Abstract
Carbonaceous adsorbents have been pointed out as promising adsorbents for the recovery of methane from its mixture with carbon dioxide, including biogas. This is because of the fact that CO2 is more strongly adsorbed and also diffuses faster compared to methane in these materials. Therefore, the present study aimed to test alternative carbonaceous materials for the gas separation process with the purpose of enriching biogas in biomethane and to compare them with the commercial one. Among them was coconut shell activated carbon (AC) as the adsorbent derived from bio-waste, rubber tire pyrolysis char (RPC) as a by-product of waste utilization technology, and carbon molecular sieve (CMS) as the commercial material. The breakthrough experiments were conducted using two mixtures, a methane-rich mixture (consisting of 75% CH4 and 25% CO2) and a carbon dioxide-rich mixture (containing 25% CH4 and 75% CO2). This investigation showed that the AC sample would be a better candidate material for the CH4/CO2 separation using a fixed-bed adsorption column than the commercial CMS sample. It is worth mentioning that due to its poorly developed micropore structure, the RPC sample exhibited limited adsorption capacity for both compounds, particularly for CO2. However, it was observed that for the methane-rich mixture, it was possible to obtain an instantaneous concentration of around 93% CH4. This indicates that there is still much potential for the use of the RPC, but this raw material needs further treatment. The Yoon–Nelson model was used to predict breakthrough curves for the experimental data. The results show that the data for the AC were best fitted with this model.
Highlights
The development of fuel production based on renewable resources is one the major trends in science and the economy
In this paper we focus on adsorption technologies, especially materials, for which proper selection is a key factor in the successful use of this technology in biogas upgrading and cleaning [22]
Three types of carbonaceous materials were examined: carbon molecular sieve (CMS, Carbo-Tech) as a commercial material, coconut shell activated carbon (AC, Cocarb Solution) as an adsorbent derived from bio-waste, and rubber tire pyrolysis char (RPC, ReOil) as a Materials 2021, 14, 7759
Summary
The development of fuel production based on renewable resources is one the major trends in science and the economy. Taking into consideration the adsorption-based process, especially pressure swing adsorption (PSA), as a method to enrich methane from biogas [52], a useful tool to check the viability of such a separation is the performance of a breakthrough curve experiment [12,27] In this way, it is possible to evaluate the performance of potential adsorbent materials and their use for upgrading biogas for transport applications or to satisfy pipeline specifications, naturally, without complicated full adsorption–desorption PSA cycles. The main objective was to analyze the effect of the extreme contents of CH4 and CO2 in the feed stream and, based on these results, to prove that these materials are suitable for biogas separation
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