Reactive Extractive Distillation Research Articles

Design and optimization of reactive dividing-wall extractive distillation process for dimethyl carbonate synthesis based on quantum chemistry and molecular dynamics calculation

• Selection of extractants based on quantum chemistry and molecular dynamics calculation. • The process of dimethyl carbonate production by transesterification was designed. • Economic and environmental optimization of several different production separation processes. The preparation of dimethyl carbonate by transesterification of ethylene carbonate and methanol has an important application in industry. The preparation of dimethyl carbonate by reactive distillation and the efficient separation of dimethyl carbonate and methanol are the inevitable requirements of the sustainable development of extractive distillation. Based on the quantum chemistry calculation and molecular dynamics calculation analysis, a better extractant (2-Furaldehyde) was selected. The simulated extractive distillation was designed to separate dimethyl carbonate methanol. The σ - profile was drawn by using COSMO-SAC model, and three different separation processes of dimethyl carbonate production were compared and optimized. Taking TAC as the objective function, the separation process of reactive dividing-wall extractive distillation can reduce about 21% and carbon dioxide emission by about 10% compared with the common reactive distillation process, which has obvious economic advantages and environmental performance. Through the economic and environmental optimization analysis of the production and separation process of dimethyl carbonate, it provides a certain guiding significance for the actual production of dimethyl carbonate and the separation of dimethyl carbonate methanol.

Exergy, economic and environmental assessment of sec-butyl acetate hydrolysis to sec-butyl alcohol using a combined reaction and extractive distillation system

Sec-butyl alcohol (SBA), an important chemical intermediate, is widely used in the synthesis of methyl ethyl ketone, herbicides and other products. However, there are some problems, such as high energy consumption and high equipment investment, in the traditional method of SBA production. With the mature application of the synthesis method of sec-butyl acetate (SBAC) in industry, the excess capacity of SBAC gradually appears. The synthesis of SBA from SBAC has become a research hotspot. SBA synthesized via the hydrolysis of SBAC has the advantages of fewer byproducts and wide sources of raw materials, but it has the limitation of a low degree of hydrolysis. In this study, based on Douglas’s economic optimization model, taking the total annual cost (TAC) as the objective function, the influencing factors and suitable operating conditions of the SBAC hydrolysis reactive extractive distillation process were explored, and TAC was obtained under the optimal operating conditions. The environmental performance of the process was studied according to life cycle analysis. The exergy efficiency was obtained based on thermodynamic analysis. The process was analyzed from the aspects of exergy, environment and economy, which provided theoretical guidance for the industrial design of the new SBA process.

Investigation on ternary system tetrahydrofuran/ethanol/water with three azeotropes separation via the combination of reactive and extractive distillation

In this work, a systematic method for conceptual design and multi-objective optimization of an energy-efficient and sustainable reactive/extractive distillation (RED) process is proposed to separate a ternary wastewater mixture with multi-azeotrope tetrahydrofuran/ethanol/water. Conceptual design of the proposed scheme is carried out by the analysis of thermodynamic feasibility (e.g., residue curve maps and iso-volatility line). In the proposed process, the component of water in the ternary system is firstly removed by adding the reactant in a reactive distillation column and the remaining binary azeotropic mixture is then separated via ED. During the ED process, the best entrainer dimethyl sulfoxide could be determined via the comparison of iso- and uni-volatility. An improved multi-objective genetic algorithm is employed for optimizing the established process with some key decision variables (e.g., feed locations and distillate rate). The results illustrated that the economic and environmental benefits of the proposed RED process will be greatly improved.

Process intensification and energy saving of reactive distillation for production of ester compounds

Abstract Reactive distillation (RD) process is an innovative hybrid process combining reaction with distillation, which has recently come into sharp focus as a successful case of process intensification. Considered as the most representative case of process intensification, it has been applied for many productions, especially for production of ester compounds. However, such problems existing in the RD system for ester productions are still hard to solve, as the removal of the water which comes from the esterification, and the separation of the azeotropes of ester–alcohol (–water). Many methods have been studying on the process to solve the problems resulting in further intensification and energy saving. In this paper, azeotropic–reactive distillation or entrainer enhanced reactive distillation (ERD) process, reactive extractive distillation (RED) process, the method of co-production in RD process, pressure-swing reactive distillation (PSRD) process, reactive distillation–pervaporation coupled process (RD–PV), are introduced to solve the problems above, so the product(s) can be separated efficiently and the chemical equilibrium can be shifted. Dividing-wall column (DWC) structure and novel methods of loading catalyst are also introduced as the measures to intensify the process and save energy.

Process integration of dimethyl carbonate and ethylene glycol production from biomass and heat exchanger network design

This work proposed an integrated production process of dimethyl carbonate (DMC) and ethylene glycol (EG) from biomass. The process started with biomass gasification, CO2 separation and CO2 conversion to ethylene carbonate. DMC and EG were produced via transesterification using reactive distillation and extractive distillation. Various key parameters were examined to optimize operating condition focusing on heat consumption. DMC and EG can achieve 99.5mol% purity. The process can sustain itself without any external heat sources by using biomass combustion, and all performance indicators were considered under the energy self-sufficient conditions. The ratio of biomass fed to the gasifier and the combustor was found to be 0.38:0.62 where the C, H and O atom efficiencies of the process achieved were 35.83, 53.19 and 40.31%, respectively. When employing heat exchanger network, the atom efficiency of the process could be improved (C: 42.49, H: 61.83, O: 45.21), while the ratio of biomass fed to the gasifier and the combustor increased to 0.46:0.54. The energy consumptions were reported by mass allocation as 143MJ/kg-DMC. Since all energy was supplied by biomass itself, the process was considered as carbon neutral with a fraction of carbon dioxide fixation from biomass into chemicals of 0.31.

Production of glycerol carbonate via reactive distillation and extractive distillation: An experimental study

A process for the production of glycerol carbonate (GC) is proposed with the transesterification of glycerol (GL) and dimethyl carbonate (DMC) with CaO as catalyst by reactive distillation and extractive distillation. The performance of solvents in separating DMC-methanol azeotrope and the effects of operation parameters on the reactive distillation process are investigated experimentally. The results indicate that both the GL conversion and GC yield increase with the DMC/GL molar ratio, reflux ratio, final temperature of tower bottom, and CaO/GL molar ratio and decrease as the recycle number of CaO increases. The calcium concentration in the residual reaction mixture also decreases remarkably as the DMC/GL molar ratio increases. At DMC/GL molar ratio 4.0, reflux ratio 1.0, final temperature of tower bottom 358K, and CaO/GL molar ratio 0.05, both the GL conversion and GC yield can reach above 99.0%, and the mass concentration of calcium in the product is less than 0.08%.

Feasibility Evaluation of Quinary Heterogeneous Reactive Extractive Distillation

This study addresses a feasibility evaluation method for the heterogeneous reactive extractive distillation of azeotropic quinary mixtures based on visualization in composition space. A critical composition region, that is, thermodynamically infeasible region for heterogeneous reactive extractive distillation, is determined by the constraint of reaction and phase equilibria. In addition, operating constraints are imposed on the feasibility evaluation in terms of the upper and lower internal reflux boundaries. Using these two kinds of feasibility constraints, we examine how the ethyl and isopropyl acetate reactive distillation systems, which cannot produce pure products because of four minimum-boiling azeotropes, lead to a full conversion and pure product recovery with the introduction of an external entrainer inducing L–L splits. The pure acetate production in a single reactive extractive distillation column is possible because the composition trajectory approaches the desired region in composition space ...

Olefin isomer separation by reactive extractive distillation: Modelling of vapour–liquid equilibria and conceptual design for 1-hexene purification

A thermodynamic model was developed to describe the vapour–liquid equilibria encountered in the reactive extractive distillation of 1-hexene mixed with n-hexane and 2-methyl-1-pentene, used to represent a Fischer–Tropsch stream. Experimentally it is determined that the feed mixture behaves nearly ideal in the absence of any solvent and that the obtained selectivities are near unity. A non-reactive solvent (D2EHPA) increases the activity coefficients but does not significantly improve the selectivity. The selectivity can only be increased by enriching the solvent with a metal-ion (Ag). The model uses the Wilson equation to describe the activity coefficients and can represent the vapour–liquid equilibria accurately as function of composition, pressure and temperature. To produce 1-hexene with a 99% recovery and at 99.5% purity, the solvent-to-feed ratio should be around 5 (at 0.2 bar, T = 311 K). Under these conditions the selectivity is 1.34 (2-methyl-1-pentene/1-hexene) and 1.55 ( n-hexane/1-hexene) and the minimum number of equilibrium trays approximately 42.

Functionalized Solvents for Olefin Isomer Purification by Reactive Extractive Distillation

Olefin isomer separations are difficult, energy intensive and thus expensive. An overview is presented to investigate the feasibility of metal–ligand complexes as functionalized solvents applied in a novel separation technology, reactive extractive distillation, for the separation and purification of α-olefins like 1-hexene from other C6-olefin isomers (internal, branched, cyclic and diolefins) and paraffins by using π-complexation. Functionalized metal–ligand complexes were synthesized based on commercial available ligands from hydrometallurgy. In screening experiments they were evaluated for ρ-complexation with ethylene. The best solvents were selected for evaluation of preferential complexation of 1-hexene relative to other olefin isomers. D2EHPA and DNNSA yield both stable metal–ligand complexes and triple the solubility of ethylene. Next, three different phosphoric acid ligands: D2EHPA, DBPA and MEHPA and two sulphonic acid ligands: DNNSA and DBSA, were investigated for a variety of C6-olefin isomers. The highest selectivities were obtained for silver-DBPA (20 wt% Ag, S/ F = 3): 1.23 for 2-methyl-1-pentene and 1.42 for n-hexane. An equilibrium model is used to conceptually design a reactive extractive distillation column applying the functionalized solvent silver-D2EHPA. Such a column should be operated at a solvent to feed ratio of around 5( P = 0.2 bar, T = 311 K) for 99.5% purity and 99% recovery. Under these conditions, the minimum number of equilibrium trays ( N min) to separate 1-hexene from 2-methyl-1-pentene is approximately 42, a dramatic decrease compared to N min of about 310 in the absence of silver.

Feasible products in complex batch reactive distillation

AbstractA new feasibility evaluation procedure for reactive mixtures is presented, where simple homogeneous reactive batch columns cannot produce pure products. Such columns are not feasible for producing pure products if no node products exist that are reachable by residue curves from the reaction equilibrium manifold. Three alternatives are presented. If an unstable node heterogenous azeotrope decants to an almost‐pure product, and that azeotrope is always reachable from the reaction equilibrium manifold, then a batch reactive rectifier can produce pure products with a decanter. If a homogeneous entrainer allows extractive section profiles to connect the reaction equilibrium manifold to an entrainer‐product binary edge, then a homogeneous batch reactive extractive distillation (BRED) column can produce a pure product. If these criteria are not met, then an entrainer that induces an unstable node heterogenous azeotrope between itself and one of the products should be used in a rectifier, a middle‐vessel column, or a BRED column. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Effects of Ligand Structure on Reactive Vapor−Liquid Distribution Ratio and Selectivity for C6-Olefin Isomers

Vapor−liquid equilibrium experiments are performed to evaluate the suitability of π-complexing silver of various phosphoric and sulfonic acids for application as functionalized solvents in Reactive Extractive Distillation to separate 1-hexene from other C6-olefin isomers. The effect of solvent structure is investigated by testing five different ligands, di (2-ethylhexyl) phosphoric acid (D2EHPA), di (butyl) phosphoric acid (DBPA), mono (2-ethylhexyl) phosphoric acid (MEHPA), di (nonyl) naphthalene sulfonic acid (DNNSA), and dodecyl benzene sulfonic acid (DBSA), for a variety of C6-olefin isomers (1-hexene, 2-methyl-1-pentene, n-hexane, 1,5-hexadiene, trans-2-hexene). The introduction of silver in the solvent increases the solvent selectivity for 1-hexene. At equal silver concentration the ligand size does not influence the selectivity of chemically similar components (1-hexene/2-methyl-1-pentene) but increases that of chemically different components (1-hexene/n-hexane). A lower pressure, a higher silver concentration, or higher solvent-to-feed (S/F) ratio are beneficial for the 1-hexene selectivity. The highest selectivity is obtained for Ag−DBPA (20 wt % Ag, S/F-ratio of 3): 1.23 for 2-methyl-1-pentene and 1.42 for n-hexane, relative to 1.04−1.06 for unreactive solvents.

Effect of C6-olefin isomers on π-complexation for purification of 1-hexene by reactive extractive distillation

Separation of α-olefins from other olefin isomers is a difficult and expensive operation because of the low selectivities encountered. A promising alternative is π-complexation in combination with extractive distillation: reactive extractive distillation (RED). In this paper, silver nitrate dissolved in ethylene glycol is investigated as a potential reactive solvent for the separation of 1-hexene from a stream containing cis/ trans-2-hexene, 1-methylcyclopentene, 2-methyl-1-pentene and 1,5-hexadiene typical for a Fischer–Tropsch stream. The solubility of 1,5-hexadiene is increased the most, but of the tested mono-olefins, 1-hexene has the highest increase. The results indicate that all olefins form 1:1 (silver:olefin) complexes. In addition, 1-hexene also produces 1:2 complexes and 1,5-hexadiene 2:1 complexes. The differences in complexation ability are the consequence of steric hindrance and mainly alter the entropy change of complexation. The 1:1 complexes with mono-olefins therefore exhibit an equal change in enthalpy of complexation (15.6 kJ/mol). The obtained selectivities for 1-hexene compared to the tested C6-olefin isomers are: 4.94 ( trans-2-hexene), 1.8 (2-methyl-1-pentene), 1.29 ( cis-2-hexene), 0.9 for 1-methylcyclopentene and 0.37 (1,5-hexadiene). Although technically feasible, it turned out that the developed solvent is industrially not applicable to separate 1-hexene from most of the isomers due to the too low solubility of 1-hexene in the reactive solvent and consequently the too high solvent-to-feed ratio's needed.

Feasible products in batch reactive extractive distillation

AbstractA systematic feasibility evaluation method is presented for batch reactive distillation columns with extractive feed streams. In this batch configuration, one feasibility criterion is obtained for quaternary reactive systems by using residue curve maps and reaction equilibrium manifolds. If all reaction products are saddles and one of the binary azeotropes between the desired products and the other components is an unstable node, then a reactive rectifier with a side‐feed entrainer can produce pure products regardless of the type and number of azeotropes involved in the system. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1484–1492, 2004

Analysis of Complex Separation Schemes in the Presence of Chemical Reactions

A key feature in the analysis of extractive distillation columns is the use of difference points representing the flow rate and composition difference between the cascade section end-product and the extractive side feed(s). Also referred to as a Δ-point, it may be used to assess feasibility for complex cascades with highly non-ideal VLE behavior. We have recently generalized the concept of difference points to systems where chemical reactions take place. We have also shown that the analytical insights are independent of the actual configuration of physical equipment and apply to any partial or complete flowsheet. This paper will demonstrate how the theory of generalized difference points may be applied to the design of complex separation cascades with reaction. Two example designs with integrated reaction and separation will be presented and analyzed for 3 and 4 components, respectively: (a) reactive distillation for the production of acetic acid from acetic anhydride and water and (b) reactive extractive distillation for the production of methyl acetate from acetic acid and methanol with water as a side product. The acetic acid example will illustrate how composition space can be divided into regions where feasibility with respect to distillate placement and internal reaction distribution can be performed using difference point theory. The methyl acetate design will show how a complex column can be divided into sections and analyzed using difference points to expose the role each section plays in making a feasible design.

Separation of aqueous isopropanol by reactive extractive distillation

AbstractA new separation method of reactive extractive distillation is proposed for the separation of isopropanol and water, using the mixture of ethylene glycol (C2H6O2) and glycollic potassium (C2H5O2K) as an entrainer. Vapor–liquid‐equilibrium (VLE) measurements confirmed that the entrainer was effective for this separation. Using a feed/solvent volume ratio of 1:1, isopropanol with a concentration over 96.0% weight fraction was obtained by the reactive extractive distillation process and the azeotropic point was eliminated. A novel process of separating isopropanol and water is designed on the basis of reactive extractive distillation to obtain the product with different concentrations, which may have a lasting value in industry.© 2002 Society of Chemical Industry

Combined process of reaction, extraction and distillation in a multistage column.

Reactive-extractive distillation in a multistage column is numerically investigated to improve the yield of desired intermediate product in a complex reaction combining reversible and consecutive reactions which are of the first order. On the assumption of phase equilibrium, mass balance equations are formulated in terms of a phase-splitting parameter and solved by use of the modified relaxation method. The optimal value of each decision variable is determined for tentatively chosen parameter values. Then the effect of each parameter on yield is evaluated for fixed values of the remaining parameters. The proposed combined process may have advantages over extractive reaction, reactive distillation and reaction without simultaneous separation singly if the system parameters can be chosen favorably.