• Energy Research
• 2021-2025close

This work provides insights into the relationship between the pyrolysis products distribution and the structural features of xylose-based hemicelluloses. Three xylose-based hemicelluloses differing in composition, molecular weight, chain branching and origin were selected, structurally characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis and nuclear magnetic resonance and then used as feedstocks for slow pyrolysis tests up to 700 °C in nitrogen environment. Commercial beechwood xylan was selected as representative of the glucuronoxylan hemicellulose type, typical of hardwood species. Commercial corncob xylan was selected as it is composed by a mixture of low molecular weight xylo-oligosaccharides with a low acetylation degree. In the end, the xylan extracted from grape pruning, being an arabinoglucuronoxylan, was chosen as representative of hemicellulose structure common to most annual plants and agricultural wastes. Low-branched material (corncob xylan) produced the lowest yield of char and the highest yield of pyrolysis liquids, while highly-branched material (grape pruning xylan) exhibited an opposite trend. The liquid composition was qualitatively similar for all the considered xylans. However, the comparison of the quantifiable species showed different relative abundances. The pyrolysis products distribution indicated that the chain branching degree affected at a higher extent the feedstock pyrolytic behavior with respect to the ash content.

This work provides insights into the relationship between the pyrolysis products distribution and the structural features of xylose-based hemicelluloses. Three xylose-based hemicelluloses differing in composition, molecular weight, chain branching and origin were selected, structurally characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis and nuclear magnetic resonance and then used as feedstocks for slow pyrolysis tests up to 700 °C in nitrogen environment. Commercial beechwood xylan was selected as representative of the glucuronoxylan hemicellulose type, typical of hardwood species. Commercial corncob xylan was selected as it is composed by a mixture of low molecular weight xylo-oligosaccharides with a low acetylation degree. In the end, the xylan extracted from grape pruning, being an arabinoglucuronoxylan, was chosen as representative of hemicellulose structure common to most annual plants and agricultural wastes. Low-branched material (corncob xylan) produced the lowest yield of char and the highest yield of pyrolysis liquids, while highly-branched material (grape pruning xylan) exhibited an opposite trend. The liquid composition was qualitatively similar for all the considered xylans. However, the comparison of the quantifiable species showed different relative abundances. The pyrolysis products distribution indicated that the chain branching degree affected at a higher extent the feedstock pyrolytic behavior with respect to the ash content.

Glycerol is the main by-product of biodiesel production; its upgrading to more valuable products is a demanding issue. Hydrogenolysis to 1,2-propanediol is one of the most interesting processes among the possible upgrading routes. In this study, we propose novel copper/zirconia catalysts prepared by advanced preparation methods, including copper deposition via metal–organic framework (MOF) and support preparation via the sol–gel route. The catalysts were characterized by N2 physisorption, X-ray diffraction, Scanning Electron Microscopy, H2-TPR and NH3-TPD analyses and tested in a commercial batch reactor. The catalyst prepared by copper deposition via MOF decomposition onto commercial zirconia showed the best catalytic performance, reaching 75% yield. The improved catalytic performance was assigned to a proper combination of redox and acid properties. In particular, a non-negligible fraction of cuprous oxide and of weak acid sites seems fundamental to preferentially activate the selective pathway. In particular, these features avoid the overhydrogenolysis of 1,2-propanediol to 1-propanol and enhance glycerol dehydration to hydroxyacetone and the successive hydrogenation of hydroxyacetone to 1,2-propanediol.

Glycerol is the main by-product of biodiesel production; its upgrading to more valuable products is a demanding issue. Hydrogenolysis to 1,2-propanediol is one of the most interesting processes among the possible upgrading routes. In this study, we propose novel copper/zirconia catalysts prepared by advanced preparation methods, including copper deposition via metal–organic framework (MOF) and support preparation via the sol–gel route. The catalysts were characterized by N2 physisorption, X-ray diffraction, Scanning Electron Microscopy, H2-TPR and NH3-TPD analyses and tested in a commercial batch reactor. The catalyst prepared by copper deposition via MOF decomposition onto commercial zirconia showed the best catalytic performance, reaching 75% yield. The improved catalytic performance was assigned to a proper combination of redox and acid properties. In particular, a non-negligible fraction of cuprous oxide and of weak acid sites seems fundamental to preferentially activate the selective pathway. In particular, these features avoid the overhydrogenolysis of 1,2-propanediol to 1-propanol and enhance glycerol dehydration to hydroxyacetone and the successive hydrogenation of hydroxyacetone to 1,2-propanediol.

Urban waste management is a hard task: more than 30% of the world’s total production of Municipal Solid Wastes (MSW) is not adequately handled, with landfilling remaining as a common practice. Another source of wastes is the road pavement industry: with a service life of about 10–15 years, asphalts become stiff, susceptible to cracks, and therefore no longer adapted for road paving, so they become wastes. To simultaneously solve these problems, a circular economy-based approach is proposed by the ReScA project, suggesting the use of pyrolysis to treat MSW (or its fractions as Refuse Derived Fuels, RDFs), whose residues (oil and char) can be used as added-value ingredients for the asphalt cycle. Char can be used to prepare better performing and durable asphalts, and oil can be used to regenerate exhaust asphalts, avoiding their landfilling. The proposed approach provides a different and more useful pathway in the end-of-waste (EoW) cycle of urban wastes. This proof of concept is suggested by the following two observations: (i) char is made up by carbonaceous particles highly compatible with the organic nature of bitumens, so its addition can reinforce the overall bitumen structure, increasing its mechanical properties and slowing down the molecular kinetics of its aging process; (ii) oil is rich in hydrocarbons, so it can enrich the poor fraction of the maltene phase in exhaust asphalts. These hypotheses have been proved by testing the residues derived from the pyrolysis of RDFs for the improvement of mechanical characteristics of a representative bitumen sample and its regeneration after aging. The proposed approach is suggested by the physico-chemical study of the materials involved, and aims to show how the chemical knowledge of complex systems, like bituminous materials, can help in solving environmental issues. We hope that this approach will be considered as a model method for the future.