摘要:

Kraft delignification of Douglas-fir (Pseudotsuga menziesii) wood meal was carried out under an instantaneous isothermal condition with a liquor-to-wood ratio of 50 to investigate the effects of reaction temperature and chemical concentration on the rate of delignification. The temperatures studied were in the range of 120 to 175°C. Three levels of [HO−l] and three levels of [HS−l] concentrations were investigated. In each case an efficient mechanical agitation of the pulping liquor was maintained and the delignification was extended to reach its completion. Using a nonlinear regression analysis on the delignification results, a single kinetics equation was resolved to describe the effect of temperature and chemical concentration on the rates of delignification for the initial, bulk, and final phases. This equation also revealed that the amounts of lignin removed due to the chemical reactions in the initial, bulk, and final phases were 18.8, 71.4, and 3.8%, respectively. About 6% of the total lignin was dissolved into the pulping solution before any significant chemical reaction occurred to the lignin core. The activation energies of delignification reactions in the initial, bulk, and final phases were 85.8, 123.8, and 110.0 kJ/mole, respectively. The Ln(pre-exponential factors) were 22.5, 30.5, and 23.4 m−l1for the initial, bulk, and final phases, respectively. The rate of delignification was strongly affected by the presence of [HO−l] in the bulk and final phases. Whereas, [HS−l] had a significant effect on the rate of delignification only in the bulk phase. These chemical effects were also quantified.

ISSN:0277-3813    

DOI:10.1080/02773819008050241

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Laboratory experiments show that pretreatment with NO2including heating and ripening at 5% consistency and 90°C for 3 hours in the presence of NO3- and H+led to a dissolution of approximately 50–60% of the lignin in unbleached kraft pulp. Only 5–15% were dissolved when the treatment was terminated after heating to 90°C. An extensive fragmentation of the lignin during the ripening explains the extensive delignification in acid medium.

ISSN:0277-3813    

DOI:10.1080/02773819008050242

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Both residual lignins and lignins isolated from the pulping liquor of 20 l batch cookings of spruce chips according to the organocell process were subjected to HPSEC. Checking the resulting Mn-values by vapor pressure osmometry confirmed the HPSEC data except for first stage lignins with short cooking times, where the different elution behavior caused by high portions of organic nonlignin substances is held responsible for these discrepancies.

ISSN:0277-3813    

DOI:10.1080/02773819008050243

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Soluble and residual spruce lignins were subjected to permanganate oxidation and thioacidolysis to elucidate changes in lignin's structure during Organocell pulping.

ISSN:0277-3813    

DOI:10.1080/02773819008050244

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Oxidation of woodmeals with an excess of aqueous sodium periodate solution at 4°C released an amount of methanol approximately equivalent to the phenolic hydroxyl content of the lignin as determined by the aminolysis method. The periodate and aminolysis methods gave very comparable data for Norway spruce and aspen woodmeal samples.

ISSN:0277-3813    

DOI:10.1080/02773819008050245

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Sweetgum wood was hydrolyzed at 20°C and 50°C for different time periods with 68% sulfuric acid. The lignin residues obtained were subjected to a phenolation reaction. For lignin prepared at the lower temperature the maximum phenol uptake was 9.5%, and at the higher temperature only 5–6%. When wood prehydrolyzed with dilute acid was used the phenol uptake rose to 12.5%. However, all the sulfuric acid hydrolysis lignins showed much lower reactivity toward phenol than the 20% phenol uptake exhibited by lignin isolated using concentrated hydrochloric acid.

ISSN:0277-3813    

DOI:10.1080/02773819008050246

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Exposure of 1.5 cm diameter × 1.2 cm long white fir and Douglas-fir heart-and sapwood samples to the action of cold radiofrequency oxygen, nitrogen, and helium plasmas strongly increased wood permeability to nitrogen flow along the grain. Oxygen was most effective, followed by nitrogen and helium. While an increase in radiofrequency energy level increased the effect, the opposite was true for an increase in reactant gas flow rate. With white fir the rate of permeability increase was higher at the beginning of the plasma treatment. This was attributed to differing ablation rates of cellulose, hemicelluloses, and lignin. No significant time difference in the rate of permeability increase was observed with Douglas-fir. Extractives suppressed the plasmainduced permeability increase; thus extraction with water and ethanol, followed by oxygen plasma treatment increased permeability of Douglas-fir heartwood 32 times, while plasma treatment of the unextracted Douglas-fir increased permeability only 8 times. The permeability of extracted and oxygen plasma-treated wood did not vary much across the grain, but did decrease with distance from the ends of the samples due to incomplete removal of extractives from the center.

ISSN:0277-3813    

DOI:10.1080/02773819008050247

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A series of condensed tannin derivatives with non-, mono-, di- and tri-hydroxylated B-rings were synthesized starting from phloroglucinol and benzaldehyde derivatives. The protein-precipitating capacity of these condensed tannin derivatives showed 1) A condensed tannin with only a 4′-hydroxylated B-ring has almost the same protein-precipitating capacity as that of a condensed tannin with 3′,4′-dihydroxylated or 3′,4′,5′-trihydroxylated B-rings. 2) The complexing ability of phenolic hydroxyl groups in the B-ring are effective in the order ofp- >m- >o-positions.

ISSN:0277-3813    

DOI:10.1080/02773819008050248

出版商:Taylor & Francis Group    

年代:1990

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:10.1080/02773819008050240

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor