FI61211B - FOERFARANDE FOER FRAMSTAELLNING AV EN HOEGUTBYTESMASSA LAEMPLIG FOER ABSORPTIONSPRODUKTER - Google Patents

Description

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Patent · och registerstyralsan 'Ansekan uthgd och utUkrlfcM publkarad 26.02.82 (32) (33) (31) »Vrd« tty Muoikuut — Begird prior * · »13.11.75

Sweden-Sverige (SE) 7512777 “9 (Tl) Mo och Domsjö Aktiebolag, Fack, S-891 01 Örnsköldsvik, Sweden-Sverige (SE) (72) Jonas Arne Ingvar Lindahl, Domsjö, Sweden-Sverige (SE) (7 ^ ) Berggren Oy Ab (5 ^) Method for the production of high-yield mass suitable for absorption products -Förfarande för framställning av en högutbytesmas warmplig för absorptionsprodukter

The present invention relates to a pulp having improved properties for absorption purposes and to a process for producing such a pulp in high yields from a lignocellulosic raw material such as wood, bagasse and straw. The pulp according to the invention is particularly suitable for the production of absorbent articles such as various tissue papers, pulp wadding, gauze bandages, menstrual pads and tampons.

At present, only chemical pulps such as sulphite and sulphate pulp are used to make such absorption products. However, in the production of these pulps, hardly half of the wood fibers are recovered, which is a considerable drawback given the worsening of the fiber shortage. If wood raw material is to be used more efficiently, on the one hand, the yield of pulp must be increased and, on the other hand, the fibers must be reused. However, the recovery of toilet paper has proven difficult to perform economically. Thus, the only way to make more complete use of the limited fibrous raw material is to increase the fiber yield. Nk. in the production of high-yield pulp, wooden logs are ground against a rotating stone or the wood is first reduced to small pieces into so-called wood chips.

2,61211 which is then fed to a disc mill having one or two rotating plates with grooves, .the wood fibers detach as the chips pass between the boards. According to one development of this wood chipping process, the wood chips are preheated with steam before being fed to a plate shredder, whereby the preheating softens the lignin in the wood so that the release of the fibers is facilitated. This so-called hot rubbing pulp gives a higher proportion of long fibers than the cold rubbing pulp or groundwood. However, these processes have the downside that they consume a lot of energy. It is further known to carry out only partial delignification of the lignocellulosic material with sulfur-containing compounds at high temperature (> 160 ° C) before defibering and thus to obtain a high pulp yield. By adjusting the dissolution conditions, pulp yields can be obtained which vary between 60 and 93% (so-called chemimechanical mass). The energy consumption of a chemimechanical process is substantially lower than that of mechanical processes of the type mentioned above, but it has the disadvantage that it requires considerable amounts of sulfur-containing chemicals, which require an expensive chemical recovery plant. Another disadvantage of this method is that it dissolves large amounts of organic matter, which must be recovered and treated to avoid environmental contamination. The production of unbleached and bleached mechanical pulps also generates waste that I do not need to clean before it can be released into the environment.

A common disadvantage of all the pulp manufacturing processes described above is that the pulps must be sieved in various expensive and bulky equipment to separate the coarser particles and to enrich the suitable fibers, respectively. When screening is performed at very low fiber densities, only low concentrations of chemicals and dissolved organic matter are obtained in the filtrate, which makes recovery and purification cumbersome and less economically attractive.

Another disadvantage of known high yield pulps is that they lower during transport and storage in such a way that their bulk is significantly reduced.

In the practice of the present invention, the disadvantages listed above are drastically reduced. In addition, the pulp obtained has been shown to have properties which are superior to those of previously known high-yield pulps.

According to the present invention, the present invention relates to a light pulp having a low resin content, a high bulk content, good liquid absorption properties and better deposition stability, which cellulose pulp is characterized in that it contains 0.1 to 1.0 % by weight of sulfur, leaving more than 25% on a 20 Mesh sieve in a fiber classification analysis carried out on a Bauer Mc Nett apparatus, containing at least 10% of bundles of 2 to 4 individual fibers, having a resin content of less than 0,8% as determined by extraction with dichloromethane According to SCAN and that its bulk dry fiber content exceeds 20 x 10 m / kg. The pulp with these characteristics has proven to be clearly better than the previously known cellulose pulps for absorption purposes and, moreover, has much lower manufacturing costs due to low wood consumption and low energy consumption.

Preferably, the pulp of the invention has a sulfur content of 0.2-0.6%, leaving 30-60% fibers on a 20 Mesh screen in a fiber classification analysis performed on a Bauer Mc Nett apparatus, has 15-30% bundles of 2-4 individual fibers and has a dry dry fiber bundle. exceeds 25 x 10 ”^ m ^ / kg.

It is also particularly advantageous to adjust the pH of the pulp according to the invention in the dried pulp to a value greater than 6, preferably between 7 and 10, whereby the acidic products in the absorbed liquid are neutralized, which reduces skin irritation.

The present invention also relates to a process for producing a light pulp having a low density and good liquid absorption properties as described above, which process comprises washing fresh or preserved chips with water, impregnating with a sulfur-containing dissolving chemical, partially dissolving at elevated temperature and then mechanically defibering. and bleached, characterized in that the partial dissolution is carried out to a degree of sulfonation corresponding to 0.1-1.0, preferably 0.2-0.6% by weight of sulfur, based on the weight of the pulp treated, at a temperature of 373-443 K, and that the mechanical the defibering is carried out in part so that the fibrous pulp after defibering contains at least 10% of bundles of fibers consisting of 2 to 4 individual fibers.

4,61211

Suitable dissolving chemicals for use in accordance with the present invention include sodium, potassium, ammonium, calcium or magnesium bisulfite and sulfite, of which sodium bisulfite and sodium sulfite are most suitable. The concentration of dissolution chemicals in the dissolution liquid must not exceed 20 g SO2 per liter, the pH of the impregnation of the pulp must be between 5-11, preferably between 6-9, and the impregnation must be carried out in such a way that each kilogram of dry chips absorbs 0.9- 1.5 liters of solution. The temperature used in the dissolution must be lower than that normally produced in the preparation of corn-mechanical pulp in order to obtain a suitable partial dissolution according to the invention to a suitable degree of sulfonation. A suitable temperature for this is 373-443 K, preferably 383-403 K. During impregnation it is suitable to maintain the same temperatures as during dissolution and it is particularly suitable to roast the water-washed chips with steam before impregnation.

The partial dissolution according to the invention is essential for achieving the advantageous properties of the product according to the invention. In this case, the lignin contained in the lignocellulosic material softens and some of it is sulfonated so that it can be dissolved later. A suitable degree of sulfonation corresponds to 0.1-1.0, preferably 0.2-0.6% sulfur, based on the weight of the treated lignocellulosic material. Within the above-mentioned framework, different wood species require different dissolution conditions to achieve the above-mentioned degree of sulfonation. It is essential that the dissolution is carried out in such a way that there is no free or bound sulfur dioxide in the dissolution liquid after the partial dissolution has been completed. Therefore, the residence time and temperature must be adjusted accordingly. A suitable residence time in the impregnation step is 0.5-5 minutes and a suitable residence time in the dissolution step is 0.5-50 minutes, preferably 2-10 minutes.

The pulp obtained after partial dissolution according to the invention is mechanically defibered in an defibering device in such a way that the defibered pulp will contain at least 10% of fiber bundles. By fiber bundles is meant here soft fiber bundles containing 2-4 individual fibers. Instead, hard fiber bundles containing unsulfonated wood and fiber bundles containing 5 or more individual fibers (so-called sticks) are not meant. This partial mechanical defibering is preferably carried out in such a way that the defibered material will contain at least 15-30% of the above-mentioned fibrous ladders. Partial mechanical defibering must also be carried out in such a way that no shortening of the fibers occurs during defibering, which can be achieved by treatment in a high-density grinder. By carrying out the partial mechanical defibering as mentioned above, the partial dissolution gives the finished product particularly suitable properties for absorption purposes, such as high bulk, good water absorption including absorption rate and retention, good settling resistance under storage conditions, low resin content and good brightness.

According to the invention, it is suitable for partial mechanical defibering to include resin removal and bleaching chemicals. Suitable resin removal chemicals include phosphates, complexing agents and / or surfactants, of which phosphates are particularly suitable, and the resin removal is carried out in an alkaline environment, with alkali metal hydroxides such as sodium hydroxide being particularly suitable as alkali. The pH of the resin removal liquid added to the defibering device must be above 11 in order for the initial pH of the pulp slurry to be above 9 and preferably to be kept higher than 10, which is suitable according to the present invention. Suitable bleaching chemicals to be added to the defibering device at the same time as the resin removal ceramics are alkali metal peroxides such as sodium peroxide and hydrogen peroxide, but so-called reducing bleaching agents such as dithionite, hydroxylamine, thiourea and thioglycolic acid can also be used. Other oxidizing bleaches such as ozone, persulfates, oxygen gas, peracetic acid and borax may also be used as bleaching agents in accordance with the present invention. The defibering results in a homogeneous mixing of the added chemicals and rapid and efficient saponification of the fatty and rosin acids, which later facilitate the dispersion of the unsaponifiable parts of the extracts. Relatively high temperature and intensive mechanical treatment also contribute to these reactions.

After partial defibering, according to the invention, dewatering of the pulp slurry obtained is suitably carried out to a dry content of at least 30%, preferably 45-55%, at a high temperature, suitably above 348 K. This high temperature results in the best possible separation of the saponified and dispersed extracts as well as a high dry content in the pulp, which must then be dried. In addition, the said dewatering causes the chemicals and dissolved organic substances to be recovered to be concentrated.

One advantage of using the present invention is that the fiber yield becomes very high, i.e. between 85-95%, preferably between 90-94%. In addition, the invention provides an inherently low energy consumption, i.e. between 200 and 1100 kWh per tonne of dry cellulosic fiber produced. The invention also has the further advantage that the volume of excess liquid leaving the process remains small and its concentration relative to the impurities, and that the liquid can be removed from a single location. This makes it possible to recover used chemicals and / or treat process effluents in a simple and conventional manner. It is also essential that the equipment [investment costs] are low, as there is no need to sift the pulp material, which, moreover, further reduces energy consumption. An additional advantage of the invention is that the heat generated in the process can be easily recovered and utilized. Thus, low-pressure steam is obtained from the process, which can be utilized, for example, in evaporation or district heating. A further advantage of the invention is that the consumption of water 3 remains extremely low, i.e. about 3 m of water per tonne of dried pulp produced. The corresponding figures for the production of chemical pulp 3 are about 250 m and for the production of groundwood or hot mill 3 about 20 m.

According to the present invention, a lignocellulosic material such as wood, bagasse or straw is used as a raw material. Particularly suitable is the use of wood fibers, which also includes some mixing of the recovery fibers. When using fresh or stored wood, the logs are first chipped in a chipper, after which the resulting chips are washed in hot water. At the same time, iron objects are separated by electromagnets, which can otherwise damage the moving parts of the machines. The defibering device used in the process is particularly susceptible to damage.

According to a preferred embodiment of the invention, which can be implemented in the device according to Figure 1, the well-washed and hot chips in the chip washer 1 are transferred to a roasting vessel 2, where it is treated with saturated steam at atmospheric pressure. This stage of the process is called steam roasting and its function is to remove air from the chips and to equalize the moisture content. After steam roasting, the chips are fed to a spiral feeder 3, which opens into the impregnation chamber 5.

61211

Alternatively, the washed chips are fed directly to the spiral feeder 3, i. this conversion does not perform steam roasting. As the chips pass through the helical feeder 3, it is compressed so that the excess liquid flows out through the drain line 4 in the helical feeder.

Once the chips have passed through the helical feeder 3, they are allowed to swell freely in the impregnation chamber 5. The impregnation chamber 5 is filled with a dilute solution of Na, K, NH 4, Ca or Mg bisulphite and / or sulphite. It is particularly suitable to use sodium bisulfite or bisulfite. In order for the lignin sulfonylation to occur rapidly during processing in the impregnation chamber and digester 10, the pH of the impregnation solution must be between 5 and 11, preferably between 6 and 9. The total amount of chemicals in the impregnation solution, expressed as sulfur dioxide, shall not exceed 20 g SO2 per liter. When the chips swell freely in solution, experience has shown that each kilogram of dry chips absorbs 0.9-1.5 liters of solution. The volume of solution absorbed varies according to the species of wood. The impregnation chamber has two vertical helices 6.7 which carry the chips upwards to the upper level of the chamber. In order to make the impregnation homogeneous and to achieve a short-term sulfonation in the liquid phase, the chips are then slowly transported upwards in the impregnation chamber. At the same time, the liquid level in the impregnation chamber is kept as high as possible. This is achieved automatically by means of measuring sensors and control valves, which are not shown in Figure 1. The treatment in the impregnation chamber is preferably carried out at a temperature of 373-443 K, preferably at a temperature of 383-403 K and lasts 0.5-5 minutes. From the top of the chamber, the chips fall into the digester 10 below. The dry matter content of the chips leaving the impregnation chamber 5 is about 35%. In digester 10, the chips are partially sulfonated at 373-443 K, preferably 383-403 K.

Said temperatures also prevail in the impregnation chamber 5, since this part is in direct contact with the cooking part 10. The heating in the digester is carried out by passing saturated steam together 8 through it, i.e. further sulfonation of the wood is performed in the vapor phase. The residence time in the cooking section is normally 0.5-30 minutes. A residence time of 2-10 minutes has proven to be particularly suitable. According to the invention, the residence time and temperature are adjusted so that no free or bound SO2 is present in the dissolution liquid at the bottom of the digester, from which the partially sulphonated chips are removed. This is essential to prevent reduction and decomposition of the peroxide solution used as bleach and to avoid the formation of sulfuric acid, which precipitates extractants on the pulp fibers, which affects the brightness and absorbency of the finished product.

The partially sulfonated chips are then fed out of the digester by a conveyor coil 12. According to a preferred embodiment of the invention, the conveyor coil takes the chips to a plate mill 13 or other defibering means, e.g. a high density helical fiberizer, which provides a kneading and shearing effect without cutting fibers. Equipment of the latter type is sold by MoDoMekan AB under the trade name FROTAPULPE ^. The mechanical defibering is carried out at a pressure equal to or slightly lower than that prevailing in the digester. It is further essential according to the invention that the pulp material is only partially defibered during mechanical defibering, i. after pulping, the pulp must contain bundles of fibers consisting of 2 to 4 individual fibers, which is very advantageous for the bulk of the finished product. According to the invention, the partial mechanical defibering must be carried out so that the defibered pulp after defibering contains at least 10% and preferably 15-30% of fiber bundles. In addition, any shortening of the fibers during defibering must be avoided, which is likewise achieved by treatment in high-density grinders of the disc mill type or in the above-mentioned devices sold under the trade name FROTAPULPEI ^. In addition, partial sulfonation avoids the formation of hard bundles of fibers, also called sticks, which are always formed when more than 2% of the total amount of fibrous material is produced during the production of mechanical pulp.

The resin removal and bleaching chemicals are added to the helical feeder 12 before the fiberizer 13 through one of the 11. The addition of a resin remover, for example Na 2 PO 2 sn, can vary between 0.1 and 1.5% by weight of the pulp. Preferably it is used at 0.2-0.4%. Surfactants are added up to 0.2% and complexing agents such as NTA, EDTA and DTPA up to 0.3% by weight of the pulp. When hydrogen peroxide is used, it is added up to 4%, preferably 1.0-2.0% by weight of the pulp. The sodium hydroxide content must be at least 65% and not more than 200% of the peroxide addition. To stabilize the peroxide, 0.5-4.0% sodium silicate and / or 0.05-0.5% magnesium sulfate must be added. When chemicals are recovered from process effluents, the addition of sodium silicate must not exceed 0.5%. The defibered pulp material is then pushed down line 14 to a cyclone 15 to separate the low pressure steam 17 from the pulp fibers. The cyclone is equipped with a valve 16 for adjusting the amount of steam outlet and steam pressure. In addition, the cyclone is mounted immediately together with the press 18, where the pulp leaving the cyclone is collected and dewatered. Steam is taken from the cyclone at a pressure slightly lower than the pressure in the grinding chamber of the plate grinder. The resulting steam can be used for various purposes, e.g. heating rooms or evaporating chemical liquids. In the press 18, at least 30%, preferably 45-55% of the fibrous cellulosic material is dewatered at a high temperature. The liquid leaving the press contains chemicals and dissolved organic matter, which is suitably recovered through the discharge pipe 19 by evaporation, separation of the fibers and incineration, or by other means of recovering the chemical content. Since the defibering is carried out at a consistency of 20% to 40% of the pulp, little excess liquid is obtained. The consistency of the pulp decreases during the grinding treatment due to the need to add sealing water to the grinder.

Once the pulp has passed through the cyclone and press, it may, if deemed appropriate, be passed through another cyclone and press to separate the steam and increase the dry matter content of the pulp, respectively.

According to the invention, the pulp material, after dewatering, is without further intermediate treatment taken directly to a drying plant in which the moisture content of the cellulosic material is reduced to less than 14%, preferably less than 10%. The drying plant can be a drying machine with a wire and cylinders or a flake dryer. In the former case, however, the pulp must first be diluted to a suitable consistency with circulating water.

The reaction of the dried pulp treated according to the invention is neutral or weakly alkaline. The pH of the pulp should preferably be above 6 and most preferably between 7-10.

The present invention is not limited to the embodiments described above. Thus, for example, the partially sulfonated material can be introduced directly from the digester into a pressure cyclone and then defibered by the addition of bleaching and resin removal chemicals, and extruded. Furthermore, liquid phase cooking can be used instead of steam phase cooking.

1 ° 61211

The ratio of the proportion of long-fiber material in the pulp according to the invention to the normally produced hot-milled pulp with a grinding degree of 240 ml according to the Canadian Standard Freeness can be seen from the following fiber classification analysis carried out in a Bauer Mc Nett apparatus.

Mesh size Mass according to the invention Hot rubbing mass

Mesh Remaining% Permitted% Remaining% Permitted% 20 40 60 10 90 150 43 12 60 30

The pulp made according to the invention thus contains about four times more long-fiber material than the hot-milling pulp and thus approaches the fibrous composition of the chemical pulp. Surprisingly, as will be shown below, the absorption rate and water retention capacity of the pulp prepared according to the invention are very good despite the relatively high degree of grinding, which is not about 450 ml according to Canadian Standard Freeness. In addition, the long fiber content of the pulp made according to the invention gives considerably better thief stability to the absorption products made therefrom compared to the hot-rubbing pulp. The latter contains such a large proportion of short fibers that, when used in absorption products, it settles during storage, so that the product becomes unusable for its intended purpose.

As can be seen from the following experiments, the composition according to the invention is excellently suitable as an absorbent for products such as bandages, menstrual pads, tampons and wound dressings. Due to its low resin content, it can also be processed quite well for further use as pulp. Fully bleached sulphite pulp, peroxide bleached groundwood and peroxide bleached hot milling were used as reference masses in the experiments. The control masses were dried to a dry content of 94% and then conditioned to a moisture content of 10% after 2 days. The samples were then dry fiberized (ground down) in a plate grinder with a plate diameter of 300 mm. The water absorption and bulk of the fluff masses were then tested. The following method was used in the analysis: In a special apparatus, sample pads with a diameter of 50 mm and a weight of 2.00 g were formed from the fluff. By loading the sample at 100 g and measuring the thickness of the sample, a measure representative of the peak was obtained. The thickness of the sample was set to 15 mm 11 61211 and it was then allowed to absorb from below water at a temperature of 293 K, at which time the absorption time was measured. The absorption capacity was then determined with a load of 1000 g. The test results for the reference masses are shown in Table 1.

table 1

Test of reference masses

Yield, Extract- Brightness Bulk Absorption- Absorption% content% SCAN m / kg speed, g H? 0 / g DKM,% sec. 1 'mass

Sulphite mass 52 0.40 92 28-10 26 10.9

Grinding 96 1.05 72 15-10-3 19 10.7

Heat massage - 95 1.02 71 17-10-J 9 10.9

High bulk and short absorption time are criteria for the viscosity to be a good starting material for pieces, for example. As shown in Table 1, the sulfite pulp has a large bulk but a relatively long absorption time. The groundwood has a small bulk and a relatively long absorption time. The hot mill has a small bulk but a short absorption time. The absorption capacity of the absorbed water is approximately equal for all samples and can be considered to be at a perfectly acceptable level.

The invention is illustrated by the following application examples. Example 1

Two masses A and resp. B, of which Sample B was treated according to the present invention. Spruce wood was chipped in a chipper into chips with a length of 30-50 mm, a width of 10-20 mm and a thickness of 1-2. The chips were washed in hot water and emptied into a steam roasting vessel where they were treated with saturated steam at atmospheric pressure for 10 minutes. The steam-roasted chips are transferred to the impregnation chamber with a spiral feeder. The impregnation drill was filled with a sulfite solution having a pH of 7.5. The SO 2 content was 5 g / l and the NaOH content was 6.5 g / l. Upon impregnation, the chips absorb an average of 1.1 liters of sulfite solution per kg of dry chips. The concentration of absorbed SO 2 thus became 1.1 x 5 = 5.5 g per kg of chips, i.e. 0.55%. The temperature in the impregnation vessel was maintained at 398 K. The total residence time of the chips in the impregnation chamber was about 2 minutes. During this residence time, the wood material became slightly 12,61211 sulfonated in the liquid phase. The impregnated chips were transferred to a digester fed saturated steam so that a temperature of 398 K was reached. The residence time of the chips in the digester was 4 minutes. Including the residence time in the impregnation chamber, the total sulfonation time thus became 2 + 4 = 6 minutes. From the bottom of the digester, the chips were then fed by a conveyor screw to a plate grinder with a steam overpressure of 150 kPa (1.5 aty).

In a disc grinder, the chips were partially defibered, i. a certain number of fiber bundles of 2 to 4 fibers were detectable after defibering. The dry content in the center of the disc grinder was 30% and in the circumference of the plates 32%. Energy consumption in the defibering was obtained by measuring 750 kWh per tonne of dry pulp produced. Upon leaving the grinding chamber of the grinder, the pulp was diluted to 27% consistency with condensing water. The defibered pulp was buffered into a pressurized cyclone to separate excess steam from the pulp fibers. The pulp fibers were collected with a press mounted together with the cyclone. The press removed water from the pulp so that its consistency increased from 27% to 42% at 363 K. The amount of water displaced 3 thus became, in m calculated per ton of dry pulp 3, only 1.3 m. The concentration of organic matter in the solution was 60 kg, i.e. 4 g / l, and no free or bound sulfur dioxide was detected. The pulp yield was 94%. The pulp with a dry content of 42% was dried in a flake dryer to a dry content of 94%, conditioned and dry fiberized and tested in the same manner as the reference pulps above. The mass thus treated was marked with the letter A.

In another experiment according to the preparation of Sample A, the following resin removal and bleaching chemicals (amounts expressed as 100% chemicals as a% of dry weight) were added to the center of the fibrous abrasion plates: 0.1% EDTA (ethylenediaminetetraacetic acid) 0.3 % Na5P3010 0.05% BEROCELL-25 (wetting agent) 2.0% H 2 O 2

1.8% NaOH

2.0% Sodium silicate (water glass) 40 ° B5 61211 13 After defibering and dehydration according to the preparation of sample A, the pulp marked B was dried as above and tested as for control samples and sample A. The results are shown in Table 2.

Table 2 Test results for samples A and B.

Yield Extract- Brightness Bulk Absorption- Absorption% concentration% SCAN 3y. speed, g H-O / g DKM% / "sec mass Sample A 94 1.52 59 31 * icf3 100 5.2 Sample B 94 0.58 71 30-10-3 8 11.3

As can be seen from Table 2, the bulk of both Sample A and Sample B has become surprisingly large, even larger than the bulk shown in Table 1 of the sulfite pulp. Compared to the peaks of mechanical pulps, the pulps according to the invention have twice the bulk. Despite the fact that sample A is partially sulfonated, its water absorption is very poor.

Instead of adding bleaching resin removal chemicals according to the present invention, a surprisingly good absorption rate and good absorption of absorbed water are obtained, and the pulp prepared according to the invention (sample B) is thus completely superior to reference masses and sample A as an absorbent in absorption products.

When comparing the wood consumption and energy consumption of the pulps according to the invention and conventional pulps, there are considerable advantages in using the present invention.

Wood consumption and energy consumption for the production of 1 tonne of dry pulp_

Yield Wood kWh% condition m3

Sulphite pulp 52 5.01 800

Hioke 96 2.71 1400

Hot milling 95 2.74 2100 Samples A and B 94 2.77 750

The method according to the invention thus gives the lowest energy consumption and at the same time low wood consumption.

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Moreover, given the lower investment cost required to produce the pulp according to the invention due to the omission of the screen compartment, it is obvious that the process according to the invention can produce high quality pulp for absorption products at a much lower cost than previously possible, while reducing emissions. the conditions for achieving a high degree of purification of emissions are improving.

About 5-30% of the chemical pulp can also be mixed into the pulp according to the invention in order to achieve special effects.

Claims (12)

1. Light, absorbent, lignin-rich high-yield cellulose pulp with low resin content, low bulk density and good absorption properties for liquid, and improved layer stability noted from a content of 0.1-1.0% by weight sulfur, present in the form of ligniribound bisulfite and sulphite ions, by an amount of fiber group analysis of mesh size 833 micron retained fibers of over 25%, of an amount of fiber bundles consisting of 2-4 single fibers of at least 10%, of an amount of dichloromethane extractable resin less than 0.8% and of a cloud density in dry defibrated form of less than 50 kg / m 2. High yield mass according to claim 1, characterized by a sulfur content of 0.2-0.6% present in the form of lignin-bonded bisulphite and sulphite ions, of an amount of fiber group analysis of mesh size 833 millisons retained between 35 and 65%, of a plurality of fiber bundles consisting of 2-4 single fibers of between 15 and 30% and of a bulk density in a dry defibrated form of less than 40 kg / m 2. High yield pulp according to claims 1-2, characterized in that the pH of the dried pulp is above 6, preferably 7-10. 4. High yield pulp according to claims 1-3, characterized in that it contains 5-30% chemical pulp. A process for producing a light, low bulk density absorbent mass and good liquid absorption properties according to claims 1-3, wherein fresh or stored chips are water-washed, pressed, impregnated with sulfur-containing digestive material, partially dissolved at elevated temperature and then mechanically defibrillation and bleaching, characterized in (a) that the content of the impregnating liquid is maximally raised to 20 grams of SO2 per liter and that the pH of the impregnating liquid is kept at 5-11, preferably 6-9, b) that the partial digestion is carried out to a degree of sulfonation. corresponding to 0.1-1.0, preferably 0.2-0.6% of sulfur bonded in the form of lignosulfonates, based on the dry weight of the treated cellulose material, at a temperature of 373-443 K, preferably 383-403 K under a temperature of time of 0.5-30 minutes and in such a way that the digestion fluid at the end of the digestion does not contain any free or bound SO2