Integrated autothermal reactor concepts for oxidative coupling and reforming of methane

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.

Conceptual Process Design and Economic Analysis of Oxidative Coupling of Methane

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

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

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

This thesis illustrates catalytic activity, stability and intrinsic kinetics of methane steam reforming (MSR) reaction over noble metal catalysts. The main objective of this thesis is to evaluate a best performing catalyst based on the maximization of H2 production and minimization of CO in the synthesis gas produced from MSR reaction. The noble metal catalysts tested towards MSR reaction were Rh, Ru and Pt supported on different reducible and irreducible oxides. The oxides (CeO2, MgO and Al2O3) used in this work were synthesized from their nitrite precursor by Simultaneous combustion synthesis (SCS) while Nb2O5 was prepared by heat treatment of Niobic acid obtained from Companhia Brasileira de Metalurgia e Mineracao (CBMM, Brasil). In all the catalysts the noble metals were deposited on the support by wetness impregnation method, except Pt/CeO2 which was prepared by one shoot SCS method. All the prepared catalysts were calcined under different calcination regimes. The best performing catalysts were characterized by different techniques BET, CO chemisorption, porosiometery, XRD, XPS, ICP, TEM and SEM analyses. Efforts have been made to correlate the catalytic activity with the physical characterization. All the catalysts prepared were initially screened by MSR reaction in a tubular fixed bed quartz reactor of 4mm ID containing 30mg of catalyst diluted with 50mg of inert. For catalytic screening and stability test the feed was introduced at a weight hourly space velocity of 20 NLh-1g-1cat and steam to carbon ratio 3-4 depending upon the catalyst. The results obtained from basic screening of the catalysts were analyzed in terms of methane conversion, H2 produced in dry reformate and CO2 selectivity. Among all the catalysts tested towards MSR only two were chosen based on initial screening, Rh/CeO2 and Pt/CeO2, for the further test concerning catalyst stability. The stability of Rh/CeO2 and Pt/CeO2 catalysts was determined based on daily start up and shut down cycle (DSS) with a 6h performance period. The Pt/CeO2 catalyst was tested for a total of 150 h in which 100h performance was with DSS in N2 environment while 50h of catalyst activity with DSS in reaction environment. The Rh/CeO2 catalyst was tested for a total of 25 h catalyst activity with DSS in N2 environment. Additionally the Rh/CeO2 catalyst was also tested in 100h continuous ageing. Both the catalysts showed good results in terms of catalyst activity and stability during the time period. As Rh/CeO2 catalyst showed good activity during 100h continuous endurance this catalysts was chosen to evaluate the intrinsic kinetics of methane steam reforming. For the kinetics test firstly the heat and mass transfer limitations were evaluated both experimentally and theoretically. The reactor was operated in an integral mode and no inert was used in feed for the kinetic experiments. The effect of WHSV at constant S/C 3 on the methane conversion and product composition was also determined. The partial pressures of the reactants were varied by varying the steam-to-carbon ratio of the feed. An attempt was made to fit kinetic data obtained using the models available in literature. The kinetic data obtained was perfect fit for the model proposed by Berman, and the activation energy of Rh/CeO2 was found to be 38.6 kJ/mol

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.

Performance and reaction mechanism of Mg-doped and Li-doped La2O3 catalysts in oxidative coupling of methane: DFT and experiment study

Techno-economic analysis of oxidative coupling of methane: Current state of the art and future perspectives

In the second part of this paper (Part II), the potentials and characteristics of an industrial-scale Oxidative Coupling of Methane (OCM) process integrated with CO2-hydrogenation, ethane dehydrogenation, and methane reforming processes are highlighted. This novel process concept comprises a direct conversion of methane to ethane and ethylene and further conversion of the resulted carbon dioxide and remaining unreacted methane, respectively, to methanol and syngas. In this context, the selected experimental results of the catalytic CO2-hydrogenation to methanol reported in the first part of this paper (Part I), were utilized to represent its industrial-scale performance. The experimental results of the mini plant-scale operation of an OCM reactor and CO2 removal units along with the experimental and industrial data available for representing the operation and performance of all process-units in the integrated process structures were utilized to perform a comparative techno-economic environmental analysis using Aspen-Plus simulation and an Aspen Economic Process Analyzer. The experimental procedure and the results of testing the sequence of OCM and CO2-hydrogenation reactors are particularly discussed in this context. It was observed that in the sequential operation of these reactors, ethylene will be also hydrogenated to ethane over the investigated catalysts. Therefore, the parallel-operation of these reactors was found to be a promising alternative in such an integrated process. The main assumptions and the conceptual conclusions made in this analysis are reviewed and discussed in this paper in the light of the practical limitations encountered in the experimentations. In the context of a multi-scale analysis, the contributions of the design and operating parameters in the scale of catalyst and reactor as well as in the process-scale represented by analyzing the type and operating conditions of the downstream-units and the process-flowsheets on the economic and environmental performance of the integrated process structures were studied. Moreover, the economic impacts of extra ethylene and methanol produced respectively via the integrated ethane dehydrogenation and CO2-hydrogenation sections were analyzed in detail. The required capital investment was found to be even smaller than the yearly operating cost of the plant. The environmental impacts and sustainability of the integrated OCM process were found to be enhanced by securing a minimum direct CO2-emission and energy-efficient conversion of CO2 and the unreacted CH4, respectively, to methanol and syngas. Besides producing such value-added by-products, efficient operation of downstream process-units was secured by minimizing the energy usage and ethylene losses. Under the considered conditions in this analysis, the specifications of the finally selected integrated OCM process structure, providing the fastest return of investments (less than 8 years), are highlighted.

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

Simultaneous Synthesis of the Downstream Process and the Reactor Concept for the Oxidative Coupling of Methane (OCM)

An oxidative coupling of methane (OCM) is a promising process to convert methane into ethylene and ethane; however, it suffers from the relatively low selectivity and yield of ethylene at high methane conversion. In this study, a membrane reactor is applied to the OCM process in order to prevent the deep oxidation of a desirable ethylene product. The mathematical model of OCM process based on mass and energy balances coupled with detailed OCM kinetic model is employed to examine the performance of OCM membrane reactor in terms of CH4 conversion, C2 selectivity, and C2 yield. The influences of key operating parameters (i.e., temperature, methane-to-oxygen feed ratio, and methane flow rate) on the OCM reactor performance are further analyzed. The simulation results indicate that the OCM membrane reactor operated at higher operating temperature and lower methane-to-oxygen feed ratio can improve C2 production. An optimization of the OCM membrane reactor using a surface response methodology is proposed in this work to determine its optimal operating conditions. The central composite design is used to study the interaction of process variables (i.e., temperature, methane-to-oxygen feed ratio, and methane flow rate) and to find the optimum process operation to maximize the C2 products yield.

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.