Methanol carbonylation with improved aldehyde removal

A method of making acetic acid while controlling aldehyde and aldehyde-derived impurities comprising:

• (a) carbonylating methanol or reactive derivatives thereof in a reactor of a production system in the presence of a Group VIII metal catalyst and a methyl iodide promoter while maintaining a concentration of water in the reactor of from 1-10% by weight of the reaction medium and concurrently maintaining in the reactor a predetermined partial pressure of carbon monoxide;
• (b) venting non-condensibles from the production system as to provide vent gas containing light ends and aldehyde impurity;
• (c) feeding the vent gas from the production system to an absorber tower;
• (d) supplying a scrubber solvent to the absorber tower, the scrubber solvent comprising acetic acid, methanol, methyl acetate or mixtures thereof;
• (e) contacting the vent gas with the scrubber solvent thereby removing light ends and aldehyde impurity from the gas and absorbing into the scrubber solvent;
• (f) stripping absorbed light ends and aldehyde impurity from the absorber solvent to provide a vent-recovered light ends stream having more than 1 percent acetaldehyde by weight;
• (g) purifying the vent-recovered light ends stream to remove aldehyde impurity;
• and
• (h) recycling purified light ends from the vent-recovered light ends stream to the production system.