Dilute acid hydrolysis of presscakes from silage and grass to recover hemicellulose-derived sugars.

Grass and silage presscakes from various types of raw materials were hydrolyzed with dilute acid at moderate conditions to recover hemicellulose-derived sugars. Extracting the material with cold water prior to hydrolysis significantly increased the yield. The poor performance without extraction was due to the high buffer capacity of the material. The best results were obtained with extracted grass and silage from a permanent pasture and extracted clover/grass silage. The highest observed sugar yield was 16.43 g/100 g dry-matter, which represents approximately 25% of the available sugars and 60% of the hemicellulose fraction. Including the soluble sugar oligomers, the yields were even higher (up to 20 g/100 g dry-matter). A statistical experiment design with extracted clover/grass silage was performed to estimate the effects of temperature, time, and dry-matter concentration. Acid and dry-matter concentration had the highest effect on sugar yield, whereas temperature and acid concentration were mainly responsible for forming sugar degradation products. These findings agree with recent kinetic theories. Yields in this experiment were comparable to those of other lignocellulosic materials.