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Report RSE 17000278

Development and field validation of upgrading processes of biogas to biomethane with solid sorbents based on ammine or with physical adsorbents



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M. Scagliotti (RSE SpA), M. Notaro (RSE SpA) , A. Rossetti (RSE SpA)

BIOENERGY 2016 - Bioenergy

Results of the in-field tests performed on a small pilot plant installed at an anaerobic digester in order to validate in real operating conditions an innovative technology for the upgrading of biogas to biomethane by the carbon dioxide selective adsorption on a solid amine-based sorbent and on the MS C544 zeolite.

The upgrading of biogas to biomethane is a promising option for the biogas valorization. Biomethane which is obtained by the biogas upgrading is a fuel comparable to conventional natural gas, in terms of composition and heating value, and suitable for the injection into the natural gas network or to be directly used as biofuel in transport. In this frame, RSE has proposed an innovative upgrading technology, based on amines anchored on solid supports (solid sorbent) which allows to reduce the energy demand of the process, while keeping high performances and selectivity. RSE has developed a technology that uses amine-based solid sorbents in a process easier to operate and with a significant energy savings. For the evaluation and validation of this technology under real operating conditions, a pilot plant called BioMet-up was realized by RSE and installed near the anaerobic digester of the Biotreatment Center of ETRA in Camposampiero (PD). The pilot plant has been operated for a period of about six months during which, unfortunately, a slow and continuous decreasing of sorbent capture capacity was noticed.

In the reference period the efforts has been then devoted to: i) start a second field test at ETRA site by using a new load of freshly prepared solid diethanolamine sorbent; ii) investigate in parallel the degradation causes by laboratory tests on the sorbent that was previously operated in real conditions at ETRA site.

The amine sorbent degradation under real operational conditions was confirmed by the new field test too. Although not fully clarified, the causes of the degradation seem to be attributable to the loss by evaporation of the amine phase deposited on the sorbent and/or its decomposition by oxidation due to air intake in the reactor during the regeneration step carried out by raising the temperature and pumping vacuum. Due to the performance degradation in the real application conditions, the amine based sorbent does not appear suitable for an industrial-scale up of the biogas upgrading process. Therefore, other types of solid sorbents have been tested which could represent a valid alternative. Specifically, the investigations have been redirected to two distinct categories of materials: a) amino acids supported on porous alumina and b) physical adsorbents, such as zeolites and activated carbons.

Among the different investigated materials, a zeolite was identified that showed a CO2 capture capacity in the laboratory test more than twice of the amine sorbent. The high performance of zeolite was also confirmed in the preliminary tests performed in real operation conditions at the ETRA site. Conversely, the zeolite did not show 100% selectivity in the separation of the CO2/CH4 mixture and initially it completely retains both CO2 and CH4. However, this phenomenon was limited to the first minutes of the adsorption phase, after which only CO2 continued to be absorbed while the CH4 is totally released.

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