Fractionation lignosulfonate

The use of the lignin fraction is much more cumbersome currently the best-known chemical of a real commercial importance is vanillin, which is obtained by oxidation of the black liquor. Another example is a product called spray-dried lignosulfonate (as sodium salt) obtained from the older, acidic sulfite pulping process. It is sold as a commercial product primarily as a concrete additive for enhanced strength. Since the cement industry is one of the big contributors of carbon dioxide emissions (due to the production of calcium oxide from calcium carbonate), the use of this renewable, wood-derived product not only is fossil-carbon neutral in itself but also reduces carbon dioxide emission due to the diminished need for cement in large infrastructures made of concrete. 

In order to study birch lignosulfonates, spent sulfite liquor, from which monosaccharides had been removed by ion exclusion chromatography, was fractionated on the basis of molecular size by preparative GPC (Fig. 1). 

The fractions in the region 700-1230 mL in Figure 1 were combined in order to study the structure of the polymeric portion of the birch lignosulfonates. The combined solution was then refractionated by preparative RPC into five fractions (Fig. 2). 

Figure 1. Fractionation of birch lignosulfonates by preparative gel permeation chromatography.

Figure 2. Fractionation of high molar mass birch lignosulfonates (fraction A in Figure 1) by preparative reversed-phase chromatography.

Table I. Carbohydrate and Lignosulfonate Contents of the Hydrolyzed Fractions I-V...

It can be seen from Figures 2 and 3 that the virtually carbohydrate-free fractions III-V are eluted by RPC in order of increasing molar mass and that fraction V contains the highest molar mass lignosulfonates. A large part of fraction I is eluted by GPC in the same region as fraction V. This supports the supposition that the lignosulfonates of fraction I are bound to carbohydrates. Otherwise they would have been eluted by RPC in fraction V. 

It was shown that high molar mass lignosulfonate compounds can be fractionated by RPC into hydrophilic and hydrophobic compounds. It can be seen from Figures 4 and 5 that the birch lignosulfonates with low molar mass (fractions B and C in Figure 1) were also fractionated into hydrophilic and hydrophobic portions with no clearly resolved peaks. 

The results show that RPC will also separate low molar mass lignosulfonates into hydrophilic and hydrophobic fractions as well as into a far greater number of individual components than obtained by fractionation with GPC. 

Eisenbraun EW (1963) The separation and fractionation of lignosulfonic acids from spent sulfite liquor with tn-n-hexylamme m organic solvents Tappi 46.104-107 Felicetta VF, McCarthy JL (1957) Tappi 40.851-866 Forss KG, Pirhonen IMJ (1974) U S Patent No 3825526... 

Harris EE, Hogan D (1957) Isolation and fractionation of lignosulfonates in spent sulfite liquors Ind Eng Chem 9 1393 Hough WJ (1910) U S Patent No 949324... 

Kontturi AK, Sundholm G (1986) The extraction and fractionation of lignosulfonates with long chain aliphatic amines Acta Chem Scand 40 121-125 Wada S, Iwamida T, Iijima R, Yabe K (1962) Fractional precipitation of kraft black liquor from spruce wood Chem High Polymers (Kabunshi Kagaku) 19 699-705... 

Fig. 5.1.6. Concentration of phenol in softwood lignosulfonate (weight fraction in the mixture) as revealed by second derivative spectra. (Lin 1982)...

Forss K, Schott O, Stenlund B (1967) Light absorption and fluorescence of lignosulfonates dissolved in water and dimethylsulfoxide Pap Puu 49 525-530 Forss K, Stenlund B (1969) Molecular weights of lignosulfonates fractionated by gel permeation chromatography Pap Puu 51 93-105... 

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