Catalytic cracking and skeletal isomerization of n-hexenes on HY zeolite

The catalytic cracking and skeletal isomerization of n-hexenes on 80/100 mesh HY zeolite has been studied in the temperature range 350–405°C, and compared with results previously obtained on ZSM-5 zeolites. Species with less than three carbon atoms were not observed as primary cracking products, with traces of ethylene formed only as a secondary product. Although propylene and propane may be formed partially by monomolecular cracking of n-hexenes, the dominant cracking process is bimolecular. Dimerization, followed by disproportionation gives stable C₃, C₄ and C₅ species, in addition to C₉, C₈ and C₇ fragments. The probability of these larger fragments undergoing further cracking before desorption increases with temperature, but is significantly less than found on ZSM-5 zeolites. The main products of skeletal isomerization were monomethylpentenes, with those isomers which can originate from tertiary carbonium ions dominant. Dimethylbutenes were formed mainly as secondary products. The rate of the dimerization-cracking process in which two n-hexene species participate is ? six times slower than the reaction involving a monomethylpentene species and a linear hexene. The increase in the rate of the latter process with respect to the former is reduced on ZSM-5, and this can be attributed to the narrower pore size within this zeolite. In contrast to ZSM-5, there is significant formation of alicyclics, paraffins and aromatic species. The residual coke was found to be considerably poorer in hydrogen content than comparable material formed on ZSM-5.     

In-situ synthesis and catalytic activity of ZSM-5 zeolite

ZSM-5 zeolite has been hydrothermally synthesized in-situ on the external surface of calcined kaolinite in the presence of n-butylamine. This supported zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and N₂ adsorption. Several synthesis variables were systematically investigated, including SiO₂ to Al₂O₃ ratio, pH, crystallization time, and crystallization temperature. After mixing the ZSM-5 with a Fluid Catalytic Cracking (FCC) catalyst, catalytic performance was evaluated by cracking vacuum gas oil (VGO) in a micro-fixed bed reactor. ZSM-5 addition was favorable for the production of light olefins by catalytic cracking of VGO.     

Catalysts based on zeolite ZSM-23 for isodewaxing of a lubricant stock

Granular Pt/(ZSM-23-γ-Al₂O₃) catalysts with different platinum and zeolite contents have been synthesized with the aim of developing efficient isodewaxing catalysts for lowering the pour point of lubricants and diesel fuels. Their physicochemical properties have been studied by X-ray diffraction, temperature-programmed desorption of ammonia, and low-temperature nitrogen adsorption/desorption. The effects of catalyst composition and process conditions (1.0–3.0 MPa, 220–400°C) on the outcomes of the isodewaxing of the 280°C-EBP lubricant fraction isolated from the hydrocracking product of vacuum gas oil have been investigated. The highest yields of products with the same pour points have been obtained with a 0.30 wt % platinum catalyst supported on the 20 wt % zeolite ZSM-23 + 80 wt % γ-Al₂O₃ material. An analysis of the basic performance characteristics of the isodewaxing catalysts based on zeolite ZSM-23 and dewaxing catalysts based on zeolite ZSM-5 has demonstrated that the catalysts based on ZSM-23 ensure higher yields of dew-axed products than the laboratory and commercial catalysts based on ZSM-5.     

Effect of Temperature in Hydrocracking of Light Cycle Oil on a Noble Metal‐Supported Catalyst for Fuel Production

The effect of temperature has been studied in hydrocracking of light cycle oil (LCO), byproduct of fluidized catalytic cracking (FCC) units on a bifunctional catalyst (Pt‐Pd/HY zeolite). The increase in both temperature and H₂ partial pressure have an important attenuating effect on catalyst deactivation, given that they decrease sulfur equilibrium adsorption and enhance hydrocracking of coke precursors. Therefore, the catalyst maintains significant hydrodesulfurization and hydrocracking activity. As the temperature is increased, hydrocracking conversion and naphtha selectivity increase, although there is no significant dearomatization of the medium distillate fraction in the range of the studied experimental conditions. 400 °C is the more suitable temperature for obtaining a high yield of naphtha with a high content of i‐paraffins.     

Hydrocracking of Fischer‐Tropsch Wax with Tungstovanadophosphoric Salts as Catalysts

The synthesis of liquid hydrocarbons from CO₂ and H₂, based on renewable energy and H₂O electrolysis, respectively, in a power‐to‐liquid process is a promising concept for the substitution of fossil fuels. Such a process is based on Fischer‐Tropsch synthesis followed by hydrocracking to convert waxy products into transportation fuels such as gasoline and diesel oil. Heteropolyacid cesium salts as catalysts show appropriate activity for hydrocracking, and the selectivity in cracking model hydrocarbons and Fischer‐Tropsch wax can be tuned by the vanadium content of the catalyst. Thermal stability and surface properties were investigated, and the catalysts are compared with a classical H‐Y‐type zeolite used for hydrocracking.     

Technological Applications of Zeolites in Catalysis

Abstract

Zeolites have been used as catalysts in industry since the early 1960s. The great majority of commercial applications employ one of three zeolite types: zeolite Y (faujasite); mordenite; ZSM-5. By far the largest use of zeolites is in catalytic cracking, and to a lesser extent in hydrocracking. Table 1 presents some data showing the commercial importance of this field [1]. The data are for United States refineries only and must be multiplied by a factor to arrive at worldwide use. Better than 90% of free-world cracking units now use zeolite catalysts. For many years it had been assumed that crystalline aluminosilicates with their uniform pore structure would make inferior catalysts to amorphous silica-slumina with a rather wide pore size distribution. The tremendous acid activity of hydrogen zeolites also was not recognized. Rabo and co-workers [2] showed at the 2nd International Congress on Catalysis that hydrogen exchanged faujasites possessed good isomerization ability, but commercial application in catalytic cracking became feasible only after Plank and Rosinsky at Socony-Mobil Oil Co. succeeded in stabilizing zeolite Y against steam and heat sintering by exchange with rare earth ions and by separating zeolite crystallites by incorporating them into a silica-alumina matrix which provided a heat reservoir along with some synergistic cracking effects. Modern cracking catalysts comprise 10–40% rare earth exchanged H-Y zeolite dispersed in a matrix of silica-alumina, semisynthetic clay, or natural clay.     

Translating clean liquid fuels synthesis with low aromatics over NaFe@C/HZSM-22 directly in CO2 hydrogenation

Fuel production is an option for valorizing CO₂, yet deficient catalysts meeting the standard fuel production has impeded progress of this promising technology. Herein, liquid fuel synthesis is rationalized over a catalyst consisting ‘C′, ‘Na’, and ‘Fe’, as in NaFe@C, configured with ZSM-22 and ZSM-5 in CO₂ hydrogenation. While the ‘Na’ and ‘C′ functioned as structural promoters on Fe to enhance CO₂ conversion and olefins synthesis, the characteristics of the zeolites facilitated oligomerization of lighter hydrocarbons. A high C₅ + selectivity was obtained over the HZSM-22 composite in CO₂ hydrogenation dominated by olefins and isoparaffins. Model reactions for exemplar oligomerization activity over the zeolites revealed ZSM-5 as highly active with selectivity towards isoparaffins and aromatic. The ‘Na’ cations induce Lewis’s acid sites (LAS) which suppresses hydrocracking during chain growth. This consistency, revealed between the model and CO₂ hydrogenation unlocks a door to zeolite usage in CO₂ hydrogenation to clean heavy hydrocarbons.     

Catalytic behavior of hybrid Co/SiO2-(medium-pore) zeolite catalysts during the one-stage conversion of syngas to gasoline

The catalytic properties of 10-MR (membered ring) zeolites (ZSM-5, MCM-22, IM-5, ITQ-2, all with a similar Si/Al ratio of ca. 15) in hybrid Co/SiO₂-zeolite catalysts for the direct conversion of syngas to mainly high-octane gasoline-range hydrocarbons has been studied under typical Fischer-Tropsch (FT) conditions: 250 °C, 2.0 MPa, and H₂/CO = 2. Special emphasis has been given to the deactivation behavior and the characterization of the amount and nature of the carbonaceous deposits formed by a combination of techniques (elemental analysis, TGA (thermogravimetric analyses), GC–MS, and DR (diffuse reflectance) UV–vis spectroscopy). The presence of the medium-pore zeolite increases the gasoline yield by about 20–50%, depending on the particular zeolite, and enhances the formation of branched products with respect to the base Co/SiO₂ catalyst, which is explained by the promotion of isomerization and cracking of long-chain (C₁₃₊) n-paraffins formed on the FT component. The initial zeolite activity is mostly determined by the surface acidity rather than by the total amount of Brønsted acid sites, pointing out to the existence of limitations for the diffusion of the long-chain n-paraffins through the 10-MR channels under FT conditions. Thus, ITQ-2 bearing the largest surface area presents the highest initial yield of branched gasoline-range products, followed by ZSM-5, IM-5, and MCM-22. All zeolites experience a loss of activity with TOS, particularly during the initial reaction stages. This deactivation is governed by the morphological and structural properties of the zeolite, which finally determine the amount and location of the coke species, and not by the acidity.     

The mechanism of catalytic cracking of n-alkenes on ZSM-5 zeolite

The catalytic cracking of n-alkenes on ZSM-5 zeolite at 405°C can occur both by a monomolecular mechanism and a bimolecular process. In the latter, cracking is preceeded by dimerization. We show that pentenes are cracked exclusively by the bimolecular process. The dominant cracking mechanism for n-hexenes also requires initial dimerization, although a small proportion (<19%) of the total cracking may proceed by a monomolecular process. Cracking of n-heptenes is predominantly monomolecular, with only 13% of the total occurring via an initial dimer formation. The cracking of n-octenes and n-nonenes can be interpreted by assuming a monomolecular mechanism only. Thus it appears that at 405°C olefins smaller than C₆ are stable with respect to direct cracking and must dimerize before a species is formed which is unstable enough to crack. No molecular hydrogen was produced in any of the cracking reactions reported here in the range of conversions studied.     

Crystal-size–dependent external surface diffusion barriers in Pt/ZSM-5 catalyzed n-pentane isomerization

Surface barriers persist in the molecular transport across external crystal surface of zeolites, which brings strong influences on zeolite catalysis. This study probes the role of crystal-size–dependent surface barriers in zeolite catalysis, with n-pentane isomerization catalyzed by Pt/ZSM-5 as a model reaction system. Chemical liquid deposition of SiO₂ is performed to reduce surface barriers on ZSM-5 crystals with different sizes. After SiO₂ deposition, surface barriers on both small (266 nm) and large (1304 nm) crystals are significantly reduced, while the improvement in catalytic activity for the large crystals (76.1%–129.1%) is much higher than that for the small ones (−17.4% to 16.7%). For the large ZSM-5 crystals, diffusion limitation is stronger, and thus the effect of surface barriers on catalytic activity is more important. This study reveals the unique role of crystal-size–dependent surface barriers in zeolite catalysis, and understanding this is important for the optimal design of zeolite catalysts.     

Novel Ni2P/zeolite catalysts for naphthalene hydrocracking to BTX

Ni₂P catalysts supported on ZSM-5, Beta, and USY zeolites were prepared by temperature-programmed reduction (TPR), applied for the hydrocracking of naphthalene, and characterized by BET, CO uptake, NH₃-TPD, TEM, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS). The catalytic activity was tested at 673 K and 3.0 MPa in a three-phase fixed bed reactor for hydrocracking of naphthalene. The Ni₂P/Beta exhibited best activity with a naphthalene conversion of 99%, and a BTX yield of 94.4%. Well-dispersed Ni₂P particles combined with moderate acidity and porosity of zeolite Beta contributed to the enhanced hydrocracking activity of naphthalene into BTX.     

Effect of process conditions on the composition of products in the conventional and deep catalytic cracking of oil fractions

With the purpose of increasing the yield of light C₂-C₄ olefins in comparison with that in conventional catalytic cracking, we experimentally study the effect of temperature and catalyst-to-oil ratio on the distribution of the basic products of oil catalytic cracking on the bizeolite and industrial LUX catalysts. The bizeolite catalyst contains ZSM-5 and ultrastable Y zeolites in equivalent amounts, while the LUX catalyst contains 18 wt % of Y zeolite in the HRE form. As shown by the results of our tests, the yield of C₂-C₄ olefins and gasoline in the deep catalytic cracking of hydrotreated vacuum gasoil on the bizeolite catalyst within a range of catalyst-to-oil ratios of 5–7 and temperatures of 540–560°C reaches 32–36 and nearly 30 wt %, respectively. In cracking on the LUX catalyst under similar conditions, the yield of light olefins and gasoline is 12–16 and 37–45 wt %, respectively. The distribution of target products in the deep catalytic cracking of different hydrocarbon fractions (vacuum gasoil, gas condensate, its fraction distilled from the cut boiling below 216°C, and the hydrocracking heavy residue) on the bizeolite catalyst is studied. It is shown that the fractions of gas condensate and hydroc-racking residue can serve as an additional source of hydrocarbon raw materials in the production of olefins.     

Conversion of vegetable oils under conditions of catalytic cracking

The effect of the composition of zeolite containing catalyst, the conditions of conducting the process, and the nature of oils on the distribution of target products during conversion under conditions of catalytic cracking is studied. The study is performed on bizeolite catalysts containing zeolites (ultrastable Y and ZSM-5 at different ratios) and on catalyst LUX containing18 wt % of zeolite Y in the HREY form. It is shown that the presence of zeolite ZSM-5 in the catalyst composition promotes the formation of olefines C₂–C₄. An increase in the severity of cracking process (elevated temperatures and catalyst: raw material ratios) improves the yield of gaseous products and coke with a simultaneous reduction in the yield of the gasoline fraction. The effect the nature of vegetable oils has is studied using the examples of palm, rapeseed, mustard, and sunflower oils. It is demonstrated that for the maximum yield of olefines C₂–C₄ and gasoline, we must use oils with elevated contents of saturated fatty acids. The regularities of the simultaneous cracking of sunflower oil and vacuum gas oil are studied. It is been found that upon simultaneous cracking, the total conversion of the mixed feedstock and yield of gasoline fraction increase; the maximum effect is attained with the addition of 3–10 wt % of vegetable oil.     

小晶粒ZSM-22的可控合成及其催化长链正构生物烷烃制航空煤油性能

由生物脱氧油制生物航空煤油具有较大应用潜力和发展前景,为了提高生物航煤的收率,开发性能更好的加氢裂化/异构化催化剂是关键。本文采用水热合成法,在低温陈化、加入晶种、提高合成凝胶的碱度或加入有机碱条件下,合成了平均c轴尺寸在100~330nm的小晶粒ZSM-22分子筛,进行了XRD、SEM、N₂物理吸附、NH₃-TPD和吡啶红外表征,并以生物质油加氢脱氧得到的长链正构生物烷烃为原料,考察了不同晶粒尺寸 ZSM-22催化剂催化裂化和异构化制生物航空煤油的性能。结果表明,通过提高碱度合成的小晶粒H-ZSM-22 具有较强的酸中心,较多可及的强B酸中心数量,其长链正构烷烃转化率可达80%以上。在此基础上,制备的Pt/ZSM-22催化剂具有较高的Pt分散度,表现出很好的加氢裂化/异构化性能,其长链正构烷烃的转化率高达97.79%,生物航煤收率达50.25%,航煤产物异正比为7.55。     

Structure, energetics and diffusion properties of isomers of trimethyl benzene in β zeolite: Uptake and Monte Carlo simulation study

A Monte Carlo study along with experimental uptake measurements of 1,2,3-trimethyl benzene, 1,2,4-trimethyl benzene and 1,3,5-trimethyl benzene (TMB) in β zeolite is reported. The TraPPE potential has been employed for hydrocarbon interaction and harmonic potential of Demontis for modeling framework of the zeolite. Structure, energetics and dynamics of TMB in zeolite β from Monte Carlo runs reveal interesting information about the diameter, properties of these isomers on confinement. Of the three isomers, 135TMB is supposed to have the largest diameter. It is seen TraPPE with Demontis potential predicts a restricted motion of 135TMB in the channels of zeolite β. Experimentally, 135TMB has the highest transport diffusivity whereas MD results suggest this has the lowest self diffusivity.     

Technological Applications of Zeolites in Catalysis

Zeolites have been used as catalysts in industry since the early 1960s. The great majority of commercial applications employ one of three zeolite types: zeolite Y (faujasite); mordenite; ZSM-5. By far the largest use of zeolites is in catalytic cracking, and to a lesser extent in hydrocracking. Table 1 presents some data showing the commercial importance of this field [1]. The data are for United States refineries only and must be multiplied by a factor to arrive at worldwide use. Better than 90% of free-world cracking units now use zeolite catalysts. For many years it had been assumed that crystalline aluminosilicates with their uniform pore structure would make inferior catalysts to amorphous silica-slumina with a rather wide pore size distribution. The tremendous acid activity of hydrogen zeolites also was not recognized. Rabo and co-workers [2] showed at the 2nd International Congress on Catalysis that hydrogen exchanged faujasites possessed good isomerization ability, but commercial application in catalytic cracking became feasible only after Plank and Rosinsky at Socony-Mobil Oil Co. succeeded in stabilizing zeolite Y against steam and heat sintering by exchange with rare earth ions and by separating zeolite crystallites by incorporating them into a silica-alumina matrix which provided a heat reservoir along with some synergistic cracking effects. Modern cracking catalysts comprise 10-40% rare earth exchanged H-Y zeolite dispersed in a matrix of silica-alumina, semisynthetic clay, or natural clay.     

Isobutane/2-butene alkylation on MCM-22 catalyst. Influence of zeolite structure and acidity on activity and selectivity

The catalytic behavior of the novel MCM-22 zeolite for the continuous alkylation of isobutane with 2-butene has been investigated at a temperature of 50°C, 2.5 MPa total pressure, and a variety of olefin space velocities. At high olefin conversions the MCM-22 zeolite showed a very high initial cracking activity attributable to strong Brønsted acid sites, as well as to the existence of strong diffusional restrictions of the TMP's (formed inside the zeolite) to exit through the channels. At short times on stream (TOS), TMP's account for ca. 40% of the C₈ fraction. The olefin conversion and the cracking activity rapidly decline with TOS, while the alkylate product became richer in dimethylhexenes, indicating a predominance of 2-butene dimerization and a loss of hydrogen transfer activity as the catalyst aged. Moreover, MCM-22 gives less TMP's than large-pore zeolites (USY, beta, mordenite), but more than the mediumpore ZSM-5 at similar 2-butene conversion. The latter catalyst was much more selective for olefin dimerization than for isobutane alkylation, presumably because formation of the bulkier TMP's was strongly impeded in its smaller pores.     

Comparison of cracking and hydrocraking of n-heptane on H-ZSM-5 catalysts

Acid catalyzed cracking and bifunctional cracking of n-heptane were investigated on HZSM-5 catalysts. At a reaction temperature of 543 K, the cracking on metal-free zeolite was found to be directly proportional to hydrogen partial pressure. Hydrogen influences the hydrogenation of product olefins and carbon deposits and therefore enhances the overall activity. Under the same conditions, in the presence of platinum, the hydrocracking rate reaches a maximum with increasing hydrogen partial pressure. The reaction can be formally described by a Langmuir Hinshewood mechanism: hydrogen is adsorbed on Pt in competition with hydrocarbons. The maximum reaction rate depends on a favourable ratio of the two adsorbed reactants. The energy of activation of hydrocracking was over 100 kJ/mol higher than that of acid cracking.     

Effect of Si/Al ratio on performance of Pt–Sn-based catalyst supported on ZSM-5 zeolite for n-butane conversion to light olefins

The performance of Pt–Sn-based catalyst, supported on ZSM-5 of different Si/Al ratios were investigated for simultaneous dehydrogenation and cracking of n-butane to produce light olefins. The catalysts were characterized by number of physio-chemical techniques including XRF, TEM, IR spectra, NH₃-TPD and O₂-pulse analysis. Increase in Si/Al ratio of zeolite support ZSM-5 significantly increased light olefin's selectivity, while feed conversion decreases due to lower acidity of support. The results indicated that both the n-butane cracking and dehydrogenation activity to light olefin's over Pt–Sn/ZSM-5 samples with increasing Si/Al ratios greatly enhanced catalytic performance. The catalysts were deactivated with time-on-stream due to the formation of carbon-containing deposits. A coke deposition was significantly related to catalyst activity, while at higher Si/Al ratio catalyst the coke precursors were depressed. These results suggested that the Pt–Sn/ZSM-5 catalyst of Si/Al ratio 300 is superior in achieving high total olefins selectivity (above 90 wt.%). The Pt–Sn/ZSM-5 also demonstrates resistance towards hydrothermal treatment, as analyzed through the three successive reaction-regeneration cycles.     

Characterization and application of a Pt/ZSM-5/SSMF catalyst for hydrocracking of paraffin wax

The microstructured Pt/ZSM-5/SSMF catalysts, for hydrocracking of paraffin wax, have been developed by impregnation method to place Pt onto thin-sheet ZSM-5/SSMF composites obtained by direct growth of ZSM-5 on the sinter-locked stainless steel microfibers (SSMF). The best catalyst is the one with ZSM-5 having a SiO₂/Al₂O₃ weight ratio of 200, delivering ~ 95% conversion with 77.5% selectivity to liquid products or 64.4% selectivity to naphtha at 280 °C. This new approach is capable of increasing the naphtha selectivity with high activity maintenance in comparison with the literature catalysts.