Effective catalysts derived from waste ostrich eggshells for glycolysis of post-consumer PET bottles

Article abstract of DOI:10.1007/s11696-019-00710-3

Herein, we report an effective chemical recycling of poly(ethylene terephthalate) (PET) using sustainable sources of catalysts, calcium oxide (CaO) derived from ostrich eggshells. The active catalysts were demonstrated in the chemical depolymerization of post-consumer PET bottles. Beverage bottles were proceeded with 1 wt% catalyst derived from ostrich eggshells in the presence of ethylene glycol at 192?°C under atmospheric pressure to give the major product as bis(2-hydroxyethyl terephthalate) (BHET) which was confirmed by melting point, IR spectroscopy, ¹H-, ¹³C-NMR spectroscopy and mass spectrum. The catalyst could fully depolymerize PET within 2?h, producing a good yield of highly pure BHET monomer. The catalysts were successfully characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy analysis (FE-SEM), and thermo-gravimetric analysis (TGA). Furthermore, catalysts derived from chicken eggshells, geloina, mussel, and oyster shells were run to compare the catalytic activities. For better understanding of catalytic parameters, effects of calcination temperatures of catalyst, weight ratio of catalyst, ratio of weight of solvent, and time of depolymerization for the ostrich eggshells catalyst were also investigated.

Full text of DOI:10.1007/s11696-019-00710-3

Chemical Papers
https://doi.org/10.1007/s11696-019-00710-3
ORIGINAL PAPER
Efective catalysts derived ꢀrom waste ostrich eggshells ꢀor glycolysis
oꢀ post‑consumer PET bottles
Isti Yunita1,2 · Siraphat Putisompon · Peerapong Chumkaeo · Thinnaphat Poonsawat · Ekasith Somsook
1
1
1
1
Received: 21 October 2018 / Accepted: 5 February 2019
©
Institute of Chemistry, Slovak Academy of Sciences 2019
Abstract
Herein, we report an efective chemical recycling oꢀ poly(ethylene terephthalate) (PET) using sustainable sources oꢀ catalysts,
calcium oxide (CaO) derived ꢀrom ostrich eggshells. The active catalysts were demonstrated in the chemical depolymeriza-
tion oꢀ post-consumer PET bottles. Beverage bottles were proceeded with 1 wt% catalyst derived ꢀrom ostrich eggshells
in the presence oꢀ ethylene glycol at 192 °C under atmospheric pressure to give the major product as bis(2-hydroxyethyl
1
13
terephthalate) (BHET) which was conꢁrmed by melting point, IR spectroscopy, H-, C-NMR spectroscopy and mass
spectrum. The catalyst could ꢀully depolymerize PET within 2 h, producing a good yield oꢀ highly pure BHET monomer.
The catalysts were successꢀully characterized by X-ray powder difraction (XRD), X-ray photoelectron spectroscopy (XPS),
ꢁ
eld-emission scanning electron microscopy with energy dispersive X-ray spectroscopy analysis (FE-SEM), and thermo-
gravimetric analysis (TGA). Furthermore, catalysts derived ꢀrom chicken eggshells, geloina, mussel, and oyster shells were
run to compare the catalytic activities. For better understanding oꢀ catalytic parameters, efects oꢀ calcination temperatures
oꢀ catalyst, weight ratio oꢀ catalyst, ratio oꢀ weight oꢀ solvent, and time oꢀ depolymerization ꢀor the ostrich eggshells catalyst
were also investigated.
Keywords Ostrich · Eggshells · Glycolysis · Poly(ethylene terephthalate) · Depolymerization
Introduction
This material is considered as a harmꢀul substance that
causes chain oꢀ environmental damages (Webb et al. 2013).
Thus, this phenomenon, an issue related to human viability,
is the main reason ꢀor PET waste recycling to gain more
attentions today (Khoonkari et al. 2015).
Drinking bottles are plastics made ꢀrom poly(ethylene tere-
phthalate) (PET) with the highest consumption growth.
The demand ꢀor poly(ethylene terephthalate) bottles is pro-
gressing with dramatic applications in beverage containers
Four major approaches have been proposed ꢀor PET recy-
cling: “in-plant” recycling, mechanical recycling, chemi-
cal recycling and energy recovery through incineration
(López-Fonseca et al. 2010). However, some researchers
have endeavored to develop methods that essentially involve
the recovery oꢀ monomers and the production oꢀ chemicals
with attractive added value or intermediates oꢀ PET wastes.
Among those methods, chemical recycling materials show
the highest consistency with the principle oꢀ sustainable
development leading to the recovery oꢀ raw materials ꢀrom
PET which have been made (Imran et al. 2013).
(
López-Fonseca et al. 2011). PET resins are also in demand
ꢀ
or ꢂexible packaging ꢁlms due to its high clarity, low per-
meability, and excellent printing capabilities. However, PET
waste poses an indirect hazard to the environment. It has
high resistance to atmospheric and biological substances.
*
Ekasith Somsook
ekasith.som@mahidol.ac.th
1
NANOCAST Laboratory, Center ꢀor Catalysis Science
and Technology, Department oꢀ Chemistry and Center
oꢀ Excellence ꢀor Innovation in Chemistry, Faculty
oꢀ Science, Mahidol University, 272 Rama VI Rd., Thung
Phaya Thai, Ratchathewi, Bangkok 10400, Thailand
There are several chemical recycling methods proposed
ꢀor PET depolymerization, such as hydrolysis, methanoly-
sis, ammonolysis, aminolysis, and glycolysis. The glycolysis
is the most efective method ꢀor the production oꢀ a high-
priced virgin monomer, bis(2-hydroxyethyl terephthalate)
2
Department oꢀ Chemistry Education, Yogyakarta State
University, Colombo Road No. 1, Yogyakarta 55281,
Indonesia
(
BHET) by breaking down the ester bond ꢀollowed by the
Vol.:(0
1
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Chemical Papers
replacement oꢀ the hydroxyl terminal (George and Kurian
014). This product can be easily integrated into a conven-
nanotubes (MWCNT) as a sustainable and ꢀriendly cata-
lyst in PET glycolysis with 100% yield oꢀ BHET at 190 °C
ꢀor 2 h. Using metal oxide as a catalyst in the glycolysis
can be a promising alternative process in addition to using
conventional catalysts. It is associated with high monomer
yield, high mechanical strength, high reusability, and ease oꢀ
separation. More over, low temperatures succesꢀully applied
in those work (Al-Sabagh et al. 2016), although, the high
quality oꢀ catalyst was diꢃcult to be denied as it was an
important ꢀactor to enhance the percentage oꢀ yield.
2
tional PET manuꢀacturing plant. Furthermore, this monomer
can be used as a building block ꢀor other polymer syntheses
with higher economic value, ranging ꢀrom unsaturated poly-
ester resins and polyethylene terephthalate (PET) to a new
biocompatible system (Wang et al. 2009). From these points
oꢀ views, it can be concluded that this process is promising
ꢀ
or environmental sustainability.
Catalysts play a key role in the glycolysis to obtain a max-
imum yield (Nica et al. 2015). One oꢀ the various catalysts
commonly used in PET glycolysis is zinc acetate, as the
activation oꢀ reaction by this catalyst is remarkable (Xi et al.
The aims oꢀ this investigation are to prepare Ca-based
metal oxide derived ꢀrom by-products oꢀ ꢀood sources and
then to apply them as catalysts in the glycolysis oꢀ waste
drinking bottles made ꢀrom PET to solve waste problems.
The sources oꢀ calcium to be used are household wastes
ꢀrom eggshells and seaꢀood shells. To the best oꢀ our knowl-
edge, there is no report on the production oꢀ calcium oxide
ꢀrom ostrich eggshells, chicken eggshells or various shells as
catalysts ꢀor the glycolysis oꢀ poly(ethylene terephthalate).
In this study, calcium oxide catalysts made ꢀrom various
calcium sources were prepared, characterized and tested in
the glycolysis oꢀ waste drinking bottles made ꢀrom PET.
2
005). Other salts, such as metal acetate (Co, Pb, and Mn)
Ghaemy and Mossaddegh 2005), chloride (Zn, Li, Didym-
ium, Mg, and Fe) (Pingale et al. 2010), titanium phosphate
Troev et al. 2003), hydroxide (Li, K) (Shukla and Harad
005; Nikje and Nazari 2007), sulphate (Na, K) (Shukla and
Harad 2005), and sodium carbonate (Duque-Ingunza et al.
(
(
2
2
013; Shukla and Kulkarni 2002) have been investigated.
Recently, a series oꢀ novel catalysts in the process oꢀ glyco-
lysis, including Lewis acid ionic liquids (Al-Sabagh et al.
2
014; López-Fonseca et al. 2010; Wang et al. 2009) and
metal oxides (Imran et al. 2011, 2013), have been studied. In
addition, diferent methods ꢀor using microwave irradiation
on PET glycolysis have also been reported (Choudhary et al.
Experimental
2
013; Pingale and Shukla 2008), but it has a shortcoming
Materials
like the use oꢀ a sophisticated set oꢀ instruments. However,
these ionic liquids catalyst is impractical in synthetic pro-
cess, has high toxicity and erosivity, lower percentage in
PET conversion and BHET selectivity compared to metal
oxide as a catalyst (Al-Sabagh et al. 2014; Imran et al. 2011,
Post-consumer PET bottles were collected, ꢀurther cleaned,
2
and cut into 3 × 3 mm square chips aꢀter lids, label and
bottom parts were removed. Flake PET was cleaned by
−
3
1 mol dm oꢀ sodium hydroxide solution, type 1 ultrapure
water and dried at 80 °C ꢀor 12 h. Ethylene glycol (EG)
(analytical grade) was purchased ꢀrom RCI Labscan. Ostrich
eggshells, chicken eggshells, oyster shells, geloina shells,
and mussel shells were collected ꢀrom local markets.
2
013; López-Fonseca et al. 2010; Wang et al. 2009). Many
eforts have been made by researchers to ꢁnd afordable
catalysts and reaction systems.
Various heterogeneous catalysts based on metal oxides
have been tested in PET glycolysis. Imran et al. (2013)
reported that mixed-oxide spinels showed high catalytic
activity when tested on PET glycolysis at 260 °C with a pres-
sure under 5.0 atm. Park et al. (2012) investigated glycolysis
oꢀ post-consumed PET using graphene oxide–manganese
nanocomposite (GO–Mn O ) in a stainless-steel batch auto-
Preparation of catalysts
All shells were cleaned and dried beꢀore crushing and siꢀt-
ing to yield powder. The dried waste shells are calcined at
a temperature oꢀ 600–1000 °C in the air atmosphere with a
3
4
−
1
clave reactor at 300 °C and 1.1 MPa ꢀor 80 min. The lowest
heating rate oꢀ 5 °C min ꢀor 5 h. All calcined samples are
stored in a desiccator to avoid moisture in the air beꢀore use.
amount oꢀ Mn O loading on graphene oxide (GO) yields
3
4
the highest percentage oꢀ BHET about 96.4%, whereas in
PET glycolysis with Mn O without graphene oxide (GO)
Glycolysis of PET
3
4
produced 82.7% yield oꢀ BHET. Bartolome et al. (2014)
reported the high yields oꢀ BHET aꢀter 1 h oꢀ glycolysis at
Each experiment was repeated ꢀor 3 times. The glycolysis
3
3
00 °C using γ-Fe O nanoparticles.
reaction was set in a 100 cm two-neck round bottle equipped
2
3
The utilization oꢀ high temperature, sophisticated appa-
with a magnetic stirrer with condenser and thermometer. 5 g
oꢀ ꢂake PET, desired catalyst (the weight ratio oꢀ catalyst to
EG oꢀ 0.01, 0.02, 0.05, 0.1), and ethylene glycol (the weight
ratio oꢀ EG to PET oꢀ 5, 10, 15, 20) were mixed and the
ratus and high pressure is seen as major disadvantages ꢀor
the use oꢀ these catalysts in PET glycolysis. Al-Sabagh et al.
(
2016) reported that Fe O -boosted multiwalled carbon
3 4
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Chemical Papers
1
13
reaction temperature was set at 192 °C with varying reaction
times (in the range 1 until 4 h). Aꢀter completion oꢀ glyco-
lysis, the obtained product was ꢀrozen ꢀor 12 h ꢀollowed by
H- and C-NMR spectra oꢀ the isolated product in
DMSO-d were collected on a 400-MHz Bruker Avance
6
NMR Spectrometer. The NMR parameters were set up at 16
3
extraction with 500 cm oꢀ boiling distilled water. The mix-
and 512 scans, relaxation times oꢀ 1 s and 1.5 s, pulse widths
1
13
ture was separated into solid and liquid phases by ꢁltration.
The solids were washed, dried, and weighed as oligomers.
All ꢁltrates were heated at 90 °C until a clear extract solu-
tion existed. Flake BHET obtained ꢀrom the liquid phase
with vacuum ꢁltration aꢀter being stored in ꢀreezer at 0 °C
oꢀ 15 and 11 μs ꢀor H- and C-NMR spectra, respectively.
Gas chromatography with mass spectrometry (GCMS) spec-
tra were obtained by Agilent 7950 (GC) and Agilent 5975
(MS) with an HP-5 capillary column. Electrospray ioniza-
tion (ESI, m/z) mass spectrometry was perꢀormed using
microTOF in positive ion mode. Fourier transꢀorm-inꢀrared
spectroscopy (FT-IR) analysis was perꢀormed using Perkin
Elmer Series Spectrometer (Frontier Model), in the range
ꢀor 12 h was transꢀerred to a chiller ꢀor 24 h.
The obtained BHET ꢂakes were then washed with cold
water and dried at 80 °C ꢀor 12 h and the weight oꢀ the
BHET result was used ꢀor the calculation oꢀ yield oꢀ BHET.
The conversion oꢀ PET is deꢁned by Eq. (1) and yield oꢀ
BHET product was calculated by Eq. (2).
−
1
oꢀ 4000–400 cm .
Results and discussion
u
1
Conversion of PET =
× 100%
(1)
u
0
Morphology, structure and elemental analyses
of catalysts
ꢀ
ꢁ
m ∕MW
1
BHET
Yield of BHET = ꢀ
ꢁ × 100%
(2)
The XRD patterns oꢀ calcined shells are shown in Fig. 1. All
samples were calcined at 1000 °C ꢀor 5 h. Aꢀter calcination,
m ∕MW
0
PET
it was observed ꢀor the transꢀormation oꢀ CaCO to CaO ꢀor
In the equation, u , u represented initial weight and unde-
3
0
1
seaꢀood shells and eggshells. The main difraction peak was
in good agreement with the JCPDS card no. 00-002-1088
ꢀrom typical cubic CaO crystals. Thereꢀore, the occurrence
oꢀ intense and narrow peaks in calcined solids deꢁnes the
crystal structure oꢀ calcium oxide as a compound, indicating
that the catalyst must be activated thermally beꢀore being
used in the reaction oꢀ glycolysis. In addition, traces oꢀ
polymerized weight oꢀ PET. m , m represented theoretical
0
1
weight and actual weight oꢀ BHET. MW
and MW
PET
BHET
−
1
reꢀer to the molecular mass oꢀ BHET which is 254 g mol
−
1
and PET repeating unit which is 192 g mol , respectively.
Characterization
Ca(OH) impurities derived ꢀrom the reaction oꢀ CaO and
2
The morphology, structure and elemental analyses oꢀ cal-
cium oxide ꢀrom waste shells-derived catalyst were utilized
by ꢁeld-emission scanning electron microscopy (FE-SEM,
Hitachi SU8010) which has SE resolution 1.3 nm and ꢁeld
emission tip as the ꢁlament source. The micrographs were
taken in various magniꢁcations at electron acceleration volt-
age oꢀ 4.0 kV. Using the same instrument, the analysis by
energy dispersive X-ray spectroscopy (EDX) was conducted
at electron acceleration voltage oꢀ 15 kV.
water in the air were ꢀound at 2θ oꢀ 18.3° in a good agree-
ment with the JCPDS card no. 87-0674.
X-ray photoelectron spectroscopy (XPS) was obtained
ꢀ
rom Axis Ultra DLD, Kratos Analytical Ltd., UK.
X-ray powder difraction (XRD) characterization oꢀ the
waste-shells catalyst was completed using Bruker D8
Advance difractometer (Germany) with Cu-Kα radiation
(
λ=0.15418 nm), 30 kV and 15 mA over a 2θ range oꢀ 10°
to 80° with a step size oꢀ 0.02° at a scanning speed oꢀ 6°/
min.
Thermo-gravimetric analysis–diferential scanning calo-
rimetry (TGA–DSC) was perꢀormed using a TA instruments
−1
SDT2960 simultaneous at the heating rate oꢀ 20 °C min in
the range ꢀrom room temperature to 900 °C under nitrogen
gas.
Fig. 1 XRD patterns oꢀ a geloina, b chicken, c mussel, d oyster, e
ostrich eggshells
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Chemical Papers
Due to the excellent mechanical properties oꢀ ostrich egg-
shells, they were selected ꢀor the ꢀurther studies in the calci-
nation oꢀ samples at diferent temperatures ꢀor 5 h as shown
in Fig. 2. In the difractograms oꢀ uncalcined ostrich egg-
shells and calcined ostrich eggshells at 600 °C and 700 °C,
The CaO lattice constant oꢀ the sample is determined by
identiꢀying the peak position (2θ) oꢀ the XRD pattern using
Bragg’s Law. The lattice constants in the sample were ꢀound
to be 4.7418 Å, which corresponded to the lattice constant
in pure CaO.
the peaks associated with CaCO at 2θ=23°, 30°, 37°, 44°,
The morphology and elemental analyses oꢀ shells were
examined by FE-SEM/EDX at 4.0 kV and 15 kV oꢀ the
acceleration voltage, respectively, aꢀter coating with Pd/Pt,
due to the non-conductivity oꢀ calcium oxides as shown in
Figs. 3 and 4. Calcined chicken, geloina, mussel and oyster
shells in Fig. 3 show the morphological similarities oꢀ par-
ticles with calcined ostrich eggshells. The calcined waste
shells showed a regular shape and most oꢀ them were bound
together as aggregates with varying aggregate sizes. How-
ever, larger sizes oꢀ aggregates were observed on ostrich
eggshells, which were detected as groups oꢀ agglomerated
particles ꢀrom small particles, ranging up to several tens
oꢀ microns (Viriya-empikul et al. 2012). In this case, the
smaller grain size and aggregate provided a higher speciꢁc
surꢀace area. On the other hand, the higher magniꢁcation
showed the layered surꢀaces which were the same charac-
teristic oꢀ cracking on the all types oꢀ shells.
3
4
8°, 49°, 58°, 61°, and 65.2° (in the agreement with JCPDS
ꢁ
le no. 47-1743) were observed. As the temperature ꢀor the
calcination increased, it resulted in the change in the compo-
sition oꢀ the ostrich eggshells. The peaks ꢀor calcined ostrich
eggshells at 1000 °C ꢀor 5 h showed identical, clear and
sharp reꢂection peaks at 2θ oꢀ 35°, 38°, 54°, 64° and 68°,
the characteristic peaks oꢀ calcium oxide (JCPDS ꢁle no.
0
0-002-1088), which indicates a single crystalline phase.
The presence oꢀ irregular particle shapes ꢀrom ostrich
eggshells at Fig. 4 beꢀore calcination was signiꢁcant. The
size oꢀ the calcined ostrich eggshells particles decreased and
the shape oꢀ the particles became more regular along with
the calcination process. The microstructural architectures oꢀ
shells were not changed drastically ꢀrom layered to porous
structures (Buasri et al. 2013).
The small particles in the calcined ostrich eggshells com-
bined to make large agglomerates that could be observed
aꢀter calcination at a temperature oꢀ 800 °C and continue to
enlarge aꢀter calcination at a temperature oꢀ 1000 °C. The
agglomeration oꢀ the calcined catalyst was caused by the ꢀor-
mation oꢀ suꢃciently uniꢀorm oxides. Changes in the shells
structure could be caused by changes in composition. Cal-
cium carbonate which was a largest part oꢀ the components
Fig. 2 XRD patterns oꢀ a uncalcined ostrich eggshells, calcined
ostrich eggshells at b 600 °C, c 700 °C, d 800 °C, e 900 °C, f
1
000 °C
Type of Catalysts
Level of
Magnification
Chicken
Geloina
Mussel
Ostrich
Oyster
2.0 k
40.0 k
Fig. 3 FE-SEM images oꢀ calcium oxide particles obtained ꢀrom calcined diferent shells
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Chemical Papers
Temperature of Calcination
700 °C 800 °C
Level of
Magnific
ation
Uncalcined
600 °C
900 °C
1000 °C
2.0 k
40.0 k
Fig. 4 FE-SEM images oꢀ ostrich eggshells obtained ꢀrom diferent temperatures oꢀ calcination
Table 1 Elemental analysis oꢀ the calcined catalysts at 1000 °C,
a temperature below 700 °C and the other stage occurring
between 700 and 800 °C. The waste eggshells were ana-
lyzed by TGA/DSC to determine the appropriate calcina-
tion temperature to produce calcium oxide as the catalyst
uncalcined ostrich eggshells and their atomic/weight concentrations
(
%) determined by FE-SEM–EDX
Catalyst
Weight % oꢀ element
Atomic % oꢀ ele-
ment
ꢀor glycolysis. The thermal behaviors oꢀ diferent type uncal-
Ca K
O (K)
Ca K
O (K)
cined catalysts showed the similar pattern oꢀ TGA curve,
which had a diferent stage oꢀ weight loss. At a temperature
below 370 °C, it was associated with evaporation oꢀ mois-
ture which was physically trapped in the eggshells and also
removing the organic matter; ꢀurthermore, the weight loss
continued aꢀter 370 °C–550 °C associated with dehydration
Chicken
Geloina
Mussel
Oyster
Ostrich
Uncalcined ostrich
60.55
54.46
54.41
49.96
65.26
47.00
39.45
45.54
45.59
50.04
34.74
53.00
37.99
32.32
32.27
28.50
42.85
26.15
62.01
67.68
67.73
71.50
57.15
73.85
oꢀ Ca(OH) (~4 wt%). The next decomposition was occurred
2
ꢀ
rom 700 °C and end around 800 °C, ꢀound throughout 5
samples, which showed the dissociation oꢀ remaining
organic material and the presence oꢀ calcium carbonate. The
major weight loss around those temperatures,~42 wt%, was
contained in the shell broken down into CaO by evolving
carbon dioxide upon the heating process.
due to the transꢀormation oꢀ CaCO phase to CaO phase
3
The ostrich eggshells that were calcined at 600 °C and
and carbon dioxide as the by-product. As the sample weight
remained constant aꢀter 800 °C and the main composition oꢀ
the sample calcined at and above 900 °C is calcium oxide,
conꢁrmed by XRD difraction, the temperature oꢀ 1000 °C
was suitable ꢀor the use as the calcination temperature to
ensure complete conversion into CaO, conꢁrmed by the
TGA and DSC curves (Viriya-empikul et al. 2012). The
results oꢀ the TGA analysis were supported by the results
oꢀ the DSC analysis. The endothermic peak that occurred at
7
00 °C exhibited irregular and modulated non-uniꢀorm
particle shapes. Furthermore, ostrich eggshells which were
calcined at higher temperatures, aꢀter 800 °C, showed micro-
structures oꢀ calcium oxide. Aꢀter applying the high tem-
perature oꢀ calcination, the morphology oꢀ the catalyst was
changed ꢀrom irregular shapes to interconnected ꢀorms such
as skeletal structures. Some surꢀace cracks in SEM images
were observed ꢀrom the changing oꢀ the calcination tempera-
ture in SEM images. In addition, calcium oxide as a neces-
sary active site in the reaction oꢀ glycolysis is successꢀully
produced, which is supported by XRD difractogram.
Analysis oꢀ the elemental composition oꢀ samples is
shown in Table 1. The elements determined were Ca and
O. Calcined ostrich eggshells had the highest calcium and
oxygen deposits on the outer surꢀace, each oꢀ which was
760 °C proved the decomposition oꢀ CaCO to CaO.
3
A slightly diferent ꢁnding in the TGA curve in each shell
was in agreement with Mohamad et al. (2016) that smaller
particles undergo rapid changes compared to larger particles.
This observation may be due to the large surꢀace area associ-
ated with smaller particle size that contributes to higher heat
exchange rates needed to promote decomposition (Mohamed
et al. 2012).
6
5.26% and 34.74% by weight oꢀ the element. The amounts
oꢀ calcium in calcined oysters and uncalcined ostrich egg-
shells were slightly diferent.
X-ray photoelectron spectroscopy (XPS) is the important
technique ꢀor the elucidation oꢀ the catalyst surꢀace com-
position and the chemical state oꢀ its constituent elements.
Table 2 shows the binding energy (BE) values (in eV) and
As shown in Fig. 5, the thermograms oꢀ uncalcined
samples show two diferent stages oꢀ weight loss: one at
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Chemical Papers
Fig. 5 TGA curves oꢀ a geloina, b mussel, c chicken, d oyster, e ostrich, f all shells
atomic concentration values (in %) oꢀ elements ꢀrom ostrich
and calcined ostrich eggshells.
and carbon element. In the uncalcined ostrich eggshells
(Fig. 6), the relative mass ratio ꢀor oxygen, calcium and car-
bon is 37.82%, 29.14% and 33.03%, respectively. On the
contrary (Fig. 7), aꢀter calcination at 1000 °C, the resultant
The XPS data revealed that the uncalcined and calcined
ostrich eggshells predominantly conꢁned oxygen, calcium
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Chemical Papers
Table 2 Binding energy values oꢀ the constituent elements oꢀ uncal-
cined and calcined eggshells and their atomic concentrations (%)
determined by XPS
Element
Uncalcined ostrich eggshell Calcined ostrich eggshell
at 1000 °C
BE (eV)
% atomic con- BE (eV)
centration
% atomic
concentra-
tion
O 1s
531.2
–
–
40.47
530.8
531.8
533.4
32.1
15.7
1.5
Total O
Ca 2p
Ca 2p
Ca 2p
Ca 2p
49.3
6.1
7.4
3.1
3.4
–
–
8.45
–
346.3
347.2
349.7
350.6
347.0
–
350.6
4
Total Ca
12.45
20
displayed mainly three typical peaks oꢀ O 1s, Ca 2p, and
C 1s in relative mass ratios between oxygen and calcium
ꢀ
or 1:1, vis. 40.34%, 40.84%, and 18.82%, respectively. The
Ca 2p spectrum on the calcined ostrich eggshells, showed
2
+
ꢀ
our relative calcium species, which corresponded to Ca
3
/2
in CaO, in the ꢀorm oꢀ Ca 2p (346.3 eV) and (347.2 eV),
1
/2
Ca 2p (349.7 eV) and (350.6 eV). The C 1s spectrum
could be deconvoluted into three peaks corresponding to
the presence oꢀ carbon and organic matter (284.5 eV), C–O
(
285.8 eV), and O–C–O and C=O (289.4 eV) ꢀunctional
groups. In addition, the deconvolution oꢀ the O 1s spectrum
at calcined ostrich eggshells revealed peaks originating
2
−
ꢀ
rom O (530.8 eV) were determined to be metal oxide,
adsorbed water (H O at 533.4 eV), predominant existence
2
−
oꢀ OH groups (531.8 eV).
Efect oꢀ diferent catalysts on the depolymerization
oꢀ drinking water bottles
The ꢀormation oꢀ calcium oxide in each shell aꢀter calcina-
tion at the temperature oꢀ 1000 °C was the main reason ꢀor
using calcined eggshells at 1000 °C to study the efects oꢀ
various shells in the reaction oꢀ glycolysis. Glycolysis reac-
tion with commercial zinc acetate (Zn(OAc) ) as the catalyst
2
was set as a controlled experiment. Zinc salt is a well-known
catalyst used in glycolysis with high-yield products. From
this work, 75% yield oꢀ BHET was obtained using 1 wt%
oꢀ commercial Zn(OAc) . This result was slightly diferent
2
with the reaction using calcined ostrich eggshells which can
produce 76% yield oꢀ BHET (Fig. 8). Catalysts derived ꢀrom
ostrich eggshells showed the best catalytic activity which
produced the highest yield percentage and were selected ꢀor
the ꢀurther studies. According to the result in Fig. 8, the
higher calcium content in the catalyst did not guarantee the
Fig. 6 XPS spectra oꢀ uncalcined ostrich eggshells showing the ꢁtted
peaks a Ca 2p, b O 1s, c C 1s
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Fig. 8 The efect oꢀ diferent catalysts on the yield oꢀ BHET. Reac-
tion was set at 192 °C ꢀor 2 h. All types oꢀ catalyst were loaded at 1
wt% into each batch and the ratio between PET and ethylene glycol
was 1:15. 100% conversion
and 61% yield oꢀ BHET, respectively. Both oꢀ these catalysts
contained around 54% by weight oꢀ calcium.
Efect oꢀ calcination temperatures oꢀ catalysts
The efect oꢀ calcination temperature oꢀ catalysts derived
ꢀ
rom ostrich eggshells on the glycolysis was investigated
as shown in Fig. 9. It was clear that increase in temperature
or calcination oꢀ catalyst increased the catalytic activities.
ꢀ
According to XRD data, the peak oꢀ CaO became clearer
and was ꢀormed by increasing the temperature oꢀ calcination.
No signiꢁcant ꢀouling or second phase was detected, which
showed that high purity oꢀ CaO was obtained. The crystal-
linity oꢀ CaO increased linearly during the sintering process
until the calcination temperature reaches 1000 °C. This was
the reason that catalyst derived ꢀrom ostrich eggshells cal-
cined at 1000 °C was proved to be the most efective cata-
lyst. Hereaꢀter, in the case oꢀ ostrich eggshells, based on
the TGA/DSC analysis, it was shown that the conversion oꢀ
CaCO into CaO occurred exquisitely at temperatures above
3
9
00 °C which were ꢀollowed by completely releasing oꢀ CO
2
(
Tan et al. 2015).
Efect oꢀ weight ratio oꢀ PET–ethylene glycol
In our study, the efect oꢀ weight ratio oꢀ PET–ethylene gly-
col (EG) on the resulting product yield was also investigated
as shown in Fig. 10. It can be seen that the observed cata-
lyst perꢀormance increased when the weight ratio oꢀ PET to
ethylene glycol applied in glycolysis system with catalyst
derived ꢀrom ostrich eggshells calcined at 1000 °C was 1:15.
On the other hand, when the weight ratio oꢀ PET–ethylene
Fig. 7 XPS spectra oꢀ calcined ostrich eggshells at 1000 °C showing
the ꢁtted peaks a Ca 2p, b O 1s, and c C 1s
higher yield oꢀ BHET products. This ꢀact was consistent
with data obtained in glycolysis reactions using catalysts
derived ꢀrom mussel and geloina shells which produced 63%
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Fig. 9 The efect oꢀ calcination temperatures on the catalytic activity
Fig. 11 The efect oꢀ weight ratio oꢀ catalyst–PET on the yield oꢀ
BHET. Reaction was set at 192 °C ꢀor 2 h, 5 g oꢀ PET. The ratio
between PET and ethylene glycol was 1:15. 100% conversion
oꢀ ostrich eggshells ꢀor glycolysis oꢀ water bottles. Reaction was set at
1
92 °C ꢀor 2 h. All types oꢀ catalyst were loaded at 1 wt% into each
batch and the ratio between PET and ethylene glycol was 1:15. 5% oꢀ
conversion on the 600 °C and 7% oꢀ conversion on the 700 °C
Fig. 12 The efect oꢀ depolymerization time on the yield oꢀ BHET.
Reaction was set at 192 °C, 5 g oꢀ PET. Catalyst was loaded at 1 wt%
into each batch. The ratio between PET and ethylene glycol was 1:15.
Fig. 10 The efect oꢀ weight ratio oꢀ PET–EG on the yield oꢀ BHET.
Reaction was set at 192 °C ꢀor 2 h, 5 g oꢀ PET. Catalyst was loaded at
1
00% conversion
1
wt% into each batch. 100% conversion
Efect oꢀ weight ratio oꢀ catalyst–PET
glycol was less than 1:15, the percentage oꢀ BHET was
below 70%. Due to an increase in the PET–EG ratio, this
will lead to an increase in the rate oꢀ decomposition and pro-
duce oligomers oꢀ lower molecular weight. However, when
the ratio oꢀ PET–EG reaches the optimal value, there will
be a balance between EG, oligomers, and ꢁxed BHET, so
that the degradation rate reaches a constant value. Whereas,
a high proportion oꢀ PET–EG ratio, resulted in mixing diꢀ-
The efects oꢀ catalyst loading were investigated and the
results are demonstrated in Fig. 11. A similar catalytic per-
ꢀ
ormance in the 100% conversion was observed ꢀor the cata-
lyst derived ꢀrom ostrich eggshells calcined at 1000 °C. The
major component oꢀ catalyst was calcium oxide. Thereꢀore,
the BHET production was investigated ꢀor the ratio oꢀ cal-
cium oxide–PET. By increasing the catalytic loading to 5%
ꢁ
culties in the glycolysis reactions (Jehanno et al. 2018).
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Fig. 13 1H- and 13C-NMR spectra oꢀ BHET product
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3

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Fig. 14 a GC chromatogram oꢀ
BHET product, b mass spec-
trum oꢀ BHET product
by weight and continued to 10% by weight, the catalytic
activities oꢀ catalyst were lowered. The high possibility may
be due to the high composition oꢀ calcium in the system
inducing generated oꢀ by-product ꢀrom the side reactions.
The highest yield oꢀ glycolysis product is obtained at 1%
by weight oꢀ catalyst loading, which has 100% conversion
and 76% oꢀ BHET yield. This result was promising as com-
pared to the percentage yield produced by the reaction using
commercial zinc acetate as a catalyst. Likewise, reduction
in yield was obtained due to reduction in catalyst loading,
which resulted in 36% oꢀ oligomers and 64% oꢀ BHET,
reꢀerring to Fig. 11. The reduction in BHET results was
continued by increasing the catalyst concentration to 5% by
weight oꢀ the substrate.
Efect oꢀ the depolymerization time
To determine the efect oꢀ depolymerization time on the
yield oꢀ product, the glycolysis oꢀ PET was perꢀormed using
1 wt% oꢀ catalyst derived ꢀrom ostrich eggshells calcined at
Fig. 15 ESI–MS spectrum oꢀ BHET product
Fig. 16 FTIR spectra oꢀ BHET product
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Table 3 Functional group ꢀrequencies oꢀ BHET determined by FTIR
Zhao et al. 2018)
ꢀrom the benzene ring (δ =8.12 ppm, s, 4H). Signals at δ
H
(
4
.32 ppm and δ 3.71 ppm were characteristics oꢀ the meth-
ylene protons oꢀ CH –COO (δ = 4.32 ppm, t, 4H) and
Wave number
Types oꢀ vibration
Functional groups
2
H
−
1
(
cm
)
CH –OH (δ =3.71 ppm, m, 4H), respectively. The signal
2 H
at δ 4.99 ppm was the characteristic oꢀ the hydroxyl proton
δ =4.99 ppm, t, 2H) (Imran et al. 2013).
3
2
2
1
1
1
1
448.72
963.96
880.14
716.11
504.25
411.59
135.40
Stretching
Stretching
Stretching
Stretching
Stretching
Stretching
Stretching
O–H band
C–H alkyl
C–H alkyl
C=O group
C=C aromatic
C=C aromatic
C–O band
(
H
1
3
In the C-NMR spectrum, the signal at 59.00 ppm
represented the carbon in the methylene group adjacent
to the hydroxyl group, and the signal at 67.06 ppm indi-
cated the presence oꢀ carbon in the methylene group next
by the –COO– group. Signals at 129.54 and 133.76 ppm
were given aromatic carbon associated with the hydrogen
and –COO– groups, respectively. The signal at 165.19 ppm
indicates carbon in the –COO– group. The NMR spectrum
oꢀ the monomers produced in this study is identical to that
reported in the literature (Lima et al. 2017) and veriꢁes the
high purity level oꢀ the monomers produced.
1
000 °C as shown in Fig. 12. It can be seen that the BHET
yield increases by lengthening the reaction time. In the
presence oꢀ the catalyst, the PET conversion reached 100%
within 1 h with 33% oꢀ the BHET yield. The yield oꢀ BHET
increased to 71% as the reaction time was extended to 1.5 h.
Furthermore, when the reaction time was extended to 2 h,
the BHET yield reached the highest value oꢀ 76%. The aug-
ment oꢀ reaction time ꢀor more than 2 h does not show a
signiꢁcant increase in BHET.
The main product obtained in PET glycolysis on ethylene
glycol catalyzed by calcined ostrich eggshells at 1000 °C
was conꢁrmed by GC–MS (Fig. 14). The product showed a
high purity, since no extra peak was ꢀound. It is clear ꢀrom
ESI–MS in Fig. 15 that the peak up to m/z 277 was obtained.
+
This peak was related to the main product ionized by Na (in
+
To conꢀirm that the major product oꢀ glycolysis was
electrospray ionization, the ꢀraction can be ionized by H ,
1
13
+
+
BHET, H- and C-NMR spectra oꢀ the BHET prod-
Na , or K ). Thus, the molecular weight oꢀ the main product
−
1
uct were conꢁrmed as shown in Fig. 13. The signal at δ
was 254 g mol , the amount equal to the molecular weight
oꢀ the BHET.
8
.12 ppm indicated the presence oꢀ ꢀour aromatic protons
Scheme 1 A proposed mechanism oꢀ the glycolysis oꢀ PET catalyzed by CaO
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3

Chemical Papers
The FTIR (KBr) spectrum oꢀ the puriꢀied monomer
clearly is shown in Fig. 16 and Table 3. Furthermore, the
Republic oꢀ Indonesia, the Thailand Research Fund (RSA6080010)
and the Royal Golden Jubilee Scholarship to PC [PHD/01242556]. On
behalꢀ oꢀ all authors, the corresponding author states that there is no
conꢂict oꢀ interest.
−
1
peaks in the absorption band oꢀ about 3400 cm belonging
to the hydroxyl group did not appear in PET (Zhao et al.
2
018), ꢀollowed by the appearance oꢀ peaks in the spectrum
oꢀ product indicating a successꢀul breakdown oꢀ PET by eth-
ylene glycol in the presence oꢀ CaO as a catalyst. The melted
PET material which was ꢀurther depolymerized into chemi-
cals with less molecular weight including richer hydroxyl
was conꢁrmed by a sharper absorption peak between 3000
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