| Biomass ethanol is currently the most promising industrialized scale of liquid fuel green energy.As a large agricultural country,China's wood fiber resources are huge,and it is an important raw material for biomass ethanol.Since lignocellulosic materials have inherent properties that are difficult to degrade and utilize,they need to be pretreated.Most of the pretreatment costs are generally high,and the technology has limitations,which makes it difficult to achieve large-scale application of biomass ethanol.Seeking economically viable pretreatment methods is critical to the development of biomass ethanol.A single formic acid or hydrogen peroxide exhibits a positive effect on biomass pretreatment.The two are mixed at a certain ratio and temperature,have a good delignification effect,and significantly improve substrate utilization.The main contents and results of this paper are as follows:(1)The optimum conditions for pretreatment of straw with hydrogen peroxide-formic acid method were studied by single factor experiment and response surface design: volume ratio of hydrogen peroxide to formic acid was 6:4,reaction temperature was 62.5 °C,reaction time was 110.Min,solid-liquid ratio 1:10.After treatment,the concentration of reduced sugar in the straw was 10.56 g/L.Compared with the untreated raw materials,the pretreated straw cellulose content increased significantly,and the lignin removal rate reached 74.85%.Fourier transform infrared(FT-IR)analysis showed that the lignin-related absorption peaks in the pretreated straw were weakened and the lignin was effectively removed.Enzymatic comparison experiments showed that hydrogen peroxide-formic acid treatment of straw biomass increased the enzymatic yield by 49.25%.(2)The single-factor experiment and orthogonal design were used to optimize the saccharification and fermentation of the treated straw.The optimal culture conditions were: substrate concentration 4%,cellulase amount 25 FPU/g(substrate),yeast inoculum 8%,fermentation temperature 32.5 °C,initial pH 5.After 72 h of fermentation,the ethanol concentration reached 9.18 g/L.Pre-saccharification of pretreated straw before simultaneous saccharification and fermentation cansignificantly increase the ethanol conversion rate of alcohol yeast,shorten the fermentation time,and increase the ethanol end point concentration to some extent.(3)Investigating the fermentation of ethanol with different concentrations of reaction aids Tween-20,Triton X-100,Tween-80,bovine serum albumin(BSA)and polyethylene glycol-4000(PEG-4000)influences.The results showed that the addition of reaction auxiliaries promoted the simultaneous saccharification and fermentation of ethanol.The optimum addition amount of each reaction auxiliaries was 0.03,0.03,0.02,0.02,0.03 g/g(substrate).It was found that 0.03 g/g(substrate)Triton X-100 promoted the best among the five kinds of reaction auxiliaries,and the ethanol concentration and alcohol conversion rate increased by 10.60% and 6.92%,respectively.(4)The effects of a single inhibitor of formic acid,acetic acid,furfural and5-hydroxymethylfurfural on ethanol production by alcohol yeast were studied.The results showed that the four inhibitors had significant effects on the ethanol production of yeast fermentation and the reduction of sugar in fermentation broth.As the concentration of fermentation inhibitors increased,the concentration of ethanol showed a downward trend,and the concentration of reducing sugars increased,eventually reaching a certain limit.The range of effects of the four inhibitors on fermentation alcohol production was: 1 g/L-3 g/L for formic acid,2 g/L-8 g/L for acetic acid,and 2 g/L-9 g/L for furfural.5-hydroxymethylfurfural is 0.5 g/L-3 g/L.In addition,the concentration of formic acid is 1 g/L-2.5 g/L,the concentration of acetic acid is 1 g/L-7 g/L,the concentration of furfural is 2 g/L-8 g/L,and the concentration of 5-HMF is 0.5 g/L-3 g/L,which have the most significant effect on reducing sugar in the fermentation system. |
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