JPH05500835A - How to treat fiber pulp with chemical solutions - Google Patents

Abstract

The process relates to continuous treatment of a fiber pulp with a chemical solution by forming on a filter surface a bed of a fiber material suspension and by feeding it through one or several chemical treatment steps in which the chemical solution is displaced through the bed. According to the method, there are used in each treatment step two different treatment liquids which are successively displaced through the bed. The first treatment solution is a chemical solution which contains a greater amount of active chemicals than is consumed in the reactions occurring in the pulp bed, preferably approx. twice the amount. The second treatment liquid is a solution which does not contain active chemicals in an amount significant in terms of the reaction. Its purpose is not only to displace that portion of the first treatment liquid from which the active chemicals have been spent but also that portion which still contains active chemicals upon leaving as a filtrate. Of the filtrate of the treatment step, that fraction is recovered which has the highest concentration of active chemicals and contains most of the active chemicals leaving the bed and is in its amount only so large that, when reinforced with a fresh chemical solution, it can be used in its entirety as the first treatment solution. The total liquid volume of the treatment liquids is substantially greater than the liquid volume present in the bed upon its leaving the treatment step - preferably 2- to 3-fold.

Description

[Detailed description of the invention] How to treat textile valves with chemical solutions The present invention forms a valve bed with a valve suspension on the filter surface. It can also be used with one of several chemical treatment steps that displace the chemical solution with a valve bed. Concerning the continuous treatment of fiber valves with chemical solutions by providing said bed . When using this type of method for bleaching cellulosic materials, it is generally It is called catalytic bleaching or dynamic bleaching.

If it is desired to produce saleloin fibers with a high degree of whiteness, the fibers are removed. Must be bleached after the cellulose process. For example, a highly white sulfate valve To obtain the extract, use chlorine and chlorine dioxide as bleaching agents and sodium hydroxide as the extraction chemical. It must be bleached in 5 steps using bleach.

The most common method for this is to first mix the drug solution with the valve suspension and then This mixture (valve + chemicals) is then introduced into a retention tank and charged to react with the fiber material. Allow sufficient diffusion time. Then, the generated reaction products are washed away.

Although it varies depending on the chemical, a relatively long residence time is required to ensure sufficient diffusion. Ru. For example, when using chlorine dioxide, typical residence times are 3 to 5 hours.

As a result, the devices are generally large and expensive.

The required residence time can be reduced by using the displacement method instead of the mixing method. I've known this for a while now. Development of equipment suitable for this method began in the 1960s. It was. Some of the expected benefits were achieved, e.g. In comparison, the heat usage and water consumption of the bleaching process could be significantly reduced. just However, the amount of bleaching chemicals increased somewhat.

However, at the same time, conventional technology has evolved, particularly mixers. For this reason, replacement techniques The technical system was not as competitive as expected. Today, displacement bleaching is It is mainly used when the textile material can be easily bleached.

Conventionally used substitution bleaching methods are briefly as follows: The pre-formed valve bed allows the liquid content to be approximately equal to that of the same bed. Replace the chemical solution with a large amount of liquid. Usually, quantity coef ficient) is 1 to 1.1 (quantity rate = volume of chemical used/liquid content of bed ). The concentration of active chemical in the replacement chemical solution is determined by the amount of active chemical in the valve bed treatment. Adjust as portions are consumed.

The above chemical solution and the generated reactants are transferred from the bed to the chemicals used in the next step. Before separation by one exchange or in the case of a final bleaching step with water, This is aimed at the so-called steady step with a long residence time, which is This is because the concentration distribution that occurs in the area has time to level out due to the influence of diffusion.

In order to obtain similar results with this method as with conventional methods, the above-mentioned steady-state steps must be completed. It is known that the residence time should be of the same order of magnitude as that of conventional methods.

The purpose of the present invention is to provide uniform chemical treatment throughout the valve bed. The above disadvantages can be overcome by using a substitution process that does not require stationary steps. It's about avoiding.

Displacement bleaching is similar in many ways to displacement cleaning; There are significant differences between is important. In both methods, liquid flow by dispersion and also in the fiber bed A similar liquid mixing occurs due to the fact that the flow is laminar. For these reasons When the liquid in the valve bed is replaced by another liquid, the ideal position is No exchange occurs, and there is always mixing between the two solutions, even in the cleaning method and in the replacement method. But this is a disadvantage. This disadvantage in both methods is due to the principle of self-sufficiency. It can be reduced by performing substitutions. However, as the number of replacement steps increases, However, the cost of equipment increases.

Although reactive chemistry occurs when cleaning valves, the main purpose of this method is to clean the valves. The goal is to be as careful as possible to separate the chemicals in the solution in the valve bed. of the valve Increasing the rate of displacement during cleaning improves chemical recovery. Therefore relatively High mass rates are generally used. However, as the amount recovered increases, the evaporation of recovered The need will increase.

On the other hand, in the case of conventional bleaching, it is disadvantageous to use high loading rates. Ru. This is because in this case the active chemical displaced in the valve bed is not recovered. This is because the loss of effective chemicals during bleaching increases.

In both the cleaning method and the bleaching method, replacement is performed by the cross-flow method, and the liquid flow is carried out during the replacement operation. passes through the bed at right angles to the direction of bed movement.

Since the valve fibers are compressible, the density of the valve bed is not constant within the bed. It increases exponentially towards the filter surface. Of course, this distribution is the type of valve involved and the size of the pressure difference used to create the liquid flow. It is taking place. Usually the density value is about 2% to about 20%, with an average of about lO%. be.

This phenomenon does not have much significance in terms of cleaning effectiveness, but in the case of bleaching, , it is important that all fibrous layers of the bed receive a large amount of active chemical, which is This is of great significance, especially when the concentration of the active chemical in the solution is This is because it decreases as it flows towards. This is due to the above-mentioned dispersion phenomenon and drug This is because the product flows through the valve layer and reacts with the valve layer, resulting in a decrease in Ru.

For these reasons, conventional displacement bleaching methods require that the buffer be removed far from the filter surface. The lube layer is treated with a chemical solution containing a large excess of chemicals over the required amount. Therefore Therefore, layers near the filter surface may not receive a sufficient amount of active chemical during replacement or receive no active drugs. Therefore, the bleaching of the valve bed is quite non-uniform. .

However, using too much active chemical can be dangerous if process conditions such as temperature and pH If the conditions are at the right level, cellulose and S fibers can be decomposed. It is understood that there is no disadvantage caused by causing an inappropriate secondary reaction. There is. However, excess chemicals must be removed prior to the next chemical treatment.

This is because the process conditions will be different in the next step.

When using displacement techniques for bleaching valves, it is most important to clean all layers of the valve bed. be treated with sufficient amounts of chemicals, and to ensure this A solution in which the amount of effective chemical is substantially greater than the amount of effective chemical required to completely treat the entire bed. Use liquid.

The purpose of the present invention is to provide this type of valve bed treatment, but with effective chemical The chemical consumption is not greater than that of ordinary bleaching methods due to the loss of .

The main features of the invention are shown in the attached figure 1/-.

Briefly, the method of the invention is as follows.

The valve bed is formed from cleanly washed valves to be bleached; The cleaning solution present in the first bleaching solution (e.g. chlorine and/or (containing chlorine dioxide) as a displacement liquid. However, first The bleach solution contains an excess of active chemicals and preferably completely chemically treats all valve beds. It contains approximately twice the amount required in the first step. Immediately after this replacement Subsequent substitutions are made using another solution or several solutions. In this case the first replacement Replace the solution used in the bed with the active drug or most of it.

The filtrate displaced from the bed during these displacements is divided into fractions. this place The combined first fraction contains the wash solution and the first displaced bleach solution contains the wash solution. reacts with bleach and contains primarily only used bleach and bleach reactants. Ru. The second fraction of the filtrate contains most of the bleach that was not consumed during displacement. have This solution fraction is collected prior to reuse in the chemical processing step. and then fortified with fresh bleach equal to the amount of active chemical consumed in the same step. I'll keep it.

In the method of the invention, one bleaching step consists of at least two solutions. Not only substitutions but also several substitutions are made. Therefore, there are at least two filtrate divided into fractions.

Several of the above bleaching steps can be included in succession during the process.

In the above method, the amount used in the replacement can be freely selected, and the loss of bleach It is substantially greater than 1 in terms of increasing losses. On the contrary, for example during the cleaning process. As a result, efficiency and chemical usage and recovery are improved using higher dosage rates.

As mentioned above, in this bleaching method, there are one or several liquid zones within the same cross section. However, this is due to the high local dose rates used for the different solutions.

The volume rate of recovered filtrate containing active chemicals is determined by how efficiently unused active chemicals are recovered. This determines whether the The higher the quantity rate, the better the recovery. This results in The quantity rate is also determined for the chemical solution used for replacement.

This is because it is the same as the volume rate of the recovered filtrate under the influence of the new chemical. Because you should.

Recovery of the above effective chemicals effectively dispersed in the bed by effective use of bleach ensure that as little solution as possible from the previous step containing the active chemical is used in subsequent steps. This is important to ensure that it mixes with the active drug being used. For these reasons It also allows for higher total mass rates in the processing steps, thereby increasing the loss of active chemicals. Because it can be used without The active chemical in the step is not used to replace the active chemical in the related step; For the step, use a solution as neutral as possible, e.g. preferably at a suitable temperature. Pure water is used. If, for example, a chlorine solution is directly replaced with a sodium hydroxide solution, If so, the solutions will mix in the boundary zone due to dispersion.

In this way they offset each other's advantages by bleaching, and even have disadvantageous secondary effects. A reaction occurs. For example, extreme pH changes can cause a chlorine solution to become a hypochlorite solution. can change to.

However, in some cases the filtrate containing only chemicals or the bleaching process It is advantageous to utilize the spent reaction products.

Replace the active chemical solution used in this step with a neutral solution, thereby The filtrate separated from the fiber bed via the filter surface during treatment is The drug concentration changes as the bed progresses. The first fraction is mainly Contains chemicals and reaction products used and consumed in the previous process. This hula The filtrate changes more slowly or rapidly depending on the strength of dispersion by the bed. However, the filtrate contains the active drug used in the processing step in question, and The product reacts with the fibrous material of the valve bed and the reaction products already formed and becomes inactive. It becomes sexual.

This fraction was consumed by the reaction and used in the processing step. Contains primarily active chemicals used in processing steps to accommodate excess active chemicals. It changes in a way that corresponds to the fraction present. This fraction is When transferring, add the neutral solution used as the replacement solution for this step immediately after the active chemical solution. Changes in a manner that corresponds to fluids containing mainly drugs obtained from liquids . If the solution is pure water, as recommended by Jintong, it will contain the active drug. The above fractions contain the chemicals consumed as well as the chemicals formed in the subsequent processing steps. The solution containing the reaction products changes to nearly pure water before changing again. However, the book Assume that the step is not the final process.

a third filtrate as described above containing active chemicals not consumed in the reaction in the processing step; Fractions are collected as carefully as possible and combined with chemical solutions from the same processing step. and reused with new additive chemicals.

The portion of this solution that can be recovered is the amount of this step minus the amount of new chemical, of course. Effective chemical solution amount.

In the above method, the amount of solution recovered is limited, and it is necessary to disperse it in the fiber bed. Therefore, it is not possible to recover 100% of all the active chemicals displaced in the bed. It is Noh. i.e. a small part of it ('tail J') was previously displaced from the bed. will always remain in the filtrate fraction that is During the tion, another "tail j remains.

The maximum recovery amount of active drug is determined when the maximum active drug concentration in both tails is equal, i.e. that is, the concentration of active drug in the filtrate is the same at both separation points of the filtrate fraction. Sea urchins are obtained when it is possible to control the separation of the filtrate fraction.

A partition that seals tightly to the screen allows for easy access to the filtrate chamber behind the screen. The filtrate can be divided into various fractions by dividing the filtrate into different fractions. death However, in this case it is not possible to maximize chemical recovery under all operating conditions. Ru. This is because the position of the chemical distribution in the equipment used depends on the flow rate of the replacement liquid and the filter. - because it shifts when the ratio of the moving speeds of the surface changes. In addition to this, the reaction The location of the drug distribution of the consumed drug and the still active drug in the bed process This percentage is influenced by the proportion of chemicals used, which, among other things, Depends on how much residual lignin or similar chemically consuming components are present in the lube bed. It's on.

Our co-pending Finnish patent application for implementing the method disclosed in this application By using the device system disclosed in Application No. 891661, the above species can be active drug recovery in a manner that always maximizes active drug recovery under each operating situation. It is possible to control the withdrawal of the filtrate fraction containing the product.

The filtrate chamber is separated by a partition giving slits of equal width with respect to the filter surface. The slit part of the filtrate fraction passes through the slit part and passes through the slit part of the filtrate fraction. can flow in during the session. The filtrate fraction contains active drug from other filtrate fractions. The concentration of active chemicals is measured in the slits in both partitions separating the tractions. , and adjust the juice extracted from the other filtrate fractions so that the constant concentrations on both sides are equal. Then, as described above, the optimum drug recovery rate can be obtained.

Device system according to our co-pending Finnish patent application no. 891661 When used to carry out this bleaching method, the most recommended embodiment is its main The variables are of the same order of magnitude as when the same device is used for valve cleaning. Ba The thickness of the lube bed is between 20 and 100 mm, preferably about 50 mm. liquid replacement The pressure difference for this is 1 to 4 meters of water head. The screen movement speed is The speed is 0.2 to 1 m/s, preferably about 0.5 m/s. - location of processing steps; The total rate of conversion is >1.5, preferably >2. The volume rate of active chemical solution is these values. It is about half of that. Based on the above values, - the total retention of the fiber bed of the processing step The time is 10-50 seconds, usually about 20 seconds.

In the most preferred embodiment of the invention, a high quantity rate is used in each substitution step, i.e. This method uses approximately twice the amount of the conventional replacement method, and each step is performed in at least two portions. Divide into steps. Therefore, to use this bleaching method, carry out this method and necessary to make it possible to carry out several successive displacement steps in one and the same device. Methods and equipment must be available, and when adding a stem, Their marginal cost is relatively low and the computational cost of the device per effective screen is economical. It is necessary to be objective.

It is not possible to perform all bleaching steps on the same equipment and If the liquid must be transferred from one device to another between bleaching steps, use this method. The valve bed and liquid are almost completely mixed by this movement. In this case different In order to avoid mutual mixing of chemical solutions, the transfer should be The liquid content is mainly C and only one chemical solution, preferably water or a neutral solution. It must be done in this way. This means that the partial volume rate of the drug solution is at least 1 , which means it should preferably be high.

In this method, the surface layer of the fiber bed is treated with approximately twice the amount of chemicals compared to the lower layer. be managed. However, this non-uniform distribution does not affect the uniform treatment of the bed. That's called The reason is that if we examine the individual fiber layers of the bed, the active chemical will flow through each layer; The amount approaches infinity in proportion to the amount consumed by the fiber layer for a complete reaction. It is from.

In this way, the reaction between bleach and residual lignin is ensured in each fiber. A high probability is achieved, which probability is independent of processing time. i.e. bleaching It is independent of the residence time of the bed in the step. From this, the valve bed It also happens that the bed does not need to be thick, i.e. its optimal thickness depends on the liquid dispersion by the bed. is based on the fact that it is small enough without requiring an unnecessarily large filter surface. It can be decided accordingly.

This is advantageous for the present method in forming and maintaining a uniform valve bed. It means that. Additionally, the two filtrate fractions are Of particular importance to this method is the ability to separate these filtrate fractions into The first one contains mainly the reaction products, the second one contains the active drug. ing.

Furthermore, it is possible to measure the chemical concentration directly behind the filter surface in an optimal manner. It is recognized that the filtrate rate can be measured and adjusted accordingly.

This method requires the highest velocity of chemical movement, which is important not only around the fibers but also at them. due to forced and directed liquid flow through the This is because the distance is so short that no significant movement of substances occurs due to diffusion. These principles Due to this reason, it is also necessary for the system to maintain a two-phase system. for that purpose , it is necessary that the pressure of the system is not less than the equilibrium total pressure of the gas and vapor. in this case The largest portion of the gases and vapors remains dissolved in the liquid phase and enters the bed during processing. No interfering bubbles or gas phases are formed.

If methods and devices have been developed for this purpose and meet these prerequisites and conditions, then our It is disclosed in currently pending Finnish Patent Application No. 891,661. For this bleaching method By utilizing the method and apparatus of the said application to It also has the following advantages over the displacement bleaching methods used up until now: It will be done.

- The method and equipment technology make this bleaching process simple. That is because some This is because the bleaching step is carried out in one device.

- Low energy consumption. This is because there is less need for bonpin, and there is no need for mixing. This is because there is no need.

- Bleach consumption is less than conventional bleaching methods. This is because a solution containing a medicinal agent is , a bleaching process that contains reaction products and even consumes bleach if they are mixed. This is because it can be efficiently separated from the solution generated during the process.

- It is possible to maintain optimal conditions during the various bleaching steps and The slightly deligned fiber bundle is treated with a sufficient amount of chemicals. these With this factor, you can obtain a bulb with high and even whiteness, and it is also free from dirt. Fewer prerequisites are introduced and excellent strength properties are retained.

IF1i original side] Translation submission form (Sho) (Article 184-8 of the Patent Law) October 7, 1991

Claims (5)

[Claims] 1. By forming a bed of fibrous material suspension on the filter surface, the chemical solution can also be The bed is provided by one or several chemical treatment steps that replace the During the continuous treatment of textile valves with chemical solutions by Two different processing liquids are used which are continuously displaced by the bed in the process. , the initial process liquid contains a larger amount of active chemical than is consumed by the reactions occurring in the valve bed. , preferably about twice the volume, and the second treatment liquid is in the method The solution does not contain a significant amount of the active drug, and the purpose of this method is to remove the active drug. is not only to displace the initial liquid portion that is not consumed, but also to be separated as filtrate. It also replaces parts that still contain active drug when separated, and then It has the highest concentration of active drug and contains most of the active drug separated from the bed. fraction is recovered, and it is only in large quantities that new drugs can be used. It is characterized by the fact that it can be reused as the initial treatment solution after being strengthened with a product solution. Method of continuous processing of fiber valves. 2. The total liquid volume of the two process liquids in each process step is substantially more than the liquid volume present in the fiber bed, preferably 2 to 3 times A method according to claim 1, characterized in that: 3. The second treatment liquid used in the treatment step may contain water and/or other treatment liquids. It is characterized by the fact that it is a displaced liquid from the pump and mainly contains only reaction products. The method according to claims 1-2. 4. In bed chemical processing, the filtrate leaving the bed is divided into three successive fractions. The middle fraction is divided into fractions, of which the active drug leaves the bed. central The dividing point of the fraction and the first fraction and the middle fraction and the third This can also be done by measuring the concentration of the active drug at the point of separation of the fractions. Based on the measurement results, the volume ratio of the first and third fractions is calculated based on the active drug at both dividing points. The maximum ratio displaced from the bed by adjusting the concentrations of Claims 1 to 3 are characterized in that an amount of the active drug can be recovered for reuse. The method described in Section 3. 5. In the chemical processing step, fibers and fine particles are formed at right angles to the direction of bed movement. The separated materials are sent horizontally, and the liquid is filtrated and replaced on a horizontal bed. The filter surface is continuously immersed in the liquid and is related to the horizontal movement direction. While the filter is in a vertical position, the filtration and displacement of liquid is carried out by the water pressure difference between the filter surfaces. 5. A method according to claims 1 to 4, characterized in that it is carried out.