(401bf) Synthesis of Highly Performing Nanoporous Carbon Adsorbent for Separation of Siloxane and Ammonia Impurities from Land-Fill Gas

Land-fill gas or bio-gas is composed of large portion of methane and carbon dioxide, and small amount of impurities such as nitrogen, oxygen, hydrogen sulfide, siloxane and ammonia. For example, in Metropolitan Landfill area in Republic of Korea, land-fill gas is recently composed of 47% of methane, 38% of carbon dioxide, 13% of air, 1.8% of hydrogen sulfide, 50ppm of siloxane, and 1ppm of ammonia. Land-fill gas is sometimes separated to form high-purity methane gas by removing other species [1,2]. Hydrogen sulfide can be removed by absorption method using sodium hydroxide solution, and carbon dioxide can be removed by several methods such as water scrubbing absorption, pressure-swing adsorption, and membrane separation. Tiny amount of siloxane and ammonia can be separated via adsorption process, but non-recyclable adsorbents have been so far used for the separation of these species [3,4]. Most challenging part is the separation of air. Cryogenic distillation method is commonly used for this step, but this process is highly energy demanding and highly cost.

Recently, we have been developing low-cost separation process to upgrade land-fill gas to medium-grade-purity (~70%) methane gas which can be still utilized to fuel for various industrial uses such as sewage drying. This process is quite economic, because separation of air is not included. In addition, we developed separation process of siloxane and ammonia residues using recyclable and highly-performing adsorbents. For the synthesis of suitable adsorbent of each component, it was quite necessary to consider the chemical properties of siloxane and ammonia. Siloxane species are known to be polymerized in acidic or basic condition to form bulkier species. The polymeric bulky siloxane can cause adsorbent deactivation due to pore blocking and difficult regeneration. The ammonia gas is well known as basic molecules which have strong affinity to acidic species. In these reasons, siloxane separation, we synthesized neutral carbon materials with large surface area by various methods. In addition, we developed carbon-based acidic ammonia-adsorbent by simple methods. In parallel, adsorption-desorption isotherms and breakthrough curve of siloxane and ammonia were measured for thus synthesized adsorbents. Regeneration tests of those adsorbents were also performed. Our new adsorbents for siloxane and ammonia species exhibited higher adsorption capacity and breakthrough amount than previous commercial adsorbents. More notably, the adsorption performance of new siloxane adsorbent could be completely regenerated by heat treatment. In the case of ammonia adsorbent, we are modifying the ammonia adsorbent to be easily regenerated by simple heat treatment. And then, we will develop adsorption-regeneration process of siloxane and ammonia residue. Detail results for synthesis and the adsorption measurement of the synthesized adsorbents will be presented in the conference.

[1] S. Cavenati, C.A. Grande, A.E. Rodrigues, Energy&Fuels 6 (2005) 2545.

[2] E. Ryckebosch, M. Drouillon, H. Vervaeren, Biomass and Bioenergy 35 (2011) 1633.

[3] A. Cabrera-Codony, M.A. Montes-Moran, M. Sanchez-Polo, M.J. Martin, R. Gonzalez-Olmos, Environ. Sci. Technol. 48 (2014) 7187.

[4] A. Qajar, M. Peer, M.R. Andalibi, R. Rajagopalan, H.C. Foley, Micropor. Mesopor. Mater. 218 (2015) 15.