Abstract：The main catalyst for ethylene oligomerization synthesis of 1-hexene is organic chromium catalyst, in which Cr(Ⅲ) can form a complex with the cocatalyst alkyl aluminum. Since Cr(Ⅵ) can react with the alkyl aluminum, which reduces the catalytic capacity of the catalyst, it is necessary to accurately determine the content of Cr(Ⅲ) in chromium catalyst. Cr(Ⅵ) in organic chromium catalyst was treated by p-methylbenzene sulfonic acid complexation and isoamyl alcohol extraction under acidic condition in experiments, realizing the separation of Cr(Ⅲ) and Cr(Ⅵ). Finally, the content of Cr(Ⅲ) in inorganic phase was determined by inductively coupled plasma atomic emission spectrometry(ICP-AES). The concentration and dosage of nitric acid as well as the dosage of complexing agent and extraction agent were investigated. It was found that the Cr(Ⅲ) and Cr(Ⅵ) in sample could be fully separated with 2.0 mL of p-methylbenzene sulfonic acid and 20 mL of isoamyl alcohol after adding 10 mL of 10% (volume fraction, similarly hereinafter) nitric acid. The correlation coefficient of calibration curve for Cr(Ⅲ) was greater than 0.999. The limit of detection was 1.45 μg/g. The content of Cr(Ⅲ) in sample of organic chromium catalyst was determined according to the experimental method. The relative standard deviation (RSD, n=6) of determination results was less than 4%. The recoveries were between 94% and 103%.
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