Low-temperature Hydrocracking Research Articles

Enhanced hydroconversion of polyethylene via dual-functional catalysis: Exploiting ZSM-22 pore-mouth catalysis and Ru electronic effect

The subject of extensive research, the low-temperature hydrocracking of polyethylene reveals the one-step synthesis of iso-alkanes via metal–acid bifunctional catalysis as an emerging strategy. Zeolites, with their superior compatibility with existing petrochemical infrastructure, serve as the acidic supports of choice. In this research, Ru nanoparticles were loaded onto ZSM-22, a zeolite known for its effective pore-mouth catalysis. Mechanical ball milling enhanced the pore-mouth area and the proximity of metal–acid sites, significantly boosting the hydrocracking reaction. The electronic properties of Ru were modified by selecting various Ru precursors and adjusting loading amounts. In-situ infrared studies showed the detachment of olefin intermediates from Ru sites as a critical factor in controlling hydrocracking and the terminal hydrogenolysis reactions. By combining catalyst characterization with reaction barrier calculations from density functional theory (DFT), it was found that oxidized Ru species aid in the release of olefin intermediates, facilitating Brønsted acid-driven β-scission and isomerization reactions. The study achieved a liquid-phase yield exceeding 82 wt% and an iso/n ratio surpassing 60% under low-energy consumption conditions using commercially available catalysts.

Low-temperature selective transformation of diethylbenzene to isobutane and cyclohexanes via the interplay of Pt and acid centres in Pt/H-*BEA zeolites

The hydrocracking of aromatic hydrocarbons on bifunctional catalysts comprises parallel reactions that provide a wide distribution of products and byproducts. This work demonstrates on diethylbenzene (DEB) hydrotreatment that Pt/H-Al-rich *BEA zeolite catalysts can significantly reduce the hydrocracking temperature so that only the selected reaction mechanisms prevail in the process, providing high selectivity. The interplay of high activity of Pt clusters in hydrogenation/dehydrogenation and Brønsted acid sites in acid-catalysed reactions allows selective hydrocracking of DEB to isobutane and methylcyclopentane by the paring reaction at 200 °C. Low-temperature hydrocracking consists of hydrogenation of DEB to diethylcyclohexane, its rapid skeletal hydroisomerization to C10 branched alkylcycloalkanes followed by their A type β scission providing isobutane and methylcyclopentane with 80% selectivity at 68% DEB conversion, practically without subsequent reactions of the formed products. The reactive CC bond in tribranched alkylcycloalkanes selectively undergoes A type β scission, while more stable CC bonds in less or unbranched hydrocarbon chains or rings do not crack to a substantial extent at low temperatures. The study demonstrates that the low-temperature hydrotreatment of aromatics over highly active catalysts allows controlling the involvement of individual reaction mechanisms in the complex hydrocracking process and provides tailored selectivity.

Fabrication of single-walled carbon nanotubes in the channels of CoAPO-5 membrane by low-temperature hydrocracking

Abstract The defect-free CoAPO-5 membrane was fabricated on the porous α-Al2O3 substrate by using in-situ crystallization, and the prepared CoAPO-5 membrane was used as the template for the preparation of single-walled carbon nanotubes (SWCNTs) inside the liner channels (0.73 nm in diameter) by low-temperature hydrocracking, utilizing the organic precursor (tripropylamine) as the carbon source. The results of X-ray diffraction and scanning electron microscopy indicated that the synthesized membrane covered tightly on the α-Al2O3 substrate was 50 μm in thickness, which was composed of well-intergrown and randomly oriented CoAPO-5 molecular sieves. According to the characterization using high-resolution transmission electron microscopy, polarized Raman scattering and thermal-gravimetric analysis, 0.4 nm SWCNTs were synthesized inside the zeolitic channels of the CoAPO-5 membrane, and 45.47% tripropylamine were successfully converted into SWCNTs after hydrocracking for 12 h at 350 °C. On the basis of N2 adsorption/desorption isotherms for the CoAPO-5 molecular sieves and SWCNTs/CoAPO-5 composite material, it can be concluded that the fraction of channels not containing SWCNTs in the resulting SWCNTs/CoAPO-5 composite membrane is small. The results of single-component pervaporation demonstrate that the inter-crystal defects in the as-synthesized SWCNTs/CoAPO-5 composite membrane are negligible.

Influencing Factors on Formation of SWCNTs in the Channels of AFI Molecular Sieves by Low-temperature Hydrocracking

Influencing Factors on Formation of SWCNTs in the Channels of AFI Molecular Sieves by Low-temperature Hydrocracking

Formation mechanism of 0.4-nm single-walled carbon nanotubes in AlPO4-5 crystals by low-temperature hydrocracking

The carbonization mechanism of tripropylamine (TPA) in low-temperature hydrocracking was studied with the aim of increasing the quality and filling density of single-walled carbon nanotubes (SWCNTs) produced in the channels of AlPO4-5 crystals. The conversion process of TPA was investigated using a combination of Fourier transform infrared spectroscopy, mass spectrometry, 13C nuclear magnetic resonance spectroscopy, thermogravimetric analysis and micro-Raman spectroscopy at various hydrocracking temperatures. During the hydrocracking process, hydrogen participated in the cracking reaction of TPA and decreased the required activation energy. The protonated TPA converted into neutral TPA at 210 °C. When the hydrocracking temperature exceeded 260 °C, dipropylamine, n-propylamine, propylene, propane, ethane and methane were produced. The hydrocracking rate of TPA increased with increasing hydrocracking temperature. A small amount of aromatic compounds was also detected in the AlPO4-5 crystals hydrocracked at 280–350 °C; this amount decreased with increasing hydrocracking temperature. The content of residual TPA and amorphous carbon compounds in the AlPO4-5 crystals also decreased with increasing hydrocracking temperature. TPA decomposed completely after hydrocracking for 10 h at 350 °C. SWCNTs with a diameter of 0.4 nm were synthesized at 280–350 °C, and the filling density of SWCNTs increased with increasing hydrocracking temperature.

Importance of hydrogen for low-temperature detemplation of high-silica MFI zeolite crystals

Many attempts have been made for template removal from inorganic porous materials at mild temperature (below 350 °C), because high-temperature calcination is attributed as the trigger of the framework damages. In this study, a new two-step method, coupling by low-temperature hydrocracking and oxidation, is proposed for efficient removal of the organic templates in high-silica MFI zeolite crystals of different size at a mild temperature (300 °C). With this approach, unlike in conventional calcination above 400 °C, the pristine zeolite framework is preserved and no coke-like residues are formed, consistently verified by NMR, TGA, and Raman spectra. The reason for this phenomenon is proved as a special propyl-radical- mechanism in H2 atmosphere, indicated by GC measurement and analysis online. This provides an alternative option for the low-temperature detemplation of high-silica microporous materials.

Synthesis and Low-Temperature Detemplation of High-Silica MFI Zeolite Membranes

High-silica MFI zeolite membranes supported on porous a-alumina discs were prepared by a seeded secondary growth method, using tetrapropylammonium hydroxide (TPAOH) as organic template. First, nanocrystals were deposited on rough alpha-Al2O3 discs by a spin-on process. Then, based on controlling the H2O/Si molar ratio of the synthetic solution, a restricting in-plane hOh-oriented growth method with an ultra-dilute precursor was designed to prepare non-defective zeolite membranes that were as thin as possible. Finally, cross linked and dense MR zeolite membranes were prepared after the third synthesis step, giving a membrane layer thickness of about 8 mu m, including similar to 5 mu m dense layers and 3 pm intermediate layers. A novel, two-step method, coupling by low-temperature hydrocracking and oxidation, is proposed for efficient removal of the template from zeolite membranes. Compared with traditional high-temperature calcination, template removal by the two-step method could eliminate the grain boundary defects formed in response to stresses induced by heat treatment. As a result, the membranes treated by the two-step detemplation method displayed a preferable CO2/N-2 separation factor (about 5.2) and high CO2 permeance (5.8 x 10(-7) mol.m(-2).s(-1.)Pa(-1)) at 30 degrees C.

Single-walled carbon nanotubes prepared in small AlPO4-5 and CoAPO-5 molecular sieves by low-temperature hydrocracking

Single-walled carbon nanotubes (SWNTs) were prepared in the channels of small AlPO4-5 and cobalt-incorporated AlPO4-5 (CoAPO-5) crystals (4–6 μm in diameter and 10–30 μm in length), by hydrocracking at 350 °C. The effects of Co content in the precursor gel and carbon density of the structure-directing agent on the resulting SWNTs were investigated. The results of high-resolution transmission electron microscopy and polarized Raman scattering indicated that SWNTs formed in the channels of AlPO4-5 and CoAPO-5 crystals, after hydrocracking for 10 h at 350 °C. The SWNTs were 0.4 nm in diameter, and possessed well-defined symmetry. When the Co/Al ratio of the precursor gel was 0.075, the relative intensity ratio of Raman D to G band (ID/IG) was 0.286, and the weight loss (500–700 °C) of the SWNTs formed in CoAPO-5 was 3.27 wt%. This Co/Al ratio yielded the lowest obtained ID/IG value and the highest weight loss of SWNTs, which indicated the lowest amorphous carbon density and the highest SWNT quantity. The density and quantity of SWNTs in the AlPO4-5 crystals increased when the structure-directing agent was changed from triethylamine to tripropylamine, because of the higher carbon content of the latter's unit cell. Low-temperature hydrocracking can be used to prepare SWNTs in the channels of AlPO4-5 and CoAPO-5 crystals, even for small low-quality crystals.

TPAOH Template Removal from High-Silica ZSM-5 by Low-Temperature Hydrocracking

zeolite membranes, especially the mfi-type zeolite membranes, have attracted significant attention for decades because of their special properties. while organic templates such as tetrapropylammonium hydroxide (tpaoh) have typically been used for the synthesis of zsm-5 zeolite and zeolite membranes, the templates remain trapped in the as-synthesized zeolite crystals. a common method for removing organic templates and generating porous frameworks is calcination; however, during this process, the channel structure may be affected. in particular, for zsm-5 membranes, membrane defects may be produced and the separation efficiency therefore may decrease to some extent. in this study, the low-temperature hydrocracking of tpaoh in zsm-5 zeolite crystals was studied under h-2/n-2, while n-2 adsorption, thermogravimetric (tg) analysis, fourier transform infrared (ftir) spectroscopy, temperature-programmed desorption of ammonia (nh3-tpd), and raman spectroscopy were used to characterize zeolite samples. the results show that the organic template in the pores of zsm-5 can be effectively removed below 350 degrees c by low-temperature hydrocracking. characterization analyses by bet specific surface area, tg, ftir, and raman spectroscopy demonstrated that a reducing atmosphere containing h-2 was more conducive to template removal at low temperature than atmospheres of air or n-2. the degree of template removal increased with temperature increasing. the bet surface area of the crystal after hydrocracking at 280 degrees c reached 252 m(2).g(-1), although a small amount of organic residue remained. furthermore, after hydrocracking at 350 degrees c, the bet surface area reached 399 m(2).g(-1), and only trace amount of inorganic carbon residue remained. in addition, the introduction of hydrogen at low temperatures could prevent coke deposits on acid sites and thus zsm-5 zeolite crystals had greater numbers of acidic sites after low-temperature hydrocracking.

Selectivity of platinum–zirconia catalysts in n-paraffins hydroisomerisation process

Tungstated and sulphated zirconium hydroxides produced by MEL Chemicals were used as a raw material for preparation of n-paraffins hydroisomerisation catalysts. The preparation involved forming of zirconium hydroxides with peptised aluminium hydroxide, thermal treatment and impregnation of the obtained supports with platinum hexachloric acid solution. The obtained catalysts, 0.5 wt.% Pt/(SO 4/ZrO 2+Al 2O 3) and 0.5 wt.% Pt/(WO 3/ZrO 2+Al 2O 3) were tested in a continuous flow process of n-cetane hydroisomerisation. It was occurred, that the applied doped zirconium oxides are mesoporous materials of relatively low pore volume in comparison with other known support materials, mesopores consists ca 80% of the total pore volume and 65% of the specific surface area. Addition of the alumina binder in the support forming stage increased pore volume and specific surface area of the obtained supports, mainly in the range of the mesopores diameter size. We have stated that the sulphated zirconia–alumina based platinum catalyst is highly active, low temperature hydrocracking catalyst; it gives total conversion (hydrocracking) of the feed at temperature process below 200 °C. In our opinion the sulphated zirconia is not the suitable support component for the preparation of catalysts for hydroisomerisation of long chain hydrocarbons. The second of the prepared catalysts, the tungstated zirconia based one, is far more promising; it is less active but more selective in the n-paraffins hydroisomerisation process. Selection of the proper process parameters, hydrogen pressure and LHSV of the feed, makes it possible to attain 50–60% conversion with almost 90% hydroisomerisation selectivity. Products of hydrocracking (C 5–C 13 hydrocarbons) obtained at low conversion level (e.g. 28%) are mainly linear isomers (70%), but the increase in the conversion level up to 60–70% causes that products of hydrocracking were mainly branched isomers (≈80%).

Low temperature hydrocracking of n-heptane over Ni-supported catalysts: study of global kinetics

Two kinetic models were applied to n-heptane hydrocracking on a Ni-Re/ZSM-5 catalyst over a wide range of operating experimental conditions (temperature=433–493 K, and pressure=760 mm Hg). In the first model, the hydrogen is adsorbed on the catalyst surface without dissociation, while the second model assumes hydrogen dissociation. Both models assume that the adsorption follows Langmuir isotherm. The molecular hydrogen associated with an active site is most likely involved in the CC bond rupture, which is concluded to be the rate controlling step in this work. The extracted intrinsic kinetics were estimated via the derivation of the reactor model. The apparent activation energy for n-heptane cracking is found to be 83 kJ/mol. Both models describe well the n-heptane consumption rate. The simulation results revealed that the hydrogen adsorption constant is smaller than the n-heptane adsorption constant.

Low temperature hydrocracking of hydrocarbons on Ni-supported catalysts

Metal vapor method was employed to design a new method for preparation of nickel-containing supported catalysts on different metal oxides such as Al 2O 3, MgO, ZSM-5. The activation of carbon–carbon bonds in some n-alkanes and cycloalkanes was investigated. Results have shown that these catalysts retained very high activity, selectivity and stability toward hydrocracking and isomerization of hydrocarbons. Since metal vapor method yielded metal particles in a highly dispersed state, these particles were unique and demonstrated considerable decrease in the cleavage temperature of C–C bonds in hydrocarbons. The most significant difference was observed in the presence of bimetallic Ni–Re/ZSM-5 catalyst: it caused almost complete conversion of tested hydrocarbons at 463–493 K under normal pressure. n-Heptane could be converted virtually to isobutane and propane only. Hydrocracking of high alkanes (C 16) on these catalysts produced high liquid products and lower gas products.

The Role of Ion Exchange Method of Na-ZSM-5 Zeolite and Influence Hydrogenation Components on Properties and Activity of Dewaxing Catalysts

Hydrocracking of n-hexane and diesel oil fraction over presulfided NiMo, Mo and Ni catalysts has been carried out using a high pressure flow reactor system. The ion-exchanged form of ZSM-5 extrudates (50% alumina binder) was loaded with 2-20 wt.% of metals. The results indicate that, using Ni/H-ZSM-5 zeolite obtained by incorporation of nickel by ion exchange treatment of NH4-ZSM-5 from nickel nitrate solution, it is possible to obtain sufficiently active catalysts for low-temperature hydrocracking process. The catalysts containing Ni-ZSM-5 zeolites (Ni/H-ZSM-5 or Ni/Na-ZSM-5) were superior to catalyst prepared by using P/H-ZSM-5. It was found that nickel was an essential hydrogenation components of low temperature hydrocracking catalysts.