Determination of total base number (TBN) in lubricating oils by mid-FTIR spectroscopy

摘要

A Fourier transform infrared (FTIR) spectroscopic method was developed to rapidly and quantitatively determine the Total Base Number (TBN) of hydrocarbon lubricating oils by spectroscopically measuring the COO functional group of the salt produced when trifluoroacetic acid (TFA) reacts with basic constituents present in an oil. FTIR quantification was based on a differential spectrum derived from two oil spectra collected separately, one recorded prior to and the other after the addition of a TFA reactant solution, the first spectrum being subtracted from the second. Since the TFA/base reaction is rapid, complete and stoichiometric, the FTIR method was found to be very robust and capable of reliably monitoring relatively small changes in TBN, with a reproducibility of ±0.17 mg KOH/g and an accuracy of ～±0.20 mg KOH/g, as determined by standard addition. The method is simple to execute and avoids the environmentally unfriendly solvents associated with the ASTM wet chemical methods. Implemented with appropriate software, the determination of TBN by FTIR spectroscopy would be a simple and convenient procedure, useful for routine condition monitoring and a significant improvement over the methods presently available.