SE442880B - PROCEDURE FOR DELIGNIFICATION / WHITING OF CELLULOSAMASSA WITH CHLORIDE Dioxide / CHLORINE IN THE SAME STEP - Google Patents

Abstract

16-256 PROCESS FOR DELIGNIFYING AND/OR BLEACHING CELLULOSE PULP The process for delignifying and/or bleaching cellulose pulp comprises adding chlorine dioxide first to the cellulose pulp, and then chlorine, the chlorine being supplied to the cellulose pulp sequentially in two or more increments in the Course of this stage of the delignifying and/or bleaching process.

Description

10 IS 20 25 35 8008336-5 2 The production of chlorine is significantly cheaper than chlorine dioxide in terms of energy requirements per quantity active clone but chlorine reacts with lignin and the carbohydrate moiety in cellulose pulp and gives rise to toxic substances, of the type chlorinated hydrocarbons and chlorinated lignin, which released to the recipient. Chlorine dioxide reacts only with lignin without appreciable formation of organic chlorine compounds and attack on cellulose and hemicellulose.

By incorporating chlorine dioxide into chlorine, a reduction is obtained attack on the carbohydrate portion of the cellulose pulp.

At s.k. displacement bleaching is displaced one ink chemicals, e.g. chlorine after some time with water or alkali solution, after which after some time this liquid in turn is displaced with another bleaching chemical solution, for example containing chlorine dioxide, which gives the advantage of simplified apparatus.

All bleaching chemicals have both benefits as disadvantages.

Disclosure of the invention Technical problem In prior art, non-bleaching agents have potassium and chlorine dioxide could be used on timely manner, i.e. so that the advantage of the respective bleaching chemical is used at the same time as its disadvantages work.

Solution The present invention describes an optimal use of the above-mentioned bleaching chemicals and relates to a procedure for delignification and / or bleaching of cellulose pulp by means of the chemicals chlorine and chlorine oxide, the cellulosic mass in one and the same deligni- Chlorination dioxide is first applied and bleaching steps and then for a time chlorine is added, characterized in that the chlorine the cellulose mass is applied sequentially at two or several times during the delignification / bleaching process the course of the race and that the acidity of the cellulose pulp before the delignification / bleaching step is set so that cellulose pulp pH at delignification / bleaching the end of the process amounts to 3.5-6.0, preferably 4.5-5.5, preferably 4.75-5.25. 10 15 20 25 30 s 8008336-3 The bleaching step according to the invention can be inserted anywhere any time in a spell sequence, i.e. in its beginning, middle or end. 'It is especially advantageous to deposit the bleaching step according to the invention in the places where previous chlorine dioxide steps have been used. It is entirely possible, to also replace the chlorine step with the bleaching step according to the invention for example, as a first bleaching step in a bleaching sequence.

The method according to the invention is applicable Though the cellulosic pulp fibers must contain and preferably be surrounded of water. According to a preferred embodiment of the The cellulose mass is present in the form of a cellulose pulp of varying pulp concentration. suspension with a pulp concentration of 2-30%, preferably approximately 2.5-12%.

The cellulose pulp usually comes from one washing filter and leaves this in the form of a coherent pulp web with a pulp concentration of 11-16%.

The pulp web usually falls into a screw where it crumble.

The pulp suspension is then fed to an apparatus, where admixture of chlorine dioxide in the form of an aqueous solution takes place, whereby a pulp concentration of approx. 6-12% arises. The total amount of active chlorine as well as the amount chlorine dioxide, which is added to the pulp suspension is in the first depending on the lignin content of the cellulose pulp and can therefore vary considerably. Usually it lies total batch of active chlorine, i.e. chlorine and chlorine dioxide, between 0.2 and 10%, calculated on absolutely dry mass.

The amount of chlorine dioxide invested in the above-mentioned apparatus is 30-90%, preferably 40-85%, preferably 50-70% of the total active chlorine batch to the step. Mass suspension the reaction is allowed to react with the chlorine dioxide for a certain period of time time. This residence time can be achieved by transporting the pulp suspension through a conduit of a certain length and / or by storing the pulp suspension in a vessels of some kind, such as a small bleaching tower. 10 15 20 ZS 30 55 8008336-3 4 The pulp is then transported to a chemical mixing site, where chlorine is usually in the form of a water solution is added. The time between chlorine dioxide the rate and initial addition of chlorine may vary considerably, i.a. depending on the temperature the suspension exhibits. However, it is preferred that the first the partial addition of chlorine is done within 30 minutes, preferably within 15 minutes, preferably within 5 minutes the chlorine dioxide additive. The pulp suspension is transported then on to another chemical admixture place, where additional chlorine is added. The time period between the two chlorine additives may correspond to those above, but do not need to do so.

According to a preferred embodiment of the invention the pulp suspension is transported to further chemical mixing sites, where chlorine is added.

The chlorine additive is thus divided on at least two occasions and the amount of chlorine charged at each occasion should be 10-25%, preferably 15-25%, preferably 20- 24% of the amount of active chlorine that accompanies the mass pension and is unused at the time of addition.

The amount of unused active chlorine in the pulp suspension determined by analysis according to any of the known methods. Because the consumption of bleach chemicals is larger at the beginning of the bleaching step, the main part of is added chlorine during the first half of the bleaching step.

The temperature during the bleaching step is connected with and depending on several parameters, for example the bleaching step according to the invention in the bleaching sequence then, total batch of active chlorine and time, and lies usually at 20 DEG-90 DEG C., preferably at 70 DEG-70 DEG C., preferably at 40-60 ° C. The pH of the pulp suspension when it is introduced in the bleaching step according to the invention varies, depending on the immediately preceding treatment. For example, the bleaching step according to the invention is not always followed by a 10 8008336-3 washing steps, without the cellulose pulp can be transported directly from a chemical treatment step to bleaching the step according to the invention. It is therefore of the utmost weight, to a good result of the bleaching according to the invention is to be achieved, that the incoming cellular the acidity of the loose material is checked and set to described above.

The hallmark of the present invention is as shown above, that the cellulosic pulp first chlorine dioxide is added and then chlorine quenically on two or more occasions in the bleaching step.

In addition to pure chlorine dioxide, chlorine dioxide also means chlorine dioxide mixtures, where chlorine dioxide is the predominant rande kemikalíen. As is well known, it is difficult to set completely pure chlorine dioxide. Technical chlorine dioxide usually contain a certain amount of chlorine and even if the proportion amounts to up to 30%, this is included mixture in the concept of chlorine dioxide. Similarly means chlorine in addition to pure chlorine also chlorine mixtures, where chlorine is the dominant chemical.

Regarding the addition of chlorine dioxide and chlorine to the pulp suspension, it is done as follows.

Chlorine dioxide in the form of an aqueous solution is added a mixing apparatus, where it is mixed into the pension. The mixing device is called a mixer. These can be divided into two types, namely dynamic mixer containing one or more moving parts of the pin type mixer and static mixer, which does not contain any moving parts. Both mixer types can be used for incorporation of chlorine dioxide into the pulp suspension in accordance with the invention.

Chlorine can be added to the pulp suspension either in in the form of gas or an aqueous solution. An aqueous solution of chlorine is preferable. The apparatus described above can can also be used for the incorporation of chlorine into the pulp suspension 10 15 Z0 25 1 ,; UI 8008336-3 sionen. It is important that the mixture of chlorine and the mass suspension is intensive. According to a preferred embodiment of the invention, the chlorine is mixed into the mass. the suspension by means of a long tube through which the pulp suspension is pumped. The pipe is provided inside with fixed baffles, placed at certain intervals in longitudinal path between each other. In direct connect to the baffles, more specifically something after the baffles in the direction of transport of the pulp suspension, there are lines for the introduction of the chlorine connected. When the mass suspension pumped through the pipe, it is subjected to a strong turbulent movement with the passage of the baffles.

It is in these places that the chlorine is added in the form of a aqueous solution. It is especially beneficial if the chlorine mixed into the water following the cellulose pulp the solution, during a partial separation of the pulp and the liquid. This can be achieved, for example, by that narrower pipes provided with slits or other per- linings in the mantle surface are inserted into the coarser 1ängs ~ walking pipe in the places where the supply lines for chlorine are connected. Through these perforations are pressed liquid but not cellulose pulp and to this liquid the chlorine solution is passed, then the cellulose mass and the liquid remixed after passing the aforementioned baffles.

Benefits By bleaching the cellulose pulp in accordance with The invention provides a number of advantages.

A large part of the chlorine dioxide, as before used in bleaching in different bleaching sequences, put with the cheaper ink chemical chlorine, without the amount of organically bound chlorine (ie the most toxic substance) increases in the bleach liquor. This means that it from an economic point of view very important connection between use of chlorine and sodium hydroxide in the bleaching sequence can be maintained in a meritorious manner. One for excessive use of chlorine leads to a too low production sodium hydroxide relative to afterxagan 10 15 20 25 30 8008336-3 in the cellulose industry, which in turn leads to more expensive sodium hydroxide and higher total production cost of bleached cellulose pulp.

The amount of chlorine dioxide added is utilized in one better way, probably due to the decay of HClO 2 to HClO and HClO 3 are counteracted by the addition of chlorine in accordance with the invention. The treatment temperature can be lowered and the time shortened compared to conventional chlorine dioxide bleaching due to the high efficiency (high reaction rate) of the bleaching process according to the invention. Lowering the temperature means energy profit and shorter time means, that the residence volumes for example in the form of bleach becomes smaller, which reduces investment and operating costs.

Figure description Figure 1 shows a flow chart for an output embodiment of the method according to the invention.

Best embodiment Experiments with the method according to the invention have and the results obtained are set out below. standing embodiment.

Example 1 Pine sulphate pulp with kappa number 3.0 and viscosity 995 dmš / kg was bleached partly with chlorine dioxide according to conventional technology and partly with chlorine dioxide and chlorine in in accordance with the invention.

When bleached with chlorine dioxide only [O-sample) 417 grams of a pulp suspension with a concentrated 12% in an ink vessel. 778.7 g of water were added.

The mixture was tempered in a water bath to 40 ° C. 54.3 ml of a chlorine dioxide solution with a strength of 15 g active chlorine / liter was added. The mixture of the bleach in the pulp suspension was made by means of a propeller stirrer for a period of 2 minutes from the time of addition. 10 15 0000336-3 The ink vessel was stored in the water bath for 30 minutes.

Thereafter, the bleaching and pH suspension of the pulp suspension was stopped. value and residual chlorine content were determined. Of the washed cellulose mass was made sheets for determining brightness.

In bleaching in accordance with the invention, also weighed 417 grams of 12% cellulose pulp in a bleach vessel and to this was added 720.8 g of water.

The mixture was tempered in a water bath to 40 ° C.

Alkali in an amount of 0.1 g was added to the pulp suspension with the intention of slightly raising its pH.

Under powerful stirring by means of a propeller stirrer was added 33.3 ml of a chlorine dioxide solution with a strength of 15 g active chlorine / liter. With the addition of chlorine dioxide the time measurement began. After a time of 2 minutes 28.8 ml was added, after 4 minutes 26.3 ml and after 6 minutes 23.8 ml of a chlorine solution with a strength of 4.0 g active chlorine / liter with continued stirring.

Stirring continued for another 2 minutes before stopping.

The bleaching continued until a total of 30 minutes before flutit. Thereafter, the pH of the pulp suspension was determined and residual chlorine content. Of the washed cellulosic pulp sheets were made for determining brightness.

Terms and results are summarized in the following standing table 1.

Table 1 0-prov Mass concentration,% 4.0 Temperature, OC 40 Time, minutes 30 Batch, chlorine dioxide, 0 active chlorine 1.63 Rate, chlorine,% End pH 2.9 Residual chlorine,% active chlorine 0.48 Brightness,% ISO 68.8 viscosity, anF / kg 965 Organic chlorine in bleach liquor, mg / kg organic material 13 According to the invention 4.0 40 30 LO 1 z '- 1.63 oßzJ 4.8 0.13 75.0 950 14 10 15 20 25 30 35 8008336-3 9 The batch of ink chemicals was counted in% of absolutely dry mass, the brightness was determined according to SCAN-C 11: 7S, viscosity was determined according to SCAN-C 15:62 and the amount of technically bound chlorine was determined after extraction with leumeter.

As can be seen from the table above, the bleaching the method according to the invention is much more efficient than conventional chlorine dioxide bleaching, which is reflected in a considerably higher brightness of the cellulose pulp and significantly lower residual chlorine content in the pulp suspension.

Despite the great difference in brightness of the masses according to the 0-test and according to the invention, respectively the viscosity of the pulp according to the invention only slightly lower than in the mass according to the O-test. Further shows that the amount of organically bound chlorine in bleach the liquor is essentially the same in the two experiments.

In the example shown above, the chlorine additive has divided into three occasions. According to a preferred embodiment of the invention, chlorine addition must be made on three or more occasions during the bleaching step.

Example_Y Experiments with the method according to the invention have performed in experimental equipment in the factory.

The experiment according to the invention was carried out accordingly flow chart, shown in Figure 1 with a birch sulphate mass with kappa number 2.7. For comparison, it faded the mass in a conventional chlorine dioxide step, i.e. all chlorine dioxide was charged at the start of the bleaching (O-sample).

The pulp concentration in this step was 4.2%, the temperature the trip 4ZoC and the time 30 minutes. Amount of chlorine invested dioxide was 1.6% active chlorine, calculated on absolutely dry pulp, and the pH of the pulp suspension at the end of the bleaching var 3.4.

In the experiment according to the invention were transported a pulp suspension of the abovementioned birch sulphate pulp through line 1 to a mixer 2. In this mixer was mixed the cellulose pulp with an aqueous solution of chlorine dioxide, which 10 15 20 25 30 8008336-3 10 was added through the line 3.- Invested amount of chlorine dioxide was O.8% active chlorine, calculated on absolutely dry mass.

Thereafter, the pulp suspension was transported through 4 to an elongate treatment vessel 5. This treatment vessels were divided into chemical admixture spaces 6, 7, S etc. and intermediate residence volumes 9, 10, ll, etc. The chemical mixing spaces were provided with fixed baffles 12, which caused one turbulent flow of the pulp suspension. In connection with to the baffles 12 in spaces 6, 7 and 8 chlorine was added in the form of an aqueous solution. Waterless the line was supplied via the main line 13 and the side line 14, 15 and 16. In the present experiment, the chlorine additive was divided into 13 substreams. showing a schematic flow chart of principle nature, only three additives have been shown. Overall amount of chlorine invested was 0.8%, calculated on absolutely dry pulp. After the chlorine additions, the pulp suspension was carried out through line 17 to a bleaching tower 18, where the pulp completely bleached. 30 minutes after the chlorine dioxide addition the bleaching process was interrupted by the mass was ported through line 19 to a wash filter (no The temperature of the pulp suspension was 42 ° C After the last chlorine addition In Figure 1, shown). during the entire bleaching step. the mass concentration of the suspension was 4.Z%. It through line l the acidity of the bulk suspension included was so adjusted that the pH of the pulp suspension at the end of the bleaching was 5.2.

The breakdown of the chlorine additive is shown below. standing table 2. 10 8008336-3 ll Table 2 Time from the start of bleaching in Invested amount of chlorine, calculated on minutes absolutely dry mass 3 0.180 4 0.135 5 0.095 6 0.075 7 0.064 8 0.052 9 0.042 10 0.037 ll 0.030 12 0.027 13 0.023 14 0.021 15 0.020 In both bleaching experiments it was determined after bleaching end up remaining amount of unused active chlorine and off it sheets were washed, on which the brightness was determined des en1igr sem-c 11:75. of Table 3 below.

The measured values are shown Table 3 0-sample According to the invention Residual amount of active chlorine,% 0.53 0.10 Brightness Iso, 2, 69.2 75.3 The above values show that the bleaching process according to the invention are much more efficient than conventional chlorine dioxide bleaching, which is understood by the lower the residual chlorine content of the pulp suspension and the higher the heat of the mass. 8008336-3 12 Exemgel 3 The same birch sulphate mass as in Example 2 was again laid in accordance with the invention and in accordance with the flow chart shown in Figure 1.

In these experiments the alkali addition was varied to the pulp suspension coming through line 1 so that five different pH values of the pulp suspension at the end of the bleaching was reached.

The bleaching conditions are shown below table 4.

Table 4 Mass concentration,% 4.2 Tenlperatur, OC 42 Time, nünuter 30 Acidity of the mass suspension 2.7, 3.5, 4.6 at the end of bleaching, pH 5.0 and 6.0 Chlorine dioxide batch, active chlorine,% 1.0 Chlorine charge, 0.6% The chlorine was charged according to the following schedule regarding time from the start of bleaching in ' .l60 minutes and amount in% 3 0 4 0.120 5 0.080 6 0.060 7 0.049 8 0.037 9 0.027 10 0.022 11 0.015 12 0.012 13 0.008 14 0.006 15 0.005 10 15 20 ZS 8008336-5 13 After the end of the bleaching, the remaining amount was determined unused active chlorine in the pulp suspension and of it washed mass was made sheets, on which the brightness was sued in accordance with SCAN-C 11:75. is shown in Table 5 below.

The measured values Table 5 The pH of the suspension at the end of the bleaching 2.5 3.5 4.6 5.0 6.0 Residual amount of active chlorine% 0.20 0.22 0.23 0.24 0.24 Brightness ISO,% 70.0 73.0 75.0 75.6 75.9 As can be seen from the above values, the residual chlorine content is at all attempts were low. The brightness of the mass becomes special high about the pH value in the pulp suspension at bleaching end is in the range 3.5-6.0.

Example1_í A birch sulphate mass with a coat number of 4.5 and light 50.9% ISO was treated partly according to conventional chlorine dioxide bleaching, i.e. with the addition of all chlorine dioxide at the start of the bleaching step, and partly according to the invention, i.e. according to the flow chart shown in Figure 1. The intention with the attempts was to achieve the same brightness of the bleached the masses.

In the experiment with conventional chlorine dioxide bleaching (0-sample) the pulp concentration was 6%, temperature 70 ° C and the time 180 minutes. Amount of chlorine dioxide invested was 2.8% active chlorine, calculated on absolutely dry mass. pH the value of the pulp suspension at the end of the bleaching was 2.3.

In the experiment according to the invention, concentration 4.Z%, temperature SOOC and time 30 minutes. The pH of the pulp suspension during bleaching end was 5.8. At the start of the bleaching, chlorine dioxide was used in cn amount of 0.93% active chlorine, calculated on absolutely dry . ....__.........._...-. 10 l5 8008356-3 14 pulp. Chlorine was charged in an amount of 0.80%, calculated on absolutely dry mass. Chlorine was charged according to a schedule, as shown in Table 6 below.

Table 6 Time from the start of bleaching in Invested amount of chlorine calculated on absolutely dry mass fl O minutes 0.210 0.162 0.118 0.096 0.084 0.052 0.042 0.037 ROOOQQLFI-Iäb-XKQ After the end of the bleaching, the remaining amount was determined unused active chlorine in the pulp suspension and of it washed mass was made sheets, on which the brightness was sued in accordance with SCAN-C 11:75. The measured values can be seen from Table 7 below.

Table 7 0-sample According to the invention Residual amount of active chlorine,% 0.20 0.08 Brightness ISO,% 77.3 77.5 As can be seen, the bleached masses have the same brightness obtained. have been widely differing.

This has been achieved despite the bleaching condition ~ In the procedure according to invention, the chemical rate was lower, the temperature lower and the time shorter compared to the conventional the chlorine dioxide bleaching process. This means a superior economics of the process according to the invention. Low 10 20 25 50 8008336-3 15 chemical rate leads to low chemical cost, low temperature leads to low energy costs and short time leads to the volume of ink vessels becoming small, which means low acquisition and operating costs. This with low acquisition and operating cost is valid even if the savings are partly offset by the acquisition of apparatus, for example, similar to that indicated by the number 5 nade in figure l.

Example 5 A birch sulphate mass with a coat number of 4.5 and light 50.9% ISO was treated in three different ways, partly according to conventional chlorine dioxide bleaching (0-sample), i.e. with the addition of chlorine dioxide at the start of the bleaching step, partly with the addition of chlorine dioxide at the start of the bleaching step followed by a chlorine additive (D / C) and finally according to a embodiment of the invention.

In the 0-sample, the pulp concentration was 4.2%, the temperature SOOC and the time 30 minutes. The amount invested chlorine dioxide at the start of bleaching was 2.1% active chlorine, calculated on absolutely dry mass.

In the experiment with the addition of chlorine dioxide first and then chlorine (D / C) the pulp concentration was 4.2%, the temperature SOÜC and the time 30 minutes. The amount invested chlorine dioxide at the start of bleaching was 1.9% active chlorine, calculated on absolutely dry mass. After 2 minutes bleaching time 0.21% chlorine was charged, calculated on absolutely dry mass.

In the experiment according to the invention, concentration 4.2%, temperature SOOC and time 30 minutes. The amount of chlorine dioxide charged during bleaching start was 1.13% active chlorine, calculated on absolutely dry pulp. After 2 minutes of bleaching time, 0.2]% chlorine was charged, calculated on absolutely dry mass and after additional l minute bleaching time, 0.16% chlorine was charged, calculated on absolute dry mass. The pH value of the pulp suspension during bleaching was controlled to 5.0 by the addition of a small amount alkali. 10 8008336-5 M After the end of the bleaching in the various experiments the remaining amount of unused active chlorine was determined in the pulp suspension and of the washed pulp were made sheets on which the brightness was determined according to SCAN-Cll: 75. IN Table 8 lists the bleaching conditions and achieved results.

Table 8 0-sample D / C Enl. opg.

Capacity of starting mass 4.5 4.5 4.5 "brightness, ISO% 50.9 50.9 50.9 Mass concentration,% 4.2 4.2 4.2 Temperature, C 50 50 50 Total bleaching time, minutes 30 30 30 Chlorine dioxide charge at start-up 2.10 1.90 1.13 % active chlorine Added chlorine after 2 min,% - 0.21 0.21 Added chlorine after 3 min,% ~ - 0.16 pH at the end of bleaching 2.5 2.2 5.0 Residual amount of active chlorine,% 1.20 0.80 0.20 Brightness, ISO% 67.0 69.0 74.0 Consumed active chlorine,% 0.90 1.31 1.50 As shown in the results reported in Table 8 the method according to the invention occupies a special position in terms of the brightness improvement of the mass. About D / C- the bleaching, i.e. addition of chlorine dioxide in bleaching start followed by a chlorine additive, compared with 0- the test, i.e. conventional chlorine dioxide bleaching, finds one a brightness difference of 2 units in favor of D / C procedure. However, this improvement has taken place the price of significantly increased consumption of active chlorine. If the method according to the invention is studied one finds further increase the brightness of 5 units, despite that the consumption of active chlorine does not exceed the use according to the D / C procedure. When comparing 8008336-3 residual amount of active chlorine in the various processes is found that in the process according to the invention they are taken the blekkerrlikalías invested in something completely different than in the other two procedures.

Claims (5)

8008336-3 18 Patent claims Process for delignification and / or bleaching of cellulose pulp by means of the chemicals chlorine and chlorine dioxide, wherein the cellulose pulp in one and the same delignification / bleaching step is first added to chlorine dioxide and after a time chlorine is added, characterized in that the chlorine is added to the cellulose sequentially on two or more occasions during the delignification / bleaching process and that the acidity of the cellulose pulp before the delignification / bleaching step is adjusted so that the pH of the cellulose pulp at the end of the delignification / bleaching amounts to 3.5-6.0, preferably 4.5-5.5, preferably 4.75-5.25. 2. A method according to claim 1, characterized in that the cellulose pulp is present in the form of a suspension with a pulp concentration of 2-30%, preferably 2.5-12%. J. Process according to claim 1-2, characterized in that the chlorine dioxide content consists of 30-90%, preferably 40-85%, preferably 50-70% of the total active chlorine batch. 4. A method according to claims 1-3, characterized in that the first partial addition of chlorine takes place within 30 minutes, preferably 15 minutes, preferably 5 minutes after the chlorine dioxide addition and that the bulk of the amount of chlorine is added to the cellulose pulp during the first half. of the delignification / bleaching step. 5. A process according to claims 1-4, characterized in that the amount of chlorine added to the cellulose pulp at each addition is 10-25%, preferably 15-25 Z, preferably 20-24 Z of the amount of active chlorine. , which accompanies the mass at the time of application.