Method for catalytic phase oxidation to (meth) acrolein and/or (meth) acrylic acid

#The present invention relates to a process for the continuous gas-phase oxidation to (meth)acrolein and/or (meth)acrylic acid. Below, the term (meth)acrolein represents acrolein or methacrolein and analogously (meth)acrylic acid designates the substances acrylic acid or methacrylic acid.

#(Meth)acrolein and (meth)acrylic acid are key chemicals.

#The known industrial processes for the gas-phase oxidation to (meth)acrolein and/or (meth)acrylic acid (for example according to DE-A-196 24 31) are carried out as a rule in tube-bundle reactors which have a large number of reaction tubes, currently up to 28 000, welded in between tube sheets. Here, preferably temperatures of from 200 to 450° C. and, if required, superatmospheric pressure are employed. The reaction tubes are filled with the heterogeneous oxidation catalysts and reaction mixture flows through said tubes. A heat-exchange composition, as a rule a salt melt, frequently a mixture of potassium nitrate, sodium nitrite and sodium nitrate, which removes the heat of reaction, flows through the interior of the reactor, between the reaction tubes.

#The invention is explained in more detail below with reference to a drawing.

#In the figures, identical or corresponding features are provided with identical reference numerals.

#FIG. 1 shows, in longitudinal section, a particularly preferred embodiment of a reactor which is particularly suitable for carrying out the process,

#The reactor shown in longitudinal section in FIG. 1 has the shape of a cylinder with feeding of the reaction mixture 1 in the upper region and removal of the reaction mixture 2 in the lower reactor region. The preferably gaseous reaction mixture itself is denoted by 5. Heat exchanger plates 8 which have the particularly preferred wedge-shaped formation are arranged in the interior of the reactor, in the longitudinal direction thereof. A heat exchange composition flows through the reactor plates and is introduced via a feed 3 and a distributor line 6 and removed via a collecting line 7 and a removal line 4. The cross section in FIG. 1A illustrates the substantially parallel arrangement of the heat exchanger plates 8.

#FIGS. 1B and 1C clearly show the preferred wedge-shaped formation of the heat exchanger plates 8 and their formation by metal sheets spot-welded to one another.

#FIG. 2 shows, by way of example, a longitudinal section through a reactor having cocurrent flow of the reaction mixture and heat exchange composition. FIG. 2 clearly shows that, in the heat exchanger plates 8, the liquid level of the heat exchange composition ranges only to a specific height, i.e. the heat exchange composition vaporizes above this. The heat removal thus takes place through evaporative cooling.