pH电位滴定法测定发动机油碱值  

Determination of alkaline value of engine oil by pH potentiometric titration

作　　者：常高 冯程 李良 张静茹 张作煜 CHANG Gao;FENG Cheng;LI Liang;ZHANG Jingru;ZHANG Zuoyu(Sdic Qinzhou Port Co.,Ltd.,Qinzhou 535008,China;Jilin Provincial Ecological Environment Monitoring Center,Changchun 132000,China;Guangzhou Mechanical Engineering Research Institute Company Limited Equipment Lubrication and Testing Institute,Guangzhou 510700,China)

机构地区：[1]国投钦州港口有限公司,广西钦州535008 [2]吉林省生态环境监测中心,吉林长春132000 [3]广州机械科学研究院有限公司设备润滑与检测研究所,广东广州510700

出　　处：《冶金分析》2024年第11期66-71,共6页Metallurgical Analysis

基　　金：广东省工业摩擦学企业重点实验室(2023B1212070025)。

摘　　要：碱值测试可用于评估发动机油中碱性添加剂含量,是发动机油性能评价的重要指标之一。本文将20种发动机油的解离常数带入汉德森-海森巴赫方程,结合能斯特方程计算得到不同发动机油的理论终点pH值,通过统计学中稳健统计算法A进行统计分析,确定适用于所有发动机油的终点pH值为-4.5;再以冰乙酸和氯苯混合溶液为溶剂,使用高氯酸冰乙酸进行滴定,建立了pH电位滴定法测定发动机油碱值的测定方法。方法检出限为0.0041 mgKOH/g。将碱值发动机油标准物质用不含碱性物质的基础油进行稀释,混合均匀后配制成碱值依次为2、5、20mgKOH/g的空白加标样品,采用实验方法进行测定,测定结果的相对标准偏差(RSD,n=6)为0.60%~1.2%,空白加标回收率为99%~102%。采用实验方法对不同发动机油样品进行测定,并采用行业标准SH/T0251—1993《石油产品碱值测定法(高氯酸电位滴定法)》进行方法比对,结果表明,两种方法测定值的差值均在行业标准SH/T0251—1993要求的重复性限要求范围内。选择4个不同碱值水平的发动机油标准物质,按照选定的实验方法进行测定,测试结果在标准值偏差范围内,相对标准偏差(n=6)为0.37%~0.81%。按照实验方法对5种发动机油样品进行测定,测定结果的相对标准偏差(n=10)均小于1%。The test of alkaline value can be used to evaluate the content of alkaline additives in engine oil,and it is one of important indicators for evaluating the performance of engine oil.In this study,the dissociation constants of 20 types of engine oils were introduced into the Henderson-Hasselbalch equation.By combining with the Nernst equation,the theoretical endpoint pH values of different engine oils were calculated.The statistical analysis was conducted using the robust statistical algorithm A in statistics,and it was found that the endpoint pH value applicable for all engine oils was-4.5.A method for determining the alkaline value of engine oil by pH potentiometric titration was established using the mixture of acetic acid and chlorobenzene as the solvent and using the mixture of perchloric acid and acetic acid as the titrant.The limit of detection of this method was 0.0041 mg KOH/g.The standard substance of alkaline engine oil was diluted with base oil that contained no alkaline substances.After well mixing,the blank spiked samples with alkaline content of 2,5,and 20 mg KOH/g were prepared and determined according to the experimental method.The relative standard deviations(RSD,n=6)of the measurement results were between 0.60%and 1.2%,and the recoveries of blank spiked samples were between 99%and 102%.Various engine oil Petroleum Product Alkalinity Determination Method(Perchlorate Potentiometric Titration Method)was used for method comparison.The results showed that the difference between the two methods was within the repeatability limit required by the industry standard SH/T 0251-1993.Four standard substances of engine oil with different alkaline levels were selected and determined according to the experimental method.The test results were within the range of standard deviation,and the RSDs(n=6)were between 0.37%and 0.81%.The proposed method was applied for the determination of five types of engine oil samples,and the RSDs(n=10)of measurement results were less than 1%.

关 键 词：发动机油 碱值 pH 能斯特方程 电位滴定法 高氯酸 冰乙酸 氯苯 

分 类 号：O657[理学—分析化学]