Separation Of Dimethyl Carbonate Research Articles

Molecular simulation and experimental insights into the separation of dimethyl carbonate and isopropyl alcohol using imidazolium ionic liquids

Molecular simulation and experimental insights into the separation of dimethyl carbonate and isopropyl alcohol using imidazolium ionic liquids

Pilot-scale azeotrope purification of dimethyl carbonate by cost-efficient pervaporation-assisted distillation

The production processes of dimethyl carbonate (DMC) typically involve an excess amount of methanol, and therefore, the separation of DMC from methanol is essential in the chemical industry. While pressure swing distillation is commonly used for this separation, it is an energy-intensive process. Pervaporation, on the other hand, has been found to be a more energy-efficient method, especially when a suitable inorganic or ceramic membrane is used. The use of polymeric membranes is not recommended due to the high operating temperatures required. Hybrid silica membranes, such as HybSi®, have emerged as a promising option for this purpose. In this study, we conducted both laboratory and pilot-scale pervaporation experiments along with pilot-scale pervaporation-assisted distillation experiments, and carried out process simulations to evaluate the potential cost savings in DMC purification using a HybSi® membrane. The cost of purification was calculated per ton of DMC produced, and results demonstrated cost savings compared to the base case using pressure swing distillation. These savings were attributed to reduced operating and capital expenditures resulting from lower energy consumption and a more compact design. Our results indicate that the use of HybSi® membranes has the potential to revolutionize the DMC production process and provide a more sustainable and cost-effective solution.

Studies on the Prediction and Extraction of Methanol and Dimethyl Carbonate by Hydroxyl Ammonium Ionic Liquids.

The separation of dimethyl carbonate (DMC) and methanol is of great significance in industry. In this study, ionic liquids (ILs) were employed as extractants for the efficient separation of methanol from DMC. Using the COSMO-RS model, the extraction performance of ILs consisting of 22 anions and 15 cations was calculated, and the results showed that the extraction performance of ILs with hydroxylamine as the cation was much better. The extraction mechanism of these functionalized ILs was analyzed by molecular interaction and the σ-profile method. The results showed that the hydrogen bonding energy dominated the interaction force between the IL and methanol, and the molecular interaction between the IL and DMC was mainly Van der Waals force. The molecular interaction changes with the type of anion and cation, which in turn affects the extraction performance of ILs. Five hydroxyl ammonium ILs were screened and synthesized for extraction experiments to verify the reliability of the COSMO-RS model. The results showed that the order of selectivity of ILs predicted by the COSMO-RS model was consistent with the experimental results, and ethanolamine acetate ([MEA][Ac]) had the best extraction performance. After four regeneration and reuse cycles, the extraction performance of [MEA][Ac] was not notably reduced, and it is expected to have industrial applications in the separation of methanol and DMC.

Evaluation of task-specific ionic liquids applied in pervaporation membranes: Experimental and COSMO-RS studies

The production of dimethyl carbonate (DMC) from CO2 and methanol (MeOH) is an attractive route for CO2 capture and utilization. In this process, the separation of DMC from the reaction medium is critical to maximize the conversion of CO2. However, DMC and MeOH form an azeotropic mixture that is difficult to separate. This work investigates the possibility of using task-specific ionic liquids (TSILs) in the form of supported ionic liquid membranes (SILMs) to separate and purify DMC by using pervaporation. Two tertiary amine ILs, i.e., 1-octyl-3-methylimidazolium bromide ([Omim][Br]) and 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Omim][NTf2]), and one cyclic quaternary ionic liquid, i.e., 1-octyl-1,4-diazabicyclo[2.2.2]octanium bromide ([ODABCO][Br]), were prepared. The structure and purity of the synthesized ILs were confirmed by NMR and FTIR, and the as-synthesized ILs along with one commercial quaternary ammonium IL, tetrabutylammonium bromide ([TBA][Br]), were further characterized using TGA/DSC. SEM-EDX, tensile tests and stability tests were also performed to characterize the SILMs. During the pervaporation experiments, the SILMs showed an initial decrease in DMC and MeOH permeance over time, followed by a gradual stabilization, with a relatively stable DMC/MeOH selectivity as pure liquids. In addition, an increase in temperature is shown to have negative effect on DMC and MeOH permeance because sorption, which is an exothermic process, governed the transport of molecules across the membrane. The studied SILMs exhibited higher selectivity at low temperatures, especially at 30 °C. Furthermore, the COSMO-RS model provided insights of the effect of IL structures on the separation of DMC from MeOH at molecular level.

Phase behavior and molecular insights on the separation of dimethyl carbonate and methanol azeotrope by extractive distillation using deep eutectic solvents

Deep eutectic solvents (DESs) exhibit good separation performance as extractants in extractive distillation. In this study, choline chloride (ChCl)-based and tetrabutylammonium bromide (TBAB)-based DESs were prepared using ChCl and TBAB as hydrogen bond acceptors (HBAs) and urea, glycerol (G), malonic acid (MA), and levulinic acid (LA) as hydrogen bond donors (HBDs). Based on the COSMO-SAC model, the possibility of separating the binary azeotropes of methanol (MeOH) and dimethyl carbonate (DMC) using five DESs was verified. The binary azeotropes of MeOH and DMC were separated by extractive distillation using five DESs, and their separation performance was investigated. The experimental results revealed that ChCl-urea had the best separation effect on the binary azeotropes MeOH and DMC. The macroscopic separation phenomenon and microscopic molecular mechanisms were studied systematically. The interaction of the DESs with MeOH and DMC was investigated at the molecular level by quantum chemical (QC) calculations, and the important role of the hydrogen bond of the DESs in extractive distillation was revealed. The experimental and QC results demonstrate that DESs have a significant effect on the intermolecular forces and can effectively separate azeotropes.

High-performance ZIF-8/biopolymer chitosan mixed-matrix pervaporation membrane for methanol/dimethyl carbonate separation

The separation of dimethyl carbonate (DMC) –an ecofriendly organic compound– from a reaction medium is oftentimes complicated due to the presence of other organic compounds, particularly when the mixture forms an azeotrope. To this end, pervaporation is proposed in this work as the perfect candidate to solve this separation puzzle, using novel membranes which flipped the ratio of the binary mixture methanol (MeOH) and DMC (from 10:90 to ∼90:10). ZIF-8 fillers were incorporated into chitosan (CS) biopolymer matrix to prepare these mixed-matrix membranes (MMM). At 15 wt% loading of ZIF-8/CS, the～30 μm-thick MMM showed an exceptional selectivity of 11.2, with MeOH permeance of 97.7 GPU at 50 ℃. This superior separation performance is attributed to the higher MeOH affinity to the CS matrix, further reinforced with the preferential channels of ZIF-8 fillers for MeOH. This successful separation of binary organic mixtures elevates a crucial part of downstream processing, merely achieved with conventional distillation, and most importantly, open doors to greener fuels.

Thermodynamic and economic comparison of extractive distillation sequences for separating methanol/dimethyl carbonate/water azeotropic mixtures

The separation of dimethyl carbonate (DMC)/methanol/water azeotropic mixtures has been a hot topic in the study of DMC synthesis process. In this work, the efficient organic solvent methyl salicylate, ionic liquids (ILs) 1‐butyl‐3‐methylimidazolium chloride ([BMIM][Cl]), or 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) was employed to break azeotropic mixtures. Interaction mechanisms between DMC/methanol/water and entrainers were revealed by sigma-profile. Energy and economic comparison of two alternative separation sequences including pre-separation integration with extractive-heterogeneous distillation and direct extractive distillation processes were investigated. The average relative deviations (ARD) were used to check the reliability of the NRTL model. The effect of high viscosity fluid on the mass transfer was analyzed from the perspective of the overall efficiency of column. For [BMIM][Cl], the separation mechanism is the formation of H-bond between [BMIM][Cl] and methanol/water. Direct extractive distillation process is superior to pre-separation integration with extractive-heterogeneous distillation process in terms of steam consumption, capital cost, mass transfer efficiency and total annual cost (TAC), and [BMIM][Cl]-based direct extractive distillation process is the best. This work provides a green and efficient separation route for replacing organic solvent-based process.

Pervaporation and vapour permeation of methanol – dimethyl carbonate mixtures through PIM-1 membranes

The separation of dimethyl carbonate (DMC) from its mixtures with methanol was studied using pervaporation (PV) and vapour permeation (VP) through thick (∼0.5 mm) PIM-1 membranes; PV characteristics of PDMS and PTMSP membranes are provided for comparison. DMC is a “green” chemical with numerous applications in chemistry, but its production is energy- and cost-intensive. As their azeotrope contains 82 mol.% of methanol at 40 °C, DMC-selective rather than common methanol-selective membranes can allow for energy efficient separation and thus production of this “green chemical”. PV of the azeotropic mixture through the PIM-1 membrane showed a separation factor of 2.3, which is comparable to that observed for PV through the PDMS membrane; the PTMSP membrane showed practically no separation. The total PV fluxes followed the order: PTMSP ≫ PIM-1 > PDMS. When the PIM-1 membrane was operated in the VP mode, a separation factor of up to 5.1 was reached for the vapours having the azeotropic composition, while total fluxes dropped ca 50-times compared to PV. The highest observed separation factor of 6.5 was found for VP of DMC-rich vapour mixtures highly diluted with inert gas. To our knowledge, VP through PIM-1 membranes enables to date the most selective membrane-based removal of DMC from its azeotrope with methanol.

Choline chloride based deep eutectic solvents selection and liquid-liquid equilibrium for separation of dimethyl carbonate and ethanol

Dimethyl carbonate (DMC) is an excellent gasoline and diesel additive in the field of fuel. However, it can form azeotrope with ethanol, so separation of DMC with high purity from the azeotrope is of significance. To separate the azeotrope of DMC and ethanol, the σ-profiles were calculated by the COSMO-SAC model to determine suitable deep eutectic solvents (DESs). On the basis of σ-profiles analysis, four choline chloride based DESs were selected and evaluated as extractant. The liquid−liquid equilibrium (LLE) data for the ternary systems DMC + ethanol + DESs were determined at T/K = 298.15 and 308.15 K under 101.3 kPa. The distribution coefficient and selectivity were calculated to evaluate the extraction ability of the DESs. And the influence of different temperature on phase behavior was explored. In addition, the 1H NMR spectrums of the DESs distributed in the upper and lower phases were obtained to check the integrity of the DESs. Meanwhile, the LLE experimental data were correlated by the NRTL model, the correlation results show an agreement with the experimental data.

Separation of Dimethyl Carbonate and Methanol by Deep Eutectic Solvents: Liquid–Liquid Equilibrium Measurements and Thermodynamic Modeling

To separate the mixture of dimethyl carbonate and methanol, two deep eutectic solvents (DESs), choline chloride with glycerol and ethylene glycol, with the molar ratio of 1:2 were prepared to separate dimethyl carbonate from the mixture by liquid–liquid extraction. The liquid–liquid equilibrium (LLE) data for the ternary systems of dimethyl carbonate + methanol + DESs were determined at temperature of 298.15 and 308.15 K under 101.3 KPa. The measured tie-line data were validated by the Bachman equation, and the correlation coefficients (R2) were all close to 1. Meanwhile, the distribution coefficient and selectivity were calculated from the experimental results. The LLE experimental data were correlated using the nonrandom two-liquid (NRTL) model, and the correlated results agree well with the LLE experimental data. Also, the parameters of the NRTL model were regressed.

Development of alternative methanol/dimethyl carbonate separation systems by extractive distillation — A holistic approach

Separation of dimethyl carbonate (DMC) with methanol (MeOH) is fundamentally difficult as DMC forms an azeotrope with MeOH. In this context, a holistic, three-tiered approach was undertaken to develop alternative MeOH/DMC separation systems by extractive distillation. To that end, a preliminary entrainer screening was conducted in the first tier using predictive UNIFAC-DMD and COSMO-SAC models. Based on calculated selectivities at infinite dilution (Sij∞), twelve potentially promising candidates were chosen out of 35 solvents. These mass separating agent (MSA) candidates were allowed to be advanced to the next level of screening in which the limiting activity coefficients of methanol as well as dimethyl carbonate in those selected solvents were experimentally measured by the technique of headspace gas chromatography. At this level of screening, a composite Z-score taking both selectivity and solvency factors into account was employed. Two solvents — methyl salicylate and ethyl benzoate with relatively high values of the composite Z-score were identified for further vapor ​– liquid equilibrium (VLE) experiment in the second tier where four sets of data were measured using a dynamic recirculation cell. The effectiveness of the two solvents acting as entrainers was further quantitatively assessed by simulation in the last tier, and compared with that of others being used industrially or proposed in the literature. Through a sequential iterative optimization scheme, extractive distillation system for each entrainer was optimized based on both conventional and heat-integrated schemes. The simulation results reveal that the effectiveness of methyl salicylate as an MSA outperforms all other entrainers.

Novel Procedure for the Synthesis of Dimethyl Carbonate by Reactive Distillation

A novel energy saving procedure for the synthesis and separation of dimethyl carbonate by reactive distillation is proposed, and its principle technical feasibility is demonstrated based on the physical properties of a dimethyl carbonate synthesis system. The steady-state simulation is performed with Aspen Plus, and the UNIQUAC-RK model is used in this work. The simulation result shows that the novel procedure can simplify the process and reduce energy consumption. The new procedure can save energy costs by 29.50% compared with the traditional processes. For further energy consumption reduction, heat integrations between the low-pressure column and the high-pressure column are adopted. It is found that energy savings of 53.80% are achieved for this novel process. The total annual costs of the four procedures are estimated and compared. It is shown that costs can be reduced by more than 31.54% by using the new processes. To sum up, the new procedure has a better economic investment than the original.

Pervaporation separation of dimethyl carbonate/methanol binary mixtures with poly(vinyl alcohol)-perfluorslulfonic acid/poly(acrylonitrile) hollow fiber composite membranes

Using poly(vinyl alcohol) (PVA) and perfluorslulfonic acid (PFSA) as coating materials, poly(acrylonitrile) (PAN) hollow fiber ultrafiltration membrane as substrate, PVA-PFSA/PAN composite membranes were fabricated by dip-coating method. The fabricated composite membranes were used to the separation of dimethyl carbonate (DMC)/methanol (MeOH) binary mixtures by pervaporation process. SEM images verify that the coated layer is well combined with substrate and the thickness nearly linearly increases with the coating solution concentration. The separation factor increases but at cost of the decline of permeation flux when the concentration of the coating solution or its PVA mass fraction increase. The permeation flux increases and separation factor slightly increases with the feed temperature increasing at 30–60 °C. The increase of feed MeOH concentration leads to an improvement of permeation flux and a decline of separation factor.

Experimental investigation, modeling and scale-up of hydrophilic vapor permeation membranes: Separation of azeotropic dimethyl carbonate/methanol mixtures

The separation of azeotropic mixtures is a challenging task that is currently performed by special distillation processes, such as heteroazeotropic, extractive or pressure-swing distillation. In recent years, membrane materials that are used to separate different combinations of chemical compounds have constituted an energy-efficient and competitive alternative to special distillation processes. Vapor permeation is a promising type of membrane separation processes which enables to overcome limitations caused by the thermodynamic phase equilibrium. This characteristic facilitates the separation of azeotropic mixtures. However, the membrane needs to be large to handle high throughputs or to achieve high purities. Thus, the use of membranes in combination with established unit operations in so-called membrane-assisted separation processes is advantageous. Nevertheless, in addition to the reliable selection of a suitable membrane polymer for a given design task, a model-based scale-up is still challenging and complicates the design of said membrane separations. These disadvantages limit the application of vapor permeation in the chemical industry. Therefore, the aim of this paper is to enable scale-up by systematically identifying the influence of vapor permeation operating parameters at two different experimental scales with a scale-up factor of 50. Based on these experiments, a rigorous model was developed using experimental data from lab-scale to predict the separation characteristics in pilot-scale. These findings were validated against experimental data from this scale. In this work, the separation of dimethyl carbonate and methanol showing a low-boiling azeotrope with high methanol content was used as a case study. The separation of these two compounds is of significant interest because valuable dimethyl carbonate is usually produced from methanol feedstocks, thus necessitating the separation of both components.

Separation of dimethyl carbonate/methanol/water mixtures by pervaporation using crosslinked chitosan membranes

This study deals with the separation of dimethyl carbonate (DMC) by pervaporation using crosslinked chitosan membranes. DMC, an environmentally benign chemical, is commercially produced by oxidative carbonylation of methanol, and the separation and purification of DMC is critical to DMC manufacture due to azeotropic nature of the reaction mixtures. In this study, chitosan membranes crosslinked by dilute sulfuric acid were prepared for DMC separation by pervaporation. The membranes were tested for separation of binary DMC/water, DMC/methanol and methanol/water mixtures and ternary DMC/methanol/water mixtures in a temperature range of 25–55 °C. The experimental results showed that the membrane could be used effectively to break the DMC/methanol azeotrope and to remove a small amount of water from DMC. It was also shown that coupling effect was important in pervaporation separation of multi-component mixtures due to interactions among the permeating species.

Separation of Dimethylcarbonate from Dimethylcarbonate-Methanol Mixture by Pervaporation.

Using poly (dimethylsiloxane) membranes, the sorption amount of dimethylcarbonate-methanol mixture into the membranes at the equilibrium was measured and pervaporation of dimethylcarbonate-methanol mixture was performed. The equilibrium concentration of the mixture in the membrane increased with increasing dimethylcarbonate concentration in the liquid phase. The membrane was permselective to dimethylcarbonate in the range of dimethylcarbonate weight fraction in the feed up to 0.8 in pervaporation. The permeation fluxes of both components increased and the separation factor remained almost constant as the operating temperature increased.The permeation fluxes through the membrane were analyzed by the solution-diffusion model considering the swelling effect of dimethylcarbonate on the membrane, and diffusion coefficients and swelling parameters were evaluated. The calculated values of separation factor based on the model were in good agreement with the experimental ones.