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Produção de biocombustíveis líquidos a partir de glicerina não refinada, num contexto de biorrefinaria
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Resumo(s)
A presente dissertação teve como principal objetivo a produção de biocombustíveis líquidos a partir de glicerina não refinada proveniente de um processo de produção de biodiesel. Foram cedidas para este trabalho 3 amostras diferentes de entre as quais se escolheu a que apresentava maior potencial para aproveitamento. Essa amostra apresentava um valor de pH de 12 e continha: glicerol (70,6 ± 0,6 % m/m), sabões (3,5 ± 0,3 % moleato/m), cinzas (3,75 ± 0,13 % m/m), metanol (23,96 ± 0,02 m/m) e água (0,83 ± 0,01 m/m). Para separar os ácidos gordos presentes na forma de sabões e enriquecer a fase aquosa em glicerol, foi realizado um processo de acidificação/neutralização seguido de separação das fases obtidas por centrifugação. Através de estudos de otimização do processo, e tendo em vista uma eventual aplicação industrial, concluiu-se que a adição de ácido clorídrico (HCl) para uma redução do valor de pH da glicerina não refinada para 5, permite obter uma fase rica em glicerol contendo 94,6% do original e uma fase orgânica contendo 75% de ácidos gordos livres (AGL). Apesar de não ter um existido aumento de pureza da fase contendo glicerina, este processo permitiu reduzir o nível de alguns parâmetros contaminantes de modo a possibilitar o seu uso como fonte de carbono em ensaios fermentativos de produção de etanol e de biomassa oleaginosa.
Com vista à produção de etanol foram realizados ensaios envolvendo diversas leveduras específicas inoculadas em meio contendo uma composição base de sais e extrato de levedura, ou apenas sais, e glicerina não refinada tratada a pH 5 com HCl numa concentração final de 7,5 g/L em glicerina. Os resultados destes ensaios foram comparados com ensaios semelhantes realizados com glicerina comercial pura (87%). Verificou-se que as leveduras Pichia stipitis e Saccharomyces uvarum apresentavam uma melhor capacidade de adaptação para conversão da glicerina tratada em biomassa. Contudo, o processo fermentativo não ocorreu de modo significativo tendo-se detetado concentrações mínimas de etanol (< 250 mg/L). Na avaliação da viabilidade da produção de biomassa rica em óleo por conversão de glicerina proveniente da produção de biodiesel, verificou-se que as leveduras Rhodosporidium toruloides e Rhodotorula mucilaginosa apresentaram rendimentos de conversão em biomassa de aproximadamente 50%. Os teores de ácidos gordos presentes na biomassa no final do processo eram cerca de 20% do inicial, mostrando que a adaptação das células à glicerina ocorreu à custa de alteração no metabolismo de produção de lípidos.
The main goal of this work was the production of liquid biofuels from crude glycerine from biodiesel production. Three different crude glycerine samples were obtained and characterized. Taking into consideration the potential for biofuels production, the sample chosen for the following studies was the sample containing 70.6 ± 0.6% m/m of glycerol, 3.5 ± 0.3 % moleate/m of soaps, 3.75 ± 0.13 % m/m of ash, 23.96 ± 0.02% m/m of methanol, 0.83 ± 0.01% m/m of water and a pH level of 12. In order to separate the fatty acids, present in the soap form obtaining a glycerol rich phase, was carried out an acidification/neutralisation step followed by centrifugation to promote phase separation. Several studies to optimize the process for industrial scale application were performed. Addition of hydrochloric acid (HCl) until pH 5 revealed to be the best way to obtain a glycerine rich phase containing 94.6% of the original compound and an organic phase with 75% of free fatty acids (FFA) corresponding to a recovery of 59.4%. Although there was not observed an increase in the purity of the glycerine phase as expected, some important contaminant levels were reduced in the process allowing a posterior use of this material, as carbon source in ethanol fermentation and oleaginous biomass production assays. Regarding the ethanol production, fermentative experiments were carried out with 4 different yeasts. The microorganisms were inoculated in media containing either inorganic salts and yeast extract or only inorganic salts and crude glycerine treated at pH 5 with HCl (final concentration – 7.5 g/L) as carbon source. The results obtained were compared to similar ones where technical grade commercial glycerine (87%) was used. It was found that the yeasts Pichia stipitis and Saccharomyces uvarum showed higher capability to use crude glycerine and grow. However, the fermentation ability seemed to be inhibited as no significant ethanol levels were detected in the medium (<250 mg / L). Also, several experiments were performed to evaluate the feasibility of using crude glycerine to produce oleaginous biomass. It was observed that yeasts, such as Rhodosporidium toruloides and Rhodotorula mucilaginosa, were able to grow with a biomass conversion yield of around 50%. Nevertheless, the final fatty acid content in the cells was about 20% of the initial level, indicating that cell adaptation to crude glycerine resulted in changes in the lipid metabolism.
The main goal of this work was the production of liquid biofuels from crude glycerine from biodiesel production. Three different crude glycerine samples were obtained and characterized. Taking into consideration the potential for biofuels production, the sample chosen for the following studies was the sample containing 70.6 ± 0.6% m/m of glycerol, 3.5 ± 0.3 % moleate/m of soaps, 3.75 ± 0.13 % m/m of ash, 23.96 ± 0.02% m/m of methanol, 0.83 ± 0.01% m/m of water and a pH level of 12. In order to separate the fatty acids, present in the soap form obtaining a glycerol rich phase, was carried out an acidification/neutralisation step followed by centrifugation to promote phase separation. Several studies to optimize the process for industrial scale application were performed. Addition of hydrochloric acid (HCl) until pH 5 revealed to be the best way to obtain a glycerine rich phase containing 94.6% of the original compound and an organic phase with 75% of free fatty acids (FFA) corresponding to a recovery of 59.4%. Although there was not observed an increase in the purity of the glycerine phase as expected, some important contaminant levels were reduced in the process allowing a posterior use of this material, as carbon source in ethanol fermentation and oleaginous biomass production assays. Regarding the ethanol production, fermentative experiments were carried out with 4 different yeasts. The microorganisms were inoculated in media containing either inorganic salts and yeast extract or only inorganic salts and crude glycerine treated at pH 5 with HCl (final concentration – 7.5 g/L) as carbon source. The results obtained were compared to similar ones where technical grade commercial glycerine (87%) was used. It was found that the yeasts Pichia stipitis and Saccharomyces uvarum showed higher capability to use crude glycerine and grow. However, the fermentation ability seemed to be inhibited as no significant ethanol levels were detected in the medium (<250 mg / L). Also, several experiments were performed to evaluate the feasibility of using crude glycerine to produce oleaginous biomass. It was observed that yeasts, such as Rhodosporidium toruloides and Rhodotorula mucilaginosa, were able to grow with a biomass conversion yield of around 50%. Nevertheless, the final fatty acid content in the cells was about 20% of the initial level, indicating that cell adaptation to crude glycerine resulted in changes in the lipid metabolism.
Descrição
Tese de mestrado integrado em Engenharia da Energia e do Ambiente, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, em 2018
Palavras-chave
Glicerina não-refinada Biodiesel Bioetanol Lípidos Leveduras Teses de mestrado - 2018