Enriching Low-Concentration Coalbed Methane Using a Hydrophobic Adsorbent under Humid Conditions
Hua Shang, Feifei Zhang, Jiaqi Liu, Xinran Zhang, Jiangfeng Yang, Libo Li, Jinping Li
Abstract
Under practical conditions, the mixture of gases that enters a pressure swing adsorption (PSA) unit must be completely dehydrated; water vapor could have negative impacts on the uptake capacity and long-term stability of many sorbents. The use of hydrophobic adsorbents may eliminate the dehydration step. In this work, the superhydrophobic sorbent silicalite-1 was chosen and the hydrophobic mechanism was studied using density functional theory (DFT) calculations. For the separation experiments, the wet gas mixture (CH4/N2/H2O(v)) with varying relative humidities (30, 50, and 100% RH) was fed to a fresh bed. There was almost no change of CH4 breakthrough time compared with the dry condition. Only a slight reduction (less than 0.5 min) was observed in a water vapor-presaturated (continuous 36 h) bed. These breakthrough results show that the presence of water has limited influence on CH4/N2 separation using silicalite-1. Finally, PSA experiments were conducted under both dry and humid conditions (100% RH); after 60 cycles, the fluctuation of purity and recovery was less than 2%, confirming that the presence of water vapor had negligible influence on CH4 enrichment performance using a hydrophobic sorbent.