甲烷制卤代甲烷研究进展

甲烷的化学性质很不活泼,需经中间体才能将其转变成高附加值的化工产品。以卤代甲烷为中间体具有能耗低的优势,是一种潜在的甲烷活化方式。综述国内外甲烷制卤代甲烷研究进展,主要介绍不同卤素源条件下的反应机理及催化剂性质、反应条件对单卤代甲烷选择性的影响。甲烷经氯代甲烷活化时,产物中一氯甲烷选择性与催化剂性质密切相关,亲电型催化剂能高选择性生成一氯甲烷;甲烷经溴代甲烷活化时,贵金属和非贵金属均可作为催化剂活性中心,且该反应可以根据后续产物的需要,调节产物组成和比例。甲烷溴代反应单卤代产物选择性高于甲烷氯代反应,但溴代反应需在较高温度进行。     

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的工作,但仍不能满足工业化生产要求。围绕这一反应,主要介绍甲烷通过气固相催化氧化、液固相催化氧化反应制备甲醛和甲醇的研究进展,并对这些催化体系的作用机理、活性物种类型和活性位结构进行科学认识。期望通过对甲烷选择性氧化催化剂的深入探究,最终指导高活性、高选择性催化剂的设计与开发。     

我国科学家在丙烯的催化环氧化合成环氧丙烷方面取得突破

美国《科学》杂志 (2 0 0 1 ,2 92 :1 1 39)刊发了中国科学院大连化学物理研究所奚祖威研究员等撰写的论文“反应控制相转移催化丙烯环氧化合成环氧丙烷”,该研究组开发的一种含钨的金属有机催化剂应用于丙烯和 H2 O2 的环氧化反应中 ,显示了较高的催化活性和选择性 (只有目标产物和水生成 ) ,更引人注目的是这项工作在催化剂回收利用方面取得了突破 ,而其深远的应用背景在于相对于如今世界范围内采用的路线长、成本高、污染严重的卤醇法和间接氧化法 ,该催化体系为一条更经济和更环境友好的生产环氧丙烷的路线提供了良好前景。文章发表后…     

甲烷部分催化氧化合成甲醇和甲醛

本文综述了由甲烷部分催化氧化制甲醇和甲醛研究中所用催化剂的制备条件及催化反应条件,并对用于该反应的催化剂开发和最佳合成工艺条件的选择指出了方向。     

合成甲醇催化剂的新进展

综述了合成甲醇的低温液相合成法、甲烷催化氧化法和二氧化碳催化加氢法等新工艺所使用的催化剂及其活性中心、催化反应条件和反应机理的研究近况。与传统的合成气合成甲醇技术相比 ,在催化剂性能、原料成本及发展前景等诸方面各有优点 ,提倡大力开发以二氧化碳或甲烷生产甲醇的绿色化学新工艺。     

V2O5催化甲烷液相部分氧化工艺过程研究

以V2O5为催化剂,在发烟硫酸中进行了甲烷液相选择性氧化的研究工作,考察了V2O5催化剂用量、反应温度、反应时间、发烟硫酸浓度等工艺条件对反应收率的影响,进行了甲烷液相选择性氧化的催化机理探讨和宏观动力学推导.甲烷在部分氧化反应中首先转化为硫酸甲酯,后者进一步水解得到甲醇.甲烷转化率可达54.5%,选择性45.5%,相应的工艺条件为催化剂用量0.0175 mol、反应温度180C、发烟硫酸中SO3含量50%(wt)、反应时间2 h.V2O5催化甲烷液相部分氧化反应遵循亲代取代机理,甲烷液相部分氧化反应为一级反应.     

丝光沸石择形催化合成甲胺反应的性能研究

制备了经阳离子改性的合成丝光沸石催化剂 ;以氨和甲醇为原料 ,在常压固定床上进行了合成甲胺反应研究 ,考察了工艺条件对催化剂催化性能的影响 ,并通过正交试验筛选出最佳工艺条件。结果表明 :经钙、镁离子交换的丝光沸石催化剂具有较高活性和良好选择性 ,甲醇转化率 >90 % ,对二甲胺的单程选择性 >40 %。自制的这种钙离子改性丝光沸石催化剂(CaHM)的催化性能优于目前国内工业化的甲胺生产催化剂 ,而且CaHM是经添加粘接剂焙烧成型的样品 ,可直接供产品的中试放大。     

炼厂硫化氢合成二甲基亚砜技术开发

开发了以炼厂硫化氢为原料制备二甲基亚砜的绿色清洁生产技术。硫化氢合成二甲基硫醚,采用分子筛催化剂,运行2048h后,甲醇转化率和二甲硫醚选择性保持在95%以上,催化性能优异;以二甲基硫醚和过氧化氢制备二甲基亚砜,过氧化氢和二甲硫醚的转化率均在95%以上,二甲亚砜的选择性在99%以上,产品经分离纯度可达99.5%以上,达到工艺一级品要求。该工艺条件温和、路线简单,具有绿色、环保等特点,具有较好的工业化应用前景。     

无定型MnO2的制备及其催化苯甲醇选择氧化性能

用KMnO₄和MnSO₄为原料，通过简单的氧化还原过程合成了无定形MnO₂，并用于催化苯甲醇氧化制苯甲醛，发现制得的无定形MnO₂在催化苯甲醇氧化制苯甲醛中表现出较高的活性和苯甲醛选择性（100%）。考察了反应温度、氧浓度、催化剂用量以及反应时间对苯甲醇氧化的影响。结果表明，较高的反应温度和氧浓度以及合适的催化剂用量有利于无定形MnO₂催化苯甲醇氧化生成苯甲醛，在反应温度110 ℃、常压和通氧条件下反应3 h, 苯甲醇转化率和苯甲醛选择性均为100%。     

等离子体技术及其在催化领域中的应用

本文介绍了等离子体的特性，发生技术及其在催化剂的制备、再生和改性中的应用。并以甲烷与二氧化碳反应制合成气，甲烷与二氧化碳反应制乙酸及甲烷部分氧化制甲醇，甲烷偶联反应制低碳烃等为例介绍了等离子体技术在催化反应中的应用，分析了等离子体状态下的催化反应机理，从而预测了等离子体技术在催化领域中的应用前景。     

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.     

Methane Partial Oxidation by Unsupported and Silica Supported Iron Phosphate Catalysts: Influence of Reaction Conditions and Co-Feeding of Water on Activity and Selectivity

The partial oxidation of methane to methanol and formaldehyde by molecular oxygen has been investigated over crystalline and silica supported FePO₄at a pressure of 1 atm and in the temperature range of 723–973 K. The quartz phase of FePO₄, as well as silica supported FePO₄prepared by impregnation (5 wt%), were examined in a continuous flow reactor. Experiments carried out over FePO₄show high selectivity to formaldehyde at low conversion and suggest that formaldehyde is the primary reaction product, but selectivity decreased rapidly as conversion was increased. The highest space-time yield of formaldehyde observed for this catalyst was 59 g/kg_cat-h. Above 5% methane conversion, carbon oxides were the only products. For silica-supported FePO₄, formaldehyde selectivity did not fall off rapidly, exhibiting a formaldehyde selectivity of 12% at about 10% conversion (STY=285 g/kg_cat-h). Quantifiable yields of methanol were observed at very low conversion levels, i.e. below 3% (STY=11 g/kg_cat-h). Addition of steam (up to 0.1 atm partial pressure) into the feed stream increased the selectivity to methanol (∼25 g/kg cat/h with up to 3% selectivity) and formaldehyde (∼487 g/kg cat/h with up to 94% selectivity) for the silica-supported FePO₄catalyst. Steam addition had little effect on catalyst activity. Characterization results indicate the presence of FePO₄, as well as fivefold coordinate Fe³⁺in silica supported catalyst samples, and this species is proposed to be responsible for methane activation. After catalysis in the presence of steam, the fivefold coordinate iron is present, but a significant fraction of the FePO₄has been reduced to Fe₂P₂O₇. Enhanced selectivity in the presence of steam is attributed in part to the ease of the reversible formation of surface hydroxyl groups (P-OH) from pyrophosphate (P-O-P) groups.     

Systematic Study of the Oxidation of Methane Using Supported Gold Palladium Nanoparticles Under Mild Aqueous Conditions

The oxidation of methane using hydrogen peroxide has been studied using supported gold palladium catalysts prepared using the incipient wetness technique. The effect of reaction conditions and catalyst parameters has been investigated. The supported gold palladium nanoparticles produce methyl hydroperoxide as the primary reaction product which is subsequently converted to methanol with high selectivity, ca. 40–70 %. The selectivity to methanol is influenced by the oxidation state the palladium component of the catalyst. In contrast to homogeneous gold and palladium catalysts the heterogeneous gold palladium nanoalloys are reusable and affords high oxygenate selectivity (ca. 90 %).     

Direct synthesis of LPG from syngas derived from air-POM

Direct synthesis of liquefied petroleum gas (LPG) from a low-cost syngas derived from partial oxidation of methane with air (air-POM) was investigated over a hybrid catalyst consisting of methanol synthesis catalyst and Pd-modified Y-zeolite. The hybrid catalyst demonstrated a high activity and more than 73% selectivity for LPG fraction. BET, NH₃-TPD and TPO-MS were carried out to study the properties of Pd-Y before and after reaction. The results indicated that coke deposition on Pd-Y was the main contribution to the slow deactivation of hybrid catalyst.     

MK-121型甲醇合成催化剂的升温还原

介绍了甲醇合成回路流程及MK-121型甲醇合成催化剂的升温还原情况。从出水量、耗氢情况来看,催化剂还原得非常彻底;另外,在催化剂还原过程中,循环量、甲醇合成塔进出口气体温度、顶部绝热层温度、进口H_2含量、系统压力等指标都非常平稳。实际运行情况证明,该催化剂具有较高的转化率、选择性、活性和稳定性。     

CuZnTiO2/SAPO-34双功能催化剂的设计、制备及其用于CO2加氢制烯烃性能

CO₂加氢经甲醇（含氧中间体）制低碳烯烃工艺路线，可实现成醇、脱水两步反应串联协同进行，打破费托合成产物Anderson-Schulz-Flory（ASF）分布限制，高选择性地制取低碳烯烃。传统甲醇合成Cu基催化剂加氢能力较强，在两步反应中产物以CH₄、低碳烷烃为主。实验设计、制备了CuZnTiO₂/(Zn-)SAPO-34复合催化剂，实现了CO₂加氢在Cu基复合催化剂上高选择性合成C₂～C₄烯烃（约60%）。研究表明，两步反应过程中甲醇体积分数较低（＜6%），且高温下逆水煤气变换反应严重，导致催化剂酸性变化对产物分布的影响较大。调变两类活性位点比例发现，CH₄的产生与串联反应存在竞争关系，SAPO-34酸量的增加抑制了CH₄的生成，促进串联反应正向进行；合适的酸性有助于生成C₂～C₄烯烃。控制成醇、脱水两类活性位点接触距离可调变烯烃的二次反应，降低加氢能力，改善产物分布。     

Manganese oxide catalyzed methane partial oxidation in trifluoroacetic acid: Catalysis and kinetic analysis

Direct oxidation of methane to methanol has been studied for decades, and has yet to be commercialized. Three years ago, UOP LLC, a Honeywell Company, started a government co-sponsored project (NIST/ATP Award 70NANB4H3041) for selective liquid phase oxidation of methane to methanol. Recently we have discovered an efficient methane oxidation by manganese oxide. When used as stoichiometric oxidant, quantitative metal oxide-based yield was observed for methane oxidation. The spent catalyst activity can be 100% regenerated with air under basic conditions. A high methane-based yield (36%) with high selectivity (>95%) was achieved when manganese oxide was used in catalytic amount in the presence of air for methane oxidation. Our online GC analysis showed that catalytic methane oxidation occurs with two-stage reaction kinetics with constant reaction rate at the active stage, which can be explained by a low steady-state active catalyst concentration as observed by in situ UV–vis spectrometer.     

浆态床中二氧化碳加氢合成甲醇

研究了浆态床中自行开发的LP201甲醇合成催化剂上二氧化碳加氢合成甲醇的过程。探讨了不同操作条件，如温度、压力、气体空速、原料气配比等对反应的影响；考察了该催化剂在浆态床二氧化碳加氢合成甲醇过程中的稳定性。实验结果表明，浆态床二氧化碳加氢合成甲醇过程中主要产物为甲醇、CO和水；随温度的增加，CO2的转化率和甲醇产率呈现上升的趋势，但甲醇的选择性明显下降；压力的升高有利于CO2的转化率、甲醇产率以及甲醇的选择性提高；原料气空速的提高会增大甲醇产率，但同时降低CO2的转化率以及甲醇的选择性；CO2的转化率、甲醇收率以及甲醇的选择性在氢碳摩尔比4～5获得极大值。LP201催化剂的寿命考察结果表明，该催化剂具有较好的催化活性和稳定性。     

Partial oxidation of methane to synthesis gas via the direct reaction scheme over Ru/TiO2 catalyst

The partial oxidation of methane to synthesis gas has been investigated over various supported metal catalysts. The effects of operational variables on mass and heat transport resistances were investigated for defining the kinetic regime. It is observed that, in the absence of significant mass and heat transfer resistances, high selectivity (up to 65%) to synthesis gas is obtained over Ru/TiO₂ catalysts in the low methane conversion range ( ) whereas only negligibly small selectivity to synthesis gas is observed over all other catalysts investigated under similar conditions. This indicates that the Ru/TiO₂ catalyst possesses unique properties, offering high selectivity to synthesis gas formation via the direct reaction scheme, whereas the other catalysts promote the sequence of total oxidation of methane to CO₂ and H₂O, followed by reforming reactions to synthesis gas. An increase of selectivity to synthesis gas, in the presence of oxygen, is achieved over the Ru/TiO₂ catalyst by multi-feeding oxygen, which is attributed to suppression of deep oxidation of H₂ and CO.     

费托合成蛋壳型催化剂活性组分厚度的模拟计算

采用Comsol-Multiphysics软件对蛋壳型Co基催化剂费托合成反应体系进行了CFD模拟计算。通过建立合理的费托合成催化剂颗粒三维模型进行计算,重点研究了催化剂活性组分厚度对费托合成反应产物分布、温度分布以及转化率的影响。结果表明：费托合成反应内扩散阻力较大,CO在催化剂表面和内部存在明显的浓度差。且由于H₂的扩散速率远大于CO的扩散速率,导致催化剂颗粒内部氢碳比很高,不利于油类和蜡类物质的生成;随着催化剂活性组分厚度的增加,CO转化率逐渐提高,甲烷和低碳烃的选择性逐渐增大,而C₁₀H₂₂和C₂₂H₄₆的选择性逐渐减小;催化剂颗粒内部的温度峰值逐渐向催化剂内部移动,不利于反应热的转移。对于尺寸为?2.5 mm的蛋壳型球形催化剂,较佳的催化剂活性组分厚度为0.125 mm。