One way of utilization of PVC wastes, a source of pollution, is suggested to produce an activated carbon which is used as an absorbent and a catalyst.
There are two steps in the process of activated carbon production: carbonization of PVC wastes and activation of carbonized material.
The objective of this research is to investigate the effect of thermal stabilizers, such as the stearate salts of zinc and calcium on the carbonization and activation in the production of activated carbon from PVC.
PVC wastes with thermal stabilizers were carbonized using the mixture of nitrogen and oxygen, and then activated at around 900℃ with steam.
Infrared spectrophotometer and ultra-violet spectrophotometer were used to find how the structure of PVC wastes was transformed during carbonization. PVC with zinc stearate was carbonized and transformed to more crosslinked polyene chains than pure PVC and PVC with calcium stearate because the zinc chloride generated during the carbonization catalyzed the initial dehydrochlorination, subsequent polyene formation and crosslinking in PVC.
Therefore, it had more stable structure in the second stage of carbonization and higher yield of char.
It was shown that calcium stearate suppressed the formation of zinc chloride in carbonization when PVC contained the mixture of calcium and zince stearates.
Aromatic acid such as phenol and benzoic acid was produced at high temperature in carbonization of PVC with zinc-stearate because zinc chloride functioned as Friedel-craft catalyst for the production of aromatic acid from benzene.
Effects of thermal stabilizers on kinetics of first stage carbonization of PVC and activation of char were studied.
Steam was used for the activation of char.
The carbonization has the reaction mechanism as S + gG → g'G' + rR, that is, one gram of PVC (S) is decomposed to the g' grams of gas (G') and r gram of residue (P).
The reaction rate was studied using TGA by the method of continuous increase in sample temperature. The effects of thermal stabilizers and the amount of oxygen on the reaction rate were examined.
Pure PVC has the reaction order of $\frac{3}{2}$ with respective to solid, while PVC with thermal stabilizers have first order reaction, no matter what kind of atmosphere is given for the carbonization. From these results it is recognized that thermal stabilizer affects the carbonization mechanism.
The activated carbons from PVC were examined using scanning electron photomicroscope.
Activated carbons from PVC with thermal stabilizer are comparatively more porous than activated carbon from pure PVC. Especially, activated carbon from PVC with mixture of calcium and zinc stearate is most porous.
Because of activating effect of zinc chloride and zinc oxide, it is not necessary for PVC with zinc stearate to treat activation.
The ultimate structure of char produced from carbonization of PVC is Hexagon type.
