Effects of Metal Chlorides on the Solubility of Lignin in the Black Liquor of Prehydrolysis Kraft Pulping

The effects of CaCl2, MgCl2, FeCl3, NaCl, and AlCl3 on the solubility of lignin in the prehydrolysis kraft black liquor of Masson pine were studied using a focused-beam reflectance measurement (FBRM) instrument and UV spectra. The results showed that NaCl and AlCl3 have no obvious effects on the coagulation or solubility of lignin in the prehydrolysis kraft black liquor at high effective alkalinity. However, CaCl2, MgCl2, and FeCl3 have significant effects on the solubility of lignin in the black liquor. According to the reduction rate of UV absorbance, the effects of these chloride salts on the black liquor lignin solubility at high alkali content were as follows: AlCl3≈NaCl＜MgCl2＜CaCl2＜FeCl3.