PREDICTION OF LIGNIN CONTENT AND PULP YIELD - FROM BLACK LIQUOR COMPOSITION USING NEAR-INFRARED SPECTROSCOPY AND PARTIAL LEAST-SQUARES REGRESSION

A concept is presented for monitoring the delignification process duri ng a laboratory kraft cook on softwood. Two series of cooking liquors were analyzed by near-infrared spectroscopy. The first series of liquo rs was withdrawn from pulping experiments covering the initial, bulk a nd final phase of the cook. The second series of liquors was taken fro m experiments associated with the final delignification phase in order to be a better learning set for the prediction of kappa numbers. By u sing a partial least squares regression technique, the pulp yield and the Klason lignin content could be predicted accurately from spectrosc opic data obtained on the first series of liquors. Similarly, when nea r-infrared data were used from the second series of cooking liquors, a very good correlation was found between observed kappa numbers and th e predicted ones.