5-7 OCTOBERISFR2011

45

TOLEDO (SPAIN)

EMISSION CONTROL OF BROMINATED COMPOUNDS BY METAL OXIDES INPYROLYSIS OF TETRABROMOBISPHENOL A AND A PRINTED CIRCUIT BOARD
T. Suzuki, O. Terakado, R. Ohhashi and M. Hirasawa
Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya University, Japane-mail: teramon@numse.nagoya-u.ac.jp

Abstract
Pyrolysis of tetrabromobisphenol A, a common flame retardant, has been studied under the presence of metal oxide. Theformation of hydrogen bromide and brominated organic compounds is significantly suppressed by the addition of metaloxides. The bromine fixation ability of various oxides is compared and discussed. A preliminary work on thermal
degradation of mixtures of a print circuit board and oxide has been also carried out. The results show that the presence ofoxide is effective for the suppression of hydrogen bromide as well as brominated organic compounds.

Keywords: tetrabromobisphenol A, hydrogen bromide, brominated organic compounds, metal oxides, printed circuitboard

1. Introduction
Pyrolysis treatment is an attractive method that enables
feedstock recycling of synthetic polymers withsimultaneous volume reduction of wastes. However,most of waste polymers contain various flame retardants,
the influence of which should be carefully examined in
the pyrolysis treatment. Tetrabromobisphenol A or 2,6,2’,6’-tetrabromo-4,4’-isopropylidene-diphenol, denotedhereafter as TBBA, is commonly used as brominatedflame retardant. Thermal treatment of waste resins
containing TBBA results in the formation of various
brominated compounds. It is known that the majordegradation product of TBBA is hydrogen bromide, HBr,
with some by-products of brominated phenols [1].
Uncontrolled thermal treatment of waste containing
TBBA can develop polybrominated dibenzo-p-dioxins(PBDDs) and dibenzofurans (PBDFs) [2]. The emission
control of such harmful compounds is becoming
important in the view of the significant increase of waste
electronic and electric equipment (WEEE). In the present
study, we have carried out pyrolysis of TBBA in thepresence of metal oxide in the view of simultaneous
treatment of waste plastics and oxide wastes, such as
metallurgical dust. A preliminary work has been also
conducted for pyrolysis of a printed circuit board
containing bromine as flame retardant.

2. Materials and Methods
Powder form of TBBA, C15H12Br4O2 supplied from Aldrich,
was used in the present study. The typical diameter wasof ~50 μm. Pyrolysis samples were prepared bymechanical mixing of the TBBA and metal oxide powderof reagent grade (La2O3 from Kishida Chem. Co., Ltd.,and ZnO, CaO, CuO and Fe2O3 from Kanto Chem. Co.,
Ltd.) in mortar for ca. 5 min. The mixture wasconsequently pelletized with the load of ca. 2.5×108 Pa.

interiores libro.indd 45

The oxides have the particle diameter of 1-10 m, andthe BET surface area of the order of 1 m2/g [3]. It is
expected that bromine released from TBBA reacts withmetal oxide to form the corresponding metal bromide oroxybromide. The composition of [TBBA]:[Fe2O3] = 1:1
and [TBBA]:[other oxide] = 1:2 in molar ratio was mainlyexamined. This is based on the stoichiometry of thecorresponding metal bromides and oxybromide, i.e.
ZnBr2, CaBr2, CuBr2, FeBr2 and LaOBr. A printed circuitboard was supplied from Hitachi Kasei Co., Ltd. (FR-4type). The copper plate was removed by iron chloride
solution. The Cu-free board was then crushed andground down to < 250 m. The preparation of pyrolysis
sample was similar to that of TBBA – metal oxide
mixtures.
Pyrolysis experiments were carried out with a horizontal
type reactor (700 mm in length and 26 mm in i.d.) under
helium atmosphere [4]. Detailed analytical methods ofpyrolysis products are described elsewhere [4]. The
formation of hydrogen bromide captured in a water trap
was monitored through the amount of bromide ion, Br-,with an ion meter (IM-40S, TOA Electronics). A bromideion-selective electrode (TOA Br-125) was employed as
the working electrode. The reference electrode (TOA HS305DS) was a double junction-type Ag/AgCl electrodewith saturated KCl solution as an inner solution and 0.1
M KNO3 solution as an outer solution adjacent to thesample solution. Gaseous and liquid products wereanalyzed by GC-MS.

3. Results and Discussion
The formation of hydrogen bromide and brominatedorganic compounds is observed in pyrolysis of TBBA. As
seen in Table 1, the addition of metal oxide gives rise toconsiderable suppression of HBr. In the case of theaddition of lanthanum oxide with the composition of 1:2,

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6th International Symposium on Feedstock Recycling of Polymeric Materials

the formation of HBr is almost insignificant. As
summarized in Table 2, the formation of the brominatedorganic compounds is substantially reduced by theaddition of calcium oxide and La 2O3. Thus, these oxides
can be applied for the emission control of harmfulbominated organic compounds.
Table 1. The ratio of trapped Br- in water trap and theinitial bromine at 800 oC (in %). The composition of TBBA
– oxide mixture denotes [TBBA] : [oxide] in molar ratio.
TBBA
TBBA-ZnO

TBBA-Fe2O3

TBBA-CaO

TBBA-La2O3

1:1
1:2
1:3
1:1
1:2
1:3
1:1
1:2
1:3
1:1
1:2

Trapped Br (wt.%)
92
38
23
4.0
4235
1746
139.1
300.5

Table 2 Product yield for pyrolysis at 800 oC,100×(mass of product)/(initial mass of TBBA). The
sample composition is [TBBA] : [Fe2O3] = 1:1 and[TBBA] : [other oxide] = 1:2.
TBBA
Phenol
0.019
pbromo6.8
phenolm-cresol 0.057
2bromo0.20
4methylphenol
3,5dibromo- 0.0026
toluene2,6dibromo- 2.15
phenol
2,4,6tribromo- 2.48
phenol+ZnO
2.4+Fe2O3 +La2O3
2.8
0.26+CaO
0.21

0.74

0.94

0.10

0.095

0.019

0.027

0.0024

0.018

0.053

0.027

0.023

0.051

0.00110.00640.00100.0024

0.41

0.36

0.078

0.25

0.16

0.20

0.0071

0.10(4 
(4  <P1   (4  <P1   (4  (G1   

RDTQO QRJGPQN
FKDTQO QRJGPQNVTKDTQO QRJGPQN

(4  (G1   (4  .C1   (4  .C1   (4  % C1   

9 RTQFWEVU9 (4 ‫ޓ‬Fig. 1. Comarison of the yield of bromophenols in thermal
degradation of printed circuit board, FR-4, at 800
degrees celsius. The composition in molar ratio isindicated in the parenthesis, where the mole of thecorresponding TBBA in the board and that of each oxide
is shown.

4. Conclusions
The addition of some metal oxides reduces the formationof HBr and brominated organic compounds in thermal
degradation of TBBA. Lanthanum oxide is especiallyeffective for the suppression of HBr, and the formation of
the brominated organic compounds are substantiallyreduced by the addition of La2O3 and CaO. Similar
suppression is observed in pyrolysis of a printed circuitboard under the presence of metal oxide, though a slightdifference in the role of oxides is observed. The influenceof polymer matrix may not be negligible, so that furtherstudies on thermal decomposition of various polymers
containing TBBA should be carried out.

References

Similar effect is observed in the pyrolysis treatment of a
printed circuit board, containing bromine as frame
retardants. Fig. 1 shows the product yield of
bromophenols in pyrolysis of the board material at 800 oC.
It is clearly seen that the formation of brominatedcompounds is substantially reduced by the addition ofmetal oxide. In comparison of the present results withthose of the TBBA-oxide mixtures, it is obvious thatcalcium oxide plays a different role in the fixation of theinteriores libro.indd 46

bromine. Further studies are needed in order to clarify
the detailed role of the oxides in the fixation of bromine inthe pyrolysis treatment.

[1] K. Marsanich, S. Zanelli, F. Barontini and V. Cozzani,
Evaporation
andthermaldegradation
oftetrabromobisphenol A above the melting point,
Thermochim. Acta 421 (2004) 95-103.
[2] H. Wichman, F.T. Dettmer and M. Bahadir, Thermal
formation of PBDD/F from tetrabromobisphenol A – acomparison of polymer linked TBBP A with its additive
incorporation in thermoplastics, Chemosphere 47 (2002)
349-355.
[3] Y. Masuda, T. Uda, O. Terakado and M. Hirasawa,Pyrolysis study of PVC - metal oxide mixtures:
Quantitative products analysis and chlorine fixation abilityof metal oxides, J. Anal. Appl. Pyrolysis 77 (2006) 159.
[4] O. Terakado, R. Ohhashi and M. Hirasawa, Thermal
degradation study of tetrabromobisphenol A under thepresence metal oxide: Comparison of bromine fixation
ability, J. Anal. Appl. Pyrolysis (2011) in press.

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