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).
|Published (Last):||18 March 2011|
|PDF File Size:||8.36 Mb|
|ePub File Size:||16.75 Mb|
|Price:||Free* [*Free Regsitration Required]|
Process for acid bleaching of lignocellulose-containing pulp with a magnesium compound. At this point, the fibers are in a solution of dissolved lignin and pulping chemicals, called dilute hemmicellulases weak black liquor.
Enzymes, like other proteins, are ampholytes and possess many hrmicellulases groups. This is applied before carrying out the normal mechanical or chemical pulping.
The suspension was vacuum-filtered and the filter cake was washed with ml deionized water to remove all the soluble xylan.
US5591304A – Method for the use of enzymes in bleaching paper pulp – Google Patents
The pulp should have a residence time of preferably over one hour in this brownstock storage tank. Use of enzymes can modify the bemicellulases material.
A further preferred enzyme system also contains mannanase and other enzymatic components of T. In fact, it has such a strongly positive impact that it almost completely, and unexpectedly, cancels out the well known negative effects of increasing pH beyond the optimum level of performance for the enzymes. The culture supernatant was harvested by centrifugation rpm, min. The following relationship between AOX production and bleaching chemical usage has been recognized: In fact, the preferred optimum is in a range normally believed to lead to rapid enzyme inactivation.
From This Paper Topics from this paper. Pulp bleaching process comprising oxygen delignification and xylanase enzyme treatment. Keywords Biotechnology, Pulp and paper industry, Water recycling Introduction Indian paper industry contributes to about 2.
Thermostable and alkaline-tolerant microbial cellulase-free xylanases produced from agricultural wastes and the properties required for use in pulp bleaching bioprocesses: This, in turn, leads to a significantly reduced chlorine requirement to bleach pulp.
If nemicellulases function depends on certain special groupings, these may have to be present in some instances in the un-ionized state and, in others, as ions. Social factors like poverty, literacy, corporate spending are the factors behind low level consumption. A method to improve the bleachability of wood pulp obtained by standard pulping processes that produce incompletely washed brownstock of more than 1 Kg soda per ton of pulp, comprising treating said brownstock at a pH range of approximately 7.
Hydroxide bleachiing may be combined with hydrogen peroxide E P or oxygen E o.
The procedures were as described in Example 5, except the initial multistage water washing was omitted. Equilibrium pH is reached after roughly 90 minutes. Also, a method and apparatus for treating wood pulp containing incompletely washed brownstock in which the brownstock is treated at a pH range of approximately 6. In the bleaching process chemical pulp is then routinely reacted with chlorine and other delignifying chemicals to further remove lignin and then reacted with bleaching agents to modify the lignin from pulp, whereby providing a stably brightened pulp.
A ReviewTappi J.
Hemicellulases in the bleaching of chemical pulps. – Semantic Scholar
The brownstock slurry should be mixed, for example with a mixing pump, to ensure uniform distribution of enzyme and then held in a storage tank or line for a period of at least 15 minutes, and preferably at least 1. Enzymes differ most strikingly from ordinary chemical hemicellulaases in their substrate specificity and catalytic efficiency.
Sodium hydroxide is added to the pulp to remove the residual reaction products that were not solubilized in the acidic chlorination stage but readily dissolve in an alkaline medium. Enzymatic bleachiny are catalytic, highly selective, and operable under mild temperature and pressures. Biotechnology-based processes for paper industry should reduce the bleacihng costs of pulp production, generate higher value fiber resources, lower total manufacturing costs and make it commercially feasible.
We can only speculate that several complex factors are working together to cause this effect.
Oxygen bleached spruce Kraft pulp with a Kappa number of Xylanase activities of around 5 Ul -1 and mannanase activities of around 1 Ul -1 were obtained for cultures grown on oat spelt xylan and 3 Ul -1 and 0. To avoid these problems, hemicellulased liquor was squeezed out of a sample of the pulp and the pH of this liquor measured. While the well washed samples of brownstock used in hemidellulases laboratory testing had residual soda levels below 1 Kg per ton, one often finds residual soda levels ten times this high in operating mills.
The results are shown in FIG. Although lignin is present in lower grades of paper such as newsprint, complete lignin removal is essential for the production of fine paper.
The enzymes of Bemicellulases.
While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification and that this application is intended to cover any variation, uses or adaptations pu,p the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth pup as fall within the scope of the invention.
Process for treating hardwood pulp with an enzyme mixture to reduce vessel element picking. Unfortunately, the effluent from this chlorine-based bleaching process contains several classes of toxic compounds, namely organochlorines.
After adding 5 ml of H 2 O the absorption was measured at nm. In addition, the new strain had the following biochemical properties typical for Thermomonospora fusca: This is the complete opposite of what it does at the normally preferred conditions of operation for enzyme treatment. Treatment of mechanical pulps with enzymes for improved drainability EP Karsila et al. Biotechnology can play a leading role, including: Hemicellklases slurries are so thick as to make pH measurement by the usual method i.
It has been found, in accordance with this invention, that the enzyme systems of Thermomonospora strains comprising at least one hemicellulase acting enzyme can be used to selectively treat a variety of pulps at a high temperature and under alkaline conditions, whereby the lignin content is reduced while the cellulosic content of the pulp remains substantially unaffected.
Such extractants essentially solubilise the affected lignin component and suitable extractants include but are not limited to bases such as alkali metal hydroxides EDMF, dioxane, acetone, and alcohol.
The procedures of Example 7 were carried out, except the pulp was treated with enzyme immediately after the addition of the sulfuric acid. Genetically engineered microorganisms and enzymes can displace many of the environmentally adverse practices used in pulp processing http: Xylanase focuses in a band corresponding to an isoelectric point pI of 9.
Making pulp using enzymes Biopulping Biopulping is the treatment of wood chips with lignin- degrading hemicelluulases. It also improves the runnability of the pulping, bleaching and papermaking processes.