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排序方式: 共有262条查询结果,搜索用时 10 毫秒
1.
Fernando M. Lanas Janete H. Y. Vilegas Srgio Martins Elaine A. F. Gobato 《Journal of separation science》1994,17(4):237-244
An overview is presented of the analytical approaches developed by our research group over the last ten years for analysis of alternative fuel, both biomass and fossil. The alternative fuels are analyzed successively by PLC-8 (preparative liquid chromatography–group-type) fractionation and high resolution gas chromatography. Some of the possibilities for fractionation and characterization of alternative fuels are herein exemplified with sugar cane bagasse pyrolysis products. 相似文献
2.
A way of determining the flexibility of wood-pulp fibres is developed, which involves i) a precise measurement of the topology
of single-fibres by using a confocal laser scanning microscope and ii) the measurement of the elastic modulus of the fibres
by using a single-fibre fatigue cell. Reported in this paper are the initial results of tests carried out on black spruce
fibres, which have been subjected to three different levels of mechanical refining energy, namely ∼1100, 2300, and 3500 kWh/t.
It is found that the fibre flexibility rises significantly between the first and second energy levels, but it does not change
to the same degree between the second and third ones. The described procedure of measuring the flexibility of fibres may be
used to establish the appropriate refiner energy necessary for the production of a specific grade of paper.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 115–128, January–February, 2006. 相似文献
3.
Veronica?StigssonEmail author G?ran?Kloow Ulf?Germg?rd Niclas?Andersson 《Cellulose (London, England)》2005,12(4):395-401
Controlling the reduction in molecular weight of the cellulose chains is essential in the production of carboxymethyl cellulose
(CMC). Such a reduction can be achieved by the addition of cobalt during the process of cobalt(II) ions, which act as a catalyst
for oxidative cleavage, and the influence thereof has been studied under a variety of conditions. This study has resulted
in a model that summarises the effects of the added amount of cobalt, the time for the cobalt reaction, the temperature in
the mercerisation stage of the CMC-manufacturing process and finally the effect of the temperature in the etherification stage.
It is shown that it is important for cobalt to be present during the mercerisation stage in order to achieve the desired viscosity. 相似文献
4.
E. Fleury J. Dubois C. Léonard J. P. Joseleau H. Chanzy 《Cellulose (London, England)》1994,1(2):131-144
Solutions of cellulose diacetate (CDA) from two sources (cotton linters and wood pulp Floranier) were analysed in various solvents by size exclusion chromatography (SEC). Without special precautions, the SEC chromatograms presented three peaks — or prehumps — before the main polymer peak. The first prehump which could be eliminated by ultracentrifugation corresponded to microgels whose sugar composition was determined. These microgels were also investigated by electron microscopy, X-ray and electron diffraction analysis. They corresponded mainly to cellulose triacetate (CTA-II) in the case of CDA from cotton linters and a mixture of CTA-II and xylan diacetate (XDA) in the case of CDA from the wood pulp Floranier. The second and third prehumps could be attributed to ionic effects corresponding to the association of remaining sulfate groups on the CDA molecules with residual calcium. It was found that these ionic effects could be eliminated by the addition of LiBr or LiCl to the elution solvents. This led to chromatograms devoid of prehumps.Presented in part at the Cellulose '91 meeting in New Orleans. 相似文献
5.
Wolfgang?Gutleben Verena?Unterholzner Dietmar?Volgger Andreas?ZemannEmail author 《Mikrochimica acta》2004,146(2):111-117
In the course of this investigation, a method for the characterization and differentiation of paper pulps was developed. After hydrolyzation of the papers and the respective raw pulps with trifluoroacetic acid, the hydrolyzates were analyzed with respect to their carbohydrate composition using ion exchange chromatography. The variations in carbohydrate composition mainly arise from the various hemicelluloses of the papers and pulps. The chromatographic results were then further processed using principal component analysis which allows correlating the various papers to different pulp materials. 相似文献
6.
M. Costa-Ferreira A. Dias C. Maximo M. J. Morgado G. Sena-Martins J. Cardoso Duarte 《Applied biochemistry and biotechnology》1994,44(3):231-242
Production of xylanolytic enzymes by anAspergillus niger CCMI 850 isolate was investigated in batch cultures. The effect of the composition of a fermentation medium that did not
include chemical inducers, on β-xylanase, β-xylosidase, α-l-arabinofuranosidase, and total cellulase activity was studied. With 4% xylan as the carbon source, about 65 U/mL of β-xylanase
was obtained, whereas the total cellulase activity was undetectable, under the specified conditions. This β-xylanase activity
represents the highest reported for a wild-type strain ofA. niger. The effect of pH and temperature on the activity of β-xylanase was studied. Partial characterization of the β-xylanase showed
that with insoluble birchwood as substrate theK
m
andV
max were 0.3 mM and 19 μmol/min, respectively. Aspects of using the crude β-xylanase preparation for applications in the pulp and paper industry
were discussed. 相似文献
7.
Nishi K. Bhardwaj Viet Hoang Vinh Dang Kien L. Nguyen 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,290(1-3):222-228
A wide range of kraft pulps from radiata pine produced by low-temperature kraft pulping in flow-through reactors was assessed for carboxyl and hexenuronic acid (HexA) contents using the conductometric titrations and UV spectrophotometer, respectively. The Kappa number of pulps varied from 20.8 to 84.7 when using a cooking liquor of 1 M effective alkali as Na2O, 25% sulfidity, and cooking time of 100–250 min. The experimental results showed that the carboxyl groups (including HexA) and HexA groups dissolved and their residual values in the pulp samples correlate linearly with Kappa number and pulp yield. The dissolving rate of all carboxyl groups is much faster than the loss of HexA. The HexA/lignin ratio decreased non-linearly with Kappa number. 相似文献
8.
Silva Silvio S. Ribeiro JoÃo D. Felipe Maria G. A. Vitolo Michelle 《Applied biochemistry and biotechnology》1997,(1):557-564
Batch fermentations of sugar cane bagasse hemicellulosic hydrolysate treated for removing the inhibitors of the fermentation
were performed byCandida guilliermondii FTI20037 for xylitol production. The fermentative parameters agitation and aeration rate were studied aiming the maximization
of xylitol production from this agroindustrial residue. The maximal xylitol volumetric productivity (0.87 g/L h) and yield
(0.67 g/g) were attained at 400/min and 0.45 v.v.m. (KLa 27/h). According to the results, a suitable control of the oxygen input permitting the xylitol formation from sugar cane
bagasse hydrolysate is required for the development of an efficient fermentation process for large-scale applications. 相似文献
9.
Regina Y. Moriya Adilson R. Gonçalves Fabrícia P. Faria 《Applied biochemistry and biotechnology》2005,121(1-3):195-203
Organosolv (ethanol/water and acetosolv) pulps were treated with Humicola grisea var. thermoidea and compared with Cartazyme HS xylanase-treated pulp. The ethanol/water pulps treated with H. grisea had the same viscosity as unbleached pulps (8 cP). Ethanol/water pulps treated with Cartazyme had higher viscosity than H. grisea-treated pulps (12 cP). Acetosolv pulps treated with H. grisea and Cartazyme presented a reduction in viscosity; however, the pulps treated with H. grisea had a lower reduction in viscosity than Cartazyme-treated pulps. Ethanol/water pulps treated with H. grisea had a 23% reduction in kappa number in 4 and 8 h of treatment, compared with the unbleached pulps. Cartazyme-treated pulps
had a kappa number similar to that of the control pulps for 4 h of treatment. Extending the treatment time to 12 h resulted
in a reduction of 33%. The acetosolv pulp treated with H. grisea had a kappa number reduced to 23% in 4 h. Cartazyme treatment resulted in a reduction of 55 and 44% in kappa number for 4
and 8 h of treatment, respectively, when compared with control pulp. Extending the treatment time to 12 h decreased the kappa
number 72%. Fourier transform infrared spectra and principal component analysis showed differences among unbleached, H. grisea-treated, and Cartazyme-treated pulps. 相似文献
10.
Brightness reversion of softwood (SW) and hardwood (HW) bleached chemithermomechanical pulps (BCTMP) with a 300–400nm light source under argon, oxygen, and air were studied in the absence and presence of UV-screens using UV–Vis reflectance difference spectroscopy. The UV-Vis difference absorption spectra of control SW and HW BCTMP testsheets indicate that as the concentration of atmospheric oxygen is increased, the absorption at max 360nm increases and a blue shift occurs. In all of the cases studied, brightness reversion was observed to occur under an argon atmosphere. The addition of benzophenone and benzotriazole additives to BCTMP testsheets resulted in a significant decrease in formation of chromophores absorbed at 400nm and 360nm. The possible mechanisms contributing to these effects are discussed in terms of the photoformation of lignin chromophoric structures. 相似文献