JPH0718113B2 - Bleaching of lignocellulosic materials with dioxirane - Google Patents

Description

The present invention relates to a method for bleaching chemical pulp.

In the manufacture of paper, wood is usually converted by chemical means into pulp, then spread on wires and dewatered to form paper.

Kraft pulping is the most widely practiced form of chemical pulp formation in North America. This pulp is relatively dark in color, so the pulp is generally bleached before it is formed into paper to produce a commercially acceptable paper.

Various bleaching agents are used. These include chlorine, chlorine dioxide, hypochlorite, hydrogen peroxide and oxygen. Typically, more than one of these chemicals is required, but they are used individually or mixed sequentially. In the art, these various bleaching compounds are designated by letters. That is, chlorine is C, chlorine dioxide is D, caustic extraction is E, hypochlorite is H, hydrogen peroxide is P, and oxygen is O.

Although the above compounds include chlorine and certain chlorine-containing compounds, there are concerns about the use of chlorine and chlorine compounds in bleaching pulp. That is, chlorine and chlorine-containing compounds react with pulp components-primarily lignin, fatty acids and resin acids-to produce chlorinated organic compounds. Some of these chlorinated organic compounds are environmentally hazardous, and some major pulp-producing countries have limited the amount that can be discharged into the waterways from the bleaching process.
It makes sense to take legislation to limit the emission of such compounds in most countries.

Elimination of elemental chlorine and its related compounds in the bleaching process appears to prevent the formation of chlorinated organic compounds in the effluent, but efforts in line with this policy have been ineffective.

The use of elemental chlorine and related compounds during bleaching forms tetrachlorinated dioxins (TCDD) and furans (TCDF). These compounds are found in pulp and pulp mill effluent. However, the formation of these two toxins, or toxins, can be eliminated by reducing the amount of chlorine applied. Unfortunately, however, it is difficult to do this with existing technology without sacrificing certain qualities of pulp or introducing additional problems to the pulp making process.

The delignification with oxygen is performed by heating the pulp at a temperature of about 80 to 120 ° C and at an oxygen pressure of about 7.03 Kg / cm ² · g (100 psig) for about 30
It is a method of processing for a long time of ~ 90 minutes. In this oxygen delignification method, if the delignification is carried out for too long, that is, if the kappa value is lowered to about 10, weak pulp tends to be produced. In this respect, the kappa value of the pulp is a measure of the bleachability of the pulp. It is 1
A value corrected for 50% consumption of permanganate, showing the number of milliliters of 0.1 normal potassium permanganate solution that can be consumed under standard conditions in grams of pulp (on oven dry basis).

U.S. Pat. No. 4,439,271 to O. Samuelson discloses a method which employs a nitrogen dioxide pretreatment prior to oxygen delignification.
This method delays the depolymerization of cellulose during bleaching with oxygen. However, the release of nitrogen-containing compounds from the bleaching effluent can introduce other problems and these nitrogen compounds cannot be recovered by existing kraft pulp forming chemical recovery systems.

US Patent No. 4,404, granted to JJ Cael
No. 061 discloses that pulp produced by standard alkaline pulp forming processes can be bleached with monoperoxysulfate to produce papermaking pulp and bleached pulp. Also, U.S. Pat. No. 4,756,800 to EL Springer discloses a method of making salts of monoperoxysulfate and simultaneously bleaching pulp. However, neither patent specification describes the strength properties of fully bleached pulp.

There is a need for a bleaching process that produces pulp of good quality and reduces environmental concerns in carrying out such production.

Dioxirane has the following general structural formula (In the formula, R ₁ and R ₂ may be an aliphatic or aromatic group, or both groups may be bonded to each other to form a cyclic compound). These dioxirane compounds and their production are described, for example, in RW Muley (RWMu
rray) and R. Jeyaraman Journal of Organic Chemistry (Journal)
of Organic Chemistry), 50 , 20847-20853 (1985).

The present invention bleaches chemical pulp without the use of elemental chlorine, or by using elemental chlorine at lower levels than in the prior art, thus the toxin TC.
This is a method to avoid generation of DD and TVDF.

Accordingly, in its broadest aspect, the present invention is a chemical pulp bleaching process comprising the step of contacting a chemical pulp with a dioxirane.

The dioxirane may be used in combination with known bleaching agents or may be used in sequence with known bleaching agents.

Desirably, the pulp has a kappa value in the range of 15-60 if it is from a softwood species, and a kappa value in the range of 5-25 if it is still from a hardwood species. Dioxirane is
The pulp is preferably contacted with the pulp at a temperature in the range of about 5 to 50 ° C. for about 90 minutes or less. The dioxirane is preferably used in an amount of 0.2 to 1.0% active oxygen charge based on oven dried pulp, i.e., an amount sufficient to provide one active oxygen atom per dioxirane molecule. Dioxirane has the following structural formula: (In the formula, R ₁ and R ₂ may be the same or different and each is an aliphatic or aromatic group, and both groups are bonded together to form a ring. May be). One dioxirane compound that has proven to be useful is dimethyldioxirane, but any such dioxirane is such that R ₁ and R ₂ are each an alkyl group having from 1 to 4 carbon atoms. Is also appropriate.

If a subsequent bleaching step is used subsequently, ie following the dioxirane treatment, the subsequent bleaching of the pulp may be carried out with chlorine dioxide (D) alone when the dioxirane treated pulp contains less than 10 kappa residual lignin. Alternatively, the sequence may be chlorine dioxide, caustic extraction, chlorine dioxide sequence (DED). If the bleaching is done using the DED sequence, this sequence can also be described as D ₁ ED ₂ . Chlorine dioxide in stage D ₁ is in the range 0.5-1%, preferably about 0.8%, and caustic in stage E is in the range 0.2-0.7%, preferably about 0.4%.
And chlorine dioxide in the D ₂ stage is used in the range of 0.2 to 0.7%, preferably 0.4%. All percentages are expressed as weight on oven dried pulp. When chlorine dioxide is used alone, its amount is in the range 0.5 to 1% by weight, preferably about 0.8%, based on oven dried pulp.

When the dioxirane treated pulp has a residual lignin content corresponding to a kappa value of greater than 10, subsequent bleaching is chlorine;
Caustic Extraction; Chlorine Dioxide: Caustic Extraction; Chlorine Dioxide Sequence (CEDED) can be used. In this sequence, which describes the sequence as CE ₁ D ₁ E ₂ D ₂ , a substantially reduced chlorine charge was used in stage C, where the caustic charge in stage E ₁ was 60% of the amount in stage C. , In stage D _{1 a} chlorine dioxide charge of 0.5-1.2% is used, in stage E ₂ the caustic charge is 50% of the amount used in stage D ₁ , and in stage D ₂
A chlorine dioxide charge of 0.25-0.6% is used. Percentages are based on the weight of oven dried pulp. The chlorine used in Stage C is generally applied in combination with varying amounts of chlorine dioxide.

The invention is illustrated by the examples, which are included for purposes of illustration and are not intended to limit the invention.

Example 1 16.4 at 39% pulp consistency with the Kraft process
Aspen pulp (50 g dry weight in an oven) manufactured to a kappa value of 25 ° C. with an acetone solution of dimethyldioxirane (DMD) (280 mL; concentration 4.59 g / L, ie 0.55 wt% active oxygen based on oven dried pulp) Was processed for 1 hour. The dimethyldioxirane treated pulp was then bleached with chlorine dioxide (0.8 wt% based on oven dried pulp) at 70 ° C for 3 hours.

A second sample of the same aspen kraft pulp (100 g oven dry weight) was used with sodium hydroxide (4 wt% based on oven dried pulp), magnesium sulfate (0.5 wt% based on oven dried pulp), molecular oxygen (7.03 Kg / cm ²・ g; 1
Pulp consistency of 10.7% and 11
It was delignified with molecular oxygen at 5 ° C for 1.5 hours. This pulp, which has been delignified with molecular oxygen, is then bleached with elemental chlorine (1.8% available chlorine based on oven-dried pulp) at a pulp consistency of 3% and 1 hour at 20 ° C. and sodium hydroxide (oven dried). Pulp consistency 12 due to 1.1% by weight of pulp)
% And 74 ° C. for 2 hours and further delignified with chlorine dioxide (0.5 wt% based on oven dried pulp) at 6% pulp consistency and 74 ° C. for 3 hours. This bleaching sequence is called OCED.

A third sample of the same aspen kraft pulp (50 g oven dry weight) was also bleached in the conventional manner using the CED sequence. That is, bleaching with elemental chlorine was performed at a pulp consistency of 3% and 20 ° C. for 1 hour using an effective chlorine charge of 3.3% based on oven-dried pulp, and extraction with sodium hydroxide (2.0% based on oven-dried pulp).
Wt%) with 12% pulp consistency and 74 ° C
For 2 hours, and delignification with chlorine dioxide (1.0% based on oven-dried pulp) for 3 hours at a pulp consistency of 6% and 74 ° C.

The results shown in Table 1 show that DMD delignification level 8
It illustrates that aspen kraft pulp treated to 0% has better mechanical properties than the same pulp treated to a delignification level of 67% with molecular oxygen. This fully bleached pulp with DMD treatment and 86.8% Elrepho whiteness has the same zero span tensile strength as the 89.9% Elrepho whiteness bleached with conventional CED bleaching. Have.

In these examples, the Erlefo whiteness was measured at 457 nm using a Technobrite (TM) Micro TB-1C instrument. This standard test method is T
APPI T-452om-87 and CPPA E.1.

Zero span tensile strength was measured according to TAPPI T231 cm-85 using a The Troubleshooter (TM) zero span tester from Pulmac Instrument.

Example 2 At a pulp consistency of 39% by Kraft method
A fourth sample of aspen pulp (oven dry weight 50 g) produced to a kappa value of 16.4 was added to an acetone solution of DMD (170 m
L; concentration 4.44 g / L, ie 0.33% by weight active oxygen based on oven-dried pulp) and 80 mL of acetone at 25 ° C. for 3 hours. The DMD treated pulp was filtered and washed with a large amount of distilled water. The resulting pulp is then further delignified with chlorine dioxide (1.0% by weight based on oven-dried pulp) for a pulp consistency of 6% and 74 ° C. for 3 hours and with sodium hydroxide for a pulp consistency of 10% and 74 ° C. For 2 hours, and another chlorine dioxide stage (0.
Bleached for 3 hours at 6% pulp consistency and 74 ° C.

A fifth sample of the same aspen kraft pulp (100 g oven dry weight) was used with sodium hydroxide (4 wt% based on oven dried pulp), magnesium sulfate (0.5 wt% based on oven dried pulp) and molecular oxygen (7.03 Kg / cm ²
g.100 psig) and delignification with molecular oxygen for 1.5 hours at 12% pulp consistency and 110 ° C. This aspen pulp delignified with molecular oxygen was further bleached with elemental chlorine (2% available chlorine based on oven-dried pulp) at a pulp consistency of 3% and 1 hour at 20 ° C. and sodium hydroxide (oven dried). 1.2% by weight pulp (12% by weight) and 2% pulp consistency at 74 ° C for 2 hours and chlorine dioxide (0.5% by weight oven dried pulp) 6% pulp consistency and further bleaching at 74 ° C for 3 hours .

In this particular example, the aspen kraft pulp is
The same degree (6
3%) was delignified. The results shown in Table 3 are DMD
Fully bleached aspen pulp produced by treatment followed by DED bleaching without elemental chlorine is 2% effective based on oven-dried pulp based on delignification with molecular oxygen and subsequent elemental chlorine step. It demonstrates that it has a better zero span tensile strength than the same pulp produced by CED bleaching with a chlorine charge. DMD treated pulps, on the other hand, produce fully bleached pulps with zero-span tensile strength similar to pulps produced by conventional methods involving the use of elemental chlorine for bleaching.

Example 3 Pulp consistency at 35% by Kraft method
A DMD of a sixth sample of aspen pulp (oven dry weight 50 g) manufactured to a kappa value of 16.4 was added to an acetone solution (643 m
L; concentration 2.0 g / L, i.e. 0.55 wt% active oxygen based on oven-dried pulp) at 25 ° C for 1 hour. The resulting pulp was then thoroughly washed with copious amounts of deionized water.

A seventh sample of the same aspen kraft pulp (100 g oven dry weight) was used with sodium hydroxide (4 wt% based on oven dried pulp), magnesium sulfate (0.5 wt% based on oven dried pulp) and molecular oxygen (7.03 Kg / cm ²
g; 100 psig) with a pulp consistency of 12% and 1
It was delignified with molecular oxygen for 1.5 hours at 15 ℃. The resulting oxygen delignified pulp was thoroughly washed with a large amount of deionized water.

The results shown in Table 3 demonstrate that the DMD treated pulp has a better yield than pulp bleached to the same degree of delignification with molecular oxygen. This illustrates that DMD has better selectivity for lignin than does molecular oxygen.

Example 4 Harimomi pulp (50 g oven dry weight) produced by the Kraft process at a pulp consistency of 37% to a kappa value of 32 was added to an acetone solution of DMD (330 mL; concentration 4.6 g / L, ie 0.65 wt% based on oven dried pulp). % Active oxygen) 25
It was treated at 0 ° C for 0.5 hour. CED this DMD treated pulp
Further bleached in sequence. That is, bleaching with elemental chlorine was performed at a pulp consistency of 3% and 20 ° C. using 2.8% by weight of available chlorine based on oven-dried pulp.
12% pulp consistency with sodium hydroxide (1.7% by weight based on oven-dried pulp) for extraction
And 74 ° C. for 2 hours, and delignification with chlorine dioxide (0.8% by weight based on oven-dried pulp) at 6% pulp consistency and 74 ° C. for 3 hours, respectively.

A second sample of the same Harimomi kraft pulp (50 g oven dry weight) was further bleached in a conventional manner using the CED sequence. That is, bleaching with elemental chlorine using 6.4% available chlorine based on oven-dried pulp, pulp consistency 3% and 1 hour at 20 ° C., extraction with sodium hydroxide (3.8% by weight oven-dried pulp). Bleaching at 12% pulp consistency and 74 ° C. for 2 hours and chlorine dioxide (1% on oven dried pulp basis) bleaching at 6% pulp consistency and 74 ° C. for 3 hours, respectively.

The results, shown in Table 4, demonstrate that DMD treated pulp can be bleached to the same brightness as that of bleached pulp in the conventional manner. The former uses a significantly smaller amount of elemental chlorine than the elemental chlorine required by conventional methods. Zero-span tensile strength and viscosity of pulp bleached by both methods are comparable.

Thus, according to the present invention there is provided a method of treating pulp which can be sufficiently bleached up to 90% El Repho whiteness with or without very small amounts of elemental chlorine in subsequent steps. DMD with a residual lignin content of less than 5 kappa
The treated pulp has a pulp strength equivalent to that of untreated pulp. The fully bleached pulp produced by the process of the present invention has the same strength properties as pulp produced by the conventional bleaching process using high loadings of elemental chlorine.

Bleaching of chemical pulp with dioxirane compounds is modified for a range of bleaching conditions, bleaching sequences and combinations with molecular chlorine and other bleaching agents not specifically exemplified above, such as hydrogen peroxide, oxygen and monoperoxysulfate. can do. Treatment with dioxirane can also be combined with delignification with oxygen, which is placed before and after oxygenation. Two
The use of oxygen-containing compounds can have the advantage that chlorine and chlorine compounds eliminate the cleaning steps required between each step of the sequence.

The pulp used in the present invention can be kraft pulp, sulfite pulp, soda pulp or other types of chemical pulp from hardwood and softwood species. The invention extends to chemical pulp, but the term also extends to pulp produced by the treatment of wood species with organic solvents to separate wood components.

Claims (13)

[Claims] 1. A method of bleaching chemical pulp, comprising the step of contacting the chemical pulp with dioxirane. 2. A chemical pulp having a kappa value in the range of 15 to 60 when it is derived from a softwood species and a pulp having a kappa value in the range of 5 to 25 when derived from a hardwood species. The method of claim 1 having. 3. The method of claim 1 wherein the dioxirane is contacted with the pulp at a temperature in the range of about 5 to about 50 ° C. for a time of about 90 minutes or less. 4. When the pulp which has been subjected to dioxirane treatment contains residual lignin corresponding to less than 10 kappa units, the sequence of chlorine dioxide (D) or chlorine dioxide, caustic extraction, chlorine dioxide sequence (DED The method according to claim 1, which comprises a bleaching step according to (1). 5. Bleaching with chlorine dioxide at 0.5 in D ₁ stage
In the range of ~ 1%, caustic is 0.2 ~ in the E stage.
In the range of 0.7% and chlorine dioxide in the D ₂ stage of 0.2
5. The method according to claim 4, which is carried out with a D ₁ ED ₂ sequence (percentages are all based on the weight of the oven-dried pulp), each used in the range from 0.7% to 0.7%. 6. The method of claim 5 wherein chlorine dioxide in stage D ₁ is about 0.8%, caustic in stage E is about 0.4%, and chlorine dioxide in stage D ₂ is about 0.4%. Method described in 7. A bleaching amount of 0.5-0.5% with respect to oven-dried pulp.
A process according to claim 4, which is carried out with chlorine dioxide in the range of 1% by weight. 8. The method of claim 7 wherein the chlorine dioxide is about 0.8% based on oven dried pulp. 9. A chemical pulp having the following structural formula: (In the formula, R ₁ and R ₂ are each an aliphatic or aromatic group,
Further, both groups may be bonded together to form a ring. ) For dioxirane and oven-dried pulp.
Contacting at an active oxygen charge of 2 to 1% by weight; (b) using the sequence chlorine dioxide (D) when the pulp obtained has a residual lignin content corresponding to a kappa value of less than 10, or Chlorine dioxide, caustic extraction, bleaching using the chlorine dioxide sequence (DED); and (c) when the pulp has a residual lignin content corresponding to a kappa value of greater than 10, the pulp is significantly reduced in elemental form. Bleaching with a chlorine charge, chlorine, caustic extraction, chlorine dioxide, caustic extraction, chlorine dioxide sequence (CEDED); bleaching of chemical pulp comprising steps. 10. The method according to claim 9, wherein the dioxirane is dimethyldioxirane. 11. The method of claim 9 wherein the dioxirane is contacted with the pulp at a temperature in the range of about 5-50 ° C. for a period of about 90 minutes or less. 12. The method according to claim 9, wherein the aliphatic group is an alkyl group having 1 to 4 carbon atoms. 13. The sequence uses chlorine in step C in an amount suitable for the kappa value of the pulp after contact with dioxirane, and in step E ₁ the caustic charge is 60 times the charge used in step C. %, 0.5 to 0.5 in stage D ₁ .
Using a chlorine dioxide charge of 1.2%, the caustic charge in stage E ₂ is the same as the charge used in stage D ₁ .
10. CE ₁ D ₁ E ₂ D ₂ (percentages are based on oven dried pulp) which is 50% and uses a chlorine dioxide charge of 0.25 to 0.6% in stage D ₂ , according to claim 9. The method described.