Simulation And Energy-saving Design Of Benzoic Acid Separation Process

Benzoic acid is an important intermediate or monomer in the chemical industry, which has a wide range of applications in food, pharmaceutical and fine chemical industry. Generally, liquid phase catalytic oxidation of toluene is used to prepare benzoic acid, and distillation is used to separate the product of the reaction to get high-purity benzoic acid. Energy consumption of distillation accounts for a significant proportion in the total energy consumption of benzoic acid preparation process, so research on energy saving of distillation is of great significance.Chemical process simulation software Aspen plus was used to simulate benzoic acid separation process. Short-cut design model and rigorous calculation model were selected to simulate distillation columns, and NRTL activity coefficient model was used to calculate thermodynamic properties of the materials. Sensitivity analysis tool was used to study the effect of operating pressure, number of theoretical plates, feed location, distillate mass and reflux ratio on product purity and energy consumption, and operating parameters were optimized to ensure high purity of product and low energy consumption. With optimized operating parameters, the separation system could export benzoic acid product with mass purity of99.5%and benzaldehyde by-product with mass purity of99.5%. Energy consumption maintained at a low level.Analyzed the original process, and made a process modification plan to save energy. Steam stripping method that used in the removal of toluene in the original process was changed to general distillation operation. Despite the requirement of more theoretical plate, it could save equipment investment and significantly reduce energy consumption. Energy needed to remove toluene dropped to49.57kw from60.22kw. The feasibility of heat integration between the distillation columns was studied, and a plan of integrating the condenser of benzoic acid column with the reboiler of lightness-removing column was proposed. Adjusted the operating pressure of lightness-removing column to meet the requirement of minimum heat transfer temperature difference, and heat transfer temperature difference reached15.64℃. The reboiler of lightness-removing column could be canceled and the condenser heat duty of benzoic acid column was reduced due to the use of heat integration. By taking the modification plan, heat load could be21.6%lower, and cooling load could be34.5%lower than the original process.