摘要:

Two wood species - the softwood Pinus radiata and the hardwood Eucalyptus regnans have been examined by CP/MAS13C NMR spectroscopy before and after treatment by two steam explosion processes, namely, the Canadian Iotech Process and the Australian Siropulper process.1,2While the main effects of treatment appeared to be, in general, similar for both processes and both species of wood, e.g. an apparent increase in cellulose crystallinity, hydrolysis of the hemicellulose component, de-etherification and depolymerization of the lignin component, some differences were also detectable, particularly in samples of extracted exploded wood. These included differences in cellulose crystallinity, composition and residual lignin structure. In some cases, signal area ratios could be used both to confirm and to provide a comparative measure of these effects and differences. Signal ratios were also the basis for development of a useful, non-destructive method of examining lignin content, which may have an advantage over the Klason method for comparing exploded wood and extracted exploded wood samples, in that it does not degrade carbohydrate. Some implications of the results for bioconversion processes are mentioned briefly. CP/MAS NMR spectroscopy is thought to be a valuable and promising technique for examining and comparing the effects of pretreatment on the structure and composition of biomass substrates, as it provides estimates, from a single experiment, of cellulose crystallinity and lignin content, as well as qualitative comparisons, e.g. of lignin structure.

ISSN:0277-3813    

DOI:10.1080/02773818508085186

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The alkaline cleavage of β-ether bonds of phenolic lignin model compounds by reducing sugars has been shown to occur by the reaction of the quinone methide of the lignin model with a sugar-derived enediol. Reaction of the quinone methide of 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)ethanol with L-ascorbic acid in the absence of base gives a carbon-carbon bonded intermediate formed by reaction of the C-2 carbon of the ascorbic acid enediol with the α-carbon of the quinone methide. This intermediate then fragments under alkaline conditions to guaiacol and vinylguaiacol, the same products as obtained from heating the β-ether itself with ascorbic acid or reducing sugars under alkaline conditions. The isolated intermediate was obtained as a one to one mixture of two stereoisomers, isomeric at the benzylic carbon, from which one isomer was selectively crystallised. The generality of the reaction and its relevance to the development of alternative pulping processes is discussed and the possibility of carbon-carbon bonded lignin carbohydrate complexes being formed via enediols is suggested.

ISSN:0277-3813    

DOI:10.1080/02773818508085187

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

At pH 11 and 140°C, the rate of end-wise degradation (“peeling”) of hydrocellulose is approximately 27 percent of that in 1 N NaOH. As the pH is reduced further, the rate of peeling declines by a factor of 0.34 per pH-unit. This decline is less than expected on the basis of end-group ionization. Consequently end-wise degradation can be a significant reaction even at neutral pH.

ISSN:0277-3813    

DOI:10.1080/02773818508085188

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

An equation has been developed to relate the viscosity of unbleached pulp to the residual alkali in the spent liquor, and the time-temperature profile of the cook (expressed as the G-factor). The equation is applicable to kraft, kraft-AQ and soda-AQ pulping and to a variety of wood species.

ISSN:0277-3813    

DOI:10.1080/02773818508085189

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Lignin model fragmentation studies done in alkaline aqueous DMSO exhibited a high degree of β-aryl ether cleavage, a degree equal to that of a comparable soda/AQ system. Pulping studies with loblolly pine in aqueous DMSO demonstrated that DMSO accelerates delignification, but the quantities required appear Impractical. Several lignin model compounds have been heated at 150°C with alkali in aqueous DMSO to give complex product mixtures containing oxidation, reduction, and methyl sulfide addition products. Low temperature reactions of DMSO and dirasyl anion with in situ generated quinonemethides afforded unique products. Reactions attributed to DMSO were not observed when an oxidized analog, dimethylsulfone, was substituted for the DMSO.

ISSN:0277-3813    

DOI:10.1080/02773818508085190

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The products formed when methyl mercaptan reacts with polysul-fide in an alkaline solution have been identified, using1H NMR, as dimethyldisulfide, dinethyltrisulfide, dimethyltetrasulfide and methyldisulfide anion (CH3SS−). Analogously, methyl mercaptan and polythionate were found to give methylthiosulfate anion (CH3SSO3−), in addition to these dimethylpolysulfides. The reactions are interpreted in terms of nucleophilic displacements of the SN2 type. The formation of these anionic products constitutes the basis for the potential use of polythio compounds for reduction of air pollution in the kraft pulping process.

ISSN:0277-3813    

DOI:10.1080/02773818508085191

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

To elucidate the mechanism of anthrone-promoted β -ether cleavage reactions, the phenolic lignin model compound 1, 1-(4-hy-droxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol, was heated with 0.1 mole of anthrone (AN) or anthrahydroquinone (AHQ) at 140 °C for 1/2, 1, 2, 3 and 5 hours in 1 M sodium hydroxide solution. The cleavage products [2-methoxyphenol and (2-meth-oxy-4-propenyl)phenol] were the same as in experiments with equimolar amounts or excess of AN and the yields increased as a function of reaction time to a maximum corresponding to the cleavage of four to five moles of1per one mole of AN. AHQ was found to react in a similar manner. This “catalytic” effect is tentatively attributed to sequential transformations of AN and AHQ to products capable of causing further reductive cleavages. GC-MS analysis of the reaction mixture showed the presence of by-products which indicate that some catalyst regeneration through oxidation of 1 or its hydrolysis products may have occured. 1-Hydroxyanthrone had a similar “catalytic” effect in cleaving β-ether bonds, but glucose did not.

ISSN:0277-3813    

DOI:10.1080/02773818508085192

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Arylglycerol-ether bonds of lignin samples or model compounds vera selectively cleaved by treatment with dioxane-ethanethiol (9/1, v/v) and 0.2 N HBF4etherate or 0.2 N BF3etherate at 100°C for four hour3. Monomers resulting from “thioacidolysis” were identified by gas chroraatography-mass spectrometry of their trimethylslly derivatives. Compared to acidolysls (dloxane-water, 0.2 N HCL, 100°C 4h), thioacidolysis yields less complex mixtures of monomers. The monomer yields for lignin thioacidolysis were also higher than for acidolysls. This increase was particularly evident for hardwood lignins.

ISSN:0277-3813    

DOI:10.1080/02773818508085193

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0277-3813    

DOI:10.1080/02773818508085185

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor