Technology Type

Caustic treatment is used to upgrade a wide range of liquid fractions from LPG to diesel fuels and heating oils. As the caustic solution (and often a catalyst) mixes with the hydrocarbon feed it either extracts or sweetens mercaptans, depending on the process used.

However, the combination of the hydrocarbon and mercaptan rich caustic also forms a very stable emulsion that is difficult to separate, causing significant quantities of caustic carryover in the product. This results in off-specification products due to haze or elevated sodium concentration and loss of caustic. In many cases the entrained caustic is fed to processes where sodium is a poison to the catalyst.

Because the emulsion is so stable, knock-out drums, sand filters and packed vessels are not able to efficiently separate the caustic emulsion from the hydrocarbon streams. High efficiency phase separators such as Liquid/Liquid Coalescers reliably meet ‘clear and bright’ product specification and sodium levels downstream. Filter elements are employed to reduce suspended solids to improve the efficiency and life of the Liquid/Liquid Coalescer.

Example of fuels caustic processes are:

• UOP Merox™ Process
• Merichem Napfining™ Process
• Merichem Mericat Processes

Source: Pall Corporation >  Oil & Gas > Downstream Refining > Refinery Caustic Treating > Causting Treating in Refineries.