An update of the ZeaChem process for increased ethanol production

The technical and economic investigation of the ZeaChem process for increased production of ethanol from sugar process streams has been completed at SRI and this paper reports on these investigations. The main benefit of the process is the theoretical increase in ethanol production by up to 50% per unit dextrose sugar feed. The ZeaChem process utilises bacteria to convert fermentable sugars to acetic acid either in a one step direct fermentation process or in a two step fermentation process via lactic acid. The production of lactic acid can provide an additional revenue source from the sale of single cell protein produced in the two step process. After fermentation, the acetic acid is extracted from the fermentation broth in an acid recovery stage, esterified in a reactive distillation process and converted to ethanol by hydrogenolysis. The ZeaChem process has four main production stages. In order to achieve high yields of ethanol, high yields are required for each stage of the process. High yields are obtained for each stage of the process. Several sugar process streams were considered for the process and these included clarified juice, syrup, A molasses, B molasses and C molasses. However, the fermentation process is inhibited if C molasses only is used as feed. Large dilutions of C molasses are required to obtain high yields during the fermentation stage. The reasons for the inhibition of the fermentation of C molasses are not understood and should be targeted in further laboratory scale testing, while the project is progressed to pilot plant trials. The evaluation of the ZeaChem ethanol process has confirmed the potential of the process to achieve significantly higher yields than the conventional yeast fermentation process.