Porous Solid Particles Characteristics Of Biomass And Its High-solids Enzymatic Hydrolysis And Fermentation Process

High-solids enzymatic hydrolysis fermentation of biomass has a lot of advantages,such as high sugar concentration,high product concentration,low separation cost and less waste water discharge etc.,which is the trend of biomass energy industry and the hot spot of green biological industry.However,the lack of theoretical knowledge and process strengthening technologies caused by the complex porous structure and particle characteristics of solid materials,leads to the low conversion efficiency and the difficulty of breaking through the industrial technical economy during the high-solids enzymatic fermentation.Thus,we believe that starting from the cognition of the characteristics of biomass porous solid particles,may be the key way to break through the biomass high-solids enzymatic hydrolysis fermentation.In this thesis,the characteristics of porous solid particle medium was analyzed,the transfer and reaction law during high-solids enzymatic hydrolysis fermentation was studied,effectively strategies of process intensification and targeted regulation were explored,and then to guide process optimization and reactor design for high-solids enzymatic hydrolysis fermentation.The main results are as follows:(1)The multi-scale porous structure of lignocellulosic biomass affects the water distribution and the water flow characteristics,and then affects the enzymatic hydrolysis efficiency.With steam-exploded straw(SES)as the representative of lignocellulose,the effects of the porous properties on the transfer and hydrolysis efficiency during high solids enzymatic hydrolysis of SES were explored.The results showed that the capillary pores accounted for more than 90%of the total pore volume of the SES,and the capillary water accounted for 90%?95%of the total volume of water at liquid-to-solid ratio(LSR)of 3?10.The capillary water can be driven by the external force,thus the capillary water becomes the main mass transfer carrier for high-solids enzymatic hydrolysis.Furthermore,after capillary water transfer driven by external force,enzymatic hydrolysis yield could be improved by 58.3%?106.7%,while when the capillary water disappeared at 12 h,the enzymatic hydrolysis yield was as high as 96%but no longer increased.Thus,capillary water transfer in porous media is the limiting factor for high solids enzymatic hydrolysis of lignocellulose.Moreover,the periodic peristalsis with the normal force as the power source was proposed to strengthen the capillary water transfer in the media.Periodic peristalsis could promote the efficient mass transfer of fluid and enzyme molecules in the media,and then significantly improve the enzymatic hydrolysis efficiency.Therefore,the LSR of SES can be reduced to 3,the solids content can be increased to 25%,and the sugar concentration can reach up to 160 g/L under periodic peristalsis.Meanwhile,periodic peristalsis can effectively reduce the enzyme dosage of 5?8 times,saving a lot of enzyme costs.(2)The enzymatic hydrolysis of lignocellulosic biomass is a solid-liquid phase transition(SLPT)process from solid particle to soluble sugar.The impact of porous solid particles effect on the mass transfer and accessibility at the initial stage of enzymatic hydrolysis is significant.Thus,from the perspective of SLPT,it is likely to be an effective way for in-depth understanding the enzymatic hydrolysis mechanism and improving enzymatic hydrolysis efficiency of lignocellulose.In this thesis,the method for characterization of SLPT turning point and the kinetics of SLPT during lignocellulose enzymatic hydrolysis were established firstly,then the rate-limiting step,influencing factors and targeted strengthening measures were proposed.Results showed that the criteria of SLPT for SES enzymatic hydrolysis were apparent viscosity of 0.493 Pa s and compressive modulus of 29.4 kPa.The enzymatic hydrolysis conversions at SLPT turning point were>0.85,thus the stage before SLPT was the key stage for lignocellulose hydrolysis.The rate of SLPT was positively related with increasing of mass transfer coefficient D2,enzyme dosage E0 and liquid-to-solid ratio LSR but negatively related to increasing of particle size R0.The periodic normal stress can significantly improve D2,thus the rapid SLPT under the system with E0 10 times lower,LSR 7 times lower and R0 87 times higher is achieved,then enzymatic hydrolysis efficiency was improved significantly.(3)Solid-state fermentation(SSF)is an extreme case of high-solids conversion of biomass.The properties of porous solid substrate composed of gas,liquid and solid three phases resulted in the difficulties of heat and mass transfer and process monitoring.In this thesis,three SSF process monitoring systems based on infrared thermal imaging,visible light imaging and low-field nuclear magnetic imaging coupled digital image processing technology were established.The real-time mycelium temperature,mycelium growth dynamics and contamination can be monitored.Secondly,the relationships among the mycelium temperature,the average substrate temperature and the gas temperature during SSF process was established,that is,(?)T2/(?)t=-Q/C2m2+(C3m/C2m2)(?T3+(?)t)?(C1k2/C2m2)((?)T1/(?)t)2,to guide the temperature regulation and optimize the fermentation process.Finally,the effect of water retention and humidification in the gas-double dynamic SSF process was revealed.The theoretical analysis showed that the evaporation area A1,the pulsating pressure P,the volume of the tank V and discharge port area A2 are the key factors for the humidification or the desiccation of gas-double dynamic SSF process.Thus,those factors can be regulated to guide the pressure pulsation process optimization.(4)From the perspective of mechanical properties of SSF meidum,relationships among the medium's physical properties and heat and mass transfer as well as fermentation performance were established,to guide culture medium preparation and thick-layer packing design of SSF.We established an integrated mechanical property index Imp to fully characterize medium physical properties of water retention,gas permeability,thermal conductivity and thermal diffusivity.When Imp?4.37×10-2,water retention and heat conduction was promoted in the medium,which was beneficial to cell growth.When Imp>4.37×10-2 heat accumulation and poor permeability reduced fermentation performance.Thus,Imp could well comprehensively characterize physical properties of medium,which could be useful for guiding culture medium preparation and dynamic process control in SSF.In addition,based on the silo effect of the particulate matter,that is,the Coulomb's friction characteristics of the particulate matter result in the baffle or wall to share part of the self-weight stress of the medium,the SSF thick-layer packing pattern with built-in partition was designed.The center temperature of fermentation medium was 34? and the biomass was up to 0.75 g/g dry basis under the bed height of 25 cm in the gas-double dynamic SSF bioreactor.Therefore,the addition of partitions in the packing,reducing the unit area of the packing,relieving the consolidation and settlement caused by self-weight stress,and coupled with pressure pulsating to enhance the heat and mass transfer,the thick-layer packing SSF and the increase of the loading coefficient can be achieved.