Thermal degradation of synthetic lubricants under oxidative pyrolytic conditions G. Mascolo a, * , R. Rausa b , G. Bagnuolo a , G. Mininni c , L. Tinucci b a C.N.R. Istituto di Ricerca sulle Acque, Sezione di Bari, Via De Blasio 5, 70123 Bari, Italy b EniTecnologie S.p.A., Via Maritano 26, 20097 S. Donato Milanese, Italy c C.N.R. Istituto di Ricerca sulle Acque, Sezione di Roma, Via Reno 1, 00198 Roma, Italy Received 10 December 2004; accepted 13 May 2005 Available online 1 July 2005 Abstract The gaseous phase thermal degradation, under oxidative pyrolysis conditions, of three commercial industrial lubricants (two of different triaryl phosphate composition and one based on fatty acid methyl and ethyl esters) was investigated between 400 and 1000 8C. The main objective of the study was to investigate their behavior in simulated ‘‘hot spot’’ conditions, i.e. compare the thermal stability and identify the products of thermal decomposition as a function of exposure temperature. Experimental results showed that the fluid based on fatty acid methyl and ethyl esters has the lowest thermal stability, being completely degraded at 700 8C with respect to 800 and 900 8C for the two phosphorus-based lubricants. Several by-products were identified during the thermal degradation of all lubricants. The majority of them consisted of aromatic compounds, amongst which benzene was the most abundant, and polycyclic aromatic hydrocarbons (PAHs). The formation of such by-products peaked at 700 and 800 8C respectively for the lubricants without and with phosphorus. Two main mechanisms were proposed for the formation of these products. In first hypothesis, degradation of the fatty acid methyl and ethyl esters lubricant is assumed to start with the breakdown of the aliphatic moieties generating vinyl radicals which, in turn, through displacement and cyclization reactions gave rise to benzene radicals and PAHs. According to the second hypothesis, phosphorus-based lubricants degrade directly forming benzene radicals and PAH structures by consecutive reactions. At temperatures greater than 700 8C, the amounts of benzene and PAHs produced as a result of the degradation of the fatty acid methyl and ethyl ester based lubricant were much lower than those of the two triaryl phosphate lubricants. The experimental results showed that fewer and less hazardous by-products are formed during the thermal degradation of the fatty acid methyl and ethyl ester based lubricant with respect to the lubricants based on triaryl phosphate. # 2005 Elsevier B.V. All rights reserved. Keywords: Aryl phosphates; Fatty acid methyl and ethyl esters; Lubricants; Oxidative pyrolysis; PAHs; Thermal degradation 1. Introduction Triaryl phosphates are commonly used world-wide as lubricants due to their superior performance compared to natural or synthetic hydrocarbon oils [1–3] with an annual consumption of several thousands of tons [4]. They are mainly used as a synthetic lubricant in several high temperature industrial applications (ovens, electric soldering and indus- trial press) and as an anti-wear additive in several synthetic ester formulations of aviation turbine engines [5,6]. In addition, other triaryl phosphate applications exist, the most important being use as a hydraulic fluid, as a plasticizer in lacquers and varnishes and as a flame retardant [6,7]. However, there is concern about the widespread use of these compounds because their chemical structures are phosphorus-based esters as those of other compounds known to be highly toxic to mammals, such as the well known neurotoxins used in biological weapons (Sarin 1 , Tabun 1 and Soman 1 ) and to the insecticide Salithion 1 [8,9]. The toxicity of triaryl phosphate lubricants principally depends upon the substituent group and its location on the benzene ring. The substituents are usually methyl and tertiary-butyl, giving rise to tricresyl phosphate (TCP) and to t-butylphenyl www.elsevier.com/locate/jaap J. Anal. Appl. Pyrolysis 75 (2006) 167–173 * Corresponding author. Tel.: +39 080 5820519; fax: +39 080 5313365. E-mail address: giuseppe.mascolo@ba.irsa.cnr.it (G. Mascolo). 0165-2370/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2005.05.005