Low sodium salt manufacturing method

Abstract

To provide a method for producing a low-sodium salt, which can efficiently produce a low-sodium salt containing sodium chloride and potassium chloride at low cost. [Solution] This method for producing low-sodium salt uses brine produced during the salt production process, in which seawater is concentrated in an electrodialysis cell equipped with an ion exchange membrane and then boiled down to produce table salt. The method comprises a salt solution preparation step in which the brine produced during the salt production process is boiled down to a value lower than the Baume degree limit for potassium chloride precipitation to obtain a salt solution; a slurry acquisition step in which the salt solution obtained in the salt solution preparation step is further boiled down to a value higher than the Baume degree limit for potassium chloride precipitation to obtain a slurry containing precipitated sodium chloride and potassium chloride crystals; and a dehydration treatment step in which the slurry obtained in the slurry acquisition step is dehydrated to separate and recover low-sodium salt containing sodium chloride and potassium chloride.

Description

[Technical Field]

[0001] The present invention relates to a method for producing low-sodium salt using brine produced during the salt production process of producing common salt from seawater. [Background technology]

[0002] In recent years, it has become widely recognized that excessive intake of salt (sodium chloride) increases health risks, such as high blood pressure, heart disease, and kidney disease. As part of its "Healthy Japan 21" initiative, the Ministry of Health, Labour and Welfare recommends that adult salt intake be limited to less than 7.5g / day for men and less than 6.5g / day for women.

[0003] Therefore, in the food industry, seasonings, processed foods, retort foods, etc. that use low-sodium salt, which is a reduced-sodium product, are manufactured and sold. However, most of the low-sodium salts available on the market are produced by adding potassium chloride to table salt to adjust the blending ratio to about 7:3, which makes production time-consuming and costly (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-7111 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for producing a low-sodium salt, which can produce a low-sodium salt efficiently and at low cost. [Means for solving the problem]

[0006] The present inventors have discovered that sodium chloride and low-sodium salts containing potassium chloride can be produced efficiently and at low cost by boiling down brine, which is produced in the process of producing salt from seawater, to a Baume degree value lower than the limiting point at which potassium chloride precipitates, to obtain a salt solution, and then further boiling down this salt solution to a Baume degree value higher than the limiting point at which potassium chloride precipitates, and have thus completed the present invention.

[0007] That is, the present invention is as follows. [1] A method for producing low-sodium salt using brine produced during a salt production process in which seawater is concentrated in an electrodialysis cell equipped with an ion exchange membrane and then boiled down to produce table salt, A salt solution preparation step in which the brine produced during the salt production process is boiled down to a value lower than the Baume degree at the potassium chloride precipitation limit to obtain a salt solution (also called bittern); a slurry obtaining step of further boiling the salt solution obtained in the salt solution preparing step to a Baume degree higher than the potassium chloride precipitation limit to obtain a slurry containing precipitated sodium chloride and potassium chloride crystals; a dehydration treatment step of dehydrating the slurry obtained in the slurry obtaining step to separate and recover low-sodium salts including sodium chloride and potassium chloride; A method for producing a low-sodium salt, comprising the steps of:

[0008] [2] The method for producing a low-sodium salt according to [1] above, wherein in the salt solution preparation step, the brine is boiled down to a value 1.0 to 5.0 degrees lower than the Baume degree at which potassium chloride precipitates. [3] The method for producing a low-sodium salt according to [2] above, characterized in that in the slurry obtaining step, the salt solution is boiled down to a value 1.0 to 3.0 degrees higher than the Baume degree at the potassium chloride precipitation limit.

[0009] [4] The method for producing a low-sodium salt according to any one of [1] to [3] above, wherein the ratio of sodium chloride to potassium chloride contained in the produced low-sodium salt is 55:45 to 95:5. [5] The method for producing a low-sodium salt according to [4] above, wherein the ratio of sodium chloride to potassium chloride contained in the produced low-sodium salt is 60:40 to 80:20.

[0010] [6] The method for producing a low-sodium salt according to any one of [1] to [5] above, wherein the sodium chloride and potassium chloride contained in the produced low-sodium salt are 80 mass % or more, calculated on solid matter. [7] The method for producing a low-sodium salt according to any one of [1] to [6] above, wherein the magnesium chloride contained in the produced low-sodium salt is 10 mass % or less, calculated on solid matter. [Effects of the Invention]

[0011] According to the present invention, low-sodium salts containing sodium chloride and potassium chloride can be produced efficiently and at low cost. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an explanatory diagram of a low-sodium salt production facility according to one embodiment of the present invention. [Figure 2] 1 is a graph showing the relationship between the concentration of boiled seawater (brine) and the solubility of sodium chloride and potassium chloride. [Figure 3] 1 is a graph showing the relationship between the boiled concentration of a salt solution and the composition ratio of precipitated sodium chloride and potassium chloride. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method for producing low-sodium salt of the present invention is a method for producing low-sodium salt using brine produced during a salt production process in which seawater is concentrated in an electrodialysis cell equipped with an ion exchange membrane and then boiled down to produce table salt. The method is characterized by comprising: a salt-solution preparation step in which the brine produced during the salt production process is boiled down to a value lower than the Baume degree at which potassium chloride precipitates, thereby obtaining a salt-solution; a slurry obtaining step in which the salt-solution obtained in the salt-solution preparation step is further boiled down to a value higher than the Baume degree at which potassium chloride precipitates, thereby obtaining a slurry containing precipitated crystals of sodium chloride (NaCl) and potassium chloride (KCl); and a dehydration treatment step in which the slurry obtained in the slurry obtaining step is dehydrated to separate and recover low-sodium salt containing sodium chloride and potassium chloride.

[0014] The Baume scale (also written as Be') used in the present invention is a unit used to indicate the concentration of concentrated water, and is also called the Baume specific gravity value, with a larger value meaning a higher concentration.

[0015] The potassium chloride precipitation limit used in this invention is the point where the potassium chloride concentration line obtained when evaporating and boiling down brine in a salt production method using an ion exchange membrane intersects with the potassium chloride solubility curve, which depends on the evaporation temperature. Specifically, in the process of boiling down brine (concentration process), the solubility of sodium chloride reaches a maximum and then drops, while the solubility of potassium chloride reaches a maximum. If the brine is boiled down beyond the potassium chloride precipitation limit, potassium chloride will precipitate (see Figure 2).

[0016] The low-sodium salt produced by the production method of the present invention contains sodium chloride and potassium chloride, and therefore is a salt that can reduce sodium chloride intake compared to table salt consisting of sodium chloride.It can be used alone, and can also be used, for example, as a seasoning to be added to condiments, processed foods, retort foods, etc.

[0017] Here, the ratio of sodium chloride to potassium chloride contained in the produced low-sodium salt is preferably 55:45 to 95:5, more preferably 60:40 to 80:20, and even more preferably 65:35 to 75:25, which can make it less likely that the saltiness will be unsatisfactory and make it easier to achieve the effect of reduced salt intake.

[0018] Furthermore, the content of sodium chloride and potassium chloride contained in the low-sodium salt produced by the production method of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, calculated on a solid basis.

[0019] Furthermore, the content of magnesium chloride (MgCl) contained in the low-sodium salt produced by the production method of the present invention is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less, calculated on a solid basis.

[0020] The method for producing low-sodium salt of the present invention is a novel technique in which brine produced in the salt production process from seawater is boiled down to a value lower than the Baume degree, rather than to the Baume degree at which potassium chloride precipitates, which is the standard for normal salt production, to obtain a salt solution containing sodium chloride and potassium chloride in a predetermined mass ratio, and then low-sodium salt is produced using this salt solution.

[0021] That is, in a typical salt production process, brine is boiled down to a Baume degree to obtain precipitated sodium chloride of high purity, and the salt solution with a high potassium chloride concentration, from which the precipitated sodium chloride slurry has been removed, is used, for example, as a raw material for obtaining potassium chloride in the next step. However, in the present invention, sodium chloride is intentionally left in the solution in the former step to increase the sodium chloride concentration above normal, resulting in a salt solution in which sodium chloride and potassium chloride have a predetermined mass ratio, and a low-sodium salt is obtained from this solution.

[0022] According to the production method of the present invention, since there is no need to previously produce sodium chloride and potassium chloride and then mix them in a predetermined ratio, a low-sodium salt in which sodium chloride and potassium chloride are uniformly mixed can be produced efficiently with good workability, and therefore the low-sodium salt can be produced at low cost.

[0023] The method for producing a low-sodium salt of the present invention includes a salt solution preparation step, a slurry obtaining step, and a dehydration treatment step, but other steps may be included before, after, or between each of these steps. Specifically, for example, a storage step for temporarily storing the slurry may be included between the slurry obtaining step and the dehydration treatment step.

[0024] Each step of the present invention will be described below.

[0025] (Salt solution preparation process) The salt solution preparation process involves boiling down the brine produced during the salt production process to a value lower than the Baume degree limit at which potassium chloride precipitates, to obtain a salt solution (see Figures 1 and 2).

[0026] Here, the salt production process refers to a process in which seawater is concentrated in an electrodialysis tank equipped with an ion exchange membrane and then boiled down to obtain precipitated sodium chloride (table salt). The brine produced in this process is used in the salt solution preparation step. As the brine, it is preferable to use the most concentrated brine (mother liquor) in the salt production process. In other words, it is preferable to use the final brine used to obtain precipitated sodium chloride in a normal salt production process.

[0027] Seawater contains, for example, about 3 to 4% salt, and contains, as components, for example, sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate (MgSO4), calcium sulfate (CaSO4), and the like.

[0028] An electrodialysis cell is a cell equipped with ion exchange membranes that concentrate seawater to increase its salinity, for example, to 15-20%. A specific example of this is a cell constructed by alternating cation exchange membranes (positive membranes) that allow only cations to pass and anion exchange membranes (negative membranes) that allow only anions to pass, creating small chambers with electrodes placed on both ends. When seawater is passed through every other chamber in this cell and a direct current is applied, anions move along the current flow (from the negative pole to the positive pole), passing through the negative membrane and being blocked by the positive membrane, while cations move in the opposite direction, toward the positive pole, passing through the positive membrane and being blocked by the negative membrane. As a result, the chamber through which seawater flows (called the desalination chamber) contains fewer ions, while the adjacent chamber (called the concentration chamber) is enriched with more ions, producing brine.

[0029] To obtain a salt solution in the salt solution preparation step, the brine is preferably boiled down to a value 1.0 to 5.0 degrees lower than the Baume degree at the potassium chloride precipitation limit, more preferably 1.0 to 4.0 degrees lower, even more preferably 1.0 to 3.0 degrees lower, and particularly preferably 1.2 to 2.0 degrees lower (see Figure 2). This makes it possible to adjust the dissolution ratio of sodium chloride and sodium chloride in the salt solution, and in the next step, a low-sodium salt with the desired sodium chloride to potassium chloride ratio can be obtained.

[0030] Here, the Baume degree at the potassium chloride precipitation limit is specifically, for example, 27.0 to 35.0 degrees, preferably 27.0 to 33.0 degrees, more preferably 30.0 to 33.0 degrees, and even more preferably 31.0 to 32.0 degrees.

[0031] (Slurry obtaining process) The slurry obtaining step is a step in which the salt solution obtained in the salt solution preparation step is further boiled down to a Baume degree higher than the limit of potassium chloride precipitation, to obtain a slurry containing precipitated sodium chloride and potassium chloride crystals (see Figures 1 and 2).

[0032] To obtain a slurry in this step, the salt solution is boiled down to a value 1.0 to 3.0 degrees higher than the Baume degree at which potassium chloride precipitates, more preferably 1.0 to 2.5 degrees higher, even more preferably 1.0 to 2.0 degrees higher, and particularly preferably 1.2 to 2.0 degrees higher (see Figure 2). This makes it possible to minimize the precipitation of magnesium, which causes bitterness.

[0033] (Storage process) The storage process is a process in which the slurry obtained in the slurry obtaining process is temporarily stored in a tank or the like (see Figure 1). This allows the slurry to be sent downstream of the storage process without being affected by the amount of slurry supplied from the slurry obtaining process.

[0034] (Dehydration process) The dehydration step is a step of dehydrating the slurry obtained in the slurry obtaining step to separate and recover low-sodium salts including sodium chloride and potassium chloride. This dehydration step can remove most of the water from the slurry. This allows the production of a low-sodium salt. The low-sodium salt may be in a wet state, but is usually dried, then packaged, or the like, and shipped as a commercial product.

[0035] Next, a production facility for a low-sodium salt to which the above-described production method for a low-sodium salt can be applied will be described, but the present invention is not limited to these embodiments. Here, Figure 1 is an explanatory diagram of the production facility for a low-sodium salt. As shown in FIG. 1, a low-sodium salt production facility 10 includes a salt solution preparation device 11, a slurry acquisition device 12, and a dehydration treatment device 13, which are arranged in this order. A detailed explanation is provided below.

[0036] (Salt solution preparation device) The salt solution preparation device 11 is equipped with a container 14 for receiving brine produced during the salt production process, a circulation path 15 connecting the upper and lower parts of the container 14, and a heater 16 provided in the circulation path 15. While circulating the brine, the brine is boiled down to a value lower than the Baume degree limit at which potassium chloride precipitates, thereby obtaining a salt solution.

[0037] This vessel 14 is a spindle-shaped can for boiling water, and with its axis aligned vertically, the upper and lower sides of vessel 14 are connected by circulation path 15. Heater 16 is provided in circulation path 15, and a circulation pump 17 is provided below (upstream of) heater 16. The brine is circulated from the bottom to the top of vessel 14 by circulation path 15 and circulation pump 17, while the brine flowing through circulation path 15 is boiled down by heater 16, precipitating sodium chloride and obtaining a salt-dissolved solution.

[0038] (Slurry obtaining device) The slurry obtaining device 12 is equipped with a container 18 for receiving the salt solution obtained in the salt solution preparing device 11, a circulation path 19 connecting the upper and lower parts of the container 18, and a heater 20 provided in the circulation path 19, and while circulating the salt solution, further boils it down to a value higher than the Baume degree at which potassium chloride precipitates, thereby obtaining a slurry.

[0039] This vessel 18 is a spindle-shaped concentrator, and with its axis aligned vertically, the upper and lower sides of vessel 18 are connected by a circulation path 19. A heater 20 is provided in this circulation path 19, and a circulation pump 21 is provided below (upstream of) heater 20. The salt solution is circulated from the bottom to the top of vessel 18 by circulation path 19 and circulation pump 21, while the salt solution flowing through circulation path 19 is further boiled down by heater 20, to obtain a slurry containing precipitated sodium chloride and potassium chloride crystals.

[0040] (Dehydration treatment device) The dehydration treatment device 13 is a device that dehydrates the slurry that has been extracted from the slurry obtaining device 12 and passed through the slurry tank 22, to separate and recover low-sodium salts including sodium chloride and potassium chloride. Here, an inverted triangular pyramid-shaped tank can be used as the slurry tank, and the liquid that overflows from the tank is recovered. The dehydration treatment device is not particularly limited as long as it can separate and recover the low-sodium salts, and examples thereof include a centrifuge, a vacuum dehydrator, a pressure filter (filter press), and a belt press filter, and the separated liquid generated from the dehydration treatment device is recovered.

[0041] The liquid overflowing from the above-mentioned slurry tank 22 and the separated liquid generated from the dehydration treatment device 13 can be recovered, for example, in a crystallization tank and cooled, thereby making it possible to recover the raw material for potassium chloride and also to recover bittern (a substance containing magnesium chloride). [Example]

[0042] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0043] (Preliminary Exam 1) We investigated the relationship between the boiled-down concentration of seawater and the solubility of sodium chloride and potassium chloride when seawater was concentrated in an electrodialysis cell equipped with an ion exchange membrane and then boiled down. Figure 2 is a graph showing the relationship between the boiled-down concentration of seawater (Baume degree) and the solubility of sodium chloride and potassium chloride.

[0044] As shown in Figure 2, in the process of boiling seawater down to the limit of potassium chloride precipitation, for example, a salt solution with a dissolution ratio of 70% sodium chloride and 30% potassium chloride can be obtained at around 30 degrees, which is lower than the limit of potassium chloride precipitation (approximately 31.5 degrees Baume).

[0045] (Preliminary Exam 2) Based on the results of Preliminary Test 1, three salt solutions with Baume degrees of 28.5, 30.0, and 31.5 were prepared. An evaporation test was conducted in a beaker using these salt solutions, and the precipitated crystals were analyzed. The evaporation test corresponds to the slurry preparation process of the present invention, in which the salt solution was further boiled down to a Baume degree of 33.0. Specifically, 33% of the water was evaporated. Figure 3 is a graph showing the relationship between the boiled-down concentration of the salt solution and the composition ratio of precipitated sodium chloride and potassium chloride.

[0046] As shown in Figure 3, when the evaporation test was performed on a salt solution with a Baume degree of 31.5, the composition ratio of the precipitated sodium chloride and potassium chloride was 1:1. It can be seen that the composition ratio of the precipitated sodium chloride and potassium chloride changes as the Baume degree of the salt solution decreases. For example, when the Baume degree of the salt solution is in the range of 30.0 to 30.5, a low-sodium salt with a sodium chloride to potassium chloride ratio of about 7:3 can be obtained.

[0047] Here, when the Baume degree of the salt solution is 30.5 degrees, the composition ratio of the precipitated sodium chloride and potassium chloride is 60% by mass sodium chloride and 20% by mass potassium chloride, and when converted back to just sodium chloride and potassium chloride, it becomes 75% by mass sodium chloride (= 60 / (60 + 20)) and 25% by mass potassium chloride (= 20 / (60 + 20)), which shows that a low-sodium salt with a sodium chloride to potassium chloride ratio of 75:25 can be produced.

[0048] (Example) Brine produced during the salt production process was boiled down to 30.5°C (below the limit of potassium chloride precipitation) to obtain a salt solution. One liter of this salt solution was placed in a beaker and further boiled down to 33.0°C (above the limit of potassium chloride precipitation) to obtain a slurry containing precipitated sodium chloride and potassium chloride crystals. The precipitated crystals were then dehydrated and analyzed for their components. Analysis was based on the "Salt Testing Methods" published by the Salt Industry Center (public foundation), with Cl ions measured by the Mohr method (silver nitrate titration), K ions measured by flame photometry, Ca ions and Mg ions measured by chelate titration, SO ions measured by ion chromatography, and Na ions measured by stoichiometric conversion to Cl ions. For reference, commercially available products were also analyzed. The analytical results of the composition of the low sodium salt obtained in this test are shown in Table 1. The values ​​shown in Table 1 are calculated on a solid basis.

[0049] [Table 1]

[0050] From Table 1, it can be seen that the ratio of sodium chloride to potassium chloride in the low sodium salt of the example was approximately 68:32, which is the same ratio as that of the reference product. Therefore, it was found that low-sodium salts can be produced efficiently and at low cost. [Industrial Applicability]

[0051] The present invention is industrially useful because it enables low-sodium salts to be produced efficiently and at low cost. [Explanation of symbols]

[0052] 10. Low-sodium salt manufacturing facility 11 Salt dissolving solution preparation device 12 Slurry obtaining device 13 Dehydration treatment equipment 14 Container 15 Circulation path 16 Heater 17 Circulation pump 18 Container 19 Circulation path 20 Heater 21 Circulation pump 22 Slurry tank

Claims

1. A method for producing low-sodium salt using brine produced during a salt production process in which seawater is concentrated in an electrodialysis cell equipped with an ion exchange membrane and then boiled down to produce table salt, comprising: a salt solution preparation step of boiling down the brine produced during the salt production process to a value lower than the Baume degree at which potassium chloride precipitates, thereby obtaining a salt solution; a slurry obtaining step of further boiling the salt solution obtained in the salt solution preparing step to a Baume degree higher than the potassium chloride precipitation limit to obtain a slurry containing precipitated sodium chloride and potassium chloride crystals; a dehydration treatment step of dehydrating the slurry obtained in the slurry obtaining step to separate and recover low-sodium salts including sodium chloride and potassium chloride; A method for producing a low-sodium salt, comprising the steps of:

2. 2. The method for producing low-sodium salt according to claim 1, wherein in the salt solution preparation step, the brine is boiled down to a value 1.0 to 5.0 degrees lower than the Baume degree at which potassium chloride precipitates.

3. 3. The method for producing a low-sodium salt according to claim 2, wherein in the slurry obtaining step, the salt solution is boiled down to a value 1.0 to 3.0 degrees higher than the Baume degree at the potassium chloride precipitation limit point.

4. 2. The method for producing a low-sodium salt according to claim 1, wherein the ratio of sodium chloride to potassium chloride contained in the produced low-sodium salt is 55:45 to 95:

5.

5. 5. The method for producing a low-sodium salt according to claim 4, wherein the ratio of sodium chloride to potassium chloride contained in the produced low-sodium salt is 60:40 to 80:

20.

6. 2. The method for producing a low-sodium salt according to claim 1, wherein the sodium chloride and potassium chloride contained in the produced low-sodium salt are 80% by mass or more in terms of solid matter.

7. 2. The method for producing a low-sodium salt according to claim 1, wherein the magnesium chloride contained in the produced low-sodium salt is 10% by mass or less in terms of solid matter.

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