Artigos Técnicos | ARTIGO TÉCNICO/ TECHNICAL ARTICLE | 23.10.2021

Autores: Felipe Pedersoli Borges1, Jéssica Silva Gomes1,2, Iara Fontes Demuner1,
Fernando José Borges Gomes3, Ana Márcia Macedo Ladeira Carvalho1
1 Department of Forest Engineering, Federal University of Viçosa. Brazil
2 Department of Chemistry, Federal University of Viçosa. Brazil
3 Department of Forest Products, Federal Rural University of Rio de Janeiro. Brazil

O PAPEL vol. 82, N.o 10, pp. 68 - 72 - OCT 2021

Lignin is the main organic compound present in residual
liquors produced by pulping processes. It is estimated that
only 1 to 2% of this lignin is used to generate value-added
products, such as lignosulfonates produced by the sulfite
process. The remaining 99% is incinerated to generate
energy for the kraft process. The commercial application
of kraft lignin is still underperformed due to the difficult
workability of this polymer, which has low reactivity, high
heterogeneity and great complexity. One of the ways used to
increase the uniformity of molecular weight and, therefore,
reduce polydispersity, is the fractionation technique with
organic solvents. Thus, this study aims to evaluate the
yield of eucalyptus kraft lignin fractionation in different
organic solvents, in order to allow realizing the subsequent
assembly of an eluotropic series suitable for sequential
solvent fractionation of lignin. Two grams of kraft lignin
were fractionated using 20mL of organic solvents ethanol,
methanol, acetone, dichloromethane and a mixture of
methanol/dichloromethane separately. The systems
were subjected to stirring at 140rpm for 2 hours at room
temperature. The suspensions were filtered through glass
crucibles covered with vacuum-packed aluminum oxide
and the retained fractions were subsequently dried in an
oven at 105ºC to determine the masses of insoluble lignin.
The filtrate was dried by the solvent recovery method in an
extraction battery, and the residual material was weighed.
The percentages of soluble and insoluble fractions of kraft
lignin with each solvent were calculated based on the total
mass of the material. The yields of the soluble fractions
obtained for methanol, ethanol and acetone were 86.6%;
80.4% and 84.5%, respectively. These yields were considered
high and satisfactory, being greater for methanol. Methanol
obtained higher soluble fraction yields than ethanol, when
comparing alcohols. The result is in accordance with the
predicted, since, for a homologous series, the greater the
carbon chain of the solvent, the smaller the solubility of kraft
lignin. The methanol/dichloromethane mixture solubilized
more lignin than each solvent separately. The conclusion
is that methanol is the solvent that leads to the best yield
of soluble fraction of eucalyptus kraft lignin. It is also
observed that the three solvents are adequate to compose
the eluotropic series for sequential fractionation. Finally,
it is noted that dichloromethane and methanol act in quite
different fractions of lignin.
Keywords: fractionation; organic solvent; lignin; kraft;

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