二甲醚部分氧化重整制氢的实验研究

应用自制二甲醚(DME)部分氧化重整制氢实验装置,研究了温度、空醚比、DME进气流量、催化剂用量和重整器管内径对DME转化率和H2产率的影响。结果表明,常压下,在300℃～500℃,随着温度升高,DME转化率和H2产率增大,DME转化率的最大值接近100%,H2产率的最大值约为95%,产气中H2、CO和CH4的体积分数增大,CO2和DME的体积分数减小。空醚比从0.5增大到3.0时,DME转化率和H2产率增大,产气中H2和CO的体积分数先增后减。增大DME进气流量,DME转化率、H2产率、产出的气体中H2和CO的体积分数都减小。增加催化剂用量、减小重整器管内径都能增大DME转化率和H2产率。     

A comprehensive modeling study of hydrogen oxidation

A detailed kinetic mechanism has been developed to simulate the combustion of H₂/O₂ mixtures, over a wide range of temperatures, pressures, and equivalence ratios. Over the series of experiments numerically investigated, the temperature ranged from 298 to 2700 K, the pressure from 0.05 to 87 atm, and the equivalence ratios from 0.2 to 6. Ignition delay times, flame speeds, and species composition data provide for a stringent test of the chemical kinetic mechanism, all of which are simulated in the current study with varying success. A sensitivity analysis was carried out to determine which reactions were dominating the H₂/O₂ system at particular conditions of pressure, temperature, and fuel/oxygen/diluent ratios. Overall, good agreement was observed between the model and the wide range of experiments simulated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 603–622, 2004     

基于火花放电等离子体部分氧化重整二甲醚制氢研究

应用自制的多级式等离子体富氢气体制备装置，进行了二甲醚部分氧化重整制氢实验。实验结果表明，常温常压下二甲醚的转化率和氢产率随占空比的增大先增大后减小，当占空比为80%时最大值分别为87.6%和39.4%。随着电源电压的增加，放电能量和持续时间逐渐增加，转化率和氢产率逐渐增加。当反应器采用保温措施或对反应物进行加湿时，转化率和氢产率均有明显提高，同时制氢能耗下降，热效率有一定提高。实验过程中附着在电极上的积炭主要是由于氧气不足造成，随空醚比的增大，积炭明显减少。     

High-temperature pyrolysis of dimethyl ether

The kinetics of pyrolysis of dimethyl ether wexre studied in an adiabatic flow reactor at temperatures between 790 and 950°C. The unimolecular rate constant for the initiating step CH₃OCH₃ = CH₃O + CH₃ was found to be k₁ = 2.16 × 10¹⁵e^?76,600/RTsec^?1. Aspects of the kinetic mechanism are discussed and a system postulated to account for the high-temperature products.     

Partial oxidation of dimethyl ether to H2/syngas over supported Pt catalyst

Dimethyl ether （DME） is a non-toxic fuel with high H/C ratio and high volumetric energy density, and could be served as an ideal source of H2/syngas production for application in solid oxide fuel cells （SOFC）. This study presents results of DME partial oxidation over a 1.5 wt% Pt/Ce0.4Zr0.6O2 catalyst under the condition of gas hourly space velocity （GHSV） of 15000-60000 ml/（g·h）, molar ratio of O2/DME of 0.5 and 500-700 ℃, and this temperature range was also the operation temperature range for intermediate temperature SOFC. The results indicated that the catalyst showed good activity for the selective partial oxidation of DME to H2/syngas. Under the working conditions investigated, DME was completely converted. Increase in reaction temperature enhanced the amount of syngas, but lowered the H2/CO ratio and yield of methane; while increase in reaction GHSV resulted in only slight variation in the distribution of products. The good catalytic activity of Pt supported on Ce0.4Zr0.6O2 for the partial oxidation of DME may be directly associated with the good oxygen storage capacity of the support, which is worth of further investigation to develop materials for application in SOFC.     

A short asymmetric synthesis of (+)-lyoniresinol dimethyl ether

A short, efficient synthesis of the lignan (+)-lyoniresinol dimethyl ether is described. The synthesis is achieved by asymmetric photocyclization of an achiral dibenzylidenesuccinate to a chiral aryldihydronaphthalene. (-)-Ephedrine is used as a chiral auxiliary to bias the atropisomeric equilibrium in the dibenzylidenesuccinate prior to the photochemical reaction. The synthesis of the title compound was accomplished in five steps, and the final product was recrystallized to constant melting point and rotation.     

A mass spectrometric study of dimethyl ester trimethylsilyl ether derivatives of some 3-hydroxydicarboxylic acids

The fragmentation pathways for the dimethyl ester trimethylsilyl ether derivatives of some 3-hydroxydicarboxylic acids have been found by using B/E 2nd B²/E linked scans and isotope substitution techniques. Most of the fragments are due to ionization at silicon, which induces a fragmentation pattern that intimately reflects the structure of the compounds.     

Ethylene pyrolysis and oxidation: A kinetic modeling study

Ethylene oxidation and pyrolysis was modeled using a comprehensive kinetic reaction mechanism. This mechanism is an updated version of one developed earlier. It includes the most recent findings concerning the kinetics of the reactions involved in the oxidation of ethylene. The proposed mechanism was tested against ethylene oxidation experimental data (molecular species concentration profiles) obtained in jet stirred reactors (1–10 atm, 880–1253 K), ignition delay times measured in shock tubes (0.2–12 atm, 1058–2200 K) and ethylene pyrolysis data in shock tube (2–6 atm, 1700–2200 K). The general prediction of concentration profiles of minor species formed during ethylene oxidation is improved in the present model by using more accurate kinetic data for several reactions (principally: HO₂ + HO₂ → H₂O₂ + O₂, C₂H₄ + OH → C₂H₃ + H₂O, C₂H₂ + OH → Products, C₂H₃ → C₂H₂ + H).     

Analysis of HO2 and OH formation mechanisms using FM and UV spectroscopy in dimethyl ether oxidation

Product formation pathways in the photolytically initiated oxidation of CH3OCH3 have been investigated as a function of temperature (298-600 K) and pressure (20-90 Torr) through the detection of HO2 and OH using Near-infrared frequency modulation spectroscopy, as well as the detection of CH3OCH2O2 using UV absorption spectroscopy. The reaction was initiated by pulsed photolysis with a mixture of Cl2, O2, and CH3OCH3. The HO2 and OH yield is obtained by comparison with an established reference mixture, including CH3OH. The CH3OCH2O2 yield is also obtained through the procedure of estimating the CH3OCH2O2/HO2 ratio from their UV absorption. A notable finding is that the OH yield is 1 order of magnitude larger than those known in C2 and C3 alkanes, increasing from 10% to 40% with increasing temperature. The HO2 yield increases gradually until 500 K and sharply up to 40% over 500 K. The CH3OCH2O2 profile has a prompt rise, followed by a gradual decay whose time constant is consistent with slow HO2 formation. To predict species profiles and yields, simple chlorine-initiated oxidation model of DME under low-pressure condition was constructed based on the existing model and the new reaction pathways, which were derived from this study. To model rapid OH formation, OH direct formation from CH3OCH2 + O2 was required. We have also proposed that a new HCO formation pathway via QOOH isomerization to HOQO species and OH + CH3OCH2O2 --> HO2 + CH3OCH2O are to be considered, to account for the fast and slow HO2 formations, as well as the total yield. The constructed model including these new pathways has successfully predicted experimental results throughout the entire temperature and pressure ranges investigated. It was revealed that the HO2 formation mechanism changes at 500 K, i.e., HCO + O2 via HCHO + OH and the above proposed direct HCO formation dominates over 500 K, while a series of reactions following CH3OCH2O2 self-reaction and OH + CH3OCH2O2 reaction mainly contribute below 500 K. The pressure dependent rate constant of the CH3OCH2 thermal decomposition reaction has been separately measured since it has large negative sensitivity for HO2 formation and is essential to eliminate the ambiguity in the CH3OCH2 + O2 mechanism at higher temperature.     

A mass spectrometric study of the dimethyl ester trimethylsilyl enol ether derivatives of some 3-oxodicarboxylic acids

The fragmentation pathways for the dimethyl ester trimethylsilyl enol ether derivatives of some 3-oxodicarboxylic acids have been found by using B/E and B²/E linked scans, collisional activated decomposition and isotope substitution techniques. The trimethylsilyloxy group strongly directs the decomposition processes, and induces a fragmentation pattern that intimately reflects the structure of the compounds.     

Transient kinetic studies and microkinetic modeling of primary olefin formation from dimethyl ether over ZSM-5 catalysts

The formation of primary olefins from dimethyl ether (DME) was studied over ZSM-5 catalysts at 300°C using a novel step response methodology in a temporal analysis of products (TAP) reactor. For the first time, the TAP reactor framework was used to conduct single- and multiple-step response cycles of DME (balance argon) over a shallow bed with the continuous flow panel. Propylene is the major primary olefin and portrays an S-shaped profile with a preceding induction period when it is not observed in the gas phase. Methanol and water portray overshoot profiles due to their different rates of generation and consumption. DME effluent shows a rapid rise halfway to its steady-state value leading to a slow rise thereafter because of its high desorption rates followed by subsequent reactions involving DME in further steps during the induction period. To analyze the experimental data quantitatively, nine reaction schemes were compared, and kinetic parameters were obtained by solving a transient plug flow reactor model with coupled dispersion, convection, adsorption, desorption, and reaction steps. The methoxymethyl pathway involving dimethoxyethane and methyl propenyl ether gives the closest match to experimental data in agreement with recent density functional theory studies. Gaseous dispersion coefficients of ca. 10⁻⁹ m² s⁻¹ were obtained in the TAP reactor. The novel experimental data validated against the transient kinetic model suggests that after the formation of initial species, the bottleneck in propylene formation is the transformation of the initial C–C bond, that is dimethoxyethane formed initially from DME and methoxymethyl groups. DME adsorption on ZSM-5 catalyst generates surface methoxy groups, which further react with the feed to give methoxymethyl groups. These methoxymethyl groups are regenerated through a series of reactions involving intermediates such as dimethoxymethane and methyl propenyl ether before propylene formation.     

Numerical analysis and experimental study of hydrogen production from dimethyl ether steam reforming

An experimental and theoretical study of steam reforming of dimethyl ether was carried out in a processor for fuel cell vehicles to explore the effect of temperature gradient and hydrogen content of the processor.A steady-state,laminar,two-dimensional axi-symmetric model was proposed to investigate the fluid flow,heat transfer and chemical reactions in the dimethyl ether steam reforming processor using porous medium approach.The numerical model was established with Star-CD program using SIMPLE algorithm and finite volume method.Experimental verification of the two-dimensional mathematical model was conducted.The numerical results coincided well with the experimental data.The effects of the parameters on the temperature gradient and hydrogen content of the processor were studied using the numerical model.     

A highly sensitive and selective dimethyl ether sensor based on cataluminescence

A sensor for detecting dimethyl ether was designed based on the cataluminescence phenomenon when dimethyl ether vapors were passing through the surface of the ceramic heater. The proposed sensor showed high sensitivity and selectivity to dimethyl ether at an optimal temperature of 279 °C. Quantitative analysis were performed at a wavelength of 425 nm, the flow rate of carrier air is around 300 mL/min. The linear range of the cataluminescence intensity versus concentration of dimethyl ether is 100-6.0 × 10³ ppm with a detection limit of 80 ppm. The sensor response time is 2.5 s. Under the optimized conditions, none or only very low levels of interference were observed while the foreign substances such as benzene, formaldehyde, ammonia, methanol, ethanol, acetaldehyde, acetic acid, acrolein, isopropyl ether, ethyl acetate, glycol ether and 2-methoxyethanol were passing through the sensor. Since the sensor does not need to prepare and fix up the granular catalyst, the simple technology reduces cost, improves stability and extends life span. The method can be applied to facilitate detection of dimethyl ether in the air. The possible mechanism of cataluminescence from the oxidation of dimethyl ether on the surface of ceramic heater was discussed based on the reaction products.     

Activation of dimethyl ether with transition metal atoms

The cocondensation of iron or manganese atoms with dimethyl ether at ?196°C leads to organometallic products which upon hydrolysis at 25°C yield a mixture of mainly alkenes and alkanes.     

A new catalyst for direct synthesis of dimethyl ether from synthesis gas

A new catalyst has been prepared by coprecipitation sedimentation method developed in our laboratory. It exhibits excellent catalytic activity, selectivity and stability for conversion of synthesis gas to dimethyl ether: conversion of CO 92%, selectivity of dimethyl ether 98%. Catalytic properties of the catalyst show no evident change after being used for 100 h.     

Synthesis of gasoline from syngas via dimethyl ether

Zeolite H-TsVM has been loaded with palladium by different methods. The properties of the resulting catalysts in gasoline synthesis from syngas via dimethyl ether depend on the way in which palladium was introduced. The catalysts have been characterized by ammonia temperature-programmed desorption (TPD), temperature-programmed reaction with hydrogen, and X-ray photoelectron spectroscopy. According to ammonia TPD data, use of a palladium ammine complex instead of palladium chloride reduces the concentration of strong acid sites and raises the concentration of medium-strength acid sites, thereby reducing the yield of C1–C4 hydrocarbons and increasing the yield of gasoline hydrocarbons. At T = 340°C, P = 100 atm, and GHSV = 2000 h^?1, the dimethyl ether conversion is 98–99%, the gasoline selectivity is >60%, the isoparaffin content of the product is ～61%, and the arene content is not higher than 29%.