Dilute-acid hydrolysis

Hydroxyall l Hydroperoxyall l Peroxides. There is evidence that hydroxyalkyl hydroperoxyalkyl peroxides (2, X = OH, Y = OOH) exist in equihbrium with their corresponding carbonyl compounds and other a-oxygen-substituted peroxides. For example, reaction with acyl haUdes yields diperoxyesters. Dilute acid hydrolysis yields the corresponding ketone (44). Reduction with phosphines yields di(hydroxyalkyl) peroxides and dehydration results in formation of cycHc diperoxides (4). 

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

Dilute acid hydrolysis of 17,21-alkylorthoesters (43) of corticosteroids usually gives the 17-monoesters (44) together with small amounts of 21-monoesters, although in certain cases the 17-monoesters (44) are the exclusive products. ... 

Arsine, AsHs, is formed when many As-containing compounds are reduced with nascent hydrogen and its decomposition on a heated glass surface to form a metallic mirror formed the basis of Marsh s test for the element. The low-temperature reduction of AsCls with LiAlH4 in diethyl ether solution gives good yields of the gas as does the dilute acid hydrolysis of many arsenides of electropositive elements (Na, Mg, Zn, etc.). Similar reactions yield stibine, e.g. ... 

Maloney, M.T., Chapman, T.W., and Baker, A.J. (1986) An engineering analysis of the production of xylose by dilute acid hydrolysis of hardwood hemicellulose. Biotechnol Progr., 2, 193. 

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

Dialkylaminofurans (169) are prepared from tertiary amides of /3-aroylpropionic acids (167), which on treatment with acetic anhydride and perchloric acid yield 2,3-dihydrofuran-2-furylideneammonium salts (168) from which stable dialkylaminofurans. (169) can be obtained. Dilute acid hydrolysis gives the butenolides (170) (73JCS(P1)2523). 

Dilute Acid Hydrolysis. Data relative to the acid saccharification of the four substrates at various levels of vibratory ball milling are given in Table III and plotted as rate and yield curves in Figures 7 and 8. Table IV summarizes the half-life and maximum sugar yield values derived from these curves. 

The effect of ball milling on the dilute acid hydrolysis of cellulose is similar in many ways to the effect electron irradiation has on enhancing saccharification (18). In the case of cotton linters, for example, maximum irradiation lO d) resulted in a half life of hydrolysis of about 7 min... 

Table IV. Effect of Vibratory Ball Milling on the Kinetics of Dilute Acid Hydrolysis ...

The relative influence of vibratory milling on the course of enzymatic and dilute acid hydrolysis of four cellulosic substrates was investigated. The four substrates—cotton linters, newsprint, Douglas fir, and red oak— were vacuum-dried and then milled for various time periods ranging up to 240 min. Assays were then made of rate and extent of hydrolysis, maximum yield of reducing sugar, and cellulose crystallinity. 

Vibratory milling also yields substantial increases in the rates of dilute acid hydrolysis of all four substrates nearly nine-fold for cotton linters and roughly five-fold for the three lignocelluloses. Increases in maximum sugar yields under simple batch conditions ranged from 60% to 140% over the yields for the unmilled materials. 

Ruiz, R. and Ehrman, T. (1996), Dilute acid hydrolysis procedure for determination of total sugars in the liquid fraction of process samples, in Laboratory Analytic Procedure LAP-014, National Renewable Energy Laboratory, Golden, CO. 

A second effect on hydrogen ion activity not previously considered in dilute-acid hydrolysis of hemicellulose is the shift to bisulfate that occurs with neutralization. Neutralization products are water and mineral sulfates (Eq. 5). These mineral sulfates, if not removed from the system, will form bisulfates from some of the remaining hydronium ions to reestablish equilibrium as follows (Eq. 7) ... 

The main factors affecting monosaccharide recovery in dilute-acid hydrolysis are catalyst concentration, reaction time, and temperature, whereas enzymatic hydrolysis is also dependent on additional factors such as substrate structure, and type and ratio of enzymatic activities present in the commercial enzyme preparations. The most important enzymes for xylan hydrolysis are endo-l,4-(3-xylanases (which attack the main chain) (3-xylosidases (which hydrolyze xylooligosaccharides to xylose) and accessory enzymes, such as acetyl xylanesterases, a-glucu-... 

Optimization of Brewery s Spent Grain Dilute-Acid Hydrolysis for the Production of Pentose-Rich Culture Media... 

Index Entries Brewery s spent grain dilute-acid hydrolysis pentose-rich media Debaryomyces hansenii. 

Dilute-acid hydrolysis is therefore the main choice for the hydrolysis of hemicellulose to monosaccharides once it is a fast and efficient method (19). However, a careful optimization of operational conditions used for hydrolysis is important to ensure high monosaccharide recovery and minimize coformation of microbial inhibitors. 

The high pentose yields obtained in the current study are favorable when compared to those previously reported for dilute-acid hydrolysis in batch processes (28-31). However, the hemicellulosic sugar yield reported in the literature is often expressed as xylose equivalents, which is difficult to compare to monosaccharide recovery. The highest monosaccharide recovery was obtained with low CS values, which is in agreement with previous findings for sulfuric acid-catalyzed steam explosion, in which also better hemicellulosic sugar recoveries were obtained at relatively low severities (28,32) of <2.2 (22). 

Since dilute-acid hydrolysis mainly solubilizes the hemicellulose components, the changes in solid yield (a measure of dry weight loss) are useful for monitoring the progress of the treatment. Table 1 shows the yield and... 

Fig. 1. Yield of monosaccharides after dilute-acid hydrolysis of BSG as a function of CS. (A), Xylose ( ), arabinose ( ), glucose. The lines only show trends.

Effect of CS Parameter on Solid Yield and Polymeric Composition of Processed Solids Obtained After Dilute-Acid Hydrolysis of BSG... 

From the reported data (Figs. 1 and 2, Table 1) the optimum condition to obtain a pentose-rich hydrolysate from dilute-acid hydrolysis of BSG at 130°C was 15 min (CS 1.94). Such hydrolysate contains about 43.5 g/L of glucose, xylose, and arabinose (ratio of 10 67 32), together with a low content of furfural, HMF, acetic acid, formic acid, and total phenolic compounds (Table 2). This condition was chosen for subsequent production of hydrolysates for fermentation. 

Kinetics of Glucose Decomposition During Dilute-Acid Hydrolysis of Lignocellulosic Biomass... 

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