SU1064873A3 - Process for producing cellulose sulfate - Google Patents

Abstract

METHOD FOR PRODUCING kraft pulp by cooking wood raw material with liquor and control varkoyg comprising selection liquor sample, determining alkali concentration in the selected sample by the value of electrical conductivity, subsequent adjustment of operating concentration of alkali time and cooking temperature depending on the set value of alkali concentration in the selected sample, characterized by that, in order to stabilize the degree of delignification of the target product, sampling is carried out after the time from the beginning of the process in the arches during which 44.972 were consumed, 4% of the liquor from the total amount introduced for boiling, after which the sampled sample was titrated with acid until the moment at which the electroplating value becomes constant, the amount of acid consumed for the titration is measured, and the alkali concentration value in the sample is adjusted by the measured amount of acid.

Description

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mLHf50it (2.5N) The invention relates to a process for the preparation of sulphate pulp and can be used to produce pulp under the conditions necessary to achieve the desired degree of delignification. A known method of obtaining sulphate cellulose by boiling wood raw material with lye and controlling cooking, including och10 (ts11y liquor sample, determining the alkali concentration in the sample taken by the value of electrical conductivity, then adjusting the working concentration of alkali, time and temperature of cooking depending on the set alkali concentration in the sample. According to this method, the concentration of hydroxyls in the cooking liquid is controlled by determining the differential fluid conductivity stages of the cooking process, the trace is followed by the concentration of alkali during cooking. Conductivity is measured before and after neutralization and maintained at the desired level during cooking by adding white or black liquor or by adjusting the cooking temperature and / or cooking time 1. However, according to a known method, no better results are obtained than by direct measurement of the conductivity of the cooking liquid, moreover, according to this method, it is impossible to provide uniform cooking that can produce pulp with a pre-selected number K appa I The purpose of the invention is to stabilize the degree of delignification of the target product. The goal is achieved according to the method of obtaining pulp cellulose by boiling wood raw material with lye and controlling the cooking, including sampling liquor, determining the concentration of lye in the sample taken by the value of electrical conductivity, then adjusting the working concentration of alkali, time and temperature of cooking Depending on the set value of the alkali concentration in the sample, the sample is taken after the time from the start of the process, during which H3pacxoj; oBaHO 44.9-72.4% liquor of the total amount introduced for cooking, after which the sample was titrated with the selected acid to a point at which the conductivity value becomes constant, measured the amount of acid consumed for titration, and a value of the concentration of the liquor in the sample is corrected by the measured amount of acid. The method is carried out in the following 6 times. Sulfate cooking is started in the usual way by loading and mixing wood chips and sulphate cooking liquid in the digester. Cooking is continued during the initial period, during which 44.9 - 72.4% of the alkali consumed immediately after the start of cooking is consumed. After that, a sample of the cooking liquid is taken, which is titrated with acid to the point defined as the boundary conductivity of the sample. During initial cooking, the temperature is increased gradually or quickly. For initial heating rates and temperatures, the correct definitions approaching temperatures when sampling. When preparing the sample for titration, the rate of temperature rise during the initial cooking cycle is in the range of 0.1 - 25 s / min (preferably 0.2 - 10 ° C / min). Initially, as the acid is added, the conductivity rapidly decreases, but after adding a certain amount of acid depending on the alkalinity of the sample, the change in conductivity becomes very small or completely stops. The point of noticeable decrease or change in conductivity is the end point, which is characterized by a change in the slope of the curve. This point is taken as the limiting value of conductivity, in which conductivity becomes relatively constant. FIG. 1-5 are the titration curves for acid cooking A-E respectively, which show the dependence of conductivity on the amount of added acid (the point where the conductivity reaches or approaches the limit value is taken as the end point (P); in Fig. 6, the plot of the coefficient H against the percentage of alkali (NaOH); Fig. 7 shows the reference graph of the curves of the coefficient H on the Kappa number for a series of alkali concentrations in the range of 12.5-40 g / l; in Fig.8 an equipment diagram for carrying out the method. conductivity applied Any device suitable for this purpose, such as a four-electrode device of the Kemotron type, which makes it possible to record conductivity with various amounts of acid. An inorganic or organic acid (preferably inorganic) that is not an oxidizing agent under titration conditions is used for titration. Acid is used in the form of diluted 0.1-6.0N aqueous solutions.The best acids for titration are sulfuric and hydrochloric (the preference of sulfuric acid is high sulfur content, corresponding to boiling liquid); It is possible to use pr-adeny and orthophosphoric, hydrobromic and hydroiodic, metaphosphoric or pyrophosphoric, as well as organic acids, for example, acetic, formic, trichloroacetic or pro pionic. The amount of acid added during the titration to the end point corresponds to the amount of alkali present, so the latter can be calculated from the amount of acid consumed for the titration. The alkali content (NaOH) is calculated in g / l. The concentration of alkali makes it possible to choose the correct curve when determining the coefficient And for a given Kappa number on the reference graph. The reference graph is composed of curves, each of which is intended for a specific alkali concentration (NaOH in g / l), at which cooking can be carried out. For each type of wood it has a reference graph, for example, for spruce, fir, pine, birch, eucalyptus , beech, oak, maple, aspen, cedar, hemlock, cherry, chestnut, acacia, for, these curves are based on the Kappa numbers obtained for cellulose processed at these H coefficients in the digesters used. After the correct curve has been chosen to determine the alkali concentration, the H coefficient for the Kappa number of the desired pulp is found and the temperature and the cooking time are determined. The coefficient H corresponds to the unit of cooking and represents the number of hours of cooking at 100 ° C. At a higher temperature in a given period of time, more single I cooks can be completed, and at a lower temperature less. Thus, the coefficient H is a measure of the duration of cooking at or above and the same temperature. Cooking temperatures of 150-190 ° C are used, the duration of cooking is 1 min - 10 hours (preferably 160– 180 ° C, 15 min –3 h). The coefficient H determines the duration of cooking at a selected temperature and, conversely, for a given Kappa number with an alkali concentration determined by titration. To calculate the H coefficient and the cooking conditions, computers are used which set up to regulate automatic cooking, sending a direct signal to the control board that sets the cooking conditions. With a batch or continuous method, a sampling operation can be adapted to this type of cooking pot, for example, continuous cooking boilers with two cooking zones and a controlled cooking sequence in these zones. During periodic cooking, more than one sample can be taken to better control the cooking, however cooking mode can be set by the results of one sample. With known pulping, the same temperature and time schedule is used for periodic or continuous operation, and for the proposed one, on the contrary, the conditions for each cooking or for a continuous process vary depending on the coefficient H determined for the given batch. I- The cooking temperature or cooking time may vary, this usually happens in practice, but the concentration of alkali 1 can be adjusted by adding either water, black liquor or alkali. To shift to another curve of alkali concentration on the reference graph, thus obtaining a more favorable or convenient ratio. H. It may be necessary to take another sample if more alkali has been added, since its greater concentration may affect the wood. If an additional amount of alkali is added at a late stage of cooking, the effect is minimal and the selection of a second sample is not necessary. The equipment (Fig. 8), intended for the continuous cooking process, contains a preheater 1, through which Diena is fed through lines 2 and 3. In chip heater 1, it is heated with steam and hot gases and then continuously fed through high pressure feeder 4 and line 5 to the digester 6 using cooking liquid circulating through line 7. The reactor is an elongated boiler through which chips and liquid are advanced at a low speed, the temperature of the circulating mass is raised in the steam preheater 8, through which the mass passes through lines 9-12; at the same time, the desired rate of temperature rise and cooking temperature is carried out. Sampling lines go from lines 11 and 12 to an analyzer (not shown), signals from the analyzer are sent to a computer (not shown programmed to control the temperature of heaters 8, alkalinity control is carried out by adding white and black liquor through lines 13 and 14. Cellulose removed from the bottom of the digester and fed to the blow tank via line 15. The selected black liquor enters the regeneration plant via lines 16 and 17 and evaporators 18 and 19, and hot gases from evaporators 18 and 19 are directed through lines 3, 20 and 21 in ho Loudspeakers and heaters Example: Five different batches (A-E) of pine chips load Cooking A NaOH, g / l 21.0 19 61.3 (A) - 72.4 (E)% NaO were consumed in the instructions of the experiments For the preparation of reference graphs shown in Figures B and 7, boiling is performed using pine chips under the same cooking conditions, i.e., with a liquid: wood ratio of 3: 5, the rise-temperature rate is from 80 ° C to the cooking temperature of 0.5 s / min and the final cooking temperature of 170 s, then the Kappa numbers of the obtained pulps are recorded. Kappa numbers are plotted as a function of the H coefficient for each alkali concentration from 12.5 to 40 g / l, and a reference graph is obtained (Fig. 7). A graph of the dependence of the coefficient H on the alkali concentration is also constructed (Fig. 6). The conditions for each cooking (from A to E) are easily determined to produce pulp with the desired Kappa number by selecting the curve in Fig. 7, the corresponding alkali concentration in the given cooking, selecting the Kappa number and finding the H coefficient on the cryA

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1870 98 90

Then cook under the specified conditions. The mass is heated to 170 ° C and this temperature is maintained at five, five, 98, 117, 126 and 172 minutes, respectively.

The cooking is then interrupted and the resulting pulps are sorted and washed, after which the kappa number is determined.

The following ftts are obtained: in a brewing vessel of periodic operation together with sulphate cooking, NaOH - liquid. The amount of wood and chemicals loaded into the digester for each cooking is accurately determined. Wood quality fluctuations do not take into account. Alkali consumption 20% of active (% NaOH) sulfur content 30%; the ratio of wood to liquid 1: 3.5 kg / l; rate of temperature rise from 80 to 0.5 ° C / min. When the temperature of the digester reaches 140 ° C, 100 ml of the cooking liquid are sampled, the titration is carried out with 2.5% aqueous sulfuric acid, and conductivity measurement is carried out on a conductivity meter. The addition of acid is carried out until a constant value of conductivity is reached, which is plotted on the graph. The limit value characterizes the change in state upon reaching the end point P. The following alkalinity values (in the form of NaOH, g / l) of cooking liquids are obtained: I C D E 7.5 16.6 15.0 I. The ratio of the curves of FIG. 7 corresponds to the empirical formula Kappa number g .. f d2. nj X / (, where k 0.1806; k, 80.7;, 9388; A is the alkali concentration, NaOON, g / l; H is the H coefficient, the K values, k-k, and k depend on the rate of temperature rise The sampling time and the cooking time and cooking temperature at which the sample is taken are determined empirically for each profile of the cooking conditions. However, this formula is applicable to all possible cooking conditions i The coefficient H, necessary to obtain the Kapp number 33 with this alkalinity. Cooking time at 170 ° C.

Cooking Number

32.1 Kapp

From these data it can be seen that the Kapp numbers obtained are close to the calculated Kapp numbers, equal to 33.

For comparison, a second series of five brewings are carried out with the same chips and under the same cooking conditions. From these data it is clear that cellulose has different Kappa numbers, i.e. standard conditions do not give uniform Kappa numbers. The proposed method makes it possible to avoid such scatter of data. And to obtain in each case cellulose with uniform dimensional properties with a predetermined degree of delignification. Example. Pine chips of the same batch and cooking liquor are loaded into the digester of intermittent operation as in Example 1, cooking is carried out under the following conditions: alkali loading (NaOH) 24%; sulfur content 30%; the ratio of wood to liquid 1: 3.5 kg / l; the rate of temperature rise is from 80 to 170 C; 0.5 C / min; maximum temperature. After the cooking temperature reaches 140 ° C, a sample of the cooking liquid is collected, the alkali content (g / l NaOn) is determined by conduction titration. At the same time spend 44.9% of NaOH. By the above formula, the H coefficient for a Kappa number of about 33 is 1200, which corresponds to 61 minutes of cooking at. At the end of cooking, under these conditions, the pulp is washed and sorted. The kappa number of the obtained pulp is 31.5, which is close to the calculated value. ma c-m-f 1К) th 12 g S S 10 yy It miHiSOit

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but in each case the cooking temperature is maximum for 120 minutes. At the end of the cooking, the resulting celluloses are sorted, washed and the kappa number for them is determined.

The following values are obtained: H I J 32.0 34.5 39.2 For comparison, pine chips from the same batch are cooked for 2 hours at a maximum temperature of 170 seconds. Other conditions as above. The kappa number for the resulting pulp is 19.9, which is different from the calculated one. All this shows that the proposed method makes it possible to control fluctuations in alkali content caused by uneven amounts of wood and alkali. Under standard cooking conditions, the kappa number is 19.9, which indicates a deterioration in the hardness of the pulp while reducing its yield. Froze Example 2 is repeated using pine chips of example 2. A sample of cooking liquor is taken at, using the above formula, to obtain a kapp number 33, a coefficient H equal to 1300, corresponding to 120 minutes of cooking and the maximum temperature maintained at this level for 120 minutes, is required. then stop cooking. The resulting pulp has a kappa number of 32, which is very close to the calculated value. Thus, the proposed method allows to obtain cellulose with a practically specified Kappa number, i.e. significantly stabilize the degree of delignification of the target product. tLg / pf2 If S 8 20 mlHfSO f 2 H S

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Claims (1)

METHOD FOR PRODUCING SULPHATE CELLULOSE by cooking wood raw materials with liquor and controlling cooking, including sampling the liquor, determining the alkali concentration in the selected sample by the conductivity value, then adjusting the working alkali concentration of the cooking time and temperature depending on the set value of the alkali concentration in the selected sample, differing the fact that, in order to stabilize the degree of delignification of the target product, sampling is carried out after a period of time from the start of the cooking process, in the cross-section of which is consumed 44.972.4% of the liquor of the total amount introduced for cooking, after which the selected sample is titrated with acid until the conductivity becomes constant, the amount of acid used for titration is measured, and the alkali concentration in § the sample is adjusted according to the measured amount of acid. SU, "1064873