EP2029808A2

EP2029808A2 - Method for producing fibrous material made of wood

Info

Publication number: EP2029808A2
Application number: EP07723955A
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: US8758557B2; BRPI0712854A2; US20100032111A1; WO2007140839A2; WO2007140839A3; JP2009540134A; CA2634380C; CA2634380A1

Abstract

The invention relates to a method for producing fibrous material consisting of the following steps: production of a chemical solution with less than 25% sulfite (calculated as NaSO3), relative to the oven-dry quantity of the lignocellulosic raw material; mixture of the chemical solution with wood in a predefined bath ratio; heating the chemical solution and the wood to a temperature higher than room temperature; and then either (1st alternative) removal of free-flowing chemical solution and pulping of the wood in the vapor phase, or (2nd alternative) pulping of the wood in the liquid phase, and separation of the free-flowing chemical solution and the wood.

Description

Description Method for producing wood pulp

The invention relates to a process for the production of pulp from lignocellulosic raw materials with low use of chemicals. In particular, the invention relates to a process for the production of high lignin content pulp, e.g. B. for softwoods of more than 15% and for hardwoods of more than 12%, each based on the produced otro pulp, the pulp usually 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 (Semichemical Pulping for Grading Grades, page 130 ff; in PuIp and Paper Manufacture, 3 ^rd Edition, Vol. 4, Sulfite Science and Technology - ISBN 0- 919893-04-X). In addition to sodium sulphide, this process always involves an alkaline component, typically sodium carbonate. nat, used in the digestion solution. However, other processes such as the soda process and the soda process can be modified to produce high yield pulps (see "Choosing the best brightening process", N. Liebergott and T. Joachimides, PuIp & Paper Canada, Vol 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 amount of chemicals is metered 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 ⁰ SR, to look at, as they z. In "Choosing the best brightening process", N. Liebergott and T. Joachimides, PuIp & Paper Canada, Vol. 12, December 1979, for high yield pulps of softwood. A high degree of grinding is achieved by using mechanical energy. 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 propose a process for the production of pulp, with which fibers of high strength can be produced in an economical manner.

This object is achieved with a process for the production of pulp from lignocellulosic raw material with the following steps:

Producing a chemical solution with less than 25% sulphite (calculated as Na SO3), in each case based on the otro amount of the wood used, mixing the chemical solution with the wood in a predetermined liquor ratio,

Heating the chemical solution and the wood to a temperature above room temperature and then either (1st alternative) - removing free-flowing chemical solution and digesting the wood in the vapor phase or (2nd alternative) digesting the wood in the presence of the liquid-phase chemical solution and Separate the free-flowing chemical solution and the wood.

The method according to the invention is based on the fact that a minimum of chemicals is used for the production of high-yield fibers. Despite the low use of chemicals, the process according to the invention yields fibers with good yield and excellent strength properties. Thus, for softwood fibers, which are produced according to a preferred embodiment of the method according to the invention, at grindings of only 12 ⁰ SR to 15 ⁰ SR tensile lengths of more than 8 km, but also tensile lengths of more than 9 km and more than 10 km measured , For hardwood fibers, which are produced according to an advantageous embodiment of the method according to the invention, measured at only 20 ⁰ SR values of more than 5 km, but also tear lengths of more than 6 km and more than 7 km. This achieves the desired high level of strength.

In the process described in DE 10 2006 027006, which is regarded as the closest prior art, it was initially considered that the quality of the high-yield pulp produced there was more than 10% (calculated as NaOH) for the high chemical input. for softwood and more than 7% (calculated as NaOH) for hardwood. Experiments have shown, however, that a pulp can be produced with the same qualities, if much smaller amounts of sulfite are used and if the use of alkali, eg. B. of NaOH or Na2CO3 is omitted. The requirement for sulphite can be reduced by 10% to 50%, in most cases by 20% to 40%, usually by 25% to 35%, compared to the process according to DE 10 2006 027006 in the process according to the invention. This is a significant advance on the one hand achieved in the process costs. On the other hand, the inventive method works much more environmentally friendly, because a total of a minimum of chemicals is used to produce a particularly high quality and versatile fiber. In addition, only a small and therefore particularly economical and environmentally friendly chemical reprocessing is required to close this process.

The inventive method is used according to an advantageous embodiment for the production of high yield fibers. These high strength values are for Fibers with a lignin content of more than 15% for softwood pulps and more than 12% for hardwood pulps previously unknown. However, the high strength level can also be maintained for fibers with an even higher lignin content. The inventive method is also suitable for the production of softwood pulps with a lignin content of more than 17%, preferably more than 19%, advantageously more than 21% based on the otro fiber mass. Hardwood fibrous materials with a lignin content of more than 14%, preferably more than 16%, particularly preferably more than 18%, can likewise be prepared by the process according to the invention and exhibit a high level of strength.

The advantages described above are fully applicable to such high yield pulps. It is to be regarded as an extraordinary advantage of the method according to the invention that the described strength values are achieved even at extremely low degrees of grinding, which hitherto were not available for high yield fibers in combination with high strength values. 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 hitherto yielded fibers at these low degrees of grinding which did not have sufficient binding capacity and which accordingly did not offer sufficient strength properties for an economical use of such fibers.

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 levels of grinding are also achieved with a low specific demand for grinding energy, which is less than 350 kWh / t of pulp for softwood pulps, and for hardwood pulps the demand for grinding energy may even be less than 250 kWh / t of pulp. The realization that the high level of strength is already achieved at low grinding degrees of 12 ⁰ SR to 15 ⁰ SR for softwood and 20 ⁰ SR for hardwood and below, is an essential part of the invention. The composition of the chemical solution used for the digestion can be determined in agreement with the wood to be digested and the desired pulp properties. As a rule, only one sulfite component is used. Alternatively or in addition, a sulfide component can 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.

It is considered as an independent inventive achievement to have recognized the advantages of using a quinone component for the high yield digestion of the present invention. Quinone components, especially 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 they significantly increase the speed of lignin sulfonation in the production of high yield pulps. The duration of the digestion can z. B. in the manufacture 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 process of the invention can be carried out in a wide pH range. Depending on the amount of sulfite used or on the composition of the chemical solution, a pH value between 6 and 11, preferably between 7 and 11, particularly preferably between 7.5 and 10, can be set at the beginning of the process. 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 for chemicals.

Without further addition of acid or alkaline components arises, for. For example, for softwood, at the end of the digestion, a pH between 5.5 and 10, usually between 7.5 and 8.5 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, that is the ratio of the amount of otro wood 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 chips is preferably carried out 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, a period of time of up to 30 minutes, preferably of up to 60 minutes, particularly preferably of up to 90 minutes, is advantageous. The The optimum time depends, among other things, on the amount of chemicals and 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 decomposition temperatures between 155 ⁰ C and 170 ⁰ C is set. Higher or lower temperatures can be set, but in this temperature range, the energy required to heat up and accelerate the digestion is in an economic relationship. Higher temperatures can also have a negative impact on the strength, yield and whiteness of the pulp. The pressure generated by the high temperatures can be easily absorbed by appropriate design of the digester. The duration of the heating depends on the capacity of the digester and is at low mass entry, that is, a low liquor ratio only a few minutes, usually up to 30 minutes, advantageously up to 10 minutes, especially when heated by 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. The use of a quinone component, in particular anthraquinone, allows a reduction of the digestion time to up to 25% of the time required without the addition of anthraquinone. If the use of quinone components is dispensed with, it will be extended for comparable digestion results the digestion time by more than one hour, for example from 45 minutes to 180 minutes.

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 amount of chemicals to be used according to the invention for the production of a pulp with a yield of at least 70% is up to 25% sulphite for softwood and up to 18% sulphite for hardwood, in each case based on the otro wood pulp to be broken up. The quality of the pulp produced shows the best results with a chemical use of up to 15% sulphite for softwood and hardwood. Preference is given to adding up to 20% sulphite, particularly preferably up to 15% sulphite, based on the amount of otro coniferous wood used. For hardwoods, the use of chemicals is rather lower, preferably up to 12% sulfite, more preferably up to 10% sulfite. In order to achieve fibers with the high strength properties according to the invention, a sulphite use of at least 7% based on the otro wood mass to be broken up is required.

Further investigations have shown that only part of the chemicals, in particular sulfite, are consumed during the partial digestion of the lignocellulosic raw material. The majority of the chemicals are discharged unused, either before digestion (vapor phase digestion) or after digestion (digestion in the liquid phase). The consumption of chemicals is below the levels used in the digestion solution.

The chemical consumption is recorded as the amount of chemicals (sulfite) that - relative to the originally used amount of chemicals - after removal or separation of the chemical solution and, if necessary, detection of chemical solution after defibering or in connection with detection of the chemical solution is measured. The consumption of chemicals depends on the absolute amount of chemicals used for the digestion, based on the chemicals to be broken down otro wood pulp. The higher the use of digestion chemicals, the lower the direct sales of chemicals. When using 25% sulfite based on otro wood pulp, for example, only about 40% of the chemicals used are consumed. However, when using 16% sulphite in relation to otro wood, about 45-50% of the chemicals used are consumed, as could be proven in laboratory experiments.

The consumption of sulphite during digestion depends on the lignin content of the starting raw material. Derived from lignin degradation and other chemical reactions, chemical consumption to produce one tonne of pulp is up to 13% sulfite for lignocellulosic feedstock with a lignin content of more than 25% based on otro raw material (typically softwood, numerous hardwoods), up to 10% sulfite for lignocellulosic raw material with a lignin content of 20% up to 25% based on otro raw material (typically annual plants or

Hardwood with low lignin content such as poplar or beech). In the case of lignocellulosic raw material with a lignin content that is significantly below 20%, based on otro raw material, typically annual plants such as grasses or bananas, the consumption of sulphite initially used for digestion may also be less than 10%, but at least 7%.

In order to ensure a uniform process result and possibly to obtain special, desired pulp properties, according to the invention only this relatively small amount of sulphite is consumed. These 7% to 13% sulfite, which are actually consumed during the digestion, represent only a subset of the total sulfite used for the digestion. A chemical solution with up to 25% sulfite based on the lignocellulosic raw material to be digested is nevertheless economical and useful according to the invention z. B. to influence the reaction rate positive or to suppress unwanted side reactions. Only the amount of chemicals actually consumed in digestion, especially sulphite, must be added fresh during the preparation of chemical solution for the next digestion. The excess unused sulphite contained in the chemical solution already used is, according to a preferred embodiment of the present invention, recycled and is available again for the subsequent digestion of lignocellulosic raw material.

It follows from the above that the digestion solution of the previous digestion, which contains considerable amounts of unused sulphite, is available for the preparation or preparation of chemical solution for the next digestion. In addition, however, the use of fresh or reprocessed chemicals is required. It has proved to be advantageous according to a preferred embodiment of the method according to the invention to divert a partial flow of the already used chemicals or digestion solution. This diverted partial stream of the already used chemical solution is recycled to the digestion chemicals, in particular the sulfite. It is sufficient if only a partial stream of the chemical solution is fed to the reprocessing after digestion. A proportion of the chemicals, in particular of the sulfite, which is consumed during the digestion can thus be recovered by recycling only a partial stream of the chemical solution as fresh sulfite. The other part of the chemical or digestion solution, which is recycled without special treatment, directly from the recycling of used chemical solution in circulation, and contains the unused sulfite, is another essential ingredient of the digestion solution, usually with an above-mentioned proportion of freshly added or recycled sulfite as described above. Unused sulfite recycled without treatment is used in a total amount of up to 75% of the total sulfite required for digestion. Finally, fresh sulfite can be added or recycled in the reprocessing of the chemicals, or fresh sulfite can be added directly to the chemical solution.

According to an advantageous variant of the process according to the invention, up to 30% by weight, preferably up to 50% by weight, particularly preferably up to 75% by weight, of sulfite from the recirculation of chemical solution already used for the digestion is used in the preparation of the chemical solution to 70% by weight, preferably up to 50% by weight, more preferably up to 25% by weight of sulfite fresh or equivalent fresh, from the reprocessing. 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 strengths 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 that is removed before or after the wood is thinned 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 to determine the consumed proportions of, for 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 even if it is removed before the digestion, but also when it is removed after the digestion, no or only very few substances that are in a re-use of the strengthened chemical solution for the next digestion. The method according to the invention, which aims to provide an oversupply of digestion chemicals in the impregnation, can thus be extremely economical despite the initially uneconomical approach of high chemical use, since the removal or separation and the strengthening of the chemical solution can be carried out easily and inexpensively.

Another advantage of this measure is that the solids content of the used digestion solution increases after a partial recirculation. An increase of z. B. 9% up to 22% solids content is possible after a multiple recirculation. The calorific value of the spent digestion solution increases by up to 20%. In particular, the content of organic solids increases. The content of inorganics (sulfite, etc.) drops from 56% absolute solids content after a first digestion to up to 44% absolute solids content after repeated recycling of the digestion solution.

The process of the invention is specifically controlled so that only as little as possible of the lignocellulosic starting material used is degraded or dissolved. The aim is to produce a pulp, the z. For example, for softwood has a lignin content of at least 15% based on the otro fiber mass, preferably a lignin content of at least 18%, more preferably 21%, advantageously at least 24%. For hardwood it is desired to achieve a lignin content of at least 12% based on the fiber mass, preferably of at least 14%, more preferably of at least 16%, advantageously of at least 18%.

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 lignocellulosic raw material used. This yield correlates with the lignin content of the pulp stated above. The original lignin content of a lignocellulosic raw material is specific to the species. The loss of yield in the present process is predominantly a loss of lignin and easily hydrolyzable hemicelluloses. In non-specific digestion processes, the proportion of carbohydrates is significant. lent increased, z. 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 the 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 further contained in the filtrate chemicals 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-technical properties were determined on test sheets, which were prepared according to Zellcheming leaflet V / 8/76. The degree of beating was determined according to Zellcheming leaflet V / z / (> 2. The density was determined according to Zellcheming regulation V / 11 / 57. The tearing length was determined according to Zellcheming regulation V / 12 / 57. The tear propagation resistance became DIN 53 128 Elmendorf determined.

Tensile, Tear and Burst indices were determined 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 should 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 given in weight percent as the particular chemical used unless otherwise stated.

Example i - Digestion in the liquid phase After a damping (30 minutes with saturated steam at 105 ^° C.), spruce wood chips are mixed with a sodium sulfite digestion solution at a liquor ratio of wood: digestion solution 1: 3. The total use of chemicals was 23.6% calculated as sodium sulfite, based on otro spruce wood chips. The spruce wood chips impregnated with the chemical solution were heated to 170 ^° C. over a period of 90 minutes and digested for more than 180 minutes at this maximum temperature. The initial pH was in the range of pH 8.0 to 9.5.

Subsequently, the free-flowing liquid was removed by centrifugation, collected and analyzed in an arrangement for recycling unused liquid and fortified and thus provided for the next digestion. Intensifying means that the specified sulphite concentration is adjusted again by the addition of fresh or recycled sulphite for the next digestion. The chemical consumption in this first digestion is 82%.

The open-grained spruce 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 for defibering the partially digested spruce wood chips was less than 300 kWh / t of pulp.

The yield is 78.6% based on otro pulp. The tenacity was measured at 14 ⁰ SR at 8 km, the Tear index at 8.5 mN * m ² / g. The whiteness was determined after digestion at 41% ISO.

The solids content of the digestion solution was determined to be 10.2% after the first digestion. The same digestion solution was in each case boosted again to the starting content of sulfite described above, further digestions were carried out under the same conditions. After the fifth digestion the Solids content of the digestion solution determined again at 20.4%.

The calorific value of the digestion solution after the first digestion was determined to be 9.507 J / g. After the fifth digestion with each reused, strengthened digestion solution, the calorific value was determined to be 11,313 J / g.

After each of the five digestions under the conditions of Example 1, the consumption of sulphite was recorded. On average, it was 46%. For the fifth digestion, in which the waste liquor from the previous digestions was collected, the sulfite content was determined and the predetermined sulfite content was re-adjusted by adding fresh sulfite to prepare the digestion solution, 30% of the sulfite from unused sulfite of the digestion solution was preceded by the latter Digestion and 70% fresh sulfite added.

Example 2

The pulp according to Example 2 was prepared from spruce woodchips under the conditions of Example 1, with the following changes: In addition to the 23.6% sulphite, the chemical solution was admixed with 0.1% anthraquinone, based on the amount of wood used. The duration of the digestion was shortened to 45 minutes.

At 15 ^° SR, a tenacity of 10.9 km and an ultimate tensile strength of 82 cN / 100 g / m ² paper weight were determined for the spruce pulp of Example 2. The whiteness was determined to be 53.1% ISO and the yield was 76.7%.

The outcrops according to Examples 3 and 4 explained below relate to vapor-phase digestions.

Example 3

Spruce wood chips are impregnated with 23.6% sulfite at a liquor ratio of wood: chemical solution = 1: 5 at 120 ⁰ C in the vapor phase for 120 minutes. The chemicals used are sulfite and 0.1% anthraquinone. At the beginning of the impregnation, a pH of 9.4 sets. After impregnation, the chemical solution is removed. The chips impregnated with the chemical solution are heated to 170 ^° C. with steam in about 5 minutes. This vapor phase at 170 ⁰ C is held for 60 minutes. Then the steam is released and within 30 seconds, the cooker is cooled to 100 ⁰ C, and it sets ambient pressure. The wood chips are removed from the stove and shredded. Aliquots of the spruce pulp so produced are ground and the ground fractions and pulp properties are determined for the ground portions.

At 14 ^° SR, 9.3 km tenacity and 102 cN / 100 g / m ² paper weight were measured. The whiteness was determined to be 42.6% ISO and the yield was 78.9%.

For the following examples of hardwood outcrops, Table 1 shows the experimental data in summary.

Example 4, Example 5

Birch wood chips are after a damping (90 minutes in saturated steam at 105 ⁰ C) with a sodium sulfite digestion solution with the addition of 0.1% anthraquinone at a liquor ratio of wood: digestion solution 1: 3 added. The total use of chemicals was 16.5% calculated as sodium sulfite, based on otro birch wood chips. The birch chips impregnated with the chemical solution were heated to 170 ^° C. and digested at this maximum temperature for 60 minutes (Example 4) or over 80 minutes (Example 5).

26, 32% of the sulfite used (Example 4) or 32, 52% of the sulfite used (Example 5) were consumed during the course of the digestion.

For Example 4, a yield of 85.34% and a whiteness of 68.81% ISO were detected after digestion. At 20 ⁰ SR, the birch has a tearing length of 8.4 km and a tear index of 6.9 mN * m ² / g. For Example 5, a yield of 83.99% ^and a whiteness of 69.82% ISO were detected after digestion. Example 6, Example 7, Example 8

Beech wood chips are after a damping (90 minutes in saturated steam at 105 ⁰ C) with a sodium sulfϊt digestion solution with the addition of 0.1% anthraquinone at a liquor ratio of wood: digestion solution 1: 3 added. The total use of chemicals was 16.5% calculated as sodium sulfite, based on otro beech wood chips. The beech wood chips impregnated with the chemical solution were heated to 170 ^° C. (Examples 6, 7) or to 160 ^° C. (Example 8) and heated for 60 minutes (Example 6) or 48 minutes (Example 7) and over 55 minutes ( Example 8).

The consumption of sulfite in Example 6 was 54.3% of the sulfite originally used, in Example 7, a consumption of 48.5% was recorded and in Example 8, the consumption of sulfite was 35, 4% based on the sulfite originally used.

The yield was recorded for Example 6 at 74.1%, for Example 7 a yield of 75.2% was determined and for Example 8 the yield was 82.4%. The whiteness was determined for example 6 with 66.3% ISO, for example 7 with 62.9% ISO and for example 8 with 69.9% ISO.

For the beech pulp thus produced, a breaking length of 5.5 km was determined at 20 ^° SR. The tear index was found to be 4.8 mN * m ² / g.

Example 9, Example 10

Poplar wood chips are after a damping (90 minutes in saturated steam at 105 ⁰ C) with a sodium sulfite digestion solution with the addition of 0.1% anthraquinone at a liquor ratio of wood: digestion solution 1: 4 added. The total use of chemicals in Example 9 was 19.7%, in the example 10 16.5%, calculated in each case as sodium sulfite, based on otro poplar wood chips. The poplar wood chips impregnated with the chemical solution were heated to 170 ^° C. and digested for more than 60 minutes.

The consumption of sulfite in the example was 947.5%, in example 10 a consumption of 55.8% was recorded, based in each case on the sulfite originally used. The yield was recorded for example 9 at 76.5%, for example 10 a yield of 77.2% was determined. The whiteness was determined for Example 9 at 67.1% ISO, for Example 10 at 63.5% ISO.

For the poplar pulp thus produced, a breaking length of 9.9 km was determined at 20 ^° SR. The tear index was found to be 6.9 mN * m ² / g.

Example 11, Example 12 Poplar wood chips are after a damping (90 minutes in saturated steam at 105 ⁰ C) with a sodium sulfite pulping solution with the addition of 0.1% anthraquinone at a liquor ratio of wood: digestion solution 1: 3 added. The total use of chemicals was 16.5% calculated as sodium sulfite, based on otro poplar chips. The poplar wood chips impregnated with the chemical solution were heated to 170 ^° C. (Example 11) or 160 ^° C. (Example 12) and digested for 45 minutes (Example 11) or 90 minutes (Example 12).

The consumption of sulfite in the example was 1151.4% of the sulfite originally used. The sulfite consumption for Example 12 was not recorded.

The yield was recorded for example 11 at 80.2%, for example 12 a yield of 80.7% was determined. The whiteness was determined for example 11 with 64.1% ISO, for example 12 with 69.3% ISO.

Claims

claims

1. A process for producing pulp from lignocellulosic raw material comprising the steps of - preparing a chemical solution with less than 25% sulfite (calculated as

NaSθ3) based on the otro amount of the lignocellulosic raw material mixing the chemical solution with wood in a predetermined liquor ratio heating the chemical solution and the wood to a temperature above room temperature and then either (1st alternative)

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

Separate the free-flowing chemical solution and the wood.

2. The method according to claim 1, characterized in that a pulp with a content of at least 15% lignin, preferably at least 17% lignin, advantageously at least 19% lignin, more preferably at least 21% 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 is produced.

3. The method according to claim 2, characterized in that a pulp with a content of at least 15% lignin based on otro pulp is produced for softwood, with a freeness of up to 15 ⁰ SR a tearing length of more than 8 km, preferably from more than 9 km, advantageously more than 10 km.

4. The method according to claim 2, characterized in that a pulp with a content of at least 12% lignin based on otro pulp for hardwood is produced, which has a breaking length of more than 5 km, preferably of more than 6 km, more preferably of more than 7 km at a freeness of up to 20 ⁰ SR.

5. The method according to claim 1, characterized in that for the preparation of the chemical solution sulfites and sulfides, used singly or in mixture.

6. The method according to claim 5, characterized in that for the preparation of the chemical solution of sodium, potassium, magnesium and / or ammonium sulfites are used.

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

8. The method according to claim 1, characterized in that the method is carried out at a pH between 5.5 and 11, preferably between 5.5 and 10, more preferably between 7.5 and 8.5.

9. The method according to claim 1, 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.

10. The method according to claim 1, characterized in that the heating of the chemical solution and the wood to up to 130 ⁰ C, preferably up to 120 ⁰ C, advantageously up to 110 ⁰ C.

11. The method according to claim 1, characterized in that the heating of the wood and optionally the chemical solution up to 90 minutes, preferably up to 60

Minutes, advantageously up to 30 minutes, particularly advantageously takes up to 10 minutes.

12. The method according to claim i, characterized in that the digestion of the wood at temperatures between 120 ⁰ C and 190 ⁰ C, preferably at temperatures between 150 ⁰ C and 180 ⁰ C, particularly preferably at temperatures between 160 ⁰ C and 170 ° C. is carried out.

13. The method according to claim 1, characterized in that the digestion of the wood takes up to 180 minutes, preferably up to 90 minutes, more preferably up to 60 minutes, advantageously up to 30 minutes, particularly advantageously takes up to 2 minutes.

14. The method according to claim 13, characterized in that the duration of the opening is selected depending on the liquor ratio.

15. The method according to claim 1, characterized in that for the digestion of lignocellulosic raw material with a lignin content of more than 25% based on otro raw material up to 13% sulfite based on otro lignocellulosischen raw material are used that for digesting lignocellulosic raw material with a lignin content of 20% to 25% based on otro raw material consumed up to 10% sulfite, and that are used to digest lignocellulosic raw material with a lignin content of up to 20% based on otro raw material less than 10% sulfite, but at least 7% sulfite used become.

16. The method according to claim 1, characterized in that for the digestion of softwood up to 25% sulfite, preferably up to 20% sulfite, preferably up to 15

% Sulfite, but at least 7% sulfite can be used.

17. The method according to claim 1, characterized in that for the digestion of hardwood up to 15% sulfite, preferably up to 12% sulfite, more preferably up to 10% sulfite, but at least 7% sulfite are used.

18. The method according to claim 1, characterized in that the consumption of sulfite during the digestion up to 80%, preferably up to 60%, particularly Preferably up to 40% of the sulfite is used at the beginning of the digestion.

19. The method according to at least one of the preceding claims, characterized in that for the preparation of the chemical solution up to 75% by weight of the sulfite from the recycling of already used for the digestion of the chemical solution is used, and that at least 25% by weight of the sulfite are freshly added ,

20. The method according to claim 19, characterized in that for the preparation of the chemical solution up to 50% by weight of the sulfite from the recycling of already used for the digestion of the chemical solution is used, and that at least 50% by weight of the sulfite are freshly added.

21. The method according to claim 19 or 20, characterized in that in the preparation of the chemical solution fresh sulfite is added in the following amounts: up to 13% for lignocellulosic raw material of more than 25% lignin based on otro raw material, up to 10% for lignocellulosic raw material with a lignin content of 20% to 25% based on raw material and less than 10% for lignocellulosic raw material with a lignin content of less than 20%, calculated as NaSO 3 in terms of otro lignocellulosic raw material.

22. The method according to claim 1, characterized in that the composition of the removed or separated chemical solution is detected and then adjusted for re-use for the production of fibers to a predetermined composition.

23. The method according to claim 1, characterized in that after the pulping and possibly grinding the digested lignocellulosic material released chemical solution is removed and is supplied to further use.

24. The method according to claim 1 or 23, characterized in that by recycling the digestion solution, the solids content of these circulated Digestion solution by up to 5%, preferably by up to 10 96, more preferably increases by up to 15%.

25. The method of claim 1, 23 or 24, characterized in that the circulated digestion solution has up to 1.5 M J / kg higher calorific value than a freshly prepared digestion solution.