Ester-based Oils Research Articles

Ionic liquid-functionalized ZnO nanomaterial: Multifunctional additives enhancing tribological performance and corrosion resistance in ester oil

A multifunctional nanomaterial (ZnO-IL), comprising zinc oxide modified with corrosion-resistant ionic liquid groups, was designed and synthesized. It was used as an additive in bis(2-ethylhexyl) sebacate (DIOS) to evaluate its tribological and corrosion resistance properties, and compared with the commercial additive sulfurized isobutylene (SIB). ZnO-IL exhibited good solubility and thermal stability in DIOS. Lubricants containing ZnO-IL showed excellent anti-wear performance under various loads and temperatures. Its deposition on metal surfaces and the synergistic action of benzotriazole groups in the anions effectively prevented corrosion on the surfaces of metal friction pairs, thereby addressing the challenge of friction pair corrosion caused by the hydrolysis of ester-based oils. The ZnO-IL nanomaterial rapidly formed an organic-inorganic multilayer adsorption film on metal surfaces through electrostatic interactions. During friction, a boundary lubrication film composed of ZnO deposition and friction chemical reaction films was formed, thereby avoiding direct metal contact, reducing contact pressure, and exhibiting outstanding friction reduction and anti-wear properties.

Lubrication antagonism mechanism of nano-MoS2 and soot particles in ester base oil

Spherical nano-MoS2 (S-MoS2) has excellent lubricating properties and potential application value in engine oil additives. Engine soot can enter the engine oil, so the tribological interaction between S-MoS2 and diesel combustion soot (DCS) should be investigated. In this study, DCS was used to simulate engine soot. The interaction was investigated in dioctyl sebacate (DOS), and the interaction mechanism was full characterized. Results showed that S-MoS2 and DCS had obvious antagonism effects on lubrication. The 0.5% S-MoS2 exhibited good lubricating properties in DOS, which could reduce friction by ∼22% and wear by ∼54%. However, after 0.5% S-MoS2 was added to the 0.5% DCS contaminated DOS, the lubrication performance was not improved and was even worse than that without S-MoS2. When S-MoS2 was added for DOS lubrication, a tribofilm containing MoS2 formed on the friction surface, but simultaneously adding 0.5% DCS resulted in the disappearance of the MoS2 tribofilm. Moreover, under the action of friction heat, DCS and S-MoS2 could form hard MoxCy, thereby increasing abrasive wear. Finally, a preliminary deantagonism method was provided. After 2.0% zinc isooctyl dithiophosphate was added to the above antagonistic system, the friction coefficient did not show visible changes, but the wear recovered to a level close to that when only S-MoS2 was added. The antiantagonism method is not very satisfactory and some more efficient methods need to be further explored.

Dual surface-modification by oleic acid and epoxy-based silane coupling agent providing cerium oxide nanoparticles as additive in pentaerythritol oleate with improved high-temperature adsorption performance and tribological properties

An epoxy-based silane coupling agent (KH560) was grafted onto the surface of oleic acid-modified cerium oxide (CeO2-OA) nanoparticles in order to improve the competitive adsorption ability of the anti-wear additives in ester oils and simultaneously hinder the additive desorption owing to thermal disturbance under high-temperature condition. The as-prepared oleic acid-epoxy silane co-modified cerium oxide (CeO2-OA/E) nanoparticles were characterized. The effect of temperature on the adsorption behavior of trityl phosphate (TCP, a commercial high-temperature antifriction agent), CeO2-OA and CeO2-OA/E in PETO was studied using a dissipative quartz microbalance. Their tribological properties as the additives in pentaerythritol oleate (PETO), a polar ester base oil, were evaluated with a four-ball machine and a ball-on-block friction and wear tester; and their tribomechanism was explored with respect to their adsorption behavior on rubbed steel surfaces at elevated temperatures. It was found that the secondary surface-capping of CeO2-OA by the KH560 silane coupling agent resulted in great increases in the surface potential (from 54 mV to 396 mV) and thermal stability as well (the thermal decomposition temperature rose from 185 °C to 254 °C). Among the tesetd lubricant additives, CeO2-OA/E exhibited the highest adsorption mass, because of the highest surface potential the chemisorption ascribed to the epoxy group of the silane coupling agent. Particularly, CeO2-OA/E added in PETO exhibited better friction reduction and anti-wear properties at 150 °C than CeO2-OA and TCP, because CeO2-OA/E added in PETO formed tribofilm composed of CeO2 and SiO2 with excellent thermal stability as well as friction-reduction and antiwear effects through stable chemical adsorption and tribochemical reaction at elevated temperatures.

Tribological study of two ammonium chloride-decanoic acid deep eutectic solvents (DESs) as high-performance lubricants

Deep eutectic solvents (DESs) are acknowledged as a novel class of functional liquid. DESs share similar physical properties with ionic liquids (ILs) and have the potential to be a novel class of lubricants. In this study, two DESs, namely tetrabutylammonium chloride-decanoic acid DES (C4-DES) and methyl tricaprylmethylammonium chloride-decanoic acid DES (C8-DES), were synthesized, and their physico-chemical properties and tribological performances were evaluated. Post-analysis of the rubbing surfaces used multiple techniques to gain insights into the lubrication mechanisms. Results show that the coefficient of friction (COF) and wear were reduced by approximately 29% and 91% for the C4-DES, and 36% and 94% for the C8-DES, compared to an ester base oil. The friction reduction behavior of the DESs is attributed to the monolayer adsorption of the polar group in the decanoic acid (DEAC), whose effectiveness is affected by the component of the ammonium salts in the DESs and the operating temperatures. In addition to the adsorbed film, worn surface analysis revealed that an ultra-thin tribochemical film with a thickness of 3–7 nm was formed on the surfaces lubricated with the C8-DES. The composition of the film was studied, and the lubrication mechanisms of the two DESs were discussed.

Adaptive accelerated reactive molecular dynamics driven by parallel collective variables overcoming dimensionality explosion.

ReaxFF reactive molecular dynamics has significantly advanced the exploration of chemical reaction mechanisms in complex systems. However, it faces several challenges: (1) the prevalent use of excessively high temperatures (>2000K), (2) a time scale considerably shorter than the experimental timeframes (nanoseconds vs seconds), and (3) the constraining impact of dimensionality growth due to collective variables on the expansiveness of research systems. To overcome these issues, we introduced Parallel Collective Variable-Driven Adaptive Accelerated Reaction Molecular Dynamics (PCVR), which integrates metadynamics with ReaxFF. This method incorporates bond distortion based on each bond type for customized Collective Variable (CV) parameterization, facilitating independent parallel acceleration. Simultaneously, the sampling was confined to fixed cutoff ranges for distinct bond distortions, effectively overcoming the challenge of the CV dimensionality explosion. This extension enhances the applicability of ReaxFF to non-strongly coupled systems with numerous reaction energy barriers and mitigates the system size limitations. Using accelerated reactive molecular dynamics, the oxidation of ester-based oil was simulated with 31 808 atoms at 500K for 64s. This achieved 61% efficiency compared to the original ReaxFF and was ∼37 times faster than previous methods. Unlike ReaxFF's high-temperature constraints, PCVR accurately reveals the pivotal role of oxygen in ester oxidation at industrial temperatures, producing polymers consistent with the sludge formation observed in ester degradation experiments. This method promises to advance reactive molecular dynamics by enabling simulations at lower temperatures, extending to second-level timescales, and accommodating systems with millions of atoms.

In situ preparation of Cu-Mo-S nanoparticle additive with multi-functional tribological properties

Complex operating conditions pose greater challenges for lubricants, making the development of multi-functional additives a trend. This research introduces a multifunctional Cu-Mo-S nanoparticle (CMS) additive, synthesized using a unique one-pot in situ method. The CMS significantly improved the tribological performance and oxidation stability of base oils. Specifically, 0.5 wt% CMS manifested a remarkable reduction in the friction coefficient and wear volume of ester-based oils by 74.75% and 95.91%, accompanied by a noteworthy increase in the extreme pressure capabilities exceeding 50%, outperforming the individual copper nanoparticles, organic molybdenum, and their mixtures. The remarkable results are attributed to the distinctive structure of CMS, which decomposed during the friction process, forming a continuous friction film containing copper, molybdenum, and iron compounds.

Performance of Hybrid Nanofluids of Mineral Oil and Vegetable oil based Ester

The prosperity and economic development of a nation depend on its capability to maintain reliable and high-quality electric power management. It is achieved through the availability of extremely reliable ancillary electrical equipment. A power transformer is one such piece of crucial equipment that transfers electricity from one circuit to another without altering the frequency. Mineral oil has been conventionally used as a liquid dielectric in transformers since the last century. However, in recent days, vegetable oil-based esters have emerged as a favourable alternative to mineral oils due to their biodegradability and sustainability. The introduction of nanotechnology led to massive studies to enhance the quality of liquid dielectrics. Further, the addition of more than one nanoparticle to the base fluid has broadened the scope of nanofluids’ property enhancement. This study focused on the assessment of the dielectric properties of hybrid nanofluids consisting of ZnO and reduced graphene. Mineral oil and vegetable-based transformer oil were chosen as base fluids to prepare the nanofluids. The mass of the added nanoparticles was 0.01%. The ratio between the nanoparticles was selected as 1:1. The hybrid nanofluids were characterized for breakdown voltage viscosity at temperatures ranging from 40 °C to 100 °C, interfacial tension, tan delta, and resistivity. The overall properties of hybrid nanofluids were found to be improved due to the inclusion of ZnO and reduced graphene.

Synthetic Ester-Based Oils and Their Application in Power Industry

Suitable (biodegradable) substitution of classic mineral petroleum-based oils used in power transformers is studied. Paper presents test results of six paper-oil insulation systems varying by different type of oil. Three common transformer oils and three new synthetic oils (never used in power transformers before) were selected for the purpose of experiment. The oils have been exposed to accelerated thermal aging (at the temperature of 90 °C) and their properties were measured in time intervals of 0, 50, 125, 225, 500, 1000 and 2000 hours.

Low-viscosity oligoether esters (OEEs) as high-efficiency lubricating oils: Insight on their structure–lubricity relationship

Development of energy-efficient lubricants is a way to reduce energy consumption for transportation, with the tendency to design molecules that are beneficial in reducing the viscosity of synthetic oils. Oligoether esters (OEEs), as a low-viscosity ester base oil, have characteristics such as simple synthesis and excellent lubrication effect, however, the application of OEEs in tribology field has rarely been investigated. The objective of the present study is to investigate the effect of structure on the lubricating performance of OEEs and to develop a predictive model for OEEs based on quantitative structure-property relationship (QSPR) through a combination of experiment and statistical modeling. Results showed that glycol chains contribute positively to lubrication with the ether functional groups increasing the sites of adsorption. Compared to branched-chain OEEs, straight-chain OEEs exhibited reduced wear, which was mainly due to the thicker adsorption film formed by the straight-chain structure. Furthermore, carbon films were detected on lightly worn surfaces, indicating that OEEs underwent oxidation during the friction process. Based on the results of principal component analysis (PCA) and partial least squares (PLS), it could be found that the predictive models of viscosity–temperature performance, thermal stability performance, coefficient of friction (COF), and wear volume (WV) performed well and robustly. Among them, COF and WV can be best predicted with an R2 of about 0.90.

Dialkyl phosphonate with carboxylic acid as antiwear additives for ester-base lubricants

Ester-base oils are commonly used in environmentally adapted lubricants (EALs) because of their biodegradability. However, their antiwear performance is difficult to improve using the conventional lubricant additives developed for mineral-base oils. In this study, dialkyl phosphonates with various functional groups were designed as antiwear additives for ester-base oils. The antiwear performances of these phosphonates were evaluated using four-ball tests. The results suggest that dialkyl phosphonate with carboxylic acid (DAPA) has better antiwear performance in ester-base oils than that of other phosphonates and conventional phosphorus additives. Remarkably, DAPA exhibits better antiwear performance under severe test conditions in ester-base oils than in poly-alpha olefin. X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to study the chemical compositions of steel surfaces after friction and better understand the antiwear mechanism of DAPA, particularly in ester-base oils.

A monosurfactant-stabilized dual-responsive and versatile emulsion lubricant

Emulsions consisting of lubricating base oil and water have extensive applications in the fields of metalworking and heavy-duty machinery. Due to the compositional complexity that confines an effective recycling of emulsion constituents and the frequent use of toxic, non-biodegradable mineral base oil, an industrial emulsion lubricant is usually easy to produce severe environmental burdens and health issues. Here we report a dual-responsive and versatile lubricating emulsion solely consisting of water, an eco-friendly ester base oil and a synthetic cationic emulsifier. Taking advantage of the inclusion of azobenzene moiety, [CeCl3Br]- anion and methylimidazole head-group, the surfactant can not only undergo tribochemical reactions to function as a lubricant additive to achieve very low interfacial friction, but also endow the resulting emulsion efficient anticorrosion, antibiosis and both light- and magneto-responsiveness. Based on a reversibly photo-triggered variation in the hydrophobicity of surfactant, an on-demand separation and recycling of emulsion component followed by a nearly one order of magnitude conversion in the friction can be realized. Together with its magneto-controlled migration and adaptivity to high normal loads, we envision that the emulsion lubricant may find potential applications in a broad range of industrial systems requiring lubrication and heat dissipation as well as smart devices needing control over the friction between two contacting surfaces.

Experimental investigation on the impact of NOx emission in CI engine fueled with rapeseed biodiesel with antioxidant additives

The proposed research aims to investigate the impact of an oxidant, l-ascorbic acid, on the performance and exhaust of a diesel engine that drives on neat rapeseed methyl ester-based oil (RSOME). The antioxidant is supplemented with rapeseed oil methyl ester in a range of amounts (100–400 mg). This research revealed that, without altering the engine, the reactive additives mixture (MERSO + LA300) substantially lowered the NOX and HC emissions of methyl ester in rapeseed oil-fueled engines.

High-Pressure Thermophysical Properties of Eight Paraffinic, Naphthenic, Polyalphaolefin and Ester Base Oils

In this work, the thermophysical properties of four mineral (paraffinic and naphthenic) and four synthetic (polyalphaolefin and ester) base oils are measured. Knowledge of these properties is of vital importance for the correct and optimal formulation and design of lubricants, and for the development of equations of state and transport models that adequately represent their properties. Density, isothermal compressibility, thermal expansion coefficient, dynamic viscosity, pressure–viscosity coefficient, and contact angle were determined. To carry out this work, a pρT apparatus, a rotational viscometer, a falling body viscometer, and a contact angle analyzer were used. Highest densities were found for the polyalphaolefin and ester synthetic oils, increasing around 5% from 0.1 to 100 MPa for all the base oils. The density of the synthetic oils is less dependent on temperature changes. For the expansivity and compressibility of all the base oils, decreases with pressure of up to 35% and 45% were observed. From the contact angle measurements, it was observed that base oils with a higher viscosity grade have a worse wetting. The greatest effect of pressure on the dynamic viscosity was obtained for the naphthenic mineral oil and the lowest effect for the polyalphaolefin oil. Paraffinic and naphthenic oils present the highest universal pressure–viscosity coefficients.

Solubility, miscibility and compatibility studies of low GWP non-flammable refrigerants and lubricants for refrigeration and air conditioning applications

Majority of currently used refrigeration and air conditioning systems utilize high GWP refrigerants such as R410A, R404A and R134a. These systems have large leak rates which leads to significant amount of release of HFC's to the environment. The growing environmental concerns are driving stringent regulations to phase out these high GWP refrigerants and move towards adoption of lower GWP refrigerants. This transition would require understanding of interaction between low GWP refrigerants and lubricating oil as well as the material compatibility with commonly used thermoplastics and elastomers. In this article, nonflammable low GWP refrigerants, R515B and R471A are introduced as the potential replacements for R410A, R404A and R134a in an air-conditioning and medium temperature refrigeration applications. Solubility and miscibility of R515B and R471A with polyol ester-based oil (POE32) is experimentally investigated over a temperature range of −20 °C to 120 °C and −30 °C to 75 °C, respectively. Further this article also presents the compatibility results of R515B and R471A (POE32) with thermoplastics and elastomers used in refrigeration and air-conditioning systems.

Tribological properties and lubrication mechanism of protic ionic liquid-modified nanosilica as high-temperature antiwear additive for pentaerythritol ester

Protic ionic liquid-modified nanosilica (SiO2-PIL) hybrid with excellent dispersion stability and thermal stability was prepared. The SiO2-PIL hybrid was used as a high temperature antiwear additive for pentaerythritol ester (PE) base oil, which exhibited better antiwear ability and load-carrying capacity at high temperature compared with triphenyl phosphate (TCP). This is attributed to the synergistic friction-reducing and antiwear effects of nanosilica and ionic liquid during sliding at elevated temperatures. Findings indicate that a protective tribofilm with sandwich structure composed of phosphate and amorphous carbon as the outer layer and silica nanoparticles as the interlayer was formed on the worn surface. Finally, combined with the adsorption behavior and the results of worn surface analysis, the high-temperature lubrication mechanism of SiO2-PIL was proposed.

Frictional Power Evaluation of Additive-Mixture in Trimethylolpropane Trioleate Oil using Single Cylinder Diesel Engine

Rapid depletion of petroleum sources and increase of demand for environmentally friendly products has urged the need for biodegradable lubricants to be utilized in various applications, especially for internal combustion (IC) engine lubrication. To perform on par with the commercial engine oils, bio-based lubricants need to be further improved through the addition of appropriate additives. This study investigates the synergistic performance of additive-mixture comprising of ionic liquids (IL), glycerol monooleate (GMO), molybdenum dithiocarbamate (MoDTC) and titanium dioxide (TiO2) nanoparticle in trimethylolpropane trioleate (TMPTO) ester base oil. Lubricity performances of the prepared sample were evaluated in the context of tribological improvement using laboratory tribotester as well as friction power reduction in actual single-cylinder diesel engine. From a prior study, it was found that additive mixture containing 0.93 wt.% IL, 1.49 wt.% GMO, 0.52 wt.% MoDTC, and 1.25wt.% TiO2 was able to provide substantial friction and wear as well as extreme pressure improvements. The present study was conducted to evaluate whether the formulation can offer the same performance on the actual engine in conjunction to the laboratory bench test. To do so, two different types of engine tests were conducted which are that standard engine performance test and also the Willans line test to evaluate the engine frictional power. The performance of the additives-TMPTO mixture was compared directly to those of commercial SAE 0W-30 engine lubricant. In the standard engine performance test, it was found that the additives-TMPTO mixture performed better than commercial SAE 0W-30 engine lubricant in terms of 2.5% higher maximum torque value, 3% higher overall brake power output, 10% lower brake specific fuel consumption and 12% higher brake thermal efficiency throughout the conducted test speed of 800 to 2300 rpm. Through the Willans line test, it was found that the additives-TMPTO mixture showed better results than the commercial SAE 0W-30 engine lubricant in terms of 20-25% lower frictional power at 900, 1200 and 1500 rpm. Overall, these results further justify the enhanced lubrication properties of the formulated bio-based oil in addition to the prior conducted tribological analyses.

Assessment of Thermophysical Performance of Ester-Based Nanofluids for Enhanced Insulation Cooling in Transformers

Nanotechnology provides an effective way to upgrade the thermophysical characteristics of dielectric oils and creates optimal transformer design. The properties of insulation materials have a significant effect on the optimal transformer design. Ester-based nanofluids (NF) are introduced as an energy-efficient alternative to conventional mineral oils, prepared by dispersing nanoparticles in the base oil. This study presents the effect of nanoparticles on the thermophysical properties of pure natural ester (NE) and synthetic ester (SE) oils with temperature varied from ambient temperature up to 80 °C. A range of concentrations of graphene oxide (GO) and TiO2 nanoparticles were used in the study to upgrade the thermophysical properties of ester-based oils. The experiments for thermal conductivity and viscosity were performed using a TC-4 apparatus that follows Debby’s concept and a redwood viscometer apparatus that follows the ASTM-D445 experimental standard, respectively. The experimental results show that nanoparticles have a positive effect on the thermal conductivity and viscosity of oils which reduces with an increase in temperature.

Improvement of the lubrication performance of an ester base oil with coated ferrite nanoadditives for different material pairs

In the present work, lubrication properties (friction and wear) of a synthetic ester oil, tris(2-ethylhexyl) trimellitate (TOTM) containing ferrite nanoparticles coated with oleic acid (F3O4-OA) were investigated for two different material pairs: steel ball-steel disc and silicon nitride ball-steel disc. Thus, four TOTM nanolubricants were formulated: TOTM + 0.010 wt% Fe3O4-OA, TOTM + 0.015 wt% Fe3O4-OA, TOTM + 0.020 wt% Fe3O4-OA and TOTM + 0.025 wt% Fe3O4-OA showing all of them a moderate time stability due to the oleic acid coating. Wettability behaviour of the ferrite-based nanolubricants on steel surface was analysed, revealing that the addition of Fe3O4-OA nanoparticles in TOTM decreases the contact angle between the steel surface and TOTM lubricant surface. Friction sliding tests were performed with the neat TOTM and with the formulated nanolubricants under a 20 N of load. All nanolubricants showed lower coefficients of friction than those reached with TOTM base oil for both material pairs. Worn area was significantly reduced for all Fe3O4-OA concentrations in the steel-steel contact and for the highest concentrations in the silicon nitride-steel contact. Specifically, the largest achieved reductions were for the TOTM + 0.010 wt% F3O4-OA nanolubricant: 43% reduction in friction (silicon nitride-steel) and reductions of 17% in wear track width, 42% in wear track deep and 36% in area (steel-steel). In addition, roughness analysis and Raman microscopy of the tested discs showed that tribofilm formation and surface repairing mechanisms occur.

Production of sustainable two-stroke engine biolubricant ester base oil from palm fatty acid distillate

In this study, palm fatty acid distillate (PFAD) was selected as the feedstock for biolubricant base oil production in two-stroke engine oils’ formulation. PFAD is a low-cost palm refinery by-product with a high free fatty acid (FFA) content (85%). The esterification of PFAD with neopentyl glycol (NPG) was conducted in the presence of a solid acid catalyst (SO42-/Fe2O3/Al2O3) to produce PFAD-NPG ester. Optimization profile indicated that PFAD conversion and PFAD-NPG ester yield were 84% and 82%, respectively, under optimum reaction conditions of 180 °C, 4 h, 2.0 wt% SO42-/Fe2O3/Al2O3 catalyst loading and a 2:1 PFAD to NPG molar ratio. The physicochemical properties of the base oil successfully comply with the Japanese Automotive Standards Organization (JASO) M345:2018 requirements for two-stroke oils in terms of sulfated ash content, kinematic viscosity at 100 °C and flash point. In addition, reusability of solid acid catalyst, SO42-/Fe2O3/Al2O3 was investigated, where PFAD conversion and PFAD-NPG ester yield were found to be excellent at 81% and 80%, respectively, which showed that the catalyst had good consistency after 5 cycles.

Alternative liquid dielectrics in power transformer insulation: a review

Transformer liquid dielectrics evolved where mineral oil has been the dominant choice until emergence of synthetic esters and natural esters. Natural ester-based oils have been under extensive investigations to enhance their properties for replacing petroleum-based mineral oil, which is non-biodegradable and has poor dielectric properties. This paper focuses on exposition of natural ester oil application in mixed transformer liquid dielectrics. Physical, chemical, electrical, and ageing characteristics of these dielectrics and the dissolved gas analysis (DGA) were reviewed. Physical properties include viscosity, pour point, flash and fire point which are vital indicators of heat insulation and fire risk. Chemical properties considered are water content, acid number, DGA, corrosive sulphur, and sludge content to limit and detect degradation and corrosion due to oil ageing. Electrical properties including breakdown voltage were considered for consistent insulation during overload and fault conditions. These properties of evolving alternative dielectrics were reviewed based on ASTM International standards and International Electro technical Commission standards for acceptable transformer liquid dielectrics. This review paper was compiled to avail modern methodologies for both the industry and scholars, also providing the significance of using mixed dielectrics for power transformers as they are concluded to show superiority over non-mixed dielectrics.