Fumaric acid is an important food additive and industrial intermediate compound. The traditional methods of producing fumaric acid were catalyzed by maleic acid isomerization. In this study, isomerization of maleic acid in water without catalyst was investigated at elevated temperature, which addressed the problem of sewage discharge. HPLC analysis showed maleic acid converted into fumaric acid and small amount of malic acid simultaneously. The effects of concentration of maleic acid, reaction temperature, reaction time, and stirring on the yield of fumaric acid were investigated. The optimum reaction conditions were also explored. The results showed the isomerization of maleic acid reached equilibrium at about 1 h, stirring did not affect the reaction rate, and conversion due to the monomolecular mechanism. In order to achieve "zero emission," the recycle of filter liquor was also studied. The pH of filter liquor changing signifies the lower pH was in favor of the conversion of maleic acid to fumaric acid. The high yield and recyclability suggested that this process had promising application in fumaric acid production.
The catalytic performance of mixed metal oxides was evaluated for the synthesis of diethylene glycol bis(allyl carbonate) (ADC) by transesterification of diethylene glycol (DEG), dimethyl carbonate (DMC). and allyl alcohol (AAH), and MgO–PbO was found to show the highest catalytic activity. The influence of preparation conditions on the catalytic performance of MgO–PbO was studied and its suitable preparation conditions were as follows. A calcination process was used, with Mg(OH)2 and Pb(CH3COO)2·3H2O as precursors, molar ratio of Mg:Pb = 6:1, and calcination temperature of 650 °C. Under the following reaction conditions, molar ratio of DEG:DMC:AAH = 0.08:1:2, weight percentage of MgO–PbO = 1.5% of total weight of all reactants, 100 °C, 6 h, and vacuum of 0.08 MPa, the yield of ADC was 97.3%. Moreover, MgO–PbO showed a good recyclability; ADC yield of 95.4% could be achieved after the catalyst was reused for two times. The results of N2 adsorption–desorption measurement and XPS analyses for MgO–PbO indicate there exists an interaction between MgO and PbO, which promotes the catalytic performance and recyclability of MgO–PbO. Furthermore, the reaction pathway for ADC synthesis was elucidated by means of GC-MS analysis and experimental verification.
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