Data on the effects of reaction temperature on degradation of HDPE into various products using HZSM-5 (80) catalyst are shown in Table 3 while Table 4 presents the yields of degradation products using AlSBA-15 catalyst. It is clear that gen­erally the yield of volatile products increased with increasing reaction tempera­ture. It was well noted that by increasing the temperature, cracking probability was increased to result in higher yield of volatile products. At higher tempera­ture, the reaction was generally accelerated, and the accessibility of the reaction products resulting from interaction with external active sites and the reactant was improved. Thus, cracking reactions to give smaller molecular-sized sub­stances were improved. On other hand, the small internal pores of the HZSM-5 and AlSBA-15 catalysts could create hindrance toward the formation of liquid

Fig. 4 Effects of different catalysts on liquid products yield at 623 K with 10 % catalyst loading

products with relatively larger molecular sizes. The effect was more severe in the case of zeolite catalyst with internal pores in the micropore size range. However, it was also noted that the HZSM-5 (Si/Al = 80) catalyst had better capability to con­vert liquid products into gaseous products especially at high temperatures. Similar observations have been reported in literature (Mastral et al. 2006). For exam­ple, it was found that the liquid yield decreased with increasing temperature and higher temperature evidently caused decreases in boiling points of liquid products (Hernandez et al. 2006).

Findings made in this study were in good agreement with those reported by Mastral et al. (2006). They found that zeolitic materials were suitable to be used in

Fig. 5 Effects of reaction temperature on gas products yield by 10 % loading of HZSM-5(80) catalyst

catalytic degradation of polyethylene due to their acidity and structural suitability. As observed in this study, the highest gas yield was achieved by increasing the experi­mental temperature from 350 to 400 °C. Our results regarding the effects of tempera­ture on AlSBA-15 catalyst were also in good agreement with those of Sinfronio et al. (2006) who used Al-MCM-41 as the mesoporous catalyst. Based on these observa­tions, it could be concluded that the most suitable temperature range for maximum liquid fuel yield using HZSM-5 catalyst was 350 °C while it was 400 °C for AlSBA — 15 catalyst. However, higher coke deposition could sometimes correspond to the increasing reaction temperatures, and formation of waxy compound might prevent the accurate calculation of the yield of liquid and gaseous products.

Data regarding the effect of reaction temperature on the gaseous product yield using HZSM-5(80) catalyst are presented in Fig. 5. It is shown that 500 °C gave the most uniform products distribution with highest composition showed by C3 (34.5 %) and the lowest by C5 (11.2 %). By carrying out the reaction at 400 °C, remarkable reduction on the C1 while at the same time an increase in the propor­tion of carbon chain C5 was observed.

In order to compare the effect of temperature when a mesoporous catalyst was used, similar experimental run was carried out using AlSBA-15 catalyst. Figure 6 presents data that were obtained using the mesoporous catalyst. In this case, 350 °C showed the highest gaseous products yield with the highest composition showed by C4 while for the other two reactions, i. e., 400 and 500 °C, C3 predominated. Generally, temperature does not have dominant effects on the gaseous products dis­tribution. However, the difference in gaseous products distribution was significant when comparing results obtained with microporous HZSM-5 (80) and mesoporous AlSBA-15 catalysts. AlSBA-15 catalyst under same 10 % catalyst loading did not produce detectable C1 gas products. This mesoporous catalyst also led to increases in C5 (11.6 and 12.7 %) as compare to those of HZSM-5 microporous catalyst (4.4 and 7.0 %) for the reaction temperatures of 350 and 400 °C, respectively.

However, degradation of liquid products using HZSM-5 (80) showed a decreas­ing trend for increasing carbon chain from C8 to C25+. As shown in Fig. 7, the highest proportion of liquid products for all four reaction temperatures was in

Fig. 6 Effects of reaction temperature on gas products yield by 10 % loading of AlSBA-15 catalyst

Fig. 7 Effects of reaction temperature on liquid products yield by 10 % loading of HZSM-5 (80) catalyst

the carbon chain range of C8-C12. The lowest proportion of carbon chain range was the heaviest carbon chain, i. e., C25+ for all reaction temperatures studied. Increasing reaction temperature had the tendency to produce higher amount of shorter carbon chain molecules while simultaneously reducing the longer carbon chain molecules in the products mixture.

Figure 8 presents the data obtained using AlSBA-15 catalyst under the effect of varying temperatures. Generally, the results showed similar downward trend as observed in the case of using HZSM-5 (80) catalyst. The highest proportion was recorded by carbon chain range of C8-C12 for all three reaction tempera­tures. The second highest composition was recorded by the carbon chain range of C13-C16. This composition also dropped steadily as the reaction temperature increased. The lowest fraction of carbon chain range for the overall liquid prod­uct was C25+. By comparing the effect of varying reaction temperatures to both microporous HZSM-5 (80) and mesoporous AlSBA-15 catalysts, it was concluded that generally liquid degradation products for AlSBA-15 consisted of shorter

carbon chain range molecules. This could be seen for carbon ranges of C8-C12 and Сіз-Сі6 at 350 °C. AlSBA-15 catalyst produced nearly 78.2 % of overall liquid composition while it was only around 63.5 % for HZSM-5(80) catalyst.