Heat-integrated Pressure-swing Distillation Process Research Articles

Energy-saving strategy for separation of methylcyclohexane/tert-butanol azeotrope

With the increase in industrialization, researchers are striving to pursue energy-saving and environment-friendly separation technologies. In this regard, effective separation of azeotropes is one of the focus areas in recent years. According to the characteristics of methylcyclohexane (MCH) and tert-butanol (TBA) azeotropes, a pressure-swing distillation (PSD) process is established in the current work. Combined with steam recompression and heat integration, two improved separation processes for reduced energy consumption are designed. The operating parameters had a significant effect on the efficiency and cost of the process. Therefore, the selection of parameters was discussed in detail. The proposed PSD processes were evaluated according to the assessment indices including total energy consumption (TEC), CO2 emissions and total annual cost (TAC). The results showed that the improved processes obviously decreased the energy consumption and improved the economy whether it is heat pump pressure swing distillation (HP-PSD) or heat integrated pressure swing distillation (HI-PSD). The HI-PSD process can achieve a TAC savings of 30.86%, TEC reduction of 37.59% and CO2 reduction of 36.34%. The HP-PSD process is found to be the most economical and environment-friendly process among the studied processes, and could achieve 34.92% TAC savings, 42.89% TEC reduction and 50.98% CO2 reduction.

An advanced optimization strategy for enhancing the performance of a hybrid pressure-swing distillation process in effective binary-azeotrope separation

The separation of binary azeotropes with low cost and energy consumption is important and challenging for the production of chemicals. A hybrid heat-integrated pressure-swing distillation process (HHIPSD) with heat pump was proposed for the separation of both maximum- and minimum-boiling azeotropes in this work. Compared to the conventional fully heat-integrated pressure-swing distillation process (FHIPSD), the HHIPSD process showed lower total annual cost and higher thermodynamic efficiency in the separation of seven minimum-boiling azeotropes of benzene-ethanol, methanol-acetone, methanol-ethyl acetate (EA), ethanol-EA, acetonitrile-ethanol, isobutanol (IBA)/isobutyl acetate (IBAc) and diisopropyl ether (DIPE)-isopropyl alcohol (IPA), and two maximum-boiling azeotropes of water-ethylenediamine (EDA) and acetone-chloroform. For the best performance of HHIPSD process, robustness and algorithm optimization were studied in this paper. Scenario analysis method was proven to greatly enhance the convergence of HHIPSD models. The improved genetic algorithm (GA) was modified by particle-swarm optimization and pattern search method and validated by 13 benchmark functions. Meanwhile, different constraint handling methods were studied to ensure the better performance of the improve GA method. With the improvement of model robustness and optimization algorithm, the HHIPSD process achieved 21.6 % and 4.2 % decrease of TAC for water-EDA and methanol-acetone separation, respectively, compared to FHIPSD process. The proposed HHIPSD process together with the optimization strategy suggests the pressure-swing distillation technology can be highly effective in azeotrope separation.

Study on energy saving of heat integrated distillation process for methyl acetate–methanol–tetrahydrofuran–water

ABSTRACT Based on the characteristics of binary azeotropic composition in the mixture of methyl acetate–methanol–tetrahydrofuran–water sensitive to pressure, pressure swing distillation (PSD) and double-solvent extraction distillation (DSED) were proposed to study the separation of the quaternary system. Numerical simulations were performed by ASPEN PLUS software (version 10.0) environment under the WILSON thermodynamic model. The economy of PSD and DSED process was performed, and the heat integration of two distillation processes was compared based on total annual cost (TAC). Research results of PSD indicated that compared with conventional PSD (CPSD), heat-integrated PSD (HIPSD) can save energy consumption and TAC by 33.87% and 30.70%, respectively, and moreover increase thermodynamic efficiency by 1.77%, so it had obvious energy-saving effect and economic advantage. Simulation results of DSED showed that water (H2O) and ethylene glycol (EG) were most suitable extractants for the system, and the suitable solvent ratios for H2O and EG were 0.28 and 0.38, respectively. Compared with conventional double-solvent ED (CDSED), heat-integrated double-solvent ED (HIDSED) can save energy consumption and TAC by 43.29% and 28.12%, respectively, and moreover increase thermodynamic efficiency by 3.25%, so it was superior to CDSED. The results indicated that the energy consumption and TAC of HIDSED are respectively 63.56% and 44.01% less than the HIPSD process, and the thermodynamic efficiency of the former is 3.9% larger than the latter, so the HIDSED process shows better economic and energy-saving effect.

Evaluation of membrane-assisted hybrid processes for the separation of a tetrahydrofuran-methanol-water mixture

The combination of pervaporation (PV) and distillation provide considerable potential for the separation of azeotropic multicomponent mixtures. However, only a proper techno-economic evaluation of these processes compared to a reference process enables a reliable evaluation of benefits. Within this work, the potential of a PV-assisted distillation process is evaluated for the mixture of tetrahydrofuran methanol and water compared to a heat-integrated pressure-swing distillation process. Since initial evaluations reveal a significant potential of the PV-assisted processes regarding the required energy demand, experimental investigations of three polymeric and two inorganic membranes were conducted. A detailed characterization of the most promising membranes PERVAP™ 4155–40 and Hybrid Silica HybSi® AR was performed, and the latter one provided the highest permeance and selectivity. Based on the derived flux models, an economical optimization was performed. Despite the energy-benefits of the PV-assisted processes, the reference process was still evaluated more favorable under the considered framework, mainly caused by high investment and cooling costs. The current study illustrates the benefits of a tight integration of model-based process design and experimental investigations. Despite possible energy savings and promising performance metrics of the membrane, an assessment of the techno-economic performance of these processes is of major importance to identify applications.

Design and control of ethyl acetate/n-hexane azeotropic system separation via different heat-integrated pressure-swing distillation process

Design and control of ethyl acetate/n-hexane azeotropic system separation via different heat-integrated pressure-swing distillation process

Dynamic control analysis of partially heat-integrated pressure-swing distillation for separating a maximum-boiling azeotrope

Dynamic control behavior of partially heat-integrated pressure-swing distillation process is investigated by taking a separation of maximum-boiling ethylenediamine/water azeotrope as the example. The feasibility of using a single-end control strategy is affirmed by the method of feed composition sensitive analysis, and a series of novel control structures are developed to eliminate or attenuate the snowball effect, wherein the special control loops are that the flow in bottoms recycle line is controlled by regulating the set-point of a flow controller placing in recycle loop through two alternative ratio controllers including flow and thermal ratios. Both the robust and stable regulatory control are achieved with dual-product composition restored to their steady-state design specifications for handling large (20%) step changes in throughput and feed composition. The effectiveness of control structure with flow ratio option works better than that of another alternative taking the comprehensive consideration of product transient deviations, product offsets and settling time. Besides, there is no product offset for distillate ethylenediamine composition, although only the temperature control loops are used in the low-pressure column for control structure with thermal ratio option, which is the advantage of this control structure since the dual-end product composition control loops are required for that with thermal ratio. Of the particular importance is that the severer and stronger oscillatory effect of product composition is weakened by taking the proportional-only cascaded temperature controller for facing throughput perturbations.

Exploration of a heat-integrated pressure-swing distillation process with a varied-diameter column for binary azeotrope separation

The pressure-swing distillation (PSD) processes with varied-diameter columns (VDCs) for separating methanol–chloroform and n-heptane–isobutanol are studied. Furthermore, two heat-integrated PSD processes, partial integration and full heat integration, are discussed with ordinary and VDCs. The results show that whether it is heat integrated or non-heat integrated, the processes using VDC have an advantage in the economy. Based on the minimum total annual cost (TAC), the dynamic controllability without and with full heat integration for an azeotrope system methanol/chloroform is explored. The dynamic controllability without and with partial heat integration for the azeotrope system n-heptane/isobutanol is discussed. The results indicated that compared with the dynamic responses without heat integration process, the heat-integrated PSD with a VDC did not increase the control difficulty while maintaining its economy. More azeotropic systems should be studied to investigate their economics and control effects, which will benefit PSD design and industrial application.

Heat-integrated pressure-swing distillation process for separation of the maximum-boiling azeotrope diethylamine and methanol

Abstract The steady-state economics and dynamic controllability of heat-integrated pressure-swing distillation (PSD) processes are explored by taking the separation of maximum-boiling azeotrope diethylamine and methanol as demonstrating example. Compared to the conventional process, the B-E configuration (hot stream preheating the feed of high-pressure column) is attractive than others due to reducing 36.83% in energy consumption, 20.49% in CO2 emissions and 25.69% in total annual cost (TAC) and enhancing 49.48% in thermodynamic efficiency, respectively. Dynamic controllability of the economic efficient backward-integrated processes is also investigated by teaching the terminology of “simultaneous design”. The effectiveness of single-end control strategy is determined by the method of feed composition sensitive analysis, and a series of control structures are devised and assessed by the perturbations of feed flowrate and composition. The robust control scheme (CS5) with the ratio strategy to manipulate recycle stream flowrate is constructed to eliminate snowball effect and oscillation phenomena for partially case. It is also used to the combinational heat-integrated processes, and the differences of integral absolute error (IAE) are small between the alternative arrangements, demonstrating that the performance of single-end control scheme with the feedforward strategy of molar ratio reflux-to-feed (R/F) is robust and efficient.

Design and control of extractive distillation process for separation of the minimum-boiling azeotrope ethyl-acetate and ethanol

Design and control of extractive distillation process is explored by taking the separation of minimum-boiling azeotrope ethyl-acetate and ethanol as an example. The two evaluation indicators of second-law efficiency and CO2 emissions are employed to evaluate different alternatives, which consist of conventional case, F-E process (hot solvent stream to preheat fresh feed of extractive column), B1-E process (hot solvent stream to preheat feed of recovery column), and F-B1-E process (hot solvent stream to preheat feed of extractive and recovery column). The conventional case can reduce 32.23% in total annual cost (TAC), 28.81% in energy-saving comparing to economically optimum fully heat-integrated pressure-swing distillation process. Besides, it can further cut 4.38% in TAC and 9.79% in steam cost by heat integration B1-E configuration while others are 1.11% (1.30%) in TAC and 10.45% (12.11%) in steam cost, where, data in the brackets are for F-B1-E process. Furthermore, the control of extractive distillation process is explored since the interaction of parameters is complicated. For conventional process, the effectiveness of single-end control strategy is determined by the method of feed composition sensitive analysis. The appropriate control scheme (CS3) is screened by the indicator of integral absolute error (IAE) since its deviations of product purities to specifications are the least. A new control scheme of bypassing portion of hot stream around economizer with dual-point temperature control strategy is proposed for the efficient economics thermal integration alternative, and it can still achieve robust control performance at facing feed flowrate and composition disturbances.

Heat-integrated pressure-swing distillation process for separating the minimum-boiling azeotrope ethyl-acetate and ethanol

Abstract Design and control of the forward integration of pressure-swing distillation processes is explored with the aid of the tools of Aspen plus and Aspen dynamics taking the separation of the minimum-boiling azeotrope ethyl acetate and ethanol as an example. The optimized separation configuration is obtained by taking the minimization of total annual cost (TAC) as an objective function. The two key performance indicators of second law efficiency (η) and carbon dioxide emissions are employed to evaluate the three operations, which consist of conventional non-heat integration and the corresponding partially and fully heat integration processes. Compared to the non-heat integration process, the fully heat integration process is more attractive since it can achieve 33.33% energy consumption saving, reduction of 31.33% CO 2 emissions and 26.64% TAC. Furthermore, the control of the PSD processes with heat integration are explored since the interaction of parameters are complicated for this neat configuration. The effectiveness of the single-end control strategy is evaluated and determined by method of the feed composition sensitive analysis, and a series of control structures are devised and assessed by the perturbations of the feed flow rate and feed composition. It is concluded that the small disturbances are addressed for fully heat integration in comparison with the partially heat integration owing to the degree of freedom reduction. In addition, the efficient control strategy with the ratio scheme to manipulate the cascade flow controller is developed to eliminate the snowball effect for PSD with partially case.

Control of a Heat-Integrated Pressure-Swing Distillation Process for the Separation of a Maximum-Boiling Azeotrope

Methanol and trimethoxysilane form a maximum-boiling homogeneous azeotrope whose composition changes fairly significantly with pressure, so separation into high-purity products is viable using pressure-swing distillation. Heat integration of the two columns can be used to reduce energy costs since they operate at different temperatures. The pressure in the high-pressure column is not controlled but “floats” depending on conditions in the base of the low-pressure column. An auxiliary reboiler is required to balance the heat duty in the low-pressure column. Since pressure affects the composition of the azeotropic, this variable pressure increases the complexity of the required control structure. The purpose of this paper is to develop a control scheme that can effectively handle large disturbances in feed flow rate and feed composition.

Design and control of distillation processes for methanol–chloroform separation

The binary mixture of methanol–chloroform exhibits a minimum-boiling azeotrope with ∼34mol% methanol at 327K under atmospheric pressure. In this paper, design and control of alternative distillation processes for separation of methanol–chloroform azeotropic mixture are explored. The steady-state and dynamic simulations are carried out with Aspen Plus and Aspen Dynamics. The comparison in terms of steady-state design is done between homogeneous extractive distillation and pressure-swing distillation processes. The pressure-swing distillation process is found significantly more economical than the homogeneous extractive distillation process. Based on results, a heat-integrated pressure-swing distillation process is considered, and found economically feasible. Thus, the dynamic comparison is done between pressure-swing distillation systems with and without heat integration. The pressure-swing distillation process without heat integration can be controlled using a basic control structure, while the heat-integrated pressure-swing distillation system requires a pressure-compensated temperature control structure. Results show that dynamic controllabilities of both processes are quite similar.