Ayman Ali, ExxonMobil EAME Industrial Marketing Advisor for Europe, Africa and the Middle East, outlines the current state of the environmentally acceptable lubricants (EAL) market
The biodegradable lubricants market has evolved over the past three decades, with everything from rapeseed to sea water used to lubricate ships and hydraulic systems. A myriad of tests and definitions have been put forward by bodies in a bid to harmonise certification and encourage uptake. Yet the advantages, disadvantages and technical considerations of switching to these products are often ill understood.
Lubricants exist to optimise and protect a vast range of applications in exploration and production machinery. From gas engine, hydraulic, turbine, compressor and gear oils through to synthetic greases and diesel engine oils, they are used in almost every variety of severe applications.
Despite significant recent technological advances in these oil and gas applications, there are a number of challenges operators often face. Leaks in connectors, hoses and seals can still result from misapplication, improper assembly and simple wear and tear of the equipment. Even a small leak of one drop per second could lead to the release of up to 200 litre of lubricant in a month . As environmental impact rises up the agenda of policymakers and regulators, regulatory bodies are increasingly introducing fines and penalties to control spills, coupled with incentives to encourage the use of environmentally acceptable lubricants (EALS). This in turn is generating a gradual shift towards what had previously represented a small share of lubricant sales.
This has in turn led to a tighter definition of what constitutes biodegradable and environmentally acceptable lubricants, stricter labelling and higher sales, particularly in Europe. A further significant trend in the biodegradable lubricants arena is the increased research and development (R&D) effort that has gone into developing these specialised oils. Such advances have given rise to a new breed of environmentally acceptable and biodegradable lubricant that does not compromise on efficiency and performance compared to conventional lubricants in the way that many predecessors did.
Biodegradation: what actually is it?
Biodegradation is one of three processes that transform or break down materials that enter the environment (the other two being chemical or photoxidation and weathering). The biodegradation process relies on micro-organisms (or their enzymes) such as bacteria, yeast, protozoans and fungi in the environment and typically releases carbon dioxide and water. There are two main types of biodegradability: “inherently” and “readily” biodegradable. The Organisation for Economic Co-operation and Development (OECD), the Paris-based body of developed economies, defines these as:
Inherently biodegradable – classification for a product that has a biodegradation better than 20% in 28 days, which includes most mineral oil lubricants;
Readily biodegradable – classification for a product that has a biodegradation of more than 60% within 28 days, which eliminates most, if not all, mineral oils.
Another widely used industry standard to measure biodegradation is the 21-day test of the Co-ordinating European Council (CEC), the trade body that develops performance tests for fuels and lubricants. The CEC L-33-93 test measures the loss of oil and oil-soluble metabolites in a nature-like aqueous environment. The benchmark for qualifying a lubricant as biodegradable is biodegradability of more than 80% by the CEC L-33-93 method or more than 60% by the OECD 301B method.
Lubes that break down: the basics
Although biodegradables and environmentally acceptable lubricants have been in commercial production for decades, they comprise a small portion of the total lubricant market and are still regarded as niche. Biodegradable lubricants can be classified in four categories. These are vegetable oils, polyalkylene glycols, synthetic esters and saltwater. The different lubricants types have different qualities and drawbacks, enjoying differing levels of popularity in industry.
Vegetable oils are made up mostly of natural esters (triglycerides), although the exact chemical nature varies according to plant species – e.g. rapeseed, sunflowers, canola and soybeans. Their most common commercial application is in hydraulic fluids. In addition to high biodegradability and low aquatic toxicity vegetable oils have a higher viscosity index (resistance to thinning at high temperatures) than mineral oils and high lubricity and high flash point (combustion temperature). They perform well at extreme pressures, and do not react with paints or varnishes but have various disadvantages, which have limited their popularity.
Changing from a mineral to a vegetable oil lubricant is simple, as the two types of oils are compatible and vegetable oil lubricants will perform properly if some mineral oil residue remains. Disposal costs are also generally lower because of their non-toxic overall formulation. However, they perform poorly and thicken quickly at the sorts of low temperatures that are common in the oil and gas industry and exhibit poor oxidative instability at high temperatures, necessitating more frequent oil changes and making them poorly compatible with the growing technical requirements of modern hydraulic systems.
Lubricants based on synthetic esters are actually the oldest class of bio-degradable lubricant, hailing from the 1950s, when they were first used for jet engine lubrication. They are created from the esterification of bio-based materials (modified animal fat and vegetable oil) and can be specifically adapted for their intended application. Generally synthetic esters have a high viscosity index and high lubricity, perform well across a wide range of temperatures, boast high oxidative stability (meaning long lubricant life) and provide corrosion protection. Their bio-based formation means they generally satisfy testing requirements for biodegradability and aquatic toxicity, albeit they are recognised as less easily and readily biodegradable than pure vegetable oil-based lubricants, and they occasionally exhibit incompatibility with certain paints and seal materials. EALs based on synthetic esters are also, in general, compatible with mineral oils, provided that no more than 2% of the previous oil charge remains (as per ISO 15380 requirements). It is recommended to drain down the system as far as possible to maximise the benefits of the new product's technology.
The third type of biodegradable lubricant is one made up of polyalkylene glycols (PAG). These are synthetic lubricant base oils, typically made by the polymerisation of the hydrocarbon ethylene, a natural plant hormone, or propylene oxide. They can be soluble in either oil or water and exhibit highly biodegradable qualities (notably the water-soluble PAGs). The major disadvantage of PAG-based products is poor compatibility with seals, gaskets and linings and poor miscibility with standard mineral oils. Some reports have indicated that a growing number of companies are turning to the fourth type of biodegradable lubricant. Seawater is used in ship stern tube systems that use non-metallic bearings in place of metal bearings.
Biodegradable lubricants are experiencing substantial growth in Europe, with more robust and harmonised certification becoming increasingly widespread. To help operators comply with environmental legislation and optimise the performance of their equipment, a switchover to biodegradable lubricants should be considered. Although that process can be straightforward, it is important to note that not all biodegradable lubricants are the same and that newly developed synthetic ester products are becoming available that offer protection and long oil drain intervals and reach new heights of hydraulic efficiency levels.