FI65607C - FOERFARANDE FOER KONTINUERLIG FRAMSTAELLNING AV EN BLANDNING INNEHAOLLANDE KLORDIOXID OCH KLOR SAMT FOER AOTERVINNING AV ALKALIMETALLKLORIDSLAM - Google Patents

Description

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This invention relates to the preparation of a mixture of chlorine dioxide and chlorine and to the recovery of an alkali metal chloride slurry. More specifically, this invention relates to improvements in the process for treating alkali metal bisulfate slurries obtained from single vessel process chlorine dioxide generators.

Given the considerable commercial interest and importance of chlorine dioxide in the fields of cellulose bleaching, water purification, degreasing, phenol removal from industrial waste, textile bleaching, etc., it is highly desirable to provide methods for economically producing chlorine dioxide and using the type of effluents produced. stay up.

One way to produce chlorine dioxide is by the reaction of an alkali metal chlorate, an alkali chloride and a mineral acid such as sulfuric acid. Examples of reactions that can take place are: (1) NaClO3 + NaCl + H2SO4 »C102 + 0.5 Cl2 + Na2SO4 + H2O

(2) NaClO3 + 5NaCl + H2SO4— * C102 + 3 Cl2 + 3 Na2SO4 + SHjO

Such reactions are used commercially by continuously feeding the reagents into the reaction vessel and continuously removing the chlorine and chlorine dioxide formed therein from the reaction vessel.

Reaction 2, which is preferred because it produces primarily chlorine dioxide, results in the use of approximately equivalent amounts of chlorate and chloride.

A one-pot process for producing chlorine dioxide is disclosed in U.S. Patent 3,563,702, which discloses that alkali metal chlorate, alkali metal chloride, and a mineral acid solution are continuously fed to a single-vessel generator-evaporator crystallizer in amounts sufficient to generate chlorine dioxide and chlorine at about 65-85 ° C. about 2 in the presence of 4-N catalyst or 4-11 N without catalyst, removing water by vacuum evaporation at 100-400 mmHgn absolute pressure while simultaneously removing chlorine dioxide and chlorine, crystallizing the mineral acid salt inside the generator and removing crystals from the vessel.

When the reaction takes place inside a vessel, in reactions in which sulfuric acid is used as a mineral acid reagent, crystals of sodium sulfate and sodium bisulfate, the amount and presence of which generally depend on the acid concentration used, crystallize from solution and settle to the bottom of the generator.

In addition to the use of sulfuric acid, hydrochloric acid can also be used as a mineral acid reagent, in which case the crystals removed from the generator are alkali metal chloride crystals. However, the hydrochloric acid process produces alkali metal chloride as a by-product, which product is often less desirable than alkali metal sulfate. Sodium sulfate is a valuable by-product that is useful in sulfate cellulose cooking processes as well as chlorine dioxide. Therefore, systems that produce chlorine dioxide and sodium sulfate are particularly useful because on-site coordination with cooking operations can be accomplished using both the primary chlorine dioxide product and the sodium sulfate recovered in the cooking process, especially in sulfate cooking operations.

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In some cases, however, the need for sodium sulfate has been greatly reduced or counteracted. Sodium sulfate is not required for certain types of cooking processes. In certain sulphate cooking operations, the need for sodium sulphate can be reduced or varied and the placement of excess salt poses problems for current environmental standards. Although the need for reduced amounts of sodium sulfate may vary, the need for chlorine dioxide remains unchanged.

In cases where reduced amounts or no sodium sulfate are required, the one-pot process can be modified to use hydrochloric acid as the mineral acid reagent, with the by-product being sodium chloride. However, such systems are not as efficient as systems using sulfuric acid. Furthermore, only sodium chloride is obtained and in cases where varying amounts of sodium sulphate are required, the development of the required amount of sodium sulphate would make it necessary to switch back and forth from the catalyzed sulfuric acid system to the catalysed hydrochloric acid system with all its associated problems.

It is an object of the present invention to provide a process in which a one-pot process can be used very efficiently to produce chlorine dioxide and the recovery of chlorine and by-product salt to produce the desired salt without having to change the conditions in the reactor.

It is a further object of this invention to provide an improved process for treating crystal slurry produced in single vessel processes to return valuable chlorate and sulfate moieties contained in a solids effluent to a generator for further reaction and converting the sulfate salt to the chloride salt as desired.

According to the process of the present invention, a single vessel process slurry containing alkali metal bisulfate crystals and valuable chlorate moieties is fed to the top of a metathesis column. An aqueous solution of hydrochloric acid having a concentration of about 32-37% by weight and a temperature above about 20 ° C is added continuously or intermittently through a feed opening near the bottom of the metathesis column to the downstream slurry stream, the crystals in the slurry reacting with hydrochloric acid to give sodium sulfuric acid, with the regenerated sulfuric acid and valuable chlorate ions being leached from the column to the generator and the sodium chloride leaving the aqueous slurry through an outlet located near the bottom of the metathesis column.

There are many benefits to using this process. The process makes it possible to use a more efficient sulfuric acid reaction in a single-vessel generator-evaporator crystallizer without switching to a less efficient hydrochloric acid reaction process in those cases where reduced amounts of by-product sodium sulfate are required. In those cases where an increased or maximum amount of sodium sulfate is desired, the process allows such addition or maximization by simply reducing or replacing the hydrochloric acid stream going to the bottom of the metathesis column with a stream of fresh water. In those cases where maximum sodium sulfate production must be achieved, the upstream flowing water works to return substantially all of the valuable chloride, chlorate, and sulfuric acid components to the generator continuously, requiring a relatively small energy supply to the system. In addition, under these conditions and when the generator is operated at high acid concentrations of the order of 10-11 N, water washing allows recovery of sodium sulfate as neutral sodium sulfate as opposed to undesired acidic sodium sulfates recovered by the sludge filtration technique previously used in the art.

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The rates at which hydrochloric acid or water is fed to the bottom of the metathesis column will, of course, depend on the desired conversion or washing to be accomplished. In cases where complete conversion of sodium bisulphate to sodium chloride is required, the amount of hydrochloric acid continuously fed to the metathesis column must be at least twice the amount of sodium sulphate produced in the reactor, expressed in moles.

In cases where the sodium bisulfate to be removed has to be reduced by predetermined amounts, the flow of hydrochloric acid to the metathesis column is adjusted to allow the desired amount of conversion, with unconverted sodium sulfate being recovered from the bottom of the column.

The rates of downward flow of sodium bisulfate slurry and upward flow of hydrochloric acid are adjusted to provide maximum conversion efficiency without substantially increasing the steam requirement for vacuum evaporation in the generator.

In general, the washing and conversion reaction require the flow rates to be adjusted to provide a residence time of about 10-60 minutes, and preferably about 15-40 minutes.

Figures 1 and 2 show metathesis columns that are preferred for use in this process. Figures 1 and 2 are schematic vertical sections.

Referring now to Figure 1, the apparatus comprises a metathesis column or tower 1 made of a corrosion resistant material such as titanium, plastics, ceramics, glass, etc. The column is preferably, although not necessarily substantially cylindrical, having a feed device 10 at its top for feeding one crystal slurry not visible). The lower end of the metathesis column is equipped with a hydrochloric acid and / or hot water supply pipe 7 and a device for varying the inflowing hydrochloric acid 65607 6 and hot water (not shown) and the crystal slurry outlet or outlet generally shown in section 6. The column 1 is divided into several reaction / washing zones 9, 11, etc. with downwardly and inwardly tapering, funnel-shaped projections 4 with openings 5 at the tip for discharging the crystalline slurry downwards into the swirling washing / reaction zones 9, 11, etc .; the flow of crystalline-containing slurry is directed downwardly from one protrusion to another and to successive vortices of reaction / wash zones.

Each funnel-shaped protrusion is provided with a plurality of openings 3 located at or near the junction between the top of the protrusion and the column wall. As the crystal-containing slurry moves downward to the protrusion and through the orifice 5, the upward flow of hydrochloric acid is partially directed through the orifices 3, creating turbulence in zones immediately below the protrusion openings and continuously converting sodium sulfate to sulfuric acid and valuable chlorate . The control of the amount of downward flow and turbulence of the crystals is effortless to realize by controlling the relative sizes of the crystal outlets 5 and 3.

Zone 8 of the column is a relatively stationary or turbulent zone.

The metathesis column can be placed immediately below the single-vessel generator, in which case the crystal slurry moves as a gravity flow from the generator 10 to the column and the valuable chlorate and sulfuric acid portions are continuously returned directly to the generator in an upward flow.

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The total number of protrusions placed on the metathesis column can be varied depending on the commonly used reaction efficiency and the amount of material. In practice, using commercially available single-vessel generators with a capacity of about 2300 L, metathesis columns of the type described and having about 1.7 to 3.3 protrusions per linear meter of column have been found to be effective. In general, columns of about 3-4.5 m in length with 8-10 protrusions spaced approximately 30 cm apart are preferred.

In cases where spatial and other factors dictate the placement of the metathesis column at a location adjacent to the single vessel generator, the slurry containing crystals removed from the bottom of the generator is pumped to the top of the metathesis column by a suitable pumping device (not shown). by means of a transfer device (not shown).

Figure 2 shows another metathesis column that can be used in the process of this invention. Like the column of Figure 1, this metathesis column can be placed either adjacent to or immediately below the single vessel generator. In cases where the metathesis column is located immediately below the single vessel generator, the crystal slurry is continuously removed from the bottom of the generator (not shown) to the top of column 1 in zone 1. Hydrochloric acid is continuously introduced into valuable parts of chlorate and sulfuric acid to the generator from the top of the column. Sodium chloride moves down to the collection zone 5, from where it is removed through the outlet 3. The outlet 3, which is shown to be located at a point in the column 1 above the hydrochloric acid inlet 2, can be varied in position close to the bottom of the column.

As with the metathesis column of Figure 1, this metathesis column can also be placed next to a single vessel generator, in which case it is equipped with a pumping device for continuously feeding crystal sludge from the generator to the metathesis column, and water containing valuable chlorate and sulfuric acid components is continuously removed from the top of the column and through the feed pipe device.

The following example is intended to illustrate the present invention.

Example Using the metathesis column with 11 protrusions shown in Fig. 1, a dilute hydrochloric acid feed port was placed between the fifth and sixth protrusions from the bottom, with the water feed port located at the bottom of the column. The reaction producing chlorine dioxide in a single vessel generator was adjusted to produce sodium bisulfate at a rate of 26 kg / h. The aqueous hydrochloric acid solution was fed as a 36% acid to the metathesis column at a rate of about 13 kg / h and hot water was added to the bottom of the column at about 23 kg / h to wash the sodium chloride produced in the metathesis column. Sulfuric acid was recovered in an amount of about 10.5 kg / h from the top of the column. Analysis of the brine recovered from the column showed 12.8 kg / h recovery for sodium chloride, 19.9 kg / h removal to water, 0.04 kg / h hydrochloric acid and 0.009 kg / h sodium bisulfate, indicating essentially complete conversion of sodium bisulfate to sodium chloride in the column. .

Claims (6)

A process for the continuous preparation of a mixture containing chlorine dioxide and chlorine and for recovering an alkali metal chloride slurry, comprising (a) continuously reacting an alkali metal chlorate, alkali metal chloride and sulfuric acid in a single vessel generator-evaporator-crystallizer in chlorine dioxide (b) the temperature is maintained between about 65-85 ° C? (c) the acidity of the reaction solution is maintained between about 4-11 N? (d) subjecting the reaction solution to an absolute vacuum of about 100-400 mmHg to cause evaporation of water vapor; (e) the chlorine dioxide and chlorine produced by said reaction are removed as a mixture with water vapor? and (f) the alkali metal bisulfate is continuously crystallized in and continuously removed from the single vessel reactor, characterized in that the alkali metal bisulfate crystals produced in one vessel are continuously passed in the form of a slurry directly downstream to the top of the unitary metathesis column; directing a countercurrent flow of dilute hydrochloric acid through the column at a rate and in amounts sufficient to react with the early metal sulfate to convert the alkali metal sulfate to sulfuric acid and alkali metal chloride, continuously returning the valuable chlorate and sulfuric acid portions to substantially one vessel slurry? and continuously removing the alkali metal chloride slurry from the bottom of the metathesis column. Process according to Claim 1, characterized in that the early metal chlorate is sodium chlorate and the alkali metal chloride is sodium chloride. Process according to Claim 1 or 2, characterized in that the concentration of the aqueous hydrochloric acid solution is about 32 to 37% by weight. 65607 10 Process according to Claim 1, 2 or 3, characterized in that the temperature of the aqueous hydrochloric acid solution is about 20 to 35 ° C. Process according to Claim 1, 2, 3 or 4, characterized in that hot water is continuously fed to the metathesis column on its basis in order to effect washing of the alkali metal chloride. 1. A compound for the treatment of alkali metal chlorides and alkali metal chlorides and alkaline metal chlorides, including alkali metal chlorides and alkali metal crystals, such as an alkali metal reactor, an reactor, a reactor the proportion of chlorine dioxide, chlorine and alkali metal sulphate in the catalyst, including the catalyst; (b) a temperature between about 65 ° C and about 85 ° C; (c) reacting at a rate of about 4 to about 11 N; (d) reacting the reaction with an absolute vacuum of about 100-400 mmHg for water treatment; (e) chlorine dioxide and chlorine, in which case the reaction is carried out; and (f) alkali metal sulphate in a continuous ring of crystals in an enrichment reactor and in a continuous reactor; kännetecknat av att alkalimetallvätesulfatkris-tallerna, som bildas i enkärlsreaktorn, kontinuerligt i forma av en uppslamning överföres direkt account överdelen päen integrerad utbyteskolonn, i nedätgäende strömning; variables of the same color as the compounds of the alkali metal salt of the bracket of the genomic columns of the solid state and alkali metal chlorides of the reaction group with the addition of alkali metal and alkali metal chlorides enkärlsreaktorns