As a kind of important industrial raw materials and pharmaceutical intermediates, 3-mercaptopropionic acid (3-MPA) has attracted wide attention because of its various uses. At present, acrylonitrile and sodium hydrosulfide are generally used as raw materials to synthesize 3-MPA. The reaction process of this method is complicated, and the temperature control of each step of the reaction process is strict. With the increasing awareness of resource recycling, the method of synthesizing 3-mercaptopropionic acid with acrylic acid (AA) and petrochemical refinery by-product hydrogen sulfide as raw materials has gradually gained the attention of petrochemical refineries. The use of hydrogen sulfide as a by-product to synthesize 3-mercaptopropionic acid not only turns hydrogen sulfide into a waste, but also has a significant cost advantage over other synthetic methods. In view of the relatively lack of systematic research on the process of synthesizing 3-mercaptopropionic acid from hydrogen sulfide and refinery by-products at home and abroad, the heterogeneous reaction system and the synthesis process conditions of the homogeneous reaction system are respectively carried out. Detailed optimization and research were conducted to investigate the effects of various factors on the synthesis of 3-mercaptopropionic acid in the two reaction systems. The main work and conclusions are as follows:
The solid catalyst of heterogeneous reaction system was studied. The product prepared by precipitation method using magnesium acetate and oxalic acid as precursor and high temperature calcination was determined as catalyst for synthesizing 3-MPA. The liquid alkali for homogeneous reaction system A study was conducted to determine the reaction of triethylamine as a reaction system.
The product was analyzed by HPLC, GC-MS and IR. The formation of the target product 3-MPA was confirmed, and the composition and formation of by-products were analyzed.
3. Quantitative analysis of the reaction product was completed by HPLC external standard method. Based on the yield of 3-MPA, the optimum process conditions for the synthesis of 3-MPA were determined. The optimum process conditions for the heterogeneous reaction system are: using 1,4-dioxane as solvent, reaction temperature 80 ° C, H 2 S pressure 0.5 MPa, reaction time 5 h, n (catalyst): n (acrylic acid) = 0.2: 1, V (1,4-dioxane): V (acrylic acid) = 5: 0.2, at this time AA conversion rate of 100%, 3-MPA selectivity of 35.6%; the best homogeneous reaction system The process conditions are as follows: a reaction sequence in which triethylamine is first reacted with H2S and then added to AA, n(triethylamine): n(AA)=2.08:1, reaction temperature 80-C, reaction time 6h, first The amount of secondary H2S was 0.1 Mpa, and the amount of H2S introduced to the second time was 0.6 MPa. At this time, the conversion rate of AA was 99.95%, and the selectivity of 3-MPA was 60.03%. In general, the conversion rates of the two reaction systems are not much different, and the selectivity of the 3-MPA in the homogeneous reaction system is much better than that of the heterogeneous reaction system.
Based on the reaction principle of the synthesis of 3-MPA between acrylic acid and hydrogen sulfide proposed by the predecessors, the reaction principle of the synthesis of 3-MPA was discussed.