Rapid determination of viscosity and viscosity index of lube base oil based on near-infrared spectroscopy and new transformation formula

Viscosity and viscosity index are the key product properties in lubricating oil production process. Rapid and even online analysis of viscosity and viscosity index through near-infrared (NIR) spectroscopy combined with chemometrics is helpful to optimize the production process. However, due to the nonlinear effect, the commonly used linear multivariate correction method is not effective. In this work, the feasibility of four existing viscosity linear transformation formulas for establishing NIR models was studied, and a new viscosity linear transformation formula was developed based on the viscosity-gravity constant. The experimental results showed that three of the four existing viscosity linear transformation formulas made some improvement on the viscosity prediction of base oil, but not as good as the newly established viscosity linear transformation formula. For viscosity index, the accuracy of modeling with reference viscosity index directly was much better than calculating by prediction viscosity value. Both of the viscosity and viscosity index prediction results of NIR analysis were in good agreement with the results of reference method, indicating that the determination can meet the needs of rapid and on-line analysis in industrial field.