Hamid Reza Godini

Performance analysis of the adsorptive separation of ethylene downstream of an oxidative coupling of methane (OCM) process, being an alternative process for converting methane content of natural gas or other methane-rich sources to ethylene, was studied in this research for a production capacity of 1 Mt/yr. This was motivated by observing promising adsorption characteristics and efficiency in the selective adsorption of ethylene using 13X zeolite-based sorbent. The energy and economic performance of alternative scenarios for retrofitting the adsorption unit into an integrated OCM process were analyzed. Simulations of the integrated OCM process scenarios include OCM unit, CO₂-hydrogenation, ethane dehydrogenation and methane reforming sections. The use of efficient ethylene adsorption separation enabled the improvement of the economic and energy efficiency of the integrated OCM process under specific operating conditions. For instance, the invested amount of energy and the associated energy cost per ton of ethylene in the cryogenic ethylene-purification section of the integrated process using adsorption unit are, respectively, 75% and 89% lower than the reference integrated OCM process. Under the conditions considered in this analysis, the return on investment for the final proposed integrated OCM process structure using adsorption separation was found to be less than 9 years, and the potential for further improvement was also discussed.

This work presents multi-scale approaches to investigate 3D printed structured Mn–Na–W/SiO₂ catalysts used for the oxidative coupling of methane (OCM) reaction. The performance of the 3D printed catalysts has been compared to their conventional analogues, packed beds of pellets and powder. The physicochemical properties of the 3D printed catalysts were investigated using scanning electron microscopy, nitrogen adsorption and X-ray diffraction (XRD). Performance and durability tests of the 3D printed catalysts were conducted in the laboratory and in a miniplant under real reaction conditions. In addition, synchrotron-based X-ray diffraction computed tomography technique (XRD-CT) was employed to obtain cross sectional maps at three different positions selected within the 3D printed catalyst body during the OCM reaction. The maps revealed the evolution of catalyst active phases and silica support on spatial and temporal scales within the interiors of the 3D printed catalyst under operating conditions. These results were accompanied with SEM-EDS analysis that indicated a homogeneous distribution of the active catalyst particles across the silica support.

The present study aims to conduct a systematic assessment of Al‐SBA‐15 as the aluminum‐substituted mesoporous catalyst for raw methanol dehydration to dimethyl ether (MTD). The catalysts are synthesized by varying the pretreatment variables (pH of the preparation and Si/Al ratio), the posttreatment variable (steaming time), and by the addition of aluminophosphate as the binder. The experimental design and the analysis of the results, especially the relation of characterization results and reactor performance, are performed by the optimal response surface method in Design‐Expert software. The prepared micro‐mesoporous catalyst exhibits an excellent activity, stability, and DME selectivity; therefore, it can be introduced as an efficient catalyst for raw methanol dehydration.

A multi-aspect analysis of low-pressure catalytic hydrogenation of CO₂ for methanol production is reported in the first part (part I) of this paper. This includes an extensive review of distinguished low-pressure catalytic CO₂-hydrogenation systems. Specifically, the results of the conducted systematic experimental investigation on the impacts of synthesis and micro-scale characteristics of the selected Cu/ZnO/Al₂O₃ model-catalysts on their activity and stability are discussed. The performance of the investigated Cu/ZnO/Al₂O₃ catalysts, synthesized via different methods, were tested under a targeted range of operating conditions in this research. Specifically, the performances of these tested Cu/ZnO/Al₂O₃ catalysts with regard to the impacts of the main operating parameters, namely H₂/CO₂ ratio (at stoichiometric -3-, average -6- and high -9- ratios), temperature (in the range of 160–260 °C) and the lower and upper values of physically achievable gas hourly space velocity (GHSV) (corresponding to 200 h⁻¹ and 684 h⁻¹, respectively), were analyzed. It was found that the catalyst prepared by the hydrolysis co-precipitation method, with a homogenously distributed copper content over its entire surface, provides a promising methanol yield of 21% at a reaction temperature of 200 °C, lowest tested GHSV, highest tested H₂/CO₂ ratio (9) and operating pressure (10 bar). This is in line with other promising results so far reported for this catalytic system even in pilot-plant scale, highlighting its potential for large-scale methanol production. To analyze the findings in more details, the thermal-reaction performance of the system, specifically with regard to the impact of GHSV on the CO₂-conversion and methanol selectivity, and yield were experimentally investigated. Moreover, the stability of the selected catalysts, as another crucial factor for potential industrial operation of this system, was tested under continual long-term operation for 150 h, the reaction-reductive shifting-atmospheres and also even after introducing oxygen to the catalyst surface followed by hydrogen reduction-reaction tests. Only the latter state was found to affect the stable performance of the screened catalysts in this research. In addition, the reported experimental reactor performances have been analyzed in the light of equilibrium-based calculated achievable performance of this reaction system. In the performed multi-scale analysis in this research, the requirements for establishing a selective-stable catalytic performance based on the catalyst- and reactor-scale analyses have been identified. This will be combined with the techno–economic performance analysis of the industrial-scale novel integrated process, utilizing the selected catalyst in this research, in the form of an add-on catalytic system under 10 bar pressure and H₂/CO₂ ratio (3), for efficiently reducing the overall CO₂-emission from oxidative coupling of methane reactors, as reported in the second part (part II) of this paper.

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.