Method of controlling the degree of digestion of lignocellulose-containing materials

p0001The invention relates to a method for controlling the decomposition degree of lignocellulosic materials by spectroscopic analysis of the digestion solutions.

p0002Since a continuous direct measurement of lignin in the cooking liquor during the cooking process to date is not yet possible, is at previously developed process control systems on the secondary data that affect the digestion, resorted. The degree of digestion factors affecting the cooking temperature, the cooking time, the boiler pressure and the chemical concentration and composition of the cooking liquor. Even in so-called feedback / feed forward system (Bylund, L .; Hägglund, S .; Thorsell, L .; Wallin, G .: On-line cooking liquor analyzer -. A Means for effective control of sulfite digesters 1982 Internatinal sulfites Pulping Conference , Toronto, Oct. 20-22, 1982, TAPPI Proceedings 285-292) but leaves it to only an indirect determination of the decomposition degree, and therefore the resulting kappa number of deviations erkochten pulps predetermined target value is relatively high. The kappa number is a measure of the residual lignin content of the pulp. It is determined according to TAPPI standard T 236 or Zellcheming IV / 37 / 80th

p0003For this reason, for a long-term studies have been conducted that the applicability of fluorescence spectroscopy (Bublitz, WJ: Fluorescence of pulping liquors: A tool for digester control TAPPI <u>64</u> (6), 73-76 (1981)) as well as light and UV photometry (Helmke, D .: Analysis of the suitability of UV absorption measurement of Bisulfitablaugen to pulping control in Zellstoffkochungen Dissertation, University of Hamburg, 1973 and Tikka. . PO; Virkola, N. e .: A new cooking liquor analyzer for monitoring organic and inorganic substances in 1984 pulping Conference, San Francisco, November 12 to 14, 1984, TAPPI Proceedings 291-296) for determining the lignin concentration in the digestion solution had the subject. It turned out, however, that either no good correlation between the residual lignin content of erkochten pulps and the measured concentration of lignin in the pulping liquor at the end of cooking consisted or the time required for the accurate measurement of lignin was very large.

p0004The reference "Abstract Bulletin of the Institute of Paper Chemistry" Volume 56 No. 6, December 1985, page 702 is concerned with the hydroxyl-determination of modified lignins in the solid phase (so-called after the KBr pellet method) using a Dispersiv- IR spectrometer, but not with the analysis of pulp cooking waste liquors in the liquid phase by means of FTIR spectroscopy. Pulp liquors can not be equated with lignin, since it is complex composite multi-component mixtures containing a plurality of diverse carbohydrate Abbaupordukten, lignin fragments, phenols, extractives and inorganic chemicals.

p0005The invention is based, to achieve better control of the decomposition degree of lignocellulosic materials for the purpose of optimizing the process control on the object.

p0006This object is in the process defined at the outset achieved in that (1) the IR spectroscopic behavior of the digestion solution before and during the cooking process and (2) draws on the derived IR data for determining the cooking end point and process control of the pulping process, by which the composition or the concentration of the cooking chemicals concerned record one hand and the analytical data of the erkochten cellulose-containing materials on the other hand these correlated data and the set correlation data used for optimization of the cooking process.

p0007The inventive method can be performed in all pulping process, which means you can perform the decomposition at pH values ​​in the range 1 to 14 In particular, one can perform the digestion as sulphite or sulphate process, although other methods, such as the soda process can be applied.

p0008In the method according to the invention can be the entire IR spectrum or parts of it in the near and / or mid-IR region (12000-400 cm⁻¹) using it to create an IR data set.

p0009The inventive method makes it possible to determine within a short time both the change in cooking chemicals composition and concentration as well as the increase in the concentration of dissolved out of the lignocellulosic materials substances in the course of cooking with very great precision directly in the digestion solution. The IR-measuring data are determined here preferably by Fourier transform infrared (FTIR) spectroscopy. The IR measurement data can be determined using the baseline-corrected band heights and / or integral surfaces and / or spectra curves.

p0010The sampling and measurement is carried out either manually or automatically by means of a connecting pipe between boiler and IR spectrometer using a flow cell. In contrast to other methods, it is not necessary to dilute the digest solution to fractionate or to modify them in some other way. There was no influence of cooking temperature, the boiler pressure or the chemical concentration of the cooking liquor are found on the Ligninkonzentrationsmessung by IR absorption.

p0011The IR measurement data of digestion solution in the medium and / or near IR range can be measured either by means of transmission measurement or by attenuated total reflection (ATR measuring technique), wherein a specific for the respective pulping process and for each used wood IR data from the entire spectrum or parts thereof is formed, which consists of various band heights and / or band integrals and / or spectra curves. The IR measurement data can be determined in particular in a circular ATR cuvette, namely intermittently or continuously in a flow cell.

p0012This IR-data set is associated with preserved according to other methods of analysis records to the composition or the concentration of the cooking chemicals as well as with the analytical data of the erkochten cellulose-containing materials, for example, the residual lignin content, so that after a sufficient number of cookings, the correlations between the data sets are determined can. Through constant checkups of erkochten cellulosic materials as well as the disintegration solutions and entering the values ​​obtained in the correlation equations, the statistical relevance is continuously improved.

p0013The data relating to the cooking chemicals can eg be determined by titration, while the data relating to the residual lignin can be determined by determining the kappa number.

p0014An FTIR spectrometer with a matched to the mathematical / statistical evaluation methods Software is able to provide reliable data to the cooking end point determination. The calculated IR characteristics can in this case be supplied by conventional process control systems, where they are used to optimize the cooking to deliver as the cooker guards information about when to start with the exhaust gases along with the other characteristic data by manual input or on-line data storage is.

p0015The invention is illustrated by the following examples but not limited to.

example 1

p0016A boiler, which operates according to the sulphite, are removed during the pulping process either batchwise or continuously by hand by means of direct connection cable between boiler and flow cell samples and immediately measured this directly in the FTIR spectrometer and recorded the IR spectroscopic characteristics. The progression of Magnesiumbisulfitkochung of carrying wood chips in<ul><li>a) a Laborkochung and</li><li>b) a Industriekochung</li></ul> is represented by a rise in lignin concentration in the digestion solution, depending on the cooking time. In the Figures 1a and 1b, the increase in absorption of two bands with the maxima is approximately 1515 and 1465 cm⁻¹ in cm⁻¹ visible.

p0017In Figures 2a and 2b, the increase of the integral surfaces (I₁, I₂) and the band height (H₁, H₂) is plotted against the same bands, the cooking time. When evaluating a baseline correction is performed in both cases, the minimums are considered cm⁻¹ at about 1540, 1485 and 1445th

p0018Digestion conditions for<ul><li>a) the Laborkochung: Koch acid concentration: 6.65% total SO₂, 3.38% free SO₂, 2.13% MgO wood Quantity: 800 g absolutely dry (bd) Kettle Type: Mini-mill Digester M / K Systems Inc. Liquor ratio: 3.5: 1 Heating time: 65 min Cooking time at maximum temperature (T_Max): 360 min T_Max: 140 ° C Boiler pressure (p) at T_Max: 6,3 bar Kappa number of erkochten Zellstofs: 22.3</li><li>b) the Industriekochung Koch acid concentration: 5.50% total SO₂, 1.08% free SO₂, 1.38% MgO Wood Quantity: 64 t (bd) Cooker: 225 m³ stainless steel kettle Liquor ratio: 2.5: 1 Heating time: 195 min Cooking time T_Max: 265 min T_Max: 139 ° C p T_Max: 5.5 bar Kappa number of pulp erkochten: 17.2</li></ul>

example 2

p0019The cooking course of Laborkochung of spruce chips by the sulphate process is shown in Figure 3 with reference to the increase in concentration of dissolved ligno-cellulose depending on the cooking time using the example of the band level rise at about 1494 cm⁻¹ on the cooking time. Digestion conditions: Chemicals: 19% NaOH / od wood, 8% Na₂CO₃ / absolutely dry wood, 10% Na₂S / od wood Wood Quantity: 800 g atro Kettle Type: Mini-mill Digester M / K Systems Inc. Liquor ratio: 4: 1 Heating time: 95 min Cooking time T_Max: 120 min T_Max : 170 ° C p T_Max: 7.7 bar Kappa number of pulp erkochten: 23.5

example 3

p0020Figure 4a shows the infrared spectra of chemicals kochungsrelevanten an acidic Natriumsulfitkochung are shown. The chemical composition and concentration of the digestion solution is using a multi-component analysis in FTIR spectrometer, for example on the ratio of the characteristic for each cooking chemical bonds or bonds with each other, determined. For sodium a characteristic band is about 960 cm⁻¹ for sodium hydrosulfite cm⁻¹ at about 1215 and is SO₂-water ( "free SO₂") at approximately 1330 cm⁻¹. The change in the chemical composition in the course of a pulping of spruce chips by the sulfite is shown in Figure 4b by the decrease of absorbance of the band at about 1330 cm⁻¹ for free SO₂. Digestion conditions: Koch acid concentration: 7.82% total SO₂, 5.10% free SO₂, 0.86% MgO Wood Volume: 58.2 bdt Cooker: 320 m³ brick-lined steel cooker Liquor ratio: 3.4: 1 Heating time: 180 min Cooking time T_Max: 270 min T_Max: 138 ° C p T_Max: 6.6 bar Kappa number of erkochten pulp: 7.2

example 4

p0021There were 10 of Magnesiumbisulfitkochungen book chips from industry in accordance with the procedure of Example 1 examined and then correlates the baseline and fleet ratio corrected integral values ​​and band heights with the Kappa number of pulps erkochten by regression analysis. The results are shown in Figures 5 and 6. FIG. There were correlation coefficients were from 0.79 to 0.95. Field of Aufscflußbedingungen: Koch acid concentration: 5.5 to 5.8% total SO₂ 0.8 to 1.1% of free SO₂ 1.35 to 1.45% MgO Wood Volume: 64 - 75 tonnes bone dry Cooker: 225 m³ stainless steel kettle Liquor ratio: 2.1: 1 - 2.8: 1 T_Max: 137 ° - 143 ° C Cooking time T_Max: 240-330 min p T_Max: 5,0 - 5.8 bar Kappa number of pulps erkochten: 12-26

example 5

p0022It was, for procedural 8 Magnesiumbisulfitkochungen of spruce chips, also from the industry, which served to produce tiefviskoser pulps according to Example 1 and 4. FIG. The correlations are shown in Figures 7 and 8. FIG. The correlation coefficients determined were in this case from 0.75 to 0.94. Field of digestion conditions: Koch acid concentration: 7,5 - 8.5% total SO₂ 5.0 to 6.6% of free SO₂ 0.75 to 0.95% MgO Wood Quantity: 55 - 66 bdt Cooker: 320 m³ brick-lined steel cooker Liquor ratio: 3.3: 1 to 4.1: 1 T_Max: 136 ° - 142 ° C Cooking time T_Max: 160-270 min p T_Max: 6,5 - 7,0 bar Kappa number of pulps erkochten: 5 - 10