Ethane Aromatization Research Articles

Oxidative Aromatization of Ethane

This study is focused on examining the incorporation of oxidative dehydrogenation into the aromatization of ethane, utilizing thermodynamic analysis and catalytic experiments. The catalysts were characterized by inverse temperature programmed reduction, X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD). The results indicated that a blend of the M1 catalyst, containing oxides of vanadium, niobium, and tellurium, with H‐ZSM‐5, serves as an effective catalyst system for the oxidative aromatization of ethane at T = 380 °C. The M1's role in the oxidative dehydrogenation of ethane contributes to de‐bottlenecking the essential step of the reaction. On the zeolitic catalyst aromatic compounds are formed from a surface hydrocarbon pool. In parallel, the oxidation of these intermediates was observed. Also, the formation of paraffins through H‐transfer was evident from the catalytic results. While the zeolite underwent significant deactivation due to coking, the M1 catalyst demonstrated highly stable activity. Interestingly, the system did not show any synergistic effects. Based on the structure‐activity relation of the catalytic system a reaction mechanism is proposed.

CO2-assisted ethane aromatization over zinc and phosphorous modified ZSM-5 catalysts

The tandem reactions of CO2-assisted oxidative dehydrogenation and aromatization (CO2-ODA) of ethane were investigated over ZSM-5 modified with zinc (Zn) and phosphorus (P) by experimental studies and DFT calculations. The nature of active Zn species and their interaction with P were elucidated for understanding Zn/P-ZSM-5 catalyzed CO2-ODA reaction of ethane. Compared to the direct dehydrogenation and aromatization (DDA) reaction, the Zn/P-ZSM-5 catalyst possessed higher ethane conversion, enhanced aromatics yield, and better stability in the CO2-ODA reaction. The presence of CO2 reduced the carbon deposition, stabilized the Zn species, and thereby facilitated the generation of more liquid aromatics in CO2-assisted ethane aromatization. In situ characterization and DFT calculations provided insight into the mechanisms of CO2-ODA over the Zn/P-ZSM-5 catalyst.

Coupling CO2 reduction with ethane aromatization for enhancing catalytic stability of iron-modified ZSM-5

The shale gas revolution and the carbon-neutrality goal are motivating the landscape toward the synthesis of value-added chemicals or fuels from underutilized ethane with the assistance of greenhouse gas CO2. Combining ethane aromatization with CO2 reduction offers an opportunity to directly produce liquid products for facile separation, storage, and transportation. In the present work, Fe/ZSM-5 catalysts showed promise in the simultaneous CO2 reduction and ethane aromatization at atmospheric pressure and 873 K. The catalysts were further investigated using X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) measurements under in-situ conditions, indicating that most of Fe species existed in the form of Fe oxides and a portion of Fe was incorporated into the ZSM-5 framework generating Lewis acid sites. Both types of Fe species remained almost unchanged under reaction conditions, contributing to an enhanced aromatization activity of Fe/ZSM-5. The effects of CO2 and steam on the acid sites and in turn aromatization activity were also investigated by transient studies, which exhibited a reversible modification behavior. Moreover, CO2 was identified to be critical to enhance coke resistance and in turn catalyst stability. This work highlights the feasibility of using CO2 to assist the upgrading of abundant ethane from shale gas to aromatics over non-precious Fe-based zeolite catalysts.

Comparative study on the catalytic behaviors of zeolites with different diffusion limitation in ethane aromatization

The design of zeolite-based catalysts with reduced diffusion limitation has attracted much attention for the enhanced activity and stability in light alkane aromatization. Here we employed three types of zeolite-based catalysts including micron zeolite, solid nano zeolite, and hollow zeolite with nano size to investigate the effects of diffusion length and pore structure of zeolites on their mass transport efficiency and catalytic performance during ethane aromatization. It was indicated that the shortened diffusion length and increased mesoporosity of Zn/hollow-HZSM-5 endow it with substantial improvement in mass transport, leading to enhanced accessibility to active acid sites and rapid escape of formed lighter aromatics rather than further polymerization to form coke. Contrarily, the solid micron zeolites with long diffusion path experience strong diffusion limitation, which extends the contact time of reactants and products with the active acid sites within zeolites thus resulting in severe coke deactivation. After being subjected to ethane aromatization for 400 min, the aromatics selectivity toward Zn/hollow-HZSM-5 catalyst retained 50%, which is almost threefold with respect to that of the solid Zn/micro-HZSM-5 and Zn/nano-HZSM-5. Based on the Thiele modulus, it can be suggested that shortening diffusion length and introducing mesopores into zeolites can effectively alleviate diffusion resistance, then enhance their catalytic activity and stability toward ethane aromatization.

Mechanism and Kinetics of Ethane Aromatization According to the Chemical Transient Analysis

The need for on-purpose techniques for the conversion of cheaper and abundant light alkanes to petrochemical products has revitalized research interests on light alkanes aromatization. Here ethane/propane aromatization and ethylene oligomerization over the representative Zn-HZSM-5 and Pt/HZSM-5 catalysts have been studied by the step-perturbation transients to provide insight into the kinetics and mechanisms leading to higher olefins and aromatics formation from ethane aromatization. The time-dependent catalytic behavior during the build-up and back-transient between ethane and inert, ethane and propane, as well as ethylene and inert, has been extensively discussed. We suggested that the hydrocarbon-pool mechanism be involved once ethylene was produced from the dehydrogenation of ethane. The oligomerization/cracking, cyclization, and dehydrogenation/hydride transfer reactions involved with the hydrocarbon-pool species reach the thermodynamic equilibrium quickly. The initial ethane dehydrogenation and the final formation of aromatics from their corresponding intermediates are slow surface-reactions. The rate constants k for benzene, toluene, and xylene formation from the “lumped hydrocarbon-pool” have been evaluated based on the first-order kinetic model of the back-transient. The rate constants k for aromatics over the Pt0 clusters/particles in the Pt/HZSM-5 are ⁓ 20–30% higher than that over the Zn (II) cations in the Zn-HZSM-5 catalyst.

Mesoporous HZSM-5 Supported Zn Catalyst for Improved Ethane Aromatization

Ethane aromatization is a promising process to achieve the efficient utilization of abundant ethane into high value-added chemicals. However, rapid coking deactivation has hindered the application of this technique. In this work, to improve catalyst stability, mesopores are introduced into the conventional Zn modified HZSM-5 catalysts. ICP, XRD, N2 adsorption–desorption, HRTEM, NH3-TPD, TG, and XPS are used to study the structure property, acidity, and coke formation of conventional and mesoporous catalysts. For ethane aromatization, upon reacting for 262 min, the yield of main products including benzene, toluene, and ethylene decreased by 48.7% for conv-Zn/HZSM-5 while only 16.6% for meso-Zn/HZSM-5. The significantly enhanced catalytic activity and stability of meso-Zn/HZSM-5 is primarily ascribed to the generation of mesopores after alkali treatment. As suggested by TG and N2 adsorption–desorption, conv-Zn/HZSM-5 exhibited not only faster coke deposition than meso-Zn/HZSM-5, but also major coke formation within the micropores, thus accelerating the catalyst deactivation. In contrast, the introduction of mesopores seems to availably facilitate the diffusion and escape of products from zeolite channels and subsequently suppress the internal coke formation, resulting in improved catalyst stability. In addition, a reaction-regeneration protocol was operated on meso-Zn/HZSM-5, which can effectively remove the deposited coke and extend the life of catalyst.

Nickel/gallium modified HZSM-5 for ethane aromatization: Influence of metal function on reactivity and stability

Bimetallic catalysts often outperform their monometallic counterparts due to the synergistic effect. Here we reported that the Ni/Ga co-functionalized HZSM-5 catalyst, specifically with Ni1/Ga1 stoichiometric ratio, shows significantly improved selectivity (above 80 %) and stability than the Ni/HZSM-5 catalyst and higher activity (with identical selectivity) than the Ga/HZSM-5 catalyst in ethane aromatization. According to the transient experiment, the Ga and Ni1Ga1/HZSM-5 catalysts show an induction period of a few minutes. However, for Ni/HZSM-5 and Ni1Ga1/3/HZSM-5, the induction period increased to >10 min and >30 min, respectively, where up to 100 % of ethane was converted into methane and coke through cracking/hydrogenolysis. Based on the generalized power-law equation model, a modified model for deactivation kinetic was proposed. Consequently, the influence of the metal function on the kinetic parameters was discussed. We anticipate the formation of Ni3Ga intermetallic alloy and its synergy with the exchanged Gaδ+ to be responsible for optimal BTX formation.

Improved ethane conversion to ethylene and aromatics over a Zn/ZSM-5 and CaMnO3-δ composite catalyst

Abstract Ethane conversion to ethylene and aromatics over Zn/zeolite catalysts is a promising technology for efficient exploitation of light alkanes. However, the reaction faces two major hurdles including the limited ethane conversion due to thermodynamics and the drastic catalyst deactivation by kinetical coke accumulation. Here we present a route to improve ethane conversion using a composite catalyst, involving Zn/HZSM-5 for ethane dehydroaromatization and CaMnO3-δ perovskite for in situ selective hydrogen oxidation. The in situ H2 consumption shifts ethane dehydrogenation equilibrium to the desired side and can obviously increase the yield of target product. Furthermore, it is found that the in situ generated H2O through H2 combustion can significantly suppress the coke formation and consequently enhance the stability of the composite catalyst. After 400 min reaction, a product yield of 23% was retained over the composite catalyst, almost a threefold increase with respect to the Zn/HZSM-5 reference (8%). It is anticipated that this novel composite catalyst combined with an efficient reactor technology may improve the viability of ethane aromatization in utilization.

Different mechanisms of ethane aromatization over Mo/ZSM-5 and Ga/ZSM-5 catalysts

Aromatization of light hydrocarbons can contribute to a secure supply of aromatics for the chemical industry. In this work, we investigate the influence of modification of zeolite ZSM-5 with Ga and Mo on the reaction mechanism underlying the activation and aromatization of ethane. Well-defined Mo/ZSM-5 and Ga/ZSM-5 zeolites efficiently promote ethane aromatization to benzene-toluene-xylene mixtures. Both catalysts suffer from coke formation, which leads to rapid deactivation. From catalytic tests, temperature-programmed surface reaction and pulsed reaction experiments, we infer that ethane conversion on Ga/ZSM-5 follows a conventional sequential dehydrogenation-oligomerization-aromatization mechanism, while the reaction over Mo/ZSM-5 involves reactive surface carbon (hydrocarbon pool) species.

Ethane aromatization and evolution of carbon deposits over nanosized and microsized Zn/ZSM-5 catalysts

Nanosized Zn/HZSM-5 facilitated the faster escape of light aromatics from zeolite channels and exhibited higher product yield and improved stability.

Tandem Reactions of CO2 Reduction and Ethane Aromatization.

Aromatization of light alkanes is of great interest because this can expand the raw materials used to produce aromatics to include fractions of natural gas that are readily available and inexpensive. Combining CO2 reduction with ethane dehydrogenation and aromatization can also mitigate CO2 emissions. A one-step process that can produce liquid aromatics from the reactions of CO2 and ethane using phosphorus (P)- and gallium (Ga)-modified ZSM-5 has been evaluated at 873 K and atmospheric pressure. The addition of P improves the hydrothermal stability of Ga/ZSM-5, reduces coke formation on the catalyst surface, and allows the formation of more liquid aromatics through the tandem reactions of CO2-assisted oxidative dehydrogenation of ethane and subsequent aromatization. Density functional theory calculations provide insights into the effect of Ga- and P- modification on ethane dehydrogenation to ethylene as well as the role of CO2 on the production of aromatics.

Ethane Aromatization over Zn-HZSM-5: Early-Stage Acidity/Performance Relationships and Deactivation Kinetics

Catalytic conversion of ethane to aromatics (BTX) over metal/HZSM-5 catalysts involves significant catalyst deactivation due to coking. Consequently, true acidity/performance relationships are escaped if the intrinsic catalyst acidity was correlated to the “steady-state” performance. Here, the effect of acidity on the early-stage performance and time-dependent deactivation kinetics has been investigated. The early-stage ethane conversion and BTX selectivity both increased with decreasing Si/Al2 ratios. Specifically, the space–time yields of BTX increase linearly with increasing Brønsted acidity, indicating Brønsted acids as the main active sites for BTX. Further evidence can be found from the transient experiment (C2H6/Ar ↔ C2H6/NH3) and C2H4-TPSR. A promotion effect of the Zn(II) sites (mainly responsible for ethane dehydrogenation) on BTX formation was also observed. With time-on-stream, the catalytic performance attenuated due to coking, which can be modeled as “r(t) = r0/(1 + ktα)” kinetically, and the parameters (for aromatics) k decreased and α increased with decreasing acidity.

Transient Kinetic Study of Ethane and Ethylene Aromatization over Zinc-Exchanged HZSM-5 Catalyst

The conversion of ethane and ethylene to aromatics over a zinc-exchanged HZSM-5 catalyst has been studied by chemical transient kinetic analysis in a flow reactor under atmospheric pressure. Time-dependent early stage/build-up catalytic behavior and the kinetic parameters of products decay during the back-transient have been discussed extensively at different reaction temperatures. For both ethane and ethylene aromatization, the delay times (relevant to the initial appearance of the reactant in the gas phase) of the formation of aromatics are 10–15 s during the build-up, which decreases with increasing temperature. On the basis of quantitative back-transient analysis, the rate constants for the formation of benzene, toluene, and/or xylene range from 5 to 30 × 10–3 s–1 dependent upon the reaction temperatures. According to the Arrhenius equation, the activation energies for the formation of benzene and toluene during ethane aromatization are 57 and 73 kJ/mol, respectively, which are relatively higher than ...

Deactivation Mechanism and Regeneration Study of Ga–Pt Promoted HZSM-5 Catalyst in Ethane Dehydroaromatization

Direct nonoxidative conversion of ethane to aromatics has become an effective way of upgrading shale gas. Metal-promoted shape selective zeolite catalysts are often used for aromatization. Although the coking issue of the catalysts in ethane aromatization has been reported, the deactivation mechanism and the performance of regenerated Ga–Pt promoted HZSM-5 needs to be further investigated. The objective of this study is to elucidate deactivation mechanism of Ga–Pt promoted HZSM-5 and investigate the feasibility of regenerating deactivated catalysts for commercial viability. When using lower concentration of oxygen (2 vol %) for regeneration, decreased catalyst deactivation rate was observed. The metal particle size, crystalline structures, and acidity are characterized by various analytical instrumentations (TEM, XRD, NH3-TPD). The change of Bronsted acidity was observed on regenerated catalysts. The results showed that metal agglomeration and leaching of Pt from homogeneous Ga–Pt particle were the main causes of deactivation other than coke deposition, indicating that stabilization of bimetallic metal particles on zeolite surface is critical.

Progress and prospects in catalytic ethane aromatization

Optimal ethane-to-aromatics catalyst design requires carefully tuning metal and zeolite catalytic sites to work in conjunction.

Conversion of Light Alkane to Value-Added Chemicals over ZSM-5/Metal Promoted Catalysts

Gallium–platinum promoted HZSM-5 is found to be a promising catalyst for ethane aromatization reaction. The influence of Pt as a promoter on the activity of Ga/HZSM-5 catalyst for ethane aromatization has been investigated. Comparative study was performed between bimetallic Ga–Pt based and Mo based HZSM-5, where the GaPt/HZSM-5 showed better aromatic and hydrogen selectivity. Pt promoted Ga/HZSM-5 catalyst exhibited higher activity compared to pure Ga/HZSM-5 catalyst. The presence of platinum in the gallium zeolite considerably accelerated dehydrogenation step in ethane aromatization. In addition, GaPt/HSZM-5 deactivated significantly slower than Mo/HZSM-5 and Ga/HZSM-5. TPO study of spent catalysts revealed that carbonaceous deposit on GaPt/HZSM-5 catalyst was burnt off at lower temperature compared to pure Ga/HZSM-5 catalyst, indicating the presence of Pt facilitated hydrogen spillover resulting in hydrogenolysis of coke precursors. The reaction mechanism associated with aromatic formation is postulated...

Upgrading of stranded gas via non-oxidative conversion processes

Ethane aromatization was carried out using metal promoted ZSM-5 catalysts. Desired products including ethylene and aromatics were obtained over Pt and Mo promoted ZSM-5 zeolite under reaction conditions of 600°C, 0.1MPa and GHSV=1000h−1. Results indicated that aromatics were formed via ethylene intermediate. Although ethane conversion and selectivity to aromatics were influenced by metal promoters, the distribution of benzene, toluene, xylenes and C9 aromatics depends mainly on the shape selective property of the ZSM-5. Ethane aromatization catalyst deactivated over time due to carbon deposition and metal leaching. Although oxidative regeneration could recovered 90% activity, the catalyst deactivated even faster after regeneration. For the purpose of economic comparison between direct and indirect natural gas conversion, the performance of edge coated Co-Re/γ-Al2O3 Fischer-Tropsch synthesis catalyst was presented. Even with capital savings on downstream refining, indirect natural gas conversion shows lower internal rate of return (IRR), largely because of higher capital and operating costs in syngas production.

Ethane and ethylene aromatization on zinc-containing zeolites

The importance of balance between the number of Zn and Brønsted acid sites for aromatization of ethane and ethylene on Zn-ZSM-5 is discussed.

Deactivation of a Zn-Containing zeolite in ethane aromatization

Ethane conversion into aromatic hydrocarbons over a high-silica ZSM-5-type zeolite doped with zinc by impregnation has been investigated. The deactivation of the Zn-containing zeolite at different stages of ethane conversion has been studied by temperature-programmed ammonia desorption, differential thermal analysis, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The nature and distribution of active phases and coke deposits on the catalyst surface have been determined. The Zn/ZSM-5 catalyst shows a relatively high activity and stable performance in ethane aromatization.

Catalytic aromatization of ethane on zinc-modified zeolites of various framework types

Zeolites of the ZSM-5, ZSM-8, ZSM-11, and ZSM-12 framework types have been prepared by hydrothermal synthesis from alkaline alumina-silica gels, and modified with zinc by the impregnation method. The acid properties of the zeolites have been examined, and it has been found that the catalysts differ from one another in distribution and relative amount of acid centers of various types. The feasibility of the direct chemical conversion of ethane to aromatic hydrocarbons on the zinc-containing zeolites of various framework types has been shown. It has been found that the structure of high-silica zeolites affects the activity and selectivity of the zinc-containing catalysts prepared from them. It has been shown that the most effective catalyst for the ethane-to-aromatics conversion process is the zinc-modified ZSM-5 type zeolite.