Ethanol Production via In-Situ Detoxification of Spent Sulfite Liquor

The spent liquor of sulfite pulping process contains a significant amount of monosugars. The objective of this paper is to investigate the performance of Saccaromyces cerevisiae in producing ethanol from the monosugars of spent sulfite liquor (SSL). The SSL contains lignosulfonate, furfural and acetic acid that are inhibitors of fermentation processes, and thus should be removed via a detoxification process. Model SSL solutions were prepared, and the removal of inhibitors was studied via the adsorption concept by using activated carbon (AC), precipitated calcium carbonate (PCC), or XAD-4 resin at pH 3.8 or 6. The results showed that AC was the most effective adsorbent with the removal of 100% furfural, 48% acetic acid and 70% lignosulfonate from SSL at pH 3.8. To produce ethanol, detoxification and fermentation can be subsequently conducted (pre-detoxification process) or combined in one process (in-situ detoxification process). In another set of experiments, the performance of these two processes was compared. It was revealed that the in-situ detoxification process produced slightly lower ethanol than the pre-detoxification process did, but the monosugar consumption was the same in both processes. It was concluded that the in-situ detoxification process can effectively minimize the negative effect of the inhibitors during the yeast fermentation process and that the yeast effectiveness was not decreased by the presence of AC. The slightly lower ethanol concentration in the in-situ detoxification process is caused by the fact that a small amount of ethanol adsorbed on the AC.