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Environmentally adapted lubricants, Part I. An overview
Abstract
The requirement for environmentally adapted lubricants has begun to play an increasingly important role in many industrial applications, particularly in the last two decades. The present-day requirements for biodegrable and eco-friendly lubricants imply that lubricants have properties that can minimise, if not eliminate, negative environmental impact, such as contamination of soil and water, caused by lost lubrication, leakage and accidents. The dominant factors that have a direct impact on the environment and which characterise the lubricant and its chemical composition, are toxicity, bio-accumulation and biodegradability. Biodegradability is perhaps the most important factor which determines the fate of lubricant in the environment. Various commercial, governmental, and regulatory initiatives exist that protect the interests of the consumer. Life cycle analysis can help in assessing the total environmental impact of lubricants. This paper reviews the essential requirements of environmentally adapted lubricants, i.e., chemical composition, eco-toxicity, biodegradability, bio-accumulation, and eco-labelling schemes, and life cycle analysis.
The development and current status of environmentally friendly lubricating base stocks and additives were reviewed. Thus the biodegradability of various base oils and additives and the methods to test biodegradability and eco-toxicity were summarized. It is pointed out that, owing to the good biodegradability, good lubricating performance, non-toxicity, and huge output of various vegetable oils, more attention should be paid to vegetable oils in the domestic study and development of environmentally friendly lubricating oils and greases. Moreover, it is suggested that more efforts should be made with respect to the research and development of novel multifunctional environmentally-friendly lubricant additives.
Lubricants are essential in engineering, however more sustainable formulations are needed to avoid adverse effects on the ecosystem. Bio-based lubricant formulations present a promising solution. Biolubricants: Science and technology is a comprehensive, interdisciplinary and timely review of this important subject. Initial chapters address the principles of lubrication, before systematically reviewing fossil and bio-based feedstock resources for biodegradable lubricants. Further chapters describe catalytic, (bio) chemical functionalisation processes for transformation of feedstocks into commercial products, product development, relevant legislation, life cycle assessment, major product groups and specific performance criteria in all major applications. Final chapters consider markets for biolubricants, issues to consider when selecting and using a lubricant, lubricant disposal and future trends. With its distinguished authors, Biolubricants: Science and technology is a comprehensive reference for an industrial audience of oil formulators and lubrication engineers, as well as researchers and academics with an interest in the subject. It provides an essential overview of scientific and technological developments enabling the cost-effective improvement of biolubricants, something that is crucial for the green future of the lubricant industry.
The synthesis of high molecular weight esters such as bis (2-ethylhexyl) sebacate is of significance for its use as a lubricant. This ester is synthesized by the transesterification of dimethyl sebacate with 2-ethylhexanol. Therefore, the solubilities of bis (2-ethylhexyl) sebacate and dimethyl sebacate were determined at 308–328 K at pressures of 10–18 MPa in supercritical carbon dioxide. The solubility of dimethyl sebacate was always higher than bis (2-ethylhexyl) sebacate at a given temperature and pressure. The Mendez-Teja model was used to verify the self-consistency of data. Further, a new semi-empirical model with three parameters was developed using the solution theory coupled with Wilson activity coefficient. This model was used to correlate the experimental data of this work and solubilities of many high molecular weight esters reported in the literature.
Purpose
– The paper presents the results of research carried out on esters of carbonic, adipic, and sebacic acids with respect to their use as components of fully synthetic lubricating oil produced from a polyalphaolefin base. Straight dicarboxylic acid esters were synthesized in a transesterification reaction of dimethyl carbonate, dimethyl adipate, and dimethyl sebacate with 2‐ethylhexanol and 3,5,5‐trimethylhexanol.
Design/methodology/approach
– Oligomeric esters of adipic acid and sebacic acid were synthesized using neopentyl glycol, appropriate dimethyl adipate or dimethyl sebacate and 2‐ethylhexanol as the starting material. The basic physicochemical properties of esters were determined and their compatibility with synthetic oils were defined. They were also evaluated with respect to resistance under the influence of thermo‐oxidative factors, evaporation and susceptibility to hydrolytic decomposition. The selected esters were complemented with commercial additives to make up a fully synthetic lubricating oil with a polialphaolefin base. A special attention was paid to the effect of ester compounds on the physicochemical properties of the formulated oil.
Findings
– The obtained results show that straight adipates and sebacates of 2‐ethylhexanol and 3,5,5‐trimethylhexanol as well as oligomeric esters in which molecules are terminated with 2‐ethylhexyl group can be used as component of lubricating oils. The addition of these esters reduced the pour point by a few degrees in comparison with the tested base oil. The temperature fell below 40°C. The presence of esters significantly improved the viscosity index. A positive influence of esters on the lubricating properties of the formulated oil was also observed. On the contrary, dialkyl carbonates show too low boiling point, which is indicated by the high amount of volatile components, 19‐22 percent, in final product. Adipic and sebacic oligomers containing methoxyl groups in their structures proved to be immiscible with polyalphaolefins.
Originality/value
– The achievement of this work is the synthesis of new oligomeric esters of dicarboxylic acids, which can be excellent additives for improving properties of synthetic oils. Further studies will be focused on the use of esters as components of engine oils. This requires real motor tests.
Five samples of dibasic acid esters with varied chemical structures were synthesized. These included didecyl carbonate, didecyl adipate and didecyl sebacate as well as modern oligomeric esters of adipic acid and sebacic acid. These esters were tested in terms of their suitability as additives of fully synthetic engine oils. It was noted that an addition of 10% of the respective esters to oils based on polyalphaolefins led to an improvement of their properties. The pour point of the oils as well as their low temperature viscosity were reduced. The viscosity index rose and oil lubricity improved. Esters of oligomeric structures synthesized by the transesterification of dimethyl adipate or dimethyl sebacate with a mixture of neopentyl glycol and decanol showed particularly suitable properties. The tested esters were compatible with the other oil components, forming a stable solution in a wide temperature range.
This paper highlights past and current work on the toxicity of petroleum lubricants and the base oils from which they are made. The review includes a discussion of short-and long-term toxicity studies carried out to determine potential hazards following skin contact, ingestion, or inhalation of petroleum products and covers the relationship between refining severity and the carcinogenicity of petroleum base oils.
As part of the OECD Chemicals Group program, much effort has gone into trying to identify and develop methodologies for predicting human and environmental exposure to new chemicals. This paper reviews this activity and discusses the applicabilities and limitations of the methodologies. Of special interest is the model developed by Mackay and adapted by Wood that can be used at several levels of sophistication depending on the chemical and environmental data available.
Up until the 1980's the problems facing lubricant formulators and marketers were simply those of meeting the technical requirements set by Original Equipment Manufactures (OEMs) and customers. However in the last ten years a whole extra set of requirements have been introduced, through legislation, public concern and OEM pressures, dealing with a lubricant's impact on the natural environment. Such impacts must be examined through a lubricants full life cycle all the way from the original product development programme through to ultimate disposal. Although a full life cycle analysis is needed in order to assess the total impact of lubricants in the environment, a subject well beyond the scope of this paper, we have attempted to highlight some recent developments in the following critical areas:(a) Choices during formulation, especially those dictated by current and emerging legislation,(b) Impacts during use of the product including such aspects as fuel economy, oil consumption and tailpipe emissions,(c) Fate in the environment, with emphasis on the disposal and/or recycling of used lubricants.