Influence of nanocatalyst on oxidative coupling, steam and dry reforming of methane: A short review

A direct method of converting natural gas into ethylene is the heterogeneously catalyzed oxidative coupling of methane (OCM), however, only with hydrocarbon yields limited to 30-35% despite enormous efforts to optimize the catalysts. By combining the exothermic OCM with a secondary process, namely steam reforming of methane (SRM), the methane conversion can be increased significantly while improving temperature control and simultaneously producing valuable synthesis gas. In this thesis, two different reactor concepts were developed to integrate the OCM and SRM reactions in an overall autothermal process, so that the OCM process is effectively cooled and the generated reaction energy is efficiently used to produce synthesis gas. The integration is most optimally achieved on the catalyst particle scale, which would eliminate the need for external heat exchange and opens up the possibility to use distributive oxygen dosing with which much higher product yields can be achieved. It is proposed to use a dual function catalyst particle in which the two chemical processes are physically separated by an inert, porous layer, such that additional diffusional resistances are intentionally created to control the reaction rates. This concept was studied with numerical simulations on the scale of a single catalyst particle and on reactor scale. It was found that the SRM and OCM reaction rates could be effectively tuned to achieve autothermal operation at the reactor scale, while the methane conversion was enhanced from 44% to 55%. An alternative integrated process can be achieved by combining OCM and SRM in a heat exchange reactor comprising of two separate reaction chambers which are thermally coupled. The OCM is carried out in packed bed reverse flow membrane reactor tubes submerged into a fluidized bed where the unconverted methane and byproducts from OCM are reformed, thus producing synthesis gas and consuming the reaction heat liberated by OCM. The feasibility of this concept is supported by experiments of OCM on a Mn/Na2WO4/SiO2 catalyst in a packed bed (porous Al2O3) membrane reactor. The results demonstrated that a C2 yield of 25-30 % can be achieved and that distributed feed of oxygen is optimal for the combined OCM/SRM reactor concept.

Combined steam reforming and dry reforming of methane using AC discharge

Dual-membrane reactor for methane oxidative coupling and dry methane reforming: Reactor integration and process intensification

The current study reviews the recent development in the direct conversion of methane into syngas, methanol, light olefins, and aromatic compounds. For syngas production, nickel‐based catalysts are considered as a good choice. Methane conversion (84%) is achieved with nearly no coke formation when the 7% Ni‐1%Au/Al2O3 catalyst is used in the steam reforming of methane (SRM), whereas for dry reforming of methane (DRM), a methane conversion of 17.9% and CO2 conversion of 23.1% are found for 10%Ni/ZrOx MnOx/SiO2 operated at 500 °C. The progress of direct conversion of methane to methanol is also summarized with an insight into its selectivity and/or conversion, which shows that in liquid‐phase heterogeneous systems, high selectivity (>80%) can be achieved at 50 °C, but the conversion is low. The latest development of non‐oxidative coupling of methane (NOCM) and oxidative coupling of methane (OCM) for the production of olefins is also reviewed. The Mn2O3–TiO2–Na2WO4/SiO2 catalyst is reported to show the high C2 yield (22%) and a high selectivity toward C2 (62%) during the OCM at 650 °C. For NOCM, 98% selectivity of ethane can be achieved when a tantalum hydride catalyst supported on silica is used. In addition, the Mo‐based catalysts are the most suitable for the preparation of aromatic compounds from methane.

Methane, which is the principal component of natural gas reserves, is currently being used for home and industrial heating and for the generation of electrical power. Methane is an ideal fuel because of its availability in most populated centres, its ease of purification and the fact that is has the largest heat of combustion compared to the amount of CO2 formed, among all hydrocarbons. On the other hand, methane is an under-utilised resource for chemicals and liquid fuels. Known resources of natural gas are enormous and rival those of liquid petroleum. Transportation problems with methane and the increasing oil price have led to world-wide efforts for directly converting methane into easy transportable value added products, such as ethylene (feedstock for petrochemicals), aromatics and liquid hydrocarbon fuels. The main goal of the work described in this thesis was the development of an auto thermal process, combining the exothermic oxidative coupling of methane and highly exothermic combustion (side)reactions with the endothermic processes of methane steam reforming and methane dry reforming. The desired products are ethylene and synthesis gas. Two concepts for the combined process of oxidative coupling and reforming of methane are proposed. Because of the high reforming activity of ethane and ethylene, contact between C2 hydrocarbons and the reforming catalyst should be avoided. One concept combines oxidative coupling and reforming in structured spherical catalyst particles, consisting of an outer layer of oxidative coupling catalyst and a core of a reforming catalyst. The second concept combines oxidative coupling and reforming in different reactor compartments, still facilitating heat exchange between both processes. After oxidative coupling, reactive separation of ethylene by alkylation with benzene is performed. The remaining mixture converted with reforming reactions to synthesis gas. The total process will convert methane, oxygen and benzene to synthesis gas and ethylbenzene.

Methane is one of the promising alternatives of petroleum, which should be used for not only a fuel but also a resource for hydrogen and more useful chemicals as with the petroleum. However, the selective methane conversion to them is still difficult in contrast to the combustion. Three types of photocatalytic reactions for methane conversion, i.e., the photocatalytic non-oxidative coupling of methane (2CH4 → C2H6 + H2), the photocatalytic dry reforming of methane (CH4 + CO2 → 2CO + 2H2) and the photocatalytic steam reforming of methane (CH4 + 2H2O → 4H2 + CO2), can take place around room temperature or at a mild condition such as 473 K using photoenergy and semiconductor photocatalyst. In the present short review, the details of each photocatalytic reaction and the design concept of the semiconductor photocatalysts for each photocatalytic methane conversion were summarized and discussed.

The growing concern of many countries globally about the greenhouse gas emissions have emphasized interest towards dry reforming of methane (DRM). For an oil and gas based economy such as the state of Qatar, CO2 emission is a big challenge, as it has rendered Qatar as the highest CO2 emitting country per capita in the world. The potential of DRM process for integration in the existing infrastructure of Qatar is a key aspect of this research as a part of exceptional proposal granted to Dr. Nimir Elbashir by QNRF aimed at CO2 fixation. DRM is a heterogeneous chemical reaction in which the two greenhouse gases; CH4 and CO2 are converted to synthesis gas. Synthesis gas or ‘syngas’ is a precursor to a large variety of value added chemicals including hydrocarbons via Fischer-Tropsch Synthesis (FTS). In addition to CO2, steam can also be used to reform methane into syngas in a process known as steam reforming of methane (SRM). Steam Reforming of Methane (SRM) ΔH298 = 206 kJ/mol (1) Dry Reforming of Methane (DRM) ΔH298 = 247 kJ/mol (2) In addition to these two processes, there is also an exothermic reforming process, known as the partial oxidation of methane (POX), where methane is combusted to yield syngas. DRM process is beset by numerous major process limitations including its high endothermicity, high rate of catalyst deactivation (due to carbon formation) and low-quality syngas yield ratio (H2:CO⇐1:1). These challenges have posed severe obstruction towards widespread commercialization of this technique. A synergistic amalgamation of the reforming of methane as DRM+SRM, DRM+POX and DRM+SRM+POX have been recommended in the literature as a way to tackle the intrinsic limitations of the DRM process. In the current work, such combinations of methane reforming processes have been simulated thermodynamically using direct Gibbs free energy (GFE) minimization method. Energy valuations of various case scenarios have been carried out under varying operating conditions (temperature, presssure and feed mole ratios) assuming both ideal gas conditions and non ideal regimes using cubic equations of state (Peng Robinson (PR), Redlich Kwong (RK) and Soave Redlich Kwong). The main objective of the thermodynamics aspect of this study is to find optimized condition of reduced energy requirement and reduced carbon deposition while maintaining considerable CO2 fixation in a combined reforming process. In order to completely understand the system, a one-dimensional pseudo-homogeneous fixed bed reactor model which incorporates all the transport limitations (heat, mass and momentum) for combined SRM/DRM processes is developed. Reaction kinetics utilizing Langmuir-Hinshelwood Hougen-Watson (LHHW) type rate expressions published in the literature for SRM and DRM under analogous operating conditions have been used in the reactor bed model. These model results will be further validated against the experimental data published in literature. The kinetic conversion profiles are then compared with the thermodynamic results to systematically determine the regimes of kinetic deviation (from equilibrium) for the combined SRM/DRM system. This approach of carrying out both thermodynamic and reaction engineering analysis is advantageous in understanding the reforming process in a broader view and will also help in setting base for experimental investigations. These modeling results will be used as pre-experimental initial findings for the NPRP exceptional project aimed towards development of highly effective and coke resistant catalysts.ReferencesPakhare, D. and J. Spivey, A review of dry (CO2) reforming of methane over noble metal catalysts. Chemical Society Reviews, 2014. 43(22): p. 7813-7837.Song, C., Tri-reforming: a new process for reducing CO2 emissions. Chemical Innovation, 2001. 31: p. 21-26.Jiang H, Li H, Zhang Y., Tri-reforming of methane to syngas over Ni/Al2O3—thermal distribution in the catalyst bed. Journal of Fuel Chemistry and Technology 2007. 35: p. 72-78.Noureldin, M.M.B., N.O. Elbashir, and M.M. El-Halwagi, Optimization and Selection of Reforming Approaches for Syngas Generation from Natural/Shale Gas. Industrial & Engineering Chemistry Research, 2014. 53(5): p. 1841-1855.

A new and very promising application of auto-thermal reactors is the coupling of endothermic and exothermic reactions where the product of the endothermic reaction is the desired one. Therefore, in this work, a reactor in which oxidative coupling of methane (OCM) and steam re-forming of methane (SRM) reactions take place simultaneously was modeled. The results were obtained in a wide range of different conditions such as inlet feed, inlet temperature, portions of OCM and SRM catalysts, and inlet velocity. In selection of the catalysts, more attention was drawn to prevent re-forming of OCM products. The main parameters of each reaction under different conditions such as conversion of the feed components, products selectivity and yield, temperature in the length of reactor, and component's concentration in the reactor were considered in course of this study. The results revealed that simultaneous OCM and SRM reactions in one reactor will tend to be auto-thermal, and the waste of energy will be reduced. The results also show that complete conversion of water and majority of methane and oxygen will decrease the amount of unwanted products at the reactor's discharge-a constraint that exists in single reactors of each reaction specially OCM.

Techno-economic analysis of integrating the methane oxidative coupling and methane reforming processes

Solid oxide electrolysis cell (SOEC) has emerged as a key enabling technology for achieving carbon-neutral energy systems, owing to its high efficiency and intrinsic compatibility with renewable energy sources. To date, research has primarily focused on three major processes in SOEC: H2O electrolysis, CO2 electrolysis, and H2O/CO2 co-electrolysis. In contrast, the electrochemical conversion of hydrocarbon fuels, despite its significant potential for value-added chemical production, remains underexplored and lacks a comprehensive systematic review. This review addresses recent progress in SOEC-mediated hydrocarbon conversion, including H2O/CO2 co-electrolysis for syngas generation, methane-assisted electrolysis, and the electrochemical transformation of C2H4 and other hydrocarbons. Particular attention is given to the integration of SOEC with partial oxidation, dry reforming, and oxidative coupling of methane. The review first outlines the structure and key materials of SOEC. It then summarizes the reaction mechanisms, current progress, and major technical challenges associated with each conversion pathway. Finally, it analyzes how advances in electrode material design, reaction mechanism modulation, and reactor engineering influence SOEC performance and long-term durability. Several critical technical bottlenecks, including carbon deposition, electrode degradation, and limited selectivity, are identified. A forward-looking research roadmap is proposed to guide the scale-up and practical deployment of SOEC for sustainable hydrocarbon fuel conversion.

Production of a hydrogen-enriched syngas by combined CO2-steam reforming of methane over Co-based catalysts supported on alumina modified with zirconia

CH4 valorisation reactions: A comparative thermodynamic analysis and their limitations

The development of society is dependent on commodities such as fuels and chemical feedstock. Most of these commodities are obtained from oil as raw material. Although the need to find a friendly solution to couple an economically viable energy model with a greener solution, it is known that technologies applying renewable sources are in an early stage of development. The conversion of methane into clean fuels or chemical feedstock with high commercial value, such as hydrogen, ethylene, or methanol is interesting from the energetic and economic point-of-view. Among the methods of methane conversion, the industrially used is the steam reforming (MSR), in which methane reacts with water to produce syngas, a mixture of CO and H2. Nevertheless, this reaction is highly endothermic and responsible for a large volume of CO2 emitted by the reactor burners that provide energy to the reactors. An interesting alternative process for methane conversion is the dry reforming of methane (DRM), which consists of the reaction of methane with CO2, also yielding syngas. The advantage of this reaction is the utilization of two harmful gases to the atmosphere. The disadvantage of this reaction is due to the catalyst deactivation by carbon deposition. In heterogeneous catalysis, there is a strong relationship between catalytic performance and surface and textural properties, that are outlined by the number and distribution of available active sites. In this way, different synthetic routes may be used to design these properties and obtain products of commercial interest, such as ethylene. The commercial production of ethylene occurs by the recuperation of refinery gases, thermal cracking of light hydrocarbons, mainly ethane and propane, or a combination of both processes. An alternative process of ethylene production may be from natural gas and or biogas. This process can be performed by the syngas route or by oxidative coupling of methane (OCM). The first process is an indirect conversion of methane and involves several steps, which increases the process costs. The second one is a direct conversion, where methane is directly converted into C2 (ethane and ethylene) hydrocarbons. Although the OCM is not yet a reaction on an industrial scale, several efforts are being made to design a catalytic system to achieve C2 hydrocarbons yields above 30%, the minimum required. Besides that, another technology has been studied to directly produce ethylene via the oxidative coupling of methane using CO2 as a mild oxidant (CO2-OCM). These technological routes for the valorization of methane and CO2 will be addressed in this review.

Design of a microchannel-based reactor module for thermally coupled reactions: Oxidative coupling and steam reforming of methane

99/01302 Polymer-oxide anode materials : Kerr, T. A. et al. Mater. Res. Soc. Symp. Proc., 1998, 496, 499–504