Two-step acid hydrolysis process kinetics in the saccharification of low-grade biomass: 1. Experimental studies on the formation and degradation of sugars

Two-step acid hydrolysis studies were performed on various types of low-grade biomass, such as bakery waste, grain dust, wood chips and wheat straw. These wastes contain predominantly starch, cellulose, hemicellulose, or combinations of these carbohydrates. The hydrolysis conditions for each step were determined by using pure starch and cellulose as substrates. Starch and hemicellulose were hydrolyzed at 132°C for 40 min using 2% H2SO4. Cellulose was hydrolyzed at 132°C for 70 min using 15% H2SO4. Dilute acid hydrolysis of bakery waste provided 92% conversion to glucose with no xylose in the hydrolyzate. In the case of wood chips, grain dust and wheat straw, substantial quantities of xylose were obtained at the end of the second hydrolysis step. Bakery waste has good potential for use as a feedstock for the production of chemicals due to the high yield of almost 80 g glucose/100 g substrate. Two-step hydrolysis gave 40–50 g of total sugars/100 g of substrates in the case of wood chips, grain dust and wheat straw. The observed trends for starch and cellulose hydrolysis indicate that the conversion of biomass to sugars can be maximized by using a two-step hydrolysis process.