Conversion of low density polyethylene into petrochemical feedstocks usinga continuous screw kiln reactor

Thermal and catalytic degradation of low-density polyethylene (LDPE) has be en investigated using a screw kiln reactor provided with two zones of react ion temperature. Thermal degradation experiments carried out at different t emperatures and screw speeds have shown that this continuous system is suit able for the LDPE degradation, product outputs up to c.a. 100 g/h being obt ained. Compared to a conventional batch reactor, the screw kiln system lead s to a lower formation of gaseous products, whereas overcracking of the hea vy fractions is also reduced. These differences are probably originated by the intimate contact and the same residence times for all the product fract ions that exist within the screw reactor, which is in contrast with the sel ective and fast withdrawal of volatile products taking place in the batch s ystem. In the catalytic experiments, a mesoporous MCM-41 type aluminosilica te has been used as catalyst, being continuously fed to the screw reactor m ixed with the raw plastic material. In these conditions, yields up to 80% t owards hydrocarbons within the gasoline range (C-5-C-12) have been obtained . Moreover, high amounts of C-7 and C-8 hydrocarbons are present in the gas oline fractions, which is assigned to catalytic oligomerization reactions t hat selectively affect to C-3 and C-4 gaseous hydrocarbons. (C) 2001 Elsevi er Science B.V. All rights reserved.