development of a high-performance pressure swing sorption process for natural gas dehydration

Abstract

Natural gas is an important energy source for industry, transportation, and homes. It is also used as a chemical feedstock in the manufacturing of plastics and other commercially important organic chemicals. The presence of water in natural gas not only substantially decreases the heating value of natural gas, but also damages the transportation pipeline by corrosion and methane hydrate formation. To dehydrate natural gas, technologies such as absorption, adsorption, condensation, and supersonic separation have been developed. Despite satisfactory results from these technologies, problems with pollution and high processing costs still exist. In this research project, a new pressure swing sorption process for dehydration of gases using biosorbents was developed, which is efficient, environmentally friendly, and economically favorable. Biosorbents were made from flax shives and oat hulls, which had high water vapor sorption capacity and selectivity compared to numerous commercial adsorbents. Six-step and four-step PSA cycles were designed and dual-column pressure swing experiments were conducted. The process worked for over 450 cycles without observable degradation and pipeline-quality dry gas was achieved. Equilibrium and kinetic modeling were performed to further investigate the water vapor sorption characteristics and mechanisms. In addition, the properties of the biosorbents such as sorption capacity, selectivity, pore size and pore volume distributions, surface functional groups, packing and true densities, thermal stability, and biopolymer/elemental compositions were determined. Furthermore, a life cycle assessment was performed to compare the environmental impacts of biosorbent production with those of molecular sieves production. The results showed that both the PSA process and the biosorbents developed in this work are environmentally friendly and efficient, and have a potential for industrial applications such as dehydration of natural gas, biogas, syngas, and air. The value propositions of the developed process are efficient gas dehydration with low negative environmental impacts and a potential market for agricultural residues as industrial biosorbents in this process.