Catalytic gas-phase oxidation of propene to acrolein

A process for the catalytic gas phase oxidation of propene to acrolein, comprising:

• passing a reactant gas mixture comprising propene and oxygen, preheated to the temperature of heat-exchange medium in a fixed bed reactor, through a plurality of catalyst containing contact tubes in said fixed bed reactor arranged to leave an essentially circular free space in the center of the reactor of about 10 to 30 vol. % of the reactor internal diameter and containing an arrangement of horizontally positioned baffles, non-equidistantly spaced apart in order to restrict temperature differences and pressure drops in horizontal sections within zones of the reactor, which baffles are positioned to leave alternate heat-exchange medium flow passageways at the center and outer periphery of the reactor, said contact tubes extending through holes in the baffles where the size of the holes is such to accommodate passage of the contact tubes through the baffles and leaving gaps between the outer surfaces of the tubes and the baffles such that the heat-exchange medium passes at a transverse flow rate within a zone between baffles at a constant rate;
• simultaneously passing a heat-exchange medium at elevated temperature over the exterior surfaces of the contact tubes in a longitudinal flow pattern which is cocurrent with the direction of flow of reactants through said tubes and superposing a transverse flow on the longitudinal flow of heat exchange medium through the reactor, wherein heat-exchange medium enters a reactor through two ring-shaped pipelines which are attached to the two ends of the reactor and have windows distributed over the entire periphery thereof, the window openings being designed in such a way that the same amount of heat-exchange medium passes through each window per time unit and wherein heat-exchange medium is withdrawn from the reactor as the gas phase oxidation reaction proceeds in an amount of 30 to 70% of the total amount of heat-exchange medium fed into the reactor, the flow rate of heat exchange medium being such that the temperature between the point of entry of the heat exchange medium into the reactor and its point of exit increases by 2.degree. to 10.degree. C.;
• and
• obtaining product acrolein at a selectivity .gtoreq.85 mol % from the reactor at a single pass propene conversion .gtoreq.90 mol %.