JP3534412B2 - Method for removing hexenuronic acid groups in cellulose pulp by heat treatment - Google Patents

Description

The present invention relates to a method for treating cellulose pulp according to claim 1.

Pulp mills have recently tended to abandon the use of elemental chlorine and partially chlorine dioxide. The reason is due to both environmental protection and market factors. Disadvantages caused by elemental chlorine include both significant offensive gas emissions from the chemical pulp industry and liquid effluent to the water system. Primarily for impact on water systems, chlorine dioxide does not cause such large-scale malodorous defects. Comparing these chlorine chemicals with the AOX number, which determines the burden on the water system, shows that elemental chlorine is many times more harmful than chlorine dioxide.

In addition to chlorine and chlorine dioxide-based methods, numerous chlorine-free bleaching methods have been developed over the last few years. For example, oxygen, ozone and peroxides have been used in these methods. However, methods using chlorine dioxide are also widely practiced in many countries, and they may be related to environmental problems as well. There are various reasons why it is widely used. The price of chlorine dioxide is very competitive compared to the prices of other chemicals, and today it is, for example, about half the price of competing peroxides. Also, the strength and whiteness achieved by dioxide bleaching are good, in fact at least about the same as with peroxides at the same chemical consumption (kg / adt).

If the bleaching of cellulose pulp is carried out on the basis of bleaching chemicals such as oxygen, peroxides or ozone, the removal of heavy metals forms an essential processing step. Hazardous metals include manganese, copper and iron, which have a deleterious catalytic reaction on pulp quality. They degrade bleaching chemicals, which reduces bleaching efficiency and increases chemical consumption. In cellulosic pulp, heavy metals are mainly bonded to carboxylic acid groups.

It has been proposed to carry out the metal removal in such a way that the pulp is pretreated with an acid, for example sulfuric acid, before the requisite bleaching step. Published FI patent application 76134 (CA 1206704)
Describes that the acid treatment is carried out at a temperature of at least 50 ° C., preferably 60-80 ° C. and a pH of 1-5. Although acid treatment at lower temperatures results in fairly good removal of harmful metal ions in the literature, acid treatment at temperature in the literature modifies lignin and, as a result, acid treatment is followed by alkaline peroxidation. It has been stated that oxide treatment significantly improves its dissolution [Lachenal].
D. Others, 1982 Tappi Pulp Bleach International Conference, Proceedings,
Pp. 145 to 151] As described above, while the acid treatment step reduces the Kappa number in the peroxide treatment step, no reduction in the Kappa number has been found in the acid treatment step. Literature FI
76134 also states that theoretically the acid treatment can be carried out at a temperature of 100 ° C. but this will result in poor quality pulp.

In EP patent application 511695 it is proposed that after acid treatment a metal ion such as magnesium ion, which favors peroxide bleaching, should be added. This is because a part of these metals is also removed by the acid treatment. According to this document, acid treatment is 10-95 ° C, most preferably 40-80 ° C.
At a temperature of 1 to 6, most preferably at a pH of 2 to 4. The acid treatment is followed by the step of adding the appropriate alkaline earth metal. It is further stated that the acid treatment allows the pulp to be treated with a suitable bleaching chemical such as chlorine dioxide and / or a delignification chemical.

Removal of harmful metals can be made more effective by using chelating agents to bind the metal in connection with acid treatment. One such method is SE Patent 5016.
51, which has the same acid treatment as in the above-mentioned EP511695 publication, except that the acid treatment is performed in the presence of a chelating agent. However, the chelating agents used to bind the metal serve to increase the bleaching cost.

The main purpose of the acid treatment of the pulp described above is to achieve a favorable metal composition for chlorine-free bleaching chemicals. At these stages the Kappa number may be reduced by 1-2 units due to washing and extraction phenomena. As previously mentioned, the composition of the metal affects the consumption of bleaching chemicals and the reason for using the known acid treatment step is therefore to remove the metal from the pulp.

One of the most important drawbacks of conventional bleaching is that the consumption of bleaching chemicals, especially those free of chlorine, is rather high, which considerably increases the production costs of bleached pulp. Bleaching with chlorine dioxide also requires attempts to reduce the consumption of the chemical for both economic and environmental reasons. Furthermore, the occurrence of, to some extent, a large degree of whiteness reversion is a typical feature of oxygen and peroxide bleached pulp.

The object of the present invention is to eliminate or minimize the disadvantages of the prior art process by allowing cellulosic pulps, in particular cellulosic pulps produced under alkaline conditions, to be treated with bleaching chemicals containing no chlorine or chlorine dioxide which is still important for pulp bleaching. To achieve a completely new composition for bleaching. A further object of the invention is to produce cellulose pulp which is easily bleached, for example with oxygen and / or peroxide.

Cellulose pulp is known to contain a 4-O-methyl-α-D-glucuronic acid group (glucuronic acid group). According to our recent findings, sulphate pulp has, in addition to the glucuronic acid groups, a significant amount of 4 bound to xylan.
It also contains a -deoxy-β-L-threo-hexe-4-enopyranosyluronic acid group (hexeneuronic acid group).
The amount of these groups is even higher in some pulps than the known amount of glucuronic acid groups.

When bleaching pulp, hexenuronic acid groups have been found to consume electrophilically reacting bleaching chemicals such as chlorine, chlorine dioxide, ozone and peracids [Buchert et al. 3rd European debate on lignocellulosic compounds and pulp (Stockholm, 28-31 August 1994). However, the hexenuronic acid groups do not affect the consumption of oxygen and hydrogen peroxide used as bleaching chemicals in alkaline conditions. Because they do not react with such chemicals. Therefore, oxygen and / or peroxide bleaching does not result in the decomposition of hexenuronic acid groups. Instead, a particular problem with acid and / or peroxide bleached pulps is that they have a relatively low whiteness and / or such pulps tend to undergo whiteness reversal.

Based on what has been stated above, our invention contemplates that the consumption of bleaching chemicals can be reduced by the selective removal of hexenuronic acid groups from cellulose pulp in connection with bleaching. Is based. At the same time, it was completely unexpected to discover that the tendency of pulp brightness reversal decreased. Also, bleaching becomes more selective because heavy metals can be removed more effectively.

  The features of the invention will be apparent from the appended claims.

The above selective removal of hexeneuronic acid groups according to the present invention adjusts the aqueous suspension of cellulose pulp to be slightly acidic, typically setting the pH to about 2 to about 5, and further adding the aqueous suspension. Is performed at an elevated temperature. For preferred results, the temperature is at least 85 ° C, most preferably at least 90 ° C. The use of such high temperatures has been avoided in conventional acid treatments. This is because it was estimated that the quality of pulp would be poor. The main purpose of the acid treatment was to remove harmful metals. In the acid treatment described above, the purpose is to remove the metal and temperature does not play a significant role. The important point is that the pH of the pulp is low so that the metal separates from the fiber. In the laboratory, processing is typically done at room temperature. In the factory, metal removal is typically carried out in the temperature range of 60-85 ° C, which is the temperature prevailing in the acid treatment stage due to the circulation of water. If for some reason you want to do acid treatment at a higher temperature in the factory,
The acid treatment step would have to be heated separately, such as with steam. This was naturally avoided because it was presumed to degrade the strength properties of the pulp, and therefore, according to what was previously known, 85
There was no reason to use a high temperature acid treatment step above ° C. The high temperatures referred to in the prior art (eg FI 76134) merely mean that metal removal is possible even at those high temperatures.

As long as the treatment time is long enough, typically longer than 10 minutes, it does not play a significant role in terms of metal removal. The extra time is not detrimental to metal removal, but of course results in extra factory cost. This is because long processing times require the use of larger tanks. Large tanks have also been avoided. This is because the strength characteristics of pulp could be adversely affected by the acid treatment step. Therefore, the long treatment times associated with acid treatment steps as referred to in the prior art only mean that the long treatment times do not have a detrimental effect on metal removal.

Especially in factory conditions, it is long and high temperature (for example, 2-3
It should be noted that there was a clear reason to avoid acid treatment (85 ° C in time). The above-mentioned reasons are very important since prior to the present invention it has not been discovered that this type of treatment can reduce the Kappa number of the pulp by 2-9, preferably 3-6. This was not discovered even in laboratory experiments. Because all this thought was regarded as contrary to all the existing knowledge. Particularly surprising is the deterioration of the strength properties of the pulp if the Kappa number of the pulp to be treated has been reduced significantly by steaming or possibly further delignification, i.e. below 24, preferably below 14. That is, it is possible to perform such an acid treatment without causing it. Acid (stage A)
It must also be taken into account that pulp treatment with both chelators and chelating agents (stage Q) has been investigated in great detail in the last 5 years in relation to the peroxide stage. Therefore, it is quite surprising to propose a long high temperature acid treatment step, under the circumstances where both high temperature and long time are considered as detrimental factors for acid treatment of pulp, even when used separately. Is new.

The pH with known acid treatments is rather low, for example to lower the manganese content of the pulp considerably, i.e. from 1.5 to
It should also be noted that it must be 2. Two
In the lower pH range, the carboxylic acid type groups will be fully protonated, resulting in low metal levels. pH2
At ~ 6, the metal ion competes with the hydrogen ion for carboxylic acid sites, resulting in an increase in metal content as the pH increases. [Devenyns J. Others,
1994 Tappi Pulp Manufacturing Conference, Proceedings, pp. 381-388
Bouchard J. et al., 1994 International Conference of Pulp Bleaching, pages 33-39]. On the other hand, in the method of the present invention, the carboxylic acid type group (hexenuronic acid) is removed,
This means that the amount of carboxylic acid sites is reduced and the pulp is less occupied by the metal.

According to the present invention, bleached cellulose pulp can be easily produced by the sulfate method of bringing hexenuronic acid into pulp or an equivalent alkaline method. The characteristic of the pulp produced according to the invention is that it contains at most a small amount of hexenuronic acid, can be easily bleached without using chlorine (ECF) or chlorine chemicals (TCF), and is simply oxygen gas. And / or can be easily bleached even with peroxides. The consumption of bleaching chemicals can also be significantly reduced. In addition, the brightness reversal expressed as pc-number (brightness rev
An ersion) of less than 2 is typical of pulp produced by this method.

According to the present invention, the treatment of pulp in water suspension carried out under acidic conditions at a temperature of at least 85 ° C. will be referred to as “acidic pretreatment”
Also called.

According to the present invention, the cellulose pulp is treated in the presence of water at a temperature of at least 85 ° C. at a pH in the range of about 2 to about 5 (typically a pH in the range of 2 to 5). Remove the hexenuronic acid group from. It is particularly preferred to maintain the pH value of the aqueous suspension of cellulose pulp at 2.5-4. The lowest pH value (2.5-3.5) is preferred for conifers and the highest pH value (3-4) is preferred for hardwood.

Various acids-inorganic acids, for example mineral acids such as sulfuric acid, nitric acid, and hydrochloric acid, and organic acids such as formic acid and / or acetic acid-to set the pH value for slush pulp Can be used. If desired, use formate (formia) to keep the pH as constant as possible during processing.
These acids may be buffered with salts of acids such as te). The temperature can vary from 85 ° C to above. The temperature is preferably maintained at about 90-110 ° F. If the treatment is carried out under atmospheric conditions, 100 ° C is the natural maximum. Higher temperatures are possible if a pressure vessel is used. In this way, the temperature is 200-500 at the temperature of 100-130 ℃.
It may be carried out in a bleaching tank at a pressure of kPa. The upper temperature limit is usually set at about 180 ° C to avoid excessive degradation of the fibers.

The time of treatment varies according to pH value, temperature and the material to be treated. Of course, it also depends on how completely you want to remove hexenuronic acid. Generally, the processing time is at least t minutes, and t = 0.5exp (10517 / (T + 273) -2.
4), [t = 0.5e ^{(10517 / (T + 273) -24} ].
(° C.) is the temperature of acid treatment. The decomposition of the hexenuronic acid group follows the first-order reaction rate. Reaction rate constant k and temperature T
The relationship between (K) is k = Ae- ^{E / RT} (Arrhenius relationship) (where A is the constant due to the reaction in question, E is the activation energy, and R is the gas constant). Is known to be. On the other hand, for the first-order reaction, the reaction time is t = (1 / k) ln (c ₀ / c), where c is the concentration of hexenuronic acid and c ₀ is the initial concentration. It has been known. Arrhenius equation and t = (1 / k) l
By using n (c ₀ / c) and the test results (eg, Example 8 below), t = 0.5exp (10517 / (T + 273) −2
The formula of 4) was obtained. Generally, t is 5 minutes to 10 hours. In the examples described below, the treatment was carried out at atmospheric pressure conditions. Typical processing time at a temperature of 90 ° C is 1.5 to 6 hours, about 50 minutes to 5 hours at 95 ° C, about 0.5 to 100 ° C.
45 hours. Under pressure, for example at temperatures of 120 to 130 ° C., the treatment typically takes place within about 5 to 50 minutes.

The present invention provides for as much hexenuronic acid moiety as possible,
It is preferably at least 50%, particularly preferably at least about 75%, and most suitably at least about 90%. The concept `` the pulp contains at most a small amount of hexenuronic acid '' means that the amount of hexenuronic acid is up to 50% in the amount present after cooking in the corresponding untreated pulp, particularly preferably up to 25%. %, Most suitably up to 10%.

To prevent excessive degradation of carbohydrate substances, one usually does not try to completely remove hexenuronic acid groups.

The treatment may be carried out in the flow reactor as a continuous treatment or as a batch treatment. The pulp is treated in the presence of water, in other words, the pulp received from the pulp cooking process is slushed into water, and the consistency of that slush in the pretreatment according to the invention.
Is about 0.1 to 50%, preferably about 1 to 20%. Mixing is preferred for pretreatment. For continuous mixing, a static mixer can be used.

The arrangement according to the invention can be applied to pulps produced by the sulphate method or other alkaline methods and containing hexeneuronic acid groups.

The term "sulfate method" means a cooking method in which the main cooking chemicals are sodium sulfide and sodium hydroxide. Other alkaline cooks include, for example, long-term cooks based on continuing conventional sulfate cooks until the Kappa number of the pulp drops below a value of about 20. These methods typically include oxygenation. The long-term steaming method includes, for example, long-term batch steaming (+ AQ), EMCC (long-term modified continuous steaming), batch steaming, and super batch (Super-Bat).
ch) / O ₂ , MCC / O ₂ , and continuous steaming / O ₂ . In our experiments, hexenuronic acid forms about 0.1-10 mol% of the hydrolysis product of xylanase treatment of softwood pulp obtained from the above cooking process. After pretreatment according to the present invention, the concentration of hexenuronic acid is reduced to about 0.01-1 mol%.

In the present application, the term "in connection with bleaching" means that the acidic pretreatment is carried out before bleaching, during bleaching and at the latest after bleaching. When an electrophilically reacting substance such as chlorine, chlorine dioxide, ozone or peroxide is used as the bleaching chemical, it is particularly preferable to carry out a pretreatment before bleaching. This is because the consumption of bleaching chemicals can be reduced in this way. Characteristics of cellulose pulp,
For example, it can be said that the unbleached pulp is subjected to the treatment in order to change the bleaching property. On the other hand, when oxygen gas and / or peracid is used for bleaching (bleaching treatment), the pretreatment can also be performed after bleaching. In the latter case, the treatment is preferably carried out immediately after bleaching and before any possible drying of the pulp (ie undried pulp). The pretreatment may be performed between the bleaching stages of the continuous bleaching process.

Next, examples of suitable bleach successive steps: A-O-Z-P AQ-O-Z-P A-O-ZQ-P A-O-P n AQ-O-P n O-A- Z-P O-AQ-Z-P O-A-ZQ-P O-A-P _n O-AQ-P _n O-A-D-E-D O-AD-E-D A-O-D -E-D O-A-X- _Pn A = Acid pretreatment according to the invention at elevated temperature O = Oxygen treatment P = Peroxide treatment _Pn = Several subsequent peroxide treatment steps E = Alkali stage Z = Ozone treatment (ZQ means that the complexing agent was added by ozone treatment) Q = Complexing agent treatment (AQ means that the complexing agent was added by acid treatment) D = Chlorine dioxide treatment (AD means not washed between steps) X = Enzymatic treatment An alkaline step may be included between the bleaching steps with oxygen chemicals. Known enzymes such as cellulases, hemicellulases, and lignases may be used to make the bleaching more effective.

The pretreatment according to the invention may be carried out during the continuous bleaching process, before the oxygen or peroxide stage, or after, but in the chlorine dioxide stage,
It is performed prior to the ozone stage or the peracid stage (eg, formic acid or peracetic acid stage) to reduce ozone and / or peracid consumption. Since the bleachability of the pulp can be improved by pretreatment, the present invention can decisively reduce the consumption of said bleaching chemicals, and / or chlorine dioxide, ozone in bleaching, previously The use of peracid can be omitted.

Many chemical processes for producing chemical pulp have an oxygen delignification step as the last step. Treatment may occur before or after this oxygen stage, preferably after the oxygen stage. In bleaching hardwood pulp, chlorine dioxide consumption is reduced by 30-40% at ISO whiteness of 88% when the bleaching continuous process is O-A-D-E-D. Bleaching softwood pulp has a corresponding reduction in consumption of 10 to 20%. In both cases, the yield is almost unchanged compared to bleaching without stage A. Furthermore, experiments have shown that step A, which follows step A, may be carried out without washing between them, so in other words the process sequence is O-AD-E-D. become.

In a chlorine-free bleaching continuous process involving a bleaching step with an electrophilic bleaching chemical, for example ozone or peracid,
It is preferred that the oxygen treatment be carried out before the first stage Z, preferably in such a way that the pulp is washed before going to stage Z to ensure the effective removal of hexenuronic acid from the pulp. The savings in ozone consumption produced by hexenuronic acid (HexA), and thus the chemical consumption achieved by the method according to the invention, take into account that hexenuronic acid consumes 1 equivalent of ozone (1 equivalent O ₃ / HexA). Can be calculated theoretically. Typically, the consumption savings are 1-3 kg O _{3 /} t pulp. In the acid treatment, the furan derivative formed from hexenuronic acid consumes twice as much ozone, so it is preferred to wash the pulp as effectively as possible after the acid treatment and before the bleaching step. The above is true for all peracetic acid, persulfuric acid, and all other chlorine-free electrophilic bleaching chemicals such as peroxomolybdate.

The reduction in the consumption of bleaching chemicals by acid treatment is due to the fact that removal of hexenuronic acid reduces the amount of reactive acid groups during bleaching, and thus less material to be bleached.

According to one preferred embodiment, the main bleaching chemical used is a peroxide containing material (usually hydrogen peroxide). For example, it is possible to produce a pulp having a tendency of whiteness reversal less than 2, expressed as a pc-number. The whiteness inversion tendency cannot be effectively prevented except by removing hexenuronic acid. Since the harmful heavy metal concentration can be reduced even by the acid treatment according to the present invention, it is preferable to perform the acid treatment before the first P step.
Most suitably, the peroxide treatment involves an oxygen gas pretreatment.

The pH of slush pulp treated with oxygen is initially about 3
Set to a value of ~ 4, raise the temperature of the pulp to 90-130 ° C and maintain at that temperature for at least 5 minutes, then treat with hydrogen peroxide under alkaline conditions to produce a bleached pulp . Instead of hydrogen peroxide, the peroxide-containing substance may be, for example, Caro's acid or a substance equivalent thereto, which decomposes under suitable conditions to form hydrogen peroxide or peroxo ions (eg alkaline conditions).

In order to remove the heavy metals bound to the cellulose pulp, the pretreatment according to the invention may be carried out with a chelating agent which binds the heavy metals. EDTA and DTPA can be mentioned as examples of these chelating agents. Generally, the chelating agent is introduced into the pulp at a rate of about 0.2% of the pulp. However, one particular advantage of the acidic pretreatment according to the present invention is that, as described in Example 10, it is possible to remove the metal effectively without the treatment with a chelating agent. be able to.

Acidic pretreatment changes the properties of paper quality,
It can also be carried out on bleached or unbleached pulp. For example, removal of acid groups can reduce the water holding capacity of the pulp, thereby producing, for example, a relatively stiff pulp suitable for use in packaging boards.

The invention and its aspects are described in detail below by means of examples.

FIG. 1 is a graph illustrating the influence of acidity on the hydrolysis rate of arabinose acid groups and hexenuronic acid groups of pine sulfate pulp at a temperature of 80 ° C. The points obtained in the experiment fit the theoretical curves according to the formulas illustrated in Example 2, respectively.

FIG. 2 illustrates the temperature dependence of the time required to remove hexenuronic acid groups in the range 80-140 ° C. for birch sulfate pulp treated with an acid at pH 3.5. The reaction rate is almost maximum at this pH. At higher pH values, the holding time at a given temperature will be longer. The upper three curves are 95 of the hexenuronic acid group,
It illustrates the optimum operating range when 90 and 80% are removed. The dotted line illustrates the minimum maintenance time when 50% of the hexenuronic acid groups are removed.

In the examples, the Kappa number of pulp is standard SCAN-C 1:77.
Viscosity according to standard SCAN-CM 15:88.
Accordingly, the whiteness is determined according to the standard SCAN-C 11:75. The tendency of whiteness inversion is the dry heating method (24 hours, 10
5 ° C). The pc-number was calculated from those results.

Example 1 4-O-methylglucuron oxirane isolated from hardwood was treated in a 1M sodium hydroxide solution at a temperature of 160 ° C. for 2 hours. The xylan was precipitated from the liquid by cooling the liquid and adjusting the liquid to neutral. The precipitated xylan was washed, dried and then treated with endoxylanase. The hydrolyzed material was fractionated using anion exchange chromatography and gel filtration. The oligosaccharide moiety is thus isolated, which contains 4-deoxy-β-L-threo-hex-4-eneuronoxylotriose (80%) and -tetraose (20%) by NMR spectroscopy. It was discovered.

A portion of the oligosaccharide liquid was placed in deuterium oxide
Dissolved in 10 mM acetate buffer (pH 3.7). The liquid is N
Put in MR tube, change in it for ¹ hour at 80 ℃ for ¹ hour
Followed by NMR spectroscopy.

Decomposition of the hexenuronic acid group followed a first-order reaction.
The conversion rate was 55% at the reaction time of 17 hours. No hydrolysis of the xyloside bond was found. When the hexenuronic acid group decomposes, almost equivalent compounds are generated, and these compounds are furan-2-carboxylic acid (δ _H3 = 7.08 ppm, J
_{H3, H4} = 3.5 Hz, J _{H4, H5} = 1.7 Hz, J _{H3, H5} = 0.8 Hz) and formic acid (δ _H = 8.37 ppm). Furthermore, 2
-Furaldehyde-5-carboxylic acid (δ _H3 = 7.13 ppm,
A small amount of components identified as δ _H4 = 7.52 ppm, δ _CHO = 9.60 ppm, J _{H3, H4} = 3.5 Hz) was generated.

According to this example, the hexene uroside bond can be selectively hydrolyzed under mild conditions without significantly hydrolyzing the xyloside bond. Correspondingly,
It can be concluded that the glucosidic and mannosidic bonds of cellulose and glucomannan are stronger than those of xylan and are stable under these conditions.

Example 2 Pine sulphate pulp (Kappa number 25.9) was incubated in buffer (pH 1.5-7.8) for 2 hours at different temperatures (25, 50 and 80 ° C). Following the treatment, the pulp sample was washed with water. The washed pulp was treated with xylanase and the hydrolyzate was analyzed by ¹ H NMR spectroscopy.

Changes in the carbohydrate content of pulp were found only at the highest temperature used (80 ° C). Unlike normal hydrolysis of glucosides, hydrolysis of hexenuronic acid groups is not directly proportional to hydronium ion concentration (Equation 1), but the pH dependence of reaction rate is caused by free hexenuronic acid groups in the absence of catalyst. The reaction clearly showed that it was carried out by the hydronium ion (Equation 2, FIG. 1).

(1) κ = κ _Q [H ₃ O ⁺ ] (2) κ = κ _Q {1 / (1 + K _a / [H ₃ O ⁺ ]} According to this example, the hexeneuronic acid group of the cellulose pulp is slightly acidic. It can be selectively removed at elevated temperature under conditions (pH> 2) .The partial hydrolysis of the arabinose group occurs, which results in a decrease in yield due to the low concentration of arabinose in the cellulose pulp. Especially smaller (1% for softwood pulp, 0 for hardwood pulp)
%).

Example 3 An oligosaccharide solution (15.5 mg, 0.025 mM) was added into a boiling 0.01 M formiate buffer (pH 3.3, 27 ml). The liquid was refluxed for 3 hours. Samples (0.5 ml) were taken at appropriate time intervals and diluted with water (5 ml). 200 to absorb light
It was measured in the wavelength range of 500 nm. The formation of furan-2-carboxylic acid (λ _max = 250 nm) followed a first-order reaction (κ =
0.44h ^-1 ). The molar absorptivity calculated per unit amount of hexenuronic acid groups was 8,700. This absorbency value can be used to determine the hexenuronic acid concentration of the cellulose pulp.

Example 4 An oligosaccharide mixture (2.0 mg, 3.22 μM) was dissolved in water (4.8 ml). 0.6 ml of 2M sulfuric acid and 0.6 ml of 0.02M potassium permanganate (12.0 μM) were added to the liquid. Ten
In minutes 0.12 mM 1 M potassium iodide and 100 ml water were added to the liquid. The iodine concentration of the liquid was determined by a spectrophotometer (350 nm, ε = 16,660). The permanganate ion consumption was calculated based on Equation 3.

(3) 2MnO ₄ ⁻ + 10I ⁻ + 16H ⁺ → 2Mn ²⁺ + 5I ₂ + 8H ₂ O The consumption of permanganate ion was 7.98 μM, that is, 2.5 per 1 mol of hexenuronic acid group. Since the determination of the Kappa number used to describe the lignin concentration of cellulose pulp was done under exactly the same reaction conditions, the hexenuronic acid groups may give rise to considerable error with respect to the actual lignin concentration.

Example 5 0.06 M of birch sulfate pulp (3 g, kappa number 16.5)
4 in 100 ml of formate buffer (pH 3.2, 250 ml)
Time processed. Absorption of light (250 nm, ε = 8,7) caused by decomposition of hexenuronic acid group by 2-furan-carboxylic acid
00) tracked by. The total amount of hexenuronic acid groups was calculated to be 70 meq / kg pulp. The Kappa number of the treated pulp was 10.6.

With the present invention, a significant amount of hexenuronic acid groups can be removed from sulfate pulp, which significantly reduces the Kappa number used to represent the degree of delignification.
A similar decrease can be expected to occur with consumption of electrophilic bleaching chemicals that react with hexenuronic acid groups.

Example 6 Pine sulphate pulp bleached with oxygen and peroxide (9 g, Kappa number 5.3) was mixed with 0.06 mol formate buffer (pH 3.2, 60).
0 ml) at a temperature of 100 ° C. for 2.5 hours. Degradation of the hexenuronic acid group was followed by absorption of light (250 nm, ε = 8,700) caused by 2-furan-carboxylic acid.

The total amount of hexenuronic acid groups was calculated to be 48 meq / kg pulp. All hexenuronic acid groups were removed from the pulp with a reaction time of about 30 minutes. The treated pulp was filtered on a Buchner funnel and washed with water. The treated pulp penetrated very easily compared to the original pulp.
The treated pulp had a Kappa number of 2.3. The Kappa number of sulfate pulp bleached with oxygen and peroxide according to the invention was very low after the treatment to remove the hexenuronic acid groups. The treatment according to the invention significantly increases the possibility of producing fully bleached TCF pulp without the use of ozone bleaching.

Example 7 Oxygen-bleached birch sulphate pulp (100 g, kappa number 11.5) was mixed in water (3 liters). PH of suspension
Was adjusted to a value of 3.4 by adding 2 ml of strong formic acid. The suspension thus formed was kept at a temperature of 100 ° C. for 4 hours. 2-furan-
UV absorption caused by carboxylic acid (250 nm, ε = 8,70
0) tracked by. The amount of hexenuronic acid groups removed was calculated to be 54 meq / kg of pulp, which was about 98% of the total amount of hexenuronic acid groups in the pulp. The treated pulp had a Kappa number of 6.2.

Chelation with EDTA (0.2% of pulp) was performed at a concentration of 3.5% for both treated and untreated pulp. The treatment was carried out at a temperature of 60 ° C. and the time was 45 minutes.

After washing, peroxide bleaching (3% of pulp is hydrogen peroxide)
Was performed on a pulp with a concentration of 10%. Magnesium sulphate (0.5% of pulp) was used as stabilizer and sodium hydroxide (1.8% of pulp) was used as alkali. The temperature was 90 ° C and the bleaching time was 180 minutes. Kappa number, viscosity, whiteness, and whiteness inversion tendency (brightness
The reversion tendency (pc-number) was determined for the washed pulp. The properties of the pulp are shown in Table 1.

The results show that the pretreatment strongly influences the action of the peroxide stage pulp. Peroxide consumption has decreased dramatically, nevertheless the increase in whiteness is more than doubled compared to untreated pulp.
The whiteness reversal tendency of the pretreated pulp expressed as pc-number is
It is more than 50% lower than the whiteness reversal tendency of untreated pulp.

Example 8 Unbleached birch sulphate pulp (Kappa number 15.4) was treated with 5% strength formic acid so that the pH of the slurry was 3.0, 3.5 or 4.0. Pulp treated in this way
0.2 at a temperature of 85, 95, 105, and 115 ° C in a 150 ml pressure vessel.
Digested for ~ 24 hours. The dissociation of hexenuronic acid groups was followed by determining the concentration of furan derivatives formed from hexenuronic acid groups in the filtrate. Kappa number and viscosity were determined for digested pulp.

The decrease in kappa number was linearly dependent on the decrease in hexenuronic acid concentration. The maximum decrease in hexenuronic acid concentration was 60 meq / kg, corresponding to a decrease in Kappa number of 6.3 units. When 90% of the hexenuronic acid groups are removed,
The treatment yield was 98% calculated based on TOC. Decomposition of the hexenuronic acid group followed the first-order reaction rate.
The minimum retention time required by the treatment (50% reduction in hexenuronic acid concentration) and the optimal retention time (80-95% reduction in hexenuronic acid concentration) are illustrated by curves fitted to the experimental points (Fig. 2). ). At pH 3.0-3.5, the decomposition rate of hexenuronic acid groups was very close to its maximum value. At higher pH values, the required retention time is longer due to the slower reaction rate.

Example 9 Birch Sulfate Sulfate Pulp Bleached with Oxygen (Kappa Number 10.
3) was treated under the conditions according to Example 8 to remove the hexenuronic acid groups. The Kappa number after the treatment was 5.4. Both acid treated and untreated pulp were bleached in a continuous DED process with several doses of chlorine dioxide and alkali. When bleached to ISO whiteness of 88.0%, acid-treated pulp consumes 2.5% of chlorine dioxide calculated as active chlorine,
1.4% consumption of sodium hydroxide. % Consumption of Corresponding Chlorine Dioxide and Sodium Hydroxide by Untreated Pulp
Were 4.3 and 0.8, respectively. The yield of the DED continuous process is
The acid treated pulp was 97.1% and the untreated pulp was 95.5%. Therefore, the consumption of ECF bleaching chemicals was reduced by 42-43% without reducing the yield of bleaching by removal of hexenuronic acid groups. The specific tensile strength and the specific tear index of the sheets made from these pulps were the same for sheets of the same density.

Example 10 Pine sulfate pulp (100 g, Kappa number 25.9) was mixed in water (3 liters). The pH of the suspension was adjusted to a value of 3.5 by adding 1.5 ml of strong formic acid. The suspension thus formed was digested at a temperature of 100 ° C. for 2.5 hours. Degradation of the hexenuronic acid group was followed by UV absorption (250 nm, ε = 8,700) caused by 2-furan-carboxylic acid. The total amount of hexenuronic acid groups removed is 1 kg of pulp
It was calculated to be 32 meq per unit, corresponding to about 95% of the total amount of hexenuronic acid groups in the pulp. EDTA
Chelation with (0.2% of pulp) was performed on both untreated and treated pulp at a concentration of 3%. The treatment was carried out at a temperature of 50 ° C. and the time was 45 minutes. The metal concentration of the pulp was determined by atomic absorption spectrophotometer.

Treatment to remove hexenuronic acid groups reduced the iron and manganese concentrations in the pulp in particular (Table 2). In this case, the reduction of iron was significantly greater than with the chelation treatment, and even the reduction of manganese was as great as with the chelation treatment.

Iron and manganese are among the most harmful metals for TCF bleaching, and the use of chelating agents can partially or completely replace the treatment to remove hexenuronic acid. If chelating agents are used, it is preferred to add them in connection with the treatment to remove the hexenuronic acid groups.

While the present invention has been described in relation to what is presently considered to be the most practical and preferred embodiments, it is not intended that the invention be limited to the disclosed embodiments, but, within the true spirit and scope of the appended claims. It is to be understood that it includes various modifications and equivalent configurations included in.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Telemann, Anita Finland 02-01 Espoo, Ranatier 7 B 7 (72) Inventor Tenkanen, Mayya Finland 02-03 Espoo, Soukanni Ementier 9 B (56 Reference: Japanese Patent Application Laid-Open No. 4-228690 (JP, A) Japanese Patent Application Laid-Open No. 5-148784 (JP, A) Acid Extraction The He Alkaline Wood Pulps (Kraft or Soda, AQ) Before or During Reaching Bleach. JOURTNA L OF WOOD SHEMISTRY AND TECHNOLOGY, USA, 1993, 13 2), 261-281 (58) investigated the field (Int.Cl. ^7, DB name) D21C 9/00 - 9/16

Claims (11)

(57) [Claims] 1. A method for treating a cellulose pulp having a kappa number lower than 24 produced by an alkaline method, wherein the cellulose pulp is treated at a temperature of 85 to 150 ° C. and a pH of 2 to 5 for a sufficient time, At least 50% of the hexenuronic acid groups in the cellulose pulp are removed, and the Kappa number of the pulp is reduced by 3 to 6 units, but the time is 5 minutes to 10 hours, and at least t (minute) = 0.5e.
^{(10517 / (T + 273) -24)} [where T (° C) is the temperature of the acid treatment] and the treatment is carried out in a continuous bleaching step before the chlorine dioxide step or before the ozone step or before the peracid step. A method for treating cellulose pulp, wherein the method is carried out to reduce the consumption of chlorine dioxide, ozone or peracid, respectively. 2. Cellulose pulp at a temperature of 90 ° C. is 1.5-6.
Treatment for 50 minutes to 5 hours at a temperature of 95 ° C,
The method according to claim 1, wherein the treatment is performed at a temperature of 100 ° C for 0.5 to 5 hours. 3. The method of claim 1 wherein the acid treated pulp is washed prior to the ozone bleaching step. 4. A process according to claim 1, wherein the acid treated pulp is bleached with chlorine dioxide without washing between stages. 5. The method of claim 1 wherein the acid treated pulp is washed prior to the peracid bleaching step. 6. The method according to claim 1, wherein the treatment is carried out at a consistency of 0.1 to 50%. 7. The method according to claim 1, wherein the treatment is carried out at a pH value of 2.5-4. 8. The method according to claim 1, wherein the pH of the cellulose pulp is set by an inorganic or organic acid. 9. The method according to claim 1, wherein the cellulose pulp is treated with oxygen before the treatment. 10. The method according to claim 1, wherein the temperature is 90 to 110 ° C. 11. The method according to claim 1, wherein the alkaline method is a sulfate method.