Study On Enhancing Hydrolysis Of Lignocellulosic Biomass By NaOH/Urea Pretreatment

The economic dependency on fossil fuels and the resulting effects on climate and environment have put tremendous focus on utilizing fermentable sugars from lignocellulose, the largest known renewable carbohydrate source and significant environmental benefits. However, there still exist some problems in the pretreatment, such as, formation of toxic substances and operated at high pressure or high temperature. The high costs for pretreatment and enzymatic hydrolysis currently deter the commercialization of lignocellulose bioconversion processes. Lignocellulosic biomass, including energy plants, soft wood, crops and tobacco, pretreated by using sodium hydroxide/urea was studied in this paper. The results were summarized as follows,1. The substrate enzymatic digestibility(SED) of grass-like plants, including miscanthus, saccharum spontaneum linn, wheat straw and corn straw, was improved significantly by Na OH/Urea pretreatment at low temperature. Espacially, the SED of tobacco leaf pretreated by Na OH/Urea increased to 99.48%. Pretreatment performance of Na OH/Urea is better than that of organosolv pretreatment, including acetone or benzene/ethanol/aether.2. The SED of masson pine pretreated by Na OH/Urea was 13.5% higher than that pretreated by dilude acid. Both Na OH/Urea and dilude acid pretreatment can efficiently convert cellulose I to cellulose II. SEM shows that structure of masson pine pretreated by dilude acid still tight due to the low removal rate of lignin. However, Na OH/Urea effectively removed more lignin and resin, and also recovers more cellulose and hemicellulose in solid state, thus could enhance the sugar platform conversion process. It shows that structure of masson pine pretreated by Na OH/Urea collapsed significantly and crystallinity decreased. Lignin in masson pine have higher ratio between guaiacyl and syringyl structural units than that in masson pine pretreated by dilude acid.3. The optimized conditions of Na OH/Urea pretreatment for miscanthus are: dosage of Na OH 6wt%, dosage of urea 12 wt%, temperature 21°C and liquid-to-solid ratio 10 mL?g-1. The removal rate of lignin and hemicellulose was increased when pretreatment temperature or Na OH dosage was increased. It was found that galactose in hemicellulose side chain was easy to be removed firstly in the pretreatment. The effect of the Na OH dosage in different chemical substances removal rate were lignin, xylan, araban, galactan in turn. The enzymatic hydrosis of miscanthus that pretreated under room temperature was improved most significantly by adding 12wt% urea. It is supposed that urea hydrates serve as hydrogen bonding donor and receptor to prevent lignin droplets deposit on cellulose, thus enhanced enzymatic hydrolysis of miscanthus. It is revealed that lignin removal rate increased when urea dosage was increased. Conversely, hemicellulose removal rate decreased when urea dosage was increased.