Polystyrene Destruction Temperature

case of polypropylene the exothermic region follows endothermic region. The exothermic region evolves from the combustion of gases evolved from the initial pyrolysis of the material. The TGA results on polystyrene show that this material almost does not have any impurities, and at high heating rate in oxidative conditions the thermal decomposition does not follow the usual smooth decay (compare the TGA curves in Figs. 15.33 and 15.35).

Styrofoam Decomposition Temperature
Temperature (°C) Figure 15.33. Thermal decomposition of polystyrene in nitrogen.
Dsc Molecular Weight Polystyrene

Temperature (°C)

Figure 15.34. Thermal decomposition and heat of pyrolysis of polystyrene in nitrogen.

Temperature (°C)

Figure 15.34. Thermal decomposition and heat of pyrolysis of polystyrene in nitrogen.

The DSC results suggest that polystyrene does not go through melting point before decomposition. Under inert conditions the results suggest decomposition in a single stage with endothermic heat of pyrolysis (see DSC curves in Fig. 15.34). Therefore in oxidative conditions the decomposition behavior varies between lower heating rate and higher heating rate. At lower heating rate it has a large amount of exothermic heat of pyrolysis, but at higher heating rate at first it shows

Decomposition Temperature

Temperature (°C)

Figure 15.35. Thermal decomposition of polystyrene in air.

Temperature (°C)

Figure 15.35. Thermal decomposition of polystyrene in air.

Sulphonated Polystyrene Tga

Temperature (°C)

Figure 15.36. Thermal decomposition and heat of pyrolysis of polystyrene in air.

Temperature (°C)

Figure 15.36. Thermal decomposition and heat of pyrolysis of polystyrene in air.

exothermic behavior and then it shows endothermic behavior (see DSC curves in Fig. 15.36). The results for the thermal decomposition of polyethylene and polyvinyl chloride in nitrogen are given in Figures 15.37 and 15.38, respectively.

Cellulose contained approximately 2% moisture and approximately 6% fixed carbon by weight. At the end of the TGA tests about 95% of weight loss was achieved. The remaining residue represents mainly the impurities present in the original sample. In contrast for polypropylene and polystyrene almost complete

Polyethylene Tga
Temperature (°C) Figure 15.37. Polyethylene decomposition in nitrogen.
Polyvinyl Chloride Temperature
Figure 15.38. Polyvinyl chloride decomposition in nitrogen.

weight loss was achieved at the end of the TGA tests. The results show that under oxidative conditions all samples decompose in a single stage except for the drying process at the beginning of the test (up to 110°C for cellulose). The initial weight loss on each TGA curve for cellulose is due to the volatiles release during the pyrolysis.

The use of TGA was made in order to obtain information on the overall kinetics of the decomposition process for the surrogate waste materials. The decomposition rates for cellulose are shown in Figures 15.25-15.28, in Figures 15.29-15.32 for polypropylene, in Figures 15.33-15.36 for polystyrene, in Figure 15.37 for polyethylene, and in Figure 15.38 for polyvinyl chloride. The results provide the function ln[—ln(1 — a)] versus 1/T from which the Arrhenius parameters A (the pre-exponential factor) and E (the activation energy) can be evaluated from the graphically determined slope and intercept of the function ln[—ln(1 — a)] versus 1/T.

The calculated results for ln(A), E, and maximum decomposition temperature are given in Tables 15.13-15.15. The results for cellulose and polystyrene show that the activation energy E decreases with increase of heat ramp rate. However, for polypropylene under inert conditions the results show an increase of activation energy E with an increase of heat ramp rate. The thermal decomposition temperature increases with increase in the ramp rate. In any case the amount of heat of pyrolysis is relatively larger under oxidative condition than in inert condition except for the high heating rate of polystyrene. The temperature dependence of heat of pyrolysis depends on the material properties. The reason for high endothermic heat of pyrolysis at high heating rate for polystyrene in oxidative condition is as follows. In the experiments we chose approximately constant mass and constant heat flow so that at different heating rate the sample receives different amounts of air per gram of sample. It is to be noted that the temperature of the air is at the sample temperature at the given condition. In real practice excess air levels may be 50-100% of the stoichiometric amount. Our results obtained can still be used under these conditions.

The results show that at higher heating rate the ratio of required amount of air to that provided to combust the polystyrene is not so high. So the assumption of constant partial pressure of oxygen becomes weak. Thus the correlation between

Table 15.13 Arrhenius Parameters and Maximum Decomposition Temperature for Cellulose in Nitrogen and Air

Was this article helpful?

0 0
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment