Study On Biofuel Ethanol Production From Wheat Straw Pretreated By Magnesium Bisulfite And Process Simulation

This study focused on the biofuel ethanol production from wheat straw by low energy consumption magnesium bisulfite pretreatment process(MBSP).The critical parameters that affected pretreatment energy consumption were probed.And the effects of hydrolysate components of MBSP on enzymatic hydrolysis(EH)and ethanol fermentation were investigated.Finally,On this basis,the process of biofuel ethanol production from wheat straw pretreated by low energy consumption magnesium bisulfite was established.Furthermore,the process was simulated to verify its feasibility.Firstly,the critical factors that affected MBSP energy consumption,such as the ratios of solid to liquid,milling method and washing ratios,were optimized.The research results demonstrated that the optimal conditions were: 1:5(w/v)of solid to liquid ratio,post-pretreatment milling for 4 min by beater(PFI)and washing with the ratio of 1:4(w/v).The lignin and hemicellulose removal could be realized under relative low solid to liquid ratios among wheat straw pretreated by MBSP.Then the efficiency of EH could be affected mainly by the lignin removal.Comparing with milling before pretreatment,EH time could be shortened effectively and it also benefits to solid and cellulose recovery by post pretreatment milling.After pretreatment,increasing of washing ratios could promoting acid-soluble lignin removal and soluble degradations digestion effectively.Wheat straw pretreated by MBSP without any detoxification processes could be directly used for EH.The efficiency EH from wheat straw pretreated by MBSP would not be affected when increasing wahsing ratios after pretreatment.With 30 g/L of unwashing wheat straw pretreated by MBSP(based on cellulose),91.37% of 48-h cellulose EH yield was obtained.Rising substrate concentration to 50,70,90 and 100 g/L,the highest EH yield was 89.71%,86.11%,81.88% and 78.82%,respectively which were near to the EH yield of washing pretreated wheat straw.Investigating the influence of hydrolysate components of MBSP on cellulose EH,EH from Avicel and washing wheat straw pretreated by MBSP both could be enhanced by low addition hydrolysates(lower than 4 g/L).However,EH could be inhibited obviously by addition high dosage of hydrolysates(higher than 4 g/L).Magnesium lignosulfonate and XOS in MBSP hydrolysates were the main effectors that affecting on cellulose EH.EH was inhibited obviously with high dosage of MBSP hydrolysates due to high XOS content.The results of separate and simultaneous saccharification fermentation from pretreated wheat straw with different washing ratios were compared.The results indicated that the fermentation results were similar comparing unwashing and washing pretreated wheat straw among separate saccharification fermentation;However,among simultaneous saccharification fermentation,the results fermentated by unwashing wheat straw were slightly worse than washing wheat straw because that high concentration of acetic acid(higher than 2 g/L)inhibited ethanol fermentation seriously.On the basis of experimental studies,the ethanol factory with annual using 300-thousand t wheat straw by MBSP was designed by Aspen plus.Analysis of process energy consumption,the net production energy was 1.05-fold than producing energy;Analysis of water consumption,only 2.21 t water was needed when producing 1 t ethanol.The manimum ethanol sell price was $1.82/gal which was lower than National Renewable Energy Laboratory(NREL)model with $2.15/gal.These results showed that this process had well potential in applications.