| The conversion of lignocellulose into fuel ethanol is a hot spot in the development of the biomass energy industry.However,the current economic efficiency of lignocellulosic ethanol is poor,leading researches on the key technologies of lignocellulosic ethanol conversion are important for solving the current problems.In this dissertation,from the perspective of process intensification,a new process of green medium coupled steam explosion was developed to reduce the intensity of pretreatment and enzymatic fermentation inhibitors.The limitation of minute amount of enzymes premixing was proposed and periodic vibration premixing process was developed for the related process intensification.A bio-chemical method,which was based on pre-enzymatic hydrolysis with Fenton reagent,was developed to reduce the enzyme dosage.A solid-state fermentation process with N2 periodic pulsation as the core was developed for realizing high productivity ethanol using Zymomonas mobilis.The main research results obtained in the dissertation are as follows:(1)Aiming at the problems of high steam explosion intensity,high inhibitor concentration and other problems existing in the steam explosion pretreatment,green medium coupled steam explosion pretreatment was developed.The coupling of green medium can effectively strengthen the removal of lignin and acetyl groups during steam explosion,and at the same time reduce the generation of inhibitors.Among them,the green medium coupled steam explosion pretreatment represented by urea can not only achieve the removal of 29.10%of lignin and 94.96%of acetyl groups,but also lead to 67.95%5-hydroxymethyl furfural reduction and non-production of furfural.Besides,the addition of green medium can reduce the steam explosion intensity required for corn stover.Under low steam explosion intensity(0.8 MPa,30 min),the glucose concentration after high-solids enzymatic hydrolysis of green medium(urea or Fenton reagent)coupled steam exploded corn stover was 4.87%and 9.57%higher than that of high-strength without green medium coupling steam exploded(1.1 MPa,30 min)corn stover,respectively.(2)The trace cellulase(0.50%,w/w)was difficult to be premixed in high-solids which would reduce the enzymatic hydrolysis efficiency.From the perspective of the enzyme premixing process in high-solids,mixing degree of cellulase were explored for the identification of distribution of enzymes in high-solids substrates and the development of periodic vibration premixing.The results show that the premixing of trace enzyme in high-solids has the characteristics of stages.The effects of cellulase premixing on the high-solids enzymatic hydrolysis process was investigated.Sufficient premixing at 20%solid loading would cause 63.96%enzymatic hydrolysis efficiency increasement,87.5%enzyme dosage reduction and early advent of liquification.Periodic vibration premixing process was developed.At 30%solid loading,compared with shaking premixing,the enzymatic hydrolysis efficiency after periodic vibration premixing was increased by 55.75%.Combining water state and enzymatic hydrolysis process,periodic vibration premixing was proved the ability for enhancing the mass transfer at pore scale.(3)Aiming at the problems of low enzymatic hydrolysis efficiency and large enzyme dosage in high-solids enzymatic hydrolysis process,the Fenton reagent pre-enzymatic hydrolysis method was developed for enhancing the high-solids enzymatic hydrolysis of steam exploded corn stover.The synergic action of Fenton reagent and cellulase was explored,and it was found that Fenton reagent can effectively enhance the high-solids enzymatic hydrolysis process by pre-enzymatic hydrolysis.By optimizing key parameters such as Fenton reagent composition and reaction temperature,the glucan conversion rate was improved by 25.57%after 96 h enzymatic hydrolysis.Besides,76.19%cellulase dosage reduced was achieved after Fenton reagent pre-enzymatic hydrolysis.Based on the low field nuclear magnetic resonance and specific surface area analysis,Fenton reagent was proved to be conducted to promote the release of bound water.Besides,the specific surface area of the substrate increased from 1.0920 m2/g to 1.6499 m2/g,thereby promoting high solids enzymatic hydrolysis.(4)Aiming at the problem that Zymomonas mobilis is sensitive to oxygen,which is difficult to achieve ethanol solid-state fermentation.A high-intensity ethanol solid-state fermentation process of Zymomonas mobilis with N2 periodic pulsation as the core was developed.Ethanol solid-state fermentation and ethanol low-solids fermentation were compared for exploring the effects of solid loading on Zymomonas mobilis.Results shows that obvious oxygen inhibition effect would exist in solid-state fermentation.The N2 periodic pulsation enhancing Zymomonas mobilis ethanol solid-state fermentation was developed,which can increase the 30.38%ethanol production and the 17.64%biomass while reducing 84.56%acetic acid and 58.76%glycerol.In order to further increase the ethanol concentration,a high-intensity ethanol solid-state fermentation process was developed by coupling N2 periodic pulsation,periodic peristalsis enzymatic hydrolysis and fed-batch fermentation.The ethanol fermentation concentration reached 55.06 g/L,which was 62.90%higher than that of the blank group.(5)Based on the modeling of lignocellulosic ethanol production,SuperPro Designer was used to analyze the key parameters to guide and evaluate the ethanol production process intensification.The results showed that the enzyme dosage and mixing energy consumption accounted for 34.07%and 12.96%of the operating cost,respectively.Aiming at the critical point of ethanol economy,it was found that enzyme dosage needs to be reduced to 5.74 FPU/g DM,the enzymatic hydrolysis stirring power need to be lower to 0.335 kW/m3 and the ethanol conversion rate need to be above 90.66%.Based on the economic model,the developed processes were evaluated,which shown the economic advantages on reducing the cost of ethanol production. |
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