Recovery of succinic acid by integrated multi-phase electrochemical pH-shift extraction and crystallization

Abstract

This work presents a novel approach for the recovery of succinic acid from aqueous solutions by electrochemically induced extraction and crystallization. The suggested process allows purification by electrical energy via pH-shift downstream operations. Experimental results show that direct electrochemical extraction can recover succinic acid from aqueous solution containing approximately 50 g/L succinic acid at bulk pH of 5–7 without prior acidification by strong inorganic acid. Simultaneously, an alkaline solution was obtained from the cathode reaction, which can potentially reduce the base consumption for pH maintenance in succinic acid fermentation. Replacing salt waste generating base and acid addition by electrochemically operated pH-shift unit operations can provide more environmentally benign separation strategies for the production of bio-based succinic acid. Experimental examples for electrochemical extraction, back-extraction and crystallization are given. For extraction and back-extraction, a faradaic efficiency of 22–36% was recorded. Crystal size distribution of succinic acid from electrochemical crystallization was found to be comparable to commercially available succinic acid. Based on the experimental results we suggest a concept for the recovery of solid succinic acid from aqueous solution and pH-control in fermentation by a series of four electrochemical downstream operations, which can be coupled into two electrochemical cells. This process layout enables operating fermentation at optimal pH for maximal space-time-yield and independent pH-shift separation in the downstream, while product losses can be minimized by closed recycle streams. In the long-term perspective, electrochemical unit operations provide a way to utilize electricity for the purification of carboxylic acids.