Poplar Wood Pretreated By Diluted Acid Combined With Steam Explosion Of Composite Enzyme Fermentation Process Control And Dynamics Exploration

Bioethanol is an important part of renewable energy.Using lignocellulose to transform into bioethanol has got widely attention and support from our society. In recent years,scientific research has made great progress, but efficient wood fiber pretreatment, enzymatic saccharification, C5/C6 sugars synergistic fermentation technology are still the key research prioritiesat at home and abroad.To improve the ethanol yield, simplify process and reduce cost, the research of the key technology for poplar fiber bioconversion ethanol are as follow:(1) Analyzed the main components about the poplar wood pretreated by dilute phosphate acid combined with steam explosion(referred to as the acid explosion poplar). An observation of the structural changes by scanning electron microscopy, cellulose meter measuring the change in cellulose, hemicellulose and lignin.The results show that, Pretreated under the conditions in 2% (w/w) concentration of phosphoric acid, solid-liquid ratio of 1:2.5, prepreg 1h, steam explosion pressure is 2Mpa and maintaining time is 180s.It is effective to destroyed the lignocellulosic structure,the hemicellulose degradation rate achieve 64.71%,the cellulose degradation rate is 20.59%.(2) The acid explosion poplar as test material,researched the reaction temperature, value of initial pH, hydrolysis time, amount of enzyme and the percentage of enzyme complex to hydrolysis effect.The concentration of reducing sugar as the main target to evaluate the effect of hydrolysis. The results show that, the optimum conditions for enzymatic hydrolysis temperature is 45 ℃, initial pH value is 5.5, the amount of enzyme is 15-20IU/mL, hydrolysis time is 8-16h,The ratio of β-glucosidase enzyme and enzyme filter paper is 1.56, the highest sugar concentration reach 61.86mg/mL, reducing sugar yield as high as 72.78%.Response surface experiments show the factors that enzyme affect the size of the order is the percentage of composite enzyme> initial pH value> hydrolysis temperature,theoretical resulting in the most excellent combination:initial pH value is 5.2, hydrolysis temperature is 46 ℃, percentage of composite enzyme is 1.62.(3) By chose good bacteria, compare different enzymatic hydrolysis and fermentation progress, obtain better strains and processes to ethanol production, and then control the fermentation process. GC Determination of ethanol content of fermented evaluating results. The specific test is as follows: ① With pure sugar fermentation, original Saccharomyces cerevisiae S1, advantages Saccharomyces cerevisiae by domesticated breeding S2 and mutagenesis Saccharomyces cerevisiae by UV combined y-ray S3 was evaluated. Get the best strain S2,fermentation ethanol concentration of 34.89g/L, the ethanol yield (glucose calculate the theoretical yield) of 91.22%.②Poplar wood pretreated by the dilute phosphoric acid prepreg combine with steam explosion as material, test and verify effect of unitary enzyme and composite enzymatic hydrolysis on fermentation. The unitary enzymatic fermentation concentration of ethanol was 19.85g/L, the highest yield was 45.17%; complex enzymatic fermentation concentration of ethanol attained 31.09g/L, the highest ethanol yield was 71.72%, ethanol yield improved 26.55%.③ Poplar wood pretreated by the dilute phosphoric acid prepreg combine with steam explosion as material,Comparison of simultaneous saccharification and fermentation (SSF) and simultaneous saccharification and co-fermentation (SSCF)process.Results showed that, E. coli KO11 and S. cerevisiae S2 SSCF result was the best, ethanol concentration reached 35g/L, the ethanol yield was 80.74%. Domesticated breeding dominant strains of Saccharomyces cerevisiae S2 fermentation ethanol concentration reached 34.04g/L.④ Considering the strain from the fermentation tolerance, simplify the process and to obtain a higher ethanol yield,chose good bacteria S2, composite enzymatic fermentation process control, explore the impact of reaction time and ventilation time of fermentation. Results showed that,ethanol concentration increased with hydrolysis time, there was good results about 8-16h ethanol concentration reached 30g/L or more. With increasing ventilation time, the sugar being exploited more thoroughly, the concentration of ethanol is rising. The best time ventilation time was 6-8h, the ethanol concentration up to 34.91gL, ethanol yield was 80.53%.By scanning electron microscopy, GC./MS analysis of the impact of acid hydrolysis fermentation burst Poplar.The acid explosion poplar with hydrolysis, fermentation progresses the degree of structural damage was gradually deepened.GC/ MS analysis identified a dozen compounds (phenols, benzene, n-type) and component changes in the liquid inclusive. The results show that the acid pretreatment produced inhibitor, with enzymatic process the inhibitor increased.Fermentation liquid emerged acids,and different palmitic acid concentration is likely to be an important factor affecting fermentation effects.(4) A preliminary study on the fermentation dynamics analysis the correlation between substrate consumption and product generated in pure sugar and poplar wood pretreated by diluted acid combined with steam explosion of composite enzyme fermentation process.The result show that their linear relation is consistent.Reducing sugar rate proportional to ethanol productivity and decline.Meanwhile,determined fermentation strains change and drawn production curve.According to the specific circumstance in poplar wood composite enzyme fermentation process,preliminary analysis assumes that dynamic model of reducing sugar G.