利用二氧化碳进行乙苯脱氢反应的研究

本文介绍了利用CO₂进行乙苯脱氢反应的新工艺和新催化剂。据估算,新工艺比工业上现行以水蒸汽作脱氢介质的传统工艺能耗大幅下降,并为新工艺配套开发了高性能的Fe-Ca-Al系复合氧化物催化剂。     

CO2氧化乙苯脱氢制苯乙烯钒基氧化物催化剂研究进展

与现有乙苯直接脱氢工艺技术相比,CO₂氧化乙苯脱氢工艺具有缓解直接脱氢热力学平衡限制、苯乙烯选择性高、能耗低和二氧化碳资源化利用等显著优势,有望成为一条从乙苯生产苯乙烯的绿色工艺路线。为此,在总结乙苯直接脱氢反应体系和现有工业技术特点、面临的问题和发展方向的基础上,本文较为全面地分析了CO₂氧化乙苯脱氢的特点和反应机理,探讨了现有催化剂体系普遍快速失活的关键原因,表明高性能催化剂研究依然是推进CO₂氧化乙苯脱氢工业化应用的关键。鉴于钒基氧化物催化剂表现出较高的活性,成为近年来CO₂氧化乙苯脱氢相关研究关注的重点。为此,从钒物种含量及其聚集态结构、催化剂的氧化还原和酸碱性、催化剂表面积炭及其作用等角度,综合分析了活性中心结构、反应机理等方面的相关研究进展,认为孤立态V⁵⁺及其含量可能是决定钒基氧化物催化剂活性的关键,其稳定性主要取决于催化剂的氧化还原特性,而积炭对催化剂活性和稳定性的影响则与其组成和石墨化程度密切相关。基于上述认识,认为强化CO₂的高效活化、抑制V⁵⁺的深度还原等是今后钒基氧化物催化剂研究的重点发展方向,而利用移动固定床或提升管反应器等进行工艺优化,对推进CO₂氧化乙苯脱氢工业化应用具有重要的研究价值。     

乙苯脱氢催化剂的发展动态

通过对乙苯脱氢制苯乙烯工业催化剂演变过程的分析。认为近年催化剂组成已经历由Ｆｅ－Ｋ－Ｃｒ系列向Ｆｅ－Ｋ－Ｃｅ系列以及由高钾含量向低钾含量的过渡。催化剂制备工艺也有诸多改进,颗粒形状由传统圆柱形向齿轮柱形及三叶柱形等异型颗粒演变。关于催化活性本质的研究渐趋活跃,多数研究者认为活性相是Ｋ２ｆｅ２Ｏ４钾流失是催化剂在正常操作条件下逐渐老化的根本原因。     

引入ZnO对Fe-K系乙苯脱氢催化剂性能的影响

用BET、XRD、XPS、Mssbauer以及乙苯脱氢反应等手段详细考察了添加ZnO对Fe-K系催化剂性能的影响。实验结果表明，ZnO的引入加强了主催化剂Fe₂O₃和助催化剂K₂O间的相互作用，使稳定晶相KFe₁₁O₁₇的形成温度降低了50℃以上，从而有利于提高样品的耐水性能和机械强度。同时，ZnO的加入进一步促进了Fe³⁺/Fe²⁺电子对之间的转化，使样品的脱氢温度降低6～13℃，脱氢活性和选择性亦得到提高。     

Amorphous porous MxTi mixed oxides as catalysts for the oxidative dehydrogenation of ethylbenzene

The properties of different metal‐oxide‐doped porous titanium oxides as catalysts for the oxidative dehydrogenation of ethylbenzene were investigated. Amorphous porous mixed oxides based on the amorphous titania matrix with selected metal ion centers as active sites have been prepared by an acid‐catalyzed sol–gel method. The dehydrogenation of ethylbenzene was studied in a continuous gas phase flow reactor under different reaction temperatures at ambient pressure. Among the 23 catalysts studied the amorphous porous AM‐Cr₅Ti mixed oxide is the most promising catalyst. At 350 °C a 75% selectivity to styrene at a 29% conversion of ethylbenzene was obtained. BET, HRTEM, XRD, GC, MS, TGA and optical microscopy were employed to characterize the fresh and used AM‐Cr₅Ti catalyst. This revised version was published online in August 2006 with corrections to the Cover Date.     

低钾型乙苯脱氢催化剂的研制

通过引入活性调节剂，双重性能调节剂，结构稳定剂等助催化剂，利用4段连续升温活化技术，制备出了氧化钾质量分数为10％的乙苯脱氢催化剂。结果表明，在反应温度610－620℃，空速0.8-1.0h^-1，水油质量比1.6-2.0的条件下，乙苯转化率，苯乙烯收率，苯乙烯选择性分别为80％，75％，95％，催化剂钾流失现象得到缓解，抗湿性能良好。     

VxTi复合氧化物催化剂用于二氧化碳气氛乙苯脱氢的研究

采用溶胶-凝胶法制备了以TiO₂为基体的VxTi复合氧化物催化剂,该催化剂用于乙苯二氧化碳低温氧化脱氢制苯乙烯反应。考察了活性组分含量和焙烧温度对催化剂活性的影响。结果表明,活性金属钒的添加有助于提高脱氢反应性能,但存在一适量值,摩尔分数超过5%,催化脱氢活性下降。通过XRD分析发现,不同焙烧温度制备的VxTi催化剂中TiO₂的晶相不同,随着温度的升高,TiO₂的晶相将由锐钛矿型转变为金红石晶相。TiO₂锐钛矿型晶相有利于苯乙烯选择性的提高,而金红石晶相则不利于催化剂的脱氢反应。     

Effect of chromium promoter on copper catalysts in ethanol dehydrogenation

A series of chromium-promoted copper catalysts with various Cr to Cu molar ratios were prepared with the co-precipitation method. The promotional effects of chromium on copper catalysts were examined by X-ray powder diffraction (XRD), nitrous oxide decomposition, and the dehydrogenation reaction of ethanol. The dehydrogenation reaction was carried out in a continuous-flow microreactor between 523 and 583 K under atmospheric pressure. The results indicated that the promotional effect was dependent on the Cr/Cu molar ratio, and the predominant decay of catalysts in this study was caused by sintering. The catalyst with the Cr/Cu molar ratio of 4/40 has the highest activity and stability. The surrounded well-dispersed chromia strongly influenced the catalytic properties of copper metal. It also showed that the over-promotation of a catalyst has a disastrous effect on the total make of product. The ethanol dehydrogenation reaction follows a first-order reaction, and the kinetics for deactivation can be described by a second-order expression.     

逆水煤气变换耦合乙烷脱氢反应中载体对氧化铬催化剂性能的影响

研究了在逆水煤气变换耦合乙烷脱氢反应中担载型氧化铬催化剂的活性,考察了多种载体对于催化剂反应性能的影响。结果表明,不同的载体所担载的氧化铬催化剂具有不同的催化性能。其中二氧化硅担载的氧化铬催化剂具有较高的乙烷转化率和乙烯选择性,在700℃时分别达到30.7%和96.5%。CO₂的作用是通过与H₂反应促进乙烷脱氢、并减少催化剂表面积炭。运用XRD、TPR、 XPS、UV-DRS和微量吸附量热技术对催化剂体相与表面结构、表面酸性和铬物种价态等进行了表征,结果显示催化剂表面酸中心适当的强度、数量和分布有利于乙烷的活化和催化转化,Cr³⁺和Cr⁶⁺物种是反应的活性中心。     

Oxidative dehydrogenation of ethylbenzene with carbon dioxide on alkali‐promoted Fe/active carbon catalysts

Well defined Mo²⁺ surface sites of silica-supported catalyst, produced by H2 reduction of the fixed molybdenum tetraallyl precursor, show a characteristic IR signal at 2170 cm^-1 due to adsorbed carbon monoxide. Higher oxidation states of Mo in the same catalyst do not show any signal related to this probe molecule. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dehydrogenation of ethylbenzene to styrene over Fe2O3/Al2O3 catalysts in the presence of carbon dioxide

An Fe₂O₃ (10 wt%)/Al₂O₃ (90 wt%) catalyst prepared by a coprecipitation method was found to be effective for dehydrogenation of ethylbenzene to produce styrene in the presence of CO₂ instead of steam used in commercial processes. The dehydrogenation of ethylbenzene over the catalyst in the presence of CO₂ was considered to proceed both via a one-step pathway and via a two-step pathway. CO₂ was found to suppress the deactivation of the catalyst during the dehydrogenation of ethylbenzene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of the dehydrogenation of ethylbenzene to styrene over unpromoted and K-promoted model iron oxide catalysts

The dehydrogenation of ethylbenzene to styrene over unpromoted and potassium-promoted model iron oxide catalysts has been studied using ultrahigh vacuum techniques in conjunction with elevated pressure reaction kinetics. Model iron oxide catalysts were prepared by oxidizing a polycrystalline Fe sample that was subsequently dosed with metallic potassium. At 875 K the unpromoted catalyst exhibited a turnover frequency of 5×10^–4 molecules/ site s and an activation energy of 39 kcal/mol, both in excellent agreement with the results found for an analogous iron oxide powder catalyst. Potassium promotion increased the turnover frequency to 1.0×10^–3 molecules/site s and lowered the activation energy to 36 kcal/mol for the dehydrogenation reaction. Similarities between the activation energies on the unpromoted and promoted catalysts indicate that the active site is the same on both catalysts. Creation of the active site was dependent upon the formation of an Fe³⁺ metastable species, consistent with the formation of a KFeO₂ phase, upon the addition of potassium.     

Pd/C催化剂在环己二醇脱氢反应中失活原因研究

针对Pd/C催化剂在环己二醇脱氢反应过程中的失活问题,采用XRD、N_2物理吸附-脱附、SEM-EDS、TEM、XPS、ICP-OES、TGA、FT-IR和Visible Raman光谱对反应前后催化剂进行表征。从催化剂的织构性质、催化剂表面活性物种的定性和定量分析以及催化剂积炭行为方面系统研究催化剂失活原因。     

二氧化碳法制备活性氧化锌的过程研究

以次硫酸氢钠甲醛副产锌泥为原料，用高剪切乳化机乳化锌浆，采用双氧水作为氧化剂氧化锌浆中的金属锌使之转化为氢氧化锌，采用二氧化碳作为沉锌剂碳化锌浆后得到碱式碳酸锌沉淀，沉淀通过脱水、洗涤、干燥、煅烧后可得到活性氧化锌产品。该方法充分利用了锌资源，有效处理了大量闲置的锌泥，制得的活性氧化锌产品质量可达到HG2572-1994合格品标准。     

非晶态Ni-B/MCM-22催化剂上二氧化碳甲烷化的研究

本文采用固定床反应装置考察了非晶态镍基催化剂CO2甲烷化催化反应活性。研究结果表明:以化学还原法制备的非晶态镍基催化剂的二氧化碳甲烷化活性较高;由XRD及TEM结果可知,非晶态镍基催化剂中镍的分散度较高;以MCM-22分子筛为催化剂载体的非晶态镍基催化剂CO2的转化率高于以γ-Al2O3为载体的非晶态催化剂。     

Hydrogenation of carbon dioxide on iron catalysts doubly promoted with manganese and potassium

The effect of addition of manganese and potassium promoters onto iron catalysts for hydrogenation of carbon dioxide was investigated. Catalyst characterizations were performed using BET surface area measurement, carbon monoxide chemisorption, temperature-programmed reduction and Mössbauer spectroscopy. It was noted that metallic iron catalysts were carburized to θ-Fe₃C and χ-Fe₅C₂ as well as oxidized to Fe₃O₄ during the course of reaction. The promotional effect of manganese was reflected in stabilization of catalytic behavior owing to a higher resistance to bulk oxidation. However, the distribution of hydrocarbon products did not change significantly in the presence of manganese promoter. With further addition of potassium promoter, the bulk phase was more likely to transform to carbides, and the selectivity toward olefins and long-chain hydrocarbons was remarkably enhanced.     

Investigations on the oxidative dehydrogenation of n-butane over VMgO-type catalysts

The oxidative dehydrogenation of n-butane was investigated over VMgO mixed oxide and pure magnesium ortho- and pyrovanadate catalysts. The formulation containing 30 wt% V₂O₅ and consisting of the Mg₃(VO₄)₂ and MgO crystal phases is more selective than the pure Mg₃(VO₄)₂, while the Mg₂V₂O₇ phase is the least selective. The selectivity to butenes and butadiene increases with the reaction temperature and the feed molar ratio of butane/oxygen. Addition of water tends to decrease the conversion of butane and enhances the oxydehydrogenation product selectivity. The relative importance of the primary and secondary paths of the reaction network was analyzed by the method of addition of intermediate products.     

乙苯脱氢制苯乙烯催化剂使过程中特性变化研究

用穆斯堡尔谱、X-射线、XPS和EPMA等手段考察了乙苯脱氢制苯乙烯GS-05型催化剂在工业装置上使用不同周期后的相组成、钾含量及电子结合能等特性的变化,并与相应周期的活比评价数据相关联。实验结果表明, GS-05型催化剂的活性相为Fe₃O₄,工业装置上催化剂活性的部分衰退是由于主要活性组份Fe₂O₃的部分流失、助剂钾的迁移和少量流失所引起的。     

Kinetic model and simulation for catalyst deactivation during dehydrogenation of methylcyclohexane over commercial Pt-, PtRe- and presulfided PtRe-Al2O3 catalysts

The catalyst deactivation kinetics for the dehydrogenation of methylcyclohexane were studied with Pt-, PtRe-, and presulfided Presulfided PtRe-Al₂O₃ Catalysts in a fixed-bed differential reactor. The kinetic analysis was made based on a Langmuir-Hinshelwood model assuming that the dehydrogenation of methylcyclohexene into methylcyclohexadiene was the rate-controlling step for the main reaction, and the polymerization of adjacently adsorbed methylcyclohexadiene as coke precursor molecules was the rate-controlling step for the deactivation reaction. The experimental data for the three catalysts at varying partial pressures of methylcyclohexane and hydrogen were well correlated by the hyperbolic deactivation function derived. The number of active sites involved in the rate-controlling step of the deactivation was evaluated to be 2.7 in average. The enhanced activity maintenance by the addition of Re as well as sulfur was attributed to a reduction in the concentration of multiple sites occupied by coke precursors adjacently adsorbed, leading to a decrease in the rate constant of the deactivation reaction.     

稀土La改性的非晶态Ni基催化剂CO_2甲烷化催化性能的研究

本文采用固定床反应装置考察了稀土镧改性的非晶态镍基催化剂二氧化碳甲烷化催化反应活性。实验结果表明:氧化镧的添加,提高了非晶态镍的晶化温度,阻止了镍的聚集,提高了镍的分散度,从而提高了二氧化碳甲烷化的活性和稳定性。