Síntese de ésteres como alternativas sustentáveis e ecológicas no desenvolvimento de novos lubrificantes

Abstract

Vegetable oils are emerging as a sustainable alternative to petroleum-based lubricants because they offer good viscosity and thermal stability and are biodegradable, reducing the environmental impact of spills. Chemical modifications, such as ester production, expand their industrial applications and support cleaner technologies, reducing dependence on fossil resources. They thus contribute to sustainability by promoting responsible industrial practices and replacing traditional substances with lower environmental impact. This research aimed to synthesise new esters from pequi oil using commercial polyols and to study the epoxidation kinetics of soybean, cotton and linseed vegetable oils. The ester synthesis involved two processes: hydrolysis of the triglycerides from pequi oil, followed by esterification with β-hydrogen-free polyols: 2-ethylhexan-1-ol (2EH), neopentylglycol (NPG), trimethylolpropane (TMP) and pentaerythritol (PE), using p-toluenesulphonic acid (p-TSA) as a catalyst. Epoxidation of vegetable oils was carried out using propionic acid and Amberlite IR-120 as catalyst in a two-phase system. The reaction kinetics were analysed using parameters such as temperature, ratio of hydrogen peroxide to propionic acid (HP/PA) and Amberlite IR-120 concentration through an experimental design. The synthesised esters showed high conversion rates (> 98%) and physicochemical properties suitable for use as lubricants. Furthermore, they exhibited ISO viscosities VG 7, 22 and 46, indicating their suitability for general lubrication of machinery, hydraulic systems and gears. These esters also exhibited SAE viscosities of 16, 30, 70W, 75W, 80 and 80W, ensuring good fluidity at low temperatures and efficiency at high temperatures. Thermal analysis showed oxidative stability (Tonset between 223 and 283 °C) and ideal flow behaviour at low temperatures, with melting points ranging from -58.0 to -2.0 °C. Rheological tests confirmed that the esters behaved as Newtonian fluids at temperatures of 20, 40 and 60 °C, maintaining a stable viscosity even with variations in temperature and shear rate. The tribological behaviour of NPG and TMP esters and their blends with NH10 showed the formation of tribofilm with a coefficient of friction (COF) in the ideal lubrication range (0.001 < COF < 0.2). Safety tests with adult zebrafish showed that all synthesised esters were non-toxic after 96 hours of exposure without affecting fish locomotion. The epoxidation kinetics of soybean (SBO), cottonseed (CSO) and linseed (LSO) oils and their methyl esters were confirmed by 1H NMR and FTIR spectroscopy, with conversion and selectivity rates higher than those observed for methyl derivatives. The HP/PA ratio (7:3 mol L-1) was identified as the parameter most influencing conversion and double bond consumption. The reactivity of the oils followed the order CSO > SBO > LSO, demonstrating the influence of chemical composition on epoxidation kinetics. The results suggest that vegetable oils are a viable alternative to fossil-based lubricants as they are natural, safe and renewable sources with significant industrial potential.