Direct DME Synthesis Research Articles

Does Direct Dimethyl Ether Synthesis from Carbon Dioxide and Hydrogen Yield More Valuable Products than the Equivalent Methanol Production? A Review on Recent Work

AbstractDimethyl ether (DME) has promising properties as e‐fuel and platform chemical. Its direct synthesis from CO2 and hydrogen, which is thermodynamically more favorable than the indirect route over methanol, is reviewed. Systematic thermodynamic equilibrium calculations are evaluated and compared to bifunctional catalysis experiments performed with Cu/ZnO/ZrO2 methanol catalyst and ferrierite or heteropolyacid‐coated dehydration catalysts under thermodynamic and kinetic conditions. In the thermodynamic region, the methyl yield of direct DME synthesis is superior over sole methanol synthesis. Significant differences among the solid acids used are absent. However, under kinetic conditions, the heteropolyacid‐coated catalysts show superior performance for dehydration over zeolites.

Biomass-derived activated carbon catalysts for the direct dimethyl ether synthesis from syngas

The direct DME synthesis from syngas was studied by using activated carbon-based bifunctional catalytic beds. Two kinds of activated carbons, prepared by physical (by CO2 partial gasification) and chemical (with phosphoric acid) activation of olive stones, were used as supports for the preparation of the catalysts. The chemically activated carbon presented a considerable amount of thermally and chemically stable surface phosphorus complexes, which played an important role on the catalytic performance of the prepared catalysts. A Zr-loaded P-containing activated carbon presented a relatively high activity, selectivity and stability for the production of DME from methanol and was used as methanol dehydration catalyst. On the other hand, Cu-Zn was loaded on both P-containing and P-free activated carbon supports for the preparation of methanol synthesis catalysts. The presence of surface-phosphorus on the carbon support resulted in a strong metal-support interaction, hindering the catalytic activity for the hydrogenation of CO to methanol. However, the catalyst that did not contain phosphorus showed noticeable activity for this reaction. The physical mixing of the methanol synthesis and methanol dehydration catalysts resulted in the preparation of carbon-based bifunctional catalytic beds, which performed very efficiently in the direct DME synthesis from syngas in a fixed-bed reactor. Different mass ratios of the individual (metallic and acid) catalysts were studied. An acid/metallic catalyst mass ratio of 2 provided the catalytic bed with enough acid sites to promote methanol dehydration to its maximum extent and make the overall product distribution controlled by the methanol synthesis reaction on the metallic phase.

Sustainability analysis of the bio-dimethyl ether (bio-DME) production via integrated biomass gasification and direct DME Synthesis Process

The sustainability analysis based on life cycle assessment (LCA) of bio-dimethyl ether (bio-DME) production via an integrated biomass gasification and direct DME synthesis (IBG-DME) process, using oil palm residue as feedstock, was performed. The IBG-DME process was simulated in Aspen plus. Operating at selected condition, the IBG-DME was an exothermic process, whereas for 1 kg h−1 of oil palm trunk, bio-DME of 0.3456 kg h−1 and bio-methanol of 0.015 kg h−1 were produced as main product and by product, respectively, with energy efficiency at 59.5%. The energy consumption increased as gasifying temperature increased and reached thermal self-sufficient condition at approximately 890 °C but the CO2 emission showed opposite trend. LCA result indicated that the carbon footprint of each unit operation relied on the energy consumption. For biomass gasification section, the global warming potential (GWP) accounted for approximately 91% of the total impact. The DME production section highly contributed toward the ozone depletion potential (ODP), eco-toxicity (ET), and human toxicity-non-carcinogenics (HTNC) whereas the syngas cleaning and conditioning section highly contributed toward GWP, human toxicity potential by ingestion (HTPI), and aquatic toxicity potential (ATP). The endpoint impact on the ecosystem were higher than the human health for all process sections.

Comparison of different sampling and surrogate modelling approaches for a multi-objective optimization problem of direct dimethyl ether synthesis in the fixed-bed reactor

It is a difficult task to select one proxy model with the proper range of accuracy and speed among various models. In the current study various types of sampling and surrogate models of a catalytic fixed-bed reactor (direct synthesis of DME) have been compared to perform a multi-objective optimization problem based on data. The challenge is to present a proper model which is capable of introducing a group of optimum points (as the Pareto front) in a single run in a multi-objective optimization problem based on Genetic Algorithm (GA) with comparable accuracy to the exact model but lower computational time during optimization. The initial database has been produced by different sampling methods. By applying the proposed method, the Pareto Front using surrogate models is achieved faster than the exact model, with quite satisfying accuracy. Different types of errors have been studied in sampling methods such as Random, Latin Hypercube Sampling (LHS), Sobol, and Halton, as well as alternative models, Linear Regression, Multilayer Perceptron Neural Network (MLP), Radial Basis Function Neural Network, Support Vector Regression, and Automatic Learning of Algebraic Models (ALAMO). Obtained results indicated that LHS as the sampling method and MLP and ALAMO as the surrogate models have the best ability to predict and optimize the steady-state behavior of the direct dimethyl ether synthesis in the fixed-bed reactor with the lowest mean square error (MSE) of 0.00027.

Kinetics of the Direct DME Synthesis: State of the Art and Comprehensive Comparison of Semi-Mechanistic, Data-Based and Hybrid Modeling Approaches

Hybrid kinetic models represent a promising alternative to describe and evaluate the effect of multiple variables in the performance of complex chemical processes, since they combine system knowledge and extrapolability of the (semi-)mechanistic models in a wide range of reaction conditions with the adaptability and fast convergence of data-based approaches (e.g., artificial neural networks—ANNs). For the first time, a hybrid kinetic model for the direct DME synthesis was developed consisting of a reactor model, i.e., balance equations, and an ANN for the reaction kinetics. The accuracy, computational time, interpolation and extrapolation ability of the new hybrid model were compared to those of a lumped and a data-based model with the same validity range, using both simulations and experiments. The convergence of parameter estimation and simulations with the hybrid model is much faster than with the lumped model, and the predictions show a greater degree of accuracy within the models’ validity range. A satisfactory dimension and range extrapolation was reached when the extrapolated variable was included in the knowledge module of the model. This feature is particularly dependent on the network architecture and phenomena covered by the underlying model, and less on the experimental conditions evaluated during model development.

One-step synthesis of dimethyl ether from biomass-derived syngas on CuO-ZnO-Al2O3/HZSM-5 hybrid catalyst: Combination method, synergistic effect, water-gas shift reaction and catalytic performance

The hybrid systems of CuO-ZnO-Al2O3/HZSM-5 for the one-step synthesis of DME from biomass-derived syngas were prepared by four different combination methods (granule-mixing, powder-mixing, physical coating and dual-bed fixing) and characterized by N2 adsorption, XRD, N2O titration, H2-TPR, NH3-TPD and TG techniques. The influences of combination method on the physicochemical properties and catalytic performances of hybrid catalyst were investigated, and the relationship among the combination method, the synergistic effect and the WGS reaction was discussed based on the composition features of the biomass-derived syngas (CO2-rich and H2-deficient). A maximum of CO conversion and DME yield was obtained over the hybrid catalyst prepared by granule-mixing method. There is a synergistic effect, which remarkably promotes the formation of DME, between the methanol synthesis and the methanol dehydration over the hybrid catalysts except for the hybrid system configured using the dual-bed fixing method. The WGS reaction, playing a pivotal role in the direct DME synthesis because of the in-situ produced hydrogen, relates to the combination method closely. An interaction between the two catalyst components arising in the combination process affects the properties of active sites and further the catalytic performances. The deactivation of the hybrid catalyst is ascribed mainly to the increase in the particle size of Cu in CuO-ZnO-Al2O3.

Experimental investigations and model-based optimization of CZZ/H-FER 20 bed compositions for the direct synthesis of DME from CO2-rich syngas

Kinetic investigations and model-based optimization of CuO/ZnO/ZrO2 : H-FER 20 catalytic systems for direct DME synthesis from CO2-rich syngas.

Direct Synthesis of Dimethyl Ether on Bifunctional Catalysts Based on Cu–ZnO(Al) and Supported H3PW12O40: Effect of Physical Mixing on Bifunctional Interactions and Activity

We studied different preparation methods to synthesize a series of bifunctional hybrid catalytic systems for the direct synthesis of DME from syngas. The objective was to optimize the contact and interaction between the methanol synthesis catalyst and the methanol dehydration catalyst (Cu/ZnO/Al2O3 and H3PW12O40 supported on TiO2, respectively) by using different mixing methods (simple mixing, mixing–milling, suspension, and mixing–pressing). It has been found that the close contact between methanol synthesis and acidic functions is highly dependent on the degree of mixing of the two catalysts. In this respect, the hybrid catalyst prepared by mixing–pressing, which represents the closest contact, shows the strongest alterations in both catalytic functions. These modifications are associated with a decrease in copper surface area and a decrease in strong acid sites caused by the physical blocking of active sites or by cation exchange of the Cu2+/Zn2+ species from Cu–ZnO(Al) and the H+ from the H3PW12O40 units. The activity results demonstrated that the mixing–pressing method leading to a closer contact between the two catalytic functions led to a very low dimethyl ether time yield compared to the other bifunctional catalysts prepared by less severe mixing methods (19.4 vs 205–335 μmol/min·gcat). This work clearly indicates the importance of the mixing method in the synthesis of the hybrid catalyst to optimize the distance and interaction between the metal and acid sites.

Simulation of Reactors under Different Thermal Regimes and Study of the Internal Diffusional Limitation in a Fixed-Bed Reactor for the Direct Synthesis of Dimethyl Ether from a CO2-Rich Input Mixture and H2

This paper presents the simulation of reactors under different thermal regimes using the most used kinetic models for the simulation of the direct synthesis of DME with the objective of optimizing the coupling between heat and mass transfer. A pseudo-homogeneous and a heterogeneous plug-flow model are developed to simulate isothermal, adiabatic, and isoperibolic fixed-bed (shell-and-tube) reactors for the direct synthesis of DME from CO2 and H2, enabling the analysis of the limitations by the internal mass transfer. Concentrations, reaction rates, and temperature gradients within the catalyst are assessed. Catalytic efficiency factors are calculated and represented along the reactor tube. The results show that the choice of the kinetic model is crucial for optimal coupling of these functions since it strongly influences the design and sizing of the reactor for synthesis of DME from CO2-rich feedstocks. Therefore, this analysis demonstrates that the direct synthesis of DME can be limited by internal mass transfer, which promotes the DME synthesis at low conversions, therefore requiring particular attention for future reactor optimization.

Kinetics of the direct DME synthesis from CO2 rich syngas under variation of the CZA-to-γ-Al2O3 ratio of a mixed catalyst bed.

The one-step synthesis of dimethyl ether over mechanical mixtures of Cu/ZnO/Al2O3 (CZA) and γ-Al2O3 was studied in a wide range of process conditions. Experiments were performed at an industrially relevant pressure of 50 bar varying the carbon oxide ratio in the feed (CO2 in COx from 20 to 80%), temperature (503–533 K), space-time (240–400 kgcat s mgas−3), and the CZA-to-γ-Al2O3 weight ratio (from 1 to 5). Factors favoring the DME production in the investigated range of conditions are an elevated temperature, a low CO2 content in the feed, and a CZA-to-γ-Al2O3 weight ratio of 2. A lumped kinetic model was parameterized to fit the experimental data, resulting in one of the predictive models with the broadest range of validity in the open literature for the CZA/γ-Al2O3 system.

Study of catalyst bed composition for the direct synthesis of dimethyl ether from CO2-rich syngas

In this work, we study the direct synthesis of DME using CO2-rich syngas, with a CO2/CO ratio similar to that obtained from the gasification of biomass, i.e., 1.9. We used catalytic beds consisting of physical mixtures of the benchmark catalysts used for the synthesis of methanol from syngas and for methanol dehydration to DME, namely Cu/ZnO/Al2O3 and γ-Al2O3, respectively. Our results show that the ratio between each catalytic phase determines the productivity and selectivity to DME, as well CO and CO2 conversions. Thus, higher total carbon conversions were obtained with the catalytic bed with the highest content of the Cu/Zn/Al2O3 phase. The presence of γ-Al2O3 allows to exceed the equilibrium conversion of CO for the syngas to methanol synthesis. The highest DME productivity is obtained with the catalytic bed containing equal amounts of both catalytic phases. In addition, we also show that other reaction variables such as temperature, pressure, and contact time also play an important role in terms of DME productivity. The presence of a high fraction of CO2 in the syngas results in a high production of H2O, which after long times on stream result in the deactivation of the Cu/ZnO/Al2O3 catalytic phase due to the sintering of the copper particles. The in situ removal of H2O via the addition of an H2O sorbent, zeolite 3A, into the catalytic bed, results in a significant enhancement of both carbon conversion and DME productivity.

Reactor modelling and design for sorption enhanced dimethyl ether synthesis

Sorption Enhanced DiMethyl Ether Synthesis (SEDMES) is a promising option to overcome thermodynamic limitations of conventional DME production processes. In this work a 2D + 1D heterogeneous dynamic model of the reaction/adsorption step in a tube of an externally cooled multitubular fixed bed SEDMES reactor is developed in order to investigate the effect of design and operating parameters on thermal behavior and DME yield performances of the reactor. The model is validated by comparison with experimental results from a bench scale unit, including the dynamics of the outlet composition and the temperature trajectories in different points along the axial coordinate. Simulations with the validated model address the effect of the CO/CO2 ratio in the feed. The results confirm that, thanks to the effective in-situ H2O removal, the DME yield performances (65–70% in this work) of SEDMES are poorly sensitive on the CO/CO2 ratio. Accordingly, on increasing the CO2 content in the feed, SEDMES provides larger advantages with respect to conventional DME direct synthesis. Calculations of maximum temperatures achieved along the axial coordinate show that catalyst thermal stress in the hottest inlet zone of the SEDMES reactor slightly increases with the CO content in the feed due to faster kinetics of the DME production reactions. However, thanks to the dilution effect provided by the adsorption material, maximum bed temperature keeps ∼ 20–30 K below the catalyst stability limit reported in the literature (573 K). Accordingly, larger tube diameters (up to 46.6 mm) than in conventional reactors for the direct synthesis of DME can be adopted with less than 2% loss in DME yield.

ZSM-5-decorated CuO/ZnO/ZrO2 fibers as efficient bifunctional catalysts for the direct synthesis of DME from syngas

CuO/ZnO/ZrO2-ZSM-5 fibrillar bifunctional catalysts, with a mean diameter of 1.5 μm, were prepared in flexible non-woven mats. The use of electrospinning technique allowed obtaining, in only one step, both a high Cu dispersion on the surface of the ZrO2 fibers and well-dispersed zeolite aggregates, with a mean size of 300 nm, decorating the CuO/ZnO/ZrO2 fiber surfaces. These fibers, without further modifications, were very efficient as catalysts for the direct synthesis of DME from syngas in a packed-bed reactor (low pressure drop and enhanced mass and heat transfer). The catalytic activity was well-correlated with the physicochemical properties of the catalysts. The enhanced interaction between the two active phases involved in the direct syngas-to-DME process gave rise to high CO conversions and selectivity to DME values, even when working with a syngas presenting a low H2/CO ratio, such as that obtained from biomass gasification.

Sorption enhanced dimethyl ether synthesis for high efficiency carbon conversion: Modelling and cycle design

Dimethyl ether is one of the most promising alternative fuels under consideration worldwide. Both the conventional indirect DME synthesis and the improved direct DME synthesis process are constrained by thermodynamics, which results in limited product yield, extensive separations and large recycle streams. Sorption enhanced DME synthesis is a novel process for the production of DME. The in situ removal of H2O ensures that the oxygen surplus of the feed no longer ends up in CO2 as is the case for direct DME synthesis. As a result CO2 can be converted directly to DME with high carbon efficiency, rather than being the main byproduct of DME production.The sorption enhanced DME synthesis process is a promising intensification, already achieving over 80 % single-pass CO2 conversion for a non-optimized system. The increased single-pass conversion requires less downstream separation and smaller recycle streams, especially for a CO2-rich feed. A key optimization parameter for the process performance is the adsorption capacity of the system. This capacity can be improved by optimizing the reactive adsorption conditions and the regeneration procedure. In this work, a detailed modelling study is performed to investigate the impact of various process parameters on the operating window and the interaction between different steps in a complete sorption enhanced DME synthesis cycle, and to compare its performance to other direct DME synthesis processes. The development of sorption enhanced DME synthesis, with its high efficiency carbon conversion, could play a significant role in the energy transition in which the carbon conversion will become leading.

Optimization of the direct synthesis of dimethyl ether from CO2 rich synthesis gas: closing the loop between experimental investigations and model-based reactor design

Kinetic modeling, model-based optimization and experimental validation for the direct DME synthesis.

Preparation of Catalyst Cu-ZnO-MgO-Al2O3 for Direct Synthesis of DME

Direct synthesis of DME catalyst was prepared using the co-precipitation method. The catalyst contained CuO/ZnO/Al2O3 about 40/27/33 (%-wt). Two types of catalyst were prepared, i.e. CZMA0 (Mg 0%-wt) and CZMA20 (Mg 20%-wt). Both of catalysts were activated using reducing gas (5% H2 and N2). The activity test was conducted by syngas model which contained (%-mole) 65% H2, 28% CO and 7% N2. The reaction was carried out in a fixed bed reactor at 5 bar, and temperature of 240, 250 and 260°C. Synthesis shown CZMA20 catalyst gave the highest catalytic activity with 73% of CO conversion and 66% of H2 conversion (5 bar and 260°C). Direct synthesis of DME was also carried out using a dual-catalyst, i.e. catalyst for methanol synthesis (M151, the commercial catalyst of methanol synthesis) and methanol dehydration (γ-Al2O3-ITB). The activity of dual catalyst shown 93% of CO conversion and 91% of H2 conversion. This activity was more stable than two other catalysts (CZMA0 and CZMA20).

Influence of the operating conditions on the behavior and deactivation of a CuO-ZnO-ZrO2@SAPO-11 core-shell-like catalyst in the direct synthesis of DME

The behavior of the CuO-ZnO-ZrO2@SAPO-11 core-shell catalyst in the direct synthesis of DME from H2 + CO + CO2 mixtures has been assessed. The effect of the reaction conditions (temperature, pressure, space-time) and feed composition (CO2 and H2 concentration) on the DME yield and selectivity, CO2 and COx (CO2+CO) conversions and stability of the catalyst have been studied. The experiments have been carried out in a fixed-bed reactor in the following condition ranges: 250–325 °C; 10–50 bar; space-time, 1.25–15 g h molC−1; CO2/COx molar ratio in the feed, 0–1; and H2/COx molar ratio in the feed, 2.5–4; time on stream, up to 48 h. Under mild conditions (275–300 °C range, 20–30 bar, space-time over 5 g h molC−1, CO2/COx molar ratio in the 0.5–0.75 range, and H2/COx molar ratio around 3) a good compromise is reached between the yield of DME and the conversion of CO2, with high catalyst stability. Coke deposition is the main cause of catalyst deactivation, formed by condensation of the hydrocarbon byproducts, blocking the metallic sites in the core. The formation rate of this fraction of coke is greater than that of the coke deposited in the SAPO-11 of the shell. Increasing reaction temperature favors the formation of coke, while co-feeding CO2 attenuates this formation, due to the increase of H2O concentration.

An intermetallic Pd2Ga nanoparticle catalyst for the single-step conversion of CO-rich synthesis gas to dimethyl ether

Well-defined Pd/Ga-nanoparticles were prepared and used as a precursor for the methanol active component in a bifunctional syngas-to-dimethyl ether catalyst. In situ X-ray absorption spectroscopy experiments were employed both to unravel the initial formation of the active catalyst phase in reductive H2 atmosphere and to further monitor changes of the nanoparticles under conditions of dimethyl ether synthesis at a pressure up to 20 bar (250 °C). The catalytic studies were conducted using simulated biomass-derived, CO-rich syngas in a continuous-flow reactor, with the bifunctional catalyst offering the two types of active sites, i.e. for methanol synthesis (Pd/Ga nanoparticles) and its subsequent dehydration (γ-Al2O3), in close proximity. As compared to the conventional Cu/Zn-based reference catalyst prepared via a similar procedure, the Pd/Ga-based catalyst showed a promising activity together with a notable stability with time on stream and a high temperature tolerance (up to 300 °C). A kinetic model which considers the individual reactions involved in direct DME synthesis based on power law equations was used to fit the experimental data, and the apparent activation energies were compared to the Cu/Zn-based catalyst.

Catalyst configuration for the direct synthesis of dimethyl ether from CO and CO2 hydrogenation on CuO–ZnO–MnO/SAPO-18 catalysts

Three catalytic bed configurations for the direct DME synthesis have been studied using CuO–ZnO–MnO and SAPO-18 as metallic and acid functions, respectively. The runs have been carried out in a fixed bed reactor under the following conditions: Feed, H2 + CO + CO2; 275 °C; 30 bar; 5.02 gcat h mol C −1 ; H2/COx = 3. The results (COX conversion, DME yield and selectivity) show that a better contact between phases, thus, incorporating both functions in a bifunctional catalyst (CZMn/S-18) results in a mayor DME yield and selectivity than the other configurations. The effects of the fed CO2 content and reaction temperature have been assessed for the bifunctional catalyst. Although the production of DME decreases with co-feeding CO2 with syngas, for a CO2/(CO2 + CO) ratio in the feed higher than 0.5 this effect is attenuated, which is interesting for the conversion of CO2. The highest DME selectivity (> 94%) is obtained at 275 °C, with moderate deactivation by coke.

Adsorption/heat exchanger (HEX) reactor for simultaneous DME and hydrogen production: A theoretical investigation

Heat exchanger (HEX) reactor is recognized as one of the most promising configurations for production of DME and hydrogen, simultaneously. In the current study, dehydration of methanol to DME is carried out in exothermic side, which is a fixed bed reactor assisted by regenerative zeolite 4A particles and coupled with benzene synthesis in endothermic side. The mathematical modeling results prove that selective water adsorption from direct DME synthesis leads to an intensification of DME production compared to non-adsorbent configuration as well as conventional one. Furthermore, the simulation results represent 336.52 ton/day enhancement in the hydrogen production rate in comparison with non-adsorbent configuration using the same catalyst loading and duty. Finally, the effects of main operating variables are considered on DME molar flow rate and cyclohexane conversion. The results suggest that the coupling of these reactions in the presence of zeolite 4A adsorbent could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the novel reactor.