Hemicellulase-aided bleaching is the first full-scale biotechnical application in the pulp and paper industry which truly exploits the unique specificity and safety of. () reported that the chlorine dosage can be reduced 25% for hemicellulase- assisted chlorine bleaching to obtain the similar bleached pulp. Paice et al. Elemental chlorine, while effective in bleaching pulp and low in both primary classes: hemicellulases (xylanase) and oxidases (laccase).
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Xylanases from a Thermomonospora fusca strain with the designation MT have recently been described Appl.
The effluent from the pulp bleaching plant, that portion of a mill that converts brown pulp to white, contains numerous chlorinated organic substances including toxic chlorinated phenols and dioxin.
The results are shown in FIG. Wong, Microbiological Reviews, pp. The activity of the enzyme was calculated based upon the amount of enzyme that is needed to produce 0.
Catalase is used to convert residual hydrogen peroxide to water and oxygen. All of these studies carried out the enzyme treatment of pulp at pH 5, which is recognized as the optimum for the activity of these enzymes. Social factors like poverty, literacy, corporate spending are the factors behind low level consumption.
The following relationship between AOX production and bleaching chemical usage has been recognized:.
US5591304A – Method for the use of enzymes in bleaching paper pulp – Google Patents
In addition, the new strain KW3 shows a resistance towards crystal violet which is considered atypical for Thermomonospora fusca. In the enzymatic process, cellulase and hemicellulase enzymes are mixed with the paper pulp. Induction, isolation and testing of stable Trichoderma reesei mutants with improved production of solubilizing cellulase. Hemkcellulases of the finite time for diffusion of acid into the fibers, the pH rises over time.
Bleaching pulp with an enzyme system, containing thermostatic xylanose activity, blecahing from a strain of Thermomonospora fusca and more specifically from a new strain with the designation KW3 and deposition number DSM bleacjing The influence of pH on enzymatic reactions may involve several different types of effects. To achieve this low cellulase activity the xylanases have to be either separated from cellulases by e.
The C and E bleaching stages reduce the lignin content of the pulp to less than 0. The optimum pH for the xylanase enzymes is determined by isolating the substrate for the enzyme, in this case xylan, and measuring the ability of hemixellulases enzyme to hydrolyze it in a dilute buffer solution. In the subsequent testing, pulp was used that had been allowed to sit and have its pH equilibrate, as well as pulp that had just had acid added to it. The method of claim 5 wherein henicellulases black liquor is mixed with the acid or base and added to the delignified wood in step b.
The present inventors have discovered hemiceplulases, contrary to all expectations, in the Kraft brownstock that has not been fully washed, and contains residual dilute black liquor i. The same procedure showed 4 mannanase isoenzymes. Dekker, Biotechnology and Bioengineering, vol.
An example of such a strain is T.
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Topics Discussed in This Paper. A process according to claim 1 wherein the pulp is chemical pulp. A xylan substrate was made using oat spelt xylan from the Sigma Chemical Co. As a result, the preferred pH for enzyme treatment is significantly higher than the enzyme’s optimum pH for hydrolysis. Operating pulp mills must make compromises between the costs and hemiceolulases of washing.
The resulting pulp was further bleached chemically using the following sequence under standard conditions: The laccase is used for direct delignification of pulp, enabeling replacement of current bleaching chemical stages such as oxygen or ozone stage. Enhanced bleaching by enzymes is quantified by the increased brightness of enzyme-treated pulp after pulpp relative to pulp bleached without enzyme treatment.
It is preferred in the practice of this invention that the specific cellulase content of the enzyme preparation contemplated be very low so that not more than about 10, FPU of cellulase activity is added per ton of pulp see Examples 1 and 2and more preferably about 2, FPU or even about FPU or less per ton of pulp.
Bark of wood is removed. The following relationship between AOX production and bleaching jn usage has been recognized: High-level of xylanase production by the thermophilic Paecilomyces themophila J18 on wheat straw in solid-state fermentation.
The present inventors have further discovered that dilute or weak black liquor, which might previously have been expected to be harmful to enzyme action, can be used as a buffer solution and mixed with acid and enzyme for simultaneous addition to the brownstock.
The total enzyme system produced by T. Preferably, the incompletely washed pulps should have a residual soda in pulp of between 1 and 50 kg per ton of pulp. Cellulases are used to improve rates of ih of pulp; and pectinases for digesting pectins.
A further embodiment of this invention, as it may be applied to a mill with a flow sheet as outlined in FIG. The caustic charge was 3.
Hemicellulases in the bleaching of chemical pulps.
VTT reported that treatment of pulp hemicellulasee hemicellulases from Aspergillus awamori and Streptomyces olivochromogenes increased the brightness of the pulp after bleaching by up to 5 ISO points Viikari, et al.
In mechanical pulping, debarked logs are forced through rotating toothed steel discs. In this case, 12 micro-liters of the enzyme were added to each 17 g sample of pulp.
Operating at an elevated pH, however, is done at the expense of a significant reduction in the brightness boosting of the xylanase. The preferred enzyme system comprises xylanase. The amount of organochlorines discharged from a pulp mill is closely related to the bleaching process used and, in particular, to the amount of chlorine used for bleaching.
While the brownstock contemplated herein should be at least partially washed, this invention is particularly concerned with providing an effective means for treating incompletely washed pulps, as for example pulps that still have a residual soda level of 1 Kg per ton or greater. The discs tear the logs and remove the lignin.