CONVERSION OF WASTE POLYETHYLENE TEREPHTHALATE (PET) INTO HYDROCARBONS BY PYROLYSIS USING LOCAL MATERIALS AS CATALYSTS
Polyethylene terephthalate (PET) have become a general use for various applications such as storage for food and beverages because of its excellent tensile and impact strength, chemical resistance, and thermal stability. However, due to its non-degradability, its waste has continued to generate great concern globally. The recycling of PETs has become a good option for the clean-up of waste PETs in the environment. To this effect, this research aimed at converting waste PETs by pyrolysis into hydrocarbons using local materials as catalyst. Varying ratio of plantain peel and kaolin clay, corn shaft and kaolin and banana peel and kaolin were the local materials used. Agilent 7820A Gas chromatograph attached to a 5977E Mass Spectrometer was used for the analysis. The results indicated that hydrocarbons such as biphenyl, benzonitrile, benzaldehyde, styrene, phenol, benzene, ethylbenzene and naphthalene were among the prominent compounds detected. The results were similar to other research works of PETs pyrolysis using inorganic materials as catalysts hence, the local materials proved to be equally efficient catalysts for PET pyrolysis.
Comparing Tables, A, B, C, D, E and F, toluene, benzene, phenol, biphenyl, benzonitrile, benzoic acid, nonadecane, naphthalene, diethylphtalate were the compounds that occurred most amongst the components listed in the tables. For samples A, C, D and E benzonitrile had the highest area percentages of 1.55, 0.68, 2.09 and 1.81 % respectively. Biphenyl had the highest area percentage of 2.32 for sample C. Naphthalene had the highest area percentage of 1.52 % for sample E, nonadecane had the highest area percentage of 1.3 % for sample C while phenol had the highest compostion of 1.7 % for sample B. The hydrocarbons listed were present in almost every minute amount most especially benzene and benzonitrile (Figure 2).
Figure 2: Comparison of samples A – F showing the most occurring components and their percentage area.
The analysis showed that apart from hydrocarbons, some other elements such as oxygen, nitrogen and alcoholic groups were present. This was similar to the work of Moinuddin and Mohammed, (2011) who used ZnO and Al2O3 as catalyst. That implied that plantain peel and Kaolin were suitable catalyst for PET pyrolysis. The advantage however with the plantain peel and kaolin over the use of ZnO and Al2O3 is that the latter temperature range for the pyrolysis was between 90°C and 405°C, while the plantain peel and kaolin clay temperature range was between 90°C and 300°C. Vakili and Fard, (2010), Siddiqui and Redhwi, (2011), Khaing and Chaw, (2015) and Ogunyemi et al., 2019 all got similar results using various inorganic catalysts.
Figures 3 and 4 shows the result of the yields from the thermal degradation of PET using Corn shaft/ kaolin clay and banana peel/kaolin respectively. Benzonitrile, biphenyls, benzoic acid, fluorene, 1,1 – biphenyl, benzaldehyde, styrene, phenol, benzene, ethylbenzene and naphthalene were among the compounds detected. These compounds are important industrial raw materials. These compounds were also detected when plantain peel was used. The results of this study was in agreement with most research works done on PET pyrolysis (Saha and Ghoshal, 2005; Al -Salam and Lettieri, 2010; Sarker et al., 2011; Claudinho and Ariza, 2017).
Figure 3: Thermal degradation of PET using Corn shaft and kaolin clay
Figure 3: Thermal degradation of PET using banana peel and kaolin clay
Pyrolysis is a strong ally for revaluation of PET waste; it is of great advantage in the industrial production processes thereby generating a new purpose for this type of waste. The use of local materials such as plantain peel/kaolin; corn shaft/kaolin and banana peel/kaolin as catalyst have proved to be efficiency in the catalytic pyrolysis process by reducing the temperature and reaction time. Since plantain peels, banana peels and corn shafts are waste products, their use will serve as both reduction of solid waste and reducing the cost of PET pyrolysis. Hydrocarbons and other compounds produced by the pyrolysis of PET serves as primary feed stocks for petrochemicals industries such as pharmaceutical and pesticides. The GC – MS analysis of this present study using local materials indicated that waste PET can be converted into useful hydrocarbons and other petrochemicals.
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