Abstract
Abstract Based on a systematic review, 19 case studies were selected, focusing on the production of biochar through pyrolysis of five lignocellulosic biomasses (olive husk, beech wood, corncob, spruce wood, and hazelnut shell), under constant pressure (0.1 MPa) and temperature from 650.2 to 973.0 K. Interactions between process variables (temperature, residence time of the vapor phase and heating rate), biomass chemical composition variables (lignin, holocellulose, ash, carbon, nitrogen, oxygen and hydrogen content) and biochar yield-CY were evaluated by Pearson’s correlation matrix and Principal Component Analysis-PCA. Strong correlations (|r| ≥0.75, p<0.05) were found for lignin and CY (0.78); carbon and CY (0.76); nitrogen and CY (0.77). Three variables of biomass chemical composition were the most important ones for the first principal component-PC1; process variables (heating rate and the vapour residence time) were the most important ones for the second principal component-PC2. Experiments with hazelnut shell as feedstock were associated with higher CY.
Highlights
AND OBJECTIVESThermochemical char is a stable carbon-rich by-product (65% to 95% carbon) (Debiagi et al, 2018) resulting from thermochemical degradation of plant or animal biomass (Ahmad et al, 2014) under O2-free or limited quantities of O2 (Pandey et al, 2020).Traditionally, the production of char – known as “charcoal” occurs through direct burning of woody biomass and reactional atmosphere in contact with oxygen used for thousands of years (Weber & Quicker, 2018) in systems such as “earth-mound kiln” (Adam, 2009)
When the biochar yield (CY) is correlated to the first and to the second principal components (PC1 vs CY and PC2 vs CY respectively) the results revealed that PC1 has a strong positive correlation with CY (r = 0.8282), but PC2 has not (r = -0.3121)
The investigation focused on biochar yield (CY) as the main product of interest after pyrolysis has been applied to five types of biomasses with similar energy content selected as feedstocks
Summary
AND OBJECTIVESThermochemical char is a stable carbon-rich by-product (65% to 95% carbon) (Debiagi et al, 2018) resulting from thermochemical degradation of plant or animal biomass (Ahmad et al, 2014) under O2-free or limited quantities of O2 (Pandey et al, 2020).Traditionally, the production of char – known as “charcoal” occurs through direct burning of woody biomass and reactional atmosphere in contact with oxygen used for thousands of years (Weber & Quicker, 2018) in systems such as “earth-mound kiln” (Adam, 2009). Thermochemical char is a stable carbon-rich by-product (65% to 95% carbon) (Debiagi et al, 2018) resulting from thermochemical degradation of plant or animal biomass (Ahmad et al, 2014) under O2-free or limited quantities of O2 (Pandey et al, 2020). Most charcoal production still occurs in traditional (rudimentary) kilns, resulting in inefficient carbonization, CO2, and nonCO2greenhouse gases (VOCs) release and economic losses (Pereira et al, 2017). To overcome these issues, modern technologies and lifecycle assessment are helping to improve efficiency, to reduce VOC generation (Azzi et al, 2019). The natural polymeric constituents (i.e. lignin, hemicellulose, cellulose, fats and starches) are thermally broken down into three different fractions: tars, bio-oil (condensed vapours), char (solid fraction) and non-condensable gases (Mohan et al, 2006; Ciubota-Rosie et al, 2008).
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