Esterification synthesis of n-butyl propionate by reactive distillation

• Main Authors: Liu, Wen-Tzong, 劉文宗
• Other Authors: Tan, Chung-Sung
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/29448513497004518347

博士 === 國立清華大學 === 化學工程學系 === 90 === The objective of this study was to investigate the reactive distillation technique, a promising technology combining distillation and reaction in one column in order to reduce capital and operating cost, using the esterification of n-butyl propionate from propionic acid and n-butanol as the model system. The research contents included investigation of chemical equilibrium between each pair in product mixtures and screening of catalysts among the commercial solid acids like acidic exchange resins. A 50 mm column was used to carry out the catalytic distillation experiments and three kinds of catalysts installation methods were tested. The computer simulation was performed to investigate how the operating variables such as reflux ratio, stripping area, reaction area, rectification area, and boil-up ratio affect the purity of the product and the conversion of propionic acid. The obtained results of this study are listed as follows: 1.The VLE data of propionic acid + n-butyl propionate were established from the VLE experiments conducted at pressures ranged from 60 kPa~101.3kPa. The NRTL model was found to be the most appropriate to represent liquid phase non-idealities. The Hayden-O’Cornell equation was used to account for vapor phase association. The UNIFAC was found not to describe the VLE because it predicted an azeotrope that was not observed in the experiments. The NRTL-HOC model predicted the existence of a double azeotrope at low pressures that has been reported in the literature. 2.The Amberlyst 35 was observed to possess the highest activity and physical strength among the acidic exchange resins used in the catalyst screening. From the study on chemical reaction kinetics, it was found that the reaction was endothermic with a heat of reaction of 0.46 kcal/mol. Heat due to dissociation of propionic acid was postulated to contribute to the total heat of reaction. The mechanism for this reaction was believed to follow the Eley-Rideal model in which the adsorbed propionic acid reacted with n-butanol in the bulk liquid. The controlling step was the adsorption of propionic acid. 3.N-Propionate with a high purity could be produced from the bottom of a reactive distillation column. The co-jet tray method for the installation of solid catalysts was recommended because of high liquid holdup, low cost, and easy replacement of catalysts. 4.The key to produce n-butyl propionate with a purity of >99.5 wt% was to maintain the bottom temperature of a reactive distillation column sufficiently close to the boiling point of n-butyl propionate. The key to assure a complete conversion of propionic acid in order to prevent from a high separation cost of propionic acid was the setup of a reaction zone, including catalysts amount, liquid holdup, etc. The presence of redundant n-butanol did not result in a higher conversion of propionic acid because it lowered temperature in the reaction zone. The simulation based on the equilibrium stage model using the Aspen plus simulator was found to correlate the experimental data on temperature profile in column and composition in the bottom and top well. The regressed kinetic parameter could represent both mass transfer and chemical kinetic effects.