110th Anniversary: Fluidized-Bed Chemical Reactors for Heterogeneously Catalyzed Gas–Solid Reactions: Old and New Applications

In this review, the potential of fluidized-bed technology for heterogeneously catalyzed gas–solid reactions is discussed. This reaction class can be divided into three reaction categories: gas-to-solid (G2S), solid-to-gas (S2G), and solid-to-gas-to-gas (S2G2G). The established examples of G2S reactions are the gas-phase polymerizations of ethylene and propylene. However, other concepts, such as polymerization to butadiene rubber and synthesis of carbon nanotubes, are also discussed. It is a common feature of this reaction class that the catalyst remains a residue in the product and can influence its quality. S2G reactions are represented on a large scale by the synthesis of organosilanes. Another example is given by the hydrochlorination of silicon. In this reaction class, a particulate catalyst is anchored to the surface of the fluidized particles and should not be lost during the progressive conversion of the substrate. The fluidized-bed reactor is also suitable for performing the S2G2G reactions. Catalytic pyrolysis of biomass or waste is a good example of this class. In the first step, solid particles are thermally decomposed to gas and solid residue. In a consecutive step, gas released during pyrolysis is catalytically converted to value-added products.