JPS62223006A - Method and apparatus for manufacturing sodium hydrosulfite - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] This invention relates to an improved method and apparatus for producing sodium hydrosulfite.

PRIOR ART AND PROBLEM SOLVED BY THE INVENTION Sodium hydrosulfite NazStOa, also known as sodium dithionite, is widely used as a bleaching agent in the paper and textile industries and is also used in a wide range of other Because it is relatively unstable, it is generally manufactured in situ, for example in a pulp mill, just before use.

Conventionally used methods for producing sodium hydrosulfite include dissolving zinc in a solution of sodium bisulfite and precipitating the sodium zinc sulfite with milk of lime, leaving the hydrosulfite in solution; , involving reacting sodium formate with sodium hydroxide and sulfur dioxide.

More recently, the applicants of the present application have developed a method for preparing an aqueous solution of sodium hydrosulfite by mixing sodium hydroxide and sulfur dioxide with sodium borohydride in an aqueous medium. Sodium borohydride is generally used in this process as a mixture with an aqueous sodium hydroxide solution. This mixture, available from the Ventr, on division of Morton Thiocol Incorporated under the trade mark BOROL, is a product of the acid hydrolysis of sodium borohydride.
It has good stability since hydrolysis is prevented. For convenience, this type of method will hereinafter be referred to as the Bolor method.

The theoretical reaction of the Bolor method is as follows, assuming ideal conditions and 100% yield.

NaO+4+8Na011+8SOz-1→4NatSzOa+NaBO=+6tlzO However, there is a side reaction in which the sodium borohydride is hydrolyzed, thus reducing the overall efficiency of the reaction.

NaBH4+ 2HzO--Nini → NaBOz + 4
11z ↑This reaction is a function of pl+, and pl+
increases as the value decreases. However, this problem cannot be overcome simply by raising pl+, since raising pl+ has an opposite effect on the main reaction. The reaction actually occurs in two steps as follows:
a> Reaction between sulfur dioxide and sodium hydroxide to yield sodium bisulfite (1), (b) Reaction between sodium bisulfite and sodium borohydride to yield sodium hydrosulfite (II).

(E) 8NaOH+ 8SOz
8NallSO3(n) 8NaH5Oz + Na
BIla −→4NazSzOn + NaBOz
+ 61120 There is also an equilibrium (I[I) relationship between the bisulfite and sodium sulfite, which is a function of pl+.

Here it is! :;■? White (II a) 1lzO+ 1ISOz--11 Nini 1--- ■, 0 meeting + sot"-Kt = 1.02x
lO-' (18℃)K, = 1.54X10-"
(18°C) p) Above I=7, the bisulfite concentration is inversely proportional to the pH. Below pH=2, the bisulfite concentration is directly proportional to pH. This style of method is generally p
H is carried out in the range of 5 to 7, and in this pH range lowering the pH favors the formation of bisulfite.

Therefore, to determine the optimum pH for this process, this equilibrium issue must be considered in light of the acid hydrolysis issues discussed above. In conventionally used methods, a pH of 6.5 has been found to give the best yields. Nevertheless, it has proven difficult to achieve yields higher than 85%.

In the borole process used so far, S02, water, sodium hydroxide, and a sodium borohydride/sodium hydroxide/water mixture (borole) are fed into a flow line in that order. This flow line leads to a static mixer and then to a degassing tank which discharges the entrained gas to the atmosphere. An aqueous solution of sodium hydrosulfite is pumped from the degassing tank, a portion of which is delivered to a storage tank for use when needed, and the remainder is added to the SO, water, and N a Otl inlets. Recirculation is provided to the flow line downstream and upstream of the inlet of the boron. The input amount of each reactant can be automatically controlled in response to the upper or lower limit of the liquid level in the degassing tank or storage tank, or to changes in pressure, flow rate, and/or pH.

Applicants of the present application have attempted to improve the yield of the above process by varying the proportions of chemicals and the measurement and control of pH, as well as by alternative methods of addition.
1 Margin [Means and Effects for Solving the Problem] According to one aspect of the present invention, by feeding the reactants into a constantly circulating reaction mixture from which sodium hydrosulfite is withdrawn, The feature of the method for producing sodium hydrosulfite by reacting a mixture of borohydride].lium/sodium hydroxide/water with sulfur dioxide and sodium hydroxide and/or sodium bisulfite in an aqueous solution is that the sodium hydrosulfite is The recycled IO reaction mixture is divided into two streams downstream of the point where it is withdrawn and upstream of the point where the reactants enter the system. One of these streams is fed with a reactant other than the sodium borohydride mixture, which stream is then recombined with the other stream to form a single stream, and the single stream is supplied with a reactant other than the sodium borohydride mixture. Sodium boronate/
Add sodium hydroxide/water mixture.

Reactants other than the sodium borohydride mixture are preferably fed to the system as sodium hydroxide, sulfur dioxide, and water, but are generally formed by prereacting a sulfur dioxide/water mixture with sodium hydroxide. A variety of reactants could be used, including sodium bisulfite.

According to another aspect of the invention, a process in the above manner provides that sulfur dioxide is fed into the system rather than upstream of the point at which sodium hydroxide is introduced into the system, as in previously used processes. It is characterized by being supplied to the system at a downstream location. Preferably, the SO□ is mixed with water before being fed to the reactant stream containing sodium hydroxide.

Applicants have discovered that the yield in a process in the general manner described above can be improved by any or all of the following: 1) increasing the pH range to 5.5;
6.5, preferably 5.7 to 6.2; 1i) carrying out the reaction at a temperature lower than 12°C; iii)
) Adjusting the concentration of the reactants so that the concentration of hydrosulfite at the point of withdrawal is between 9 and 12% by weight. Concentrations higher than this range can lead to crystallization of the hydrosulfite during storage.

According to a preferred feature of the invention, the reactants are placed at suitable locations in the center of the reactant streams such that each reactant joins the other reactant streams at a generally prevailing flow rate to reduce turbulence. The reactant stream is fed through a nozzle positioned and aligned in the direction of flow. The improved kinetic mixing thus obtained prevents or reduces sudden changes in the pH of the reaction mixture.

In the process of the invention, when sodium hydroxide and sulfur dioxide are fed into the system, the reaction N) is as outlined above.
occurs, producing a mixture of sodium bisulfite and sulfur dioxide. The SO□ depth of this mixture is preferably 9
5~120g/j! , more preferably 100-115
g/Il. Bisulfite (bisu) in the mixture
The ratio of lfite) /SO□ is preferably l :
It ranges from 1.20 to L: 1.50, most preferably about 171.35. Alternatively, an aqueous mixture of sulfur dioxide and sodium bisulfite could be fed to the system, for example one of the solutions disclosed in EP-A-0202210.

The reaction mixture should typically be kept at a pressure of at least 300 kPa to keep the SOW liquid. The preferred pressure range is 300-350 kPa, but higher pressures could be used.

The preferred reaction temperature is below 12°C, more preferably between 7 and 10°C. At such relatively low temperatures, the loss of Na[lHn due to acid hydrolysis is substantially reduced;
It was discovered that. One possibility is that the lower temperature simply reduces the kinetic rate for hydrolysis of sodium borohydride. Whatever the actual mechanism, this reduction in hydrolysis in turn occurs at a slightly lower pH than in conventionally used methods, e.g. between 5.5 and 6.0 (II). make it possible to do This favors bisulfite in equilibrium (III) and thus increases the yield of the sodium bisulfite/sodium borohydride reaction (11).

Another possibility is that under these temperature and pressure conditions at least a portion of the sulfur dioxide is converted to the hexahydrate SO□.61
hOO form, which can to some extent suppress the direct contact between the strong acid free SO2 and the NaB114 it encounters further downstream, thus reducing the acid hydrolysis of NaBH4.

The sodium borohydride/sodium hydroxide/water mixture used in the process of the invention preferably contains 10-15 wt.% NaB, 4.35-45 wt.% Na0Hs and 40-60 wt.% water. It becomes. The Borol™ mixture of Morton's thiochol incorphoratide comprises 12% NaBIIa, 40% NaOH1 and 48% water.

According to another aspect of the invention, it comprises a static mixer with cooling means, a degassing tank downstream of the static mixer, a circulation pump, and a recirculation loop comprising a withdrawal point for sodium hydrosulphite. An apparatus for producing sodium hydrosulfite, wherein the recirculation loop is divided into first and second flow lines downstream of the withdrawal point, the first flow line containing water, carbon dioxide, There are one or more input points for sulfur and sodium hydroxide or sodium bisulfite or various mixtures thereof, and a second flow line is connected again with the first flow line downstream of said input points. A companion device is provided.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings.

Referring first to FIG. 1 to describe the prior art method described above, liquid sulfur dioxide from tank 10, supply line 14
, sodium hydroxide from storage tank 15 , and a sodium borohydride/sodium hydroxide/water mixture (hereinafter referred to as Borol™) from storage tank 16 are fed to flow line 12 . When thorium hydroxide joins flow line 12, reaction (1) described above occurs and sodium bisulfite is produced. Further downstream, when the borole mixture joins the system, a reaction (IT) begins to occur to form sodium hydrosulfite.

The reaction mixture is sent to a static mixer 18 and then to a degassing tank 19 where gaseous products, such as hydrogen, are vented from the system to the atmosphere through a vent tube 20.

Connected to the bottom of the degassing tank 19 is a flow line 22 through which the sodium hydrosulphite solution from the degassing tank is circulated by a pump 24. This flow line is connected to a first line 2 downstream of the pump.
6 and a second line 32, the first line 26 leading to a sodium hydrosulfite storage tank 28 and the second line 32 supplying a portion of the sodium hydrosulfite solution to the sodium hydroxide solution. It is recycled into the flow line 12 downstream of the input point and upstream of the Volol® input point. A small portion of the solution is withdrawn from flow line 32 along flow line 30 and recycled directly to degassing tank 19 .

The bulk plant or the like is supplied with thorium hydrosulphite solution directly from the storage tank 28. While the sodium hydrosulfite solution is being withdrawn from this tank, a level transmitter ('LT) 34 detects a drop in the level and sends an electrical signal to a level indicating controller (LIC) 36, which in turn The surface indicating controller 36 is the flow rate indicating controller (FIC) 3
7, this flow indicating controller 37 in turn activates a current/pressure converter (1/P converter), which in turn operates a pressure valve.
40 to increase water flow into the system.

The flow rate of water passing through the supply pipe 14 is measured by an electromagnetic fL meter (MM) 4.
2, and this electromagnetic current meter 42 is detected by FIC37
to regulate the flow rate, and also send a signal to a flow ratio indicating controller (FRIC) 44 which outputs a current/pressure conversion H(1) which actuates a pressure operated valve 48. / p converter) 46 to regulate the supply of Volol™. The flow rate of the borole mixture is detected by an electromagnetic flowmeter 50, which includes a PRIC 44 and a current/pressure converter (1/P converter).
54 and a flow ratio indicating controller (FRIC) 52 that regulates the amount of N a OH input by means of a pressure operated valve 56 . The flow rate of Na01l into the system is also measured using an electromagnetic flowmeter 58.
This electromagnetic flowmeter 58 is monitored by a PRIC52
■Sends the measurement signal back.

The various control functions 36, 37, etc. are shown in FIG. 1 as separate microprocessor functions for simplicity. In reality, of course, all of these functions are performed by a single central processing computer.
ss computer) suitable! ,: fulfilled.

The input to the SO□O system is adjusted as a function of the pH of the re-14-ring reaction mixture. pH of the solution in branch pipe 30
is monitored by a pl+ electrode (pHE) 60, which is a current/pressure transducer (1/P transducer).
64 and a pressure-operated valve 66 to send a signal to a pH indicator controller (pHlc) 62 that regulates the amount of SO□ input.

As previously mentioned, this prior art method generally requires about 6.
Operated at a pH of 5. When the monitored pit becomes higher than a predetermined value, pH1c62 works and S
Increase the flow of O□ and decrease the input of SO2 if the pH decreases as well.

When the liquid level in the degassing tank 19 drops below a predetermined liquid level, the liquid level transmitter 70 activates the liquid level indicator controller 72.
to reduce the flow rate of sodium hydrosulfite through flow line 26 to storage tank 28 through current/pressure converter 3 (1/P converter) 74 and pressure operated valve 76 .

Using a Borol™ solution with the composition specified above and a molar ratio of Na011 to NaBL of 3.2:1, the overall equation for reactions (+) and (II) above is: It will be as follows.

Based on this, assuming an overall reaction efficiency of 85% for the prior art process above, the actual total of each reactant required to produce 1 kg of 100% active sodium hydrosulfite is , is shown as follows.

Borol mixture 0.533kg NaOH0,325kg (based on 100%) S0□
0.865 kg The amount of water depends on the desired concentration of the final sodium hydrosulfite solution. The concentration of the sodium hydrosulfite solution is
It is usually 2 to 6% by weight.

Referring to FIG. 2 of the accompanying drawings, which illustrates a first aspect of the invention, certain features that are essentially identical to those shown in FIG. 1 are designated by the same reference numerals. As in the embodiment of FIG. 1, the sodium hydroxide, water, and sulfur dioxide are mixed to begin the production of sodium bisulfite, then the Volol™ mixture is added, and the reaction mixture is passed through the static mixer 18. , and then sends it to the degassing tank 19. The temperature of the mixture entering the static mixer is preferably about 10°C. The static mixer 18 is equipped with a water cooling jacket 17, which reduces the temperature of the reaction mixture to about 8°C. The flow rate of the sodium sulfite solution from the degassing tank to the storage tank is determined by the liquid level transmitter 70 and the liquid level indicator controller 7.
2, a current/pressure transducer 74, and a pressure operated valve 76. A control valve 89 is also provided, and an electromagnetic flow valve CMFT) 77 is also provided so that the flow rate of sodium hydrosulfite into the storage tank can be monitored.

Hydrosulfite (h) separating from the recirculating stream
The concentration of hydrosulfite is generally between 9 and 1
It is in the range of 2% by weight. By operating the process at this relatively high concentration, yields can be increased, but storage stability is reduced. Therefore, if you are not using sodium hydrosulfite immediately, add 4 to 5 ffiffs of it.
It should be diluted to a concentration of i%. For this purpose, water is supplied through a conduit 170 taken from the main water supply pipe 114. The dilution water supply to the sodium hydrosulfite solution is controlled by a five conductivity regulating microprocessor (C
CD) 173 and current/pressure converter (1/P converter) 1
regulated by valve 171 operated by 72.

Pump 24 for sodium hydrosulfite recirculation flow
In this embodiment, the pH electrode 61 is placed at an appropriate position downstream of the pH electrode 61 which controls the amount of Sow input as described below. Downstream of the pump 24 and the point where the sodium hydrosulfite is withdrawn to a storage tank, the solution is transferred to a heat exchanger 90.
, another control valve 91, and rotameter (RM)
Pass 92. This heat exchanger cools the reaction mixture from about 12°C, which has risen as a result of the exothermic reaction, to about 7°C. The flow line then branches at a point indicated at 80 into a first flow line 82 and a second flow line 84.

The relative proportions of flow through these two flow conduits are:
Adjustment is made by a manual control valve 81 in the flow line 84. Preferably 20 to 60% of the flow rate, typically 40% of the flow rate, passes through the first flow line 82 and 40 to 80% of the flow rate, typically 60% of the flow rate passes through the second flow line 82. It passes through the conduit 84.

Sodium hydroxide from supply tank 115 is supplied to flow line 82 at 100.

The SO□ from the supply tank 110 joins the water supply line 114 at 102, and the resulting mixture is not upstream of the Na0ll input point as in previous Volor processes, but downstream thereof. is supplied to flow line 82 at location 104 . The reaction mixture then passes through a static mixer 98 and proceeds to the main static mixer 18 where the borole mixture from the feed tank 16 is fed to the system.

The second flow line 84 connects two static mixers 9
It rejoins the first flow line 82 at a position 86 between 8 and 18. The flow rate of the recirculated mixture entering the static mixer 18 is monitored by a pressure indicator (PI) 94, which is connected to a pressure indicator controller (CPIC) 95.
This pressure indicating regulator 95 in turn provides a signal to a current/pressure converter (1/P converter) 96 which actuates a pressure operated valve 97 to regulate flow to the static mixer 18.

A portion of Na011 (conveniently 10-50% of the total NaOH flow, preferably 3
5 to 40%) is supplied to the SO2 input line through the bypass line 101. This N a OIf joins this line downstream of location 102 where SO2° joins the water stream. ``The flow rate through the bypass line is regulated by a valve 103, which controls water, Na011. and Sot's monitored flow rate.

Although the sodium hydrosulfite storage tank of FIG. 1 is not shown in FIG. 2, it will be appreciated that the system of FIG. 2 would feed the storage tank in exactly the same manner as in FIG.

The equipment of FIG. 2 (sys tea+) has an automatic control system that operates in a similar manner to the automatic control system of FIG. 1st
An input signal S, which can correspond to the liquid level signal from the storage tank in the figure, is supplied to a flow rate indicating controller CF I C) 137, which in turn is connected to a current/pressure converter (1/P converter). ) 138 to actuate the pressure operated valve 140 in the water supply line 114. The flow rate indicating controller 137 also receives flow rate data from the electromagnetic flow tube (MFT) 142 of the water flow line and transmits the flow rate data to a flow rate ratio indicating controller (1' RIC) 144 to determine the flow rate. A ratio indicating controller 144 controls the supply of borole mixture to the static mixer 18 via a current/pressure transducer (1/P transducer) 146 and a pressure operated valve 148, and a electromagnetic flow tube (MFT) 150.
Monitor the flow rate by

Flow rate data for water and borole mixtures are provided by a flow ratio indicating controller (PRIC) 144 to a flow ratio indicating controller (PRIC) 152 and also by a flow ratio indicating controller (PRIC) and a pH indicating controller (pHIc). It is also transmitted to a composite controller 162 comprising controllers that adjust the sodium hydroxide and sulfur dioxide inputs, respectively. Flow rate ratio indicating controller (PRIC) 15
2 adjusts the input amount of Na011 by a current/pressure converter (1/P converter) 154 and a pressure-operated valve 156;
Na by electromagnetic flow tube (MFT) 15B
Monitor the input amount of OIt. The control device 162
, and also receives pH data from the pH electrode 61, as well as from the micromass meter 160 that monitors the flows of. This flow rate is determined by the current/pressure converter ([/P converter) 16.1
and a pressure operated valve 166.

The signal from controller 162 to current/pressure transducer 164 is preferably determined to a greater extent by flow rate data than by pH data.

The signal is suitably based on flow ratio data to a range of 75-85%, preferably about 80%, and 15-2.
Up to a range of 5%, preferably up to about 20%, is based on pi1 data.

By splitting the recycle stream at 80, a more balanced reactant charge is obtained because there is less volume difference between the recycle stream and the reactants entering it. Extreme dilution of the reactants is also reduced.

The equipment (sys tea+) shown in Fig. 3 is Na01
1. Instead of independently dosing SOx and water, a single aqueous solution of sodium bisulfite and sulfur dioxide is introduced.

In this drawing, components that are identical to those in FIG. 2 are designated with the same reference numerals and will not be described in detail. This equipment consists of cooling type static mixer 1
8. A recirculation system with a degassing tank 19, a pump 24, a withdrawal point and dilution facility for the product, a heat exchanger 90, and a split flow comprising an input line 82 and a bypass line 84. In the range including
This is the same as in 1.

The input pipe 82 is supplied with SO□/ from the supply tank 210.
There is a single input point 204 for the Na11SO3 aqueous solution. The meteor of this solution is the flow rate ratio indicator 1!1 meter (F
RIC)/1) Current/pressure transducer <1 controlled by a control device 262 comprising 11 indicating controllers (pold C)
/P conversion WS) 238 is regulated by a valve 240 actuated by This controller receives and receives signals from the same pH electrode 61 as in the facility of FIG. Flow rate indicating controller (F) that monitors the flow rate of sodium boron solution
It also receives signals from IC) 244. This flow rate indicating controller (FIC) 244 is connected to the electromagnetic flow tube 1.
Since it only receives the flow rate data from 50, it is replaced with the flow rate ratio indication adjustment ;1 (FRIC) 144 in FIG. As in the installation of FIG. 2, the controller 262 preferably controls the sodium bisulfite/S (h solution) based on flow rate data to a range of about 80% and pH data to a range of about 20%. Adjust amount of input.

FIG. 4 shows various reactant injection points 100, 102,
and 104 show the preferred mode of feeding the system according to the present invention. A similar approach can be used to feed into the Borol mixture rather than directly into the static mixer as shown in FIG. The main flow line is indicated at 180 and is NaO
Added components, such as H or SO□/water mixtures, enter the system through 1 ffl nozzle 182, which is appropriately positioned with its end substantially coaxial with the main flow line. The nozzle is such that the flow rate of reactants entering the system is substantially the same as that of the circulating reaction mixture in the main flow line. This means that all of the reactants entering the system at this point are carried along by the circulating reaction mixture without any adhesion to the sides of the flow lines surrounding it. this is,
It helps to ensure that a homogeneous mixture is obtained and that sudden changes in composition and especially pH are avoided.

FIG. 5 is a phase diagram for the sulfur dioxide/water system supplied to the apparatus of the present invention, in which the percentage of SO is plotted against temperature at a pressure of 500 kPa. The method of the invention typically uses 250-300kf
Although it is operated at a slightly lower pressure like 'a,
The relevant parts of this phase diagram are tree-like. It can be seen from this that at the temperatures and concentrations normally used in the process of the invention, a portion of the SO7 is in the above-mentioned hydrate form.

The above-described system provides yields that are substantially improved over those obtained using the previous Bolor method, with 90% yields and even yields of over 95% easily achieved. I found out that it is possible.

Important factors in achieving this include feeding Na011 into the recycle stream upstream of the SO2 input to avoid excessive pH drops, and the These include the dynamic mixing obtained by using a nozzle such as 182 in the figure, the 302/water and sodium bisulfite/SO2 ratios, and relatively low temperatures.

Add a small excess of sodium bisulfite (typically 1
Taking into account the operation of the equipment (0-15% excess), the balance equation (balanced equation H based on 90% yield) can be modified as follows.

Na[1II4+3.2NaOH+2.6NazSzO
s+3.5SOz −-→Based on this formula, 100
The actual amounts of each substance required to produce 1 kg of % active sodium hydrosulfite are: Borol mixture 0.503 kg Na0II (100%) 0.332 kg5
It is revealed that the weight is 0□ 0.889 kg.

There are various ways in which the percentage yield obtained by the method of the invention may be calculated. Three such methods mentioned here are:

``If the relationship between borole solution and bisulfite is quantitative, no hydrogen will be generated.In reality, hydrogenation in borole solution Due to the undesired decomposition (hydrolysis) of the sodium boron, some hydrogen evolution occurs which does not react with the bisulfite.

By measuring the flow rate of hydrogen in comparison with the flow meter of the borole solution, the efficiency of the mono-lithium hydrosulfite production reaction can be calculated.

This yield measurement method is based on the balance equation stoichiometry of the conversion of the reactant feed chemical to the product sodium hydrosulfite.

The actual yield of sodium hydrosulfite is determined by titrating the concentration of sodium hydrosulfite in the product solution. Then, the yield percentage is calculated by the ratio of the sodium hydrosulfite actually produced to the sodium hydrosulfite theoretically produced according to the stoichiometry of the balance equation and the chemical supply amount of the reactants. Li-F
ee Poloru appearance? This yield percentage calculation method calculates the amount of sodium borohydride in the borohydride solution that supplies the reactant chemicals that is actually consumed in the production of the product sodium hydrosulfite. Use boron analysis to

The boron in commercially available borol solutions is predominant in the form of sodium borohydride, although a small amount of boron is also present as sodium metaborate. This latter impurity is determined analytically by first analyzing the borole solution for sodium borohydride concentration and then measuring total boron by atomic absorption or mannitol titration of the hydrolyzed sample. From the difference between these measured values, calculate the ■ value of boron as sodium metaborate.

Next, the product sodium hydrosulfite was converted into boron-containing (T
Let's analyze I. The contribution of boron as metaborate in the reactants of the borole solution is subtracted because it is an impurity, and the remaining boron is used in the hydrogenation process to form sodium hydrosulfite in the stoichiometric balance equation. Attributed to sodium boron. From the titration of the product for actual sodium hydrosulfite and theoretically possible sodium hydrosulfite (based on boron analysis):
Calculate the yield percentage.

The following examples further illustrate the method of the invention.

〔Example〕

The equipment shown in Figure 2 is operated with the fixed process parameters listed below.

Reactant feed pressure (bar) Borol? Liquid content 4.65NaO
H4,58 Sot
5.92 WtN flow rate (m/h):
20 Other operating parameters are varied as shown in the table below and the yield of thorium hydrosulfite is determined using the mass balance method described above.

The equipment shown in FIG.
Run as shown in Example 1, varying the ratios of and borole feed. The yield of sodium hydrosulfite is determined by the mass balance method described above.

It can be seen from the table above that even at the pH values used in the previous Bolor process and its equipment (FIG. 1), greatly improved yields are obtained. At lower values of 9H, such as 5.5 to 6.0, which are preferred for the process of the invention, yields of over 95% are obtained. The optimum pH for this method is believed to be 5.9.

①--Operate the equipment shown in Figure 2 with the following process parameters.

p 11 5.91 Temperature ("C) 9.8 Recycle flow St (n?/h) 12-20 Split flow ratio (percentage of feed stream directed to the side that supplies the chemical) 40 Sodium hydrosulfite The yield is determined by the two methods mentioned above,
That is, it is measured by the total boron method and the mass balance method.

The setup 6iif shown in FIG. 3 is operated with the following process parameters.

Below margin temperature ('C) 1O-11p
H5, 6-5.8 Recirculation flow rate (rrr/h) 25-30 Hydrosulfite concentration (wt%) 12 Three methods mentioned above, namely hydrogen and borol solution flow method, mass balance method, and total boron method Determine the yield of sodium hydrosulfite.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified flowchart illustrating two conventional methods described in the Detailed Description of the Invention section.

FIG. 2 is a flowchart diagrammatically illustrating a method according to the first aspect of the invention.

FIG. 3 is a flowchart diagrammatically illustrating an installation according to a second aspect of the invention.

FIG. 4 is an explanatory diagram of a dynamic mixing nozzle used in the method of the present invention.

FIG. 5 is a water/SO2 phase diagram showing the concentration and conditions under which SO□ forms a hydrate.

In the figure, 18 is a static mixer, 19 is a degassing tank, 24 is a Wi ring pump, 80 is a branch point of circulation flow, 8
2 is a first flow pipe, 84 is a second flow pipe, 86 is a confluence point of circulating flow, 100 and 104 are reactant injection points,
101 is a bypass pipe, 103 is a valve, 114 is a water supply pipe, and 182 is a nozzle.

Claims (1)

[Claims] 1. A method for producing sodium hydrosulfite by reacting sodium borohydride with sodium bisulfite, sodium hydroxide, and sulfur dioxide in an aqueous solution, comprising:
The reactants are fed to a continuously recirculating reaction mixture from which the sodium hydrosulfite solution is withdrawn, and the sodium borohydride is in the form of an aqueous mixture with sodium hydroxide and the other reactants are input. Location (100, 104)
In the production method, the sodium hydrosulfite solution is supplied to the system at a position downstream of the position and upstream of the position from which the sodium hydrosulfite solution is extracted, and a position where the reactant is introduced and downstream from the position from which the sodium hydrosulfite solution is extracted. splitting said recycled reaction mixture into a first stream (82) and a second stream (84) at a point (80) upstream of said sodium borohydride aqueous solution into said first stream (82). A reactant other than the mixture is supplied, and then the first and second reactants are supplied.
(86) to form a single stream and supplying said sodium borohydride mixture to said single stream. 2. Sodium hydroxide is supplied to the first stream (82), and at least a portion thereof is introduced into the first stream at a position (100) upstream of the input point of other reactants. , the method according to claim 1. 3. Water supply pipe (11) leading to the first flow (82)
4) and a location (104) upstream of the location (104) at which the sulfur dioxide/water mixture enters the system.
100), supplying a portion of the sodium hydroxide to the first stream (82) and supplying the remainder to the water supply line (114) to mix with the sulfur dioxide/water mixture. The method according to claim 1 or 2, wherein: 4. The above reaction for producing sodium hydrosulfite is carried out in 5.
4. A method according to claim 1, characterized in that it is carried out at a pH in the range from 5 to 6.5. 5. The above reaction for producing sodium hydrosulfite is carried out in 12
5. Process according to claim 1, characterized in that it is carried out at a temperature below 0.degree. 6. Adjust the concentration of the reactants in the circulating reaction mixture to reduce hydrosulfite (hy
6. Process according to claim 1, characterized in that the concentration of drosulfite is between 9 and 12% by weight. 7. feeding said reactants to said reactant stream through a nozzle (182) placed at a suitable location in the center of said reactant stream and aligned with the direction of flow, so that each reactant is generally distributed; 7. A method according to claim 1, characterized in that the flow rate is combined with the flow at a flow rate. 8. Reactants other than the sodium borohydride mixture are fed to the first stream (82) in the form of an aqueous mixture of sodium bisulfite and sulfur dioxide. The method according to any one of paragraphs 7 to 7. 9, static mixer (18), degassing tank (19) downstream of the static mixer, circulation pump (
24) and a recirculation loop comprising a withdrawal point for sodium hydrosulfite, the recirculation loop comprising a first flow downstream of the withdrawal point. Pipeline (8
2) and a second flow conduit (84);
The flow conduit (82) has one or more input points (100, 104) for sodium hydroxide, sulfur dioxide, and water, or mixtures or reaction products thereof; The conduit (84) rejoins said first flow conduit (82) at a location (86) downstream of the input point in said first flow conduit (82) and also connects said first and Said position (86) where the second flow conduits come together again
), an input point for the sodium borohydride/sodium hydroxide/water mixture is provided downstream of the device. 10. Each of the one or more input points (100, 104) of the first flow conduit (82) is positioned at a suitable position in the center of the flow conduit and aligned in the direction of flow; 10. The device of claim 9, comprising a nozzle (182). 11. characterized in that said first flow line (82) has an input point (100) for sodium hydroxide and downstream thereof an input point (104) for a sulfur dioxide/water mixture; The device according to claim 9 or 10, wherein 12. A bypass pipe (101) including a valve (103) is provided to supply a portion of the sodium hydroxide to the water supply pipe (114) leading to the sulfur dioxide injection point (104), and the water supply pipe is provided with a bypass pipe (101) including a valve (103). Claim 11, characterized in that a sulfur dioxide supply line is provided at a position (102) upstream of the point at which the sodium hydroxide is introduced into the water supply line for supplying the sulfur dioxide. The device described.