US 10,118,886 B2  11  12  FIG.  2  shows a schematic diagram of a downstream  processing that incorporates an iteration of the present  esterification process. In particular, FIG.  2  depicts an  example of using succinic acid or any other kind of carbox› ylic acid derived from a fermentation broth is extracted and  reacted with an alcohol in the presence of excess CO$_{2 }$ to  generate esters. According to this iteration of the process,  glucose, com steep liquor, or other sugars, and Mg(OH)$_{2}$ /  NaOH are introduced into a fermentation reactor  21  and  fermented  23  to produce carboxylic acids. A fermentation  broth liquid  25  containing a mixture of carboxylic acids,  salts (e.g., succinic acid and its sodium or magnesium salt),  and other by-products is filtered  27  to remove cell mass and  other insoluble matter  27a.  The fermentation is performed at  a low pH value, in which one starts at a higher pH ( e.g., pH  - 7 or 8) and during the course of the fermentation, the pH  value drops to about 2-3. One will produce a mixture of salts  and free acid present, for example, in a ratio range of about  9:1 w/w to 7:3 w/w of salt to acid. The fermentation broth  is retrieved from a fermentation reactor at a pH value of less  than the pKa of the carboxylic acids, (e.g., pH 5). Typically,  the fermentation broth is at a pH value in a range between  about 1.5 and about 4.5.  The broth extract is then dried  29  to a powder. When  drying the mixed acid filtrate should remove as much water  as possible. The drying step can be accomplished, for  instance, by means of spray drying, drum drying, or cryo› desiccation. As with esterification in general, relatively low  water content is desired, otherwise the reversible reaction  will tend to hydrolyze back to the dicarboxylic acid. In the  present process, a maximum residual moisture content of  about 5% by weight should be maintained. One would  expect an increase in ester yield of up to about 98 or 99%  with samples that contain less than 3% wt. of water.  The dried powder (average moisture content between  about 1 wt. % and 5 wt. %, desirably s3 wt. % ) is then  reacted  31  with an alcohol  33  which serves as an alkylating  agent, in excess CO$_{2 }$ at a temperature between about 180°  C.  to about 250°  C. for a duration of about 4 hours or more to  esterify the carboxylic acids. In this example, succinic acid  is reacted in methanol and CO$_{2 }$ to generate dimethyl succi- nate. Along with the free carboxylic acid, any remaining free  amino acids which were in the fermentation broth are also  esterified.  Once the carboxylic acid esters are generated and recov› ered from the fermentation broth they can be further pro› cessed as feed stock in either hydrogenation or hydrogenoly- sis systems. Hydrogenation or hydrogenolysis can be  conducted according to various different methods, systems,  and their permutations, such as described in U.S. Pat. No.  7,498,450B2 (relating to homogenous hydrogenation of  dicarbocilic acids and/or anhydrides), U.S. Pat. No. 6,433,  193B, or 5,969,164, (relating to a process for production of  tetrahydrofuran and y-butyrolactone by hydrogenation of  maleic anhydride); U.S. Pat. No. 4,584,419A (relating to  process for the production of butane-1,4-diol involving the  hydrogenation of a di(C$_{1 }$ to C$_{3 }$ alkyl) ester of a C$_{4 }$ dicar› boxylic acid); UK Patent Application No. GB2207914A  (relating to a process for production of a mixture of butane  1,4-diol, y-butyrolactone, and tetrahydrofuran from maleate  and fumerate);  International  Patent Application Nos.  WO8800937 A (relating to a process for the co-production of  butane-1,4-diol and y-butyrolactone by means of hydroge› nation of dialkyl maleate) or WO 82/03854 (relating to a  process for hydrogenolysis of a carboxylic acid ester), or an  article by S. Varadarajan et al., "Catalytic Upgrading of  Fermentation-Derived Organic Acids," BroTECHNOL. PRoG.  1999, 15, 845-854, the content of each of the preceding  disclosures is incorporated herein in its entirety by reference.  As the example illustrates in FIG.  2,  when reacted with  methanol in accord with the reaction temperatures and  pressure parameters defined above, succinic acid esterified  to produce dimethyl succinate (as predominant product),  NaHCO$_{3}$ ,  MgCO/Mg(HCO$_{3}$ ) 2  and excess methanol  35.  The dimethyl succinate and methanol  37  are separated from  NaHCO$_{3 }$ and MgCO$_{3 }$ 39.  The carbonates, unlike CaSO$_{4}$ ,  can be recycled  41  back into the reactor  21,  either for a  continuous process or in a fresh batch process. The dimethyl  succinate and methanol are further separated  43  from each  other with the methanol  33  being recycled  45.  Subsequently,  the dimethyl succinate  47  is subjected to either hydrogena› tion or hydrogenolysis  49  and transformed into a variety of  biofuel products  51,  including alkanes and/or alcohols, for  instance: ethane, ethanol, propane, propanol, butane, or  butanol.  Another advantage of the present process is that it can  simplify the transport and processing of crops for fermen- tation products. For instance, with a dried fermentation broth  powder one is freed from issues associated with working  with wet or liquid stock. A dried fermentation broth powder  can be more economically shipped to a location different  from where the fermentation broth is made or obtained. This  will enable the reaction for ester synthesis to be performed  at a remote location different from where the fermentation  broth is obtained, and expand the geography of where the  final processing facilities can be situated.  Section IL-Examples  A  Examples prepared according to the present esterification  method are integrated into a process for isolating free  carboxylic acid from a fermentation broth. The method  involves generally the following steps: a) filtering a crude  fermentation broth to remove cell mass and other biological  debris from a fermentation broth; b) desiccating the fermen› tation broth; c) reacting the dried fermentation broth with an  excess of methanol (CH$_{3}$OH) or ethanol (C$_{2}$H$_{5}$OH) and  carbon dioxide (CO$_{2}$ )  at a temperature about 150°  C. up to  the near critical or critical temperature and under near  critical or critical pressure of the alcohol and/or CO$_{2 }$ reagents, to produce a mixture of monoesters and diesters  and carbonate (NaHCO3/MgCO$_{3}$ );  d) filtering the reaction  product to remove by-products; and e) purifying by distilling  the esters.  The fermentation broth filtrate was dried to remove all or  nearly all of the water to produce a powder of mixed  organics. Using a spray dryer or  drum  dryer, one aerosolizes  the raw solution containing mixed carboxylic acids to des› iccate into a powder. The desiccated powder is suspended in 