Contacting fine particles with a gas phase in a stirred bed reactor

A process for producing products, comprising:

• contacting particles of Geldart class C having a particle size d90<20 μm in a stirred fixed bed with a gas phase;
• treating the particles in a process zone of a gas-traversed reactor, wherein the process zone is the region in a reactor in which the stirred particle bed is brought into contact with the gas phase;
• and
• circulating the particles in the process zone by use of a close-clearance stirrer during the contacting with the gas phase,
• wherein the stirrer mechanism is close-clearance when in equation 1
• W
• ⁡
• (
• h
• )
• =
• u
• R
• (
• h
• )
• u
• B
• (
• h
• )
• (
• 1
• )
• wherein for half of all values of h the close clearance W(h) in the process zone W(h) is >0.9,
• wherein uR(h) is equal to the outer circumference of the stirrer mechanism in the sectional face at the height coordinate h, and
• wherein uB(h) is equal to the inner circumference of the reactor in the sectional face at the height coordinate h.