Analytical Instrumentation 17 Engine oils


At the elevated temperature of operation within engines, high levels of acid are generated. The acid increases oil viscosity, causing reduced efficiency and damage to the exposed engine parts. The TAN value assists service operations by giving an indication of oil change requirements.


A customer using traditional methods of TAN analysis wanted to compare results against the micro TAN titrator. The results were consistent with that of the customer.


Details are given below. Engine oil: expected TAN 3.4


Weight (g) 0.51 0.51 0.50


0.52 0.50 0.50


Transformer oils – optimised method


After discussions with customers analysing transformer oils, it was decided to spend time optimising the method for these sample types.


Typically, samples have the same, known density, of 0.875. It follows that 1mL of sample weighs 0.875g. A fixed volume of sample can be put into the titration vessel using the calibrated syringe, optimised for coloured samples. The weight of the sample can be keyed into the titrator. (at 0.875g per mL of sample).


The titration is then started. At endpoint, the result is read directly on the display.


A number of samples were run. The system was standardised with a known solution. Good correlation was achieved. UK transformer oil data


Sample


Low TAN 0.06 expected Low TAN 0.06 expected Low TAN 0.06 expected


MXN 0.17 MXN 0.17 STAN 2


Lubricant sample


Another UK customer has used the colorimetric method of analysis of lubricants for many years. As part of a laboratory upgrade scheme, the customer needed to assess the micro TAN system for his samples. The sample gave good, accurate results. These were slightly higher than those achieved with the colorimetric method. However it does show the limitations of the colorimetric method whose endpoint is determined by visual colour comparison against a standard colour chart.


UK lubricant sample: expected TAN 0.8 (customer colorimetric result) Weight (g) 1.16 1.00


1.01 1.00 1.00 1.00


Titre (ml) 0.408 0.353 0.391


0.391 0.371 0.371


TAN result 1.05 0.91 1.11


1.12 1.01 1.02


These results do show the accuracy provided by automatic titration systems compared to the traditional colorimetric methods. The importance of the TAN parameter to the performance of lubricant and transformer oils cannot be understated. The performance of engines and transformers are key to many industries. An optimized system that offers costs savings and health and safety benefits, while maintaining high performance is a great addition to the oil analysis laboratory.


ASTM D664 method for TAN


• ASTM D 664-09 Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration.


• Sample is titrated with 0.1mol/L potassium hydroxide 2-propanol solution and the endpoint is determined on titration curve.


• Result is calculated from titration volume of potassium hydroxide/ 2-propanol solution reaching the endpoint.


• The Total Acid Number (TAN) result is given as the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil.


Weight (g) 5.63 5.81 5.91


8.17 6.40 5.63


Titre (ml) 0.283 0.301 0.298


0.532 0.474 2.013


TAN result 0.092 0.107 0.102


0.234 0.248 1.950


Examples: US sample


10 – 12g was taken and a ‘more workable’ titration volume of 0.85mL was given. Results of 0.034, 0.032 and 0.035 show the sensitivity and accuracy of the unit.


UK transformer oil with very low TAN value


12 – 15g of sample was taken and gave a titration volume of 0.3mL. With a standard system, a large weight of sample, and corresponding large volume of solvent, would be needed to get even the smallest titre above the blank value. Excellent results of 0.005, 0.004 and 0.005 were given.


North Sea crude oils – preliminary data Work has just started to evaluate the system for crude oil samples.


Early results from the North Sea samples are promising but more data from different crude oils is needed to prove the system.


Sample Crude 1 Crude 1 Crude 2


Crude 2


Weight (g) 0.11 0.14 0.12


0.08


Titre (ml) 1.077 1.301 1.896


1.241


TAN result 3.97 4.02 7.40


6.60


Titre (ml) 0.497 0.510 0.515


0.510 0.508 0.482


TAN result 3.36 3.51 3.63


3.44 3.56 3.26


Low level TAN values


There are also many customers analysing samples for TAN values below the limit of ASTM D664- 09. The problem with the standard micro system in this case is that the titre values are very small in comparison to the solvent blank values. One way to approach this issue is to use a reduced molarity titrant. For low level TAN values, the reduction of the KOH strength to 0.01M gives workable titre values. Samples from the UK and USA were analysed and consistent results achieved. This does increase the scope of the micro TAN analyser for very low acid levels in oil samples.


Key features


• Conforms to ASTM D 664-09 • Very easy to use with intuitive keypad and function guide display. • Automatic data storage of last 55 analysis results. • 10ml high precision syringe featuring 40,000 stepper motor. • Connects to external PC keyboard for easy text and sample information data entry. • Connects to different types of printers, PC and balances. • 2 x RS 232C sockets for printer/PC/balance connection.


Future development and evaluation work


Further work on varying crude oil sample types is required to prove the system. At present just two samples have been analysed but early results are promising. The technique could also be developed for additional parameters such as Total Base Number (TBN). The application to TBN analysis would give the same benefits to the customer as the micro TAN system. Finally, the micro approach could be utilised in future product development by GR Scientific, ensuring that all customers could benefit from reduced solvent use, reduced budget spend and enhanced health and safety considerations.


Summary


Conforming to ASTM D664-09 standards the Aquamax MicroTAN incorporates new technology in the form of a micro combination pH electrode and an optimised titration vessel


Applicable to petroleum products, lubricants and transformer insulating oils; new & used petroleum products; biodiesel and biodiesel blends, it has been shown to reduce use of organic solvents; reduce cost of waste disposal; offer improved analytical precision and accuracy; offer enhanced health and safety benefits and bring overall savings to budgetary spend.


*PittCon 2012, Orlando, USA, Wednesday March 14th


April / May 2012 • www.petro-online.com


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