EP2029806A2

EP2029806A2 - Method for producing fibrous material

Info

Publication number: EP2029806A2
Application number: EP07723953A
Authority: EP
Inventors: Esa-Matti Aalto; Hans-Ludwig Schubert
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2006-06-08
Filing date: 2007-04-04
Publication date: 2009-03-04
Also published as: US20090314443A1; JP2009540132A; CA2634378A1; WO2007140837A3; BRPI0712857A2; WO2007140837A2

Abstract

The invention relates to a method for producing fibrous material with a lignin content of at least 15% for softwood, at least 12% for hardwood, or at least 10% for annual plants, relative to the oven-dry fiber mass in each case, consisting of the following steps: production of a chemical solution comprising more than 5% chemicals (calculated as NaOH) for softwood, or comprising more than 3.5% chemicals (calculated as NaOH) for hardwood, or more than 2.5% for annual plants, relative to the oven-dry quantity of the wood in each case; mixture of the chemical solution with wood or annual plants in a predefined bath ratio; heating of the chemical solution and of the wood or the annual plants to a temperature higher than room temperature; and then either (1st alternative) removal of free-flowing chemical solution and pulping of the wood or the annual plants in the vapor phase, or (2nd alternative) pulping of the wood or the annual plants in the liquid phase, and separation of the free-flowing chemical solution and the wood or the annual plants.

Description

Process for producing pulp

The invention relates to a process for the production of pulp from wood or annual plants with a lignin content of more than 15% for softwoods, for hardwoods of more than 12% and for annual plants of more than 10%, in each case based on the produced otro pulp, wherein the Fiber has predetermined strength properties.

Processes are known which produce pulps with a relatively high lignin content of over 15% for softwood and over 12% for hardwood. They provide a yield of 70% or more based on the starting material used. These methods are based on chemical and / or mechanical decomposition of the wood.

With mechanical defibration of the wood this is - usually after a pre-damping - decomposed into grinding aggregates into fiber bundles. These fiber bundles are then defibrillated by further grinding into individual fibers. The yield is very high, but also the required grinding energy. The strength of the wood fibers is very low, even after grinding, because the fibers contain much native lignin and therefore have little bonding potential. They are also degraded by the mechanical defibration, which impairs their recyclability.

In the case of chemical decomposition of the wood, chemicals usually act on the wood under increased pressure and elevated temperature. A typical process for high yield pulps is the NSSC process. However, other processes such as Kraft or soda may also be modified to produce high yield pulps (see Choosing the Best Brightening Process, N. Liebergott and T. Joachimides, Puck & Paper Canada, Vo. 80) , No. 12, December 1979). If the extraction of the originally used wood is to be limited to a maximum of 30%, far fewer chemicals are needed and used than in the production of pulps that are to be completely lignin-free. For the production of high yield pulps, the Quantity of chemicals dosed depending on the desired yield. In order to achieve a yield of about 70% based on otro wood use, it is recommended in the prior art to use up to 10% of chemicals based on the starting material. In the case of solid pulps, the use of chemicals is often 30% of the chemicals related to the otro wood or more.

Chemicals determine the process costs, so they are used as sparingly as possible. CTMP pulps are typically made with chemical levels of 3% to 5%. In known, industrially established processes for the production of high yield fibers, eg. As the NSSC process, up to 10% chemicals are used based on the starting material. With such a limited use of chemicals, no recovery for the recovery of the chemicals is yet to be installed. Despite the relatively small amounts of chemicals, this type of pulp production leads to a considerable environmental, especially water pollution, not only because of the chemical entry but mainly because of the organic cargo that is discharged into the receiving waters.

With regard to the cost situation, it should be noted that in the case of mechanically produced fibrous materials, the sharp rise in energy prices weighs on production costs. For chemically produced high yield pulps, production is burdened with the cost of the lost chemicals.

High yield pulps are ground to high levels of grinding for current uses. Only then will they reach an acceptable level of strength. As a high grinding degrees are here values of about 300 ml CSF (Canadian Standard Freeness), equivalent to 41 ⁰ SR (Schopper-Riegler, see below) and 500 ml CSF, equivalent to 26 "SR to look at as it z. B. 80, No. 12, December 1979, for high yield pulps from softwood The fibers are rubbed against each other or on a grinder or on a grinding media and thus changed in their surface properties towards a better bonding behavior. The high degree of grinding is therefore not an end in itself. It results rather from the requirements of the strength properties of the fiber.

The high yield fibers produced by mechanical and / or chemical means are used in particular where it is not absolutely necessary to have a high final whiteness and high whiteness stability. They could open up many more applications if the strength level could be increased.

It is therefore an object of the invention to provide a process for the production of pulp with a lignin content of more than 15% for softwood, more than 12% for hardwood and more than 10% for annual plants, with which fibers of high strength can be produced in an economical way ,

This object is achieved with a method for the production of pulp from wood or annual plants with a lignin content of at least 15% for softwood and 12% for hardwood and 10% for annual plants, each based on the otro fiber mass, with the steps:

- Make a chemical solution with more than 5% chemicals (calculated as

NaOH) for softwood or with more than 3.5% chemicals (calculated as NaOH) for hardwood or with more than 2.5% chemicals (calculated as NaOH), in each case based on the otro amount of wood used,

Mixing the chemical solution with the wood or annual plants in a predetermined liquor ratio,

Heating the chemical solution and the wood or annual plants to a temperature above room temperature and then either (1st alternative)

Removal of free-flowing chemical solution and - digesting the wood or annual plants in the vapor phase or (2nd alternative) - digesting the wood or annual plants in the presence of the

Chemical solution in liquid phase and

Separating the free-flowing chemical solution and the wood or the Annual plants.

The method according to the invention is based on the fact that higher quantities of chemicals are used for the production of high-yield fibers than has hitherto been customary. More than 5% of softwood chemicals are well above the hitherto common chemicals levels for engineering pulp production, also more than 3.5% for hardwood and 2.5% for annual plants. This high use of chemicals yields fibers with good yield and excellent strength properties. Thus, for softwood at grinding degrees of only 12 ⁰ SR to 15 ⁰ SR, breaking lengths of more than 8 km, but also breaking lengths of more than 9 km and more than 10 km are measured. For deciduous trees, values of more than 5 km, but also breaking lengths of more than 6 km and more than 7 km are measured at only 20 ⁰ SR. This achieves the desired high level of strength.

It is to be regarded as an extraordinary advantage of the method according to the invention that these strength values are achieved even at extremely low degrees of grinding, which were previously unavailable for high-yield fibers. Fibrous materials according to the prior art exhibit an unacceptable level of strength at freenesses of 12 ⁰ to 15 ⁰ SR SR for softwood pulps or 20 ⁰ SR for hardwood. Known pulps have so far yielded fibers at these low degrees of grinding which have not exhibited sufficient binding power and which accordingly have not provided sufficient strength properties for economical use of such fibers.

Suitable annual plants are, in particular, bamboo, hemp, rice straw, bagasse, wheat, miscanthus or the like.

By contrast, the fibrous materials produced by the process according to the invention have tear lengths of more than 8 km up to 11 km and tear strengths of more than 70 cN up to more than 110 cN, even at degrees in the range from 12 ^° SR to 15 ^° SR Leaf weight of 100 g / m ² . These low freeness levels are also achieved with a low specific demand for grinding energy, which is less than 500 kWh / t pulp for softwood pulps, and for hardwood pulp the demand for grinding energy may even be less than 300 kWh / t pulp. The realization that the high level of strength already at low degrees of grinding of 12 ⁰ SR to 15 ⁰ SR for softwood and 20 ⁰ SR for hardwood and below is achieved is an essential part of the invention.

These high strength values have hitherto not been known for pulps having a lignin content of more than 15% for softwood pulps, more than 12% for hardwood pulp or more than 10% for annual plants. The high

Strength level can also be higher for fibrous materials

Lignin content can be maintained. The inventive method is also suitable for the production of softwood pulps with a lignin content of more than 18%, preferably more than 21%, preferably more than 24% based on the otro

Fiber mass. Hardwood fibrous materials with a lignin content of more than 14%, preferably more than 16%, more preferably more than 18% and also

Annual plants with a lignin content of more than 10%, preferably more than 12

%, in particular more than 19% can also be produced by the process according to the invention and show a high level of strength.

The composition of the chemical solution used for the digestion can be determined in accordance with the wood to be broken or the annual plants and the desired pulp properties. As a rule, only one sulfite component is used. Alternatively or in addition, a sulfide component may be added. Digestion with a sulfite component is not disturbed by the presence of sulfide components. Technically, sodium sulfite is usually used, but also the use of ammonium or potassium sulfite or magnesium bisulfite is possible. In particular, when high amounts of sulfite are used, can be dispensed with the use of an alkaline component, because even without the addition of alkaline components, a high pH value sets, which favors the digestion.

To adjust the pH and to support the delignification, an acidic and / or an alkaline component can be added. The alkaline component is usually sodium hydroxide (NaOH) is used. However, it is also possible to use carbonates, in particular sodium carbonate. All information on chemical quantities of the digestion process in this document, eg. As for the total use of chemicals or for the distribution of the sulfite component and the alkaline component, unless otherwise stated, are each calculated and reported as sodium hydroxide (NaOH).

As an acid component, acids can be added to adjust the desired pH. However, preference is given to the addition of SO ₂ , if appropriate in aqueous solution. It is inexpensive and readily available, especially if the spent chemical solution z. B. based on sodium sulfite, after digestion is prepared for further use.

It is considered an independent inventive achievement to have recognized the advantages of using a quinone component for the high yield digestion of the invention. Quinone components, particularly anthraquinone, have heretofore been used in the manufacture of pulps with minimal lignin content to prevent unwanted attack on the carbohydrates towards the end of the digestion. The addition of quinone components makes it possible to continue the digestion of wood until almost complete degradation of the lignin. It has been found to be an unprecedented, unexpected property of quinone components that significantly increase the rate of lignin degradation in the production of high yield pulps. The duration of the digestion can z. B. in the production of softwood pulps by more than half, depending on digestion conditions shortened by more than three quarters. This remarkable effect is achieved with minimal use of quinone. Optimal is a use of z. As anthraquinone, which is between 0.005% and 0.5%. Use of anthraquinone of up to 1% also provides the desired effect. A use of more than 3% anthraquinone is usually uneconomical.

From single or several of the aforementioned chemicals, a chemical solution is prepared. Mostly an aqueous solution is used. Optionally, the use or addition of organic solvents may be provided. Alcohol, especially methanol and ethanol, in combination with water, result in particularly effective chemical solutions for the production of high-quality high-yield fibers. The Mixing ratio of water and alcohol can be optimized for the respective raw material in a few experiments.

The amount of chemicals to be used according to the invention for producing a pulp with a yield of at least 70% is at least 5% for softwood, at least 3.5% for hardwood and at least 2.5% for annual plants, in each case based on the otro wood or annual plant mass to be broken up. The quality of the produced pulp shows the best results with a chemical use of up to 15% for softwoods up to 10% for hardwood and up to 10% for annual plants. Preference is given to between 9% and 11% chemicals based on the used otro wood in softwood added. For hardwoods, the use of chemicals is rather lower, preferably between 4% and 10%, more preferably between 6% and 8% and in annual plants between 3 and 10%.

As already explained above, setting a specific pH is by no means required. Only if, for example, special properties of the pulps (particularly high whiteness, a certain ratio of breaking lengths and tear strength) are to be achieved with the digestion, it may be useful to add acid or an alkaline component before or during the digestion. According to an advantageous embodiment of the method according to the invention, regardless of the chosen use of chemicals as a whole, a ratio between an alkaline component and sulfur dioxide (SO ₂ ) can be adjusted within a wide range. SO ₂ is mentioned here as representative of the above-mentioned acidic component. So it can be used instead of SO ₂ and an acid. Since the possibly added quinone component is used only in minimal amounts, usually well below 1%, it is negligible for setting this ratio. A ratio of alkaline component: SO ₂ in a range of 4: 1 to 1.6: 1 is well suited to carry out the process according to the invention and to achieve fibers with high strength properties. A customary, particularly suitable range is between 2: 1 and 1.6: 1. The adjustment of the proportionate components takes place depending on the raw material to be digested and the respectively selected process control (digestion temperature, digestion time, impregnation). The process of the invention can be carried out in a wide pH range. The ratio of alkaline component to acidic component or the use of an acidic or an alkaline component can be adjusted so that at the beginning of the process, a pH between 6 and 11, preferably between 7 and 11, more preferably between 7.5 and 10 is set. The more alkaline pH's between 8 and 11, which are beneficial to the process of the invention, also favor the effect of the quinone moiety. The method according to the invention is tolerant with regard to the pH; There are few chemicals required for pH adjustment. This has a favorable effect on the costs of chemicals.

Without further addition of acid or alkaline component arises, for. For example, for softwood, at the end of the digestion, a pH between 8 and 10, usually between 8.5 and 9.5 in the free-flowing chemical solution and the dissolved organic components that have been liquefied by the digestion, a. Among the dissolved organic components are mainly lignosulfonates.

The liquor ratio, ie the ratio of the amount of otro wood or annual plants to the chemical solution, is set between 1: 1, 5 and 1: 6. A liquor ratio of 1: 3 to 1: 5 is preferred. In this range, a good and simple mixing and impregnation of the material to be digested is ensured. For softwood a liquor ratio of 1: 4 is preferred. For wood chips with a large surface, the liquor ratio can also be significantly higher to allow rapid wetting and impregnation. At the same time, the concentration of the chemical solution can be kept so high that the liquid volumes to be circulated are not too large.

The mixture or impregnation of the wood or Einjähraufschlussgut preferably takes place at elevated temperatures. Heating the chips and the chemical solution up to 110 ⁰ C, preferably up to 120 ⁰ C, more preferably up to 130 ⁰ C leads to a rapid and uniform digestion of the wood. For the mixing or impregnation of the wood chips is a period of up to 30 minutes, preferably up to 60 minutes, more preferably from to advantageous to 90 minutes. The optimum time depends, among other things, on the amount of chemicals and the liquor ratio and the type of digestion (liquid or vapor phase).

The digestion of the mixed with the chemical solution or impregnated lignocellulosic material is preferably carried out at temperatures between 120 ⁰ C and 190 ⁰ C, preferably between 150 ⁰ C and 180 ⁰ C. For most woods are digestion temperatures between 155 ⁰ C and 170 ⁰ C. set. Higher or lower temperatures can be adjusted, but in this temperature range, the energy required to heat and accelerate the digestion are in an economic relationship. Higher temperatures can also have a negative effect on the strength and whiteness of the fibers. The pressure generated by the high temperatures can be easily absorbed by appropriate design of the digester. Usually, the duration of the heating is only a few minutes, usually up to 30 minutes, advantageously up to 10 minutes, in particular when heated by means of steam. The duration of the heating can take up to 90 minutes, preferably up to 60 minutes, z. B. when it is digested in the liquid phase and the chemical solution is to be heated together with the wood chips.

The duration of the digestion is chosen especially depending on the desired pulp properties. The duration of the digestion can be shortened to up to 2 minutes, z. B. in the case of a vapor phase digestion of a hardwood with low lignin content. But it can also be up to 180 minutes, if z. B. the digestion temperature low and the natural lignin content of the aufzuschließenden wood is high. Even if the initial pH of the digestion is in the neutral range, a long digestion time may be required. Preferably, the digestion time is up to 90 minutes, especially in coniferous wood. Particularly preferably, the digestion time is up to 60 minutes, advantageously up to 30 minutes. A digestion time of up to 60 minutes is mainly considered for hardwoods.

In annual plants, the digestion time is up to 90 minutes. The use of a quinone component, in particular anthraquinone, allows a reduction the digestion time up to 25% of the time required without addition of anthraquinone. If the use of quinone components is omitted, the digestion time is extended by more than one hour, for example from 45 minutes to 180 minutes, for comparable digestion results.

According to an advantageous embodiment of the method according to the invention, the duration of the digestion is set as a function of the selected liquor ratio. The lower the liquor ratio, the shorter the process duration can be set.

The production of high yield pulp with high chemical input of more than 5% for softwood, of more than 3.5% for hardwood and at least 2.5% for annual plants initially appears uneconomical. Experiments have shown, however, that only some of the chemicals are consumed during the partial digestion of the lignocellulosic material. The majority of the chemicals are discharged unused, either before digestion (vapor phase digestion) or after digestion (digestion in the liquid phase). The actual consumption of chemicals is below the amounts used in the digestion solution.

Chemical consumption is recorded as the amount of chemicals measured in terms of the original amount of chemicals after removal or separation of the chemical solution and, if necessary, detection of chemical solution measured after defibration or in conjunction with detection of the chemical solution. The consumption of chemicals depends on the absolute amount of chemicals used for the digestion, based on the otro wood mass to be digested. The higher the use of digestion chemicals, the lower the direct sales of chemicals. When using 27.5% of chemicals based on otro wood pulp, for example, only about 30% of the chemicals used are consumed. However, when 15% of the chemicals are used in relation to otro wood, 60% of the chemicals used are consumed, as demonstrated in laboratory tests. The consumption of chemicals for the process according to the invention is up to 80%, preferably up to 60%, according to a preferred embodiment of the process during the digestion. particularly preferably up to 40%, advantageously up to 20%, particularly advantageously up to 10%, of the chemical used at the beginning of the digestion.

The chemical consumption for producing one ton of pulp is about 6% to 14% sulfite and / or sulfide component and possibly alkaline and / or acidic component and possibly quinone component based on otro pulp (hardwood and softwood or annual plants). According to the invention, this amount of chemicals is sufficient to produce a pulp having the predetermined properties. However, in order to ensure a uniform process result and possibly to obtain special, desired pulp properties, it may prove useful to use higher amounts of chemicals for the digestion, z. As the above mentioned up to 30% chemicals based on otro wood or annual plant mass. The use of these amounts of chemicals at the beginning of the digestion shows advantageous effect, since the fibers obtained in this way have previously unavailable properties, in particular high strength properties and high degrees of whiteness. In particular, no digestion process is currently available that produces high strength pulps over a broad pH spectrum from the neutral to the alkaline range. As economically particularly attractive has been found that the fibers produced according to the invention are to be ground with much lower energy consumption to predetermined degrees of grinding than known fibers. In addition, they develop the high strengths even at unusually low grinding grades from 12 ⁰ SR to 15 ⁰ SR for softwood and 20 ⁰ SR for hardwood.

Excess chemicals are present after mixing and impregnating the wood with the chemical solution or after digestion in the free flowing liquid. This excess is deducted before digestion (1st alternative) or after digestion (2nd alternative). According to an advantageous embodiment of the method, the composition of the removed chemical solution is detected and then adjusted to a predetermined composition for re-use for the production of fibers. The chemical solution, before or after the decomposition of the wood or the Annual plant is removed, no longer has the original composition. At least some of the chemicals used for digestion have - as described above - penetrated into the material to be digested and / or has been consumed in the digestion. The unused chemicals can easily be used again for the next digestion. However, it is proposed according to the invention to first determine the composition of the removed chemical solution and then the consumed proportions of z. As sulfite, alkaline component, quinone component or water or alcohol to supplement to restore the predetermined composition for the next digestion. This supplementary step is also called strengthening.

It is to be regarded as a considerable advantage of this measure that the chemical solution contains no or only very few substances, especially when removed before digestion, but also when removed after digestion, which is the next time the recovered chemical solution is used again Disruption proves to be annoying. The method according to the invention, which aims to provide an oversupply of digestion chemicals during impregnation, can thus be extremely economical despite the initially uneconomic approach of high chemical use, because the removal or separation and the strengthening of the chemical solution can be carried out easily and inexpensively.

The process of the invention is specifically controlled so that only as little of the starting material used is degraded or dissolved. The aim is to produce a pulp which has a lignin content of at least 15% based on the otro fiber mass for softwood, preferably a lignin content of at least 18%, more preferably 21%, advantageously at least 24%. For hardwood is sought to achieve a lignin content of at least 12% based on the otro fiber mass, preferably of at least 14%, more preferably of at least 16%, advantageously of at least 18%. In annual plants, the preferred lignin content is between 10 and 28%, in particular between 12 and 26%. The yield of the process according to the invention is at least 70%, preferably more than 75%, advantageously more than 80%, in each case based on the wood used. This yield correlates with the lignin content of the pulp stated above. The original lignin content of wood is specific to the species. In the present process, the yield loss is predominantly a loss of lignin. In the case of nonspecific digestion processes, the proportion of carbohydrates is markedly increased, eg. B. because digestion chemicals in an undesirable manner also bring cellulose or hemicelluloses in solution.

A further, advantageous measure is to remove after defibering and optionally grinding the lignocellulosic material, the remaining chemical solution and feed it to a further use. In a preferred embodiment, this reuse can include two aspects. On the one hand, the decomposed during the partial digestion or dissolved in organic material, mainly lignin, continue to be used. It is burned, for example, to gain process energy. Or it is prepared to be used elsewhere. On the other hand, the used and unused chemicals are reprocessed so that they can be used for a renewed, partial digestion of lignocellulosic material. This includes the treatment of used chemicals.

According to a particularly preferred variant of the method according to the invention, the chemical solution used is used extremely efficiently. After defibering and optionally grinding, the pulp is washed to displace the chemical solution as much as possible through water. The filtrate produced in this washing or displacement process contains considerable amounts of chemical solution and organic material. According to the invention, this filtrate is supplied to the removed or separated chemical solution before the chemical solution is fortified and fed to the next digestion. The chemicals and organic components contained in the filtrate do not disturb the digestion. To the extent that they still contribute to delignification during the next digestion, their content is recorded in the chemical solution and taken into account in determining the amount of chemicals required for this digestion. The chemicals further contained in the filtrate behave inert during the pending digestion. They do not bother. The organic constituents contained in the filtrate are also inert. They will continue to be used in the processing of the chemical solution after the next digestion, either to generate process energy or otherwise.

It is considered to be particularly advantageous that less filtrate water and fewer chemicals are used for digestion by this filtrate. At the same time a maximum of dissolved organic material is detected. This improved use of the dissolved organic material also improves the economy of the process according to the invention.

Details of the method and the device according to the invention are explained in more detail below with reference to exemplary embodiments.

The following tests were evaluated according to the following rules:

The yield was calculated by weighing the raw material used and the pulp obtained after the pulping, in each case dried at 105 ^° C. to constant weight (atro). The lignin content was determined as Klason lignin according to TAPPT T 222 om-98.

The acid-soluble lignin was determined according to TAPPI UM 250

The paper technology properties were determined on test sheets which were produced according to Zellcheming leaflet V / 8/76.

The freeness was measured according to Zellcheming leaflet V / 3/62. - The density was determined according to Zellcheming regulation V / 11/57.

The breaking length was determined according to Zellcheming regulation V / 12/57. The tear resistance was determined according to DIN 53 128 Elmendorf.

The determination of Tensile, Tear and Burst Index was carried out according to TAPPI 220 sp. 96. The whiteness was determined by preparing the test sheets according to Zellcheming leaflet V / 19/63, measured according to SCAN C 11:75 with a Datacolor elrepho 450 x photometer; the whiteness is given in percent according to ISO standard 2470. - The viscosity was determined according to the leaflet IV / 36/61 of the Association of Pulp and Paper Chemists and Engineers (Zellcheming).

- All% figures in this document are to be read as weight percent unless otherwise specified. - The term "otro" in this document refers to "oven-dry" material which has been dried at 105 ^° C. to constant weight. The digestion chemicals are reported in weight percent as sodium hydroxide, unless otherwise specified.

Example 1 - Softwood pulping in the liquid phase

A mixture of spruce wood and Douglas fir wood chips was after a damping (30 minutes in saturated steam at 105 ⁰ C) with a sodium sulfite pulping solution at a liquor ratio of wood: digestion solution 1: 3 added. The total use of chemicals was less than 15% based on otro woodchips. The pH at the beginning of the digestion was adjusted to pH 6 by addition of SO ₂ .

The impregnated with chemical solution spruce wood chips were heated over a period of 90 minutes at 170 ⁰ C and digested for 60 minutes at this maximum temperature.

Subsequently, the free-flowing liquid was removed by centrifugation, collected and analyzed and strengthened in an arrangement for recycling unconsumed liquid and thus provided for the next digestion.

The open-ended wood chips were shredded. Aliquots of the pulp so produced were ground for different lengths to determine the strength at different degrees of grinding. The energy required to shred the partially digested chips was less than 300 kWh / t of pulp.

The yield in this experiment was 77% based on the wood pulp used. This corresponds to a pulp with a lignin content of well over 20%. The average lignin content for spruce wood is given as 28% in relation to the otro wood mass (Wagenführ, Anatomie des Holzes, VEB Fachbuchverlag Leipzig, 1980). The actual lignin content of the pulp is higher than 20%, because during digestion mainly but not exclusively lignin is broken down. Carbohydrates (cellulose and hemicelluloses) are also dissolved in small amounts. The values given show that the digestion has a good selectivity with regard to lignin and carbohydrate degradation.

The whiteness is unexpectedly high with values of over 55% ISO and thus provides a good starting point for a possible subsequent bleaching, in the whiteness of 75% ISO can be achieved.

At a starting grinding degree of 12 ^° SR, these substances already have 6 km of breaking length with a specific weight of 1.87 cm ³ / g.

To grind the fibers to a degree of grinding of 15 ⁰ SR, a grinding time of 20 to 30 minutes is required. Up to a grinding time of 20 minutes (freeness SR 12 ⁰ - 15 ⁰ SR), the freeness developed independently of the pH value at the start of the digestion (pH 6 to pH 9.4) in a narrow corridor.

Also regardless of the initial pH of the digestion and the grinding time required to reach the degree of grinding a high level of strength is achieved at a freeness of 15 ⁰ SR.

Example 2

The pulp was made from spruce wood chips with the pH at the beginning of the digestion being 9.4.

In addition to the 15% total chemicals (sulfite and NaOH in predetermined proportions), the chemical solution 0.1 anthraquinone was added based on the amount of wood used.

The duration of the digestion was 60 minutes. The following values resulted:

Yield (%): 81, 1 lignin content: 22.7

Whiteness (% ISO): 53.7

Tear length (km): 9.6

Tear resistance (cN, 100 g / m ² ): 75.0

By adding 0.1% anthraquinone, the duration of digestion can be reduced from approx. 180 minutes to 60 minutes under otherwise unchanged digestion conditions. This time saving is valuable, above all because the plants for producing pulp can be made smaller. Further savings potential lies in the fact that the temperature required for digestion only needs to be maintained for a much shorter period of time.

Furthermore, it was determined that with decreasing use of total chemicals up to values of between 5 and 15% softwood pulp is produced with largely equally good properties. These results are not dependent on the use of anthraquinone. The anthraquinone causes an acceleration of the digestion, the desired pulp can also be digested without the addition of anthraquinone.

Example 3: Hardwood pulping in the liquid phase

Eucalyptus chips were added after attenuation with a sodium sulfite digestion solution at a liquor ratio of wood digestion solution 1: 3. The use of chemicals here was 10.5% (as NaOH) on otro woodchips.

In the period of 90 minutes, the pulp was impregnated and the food was heated to the maximum digestion temperature of 170 ⁰ C. The cooking time was 50 minutes. Digestions with eucalyptus wood show that these substances can be produced with a specific energy input for defibration of less than 250 kWh / t.

The yield in these experiments was 77% based on the wood pulp used. In an initial freeness of 14 SR these substances have already 3.5 kilometers tenacity / g at a specific of 2.05 cm ^3. These substances bleached to whiteness of 79.6% ISO in the following bleach.

Experiments have shown that the vapor phase digestions have a low overall time requirement. Compared to the digestion in the liquid phase, the heating up to the maximum digestion temperature takes place much faster. The actual digestion then takes the same duration as a boiling in the liquid phase. There is no free-flowing chemical solution during vapor phase digestion, which is removed after impregnation and before digestion. It is therefore less mixed with organic material than the chemical solution, which is withdrawn after digestion in the liquid phase. However, this does not affect the quality of the pulp produced.

While in the case of vapor-phase digestions similar values can be achieved in the yield, the whiteness of the fibers produced during the steam digestion is significantly lower. A significant effect is the reduction of the maximum digestion temperature from 170 ⁰ C to 155 ⁰ C: the whiteness increases.

The fibers produced in the vapor phase have excellent strengths. The tenacity was measured, for example, at 10 km and at 11 km at 15 "SR The tearing resistance was measured, for example, at 82.8 cN and at 91.0 cN These values correspond to the best values for high lignin content pulps for pulps in For pulps with a high lignin content from the prior art comparable strength values are not known. It can be seen particularly clearly from the examples that the fibrous materials according to the invention require only a small amount of energy during grinding in order to build up high breaking lengths without reducing the tear propagation resistance. Grinding 12 ⁰ SR was achieved in 0-10 minutes; Grinding degree 13 ⁰ SR 5-30 minutes, usually 10-20 minutes. In order to reach grind level 14 ⁰ SR, the Jokro mill had to work for 30-40 minutes and for grind level 15 ⁰ SR it took between 35 and 40 minutes. It is obvious that a grinding up to Mahlgrade by 40 ⁰ SR would require an enormous amount of grinding energy. A particular advantage of the method according to the invention is therefore to be seen in the fact that with low energy consumption to be milled fibers are produced with high strengths.

Claims

claims

1. A method for producing pulp from wood or annual plants with a lignin content of at least 15% for softwood, of at least 12% for hardwood and of at least 10% for annual plants, each based on the otro pulp, with the steps

- manufacture a chemical solution with more than 5% chemicals (calculated as NaOH) for softwood or with more than 3.5% chemicals (calculated as NaOH) for hardwood or with more than 2.5% chemicals (calculated as NaOH) for annual plants, each related to the otro

Amount of wood

- Mixing the chemical solution with wood or annual plants in a given liquor ratio

- Heating the chemical solution and the wood or the annual plants to a temperature above room temperature and then

- either (1st alternative)

Remove free-flowing chemical solution and

Digesting the wood or annual plants in the vapor phase - or (2nd alternative)

Digesting the wood or annual plants in the liquid phase and separating the free-flowing chemical solution and the wood or annual plants.

2. The method according to claim 1, characterized in that a pulp having a content of at least 15% lignin, preferably at least 18% lignin, advantageously at least 21% lignin, in particular at least 24% lignin based on otro pulp for softwood or with a content of At least 14% lignin, preferably at least 16% lignin, more preferably at least 18% lignin based on otro pulp for hardwood or containing at least 10% lignin, preferably at least 12% lignin, especially at least 19% lignin based on otro pulp for annual plants will be produced.

3. The method according to claim 1 or 2, characterized in that for the preparation of the chemical solution, a quinone component is used.

4. The method according to any one of the preceding claims, characterized in that for the decomposition of softwood at most 15% chemicals, preferably between 9 and 11% chemicals are used.

5. The method according to any one of the preceding claims, characterized in that for the digestion of hardwood at most 10% chemicals, preferably between 4 and 10% chemicals, in particular between 6 and 8% chemicals are used.

6. The method according to any one of the preceding claims, characterized in that for the digestion of annual plants at most 10%, preferably between 3 and 10% chemicals are used.

7. The method according to any one of the preceding claims, characterized in that for the preparation of the chemical solution sulfites and

Sulfides, used singly or in mixture.

8. The method according to claim 7, characterized in that for the preparation of the chemical solution, an acidic and / or an alkaline component, in particular an acid, sulfur dioxide, sodium hydroxide and / or a

Carbonate is used.

9. The method according to any one of the preceding claims, characterized in that for the digestion of an alkaline component and an acidic component, in particular SO ₂ are used, wherein the

Alkaline component ratio: SO _{2 is} adjusted in a range of 4: 1 to 1.6: 1, preferably 2: 1.

10. The method according to any one of the preceding claims, characterized in that the method at a pH between 6 and 11, preferably between 7 and 11, more preferably between 7.5 and 10 is performed.

11. The method according to any one of the preceding claims, characterized in that a liquor ratio wood: chemical solution between 1: 1, 5 and 1: 6, preferably between 1: 3 and 1: 5 is set.

12. The method according to any one of the preceding claims, characterized in that the heating of the chemical solution and the wood or the annual plants up to 130 ⁰ C, preferably up to 120 ⁰ C, advantageously up to 110 ⁰ C.

13. The method according to any one of the preceding claims, characterized in that the heating of the wood or the annual plants and optionally the chemical solution takes up to 90 minutes, preferably up to 60 minutes, advantageously up to 30 minutes, particularly advantageously up to 10 minutes ,

14. The method according to any one of the preceding claims, characterized in that the digestion of the wood or annual plants at temperatures between 120 ⁰ C and 190 ⁰ C, preferably at temperatures between 150 ° C and 180 ⁰ C, particularly preferably at temperatures between 160 ⁰ C and 170 ⁰ C is performed.

15. The method according to any one of the preceding claims, characterized in that the digestion of the wood or annual plants up to 180 minutes, preferably up to 90 minutes, more preferably up to 60 minutes, advantageously up to 30 minutes, particularly advantageously up to 2 Takes minutes.

16. The method according to claim 15, characterized in that the duration of the digestion is selected depending on the liquor ratio.

17. The method according to any one of the preceding claims, characterized in that the consumption of chemicals during the digestion up to 80%, preferably up to 60%, more preferably up to 40%, advantageously up to 20%, particularly advantageously up to 10% of

Use of chemicals at the beginning of digestion.

18. The method according to any one of the preceding claims, characterized in that the composition of the removed or separated chemical solution detected and then for reuse for

Production of fibers is adjusted to a predetermined composition.

19. The method according to any one of the preceding claims, characterized in that released after the defibration and optionally grinding the digested lignocellulosic material

Chemical solution is removed and sent for further use.