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

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.

Integrated autothermal oxidative coupling and steam reforming of methane. Part 2: Development of a packed bed membrane reactor with a dual function catalyst

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.

Sol–gel method for synthesis of Mn–Na2WO4/SiO2 catalyst for methane oxidative coupling

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

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

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.

In this study, three different reactor concepts for the oxidative coupling of methane (OCM) reaction are examined at the miniplant scale. Their performance and response to variations in key process parameters, such as temperature and gas hourly space velocity (GHSV), are evaluated over a wide range. In addition to the conventional Packed Bed Reactor (PBR), Packed Bed Membrane Reactor (PBMR), and Chemical Looping Reactor (CLR) approaches were tested. The PBMR was realized with a porous ceramic α-Alumina membrane as air/O2 distributor. The CLR was operated in a poly-cyclic operation. Similarities of the different reactor concepts as well as layout-immanent differences with regard to changes in reaction conditions could be identified and advantages and disadvantages of the processes highlighted. The results show that C2 selectivity can be improved by both PBMR and CLR in comparison to conventional PBR, possibly reducing cost-intensive downstream units. While a PBMR can slightly improve selectivity (23%) while keeping the same conversion compared to a PBR, the use of a CLR allows for achieving exceptionally high selectivities of up to 90%. In order to address the low conversion, CLR tests were carried out with an additional O2 carrier material, which led to a significant improvement in terms of C2 yield. In addition to an evaluation and comparison of the different reactor concepts, the findings at the miniplant scale provide estimates of their potential use and scalability.

A novel autothermal reactor concept for thermal coupling of the exothermic oxidative coupling and endothermic steam reforming of methane

Oxidative coupling of methane (OCM) in a catalytic membrane reactor and comparison of its performance with other catalytic reactors

Analysis of oxidative coupling of methane in membrane reactors

The oxidative coupling of methane (OCM) reaction system was investigated in a packed-bed membrane reactor (PBMR) numerically via a comprehensive computational fluid dynamics (CFD) study. In this context, the complete set of momentum, mass, and energy balances were solved through finite-volume method in cylindrical coordinate system. The fractional-step method was utilized to decouple the reaction source terms from the convection-diffusion terms. The general observed trends for variation of the components' concentrations along the bed were successfully explained by analyzing the rate of reactions. In this study, the effect of membrane thermal conductivity, and oxygen permeation were also examined which can affect the OCM reactor and process performance significantly. Finally, the dynamics behavior of the system was studied and by following the reaction rates and the shift of reactions along the catalytic-bed and with time, the reaction mechanisms were discerned. The results of the performed CFD simulation can be used as a baseline for a possible optimization approach for OCM reactor performance improvement.

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.

The effects of the introduction of tetrachloromethane into the feedstream for the partial oxidation 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.