Group II base stocks are increasingly being used in marine oils. Winson Ang, Lead Technologist for Infineum Lubes Deployment, talks about the drivers for their use, the benefits they offer, and the solutions Infineum has developed to overcome the challenges they present.

Trunk piston engine oils formulated using Group I base stocks and salicylate technology have delivered robust lubrication performance to medium-speed, four-stroke ship engines, burning heavy fuel oil, for many years. However, trends in automotive crankcase lubricant formulations, which account for over half of the base stock utilisation, are impacting the supply and demand balance of base stocks globally. As the automotive sector looks to improve fuel economy and reduce emissions their use of high quality Group II and III base stocks is growing, which has resulted in a reduction of Group I capacity over a number of years.

Over the same timeframe there has been a significant increase in the availability of Group II base stocks as new plants and capacity additions have come on stream. This increased availability has driven down the cost of Group IIs, making their use in applications other than automotive crankcase oils increasingly attractive.

With no investment in Group I production on the horizon, a shift to Group II for TPEO seems inevitable.

Although this change has the potential to bring benefits to future TPEO formulations there are challenges that must first be overcome.

Group II – the challenges

The main challenge of using Group II base stocks in TPEO formulations is related to fuel contamination of the lubricant. Most four-stroke medium speed engines run on HFO, which contains asphaltenes – large polyaromatic species of undefined structure. During engine operation, these species can migrate into the oil via fuel contamination where they may agglomerate.

Marine lubricants must be able to handle asphaltenes to prevent them from agglomerating and forming ‘black sludge’ in the engine.