Effect of HCl Pretreatment on the Performance of Natural Zeolite in aSequential Pyrolysis and Catalytic Reforming of Polypropylene
Shuo Cheng1,*, Mochamad Syamsiro 1, Harwin Saptoadi2 and Kunio Yoshikawa 1
1 Department of Environmental Science and Technology, Tokyo Institute of Technology, Japan
2 Department of Mechanical and Industrial Engineering, Gadjah Mada University, Indonesia

Tel: +81 45 924 5507 , Fax: +81 45 924 5518, E-mail: cheng.s.ab@m.titech.ac.jp;

Abstract
This study investigated the performance of three kinds of natural zeolites (NZ) after HCl pretreatment in differentconcentration and one commercial zeolite catalyst (HY-zeolite) in a sequential pyrolysis and catalytic reforming ofpolypropylene. The natural zeolite was pretreated by 0.5, 1, 6 mole HCl solution under the reflux condition. The untreatednatural zeolite and HY-zeolite were also used as catalyst in this experiment for comparison. The experiments were carriedout on two stage reactor using semi-batch system. Pyrolysis process was implemented in the absence and presence ofcatalyst. The crystalline structure, the chemical composition, the Si/Al ratio, and the BET surface area were checked todetermine the basic physical and chemical properties of the treated and untreated natural zeolite. The yields of liquid andgaseous products were compared respectively to understand the effect of HCl pretreatment. The results show that thepretreatment in HCl solution could increase the surface area and the Si/Al ratio of natural zeolite. The natural zeolite, in thisstudy, belonging to mordenite-type zeolite, is comparable to commercial zeolite catalyst in terms of the performance.
Keywords: HCl pretreatment, pyrolysis, natural zeolite, catalytic reformer, fuels2. Materials and Methods
1. Introduction
Plastic, as a great invention, is becoming one kind of
substantial materials and was applied widely in themodern world. However, in decades, plastic wastes havebecome a major stream in solid waste and caused
significant environmental problems to human being. To
minimize the environmental impact and alleviate energy
shortage, a possible method is to extract energy fromwaste plastics by thermal or chemical conversions.
Therefore, pyrolysis of plastics into fuel has been
introduced not only for waste reduction but also forenergy recovery.
Pyrolysis or thermal cracking involves degradation ofpolymeric materials by heat in the absence of oxygen.
These pyrolytic products composed of a liquid fraction, agas fraction and solid residues [1]. However, thedegradation rate is relatively low. As such, the catalytic
degradation of plastic waste has been investigatedextensively by many researchers. The presence of
catalyst indeed promotes the chemical reaction resulting
in the selectivity toward specific products with high added
value. However, high cost of catalyst is the otherobstacle for pyrolysis of plastics. Natural zeolite, which
can be found in many places worldwide, might be used
as a promising alternative catalyst to lower costassociated with the usage of commercial catalysts. This
study focused on the effect of HCl pretreatment on thecatalyst performance of natural zeolite. The X-ray
analysis technique and the BET analysis were employed
to characterize the properties of the natural zeolite.

2.1 Materials
The catalysts used for these experiments were thenatural zeolite (NZ) obtained from Klaten, Indonesia andthe HY-zeolite (CBV 780) came from Zeolyst
International Company. Polypropylene (PP) andpolystyrene (PS) granules were provided by Tosoh Co.,Ltd in Japan. HCl and distilled water were obtained from
Waco chemicals.
2.2 HCl pretreatment of catalyst
Four types of natural zeolite (NZ) and one commercialzeolite catalyst (HY-zeolite) were used in the pyrolysis ofpolypropylene (PP). The raw natural zeolite was ground,sieved to 100 mesh particles size and washed with
distilled water at room temperature to remove the watersoluble impurities. The washed NZ was dried in an ovenat 120 ºC for 5 h and calcined at 500 ºC for 3 h, which
was named as NZ and used as the first catalyst. The NZ
sample was also the raw material in the subsequent
treatment steps.
As for the HCl pretreatment, the acid treated form wasprepared by mixing 20 g of NZ with 500 ml of 0.5M, 1 M
or 6 M HCl solution under the reflux condition under theatmospheric pressure for 1 h. After the HCl pretreatment,
the zeolite was filtered and washed with distilled water,
after which it was dried at 120 ºC for 5 h and calcined at500 ºC for 3 h. The products were named as 0.5M-NZ,
1M-NZ and 6M-NZ according to the concentration of HClsolution. The HY-zeolite was used as received
2.3 Pyrolysis and catalytic reforming of plastics
In this step, pyrolysis and catalytic reforming process ofPP were carried out in a two stage system, which

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

consisted of pyrolyzer and catalytic reformer. The
pyrolyzer with inner diameter and height of 30 mm and250 mm was made of stainless steel. It was wrapped upin an electric heater. The stainless steel reformer with
inner diameter and height of 10 mm and 250 mm wasalso wrapped up in an electric heater. At the outlet of thereformer, a water-cooled condenser was installed to cooland separate gas and liquid products.
50 g of the feedstock and 1 g of the catalyst were placedin the pyrolysis reactor and the reforming reactor,
respectively, beforehand. First, the reformer was heated
up to 450 ºC to removal the moisture in the catalyst andthe air in the reactors was replaced with N2 carrier gas(100 ml min-1) at the same time. The feedstock washeated in the pyrolyzer at 500 ºC, and then the vapors
went through the catalytic reformer. After finishing thecatalytic reaction, the gas was cooled to recover liquid
products in the condenser. Liquid products werecollected and weighed, and gaseous products werecollected in a gas-sampling bag. All the experiments
were implemented under the same operation conditions.
To evaluate the performance of the catalysts,experiments with HY-zeolite and without any catalysts
were also conducted with the same procedures.
2.4 Characterization of catalyst and productThe crystalline structure of the natural zeolite before andafter the HCl pretreatment was determined by the XRD
analysis (Rigaku Corp., Japan) using the Copper K alpharadiation. The chemical composition and the Si/Al ratio ofcatalyst samples were confirmed by the X-ray
Fluorescence (XRF) analyzer. The BET surface area wasdetected by the nitrogen adsorption-desorption
measurements, which were measured at 77 K on aBelsorp-mini II (Bel Japan). The Transmission Electron
Microscope (TEM/STEM: JEM-2100F, JEOL Co., Ltd)was employed to identify the surface and threedimensional structure of catalysts. The liquid productcomposition was analyzed by GC-MS, and the gaseous
product composition was measured by GC-TCD (AgilentTechnologies Inc. USA).

3of NZ could increase the Si/Al ratio. The surface area
also increased with the increase of the concentration ofHCl solution.

Fig.1. X-Ray powder diffraction pattern of natural zeolite
samples before and after HCl treatment.
It can be seen from Table 1 that the HCl treatment of theNZ catalyst could increase the Si/Al ratio. The surface
area also increased with the increase of theconcentration of HCl solution. In the BET surface case, itchanged a lot from NZ to 1M-NZ. However, thedifference is not so obvious between 1M-NZ and 6M-NZ.
In consideration of 6 M HCl would damage the crystalline
structure and the cost factor, pretreatment by 1 M or
below HCl solution is more attractive.
Table 1 Chemical composition and BET surface area ofHY-zeolite, NZ before and after the HCl pretreatment.
SiO2/Al2O3
Fe
SBET
NZ
4.78
2.99
91.1
0.5M-NZ
174.0
1M-NZ
7.66
1.39
233.9
6M-NZ
12.590.28282.1
HY-zeolite
80.00
780.0
3.2 The product yield of polypropylene
According to Fig.1, all of the liquid yields were over 85%.
However, there is a trend that the liquid yield frompolypropylene increased with the increase of theconcentration of HCl pretreatment solution.

Results and Discussion

3.1 Characterization of catalysts
The XRD analysis has been done, in order to examine
the change of the pore structure in the NZ and its HCl
pretreated samples. The concentrated peaks shown inFig. 1 indicated that these natural zeolite samples haveregular crystal form. The main structure of the NZ
catalyst could be identified to be mordenite type by threecharacteristic peaks 2T (degree) = 25-30. Most of thepeaks observed at 2T (degree) = 5-35 also proved thisestimate. Some impurity peaks of the NZ catalyst
disappeared in the diffractograms of those pretreatedwith HCl, which indicates that the pretreatment could
remove a part of impurities. However, in the 6 M figure,some main peaks are weaken, which means that 6M HClsolution would destroy the crystalline structure. Thechemical composition and the BET surface area fornatural zeolite before and after the HCl pretreatment arelisted in Table 1. It can be seen that the HCl pretreatment

Fig. 1. Product yield obtained from the pyrolysis
and catalytic reforming of polypropylene.

4Conclusions

The natural zeolite used in this experiment belonged tomordenite type. The HCl pretreatment could increase theSi/Al ratio and the surface area of natural zeolite.
However, high concentration of HCl would damage thecrystalline structure. The liquid yield from polypropylene
increased with the increase of the concentration of HCl
pretreatment solution.

References[1] Buekens, A.G. and H.Huang. Resources,Conservation and Recycling 23 (1998) pp. 163-181.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013