Commercial Plastic Pyrolysis Processes

This book covers thermal and catalytic pyrolysis processes that produce liquid fuels (or other useful chemicals) from waste plastics. The book provides a comprehensive overview of the main commercial plastics pyrolysis processes, the types of plastics that can be processed, the properties of the respective fuels produced and the key variables influencing the pyrolysis of plastics such as temperature, residence time, pressure and catalyst types. 

The development of commercially viable plastic pyrolysis processes has up to now been hindered by the need to engineer around various process problems such as reactor fouling by carbon deposits, poor heat transfer of molten plastics, the requirement for integrated fractionation of products, separation of water and suspended carbon from the liquid fuels and integrated desulphurization. 

The use of pyrolysis for the recycling of mixed plastics is discussed and it is shown that fluidised bed pyrolysis is particularly advantageous. It is demonstrated that 25 to 45% of product gas with a high heating value and 30 to 50% of an oil rich in aromatics can be recovered. The oil is found to be comparable with that of a mixture of light benzene and bituminous coal tar. Up to 60% of ethylene and propylene can be produced by using mixed polyolefins as feedstock. It is suggested that, under appropriate conditions, the pyrolysis process could be successful commercially. 23 refs. 

Overview of Commercial Pyrolysis Processes for Waste Plastics... 

The Beijing Roy Environment Technology Co., Ltd (also known as Royco) has developed a commercial pyrolysis process for turning waste plastics into oil known as the EZ-Oil Generator process. 

Mixing carbon with microwave-transparent materials, particularly plastics, and subjecting the mix to microwave radiation, is a very efficient way to heat up such materials, increasing their bulk temperature to a point where pyrolysis occurs. In this chapter the main characteristics of a number of microwave pyrolysis processes, for plastics and other materials, have been introduced, showing that these processes combine the advantages of microwave heating with the commercial and environmental opportunities intrinsic to the pyrolysis of wastes. 

Scientific studies have found that the differences between microwave and conventional pyrolysis go beyond the obvious difference in the source of heat. Other differences arise from the very high rates of heat transfer from the microwave-absorbent to the waste, the amount heat received by the primary pyrolytic products once they leave the absorbent bed and the highly reducing environment. These three aspects have been shown to have an important effect in the final products since they modify the extent of secondary and tertiary reactions. Moreover, the scientific studies have shown that a nonthermal microwave effect in these processes is unlikely to exist. Tests have showed the potential of the microwave-induced pyrolysis process for the treatment of real plastic-containing wastes and it is believed that a commercial process could be developed, for example, to recover clean aluminium from plastic/aluminium laminates. Other materials, in particular tyres, coal and medical wastes are very good candidates to be treated/recycled using microwave pyrolysis and there have been a considerable number patents filed with this goal in mind. 

The research and development carried out so far in has shown that, even though microwave pyrolysis will not be the solution to the whole problem of plastic disposal, it certainly has the potential to help reducing the number of resources currently committed to landfill. Evidence of this potential is the number of companies interested in the development of the process and that are currently active, trying to commercialize proprietary microwave pyrolysis processes. However, this chapter has shown that in order to accomplish a more widespread utilization of this kind of processes a better communication between the commercial and scientific communities is needed. The companies with their patents would be able provide many innovative ideas that may help to increase processes efficiency and the scientific community would provide explanations for the improvements, that would in turn generate even more ideas in a self-sustaining cycle of improvement. 

The majority of the cyanuric acid produced commercially is made via pyrolysis of urea [57-13-6] (mp 135°C) primarily employing either directiy or indirectly fired stainless steel rotary kilns. Small amounts of CA are produced by pyrolysis of urea in stirred batch or continuous reactors, over molten tin, or in sulfolane. The feed to the kilns can be either urea soHd, melt, or aqueous solution. Since conversion of urea to CA is endothermic and goes through a plastic stage, heat and mass transport are important process considerations. The kiln operates under slight vacuum. Air is drawn into the kiln to avoid explosive concentrations of ammonia (15—27 mol %). 

In a number of processes the plastics prior to pyrolysis are dissolved into product oil for example, so that the viscosity is quite controllable. Other options, though today somewhat obsolete, are the use of a molten lead, tin or salt bath. Unfortunately, residues accumulate on top of this bath, and periodic shut-down for cleaning is inevitable. The process has been used commercially for PMMA. 

Furthermore, a study of the behaviour of a fluidized-bed reactor is very important as one of the options for a possible commercialization of such a pyrolysis recycle process is to co-feed plastic waste into the FCC cracker unit of an oil refinery. Studies of plastic being a fraction of the feed of a cracking process have been carried out by Ng et al. [7] and Arandes et al. [12, 27, 28]. They not only showed the applicability of the method, but discovered a synergetic effect on the cracking of the oil decreasing the amount of aromatics. 

Figure 15.6 Process flow for commercial pyrolysis plant (Thermofuel ) for converting waste plastics into diesel fuel. The plastic is heated to 375-425°C and the pyrolysis vapours are catalytically cracked and then selectively condensed. Note that the pyrolysis vessel is purged with nitrogen gas and that the hot pyrolytic vapours pass from the pyrolysis vessel to the catalytic reaction tower where they are cracked and reformed to give a high-purity diesel stream. (Reproduced by permission of Ozmotech Pty Ltd)...

Microwave pyrolysis of plastic (or plastic-containing) wastes is a relatively new area that has been studied only in the last decade or so. Because of this, there is considerably less information in the scientific literature compared with other approaches to the pyrolysis of plastics. Also, there is a substantial amount of information contained in patents, which suggests that the development of microwave pyrolytic processes has been more intuitive rather than strictly scientific. This chapter will summarize the developments in this area that are described both in scientific and commercial literature. 

Piezoceramic materials are chemically inert and physically strong. In fibre form, they have anisotropic structures. Usually, ceramic fibres are produced by the spinning of an organic or mineral precursor fibre, followed by heat treatment and pyrolysis (Hearle, 2001). Piezoceramic fibres comprising lead zirconate/lead titanate exhibit better sensitivity in terms of piezoelectric activity and elevated operating temperatures (Swallow et al., 2008). PZT fibres can be manufactured by various processes, such as sol-gel, viscous suspension spinning, extrusion and viscous plastic processing, some of which are already commercially available (Strock et al., 1999 Meyer et al., 1998 French and Cass, 1998 Meister et al., 2003 Bowen et al., 2006). 

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