Silica Gel as a Selective Adsorbent for Biogas Drying and Upgrading

Biogas upgrading (CO₂ removal) is an essential step toward the production of biomethane. Biomethane can be transported in the existing natural gas grids or used directly as a vehicular fuel with proven environmental benefits. Before or after upgrading (depending on the technology), biomethane needs to be dried to avoid corrosion issues in pipelines and storage devices. While the trend now is to evaluate advanced and eventually expensive adsorbents, we have revisited the possibility of using silica gel as a cheap material to decrease the cost of biomethane production. Silica gel does not present a very high selectivity toward CO₂, but Pressure Swing Adsorption (PSA) engineers can handle the lack of selectivity by tuning the unit operation. The advantage of silica gel is that the adsorption isotherms of CO₂ are not very steep. Moreover, an additional advantage is that the same adsorbent can do the drying and the upgrading steps in the same column. We have evaluated two different samples of silica gel with wide and narrow pores, and we have seen that the material with higher density and higher surface area has more potential to be used for biogas upgrading.