Downstream separation and purification of succinic acid from fermentation broths using spent sulphite liquor as feedstock

Spent sulphite liquor produced as side stream from sulphite pulping of Eucalyptus globulus hardwood could be used for the separation of lignosulphonates by nanofiltration in the retentate stream and succinic acid production via fermentation of the permeate stream by Actinobacillus succinogenes or Basfia succiniciproducens. The potential integration of this process in conventional pulp mills towards the development of a novel biorefinery is dependent on the efficient downstream separation of succinic acid crystals at high yield and purity. This study focuses on the evaluation of five downstream separation processes, namely calcium precipitation, direct crystallisation using acidification or cation-exchange resins, salting-out and reactive extraction, for the purification of succinic acid from crude fermentation broths. Reactive extraction using trioctylamine in 1-hexanol and direct crystallisation coupled with cation-exchange resins led to succinic acid recovery yields of 73% and 79%, respectively. 1H NMR analysis showed that these downstream separation processes led to succinic acid crystal purities of ca 98.5% for reactive extraction and higher than 99% for the direct crystallisation method coupled with cation-exchange resins with no detectable acetic acid content when re-crystallisation was employed. It has been demonstrated that succinic acid produced via fermentation using side streams from pulp and paper mills could be separated at high purity and yield from crude fermentation broths rendering feasible its utilisation for poly(butylene succinate) production.