Komplexbildner in alkalischen Reinigern

Abstract

Using a laboratory-scale CIP test rig under process conditions (temperature fluid dynamics, time) based on values found in practical cleaning of dairy plant heat exchangers comparative cleaning experiments were carried out. For testing circular stainless steel elements of 50 mm in diameter were used which had been soiled with deposits consisting mainly of denatured whey proteins in a specific heating procedure using fresh raw milk. Deposit removal was monitored by use of a video camera. Single digitized frames showing different stages of soil removal were transmitted to a computer and analyzed with the aid of an image processing software (surface clean/ still soiled). As a basic substrate an aqueous solution of sodium hydroxide in tap water (17°dH) was used to which 12 complexing agents had been added in a comparable concentration. According to the test results EDTA is still the most efficient product, although due to its poor biodegradability in conventional sewage treatment plants, it should be substituted by other substrates. Na3-SDA proved to be nearly as efficient as EDTA, but due to its high production costs it is, at present not competitive on the market. NTA, which is recommended by the Ministry for Environment and Reactor Safety, Bonn, and the Federal Health Office, Berlin, was found as a well suited biodegradable substitute for ETDA. The biodegradable structures Na 3 -MGDA (Trilon ES 9964), Na 3 -EGDA and Na 4 -ASDA were as effective as NTA, whilst IDA and Na 2 -IDA as well as Na 2 -MIDA, Na 2 -HEIDA, and NA 3 -ISDA produced no effect. With respect to its comparability to NTA, and the justifiable production costs, Na 3 -MGDA (Trilon ES 9964) is the product of choice for a field test for cleaning a plate heat exchanger in a dairy plant.