In situ analysis of volatiles obtained from the catalytic cracking of polyethylene

The effects of the solid‐acid‐catalyst pore size and acidity on polyethylene catalytic cracking were examined with a comparison of the temperature‐dependent volatile‐product‐slate changes when the polymer was cracked with HZSM‐5 and HY zeolites and the protonated form of MCM‐41. Volatile‐product distributions depended on the catalyst acidity and pore size. With HZSM‐5, paraffins were detected initially, and olefins were produced at somewhat higher temperatures. Aromatics were formed at temperatures 30–40°C higher than those required for olefin production. Small olefins (C₃–C₅) were the most abundant products when HZSM‐5 and MCM‐41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily paraffin volatile products (C₄–C₈). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which led to the formation of volatile paraffins. Compared with the other catalysts, HZSM‐5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile‐product variations could be rationalized by a consideration of the combined effects of catalyst acidity and pore size on carbenium ion reaction pathways. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3118–3125, 2001     

Catalytic Activity of Copper Oxide Impregnated HZSM‐5 in Methanol Conversion to Liquid Hydrocarbons

A number of CuO/HZSM‐5 catalysts have been studied in a small scale fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. All the catalysts were prepared by wet impregnation technique. The copper oxide loading over HZSM‐5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, surface area analyzer, metal trace analyzer, SEM techniques and TGA were used to characterize the catalysts. Incorporation of CuO onto HZSM‐5 zeolite significantly increased conversion and liquid hydrocarbon product yields. The major liquid products of the reactions were ethyl benzene, toluene, xylene, isopropyl benzene, ethyl toluene, trimethyl benzene and tetramethyl benzene. The maximum methanol conversion and hydrocarbon product yield was obtained at a copper oxide loading of 7 wt%. Effect of run time on conversion and product distribution was also investigated to compare the performance of these catalysts and coke on the catalyst was determined. Effect of space‐time and temperature on methanol conversion and products yield with 7 wt% CuO/HZSM‐5 has also been investigated and analyzed qualitatively.     

Zeolite catalysis studied by radiolysis/EPR. Transformations of cyclic olefins

The Brønsted acid-catalyzed transformations of cyclic olefins in zeolites HZSM5 and H-mordenite were elucidated by the radiolysis/EPR method. Products of catalytic reactions were spin- labeled by radiolytic means and identified by using EPR spectroscopy. Comparison of reactions on HZSM5 and H-mordenite reveals strong shape selectivity on reactions in these catalysts. The radiolysis/EPR method is a new in situ spectroscopy with excellent sensitivity and structural specificity for the study of reaction mechanisms in zeolite catalysts.     

One-step conversion of syngas to light olefins over bifunctional metal-zeolite catalyst

Light olefins(C_2–C_4) are fundamental building blocks for the manufacture of polymers, chemical intermediates,and solvents. In this work, we realized a composite catalyst, comprising Mn_xZr _yoxides and SAPO-34 zeolite,which can convert syngas(CO + H_2) into light olefins. Mn_xZr_yoxide catalysts with different Mn/Zr molar ratios were facilely prepared using the coprecipitation method prior to physical mixing with SAPO-34 zeolite. The redox properties, surface morphology, electronic state, crystal structure, and chemical elemental composition of the catalysts were examined using H_2-TPR, SEM, XPS, XRD, and EDS techniques, respectively. Tandem reactions involved activation of CO and subsequent hydrogenation over the metal oxide catalyst, producing methanol and dimethyl ether as the main reaction intermediates, which then migrated onto SAPO-34 zeolite for light olefins synthesis. Effects of temperature, pressure and reactant gas flow rate on CO conversion and light olefins selectivity were investigated in detail. The Mn_1Zr_2/SAPO-34 catalyst(Mn/Zr ratio of 1:2) attained a CO conversion of 10.8% and light olefins selectivity of 60.7%, at an optimized temperature, pressure and GHSV of 380 °C, 3MPa and 3000 h~(-1) respectively. These findings open avenues to exploit other metal oxides with CO activation capabilities for a more efficient syngas conversion and product selectivity.     

全馏分催化裂化汽油临氢芳构化研究

程序升温还原法制备了MoP/HZSM-5催化剂,并进行了XRD表征。以催化裂化全馏分油为原料,在小型连续固定床反应装置上,考察了工艺条件对催化剂芳构化降烯烃性能的影响。结果表明,MoP/HZSM-5催化剂具有较高活性和稳定性。在反应温度380 ℃、压力2.0 MPa、空速1.0 h^-1和氢油体积比400∶1条件下,芳烃体积分数36.90%,烯烃体积分数26.16%,液收66.70%。     

分子筛上甲醇转化过程的热力学和拓扑结构

现代新型煤化工是我国当今基础有机化学工业发展的新亮点,也是世界化工界的又一次革命。煤制化学品路线经历气化、变换、甲醇合成、甲醇制烃类等过程,其中,最为重要的是分子筛上甲醇转化的过程。本文综述了分子筛上甲醇转化的相关研究,一方面从ZSM-5上甲醇转化的生成烃池及烯烃的热力学机制和产物分布出发,介绍了多甲基苯生成烯烃热力学平衡模型和其中的芳烃池生成烯烃热力学机制,另一方面,介绍了基于Ising模型的分子筛离散拓扑结构模型。利用分子筛孔道堵塞与围棋中“气”的有无的类似性,能够很好地再现SAPO-34上的相变失活现象和不均匀的积炭分布现象。以模型为指导,介绍了一些分子筛多级结构构筑的工作,这些工作很好地提升了催化剂选择性和寿命。这些概念对于准确理解甲醇在分子筛上的反应与失活机制、产品分布及提高选择性有指导意义。     

An infrared spectroscopic study of the mechanism of chloromethane conversion to higher hydrocarbons on HZSM5 catalyst

Investigation of the reaction mechanism of chloromethane on ZSM5 is a new topic. In this work an in situ FTIR technique was employed to study the conversion processes of chloromethane, the active sites on HZSM5, and the desorption state of surface species. The catalytic conversion of chloromethane to higher hydrocarbons was also studied. It is demonstrated that chloromethane can be reversibly adsorbed on acidic sites of HZSM5 at room temperature. At 100°C chloromethane is irreversibly and dissociatively adsorbed on the strong acidic sites of HZSM5, on which surface methoxyl is formed as proved by infrared characteristic C-H stretchings of-CH₃ at 2960 and 2870 cm^–1. Alkoxyls are produced and adsorbed on the catalyst surface as characterized by the infrared absorption bands of -CH₂-groups at 1460 and 2930 cm^–1. At 100°C the adsorbed methoxyl and alkoxyls are the main surface species, and a small amount of aromatics might exist as detected by a characteristic absorption band at 1510 cm^–1. Between 100 and 200°C the adsorbed surface methoxyl and alkoxyls are converted to aromatics, and the occupied OH groups partially appear. At temperature higher than 300°C the adsorbed aromatics are thermally desorbed into the gas phase. Aromatics and alkanes are the main products in catalytic conversion. These results reveal that the formation of aromatics from methoxyl and alkoxyls is easier than the desorption of aromatics from HZSM5 catalyst. An alkoxyl mechanism is proposed for the conversion of chloromethane on HZSM5 based upon the experimental results and the three assumptions: (a) The primary C-C bond is formed from surface methoxyl groups via the methoxyl group polarization and C-H bond weakening, (b) The adsorbed alkoxyls are converted to aromatics via hydrogen transfer and bond rearrangement similar to the conventional carbenium ion mechanism for the aromatization of olefins and alkanes on HZSM5. The hydrogen atoms from the aromatization stimulate the desorption of alkoxyls to alkanes. (c) At temperature higher than 300°C surface reactions and desorption of adsorbed species take place simultaneously, determining the product distribution in the catalytic conversion.     

In situ synthesis of SAPO-34 crystals grown onto α-Al2O3 sphere supports as the catalyst for the fluidized bed conversion of dimethyl ether to olefins

SAPO-34 is an excellent catalyst for the conversion of dimethyl ether (DME) to olefins, but because conventionally synthesized SAPO-34 crystals are too small to be used directly in a fluidized bed, they have to be used as, and have the disadvantages of, a spray-dried catalyst. In this study, SAPO-34 crystals were synthesized in situ to grow on the surface of small α-Al₂O₃ spheres to produce a zeolite catalyst for a fluidized bed reactor. The influences of the composition of the crystal gel and surface structure of the support were investigated. The catalytic performance of the zeolite crystals grown on the support (surface zeolite) for the conversion of DME to olefins was investigated in a fixed bed microreactor and a fluidized bed reactor. The experiments showed that these surface SAPO-34 crystals gave the same activity and product selectivity as conventionally synthesized free SAPO-34 crystals and a higher reaction rate (normalized to the weight of SAPO-34) than the spray-dried catalyst. In situ synthesis is a simple and effective way to produce a SAPO-34 catalyst for a fluidized bed reactor.     

Production of olefins from ethanol by Fe and/or P‐modified H‐ZSM‐5 zeolite catalysts

BACKGROUND: Much attention has been paid to the catalytic conversion of ethanol to olefins, since biomass resources such as ethanol are carbon‐neutral and renewable, and olefins are useful as both fuels and chemicals. It has been reported that zeolite H‐ZSM‐5 is effective for converting ethanol to hydrocarbons, with the chief products being aromatic compounds. RESULTS: Successive addition of Fe and P to the H‐ZSM‐5 improved the initial selectivity for propylene, while the sole addition of Fe or P and co‐addition of Fe and P showed medium initial selectivity. In general, catalysts showing higher initial selectivity for propylene exhibited a steeper decrease in propylene selectivity with time on‐stream. The cause of the change in product selectivity may be carbon deposition during reaction. Addition of Fe and P can improve catalytic stability when processing both neat and aqueous ethanol. The catalytic performance was regenerated by calcination in flowing air. CONCLUSION: Fe‐ and/or P‐modified H‐ZSM‐5 zeolite catalysts efficiently produced olefins (especially propylene) from ethanol. Effective catalyst regeneration was achieved by calcination in flowing air. Copyright © 2010 Society of Chemical Industry     

正己烷在HZSM-5分子筛上的催化裂解研究

为筛选反应活性和烯烃选择性相对较高的催化剂用于研究吸热型碳氢燃料的催化裂解,以正己烷的催化裂解作为探针反应,探讨其在不同硅铝物质的量比HZSM-5［n(Si)∶n(Al)=25、36、100］分子筛上催化裂解的反应活性和产物分布。结果表明,正己烷在HZSM-5分子筛上的裂解转化率随温度的升高和分子筛中硅铝物质的量比的减小而增大;裂解产物中乙烯、丙烯和总烯烃的选择性均随裂解温度的升高和分子筛中硅铝物质的量比的增加而增加,在（300~550） ℃,HZSM-5［n（Si)∶n(Al)=36］上的总烯烃收率最高,芳烃含量随分子筛中硅铝物质的量比的增加而减小;基于裂解转化率、烯烃和芳烃收率等因素综合考虑,HZSM-5 n(Si)∶n(Al)=36］分子筛为优选催化剂。     

Introduction of gallium in HZSM5 and HY zeolites by post-synthesis treatment with trimethylgallium

Framework gallium was introduced in dealuminated HZSM5 and HY zeolites by treatment with trimethylgallium (TMG). The experiments were successful for both zeolites, particularly when performed in a hydrogen atmosphere. Side reactions of TMG with isolated silanol groups or Brxnsted acid sites resulted in the formation of extra-framework gallium. The Ga/HZSM5 zeolite showed an enhanced selectivity to aromatics in the propane conversion.     

Study on products distribution of iron and iron–zeolite catalysts in Fischer–Tropsch synthesis

The dependencies of hydrocarbon product distributions of iron and physical mixture of iron–zeolite catalyzed Fischer–Tropsch synthesis on reaction conditions include: reaction temperature, reaction pressure, H₂/CO feed ratios; space velocity and effect of zeolite presence have been investigated. The concept of two superimposed Anderson–Schulz–Flory distributions has been applied for the representation of the product distribution for both iron and iron–zeolite catalysts. Zeolite presence increased secondary reactions that include cracking of heavier products and light olefins oligomerization. Product distribution of iron–zeolite catalyst was comparable with iron catalyst at high space velocity, because the role of the zeolite on overall reaction declined.The results of the product distribution dependency on the reaction conditions over both iron and iron–zeolite catalysts showed that the average number of carbon decreases with H₂/CO ratio increasing and the reaction temperature in product.     

Influence of operating conditions,Si/Al ratio and doping of zinc on Pt-Sn/ZSM-5 catalyst for propane dehydrogenation to propene

The direct catalytic dehydrogenation of propane to propene is an important route to enhance propene production. In the present experimentation the focus was to investigate the influence of incipient operating conditions, Si/Al ratio of zeolite support and effect of zinc doping on Pt-Sn/ZSM-5 catalyst performance. The catalysts were extensively investigated by reaction tests in a continuous plug-flow quartz micro-reactor. The experimental data shows that the manipulation of operating parameters significantly improves the reaction performance, while huge dynamicity is observed in product distribution. Reaction temperature, 600 °C is found to be most suitable, while increasing the weight hourly space velocity (WHSV), propene selectivity improves at the expense of lower conversion. The OPE was drawn to observe overall reaction network. It was found that the acidity of zeolitic support plays a more important role in achieving desired product selectivity than additional metallic content. Accordingly, the Si/Al ratio of the ZSM-5 zeolite the pro- pene selectivity was enhanced, leading to remarkable improvement in the total olefins selectivity which was remarkably improved owing to a suppression of secondary reactions. At Si/Al ratio 300, the selectivity of propene and total olefins becomes stable at 73% and 90% respectively. The doping of Zn on Pt-Sn/ZSM-5 improves only propene selectivity, but is severely affected by quick deactivation.     

全结晶ZSM-5分子筛催化剂研究及工业应用

制备了全结晶ZSM-5分子筛催化剂,采用XRD、SEM、N2物理吸附-脱附及NH3-TPD等对催化剂进行表征,并考察其用于碳四烯烃催化裂解制丙烯(OCC)反应的催化性能。结果表明,制备的全结晶ZSM-5分子筛催化剂比常规成型的催化剂具有更高的结晶度、更大的比表面积、更丰富的孔结构以及更多的活性中心。高空速有利于反应的进行,提高压力对反应不利,升高温度有利于提高产物丙烯收率。在实验室研究的基础上,将全结晶ZSM-5分子筛催化剂用于OCC工业装置,取得良好的应用效果。     

Influence of the post-treatment of HZSM-5 zeolite on catalytic performance for alkylation of benzene with methanol

The porous material HZSM-5 zeolite with micro-mesopore hierarchical porosity was prepared by post-treatment (combined alkali treatment and acid leaching)of parent zeolite and its catalytic performance for benzene alkyl-ation with methanol was investigated.The effect of post-treatment on the textural properties was characterized by various techniques(including ICP-AES,XRD,nitrogen sorption isotherms,SEM,NH3-TPD,Py-IR and TG).The results indicated that the post-treatment could modify the structural and acidic properties of HZSM-5 zeolite.In this procedure,not only additional mesopores were created by selective extraction of silicon but also the acidity was tuned.Consequently,the modified HZSM-5 zeolite showed larger external surface area with less acid sites as compared to the parent zeolite.It was found out that the modified zeolite exhibited a higher benzene conversion and xylene selectivity for alkylation of benzene with methanol as well as excellent life span of the catalyst than conventional ones.This can be explained by the facts that the presence of additional mesopores improved the diffusion property in the reactions.Furthermore,the modified zeolite showed an appropriate Br?nsted acidity for effective suppression of the side reaction of methanol to olefins,thus reduced the accumulation of coke on the HZSM-5 zeolite,which was favorable for the catalyst stability.In comparison with the parent HZSM-5 zeolite, the modified zeolite by alkali treatment and acid leaching showed better performance for the benzene alkylation with methanol.     

Controllable fabrication and catalytic performance of nanosheet HZSM‐5 films by vertical secondary growth

Nanosheet HZSM‐5 film vertically grown on the substrate with the tailorable macro‐ and meso‐pores between the layers of nanosheets is hydrothermally synthesized by seed‐assisted secondary growth method. The as‐prepared nanosheet HZSM‐5 film exhibits reaction rate enhancement up to 312% in catalytic cracking of n‐dodecane as well as twice light olefins selectivity, ascribed to the better mass transfer of reactants in the hierarchical porous structure and the ultra‐thin b‐axis pores of nanosheets. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1923–1927, 2018     

Molybdenum ZSM-5 zeolite catalysts for the conversion of methane to benzene

This paper describes characterization studies of Mo-HZSM-5 zeolite catalysts active for the non-oxidative conversion of methane to benzene. FTIR, and NMR evidence is presented for migration of molybdenum into the zeolite pores during catalyst calcination at high temperatures. Mo K-edge EXAFS confirms that calcination produces highly dispersed oxomolybdenum or molybdate species which are converted to a molybdenum carbide phase under reaction conditions. Factors determining catalyst performance are discussed.     

Propane Aromatization over HZSM‐5 and Ga/HZSM‐5 Catalysts

The selective transformation of light alkanes to aromatics that are more valuable and versatile feedstocks for the chemical industry is one of the major challenges of catalytic chemistry. The complexity of the aromatization chemistry makes it difficult to unravel reaction mechanisms and, mechanistic information is largely developed from observed product distributions. This article reviews the current mechanistic understanding for the conversion of propane to aromatic compounds over HZSM‐5 and Ga/HZSM‐5 catalysts based on experimental as well as theoretical studies.

Following a general discussion of acidity and confinement effects in these systems, this review focuses on understanding specific reactions occurring on Brønsted acid sites in HZSM‐5. Mechanistic details available from Density Functional Theory (DFT) calculations, as well as kinetic modeling efforts for various complex hydrocarbon systems are critically reviewed. A detailed, tabulated review of the literature compares the catalytic performance of gallium modified ZSM‐5 catalysts and subsequently the promotional effect of gallium as an additive is critically discussed in terms of the nature of the active sites, as well as the new reaction pathways introduced by gallium addition.     

Catalytic conversion of commingled polymer waste into chemicals and fuels over spent FCC commercial catalyst in a fluidised-bed reactor

A commingled post-consumer polymer (CPW#1) was pyrolysed over spent fluid catalytic cracking (FCC) commercial catalyst (ECat-1) using a laboratory fluidised-bed reactor operating isothermally at ambient pressure. The influence of reaction conditions including catalyst, temperature, ratios of commingled polymer to catalyst feed and flow rates of fluidising gas was examined. The conversion for spent FCC commercial catalyst (82.7 wt%) gave much higher yield than silicate (only 14.2 wt%) and the highest yield (nearly 87 wt%) was obtained for ZSM-5. Greater product selectivity was observed with ECat-1 as a recycled catalyst with about 56 wt% olefins products in the C₃–C₇ range. The selectivity could be further influenced by changes in reaction conditions. Valuable hydrocarbons of olefins and iso-olefins were produced by low temperatures and short contact times used in this study. It is also demonstrated that the use of spent FCC commercial catalyst and under appropriate reaction conditions can have the ability to control both the product yield and product distribution from polymer degradation, potentially leading to a cheaper process with more valuable products.     

The effect of pretreatment procedures on the activities of Fe- and Mn-promoted sulfated zirconia catalysts

The vapour phase acylation of furan and pyrrole was carried out over HZSM‐5(19.7), HZSM‐5(30), HZSM‐5(280), CeHZSM‐5(30), LaHZSM‐5(30), HY and CeHY zeolites in a fixed bed reactor at atmospheric pressure using acetic anhydride as an acylating agent. The catalytic activity of the zeolite catalysts was dependent on the reaction temperature and the type of cation promoter used in the modification of the zeolite surface. The activity of the catalysts varied with the acidity of the zeloite systems tested. The yields of 2‐acetylfuran and 2‐acetylpyrrole with respect to the conversion of furan and pyrrole were 67.5% and 75.5% respectively. The acylation was found to be more active on Brønsted acidic sites available over zeolite systems.