A data-driven approach for the study of coagulation phenomena in waste lubricant oils and its relevance in alkaline regeneration treatments

• Published in: The Science of the total environment 2017-12, Vol.599-600, p.2054-2064
• Main Authors: Pinheiro, C.T., Ascensão, V.R., Reis, M.S., Quina, M.J., Gando-Ferreira, L.M.
• Format: Article
• Language: English
• Subjects: Characterization; Classification; Coagulation phenomena; FTIR spectroscopy; Regeneration; Waste lubricant oil
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2017.05.124

[Display omitted] Coagulation phenomena can occur in certain types of waste lubricant oils (WLO) during regeneration processes involving alkaline treatments, causing plant shutdowns. In this context, this study addresses the nature of the compounds responsible for the coagulation phenomena after the alkaline treatment. For such, an empirical test was developed to assess the coagulation behaviour of WLO, consisting in the addition of KOH to the WLO followed by heating under stirring conditions. This test was performed on 133 samples and four coagulation classes were identified: A; B1; B2 and C. Moreover, a physicochemical characterization of WLO was carried out regarding viscosity at 40°C, saponification number (SN), total acid number (TAN), surface tension, water content, elemental analysis and functional groups (FTIR). 56 samples of fresh lubricant oils for different applications were also characterized and their properties assessed and compared. Multivariate methods were applied to WLO to discriminate among coagulation classes based on FTIR spectra. It was found that coagulation classes A and B1 exhibit statistically similar patterns for all properties determined. Spectral discriminating analysis did not reveal discriminant peaks for class B1 samples, and the presence of specific additives was pointed as the possible factor underlying the increase in viscosity in this oils. Class B2 presents the absence of additives and oxidation products as differentiating features. In addition, B2 samples showed lower TAN SN, and lower concentration of some elements. Lubricants from gear or hydraulic applications can give rise to this class of WLO. Oils of Class C are mainly composed by synthetic ester type base oils, which hamper regeneration processes using alkaline pretreatments. In future studies, WLO type A and B1 can be classified as a single class. The coagulation phenomena classification becomes A – negative, B – precipitate formation and C – positive. •Regeneration of waste oil by alkaline treatment is dependent on coagulation phenomena.•Coagulation test indicated three classes of waste oils (A, B and C).•Chemometric methods based on FTIR spectra properly classified 83% of the samples.•Discriminant analysis showed differences in the chemical composition between classes.•The data-driven approach adopted is useful for predicting coagulation phenomena.