FI122612B - Process for Extraction of Aliphatic Carboxylic Acids, Lignin and Extractive Substances from Alkaline Cellulose Cook - Google Patents

Description

This invention relates to a process for the preparation of aliphatic carboxylic acids, lignin and extracts from the waste liquors of alkaline cellulosic soups. formed in a separate initial stage of the so-called alkaline soups, in particular pine and birch sulfate soup. pre-processing stage. The method is primarily applicable to pretreatment broths from both softwood and hardwood soups, but it can also be applied to the fractionation of organic matter from the waste liquors from alkaline soils of other cellulosic plant materials (including grasses and agricultural and industrial waste). The alkaline pretreatment disclosed in the present invention is typically carried out with an aqueous solution of sodium hydroxide (NaOH) only (an aqueous solution of NaOH and sodium sulfide (Na 2 S) is used in the sulphate cooking) to form readily chemically usable sulfur-free organic materials. Another significant advantage of using pretreatment solutions for the recovery of organic material is that in the alkaline cooking process, the low calorific value and the carbohydrate based material dissolve significantly higher than the higher calorific value lignin. This fact is particularly important for the energy efficiency of the mill, since the thermal energy bound to the organic matter of the actual waste liquor (black liquor) is recovered when the black liquor is burned in connection with the regeneration of inorganic cooking chemicals. recovery boiler. On the other hand, the redirection of the organic material soluble in the soup (about a quarter of the original raw material in this invention) before the recovery boiler provides an opportunity for increased production, which in turn is important if the recovery boiler has become a traditional production bottleneck.

3 0 For many reasons, the use of renewable natural resources such as wood and other non-wood based materials (biomass), either as such or in the form of waste 2, will increase and become even more important in the near future. In addition to producing "green energy" (eg electricity and bioliquids such as biodiesel and ethanol), the aim is to produce value-added chemicals. Although the major component of biomass is cellulose, it also contains significant amounts of other carbon hydrates (hemicelluloses) and, e.g. lignin and extracts / 1-3 /. The prerequisite for a successful biomass utilization concept is to be able to efficiently utilize all of the material components present in the raw material. Current biorefinery processes thus aim to comprehensively process chemical products, special materials, and energy and liquid fuels from wood or vegetable materials.

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Biomass has traditionally been treated chemically (acids) or biochemically (enzymes), whereby the polysaccharides are selectively hydrolyzed to fermentable sugars and convertable into a variety of chemicals / 1,4-10 /. In addition, thermochemical processes provide a direct opportunity to produce gaseous and liquid product mixtures / 1,5,7,10 /. Of these methods, the most straightforward method is gasification, which produces either synthesis gas directly used for the production of energy or the production of chemicals (including the traditional Fischer-Tropsch process). In principle, both approaches (chemical and thermochemical conversion) are part of the biorefinery concept that replaces fossil feedstocks. Today, about 90% of the chemical-20 pulp is produced by an alkaline sulphate cooking process which has been used in principle for almost 150 years / 11 /. According to the current concept of biomass refinery, this method quite effectively separates the modified chemical components of the raw material to produce its main product, chemical pulp, thus forming a natural and functional biorefinery as such / 2,3,5,12 /.

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In alkaline cooking processes, the lignin contained in the raw material that binds the cellulose fibers together is strongly removed under alkaline conditions. At the same time, the digestion of the polymeric carbohydrate material, cellulose and hemicelluloses, which reduce the total yield of the cooking process, and the simultaneous dissolution in the broth also occur (2,11). Thus, the organic matter dissolved in the black liquor, after partial separation of the crude extract from the wood extracts, consists mainly of both lignin depletion products and aliphatic carboxylic acids formed by cleavage reactions in the 3 carbohydrate chains (Figure 1). Most of the sodium consumed during cooking is bound to these acids, while most of the sulfur is in the inorganic material. The main organic components of black liquor are utilized as chemical products 5, practically only the fraction derived from extractives, tall oil / 11 /. Other organic material is burned in a recovery boiler in connection with the regeneration of cooking chemicals and used for the production of thermal energy. However, due to the high oxygen content of the aliphatic carboxylic acid fraction, its heat content corresponds to only a quarter of the effective calorific value of the black liquor organic matter. Since the modern sulphate mill 10 is more self-sufficient in energy, it would be possible to recover at least part of these acids in particular. In addition, recovery of acids (and other organic matter) would be advantageous especially when the recovery boiler, as mentioned above, constitutes a bottleneck in production.

15 The aliphatic acid fraction of black liquor contains both volatile (formic and acetic) and hydroxy acids having either one or two carboxylic groups (Figure 1) / 11 /. Hydroxymmonocarboxylic acids form the most significant concentration of the acid in black liquor. The total amount of acids formed in deciduous soup is almost the same as in coniferous soup, but the relative proportions of acids 20 differ. In addition, the acid composition varies somewhat depending on the cooking conditions used. The utilization of aliphatic acids, as well as lignin, requires that they be isolated from the other constituents of the black liquor in their pure fractions. Especially for lignin, its sulfur-free content (normal sulfate lignin contains 1-3% sulfur / 11 /) would be preferable. However, in all cases, it is a requirement that the recovery of organic fractions must be seamlessly incorporated into the normal operation of the mill, and particular account must be taken of interferences caused by the process in the regeneration of cooking chemicals. In practice, this means that only partial recovery of organic material is possible. On the other hand, it is not possible to make very significant changes in the normal operation of the mill, since the main product of the delignification processes, fiber, is suitable as a base material for many paper and board products / 11-14 /.

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In addition to the above, the development of the method of the invention was based on the boundary conditions listed below. In addition, the basic idea was that a substantial advantage would be obtained if the waste liquor needed for the separation of organic matter was taken from the initial stage of cooking. Namely, at this stage, a large proportion of the carbohydrates are relatively selectively soluble without the corresponding lignin depletion, allowing significantly more low-heat (aliphatic acids) to be recovered than high-heat (lignin) / 2,15 /. Thus, the overall aim was thus to maximize the carbohydrate-based material and, on the other hand, to minimize the recovery of the lignin-based material. Generally, the removal of lignin during cooking can be divided into three steps, whereby the first so-called "lignin" is removed. in the extraction step, 15-25% of the original lignin is soluble (16) and at the same time the lignin is slightly lower in molecular weight than the normal sulfate lignin. Similarly, in the early stages of cooking, the volatile extracts contained in the raw material (among them, the turpentine of conifers) are almost completely eliminated and the fatty acid esters (the largest fraction of non-volatile extracts) are rapidly hydrolyzed to form fatty acid salts / 2,11 /. In addition to the above, this extraction can be performed at a lower alkali dosage, which results in less acid formation and, in addition to the removal of extracts and lignin, results in significant dissolution of the hemicelluloses (glucomannan and xylan) contained in the raw material. Unless sulfur-free products are considered as an indispensable advantage, the process can be modified to use white liquor (NaOH + Na 2 S + water), green liquor (Na 2 CO 3 + Na 2 S + water) or their oxidized aqueous solutions (NaOH + Na 2 SO 4 + water and Na 2 CO 3). + water). Boundary Conditions for Developing the Invention: • Cellulose is the main product of the mill and its strength properties must be maintained.

• The recovery process must not interfere with the regeneration of cooking chemicals, whereby only partial removal of organic matter from the waste liquor is possible - the recovery process increases the capacity of the mill's soda recovery boiler (basically reducing the amount of black liquor organic matter by one third).

• The undisturbed separation of extractives should be maintained.

• Ability to manufacture sulfur-free products.

• Seek to use simple unit processes in the recovery process 5.

• There must be multiple opportunities for further modification and utilization of the isolated products.

According to the present invention, the raw wood is treated with an aqueous solution of NaOH or an aqueous solution containing it as an active chemical so that about one fifth of the original raw material is removed (Figure 1). The spent liquor is then passed to organic material recovery and the alkali-treated raw material is further comforted by either normal sulfate cooking or soda anthraquinone (AQ) cooking. It is understood that the fibrous raw material may be any suitable biomass material for this purpose.

15 Alkaline treatment also removes a significant amount of foreign metals and nitrogenous compounds from the raw material while facilitating the normal operation of the mill. In particular, it is important to emphasize that in such a breeding concept, the raw material of logging and bark waste (Figure 1 mainly shows the Nordic situation), which can be utilized by other known methods, has already been partially implemented / 1,4-12 /.

The following example further illustrates the method of claim 1 of the invention. It will be apparent to one skilled in the art that the main method shown in the example can be modified in many ways on a case-by-case basis to achieve the optimum result. 25

Example 1: Chips made from pine (Pinus sylvestris) and birch (Betula pendula) were subjected to alkali pretreatments under the following conditions: 2-14% NaOH in dry wood, liquid / wood ratio 4 L / kg, treatment time 30-90 min and a treatment temperature of 150 ° C (pine) or 160 ° C (birch). The spent liquor from the pretreatment was recovered and the 6 chips were subsequently defibrated according to both sulfate and soda AQ cooking under normal conditions. In this case, it was found that no differences were found in the bleaching and strength properties of the pulp (tear and tensile index and pulverization) with reference cooking, but the overall yield was slightly lower (5-1.5% of wood) and the cooking time to target increased slightly.

The composition of the resulting waste broths was according to Table 2, with only cases (8% NaOH / 30 min) and (10% NaOH / 30 min) for each of the raw materials. Significantly, the mass ratio of aliphatic acids / lignin in these cases was between 1.8 and 2.3 (Table 3), while the corresponding ratio for normal black liquor is 0.9-1.2 / 11 /. The extracts were almost completely removed from the raw material during the pretreatments and the proportion of other compounds was low, especially in the case (8% NaOH / 30 min). In contrast, in the case (10% NaOH / 30 min), a higher alkaline dose resulted in a significant dissolution of the hemicelluloses without cleavage.

15 The acid composition of the pretreatment broths (Table 4) showed a significant proportion of volatile acids (about half) compared to normal black liquor due to the cleavage of the acetyl groups of hemicelluloses (pine glucomannan and birch xylan) / 11 / (formation of acetic acid). In addition, it is generally noted that the major hydroxy acids 3,4-dideoxy-pentonic and glucose isosaccharic acid are composed of glucomannan and cellulose, whereas 2-hydroxybutane and xylisosaccharic acid are derived from xylan. Instead, formic, glycolic, lactic, and 3-deoxy-pentonic acid consist of all the polysaccharide components.

Table 5 shows the potential annual production of organic fractions in an example case (8% NaOH / 30 min) at a mill with an annual unbleached kiln dry mass of 500,000 tonnes. This production loss of black liquor organic matter material and heat content can be seen in Table 6. In practice, this recovery slightly increases the relative amount of lignin introduced into the recovery boiler, which may be reflected in the evaporated black liquor droplet performance /.

Fractionation of the spent liquor from the pre-treatment can be carried out using unit-5 processes known per se (Figure 2). Extractives are recovered from evaporated (dry matter 25-30%) waste liquor according to standard practice (volatile extracts are already released during pre-treatment) / 11 /. Sulfur free lignin precipitation can be effected from the same evaporated waste liquor preferably in two steps first with mill flue gas and carbon dioxide (pH down to about 8) and then to complete lignin precipitation in a second step with mineral acid (H2SO4, pH down to about 3) / 18-20 /. Since the pK values of the aliphatic acids are in the range of 3.5-5.0, the acids are also largely released from their sodium salts. Sodium released during carbonation occurs as a mixture of sodium carbonate and sodium hydrogencarbonate and can be reused in the process after causticization. The Na 2 SO 4 4 produced using sulfuric acid can be used as such in the chemical industry, as a make-up chemical for a sulphate mill, or it can be decomposed back to sulfuric acid and sodium hydroxide by electrodialysis / 21,22 /. If hydrochloric acid (HCl) is used for acidification, the sodium chloride (NaCl) formed will, in turn, obtain chlorine (Cl 2) and NaOH which may be used in bleaching. On the other hand, the acids can also be liberated directly, preferably directly by electrodialysis, whereby free acids and NaOH can be formed by suitable process analysis in the event of partial precipitation of residual lignin.

In addition to the aliphatic acids, the post-acidification solution contains mainly inorganic salts. If the volatile acids (formic and acetic acid) are removed from the resulting solution by distillation, additional corresponding salts (eg Na 2 SO 4) are precipitated during the distillation. However, they are almost completely eliminated if the non-volatile hydroxy acids present as the main distillation residue are dissolved in concentrated acetic acid (the salts are insoluble). Indeed, one of the advantages of the invention is the high volatile acid content, since it is easy to separate them by distillation. Formic acid and acetic acid can be separated, for example, by azeotropic distillation using ethylene dichloride as an auxiliary / 23 /. The hydroxy acids can be purified, for example, by vacuum distillation (0.067-0.173 kPa) / 24 / or by chromatographic methods applied by the sugar industry, such as ion-exclusion technology / 25 /. In the latter case, removal of formic and acetic acid and inorganic salts is not necessary prior to the separation of the hydroxy acid. Due to the instability of certain acids, the distillation yields were about 50% (pine) and 5 75% (birch), which corresponded to total acid yields of about 70% (pine) and about 85% (birch). In practice, the acid fractions were, in addition to volatile acids (formic and acetic acid), either fractions' 'low molecular weight acids' (a mixture of glycolic, lactic and 2-hydroxybutanoic acids) or' high molecular weight acids' (3,4-dideoxy-pentonic, 3-deoxy). pentonic acid, xylisosaccharic acid and glucose isosaccharic acid).

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Utilization of the extractants can be carried out according to standard practice, whereupon release of the acids (plating) yields distillable crude tall oil. However, pyrolysis of the extractant fraction was also attempted in connection with the invention, whereby a readily utilizable sodium carbonate and a liquid having the characteristics of 15 diesel fuels was formed, e.g. hydrocarbons (straight chain alkali, 1-alkene and dialkene series), straight-chain 2-ketones and aromatics (including benzene, naphthalene and phenanthrene / anthracene derivatives) and small amounts of terpenoids (including resin acids and steroids), fatty acids. Recovery of lignin as such (including use in phenolic and polyurethane resins) or after pyrolysis as fuel and chemical products (phenols and carbon fiber) is also possible / 26 /. Acidic, formic, acetic, glycolic and lactic acids are well-known chemicals and are used in a wide variety of applications / 27 /. For other acid components, potential industrial applications using either free acids or their salts have also been studied. An interesting alternative is to esterify them to form surfactants with fatty acids or to use them as a component in polyester resins. Pyrolysis of the acid fraction was also attempted in connection with the invention, whereby the acid salts led to the formation of sodium carbonate and gases, e.g. various aldehydes and ketones.

References: 1. Goldstein, I.S., (ed.), Organic Chemicals from Biomass, CRC Press, Inc., Boca Raton, FL, USA, 1981.

5 2. Sjöström, E., Wood Chemistry - Fundamentals and Applications, second edition,

Academic Press, Inc., San Diego, CA, USA, 1993.

3. Alen, R., Structure and Chemical Composition of Wood, in: Forest Products Chemistry, P. Stenius, (Ed.), Fapet Oy, Helsinki, 2000, pp. 11-57.

4. Wise, D.L. (Ed.), Organic Chemicals from Biomass, The Benjamin / Cummings 10 Publishing Company, Inc., London, UK, 1983.

5. Alen, R., Conversion of Cellulose-Containing Materials into Useful Products, in Cellulose Sources and Exploitation - Industrial Utilization, Biotechnology, and Physico-Chemical Properties, J.F. Kennedy, G.O. Phillips, and P.A. Williams (Ed.), Ellis Horwood, Ltd., Chichester, West Sussex, 15 England, 1990, pp. 453-464.

6. Kamm, B., Gruber, P.R. and Kamm, M., (Eds.), Biorefiners - Industrial Processes and Products, Status Quo and Future Directions, Volumes 1 and 2, Wiley-VCH Verlag GmbH & Co., Weinheim, Germany, 2006.

7. Mabee, W.E. and Saddler, J.N., Pulp Paper Can. 107 (6) (2006) 34-37.

20 8. Amidon, T.E., Pulp Paper Can. 107 (6) (2006) 47-50.

9. Chamboast, V., Earner, R. and Stuart, P.R., Pulp Paper Can. 108 (6) (2007) 30-35.

10. Argyropoulos, D.S., (Ed.), Materials, Chemicals, and Energy from Forest Biomass, ACS Symposium Series 954, American Chemical Society, Washington, DC, USA, 2007.

25 11. Alen, R., Basic Chemistry of Wood Delignification, in: Forest Products Chemistry, P. Stenius (Ed.), Fapet Oy, Helsinki, 2000, pp. 58-104.

12. Sjöström, E., J. Appl. Polym. Sci. 37 (1983) 577-592.

13. Axegard, P., Utilization of Black Liquor and Forest Residues in a Pulp Mill Biorefinery, Forest Based Sector Technology Platform Conference, Lahti, 2006.

30 14. van Heiningen, A., Pulp Paper Can. 107 (6) (2006) 38-43.

15. Aurell, R. and Harder, N., Svensk Papperstidn. 68 (3) (1965) 59-68.

10 16. Kleppe, P.J., Tappi 53 (1) (1970) 35-47.

17. Alen, R., Combustion Behavior of Black Liquors from Different Delignification Conditions, Proc. International Recovery Boiler Conference, 40 Years Recovery Co-operation in Finland, Haikko Manor, Porvoo, May 12-14, 2004, pp. 31-42. .

18. Alen, R., Patja, P., and Sjöström, E., Tappi, 62 (11) (1979) 108-110.

19. Wising, U., Algehed, J., Bemtson, T., and Delin, L., Tappi J. 5 (1) (2006) 3-8.

20. Wallmo, H., Richards, T. and Theliander, H., Paperi Puu 89 (7-8) (2007) 436-442.

21. Raucq, D., Pourcelly, G. and Gavach, G., Desalination 91 (12) (1993) 163-175.

22. Paleologou, M., Thibault, A., Wong, P.-Y., Thompson, R. and Berry, R.M. 10 Optimization of a two-compartment bipolar membrane electrodialysis system for the production of sodium hydroxide and sulfuric acid from sodium. sulfate generated at krafit Mills using ECF and TCF bleaching sequences, Proc.

Symposium on Minimum Effluent Mills, Atlanta, GA, USA, TAPPI Press, 1996, pp. 381-384.

15 23. Biggs, W.A., Jr., Wise, J.T., Cook, W.R., Baxley, W.H., Robertson, J.D. and

Copenhaver, J.E., Tappi 44, 385-392 (1961).

24. Alen, R. and Sjöström, E., Paper Wood 62 (8) 469-471 (1980).

25. Alen, R., Sjöström, E. and Suominen, S., J. Chem. Tech. Biotechnol. 51 (1990) 225-233.

26. Glasser, W. and Sarkanen, S., (eds.), Lignin - Properties and Materials, ACS.

Synposium Series 397, American Chemical Society, Washington, DC, USA, 1989. 27. Alen, R., Chemistry-Chem. 15 (6) 565-569 (1988).

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Claims (7)

A process for recovering organic matter fractions, such as aliphatic carboxylic acids, lignin and extractives, formed in the alkaline delignification of wood or other cellulosic plant material, characterized in that the recovery is effected from a separate alkaline pretreatment of the soup. Process according to Claim 1, characterized in that the delignification process is either sulphate or soda anthraquinone cooking and the alkaline pretreatment of the raw material is carried out with either an aqueous sodium hydroxide solution or an aqueous solution in which the active alkali is sodium hydroxide. Method according to claims 1 and 2, characterized in that the pretreatment is carried out with an alkali content of 2-14% of the dry matter of the raw material, preferably 8% (liquid / wood ratio about 4 kg / L), with a treatment time of 30-90 minutes, preferably 30 minutes and at a temperature of 150-180 ° C, preferably 150-160 ° C. Process according to Claim 1, characterized in that the substance fractions separated by methods known per se can be used as such or after modification as chemical products or parts thereof, or as different types of fuels. Process according to claims 1 and 4, characterized in that the sodium sulfate formed by the sulfuric acid used in the release of the aliphatic carboxylic acids can be broken down into sulfuric acid and sodium hydroxide by electrodialysis. Process according to claims 1 and 4, characterized in that the sodium chloride formed by the hydrochloride (hydrochloric acid) used in the release of the aliphatic carboxylic acids can be broken down to the hydrochloride and sodium hydroxide by electrodialysis. Process according to claims 1 and 4, characterized in that the substance fractions 5 can be utilized either in their sodium salts or in their free forms. 10 15 20 25 30