SE534004C2 - Process for preparing chemical mechanical pulp - Google Patents

Description

25 30 35 40 534 004 different size for asp. As the alkalide dose (eg, the amount of NaOH) is increased from 0.6% to 3%, the yield of aspen wood decreases linearly from about 95% to 89% in a conventional process.

Some of the yield loss takes place already during the impregnation, and some does not take place until the subsequent refining step at a high temperature.

In practice, a large alkaloid dose must be used to ensure maximum impregnation. The penetration of the alkali solution into the fl ice is slow and alkali tends to be consumed in the outer parts of the fl ice, leaving insufficient amount of alkali for the inner part of the fl ice. In the refining step, this turns out to be a higher percentage of coarse projects.

The effect of alkali on the spreading qualities of the chemical mechanical pulp is particularly problematic. The spreading qualities decrease with increasing alkalidose and, when the refining level is the same, the spreading is always smaller when the alkalidose is larger. Bleaching also reduces the spread further.

In order to produce high-quality printing paper, it is necessary that the scattering and brightness properties of the pulp are good. It is possible to produce CTMP pulps from hardwood with a high brightness, even up to an ISO brightness of 88%.

The object of the present invention is to eliminate at least some of the disadvantages associated with the known technology, and to provide a new solution for the production of chemical mechanical pulp.

The present invention is based on the principle that, when producing chemical mechanical pulp, the impregnation of the ice is carried out under overpressure.

Richardson and LeMahieu have described a process for producing a superabrasive mass, in which process aspen is impregnated at a temperature of about 75 ° C and a pressure of 4 bar using a mixture of sodium hydroxide and sodium salt, before refining the ice [Tappi 1965 (48), no. 6, pages 344 - 3461. According to the article, by increasing the concentration of alkali, the strength of the pulp can be improved, and at the same time the energy consumption can be reduced. A problem with the known solution, however, is that the increase in alkali reduces the bleachability of the pulp.

In connection with the present invention, it has been unexpectedly discovered that, when combining an efficient deaeration of the ice, which is most conveniently carried out by steaming, and a pressure impregnation, it is possible to carry out the impregnation more efficiently and to reduce the alkali dose significantly. Comparison with the same freene number, it is possible to use a significantly smaller alkaloid dose to achieve the same or even lower coarse project percentage and at the same time the spread of the pulp is made higher than with a conventional impregnation which is not carried out under pressure.

The method according to the present invention is practiced by means of device in series of equipment comprising the following units: fl ice drain unit, fl ice impregnation unit and fl ice refining unit, in which case the impregnation unit comprises a closed vessel inside which the impregnation treatment can be performed at overpressure.

More particularly, the method according to the present invention is characterized mainly by what is stated in the characterizing part of claim 1.

The pulp according to the invention is again characterized by what is stated in the characterizing part of claim 14.

Significant advantages are achieved by the invention. Pilot-scale experiments have thus shown that using pressurized impregnation makes it possible to reduce the alkali dose by 50% or more. In addition, the invention increases the dispersion of the pulp: in the experiments, the dispersion has unexpectedly even been higher than in the TMP reference (0% alkali). It is also worth noting that it has been possible to increase the spread without increasing the percentage of rough projects. At the same freeness rate, the bulk value is also improved.

With pressurized impregnation, a degree of penetration exceeding 95% has been achieved in laboratory experiments. At the reference points used in the experiments, the maximum degree of penetration has been 63 - 74%. In pilot test runs, it has also been possible to reduce the alkali concentration from the known content of 0.8 - 1.2% per Adt (tonne of dry matter) to a content of 0.25% per Adt without increasing the percentage of coarse rejects. . At all test points, the spread has been significantly higher than in the reference.

Pressure impregnation enables the improvement of the quality of chemical refiner pulp for various end-use applications.

In the following, the invention will be explained in more detail with the aid of a detailed explanation and with reference to, for example, which are described below.

The accompanying figure illustrates a simplified drawing of the equipment utilized in the method of the present invention.

As explained above, the process according to the invention comprises three steps, which are - firstly, at least most of the lu fi contained in the wood raw material comprising fl ice is removed (ie fl the ice is deaerated), - secondly, the raw material thus obtained is impregnated with an alkali solution under overpressure in order for alkaline to be efficiently absorbed into the ice, and - thirdly, the treated ice is refined to a predetermined drainage capacity.

As described above, the pulp is prepared by a chemical mechanical process. In the present invention, chemical mechanical pulping generally involves a process that includes both a chemical and a mechanical blending step, as described above. The CMP and CTMP processes are chemical mechanical processes. In the CMP process, the raw material is refined at normal atmospheric pressure, while in the CTMP process fi- refined refined pulp is produced. Due to the fact that a higher content of chemicals is used in the CMP, its yield is usually less than the yield of the CTMP process (less than 90%). In both cases, the chemical treatment of the wood is traditionally carried out with sodium salt (sulfonation treatment), in which case leaf can also be treated with sodium hydroxide. This case is a typical content of chemicals in the CTMP process about 0 - 4% sodium salt and 1 - 7% sodium hydroxide, and the temperature is about 60 - 120 ° C. In contrast, the content of chemicals in the CMP process is 10 - 15% sodium sulphite and / or 4 - 8% sodium hydroxide (calculated with respect to dry wood), and the temperature is 130 - 160 ° C and the corresponding 50 - 100 ° C.

In a chemical mechanical process, fl ice can also be impregnated with an alkali oxide solution (APMP process). The peroxide content is usually 0.1 - 10% (of the dry mass weight), typically about 0.5 - 5%. The amount of alkali added, such as sodium hydroxide, is approximately the same, ie about 1-10% by weight.

The present invention relates in particular to the CTMP process in which the ice coming from the impregnation is fibrous using the pressure pulp printing process.

The initial material of the process of the present invention is ice comprising coniferous or deciduous. Particular use is made of hardwood ice in production, where the ice is made from birch (usually a type of wood of the genus Betula) or a type of wood of the genus Poplar or a mixture of them. Examples of suitable wood types of the genus Betula are B. pendula and B. pubescens, and wood types of the genus Poplar are in particular the following: B. tremula, P. tremuloides, P. balsamea, P. balsamifer, P. trichocarpa, P. heterophylla , P. deltoides and P. grandidentata. Aspen (European aspen, P. tremula; American aspen (Quaking aspen), P. tremuloídes), aspen species that are hybrids of different stock aspens, hybrid aspen (eg 10 15 20 25 30 35 40 534 004 P. tremula x tremuloides, P. tremula x tremula, P. deltoides x trichocarpa, P. trichocarpa x deltoides, P. deltoides x nigra, P. maximowiczii x trichocarpa) and other types produced by genetic engineering, together with poplars, are considered to be particularly preferred.

In addition to firewood from the genus Betula and Populus, other deciduous tree species can also be used as raw material, such as eucalyptus and mixed tropical deciduous trees. Among conifers, special mention should be made of spruce (Picea abies) and pine (Pínus silvestris) and other species of the genus Picea and Pinus.

According to one application, a chemical mechanical pulp is produced comprising up to 100% of the wood fibers.

With the present invention, however, it is possible to produce a chemical mechanical pulp, which consists of a mixture of hardwood and softwood fibers, and which pulp comprises at least 5% softwood fibers, for example it may comprise 50-99% hardwood fibers and 1-50% coniferous trees. It is possible to increase the bulk value, the strength properties and the stiffness of the pulp by utilizing softwood fibers, in particular by utilizing spruce fibers.

The size of the ice in the form of wood raw material is usually about 20 - 50 mm x l - 10 mm, typically about 35 -40mmx3-5mm.

First, remove as much of the air in the ice as possible. Usually the purpose is to remove at least 70%, especially about 80 - 100% of the air contained in the ice. The air is usually present in the form of gas. As will be apparent from the accompanying d flow chart, this elution can be performed by steaming fl the ice in an evaporator 1. In the process according to the figure, the ice of the original material is fed by means of the screw conveyor 2 into steam silo 1, in which steam is either fed from a feed nozzle , as the figure shows, from fl your nozzles 3a - 3c, to distribute the steam evenly in the fl ice in the silo.

The purpose of steaming is to remove air from the ice. At the same time, steam remains in the ice. The steaming can be carried out, for example, in a continuous evaporator 1, as shown in the figure, in which the ice moves through the steam silo 1, where they are brought into contact with the saturated or almost saturated steam for a period of about 0.5 - 20 minutes, especially about 1 - 10 minutes. Steaming can be performed at overpressure, but usually steaming at normal atmospheric pressure is fully adequate. More specifically, an elevated temperature is used, eg about SO - 100 ° C, especially about 80 - 100 ° C, depending on how saturated the steam is used. Instead of using steam, the deaeration can be performed at low pressure / i a vacuum or steaming can be made more efficient with vacuum treatment.

The treated ice is removed from the steam silo via the outlet nozzle 4, after which the ice is most suitably compressed in the plug screw 5. After this step, typically at least 95%, preferably at least 98%, of the air has been removed, and at the same time some of the steam has also been removed.

For the sake of completeness, it should be mentioned that the evaporation of the fl ice is used in the production of both sulphate pulp and chemical refiner pulp. Until the present invention, however, it has never before been proposed that a combination of steaming of chips and impregnation under pressure can be used in the production of chemical mechanical pulp.

After the deaeration step, the ice is led to the impregnation treatment step 6. According to a preferred embodiment of the present invention, the steamed ice, especially still at the temperature of the steam step, is brought to the impregnation step, which is performed in the absorber 6. The temperature of the lower impregnation solution used in the impregnation than the temperature of the steam in the steam stage.

In practice, the impregnation step is performed in a closed vessel, ie a pressure vessel, which is arranged downstream of the steam device. The absorbent device illustrated in the watch comprises on the whole an elongate absorbent device, the longitudinal axis of which is arranged substantially vertically and which has an upper and a lower part, in which case they are coming from the deaeration unit can be fed into the upper part of the absorber and discharged via the lower part of the absorber. In the absorbent device according to the present invention it is substantially possible to achieve an absolute pressure of at least 1.5 bar, preferably about 1.5 - 15 bar.

When the ice is fed quickly into the impregnation vessel, their temperature can drop by a maximum of approx. 10 -20 ° C before the impregnation step starts.

In the absorber 6 there is an upper separator 7. Via its feed nozzle 7a the ice is fed into the absorber and into the separator, liquid is separated from the ice. This liquid is recycled to reject fl fate from steam silo l.

According to a preferred embodiment, the steaming fl ice is fed into the impregnation step together with the impregnation chemicals, in which case the impregnation chemicals are fed via separate feed nozzles 10a - 10c to the pipeline 11, which connects the outlet nozzle 4 of the steam device 1 to the absorber nozzle nozzle 6. To create pressure, pumps 20, 21 or similar devices are suitably arranged in the pipeline.

In the impregnation step, an impregnation solution is used, which comprises an aqueous solution of alkaline material, which solution optionally comprises sulfonation chemicals. Typically, an aqueous solution of either an alkali metal hydroxide, such as NaOH or KOH, or an alkaline earth metal hydroxide, such as magnesium hydroxide, Mg (OH) 2, or calcium hydroxide or mixtures thereof is used. If desired, this solution also comprises, for example, salt compounds, such as sodium salt, the concentration of alkali hydroxide is typically about 2 - 12 kg / Adt (tons of air-dried pulp), however preferably not more than about 6 kg / Adt, especially not more than about 4 kg / Adt. Alkaline earth metal hydroxides are used in (molarity) corresponding levels. The pH value of the solution is about 9 - 11. The consumption of the sulphate compound is about 1 - 20 kg / Adt, for hardwood in particular not more than 3 kg / Adt.

In addition to pure solutions, aqueous solutions of compounds of alkaline materials can also be used for impregnation, such as the boiling liquor obtained from pulp boiling, for example white or green liquor. The temperature in the impregnation step is about 30 - 95 ° C, preferably about 40 - 90 ° C, which temperature can be achieved at least in part by the heat carried by the ice. Usually the temperature in the impregnation step is lower than the temperature in the elution step. According to the present invention, the pressure in the impregnation step is about 1.5 - 15 bar, preferably about 2 - 10 bar absolute pressure. As a result, an overpressure of at least about 0.5 bar is used during the impregnation. The ratio of wood to liquid (p / p) is usually about 1:20 1: 4, especially about 1:15 1: 6.

The content of the impregnation chemicals can be regulated depending on the fl ice to be treated and, if necessary, it can be increased.

The duration of the impregnation treatment is about 1 - 240 minutes, preferably about 5 - 120 minutes, especially about 10 - 60 minutes.

During the impregnation step, the ice is impregnated with alkali to the highest possible extent. Usually at least 85%, preferably at least 90%, in particular at least 95% of the volume of pores of the ice should be filled with the impregnation solution.

The impregnation can be performed in one or more steps, in which case at least one impregnation step is performed at overpressure. According to a preferred form of drying, the hot ice is first impregnated under overpressure under the conditions mentioned above, after which the impregnation process still continues in an open container or vessel at the same or at a different temperature. About 10 - 80% of the time for the impregnation treatment can be performed under pressurized conditions. In the application described below, the duration of treatment under pressure and treatment under non-pressure were equally long, the total time being 40 minutes.

The fl ice coming from the impregnation step is removed via the outlet nozzle 6a. The reference numeral 6b refers to the dispensing device of the absorbing device. With this dispensing device, the residual fraction which has accumulated at the bottom of the device can be removed.

There, the ice is fed to a refining step 12 for conventional chemical mechanical pulp, which can be carried out, for example, in a refiner equipped with grooved refining blades. The wood material is refined to a drainability of 50 - 500 ml CSF, especially about 90 - 150 ml CSF.

Drawing 1 shows in practice how the fl ice fl fate generated from the impregnation step can be further processed before refining. Consequently, the excess impregnating liquid in the screw press 13 is first removed, after which the reaction of the chemicals can continue in the reaction silo 14, before the ice is transported with the screw conveyors 15a and 15b to the pipe. The reaction time in reaction silo 14, if such a silo is used, is typically about 0.1 to 10 hours.

In the screw press 13 it is possible to separate contaminants and supporting materials which are not suitable for refining, and they are removed via the screen 16 to the reject channel. The liquid phase 17, which is generated from the screw press, can be recycled to the pipeline 10, possibly in combination with the addition of new water. Reference numerals 20 and 23 refer to pumps which are arranged for feeding the liquid phase. In particular, as the figure shows, the impregnation solution is recycled in the process and its alkali concentration can be controlled (increased) by adding new alkali.

It should be mentioned that two essential factors in the present invention are that a good elimination is achieved before the impregnation solution and the ice are brought together, and that the impregnation takes place under pressure. These two factors together enable an efficient penetration of the impregnation solution into the ice. The residence time and the temperature in the pressure vessel are selected in such a way that it is possible to regulate the diffusion time and the reaction time. The time must be long enough for the diffusion to take place, whereby the reaction rate must not be too high.

The chemical mechanical pulp, as described above, has extraordinary good properties. As described in the introduction, the light scattering qualities of the pulp are improved and have been achieved without increasing the percentage of coarse projects. Consequently, at the same freeness rate, the light scattering qualities of the pulp according to the invention are at least 5%, even 10% better compared to the high alkali reference. At the same time, the percentage of coarse rejects of the pulps of the present invention is lower than the percentage of coarse rejects of the TMP reference and unexpectedly even lower than the percentage of coarse rejects of the high-calorie reference. At the same freeness rate, the bulk value is also improved by as much as 5%.

A notable example is that the light scattering qualities of the CTMP pulp produced from aspen can be higher than 45 mz / kg and the percentage of coarse rejects lower than 0.3%. For birch, it is correspondingly possible to produce a pulp which has spreading qualities which are higher than 45 mz / kg and a percentage of coarse rejects which is lower than 1.5%. These are only examples of the properties of pulp, and it should be mentioned that for a pulp producer, within the limits of the present invention, it is possible to freely choose either a desired degree of dispersion or percentage of coarse projects and, by means of the present invention, that achieve a significant improvement of one of the parameters.

The pulp according to the present invention can be used for the production of paper and board products.

Accordingly, after the coating described above, the pulp is usually bleached using, for example, hydrogen peroxide under alkaline conditions to a brightness of about 75-88%. If desired, it is possible to tailor the properties of the initial material by mixing the pulp with a chemical pulp in such a way as to provide a storeable, initial material, one which, however, comprises a significant amount (at least 30% by weight) of chemical mechanical pulp Coniferous pulp is preferably used as chemical pulp and in this case its percentage is 1 - 50% of the dry weight of fi brema in the raw material. However, it is also possible to use only chemical mechanical aspen pulp.

The pulp is first spread to a leathery consistency in a manner known per se (typically to a percentage of solids of about 0.1 - 1%), after which it is spread on the wire, where it is made into a web to form paper or paper. cartonboard. It is possible to add a filler, such as calcium carbonate, usually about 1 to 50% by weight of the weight of fibers to the fiber slurry.

The paper barium can be surface glued and / or provided with a coating layer and, if desired, calendered. Coating pastes can be used for a single coating, for pre-coating and for surface coating. Triple coating is also possible. In general, a coating according to the present invention contains 10 to 100 parts by weight of at least one pigment or a mixture of pigments, 0.1 to 30 parts by weight of at least one binder and 1 to 10 parts by weight of other additives known per se.

In the manner described above, it is possible according to the present invention to produce from the pulp webs of material which have excellent printing properties, good uniformity and high opacity and brightness.

Examples of applications are paper, coated printing paper and brochure paper, cover paper for multilayer cardboard.

The following non-limiting examples illustrate the present invention.

Example 1 CTMP pulp of aspen was prepared in the laboratory under the following conditions: Chips of aspen, which had been steamed at 100 ° C for a period of 2 - 5 minutes, were impregnated with different amounts of sodium hydroxide at a pressure of 5 bar (a), at 80 ° C for a period of 20 minutes in a closed container. Thereafter, the impregnation was continued for another 20 minutes in an open reaction silo at 80 ° C.

The following methods, among others, were used to determine the properties of the pulp: ~ bulk cm3 / g: EN 20534 - spread mz / kg: ISO 9416 - CSF ml: ISO 5267-2 - tip: 'Pulmac shives', sample amount 3 g and a 0.08 mm perforated disk for 150 ml CSF pulp and 0.1 mm for 325 ml CSF pulp.

Table 1 shows what happens when the aspen chips treated in this way were refined to a drainage capacity of 150 ml CSF.

Table 1 NaOH dose,% NaOH, g / l NaOH, mol / l Spread, mz / kg Spet,% 1.2 4.8 0.12 53.5 0.43 0.41 1.68 0.042 58.5 0 .07 0.33 1.32 0.033 56.4 0.04 0.23 0.92 0.023 59.0 0 .14 0 0 0 57.3 0.62 As the table shows, using the present invention it is possible to reduce dose of alkali hydroxide, in which case the spread clearly increases without increasing the percentage of coarse rejects. Compared to the case in which a conventional amount of alkali was used, the dispersion was increased by more than 10%. Unexpectedly, the percentage of coarse rejects was even lower than in the reference with 1.2% alkali.

Table 2 shows the bulk value of the masses described above.

Table 2 NaOH dose,% Bulk, cm / g 1.2 2.66 0.41 2.70 0.33 2.81 0.23 2.74 0 2.83 As can be seen, the bulk value is also slightly better at the same CSF level.

The experiments were repeated with birch ice. Pressurized impregnation of birch (80 ° C, 5 bar, 20 minutes) at the CSF level of 325 ml produced the following dispersion values: Table 3 NaOH dose,% NaOH, g / l NaOH, mol / l Propagation, mz / kg Tip ,% 1.1 4.4 0.1 1 41.3 - 42.5 2.24 0.42 1.68 0.042 45.1 1.40 Even in this case, a significant improvement in the spread was achieved, even if the percentage - the coarse project part remained high in the experiment. However, it was one third lower than in the reference.

In the case of birch, the reduction of the alkali dose had no significant effect on the bulk value.

Example 2. Laboratory impregnations In the laboratory, impregnations were carried out using aspen and birch at normal atmospheric pressure using alkali doses of 2.5, 5 and 10 kg NaOH / Adt fl ice. The wood / liquid ratio was 1: 8, and the temperature was 80 ° C.

Samples were taken from the impregnation solution at the following times: 15 minutes, 30 minutes, 1 hour and 3 hours from the start of the impregnation process. The organic material, which was dissolved in the impregnation solution, increased dramatically with increasing alkalidose and as a function of the impregnation time. At the same time, the dissolved COD increased dramatically.

The table below shows the results obtained in the example of the effect of the alkali dose on the fiber loss during 40 minutes of laboratory impregnation of aspen.

It should also be noted that the loss was determined from the impregnation solution before the refining. Refining increases the amount of dissolved material and consequently increases the loss of contact, with the larger the alkalide the greater the loss.

Table 4 NaOH% NaO NaO mol / 1 1 1 43 0 035 0m5 O 71 0017 0 0

Claims (14)

10 15 20 25 30 35 40 45 50 534 0011 PATENT CLAIMS A process for producing a chemical mechanical pulp from a wood material comprising wood chips, according to which process - - the ice is brought into contact with an alkaline impregnation solution in an impregnation step under conditions under which the impregnation solution penetrates into the ice, and - the behand ice treated with the impregnation solution, is refined to a desired drainage capacity for the production of the pulp, characterized by - exposing the ice to deaeration at a temperature of 50-100 ° C, and - impregnating the thus obtained, de-leached ice with an alkaline impregnation solution at overpressure, at a temperature of about 30-95 ° C, in such a way that the impregnation solution is effectively absorbed into the fl ice before being refined. A method according to claim 1, wherein the wood raw material is steamed at an elevated temperature, in particular about 80 - 100 ° C, to remove the lu fi from the ice. A method according to claim 1 or 2, wherein - the steamed fl ice is passed substantially at the temperature of the steam treatment to the impregnation step, and - in the impregnation step the temperature of the impregnation solution is kept below the temperature of the steam treatment. A method according to claim 2, wherein the steamed ice is fed to the impregnation step via a screw press. A method according to any one of the preceding claims, wherein, in the impregnation step, an impregnation solution is used which comprises an alkali metal hydroxide, the dose of which is at most about 6 kg / Adt, preferably at most about 4 kg / Adt. A process according to any one of the preceding claims, wherein an aqueous solution of an alkali metal hydroxide, such as sodium hydroxide, cooking liquor obtained from chemical pulp boiling, for example white or green liquor, or salt compounds, such as sodium sulphite, or mixtures thereof, is used as the impregnation solution. . Process according to any one of the preceding claims, wherein the ice is impregnated with the alkaline impregnation solution for about 1 - 240 minutes, preferably about 5 - 120 minutes, in particular about 10 - 60 minutes. A method according to any one of the preceding claims, wherein the wood raw material is refined to a drainage capacity which is 50 - 500 ml CSF, preferably about 90 - 150 ml CSF. A method according to any one of the preceding claims, wherein the temperature at the impregnation step is about 40 - 90 ° C. A method according to any one of the preceding claims, wherein the pressure at the impregnation step is about 1.5 - 15 bar, preferably about 2 - 10 bar absolute pressure. A method according to any one of the preceding claims, wherein, in the impregnation step, at least 85%, preferably at least 90%, in particular at least 95% of the volume of pores in the ice is filled with the impregnation solution. A method according to any one of the preceding claims, wherein the impregnation is carried out in fl your steps, in which case at least one of the steps is performed at overpressure and at least one of the steps at normal atmospheric pressure. 53-'4 004 10 A method according to any one of the preceding claims, wherein the steaming of the chips is carried out at least substantially at normal atmospheric pressure using saturated or almost saturated steam. Chemical mechanical pulp produced by the process according to any one of claims 1 to 13.