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Analytical Instrumentation
Reduced Volume TAN System Saves Cost and Use of Organic Solvents
Trevor Blows, Application Chemist. GR Scientific Ltd.
P.O.Box 242, Ampthill, Bedfordshire, MK45 5AQ, UK Tel: +44 (0) 1525 404747 • Email:
info@grscientific.com
In a presentation given during Pittcon 2012,* (Session 2035 –Fuel Analysis), Trevor Blows, Application Chemist, of GR Scientific, described a new micro system for TAN Analysis which operates with a reduced solvent volume requirement, bringing associated cost savings and environmental benefits. Tis article looks at how this system was developed as a different approach to meeting customer needs.
Introduction -What is TAN
Oils continually react with atmospheric oxygen to produce organic oxidation products that are acidic in nature. At ambient temperature, this reaction is very slow and has little effect upon oil conditions. At the elevated temperatures that exist within an operating engine, reaction rates are much higher. Elevated operating temperatures can generate high levels of weak organic acids. They cause increased oil viscosity and can deposit as lacquers on hot surfaces.
Total Acid Number or TAN is the measure of both the weak organic and strong inorganic acids present in oil. It is applicable to gearbox, gas engine, gas turbine and hydraulic lubricants. It is an important quality measurement of crude oil. The TAN value indicates to the crude oil refinery the potential of corrosion problems. Total Acid Number is an analytical test to determine the deterioration of lubricants. The more acidic a lubricant is, the further its degradation has proceeded.
Features
Following a consultation period with customers GR Scientific developed and refined a micro system for Total Acid Number (TAN) analysis which incorporates a newly developed micro combination pH electrode and optimised titration vessel. Providing for enhanced health and safety in use and also meeting environmental impact considerations, the newly introduced Aquamax MicroTAN system has been shown to save up to 75% of the volume of organic solvent used in analysis, reducing cost per test to around $2, while also bringing down costs of waste solvent disposal.
Conforming to ASTM D 664-09: Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration - the analyser has been developed specifically for the wide range of TAN values expected from oil industry samples.
How it works
The system, designed for ease of use, is calibrated using aqueous pH11 buffer and the blank value for the titration solvent determined. This value is stored automatically for use in later TAN calculations. Following titration the results, expressed as mg KOH/g, are displayed on the screen and stored in the data logger. Printer or PC options are available and can be configured to suit user requirements.
Micro system development – why?
During meetings and demonstrations with companies in the UK and Northern Ireland during 2010, it became apparent that existing technology was no longer addressing some of the users’ needs. Common issues raised by customers included :-
‘Macro System works well but we spend a lot of money on solvents’. Budgets were being reviewed.
High cost to dispose of organic solvent waste. Health and safety issues. “Surely you can reduce sample volume?”
Electrode performance check for ASTM D664-09 compliance
• The D664-09a recommends the use of aqueous buffers to check electrode performance and to determine the TAN titration end point when no definite point of inflection is obtained.
• The basic manual system described in the ASTM text is a mV meter (or pH meter with mV mode). It measures electrode performance/Nernstian slope efficiency in aqueous pH 4 and 7 buffers. The electrode system is then conditioned to measure the mV response of non-aqueous oil samples. This is the basis of the TAN test.
• The measurement of electrode performance/Nernstian slope efficiency is not part of the TAN test. It only ensures that the electrode system is functioning correctly before being used for the non aqueous titration.
• The GR Scientific micro system is used for TAN measurement. It uses the mV reading taken from a pH11 buffer as the end point for the TAN titration. The system does not measure Strong Acid Number so the use of pH4 calibration is not required.
• D664-09a Appendix X1, is a non mandatory check for electrode performance. It is noted that X1.1 states that ‘a manual check can be carried out with a pH meter or titrator with mV reading capability’. So D664-09a does allow the use of a pH meter to check electrode performance.
Setting out to address these changes GR Scientific tested the analytical system with a customer using glass vessels resulting in 40mL capability. This was reduced further to 25mL with the development of a micro combination pH electrode. Further trials went well with the customer adopting the system almost immediately and it is now in regular use.
Electrode selection and development
Key to the success of the instrument has been the electrode technology. GR Scientific worked closely with a UK sensor company to develop a micro combination electrode. It provides:
• Excellent stability for non-aqueous titrations. • An easy to clean design which is an important feature necessary for oil analysis systems. • Regeneration to optimum efficiency in minutes. • Electrode designed to meet titration vessel geometry. • Minimised effect from stirrer vortex.
Case studies
The following case studies indicate how the Aquamax MicroTAN compared with other methods of analysis.
April / May 2012 •
www.petro-online.com
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