An Integrated Bioprocess Combining Biodiesel With 1, 3-Propanediol Production

The predicted shortage of fossil fuel and the pollution of environment encourage thesearch for substitutes for petroleum derivatives. Biodiesel is a clean, renewable alternativefuel of petroleum diesel. The production techniques of biodiesel, the utilization of byproduct(glycerol), the combined productions of biodiesel and 1,3-propanediol (1,3-PD), and anintegrated bioprocess combining biodiesel production by lipase with microbial production of1,3-PD were studied in this paper.Firstly, the methanolysis of different oils by alkali-catalysis and lipase-catalysis werestudied. A novel two-step method was proposed, by which biodiesel was produced from ferricchloride (2.0%) catalyzed reaction followed by alkali (1.0% potassium hydroxide)transesterification. This new two-step process showed advantages of high efficiency, noacidic wastewater, low equipment cost. The conversion of waster cooking oil into biodiesel inthis method was 85%, while the conversion of model refined waster cooking oil was 94%.The optimal reaction parameters of methanolysis of soybean oil by lipase-catalysis weredetermined as follows: 15wt% of lipase, 55℃of temperature, petroleum ether as solution,methanol was added by 6 times. The methanolysis of soybean oil and waster cooking oil bylipase-catalysis were not significant different, which showed that lipase was an effectivecatalyst on transesterification of oils having high concentration of free fatty acids.Secondly, the utilization of byproduct (glycerol), i.e., microbial production of 1,3-PD byKlebsiella pneumoniae was investigated. The similar results were obtained from reagent andindustrial glycerol materials. In batch fermentations, the 1,3-PD yields of 0.73 and0.75mol/mol on reagent and industrial materials under microaerobic conditions were higherthan that of 0.67 and 0.68mol/mol under anaerobic conditions. In fed-batch fermentations, the1,3-PD yields of 0.55 and 0.53mol/mol on reagent and industrial materials undermicroaerobic conditions were comparable to that of 0.57 and 0.54mol/mol under anaerobicconditions. Organic acids in 1,3-PD fermentation broth were determinated by ion-pairchromatography and high performance liquid chromatography (HPLC). The products of1,3-PD fermentation under anaerobic and microaerobic conditions obtained were compared.Citrate, succinate and fumarate were determinated by ion-pair chromatography. Formate,lactate, acetate, citrate, succinate and fumarate were determinated by HPLC. Apart from 2,3-butanediol and fumarate concentrations, other product concentrations under anaerobicconditions were higher than those under microaerobic conditions.Thirdly, the combined production of biodiesel and 1,3-PD was studied. The crudeglycerol from biodiesel production could be directly converted to 1,3-PD without any priorpurification. In flask cultures, the 1,3-PD yields of 0.62 and 0.44mol/mol on crude glycerolfrom lipase-and alkali-catalyzed methanolysis of soybean oil were lower than that of0.68mol/mol on pure glycerol. In fed-batch fermentations, the 1,3-PD yields of 0.47 and0.46mol/mol on crude glycerol were comparable to that of 0.49mol/mol on pure glycerol. Theproductivity of 1.7g 1^-1 h^-1 on crude glycerol was comparable to that of 2.0g 1^-1 h^-1 on pureglycerol.Lastly, an integrated bioprocess combining biodiesel production by lipase with microbialproduction of 1,3-PD was proposed. Glycerol dialysis with model solutions by a hollow fibermembrane was carried out. 80% of the initial glycerol was removed within 1h when glycerolconcentration was in the range of 1-6wt%. Glycerol formation rate accompanied withbiodiesel production was consistent with the glycerol consumption rate in 1,3-PDfermentation. Two types of integrated bioprocess were investigated. In the combinedbioprocess contained one batch of transesterification, the methyl esters conversion was 86%,and 1,3-PD concentration obtained was 61.1g/L. In the combined bioprocess contained twobatch of transesterification, the methyl esters conversion was 84%, and 1,3-PD concentrationobtained was 50.7g/L. The highest cell dry weights were 5.2g/L and 4.9g/L, respectively. Theconcentration of methanol penetrated into fermentation broth reached 19.0g/L (11% of thetotal metnanol).In conclusion, the results suggest that the two-step method was an effective way totransesterify oils having high concentration of free fatty acids and the integrated bioprocessreduces the production cost and raises productivity for biodiesel and 1,3-PD, which makes theoperation more economically appealing.