17702: A Novel Integrated Biological Process for Conversion of AFEX-CS to Ethanol Featuring High Ethanol Productivity, Enzyme Recycling, and Yeast Cells Reuse

There are two major problems in current cellulosic ethanol production process: low ethanol productivity and high enzyme loading. Based on the current Separate Hydrolysis and Fermentation (SHF) process, it takes at least 96h to perform enzymatic hydrolysis to convert AFEX-CS to fermentable sugars at 6% glucan loading. It will then take another 96-168h to ferment those sugars to ethanol. By simply integrating enzymatic hydrolysis and fermentation, which is SSCF (simultaneously saccharification and co-fermentation), it still requires at least 168h to reach comparable results as SHF.  

Here we will present a novel continuous SSCF process. In this process, the easily hydrolyzed part of biomass is converted to ethanol first, which can be done in 48h. The liquid is then harvested by centrifuge and subjected to distillation. The residue solids (difficult hydrolyzed part of biomass (DHPB)), which carries enzymes and yeast cells, are transferred to the next cycle. This way, enzymes and yeast cells are largely reused. After five cycles, the difficult hydrolyzed part is collected and SSCF is performed to convert it to ethanol. Since enzymes are accumulated to a relatively high concentration and part of the decomposition products are removed with liquid during the five cycles, the hydrolysis of DHPB would be easier to achieve high sugar conversion. Our results showed that ethanol concentrations produced in this process were all above 40g/L; the cellulosic ethanol production was shortened from 192h to 48h; enzyme loading was reduced by about 30%; ethanol yield was enhanced from 191.5g/kg AFEX-CS to around 205g/kg AFEX-CS.