Hamid Reza Godini

Oxidative Coupling of Methane: Reactor Performance and Operating Conditions

Abstract In this work, the achievable performance in case of desired-product selectivity, yield and conversion are evaluated systematically for different reactors in order to find the optimum range of operation for the OCM process. This approach is applied to a nonisothermal plug flow reactor and a nonisothermal porous packed bed membrane reactor using different types of catalysts in the wide range of operating conditions. Moreover, a fluidized bed reactor is also considered. The results show that tracking the optimum area of operation has a monotonic direction under some range of operating conditions, whereas it reflects a qualitative trade-offs under some other ranges of operating conditions. For all investigated reactor concepts the likelihood of optimal operating conditions are found, and the best corresponding performance for all of them are reported.

Feasibility study of the Mn–Na2WO4/SiO2 catalytic system for the oxidative coupling of methane in a fluidized-bed reactor

The catalytic system Mn–Na2WO4/SiO2, known for its relatively stable performance for oxidative coupling of methane (OCM), has been thoroughly investigated in the past. In order to evaluate its catalytic performance, micro-fixed-bed reactors were used almost exclusively. This study aims to answer the question of whether this catalytic system would be applicable on a larger scale using a miniplant fluidized-bed quartz glass reactor. Special consideration was given for finding the optimal operating conditions and investigating whether catalyst abrasion and agglomeration could be limiting factors. In this study different compositions of the Mn–Na2WO4/SiO2 catalyst were tested. High sodium content catalysts were difficult to fluidize at the optimal reaction temperature due to severe agglomeration by melting. Low sodium content catalysts showed low selectivity to C2+ hydrocarbons. Catalysts containing intermediate levels of sodium were used for detailed testing as they showed promising performance as well as good fluidizability. The influence of the different reaction parameters on performance was tested, resulting in 19.4% C2 yield at 40% C2 selectivity. Catalysts before and after reaction were characterized regarding composition, crystalline phases, surface morphology and thermal stability. After time on stream, all catalysts exhibited a reduction in specific surface area, changes in Mn valence state (Mnδ+ (2 ≤ δ ≤ 3)) and changes in morphology due to grain growth.

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

Abstract The Oxidative Coupling of Methane (OCM) is a promising alternative for the oil based production of olefins. The aim is the catalytically conversion of methane containing natural gas to ethylene, which builds up a base for olefins and further synthesis. The overall yield is still limited to 30%. Beside new catalysts and reactors, new concepts for integrated downstream processes are necessary to overcome the exist limitations [3]. To meet this target as fast as possible, the downstream process, the reactor and the catalyst are designed simultaneously. This novel strategy causes particular interactions between the downstream process, the reactor and the catalyst design. Design specifications for each part of the plant are established as targets such as carbon dioxide concentration. In order to modify and investigate the different approaches in our mini plant easily, the whole process is designed and built up modular. The entire process is divided into three units: reaction, purification and separation unit. On each unit interfaces of each unit the targets and the process specification are defined by laboratory screenings. Due to the novel process design strategies, the downstream impose specification to the reaction unit and the catalyst too e.g. maximum carbon dioxide concentration for the reaction product. For this purpose different reactor concepts like membrane reactors, fluidized bed and fixed bed reactors have to be investigated along with different integrated downstream concepts. The most promising reactor concepts are discussed in this article regarding their implementation and their influence on the separation process. The downstream concept should also be design appropriately for the OCM Process. Therefore a novel hybrid purification process, a combination of a membrane and an amine unit for the carbon dioxide removal could be implemented and is presented in this article. The modification results of this novel hybrid process are presented along with the simulation results for the hybrid process and they are discussed regarding the whole OCM Process. Thus the results have to be validated in our mini plant.

Sequential Flowsheet Optimization: Maximizing the Exergy Efficiency of a High-Pressure Water Scrubbing Process for Biogas Upgrade

Abstract Biogas is an important renewable energy source and potential raw material for the chemical industry. Its utilization frequently requires a treatment and/or upgrade step. The aim here is to maximize the exergy efficiency of a high-pressure water scrubbing process for upgrading biogas into biomethane by coupling a sequential modular simulation flowsheet with different optimization algorithms. By setting adequate operating pressures, and reducing cycle water and stripping air flowrates, an exergy efficiency of 92.4% is reached.

Use of RSM for the multivariate, simultaneous multiobjective optimization of the operating conditions of aliphatic carboxylic acids ion-exclusion chromatography column: Quantitative study of hydrodynamic, isotherm, and thermodynamic behavior

The present study evaluates the capability of ion exclusion chromatography (IEC) of short chain aliphatic carboxylic acids using a cation exchange column (8% sulfonated cross-linked styrene-divinylbenzene copolymer) in different experimental conditions. Since one of the prerequisites to the development of an efficient carboxylic acid separation process is to obtain the optimum operational conditions, response surface methodology (RSM) was used to develop an approach to evaluate carboxylic acids separation process in IEC columns. The effect of the operating conditions such as column temperature, sulfuric acid concentration as the mobile phase, and the flow rate was studied using Central Composite Face (CCF) design. The optimum operating conditions for the separate injection of lactic acid and acetic acid is temperature of 75 °C, sulfuric acid concentration of 0.003 N for both acids and flow rate of 0.916 (0.886) mL/min for acetic acid (lactic acid). Likewise, the optimum conditions for the simultaneous injection of acetic and lactic acid mixture are the column temperature of 68 °C, sulfuric acid concentration of 0.0003 N, and flow rate of 0.777 mL/min. In the next step, the adsorption equilibria of acetic acid and lactic acid on the stationary phase were investigated through a series of Frontal Analysis (FA), Frontal Analysis by Characteristic Points (FACP), and using Langmuir isotherm model. The results showed an excellent agreement between the model and experimental data. Finally, the results of thermodynamic studies proved that the IEC process for separation of acetic and lactic acid is a spontaneous, feasible, exothermic, and random process with a physical adsorption mechanism. The results of the current paper can be a valuable information in the stages of designing IEC columns for separation of aliphatic carboxylic acids.

CHAPTER 3:Oxidative Coupling of Methane in Membrane Reactors

Oxidative Coupling of Methane (OCM) processes have been investigated as an alternative promising approach for ethylene production for the last three decades. Having considered the performance of the state-of-the-art OCM catalysts and the OCM reaction mechanism, improving the performance of the OCM membrane reactor could be considered as an important contribution to address such a complicated reactor engineering task. In this context, a systematic methodology implementing inorganic membranes, properly modified via silica-based materials, and the thereby achieved outstanding OCM membrane reactor performances are reported here. Moreover, the most important aspects of the performance analysis of OCM membrane reactors, especially in the context of the thermal-engineering characteristics of these systems, are discussed. Such analysis, for the most part, can be applied similarly to analyze other highly exothermic reaction systems in membrane reactors. Interactions between the membrane and the benchmark Mn–Na2WO4/SiO2 catalyst are also discussed. Furthermore, along with reviewing the general aspects of the model-based analysis of OCM membrane reactors, the potential of integrated OCM membrane reactors, such as dual-membrane reactors, is also highlighted. The special characteristics of modeling such non-isothermal reaction systems with significant mass and heat integration in both radial and axial dimensions are also reviewed.

The systematic design of CO2 capture rocesses applied to the oxidative coupling of methane

The Systematic Design of CO2 Capture Rocesses Applied to the Oxidative Coupling of Methane

Modeling, Simulation, and Economic Evaluation of a Hybrid CO2 Capture Process for Oxidative Coupling of Methane

Abstract The Oxidative Coupling of Methane (OCM) is a direct path for the conversion of methane into ethene. Carbon dioxide is generated as an undesired reaction by-product and must be removed in the downstream separation section. This is commonly achieved by amine scrubbing, which is an energy-intensive process. An alternative hybrid process employing gas separation membranes and absorption is investigated in this contribution. Membrane and absorption processes are modeled and simulated. Several flowsheet configurations and gas compositions, reflecting different OCM reactor concepts, are considered. Preliminary economic analysis is carried out to assess the feasibility of applying this process industrially.