对甲基苯磺酸络合-异戊醇萃取铬(Ⅵ)在有机铬催化剂中铬(Ⅲ)测定中的应用

乙烯齐聚合成1-己烯的主催化剂为有机铬系催化剂,铬系催化剂中铬(Ⅲ)能很好地与助催化剂烷基铝形成络合物,而铬(Ⅵ)会与烷基铝发生反应,降低催化剂的催化能力,因此需要准确测定铬催化剂中铬(Ⅲ)含量。实验提出在酸性条件下用对甲基苯磺酸络合、异戊醇萃取有机铬催化剂中铬(Ⅵ),使铬(Ⅲ)和铬(Ⅵ)分离,最后采用电感耦合等离子体原子发射光谱法(ICP-AES)测定无机相中铬(Ⅲ)。实验考察了硝酸的浓度和用量,以及络合剂和萃取剂的用量。研究表明:加入10 mL 10%(体积分数,下同)硝酸,用2.0 mL对甲基苯磺酸络合、20 mL异戊醇萃取就可以完全将样品中的铬(Ⅲ)和铬(Ⅵ)分离。铬(Ⅲ)校准曲线的线性相关系数大于0.999;方法检出限为1.45 μg/g。按照实验方法测定有机铬催化剂实际样品中铬(Ⅲ),结果的相对标准偏差(RSD,n=6)小于4%,回收率为94%～103%。

Application of p-methylbenzene sulfonic acid complexation-isoamyl alcohol extraction of Cr(Ⅵ) for determination of Cr(Ⅲ) in organic chromium catalyst

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%.