Crude glycerol, a byproduct of biodiesel, can be used as raw material to prepare a variety of chemical products, such as 1,2-propanediol, 1,3-propanediol, polyester and polyglycerol. They are important chemical raw materials and products, and have a wide range of applications.
1,2-propanediol
1,2-propanediol is an important chemical raw material. The preparation of 1,2-propanediol from crude glycerol is usually carried out by chemical catalytic hydrogenolysis. It was found that the catalytic hydrogenation of glycerol to 1,2-propanediol was catalyzed by Cu/Mgo. The preparation method of the catalyst was investigated. It was found that when the catalyst was prepared by coprecipitation, the activity of the catalyst was the highest, the conversion of glycerol could reach 72%, the selectivity of 1,2-propanediol was 97.5%, and the conversion of glycerol could be further increased to 82% by adding trace NaOH. 1,2-propanediol was synthesized from glycerol by two-step method. First, glycerol was synthesized into acetone alcohol at atmospheric pressure. Then, acetone alcohol was hydrogenated to 1,2-propanediol under the action of copper chromate catalyst. The yield reached 75%. The results show that the technology of catalytic hydrogenation of glycerol to bio-1,2-propanediol has made great progress. However, in order to maintain the high activity of the catalyst, the purity of glycerol is generally high, and further treatment and purification of crude glycerol are needed.
1,3-propanediol
1,3-propanediol is an important intermediate in organic synthesis and an important raw material for the synthesis of polyester PTT (polypropylene terephthalate). With the continuous promotion of biodiesel technology, the production of 1,3-propanediol from crude glycerol by biological method has attracted extensive attention of researchers all over the world. Several strains of 1,3-propanediol fermentation have been reported in the literature, such as Klebsiella pneumoniae, Lactobacillus brevis, Citrobacterfreundii, Clostridium butyricum, Clostridium pasteurianum and so on. Hu Qiulong et al. fermented 1,3-propanediol from glycerol, a by-product of biodiesel, Klebsiella spp. as a strain. The production efficiency and economic feasibility of glycerol with different purity were investigated. The results showed that the conversion rates of 1,3-propanediol from refined glycerol (purity & gt; 98%), crude glycerol A (purity 83%), crude glycerol B (purity 78%) and crude glycerol C (purity 68%) were respectively. The cost of 1,3-propanediol in crude glycerol A and B production units is lower than that of refined glycerol and crude glycerol C through rough economic evaluation, which is 52.38%, 48.08%, 45.22% and 39.95%. MARIA et al. improved Clostridium butyricum by metabolic engineering. A recombinant strain DG1 was obtained. It was found that when glycerol was used as substrate, 1,3-propanediol could be produced efficiently by fermentation, and it could be operated continuously for a long time at a high volumetric yield of 3g/(L.h). Using Klebsiella neumoniae ATCC15380 as strain, crude glycerol as byproduct of biodiesel as raw material, ANAND et al. fermented to produce 1,3-propanediol. Among them, the yield of propanediol can reach 56g/L, the molar conversion rate of glycerol is 0.85. The purity of 1,3-propanediol can be obtained by separating and purifying the fermentation broth, and PTT products can be successfully prepared from it to meet the requirements of polymerization grade. Biological production of 1,3-propanediol has the characteristics of mild reaction conditions, low environmental pollution and renewable resources. However, there are still some difficulties in its large-scale industrialization. The main limiting factors are the high cost of raw materials and the high cost of separation and purification process. The production of 1,3-propanediol from crude glycerol is an effective way to reduce the cost of raw materials.
