The Heat Treatment Severity Index: A new metric correlated to the properties of biochars obtained from entrained flow pyrolysis of biomass

Abstract

The properties of biochars produced in biomass pyrolysis processes highly depend on the pyrolysis conditions, specifically the pyrolysis temperature and thermal treatment duration. The higher the temperature and the duration, the more severe is the heat treatment. The present work proposes a new Heat Treatment Severity Index (HTSI) for the quantification of the heat treatment severity during the pyrolysis reaction. This metric takes into account both effects of reactor temperature and heat treatment time inside the reactor. The relevance of this HTSI is assessed through analyzing the evolution of some properties of biochars obtained after pyrolysis of 370 µm beech wood particles in an entrained flow reactor. These biochars were characterized for their chemical composition (elemental analysis), structure (Raman spectroscopy) and reactivity towards oxygen (thermogravimetric analysis). These properties were well correlated with the HTSI following remarkable mathematical relationships. This finding demonstrates the possibility to engineer biochars with controlled properties by a careful mastering of the experimental conditions of the pyrolysis process in terms of temperature and heat treatment time.

Aromaticity, polarity, and longevity of biochar derived from disposable bamboo chopsticks waste for environmental application

“…It is worth noting that the ash content in the DBC feedstock was lower than that in bamboo, based on Hernandez-Mena et al [ 42 ] (2.57%), Wang et al [ 37 ] (2.10%), and Sahoo et al [ 36 ] (1.58%). The FC content in woody biomass varies depending on plant type; therefore, the FC of DBC was 10.24% different from that of other wooden feedstocks, such as 15.2% for beech wood [ 49 ], 35% of tree bark (Pinus pinaster), and 19% of applewood [ 45 ] .…”

“…The results showed that with increasing temperature, the DBC biochar had progressively higher C content, resulting from the removal of dissociated bonds between C and functional groups on the surface of the biomass, including –OH, aliphatic C–O, and aliphatic C–H groups [ 9 , 19 , 33 , 47 ]. The aromatization process begins at approximately 350 °C and continues at higher temperatures [ 40 , 49 ]. The aromatic C–H deformation increased until the temperature reached 500 °C [ 43 ].…”

“…However, many studies have noted that feedstock, temperature, and time are important factors that significantly affect the properties of biochar [ 36 , 46 , 47 ]. Additionally, in the case of the same feedstock type, the properties of biochar are significantly affected by the temperature [ 20 , 48 , 49 ]. However, wooden feedstocks have complex structures and compositions; as a result, the various components of the biomass break down at different temperatures, which makes the biochar properties highly diverse, even when produced from the same feedstock [ 41 , 43 , 50 ].…”

Influence of Pyrolysis Temperature and Time on Biochar Properties and Its Potential for Climate Change Mitigation

“…With the various types of feedstocks and the complexity of the production process, designing a suitable pyrolysis process to control the excellent quality of biochar is challenging [11,39]. Typically, biochar quality is strongly influenced by temperature and holding time and is determined by the C content and the atomic ratios of H/C, O/C, and (O+N)/C, representing the degree of carbonization, aromaticity, polarity, and stability of biochar, respectively [11,57].…”

“…Although many pyrolysis conditions can affect biochar properties, a meta-analysis of the literature performed by Ippolito et al [37], Wang et al [38], and Guizani et al [39] showed that temperature and holding times are considered strong factors that directly influence biochar properties, the breakdown of lignocellulosic feedstocks and chemical bonds, and the physical and chemical structure of the resultant biochar [32,40,41]. A comprehensive review of the literature on biochar shows that the properties of biomass feedstocks change with the techniques and conditions employed in the pyrolysis process [42][43][44].…”