​​​​Prahar Vaidya​, M.S.

My research work "Pure and Binary Adsorption of Methane-Nitrogen on Silicalite" review the issues with the conventional separation of Natural gas using cryogenic distillation and suggesting a convenient and efficient separation method using novel adsorption separation process.
 
The only technology that is currently being used for nitrogen removal from methane till date is cryogenic distillation, which is highly energy-intensive and costly. The combined costs of liquefaction and subsequent re-compression of the low pressure product makes this an expensive process. It is economical only for large, highly contaminated gas. Since a high feed pressure is already available through natural means, Pressure Swing Adsorption (PSA) show a high potential for future use. 
 
It also covers environmental issues. Methane is the most important non-CO2 greenhouse gas responsible for global warming, responsible for more than 10% of total greenhouse gas emissions. Thus, it is imperative to catch methane from the landfill gases and to use it as a alternative to fossil fuels. Impure natural gases contain significant amounts of nitrogen. The separation of nitrogen from methane is therefore increasingly important for upgrading LGF (Landfill gas), coal gas, and natural gas into a more pure form of methane containing gas.

Despite the advantages of using adsorption for upgrading methane, this separation has been found particularly difficult because of the lack of satisfactory adsorbent. Potential adsorbent needs to have high nitrogen/methane selectivity. The equilibrium selectivity favors methane over nitrogen (or high methane/nitrogen selectivity) for all known adsorbents, such as activated carbon, silica gel, activated alumina, large-pore zeolites and molecular sieves. Therefore, the development of such adsorbents and its adsorption property is desirable.
 
This study reviews one of the most commonly used technique (i.e. volumetric measurement) for pure and binary adsorption isotherm measurement of methane and nitrogen on silicalite adsorbent. This method involves measuring the pressure change in a known volume of gas subjected to adsorption. As the gas is adsorbed and allowed to reach equilibrium, the measured decrease in the system pressure yields the amount of gas adsorbed under the given conditions.

Pure adsorption equilibria for the gases listed above was measured at three different temperatures (283.15 K, 308.15 K and 338.15 K). The virial equation of state was used to correlate the experimental data, to calculate the Henry’s law constants and the heats of adsorption at zero loading. Ideal separation factor (selectivity) was obtained from the experimental pure adsorption isotherms by using the virial isotherm model. Binary adsorption behavior for methane and nitrogen mixture, covering the whole concentration range at 308.15 °K and at 504 kPa was determined experimentally. The corresponding x-y diagrams and selectivity were obtained from these data. The experimental results were compared with the results predicted from a mixture adsorption model, IAST. It was found that IAST successfully predicted the total amount adsorbed throughout the concentration range. There is a considerable deviation in selectivity as well as partial amount adsorbed for both the species at higher pressure. The reason is attributable to the fact that selectivity is much more sensitive to uncertainties in the measurement.
 

​

For more information, visit author's publisher, Ohiolink ETD Or EngagedScholarship :