| As an important chemical product and organic synthesis intermediates, propionic acid is well known as one of the most economical, effective and safest food preservative, which is extensively applied in antisepsis and preservation for corn, feedstuff and food. The propionic acid production capacity is gravely insufficient in our country, and large quantities of propionic acid is imported every year. In the production methods of propionic acid, hydrocarboxylation, propionaldehyde oxidation and light hydrocarbon oxidation has been industrialized, but these process have some disadvantage like harsh reaction conditions and complex technology, etc. The process of propionic acid production by vapor phase carbonylation of ethanol has such advantage as abundant raw materials, mild conditions, low cost and no pollution, etc. that was future development direction, and the study on catalyst in the reaction system has important theoretical value and practical significance. The vapor-phase carbonylation of ethanol to propionic acid and ethyl propionate under atmospheric pressure was investigated, combining the performance of the catalyst evaluation and characterization of its physical and chemical properties, the preparation of the catalysts and reaction process were optimized and the reaction kinetics were investigated.The physical properties and surface chemical properties of different activated carbon support materials were analysised. The results showed that wood charcoal had an amount of mesopore structure, higher surface area, less ash content and impurity, good thermal stability and more oxygen-containing functional groups. These factors were conducived to the dispersion and positioning of active components. Catalyst structure was analyzed and characterized by TPR, SEM and TG. The results showed that precursors of catalysts was more easily be reduced, A considerable number of active site were formed, the metal dispersion and distribution consistency of nickel were highest. Ethanol conversion rate and product selectivity were the highest, 67.62% and 65.48%, respectively.The result of surface modification for activated carbon indicated that acid modification had increased surface area, mesopore structure and the number of oxygen-containing functional groups, and it was the ideal pretreatment methods. The optimum acid concentration was 5mol/L. The catalyst of activated carbon after modification as the support was prepared. The influence of preparation factors for catalyst was investigated. The preparation conditions of catalyst were optimized and the result showed that optimum nickel loading was 10%, calcination temperature was 400 ℃ in the beginning 2 hours, and reduction temperature was 450 ℃ in the next 2 hours. In addition, the second component zinc had a promoting effect on catalyst performance, especially when the nickel loading was 7%, and when active components zinc was impregnated in second step, the catalyst worked particularly well. Ultrasonic treatment was good for dispersion of active components.Reaction process conditions of ethanol carbonylation were investigated, the optimum reaction conditions were obtained: reaction temperature: 260℃; the space velocity of ethanol: 1.3mLC2H5OH/(gCat·h); n(CO)∶n(EtOH)∶n(EtI)=20∶10∶1(mol); Under forementioned conditions, ethanol conversion of 86.78%, and carbonylation selectivity of 81.6%. The catalyst achieved higher activity after the induction period of 2 hours, in the study period, the stability of the catalyst was higher.Ethanol and carbon monoxide had participated in the catalytic cycle by intermediate CH3CH2-(CO)-Ni-I in transition state active, and synthesized propionic acid and propionic ether as final products. Ethanol carbonylation dynamics equation was obtained, Combining with reaction mechanism, it can be inferred that CO insertion step and ethanol reduction alcoholysis step were control steps to generate propionic ether. |
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