5-7 OCTOBERISFR2011

129

TOLEDO (SPAIN)

SIMULTANEOUS SILVER AND BENZENE RECOVERY FROM X-RAY FILM
S. Kumagai, G. Grause, T. Kameda, and T. Yoshioka
Graduate School of Environmental Studies, Tohoku University
e-mail: yoshioka@env.che.tohoku.ac.jp

Abstract
X-ray film consisting of poly(ethylene terephthalate) (PET) was hydrolyzed at a temperature of 450 °C in a steam
atmosphere resulting in terephthalic acid (TPA). It was found during earlier investigations that TPA is decarboxylated in thepresence of calcium oxide (CaO), and benzene is selectively produced. In this work, silver was recovered during the thermal
decomposition of X-ray film and the effect of CaO on the liquefaction of X-ray film was investigated. Benzene yield and purity
were promoted in the presence of CaO, resulting in 42% and 78%, respectively. For the purpose of comparison, PET fromone-way bottles was pyrolyzed under the same conditions with results showing a similar tendency. Furthermore, 95% of thesilver content was recovered during the liquefaction of X-ray film. These results imply that this method can also be applied toother PET based materials containing inorganic substances, which cannot be recycled effectively otherwise.

Keywords: Pyrolysis, PET, Calcium oxide, Metal recovery, Feedstock recycling

2. Materials and Methods“TPA decarboxylation chamber”, which was filled withCaO. The sample was kept in a perforated sample holder
inside the hydrolysis chamber. The CaO bed wascalcined prior to the experiment in the decarboxylationchamber for 1h at 900 °C in a He atmosphere in order todecompose potential calcium carbonate (CaCO3). After
calcination, the sample was hydrolyzed in the hydrolysis
chamber at 450 °C in a steam flow of 327 mL min-1(steam:88 vol%, He:12 vol%). Gaseous TPA from thePET hydrolysis was carried with other gases by thesteam flow into the decarboxylation chamber, where it
reacted with CaO at 700 °C. Liquid products weregathered in cooling traps cooled by ice and liquid
nitrogen. Gaseous products were collected in a gas bag.
Silver remained with carbonaceous residue in the samplebag.
For qualitative and quantitative analysis, gaseous
products and liquid products were analyzed by gas
chromatography (GC-FID, GC-TCD and GC-MS).
Recovered silver was analyzed by XRD and ICP-AES.
Spent CaO was analyzed by XRD.
All products were standardized on the basis of thesample weight (100 wt%).

2.1. Materials

3. Results and Discussion

Cut PET bottles and X-ray film (2.8 mm 2.8 mm) wereused for pyrolysis experiments. Samples were preparedby the quartering method. CaO, with a particle sizes
between 1.0 and 3.0 mm was used as a catalyst.

Table 1 shows the elemental composition of PET bottles
and X-ray film determined by elemental analysis. The
CHO content of PET bottles and X-ray film used for thepyrolysis experiments was approximately the same.
Differences to the theoretical composition of PET werenegligible. X-ray film contained further silver and bromine
from the photosensitive material, and nitrogen fromgelatin.
The fractions of benzene, TPA and BA, as well as thebenzene purity were slightly higher for PET bottles than

1. Introduction
Thermal decomposition of waste PET is a feasible
alternative for materials containing inorganic substances,which cannot be recycled mechanically. However,terephthalic acid (TPA) and benzoic acid (BA) are formed
during the pyrolysis of PET, causing concerns forcorrosion and blockage of pipes in the treatment facilities.
From our previous work,1-3 to prevent such negative
effects, PET and TPA were pyrolyzed in the presence of
calcium oxide (CaO), resulting in oil with a high benzene
content and without sublimating substances such as TPA.
In this study, X-ray film consisting of PET and theremaining silver from the photosensitive layer of the film
was converted into benzene. Simultaneously, silver wasrecovered, applying the previous developed process. Thefilm was pyrolyzed in the presence and absence of CaO
in order to investigate the effect of CaO on theliquefaction of PET containing silver as an additve.
Furthermore, silver recovery yields were investigated. For
the purpose of comparison, PET bottles were also
pyrolyzed under the same conditions.

2.2. Pyrolysis experiments and analytical methods
The experiments were carried out in a quartz tube,
embedded in two independently heated electric furnaces
which separated the quartz tube in two heating zones:
one assigned as “PET hydrolysis chamber” and one asinteriores libro.indd 129

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6th International Symposium on Feedstock Recycling of Polymeric Materials

for X-ray film in the absence of CaO (Fig 1), since PETbottles have a higher PET content. However, the same
pyrolysis products were observed from PET bottles andX-ray film. More carbonaceous residue was obtained
from X-ray film than from PET bottles, since X-ray film
might contain high molecular stabilizers.
Table 1. Elemental composition of PET bottles and X-rayfilm.
PET (theoretical)

PET bottle

X-ray filmCarbon

62.5

61.961.5

Hydrogen

4.2

4.3

4.4

Oxygen

33.3

33.7

32.8

Nitrogen--

0.4

Bromine--0.5

Silver--

0.4

The pyrolysis of X-ray film in the presence of CaO
resulted in a strongly increased benzene fraction of 16.9
wt% (yield: 42%) and purity of 78%, respectively. In
accordance with the promotion of the benzene fraction,
carbonaceous residue decreased. Furthermore, the CO2
fraction increased, as well, since the decarboxylation ofcarboxyl groups from TPA was accelerated. The values
from the present experiments are smaller than themaximum benzene yield of 74% and purity of 97%,
reported in our previous work2 due to the inefficienthydrolysis of PET.
0.6

16.9

10080

80

60

79.1

20060

78.0

53.9

40

57.7

26.8

40
46.0

37.7

20

16.0

PET bottle PET bottle X-ray film X-ray film
/CaO
/CaO

:Benzene,

0:TPA and BA,:ResidueFig. 1. Pyrolysis product distribution and benzene purityof the product oil.
1) Hydrolysis of PETOOO CSteamC OCH2 CH2HOOOOHOHTPA2) Decarboxylation of TPAHOOOnPET2OOOOCa2+ CaOCalcium terephthalate0302θ/degree

6090Fig.2. XRD pattern of silver and carbonaceous residue
from the hydrolysis chamber.

4. Conclusions
The aim of this research was the investigation of theeffect of CaO on the recovery rate of silver and benzene
from PET containing X-ray film. From the elemental
analysis, it was confirmed that PET bottles and X-ray film
have a similar elemental composition. In addition,benzene yield and purity from the degradation of X-ray
film were promoted in the presence of CaO, showing
42% and 78% respectively. Furthermore, an average of95% of silver was recovered from the hydrolysis chamber.
Hence, these results imply that the existing process of
converting PET into benzene can be applied to X-ray film,
and possibly also to PET materials containing otherinorganic materials.

References:CO2,:Other liquid products,:Other gaseous products,

Benzene purity[%]

Weight fraction[wt%]20.3

1.4100Ag

Intensity/cps
2000 cps

Elementhydrolyzed in steam atmosphere resulting in TPA. The
produced TPA is adsorbed at the CaO surface forming
calcium terephthalate.3 In a second step, the carboxylgroup of TPA is decarboxylated, resulting in benzene andCaCO3. CaCO3 is decarbonated and CaO is regenerated,allowing readsorption of TPA.
Fig.2 shows XRD pattern of the recovered silver,incorporated in the carbonaceous residue from thehydrolysis chamber. The result indicates that the silver
remained as metallic silver. An average of 95% silver
was recovered from the initial silver content.

+ CaCO3Benzene[1] T. Yoshioka, E. Kitagawa, T. Mizoguchi and T.
Okuwaki. High Selective Conversion of Poly(ethyleneterephthalate) into Oil Using Ca(OH)2. Chem. Lett.
33(2004), 282-283.
[2] G. Grause, T. Handa, T. Kameda, T. Mizoguchi andT.Yoshioka. Effect of temperature management on thehydrolytic degradation of PET in a calcium oxide filledtube reactor. Chem. Eng. J. 166(2011), 523-528.
[3] S. Kumagai, G. Grause, T. Kameda, T. Takano, H.
Horiuchi and T. Yoshioka. Decomposition of Gaseous
Terephthalic Acid in the Presence of CaO. Ind. Eng.
Chem. Res. 50(2011), 1831-1836

Scheme 1. Reaction scheme of the degradation of PET
in the presence of CaO.
Scheme 1 shows the reaction scheme of the degradationof PET in the presence of CaO. At first, PET isinteriores libro.indd 130

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