Influence of prefiltration on membrane performance during isolation of lignin-carbohydrate complexes from spent sulfite liquor

• In this study, we examined the isolation of lignin-carbohydrate complexes (LCCs) from sodium-based spent sulfite liquor, in conjunction with minimization of membrane fouling. We screened 3 polysulfone (PS) membranes with cutoffs of 100, 50, and 25 kDa, respectively. Flux and retention for the 100- and 50-kDa membranes had the same order of magnitude, indicating that these properties were determined by fouling that formed on the membrane—not pore size. The PS membrane with the 50-kDa cutoff performed best in terms of flux and retention of lignin-carbohydrate complexes and experienced the least membrane fouling. Two prefiltration methods were used to decrease the fouling of the 50-kDa membrane: a 0.2-μm PS microfiltration membrane and dead-end filtration with 10-um filter cloth and a 4 wt% mixture of kieselguhr (diatomite) and spent sulfite liquor prior to filtration. Prefiltration of the SSL with microfiltration increased the flux 3-fold and decreased the fouling grade from 49% to 7.2%. Dead-end filtration effected a 16% increase in flux and a fouling grade of 17%. The retention of LCC during microfiltration was high, which resulted in a loss of high-molecular-weight products, whereas the loss of LCC during dead-end filtration was negligible. A 50-kDa PS membrane performed best with regard to the recovery of lignin-carbohydrate complexes from spent sulfite liquor. Also, dead-end filtration is a promising method for eliminating membrane fouling.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Kemiska processer (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Chemical Process Engineering (hsv//eng)

Nyckelord

Dead-end filtration

Fouling

Galactoglucomannan

Lignin

Lignin-carbohydrate-complex

Microfiltration

Prefiltration

Spent sulfite liquor

Ultrafiltration

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