Critical solubility of dimethyl ether (DME)+diesel fuel and dimethyl carbonate (DMC)+diesel fuel

An experimental apparatus was developed for measuring the critical solubility. The critical solubilities were determined for binary mixtures of DME+diesel fuel and DMC+diesel fuel. For DME+diesel fuel their critical solubility temperatures ranged from 272.83 to 255.13 K while the mass fractions of DME varied from 3.44 to 95.8%; For DMC+diesel fuel, their critical solubility temperatures were between 273.58 and 302.72 K while the mass fractions of DMC varied from 1.22 to 89.6%.     

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 pre-pared 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.     

合成气一步法制二甲醚催化剂的研究

在Cu-Zn-Al甲醇催化剂制备工艺的基础上,研制出合成气一步法制二甲醚催化剂。经过实验室试验和评价,确定了催化剂使用的最佳工艺条件：压力40 MPa,温度270～310 ℃,空速1 000～2 000 ｈ^-1,合成气中H2体积分数为70%～80%,CO体积分数6%～12%,CO₂体积分数3%～4%。在该条件下,CO转化率大于85％,二甲醚选择性大于90％,二甲醚的收率达65％以上。催化剂表现出良好的活性、选择性和稳定性。     

二甲醚精馏塔实验研究与模拟计算

建立了用于二甲醚精制的精馏塔实验流程,实验测定了在操作工艺条件下的精馏结果。以平衡级理论为依据建立二甲醚精馏过程的数学模型,根据研究体系在通常情况下沸点相差较大、液相非理想性的特点,建立序贯收敛的循环嵌套迭代计算方法对模型进行求解,模拟计算结果与实验数据结果吻合较好。对二甲醚精馏塔的模拟分析结果表明：塔顶要得到含量不小于99 %(mol)二甲醚产品,维持操作压力1 MPa、在精馏塔中部进料的情况下,进料量不超过22 mol·h^-1为宜;回流比要根据进料液中二甲醚组分含量控制在一定范围内;进料液中二氧化碳含量高低对产品二甲醚纯度和收率影响显著,在进入精馏塔之前尽可能地将二氧化碳除去是必要的。     

一步法合成二甲醚反应器的研究进展

综述了合成气一步法合成二甲醚反应器的发展近况,着重介绍了固定床、浆态床及组合床的研究进展,并根据国内外的研究对几种反应器进行了工艺比较。     

Investigation on idle performance of a spark-ignited ethanol engine with dimethyl ether addition

Dimethyl ether (DME) and ethanol are thought to be alternative fuels for future internal combustion (IC) engines. The experiments in this paper were carried out at idle and stoichiometric conditions to investigate the effect of DME addition on the idle performance of a spark-ignited (SI) ethanol engine. The engine was modified to be fueled with the mixture of DME and ethanol which were injected into the engine intake ports simultaneously. A hybrid electronic control unit (HECU) was specially developed to control the injection timings and durations of ethanol and DME, accomplishing specified excess air ratios and DME addition fractions in the total ethanol-DME fuel mixture. The experimental results demonstrated that, the indicated thermal efficiency was increased by over 20% after DME blending and the flame development and propagation durations were shortened with the increase of DME addition fraction. Meanwhile, HC emissions were obviously decreased with the increasing fraction of DME addition, while NOx emissions were slightly increased. Therefore, DME addition is a potentially applicable method to improve the idle performance of SI ethanol engines.     

Characteristics of integrated micro packed bed reactor-heat exchanger configurations in the direct synthesis of dimethyl ether

The performance of three integrated micro packed bed reactor-heat exchangers (IMPBRHEs) for direct DME synthesis over physical mixtures of CuO–ZnO–Al₂O₃ and γ-Al₂O₃ catalysts was experimentally investigated. Systematic variations in reactor and slit dimensions and configuration were analyzed in terms of thermal behaviour, mass transfer, pressure drop and residence time distribution (RTD). The pressure drop was always small (<0.12 bar) relative to the total pressure (50 bar), and linear dependence with GHSV confirms the predicted laminar flow for Re = 0.1–2. A narrow RTD was estimated by the dispersion analysis. Careful temperature measurements confirmed that the reaction temperature is mainly controlled by the oil heat exchange to give a practically uniform temperature profile for set inlet oil temperatures of 220–320 °C. The micro packed beds were found free of the internal as well as external mass transfer limitations, as showed by no significant change in the CO conversion and DME yield for different catalyst particle sizes, no effect of varying the linear gas velocity, and no effect of manipulating reactant diffusion coefficient. Packed bed microstructured reactors hence provide an isobaric and isothermal environment free from transport limitations for the direct DME synthesis, in the kinetic regime as well as at equilibrium conversion.     

Synthesis of dimethyl ether (DME) by catalytic distillation

The intrinsic kinetics of liquid phase catalytic dehydration of methanol to dimethyl ether over a macroporous sulphonic acid ion exchange resin was determined in a fixed-bed micro-reactor in the temperature range of 391–423 K and pressures up to 2.0 MPa. The kinetic model based on Eley–Rideal mechanism, as well as the power-rate law model, was adopted for fitting the experimental data. However, the Langmuir–Hinshelwood mechanism is not feasible for describing the dehydration reaction of methanol, as deduced from the macroscopic kinetic data and/or no dependence of methanol conversion on initial methanol concentration in the absence of water at the inlet using acetone as inert solvent. Moreover, an improved process consisting of the combination of a fixed-bed reactor and a catalytic distillation column for the synthesis of DME (Process A) was proposed, and a mathematical model was established, into which the intrinsic kinetics obtained in this work was incorporated. The comparison of operating performance among the improved process, Process B consisting of a fixed-bed reactor and two ordinary distillation columns, and Process C consisting of a catalytic distillation column and an ordinary distillation column was also made. It was found that the improved process is more promising than others in energy consumption, production capacity and column number under the same product purity, and is easy to be implemented based on Process B that is currently used in the actual industrial plants with a long catalyst lifetime.     

Investigation on the fuel spray and emission reduction characteristics for dimethyl ether (DME) fueled multi-cylinder diesel engine with common-rail injection system

The aim of this study is to investigate the effects of dimethyl ether (DME) fuel on the engine performance and the exhaust emission reduction characteristics in a DME fueled four-cylinder diesel engine with a common rail injection system, as well as an injection characteristics and a spray behavior. The injection rate meter and the spray visualization system are utilized for the analysis of the injection characteristics and the spray behavior. Also, the modified four-cylinder diesel engine with 1.6 liter engine size is used for the investigation of the engine performance and the exhaust emission reduction characteristics of DME fuel.Based on the experimental investigation, it revealed that the injection quantity of DME fuel was larger than that of the ultra low sulfur diesel (ULSD) due to the high return fuel pressure at the same injection pressure and energizing duration. In this case, the injection quantity of DME fuel is increased by extension of real injection duration due to return fuel pressure.In combustion characteristics, the peak combustion pressure and the ignition delay of DME fuel are higher and faster than those of ULSD, respectively. The NO_x emission of DME fuel shows slightly higher than that of ULSD at the same engine load condition, and the soot emission of DME fuel is nearly zero level. The oxygenated component and volatility of DME resulted in HC and CO emissions that were lower than those of diesel.     

合成气一步法5000t/a二甲醚管式反应器设计

应用实验所得动力学数据,建立管式固定床反应器的一维数学模型。通过计算典型工况下5000t/a二甲醚反应器,得到了反应器的工艺与设备设计参数。     

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.     

A study on the macroscopic spray behavior and atomization characteristics of biodiesel and dimethyl ether sprays under increased ambient pressure

The aim of this work is to investigate the spray behaviors of biodiesel and dimethyl ether (DME) fuels using image processing and atomization performance analysis of the two fuel sprays injected through a common-rail injection system under various ambient pressure conditions in a high pressure chamber. In order to observe the biodiesel and DME fuel spray behaviors under various ambient pressures, the spray images were analyzed at various times after the start of energization using a visualization system consisting of a high speed camera and two metal halide light sources. In addition, a high pressure chamber that can withstand a pressure of 4 MPa was used for adjusting the ambient pressure. From the spray images, spray characteristics such as the spray tip penetration, cone angle, area, and contour plot at various light intensity levels were analyzed using image conversion processing. Also, the local Sauter mean diameters (SMD) were measured at various axial/radial distances from the nozzle tip by a droplet measuring system to compare the atomization performances of the biodiesel and DME sprays.The results showed that the ambient pressure had a significant effect on the spray characteristics of the fuels at the various experimental conditions. The spray tip penetration and spray area decreased as the ambient pressure increased. The contour plot of the biodiesel and DME sprays showed a high light intensity level in the center regions of the sprays. In addition, it was revealed that the atomization performance of the biodiesel spray was inferior to that of the DME spray at the same injection and ambient conditions.     

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

Various dehydration catalysts were studied in the synthesis of dimethyl ether (DME) directly from carbon-monoxide-rich synthesis gas under a series of different reaction conditions. The investigated catalyst systems consisted of combinations of a methanol catalyst (CuO/ZnO system) with catalysts for methanol dehydration based on γ-Al₂O₃ or zeolites and γ-Al₂O₃ was identified as the most favorable dehydration catalyst. Various reaction parameters such as temperature, H₂/CO ratio and space velocity were studied. The impact of water on Cu/ZnO/Al₂O₃-γ-Al₂O₃ catalysts was investigated and no deactivation could be observed at water contents below 10% during running times of several hours. A running time of several days and a water content of 10% led to a significant increase of CO conversion but the water gas shift reaction became dominating and CO₂ was the main product. After termination of water feeding significant deactivation of the catalyst system was observed but the system returned to high DME selectivity. Catalyst stability and the influence of CO₂ in the gas feed were studied in experiments lasting for about three weeks. The presence of 8% of CO₂ caused an approximately 10% lower CO conversion and an about 5% lower DME selectivity compared to the reaction system without CO₂.     

Macroscopic spray characteristics and breakup performance of dimethyl ether (DME) fuel at high fuel temperatures and ambient conditions

The purpose of this work was to investigate, both experimentally and numerically, the spray behavior and atomization characteristics of dimethyl ether (DME) at high fuel temperatures and under various ambient conditions. In order to compare the theoretical and measured spray characteristics of DME fuel, macroscopic characteristics such as spray tip penetration and spray cone angle were investigated using spray visualization system with a heating system. DME atomization performance was calculated under various conditions from KIVA-3 V code and studied via analysis of the overall Sauter mean diameter (SMD) map, which is related to ambient gas temperature, ambient pressure, and fuel temperature.DME spray was found to exhibit behavior that differs from diesel spray under atmospheric condition. However, at high ambient pressure conditions, DME and diesel sprays display similar behavior. At ambient atmospheric condition, the spray cone angle of DME fuel is larger than that of diesel spray due to the occurrence of flash boiling. Variation in DME fuel temperature had little effect on spray tip penetration and spray cone angle characteristics. An increase in ambient air temperature caused an increase in DME spray cone angle due to an enhancement of the flash boiling effect. However, the DME spray cone angle showed a decreasing trend at high ambient pressure conditions when the ambient air temperature was increased. This was due to the disappearance of flash boiling and the evaporation of droplets at the exterior of the spray cone. In the overall SMD map, the increase of the ambient gas temperature and fuel temperature induced the increase of DME overall droplet size. On the other hand, the ambient gas pressure have slightly influenced on the overall SMD at a low ambient gas temperature and low fuel temperature, but the effect of the ambient gas pressure is significant at high ambient gas temperature and high fuel temperature. At high ambient gas temperature, the increase of the ambient gas pressure causes the increase of the overall SMD. At high DME fuel temperature, the decrease of the ambient gas pressure induces the increase of the overall SMD.     

Experimental and analytical study on the spray characteristics of dimethyl ether (DME) and diesel fuels within a common-rail injection system in a diesel engine

This paper investigates the effect of injection parameters on the characteristics of dimethyl ether (DME) as an alternative fuel in a diesel engine with experimental and analytical models based on empirical equations. In order to study macroscopic and microscopic characteristics of DME fuel, this work focuses on the atomization characteristics of DME and compares experimental and predicted results for spray development obtained by empirical models for diesel and DME fuel. Detailed comparisons of spray tip penetration from three different empirical correlations and from visualization experiments of diesel and DME fuels were conducted under various fuel injection conditions. In comparison with the results of different empirical equations for measured spray tip penetration, the experimental results of this study provide good agreement with the calculation results based on empirical equations, except during the earliest stage of the injected spray sequence. The results of atomization characteristics indicate that DME showed better spray characteristics than conventional diesel fuel. Also, the fuel injection delay and maximum injection rate of DME fuel are shorter and lower than those of diesel fuel at the same injection conditions, respectively.     

Influence of ambient flow conditions on the droplet atomization characteristics of dimethyl ether (DME)

This paper describes the effects of ambient flow conditions on the droplet atomization characteristics of dimethyl ether (DME) both experimentally and numerically.In this investigation, the droplet atomization of DME fuel affected by ambient flow conditions was studied in terms of droplet mean size and detected droplet percentage under elevated ambient pressures and temperatures. In order to predict the DME spray atomization, the hybrid breakup model combined with KH-RT (Kelvin-Helmholtz and Rayleigh-Taylor) and KH-DDB (Kelvin-Helmholtz and Drop Deformation Breakup) models was applied in this study.It was revealed that the spray arrival time of DME fuel under a high ambient pressure increased in accordance with the increase in ambient pressure in the spray chamber. It can be seen that more small droplets are distributed at high ambient flow pressure conditions than at atmospheric conditions. This is a consequence of enhanced atomization of DME fuel. On the other hand, when the ambient pressure increases to 2 MPa, the Sauter mean diameter (SMD) increases only slightly compared with that at 1 MPa of pressure. The SMD value of droplets is increased as ambient temperature is increased. Under the high temperature condition in the chamber, the small droplets of DME fuel evaporate quickly and mix with the ambient air. As a result, it promotes the air-fuel mixing in a combustion chamber.     

以联醇气为原料合成二甲醚的工业侧流试验

介绍了以联醇气为原料合成二甲醚的工业侧流试验,考察了联醇气制二甲醚用催化剂的性能。试验结果表明,该二甲醚合成催化剂的转化率、选择性、稳定性等性能达到了国内同类催化剂的先进水平。     

Simulation of fixed bed reactor for dimethyl ether synthesis

Dimethyl Ether (DME) is considered as one of the most promising candidates for a substitute for LPG and diesel fuel. We analyzed one-step DME synthesis from syngas in a shell and tube type fixed bed reactor with consideration of the heat and mass transfer between catalyst pellet and reactants gas and effectiveness factor of catalysts together with reactor cooling through reactor wall. Simulation results showed strong effects of pore diffusion. We compared two different arrangements of catalysts, mixture of catalyst pellets (methanol synthesis catalyst and methanol dehydration catalyst) and hybrid catalyst. Hybrid catalyst gave better performance than a mixture of pellets in terms of CO conversion and DME productivity, but more difficulties with reactor temperature control. Use of inert pellets and inter-cooling was also simulated as a means of controlling maximum reactor temperature.     

Experimental study on the hazards of the jet diffusion flame of liquefied dimethyl ether

Dimethyl ether (DME) has been considered as a substitute for diesel fuel because it has a low auto-ignition temperature and produces less NO_x, SO_x, and particulate matter. However, the introduction of DME vehicles needs widely available DME supply stations. Moreover, the preparation of safety regulations for DME supply stations is very important, and so safety data is needed. Therefore, the present paper reports the hazards of the DME jet diffusion flame, which is one of several hazardous properties of DME, by studying the results of leaking gas and liquid DME. DME jets were released horizontally from circular nozzles whose diameters were 0.2, 0.4, 0.8 and 2 mm, and the release pressure was varied from the saturated vapor pressure to 2 MPa. When gaseous DME was released at the saturated vapor pressure, the flame was blown out. However, when liquefied DME was released, the flame formed. We obtained the experimental equations for estimating the scale and thermal hazards of DME diffusion flames.     

Electro-oxidation of dimethyl ether on Pt/C and PtMe/C catalysts in sulfuric acid

The electro-oxidation of dimethyl ether (DME) on PtMe/Cs (Me = Ru, Sn, Mo, Cr, Ni, Co, and W) and Pt/C electro-catalysts were investigated in an aqueous half-cell, and compared to the methanol oxidation. The addition of a second metal enhanced the tolerance of Pt to the poisonous species during the DME oxidation reaction (DOR). The PtRu/C electro-catalyst showed the best electro-catalytic activity and the highest tolerance to the poisonous species in the low over-potential range (<0.55 V, 50 °C) among the binary electro-catalysts and the Pt/C, but at the higher potential (>ca. 0.55 V, 50 °C), the Pt/C behaved better than PtRu/C. The apparent activation energy for the DOR decreased in the order: PtRu/C (57 kJ mol⁻¹) > Pt₃Sn/C (48 kJ mol⁻¹) ≈ Pt/C (46 kJ mol⁻¹). On the other hand, the activation energy for the MOR showed a different turn, decreased in the following order: Pt/C (43 kJ mol⁻¹) > Pt₃Sn/C (35 kJ mol⁻¹) ≈ PtRu/C (34 kJ mol⁻¹). The temperature dependence of the DOR was greater than that of the oxidation of methanol (MOR) on the PtRu/C.