JP2008266798A - Method for measuring hexenuronic acid content in bleached pulp, method for producing bleached pulp, and method for producing paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring a hexenuronic acid content in bleached pulp, which nondestructively and accurately measures a hexenuronic acid in bleached pulp by ECF bleaching or TCF bleaching in a short time. <P>SOLUTION: The method for measuring a hexenuronic acid content in bleached pulp comprises: using bleached pulp as a measurement sample obtained by using a pulp raw material prepared from lignocellulose to elementary chlorine-free bleaching or totally chlorine-free bleaching until ISO brightness reaches ≥80% and obtaining a hexenuronic acid content from the ultraviolet absorbance of the measurement sample at 230-240 nm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention measures the content of hexeneuronic acid contained in a bleached pulp obtained by subjecting a pulp material prepared from lignocellulose to elementary chlorin-free bleaching (hereinafter referred to as ECF bleaching) or totalary chlorin-free bleaching (hereinafter referred to as TCF bleaching). On how to do.
Moreover, it is related with the manufacturing method of bleached pulp, and the manufacturing method of paper.

When obtaining paper pulp, the pulp material may be bleached with chlorine-based bleaching chemicals such as molecular chlorine, hypochlorite, and chlorine dioxide. Among chlorine-based bleaching chemicals, molecular chlorine has been particularly used because of its high bleaching action, low reactivity with cellulose, and prevention of pulp strength reduction.
However, when bleaching with molecular chlorine, since many organic chlorine compounds having a large environmental load are easily produced as by-products, recently, there is a tendency to shift to a bleaching method that does not use molecular chlorine. As bleaching methods not using molecular chlorine, molecular chlorine is not used, but ECF bleaching using other chlorine-based chemicals and TCF bleaching using no chlorine-based chemicals are known.

 However, pulp obtained by ECF bleaching or TCF bleaching has a problem of fading easily. In recent years, research on the cause of fading of pulp obtained by ECF bleaching or TCF bleaching has progressed, and it has been found that the causative agent of fading is hexeneuronic acid remaining in the bleached pulp. In addition, since this hexeneuronic acid is easily decomposed by molecular chlorine, the amount of hexeneuronic acid in the pulp bleached with molecular chlorine is small, fading is unlikely to occur, and it seems that this was not a problem.

As a method of preventing fading due to hexeneuronic acid, a method of increasing the amount of hexeneuronic acid decomposed by increasing the amount of chlorine dioxide added as a bleaching chemical (see Patent Document 1), acid treatment at high temperature, and acid hydrolysis of hexeneuronic acid And a method for promoting acid hydrolysis of hexeneuronic acid by performing a treatment with chlorine dioxide at a high temperature (see Patent Document 3) and the like.
However, it is difficult to completely eliminate hexeneuronic acid from the bleached pulp by any method. Therefore, it is necessary to control the quality of the pulp by measuring the hexeneuronic acid content in the bleached pulp.

  As a method for measuring the hexeneuronic acid content in the pulp, a method is known in which the pulp is acid-treated at a high temperature to measure furan which is a decomposition product of hexeneuronic acid (see, for example, Patent Document 2). However, this measuring method has a problem that it requires labor and time, and the pulp has to be decomposed, making online measurement difficult.

A method for measuring the content of hexeneuronic acid in pulp in a non-destructive state is also known. For example, Non-Patent Document 1 discloses a method of irradiating unbleached pulp with ultraviolet light and calculating the amount of hexeneuronic acid in the pulp from the absorbance at 232 nm and the absorbance at 280 nm. However, the measurement method described in Non-Patent Document 1 sometimes fails to accurately determine the hexeneuronic acid content.
JP 2003-96680 A Japanese National Patent Publication No. 10-508346 Special table 2004-522008 gazette M. Ragnar, Nordic Pull and Paper Research Journal Vol. 68 no. 1/201

An object of the present invention is to provide a method for measuring the hexeneuronic acid content in bleached pulp, which can measure the hexeneuronic acid content in bleached pulp subjected to ECF bleaching or TCF bleaching in a non-destructive manner in a short time and accurately. To do.
Another object of the present invention is to provide a method for producing bleached pulp capable of producing bleached pulp in which discoloration is prevented and a method for producing paper capable of producing paper in which discoloration is prevented.

  As a result of investigating the reason why the hexeneuronic acid content cannot be obtained accurately even when measuring the ultraviolet light absorbance at 230 to 240 nm, the present inventors have found that lignin is contained in the pulp. It was found that it cannot be measured. Furthermore, it has been found that if delignification is advanced until the ISO whiteness of the pulp reaches 80% or more, the influence of lignin on the absorbance at 230 nm to 240 nm can be eliminated. Based on these findings, the inventors have invented the following method for measuring the hexeneuronic acid content in bleached pulp, a method for producing bleached pulp, and a method for producing paper.

That is, the present invention includes the following aspects.
[1] A pulp raw material prepared using lignocellulose is subjected to elementary chlorin-free bleaching or total chlorin-free bleached pulp until an ISO whiteness of 80% or more is used as a measurement sample.
A method for measuring a hexeneuronic acid content in bleached pulp, wherein the hexeneuronic acid content is determined from an ultraviolet light absorbance at 230 to 240 nm of a measurement sample.
[2] The method for measuring a hexeneuronic acid content in a bleached pulp according to [1], wherein the bleached pulp is in a slurry state.
[3] The method for measuring the hexeneuronic acid content in the bleached pulp according to [1], wherein the bleached pulp is a sheet.
[4] Pulp raw material prepared using lignocellulose is continuously subjected to elementary chlorin-free bleaching or total chlorin-free bleaching until the ISO whiteness reaches 80% or more to continuously produce slurry-like bleached pulp A way to
A collecting step for continuously collecting a part of the slurry-like bleached pulp and a hexeneuronic acid content in the collected slurry-like bleached pulp are continuously measured by the method for measuring a hexeneuronic acid content in the bleached pulp according to claim 2. A method for producing bleached pulp, characterized by comprising a measuring step for measuring automatically and a management step for managing bleached pulp based on the measured hexeneuronic acid content.
[5] The bleaching process according to [4], wherein the bleaching conditions of elementary chlorin-free bleaching or total chlorin-free bleaching are changed so that the hexeneuronic acid content measured in the measuring process falls within a predetermined range in the management process. Pulp manufacturing method.
[6] A method for producing paper, characterized in that the bleached pulp obtained by the method for producing bleached pulp according to [4] or [5] is made under acidic conditions.

According to the method for measuring the hexeneuronic acid content in the bleached pulp of the present invention, the hexeneuronic acid content in the bleached pulp subjected to ECF bleaching or TCF bleaching can be measured accurately in a short time in a non-destructive manner. Therefore, the bleached pulp can be easily managed by measuring the hexeneuronic acid content in the bleached pulp. For example, it can be managed by changing the bleaching conditions so that the hexeneuronic acid content in the bleached pulp is within a predetermined range.
According to the paper manufacturing method of the present invention, paper that is prevented from fading can be manufactured.

<Measurement method of hexeneuronic acid content in bleached pulp>
The method for measuring the hexeneuronic acid content in the bleached pulp of the present invention uses bleached pulp obtained by ECF bleaching or TCF bleaching of a pulp raw material prepared using lignocellulose as a measurement sample, and the hexeneuronic acid content is determined from the ultraviolet light absorbance of the measurement sample. It is a method to seek.

(Pulp raw material)
The pulp raw material can be obtained, for example, by digesting lignocellulose.
Here, lignocellulose refers to cellulose containing lignin, such as a woody material. Lignocellulose is commonly used as a raw material for pulp.
Examples of lignocellulose include hardwood, softwood, non-wood such as bamboo and hemp, and mixtures thereof. Among these, hardwood is preferable in that it contains a large amount of methylglucuronic acid that generates hexeneuronic acid, and the measurement method of the present invention is particularly useful.

  As the lignocellulose cooking method, for example, known cooking methods such as kraft cooking, polysulfide cooking, soda cooking, alkali sulfite cooking and the like can be applied. Among these, considering pulp quality, energy efficiency, etc., kraft cooking method or polysulfide cooking is preferable.

In the case of kraft cooking of 100% by mass of hardwood, the kraft cooking solution preferably has a sulfidity of 5 to 75%, more preferably 15 to 45%. The effective alkali addition rate is preferably 5 to 30% by mass, more preferably 10 to 25% by mass, based on the mass of the absolutely dry wood. The cooking temperature is preferably 130-170 ° C.
By setting it as such conditions, it can fully digest and can suppress the waste of a raw material and energy.

  The cooking method may be either a continuous cooking method or a batch cooking method. When the continuous cooking method is applied, a modified cooking method in which a cooking solution is added at multiple points may be applied, and the method is not particularly limited.

A cooking aid can be used for cooking. As the cooking aid, a known cyclic keto compound, for example, benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone, and a nuclear substituent such as alkyl or amino of the cyclic keto compound, or a reduced form of the cyclic keto compound. And hydroquinone compounds such as anthrahydroquinone. Moreover, as a cooking aid, the 9,10-diketohydroanthracene compound which is a stable compound obtained as an intermediate body of the anthraquinone synthesis method by Diels Alder method is mentioned. A cooking aid may be used individually by 1 type, and may use 2 or more types together.
The amount of the cooking aid added is preferably 0.001 to 1.0% by mass based on the absolute dry mass of lignocellulose. If the amount of the cooking aid added is 0.001% by mass or more per the absolutely dry mass of lignocellulose, cooking can be further promoted. However, even if the cooking aid is added in excess of 1.0% by mass, the effect corresponding to the amount added is not exhibited and only the cost is increased.

(Bleached pulp)
Bleached pulp is obtained by subjecting the above pulp material to ECF bleaching or TCF bleaching.
In ECF bleaching, for example, chlorine dioxide, ozone, hydrogen peroxide, peracid or the like is used as a bleaching chemical without using molecular chlorine.
In ECF bleaching, bleaching can be performed in multiple stages. For example, a chlorine dioxide stage (hereinafter sometimes referred to as D stage or D), an ozone stage (hereinafter sometimes referred to as Z stage or Z), and an alkali extraction stage (hereinafter referred to as E stage or E). ), Oxygen-added alkali extraction stage (hereinafter sometimes referred to as Eo stage or Eo), hydrogen peroxide-added alkali extraction stage (hereinafter also referred to as Ep stage or Ep), oxygen and hydrogen peroxide-added alkali extraction Stages (hereinafter sometimes referred to as Eop stages or Eop), peracid stages such as persulfuric acid and peracetic acid (hereinafter sometimes referred to as Pa stages or Pa), acid treatment stages (hereinafter referred to as A stages or A). A bleaching sequence in which each bleaching stage is combined can be applied. The number of stages to be combined may be appropriately selected according to the purpose. For example, when it is desired to increase bleaching, the number of stages may be increased.
Specific bleaching sequences in ECF bleaching include D-E-D, Z-E-D, Z / D-E-D, D-Eo-D, Z-Eo-D, and Z / D-Eo-D. , D-Ep-D, Z-Ep-D, Z / D-Ep-D, D-Eop-D, Z-Eop-D, Z / D-Eop-D, Pa-D-Ep-D, D -Ep-D-Pa, D-Eop-D-Pa, AD-Eop-D, AZ-Eop-D, AZ / D-Eop-D, etc. are mentioned.

  Chlorine dioxide bleaching conditions, ozone bleaching conditions, ozone / chlorine dioxide bleaching conditions, alkali extraction conditions, oxygen-added alkali extraction conditions, oxygen-hydrogen peroxide-added alkali extraction conditions, and peracid bleaching conditions are not particularly limited. It can be changed as appropriate.

In TCF bleaching, for example, ozone, hydrogen peroxide, peracid or the like is used as a bleaching chemical without using a chlorine-based chemical.
In TCF bleaching, multi-stage bleaching can be performed. For example, a bleaching sequence in which bleaching stages of Z stage, E stage, Eo stage, Ep stage, and Pa stage are combined can be applied.
Specific bleaching sequences in ECF bleaching include Z-Eo-P, Z-Eop-P, Pa-Eop-P, Z / Pa-Eop-P, Z-Eop-Pa, and Z-Eop-Pa-P. Etc.

Bleaching is performed until the ISO brightness is 80% or more. Here, ISO whiteness is whiteness by the diffuse reflection method measured according to JIS P8148. The ISO whiteness can be measured by, for example, a commercially available whiteness meter, a spectrophotometer capable of measuring the ISO whiteness, or the like.
If the ISO whiteness is less than 80%, the amount of residual lignin increases, affecting the ultraviolet light absorbance at 230 to 240 nm, and the hexeneuronic acid content cannot be measured accurately.
In order to increase the ISO whiteness to 80% or more, for example, the amount of bleaching chemical added may be increased, the temperature during bleaching may be increased, or the number of bleaching stages may be increased.

  The bleached pulp preferably has an ISO whiteness of 90% or less, and more preferably 85% or less. When the ISO whiteness of the bleached pulp is 90% or less, a problem of fading is likely to occur, so that the effect of the present invention is further exhibited.

As a form of bleached pulp, a slurry form may be sufficient and a sheet form may be sufficient. However, in order to measure on-line at the time of manufacturing papermaking pulp, it is preferable to measure in a slurry state.
When the hexeneuronic acid content is measured off-line, the bleaching pulp is preferably in the form of a sheet because the measurement becomes easy. In the case of a sheet, it may be in a dry state or a wet paper state.

  Prior to ECF bleaching or TCF bleaching, alkaline oxygen bleaching and washing can be performed. Further, before the alkaline oxygen bleaching, the pulp raw material may be washed, roughly selected, and carefully selected.

Alkaline oxygen bleaching is a process of bleaching with oxygen and alkali.
As the alkaline oxygen bleaching, a known medium concentration method or high concentration method can be applied, but the medium concentration method is preferable from the viewpoint of versatility.
In the medium concentration method, oxygen gas and alkali are added to the pulp slurry with a mixer and mixed thoroughly. Then, the mixture is sent to a reaction tower capable of holding a mixture of pulp, oxygen and alkali under pressure for a certain period of time. Delignify and bleach.
Examples of the alkali used in the alkali oxygen bleaching method by the medium concentration method include sodium hydroxide (caustic soda) or oxidized kraft white liquor.
Examples of the oxygen gas include oxygen obtained by a cryogenic separation method, oxygen obtained by PSA (Pressure Swing Adsorption), and VSA (Vacuum Swing).
The oxygen obtained by Adsorption) can be used.

In alkaline oxygen bleaching in the medium concentration method, the pulp concentration is preferably 8 to 15% by mass. When the pulp concentration is lower than 8% by mass, the volume of the pulp slurry increases and the reaction tower becomes large, which is not suitable. On the other hand, if it exceeds 15% by mass, the load on the reaction mixer increases and the equipment must be made heavy, which is not suitable.
The amount of oxygen gas added is preferably 0.5 to 3% by mass based on the mass of the absolutely dry pulp. An oxygen gas addition amount of less than 0.5% by mass is not suitable because the bleaching effect is reduced. On the other hand, even higher than 3% by mass is not suitable because the bleaching reaction does not proceed any further and becomes uneconomical. The amount of alkali added is preferably 0.5 to 4% by mass per mass of absolutely dry pulp. When the amount of alkali added is lower than 0.5% by mass, the bleaching effect is reduced, which is not suitable. On the other hand, even higher than 4% by mass is not suitable because the bleaching reaction does not proceed further and becomes uneconomical.
The reaction temperature during bleaching is preferably 80 to 120 ° C. A reaction temperature lower than 80 ° C. is not suitable because the bleaching effect is reduced. On the other hand, even if the temperature is higher than 120 ° C., not only the bleaching reaction does not proceed any more, but also the pulp yield is lowered and it becomes uneconomical.
The reaction time is preferably 15 to 100 minutes. If the reaction temperature is shorter than 15 minutes, the bleaching effect is reduced, which is not suitable. On the other hand, even if the time is longer than 100 minutes, the bleaching reaction does not proceed any more and the reaction tower becomes large, which is not suitable.
The alkaline oxygen bleaching is preferably repeated a plurality of times. If alkaline oxygen bleaching is repeated, lignin can be removed and bleached more, and the content of heavy metals can be reduced.

(Measurement of UV light absorption)
The ultraviolet light absorbance of the measurement sample is measured by ultraviolet light of 230 to 240 nm, preferably 232 to 234 nm. Measuring absorbance at wavelengths less than 230 nm or greater than 240 nm is not suitable because it does not correlate with the amount of hexeneuronic acid in the bleached pulp.

The instrument for measuring the ultraviolet light absorbance is not particularly limited, and when measuring bleached pulp in a sheet form offline, a general-purpose desktop spectrophotometer or the like can be used.
When the bleached pulp is in the form of a slurry, it is possible to use a general-purpose online copper valence meter that changes the absorption wavelength to 230 to 240 nm, which measures the absorbance at 280 nm during multistage bleaching. By using a modified version of the copper valence meter in this way, online measurement is possible.

In order to obtain the hexeneuronic acid content from the ultraviolet light absorbance, a calibration curve of the hexeneuronic acid content with respect to the ultraviolet light absorbance is prepared in advance. Then, the ultraviolet light absorbance of the measurement sample is measured, and the hexeneuronic acid content is determined based on the ultraviolet light absorbance and the calibration curve.
Examples of methods for creating a calibration curve include the following methods.
That is, first, three or more types of bleached pulp having an ISO whiteness of 80% or more and different ISO whiteness are prepared, and the ultraviolet light absorbance at 230 to 240 nm of these bleached pulps is measured. Further, water, formic acid, and sodium formate are added to each bleached pulp, and hexeneuronic acid is acid hydrolyzed, filtered, and 2-furanic acid, which is an acid hydrolyzate of senuronic acid present in the filtered solution, and 5 -Carboxy-2-furanaldehyde is quantified by high performance liquid chromatography (HPLC), and the original hexeneuronic acid content is determined from the total molar amount. Then, a calibration curve is prepared by plotting the ultraviolet light absorbance of 230 to 240 nm against the hexeneuronic acid content.

In the method for measuring hexeneuronic acid described above, bleached pulp having a small amount of lignin is used as a measurement sample by performing ECF bleaching or TCF bleaching until the ISO whiteness reaches 80% or more. Since the ultraviolet light absorbance of lignin is 230 to 240 nm, similar to hexeneuronic acid, it is difficult to accurately determine the hexeneuronic acid content even if the ultraviolet light absorbance at 230 to 240 nm is measured if there are many coexisting substances such as lignin. is there. However, since the amount of lignin in the measurement sample is reduced in the measurement method of the present invention, the ultraviolet light absorbance at 230 to 240 nm correlates with the hexeneuronic acid content. Therefore, the content of hexeneuronic acid can be accurately determined by measuring the ultraviolet light absorbance at 230 to 240 nm.
In general, since ultraviolet light is less absorbed by water, it is considered that the correlation between the ultraviolet light absorbance at 230 to 240 nm and the hexeneuronic acid content is established even when the bleached pulp is in a slurry state. Therefore, even if the bleached pulp is in the state of pulp slurry, if the ISO whiteness is 80% or more, the hexeneuronic acid content in the bleached pulp can be accurately measured from the ultraviolet light absorbance of 230 to 240 nm.

  In addition, ultraviolet light absorbance measurement is non-destructive and can be measured in a short time, so the hexeneuronic acid content in bleached pulp can be measured non-destructively and in a short time. Can be measured and managed.

  By measuring the hexeneuronic acid content by this measuring method, only bleached pulp within a predetermined range can be used as papermaking pulp, so that troubles of discoloration can be prevented.

  In TCF bleaching and ECF bleaching, for example, the temperature at the time of acid treatment or high-temperature chlorine dioxide bleaching can be appropriately changed according to the hexeneuronic acid content in the bleached pulp. Specifically, when the hexeneuronic acid content in the bleached pulp is high, the temperature during bleaching can be increased, and when it is low, the temperature can be decreased. Thus, waste of energy can be prevented by changing the temperature during bleaching according to the hexeneuronic acid content in the bleached pulp.

  Furthermore, in TCF bleaching and ECF bleaching, the amount of bleaching chemical used can be appropriately changed according to the hexeneuronic acid content in the bleached pulp. For example, when using chlorine dioxide with the resolution of hexeneuronic acid or ozone and hydrogen peroxide with no resolution as bleaching chemicals, the chlorine dioxide and hydrogen peroxide concentration is determined based on the hexeneuronic acid content of the bleached pulp. The usage ratio can be changed as appropriate. Specifically, when the content of hexeneuronic acid in the bleached pulp is high, the usage rate of chlorine dioxide can be increased, and when the content is low, the usage rate of hydrogen peroxide can be increased. Thus, if the bleaching chemical is changed according to the hexeneuronic acid content, the amount of expensive chemical used can be reduced, and the bleaching chemical cost can be reduced.

<Method for producing bleached pulp>
An embodiment of the method for producing bleached pulp of the present invention will be described.
In the bleached pulp production method of the present embodiment, a bleaching device for producing a slurry-like bleached pulp, a sampling tube for continuously collecting a part of the bleached pulp from the bleaching device, and a slurry-like sample collected by the sampling tube The hexene uron which continuously measures the hexene uronic acid content in the slurry-like bleached pulp collected by the sampling tube by the whiteness meter for measuring the whiteness of the bleached pulp and the method for measuring the hexene uronic acid content in the bleached pulp described above A manufacturing apparatus provided with an acid content measuring apparatus (hereinafter abbreviated as a measuring apparatus) is used.

  As the whiteness meter, a commercially available on-line whiteness meter can be used, and a spectrophotometer capable of measuring ISO whiteness can be used as the whiteness meter.

As the measuring device, for example, a device having a sample container for storing a measurement sample of bleached pulp and an ultraviolet light absorbance measuring device for measuring the ultraviolet light absorbance of the bleached pulp in the sample container at 230 to 240 nm is used. Is done.
In this measuring apparatus, the bleached pulp collected by the collecting tube can be continuously supplied to the sample container, and the hexeneuronic acid content can be continuously measured by an ultraviolet light absorbance measuring device.

In the production method of the present embodiment, the pulp raw material prepared using lignocellulose is continuously ECF bleached or TCF bleached until the ISO whiteness measured by the whiteness meter reaches 80% or more by a bleaching apparatus, Slurry bleached pulp is continuously produced.
Further, in the production method of the present embodiment, a part of the slurry-like bleached pulp is continuously collected from the bleaching device by the collecting tube, and the hexeneuronic acid content in the sampled slurry-like bleached pulp is measured by the measuring device. Measured continuously by the method of measuring hexeneuronic acid content in the bleached pulp.
The bleached pulp is managed based on the measured hexeneuronic acid content. From the viewpoint that the bleached pulp can be managed with high accuracy, it is preferable to change the bleaching conditions for ECF bleaching or TCF bleaching so that the measured hexeneuronic acid content falls within a predetermined range. For example, when the hexeneuronic acid content exceeds a predetermined range, the amount of bleaching chemical added is increased or the bleaching temperature is increased.
The bleached pulp can also be managed by preventing bleached pulp having a hexeneuronic acid content outside the predetermined range from being conveyed to the papermaking process.

  According to the method for producing bleached pulp, the hexeneuronic acid content of the obtained bleached pulp can be easily within a predetermined range. Therefore, it is possible to obtain a bleached pulp that prevents discoloration. Therefore, if this bleached pulp is made, paper that is prevented from fading can be produced.

  In addition, the manufacturing method of the bleached pulp of this invention is not limited to the said embodiment. For example, the whiteness meter can be omitted when ECF bleaching or TCF bleaching is performed to ensure that the ISO whiteness of the bleached pulp is 80% or more. If the whiteness meter is omitted, bleached pulp is used as papermaking pulp based solely on the hexeneuronic acid content.

<Paper manufacturing method>
The paper manufacturing method of the present invention is a method for papermaking bleached pulp manufactured by the above-described bleached pulp manufacturing method under acidic conditions.
Examples of the paper making method include a method using a paper machine such as a long net paper machine, a circular net paper machine, and a twin wire type paper machine.
The acidic condition is that the pH of the pulp slurry is less than 7.0, but a pH of 6.5 or less is preferable. Since the paper obtained by papermaking at pH 6.5 or less is liable to fading, the effects of the present invention are particularly exhibited.
As a method for adjusting the pH, for example, sulfuric acid or a sulfuric acid band is generally added, but is not particularly limited.
After paper making, dehydration, drying and smoothing can be performed by known methods.

  In the paper production method of the present invention, bleached pulp produced by the above-described bleached pulp production method, that is, bleached pulp having a hexeneuronic acid content within a predetermined range, is produced, so that paper that is prevented from fading can be obtained. .

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, “%” means “mass%”.

Measurement of ISO whiteness, ultraviolet light absorbance and hexeneuronic acid content of pulps in Examples and Comparative Examples was performed by the following methods.
(Measurement of whiteness and ultraviolet light absorbance of pulp)
After the bleached pulp was disaggregated, a sheet having a basis weight of 60 g / m ² was prepared according to JIS P 8209, air-dried, and the ISO whiteness was measured according to JIS P 8148 using a spectral whiteness colorimeter (manufactured by SUGA). .
Further, UV absorbance of the sheet from 200 nm to 500 nm was measured using UV3100PC (manufactured by Shimadzu Corporation).

(Quantitative analysis of hexeneuronic acid in pulp)
5 g of the completely washed pulp was taken at an absolutely dry mass, and ultrapure water was added so that the total water content was 150 ml, and then 0.0564 g of formic acid and 0.0208 g of sodium formate were added and stirred well. After stirring, the entire amount was transferred to a pressure vessel and treated at 110 ° C. for 5 hours to hydrolyze hexeneuronic acid. Thereafter, the mixture was filtered and 2-furanic acid and 5-carboxy-2-furanaldehyde, which are acid hydrolysates of hexeneuronic acid present in the filtered solution, were quantified by high performance liquid chromatography (HPLC), The original amount of hexeneuronic acid was determined from the total amount.

Example 1
200g of dry Acacia mangum collected, liquid ratio 4, 22% effective alkali per mass of dry chip, 28% sulfidity of cooking liquor, cooking temperature 155 ° C, cooking time 120 minutes Kraft cooking was performed using an autoclave. After cooking, the waste liquid and the pulp were separated, and the pulp was carefully selected using a flat screen equipped with a 10-cut screen plate. Next, 70.0 g of unbleached kraft pulp after selection is collected at an absolute dry mass, 2.0% of sodium hydroxide is added per mass of the absolute dry pulp, and then diluted with ion-exchanged water to a pulp concentration of 10%. It was adjusted. The unbleached pulp slurry whose concentration was adjusted was placed in an indirect heating autoclave, and 99.9% of commercially available compressed oxygen gas was further injected to react the gauge pressure at 1 MPa for 60 minutes to perform alkaline oxygen bleaching. After completion of the reaction, the pressure was reduced until the gauge pressure became 0.05 MPa or less, the pulp was taken out from the autoclave, washed with 7 liters of ion-exchanged water, and dehydrated.

60 g of the kraft pulp after the alkali oxygen bleaching was collected in an absolutely dry mass, put in a plastic bag, and the pulp concentration was adjusted to 10% using ion-exchanged water. Furthermore, after adding 1.2% chlorine dioxide per mass of dry pulp and stirring well, it was immersed for 30 minutes in a constant temperature water bath having a temperature of 70 ° C. to perform the first D-stage treatment. After completion of the treatment, the pulp was diluted to 3% with ion-exchanged water, and then dehydrated and washed with a Buchner funnel.
50 g of the pulp after the first D stage was collected at an absolutely dry mass, put in a plastic bag, and ion-exchanged water was added to adjust the pulp concentration to 10%. Furthermore, after adding 1.0% sodium hydroxide and 0.1% hydrogen peroxide per mass of dry pulp, mix well, then immerse in a constant temperature water bath at 70 ° C for 90 minutes to extract the Ep stage Went. After completion of extraction, the pulp was diluted to 3% with ion-exchanged water, and then dehydrated and washed with a Buchner funnel.
45 g of the pulp after the Ep stage was collected at an absolutely dry mass, put into a plastic bag, and adjusted to a pulp concentration of 10% using ion-exchanged water. Further, after adding 0.2% of chlorine dioxide and 0.05% of sodium hydroxide per mass of dry pulp, the mixture was thoroughly stirred and immersed in a constant temperature water bath at a temperature of 70 ° C. for 180 minutes. Was bleached. After completion of bleaching, the pulp was diluted to 3% with ion-exchanged water, and then dehydrated and washed with a Buchner funnel. In this way, bleached pulp was obtained.
Table 1 shows the whiteness, hexeneuronic acid content, and ultraviolet light absorbance at 230 nm, 232 nm, 234 nm, and 240 nm of the obtained bleached pulp.

Example 2
The acacia mangum of Example 1 was changed to an acacia hybrid (a hybrid of acacia mangum and aurikal horumis), the effective alkali during cooking was 20%, and the chlorine dioxide addition rate in the first D stage was 0. Except for changing to 95%, cooking, alkaline oxygen bleaching and multistage bleaching were carried out in the same manner as in Example 1 to obtain bleached pulp.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Example 3
Same as Example 1 except that the Acacia mangum of Example 1 was changed to Eucalyptus nightens, the effective alkali during cooking was changed to 16%, and the chlorine dioxide addition rate in the first D stage was changed to 0.45%. Digestion, alkaline oxygen bleaching and multistage bleaching were carried out to obtain bleached pulp.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Example 4
Same as Example 1 except that the Acacia mangum of Example 1 was changed to Eucalyptus globulus, the effective alkali during cooking was changed to 15%, and the chlorine dioxide addition rate in the first stage D was changed to 0.30%. Digestion, alkaline oxygen bleaching and multistage bleaching were carried out to obtain bleached pulp.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Example 5
Example 1 except that the acacia mangum of Example 1 was changed to Eucalyptus chamaldrensis, the effective alkali during cooking was changed to 19%, and the chlorine dioxide addition rate in the first stage D was changed to 0.40%. In the same manner as above, bleaching, alkaline oxygen bleaching and multistage bleaching were carried out to obtain bleached pulp.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Example 6
50 g of kraft pulp after bleaching alkaline oxygen using the same eucalyptus and globulas as in Example 4 in an absolutely dry mass was taken, put in a plastic bag, added with ion-exchanged water and sulfuric acid, and a pulp concentration of 10%, pH 2.5. Adjusted. The pulp slurry whose concentration was adjusted was placed in a medium-concentration mixer, 0.7% ozone was added per mass of the absolutely dry pulp, and the mixture was stirred and reacted at 50 ° C. for 1 minute. The pulp after the reaction was diluted to 3% with ion-exchanged water, and then dehydrated and washed with a Buchner funnel.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Example 7
Digestion in the same manner as in Example 5, except that the chlorine dioxide addition rate in the first D stage of Example 5 was changed to 0.55% and the hydrogen peroxide addition rate in the Ep stage was changed to 0.5%. Alkaline oxygen bleaching and multistage bleaching were performed to obtain bleached pulp.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Comparative Example 1
A bleached pulp was obtained by performing the same operation as in Example 6 except that the ozone addition rate in Example 6 was changed to 0.5%.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Comparative Example 2
A bleached pulp was obtained by performing the same operation as in Example 6 except that the ozone addition rate in Example 6 was changed to 0.3%.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Comparative Example 3
30 g of kraft pulp after alkaline oxygen bleaching using the same eucalyptus and globulas as in Example 4 in an absolutely dry mass was collected, placed in a plastic bag, and the pulp concentration was adjusted to 10% using ion-exchanged water. Furthermore, after adding 1.2% chlorine dioxide per mass of dry pulp and stirring well, it was immersed for 30 minutes in a constant temperature water bath having a temperature of 70 ° C. to perform the first D-stage treatment. After completion of the treatment, the pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel to obtain bleached pulp.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

Comparative Example 4
A bleached pulp was obtained in the same manner as in Comparative Example 3 except that the chlorine dioxide addition rate in Comparative Example 3 was changed to 1.2%.
Table 1 shows the ISO whiteness, hexeneuronic acid content, and ultraviolet light absorbance of the obtained bleached pulp.

FIG. 1 shows a plot of the hexeneuronic acid content against the ultraviolet light absorbance at 232 nm. As is apparent from this figure, when the bleached pulp has an ISO whiteness of 80% or more, the ultraviolet light absorbance at 232 nm of the sheet has a correlation with the hexeneuronic acid content in the bleached pulp. Therefore, the hexeneuronic acid content in the bleached pulp can be accurately determined by measuring the ultraviolet light absorbance at 230 to 240 nm of the bleached pulp bleached until the ISO whiteness becomes 80% or more.
On the other hand, when the ISO whiteness was less than 80%, the ultraviolet light absorbance at 232 nm did not correlate with the hexeneuronic acid content in the bleached pulp.

It is the graph which plotted the hexeneuronic acid content in bleached pulp with respect to ultraviolet light absorbance.

Claims (6)

Using the pulp material prepared using lignocellulose as a measurement sample, bleached pulp that has been subjected to elementary chlorin-free bleaching or total chlorin-free bleaching until the ISO whiteness is 80% or more,
A method for measuring a hexeneuronic acid content in bleached pulp, wherein the hexeneuronic acid content is determined from an ultraviolet light absorbance at 230 to 240 nm of a measurement sample.   The method for measuring a hexeneuronic acid content in bleached pulp according to claim 1, wherein the bleached pulp is in a slurry state.   The method for measuring the hexeneuronic acid content in bleached pulp according to claim 1, wherein the bleached pulp is in sheet form. A pulp raw material prepared using lignocellulose is continuously subjected to elementary chlorin-free bleaching or total chlorin-free bleaching until the ISO whiteness reaches 80% or more, thereby producing a slurry-like bleached pulp continuously. There,
A collecting step for continuously collecting a part of the slurry-like bleached pulp and a hexeneuronic acid content in the collected slurry-like bleached pulp are continuously measured by the method for measuring a hexeneuronic acid content in the bleached pulp according to claim 2. A method for producing bleached pulp, characterized by comprising a measuring step for measuring automatically and a management step for managing bleached pulp based on the measured hexeneuronic acid content.   The bleaching pulp production according to claim 4, wherein in the management step, the bleaching conditions of elementary chlorin-free bleaching or total chlorin-free bleaching are changed so that the hexeneuronic acid content measured in the measuring step falls within a predetermined range. Method.   6. A method for producing paper, wherein the bleached pulp obtained by the method for producing bleached pulp according to claim 4 or 5 is subjected to papermaking under acidic conditions.

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