Reactive Distillation Process Of Ethyl Acetate Synthesis Catalysed By 12-molybdophosphoric Acid

Ethyl acetate (EA) is a important organic chemical and one of green solvents. The main methods of EA synthesis include the estenfication of acetic acid with ethanol and the condensation of acetaldehyde. Along with the exhaustion of petroleum resources, the esterification method is putting on the schedule because it could use biological resources indirectly.The research work of this dissertation focus on two key points for energy-saving and pollution-reducing in the industrial production of EA by esterification: catalysts and separation. The feasible schemes were suggested.Based on the investigation of published literatures, a composite catalyst of (phosphomolybdic acid + phosphoric acid) was designed: phosphomolybdic acid acts as the function component of catalysis and phosphoric acid acts as that of corrosion-inhibition, which gives both the high effectiveness of catalysis and the great reduction of corrosion to equipment. The two components are miscible in reactants and products to form homogeneous catalysis system which eliminates the influence of interphase mass transfer on catalyzing efficiency. The two components are involatile so that they can be excluded from entering the product and by-product streams in the sequential separation steps to avoid the loss of catalyst and the pollution. Comparing with the conventional catalyst sulfuric acid, the new catalyst gets over the disadvantages: severe corrosion to equipment, inevitable side reactions, and pollutants of sour water and sour residue. Comparing with the acidic ion-exchange resin recently applied in industry, the new catalyst overcomes the disadvantages: non-negligible resistance of interphase mass transfer, periodical regeneration and reinstallation, and pulverization of resin particles to result in loss of catalyst.Due to the lack of reference data for the new catalyst, the experiments about the reaction rate of esterification and the corrosion rate of three steel materials commonly used were carried out first to investigate the functions of the twocomponents in catalysis system. The function feasibility of the new catalyst was verified. Then the reaction kinetics of the catalyst were measured under conditions of atmospheric pressure and temperature range of 333.15K～393.15K, which provides the quantitative calculation in the process of EA synthesis with necessary basic kinetic data.In present reactive distillation process, the top-water-ejection scheme, in which ethanol, EA and water are drawn out of column at the top, is widely used. This scheme results in disadvantages of a large reflux ration, multiple recycle streams in sequential separation steps and high consumption of energy. Against these, a bottom-water-ejection scheme based on a reactive extractive distillation process was proposed. The excessive acetic acid was fed into the upper middle section of column to increase the conversion of ethanol and, at the same time, to extract water from the up-flow mixture to break the formation of azeotropes of ethanol, EA and water in that section. The product EA of high concentration was drawn out of column as a side stream at the upper section. A little of distillate containing water at the top was recycled to middle section. The by-product water and superfluous acetic acid were drawn out of column at bottom and were separated in a dehydration column. The dehydrated acetic acid with catalyst in it was recycled to the upper-middle section of column.Aspen Plus was used to carry out a simulation study on the above process. The influence of stage number in reactive section, molar ratio of acetic acid to ethanol in column, reflux ration and position of side stream on the performance of esterification column was investigated. The simulation results showed that this process was feasible and that the concentration of EA obtained as upper side stream is about 98%, the bottom mixture of acetic acid and water contained also 1% of EA and trace ethanol. The reflux ratio of esterification column was only 2.5 to 3, which reduced the energy consumption of the column obviously.