Process Intensification Of High Solids Enzyamtic Hydrolysis And Fermentation Of Steam Exploded Straw

High solids lignocellulose refinery has many advantages including higher fermentable sugar and product concentration, lower cost of separation, and less wastewater discharge. It is an important approach to realize lignocellulose refinery industrialization. The main challenges of high solids lignocellulose refinery for ethanol production includes (1) how to increase fermentable sugars by pretreatment; (2) how to remove the "solids effect" and improve the efficiency of high solids enzymatic hydrolysis and fermentation; (3) how to realize the high co-fermentation efficiency of glucose and xylose, and how to construct the integration process of each unit operation to achieve efficient refinery. In order to solve these problems, the core unit operation of lignocellulose refinery for ethanol production including pretreatment, hydrolysis and fermentation were studied in the present study, and the research results was given as follows:(1) The polysaccharide recovery was low, the degradation products yield was high, and the enzymatic hydrolysis efficiency was poor in conventional steam explosion (SE). A novel steam explosion pretreatment strategy, low holding temperature and high explosion pressure (LHT/HEP), was developed. Under the optimal steam explosion conditions (160℃,48 min), glucan and xylan recovery was 93.4% and 71.6%, glucan and xylan conversion was 82.3% and 79.6%, glucose, xylose and total sugar yield reached 77.3% and 62.8% and 72.3%, respectively, which were better than these under conventional steam explosion (200℃,6 min). LHT/HEP-SE had low holding temparture and pretreatment severity and it was a novel pretreatment method.(2) The "solids effect" of high solids enzymatic hydrolysis leads to the low efficiency of enzymatic hydrolysis. Based on the principle of bionics, a novel intensification method, periodic peristalsis, was developed by simulating the structural features of rumen to intensify high solids enzymatic hydrolysis. A novle preparation process of peristalsis materials was developed using agricultural straw as raw material. In this process, xylose and furfural was obtained from agricultural straw by SE to prepare polyurethanepolytetramethylene glycol, which can be further used to prepare polyurethane.(3) The effects of periodic peristalsis on sugar conversion, apparent viscosity and enzyme activity loss in high solids enzymatic hydrolysis was studied. Compared with incubator shaker, periodic peristalsis increased glucan and xylan conversion by 4.1%-11.2% and 2.8%-9.2% at 15%-30% solid loadings, respectively. Compared with incubator shaker, periodic peristalsis reduced apparent viscosity, shortened transition point from the solid state to slurry state by 6-14 h, and reduced the cellulase loss by 3.2%-7.9% at 15%-30% solid loadings. Results showed that periodic peristalsis was an efficient intensification method to improve the efficiency of high solids enzymatic hydrolysis of steam exploded corn stover.(4) The interactions between biomass and water and its correlations with high solids enzymatic hydrolysis of steam exploded corn stover were studied. Results suggested that exponential model can express well the interactions between untreated/steam exploded corn stover and water. SE increased glucan content, biomass crystallinity, specific surface area, pore volume, average pore diameter, porosity, oxygen to carbon ratio, thereby enhanced the interactions between corn stover and water. SE increased the binding strength and water content on the surface of corn stover, hence increased the accessibility of polysaccharide to water and enzyme. Combined with these, the release of water constraint before 36 h improved the efficiency of high solids enzymatic hydrolysis.(5) The effects of periodic peristalsis on the water constraint and its relationship with the efficiency of high solids enzymatic hydrolysis were analyzed. Compared with that by incubator shaker, the pool peak height of water pool in high solids enzymatic hydrolysis increased by 7.7%-43% before 24 h by periodic peristalsis, which was consistent with the increase trend of glucan conversion. During the initial stage of hydrolysis, the periodic peristalsis released the water constraint, and thus improved sugar conversion. Results suggested that the effects of chemicals on water constraint followed the order:Tween 80, ethanol, xylose, glucose and microcrystalline cellulose. Submicroscopic particles and large particles residue are two main factors affecting water constraint.(6) Biomass heterogeneity is closely related with the efficiency of high solids enzymatic hydrolysis. The selectively structural and functional fractionation and the stress-strain behavior of agricultural straw were studied in SE and high solids enzymatic hydrolysis. Compared with steam exploded steam node and stem rind, steam exploded pith, leaf sheath, leaf and whole corn stover had lower hardness and less total work done, which facilitated the efficiency of mixing and high solids enzymatic hydrolysis. Compared with incubator shaker, periodic peristalsis reduced the hardness and total work done of high solids enzymatic hydrolysis within 12 h, and thus increased sugar conversion. Selectively structural and functional fractionation obtained the higher conversion efficiency of different morphological fractions under their optimum steam explosion and enzymatic hydrolysis conditions, respectively. Periodic peristalsis changed the stress-strain behavior of high solids enzymatic hydrolysis, and thus increased the sugar conversion. The analysis of the stress-strain behavior and its correlations with the efficiency of enzymatic hydrolysis provided a new theoretical basis for the development and design of high solids enzymatic hydrolysis.(7) The high solids enzymatic hydrolysis and fermentation process was studied by S. cerevisiae IPE003, and several fermentation strategies including separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), separate hydrolysis and co-fermentation (SHCF), and simultaneous saccharification and co-fermentation (SSCF) were compared. Glucan and xylan conversion were 82% and 82.1%, respectively, and ethanol concentration, yield, and productivity was 60.8 g/L, 75.3%, and 0.63 gL-1h-1 in SSCF of steam exploded corn stover after 96 h by S. cerevisiae IPE003. S. cerevisiae IPE003 can efficiently co-ferment glucose and xylose, and increase the concentration, yield and productivity of ethanol.In summary, LHT/HEP-SE overcome biomass recalcitrance and improved the refinery efficiency of agricultural straw. The novel intensification method, periodic peristalsis, can effectively remove "solid effect" and hence enhance the efficiency of high solids enzymatic hydrolysis. S. cerevisiae IPE003 can co-ferment glucose and xylose effectively; the integration process of pretreatment, enzymatic hydrolysis and fermentation can effectively improve the refinery efficiency of agricultural straw with high solids. These results provided a theoretical foundation for lignocellulose refinery and lignocellulosic ethanol industrialization.