FI109545B - Process for the production of fibrous pulp from herbaceous plants - Google Patents

Description

109545

Process for the production of fibrous pulp from herbaceous plants Förfarande för att framställa fibermassa av växter med örtstam 5

The invention relates to a process for the production of pulp suitable for papermaking from herbaceous plants, in which the fiber raw material is chopped, boiled and bleached.

10 In addition to forests, cereal straw and other annual grasses are the world's largest potential fiber resource. In many scarce wooded countries, herbaceous plants have long been the main raw material for paper pulp. Practical problems in the utilization of herbaceous plants are caused by the availability, collection, transportation, storage and cleaning of the raw material. In order to be economically competitive in the use of non-wood fiber raw material, it is advantageous to carry out mass production in relatively small units with an annual output of the order of 30,000 to 50,000 tons / year. This requires that the pulp production line be simple.

The term herbaceous plants is used hereafter to cover all non-wood fiber materials that can be used to make pulp. The characteristics of grassy plants and their suitability for pulping vary. In general, they contain less lignin than the wood raw material, but their silicate and ash content may be remarkably high. This creates its own specific requirements for the pulping process used.

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For the delignification of non-wood fibrous raw materials, cooking methods such as sulphate and soda soup and their variants are commonly used to delignify wood. The recovery of cooking chemicals in these processes is often hampered by the high silicate content of the plants. In alkaline cooking, the silicates dissolve in the cooking liquor and then * · 30 are precipitated in the chemical cycle on the heat surfaces of the evaporator, unless a separate silicate removal step is provided. Unfortunately, often in developing countries, soup 109545 2 is still discharged directly into the water because of the difficult and costly recovery of chemicals. Yields in low cooking methods also remain low.

A solution has also been sought for the cooking of herbaceous plants using organosolv cooking methods based on the use of various organic solvents. In Paper and Wood, Vol. 78 (1996), No. 10, E. Rousu, "Formic Acid as a Cooking Chemical", pp. 594-596, describes one such cooking method. However, it requires the use of high acid concentrations, resulting in high acid consumption. operating costs.

10 FI patent application 940638 describes a so-called. fertilizer soup, in which the soup slurry is suitable for direct use in the field as fertilizer. However, the economic viability of the method has been questioned. The cooking method is best suited for areas with a water irrigation system.

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It is an object of the present invention to provide a novel method of making pulp for papermaking from herbaceous plants which avoids the drawbacks of known methods.

* * · 20 The object of the invention is a mass-production process which is environmentally friendly and simple in technical terms, and which is economically viable even when the unit is small.

In order to achieve the above objects, the process according to the invention is characterized in that the cooking is carried out at a temperature of 60 to 130 ° C and that the water used is acidified so that the final pH of the cooking is below 7 but above * 3.

'· · ·' Known cooking methods generally use concentrated chemical solutions and high cooking temperatures of:: 30. When the cooking step is carried out in accordance with the invention in acidic water and at a relatively low temperature, the yield loss in cooking is low, but the mass is 3,109,545 easily bleached in the subsequent bleaching of the cooking. The majority of the fiber-binding lignin in the fiber material is not dissolved until bleaching.

Since high doses of chemicals are not used in cooking, it is not necessary to provide a heavy chemical recovery system. The cooking liquor and washings can be led to a sewage treatment plant for treatment by known biological purification methods. As a result, the investment and operating costs of the process are inexpensive, making it profitable even for small units. The relatively simple pulping process can be easily integrated with the paper mill to produce either reinforcement pulp or short fiber pulp, depending on the fiber raw material, for the paper machine 10. The process produces a good quality pulp which is suitable for a variety of end products. The yield of the pulp is somewhat better than that of non-wood pulps produced by conventional methods.

The water cooking method according to the invention is suitable for delignification of many different herbaceous plants. The need for pre-treatment of the fiber raw material depends, e.g. whether the whole plant is recoverable as such or whether the fiber fraction has to be mechanically separated from the plant material. Many cereals are often enough for pre-treatment alone. 4 shredding straw, for example, linen must be trapped and pressed before cooking: mechanically fractionate v. 20 or otherwise to separate * * I · for cooking. ·. ·. its fibrous material.

• · ·. ':: For long fiber plants, the pulp used for pulping must be relatively short to prevent the fiber bundles from twisting with each other during cooking. 25 Linen seems to be a suitable chopping length of 5 ... 10 mm. With short fiber plants! the length of the chipper can be up to 50 mm.

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. '. ·. The fiber shred is boiled in water to which the acid has been added to the final pH of the soup

will be less than 7 but more than 3. The acid used may be any inorganic or organic acid. Preferably, organic acids such as · · ·: formic acid or acetic acid or a mixture thereof are used to adjust the pH. The acid addition used is so.

• »» • · 109545 4 that there is no organosolv soup. Organosolv soups generally contain from 20 to 100% organic solvent in the cooking solution. In the aqueous cooking according to the invention, the acid addition is always less than 2% of the total volume of the cooking solution, preferably less than 1%. Good results have already been obtained with about 0.06% acid addition.

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The cooking is carried out at a temperature of 60-130 ° C, preferably 70-100 ° C. After cooking, the waste liquor is separated from the fiber shingle and led to waste water treatment.

The yield loss in acidic water boiling is relatively small. Thus, without mechanical pre-treatment, the cooked fiber raw material may not be converted to fiber after cooking. Therefore, water boiling is followed by bleaching, which aims not only to increase the brightness of the pulp but also to dissolve the lignin and cause the pulp to fiberize. Any known bleaching method can be used for bleaching. Preferably, however, chlorine-free bleaching chemicals such as peroxide are used.

15

When using peroxide bleaching, the fiber shred must be chelated prior to bleaching to stabilize heavy metal ions so that they do not accelerate peroxide degradation during bleaching.

For this purpose, the pulp is treated in a manner known per se with a suitable chelator. generator. Chelation can be performed either as a separate step before bleaching or * * * 20 during cooking by adding a small amount of chelating agent to the cooking water.

•: · · j Bleaching is carried out in the usual manner, however, using dosages of chemical and conditions which dissolve some of the lignin contained in the fiber material.

The process according to the invention for preparing fibrous pulp from grassy plants. · T: The unit can be positioned adjacent to a paper mill to form part of the paper:.:: Pulp system of the machine. In this case, the pulp produced by the process can be utilized: Y: directly mixed with a normal pulp on a paper machine. Depending on the fiber raw material: '': either cheap short-fiber filler pulp or long-fiber reinforcement pulp may be produced. The masses of herbaceous plants generally do not need very much. *. : vigorous milling, but pulping or pulping may be sufficient.

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Short fiber pulp (straw, etc.) can be used e.g. interlayer of multi-ply paperboard to replace recycled or wood fiber. Long fiber pulp (flax, hemp, kenaf) can be used to replace wood fiber, for example in the manufacture of recycled paper. The process of the invention can also be used to make paper pulp from a mixture of short fiber and long fiber plants for use as such in papermaking.

The method according to the invention requires little investment since the recovery of chemicals does not have to be arranged. Consumption of chemicals in cooking is low, but similarly, more chemicals need to be used in the bleaching process if the goal is to fully bleach the pulp. The process is also environmentally friendly because sulfur compounds are not used in cooking and preferably chlorine compounds are not used in bleaching.

In the following, the pulping process according to the invention will be described by means of three further examples, which, however, are not to be limited in scope and scope.

Example 1: Soaking and bleaching of wheat straw, Wheat straw was subjected to water cooking and peroxide / peracetic acid bleaching laboratory: *. ·. 20 conditions. The straw was initially chopped to a length of about 50 mm and cooked in 15-liter rotating electric heaters. The conditions and yields of the two soups at different temperatures are set out in Table 1.

Water made acidified by adding a small amount of 25 acid solutions prepared by mixing concentrated formic acid and concentrated acetic acid: 1: 3 was used as the cooking solution. In addition to the acid solution, the required amount of v: water was added to the digester to achieve the desired liquid to straw ratio of 10: 1. The acid addition was thus 0.064% of the volume of the broth in both soups.

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Table 1. Conditions and yields of wheat straw water soups.

Soup 1 Soup 2

Amount of straw, g 875 1000

Acid solution *, ml 5.6 6.4 5 Temperature, ° C 100 130

Cooking time, min 240 240

End pH 5.5 5.0

Yield,% 92.1 88.6 10 * The acid solution contained concentrated formic acid and concentrated acetic acid in a ratio of 1: 3.

After cooking, the straw chips were washed and chelated for 1 hour with a 0.3% EDTA dose at 3% consistency and 70 ° C. After chelation, the still non-fibrous straw chips were bleached under the conditions described in Table 2. The bleaching comprised two peroxide-15 steps, a peracetic acid step and a third peroxide step. The results of bleaching are shown in Table 3. The bleached pulps were milled and the paper properties were determined.

Table 2. Wheat straw bleaching conditions, 10% consistency.

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v · Bleaching Chemical - Temperature, Time, min NaOH,% Final pH

step dose,% ° C

I peroxide 4.0 85 180 7.5 9.0 / 9.1! : Y: Peroxide II 2.0 85 180 3.5 9.5 25 Peracarp 1.085 60 0.5 4.8 / 4.9. Peroxide III 2.0 85 240 3.0 10.4 109545 7

Table 3. Bleaching results for wheat colts soups 1 and 2.

Soup 1 Soup 2

Brightness,% 80.9 76.4 5 Yield,% of raw material 51.5 50.9 Consumption of H2O2,% 7.49 7.34

Peracetic Acid Consumption,% 0.84 0.85 10 After cooking, the raw material was still in straw form, but it was fiber-fiberized during the second peroxide step. Based on the yields, the material loss in the cooking was about 10% and in the bleaching about 40% of the weight of the original raw material.

The water cooking method and the peroxide / peracetic acid bleaching resulted in a bleaching straw pulp of 15% to 80% with a relatively high tensile strength at the very beginning of refining and a low tear index. During the grinding process, the pulp properties did not develop. in a positive direction, so it is not worth much to grind the straw mass. Pulp water '. the removal capacity was poor due to the short fiber length and high fines content.

t I · *: · i 20 Of the two cooking temperatures used, lower than 100 ° C appeared to be more favorable than 130 ° C for pulp yield, lightness, and paper technical properties.

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Example 2: Flax soup and bleaching »·» »· ti» v: 25 The raw material used for the production of the flax pulp is partially field-soaked, trapped: Y and condensed flax, which is cut to a length of about 12 mm. The purpose of the mechanical pre-treatment was to separate the fiber fraction from the rest of the plant material. Long fiber linen #i was shredded to prevent the fiber bundles from twisting into the knot during cooking and pulp processing.

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The purified and shredded flax fiber fraction was boiled in acidic water for 240 minutes at 100 ° C. The cooking conditions were essentially the same as in cooking 1 of Example 1. An acid solution containing one part concentrated formic acid and three parts concentrated acetic acid was used in 6.1 ml / 950 g of flax, with a 10: 1 acid addition to 0.064% cooking solution. by volume. The final pH of the flax soup was 5.1 and the yield was 92.0%.

After cooking, washing and chelating, the flax mass was bleached in three steps with the peroxide-peracetic acid-peroxide sequence. The bleaching conditions are shown in Table-10. 4. The flax pulp was blended into its birch pulp.

Table 4. Conditions used for bleaching the flax pulp, 10% consistency.

Bleaching Chemical- Temperature, Time, min. NaOH,% End-pH 15 Step Dose,% ° C

Peroxide I 4.0 85 240 4.3 9.7

Peroxide 1.0 85 150 0.5 4.7: peri: II Peroxide 2.0 85 300 2.4 10.2 t · · t · · 20 The yield of bleached flax pulp was 75.0% of the original fibrous raw material. Massan. The lightness was 86.9%, which is significantly better than that of Example 1. This scale * · · t-; ·. less bleaching chemicals were needed to reach the leukine level than the straw pulps.

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The total consumption of peroxide was 4.25% and that of peracetic acid 0.81% based on the dry matter of boiled flax.

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In laboratory bleaching, the flax fibers twisted into small, tight cores, which made it difficult to determine the paper technical properties of the pulp in the milling experiments. The addition of 20% flax significantly improved the tear strength of the birch pulp sheet.

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Example 3. Stir-bleaching and bleaching of straw and flax

Wheat straw and flax were made into a mixture by boiling them together at a relatively low temperature in the presence of chelate. 645 g of chopped wheat straw (length 5 50 mm) and 100 g of partially steeped, trapped, pressed and chopped flax fiber fraction (length 12 mm) were boiled for 60 minutes at 70 ° C. 0.3% EDTA by weight of the fibrous raw material was added to the cooking water and 6.4 ml of a concentrated formic acid / concentrated acetic acid mixture (1: 3) was added to the chelating agent to adjust the pH to 0.086% v / v in the cooking medium. The final pH of the soup was 4.9.

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The blend of flax and straw was bleached with the same four-step sequence and under the same conditions as pure straw pulp, cf. Table 2. Due to the different yields of flax and wheat, the final blend ratio in the bleached pulp was about 20:80. The yield of bleached pulp was 62.7% of the original raw material and the brightness was 84.6%. Consumption of peroxide 15 in bleaching was 7.2% and consumption of peracetic acid was 0.9%.

The bleaching of the pulp was not adversely affected by the fact that the cooking was carried out at a lower temperature and for a shorter duration than in Examples 1 and 2. Chelation,, ·. can be well done already during cooking. The experiment also showed that different fiber raw materials can be cooked and bleached together, as long as bleaching conditions are selected taking into account the requirements of a more lighter raw material.

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Claims (15)

A process for producing fibrous pulp suitable for papermaking of plants with herb stock, wherein the method of fiber raw material is chopped, boiled and bleached, characterized in that the cooking is carried out at a temperature of 60 ... 130 ° C, and that as a boiling solution water is used in which acid has been added in such a way that the final pH of the boiling is below 7 but over 3. 2. A method according to claim 1, characterized in that such bleaching dosages and bleaching conditions with which the fiberization of the fibrous raw material is ensured are used in the bleaching 10. Process according to claim 1 or 2, characterized in that an inorganic acid is added to the boiling solution for pH control. 15 4. A process according to claim 1 or 2, characterized in that the acid used for pH control is an organic acid, such as formic acid or acetic acid or a mixture thereof. «* ·: V 20 5. A process according to claim 3 or 4, characterized in that the addition of acid is not more than 2% of the volume of the boiling solution, advantageously below 1% by volume. Process according to any of the preceding claims, characterized in that the cooking is carried out at a temperature of 70 ... 100 ° C. 25 7. A process according to any of the preceding claims, characterized in that chlorine-free bleaching chemicals are used in the bleaching following: 8. A process according to claim 7, characterized in that peroxide is used as a bleaching chemical and the pulp is chelated before bleaching. 105545 9. A process according to claim 8, characterized in that the chelation is carried out already in connection with the cooking. Method according to any of the preceding claims, characterized in that the fibrous raw material is chopped before cooking to chop with the dimension of 5 ... 50 mm depending on the type of plant. Method according to any of the preceding claims, characterized in that from the fibrous raw material prior to cooking, the fiber-containing component thereof is separated separately. Process according to any of the preceding claims, characterized in that the method is applied in a process placed adjacent to a paper mill and the pulp produced by the process is utilized in the paper mill involved in traditional pulp of wood. Process according to any of the preceding claims, characterized in that the fiber pulp produced by the process is used in the desired layers in a multilayer web. V 20 A method according to any of the preceding claims, characterized in that two or more plants with herb stock are boiled and blended together. j 15. A method according to claim 14, characterized in that a long-fiber plant and a short-fiber plant with herb stock are boiled and blended together.