FI80731B - FOERFARANDE FOER STYRNING AV ALKALISK CELLULOSAKOK. - Google Patents

Description

! 80731

METHOD FOR CONTROL OF ALKALINE CELLULOSE SOUP-FÖRFARANDE FÖR STYRNING AV ALKALISK CELLULOSAKOK

The invention relates to a method for controlling an alkaline cooking process of a cellulosic material, such as wood, in particular sulphate and soda cooking.

In temporal cooking processes, the lignin contained in the raw wood, which binds the cellulose fibers together, is strongly removed under temporal conditions, with partial cleavage of the wood polymeric carbohydrate, cellulose and hemicelluloses into aliphatic carboxylic acids; New York, 1981). The organic matter dissolved in the waste liquor thus consists not only of the decomposition products of lignin 15 but also of said decomposition products of carbohydrates and, to a lesser extent, of wood extractants.

The aliphatic carboxylic acid fraction contained in the waste liquor, in turn, consists not only of volatile acids (acetic-20 and formic acid) but also of hydroxymonocarboxylic and hydroxydicarboxylic acids (Alen, R., Niemelä, K. & Sjöström, E., J. Chromatogr. 301 (1984) 273; K. & Sjöström, E., Holzforschung 40 ^, 1986, 361). Although the total amount of acids produced in hardwood cooking is slightly lower than in softwood cooking due to the higher cooking yield, the different carbohydrate compositions of the raw materials also cause significant differences to the corresponding acid compositions. In addition, differences in acid formation rates have been observed, as a result of which the acid composition of the effluent 30 changes as delignification progresses. The acetyl groups contained in both coniferous and deciduous hemicelluloses (glucomannans and xylans) are easily cleaved by alkali in the early stages of cooking, leading to the formation of acetic acid (Olm, L. & 35 Tistad, G., Svensk Papperstidn. 82, 1979, 458). Later, acetic acid is formed more slowly and is formed mainly as a result of cleavage reactions in carbohydrate chains. Due to the high acetyl group content of deciduous trees, the corresponding black liquor contains significantly more acetic acid than softwood black liquor. Formic acid is instead formed e.g. in the case of cleavage-5 cleavage reactions, as one of the reaction products of the cleaved carbohydrate terminal unit, and its concentration in the black liquor increases more regularly than the acetic acid concentration as the cooking progresses. The amount of formic acid in black liquor, on the other hand, is not greatly affected by the wood raw material added to the 10 soups.

According to a granted Finnish patent (no. 71584), the control of alkaline soups can be carried out with surprisingly precise analysis by chromatographic analysis of the relative composition of the hydroxymonocarboxylic acids contained in the broth. In addition, it has later been found (FI 875248) that on the basis of the corresponding decomposition product compositions it is possible to determine the composition of the softwood and hardwood chips added to the soup. The object of the invention is to provide a new method for controlling an alkaline / cellulose soup more easily and simply than before and with a more precise degree of cooking. 'answering.

With respect to the features of the invention, reference is made to claim 1. The invention makes a new and surprising finding, namely that temporal cellulose soups can be successfully controlled by the fraction of volatile acids (acetic and formic acid) formed in the cooking over a period of time. The control is based on monitoring the change in the ratio of acetic and formic acid concentrations as delignification progresses. In this case, it is possible to predict the time required for the desired degree of delignification under the currently applicable cooking conditions. The main features of the invention appear. 35 of the appended claims.

During the development of the method according to the invention, it turned out that a certain linear relationship can be found between the ratios of acetic and 3 80731 formic acid concentrations during cooking and the total yield of cooking (or alternatively the amount of lignin remaining in the raw material) depending on the degree of delignification. This arithmetic dependence is also slightly affected by random variations in cooking conditions, such as total alkali dosage or sulfidity. If samples are taken at regular intervals during cooking, this acid ratio 10 can be used to determine the time taken to reach the desired degree of cooking.

It is also essential to the invention that the acetic and formic acid contained in the black liquor can, if desired, be analyzed by chromatographic methods without prior preparation of derivatives which increase the volatility of the acids. In this respect, a significant advantage is obtained with the previous method based on the monitoring of poorly volatile hydroxymonocarboxylic acids (Finnish Patent No. 71584). In addition, there is a significant advantage over this method in that there are only two acid components to be analyzed in this method compared to several tens of hydroxy acids. In view of the foregoing, it is self-evident that the reliable analytical information required by the control information 25 obtained by computer technology is obtained almost immediately from the time of sampling, which contributes significantly to the usability of the method.

The following examples further illustrate the method of the invention. Although these Examples 30 deal with sulfate soup for pine and birch chips, it will be apparent to one skilled in the art that the method is also applicable to other temporal soups (e.g., soda-anthraquinone soup) and other wood species used as raw materials (and possibly 35 other cellulosic plant material). . In this case, the change in the ratio of acetic and formic acid to the total yield of the soup and the dissolution of lignin, respectively, is first determined in each case, taking into account the quality and composition of the raw material in question (eg mixed soups).

5 EXAMPLE 1:

Chips made of birch wood (Betula verrucosa / B. Pubescens) (screened fraction 2-4 mm) were subjected to a normal sulphate digestion of 20% (as sodium hydroxide) wood, a sulphide thetate of 30% and a liquid / wood ratio of 4 L / kg. . The cooking temperature was raised at a constant rate for 90 min (from 30 ° C to 168 ° C, and cooking was continued at a maximum temperature of 90 min. During the cooking time, waste sludge samples were taken at regular intervals (20 min) and analyzed for acetic and formic acid (Alen, R., Jännäri, P. & Sjöström, E., Finn. Chem. Lett., 1985, 190) As the dependence of the total yield of the soup on the chlor-20 number is well known from the previous data (the number can be used to calculate the amount of lignin in the pulp), it is not determined in this case.

• / Figure 1 shows the dependence of the acetic acid / formic acid ratio on the cooking time and Figure 2: the change in this ratio in relation to the substance dissolved in the cooking. In the latter case, it can be clearly seen in the acid ratio in the different cooking stages ha-! assertive turning point. By taking a sufficient number of waste liquor samples from a similar digestion with that digester during the temperature raising step and immediately thereafter, it is possible to use the available information to determine mathematically the period in which the desired degree of cooking is achieved.

EXAMPLE 2: 35 According to Example 1, a corresponding sulphate soup was made for pine chips (Pinus sylvestris) under the following conditions: active alkali 24% (as sodium 5 80731 as hydroxide) of wood, sulphidity 30% and liquid / wood ratio 3.5 L / kg. The cooking temperature was raised at a constant rate for 60 min from 20 ° C to 170 ° C, and cooking was continued for 150 min. During the cooking time, effluent samples were taken at certain intervals (30 min) and the acetic and formic acid contents were determined according to Example 1. Figures 3 and 4 show, in this case, the change in the acetic acid / formic acid ratio as a function of the cooking time and the substance dissolved in the cooking 10. Also in this case, the information required for the control of the cooking of the dependence between the total yield and the chlorine number is a previously known fact.

The working examples are intended only to illustrate the invention without limiting it in any way.

Claims (5)

A process for controlling an alkaline process for boiling a cellulosic material such as wood, in particular sulfate and soda cooking, characterized in that the acetic and formic acid formed in connection with the delignification is analyzed during the course of boiling. and the time period required to achieve a desired boiling rate is determined on the basis of the concentration ratio of the acids present in the black liquor. 2. A process according to claim 1, characterized in that the acetic and formic acids are separated and analyzed by a chromatographic method based on gas chromatography or high pressure liquid chromatography. 3. A process according to claim 1 or 2, characterized in that the acetic and formic acid present in the effluent is analyzed in the form of sodium salts, free acids and / or derivatives. 4. A process according to any of claims 1-3, characterized in that the boiling stage at present and the required additional delignification time are determined on the basis of the black liquor content of the acetic acid and the formic acid, in which the ratio is compared with that for which cooking application separately determined corresponding to relationship dependency. Process according to any of claims 1-4, characterized in that a sufficient amount of sample for analyzing the acids is taken from the boiling ends during the course of the boiling.