The Effect of Initial Acid Concentration on the Lignin Isolated by the Acidolysis of Aspen Wood

158

MIRANDA G. S. CHUA and MORRIS WAYMAN. Can. J. Chem. 57, 1141Chem. 57, (1979. Extractive-free aspen wood meal was subjected to autohydrolysis at 195'C for 5 min to 2 h, and the lignin extracted with 90% dioxane. Extracted autohydrolysis lignin was found to be higher in carbon but lower in hydrogen and oxygen content than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. These differences have been attributed to condensation and incorporation into the lignin of non-lignin components. A lignin extractability curve with a maximum delignification at autohydrolysis time of 30-40 min was found. From molecular weight distribution studies the ratio of high molecular weight to low molecular weight materials varied for the different extracted lignins and reached a maximum at autohydrolysis time of 40 min. A mechanism of depolymerization/repolymerization of the lignin via carbonium ions has been proposed. p-Hydroxybenzoic acid is postulated as contributing to the extractability of aspen lignin by acting as a blocking agent.MIRANDA G. S. CHUA et MORRIS WAYMAN. Can. J. Chem.,57, 1141Chem.,57, (1979. On a soumis de la sciure de bois de tremble (ne contenant plus de produits pouvant dtre extraits) a une autohydrolyse k 195'C pour des temps allant de 5 min k 2 h puis on en a extrait la lignine par du dioxanne a 90%. On a trouvk que la lignine extraite de l'autohydrolyse contient plus de carbone et moins d'hydrogkne et d'oxygene que la lignine provenant de bois de tremble broy6. La quantitk de methoxyle qui y est contenue est aussi plus faible que celle contenue dans la lignine de rkfkrence. On a attribuk ces diffkrences k la condensation et k I'incorporation dans la lignine de composants qui ne sont pas des lignines. On a dktermink une courbe permettant d'kvaluer la facilitk d'extraction de la lignine; elle prksente un maximum de dklignification a des temps d'autohydrolyse de 30 ti 40 min. En se basant sur des Btudes de distribution de masses moleculaires, on a determine que le rapport des produits de masses molkculaires klevBes/produits de masses molkculaires plus faibles varie suivant les diffkrentes lignines extraites et qu'il atteint un maximum k un temps d'autohydrolyse de 40 min. On propose un mkcanisme de dkpolymkrisation/repolymkrisation de la lignine par l'intermkdiaire de carbocations. On croit que I'acide p-hydroxybenzoi'que facilite l'extraction de la lignine de tremble en agissant cornrne agent bloqueur.[Traduit par le journal]

Section: Elemental Analyses Of Extracted Autohydrolysismentioning

confidence: 77%

Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 1. Composition and molecular weight distribution of extracted autohydrolysis lignin

Chua¹,

Wayman²

1979

158

“…This depolymerization technique has been widely used for characterizing protolignin in order to deduce its structural features as well as any changes in extracted lignins caused by the method of isolation (24)(25)(26). As has been demonstrated by Leopold (27) in studies on lignin model compounds, lower yields of aromatic aldehydes are obtained upon the alkaline nitrobenzene oxidation of condensed lignin structures (i. e., carbon-carbon linked).…”

Section: Alkaline Nitrobenzene Oxidationmentioning

confidence: 99%

Fractionation of woodmeal by prehydrolysis and thermal organosolv. Alkaline depolymerization, chemical functionality, and molecular weight distribution of recovered lignins and their fractions

Thring¹,

Chornet²,

Overend³

1993

. Can. J . Chem. 71, 779 (1993). Thermal organosolv glycol lignins and their fractions have been characterized by means of elemental composition, molecular weight distribution, and 'H and I3c NMR spectroscopy. Fractionation of each lignin by sequential solvent extraction produced fractions of increasing molecular weight and polydispersity. Structures in the highest molecular weight fractions were found to be linked by a high proportion of P-0-4 type bonds, whilst the lowest molecular weight fractions consisted of a high content of saturated aliphatic side-chain structures. A noticeable difference in the content of carbohydrate contaminants in both starting lignins indicated the formation of relatively stable lignin-carbohydrate complexes, especially in the lignin recovered from pretreated wood. In addition, depolymerization of the lignins and their fractions to monomeric compounds was explored using alkaline hydrolytic and nitrobenzene oxidative routes. The highest molecular weight fractions from each lignin were identified as the best candidates for production of useful monomeric phenolic compounds. En se basant sur la composition ClCmentaire, la distribution des poids molCculaires et la RMN du 'H et du I3c, on a caractCrisC les lignines thermiques de l'organosolv glycol et leurs fractions. Le fractionnement de chaque lignine par extraction ~Cquentielle par les solvants a fourni des fractions de poids molCculaires et de polydispersitCs croissants. On a trouvC que les structures des fractions de poids molCculaires les plus ClevCs sont likes en grande partie par des liaisons de type P-0-4 alors que celles des fractions de poids molCculaires plus faibles comportent de grandes quantites de chaines laterales aliphatiques saturkes. On a not6 une difference notablehans le contenuen hydrates de carbone des deux lignines; elle indique qu'il y a formation de complexes lignine -hydrate de carbone relativement stables, particulikrement dans la lignine rCcupCrCe du bois prCtraitC. On a de plus examine la dCpolymCrisation des lignines et de leurs fractions en composCs monomeres par hydrolyse alcaline et par oxydation avec du nitrobenzkne. Pour la production de composCs phCnoliques monomkres utiles, on a identifiC que les fractions de poids molCculaires les plus ClevCs de chacune des lignines seraient les plus appropriCes.[Traduit par la rCdaction]

“…T h e very rapid increase in the yield of chloroformsoluble material from the 1.3-hour to the 3-hour reaction time may be due to the autocatalytic effect of the released phenolic compounds. I t is well known that the addition of even traces of mineral or organic acids aid markedly in any lignin isolation procedure (13) With increasing time of reaction there is a similar total increase in aromatic derivatives but less secondary reduction or cracking than in the case of those runs with temperatures over 195". Again the increasing molar ratio of type B over type A compounds, with increasing time, is a result of a relative decrease in compounds of the latter type since there is no significant decrease in the yield of compounds of t h e former type.…”

mentioning

confidence: 99%

“…After removal of the chloroform and precipitation in t o water, a cream-colored solid was collected and dried over Pz05. This material analyzed for C, 63.23; H , 6.59; ash, 0.81; methoxyl, 21.8y0, had an average molecular weight above 2480, and gave an infrared spectrum typical of that of an isolated dioxane aspen lignin (13). Similarly, the chloroform-insoluble lignins were examined for the presence of any medium molecular weight substances.…”

mentioning

confidence: 99%

The Effect of Time and Temperature on the Hydrogenation of Aspen Lignin

Pepper¹,

Steck²

1963

Self Cite

X study has been made of the hydrogenation of preextracted aspen sapwood meal under conditions whereby the lignin is degraded to identifiable products. By gas liquid chromatography, guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-n-propylguaiacol, dihydroconiferyl alcohol, syringol, 4-methyls~ringol, 4-ethylsyringol, 4-n-propylsyringol, and dihydrosinapyl alcohol were separated and identified.The relative abundance of these 10 compounds was determined in the chloroform-soluble product after hydrogenation using a dioxane-water (1:l) solvent medium, Raney nickel catalyst, a n initial hydrogen pressure of 500 p.s.i. and temperatures of 150°, 16j0, 185", 195", 210°, and 220" for a reaction time of 5 hours and a temperature of 195" for times of 0, 1.3, 5.0, and 24 hours. The best yield (52.27, of the Klason lignin) of such phenolic derivatives was obtained a t a reaction temperature of 195" for 5 hours.The significance of the obser~red variation in the yields of these compounds with time and temperature and the relationship of these yields t o the structure of lignin is discussed. Evidence is presented in support of both 7-alkyl ether and p-aryl ether linkages in the lignin substance.In 1938, Harris, D'Ianni, and Adkins (1) reported a successful catalytic hydrogenolysis of an isolated aspen lignin and isolated and identified lignin derivatives of a cyclohexylpropyl nature. Since that time this technique has been applied to the study of various wood and straw meals and isolated lignins, under a variety of conditions involving different catalysts, solvents, times, temperatures, and initial pressures of hydrogen (2, 3). A significant contribution was made in 1948 by Brewer, Cooke, and Hibbert (4), who reported the degradation of maple wood lignin under much milder conditions of hydrogenation than those used by earlier workers and obtained phenylpropyl lignin derivatives, thus providing direct evidence for the aromatic nature of the lignin substance. Subsequently, other workers (5-9) have extended these studies to other lignified materials and various isolated lignins and have thereby added to the variety of aromatic compounds that have been isolated and identified. Of particular interest is the recent work of Coscia, Schubert, and Nord (10) and of Olcay ( l l ) , who obtained aromatic lignin derivatives by the hydrogenation of the milled wood lignins from birch, oak, pine, and spruce under conditions which, when applied earlier to other isolated lignins, had given rise to cyclohexyl derivatives. These workers introduced the use of gas-liquid chromatography for the separation and quantitative estimation of the lignin derivatives.Earlier, in these laboratories, a study had been made of the conditions affecting the isolation, as a chloroform-soluble fraction, of the lignin derivatives resulting from the catalytic hydrogenation of aspen wood meal (8). I t was thus found that a t temperatures of 170"-180" for a reaction period of 3 hours, using a dioxane-water (1: 1) medium, Raney nickel catalyst, and an initial hydr...