Experimental and Modeling of Low Pressure Plasma as a Complementary Process for Thermal Waste Treatment

Sharona Atlas, NRCN, Beer-Sheva, Israel
Amir Kaplan, Nrcn, Beer-sheva, Israel
Ofra Klein-BenDavid, Nrcn, Beer-sheva, Israel
Hadas Raveh-Amit, Nrcn, Beer-sheva, Israel
Nissim Banano, Nrcn, Beer-sheva, Israel
Avi Ben-Shabat, Nrcn, Beer-sheva, Israel
Gabriela Bar-Nes, Nrcn, Beer-sheva, Israel
Avi Raveh, Nrcn, Beer-sheva, Israel

Thermal decomposition of plastic waste results in gas products, mainly hydrocarbon molecules (C2-C6), which cannot be released to the atmosphere for environmental reasons. Here, we propose a secondary gas treatment by inductive radio-frequency (13.56 MHz RF) in order to decompose the hydrocarbon gas products into shorter molecules.  As a case study, we studied and compared the plasma treatment of two gas sources: the first source was a mixed gaseous product collected online from the decomposition of HDPE in a thermal pyrolysis reactor, while the second source was industrial butane gas.

In this study, we focused on decomposition of the two sources of gas using data from optical emission spectroscopy (OES) obtained from the center of the inductive RF coil. Systematic addition of Ar, N₂ and Ar+N₂ mixtures to the treated gas were studied. The main emissions from discharges in the gases or their mixtures in the spectral region 200-700 nm. Their relative intensities were found to depend strongly on the plasma excitation mode, N₂ flow rate and gas feed composition, while keeping a constant gas pressure of 5 mbar, flow rate of 100 sccm and RF power input of 700 W.  It was found that the addition of N₂ to the origin gas enhanced gas decomposition as compared to the addition of Ar only. This can be attributed to the decomposition by etching process rather than by the sputtering particle process. Moreover, our preliminary modeling results showed plasma behavior from ignition to steady state, which takes less than 0.01 sec. This will help us to better understand and optimize a variety of thermal decomposition reactions.

This study suggests that coupling low pressure plasma to conventional thermal decomposition techniques can provide an effective treatment process for solid plastic waste.