Abstract
The zero-waste city challenge of the modern society is inevitably addressed to the development of model’s waste-to-energy. In this work, carob waste, largely used in the agro-industrial sector for sugar extraction or locust beangum (LBG) production, is considered as feedstock for the slow pyrolysis process. According to the Food and Agriculture Organization of the United Nations (FAO), in 2012, the world production of carobs was ca. 160,000 tons, mainly concentrated in the Mediterranean area (Spain, Italy, Morocco, Portugal, and Greece). To evaluate the biomass composition, at first, the carob waste was subjected to thermo-gravimetric analysis. The high content of fixed carbon suggests that carobs are a plausible candidate for pyrolysis conversion to biochar particles. The thermal degradation of the carob waste proceeds by four different steps related to the water and volatile substances’ removal, degradation of hemicellulose, lignin and cellulose degradation, and lignin decomposition. Considering this, the slow pyrolysis was carried out at three different temperatures, specifically, at 280, 340, and 400 °C, and the obtained products were characterized. Varying the processing temperature, the proportion of individual products’ changes with a reduction in the solid phase and an increase in liquid and gas phases, with an increase in the pyrolysis temperature. The obtained results suggest that carob waste can be considered a suitable feedstock for biochar production, rather than for fuels’ recovery.
Highlights
In recent years, an increasing number of studies have been focused on the conversion of waste, biomass, and various residues into energy, fuels, and other useful materials that should otherwise be disposed of, with the aim of achieving a circular economy and, above all, a zero-waste society
The high value of fixed carbon suggests that the carob waste can be considered suitable feedstock for biochar particles’ production
After sugar extraction, was subjected to slow pyrolysis, and the collected gas, liquid, and solid phases were characterized in order to optimize the process conditions and to maximize the products’ yields
Summary
An increasing number of studies have been focused on the conversion of waste, biomass, and various residues into energy, fuels, and other useful materials that should otherwise be disposed of, with the aim of achieving a circular economy and, above all, a zero-waste society. One of the ways to valorise waste, obtaining energy, in terms of fuel and gas, is the pyrolysis process. Fast pyrolysis is the most efficient method to produce biofuel, whereas gasification is the most efficient method to produce syngas, and is used to generate energy and heat [4]; instead, slow pyrolysis tends to yield higher proportions of biochar owing to the slow heating rates and longer residence time [5,6,7]. There are many studies on the possibility to obtain biofuels via biomass slow pyrolysis [6,7,9,10,11]. Lehmann studied the implications for greenhouse gas (GHG) emissions of a slow pyrolysis-based bioenergy system for biochar and energy production [8]
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