Patent ID: 7537745

Claim:
Process for producing cyclohexanone oxime comprising: cycling an aqueous reaction medium containing residual hydroxylammonium from a cyclohexanone oxime synthesis reactor in which cyclohexanone oxime is produced by reaction of hydroxylammonium with cyclohexanone to a hydroxylammonium synthesis reactor in which hydroxylammonium is prepared by catalytic reduction of nitrate with hydrogen; providing a first acidic aqueous solution comprising hydroxylammonium and phosphate from at least a portion of the cycled aqueous reaction medium; and mixing the first acidic aqueous solution with a second acidic aqueous solution comprising nitric acid within or upstream of the hydroxylammonium synthesis reactor, resulting in a third acidic aqueous solution comprising hydroxylammonium, phosphate and nitric acid, wherein the third acidic aqueous solution has a total acid concentration minus the phosphate concentration which is lower than 0.523*In([hydroxylammonium]/1.25)+422/(T+81) whereby [hydroxylammonium] is the concentration of hydroxylammonium in the third acidic aqueous solution, T is the temperature of the third acidic aqueous solution expressed in ° C. and all concentrations are expressed in mol/l.