FI123577B - Method for recovering aliphatic carboxylic acids, lignin and extracts from waste liquors of alkaline cellulose soups - Google Patents

Description

The present invention relates to a process for the production of organic materials and to the elimination of organic materials. 10 waste liquors formed in a separate oxidative alkaline initial stage of alkaline soups, in particular pine and birch sulfate, 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 and further utilization of organic matter from the waste liquors from alkaline soils of other cellulosic plant materials (including grasses and agricultural and industrial wastes).

Prior art application (1) discloses a process in which such an alkaline pretreatment is carried out only with aqueous sodium hydroxide (NaOH). An important advantage of this is that the recovery of the soluble constituents (aliphatic carboxylic acids, lignin and extracts) is obtained by utilizing the pre-treatment waste solution 20 formed during pre-treatment to recover its soluble constituents. Generally considered in this way, utilizing pretreatment solutions for organic material recovery has the advantage that, in alkaline cooking, the low calorific and carbohydrate based material first dissolves significantly more than the higher calorific lignin. This fact is particularly important for the energy efficiency of the mill, since the thermal energy bound to the organic matter of the mill's actual waste liquor (black liquor) is recovered by burning the black liquor in the process of regeneration of inorganic cooking chemicals. recovery boiler. On the other hand, the use of Aarni -30 in organic cooking material (less than one-fifth of the original raw material) for other purposes prior to the recovery boiler provides an opportunity to increase production.

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! which in turn matters if the recovery boiler has become a traditional bottleneck in production.

In the present invention, it has been found advantageous to carry out said alkaline pretreatment under oxidizing conditions, whereby an oxidizing chemical such as hydrogen peroxide (H2O2) or oxygen (O2) is added to the aqueous NaOH solution. In addition to the foregoing advantages, a substantial improvement in the basic process is achieved in that the formation of aliphatic carboxylic acids from the carbohydrate material of the raw material chips under alkaline conditions is directed to the lowest molecular weight acid components. In practice, this means that, under oxidizing conditions, more so-called "quenching" is achieved than pretreatment with NaOH alone. small molecule volatile acids (formic and acetic acid) as well as certain other small molecule acids, small molecule hydroxy acids (including glycolic and deoxytetronic acid) and on the other hand these lesser 'large molecular hydroxy acids' (including deoxy-pentonic acid) . This has a very beneficial and decisive effect on the recovery and utilization of acids, as small molecule acids are generally more easily distinguishable and also industrially available than large molecule acids.

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In sulphate cooking (more than 90% of the chemical pulp in the world is currently produced by this process), the lignin from the raw material that binds the cellulose fibers together is strongly removed under alkaline conditions. At the same time, the total yield of the polymeric carbohydrate material of wood, cellulose and hemicelluloses, which reduces the total yield of the cooking process, and is simultaneously dissolved in the broth / 2,3 /. Thus, the organic matter dissolved in the black liquor, after partial separation of the crude leachate from the wood extracts, consists mainly of both lignin depletion products and aliphatic carboxylic acids formed by cleavage reactions in the carbohydrate chains. Most of the sodium consumed during cooking is bound to these acids, while most of the sulfur is in the inorganic material. Of the main organic components of black liquor, virtually only the fraction derived from extractants I 3, pine soap 131, is utilized as chemical products. Other organic matter 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 thermal content corresponds to only a quarter of the effective thermal value of the black liquor organic matter. Since the modern sulphate mill is more energy-efficient than self-sufficient, this would allow at least partial recovery 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.

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The aliphatic acid fraction of black liquor contains both volatile (formic and acetic acid) and hydroxy acids having either one or two carboxyl groups (Table 1). Hydroxy monocarboxylic acids form the most significant acid fraction in black liquor. The total amount of acids formed in hardwood soup is almost the same as that of softwood soup, but the relative proportions of the acids differ characteristically. 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 as a pure fraction. Particularly for lignin, its sulfur-free (normal sulfate lignin 20 contains 1-3% sulfur 131) would be preferred. However, it is a requirement in all cases that the recovery of organic fractions must be seamlessly incorporated into the normal operation of the plant, which must take particular account of the disturbances 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 de -ignification processes, fiber, has to be used as a base material for many paper and board products / 3-6 /.

The development of the process according to the invention was based on the general boundary conditions set forth in patent application / 1 / list-30, whereby the basic idea was to take the waste liquor necessary for the separation of organic material from the initial stage of the cooking. alkaline pre-treatment

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lyn. Thus, at the same time, it was possible to maximize the carbohydrate-based material and, on the other hand, to "minimize" the formation of the "lignin-based" impurity material. However, in addition to this, the fact that an oxidizing chemical which was more advantageous in terms of the separation and utilization of the acids, in addition to alkali, was present during the pre-treatment, was further found to improve the process. The isolation and purification of the dissolved sulfur-free substance fractions (aliphatic carboxylic acids, lignin and extracts) were also performed in this case according to the unit processes disclosed in patent application / 11.

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The following Examples 1 and 2 further illustrate the process of claim 1 of the invention. It will be apparent to one skilled in the art that there are many ways in which the main method described in the Examples can be modified on a case-by-case basis to achieve the desired optimum result. Thus, it is also clear that the fibrous raw material may be any suitable biomass material for this purpose and that the pretreated raw material may be further defibrated, for example, by either normal sulfate cooking or soda anthraquinone (AQ) cooking. In all cases, however, the pretreatment waste liquor is directed to the organic material recovery.

Example 1 Chips made from pine (Pinus sylvestris) were subjected to alkali pretreatments under the following conditions: 4% and 8% NaOH in the dry matter, 5 L / kg ratio of wood, 60 min treatment time and 150 ° C treatment temperature. In addition, alkali treatments were carried out using 6% and 8% NaOH in the dry solids, 5 L / kg ratio of wood dry matter, 60 min treatment time and 150 ° C treatment temperature. In both cases, the treatments were then performed either by adding 2% ELCl 2 or O 2 (5 atm). The spent liquor from the pretreatment was recovered and the chips were then carefully washed with running water to determine the total yield of the treatment (solute = (amount of oven-dry chips before treatment) - (amount of oven-dry chips after treatment)).

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The composition of the resulting waste broths was according to Table 2. The mass ratio (volatile acids) / (hydroxy acids) was either 1.9 (4% NaOH) or 1.0 (8% NaOH), in the presence of Η2θ2: η, either 1.5 (6% / H2O2) or 1.3 (8%) / H 2 O 2) and O 2 in the presence of either 1.0 (6% / O 2) or 1.3 (8% / O 2) (Table 3). In the case of pretreatment with alkali alone, the mass ratio (volatile 5 acids / hydroxy acids) was quite high at the lower alkali dose (4% NaOH). This was clearly due to the fact that the acetyl groups of the major hemicellulose component of the pine tree, the Glu-coman, cleave almost immediately at the start of treatment to form acetic acid / 31, whereas hydroxy acids are uniformly formed during treatment and are also affected.

The oxidizing additive (H 2 O 2 or O 2) also produced relatively less soluble material other than aliphatic acids, which in this case contributed to the total yield (Table 2) and to the mass ratios (aliphatic acids) / (other organic matter) (Table 3). In this regard, the alkali treatments, especially in the presence of H2O2, were clearly different from the other treatments (about 75% of the organic material acids, 50-60% in the other treatments). The total amount dissolved in oxidative pretreatments ranged from 8.0 to 13.2% of the dry matter of the chips (Table 2).

Generally, in all pretreatment cases, the volatile acids (formic and acetic acid) were 50-64% of the aliphatic carboxylic acids (volatile acids + hydroxy-20 acids) (Table 4). Since previous experience (1) makes it easier to isolate and purify hydroxy acids, which are more easily industrially utilizable, this is of great practical importance - only about 35% of the total aliphatic carboxylic of total organic matter / 3 /. The presence of Η202: η and O2 also led to the positive phenomenon that high molecular weight hydroxy acids (including deoxy-pentonic acid and isosaccharic acids) were partially cleaved into low molecular weight acids (including formic, glycolic and deoxy-tetronic acid). This also contributes to the beneficial effect on the final isolation and utilization of acids, as the small molecule hydroxy acids utilized in industry are more easily isolated than the large molecule hydroxy acids, which, moreover, have not yet been established for large scale use. On the other hand, 6 H2O2 cleaved slightly more wood components (including lignin) into aliphatic carboxylic acids in the alkali, which was particularly evident at the higher alkaline dose level (6ΨΨίΆ2θ2 vs. 8% / H2C >2).

The pH values of the pretreatment waste solutions were in the range of 6.4 to 9.7, indicating the presence of acids in their sodium salts, taking into account the pK values of the acids (3-5), while the amount of NaOH delivered was not too high or too low. Extracts, lignin and acids were isolated by the unit processes disclosed in patent application / 1 /. Alternatively, the acids were liberated from their sodium salts, either by using mineral acid or electrodialysis. In general, three acid fractions were obtained by various purification methods (including distillation and chromatographic methods): (i) volatile acids (formic and acetic acid), (ii) low molecular weight hydroxy acids (mainly glycolic, lactic, hydroxybutanic and deoxy-tetronic acid, -C4) and iii) high molecular weight hydroxy acids (mainly deoxy-pentonic acid and isosaccharic acids, C5-C6). In all cases, the chips that were pre-hand-15 could be defibrated normally, e.g., without loss of yield, by sulfate cooking.

Example 2 20 Chips made of birch wood (Betula pendula) were subjected to alkali pretreatments under the following conditions: 4%, 6% and 8% NaOH in the dry matter of the wood, 5 L / kg ratio of wood, 60 min. ° C. In addition, alkaline treatments were carried out using 6% and 8% NaOH in the dry matter of wood, with a liquid / wood ratio of 5 L / kg, a treatment time of 60 min and a treatment temperature of 150 ° C. In both cases, the treatments were then carried out either by adding 2% H 2 O 2 or C 2 (5 atm). The spent liquor from the pretreatment was recovered and the chips were then carefully washed with running water to determine the total yield of the treatment (solute = (amount of oven-dry chips before treatment) - (amount of oven-dry chips after treatment)).

The composition of the resulting waste broths was as shown in Table 5. The total amount dissolved in oxidative pretreatments ranged from 11.0 to 14.7% of the dry matter of the chips.

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This, at the same time, demonstrated the effectiveness of the oxidizing chemicals in reacting e.g. birch neutral extracts and low molecular weight lignin material, converting them to a soluble form. The mass ratio (volatile acids) / (hydroxy acids) in this case was 5.8-3.3 (8% NaOH-4% NaOH), in the presence of H2O2 either 4.8 (6% / H2O2) or 3.7 (8%) / Η2θ2) and in the presence of O2, either 4.2 (6% / 02) or 3.3 (8% / C2) (Table 6). The pH values of the pretreatment waste solutions were in the cases (6% and 8% / H2O2) and (6% and 8% / 02) between 5.4 and 7.0, indicating that the amount of NaOH administered was sufficient. In general, however, the use of oxidizing chemicals did not appear to be as advantageous for acid recovery as the pine pretreatment, due to the increased solubility.

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The carbohydrate fraction of birch chips differs to some extent from the composition of the corresponding fraction of pine chips / 8 /, which is also reflected in the acid components formed (Tables 4 and 7). In particular, the high acetyl group content of the most important hemicellulose component of birch wood, xylan, results in high acetic acid content. Generally, in all birch chip pretreatment cases, volatile acids (formic and acetic acid) were 75-86% of aliphatic carboxylic acids (volatile acids + hydroxy acids) (Table 7). However, as expected, the effect of oxidizing chemicals (H 2 O 2 or O 2) on the formation of hydroxy acids was similar to that of pine chips. In this case, the acids were 58-68% of the organic matter.

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Isolation of extracts, lignin and acids was performed as in Example 1. Again, three acid fractions were obtained by different purification processes - (i) volatile acids (formic and acetic acid), (ii) low molecular weight hydroxy acids (mainly glycolic, lactic, hydroxybutanic and deoxy-tetronic acid, C2-C4) and Hi) high molecular weight (hydroxy) acids. mainly deoxy-pentonic acid and isosaccharic acids, Cs-C 6) and pre-handled chips were able to be defibrated normally without loss of yield by sulfate cooking.

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References 1. Aldn, R., Process for the preparation and recovery of aliphatic carboxylic acids, lignin and extracts from waste liquors of alkaline cellulose soups, 5 Patent Application 20070906 (27.11.2007).

2. Sjöström, E., Wood Chemistry - Fundamentals and Applications, second edition, Academic Press, Inc., San Diego, CA, USA, 1993.

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

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

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

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

7. Alen, R., A Collection of Organic Compounds - Properties and Applications, 15 Consalen Consulting, Helsinki, 2009, 1370 pages.

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

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Claims (5)

A process for recovering organic matter fractions produced by alkaline delignification of wood or other cellulosic plant material and soluble in broth, such as aliphatic carboxylic acids, lignin and extracts, characterized in that the recovery is carried out separately from the alkalizing agent and the stalk. 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 an aqueous solution of sodium hydroxide, preferably with either hydrogen peroxide or oxygen. Process according to claims 1 and 2, characterized in that the pretreatment is carried out with an alkali content of 4-8% of the dry matter of the raw material, preferably 6%, the other conditions preferably being a liquid / wood ratio of 5 kg / L, treatment time 60 minutes and temperature 150 ° C. Process according to Claim 1, characterized in that the sulfur-free substance fractions separated by methods known per se can be utilized either directly 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 substance fractions can be utilized either in their sodium salts or in their free forms. 30 1. Förfarande för utvinning av organic bulk fraction, säsom aliphatic carboxylsyror, 5 lignin och extraktivämnen, som bildas vid alkalisk delignifiering av veder annulat cellulosahaltigt växtmaterial och upbing fråt försvant förfinger, kokningen. 10 2. Förfarande enligt patentkrav 1, a transcription method for the attenuation / alkali-delignification of sulfate-anhydrous soda-anthraquinones and an alkaline-deleterious solution of sodium hydroxide for the elimination of sodium hydroxide. 15 3. Förfarande enligt patentkrav 1 och 2, kännetecknat av att förbehandlingen görs med en alkalimängd 4-8%, företrädesvis 6%, frän torrämnet i rämaterialet, varvid de övriga förhällandena företrädesvis är som topjer: lts / ved-för kg. , behand-lingstiden 60 minuter at 150 ° C. 20 4. Förfarande enligt patentkrav 1, kännetecknat av att de svavelfria ämnesfraktioner som har separerats genom i och för sig stump förfaranden the user of antingen som radiation after modification of the chemical product eller deras delar, eller som bränslen av olika typ. 25 5. Förfarande enligt patentkrav 1 och 4, kännetecknat av att ämnesfraktionema kan utttttttjas antingen som you sodium salter eller i you fria former. 30