Flash-Pyrolyzed Product Distribution of Major Plastics in a Batch Reactor

Abstract

This study is a starting point for the creation of a new plastic recycling process. The process consists of two successive pyrolyzing reactors, for which a spouted bed type seems to be most appropriate for the time being. In the first reactor, plastic chips are fed and instantaneously pyrolyzed into lower hydrocarbons (gas or vapor). In the second reactor, the hydrocarbons are further pyrolyzed into hydrogen and carbon. Hydrogen is a useful and clean fuel (no carbon dioxide evolution) and a chemical raw material. Carbon can be utilized as carbon black, activated carbon, and so forth. In this study, flash pyrolysis of plastics was investigated to obtain basic data for the first reactor of the process. Six types of plastics, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET), were flash-pyrolyzed by putting them into a pre-heated batch reactor (873 K, 5 × 10^-5 m³), which was made from stainless steel and contained 5 mm-diameter non-porous α-alumina balls as a thermal medium. The products (gas, condensate and solid residue) were collected and analyzed. In most cases, solid residue (in the reactor) yield was less than 3%. Gas yield was 1 to 30%. Condensate yield was 10 to 90%. These results show that in the first reactor of the proposed process most of the fed plastics can be pyrolyzed into gas and vapor, which will move to the second reactor as a fluid.