The present study continues the development and enhancement of a highly efficient unique hybrid technique—membrane-assisted gas absorption in designing the separation unit, which provides the improvement in mass-transfer of a target component during the ammonia capture process from a process loop of the Haber–Bosch technological route. In order to minimize the absorbent volume to membrane area ratio, the special separation cell was designed based on a combination of two types of hollow fiber membranes, dense gas separation membrane and porous pervaporation membrane. The separation performance tests were implemented under two sets of conditions, sweeping the bore (permeate) side of a cell with helium and hydrogen-nitrogen mix. For both cases, the membrane-assisted gas absorption cell demonstrated high separation efficiency, and the ammonia concentration in the permeate was never lower than 81 mol%; meanwhile, under the hydrogen-nitrogen bore sweep conditions, the ammonia concentration in the permeate reached 97.5 mol% in a single-step process. Nevertheless, there is a product purity–recovery rate trade-off, which is a typical issue for separation processes.

Herein, we report for the first time a study dedicated to acidic gases’ solubility in ionic liquids with sterically hindered bulky anion, namely bis(2-ethylhexyl) sulfosuccinate ([doc]), experimentally evaluated at low pressures. The effect of cation change (imidazolium, pyridinium, and pyrrolidinium) on the thermophysical properties and sorption capacities was also discussed. The densities and the activation energies of the tested ILs exhibited minor differences. Furthermore, the COSMO-RS model was used to predict the free volumes of ILs aiming to investigate its influence on gas solubilities. The conducted calculations have revealed an antibate correlation between the fractional free volume (FFV) and Henry’s law constant. In particular, the lowest FFV in 1-methylimidazolium [doc] corresponded to the minimal sorption and vice versa. In addition, it was shown that the presence of protic cation results in a significant reduction in CO₂ and H₂S solubilities. In general, the solubility measurement results of the synthesized ILs have shown their superiority compared to fluorinated ILs based on the physical absorption mechanism.

This work is carried out in order to identify the most effective mode of operation of the membrane-assisted gas absorption setup in the problems of ammonia recovery. The study was conducted to determine the effect of the adsorbent layer thickness on the efficiency of ammonia separation from a binary mixture of NH₃/N₂, with an ammonia content of 15 vol.%, by the method of membrane-assisted gas absorption. The study used a commercially available elastomeric poly(dimethylsiloxane)poly(diphenylsesquioxane) membrane (LESTOSIL™) as the membrane, and an aqueous solution of PEG-400 was used as the absorbent. The experiment was carried out at seven different thicknesses of the absorbent layer, from 0 (without absorbent) to 6.5 mm, for each of them the separation efficiency value was obtained at a gas flow of 30 ml/min. There is an inversely proportional dependence of the ammonia concentration in the retentate stream on the thickness of the liquid absorbent layer. The highest separation efficiency (4375.48) was achieved with an absorbent layer thickness of 6.5 mm.