KINETIC INVESTIGATION OF METHYLCYCLOPENTANE REFORMING ON FRESH AND DEACTIVATING Pt/Al2O3 CATALYST

ABSTRACT

The conversion of methylcyclopentane (MCP) in hydrogen on fresh and deactivating Pt/Al₂O₃ catalyst to hydrogenolysis products (2-methylpentane, 3-methylpentane and n-hexane), cyclohexane and benzene was studied in a Berty CSTR at various partial pressures of MCP and H₂, and at a total pressure of 1 atm. For the kinetic studies, temperatures between 370 – 400° and W/F values up to 0.33 g min/cm³ were used. The conversion of MCP was found to increase with increase in temperature at all the MCP partial pressures investigated. The hydrogenolysis products and benzene composition generally increased with increase in temperature and W/F. The mechanism for the reforming of MCP was similar to that proposed by Dartigues et al. (1978) except that the formation of hydrogenolysis products was accounted for in this formulation. Eleven rate models were developed and tested and six satisfied the set criteria. Since hydrogenation/dehydrogenation and desorption steps are relatively rapid, the conversion step to hydrogenolysis products was deemed the only rate determining step with an activation energy of 36.31 kcal/gmol. For the deactivation studies, the model of Corella and Asua (1982) was used for the development of two deactivation models. The only model found to predict the deactivation behavior was the step leading to the formation of the coke precursor as rate controlling.     

ESTIMATION OF TOXIC COKE DEPOSITS ON FRESH AND REGENERATED Pt/Al2O3 CATALYST FROM METHYLCYCLOPENTANE REFORMING IN H2 AND N2 ATMOSPHERES.

An estimate of the quantity of toxic coke deposited on fresh and regenerated Pt/Alj₂O₃ catalyst has been determined for methylcyclopentane (MCP) reforming in a Berty CSTR at 390°C, W/F=0·11 g min cm^-3, total pressure of 1 atm and MCP partial pressure of 9·2 × 10^-2 atm in H₂ or N₂ carrier. Eleven cycles consisting each of catalyst deactivation, regeneration and reduction were investigated with 3 in H₂ and 8 in N₂. Oxidizable (primary) coke deposits were higher in N₂. However, higher levels of toxic (secondary) coke were deposited in H₂. The ratio of oxidizable to toxic coke lies between 1-15×10³ in H₂ and 22 - 55 × 10³ in N₂ The coke-time profiles for secondary coke removal exhibited maxima suggestive of three types of secondary coke with varying reactivity in H₂. Furthermore, the results strongly suggest that the cokes were layered on acidic coke forming sites with the solid phase transformation of primary to secondary coke occurring at the catalyst-coke interface.     

REFORMING OF N-OCTANE ON A Pt/Al2O3 CATALYST. II. KINETIC ANALYSIS OF HYDROGEN DEPENDENCE.

The conversion of n-octane on Pt/Al₂O₃ catalyst was found to pass through pronounced maxima with the variation of the partial pressure of hydrogen at temperatures between 420°C-460°C, P_N = 7·63 × 10^-3 atm and W/F = 0·11lg min cm_-3. The products of reaction were hydrocracked products, octane, ethylbenzene, o-.p-,m,-xylene and toluene. The order of appearance of the optimum PH for the various reactions were: Isooctane>Dehydrocyclized products>Hydrocracked products.

A sequence of elementary steps earlier postulated was found to predict the maximum in the n-octane P_H profiles for the three temperatures investigated. The rate determining steps for the two rate equations that were found suitable were conversion of adsorbed isooctane to adsorbed o-xylene and ethylbenzene.     

KINETIC ANALYSIS OF THE ISOMERIZATION OF 2,2,4-TRIMETHYLPENTANE ON A FRESH AND DEACTIVATING Pt-Alumina CATALYST

The isomerization of 2,2,4-trimethylpentane (2,2,4-TMP) was investigated in a Berty CSTR at various partial pressures of the reactant and hydrogen, 1 atm total pressure and temperatures between 370 - 430^°C on fresh and deactivating 0.3 and 0.6% Pt/Al₂O₃ catalysts. The sole product of the reaction was the production of the isomer, 1,1,3-trimetylpentane (1,1,3-TMP). For the kinetic investigation on the fresh catalysts, there was no difference in conversion between the catalysts at these two loadings. Mechanistic rate equations were derived on the basis of the generally accepted mechanism for skeletal isomerization on an ideal bifuctional catalyst. Two of the three models developed on the basis of the isomerization on the acidic site and the diffusion of the dehydrogenated product from the acidic site to the metal site, were found to predict the conversion - W/F profiles. However, only the second model was found kinetically appropriate due to its reasonable prediction of an activation energy that is consistent with the high activity data. Deactivation data was affected by catalyst loading and the kinetics of deactivation was predicted by a model where the formation of the coke precursor was rate controlling.     

REFORMING OF N-OCTANE ON A Pt/Al2O 3 CATALYST. 1. PRODUCT DISTRIBUTION AND KINETIC ANALYSIS.

The conversion of n-octane on Pt/Al₂O₃ catalyst to hydrocracked products, isooctane, ethylbenzene, o-,p-,m-xylene and toluene was investigated in hydrogen in a Berty CSTR at three different partial pressures of n-octane, 101·325 KPa total pressure, temperatures between 400°C-460°C and W/F values up to 0·33gmincm^-3. The hydrocracked products were the most predominant. Of the other products, isooctane was present in the highest yield. A sequence of elementary steps based on the suggested reaction network of Ako and Susu (1986) was found to predict the experimental conversion-W/F data with the conversion of adsorbed isooctane to adsorbed o-xylene as the rate determining step. The activation energies for the forward and backward reactions of this step were determined to be 21·2 and 14·3 Kcal/gmol, respectively.     

REFORMING OF N-OCTANE ON A Pt/Al2O 3 CATALYST. 1. PRODUCT DISTRIBUTION AND KINETIC ANALYSIS.

ABSTRACT

The conversion of n-octane on Pt/Al₂O₃ catalyst to hydrocracked products, isooctane, ethylbenzene, o-,p-,m-xylene and toluene was investigated in hydrogen in a Berty CSTR at three different partial pressures of n-octane, 101·325 KPa total pressure, temperatures between 400°C-460°C and W/F values up to 0·33gmincm^-3. The hydrocracked products were the most predominant. Of the other products, isooctane was present in the highest yield. A sequence of elementary steps based on the suggested reaction network of Ako and Susu (1986) was found to predict the experimental conversion-W/F data with the conversion of adsorbed isooctane to adsorbed o-xylene as the rate determining step. The activation energies for the forward and backward reactions of this step were determined to be 21·2 and 14·3 Kcal/gmol, respectively.     

REFORMING OF N-OCTANE ON A Pt/Al2O3 CATALYST. II. KINETIC ANALYSIS OF HYDROGEN DEPENDENCE.

ABSTRACT

The conversion of n-octane on Pt/Al₂O₃ catalyst was found to pass through pronounced maxima with the variation of the partial pressure of hydrogen at temperatures between 420°C-460°C, P_N = 7·63 × 10^-3 atm and W/F = 0·11lg min cm_-3. The products of reaction were hydrocracked products, octane, ethylbenzene, o-.p-,m,-xylene and toluene. The order of appearance of the optimum PH for the various reactions were: Isooctane>Dehydrocyclized products>Hydrocracked products.

A sequence of elementary steps earlier postulated was found to predict the maximum in the n-octane P_H profiles for the three temperatures investigated. The rate determining steps for the two rate equations that were found suitable were conversion of adsorbed isooctane to adsorbed o-xylene and ethylbenzene.     

柠檬酸对NiW/Al2O3加氢脱硫催化剂硫化行为的影响

在NiW/Al2O3催化剂中引入柠檬酸络合剂,考察了柠檬酸对不同温度硫化的NiW/Al2O3催化剂4,6-DMDBT加氢脱硫活性的影响,并采用程序升温氢还原（H2-TPR）、X射线光电子能谱（XPS）和高分辨透射电镜（HRTEM）进行了表征。结果表明,硫化温度较低时(<300℃),柠檬酸对NiW/Al2O3催化剂的加氢脱硫活性没有促进作用,硫化温度较高时（≥300℃）,明显促进了NiW/Al2O3催化剂的脱硫活性,并对加氢脱硫途径表现出选择性促进效应。柠檬酸不仅减弱了金属W与载体之间的相互作用,促进了W物种的还原和Ni-W-O混合相的生成。而且还降低了金属W的硫化温度,促进了W物种的硫化和小尺寸WS2晶粒的生成。     

NiW/Al2O3上喹啉对二苯并噻吩 加氢脱硫的抑制作用及反应动力学

 以二苯并噻吩(DBT)为含硫模型化合物，在中压滴流床反应装置中研究了工业NiW/Al₂O₃催化剂(RN-10)上喹啉对DBT加氢脱硫(HDS)的抑制作用，考察了喹啉质量分数(0.5%~1.5%)、反应温度(290~380℃)、反应压力(4.0~5.6MPa)对DBT的HDS的影响。结果表明，喹啉的存在对于DBT的HDS反应有很强的抑制作用，且喹啉浓度越高，抑制作用越大；对DBT的先加氢饱和再脱硫路径(HYD)的抑制作用比对直接脱硫路径(DDS)更大；提高反应温度对DDS和HYD路径的脱硫活性均有提升，但由DDS路径生成联苯的选择性降低；较高反应压力有利于提高HYD路径产物的选择性。采用带有氮化物吸附(中毒项)的拟一级反应动力学模型对实验数据进行拟合，得到不同喹啉质量分数下DBT的HDS表观反应速率常数。经检验，模型计算结果与实验结果吻合。     

Pt-K/Al_2O_3TiO_2常压催化糠醛脱羰制呋喃的研究

常压下 ,在固定床连续反应器中以Pt K/Al2 O3 TiO2 为催化剂进行了糠醛催化脱羰制呋喃的研究。确定了较优的工艺条件 :温度 30 0℃ ,n(H2 )∶n(糠醛 ) =2∶1,空速为 1h-1。反应过程中催化剂稳定性下降的原因是反应物糠醛的自身结焦。     

载体Na含量对NiMo/Al_2O_3催化剂加氢性能的影响

采用饱和浸渍法制备了Na含量不同的γ-Al_2O_3载体,并采用相同方法制备了负载量相同的NiMo催化剂,以加氢后的西太平洋常压渣油为原料对催化剂性能进行了评价,用BET,IR-OH,LRS,H_2-TPR等方法对载体和催化剂进行了表征。结果表明:随载体Na含量的增加,对应催化剂的加氢性能下降;Na的引入对载体的孔道结构和酸量没有显著影响,但使载体表面的碱性羟基增多,酸性羟基减少,在增强活性金属与载体间相互作用的同时,使八面体Mo物种向四面体Mo物种转变,导致催化剂的加氢性能有所下降。     

纳米Pd/Al2O3催化剂的表征及其选择性加氢反应性能

 采用氢电弧等离子体法制备的纳米钯粉制备了纳米Pd/Al2O3催化剂，采用X射线粉末衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）、X光电子能谱（XPS）和程序升温还原（TPR）等物理化学手段对其进行了表征，并在裂解汽油一段加氢反应中考察了其催化活性和选择性。结果表明，纳米Pd/Al2O3催化剂表面的Pd原子排列有序，表面呈蜂窝状，其载体的内部没有Pd元素，而浸渍法所得的Pd/Al2O3催化剂载体内部有Pd元素；纳米Pd/Al2O3的Pd3d5/2结合能比壳型Pd/Al2O3的Pd3d5/2结合能高；前者XRD谱图中未发现Pd和PdO的特征峰。两种样品的程序升温还原研究表明纳米Pd和载体Al2O3发生了强相互作用。在裂解汽油一段加氢选择性反应中，纳米Pd/Al2O3催化剂显示出较高的催化活性和优异的选择加氢性能。     

新型Pt/Al_2O_3苯加氢催化剂的研制

开发了一种新型的苯气相加氢制环己烷的Pt/A l2O3催化剂,并在模拟苯加氢制环己烷工业装置建成的催化剂原粒度活性评价装置上评价催化剂的性能。考察了催化剂的制备方法、A l2O3载体物性、催化剂制备时竞争吸附剂对催化剂性能的影响。确定了适用于该新型催化剂的最佳的工艺操作条件。本催化剂具有与参比的工业催化剂类似的催化性能,但侧压强度明显高于参比催化剂。     

NiMo/Al2O3加氢脱硫催化剂的电镜表征

 采用常规透射电子显微技术（TEM）和扫描透射电子显微技术结合X射线能谱分析的测量技术（简称分析电子显微技术- —AEM）对NiMo/Al₂O₃系工业加氢脱硫催化剂的氧化态和硫化态进行对比研究。结果表明，对于硫化态加氢脱硫催化剂，TEM可以给出清晰的活性相的形貌和分布信息，活性相条纹的长度、堆叠层数等活性相参数特征的统计与其催化活性具有良好的关联。通过AEM的Mapping技术对NiMo/Al₂O₃催化剂氧化态和硫化态活性组分Ni、Mo的微区成分分布的测定，可获得催化剂活性相前体和硫化态活性组分的成分分布信息，克服了单一TEM不能提供成分信息的缺点，增加了对催化剂制备过程中活性组分变化的了解。     

活化温度对NiW/Al_2O_3催化剂中金属-载体相互作用的影响

考察了活化温度对NiW/Al_2O_3催化剂4,6-二甲基二苯并噻吩加氢脱硫活性和金属-载体相互作用的影响。研究结果表明,350～400℃是催化剂获得高脱硫活性的适宜活化温度,在该温度下对催化剂进行活化有利于金属.载体之间保持适度的相互作用,并促进W金属的硫化。高温活化(450℃)会导致Ni与氧化铝载体的相互作用增强,生成尖晶石物相,破坏Ni-W-O混合相物种,使金属W不易硫化,导致催化剂活性下降。     

乙二醇对Ni-W/Al2O3催化剂的加氢性能影响

以Ni、W为活性组分,Al2O3为载体,制备催化剂Ni-W/Al2O3,并采用乙二醇后处理未焙烧的催化剂Ni-W/Al2O3,得到催化剂Ni-W/Al2O3-AT。通过X射线衍射（XRD）、氢气程序升温还原（H2-TPR）、紫外拉曼光谱（LRS）、透射扫描电子显微镜（TEM）、XPS等表征方法研究催化剂的物化性质。结果表明：催化剂Ni-W/Al2O3经乙二醇后处理后,改善了载体氧化铝表面的羟基基团的分布,促使W物种以八面体配位多核聚钨酸的形态存在;并有效削弱了载体与活性金属之间的强相互作用,提高了W物种的分散度与硫化度,最终使得催化剂形成更多“Ni-W-S”加氢活性相,提高了催化剂Ni-W/Al2O3-AT的加氢活性。与催化剂Ni-W/Al2O3相比,催化剂Ni-W/Al2O3-AT对舟山石化焦化轻蜡油具有更高的加氢脱硫、脱氮与芳烃饱和性能,硫质量分数可从6 850 μg/g降至10 μg/g,氮质量分数由3 720 μg/g降至12 μg/g,双环以上芳烃质量分数可从25.8%降至3.2%。     

Al2O3对Zn/HZSM-5芳构化催化剂的影响

研究了Ａｌ２Ｏ３的加入对Ｚｎ改性ＨＺＳＭ－５催化剂性能的影响,应用分析电镜（ＴＥＭ－ＥＤＳ）对催化剂进行了微区元素组成分析,比较了Ａｌ２Ｏ３、Ｚｎ／Ａｌ２Ｏ３、ＨＺＭ－５以及Ｚｎ／Ａｌ２Ｏ３＋ＨＺＳＭ－５机混催化剂的芳构化性能和Ｚｎ分布,并初步探讨了影响Ｚｎ组元分布的因素,结果表明,加入Ａｌ２Ｏ３的Ｚｎ改性ＨＺＳＭ－５催化剂在经过高温焙烧或水热处理后,原来处于分子筛上的Ｚｎ组元部分迁移至Ａｌ２Ｏ３     

氯化条件对正己烷异构化Pt/Al2O3催化剂性能的影响

采用浸渍法制备了Pt/Al2O3催化剂,在250和300℃下氯化不同时间,得到两个系列的Pt/Al2O3 Cl催化剂。采用BET、NH3 TPD、Py IR等方法表征了制备的催化剂。以正己烷为原料,在反应温度140℃、压力20 MPa、体积空速12 h-1、氢/油摩尔比2的条件下,考察了Pt/Al2O3 Cl催化剂的异构化催化活性和异构产物选择性。结果表明,在相同温度下,氯化时间越长,Pt/Al2O3 Cl的比表面积越小,孔径越大。在250℃氯化时,氯化时间越长,催化剂酸量和氯质量分数越高,催化正己烷异构化活性和异构产物选择性越高;但在300℃氯化时,氯化时间超过1 h,所得Pt/Al2O3 Cl的酸量和氯质量分数下降,催化性能变差。氯化后的Pt/Al2O3 Cl催化剂只有L酸位,经异构化反应评价后催化剂既有L酸又有B酸。300℃氯化1 h最佳,所得Pt/Al2O3 Cl催化正己烷异构化的转化率为8405%,2〖DK〗,2 二甲基丁烷选择性为2654%;连续运行300 h,催化剂活性几乎不改变。     

催化裂化汽油重馏分在MoCo/Al2O3催化剂上的加氢脱硫性能

以FCC汽油为原料,在中型试验装置上考察了230～400 ℃范围内硫化温度对MoCo/Al2O3催化剂加氢脱硫率及烯烃加氢饱和率、辛烷值损失性能的影响。结果表明在260 ℃反应温度下,随着硫化温度的提高,加氢脱硫率由84.4%逐步提高到91.1%;在280 ℃反应温度下,随着硫化温度的提高,加氢脱硫率维持在96.0%以上基本不变。在上述两种情况下,250 ℃硫化催化剂烯烃加氢饱和率最低,辛烷值损失最小。表明250 ℃硫化催化剂加氢脱硫选择性最好。250 ℃下硫化充分且碳含量较少是FCC汽油加氢脱硫选择性最好的原因。