Kinetics of scrap tyre pyrolysis under vacuum conditions Gartzen Lopez, Roberto Aguado, Martín Olazar * , Miriam Arabiourrutia, Javier Bilbao Departamento de Ingeniería Química, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain article info Article history: Accepted 3 June 2009 Available online 8 July 2009 abstract Scrap tyre pyrolysis under vacuum is attractive because it allows easier product condensation and control of composition (gas, liquid and solid). With the aim of determining the effect of vacuum on the pyrolysis kinetics, a study has been carried out in thermobalance. Two data analysis methods have been used in the kinetic study: (i) the treatment of experimental data of weight loss and (ii) the deconvolution of DTG (dif- ferential thermogravimetry) curve. The former allows for distinguishing the pyrolysis of the three main components (volatile components, natural rubber and styrene–butadiene rubber) according to three suc- cessive steps. The latter method identifies the kinetics for the pyrolysis of individual components by means of DTG curve deconvolution. The effect of vacuum in the process is significant. The values of acti- vation energy for the pyrolysis of individual components of easier devolatilization (volatiles and NR) are lower for pyrolysis under vacuum with a reduction of 12 K in the reaction starting temperature. The kinetic constant at 503 K for devolatilization of volatile additives at 0.25 atm is 1.7 times higher than that at 1 atm, and that corresponding to styrene–butadiene rubber at 723 K is 2.8 times higher. Vacuum enhances the volatilization and internal diffusion of products in the pyrolysis process, which contributes to attenuating the secondary reactions of the repolymerization and carbonization of these products on the surface of the char (carbon black). The higher quality of carbon black is interesting for process viabil- ity. The large-scale implementation of this process in continuous mode requires a comparison to be made between the economic advantages of using a vacuum and the energy costs, which will be lower when the technologies used for pyrolysis require a lower ratio between reactor volume and scrap tyre flow rate. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The devolatilization of wastes generated by human activity (such as plastics and tyres) is one of the 21st century’s greatest challenges and its technological progress is crucial for sustainable development. This valorisation must be carried out following routes that contribute to a better exploitation of raw materials that attenuate climate change and decrease fossil fuel consumption. The pyrolysis of scrap tyres produces flammable gases, high en- ergy density liquids and an adulterated carbon black. The viability of its industrial implementation requires maximizing jointly the efficiency of pyrolysis process and the valorisation of each product stream (Zhang et al., 2008). The gas has a higher heating value of around 38 MJ/N m 3 , which is sufficient to sustain the process of pyrolysis and offset heat losses (Aylon et al., 2007). The pyrolysis liquid has a higher heating value of around 42 MJ/kg (Laresgoiti et al., 2004; Olazar et al., 2008a) and a high content of BTX and lim- onene (Islam et al., 2008; Olazar et al., 2008a), which has promoted studies on its use for the replacement of conventional liquid fuels and as a source of chemicals and raw materials for the petrochem- ical industry. The yields of BTX and light olefins may be increased by using in situ acid catalysts (HY or HZSM-5 zeolites) or by reforming the volatile stream at the outlet of the pyrolysis reactor by using these catalysts (Arabiourrutia et al., 2008). The carbon black obtained in thermal flash pyrolysis has a high heat value of 29 MJ/kg and a sulphur content of 2.0–2.8% (Olazar et al., 2008a), which should be removed for most of the applications. The pyrolysis of scrap tyres has already been studied and re- ported in the literature and encouraging results have been ob- tained at different scales and using different technologies, amongst which the following are worth mentioning: fixed bed (Berrueco et al., 2005; Islam et al., 2008), fluidized bed (Kaminsky and Mennerich, 2001; Dai et al., 2001), rotary oven (Li et al., 2004), vacuum moving bed (Pantea et al., 2003; Gupta et al., 2004) and conical spouted bed reactor (Arabiourrutia et al., 2007). The interest of vacuum pyrolysis lies in the advantages associ- ated with the decrease in the inert gas flowrate and residence time of volatiles in the reactor: (a) lower energy requirements for the process (although this advantage depends largely on the technol- ogy used, given that it will condition the energy requirement for vacuum); (b) simpler devices for volatile product condensation; (c) higher liquid yield and better control of its composition, either for increasing the yield of high value added components, such as dl-limonene (Pakdel et al., 2001) or for improving its fuel quality (Zhang et al., 2008) and (d) better quality of the carbon black, given 0956-053X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2009.06.005 * Corresponding author. Tel.: +34 946 015 363; fax: +34 946 013 500. E-mail address: martin.olazar@ehu.es (M. Olazar). Waste Management 29 (2009) 2649–2655 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman