Caustic Treating Systems

Caustic treating is used to remove or sweeten mercaptan compounds in hydrocarbon streams. The process is used on a wide range of liquid fractions from LPG to diesel fuels and heating oils. As the caustic solution mixes with the hydrocarbon feed it extracts mercaptans. However, the combination of the hydrocarbon and mercaptan rich caustic also form a very stable emulsion that is difficult to separate, causing significant quantities of caustic to carry over into the product. This results in off-specification product due to haze or sodium concentration and loss of caustic. In many cases the caustic is fed to processes where sodium is poison to the catalyst.  (more)

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Because the emulsion is so stable, knock-out drums, sand filters and packed vessels are not able to efficiently separate the caustic solution from the hydrocarbon.

Pall Solution

Pall PhaseSep® Liquid/Liquid coalescers installed in caustic treating systems have removed caustic from the hydrocarbon product to concentrations of less than 0.5ppm wt. This eliminates haze and sodium product quality problems for gasoline, jet fuel, diesel and lighter hydrocarbons and extends the run life of catalysts in downstream processes. The stability of an emulsion containing caustic and hydrocarbons from a caustic treating is very difficult to separate. An interfacial surface tension as low as 1 dyne/cm has been measured in the hydrocarbon stream. Most liquid/liquid dispersions with an interfacial tension less than 20 dyne/cm cannot be separated in knock-out drums, packed vessels, sand filters, or other conventional coalescers.

Figure 1: Caustic Treating Systems


Table 1: HCP Filter Recommendations

Filter Location Recommended Pall Assembly Purpose of Separation Benefits of Separation
1* Prefilter with Pall Nylon Profile cartridges Removal of Solids Improve efficiency and life of PhaseSep Liquid/Liquid coalescer
2* Pall PhaseSep Liquid/Liquid Coalescer in horizontal assemblyLCS4H1AH Remove carried over caustic from hydrocarbon product
  • Meets product quality specifications for haze and sodium
  • Extends run life of downstream catalytic

* Both filter locations 1 and 2 required for this application

Petroleum Refineries
Gas Processing Plants
Chemical and Petrochemical Plants