Understanding the role played by moisture in CO2 sorption is key for designing the next generation of solid sorbents such as metal–organic frameworks, which can be used for carbon capture and conversion as well as for molecular sieving, energy storage, etc. The abundance of water in nature and industrial processes, including in anthropogenic sources of CO2 has been shown to significantly affect commercial adsorbent performances, including their uptake capacity and selectivity. However, less is known about the role of humidity on CO2 diffusion, even though it is crucial for economically viable rapid capture processes. In this work, we have used atomistic simulations and experiments to gain insight into the effect of humidity on CO2 adsorption, diffusion and transport properties in UiO-66­(Zr), here described as a flexible structure. We show that depending on the water concentration adsorbed in the host nanoporosity, the CO2 adsorption can be enhanced or reduced depending on thermodynamic conditions. At low water loading, isolated molecules interact with low-energy sites of the sorbent. At higher loading, nucleation drives water cluster formation, followed by cluster percolation resulting in a sub-nanoporous adsorbing media decreasing the overall CO2 diffusion compared to the dry structures. We finally show that equilibrium parameters such as self-diffusion coefficients and isotherms can be used to describe the CO2 transport in dry and humid structures through the nano-Darcy equation.

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In the current energy transition scenario, gas represents one of the main pillars for a greener energy mix. In 2015, we presented two promising schemes to produce a challenging notional gas field located 2500 meters water depth and 300 km from shore using only subsea processing [1]. The first scheme consists of subsea gas/liquid separation, gas compression and liquid boosting for multiphase export to shore; the second, developing a subsea high-pressure dehydration system for up to 300 Bara, using adsorption, to avoid the use of a monothylene glycol (MEG) loop and export dry gas directly from subsea. Performance of desiccants at such high pressure has not been studied thoroughly and qualification was necessary. This paper presents the proof-of-concept of a subsea dehydration technology at high pressure. Several criteria were used to evaluate the potential technologies: treatment performance, power consumption, production at varying pressure, sensitivity to feed contaminants, CAPEX, OPEX, weight & size, among others. The preferred solution was concluded to be temperature swing adsorption (TSA). Once TSA was selected as the most promising dehydration technology, different laboratory tests were performed and several parameters were identified to screen the potential desiccants: adsorbent working capacity, water/CH4 selectivity, water adsorption energy and regeneration temperature. Finally, a pilot was built and a test matrix was run in order to prove the concept. The adsorption, and specifically a TSA Process, was the technology selected in the first part of the study. The choice was based mainly on the energy efficiency and the technology readiness level. In the second part of this project, the feasibility of the process at high pressure (up to 300 Bara) and its application subsea were proven through experimental tests performed at a laboratory pilot. Characterization tests and water and methane adsorption/desorption isotherms are briefly presented. Based on these results, zeolite, alumina and activated carbon adsorbents were identified. Finally, complete adsorption/desorption cycles at different pressures and temperatures were performed, proving the concept and its potential. This is the first study proving experimentally the concept, and presenting the potential, of the TSA Process for subsea dehydration at high pressure. This is one of the subsea processing building blocks identified in many gas field architectures and it is especially required to produce remote and deep reservoirs at competitive costs.