HYDROGEN TRANSFER IN CATALYTIC CRACKING

Hydrogen transfer is an important secondary reaction of catalytic cracking reactions, which affects product yield distribution and product quality. It is an exothermic reaction with low activation energy around 43.3 kJ/mol. Catalyst properties and operation parameters in catalytic cracking greatly influence the hydrogen transfer reaction. Satisfactory results are expected through careful selection of proper catalysts and operation conditions.     

Selective Hydrogen Transfer Reaction in FCC Process：Characterization and Application

The product distribution and gasoline quality of FCC process, especially the olefin content,heavily depends on the catalyst performance in terms of selective/non-selective hydrogen transfer reaction selectivity. A reliable experimental protocol has been established by using n-dodecane as a probe molecule to characterize the selective hydrogen transfer ability of catalytic materials. The results obtained have been correlated with the performance of the practical catalysts.     

Catalytic Cracking Characteristics of Plant Oil for Producing Light Olefins and Light Aromatics

Catalyst containing shape selective zeolite is used to investigate the catalytic cracking characteristics of palm oil and three types of hydrocarbon VGOs on a fixed fluidized bed(FFB) unit. The advantage of producing light olefins and light aromatics by catalytic cracking of plant oil is discussed. Results indicate that the hydrocarbyl group of the plant oil molecule is quite readily crackable; the C_6—C_8 aromatics yield is well above and the light olefins yield is about the same with the hydrocarbon feeds, while the yields of low value products are lower; the hydrocarbyl group of the plant oil molecule has strong tendency of aromatization, and can enter the zeolite pores to selectively form C_6—C_8 aromatics; during catalytic cracking of plant oil and fatty acids, a portion of the oxygen is removed in the form of water through hydrogen transfer reaction, while olefins are prevented from being saturated, which can ensure proper yields of both low-carbon olefins and light aromatics.     

金属氧化物对ZSM-5分子筛催化裂化性能的影响

Effects of metal oxide in ZSM-5 zeolite on its catalytic performance in fluid catalytic cracking reaction were studied via characterization by XRD and FT-IR spectroscopy using pyridine and collidine as molecular probes,and the modified ZSM-5 zeolite was evaluated in a micro reactor using standard light diesel fraction as the feedstock.Test results indicate that the metal species introduced into the ZSM-5 zeolite had led to the formation of Lewis acid centers.When the modified ZSM-5 zeolite with the metal species on its surface was used as the catalyst in FCC reaction,both the propylene yield and the propylene concentration in the liquefied petroleum gas increased,but in the meantime,more hydrogen and coke were formed at high conversion rate under the joint action of nonselective cracking of Lewis acid centers and dehydrogenation at metal centers on its outside surface.     

加氢苛刻度对烃类组成和催化裂解产品分布的影响

Residue deep hydrotreating (RDHT) process was developed by the Research Institute of Petroleum Processing (RIPP) to provide high quality feedstock for deep catalytic cracking (DCC) process. In this research work, the effects of RDHT process and reaction severity on heteroatom removal, hydrogen content increase, hydrocarbon composition improvement, and DCC product yields were studied. It was showed that the RDHT process can effectively reduce heteroatoms, increase hydrogen content and improve the hydrocarbon compositions, which can contribute to an increase of light olefins yield in DCC unit.     

环烷烃混合烯烃催化裂化: 1. 单事件动力学模型 (SEMK)建立

Single-event microkinetic(SEMK) model of the catalytic cracking of methylcyclohexane admixed with 1-octene over REUSY zeolites at 693 K—753 K in the absence of coke formation is enhanced. To keep consistency with the wellknown carbenium ion chemistry, hydride transfer forming and consuming allylic carbenium ions in the aromatization of cycloparaffins are further investigated and differentiated. The reversibility of endocyclic β-scission and cyclization reactions is refined by accounting explicitly for the reacting olefins and resulting cycloparaffins in the corresponding thermodynamics. 24 activation energies for the reactions involved in the cracking of cycloparaffins are obtained by the regression of 15 sets of experimental data upon taking the resulting 37 main cracking products, i. e., responses into account. The enhanced SEMK model can adequately describe the catalytic behavior of 37 main products with conversion and temperature.     

Commercial Application of RMC Technology in the 1.5 Mt／a Hydrocracking Unit at Shanghai Petrochemical Company

The RMC technology developed by RIPP has been applied in a 1.5Mt/a medium pressure hydrocracking unit at Shanghai Petrochemical Company. The unit was successfully put on stream in September 2002. Calibration of the performance of the commercial unit has shown that the RMC technology has higher hydrogenation activity and selectivity, and high quality product can be obtained under lower reaction temperature. The heavy naphtha with less than 0.5 ppm of sulfur and 58.5 m% potential aromatic content is a good feedstock for catalytic reforming unit. The diesel with less than 0.5 ppm of sulfur, 6.6 m% aromatics and cetane rating of 56 is a high-grade diesel fuel. The hydrocracked tail oil containing more than 14 m% hydrogen and mere 1.7m% aromatics could be used as a good feedstock for steam cracking process to produce ethylene.     

Effect of Operating Parameters on Composition of Dry Gas Obtained During Gasoline Cracking Process

The influence of operating parameters on ethylene content in dry gas obtained during catalytic cracking of gasoline was investigated in a pilot fixed fluidized bed reactor in the presence of the MMC-2 catalyst.The results have shown that the majority of dry gas was formed during the catalytic cracking reaction of gasoline,with a small proportion of dry gas being formed through the thermal cracking reaction of gasoline.The ethylene content in dry gas formed during the catalytic cracking reaction was highe...     

Effect of Water Vapour on the Acidity of ZSM-5 Zeolite Used for Catalytic Cracking of Naphtha to Manufacture Ethylene and Propylene

The change in acidity of the ZSM-5 zeolite was investigated after it was treated with water vapour, and its capability on ammonia adsorption was also studied after having adsorbed water vapour. The effect of water vapour on products distribution was studied during catalytic cracking of naphtha, the changes in the adsorption ability and catalytic performance of the ZSM-5 zeolite was investigated after the catalyst was loaded with phosphorus species. These results all indicated that water vapour could reduce the acid strength and acid density of ZSM-5 zeolite and affect the capability of ZSM-5 on adsorption of gases, therefore the activated energy contributed by the ZSM-5 zeolite to the catalytic cracking reaction would be low to prevent the feedstock from deepened catalytic cracking and coke formation.     

CFD Simulation on Ethylene Furnace Reactor Tubes

1. Introduction Thermal cracking of hydrocarbons for olefin production is normally carried out in long thin reactor tubes. Complicated transfer and reaction processes, including mass transfer, momentum transfer, and heat transfer, as well as thermal cracking reactions, which are closely related with each other, take place in reactor tubes. It is difficult to obtain the detailed operating parameters in reactor tubes by direct measurements due to technical limitations. The lack of understanding …     

FCC 汽油烯烃双分子裂化反应及其与双分子氢转移反应之比的研究

以催化裂化汽油为原料在不同类型的催化剂上进行了催化转化试验，探讨了不同类型的氢转移反应在烯烃转化中的作用。结果表明，汽油烯烃在不同类型的催化剂上发生裂化反应强弱及其与氢转移反应之比大小是不同的；再生催化剂有利于裂化反应，有利于提高裂化反应与氢转移反应之比；较高的反应温度和较高的重时空速有利于裂化反应，有利于提高裂化反应与氢转移反应之比。     

直链烯烃在裂化催化剂基质上的反应机理研究

用溶胶-凝胶法制备了一系列FCC催化剂的基质材料SiO2Al2O3,采用XRD、BET及IR对其结构和酸性特征进行了表征。在FCC操作条件下,以n-C7=-1为模型化合物,考察了反应产物分布与基质材料酸中心特性的关联,提出了n-C7=-1的裂化反应网络,对n-C7=-1的异构化、氢转移、芳构化等二次反应机理进行了探讨。结果表明:异构化反应过程同时以单分子和双分子两种机理进行,但双分子反应选择性较低;氢转移反应不仅与基质的酸中心密度有关,对酸类型的影响更为敏感,在只有L酸的基质上,氢转移以Rideal机理进行,其活性随酸中心密度呈线性增加;在既有B酸又有L酸的基质上,氢转移更倾向于L-H机理,其活性随酸中心密度呈指数增加;烯烃二次反应之间选择性的竞争很大程度上取决于B酸与L酸在总酸量中的分配;以烯烃在B酸与L酸上形成结构不同的正碳离子为前提,提出了两种正碳离子进一步反应的机理模型,并较好地解释了烯烃的反应机理与产物分布。     

甲基环己烷催化裂化的研究进展

详述了近年来国内外在甲基环己烷(MCH)催化裂化转化途径和机理研究中取得的成果。从单环环烷烃的催化裂化反应机理出发,分析了不同催化剂和工艺条件下的MCH转化反应特点。在催化裂化条件下,MCH主要发生开环、β-裂化、氢转移、异构化、烷基转移和脱烷基等六大类反应。着重讨论了MCH在不同催化体系下的反应性能、反应机理及动力学模型的建立;在此基础上,进一步总结了典型的MCH催化裂化反应网络。展望了环烷烃催化裂化催化剂研制和工艺优化的发展方向。     

催化裂化过程中骨架异构化反应的研究Ⅱ.催化裂化工艺过程中操作参数对骨架异构化反应的影响

在小型固定床反应器、美国Xytel公司ACE(R型)装置和提升管催化裂化装置(Riser unit，RU)上，以Marbon减压馏分油、中间基性质的混合油(85％管输VGO掺混15％管输VR，质量分数)和石蜡基性质的减压蜡油(VGO)掺减压渣油(VR)构成的混合油(70％大庆VGO掺混30％大庆VR，质量分数)为催化进料，考察了主要操作参数对骨架异构化反应的影响。研究表明，反应温度、剂／油质量比(m(Catalyst)／m(Oil))、催化剂上焦炭沉积状况、反应质量空速和蒸汽注入量等操作参数对催化裂化过程中的骨架异构化反应均有影响。催化裂化过程中骨架异构化反应是放热过程，高反应温度会抑制骨架异构化反应。提高m(Catalyst)／m(Oil)可以增强催化裂化过程中的骨架异构化反应。焦炭对催化剂酸中心的覆盖能抑制骨架异构化反应，但其影响幅度小于对裂化反应的影响。骨架异构化反应是一个快速反应，低反应温度下减少反应时间会增强催化过程中的骨架异构化反应。水蒸气注入量的增加(即降低烃分压)会减少催化过程中的骨架异构化反应。     

催化裂化反应热计算方法的研究

在分析现有催化裂化反应热测算方法的基础上,提出了用典型反应计算催化裂化反应热的方法（简称典型反应法）。该方法把流化催化裂化装置（FCCU）反应器中发生的反应划分为裂解、脱氢、氢转移、异构化、H₂S生成和缩合生焦6类典型化学反应,利用每类典型反应的热效应数据和反应数量来计算催化裂化的反应热。用该方法计算了6套大型工业FCCU的反应热数据,并与分子膨胀法、催化焦法和反应-再生系统热平衡法的计算结果进行了对比。结果表明,典型反应法因考虑了氢转移和异构化等二次反应放热,计算得到的反应热平均比分子膨胀法和催化焦法低45.8%和31.8%,比反应-再生系统热平衡法高77.8%,但低于基于碳差法催化剂循环量的反应系统热衡算方法的计算结果。     

催化裂解多产丙烯过程中的反应化学控制

在固定床微反实验装置上,选择正十六烷和大庆蜡油为原料,通过改变反应条件和催化剂类型研究了单、双分子反应对丙烯和干气生成的影响。结果表明,强化单分子反应有利于液化气中丙烯含量的提高,但干气产率也会同时增加;而一定程度上促进双分子反应,尤其是负氢离子转移反应的发生有助于抑制干气的生成,但程度太高时却不利于丙烯的生成。利用单、双分子反应的可控制性,采取措施合理调节反应过程中各自的比例和程度是降低现有催化裂解多产丙烯技术干气产率的有效途径。     

催化裂化过程中氢转移反应的研究

氢转移反应是催化裂化过程中十分重要的二次反应,是一个低活化能、快速、放热的过程,其活化能仅为43.3kJ/mol。研究表明催化剂的酸结构和孔结构特性、反应温度、焦炭污染状况和反应接触时间能显著地影响催化裂化过程中的氢转移反应,决定着裂化产物中的烯烃含量、产物的组成和相对分子质量分布。     

FCC汽油加氢脱硫及芳构化催化剂的设计与验证

分析了FCC汽油中各种烯烃的加氢饱和对汽油辛烷值的影响，其中支链化程度不高且碳数大于6的烯烃的加氢饱和是FCC汽油加氢后辛烷值降低的主要原因。探讨了提高FCC汽油辛烷值的各种反应，提出了在研制FCC汽油加氢脱硫催化剂时，应考虑催化剂的异构化、芳构化、氢转移、烷基化和选择性裂化等功能；通过提高烯烃和烷烃的支链化度，将部分烯烃转化为高辛烷值的芳烃，或将低辛烷值的正构烃类选择性异构等措施，达到保持加氢FCC汽油辛烷值的目的，并对研制的催化剂进行了验证。     

异丙苯在酸性催化剂上的主要化学反应路径

 采用小型固定流化床装置(ACE-Model R), 研究了反应温度在450～600℃范围内, 异丙苯在酸性催化剂上的主要化学反应路径。结果表明, 异丙苯在酸性催化剂上的主要化学反应有脱烷基反应、烷基侧链裂化反应、烷基转移反应和氢转移反应等, 其中脱烷基反应是最主要的化学反应, 其选择性为67%～88%;烷基侧链裂化反应选择性为1%～2%;烷基转移反应选择性为1%～10%; 氢转移反应选择性为1%～3%。提高反应温度既有利于脱烷基反应又有利于烷基侧链裂化反应, 烷基侧链裂化反应选择性的增加有利于C₁～C₂等小分子烃类和短侧链芳烃的生成, 但高温不利于烷基转移反应和氢转移反应.