n-Pentane Hydroconversion Using Pt-loaded Zeolite Catalysts

Abstract

Pt/H-ZSM-5 and Pt/H-MOR catalysts with different Pt contents were prepared via impregnation using H₂PtCl₆ · 6H₂O or via exchange using Pt(NH₃)₄Cl₂, calcination in air at 530°C and reduction in H₂ at 500°C. The prepared catalysts were tested for n-pentane hydroisomerization and hydrocracking via bifunctionality at 250–500°C using a micro-catalytic pulse reactor. It is found that the dispersion of Pt-exchanged zeolites is higher than the corresponding Pt-impregnated zeolites at all Pt contents. It is also found that the dispersion of Pt/H-ZSM-5 catalysts either exchanged or impregnated are higher than the corresponding Pt/H-MOR catalysts. Temperature-programmed desorption (TPD) data showed that the impregnated catalysts possess a higher acid sites number than the exchanged catalysts; and that the Pt/H-ZSM-5 catalysts have a higher number of acid sites than do the Pt/H-MOR catalysts, whereas the latter catalysts possess higher strength of acid sites at all Pt contents. The hydroisomerization activities using Pt exchanged catalysts, supported either on H-ZSM-5 or H-MOR, are higher than the impregnated catalysts at almost all Pt contents. It is also concluded that the H-ZSM-5-supported catalysts, either exchanged or impregnated, are more active than the H-MOR supported ones. Hydrocracking is higher using all loaded H-MOR catalysts.     

Role of Structure and Acidic Nature on Catalytic Behavior of Nickel Supported H-mordenite,H-ZSM-5, and γ–alumina Catalysts

Abstract

Nickel metal was loaded in different percentages (7, 10, and 13% w/w) on different supports (H-mordenite, H-ZSM-5, and γ–alumina). The prepared catalyst samples were tested in cyclohexane conversion using microreactor pulse technique. Structure was followed up by XRD analysis. Chemisorption of tert-butylamine (TBA) was adopted for estimating the number of surface acid sites. It was found that all prepared samples displayed cracking activity, being mostly related to the fraction of acid sites remaining on the surface after coverage with supported Ni atoms. H-mordenite-supported samples exhibited mainly isomerization functionality by showing a larger portion of surface acid sites. H-ZSM-5-supported samples showed higher dehydrogenation activity. Agglomeration seemed to be responsible for lower activity of the sample of higher Ni content. The formed NiOOH phase was suggested to be responsible for increased dehydrogenation activity on H-ZSM-5 samples and increased cracking activity on γ–alumina-supported samples of higher Ni content.     

脱氯温度对Pt-θ-Al2O3催化剂丙烷脱氢性能的影响

Several Pt-θ-Al2O3 catalysts with similar ultra-low Cl contents were used to investigate the influence of the dechlorination temperature on the propane dehydrogenation reaction. The Pt-θ-Al2O3 catalyst with the highest dechlorination temperature showed the lowest propane rates and propylene selectivity. Scanning transmission electron microscopy showed that the dispersions of Pt nanoparticles decreased with the increasing dechlorination temperatures. Temperature-programmed reduction showed that the higher dechlorination temperature led to strong interactions between the metal and support and made it difficult to reduce Pt nanoparticles. Temperature-programmed reduction implied that more coke was deposited on the metal for catalyst with higher dechlorination temperatures. The Raman spectra and value of H/C showed that more side-reactions, such as cracking and severe deep dehydrogenation reactions, occurred for catalysts with higher dechlorination temperatures. Therefore, the lower dispersion of Pt nanoparticles, the stronger metal-support interactions and increased side-reactions, resulting in lower catalytic activities for Pt-θ-Al2O3 with higher dechlorination temperatures.     

Nanosized Platinum-Loaded H-ZSM-5 Zeolite Catalysts for n-Hexane Hydroconversion

Abstract

A series of nanosized platinum-containing catalysts was successfully loaded on/in zeolite H-ZSM-5 via exchanging the zeolitic proton with platinum from Pt tetramine dichloride complex. Another series of Pt/H-ZSM-5 catalysts was prepared via wet impregnation of H₂PtCl₆ solution for comparison. The latter series was found to produce lower Pt dispersion. Pt dispersion was determined by H₂ chemisorption. Catalyst characterization via ammonia temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), and transmission electron microscopy (TEM) was examined for all catalysts and showed large differences in particle sizes. The data on n-hexane reactions of the catalysts of both series confirmed the formation of Pt nanoparticles in the exchanged catalysts. The relatively lower density and strength of acid sites acquired by Pt-exchanged catalysts contributed to this difference; stronger acid sites in the impregnated catalysts are in favor of hydrocracking reactions, which inhibit isomerization selectivity.     

Transformation of Cycloparaffin over Zeolite-Supported Metal Catalyst for Improving the Octane Number of Gasoline

Abstract

In order to improve the octane number of gasoline, Ni/HZSM-5 and NiMo/HZSM-5 catalysts were prepared by impregnation method, and their activities for hydrocracking, hydroisomerization, and aromatization were investigated by the transformation of cylcohexane. The experimental results show that the conversion of cyclohexane is affected greatly by the reaction temperature. The production of methyl-cyclopentane is the result of the hydroisomerization of cyclohexane. The olefin distribution reveals that the hydrocracking reaction of cyclohexane over acidic zeolite catalyst probably obeys the dimolecular mechanism and the C₅ and C₇ olefins come from the cracking of the dimer of cyclohexane. The activities of the presulfided Ni/HZSM-5 and NiMo/HZSM-5 catalyst for the transformation of cyclohexane were evaluated and the product selectivities for two presulfided catalysts are similar to those obtained over reduced Ni/HZSM-5 catalyst.     

Para-xylene Maximization—Part VI: Shape-Selective Platinum-Promoted Methylation of Toluene

Abstract

The need for increased production of para-xylene, which is the primary material for producing the polyester fibers, activated this research. Although the alkylation reaction is acid catalyzed, we found that a Pt promoter activates this reaction by virtue of the presence of a vacant d-orbital in the Pt atom. In this work, a series of catalysts containing 0.1, 0.2, or 0.3% Pt in H-ZSM-5 zeolite was tested for alkylating toluene with methanol, aiming to produce the xylenes and maximizing para-xylene production in a temperature range of 300°C–500°C in the presence of hydrogen flow in a continuous-flow fixed-bed reactor. The catalysts were characterized by temperature programmed desorption (TPD) of ammonia for acid sites distribution analysis and platinum dispersion in the catalysts by hydrogen chemisorption. Moreover, the diffusion resistance extent in the current catalysts during the alkylation reaction has been evaluated via estimation of the Thiele modulus, Φ _L . The selectivity for para-xylene production was found to increase systematically with increasing the Pt content in the catalysts, whereas the unloaded zeolite did not follow this order. The Φ _L values calculated were accordingly found to increase also with increasing Pt content in the catalysts. Although para-xylene was the highest on the 0.3% Pt/H-ZSM-5 catalyst, the heavy undesired trimethylbenzenes were the lowest to be formed on this catalyst.     

Role of Structure and Acidic Nature on Catalytic Behavior of Nickel Supported H-mordenite, H-ZSM-5, and γ-alumina Catalysts

Nickel metal was loaded in different percentages (7, 10, and 13% w/w) on different supports (H-mordenite, H-ZSM-5, and γ-alumina). The prepared catalyst samples were tested in cyclohexane conversion using microreactor pulse technique. Structure was followed up by XRD analysis. Chemisorption of tert-butylamine (TBA) was adopted for estimating the number of surface acid sites. It was found that all prepared samples displayed cracking activity, being mostly related to the fraction of acid sites remaining on the surface after coverage with supported Ni atoms. H-mordenite-supported samples exhibited mainly isomerization functionality by showing a larger portion of surface acid sites. H-ZSM-5-supported samples showed higher dehydrogenation activity. Agglomeration seemed to be responsible for lower activity of the sample of higher Ni content. The formed NiOOH phase was suggested to be responsible for increased dehydrogenation activity on H-ZSM-5 samples and increased cracking activity on γ-alumina-supported samples of higher Ni content.     

Catalytic para-xylene maximization. Part X: Toluene disproportionation on HF promoted H-ZSM-5 catalysts

H-ZSM-5 zeolite catalysts were doped with 2%, 3% and 4%HF to be used for investigating their activities and selectivities for xylenes production and for para-xylene maximization at temperatures of 300–500 °C via toluene disproportionation. This doping caused pore size modification of the H-ZSM-5 catalyst. The reaction was carried out in a fixed bed flow type reactor. The ratio of produced para-xylene relative to its thermodynamic composition reached as high as 3.29 at 300 °C on the 4%HF doped H-ZSM-5 catalyst although this catalyst possessed the lowest amount of the largest pores (3.0–5.7 nm) and the smallest pores (0.4–1.7 nm). The overall activities of the catalysts were decreased with an increase in HF doping because of diffusion restriction. The kinetics of the reaction were simply treated and found to give E_a and ΔS¹ values compatible with the characterization data of the catalysts.     

Cd-ZSM-5沸石催化剂的制备、表征和芳构化催化性能

采用离子交换、浸渍和混合三种方法制备镉改性ZSM-5沸石催化剂,考察了改性方法和镉含量对催化剂的表面酸性和Cd状态以及芳构化性能的影响。结果表明,加入镉降低了B酸性,Cd~(2+)与沸石结合形成了L_(1612)酸中心,其生成量取决于改性方法和Cd含量,并与芳构化活性提高有直接关系。     

Hydroisomerization of n-Hexane Using Unloaded and Low-Platinum-Loaded H-ZSM-5 and H-MOR Catalysts

Abstract

The applicability for investing and comparing two zeolites (H-ZSM-5 and H-MOR) as supports for low-platinum (less expensive) catalysts used principally for hydroisomerization of n-paraffins in light petroleum naphtha is investigated using n-hexane as a model n-paraffin feed at temperatures of 250°C–500°C in a flow-type reactor with a hydrogen flow of 20 cm³ min^?1 at atmospheric pressure. H-ZSM-5 zeolite acquires higher density of strong acid sites, which are still somewhat weaker than the respective sites in H-MOR. These milder sites in H-ZSM-5 zeolite enhanced hydroisomerization and dehydrocyclization but suppressed hydrocracking after incorporating 0.15% Pt. Hydrochlorination (HCl) and hydrofluorination (HF) of 0.15% Pt/H-ZSM-5 were carried out to modify its acidity and Pt dispersion with the goal of maximizing n-hexane hydroisomerization. The HCl treatment seems to have significantly approached the requirement for optimum catalytic bifunctionality, whereas HF treatment appears mostly deteriorative.     

八氢菲在分子筛催化剂上的环烷环开环反应

在小型固定流化床(FFB)装置上,以Y与ZSM-5分子筛为催化剂进行八氢菲的催化裂化反应,考察了分子筛类型、反应温度、剂/油质量比对八氢菲裂化反应的影响。结果表明,八氢菲在分子筛催化剂上容易发生环烷环开环反应,生成丙烷、丙烯、丁烷、丁烯、甲基戊烷和环戊烷、环己烷类环烷烃以及苯、C₁~C₄烷基取代苯等,烷基苯再发生二次反应生成萘、烷基萘、联苯等;少量八氢菲通过脱氢缩合,生成菲、芘等三环以上多环芳烃,甚至焦炭。由于扩散和吸附性能的影响,八氢菲的环烷环开环反应与催化剂的孔径和B酸量有关;其环烷环开环反应选择性,在孔径和B酸量适宜的Y分子筛催化剂上比在ZSM-5催化剂上高。在Y分子筛催化剂上,当温度为450~525℃、剂/油质量比为3~9,随着反应温度的升高,或者剂/油质量比的增加,八氢菲脱氢缩合反应增强,而环烷环开环反应选择性降低。     

High Yields of LPG Via n-Hexane Hydrocracking Using Unloaded Acidic Zeolite Catalysts

This work includes investigating the hydrocracking of n-hexane, as a low-octane naphtha component to high-octane gaseous motor fuel (LPG) in a pulse flow atmospheric microreactor using untreated and steam-treated H-MOR, H-BEA, or H-ZSM-5 zeolite catalysts. All zeolites were metal-free and their bifunctionality depended only on the Brønsted zeolitic acid sites. The temperature programmed desorption analysis was performed to compare the weak and strong acid sites in the current catalysts. The catalytic activities of the catalysts were found to correlate well with their acid strengths. The most active catalyst was St-H-MOR, which acquired the strongest acid sites and highest densities. On this catalyst, 92.1% LPG was produced at 350°C, whereas on the un-steamed one (H-MOR), the LPG yield amounted to 88.0% at the same temperature. Maximum LPG production on H-BEA acquired 84.6% at 400°C, whereas on St-H-BEA, it acquired a close yield (85.7%). Zeolites H-ZSM-5 and St-H-ZSM-5 acquire very low catalytic activities mainly due to their narrow pore structure, as well as due to their partial pore filling by Al debris in case of St-H-ZSM-5.     

Transformation of Cycloparaffin over Zeolite-Supported Metal Catalyst for Improving the Octane Number of Gasoline

In order to improve the octane number of gasoline, Ni/HZSM-5 and NiMo/HZSM-5 catalysts were prepared by impregnation method, and their activities for hydrocracking, hydroisomerization, and aromatization were investigated by the transformation of cylcohexane. The experimental results show that the conversion of cyclohexane is affected greatly by the reaction temperature. The production of methyl-cyclopentane is the result of the hydroisomerization of cyclohexane. The olefin distribution reveals that the hydrocracking reaction of cyclohexane over acidic zeolite catalyst probably obeys the dimolecular mechanism and the C₅ and C₇ olefins come from the cracking of the dimer of cyclohexane. The activities of the presulfided Ni/HZSM-5 and NiMo/HZSM-5 catalyst for the transformation of cyclohexane were evaluated and the product selectivities for two presulfided catalysts are similar to those obtained over reduced Ni/HZSM-5 catalyst.     

II. Electrical Properties of Ni/Silica Gel and Pt/γ-Alumina Catalysts in Relation to Catalytic Activity

Abstract

The catalytic activity of silica gel and silica gel—supported nickel (2, 5, and 8 wt% Ni) and γ-alumina—supported platinum (0.3 and 0.6 wt% Pt) was studied for n-hexane or n-pentane cracking and cyclohexane dehydrogenation adopting pulse technique. The results showed that Pt/γ-alumina could be a selective catalyst for cyclohexane dehydrogenation reaction. Ni/silica gel catalyst was a good cracking catalyst, the activity of which increased by increasing the metal content up to 8% Ni. For cyclohexane, dehydrogenation over Ni/silica gel, the activity increased by increasing the metal loading. N2 sorption characterizations showed that both silica gel- and γ-alumina—supported catalyst samples exhibited mesoporous structures. Silica gel and silica gel—supported samples have ink-bottle type pores while γ-alumina and γ-alumina—supported platinum samples have platelike pores. BET surface area and total pore volume decreased by increasing metal loading for both catalyst samples.

Electrical properties of pure γ-alumina and silica gel supports were functions of metal content and frequency of the applied field. The increase of conductivity is considered a good indicator of the decrease in the activation energy (increase of catalytic activity). The observed increase in conductivity with the increase of metal loading may be due to increase in the mobility of the free charge carriers (i.e., ions and free radicals taking part in the mechanism of catalytic conversion of hydrocarbons over the catalyst polarized active centers that increased by increasing metal loading). These charge carriers diffuse in the bulk of pores and reach electrodes where they discharge, giving rise to diffusion impedance (Warburg impedance).     

Catalytic Dewaxing for Lube Oil Production

Abstract

The selective cracking of long-chain normal paraffin's of medium neutral raffinate, derived from a lube oil-phenol extraction unit, by the catalytic dewaxing technique over H-ZSM-5 and NiMo-H-mordenite catalysts was studied. The runs were conducted to produce lube oils with acceptable cold flow properties. The influences of zeolite types, metals loading, and operating reactor temperatures (290°C–475°C) can have a great effect on cracking high pour point n-paraffins into lower ones, and hence a reduction in pour points. An increase in temperature (between 290°C and 375°C) increased wax conversion (percent dewaxing) on H-ZSM-5 compared with NiMo-H-mordenite catalysts due to its higher cracking activity. As a result, large amounts of C₁-C₄ gases and C₅-170°C naphtha were produced. The low pour point lube oils produced from catalytic dewaxing over H-ZSM-5 compared with NiMo-H-mordenite catalyst indicates that the former was more selective for removing wax components than the later. On the other hand, high concentrations of aromatics were obtained on both catalysts, since the waxy paraffins are converted to lower boiling products. The reduction in dewaxed pour points (Δpp) was observed to be in the range of 38°C–42°C over H-ZSM-5, compared to 37°C–40°C over NiMo-H-mordenite at the same reaction temperature ranges (290°C–375°C), but NiMo-H-mordenite has advantages at higher temperature ranges (above 375°C) in pour point reduction (Δpp range: 41°C–42.5°C). The addition of bimetallic components to the mordenite-catalyst enhances its activity, and the rate of normal paraffin cracking was increased due to the hydrogenolysis activity of the active metals. This means that the bimetallic H-mordenite catalyst has the advantage over H-ZSM-5 in its refining activities (hydrodesulfurization [HDS] and hydrodenitrogenation [HDN]) under the tested operating conditions. These results may be attributed to shape-selective discriminating behavior due to differences in zeolite pore openings (i.e., 6.5 × 7.0 Å for mordenite and 5.3 × 5.6 Å for ZSM-5). In other words, a combination of isomerization and selective cracking reactions of high n-paraffins may occur during the dewaxing process using NiMo-H-mordenite catalyst. The influences of process parameters (temperature, pressure, and liquid hourly space velocity [LHSV]) on the relations between wax conversion to maintain maximum low pour points and maximum dewaxed oil yields or minimum yields of the least desired gases were optimized to produce dewaxed lube oils of acceptable characteristics.     

Cu/ZSM-5催化剂的表征及其环己醇脱氢性能

以制备的ZSM-5分子筛为载体,采用浸渍法制备了一系列Cu负载量不同的Cu/ZSM-5催化剂。采用X射线衍射、氢气程序升温还原、吸附氨气程序升温脱附和BET等方法对Cu/ZSM-5催化剂进行了表征,用H2-N2O滴定法测定了Cu金属的比表面积和分散度。以环己醇气相脱氢制备环己酮为探针反应对Cu/ZSM-5催化剂的催化性能进行了评价。实验结果表明,Cu负载量影响Cu物种在载体表面的状态和分布,Cu是环己醇脱氢反应的活性中心,其比表面积、分散度与Cu/ZSM-5催化剂的活性相关,Cu/ZSM-5催化剂的B酸中心与环己醇脱氢反应的选择性相关。Cu质量分数5%的Cu/ZSM-5催化剂上Cu金属的比表面积较大而B酸中心较少,显示出很高的环己醇转化率(58.7%)和较好的环己酮选择性(97.2%)。     

Computerized Solution of the Dynamic Sorption Process for Binary System in Heterophase Medium

Abstract

A mathematical model equation for binary adsorption-reaction process is developed and illustrated for the catalytic dehydrogenation of cyclohexane to benzene on Platinum-Rhenium/Alumina catalyst with unadsorbed hydrogen in inert (argon, he lium) and active (hydrogen) carrier gases using pulse and continuous flow techniques. The optimization routine of Nelder-Mead simplex algorithm is developed with a view to estimating surface reaction rate and adsorption equilibrium constants at different temperatures, which in turn are used to determine activation energies and adsorption equilibrium energies for cyclohexane dehydrogenation in inert and active carrier gases using pulse and continuous flow techniques.     

有机氢载体低温高效脱氢催化剂的研究进展

有机氢化物储氢作为一种大规模、长距离、长期氢能储存和输送的储氢技术,应用潜力巨大,主要问题是常规脱氢催化剂在低温下的活性偏低和稳定性较差。在理论分析开发十氢化萘、甲基环己烷和环己烷等有机氢载体低温高效脱氢催化剂可行性的基础上,综述了国内外的研究现状。指出对传统脱氢催化剂进行改性、采用新型活性炭和覆炭γ-Al2O3载体,都可在一定程度上改善有机氢载体在低温下的脱氢效率;而反应蒸馏条件下催化剂以过热液膜状态催化,或采用pH摆动法制备孔分布集中且pH可控的γ-Al2O3作载体,则可能使有机氢载体在低温下高效脱氢,是有机氢载体高效脱氢催化剂的开发方向。     

Transformation of Paraffins to Improve the Octane Number of the Cracked Naphtha Over Ni/HZSM-5 Catalyst

Abstract

Paraffins in the cracked naphtha can be transformed into aromatics and isoparaffin to improve the octane number. In this article, a series of Ni/HZSM-5 bifunctional catalysts were prepared and were characterized by temperature-programmed desorption of NH₃ (NH₃-TPD), FT-IR analysis with adsorbed pyridine as well as by x-ray powder diffraction analysis. The monolayer dispersion threshold value of Ni on HZSM-5 was determined and the cracking and aromatization activities of the catalysts were investigated in the transformation of n-heptane. The experimental results show that the catalyst with a monolayer dispersion threshold value of Ni shows the best aromatization and isomerization activity. The products selectivity of n-heptane over different catalysts was analyzed and it was revealed that low hydrogen pressure can reduce the conversion of n-heptane, but at the same time accelerate the production of aromatics. The aromatization activity of the catalysts increases with the elevation of the reaction temperature, and the incorporation of metal in HZSM-5 decreases the cracking reaction on the catalysts, while at the same time increases the reactions that may result in the production of aromatics.     

催化剂焙烧设备的工业放大对乙苯脱氢催化剂影响的剖析

 催化剂的焙烧是催化剂制备的重要步骤，本文以乙苯脱氢制苯乙烯催化剂为研究对象，对隧道窑和连续式回转炉等常用工业设备焙烧的催化剂，与试验室马弗炉焙烧的催化剂分别进行了评价和分析。结果表明，回转炉焙烧的催化剂平均抗压碎强度和抗压碎强度方差略优于隧道窑焙烧的催化剂；回转炉焙烧的催化剂在反应活性、选择性以及比表面、孔容、平均孔径、晶粒形貌等各项特征上均达到试验室马弗炉的焙烧水平，更优于隧道窑焙烧的催化剂。催化剂的比表面、孔容、平均孔径及晶粒形貌的差别是焙烧的催化剂活性存在差异的主要原因。研究表明，从试验室小试装置到工业大规模设备存在不容忽视的催化剂焙烧过程的放大效应。