Determination of phenol in phenol tars from the cumene-to-phenol process streams with C-13-NMR spectroscopy

C-13-NMR spectroscopy has been employed for the determination of phenol in phenol tars originating from the process of phenol industrial synthesis. Re laxation times T-1 of C-13 nuclei in phenol and in dioxane (used as a stand ard for quantitation) have been measured in order to establish appropriate conditions for the acquisition of quantitative spectra. The results of C-13 -NMR analyses are compared with the results obtained with H-1-NMR, infrared spectroscopy, ultraviolet spectroscopy, gas chromatography and bromometric titration. The accuracy and repeatability of the determinations have been tested on samples with added weighed amounts of phenol. A great advantage o f the C-13-NMR method is that three results from each spectrum are obtained , which may be averaged, while those involving large errors can be rejected . The scatter of the relative errors for single results has been tested and evaluated at the level +/- 0.8%.