GROTTOLA, CORINNA MARIA (2017) Yields and properties of char produced by slow pyrolysis of lignocellulosic biomasses. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Lingua: English
Title: Yields and properties of char produced by slow pyrolysis of lignocellulosic biomasses
Date: 11 December 2017
Number of Pages: 101
Institution: Università degli Studi di Napoli Federico II
Department: dep08
Dottorato: phd038
Ciclo di dottorato: 30
Coordinatore del Corso di dottorato:
Cavaliere, AntonioUNSPECIFIED
Date: 11 December 2017
Number of Pages: 101
Uncontrolled Keywords: pyrolysis; char; phytoremediation; heavy metals.
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/25 - Impianti chimici
Date Deposited: 06 Jan 2018 03:19
Last Modified: 19 Mar 2019 11:58


Restoration of soils contaminated by potentially toxic elements (PTEs) can be carried out through phytoremediation technique. Biomasses to be used in the phytoremediation process are generally selected to match agronomic parameters and heavy metals uptake ability. The environmental sustainability of the phytoremediation could be supported in combination with further process useful for the disposal of the contaminated biomasses. The safe disposal of contaminated biomasses in landfills remains an unresolved problem. To implement phytoremediation properly, a plan for the disposal or valorization of the contaminated plant material after harvesting is required. Pyrolysis can represent an environmentally sustainable strategy capable to reduce the volume and weight of contaminated matter with respect to the original biomass; concentrate the potentially toxic elements (PTEs) in the solid product and produce a vapour phase heavy metal free energy carrier. The stability of PTEs and the physico-chemical properties of the produced chars are relevant to assess if the contaminated char could be converted into a valuable resource. Such issues are currently largely unexplored in literature. Mainly the char characteristics depend on the feedstock composition and pyrolysis conditions, a proper selection, of the biomasses suitability for the phytoremediation, could be greatly effective if the knowledge of the possible properties of the residual char from pyrolysis is available to identify possible valorization routes. In this Ph.D. thesis, a comparative analysis of the yields and phisco-chemical characteristics of char obtained from slow pyrolysis (at constant heating rate, HRsp = 4 K/min, and pressure, P = 5*105 Pa) of five uncontaminated biomasses (Populus nigra, Salix alba, Fraxinus oxyphylla, Eucalyptus occidentalis and Arundo donax) is carried out under steam atmosphere to better develop char porosity. Moreover, the dependence of the properties of solid residue on the process final temperature is studied for E. occidentalis in the temperature range of 688–967 K. The results demonstrate that, among the studied biomasses, chars from P. nigra and E. occidentalis have to be preferred for applications regulated by surface phenomena given their highest surface area (270–300 m2/g), whereas char from E. occidentalis is the best choice when the goal is to maximize energy recovery. On the basis of the experimental results from the two sets of pyrolysis tests, Eucalyptus occidentalis, Populus nigra and Arundo donax are selected for phytoremediation test. Arundo donax is included within the phytoremediation test, due to its spontaneous growth in contaminated soils and easily harvesting. The results of the feedstock characterization have shown that no heavy metals content is accumulated in Eucalyptus occidentalis, whereas Pb, Cd, Zn, Cu are stabilized in different plant parts of Populus nigra and Arundo donax. The effect of the variable feedstock (branches and leaves for Populus nigra; rhizomes and culms for Arundo donax).and of the temperature, in the range 613-873 K, are studied for the investigation of the fate of Pb, Cd, Cu and Zn during pyrolysis. The results obtained in this work of thesis show that when a slow pyrolysis process in has to be used for the treatment of the heavy metals contaminated biomasses the type of pollutants should be assessed. In presence of Cd it is necessary to operate at low temperature conditions (less than 553 K) to avoid the release of Cd into the combustible gaseous phase. However, under these conditions, the char characteristics do not allow to use it in processes that involve solid-fluid interface phenomena (e. g. adsorbing material, catalysis, synthesis of composite materials). The pyrolytic treatment represents only a safe biomass disposal process that combines the reduction of the volume of contaminated solid, with an increase in its recalcitranza, and a reduction of the mobility of heavy metal, that remain confined in the char in a more stable form. If the biomasses are only contaminated with one or more metals between Pb, Cu and Zn, it is possible to conduct a pyrolytic treatment at higher temperatures, thus obtaining a solid residue of interest in all applications that require a high specific surface, with retained metals present in more stable form hardly and bioavailable, except for specific cases as was the case of Arundo rhizomes. �

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