Process for preparing acrylic acid

A process for preparing acrylic acid, including a step of oxidizing acrolein, wherein the reaction mixture obtained in this oxidation is contacted with water as quenching agent in an apparatus consisting essentially of

• a feed containing a reaction mixture arranged below the middle of the apparatus,
• a quenching agent inlet arranged above the feed,
• an outlet arranged below the feed and
• a draw arranged above the quenching agent inlet,
• the apparatus having, between the quenching agent inlet and the feed containing the reaction mixture, a region provided with one or more packing elements, wherein 2 or 3 sieve trays or ripple trays which ensure the formation of a liquid layer having a height of at least 1 cm is present between the quenching agent inlet and a packing element present between the quenching agent inlet and feed containing the reaction mixture, the liquid layer being arranged in the apparatus such that gaseous substances which pass through the feed containing the reaction mixture into the apparatus have to pass through the liquid layer in order to get into the top of the apparatus.