pH Measurement and Control of Ethylene Quench Waters

Ethylene is produced at high temperatures (750-1000°C) in a steam cracker. Olefins, Naphtha or LNG feedstock is steam cracked in a cracking furnace. The ethylene is produced when the high temperature process is stopped by water quenching. Accurate pH measurement and control, by the addition of caustic, to remove acid gases such as hydrogen sulphide and carbon dioxide of these quench waters is necessary to prevent unwanted emulsions forming.

Porous reference electrodes fail due to serious fouling and hydrogen sulphide poisoning present in the quench waters.

Accurate, Low-Maintenance, Long Life pH measurement and control is assured when the quench water process is controlled using the unique and patented Refex pH/mV electrodes.  The Refex patented reference electrode uses a Non-Porous, ionically conducing, hard polymeric material replacing the need for porous liquid-junctions (Diaphragma). The Refex polymeric material doubles as an immobilised non-porous electrolyte and also as a protective interface/barrier that separates the quench waters from the reference Ag/AgCl half-cell and KCl electrolyte. As a result there is no liquid exchange or contact.

The Refex electrodes cannot be poisoned or fouled and continue to perform accurately even when completely coated with crude oil for examples. The coatings must remain wet and conductive. 

The Refex electrodes are compatible with most pH transmitters. The electrodes shown in the image are compatible with Yokogawa pH transmitters (retrofit directly to the Yokogawa flow cell) and connect directly with the Yokogawa connecting cables.