Valorisation of by-Products/Waste of Agro-Food Industry by the Pyrolysis Process

Abstract

Waste valorization practices have attracted a great deal of attention in recent years with the aim of managing waste in the most sustainable way. Agro-food industry waste of the Piedmont Region such as coffee powder, cocoa husks, pellets of parchment coffee, rice husk and hazelnut shell, has been pyrolysed via a lab-scale reactor system. This work studies the yields and properties of pyrolysis products (bio-oil, gas and char) produced from the different feedstocks under two heating rates, 360 and 750 °C/h with the maximum temperature of 750 and 800 °C, respectively. The results show that the bio-oil yield increased when increasing heating rates and temperatures while the char yield decreased.

The main gas products were CO₂ (28-43%), H₂ (19-26%), CO (13-26%) and CH₄ (12-18%). The high heating value (HHV) of the products ranged between 13-17, 27-35 and 18-31 MJ/kg for gas, bio-oil and char, respectively. The HHV of the tar was relatively higher than that of diesel fuel, which is approximately 42 MJ / Kg. The chemical energy yield varied from 72% to 86%, with the highest value for the hazelnut shell. The solid residue was mainly composed of carbon (81-98,6%). The solid rice husk residue presented a particularly high quantity of silica (14,4%).

This study also aimed to investigate the feasibility of applying high-carbon bio-char particles additive to concrete to improve the sustainability of the pyrolysis process to valorize the solid output. As a result, this research developed a cement admixture using nano/micro carbonized bio-char particles from pyrolyzed coffee powder waste to enhance its mechanical strength and toughness without losing its ductility. The flexural test results showed that the strength and ductility increased by adding a percentage equal to 0.08 wt% of Carbon-Coffee particles into the matrix. In fact, the FMAX grows from 130 N to about 180 N and, at the same time, the fracture energy increases by 40%.