It is very important today to address the impacts of climate change as its effects can be observed every day. Nowadays many scientists believe that earth's climate is changing as a result of human-caused greenhouse gas emissions such as carbon dioxide and methane. Global energy demand is also rapidly evolving. A sustainable approach that balances economic growth with social and environmental responsibility should be considered as an effective and long-term strategy. Carbon dioxide is the foremost greenhouse gas of anthropogenic origin, responsible for the majority of the earth's warming effects. It is estimated that around 60% of the global warming impact can be traced back to the release of carbon dioxide into the atmosphere. Lowering methane emissions offers a range of notable advantages in terms of energy, safety, economy, and the environment. Firstly, since methane is a potent greenhouse gas (25 times more powerful than CO2 over a 100-year period), reducing methane emissions will contribute significantly to mitigating climate change in the short term. Additionally, methane is the primary component of natural gas and biogas, which means collecting and utilizing methane can be a valuable source of clean energy that fosters local economic growth and minimizes local environmental pollution. Generating energy through methane recovery eliminates the need for traditional energy resources, thus lessening end-user and power plant CO2 and air pollutant emissions. Physical adsorption separation processes have proven to be an effective technique for simultaneous carbon dioxide capture and methane enrichment applications. The objective of this study is to conduct a thorough assessment of the adsorption separation of methane and carbon dioxide gases employing a commercially available carbon molecular sieve, CMS(C), and an activated carbon, AC(B). The accomplishment of the objective involved conducting an in-depth characterization of the adsorbents. Part of the characterization included measurements of the internal surface area and pore size distributions, as well as the measurements of the equilibrium adsorption isotherms using gravimetric techniques. These isotherms enabled detailed kinetic analyses, such as evaluating diffusivity and mass transfer coefficients at various temperatures and pressure steps. The prediction of binary isotherms were based on theoretical models, which can describe the gas mixture adsorption equilibria using pure component equilibrium data. Breakthrough curves were generated to describe the dynamic response of an adsorption column under different pressures, temperatures, and flow rates. A mechanistic model was developed utilizing gPROMS simulation software for adsorption breakthrough process and it was validated by comparing its results to the experimental breakthrough curves. Parametric studies were conducted to determine the optimal operating conditions for gas adsorption separation of CO2 and CH4 gases. By examining the data obtained from breakthrough curves, pure and predicted binary adsorption equilibria, we calculated adsorption capacities, selectivity, sorbent selection parameter (S parameter), and the adsorbent performance indicator (API). These calculations were carried out to evaluate the initial potential for gas adsorption separation of the carbon molecular sieve (CMS(C)) and the activated carbon (AC(B)) under a range of operating conditions. Increasing pressure, decreasing temperature, and reduced feed flow improved breakthrough time and adsorption capacity for both gases on these adsorbents. CMS(C) showed superior selectivity, while AC(B) had a higher API value at specific conditions. The API was considered a more practical parameter for evaluating the initial gas separation potential. CMS(C) proved to be the better choice for methane purification, achieving the longest purification time under optimal conditions. Additionally, the study explored the kinetic behavior of methane and carbon dioxide with these adsorbent materials, revealing faster carbon dioxide uptake rates and the potential advantages of activated carbon in reducing adsorption/desorption cycle times in separation processes. At a pressure of 1 atm, a temperature of 294 K, and a flow rate of 400 ml min-1, CMS(C) had the highest values of selectivity and the S parameter, while AC(B) had the highest API value at 9 atm of pressure, a temperature of 294 K, and a flow rate of 400 ml min-1. The API was considered a more practical parameter for evaluating the initial gas separation potential. CMS(C) proved to be the better choice for methane purification, achieving the longest purification time of 420 seconds at a pressure of 9 atm, a temperature of 294 K, and a flow rate of 400 ml min-1. Additionally, the study explored the kinetic behavior of methane and carbon dioxide with these adsorbent materials, revealing faster carbon dioxide uptake rates and the potential advantages of activated carbon in reducing adsorption/desorption cycle times in separation processes. The analysis of the study, when compared to existing literature, reveals a coherent and logical progression. Our results align with similar studies, validating key points such as the improvement of methane purification through reduced feed flow rates and increased pressures, enhanced adsorption separation performance at lower temperatures and pressures, the superior adsorption capacity of activated carbon over carbon molecular sieves, and the greater selectivity of carbon molecular sieves over activated carbon and faster diffusion of carbon dioxide compared to methane within the carbon porous materials.

The objective of this research was to determine an appropriate adsorbent for the separation of CH₄ from CO₂, N₂, and O₂. To screen different adsorbents for this purpose, pure component adsorption isotherms and gas mixture isotherms were measured. Adsorption isotherms are critical data for modeling adsorption processes. Thus, determining an accurate and reliable method of measuring gas adsorption isotherms is crucial. Concentration pulse chromatography can be used to measure the slope of the isotherm. In the case of pure component adsorption, the slope at different partial pressures of adsorbate can be integrated to determine the adsorption isotherm. The accuracy of the concentration pulse chromatography method was compared to that of gravimetric analysis to find an appropriate technique to obtain pure component gas adsorption isotherms by measuring CH₄ isotherms on activated carbon at 25°C and up to 6.3 atm. Isotherm results from concentration pulse chromatography were identical to gravimetric results, but the use of a sufficiently long column for concentration pulse chromatography was crucial. Afterwards, gravimetric analysis was used to determine the performance of activated carbon (AC A-C) and carbon molecular sieve (CMS A-D) adsorbents for adsorbing CO₂ and N₂. Additionally, O₂ adsorption isotherms were measured for CMS's. At 25°C and above atmospheric pressure, AC-B showed the highest CO₂ capacity and CO₂/N₂ selectivity. The isosteric heat of adsorption values of CO₂, N₂, and O₂ for the CMS's were calculated; CMS-A and CMS-C had high isosteric heat of adsorption values for CO₂, above 40 kJ mol⁻¹. Finally, the performance of activated carbon in separating a binary mixture of CO₂ and N₂ was experimentally measured by obtaining binary gas mixture adsorption isotherms using concentration pulse chromatography technique between 30-70°C and 1-5 atm total pressure. The OLC activated carbon showed selectivity for CO₂ over N₂, with the experimental results showing a slight deviation from theoretical predictions of the binary adsorption isotherms. Compared to other adsorbents in the literature, OLC had similar CO₂ and N₂ adsorption capacities but higher CO₂/N₂ selectivity.

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