Highest Aromatic Yield Research Articles

Decoupling Aromatic Yield and Coke Formation in Methanol‐to‐Aromatic Reaction on Zn(II) Exchanged H‐ZSM‐5 Zeolite

AbstractMethanol to aromatic reaction is an alternative pathway to produce aromatics from non‐petroleum resources. Zn‐modified ZSM‐5 zeolite is the widespread catalyst for MTA due to its high activity and selectivity to aromatics. However, a desired high yield of aromatics is usually accompanied with undesired coke formation and fast deactivation of catalyst, because aromatic molecules also serve as the precursor for coke formation. To decouple the aromatic yield and coke formation rate, in this work we use Zn‐ZSM‐5 to investigate coke formation and catalyst deactivation. The coke distribution along the catalyst bed was analyzed and its correlation with the concentration gradient of methanol, olefins and aromatics along the bed was deciphered. Coke was found to form very fast at catalyst bed in the copresence of methanol and aromatics. On the contrary, much less coke was observed at the later layers of the catalyst bed where methanol had been fully converted and aromatics were present in the highest concentration. Based on this finding, we adjusted the reaction conditions to successfully improve the yield of aromatics without reducing catalyst lifetime in compromise, by applying a higher methanol partial pressure that enables a faster consumption of methanol and reduces the period of copresence of methanol and aromatics.

Upgrading CO2 to sustainable aromatics via perovskite-mediated tandem catalysis

The directional transformation of carbon dioxide (CO2) with renewable hydrogen into specific carbon-heavy products (C6+) of high value presents a sustainable route for net-zero chemical manufacture. However, it is still challenging to simultaneously achieve high activity and selectivity due to the unbalanced CO2 hydrogenation and C–C coupling rates on complementary active sites in a bifunctional catalyst, thus causing unexpected secondary reaction. Here we report LaFeO3 perovskite-mediated directional tandem conversion of CO2 towards heavy aromatics with high CO2 conversion (> 60%), exceptional aromatics selectivity among hydrocarbons (> 85%), and no obvious deactivation for 1000 hours. This is enabled by disentangling the CO2 hydrogenation domain from the C-C coupling domain in the tandem system for Iron-based catalyst. Unlike other active Fe oxides showing wide hydrocarbon product distribution due to carbide formation, LaFeO3 by design is endowed with superior resistance to carburization, therefore inhibiting uncontrolled C–C coupling on oxide and isolating aromatics formation in the zeolite. In-situ spectroscopic evidence and theoretical calculations reveal an oxygenate-rich surface chemistry of LaFeO3, that easily escape from the oxide surface for further precise C–C coupling inside zeolites, thus steering CO2-HCOOH/H2CO-Aromatics reaction pathway to enable a high yield of aromatics.

Highly selective production of light aromatics from co-catalytic fast pyrolysis of pre-deoxygenated biomass and hydrogen-rich polyethylene using a dual-catalyst system

Co-catalytic fast pyrolysis of torrefaction deoxygenated pine wood (PW) and high-density polyethylene (HDPE) in dual-catalyst (metal oxidize and zeolite) system is an effective technology to produce renewable bio-aromatics. In this work, the torrefaction deoxygenation pretreatment (TDP) was carried out to remove oxygen element from PW prior to catalytic fast pyrolysis (CFP). 56.90 % oxygen could be removed at TDP temperature of 300 °C, releasing in the oxygen carrier of CO2, CO, H2O, alcohols, acids, phenols, etc. Then, the synergistic effect between the metal oxide and the HZSM-5 in dual-catalyst system was also investigated. Among these metal oxides (Al2O3, MgO, CaO, ZnO, and Fe2O3) and hierarchical HZSM-5, the dual-catalyst of CaO and hierarchical HZSM-5 (treated by 0.2 M NaOH) was the optimal combination. The layout mode between feedstock and dual catalyst was also optimized. The highest yield of aromatics was produced in layout Mode 8, where the CaO was mixed with torrefied PW, but the hierarchical HZSM-5 and HDPE were laid in separated layers. The mixing of CaO and torrefied PW promoted the conversion of the macromolecular oxygenates into micromolecular oxygenates. Then, these small-molecular oxygenates could enter the hierarchical channel of HZSM-5, being converted into aromatics by undergoing the Diels-Alder reaction.

A site distance dependence of product selectivity in n-hexane dehydrogenation over alumina-supported chromium catalyst

Although CrOx/Al2O3 has been widely applied for light alkanes dehydrogenation, there is insufficient understanding on the dehydrogenation of long-chain alkanes that no solutions to the poor selectivity to mono-olefins and high yield of aromatics. Herein, dehydrogenation of n-hexane was studied on a series of CrOx/γ-Al2O3 catalysts with different densities of Cr sites, and it finds that the dehydrogenation performance is closely related to the distance between Cr sites. With densely populated Cr sites, multiple H atoms of n-hexane are adsorbed on the CrOx/γ-Al2O3 simultaneously (i.e., multi-point adsorption), promoting the formation of n-hexadiene, n-hexatriene and the resultant benzene and/or coke. Therefore, when the Cr loading exceeds the mono-layer coverage (5 wt% Cr loadings), the selectivities to n-hexenes and benzene are kept constant (about 23 wt% and 68 wt%, respectively). While decrease of Cr content in the mono-layer regime leads to a significant decrease in both the distance between Cr sites and the number of adsorbed H atoms, resulting in improved selectivity to n-hexenes. The CrOx@γ-Al2O3 catalyst with 3.6 Cr atoms/nm2 prepared by the equilibrium adsorption method (and the complexation of CrIII and 3,5-dimethylpyridine), exhibits 89 wt% selectivity to n-hexenes (<2 wt% for benzene). This work provides theoretical guidance for the precise design and synthesis of the high-performance CrOx-based catalyst for the dehydrogenation of alkanes, especially for long-chain alkanes.

Catalytic co-pyrolysis of low-density polyethylene and lignin over Cu-modified HZSM-5: Insight with online photoionization mass spectrometry

Catalytic pyrolysis of lignocellulosic biomass usually suffers from coking because of its hydrogen-deficient and oxygen-rich nature. The co-feeding of biomass with plastics may enhance product quality. Herein, we studied the catalytic co-pyrolysis of low-density polyethylene (LDPE) and lignin (LG) over HZSM-5 modified with Cu. The effects of Cu valence and feedstock mass ratio on the product distributions were characterized by online photoionization mass spectrometry. Our results show that the addition of Cu limits the formation of aliphatics and promotes the aromatization reaction to produce monocyclic aromatic hydrocarbons (MAHs). The Cu2O/HZSM-5 catalyst exhibits better dehydrogenation activity and promotes the formation of phenolics, while the CuO/HZSM-5 catalyst has a better selectivity for MAHs. In addition, the feedstock mass ratio was also screened, indicating that the highest yield of aromatics was obtained at a mass ratio of 1:3 (LG: LDPE). This work provides new insights into the efficient use of biomass and plastics.

Chemical recycling of plastic waste to monomers: Effect of catalyst contact time, acidity and pore size on olefin recovery in ex-situ catalytic pyrolysis of polyolefin waste

The catalytic upgrading of post-consumer mixed polyolefinic waste pyrolysis vapors has been studied over five different solid acid catalysts to understand the effect of vapor-catalyst contact time and catalyst properties on the recovery of light olefins (C2-C4). HZSM-5 with Si/Al ratio of 11 and 27 produced the highest light olefins yields (83.4 wt% and 72.1 wt%, respectively) at a very short contact time of ∼5 ms while extending the contact time (≥23 ms) decreased the olefin yields and resulted in higher yields of aromatics (∼30.0 wt% and ∼40.0 wt%, respectively). Short contact time (5 ms) was not sufficient for HZSM-22 to crack pyrolysis vapors to C2-C4 olefins (8.0 wt%) but increasing contact time improved C2-C4 yields to 53.5 wt% without increased production of aromatics, which may be attributed to its small pore size (shape selectivity). SAPO-34, SAPO-11, and Al-MCM-41 were not selective to light olefins at any studied contact time.

Catalytic pyrolysis of rice straw for high yield of aromatics over modified ZSM-5 catalysts and its kinetics

The fabrication of ZSM-5 for the catalytic pyrolysis of biomass into highly selective valuable aromatics remains a challenge. This study investigates the product selectivity of rice straw pyrolysis without and with P-ZSM-5, alkali (0.4 M ZSM-5) and metal (8 wt% Ni-ZSM-5) modified catalysts via Py-GC/MS. Results revealed that the addition of catalysts significantly affected product distribution, with maximum selectivity of aromatics (47%) over 8 wt% Ni-ZSM-5 followed by P-ZSM-5 (44%) and 0.4 M ZSM-5 (42%). 8 wt% Ni-ZSM-5 exhibited the additive effect for monoaromatics with a maximum yield of BTX (67.23 mg/g) due to improved acidity responsible for the promotion of acid catalyzed reactions. Furthermore, the thermo-kinetics of rice straw without and with catalysts were investigated using thermogravimetric analysis. Thermogravimetric analysis shows that the degradation rate of rice straw reduced after the addition of catalysts. From the kinetic analysis, the value of activation energy of rice straw (114.43 kJ mol−1) decreased after the addition of catalysts, which was 102.48 kJ mol−1 (P-ZSM-5), 93.11 kJ mol−1 (0.4 M ZSM-5) and 61.89 kJ mol−1 (8 wt% Ni-ZSM-5). Thermodynamic parameters (ΔHandΔG) show that catalytic pyrolysis of rice straw is an endothermic and nonspontaneous process.

Higher BTX yield in coaromatization of n-hexane and methanol over [Zn,Ga]/HZSM-5 catalyst

A series of [Zn,Ga]/HZ catalysts were prepared by impregnation and their catalytic performance in coaromatization of n-hexane and methanol, a heat-coupling reaction, were studied in detail. The crystallization, textural properties, morphology, acidity, composition and chemical state were characterized by XRD, N2 adsorption/desorption isotherms, TEM, py-FTIR, ICP-OES and XPS. The modification of Zn and Ga tunes the acid distribution, and more importantly Ga introduction greatly increases the content of active centers Zn(OH)+ from 30 % (1Zn/HZ) to 60 %. As a result, [Zn,Ga]/HZ improves the dehydroaromatization ability and provides higher aromatics yield. The analysis of organic species in catalyst by TG and GC–MS confirms that [Zn,Ga]/HZ produces more aromatics precursors than HZ. Under the conditions of feed ratio (n-hexane/methanol) 3:7, reaction temperature 530 °C, and WHSV 1.0 h−1, the BTX yield was significantly increased to 70 %.

Influence of metal chloride modified biochar on products characteristics from biomass catalytic pyrolysis

In this study, the pyrolysis temperature of peanut shells was optimized, and biochar was prepared and modified with HCl to obtain better surface characteristics and pore structure. The incipient wetness impregnation method was used to load one or two of NaCl, MnCl2, FeCl3 on HC, and their influences on the characteristics of the pyrolysis products were studied. The results show phenols have completed the evolution from methoxyphenols to benzenediols to alkylated phenols and aromatics from 440 °C to 660 °C. FeCl3 modified biochar has high phenol selectivity, reaching the maximum value of 46.63% when the loading is 8%. And it also has the highest aromatics selectivity. When the loading is 16%, the aromatic content is 38.33%. The selectivity of phenols and aromatics of MnCl2 is slightly lower than that of FeCl3, but it has the highest decarboxylation activity. The selectivity of NaCl is low, but it has the highest yield of aromatics at low loading. The advantage of bimetal modification is that it can take into account the selectivity of phenol and aromatics. The study indicates peanut shells have the potential to be widely used as raw materials and catalysts for the production of high value-added chemicals.

Low energy consumption and high quality bio-fuels production via in-situ fast pyrolysis of reed straw by adding metallic particles in an induction heating reactor

An in-situ fast pyrolysis of biomass by adding metallic particles in an induction heating reactor was proposed to produce high quality bio-fuels. After adding metallic particles into biomass, the times required to reach complete pyrolysis during reed straw pyrolysis process were significantly reduced up to 28.9%. The yields of combustible gas and bio-oil products were significantly increased. Furthermore, higher-quality combustible gas and bio-oil products were obtained with the LHV of gas products and HHV of bio-oil (dry basis) increased by 14.2%–19.1% and 4.16%–16.35%, respectively, under 400–600 °C. The lower oxygen content and higher yields of aromatics, alkenes and alkanes contents in bio-oil were obtained after metallic particles addition. More importantly, up to 26.5% of the total energy consumption during pyrolysis process was reduced after adding metallic particles into biomass in an induction heating reactor. The results indicate that adding metallic particles into biomass in an induction heating reactor can significantly enhance the heat transfer, decomposition reaction intensity and energy utilization efficiency of biomass pyrolysis process with lower energy consumption and higher-quality bio-fuel production.

Effect of alkali modification to ZSM-5 zeolite on the aromatization of methanol

ZSM-5 zeolites were modified by desilication with sodium acetate and sodium citrate. The physicochemical properties of ZSM-5 zeolites, such as crystal structure, acid content, surface area and pore volume, were characterized by XRD, SEM, NH3-TPD, 27Al MAS NMR, pyridine adsorption infrared spectroscopy and N2 adsorption-desorption isotherms. Theresultsindicatethat pore size of the zeolite increases and mesoporous structures are formed by alkali modification, and the amount of Lewis and Brönsted acid contents decreased obviously. When the concentration of sodium acetate solution is 0.5 mol/L, the modified zeolite has a suitable B/L value for the aromatization of methanol while forming a large number of mesoporous structures. Compared with microporous ZSM-5, the catalyst life is increased from 20 h to 74 h, and the highest yield of aromatics is increased from 20.97% to 40.05%.

New Mechanistic Insights into the Lignin β-O-4 Linkage Acidolysis with Ethylene Glycol Stabilization Aided by Multilevel Computational Chemistry.

Acidolysis in conjunction with stabilization of reactive intermediates has emerged as one of the most powerful methods of lignin depolymerization that leads to high aromatic monomer yields. In particular, stabilization of reactive aldehydes using ethylene glycol results in the selective formation of the corresponding cyclic acetals (1,3-dioxolane derivatives) from model compounds, lignin, and even from softwood lignocellulose. Given the high practical utility of this method for future biorefineries, a deeper understanding of the method is desired. Here, we aim to elucidate key mechanistic questions utilizing a combination of experimental and multilevel computational approaches. The multiscale computational protocol used, based on ReaxFF molecular dynamics, represents a realistic scenario, where a typical experimental setup can be reproduced confidently given the explicit molecules of the solute, catalyst, and reagent. The nudged elastic band (NEB) approach allowed us to characterize the key intermolecular interactions involved in the reaction paths leading to crucial intermediates and products. The high level of detail obtained clearly revealed for the first time the unique role of sulfuric acid as a proton donor and acceptor in lignin β-O-4 acidolysis as well as the reaction pathways for ethylene glycol stabilization, and the difference in reactivity between compounds with different methoxy substituents.

Green BTX production from methyl oleate over hierarchical HZSM-5 zeolites prepared by NaOH treatment

BTX production from methyl oleate over four HZSM-5 zeolites with various pore structure was evaluated in a fixed-bed microreactor. HZSM-5 zeolite (SiO2/Al2O3 = 38) was synthesized by the hydrothermal method, and treated using NaOH solutions with different concentrations (0.1 M, 0.3 M, and 0.5 M) to prepare hierarchical HZSM-5 zeolites with different cavity volumes and mesopores in shells. Multi-characterizations (including XRD, NH3-TPD, SEM, TEM, Py-IR, XPS and N2 adsorption–desorption isotherms) revealed that the NaOH treatment induced the formation of hollow structures and mesopores in the HZSM-5 crystals without destroying the topological structure, increased the acid amount and pore volume and decreased the molar SiO2/Al2O3 ratio and BET surface, resulting in high aromatic yields in the catalytic aromatization of methyl oleate. The BTX yields and aromatic content in liquid over hierarchical HZSM-5 zeolites increased with increasing NaOH concentration. The HZSM-5 zeolite treated with a 0.5 M NaOH solution with a high amount of acid and large cavity volume led to a high aromatic yield of 51.28 wt%.

Enhancing Methane Aromatization Performance by Reducing the Particle Size of Molybdenum Oxide.

Efficient use of natural gas to produce aromatics is an attractive subject; the process requires catalysts that possess high-performance active sites to activate stable C–H bonds. Here, we report a facile synthetic strategy to modify HMCM-49 with small molybdenum oxide nanoparticles. Due to the higher sublimability of nano-MoO3 particles than commercial MoO3, they more easily enter into the channels of HMCM-49 and associate with Brønsted acid sites to form active MoCx-type species under calcination and reaction conditions. Compared with commercial MoO3 modified MCM-49, nano-MoO3 modified MCM-49 exhibits higher methane conversion (13.2%), higher aromatics yield (9.1%), and better stability for the methane aromatization reaction.

Catalytic fast Co-Pyrolysis of sewage sludge−sawdust using mixed metal oxides modified with ZSM-5 catalysts on dual-catalysts for product upgrading

Catalytic fast co-pyrolysis of sewage sludge and sawdust was performed using Py/GC-MS for pyrolytic product upgrades. Metal oxides (NiO and MoO3) and ZSM-5 catalysts had been introduced into single catalytic pyrolysis. The combination of NiO + MoO3 in mixed metal oxides (MMOs) was modified with ZSM-5 under a dual-catalyst with different catalytic layouts. In the pyrolysis process, the metal oxides specifically promoted the formation of phenols, ketones, and furans. ZSM-5 was proven to be more effective in producing aromatic hydrocarbons and phenols and in reducing the oxygenated compounds. The combination of MMOs with ZSM-5 effectively improved product distribution by increasing the production of aromatics and phenols. MMOs promoted the aromatics selectivity of undesirable PAHs (70.5%), however, the addition of ZSM-5 to MMOs appeared to reduce and inhibit the formation of PAHs by 0.85%. The highest yield of aromatics was obtained by the layout of the ZSM-5/MMO dual catalysts layout which was 21.6%. Dual catalysts of MMOs and ZSM-5 in separated layout created promising effects in further increasing the production of aromatic hydrocarbons and phenols compared to the mixture of MMOs modified ZSM-5.

Catalytic upgrading of coal tar coupling with methanol using model compound over hierarchal ZSM-5 for increasing light aromatic production under atmosphere pressure

A new route for upgrading coal tar to aromatics was investigated. o-Cresol as model compound was investigated the coupling reaction of coal tar with methanol. ZSM-5 zeolite by 0.3 mol L−1 NaOH treatment showed the best catalytic performances due to higher Brønsted acid sites and larger mesopores. Compared with cresol as sole reactants, mixing methanol significantly promoted the production of aromatics and restrained coke deposition through methylation and hydrogen transfer. Higher yield of aromatics was obtained with increasing methanol/cresol molar ratio, indicating that more aromatic hydrocarbons were produced via providing methyl groups rather than active hydrogen from methanol. Moreover, the types of aromatic hydrocarbons could be tuned by alkylation of methylbenzene with methanol. Main products were toluene, xylene and trimethylbenzene due to the effect of steric hindrance of larger molecules of polymethylbenzene.

In situ and Ex situ Catalytic Pyrolysis of Microalgae and Integration With Pyrolytic Fractionation.

Microalgae are attractive feedstocks for biofuel production and are especially suitable for thermochemical conversion due to the presence of thermally labile constituents—lipids, starch and protein. However, the thermal degradation of starch and proteins produces water as well as other O- and N-compounds that are mixed-in with energy-dense lipid pyrolysis products. To produce hydrocarbon-rich products from microalgae biomass, we assessed in situ and ex situ catalytic pyrolysis of a lipid-rich Chlorella sp. in the presence of the HZSM-5 zeolite catalyst over a temperature range of 450–550°C. Results show that product yields and compositions were similar under both in situ and ex situ conditions with benzene, toluene and xylene produced as the primary aromatic products. Yields of aromatics increased with increasing temperature and the highest aromatic yield (36.4% g aromatics/g ash-free microalgae) and selectivity (87% g aromatics/g bio-oil) was obtained at 550°C. Also, at this temperature, oxygenates and nitrogenous compounds were not detected among the liquid products during ex situ catalytic pyrolysis. We also assessed the feasibility of a two-step fractional pyrolysis approach integrated with vapor phase catalytic upgrading. In these experiments, the biomass was first pyrolyzed at 320°C to degrade and volatilize starch, protein and free fatty acids. Then, the residual biomass was pyrolyzed again at 450°C to recover products from triglyceride decomposition. The volatiles from each fraction were passed through an ex situ catalyst bed. Results showed that net product yields from the 2-step process were similar to the single step ex situ catalytic pyrolysis at 450°C indicating that tailored vapor phase upgrading can be applied to allow separate recovery of products from the chemically distinct biomass components—(1) lower calorific value starch and proteins and (2) energy-dense lipids.

The Experimental Research on Efficient Process of Bio-aromatics Production

The process research of biomass catalytic cracking for production of bio-aromatics was performed with a 50kg/h riser reactor designed by China Energy Conservation and Environmental Protection Group (CECEP). The catalyst was chosen on the basic of a previous study, were Zn2+ exchanged zeolite type catalyst supplied by China University of Petroleum. Via analysis of the liquid product collected in different temperatures, influence of reaction temperature on the yield of bio-aromatics is investigated in this paper, the high yield of aromatics form corn stalk is 15.5wt%, obtained at 500°C, while gas yield is 33.5wt%. The creative process described in this paper provides a new efficient and easily scaled method for bio-aromatics production, also could be available to industrial pilot plant design studies.

Direct conversion of CO2 to aromatics with high yield via a modified Fischer-Tropsch synthesis pathway

The direct conversion of CO2 to aromatics not only reduces carbon emissions but also provides an alternative way for value-added chemicals synthesis. Even though the hydrogenation of CO2 to aromatics has been realized via a methanol-mediated pathway or a modified Fischer-Tropsch synthesis route, low yield of aromatics is still the bottleneck of this strategy. Here, we develop a multifunctional catalyst composed of Na modified Fe-based catalyst and hollow acidic zeolite H-ZSM-5 to catalyze the hydrogenation of CO2 to aromatics by single pass. Na modified Fe-based catalyst prepared by pyrolysis of Fe-based metal-organic frameworks (Fe-MOFs) can boost the formation of alkenes intermediates because of its high active sites accessibility and precisely tailored catalytic interfaces. Thereafter, the produced alkenes can be converted to aromatics via the dehydrogenation and cyclization reactions when they diffuse to the acid sites of H-ZSM-5. The hollow H-ZSM-5 with short diffusional channels, appropriate density and strength of acid sites guaranteed the high yield of aromatics (203.8 gCH2 kgcat−1 h−1). Furthermore, the driving force in the tandem process can be attributed to the cooperative interplay between the multifunctional catalysts. The CO2 adsorbed on Fe-based catalyst can be employed as acceptors for H species produced from the dehydrogenation and cyclization reactions, thereby increasing the yield of aromatics by shifting the chemical thermodynamic equilibrium.

Investigation of hot char catalytic role in the pyrolysis of waste tires in a two-step process

This study pursues the valorization of waste tires by pyrolysis using a different approach for tire parts, specifically, the tire tread rubber and side wall rubber. Tire tread rubber was used to produce hot char with the purpose of using it as cracking catalyst. Side wall rubber was valorized by pyrolysis and online catalytic pyrolysis over tire tread rubber derived hot char in two fixed bed reactor. This work aims to improve the quality of pyrolysis products using tire tread rubber derived hot char as catalyst. The thermal decomposition behavior and products characteristics were tested by means of TG-FTIR, GC, GC-MS, nitrogen adsorption and SEM. Under catalytic pyrolysis temperature of 500−550 °C, a high yield of valuable single ring aromatics (concentration in the oil of 50 %) was obtained. The yield of gas can reach 10.5 wt.% after catalytic pyrolysis, which only 3.0 wt.% without catalytic pyrolysis. The yield of undesirable byproducts as PAHs and carbon deposits was also limited. This strategy represents a novel and feasible alternative to traditional waste tire catalytic pyrolysis processes using expensive catalysts as zeolite.