Kraft Pulping Of Wood Research Articles

Structure of hardwood glucuronoxylans: modifications and impact on pulp retention during wood kraft pulping

The behaviour of different hardwood glucuronoxylans during the kraft pulping process was investigated. Woods and pulps xylans were isolated and characterized by size exclusion chromatography, methylation (linkage) analysis and 1H NMR. Eucalyptus globulus and Eucalyptus urograndis showed xylan retention significantly higher than that of Betula pendula. The higher retention of Eucalyptus xylans was assigned to (i) their higher average molecular weight (31 against 24 KDa in B. pendula) and to (ii) the presence of O-2 substituted 4- O-methyl-α- d-glucuronic acid groups ([→2)-Glc pA-(1→]) with galactopyranosyl/glucopyranosyl residues belonging to fragments of galactan/glucan chains that were absent in B. pendula xylans. A significant part of uronic acids, particularly [→2)-Glc pA-(1→] units, remain in fibres until the end of pulping. The acetylation degree and distribution of acetyl groups between Xyl p units, in general terms, was similar in the three types of xylans. Unexpectedly, about 20% of the acetyl groups persisted in pulps xylans till the end of pulping.

Swelling Behavior of Black Liquor from Soda Pulping of Wheat Straw

The primary aim of this research work was to characterize the swelling properties of black liquor and their dependence on the temperature and gas composition of the combustion or gasification environment. The measurements were made using an industrial black liquor from soda pulping of wheat straw. The swelling measurements were carried out in a single droplet reactor. This paper presents data that show the influence of the reactor temperature and the gas composition on the swelling during devolatilization, and compares the swelling characteristics of a straw black liquor with similar published data on black liquors from kraft pulping of wood. Experiments were carried out in inert, oxiding, and gasifying environments, at temperatures from 500 to 900 °C. One interesting result was that the straw liquor swelled much more than most kraft or soda liquors from pulping of wood. Another result was that droplets subjected to hot gas atmospheres containing O2, CO2 and/or H2O(v) swelled less than those subjected to hot N2 atmospheres. The data obtained suggest that the straw soda black liquor would burn more rapidly than most kraft liquors from pulping of wood because of its high external surface area when swollen. This highly swelling liquor caused problems with fluidization when straw liquors were injected in a laboratory-scale fluidized bed gasifier.

Effect of Pulping Conditions on the ECF Bleachability of Eucalyptus globulus Kraft Pulps

The effect of Eucalyptus globulus wood kraft pulping conditions on the chlorine dioxide consumption in elemental chlorine free bleaching of pulps was investigated. When the pulping is extended (kappa number decreases), the bleachability [as (OXE/ton)/kappa number] is reduced, suggesting that residual lignin and other oxidizable unsaturated structures in pulp become less reactive as their content in the pulp decreases. For the same unbleached pulp kappa number, the increase in active alkali and sulfidity used in pulping improves bleachability, whereas the pulping temperature (150-170°C) does not affect the bleaching response. The increase in liquor-to-wood ratio has a detrimental effect on the bleachability. No clear correlation could be established between unbleached pulp brightness and its bleaching response. Overall, the results obtained show a good correlation between the integral of the relative reaction rate constant (H factor) used in the pulping and pulp bleachability, with a low H factor being beneficial to the bleaching response of the pulp.

Experimental Methodology for Heterogeneous Studies in Pulping of Wood

The heterogeneous nature of the kraft pulping of wood is experimentally demonstrated in this paper, and a new methodology for kraft pulping investigation is presented. The strategy proposed here enables the measurement of alkali and of lignin concentrations in the pulping liquor, both inside and outside of the wood chips. With this procedure, it is possible to independently determine, in both entrapped and free liquors, the time histories of the concentrations of alkali and lignin as well as total dissolved solids, which are a direct result of the mass transfer and of the chemical reactions that take place during this heterogeneous process. The influence of the chip thickness and of temperature on the relative rates of these two phenomena is also highlighted. This experimental methodology establishes the foundations for the development of a macroscopic heterogeneous kraft pulping model that can be experimentally validated in pulping conditions, even for modified digester processes.

Pulping and bleaching of pulp from olive tree residues

The influence of operating conditions (active alkali concentration, temperature and time) used in the kraft pulping of wood from olive trimming residues on the yield and kappa index of the pulp and the stretch index, burst index and tear index of paper sheets obtained from it, as well as that of the chlorine dioxide concentration used to bleach the pulp according to the D 1ED 2 sequence (chlorine dioxide-alkaline extraction-chlorine dioxide) on the yield, kappa index, brightness and viscosity of the bleached pulp, were studied. A 2 n central composite factor design was used to derive equations that relate the dependent variables to the operating variables considered in the pulping and bleaching processes. The equations reproduce the experimental results with errors less than 10%. Based on the pulping results, obtaining readily bleached pulp of acceptable strength-related properties entails using an active alkali concentration of 25%, a temperature of 175°C and a time of 93 min. Based on the bleaching results, using chlorine dioxide concentrations of 7.5 and 1% in steps D 1 and D 2, respectively, ensures the obtainment of acceptably bright (>88%) pulp with little loss of yield (<2%) and viscosity (<3%).

On-Site Production of Xylanase and its Application on Hard Wood Kraft Pulp Bleaching

Xylanase treatment with on-site enzyme production was introduced into the hardwood kraft pulp bleaching process (C-E/O-dnD) at Yonago mill in October, 1998.A thermostable xylanase from a microorganism, Bacillus sp.S-2113, that we isolated through screening was selected for use in this process.The xylanase-containing culture was applied to the bleaching process without removing the bacterial cells from the culture medium.Two years have passed since the xylanase treatment operation, with onsite enzyme production, was begun, and so far, this operation has been working well.The ECF bleaching sequence will start operation within the year 2000in Yonago mill.The effects of enzyme bleaching in the ECF bleaching process are expected to be even greater then.

A Possible Role of Manganese Peroxidase during Biobleaching by the Pulp Bleaching Fungus SKB-1152

The fungus SKB-1152 bleaches oxygen-alkaline treated hard wood kraft pulp (OKP) rapidly. In the initial phase of fungal treatment, maximum production of manganese peroxidase (MnP) was observed. The filtrate from a 1-day fungal treatment could bleach OKP when manganese, glucose, and glucose oxidase were added. A possible role of MnP in the initial fungal bleaching process is suggested.

The Relative Behavior of Benzylic Alcohols and Mercaptans Toward Oxidation By Sodium Anthraquinone-1-Monosulfonate (Ams)

Abstract The reactions of 1-phenylethanol and 1-phenylethanethiol, either alone or together, with AMS in alkaline 50Z aqueous dioxane at 88∗ have been studied. The mercaptan is oxidized several hundred times faster than the alcohol. The results imply that benzyl mer-captans, such as those produced during the kraft pulping of wood, could serve as reaction partners in the reduction of anthraquinone to anthrahydroquinone during kraft/anthraquinone pulping.