Direct Synthesis Of Dimethyl Ether Research Articles

Co-feeding water to attenuate deactivation of the catalyst metallic function (CuO–ZnO–Al2O3) by coke in the direct synthesis of dimethyl ether

Co-feeding water with syngas in the direct synthesis of dimethyl ether has been studied in order to reduce the deactivation by coke deposition on the CuO–ZnO–Al2O3 metallic function in the CuO–ZnO–Al2O3/γ-Al2O3 bifunctional catalyst. The runs (synthesis of methanol and synthesis of DME) have been carried out in an isothermal fixed bed reactor under conditions avoiding catalyst deactivation due to the sintering of the metallic function (<325°C) and the deactivation of the acid function (with an excess of γ-Al2O3 in the catalyst). The results of long-term experiments evidence that water in the reaction medium attenuates coke deposition during the methanol synthesis step, which is the limiting one. Water is understood to partially inhibit the formation of coke precursor methoxy ions. Furthermore, the formation of paraffins is attenuated by co-feeding water.

The influence of different methanol synthesis catalysts on direct synthesis of DME from syngas

Methanol synthesis catalysts based on Cu–Zn–Al prepared under different precipitation conditions with the use of Zr or not as a promoter were studied in the direct synthesis of dimethyl ether (DME) using H-ferrierite as a dehydration component. Samples prepared under high supersaturation conditions showed textural and structural changes without any relation to the CO conversion. Samples containing zirconium favored an increase of Cu surface area, but other factors were involved in the improvement of the catalyst activity. The presence of aluminum in the methanol synthesis catalyst produced structural changes that could be related to the catalytic activity.

Direct synthesis of dimethyl ether from carbon-monoxide-rich synthesis gas: Influence of dehydration catalysts and operating conditions

Various dehydration catalysts were studied in the synthesis of dimethyl ether (DME) directly from carbon-monoxide-rich synthesis gas under a series of different reaction conditions. The investigated catalyst systems consisted of combinations of a methanol catalyst (CuO/ZnO system) with catalysts for methanol dehydration based on γ-Al 2O 3 or zeolites and γ-Al 2O 3 was identified as the most favorable dehydration catalyst. Various reaction parameters such as temperature, H 2/CO ratio and space velocity were studied. The impact of water on Cu/ZnO/Al 2O 3-γ-Al 2O 3 catalysts was investigated and no deactivation could be observed at water contents below 10% during running times of several hours. A running time of several days and a water content of 10% led to a significant increase of CO conversion but the water gas shift reaction became dominating and CO 2 was the main product. After termination of water feeding significant deactivation of the catalyst system was observed but the system returned to high DME selectivity. Catalyst stability and the influence of CO 2 in the gas feed were studied in experiments lasting for about three weeks. The presence of 8% of CO 2 caused an approximately 10% lower CO conversion and an about 5% lower DME selectivity compared to the reaction system without CO 2.

A double-shell capsule catalyst with core–shell-like structure for one-step exactly controlled synthesis of dimethyl ether from CO 2 containing syngas

A zeolite capsule catalyst Cr/ZnO–S–Z was prepared successfully by a novel dual-layer method, in which one layer of neutral Silicalite-1 zeolite shell was first synthesized on the bimetallic Cr/ZnO core catalyst, acting as the intermediate layer for the following H-type H-ZSM-5 zeolite shell direct synthesis on its surface. By using this dual-layer method, it can be easily realized that the formation of H-ZSM-5 zeolite membrane on the millimeter-sized bimetallic substrates. Direct synthesis of dimethyl ether (DME) from syngas at higher reaction temperature was the application of this zeolite capsule catalyst to test its catalytic performance. In reaction, this zeolite capsule catalyst could realize the exactly controlled synthesis of DME, suppressing the formation of other alkane/alkene by-products simultaneously, demonstrating its exclusive ability for the selective synthesis of target product compared with the conventional hybrid catalyst.

Modeling and simulation of tube-shell reactor for dimethyl-ether synthesis from coal-based synthesis gas

Mathematical simulation was performed on tube-shell reactor for dimethyl ether (DME) synthesis from coal-based syngas. The model was established based on kinetics of dimethyl-ether synthesis from syngas over a bifunctional catalyst, which is mixed by methanol synthesis catalyst and dehydration catalyst as 1:1 mass ratio. Methanol synthesis from CO and CO2 and methanol dehydration were selected as three-independent reactions, CO, CO2, and DME as key components to establish the one-dimensional mathematical model of the reactor. The gas concentration and temperature profiles inside the reactor tubes were obtained. The operating conditions affecting DME synthesis were also discussed based on the model. The simulations indicate that higher pressure and lower temperature at the inlet and rich hydrogen in the reactant are favorable in direct DME synthesis in fixed-bed process, and the temperature of boiling water affect the reactor performance seriously.

The effect of flow type patterns in a novel thermally coupled reactor for simultaneous direct dimethyl ether (DME) and hydrogen production

Dimethyl ether (DME) has gained wide interest in chemical industry regarding its use as a multi-source, multi-purpose fuel either for diesel engines or as a clean alternative for liquefied petroleum gas (LPG). The direct synthesis of DME from syngas would be more economical and beneficial in comparison to the indirect process via methanol dehydration. In this study, one type of the multifunctional auto-thermal reactors (the recuperative one) is selected in which the direct synthesis of dimethyl ether (DME) is coupled with the catalytic dehydrogenation of cyclohexane to benzene in a two fixed bed reactor separated by a solid wall, where heat is transferred across the surface of tube. Steady-state, heterogeneous, one-dimensional model has been used to describe the performance of this novel configuration. Both co-current and counter-current operating modes are investigated and the simulation results are compared with the available data of a pipe-shell fixed bed reactor for direct DME synthesis which operates at the same feed conditions. In addition, the influence of the molar flow rate of exothermic and endothermic stream on the reactor performance is also investigated. The results suggest that coupling of these reactions could be feasible and beneficial and the co-current mode has got better performance in DME and hydrogen production. In order to establish the validity and safety handling of the new concept, an experimental proof is required.

Direct dimethyl ether (DME) synthesis through a thermally coupled heat exchanger reactor

Compared to some of the alternative fuel candidates such as methane, methanol and Fischer–Tropsch fuels, dimethyl ether (DME) seems to be a superior candidate for high-quality diesel fuel in near future. The direct synthesis of DME from syngas would be more economical and beneficial in comparison with the indirect process via methanol synthesis. Multifunctional auto-thermal reactors are novel concepts in process intensification. A promising field of applications for these concepts could be the coupling of endothermic and exothermic reactions in heat exchanger reactors. Consequently, in this study, a double integrated reactor for DME synthesis (by direct synthesis from syngas) and hydrogen production (by the cyclohexane dehydrogenation) is modelled based on the heat exchanger reactors concept and a steady-state heterogeneous one-dimensional mathematical model is developed. The corresponding results are compared with the available data for a pipe-shell fixed bed reactor for direct DME synthesis which is operating at the same feed conditions. In this novel configuration, DME production increases about 600 Ton/year. Also, the effects of some operational parameters such as feed flow rates and the inlet temperatures of exothermic and endothermic sections on reactor behaviour are investigated. The performance of the reactor needs to be proven experimentally and tested over a range of parameters under practical operating conditions.

Equilibrium calculations for direct synthesis of dimethyl ether from syngas

Thermodynamic analysis of single-step synthesis of dimethyl ether (DME) from syngas over a bi-functional catalyst (BFC) in a slurry bed reactor has been investigated as a function of temperature (200–240°C), pressure (20–50 bar), and composition feed ratio (H2/CO: 1–2). The BFC was prepared by physical mixing of CuO/ZnO/Al2O3 as a methanol synthesis catalyst and H-ZSM-5 as a methanol dehydration catalyst. The three reactions including methanol synthesis from CO and H2, methanol dehydration to DME and water–gas shift reaction were chosen as the independent reactions. The equilibrium thermodynamic analysis includes a theoretical model predicting the behaviour and a comparison to experimental results. Theoretical model calculations of thermodynamic equilibrium constants of the reactions and equilibrium composition of all components at different reaction temperature, pressure, and H2/CO ratio in feed are in good accordance with experimental values. L'analyse thermodynamique de la synthèse en une étape du méthoxyméthane du gaz de synthèse sur un catalyseur bifonctionnel dans un réacteur à lit bouillonnant a été étudiée comme une fonction de température (200 à 240 ∘C), de pression (20 à 50 bars) et de rapport d'alimentation compositionnel (H2/CO: 1–2). Le catalyseur bifonctionnel était préparé par un mélange physique de CuO/ZnO/Al2O3 comme un catalyseur de synthèse de méthanol et de H-ZSM-5 comme un catalyseur de déshydratation du méthanol. Les trois réactions, soit la synthèse du méthanol du CO et du H2, la déshydratation du méthanol en méthoxyméthane et la conversion catalytique, ont été choisies comme réactions indépendantes. L'analyse thermodynamique de l'équilibre comprend un modèle théorique qui prédit le comportement et une comparaison par rapport aux résultats expérimentaux. Les calculs du modèle théorique des constantes de l'équilibre thermodynamique des réactions et la composition d'équilibre de tous les composants à différentes températures de réaction, différentes pressions et un différent rapport H2/CO dans l'alimentation cadrent bien avec les valeurs expérimentales. Additional Supporting Information may be found in the online version of this article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis of dimethyl ether from syngas in a microchannel reactor—Simulation and experimental study

Dimethyl ether (DME) is considered an alternative fuel for diesel engines with improved emission properties. The direct synthesis of DME from synthesis gas is a highly exothermic process. In this work, a microchannel reactor with improved heat and mass transfer has been used to produce DME from syngas. The experiments have been carried out in a wide range of reaction temperatures (210–300°C), pressure (10–50bar) and GHSV (4500–60,000Nml/gcat/h), and the H2:CO ratios of 1, 2 and 4 have been applied. The temperature profile along the catalytic bed and an evaluation of the heat removal capacity of the reactor are investigated by a 2D pseudo-homogeneous dispersion model. The experiments and modelling results demonstrate that the DME production is conducted under practically isothermal conditions in the microchannel reactor.

A study on the catalytic performance of Pd/γ-Al2O3, prepared by microwave calcination, in the direct synthesis of dimethylether

A series of Pd/γ-Al2O3 hybrid catalysts were prepared by impregnation and subsequent calcination under microwave irradiation. The catalysts were used for direct synthesis of dimethylether (DME) from syngas. The results show that calcination under microwave irradiation improved both the activity and selectivity of the catalysts for DME synthesis. The optimum power of the microwave was determined to be 420 W. Under such optimum conditions, CO conversion, DME selectivity and time space yield of DME were 60.1%, 67.0%, and 21.5 mmol·mL−1·h−1, respectively. Based on various characterizations such as nitrogen physisorption, X-ray diffraction, CO-temperature- programmed desorption, and Fourier transform infrared spectral analysis, the promotional effect of the microwave irradiation on the catalytic property was mainly attributed to both the higher dispersion of Pd and the significant increase in the adsorption on the CO-bridge of Pd. Microwave irradiation with very high power led to the increase in CO-bridge adsorption and thereby decreased the catalytic activity, whereas the coverage by metallic Pd of the active sites on acidic γ-Al2O3 significantly occurred under microwave irradiation with very low power, resulting in a decrease in the selectivity to DME.

Study on direct alcohol/ether fuel synthesis process in bubble column slurry reactor

The recent studies of direct alcohol/ether synthesis process in slurry reactors were reviewed, and the research work in our laboratory was carried out in this paper. a global kinetics model for direct dimethyl ether (DME) synthesis from syngas over a novel Cu-Zn-Al-Zr slurry catalyst was established according to the total of 25 experimental data, and a steady-state one-dimensional mathematical model was further developed in bubble column slurry reactor (BCSR), which was assumed that the bubble phase was plug flow, and the liquid phase was fully mixed flow. The numerical simulations of reactor design of 100000 t/a dimethyl ether pilot plant indicate that higher pressure and lower temperature were favorable to the increase of CO conversion, selectivity of dimethyl ether, product yield and height of slurry bed. The optimal operating conditions for DME synthesis process were obtained: reaction temperature at 240°C, reactor pressure at 5 MPa and reactor diameter of 2.5 m.

Catalytic activity of Cu–Zn–Al–Mn admixed with gamma-alumina for the synthesis of DME from syngas: manganese effect or just method of preparation?

A series of methanol synthesis catalysts, CuO/ZnO/Al2O3 and CuO/ZnO/Al2O3 containing 5 mol% of manganese physically admixed with γ-Al2O3 were tested for the direct synthesis of dimethyl ether from syngas. The catalysts were prepared by coprecipitation of the metal nitrates with several types of alkali carbonate solution. Aqueous solutions of Na2CO3, NaHCO3/Na2CO3 buffer, and NaHCO3 were used as the precipitating agents to investigate the effects of the preparation method on the microstructure of the precursors and on the physicochemical properties and reactivity of the resulting catalysts. It was found that the most responsible factor in determining the catalytic activity of the methanol synthesis catalyst is the preparation method rather than the incorporation of manganese as the structure modifier. There is a substantial correlation between the copper metal surface area and the activity of the catalyst derived from the structurally active precursor, hydrotalcite-like layered double hydroxides.

Confinement Effect and Synergistic Function of H-ZSM-5/Cu-ZnO-Al2O3 Capsule Catalyst for One-Step Controlled Synthesis

Dimethyl ether (DME) is an industrially important intermediate, as well as a promising clean fuel, but the effective production through traditionally consecutive steps from syngas to methanol and then to DME has been hindered by the poorly organized structure of the conventional physical mixture catalyst. Here, a novel zeolite capsule catalyst possessing a core-shell structure (millimeter-sized core catalyst and micrometer-sized acidic zeolite shell) was proposed initially through a well-designed aluminum migration method using the core catalyst as the aluminum resource and for the first time was applied to accomplish the DME direct synthesis from syngas. The selectivity of the expected DME on this zeolite capsule catalyst strikingly exceeded that of the hybrid catalyst prepared by the traditional mixing method, while maintaining the near-zero formation of the unexpected alkanes byproduct. The preliminary methanol synthesis reaction on the core catalyst and the following DME formation from methanol inside the zeolite shell cooperated concertedly and promoted mutually. This zeolite capsule catalyst with a synergetic confinement core-shell structure can be used to efficiently realize the combination of two and more sequential reactions with many synergistic effects.

Highly efficient synthesis of dimethyl ether from syngas over the admixed catalyst of CuO–ZnO–Al 2O 3 and antimony oxide modified HZSM-5 zeolite

A series of HZSM-5 zeolites modified with various contents of antimony oxide (0–30 wt.%) were prepared by solid state ion reaction at 500 °C, and the acidities of the resulted materials were characterized by temperature-programmed desorption of NH 3. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the admixed catalysts of an industrial CuO–ZnO–Al 2O 3 methanol synthesis catalyst and the parent and antimony oxide modified HZSM-5 zeolites under pressurized fixed-bed continuous flow conditions. The results indicated that modification of HZSM-5 with suitable amount of antimony oxide significantly decreased the selectivity for undesired byproducts like hydrocarbons and carbon dioxide from 9.3% and 32.4% to less than 1% and 28%, respectively, so the selectivity for DME was enhanced greatly from 55% to 69% under temperature of 260 °C, pressure of 4 MPa and gas hourly space velocity of 1500 mL h −1 g cat - 1 . The decrease in the formation of hydrocarbons and carbon dioxide can be attributed to the significant decline in the amount of strong acid sites of the HZSM-5 zeolite induced by antimony oxide modification. Additionally, the influences of the operating parameters on the performance of the most efficient catalyst were also investigated. The results showed that high reaction temperature and high gas hourly space velocity resulted in both lower carbon monoxide conversion and lower dimethyl ether selectivity, so they should be no higher than 280 °C and 3000 mL h −1 g cat - 1 , respectively.

Enhanced Catalytic Performance for Dimethyl Ether Synthesis from Syngas with the Addition of Zr or Ga on a Cu−ZnO−Al2O3/γ-Al2O3 Bifunctional Catalyst

Direct synthesis of dimethyl ether (DME) from synthesis gas was investigated on bifunctional catalysts, containing Cu−ZnO−Al2O3 promoted with Zr or Ga on γ-Al2O3 as a methanol dehydration catalyst. In comparison to an unpromoted bifunctional catalyst, promoted catalysts with Zr or Ga showed a higher catalytic performance and stability. The facile reducibility of copper particles with high dispersion and an appropriate acidity and electronic state of copper species are mainly responsible for the superior catalytic performance with the help of structural promoting effects of Ga or Zr components on Cu−ZnO−Al2O3. The high formation rate of methanol by CO hydrogenation on the Zr-promoted Cu−ZnO−Al2O3 and the dehydration rate of methanol to DME on the modified acidic sites of γ-Al2O3 are mainly responsible for the superior catalytic activity and stability.

Deactivation Kinetics for Direct Dimethyl Ether Synthesis on a CuO−ZnO−Al2O3/γ-Al2O3 Catalyst

A kinetic model has been established for the deactivation of a CuO−ZnO−Al2O3/γ-Al2O3 catalyst in the direct synthesis of dimethyl ether. The model allows calculating the effect of the operating conditions and the evolution of component concentration in the reaction medium (dimethyl ether, methanol, paraffins, H2, CO, CO2, and H2O) with time on stream. The results of the model fit the experimental results in a wide range of conditions: 225−350 °C; 10−40 bar; space time, 0.1−68.0 (g of catalyst) h (mol of reactants)−1; molar ratio (H2/CO) in the feed, 2−4; time on stream, 30 h. The model considers the cause of deactivation to be coke deposition on the metallic function and that this coke is formed by degradation of oxygenates (dimethyl ether and methanol). The effect of water in the reaction medium has been quantitatively considered in the kinetic model, whose drawback is the attenuation of the methanol synthesis rate and whose benefit is the attenuation of deactivation by coke deposition. The kinetic model...

Regeneration of CuO-ZnO-Al2O3/γ-Al2O3 catalyst in the direct synthesis of dimethyl ether

This paper deals with the regeneration of a CuO-ZnO-Al2O3/γ-Al2O3 catalyst used in the direct synthesis of dimethyl ether. When coke combustion (subsequent to aging treatment) is performed in a thermobalance, two coke fractions with different combustion kinetics are identified. One coke fraction, deposited on the metallic sites and whose combustion is activated by these sites, has a kinetic constant of combustion 7–26 times higher than that corresponding to the coke located at the Al2O3 support. Uninterrupted operation is feasible in reaction–regeneration cycles in a fixed bed reactor as long as the reaction and regeneration steps are carried out at 325°C, which are limiting conditions in order to avoid irreversible deactivation by sintering of the metallic function. The regeneration with O2 diluted with He (5% of O2) allows the complete combustion of coke. Under conditions of partial coke combustion it is observed that the removal of the fraction deposited on the metal makes it possible to recover the initial activity of the catalyst, which subsequently undergoes fast deactivation.

100 t/a-Scale demonstration of direct dimethyl ether synthesis from corncob-derived syngas

Direct conversion of biomass-derived syngas (bio-syngas) to dimethyl ether (DME) at pilot-scale (100 t/a) was carried out via pyrolysis/gasification of corncob. The yield rate of raw bio-syngas was 40–45 Nm 3/h with less than 20 mg/Nm 3 of tar content when the feedrate of dried corncob was 45–50 kg/h. After absorption of O 2, S, Cl by a series of absorbers and partial removal of CO 2 by the pressure-swing adsorption (PSA) unit sequentially, the obtained bio-syngas (H 2/CO≈1) was directly synthesized to DME over Cu/Zn/Al/HZSM-5 catalyst in the fixed-bed tubular reactor. CO conversion and DME space-time yield (STY) were 67.7% and 281.2 kg/m cat 3/h respectively at 260 °C, 4.3 MPa and 3000 h −1(GHSV, syngas hourly space velocity). Synthesis performance would be increased if the tail gas (H 2/CO > 2) was recycled to the reactor when GHSV was 650–3000 h −1.

Simulation of DME synthesis from coal syngas by kinetics model

DME (Dimethyl Ether) has emerged as a clean alternative fuel for diesel. There are largely two methods for DME synthesis. A direct method of DME synthesis has been recently developed that has a more compact process than the indirect method. However, the direct method of DME synthesis has not yet been optimized at the face of its performance: yield and production rate of DME. In this study it is developed a simulation model through a kinetics model of the ASPEN plus simulator, performed to detect operating characteristics of DME direct synthesis. An overall DME synthesis process is referenced by experimental data of 3 ton/day (TPD) coal gasification pilot plant located at IAE in Korea. Supplying condition of DME synthesis model is equivalently set to 80 N/m3 of syngas which is derived from a coal gasification plant. In the simulation it is assumed that the overall DME synthesis process proceeds with steadystate, vapor-solid reaction with DME catalyst. The physical properties of reactants are governed by Soave-Redlich-Kwong (SRK) EOS in this model. A reaction model of DME synthesis is considered that is applied with the LHHW (Langmuir-Hinshelwood Hougen Watson) equation as an adsorption-desorption model on the surface of the DME catalyst. After adjusting the kinetics of the DME synthesis reaction among reactants with experimental data, the kinetics of the governing reactions inner DME reactor are modified and coupled with the entire DME synthesis reaction. For validating simulation results of the DME synthesis model, the obtained simulation results are compared with experimental results: conversion ratio, DME yield and DME production rate. Then, a sensitivity analysis is performed by effects of operating variables such as pressure, temperature of the reactor, void fraction of catalyst and H2/CO ratio of supplied syngas with modified model. According to simulation results, optimum operating conditions of DME reactor are obtained in the range of 265–275 °C and 60 kg/cm2. And DME production rate has a maximum value in the range of 1–1.5 of H2/CO ratio in the syngas composition.

Scale study of direct synthesis of dimethyl ether from biomass synthesis gas

We investigated the synthesis of dimethyl ether (DME) from biomass synthesis gas using a kind of hybrid catalyst consisting of methanol and HZSM-5 zeolite in a fixed-bed reactor in a 100 ton/year pilot plant. The biomass synthesis gas was produced by oxygen-rich gasification of corn core in a two-stage fixed bed. The results showed that CO conversions reached 82.00% and 73.55%, the selectivities for DME were 73.95% and 69.73%, and the space–time yields were 124.28 kg m − 3 h − 1 and 203.80 kg m − 3 h − 1 when gas hourly space velocities were 650 h − 1 and 1200 h − 1 , respectively. Deoxidation and tar removal from biomass synthesis gas was critical to the stable operation of the DME synthesis system. Using single-pass synthesis, the H 2/CO ratio improved from 0.98–1.17 to 2.12–2.22. The yield of DME would be increased greatly if the exhaust was reused after removal of the CO 2.