Energy-efficient Extractive Distillation Research Articles

Study on the separation of methyl-ethyl-ketone / isopropanol / water ternary mixture by energy-efficient extractive distillation processes

The separation of ternary mixtures of methyl-ethyl-ketone (MEK)/isopropanol (IPA)/water, which are produced through chemical processes, is an imperative task aimed at reducing energy expenditures and mitigating environmental contamination. In the industry, Ethylene glycol (EG) and dimethyl sulfoxide (DMSO) are commonly employed as extractants. The selection of EG as the extractant was based on an investigation into the impact of relative volatility. Three distinct processes, namely conventional extractive distillation (CED), side-stream extractive distillation (SED), and heat pump extractive distillation (HPED), were evaluated by total annual cost (TAC), total energy consumption (TEC) and carbon dioxide emissions (CO2 emissions). The results demonstrate that both the enhanced SED and HPED processes effectively decrease energy consumption. Specifically, the TEC for the SED process exhibits a reduction of 15.36% compared to the CED process, resulting in a TAC saving of 9.06% and a decrease in CO2 emissions by 12.37%. Similarly, the HPED process surpasses the CED process by achieving a TAC saving of 15.41% and a CO2 emissions reduction of 22.61%. Consequently, this research presents a novel approach for the separation of MEK/IPA/water, offering significant practical implications.

Structure optimization of task-specific ionic liquids targeting low-carbon-emission ethylbenzene production

The production of ethylbenzene from dry gas is a representative of an energy-intensive process in oil refineries, and the distillation process accounts for the major energy consumption and carbon emissions. Due to the increasing energy and environmental challenges, there is a strong demand for new technologies or intensified process designs that enable us to have energy-efficient and sustainable process operations. In this work, an ionic liquid (IL)-based energy-efficient extractive distillation (ED) process with low carbon emission is proposed for the distillation process of ethylbenzene production from dry gas. First, the structure of task-specific ILs is optimized through the computer-aided IL design (CAILD) method with a novel design objective. An ammonium-based IL ethylammonium trifluoromethanesulfonate ([C2H8N][TfO]), that has the best objective performance, is identified by solving a mixed-integer nonlinear programming (MINLP) problem. The energy, environmental (carbon emission), and economic performance of this [C2H8N][TfO]-based ED process in the ethylbenzene production is then thoroughly evaluated on the basis of optimized process operations in Aspen Plus. For demonstration purposes, a case study for the separation process of an industrial-scale ethylbenzene production in a Chinese refining industry is performed. When compared to the conventional process that is currently used in the petrochemical industry, our proposed [C2H8N][TfO]-based ED separation process has 40 % energy (hot utility) savings and a 11 % cost reduction. Notably, the IL-based ED separation process has 40 % lower carbon emissions versus the conventional process, indicating its great potential for sustainable operation in the production of ethylbenzene from dry gas.

Energy-efficient separation of propylene/propane by introducing a tailor-made ionic liquid solvent

In the petrochemical industry, the separation of propylene/propane is usually paid much attention due to its high energy-consuming and environmental challenges. In this work, an energy-efficient extractive distillation (ED) separation process of propylene/propane is proposed by introducing a tailor-made ionic liquid (IL) solvent. The structure optimization of ILs is performed with a novel design objective in the computer-aided ionic liquid design (CAILD) method. By solving a formulated CAILD-based mixed-integer nonlinear programming (MINLP) problem, the ethylimidazolium ethyl sulfate ([C2IM][EtSO4]) is identified as the best IL solvent. The separation performance of [C2IM][EtSO4] in the ED process of propylene/propane is then evaluated through rigorous process simulation in Aspen Plus. For comparison, the conventional separation process of propane/propylene is also simulated and optimized. Based on the optimized operations, in-depth energy and economic assessment are conducted for an industrial-scale separation of propane/propylene in a Chinese refining industry. Remarkably, the [C2IM][EtSO4]-based ED process has 68.9% energy savings and 74.7% cost reduction when compared to the conventional process.

Investigation on energy-efficient extractive distillation for the recovery of ethyl acetate and 1,4-dioxane from industrial effluent

Conventional extractive distillation processes have been proposed to separate the ternary ethyl acetate-1,4-dioxane-water system with azeotropes. Energy-efficient extractive thermally coupled processes with heat integration have been developed to reduce energy consumption. A macro-analysis of the energy, exergy, economy, and environment is conducted to estimate the economic and environmental benefits. The results proved that an extractive dividing-wall column with a heat-integrated process possessed the greatest energy-saving potential, delivered best economic performance and exhibited highest exergy efficiency. Compared to those of a conventional direct extractive distillation process, the total energy requirement and total annual investment cost are reduced by 28.18% and 24.28%, respectively, by the best energy-saving process. The total exergy efficiency of it is 1.779%. The proposed cleaner and sustainable extractive dividing-wall column configuration could achieve energy saving, investment reduction, and effectively enhance the exergy efficiency.

Energy-efficient extractive distillation combined with heat-integrated and intermediate reboilers for separating acetonitrile/isopropanol/water mixture

A conventional triple-column extractive distillation is researched for the separation of acetonitrile/isopropanol/water mixture with ethylene glycol (EG) as entrainer. In this article, the pressure-relative volatility curve is investigated to find the suitable pressure of column. To achieve the further energy saving, three heat-integrated schemes and two heat-integrated combined with intermediate reboilers schemes are researched based on the conventional extractive distillation. Both two heat integration with intermediate reboilers schemes shown the better performance than other schemes since the further analysis of the energy, exergy, economic and environment (4E) were investigated. For the most energy saving design, PHI-IHI2, it has 48.50% energy-saving, 70.73% exergy efficiency enhanced, 36.24% reduction in total annual cost (TAC) and 48.55% reduction in gas emissions with the comparison of the conventional extractive distillation (CED) process. The result shows the extractive distillation combined with heat-integrated and intermediate reboilers presented great energy-efficient, economy saving and environment friendly for separating acetonitrile/isopropanol/water mixture.

Comparison of heterogeneous azeotropic distillation and energy-saving extractive distillation for separating the acetonitrile-water mixtures

The separation of acetonitrile-water mixtures is a challenging and significant task due to the presence of azeotrope, for which three separation alternatives are proposed, including an energy-efficient extractive distillation strategy (ED), an pressure-swing distillation strategy (PSD) and an novel azeotropic distillation strategy (EAD). Concept design based on ternary phase diagrams of various solvents demonstrates that benzene is a suitable solvent for the newly proposed EAD scheme. The separation sequence and operating parameters are optimized via using different sequential iterative procedures based on the minimal total annual cost (TAC). Under temperature-enthalpy (T-H) diagram guidance, heat integration applied to this three sequences significantly is completed, which reduces TAC by 27.45%, 30.42%, and 46.67%, respectively. Comprehensive evaluation of the three separation alternatives from the economic and environmental perspectives indicates that the heat-integrated EAD scheme is more attractive, since its TAC decreases by 52.03% and 55.30%, respectively, and CO2 emissions decreases by 56.63% and 61.63% compared with ED and PSD schemes. It is worth noting that the conceptual design of the EAD scheme also provides an energy efficient alternative for other systems that form azeotropes with water.

Rigorous design and simultaneous optimization of extractive distillation systems considering the effect of column pressures

Column pressure is one of the most important decision variables in the design and optimization of energy-efficient extractive distillation (ED) as it impacts on phase equilibrium, column temperature, and azeotropic concentration. However, many previous works fixed column pressure heuristically before optimization, resulting in divergence from the global optimum with variable column pressures. This ignorance gives this work the target to simultaneously optimize ED systems with fully considering the effect of column pressures. In detail, the task is carried out through combining the genetic algorithm programmed in MATLAB with Aspen Plus. Three binary systems are investigated to demonstrate the importance of pressure optimization – two sensitive (n-heptane/isobutanol and acetonitrile/water) and one insensitive (isopropanol/water) to pressure. Significant economic benefits are validated through optimizing pressure in the results for pressure sensitive systems, with the pressure insensitive system on the contrary. This suggests an optional pre-exclusion of pressure optimization, which requires to decipher the pressure sensitivity of the target system.

Energy-Saving Reduced-Pressure Extractive Distillation with Heat Integration for Separating the Biazeotropic Ternary Mixture Tetrahydrofuran–Methanol–Water

There is rich literature on the separation of binary azeotropic mixtures, whereas few studies exist on the separation of biazeotropic ternary mixtures. In this work, we propose a systematic approach for energy-efficient extractive distillation processes for the separation of a biazeotropic mixture that involves thermodynamic insights via residue curve maps and the univolatility line to find the optimal entrainer and operating pressure, global optimization based on a proposed two-step optimization procedure, and double-effect heat integration to achieve further saving of energy consumption. An energy-saving reduced-pressure extractive distillation (RPED) with a heat integration flowsheet is then proposed to achieve the minimum total annual cost (TAC). The results show that the TAC, energy consumption, and exergy loss of the proposed RPED with heat integration are reduced by 75.2%, 80.5%, and 85.8% compared with literature designs.

Combining the preconcentration column and recovery column for the extractive distillation of ethanol dehydration with low transition temperature mixtures as entrainers

Extractive distillation using low transition temperature mixtures (LTTMs) is a promising technology to separate ethanol and water azeotrope. In this work, the separation of water and ethanol by extractive distillation using LTTMs (choline chloride/urea 1:2) as entrainer was designed and simulated in Aspen Plus. Firstly, database of ChCl/urea = 1:2 (Reline) was established in Aspen Plus. Secondly, the simulation and optimization of the conventional extractive distillation process for ethanol dehydration with Reline or ethylene glycol as entrainer were worked out. The results showed that the TAC (total annual cost) of the process with Reline as entrainer was reduce by 14.61% than that of the process with EG as entrainer. In addition, in order to reduce energy consumption in distillation, an energy-efficient extractive distillation process which combining the preconcentration section and entrainer recovery section in one column was developed. The results showed that the proposed process with Reline as entrainer could save 29.48% and 17.42% of TAC compared with the conventional extractive distillation with EG and Reline as entrainer, respectively.

Control of Highly Heat-Integrated Energy-Efficient Extractive Distillation Processes

In our previous papers, two highly heat-integrated energy-efficient extractive distillation processes were presented by combining a preconcentration distillation column with an extractive distillation column or entrainer recovery column (Ind. Eng. Chem. Res. 2014, 53, 7121; Chem. Eng. Sci. 2015, 135, 166). However, these novel synthesis systems with highly heat-integrated configurations may exhibit complicated issues of dynamic controllability. Thus, this paper extends the previous work to investigate the dynamic controllabilities of these new synthesis systems. The singular value decomposition method is applied to analyze the temperature profiles and select the appropriate control trays. As the main column is highly heat-integrated from two columns, several degrees of freedom are lost. Thus, three temperature control loops are installed in the combined column. The dynamic performances of each system are tested by introducing ±20% disturbances of feed flow rate and composition, respectively. The results s...

Energy-Efficient Extractive Distillation Process by Combining Preconcentration Column and Entrainer Recovery Column

An energy-efficient two-column process based on a conventional extractive column process is explored by combining a preconcentration column and entrainer recovery column, which provides potential energy savings and capital investment reduction. Two case studies are demonstrated to verify the above-mentioned energy and economic advantages: the separation of isopropyl alcohol–water using DMSO as the entrainer and the separation of acetonitrile–water using ethylene glycol as the entrainer. In both cases, based on the global economic optimization, a design with optimized operation conditions for the conventional and improved processes is developed. It is revealed that the new process offers energy savings of 13.7% and 16.3%, respectively, and a similar reduction in total annual costs as compared to those of the conventional process.