Catalyst For Dimethyl Ether Synthesis Research Articles

CFD modeling of DME synthesis based on methanol dehydration process by an adiabatic reactor: Characterization

Today, Dimethyl ether (DME) can be used as a fuel in various applications, including as a substitute for diesel fuel. Despite its advantages, there are some challenges associated with DME as a fuel. One of the main challenges is the limited availability of DME refueling stations and the need for dedicated storage facilities due to their different properties compared to traditional fuels. DME shows promise as a clean-burning alternative fuel with the potential to reduce emissions and dependence on fossil fuels, especially in the transportation and power generation sectors. Ongoing research and development efforts are focused on improving production methods, expanding infrastructure, and exploring new applications for DME as a fuel. DME is a colorless gas that can be used as a fuel or as a precursor for the production of other chemicals. The most common method for DME synthesis involves the dehydration of methanol. Methanol is first converted to dimethyl ether by removing a molecule of water. This reaction is typically catalyzed by acidic materials such as alumina or zeolites. In this work, to study the physical properties of the methanol dehydration reaction, CFD modeling of the adiabatic reactor has been accomplished. The researchers showed that the use of an alumina catalyst, which has selective mechanical properties and unique surface properties, is a suitable choice as a catalyst for DME synthesis. The results of this study indicate that laboratory data such as pressure, energy, and velocity in the adiabatic reactor satisfy the reaction conditions well. Also, temperature profile diagrams with changes in temperature, pressure, and velocity show that the reaction of methanol dehydration is strongly dependent on environmental factors and presents different results under the influence of other conditions.

Enhanced catalytic stability of non-stoichiometric Cu–Al spinel catalysts for dimethyl ether synthesis from syngas: Effect of coordination structure

Cu–Al spinel catalysts were synthesized by various preparation methods, and its CO hydrogenation performance was evaluated. Characterization results showed that different preparation methods can effectively regulate the coordination distribution of cations in surface spinel structure. The sustained release property of Cu–Al spinel was related to its coordination structure. The catalyst containing a large amount of octahedral spinel Cu2+ ions was capable of delaying the reduction of copper, and small Cu nanoparticles (Cu NPs) were produced and highly dispersed on the defective spinel surface, which may be that the vacancy derived on the surface of defective spinel anchored small Cu NPs, which was the key to improve catalytic stability. We also discussed the real reason for poor catalytic stability, and this was due to that the easily-reducible spinel possessed extensive tetrahedral spinel Cu2+, which accelerated the reduction and release of copper, resulting in that the formed copper was unstable and aggregated readily. The Cu–Al spinel catalyst prepared by the solid phase method included octahedral coordination Cu2+ ratio as high as 59%, and the corresponding average size of Cu particles produced from spinel was measured as about 11.3 nm by N2O titration method, exhibiting enhanced stability and excellent catalytic performance.

A Review on Deactivation and Regeneration of Catalysts for Dimethyl Ether Synthesis

The deactivation of catalysts and their regeneration are two very important challenges that need to be addressed for many industrial processes. The most quoted reasons for the deterioration of dimethyl ether synthesis (DME) concern the sintering and the hydrothermal leaching of copper particles, their migration to acid sites, the partial formation of copper and zinc hydroxycarbonates, the formation of carbon deposits, and surface contamination with undesirable compounds present in syngas. This review summarises recent findings in the field of DME catalyst deactivation and regeneration. The most-used catalysts, their modifications, along with a comparison of the basic parameters, deactivation approaches, and regeneration methods are presented.

Roles of interaction between components in CZZA/HZSM‐5 catalyst for dimethyl ether synthesis via CO2 hydrogenation

AbstractThe roles of interaction between two catalyst components in CuO–ZnO–ZrO2–Al2O3 (CZZA)/HZSM‐5 bifunctional catalyst for dimethyl ether (DME) synthesis via carbon dioxide hydrogenation were investigated. It was found that CZZA catalyst showed excellent stability during methanol (MeOH) synthesis for 100 h, while there was a severe loss of catalytic activity in the bifunctional catalyst for DME synthesis. Hence, the effects of different degrees of intimacy of two catalyst components were studied for DME synthesis, including mixed and separated modes. For the mixed mode, the particle size of catalysts and the amount of reaction intermediates were proven to influence the catalyst deactivation. For the separated mode, the catalysts showed rapid deactivation within a short time. Various characterizations indicated that the remarkable deactivation of separated mode was mainly caused by the decrease of copper active centers (e.g., sintering and oxidation) and blockage of acid sites via increased coke deposition on HZSM‐5.

Enhanced stability of Fe-modified CuO-ZnO-ZrO2-Al2O3/HZSM-5 bifunctional catalysts for dimethyl ether synthesis from CO2 hydrogenation

A series of iron (Fe) modified CuO-ZnO-ZrO2-Al2O3 (CZZA) catalysts, with various Fe loadings, were prepared using a co-precipitation method. A bifunctional catalyst, consisting of Fe-modified CZZA and HZSM-5, was studied for dimethyl ether (DME) synthesis via CO2 hydrogenation. The effects of Fe loading, reaction temperature, reaction pressure, space velocity, and concentrations of precursor for the synthesis of the Fe-modified CZZA catalyst on the catalytic activity of DME synthesis were investigated. Long-term stability tests showed that Fe modification of the CZZA catalyst improved the catalyst stability for DME synthesis via CO2 hydrogenation. The activity loss, in terms of DME yield, was significantly reduced from 4.2% to 1.4% in a 100 h run of reaction, when the Fe loading amount was 0.5 (molar ratio of Fe to Cu). An analysis of hydrogen temperature programmed reduction revealed that the introduction of Fe improved the reducibility of the catalysts, due to assisted adsorption of H2 on iron oxide. The good stability of Fe-modified CZZA catalysts in the DME formation was most likely attributed to oxygen spillover that was introduced by the addition of iron oxide. This could have inhibited the oxidation of the Cu surface and enhanced the thermal stability of copper during long-term reactions.

Effect of acidic MCM-41 mesoporous silica functionalized with sulfonic acid groups catalyst in conversion of methanol to dimethyl ether

The global issue of contamination and power reserves has given dimethyl ether (DME) considerable attention. It is an encouraging and clean green material for the future resulting from its clean combustion properties. In this paper, a novel MCM-41-propyl-SO3H catalyst was successfully prepared with tethering of the active sulfonic acid groups onto the support via covalent bonds. This material was investigated as catalyst for DME synthesis via methanol dehydration in a fixed bed flow reactor at different experimental settings. TGA, NH3-TPD, SEM, XRD and BET techniques​ were utilized to characterize the synthesized material. MCM-41 sulfonated catalyst showed great thermal stability, high surface area and significant acid loading. The catalytic tests also demonstrated that the maximum methanol conversion was observed at 350 °C and catalyst contact time of 8 s. In addition, the catalyst showed a total selectivity to DME; light hydrocarbons and higher oxygenated compounds were not formed at temperatures above 300° C.

The catalytic activity of Co/kaolinite catalyst for dimethyl ether synthesis via methanol dehydration

The production of dimethyl ether (DME), renewable fuel, using dehydration of methanol over Co supported on kaolinite catalysts was investigated. In this study, kaolinite was modified by impregnation of the various percentage of Co (5%Co/KN, 10%Co/KN, and 15%Co/KN) to improve the activity of the catalyst. The prepared catalysts were characterized by nitrogen gas adsorption using the Brunauer–Emmett–Teller (BET) method, and the X-ray diffractometer (XRD). The thermogravimetric analysis (TGA) was used to analyze of coke formation on spent catalysts. The catalytic performances of catalysts were tested in a fixed-bed reactor at atmospheric pressure at the temperature range of 250–350 °C with a fixed weight hourly space velocity (WHSV) of 2.054 h−1. It was found that 5%Co/kaolinite showed the highest methanol conversion of 81.7% among the Co/KN catalysts; however, the DME selectivity was less than 80%. The presence of Co gave the less formation of coke on used catalysts indicating that the Co/KN catalyst had more stable than unmodified kaolinite. The 15%Co/KN is an active, selective, and durable catalyst for DME production at the temperature of 300 °C.

Bifunctional Silicotungstic Acid and Tungstophosphoric Acid Impregnated Cu–Zn–Al & Cu–Zn–Zr Catalysts for Dimethyl Ether Synthesis from Syngas

In the present study, a set of methanol synthesis catalysts with different Cu/Zn/Al or Cu/Zn/Zr molar ratios were synthesized by a co-precipitation method. Silicotungstic acid and tungstophosphoric acid were impregnated into these materials to synthesize new bifunctional catalytic materials to be used in direct synthesis of dimethyl ether (DME) from syngas. In the case of methanol production, synthesized Cu/Zn/Al catalysts exhibited quite high methanol selectivity, reaching to approximately 87%. These results indicated that the dispersion of copper particles profoundly affected the selectivity of methanol. Direct synthesis of DME was investigated in the presence of heteropoly acid impregnated copper-based novel hybrid type bifunctional catalysts. Results revealed that product distributions were strongly influenced by the reaction temperature, pressure, heteropoly acid content, and type. Results proved that silicotungstic acid (STA) impregnated bifunctional catalysts showed much better catalytic performance than the tungstophosphoric acid (TPA) impregnated ones in DME synthesis from syngas. Very high dimethyl ether selectivity values were achieved in direct synthesis of dimethyl ether over the 25%, and 30% STA impregnated methanol synthesis catalysts, at 275 °C and 50 bar. DME selectivity presented an increasing trend due to the increase in heteropoly acid content over methanol synthesis catalysts. The silicotungstic acid incorporated (30%) Cu/Zn/Al catalyst, having a composition of 6/3/1 (30STA@CZA:631), showed the highest CO conversion and DME selectivity. However, coke formation over this catalyst was much more than the catalyst containing 25% STA. This is mainly due to the higher Bronsted acidity of 30STA@CZA:631 than 25STA@CZA:631. Low coke formation, together with quite high DME selectivity values achieved with 25STA@CZA:631, is a worthy distinction of this catalyst for the direct synthesis of DME from synthesis gas. Novel hybrid type catalysts are successfully synthesized for direct synthesis of dimethyl ether process. Heteropoly acid incorporated methanol synthesis catalysts are very active and stable in the direct synthesis of dimethyl ether process. Silicotungstic acid (STA) impregnated copper-based catalyst exhibits a superior performance than the tungstophosphoric acid impregnated catalyst.

Ethanol as a Binder to Fabricate a Highly‐Efficient Capsule‐Structured CuO−ZnO−Al2O3@HZSM‐5 Catalyst for Direct Production of Dimethyl Ether from Syngas

AbstractThis work reports a highly efficient capsule‐structured CuO−ZnO−Al2O3@HZSM‐5 (CZA@HZSM‐5‐EtOH) core‐shell catalyst for the direct conversion of syngas to dimethyl ether by a facile physical coating method with ethanol as a binder through coating micrometer‐sized HZSM‐5 shell on the prior‐shaped millimeter‐sized CZA core, it shows 2.9 times higher CO conversion with the 2.7 times higher turnover frequency and 9.2 times higher dimethyl ether space‐time yield of the CZA@HZSM‐5‐SS catalyst prepared by a similar process but with silica sol as a binder (315.5 vs 34.3 gDME kgcat−1 h−1). The relationship between the structure and performance was explored by a variety of characterization techniques including X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X‐ray diffraction (XRD), ammonia temperature programmed desorption (NH3‐TPD), nitrogen adsorption‐desorption, H2‐temperature‐programmed reduction (H2‐TPR) and H2‐TPR after oxidation of the samples by N2O. CZA@HZSM‐5‐EtOH can be considered as a highly efficient and practical catalyst for dimethyl ether synthesis from syngas. This work presents a new avenue to design other bifunctional catalysts for the cascade reactions in which the raw materials can be converted into an intermediate over the core and then the as‐formed intermediate over the core can be subsequently converted into the final product.

Direct dimethyl ether synthesis over mesoporous Cu–Al2O3 catalyst via CO hydrogenation

Syngas conversion to dimethyl ether (DME) is an important reaction (STD) in C1 chemistry since DME not only possesses high value but also can be used as a vital chemical intermediate. Here, we design a Cu-based mesoporous alumina catalyst to realize the DME synthesis reaction. It exhibits high catalytic activity in terms of CO conversion of 21.2% and DME selectivity of 95.9% according to its synergistic effect between the Cu and alumina. In the Cu-based alumina catalyst, the Cu–Cu bond is for converting CO to methanol and the Cu–Al bond is for the formed methanol dehydration to DME. Therefore, the well-dispersed Cu nanoparticles provide amounts of active sites for methanol synthesizing, at the same time as the strong metal–support interaction between the Cu nanoparticles and mesoporous alumina offering Cu–Al active sites for methanol quick dehydration to DME. In addition, the mesopores supplied by alumina support also accelerate the mass transfer and diffusion, boosting the CO activation. This study points out the real active phase for DME synthesis, which plays an important guiding role in design of related catalysts for DME synthesis. The process of syngas conversion to DME over Cu-based mesoporous alumina catalyst.

A novel UiO-66 encapsulated 12-silicotungstic acid catalyst for dimethyl ether synthesis from syngas

Abstract Dimethyl ether (DME) has received great attention as a promising clean fuel and industrially important intermediate. Tremendous efforts have been made to develop highly active and stable catalysts for DME production. Here, we present the first example of the application of metal-organic framework (MOF) catalyst in DME synthesis from syngas. A Zr-MOF (UiO-66) was selected as the catalyst host and support owing to its exceptionally high stability and porosity. UiO-66 was firstly functionalized by silicotungstic acid (H4SiW12O40, STA) via a one-pot synthesis method and then loaded with Cu by a facile solid grinding method. The prepared catalysts were characterized using XRD, TGA, FT-IR, N2 adsorption and TEM. The high porosity and thermal stability of acidified UiO-66 were maintained after 15% wt STA incorporation without any destruction of the Keggin structure of STA. The catalyst was tested for one step DME synthesis from syngas, showing higher DME selectivity and space-time yield than control catalysts. The superior activity of Cu/STA-UiO was attributed to the uniform dispersion of active centres with close intimacy and high density of Bronsted acid sites, as well as strong metal support interaction between Cu and Zr oxide SBU evidenced by XPS analysis.

Stability of a Bifunctional Cu-Based Core@Zeolite Shell Catalyst for Dimethyl Ether Synthesis Under Redox Conditions Studied by Environmental Transmission Electron Microscopy and In Situ X-Ray Ptychography.

When using bifunctional core@shell catalysts, the stability of both the shell and core-shell interface is crucial for catalytic applications. In the present study, we elucidate the stability of a CuO/ZnO/Al2O3@ZSM-5 core@shell material, used for one-stage synthesis of dimethyl ether from synthesis gas. The catalyst stability was studied in a hierarchical manner by complementary environmental transmission electron microscopy (ETEM), scanning electron microscopy (SEM) and in situ hard X-ray ptychography with a specially designed in situ cell. Both reductive activation and reoxidation were applied. The core-shell interface was found to be stable during reducing and oxidizing treatment at 250°C as observed by ETEM and in situ X-ray ptychography, although strong changes occurred in the core on a 10 nm scale due to the reduction of copper oxide to metallic copper particles. At 350°C, in situ X-ray ptychography indicated the occurrence of structural changes also on the µm scale, i.e. the core material and parts of the shell undergo restructuring. Nevertheless, the crucial core-shell interface required for full bifunctionality appeared to remain stable. This study demonstrates the potential of these correlative in situ microscopy techniques for hierarchically designed catalysts.

Catalytic hydrogenation of CO2 into methanol and dimethyl ether over Cu-X/V-Al PILC (X = Ce and Nb) catalysts

The production of methanol (MeOH) and dimethyl ether (DME) through CO2 hydrogenation is an attractive route to recycle CO2 and control its emission to the atmosphere. In the present work, the hydrogenation of CO2 into MeOH and DME over Al-pillared clays impregnated with different metals (Cu-X/V-AI PILC, where X=Ce and Nb) was investigated in the temperature range 200–300°C. The influence of additives on the physico-chemical properties of the catalysts was evaluated by N2 adsorption, ex situ XRD, TPR analysis, and in situ XANES and XRD. The acid sites were analyzed by FTIR analysis after adsorption of pyridine and NH3-TPD. The basic and metallic sites were analyzed by CO2-TPD and N2O-TPD, respectively. In situ XANES was used to investigate the Cu+ and CuO species. MeOH and DME selectivities were directly related to the presence of acid, basic and metallic sites and with the reaction temperature. The results indicated that the CuCe/V-Al PILC catalyst was the most promising catalyst for DME synthesis from CO2.

Influence of Compound Additive CeO2-MxOy on Catalytic Performace of Pd/γ-Al2O3 Catalyst for One-step Synthesis of Dimethylether

A series of Pd/γ-Al2O3 catalysts with different types of compound additives were prepared by impregnation under microwave calcination; the physicochemical properties and catalytic performance of catalysts for one-step synthesis of dimethylether from sulfur-containing syngas were investigated. The results show that the catalysts added CeO2-ZrO2 showed much better catalytic performance and sulfur tolerance than those added CeO2-ZnO or CeO2-CaO in terms of CO conversion, methanol, and dimethylether selectivities and time space yield of dimethylether, which are closely related to higher pore volume and Pd dispersity, moderate CO adsorption, and moderate surface acidity of the catalyst. The optimum compound additive content was determined to be 2%CeO2-1%ZrO2. Under such optimum conditions, CO conversion, dimethylether selectivity, and time space yield of dimethylether are 63.2%, 68.5%, and 30.92 mmol·(ml·h)−1, respectively.

Hierarchically structured ZSM-5 obtained by desilication as new catalyst for DME synthesis from methanol

A new type of micro–mesoporous materials with properties of ZSM-5 zeolite was tested as catalysts for the synthesis of dimethyl ether (DME) from methanol. The catalytic performance of ZSM-5 was improved by generation of mesoporosity using desilication method (alkaline leaching of framework Si). It was shown that controlled modification of the porous structure and acidity of the zeolitic samples strongly influences their catalytic activity, selectivity and stability in the process of DME synthesis. Desilication of ZSM-5 zeolite resulted in a development of the mesoporous structure and enhancement of its acidity, what was confirmed by N2-sorption measurements, IR-DRIFT spectroscopy and NH3-TPD. Desilicated zeolite samples exhibited higher catalytic activity and stability in the process of DME synthesis in comparison to parent ZSM-5. Moreover, micro–mesoporous zeolites were more resistant for poisoning by coke deposits in comparison to conventional ZSM-5 catalyst.

V-modified CuO–ZnO–ZrO2/HZSM-5 catalyst for efficient direct synthesis of DME from CO2 hydrogenation

A series of V-modified CuO–ZnO–ZrO2/HZSM-5 catalysts for direct synthesis of dimethyl ether (DME) from CO2 hydrogenation were prepared by an oxalate co-precipitation method. The catalysts were also characterized by XRD, BET, H2-TPR, N2O chemisorption, NH3-TPD, and XPS techniques. The results show that the catalytic performances of the catalysts are strongly dependent on the content of V added in the preparation.

Pd/CNT-promoted Cu[sbnd]ZrO2/HZSM-5 hybrid catalysts for direct synthesis of DME from CO2/H2

A type of bi-functional hybrid catalyst of Pd-decorated CNT-promoted Cu-ZrO2 admixed with HZSM-5 zeolite was developed, and displayed excellent performance for the direct synthesis of dimethyl ether (DME) from CO2/H2 via CH3OH in a single fixed-bed continuous flow reactor. Over a CuZr–PdCNTs/HZSM-5 hybrid catalyst under reaction conditions of 5.0MPa, 523K, V(H2)/V(CO2)/V(N2)=69/23/8, GHSV=25,000mLSTP/(h g-hydr. catal.), the observed specific rate of CO2 hydrogenation-conversion reached 0.39μmol/(s m2-Cu0-SA), which was 1.22 times that of the corresponding Pd/CNTs-free counterpart CuZr/HZSM-5. The addition of a minor amount of the Pd-decorated CNTs into the CuZr/HZSM-5 host catalyst caused little change in the apparent activation energy for CO2 hydrogenation, but led to an increase of metal Cu exposed area (catalytically active Cu surface-sites closely associated with the CO2 hydrogenation to methanol) and marked improvement of adsorption performance of the catalyst for H2 and CO2. The latter would help generate a micro-environment with higher concentration of active H and CO2 adspecies at the surface of the functioning catalyst, thus increasing the rate of the surface hydrogenation reactions. The present study also demonstrated that combining the methanol-synthesis and methanol-dehydration-to-DME processes in heterogeneous “one-pot” reactions by using the bi-functional hybrid catalyst could indeed enhance the driving force for CO2 hydrogenation conversion.

One-step synthesis of dimethyl ether from the gas mixture containing CO2 with high space velocity

Dimethyl ether (DME) has been considered as a potential hydrogen carrier used in fuel cells; it can also be consumed as a diesel substitute or chemicals. To develop the technique of DME synthesis, a bifunctional Cu–ZnO–Al2O3/ZSM5 catalyst is prepared using a coprecipitation method. The reaction characteristics of DME synthesis from syngas at a high space velocity of 15,000mL (gcath)−1 are investigated and the effects of reaction temperature, pressure, CO2 concentration and ZSM5 amount on the synthesis are taken into account. The results suggest that an increase in CO2 concentration in the feed gas substantially decreases the DME formation. The optimum reaction temperature always occurs at 225°C, regardless of what the pressure is. It is thus recognized that the DME synthesis is governed by two different mechanisms when the reaction temperature varies. At lower reaction temperatures (<225°C) the reaction is dominated by chemical kinetics, whereas thermodynamic equilibrium is the dominant mechanism as the reaction temperature is higher (>225°C). For the CO2 content of 5vol.% and the pressure of 40atm, the maximum DME yield is 1.89g (gcath)−1. It is also found that 0.2g of ZSM5 is sufficient to be blended with 1g of the catalyst for DME synthesis.

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.

Nafion-Incorporated Silicate Structured Nanocomposite Mesoporous Catalysts for Dimethyl Ether Synthesis

Being chemically and thermally stable, Nafion resin is considered to be an attractive solid acid catalyst. Although it has high acid strength and the ability to catalyze a wide range of reactions, the catalytic activity of Nafion is limited, because of its very low specific surface area. In this study, mesoporous Nafion−silica nanocomposites were developed by following a one-pot acidic hydrothermal synthesis procedure. Synthesized catalysts were determined to have well-dispersed structures with high surface area values (595−792 m2/g) and strong Brønsted, as well as Lewis, acid sites. The activities of these novel catalysts were tested in dimethyl ether synthesis from methanol in a flow system. The effects of modifications in the synthesis procedure and Nafion loading showed that the material synthesized from a solution containing a Nafion/silica weight ratio of 0.15 and refluxed with a 2 M sulfuric acid−ethanol (SAE) mixture for surfactant removal was the best catalyst for this reaction. Production of the green transportation fuel alternate dimethyl ether (DME) was achieved with this catalyst at very high yields with almost 100% DME selectivity at >180 °C.