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

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.

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.

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

Integrated autothermal oxidative coupling and steam reforming of methane. Part 1: Design of a dual-function catalyst particle

The effects of the introduction of tetrachloromethane into the feedstream for the partial oxidation and oxidative coupling of methane

Investigations of the selective partial oxidation of methanol and the oxidative coupling of methane over copper catalysts

The effect of heat transfer on products of a thermally coupled shell and tube reactor consisting of two processes: Steam reforming of methane and oxidative coupling of methane

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.

The catalytic oxidative coupling of methane (OCM), which can be used to obtain ethylene, is a major challenge in heterogeneous catalysis. This chapter mainly discusses the active sites of OCM catalysts, their reaction mechanisms, and their catalytic performance under various oxidative reaction conditions, including the OCM reaction network. In the OCM reaction, CH4 is oxidatively converted to C2H6 and then C2H4. After activation of CH4 on catalysts such as metal oxides, the formation of C2H6 proceeds in a homogenous gas phase via a free-radical mechanism. Thus, C2H6 is produced mainly by the coupling of the surface-generated •CH3 radical (methyl radical) in the gas phase. The C2H4/C2H6 yields are limited by the secondary reaction of •CH3 radicals with the catalyst and reactor surfaces and the further oxidation of C2H4 on the catalyst surface and in the gas phase. The nature of the active sites and the reaction mechanism have been investigated. Reactive oxygen ions, such as O− or O22−, are required for the activation of methane on catalysts. However, no feasible processes have resulted, despite a reasonable understanding of the elementary reactions in the OCM reaction. The non-oxidative coupling of methane (dehydrogenative coupling of methane) gives C2H4 and aromatic hydrocarbons at ~1000 K. Although the dehydrogenative coupling of methane is thermodynamically disadvantageous due to the large positive change in free energy, over-oxidation does not occur, and CO and CO2 are not formed. The catalytic performance of supported Fe catalysts, such as SiO2-supported Fe, are discussed, along with their catalytic properties.

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.

Oxidative coupling of methane over mixed metal oxide catalysts: Steady state multiplicity and catalyst durability

For more than three decades, Oxidative Coupling of Methane (OCM) process has been comprehensively investigated as an attractive alternative for the commercially available ethylene production technologies such as ethane and naphtha cracking. Developing a suitable catalyst and proper reactor feeding policy, reviewing and deploying the efficient methods in the separation and purification of the undesired and desired products, possible energy saving and process intensification in different sections of the OCM process, each has been the subject of many researches in the past. In this paper, the interconnections of these aspects will be addressed by reviewing the performance of different alternative structures and unit operations in different sections of the OCM process. As a systematic approach in this analysis, a concurrent engineering approach supported by the experimental data which was extracted from an OCM miniplant scale facility was applied. Using an efficient porous packed bed membrane reactor and a proper set of operating conditions, up to 25% C2-yield, 20% C2H4-yield, and 52% C2H4-selectivity and the highest observed fluidized bed reactor C2-yield was achieved in this OCM miniplant. This experimental analysis was performed in the chair of process dynamics and operation at Berlin Institute of Technology under the main framework of Unifying Concepts in Catalysis (UniCat) project. The economic analysis of the industrial-scale operation showed promising potentials and also advantages of the final proposed OCM process-structure in this research.

Oxidative coupling of methane has been studied over (Mn+A+W)/SiO2 catalysts in a continuous–flow micro reactor, where A represents an alkali ion of Li, Na, K or Cs having different weight percents. The main aim of this study is to find the role of alkali ions in interaction between Mn and W species with SiO2 to make a proper structure for catalyzing oxidative coupling of methane (OCM) reaction. The catalysts were characterized by XRD, SEM, FTIR, TPR and also the electrical conductivity was measured in air and under OCM reaction. It was found that for the formation of crystallized catalyst, the amount of alkali ion should be such that the catalyst containing tungsten transforms into A2WO4. Using a smaller amount of alkali ions does not result in crystalline catalyst by calcination under the same condition of temperature and atmosphere. However, under the OCM reaction condition the catalyst gradually turns into a crystalline structure and its catalytic performance, i.e. conversion and selectivity, for the OCM reaction is almost similar to the (Mn+A2WO4)/SiO2 catalyst. The transformation of the catalyst containing alkali ions from amorphous to crystalline one indicates a kind of structural flexibility of the catalyst under OCM atmosphere. The structural flexibility of the catalyst under the OCM reaction is considered to be the main chemical role of the alkali ions.

The catalytic oxidative coupling of methane (OCM) to C2 hydrocarbons with oxygen (O2 -OCM) has garnered renewed worldwide interest in the past decade due to the emergence of enormous new shale gas resources. However, the C2 selectivity of typical OCM processes is significantly challenged by overoxidation to COx products. Other gaseous reagents such as N2 O, CO2 , and S2 have been investigated to a far lesser extent as alternative, milder oxidants to replace O2 . Although several authoritative review articles have summarized OCM research progress in depth, recent oxidative coupling developments using alternative oxidants (X-OCM) have not been overviewed in detail. In this perspective, we review and analyze OCM research results reporting the implementation of N2 O, CO2 , S2 , and other non-O2 oxidants, highlighting the unique chemistries of these systems and their advantages/challenges compared to O2 -OCM. Current outlook and potential areas for future study are also discussed.

The study of composition of novel high temperature catalysts for oxidative conversion of methane