Effect Of Rice Straw Prehydrolysate On Enzymatic Cellulose Hydrolysis And Its Resource Utilization

Bioconversion of cheap, renewable and abundant lignocellulosic biomass to produce biofuels or biochemicals is very meaningful in sustaining the development of our economy and society. In this dissertation, the effect of alkali lignin with different molecular weights on cellulase, the inhibition mechanism of inhibitors (phenolics) produced by pretreatment, alkali recycling, the separation and concentration of phenolics, and the membrane fouling mechanism during nanofiltration (NF) applied in dilute acid hydrolysate were systematically investigated. The main results can be sumaried as follows:(1) The effect of alkali lignins with different molecular weight on the enzymatic hydrolysis of lignocellulose was studied. The results showed that the addition of all the alkali lignins enhanced the hydrolysis of rice straw. The level of enhancement was related to the molecular weight of lignins. The level of enhancement was related to the molecular weight of lignins. Langmuir adsorption results showed that the alkali lignin with higher molecular weight had low affinity with cellulase. And the surface charge and hydrophobicity of alkali lignins also confirmed the results.(2) The effect of vanillin on cellulase activity for the hydrolysis of cellulose was investigated in detail. The results clearly showed that vanillin could reversibly and non-competitively inhibit the cellulase activity. Moreover, investigation of the effect of each group on phenyl ring of vanillin on cellulase activity demonstrated that aldehyde group and phenolic hydroxyl groups of vanillin had inhibitory effect on cellulase.(3) Lignin recovery from the alkaline rice straw hydrolyzate by ceramic ultrafiltration was investigated in terms of lignin retention and fouling mechanisms. The results showed that the relative higher cross-flow velocity and lower pressure led to less resistance and membrane fouling. The alkaline solution from ultrafiltration permeate was recycled for the pretreatment of fresh rice straw after simple pH adjustment. It was found that the reuse of alkali was feasible. The consumptions of NaOH and water were reduced by 42% and 50% respectively during pretreatments with reuse of alkali.(4) The separation and concentration of hydroxycinnamic acids from phenolic aldehydes were investigated using nanofiltration (NF) membrane with model solution and practical hydrolyzate. The results indicated that the separation performance of hydroxycinnamic acids from aldehydes was optimal at neutral pH. Salt and pH acted synergistic effect on phenolic aldehydes retention. When the practical alkaline hydrolyzate was treated under concentration-diafiltration mode, the purity of hydroxycinnamic acids was high up to 91.4%.(5) The influence of five pre-treatments i.e. on NF performance and membrane fouling were examined. The results showed that AC adsorption achieved the biggest volume reduction ratio (VRR) and decreased the membrane fouling. The results indicated that AC adsorption could be a useful pre-treatment before NF. In addition, phenolics and pigment might be the main components leading to severe fouling during NF process.