Pyrolysis of tyres

Pyrolysis of tyres is a feasible, yet technically difficult operation. The handling of the remnants of the steel carcass, the carbon black, the zinc oxide, as well as the tendency to repolymerize of the major products are serious stumbling blocks. Various rubber pyrolysis technologies have been developed, using, e.g. fluid bed, rotary kiln (Sumitomo Cement), molten salts, or cross-flow shaft systems (WSL/Foster Wheeler). 

A. M. Cunliffe and P. T. Wilhams, Composition of oils derived from the batch pyrolysis of tyres. J. Anal. Appl. Pyrol, 44, 131-152 (1998). 

C. Diez et al.. Pyrolysis of tyres. Influence of the final temperature of the process on emissions and the calorific value of the products recovered. Waste Management, 24, 463-469 (2004). 

P. T. Williams S. Besler and D. T. Taylor, The batch pyrolysis of tyre waste - fuel properties of the derived pyrolytic oil and overall plant economics. Proceedings of the Institution of Mechanical Engineers Part A. Journal of Power and Energy, 207, 55-63 (1993). 

The feasibility of using the char generated by tyre pyrolysis as a precursor in the manufacture of activated carbon has been studied by various authors.119,131 Merchant and Petrich131 have obtained carbons with surface areas above 500 m2 g 1 from tyre pyrolysis in batch reactors and subsequent activation of the chars by treatment with superheated steam at temperatures in the range 800-900 °C. Teng et a/.119 have obtained activated carbons with surface areas above 800 m2 g 1 by pyrolysis of tyres up to 900 °C, followed by activation of the resulting chars in C02 at the same temperature. These surface areas are... 

The Toxic Substance Control Act (TSCA) requires that companies that are producing carbon black and other chemicals as a result of the pyrolysis of tyres have to report them to the EPA. The specific requirements of this reporting are laid down in the TSCA. 

Williams, P. T. Taylor, D. T. 1993. Aromatiza-tion of tyre pyrolysis oil to yield polycyclic aromatic hydrocarbons. Fuel, 72, 1469-1474. 

Carbon black is made by the vapour-phase incomplete pyrolysis of hydrocarbons to produce a fluffy fine powder. Worldwide, about 7 million tons a year are produced. It is used as a reinforcing agent in rubber products such as tyres (20-300 nm), as a black pigment (<20 nm) in printing inks, paints, and plastics, in photocopier toner, and in electrodes for batteries and brushes in motors. 

An oil of low flash point in the range 14-18°C, and of 41-43 MJ Kg gross calorific value has been obtained in batch pyrolysis [36] of automobile tyre waste. In a pilot plant with semi-continuous feeding [37] the liquid yield of tyre waste decreased seriously with increasing temperature, and it was always lower in an atmosphere containing oxygen that in nitrogen. 

O. Senneca, P. Salatino and R. Chirone, A fast heating-rate thermogravimetric study of the pyrolysis of scrap tyres. Fuel, 78, 1575-1581 (1999). 

J. F. Gonzalez, J. M. Encinar, J. L. Canito and J. J. Rodriguez, Pyrolysis of automobile tyre waste. Influence of operating variables and kinetics study. J. Anal. Appl. Pyrol., 58-59, 667-683 (2001). 

W. Kaminsky and H. Sinn, Pyrolysis of plastic wastes and scrap tyres using a fluidised bed process.In J. L. Jones and S. B. Radding(eds) Thermal Conversion of Solid Wastes and Biomass.ACS Syposium Series 130, American Chemical Society, Washington,D.C (1980). 

H. W. Schnecko, Pyrolysis of used tires, Chem. Ing. Techn., 48, 443-447 (1976). W. Kaminsky, Pyrolysis of plastic waste and scrap tyres in a fluid bed reactor. Resource Recovery Conserv., 5, 205-216 (1980). 

There are a few companies that advertise on the Internet proprietary processes for micro-wave pyrolysis of wastes. Not surprisingly, considering what was presented in the previous section, most of these refer specifically or specially to the pyrolysis of waste tyres. 

D. Boukadir et al.. Preparation of a convenient filler for thermoplastics by pyrolysis of rubber powder recovered from tyres. Journal of Analytical and Applied Pyrolysis, 3, 83-89 (1981). 

P. T. Williams and A. J. Brindle, Fluidised bed pyrolysis and catalytic pyrolysis of scrap tyres. Environmental Technology, 24, 921-929 (2003). 

The gas fluidized-bed reactor is the most efficient approach to pyrolysis. In this reactor the waste plastic is suspended around the heating medium and snbjected to pyrolysis by means of immersed heating tubes and gas-solid convective heat transfer. At present the only difficulty with this reactor is the problem of its structure. Fluidized-bed pyrolyzers have been designed for pyrolysis of waste tyre mbber in Taiwan and in Hangzon. A schematic apparatus of a fluidized-bed pyrolyzer is shown in Fignre 27.2. 

Roy et al. [11] carried out vacuum pyrolysis of used tyres, with a bench-scale reactor and with cross-ply tyres as feedstock. When the pyrolysis of rubber is carried out under vacuum the spectrum of quality products obtained is distinct from the usual atmospheric... 

At the University of Hamburg we have been developing a fluidized bed process for the pyrolysis of plastic waste and scrap tyres since 1970. We used three stages of up-scaling - 0.1 kg/h ... 

Products of fluidized bed pyrolysis of plastic waste and scrap tyres (wt-%)... 

Type quantity and quality of the reaction products naturally depend upon the properties of the input material. The following are examples of products obtained by the pyrolysis of used tyres (Figures 3 and 4). Gas ... 

The gas which is cleaned by scrubbing can be used advantageously for the aspired, self-sufficient operation of the plant in respect to energy. Excess quantities of the gas may be flared off. The composition of the high-calorific gas obtained from the pyrolysis of old tyres is shown in table 1. 

These consist primarily of material high in carbon content, which is practically odourless. Because of their high calorific values of more than 30.000 kJ/kg it is possible to use them as fuel or as raw material for gas generators. If properly treated, they can also be used as filler materials by the rubber industry or as fillers or dyes by the chemical industry (see table 3). In our case the pyrolysis of 1 ton of used tyres produced 365 kg of solid residues, most of which, namely 49.7 % had a grain size between 0.1 and 0. 5 mm. 

The solid residues contain metallic substances which can be removed with ease from the soot after pyrolysis because they are the shredded steel components of tyres. 

The PAHs are substances mainly formed from incomplete combustion processes (e.g. pyrolysis) of petroleum and coal in connection with energy production, industrial activities, transport, etc. but also from graphite electrodes in industrial processes, from wood preservatives made up from coal tar and from products such as car tyres. The occurrence of PAHs is widespread, although often more or less concentrated to hot spots associated with anthropogenic activities. Of course, PAHs being products from combustion processes, are also formed in natural combustion processes such as forest fires, volcanic activities, etc. and they are... 

Thermal processes are mainly used for the feedstock recycling of addition polymers whereas, as stated in Chapter 2, condensation polymers are preferably depolymerized by reaction with certain chemical agents. The present chapter will deal with the thermal decomposition of polyethylene, polypropylene, polystyrene and polyvinyl chloride, which are the main components of the plastic waste stream (see Chapter 1). Nevertheless, the thermal degradation of some condensation polymers will also be mentioned, because they can appear mixed with polyolefins and other addition polymers in the plastic waste stream. Both the thermal decomposition of individual plastics and of plastic mixtures will be discussed. Likewise, the thermal coprocessing of plastic wastes with other materials (e.g. coal and biomass) will be considered in this chapter. Finally, the thermal degradation of rubber wastes will also be reviewed because in recent years much research effort has been devoted to the recovery of valuable products by the pyrolysis of used tyres. 

Figure 4.35 Pilot plant for the vacuum pyrolysis of used tyres.129...

Various alternatives have recently been proposed for the valorization of the solid carbon residue of tyre pyrolysis. Napoli et al.ni have compared the properties of the char with those of coal. The calorific value of the char is slightly higher than that of coal due to the lower ash content of the former, while... 

Likewise, Orr et al.29,30 have explored the possible use of tyre pyrolysis oil as a solvent for coal liquefaction. The potential of this alternative was demonstrated by the fact that coal-TPO mixtures were transformed with higher conversion than when coal was reacted directly with ground waste rubber tyres. It is proposed that the polyaromatic compounds present in the TPO favour coal dissolution during liquefaction. Treatment of coal-TPO mixtures (50/50%) at 430 °C under 68 atm of cold-hydrogen pressure in the presence of a Mo catalyst led to a high coal conversion in just 10 min of reaction. From electron probe microanalysis of the coal particles after the reaction, the authors conclude that TPO favours the catalyst dispersion and its contact with coal, which results in enhanced coal conversion. 

A new version of MCFC technology - the direct carbon fuel cell (DCFC) - is under development at the Lawrence Livermore National Laboratory in the USA. Instead of using gaseous fuel, a slurry of finely divided carbon particles dispersed in molten alkali metal carbonates is fed to the cell. The carbon is made by the pyrolysis of almost any waste hydrocarbon e.g., petroleum coke), a process that is already carried out industrially on a large scale to produce carbon black for use in the manufacture of tyres, inks, plastic fillers, etc. The pyrolysis reaction yields hydrogen that can itself be utilized in another fuel cell ... 

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