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Digital archive of theses discussed at the University of Pisa


Thesis etd-01092015-181947

Thesis type
Tesi di dottorato di ricerca
Thesis title
Complete catalytic exploitation of lignocellulosic biomass to give fine chemicals and biofuels
Academic discipline
Course of study
tutor Prof. Raspolli Galletti, Anna Maria
correlatore Salvini, Antonella
  • catalisi omogenea
  • conversione biomasse
  • idrolisi
Graduation session start date
Release date
This PhD work is focused on the complete catalytic exploitation of lignocellulosic biomass to give fine chemicals and biofuels. Among the biomass conversion routes, the hydrothermal one will be chosen for the depolymerization/conversion of the three major components of lignocellulosic biomass: cellulose, hemicellulose and lignin. The exploitation of non-food lignocellulosic crops, e.g. second generation feedstocks, such as giant reed (Arundo Donax L.), miscanthus (Miscanthus x Giganteus), and sorghum (Sorghum Bicolor L.), is extremely advantageous, thanks to their high content of macroconstituents (cellulose, hemicellulose and lignin), low-cost of production and abundance in the Italian territory. According to the hydrothermal route, the acid-catalyzed hydrolysis of hemicellulose/cellulose biomass fraction gives furfural/levulinic acid, respectively. These platform chemicals are receiving great attention, thanks to their high reactivity, low cost of production and high added-value of their derivatives. Starting from these statements, giant reed, miscanthus and sorghum will be hydrolyzed to furfural and levulinic acid and the yields will be optimized, by using dilute hydrochloric acid as homogeneous catalyst and water as green solvent. At first, the hydrolysis reaction will be studied in a microwave reactor, optimizing the main reaction parameters, that is concentration of hydrochloric acid, solid/liquid ratio of the starting reaction mixture, hydrolysis temperature and time. This innovative approach allows, with respect to the traditional heating, significant time and energy savings, thus dramatically reducing the time required the reaction screening/optimization. Subsequently, the hydrothermal conversion to furfural and levulinic acid will be further optimized, starting from characteristic real agronomic parameters, such as harvest time, dry matter yield and cost of biomass production. Our process applies the “biorefinery concept”, according to which it is necessary to exploit all biomass macrocomponents, e.g. hemicellulose, cellulose and lignin. However, lignin fraction is recovered as solid residue at the end of the two hydrolysis steps, and it is very degraded. The use of this hydrolysis residue for the synthesis of polyurethane foams for packaging uses, will be discussed, thus demonstrating that this degraded lignin can still partly substitute polyether polyol of traditional petrolchemical source. As above stated, the used lignin coming from the hydrothermal giant reed conversion, is very degraded respect to the technical ones, and has a carbonaceous behaviour, being an “hydrochar”, and, as such, it can be better exploited as soil amendment, as porous material for biological and chemical uses, or for energy production. This last exploitation possibility is evaluated. About this line of research, at the adopted process temperatures, hemicellulose/cellulose have been converted into furfural and levulinic acid, but also partly degraded to humins, which are the main by-products of the hydrothermal process. Humins are polyaromatic compounds of furan source and, therefore, from a thermal/energetic point of view, it is more useful to investigate the behavior of these bio-wastes, rather than that of technical lignins. Therefore, giant reed hydrolysis residue will be further characterized and compared with xylose- and glucose-derived humins, and the similarity (from the point of view of the energy content) among these charred bio-wastes will be
demonstrated, thus further closing the biorefinery circuit of the giant reed biomass. After the exploitation of the most abundant components of the giant reed biomass, a preliminary investigation about the extractives composition of giant reed biomass will be considered. Despite these compounds are not abundant, they can be advantageously exploited as effective natural antioxidants of for nutraceutical purposes, thanks to the contribute of healty compounds, such as phenols and fatty acids. Following this line of research, some phenols can be isolated by solvent extraction from the giant reed hydrolysis residue. Lastly, efficient antioxidants can be recovered from olive mill waste water (OMWW), which contain high amounts of free bio-phenols, in particular hydroxytyrosol, tyrosol and oleuropein. A preliminary investigation about the recovery of these bio-phenols by solvent extraction will be reported. By this way, the exploitation of less abundant fractions can become very affordable, thanks to the high economic value and the healthy properties of the recovered bio-products, which can be immediately used, without any upgrading step, which is instead necessary in the case of the considered sugar-derived platform chemicals, e.g. furfural and levulinic acid.