Abstract: When the virtual component method is used to characterize the complex chemical composition of crude oil and its fractions, the distillation curve is often discontinuous and fluctuating, and the reliability of the results is poor because of insufficient distillation data. The traditional quadratic and cubic polynomial spline interpolation functions are commonly used to keep the distillation curve continuous and smooth, but those interpolation results sometimes are not accord with the monotonic increasing characteristics of the distillation curve. An exponential spline interpolation with three parameters was designed to guarantee the monotone increasing of distillation curve in theory. Furthermore, the real boiling point distillation data of 52 kinds of crude oils were interpolated and verified. The results showed that the method of exponential spline interpolation could guarantee the monotone increasing of the distillation curve after interpolation. Among the 52 kinds of interpolation results, there were 37 kinds whose fitting determination coefficient (R²) of exponential spline interpolation was greater than 0.99, accounting for 71.2%, and only 21 kinds whose R² of cubic spline interpolation was greater than 0.99, accounting for 40.4%. There were 50 kinds whose accuracy of exponential spline interpolation was higher than that of cubic spline interpolation, which showed that exponential spline interpolation was better than cubic spline interpolation. Therefore, based on the exponential spline interpolation method, the accuracy of the virtual component method could be obviously improved.

Key words: distillation curve of crude oil, spline interpolation, monotonically increasing, pseudo-component