(447g) Energy Efficient Solvent Recovery Via Reactive Distillation

Reactive separations are powerful technologies for separation of azeotropic multicomponent carboxylic acid mixtures. By reducing the boiling point and the enthalpy of evaporation via chemical reaction energy savings can be achieved and separation into pure constituents is possible.

Waste from the pulping industry may be a perfect feedstock material for biobased chemicals. The black liquor thickening condensate for example contains acetic acid and formic acid. Liquid-liquid extraction is perfectly suited for the wastewater treatment of this condensate to remove the carboxylic acids with low energy demand. But the solvent recovery is normally done by energy intensive distillation and additionally, the crude distillate is an azeotropic multicomponent mixture. By extending the solvent recovery to reactive distillation with an appropriate reactive agent, the energy demand can be reduced by lowering the boiling points and the enthalpy of evaporation of the reaction products. Esterification with methanol as example produces the low boiling methyl esters methyl formate and methyl acetate with an enthalpy of evaporation four times smaller compared to water. The combination of distillation and chemical reaction may lead to complete conversion by shifting the equilibrium of the esterification reaction to the product side via continuous removal of the products. The elevated temperature in the reboiler enhances the reaction rates whereby the application of a catalyst is not mandatory. Additionally the reaction products have higher market values compared to the carboxylic acids. Reactive distillation experiments in batch and continuous mode showed complete conversion of formic acid. Acetic acid is converted to a lesser extent. Methyl formate can be isolated in high grade quality in a first step. For acetic acid removal different routes are applicable. Exemplarily acetic acid conversion may be completed and methyl acetate removed from the solvent in a second step.