Determination of Diffusion Coefficient of Palm Oil in n-Hexane Using Laser Deflection Method and Image Processing

Abstract

Determination of diffusion coefficient using the Wiener method has shown a high level of agreement with literature in previous studies, particularly for liquids with a mass of less than hundreds of amu and a small molecule-sized order of Angstrom (atomic mass unit). This method involves a laser beam deflection and refraction phenomenon on the inter-diffusion zone of two fluids with different refractive indexes. Palm oil, vegetable oil with a composition and structure that is quite complicated and size relatively large molecule, has abundantly available and has become one of the primary raw materials for biodiesel production and cooking. This study used the method to examine the diffusivity of palm oil in n-hexane, which is still rare and hard to find, so challenging to be studied. A camera is used to catch the trace of a deflected laser beam on a screen after it passes through a diffusion cell in the measurement. This image was then corrected, made grey, and digitized to extract the laser image coordinate data. An averaging window algorithm is used in digitizing. The digitized results are then processed to calculate the diffusion coefficient. Measurements were made three times to test the consistency of the results. Camera and digitizing techniques are used here to speed up and facilitate measurement. The measured value of diffusion coefficient of palm oil in n-hexane is 2.18×10-4 ± 5.05×10-5 cm2/minute. The results showed consistency in measure, i.e., precision with a maximum error range of 10.6%, but not good suitability value with literature data, i.e., accuracy was less than 10%. These results found that the measurement system that applied the laser deflection method and the image processing of averaging window could not measure the diffusion coefficient of large molecules and complexes such as palm oil quite well.