Volatility and Viscosity
Figure 2. Typical volatility / viscosity relationships for high VI single-structure and mixed-structure fluids.
The second key question is “should we do it?” There are relatively few applications where bio-based materials are required by legislation or demanded by customers. The drivers for adoption of bio-based materials in lubricants will have to be either cost or performance.
Lubricant performance requirements are continually evolving, while existing formulations tend to stay in use for the service lifetime of the equipment they were designed for, so the challenge for suppliers of new materials is to anticipate the needs of the next generation of products. Fortunately, the established processes for defining industry standards mean that it is easier to predict future requirements in lubricants than in many other sectors.
For example, in automotive crankcase oils there will be an ongoing requirement to deliver improved fuel efficiency, maintained throughout the lubricant lifetime. An obvious approach is to reduce the fluid viscosity as far as is possible while still providing adequate lubrication at high temperatures. Lower viscosity fluids generally have higher volatility, so it will be necessary to use materials offering the optimum balance of viscosity and volatility. This requirement favours fluids with narrow ranges of carbon number and chemical structure. Figure 2 illustrates how the flash point, which is an indicator of volatility, varies with viscosity, showing typical ranges for mixed fluids such as high VI mineral oils and for single structure synthetics. The best viscosity / volatility performance is obtained with single substances having a predominantly linear alkyl structure, but with just enough branching to prevent wax formation at low temperatures.
The same structures which give the best viscosity / volatility trade-off also generally have high VI. These properties are already exploited in established synthetic lubricants like fossil-
based PAOs and partially bio-based polyol esters based on short chain natural fatty acids. However, for both product types, cost and availability are currently limited by unselective manufacturing routes. PAOs are produced by converting ethylene to alpha-olefins, separating the desired fraction and oligomerising to give mixed PAOs which then require further separation to give the desired products. The unselective reactions mean that increasing production of a PAO means finding balancing outlets for a complex set of co-products. Similarly, for polyol esters, the desirable short chain fatty acids are only minor components of the natural mix and their availability is limited.
Other lubricant sectors will have different performance challenges, but it will always be true that the more tightly you can control the fluid structure, the more closely you can approach an optimum balance of properties. And the more selective the manufacturing process, the better. So perhaps this will be the opportunity for novel bio-based materials to add value in lubricant applications. Industrial chemists have always envied nature’s highly selective chemical transformations. If biotechnology can harness this capability and deliver selective and cost effective routes to high performance synthetic fluids, there will certainly be opportunities in lubricant applications.
Stephen Boyde
stephen.boyde@
bm4tech.com
LINK
www.bm4tech.com
LUBE MAGAZINE NO.128 AUGUST 2015
39
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53
