Monday, May 4, 2009
9-25
A new low capital process to convert municipal solid waste fiber into ethanol
Benjamin Levie1, Johnway Gao1, Jeff Mayovsky2, and Krishna Chundakkadu2. (1) Catchlight Energy LLC, 32901 Weyerhaeuser Way, Federal Way, WA 98001, (2) Weyerhaeuser, 32901 weyerhaeuser way south, Federal Way, WA 98001
Adequate enzymatic hydrolysis of paper from the municipal solid waste has been found by others to require intensive pretreatment which increases capital and operating costs and ultimately the minimum ethanol selling price. We have developed a low cost pretreatment specifically for waste paper which significantly reduces these costs as well as the potential for producing inhibitors to ethanol production. This patent pending approach makes use of differences in physical fiber characteristics to make an 80/20 split of a more hydrolyzable fiber and a smaller less hydrolyzable fraction of fiber that either can be pretreated by itself and added back in, or eliminated from the process entirely depending on economic analysis. A 200 kg mix of waste papers blended to simulate the concentrations expected in the waste stream based on California waste characterization studies was created, pulped, cleaned and fractionated using standard pilot scale sized equipment. Simultaneous saccharification and fermentation (SSF) of the more hydrolyzable fraction using Saccharomyces cerevisiae produced ethanol concentrations of 4% ethanol at 0.29 g/g untreated fiber at 14% solids loading within 68 hours 4% yields of 0.34g ethanol/g wet oxidated clean fiber within 52 hours at 12% solids loading using enzyme additions for both of only 20 FPU/g fiber. The smaller and less hydrolyzable fraction requires more pretreatment. The less hydrolysable fraction has about ½ the conversion in untreated state as more hydrolyzable fraction, but further cleaning (removal of ash) followed by a more concentrated wet oxidation or addition of surfactants before hydrolysis can optimize the overall process economics.