At present, chemical synthesis is commonly used in industry, that is, fatty acids and fatty acid derivatives (oils, fatty acid esters, etc.) are reacted with polyglycerol in the presence of acid or base catalysts. Zhou Xing used lauric acid and capric acid as raw materials, sodium hydroxide as catalyst, and reacted with polyglycerol by direct esterification method at 220 ℃ under nitrogen protection to synthesize lauric acid polyglycerol ester and capric acid polyglycerol ester. . Usha et al. prepared Polyglycerol Fatty Acid Ester by esterification of fatty acids obtained by hydrolysis of cottonseed oil and castor oil with polyglycerol at 230-235 °C. Shikhaliev et al. used caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid and stearic acid as raw materials, respectively, and prepared corresponding fatty acid methyl esters through methyl esterification, and then mixed with polyglycerol (average degree of polymerization of 5). A series of Polyglycerol Fatty Acid Esters with different carbon chain lengths and different degrees of esterification are prepared by transesterification under the action of alkali catalysts. The alkali catalysts used include sodium hydroxide, sodium carbonate, sodium methoxide, potassium hydroxide and potassium carbonate, among which sodium methoxide has the best catalytic effect. According to the different carbon chain lengths of fatty acids, the temperature of transesterification reaction is 180-220 °C.
The aforementioned homogeneous catalytic reaction using inorganic bases or acids as catalysts has the following problems: 1) The process reaction temperature is high (usually above 200 °C), the energy consumption is high, the equipment requirements are high, and the final product usually has Unpleasant color, odor, etc., limit the application of Polyglycerol Fatty Acid Ester in food, personal care products and other fields. 2) Due to the low catalyst selectivity and many by-products, and in order to obtain a valuable product with a low degree of esterification, a large excess of polyglycerol needs to be added, resulting in great difficulty in separation and purification. In addition, the production process generates a large amount of waste, because the inorganic acid or base that acts as a catalyst must be neutralized, and bleaching agents and adsorbents are usually added to remove the undesirable color and odor of the final product.
The development of new and green catalysts has been a hot research topic in recent years, such as solid heterogeneous catalysts, which can overcome the disadvantages of many side reactions, high energy consumption, waste of resources, and environmental pollution, and have the advantages of high efficiency and reusability. Nie Rongrong studied 4 kinds of solid catalysts (KOH/MgO, NaOH/MgO, KOH/Al2O3, NaOH/Al2O3) for the synthesis of medium-carbon chain fatty acid polyglycerol esters. After screening, KOH/Al2O3 has the best catalytic effect. And the catalyst can be reused, and the green synthesis process of Polyglycerol Fatty Acid Ester has been developed, which reduces the pollution to the environment. Márquez-Alvarez et al. proposed that solid catalysts based on MCM-41 and other mesoporous structures are more effective new methods for large-scale production of Polyglycerol Fatty Acid Ester and other polyol fatty acid ester emulsifiers, which have strong research significance and economic value. In addition, Zou Qiang used ionic liquid [HSO3-pmim]+[HSO4]- as a catalyst to catalyze the esterification of triglycerol and medium carbon chain fatty acid to synthesize triglyceride of medium carbon chain fatty acid, which has good catalytic performance and can be reused. After 5 times, the esterification rate of the reaction system is still maintained at about 90%, and it has good reusability.
New catalysts such as solid catalysts and ionic liquids have good catalytic performance and are reusable, and have good application prospects. However, the esterification reaction used in the synthesis of Polyglycerol Fatty Acid Ester still requires a reaction temperature above 200 °C, high energy consumption, and the color of the final product. Issues such as smell are not well addressed. In recent years, the synthesis of polyglycerol fatty acid esters by enzymatic catalysis has attracted worldwide attention. This method has mild reaction conditions (the reaction temperature is usually lower than 100 °C), and the enzyme catalyst has high selectivity, few side reactions and good product quality. , High security.
Xiao Yisha et al. used industrial oleic acid and oligoglycerol as raw materials, and prepared low Polyglycerol Fatty Acid Ester by esterification catalyzed by phospholipase A1. The reaction temperature was 45 °C, the amount of enzyme added was 1.6% (accounting for the total mass of the substrate), and the amount of water added was 4 % (accounting for the total mass of the substrate), the molar ratio of the substrate is 1:1, the reaction time is 12 h, and the esterification rate can reach 56.6%. Wan et al. used lipase Lipozyme 435 as a catalyst to catalyze the esterification of oleic acid and oligoglycerol in a solvent-free system to prepare oligoglycerol fatty acid esters. The reaction time was 4.5 h, the reaction temperature was 90 °C, and the amount of enzyme was 2% (accounting for 2%). The total mass of the substrate), the esterification rate can reach more than 95%. Peng et al. used long-carbon fatty acids, medium-carbon fatty acids and short-carbon fatty acids as raw materials, respectively, and used lipase Lipozyme 435 as a catalyst to carry out esterification with polyglycerol in a solvent-free system to prepare polyglycerol fatty acid esters with different carbon chain lengths. The reaction temperature was about 84 ℃, the reaction time was 6 h, and the esterification rate was 67%-72%. Wang et al. used methyl laurate and deca-glycerol to carry out transesterification reaction catalyzed by lipase (novozyme 435) to prepare deca-glycerol laurate. The reaction temperature was 65 °C. Under the optimal conditions, the conversion of methyl laurate was 84.4%.
