JPS6020321B2 - Process for producing sodium dithionite from sulfur dioxide, sodium formate and sodium carbonate using a minimum of solvents - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing anhydrous alkali metal salts of dithionite from formate and sulfur dioxide.

Specifically, this is a method for producing sodium koji dithionate in a methanolic aqueous solution in which both sodium formate and sulfur dioxide are dissolved. Dithionite is required as a bleaching agent, for example for bleaching groundwood pulp.

Zinc dithionite has been replaced by sodium indigo dithionite because of the scarcity and cost of zinc powder for its production and because it is not economically desirable for the disposal of zinc-containing waste. ing. Sodium dithionite can be produced by electrolysis and hydrogenation shelf-life processes, but the most economical means to make a high-grade solid product is to use a formate group to reduce the sulfur atom's hydration mark. is to use.

This process was first disclosed in 1933 Wang et al., U.S. Pat. A method is described for producing anhydrous sodium dithionite by introducing the SO2-methanol solution to a temperature at which the formation of sodium dithionite begins.

In one example of the Kamiyoshi specification, Na2C03 is 19.0% of sodium formate. This method requires a significant excess of sodium formate to buffer the acidity of the solution and also produces significantly finer, less stable crystals. Over the past 30 years, a series of improved methods using sodium hydroxide as an alkaline source have been developed, including, among others, U.S. Pat.
No. 4340, No. 3718732, No. 72221
No., No. 7695, and Specification No. 97, No. 4,
Special Publication No. 43-7003 and Publication No. 46-2405,
and Belgian Patent No. 698247.

These improved methods involve adding sulfur dioxide-containing methanol and an alkaline agent to an aqueous solution of an alkali metal formate and bringing the resulting aqueous methanol solution to a reaction temperature above the dehydration point of the hydrated alkali metal dithionite. The purpose is to prevent the formation of a crystalline body having crystal water introduced into the crystalline body.

The above addition rate needs to be adapted to the production ratio of dithionite; if it is too fast, the dithionite ion will decompose and the yield will therefore decrease. These improved methods involve absorbing sulfur dioxide into an alcohol that is miscible with water as a first feed solution, and dissolving sodium hydroxide and sodium formate outside the reactor in extremely hot water as a second feed solution. and feeding these two solutions to a reactor maintained at 60 to 90 degrees zero and containing a small amount of alcohol under overpressure.

In order to increase the production per unit volume of the reactor and per unit volume of alcohol, high concentrations of the reaction components are used and tertiform formate (which may be a by-product of the previous reaction) is added in the reactor. Dissolve in methyl alcohol, which was used as a solvent for the additive solution (US Pat. No. 3,7695).

In each of the above-mentioned specifications, sodium hydroxide is used as an alkali source, and sodium carbonate is only exemplified, but in Taruko No. 43-7003, sulfur dioxide is absorbed into methanol and concentration and then gradually adding an alkaline aqueous solution containing both sodium formate and sodium carbonate (containing % sodium carbonate by weight of sodium formate).

In this case the yield is about 5% by weight of the tablets based on sulfur dioxide and about 54% by weight based on sodium. Table 1 and 0
The table shows comparative experimental data, including the results for 19 examples of the four most relevant US patent specifications mentioned above.

Product dust index data are not shown. Table □ From the examples showing experimental results in the public literature, it is clear that: 'a} Sodium hydroxide is routinely chosen as the alkali source; 'b} Sodium carbonate is rarely used. It is merely an example.

[c- In Wakachi's case of using sodium carbonate as the alkali source, the yield is clearly inferior to that when sodium hydroxide is used in the production of sodium dithionite.

Nevertheless, the use of sodium carbonate is highly desirable since it is significantly less expensive than sodium hydroxide.

Furthermore, the production rate per unit volume of the reactor is an extremely important economic issue for reactions where relatively slow reactions and repeated batch pressurized reactions are desired. Also West German Patent No. 20
As shown in No. 00877 and U.S. Patent No. 7695, it is difficult to increase the yield of the reaction system by reducing the amount of alcohol added to the reaction system, especially along with sulfur dioxide. , since the water is accompanied by and chemically combined with the caustic soda (generally added as a concentrated solution), and the ratio of alcohol to water does not increase the solubility of the dithionite. This is because the dissolved dithionite cannot lower the reaction pH.
(the yield and efficiency of the process are both reduced). It is therefore an object of the present invention to provide a process for producing anhydrous sodium dithionite from sulfur dioxide and formate, in which the majority of the sodium ions are produced by sodium carbonate or by the combination of sodium carbonate and sulfur dioxide. provided by the reaction product.

Another object is to obtain a process for the production of dithionite by a batch process with a high output per unit volume of reactor.

According to the idea and object of the invention, the method comprises combining sulfur dioxide dissolved in methanol with sodium formate dissolved in water at about 120°C and also a methanol solution (to which S02-methanol and an aqueous formate solution are added). by reacting with sodium carbonate added as a dry powder to
It can be used to produce sodium dithionite in a reactor of a given volume.

Methanol and water are present in selected weight ratios, with the amount of water being the minimum amount required to dissolve the sodium formate at high concentrations and elevated temperatures. Sulfur dioxide, methanol, sodium formate, water and sodium carbonate leather
Preferably, a given volume of the reactor is fully utilized. Each methanol solution contains about 4% by weight of methyl formate. Methanol is additionally added to the reflux condenser to keep the loss of ethyl formate and other by-products to a minimum. The amount added is approximately 15% by weight of the total methanol used. The weight ratio of methanol to water is about 4.2-5.2. The ratio of sulfur dioxide to methanol based on equivalent weight is approximately 0.
20 to 0.25. The ratio of sulfur dioxide to water by weight is about 1.7 to about 2.4. The ratio of sulfur dioxide to formate ions by equivalent weight is about 1.4. Sodium carbonate is about 60% of sodium formate by weight, and the Na2C03/HCOONa ratio on an equivalent basis is about 0.8. When the weight ratio of methanol to water is greater than 5.2,
Therefore, if the amount of water is too small or the amount of methanol is too large, two undesirable results will occur. One is that the particle size of the head dithionate product becomes smaller and the agglomerates become more powdery, and the other is that substances normally present in the flow are mixed with the product. The analytical purity of the product is reduced due to precipitation. S02
Regarding the weight ratio of water to water, many disadvantages arise if the S02 base is changed in relation to the other compounds involved in the reaction, which can also occur due to changes in the amount of water.

That is, when the water increases, the dithionite tends to dissolve and decompose, thus reducing the yield. Also, if the amount of water is reduced, the two undesirable consequences described above with respect to the weight ratio of methanol to water occur. That is, small particles and powdery head dithionate are formed, and the analytical purity thereof is reduced. Furthermore, if the amount of sodium carbonate is reduced to less than 50% by weight of sodium formate, sodium from other alkaline sources is required.

If sodium formate is additionally used as an alkali source of this kind, an excess of formic acid is produced, which is used only in the first stage and cannot be recycled. Based on sulfur dioxide, the yield is about 74-8a% by weight.

The yield is about spherical to 5% by weight based on the formate. The yield is about 65-75% by weight based on sodium. This method uses approximately 1.04 g/gal of reaction volume.
[9 (about 2.3 pounds) and about 3.78〆 (1 gallon)
approximately 0.6 pounds of sodium dithionite per hour. Soda ash has been found to be at least 7% more effective by weight than caustic soda in terms of Na20 usage in the process of the present invention, which is an improvement on the process described in US Pat. No. 7,695.

The reason for this is not completely understood, but perhaps the extremely strong alkalinity of the NaOH present when the increased NaOH solution contacts and dissolves in the reaction medium produces insoluble and highly inert by-products. For example, it seems to be due to the formation of Na2S03. Soda ash, on the other hand, does not dissolve immediately upon addition, and therefore its alkalinity tends to be released at a slower rate. However, based on alkaline sodium vs. total Na added, Na20
The results of known comparative calculations may lead to misunderstandings regarding these examples (for example, Example 4 of US Patent No. 97-4).

In this case no caustic soda is added and all the sodium is supplied by sodium formate. This is due to the fact that the process cannot be continued with circulating alcohol. Thus the desired reaction requires 1 mole of formic acid and 2 moles of bisulfite: HCOOH+2NaHS03→N
a2S204 10C02 20 U.S. Patent No. 9754
When S02 is added to sodium formate as described in Example 4 of Specification No. 4, 2 moles of formic acid are produced for 2 moles of NaHS03: ratio ○ 1 $ 0 2 1 2 HCOON
a. 2HCOOH+2NaHS03 Excess formic acid reacts with excess methanol to produce terityl formate.

Excess formic acid also decomposes dithionite. This problem arises when methanol is recovered for use in the next batch. In this case, a large amount of formic acid is involved, and when used in Example 4 of U.S. Pat. dithionite will be violently decomposed due to the change ≠ impossibility). The methods shown in the examples below in which sodium formate is in balance with NaOH or N also with C03 also require that the methanol containing tertyl formate is recovered from the previous reaction step and therefore the added tyl formate is consumed. Based on the assumption that it will never be generated.

These examples therefore resemble conventional processes in which methyl alcohol is repeatedly circulated. For fresh batches, as in the examples of the above-mentioned publication, where caustic soda is used, no formic acid is supplied.

As a result, formate ions have to be supplied exclusively from HCOONa, and NaOH has to be reduced accordingly. As a result, the circulation method in each example described later cannot be strictly compared with the fresh method in the examples of known literature.

Comparisons between the two are therefore based on the total amount of sodium used, although the total amount of Na consumed is not clear since sodium formate has a diluting effect. The process of the invention can be summarized as comprising the following steps: dissolving sodium formate in water at elevated temperature to maximum concentration to form an aqueous formate solution;
B' Dissolve sulfur dioxide in methanol, prepare a methanol solution in a designated reactor, and add the following: [1
1. To prepare at least the actual base of the alkali required for the reaction, firstly sodium carbonate, especially as a dry powder (sodium carbonate is at least 50% by weight of the sodium formate), then an aqueous formate solution, and '31 Finally, S02-methanol solution (approximately 80% is “
(added as a "fast" S02 feed, the remainder added as a "slow" SQv feed at progressively slower addition rates).

Even better results than in the modified soda ash example were obtained by pre-reacting the sulfur dioxide with sodium carbonate suspended in methanol and then adding a slurry of sodium bisulfite in methanol to a concentrated solution of sodium formate. and added to the main reactor under controlled rate.

This example yields sodium dithionite with acceptable particle size and dust properties, and the analytical results are at least as good as those of the standard caustic process described in U.S. Patent No. 7,695. It is equally good, with yields 22-25% higher by weight than standard caustic process yields, and consumption of about 3.0% by weight for sulfur dioxide and equivalent N
About 8.6% less with respect to aOH. Another soda ash example involves slurrying sodium metabisulfite (a stoichiometric reaction product of total soda ash and about half the sulfur dioxide) with most of the methanol and the other half of the S02 % in methanol and then adding this metabisulfite slurry to the main reactor along with a concentrated aqueous solution of sodium formate.

This second improved method produces sodium dithionite with excellent particle size and dust properties, as disclosed in U.S. Pat. No. 3,897,544
Approximately 20% by weight compared to the standard caustic method according to No.
Improved yields also result with approximately 5.4% lower consumption in terms of sodium hydroxide. In comparison with a series of known experiments using Na2C03, these results show that when the reaction components are made at an optimum ratio and the experimental procedure is maintained at an optimum level, a significantly reduced amount of sulfur dioxide with formate ions in an aqueous methanol solution is obtained. It has been discovered that sodium carbonate can be used as an added alkali source in amounts.

The novel process according to the invention can be carried out when the alkali is in the form of sodium carbonate, sodium bicarbonate, sodium sulfite, sodium metabisulfite or sodium hydroxide.

Particularly advantageous, however, is the use of sodium carbonate due to its low cost and for various reasons. Attempts to replace sodium hydroxide with sodium carbonate in a standard manner as described in U.S. Pat.
This was followed by maintaining the same amount of water, including water chemically bound in the NaOH.

In this case an undesirable amount of dust was obtained and the product was of low purity. The amount of soda ash was then reduced, all other conditions held constant. In this case the analytical purity of the product was improved and the dust was reduced. In this series of experiments, dust was reduced by adding Na2C0345.
50 to 307, and further increased the supply of Na2C03 by 5
It was reduced to 215 by deferring for a minute.

However, the most effective way to reduce Dato is to reduce S0
It was found that there were two distributions (split addition of S02).In the table below, the numerator indicates the rapid supply of S02 and the denominator indicates the slow supply, respectively in weight %): Distribution
Dust number 81/19
26082/18
19683/17
14784/16
97 The amount of dust in the batch production of sodium dithionite is checked with a colorimetric method using Rubin's solution to determine the sodium dithionite dust in the sample.

In this way, Na2S2040.0256 is reacted together and the Rubin solution 25' is decolorized to measure the dust of each produced batch. A dust meter is installed in the device to carry out this dust measurement operation.

Inner flea approximately 2.54 knots (1 inch), length approximately 86.3 mm (
34 inches) and a well-cleaned and dried Oertriator tube with a ball joint at each end vertically. The inner diameter is about 2.54 feet (1 inch), the length is about 20.32 feet (8 inches), and the thickness at the bottom is about 2.5 inches. A well-washed and dried Eltriator sample-containing tube placed with a layer of glass wool (approximately 1 inch) is connected vertically to the bottom of the Eltriator tube. A 5-1 cape sig nitrogen source is connected to the bottom of the sample-containing tube via a needle control valve and rotameter.

Connect a J-type inlet tube with an inner diameter of 4 to 5 female in an inverted manner to the upper ball joint of the Eltriator tube, so that the straight part of the J-type is located at the bottom of a 500' female cylinder containing 450' of water. Try to reach within 1 inch of the enemy. The doorbell buzzer is “J”
The curved part of the variac is connected to the power source.
). Connect the 50' pureet containing Rubin's solution to the top of the graduated cylinder. To begin the test, mix thoroughly by gently shaking the bottle containing part of the production batch and rolling the pin (if the contents of the pin are shaken, a dust film that collects on the top will prevent the test from being carried out). to disturb).

Remove 0.1 μl of the sample from the bottle and carefully pour it into the Ertriator sample tube, this care is necessary to avoid loss of dust during the transfer, and also remove all particles using a camel hair brush. Transfer to the sample-containing tube. Add Rubin's solution 3.0 to the water in the graduated cylinder.

Vibration is initiated and adjusted by the rate of vibration that violently strikes the lower side of the J-type inlet tube approximately at the center of the arc. When the buzzer operates under the precise and proper control of the variac, the operator can detect approximately 7.62 to 10.16 seconds from the point where the vibrating comb strikes.
When I put my finger on the tube at the tip (approximately 3 to 4 inches), I felt a vibration. If the device is tightened too tightly,
The vibrations are weak and cannot push out the dust, so the dust accumulates outside and inside the inlet tube. The needle valve that controls the flow of nitrogen through the Ertriator column is carefully and quickly opened, at approximately 2.67 m/min (0.09425 m/min).
Adjust the flow rate to the desired flow rate.

This flow ratio remains constant during operation. A timer is started when the flow of nitrogen to the bottom of the Ortriator column and to the sodium dithionite sample reaches a sufficient amount to form a dust film. As soon as the Rubin solution is decolorized, add a few more drops of Rubin solution. The scream count of Rubin's solution is recorded at 1 minute intervals. The flow of Hertorgeta takes about 5 minutes (
Lasts for 3 days (Tochisa). The volume of the Rubin solution is approximately 0.1 shipboard, and the time is approximately 0.1 minute. The dust coefficient or dust grade is calculated as follows:
0=number of dust Generally, SQ is added in two steps.

The "fast" S02, which is 80-85% by weight of the total amount, is fed during the first 80 minutes, and the remaining "slow" S02 is fed during the next 80 minutes.
Introduced in minutes. The reaction is run for a third 80 minute period without the addition of any additives other than the "scrub" alcohol to avoid loss of volatile reaction components. then reduce the excess water and methanol brought about by the use of NaOH,
Finally, the amounts of reaction components are increased until the entire volume of the reactor is utilized and the maximum output per unit of volume used is obtained.

Na2C described in Examples 2, 3, 4, 6 and 7 below
The laboratory and test factory experimental data for 03 are shown in Section V.
Examples 1 and 5 for NaOH shown in Table a and also Section V
Compare with the data of 15 examples for known NaOH and Na2C03 shown in Table b. Examples 1-4 The data and results for Examples 1-4 are shown in Table m.

EXAMPLE 1 A comparative example uses the method described in U.S. Pat.
Average values are shown for a 7 day experiment used as a round weight % solution and without sodium carbonate. Example 2 is sodium carbonate 1
The results are shown for equivalent weights and the same amount of water as in Example 1. Example 3 describes the results for a smaller amount of sodium carbonate and the same amount of water as Example 2. Example 4 shows the results with even lower amounts of sodium carbonate and reductions in both water and methanol. As a representative treatment method in Table m, Example 2 was carried out by each step detailed below.

Add 851 parts of methanol and 38 parts of terityl formate to a rope pestle reactor.

Heat this charge to 70qo and 35 psig with nitrogen.
Keep under pressure. A mixture of 828 parts of 96% sodium formate is mixed with 727 parts of water and heated to boiling point.

The mixture is transferred to a stainless steel cylinder lined with 7 capes sig steam to maintain the solution at about 3000F. The level in the feeder is measured by a float, which is contacted by a metal rod that projects from the top of the cylinder into the viewing glass. The sight glass is graduated in units of ribs, so that the volume within the supply device can be known precisely. The feed rate can be controlled by reading the level of the feeder on a skin-by-skin basis and comparing this to the calculated value. A mixture of meth/ol 1702, 76 methyl formate, and sulfur dioxide 1307 is placed in another stainless steel cylinder equipped with a sight glass and a metering rod.

Therefore, this device can also accurately know the capacity. The feed rate of the mixture is controlled by a rotameter.
5 beakers of 557 ml of sodium carbonate and 100 ml each
Divide into 1 piece and 1 piece of 57 pieces.

The feeding mechanism for soda ash consists of two valves and one 4-inch hopper. Hopper holds 100 units. The space between each valve holds 11.1 mm. Since 557 units are to be supplied over 79 minutes, 7.05 units per minute must be introduced.

The valve system is operated every 1.57 minutes since the amount of drop per drop is 11.1 minutes.

Nitrogen outflow is performed at the soda ash inlet to prevent coagulation caused by reactions that block the inlet (in later experiments, nitrogen outflow is omitted, and valves and fixtures are heated with electrical tape to prevent coagulation). ) The contents of the reactor were brought to 70°C and S02
-Start supplying methanol.

After the S02 concentration in the pot reaches 1%, start the timer and start feeding the sodium formate solution and solid soda ash. 5% by weight of the sodium formate solution is fed over 5 minutes and the remaining 95% by weight is introduced every 7 minutes. Soda ash is fed in 79 minutes as a "quick SQ" feed rate.
81% by weight of S02-methanol is fed over 8 minutes, and the remaining 1% by weight is slowly fed for 80 minutes. 8
At the end of 0 minutes, the SQ methanol feed rate is reduced to about 1/3 of the rapid SQ feed rate, reducing the flow rate to 20
Hold for a minute.

This rate is then reduced to 26% of the rapid 602 feed rate and held for one additional stream, and finally reduced to 17% of the rapid rate until the S02-methanol solution flows out (which is typically 160 minutes). let The reaction time, which was 70° C. at the beginning, reached 83° C. after about 5 minutes. The temperature at which 8 is 0 is then maintained until the end of this process.

After the slow S02 feed ends (approximately 160 minutes), the reaction proceeds for an additional 80 minutes or a total reaction time of 240 minutes.

During the entire process, 500 methanol of methanol is fed to the scrubber to reduce the loss of volatile reaction components such as ethyl formate and SQ.

Samples of the reaction liquor are taken after rapid SQ supply (80 minutes), after slow S02 introduction (16 field hours), and at the end of the reaction (240 minutes).

Sample 10' is mixed with alkaline formaldehyde solution (to bind the bisulfite) and then titrated with 0.1N standard iodide solution. The timer indicates the sodium thiosulfate content of the solution and also indicates the degree of decomposition of the dithionite. The contents of the reactor are passed through a glass-fritted Buchner funnel, creating a stream of nitrogen over the product to avoid contact with air. The product is washed with methanol, dried in a vacuum flask, and the whole is heated in a hot water bath under vacuum. The dried product was weighed to determine yield, assayed for dithionite purity, and assigned a dust number. Examples 5-7 The data and results for Examples 5-7 are shown in Table N,
This shows the test factory results for a base treatment using sodium hydroxide and the test factory results for two treatments using sodium carbonate.

The reactor is constructed and operated as described in US Pat. No. 7,695. Sodium carbonate is 6% by weight of sodium formate. In Example 6, the amount of methanol is the same as in Example 5 Comparative Example, but the amount of water present is slightly increased. In example 7, the amount of water is 2 compared to example 6.
5% less, and 20% less methanol. Table N. Comparative calculation results of reaction component ratios and production amounts between laboratory and test factory examples and known examples. Tables Va and Vb include
Calculated ratios based on the equivalent values in the table and calculated yields based on S02, formate ions and sodium ions are described for two experimental treatment examples and known examples.

Calculated production volume for reactor volume [k9 (lb)/hour/
Approximately 3.78 gallons] are shown for each example and each of the above known patent specifications. Generally, production volume is 18% by weight from laboratory data and 20% from test factory data.
It is increasing. Table Va* Contains formate equivalents in sodium formate and dimethyl formate** Table V Contains methanol equivalents in dicil formate
b* Contains formate equivalents in sodium formate and formic acid solution. ** Contains methanol equivalents in dimethyl formate. The present invention is most notable in yield and process output.

In a laboratory system using sodium carbonate instead of sodium hydroxide in Example 4 compared to Example 1, the efficiency of the process was increased for all three feedstocks. Production, measured in pounds of product produced per hour per gallon of reaction solution, is increased by this substitution. A similar increase in process efficiency and yield was seen in Example 7 vs. Example 5 at the test plant.
It is clear from the description. These results show that the products of Examples 6 and 7 shown in Table W are superior in having high analytical values and low dust counts, making these products extremely useful as industrial bleaching agents.

Examples 8 to 10 Other test factory results are standard work with caustic soda and 2 work with soda ash (Na2C03 is 62.9 of HCOONa).
% by weight) are shown in Table 1.

Pure Na per gallon of reactor volume
Significantly improved yields, measured as 2S204 (lbs), were obtained in Examples 9 and 10. Even though the amount of water used to dissolve the increased amount of sodium formate was slightly greater than the total amount of water used with NaOH and HCOONa in Example 8 Comparative Example, NaOH
By replacing Na2C03 with Na2C03, it was possible to reduce the amount of ethanol even though sulfur dioxide was additionally used. Due to the relatively low density of methanol, this reduction results in significant reactor space savings. Table 1 Generally, by using sodium carbonate as the alkali source in the process of the invention, the amount of solvent used in the reactor can be reduced as shown in Examples 8-10. The production is therefore significantly increased compared to the world standard production obtained using sodium hydroxide as the alkali source.

A reduction in the total amount of sodium is necessary when using soda ash. Although the example below is directed directly to the use of soda ash as a solid, it should be taken into account that while water is added to the soda ash in the present invention, the amount of water in the other feed streams is correspondingly reduced. be. The gist of the invention is that 'a) the total amount of water added to the reactor and the ratio of methanol to water are preset, but the amount of water in the individual feed streams is not necessary. be. Example 11 This example describes the pre-reaction of sodium carbonate and sulfur dioxide to form a composite material.

Three types of V feeders were manufactured.

V-supply "A" was prepared by suspending total parts by weight of sodium carbonate in 167 parts of methyl alcohol containing 9 parts of methyl formate and adding 167 parts of sulfur dioxide to this suspension. Feed “B” is sodium formate 1 with a purity of approximately 96%.
It was produced by dissolving 31 parts in 93 parts of water. Feed "C" was prepared by dissolving 35 parts of sulfur dioxide in 35 parts of methyl alcohol containing 2 parts of methyl formate. A first charge consisting of 115 parts of methyl alcohol containing 6 parts of methyl formate was placed in the reactor.

Pour this charge, pressure 2 imitation sig and temperature 65:00
heated to. Feed "A" and feed "B" were then introduced simultaneously at a rate such that a specified amount of each was fed into the reactor for 80 minutes. Heating the contents of the reactor at a temperature of 8.0
Continued until reaching . At this point, heating was reduced to maintain a controlled reaction at a temperature of 83°C. The heating time from 65°C to 83°C was about 10 minutes.

After a further 10 minutes, the reactor pressure reached 5 sig due to the release of carbon dioxide gas due to the reaction. The reaction pressure was then maintained at 5 sig by controlling the release of carbon dioxide produced in the reaction. The released gas is first transferred to the water-cooled condenser (360) and then to the frozen condenser (360).
10q0) and then fed the frozen scrubber with methyl alcohol at a rate of 0.26 parts per minute. Both condensate and effluent scrubber methanol from the two condensers were re-entered the reactor.

At the end of supply period 8 minutes of supply bodies A and B, supply body C
was fed at a rate of 1.5 parts per minute.

After 15 minutes, this rate is 1. 15 minutes later, it was lowered by 0.7 per minute. A total of 72 parts of Feed C was consumed every 8 minutes. During this time, the temperature and pressure inside the reactor were maintained at 83° C. and 5 sig, respectively. The same conditions were maintained for an additional 70 minutes after the completion of the introduction of the phlegm C.

At this point (ie, 230 minutes after the start), the reactor contents were cooled to 60q0 and heated. The filter cake was then washed with 24 parts of methyl alcohol and dried under vacuum, yielding 240.5 parts by weight of a crystalline product and an analytical value of 92.3% as sodium dithionite. Example 12 [Reference Example] This example describes the use of sodium metabisulfite as a feed material.

Three types of descendant combinations were produced again.

Feed A consists of 15 parts of sodium metabisulfite suspended in 167 parts of methyl alcohol containing 9 parts of methyl formate;
It was prepared by adding 67 parts of sulfur dioxide to this suspension. Feeds B and C were the same as described in Example 11. The feed schedule, reaction conditions and overall reaction time were exactly as described in Example 11.

After filtration, washing and drying as in Example 11, 238 parts by weight of crystalline product and an analysis value of 91.0% as sodium dithionite were obtained. As mentioned earlier,
The novel process of the present invention increases the output of a given two reactors per unit time.

Claims (1)

[Scope of Claims] 1. Aqueous sodium formate, sulfur dioxide-methanol solution and sodium compound are prepared in such a manner that (a) the methanol:water weight ratio is not greater than 5.2, and (b) the SO_2:water weight ratio is 1. 7 to about 2.4, using sodium carbonate as the sodium compound in a proportion of at least 50% by weight of the sodium formate. A method for producing anhydrous sodium dithionite, which comprises reacting each reagent and recovering anhydrous sodium dithionite. 2. The sulfur dioxide-methanol solution contains methyl formate,
A method according to claim 1. 3. The method of claim 2, wherein methyl alcohol and methyl formate are placed in a reactor followed by the introduction of sulfur dioxide-methanol solution, aqueous sodium formate and sodium carbonate. 4 The ratio of SO_2 equivalents to formate equivalents is about 1.4,
A method according to claim 3. 5. The method of claim 3, wherein the sodium carbonate is added directly to the reactor as an anhydrous powder. 6 Sodium carbonate in sulfur dioxide-methanol solution
4. The method of claim 3, wherein a slurry is formed by pre-reacting with the reactor and adding the slurry to the reactor. 7 Sodium carbonate in sulfur dioxide-methanol solution
7. The method of claim 6, wherein the slurry formed by pre-reacting with sodium metabisulfite in methanol. 8 Sodium carbonate in 1 part of sulfur dioxide-methanol solution
7. The method of claim 6, wherein the slurry formed by pre-reacting the sodium bisulfite in methanol is sodium bisulfite in methanol. 9. The method of claim 6, wherein the addition of the slurry is carried out in about the first third of the time required for the reaction to obtain anhydrous sodium dithionite. 10. The method of claim 6, wherein the addition of the aqueous sodium formate solution is carried out substantially simultaneously with the addition of the srillar to the reactor. 11 80-85% by weight of sulfur dioxide-methanol solution
7. A process as claimed in claim 6, in which the remaining 15-20% is introduced within the second third of the total reaction time.