流化床裂解废塑料

Bed defluidisation during the fluidised bed pyrolysis of plastic waste mixtures *

Maria Laura Mastellone,Umberto Arena )

Department of Environmental Sciences,University of Naples II,Via Vivaldi,43-81100Caserta,Italy

Received 25October 2002;accepted 30April 2003

Abstract

The risk of occurrence of phenomena inducing worsening of fluidisation quality and eventually leading to bed defluidisation is one of the major constraints to an easier utilisation of fluidised beds for the low-temperature pyrolysis of plastic wastes.In order to investigate these phenomena,different mixtures of plastic wastes,obtained by combination of three commercially-available recycled polymers,were fed to a laboratory-scale bubbling fluidised bed reactor.Two mechanisms of defluidisation were identified and the time at which defluidisation occurred was measured and correlated to a key variable of the process.The observed phenomenology was also simulated by means of room-temperature experiments carried out with a selected mineral oil.The results allow us to demonstrate the existence of a synergistic effect between the observed mechanisms of defluidisation.Ó2004Elsevier Ltd.All rights reserved.

Keywords:Defluidisation;Plastic waste;Pyrolysis;Fluidised bed

1.Introduction

The series of advanced thermolytic technologies for plastic recycling (pyrolysis,gasification,hydrogenation),generally known as ‘feedstock recycling’,is economically and environmentally attractive when the waste has low homogeneity and is contaminated by non-polymeric constituents.The polymeric residues are processed into their basic chemical components and these can be used again as raw materials in refineries or in the petrochem-ical industry.In this way new plastics can be produced without any deterioration in their quality and any restriction to their application [1e 3].Fluidised bed pyro-lysis appears to be one of the most promising of feed-stock recycling technologies for a series of reasons.The almost constant temperature provides for uniform pro-

ducts;the suppression of side reactions increases the process controllability;the absence of moving parts in the hot region reduces the maintenance time and cost;the possibility of applying the process on a relatively small scale makes the range of investment alternatives wider.The disadvantages that are not yet completely eliminated are the necessity to limit the chlorine content in the inlet stream and the risk of fluidisation worsening as a con-sequence of solid agglomeration in the bed [4,5].

The latter aspect has been investigated in two recent papers [3,6]which refer to experiments carried out with single polymer feeding of polyethylene (PE),polypro-pylene (PP)and polyethylene terephthalate (PET).The results highlighted that the bed defluidisation can occur during the pyrolysis of plastics as a consequence of the agglomeration between the molten polymer and the inert material (which in turn depends strongly on molten polymer viscosity,and then on bed temperature and poly-mer molecular weight).The defluidisation phenomenon can occur in different ways,depending on the polymer type,and with different rates,depending on the reactor temperature,heat transfer and other operating con-ditions as the polymer feed rate and the bed amount.The sequence of steps that can occur after the injection

*

Based on a paper presented at the 2nd International Conference on Modification,Degradation and Stabilisation of Polymers (MoDeSt),Budapest,30June e 4July 2002.

)Corresponding author.Tel.:C 39-0823-274-603/274-414;fax:C 39-0823-274-605.

E-mail addresses:mlaura.mastellone@unina2.it (M.L.Mastellone),umberto.arena@unina2.it (U.Arena).

0141-3910/$-see front matter Ó2004Elsevier Ltd.All rights reserved.doi:10.1016/j.polymdegradstab.2003.04.002

Polymer Degradation and Stability 85(2004)1051e

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