JPS597641B2 - How to get the best results - Google Patents

Description

[Detailed description of the invention] This invention relates to a method for producing chlorine dioxide.

BACKGROUND OF THE INVENTION Chlorine dioxide is a valuable chemical agent, typically used in the form of an aqueous solution for the bleaching of cellulosic fiber material pulp, which generally involves the reduction of chlorate with chlorine in an acidic medium. It is known to be produced in a number of ways.

The basic reactions involved in such methods are summarized by the equation below.

Generally, the chlorate ions in the above formula are supplied by sodium chlorate, the chloride ions by sodium chloride and/or hydrochloric acid, and the hydrogen ions by sulfuric acid and/or hydrochloric acid.

In addition to the reaction explained in reaction formula (1) above, the following formula (2
), there is a competing reaction that reduces the efficiency of conversion of chlorate ion to chlorine dioxide.

As described in more detail in Canadian Patent No. 826,577, one known method for producing chlorine dioxide involves adding sodium chlorate, sodium chloride and/or hydrochloric acid and sulfuric acid to an acid solution of about 2 to 4.8N. Maintaining the aqueous reaction medium contained at a temperature of 100°C at its boiling point and at the same time maintaining the reaction vessel at a pressure below atmospheric pressure evaporates water from the reaction medium and removes chlorine dioxide and chlorine in a gaseous mixture with water vapor. This precipitates solid by-products, primarily anhydrous sodium sulfate, in the reaction vessel.

The reaction is conducted at an elevated temperature below the temperature above which substantial decomposition of the chlorine dioxide occurs.

The gaseous mixture of chlorine dioxide, chlorine and water vapor is then treated to condense the water vapor and recover an aqueous solution of chlorine dioxide, usually containing some dissolved chlorine.

The sodium sulfate precipitated as a by-product can be removed continuously or intermittently from the reaction vessel and used as a replenishment agent in the recovery cycle of pulp production in any convenient type of pulp mill, typically a kraft pulp mill. Use as.

In a kraft halp manufacturing operation, wood chips or other crude cellulosic fibrous materials are digested in a pulping liquor (white liquor) containing sodium sulfide and sodium hydroxide as the active pulping agents to produce wood pulp; is separated from the used pulping liquor (black liquor).

This pulp is then subjected to bleaching and refining operations in a bleaching device to produce a pulp with desired whiteness.

This bleaching process typically uses a chlorine dioxide solution produced in a chlorine dioxide production facility.

The black liquor is subjected to recovery and regeneration operations to prepare new white liquor and recycled to the cooking process, where it is recycled to reduce wasted white liquor.
We will also provide some of them.

Recovery and reclamation operations generally involve first concentrating the black liquor and then heating it in a furnace to produce a smelt containing sodium sulfide and sodium carbonate.

This smelt is dissolved in water to form an aqueous solution (green liquor), undissolved solids are removed, and then causticized with slaked lime to convert carbonate to hydroxide, resulting in the precipitation of calcium carbonate.

Calcium carbonate is recovered and typically used to further produce slaked lime.

The aqueous solution after separating the calcium carbonate is used as circulating white liquor.

Sodium sulfate recovered from the chlorine dioxide production unit is used as a replenishment source for the system to replenish sodium and sulfur values.

The amount of replenishment agent required is less than the amount of chlorine dioxide required, but it varies from factory to factory, as there is little loss due to the established recovery process.

The above chlorine dioxide manufacturing procedure produces chlorine dioxide 1 About 1 mole per mole of sodium sulfate}IJum and -~12 Provides moles of chlorine.

With decreasing losses in sodium and sulfur values, conventional processes typically produce more sodium sulfate than can be used in a factory, and excess amounts accumulate.

Furthermore, with the trend towards decreasing the amount of chlorine used in bleaching processes, chlorine gas is being produced in excess.

DISCLOSURE OF THE INVENTION The present invention involves applying reduced pressure to an acidic aqueous reaction medium containing hydrogen ions, chlorate ions, chloride ions, sodium ions and sulfate ions and having an overall acidic normality of 2.0 to 4.8 normal. maintaining said acidic aqueous reaction medium at its boiling point, precipitating neutral sodium sulfate from said reaction medium, removing a gaseous mixture containing chlorine dioxide, chlorine and water vapor from said reaction medium, and removing said gas from said reaction medium. A process for the continuous production of chlorine dioxide and chlorine by reduction of sodium chlorate by chlorine ions in said acidic aqueous reaction medium, which comprises dissolving all of the chlorine dioxide content of the mixture and part of the chlorine in an aqueous medium, Reacting chlorine containing chlorine in the gaseous mixture that does not dissolve in the chlorine dioxide solution with sulfur dioxide and water to produce hydrogen chloride and sulfuric acid, and supplying the thus produced hydrogen chloride and sulfuric acid to the reaction medium. and both hydrogen ions and chloride ions are 1:
The reaction medium is supplemented in a molar ratio of 10, and the hydrogen and chloride ions are supplemented in the form of hydrogen chloride or hydrochloric acid or sodium chloride and sulfuric acid in a 2:1 molar ratio or sodium chloride and sulfuric acid in a 2:1 molar ratio. 1 molar ratio of the mixture with hydrogen chloride or hydrochloric acid to bring the sodium ions and sulfate ions into a stoichiometric ratio that approximately corresponds to the formation of neutral sodium sulfate, and to provide a total A process for the continuous production of chlorine dioxide characterized in that sufficient hydrogen and chloride ions are added to meet the requirements.

According to the present invention, chlorine containing by-product chlorine undergoes an exothermic reaction with sulfur dioxide according to the following equation.

The hydrogen ions and chloride ions produced in this reaction are used to provide at least a portion of the hydrogen ions and/or chloride ions required in the chlorine dioxide production reaction.

Because the competitive reaction of formula (2) makes the chlorine dioxide production process inefficient, the relationship with the product of formula (3) becomes unbalanced, and correction is required to keep the chlorine dioxide production process stable. Must.

The present invention accomplishes this corrective action while simultaneously reducing the amount of sodium sulfate produced per mole of chlorine dioxide.

The ratio at which formula (1) dominates formula (2) in reducing chlorate ions represents the production efficiency of chlorine dioxide, and this value is expressed as E.

E is the percentage conversion of chlorate to chlorine dioxide according to formula (1)
For example, when the conversion rate is 90%, it is expressed as 0.90.

Conversion efficiency E can be adjusted by adjusting the chloride/chlorate molar ratio in the production equipment or by using a catalyst to promote chlorine dioxide production.

That is, the lower the molar ratio of chloride/chlorate in the raw material, the more efficient the production of chlorine dioxide up to a certain limit.

A catalyst for promoting the production of chlorine dioxide is known, and a typical example of this catalyst is silver ion.

The amount of hydrogen ions required to produce 1 mole of chlorine dioxide depends on the overall efficiency (8), and is expressed as follows from equations (1) and (2).

Similarly, the amount of chlorine ions required to produce 1 mole of chlorine dioxide is expressed as follows.

Further, the amount of chlorine produced from the reaction medium is expressed as:

The required amount of chlorate raw material is 1 mole of 0102 produced 1 Therefore, CI-:E in the raw material The molar ratio of CIO3- is (5-4E):1.

Therefore, if the efficiency is less than 1, all Cl -: CIO3
The molar ratio of - is always greater than 1:1.

It is preferred to operate this molar ratio in the raw material as close to 1:1 as possible.

Since chlorate is usually added as the sodium salt and sodium sulfate is the only salt that precipitates from the reaction medium, the amount of sulfate ions fed into the reaction medium will react with two moles of sodium ions introduced as sodium chlorate. Necessary to do this: Nimol E
Adjustments must be made to provide 2E sulfate ions.

In this way, in order to produce chlorine dioxide continuously in a stable state with a certain efficiency, there are certain constraints that must be carefully observed.

Naturally, it is preferable to operate the chlorine dioxide production system so that the conversion efficiency of chlorate to chlorine dioxide by the reaction of formula (1) is as high as possible.

Nevertheless, the constraint condition is
It can be applied as follows for producing 1 mole of chlorine dioxide.

These amounts of raw materials are 1 mole CIO2 and 1 mole Cl2
generate.

The basic reaction of chlorine and sulfur dioxide according to equation (3) produces H+ and CI- ions in a 2:1 molar ratio.

As can be seen from the above formula, the efficiency (6) which is the normal condition
is less than 1, H0:CI- supplied to the reaction medium
The molar ratio is always less than 2:1.

The lower the efficiency, the lower the H+:Cl- molar ratio.

That is, feeding the reaction product of sulfur dioxide and chlorine according to formula (3) directly to the reaction medium causes an imbalance in the system, which inhibits stable operation.

That is, when the amount of chlorine ions is correct, the amount of hydrogen ions becomes too high, and when the amount of hydrogen ions is correct, the amount of chlorine ions becomes too low.

Both conditions are unsatisfactory.

In the first condition, the acidity of the reaction medium increases and the reaction rate increases, resulting in a more rapid increase in acidity and an even faster reaction rate.

In this way, the reaction can become uncontrolled and may explode.

Moreover, the acidity of the reaction medium reaches a value at which acidic acid salts precipitate.

Although the precipitation of acidic sulfate removes acid from the reaction medium and serves to control the acid concentration, the use of acidic sodium sulfate in pulp mills is undesirable due to the loss of acid with the salt.

In the second state ``T: +1, the efficiency is initially higher due to a decrease in the chloride/chlorate molar ratio, but due to the need to keep the acid feed rate correct, the chloride ion feed The amount decreases and as a result the chlorine dioxide production reaction slows down and eventually stops.

Furthermore, when all of the chlorine produced by the reactions of formulas (1) and (2) is recovered together with chlorine dioxide, and the reaction of the recovered chlorine and sulfur dioxide as shown in formula (3) proceeds completely, The amount of hydrogen ions obtained by the reaction is as follows per mole of chlorine dioxide produced.

Similarly, the amount of chlorine ions obtained is as follows.

The amounts of hydrogen and chloride ions provided by the reaction of chlorine thus recovered with sulfur dioxide are not sufficient for the production of chlorine dioxide, unless the conversion efficiency of chlorate to chlorine dioxide is 100%. Exceeds the required amount of hydrogen ions and chloride ions.

However, some of the chlorine produced by formulas (1) and (2) dissolves in the chlorine dioxide solution and cannot be normally recovered.

This amount amounts to 20-40% of the chlorine present in the gaseous reactant stream removed from the chlorine dioxide production unit.

The loss of chlorine into the chlorine dioxide solution significantly reduces the amount of chlorine available from the chlorine dioxide production reaction that must react with sulfur dioxide, resulting in an insufficient amount of chlorine being recovered, as detailed below. As such, an external supply of chlorine is required.

Another important consideration is that the amount of chlorine that reacts with the sulfur dioxide must be limited to an amount that produces just enough sulfate ions to combine with the sodium ions introduced into the reaction medium along with the sodium chlorate.

In addition to these many constraints on the chlorine dioxide production reaction, there are constraints on the reaction of chlorine with sulfur dioxide to provide hydrochloric acid and sulfuric acid that must be kept in mind when producing chlorine dioxide in a stable state. It is as follows.

(1) Produce just enough sulfate ions to correspond to the amount of sodium ions introduced into the reaction medium.

(11) Less than all of the chlorine and sulfur dioxide produced in the chlorine dioxide production reaction (to deal with the excess amount of hydrogen ions and chlorine ions that are reacted and provided to others).

(m) Providing the necessary amounts of acid and chloride to replace the amount of chlorine lost to the chlorine dioxide solution.

[0110] Correcting the incorrect hydrogen ion/chloride ion molar ratio to provide the required amount in the feedstock fed to the chlorine dioxide production reaction medium at normal efficiency.

In order to provide a chlorine dioxide production system in which chlorine obtained in the chlorine dioxide production reaction reacts with sulfur dioxide, the product of the reaction is supplied to the production reaction, and the reaction proceeds in a stable state during that time. , there are a number of conditions that must be balanced in normal chlorine dioxide production efficiency.

Due to the number of constraints mentioned above, the choice of conditions to achieve proper adjustment of the feedstock is very limited.

If the conditions are not chosen as detailed below, the system will be unbalanced and the reaction will be unstable and will not produce the desired results.

≠The reaction of chlorine obtained in the chlorine dioxide production reaction with sulfur dioxide is used to produce just enough sulfate ions to correspond to the amount of sodium ions introduced with sodium chlorate, resulting in neutral sodium sulfate. is manufactured.

As mentioned above, the amount of sodium ions introduced with sodium chlorate is 1 mole per mole of chlorine dioxide, and therefore the required E1 amount of sulfate ions is 1 mole/1 mole of chlorine dioxide. be.

2E As can be seen from equation (3), the sulfate ion is exactly 1 If one mole is produced, this reaction will produce the following molar amount 2E Hydrogen ions and chloride ions are generated.

Judging from the aforementioned hydrogen and chloride ion requirements, in addition to the amount obtained by the reaction of sulfur dioxide with chlorine, additional amounts are required to meet the desired requirements of these ions to be supplied to the chlorine dioxide producing reaction medium. The following amounts of hydrogen ions and chloride ions must be replenished.

Thus, the replenishment amounts of hydrogen ions and chloride ions are the same, and according to one embodiment of the present invention, the hydrogen ions and chloride ions to be replenished provide 1 mole of hydrogen ions for each mole of chloride ions. Provided by brine hydrogen or hydrochloric acid.

A preferred aspect of this embodiment is that the hydrogen chloride or hydrochloric acid used for replenishing raw materials is produced by reacting hydrogen with a further part of the chlorine produced in the chlorine dioxide production equipment, and the required amount of hydrogen chloride is This is what we can provide.

The total amount of chlorine reacted with sulfur dioxide and hydrogen ions according to a preferred embodiment of the invention is as follows.

? However, 6-5E produced in the chlorine dioxide production reaction The amount of chlorine is mol/1 mol CIO2 Ru.

The amount of chlorine produced is therefore always in excess of the required amount of chlorine by 1 -E moles/1 mole CIO2, except in extreme cases where the efficiency is 100%.

2E However, as mentioned above, about 20-40% of the chlorine produced
% is dissolved in chlorine dioxide solution during chlorine dioxide recovery,
1-E does not participate in reactions with sulfur dioxide or hydrogen.

Therefore, if this amount of loss exceeds 1 mol/12E mol C102, it is necessary to supply chlorine from the outside to compensate for the loss.

Since chlorine dioxide and chlorine typically cannot be separated substantially completely, preferred embodiments of the invention typically require an external source of chlorine.

For this purpose, hydrogen chloride or hydrochloric acid may be mixed with the reaction product of sulfur dioxide and chlorine before being fed to the chlorine dioxide production medium, or these substances may be fed separately to the reaction medium.

A second method of such adjustment means may be to use sodium chloride as a solid or aqueous solution to replenish chloride ions.

1 mole of Na for each mole of chloride ion} Since the IJium ion is introduced into the reaction medium, it is necessary to supply enough sulfate ion to produce sodium sulfate from the sodium ion introduced with this sodium chloride. .

The hydrogen ion concentration also needs to be adjusted appropriately; in this case both hydrogen ions and sulfate ions are provided by externally supplied WFa.

In this second method, this external Sodium chloride and sulfuric acid, supplied from , are used in a molar ratio of 2:1.

This external feed may be fed to the reaction product of sulfur dioxide and chlorine before being fed to the chlorine dioxide production reaction medium.

Alternatively, only one of the external feeds may be added to the reaction product of sulfur dioxide and chlorine before being fed to the chlorine dioxide production medium, and the other feed may be added directly to the reaction medium.

Each of the feeds to the reaction medium may also be fed separately.

In a third method, part of the required hydrogen and chloride ions may be provided by hydrogen chloride or hydrochloric acid, and the remainder by a mixture of sodium chloride and sulfuric acid.

These three methods are the only possible ways to keep the reaction stable.

Other substitutions result in unbalanced reactions.

For example, in the second method described above, if the additional requirement for sulfate ions were to be provided by the reaction of sulfur dioxide and chlorine, this reaction would also produce chloride ions, thereby adjusting the sodium chloride replenishment amount appropriately. As a result, the amount of Na}IJium ions decreases,
As a result, the amount of sulfate ions becomes excessive than the required amount, resulting in failure.

Therefore, the key point of the present invention is that sodium ions and neutral sodium sulfate (Na2SO4) are fed into the chlorine dioxide production reaction medium along with sodium chlorate.
by reacting just enough chlorine with sulfur dioxide to produce an amount of sulfate ions and providing equimolar amounts of hydrogen and chloride ions to the reaction product of sulfur dioxide and chlorine to produce these ions. These equal supplementary amounts of ions may be supplied by hydrogen chloride or by a mixture of 2 moles of sodium chloride and 1 mole of sulfuric acid.

As mentioned above, the reaction between sulfur dioxide and chlorine is an exothermic reaction, and according to one embodiment of the present invention, the heat generated in this exothermic reaction exceeds the heat required to maintain the chlorine dioxide production reaction medium at the boiling point temperature. Used to provide at least two parts.

This is accomplished by providing a reactor in which the sulfur dioxide and chlorine react and exchange heat with the reaction medium.

If the heat generated by the exothermic reaction of chlorine and sulfur dioxide is insufficient to provide the heat demand of the chlorine dioxide production reaction medium, a make-up amount of heat to meet the overall heat demand will be used in the production From the heat of the steam from the ejector used to keep the equipment below atmospheric pressure, or from the heat generated during dilution when the acid produced by the reaction of sulfur dioxide with chlorine is added to the reaction medium. , or from the heat of reaction between hydrogen and chlorine.

Therefore, the present invention provides a continuous chlorine dioxide production system in which the reaction between sulfur dioxide and chlorine is integrated and proceeds continuously in a stable state.

Effects of the Invention An advantage of the process of the invention is that by using the reaction of chlorine with sulfur dioxide and water, continuous production of chlorine dioxide is possible.

The present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 shows a chlorine dioxide production system 10 having a chlorine dioxide production device 12. As shown in FIG.

The chlorine dioxide generator 12 contains a chlorine dioxide production reaction medium containing sodium ions, chloride ions, chlorate ions, sulfate ions, and hydrogen ions.

The vessel is kept under reduced pressure and the reaction medium is kept at its boiling point.

Temperature and pressure can vary over a wide range, but are usually 25-90°C.
0 to 400 mm mercury absolute pressure.

The boiling temperature of the reaction medium evaporates the water and the vapor dilutes the chlorine dioxide and chlorine produced from the reaction medium.

The resulting gaseous mixture is removed from the reaction zone by line 14.

When the reaction medium becomes saturated with sodium sulfate, anhydrous, neutral sodium sulfate precipitates from the reaction medium.

Typically, the chlorine dioxide generator 12 uses sodium chlorate, . Operated substantially continuously by replenishing an aqueous solution containing sodium chloride, chlorine and sulfuric acid in line 16, the replenishment of liquid and the amount of liquid and vapor are maintained such that the amount of liquid in maker 12 is substantially constant. The amount taken out is maintained in a well-balanced manner.

The precipitated sodium sulfate, along with some spent drug in the reaction medium, is passed through line 18 to maker 12 as a slurry.
taken from.

The withdrawn slurry is sent in part by line 19 to separator 20 where the crystalline sodium sulfate is separated from the mother liquor and by line 22 to a part of the product of system 10.
The pulp is recovered and utilized in the pulp mill as shown in detail in Figure 2.

The remaining slurry in line 18 is recycled to maker 12 as described in more detail below.

The mother liquor after separating the solids in the separator 20 is sent to the line 2.
After addition of an aqueous solution of sodium chlorate and sodium chloride in an amount sufficient to replenish the amount consumed in the manufacturer 12 by line 28, the slurry is combined with the remaining slurry in 1 and sent by line 24. It is sent to a heat exchanger 30 with a reactor 32 installed in the system.

Heat exchanger 30 and reactor 32 are comprised of the shell and tube sides of a conventional heat exchanger or other suitable device.

The heated solution from the heat exchanger 30 is sent by line 34 to a reheater 36 which provides the heat needed to increase the temperature of the aqueous solution in line 34 to the temperature required in the manufacturer 12. Ru.

The reheater may be omitted if sufficient heat can be obtained elsewhere to provide the recycled feedstock at the desired temperature.

The solution is then sent via line 38 and a mixture of hydrochloric acid and hydrochloric acid is added via line 42, followed by line 40.
If necessary, hydrochloric acid is added via line 44, and finally, via line 16, the maker 12
The circulatory system is completed by sending the

The heat of dilution of the acid in lines 42 and 44 further increases the heat capacity of the feed solution in line 16.

The gaseous mixture of chlorine dioxide, chlorine and steam in line 14, after optionally condensing some of the steam, is sent to a chlorine dioxide absorption tower 46, where water is supplied by line 48 and an aqueous solution of chlorine dioxide is supplied. is formed and is removed from absorber column 46 by line 50.

Some of the chlorine present in the gaseous mixture in line 14 dissolves into the chlorine dioxide solution during the absorption procedure.

The concentration of dissolved chlorine present in the chlorine dioxide solution is reduced by stripping the chlorine from the aqueous chlorine dioxide solution in line 50 by air supplied to a chlorine stripper 54 by line 52.

The aqueous chlorine dioxide solution resulting from the stripping operation is recovered as product of system 10 via line 56.

The mixture of air and chlorine obtained by the stripping is sent by line 58 to absorption column 46 along with some chlorine dioxide incidentally included in the stripping operation of the aqueous solution in line 50.

The gaseous chlorine obtained by the separation of chlorine dioxide in absorption column 46 is sent by line 62 to the effluent along with air from line 64.

The gaseous raw material supplied to the ejector 60 is the producer 12
is used to keep it under vacuum.

Steam is supplied by line 66 to ejector 60 and with the chlorine in line 62 forms a gaseous mixture of chlorine, steam and air in line 68.

This mixture is sent to reactor 32 by line 70.

Additional chlorine gas is introduced into line 70 by line 72 to replenish the chlorine feedstock sent to reactor 32.

Sulfur dioxide is also fed to reactor 32 by line γ3 and reacts with chlorine and steam to provide a mixture of sulfuric acid, hydrochloric acid, air and steam.

The reaction of sulfur dioxide and chlorine is an exothermic reaction, and the heat generated heats the solution passing through heat exchanger 30 and provides at least a portion of the heat demand of producer 12.

The mixture of gas and liquid phases produced in reactor 32 is sent by line 74 to phase separator 75 where the liquid phases of sulfuric acid and hydrochloric acid are separated and circulated at high temperature in line 38 by lines 76 and 42. Introduced into the manufacturer feedstock liquid.

Additional amounts of sulfuric acid may be added to the acid solution in line 76 via line 78.

The gas phase consisting of water vapor, hydrogen chloride and air obtained by the phase separation operation is sent from phase separator 75 via line 80 to absorber 82, to which cooling water is supplied via line 84.

Cooling of the gas phase condenses the water vapor, absorption of hydrogen chloride produces hydrochloric acid, and air is discharged via line 86.

The hydrochloric acid produced by the absorption of hydrogen chloride in absorber 82 is then sent by lines 88 and 44 to the hot aqueous solution in line 40.

Additional hydrochloric acid may be introduced into line 44 via line 90.

Alternatively, hydrochloric acid in line 88 can be added to line 76 or line 4.
line 38 as a single acid supply line.
may be supplied to a high temperature aqueous solution, and the replenishment line 90
The hydrochloric acid may be fed to the mixed stream or to the hydrochloric acid stream prior to mixing.

Additionally or alternatively, the mixed acid stream in line 76 may be combined with the hydrochloric acid stream in line 88 or line 44 and added to the hot circulating manufacturer feed liquid in line 40 as a single acid stream. Also good.

The make-up amount of sulfuric acid in line 78 may be supplied either before or after combination with the hydrochloric acid.

As mentioned above, the production of the chlorine dioxide solution in the line 56 from the sodium chlorate raw material in the line 28 is normally performed at an efficiency of 100% or less due to the competitive reaction of the formula (2), and the chlorine produced in the production unit 12 is Some of this is contained in the chlorine dioxide solution in line 56 and removed from the system.

In order to correct these inefficiencies and imbalances in FIG. The amounts of hydrogen ions and chloride ions in line 16 are adjusted to provide efficient conversion of chlorate to chlorine dioxide and effective separation of chlorine from chlorine dioxide.

That is, an additional amount of chlorine is provided by line 72 to replace the chlorine lost to the chlorine dioxide solution in line 56, and the reaction of chlorine with sulfur dioxide in reactor 32 provides the required amount of hydrogen ions; Hydrogen ions are supplied to the producer 12 by lines 42 and 44.

In this embodiment, the concentration of chloride ions is increased to the desired level by supplying an additional amount of sodium chloride via line 28, thus decreasing the H+:C1- molar ratio.

Or the hydrogen ion concentration is . line 7 instead of the acid produced by replenishing chlorine through line 72.
It may be replenished to a predetermined level by supplying sulfuric acid via line 72 or by supplying a portion with chlorine via line 72 and a portion with sulfuric acid via line 78.

The additional requirement for chloride ions is provided by adding additional sodium chloride via line 28 as previously described.

A further source of hydrogen and chloride ions may be hydrochloric acid supplied by line 90, with additional chloride ions supplemented by sodium chloride supplied from line 28.

Additionally, in this procedure, chlorine may be supplied via line 72 to increase the hydrogen ion concentration, and hydrogen ions and chloride ions may be replenished by hydrochloric acid in line 90.

When compared to the method of replenishing sulfuric acid described above, line 22
The amount of sodium sulfate recovered is reduced.

Given that the amount of chlorine lost to the chlorine dioxide solution in line 56 is negligible, the amount of chlorine ion supplementation provided solely by the sodium chloride in line 28 is only the amount needed to correct the efficiency of the chlorine dioxide manufacturing process. should be taken into consideration.

Instead of using reactor 32 in heat exchange relationship with recycle stream 26, the reaction between the sulfur dioxide supplied by line 73 and the chlorine supplied by line 70 can be carried out using a suitable reactor installed in the line of feed to the manufacturer. It may be carried out in a suitable device.

This latter feed line is designed so that substantially complete reaction between the chlorine, sulfur dioxide and water vapor occurs before feeding the reaction products to the chlorine dioxide generator.

The raw material line is placed in heat exchange relationship with the mother liquor of the maker so that the heat of reaction is provided to the mother liquor of the maker.

Other suitable methods may be used to effect heat exchange between the reaction vessel in which sulfur dioxide reacts with chlorine and the chlorine dioxide production reaction medium.

FIG. 2 is a system diagram of a kraft pulp mill system using the chlorine dioxide production system 10 of FIG. 1.

Wood chips or other cellulosic fibrous materials are line 110
is fed to a digester 112 where the wood chips are digested in a pulping liquor containing sodium sulfide and sodium hydroxide as active pulping agents supplied by line 114.

The resulting pulp and spent pulping liquor, known as "black liquor," are separated and the pulp is washed through a brown stock washer with water supplied by line 118.
The pulp is washed in 116 to remove black liquor from the pulp.

The wash water used in line 118 may be fresh water or "dirty condensate".

The washed unbleached pulp is sent by line 120 to a bleaching plant 122 where the pulp is subjected to a series of bleaching and refining steps.

Bleaching and purification steps generally consist of bleaching with chlorine, chlorine dioxide or mixtures thereof.

Chlorine dioxide is supplied to the chlorine dioxide production system 10 via line 56.
Supplied as a solution and chlorine (if used)
Supplied by line 124.

The purification step is generally performed by caustic extraction using an aqueous sodium hydroxide solution supplied by line 126.

Bleaching plant 122 may employ a series of consecutive steps to achieve the desired pulp refining and bleaching.

For example, the so-called CEDED,. The procedure C/DEDED or DEDED may be used, where C indicates bleaching with chlorine, C/D indicates bleaching with a mixture of chlorine and chlorine dioxide, D indicates bleaching with chlorine dioxide, and E indicates bleaching with chlorine dioxide. The caustic extraction process is shown.

Chlorine is not required in the DEDED procedure, so supply line 124 can be omitted.

The pulp is normally washed by water supplied by line 128 after each bleaching or caustic extraction operation during bleach plant operation.

The washing operation is carried out in the bleach plant 122 by countercurrent flow of pulp and wash water.

Bleached and refined pulp having a predetermined whiteness is recovered from the bleaching plant 122 by line 130 and may be sold as is or further processed to make paper or other pulp products.

The sodium hydroxide solution supplied to the bleach plant 122 by line 126 and the chlorine supplied by line 124 may be produced in a causticizing-chlorine vessel 132 where the sodium hydroxide solution supplied by line 134 is electrolyzed. to produce sodium hydroxide and chlorine.

Of the chlorine produced in vessel 132, bleach plant 122
The portion not needed is recovered via line 136 and used for various purposes.

For example, chlorine in line 136 may be used to provide all or a portion of the chlorine needed as make-up chlorine in line 72.

Alternatively, some or all of the chlorine may be used to react with hydrogen to provide hydrochloric acid that, after being dissolved in water, is used as a make-up hydrochloric acid supplied by line 90.

In this embodiment, the hydrogen that reacts with the chlorine is in line 28.
as a by-product of the electrolysis of sodium chloride solution to provide sodium chlorate solution.

Brown stock washer - 116 to line 1
The black liquor removed by 38 contains the spent wash water with which the pulp was washed and is passed to the evaporator 14 before being sent by lines 142 and 144 to a furnace 146 of suitable construction.
Evaporated at 0.

The water recovered from the evaporator 140 by line 148 is at least a portion of the water needed by the system, such as at least a portion of the water supplied to the bleach plant 122 in line 128 after appropriate washing if necessary. used to provide some.

Sodium sulfate is added to the black liquor, either directly or indirectly as a solid or as a slurry or aqueous solution, and is typically added from the chlorine dioxide production system 10 by line 22 to the concentrated black liquor in line 142.

The aforementioned sodium sulfate is used to replenish sodium and sulfur values lost from the system during chemical recovery and regeneration steps.

The black liquor is combusted in furnace 146 to remove organic matter and form a smelt containing primarily sodium sulfide and sodium carbonate.

The smelt is dissolved in water in the smelt dissolver 152, generally in line 1.
Calcium carbonate mud supplied by 54 is dissolved in the wash water after washing to produce green liquor in line 156.

After removing the grounds, the green liquor is sent to a causticizer 158 of conventional construction, where the sodium carbonate content in the green liquor is removed from the lime cauldron 162.
Most of the slaked lime supplied by line 160 is converted to sodium hydroxide.

Precipitated calcium carbonate from the resulting white liquor is separated and washed (not shown) to remove the white liquor before being returned to the lime kettle 162 by line 164.

The aqueous solution obtained by this washing is referred to as the "weak wash water" and is supplied to the smelt dissolver 152 by line 154, as previously described, and is used to provide at least 1 fB of water to form the green liquor. Ru.

The white liquor from the causticizing step in line 166 is circulated to provide at least a portion of the pulping liquor in line 114, supplemented by additional pulping liquor in line 168 as needed.

EXAMPLE 15 A chlorine dioxide generator was operated continuously according to the technique described in Canadian Patent No. 826,577 at about 70 DEG C. and the boiling point of the reaction medium under reduced pressure.

The total acid normality of the reaction medium was approximately 3 normal and neutral sodium sulfate precipitated from the reaction medium.

An aqueous solution of sodium chlorate containing sodium chloride was fed to the generator along with an acid feed stream produced as described below.

Chlorine dioxide production efficiency per supplied chlorate is approximately 92%
(E=0.92).

The chlorine dioxide and chlorine were removed from the generator as a mixture of evaporated water and contacted with the water to dissolve all of the chlorine dioxide and some of the chlorine in the water.

The remaining chlorine was reacted with sulfur dioxide in the presence of water to form an acid mixture of sulfuric acid and hydrochloric acid containing 0.54 moles of sulfate per mole of chlorine dioxide.

The resulting acid mixture also contained 2.16 moles of hydrogen ions and 1.18 moles of chloride ions.

0.36 mol of hydrochloric acid was added to this acid mixture to obtain a mixture containing chlorine dioxide per mol of produced chlorine dioxide.

This mixture was fed to the generator and at the same time 1.09 mol of sodium chlorate was also fed.

The supply amount of the above-mentioned ionic species is the required amount necessary to continuously produce chlorine oxide and chlorine with the above-mentioned efficiency.

Embodiments of the invention are as follows.

1. A patent claim consisting of reacting with sulfur dioxide and water just enough chlorine to produce an amount of sulfate ions equal to half the molar amount of sodium ions introduced in the form of sodium chlorate into the reaction medium The method described in the scope of.

[Brief explanation of the drawing]

FIGS. 1 and 2 are process diagrams showing one embodiment of the continuous production method of chlorine dioxide of the present invention.

Claims (1)

[Claims] 1. The acidic aqueous reaction is carried out by applying reduced pressure to an acidic aqueous reaction medium containing hydrogen ions, chlorate ions, chloride ions, sodium ions, and sulfate ions and having an overall acidic normality of 2.0 to 4.8 normal. maintaining the medium at its boiling point to precipitate neutral sodium sulfate from said reaction medium, removing from said reaction medium a gaseous mixture containing chlorine dioxide, chlorine and water vapor, and removing chlorine dioxide from said gaseous mixture. In a continuous process for the production of chlorine dioxide and chlorine by reduction of sodium chlorate by chloride ions in said acidic aqueous reaction medium, which comprises dissolving all of the chlorine and two parts of the chlorine in said chlorine dioxide solution. Hydrogen chloride and sulfuric acid are produced by reacting chlorine, including chlorine in the gaseous mixture that does not dissolve in the gas, with sulfur dioxide and water, and the hydrogen chloride and sulfuric acid thus produced are fed to the medium to produce hydrogen ions and chlorine. The reaction medium is supplemented with both hydrogen ions and chloride ions in the form of hydrogen chloride or hydrochloric acid or sodium chloride and sulfuric acid in a 2:1 molar ratio. in the form of a mixture of sodium and sulfuric acid in a 2:1 molar ratio and hydrogen chloride or hydrochloric acid to bring sodium ions and sulfate ions into a stoichiometric ratio approximately corresponding to the formation of neutral sodium sulfate, and A continuous process for the production of chlorine dioxide, characterized in that sufficient hydrogen and chloride ions are added to meet all requirements for these ion feeds.