Siloxane removal in the energy recovery of biogas: sequential adsorption/oxidation processes

The thesis deals with removal of organosilicon compounds in the energy recovery of biogas. Alternative adsorbents for the siloxane removal were studied, and the physical and chemical mechanisms involved in the siloxane adsorption were discovered, which improved the yield of the adsorption and regeneration technologies using both activated carbons and zeolites. Moreover, several technologies based on advanced oxidation processes have been applied in order to regenerate and reuse the exhausted adsorbents. The thesis studies the siloxane removal at lab-scale close to real scenario conditions, including the competitive adsorption with compounds usually found in biogas, in the presence of humidity and with the same gas matrix, which allowed to select the most efficient materials for this purpose. Therefore, the knowledge reported in the thesis dissertation is directly transferable to field application to upgrade the siloxane removal systemAquesta tesi estudia l'eliminació de compostos volàtis de silici (siloxans) per la recuperació energètica del biogàs. Es van estudiar diferents adsorbents per l'adsorció de siloxans, determinants les propietats físico-químiques superficials que en condicionen l'eficiència, permetent millorar el rendiment de l'adsorció i permetent la regeneració en carbons actius i zeolites esgotats. La tesi estudia l'eliminació de siloxans a escala de laboratori en condicions properes a les reals del biogàs, incloent l'adosrció competitiva amb altres compostos orgànics volàtics, en presència d'humitat i amb diferents matrius gasoses, la qual cosa va permetre seleccionar els materials òptims per aquest propòsit.Per tant el coneixement derivat d'aquesta tesi és directament transferible per tal de millorar els sistemes d'eliminació siloxane

Siloxane removal in the energy recovery of biogas: sequential adsorption/oxidation processes

The thesis deals with removal of organosilicon compounds in the energy recovery of biogas. Alternative adsorbents for the siloxane removal were studied, and the physical and chemical mechanisms involved in the siloxane adsorption were discovered, which improved the yield of the adsorption and regeneration technologies using both activated carbons and zeolites. Moreover, several technologies based on advanced oxidation processes have been applied in order to regenerate and reuse the exhausted adsorbents. The thesis studies the siloxane removal at lab-scale close to real scenario conditions, including the competitive adsorption with compounds usually found in biogas, in the presence of humidity and with the same gas matrix, which allowed to select the most efficient materials for this purpose. Therefore, the knowledge reported in the thesis dissertation is directly transferable to field application to upgrade the siloxane removal systemAquesta tesi estudia l'eliminació de compostos volàtis de silici (siloxans) per la recuperació energètica del biogàs. Es van estudiar diferents adsorbents per l'adsorció de siloxans, determinants les propietats físico-químiques superficials que en condicionen l'eficiència, permetent millorar el rendiment de l'adsorció i permetent la regeneració en carbons actius i zeolites esgotats. La tesi estudia l'eliminació de siloxans a escala de laboratori en condicions properes a les reals del biogàs, incloent l'adosrció competitiva amb altres compostos orgànics volàtics, en presència d'humitat i amb diferents matrius gasoses, la qual cosa va permetre seleccionar els materials òptims per aquest propòsit.Per tant el coneixement derivat d'aquesta tesi és directament transferible per tal de millorar els sistemes d'eliminació siloxane

Environmental Decision Support System for Biogas Upgrading to Feasible Fuel

Biogas production is a growing market and the existing conversion technologies require different biogas quality and characteristics. In pursuance of assisting decision-makers in biogas upgrading an environmental decision support system (EDSS) was developed. Since the field is rapidly progressing, this tool is easily updatable with new data from technical and scientific literature through the knowledge acquisition level. By a thorough technology review, the diagnosis level evaluates a wide spectrum of technologies for eliminating siloxanes, H2S, and CO2 from biogas, which are scored in a supervision level based upon environmental, economic, social and technical criteria. The sensitivity of the user towards those criteria is regarded by the EDSS giving a response based on its preferences. The EDSS was validated with data from a case-study for removing siloxanes from biogas in a sewage plant. The tool described the flow diagram of treatment alternatives and estimated the performance and effluent quality, which matched the treatment currently given in the facility. Adsorption onto activated carbon was the best-ranked technology due to its great efficiency and maturity as a commercial technology. On the other hand, biological technologies obtained high scores when economic and environmental criteria were preferred. The sensitivity analysis proved to be effective allowing the identification of the challenges and opportunities for the technologies considered

Investigating the impact of adsorbent particle size on column adsorption kinetics through a mathematical model

Experimental data demonstrates that the breakthrough curves of column adsorption exhibit qualitative differences related to the size of the adsorbent particles. Standard models do not account for particle size, consequently, in this paper we develop a new formulation that incorporates the diffusion of the adsorbate into the adsorbent particles. Two kinetic models are considered, Langmuir adsorption and a linear driving force. Approximate analytical solutions are developed for these two models coupled to mass flow and intra-particle diffusion equations. The accuracy of the analytical solutions is verified through comparison with numerical solutions of the full mathematical model. Comparison with experimental data confirms that the new analytical solutions show better agreement than previous models. However, in certain cases, neither form of model predicts the behaviour suggesting a combination of different effects contribute to the breakthrough form

Sewage biogas efficient purification by means of lignocellulosic waste-based activated carbons

The present paper evaluates the efficiency of sustainable activated carbons obtained from the valorization of lignocellulosic waste in removing siloxanes and volatile organic compounds for the purification of anaerobic digester biogas. Pyrolized and non-pyrolized lignocellulosic residues generated in food and wood industries were used as precursor materials to obtain experimental adsorbents by a chemical activation process using several activating agents. The highest porosity was obtained by non-pyrolized residue activated by K2CO3 at 900 °C. The performance of the experimental materials was compared with that of commercial activated carbons in gas adsorption tests of siloxanes (octamethylcyclotetrasiloxane and hexamethyldisiloxane) and volatile organic compounds (toluene and limonene). The waste-based activated carbons developed in this work proved to be more efficient for the removal of both siloxanes and VOCs than the commercial samples in most of the conditions tested. Adsorption capacities correlated with porosity, while the more relevant pore size depends on the adsorbate.This work was funded by MINECO – Spain (CTQ2014-53718-R) co-funded by FEDER and University of Girona. Eric Santos-Clotas thanks Universitat de Girona for his predoctoral grant (IFUdG-2015/51). Alba Cabrera-Codony acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and from the Agency for Business Competitiveness of the Government of Catalonia (TECSPR16-1-0045). LEQUIA has been recognized as consolidated research group by the Catalan Government (2017-SGR-1552).Peer reviewe

Efficient removal of siloxanes and volatile organic compounds from sewage biogas by an anoxic biotrickling filter supplemented with activated carbon

Producción CientíficaThe removal of siloxanes (D4 and D5) and volatile organic contaminants (hexane, toluene and limonene) typically found in sewage biogas was investigated in a lab-scale biotrickling filter (BTF) packed with lava rock under anoxic conditions. Complete removal efficiencies for toluene and limonene were recorded at all empty bed residence time (EBRT) tested. The influence of EBRT was remarkable on the abatement of D5, whose removal decreased from 37% at 14.5 min to 16% at 4 min, while the removal of D4 and hexane remained below 16%. The packing material was supplemented with 20% of activated carbon aiming at increasing the mass transfer of the most hydrophobic pollutants. This strategy supported high removal efficiencies of 43 and 45% for hexane and D5 at the lowest EBRT. CO2 and silica were identified as mineralization products along with the presence of metabolites in the trickling solution such as dimethylsilanediol, 2-carene and α-terpinene.Ministerio de Ciencia, Innovación y Universidades (CTQ2014-53718-R) cofinanciado por FEDER y la Universidad de Girona.Agencia para la Competitividad Empresarial de la Generalitat de Catalunya (TECSPR16-1-0045)Junta de Castilla y León y de la UE-FEDER (CLU 2017-09)European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement N° 712949 (TECNIOspring PLUS

From biocollagenic waste to efficient biogas purification: Applying circular economy in the leather industry

This work draws on the concept of circular economy (CE) to advance knowledge toward the obtention of low-cost and sustainable activated carbons from a biocollagenic waste from the leather industry, and using them in biogas upgrading for energy recovery. The research pursues a series of benefits across different industrial applications. The first is the production of sustainable carbon-based absorbents: using a CE approach, our experiments re-valorize solid wastes generated in the vegetable tanning from leather industry to obtain activated carbons for environmental applications. The second benefit is related to biogas energy recovery, which plays a key role in achieving the targets of the European Renewable Directive, since biogas is a renewable fuel which presents additional environmental value reducing the release of greenhouse gases in the atmosphere. Sustainable activated carbons were obtained from biocollagenic industrial waste by chemical activation (KOH, NaOH, K2CO3), with and without a previous pyrolysis step, at different activation temperature (750 °C and 900 °C) and different activating agent/precursor weight ratio. The microporous adsorbent materials obtained showed good chemical and textural properties, with BET specific surface area and total pore volume of up to 1600 m2 g−1 and 0.76 cm3 g−1, respectively. These efficient and low cost activated carbons showed a siloxane adsorption capacity of up to 500 mg g−1, higher than that of the commercial steam activated carbons supplied by adsorbent producers that reached values of up to 349 mg g−1. The industrial biocollagenic waste if vegetal tanning successfully performed as precursor for sustainable low-cost activated carbons, and the materials obtained were proved to be efficient for gaseous pollutants abatement applications. Thus, this work resulted in an efficient valorization method that assists the reduction of coal extraction by obtaining eco-friendly activated carbons that can be beneficially used for biogas upgrading in waste-to-energy applications in a circular economy scenario.The authors are grateful to Miquel Farrés Rojas S.A. for providing financial support through the PETRI project (MICINN, Spain, PET2007-0421-02) and for providing the leather waste samples.Peer reviewe