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Biogas upgrading using supported liquid membranes with deep eutectic systems and carbonic anhydrase enzyme
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A aplicação de novas tecnologias sustentáveis para processos de purificação de biogás desem-
penhará um papel fundamental não só no presente, mas também nas próximas décadas. Sol-
ventes Eutécticos (DES) têm sido considerados uma alternativa promissora para processos de
captura de CO2 quando comparados aos solventes tradicionalmente usados, nomeadamente
as soluções aquosas de aminas. Nesta tese, foram preparados 4 DES diferentes (cloreto de co-
lina:ácido malónico (1:1), ácido lático:l-prolina:água (1:1:1), l-prolina:glicerol (1:2.5) e cloreto
de colina:ácido lático (1:2)) e foram pré-equilibrados a diferentes valores de atividade de água
(aw) (entre 11.2 e 84.3%). Posteriormente, os DES foram caracterizados por FTIR, e a sua visco-
sidade, densidade, coeficiente de difusão do CO2 e constante de Henry para o CO2, foram de-
terminadas. A enzima anidrase carbónica (AC), enzima que tem a capacidade de catalisar a
reacção de conversão de CO2 em bicarbonato, foi adicionada na concentração de 1 mg/g DES
aos DES para avaliar o seu impacto no transporte de CO2. O DES l-Prolina-glicerol com uma
aw de 0.112 apresentou os melhores resultados apresentando o maior coeficiente de difusão de
CO2 dentro dos DES testados e com menor valor de constante de Henry. Por último, foram
preparadas membranas líquidas suportadas (SLM) utilizando um suporte poroso hidrofílico
de PTFE impregnado com o DES L-Prolina-Glicerol pré-equilibrado a aw=0.112. Foram reali-
zados ensaios de permeabilidade de gases para CH4 e CO2 a uma temperatura de 30ºC e pres-
são de 1 bar. A seletividade ideal e a permeabilidade foram calculadas e os resultados foram
comparados com a literatura. A membrana líquida suportada preparada neste trabalho apre-
sentou maior valor de permeabilidade ao CO2 quando comparado com a literatura, no entando
com uma selectividade ideial mais baixa ficando o seu valor abaixo do limite superior de Rob-
son. Isto prova que novas estratégias devem ser implementadas em trabalhos futuros para
aumentar a seletividade destas membranas impregnadas com Glicerol:L-Prolina.
The application of new sustainable technologies for biogas upgrading processes will have a key role not only in the present but also in the next few decades. Deep eutectic systems (DES) have been found to be a promising alternative for CO2 capture processes when com- pared to the most commonly used - aqueous amine solutions. In this thesis, 4 different DES were prepared (choline chloride:malonic acid (1:1), lactic acid:L-proline:water (1:1:1), l-pro- line:glycerol (1:2.5) and choline chloride:lactic acid (1:2)) and were pre-equilibrated in different water activity values (aw) (between 11.2 and 84.3%). Afterwards, the DES were characterized by FTIR, and their viscosity, density, CO2 diffusion coefficient and Henry’s constant were de- termined. Carbonic Anydrase, an enzyme that has the ability to catalyze the reaction of con- version of CO2 to bicarbonate, was added in a concentration of 1 mg/g DES to the DES to eval- uate its impact in CO2 transport. L-Proline-glycerol (1:2.5) conditioned in the aw=0.112 showed the best results having the highest diffusion coefficient within the group of DES tested and the lowest Henry’s constant. Lastly, a supported liquid membrane (SLM) was prepared using a PTFE hydrophilic porous support impregnated with L-Proline-Glycerol pre-equilibrated at the aw=0.112. Gas permeability experiments were carried out for CH4 and CO2 at a tempera- ture of 30ºC and pressure of 1 bar. The ideal selectivity and pure gas permeability were calcu- lated, and the results were compared with literature. The SLM prepared in this work presented a higher CO2 permeability value when compared to the other SLM using different DES and a lower selectivity, with its value falling below the Robson upper bound. This proves that new strategies need to be implemented in future works to increase selectivity of these membranes impregnated with Gly:L-Pro.
The application of new sustainable technologies for biogas upgrading processes will have a key role not only in the present but also in the next few decades. Deep eutectic systems (DES) have been found to be a promising alternative for CO2 capture processes when com- pared to the most commonly used - aqueous amine solutions. In this thesis, 4 different DES were prepared (choline chloride:malonic acid (1:1), lactic acid:L-proline:water (1:1:1), l-pro- line:glycerol (1:2.5) and choline chloride:lactic acid (1:2)) and were pre-equilibrated in different water activity values (aw) (between 11.2 and 84.3%). Afterwards, the DES were characterized by FTIR, and their viscosity, density, CO2 diffusion coefficient and Henry’s constant were de- termined. Carbonic Anydrase, an enzyme that has the ability to catalyze the reaction of con- version of CO2 to bicarbonate, was added in a concentration of 1 mg/g DES to the DES to eval- uate its impact in CO2 transport. L-Proline-glycerol (1:2.5) conditioned in the aw=0.112 showed the best results having the highest diffusion coefficient within the group of DES tested and the lowest Henry’s constant. Lastly, a supported liquid membrane (SLM) was prepared using a PTFE hydrophilic porous support impregnated with L-Proline-Glycerol pre-equilibrated at the aw=0.112. Gas permeability experiments were carried out for CH4 and CO2 at a tempera- ture of 30ºC and pressure of 1 bar. The ideal selectivity and pure gas permeability were calcu- lated, and the results were compared with literature. The SLM prepared in this work presented a higher CO2 permeability value when compared to the other SLM using different DES and a lower selectivity, with its value falling below the Robson upper bound. This proves that new strategies need to be implemented in future works to increase selectivity of these membranes impregnated with Gly:L-Pro.
Descrição
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Biogas Upgrading Deep Eutectic Systems Carbonic Anhydrase Supported Liquid Membranes