Membrane gas separation has potential for the recovery and purification of helium, because the majority of membranes have selectivity for helium. This review reports on the current state of the research and patent literature for membranes undertaking helium separation. This includes direct recovery from natural gas, as an ancillary stage in natural gas processing, as well as niche applications where helium recycling has potential. A review of the available polymeric and inorganic membranes for helium separation is provided. Commercial gas separation membranes in comparable gas industries are discussed in terms of their potential in helium separation. Also presented are the various membrane process designs patented for the recovery and purification of helium from various sources, as these demonstrate that it is viable to separate helium through currently available polymeric membranes. This review places a particular focus on those processes where membranes are combined in series with another separation technology, commonly pressure swing adsorption. These combined processes have the most potential for membranes to produce a high purity helium product. The review demonstrates that membrane gas separation is technically feasible for helium recovery and purification, though membranes are currently only applied in niche applications focused on reusing helium rather than separation from natural sources.

The absorption of carbon dioxide with alkanolamine or potassium carbonate solvents has gained widespre ad acceptance for the removal of CO2 from natural gas and H 2. However, alkanolamine solutions are prone to oxidative degradation at high temperature. The main advantages of potassium carbonate solution for CO2 removal are the high chemical solubility of CO2 in the carbonate/ bicarbonate system, low solvent costs and the low energy requirement for solvent regeneration. The major challenge concerning absorption of CO2 into aqueous solutions of potassium carbonate is a relatively slow rate of reaction in the liquid phase causing low mass transfer rates. It is often advantageous to add a promoter to increase the absorption rate. While piperazine is often used for this purpose, there are some environmental health concerns with this approach. In this work we consider boric acid as an alternative promoter.Absorption of CO2 in a wetted -wall column by aqueous potassium carbonate solution with and without various concentrations of boric acid as promoter was measured under conditions in which the reaction of CO2 was of pseudo-first order. The equilibrium partial pressure and the rate of absorption of CO2 were measured in 30.0 wt% potassium carbonate and 1.0 to 5.0 wt% of boric acid at 50 to 80 ∘C. The overall pseudo -first-order reaction rate constants were determined fro m the kinetic measurements. The addition of small amounts of boric acid to potassium carbonate resulted in a significant enhancement of CO2 absorption rates

The computational thermodynamic analysis of a samarium oxide-based two-step solar thermochemical water splitting cycle is reported. The analysis is performed using HSC chemistry software and databases. The first (solar-based) step drives the thermal reduction of Sm₂O₃ into Sm and O₂. The second (non-solar) step corresponds to the production of H₂ via a water splitting reaction and the oxidation of Sm to Sm₂O₃. The equilibrium thermodynamic compositions related to the thermal reduction and water splitting steps are determined. The effect of oxygen partial pressure in the inert flushing gas on the thermal reduction temperature (T_H) is examined. An analysis based on the second law of thermodynamics is performed to determine the cycle efficiency (η_cycle) and solar-to-fuel energy conversion efficiency (η_{solar−to−fuel}) attainable with and without heat recuperation. The results indicate that η_cycle and η_{solar−to−fuel} both increase with decreasing T_H, due to the reduction in oxygen partial pressure in the inert flushing gas. Furthermore, the recuperation of heat for the operation of the cycle significantly improves the solar reactor efficiency. For instance, in the case where T_H = 2280 K, η_cycle = 24.4% and η_{solar−to−fuel} = 29.5% (without heat recuperation), while η_cycle = 31.3% and η_{solar−to−fuel} = 37.8% (with 40% heat recuperation).