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

Thermal and catalytic degradation of low-density polyethylene (LDPE) has been investigated using a screw kiln reactor provided with two zones of reaction temperature. Thermal degradation experiments carried out at different temperatures and screw speeds have shown that this continuous system is suitable for the LDPE degradation, product outputs up to c.a. 100 g/h being obtained. Compared to a conventional batch reactor, the screw kiln system leads to a lower formation of gaseous products, whereas overcracking of the heavy fractions is also reduced. These differences are probably originated by the intimate contact and the same residence times for all the product fractions that exist within the screw reactor, which is in contrast with the selective and fast withdrawal of volatile products taking place in the batch system. In the catalytic experiments, a mesoporous MCM-41 type aluminosilicate has been used as catalyst, being continuously fed to the screw reactor mixed with the raw plastic material. In these conditions, yields up to 80% towards 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 gasoline fractions, which is assigned to catalytic oligomerization reactions that selectively affect to C-3 and C-4 gaseous hydrocarbons. (C) 2001 Elsevier Science B.V. All rights reserved.