Hydrate-Based CH4 Recovery from Low-Concentration Coalbed Methane Enhanced by CuO-Decorated Graphite Nanoparticles

Abstract

Efficient purification of low-concentration coalbed methane (LCCBM) is critical for energy utilization and greenhouse gas emission reduction. Hydrate-based gas separation is a promising approach for this application, but its practical deployment is constrained by sluggish formation kinetics and limited CH4 selectivity. This study reports the synthesis of copper oxide-decorated graphite nanoparticles (CuO@GNP) via chemical coprecipitation and develops a ternary combined system integrating CuO@GNP as a composite promoter, rhamnolipid (Rha) as a biosurfactant, and tetrahydrofuran (THF) as a thermodynamic promoter for hydrate-based CH4 separation from LCCBM. Among the prepared materials, 20 wt % CuO@GNP exhibited the most favorable properties, with well-dispersed CuO nanoparticles on the GNP surface and the highest specific surface area (24.90 m2·g–1), a 72.6% increase over pristine GNP. Under the tested conditions of 277.15 K and 3.6 MPa, the 20 wt % CuO@GNP nanofluids enhanced normalized gas consumption from 9.4 to 11.3 mmol/mol water and improved the separation factor from 6.80 to 7.40 relative to the GNP system. Liquid-phase temperature profiling and in situ microscopic observations indicated that CuO@GNP promotes multisite nucleation, accelerates hydrate growth kinetics, and facilitates heat dissipation, thereby sustaining continuous hydrate formation. The CuO@GNP-Rha-THF ternary system provides an effective strategy for hydrate-based CH4 recovery and offers insights into the design of surface-engineered nanofluids for gas separation applications.