PROCESS FOR HETEROGENEOUSLY CATALYZED GAS PHASE PARTIAL OXIDATION OF AT LEAST ONE ORGANIC STARTING COMPOUND

Abstract

A process for heterogeneously catalyzed gas phase partial oxidation of an organic starting compound over a fixed catalyst bed freshly installed into a reaction chamber, in which the reduction in the quality of the fixed catalyst bed is restored with increasing operating time by replacing a portion of the fixed catalyst bed by a replacement fixed catalyst bed part whose volume-specific activity is lower than the volume-specific activity of the replaced fixed catalyst bed part in its freshly installed state.

Description

Claims

1. A process for heterogeneously catalyzed gas phase partial oxidation of at least one organic starting compound with molecular oxygen over a fixed catalyst bed freshly installed into a reaction chamber, in which, for the purpose of the partial oxidation, a reaction gas mixture comprising the at least one organic starting compound and the molecular oxygen is conducted through the fixed catalyst bed and heat of reaction is removed by indirect heat exchange with a fluid heat carrier conducted outside the reaction chamber, and, when increasing operating time is accompanied by an increasing reduction in the quality of the fixed catalyst bed, the quality of the fixed catalyst bed is recovered by replacing not the entire fixed catalyst bed but only a portion thereof by a replacement fixed catalyst bed part, wherein the volume-specific activity of the replacement fixed catalyst bed part is lower than the volume-specific activity of the replaced fixed catalyst bed part in its freshly installed state.

2. The process according to claim 1, wherein the gas phase partial oxidation is that of propylene to acrolein and/or acrylic acid, or that of isobutene to methacrolein and/or methacrylic acid, or that of acrolein to acrylic acid, or that of methacrolein to methacrylic acid, or that of propane to acrylic acid, or that of isobutane to methacrylic acid.

3. The process according to claim 1, wherein the at least one organic starting compound is at least one organic starting compound from the group comprising propylene, acrolein, 1-butene, 2-butene, ethane, benzene, m-xylene, p-xylene, iso-butane, isobutene, tert-butanol, isobutyraldehyde, methyl ether of tert-butanol, o-xylene, naphthalene, butadiene, ethylene, propane or methacrolein.

4. The process according to any of claims 1 to 3, wherein the gas phase partial oxidation is the second stage of a two-stage gas phase partial oxidation.

5. The process according to claim 4, wherein the gas phase partial oxidation is the partial oxidation of acrolein to acrylic acid in a two-stage gas phase partial oxidation of propylene to acrylic acid.

6. The process according to any of claims 1 to 5, wherein the volume-specific activity of the replacement fixed catalyst bed part is such that, based on the same conversion of the organic starting compound in single pass of the reaction gas mixture through the fixed catalyst bed and the same composition of the reaction gas mixture and the same loading of the fixed catalyst bed with reaction gas mixture, the difference dΔT between the hotspot expansion ΔTHBn of the fixed catalyst bed after the replacement by the replacement fixed catalyst bed part has been carried out and the hotspot expansion ΔTHBv before the replacement by the replacement fixed catalyst bed part has been carried out, formed as dΔT=ΔTHBn−ΔTHBv, is ≦30° C.

7. The process according to claim 6, wherein dΔT is from −15 to +10° C.

8. The process according to claim 6, wherein dΔT is from −10 to 0° C.

9. The process according to any of claims 1 to 8, wherein the reaction chamber is the interior of a reaction tube.

10. The process according to claim 9, wherein the reaction tube is disposed in a tube bundle reactor.

11. The process according to any of claims 1 to 10, wherein the part of the fixed catalyst bed replaced by the replacement fixed catalyst bed part extends in flow direction of the reaction gas mixture to up to 80% of the bed length of the fixed catalyst bed.