Adding Speed to Lignin Analysis Straight from Black Liquors

Abstract

The isolation of lignin from black liquor (BL) is a major bottleneck for high-throughput analysis of the lignin content and molar mass. Here, we introduce a novel method for the direct analysis of diluted BL by size-exclusion chromatography (SEC), which allows for the simultaneous determination of lignin content and molar mass while avoiding tedious sample preparation. In this way, total analysis time was significantly reduced from 1-2 days down to only 30 min. Lignin quantification used UV detection at 410 or 475 nm for hardwood and softwood kraft lignins, respectively. Molar mass determination was based on conventional calibration corrected by MALLS785 nm measurements. The direct analysis provided a more authentic molar mass distribution of the lignin present in BL than analysis after conventional workup procedures─showing that lignin isolation leads to a substantial loss of low molar mass fractions. Despite the many impurities contained in BL, the presented analytical system showed excellent column stability, even after more than 250 injections. Here, we introduce a fast and efficient method for high-throughput characterization of complex lignin samples needed for close-to-real-time process control in industry and academia.