Direct Dimethyl Ether Research Articles

Pt/C anodic catalysts with controlled morphology for direct dimethyl ether fuel cell: The role of consecutive surface

Two types of Pt nanowires (NWs)/C catalysts with different aspect ratios and one type of Pt nanoparticles/C catalyst are successfully synthesized, and DME electrochemical performance on different extent consecutive surfaces is investigated. The morphology and crystallization are confirmed with electron microscopes and XRD. The electrochemical tests show that the nanowire catalysts, especially the one with higher aspect ratio, possess higher electrochemical surface areas, higher absorption capacity of DME, higher CO tolerance, higher electron transfer coefficient, and higher activity towards DME electrooxidation than those of the nanoparticle catalyst. The results prove that the consecutive surface favors for direct dimethyl ether fuel cell (DDFC) anodic catalyst, which are contributive to the study of the mechanism of DME electrooxidation on Pt surface and designing an effective catalyst for anodic DDFC.

The influence of anode diffusion layer on the performance of direct dimethyl ether fuel cell

SUMMARY The effects of the parameters of the anode gas diffusion layer (GDL), including the PTFE content in the backing layer (BL), the PTFE content in the microporous layer (MPL), and the carbon black loading on the performance of a liquid-feed direct dimethyl ether fuel cell (DDFC), were experimentally investigated. The results indicated that increase in the PTFE content can produce more cracks across the whole surface of the MPL. These cracks were benefit to the anode two-phase mass transport. The optimal PTFE content in anode BL and MPL was 18 and 40 wt%, respectively. The performances of the DDFCs tended to decline with the increase in the carbon black loading in the anode GDLs due to the difficult long path of mass transport. The maximum power density was obtained with 18 wt% PTFE in BL and 0 mg cm−2 carbon black loading, the optimal result, was 76.6 mW cm−2 at ambient pressure. Copyright © 2011 John Wiley & Sons, Ltd.

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.

Preparation of Cu-Zn-Al Bifunctional Catalyst by Sol-Gel Method with the Assistance of PEG and Its Catalytic Performance

A series of Cu-Zn-Al catalyst samples were prepared by sol-gel method with the assistance of polyethylene glycol(PEG) additive.The effect of PEG dosage on their physical and chemical properties was characterized by X-ray diffraction,N2 adsorption,X-ray photoelec-tron spectroscopy,H2 temperature-programmed reduction,and NH3 temperature-programmed desorption.The catalytic performance of the catalyst for direct dimethyl ether(DME) synthesis from syngas was evaluated in a slurry reactor.The results showed that PEG can improve the texture and surface physical and chemical properties of the catalyst and therefore enhance its catalytic activity.With the increase of PEG dosage,the specific surface area,pore volume,and pore diameter of the catalyst increased,whereas the reduction temperature decreased first and then increased,and the dispersion of active component,surface Cu content,and strong acid amount first increased and then decreased.However,adding PEG can only enhance catalytic activity and selectivity of the catalyst,but has no effect on the catalyst stability.

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.

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.

A study of the direct dimethyl ether fuel cell using alkaline anolyte

The electrooxidation behavior of dimethyl ether (DME) dissolved in acidic, neutral or alkaline anolyte has been studied. The cyclic voltammetry measurements reveal that DME in alkaline anolyte demonstrates higher electrooxidation reactivity than that in acidic or neutral anolyte. With increasing the NaOH concentration in the anolyte, the electrooxidation reactivity of DME can be further improved. Direct dimethyl ether fuel cells (DDFCs) are assembled by using Nafion membrane as the electrolyte, Pt/C as the cathode catalyst, and Pt–Ru/C as the anode catalyst. It is found that the use of alkaline anolyte can significantly improve the performance of DDFCs. A maximum power density of 60 mW cm −2 has been achieved when operating the DDFC at 80 °C under ambient pressure.

マイクロ・ナノ粒子触媒層へのグリセリン添加による直接形ジメチルエーテル燃料電池出力性能への影響

However, practical use is not advanced as thought by problems of the cost and durability, etc. Whether highly effective and lowering cost can be done is one of the keys to practical use. Up to now, direct dimethyl ether fuel cell (DDFC) that used DME as a fuel in polymer electrolyte fuel cell (PEFC) has been being researched. The research on the catalyst in them was to have done the optimization by changing the catalyst quantity of the anode or the cathode. Then, the purpose of this research is to improve the performance of DDFC without changing the catalyst quantity. The structure of the catalyst is changed by adding the glycerin when the catalyst seat is made, and the fuel often comes in contact with the catalyst and the performance is improved. The made glycerin addition catalyst is used for either of the anode or the cathode.

Investigation of a Stack for Direct Dimethyl Ether Fuel Cell

In this study, we investigated a stack of direct dimethyl ether fuel cell (DDFC). A small passive DDFC stack had been developed, and a good uniformity could be observed from all single cells. The open-circuit voltage (OCV) of the stack was around 4 V, and its maximum power was 300 mW. No matter which means was adopted, only the values of current and voltage can be changed. The total output power of the stack remains the same. Therefore, based on the different requirements of electrical appliances on discharge, different ways of electric connection can be adopted for the stack.

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.

Direct dimethyl-ether proton exchange membrane fuel cells and the use of heteropolyacids in the anode catalyst layer for enhanced dimethyl ether oxidation

In this study, polarization and impedance experiments were performed on a direct dimethyl ether fuel cell (DMEFC). The experimental setup allowed for independent control of water and DME flow rates. The DME flow rate, backpressure, and water flow rate were optimized. Three heteropolyacids, phosphomolybdic acid, H 3PMo 12O 40. (HPMo), phosphotungstic acid, H 3PW 12O 40, (HPW), and silicotungstic acid, H 4SiW 12O 40, (HSiW) were incorporated into the anode catalyst layer in combination with Pt/C. Both HPW-Pt and HSiW-Pt showed higher overall performance than the Pt control. Anodic polarizations were also performed, at 30 psig, Tafel slopes of 67 mV dec −1, 72 mV dec −1, and 79 mV dec −1 were found for HPW-Pt, HSiW-Pt and the Pt control, respectively. At 0 psig, the Tafel slopes were 56 mV dec −1, 58 mV dec −1, and 65 mV dec −1 for HPW-Pt, HSiW-Pt and the Pt control. The trends in the Tafel slope values are in agreement with the polarization data and the electrochemical impedance spectroscopy results. The addition of phosphotungstic acid more than doubled the power density of the fuel cell, compared to the Pt control. When the maximum power density obtained using the HPW-Pt MEA is normalized by the mass of Pt used, the optimal result, 78 mW mg −1 Pt, the highest observed at 30 psig and 100 °C to date.

Investigation of an Anode Catalyst for a Direct Dimethyl Ether Fuel Cell

In this work, we compared investigation of Pt/multiwalled carbon nanotubes (MWNTs) and Pt/Vulcan XC-72 anode catalysts for direct dimethyl ether fuel cells (DDFC). The homemade catalysts were characterized using a transmission electron micrograph (TEM) and X-ray diffraction (XRD). The cyclic voltammogram analyses revealed that the Pt/MWNTs showed a higher catalytic activity for dimethyl ether electro-oxidation, compared with the Pt/Vulcan XC-72 catalyst. The membrane electrode assembly (MEA) with the Pt/MWNTs anode catalyst presented the maximum power density of 38.4 mW cm−2, which was higher than that with the Pt/Vulcan XC-72 one (32.4 mW cm−2). Moreover, the performance decay rate of the MEA with Pt/MWNTs was lower than that with Pt/Vulcan XC-72 (after a 56 h test). It indicated that the Pt/MWNTs can be expected to be a more suitable catalyst for the DDFC.

Optimum compositions of membrane electrode assemblies (MEAs) for direct dimethyl ether fuel cell

We investigated the effects of the compositions of catalyst layers and diffusion layers on performances of the membrane electrode assemblies (MEAs) for direct dimethyl ether fuel cell. The performances of the MEAs with different thicknesses of Nafion membranes were compared in this work. The optimal compositions in the anode are: 20 wt% Nafion content and 3.6 mg cm−2 Pt loading in the catalyst layer, and 30 wt% PTFE content and 1 mg cm−2 carbon black loading in the diffusion layer. In the cathode, MEA with 20 wt% Nafion content in the catalyst layer and 30 wt% PTFE content in the diffusion layer presented the optimal performance. The MEA with Nafion 115 membrane displayed the highest maximum power density of 46 mW cm−2 among the three MEAs with different Nafion membranes. Copyright © 2009 John Wiley & Sons, Ltd.

Systematic Investigation of the Effects of Operating Conditions on the Liquid-Phase Dimethyl Ether (LPDME) Process

The effects of various reaction conditions including temperature (200−240 °C), pressure (20−50 bar), and H2/CO molar feed ratio (1−2) on the performance of the liquid-phase direct dimethyl ether (DME) synthesis from syngas, over a bifunctional catalyst (CuO/ZnO/Al2O3 + H-ZSM-5) have been studied. The experiments have been designed by general full factorial design (GFFD), and the effects of reaction conditions as well as their interactional effects on the yield of DME as the response variable have been determined. The investigation of the analysis of variation (ANOVA) table showed that all of the three variables and their interaction significantly affected the response. The relative order of importance of the factors on DME yield was found to be temperature > pressure > H2/CO molar feed ratio. In addition, the optimum operating conditions for the maximum yield of DME were 240 °C, 50 bar, and H2/CO = 2. Under these conditions, the yield of DME reached 51.0%.

Using Heteropolyacids in the Anode Catalyst Layer of Dimethyl Ether PEM Fuel Cells

In this study, polarization experiments were performed on a direct dimethyl ether fuel cell (DMEFC). The experimental setup allowed for independent control of water and DME flow rates. Thus the DME flow rate, backpressure, and water flow rate were optimized. Three heteropoly acids, phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA) were incorporated into the anode catalyst layer in combination with Pt/C. Both PTA-Pt and STA-Pt showed higher performance than the Pt control at 30 psig of backpressure. Anodic polarizations were also performed, and Tafel slopes were extracted from the data. The trends in the Tafel slope values are in agreement with the polarization data. The addition of phosphotungstic acid more than doubled the power density of the fuel cell, compared to the Pt control.

Fe-Ni anode in Direct-Dimethylether Fuel Cell Operated at Intermediate-Temperature Using BaCe0.8Y0.2O3-δ as a Solid Electrolyte

not Available.

Preparation of Nafion/sulfonated poly(phenylsilsesquioxane) nanocomposite as high temperature proton exchange membranes

Nafion/sulfonated poly(phenylmethyl silsesquioxane) (sPPSQ) composite membranes are fabricated using homogeneous dispersive mixing and a solvent casting method for direct dimethyl ether fuel cell (DDMEFC) applications operated above 100 °C. The inorganic conducting filler, sPPSQ significantly affects the characteristics in the nanocomposite membranes by functionalization with an organic sulfonic acid to PPSQ. Moreover, sPPSQ content plays an important role in membrane properties such as microstructure, proton conductivity, fuel crossover, and single cell performance test. With increasing sPPSQ content in the nanocomposite membrane, the proton conductivity increased and fuel crossover decreased. However, in a higher temperature range above 110 °C, Nafion/sPPSQ 5 wt.% composite membrane has the highest proton conductivity. Also, the DME permeability for the composite membrane with higher sPPSQ content increased sharply. The excessive sPPSQ content caused a large aggregation of inorganic fillers, leading to the deterioration of membrane properties. In this study, the optimal sPPSQ content for maximizing the DDMEFC performance was 5 wt.%. Our nanocomposite membranes demonstrated proton conductivities as high as 1.57 × 10 −1 S/cm at 120 °C, which is higher than that of Nafion. The cell performances were compared to Nafion/sPPSQ composite membrane with Nafion 115, and the composite membrane with sPPSQ yielded better cell performance than Nafion 115 at temperatures ranging from 100 to 120 °C and at pressures from 1 to 2 bar.

The electro-oxidation of dimethyl ether on platinum-based catalyst

Cyclic voltammetry (CV) and stripping voltammetry were used to study the electro-oxidation of dimethyl ether (DME) on powder microelectrodes (PMEs) containing Pt black and Pt–Ru black. As evidenced by current–time curves of DME oxidation, Pt–Ru was better than Pt in catalytic oxidation of DME, which is due to the high concentration of OH ads species on its surface. Results also showed that high temperature not only promotes the oxidation of DME, but also increases the concentration of OH ads species formed by water decomposition. In addition, the performance of single direct DME fuel cell was investigated combined with gas chromatographic (GC) analyses of its anode outlet stream. Based on CV tests, a mechanism of DME electro-oxidation was tentatively proposed, indicating two kinds of DME adsorption modes, Pt–CO and Pt–COH existed on Pt surface.

Effect of pressure on direct synthesis of DME from syngas over metal-pillared ilerites and metal/metal-pillared ilerites

The effect of pressure on the direct synthesis of dimethyl ether (DME) from syngas over metal (Cu, Zn) pillared ilerites and metal (Cu, Zn) impregnated metal-pillared ilerites was explored. The prepared catalysts were characterized by XRD, BET, ICP-AES, SEM and FT-IR. The direct DME synthesis reaction was carried out in a differential fixed bed reactor with the prepared catalysts at various pressures (10, 20, 30 bar), 250°C and H2/CO ratio of 2. The Cu/Zn-pillared ilerite catalyst showed the highest catalytic activity among the prepared catalysts at 20 bar, in which CO conversion was about 62% and DME selectivity was about 89%. CO conversion increased with pressure, and DME selectivity increased with pressure in the range of 10–20 bar, and above the pressure slightly decreased with pressure. The optimum pressure for this reaction was 20 bar.