초임계 아세톤과 메탄올을 이용한 폐 PS, PET의 분해에관한 연구

김 병기, 배성렬, 구마자와*, 황규철

한양대학교 화학공학과, 일본 토야마 대학*,

Degradation of waste PS, PET in supercritical  acetone & methanol

Byoung Ki Kim, Seong Youl Bae, H. Kumazawa*,

Gyou Chel Hwang

Department of Chemical Engineering Hanyang University

Department of Chemical Engineering Toyama University*

1. INTRODUCTION

The chemical recycling of waste polymers has been gaining greater as a means of obtaining valuable products from waste plastics in recent years. Waste Plastics is treated chemical to recover low molecular monomers or other useful compounds..

Traditionally, pyrolysis experiments of waste polystyrene(PS) produce large amounts of coke(carbon) and gas phase, and require high-energy. However, depolymerization of PS was increased highly in supercritical acetone of lower temperature than pyrolysis experiment and coke was found very little in the reactor.

Polyethylene terephthalate(PET) drink bottle using supercritical methanol was decomposed into dimethylterephthalate(DMT) and ethylene glycol(EG) as raw material.

In this study, degradation of PS, PET was studied using a high temperature, high pressure batch reactor in supercritical region and distibution of product is discussed.

2. EXPERIMENTS

The batch apparatus of a supercritical fluid is shown in Fig. 1. one-liter Autoclave reactor was equipped with high-power heater(4KW) in order to reach the reaction temperature as quickly as possible. The acetone and methanol used was high purity HPLC grade, before being fed to the reactor  the PET bottle was cut into 1cm × 1cm scraps in order to create maximum surface area for heat and mass transfer in the reactor.

This experiment was performed using acetone and methanol over the region of the critical point and we observed variation of yield with rising temperature and pressure. After reaction, the product is recovered by condensing it in a glass-cylinder cooled by water, it of PET was separated into solid and aqueous phases using a glass filter. The solid phase was further washed with water to remove any residual water-soluble components such as ethylene glycol. The acetone and methanol solution after reaction was analyzed by gas chromatographic, gas chromatographic-mass spectrometric.

3. RESULTS AND DISCUSSION

The total conversion rapidly increases with temperature ranging from 270 to 290℃. The conversion to non-aromatic condensates (or monoaromatic products) increases with rising temperature, whereas that to aromatic condensates (or recombination products of radical intermediates) increases with risining temperature below 290℃, but in turn slightly decreases at 300℃. This may be due to a contribution of further decomposition of aromatic condensates at the high temperature region [Fig.2]. The yields of the respective monoaromatic products except for styrene increase with rising temperature. The yield of styrene attains a maximum value at a temperature in between 280 and 290℃[Fig.2(a)] .The yield of diphenylbutene equivalent to dimer of styrene, also gets a maximum value at a temperature in between 280 and 290℃ as that of styrene does[Fig.2(b)].

The conversions to non-aromatic and aromatic condensates as well as the total conversion are affected very little by the acetone density[Fig.3]. The yields of non-aromatic condensates except for styrene decreases with increasing acetone density. It should be noted that the yield of styrene increases greatly with increasing acetone density[Fig.3(a)].

Fig.3 showed that the conversions to non-aromatic and aromatic condensates as well as the total conversion are affected very little by the acetone density, but the product distribution is considerably influenced by the acetone density; the increase in the acetone density preferentially favors the formation of diphenylbutene, whereas diphenylbutane and 1,3-diphenylpropane are gradually depressed with increasing acetone density.

Fig.4 showed that essentially complete depolymerization of PET could be achieved for less than an hour.

4. REFERENCES

1. J. R. Campanelli, M. R. Kamal, Journal of Applied Polymer Science, 48, pp.         443-451(1993)

2. P. Carniti, P. L. Beltrame, M. Armada, A. Gervasini, Ing. Eng. Chem. Res. 30,       pp. 1624-1629(1991)

3. R.J.Ehrig,  plastics recycling,  pp. 47-72(1992)

Fig.4 Effect of reaction time on total conversion at an initial

weight ratio of methaol to PET of 10 and 12.