Korean J. Chem. Eng., 20(4), 693-697 (2003) 693 † To whom correspondence should be addressed. E-mail: khwanlee@kier.re.kr ‡ This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology. Thermal and Catalytic Degradation of Waste High-density Polyethylene (HDPE) Using Spent FCC Catalyst Kyong-Hwan Lee † , Sang-Gu Jeon, Kwang-Ho Kim, Nam-Sun Noh, Dae-Hyun Shin, Jaehyeon Park, Younghwa Seo*, Jurng-Jae Yee** and Geug-Tae Kim*** Clean Energy Research Department, Korea Institute of Energy Research, 71-2 Jang dong, Yusong ku, Daejeon 305-343, Korea *Dept. of Environmental Engineering, Suwon Science College, Suwon 445-742, Korea **Faculty of Architectural Design & Engineering, Dong-A University, Busan 604-714, Korea ***Dept. of Chemical and Polymer Engineering, Hannam University, Daejeon 306-791, Korea (Received 27 November 2002 • accepted 28 February 2003) Abstract-Thermal and catalytic degradation using spent fluid catalytic cracking (FCC) catalyst of waste high-density polyethylene (HDPE) at 430 o C into fuel oil were carried out with a stirred semi-batch operation. The product yield and the recovery amount, molecular weight distribution and paraffin, olefin, naphthene and aromatic (PONA) distribu- tion of liquid product by catalytic degradation using spent FCC catalyst were compared with those by thermal degradation. The catalytic degradation had lower degradation temperature, faster liquid product rate and more olefin products as well as shorter molecular weight distributions of gasoline range in the liquid product than thermal degradation. These results confirmed that the catalytic degradation using spent FCC catalyst could be a better alternative method to solve a major environmental problem of waste plastics. Key words: Thermal & Catalytic Degradation, Spent FCC Catalyst, Waste HDPE, Liquid Product Distribution INTRODUCTION The consumption of various plastic materials has been growing continuously due to their versatility and low cost. Accordingly, the waste arising from this expanding use of waste is enormous [Patel et al., 1998]. However, the recycling of waste plastics is a small per- centage, whereas the large majority is landfilled or incinerated, caus- ing a severe environmental problem due to their chemical inert- ness. Their impact on the environment needs to be mitigated. Ade- quate alternative methods for recycling of waste plastics are needed for producing higher value products. The thermal and catalytic de- gradation processes of waste plastics are accepted alternative meth- ods, both economically and environmentally [Walendziewski, 2002; Bockhorn et al., 1998]. Pyrolysis of waste plastics could be proposed to produce the oil feedstocks in the petroleum industry as a feed for a petroleum re- finery catalytic cracker and steam cracker in the production of gaso- line and various alkenes. This method is a simple thermal process in which polymers at high temperature are melted and broken down to smaller molecules as the mixture products of gaseous, liquid and solid hydrocarbons [Pinto et al., 1999]. However, these products are not good as fuels due to their low quality. Consequently, the in- teresting method of polymer utilization is catalytic degradation. This is to convert the melted polymer to light carbon derived materials, constituting high quality components, in the presence of degrada- tion catalysts [Bagri and Williams, 2002; de la Puente et al., 2002; Jeong et al., 2001; Lee and Shin, 2003; Park et al., 2002]. For appli- cation processes, acidic catalysts such as zeolite Y, ZSM-5, silica- alumina and mordenite mainly produce C 5 -C 12 light hydrocarbon for the range of gasoline, whereas the thermal process with use of non-acidic catalysts produces C 12 -C 22 compounds with the range of kerosene+diesel [Walendziewski, 2002; Buekens and Huang, 1998; Sakata et al., 1999; Park et al., 2002]. Also, the combination of py- rolysis and catalytic reforming was known as a more efficient meth- od for processing large amounts of waste plastics [Songip et al., 1993]. In this study, thermal and catalytic degradations using spent FCC catalyst of waste HDPE, which can easily produce the low quality components, are compared. Spent FCC catalyst used in the cata- lytic degradation process is thrown away from the commercial FCC process in Korea as a few ten thousand tons per year, although it has high activity. It means that this catalyst can be reused in the liq- uid-phase cracking process. Accordingly, spent FCC catalyst with a low cost is utilized in the catalytic degradation process for waste plastics into oil recovery. FCC catalyst, which is mainly composed of zeolite and matrix such as alumina and silica-alumina, is pre- pared by spray drier to make a strong fine powder type. Catalytic degradation enables lowering of reaction temperature as well as boil- ing temperature range, compared to thermal degradation. In the prod- uct distributions for the two processes, the yields, accumulative prod- uct amount, PONA distribution and molecular weight distribution are discussed. Table 1. Physical properties of waste HDPE Items Mn a Mw b Mw/Mn Values 22550 367534 16.3 a Number average molecular weight. b Weight average molecular weight.