Method for controlling the digestion of pulp by IR spectroscopy

A process for controlling the digestion of pulp which comprises:

• (a) subjecting samples of the cooking liquor in the digestion being controlled as the cooking operation proceeds to infra-red spectroscopy at wavenumbers ranging from about 1400 to about 1550 cm.sup.-1 to produce absorbance curves of the spectra;
• (b) determining base-line corrected band heights or integrals of the absorbance curves of the spectra to the extent needed to establish an IR-data set for each sample;
• (c) obtaining the relationship between the IR spectra of samples of cooking liquor obtained from previous digestions and analytically determined kappa numbers of pulps contained in said previously obtained samples;
• (d) correlating said IR-data sets with said previously obtained relationship to determine the kappa number of the pulp in the said samples of the cooking liquor being digested;
• and
• (e) using said correlation for optimizing the digestion process by stopping the delignification process when the IR data in said IR-data sets establishes, via the said correlation, that the desired kappa number has been obtained.