基于反滴定的润滑油酸值测定方法

DETERMINATION METHOD OF ACID NUMBERS OF LUBRICANTS BY ANTI-TITRATION METHOD

酸值是衡量润滑油腐蚀性和使用性能的重要质量指标。酸值测定通常采用国家标准方法进行。对颜色浅的润滑油,标准方法可取得令人满意的结果,但对使用过的润滑油或颜色较深的润滑油,由于滴定终点不易判断,往往具有比较大的测定误差。文章基于反滴定理论,建立了一种新的酸值测定方法,以克服当前方法中存在的滴定终点不易判断的不足。测定时,含破乳剂的碱性水溶液充分与待测润滑油作用,以中和润滑油中酸性物质,分层后未反应的碱性物质进入水相。用标准酸溶液中和水相中的碱性物质,即可获得润滑油的酸值。由于滴定是在水溶液中进行的,终点易判定,特别适用于使用过的润滑油的酸值的测定。研究结果表明所建方法与国家标准方法的测定结果有很好的一致性,线性相关系数为0 .9982 ,平行测定标准偏差小于3.9% ,能满足快速测定要求。

Acid number is an important index for evaluating lubricant's corrosion behavior and applied performance. It was determined generally by national standard method. For colorless lubricants, the method can give us a satisfactory results. But for used or deep color lubricants, measuring error of the method was usually large owing to difficult judgment of titration end point. A new method for determination of acid numbers of lubricants was established based on anti-titration theory. First, alkalinity solution containing demulsifier was mixed with lubricant completely for neutralizing acid substances in lubricant, then remained alkalinity substance would be hold in aqueous solution. Acid number of lubricating oil can be obtained by neutralizing standard acid solution and alkalinity substance of aqueous phase. This method was carried out in aqueous solution; the titration end could be easily identified. The experimental results show that the established method has a good linear correlation with the national standard method (linear correlation coefficient is 0.9982) and can satisfy the request of shift measurement (maximum standard error less than 3.9%).