Hybrid fiber sorbents for odorant removal from pipeline natural gas

Abstract

Pipeline natural gas is typically odorized with about 10 ppm of mercaptans for safety purposes in case of a leak. However, when burned in air inside of gas turbines, these sulfur compounds react with alkali material present in air to form a corrosive combustion product which corrodes the inside of the turbine and reduces its efficiency and lifetime. It is therefore of interest to remove mercaptan odorants from pipeline natural gas before introduction into combustion turbines for the purposes of preventing or delaying corrosion associated with SOx production. The overall goal of the current project was to investigate several metal organic frameworks (MOFs) and zeolites for the removal of a common odorant, t-butyl mercaptan (TBM), from natural gas and to evaluate their ability to be practically and economically integrated into a cyclic adsorption system in a fiber module configuration. Several MOFs were synthesized and characterized for TBM adsorption capacity, selectivity, cyclic regenerability, and stability, and compared to benchmark zeolites using gravimetric sorption methods. These aspects are important to the economic viability of a TBM removal system. Results showed that MOFs can be advantageous over zeolites for this application, and the highest performing materials were chosen for further studies with fiber spinning. The materials were incorporated into hybrid cellulose acetate polymer fibers and their adsorption performances were reevaluated gravimetrically and in an automated temperature swing adsorption (TSA) system. Both MOF and zeolite hybrid fibers were successfully fabricated with high sorbent loadings, and continued to exhibit high sorption capacities and selectivities to TBM in the model natural gas flow, while remaining stable to multiple temperature swing regeneration cycles. Different operating conditions were varied in the TSA system to determine their effects on the breakthrough curve, adsorption capacity, and mass transfer. The overall results demonstrate a proof of concept that fiber sorbent creation and implementation is feasible and worth further investigation for odorant removal from pipeline natural gas in an industrial setting. This research ties together to the two major challenges in adsorption applications: materials design and system implementation, which pushes forward the development of an industrial scale system for odorant removal from natural gas.