[On Location at AIChE's 2011 Annual Meeting.] One effort to increase cellulosic ethanol production efficiencies using corn stover as feedstock involves a separation of and separate processing of the solid and liquid fractions of pretreated feedstock.
In addition to facilitating an increase in the productivity of ethanol fermentation and recovery, a spit stream process opens up the possibility of diverting the C5 stream to some potentially more lucrative bioproducts.
The stover is first pretreated with dilute acid. The liquids (C5 predominantly) are then separated from the solids (C6
predominantly). The liquid stream is then adjusted to pH 5.8 and then fermented. In aseparate trial, a 2-step process where the pH was first raised to 8.5 before being lowered was trialed, with negative results. The conclusion being that additional acetic acid, a known inhibitor, was formed at the elevated pH.
The solid phase undergoes enzymatic hydrolysis with Novozyme Cellic Clec2 at 48C for 120 hours, then the resultant is fermented.
SSF and a new, secret bioagent
Simultaneous Saccharization and Fermentation (SSF) is arecent approach to cellulosic ethanol production whereby multiple organisms/enzymes are used simultaneously, versus separately as in prior processes. However, with this separate stream process, a third organism, "Bacterium A" joins the party to assist in driving the conversion of xylose to ethanol in the liquid (C5) fraction. Yields without "Bacterium A" are unacceptably low.
The cellulosic (C6) portion of the fermentation proceeds in a predictable fashion, as all glucose is consumed (little inhibition-no pretreatment) and yields are constant. The goal of 85% conversion of glucan and xylan to ethanol (via glucose and xylose respectively) is also achieved. Energy use virtually the same, but water usage is slightly higher. Waste streams are mostly associated with the C5, so splitting the fractions reduces the volume of wastes produced. Dr. Aleandre Chapeaux presented the findings, and he can be reached at firstname.lastname@example.org.