Abstract
The combined production of the most abundant agricultural residues in Spain (viz. cereal straw, sunflower stalks, vine shoots, cotton stalks, olive, orange and peach tree prunings, and horticultural and related residues) amounts to over 50 million tons per year, more than 20% of which is generated by Andalusia alone. Agricultural residues must be disposed of for various reasons including the facts that they promote contamination and pest growth, occupy large expanses of land and hinder agricultural work. Ideally, the disposal method used should allow their major components (cellulose, hemicellulose and lignin) or their chemical potential energy to be exploited. Agricultural residues can be valorized by converting their components jointly (combustion, pyrolysis, gasification, liquefaction) or separately (fractionation). The most useful method for exploiting such components separately involves isolating cellulose fibres for papermaking purposes. In recent times, this valorization method has led to the development of the biorefining concept. Biorefining involves the fractionation or separation of the different lignocellulosic components of agricultural residues with a view to their integral exploitation rather than the mere use of cellulose fibre to obtain paper products. Biorefining replaces the classical pulping methods based on Kraft, sulphite and soda reagents with a hydrothermal treatment followed by organosolv pulping. The hydrothermal treatment provides a liquid phase containing hemicellulose decomposition products [both oligomers and monomers (glucose, xylose, arabinose)] and a solid phase rich in cellulose and lignin. By contrast, the organosolv process gives a solid fraction (pulp) and a residual liquid fraction containing lignin and other useful substances for various purposes.
Highlights
Agricultural residues are highly abundant in Spain
The annual production of the major residues in the country is estimated to exceed 50 million tons of which more than 20% is generated in Andalusia [1]
(c) Hydrothermal treatment, which provides a liquid fraction rich in hemicellulose degradation products mainly and a solid fraction essentially consisting of -cellulose and lignin
Summary
Agricultural residues are highly abundant in Spain ( in the Andalusian region). The annual production of the major residues in the country Cereal straw, sunflower stalks, vine shoots, cotton stalks, olive, orange and peach tree prunings, and horticultural and related residues) is estimated to exceed 50 million tons of which more than 20% is generated in Andalusia [1]. Agricultural residues consist mainly of cellulose and lignin, which jointly account for 85–90% of their dry matter content; the remaining 15–10% includes fat, wax, ash, simple sugars, starch, essential oils, pectins, gums and tannins, among other substances [2]. The body of cellulose materials present in these residues is known as “holocellulose” and includes three fractions (-cellulose, -cellulose and cellulose, the combination of the latter two being referred to as “hemicellulose”)
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