| Liquid fuel production by biorefinery technology from biomass resources has beendrawn much attention as an alternative way to reduce the problem of energy shortage andgreenhouse effect. Bioethanol seems to be an attractive alternative to fossil fuel and drawmore and more attention. Non-food biomass resources converted to bioethanol is currentlya hot subject in bioenergy conversion research, especially after the proposal of the energydevelopment strategies base on food security. In conventional process of ethanol procdutionfrom Jerusalem artichoke, there may have many problems: the risk of hydrolysate colouredby by-product, the long time of fermentation, the inhibition effect on yeast cells, andmembrane fouling in coupled system. To solve these problems, in this paper, inulinaseproduction by Kluyveromyces lactis MW270-7B strain, development of bio-membranereactor, establishment of hydrolysis kinetic model of Jerusalem artichoke, analysis ofethanol-inhibitory mechanism, ethanol production by VMD coupled with fermentationprocess and membrane fouling in this coupling process were researched.Kluyveromyces lactis strain was cultured in SD medium at30oC with170rpm for48h.Then4mL of spore suspension was inoculated into500mL Erlenmeyer flask which contains200mL YEPD culture medium and cultured at30oC with170rpm. The results showed thatthe inulinase activity reached a maximum of131U/mL after120h, while the biomass didnot increase after72h, which illustrated that enzyme production process was non couplingtype, in addition, the results also provided foundation for coupling inulinase productionwith hydrolysis of Jerusalem artichoke.To increase the dissolved oxygen concentration in the culture medium, an airliftself-circulating bio-membrane reactor (MBR) based on plat sheet/hollow fibre membranewas developed. In this novel MBR, Due to the unique design of guide shell in the device.The liquid medium can flow in extrinsic cycle or intrinsic cycle flexibly by changing theposition of pores on the support plate. Without extra agitating equipment, it saved moreenergy during the culturing process. Also, the facility is easy to operate and overallsterilized. Compare with the conventional Erlenmeyer flasks, the novel MBR can enhancesecretory expression of Kluyveromyces lactis.Enzyme hydrolysis kinetic models of inulin and Jerusalem artichoke by the inulinase were established, respectively; the corresponding Michaelis-Menten equation modelconstants were found to be related to temperature through the Arrhenius model. The kineticmodels were validated by experimental data and utilized to predict the hydrolysis reactionrates of Jerusalem artichoke for substrate concentrations ranging from2to200g/L and afairly large reaction temperature range (35-60oC). It provides an easy way to choose theoptimized reaction conditions during the hydrolysis of high concentration of Jerusalemartichoke solution.Based on the analysis of the transfer mechanism, a novel modified Knudsen-viscoustransition model to predict the VMD performance of ethanol-water mixture was established.A novel approach to determine the model parameters K and B (modified Knudsen diffusionand viscous flow membrane characteristics, respectively) consisted of membranemorphological parameters was especially developed by fitting the water VMD experimentalresults. The results showed that the simulation values agree quite well with experimentalones.Ethanol production from Jerusalem artichoke by separate hydrolysis and fermentation(SHF) and simultaneous saccharification and fermentation (SSF) were conductedrespectively. During each process, the concentration of ethanol and consume of thereducing sugar were detected. In SHF process, firstly,30%(w/w) Jerusalem artichoke washydrolysed at55oC by inulinase, at the end of hydrolysis, the Jerusalem artichokehydrolyzate containing27.6g reducing sugar was turned to fermentation process at42oC.After48h, the concentration of ethanol reached12.7%(w/w) which was93%of thetheoretical ethanol yield. Meanwhile, the effect of substrate concentration was investigated;the results revealed that that with the increase of substrate concentration, the ethanolconcentration increases, but the conversion efficiency decreased. Howeve, under the sameconditions, the results in SSF process displayed that the reducing sugar was not exhaustafter72h, the ethanol concentration increased with the initial substrate concentrations, theconversion efficiency, by contrast, decreased with the increase of substrate concentrations.The following reasons may account for this: Jerusalem artichoke was hard to be degradedcompletely at42oC, and also, the fermentation broth was highly viscous, which is bad formass transfer in this coupling process. Besides, with the accumulation of ethanol in the process, the deactivation of inulinase was occurred which lead to the incomplete ofhydrolysis. Also, it shows that SSF is not appropriate for the dydrolysis of Jerusalemartichoke and ethanol production.The batch fermentation combined with the removal of ethanol from the broth bymeans of VMD has been investigated. VMD was performed at42oC,95kPa with the flowrate of50L/h. During the coupling process, VMD was started four times and ran for30minat a time. The final residual sugar concentration was about0.25%after48h, the resultsproved that the coupling system removed ethanol from the broth which eliminated theinhibition of high ethanol concentration in fermentation broth. And the production efficency,production rate and final ethanol concentration were greatly improved in the fermentationwith vacuum membrane distillation.Separation performance of four types of flat sheet membranes was evaluated byethanol-water VMD. The PTFE-M1exhibited the best separation performance, and theseparation factor reached6.8in the experimental range, next was PTFE-M2and PTFE-M3,least was PVDF-M1. Subsequently, PTFE-M1and PTFE-M1were used for removelethanol from fermentation broth. Not only membrane fouling, but also decrease ofhydrophobic performance was found on both of the two membrane surfaces. The contactangle of original PTFE-M1membrane was about140o, but after VMD experiments, thecontact angle of PTFE-M1membrane decreased to115o for feed side, below50o for thepermeate side. However, after washed by water, the hydrophobicity returned back to theoriginal level.Finally, the effects of fermentation broth compositions on the hydrophobicity ofmembrane surface were investigated. The results revealed that the effect of5%ethanol-water solution on membrane can be neglected during the process. But the reducingsugar, by-products and yeast cells in the fermentation broth adherented on the membranesurface which lead to reduction of surface tension. But the excellent hydrophobicityrecovery after washed by water proved that the structure of membrane didn’t change by thecontaminant. Therefore, The PTFE-M1membrane was suitable for ethanol removal as longas the membrane was washed periodically. |
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