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 alka
- PDF / 1,204,269 Bytes
- 24 Pages / 439.37 x 666.14 pts Page_size
- 99 Downloads / 165 Views
Recovery of Low-Ash and Ultrapure Lignins from Alkaline Liquor By-Product Streams Mark C. Thies and Adam S. Klett
3.1
Introduction and Background
Lignin is one of the most abundant organic compounds on the planet, second only to cellulose. About 30 % of all organic carbon and 30 % of wood occurs in nature in the form of the biopolymer lignin. Although lignin is plentiful, it has been far more difficult to find uses for lignin than has been the case for its compatriot in woody biomass, namely, cellulose. In fact, probably the most common expression that one hears when lignin is mentioned is that “You can make anything that you want with lignin – except money!” In general, lignin is readily available, albeit in a raw, unpurified form, whenever cellulose is being recovered from biomass. For example, in the nascent lignocellulosic biofuels industry, cellulose and hemicellulose (the two major constituents in biomass besides lignin) are converted by hydrolysis to sugars, which can then be biologically or catalytically converted to biofuels. However, the remaining lignin is a fuel at best if it can be adequately concentrated – and a waste stream at worst. But the largest source of lignin today is not derived from cellulosic ethanol, but instead is generated as a by-product in the manufacture of cellulosic pulp in the pulp-and-paper industry. For example, in the dominant (95 % of the market) Kraft (sulfate) process, an alkaline liquor of sodium hydroxide and sodium sulfide at elevated temperatures is used to dissolve the lignin components of wood, freeing the cellulosic fibers in the form of pulp, which is then used to make paper [1]. The spent alkaline liquor by-product stream contains most of the lignin and is known as “black liquor”. Typically, this lignin-rich stream is burned at the pulp mill for its fuel value (as lignin has the same heating value as coal), with only about 0.2 % being recovered for nonfuel uses [2, 3]. However, because lignin is the only abundant biopolymer with aromaticity (see Fig. 3.1), it should have far more value M.C. Thies (*) • A.S. Klett Department of Chemical and Biomolecular Engineering, Clemson University, Earle Hall, Clemson, SC 29634-0909, USA e-mail: [email protected] © Springer Science+Business Media Singapore 2016 Z. Fang, R.L. Smith, Jr. (eds.), Production of Biofuels and Chemicals from Lignin, Biofuels and Biorefineries 6, DOI 10.1007/978-981-10-1965-4_3
55
M.C. Thies and A.S. Klett
56 CH3 CH2 CH2
CH2OH HC
CH2OH HC
H3CO
O
HC O
CH
O
OH
CH
CH2OH
CH
CHOH
CH2OH
CH CHOH
O HOH2C
OH
CH2OH O
OCH3
CH H3CO
H3CO
O
CHOH
O O
HC
O
CHOH
H C H2C
OCH3
HC
C H
CH2OH
HO
HC
CH
CH CH
O
CH2
CHOH CH2OH O
H3CO
HC Lignin
OCH3
OCH3
CH O
O
H3CO Lignin
Fig. 3.1 A portion of a structural model for spruce lignin, representing the types of linkages and structural units (Reprinted with permission from Ref. [5]. Copyright © 1977, Springer-Verlag)
as a renewable biopolymer [3, 4]. As seen in the next section, evidence is increasing that this indeed is the case.
Data Loading...
