A carregar...
Publicação
Cascade valorization of spent coffee grounds for the production of value-added products and energy: Evaluation of selective fractionation processes
| Nome: | Descrição: | Tamanho: | Formato: | |
|---|---|---|---|---|
| 2.27 MB | Adobe PDF |
Orientador(es)
Resumo(s)
Este trabalho propõe uma estratégia de valorização em cascata das borras-de-café (SCG), um
resíduo abundante a nível mundial, em biocombustíveis e produtos de valor acrescentado.
Avaliaram-se duas estratégias de produção de biodiesel: Processo em três etapas, extração,
recuperação de solventes (hexano, etanol, metanol e água) e transesterificação, e o processo de
transesterificação direta. O maior rendimento em ésteres-de-ácidos-gordos (10,88%, base seca de
SCG) foi obtido para o processo baseado na extração com etanol. No entanto, a transesterificação
direta, energeticamente mais eficiente, também apresentou um rendimento significativo, 9,28 %.
A produção de lenhina e oligossacáridos foi avaliada para SCG e SCG extraídas com etanol
utilizando um pré-tratamento alcalino suave, estudando o tempo de reação (60-240 min),
temperatura (25-75 °C) e concentração de NaOH (0-2,5 M). O fator de severidade descreve
adequadamente a cinética do processo, com severidades mais elevadas a induzirem maiores
rendimentos em produtos, 18,02% e 13,25% (base SCG seca), para lenhina e oligossacáridos
(XGMOS), respetivamente. Todas as variáveis são estatisticamente significativas para o rendimento
em sólidos que influenciam negativamente. O rendimento em XGMOS é (positivamente) influenciado
tanto pelo tempo, como pela concentração de catalisador. O rendimento em lenhina só é
influenciado (positivamente) pela concentração do catalisador. O melhor balanço entre a formação
de produtos e os custos operacionais foi identificado para [NaOH] 0,625 M, 50 °C, e 60 min. Ambas as
amostras de SGC apresentaram um desempenho comparável.
A produção de biogás por digestão anaeróbia foi ensaiada em mono e em codigestão (utilizando
SCG/chorume de porco 1/3, base sólidos voláteis, SV). Os perfis de produção de biogás foram
semelhantes, mas a codigestão permite duplicar a produção específica de biometano em
comparação com a mono-digestão.
A estratégia de valorização proposta permitiu a produção sequencial de 7,77 kg de biodiesel; 5,34
kg de lenhina, 5,44 kg de oligossacáridos e 137,08 kg de biometano por 100 kg de SCG (e 314,93 kg
de chorume de porco), num processo integrado, tecnicamente viável, eficiente em termos
energéticos, escalável e que promove a bioeconomia circular.
This work proposes a cascade valorization route of spent coffee grounds (SCG), a widespread lignocellulosic residue, into biofuels and value-added products. Biodiesel production was assayed based on two strategies: i) the classical three-step process (extraction, solvent recovery, and transesterification), and ii) a direct transesterification. Hexane, ethanol, methanol, and water were the studied solvents. The highest FAME yield (10.88%, dry SCG basis) was found for ethanol extraction, with direct transesterification also leading to significant production (9.28 %, dry SCG basis). Lignin and oligosaccharides production using a mild alkaline (NaOH) pre-treatment, was studied both for SCG and ethanol extracted SCG, for reaction time (60-240 min), temperature (25-75 ˚C) and the NaOH concentration (0-2.5 M). The severity factor suitably describes the global process kinetics, with higher severities yielding higher product yields, 18.02% and 13.25%, dry SCG basis, for lignin and oligosaccharides (XGMOS), respectively. All variables are statistically significant for solid yield and negatively impact it, XGMOS yield is (positively) influenced both by time and catalyst concentration, and lignin yield is only influenced by catalyst concentration. Optimal balance between product formation and potential operational costs was putatively identified when using 0.625 M NaOH, at 50 ˚C for 60 min, with both SGC samples presenting comparable performance. Biogas production was assayed using anaerobic digestion either in mono- or in co-digestion (using SCG samples/pig slurry 1/3, VS basis). All samples tested in both trials presented similar timedependent gas production profiles, but co-digestions led to almost double the specific biomethane production when compared to mono-digestion, with the highest specific biogas production being achieved from ethanol and NaOH extracted SCG (835.5 mL/ g VS). The proposed valorization route enabled the sequential production of 7.77 kg biodiesel, 5.34 kg lignin, 5.44 kg oligosaccharides and 137.08 kg biomethane per 100 kg of SCG (and 314.93 kg pig slurry), in an integrated process that is technically feasible, energy efficient, scalable, and promotes the circular bioeconomy.
This work proposes a cascade valorization route of spent coffee grounds (SCG), a widespread lignocellulosic residue, into biofuels and value-added products. Biodiesel production was assayed based on two strategies: i) the classical three-step process (extraction, solvent recovery, and transesterification), and ii) a direct transesterification. Hexane, ethanol, methanol, and water were the studied solvents. The highest FAME yield (10.88%, dry SCG basis) was found for ethanol extraction, with direct transesterification also leading to significant production (9.28 %, dry SCG basis). Lignin and oligosaccharides production using a mild alkaline (NaOH) pre-treatment, was studied both for SCG and ethanol extracted SCG, for reaction time (60-240 min), temperature (25-75 ˚C) and the NaOH concentration (0-2.5 M). The severity factor suitably describes the global process kinetics, with higher severities yielding higher product yields, 18.02% and 13.25%, dry SCG basis, for lignin and oligosaccharides (XGMOS), respectively. All variables are statistically significant for solid yield and negatively impact it, XGMOS yield is (positively) influenced both by time and catalyst concentration, and lignin yield is only influenced by catalyst concentration. Optimal balance between product formation and potential operational costs was putatively identified when using 0.625 M NaOH, at 50 ˚C for 60 min, with both SGC samples presenting comparable performance. Biogas production was assayed using anaerobic digestion either in mono- or in co-digestion (using SCG samples/pig slurry 1/3, VS basis). All samples tested in both trials presented similar timedependent gas production profiles, but co-digestions led to almost double the specific biomethane production when compared to mono-digestion, with the highest specific biogas production being achieved from ethanol and NaOH extracted SCG (835.5 mL/ g VS). The proposed valorization route enabled the sequential production of 7.77 kg biodiesel, 5.34 kg lignin, 5.44 kg oligosaccharides and 137.08 kg biomethane per 100 kg of SCG (and 314.93 kg pig slurry), in an integrated process that is technically feasible, energy efficient, scalable, and promotes the circular bioeconomy.
Descrição
Mestrado em Engenharia do Ambiente. Universidade de Lisboa, Instituto Superior de Agronomia
Palavras-chave
biodiesel bioeconomia circular biogás oligossacáridos produtos derivados de lenhin circular bioeconomy lignin-derived products oligosaccharides
Contexto Educativo
Citação
Ribeiro, G.M.R.M.Cascade valorization of spent coffee grounds for the production of value-added products and energy: Evaluation of selective fractionation processes. Lisboa: ISA-Universidade de Lisboa, 2023. Dissertação de Mestrado
Editora
Instituto Superior de Agronomia, Universidade de Lisboa