Chemical Composition of Spent Liquors from Acidic Magnesium–Based Sulphite Pulping of Eucalyptus globulus

Abstract

The major components of industrial thin (SSL) and thick (THSL) liquors from acidic magnesium–based sulphite pulping of Eucalyptus globulus wood have been characterized. The analysis of sugars in SSL revealed the predominance of xylose, which was present in the form of sugar monomer (ca. 70%) and as xylo-oligosaccharides (ca. 30%). Lignosulphonates (LS) were the most abundant organic fraction of spent liquor (ca. 50% of liquor dry matter) consisting of sulphonated oligomers (SO₃H ≈ 20% w/w) of low molecular weight (Mw ≈ 1000–1300 Da) and constituted mainly by syringyl units (syringyl:guaiacyl ratio = 81:19). The major phenolic extractives of THSL were pyrogallol (93 g/ton) and gallic acid (1020 g/ton), and the most abundant fatty acid and sterol were tetracosanoic acid (6 g/ton) and β -sitosterol (45 g/ton), respectively. The structural changes of macromolecular components during the liquor evaporation were discussed.

Keywords:

• Chemical composition
• Eucalyptus globulus
• lignosulphonates
• sulphite pulping
• sulphite spent liquor

This work was financially supported by the Foundation of the Science and the Technology (FCT), grant reference SFRH/BD/31463/2006, and by the innovation PRIME Program (grant SIME I&DT no. 00/22689).

Notes

∗Uronic and aldouronic acids were not quantified.

∗Corrected for the ash content.

∗∗Empirical formula for LSF and LSG per phenylpropane unit: C₉H_9.77O_3.92S_0.10(SO₃H)_0.36(OCH₃)_1.51 and C₉H_13.20O_5.61S_0.02(SO₃H)_0.79(OCH₃)_1.59, respectively.

∗Data for eucalypt wood lignin are presented in parenthesis.^{[ 12 ]}