Suppression Of Coke Formation Research Articles

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.

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.

Performance and synergistic effect of oil-coal co-hydrogenation with hydrogen-donor solvent enhancement

The synergistic effect of oil-coal co-hydrogenation and the relationship between H2 consumption and hydrogenation performance of heavy oil and low-rank coal were investigated. The feasibility of oil-coal co-hydrogenation with hydrogen-donor solvent (HDS) enhancement was studied. Results show a matching between the hydrogenation of CG residue and HS coal. H2 consumption is closely related to the severity of reaction, and positively related to the conversion of raw material and oil yield, which could be an essential index for evaluating and predicting the effectiveness of hydrogenation reactions. HDS, rich in partially hydrogenated polycyclic aromatic hydrocarbons, can enhance the synergistic effect of oil-coal co-hydrogenation, effectively inhibit coke formation and improve product distribution because of its ability to supply and transfer hydrogen. Compared to the superimposed product yield of single hydrogenation of residue and coal, the oil yield increases by a maximum of 9.18 wt%, while the gas yield and asphaltene yield decrease by a maximum of 2.72 wt% and 3.55 wt%, respectively, in the oil-coal co-hydrogenation with HDS enhancement. Under the condition of suitable H2 consumption, that is, suitable reaction severity, the synergistic effect of oil-coal co-hydrogenation with 35 wt% HDS is the optimum, and the best raw material conversion and oil yield can be obtained, which are 89.78 wt% and 67.46 wt% respectively.

The effect of water on coking and heat transfer inhomogeneity of supercritical aviation kerosene in a curved mini-channel

Water addition to aviation kerosene draws increasing attention in increasing heat sink and suppressing coke formation for regenerative cooling of scramjet engines. However, the effect of water on flow, reaction and heat transfer, particularly the thermal inhomogeneity in curved cooling channel is rarely reported. In the present study, the effect of water on coking and heat transfer inhomogeneity characteristics of China aviation kerosene, RP-3 studied in a uniformly heated curved mini-channel. A transient three-dimensional numerical simulation model with hybrid pyrolysis and steam reforming reactions of RP-3 is established and validated. The results show that there exists serious mass and thermal stratification in the curved mini-channel due to secondary flow and species diffusion. Specifically, RP-3 and water are diffused to concentrate at the bottom heating wall surface while coke deposition and light gaseous species, e.g., H2, CH4, CO are concentrated at the top heating wall surface. The thermal difference between the top and bottom heating walls is significant. Temperature and coke content of the top heating wall are much higher than those of the bottom heating wall. The gas film and coke deposition formed at the top heating wall surface lead to serious heat transfer deterioration. Therefore, the heat transfer coefficient at the bottom wall of the curved channel is much higher than that of the top wall. Water addition enhances secondary flow and thus exacerbates the coking and heat transfer inhomogeneity in the curved cooling channel. With water content increasing from 0 to 15 wt%, the secondary flow velocity increases by 288.2%, the conversion of RP-3 increases by 114.8% and the average coke content on the heating walls decreases by 40%. Meanwhile, the average heat transfer coefficient increases by 33.9% at the bottom heating wall but decreases by 18.0% at the top heating wall with the increase of water content.

Enhancement of Catalytic Activity on Crude Palm Oil Hydrocracking over SiO2/Zr Assisted with Potassium Hydrogen Phthalate.

In this study, the catalytic activity of bifunctional SiO2/Zr catalysts prepared by template and chelate methods using potassium hydrogen phthalate (KHF) for crude palm oil (CPO) hydrocracking to biofuels was investigated. The parent catalyst was successfully prepared by the sol-gel method, followed by the impregnation of zirconium using ZrOCl2·8H2O as a precursor. The morphological, structural, and textural properties of the catalysts were examined using several techniques, including electron microscopy energy-dispersive X-ray with mapping, transmission electron microscopy, X-ray diffraction, particle size analyzer (PSA), N2 adsorption-desorption, Fourier transform infrared-pyridine, and total and surface acidity analysis using the gravimetric method. The results showed that the physicochemical properties of SiO2/Zr were affected by different preparation methods. The template method assisted by KHF (SiO2/Zr-KHF2 and SiO2-KHF catalysts) provides a porous structure and high catalyst acidity. The catalyst prepared by the chelate method assisted by KHF (SiO2/Zr-KHF1) exhibited excellent Zr dispersion toward the SiO2 surface. The modification remarkably enhanced the catalytic activity of the parent catalyst in the order SiO2/Zr-KHF2 > SiO2/Zr-KHF1 > SiO2/Zr > SiO2-KHF > SiO2, with sufficient CPO conversion. The modified catalysts also suppressed coke formation and resulted in a high liquid yield. The catalyst features of SiO2/Zr-KHF1 promoted high-selectivity biofuel toward biogasoline, whereas SiO2/Zr-KHF2 led to an increase in the selectivity toward biojet. Reusability studies showed that the prepared catalysts were adequately stable over three consecutive runs for CPO conversion. Overall, SiO2/Zr prepared by the template method assisted by KHF was chosen as the most prominent catalyst for CPO hydrocracking.

Enhanced stability of CO2-assisted shale gas aromatization through the introduction of Mg promoter on Mo/ZSM-5

CO2-assisted shale gas aromatization is an effective method for directly producing benzene, toluene, and xylene (BTX) and H2 as well as for suppressing coke formation compared to non-oxidative conversion. However, Mo/ZSM-5, the conventional catalyst for aromatization, should be improved to make it more resistant to coke formation and enhance the BTX yield further for practical applications of the proposed reaction system. This study proposes Mg-promoted Mo/ZSM-5, labeled as Mg/Mo/ZSM-5, to enhance the efficiency of CO2-assisted shale gas aromatization by controlling the acidic and basic properties of Mo/ZSM-5. The addition of Mg on Mo/ZSM-5 selectively removed its Brønsted acid sites and increased its base site density, resulting in the enhanced catalytic stability by suppressing hard coke formation and protecting the active phase of Mo. Thus, the modified catalyst showed a higher BTX production than conventional Mo/ZSM-5, with the complete conversion of CO2 over a longer period than with Mo/ZSM-5. These benefits were maximized at a CO2 concentration of 10 %; moreover, the Mg/Mo/ZSM-5 catalyst improved regeneration efficiency.

Combination of torrefaction and catalytic fast pyrolysis for aromatic hydrocarbon production from herbaceous medicine waste

The combination of torrefaction pretreatment and catalytic pyrolysis of herbaceous medicine waste (HMW) was performed. The effects of torrefaction, pyrolysis temperature, SiO2/Al2O3 atomic ratio (SAR) and catalyst-to-feedstock (C/F) ratio on the distribution of aromatic hydrocarbons (AHs) was investigated. The formation of coke and its effects on the catalytic performance of the catalyst were evaluated. The results demonstrated that zeolite can effectively convert the torrefied HMW into AHs. The liquid products were dominated by monocyclic aromatic hydrocarbons (MAHs), in which toluene and xylene were formed preferentially over other aromatics. The total content of benzene, toluene, ethylbenzene, p-xylene, and naphthalene (BTEXN) reached 49.23–76.31%. Temperature, SAR and C/F ratio exhibit a greater influence on AHs formation than the torrefaction agents. A higher pyrolysis temperature and C/F ratio can inhibit coke formation, while higher SAR is beneficial to coke formation. The catalyst with a lower SAR yield more AHs and less coke. Coke was initially formed on the surface of the catalyst at low temperature, but it was more likely to form in the pores of the catalyst at high temperatures. The results show that the combination of torrefaction and catalytic pyrolysis is a potential approach for converting HMW into valuable bio-oils.

CO2-H2O assisted co-pyrolysis of petroleum vacuum residue and polypropylene to improve asphaltene reduction and coke suppression: A statistical approach

Non-catalytic co-pyrolysis of petroleum vacuum residue (VR) and polypropylene (PP) was studied under CO2 and/or steam atmospheres in a batch condition. A statistical approach was performed to analyze the effect of temperature, CO2 initial pressure, reaction time, PP and water contents using fractional factorial design methodology. A comparison of co-pyrolysis in steam, CO2, and steam + CO2 atmospheres showed that CO2 + steam is a more effective environment for reduction of asphaltene and suppressing coke formation. In detail, steam dominated the pyrolysis process, whereas CO2 enhanced the thermal cracking reactions, thereby increasing the asphaltene conversion to maltene and decreasing coke formation. Moreover, the results indicated that the addition of PP to VR improved the yield and quality of the liquid product and diminished the coke content. The optimum conditions were the temperature of 380 °C, CO2 initial pressure of 0.6 MPa, reaction time of 90 min with PP/ VR and water/ VR ratios of 0.23, and 0.25 (g/g), respectively. Pyrolysis of VR under such conditions resulted in the 86% maltene yield, 89.7% asphaltene reduction and 6.3% coke reduction. 1H NMR analysis showed that paraffins occupy the major content of the liquid (81.07 vol%), followed by aromatics (12.28 vol%) and olefinic compounds (6.65 vol%). In addition, the upgraded oil had a remarkable °API gravity of 35.9 and a low viscosity of 5.27 ± 0.02 cP. Furthermore, heavy metals of Ni and V were removed from the liquid product by 56.1% and 65.6%, respectively. Pyrolysis of VR with PP in the CO2 + steam environment would be deemed an economically viable and environmentally friendly technique of transforming the abundant low-grade VR feedstocks to valuable liquid fuels at a milder processing condition without using any catalysts.