FI66034B - FARING PROCESSING OF CELLULOSE AND CELLULOSE AOTERVINNING AV KEMIKALIER - Google Patents

Description

05034

Method for producing cellulose and recovering chemicals.

The invention relates to an alkaline cellulose soup in which sodium aluminate and sodium sulphide are used as cooking chemicals. More specifically, the invention relates to a process for the production of cellulose and the recovery of chemicals, in which hardwood or softwood chips are boiled with an aqueous solution of sodium sulphate containing sodium sulphide in a conventional sulphate cellulose digester under standard conditions. The process is characterized in that, after evaporation, the waste liquor separated from the broth is fed to a gasifier at a temperature of 700-1250 ° C, the hot inorganic material is removed from the gasifier, cooled with the air required for gasification, crushed and dissolved in water and the resulting alkaline aluminate solution As an absorption solution to give a solution containing 1-4% by weight of Na2S and NaHS and 5-20% by weight of NaA102, which is suitable as such without 20 separate causticisations for cellulose cooking, and the resulting hydrogen sulphide-free gas is burned in a suitable boiler .

In the process according to the invention, the cooking chemicals can be returned to the cooking in regenerated form without a separate causticization step. The use of aluminate as an auxiliary chemical for auto-25 causticization is known per se in the sulfite process, the so-called In the Sonoco method (Cook, W.R. Pin 57 (1974), 9, pp. 94-96), and in two-stage combustion according to FI patent publication 62,562. It has also been proposed to add aluminate to sulfur-free alkaline soup (so-called soda-30 soup) (see U.S. Pat. No. 2,601,110), however, about half of the alkali must be added in the form of sodium hydroxide, which makes autocastification impossible.

Paper and Wood No. 2, 1979, pp. 98-103 states that sodium aluminate is not a strong enough 35 base to replace sodium hydroxide in cooking.

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Paper and Wood No. 3, 1978, pp. 129-132 states that sodium aluminate autocustification can only be used in sulfur-free cooking.

Reference is now made to the accompanying Figure 1, 5 which shows the circulation of Al (OH) 2 and the gasification of the waste liquor in the process according to the invention.

The evaporated black liquor 2 obtained from boiler 1 is granulated with recycled Al (OH) 3 and NaAlCl 2 into 10-20 mm granules in granulation drums 3, in a manner known per se, after which the granules are fed to a waste liquor gasifier 4 at a temperature of 700-1250 ° C. Due to the high melting point of the sodium aluminate formed, it is constantly operated in the solid phase. Gasification of waste liquor is a known technique e.g. From the SCA-Billerud process (STFI Meddelanden, 15 series D7, 1976, pp. 132-138). The hot granules, which no longer contain organic matter or sulfur, are removed from the bottom of the carburetor and cooled, for example, by a fluidized bed condenser 5. The cooling is carried out with the air required for gasification. The granules are then crushed and, if desired, some of the sodium aluminate formed is recycled to granulation 1. The rest of the sodium aluminate is dissolved in water 6 and, if desired, the water-insoluble material can be separated and recycled.

The gas mixture obtained from the gasification of the waste liquor is cooled to 25 in a waste heat boiler 7 and possibly additionally by jet cooling. H 2 S is absorbed directly into the alkaline aluminate solution. This is a known technique that can be performed with very low H2S losses. In the absorber 8, H2S reacts with NaOH to give a solution containing 30 Na2S, NaHS and NaAlO2, the H2S-free gas is burned in a suitable boiler.

It has surprisingly been found that the solution obtained from the absorption of H2S is suitable as such without separate causticization as a cellulose cooking solution. In this way, the chemical cycle of the sulphate-35 distillate process can be simplified without compromising cooking efficiency, thus avoiding the high investment costs of traditional causticization and recovery boilers, as well as the operational difficulties and risks associated with the latter.

3 66034

The process according to the invention has the difference and advantage over known processes that the formation of melt in the waste liquor carburetor is avoided. Due to the high melting point of sodium aluminate, it is operated in a solid 5 phase all the time. In addition, the investment costs of the sulfate process when using an aluminate solution can be decisively reduced by completely avoiding causticization and simplifying heat recovery from black liquor.

The following examples illustrate the invention: ^ EXAMPLE 1 (Comparative Example)

Standard sulfate cellulose soup was performed under laboratory conditions as follows:

To a 1 liter auto-15 clavicle equipped with a rotary mixer was added 100 g of air-dried Finnish pine chips (humidity 10%)

12.6 g NaOH

6.3 g Na2S

3.5 g Na 2 CO 3 350 g H 2 O.

The autoclave was sealed and cooking was performed by raising the temperature with thermosed oil heating from 20 ° C to 80 ° C in 0.5 hours and from 80 ° C to 170 ° C in 2.0 tin. Reactor 25 was maintained at a final cooking temperature of 170 ° C for 1.5 hours.

The autoclave was cooled to 60 ° C per hour.

The reactor mixture was transferred from the autoclave to a 2 L decanter to which 300 g of cold water was added, after which the fibers were separated from the cooking liquor by filtration. The separated cellulose-30 fraction was washed twice with 5 liters of water, after which the fibers were filtered off and dried for 12 hours at 105 ° C.

The cellulose fraction thus washed and dried was weighed and found to have a pulp yield of 48.3 g in the model soup. The lignin content of the obtained cellulose was determined by the so-called based on chapter number 35 (TAPPI standard). Lignin content = 7.9%.

4 66034 EXAMPLE 2

Experimental cooking was performed under laboratory conditions in which the alkaline addition was dosed as sodium aluminate alone. Both sulfidity and total alkali in the cooking-5 solution were the same as in the control soup (Example 1).

Thus, to a 1 liter heated autoclave equipped with a rotary stirrer were added: 100 g of air-dried Finnish pine chips (moisture 10%) 10 54 g Na A1C> 2

12.6 g Na2S

3.5 g Na 2 CO 3 750 g H 2 O.

Cooking was performed using the same temperatures as in Example 1.

After the reaction, the reaction mixture was transferred to a 2 L beaker as in the previous example, 300 g of cold water was added, and the fibers were separated from the cooking liquor by filtration. The separated black liquor was collected for subsequent experiments and the cellulose fraction was washed and dried as in Example 1. The yield of washed and dried pulp was 55.6 g, the number of pieces was 66.2 and the corresponding lignin content was 9.9%.

EXAMPLE 3 A test soup according to Example 2 was performed using 100 g of air-dried birch chips (moisture 9%) instead of pine chips. After washing and drying, 54.0 g of pulp were found, the number of pieces was 36.9 and the corresponding lignin content was 5.5%.

30 The black liquor separated after cooking was collected for further experiments.

EXAMPLE 4

In the previous two Examples 2 and 3, the separated black liquor sample was concentrated and treated to regenerate cooking chemicals as follows.

35 5 66034 After concentration, the composition of the black liquor was: 43.2 g of organic matter with 9% sodium (3.9) g) 15 g of Al (OH) 3 5 3.2 g of Na 2 SO 4

0.56 g NaOH

0.2 g Na2S

80 g H 2 O.

The above black liquor sample was dried at 110 ° C to give 61.5 g of dry matter. 50 g of this solid was ground and annealed in a gasification furnace under reducing conditions (CO gas flow 30 ml / min) by raising the temperature to 800 ° C in 2 hours and keeping the product at 800 ° C for 1/2 hour before cooling.

The gas leaving the gasification reactor was washed by passing it through a 2N NaOH solution (100 mL) to collect any H2S gas released. Annealing waste 29 g were dissolved in 500 ml of distilled water and the insoluble carbonaceous residue was filtered off, dried and weighed. This soluble-20 mat residue (20 g) was annealed in a porcelain crucible at 800 ° C to burn coal; the water-insoluble annealing residue (4.9 g) was taken up as alumina (Al 2 O 3).

The water-soluble fraction of the annealing waste was analyzed. It was found that the aqueous solution did not contain carbonates and that the amount of Na 2 SO 4 dissolved in it was 0.16 g, corresponding to n 6% of the initial amount of sulfate in the sample.

The Na2S content of the solution was determined by titration. The solution was found to contain 1.2 g Na 2 SO 4 corresponding to 2.2 g Na 2 SO 4 (2.6 g Na 2 SO 4 from the original amount). An amount of sulfur-hydrogen corresponding to 0.2 g of sodium sulfate was found in the sodium hydroxide-30 wash solution. The missing sulfur had apparently been removed as hydrogen sulfide with the gas stream.

The total alkali in the solution was titrated. From this, the proportion of sodium sulfide was subtracted, and it was found that the alkalinity 35 corresponded to 0.087 mol of NaOH. Accordingly, 7.1 g of Na Al 2 O 2 were dissolved in the solution (excess aluminum hydroxide was present as previously observed in the insoluble residue after annealing as Al 2 O 3).

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According to the above, the composition of the part dissolved in water after gasification was: 7.1 g NaAlO 2> 54 g 0.16 g Na 2 SO 4 x 7.6 1.2 5 1.3 g Na 2 S 10.4 which corresponds almost exactly to the cooking chemical composition used in Examples 2 and 3 .

EXAMPLE 5 The experiment of Example 4 was performed in which the gas leaving the gas reactor was washed to recover H 2 S by first passing the gas through an aluminate solution (200 mL) having a composition of 14 g Na Al 2 O 2 0.4 g Na 2 SO 4 200 g H 2 O and then through 2N NaOH solution (100 mL).

The solutions were analyzed after the experiment, and it was found that the sodium aluminate solution contained 0.3 g of sodium sulfate equivalent to sodium sulfide (hydrogen sulfide). No sulfur was found in the second wash solution (2N NaOH).

Claims (2)

7 A method for producing cellulose and recovering chemicals, wherein hardwood or softwood chips are boiled with an aqueous solution of sodium sulphate containing sodium sulphide in a conventional sulphate cellulose digester under standard conditions, characterized in that the waste liquor separated from the boiling is the hot inorganic matter is removed from the gasifier, cooled with the air required for gasification, crushed and dissolved in water, and the resulting alkaline aluminate solution is used as an absorption solution of the i 2 S in the gas produced in the gasifier to give 1-4% by weight of Na 2 S and NaHS: and a solution containing 5 to 20% by weight of NaAlCl 2, which is suitable as such for the cooking of cellulose without separate causticization, and the hydrogen sulfide-free gas obtained is burned in a suitable boiler.