Patent ID: 7667068

Claim:
A process for the continuous esterification of citric acid to produce a citric acid tri-ester in a vertical column by reactive distillation and to reduce by-products comprising: (a) feeding a mixture comprising the citric acid as an aqueous or alcoholic solution into an upper port of the column and an alcohol containing 1 to 8 carbon atoms into a lower port of the column; (b) contacting in a reactive distillation the citric acid and the alcohol in countercurrent flow in a reaction zone between the ports at a temperature between 80 and 120° C. which reacts the citric acid and the alcohol over an insoluble acid catalyst, wherein the catalyst is: (i) mounted in structured packing elements and (ii) supported in the column as a single unit of the structured packing elements within the reaction zone to form the citric acid tri-ester; (c) removing vaporized unreacted alcohol and water from the top of the column; (d) collecting a product comprising the citric acid ester from the bottom of the column, wherein the citric acid ester is mixed with about 20 to 40% by volume of the alcohol and is reboiled in a reboiler in part into the bottom of the column and in part collected as the alcohol and the citric acid ester, and wherein the reboiler is maintained at a temperature such that the presence of alcohol exists in the composition in the reboiler and the reboiled composition maintains the temperature at the bottom of the column below a temperature that causes the citric acid or the citric acid esters to form byproducts; wherein the feeding of the alcohol relative to the feeding of the citric acid is such that the percentage of citric acid conversion to a tri-ester is greater than 50 percent.