JPS6335758B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for pulping difficult-to-digest softwood materials without using sulfur, and producing bleached pulp with high brightness from the pulp using only a small amount of chlorine-containing bleach. . [Prior art] Traditionally, difficult-to-digest coniferous materials such as cedar have been
It was not easily pulped by the method (alkaline method) and the KP method (kraft method). However, KP (kraft pulp) obtained from these softwoods is a long-fiber pulp and has high tear strength, so it has been produced in some cases as pulp for paper tapes and paper strings. However, AP (alkaline pulp) and KP (kraft pulp) obtained from these difficult-to-digest materials are extremely difficult to bleach, so these raw materials are not used alone, and mixing with general materials is also discouraged. I came. Recently, due to the lack of wood, many studies have been published on the use of hard-to-digest wood, which is produced in large quantities by thinning cedar forests. However, the pulp (AP) obtained by the AP method has a low whiteness (Hunter whiteness: 17.1%) and an extremely high Katsupar number, which is an indicator of lignin content.
It has been reported that it can even reach [Mita, Kashihara et al.; Paper and Paper Technology Association Journal 37644 (1983)]. If you attempt to obtain bleached pulp by bleaching this unbleached AP using the conventional multi-stage bleaching method, even if chlorine is added in the first stage at an amount 0.2 times the cut par value,
310 kg of chlorine will be used per ton of AP. This would be difficult to implement industrially from an environmental standpoint. On the other hand, when pulped using the KP method, the Katsupar number can be lowered to about 41, but the unbleached KP obtained in this way is extremely difficult to bleach. However, recently, 7-step bleaching that includes the use of 10% chlorine,
6-stage bleaching including oxygen/alkali treatment stage to achieve whiteness of 80
There are also reports that bleached pulp close to
37829 (1983)]. The present inventors have continued research for many years in search of a method for obtaining high-quality, easily bleachable pulp from a wide range of cellulosic raw materials, both wood and non-wood, in a high yield and without pollution. Then, a chelating agent such as EDTA or DTPA as an auxiliary agent and an anthraquinone stabilizer are added to an alkaline solution of hydrogen peroxide to form a cooking liquor, and the cellulose raw material is heat-treated (see below).
By developing the PA method (abbreviated as PA method), we succeeded in obtaining pulp that was close to the intended purpose. According to the same law, pulp with a low cut par value (hereinafter referred to as
PAP) was obtained by sulfur-free cooking. Moreover, the same pulp is unbleached and has a similar cut par value.
It was found that it is much easier to bleach than KP, and that it can be exposed to a considerable degree even with one-step hypochlorite bleaching [Mita, Kashihara et al.; Paper and Paper Technology Association Journal 37644
(1983)]. However, even when an extremely large amount of available chlorine was added to the unbleached PAP (20%) in an attempt to expose it to a high whiteness level, the Hunter whiteness level only increased to 60%. [Purpose] The present invention differs from the conventional KP method in that it can cook even difficult-to-digest materials such as cedar without sulfur, and unlike the conventional AP and PA methods, it uses extremely little chlorine bleach. An object of the present invention is to provide a method for producing bleached pulp with high brightness through three-stage bleaching. [Structure] The present inventors obtained an easily bleachable unbleached pulp by limiting the cooking conditions in the PA method, and also used an alkaline solution of hydrogen peroxide as a pretreatment for bleaching the pulp with a chlorine bleach. By repeating the process (hereinafter referred to as Pa process) twice,
The present inventors have discovered that bleached pulp with high whiteness can be produced from sulfur-free and chlorine-saving pulp from hard-to-digest softwood materials, leading to the completion of the present invention. That is, the present inventors used 100% cedar chips, which have traditionally been considered the most difficult to digest as softwood wood, and added anthraquinone stabilizers and chelating agents such as EDTA to an alkaline solution of hydrogen peroxide. By treating with the added chemical solution at 180℃ for 1 hour, the Katsupur value was 36.7 and the Hunter whiteness was 30.1%.
We were able to obtain unbleached pulp with a selective yield of 42.5%. As shown in Table 1 below, the pulp is produced by repeating the treatment twice with a hydrogen peroxide solution (Pa treatment) in which the amount of alkali used is adjusted appropriately.
Effects that could not be obtained with stage treatment were obtained. In other words, the Katsupar number was reduced to about 12, while the Hunter whiteness was increased to 60%, and it became possible to save on alkali. The pulp subjected to the two-stage Pa treatment is 1 as shown in Table 2 below.
Hunter whiteness could be increased to over 75% by treating with much less hypochlorite (2% available chlorine) than either stage-treated or untreated pulp. By treating the two-stage Pa-treated pulp with 5% chlorine dioxide, we succeeded in increasing the Hunter whiteness to 80%. In carrying out the present invention, the woods that can be used are:
100% so-called difficult-to-digest materials such as cedar and Japanese pine may also be used.
Of course, it is also possible to use a material mixed with easily digestible materials in any proportion. The form that can be used as a pulp raw material is a normal factory-sized chip, and there is no particular need to make it into planer-like thin pieces or saw-dust-like pieces. The range of the liquid ratio of the cooking chemicals is wide, but usually 3.5 to 10/Kg, preferably 4.0 to 5.0 for liquid phase cooking.
/Kg, and in the case of vapor phase cooking, it is 1 to 3.5/Kg,
Preferably it is 1.5 to 3/Kg, and such a liquid ratio is convenient for stable and easy production operations. This is also preferable from the viewpoint of economically recovering energy and chemicals by concentrating and burning the pulp waste liquid. The chemicals used as cooking chemicals (hereinafter referred to as absolute dry chips), sodium hydroxide (hereinafter referred to as absolute dry chips),
(expressed as _Na2O ) is 17-28%, preferably 18
-23%, hydrogen peroxide is 1-5%, preferably 2-3%, chelating agents such as EDTA and DTPA are 0.1-1.0%, preferably 0.2-0.5%, and anthraquinone stabilizers (e.g. anthraquinone, alkylanthraquinone, etc.) is 0.05 to 1.5%, preferably 0.2 to 0.7%. Cooking temperature is 175-200℃, preferably 175-190℃
The holding time at the same temperature is 30 in liquid phase cooking.
~120 minutes, preferably 45-90 minutes, 15 minutes for vapor phase cooking
It requires cooking for ~60 minutes, preferably 25-45 minutes, during which time an unbleached pulp with a Kuppar number below 40 is obtained. Examples of the chlorine bleach used in the bleaching process of the present invention include hypochlorite, chlorite, and chlorine dioxide. In the first and second stage Pa treatment of unbleached pulp, the sodium hydroxide used in the first stage is 2
The amount used is adjusted to 5%, preferably 2 to 4%, so that the Hunter whiteness is 45% or more. In the second step, the amount used is adjusted to 1 to 5%, preferably 1 to 3%, so that the Hunter whiteness is 55% or more. Hydrogen peroxide used in each stage is 0.5-5%.
Preferably it is 1 to 3%. Processing temperature is 50-110
C., especially 70 to 90.degree. C., is preferable since no pressure-resistant equipment is required and the process can be carried out quickly. The treatment time in each stage is 15 to 150 minutes, preferably 45 to 90 minutes. When using hypochlorite for the third stage treatment,
The amount used (hereinafter expressed as available chlorine) is 0.5~
5%, preferably 1-3%, treatment temperature 10-70
℃, preferably 30-50℃, processing time 30-210℃
minutes, preferably 45 to 90 minutes. When using chlorine dioxide, the amount used is 1 to 10%, preferably 2 to 5%, the treatment temperature is 40 to 100°C, preferably 60 to 90°C, and the treatment time is 30 to 300 minutes. Preferably it is 60 to 210 minutes. [Effects] The scope of application of the present invention is wide, the implementation is easy,
The effect is remarkable. That is, since cedar, which was conventionally considered difficult to digest, can now be made into pulp, softwood materials, which were conventionally difficult to digest due to the presence of cedar, can now be cooked and bleached.
Thinning wood from mixed forests with cedar and sawmill waste containing cedar can now be used as pulp raw material chips without being sorted. This makes it possible to significantly reduce the cost of collecting wood and increase the amount of collected material. In addition, it has enabled non-sulfur digesting (sulfur-free cooking), which has been a long-held dream in the pulp industry, and has reduced the amount of chlorine required in bleaching to 1/3 to 1/10, making it a chlorin-free bleach. This technology has become much closer to chlorine-free bleaching (chlorine-free bleaching), making it possible to reduce pollution. When carrying out this method, the equipment is simple, the operation is easy, it takes only a short time, and the environmental load associated with the operation is extremely small, which is advantageous for industrialization. In other words, as long as the equipment for producing unbleached pulp is made of stainless steel or has a stainless steel lining, it can be used in either a batch kettle or a continuous kettle, and the cooking time is around 1 hour. One cycle takes about 4 hours. This significantly increases pulp productivity compared to the 12 to 20 hours required by the SP method. In addition, bleaching requires no more than 3 stages, and only requires flat pressure (especially
(Pa treatment and hypochlorite bleaching do not generate harmful gases), so conventional KP bleaching requires a 5- to 7-stage bleaching equipment that uses chlorine, chlorine dioxide, high-pressure oxygen, etc., and is heavily equipped. Compared to
Construction of factories is economical and extremely advantageous. Although the present invention is easy to convert from the conventional KP method, it is particularly noteworthy that it is easy to convert from the SP method. In other words, the SP factories for melting, whose demand has decreased sharply due to the decline of the human silk and sufu industries, are currently located at KP.
Switching to this method required a huge amount of money, and domestic pulp production was decreasing, so it was not easy to switch from an economic standpoint. The kettle can be used as is, and the cooking cycle is 1/3 to 1/4 short with this method, increasing the productivity of unbleached pulp by 3 to 4 times.Also, since the bleaching equipment requires no more than 3 stages, it can be processed almost as is. Diversion is possible. In addition, alkaline hydrogen peroxide solution is used as a bleaching chemical in the first and second stages of bleaching wastewater, so if sodium hydroxide and hydrogen peroxide are added to this wastewater, it becomes a pulp cooking chemical solution. If the cooking waste liquid is concentrated and burned, alkali, steam, and electricity can be recovered. Therefore, the amount of organic carbon that is discarded is minimized. By implementing this law, we can expect to achieve significant resource and labor savings by converting unused resources into pulp, and at the same time promote energy savings and pollution-free production. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 A cooking chemical solution containing 200 g of sodium hydroxide, 30 g of hydrogen peroxide, 3 g of anthraquinone (AQ), and 3 g of EDTA was added to 1000 g of cedar chips (absolutely dry amount) at a liquid ratio of 5/Kg, and the mixture was heated at 180°C. The mixture was heated to a temperature of 100.degree. C. and maintained at the same temperature for 1 hour for cooking. The digested product was washed with water and then screened using an 8/1000 cut flat screen to obtain selected pulp (cut par value 36.7, Hunter whiteness 30.1%) of 42.5% and lees 0.9%. This step is the first step, and 30g of sodium hydroxide and hydrogen peroxide are added to the selected pulp obtained in the first step.
By adding 30 g and treating with Pa at 90° C. for 1 hour, the Katsupar number of the pulp decreased to 15.2 and the Hunter whiteness increased to 48%. The above process is considered as the first stage of the second process, and further as the second stage of the second process.
By repeating the Pa treatment, the Katsupar number further decreased to 11 and the Hunter whiteness increased to 60%. Next, in the third step, 3% sodium hypochlorite was added to the pulp obtained by performing two-stage Pa treatment.
In addition, by treating at 50℃ for 1 hour, high whiteness pulp with a Hunter brightness of 78% is produced compared to unbleached pulp.
A bleaching yield of 92% was obtained. The above results are shown in Tables 1 and 2.
Shown in the table.

【table】

[Table] Table 1 shows the effect of treatment with an alkaline solution of hydrogen peroxide (Pa treatment), particularly the relationship between the amount of alkali used and the pulp cut-par number, Hunter whiteness, and bleaching yield. Table 2 shows the effect of pre-treatment at the Pa stage in hypochlorite bleaching, in particular the relationship between bleaching yield and Hunter whiteness and the amount of available chlorine. Example 2 Hunter white was obtained by adding 5% chlorine dioxide to cedar pulp with a cut par number of 11 and Hunter whiteness of 60% obtained by the two-stage Pa treatment shown in Example 1 and treating at 75°C for 3 hours. Pulp with a hardness of 82% was obtained with a bleaching yield of 91% compared to unbleached pulp.

Claims (1)

[Claims] 1 Add an anthraquinone stabilizer and a chelating agent as auxiliaries to an alkaline solution of hydrogen peroxide as a cooking chemical solution, and heat difficult-to-digest coniferous wood at 175 to 200℃.
The first step is to obtain unbleached pulp with a cut par value of 40 or less. The second step is to obtain pulp with a whiteness of 60% or more, the third step is to treat the pulp with a cut par number of 15 or less with a chlorine bleach until it has a high whiteness, and the first and second steps A method for producing bleached pulp with high brightness from hard-to-digest coniferous wood, which comprises processing in the following order: and a third step.