Study On The Synthesis Process Of Dimethyl Phthalate Catalyzed By Phosphotungstic Acid In The Oscillatory Flow Reactor

Dimethyl phthalate is widely used in plastic, coatings, pesticides, building material, consumer cosmetic products and so on. At present, the most common production process of dimethyl phthalate is taking place in the batch stirred tank reactor involving the usage of phthalic anhydride, methanol as the reactants and sulfuric acid as the catalyst, which has two problems. One is serious corrosion to equipment and environmental pollution. The other one is low production efficiency and large site area.This thesis chose phosphotungstic acid which has the strongest acid in the Keggin series of heteropoly acid as the catalyst of esterification so that the problems of corrosion to equipment and environmental pollution are solved. Compared to the tubular reactor or stirred tank reactor, the oscillatory flow reactor has a better residence time distribution and mixing performance for the esterification reaction which needs long resistance time and the flow rate is slow under the continuous operation condition. So it is meaningful to study on the synthesis process of dimethyl phthalate catalyzed by phosphotungstic acid in the oscillatory flow reactor.However, information related to the quantity study on the kinetics of esterification of monomethyl phthalate with methanol catalyzed by phosphotungstic acid is scarce in the literature. In this thesis, the thermodynamics calculation and analysis of the reaction system showed that this reaction was exothermic and feasible thermodynamically because of the negative Gibbs energy change. Besides, the forward reaction rate constants and equilibrium constants were measured at the temperatures ranging from373.15K-413.15K and the catalyst concentrations ranging from0.5wt%-2.5wt%. Then the kinetic equation was obtained. The kinetic equation illustrated the esterification of monomethyl phthalate with methanol catalyzed by phosphotungstic acid is a second-order reaction. The activation energy is equal to61.10kJ mol-1and the pre-exponential factor increases linearly with the catalyst concentrations.Based on the kinetic equation, the numerical simulation on the synthesis process of dimethyl phthalate catalyzed by phosphotungstic acid in the oscillatory flow reactor with conic ring baffles was studied utilizing the method of computational fluid dynamics. The results showed that the mixing in the cell was enhanced with the oscillation intensity increasing. The relative error between the calculated data and the experimental data of monomethyl phthalate concentration was about5%which means that the mathematical model used in this thesis is applicability. Besides, the calculated and experimental results proved that the oscillatory flow reactor with conic ring baffles can be used in the continuous process to synthesize of dimethyl phthalate.