Natural gas dehydration by adsorption using MOFs and silicas: A review

Abstract

• MOFs and silicas are robust adsorbents with high chemical and thermal stability. • MOFs and silicas are highly porous and efficient adsorbents for H 2 O adsorption. • MOFs and silicas are promising for dehydration of NG operating at high pressure. Due to the discoveries of large reserves of oil and gas in unconventional reservoirs, the production of natural gas (NG) has increased significantly, becoming a component of the world's nonrenewable energy matrix, which has grown the most in the last 10 years. In Brazil, these reserves, called the pre-salt layer, corresponded to 47% of the total NG produced until 2020. However, several technological challenges need to be overcome, including the development of more efficient strategies for gas conditioning and transport, including the removal of large amounts of water in the NG stream. Water with gaseous hydrocarbons under specific conditions of temperature and pressure result hydrate formation, causing corrosion, depletion, and loss of localized pressures, compromising their transport through pipelines. Among the processes used to remove water from the NG stream, dehydration using solid desiccants stands out for the high selectivity with the adsorbate due to the high affinity in the separation of water molecules from the gas stream, high recovery of products, and being a reversible process. Mesoporous silica and metal–organic frameworks (MOFs) are highly porous adsorbents that emerge as promising alternatives for water adsorption, as they present high chemical and mechanical stability, good renewability, support various adsorption/desorption cycles, and present high selectivity and capacity with water adsorption. It is worth noting that these characteristics result in more compact adsorption units, which is valuable, especially in offshore exploration. Therefore, since practical studies using mesoporous silica (SBA-15, MCM-41, xerogel and aerogel) and MOFs in the dehydration of NG are scarce, this work will present the characteristics of these adsorbents in relation to their textural, structural, and physical–chemical properties and the challenges for their use in separating water from gases.