Gas-solid hydroxyethylation of potato starch in a stirred vibrating fluidized bed reactor

A novel reactor for modifying cohesive C-powders such as in the gas-solid hydroxyethylation of semidry potato starch is characterized, the so-called stirred vibrating fluidized bed reactor. Good fluidization characteristics are obtained in this reactor for certain combinations of stirring and vibration parameters. Channeling can be suppressed by stirring in the bed with equidistant flat blades whereas agglomerates are destroyed by vibration of the gas distributor.

Also the complex sorption, diffusion and reaction behaviour of ethylene oxide in semi-dry starch was investigated. Reaction rate equations were obtained for all four parallel reactions involved: the catalyzed and uncatalyzed hydroxyethylation of starch and the catalyzed and uncatalyzed hydrolysis of ethylene oxide. By combining all results, a pressure-controlled stirred vibrating fluidized bed reactor could be designed for the gas-solid hydroxyethylation of potato starch. This process was optimized and compared to the classical slurry process. In our novel reactor the reaction time can be reduced at least by a factor of 10 relative to the slurry process whereas the selectivity is also higher. Products with a high molar substitution can be obtained by this novel process without loss of the granular structure of the starch.