Preparation of a Water-Based Lubricant from Lignocellulosic Biomass and Its Tribological Properties

Unraveling Water-Based Lubrication with Carbon Dots of Asphaltene Origin

Despite the lower toxicity of water-based lubricants over nonrenewable petroleum-based analogues, they face challenges in achieving widespread adoption due to low stability and inadequate friction-reduction performance. To address this, a cost-effective nanoadditive is synthesized by expansive oxidation of asphaltenes to create biocompatible asphaltene-derived carbon dots [(ACDs); 5 nm]. These ACDs exhibit excellent water redispersibility, promoting long-term friction reduction and marking the first use of an asphaltene-based system for friction reduction in water or oil. Even at low loadings (0.2-4.0 wt %), ACDs significantly reduce friction on steel surfaces (>54%) with tribofilm stability surpassing pristine carbon dots, typical carbon-based graphene quantum dots, and inorganic nanomaterials (commercial 5 and 20 nm silica). The ACDs' attributes include high negative zeta potential, considerable water uptake, varied functional groups, biocompatibility, and a nanodisc shape conducive to stable tribofilm formation through effective particle stacking. The scalable synthesis, high yield, and impressive water redispersibility of ACDs position them favorably for commercial water-based lubrication.

Water-Based Lubricants: Development, Properties, and Performances

Water-based lubricants (WBLs) have been at the forefront of recent research, due to the abundant availability of water at a low cost. However, in metallic tribo-systems, WBLs often exhibit poor performance compared to petroleum-based lubricants. Research and development indicate that nano-additives improve the lubrication performance of water. Some of these additives could be categorized as solid nanoparticles, ionic liquids, and bio-based oils. These additives improve the tribological properties and help to reduce friction, wear, and corrosion. This review explored different water-based lubricant additives and summarized their properties and performances. Viscosity, density, wettability, and solubility are discussed to determine the viability of using water-based nano-lubricants compared to petroleum-based lubricants for reducing friction and wear in machining. Water-based liquid lubricants also have environmental benefits over petroleum-based lubricants. Further research is needed to understand and optimize water-based lubrication for tribological systems completely.

Synthesis of Branched Biolubricant Base Oil from Oleic Acid

The mature manufacturing of synthetic lubricants (poly-α-olefins, PAO) proceeds through oligomerization, polymerization, and hydrogenation reactions of petrochemical ethylene. In this work, we utilize the inexpensive bio-derived oleic acid as raw material to synthesize a crotch-type C₄₅ biolubricant base oil via a full-carbon chain synthesis without carbon loss. It contains several cascade chemical processes: oxidation of oleic acid to azelaic acid (further esterification to dimethyl azelate) and nonanoic acid (both C₉ chains). The latter is then selectively hydrogenated to nonanol and brominated to the bromo-Grignard reagent. In a next step, a C₄₅ biolubricant base oil is formed by nucleophilic addition (NPA) of excessive C₉ bromo-Grignard reagent with dimethyl azelate, followed by subsequent hydrodeoxygenation. The specific properties of the prepared biolubricant base oil are almost equivalent to those of the commercial lubricant PAO6 (ExxonMobil). This process provides a new promising route for the production of value-added biolubricant base oils.

The Role of Surfactant Structure on the Development of a Sustainable and Effective Cutting Fluid for Machining Titanium Alloys

In cutting operations of titanium alloys, most of the problems are related to the high consumption of cutting tools due to excessive wear. An improvement of metalworking fluid (MWF) technology would increase the productivity, sustainability, and quality of machining processes by lubricating and cooling. In this research article, the authors varied the surfactant’s charge, the hydrocarbon chain length, and the ethoxylation degree. Surfactants were dispersed at 1.2 mM in water and trimethylolpropane oleate to produce water-based MWF. Infrared reflection absorption spectroscopy and total organic carbon analysis were used to study the influence of surfactant structure on the film forming ability of the emulsion and performance was studied on Ti6Al4V using tapping torque test. The results showed that by changing the molecular structure of the surfactant, it is possible to vary the affinity between the ester and the substrate and reach an optimal combination, which improves the formation of a tribofilm. The mixture with anionic surfactants has good tribology performance, while non-ionic surfactants shorten the tool’s life. Moreover, the increase in the hydrocarbon chain length and the number of ethoxylations of surfactants promotes the adhesion of ester onto the metal surface, improving the lubricity properties of environmentally friendly MWF.

Macroscopic Friction Studies of Alkylglucopyranosides as Additives for Water-Based Lubricants

Water-based lubricants might become an interesting alternative to conventional oil-based lubricants and help to reduce wear as well as improve the energy efficiency of transport processes. Since pure water is generally a rather poor lubricant due to its low viscosity and corrosiveness, it must be tribologically optimized with suitable additives. Here, we study the friction behavior of alkyl glucopyranosides (AGPs) with varying lengths of the alkyl chain. Sliding experiments show that a significant reduction in the coefficient of friction compared to that of pure water is observed. The extent of friction reduction depends strongly on the concentration and on the shearing conditions. It is assumed that the low coefficients of friction are due to the ability of AGPs to form liquid crystalline phases with an ordered structure in the friction gap. Furthermore, the interaction of the AGPs with the surface forms a wear protection layer (boundary lubrication). The friction properties of the water-based system are compared to those of a conventional, mineral oil-based lubricant.

Branched Bio-Lubricant Base Oil Production through Aldol Condensation

Currently, lubricant base oils are derived from petroleum, a nonrenewable feedstock that contributes to greenhouse gas emissions. Bioderived, renewable lubricant base oils can mitigate environmental challenges and offer superior cold flow properties by incorporating branches to the base oil's hydrocarbon backbone with an appropriate synthetic strategy. A strategy was developed to synthesize branched alkanes for lubricant base oil in two steps from 12-tricosanone, obtained from bioderived fatty acids, and furfural, obtained from lignocellulosic biomass. The reaction pathway involves carbon-carbon coupling through aldol condensation followed by hydrodeoxygenation (HDO). Various solvents (non-polar, aprotic and polar, protic) and reaction conditions were screened to achieve a maximum yield of 94.3 % of aldol condensation products, containing the majority of a C₃₃ furan (79.5 %) followed by a C₂₈ furan (14.8 %). Subsequent HDO of aldol condensation products over an Ir-ReO_x /SiO₂ catalyst produced lubricant-ranged branched alkanes (C₂₈ and C₃₃ ) with 61.4 % yield and small fractions (<11 %) of alkanes with carbon numbers between C₁₅ and C₁₀ . The viscous properties of the produced bio-lubricant base oil were comparable to commercial petroleum-derived Group III and Group IV base oils. This approach serves as a potential stepping-stone to replace petroleumderived base oils and, in turn, reduce greenhouse gas emissions associated with current lubricant production.

Renewable lubricants with tailored molecular architecture

We present a strategy to synthesize three types of renewable lubricant base oils with up to 90% yield using 2-alkylfurans, derived from nonfood biomass, and aldehydes, produced from natural oils or biomass through three chemistries: hydroxyalkylation/alkylation (HAA), HAA followed by hydrogenation, and HAA followed by hydrodeoxygenation. These molecules consist of (i) furan rings, (ii) saturated furan rings, and (iii) deoxygenated branched alkanes. The structures of these molecules can be tailored in terms of carbon number, branching length, distance between branches, and functional groups. The site-specific, energy-efficient C-C coupling chemistry in oxygenated biomass compounds, unmatched in current refineries, provides tailored structure and tunable properties. Molecular simulation demonstrates the ability to predict properties in agreement with experiments, proving the potential for molecular design.