Characterization of Char from the Pyrolysis of Tobacco

Abstract

Pyrolysis of tobacco was studied in oxidative and nonoxidative (inert) environments at atmospheric pressure and temperatures ranging from 150 to 750 degrees C. The objective was to study the effect of pyrolysis conditions on the characteristics of the solid residue, i.e., char. The char was characterized using cross-polarization (13)C nuclear magnetic resonance (CPMAS NMR), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), the Brunauer-Emmett-Teller (BET) surface area, and the elemental composition. The char yield from pyrolysis (i.e., nonoxidative) decreased sharply with an increase in temperature to ca. 22% (dry, ash-free basis) at high temperatures. In oxidative pyrolysis, i.e., in 5% oxygen, the char was completely oxidized above 600 degrees C. The gaseous product from pyrolysis at high temperatures contained a significant concentration of hydrogen. The surface area of the char was low, with a maximum of 8 m(2)/g at 400 degrees C. SEM analysis indicated that pyrolysis of the tobacco led to a gradual accumulation of inorganic crystals on the exposed surfaces, and some constituents also melted, resulting in the formation of vesicles by evolving gas. NMR analysis showed significant changes in pectin and sugar constituents of the tobacco and breaking of glycosidic bonds of cellulose at 300-500 degrees C before the char became predominantly aromatic at high temperatures. FTIR results showed a continuous decrease in the intensity of the OH stretch with temperature and the aromatic character to be at maximum at 550-650 degrees C. The H/C ratio of the char decreased continuously with temperature, while the O/C ratio became constant above 300 degrees C due to the presence of oxides and carbonates in the char. The results are consistent with the analysis of the evolved gases.

Characterization and application of chars produced from pinewood pyrolysis and hydrothermal treatment

“…The BET surface areas were 21 m 2 /g for H300 and 29 m 2 /g for P700, respectively (Table 3). It has been reported that char surface area greatly depended on treatment temperature during biomass pyrolysis [19]. Thus the relatively low surface area of P700 accorded with previous reports that high temperature was unfavorable for the porous structure of the char [7,8,21].…”

“…SEM photographs of raw pinewood, H300 and P700. and the pores might be partially blocked as a result of the softening and melting of the pinewood constituents, which could lead to a low surface area [24].…”

“…Some papers have been published about the characterization of chars from different biomass pyrolysis [4,5]. The chars from tobacco and pectin were studied and it was found that the physical and chemical characteristics of the chars were more dependent on treatment conditions than on nature of the substrates [6,7]. Chars obtained from pyrolysis of two hardwoods were characterized and the results showed that morphological features were strongly influenced by the operating conditions, especially temperature [8].…”

“…To our best knowledge, there is no information related to the characterization and utilization of char produced from biomass hydrothermal conversion and, only limited reports on the application of chars from high-temperature pyrolysis [16][17][18][19]. In this study, pinewood was selected as a representative of waste biomass and two types of chars from pinewood thermochemical conversion processes were characterized and applied as adsorbents for copper removal from aqueous solution.…”

Comparison of high temperature chars of wheat straw and rice husk with respect to chemistry, morphology and reactivity

“…Lanning [12] concluded that silicon occurs in rice husk in a hydrated amorphous form (opal or silica gel), located mainly in the outer epidermis and filling the inner channels in the spiral structure of the epidermal cells. In addition, Liu et al [13] and Sharma et al [14] proposed that the silica in the rice husk is combined with carbohydrates. This hypothesis was examined and verified by 29 Si NMR by Freitas et al [9].…”