San Li

Cellulose pyrolysis: the kinetics of hydroxyacetaldehyde evolution

Abstract The kinetics of formaldehyde, hydroxyacetaldehyde, CO and CO 2 evolution during the pyrolysis of cellulose, Whatman 41, were studied in a fast evolved gas-FTIR apparatus (EGA). The samples were subjected to exponential temperature increases from ambient to final temperatures ranging from 400°C to 800°C within about 1 min. The yields of formaldehyde, hydroxyacetaldehyde and CO approximately doubled with heating rate over the experimental range of heating rates while that of CO 2 decreased slightly. The kinetics for CO 2 evolution are consistent with a single first order reaction. The kinetics of formaldehyde and CO formation require a pair of competing first order reactions. The behavior of hydroxyacetaldehyde is more complex. In this case a third reaction step is required following the initial pair of competing reactions. The reactions involved in the evolution of all four gases, with the exception of the third step in the hydroxyacetaldehyde mechanism, exhibit essentially identical activation parameters. This suggests their formation involves common rate limiting steps. These are, most likely, the decomposition pathways of cellulose which are followed by rapid secondary reactions to yield the individual gases.

Gas chromatography–mass spectrometry analysis of polycyclic aromatic hydrocarbons in single puff of cigarette smoke

Abstract A single puff polycyclic aromatic hydrocarbon (PAH) analysis technique was developed in our laboratory and applied to study PAH formation in each puff during the cigarette smoking process. An impaction trap was used to collect the total particulate matter (TPM) from a single puff of smoke. The TPM was then weighed and dissolved in a 5:5:1 mixture of toluene, hexane, and isopropanol. Five PAHs, including naphthalene, phenanthrene, fluoranthene, pyrene, and benzo[a]pyrene were analyzed by gas chromatography–mass spectrometry (MS) using selective ion monitoring mode. This technique offers the capability to analyze trace amounts of PAHs in a single puff of mainstream cigarette smoke and provides information on PAH formation from each puff. Comparison of relative PAH levels in the lighting puff of mainstream cigarette smoke using different types of lighters is presented to illustrate the importance of applying the single puff analysis technique in understanding smoke chemistry.

Formaldehyde in the gas phase of mainstream cigarette smoke

Abstract Formaldehyde deliveries in the gas phase of the mainstream cigarette smoke of a single puff were studied using Fourier transform infrared (FTIR) spectroscopy. The lighting puff (first puff) has significantly more formaldehyde than subsequent puffs. The differences between the first puff and later puffs in cigarette smoking, such as tobacco rod length, smoke condensate on tobacco rod and filter, and whether or not the tobacco has been exposed to the previous puff(s), were explored in this study. It was found that while the mainstream gas phase formaldehyde deliveries vary with cigarette rod length and amount of smoke condensate on the tobacco rod and filter, the heat exposure of tobacco through previous puff(s) shows a more significant effect on formaldehyde levels observed in different puffs. The results of this study seek to explain the higher level of formaldehyde detected in the first puff. Exploring the smoking process on a per puff basis will provide more insight into the smoke chemistry and increase our understanding of combustion and pyrolysis in cigarette smoking.