| Polycyclic aromatic hydrocarbons (PAHs) are a large class of organic compounds which are composed of two or more fused aromatic rings. They are primarily formed in the incomplete combustion or pyrolysis of organic matter during industrial processes. PAHs are widely distributed organic pollutants in the environment. Most of PAHs and their epoxides are highly toxic, mutagenic and carcinogenic to living organisms including human beings. Natural tocopherol (TP) was extracted from the deodorizer distillates as the by-product of edible vegetable oil refining process. PAHs will also be enriched during the enrichment process of natural tocopherol. To remove PAHs in natural tocopherol, research work has been done and discussed as the following aspects:The analytical method of the trace PAHs quantification in natural tocopherol was carefully studied. Donor acceptor complex chromatography (DACC) was used to isolate PAHs in the tocopherol. The samples were injected into the DACC column (3.0 mm i.d.×80 mm) and flushed for 40 min under 0.05 mL/min flowrate, then isopropyl alcohol was used to flush DACC column with 0.5 mL/min for 4 min to remove tocopherol and other interfering substances. Acetonitrile was used to flush DACC column with 0.5 mL/min for another 1 h and was collected using a round-bottom flask. Acetonitrile was evaporated by rotary evaporation under 35℃ until 1 mL to obtain enriched PAHs solution. The PAHs solution was then analysed by HPLC. The liquid chromatographic conditions were:PAH column (4.6 mm i.d. x 250 mm,5 μm), column temperature 35℃; mobile phase, acetonitrile-water, binary gradient condition were used:from 0 to 5 min,50% water,50% acetonitrile; from 5 min to 20 min,50% water decreased to 0%,50% acetonitrile increased to 100%; from 20 min to 28 min,100% acetonitrile; from 28 min to 32 min,0% water increased to 50%,100% acetonitrile decreased to 50%. Eight wavelength shifts were adopted to achiece the most sensitivity. Sample size was 20μL. Three natural tocopherol samples,50% α-tocopherol,93.25% d-a-tocopherol, and 89.9% mixed tocopherol were analyzed using the same method. Contents of PAHs in the three tocopherols were 395.98 ng/(g TP),58.45 ng/(g TP),109.58 ng/(g TP), respectively, indicates their contents exceeding the international standard.The adsorption amount of PAHs on activated carbon AC-4 was determined and the effects of adsorption temperature, adsorption time were studied. Secondary adsorption kinetic model was employed to fit PAHs adsorption curve, and the kinetic characteristics were investigated. The results showed that when the operation condition of the adsorption temperature is 35℃ and the adsorption time is 38 h, the adsorption amount of PAHs was highest. The adsorption kinetics curve well fitted the secondary adsorption kinetic model. At 35℃, both of Langmuir and Freundlich model can be used to fit the adsorption isotherm of PAHs. It is also worth noting that at 50℃ the Langmuir model exhibit superior fitting effect than the Freundlich model.On the basis of the static adsorption experimental results, the breakthrough curve of naphthalene was measured. When the concentration of tocopherol was 5%, naphthalene content was 100 μg/(g TP) under 3 BV/h flowrate at 25℃,8.59 g tocopherol was handled by per gram AC-4. The results showed that PAHs outflow time was relatively slow indicating that PAHs were almost completely adsorbed. At the same time, the loss of tocopherol was 4.43% that was negligible in the process. |
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