INFLUENCE OF CRUDE METHANOLIC EXTRACTS OF RICE HUSK AND SAW DUST AS ANTIOXIDANTS ON THERMO-OXIDATIVE STABILITY OF BASE LUBRICATING OIL

Abstract

Lubricating oil performs a variety of functions in an engine/machine. It provides lubrication to the moving, sliding & rolling surfaces thereby minimizing fraction, wear, hence imparts more life to the machinery. In addition, it protects metal surfaces against corrosion, acts as heat transfer agent, flush out contaminants, absorb shocks and seal leaks. However, during service, it is exposed to high load, speed, heating & oxidation hence suffered from degradation and gets spent. The spent oil no longer retains its properties and needs frequent replacement with a new one which is not only a waste of valuable resource but also contributes to the environmental pollution if carelessly disposed off. Performance improvement additives (antioxidants) are added in commercial formulations to avoid or delay the oxidation and to increase the service life of the oil. However, the antioxidants developed to date have several shortcomings and suffer from antagonistic effects which decline their abilities to withstand oxidation. Therefore, there is a need to investigate about new antioxidants to be efficient enough not only to minimize the thermo-oxidative degradation of the oil, and increase its service life but also to avoid disposal issues. The present work aimed to evaluate the antioxidant potentials of two natural antioxidants i.e. alcoholic extracts from rice husk (RHE) and saw dust (SDE) in oxidative stability of base lubricating oil under a set of experimental conditions. The oxidation stability of the mineral base oil with and without antioxidants was evaluated in an air atmosphere using temperature and time ramped oxidation experiments. The influence of a number of experimental conditions such as temperature, oxidation time, and concentration of each antioxidant was studied. The efficiency of the derived extracts at low and high temperatures was investigated. Mineral base oil (MBO), MBO additized with the RHE, and SDEwere evaluated at different temperatures and times using modified IP 48 procedure. The effect of additive concentration was also Table of contents xxii studied. With combination of the physico-chemical, conductiometric, spectroscopic, thermo-analytical, calorimetric and chromatographic analysis, the oil degradation in the absence and presence of the antioxidants understudy was monitored. Principal physico-chemical properties such as kinematic viscosity determined at 40 & 100 oC, viscosity index & viscosity ratio and complementary properties such as Conradson carbon residue, total acidity number & iodine number were determined using standard ASTM Methods. Oxidation may lead to formation of mostly carboxylic acids leading to changes in the spectroscopic properties of the oil. In order to know about the chemical changes occurring in the base oil during oxidation, FTIR analyses of the original oil, and un-additized MBO, RHE-& SDE-additized samples oxidized at optimum temperatures and time were performed in order to identify the oxidation products like carboxylic acids/carboxylates, amides, esters, etc.The conductance changes occurring in the oil samples during oxidation were recorded in order to decide about the oxidation induction times (OIT) and oxidative stability index (OSI). The changes were measured in case of the un-additized and RHE- &SDE-additized base oil samples oxidized at 100 and 200 oC for time duration of 06 h. Next to OSI analysis, the thermo gravimetric analyses (TGA) were performed in case of the un-additized and various additized base oil samples oxidized at 100 and 200 oC for time duration of 06 h in order to evaluate their thermal stabilities in terms of T onset, T offset, mass loss and weight gain.Calorimetric analyses in terms of oxidation induction time (OIT) were performed in case of the oil samples spiked with bio mass derived extracts in comparison to un-additized MBO in order to evaluate the antioxidant character of the RHE and SDE.To decide about changes in spectroscopic properties of the original and variously oxidized residual oil samples, Gas chromatographic- Mass spectrometric analysis was carried out in order to ascertain the changes in the individual compounds, the hydrocarbon range products and the hydrocarbon group type’s distributions. The results indicated that the antioxidants understudy imparted stability to the base oil at low as well as high temperatures. The results further inferred that the use of biomass derived additives reduced the oxidative degradation of the base oil to a greater Table of contents xxiii extent and thus could be used on commercial scale to eliminate the use of environmentally objectionable and costly additives. ORGANIZATION OF THE THESIS The thesis is compiled in the form of THREE chapters. 1. INTRODUCTION This chapter represents the theoretical knowledge about the lubricating oil, its composition, properties, base oil and its types, oxidative degradation, mechanism of oxidative degradation, method used to evaluate oil degradation, literature survey related to base oil degradation, and the role of antioxidants. All references cited have been given at the end of this chapter. 2. EXPERIMENTAL This chapter is devoted to the various experimental and stat of the art analytical methods used (ASTM/IP). All references cited have been given at the end of this chapter. 3. RESULTS AND DISCUSSION This chapter presents the experimentally achieved results supported by the corresponding pictorials, graphical representations, spectra, thermograms, oxidographs and chromatograms discussed in the light of the available literature. The conclusions based on the results are also provided. All references cited throughout the text have been given at the end of this chapter.