Dimethyl Ether Synthesis Research Articles

Effect of Si content on the performance of direct synthesis of dimethyl ether over slurry CuZnAl catalyst prepared by complete liquid phase technology

The effect of Si content on the performance of slurry CuZnAl catalyst prepared by complete liquid phase technology for direct synthesis of dimethyl ether from syngas was investigated. Among them, catalyst with Si/Al ratio of 0.5 showed the best catalytic performance with the CO conversion of 63.31% and the dimethyl ether selectivity of 72.96%. The catalyst was stable after 480 h reaction. As revealed by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption and desorption characterizations, the introduction of Si promoted the dispersion of Cu species nanoparticles and led to increased specific surface area, which was beneficial for improving the CO conversion. Besides, temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) characterizations showed that an electronic interaction between Cu species and other components of the catalyst (especially, Si species) could inhibit the reduction of Cu species, resulting in the abundant Cu+ species on the catalyst surface. This was conducive to the synthesis of methanol and could effectively inhibit the formation of CO2, which was a by-product of the water-gas shift reaction. Moreover, a large amount of Al species (AlOOH) was enriched on the SA0.5 catalyst surface, which might contribute to the dehydration of methanol to produce dimethyl ether. In conclusion, the synergetic catalysis of Cu+ and AlOOH in slurry CuZnAlSi system improved the catalytic activity and dimethyl ether selectivity.

Embryonic zeolites for highly efficient synthesis of dimethyl ether from syngas

Embryonic X-ray amorphous semi-formed MFI-type zeolite units mixed with the Cu–Zn–Al catalyst have been used for the direct synthesis of dimethyl ether (DME) from syngas. The hybrid catalyst with embryonic zeolite (EZ) with the particle size of 5 nm has demonstrated superior performance in terms of activity, selectivity, and stability compared to the crystalline ZSM-5 zeolite counterpart and the amorphous aluminosilicate material. The FTIR pyridine adsorption uncovered several types of active sites in EZ, including Brønsted acid sites of medium strength. The DFT modeling pointed out the key role of defect sites leading to lower strength of the acid sites in the embryonic MFI zeolite in comparison with the fully crystalline material. The effect of embryonic zeolite on the DME synthesis has been assigned to enhanced transport of methanol from Cu to ultra-small zeolite precursor units with moderate acidity, hence promoting the efficient dehydration to DME with high selectivity and stability.

Gallium nitride catalyzed the direct hydrogenation of carbon dioxide to dimethyl ether as primary product

The selective hydrogenation of CO2 to value-added chemicals is attractive but still challenged by the high-performance catalyst. In this work, we report that gallium nitride (GaN) catalyzes the direct hydrogenation of CO2 to dimethyl ether (DME) with a CO-free selectivity of about 80%. The activity of GaN for the hydrogenation of CO2 is much higher than that for the hydrogenation of CO although the product distribution is very similar. The steady-state and transient experimental results, spectroscopic studies, and density functional theory calculations rigorously reveal that DME is produced as the primary product via the methyl and formate intermediates, which are formed over different planes of GaN with similar activation energies. This essentially differs from the traditional DME synthesis via the methanol intermediate over a hybrid catalyst. The present work offers a different catalyst capable of the direct hydrogenation of CO2 to DME and thus enriches the chemistry for CO2 transformations.

Life Cycle Assessment for Full Chain CCU Demonstration in the Align-CCUS Project –Dimethyl Ether and Polyoxymethylen Dimethyl Ethers Production from CO2 and its Usages in the Mobility and Electricity Sectors

As part of three years of research and development in the European ALIGN-CCUS project, a CCU demonstration plant was erected at the lignite-fired block K of the RWE power plant at Niederaussem, Germany. It was the aim to demonstrate the full chain of CCU - beginning with the capture of CO2 from the power plant flue gas stream, via the one-step synthesis of dimethyl ether (DME) through to its usage for electricity generation in a peak power diesel engine generator. A secondary target was the synthesis of polyoxymethylen dimethyl ethers (OMEs) and their use in the mobility sector. A thorough Life Cycle Inventory was collected based on real process data for the first time, supported by process modelling with AspenPlus. This includes the inventory for construction and operation of all elements of the demonstrator chain: the power plant with its monoethanolamine (MEA)-based post-combustion capture facility, the newly developed synthesis unit based on a one-step reactor using a bifunctional catalyst (up to 50 kg DME per day) and the reconversion of the produced DME into electricity by an adapted diesel power generator (60-80 litre per hour DME consumption, output 240 kWel). Additionally to the DME-route, the synthesis and usage of OME3-5 as a fuel in an adapted 2 l diesel motor for mobility application were part of the investigation. The extensive inventory enabled a Life Cycle Assessment (LCA) according to ISO standards showing results for both applications. Benchmarking technologies like diesel- and e-mobility and gas turbines for peak power supply enable a comparative analysis identifying advantages and disadvantages of the CCU route. A sensitivity analysis is used to identify weak points along the routes together with future development targets and potentials. To investigate a broad array of results, several varying scenarios, especially regarding energy supply were considered. The use of renewable electricity sources for electrolytic hydrogen production, but also for other processes of the CCU chain was investigated. A range of different impact categories were considered: Global Warming Potential (GWP), Particulate Matter Formation Potential (PM), Fossil Depletion Potential (FDP), Photochemical Ozone Creation Potential (POCP) and Terrestrial Acidification Potential (AP). The results show that the investigated CCU technology routes are highly emission-intensive when using the current German electricity mix: the reuse of CO2 and the reduction of fossil fuel consumption that goes along with it, is outweighed by the energy-intensive nature of the synthesis processes. Using renewable energy sources can drastically reduce GHG emissions, especially to a point where the implementation of a mostly renewable energy supply for the process chain offers a viable mitigation option compared to the investigated benchmark technologies. Findings regarding sensitive LCI data, development targets and technological potentials are discussed in the results.

Probing Hydrophobization of a Cu/ZnO Catalyst for Suppression of Water–Gas Shift Reaction in Syngas Conversion

Due to the complexity of the structure and surface property of metal oxide catalysts, hydrophobization of metal oxide catalysts is a great challenge. The hydrophobization strategy and effects of hydrophobization on the surface property and catalytic performance of metal oxide catalysts deserve rigorous investigations. Herein, we adopt stearic acid to functionalize the surface of a Cu/ZnO catalyst by bridging stearic acid molecules with the Cu/ZnO catalyst surface. After functionalization, the hydrophobicity of the Cu/ZnO catalyst is greatly reinforced, while its structure and catalytic performance remain nearly unchanged. The hydrophobic Cu/ZnO catalyst exhibits a very positive inhibitory effect on the unfavorable water–gas shift reaction (WGSR) in one-step synthesis of dimethyl ether (DME) from syngas (CO + H2), while the catalytic activity of the hydrophobic Cu/ZnO catalyst for methanol synthesis is not affected. Lower CO2 selectivity and higher DME selectivity over the hydrophobic Cu/ZnO-4 catalyst, better than those of untreated catalyst, are obtained facilely. The promoted catalytic performance of the hydrophobic Cu/ZnO catalyst demonstrates that the surface hydrophobicity of heterogeneous catalysts is worthy of more attention for enriching their catalytic roles.

Identification of reaction path for the synthesis of polyoxymethylene dimethyl ethers from methanol and paraformaldehyde catalyzed by Al-MCM-41 zeolite

Polyoxymethylene dimethyl ethers (PODEn) are ideal blending components of diesel oil. However, there are few studies to identify the reaction path of PODEn synthesis, which is essential in understanding the reaction. In this work, the reaction path of PODEn synthesis from methanol and paraformaldehyde on the Al-MCM-41 zeolite was studied by density functional theory calculation and experiment. The structures of intermediates and transition states of PODEn synthesis were designed and optimized. The three possible reaction paths were analyzed by comparing the Gibbs free energy barriers in the calculation and the product distribution in the experiment. The results showed that paraformaldehyde is decomposed into formaldehyde first. Formaldehyde and methanol react to form a hemiacetal intermediate. Then methanol reacts with hemiacetal to form dimethoxymethane. This step has the highest free energy barrier (121.2 kJ·mol−1), which is the rate-determining step. The long-chain PODEn is formed by chain growth from PODEn-1 and formaldehyde.

Direct Synthesis of Dimethyl Ether from CO2: Recent Advances in Bifunctional/Hybrid Catalytic Systems

Dimethyl ether (DME) is a versatile raw material and an interesting alternative fuel that can be produced by the catalytic direct hydrogenation of CO2. Recently, this process has attracted the attention of the industry due to the environmental benefits of CO2 elimination from the atmosphere and its lower operating costs with respect to the classical, two-step synthesis of DME from syngas (CO + H2). However, due to kinetics and thermodynamic limits, the direct use of CO2 as raw material for DME production requires the development of more effective catalysts. In this context, the objective of this review is to present the latest progress achieved in the synthesis of bifunctional/hybrid catalytic systems for the CO2-to-DME process. For catalyst design, this process is challenging because it should combine metal and acid functionalities in the same catalyst, in a correct ratio and with controlled interaction. The metal catalyst is needed for the activation and transformation of the stable CO2 molecules into methanol, whereas the acid catalyst is needed to dehydrate the methanol into DME. Recent developments in the catalyst design have been discussed and analyzed in this review, presenting the different strategies employed for the preparation of novel bifunctional catalysts (physical/mechanical mixing) and hybrid catalysts (co-precipitation, impregnation, etc.) with improved efficiency toward DME formation. Finally, an outline of future prospects for the research and development of efficient bi-functional/hybrid catalytic systems will be presented.

Model Analysis of the Role of Kinetics, Adsorption Capacity, and Heat and Mass Transfer Effects in Sorption Enhanced Dimethyl Ether Synthesis.

The role of kinetics, adsorption capacity, and heat and mass transfer effects in the sorption enhanced dimethyl ether synthesis (SEDMES) is investigated by means of a 2D+1D model of a single tube of an industrial-scale, externally cooled, multitubular reactor that simulates the reaction/adsorption step of the SEDMES cycle. The effect of the adsorbent/catalyst weight ratio is analyzed, showing that a trade-off between DME productivity and yield originates from the balance of kinetics and adsorption capacity in the reactor tube. The effects of internal diffusion in catalyst particles are shown to have a strong impact on effective reaction rates: significant yield/productivity improvements are obtained when using a mechanical mixture of catalysts with small particle diameters or by rearranging the distribution of the two active phases in hybrid or core@shell pellets. The thermal effects in the reactor, which are increasingly critical upon intensifying the SEDMES process conditions, are also addressed.

Modeling of industrial-scale sorption enhanced gasification process: One-dimensional simulations for the operation of coupled reactor system

Sorption enhanced gasification (SEG) is a promising technology for producing gas derived from renewable feedstock to be used in biofuel synthesis processes. As a response to the growing need for renewable fuels, an SEG reactor design was developed for industrial-scale dimethyl ether (DME) production. A 100MWth scale SEG reactor concept for wood pellets as a feedstock was created by a model-based approach. Thus, a 1D modeling tool for the coupled circulating fluidized beds was developed. The model was used to investigate the dual fluidized bed system’s operation in the gasifier temperature range of 730–790°C. In this range, the optimal producer gas composition without external hydrogen for the downstream DME synthesis was achieved at gasifier temperature 730°C: 63 %vol,dbH2, 11 %vol,dbCO, 13 %vol,dbCO2. The model prediction was successfully compared against experimental data and modeling results from the literature. The developed 1D model enables the investigation of the composition and yield of the producer gas with different operating parameters, such as the part-load operation. This advanced capability can be used to develop new control strategies for the SEG system and investigate the impact of various operating parameters on the producer gas composition and yield.

Highly Conductive Structured Catalytic Reactors for One-Step Synthesis of Dimethyl Ether.

Several structured catalytic reactors for the direct synthesis of the DME reaction are compared with regard to catalyst hold-up, thermal conductivity, and volumetric productivity. Adherent and homogeneous catalyst layers were obtained by washcoating independent of the substrates’ shape and alloy. Moreover, the substrate nature (FeCrAl, brass, or aluminum) and shape (parallel cell monoliths and open foams) do not modify in great extent the CO conversion values and selectivity to the different compounds. This is reasonable since the catalytic phases are the same in all cases and the existence of mass and heat-transfer limitations was negligible in the experimental conditions studied. Structuring by washcoating exhibits less catalyst inventory per reactor volume than a packed-bed monolith. However, completely packing a monolith with powder catalyst produced a decrease in the CO conversion of around 25% with respect to the coated monolith. Moreover, by means of using the obtained highest catalyst hold-up by washcoating (0.33 gcat/cm3) in a brass monolith and by increasing the reaction temperature, the temperature profiles are only slightly affected. This allows to work in an almost isothermal reactor with a volumetric productivity up to 0.20 LDME/h·cm3 at 573 K.

Performance comparison of WO3/SiO2 to ZSM-5 and γ-Al2O3 in the catalytic dehydration of methanol

The performance of ZSM-5, γ-Al2O3 and WO3/SiO2 catalysts for the dehydration of methanol was studied in a fixed bed reactor over a temperature range of 150 to 450 °C and at atmospheric pressure. A parallel reaction scheme for dehydration of methanol to dimethyl ether and methane was proposed for the WO3/SiO2 catalyst, and kinetic parameters for the two reactions were identified. The WO3/SiO2 catalyst was less active than both ZSM-5 and γ-Al2O3 for dehydration. At temperatures above 400 °C, experimental data indicated that WO3/SiO2 could be producing heavier hydrocarbons than the other catalysts. The gas product for γ-Al2O3 and WO3/SiO2 also contained ethylene and methane whereas the gas product for ZSM-5 contained propane and propylene. At higher temperatures ZSM-5 produced gasoline range hydrocarbons but a similar product was absent from all experiments conducted using the WO3/SiO2 and γ-Al2O3 catalysts. It has been shown that WO3/SiO2 can function as a methanol dehydration catalyst for the synthesis of dimethyl ether.

Modeling the Direct Synthesis of Dimethyl Ether using Artificial Neural Networks

AbstractArtificial neural networks (ANNs) are designed and implemented to model the direct synthesis of dimethyl ether (DME) from syngas over a commercial catalyst system. The predictive power of the ANNs is assessed by comparison with the predictions of a lumped model parameterized to fit the same data used for ANN training. The ANN training converges much faster than the parameter estimation of the lumped model, and the predictions show a higher degree of accuracy under all conditions. Furthermore, the simulations show that the ANN predictions are also accurate even at some conditions beyond the validity range.

MCM-41-supported tungstophosphoric acid as an acid function for dimethyl ether synthesis from CO2 hydrogenation

We mixed an MCM-41-supported tungstophosphoric acid (TPA) catalyst with a commercial CuO–ZnO–Al2O3 methanol synthesis catalyst (MSC) and optimized the mixing ratios/reaction conditions towards high performance in dimethyl ether (DME) synthesis by CO2 hydrogenation. First, a series of TPA/MCM-41 catalysts were synthesized at a TPA loading of 30, 40, 60, and 80 wt% and characterized by combining various techniques. The results of X-ray fluorescence spectroscopy confirmed the loading of stoichiometric TPA amounts in each TPA/MCM-41 catalyst, while the N2 adsorption-desorption measurements and the scanning transmission electron microscopy images were showing the decoration of MCM-41 pores with TPA clusters. X-ray diffraction and infrared spectroscopy results identified some structural distortions in TPA clusters especially at relatively low loadings and the results of temperature programmed desorption of ammonia measurements quantified the consequences of these changes in TPA structure on the acid properties. The optimized TPA loading in TPA/MCM-41 was 60 wt% with CuO–ZnO–Al2O3:TPA/MCM-41 = 4:1 at 40 000 mL CO2 gcat−1 h−1 and H2:CO2 = 3:1 at 250 °C and 45 bar. At these conditions, the rate was 1551.5 gDME kgcat−1 h−1, to the best of our knowledge, the highest rate for the direct DME synthesis from CO2 hydrogenation in a single-pass reactor. This performance was originated from the high density of acid sites in TPA/MCM-41 owing to exceptionally high surface area of MCM-41 offering a monolayer dispersion of TPA even at a TPA loading of 60 wt%. These results present a broad potential of TPA/MCM-41 as an acid function in the catalyst mixture for the single-pass DME synthesis from CO2 hydrogenation, especially if used together with an MSC specifically designed for CO2 hydrogenation.

Techno-economic analysis of natural gas high CO2 content for dimethyl ether production with different CO2 separation using CFZ and membrane technologies

Development of the East Natuna gas field, the largest natural gas resources in Southeast Asia, is still highly challenging because of the presence of CO2, up to 72%. Reliable CO2 separation technology implementation with suitable CO2 handling methods is crucial to maximizing the field’s potential. Dimethyl ether is one of the chemical products that can be synthesized from natural gas that can be used as a substitute fuel for LPG. In this study, we compare the techno-economic analysis of natural gas high CO2 content to dimethyl ether using two schemes of CO2 separation: controlled freeze zone (CFZ) and membrane technology with CO2 sequestration. The process simulation is performed by Aspen Hysys V11 software. The results show that in technical aspect on dimethyl ether synthesis with CFZ feed gas (gas consumption of 0.0412 MMSCF/tonne-DME and 2.077 MWh/tonne-DME) is slightly better performance than synthesis process with membrane feed gas (0.043 MMSCF/tonne-DME and 2.077 MWh/tonne-DME). In an economical aspect, levelized cost of dimethyl ether production with CO2 sequestration of 556 US$/tonne-DME (CFZ) and 495 US$/tonne-DME (membrane) is higher than levelized cost without CO2 sequestration with the value of 378 US$/tonne-DME (CFZ) and 329 US$/tonne-DME (membrane).

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.

Macro-kinetic model for CuO–ZnO–ZrO2@SAPO-11 core-shell catalyst in the direct synthesis of DME from CO/CO2

An original kinetic model has been used to describe the performance of an original CuO–ZnO–ZrO2@SAPO-11 bifunctional catalyst on the one-stage synthesis of dimethyl ether (DME) from CO/CO2 hydrogenation. The model considers that certain individual reactions (the synthesis of methanol and the reverse water gas shift) occur in the metallic function (core) of the catalyst particle, whereas others (methanol dehydration) take place in the shell (acid function), and that the progress of these reactions is conditioned by the diffusion of the components. The kinetic parameters of the individual reactions and the deactivation kinetics have been calculated from experimental data obtained in a wide conditions range (H2/COx ratio, 2.5–4; CO2/COx ratio, 0–1; 10–50 bar; 250–325 °C; 1.25–20 g h molC−1). The use of the model for simulating the packed bed reactor has allowed evaluating the influence of the reaction conditions, as well as assessing the effect of the catalysts particle size. The model predicts DME yields of 64% for syngas (H2+CO) feeds, 38% for CO2/COx ratio of 0.50 and 17% for H2/CO2, respectively, at 70 bar and 290 °C. The maximum conversion of CO2 predicted by the model for the same space time value and temperature surpasses 30% for H2+CO2 feedstocks at 70 bar, greater than the experimental value obtained at 50 bar at the same temperature (∼25%).

Experimental implementation of a catalytic membrane reactor for the direct synthesis of DME from H2+CO/CO2

The direct synthesis of dimethyl ether (DME) by the hydrogenation of CO2 and CO2/COx mixtures has been studied in an original packed bed membrane reactor (PBMR). The role of the hydrophilic LTA zeolite membrane is to remove H2O from the reaction medium, reducing therefore the thermodynamic limitations of methanol synthesis and dehydration stages. LTA zeolite has the best permeation properties among the studied zeolites (LTX and SOD). The experiments were carried out using a CuO-ZnO-ZrO2/SAPO-11 catalyst at 275–325 °C, 10–40 bar, space time of 10 gcat h (molC)−1 and using in the permeate section a sweeping gas flowrate of the same composition as that fed to the reaction section. The results (DME yield, CO2 conversion and product distribution) of the PBMR are compared with those obtained in PBR without membrane. In the hydrogenation of CO2, a DME yield of 12% and a CO2 conversion of 20% are obtained at 275 °C, 40 bar and space time of 10 gcat h (molC)−1 with a great catalyst stability.

Separation enhanced methanol and dimethyl ether synthesis

Recent developments in separation enhanced reaction processes using membranes and adsorbents, highlighted here, have proven their potential for carbon dioxide conversion to methanol and dimethyl ether.

The high-yield direct synthesis of dimethyl ether from CO2 and H2 in a dry reaction environment

Highly efficient DME synthesis from CO2 and H2 was realized in a dry reaction environment via the incorporation of a water-conduction membrane.

Process Simulation and Environmental Aspects of Dimethyl Ether Production from Digestate-Derived Syngas.

The production of dimethyl ether from renewables or waste is a promising strategy to push towards a sustainable energy transition of alternative eco-friendly diesel fuel. In this work, we simulate the synthesis of dimethyl ether from a syngas (a mixture of CO, CO2 and H2) produced from gasification of digestate. In particular, a thermodynamic analysis was performed to individuate the best process conditions and syngas conditioning processes to maximize yield to dimethyl etehr (DME). Process simulation was carried out by ChemCAD software, and it was particularly focused on the effect of process conditions of both water gas shift and CO2 absorption by Selexol® on the syngas composition, with a direct influence on DME productivity. The final best flowsheet and the best process conditions were evaluated in terms of CO2 equivalent emissions. Results show direct DME synthesis global yield was higher without the WGS section and with a carbon capture equal to 85%. The final environmental impact was found equal to −113 kgCO2/GJ, demonstrating that DME synthesis from digestate may be considered as a suitable strategy for carbon dioxide recycling.