Studies On Bioprocess And Pilot-plant-scale Experiment For 1,3-Propanediol Fermentation

1,3-Propanediol is an important bulk chemical, which is used in the manufacture of polyesters,polyurethanes, solvents, antifreezes, and lubricants as well as foods, cosmetics, and medicines,in particular as a monomer to synthesize a new type of polyester, polytrimethyleneterephthalate (PTT). At present, 1,3-propandiol has mainly been manufactured by chemicalsynthesis that requires high temperature, high pressure and expensive catalysts. Therefore,much attention has recently been paid to its microbial production. In this paper, the effect ofthe intermediate of 3-hydroxypropionaldehyde (3-HPA) on metabolic pathways in anaerobiccontinuous fermentation of glycerol by Klebsiella pneumoniae were investigated byexperiments. Moreover, the feasibility of 1,3-propanediol production by two-stagefermentation was sdudied. Furthermore, the pilot-plant-scale experiments of 1,3-propanediolfermerntation from glycerol were achieved. Finally, a technical and economic analysis wascarried out based on the pilot-plant-scale experimental results.The transient behaviors in anaerobic continuous fermentation of glycerol by Klebsiellapneumoniae were observed under different change modes of substrate concentration in thefeed at a dilute rate of 0.2h^-1. An emphasis has been put on the effects of an intermediateproduct of 3-HPA on the activities of key enzymes for glycreol dissimilation as well as theformation of biomass and products. The experimental results showed that specific formationrate of 3-HPA (q3-HPA) in the culture is a key parameter, which inversely affects the activitiesof the two enzymes glycerol dehydrogenase (GDH) and 1,3-propanediol oxidoreductase(PDOR), but has a little effect on the activity of glycerol dehydratase (GDHt). The presentexperiments also suggested that excess glycerol indirectly inhibited cell growth through3-HPA. The results revealed several differences and new features compared with thosereported in the literature and would be favorable for 1,3-propanediol production technology.An investigation of microbial production of 1,3-propanediol in a two-stage batchfermentation by using glucose or cornstarch as raw material was carried out in this work. Incomparison with the anaerobic batch fermentation of 1,3-propanediol from saponifiedglycerol, a bioprocess of two successive microbial fermentations for the production of1,3-propanediol was feasible. Under the same initial glycerol mass concentration of 70 g/L,the yield of 1,3-propanediol on the second stage within 15h to glycerol from glucose on thefirst stage was higher than that of 1,3-propanediol directly from saponified glycerol in a 18h batch fermentation. The molar yields of 1,3-propanediol to glycerol were 47.3% and 44.2%,respectively,. However, only 26.5% (mol/mol) of glycerol produced from cornstarch on thefirst stage was converted to 1,3-propanediol on the second stage in 31h. Based on the batchexperiment, the anaerobic fed-batch fermentations using the raw fermentation glycerol toproduce 1,3-propanediol were carried out further. The results showed that the two-stepfermentation using starch as material was feasible.Finally, based on the lab-scale experiment, the fed-batch fermentations of 1,3-propanediolproduction from glycerol by Klebsiella pneumoniae had been conducted up to the scale of1m³ and 20m³ respectively. The 1m³-scale experimental results showed that, theconcentrations of 1,3-propanediol were all above 70g/L in the ultimate fermentation brothsboth under anaerobic and micro-aerobic conditions. The highest mass concentration of78.5g/L; the average mass conversion ratio of 50.6%; the average fermentation time of 29.7h;and the average productivity of 2.53g/L.h had achieved under anaerobic condition, comparedto the average mass concentration of 72.8g/L, the average mass conversion ratio of 45.8%, theaverage fermentation time of 34h, and the average productivity of 2.14g/L.h undermicro-aerobic condition. Furthermore, better results were also obtained in a 20m³-scalefermentor. The average concentration of 1,3-propanediol is 63.9 g/L, with the highest level of68.6g/L; the average mass conversion ratio of 41.2%; the average fermentation time of 34h;and the average productivity of 1.87g/L.h. The pilot-plant-scale experiments validate thefeasibility of the lab-scale control strategy. By using ethanol precipitation pretreatment andrectification patent technology, the final product 1,3-propanediol with a purity above 99% hadbeen harvested, the recovery yield of 1,3-propanediol was greater than 85%, and the productquality had met the polymerization standard of PTT (polytrimethylene terephthalate) provedby entrusted polymerization experiment to Petrochina Research Institue of LiaoyangPetrochemical Company. Based on the above experiments, the fed-batch fermentations usingthe raw fermentation glycerol to produce 1,3-propanediol were achieved in 1m³-scalefermentor further.In the end, based on the pilot-plant-scale experiments, it also discusses about theproduction cost and the anticipated economic benefit with regard to a set of equipments whichcould produce 1500 tons 1,3-propanediol from glycerol per year. The gross investment is68.7631 millions Yuan, the unit production cost is 24797 Yuan and the net profit is 15.01millions Yuan per year. The cost analysis demonstrated that microbial production of1,3-propanediol was economically feasible.