Toluene mediated fluid catalytic cracking of low density polyethylene using ionic liquids
Sachin Chalapati and Mikael Skrifvars
Swedish Centre for Resource Recovery, School of Engineering, University of Borås
Introduction
Polyethylene is one of the most widely used synthetic polymers produced by mankind and it is therefore necessary to develop new ways to recycle the polymer. Ionic liquids can replace several organic solvents due to their robust nature and novel properties that allow depolymerization of hydrocarbons into simpler short chained paraffin's.
Initial dissolution of LDPE using hot toluene followed by agitated depolymerization using super acidic EMIM-Cl (AlCl3) ionic liquid for producing fuel grade high calorie organic molecules might be proven successful. This could be a novel procedure that aims to produce fuel grade products from waste synthetic polymers like polyethylene.
Methods
A low temperature catalytic cracking of LDPE was investigated. Usage of ionic solvents for catalytic cracking of synthetic polymers is previously shown to be a green and efficient method in waste to fuel conversion [1]. The current method has shown efficient production of smaller alkane molecules from polyethylene films, the reaction involves a mixture of 535.5 ml of EMIM-Cl AlCl3 ionic solvent, 200 mg of anhydrous AlCl3 and 2 mol% conc. sulphuric acid as co-catalyst acting on 100 mg of LDPE. The polymer dissolution was enhanced by addition of 6.5 ml of toluene per reaction and the experiment is carried out at 160°C which is exceedingly lower than existing cracking techniques by pyrolysis [2]. The experiment is carried out in 1 bar pressure and the emanating gases are bubbled through methanol [3] for a qualitative analysis of the produced organic compounds. A 60% weight loss was achieved during 48 hr. reaction in a conical glass reactor with 600 rpm stirring. The extent of depolymerization is in direct correlation to reaction temperature in the current experimentation range from 60°C to 160°C and higher temperatures led to higher polymer weight loss (see Fig 1).
Results
Reactions were carried out with varying temperatures to observe the effect of temperature on amount of polymer depolymerization and DSC curves were obtained for the left out polymer to observe the effect of the reaction on polymer crystallinity (see Fig 2).
Figure 1 – Graph showing % depolymerization in relation to reaction temperature
Figure 2 – DSC analysis of treated (blue) vs untreated (green) polymer
References
1. Christopher J. Adams, Martyn J.Earle, Kenneth R. Seddon.
(2000), "Catalytic cracking reactions of polyethylene to light alkanes", Green Chemistry, 21-23.
2. Ranbir Bagri, Paul T. Williams. (2002), "Catalytic pyrolysis of polyethylene", Journal of analytical and applied pyrolysis, 63, 29- 41.
3. Ng, H.-J. and C.-J. Chen, Research Report RR-149 (1995):
"Vapour-Liquid and Vapour-Liquid-Liquid Equilibria for H2S, CO2, Selected Light Hydrocarbons and a Gas Condensate in Aqueous Methanol or Ethylene Glycol Solutions", Gas Processors Association and Gas Research Institute, Tulsa, Oklahoma.
0 10 20 30 40 50 60 70
60 80 100 120 140 160
% Depolymerization
