FI108890B - Method for determination of the charge state of the filtrate from pulp in paper and cardboard making machines - Google Patents

Description

1 108890

Method for determining the state of charge of the filtrates of pulps of paper and board machine Förfarande för bestämning av laddningstillständet hos filtrat fran massor i pappers- och boardmaskiner.

The present invention relates to a method for determining the charge state of filtrates of fibrous pulps used in paper and board production based on the amount of interfering substances.

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On paper and board machines, the amount of interfering substances is monitored by determining the charge state of the colloidal filtrates of the pulp used in paper and board production. Charging states are adjusted so that the amount of colloidal interferences they contain can be controlled to improve machine runnability Traditional methods are based on colloidal shrinkage or 15 potentiometric measurements directly from a filtered sample. In the method, an indicator and a cationic reagent are added to the filtered sample and to a representative volume of water. The equivalent positions of the control and the sample are then determined by titration with the anionic agent. The charge state of the sample is calculated based on the consumption of the anionic substance by comparing with the 0 test (control test).

20, '· *; A disadvantage of this method is the slowness and impracticality of the method and the adhesion of colloidal solutions:: 'to measuring devices.

: 1 ·! It is an object of the present invention to provide a rapid and accurate method without the disadvantages of the preceding 23 method.

In particular, the object of this method is to develop a method whereby the measurement of the charge state would be easily carried out without complicated titration.

3Θ .: The method according to the invention is mainly characterized in that the method takes a sufficient amount of: an amount of samples of the same anionic sample of the pulp filtrate used in paper and board production. Known amounts of cationic material of various sizes are added to these samples such that at least some of the samples are cationic and some of the samples are anionic. The charge states of the filtered samples are determined in the prior art, for example, by means of cathetric titration or potentiometric measurement 5 2 108890. Alternatively, anionic titration may be used if the same amount of cationic material is added to all samples so that all samples are cationic. The absorbances corresponding to the charge states of the samples are measured and a calibration curve is drawn or a table is drawn in which a given absorbance corresponds to a given charge state. A sample of the 5 fibrous pulp filtrates to be examined is filtered from the fibers through the filter into the filtrate.

In making the calibration curve, a sufficient number of samples are taken from the same anionic sample and 10 known quantities of cationic material are added to these samples in different sizes such that at least some of the samples are cationic and some of the samples are anionic. A sufficient number means that a sufficient number of points are obtained to draw a calibration curve. Already 5-6 samples can draw some kind of curve, but about 10 samples are used to get an accurate curve. The charge states of the filtered samples are previously determined by pre-cationic titration or by potentiometric measurement. The absorbances corresponding to the charge states of the samples are then measured and a calibration curve plotted, with a given absorbance corresponding to a given charge state. Equivalent point! can be defined mathematically without a drawn curve.

Alternatively, a calibration curve may be made by taking a sufficient number of samples from the same 20 anionic sample and adding to these samples different known amounts of cation; ,: the substance that at least some of the samples are cationic and some of the samples anionic, followed by the addition of the same amount of cationic substance to each sample so that all samples are cationic. The charge states of the filtered samples are then determined in a known manner, e.g. by anionic titration, after which the charge states of the samples and the corresponding absorbances are measured. The '25 'calibration curve is plotted as above, with a given absorbance corresponding to a given charge state.

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Absorbance is measured at a wavelength within the visible light range and absorbed by the indicator. This is most evident at 500 or 615 nm, most preferably at 615 nm. The absorbance is measured with a spectrophotometer.

Jei

An indicator is, for example, p -argidine or the like where the color changes as the charge state changes. The amount of indicator is such that discoloration is detectable with the naked eye during titration.

3 108890

The subject of measurement is a pulp filtrate used as a raw material for paper or paperboard, a filtrate of a coated wreck or some other fibrous pulp filtration used in papermaking.

Filtration is carried out with a black belt filter paper or the like, which is used to filter out the fibers 5.

The cationic agent is a cationic polymer, polydadmac ™ or the like.

The invention will be described in more detail below with reference to preferred principle examples and exemplary embodiments, the details of which are not limited to the invention.

Thus, the invention takes advantage of the fact that when a cationic reagent is added to an anionic sample and the indicator used, e.g.

The invention has many advantages over the known colloidal titration method, including the speed and ease of the method. One practical benefit is that used utensils and utensils, such as cuvettes and mixes, etc. remain clean.

20; The invention can also be used as a component of an automatic continuous charge meter for measuring paper processes also in the board and pulp industry.

'25: EXAMPLE1 - 'Perform Colloidal Titration' '0-Exam:

Take a 5 ml sample of distilled water or other convenient amount. Add 5 ml of the sample to 50 ml of the 36: diluted indicator, eg, p-toluidine solution. Add 5 ml of dilute polydadmac solution or equivalent cationic reagent. Determine the equivalent site by titration with dilute potassium polyvinyl sulphate or equivalent anionic agent until the solution is permanently discolored. Result = A ml.

4 108890 Titration of the sample: Titrate the sample in the same way as the blank test, except that the filtrate from the pulp used for the manufacture of wreckage or other paper is used in place of distilled water. Filtration is through a conventional laboratory paper filter paper. Result = B ml 5

Calculation of conversion:

The result is given by the formula: 10 A ml-B ml 5 ml m eq / ml (= milliequivalents / liter) A and B are defined above and the result is the anion consumption per sample as compared to the distilled water consumption.

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The effect of the solids can be eliminated by measuring the absorption before adding the color and subtracting this reading from the final result. Modern devices can do it automatically. The effect of dilution can also be eliminated by using more concentrated solutions or by programming equipment to account for dilution 20 ν ': EXAMPLE 2. · 'Calibration '25 * First, make a titration curve. Take, for example, 5 ml of the anionic filtrate 'pulp' used as the raw material for the paper. Filtration can be done with plain black paper or the like. Place the sample in a colorimeter (spectrophotometer) cuvette and add 50 ml of diluted p-toluidine '' indicator dye and mix continuously. Measure the absorbance of the solution at 615 nm (which is the wavelength at which the indicator is best absorbed) from the light passing through the sample. '30 0: Add cationic polymer, diluted polyadmac, etc. For example, in constant increments until the equivalence point is clearly exceeded. After each addition, wait until:; the titration reaction is complete and the absorbance is then measured with a colorimeter. This gives a titration curve in which the change in charge state of the sample is reflected as a change in absorption.

5 108890

The titration curve can also be plotted. back titration, that is, by first making a sample to repent with a known amount of reagent and then titrating as above, but using an anionic reagent as the titration solution. Next, the absorption pulses corresponding to a given charge state are calibrated to the titration curve.

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Take about two dl of the same mass of fiber into the required amount, about ten beakers or the like. 1% diluted polyadmac or other cationic polymer is added to the samples so that one kilogram of polymer per tonne of dry matter is added to the first sample, the next one, then one and a half, and so on and mixed. The clamp, i.e. the cationic polymer 10, is allowed to act for 10 min, after which the sample is filtered as above. The purpose is to obtain some of the samples as anionic and some as cationic. It is not harmful even if a sample is neutral

The volume of the five ml samples taken from the filtrates is determined by colloidal titration.

Then take five milliliters of each sample and mix with 50 ml of dilute indicator dye. The absorbances corresponding to the charge states of the samples are measured on a colorimeter and plotted on the titration curve above. The absorbance-charge equivalence thus obtained can be utilized to determine the charge-state of the desired wreck samples without titration, directly by colorimetry.

20; . Each mass type must have its own calibration, since impurities in the masses can: adversely affect the results. Therefore, the calibration curve of the wreck filtrate cannot read the charge states of the milled filtrate.

The effects of solid particles on absorption can be counteracted by measuring the absorbance caused by the filtered samples before adding the color reagents and reducing the turbidity error due to the absorption pore.

30; EXAMPLE 3 * Measurement i Take a coated wreck with the desired charge status.

5 6 108890

Take a 5 ml sample of the filtrate and mix with 50 ml of the diluted indicator color. Measure the absorbance of the solution at 615 nm with the colorimeter and read off the charge at the corresponding point on the titration curve.

The following are preferred examples of the invention, the details of which are not intended to limit the invention.

10 EXAMPLE 1 WATER SOLUTION

Absorbance measurements were performed on anionic and aqueous cation containing reagent and indicator alone. The assay was performed as follows: KPVS (potassium polyvinyl sulfate) was adjusted to an anionicity of 15 water to 0.1 M / L and an indicator aqueous solution was added. By adding MGC (methyl glycol chitosan), the charge space was adjusted for different samples to measure the absorbance so as to obtain six samples with a charge state of -0.1-0.1 meq / l. absorbances at 615 nm were measured in the samples, which was found to be representative of the wavelength range, where the absorbance is most pronounced when the charge breaks. Figure 1 shows the ratio of charge space to absorbance in such an aqueous solution. The change is very clear and:,: incremental absorbence plane for the second equivalent point.

'· Figure 1: Absorbance vs. charge state in aqueous solution containing anionic and cationic reagent and indicator dye. In the picture A = absorbance and V = charge state.

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Example 2 Grind

► <»30: Colloidal titration resulted in an anionic filtrate of 0.14 meq / l. Despite the clear anionicity, the addition of the indicator water lotion did not cause a noticeable discoloration.

: KPSV was added to the sample so that the anionicity was 0.3 mev / l and a clear color change was obtained.

Samples so treated were sampled for absorbance measurements by titration with MGC. The effect of the charge space on absorbance thus obtained is shown in Figure 2.

7 108890

Figure 2. Effect of charge space on groundwood absorbance.

For comparison, different amounts of MGC were added to the ground pulp. The masses were filtered. The filtrate charge state and absorbance (with indicator dye) were riveted. The curve thus obtained is 5 in Figure 3. In Figure 4, both ground curves are placed in the same image.

Figure 3. Absorbance vs. charge state from a comparison test with groundwood.

Figure 4. Curves of ground filtrate and reference filtrate.

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In the reference filtrate, the absorbances in the corresponding charge state were lower than those of the filtrate titrations. This may be due, for example, to the flocculation of the colloidal material and small particles into the fibers upon addition of the cationic reagent, resulting in a clearer, more light-permeable filtrate, which naturally affects the 15 '' baseline of absorbance.

EXAMPLE 3 COVERED REFUSE

20; · *, · The charge on the coated wreck sample was also too low for the color change reaction. To increase the anionicity, a coating paste was added to the sample to provide the filtrate from the sample. · 'An anionicity of 0.6 mev / l was obtained. The filtrate was subjected to similar tests to the groundwood.

Figure 5 shows the effect of the charge state of the filtrate on the absorbance at different charge states.

: 25 '* Figure 5. Absorbance vs. Charge Sample. The upper curve is the first day curve. The lower curve is made the next day.

Fig. 6 shows the absorbance vs. charge state curve obtained from the comparative test, respectively. The curve decreases to 30: when the charge state changes. The major contributing factor to the steady decrease in absorbance of MGC

with the additions is dilution of the sample. Changing the charge state by adding cationic reagent to the pulp required large amounts of reagent, whereby the sample was significantly diluted. The dilution at the last point was almost 1.7 times higher. Also, the possible colloidal flocculation of fibers described earlier may affect the shape of the curve. The more anionic the filtrate is, the more dispersed the colloids will be and the cloudier the solution will be. Coagulation occurs at the equivalent site and the particles tend to sink to the bottom. In Figure 7, the effect of dilution is compensated and in Figure 8 both curves are set to the same coordinate system.

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Figure 6. Absorbance vs. charge state of the control sample.

Figure 7. Absorbance vs. charge state of the control sample when the dilution error is compensated.

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Figure 8. Curves of the coated wreck filtrate and the reference filtrate in the same figure. The upper curve is the filtrate curve, the next curve below it is the filtrate the next day, and the lowest curve is the reference curve. The X-axis has an anionicity / cationicity that can be used instead of a charge state.

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COMMENTARY

The examples show that the method according to the invention works well, since especially at the 20 equivalents the accuracy is good.

• ·:,. ' The examples show the good operation of the method according to the invention and in addition the method is:: fast and pure. Purity is based on the fact that when samples do not need to be titrated as often as': in the titration-only method, the samples are not so often neutral. Eli 25: In measuring dishes, the samples are in colloidal form most of the time so that they cannot stain as much as during titration. The speed comes from the fact that the titration takes much longer than measuring the absorption with a spectrophotometer.

The differences are due to the presence of colloidal and solid particles in the sample, whereby the light passing through 3i) is scattered and thus affects the absorbance. The electrolytes used in the method also influence the condition of the sample. The negatively charged sample is relatively stable and i: remains cloudy despite long standstill times. The addition of a cation causes coagulation, whereby the particles adhere to one another and tend to sink to the bottom of the vessel or to adhere to the fibers. Such changes in the sample naturally affect the magnitude of the absorption of the transmitted light 9 108890. According to a further preferred embodiment of the invention, the method is made more accurate by measuring the absorbance against a sample prepared in exactly the same manner with only water added to the indicator, whereby the measurement results only in a change in the indicator slide.

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Claims (7)

A method for determining the charge state of Citrate fiber pulp used in the production of paper and paperboard, which charge state is based on the amount of interferents, characterized in that in the process, the following steps are performed: (a) a sufficient amount of sample is taken from San sanuna anionic free samples. as taghs a fiber pulp used in the production of paper and paperboard and thus a known amount of cationic substance of various sizes, these samples are added that at least some of the samples are cationic and in some of the samples are anionic, b) the loading state of the filtered the samples are determined in a previously known manner e.g. by cationic titration or potentiometric measurement, or ahematically with anionic titration if the same amount of cationic substance is added to all samples so that all samples are cationic, (c) the absorbances corresponding to the loading state of the samples are measured, and d) drawing a calibration curve or drawing up a table (e) the filtrate sample from the fiber mass used in the preparation of paper and paperboard to be examined is filtered from fiber through a filter; (f) indicator color is added to the filtrate; (g) the absorbance of the filtrate is measured and; · H) laser of the charge state of the solution corresponding to the matte absorbance from the previously made calibration curve or table from the corresponding location. in »· '2. Method according to claim 1, characterized in that the absorbance of the sample is corrected 2'5 'by comparing it with a sample prepared in exactly the same way, but where instead of the indicator only water is added, whereby as a result of the measurement on a more more accurate way, only the change that has occurred in the indicator solution. Method according to claim 1 or 2, characterized in that the absorbance is measured by spectrophotometer at a path length within the visible range, advantageously at the path length 500 or 615 nm, advantageously at the path length 615 nm. 108890 13 4. A process according to any one of claims 1-3, characterized in that the indicator is p-toluidine and is added to a solution or in solid form in such an amount that the color change during the titration can be observed with the naked eye. Method according to any one of claims 1-4, characterized in that the object for the measurement is a feed of a pulp used as raw material for paper or paperboard, a filtrate of coated scrap or some other fibrin pulp filtrate used in connection with papermaking. | 10 Method according to any of claims 1-5, characterized in that the filtering operation is carried out! with black band filterp app or equivalent. Process according to any of claims 1 to 6, characterized in that the cationic substance is a cationic polymer, such as polydadmac ™. 15 t t