Evaluation of polymeric membranes' performance during laboratory-scale experiments, regarding the CO2 separation from CH4

Anaerobic digestion biogas upgrading using a two-stage membrane system under pilot-scale conditions

In the present work, the construction, and operation of a pilot-scale biogas upgrading system is presented, employing 2 commercial polyimide (PI) membranes. The Upgrading system treats biogas produced via anaerobic digestion of the sludge, produced from the treatment of municipal wastewater in the facilities of Thessaloniki's Wastewater Treatment Plant. The goal of the separation unit is the production of high purity biomethane (>95%) for potential reuse in terms of energy. The fabrication of the pilot scale system includes the scale up of a laboratory setup separating CO2 from binary CH4-CO2 gas mixture. After the stability tests of the process, for the operation of 5 months (February to June 2023) the purity and recovery of CH4 in the final gas product. The experimental results showed an average recovery of CH4 of 95.7% for an average 55% feed composition, whereas the average purity in the final product was equal to 82.4%. The purity results were lower because of the N2 presence in the product stream (average 17.5%). After normalization with the help of the lab-scale binary results, the expected results assuming N2 absence would be 99.8% CH4 purity and 67% CH4 recovery. Finally, 3 different membrane configurations are compared in terms of their energy production, concluding to the efficiency of 2-stage configuration with recycling stream for the optimal combination of theoretical stage cut fractions.

Municipal solid waste treatment for bioenergy and resource production: Potential technologies, techno-economic-environmental aspects and implications of membrane-based recovery

World estimated municipal solid waste generating at an alarming rate and its disposal is a severe concern of today's world. It is equivalent to 0.79 kg/d per person footprint and causing climate change; health hazards and other environmental issues which need attention on an urgent basis. Waste to energy (WTE) considers as an alternative renewable energy potential to recover energy from waste and reduce the global waste problems. WTE reduced the burden on fossil fuels for energy generation, waste volumes, environmental, and greenhouse gases emissions. This critical review aims to evaluate the source of solid waste generation and the possible routes of waste management such as biological landfill and thermal treatment (Incineration, pyrolysis, and gasification). Moreover, a comparative evaluation of different technologies was reviewed in terms of economic and environmental aspects along with their limitations and advantages. Critical literature revealed that gasification seemed to be the efficient route and environmentally sustainable. In addition, a framework for the gasification process, gasifier types, and selection of gasifiers for MSW was presented. The country-wise solutions recommendation was proposed for solid waste management with the least impact on the environment. Furthermore, key issues and potential perspectives that require urgent attention to facilitate global penetration are highlighted. Finally, practical implications of membrane and comparison membrane-based separation technology with other conventional technologies to recover bioenergy and resources were discussed. It is expected that this study will lead towards practical solution for future advancement in terms of economic and environmental concerns, and also provide economic feasibility and practical implications for global penetration.

A comprehensive review on zeolite-based mixed matrix membranes for CO2/CH4 separation

Biogas consisting of carbon dioxide/methane (CO₂/CH₄) gas mixtures has emerged as an alternative renewable fuel to natural gas. The presence of CO₂ can decrease the calorific value and generate greenhouse gas. Hence, separating CO₂ from CH₄ is a vital step in enhancing the use of biogas. Zeolite and zeolite-based mixed matrix membrane (MMM) is considered an auspicious candidate for CO₂/CH₄ separation due to thermal and chemical stability. This review initially addresses the development of zeolite and zeolite-based MMM for the CO₂/CH₄ separation. The highest performance in terms of CO₂ permeance and CO₂/CH₄ selectivity was achieved using zeolite and zeolite-based MMM, which exhibited CO₂ permeance in the range of 2.0 × 10^{- 7}-7.0 × 10^{- 6} mol m^{- 2} s^{- 1} Pa^{- 1} with CO₂/CH₄ selectivity ranging from 3 to 300. Current trends directed toward improving CO₂/CH₄ selectivity via modification methods including post-treatment, ion-exchanged, amino silane-grafted, and ionic liquid encapsulated of zeolite-based MMM. Those modification methods improved the defect-free and interfacial adhesions between zeolite particulates and polymer matrices and subsequently enhanced the CO₂/CH₄ selectivity. The modifications via ionic liquid and silane methods more influenced the CO₂/CH₄ selectivity with 90 and 660, respectively. This review also focuses on the possible applications of zeolite-based MMM, which include the purification and treatment of water as well as biomedical applications. Lastly, future advances and opportunities for gas separation applications are also briefly discussed. This review aims to share knowledge regarding zeolite-based MMM and inspire new industrial applications.

Integration of gas-liquid membrane contactors into anaerobic digestion as a promising route to reduce uncontrolled greenhouse gas (CH4/CO2) emissions

In this research, the recovery of dissolved biogas (CO2/CH4) from synthetic anaerobic effluents was studied using non-porous, polydimethylsiloxane (PDMS), hollow-fibre gas-liquid membrane contactors towards the design of a reduced carbon-footprint integrated bioprocess. As a key parameter, the gas-to-liquid (G/L) ratio (employing argon as sweep gas) was systematically varied in the range of 0.5-2.0. The results showed on a 1 m2 PDMS module that increasing the liquid (effluent) flow rate favours the CH4 transport, while a higher sweep gas flow rate is preferable for the CO2 transport over CH4. Depending on the actual biogas composition and the CO2 content of the effluent, the methane recovery could be improved up to 63 % under steady-state conditions. In general, similar tendencies were observed when another PDMS membrane module with a smaller surface area (2 500 cm2) was applied hence, in this sense, the separation behaviour seems to be independent of the membrane size.

Morphology Effect of Zinc Oxide Nanoparticles on the Gas Separation Performance of Polyurethane Mixed Matrix Membranes for CO2 Recovery from CH4, O2, and N2

The effect of the morphology and content of zinc oxide nanoparticles (ZnO-NPs) on the physicochemical, mechanical, and gas transport properties of the polyurethane (PU) mixed matrix membranes (MMMs) with respect to CO2 recovery from CH4, O2, and N2 was studied. The MMMs based on PU with spherical and rod-shaped ZnO-NPs at various loadings, namely, 0.05, 0.1, 0.5, 1, and 2 wt. %, were prepared with membrane density control and studied using AFM, wettability measurements, surface free energy calculation, gas separation and mechanical testing. To evaluate the resistance of the ZnO-NPs to agglomeration in the polymer solutions, zeta potential was determined. The ZnO-NPs with average cross sectional size of 30 nm were obtained by plasma-enhanced chemical vapor deposition (PECVD) from elemental high-purity zinc in a zinc-oxygen-hydrogen plasma-forming gas mixture. It was established that the spherical ZnO-NPs are promising to improve the gas performance of PU-based MMMs for CO2 recovery from natural gas, while the rod-shaped NPs better demonstrate their potential in capturing CO2 in flue gases.