Increased Cellulosic Ethanol Productivity Through Enzyme Recycling and Yeast Cells Reuse
Cellulosic ethanol is produced from non-food based feedstock such as corn stover, the leaves and stalks of corn. This feedstock contains lignocellulose (cellulose, hemicellulose, and lignin), which must be hydrolyzed to release sugars, which are converted to ethanol. Three major issues impeding commercial production of cellulosic ethanol are high enzyme loading requirements, slow xylose fermentation, and low ethanol production. Researchers at MSU have developed a novel process that overcomes these production issues by recycling enzymes and reusing yeast cells. This reduces production costs and increases physical plant output significantly.
A novel process has been developed that overcomes all three problems with pre-processing of cellulosic biomass. With this process, the lignocellulosic biomass is hydrolyzed in less than 24 hours. The easily hydrolyzed part of the biomass is converted to fermentable sugars. This fast hydrolysate is removed from the solids and fermented to ethanol. Meanwhile, the unhydrolyzed recalcitrant solids (with bound enzymes) are cycled through subsequent hydrolysis cycles. Thus, easily digestible biomass is processed and removed for production of ethanol, while recalcitrant biomass is given more time to hydrolyze. Recycling unhydrolyzed enzymes bound to the solids reduces enzyme input costs. In addition, after fermentation, yeast cells are also recycled, further reducing costs. With this process, cellulosic ethanol plant output is increased 2 to 3 fold.
- Lower production costs as a result of reduced enzyme loading
- Less feedstock waste due to increased output efficiency
- Increased production rate
- Reduced capital investments since fewer fermenters are required
- Abundant availability of non-food based feedstocks
- Production of biofuel
- Lignin production (useful in carbon fiber production)
Thomas Herlache, Assistant Director, Michigan State University, herlache@msu.edu