Abstract: A process is proposed for preparing (meth)acrolein and/or (meth)acrylic acid by partially oxidizing C3 and/or C4 precursor compounds in the gas phase in the presence of a heterogeneous particulate catalyst, in a reactor having two or more thermoplates (1) arranged vertically and parallel to each other while in each case leaving a gap (2), the heterogeneous particulate catalyst being installed in the gaps (2) and the gaseous reaction mixture being passed through the gaps (2), which comprises monitoring, controlling and/or regulating the process by selecting as a monitoring, control and/or regulation parameter one or more temperatures which are measured in one or more gaps (2), at one or more measurement points which are distributed over the height of each gap (2).

Abstract: A process is proposed for monitoring, controlling and/or regulating reactions of a fluid reaction mixture in the presence of a heterogeneous particulate catalyst, in a reactor having two or more thermoplates (1) arranged vertically and parallel to each other while in each case leaving a gap (2), the heterogeneous particulate catalyst being installed in the gaps (2) and the fluid reaction mixture being passed through the gaps (2), which comprises selecting as a regulation signal the temperature which is determined in one or more gaps (2), at two or more measurement points which are distributed over the height of each gap (2).