Innovative new chemical-resistant coating for the chloralkali electrolysis process at the Euro Chlor trade show

Euro Chlor is a major conference and trade show that features presentations on the latest trends, developments and products and is held on a three-yearly basis. The theme of this year's event, which took place from the 16th to 18th of May in Berlin, was "Sustainable chlorine production: the path to continuous improvement".

As at previous Euro Chlor events, the main emphasis of the conference was on health, safety and environmental protection during the manufacture, use and transport of chlorine. Here, the focus was on the technologies and services specifically for the chloralkali industry. The
STEULER-KCH Plastics Engineering Division made an important contribution to the symposium with their presentation titled "The new generation of plastic tube materials for the chloralkali process".

In parallel to the conference, the trade show offered engineering firms, manufacturers and service providers the opportunity to demonstrate their technical knowledge and the advantages of their products and services. We were very pleased with the high level of interest shown in the Plastics Engineering Division stand, and in particular in our new ALPHARESIST tube system. This new material was jointly developed with our Spanish subsidiary, Alphaplast, and was specially conceived for the chlorine industry. There was great interest shown in the Plastics Engineering Division's other products and also in the rest of STEULER-KCH's portfolio. We also made important new contacts, both domestic and overseas, which have since been followed up.

ALPHARESIST is an innovative new development that serves as a replacement for GFRP tubes that play an indispensable role in the chloralkali process. The chloralkali process involves generating the important basic chemicals chlorine and caustic soda from a saline solution using electrolysis.
Direct current is passed through the solution via two electrodes, whereby some of the electrical energy is converted into chemical energy. Free chlorine and a depleted saline solution are generated at the anode and caustic soda at the cathode. This endothermic reaction results in temperatures of up to 95°C.

The current designs of the glass-fibre reinforced polymer (GFRP) tubes being used for this process are problematic in a variety of ways. In the anolyte region, pure GFRP tubes offer only limited chemical resistance, with ablated glass fibres accumulating in filters, valves, pipes and other components, resulting in higher maintenance costs.
Composite GFRP tubes with a post-chlorinated PVC (polyvinyl chloride) interior liner can only be used for acidic anolytes; above a pH value of approximately 3.5, post-chlorinated PVC is destroyed and degraded very rapidly.

GFRP tubes with a PP (polypropylene) interior liner are most commonly used in the catholyte region. The high operating temperatures here cause thermal ageing of the PP liner material, eventually leading to stress cracks, especially in the area of the welds. In addition to this, the different thermal expansion coefficients of the PP liner and GFRP laminate can lead to the liner detaching from the GFRP during cooling.
The purpose of the newly developed ALPHARESIST was therefore to increase the service life while simultaneously minimising the maintenance costs of anolyte and catholyte tubes used in the chloralkali process.

A pure GFRP design was preferred in the anolyte region. The idea was to engineer a chemical-resistant coating free of glass fibres and select an optimised, more durable resin matrix. The solution involved developing a chemical-resistant coating composed of a powdered ceramic filler and a cobalt-free cured resin matrix. This excludes the possibility of glass fibres entering the anolyte. It simultaneously minimises ablation thanks to the increased chemical resistance of the resin matrix, thus allowing for longer service lives together with reduced maintenance overheads.
A similar approach was taken in the catholyte area, the difference being that a durable epoxy resin matrix was selected as the laminating resin here.
Following successful laboratory testing, pilot field trials were carried out using both anolyte and catholyte tube components, and the results thus far have been extremely positive.
Over the coming months, extensive practical experience will be gathered so that in future ALPHARESIST can be fitted to new and existing chloralkali plants on a large scale.