Simulation and optimization of separation processes for the downstream of the catalytic oxidation of HCl as byproduct from the fluorochemical industry

Abstract

The catalytic oxidation of gaseous HCl with a small amount of HF to Cl₂ is of utmost importance and desire for chlorine recycling in the fluorochemical industry. Herein, based on the results from the catalytic oxidation of HCl as byproduct contaminated with HF and fluorocarbons from the production of 1,1,1,2-tetrafluoroethane (HFC-134a) over a recently developed RuO₂/MgF₂ catalyst, the separation and purification processes of the downstream from the catalytic oxidation unit were simulated and optimized using the Aspen Plus software. In the simulation and optimization, a separation flow for Cl₂ purification was built up and the corresponding mass and energy balances were made as well. The results show that both produced H₂O vapor and unconverted HCl from the catalytic reactor can be effectively removed by a two-stage cooling dehydration unit coupled with a three-stage drying tower to obtain 29.90 wt% hydrochloric acid. In addition, the relationship between the dehydration amount and the heat load of the drying tower was optimized, showing a H₂SO₄ (98.00 wt%) consumption of 11.8 kg per ton of Cl₂ produced, i.e., 11.8 kg/t, in the drying tower. Furthermore, the gaseous mixture of Cl₂ and O₂ can be separated by a pressurized distillation unit, in which the operating pressure and temperature as well as the heat load of the condenser were optimized, showing that a liquified Cl₂ concentration of 99.93 wt% with a recovery efficiency of 97.0 % can be achieved. The current research, therefore, provides some fundamental base for the industrialization of the recovery of Cl₂ from the byproduct HCl in the fluorochemical industry.