Flow-based automatic analysis systems
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Polyurethane foam is utilized by furniture, automotive, construction, insulation and footwear industries at a growing rate. A dominant prepolymer for polyurethane foam is polyether polyol. The current technique for analyzing potassium hydroxide (KOH) in polyol involves a laborious wet chemical method, in which a significant time lag exists between sample collection and availability of the analytical result. An on-line, near real time KOH analyzer to monitor the polyol is desirable. An automated flow analysis system utilizing conductivity detection was investigated. If KOH is the principal electrolyte contaminant, it will be the dominant current carrier. By mixing the polyol with an acid solution at different ratios, the neutralization point was successfully indicated by a minimum in conductivity in initial experiments. The suitability of acid introduction by permeation tubes, gaseous acids and alcohol solution injections was tested. However, the presence of significant background conductivity suggested that the method will not be feasible at low parts per million (ppm) levels of KOH. Therefore, an alternative approach was required. An automated reverse flow injection (Fl) based continuous analyzer with a fiber-optic based optical absorbance detector was fabricated and various schemes were tested. The most successful of these involved the injections of a solution of bromocresol green (BCG) in 2-propanol, with or without added mineral acid, into the sample polyol stream in a single-line Fl manifold maintained at 110°C (dispersion factor of 50-25 for a dilute aqueous stream at room temperature with 10 and 30 ^iL of solution injected). Measurements could be made In the present system every 4 minutes. Deliberate alteration of water content of the polyol stream in the range of interest was found to have no discernible effect on the measurement.