JPH0380915B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing chemical pulp in which wood chips are delignified in two steps. As is well known, the conventional alkaline method for producing chemical pulp basically consists of: - mixing wood chips with an alkaline cooking liquor containing sulfur compounds; - mixing the resulting mixture with about 150 to It consists of heating continuously to a temperature of 180° C.; - cooking the mixture for a time sufficient to reach the grinding point of the wood chips, depending on the type of raw wood; In practice, the grinding point is reached when the amount of residual lignin corresponds to a Katsupar number of 30-35 for softwoods and 15-25 for hardwoods. Although the above conventional methods are very widely used, they have two major drawbacks. First, this process significantly pollutes the atmosphere by releasing malodorous sulfur compounds such as mercaptans, SO ₂ and H ₂ S. In the case of bleached pulp, chlorine compounds are also released into the bleach effluent. This problem is only partially solved by the use of purification equipment, but unfortunately, as is well known, this equipment system is very expensive. A second drawback, and more importantly, is that the yield of pulp obtained by conventional methods is very low, for example about 40% for softwoods. In other words, only about 40 kg of dry pulp can be obtained from 100 kg of dry chips. In the kraft process, the wood chips are particularly heated in H ₂ S before cooking.
It has been suggested that pulp yield may be improved by stabilizing carbohydrates by pretreatment with or _O2 . However, these pretreatments with gas are complex and require specialized equipment;
Therefore, it is not widely used. Cooking operations for kraft pulp have also been proposed in which sulfur is added, for example, to the cooking liquor to form polysulfides in situ, whose oxidation stabilizes the carbohydrates and protects them from alkaline degradation. Although this method actually improves yields, the increased amount of sulfur increases air pollution, resulting in
This method is also not widely adopted. French Patent No. 2,373,637 proposes adding very small amounts (less than 0.1% by weight, based on the weight of dry wood) of anthraquinone to the cooking liquor. However, in contrast to the results shown in the tables of the above-mentioned patent specifications, industrial tests have shown only a very small improvement in yield and, in many cases, significant changes in certain mechanical properties of the pulp obtained. accompanied by deterioration [K.GOEL, AMAYROUD
and B.BRANCH, “Anthraquinone in Kraft
pulp”−Pulping Conference Proceedings, 24−
26 (1979.9), p. 213 ff]. In summary, the methods previously proposed for improving the yield in conventional alkaline chemical pulping processes either result in a decrease in the mechanical properties of the pulp or increase air pollution. . Despite various attempts, the dilemma described above always exists, while environmental protection is becoming increasingly important and the market demands stronger pulps. The present invention therefore provides an economical process that can be carried out in conventional pulping equipment and which not only substantially increases the pulp yield but also does not cause environmental pollution and improves the mechanical properties of the pulp. It is an object of the present invention to provide a method for producing pulp that can increase certain levels of pulp. Therefore, according to the present invention, when producing chemical pulp by cooking wood chips at high temperatures in an alkaline cooking liquor containing sulfur compounds, the amount of residual lignin in the wood chips is determined to be higher than that of coniferous wood in the pulp to be bleached. Regarding wood
Cut par value of 45-60, 30-30 for hardwood lumber
When the amount corresponding to a cut par number of 50 is reached, the cooking under heating is stopped; the wood chips thus treated are mechanically ground; and finally, the ground wood chips are cooked. There is provided a method for producing chemical pulp, which is carried out using an alkaline solution containing 0.1 to 1.5% by weight of peroxide based on the dry weight of the wood chips. In other words, the present invention discontinues the cooking of the wood chips before reaching the cut par number customary for unbleached chemical pulp and mechanically grinds the thus treated chips in a manner known per se, and then It consists of completing the cooking with an alkaline solution containing peroxide. It was found that the best results were obtained by the following method: - a first cooking step under heat, with a residual lignin content of 45 to 60 for softwoods for bleached pulp; 30~ for hardwoods)
discontinue when an amount corresponding to a Katsupar number of 40 (measured according to AFNOR standard T12018) is reached;
Specification No. 877401 or French Patent No. 2435457
the derivatives described in the specification are added to the cooking liquor of the first cooking step in an amount of not more than 0.05% by weight, based on the dry weight of the wood chips; - the grinding is carried out mechanically (disk grinder,
- in the cooking liquor of the second cooking step, in addition to the peroxide, 1 to 5% by weight, preferably 2 to 4% by weight of soda, based on the dry weight of the ground chips, is present, - In the second cooking step, the operation is carried out at 20-120℃.
Preferably carried out at a temperature of 70 to 100° C. for 30 to 180 minutes, preferably about 120 minutes; - peroxide treatment using well-known decomposition reactions for peroxides such as magnesium sulfate, calcium carbonate, sodium phosphate or organic compounds; It consists in carrying out in the presence of additives which have the effect of reducing or reducing the decomposition of cellulose. The peroxide has the general formula: R-O-O-X (R
represents various groups and X represents a metal ion or hydrogen). Such peroxides include hydrogen peroxide (which is economically preferred), sodium, potassium or calcium peroxide, perborates and persulfates. After the second cooking step, the resulting pulp is washed with water in a known manner. This pulp may optionally be bleached using conventional bleaching methods. The method of the invention and its advantages will become clearer from the examples described below. For convenience, these examples and the resulting data are summarized in the table below. In these tables, the following are shown in the following order: : - Active alkali is % based on dry weight of raw wood
- the degree of hardening is shown in % based on the active alkali; - the amount of sulphite is shown in % based on the dry weight of the raw wood.
- the time is given in minutes; - the weight of anthraquinone is in % based on the dry weight of the raw wood; - the Katsupar number is the value determined according to AFNOR standard T12018; - The yield of the first cooking step is in % based on the dry weight of the raw wood; - the amount of hydrogen peroxide, soda and magnesium sulfate in the second cooking step is in % based on the dry weight of the ground material; - the final Yield is in % based on the dry weight of raw wood; - Physical properties are measured at 40° SR according to the respective AFNOR standard; for breaking length (m) Q03 004 Rupture Index ( rupture index Q03 014 tear index Q01 011 In the examples shown in Table 1, Norwegian pine wood chips were used as the raw material. In Examples and In between the first and second steps, mechanical grinding of the chips from the first cooking step was carried out using a disc grinder. The example is a conventional method for making kraft pulp. The example is a first embodiment of the invention, namely:
The first cooking step was 45 minutes instead of 60 minutes in the example.
A method is shown in which the cooking process is stopped after 1 minute and a Kuppar number of 36.0 is obtained after the second cooking step, which is similar to that in the example, ie, 37.0 in the example. The example is a conventionally known method of adding anthraquinone to the cooking liquor in an amount of 0.05%; for ease of comparison, the operation was carried out in this case to obtain the same Kuppar number (37.0) as in the example. . The examples are improved embodiments of the invention,
In this method, anthraquinone was added to the cooking liquor in the first cooking step, but in an amount approximately half of that in the example. Comparison of these examples reveals the following: - Comparing the examples, the cut par value is the same in both cases, but the pulp yield is lower than 43.5%.
The amount of pulp has increased to 45.8% (approx.
% increase); this is a substantial improvement in terms of current production capacity (current production units are 500-600 t/day). Furthermore, despite this increase in yield, the tear and rupture indices remain constant and, in particular, the fracture length is substantially improved, an effect that could not be predicted at all and is contrary to conventional knowledge. It is something. - When comparing the results of Examples and Examples with the results of Examples, the addition of anthraquinone to the cooking liquor of the first cooking step increases the final yield (from 45.8% to 46.5%);
On the other hand, it can be seen that at the same time, the increase rate of the fracture length increases from 13% for the example to 34% for the example. In the conventional method (example), the addition of anthraquinone itself only resulted in an increase of about 6%, and moreover, the amount of anthraquinone used was almost twice that used in the method of the present invention. be. Furthermore, the method of the present invention (Examples and) does not cause more significant contamination than the conventional method (Examples and). In the examples shown in Table 2, the conditions shown in Table 1 are adopted, and these conditions are adapted to the treatment of hardwood wood (birchwood), in accordance with methods known per se. The wood was treated. The examples illustrate conventional kraft pulp production methods. The example is a first embodiment of the invention, namely:
The first cooking step was carried out using a smaller amount of active alkali (18% instead of 19.5% in the example) and after the second cooking step the same Kuppar number as in Example V, i.e. 21.2 in the example. We will show you how to set it to 20. The example shows a conventional method of adding 0.05% anthraquinone to the cooking liquor. The example shows a specific example of the present invention in which 0.03% anthraquinone is added to the cooking liquor of the first cooking step. A comparison of these examples shows that the process according to the invention produces similar effects (increased yield and improved certain physical properties) as in the case of conifers shown in Table 1. In the examples shown in Table 3, another method for producing chemical pulp using alkaline cooking containing sulfur compounds was applied to hardwood wood (beech wood). The examples illustrate conventional methods for making sulfite pulp. In the example, the first cooking step was stopped after 90 minutes, and after the second cooking step, the cut par number (27
A specific example of the present invention is shown in which 28) is obtained instead of . The results shown in these tables show that the process of the present invention increases yield while improving physical properties. French Patent No. 2298839 and Additional Patent No. 2430475 describe a method in which lignocellulosic material is treated in a two-stage cooking process, namely, initially with sodium hydroxide, after milling in the middle; A method for producing chemical pulp is described, which is treated with an alkaline peroxide solution in a second cooking step. The pulp obtained in this way is similar in properties to kraft pulp, but the degree of contamination is substantially reduced. At the same time, as mentioned above, all conventional methods for increasing the yield of kraft pulp are known to either reduce the physical properties of the pulp or substantially increase environmental pollution. Therefore, by adopting the specific two-stage cooking process as described above, and performing the second cooking process in a low concentration alkaline peroxide solution and under special conditions among the conditions of the first cooking process, It was unexpected that a result different from that taught by conventional methods would be obtained. In fact, according to the method of the invention, the pulp yield is increased without increasing environmental pollution, while some physical properties of the resulting pulp (particularly the breaking length) remain substantially unchanged. Or, in some cases, it may be improved. The unbleached chemical pulp produced by the method of the present invention has the same Kuppar number as conventional unbleached pulp. This pulp can therefore be bleached according to conventional bleaching methods.

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Claims (1)

[Scope of Claims] 1. When producing chemical pulp by cooking wood chips at high temperatures in an alkaline cooking liquor containing sulfur compounds, the amount of residual lignin in the wood chips is determined to be higher than that of softwood wood. For Katsupar value of 45-60,
For hardwood wood, the cooking process under heat is discontinued when a quantity corresponding to a cut par number of 30 to 50 is reached; the wood chips thus treated are ground mechanically; and finally, the wood chips are ground 0.1 based on the dry weight of the wood chips above.
A method for producing chemical pulp, characterized in that it is carried out using an alkaline solution containing ~1.5% by weight of peroxide. 2 For hardwood wood, the amount of residual lignin
Claim 1, wherein the cooking in the first step is stopped when a value corresponding to a Katsupar number of 30 to 40 is reached.
The method described in section. 3. Claim 1 or 2, in which the cooking liquor of the second cooking step contains a peroxide stabilizer.
The method described in section. 4 In the alkaline liquid of the first cooking step, anthraquinone, hydrogenated or unhydrogenated anthraquinone or anthracenediol derivative is added, based on the dry weight of the wood chips.
4. A method according to any one of claims 1 to 3, wherein the method is present in an amount of 0.05% by weight or less. 5. The cooking liquor of the second cooking step contains 1 to 5% by weight, preferably 2 to 4% by weight of soda, based on the dry weight of the ground wood chips. The method according to any of paragraph 4. 6. Second cooking step at 20~120℃, preferably 70~
6. A method according to any of claims 1 to 5, carried out at a temperature of 100<0>C for 30 to 180 minutes, preferably about 120 minutes.