Surfactant Properties of Inhibitors

The effectiveness of film-forming inhibitors, as already stated, depends upon strong adsorption of inhibitor molecules at the interface between the process liquid(s) and the metal surface to be protected. It is not at all unusual for materials active at a solid-liquid interface also to be active at a liquid-liquid and/or a liquid-gas interface. 

The former may cause emulsification problems, the latter may result in foaming. Emulsion problems are evidenced in water draw-offs in refinery equipment and in petrochemical plants, e.g. separation of oils and tars from ethylene quench water systems. 

Of great importance when refining products such as jet fuels is emulsification of small quantities of water into the product. The water may enter the system because of storage tanks that breathe humid atmospheres or carry water bottoms, or by contamination or careless handling. Water that does get into the jet fuel storage system often is difficult to remove with settlers or coalescers when surfactants are present in the system. 

Because of the deleterious action of emulsified water in promoting bacterial growth in storage, and in freezing and clogging of fuel injection nozzles during operation, jet fuel purchasers have strict requirements concerning such water, as well as the fuel response to it. 

This is usually determined by the ASTM method D 2550-66T (Water Separometer Index, Modified or WSIM test). The WSIM test helps to find one inhibitor among the others that is effective as a corrosion inhibitor, but produces minimal emulsification or that can be modified by a demulsifying agent without losing its corrosion inhibitive properties. 

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