甲烷部分氧化制甲醇及甲醛

综述了甲烷部分氧化制甲醇及甲醛工艺在催化剂、载体、选择反应条件及氧化反应机理等方面的研究进展。建议研制开发新型的复合型催化剂。     

甲烷直接催化氧化制甲醇催化剂及反应机理

研究甲烷合成甲醇的催化剂及催化机理是甲烷直接催化氧化制甲醇的关键。本文综述了甲烷合成甲醇的Pt系催化剂、Pd系催化剂、Rh系催化剂、Fe改性沸石催化剂、Cu改性沸石催化剂、改性金属有机框架材料催化剂以及相应的催化机理。结果表明,Pt系催化剂中K₂PtCl₄、Pt(bpym)Cl₂、Pt(bipy)Cl₂催化甲烷制甲醇机理为亲电取代反应。Pd系催化剂中Pd(OAc)₂在CF₃COOH水溶液中通过多步电子传递链将甲烷转化为甲醇;Pd/C在乙酸水溶液中催化甲烷合成甲醇是亲电取代和活性氧物种氧化两种机理共同作用的结果。Rh系催化剂中的Rh/ZSM-5、Rh/TiO₂通过锚定在载体孔道内的一价Rh与CO、H₂O和O₂作用将甲烷转化为甲醇。Fe、Cu改性沸石催化剂及改性金属有机框架材料催化剂通过均裂、异裂等自由基反应转化甲烷得到甲醇。指出研究高效活化甲烷分子和抑制甲醇深度氧化催化剂的设计、制备及深入探究其催化机理仍然是今后的研究重点。     

甲烷低温活化制甲醇研究进展

简要评述了当前国内外在甲烷直接部分氧化合成甲醇和甲烷经卤代后合成甲醇领域的研究进展。众多研究表明,甲烷多相催化氧化制甲醇是最具有工业化应用前景的技术,其中钼系催化剂的效果较好;以Pt、Pd配合物为催化剂的甲烷液相催化氧化法制甲醇方法具有较高的甲烷转化率和甲醇选择性,但是催化剂价格昂贵、反应条件苛刻、环境污染严重;甲烷气相均相氧化属于非催化反应,在高温高压下进行,且反应器须具备特殊的形式,结构复杂;虽然酶催化氧化法的选择性较高,但是生物酶的制备有一定难度,不适用于大范围应用,该路线目前仅限于实验室研究阶段;光催化氧化是一种环境友好的技术,反应条件温和、避免氧化剂应用,但是该类催化剂局限于半导体和盐类,还有待于进一步开发新型高效的催化剂。同时,甲烷经卤代后合成甲醇的方法对解决甲烷活化的难题具有独特优势,是一种比较有开发前景的路线,正在受到研究者们的密切关注。     

甲烷液相部分氧化制甲醇中溶剂介质的研究进展

甲烷液相转化具有反应条件温和、能耗低、投资少等优点,研究甲烷液相部分氧化制甲醇对实现天然气的直接转化和利用具有极为重要的战略意义。本文介绍了甲烷液相部分氧化制甲醇反应中有关反应溶剂介质的研究进展,详细叙述了各种酸性介质、水以及乙腈溶剂在甲烷部分氧化制甲醇中的应用,总结了不同溶剂介质下的反应机理、催化剂、溶剂浓度等对甲烷转化的影响,探讨了溶剂在甲烷液相部分氧化中的作用,指出依据溶剂介质的性质和作用,开发环境友好、反应条件温和、转化效率高的优良新型溶剂是甲烷液相部分氧化制甲醇的重要研究方向。     

Catalytic partial oxidation of methane to synthesis gas in a ceramic membrane reactor

Methane has been selectively converted to synthesis gas using a two-zone fixed bed of a Ni/Al₂O₃ catalyst inside a modified ceramic membrane. The first zone of the reactor was surrounded by an impervious wall, and therefore behaved as a conventional fixed bed reactor. In the second zone, some of the reaction products could preferentially diffuse out of the reactor, which yielded higher than equilibrium methane conversions. The influence of the different operating conditions has been studied, and the performance of the membrane reactor has been compared to that of a fixed bed reactor. The membrane reactor has also been used at pressures above atmospheric (2 bar), with good conversions and selectivities.     

Partial oxidation of methane using a microscale non-equilibrium plasma reactor

A flow-type, microscale, non-equilibrium plasma reactor was developed for partial oxidation of methane without a catalyst. A wide range of oxygen and methane mixtures was directly processed without dilution or explosion at ambient temperature because the microscale plasma reactor removes excess heat generated by partial oxidation, thereby maintaining a reaction field at temperatures near room temperature. Consequently, the least reactive methane was excited by high-energy electrons, whereas successive destruction of reactive oxygenates was minimized simultaneously within the extremely confined environment. A highly reactive and quenching environment is thereby obtained within a single reactor: these are paradoxical conditions in conventional thermochemical processes. A major product among liquid oxygenates was methanol, whose selectivity reached 34% at 30% of methane conversion. Selectivity of oxygenates such as methanol and formaldehyde depends strongly on the fragmentation pattern of methane dissociation by electron impact. Maximum selectivity of oxygenates, which is estimated from numerical simulation of a filamentary microdischarge, reaches 60% when the applied electric field corresponds to the breakdown field of methane (80 Td, 1 Td = 10⁻¹⁷ V cm²). The discharge current increases markedly with an applied electric field, but the selectivity of oxygenates decreases as the field strength increases.     

基于Ba-Ce-Co-Fe-O膜反应器的甲烷部分氧化反应研究

为开发稳定性和透氧量俱佳并适用于甲烷部分氧化反应(POM)的透氧膜材料,采用溶胶凝胶工艺合成了具有纯相钙钛矿结构的BaCe0.1Co0.4Fe0.5O3-δ混合导体陶瓷材料。POM操作结果表明:BaCe0.1Co0.4Fe0.5O3-δ膜反应器透氧量高于同类材料,875℃时透氧量达到了8.9 mL/(cm2.m in)。在1 000 h寿命实验中,膜反应器各项反应指标没有出现任何衰减,反应性能稳定,甲烷转化率和CO的选择性都在97%以上。SEM表征表明,反应后膜片表面微观结构的变化虽然不可避免,但是其仍然保持比较完整的结构。因此,该材料良好的透氧量和稳定性说明其具有较好的应用前景。     

Effect of particle shape on methanol partial oxidation in a fixed bed using CFD reactor modeling

Particle shape is one of the most important parameters in the design and optimization of fixed-bed processes. To address the impact of particle shape on methanol partial oxidation to formaldehyde over molybdate catalyst, packings of spheres, cylinders, rings, and trilobes are numerically generated. The generated packings are used to carry out resolved particle Computational Fluid Dynamics (CFD) simulations under industrial conditions. Pressure drop, voidage and velocity profiles, radial heat transfer, and local and overall conversion and selectivity results are presented. Despite their lower particle surface area, lower particle effectiveness and more uneven flow distribution than trilobes, and lower overall heat transfer coefficient than cylinders, rings had the best conversion and selectivity due to their balance between the factors. Three longer tubes of rings, rings and cylinders, and rings and trilobes are simulated and show a small gain in selectivity for the rings and trilobes.     

甲烷部分氧化制乙炔过程研究

The partial oxidation of hydrocarbons is an important technical route to produce acetylene for chemical industry.The partial oxidation reactor is the key to high acetylene yields.This work is an experimental and numerical study on the use of a methane flame to produce acetylene.A lab scale partial oxidation reactor was used to produce ultra fuel-rich premixed jet flames.The axial temperature and species concentration profiles were measured for different equivalence ratios and preheating temperatures,and these were compared to numerical results from Computational Fluid Dynamics(CFD)simulations that used the Reynolds Averaged Navier-Stokes Probability Density Function(RANS-PDF)approach coupled with detailed chemical mechanisms.The Leeds 1.5,GRI 3.0 and San Diego mechanisms were used to investigate the effect of the detailed chemical mechanisms.The effects of equivalence ratio and preheating temperature on acetylene production were experimentally and numerically studied.The experimental validations indicated that the present numerical simulation provided reliable prediction on the partial oxidation of methane.Using this simulation method the optimal equivalence ratio for acetylene production was determined to be 3.6.Increasing preheating temperature improved acetylene production and shortened greatly the ignition delay time.So the increase of preheating temperature had to be limited to avoid uncontrolled ignition in the mixing chamber and the pyrolysis of methane in the preheater.     

Characteristics of methane oxidation in a flooded rice soil profile

Laboratory experiments were conducted to study the variation of CH₄ oxidation patterns in flooded rice soil profiles. The results indicated that surface soil presented the strongest CH₄ oxidation activities as shown by the highest values of the two kinetic parameters of CH₄ oxidation, V_max and K_m in the ecosystem without rice plants. V_max and K_m decreased significantly from top to bottom in the paddy rice soil profile, ranging from 12.5 to 1.2 μg h^-1 g^-1 and 165 to 4.1 μg g^-1, respectively. In addition, we studied the effect of headspace N₂, O₂ and their ratio on CH₄ emission and oxidation to provide information on the sensitivity of methanogens and methanotrophs to soil redox change resulted from gas transportation through arenchyma. Methane emission rate increased, however, CH₄ oxidation rate decreased with a decrease of O₂ concentration in the headspace. Headspace H₂ increased CH₄ emission rate substantially. In addition to H₂ being a substrate for CH₄ formation, the change of soil redox potential to a considerably low level H₂ should also contribute to the increase in CH₄ emission. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quasicatalytic and catalytic selective oxidation of methane to methanol over solid materials: a review on the roles of water

ABSTRACT

To date, although no commercial process for the selective oxidation of methane has been realized, various novel processes with effective solid materials operated at low temperature have been proposed. It is found that the addition of water in any processes not only influences the activity, selectivity, and stability of the solid materials but also affects the extraction efficiency of methanol from the product. Herein, the published results on the roles of water in the methanol production via the quasicatalytic and catalytic selective methane oxidation process using various solid materials in gas and liquid phases at low temperatures are critically reviewed.     

Laboratory study of methane oxidation in paddy soils

Methane oxidation in paddy soils was investigated under laboratory conditions. Paddy soils collected before early rice transplanting could not oxidize atmospheric CH₄ but could oxidize CH₄ when the concentration exceeded 10 μl l^-1. Initial CH₄ oxidation rate increased with the increase of initial CH₄ concentration. Soil with the maximum potential to produce CH₄, also had the maximum CH₄ oxidation activity and the maximum emission flux from paddy soil. High CH₄ concentration stimulated the oxidation of CH₄. After 10 days' incubation under atmosphere containing 1000 μl^-1 or 10⁴ μl l^-1 CH₄, the soil which could not oxidize atmospheric CH₄ was able to oxidize it. This revised version was published online in August 2006 with corrections to the Cover Date.     

An efficient technique for improving methanol yield using dual CO2 feeds and dry methane reforming

Steam methane reforming (SMR)-based methanol synthesis plants utilizing a single CO₂ feed represent one of the predominant technologies for improving methanol yield and CO₂ utilization. However, SMR alone cannot achieve full CO₂ utilization, and a high water content accumulates if CO₂ is only fed into the methanol reactor. In this study, a process integrating SMR with dry methane reforming to improve the conversion of both methane and CO₂ is proposed. We also propose an innovative methanol production approach in which captured CO₂ is introduced into both the SMR process and the recycle gas of the methanol synthesis loop. This dual CO₂ feed approach aims to optimize the stoichiometric ratio of the reactants. Comparative evaluations are carried out from a techno-economic point of view, and the proposed process is demonstrated to be more efficient in terms of both methanol productivity and CO₂ utilization than the existing stand-alone natural gas-based methanol process.     

甲醇氧化重整催化剂的研究

制备并优选了甲醇氧化重整的催化剂 ,实验表明在相同的温度下 ,Pd催化剂、Cr2 O3 ZnO氧化物催化剂和Cu催化剂相比 ,活性、选择性以及氢产率都表现为Cu >Cr Zn >Pd。其中 ,Cu催化剂在低温时、Cr Zn催化剂在高温下表现出良好的活性和选择性 ,而且Cr Zn催化剂的热稳定性较好     

Microbial aerobic oxidation of methane in paddy soil

The microbial aerobic oxidation activity of methane, the population of aerobic methane oxidizers and the factors influencing the activity of methane oxidation were investigated in three types of paddy rice soil in Zhejiang Province, China. Methane oxidation activity was different among Huangsong paddy soil developed from fluvo-aquic soil, Old huangjinni paddy soil developed from quaternary red clay and Qingzini paddy soil developed from coastal saline soil. The Huangsong paddy rice soil showed the highest activity of methane oxidation. Different methane oxidation activity and populations of methane-oxidizing bacteria were found in various Huangsong soil samples that had different plant-cover. Methane oxidation returned to the same level after these soil samples were incubated and induced by extra added methane. The population of methane oxidizing bacteria was at maximum within the peak-tillering, heading and flowering stages, during which the largest population of methanogenic bacteria also appeared. Temperatures from 25 to 35 °C and pH from 6 to 8 were the optimum conditions for aerobic oxidation of methane in paddy rice soil. Soil particle size also affected the activity of methane oxidation.     

Platinum-macrocycle co-catalysts for the electrochemical oxidation of methanol

Metal phthalocyanines (Fe, Co, Ni and Sn) and ruthenium tetramethylcyclam 14 and 15 were studied as cocatalysts for methanol oxidation on platinum supported catalysts. The formation of well defined monolayers of the adsorbed complexes was inferred from the Langmuirian form of the adsorption isotherms in solutions of macrocycles. The coverage at monolayer levels was low, e.g. 1.25 to 2.25×10¹³ molecules cm⁻² or 400 to 800 Ų molecule⁻¹. Enhancement for the methanol oxidation reaction was observed for Pt co-catalyzed with Sn phthalocyanine and Ru tetramethylcyclam. Ru tetramethylcyclam showed an enhancement for methanol oxidation on a per unit weight basis over pure Pt, approaching the activity of PtRu at lower potentials. Increasing the size of the nitrogen ring from 14 to 15 resulted in a lower redox potential and increase in the activity of methanol oxidation. The activity of Pt co-catalyzed with Ru TMC 15 decreased with time suggesting that the macrocycle was desorbing from the supported catalyst surface.     

Partial oxidation of methane with air for methanol production in a post-plasma catalytic system

Partial oxidation of methane to methanol via post-plasma catalysis using a dielectric-barrier discharge was performed under mild reaction conditions. Air was used as the oxidizing co-reactant because of its economical practicality. Three catalysts impregnated with Pt, Fe₂O₃, CeO₂ on ceramic supports located downstream of the discharge zone were examined for increased selectivity towards methanol. It was found that all three catalysts had no significant effect on the conversion of methane, but enhanced methanol selectivity, which could be explained by a two-stage reaction mechanism. The Fe₂O₃-based catalyst showed the best catalytic activity, and high stability in the reaction. The methanol selectivity of the Fe₂O₃-assisted plasma process was 36% higher than that of the non-catalytic system at a rather low catalyst temperature (150 °C). In addition, the effects of input power, discharge frequency, discharge gap distance, total flow rate, and methane/air ratio on methane conversion and methanol yield were also studied.     

一氯甲烷生产中影响甲醇利用率因素的探讨

介绍甲醇法制取一氯甲烷生产工艺,对影响甲醇利用率的因素进行摸索,总结出比较合适的反应条件为：反应热点温度控制在前6个月280～290℃、7～9个月290～300℃、10～13个月310～320℃,氯化氢和甲醇间的量比控制在(1.10～1.15)：1.0,反应压力控制在0.20～0.4MPa,生产负荷控制在105％～110％。     

Factors affecting methanol photocatalytic oxidation and catalyst attrition in a fluidized-bed reactor

A resolution IV fractional factorial experimental design explored the effects of seven factors on both the methanol photocatalytic oxidation (PCO) rate and the catalyst particle size distribution using a fluidized-bed reactor. The seven factors were as follows: calcination temperature, calcination time, grinding order, particle size, vibration amplitude, carrier gas humidity, and fluidization velocity. Decreasing calcination temperature from 726 to 623 K increased the activity of TiO₂/Al₂O₃ catalysts for methanol PCO. Attrition during fluidization liberated small TiO₂ particles from the bulk catalyst and the rate of attrition increased with gas velocity. Attrition was the primary cause of catalyst elutriation and not the presence of fine particles initially present in the bed from catalyst preparation. Increasing humidity caused agglomeration of fine particles, which reduced the amount of catalyst carryover. Removal of fines from the catalyst bed prior to fluidization caused an increase in catalyst attrition until the amount of fines present in the bed was similar to that of a bed in which fines were not removed.     

甲烷选择性氧化制甲醛/甲醇多相催化剂研究进展

甲烷是天然气、页岩气等化石能源的主要成分,储量十分丰富.由于甲烷分子结构高度稳定,其高效活化与选择性转化具有很大的挑战性,被认为是催化反应领域的"圣杯",因此,如何在温和条件下实现甲烷选择性氧化为高附加值的含氧化合物(如甲醇、甲醛)成为研究热点.近几十年来,研究者在甲烷选择性氧化催化剂的设计与制备方面开展了大量卓有成效...