Optimization Of High Solid Concentration Hydrolysis Of Lignocellulosic Biomass

Lignocellulosic biomass is a widely distributed and economically beneficial renewable resource,including forest residues(branches,leaves),agricultural residues(straw),urban waste,etc.Improving the conversion of lignocellulosic biomass and obtaining high-concentration fermentable sugars to get economic values for industrial promotion are still the focus of research.In order to obtain high-concentration fermentable sugars,six kinds of raw materials were selected and three pretreatment methods were adopted to optimize the enzyme ratio of substrate hydrolysis with different concentrations,and on this basis,the batch feeding mode of high concentration hydrolysis was optimized.The main contents and results of this paper are as follows:1.Pretreatment of lignocellulosic biomassAlkaline hydrogen peroxide(AHP),dilute sulfuric acid(DSA)and supercritical CO₂pretreatment methods were used to pretreat different lignocellulose raw materials.After pretreatment,the cellulose content of most raw materials increased by 5%-10%,and the lignin or hemicellulose decreased.The results show that different raw materials have different pretreatment methods,and furfural residue,DSA-corncob and AHP-corn stover have better effect,62.14%conversion and 13.33 g/L sugar concentration(5%solid concentration)could be obtained from furfural residue without any pretreatment,which was very close to the pretreated sample.In the corncob pretreated with dilute sulfuric acid,the glucose conversion and concentration were 59.32%and 12.10 g/L were 196.45%and270.03%higher than those of the untreated corncob,respectively.After AHP treatment,the glucose conversion and concentration of corn straw were 49.18%and 10.35 g/L,which were 184.11%and 252.04%higher than those of untreated corn stover.2.Optimization of enzyme mixture for hydrolysis under different substrate concentrationsThe optimal proportion of the four enzymes under high concentration were as follows:furfural residue:76.70%,0%,23.30%,0%DSA-corncob:63.10%,0%,31.90%,5.00%mathod-corn straw:43.90%,0%,42.60%,13.50%.The optimal enzyme ratio of different raw materials at high solid concentration showed a common feature:the demand for?-glucosidase decreased,but more cellulase and hemicellulase were needed.3.Fed-batch hydrolysis optimizationThe optimized enzyme ratio was applied to fed-batch hydrolysis,and the fed-batch modes were optimized.the results show that fed-batch hydrolysis can effectively alleviate the phenomenon of lack of free water and high viscosity in high solid hydrolysis.It was found that the 20%substrate concentration optimal enzyme should be added regardless of the initial substrate concentration of the fed-batch hydrolysis.The study showed that the conversion of the four-time balanced feeding is more gentle than other feeding modes,and it could be clearly observed that the free water in the hydrolyzate was more abundant and the viscosity was relatively lower.Although the proportional enzyme feeding method could alleviate the enzyme activity decreased during the hydrolysis,it was found that the whole enzyme feeding method was more suitable for 48 h hydrolysis.Because in the initial stage of hydrolysis,the whole enzyme feeding method was more thorough,which could get more free water.But for longer hydrolysis,proportional enzyme feed might be more advantageous.It was important to get enough free water in the initial stage of hydrolysis.If free water started to appear,the hydrolysis could proceed smoothly,high-concentration hydrolysis could be performed smoothly by the fed-batch method.Through the optimization of the fed-batch mode,30%and 40%substrate concentration hydrolysis achieved 77.07%and 65.08%glucose conversion,respectively,and the fermentable sugars concentration reached 153.49 g/L and 171.88 g/L,respectively.