Suppression Of Coke Formation Research Articles

Partial upgrading of heavy oils by catalytic aquathermal visbreaking with dispersed iron oxide catalysts

The impact of water and red mud-like Fe oxide catalysts on aquavisbreaking (AVB) of heavy-oils was studied under various circumstances. Vacuum residue (VR) was employed as a good substitute for low-viscous bitumen grades. The reaction products were separated into SARA fractions using open-column liquid chromatography (OCLC), and boiling point groups were classified using thermogravimetric analysis (TGA). In addition, Fourier-transform infrared (FTIR) spectroscopy was used to study the structural features of VR and its derivatives. It was observed that the thermal visbreaking of VR led to a severe coke formation with asphaltene (ASP) to coke selectivity over 130 %, while the addition of water and Fe catalyst could increase the conversion of ASP to liquid oil products while inhibiting coke formation, resulting in improved conversion of ASP. Furthermore, the structural properties of spent catalysts recovered after reactions were analyzed using X-ray absorption near edge structure (XANES) and X-ray diffraction (XRD) to identify the active phase, confirming that the Fe precursor is converted to a 20–30 nm Fe2O3 and Fe3O4 during VR AVB. Moreover, the addition of carbon additives to AVB further improved the dispersion of ASP and catalyst particles, contributing to the decrease of the selectivity for ASP conversion to coke by 50 %.

Photothermal Dry Reforming of Methane on Yolk‐Shell Co–Ni Alloy@SiO2 Catalyst

Photothermal dry reforming of methane (PT‐DRM) is an appealing pathway to convert carbon dioxide and methane into synthesis gas, a mixture of carbon monoxide and hydrogen, via photothermal heating induced by concentrated sunlight. Coke formation and sintering of active metal nanoparticles, however, are a key issue for catalyst stability. In the present study, we demonstrated Co–Ni alloy nanoparticles encapsulated with a porous SiO2 shell exhibited improved catalytic activity and stability for PT‐DRM using visible/near‐IR light irradiation without any other external heating. The addition of a trace amount of Co (1–5 mol% relative to total metal) and SiO2 encapsulation enhanced the stability by simultaneously suppressing coke formation and sintering of the metal nanoparticles. Furthermore, we revealed that the position of the light irradiation spot has a crucial role in the conversions of methane and carbon dioxide and product selectivity, presumably due to large temperature gradient under the light irradiation. These findings would contribute to designing for effective PT‐DRM catalysts with improved activity and enhanced resistance for both coke formation and sintering and emphasize the significant contribution of the temperature gradients to the performance in PT‐DRM.

Fluoride-Treated Nano-HZSM-5 Zeolite as a Highly Stable Catalyst for the Conversion of Bioethanol to Propylene.

Fluoride treatment of ZSM-5 zeolite can effectively adjust surface acidity and generate a secondary pore structure. In this study, a series of modified nano-HZSM-5 zeolites were prepared by NH4F-HF mixed solution treatment and applied to the selective conversion of bioethanol to propylene at 500 °C, atmospheric pressure, and a WHSV of 10 h-1. The results showed that NH4F-HF modification weakened the surface acidity of nano-HZSM-5 zeolites, thus inhibiting coke formation. Additionally, the mesopores in the nano-HZSM-5 zeolites increased after NH4F-HF treatment, thereby enhancing the mass transfer rate and improving the coke-resistance ability. The NH4F-HF mixed solution modification significantly improved the stability of nano-HZSM-5 zeolites in catalyzing bioethanol to propylene and greatly extended the working life of nano-HZSM-5 zeolites. It can be seen from the characterization of the deactivated catalysts that coke deposition and weakening of acidity may be the key factors for catalyst deactivation.

Effect of active site size in dispersed MoS2 nanocatalysts on slurry-phase hydrocracking of residue

This work investigates the influence of active site size in dispersed MoS2 on the slurry-phase hydrocracking of Merey residue (MRR). MoS2 nanocatalysts with varying morphologies were synthesized using the ligand sulfurization method, employing molybdenum oleate as the Mo precursor. The results demonstrate that mono-layered or double-layered MoS2 plates with slab sizes of 3 ∼ 10 nm can be synthesized at a sulfurization temperature of 400 °C and a sulfurization time of 0.5 h. Prolonged sulfurization time results in the growth and agglomeration of MoS2 plates, leading to multi-layered slabs with increased length and larger particle size, as well as a wider distribution range. The MoS2-0.5 (prepared with a sulfurization time of 0.5 h) exhibits superior hydrocracking activity, effectively converting resin and asphaltene into light fractions and significantly suppressing coke formation. Specifically, the conversion rates of resin and asphaltene are 51.3 wt% and 92.1 wt%, respectively, with the minimal coke yield of 0.6 wt% under conditions of 430 °C, 1 h, 7 MPa initial H2, and a catalyst dosage of 500 μg/g. The catalytic activity of the MoS2 nanocatalysts exhibits a strong correlation with their size and morphology obtained at different sulfurization times. Density functional theory (DFT) calculations reveal that MoS2 with smaller slab sizes are more beneficial for the adsorption and dissociation of H2, due to higher adsorption energy (Eads) and lower activation barrier (Ea). This facilitates the generation of sufficient active hydrogen to encourage the hydrocracking of residue and suppress coke formation.

Preparation of presulfided oil-soluble NiMo catalyst for slurry bed hydrocracking of vacuum residue

Here, a method is proposed for constructing presulfided oil-soluble NiMo catalysts using tetrathiomolybdate nickel ammonium as a precursor via a chelating ligand exchange strategy. Leveraging the close chemical bonding between Ni and Mo atoms, the NiMo catalyst can undergo in-situ self-sulfidation to generate active NiMoS sites and a composite structure of Ni3S2 and MoS2 nano phase in tight contact, thus exhibiting strong synergistic effects. The NiMo catalyst exhibited outstanding performance in hydrocracking of vacuum residue (VR) achieving a 64.7 wt% VR conversion while maintaining a coke yield of 0.51 wt%, as well as the excellent hydrogenation activity of polycyclic aromatic hydrocarbons. Combined with density functional theory calculations, it was further revealed that the presence of Ni reduces the energy barrier for H2 dissociation on MoS2, thereby enhancing the hydrogenation activity of the catalyst and its ability to suppress coke formation. This work validates the efficient bimetallic synergistic catalytic effect of presulfided oil-soluble NiMo catalysts in the slurry bed hydrocracking process.

Enhanced coke resistant Ni/SiO2@SiO2 core–shell nanostructured catalysts for dry reforming of methane: Effect of metal-support interaction and SiO2 shell

Suppressing coke formation on nickel-based catalysts used in methane-dry reforming is one of the most important issues. We investigate the effect of nickel metal-support interaction and outer porous silica shells on the coke formation in methane dry reforming over Ni/SiO2@SiO2 core–shell catalysts. Using a simple ammonia evaporation method, the Ni/SiO2_AE catalyst, which has highly dispersed nickel nanoparticles with ca. 7 nm, was synthesized and coated with an outer porous silica shell to produce a Ni/SiO2_AE/SiO2 core shell catalyst. Based on the TEM and N2 isotherm results, a 20 nm thick SiO2 shell having pores with a size of about 2 nm was uniformly coated on the Ni/SiO2_AE catalyst. H2-TPR, and XPS analysis results suggest that the Ni/SiO2_AE and Ni/SiO2_AE@SiO2 catalysts have high nickel dispersion. This high dispersion is due to strong metal-support interactions and the formation of Ni phyllosilicate species. On the other hand, the ones synthesized by wet impregnation method have low nickel dispersion due to weaker metal-support interactions. The Ni/SiO2_AE@SiO2 core–shell catalyst showed stable catalytic activity under methane dry reforming conditions at 600 °C. On the other hand, the Ni/SiO2_WI and Ni/SiO2_AE catalysts showed rapid deactivation due to severe coke formation. It can be concluded that the strong metal-support interaction and the silica shell can suppress catalyst deactivation caused by coke formation very effectively.

Leaching char with acidic aqueous phase from biomass pyrolysis: Valorization of the leachate via catalytic hydrothermal gasification

Aqueous phase of bio-oil (APB) is a general stream of waste produced from biomass pyrolysis and fractional condensation of pyrolytic volatiles and has very limited applications. We have demonstrated a sequence of leaching of alkali and alkaline earth metallic species (AAEMs) from char and catalytic hydrothermal gasification (CHTG) for valorizing char and APB, respectively. The majority of AAEMs can be removed from the char by leaching with APB and the removal rates were almost equivalent to those leached with HCl (1.0 M). CHTG of an aqueous solution of the spent APB with a total organic carbon of 14,450 ppm was performed in a continuous flow reactor, employing an activated carbon-supported Ru catalyst (Ru loading, 4.6 wt%). The catalyst exhibited a stable activity for carbon conversion of 98.8 % at 350 °C for at least 360 min while gaseous product consisting of H2, CH4, and CO2 was produced with a cold gas efficiency of 101–103 %, on a higher heating value basis. The cold gas efficiency exceeding 100 % is mainly because of the generation of H2 from water through water-gas shift reaction. The CHTG performance of APB was enhanced by char leaching through the uptake of coke-forming precursors of APB onto char and the enrichment of AAEMs in the spent APB. These AAEMs played roles in suppressing coke formation and deposition onto the catalyst and maintaining Ru particle size by providing a less acidic hydrothermal environment.

Dry reforming of methane over embedded Ni nanoparticles in CeZrO2: Effect of Ce/Zr ratio and H2O addition

Biogas has emerged as renewable source of CH4 towards energy decarbonization in recent years. Among the biogas valorization routes, the dry reforming of methane (DRM) process is particularly interesting for H2 production. However, the development of new catalysts with high metal dispersion and coke resistance is a significant challenge, particularly under industrial condition. Therefore, this work studies the performance of Ni@CexZr1-xO2 catalysts with different Ce/Zr molar ratios for the dry reforming and bi-reforming of methane reactions. The addition of Zr promotes the Ni dispersion and the oxygen mobility of the support, leading to enhanced resistance to coke formation. Additionally, H2O suppresses coke formation under high CH4/CO2 molar ratio, but catalyst deactivation is still observed. Finally, an optimal Ce/Zr molar ratio (i.e., 4.0) is achieved, demonstrating remarkable resistance to coke formation and high CH4 and CO2 conversion rates through the control of Ni particle size and the promotion of oxygen mobility.

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling

AbstractCatalytic upcycling of polyolefins into high‐value chemicals represents the direction in end‐of‐life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM‐5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre‐cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1‐C7) are produced with a yield of 443 mmol gZSM‐5−1, where 74.3 % of them are C3‐C6 olefins, much superior to ZSM‐5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling.

Catalytic upcycling of polyolefins into high-value chemicals represents the direction in end-of-life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM-5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre-cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1-C7) are produced with a yield of 443 mmol gZSM-5 -1, where 74.3 % of them are C3-C6 olefins, much superior to ZSM-5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Hydroxyl radical-regulated crystallization of hierarchical H-ZSM-5 at low temperatures for palm oil conversion into high aromatic green gasoline

Biofuel is a sustainable fuel that is more environmentally friendly. Common biofuel processing is pyrolysis, which requires high energy. The use of appropriate catalysts can reduce the activation energy and increase product selectivity. H-ZSM-5 has excellent characteristics as a catalyst. However, hierarchical H-ZSM-5 has better characteristics because catalyst deactivation can be minimized and substrate diffusion increased. Generally, the H-ZSM-5 crystallization rate is relatively slow; in this research, OH radicals (OH) have successfully increased the crystallization rate of hierarchical H-ZSM-5. A successful synthesis of H-ZSM-5 was confirmed based on FTIR spectra and XRD diffractogram, which showed characteristic peaks in H-ZSM-5 for both TR-3 (H-ZSM-5 synthesized using OH for three days) and TN-3 (H-ZSM-5 synthesized without OH for three days). The use of OH shows an increase in the rate constant up to 3 times, producing highly crystalline TR-3. The use of OH also affected the morphology of H-ZSM-5, where TR-3 crystals tended to be more spheric with a larger size than TN-3. Porosity analysis showed higher porosity and better mesoporous features, where SBET increased from 309 to 373 m2/g, and Sext increased from 226 to 237 m2/g. This gave good effects on the catalytic ability of TR-3 compared to TN-3 by increasing gasoline yield in palm oil cracking from 35.91 wt% to 38.82 wt%, while the enhancement of the mesoporous features successfully inhibiting coke formation on the catalyst from 3.23 wt% becomes 2.02 wt% so that catalyst deactivation can be minimized.

Hydrothermally synthesized tremella-like monometallic Ni/SiO2 for effective and stable dry reforming of methane (DRM) to syngas

Despite its activity, monometallic Ni-catalyst is highly susceptible to coke deposition and sintering in catalyzing dry reforming of methane (DRM). To counter these, a novel tremella-like monometallic Ni/SiO2 catalyst was hydrothermally synthesized herein, realizing excellent activity, outstanding coke inhibition and robust structural stability for a durable DRM reaction. Functionality-speaking, the tapered ends of Ni-petals, sized at 8–15 nm, permit high DRM activity with suppressed coke formation while its thicker base spatially prevents Ni-sintering during high temperature reaction. Meanwhile, the open structure of catalyst resulting from such tremella-like structure also enhances the diffusion of reactants/products gas to/from catalytic surface, thus augmenting its activity for DRM. With merely 5 wt% Ni incorporated, CO2 and CH4 conversions of ∼90% could be attained with only ∼15% activity drop after 75 h of DRM. Full-restoration of activity could facilely be attained using 90 min in-situ oxidative regeneration. Mechanistic study coupling sorptive investigation, ex-situ XRD, and SEM reveals the pronounced adsorption tendency of CH4 over those of CO2, H2 and CO, confirming the adherence of DRM to Eley-Rideal reaction model in current study. Significantly, this study provides a new morphological-controlled strategy to conveniently impart excellent coke-inhibiting and sintering-resisting capability to monometallic Ni-catalyst.

Alkaline-earth ion stabilized sub-nano-platinum tin clusters for propane dehydrogenation.

The strong promotion effects of alkali/alkaline earth metals are frequently reported for heterogeneous catalytic processes such as propane dehydrogenation (PDH), but their functioning principles remain elusive. This paper describes the effect of the addition of calcium (Ca) on reducing the deactivation rate of platinum-tin (Pt-Sn) catalyzed PDH from 0.04 h-1 to 0.0098 h-1 at 873 K under a WHSV of 16.5 h-1 of propane. The Pt-Sn-Ca catalyst shows a high propylene selectivity of >96% with a propylene production rate of 41 molC3H6 (gPt h)-1 and ∼1% activity loss after regeneration. The combination of characterization and DFT simulations reveals that Ca acts as a structural promoter favoring the transition of Snn+ in the parent catalyst to Sn0 during reduction, and the latter is an electron donor that increases the electron density of Pt. This greatly suppresses coke formation from deep dehydrogenation. Moreover, it was found that Ca promotes the formation of a highly reactive and sintering-resistant sub-nano Pt-Sn alloy with a diameter of approximately 0.8 nm. These lead to high activity and selectivity for the Pt-Sn-Ca catalyst for PDH.

Design of MoS2 edge-anchored single-atom catalysts for propane dehydrogenation driven by DFT and microkinetic modeling.

The design of efficient catalysts for direct propane dehydrogenation (PDH) to inhibit coke formation and deactivation of traditional Pt-based catalysts are challenging tasks. Herein, by exploiting the unique geometric feature and tunability of single atom catalysts (SACs), a wide range of 3d-5d transition metals anchored on the MoS2 edge in the single atom form (TM1-S4/edge) are comprehensively investigated for the PDH application by first-principles calculations, ab initio molecular dynamics (AIMD) simulations and microkinetic modeling. Five criteria are assessed in terms of the feasibility of preparation, practical stability, feasibility of recovery after air oxidation, activity and selectivity. We identified Ru1-S4/edge SAC as the most promising candidate with activity six times higher than that of the conventional Pt(111) catalyst. Interestingly, AIMD simulations show that the motif region of the highly reactive TM1-S4/edge SACs (such as Ru, Os, Rh, and Ir) exhibits a dynamic change, with a TM-coordinated S atom tending to flutter at reaction temperatures and return to its initial position when the species is adsorbed on TMs, thereby affecting the PDH activities. In addition to identifying the potential PDH catalyst from a practical application point of view, we believe that this study also provides a comprehensive picture for the theoretical screening of low-coordination single-atom catalysts.

CO2-assisted propane dehydrogenation to aromatics over copper modified Ga-MFI catalysts

The acidity and Ga-species status in the zeolite play a crucial role in the CO2-assisted propane dehydroaromatization (CO2-PDA). In this work, a copper modified Ga-MFI zeolite (Cu/Ga-MFI) with well dispersed framework Ga species was fabricated. A remarkable aromatics selectivity of 73% at propane conversion of 93.6% was achieved on Cu/Ga-MFI catalyst. The Ga atoms in MFI framework can create a moderate acid strength, while the introduced Cu provide an appropriate Brønsted/Lewis acid distribution, enhancing the synergy between metal-related species and the zeolite. Besides, DFT results indicate that the acid sites in Ga-MFI are more preferable for the dehydrogenation of propane instead of the C-C cleavage. Moreover, CO2 can inhibit coke formation through reverse Boudouard and reverse water gas shift reaction, which endows Cu/Ga-MFI catalyst with superior anti-coking ability and regeneration stability. This work provides a novel approach for designing catalysts with high activity, aromatics selectivity, and stability for CO2-PDA reactions.

Highly efficient steam reforming of biomass tar model compound using a high-entropy alloy-based structured catalyst

The development of efficient Ni-based catalysts for steam reforming of biomass tar is crucial for the widespread application of biomass gasification. Multimetal high-entropy alloys (HEAs) have emerged as promising catalysts that can potentially replace conventional metallic materials in various applications. In this study, we investigate NiFeCoMnCu-HEA catalysts supported on the surface of wood carbon (WC) for highly efficient steam reforming of toluene, a model compound for biomass tar. The synergistic effect between Ni and the other four metals in the HEA composition inhibits coke formation during the reaction process, while the appropriate mole ratio of Ni: (Fe + Co + Mn + Cu) reduces the particle size of HEA nanoparticles. Furthermore, the unique structure of wood carbon, with its long, interconnected, yet distorted microchannels, enhances the dispersion of active sites and improves mass transfer efficiency. As a result, the NiFeCoMnCu-HEAs/WC catalyst exhibits outstanding catalytic activity, achieving over 95% toluene conversion for 48 h at 650 °C. This performance surpasses that of the compared catalysts prepared in this work, namely NiFeCoMn/WC (39%), NiFeCoCu/WC (31%), and NiFeCo/WC (20%), underscoring the significance of the HEA structure. The findings also offer valuable insights into enhancing the performance of other nanostructures in the steam reforming of biomass tar.

HZSM-5 zeolites undergoing the high-temperature process for boosting the bimolecular reaction in n-heptane catalytic cracking

High-temperature treatment is key to the preparation of zeolite catalysts. Herein, the effects of high-temperature treatment on the property and performance of HZSM-5 zeolites were studied in this work. XRD, N2 physisorption, 27Al MAS NMR, and NH3-TPD results indicated that the high-temperature treatment at 650 °C hardly affected the inherent crystal and texture of HZSM-5 zeolites, but facilitated the conversion of framework Al to extra-framework Al, reducing the acid site and enhancing the acid strength. Moreover, the high-temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking, promoting the conversion and light olefins yield while inhibiting coke formation. Based on the kinetic and mechanism analysis, the improvement of HZSM-5 performance caused by high-temperature treatment has been attributed to the formation of extra-framework Al, which enhanced the acid strength, facilitated the bimolecular reaction, and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking.

Synergistic effect of macroporosity and crystallinity on catalyst deactivation behavior over macroporous Ni/CexZr1-xO2–Al2O3 for dry reforming of methane

Dry reforming of methane (DRM) is an outstanding process for transforming methane and carbon dioxide into synthesis gases (H2 and CO). In this study, a special geometrical modification on Ni/CexZr1-xO2–Al2O3 catalyst was applied by introducing a macroporous structure into the support to accelerate the metal support interaction that optimized the distribution of the active sites over the catalyst. Furthermore, we investigated a synergistic effect of the macroporosity and CexZr1-xO2 (CZ) crystallinity over the Ni/CexZr1-xO2–Al2O3 catalyst on its catalytic performance in DRM. Macroporous Ni/CexZr1-xO2–Al2O3 catalysts were prepared via washing (Ni-MaCZA-W) and hydrothermal (Ni-MaCZA-H) methods. Non-macroporous Ni-CZA-H with crystalline CZ was prepared for comparison. The crystalline CZ over macroporous Ni-MaCZA-H had a strong interaction with Ni due to easy accessibility of Ni species to CZ in the macroporous support, resulting in highly dispersed Ni nanoparticles and abundant oxygen vacancies. The unique properties of Ni-MaCZA-H increased catalytic activity and stability in DRM, suppressing coke formation via efficient coke gasification. The Ni species and amorphous CZ over Ni-MaCZA-W resulted in a bimodal Ni size distribution and fast catalyst deactivation. However, even though the crystalline CZ over Ni-CZA-H generated a unimodal distribution of Ni nanoparticles, the non-macroporous Ni-CZA-H resulted in gradual deactivation in the catalytic activity and the production of a different type of coke.

Dry reforming of methane over gallium-based supported catalytically active liquid metal solutions

Gallium-rich supported catalytically active liquid metal solutions (SCALMS) were recently introduced as a new way towards heterogeneous single atom catalysis. SCALMS were demonstrated to exhibit a certain resistance against coking during the dehydrogenation of alkanes using Ga-rich alloys of noble metals. Here, the conceptual catalytic application of SCALMS in dry reforming of methane (DRM) is tested with non-noble metal (Co, Cu, Fe, Ni) atoms in the gallium-rich liquid alloy. This study introduces SCALMS to high-temperature applications and an oxidative reaction environment. Most catalysts were shown to undergo severe oxidation during DRM, while Ga-Ni SCALMS retained a certain level of activity. This observation is explained by a kinetically controlled redox process, namely oxidation to gallium oxide species and re-reduction via H2 activation over Ni. Consequentially, this redox process can be shifted to the metallic side when using increasing concentrations of Ni in Ga, which strongly suppresses coke formation. Density-functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations were performed to confirm the increased availability of Ni at the liquid alloy-gas interface. However, leaching of gallium via the formation of volatile oxidic species during the hypothesised redox cycles was identified indicating a critical instability of Ga-Ni SCALMS for prolonged test durations.

Comparative study of single- and two-stage slurry-phase catalytic hydrocracking of vacuum residue for selective conversion of heavy oil

The selective conversion of asphaltenes to light products while inhibiting coke formation is the most challenging in the heavy oil upgrading process. Herein, single- and two-stage slurry-phase catalytic hydrocracking of vacuum residue (VR) at various reaction temperatures (350–430 °C) were performed to elucidate the advantages of low temperature conditions and the synergistic effect of two-stage operation on asphaltene conversion. Despite the slow reaction rate at a low reaction temperature, almost no coke was produced, and the selective conversion of asphaltene to deasphalted oil (DAO) was improved with a large amount of H2 consumption. To overcome the low reaction rates at low temperatures, catalytic hydrocracking was performed at two-stage temperatures (380 and 430 °C). Two-stage catalytic hydrocracking showed a synergistic effect of suppressing coke formation while maintaining an enhanced reaction rate compared to single-stage catalytic hydrocracking. This is because the first stage of hydrocracking at 380 °C facilitates the saturation of heavy polyaromatic molecules, which can easily crack in the second stage at 430 °C. However, because two-stage hydrocracking requires a slightly longer reaction time than single-stage hydrocracking to achieve the same conversion, the efficiency of asphaltene conversion must be considered by setting appropriate operating conditions.