An Overview of the Biolubricant Production Process: Challenges and Future Perspectives

Optimizing the enzymatic production of biolubricants by the Taguchi method: Esterification of the free fatty acids from castor oil with 2-ethyl-1-hexanol catalyzed by Eversa Transform 2.0

The solvent-free esterification of the free fatty acids (FFAs) obtained by the hydrolysis of castor oil (a non-edible vegetable oil) with 2-ethyl-1-hexanol (a branched fatty alcohol) was catalyzed by different free lipases. Eversa Transform 2.0 (ETL) features surpassed most commercial lipases. Some process parameters were optimized by the Taguchi method (L16'). As a result, a conversion over 95% of the FFAs of castor oil into esters with lubricants properties was achieved under optimized reaction conditions (15 wt% of biocatalyst content, 1:4 molar ratio (FFAs/alcohol), 30 °C, 180 rpm, 96 h). The substrates molar ratio had the highest influence on the dependent variable (conversion at 24 h). FFAs/2-ethyl-1-hexanol esters were characterized regarding the physicochemical and tribological properties. Interestingly, the modification of the FFAs with 2-ethyl-1-hexanol by ETL increased the oxidative stability of the FFAs feedstock from 0.18 h to 16.83 h. The biolubricants presented a lower friction coefficient than the reference commercial mineral lubricant (0.052 ± 0.07 against 0.078 ± 0.04). Under these conditions, ETL catalyzed the oligomerization of ricinoleic acid (a hydroxyl fatty acid) into estolides, reaching a conversion of 25.15% of the initial FFAs (for the first time).

A Review on the Effect of Metal Oxide Nanoparticles on Tribological Properties of Biolubricants

This review provides a comprehensive and accessible literature review on the integration of nanoparticles into biolubricants to enhance wear and friction regulation, thus improving the overall lubricated system performance. Nanotechnology has significantly impacted various industries, particularly in lubrication. Nanobiolubricants offer promising avenues for enhancing tribological properties. This review focuses on oxide nanoparticles, such as zinc oxide (ZnO), aluminum oxide (Al2O3), copper oxide (CuO), titanium dioxide (TiO2), zirconium dioxide (ZrO2), and graphene oxide (GO) nanoparticles, for their ability to enhance lubricant performance. The impact of nanoparticle concentration on biolubricant properties, including viscosity, viscosity index, flash point temperature, and pour point temperature, is analyzed. The review also addresses potential obstacles and limitations in nanoparticle incorporation, aiming to propose effective strategies for maximizing their benefits. The findings underscore the potential of nanobiolubricants to improve operational efficiency and component lifespan. This review aims to provide valuable insights for researchers, engineers, and professionals in exploring and leveraging nanotechnology's potential in the lubrication industry. This review paper explores the basics of tribology along with its significance, green principles, mechanisms, and energy savings because of friction, wear, and lubrication. Condition monitoring techniques are also explored to achieve brief knowledge about maintaining reliability and safety of the industrial components. Recent advances in tribology including superconductivity, biotribology, high-temperature tribology, tribological simulation, hybrid polymer composite's tribology, and cryogenic tribology are investigated, which gives a thorough idea about the subject.

Microalgae cultivation for treating agricultural effluent and producing value-added products

Wastewater generated within agricultural sectors such as dairies, piggeries, poultry farms, and cattle meat processing plants is expected to reach 600 million m3 yr-1 globally. Currently, the wastewater produced by these industries are primarily treated by aerobic and anaerobic methods. However, the treated effluent maintains a significant concentration of nutrients, particularly nitrogen and phosphorus. On the other hand, the valorisation of conventional microalgae biomass into bioproducts with high market value still requires expensive processing pathways such as dewatering and extraction. Consequently, cultivating microalgae using agricultural effluents shows the potential as a future technology for producing value-added products and treated water with low nutrient content. This review explores the feasibility of growing microalgae on agricultural effluents and their ability to remove nutrients, specifically nitrogen and phosphorus. In addition to evaluating the market size and value of products from wastewater-grown microalgae, we also analysed their biochemical characteristics including protein, carbohydrate, lipid, and pigment content. Furthermore, we assessed the costs of both upstream and downstream processing of biomass to gain a comprehensive understanding of the economic potential of the process. The findings from this study are expected to facilitate further techno-economic and feasibility assessments by providing insights into optimized processing pathways and ultimately leading to the reduction of costs.

Developing a sustainable grease from jojoba oil with plant waste based nanoadditives for enhancement of rolling bearing performance

This paper presents a novel grease from jojoba oil and activated carbon nanoparticles (ACNPs) extracted from banana peel waste. The raw jojoba oil and ACNPs are first characterized for structural properties. Samples of jojoba grease blended with 0.5 and 1.5 wt. % ACNPs are prepared and tested for physicochemical and tribological properties as compared to plain jojoba grease. Adding ACNPs to jojoba grease improves corrosion resistance from grade 2c to 1a while increasing the dropping point from 100 to 109 °C. ACNPs enhanced the viscosity of jojoba oil by up to 33% for testing temperature range of 40-100 °C. The load-carrying capacity of jojoba grease is increased by about 60% when blended with 1.5 wt.% ACNPs. The same blending decreased both the coefficient of friction and the wear scar diameter by 38% and 24%, respectively. A customized test rig is used to test the effectiveness of the grease samples in rolling bearing lubrication in terms of vibration levels and power consumption. The novel jojoba grease proved to show exceptional reductions power consumption reaching 25%. The vibration spectra show the absence of resonant peaks at high frequencies suggesting the capability of jojoba grease to form a stable full film lubrication.

Biocatalytic production of biolubricants: Strategies, problems and future trends

The increasing worries by the inadequate use of energy and the preservation of nature are promoting an increasing interest in the production of biolubricants. After discussing the necessity of producing biolubricants, this review focuses on the production of these interesting molecules through the use of lipases, discussing the different possibilities (esterification of free fatty acids, hydroesterification or transesterification of oils and fats, transesterification of biodiesel with more adequate alcohols, estolides production, modification of fatty acids). The utilization of discarded substrates has special interest due to the double positive ecological impact (e.g., oil distillated, overused oils). Pros and cons of all these possibilities, together with general considerations to optimize the different processes will be outlined. Some possibilities to overcome some of the problems detected in the production of these interesting compounds will be also discussed.

Effects of 2,6-di-tert-butyl-hydroxytotulene and mineral-lubricant base oils on microbial communities during lubricants biodegradation

2,6-Di-tert-butyl-hydroxytotulene (BHT) is an additive commonly used in the manufacturing of lubricants to improve their antioxidant properties. However, in this study, we found that BHT affects the biodegradation of bio-lubricants by influencing the microbial community during the degradation of bio-lubricants. Specifically, BHT was found to reduce bacterial richness in activated sludge, but it increased the relative abundance of Actinobacteria (from 21.24% to 40.89%), Rhodococcus (from 17.15% to 31.25%), Dietzia (from 0.069% to 6.49%), and Aequorivita (from 0.90% to 1.85%). LEfSe analysis and co-occurrence network analysis suggested that Actinobacteria could be potential biomarkers and keystone taxa in microbial communities. Using the MetaCyc pathway database, the study found that BHT interfered with cellular biosynthetic processes. Additionally, the study also showed that mineral-lubricant base oils, which are difficult to degrade, significantly altered the diversity and composition of the microbiome. Overall, the findings demonstrate that BHT and mineral-lubricant base oils can substantially alter bacterial richness, structure, and function, potentially contributing to the difficulty in degrading lubricants. These findings have implications for the development of more biodegradable lubricants and the management of industrial waste containing lubricants.

Preparation of highly dispersed SnO/TiO2 catalysts and their performances in catalyzing polyol ester

A series of stannous oxide supported on rutile titanium dioxide (SnO/TiO₂) were prepared by a conventional incipient wetness impregnation method, and their performance as catalysts for fatty acid esterification reactions was investigated. The effects of Sn precursors (SnCl₂·2H₂O or SnC₂O₄), loading amounts (5-15%), and treating ambiences (air and N₂) were explored. The optimized 10% SnO/TiO₂-Cl with SnCl₂·2H₂O as the Sn precursor and thermal treatment in N₂ showed the best esterification performance. Specifically, 10% SnO/TiO₂-Cl catalyzed the esterification process of trimethylolpropane and n-octanoic acid with a conversion of 99.6% over 5 h at 160 °C, and 10% SnO/TiO₂-Cl was efficient for six catalytic cycles. Based on the results of X-ray diffraction (XRD), Raman spectra, high-resolution transmission electron microscopy (HRTEM), infrared spectra of pyridine adsorption (Py-IR), and ammonia temperature programmed desorption (NH₃-TPD), the improved catalytic performance is supposed to be attributable to the high dispersion of the Sn species on 10% SnO/TiO₂-Cl as the moderate Lewis acid sites.

Monitoring tert-Butylhydroquinone Content and Its Effect on a Biolubricant during Oxidation

The use of biolubricants as a replacement for petroleum-based products is becoming more and more important, due to the current global energy and crude oil scenario. Thus, the production of biolubricants (which could take place in biorefineries) should be as efficient as possible, obtaining high-quality products with suitable viscosity or oxidation stability values to compete with oil refineries. One of the ways to produce biolubricants is through double transesterification from vegetable oils, where the role of catalysts (usually homogeneous) is vital, as they can improve the yield of the process. However, they should be removed after the chemical reaction, which is difficult once the biolubricant is obtained. Otherwise, they could act as catalysts during oxidation, contributing to a further decrease in oxidation stability and provoking significant changes. To avoid this, antioxidant addition could be an interesting choice. The aim of this work was to assess TBHQ addition in frying oil biolubricants, monitoring properties such as viscosity, acid number, absorbance or TBHQ content (through voltammetry) during oxidation. TBHQ addition (2114 mg·L^-1) kept the main quality parameters during oxidation compared to control samples. In contrast, TBHQ content decreased during oxidation (to 160 mg·L^-1), which proved its antioxidant effect.

Design of Quercetin-Loaded Natural Oil-Based Nanostructured Lipid Carriers for the Treatment of Bacterial Skin Infections

The biological activity of natural plant-oil-based nanostructured lipid carriers (NPO-NLCs) can be enhanced by the encapsulation of bioactive compounds, and they in turn can improve topical delivery of the drugs. Quercetin (QR), a vital plant flavonoid, expresses antibacterial properties, and we recently showed that empty NPO-NLCs also have antimicrobial activity. The main objective of this study was to evaluate the synergetic effect of loading natural plant-oil-based nanostructured lipid carriers with quercetin (QR-NPO-NLCs) as a topical delivery system for the treatment of bacterial skin infections. Five nanostructured lipid carrier systems containing different oils (sunflower, olive, corn, coconut, and castor) were engineered. The particles’ stability, structural properties, bioavailability, and antimicrobial activity were studied. NLCs with an average size of <200 nm and Z-potential of −40 mV were developed. Stable QR-NPO-NLCs were obtained with high encapsulation efficiency (>99%). The encapsulation of QR decreased cytotoxicity and increased the antioxidant effect of nanocarriers. An increase in antibacterial activity of the systems containing QR was demonstrated against Staphylococcus aureus. QR-NPO-NLCs could transport QR to an intranuclear location within HaCaT cells, indicating that QR-NPO-NLCs are promising candidates for controlled topical drug delivery.

A review on properties, challenges and commercial aspects of eco-friendly biolubricants productions

Lubricants operate as antifriction media, preserving machine reliability, facilitating smooth operation, and reducing the likelihood of frequent breakdowns. The petroleum-based reserves are decreasing globally, leading to price increases and raising concerns about environmental degradation. The researchers are concentrating their efforts on developing and commercializing an environmentally friendly lubricant produced from renewable resources. Biolubricants derived from nonedible vegetable oils are environmentally favorable because of their non-toxicity, biodegradability, and close to net zero greenhouse gas emissions. The demand for bio lubricants in industry and other sectors is increasing due to their non-toxic, renewable, and environmentally friendly nature. Good lubrication, anti-corrosion, and high flammability are characteristic properties of vegetable oils due to their unique structure. This study presents several key properties of nonedible oils that are used to produce lubricants via the transesterification process. Bibliometric analysis is also performed, which provides us with a better understanding of previous studies related to the production of bio lubricants from the transesterification process. Only 371 published documents in the Scopus database were found to relate to the production of bio lubricants using the transesterification process. The published work was mostly dominated by research articles (286; 77.088%). Significant development can be seen in recent years, with the highest occurrence in 2021, reaching 68 publications accounting for 18.38% of the total documents. In the second step, (i) the authors with the most number of publications; (ii) journals with the most productions; (iii) most productive countries; and (iv) the authors' most frequently used keywords were evaluated. These results will provide a pathway for researchers interested in this field. Lastly, recommendation is made on research gaps to device possible strategies for its commercialization.

Enzymatic Synthesis of Fatty Acid Isoamyl Monoesters from Soybean Oil Deodorizer Distillate: A Renewable and Ecofriendly Base Stock for Lubricant Industries

In this study, soybean oil deodorizer distillate (SODD), a mixture of free fatty acids and acylglycerides, and isoamyl alcohol were evaluated as substrates in the synthesis of fatty acid isoamyl monoesters catalyzed by Eversa (a liquid formulation of Thermomyces lanuginosus lipase). SODD and the products were characterized by the chemical and physical properties of lubricant base stocks. The optimal conditions to produce isoamyl fatty acid esters were determined by response surface methodology (RSM) using rotational central composite design (RCCD, 2³ factorial + 6 axial points + 5 replications at the central point); they were 1 mol of fatty acids (based on the SODD saponifiable index) to 2.5 mol isoamyl alcohol, 45 °C, and 6 wt.% enzymes (enzyme mass/SODD mass). The effect of the water content of the reactional medium was also studied, with two conditions of molecular sieve ratio (molecular sieve mass/SODD mass) selected as 39 wt.% (almost anhydrous reaction medium) and 9 wt.%. Ester yields of around 50 wt.% and 70 wt.% were reached after 50 h reaction, respectively. The reaction products containing 43.7 wt.% and 55.2 wt.% FAIE exhibited viscosity indices of 175 and 163.8, pour points of -6 °C and -9 °C, flash points of 178 and 104 °C, and low oxidative stability, respectively. Their properties (mainly very high viscosity indices) make them suitable to be used as base stocks in lubricant formulation industries.

Current Status and Future Prospects of Biolubricants: Properties and Applications

Biolubricants generated from biomass and other wastes can reduce the carbon footprint of manufacturing processes and power generation. In this paper, the properties and uses of biolubricants have been compared thoroughly with conventional mineral-based lubricants. The biolubricants, which are currently based on vegetable oils, are discussed in terms of their physicochemical and thermophysical properties, stability, and biodegradability. This mini-review points out the main features of the existing biolubricants, and puts forward the case of using sustainable biolubricants, which can be generated from agro-residues via thermochemical processes. The properties, applications, and limitations of non-edible oils and waste-derived oils, such as bio-oil from pyrolysis and bio-crude from hydrothermal liquefaction, are discussed in the context of biolubricants. While the existing studies on biolubricants have mostly focused on the use of vegetable oils and some non-edible oils, there is a need to shift to waste-derived oils, which is highlighted in this paper. This perspective compares the key properties of conventional oils with different oils derived from renewable resources and wastes. In the authors’ opinion, the use of waste-derived oils is a potential future option to address the problem of the waste management and supply of biolubricant for various applications including machining, milling applications, biological applications, engine oils, and compressor oils. In order to achieve this, significant research needs to be conducted to evaluate salient properties such as viscosity, flash point, biodegradability, thermo-oxidative and storage stability of the oils, technoeconomics, and sustainability, which are highlighted in this review.

An Experimental Investigation of Static Properties of Bio-Oils and SAE40 Oil in Journal Bearing Applications

Considerable research has been conducted in the past decade and a half regarding the bio-lubricants potential to replace mineral-based lubricants as mainstream lubricants such as engine oil, hydraulic oil, compressor oil, and metalworking oil. This study studied several bio-lubricants (rapeseed oil, palm olein, and soybean oil) and a mineral-based lubricant, SAE40. The bio-lubricants have better physiochemical, tribological characteristics and environmental friendly nature, and are promising to replace mineral-based lubricants. In this study, a journal bearing test rig (JBTR) was developed in order to investigate the effect of journal speed on the temperature of oil film with time. Additionally, the load-carrying capacity of bio-oils was tested against the mineral-based lubricant SAE40 by adding a load on the journal. For all three speeds, i.e., 1000, 1500, and 2000 rpm, the bio-lubricants recorded minimum temperature. At 1000 rpm, rapeseed oil recorded a 9.2% lower temperature than SAE40. Similarly, at 2000 rpm, rapeseed oil recorded a minimum temperature that was 2.5% lower than SAE40; in comparison, at 1500 rpm, palm olein recorded a minimum temperature that was 1.8% less than SAE40. Overall, the results of this study revealed that bio-oils recorded a lower temperature rise than mineral oil. These results are very encouraging for further research in this area.

Prospects of Plant-Based Trimethylolpropane Esters in the Biolubricant Formulation for Various Applications: A Review

Biodegradable lubricants from renewable feedstocks have been successfully developed to meet the demands of new machines with stringent requirements of the global standards, which address sustainability and environmental policy. Trimethylolpropane ester (TMPE) has been extensively evaluated as a biolubricant base stock and occasionally used as an additive, due to their low toxicity and excellent biodegradability. The formulation of high-performance TMPE-based lubricants involves addition of surface additives, multifunctional additives, and solid nano particles. This review focuses on the development of plant-based TMPE formulation for various applications, namely food-grade lubricant, engine oil, drilling fluid, insulating fluid, metal working fluid, hydraulic and heat transfer fluids. Even though plant-based TMPE lubricants have huge advantages over mineral oils, they have other challenging issues such as limited load-bearing capacity, hygroscopic properties, and high risk of toxic emission owing to additives selection. The details on the performance characteristics of TMPE as base stocks and additives are discussed, including the current prospects and challenges in the respective areas. This review concludes with a brief discussion on suggestions and recommendations for future advancement in the usage of TMPE and the remaining issues that must be overcome to allow for its full potential to be realized.

Biocompatibility and Antimicrobial Activity of Nanostructured Lipid Carriers for Topical Applications Are Affected by Type of Oils Used in Their Composition

Nanostructured lipid carriers (NLCs) have gained significant attention as tools for the dermal delivery of therapeutics due to their stability, biocompatibility, and ability to improve drug bioavailability. The use of natural plant oils (NPO) in NLC formulations has numerous benefits for the skin due to their therapeutic potential. This work shows the effect of NLC composition on bioavailability in epidermal cells and antimicrobial activity against Staphylococcus aureus. Sixteen systems containing fixed (sunflower, olive, corn, peanut, coconut, castor, and sweet almond) and essential (eucalyptus) oils, with different solid lipid (SL): liquid lipid (LL) ratios, were engineered. The structural properties, bioavailability, and antimicrobial action of the particles was studied. The choice of NPO influenced the physicochemical stability by changing the diameter of NLC formulations (between 160 nm and 185 nm) and Z-potential (between −46 mV and −61 mV). All of the systems were characterized by concentration-dependent cytocompatibility with human epidermal keratinocytes (HaCaT) and human dermal fibroblasts (HDFn). The SL:LL ratio in some NLC systems impacted cell cytotoxicity differently. Antimicrobial properties were observed in all 16 systems; however, the type of oil and SL:LL ratio affected the activity of the formulations. Two NLC-NPO systems were found to be non-cytotoxic to human cells lines at concentrations that completely inhibited bacterial growth. These results present a strong argument that the use of natural oils in NLC formulations presents a promising tool for the treatment of skin infections.

Simplified Method to Optimize Enzymatic Esters Syntheses in Solvent-Free Systems: Validation Using Literature and Experimental Data

The adoption of biocatalysis in solvent-free systems is an alternative to establish a greener esters production. An interesting correlation between the acid:alcohol molar ratio and biocatalyst (immobilized lipase) loading in the optimization of ester syntheses in solvent-free systems had been observed and explored. A simple mathematical tool named Substrate-Enzyme Relation (SER) has been developed, indicating a range of reaction conditions that resulted in high conversions. Here, SER utility has been validated using data from the literature and experimental assays, totalizing 39 different examples of solvent-free enzymatic esterifications. We found a good correlation between the SER trends and reaction conditions that promoted high conversions on the syntheses of short, mid, or long-chain esters. Moreover, the predictions obtained with SER are coherent with thermodynamic and kinetics aspects of enzymatic esterification in solvent-free systems. SER is an easy-to-handle tool to predict the reaction behavior, allowing obtaining optimum reaction conditions with a reduced number of experiments, including the adoption of reduced biocatalysts loadings.

Single-Cell Oils from Oleaginous Microorganisms as Green Bio-Lubricants: Studies on Their Tribological Performance

Biolubricants refer to eco-friendly, biodegradable, and non-toxic lubricants. Their applications are still limited compared to mineral oils; however, their sustainable credentials are making them increasingly attractive. Vegetable oils are frequently used for this purpose. However, vegetable oils have issues of low lipid productivity, dependence on climatic conditions, and need for agricultural land. Microbial oils represent a more sustainable alternative. To ensure their widespread applicability, the suitability of microbial oils from a physicochemical point of view needs to be determined first. In this study, oils obtained from various oleagenic microbes—such as microalgae, thraustochytrids, and yeasts—were characterized in terms of their fatty acid profile, viscosity, friction coefficient, wear, and thermal stability. Oleaginous microalgal strains (Auxenochlorella protothecoides and Chlorella sorokiniana), thraustochytrids strains (Aurantiochytrium limacinum SR21 and Aurantiochytrium sp. T66), and yeast strains (Rhodosporidium toruloides and Cryptococcus curvatus) synthesized 64.5%, 35.15%, 47.89%, 47.93%, 56.42%, and 52.66% of lipid content, respectively. Oils from oleaginous microalgae (A. protothecoides and C. sorokiniana) and yeasts (R. toruloides and C. curvatus) possess excellent physicochemical and tribological qualities due to high amount of monounsaturated fatty acids (oleic acid C18:1 content, 56.38%, 58.82%, 46.67%, 38.81%) than those from oleaginous thraustochytrids (A. limacinum SR21 and Aurantiochytrium sp. T66; 0.96%, 0.08%, respectively) supporting their use as renewable and biodegradable alternatives to traditional mineral oil-based lubricants. Oil obtained from microalgae showed a lower friction coefficient than oils obtained from yeasts and thraustochytrids.

Biolubricant Production through Double Transesterification: Reactor Design for the Implementation of a Biorefinery Based on Rapeseed

The production and use of biolubricants as replacements for mineral lubricants align with the promotion of sustainable development goals, contributing to the sustainable economic growth of developing countries as well as the preservation of the environment. The implementation of biorefineries (where the production of biolubricants through transesterification could play an important role) is becoming important for these purposes, using natural feedstocks such as rapeseed, which is an interesting crop that can adapt to different climates under extreme weather conditions. The aim of this research work was to study the design of a reactor to produce rapeseed biolubricant through double transesterification of the corresponding vegetable oil. Thus, the kinetics to design a reactor was studied, sizing it according to the properties of the biolubricant and the demand in Spain. As a result, a SAE 10W30 biolubricant was obtained, which was suitable for Diesel engines. A batch reactor was selected for the production of this biolubricant at a national level, with a pseudo-first reaction order and a reactor volume of 9.66 m3.

The Lord of the Chemical Rings: Catalytic Synthesis of Important Industrial Epoxide Compounds

The epoxidized group, also known as the oxirane group, can be considered as one of the most crucial rings in chemistry. Due to the high ring strain and the polarization of the C–O bond in this three-membered ring, several reactions can be carried out. One can see such a functional group as a crucial intermediate in fuels, polymers, materials, fine chemistry, etc. Literature covering the topic of epoxidation, including the catalytic aspect, is vast. No review articles have been written on the catalytic synthesis of short size, intermediate and macro-molecules to the best of our knowledge. To fill this gap, this manuscript reviews the main catalytic findings for the production of ethylene and propylene oxides, epichlorohydrin and epoxidized vegetable oil. We have selected these three epoxidized molecules because they are the most studied and produced. The following catalytic systems will be considered: homogeneous, heterogeneous and enzymatic catalysis.

A Novel and Efficient Method for the Synthesis of Methyl (R)-10-Hydroxystearate and FAMEs from Sewage Scum

In this work, the transesterification of methyl estolides (ME) extracted from the lipid component present in the sewage scum was investigated. Methyl 10-(R)-hydroxystearate (Me-10-HSA) and Fatty Acid Methyl Esters (FAMEs) were obtained in a single step. A three-level and four factorial Box–Behnken experimental design were used to study the effects of methanol amounts, catalyst, temperature, and reaction time on the transesterification reaction using aluminum chloride hexahydrate (AlCl3·6H2O) or hydrochloric acid (HCl) as catalysts. AlCl3·6H2O was found quite active as well as conventional homogeneous acid catalysts as HCl. In both cases, a complete conversion of ME into Me-10-HSA and FAMEs was observed. The products were isolated, quantified, and fully characterized. At the end of the process, Me-10-HSA (32.3%wt) was purified through a chromatographic separation and analyzed by NMR. The high enantiomeric excess (ee > 92%) of the R-enantiomer isomer opens a new scenario for the valorization of sewage scum.

Formulation of Sustainable Water-Based Cutting Fluids with Polyol Esters for Machining Titanium Alloys

The machinability of titanium alloys still represents a demanding challenge and the development of new clean technologies to lubricate and cool is greatly needed. As a sustainable alternative to mineral oil, esters have shown excellent performance during machining. Herein, the aim of this work is to investigate the influence of esters’ molecular structure in oil-in-water emulsions and their interaction with the surface to form a lubricating film, thus improving the efficiency of the cutting fluid. The lubricity performance and tool wear protection are studied through film formation analysis and the tapping process on Ti6Al4V. The results show that the lubricity performance is improved by increasing the formation of the organic film on the metal surface, which depends on the ester’s molecular structure and its ability to adsorb on the surface against other surface-active compounds. Among the cutting fluids, noteworthy results are obtained using trimethylolpropane trioleate, which increases the lubricating film formation (containing 62% ester), thus improving the lubricity by up to 12% and reducing the torque increase due to tool wear by 26.8%. This work could be very useful for fields where often use difficult-to-machine materials—such as Ti6Al4V or γ-TiAl—which require large amounts of cutting fluids, since the formulation developed will allow the processes to be more efficient and sustainable.

The Economic and Environmental Significance of Sustainable Lubricants

Many industrial processes are dependent on the proper application of modern tribological knowledge for the purposes of maintaining equipment integrity and minimizing total energy losses. Consequently, the development of modern lubricants is vital for satisfying growing performance standards and increasingly stringent environmental regulations. Industrial lubricants are regulated based on demanding technical requirements and characteristics, such as high viscosity index, hydraulic stability, corrosion prevention, thermal stability, wide operating temperature ranges, demulsibility, and oxidative stability. Escalating environmental and sustainability concerns have shifted significance towards non-technical criteria for the evaluation of lubricants. Biodegradability and renewability are two influential factors in the discussion regarding the long-term sustainability of future tribological applications. Emphasis is placed on the development of environmentally friendly, non-toxic, and biodegradable lubricants that would minimize industrial pollution associated with oil-related spills and leakages. Bio-based lubricants, manufactured from renewable, organic resources, present themselves as viable alternatives to traditional petroleum-based lubricants. A major section of this review paper will provide a comparative analysis of renewable resource-based lubricants and mineral oil-based lubricants in terms of their chemical properties and respective advantages. Further discussion concerning biolubricants and use of non-edible plant feedstocks will highlight the clear economic and environmental incentives of implementing modern tribological knowledge. This review paper will conclude with the examination of the obstacles that modern day biolubricants must overcome and the future expectations of green tribology.

Oxidative Stability of Vegetal Oil-Based Lubricants

Lipids are widely distributed in nature and are one of the most important components of natural foods, synthetic compounds, and emulsions. To date, there is a strong social demand in the industrial sector for the use of sustainable products with a minimal environmental impact. Depending on their origin and composition, lipids can be employed as a plausible alternative as biodegradable lubricants in order to reduce the use of conventional mineral oil lubricants and mitigate their environmental impact. This perspective provides an overview of the advantages and constrains of vegetal oils under different lubrication regimes and the tribochemical reactions that can take place. Also, the different factors and pathways that influence their oxidation, the key role of moisture, and the changes of physical properties under pressure and temperature are reviewed. Special emphasis is devoted to the oxidation instability of fatty acids and vegetal oils and the physical and chemical approaches to improve oxidative and thermal stability are described in detail.

Solvent-free esterifications mediated by immobilized lipases: a review from thermodynamic and kinetic perspectives

Esters are a highly relevant class of compounds in the industrial context, and biocatalysis applied to ester syntheses is already a reality for some chemical companies.

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.

Biolubricants from Rapeseed and Castor Oil Transesterification by Using Titanium Isopropoxide as a Catalyst: Production and Characterization

The transesterification of rapeseed and castor oil methyl esters with different alcohols (2-ethyl-1-hexanol, 1-heptanol and 4-methyl-2-pentanol) and titanium isopropoxide as a catalyst, to produce biolubricants, was carried out. Parameters such as temperature, alcohol/methyl ester molar ratio, and catalyst concentration were studied to optimize the process. The reaction evolution was monitored with the decrease in FAME concentration by gas chromatography. In general, the reaction was almost complete in two hours, obtaining over 93% conversions. All the variables studied influenced on the reaction yields. Once the optimum conditions for the maximum conversion and minimum costs were selected, a characterization of the biolubricants obtained, along with the study of the influence of the kind of alcohol used, was carried out. The biolubricants had some properties that were better than mineral lubricants (flash points between 222 and 271 °C), needing the use of additives when they do not comply with the standards (low viscosity for rapeseed biolubricant, for instance). There was a clear influence of fatty acids of raw materials (oleic and ricinoleic acids as majority fatty acids in rapeseed and castor oil, respectively) and the structure of the alcohol used on the final features of the biolubricants.