Optical properties of crude oil with different temperatures

The transmittance and the optical properties play an important role in detection of crude oil. In this work, the transmittance spectra of crude oil was measured by Fourier transform infrared spectrometer IRTracer-100. The optical properties of crude oil were calculated by a double thickness method, and the effects of different temperature on transmittance spectra T and the optical properties (the refractive index n, the absorption index k, the absorption coefficient α and the reflectivity ρ) were analyzed. And the relationship between the temperature and the optical properties were studied. The results show that the transmittance spectra of crude oil has four absorption peaks: 720cm−1, 1377cm−1, 1465cm−1 and 2839 cm−1. At absorption peaks, temperature has a significant influence on the transmission spectrum and the optical properties of crude oil. With the increase of temperature, the refractive index n decreases gradually, when the temperature is 343.15K, the refractive index n reaches a minimum of 1.4622. The absorption index k and the absorption coefficient α have the same variation tendency, both of them reach the maximum at 313.15K. The reflectivity ρ fluctuates slightly under the influence of temperature and varies from 0.0127 to 0.0859. At absorption peak of 1456 cm−1, the refractive index n of crude oil has the best fitting accuracy, and the error range is 0.0081-0.35%. The fitting error ranges of the absorption index k, the absorption coefficient α and the reflectivity ρ are 11.79–96.52%, 2.74–77.08% and 0.1%–12.92%, respectively.