Adsorption decolorization and composition analysis of high melting point Fischer–Tropsch waxes

Abstract The decolorization and quality improvement of the high melting point Fischer–Tropsch wax were carried out by the method of adsorption refining, and the activated clay was selected as adsorbent. The effects of adsorption decolorization temperature on the wax products were evaluated by testing the saybolt color number and whiteness value of the waxes. Meanwhile, the influence of adsorption decolorization temperature on the composition of waxes was investigated by gas chromatography (GC), inductively coupled plasma (ICP), thermogravimetry/differential thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), thermogravimetric mass spectrometry (TG‐MS), Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and X‐ray fluorescence (XRF) characterizations of waxes and adsorbents activated clay before and after use. The results showed that the best adsorption decolorization temperature is 120°C, and the corresponding saybolt color number of decolorization waxes is +16. The reasons for the poor chromaticity of high melting point wax are not only the inorganic components mainly composed of residual ultrafine catalyst particles but also the organic components of unsaturated carbon–carbon double bonds and heteroatomic compounds containing oxygen, nitrogen, and sulfur. The oxidative deterioration of the unsaturated carbon–carbon double bond and hydrocarbons with low bond energy in waxes, as well as the oxidation of hydrocarbons containing oxygen and nitrogen heteroatoms, may be the main reasons for the yellowing of the wax products in the process of decolorization.