TWO STAGE DRYING OF SYNTHETIC DETERGENTS

A key ingredient in granular synthetic detergents is Sodium Tripolyphosphate (STP). The hexahydrate of STP is unstable during the spray drying process. The decomposition (reversion) is shown to be solely a function of particle temperature. The reversion products interact with calcium ions in the wash water and form insoluble species. This results in undesirable deposition onto the fabrics. The goal of this study is to develop a drying process with lower temperatures to reduce the decomposition. This, in turn, will improve product quality by reducing undesirable fabric deposits.

A two stage drying process is used to reduce the drying temperatures. Experimental evidence is presented to demonstrate the near-elimination of STP decomposition.

The design of a production scale fluid bed dryer uses a ‘normalization'procedure to calculate the rate constants at constant bed temperature from the data taken at constant inlet air temperature. The rate constants are corrleated to bed temperature using an Arrhenius-like equation.