https://backend.orbit.dtu.dk/ws/files/190081841/BiogasUpgrade_Review.pdf

Biogas upgrading and utilization: Current status and perspectives

Biogas as a renewable energy fuel – A review of biogas upgrading, utilisation and storage

The lack of tax incentives for biomethane use requires the optimization of both biogas production and upgrading in order to allow the full exploitation of this renewable energy source. The large number of biomethane contaminants present in biogas (CO2, H2S, H2O, N2, O2, methyl siloxanes, halocarbons) has resulted in complex sequences of upgrading processes based on conventional physical/chemical technologies capable of providing CH4 purities of 88–98 % and H2S, halocarbons and methyl siloxane removals >99 %. Unfortunately, the high consumption of energy and chemicals limits nowadays the environmental and economic sustainability of conventional biogas upgrading technologies. In this context, biotechnologies can offer a low cost and environmentally friendly alternative to physical/chemical biogas upgrading. Thus, biotechnologies such as H2-based chemoautrophic CO2 bioconversion to CH4, microalgae-based CO2 fixation, enzymatic CO2 dissolution, fermentative CO2 reduction and digestion with in situ CO2 desorption have consistently shown CO2 removals of 80–100 % and CH4 purities of 88–100 %, while allowing the conversion of CO2 into valuable bio-products and even a simultaneous H2S removal. Likewise, H2S removals >99 % are typically reported in aerobic and anoxic biotrickling filters, algal-bacterial photobioreactors and digesters under microaerophilic conditions. Even, methyl siloxanes and halocarbons are potentially subject to aerobic and anaerobic biodegradation. However, despite these promising results, most biotechnologies still require further optimization and scale-up in order to compete with their physical/chemical counterparts. This review critically presents and discusses the state of the art of biogas upgrading technologies with special emphasis on biotechnologies for CO2, H2S, siloxane and halocarbon removal.

A review on the state-of-the-art of physical/chemical and biological technologies for biogas upgrading

Biogas is a valuable renewable energy and also a secondary energy carrier produced from biodegradable organic materials via anaerobic digestion. It can be used as a fuel or as starting material for the production of chemicals, hydrogen and/or synthesis gas etc. The main constituents of biogas are methane (CH4) and carbon dioxide (CO2), with various quantities of contaminants, such as ammonia (NH3), water vapour (H2O), hydrogen sulfide (H2S), methyl siloxanes, nitrogen (N2), oxygen (O2), halogenated volatile organic compounds (VOCs), carbon monoxide (CO) and hydrocarbons. These contaminants presence and quantities depend largely on the biogas source, which could be anaerobic digestion of many substrates and landfill decompositions. The removal of these contaminants especially H2S and CO2 will significantly improve the quality of the biogas for its further uses. In parallel, biogas upgrading market is facing challenges in term of operating costs and energy consumption. The selection of appropriate technology depends on the specific biogas requirements, site specific, local circumstances and is case sensitive. This paper reviews the present state-of-the-art of biogas cleaning and upgrading technologies, including its composition, upgrading efficiency, methane recovery and loss. In addition, biogas production, utilization and the corresponding requirements on gas quality for grid injection and vehicle usage are investigated. Based on the results of comparisons of various technologies, recommendations are made on further research on the appropriate low cost technologies, especially using solid waste as low cost materials for biogas purification and upgrading.

/pdf/a-review-of-biogas-utilisation-purification-and-upgrading-1ykvn2m4o0.pdf

A Review of Biogas Utilisation, Purification and Upgrading Technologies

Hydrogen sulfide removal is a long-standing economic and environmental challenge faced by the oil and gas industries. H2S separation processes using reactive and non-reactive absorption and adsorption, membranes, and cryogenic distillation are reviewed. A detailed discussion is presented on new developments in adsorbents, such as ionic liquids, metal oxides, metals, metal–organic frameworks, zeolites, carbon-based materials, and composite materials; and membrane technologies for H2S removal. This Review attempts to exhaustively compile the existing literature on sour gas sweetening and to identify promising areas for future developments in the field.

https://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.7b00768

Hydrogen Sulfide Capture: From Absorption in Polar Liquids to Oxide, Zeolite, and Metal-Organic Framework Adsorbents and Membranes.

The use of photosynthetic CO2 reduction capacity of microalgae can be used for biogas upgrading. Such process would convert CO2 contained in the biogas into microalgal biomass, generating two products: upgraded biogas and biomass. Growth rate of Nannochloropsis gaditana was determined in atmospheres containing different levels of CH4 and CO2. Results showed no effect of CH4 rich atmosphere over microalgal development. CO2 inhibition was observed only when microalgae culture was exposed to atmospheres containing 9% of CO2. Direct contact of the biogas and the microalgal culture is not a feasible way to upgrade biogas, due to oxygen desorption to the gas phase. A two-stage process, involving a photobioreactor connected with a gas/liquid mass transfer unit showed to be an efficient way to remove CO2 from the biogas, keeping low levels of oxygen in the upgraded biogas.

Leslie Meier

Papers

A review on the state-of-the-art of physical/chemical and biological technologies for biogas upgrading

Photosynthetic CO2 uptake by microalgae: An attractive tool for biogas upgrading

Photosynthetic biogas upgrading using microalgae: Effect of light/dark photoperiod

Removal of H2S by a continuous microalgae-based photosynthetic biogas upgrading process

Evaluation of the feasibility of photosynthetic biogas upgrading: Simulation of a large-scale system