Polyethylene catalytic hydrocracking by PtHZSM‐5, PtHY,and PtHMCM‐41

The mechanisms involved in polyethylene catalytic hydrocracking are investigated by monitoring temperature‐dependent evolution profiles derived from mass spectra obtained while polymer/catalyst samples were heated at a constant rate. Repetitive injection gas chromatography/mass spectrometry (GC/MS) results are used to identify class‐specific fragment ions that represent paraffins, olefins, and alkyl aromatics. Class‐specific ion signals are used to generate isoconversion‐effective activation energy plots from which mechanistic comparisons are made. Studies using PtHZSM‐5, PtHY, and PtHMCM‐41 bifunctional solid acid catalysts in helium and hydrogen are reported. The effects of hydrogen on polyethylene cracking are dramatic and result in significant changes to isoconversion‐effective activation energies. Catalytic cracking mechanisms for the three catalysts are compared and differences are explained by a combination of pore size and acidity effects. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1293–1301, 2004     

Valorization by thermal cracking over silica of polyolefins dissolved in LCO

A study has been made of the cracking of polyethylene (PE) and polypropylene (PP) (which are the main components of post-consumer plastic wastes) dissolved in the Light Cycle Oil (LCO) product stream of a commercial Fluid Catalytic Cracking (FCC) unit. The cracking has been carried out on a mesoporous silica (pore size between 3 and 30 nm) in the 723–823 K range. This strategy for upgrading plastics and solvents together avoids heat transfer limitations and other problems inherent to the cracking of solid plastics. The polyolefins are transformed mainly into the components that make up the pool of gasoline (C₅–C₁₂). Furthermore, the incorporation of polyolefins has a synergistic effect on the cracking of LCO and causes a major decrease in the content of aromatics of the pool of gasoline and an increase in the content of olefins, paraffins and i-paraffins.     

Thermal and catalytic upgrading of a biomass‐derived oil in a dual reaction system

The thermal and catalytic upgrsding of bio‐oil to liquid fuels was studied at atmospheric pressure in a dual reactor system over HZSM‐5, silica‐alumina and a mixed catalyst containing HZSM‐5 and silica‐alumina. This bio‐oil was produced by the rapid thermal processing of the maple wood. In this work, the intent was to improve the catalyst life. Therefore, the first reactor containing no catalyst facilitated thermal cracking of blo‐oil whereas the second reactor containing the desired catalyst upgraded the thermally cracked products. The effects of process variables such as reaction temperature (350°C to 410°C), space velocity (1.8 to 7.2 h^?1) and catalyst type on the amounts and quality of organic liquid product (OLP) were investigated, In the case of HZSM‐5 catalyst, the yield of OLP was maximum at 27.2 wt% whereas the selectivity for aromatic hydrocarbons was maximum at 83 wt%. The selectivities towards aromatics and aliphatic hydrocarbons were highest for mixed and silica‐alumina catalysts, respectively. In all catalyst cases, maximum OLP was produced at an optimum reaction temperature of 370°C in both reactors, and at higher space velocity. The gaseous product consisted of CO and CO₂, and C₁‐C₆ hydrocarbons, which amounted to about 20 to 30 wt% of bio‐oil. The catalysts were deactivated due to coking and were regenerated to achieve their original activity.     

Reactions of cyclopentane on HY Zeolite

The reaction of cyclopentane has been studied on HY zeolite at 500°C. Initial reaction processes included ring cleavage to acyclic C₅ species, and cracking to produce fragments in the range C₁ - C₄. Hydrogen transfer accompanied those processes, so that paraffins as well as olefins were observed as initial products. Cyclopentene was formed as an unstable initial product by the dehydrogenation of the feed, although molecular hydrogen was not found as a primary product. Other dehydrogenated species initially formed included coke and aromatics in the range C₆ - C₁₀.     

Olefin production by cofeeding methanol and n‐butane: Kinetic modeling considering the deactivation of HZSM‐5 zeolite

The joint transformation of methanol and n‐butane fed into a fixed‐bed reactor on a HZSM‐5 zeolite catalyst has been studied under energy neutral conditions (methanol/n‐butane molar ratio of 3/1). The kinetic scheme of lumps proposed integrates the reaction steps corresponding to the individual reactions (cracking of n‐butane and MTO process at high‐temperature) and takes into account the synergies between the steps of both reactions. The deactivation by coke deposition has been quantified by an expression dependent on the concentration of the components in the reaction medium, which is evidence that oxygenates are the main coke precursors. The concentration of the components in the reaction medium (methanol, dimethyl ether, n‐butane, C₂? C₄ paraffins, C₂? C₄ olefins, C₅? C₁₀ lump, and methane) is satisfactorily calculated in a wide range of conditions (between 400 and 550°C, up to 9.5 (g of catalyst) h (mol CH₂)^?1 and with a time on stream of 5 h) by combining the equation of deactivation with the kinetic model of the main integrated process. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Chemical kinetic modeling of i‐butane and n‐butane catalytic cracking reactions over HZSM‐5 zeolite

A chemical kinetic model for i‐butane and n‐butane catalytic cracking over synthesized HZSM‐5 zeolite, with SiO₂/Al₂O₃ = 484, and in a plug flow reactor under various operating conditions, has been developed. To estimate the kinetic parameters of catalytic cracking reactions of i‐butane and n‐butane, a lump kinetic model consisting of six reaction steps and five lumped components is proposed. This kinetic model is based on mechanistic aspects of catalytic cracking of paraffins into olefins. Furthermore, our model takes into account the effects of both protolytic and bimolecular mechanisms. The Levenberg–Marquardt algorithm was used to estimate kinetic parameters. Results from statistical F‐tests indicate that the kinetic models and the proposed model predictions are in satisfactory agreement with the experimental data obtained for both paraffin reactants. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2456–2465, 2012     

Effects of HZSM-5 addition during catalytic cracking ofn-hexadecane on HY

Additions of HZSM-5 to HY during cracking ofn-hexadecane enhances formation of olefins in the range C₃–C₅, with concurrent suppression of hydrogen transfer processes. Ratios of branched to linear isomers are decreased for paraffins by addition of the pentasil, while the reverse is observed for olefinic products.     

Pools and Constraints in Methanol Conversion to Olefins and Fuels on Zeolite HZSM5

Large reserves of natural gas are causing high actual interest for olefins and automotive fuels via methanol conversion on zeolite HZSM5. The chemistry of this process involves spatial constraints in the zeolite pores and a set of reacting compounds hosted dynamically in the pores. The kinetic scheme of reactions in this pool regime is a matter of current debate––a problem being the complexity of product composition and its temporal changes. However, the multi-compound product composition, if measured accurately and even time-resolved––including the compounds retained in/on the catalyst––is a profound source of information. Methanol conversion has been studied with zeolite HZSM5 and zeolite HY accordingly. The pool mechanism has been developed further, specifically as depending on frustration for distinct reactions. Particular pools as for olefins or for gasoline are specified. Mechanism changes with reaction time and with reaction temperature are described, including the surprising phenomenon of reanimation and the mechanisms of catalyst deactivation.     

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     

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.     

Enhanced Production of C2–C4 Olefins Directly from Synthesis Gas

An attempt made for the selective production of C₂–C₄ olefins directly from the synthesis gas (CO + H₂) has led to the development of a dual catalyst system having a Fischer–Tropsch (K/Fe–Cu/AlOx) catalyst and cracking (H-ZSM-5) catalyst operate in consecutive dual reactors. The flow rate (space velocity) and H₂/CO molar ratio of the feed have been optimized for achieving higher CO conversions and olefin selectivities. The selectivity to C₂–C₄ olefins is further enhanced by optimizing the reaction temperature in the second reactor (cracking), where the product exhibited 51% selectivity to C₂–C₄ hydrocarbons rich in olefins (77%) with a stable time-on-stream performance in a studied period of 100 h.     

Ethylene polymerization with hybrid nickel diimine/Cp2TiCl2 catalyst: a new method to prepare blends of linear and branched polyethylene

Blends of linear polyethylene (LPE) and branched polyethylene (BPE) display very good mechanic properties that can be beneficial for various applications such as shear thinning and melt elasticity. LPE, BPE and amorphous polyethylene can be produced using nickel diimine (DMN) catalyst under various polymerization conditions, while LPE can be obtained using metallocene catalyst. Thus, LPE/BPE blends can be achieved by in situ polymerization using a hybrid DMN/metallocene catalyst. A novel hybrid catalyst made of DMN and Cp₂TiCl₂ was designed and used for ethylene polymerization. A synergistic effect of the two active sites in the hybrid DMN/metallocene catalyst was observed. Blends of linear and low branched polyethylene were synthesized when polymerization was conducted at low temperature (0 °C), while blends of linear and highly branched polyethylene were obtained at high temperature (50 °C). However, the miscibility of the polymers obtained at 50 °C was dramatically reduced as compared to those obtained at 0 °C. Mesoporous particles (MCM‐41) consisting of aluminosilicate with cylindrical pores were used to support the hybrid catalyst, in which MCM‐41 provides sufficient nanoscale pores to facilitate the polymerization in well‐controlled confined spaces. Blends of LPE and BPE were synthesized by in situ polymerization without adding comonomer and characterized. The miscibility of the polymer blends can be improved by supporting the hybrid catalyst on MCM‐41. Copyright © 2009 Society of Chemical Industry     

Catalytic Cracking of Heavy Olefins into Propylene, Ethylene and Other Light Olefins

Hybrid catalysts developed for the thermo-catalytic cracking of liquid hydrocarbons were found to be capable of cracking C₄ ⁺ olefins into light olefins with very high combined yields of product ethylene and propylene (more than 60 wt%) and C₂–C₄ olefins (more than 80 wt%) at 610–640 °C, and also with a propylene/ethylene weight ratio being much higher than 2.4. The olefins tested were heavier than butenes such as 1-hexene, C₁₀ ⁺ linear alpha-olefins (LAO) or a mixture of LAO. The hydrogen spillover effect promoted by the Ni bearing co-catalyst, contributed to significantly enhancing the product yield of light olefins and the on-stream stability of the hybrid catalyst.     

Catalytic hydrothermal liquefaction of D. tertiolecta for the production of bio‐oil over different acid/base catalysts

In this article, two acid catalysts (ZrO₂/SO₄^2? and HZSM‐5) and two base catalysts (MgO/MCM‐41 and KtB) were used in catalytic hydrothermal liquefaction (HTL) of Dunaliella tertiolecta (D. tertiolecta) for the production of bio‐oil. The results indicated that the acid/base property of the catalyst plays a crucial role in the catalytic HTL process, and the base catalyst is conducive to the improvement of conversion and bio‐oil yield. When KtB was used as the catalyst, the maximum conversion and bio‐oil yield was 94.84 and 49.09 wt %, respectively. The detailed compositional analysis of the bio‐oil was performed using thermogravimetric analysis, elemental analysis, FT‐IR, and GC‐MS. The compositional analysis results showed that the introduction of catalyst is beneficial for reducing the fixed carbon content in the bio‐oil, and the structure of catalyst influences on the bio‐oil composition and boiling point distribution. Based on our results and previous studies, the probable catalytic HTL microalgae model over various catalysts can be described that the main chemical reactions include ketonization, decarboxylic, dehydration, ammonolysis, and so forth. with HZSM‐5 and MgO/MCM‐41 as the catalyst; the cyclodimerization, decomposition, Maillard reaction, and ketonization are the main reactions with ZrO₂/SO₄^2? as the catalyst; the dehydration, ammonolysis, Maillard reaction, and ketonization can occur with KtB as the catalyst. Therefore, a plausible reaction mechanism of the main chemical component in D. tertiolecta is proposed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1118–1128, 2015     

A new catalytic process for high‐efficiency synthesis of p‐xylene by methylation of toluene with CH3Br

A new catalytic process for p‐xylene synthesis from the methylation of toluene with CH₃Br was proposed. CH₃Br was prepared from the catalytic bromination of natural gas (CH₄), by using H₂O + HBr + O₂ as mediator over supported Rh catalyst. The methylation conditions were investigated using HZSM‐5 or modified HZSM‐5 catalyst. Under optimal reaction conditions, p‐xylene selectivity is up to 93%, and p‐xylene yield is more than 21% at 673 k over the Si—P modified HZSM‐5 catalyst. Compared to the processes using MeOH or dimethyl carbonate (DMC) as methylation agent, this new process is very attractive in an economic standpoint since CH₄ is much cheaper than MeOH and DMC. In addition, the process has other advantages, such as mild reaction conditions, simple operation, high‐product yield, and so on. It is predicted that the process has good industrial potential for para‐xylene production. © 2012 American Institute of Chemical Engineers AIChE J, 59: 532–540, 2013     

Statistical Product Selectivity Modeling and Optimization for γ-Al2O3-Supported Cobalt Catalysts-Based Fischer–Tropsch Synthesis

The statistical selectivity models were developed for four different Fischer–Tropsch synthesis product range, including methane (CH₄), light olefins (C₂=C₄), light paraffins (C₂–C₄), and long-chain hydrocarbons (C₅₊), based on the experimental data obtained over thirteen γ-Al₂O₃ supported cobalt-based catalysts with different cobalt particle and pore sizes. The input variables consist of cobalt metal particle size and catalyst pore size. The cubic and quadratic polynomial equations were fitted to the experimental data, however, the mathematical models were subjected to model reduction for the enhancement of model adequacy, which was investigated through ANOVA. The multi-objective optimization revealed that the maximum C₅₊?selectivity (84.150%) could be achieved at the cobalt particle size and pore sizes of 14.764 and 23.129 nm, respectively, while keeping the selectivity to other hydrocarbon products minimum.

Graphic Abstract

     

Deactivation kinetics of a HZSM‐5 zeolite catalyst treated with alkali for the transformation of bio‐ethanol into hydrocarbons

The kinetics of deactivation by coke of a HZSM‐5 zeolite catalyst in the transformation of bioethanol into hydrocarbons has been studied. To attenuate deactivation, the following treatments have been carried out: (i) the zeolite has been subjected to a treatment with alkali to reduce the acid strength of the sites and (ii) it has subsequently been agglomerated into a macro and meso‐porous matrix of bentonite and alumina. The experimental study has been conducted in a fixed bed reactor under the following conditions: temperature, between 300 and 400°C; pressure, 1 atm; space‐time, up to 1.53 (g of catalyst) h (g of ethanol)^?1; particle size of the catalyst, between 0.3 and 0.6 mm; feed flowrate, 0.16 cm³ min^?1 of ethanol+water and 30 cm³ (NC) min^?1 of N₂; water content in the feed, up to 75 wt %; time on stream, up to 31 h. The expression for deactivation kinetics is dependent on the concentration of hydrocarbons and water in the reaction medium (which attenuates the deactivation) and, together with the kinetics at zero time on stream, allows the calculation of the evolution with time on stream of the yields and distribution of products (ethylene, propylene and butenes, C₁‐C₃ paraffins, and C₄‐C₁₂). By increasing the temperature in the 300–400°C range the role of ethylene on coke deposition is more significant than that of the other hydrocarbons (propylene, butenes and C₄‐C₁₂), which contribute to a greater extent to the formation of coke at 300°C. © 2011 American Institute of Chemical Engineers AIChE J, 58: 526–537, 2012.     

A ZSM-5-based Catalyst for Efficient Production of Light Olefins and Aromatics from Fluidized-bed Naphtha Catalytic Cracking

A ZSM-5-based catalyst was prepared by spray-dry method for fluidized-bed naphtha catalytic cracking. Multi-techniques, such as X-ray diffraction, scanning electron microscope, ²⁷Al MAS NMR, and NH₃–TPD, were employed for the investigation of ZSM-5 framework stability, framework dealumination, and catalyst acidity variation in hydrothermal treatment. Catalytic performances of fluidized-bed naphtha catalytic cracking at 630–680 °C indicated that light olefins and other value-added products could be more efficiently produced compared with the commercial process of thermal steam cracking. Long-term catalytic evaluation implied that naphtha catalytic cracking over the catalyst prepared with spray-dry method and hydrothermal treatment can be carried out at a variable reaction condition with a relatively high and stable light olefins yield.     

Characterization of Modified Nanoscale ZSM-5 Zeolite and Its Application in the Olefins Reduction in FCC Gasoline

Nanoscale HZSM-5 zeolite was hydrothermally treated with steam containing 0.8 wt% NH₃ at 773 K and then loaded with La₂O₃ and NiO. Both the parent nanoscale HZSM-5 and the modified nanoscale HZSM-5 zeolites catalysts were characterized by TEM, XRD, IR, NH₃-TPD and XRF, and then the performance of olefins reduction in fluidized catalytic cracking (FCC) gasoline over the modified nanoscale HZSM-5 zeolite catalyst was investigated. The IR and NH₃-TPD results showed that the amount of acids of the parent nanoscale HZSM-5 zeolite decreased after the combined modification, so did the strong acid sites deactivating catalysts. The stability of the catalyst was still satisfactory, though the initial activity decreased a little after the combined modification. The modification reduced the ability of aromatization of nanoscale HZSM-5 zeolite catalyst and increased its isomerization ability. After 300 h onstream, the average olefins content in the gasoline was reduced from 56.3 vol% to about 20 vol%, the aromatics (C₇–C₉ aromatics mainly) and paraffins contents in the product were increased from 11.6 vol% and 32.1 vol% to about 20 vol% and 60 vol% respectively. The ratio of i-paraffins/n-paraffins also increased from 3.2 to 6.6. The yield of gasoline was obtained at 97 wt%, while the Research Octane Number (RON) remained about 90.     

Conversion of isopropanol and mixed alcohols to hydrocarbons using HZSM‐5 catalyst in the MixAlco™ process. Part 2: Studies at 5000 kPa (abs)

This study employed HZSM‐5 (SiO₂/Al₂O₃ = 280 mol/mol) to produce hydrocarbons from reagent‐grade isopropanol and mixed alcohols made from lignocellulosic biomass (waste office paper and chicken manure) using the MixAlco? process. All studies were performed at P = 5000 kPa (abs). The experiments were conducted in two sets: (1) vary temperature (300–450°C) at weight hourly space velocity (WHSV) = 1.92 h^?1, and (2) vary WHSV (1.92–11.52 h^?1) at T = 370°C. For isopropanol at higher temperatures, the olefins undergo more cracking reactions to produce smaller molecules and more aromatics. At low temperatures, the molecules have less energy so they do not crack and therefore form larger molecules. At T = 300°C, the carbon distribution is bimodal at C9 and C12, which shows trimerization and tetramerization of propene. At 300°C, propene was the only gas produced, cracking did not occur and therefore preserved high‐molecular‐weight molecules. For mixed alcohols, higher temperatures show significant catalyst deactivation; however, isopropanol did not show any catalyst deactivation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1707–1715, 2016