Acid hydrolysis, lignin

Acid fracturing, friction reducers, 15 Acid hydrolysis, lignin, 173 Acid injection into carbonate reservoir, 610-611 Acid-rock reactions, rate, 15,16 Add wormholing in carbonate reservoirs, 608-620 in carbonate rocks, 610-611 Acidity-controlled redox reactions, 141-142 Addization... 

Acid-grade feldspar, aluminum fluoride production from, 2 357—358 Acid-grade fluorspar, 4 579, 580 analysis, 4 577t Acid halides, 12 188-190 Acid hydrolysis. See also Acidic hydrolysis of wood, 26 358 of wool, 26 376 Acid hydrolysis lignin, 15 21 Acidic catalysts, 10 556. See also Acid catalysts... 

Nakano et al. [404] observed that approximately 90% of an acid hydrolysis lignin residue from white birch became soluble after treatment with 3% sodium sulfite at 2(X)°C. Reactivity of the hydrolysis lignin was improved by milling, which was assumed to increase accessibility, and may also induce some chemical degradation. 

In the acid hydrolysis process (79—81), wood is treated with concentrated or dilute acid solution to produce a lignin-rich residue and a Hquor containing sugars, organic acids, furfural, and other chemicals. The process is adaptable to all species and all forms of wood waste. The Hquor can be concentrated to a molasses for animal feed (82), used as a substrate for fermentation to ethanol or yeast (82), or dehydrated to furfural and levulinic acid (83—86). Attempts have been made to obtain marketable products from the lignin residue (87) rather than using it as a fuel, but currently only carbohydrate-derived products appear practical. 

Acid hydrolysis of the polysaccharide portion of wood will release lignin but also causes major condensation reactions in the product(2l). These reactions can be minimized by using 41 wt. percent hydrochloric acid in place of other mineral acids but some condensation reactions still occur(22). This is not an effective method by which to obtain unaltered lignin. On the other hand, lignin can be solvent extracted from wood at temperature of 175°C using solvent mixtures such as 50/50 by volume water/1,4-dioxacyclohexane(23) Changes in lignin under these conditions appear to be minor. 

Oxidants are occasionally added to the hydrolysis mixture to favor the removal of lignin. For instance, the co-feed of 02 or air appeared beneficial to the deligni-fication efficiency of a lime-catalyzed hydrolysis step [57]. Similar improvements are also reported for the co-feed of H202 to formic or acetic acid hydrolysis [58],... 

The cellulosic residue used in these experiments is advantageous for acid hydrolysis compared to untreated wood. The cellulosic residue is finely divided, and of higher density than wood chips, 0.5 g/ml compared to 0.36, and has a very low lignin content. As a result, the output of fermentable sugars for a given size of digester will be about twice that obtainable with chips. 

When autohydrolysed aspen was treated with cellulase enzyme, poor results were obtained. Based on a ton of dry wood, only about 300 lb of fermentable sugars were obtained, and the fermentation was very inefficient with low yields of ethanol. These results compare poorly with those shown in Figure 5 when autohy-drolysed-caustic extracted aspen was treated with cellulase enzyme, and then fermented. It would appear from these results that the caustic extraction step for lignin removal would be necessary if the enzymatic hydrolysis process were to be adopted and advisable when acid hydrolysis is used. 

Yields of ethanol from aspen wood are 70.7% and 83.4% of theoretical where acid hydrolysis and enzymatic hydrolysis were employed. These were, respectively, 58.4 gallons and 68.9 gallons of 95% ethanol per ton of aspen wood. In addition 426 lb lignin with heat of combustion of 11,100 BTU/lb were obtained. 

This study reports the first application of universal calibration via HPSEC-DV to four acetylated hardwood lignins obtained from aspen (Pop-ulus tremuloides) wood meal by ball milling and solvent extraction steam explosion followed by alkaline extraction organosolv pulping followed by water extraction of the associated sugars and dilute sulfuric acid hydrolysis followed by sodium hydroxide extraction. 

Alkaline-extracted/acid hydrolysis (AH/NaOH) lignin samples were prepared by subjecting aspen wood flour to a one hour cook at 120°C in 0.05N sulfuric acid (22), followed by mixing the clarified supernatant with 1% w/w NaOH at 25°C with a Waring blender. The insoluble lignins were precipitated by addition of acid and water washes (32% yield). 

Universal Calibration. The aspen wood lignin samples chosen for this study were prepared by organosolv, steam explosion, dilute acid hydrolysis, and ball-milling procedures. 

Cellulosic materials are quite variable from source to source, not only in cellulose, hemicellulose, and lignin content but also in the crystallinity of the cellulose. As a consequence, each natural substrate would be expected to have its own unique set of process conditions to optimize glucose yield and minimize secondary product contamination. The next section on kinetics of acid hydrolysis will examine this point. 

Lignin is a complex phenolic cell wall polymer that is chemically cross-linked with hemicellulose and cell wall proteins. Most of the methods to determine lignin content are based on the removal of all other cell wall constituents, typically through acid hydrolysis, which will readily remove hemicellulose under mild conditions, and non-crystalline cellulose under more severe conditions. Several different methods will be discussed below. The different methods have also been extensively reviewed and compared by Hatfield et al. (1994), Brinkmann et al. (2002), Fukushima and Hatfield (2004), and Hatfield and Fukushima (2005). 

Figure 2. HPLC analysis of low molecular weight lignin products after acid hydrolysis of spruce wood (detector responses at 280 nm, positive curve, and at 350 nm, negative curve). (Two diastereoisomers of compound 13 are present as separate peaks.)...

Biphenyl structures and a-carbonyl-p-aryl ether structures, which are both assumed to be present in native lignin with a higher abundance than coniferyl alcohol structures (22,23) and both considered to be important leucochromophores, were not observed among die products, presumably because they are not present in spruce lignin as end groups. Both these types of structures are very stable and unlikely to be structurally changed during mild acid hydrolysis (24). 

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