Method for producing acrylic acid

A process for the preparation of acrylic acid, comprising:

• partially oxidizing propane, propene, acrolein or a mixture of propene and acrolein in the gas phase with molecular oxygen over a solid heterogeneous catalyst at elevated temperature thereby producing an acrylic acid containing hot product gas mixture;
• reducing the temperature of said hot product gas mixture by direct cooling by means of a quench liquid 1 which produces an unvaporized portion of quench liquid 1 which is circulated via a heat exchanger which provides indirect cooling, if necessary, and a portion of the unvaporized quench liquid 1 being removed as a purge from the circulation of quench liquid 1;
• passing the cooled product gas mixture obtained to a column equipped with baffles which have separation ability where the gas ascends the column and the gas mixture is fractionally condensed into a crude acrylic acid which is removed at a side take-off of the column and (i) a bottom liquid containing acrylic acid oligomers which is removed from the bottom of the column, or (ii) a high boiler fraction which is removed from a side take-off of the column in the vicinity of the bottom or (iii) a mixture of a bottom liquid containing acrylic acid oligomers which is removed from the bottom of the column and a high boiler fraction which is removed from a side take-off of the colunm in the vicinity of the bottom, wherein (i), (ii) or (iii) is used as the quench liquid 1;
• feeding said purged quench liquid 1 to a cleavage vessel;
• cleaving acrylic acid oligomers in the purged quenched liquid 1 at elevated temperature into acrylic acid which has escaped in gaseous form from the liquid phase;
• and
• condensing the acrylic acid vapor and feeding the resulting condensate into circulation in the process system as quench liquid 1.