Recovery of Low-Ash and Ultrapure Lignins from Alkaline Liquor By-Product Streams
Although a number of treatment methods can be used to separate cellulose and lignin components from biomass, aqueous alkaline treatment methods are dominant. Typically, the cellulose is precipitated from solution, and the lignin ends up in the highly alkaline liquor by-product stream. Today the vast majority of this lignin is burned in situ as a fuel; however, it potentially has far more value as a renewable biopolymer. Here, two new technologies are presented for recovering lignin from alkaline liquor streams generated either from a pulp-and-paper mill or a lignocellulosic biofuels refinery. With SLRPTM technology, the lignin precipitation step is carried out at above-ambient conditions such that a liquid (and not a solid) lignin phase is formed. Thus, the SLRP process for producing low-ash (1–2 %) lignin is continuous, not batch. Furthermore, the “liquid-lignin” phase can be readily fractionated by pH into fractions having different bulk and molecular properties. The ALPHA process was developed with the express purpose of taking low-ash lignins produced from alkaline-liquor by-product streams to the “ultrapure” state. The technology uses adjustable mixtures of biorenewable acetic acid and water to create a unique liquid–liquid solvent system that can be used to simultaneously fractionate, purify, and solvate lignins. Metals contents in ALPHA lignins well below 100 ppm are readily achieved in fractions of both low and high molecular weight.
KeywordsAlkaline pretreatment Lignin recovery Lignin fractionation Lignin extraction Liquid–liquid equilibrium Renewable solvents
This material is based upon work supported by the National Science Foundation under Award Numbers CBET-1403873 and CBET-1236759.
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