Processo de conversão de biomassa lignocelulósica visando a produção de ácido levulínico usando um catalisador à base de lignina
Data
2021-11-19
Autores
Santos, Miquéias Gomes dos [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Estudos que visam desenvolver tecnologias para a conversão de biomassa lignocelulósica em produtos como energia, combustíveis e químicos de valor agregado, são imprescindíveis para que, no futuro, biorrefinarias possam se estabelecer e se consolidar como sistemas alternativos às refinarias de petróleo. Partindo desse pressuposto, o presente trabalho contribuiu para o desenvolvimento de um processo que envolve a produção de um catalisador sólido ácido carbonáceo à base de lignina e sua utilização na reação de conversão de celulose em ácido levulínico, com a particularidade de que ambos, reagente e catalisador, são provenientes da mesma matéria-prima – uma mistura de palha e bagaço de cana-deaçúcar na proporção 1:1. A palha e o bagaço de cana-de-açúcar são importantes fontes de carbono renováveis produzidas em larga escala no território brasileiro e o ácido levulínico é um importante precursor sintético no setor químico que pode ser obtido por meio da catálise ácida da celulose, o constituinte majoritário dessas biomassas lignocelulósicas. O processo abrangeu as seguintes etapas: obtenção de celulose e lignina por fracionamento químico da biomassa de palha e bagaço de cana de-açúcar; carbonização incompleta da lignina obtida e sua posterior sulfonação com ácido sulfúrico concentrado para sintetizar um catalisador sólido ácido; e conversão direta da celulose em ácido levulínico via reações de hidrólise e desidratação simultâneas, catalisadas pelo sólido ácido carbonáceo. A caracterização química da mistura dessas biomassas revelou composição de aproximadamente 42% de celulose, 26% de hemicelulose e 28% de lignina. O delineamento experimental para recuperação da celulose e remoção da lignina mostrou que sob as condições reacionais relativamente brandas de 110 ºC, 117 min e relação sólido/NaOH (4,4%m/v) de 1:20, mais de 91% da lignina é dissolvida no licor negro, recuperandose um sólido com teor de celulose superior a 78%. A lignina, por sua vez, foi totalmente recuperada na forma de precipitado sólido por meio da redução do pH do licor negro para 3 (sob essa condição foram recuperados 11 g de precipitado por litro de licor) . Com a lignina recuperada foi possível, então, sintetizar um catalisador sólido carbonáceo com densidade de sítios ácidos totais de 7,3 mmol/g que foi capaz de converter 17,11 % da celulose e obter rendimentos de até 38,55% de ácido levulínico quando se aplicou uma relação catalisador/celulose de apenas 8:10 (m/m). O processo aqui proposto, portanto, tem o potencial de viabilizar a inclusão do ácido levulínico, um composto químico de alto valor agregado, entre os subprodutos do setor sucroenergético nacional, incrementando o potencial competitivo desse setor.
Developing technologies for converting lignocellulosic biomass to products such as energy, fuels, and value-added chemicals is an important step in making biorefineries a feasible alternative to the current oil-based productive system. Based on this assumption, the present work developed a solid carbonaceous acid catalyst based on lignin and used it to convert cellulose to levulinic acid, with the particularity that both reagent and catalyst came from the same raw material – a mixture of straw and sugarcane bagasse in a 1:1 ratio. Sugarcane straw and bagasse are important sources of renewable carbon, which are produced on a large scale in Brazil, and levulinic acid is an important synthetic precursor in the chemical sector that can be obtained through acid catalysis of cellulose, the major constituent of those materials. The process described in this work covered the following steps: obtaining cellulose and lignin by chemical fractionation of the biomass comprised of straw and sugarcane bagasse; incomplete carbonization of the recovered lignin and its subsequent sulphonation with concentrated sulfuric acid to synthesize a solid acid catalyst; and direct conversion of cellulose to levulinic acid via simultaneous hydrolysis and dehydration reactions catalyzed by the carbonaceous solid acid synthesized from lignin. The chemical characterization of the mixture of biomasses revealed a composition of approximately 42% of cellulose, 26% of hemicellulose, and 28% of lignin. The experimental design for cellulose recovery and lignin removal showed that under relatively mild reaction conditions of 110 °C, 117 min, and solid/NaOH (4.4% w/v) ratio of 1:20, more than 91% of the lignin was dissolved into the black liquor, recovering a solid with a cellulose content higher than 78%. Lignin was fully recovered in the form of precipitate by simply reducing the pH of the black liquor to 3 (under this condition 11 g of precipitate were recovered per litre of liquor). With the recovered lignin it was then possible to synthesize a solid carbonaceous catalyst with a total acid site density of 7.3 mmol/ g which was able to convert up to 17.11% of the cellulose and obtain yields of up to 38.55% of levulinic acid when a catalyst/cellulose ratio of only 8:10 (w/w) was used. The process proposed here, therefore, has the potential to enable the inclusion of levulinic acid, a high-value chemical compound, among the by-products of the national sugar-energy sector, increasing the competitive potential of that sector.
Developing technologies for converting lignocellulosic biomass to products such as energy, fuels, and value-added chemicals is an important step in making biorefineries a feasible alternative to the current oil-based productive system. Based on this assumption, the present work developed a solid carbonaceous acid catalyst based on lignin and used it to convert cellulose to levulinic acid, with the particularity that both reagent and catalyst came from the same raw material – a mixture of straw and sugarcane bagasse in a 1:1 ratio. Sugarcane straw and bagasse are important sources of renewable carbon, which are produced on a large scale in Brazil, and levulinic acid is an important synthetic precursor in the chemical sector that can be obtained through acid catalysis of cellulose, the major constituent of those materials. The process described in this work covered the following steps: obtaining cellulose and lignin by chemical fractionation of the biomass comprised of straw and sugarcane bagasse; incomplete carbonization of the recovered lignin and its subsequent sulphonation with concentrated sulfuric acid to synthesize a solid acid catalyst; and direct conversion of cellulose to levulinic acid via simultaneous hydrolysis and dehydration reactions catalyzed by the carbonaceous solid acid synthesized from lignin. The chemical characterization of the mixture of biomasses revealed a composition of approximately 42% of cellulose, 26% of hemicellulose, and 28% of lignin. The experimental design for cellulose recovery and lignin removal showed that under relatively mild reaction conditions of 110 °C, 117 min, and solid/NaOH (4.4% w/v) ratio of 1:20, more than 91% of the lignin was dissolved into the black liquor, recovering a solid with a cellulose content higher than 78%. Lignin was fully recovered in the form of precipitate by simply reducing the pH of the black liquor to 3 (under this condition 11 g of precipitate were recovered per litre of liquor). With the recovered lignin it was then possible to synthesize a solid carbonaceous catalyst with a total acid site density of 7.3 mmol/ g which was able to convert up to 17.11% of the cellulose and obtain yields of up to 38.55% of levulinic acid when a catalyst/cellulose ratio of only 8:10 (w/w) was used. The process proposed here, therefore, has the potential to enable the inclusion of levulinic acid, a high-value chemical compound, among the by-products of the national sugar-energy sector, increasing the competitive potential of that sector.
Descrição
Palavras-chave
Catalisador sólido ácido à base de lignina, Ácido levulínico, Palha e bagaço de cana-de-açúcar, Catalisador sulfonado