SELECTIVE SEPARATION OF VALERIC ACID FROM DIBASIC ACIDS USING SUPERCRITICAL CARBON-DIOXIDE

Separations of coproduct valeric acid from mixed dibasic acids is esse ntial for a new process of producing adipic acid for nylon production. The batch fractionation of valeric acid from mixtures of valeric acid and dibasic acids consisting of methyl glutaric acid and ethyl succin ic acid was carried Out with supercritical carbon dioxide using a cont inuous flow saturation apparatus. Phase equilibria of valeric acid and mixtures of valeric acid with methyl glutaric acid with supercritical carbon dioxide were measured in the range 35-65 degrees C and 68-140 bar. Apparent equilibrium of a mixture of valeric acid, methyl glutari c acid, and ethyl succinic acid with carbon dioxide is also reported. A high-pressure view-cell allowed visual observation of the number of phases present. Results indicate that highly selective removal of vale ric acid is possible from the mixtures of dibasic acids using supercri tical carbon dioxide at 50 degrees C and 90 bar, with loadings of vale ric acid close to 0.1 mol %. Solubility of valeric acid in the fluid p hase was increased to almost 6.5 mol % at 50 degrees C and 138 bar but with a decrease in the selectivity for valeric acid. The data obtaine d were correlated using the Peng-Robinson equation with conventional q uadratic mixing rules.