Madera M, Höflinger W, Kadnar R
Institute for Chemical Engineering, Fuel and Environmental Technology, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria.
J Chromatogr A. 2003 May 16;997(1-2):279-84. doi: 10.1016/s0021-9673(03)00060-8.
In water-based heat transfer systems, frequently glycols are added to the water to obtain freeze protection. For this purpose, ethylene glycol (EG) is the most common substance used. When heated, the glycol will slowly degrade and the pH of the glycol-water mixture will decrease, leading to corrosion and foaming problems. Carboxylic acids were identified as the main degradation products. Quantification of the carboxylic acids is of importance to monitor the degradation reactions in order to identify hot spots or overheating, caused by severe heat exchanger scaling, where pH measurements will not be sufficient due to buffer substances added for corrosion protection. In this work, ion chromatographic methods havebeen developed to identify the main degradation products of EG in heat transfer systems and to monitor the degradation process. Possible acidic reaction products of EG are glycolic acid, glyoxylic acid, oxalic acid, acetic acid and formic acid. Separations with a Dionex AS9-HC column with Na2CO3 eluents of differing concentrations showed that only trace amounts of carboxylic acids are present in aged heat transfer media. Oxalic acid can be quantified simultaneously to nitrite or molybdate which are added as corrosion inhibitors. A Dionex AS10 separation column with Na2B4O7 eluent enabled base line separation of glycolic acid, acetic acid and formic acid. Heat transfer media, which are operated in different heat transfer systems under different conditions, were analysed. A system was identified, where severe overheating due to fluid maldistribution in the heat exchanger took place.
在水基传热系统中，通常会向水中添加二醇类物质以实现防冻保护。为此，乙二醇（EG）是最常用的物质。加热时，二醇会缓慢降解，二醇 - 水混合物的pH值会降低，从而导致腐蚀和起泡问题。羧酸被确定为主要降解产物。对羧酸进行定量对于监测降解反应很重要，以便识别由严重的热交换器结垢引起的热点或过热情况，在这种情况下，由于添加了用于防腐的缓冲物质，pH测量将不足以检测。在这项工作中，已开发出离子色谱方法来识别传热系统中EG的主要降解产物并监测降解过程。EG可能的酸性反应产物有乙醇酸、乙醛酸、草酸、乙酸和甲酸。使用不同浓度的Na2CO3洗脱液在Dionex AS9 - HC柱上进行分离表明，老化的传热介质中仅存在痕量的羧酸。草酸可以与作为腐蚀抑制剂添加的亚硝酸盐或钼酸盐同时进行定量。使用Na2B4O7洗脱液的Dionex AS10分离柱能够实现乙醇酸、乙酸和甲酸的基线分离。对在不同条件下运行于不同传热系统中的传热介质进行了分析。确定了一个系统，其中由于热交换器中流体分布不均发生了严重过热。
