Product Design
Reaction Mechanism in the Burning Cigarette
Abstract
Summarizes the chemical reactions of a burning cigarette. Identifies the high temperature, pyrolysis-distillation and low temperature zones of burning cigarettes as areas of complex chemical reactions. Describes pyrolysis and the formation of end products, indicates that condensation and filtration occurs in the low temperature zone and states the reactions taking place in a burning cigarette are very complicated.
Fields
- Notes
Appears to be a publication in prep. and resembles Bates # 1000145162-5219 expect for font size.
- Author
- Osdene, Thomas Stefan, Ph.D. (Director of Science and Technology, Philip Morris [1986])Ph.D. in Organic Chemistry. Ten years of research when he started with PM in 1965. Worked in Chemical Research Division of PM 1965-66; Chemical and Biological Research Division 1966-69; Director of Research 1969-1984, also assumed independent position as Director of Research and Extramural Studies during these years; became Director of Science and Technology in 1984, reporting directly to Philip Morris USA Executive VP Mark Serrano. Involved with Center for Indoor Air Research (CIAR) 1988. Attended PM's Operation Downunder Conference in June, 1987. Retired 1993.
- Hypothesis
- Mainstream constituent yieldsModification of selected mainstream smoke constituents in response to health concerns.
- Sidestream constituent yields
Modification of selected sidestream smoke constituents in response to health concerns.- Smoke constituent testing
Development of methods for measurement of gas and particulate yields in mainstream and sidestream smoke. - Sidestream constituent yields
- Keyword
- Burn rate controlBurn rate is controlled through use of burn additives, density, paper, etc.
- Butt length (smoked)
- Environmental Tobacco Smoke ETS
- Heat flux
- Initial puffs (First puffs)
- Passive Smoking
- Puff parameters
- Pyrolysis
- Reaction products
- Secondhand Smoke (Sidestream smoke, SS)
- Total particulate matter (TPM or Tar)
- Butt length (smoked)
- Additive
- Menthol
- Smoke Constituent
- acetaldehyde
- Acetamide
- Acetic acid
- Acetone
- Acetonitrile
- Acrylonitrile
- ammonia
- Benzo(a)pyrene
- Butanedione (2,3-Butanedione)
- Butanone (2-Butanone)
- Carbon dioxide
- Carbon monoxide
- Dimethylpyrazine (2,5 and 2,6-Dimethylpyrazine)
- Formamide
- Hydrogen cyanide (HCN)
- Methanol
- Methylpyrazine
- Methylpyrrole
- Nicotine
- Nitric oxides
- Phenol
- Propionamide
- Propionic acid
- Pyridine
- Pyrrole
- Acetamide
- Design Component
- Air dilution
- Ash formation
- Ash temperature
- Burn rate
- Coal temperature
- Combustion temperature
- Cone temperature
- Dynamic mass burn rate
- Free burn rate
- Humectant
- Mass burn rate (MBR)
- Static burn rate
- Ash formation
- Named Organization
- Tobacco and Health Research Institute
- University of Kentucky
- Brand
- KENTUCKY REFERENCE
- Subject
- aerosol (technology)
- Ammoniation (Technology)
- Burn Rate (Design)
- Metabolites (Measures)
- Puff Parameters (Measures)
- Reaction Processes (Technology)
- secondhand smoke
- Secondhand Smoke/Constituents
- Smoke Constituents
- Tar (Measures)
- Test/Smoke Condensate (Testing)
- Test/Smoke Constituents (Testing)
- Test/Smoke Machine (Testing)
- Transfer to Smoke (Measures)
- Ammoniation (Technology)
Document Images
OSDENE, page 1
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, A
REACTION MECHANISMS IN THE BURNING CIGARETTE
By
Thomas S. Osdene~
.
0
Director of Research, Philip Morris U.S.A.
OSDENE, page 2
In any discussion of chemical reactions, in the burning
cigarette it is essential that we first describe the present
state of the art of what is known about the basic energy
relationships that govern the burning process. Using temperature =-
profiles and major reaction zones, I will develop in some detail "
a model of the burning cigarette that will show the major sources
and sinks of energy that determine the generation and fate of the
various classes of smoke products. I will describe the use of some'
of the modern techniques that have been used to confirm.the existence
and location of the reaction zones and to elucidate the reactions
known at the present time.
.
x
c
It is in our own laboratories,.here at the Philip Morris Research
Center, that many of the techniques using isotopes--both radioactive
ones such as carbon-14 and heavy isotopes such as nitrogen-15 and
oxygen-18--have been pioneered. I will.therefore draw heavily on
the work done by my colleagues over the last decade or so.. Perhaps
Z should say at the very outset that I am really here to represent
them and to describe their outstanding contributions to our
understanding of the reactions within the burning cigarette..
It should be noted that some 2,000 chemical components have
.been identified in cigarette smoke at the present time and that
perhaps tens of thousands are as yet undiscovered. Obviously, ~
it would be an impossible task to determine the mechanisms by ~
.
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which each individual component is formed. However, there is a N
~
great de r al to be learned from a.discussion of certain aspects ~
of the reactions where mechanisms have been elucidated. .
OSDENE, page 3
(
Before discussing temperature profiles and reaction zones,
some basic definitions are in order. When a smoker puffs on a
~
cigarette, the smoke that issues from the butt end of the cigarette
is called mainstream smoke. During the interval between
puffs the smoke that rises from the lit end of the cigarette is
sidestream smoke. Mainstream smoke is formed during dynamic
puffing and is quite different chemically from sidestream smoke
generated during static burning between puffs. Both sidestream
and mainstream smoke can be divided into a particulate phase and
a gas phase. The particulate phase has been arbitrarily defined
as that portion of the smoke collected on a conventional Cambridge
(
filter pad (99 .9°!o efficient for particles > 0.1` µ); the portion
that passes through the Oamb ridge filter is gas phase. These
terms are illustrated in Fig. 1.
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[insert Fig. 1]
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In order to compare results between laboratories, a set of
standard smoking conditions has been established. These conditions
~ are: puff volume, 35 ml; puff duration, 2 sec; interval between
:;the completion of one puff and~ initiation of the next puff, 58
, sec. Also, the Tobacco and Health Research Institute of the ~_
University of Kentucky has estab lished a series of standard ~
O
experimental b lended cigarettes called the Kentucky Reference I~
Series. One of these cigarettes, designated 1RI, has
as a
tiP
been used C4
standard by tobacco research scientists throughout the
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worl.d.N
N
,
and thus becomes a source of heat for solids behind the comhastion
zone. The major source of combustion during the puff is not
located at the periphery but rather in the center of the ciWette.
Previous deductions that the periphery was the major sourcecif _
combustion were probably due.-to the ease of measuring the sutface
hot spots. Baker's flow rate was quite low (120 ml/min)-whzds
.0
Y
w
would result in more heat transfer than at the standard flov rate
Fig. 3 shows the classical solid temperature profiles of
the burning cigarette obtained by Egerton, Gugan, and Weinbex&2
. ------------ ---.--.--------- --------------------------w w-- __-
_
[insert Fig. 3a and 3b] (
.
------------------------- -------------------------------------
Fig. 3a is for the second or third puff, while Fig. 3b is the
profile for the last puff. These temperatures were obtained v3.th
flow rates between,600 and 1200 ml/min--rates which reflect
more realistically the conditions in most machine-smoking espwiments.
Note again the hot spot in the vicinity of the char line and the
high surface temperature over the entire coal that serves to
preheat the incoming air. On the last puff (Fig. 3b) the heat
gradient from the 'pyrolysis region.of 400°C +-back toward the butt
is very sharp. This demonstrates dramatically the heat-abso6ing
quality of previously condensed material on the tobacco.
Becais e .&
.these materials are lost to the sidestream between puffs, the
temperature gradient forward of the pyrolysis region is not
appreciably altered by the puff position.
0
OSDENE, page 6 .
Based on these temperature profiles, the model of the burning
In the high-temperature zone (900-600°C) the exothermic
oxidation of carbon heats the oxygen-depleted gas stream which serves
as an energy.source for.the complex reactions that take place in
, . .
The occurrence and location of these reaction zones have been
the pyrolysis-distillation zone (600-100°C). Overall, the reactions
in this region are endothermic and the gas stream cools quite
rapidly, merging into a low-temperature zone (100°C-ambient).
burning cigarette.3 The carbon monoxide concentration measured
-----------------------------------------------------------------
[insert Fig. 4]
cigarette can be visualized as consisting of 3 major reaction
zones.
: verified recently in our lab oratories, where probing experiments
have been conducted on the concentrations of several gases.ia.the
. --------------------------.------------------------------ ------.--
through the longitudinal axis of the rod on the second puff of a..
cigarette is shown in Fig. 4. Superimposed on this plot is the-
. . .
'' longitudinal gas-temperature profile of the cigarette: Starting
from the left we see that the gas temperature, represented by
~
.,
the dotted line, precedes the exothermic combustion, represented
by the first solid-line peak. The carbon monoxide concentration
is now quite high, but drops very rapidly as carbon monoxide is
lost from the coal. (Note that we are still in.front of the char
line at this point.) The second carbon monoxide'peak represents
.not a geaneraT reaction zone but a reaction specific to carbon
.
monoxide, namelyJ reduction of carbon dioxide under the influence
,
of the hot char. The last carbon monoxide peak occurs in the
OSDENE, page 7
general pyrolysis region. Due to sampling conditions, the pyrolysis
peak actually occurs at approximately 5 mm from the char line
instead of 10 mm as indicated in Fig. 4. The negative slopes
on the carbon monoxide peaks represent areas of rapid diffusion
out of the cigarette. There*is a rapid loss of gas temperature
behind the pyrolysis region. A steady decline in the carbon
monoxide concentration continues as near-isothermal diffusion occurs
down the rod.
On the other hand, oxygen concentration, as illustrated in
Fig. 5, drastically decreases in the area of carbon oxidation, as
. . .
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jinsert Fig. 5]
------------------------------------------------------------------
one would expect, and is still quite low in the pyrolysis region.
The oxygen concentration then increases due to diffusion of oxygen
through the paper into the cigarette.
HIGH-TEMPERATURE ZONE
I will now discuss the reaction zones in more detail. As a p
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puff is taken on the cigarette, air enters the periphery of the O
coal at the char line. In the -high- temperature zone there is an ~
exothermic oxidation of carbon~and heat is transferred to the ~
rA
gas stream. The hot gas stream serves as an energy source for
the subsequent decomposition of the tobacco in the pyroJ.ysis-distillatior
.region, fThe products generated in the high-ternperature zone are
mainly gaseous, including carbon dioxide, carbon monoxide, hydrogen,
OSDENE, page 8
methane, some free radicals, and small amounts of water and organic
compounds. A portion of the products diffuses through the coal to
the sidestream. The remainder stays in the hot gas stream.
These observations have been verified in our laboratories
by a series.of oxygen-18 experiments.4 Kentucky Reference 1R1
cigarettes were smoked in an atmosphere containing oxygen-18 and
the incorporation of the isotope in various smoke components was
determined. Table I gives the results.that were obtained.
------------------------------------------------------------------
[insert Table I]
-----------------------------------------------------------------
a
by these pyrolytically derived compounds delivered to the sidestream
reduced atmospheric oxygen incorporation in water, acetone, and
acetaldehyde--compounds which are derived principally from
pyrolytic processes. Further, the uptake of atmospheric oxygen
SS/MS ratios of near unity. Contrast this.with the greatly
Combustion products such as carbon monoxide and carbon dioxide
derive more than 50% of their oxygen from the atmosphere. The
oxides of carbon incorporate atmospheric oxygen to the same extent
in both mainstream (MS) and sidestream (SS) smoke as indicated by
is much greater than the uptake by the same components delivered
to the mainstream.
Water is an important combustion product which rivals the
oxides of carbon on the basis of mass. The overwhelming
O
preference p
of "combustion" water for the sidestream leads us to propose that
~11
water rgsults mainly from the reaction of pyrolytically formed
0
Cn
hydrogen with oxygen. An alternate mechanism involving the
interaction of oxygen with hydrogen bound to a char-like solid
.-
OSDENE, page 9
structure can be rejected, since the SS/MS ratio of water by this
mechanism should parallel that of the oxides of carbon.
YYROLYSIS-DISTILLATION ZONE
The energy provided by the oxygen-depleted hot gas stream from
the combustion zone leads to a host of complex reactions which
occur in the pyrolysis-distillation zone. The tobacco decomposes
to yield high-b:oiling compounds which are the main source of
.particulates; "char" that serves as fuel for combustion; carbon
monoxide; organic gases such as acrolein, acetaldehyde, and
hydrogen cyanide; and intact distillation products such as nicotine
and the humectants. In this zone the aerosol, which is not in
thermal equil ibrium with the,gas, is rapidly forming, with the
higher-boiling compounds condensing first. The gases such as
carbon monoxide, carbon dioxide, and hydrogen diffu e out through
the paper while oxygen diffuses into the rod. The overall sum of
the reactions is endothermic, so that the gas stream cools rapidly.
All these reactions are temperature- and residence-time-dependent;
so pyrolysis and distillation reactions are subject to change by
alteration of the cigarette parameters, and/or the smoking conditions.
r
4
have led us to conclude
Our oxygen-18 incorporation studies
that gas-phase components in the sidestream smoke incorporate higher
percentages of'atmospheric oxygen than do those of the particulate
phase. (See Table II.) Certain organic compounds contain appreciable OO
amounts of atmospherically derived oxygen. These are principally A
r
aliphatic aldehydes, ketones, and carboxylic acids. Some oxygern
in phenol is also derived from the atmosphere.
OSDENE, page 11
C
The composition of products in the smoke from cigarettes
containing, these additives is dependent on the decomposition temperature
of the additive. For example, we have found that the reduction
of benzo(a)pyrene in smoke from nitrate-treated cigarettes varies -
~ with the decomposition temperature of the added salt. It has been .
,shown previously that the addition of..nitrate salts to cigarettes
o .
~ can significantly modify other chemical components in the smoke.6
These results suggest that significant modifications of smoke
chemistry may be obtained by the proper selection of additives
which decompose at temperatures coinciding with the formation o-f-
c r,n "
particular z$nes.
salts have also been useful for studying the various classes of
compounds formed when nitrogenous compounds are converted into
smoke products. With [15N]-glycine as an ammonia source, various
amides, nitriles, and N-heterocyclics were formed. Percent
The cigarettes with added [15N]-glycine and various [15N]-nitrate.
(
.
f
incorporations for these compounds are shown in Tables IV and V.
-----------------------------------------------------------------
.
[insert Tab les IV and Vj
------------------------------------------------------------------
Note that K15N03 and Oa(15N03)2 give results similar to Nai5N03.
The enrichment of amides is very similar to that of ammonia,
suggesting an ammonia route to the amides. While all the compounds O
O
show efficient enrichment of the nitrogen-15 label, note particularlyR
the nitrile enrichment, which is greater than that observed for ~
~
ammonia, amides, and the N-heterocyclics. Two possible mechanisms ~
47~
may account for nitrile formation:
OSDENE, page 12
.1. Ammonia may be generated at a temperature that enables
nitriles or suitable nitrile precursors to be formed.
2. Highly enriched nitric oxide may react with free radicals
to give oximes, which on dehydration yield nitxiles.
Our study could not distinguish between these 2 mechanisms.
~Note (Table V) that the heterocyclics are enriched to a much
lesser extent than the amides or ammonia (Table IV). This is to
be expected if one considers,other nitrogen sources such as -
alkaloids which would yield similar substances with no nitrogen-15
enrichment whatsoever. Some reactions which yield N-heterocyclics
.via ammonia are shown in Fig. 6. Thus, hydroxymethyltetrahydrofuran
a
-----------------------------------------------------------------
[insert Fig. 6]
--- ----------------------------------------------- ----------
can yield pyridine, while acrolein can yield methylpyridine and
dimethylpyrazine on reaction with ammonia.
Two additional nitrogenous compounds that should be mentioned
are nitrous oxide and nitric oxide.' With the oxygen-18 label, we
found (as indicated above) that nitrous oxide incorporates 38-65%
of atmospheric oxygen and that it is delivered almost exclusively
to the-sidestream smoke. Nitric oxide has been studied using the
K 15N03 precursor and an enrichment of 85 1SN atom-% was found,5a
This is identical to the nitrate enrichment of the unburned
tobacco, .-
indicating that nitrate is the major precursor of nitric oxide in
.smoke.
I would now like to turn to the use
materials and present some data that can
of carb on-14- l.ab e led
contribute further to
t
our understanding of the reactions in the pyrolysis-distillation
zone of the burning cigarette.
