The recovery process and esterification method can be  applied to producing chemical feedstock molecules from  free carboxylic acids derived from a fermentation broth.  An  advantage of the present invention is that one can use free  carboxylic acids directly from a fermentation broth and  generate corresponding esters therefrom without the need to  isolate or purify the acids from the fermentation broth, as is  necessary in conventional extractions from broth. In com› parison to certain fermentation processes that neutralize or  convert the carboxylic acids to their salts, the present  process provides an easier way to isolate and extract car› boxylic acids from a fermentation broth. The present process  eliminates a need for titration and neutralization of the  fermentation broth that can precipitate metal salts, and  certain purification steps to produce a stock platform chemi› cal. The free carboxylic acids are converted into esters,  which are simpler to process and extract by distillation or  other purification techniques without the use of expensive  and complicated chromatographic separation colunms or  resins. For instance in a conventional process, one would  need to use ion exchange chromatography to isolate the  acids. A small amount of salts may unavoidably carry-over  after the ion exchange. Hence, one may require multiple  units of operation to purify the acid to an acceptable quality  level. With each added operational unit the costs of the  overall process increases. Moreover, in synthesizing the  ester of the acid, one can recover the salt as a carbonate or  hydroxide, which can be used to regenerate the fermentation  broth, and minimize waste. By converting the organic acids  to their corresponding esters, we can avoid such issues.  In general terms, the present esterification method  involves a reaction of fermentation-derived, free organic  carboxylic acid with an alcohol in a carbon dioxide (CO$_{2}$ )- predominant atmosphere in substantial absence of any other  acid catalyst to produce esters. The esterification reaction is  performed in solution under conditions that are either at  supercritical, critical or near critical temperatures and/or  pressures for at least one of the alcohol or CO$_{2}$ .  Under such  conditions, we believe that CO$_{2 }$ self-generates or functions  in situ as an acid catalyst, and regenerates back after the  esterification reaction is completed. It is believed that a  reactive intermediate (monoalkylcarbonic acid) is being  made in situ in large enough quantities to drive esterification  and affect ester production. This intermediate, having a  similar pKa ( e.g., -4-5) as the free carboxylic acid, functions  as a carbonic acid, which is much weaker than the usual  strong acids. The observed trend of greater ester conversion  at higher temperatures adduces a relatively large energy of  activation for this process. As used herein, the term "sub- stantial absence" refers to a condition in which an acid  catalyst is either largely or completely absent, or is present  in de mininmis or trace amount ofless than catalytic efficacy.  In other words, no other acid catalyst is present, or is present  at a level less than 10%, 5%, 3%, or 1 % weight/weight  relative to the carboxylic acid in the reaction.  An  advantageous feature of the inventive process is that  activation of the free carboxylic acid as an acyl halide (e.g.,  fluoride, chloride, bromide) or by using strong mineral acids  is Uilllecessary. Acy! halides are inconvenient to use because  these species are inherently reactive, have issues with sta› bility, waste treatment, and can be cumbersome and costly to  make.  In the present process, carbon dioxide functioning as a  catalyst instead of the usual strong acids removes the need  to introduce a strong acid into the esterification reaction.  This feature can circumvent the usual need to adjust pH  values in order to remove the catalyzing acid, enabling a  simpler and cleaner synthesis. One can simply proceed to  filter the resultant product to remove alkali or alkaline earth  metal carbonate or other salts. A cleaner product will save  costs in purification and downstream processing for conver› sion to other chemical feedstock.  The process described herein is a more environmentally  benign way of producing esters. As it is believed that the  carbon dioxide can self-generate an acid catalyst in situ in  the presence of the alcohol during the esterification reaction,  the present method does not require the use or addition of  another acid catalyst species. In other words, the reaction  kinetics with CO$_{2 }$ alone can drive the esterification in the  substantial absence of any other acid catalyst. To reiterate,  the present process does not require activation of free acids  as, for example, an acyl chloride or by strong acids (i.e.,  Fischer esterification).  In general, the esterification is conducted at an operational  or reaction temperature between about 150°  C. to about 250°  C., at a reaction pressure of between about 400 psi and 2,500  psi or 3,000 psi (gauge), for an extended period, such as  about 4 hours, up to about 12 hours. Typically, the tempera› ture can be in a range between about 170°  C. or 190°  C. to  about 230°  C. or 245°  C. (e.g., 175°  C., 187°  C., 195°  C. or  215°  C.), and the operational pressure is between about 900  psi or 950 psi and about 2,200 psi or 2,400 psi ( e.g., 960 psi,  980 psi, 1020 psi or 1050 psi). Alternatively, the temperature  can be in a range between about 180°  C. to about 245°  C.  (e.g., about 185°  C. or 200°  C. or 210°  C. to about 220°  C.  or 235°  C. or 240°  C.), and the operational pressure is  between about 1000 psi and 2.350 psi (e.g., 1,100 psi, 1,200  psi, 1,550 psi, 1,750 psi, 1,810 psi, or 1,900 psi). Other  temperatures may be within a range, for example, from  about 160°  C. or 185°  C. to about 210°  C. or 225°  C., and  other operational pressures may be within a range, for  example, from about 1,150 psi or 1,500 psi to about 1,800  psi or 2,000 psi.  These reaction temperatures and pressures correspond to  supercritical, critical or near critical conditions for the  alcohol( s) or CO$_{2}$ .  Table 1 lists, for purpose of illustration,  critical parameters for some common solvents (i.e., metha› nol, ethanol, 1-propanol, 1-butanol, water, and CO$_{2}$ ).  7  US 9,834,531 B2  8  Conventionally, esters are produced when carboxylic  acids are heated with alcohols in the presence of an acid  catalyst. The mechanism for the formation of an ester from  an acid and an alcohol are the reverse of the steps for the  acid-catalyzed hydrolysis of an ester. The reaction can go in  either direction depending on the conditions used. In a  typical esterification process, a carboxylic acid does not  react with an alcohol unless a strong acid is used as a  catalyst. The catalyst is usually concentrated sulfuric acid or  hydrogen chloride. Protonation makes the carbonyl group  more electrophilic and enables it to react with the alcohol, 45  which is a weak nucleophile. 