High selective conversion of poly(ethylene terephthalate) into oil using Ca(OH)2

Article abstract of DOI:10.1246/cl.2004.282

It is a well known fact that sublimation substances, such as benzoic acid and terephthalic acid, are produced in the thermal decomposition of PET, and this causes problems in plastic recycling plants. However, it is clear that the addition of Ca(OH)₂ affects the high selectivity of benzene without producing sublimation substances. The yield of benzene was 35.85 wt % at 700°C and a 10.0 Ca(OH)₂/PET molar ratio. This value means that the selectivity of benzene is 78.8% for liquid products, and 85.1 wt % for aromatic ring in input PET.

Full text of DOI:10.1246/cl.2004.282

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Chemistry Letters Vol.33, No.3 (2004)
High Selective Conversion of Poly(ethylene terephthalate) into Oil Using Ca(OH)2
ꢀ
y
y
Toshiaki Yoshioka, Eisaku Kitagawa, Tadaaki Mizoguchi, and Akitsugu Okuwaki
Research Center of Supercritical Fluid Technology/Research Institute for Environmental Conservation, Tohoku University,
Aramaki-Aoba 07, Aoba-ku, Sendai 980-8579
y
Graduate School of Environment Studies, Tohoku University, Aramaki-Aoba 07, Aoba-ku, Sendai 980-8579
(Received November 19, 2003; CL-031117)
It is a well known fact that sublimation substances, such as
benzoic acid and terephthalic acid, are produced in the thermal
decomposition of PET, and this causes problems in plastic recy-
cling plants. However, it is clear that the addition of Ca(OH)2 af-
fects the high selectivity of benzene without producing sublima-
ꢁ
tion substances. The yield of benzene was 35.85 wt % at 700 C
and a 10.0 Ca(OH)2/PET molar ratio. This value means that the
selectivity of benzene is 78.8% for liquid products, and 85.1 wt
%
for aromatic ring in input PET.
Various methods for plastic recycling technology are now
being developed. One of the proposed technologies is conversion
into oil, and is being investigated by three large plants in Japan.
Polyolephine plastics, such as poly(ethylene), poly(propylene),
and poly(styrene), can be converted into oil via thermal decom-
position. However, thermal decomposition of poly(ethylene ter-
ephthalate) (PET) causes not only corrosion and blockade of pip-
ing but also a failure in efficiency by the generation of a
sublimation substances, such as terephthalic acid and benzoic
acid.
Figure 1. Experimental apparatus.
Table 1. Products of the thermal decomposition of PET and
mixture of Ca(OH)2 /PET
In chemical recycling of PET, solvolysis,1–7 such as hydrol-
ysis, methanolysis, and glycolysis, is well known and utilized by
some commercial plants. These processes are applied mainly to
PET bottle of high purity. However, it is important to extend
these applications to various types of PET materials, such as
film, tape, fiber, and card, and mixed waste plastics. Some stud-
ies were pushed forward to investigate liquefaction of PET. Ma-
Mixture ratio of Ca(OH)2 to PET
Solid / wt %
Residue
0
1
3
5
10
29.73 36.17 26.29 21.40 21.94
29.46 36.10 26.29 21.40 21.94
0.28 0.07 0.00 0.00 0.00
34.99 40.02 43.70 41.58 45.51
9.21 15.95 28.02 31.54 35.85
1.69 2.25 2.62 2.46 2.34
0.47 0.61 0.68 0.54 0.62
1.74 1.67 1.68 1.46 1.36
0.18 0.18 0.00 0.00 0.00
0.23 0.27 0.22 0.00 0.00
0.64 0.51 0.36 0.24 0.16
10.84 8.64 4.12 1.47 0.60
4.16 1.25 0.00 0.00 0.00
0.94 1.29 0.47 0.34 0.30
0.34 0.39 0.00 0.00 0.00
2.28 2.99 3.71 3.02 3.50
0.28 0.32 0.33 0.24 0.25
0.70 0.79 0.17 0.00 0.00
0.00 0.35 0.39 0.27 0.52
0.00 1.28 0.66 0.00 0.00
0.49 0.37 0.27 0.00 0.00
0.81 0.92 0.00 0.00 0.00
35.28 23.81 30.01 37.02 32.55
0.17 0.53 1.42 1.48 1.79
15.37 14.14 14.57 8.78 7.16
1.59 1.76 3.32 3.58 4.62
17.10 6.16 8.75 21.46 17.80
0.96 1.13 1.85 1.58 1.12
0.09 0.10 0.10 0.15 0.07
100.00 100.00 100.00 100.00 100.00
Terephthalic acid
Liquid / wt %
Benzene
Toluene
Ethylbenzene
Stylene
8
ꢁ
suda et al. reported that 56 wt % oil was produced at 500 C
with a steam and geothite catalyst. The oil is consisted of
Benzaldehyde
p-Methylstylene
Indene
4
6 wt % acetophenone, 28 wt % benzene, and 14 wt % phenol.
9
Obuchi et al. reported that thermal decomposition of 15 wt %
PET and 85 wt % PP mixture yielded a 70 wt % oil containing
aromatic and aliphatic hydrocarbons. However, requirements
for liquefaction of PET include the high selectivity of some use-
ful products such as benzene, toluene, xylene, and the lowering
of carbon residue. This paper remarks upon the high selectivity
of benzene without the production of sublimation substances via
the addition of Ca(OH)2.
Acetophenone
Benzoic acid
Naphthalene
5-Ethylindene
0
1,1 -Biphenyl
0
4-Methyl-1,1 -biphenyl
0
1,1 -Methylenebisbezene
Fluorene
A mixture of PET powder (60–100 mesh) of 1 g and
Ca(OH)2 powder was dropped into a reactor made of quartz
and quartz wool over a course of 20 min. The sample was placed
Diphenylmethanone
Phenanthrene
0
1
-[1,1 -Biphenyl-4-yl]ethanone
ꢁ
in the reactor, set at 700 C with a helium flow-rate of 50 mL/
min (see Figure 1). In case of steam addition, water was pumped
Gas / wt %
Hydrogen
Carbon monoxide
Methane
ꢁ
into the second reactor set at 450 C, thus producing steam. The
reaction temperature was measured at the quartz wool contained
in the reactor. The products were then trapped in the gas packs,
using the empty traps containing liquid nitrogen. Quantitative
analyses were conducted using GC–MS, FID and GC–TCD.
Products from the thermal decomposition of PET were clas-
Carbon dioxide
Etylene
Ethane
SUM
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.3 (2004)
283
Acetophenone
Naphthalene
Benzoic acid
Biphenyl
100
Benzene
Toluene
Stylene
1,1‘-Methylenebis-benzene
Indene
8
6
4
2
0
Ca(OH) /PET = 0
2
0
Ca(OH) /PET = 1
2
0
0
0
Ca(OH) /PET= 3
2
Ca(OH) /PET= 5
2
0
2
4
6
8
10
Mixture ratio of Ca(OH)2 to PET
Ca(OH) /PET =10
2
Figure 3. Effect of mixture ratio of Ca(OH)2/PET on selective
of benzene.
0
5
10
15
20
25
Retention time / min
ephthalate. Therefore, produced H2O from Ca(OH)2 accelerates
the hydrolysis of PET, and calcium terephthalate thus formed si-
multaneously. The calcium terephthalate is then decomposed to
benzene and CaCO3, and the later to CaO via decarboxylation.
Generation of sublimation substances, such as benzoic acid
and terephthalic acid, was not recognized over Ca(OH)2/PET
Figure 2. GC-MS total ion chromatogram for products of PET
and Ca(OH)2/PET.
sified into three groups: solids, liquids, and gases, as shown in
Table 1. The GC charts for liquid products are presented in
Figure 2. The values were standardized on the basis of PET
weight. The solids consist of carbon residue and were contained
in terephthalic acid. The maximum yield of solids was 36.17 wt
in Ca(OH)2/PET = 1. The yield decreased with the addition
of Ca(OH)2, moreover, formation of terephthalic acid was not
recognized over Ca(OH)2/PET = 3. The yield of liquids
=
3.
A molar ratio of 1 is ideal for the production of calcium ter-
ephthalate. However, the yield and selectivity of benzene de-
pends on molar ratio of Ca(OH)2. This indicates that raising
the contact efficiency between PET and Ca(OH)2 is important.
The amount of benzene from recycled PET is not enough in
comparison with petroleum industry. However, benzene is one
of the raw chemicals and its application is very wide in many
chemical industries. The selective production of benzene is able
to increase efficiency in oil plant for plastic waste recycling. This
means realization of material cycle by combination with petrole-
um industry.
%
(
45.51 wt %) increased with the addition of Ca(OH)2 for
Ca(OH)2/PET = 10.
The main gas components are carbon monoxide, carbon di-
oxide, hydrogen, methane ethylene, and ethane. Total gas yields
are between ca.23 and 37 wt % in each Ca(OH)2/PET ratio, and
did not depend on the addition of Ca(OH)2. However, the yields
of carbon dioxide and hydrogen increase with decreasing carbon
monoxide. This behavior contributes to the proceeding produc-
tion of calcium terephthalate. The yield of hydrogen also in-
creases with the addition of Ca(OH)2, indicating that water–
gas shift reaction utilizes the H2O produced from the decompo-
sition of Ca(OH)2 and the ethylene glycol from the hydrolysis of
PET. These reactions result in the decrease of residue. We have
been able to conclude that from the addition of Ca(OH)2 the
yields of hydrogen and carbon dioxide have increased, while
the residues and carbon monoxide have decreased, thus confirm-
We thank Ministry of the Environment and Ministry of
Education, Culture, Sports, Science and Technology, Japan.
References
1
2
3
4
Y. W. Awodi, A. Johnson, R. H. Peters, and A. V. Popoola, J.
Appl. Polym. Sci., 33, 2503 (1987).
T. Yoshioka, T. Sato, and A. Okuwaki, J. Appl. Polym. Sci.,
52, 1353 (1994).
A. Oku, L. C. Hu, and E. Yamada, J. Appl. Polym. Sci., 63,
595 (1997).
T. Yoshioka, N. Okayama, and A. Okuwaki, Ind. Eng. Chem.
Res., 37, 336 (1998).
1
0
ing the mechanism for the water–gas shift reaction.
In the case of PET, many products, such as benzene, toluene,
acetophenone, benzoic acid biphenyl etc., are produced. As the
molar ratio of Ca(OH)2/PET is increased the production of all
substances, except benzene, may be controlled; i.e. the selectiv-
ity of benzene is increased. The number of products was decreas-
ed with increasing molar ration of Ca(OH)2.
Figure 3 shows the effect of the molar ratio of Ca(OH)2/
PET for the selectivity of benzene for aromatic ring in input
PET. The selectivity was 38.5 wt % in case of PET, however,
it reached 85.1 wt % for 10 Ca(OH)2/PET molar ratio. This
clearly indicates that the addition of Ca(OH)2 affects the selec-
tivity of benzene. This is caused by the formation of calcium ter-
5
6
T. Spychaj and D. Pszun, Macromol. Symp., 135, 137 (1998).
T. Yoshioka, T. Motoki, and A. Okuwaki, Ind. Eng. Chem.
Res., 40, 75 (2000).
7
8
9
T. Yoshioka, M. Ota, and A. Okuwaki, Ind. Eng. Chem. Res.,
42, 675 (2003).
T. Masuda, Y. Miwa, K. Hashimoto, and Y. Ikeda, Polym.
Degrad. Stab., 61, 217 (1998).
E. Obuchi, M. Suyama, and K. Nakano, J. Mater. Cycles
Waste Manage., 3, 88 (2001).
10 E. Ernst, U. S. Patent, 989955 19110418 (1911).
Published on the web (Advance View) February 9, 2004; DOI 10.1246/cl.2004.282