Continuous Production of Hydroxypropyl Starch in a Static Mixer Reactor

A novel type of reactor for the chemical derivatization of starch pastes is presented. The design is based on the application of static mixers. The reactor shows excellent plug flow behaviour with a Peclet number of about 100. The viscosity behaviour of concentrated starch pastes in the static mixer reactor can be described by: ηapp = Ke[B m_starch ^{+c/T-DW+(n-l)}Inγ] where: K = 3.063.10⁻⁴ Pa-s., B = 12.03, C = 4.134.103 1/K., D = 2.83.10⁻²³ kg dry starch/kJ and n = 0.494. m_starch is the mass fraction dry starch in the paste. The reactor was used for the production of hydroxypropyl starch with a molar substitution (MS) of up to 0.5. Propylene oxide conversions of 90% were reached within 9 min of reaction time which compares favourable with conventional production processes. The reactor was modelled as a non-isotherm plug flow reactor. Experimental results on propylene oxide conversion and MS of the derived starch are in good agreement with model calculations. Papp = Ke wobei: K = 3,063. 10-⁻⁴ pa.s., B=12,03. C= 4,134, C=4,134, 1-³I/K., D = 2.83.10⁻²kg trockene Stärke/kJ, und n = 0,494. m_starch ist die Massenfraktion trockener Stärke in dem Kleister.