Study On The Solubility Of Lignin In Black Liquor Of Hardwoods Cooking

Lignin has the characteristic of the colloid. The effects of electrolytes on the solubility of kraft lignin in black liquor were determinated by focused-beam reflectance measurement(FBRM) instrument, laser particle analyzer, filtration through track membranes and UV spectra. According to the research results, some solutions which can slow down negative effects of some electrolytes on the cooking of stock, washing of pulp and bleaching could be proposed, it also can be used in lignin extraction.The effects of electrolytes on the solubility of lignin in eucalyptus kraft black liquor indicated that the criticle coagulation concentrations(CCC) of Ca2+、Mg2+、Mn2+、Fe3+ and Fe2+ were 50.10 mmol/L、64.9 mmol/L、12.5 mmol/L、1.87 mmol/L and 1.56 mmol/L respectively. The counts of lignin particle changed lightly and reduction rate of UV absorbence(at 205nm) increased slowly, when the concentrations of metal ions added into the black liquor were less than CCC. When the concentrations of metal ions added into the black liquor were more than CCC, counts of lignin particle and reduction rate of UV absorbence increased sharply. When the residual effective alkaline changed within the certain limit, CCC of Al3+ decreased with increasing of residual effective alkaline in black liquor. The others had not changed much with increasing of residual effective alkaline in black liquor. The diameter of nanoscale lignin particle increased with increasing of metal ions concentration added in black liquor. NaCl had no significant effect on the solubility of lignin in the black liquor, when the residual effective alkaline of black liquor were ranged from 3.54g/L to 17.89 g/L g/L(as NaOH). Some kinds of acid radical anion (SO42-、NO32-、 SiO32-、CO32-) had slight effects on the solubility of lignin.The effects of pH on the the solubility of lignin in eucalyptus kraft black liquor were showed that counts of lignin particle and reduction rate of UV absorbence increased slowly, when the pH of black liquor ranged from 13 to 10.6. when the pH of black liquor ranged from 10.6 to 9.3, they increased charply. when pH of black liquor was less than 9.3, they increased slowly again.The CCC of Ca2+ and Mg2+ decreased with the decreasing of solide content in the black liquor. The CCC of Mn+ and Fe3+ increased firstly, then decreased with the decreasing of solide content in the black liquor.The addition of electrolytes into the water used during eucalyptus kraft pulping and pulp washing would increase the Kappa Number of pulp.The effects of electrolytes on the solubility of lignin in the birch kraft black liquor were studied. The experiment indicated that Ca2+ and Al3+ had higher critical coagulation concentrations than Mg2+ and Mn2+. The CCC of Ca2+、Mg2+、Mn2+ and Al3+ were 40.5 mmol/L and 31.5 mmol/L,7.80 mmol/L and 4.10 mmol/L mmol/L, respectively. NaCl and some kinds of acid radical anion had no significant effects on the solubility of lignin in the black liquor with residual effective alkaline of 7.94 g/L.