SORPTION AND EXTRACTION OF LACTIC AND SUCCINIC ACIDS AT PH-GREATER-THAN-PK(A1) .2. REGENERATION AND PROCESS CONSIDERATIONS

As shown in part 1, carboxylic acids can be recovered from solutions a t pH > pK(a1) of the, acid by solid sorbents or liquid extractants tha t are sufficiently basic to maintain substantial capacities even at mo derately high values of pH. Appropriate extractants and sorbents can b e regenerated by back-extracting the acid into aqueous trimethylamine (TMA) solution, followed by thermal decomposition of the resulting tri methylammonium (TMAm) carboxylate. Polymeric sorbents and liquid extra ctants with tertiary amine functionalities are completely regenerable by leaching with aqueous TMA solutions. Fixed-bed breakthrough curves for the sorbent Dowex MWA-1 in both the uptake and regeneration modes are self-sharpening, and the regeneration curve displays a focusing ef fect. For acids having low-to-moderate solubilities thermal cracking o f the resultant TMAm carboxylate yields acid crystals and trimethylami ne vapor for recycle. Because lactic acid is more soluble and tends to self-esterify, simple cracking gives only partial regeneration. Anoth er approach is to react TMAm lactate with an alcohol to form the ester and TMA for recycle. The feasibility of this approach was demonstrate d through laboratory-scale experiments with n-butanol.