Thermogravimetric Analysis of Ammonia-Swelled Cellulose

Broido, A.; Weinstein, M.

doi:10.1080/00102206908952207

Cited by 32 publications

(13 citation statements)

References 3 publications

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“…The char is generally not pure carbon, and other gases, such as CO 2 , could equally well be evolved during the charforming step (they are certainly evolved during pyrolysis itself). Nevertheless, the char-forming process has been characterized by some workers as involving mainly a dehydration, in accord with this highly simplified model (Kilzer and Broido, 1965;Broido, 1966;Broido and Weinstein, 1970;Broido and Nelson, 1975;Arsenau, 1971;Arseneau and Stanwick, 1971;Bradbury et al, 1979). Though some features of such simple cellulose pyrolysis models have been the subject of recent challenge (Varhegyi et al, 1994), the basic feature of a competitive pathway leading to differing yields of char has been upheld.…”

Section: Resultsmentioning

confidence: 99%

Thermal Effects in Cellulose Pyrolysis: Relationship to Char Formation Processes

Milosavljevic

Oja

Suuberg

1996

Ind. Eng. Chem. Res.

273

178

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The thermochemistry of cellulose pyrolysis has been studied by a combination of differential scanning calorimetry and thermogravimetric analysis. Additionally, the vapor pressure and heat of vaporization of levoglucosan have been determined by an effusion method. The cellulose pyrolysis has been carried out under inert gas at heating rates from 0.1 to 60 K/min. The main cellulose thermal degradation pathway is endothermic, in the absence of mass transfer limitations that promote char formation. The endothermicity is estimated to be about 538 J/g of volatiles evolved. It is concluded that this endothermicity mainly reflects a latent heat requirement for vaporizing the primary tar decomposition products. Pyrolysis can be driven in the exothermic direction by char-forming processes that compete with tar-forming processes. The formation of char is estimated to be exothermic to the extent of about 2 kJ/g of char formed. Low heating rates, in concert with mass transfer limitations, serve to drive the pyrolysis in this direction. The enthalpy of cellulose pyrolysis is thus seen to be a sensitive function of the pyrolysis conditions. Pyrolysis appears to initially follow a common thermal pathway (in terms of enthalpy required per mass of volatile loss), irrespective of heating rate. Only at some finite level of conversion does the “thermal trajectory” of the process follow a heating rate dependent path, as significant char formation begins to occur.

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Section: Resultsmentioning

confidence: 99%

Thermal Effects in Cellulose Pyrolysis: Relationship to Char Formation Processes

Milosavljevic

Oja

Suuberg

1996

Ind. Eng. Chem. Res.

273

178

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“…Van Krevelen et a1.,* noting that almost the entire measurable reaction usually occurs within f 10% of T,, the temperature of maximum reaction velocity, applied the following approximations to the right-hand part of eq. (6): (11) By integrating and taking logs of both sides of eq. (6), then, one obtains…”

Section: Approximationsmentioning

confidence: 99%

A simple, sensitive graphical method of treating thermogravimetric analysis data

Broido

1969

J. Polym. Sci. A‐2 Polym. Phys.

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820

364

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Thermogravimetric Analysis (TGA) is finding increasing utility in investigations of the pyrolysis and combustion behavior of materials. Although a theoretical treatment of the TGA behavior of an idealized reaction is relatively straight‐forward, major complications can be introduced when the reactions are complex, e.g., in the pyrolysis of cellulose, and when experimental imperfections arise. Consequently, a fairly large number of analytical methods have been proposed for obtaining kinetic parameters from TGA curves. Among the proposed methods are several graphical procedures, mostly involving relatively inaccurate tehniques, such as obtaining slopes on a rapidly changing curve. Included among the proposed procedures is one which permits a linear plot of TGA data. The sensitivity with which such a plot can be used to identify and correct for a variety of experimental complications seems to have escaped even the proponents of the techniques. This paper provides an illustration of the use of this graphical procedure in a hypothetical first‐order pyrolysis typical of those occurring in the TGA behavior of cellulose.

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“…A great many thermogravimetry (TG) and differential scanning calorimetry (DSC) experiments, complemented by qualitative and quantitative product analysis, have affirmed that cellulose thermal decomposition is largely a competitive process [1,2,3,4,5,6,7]. In the big picture that has taken shape from these results and from associated modelling studies (for example, see [8,9,10,11,12,13] and the reviews in [14] and [15]) formation of volatiles and char are seen to be reciprocally linked to some extent.…”

Section: Introductionmentioning

confidence: 99%

Feedback processes in cellulose thermal decomposition: implications for fire-retarding strategies and treatments

Ball

McIntosh

Brindley

2004

Combustion Theory and Modelling

102

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A simple dynamical system that models the competitive thermokinetics and chemistry of cellulose decomposition is examined, with reference to evidence from experimental studies indicating that char formation is a low activation energy exothermal process and volatilization is a high activation energy endothermal process. The thermohydrolysis chemistry at the core of the primary competition is described. Essentially, the competition is between two nucleophiles, a molecule of water and an -OH group on C 6 of an end glucosyl cation, to form either a reducing chain fragment with the propensity to undergo the bond-forming reactions that ultimately form char or a levoglucosan-end-fragment that depolymerizes to volatile products. The results of this analysis suggest that promotion of char formation under thermal stress can actually increase the production of flammable volatiles. Thus we would like to convey an important safety message in this paper: in some situations where heat and mass transfer is restricted in cellulosic materials, such as furnishings, insulation, and stockpiles, the use of char-promoting treatments for fire retardation may have the effect of increasing the risk of flaming combustion.

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Thermogravimetric Analysis of Ammonia-Swelled Cellulose

Cited by 32 publications

References 3 publications

Thermal Effects in Cellulose Pyrolysis: Relationship to Char Formation Processes

Thermal Effects in Cellulose Pyrolysis: Relationship to Char Formation Processes

A simple, sensitive graphical method of treating thermogravimetric analysis data

Feedback processes in cellulose thermal decomposition: implications for fire-retarding strategies and treatments

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