Enrichment of Oxygen-Containing Low-Concentration Coalbed Methane with CMS-3KT as the Adsorbent

Research Progress in Microporous Materials for Selective Adsorption and Separation of Methane from Low-Grade Gas

Given that methane (CH4) and nitrogen (N2) have similar properties, achieving high-purity enrichment of CH4 from nitrogen-rich low-grade gas is extremely challenging and is of great significance for sustainable development in energy and the environment. This paper reviews the research progress on carbon-based materials, zeolites, and MOFs as adsorbent materials for CH4/N2 separation. It focuses on the relationship between the composition, pore size, surface chemistry of the adsorbents, CH4/N2 selectivity, and CH4 adsorption capacity. The paper also highlights that controlling pore size and atomic-scale composition and optimizing these features for the best match are key directions for the development of new adsorbents. Additionally, it points out that MOFs, which combine the advantages of carbon-based adsorbents and zeolites, are likely to become the most promising adsorbent materials for efficient CH4/N2 separation.

A pilot study to capture methane from the exhausted air of dairy cows using a cryogenic approach

In the agricultural sector, ruminants are the largest methane (CH4) emission source and many efforts have been undertaken to reduce these greenhouse gas emissions, while compromising animal health and physiology. On the other hand, ruminal CH4, which is biomethane, is in high demand, especially in its liquid form (LBM) that can be used as high energy density fuel. However, CH4 released from a ruminant is immediately mixed with air and highly diluted (<0.1%), challenging CH4 capture technologies. Here we aimed to construct a cryogenic pilot system to capture and liquefy enteric CH4 released from dairy cows kept in respiration chambers. To approach this aim, the outlet air from the chambers was directed through a two-step cooling trap to capture CO2 (-120 to -130 °C) as a solid in the first and CH4 and O2 as liquids in the second cooler (-160 to -180 °C). Warming the second cooler resulted in the evaporation of O2, thereby separating O2 and CH4. LBM purity was in average 90% and was lowest at warming rates higher than 0.88 °C/min. The mean CH4 capture efficiency was 92% and found to be independent of sequestration time and flow rate. However, an increase in CH4 concentration to 0.6%, as it occurs directly at the muzzle of a cow, reduced the sequestration time for CH4. These results show that cryogenic technology can be used to obtain LBM from the air containing ultra-low CH4 concentrations as it is found in cattle barns with high efficiency and purity.

Carboxymethyl cellulose/polyvinyl alcohol composite aerogel supported beta molecular sieve for CH4 adsorption and storage

Biomass aerogel is attractive in various applications due to their renewable, biodegradable and eco-friendly advantages. Herein, a novel beta molecular sieve/carboxymethyl cellulose/polyvinyl alcohol composite aerogel (beta/CP) is prepared by direct mixing and directional freeze-drying as an efficient gas adsorbent with hierarchical porosity. The beta molecular sieve is uniformly dispersed in the three-dimensional skeleton of the aerogel. By adjusting the loading mass of the beta molecular sieve to constitute a reasonable porosity and pore size distribution, the synergistic effect between pore structures of different scales improves the adsorption performance. The experiment results of beta/CP-4 show that the CH4 adsorption capacity can reach 60.33 cm3/g at 298 K and 100 bar, which is almost the same as that of the pure beta molecular sieve (62.09 cm3/g). The strong interaction between the aerogel and it prevents the molecular sieve agglomeration, improves the pore utilization, and also reduces the cost of using molecular sieve adsorbent. The above results indicate that the composite has good potential for application in the field of CH4 storage.