Abstract
Olive tree leaves, an abundant agricultural by-product without enough industrial market outlets, are presented in this study as a relevant resource of available carbohydrates to be chemically treated for monomeric sugar production. Characterization of two main granulometric fractions is the starting point for testing the specific effect and the relevance of three main factors (time, temperature, and sulfuric acid concentration) on diluted acid hydrolysis with respect to oligosaccharides, simple sugars, and fermentation inhibitory compounds production. The selected conditions (100 ∘ C, 90 min, and 6% w/w H 2 SO 4 ) to perform the small scale hydrolytic process, considering response surface methodology (2 3 factorial design with center points), implied production of acetic acid and hydroxymethylfurfural in concentrations not exceeding 1.10 kg m − 3 and 0.25 kg m − 3 , respectively. Thus, these experimental conditions were the reference framework to evaluate the effect of a meaningful scaling stage in a hydrolysis reactor, considering kinetic parameters based on hydrolysis rates and d-glucose and d-xylose generation.
Highlights
Olive tree (Olea europaea L.) is one of the most important fruit trees of a vast number of Mediterranean countries, such as Spain and Italy, and the recurring disposal of biomass from the required pruning operation [1] is becoming a serious environmental problem to be solved
The results obtained for olive tree leaves characterization in this investigation do not differ much with the ones reported by Sánchez et al [19] and Alburquerque et al [20], and even less so when taking into account the heterogeneity of the product, as the determinations depend on the starting biomass in terms of type of olive grove, geo-environmental conditions, and so on
On the other hand, according to a previous research [3], the main difference, regarding extractives content between olive tree pruning biomass and this same type of residue, but free of leaves, was much higher for the first type of residue. This is in accordance with the high content of these non-structural components noted in this study according to olive tree leaves (OTL) characterization results
Summary
Olive tree (Olea europaea L.) is one of the most important fruit trees of a vast number of Mediterranean countries, such as Spain and Italy, and the recurring disposal of biomass from the required pruning operation [1] is becoming a serious environmental problem to be solved. OTL global production is between 7.5 × and 1.5× tons [7], so its recovery and use is of considerable interest according to a residue management policy based on a circular economy perspective, to contribute to both soil protection and air pollution prevention, as an alternative to the traditional disposal of this waste material in the field and its usual uncontrolled combustion. In this context, OTL are considered as a lignocellulosic biomass that provides a good raw material of bioactives compounds, and a potential source of biopolymers. Constituents belonging to the first group can be removed by washing with water or organic solvents: extracts, with a fundamentally organic nature, such as aliphatic and aromatic hydrocarbons; alcohols; phenols (especially oleuropein, hydroxytyrosol, and flavonoids as major compounds [1,8]); aldehydes; ketones; Processes 2020, 8, 886; doi:10.3390/pr8080886 www.mdpi.com/journal/processes
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