Fig. 1. Processing of Biomass to Bioethanol
Traditionally, most of processes are based on acid hydrolysis of the lignocellulosic materials. The acids includw sulfuric acid, phosphoric acid, formic acid, hydrochloric acid, etc. Concentrated acid hydrolysis can process at ow temperature and achieve high monoer sugar yield. However, it cause significant equipment corrosion and requires energy-demanding acid recovery. Therefore, dilute acid hydrolysis has been studied intensively and still a major process to produce sugars from biomass. Its advantages include low acid consumption, short reaction time: 2-10 min. But the aisadvantages are high reaction temperature (170-220 C), low sugar yield due to sugar decomposition, equipment corrosion, by-product innhibition.
During the last decades, process based on enzymatic hydrolysis has attracted increasing attention due to more selective hydrolysis and the formation of less-by-products. It uses cellulase mix (Cellulase with b-glucosidase etc.) to enzymatically hydrolyze cellulose to monomer sugars. The aximum cellulase activity usually occurs at 50 ±5 0C and a pH of 4.0-5.0. The advantages of enzymatic hydrolysis includes low temperature, specific conversion of cellulose, and high yield and less toxic compounds formation than acid hydrolysis. But the problems still exsiting for this process are the slow conversion cellulose to sugars due to the matrix of hemicelluloses and lignin as well as enzymes. As mentioned before, it needs pretreatment step to expose cellulose or modify the pores in the materials to allow enzymes to penetrate into the fibers and hydrolyze the cellulose to monomer sugars.
No comments:
Post a Comment