pH control method of reducing nitrogen oxides emission

A process for the pH control of a silver nitrate solution used for the selective recovery of olefins from a mixture of gases, said process comprising:

• a) bringing a gaseous mixture comprising olefins and hydrogen into contact with an aqueous silver nitrate solution, whereby the olefins are absorbed into the silver nitrate solution as a complex;
• b) separating the solution comprising the complexed olefins from the non-absorbed gases;
• c) de-pressurising and heating the olefin complex solution from (b) so as to release the olefins from the complex and regenerate the silver nitrate solution;
• d) passing said regenerated silver nitrate solution through a bed comprising silver oxide so as to maintain the pH value of the silver nitrate between 3 and 6;
• and
• e) recycling the silver nitrate solution regenerated in (d) to step (a).