Thermal decomposition of decabromodiphenyl ether

Journal ofAnalytical and AppIied Pyrolysis, 13 (1988) 277-285 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

THERMAL

DECOMPOSITION

W. KLUSMEIER,

P. VijGLER,

OF DECABROMODIPHENYL

K.-H. OHRBACH,

University GH Paderborn, Department 4790 Paderbom (F. R. G.)

211

ETHER

H. WEBER and A. KETTRUP

oj Applied Chemistry

*

P. 0. Box 1621,

(Received December lst, 1987; accepted December lOth, 1987)

ABSTRACT Decabromodiphenyl ether has been decomposed by use of a vertical combustion apparatus, applying different air flow-rates and temperatures of 400, 600, 800 and 1000°C. The main decomposition products have been identified as brominated aliphatic and aromatic compounds such as tetrabromoethene, hexabromobutadiene, pentabromobenzene, hexabromobenzene, octabromostyrene, hexabromofuran, hexabromoindone, heptabromodibenzodioxin, heptabromodibenzofuran, octabromodibenzodioxin, and octabromodibenzofuran. Decabromodiphenyl ether; pyrolysis; thermal decomposition.

INTRODUCTION

At the present time our standard of living in most of the industrial countries has been influenced by the rapid expansion of the chemical industry, which prepares and produces numerous compounds. As a rule the physical properties, such as melting and boiling points, density or viscosity, as well as their chemical properties are well-known. Information about the thermal behaviour, e.g. the composition of the products evolved from heating at high temperatures, or burning of non-combustible and combustible substances is lacking. Such information is becoming increasingly important, whenever materials are thermally treated, especially with respect to fires in stores, on disposal sites: or due to technical waste management in incinerating plants and sludge pyrolysis. The thermal decomposition,. of decabromodiphenyl ether has been described previously [1,2]. Buser ‘has detected polybrominated dibenzodioxins and dibenzofurans as pyrolysis products arising from pyrolysis of decabromodiphenyl ether in closed quartz ampoules. Hutzinger et al. have carried out similar experiments in an open quartz tube, identifying and 0165-2370/88/$03.50

0 1988 Elsevler Science Publishers B.V.

278

determining a series of dibenzodioxins and dibenzofurans [3]. The results of investigations into the thermal decomposition of polymers containing brominated diphenylethers as flame retardants have been reported in previous papers [4,5]. Our investigations take up these results, by thermally decomposing decabromodiphenyl ether in a newly designed vertical combustion apparatus, developed by the ‘Verband der Chemischen Industrie of the Federal Republic of Germany’ (VCI) [6].

EXPERIMENTAL

Chemicals Decabromodiphenyl ether was used as a technical product of 88.1% purity, which is contaminated by 11.0% nonabromodiphenyl ether, 0.5% octabromodiphenyl ether and 0.1% hexabromobenzene. The adsorption resin for the decomposition products was XAD-4 from Rohm and Haas Company, and the charcoal tubes were type 226-01 from SKC Inc.

Instrumental equipment The analysis of the decomposition products was performed by means of a capillary gas chromatograph, Perkin-Elmer Sigma 2b, equipped with an electron-capture detector. The instrumental parameters were adjusted as follows: column, 60 m fused silica DB 1 (ICT Handelsgesellschaft); split, 20 cm3/min; temperature programme, from 100’ C to 300” C at 6 OC/mm; detector, electron-capture detector operating at 320 o C; injector, 320 OC; integrator, Spectraphysics Minigrator. For the identification of the degradation compounds an analysis system consisting of a high-resolution mass spectrometer, Finnigan MAT 8230, and a Varian 3400 gas chromatograph was available. All experimental and instrumental conditions were held constant, thus enabling a comparable evaluation of the data to be made.

Combustion apparatus The combustion apparatus, see Fig. 1, has been developed by a working group of the VCI [6]. It consists of a two-zone vertical furnace, capable of being openened. The combustion chamber is preheated and can be loaded with the sample material (20 mg) through a specially constructed charging device. The decomposition products will be adsorbed at a constant temperature of 20 OC on 180 mg of XAD resin. Commercially available charcoal tubes are installed behind the XAD-4 tubes to adsorb any low-boiling compounds, like tribromoethane and tetrabromoethene, which are not com-

279

Fig. 1. VCI combustion apparatus. 1= Two-zone vertical furnace; 2 = quartz tube; 3 = combustion chamber; 4 = sample material; 5 = gas input; 6 = gas output; 7 = cooling device; 8 = charging device; 9 = adsorption XAD-4; 10 = adsorption charcoal; 11= pump.

pletely adsorbed by XAD-4. The desorption processes were carried out by use of 2 cm3 carbon disulfide. Desorption and recovery rates

In view of the identification and the analytical determination of the combustion gas components, the sampling technique, followed by the sample pretreatment, is of great importance. The determination of the recovery rates and the desorption rates are on the one hand a measure of the adsorption properties of the collecting phase and, on the other hand, of the efficiency of the desorption reagent. To determine the desorption rate, a solution containing dibromoethane, 1,Cdibromobenzene and 1,2,5-tribromobenzene was prepared. From this solution a volume of 1 ~1 was injected onto the XAD-4 using a microliter syringe, followed by desorption with carbon disulfide; the desorption rates were greater than 95%. In order to determine the recovery rates in the range of 88%, aliquots of the the standard solution were taken and injected into the combustion apparatus, applying a temperature of 400°C and a nitrogen flow-rate of 200 cm3/min.

RESULTS

The chromatograms in Figs. 2, 3 and 4 represent the separation of the decomposition products of decabromodiphenyl ether evolved at 400, 600,

280

3 19

/

/. 90

~‘00

70

Ho

w

50

10

-

A-J M

20

IO

0.a

Fig. 2. Thermal decomposition of decabromodiphenyl ether at a temperature of 400 o C. Peak identification: 1 = carbon disulfide; 2 = not identified; 3 = tetrabromoethane; 4 = pentabromobenzene; 5 = hexabromobutadiene; 7 = hexabromobenzene; 8 = hexabromobenzofuran; 9 = cctachlorostyrene; 10 = hexabromoindone; 11 = not identified M+ = 775; 12 = not identified M+ = 616; 13 = octabromodiphenyl ether; 14 = heptabromodibenzofuran; 15 = heptabromodibenzodioxin; 16 = nonabromodiphenyl ether (isomer); 17 = nonabromodiphenyl ether (isomer); 18 = octabromodibenzofurann; 19 = octabromodibenzodioxin; 20 = decabromodiphenyl ether.

800” C and in an air stream of 200 cm3/min. The chromatogram of the experiment at 1000 o C was nearly the same as that at 800 o C. From a comparison of the chromatograms it can be concluded that the degradation of the relevant compound strongly depends on the applied decomposition temperature. At 400” C and 200 cm3 air flow-rate the complete series of combustion products will be formed, including the brominated dibenzodioxins and dibenzofurans. An increase of the temperature to 600 OC

8

18

tlme(min)

90

15 14

80

70

Fig. 3. Thermal decomposition identification as in Fig. 2.

I2

60

II

50

of decabromodiphenyl

40

30

20

IO

40

ether at a temperature of 600 o C. Peak

281

time

60

50

Fig. 4. Thermal decomposition identification, see Fig. 2.

LO

30

of decabromodiphenyl

20

10

O#O

ether at a temperature of 800 o C. Peak

leads to the decomposition of most of the products which have just been formed. In the range from 800 to 1000 o C only very small amounts of those compounds can be detected, due to a possible complete degradation of the organic matter into hydrogen bromide, carbon dioxide and carbon monoxide.

.L ”

106:

2

0,001

0,Ol

O,l

Fig. 5. Calibration curves of bromobenzene,

I 1.0 cone hlg/cm3)

1,4-dibromobenzene,

and 1,2,5-tribromobenzene.

282

,OoO

Loo

600

800 Temperature

loo0 (“C)

Fig. 6. Thermal decomposition of decabromodiphenyl ether as a function of temperature and air flow-rate.

A quantitative analysis of the indicated compounds could not be performed, since most of them are not available as reference materials. But, with regard to an estimation of some trends, we have recorded calibration curves for bromobenzene, 1,4-dibromobenzene and 1,2,5-tribromobenzene. The result is shown in Fig. 5. Needless to say, Fig. 4 demonstrates the sensitivity of the electron-capture detector to the degree of bromine substitution at the aromatic ring. The degradation of decabromodiphenyl ether is not only influenced by the temperature, but also by the air flow-rate, i.e. the time of direct contact in the hot zone of the furnace. This is represented in Fig. 6. A short direct contact time of the sample with air (100 cm3/min at 400” C) corresponds with an increase of the cleavage of the original compound, in contrast to the results obtained at 400 cm3/min, which gives only a small degree of decomposition. The thermal behaviour of the flame retardant at 600 o C can be described similarly. The degradation of the main part of the sample is due to the application of small air flow-rates. In the case of a 400 cm3/min flow-rate, this state is reached at 800 o C. The decomposition of the compounds mentioned in the following figures follows a similar trend to the decomposition of decabromodiphenyl ether, i.e. it depends on the temperature and the air flow-rate. This fact can be demonstrated by inspection of the results shown on the Fig. 7a-e, which are good examples for some of the decomposition products. From these examples it can be clearly demonstrated that the formation of the degradation products is significantly influenced by the temperature and the time of direct contact in the hot zone of the furnace. In general, long direct contact time lead to further decomposition of the components just

283 (b)

(a)

Lo3

800 600 Temperature (“c)

1000

Mx)

800

Temperature

,u

T

Cd)

V(x 103 60 64l

MYI 800 Temperature (“C)

1000

(“C)

t /\

WP

c=c

Br

br

600 e&l Temperature K)

1000

loo0

(e)

pvb&

Br Br Br Br +&&c 15 ‘t

&

‘Br

10

5

800 6M) Temperature (“0

1000

Fig. 7. Formation of (a) hexachlorobenzene, (b) pentabromobenzene, (c) hexabromofuran, (d) tetrabromoethene and (e) hexabromobutadiene showing dependence on the temperature and the air flow-rate.

formed. The formation of octabromodibenzofuran and octabromodibenzodioxin, represented in Fig. 8a and b, is somewhat different. It can be concluded that the formation of octabromodibenzofuran is due

284

(a)

600 Tempera%

lOo0 (“0

Temperature

(“0

Fig. 8. Formation of (a) octabromodibenzofuran and (b) octabromodibenzodioti dependence on the temperature and the air flow-rate.

Br

Br

Br

Br

Br

Br

Fig. 9. Formation of octabromodibenzofuran

Fig. 10. Formation

showing

of octabromodibenzodioxin

from decabromodiphenyl

from decabromodiphenyl

ether.

ether.

to a rearrangement of the decabromodiphenyl ether at long direct contact times by cleavage of two bromine radicals, see Fig. 9. This assumption is confirmed by the detection of octabromodibenzodioxin, which is formed at high air flow-rates and high temperatures, i.e. at a higher concentration of oxygen radicals, see Fig. 10.

ACKNOWLEDGEMENT

The authors acknowledge Dr. G. Merz of the Badische Sodafabrik for making the combustion apparatus available.

Anilin und

285 REFERENCES 1 2 3 4

H.R. Buser, Environ. Sci. Technol., 20 (1986) 404. H.R. Buser, Chemosphere, 16 (1987) 7143. H. Thoma, E. Hauschulz, E. Knorr and 0. Hutzinger, Chemosphere, 16 (1987) 277. E. Clausen, E.S. Lahaniatis, M. Bahadir and D. Bienik, Fresenius Z. Anal. Chem., 327 (1987) 327. 5 W. Klusmeier, R. Sonnemann, K.-H. Ohrbach and A. Kettrup, Thermochim. Acta, 112 (1987) 75. 6 W. Mere, H.J. Neu, M. Kuck, K. Winkler, S. Gorbach and H. Muffler, Fresenius Z. Anal. Chem., 325 (1987) 449.