Applied Basic Research On 1,3-propanediol Production By Fermentation

1,3-propanediol is an important chemical raw material with a variety of uses, such as lubricants,antifreeze agents,solvents,adhesives,and laminates;it has enormous applications in cosmetics,textiles,food and medicines.1,3-propanediol can be used as intermediate compound for the synthesis of heterocycles,and it also finds applications in the production of polymers such as polyesters and polyurethanes.Glycerol is the substrate of 1,3-propanediol fermentation,recently its production has increased due to the development of biodiesel industry,and the price decline of it saves costs for the fermentation process of 1,3-propanediol and it can speed up the commercialization of microbial approach to 1,3-propanediol production.The basic process conditions for microbial production of 1,3-propanediol were investigated in shaking flasks,a suitable nitrogen source for the seed culture was yeast powder mixed with(NH₄)₂SO₄,a suitable carbon nitrogen ratio for seed culture was 5,while the suitable organic nitrogen source for fermentation medium was corn syrup.Adding 8 g/L glucose in the fermentation medium could enhance the yield of 1,3-propanediol.The by-products have an effect on 1,3-propanediol production,a small amount of acetic acid could promote the throughput of 1,3-propanediol,and 0.6 g/L of it had a most obvious effect,while the production of 1,3-propanediol was inhibited when the concentration of acetic acid was up to 1 g/L.2 g/L ethanol could facilitate the production of 1,3-propanediol,while above 4 g/L ethanol would inhibit it.In batch fermentation,the production of 1,3-propanediol was 9.65 g/L at 96 h, with 87.2%utilization rate of glycerol and 67.0%1,3-propanediol yield.The production of 1,3-propanediol in 3.7 L self-operated fermenter was studied, the suitable process parameters were aeration rate0.2 vvm,and stirring rate 300 rpm. The concentration of 1,3-propanediol was 8.12 g/L at 96 h,while the utilization rate of glycerol and the yield of 1,3-propanediol were 79.2%and 62.1%,respectively.Fed-batch fermentation for the production of 1,3-propanediol was investigated, the results showed that an appropriate feeding medium consisted of glycerol,corn syrup and glucose.A suitable feeding process was adding 2 g/L glycerol,1.6 g/L glucose and 1.2 g/L corn syrup(final concentration) per 12 h after 48 h fermentation, the concentration of 1,3-propandiol reached 26.97 g/L at 240 h,the utilization rate of glycerol was 82.8%,and the yield of 1,3-propandiol was 62.6%.The two-stage fed-batch fermentation process for 1,3-propanediol production was the same as former process in 144 h,while after 144 h,double the concentration of feeding medium.After 360 h fermentation,the concentration of 1,3-propanediol in the broth was 58.78 g/L,the overall utilization rate of glycerol and overall yield of 1,3-propanediol was 88.2%and 67.2%,respectively.A process of using immobilized Klebsiella pneumoniae by sodium alginate to produce 1,3-propanediol was evaluated,the appropriate process parameters were as follows,immobilized gel beads volume fraction 15%,temperature 37℃,pH 6.7, and the initial glycerol concentration was 40 g/L.The fermentation period of 1,3-propanediol production by immobilized cells was 72 h,which was 24 h shorter than free cell fermentation.Repeated batch fermentation by immobilized cell was carried out for 1,3-propanediol production,the average glycerol utilization rate for 6 batches was 92.5%,with an average of 15.6 g/L 1,3-propanediol production,and 51.1%1,3-propanediol yield,indicating that the efficiency of reusing immobilized cell was stable,it would be propitious to continuous fermentation and automated control.Glycerol is a by-product in the production of biodiesel,the production of 1,3-propanediol by glycerol fermentation possesses good economic and social benefits.The results in this study laid the foundation for the further realization of 1,3- propanediol large-scale production.