In my experiment "Pyrolysis of municipal plastic waste". I performed thermal as well as catalytic cracking using ZSM-5 and activated carbon. The problem is that I'm getting wax instead of liquid at different temperatures 400-450-500-550-600.
Dr. Gaurh,
The hydrogen there is not enough. Please add H in the form of H2 if you want to get oil.
you should increase the temperature more I think. The amount of sample is also important. You should use lesser amount. Good Luck
Adding hydrogen as proposed by Prof. Fan is a very good idea, on the other hand you may reduce the amount of catalyst and make the cracking by thermal decomposition at relatively low temperature, My experience in industrial pyrolysis of thousands of tons of plastics containing waste without catalyst in a large rotating steel kiln heated from the outside with combusted process gas is that we never obtained any wax or condensate but products which were entirely gaseous at temperatures above ~ 200°C. The products were then combusted in line without recovering any intermediates.
I think that increasing the temperature shifts the product spectrum of the condensate towards carbon rich compounds (larger molecules/wax), the same will be true for using more or more active catalysts as they accelerate the decomposition reactions. The equilibrium composition in the temperature range you are working in is methane + carbon ! At higher temperature (~ 800°C) even the methane will decompose forming hydrogen and carbon.
You may solve the problem by studying the macrokinetics of your decomposition reactions using a GC/MS.Check for pore diffusion limitation (Weisz-Prater criterion)
Most probably as you use highly porous catalysts such as zeolites your reaction is pore diffusion controlled, so the reaction products take too long to get out of the pores they stay in contact with the highly active catalyst and have time enough to form large molecules.
The waxy compounds you find are most probably not the primary reaction products but formed during consecutive reactions.
By the way:
Isolating the pyrolysis oil is theoretically very nice but once some traces of chlorine containing plastics like PVC are in the feed the corrosion problem is difficult to solve and the processing of the oils becomes uneconomical.
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