Yinglong Wang

Separating an azeotropic mixture of toluene and ethanol via heat integration pressure swing distillation

Abstract A procedure is suggested to separating a minimum-boiling azeotrope of toluene and ethanol via heat integration pressure swing distillation (PSD), and an optimized separation configuration is obtained via taking the minimization of the total annual cost (TAC) as an objective function. The result demonstrates that PSD with heat integration is more economical than conventional PSD without heat integration. Based on steady-state simulation results, several control structures were explored using Aspen Dynamics. The results indicate that the composition/temperature cascade control structure and the pressure-compensated temperature control of a PSD process with partial heat integration with stage 21 selected as the control stage in the low pressure column can handle disturbances well. As for the PSD with full heat integration, stage 20 of the low pressure column can act as the control stage because of its more efficient controllability under feed flow rate and feed composition disturbances.

Application of a simulated annealing algorithm to design and optimize a pressure-swing distillation process

Abstract The design and optimization of pressure-swing distillation (PSD) have a critical impact on its economics. An optimization method based on simulated annealing algorithm (SAA) was proposed. The move generator and cooling schedule of the SAA were discussed, and suitable parameter settings were investigated. Two cases of PSD with and without heat integration were optimized by the SAA-based optimization method using procedures of pressure specified and pressure optimized. The results of the process without heat integration were compared with conventional optimization methods. For the acetone-methanol system, the total annual cost (TAC) shows a 5.69% decrease with the pressure specified and a 17.32% decrease with the pressure optimized. For the methanol-chloroform system, the TAC shows a 1.79% decrease with the pressure specified and a 9.04% decrease with the pressure optimized. The SAA-based optimization method has the advantages of a high probability to obtain the global optimum, automatic calculation, and less computing time.

Controllability of separate heat pump distillation for separating isopropanol-chlorobenzene mixture

The isopropanol-chlorobenzene mixture is separated via separate heat pump distillation (SHPD) to achieve significant energy savings. Rigorous steady state and dynamic characteristics for this SHPD process are simulated using Aspen Plus and Aspen Plus Dynamics. Optimized operation conditions including vapor flow rate to compressor are developed on the condition of minimum total annual cost. Two control strategies are proposed to solve feed disturbance issues and the improved structure with QRe/F (lower column reboiler duty/feed flow rate) ratio scheme can maintain the two product purities requirement with smaller transient deviation and shorter settling time.

An improvement scheme for pressure-swing distillation with and without heat integration through an intermediate connection to achieve energy savings

Abstract Pressure-swing distillation is widely studied in academia and industry. Energy consumption is a key criterion for judging whether a pressure-swing distillation is better than other distillation methods. An improved process with an intermediate connection was developed based on the two-column pressure-swing distillation for separating a binary azeotropic mixture to save energy and reduce the total annual cost. The proposed pressure-swing distillation was applied to three case systems, two minimum-boiling azeotropic mixtures of ethyl acetate/ethanol and methanol/chloroform and one maximum-boiling azeotropic mixture of ethylenediamine/water. According to our analysis, the proposed pressure-swing distillation and heat-integrated scheme can reduce energy consumption and total annual cost. The pressure-swing distillation with the intermediate connection is promising for saving energy. This advantage assists in promoting the application of pressure-swing distillation and overall energy savings in the chemical process industry.

Phase Behavior and Thermodynamic Model Parameters in Simulations of Extractive Distillation for Azeotrope Separation

Extractive distillation (ED) processes for separating ternary mixtures of benzene-cyclohexane-toluene with dimethyl formamide (DMF) and N-methyl-2-pyrrolidone (NMP) were studied using Aspen Plus and PRO/II simulators. The Aspen Plus built-in binary interaction parameters for the toluene-DMF, benzene-NMP and cyclohexane-NMP systems resulted in inaccurate phase behavior calculations. The vapor-liquid equilibrium (VLE) for the three binary systems was regressed to illustrate the importance of using accurate model parameters. The obtained binary interaction parameters described the phase behavior more accurately compared with the built-in binary interaction parameters in Aspen Plus. In this study, the effects of the regressed and built-in binary interaction parameters on the ED process design are presented. The total annual cost (TAC) was calculated to further illustrate the importance of the regressed binary interaction parameters. The results show that phase behavior and thermodynamic model parameters should receive more attention during the research and development of ED processes.