Customer report from a rectification facility

The company Fresenius Medical Care operates a factory in St. Wendel (Germany) where artificial kidneys, so-called dialyzers, are built. The dialysis filters contain hollow-fibre membranes. 

Hollow-fiber membranes
  Photograph by Fresenius Medical Care

In order to produce these hollow-fibre membranes, two liquids are required. Both liquids are separated after the production process and then prepared for reusing. To this purpose, Fresenius Medical Care operates a large rectification facility. The liquids prepared for reusing have to fulfil the strict requirements for new materials.

After the rectification, the pureness has to be assessed by online measurements. Laboratory measurements often show an offset due the strong hygroscopic behaviour of the solvent and the very narrow measurement range. Also, they require more effort than an online analysis. Therefore, tests of bypass methods have been conducted.

First trials with laboratory photometers yielded promising results. However, the instruments are supposed to run under operational conditons instead of a protected laboratory. Hence, online photometers were needed.

Photometer with flow-cell and temperature sensor
 Photometer with flow cell and temperature sensor

The project was given to the company PIER-ELECTRONIC GmbH who have been in the business for 50 years. In their photometer systems, the electronics are separated from the probed substances in such a way that contamination is impossible even if leakage occurs. This is a fundamental prerequisite because the probed substance is aggressive.

For safety reasons, both production lines are monitored twice with parallel measurements. Two UV photometers and two NIR photometers are used. This makes it possible to determine the concentration of the organic solvent in water as well as the concentration of water in the solvent. 

Photometers on site
Photometers on site
Both photometer versions are available from PIER-ELECTRONIC GmbH. After successful integration and due to the very high accuracy and reliability of the instruments, Fresenius Medical Care have decided to integrate additional photometers.

The integration of the photometers was conducted by Fresenius Medical Care. The piping was designed to ensure good accesibility of all components so that no extra work is required even in cases of maintenance.

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The liquids treated for recycling are filled in storage tanks. The outgoing product pipes to the users are equipped with additional photometers for monitoring purposes. The concentrations of water and of the solvents have to be determined again.

Photometer Analyzer
Photometer analyzer

So far, the only noteworthy deviations between the synchronous measurements have been caused by lamp failure (at the end of the lamp lifetime) and in one case by a technical defect in a lamp control.

In all cases, the observed data drift was directed towards higher values, which ensures higher safety. In this application, the photometers from PIER-ELECTRONIC achieve an absolute accuracy of  5 ppm. The T90 time parameter is lower than 0.2 seconds, naturally dependent on the chosen integration time. Stability is better than 1 ppm per day.