Total Acid Number Determination in Residues of Crude Oil Distillation Using ATR-FTIR and Variable Selection by Chemometric Methods

The total acid number (TAN) was determined in the atmospheric residue (AR) and vacuum residue (V R) of the petroleum distillation process using mid-infrared spectroscopy with attenuated total reflection in association with chemometric methods. Calibration and prediction sets consisted of 44 and 13 samples, respectively (16 AR samples and 41 VR samples). Calibration models were developed using three variable-selection models: interval partial least squares (iPLS), synergy interval partial least squares (siPLS), and backward interval partial least squares (biPLS). Different treatments and preprocessing steps were also evaluated for development of the models. The treatment based on the first derivative with a Savitzky- Golay filter and the mean centered was selected for model construction. A root-mean-square error of prediction of 0.164 mg g(-1) of KOH was achieved using the biPLS algorithm with spectra divided into 20 intervals and combinations of 5 intervals (2992-2826, 1823-1657, 1656-1490, 1489-1323, and 821-655 cm(-1)). This model (biPLS20) showed a correlation coefficient of 0.991 between reference and predicted values. The proposed method for TAN determination allowed a fast analysis, and it is possible to apply it for quality control in industrial processes with advantages when compared with the method recommended by American Society for Testing and Materials (ASTM D 664-09).