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Life cycle assessment of a CO2 revalorisation process using membrane contactors
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- Anthropogenic carbon dioxide (CO2) emissions are largely emitted from fossil fuel combustion. In order to avoid global warming, one potential approach to reduce the carbon footprint of industries could be the capture of CO2 via membrane technologies. This master thesis aims to study the potential interest of a novel process for carbon capture and utilisation (CCU) using membrane contactors. To do so, the environmental impacts will be evaluated in a life cycle assessment (LCA). The LCA will focus on the CCU process operating in 3 major steps. Firstly, membrane gas absorption uses a novel solvent composed of 0.5M sodium carbonates (Na2CO3) and promoted by 0.5M arginine (ARG) or 0.3M sarcosine (SAR). Chemical absorption fixes CO2 in the form of sodium bircarbonates (NaHCO3) in an aqueous solution. Secondly, the solution is distilled and NaHCO crystallised via membrane distillation-crystallisation (MDC). 3 different and potential MDC technologies will be studied: osmotic membrane distillation (OMD), direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD). Finally, a post-treatment step allows the filtration of NaHCO3 crystals and the recovery of the remaining solution. These crystals could be reused for other commercial purposes. The work of the thesis is 1) to model this CCU process as a continuous process and to scale it up such that material and energy inventories can be collected and 2) to identify key points of the process which are determinant with regards to environmental impacts. For this purpose, the 4-step LCA methodology is followed. The results show that the process, when environmentally optimised, is a possible technology to reduce CO2 emissions and achieve significant impact reduction in other impact categories. Absorption is also proven to be a key step with regard to emissions, with an emphasis on minimising the use of Na2CO3. Indeed, the use of Na2CO3 in the solvent is a relatively important factor for environmental concerns. To reduce its use, absorption must be carried out until the solvent is saturated. This minimises the solvent flowrate and thus reduces emissions in the subsequent MDC step. With regard to the preferred MDC step, there is no consensus on all impact categories. OMD and VMD have the highest emissions in several categories, whilst DCMD depicts quantitatively intermediate emissions.