Mathematical model of astaxanthin purification process using the low-pressure column chromatography method

Astaxanthin is an antioxidant compound that can be extracted from the microalgae Haematococcus pluvialis using the microwave-assisted extraction (MAE) method. Purification of the astaxanthin compound can be conducted using a low-pressure column chromatography (LPCC) method. However, the mathematical model illustrating the adsorption and desorption process using the LPCC method has not been built by the other authors yet. Therefore, the purposes of this study were (1) to build the mathematical model of the purification process using the LPCC method, and (2) to simulate the experimental data using the model to find the important kinetic constant values that can be used in the industrial scale-up in the future. The purification process was carried out with silica gel as a stationary phase and a mixture of n-hexane:acetone of 3:1 (v/v) as a mobile phase. The silica gel diameter was varied to 0.2-0.5 mm and 0.063-0.2 mm, while the eluent velocity was varied to 1.85 mL/min and 3 mL/min. The mathematical model having five kinetic constants of De1, De2, kc2, kc2.a, and H_A2 was successfully built. The De1 and De2 (m2/s) were the effective diffusivities of astaxanthin in the intraparticle direction of the adsorbent granule and in the axial direction of the column, respectively. The kc2 (m/s) was the mass transfer coefficient of astaxanthin from the solution to the adsorbent. The kc2.a (/s) was the volumetric mass transfer coefficient of astaxanthin from the solution to the adsorbent. The H_A2 (g silica gel/m3) was the Henry's constant for astaxanthin concentration at equilibrium at the liquid-solid interface. In the variation of silica gel diameter, the De2 value at the diameter of 0.2-0.5 mm was greater than that at 0.063-0.2 mm. However, the De1, kc2, kc2.a, and H_A2 values were not affected by the different diameters. In the variation of eluent velocity, the kc2 and kc2.a values at 3 mL/min were greater than those at 1.85 mL/min. However, the De1, De2, and H_A2 values were not affected by the different eluent velocities.