US 8,993,793  Bl  2  1  MULTIFUNCTIONAL MESOPOROUS SILICA  CATALYST  REFERENCE TO RELATED APPLICATIONS  GOVERNMENT FUNDING  BACKGROUND OF THE INVENTION  This application claims priority under 35 U.S.C. 119(e)  from U.S. Provisional Application Ser. No. 61/441,076 filed  Feb. 9, 2011, which is incorporated herein by reference in its  entirety.  This invention was made with Government support of the  United States Department of Energy under contracts  DE-AC02-07CH11358 and DE-SC0001298. The United  States Government has certain rights in this invention.  Recently, advances have been made which strike a more  desirable balance between maintaining fuel efficiency and  reducing the percentage of particulate emissions in fuels  through the use of blends of petroleum based fuel with alkyl  esters of the fatty acids contained in vegetable oils or animal  fats. These alkyl esters are commonly referenced to as  "biodiesel". Substantially pure alkyl esters, such as methyl or  ethyl esters of fatty acids, are generally preferred in biodiesel  over the use of the vegetable oils and animal fats themselves  because the alkyl esters have a viscosity that is more appro› priate to diesel fuel. Through the use of these fuel blends,  researchers have attained reductions in particulate emissions  from diesel engines [1]. The production of biodiesel has  received also extensive interest as a result of this fuel’s desir› able renewable, biodegradable, and nontoxic properties [2].  These fatty acid alkyl esters can be prepared by the trans› esterification of triglycerides in vegetable oils with short› chain alcohols ( e.g., methanol and ethanol) using homoge› neous alkali catalysts such as alkoxides. For example, soy  diesel (methyl soyate) is made commercially by an energy  and labor-intensive process wherein soybean oil is reacted  with methanol at 140-150°  F. ( sometimes under pressure) in  the presence of sodium methoxide. Isolation of the desired  methyl soyate from the highly caustic (toxic) catalyst and  other products such as glycerol, involves a precise neutraliza- tion process with strong acids, such as hydrochloric acid  (HCl), and extensive washes with water to remove the result› ing sodium chloride (NaCl) salt. Also, because of glycerol’s  high boiling point, it must be separated from the sodium  chloride salt by vacuum distillation in an energy intensive  operation. As more alkyl soyates with different alkyl func› tional groups, such as ethyl and isopropyl soyates, are being  rapidly developed to meet the growing needs of various appli› cations, the level of difficulty in separating the corresponding  catalysts, e.g., sodium ethoxide and sodium isoproxide cata- lysts, respectively, will unavoidably escalate due to the  increasing solubility of these basic catalysts in the reaction  mixture. Therefore, biodiesel is currently not cost competi› tive with conventional diesel fuel.  To improve the economic outlook of biodiesel and alkyl 60  esters in general, the feedstock selection becomes critical. In  particular, feeds containing high free fatty acid content, such  as found in beef tallow or yellow grease, are significantly less  expensive than vegetable oils, such as soybean or rapeseed oil  [3]. These high free fatty acid feedstocks present significant  65  processing problems in standard biodiesel manufacture since  the free fatty acid is saponified by the homogeneous alkali  Lin et al. (U.S. Pat. No. 7,122,688) discloses a method for  transesterifying glyceride containing oils by combining a  glyceride-containing vegetable or animal oil such as soy oil,  a C$_{1 }$-C$_{3 }$ alcohol, and an acidic mesoporous silicate under  conditions so that the mesoporous silicate catalyzes forma› tion of the corresponding fatty acid (C$_{1 }$-C$_{3}$ )  alkyl ester and  optionally, glycerol, and wherein the silicate comprises sul- fonic acids, sulfinic acids, phosphoric acids, phosphinic  For example, mesoporous catalysts containing sulfonic  acid groups and, optionally internal methyl groups have been  reported to be efficient catalysts in the esterification of glyc› erol with fatty acids, where high yields of mono-esters are  obtained [26].  For example, organic-inorganic hybrid mesoporous silicas  formed by co-condensation with thio-containing silanes, fol› lowed by oxidation of the SH groups yield pores functional- ized with sulfonic acid groups. The direct co-condensation  synthesis technique in which the mesostructure and func› tional group are simultaneously introduced, appears to be a  desirable route for incorporating functional groups because it  has been shown that it increases the concentration of the  sulfonic groups in the mesoporous silica relative to post› formation grafting [24]. One approach demonstrated previ› ously involves one-step synthesis based on the simultaneous  hydrolysis and condensation of tetraethoxysilane (TEOS)  with 3-(mercaptopropyl)trimethoxysilane (MPTMS) in the  presence of template surfactant using in situ oxidation of the  thiol groups with H$_{2}$ 0 2 .  Melero et al. has shown that the acid  strength of the sulfonic groups in the mesoporous materials  can be adjusted by choice of the organosulfonic precursor  [25].  Surfactant-templated  mesostructured  materials  have  received a great deal of attention as potential catalysts, sen› sors and adsorption agents owing to their combination of  extremely high surface areas and ordered, flexible pore sizes.  For example, mesoporous sieves of the type MCM-41 are  prepared by thermal treatment of silaceous gels formed by the  polymerization of alkoxysilanes around surfactant micelle  templates in aqueous base, followed by removal of the sur› factant to yield a matrix comprising fine pores in a cylindrical  array. The physical and chemical properties of these mesopo› rous materials can be modified by incorporating functional- ized organic groups, either by grafting on the preformed  mesopore surface or by co-condensation using functionalized  substituted trialkoxy silanes during synthesis [7-23]. Not  only can such catalysts be easily separated from the products  and recycled, but their large surface area (>700 m $^{2}$/g), defined  pore structure, tunable pore diameter (2-10 nm) and narrow  pore size distribution allow for precise regulation of the mass› transport properties that are crucial for many chemical trans› formations. Several recent studies have demonstrated that the  selectivity and reactivity ofMSN-supported catalysts can be  enhanced by introducing multiple functional groups onto the  3D controlled mesoporous surface [8-11, 14, 16].  One approach for improving the processing of high free  fatty acid oils and fats is to first esterify the free fatty acids to  alkyl esters in the presence of an acidic catalyst such as a  mineral acid. The pretreated oils in which the free fatty acid  content is lowered to no more than 0.5 wt  % can then be  processed under standard transesterification reaction condi› tions [5]. This pretreatment step has been successfully dem- onstrated using sulfuric acid [ 6]. Unfortunately, use of the  homogeneous sulfuric acid catalyst adds neutralization and  separation steps, as well as the esterification reaction, to the  overall process.  catalyst that is used to transesterify triglycerides leading to a  loss of catalyst as well as increased purification costs [ 4]. 