Spectroscopic Determination of Anthraquinone in Kraft Pulping Liquors Using a Nafion Membrane Interface

摘要

A spectroscopic technique for determining anthraquinone (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 passing through the membrane is converted into its reduced form, anthrahydroquinone (AHQ), using sodium hydrosulphite. AHQ has distinct 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 by dissolving alkaline wood lignin in the solutions. The solubility of AQ in a lignin-enriched solution is ～0.14 g/L at 90℃. Time-dependent dissolved AQ measurements in the kraft-AQ pulping process were demonstrated using the present method.