Monday, April 30, 2007

Optimization of Ammonia Fiber Expansion (AFEX) pretreatment and enzymatic hydrolysis of Miscanthus x giganteus to fermentable sugars

Hannah K. Murnen1, Venkatesh Balan2, Shishir P. S. Chundawat2, Bryan Bals2, and Bruce E. Dale2. (1) Department of Engineering, Thayer School of Engineering, 8000 Cummings Hall, Hanover,, NH 03755-8000, (2) Department of Chemical Engineering and Material Science, Michigan State University, 2527 Engineering building, E. Lansing, MI 48824

Miscanthus x giganteus is a tall perennial grass whose suitability as an energy crop is presently being appraised. Most research conducted so far has focused on the crop yield per hectare, optimal climatic conditions, energy, water and nitrogen input needed for growth. It is clear that Miscanthus has several advantages as a renewable energy crop, the most notable ones being; high yield per hectare, high cellulose content, low water and nitrogen input. However, there is very little information on the effect of pretreatment and enzymatic saccharification of Miscanthus to produce fermentable sugars. This paper reports sugar yields during enzymatic hydrolysis from ammonia fiber expansion (AFEX) pretreated Miscanthus.  Pretreatment conditions such as temperature, moisture, ammonia loading, residence time and enzyme loadings are varied to maximize hydrolysis yields.  In addition, further pretreatments such as grinding and soaking the biomass prior to AFEX as well as washing the pretreated material were also attempted to improve sugar yields. The optimal AFEX conditions determined were 160 ºC, 2:1 ammonia loading, 70 % moisture (dry weight basis), and 5 minute reaction time for water soaked Miscanthus. Approximately 96% glucan and 85% xylan conversions were achieved after 168 hours hydrolysis of 1% glucan loading enzymatic hydrolysis (15 FPU/g glucan of cellulase and 64 p-NPGU/g glucan of b-glucosidase along with xylanase and tween-80 supplementation). A complete mass balance for the AFEX pretreatment and enzymatic hydrolysis process is presented.