Measurement of parts per million levels of potassium hydroxide in polyether polyol streams

An automated reverse flow injection (FI) based continuous analyzer for KOH in polyols is presented. A solution of bromocresol green (BCG) in 2-propanol, with or without added mineral acid, is injected into the sample polyol stream in a single-line FI manifold maintained at 110°C (dispersion factor of 25 and 50 for a dilute aqueous stream at room temperature with 30 and 10µl of solution injected) and the blue indicator dianion formed upon reaction with KOH is measured at 605nm by a light emitting diode (LED) -fiber optic based absorbance detector. Injections of 10µl of 10mM BCG and 30µl of 15mM BCG, 50mM HCl were respectively chosen to cover desired ranges of 0-20 and 20-120mg KOH/kg polyol (ppm KOH). The absorbance signal is linear with KOH concentration (r2=0.9949 in both cases). Measurements could be made in the present system every 4min. Deliberate alteration of water content of the polyol stream in the range of interest was found to have no discernible effect on the measurement.