SECTOR FOCUS: BIODEGRADABLE LUBRICANTS
New Product Highlight: biobased biodegradable brightstock replacement
Natalia Stawniak, Ian Bancroft and Boris Zhmud, Nuspec Oil, York, UK
In the lubricant industry, the term “brightstock” usually refers to heavy petroleum base oil produced from residues of petroleum distillation by refineries producing API Group I Base Oils. Solvent-extracted brightstock, with a viscosity in the range of 28.0 to 35.0 mm2/s centistokes at 100°C is often used in heavy duty automotive, marine and industrial lubricants such as heavy duty engine oils, slow-speed engine cylinder oils, industrial gear oils or process oils amongst others.
As the Base Oil market shifts away from API Group I production, a global shortage of brightstock is anticipated in the nearest future, around 300 metric tonnes per year by 2025 according to Kline & Co. The severity of the problem may be further aggravated by the political push for decarbonisation of the energy sector: without fuel as a cash cow, the majority of oil refineries will face serious bankruptcy risks. The applications that rely on brightstock are faced with two options: continue to use brightstocks, which are getting pricier because of declining availability, or consider alternatives.
Synthetic alternatives for mineral brightstock include polyisobutylene (PIB), high viscosity polyalphaolefin (PAO), polyalkylene glycol (PAG), polyesters, heavy naphthenic oils and ionised vegetable oils. However, such alternatives tend to be much pricier than conventional paraffinic mineral brightstocks and require reformulation and re-approval of finished lubricants. Hence, it would be highly advantageous to have a one-to-one brightstock replacement that can be used in the existing product formulations without requiring costly re-approvals.
Between 25-35% of lubricants based on toxic mineral oil is lost directly to the environment. Since the biodeterioration potential of Base Oils is closely related
22 LUBE MAGAZINE NO.160 DECEMBER 2020
to their viscosities, mineral brightstocks have poor biodegradability. In the CEC L-33-A-93 test, the percent of biodegradation of mineral brightstocks is usually only around 10%, well below the commonly accepted standards for environmentally-compatible lubricants. Finally, the conventional brightstock manufacture is an energy demanding process since it requires removal of all lighter oil fractions by distillation. Base oils produced by refineries bring on average 1 to 1.5 kg CO2
per kg
of product. This excludes the end-of-life part (waste oil utilisation). In a hypothetical case where brightstock is the only value-added product, this figure will be an order of magnitude higher.
The drive to reduce environmental pollution has led to the development of numerous next-generation Base Oils for marine and industrial lubricants. Nuspec Oil has made advances using novel rapeseed oils; developing novel Base Oils as a direct replacement of mineral oils in the production of marine and industrial lubricants. Features of such brightstock replacements include excellent solvency, very good low-temperature threshold and outstanding tribological properties. The most important distinctive feature of these products is that they can be used as one-to-one replacement for mineral brightstocks, negating the need for costly reformulation and re-approvals, see Table 1 and 2.
Table 1: The typical physicochemical properties of mineral bright stocks
Table 2: The physicochemical properties of property-matched bio-based brightstock replacements
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