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•MWCNT system set of different diameters produced in FB reactor using Fe-Co catalysts.•A loss of homogeneous fluidization during the catalytic synthesis of MWCNTs is caused by adhesion of their primary agglomerates.•Catalyst morphology influences the formation of MWCNT agglomerates.•Controlling the catalyst particle concentration in FB prevents the formation of CNT clumps.•Coagulation model of the growth dynamics of MWCNT agglomerates in FB reactors was developed.
The problem of the loss of homogeneous fluidization and the formation of large clumps of MWCNTs during their catalytic synthesis in a fluidized bed reactor has been studied experimentally and theoretically in terms of the impact of catalyst properties and synthesis process parameters. It has been shown that two factors play the most important role in the formation of large clumps of MWCNTs, namely, the ability of high-performance catalyst to produce agglomerates of MWCNTs with high cohesion, and a high concentration of catalyst particles in the fluidized bed volume. A relationship has been established between chemical components of the catalyst, its structure and cohesive properties of the MWCNT agglomerates formed on it. An approximate semi-analytical scheme for calculating the formation and growth of large fractal agglomerates (clumps) of MWCNTs during their catalytic synthesis in a fluidized bed has been developed. This approach is based on the model of sequential coagulation of MWCNT agglomerates starting from the primary ones, and made it possible to formulate the requirements for characteristics of the catalyst and parameters of the synthesis process, which ensure homogeneous fluidization in the reactor.