Yields Of Toluene Research Articles

Pressurized hydrogasification and cobalt-catalyzed hydrogasification behaviors of naphthalene as a coal-based model compound

The pressurized hydrogasification/catalytic hydrogasification behaviors of naphthalene as a coal-based model compound were investigated for the first time in a batch reactor. The composition of products was roundly analyzed by gas chromatography (GC), gas chromatography–mass spectrometer (GC-MS) and laser desorption time-of-flight mass spectrometry (TOF-MS). Based on the product analysis results, the detailed reaction pathways for naphthalene hydrogasification and the effects of cobalt on reaction pathways were elucidated. Naphthalene first destabilized during hydrogasification. Subsequently, the destabilized naphthalene either underwent stepwise hydrocracking by active hydrogen atoms to ultimately produce benzene and methane, or formed naphthalene free radicals to initiate condensation. Cobalt can regulate products distribution to boost methane, benzene and toluene yield by facilitating active hydrogen generation, despite it had a limited ability to facilitate the naphthalene destabilization at temperature below 700 °C. Whereas above 750 °C, cobalt can promote naphthalene destabilization, thereby remarkably enhancing the conversion of naphthalene. Furthermore, cobalt intensified condensation leading to a shift of molecular mass distribution of condensation products from 252 ∼ 500 Da to 750 ∼ 2000 Da. These phenomena supported similar findings in coal catalytic hydrogasification. The rise in temperature, initial H2 pressure (P0), and cobalt content all facilitated the cobalt catalyzed naphthalene hydrocracking to gaseous product, with temperature exerting a particularly significant effect. This trend was similar with cobalt catalyzed coal hydrogasification. For example, when temperature increased from 650 ℃ to 750 ℃, naphthalene conversion improved from 21.2 % to 49.6 %, and gas yield rose from 2.6 % to 29.4 % at 1 % Co and 1.3 MPa P₀. The investigation serves to shed light on the molecular-level understanding of the mechanism underpinning coal hydrogasification.

Role of solvent in selective hydrodeoxygenation of monomeric phenols

The current production of aromatic hydrocarbons, crucial in fuel and polymer production, relies heavily on fossil resources. Finding carbon-neutral alternatives is necessary to address the current environmental challenges. Lignin emerges as a promising source for bio-based aromatics. However, existing catalytic hydrodeoxygenation processes often yield mixtures of cycloalkanes and aromatics. In our study, we investigated a selective route to obtain aromatics from phenols using the keto-tautomer reaction mechanism. According to this mechanism, the initial hydrogenation of the carbonyl group while a phenol compound is in its keto form leads to the removal of the hydroxyl group while preserving the aromatic structure. Our experiments focused on p-cresol, guaiacol, and mequinol, employing Pd/C and Ru/C catalysts. Experimental results revealed that aromatic hydrocarbons were favored during the hydrodeoxygenation of p-cresol and mequinol, while steric effects from the methoxy group hindered guaiacol's conversion. Furthermore, we observed significantly higher conversion rates when using hydrocarbon solvents compared to water, with toluene yields of up to 13.5 % by mass achieved on Pd/C. Our computational simulations confirmed the feasibility of the keto-tautomer mechanism on Pd cluster surfaces, similar to those found in Pd/C catalysts.

Mechanocatalytic Hydrogenolysis of the Lignin Model Dimer Benzyl Phenyl Ether over Supported Palladium Catalysts.

This work demonstrates the mechanocatalytic hydrogenolysis of the ether bond in the lignin model compound benzyl phenyl ether (BPE) and hardwood lignin isolated by hydrolysis with supercritical water. Pd catalysts with 4 wt % loading on Al2O3 and SiO2 supports achieve 100% conversion of BPE with a toluene production rate of (2.6-2.9) × 10-5 mol·min-1. The formation of palladium hydrides under H2 gas flow contributes to an increase in the turnover frequency by a factor of up to 300 compared to Ni on silica-alumina. While a near-quantitative toluene yield is obtained, some of the phenolic products remain adsorbed on the catalyst.

An experimental and density functional theory investigation of the influence of HZSM-5 on pyrolysis oils produced from vanillin, a model lignin compound

Lignin, as a renewable energy source, has attracted much attention due to its high valorization potential. Due to the complex composition of lignin, vanillin, an important intermediate of lignin, was chosen as a model compound in this study. The study examined the influence of the HZSM-5 molecular sieve on the quality of pyrolysis oils during the catalytic pyrolysis of vanillin at 600 °C using a horizontal tube furnace and Py-GC/MS analysis. The results revealed that the HZSM-5 catalyst significantly increased the yields of toluene, guaiacol, and 4-hydroxyisophthalaldehyde by 2.49 %, 19.26 %, and 1.8 %, respectively, whereas reducing the contents of phenol and 3,4-dimethoxyphenol by 6.01 % and 3.79 %, respectively. These findings indicate that the HZSM-5 molecular sieve effectively improves the quality of pyrolysis oils during the catalytic pyrolysis of vanillin. The evolution of the main functional groups in the pyrolysis of vanillin was analyzed using an in situ diffuse reflectance infrared Fourier transform spectroscopy. The addition of HZSM-5 promoted the cleavage of oxygen-containing functional groups and the generation of aromatic hydrocarbons during the pyrolysis of vanillin. Furthermore, the pyrolysis reaction pathways of vanillin were simulated under the B3LYP/6-311 g (d, p) basis set using the density functional theory. The acidic sites of HZSM-5 interacted with vanillin via the hydrogen bonds that affected the energy barriers of the pyrolysis reaction pathways of vanillin. HZSM-5 inhibited the generation of phenol and 3,4-dimethoxyphenol by increasing the energy barriers by 32.95 and 31.03 kJ/mol, respectively; however, HZSM-5 promoted toluene production by decreasing the energy barrier by 37.38 kJ/mol. The effects of HZSM-5 on the products in the simulation results were consistent with the experimental results.

Simulation of Regional Secondary Organic Aerosol Formation From Monocyclic Aromatic Hydrocarbons Using a Near‐Explicit Chemical Mechanism Constrained by Chamber Experiments

AbstractThe formation of secondary organic aerosol (SOA) is inextricably linked to the photo‐oxidation of aromatic hydrocarbons. However, models still exhibit biases in representing SOA mass and chemical composition. We implemented a box model coupled with a near‐explicit photochemical mechanism, the Master Chemical Mechanism (MCMv3.3.1), to simulate a series of chamber studies and assess model biases in simulating SOA from representative monocyclic aromatic hydrocarbons, that is, toluene and three xylene isomers (TX SOA). The box model underpredicted SOA yields of toluene and xylenes by 4.7%–100%, which could be improved by adjusting the saturation vapor pressure (SVP) of their oxidation products. After updating the SVP values, the mass concentration of TX SOA in the Yangtze River Delta region during summer doubled, and there was also an approximate 3% enhancement in the total SOA. Compared to a lumped mechanism used for simulating TX SOA, MCM predicted comparable mass concentrations but exhibited different volatility distributions and oxidation states.

Novel Staged Free-Fall Reactor for the (Catalytic) Pyrolysis of Lignocellulosic Biomass and Waste Plastics.

Pyrolysis of lignocellulosic biomass and waste plastics has been intensely studied in the last few decades to obtain renewable fuels and chemicals. Various pyrolysis devices have been developed for use in a laboratory setting, operated either in batch or continuously at scales ranging from milligrams per hour to tenths of g per hour. We report here the design and operation of a novel staged free-fall (catalytic) pyrolysis unit and demonstrate that the concept works very well for the (catalytic) pyrolysis of pinewood sawdust, paper sludge, and polypropylene as representative feeds. The unit consists of a vertical tube with a pretreatment section, a pyrolysis section, a solid residue collection section, a gas-liquid separation/collection section, and a catalytic reaction section to optionally perform ex situ catalytic upgrading of the pyrolysis vapor. The sample is placed in a tube, which is transported by gravity through various sections of the unit. It allows for rapid testing with semicontinuous feeding (e.g., 50 g h-1) and the opportunity to perform reactions under an (inert) gas (e.g., N2) at atmospheric as well as elevated pressure (e.g., 50 bar). Liquid yields for noncatalytic sawdust pyrolysis at optimized conditions (475 °C and atmospheric pressure) were 63 wt % on biomass intake. A lower yield of 51 wt % (on a biomass basis) was obtained for the noncatalytic pyrolysis of paper sludge, likely due to the presence of minerals (e.g., CaCO3) in the feed. The possibility of using the unit for ex situ catalytic pyrolysis (pyrolysis at 475 °C and catalytic upgrading at 550 °C) was also successfully demonstrated using paper sludge as the feed and H-ZSM-5 as the catalyst (21 wt % catalyst on biomass). This resulted in a biphasic liquid product with 25.6 wt % of an aqueous phase and 11 wt % of an oil phase. The yield of benzene, toluene, and xylenes was 1.9 wt % (on a biomass basis). Finally, the concept was also proven for a representative polyolefin (polypropylene), both noncatalytic as well as in situ catalytic pyrolysis using H-ZSM-5 as the catalyst at 500 °C. The liquid yield of thermal, noncatalytic plastic pyrolysis was as high as 77 wt % on plastic intake, while in situ catalytic pyrolysis gave a combined 7.8 wt % yield of benzene, toluene, and xylenes on plastic intake.

Selective hydrodeoxygenation of 5-hydromethylfurfural to 2,5-dimethylfuran over PtFe/C catalyst

2,5-dimethylfuran (DMF), a promising biomass-derived fuel, is synthesized via the hydrodeoxygenation of 5-hydroxymethylfurfural (HMF). This study focuses on the inherent activity of a 5Pt5Fe/C catalyst for HMF hydrodeoxygenation to DMF. The catalyst exhibited exceptional performance, achieving a remarkable DMF yield of 99.6 %. It displayed specific selectivity for C = O bond hydrogenation and CO bond cleavage in diverse substrates, producing high yield of 2-methylfuran from furfural and furfury alcohol, and high yield of toluene from benzaldehyde, benzyl alcohol. In-depth characterizations unveiled valuable insights into the 5Pt5Fe/C catalyst's properties, emphasizing a harmonious balance between metal and acid sites due to the interactive synergy between Pt and Fe species, enhancing hydrodeoxygenation activity. Additionally, the catalyst demonstrated satisfactory stability, maintaining a commendable DMF yield over five reaction cycles despite observed changes.

Catalytic pyrolysis of rape straw to produce light aromatic hydrocarbons over HZSM-5 loaded by metal ions from spent lithium batteries extracted with citric acid

In this study, metal-loaded HZSM-5 was prepared with metal ion extracted from the cathode materials of spent lithium batteries (lithium iron phosphate, LFP; lithium nickel-cobalt manganate, NCM) with citric acid for the improved production of light aromatic hydrocarbons by catalytic pyrolysis of rape straw. Because of the dealuminization effect of citric acid on HZSM-5, mesopores were introduced, and the diffusion and conversion of pyrolysis gas over acid sites were improved. After metal loading with acid-leaching solution, the amount of weak and total acids in metal-loaded HZSM-5 increased a lot, which was conducive to the dehydration, deoxygenation, decarbonylation and aromatization of pyrolysis, and the production of monocyclic aromatic hydrocarbons (MAHs). With 0.1 mol/L citric acid for LFP and NCM treatment, the metal-loaded catalyst showed a higher yield of benzene, toluene and xylene (BTX) of 11.10 wt% during catalytic pyrolysis of rape straw. Compared with 0.1-NCM-H5, a higher yield of MAHs was obtained over 0.1-LFP-H5 with a more favorable pore structure and higher amounts of weak and total acid sites. In general, the high-valued utilization of agricultural wastes and spent lithium batteries was realized in this study to produce clean energy.

Catalytic pyrolysis of polystyrene in different reactors: Effects of operating conditions on distribution and composition of products

The effects of temperature and pressure on product distribution were investigated by catalytic slow pyrolysis of polystyrene in a fixed bed. Simultaneously, the catalytic fast pyrolysis of polystyrene was carried out in a fixed-fluidized bed to study the effects of temperature and reaction time on the product distribution. The slow and fast pyrolysis experiments of polystyrene were conducted using γ- Al2O3 (basic) as catalyst and silica sand as control group. The compositions of oil and gas products were analyzed by GC-FID, GC-MS and GC to investigate the catalytic activity of basic catalyst. The results showed that catalytic slow pyrolysis and catalytic fast pyrolysis achieved maximum oil yields of 94.6 wt% and 92.19 wt%, respectively. In slow pyrolysis, toluene, ethylbenzene, and styrene were the main products, and the introduction of catalyst led to reduced yields of toluene, ethylbenzene, cumene, and α-methyl styrene. However, the main product of fast pyrolysis was only styrene, with a recycling rate nearly 80% under catalytic conditions. The presence of the catalyst increased the yield of styrene, with slow pyrolysis rising from 27.15% to 32.58%, and fast pyrolysis increasing from 82.28% to 86.56%. Longer residence time strengthened secondary reactions to generate more aromatics such as toluene and ethylbenzene. Both catalytic slow and fast pyrolysis yielded higher styrene contents than thermal pyrolysis because the basic catalyst reduced the occurrence of secondary reactions.

Role of the hydrocarbon molecular structure in CNT growth on Fe-Al catalysts.

Upgrading plastic wastes into high-value products via the thermochemical process is one of the most attractive topics. Although carbon nanotubes (CNTs) have been successfully synthesized from plastic pyrolysis gas over Fe-, Co-, or Ni-based catalysts, a deep discussion about the reaction mechanism was seldom mentioned in the literature. Herein, this work was intended to study the growth mechanism of CNTs from hydrocarbons on Fe-Al2O3 catalysts. C5-C7 hydrocarbons were used to synthesize CNTs in a high-temperature fixed-bed reactor, and the carbon products and cracked gas were analyzed in detail. The CNT yield was in the order of cyclohexane, cyclohexene > n-hexane > n-heptane > n-pentane, 1-hexene. It was proposed that CNT growth on Fe-Al2O3 catalysts was mainly determined by the yield and structure of six-membered cyclic species, which was tailored by the carbon chain length, C-C/CC bonds, and linear/cyclic structures of C5-C7 hydrocarbons. Compared with n-hexane, the six-membered rings of cyclohexane and cyclohexene promoted six-membered cyclic species formation, increasing CNT and benzene yields; the seven-membered carbon chain of n-heptane promoted methyl-six-membered cyclic species formation, decreasing CNT and benzene yields while increasing the toluene yield; the five-membered carbon chain of n-pentane and the CC bond of 1-hexene inhibited six-membered cyclic species formation, decreasing CNT and benzene yields. This work revealed the structure-activity relationship between C5-C7 hydrocarbons and CNT growth, which may direct the process design and optimization of CNT synthesis from plastic pyrolysis gas.

Maximizing light olefin production via one-pot catalytic cracking of crude waste plastic pyrolysis oil

Energy-efficient processes for converting polyolefinic waste plastics into light olefins are critical for mitigating environmental pollution and reducing carbon emissions. In this study, an alternative recycling scheme, the catalytic cracking of crude waste plastic pyrolysis oil (WPPO) over microspherical P-modified steam-treated ZSM-5 (ms-P-HZSM5-S), was demonstrated and compared to a state-of-the-art commercial scheme, the thermal cracking of a hydrotreated naphtha range of WPPO. The C2–C4 olefins yield achieved by the catalytic WPPO cracking (56.6 wt%) exceeded those achieved by the thermal WPPO cracking (36.1 wt%), thermal naphtha cracking (23.1 wt%), and catalytic naphtha cracking (29.7 wt%), which indicated the superiority of WPPO over naphtha as a feedstock. However, during a deactivation test over ms-P-HZSM5-S, coke accumulation resulted in a rapid decline in the yields of ethylene (from 17.2 to 14.6 wt%), propylene (from 25.8 to 23.6 wt%), and benzene, toluene, and xylenes (from 16.1 to 13.4 wt%) after a reaction time of 810 s (temperature = 680 °C, weight hourly space velocity = 16 h−1). Nevertheless, the catalytic performance was fully restored through regeneration in air at 730 °C, which confirmed the viability of continuous operation involving successive reaction–regeneration cycles. These findings can be leveraged to devise a new approach, the catalytic cracking of WPPO integrated with a continuous regeneration (e.g., circulating fluidized bed reactor) system, which could offer several advantages over the commercial strategy, including the posttreatment-free utilization of the entire WPPO range, higher light olefins yields, continuous coke removal, reduced energy consumption, and non-necessity of H2.

Optimizing support acidity of NiMo catalysts for increasing the yield of benzene, toluene and xylene in tetralin hydrocracking

Optimizing support acidity of NiMo catalysts for increasing the yield of benzene, toluene and xylene in tetralin hydrocracking

Palladium-Containing Catalysts Based on Functionalized CNFs for the Dehydrogenation of Methylcyclohexane

The activity of palladium-containing catalysts based on functionalized carbon nanofibers prepared by an incipient wetness impregnation method in the dehydrogenation reaction of methylcyclohexane was investigated. Methylcyclohexane is considered as one of the most promising liquid hydrogen carriers. The dependence of the catalytic characteristics of the samples on the functionalization conditions of carbon nanofibers has been studied. By temperature-programmed desorption, it was shown that an increase in the treatment time of carbon nanofibers in concentrated nitric acid from 1 to 3 h increases the number of hydroxyl groups on their surface, and treatment for 6 h contributes to a rise in the concentration of carboxyl groups and their derivatives (esters and anhydrides). Additional calcination of the functionalized nanofibers in an inert atmosphere at 530°C yielded a sample containing predominantly hydroxyl groups. The presence of hydroxyl groups on the surface of the carbon material has a positive effect on the performance of the catalysts, while the presence of carboxyl groups leads to a decrease in the yield of toluene. It is assumed that the observed differences in catalyst activity are due to differences in dispersion and localization of palladium particles.

Benzene methylation by acetic acid with platinum-loaded titanium oxide photocatalyst

Photocatalytic functionalization of aromatic rings with simple small molecules has been intensively studied by using metal-loaded titanium oxide photocatalyst. In the present study, the photocatalytic direct methylation of benzene was examined by using acetic acid as a promising methylation reagent. Over 15% yield of toluene was achieved with a platinum-loaded TiO2 photocatalyst (Pt/TiO2) under light irradiation without any extra solvent. The kinetic investigations with isotopic compounds and temperature-controlled experiments elucidated that Pt nanoparticles on the TiO2 surface have a dual role, i.e., working as an electron receiver to improve the charge separation and catalyzing a radical addition-elimination process to form toluene molecule. Two competitive reaction mechanisms were proposed in this reaction system.

Insight into the crucial reason causing the difference in secondary organic aerosol yields of monocyclic aromatic hydrocarbons with different methyl substituent numbers

The secondary organic aerosol (SOA) yield of toluene photooxidation was reported to substantially higher than that of trimethylbenzene due to the effect of the number of methyl substituents. However, the intrinsic mechanism for this disparity is not clear enough. In this study, a highly-sensitive thermal-desorption photoinduced associative ionization mass spectrometer (TD-PAI-MS) was used to real-time characterize the molecular composition and its evolution of the SOA generated from the photooxidation of toluene and 1,2,3-trimethylbenzene (1,2,3-TMB) in a smog chamber. In the new particle formation (NPF) stage, toluene generated more variety of nucleation precursors, such as benzaldehyde (MW 106) and benzoic acid (MW 122), resulting in a much higher nucleation rate and SOA number concentration. In the SOA growth/aging stage, the key SOA components of toluene were mainly dialdehydes, e.g., 2-oxopropanedial (MW 86) and 4-oxopent-2-enedial (MW 112), which played an important role in the formation of highly oxidized species (HOS) through oligomerization or cyclization reactions. In contrast, due to the presence of more methyl groups, 1,2,3-TMB was inclined to produce ketones, e.g., 2,3-butanedione (MW 86) and 3-methyl-4-oxopent-2-enal (MW 112), which would be cleaved into high-volatility low molecular compounds, e.g., acetic acid, through fragmentation. Taken together, relative to 1,2,3-TMB, the higher nucleation rate during NPF and the significant oligomerization/functionalization process during SOA growth are thought to be the major reasons resulting in the higher SOA yield of toluene. This work provides a reference for the insight into the different SOA yields of monocyclic aromatic hydrocarbons (MAHs) through further revealing the SOA formation mechanism during toluene and 1,2,3-TMB photooxidation.

Influences and mechanisms of pyrolytic conditions on recycling BTX products from passenger car waste tires

Pyrolysis is an effective method for waste tire disposal. However, it has rarely been used to recycle specific highly valuable components (such as benzene, toluene, and xylene (BTX)) from tire rubbers, owing to complicated pyrolytic reactions. This study investigated the pyrolysis process of passenger-car-waste-tires (PCWT) with the help of TG–DTG and Py–GC/MS. Based on response surface methodology (RSM), the effect of pyrolytic parameters on the yields of pyrolytic oil and BTX is evaluated. Furthermore, the BTX generation mechanisms are discussed from the perspective of aliphatic and aromatic hydrocarbon transformations. Additionally, pyrolytic conditions including temperature, rubber particle size, pressure, and gas flow rate were systemically investigated and the optimum pyrolytic condition for yield of BTX (26.5 g per 100 g tire rubber) was obtained [765 K, 0.7 mm, 0.52 MPa and 2.5 mL (g min)−1]. Therein, yield of benzene, toluene and xylene were 1.07, 5.03 and 20.40 g per 100 g tire rubber, respectively. During PCWT pyrolysis, BTX is primarily obtained via the Diels–Alder reactions of small-chain alkenes and transformations of limonene and aromatics. This study elucidates the BTX generation mechanisms during PCWT pyrolysis and clarifies the effects of varying pyrolytic conditions on BTX generation.

Scale-Up Foreseeable Fabrication of CoS-MoS2 for Efficient Deoxygenation of Lignin-Derived Phenolics to Arenes

Catalysis plays a key role in oriented biomass valorization, and designing a robust catalyst and developing its correspondingly easy-to-scale-up preparation are particularly crucial in boosting biorefinery concept into reality. In this study, employing sulfur vacancies in MoS3 and their preferable adsorption to Co ions, CoS-MoS2 catalyst was fabricated via decomposition of MoS3 followed by in situ sulfidation of Co oxides. Co could be located at the edges of MoS2, constructing plenty of CoS–edge interfaces. This critical feature of the interface enhanced the adsorption of the reactant and decreased the energy barrier of the rate-limiting step in the deoxygenation of 4-methylphenol, leading to as high as 100% toluene yield at a low temperature of 120 °C. Moreover, this catalyst presented high stability in the deoxygenation reaction and could efficiently convert other lignin-derived aromatic oxy-compounds into arenes. Importantly, this facile method shows good versatility in fabricating different iron family element-promoted MoS2-based catalysts, and this preparation procedure is readily scaled up 200-fold without compromising catalytic activity, showcasing the potential for large-scale applications.

Preparation of aromatic hydrocarbons from pinecone pyrolysis synergistically catalyzed by Ca–Fe and HZSM-5

In this study, a combination of Ca–Fe and HZSM-5 catalysts for enhancing the aromatic hydrocarbons yields from pinecone pyrolysis was proposed. The catalysts performance and the enhanced mechanism of aromatic hydrocarbons generation were investigated by pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS) and a bench-scaled fixed bed reactor. The catalysts crystallization and pore structure characteristics were characterized by X-ray diffraction (XRD) and N2 adsorption/desorption. The results showed that the combination of Ca–Fe and HZSM-5 catalysts produced the largest peak area and the highest relative content of aromatic hydrocarbons relative to HZSM-5, CaO/HZSM-5 and Fe/HZSM-5 catalysts. Relative to single HZSM-5 catalytic pyrolysis, the introduction of Ca–Fe components increased the yield of aromatics, especially increased the yield of benzene, toluene, ethylbenzene and xylene (BTEX) to 17.21 mg/g, with an increase of 61.60 %. The heterotopic arrangement of pinecone, Ca–Fe catalyst and HZSM-5 catalyst facilitated the production of high-quality aromatic hydrocarbons relative to the in situ catalytic pyrolysis technique. The Ca–Fe bimetallic catalyst decomposed the primary volatiles from pinecone pyrolysis into oxygenated compounds with smaller molecular weights, thereby increasing the proportions of pyrolysis volatiles entering the HZSM-5 channels, and subsequently enhancing the yield of aromatic hydrocarbons. This study implies that the combination of Ca–Fe and HZSM-5 catalyst is a promising approach for converting biomass materials into aromatic hydrocarbons.

Cooperative catalysis of Co-promoted Zn/HZSM-5 catalysts for ethane dehydroaromatization

Zn/HZSM-5 is a promising catalyst for ethane dehydroaromatization despite rapid deactivation within 13 h. Herein, the effect of introducing a cobalt promoter into the Zn/HZSM-5 catalyst was investigated to improve catalytic performance. Co-promoted Zn/HZSM-5 was superior to unpromoted Zn/HZSM-5 in terms of both catalytic activity and stability. Additionally, the total yield of benzene, toluene, and xylene over 1CoZn/HZSM-5 was 10.2%, even after 25 h of reaction, compared to the total yield over Zn/HZSM-5 catalyst at less than 1% at the time. XRD, UV–vis, TEM, and H2-TPR demonstrated that Co introduction improved ZnO dispersion in the prepared catalysts. Furthermore, the characterization of the spent catalyst via XRD, TEM, Raman, TGA, and N2 adsorption/desorption proposed that the conversion of graphite coke precursor to carbon nanotube and amorphous carbon prevented the micropores in the zeolite from being blocked. Thus, a considerable number of Brønsted acid sites in micropore could be preserved, thereby enhancing their catalytic stability. However, excessive Co clusters favored CC and CH bond dissociation, primarily producing methane and coke rather than aromatics. Therefore, adding an appropriate amount (1 wt%) of Co to Zn/HZSM-5 improves catalytic performance and the resistance to deactivation.

Preparation of monocyclic aromatic hydrocarbons from chlorine-containing mixed waste plastics via tandem catalysis coupled with hydrothermal pretreatment

Pyrolytic conversion of chlorine-containing mixed plastic (CMP) wastes into monocyclic aromatic hydrocarbons (MAHs) suffered the chlorinated pollutants and low product yield, making it difficult for continuous industrial operation. Herein, a novel method of tandem catalytic pyrolysis of CMP coupled with hydrothermal pretreatment (HY) for the clean production of high-yield MAHs was investigated. The pyrolytic kinetics of the feedstocks obtained after HY was analyzed, and the synergistic mechanism of HY and tandem catalysis over carbon-based catalyst (Fe/Ni/Mo@N/C) and zeolite (HZSM-5) was established. The results showed that the homogenization effect of HY on CMP was the key to improving its catalytic activity. High pretreatment temperature effectively weakened the branch-chain bond of the polyolefin molecules and dramatically reduced the pyrolytic activation energy of CMP. Additionally, the β-scission and alkylation reactions in the catalytic process were significantly promoted by HY, and subsequently improved the yields of toluene and xylene in HY-tandem catalysis, the selectivity of MAHs and benzene, toluene, ethylbenzene, and xylene (BTEX) reached 84.09% and 71.29%, respectively. The increased yield of BTEX favoured by the synergistic effect of pretreatment and catalysis was promoted to 351.97 mg/g in HY-tandem catalysis, whose yield was 9.52 times that of thermal pyrolysis. After the catalytic reaction of 360 min and transforming 18 times of the mixed plastic wastes, the coke amount of the microporous catalyst was still lower than 4 wt%. This work provides a potentially transformative solution to the challenge of upcycling unsorted plastic waste.