Characterization of Biochar Properties Affected by Different Pyrolysis Temperatures Using Visible-Near-Infrared Spectroscopy

Abstract

Rapid characterization of biochar for energy and ecological purpose utilization is fundamental. In this work, visible and nearinfrared (vis-NIR) spectroscopy was used to measure ash, volatile matter, fixed carbon contents, and calorific value of three types of biochar produced from pine wood, cedar wood, and cotton stalk, respectively. The vis-NIR spectroscopy was also used to discriminate biochar feedstock types and pyrolysis temperature. Prediction result shows that partial least squares (PLS) regression calibrating the spectra to the values of biochar properties achieved very good or excellent performance with coefficient of determination (R 2 ) of 0.86∼0.91 and residual prediction deviation (RPD) of 2.58∼3.32 for ash, volatile matter, and fixed carbon, and good prediction with R 2 of 0.81 and RPD of 2.30 for calorific value. Linear discrimination analysis (LDA) of the principal components (PCs) produced from PCA of wavelength matrix shows that three types of biochar can be successfully discriminated with 95.2% accuracy. The classification of biochar with different pyrolysis temperatures can be conducted with 69% accuracy for all three types and 100% accuracy for single type of cotton stalk. This experiment suggests that the vis-NIR spectroscopy is promising as an alternative of traditionally quantitative and qualitative analysis of biochar properties.

Effect of Pyrolysis Temperature and Residence Time on Bio-char Obtained from Pyrolysis of Shredded Cotton Stalk

“…The results of the proximate analysis, pH, EC, CEC, higher heating value (HHV) and bulk density of shredded cotton stalk and its bio-chars produced at different pyrolysis temperatures and residence time are given in Table 2. The volatile matter content of bio-chars was ranged from a minimum of 48.02% (d.b) at 500°C with 240 min residence time to a maximum of 79.48% (d.b) at 200°C with 60 min residence time.Similar results were also found by [13]. They reported that volatile matter of cedar wood, pine wood and cotton stalk bio-char decreased from 37.5 to 18.4%, 37.3 to 17.2% and 32.2 to 15.6% respectively as the temperature increased from 300 to 600°C.…”

“…Thus, the ash contents of the bio-chars were higher than those of cotton stalk, orange peels, and palm waste bio-chars [16,17,18]. Also similar results were also found by [13]. They reported that ash content of cedar wood, pine wood and cotton stalk bio-char increased from 1.5 to 2.1%, 2.5 to 4.7% and 6.0 to 10.1% respectively as the temperature increased from 300 to 600°C.…”

“…The value of fixed carbon of bio-char was ranged from a minimum of 15.02% (d.b) at 200°C with 60 min residence time to a maximum of 36.40% (d.b) at 500°C with 240 min residence time in this study. In similar studies with increasing temperature, fixed carbon content for rapeseed cake and palm stones was increased from 57.08% to 73.05%, 52.44% to84.19% and 31.0% to 85.10%, respectively [20,16,21].Similar results were also found by [13]. They reported that fixed carbon of cedar wood, pine wood and cotton stalk bio-char increased from 61.1 to 79.5%, 60.2 to 78.1% and 61.8 to 74.2% respectively as the temperature increased from 300 to 600°C [22].…”

Impact of Biochar on Organic Contaminants in Soil: A Tool for Mitigating Risk?

“…This finding was similar to that of dioxin and furan-contaminated soils where biochar markedly decreased the passive uptake of the toxic contaminants into POM samplers with increase in contact-time and concentration [119]. The increasing heat treatment on biochar feedstock reduces volatile matter, enhances the carbonisation, aromatic structure formation and surface area of the resultant biochar that is highly microporous [92,116,120]. Noticeably, biochar contains both carbonised (glassy) and non-carbonised (rubbery) fractions, where the former is categorised with non-linear competitive adsorption of organic contaminants and the latter is associated with linear non-competitive partitioning of organic contaminants [115,116,121].…”

Recent developments in biochar as an effective tool for agricultural soil management: a review

“…Sugar beet wastes, empty fruit bunches and rubber wood etc. have also been suggested as good feedstock for biochar production …”