TBN Titrator

The Titra-Lube laboratory method is run as follows:

A sample of the lubricant to be tested is weighed out into a disposable test tube. The amount of sample used in grams is determined by dividing 16 by the expected TBN value of the sample. The maximum amount of sample to be used is 2 grams.

The tube is filled to a 5 mL line with a high flash point hydrocarbon based solvent and the tube is capped and shaken until the sample is totally dissolved.

3.1.5 mL of 0.40 M isopropyl HCl is added to the tube and it is shaken for 30 seconds.

12 mL of aqueous extract solution is added and the mixture shaken for 30 seconds.

The two phases are allowed to separate for 3 minutes.
The aqueous layer is decanted off and 10 mL is transferred to a titration beaker.

12 mL of additional aqueous extract solution (clean) is added to the beaker and the solution is titrated with 0.0425 N NaOH to the inflection point. The titration can be done manually or with an automatic titrator.

TBN is calculated as follows:
TBN = 3.20 (Vb1-V5)/Ws, where Vb1 is the amount of titrant used to titrate a 0 TBN blank sample, Vs is the volume of titrant needed to titrate the sample being analyzed, and Ws is the weight of the sample used in the procedure.

HOW THE METHOD WORKS

Traditional TBN methods D-2896 and D-4739 require than a non aqueous hydrocarbon sample be dissolved in a solution capable of facilitating an acid-base reaction and titration. This requirement limits the method to using a limited number of powerful solvents, usually chlorinated ones. More polar solvents could not dissolve the oils and less polar ones would not permit a potentiometric titration to take place. The Titra-Lube laboratory method circumvents this problem by performing the test in two steps. In the first step, the oil is dissolved in a non-polar solvent and reacted with an isopropyl HCl solution which also easily dissolves in the solvent.

The solution is then mixed with an aqueous extractant which removes any excess acid from the non-polar solvent and isolated it in the aqueous phase. This aqueous phase is then physically separated from the oil and placed into the titration beaker. The acid/base titration then proceeds much more quickly than in other methods because the titration is taking place in a strictly aqueous medium. The titration itself takes about 3 minutes where previously it would take up to 30 minutes because of the time necessary for the elect rode to stabilize in the non-aqueous solution.