Adsorption of carbon dioxide and methane as biogas on activated carbon and porous glass based catalysts

In this study, the commercial activated carbon (AC) was modified by adding either nickel (Ni) or ammonium hydroxide (NH₄OH) on its surfaces. Various concentration of Ni on AC was used to investigate an enhancement of carbon dioxide (CO₂) and methane (CH₄) adsorption on AC at 298K and low pressures. Effects of NH₄OH on adsorption isotherms of CO₂ and CH₄ were also studied. The activated carbon with 1, 5 and 10% of Ni on carbons’ surfaces were prepared and the specific pore volume of these AC were 0.2297, 0.2375 and 0.2688 cm³/g, respectively. The purification or separation carbon dioxide from bio-methane is also interesting. In this study the synthesis porous glass with different concentration of nickel on solid surfaces were investigated to see whether it can be separated carbon dioxide from methane. The Ni concentration was varied from 0 to 10%. Adsorption isotherms were measured by using an Accelerated Surface area and Porosimetry System 2020 Plus (ASAP2020 Plus). It was observed that an increase of Ni could increase the surface area and specific pore volume. An early onset in adsorption isotherm for both CO2 and CH4 was observed at low pressures and the adsorption capacity increased by an increasing of Ni concentration like that observed in molecular simulation. 

In the case of NH4OH, three concentrations of NH4OH solution were prepared at 0.1, 0.5 and 1.0N for AC modification. The adsorption of CH4 on these carbons were less than that observed in the case of unmodified carbon and the concentration of NH4OH increased would reduce the adsorption capacity of methane. While NH4OH can enhance the adsorption of CO2 on AC compared with original AC, however the different concentration of functional group showed insignificant adsorption isotherms.

Therefore, the improving of AC by adding nickel can be used to enhance the methane storage and carbon dioxide capture. The adsorption at high pressures and optimum concentration of nickel should be investigated for further improving AC as energy storage and global warming issue. 

Raw biogas contains 50–70% methane and 30–50% CO₂, along with small amounts of nitrogen, oxygen, sulfur compounds, silicon compounds, ammonia, and other VOCs. Our result show that the adsorbed amount of CO2 and CH4 increase with an increase of Ni as shown in Figure 5 for carbon dioxide and methane. Methane adsorption in porous glass is greater than carbon dioxide, therefore, this may be used to develop the adsorbent for biogas separation and purification.