Acetic Acid Removal From the Hydrolysate Using Reactive Extraction In a Membrane Extractor/Reactor

Production of bioethanol from lignocellulosic biomass requires pretreatment of the biomass to hydrolyze hemicellulose, separate lignin and reduce cellulose crystallinity. During the pretreatment by dilute acid hydrolysis, several grams of acetic acid per liter of hydrolysate is generated. Acetic acid needs to be removed from the hydrolysate since it can dramatically reduce the efficiency of the subsequent fermentation step by inhibiting enzyme activity. Lime treatment, the current method of hydrolysate detoxification, consumes significant quantities of calcium hydroxide, involves solids handling and does not produce any valuable products.

We propose to remove the acetic acid with an alternative process whereby acetic acid is extracted into 1-octanol in a membrane extractor and reacted with 1-octanol in situ using a membrane containing an embedded catalyst to yield 1-octyl acetate. Acetic acid concentration in the hydrolysate will be reduced from 12.5 g/L to < 1 g/L. The product ester will be removed periodically from the organic phase. The product has very good solvent properties and can be sold to improve process economics.

In our study, we prepare membranes with a suitable catalyst (initial efforts utilize strong acid ion exchange resins) embedded in the membranes to achieve extraction and reaction in a single step. The effects of catalyst concentration, operating temperature and flow rates are investigated to optimize the performance of the process. Thus, the membrane extractor/reactor removes acetic acid from the hydrolysate and produces a valuable by-product in an environmentally friendly process.