Dear sirs, I'm employed as process engineer in oil refinery, Serbia. We're using 35% H2O2 for oxidizing spent refinery caustic from LPG and fuel gas MEROX processes. The caustic contains several thousands ppmw of Na2S and mercaptides (RSNa). H2O2 solution is stored in a plastic (PEHD) container; dozing is achived via reciprocating, stainless steel pump. Separate streams of peroxide and caustic are being mixed downstream of the caustic vessel, and then sent to refinery waste streams basin. The degree of oxidation is far below design, due to short reaction time and non-ideal mixing of streams. I have several questions concerning oxidation process. If you could help me in any way, it would be highly appreciated. 1) Can we modify our process plant and mix dilluted caustic stream with H2O2 stream in a carbon steel vessel (where dilluted caustic is located), equiped with recirculating centrifugal pump (carbon steel case) to ensure 100% oxidation? The vessel has an atmosphere vent. Oxidation reaction is measured and controlled by vessel temperature (<70C). I think it's the much better configuration to achieve full oxidation than the existing one. 2) Can we use some of the refinery wastewater streams for dilluting caustic, instead of demineralized water. Wastewater has several hundreds ppm of NH3 and sulfides. What chemical species are highly incompatible with H2O2? What do we have to avoid when dealing with H2O2? Thank you in advance. If you need more details, please write back. Wish you good health, Zauberberg

Dear David, Thank You for your reply. Concerning the use of carbon steel equipment in hydrogen-peroxide installations, what confuses me the most is the following: 1) Existing "reaction vessel" - located downstream of caustic/peroxide mixer - is made of carbon steel; our caustic oxidation plant works very well almost 10 years, no problems encountered. Since peroxide is used in higher volumes than the reaction stechiometric requires (due to non-ideal mixing), we could say that reaction vessel is constantly exposed to some concentration of H2O2, but no problems registered so far. What do you think about this observation? 2) Adding H2O2 sollution through SS316L distributor (similar to steam stripping assembly in distillation columns), submerged in caustic, would practically ensure instant oxidation and, therefore, minimize peroxide residence in the caustic vessel. Circulating pump would only "help" in this situation. Do You agree with that? Thank You again for your kind reply. Regards

Hi Zauberberg Since RTOL we didn’t met in the web!!! I suppose de use of H202 in your process system is beneficial for H2S corrosion reduction. I suggest you to read the text bellow “Hydrogen peroxide reduces sulphide corrosion” “Based on coupon tests, hydrogen peroxide can effectively remove hydrogen sulphide and destroy sulphate-reducing bacteria in oil field brines. Hydrogen peroxide’s effect on the corrosion of equipment is beneficial when the overall system is examined. H2S in the vapour space is a severe corrosive agent, but when hydrogen peroxide is added to the brine to destroy the sulphide, the sulphide in the vapour space is eliminated. This effectively eliminates the corrosion of steel above the fluid level. The corrosion of steel in contact with the brine does not increase significantly if the peroxide-to-sulphide ratio is kept close to 1:1. The use of peroxide eliminates severe corrosion in the vapour space while maintaining low corrosion below the fluid level”. Indy Best regards and good luck Luis Marques