JPS6020325B2 - Method for producing carbonate soda water salt - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for obtaining sodium carbonate monohydrate from an electrolyte obtained from the cathode chamber of a diaphragm salt water electrolytic cell (hereinafter simply referred to as phlegm electrolyte). The method for producing soda carbonate is as follows: 1) Absorb ammonia in purified brine, react with carbon dioxide gas to form sodium bicarbonate and ammonium chloride, separate the crystallized sodium bicarbonate, and then In the reaction shown in equation 1', the calcination decomposition is aHCQ → Na2C030 CQ 10 days 2
0 '1' obtained as soda ash (light ash), the mother liquor containing ammonium chloride containing bicarbonate of soda is reacted with milk of lime and decomposed into ammonia and calcium chloride solution, and the ammonia is recovered and reused. method (hereinafter simply referred to as method A), or the so-called salt method in which refined solid salt is added to the mother liquor containing ammonium chloride after separation of sodium carbonate, the ammonium chloride is crystallized and separated, and the filtrate is sent to the ammonia absorption process again. There is a cheap soda co-production method. 'U, (2) However, both methods also yield bicarbonate of soda, so to make soda ash, it must be calcined and decomposed using formula 01.Also, the soda ash obtained by neighboring component decomposition has a high density called light ash. It is soda ash with low carbon content, and in order to make dense ash with high bulk density, it is first hydrated and converted to monohydrate as shown in the '21 formula, and then Na2C03 Toka 20 → Na2C03
・Ratio 0

[21Na2C03・Sun 20→N
a2C03 10th 20 It must be calcined and dehydrated as shown in the formula ``3''3'' (hereinafter {21,
The process shown in formula '3 is called the dense ashing process). The disadvantages of these above-mentioned methods are that the A method requires a large amount of energy in the calcination decomposition process and the dense ashing process because it uses bicarbonate of soda, and it also requires an ammonia recovery process, which requires a large amount of lime milk and steam. This is not a preferable method from the standpoint of resource conservation, since all the coexisting chlorine ions are discarded. In addition, the method of co-production of ammonium chloride and soda has a major drawback in that the amount of production depends on the demand for the by-product ammonium chloride. As a method that does not involve bicarbonate of soda, there is a method of reacting caustic soda liquid with carbon dioxide gas to obtain carbonate of soda water salt. In this method, monohydrate is directly obtained, and if it is calcined and dehydrated, it can be obtained as dense ash. However, this method requires a concentrated caustic soda solution in terms of water balance, and when a diaphragm method electrolyte with a relatively dilute caustic soda concentration is used as a raw material for soda ash production, a step of concentrating the electrolyte is necessary. . Therefore, this method also requires a large amount of energy and is not necessarily a preferable method. In addition, bicarbonate of soda is added to a caustic soda solution with a concentration of 40% or more to produce sodium carbonate, and anhydrous soda is added in an amount that can fix all the water produced at that time and the water entrained from the caustic soda solution as crystal water. A method of reacting with a paddle mixer etc. and then burning and dehydrating it as it is to make dense ash (BP97
9378) has been proposed. However, this method still requires a concentrated caustic soda solution, and all impurities contained in the caustic soda solution are entrained in the dense ash. It cannot be used unless it is a caustic soda solution. Furthermore, the growth of monohydrate crystals is also insufficient. Therefore, even if the diaphragm electrolyte is used as it is in this method, a large amount of salt and other impurities contained in the diaphragm electrolyte will be completely entrained in the dense ash, resulting in a high-quality product. I can think of things that I can't do. As described above, it has been extremely difficult to use the diaphragm electrolyte as it is as a raw material for soda carbonate without concentrating and purifying it. To carbonate the diaphragm electrolyte without concentrating it, the diaphragm electrolyte is reacted with carbon dioxide gas and separated as sodium bicarbonate.The mother liquor is then dissolved in the raw material salt, further purified, and then subjected to diaphragm electrolysis. A method is disclosed (Japanese Patent Publication No. 51-30879). In this method, since bicarbonate of soda is obtained, a step of decomposition of neighboring components is required, and a step of dense ashing is required to obtain dense ash. Also, a method has been disclosed in which the electrolyte of the diaphragm method is mixed and combined with the process solution of the A method or the ammonium chloride soda co-production method to indirectly produce bicarbonate of soda (Japanese Patent Publication No. 1973
-26104, Special Public Service Showa 47-41236 Hakama Kai Showa 49-15
1199). However, all of these methods are aimed at producing bicarbonate of soda, and as will be described later, their technical ideas are different from the present invention. The present inventors conducted various studies on a method for producing soda carbonate using a diaphragm electrolyte as a raw material in a process that minimizes energy consumption, and arrived at the present invention. The technical idea of the present invention is to use the '11 diaphragm method electrolyte without concentrating it. '21 Do not use steam for concentration during the soda carbonation process. {31 The method is not a method for producing bicarbonate of soda that requires a calcining decomposition process and a dense ashing process, but a method for directly producing sodium carbonate-water salt for dense ash. [4} The alkali yield must be sufficiently high. [51 In other words, it must be an energy-saving manufacturing method. '61 It is a process that makes it extremely easy to produce soda ash not only for manufacturers with soda ash production plants using the A method or ammonium chloride soda co-production method, but also for manufacturers specializing in diaphragm brine electrolysis. {71 The purge liquid created during the production of soda carbonate can be reused in the salt water electrolysis process. etc. However, in order to completely satisfy the above technical idea, (1)
Even when carbon dioxide gas is blown into the diaphragm electrolyte, sodium carbonate-water salt does not precipitate, or even if it precipitates, it is very small. (2) Even if common salt is added to the electrolytic solution after blowing carbon dioxide gas into it, only a small amount of sodium carbonate-water salt is precipitated. '3' Soda carbonate - Since a large amount of soda carbonate is dissolved in the mother liquor from which the aqueous salt is separated, if it is harged directly, there will be a large alkali loss. In other words, the alkali yield is extremely low. It is difficult to use the '4' purge mother liquor in membrane electrolysis because it has a high concentration of sodium carbonate. '5) Combining the A process and the ammonium chloride soda co-production process improves the yield, but ammonia gets mixed into the process liquid, making it impossible to use the purge liquid for brine electrolysis. ■ Grown crystals cannot be obtained because the slurry concentration is low and it is difficult to allow the crystals to stay for a long time. There are problems such as these, and it has become clear that these problems need to be solved in order to establish an effective method for producing soda carbonate. The present inventors have arrived at the present invention as a result of further research. That is, in the present invention, when reacting the diaphragm method electrolyte and the sodium bicarbonate obtained in the third step described below in a crystallization tank, 20 kg to 70 kg of common salt is dissolved in advance in the diaphragm method electrolyte lt'. Alternatively, a part of the common salt is dissolved or suspended and a part is directly supplied to the crystallization tank, or all of the common salt is directly supplied to the crystallization tank, and the sodium carbonate aqueous salt is supplied. A first step of crystallization, a second step of separating the slurry obtained in the first step into crystals and a mother liquor, and washing the crystals as necessary, a reaction of carbon dioxide gas with the mother liquor obtained in the second step to form sodium bicarbonate. The gist of the present invention is a method for producing sodium carbonate monohydrate, which comprises a third step of crystallizing the crystals and supplying the crystals to the first step. Next, the present invention will be explained in more detail. The diaphragm electrolyte usually contains 5 to 15 wt% of caustic soda and 10 to 2 wt% of common salt. In the present invention, the higher the caustic soda concentration and the higher the common salt concentration, the greater the amount of sodium carbonate-water salt crystallized. Furthermore, since it is necessary to use the separated mother liquor of sodium bicarbonate in the diaphragm method brine electrolysis, it is desirable that the salt concentration be high. However, even the above electrolyte composition can be effectively used in the present invention. The amount of salt supplied to the electrolytic solution varies depending on the composition of the diaphragm electrolyte used, but the lower the caustic soda concentration of the solution, the greater the amount of salt used. In order to use just the right amount of sodium bicarbonate crystallized in the third step described below in the first step, when using a diaphragm method electrolyte, it is recommended to use 20 kg to 70 k9 of salt per lt of the electrolyte. preferable. If this amount is less than 20k9, the monohydrate yield will decrease, and if it is more than 70k9, it will not be possible to supply the amount of sodium bicarbonate required in the first step in the third step. As for the method of supplying common salt, it may be dissolved in advance in a diaphragm electrolyte and then supplied in a diaphragm method, or if it is not completely dissolved, it may be supplied in a suspended state. Alternatively, it may be directly supplied to the crystallization tank. A combination of these may also be used. Although the common salt is not particularly limited, purified salts with low calcium and magnesium content are preferred, and solid salts precipitated in the diaphragm method caustic soda concentration process are particularly desirable. Sodium bicarbonate can be used in the third step, and the amount required is equivalent to the amount of caustic soda in the diaphragm electrolyte to be supplied (1
(mole to 1 mole) is best. The composition of the mother liquor in the crystallization tank is
It is preferable that the caustic soda concentration does not exceed 1 wt % and the bicarbonate soda concentration does not exceed t %. When the caustic soda concentration exceeds lwt%, the crystalline form of the crystallized sodium carbonate-water salt deteriorates, and the physical properties when formed into dense ash deteriorate. If sodium bicarbonate becomes excessive and its concentration exceeds t%, sodium sesquicarbonate will precipitate, which is not preferable. The temperature of the crystallization bath is preferably within the range of 60°C to 100°C. If the temperature is lower than 60°C, good crystals cannot be obtained, and if the temperature is higher than 100°C, anhydrous soda carbonate will start to crystallize. When separating the generated sodium carbonate-aqueous salt, the resulting crystals will adhere to the mother liquor with a high salt concentration, so it is preferable to wash them with water or an aqueous sodium carbonate solution as necessary. te10
~15M% is sufficient. The third step of reacting carbon dioxide gas with the separated mother liquor of sodium carbonate and salt to obtain sodium bicarbonate may be carried out by the usual method, but the temperature of the reaction solution should ultimately be adjusted to 20 qo to 40 °C in order to reduce alkali loss. It is preferable to separate the bicarbonate of soda after lowering the temperature. The carbon dioxide gas used is not particularly limited, and is used in an amount sufficient to produce sodium bicarbonate. The obtained sodium bicarbonate does not need to be washed or dried, and can be recycled to the first step with the attached mother liquor. Normal separation methods such as centrifugal filtration, pressure filtration, and vacuum filtration are used to separate bicarbonate of soda, but it is also possible to circulate the bicarbonate of soda slurry concentrated in a static tank or liquid cyclone to the first step. It is. The mother liquor obtained in the third step has a salt concentration of 1
5 to 24 wt%, but since there is no ammonia contamination that causes the formation of explosive nitrogen trichloride during electrolysis, if the salt is redissolved to increase the salt concentration, it can be used as part of the brine for brine fin dissolution. Can be used cyclically. Next, the advantages of the present invention will be listed. By circulating sodium bicarbonate '11, it is possible to crystallize sodium carbonate-water salt without concentrating the ant film electrolyte, and the crystallization rate is also extremely high compared to the method of simply blowing carbon dioxide gas. ■ Diaphragm method More than 80% of the caustic soda in the electrolyte can be recovered as sodium carbonate-hydrate salt (referred to as monohydrate yield). If carbon dioxide gas is simply blown into the solution, the monohydrate yield will be 0 to 10% at most, depending on the composition of the diaphragm electrolyte. The monohydrate yield can be increased by dissolving or suspending '31 common salt in the diaphragm electrolyte in advance or by supplying it directly to the crystallization tank. [4' diaphragm method] Normally, the monohydrate yield varies and the production amount varies depending on the composition of the electrolyte solution, but since the present invention uses common salt, this variation can be suppressed. [51] By circulating the bicarbonate of soda and using common salt, the slurry concentration in the crystallization tank increases and the crystals become larger. '61 As the carbonate hydrate for dense ash, it is desired that the carbonate hydrate has sufficient hardness so that it will not form powder when it is made into soda ash. Dense ash from salt has a hardness equal to or higher than that of dense ash obtained by using conventional method of converting sodium bicarbonate into dense ash and further passing through a dense ashing process. '7) Since the sodium bicarbonate separated mother liquor in the third step is purged, alkali loss is small. '81 Sodium bicarbonate separated mother liquor has a high salt concentration, and
In the present invention, there is no contact with the process of A method or ammonium chloride soda co-production method, so the separated mother liquor of bicarbonate does not contain ammonia, which is avoided in salt water electrolysis plants, and can be easily used in salt water electrolysis. Can be used as part of brine. '91 Since the present invention is a process that is completely separated from the A method or the ammonium chloride soda co-production method, it becomes possible for even manufacturers who use the separate method to produce carbonated soda. QO The amount of bicarbonate of soda used in the first step is around the equivalent (1 mole to mole) of the caustic soda in the septum electrolyte, but there is a difference between the amount of bicarbonate of soda produced in the third step, i.e., the excess amount. It is desirable that there is no shortage; if there is an excess, the bicarbonate of soda must be purged, and if there is a shortage, it must be supplied from outside the system. However, in the present invention, the excess or deficiency can be adjusted simply by adjusting the amount of common salt supplied depending on the composition of the diaphragm electrolyte. The present invention described in detail above not only has economical advantages such as low energy consumption, but also provides soda hydrate salt with an ideal crystalline shape that becomes soda ash with good physical properties when made into dense ash. I can do it. This is due to the fact that the bulk electrolyte is used as a raw material, the crystallization tank conditions are limited to those of the present invention, the salt concentration in the crystallization tank is maintained at a high level of 13 to 2-wt%, and the process This is thought to be due to the complex effects of circulating and using bicarbonate of soda. This will be further explained below using examples. Example 1 In the first step, the caustic soda concentration was 9. Trace t%, salt concentration 16
Sakaki t% diaphragm method electrolyte 2800g/day, salt 11 days later, salt from the third step 3. is t%, water 11.8wt
% bicarbonate soda cake with a feed rate of 66 mm/day in two glass crystallization vessels (effective volume 0
．． 7 pm) and allowed to react while stirring to crystallize sodium carbonate aqueous salt. The temperature of the supplied diaphragm electrolyte and the temperature of the bicarbonate soda cake were 2g0, and the crystallization tank was maintained at 95°C. In the second step, the produced slurry was extracted at a rate of 164 mm/day and passed through a centrifugal furnace. The centrifugal furnace conditions were 70 days, and a 3% sodium carbonate-hydrate crystal cake was obtained for 36 days. Furthermore, the sodium carbonate-hydrate crystal cake was washed with 1% water and dried to obtain a sodium carbonate-hydrate crystal cake with a concentration of 0%. It contained 100% salt. The results of the hardness test were good, with a crushing rate of 8.0%. The crushing rate of sodium carbonate monohydrate obtained by method A is 10~]2
%, the target is 13% or less (the smaller the better).
In the third step, the sodium carbonate-water salt was separated and the top solution from the static zone was mixed with 12 t% of soda carbonate and 18 t% of common salt.
．． Wt% was included. This mother liquor was continuously supplied to a glass container with an effective volume of 5, and carbon dioxide gas was blown into the container. The temperature inside the container was 60:00. The obtained slurry was placed in batches of 5 into the same glass container, and while cooling to 35° C., carbon dioxide gas was further blown into the container for 1 hour. This slurry was heated in a vacuum oven using a glass filter, and salted 3. is t%, water 11. A bicarbonate soda cake containing t% Sakaki was obtained in 71 days. In addition, the monohydrate yield was Shigeru %. Example 2 Sodium carbonate-water salt crystallization temperature in the first step was set at 8° and 60°.
C, and the other conditions were the same as in Example 1. As shown in Table 1, the crushing rate is 8.5% and 10%, respectively.
It was good at 0%. Comparative Example 1 The crystallization temperature in the first step was changed to 50 pm, and the other conditions were as follows.
The same procedure as in Example 1 was carried out. The crystal form of soda carbonate-water salt is poor, and the crushing rate is 41.0.
% was not good. Comparative Example 2 The supply of common salt was stopped in the first step, and the other conditions were the same as in Example 1. The crushing rate was good at 11.0%, but the monohydrate yield was 5.
It dropped to 8%. Example 3 and Comparative Example 3 The amounts of bicarbonate soda cake and salt added in the first step were varied,
The same procedure as in Example 1 was carried out by adjusting the concentration of caustic soda or sodium bicarbonate in the crystallization tank. As shown in Table 1, unfavorable results were obtained when the caustic soda concentration exceeded IM% or when the bicarbonate soda concentration exceeded IM%. Example 4 Caustic soda concentration 10.7wt%, salt concentration 15.7wt
The procedure was carried out in the same manner as in Example 1, using a diaphragm method electrolyte of 50%. The results were good as shown in Table 1. (Note) Hardness test Soda carbonate-water salt is calcined under certain conditions, dehydrated, turned into dense ash, and then ground by impact under certain conditions.

Claims (1)

[Claims] 1. An electrolytic solution obtained from the cathode chamber of a diaphragm method salt water electrolytic cell (hereinafter simply referred to as diaphragm method electrolyte) and bicarbonate of soda obtained in the third step described below are reacted in a crystallization tank to produce carbonated soda water. In the method of obtaining salt, 20
kg to 70 kg of salt is dissolved in the electrolyte in advance,
Alternatively, a part of the common salt is dissolved or suspended in the electrolytic solution and a part is directly supplied to the crystallization tank, or all of the common salt is directly supplied to the crystallization tank, and then the salt is dissolved or suspended in the electrolytic solution. The first step is to crystallize the aqueous salt, the second step is to separate the slurry obtained in the first step into crystals and mother liquor, and wash as necessary, and the mother liquor obtained in the second step is reacted with carbon dioxide gas to create bicarbonate of soda. A method for producing sodium carbonate hydrate comprising a third step of crystallizing and supplying the crystals to the first step. 2 In the method described in claim 1, the temperature of the crystallization tank in the first step is maintained at 60°C or higher and 100°C or lower, and if there is excess caustic soda in the mother liquor, the caustic soda concentration is reduced to 1w.
A method characterized in that the sodium bicarbonate concentration is less than 2 wt% in the case of a shortage of caustic soda. 3. A method according to claim 1 or 2, in which a solid salt precipitated in the diaphragm electrolyte concentration step is used as common salt. 4. A method according to claim 1, in which the mother liquor obtained in the third step is recycled as brine for diaphragm electrolysis.