The global energy market is in a transition towards low carbon fuel systems to ensure the sustainable development of our society and economy. This can be achieved by converting the surplus renewable energy into hydrogen gas. The injection of hydrogen (⩽10% v/v) in the existing natural gas pipelines is demonstrated to have negligible effects on the pipelines and is a promising solution for hydrogen transportation and storage if the end-user purification technologies for hydrogen recovery from hydrogen enriched natural gas (HENG) are in place. In this review, promising membrane technologies for hydrogen separation is revisited and presented. Dense metallic membranes are highlighted with the ability of producing 99.9999999% (v/v) purity hydrogen product. However, high operating temperature (⩾300 °C) incurs high energy penalty, thus, limits its application to hydrogen purification in the power to hydrogen roadmap. Polymeric membranes are a promising candidate for hydrogen separation with its commercial readiness. However, further investigation in the enhancement of H 2 /CH 4 selectivity is crucial to improve the separation performance. The potential impacts of impurities in HENG on membrane performance are also discussed. The research and development outlook are presented, highlighting the essence of upscaling the membrane separation processes and the integration of membrane technology with pressure swing adsorption technology.

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Over the last few decades, the optimal design and operation of energy-intensive industries such as cryogenic process has gained considerable attention. Because of their high energy efficiency, compact design, and energy-efficient heat transfer, mixed refrigerant (MR) systems are used in several industrial applications. The optimal refrigerant compositionwhich is difficult to obtainis crucial to the efficiency of MR systems. In this research, we explore the MR cryogenic process optimization using 17 different components in the refrigerant stream with normal boiling points ranging from −268.9 to 36 °C to achieve the lowest specific energy consumption. Here, we developed a discrete-continuous genetic algorithm (DCGA) consisting of five steps to resolve the mathematical difficulties of the many-variable optimization problem. Through conducting two case studies, we proved that DCGA can locate the optimal solution in a reasonable amount of time. Compared to the best optimization practices in the literature, the new approach saved up to 12.5% of the unit specific energy consumption. In addition to MR systems, DCGA can also optimize other extreme problems with many independent variables.

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A rate-based membrane gas-solvent contactor model was programmed in Aspen Custom Modeler (ACM) and interfaced with the Aspen Plus software suite to enable flowsheet simulations of carbon capture processes. After validation with different sets of laboratory and pilot plant data, the model's rigorous approach was examined against the commercial RadFrac model of Aspen Plus used for conventional absorption−stripping column simulations. Under identical processing conditions, both models predicted similar results for the temperature, flow rate, and composition of the streams leaving the absorption and stripping units. Differences between the two models were most pronounced for liquid and gas temperature profiles, which were attributed to the different energy balance methods used in the two models, but the difference was not large enough (∼10 °C) to influence the mass transfer within the membrane contactor, as the composition and flow rate of leaving streams were almost identical to that of the RadFrac model. A process intensification factor analysis showed that membrane contactor technology could reduce the volume of equipment required by a magnitude of 44 to undertake the same carbon capture ratio as the conventional column process.

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