A spectroscopic technique for determining AQ in pulping liquor was developed to effectively separate AQ from dissolved lignin. This technique is based on a flow analysis system with a Nafion membrane interface. The AQ passed through the membrane is converted into its reduced form, AHQ, using sodium hydrosulfite. AHQ has distinguished absorption characteristics in the visible range, whereas spectral contribution from the small lignin molecules that penetrate through the membrane is insignificant. It was found that AQ can be dissolved in dissolved lignin- enriched alkaline solutions, which makes calibration of AQ using standard aqueous alkaline AQ solutions possible. The solubility of AQ in a lignin enriched solution is approximately 0.14 g/L at 90oC. Time-dependent dissolved AQ measurements in the kraft-AQ pulping process were demonstrated using the present method.
Chai, X.S.; Yang, X.T.; Hou, Q.X.; Zhu, J.Y.; Danielsson, L.-G. 2003. Spectroscopic determination of anthraquinone in kraft pulping liquors using a membrane interface. 12th ISWPC International Symposium on Wood and Pulping Chemistry : Madison, Wisconsin, June 9-12, 2003, proceedings. Volume I, Oral presentations. Madison, WI : University of Wisconsin--Madison, Dept. of Forest Ecology and Management, 2003 : 4 Pages