Optimization and Modeling of Helium Recovery from Natural Gas Through Hydrate-Based Gas Separation

As a finite strategic resource, helium is extracted from natural gas (NG). The concentration of helium in NG is very low, which makes helium hard to separate. The hydrate-based gas separation (HBGS) was proposed as a promising method for the separation of the NG with low helium content in this work. This work systematically investigated the HBGS of helium from simulated NG. The thermodynamic analysis reveals that the existence of 5.00 mol% tetrahydrofuran (THF) in the liquid phase decreased the gas-liquid-hydrate equilibrium pressure by 92.11%, compared to the deionized water system. The single-stage HBGS experimental results show that high THF concentration, low temperature, and high pressure benefited the gas processing capacity and helium purification, but they led to a low helium recovery rate. The best HBGS performance was limited by the "hydrate shell effect". The decrease in gas-liquid ratio led to an increase in helium concentration without losing the gas processing capacity, but it caused a decrease in the helium recovery rate. Through three-stage HBGS optimization, the helium concentration was increased from 0.54 mol% to 13.54 mol% (a 25.07-fold enrichment), and a total helium recovery of 87.34% was achieved. The mathematical model proposed in this work accurately predicts the performance of HGBS with 2.09% average relative error compared to the experimental data.