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Abstract(s)
Atualmente existe uma enorme necessidade em reduzir a dependência em
combustíveis fósseis, de modo a reduzir as emissões gasosas responsáveis pelas
alterações climáticas, havendo investimento em novas tenologias na recuperação de
subprodutos em diversos sectores, tais como no sector da celulose.
Licor negro do processo ao sulfito é um subproduto do processo de tratamento
químico ao sulfito na indústria de papel e celulose. Este subproduto apresenta
características adequadas para a produção de biocombustíveis devido ao seu poder
calorífico e ao seu alto teor de açúcares.
O presente trabalho teve como objetivo a valorização do licor negro do processo
ao sulfito, através da produção de bioetanol. Esta valorização foi realizada através da
fermentação dos açúcares presentes no licor negro do processo ao sulfito utilizando a
levedura Scheffersomyces stipitis, que é mais adequada para fermentar pentoses,
sendo que a concentração máxima de ácido acético que esta levedura consegue tolerar
é de 9g/L.
O estudo da evolução da fermentação dos açúcares foi realizado através da
comparação de 3 situações distintas: a fermentação do licor negro do processo ao sulfito
pré-tratado com resinas de permuta iónica, do licor negro diluído isento de prétratamento
e a fermentação com a levedura adaptada ao licor negro do processo ao
sulfito aumentando gradualmente a sua concentração de açúcares até 50 g/L.
O pré-tratamento consistiu na passagem do licor em duas resinas de permuta
iónica fortes, catiónica e aniónica. A resina catiónica teve como objetivo a eliminação
dos catiões de magnésio, enquanto a resina aniónica, a redução da concentração dos
lenhossulfonatos e do ácido acético.
Comparando os valores obtidos para o consumo de açúcar na fermentação do
licor negro do processo ao sulfito, num tempo de fermentação equivalente nos três tipos
de fermentação realizados, verifica-se que há um maior consumo no ensaio de
fermentação do licor negro sem pré-tratamento, cerca de 11 g/L, em relação aos ensaios
de fermentação do licor pré-tratado e de fermentação com a levedura adaptada,9 g/L e
3 g/L, respetivamente. Estes resultados não eram os esperados, podendo estar
relacionado com o facto destes ensaios não terem sido realizados em condições
estéreis, ao contrário do que aconteceu nos ensaios com a levedura adaptada, havendo
a possibilidade de crescimento de microrganismos contaminantes. Relativamente ao teor de etanol produzido, na fermentação com a levedura
adaptada, conclui-se que o teor obtido é baixo, cerca de 0,85% e 0,67% nos ensaios
realizados. Estes valores estão em concordância com o baixo consumo de açúcar que
houve nos dois ensaios.
Na caraterização da fermentação com a levedura adaptada, obteve-se uma
velocidade média de consumo do substrato igual a 0,08 g/(L.h), um fator médio de
conversão do substrato a etanol de 0,54 e a produtividade média em etanol igual a 0,45
g/(L.h).
Currently there is a huge need to reduce the dependence on fossil fuels to reduce gaseous emissions responsible for climate change and there is investment in new technologies for the recovery of byproducts in various sectors, such as in the cellulose sector. Sulphite spent liquor is a byproduct of the sulphite chemical treatment process in the pulp and cellulose industry and has several properties to produce biofuels due to its calorific value and high sugar content. This work aimed at the enhancement of the sulphite spent liquor, through the production of bioethanol. This enhancement was made through the fermentation of the sulphite spent liquor’s using the yeast Scheffersomyces Stipitis, which is more suitable for fermenting pentoses, and the maximum concentration of acetic acid that this yeast can tolerate is 9 g/L. The study of the evolution of the sugar’s fermentation was made through the comparison of three different situations: sulphite spent liquor pretreated with ion exchanging resins, liquor diluted without pretreatment and fermentation with a yeast adapted to the sulphite spent liquor gradually increasing sugar concentration to 50 g/L. The pretreatment consisted of percolating the liquor through two strong ion exchange resin beds, cationic and anionic. The objective of cationic resin was the elimination of the magnesium cations, while the anionic resin was the reduction of the concentration of lignosulphonates and acetic acid. Comparing the values obtained for the sugar consumption in the fermentation of the sulphite spent liquor, in equivalent time for the different fermentations, there is a higher sugar consumption in the fermentation of the liquor without pretreatment, about 11g/L and for the fermentations tests with pretreated liquor and the adapted yeast, 9 g/L and 3g/L, respectively. These results were not expected, and this may be related with the fact that the tests which were not carried out under sterile conditions, unlike the tests with the adapted yeast, have the possibility of growth of contaminating microorganisms. As for the ethanol production, in fermentation with the adapted yeast, it is concluded that the obtained content is low, about 0,85% and 0,67% in the tests carried out. These values are in agreement with the low sugar consumption that occurred in both tests. In the characterization of the fermentation with the adapted yeast, it was obtained an average substrate consumption rate of 0,08 g(/L.h), an average substrate conversion factor to ethanol of 0,54 and an average ethanol productivity of 0,45 g/(L.h).
Currently there is a huge need to reduce the dependence on fossil fuels to reduce gaseous emissions responsible for climate change and there is investment in new technologies for the recovery of byproducts in various sectors, such as in the cellulose sector. Sulphite spent liquor is a byproduct of the sulphite chemical treatment process in the pulp and cellulose industry and has several properties to produce biofuels due to its calorific value and high sugar content. This work aimed at the enhancement of the sulphite spent liquor, through the production of bioethanol. This enhancement was made through the fermentation of the sulphite spent liquor’s using the yeast Scheffersomyces Stipitis, which is more suitable for fermenting pentoses, and the maximum concentration of acetic acid that this yeast can tolerate is 9 g/L. The study of the evolution of the sugar’s fermentation was made through the comparison of three different situations: sulphite spent liquor pretreated with ion exchanging resins, liquor diluted without pretreatment and fermentation with a yeast adapted to the sulphite spent liquor gradually increasing sugar concentration to 50 g/L. The pretreatment consisted of percolating the liquor through two strong ion exchange resin beds, cationic and anionic. The objective of cationic resin was the elimination of the magnesium cations, while the anionic resin was the reduction of the concentration of lignosulphonates and acetic acid. Comparing the values obtained for the sugar consumption in the fermentation of the sulphite spent liquor, in equivalent time for the different fermentations, there is a higher sugar consumption in the fermentation of the liquor without pretreatment, about 11g/L and for the fermentations tests with pretreated liquor and the adapted yeast, 9 g/L and 3g/L, respectively. These results were not expected, and this may be related with the fact that the tests which were not carried out under sterile conditions, unlike the tests with the adapted yeast, have the possibility of growth of contaminating microorganisms. As for the ethanol production, in fermentation with the adapted yeast, it is concluded that the obtained content is low, about 0,85% and 0,67% in the tests carried out. These values are in agreement with the low sugar consumption that occurred in both tests. In the characterization of the fermentation with the adapted yeast, it was obtained an average substrate consumption rate of 0,08 g(/L.h), an average substrate conversion factor to ethanol of 0,54 and an average ethanol productivity of 0,45 g/(L.h).
Description
Keywords
Licor negro Processo ao sulfito Fermentação Bioetanol Levedura Scheffersomyces stipitis Sulphite spent liquor Fermentation Bioethanol Yeast Scheffersomyces Stipitis