Feature

Lubricants Technology - An Overview

Dr Himmat Singh

This article presents an overview of lubricants technology today. Various components that make the finished lubricants are briefly described along with an overview of the global lubricant market and systems of performance specifications.

The basic functions of a lubricant are friction and wear reduction, heat removal and contaminant suspension. Apart from important application in internal combustion engines, vehicles and industrial gear boxes, compressors, turbines or hydraulic systems, there are vast number of other applications, which mostly require specifically tailored lubricants. Designing a lubricant to perform above stated functions in different systems, is a complex task, involving a careful balance of properties both in the lube base stocks and the performance enhancing additives. Between 5000 and 10000 different lubricant formulations are necessary to satisfy more than 90% of all lubricant applications.

Lubricants today are classified into two major groups : Automotive lubricants and Industrial lubricants. Automotive lubricants have to perform in different types of vehicles both petrol and diesel under a variety of operating conditions. Modern vehicles are fuel efficient and comfortable with high levels of performance. They are required to meet stringent emission norms. Quality requirement of such lubricants are established by the Society of Automotive Engineers (SAE) and are specified in its classification system. Industrial lubricants can be subdivided into industrial oils and industrial specialities. Specialities in this case are principally greases, metal working lubricants and solid lubricant films. Quality requirements for these types of lubricants are defined by Original Equipment Manufacturers (OEM) and end users of the products. On the global lubricants market, automotive lubricants account for more than 60% of volumes sold.

Lubricant Market

The global lubricant market in the past 10 years has undergone dramatic changes due to industry consolidation. The industry has witnessed overall flat demand, sharp shifts in consumption, increased competition and greater pressure on profits. World lubricants demand has remained flat around 38 MT/A since 1991, despite some regional bright spots. Asia's demand grew 28.2% over the decade, but lube markets in central and eastern Europe (including Russia) shriveled to half of what they were in 1980s, while Western Europe fell nearly 10%. For the year 2000, Africa consumed 4.9% of total world lubricants demand. The Centre for European Economic Research has forecast the long-term lubricant demand by region up to year 2010. As per their estimates the world would consume a little over 40 MT of lubricants in the year 2010, with Africa accounting for 1.805 MT thus showing a growth of 2.6% over the years, against the total overall growth of 11.5% through 2010 as predicted by the study.

Lubrication / Tribology

Although the use of lubricants is as old as mankind, scientific focus on lubricants and lubrication technology is relatively new. Tribology - a term first introduced in 1966, is the science of friction, wear and lubrication, which is now used globally to describe this far-reaching activity. It is truly inter disciplinary in all its aspects and provides a scientific basis to understand contact and lubrication modes in a given tribological system. The lubrication efficiency and the application of lubricants is further dependent upon key parameters like consistency, flow properties or viscosity in the case of oils, which also appear in nearly all lubricant specifications.

Lubrication has always implied the use of lubricating oil, usually formulated by blending appropriate quality lube base stocks(s) and additives. On an average lubricating oil consists of about 93% base stock(s) and 7% chemical additives and other components. Base stocks used to formulate lubricants are normally of petroleum origin along with synthetic and vegetable oils, which may be incorporated for specialized applications. The performance of a finished lubricant, therefore essentially depends upon the type and quality of base stocks and on the additives used. Very little un-additized lube base stocks are used as lubricants. There are 15 world's top lubricant manufacturers as on today (Indian Oil Corporation Ltd. ranks 13) and they control between themselves more than 60% of global lube volume - due mainly to consolidation / mergers.

Lube Base Stocks

Lube base stocks (of petroleum origin) continue to constitute a major part of today's lubricant. These are complex mixtures of paraffinic, aromatics and naphthenic hydrocarbon type molecules, ranging in carbon number from 14 to 40+. They constitute a very important segment of the hydrocarbon industry. Manufacture of these base stocks in the past two decades or so underwent evolutionary changes due to a number of reasons. The variety of crude oils that need to be processed considerably increased, coupled with the introduction of new and improved refining processes. Hydroprocessing has emerged to be the most important routes for this purpose. Different processing configurations involving replacement of dearomatisation, dewaxing and hydrofinishing steps have been developed. Hydrocracking / hydroisomerisation enabled the refineries to produce High Viscosity Index (designated as VHVI or X-HVI) paraffinic base stocks / oils that are comparable in performance to synthetic base fluids. Paraffinic base stocks are preferentially used to formulate most of the world's automotive and industrial lubricants, including engine oils, transmission fluids and gear oils, due to their better oxidation stability, higher viscosity index and lower volatility relative to comparable viscosity grade naphthenic base oils. Naphthenic base oils have lower pour points and better solvency characteristics, compared to paraffinic base oils which makes them, particularly useful in formulating low temperature, hydraulic oils, refrigeration oils, rubber process oils, metal working oils, as well as cylinder lubricants for large engines and greases.

Base stocks differ widely in molecular composition, physical and chemical properties due to the crude source and processing steps used in their manufacture. These differences in base stock composition, even with similar physical properties can impact the end use performance of finished lubricants. As such lube base stocks are thus considered to be non-fungible products in many end use applications. In 1990 the American Petroleum Institute (API) established a base oil classification system to help marketers to minimize re-testing costs when blending licensed engine oils with base oils from different manufacturing sources. The system uses physical and chemical parameters to divide all base stocks (oils) into five groups as listed in table below :

API - Classification of Base Oils

It would be seen from the above data that as one moves from Group I to Group III base stocks, paraffinicity improves do the volatility characteristics due to shifts in manufacturing practice and higher isoparaffin contents. Group IV base oil contains all PAOs, which are used neat and in admixture with mineral base oils to improve lubricants properties. API Group V contains all other base stocks, including all naphthenic base oils, medium VI paraffinic stocks and synthetic fluids such as esters, silicones and polyglycols.

The fourth annual edition of 'Lubricants World' has recently published a list of '2002 Base Oil Refining Facilities' world wide, region wise distribution of which is shown in the table below :

While Europe and USA have practically the same number of lube plants but differ in over all capacity. Asia tops the list with 34 plants having practically the same capacity as in USA. Middle East and Africa two together have 15 lube refineries.

Region Wise Distribution of Global Base Oil Refining Capacity (2002)

BPD = Barrels Per Day Source : Lubricants World 4th Annual Edn. 2002
* Plants with capacities under 3000 BPD particularly in Europe and Asia have not been individually listed.

There are in total 8 lube refineries in Africa with a total production capacity of 17045 BPD (approx 0.85 MT/A) as listed below :

Lube Refineries and their Capacity in Africa

World wide base oil demand has risen by more than 10% since 1995, and is expected to keep growing briskly. Despite over supply plaguing some regions, such as Europe, new markets are developing for high quality Group II and Group III base oils to meet more stringent environmental and vehicle performance standards around the world. These standards are triggering closures or upgrades of Group I plants in the USA. and planning emphasis of higher-grade base oils elsewhere, particularly Asia.

Synthetic Base Fluids

The synthetic hydrocarbons or syn base fluids were developed simultaneously in Germany and U.S. In Germany low temperature performance and the need to over come the general shortage of petroleum base stocks was the driving force behind their development. Most of the economically important syn fluids can be synthesized starting with ethylene - mainly produced in steam crackers. Such fluids have required precise properties and the main classes used to blend lubricants and their principal applications include :

With the exception of polyglycol fluids, all the above syn fluids have viscosities in the range of lighter HVI neutral base stocks. Their VIs and flash points, however, are higher and their pour points are considerably lower. This makes them valuable blending components when formulating oils for extreme service at both high and low temperatures. Some of these fluids are considered to be environmentally more acceptable as well.

The main disadvantage of synthetic base fluids is that they are inherently more expensive than traditional base stocks, and are available in limited supply. This limits their used to make speciality lubricants and greases that command premium prices.

The Additives

As mentioned earlier, almost all commercial lubricants contain additives to enhance their performance. Their amount varies from > 1% to 25% or more. By for the largest market for additives is in the transportation field, including additives for engines and drive trains in cars, trucks, buses, locomotive and ships. The function of additives can be summarized as follows :

· Protect metal surfaces (rings, bearings, gears etc.)
· Extend the range of lubricant applicability
· Extend lubricants' life

The same general range of additive types find application in industrial lubricants as well along with other materials designed to impart specific properties.

Present day additives consist of a variety of classes. For the automotive lubricants these are :

a) Surface protective additives : antiwear and EP agent, detergent, dispersant and friction modifiers.
b) Performance additives : Pour point depressant, viscosity modifiers and seal swell agents.
c) Protective additives : antifoament, antioxidant and metal deactivators

Additive - Additive interactions have been widely studied and their performance attributed to a specific chemistry or functionalities of these interactive additive pairs. Many factors that govern their applications are : additive must be capable of being handled in conventional blending equipment, stable in storage, free of offensive odour and non-toxic by normal industrial standards.

Formulation, Specifications and Testing

The lubricant that one buys in the market and uses in his vehicle, engine and or machine is normally a formulated product comprising of base stock(s), performance enhancing additives, and other special ingredients. All the above components when put together in an appropriate concentration ensures that the formulated / finished lubricant perform the required functions and meet equipment needs, in which it is being used.

The physico-chemical and performance requirements define a lubricant identity and its ability to reduce friction, resist oxidation, minimize deposit formation, prevent corrosion and wear. These requirements may be set at national, regional or global levels by engine manufacturers public organizations or military authorities. The most widely known systems for automotive lubricants (being the major category) are API classification and the European system ACEA (Association Des Constructeurs European d' Automobiles). API system, which is, commonly use throughout the world relies on cooperation between three bodies namely : SAE, API and American Society for Testing and Materials (ASTM), each with a well defined role and responsibility.

API performance classification system, introduced in 1970, gave the gasoline engine, the prefix 'S' (for service station) followed by a series of letter from 'A' onward indicating successive level of increased quality or upgrading which currently stands at 'SJ', introduced in 1996. Similar to the above system, diesel engine oils are coded using a prefix 'C' (for commercial) which now stands at CH-4 or higher introduced in 1998 for the 4-stroke engine.

As with 4-stroke engine oils, there exist a similar system for two-stroke engine oils as well. Two stroke oils are allocated to certain performance groups, which provide information about suitable applications. API service groups, Japanese Automotive Standard Organization (JASO) Classification and the International Standards Organization (ISO) classification system are currently followed in most of the world.

Lubricant effectiveness is assessed by bench scale and full scale testing in the laboratory and in the field. The laboratory tests are accelerated test in real-world equipment that simulates actual service conditions. These tests are actual engines, transmissions, axles, hydraulic pumps and so on and are run under standard conditions according to the prescribed procedures. The tests are complex and expensive. The goal here is to ascertain the lubricants meet the performance requirements established by the various organizations, which appear in delivery conditions, in house standard and general specifications.
Lubricating greases which also form part of the lubricants industry as a whole are by definition solid to semi solid fluid products created by the dispersion of a thickening agent in a liquid lubricant, usually a metal soap along with certain additive compounds which impart special properties, processed in a grease plant to produce a gel like material. By far the most important application of greases is for the lubrication of rolling element bearings. Greases continued to be classified by the procedure defined by National Lubricating Grease Institute (NLG) USA in accordance with cone penetration method.

About the author: Dr Himmat Singh has a PhD in petroleum chemistry and has held numerous senior positions in the petroleum industry. He has over 38 years of experience petroleum refining.
E-mail : dr_himmat@vsnl.net

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