Abstract
Two commercially available CO2-adsorbent materials (i.e., zeolite 13X (13X) and Lewatit® VP OC 1065 (Lewatit)) were evaluated for their applicability in a continuous temperature swing adsorption (TSA) process for biogas upgrading. The equilibrium adsorption characteristics of carbon dioxide and methane were determined by fixed bed and TGA tests. While relatively high CO2 capacities were measured for both materials (3.6 and 2.5 mol kg−1), neither of them was found to adsorb significant amounts of CH4. Lewatit showed to be fully regenerable at 95 °C, whereas for 13X, the regeneration was not complete at this temperature. However, 13X showed no degradation up to 190 °C, whereas Lewatit started to degrade at 110 and 90 °C when exposed to N2 and air, respectively. Fluidization tests showed that Lewatit provides a high mechanical stability, while on the contrary, the tested 13X showed considerable attrition. An equilibrium adsorption model was fitted to the measured CO2 adsorption data. The adsorption model was then integrated into an existing simulation tool for the proposed TSA process to roughly estimate the expectable regeneration energy demand for both materials. It was found that depending on the operating conditions, the regeneration energy demand lies between 0.32–0.54 kWhth/m3prodgas for 13X and 0.71–1.10 kWhth/m3prodgas for Lewatit. Since heat integration measures were not considered in the simulations, it was concluded that the proposed TSA process has a great potential to reduce the overall energy demand for biogas upgrading and that both tested adsorbent materials may be suitable for application in the proposed TSA process.
Highlights
Biogas is a promising renewable energy source that is considered as carbon neutral since the contained carbon comes from organic matter [1]
There are various CO2 separation processes deployed for biogas upgrading, with the main being amine scrubbing, pressure swing adsorption, physical absorption, and membrane
Based on the mentioned findings, reported by Li [22] and Montanari [23] for NaX-type adsorbents, this material was identified as potential adsorbent material for the proposed temperature swing adsorption (TSA) process
Summary
Biogas is a promising renewable energy source that is considered as carbon neutral since the contained carbon comes from organic matter [1]. It can either be used for power and heat production or preferably sent to an upgrading process to yield biomethane. There are various CO2 separation processes deployed for biogas upgrading, with the main being amine scrubbing, pressure swing adsorption, physical absorption (water scrubbing, organic solvent scrubbing), and membrane. It can be stated that currently, there is no single optimum biogas upgrading technology available. The final selection of a specific upgrading technology is mostly governed by local site conditions and by regional quality standards
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