Pyrolysis of waste animal fats in a fixed-bed reactor: Production and characterization of bio-oil and bio-char
Introduction
Renewable energy sources are being considered as an attractive solution for overcoming the energy needs and for reducing the environmental problems. Compared to other renewable energy, biomass is the most interesting energy source since it can be converted directly into liquid, gaseous and solid fuels, usable for transport, heat and power production (Bridgwater and Peacocke, 2000, Asadullah et al., 2007, Blin et al., 2007, Goyal et al., 2008). Among a large variety of biomass resources, animal fatty wastes (AFW) are precious materials for second generation bio-fuels production as they are formed mainly of triglycerides, with high energetic value (Maher and Bressler, 2007).
In Tunisia, the amount of AFW generated, in 2010, was about 80.000 tons (ANGed, 2010). Regarding the method of treatment or disposal, a small percentage of AFW is recycled (around 22%) while its major part is buried in sanitary landfills, which are associated with environmental problems (leachate and biogas production). These environmental problems can be alleviated by converting these AFW into energy.
A wide range of technologies such as biochemical, thermochemical, and physical and/or chemical processes are available for recovering bio-fuels from triglyceride based materials. Thermochemical processes include gasification, pyrolysis and combustion (Bridgwater, 2003, Goyal et al., 2008). Among these technologies, pyrolysis is thought to be more favorable for converting AFW into mainly valuable liquid hydrocarbons (Maher and Bressler, 2007, Wisniewski et al., 2010). Pyrolysis is a thermal decomposition of organic substances under oxygen-deficient circumstances into various phases: liquid products (condensable vapors at cooling temperature); carbon-rich solid residues (bio-char); gaseous products (syngas which were not condensable gases) (Maschio et al., 1992, Bridgwater, 2003). The liquid product (bio-oil or pyrolytic oil), which is a complex mixture of oxygenated hydrocarbons and water, can be used directly as a liquid fuel or as source of synthetic chemical feedstocks (Bridgwater, 2003, Blin et al., 2007, Maher and Bressler, 2007). Pyrolysis bio-oil from fish fatty wastes has already been successfully tested as a direct fuel in Diesel engines (Varuvel et al., 2012). The solid bio-char, similar to fossil coal, is also a useful product that can be used as bio-fuel (high calorific value) or chemical adsorbent (as a substitute for activated carbon) (Maschio et al., 1992, Bae et al., 2011) or as soil amendment (Grierson et al., 2011). Moreover, the pyrolysis products quality and distributions depend mainly on some experimental parameters: pyrolysis final temperature, heating rate, residence time, type of pyrolysis reactor, type of raw material…etc. (Zanzi et al., 1996, Bridgwater, 2003). The influence of the process parameters and the pyrolysis products properties have been widely discussed for various biomass resources (Asadullah et al., 2007) but, few literature is available for fatty materials pyrolysis products (yields and properties). Maher and Bressel (2007) in a review on the thermo-chemical conversion of triglyceride materials, presented the state of the art of different pyrolysis processes, pyrolytic products properties and applications, and concluded that the obtained bio-oils composition are entirely different as a function of the feedstock. Wisniewski et al. (2010), comparing bio-oils produced from triglycerides materials and lignocellulosic biomass, showed that the first one contained mainly of alkanes, alkenes, ketones, aldehydes, aromatics and carboxylic acids and the second one was formed basically of phenols, benzenediols, furanes and their derivates.
However, compared to lingo-cellulosic materials, the pyrolysis of fatty wastes is not very established in the literature. Main research developed in the area of bio-fuels from fatty materials concerns bio-diesel production through transesterification process (Srivastava and Prasad, 2000, Fukuda et al., 2001, Demirbas, 2003, Tashtoush et al., 2004, Phan and Phan, 2008, Sabudak and Yildiz, 2010). This study aimed (i) to investigate the effects of main parameters (temperature and heating rate) and also of the nature of feedstock, on the pyrolysis products distribution; (ii) to determinate the suitable conditions for the production of the maximum of bio-oil; and (iii) to characterize bio-oils and bio-chars obtained from several AFW pyrolysis in the suitable conditions.
Section snippets
Raw material
The animal (lamb, poultry and swine) fatty wastes, used in this study for pyrolysis feed, were obtained from various meat factories around Tunis, in northern of Tunisia. Prior to pyrolysis experiments, animal wastes were freeze-dried and analyzed using elemental analysis (CHNS-O). The CHN-contents of the input materials were determined via Perkin Elmer 2400 CHN elemental analyzer. The sulfur content was measured using Horiba Jobin Yvon elemental sulfur analyzer. The oxygen content was
Feed materials characteristics
The main characteristics of studied animal fat wastes are summarized in Table 1. All studied materials have high carbon contents (up to ∼75% in the three studied samples), moderate oxygen contents (mean value of 19.3% for the three samples) and high hydrogen contents (around 12% for the three studied samples) but low nitrogen and sulfur contents (avg. close to 0.58% and 0.19%, respectively). The ash content of the input material are also very low (not exceed 0.64%).
The fatty acids compositions
Conclusion
This study confirms that animal fatty wastes are precious raw materials for bio-oil production by pyrolysis process. The investigation of the effects of experimental parameters on the quality and the distribution of pyrolysis products indicate that the temperature of 500 °C and the heating rate of 5 °C/min are the most convenient conditions to get better results (maximum bio-oil yield) from the pyrolysis of animal fats wastes. In these suitable conditions, the yields of bio-oils obtained from
Acknowledgements
We thank M. Ghaith Hamdaoui from CBBC (Centre de Biotechnologie de Borj-Cédria-Tunisia) for analytical assistance in GC/MS analyses and Mrs. Samia Jlidi from CNRSM (Centre National des Recherches en Sciences des Matériaux-Tunisia) for help in FTIR analyses.
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