Catalytic cracking of plastic wastes

K. Gobin, D. Koumantaropoulos, and G. Manos, One stage catalytic cracking of plastic waste on zeolite-based catalysts. Stud. Surf. Sci Catal, 135, 4989-4994 (2001). 

Figure 3.16 Scheme of a process for the direct catalytic cracking of plastic wastes in two steps [99]... 

In addition to the above-mentioned catalytic processes, there are some other related technologies wherein the catalytic cracking of plastic wastes is combined with the coprocessing of other substances, mainly coal and petroleum feedstocks (lube oil, LCO, VGO) or even a solvent. Hereafter, these technologies are explained more in detail. 

This chapter deals exclusively with tertiary recycling by pyrolysis and catalytic cracking of plastics waste alone and by coprocessing with petroleum residue or heavy oils to... 

P-17 - One stage catalytic cracking of plastic waste on zeolitic catalysts... 

The catalytic cracking of polypropylene waste in a flnidized-bed reactor was reported by Ji [12]. It gave a yield of liquid product of 50%, the research octane number of the gasoline prodnced from plastic waste was 86, and the cetane index of the diesel fuel produced from the plastic waste was 43. 

In the following sections of this chapter, the catalytic conversion of individual plastics (polyethylene, polypropylene and polystyrene) is first reviewed, followed by a description of the processes developed for the catalytic cracking of plastic and rubber mixtures. Finally, methods based on a combination of thermal and catalytic treatments are considered. However, taking into account that the key factor in the catalytic conversion of plastic wastes is the catalyst itself, we will first describe the main properties of the most widely used catalytic systems for the degradation of polymers. 

Most of the studies reported on the catalytic cracking of plastics use PE as starting material because it is the main polymer in plastic wastes. The first works appeared in the 1970s,8 mostly based on the use of Friedel-Crafts catalysts. 

Cracking of plastic wastes to gasoline and fuel oil in fluid catalytic cracker (FCC) should be more attractive than other pyrolysis processes except when the pyrolysis process is highly selective to high valued monomers, [3]. Most likely the presence of fillers in the waste can be compensated for by catalyst additions. Studies have shown that, in an FCC unit, the following significant product yields are obtained ... 

Catalytic cracking and conversion of plastics wastes is currently a field of intense research and open to innovative technologies to be discovered and applied. Significant advances have been carried out in recent years, with several commercial plants being already in operation based on the use of catalytic cracking for the plastic waste conversion into valuable products. However, there is still room for further developments. In this regard, the following fields of research can be foreseen in the next years ... 

A. R. Songip, T. Masnda, H. Kuwahara, and K. Hashimoto, Kinetic stndies for catalytic cracking of heavy oil from waste plastics over REY zeolite. Energy Fuels 8, 136 (1994). 

Because of inorganic components in waste plastics, thermal, noncatalytic processes present some advantages. In order to obtain high conversion Chinese inventors [52] propose a two-step process thermal cracking in the first step in order to obtain partial cracking of waste plastics and to separate inorganic components, and in the next step catalytic cracking of the product over a fixed-bed catalyst. 

CATALYTIC CRACKING OF WASTE PLASTICS WITHOUT RESIDUE... 

As it is both inexpensive and easy to handle, steam is a potential candidate carrier gas for waste plastic recycling in chemical plants. Furthermore, as mentioned in Section 2.1, the degradation temperatures for polyester resins are remarkably shifted to low-temperature regions, and the amount of carbonaceous residue produced in the degradation process is reduced in a steam atmosphere, as compared with that in a nitrogen atmosphere. Accordingly, the preparation of a catalyst that could demonstrate both stable activity for the catalytic cracking of PE-derived heavy oil, but that would also remain stable in a steam atmosphere, was examined [16],... 

The problems in catalytic cracking of MWP by direct contact with the catalyst can be overcome by two-step processing. This method involves an initial thermal cracking of waste plastics to produce low-quality hydrocarbons (vapors or liquid) that are treated afterwards in a catalytic reactor to obtain high-quality liquid fuels. 

The liquid product obtained from thermal cracking can be either catalytically cracked/ hydrocracked or co-processed with a refinery feed. Since the catalytic cracking of oil derived from MWP is more or less problematic, any cracking catalyst can be applied to oil derived from pyrolysis of plastics. But the yield and the quality of gasohne obtained from cracking step vary with the type of catalyst and the properties of the pyrolytic oil derivated from waste plastics. 

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