Optimization of Chemical Pretreatments Using Response Surface Methodology for Second-Generation Ethanol Production from
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Optimization of Chemical Pretreatments Using Response Surface Methodology for Second-Generation Ethanol Production from Coffee Husk Waste J. L. Morales-Martínez 1 & M. G. Aguilar-Uscanga 2 & E. Bolaños-Reynoso 1 & L. López-Zamora 1 Received: 23 June 2020 / Accepted: 23 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Within the strategies of substitution of energy from fossil fuels by renewable energies, the research is based on second-generation ethanol production (2G ethanol). One of the raw materials considered for this is residual biomass of the coffee industry, being the subject of study here. The cellulose contained in the coffee husk (coffee husk or coffee skin or coffee exocarp or pericarp) was maximized using pretreatment processes. In dilute acid hydrolysis (DAH), using a fixed 1:6 w:v solid to liquid ratio (SLR), process times (35, 45, 55 min) and H2SO4 concentrations (3, 4, 5% v/v) were evaluated, achieving 53.63% hemicellulose removal. A delignification process resulted in 58.82% lignin removal, evaluating the effect of process times (30, 35, 40 h) and SLR (1:8, 1:10, 1:12 w:v) at a fixed concentration of 8% v/v H2O2. A 115.59 g/L glucose concentration was obtained with an interaction of fixed concentrations of 4–6% w/w Cellic CTec3 enzyme and 6:1 to 1:12 v:w SLR. The fermentation process considered the composition variation of the culture medium (enriched culture C1 and non-enriched culture C2), generating ethanol at 48.19 and 29.02 g/L concentrations, respectively. Fermentation efficiency (ηf) was improved from 21.99 to 81.74% with the addition of inorganic nutrients (KH2PO4, (NH4)2SO4, and MgSO4·7H2O). These results confirmed that the optimization of the pretreatments in coffee husk waste favored the cellulose production and facilitated the enzymatic process to produce a high glucose concentration, revealing these residues as a carbon source promising for second-generation ethanol production. Keywords Response surface methodology . Glucose . Enzymatic hydrolysis . Renewable source . Cellulose
Introduction In the early 1970s, rising oil prices initiated an energy crisis which together with global warming and the depletion of oil reserves [1–3] aroused great interest in the study of renewable resources in order to produce alternative energy, allowing decarbonization in the environment and reducing the emissions of greenhouse gases by ~ 43% [1, 4, 5]. Different resources used to produce alternative energy have been studied. Currently, the world produces a large amount of waste daily (municipal, food, beverages, agricultural, and industrial) due
* L. López-Zamora [email protected] 1
Graduate Studies and Research Division, National Institute of Technology of Mexico/Orizaba Institute of Technology, Oriente 9 852, 94320 Orizaba, Veracruz, Mexico
2
Food Research and Development Unit, National Institute of Technology of Mexico/Veracruz Institute of Technology, Calz. M.A. de Quevedo 2779, 91860 Veracruz, Mexico
to the increase in population and new con
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