Use of a supplemental promoter in conjunction with a carbon-supported, noble-metal containing catalyst in liquid phase oxidation reactions

A process for the preparation of N-(phosphonomethyl) glycine or a salt thereof, the process comprising:

• oxidizing N-(phosphonomethyl) iminodiacetic acid in an aqueous reaction medium in the presence of an oxidation catalyst comprising a noble metal on a carbon support, thereby producing an aqueous reaction mixture comprising N-(phosphonomethyl) glycine, formic acid or formaldehyde;
• separating oxidation catalyst from said reaction mixture to produce a filtrate comprising N-(phosphonomethyl) glycine, formic acid or formaldehyde;
• evaporating water, formic acid or formaldehyde from said filtrate to produce an overhead vapor stream;
• condensing water, formic acid or formaldehyde from said overhead vapor stream and forming an aqueous treatment mixture containing water, formic acid or formaldehyde;
• contacting said aqueous treatment mixture with an oxidizing agent in the presence of a noble metal catalyst on a carbon support and a promoter metal comprising a metal effective to promote oxidation of formic acid or formaldehyde, thereby forming a treated condensate by oxidizing formic acid or formaldehyde contained in said treatment mixture;
• and
• recycling treated condensate incorporating it into an aqueous medium for N-(phosphonomethyl) iminodiacetic acid in the further oxidation thereof to N-(phosphonomethyl) glycine or a salt thereof.