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In gas chromatography, the mobile phase is gas and the static phase is usu- ally a liquid, or a solid in special cases. The main application of gas chromatogra- phy is in the analysis of complicated mixtures of many components. The high popularity of gas chromatography is due to its requirement of small sample amounts for analysis and the possibility to analyze compounds in trace amounts. The biggest disadvantage of this method is that all the compounds analyzed must be in the gaseous phase or can be evaporated into the gaseous phase. In gas-liquid chromatography, the stationary phase is a liquid which is cov- ered on an indifferent (inert) solid substance called the carrier. The carrier is either a porous adsorbent or the wall of a capillary. This analytical method corresponds to the principle of classical distribution chromatography, in which a liquid is used as the mobile phase. In gas adsorption chromatography, solid granulates with an active adsorptive surface, such as activated coal or silica gel, are used as the sta- tionary phase. Gas chromatography has been well known as a separation method for a long time. After they had invented the principle of distribution chromatography, A. J. P. Martin and R. L. Synge suggested the use of a flowing gas as mobile phase. The reason is that gas makes it possible to carry out distribution chromatography with high flow velocity, because of its low viscosity as opposed to the viscosities en- countered in the liquid phase. The rapid development of the method in the last few years has substantially contributed to the relatively simple and extremely sensitive measuring methods of gas chromatography. This makes it easy to operate continuously with connections between the separating column and the detector. Thus, separation, identification
detector sample input data evaluating column /
The detector and column are the most important parts of a gas chromato- graph. Usually, separation by gas chromatography is carried out at higher than room temperature. As such, Ihcrmostatic heating of the column is necessary. There are many types of columns used for gas chromatography and they are made from different materials. Usually, these are glass, plastics and metals such as copper or steel. All these materials have advantages and disadvantages for differ- ent types of analysis. For example, glass columns are thermally and chemically very stable, and normally these are relatively cheap columns in comparison to columns made from other materials. The disadvantage of the glass column is that it is very fragile, and thus it is an easily breakable material that is relatively diffi- cult to install. Plastic columns are not easily breakable. They are very flexible but chemically stable. However, the disadvantage of such columns is that they are not thermally stable. As such, they can be used only for analysis at a low temperature. The metal columns are now the most popular columns for gas chromatography. They are not breakable, and are thermally and chemically stable. They only have
The thin layer column, also called the analytical column, is ideal for all types of quantitative and qualitative analysis, because they provide the best possi- ble resolution in comparison to other gas chromatographic columns. A thin layer
.Impregnated carrier
The next important part of the gas chromatograph is the detector. The de- tector is the part of the gas chromatograph which detects the compounds leaving or exiting the column. It is a very important part of the gas chromatograph in the sense that even with the best column, if the detector is not able to exactly detect the compound as it exits the column, then the analysis is incomplete. There are many methods to detect the compounds present in the sample mixture. For exam- ple, in the case when the carrier gas is hydrogen, the analyzed sample can be burned as it exits from the column. The majority of compounds have unique colors of their burning flames, allowing for the detection of the compounds according their flame colors. This is just one of the simplest examples of the possibilities for detection. Even though there are many types of detectors used in gas chromatographs, it is possible to classify them as integral and deferential detectors. The latter class of detectors is currently the most well developed class of detectors. If only the carrier gas flows through the column, modern deferential detectors will show a direct zero base line. When analyzing real sample mixtures by gas chromatographs with such detectors, the detector detects the compound immediately as it exits from the column and sends a signal to the evaluating computer. After the particu- lar component or compound has exited the column completely, the detector sends a zero signal to the evaluating computer. These types of detectors are known as exact detectors.
This curve is defined by the minimal detectable level amount of the sub- stance that enters the detector. Usually, this level is accepted as two or three times higher than the magnitude of the normal noise of the detector. The area where the
Electrons formed in this reaction are dropped onto the collector electrode. These electrons form the electrical signal of the detector. It is important to ensure that synthetic air contains only oxygen and nitrogen and that the collector elec- trode is very clean from the burning residue or other pollutants. Otherwise, this can lead to a high deviation of the measured values from the real values. One example of the flame ionization detector is shown in Figure 2.6. Actually, the flame ionization detector is restricted to only the analysis of organic substances. As such, gases like CO2, SO2, NH3 and CO cannot be ana- lyzed by gas chromatographs with this detector type. However, analyzing inor- ganic gases in the petroleum chemistry becomes necessary only in some special cases such as ecological analyses of the gas formed during crude oil treatment. The Janak detector is probably the simplest detector that exists for gas chromatography. With this detector, carbon dioxide must be used as the carrier gas. Both the carrier gas and the sample analyzed go through a vessel containing concentrated Ca(OH)2 solution after exiting the column. In this way, the carbon dioxide is separated from the gas analyzed. All the gases not dissolved in the Ca(OH)2 solution are collected in a special collector. The volume of the com- pounds is automatically measured in this collector. It is obvious that this collector cannot be used for analyzing gases that are soluble in Ca(OH)2 solution.
electrode - , Analyzing V = and carrier
+ 1 <3 ik
The next and probably most important detector in gas chromatography is the thermal conductivity detector. This detector contains four cells, which are installed in a thermostat. Two of the cells are the measurement or analysis cells. The ana- lyzed gas and carrier gas flow through these cells. The remaining two cells are called the reference cells. Only the pure carrier gas flows through both these cells. Inside of all the four cells are platinum or wolfram electrodes. All the electrodes are heated up using exactly the same electrical stream. As such, the differences in temperature of the electrodes are only due to the difference in the thermal conduc- tivities of the gases flowing through them. If a difference in temperature in the electrodes in the measurement and comparison cells is detected, the detector sends a signal to the evaluating computer. The temperature difference is measured by measuring the electrical conduc- tivity of the electrodes in the cells. All these electrodes are connected in a special bridge circuit. This circuit is in equilibrium as long as the temperature of all the electrodes is the same. The electrical conductivity depends strongly on the tem- perature of the electrodes. If a different gas in the carrier gas flows through the measurement cells, then this circuit is immediately out of equilibrium. The different electrical conductivities of the electrodes lead to a change of voltage. This change is sent as the measured detector signal. One example of the cells and the bridge circuit are shown in Figure 2.7. It is obvious from the functioning principles of the detector that the thermal conductivity detector is suitable for all types of chemical compounds. This is why its use is recommended for analyzing complicated mixtures such as crude oil frac- tions or products. Another type of detector that is used relatively often for gas chromatography is called the ion trap detector. In some cases, this detector is called a mass selec-
a) b)
Fig. 2.7: a) Scheme of two cells of thermal conductivity detector; b) bridge circuit
The mass spectrometer serves for the exact determination of the masses of atoms and molecules as well as for the registration of the mass spectra from parti- cle mixtures to mass and relative proportion. The first ion trap detector was devel- oped in 1919 by F.W. Aston. An example of the ion trap detector is shown in Figure 2.8. The ion trap detector is operated all the time under vacuum. The measure- ment cell consists of two rotating symmetric pole caps and a ring electrode. The molecules of the sample are usually analyzed in the measurement cell. They are ionized by an electron beam that is only switched on for a brief period of time. The ions in the space between the pole caps and the ring electrode are captured or caught by a sturdy high-frequency field. By varying the high-frequency field, the ions leave the space between the pole caps and the ring electrode in the order of their mass to electrical charge values, and arrive at the amplifier. It is obvious from the working principle of the ion trap detector that this is equally a universal detector as is the thermal conductivity detector. The analysis of the mixtures of compounds with this type of detector is possible not only by reten- tion time of the compound in the column, but also by the composition of the ions of this compound. Usually, libraries of the compounds for the ion trap detector are much more extensive than the libraries for the thermal conductivity detector. However, the more extensive possibilities for knowing which compound exited the column makes this detector an excellent detector for the specialist, but intro- duces many difficulties for beginners.
electron source
The next detector to mention in this book is called the electron capture de- tector. The electron capture detector is a detector which possesses a special sensi- tivity for substances that can catch slow electrons. These include halogen organic compounds. The electron capture detector is much more sensitive for this com- pound class than, for example, the flame ionization detector. One example of such a detector is shown in Figure 2.9.
anode cathode + Fig. 2.9: Scheme of the electron capture detector: e" - slow electron P - P - particles (fast electrons) S e - analyzing substance molecule with caught slow electron
electrode Analyzing compound and carrier gas
Ill hydrogen Fig. 2.10: Scheme of the thermo ionic detector for the analysis of phosphor compounds.
The alkali bead consists of rubidium glass, which has semiconductor prop- erties. If it is cold, it is an insulator, and in the hot state, it has some conductivity. If there are alkali ions (Me+) in the hot alkali bead, then they react with electrons into alkali atoms, which surround the alkali bead as a cloud. The alkali atoms can become thermally innervated and react under light rays into innervated atoms Me . Radicals (R-), which are formed from the burned component analyzed, react with innervated alkali atoms by electron transfer from the alkali atom to substance radical. The innervated alkali atoms change their electrical charge and form posi- tively charged alkali ions, whereas the sample radicals react to form negatively charged ions R . The positive alkali ions are caught by the negatively charged alkali bead again, and react immediately to alkali atoms again. Also, they are ready for further reactions with the sample radicals again. The anions (negative charged ions) react to form a neutral final product. Electrons are captured or caught by the collecting electrode and the detector signal is thereby formed. The main reactions taking place in the detector with phosphorus compounds can be shown in the five reactions given below. All these reactions are written under the assumption that only reactions with the phosphorus oxides such as PO or PO2 occur in the detector room, since the organic substance is completely burned in the burner.
Nitrogen has an odd number of electrons on the outer shell just like phos- phorus. However, the nitrogen oxide radicals formed similarly to the phosphorus oxide radicals are cracked very quickly in the hot analyzing chamber in compari-
synthetic air
electrode Analyzing compound and carrier gas
I I hydrogen
Fig. 2.11: Scheme of the thermo ionic detector for the analysis of nitrogen compounds.
The reaction mechanism of the reactions running in the analysis room of the detector can be presented by the following reactions:
— C— C=N (cracking)
This type of detector is very specific and can be used in petroleum chemistry only in specific cases for the analysis of nitrogen or, very rarely, phosphorus com- pounds. Some of such cases are shown in the last chapter of this book. These are cases where crude oil is treated or coprocessed with other feeds that contain het-
i?v?\> L
Fig. 2.12: Main techniques for the input of the sample in the column: 1 - full needle technique 2 - empty needle technique 3 - air bubble technique 4 - solvent technique 5 - sandwich technique
When all the preparation work has been completed and sample is introduced in the column, analysis can begin. The analysis result consists of a chromatogram with many peaks that correspond to the compounds present in the sample mixture. At the beginning of this chapter, it was mentioned that the main idea of chroma- tography is the differential adsorption or absorption of the components in a sample mixture followed by desorption. However, what is observed in the chromatogram are wide peaks instead of thin lines that should represent the compounds of the sample. Why do we have wide peaks? One of the possible theories used to explain this occurrence is the theory of resistances. The main idea of this theory is pre- sented in Figure 2.13.
It was shown earlier that there are many reasons for the occurrence of anomalies during gas chromatographic analysis. This is why everything needed for analysis must be chosen very accurately. After the gas chromatograph for analyz- ing a specific sample is selected, the next step is to select the carrier gas. Every gas can theoretically be used as a carrier gas. However, there are some important char- acteristics that every carrier gas must have. The carrier gas must be chemically and physically inert to the filling or packing of the column. Also, it must not react with the compounds in the sample mixture. The last property of a good carrier gas is its level of purity. It is very important for the analysis that the carrier gas introduces no impurities into the gas chromatograph. Even very small amounts of foreign substances in the carrier gas can falsify the results very seriously. Presently, three gases are the most popular carrier gases used in gas chromatography. These are hydrogen, nitrogen and helium. The use of hydrogen as a carrier gas has only one disadvantage. The high tendency of hydrogen to diffuse and permeate through the smallest splits in the connections between parts of the gas chromatograph makes hydrogen relatively dangerous. If the leakage in the system is inside the thermostat, it can result in explosion because of the presence of a dangerous mixture of hydrogen and air. This is why the use of hydrogen as the carrier gas must be related to ensuring that there are no leaks between connections of parts in the gas chromatograph. Conse- quently, a very thorough leak check is a must before the start of every experiment. The next possible carrier gas is nitrogen. This is probably the cheapest and least dangerous carrier gas. However, it must be noted that nitrogen is also used as an inert atmosphere in many experiments in crude oil chemistry. This means that gas coming to the analysis contains nitrogen. The analysis of nitrogen in the gas mixture would be impossible if the carrier gas is the same as one of the compo- nents of the sample mixture. Nowadays, helium is the most popular carrier gas used in gas chromatogra- phy. The use of helium as inert atmosphere in thermal or catalytic treatment ex-
soap bubble
gas elastic bubble with soap solution
Fig. 2.16: Gas flow measurement device using the soap bubble principle.
The principle of this gas flow measurement device is simple. A push on the gummy bubble leads to soap bubble rising in the measurement cylinder. The gas flow pressures up the soap bubble. The time it takes for the bubble to pass through a defined volume of the measurement cylinder is measured by a timer. The princi- ple of soap bubble gas flow measurement is the direct measurement of the average gas flow velocity. The advantage of this device is that a very accurate average value for the gas flow velocity can be calculated from the measurements. This
T gas Fig. 2.17: Gas flow measurement device using principle of heavy sphere floatation.
The last device for measuring gas flow and for calibrating mass flow con- trollers that is discussed in this chapter is called the capillary gas flow measurer. The principle of this device is used in many modern automatic calibration devices for mass flow controllers. The scheme of such a device is shown in Figure 2.18. The main idea of this method is that the pressure needed to force the gas through the capillary is directly proportional to the gas velocity. The pressure can be measured by the method shown in Figure 2.18, by measuring the height of the liquid, which can be mercury or water or, for special cases, highly viscous liquids. However, this measurement is also possible by using other pressure measuring devices as well. After all the preparations and experiment are over comes to the time to evaluate the experimental data. There are many methods to evaluate the gas chro- matogram. Usually, every gas chromatograph is calibrated for each specific method. The most popular and simplest method is called the peak height method. The method is applicable only if the chromatographic column is not overloaded. In
pressure measurement
Fig. 2.18: Gas flow measurement device using principle of the capillary pressure.
The error obtained with this evaluation method is due mainly to the fact that the total retention time of the individual components depends linearly on the peak height only approximately. The amount of the component in the sample is often judged as too small for thin peaks and too high for wide peaks. The linear depend- ence is well suitable for homologous classes of compounds in the sample mixture analyzed. The next evaluating method is based on the multiplication of the peak height by the width of the peak at half its height. With this evaluation method, the total area of a peak, which corresponds to a Gauss distribution curve, is determined as an area of an equal-leg triangle. The height of the triangle is equal to the maximum of the detector signal. The area of the triangle is the result of the multiplication of the triangle height with its width at the half height. This method used frequently in comparison to all the other methods dis- cussed previously because it is less sensitive to the influence of temperature, change of pressure and carrier gas flow. However, this method can be used only for the evaluation of chromatograms with symmetric peaks. The advantage of the method is that the chromatogram can have symmetric peaks even if, like in some cases, the column of the gas chro- matograph is overloaded. The last method of evaluation of a gas chromatogram is called the mix method. With this method the compounds analyzed must be known. The pure compound that is to be evaluated is mixed with the sample mixture. Analysis of the sample mixture is performed twice in this method. One is in the absence of the pure compound whereas the second is a mixture with the pure compound. Evalu- ating the concentration of the component proceeds with a comparison of the peaks from both chromatograms. The advantage of this method is that this method is very accurate. On the other hand, the disadvantage is that the evaluation of the pure compounds is needed, and also there is the need of at least two chroma- tograms, which makes this method longer and more expensive than every other method discussed before. More information about gas chromatography can be found in references 54- 59 at the end of this chapter.
The setup shown in Figure 2.19 is the simplest example of liquid chroma- tography. The column diameter for such chromatographs usually varies from 1 to 5 cm. The column is filled with fine adsorbent particles. The top of the column is open for the entire duration of the experiment. The sample dissolved in a small amount of the solvent is introduced first in the column. After this, the solvent is introduced slowly but continuously into the column and separated compounds or fractions of compounds exit the column at the bottom. In this method, the solvent flows only under the influence of gravitational force. The disadvantage of this
' r column / data evaluating
^. . thermostat -,. solvent reservoir collector
solved compo- nent photo resistor
Source of reference UV light lens UV filter mobile cell phase Fig. 2.22: UV detector.
prism photo- rejistor
lamp f VS^/v / lens i - *' -~'\
solved X substance Fig. 2.23: Analysis cell of refractive index detector.
The most modern but not especially popular refractive index detectors are those that use a laser as the light source. The use of lasers brings many advantages. First of all, the resolution of a laser refractive index detector is much higher than by using classical detectors. However, the price for such detectors is relatively high and it is used only for special analytical cases. The next type of detector used in liquid chromatography is fluorescence detectors. These detectors use the ability of components in the sample analyzed to absorb and re-emit light at defined wavelengths. Each compound has a character- istic fluorescence. Ultra violet lamps are usually used as the light source in such detectors. The technique of fluorescence detectors is different as compared to the usual detectors. They contain only one flow cell. The light goes through this cell. The photoresistor measures the intensity of the light passing through the cell and the monochromator measures the re-emitted light, i.e. fluorescence. Electrochemical detectors are a very interesting example of detectors used in liquid chromatography. These detectors can detect only compounds that are able to react by oxidation or reduction reactions. Usually, this technique functions by measuring the gain or loss of electrons from the flowing sample as it passes be- tween two electrodes maintained at an electrical potential difference. The last two popular detectors in liquid chromatography are nuclear mag- netic resonance and mass spectrometers. The mass spectrometer as a detector was described in the section in this chapter on gas chromatography. On the other hand, the principles of the nuclear magnetic resonance are described in chapter 5 of this book because of its important in asphaltene chemistry.
In degassing the solvent with a helium stream, helium gas is bubbled con- tinuously through the solvent until all the solved gases are removed. In this method, it is important that the mobile phase does not come in contact with air during the degassing. This is the simplest and most popular method. In degassing with ultrasound, a glass with solvent is placed in the bath with the source of ultrasound. During the treatment with ultrasound, bubbles of the gas removed can be seen issuing from the solvent. The ultrasound treatment must be carried out until no more gas bubbles are issuing from the solvent. The last method, the distillation method, is the most effective but also the most complicated in executing. In this method, the solvent is evaporated in an inert atmosphere and then condensed again. It is important to ensure that no gas is dissolved in the solvent during the condensation. For this reason, the distillation unit must be evacuated before degassing and then filled with a gas that is insoluble in the mobile phase. Elution with the selected and degassed solvent as mobile phase can be done in two different methods. The first method is simplest, but cannot be used for all samples especially those containing complicated mixtures of compounds in crude oil fractions. As such, this method is only rarely used. It is called isocratic elution. In this method, the same composition of mobile phase is used during the entire analysis time. The main property of samples that can be analyzed by this method is that the components in the sample have approximately the same polarity. The second elution method is called gradient elution. This method can be used for complicated mixtures of compounds which have different polarities and which
3 mobile / phase mobile phase form container to column
On the back stroke, the separation column valve is closed, and the piston pulls in solvent from the mobile phase container. On the forward stroke, the pump pushes the solvent out to the column from the hydraulic chamber. A wide range of flow rates can be attained by altering the stroke frequency. As shown, the func- tioning principle of the membrane pump is relatively simple. However, there is the disadvantage that the pumping of the mobile phase is only done discontinuously or intermittently. A schematic showing the pulsating pumping of the solvent by a membrane pump is illustrated in Figure 2.25. The problem with discontinuous pumping can easily be solved by using two pumps functioning at the same time such that if one pump sucks in the solvent another pump presses the solvent to the column (out of phase with each other). This type of pump system is significantly smoother because one pump is filling
3 - 5 mm
The humidity that comes with the mobile phase filter paper ensures the evenness of the vapor pressure in the analysis chamber and acts as an accelerator for the achievement of saturated vapor with the mobile phase. The filter paper can also act as an indicator; if the solvent front reaches the upper limit of the filter paper, it is usually postulated that the analysis chamber is ready for the com- mencement of the analysis.
3-5 mm
The development of the sample begins due to the capillary action of the mobile phase on the thin layer plate, after the thin film plate has been placed in the analysis chamber. Usually, the time needed for the analysis varies from twenty to sixty minutes. However, the analysis proceeds until the solvent reaches the upper limit of the thin film. In the case where appropriate resolution is achieved earlier than when the solvent front reaches the upper limit of the plate, analysis can be stopped early to save time. Evaluation of the analysis results proceeds by measurement of the differ- ences in the distance from the start line until the analyzed spot and front of the mobile phase, as presented in Figure 2.29. After measuring the distances di and 62, a special factor Rf is calculated according to the formula (2.1) (see Figure 2.29). The Rf values depend on the solid absorbent, the compound polarity, and the eluting solvent polarity. The factor Rf for constant analysis conditions is a characteristic property of the sub- stance. If the thin-film card is calibrated for permanently analyzing similar sam- ples, the substance analyzed can be detected just by the Rf value.
Rf = d 2 / d , (2.1)
The evaluation can also be carried out visually as shown in Figure 2.29 or by transferring the data into digital form by a scanner and evaluating the results in a computer. Fluorescence active impregnation can be used in the case of analysis of almost transparent samples. The spots of such samples are hard to see in the visible spectra of light. However such substances can be easily detected by view- ing the thin film with UV light and observing the fluorescence picture.
d, analyzed spot i'femin1! M
iL d2
^•^^ start line y^r'O---.^.*»». rf**
The evaluation of some samples is sometimes not possible after the first development. This can be caused by a wrong choice of solvent or by special prop- erties of the sample. However, it is possible to develop the thin film one or more additional times. There are two methods for developing the thin-film card more than one time: one-dimensional and two-dimensional development. The thin-film card must be dried so that there are no residues of the mobile phase on the thin film before the development in the second step. After drying, the thin film is placed in the analysis chamber in the same way as was done for the first analysis. The analysis can be repeated until an appropriate resolution of the card is achieved. The Rf value for one-dimensional analysis is calculated by the formula in equation (2.2), with regard to the number of times (n) it was repeated.
I = I0-10-E-cd (2.4)
- Einitial = E = (2.5)
energy molecule quanta of light
E = mv2/2 (2.6) where v is the velocity of the center of mass of the molecule m is the mass of the molecule The velocity with which a molecule translates may be resolved into compo- nents along each of the three axes of the Cartesian coordinate system, as shown in Figure 2.31.
If the molecule motion is observed as is shown in Figure 2.31, then the energy of the translational motion is calculated by equation (2.7).
This equation shows that the total translational energy of the molecule can be made up of three parts, each of which represents the kinetic energy of the mole- cule along one of the reference directions. Any translation of the molecule may be considered to arise from the vector sum of its motions along the three axes. Thus, the kinetic energy may always be broken up into the sum of three contributions, one arising from motion along the x axis, one from motion along the y axis, and one from motion along the z axis. It means that the molecule has three transla- tional degrees of freedom, one corresponding to each axis. The next type of motion of the molecule is the rotational motion. The mole- cule can rotate about some internal axis. This axis may be resolved into compo- nents of the x-, y-, and z-axes of the coordinate system, so that any rotation of the molecule may be resolved into three mutually perpendicular components. The
The final type of the motion of molecules is called vibrational motion. This type of molecule motion is very important in infrared spectroscopy since the ab- sorption of infrared radiation by this motion forms the fingerprint of the sample analyzed. There are many types of vibrational motions, and these are shown be- low. It is important to know the right number of degrees of freedom for the vibra- tional motion of the sample molecule. This can be calculated by using the follow- ing general equation (2.9).
Z=3-N-6 (2.9) where N is number of centers of mass in the molecule
As was shown for translational and rotational motions, there are three de- grees of freedom for vibrational motion for every center of mass in the molecule. The number six on the right hand side term of equation (2.9) arises from the total number of degrees of freedom for translational and rotational motion, which do not belong to vibrational motion. It should be known that for linear molecules, there are only two degrees of freedom for rotational motion. This is why for this case there is a special equation for the calculation of the degrees of freedom for vibrational motion (2.10).
The number of the degrees of freedom for the vibrational motion (Z) calcu- lated by the equations (2.9) and (2.10) is called degrees of freedom of normal vibrations. For example one three-atom linear molecule has four degrees of freedom for normal vibrations (2.11):
This means that four types of vibrational motion are possible for such a molecule. The first motion is the symmetric vibration of the atoms in the direction of the center of mass as shown in Figure 2.32. Since this vibration is symmetric, it does
Both end atoms move asymmetric to the central atom during the second type of vibrational movement. Such a movement leads to the altering of the dipole moment of the molecule, and this type of vibration is active for infrared analysis. An example of this movement is shown in Figure 2.33.
The next two types of vibrational movement are called deformation vibra- tion. The end atoms move vertical to the central atom. The first type of vibrational movement is shown in Figure 2.34.
Fig. 2.34: First type ofdeformational vibrational motion of the linear molecule.
This type of motion leads to the altering of the dipole moment of the mole- cule as well as to an asymmetric vibrational motion. Thus, this vibration is active for infrared analysis. The last type of vibration for the molecule shown is principally the same as the third type of motion. However, the vibration proceeds horizontally to the cen- tral atom. This type of motion is shown in Figure 2.35
This type of motion is shown as an extra motion because the motion pro- ceeds in different coordinates in comparison to the first shown deformational motion. However, the vibration frequency and the altering of the dipole moment by these last two vibrations are the same. Such type of motions, where the vibra- tion frequency of two or more motion types is the same, is called downgraded motion. A special value, called degradation number, is given for characterization of such motions. This value shows the number of molecules that have the same vibration frequencies. For example, the degradation number for the linear mole- cule shown above is two. A three-atom nonlinear molecule is shown as the next example. Nonlinear molecules are more popular in petroleum chemistry, because most organic sub- stance are nonlinear. The number of degrees of freedom of normal vibrations for three-atom nonlinear molecule is calculated using equation (2.12).
This means that three vibrational motions are possible for this type of molecule. The end molecules vibrate symmetric to the central atom by the first possi- ble motion. In opposition to the linear molecule this motion by a nonlinear mole- cule leads to the altering of the dipole moment. This means that this vibration is active for infrared analysis. An example of such a vibration is shown in Figure 2.36.
As an analogue to the linear molecule the second vibrational motion for the non linear molecule is asymmetric vibration. This type of motion is shown in Figure 2.37.
The asymmetric vibration leads to the altering of the dipole moment as well, and as a result this motion is active for infrared analysis. The last possible vibrational motion is the deformational motion. This type of vibration is presented in Figure 2.38.
From Figure 2.38, it is easy to see that for nonlinear molecule, only the type of deformational motion shown is possible, because the deformational motional in different coordinates other than the ones shown in figure 2.38 are analogues to the rotational motion of the molecule. Thus, a three-atom nonlinear molecule has only three degrees of freedom of normal vibrations whereas a three-atom linear mole- cule has four degrees of freedom of normal vibrations. There are many types of vibrational motion of atoms in molecules. However the intention of this chapter is to show the fundamentals of infrared spectroscopy. In the list of references at the end of this chapter, many books and articles are recommended for a more detailed study of this type of analysis. Each of the vibrational motions of a molecule occurs with a certain fre- quency that is a characteristic value for the groups in the molecule analyzed. The energy involved in a particular vibration is characterized by the amplitude of vi- bration, so that the higher the vibrational energy, the larger the amplitude of the motion. According to the results of quantum mechanics, only certain vibrational energies are allowed for the molecule, and thus only certain amplitudes are al- lowed. Associated with each of the vibrational motions of the molecule, there is a series of energy levels. The molecule may change from one energy level to a higher one by absorption of a quantum of electromagnetic radiation. This can be calculated by equation (2.5). In undergoing such an energy of transition, the mole- cule gains vibrational energy, and this is represented by an increase in the ampli- tude of vibration. The frequency of light required to cause an energy transition for
n Fig. 2.39: Infrared spectrometer: 1 - infrared light source 2 - sample chamber 3 - monochromator 4 - detector 5 - amplifier 6 - evaluating computer
The most frequently used source of infrared light for infrared spectrometers is so called the Nernst stick. This stick is about two to four centimeters long and one to three millimeters thick, and is made from zirconium oxide with additions of yttrium oxide and oxides of other metals. This mixture of oxides has a negative temperature coefficient of electrical resistance. This means that its electrical con- ductivity increases with an increase in temperature. At room temperature, the Nernst stick is a non-conductor. Thus, an auxiliary heating is necessary for igni- tion of the Nernst stick. Even if the Nernst stick is red-hot, it can be heated further by electricity. The normal operating temperature of this infrared light source is approximately 1900 K.
The Littrow monochromator has a prism as a splitting system while the Ebert monochromator has a diffraction grid for the same purpose. The principles of the schemes of both monochromators are presented in Figures 2.40 and 2.41, respec- tively.
output rift parabolic mirror
input si
The diverged infrared radiation from the input slit is directed to a parabolic mirror and returned toward the splitting system (prism or gird). Depending on the type of optical principle, the parallel reflected infrared light passes through the prism or split by the diffraction gird. It is then reflected back by a plane mirror at the same parabolic reflector for the Littrow monochromator or at a second para- bolic reflector for the Ebert monochromator. After this, the monochromic infrared radiation is directed to the output slit. The most important part of the monochromator is the infrared radiation splitting system. One of the most popular splitting systems is the prism. The function of a prism is based on having various refraction angles for radiation with various wavelengths. The function principle of a prism is shown in Figure 2.42.
input slit
parabolic mirror
output slit
monochromic polychromic kht light wavelength
For the analysis of liquid samples, the cuvette material must chosen so that the sample is physically and chemically inert to this material. The result of an infrared spectroscopy is the spectrogram or spectrum. A typical example of the infrared spectrogram (i.e. spectrum) is shown in Figure 2.43. Usually, the infrared spectrum is drawn in terms of wave number / absorp- tion or wave number / transmittance coordinates as shown in Figure 2.43. The wave number is a characteristic value of the electromagnetic radiation, and can be calculated by equation (2. 13).
Tr = I / I 0 (2.14)
100. 4400 3900 3400 2900 2400 1900 1400 900 400 1 wave number [cm" ] Fig. 2.43: Infrared spectrum: 1 - basis line 2 - background absorption 3 - absorption peak 4 - shoulder 5 - analysis start point 6 - spikes
= -E-C-d (2.15)
It can be seen that the concentration of the substance in the sample can be calculated by comparing the input and output intensity of the infrared radiation. However, the input intensity is actually not a constant value. It varies depending on the frequency or wave number of infrared radiation. This means that the initial intensity of infrared radiation must be measured for every frequency before ana- lyzing the sample. However, this problem is solved in modern infrared spec- trometers by using a double beam technique. In this method, the beam of infrared
1 2 3
Colorimetry and photometry are the next spectral optical analysis methods. Both the methods measure absorbed light as was shown for infrared spectroscopy. However, for both these analyses, light with shorter wavelength is used. Color- imetry uses light with wavelength of only the visible spectral area and photometry uses the visible light, ultraviolet, and in some case, infrared area. A comparison of the different spectral areas is shown in Figure 2.47. Photometry is similar to infrared spectroscopy; a method for measuring the light transmitting ability of a solution in order to determine the concentration of a light absorbing material present in the solution. Crude oil chemists gener- ally use spectrometry in three ways: to determine the concentration of a substance which is not undergoing a chemical change in the spectrophotometer cell to measure the rate of change in the concentration of a substance which is participating in a chemical reaction to determine the absorption spectrum of a substance
1 5 6
Wavelength, [m] Fig. 2.47: Spectrum of electromagnetic radiation: 1 - cosmic rays 2 - gamma rays 3 - X-rays 4 - ultraviolet rays 5 - visible light 6 - infrared rays 7 - microwaves 8 - radio waves 9 - electric power
The motions that are analyzed by colorimetry and photometry are no longer of rotational or vibrational nature as was shown for all previous spectral analyses. The motions analyzed at the visible and ultraviolet spectral regions are specific for each atom or chemical group. In order to understand the nature of these motions, it is important to understand the structure of the atom. There are lots of models on the structure of the atom that can help us to understand the nature of matter. These models are simplified representations of real atoms. The models can be made by atomic physics to be more accurate but this makes the model more complicated. Today, it is possible to describe atoms very accurately by using quantum mechanics. However, the question that cannot be answered accurately is whether the true model has been found or not. Which of the models is the best depends on what it is used to describe. For example, there are applications in which it is sufficient to regard the atoms as small particles. The name "atom" derives from the Greek word "atomos" meaning indivisi- ble or unbreakable. The use of the name "atom" was initiated by Demokrit, a Greek philosopher, in the fifth century before Christ. Demokrit supported his theories about atoms through hypotheses that he did not then prove by experi- ments. His theory of the atomic structure of matter could not become generally accepted against the competing concept of a continuous universe. The first experimental verification of the existence of atoms came from chemists and was based on the clarification of the chemical nature of matter. In the nineteenth century, English chemist John Dalton formulated a law that now bears his name; according to this law, all chemical compounds are always formed by a fixed relation of the individual materials of the compound. Thus, the idea of atom
Usually, the one-ray photometer has no dynamic change possibility for the wavelength of the light used for the analysis whereas such a possibility exists for the two-ray photometers. The main difference between the two-ray photometer and the one-ray photometer is that the two-ray photometer has two cuvettes in the sample chamber. These are the sample cuvette and the reference cuvette. The reference cuvette is filled with pure solvent while the sample cuvette is filled up with a solution of the sample analyzed in the solvent. The results of photometry are evaluated by comparison of the intensity of light that passes through the sam- ple solution and the pure solvent. The scheme of the two-ray photometer is pre- sented in Figure 2.52. 1 2 3 4 5
The first method is the most used. The second and third methods are usually used in connection with high performance liquid or thin film chromatography. For quantitative evaluation according to the first method, equation (2.17) is used.
If the extinction (E) according to the Lambert-Beer law (see equation 2.4), which is calculated by equation (2.18), is less than 0.01,
E = E-C-d (2.18)
Ca = C c -I F a /I F C (2.20)
Fluoremetry has two main advantages in comparison to photometry that uses the same light spectrum for analysis. These are the high sensitivity and the high selec- tivity of the method. High sensitivity of the method can be explained on the basis of the absence of such effects as background absorption, which are typical of ab- sorption spectral methods. High selectivity is due to the difference in wavelengths
The functioning principle of the gas discharge lamps can be explained based on Figure 2.55. A small amount of the element that is analyzable by this lamp is melted under pressure in the quartz chamber. The element emits light of a certain wavelength by a high frequency electrical stream.
Concentration, [mol/l]
The concentration of the element in the sample solution can be found as the intersection point of the calibration line with the concentration axis at which point
In Figure 2.58 it is seen that the atomic emission spectrometer has no light source. Atoms emit light by the influence of the thermal energy of the burner. However, the energy needed to enable the atoms emit the light is much higher than the energy needed to only atomize them. Hence, the much higher temperature required for the burner of the atomic emission spectrometer than that for the atomic absorption spectrometer. This is also the reason why other gas mixtures such as fuel gas should be used for atomic emission spectroscopy. Mixtures of methane/air, hydrogen/air, acetylene/air, methane/oxygen and acetylene/oxygen are usually used as a fuel gas for this analysis. The next possible way to make atoms emit light is the flashover method. In this method, flashover is the source of thermal energy. The biggest advantage of this method is the ability to heat the sample up to 10000K. It is possible to analyze almost all known metals at this temperature. In most modern spectrometers, plasma sources are used as source of thermal energy. Both methods, atomic absorption spectroscopy and atomic emission spec- troscopy, are used in modern crude oil laboratories, with atomic absorption spec-
Both methods are used for the determination of the metal content. The de- termination of the concentrations of heavy metals in crude oil and its products is an important topic in environmental chemistry. Heavy metals are always present in crude oil, especially in the heavy fractions such as residual fuel. The control of the concentration of heavy metals in such fuels is very important for ecological monitoring in crude oil chemistry. More about the methods, techniques and mod- ern research results made by atomic absorption spectroscopy and atomic emission spectroscopy can be found in references 80-82 shown at the end of this chapter.
X-ray spectroscopy can be classified in the same manner as every other type of spectral analysis into absorption and emission spectroscopy. However, the most popular method of x-ray spectroscopy in crude oil chemistry is the emission spec- troscopy, also called x-ray fluorescence spectroscopy. The effect used by this type of spectral analysis is the same as was described for fluorescence analysis. How- ever, x-rays are used for this analysis instead of the ultraviolet radiation used for fluorescence analysis. The scheme of the x-ray fluorescence spectrometer is similar to that for the fluoremetry spectrometer. This is presented in Figure 2.59. X-ray pipes are used as the light source for x-ray fluorescence spectroscopy. There are very many types of x-ray pipes in the modern market. The functioning principle of the x-ray pipe is the same as for cathode lamps described in an earlier section of this chapter. The x-ray pipe contains an electrical heated cathode, anode and radiation output window. This window is made from beryllium because this material is transparent to x-rays. The x-rays pipes offered in the market differ because they have a different anode material, and consequently the spectral char- acteristics of the emitting radiation are different. The monochromator for x-ray fluorescence spectroscopy is called the ana- lyzing crystal. It differs from all the monochromators described earlier for all the other optical analytical instruments. The effect used in this type of monochromator is not diffraction, but interference. The wavelength of the analyzing light is changed by rotation of the analyzing crystal by certain angle. The homogeneity of the sample is very important for successful x-ray fluo- rescence spectrometry. Hence, the preparation of solid samples for this analysis by melting. The samples analyzed by crude oil chemist are, in most cases, liquids or
The first three methods are very similar to the methods used for other spec- troscopic methods. Statistical calculation methods can be used only in modern x- ray fluorescence instruments that come with the appropriate software. Different manufacturers or companies use different algorithms their instruments. The main purpose of this software is to minimize the influence of measurement errors when computing the results. A wide variety of statistical methods are available. The statistical calculation method saves a lot of experimenting time, because only the analysis of the sample is needed for every analysis. Calibration or analyses of sample with added substance is not required in this case.
All the separation methods used to classify physical and chemical properties of crude oil can be classified into the following classes: - chromatography - spectroscopy - adsorptive methods - evaporating methods - extraction - thermal diffusion - crystallization - complex formation methods
The first two methods were described in detail in the first two sections of this chapter. The adsorptive methods used by crude oil chemists are actually simi- lar to those described for the chromatographic methods. The setup used for this type of analysis is the same as was shown for column chromatography (see Figure 2.19). There are two different adsorptive separation methods: - desorption method - elution method
The preparation of sample for both methods is done in the same way as was shown for column chromatography. However, both methods differ in the solvents used for desorption. In the case of the desorption method, the solvents used should have a stronger absorption ability than the compounds in the sample mixtures. Solvents used for analyzing crude oil and its products include alcohols, ketones, ethers, chlorine-containing solvents, benzene, toluene and so on. It is possible to
The first two methods are described in detail in chapter 5 of this book be- cause of the high importance attached to these methods for the industrial separa- tion of crude oil. However, it will be said at this point that both methods use the difference in the boiling temperatures of the compounds in crude oil for separating the compounds. Rectification actually involves carrying out the distillation as a multistage process. The reason to carry out such a multistage process is that dis- tillation (i.e. in one stage) does not provide a satisfactory separation into the de- sired fractions. The distillation method is however frequently used, and it is a standard method in all international standards for characterization of light fractions of crude oil such as gasoline and diesel. The biggest advantage of this method in comparison to rectification is that this analysis needs less time to be carried out. The third method is molecular distillation. This is distillation under very low pressure. Usually the pressure for this analysis varies from 0.133 Pa up to 0.013 Pa. The heavy fractions of crude oil can be separated with this method. The name molecular distillation is derived from the fact that the vapor pressure of the high molecular compounds depends almost linearly on the boiling point of these com- pounds under vacuum. It means that the separations by this method proceeds ac- cording to the molecular weight of the compounds in the sample. The quality of the separation depends on the evaporation velocity of the compounds in sample mixture. Extraction methods are based on the different solubility of the compounds of sample in solvents. Usually, many different solvents or one solvent at different temperatures are used to separate the sample into fractions according their solubil- ity in the solvent. This method is important for analyzing the heavy fractions of crude oil. This is why this method is described in detail in chapter 8 that is devoted to asphaltene chemistry. The thermal diffusion method is used rarely in comparison to all the other analysis methods in crude oil characterization. However, this method is very use- ful and can be successfully used for the analysis of heavy crude oil fractions. The setup used for this analysis is really simple. It is represented in Figure 2.60. The setup for thermal diffusion analysis contains two cylinders installed one in another as shown in Figure 2.60. The sample is introduced between these two cylinders. During analysis, the wall of one cylinder is heated up to a temperature
The next method is the crystallization method. This method is very fre- quently used by crude oil chemists for the classification of lubricating oil fractions. This method is based on difference in the crystallization temperatures of the com- pounds in the sample. The samples which are analyzed by this method are usually highly viscous. This makes it difficult to separate the crystallized substances from the sample. Consequently, the sample is usually dissolved in a special solvent. Examples of such solvents are liquefied propane, ethyl ether, and a mixture of acetone and toluene. The last method that was mentioned at the beginning of this section was called the complex formation method. This method is based on formation of com- plexes of crude oil compounds with other substances. The most popular methods of complex formation are complex formation with CO(NH2)2 and CS(NH2)2. For CO(NH2)2, it is typically to form complexes with rc-alkanes and their derivates with relatively long paraffinic chains with normal structure. The formed com- plexes are crystallized from the sample. The separation of the n-alkane fraction from CO(NH2)2 can proceed by adding hot water to the crystallized complex. The CO(NH2)2 is very soluble in water whereas paraffins are insoluble. This is why two layers result in this separation: the fraction of aqueous solution of CO(NH2)2 and the paraffin fraction. Because the analysis is done at room temperature where paraffins are usually solid, the paraffin plate can be easily taken off from the top of the analysis glass. The analysis with CS(NH2)2 is carried out in the same way as the analysis with CO(NH2)2. However, CS(NH2)2 forms a complex with iso- alkanes. By using both of these methods, a relatively exact separation of rt-paraffin and j'so-paraffin fractions is made possible.
Nh = w h - 1 0 0 / w s (2.21)
2.3.3 Structural Bulk Analysis of Heavy Crude Oil Fractions: n-d-M Method
The main idea of structural bulk analysis of heavy crude oil fractions is based on the existence of the so-called average molecule. The average molecule describes the chemical and structural properties of all molecules present in the sample mixture. It means that the result of structural bulk analysis is not the de- termined amount of compounds or compound groups, but it is the amount of car- bon in certain structural groups, for example in aromatic groups, naphthenic groups and paraffmic groups. The most popular and simple method for structural bulk analysis for heavy crude oil fractions is called n-d-M analysis. The main idea behind this method is the linear dependence of aromatic, naphthenic and paraffmic carbon in heavy fraction on refractive index, density and value reverse to the molecular weight. This dependence is described by equation (2.23).
CL = a / M = b • Ad + c • An (2.23)
The refraction index, density and average molecular weight of the sample must be measured in order to use the n-d-M method. Evaluating the results of this method begins with calculating four factors: v, X, W and Y - according to equa- tions (2.23), (2.24), (2.25) and (2.26).
For the case when all the measurements are carried out at the temperature 70°C, factor X is used. If X is positive, then the amount of aromatic carbon is calculated by equation (2.29).
CA = 4 1 0 - v + 3660/M (2.29)
Factor Y is used for the evaluation of the measurements made at the tem- perature 70°C. If this factor is positive then the general amount of carbon in cyclic groups can be calculated by equation (2.33).
Average molecules can be drawn based on the results of the structural bulk analysis. For example, the molecule shown in Figure 2.61 has 33.3% of aromatic carbon, 13.3% of naphthenic carbon and 53.4% of paraffinic carbon. It should be noted that the same analysis results could be obtained, for ex- ample, for a mixture of different derivates with different lengths of the paraffinic chain or different number of aromatic rings. Now it is obvious that the information obtained from the n-d-M method describes the average structure of the molecules in the sample mixture and the amount of carbon in the different groups. This is why this method is called structural bulk analysis. The evaluation method described in this chapter was developed by Van- Ness [85]. More about the n-d-M method and similar methods for the analysis of heavy crude oil fraction can be found in many references at the end of this chapter.
The colloidal properties of the crude oil are important especially for the chemistry of the heavy fractions of crude oil, which contain high amounts of as- phaltenes and resins. The main purpose of all these methods is to determine the size of the colloidal particles in crude oil product, and consequently to estimate the colloidal stability of these products, meaning how long the product can keep the physical properties in the bulk volume in equilibrium. All the methods used for colloidal characterization of crude oil can be classi- fied as direct and indirect methods.
All the spectral methods belong to the direct methods. All these methods use interference or light scattering effect. The spectrum used for this analysis is all the wavelengths from infrared until x-ray. However x-ray scattering method is the most popular method of elucidating the colloidal properties of crude oil. The technical fundamentals of such a measurement are the same as was shown for x- ray spectroscopy. However, in this measurement, it is the intensity of radiation scattered at a certain angle that is determined. Equation (2.36) is used for evaluat- ing the measurements results. 2 T - T -l J /3) Is = IQ • e(-S 0 /T o/;-. (2. jo)
= 4-n/X-sin(9/2) (2.37)
where n = 3.14159265 A, - wavelength 6 - scattering angle
The next direct method used to characterize the colloidal properties of crude oil is the sedimentation method. It is obvious from the name of the method that this method is based on the sedimentation effect. There are two possibilities to carry out this method: the first is the sedimentation under the influence of gravita- tional force and the second sedimentation under influence of centrifugal force. The choice between these methods depends on the viscosity of the sample and the size of the particles of the disperse phase. Viscous samples or samples with relatively small particles should be analyzed by the second method. The setup used for sedimentation analysis is shown in Figure 2.62.
9 vH r= ' (2.38) [2-(d-d 0 )-t s
The sedimentation time is measured as a time from when the analysis starts until the time when the weight on the sedimentation scale does not change any further. The sedimentation method belongs to the classical methods of characteriza- tion of the colloidal properties of disperse systems. These methods can be used for the analysis of colloidal solutions with size of colloidal particles between 1 and 100 micrometer. The analysis of solutions with smaller particles leads to relatively high errors as a result of Brownian motion. The next direct method for the determination of colloidal characteristics of crude oil is the conductive method. This method is based on the measurement of the electrical conductivity of the sample during the time the colloidal particles pass through a calibrated microhole. The schematic of the setup used for measurement by the conductive method is shown in Figure 2.63. There is a constant voltage between two electrodes (see Figure 2.63). The sample is sucked out continuously by a pump system shown as 5 in Figure 2.63. Thus, there is continuous stream of the sample passing through the calibrated microhole throughout the analysis time. Because of the difference in conductivity of the discontinuous phase and the continuous phases in the sample colloidal solu- tion, the measured conductivity of the sample is changed continuously as particles of discontinuous phase pass through the calibrated microhole. The resulting elec- trical impulses are registered by a monitoring device. The frequency of these im- pulses depends on the concentration of the discontinuous phase and their intensity is influenced by the size of the particles passing through the calibrated microhole. Evaluation of the measurement results are based on calibration tables. The biggest disadvantage of the conductive method is that only colloidal solutions with a low concentration of the discontinuous phase can be analyzed. This is due to the fact that only a few particles can pass through the calibrated hole at the same time. This may lead to a wrong record of the particle size and concen-
The last direct method often used for determination of the colloidal proper- ties of crude oils is gel permeation chromatography. The principles of this method were described in section 2.1.2. Normally, this method is used for analyzing the molecular weight distribution of substances. However, it is possible to use it to analyze colloidal properties as well if an appropriate solvent is used as the mobile phase. This solvent must not change the native disperse particles. Almost all the solvents that can be used in this analysis as a mobile phase change the size of native particles. This is why this analysis is usually used for estimating the particle size in the sample solution.
All the indirect methods that are based on the determination of the colloidal properties of crude oil measure macroscopic properties such as density, viscosity, and molecular weight. An example is that the molecular weight of asphaltene
Density is not only just one of the most important physical parameters of crude oil and its products, but it is also an important characteristic for measuring the quality for crude oil and its products. The density of a sample shows its mass in specific volume. The classical definition of density is presented in equation (2.39).
d = W/V (2.39)
where d - density W - weight of the sample V - volume of the sample
da!=d./dw (2.40)
df=d./d w (2'41> where ds - density of the sample at the temperature 20°C dw - density of water at the temperature 4°C (1.00000 g/cm3)
Firstly pycnometer is weighed without sample, then filled with the sample thermostatted and weighed again. The absolute density is then calculated by using equation (2.42):
where d - density WF - weight of pycnometer with the sample WE - weight of empty pycnometer V - volume of the sample in pycnometer
Viscosity is the second most important physical parameter for crude oil. It characterizes not only one of the physical properties, but also the quality of most crude oil products such as lubricating oils and lubricants. The term viscosity is derived from the flow behavior of a liquid. It is a measure of resistance to flow. Viscosity can also be defined as inner friction or inner resistance of the sample against flow. There are two types of viscosity: - dynamic viscosity and - kinematic viscosity.
The two types of viscosity are often used by crude oil chemists for various purposes. The kinematic viscosity can be measured with the Ostwald viscometer. The Ostwald viscometer is the most popular instrument used by crude oil chem- ists for determination of kinematic viscosity. A schematic of the Ostwald vis- cometer is presented in Figure 2.66.
The sample is introduced inside the viscometer for the analysis so that the top limit of the sample is located exactly on sample level 1 (see Figure 2.66). After the sample is well thermostatted in the thermostat 5 the analysis can start. The sample is released for free motion through the capillary 4 for the analysis. The analysis result is measured in terms of the time which the sample needs to flow from sample level 1 to sample level 2. The viscosity result is evaluated from equa- tion (2.43).
Tl = k • t (2.43)
v = r| • d (2.44)
Refractive index is an important physical property of crude oil and its prod- ucts which is usually used for further evaluation of the characteristics of crude oil and its products. Such characteristics include the n-d-M method described in an earlier section of this chapter. Refractive index represents the ratio between two angles, the angle of incidence and the angle of refraction. The angle of incidence (aO is the angle of a light beam before hitting the sample, the angle of refraction (0:2) is the angle of the light beam after hitting the sample. An example of refrac- tion is shown in Figure 2.68.
The refractive index is calculated by equation (2.45) with regard to the re- fraction scheme shown on Figure 2.68.
Refractometry is the last analysis method discussed in this part of the book. However, some more analysis methods can be found in chapter 8 of this book. The reason to describe these analysis methods in another chapter is the high importance attached to these methods for asphaltene chemistry, which is an important part of crude oil chemistry.
31 J. E. Snow. Of Hess crust and layer cake, J. Nature, 374, 413-414, 1995.


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May 22, 2019 Spotlight News Opinion, Your Opinion 0I wrote a letter to Colonie Spotlight on May 8 which illustrated that the Town of Colonie made two critical errors when it used a survey in the comprehensive plan proceeding. The survey intends to...
May 22, 2019 Spotlight News Opinion, Your Opinion 0To the editor: I write to let my friends and neighbors know why I am supporting my County Legislator Joanne Cunningham for re-election. When you see through the fog of the political season and get to...
May 22, 2019 Spotlight News Opinion, Your Opinion 0Letter to the editor: The Albany Symphony Orchestra is undoubtedly one of the great cultural treasures of the Capital District, not only for its large adult audiences, but also for its youngest...
May 22, 2019 Jim Franco Galleries, High School Sports, Sports 0BETHLEHEM — The Eagles jumped out to a 7-0 lead after the first quarter of the Class A semifinals against Shen and never looked back, winning 15-5. On Tuesday, May 21 Liam Ferris scored eight goals...
May 22, 2019 Diego Cagara Community, New Scotland, News, Schools 0VOORHEESVILLE — Voorheesville Central School District residents approved the $25.4 million budget on Tuesday, May 21, with 1,120 supporting and 342 opposing it. Also, the bus proposition, which...
May 22, 2019 Jim Franco Business, News 0COLONIE — Philips Medical Systems MR presented a sketch plan of a 36,000-square-foot expansion of its existing facility at 450 Old Niskayuna Road. The project will cost $13.2 million and Empire...
May 22, 2019 Spotlight News Milestones, News, Schools 0COLONIE — The late coach Michael Ambrosio was named the first Kind Human of the Year, on Saturday, May 18, during the annual Raiderfest 2019 Hill of Heroes ceremony. Ambrosio, who died suddenly in...
May 22, 2019 Diego Cagara Government, Nature/Outdoors, News, The Spot 0ELSMERE — After an extensive discussion which endured until almost 10 p.m., the Planning Board voted unanimously to table a conservation subdivision application to be located at the historic...
May 22, 2019 Michael Hallisey Culture, Entertainment, Museums, The Spot 0COOPERSTOWN — The National Baseball Hall of Fame will open an exhibit that pays homage to the cardboard product that helped launch the popularity of the game. A baseball card exhibit opens on...
May 22, 2019 Michael Hallisey Music, The Spot 0As we sit down to talk about Frenship's upcoming tour, it's about two days before they leave Los Angeles and James Sunderland is "freaking out." The duo lives for live shows. After their 2017...
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The #EmpireStatePlaza Ice Rink is CLOSED Saturday, December 14 due to the weather #FYI ... See MoreSee Less
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CDPHP Cycle! rides surpass 40,000 trips taken for 2019CAPITAL REGION, N.Y. — The Capital District Transportation Authority (CDTA) and CDPHP wrapped up the third season of the CDPHP Cycle! riding season with more than 41,000 trips taken and
Clear out the bus stops on Rt. 9 Watervliet/Latham. Kids are standing in road! The stop right ahead of the circle had about a dozen people balancing on iced over roads. A little further down a mother was body shielding her toddler while they waited for the bus...once again in the road because the stop was snowed in. Shameful!!
Join us tonight on the Capital City trolley for the holiday light display in downtown Albany at 5pm and First Friday!
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subset: commoncrawl


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Legendary X-Men scribe Chris Claremont reunited with Bill Sienkiewicz for New Mutants: War Children, a Marvel 80th-anniversary one-shot released last Wednesday. But why doesn't Claremont, who is paid to remain a Marvel-exclusive writer, contribute more than the occasional one-shot or short story to the franchise which he played a bigger role than anyone else in building? That's a question for which we've never been able to find a logical answer, but one thing for certain is it's not because Claremont isn't interested.
Claremont was interviewed by Newarama's George R. R. Marston this week, and he revealed that even New Mutants: War Childen could have been longer if Marvel allowed it.
Marvel called up and said "We want to reunite you and Bill for this aspect of the 80th anniversary celebration. We'd like you to do a 30-page New Mutants story."
So I said, "I'm cool, ask Bill." They asked Bill and Bill was cool. Then my son came up with the next question, which was, can we have a hundred pages?
Sadly, Claremont and Sienkiewicz did not get a hundred pages for their one-shot. But when it comes to the New Mutants or the X-Men, Claremont seems just as primed to write their stories as the day he started.
It's the same reaction I still have to the X-Men. I look at these characters I've known for, heaven help me, the better part of a half-century, and they're still young and fresh and dynamic. I have an infinite score of stories I want to tell about them.
Unfortunately, it's not up to Claremont or even to X-Men fans, who certainly seem to respond to any article with the creator's name in it here on Bleeding Cool with plenty of interest. That's up to Marvel.
For me, I look at these characters and I look at the way they're presented, and even after all this time, my gut reaction is, what the heck happens next? But whether I get to tell those stories is up to the folks making the decisions.
So why doesn't Marvel make the decision to have Claremont write X-Men stories more regularly? It seems we may never find out.


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Fans Call Out New Kickstarter Game for Looking an Awful Lot Like Cuphead
A trailer for a new Kickstarter project called Enchanted Portals has been revealed and fans are accusing the game of being a rip-off of Cuphead.
A trailer for a new Kickstarter project called Enchanted Portals has been revealed and fans are accusing the game of being a rip-off of Cuphead.
Studio MDHR announces The Cuphead Show is currently in development with Netflix Animation and will have a separate story from the game.
Studio MDHR has released the first look at the upcoming Cuphead DLC "The Delicious Last Course," but the new content won't arrive until 2020.
Cuphead and Mugman haven't lost a step in their move to Switch. The game remains an immensely enjoyable and challenging romp at home or on the go.
The developers behind Cuphead are hopeful that fans will be able to drum up enough demand to have the characters appear in Smash Bros. Ultimate.
The previously Microsoft-exclusive Cuphead is coming to the Nintendo Switch, which may hint at more collaborations between the two in the future.
Video game soundtracks can make or break a game, but thankfully these 10 albums have some of the best music in gaming!
Funko announces Mega Man, Cuphead, Freddy Krueger, Jason Voorhees and Gollum cereals. Is it too much branding or just enough?
Cuphead is making a return through downloadable content, with a new adventure called The Delicious Last Course announced by Xbox at E3 2018.
From returning classics through to brilliant new properties, it's been a year to remember for video games. Here are the best games of 2017.
Cuphead, one of the most difficult games ever made, comes with secret modes that many aren't aware of. Here's how you can unlock them.


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Keep It Regular
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text:
British Orienteering announces today that Graham Patten has resigned from the Board of Directors.
Graham's resignation is due to personal reasons and increased business commitments. Graham has resigned with regret and wishes British Orienteering and the Board all the best for the future.
Chair of the Board, Drew Vanbeck stated: "On behalf of the Board of Directors and of British Orienteering, I extend our sincere appreciation to Graham for his contribution to the sport and personally I look forward to continuing to have the benefit of Graham's wise counsel."
Drew added, "We are in the process of searching for individuals who can fill the vacancy created by Graham's resignation and that of Judith Holt who is due to step down from the Board at the next AGM after serving the full 9-year maximum as a director. If you are interested or know of someone who is prepared to volunteer and help British Orienteering develop and advance its strategic agenda please do not hesitate to contact me or the Chief Executive Peter Hart."
The next World Orienteering Day will take place on Wednesday 13 May 2020.
In 2020, between Wednesday 13 May and Tuesday 19 May 2020, any activity held can be registered as a World Orienteering Day event.
The International Orienteering Federation´s goals regarding the organisation of this annual event are as follows:
Visionary course of action
Each club of all national Orienteering Federations gets in touch with at least one school. As teachers might need help to implement orienteering so the lessons are a fun and exciting experience, the IOF is working on providing teaching materials in different languages.
Find out more here.
Paul Murgatroyd, Head Coach for Talent, says:
"A truly phenomenal season for GB's juniors, with record breaking achievements at the Junior World Championships in Denmark in July, supported by some further strong performances at both European Youth Orienteering Championships and Junior European Cup in June and September respectively, is shown in a film."
Watch the film here.
British Orienteering looking to appoint a number of volunteer support roles to work with the Senior Squad for 2019. Roles are available to support the squad to prepare for and at IOF World Cups and the Nokian Tyres World Orienteering Championships.
A second Senior Squad Manager position is available to support the senior squad in 2019. The position will work alongside the incumbent Senior Squad Manager Ed Nicholas to support the athletes to prepare effectively for competitions and access appropriate training opportunities. This will be achieved by coordinating inter-squad communication and assisting athletes in identifying and communicating with clubs and coaches willing to support them.
Senior Squad Manager Role Description
This role is to be completed using communication tools and no expenses are available without prior arrangement.
Nokian Tyres World Orienteering Championship
Ostfold, Norway
World Cup 4
There are 2 positions available at each competition. For consistency, it is preferential that the positions are filled by the same people at both competitions. However, we will consider all offers of support.
Team Manager
As Team Manager you will coordinate the GB team attendance at competitions aiming to provide, as far as possible, a stress-free competition experience for the team. You will have experience of coordinating team attendance at international competitions and be able to provide time in advance of the competition to coordinate team entries and logistics.
Team Manager Volunteer Role Description
Technical Support
As Technical Support Volunteer you will work with the Team Manager to support athletes, as far as possible, to deliver their best performances at the competition. You will provide coaching/mentoring support and assist with training for athletes who require it whilst at the competition.
Technical Support Volunteer Role Description
For an informal discussion about a position please contact Craig Anthony on 07342 882530 or Ed Nicholas via email email@example.com. To apply please submit a short statement indicating your experience in relation to the role description by Sunday 13th January to firstname.lastname@example.com. Potential appointees will be asked to take part in an informal telephone interview.


text:
Silt woman on her bed when car crashes into bedroom
Post Independent Staff
Glenwood Springs, CO Colorado
SILT, Colorado – Ethel Richards surprisingly let out a giggle as she spoke about a car that smashed through her bedroom wall Wednesday night, while she was sitting on her bed.
"It was scary," said 83-year-old Richards. "You hear about these things but you never think they will happen to you."
Richards said that she was watching the news about 9:30 p.m. just before going to sleep, as she does every night, when a car crashed through her closet.
"It came right through the bedroom wall," she explained. "Right through the closet. It scared me to death."
She had just gotten up to get some popcorn and was sitting on the edge of the bed when the horrifying crash occurred.
"If I'd been in bed those closet doors would have hit me," she said.
Richards, who has lived her entire life in Silt, lives at the corner of Ballard Avenue and North Seventh Street – just two blocks up from the police station. She recalled the loud engine revving as it lay wedged in the wall of her home – like a large, steel, beached whale.
A neighbor came running over and turned the vehicle's engine off.
James Morrell, 52, was arrested by Silt Police and charged for allegedly driving under the influence of alcohol and reckless driving. Morrell was booked at the Garfield County Jail Wednesday night but bonded out Thursday about 5 p.m. on a $1,750 bond.
"All I could think about was picking up the phone and running," Richards said.
She called her son, who lives close by, and he quickly came to her aid. By Friday afternoon, Richards was working with the insurance company to get her house fixed. Her son had already put up plywood sheets to cover the gaping hole in the wall.
The closet doors were ripped off and a new air conditioner , still in the box, now has a big dent in it. A lamp and end table near the closet were untouched.
Ironically, Richards just added the bedroom to her home only two years earlier.
"He could have gone all they way through," she said.
According to Richards, the car missed her home's gas meter by about two feet.
Burning Mountains Fire Protection District Chief Brit McLin said that crews showed up to secure the scene and contacted Xcel Energy to shut off the power for safety reasons. The structure was deemed livable, power was restored, and Richards was allowed back into her home of 14 years. The bedroom still doesn't have electricity.
She said she never thought this type of thing would happen to her, but she was happy that no one was hurt.
"I'm OK," she said. "It could have been much worse."
She laughed saying that she has a good story to tell her friends now. But on Wednesday night she wasn't laughing at all. "It was very scary."
Dale Shrull contributed to this story.
Start a dialogue, stay on topic and be civil.
If you don't follow the rules, your comment may be deleted.
The final four: Glenwood Springs police chief candidates talk policing philosophies at community meet and greet
Thirty-six candidates applied for the Glenwood Springs chief of police position. None of the candidates were from within the Glenwood Springs Police Department.


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text: Chris Lattner wrote: > On Apr 30, 2009, at 9:38 AM, David Greene wrote: >> On Wednesday 29 April 2009 19:22, Chris Lattner wrote: >>> On Apr 29, 2009, at 8:39 AM, David Greene wrote: >>>> This patch changes the LLVM API. We should have a process for >>>> deprecating >>>> obsolete interfaces before removing them entirely. It's a >>>> significant >>>> maintenance headache to pull down a new release and fix all of the >>>> API >>>> issues along with tracking down new bugs introduced. >>> No, we make no attempt at being API compatible across revs of LLVM. >> That's a huge mistake going forward if we want to grow the community. > > Perhaps. However, I greatly prefer to make life easier for people who > contribute code (by preventing them from having to worry about > deprecation etc) than for those who don't. Reducing the barrier to > contributing code is a good way (IMO) to encourage contributions and > new developers. Perhaps, but it's a barrier for those who actually want to use LLVM's JIT. We'd love to keep up with the latest versions of LLVM, but stuff just keeps breaking and sometimes features are just deleted. For example, it used to be possible easily to turn on and off asm dumping, but it isn't any more. Andrew.


text:
- Publications
- Influence
Claim Your Author Page
Ensure your research is discoverable on Semantic Scholar. Claiming your author page allows you to personalize the information displayed and manage publications.
- Artur Jabłoński, Karolina Matczak, +13 authors Konrad Kowalski
- Molecules
- 2017
The synthesis of four cymantrene-5-fluorouracil derivatives (1-4) and two cymantrene-adenine derivatives (5 and 6) is reported. All of the compounds were characterized by spectroscopic methods and… (More)
Encapsulated doxorubicin armed with gH625 peptide does not damage normal endothelial cells as free doxorubicin
- K. Durka, Beata Gutarowska, +4 authors Janusz Hermann
- 2010
Effect of pirolin and doxorubicin on mitochondrial membrane potential in MCF-7 and MDA-MB-231 breast cancer cells
- K. Durka, Beata Gutarowska, +4 authors Roman Kołacz
- 2010


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text:
Kapag Ikaw ay Natutukso // When You Feel Tempted
MP3•Episode home
Manage episode 246161329 series 1037278
By Adventist World Radio - asia and firstname.lastname@example.com (AWR). Discovered by Player FM and our community — copyright is owned by the publisher, not Player FM, and audio is streamed directly from their servers. Hit the Subscribe button to track updates in Player FM, or paste the feed URL into other podcast apps.