Radicals from the Pyrolysis of Tobacco

Abstract

The fractional pyrolysis of Bright tobacco was studied in an inert nitrogen environment at atmospheric pressure over a temperature range of 200-700 °C, using a continuous-flow reactor system. The effect of pyrolysis conditions on the generation of free radicals and their distribution among total particulate matter (TPM), char residue, and the gas phase was characterized using electron paramagnetic resonance (EPR) and EPR spin-trapping techniques. It was found that the fractional pyrolysis of tobacco led to the generation of free radicals with g-factors of 2.0035-2.0040. They were formed during pyrolysis at temperatures of >380 °C and were present in both char and TPM. The concentration of these radicals in TPM varied from 0 spins/g at 240 °C to 11 × 10 16 spins/g of TPM at 620 °C. The concentration of these radicals in the char residue increased as the pyrolysis temperature increased; a maximum concentration of 1.2 × 10 19 spins/g of char at 480 °C was obtained, and then the value declined. The g-values of 2.0035-2.0040 are consistent with (i) surface-associated, carbon-centered radicals, where the unpaired electron is vicinal to an oxygen-containing functional group, or (ii) partially delocalized, polymeric, phenoxyl-type radicals. The analysis of the gas phase of tobacco smoke revealed the formation of alkoxyl radicals. The N-tert-butyl-R-phenylnitrone (PBN) adduct of the alkoxyl radicals is characterized by hyperfine coupling constants of a N ) 13.9 G and a H ) 2.0 G and a g-factor of 2.0064. The concentration of these radicals in the gas phase was insignificant ((5 ( 1) × 10 14 spins/g of tobacco) and was not dependent on the pyrolysis temperature. After exposure to air, the concentration of TPM radicals increased, because of the production of "new" radicals, in addition to the "old" radicals, with the increasing time of storage, reaching a maximum value and then declining. The g-factor of these new radicals is 2.0053 ( 0.0003, and their TPM concentration achieved a maximum for a pyrolysis temperature of 280 °C. At this temperature, the concentration of these new radicals is 8.1 × 10 15 spins/g of tobacco, which is 25 times greater than the concentration of radicals measured immediately after collection. The EPR spectra of the new radicals are consistent with oxygen-centered, semiquinone-type radicals. These results suggest that hydroquinone/ catechol-type species, which are free or chemically bound to TPM and do not produce EPR signals, are converted to semiquinone-type radicals by atmospheric oxidation.

Energy production from the pyrolysis of waste biomasses

“…The gaseous products consisted largely of CO 2 in both SBOC and SFOC. This result is consistent with previous observations in that CO 2 is major gaseous product from the pyrolysis of biomass [21][22][23][24]. The amount of CO in pyrolysis gas products from SFOC was about two times higher than that of SBOC.…”

Effects of Driving Conditions on Diesel Exhaust Particulates

“…53,54 Despite different fuels, four studies examining combustion of catechol fuel, tobacco, and cellulose char pyrolysis consistently observed that concentrations of aromatic-structured, persistent free radicals peaked at a threshold temperature and then decreased with increasing combustion temperatures. [53][54][55][56] Figure 4 shows that under the full engine load, because the DEPs from the engine speed of 3000 rpm along with an exhaust temperature of 569°C (secondary x-axis) contained less persistent free radicals than that from the engine speed of 1800 rpm with an exhaust temperature of 497°C, the threshold temperature corresponding to the most abundant persistent free radicals would be lower than 569°C, resulting in the decreasing concentration of persistent free radicals with an increase in the exhaust temperature. Figure 5 shows that TPM was emitted from the individual driving conditions in a decreasing order of 3000 rpm/100% Ͼ 1800 rpm/100% Ͼ 3000 rpm/60% Ͼ 1800 rpm/60%.…”

Electron paramagnetic resonance investigation of the free radicals in the gas and particulate phases of cigarette smoke using spin-trapping techniques

“…Secondly, there is a genuine difference in gas-phase composition on a puff-by-puff basis. [20][21][22][23][24][25] Literature shows that in aged smoke the concentration of the free radicals is unexpectedly increased; this has been explained by the radical reactions associated with NO and NO 2 . 10,18 More work is needed to address the contributions of these factors.…”