JP2000342902A - Method for producing deliquescent inorganic salt crystal delayed in deliquescence and reaction apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a deliquescent inorg. salt crystal slow in deliquescence and easy to handle such as magnesium chloride by dissolving a deliquescent inorg. salt in relatively high temp. water in the presence of other inorg. salts and gradually cooling the resulting soln. to relatively low temp. while irradiating the same with ultrasonic waves to precipitate a crystal and filtering off this crystal to dry the same. SOLUTION: In a normal recrystallization method wherein a deliquescent inorg. salt is dissolved in relatively high temp. water and the resulting soln. is gradually cooled to relatively low temp. to precipitate a crystal, the soln. is gradually cooled in the presence of other inorg. salts while irradiated with ultrasonic waves to produce a deliquenscent inorg. salt crystal delayed in deliquescence. As the other inorg. salts, salts of Fe, Ca, Mg, Na and the like are used independently or in a mixed state. The output of ultrasonic waves to be applied is different according to the size of a reaction container 1 or a liquid amt. and appropriately set corresponding to respective conditions. An ultrasonic oscillator 2 is attached to the upper part of the reaction container 1 and, as the reaction container 1, one having an internal structure irregularily reflecting ultrasonic waves is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and a reactor for producing a deliquescent inorganic salt crystal by a recrystallization method, and more particularly to a method for producing a deliquescent inorganic salt crystal with a slow deliquesce and ultrasonic irradiation suitable for the method. It relates to a reactor.

[0002]

2. Description of the Related Art Deliquescent inorganic salts such as magnesium chloride and calcium chloride are widely used in various chemical processing industries such as food processing and other various chemical industries. As a method for producing these inorganic salt crystals, methods such as recrystallization from a solution and boiling and concentrating have been used. The products of these deliquescent inorganic salts are dissolved by deliquesce as soon as they come into contact with air after opening, making them difficult to handle, or unusable, so that they are difficult to handle during production and use. Therefore, there is a demand for the development of a product whose deliquescence is suppressed (the deliquescence rate is slowed down). For example, a sequestering agent is added to magnesium chloride as a coagulant for tofu, dissolved in water, and dried or powdered. Method for obtaining a coagulant excellent in moisture absorption stability by granulation (JP-A-60-25185)
No. 4), magnesium sulfate and calcium chloride are mixed and heated in water to cause metathesis, and a mixture of magnesium sulfate, calcium sulfate, magnesium chloride and calcium chloride is formed. A method of obtaining a coagulant having a low deliquescence despite containing a considerable amount of high magnesium chloride and calcium chloride (JP-B-56-50945) has been proposed, and fatty acid esters, cyclodextrin, etc. Although a method of forming a film by using the method has been tried, a method which can be easily applied to various deliquescent inorganic salts and has a large effect has not yet been found.

[0003]

SUMMARY OF THE INVENTION In view of the state of the prior art, the present invention provides a method for producing a deliquescent inorganic salt crystal which is slow to be deliquescent and easy to handle, and a reactor suitable for the method. With the goal.

[0004]

According to the present invention, there is provided (1) a method of dissolving a deliquescent inorganic salt in relatively high temperature water in the presence of other inorganic salts, and then irradiating ultrasonic waves to a relatively low temperature. A method for producing a deliquescent inorganic salt crystal having a slow deliquescence, which comprises slowly cooling to precipitate crystals, filtering and drying; (2) the ultrasonic wave irradiation being pulse irradiation. (1) a method for producing a deliquescent inorganic salt crystal having a delayed deliquescence,
(3) The method for producing a deliquescent inorganic salt crystal with a slow deliquefaction according to the above (1) or (2), wherein the crystal is deposited, and the ripening is performed while maintaining the same temperature. An ultrasonic irradiation reactor in which an ultrasonic oscillator is mounted on an upper part of a reaction container, wherein the reaction container has a structure in which ultrasonic waves are irregularly reflected inside, wherein any of the above (1) to (3). An ultrasonic irradiation reaction apparatus for performing the method.

[0005]

DETAILED DESCRIPTION OF THE INVENTION In the method of the present invention, a general recrystallization method is described in which a deliquescent inorganic salt is dissolved in relatively high-temperature water and then gradually cooled to a relatively low temperature to precipitate crystals. It is characterized by gradually cooling while irradiating ultrasonic waves in the presence of other inorganic salts. Other inorganic salts include Fe,
Salts such as Ca, Mg and Na (may be deliquescent)
Are used alone or as a mixture. In the method of the present invention, the effect of reducing deliquescence increases in proportion to the content ratio of other inorganic salts in the raw material salt to be recrystallized. Therefore, the content ratio of other inorganic salts in the raw material salt (deliquescent inorganic salt + other inorganic salts; excluding water containing crystal water) need not be particularly limited, and the necessary deliquescent effect can be obtained. The ratio of other inorganic salts may be appropriately determined. In general, for industrial use, deliquescent inorganic salts that are commercially available for use as food additives, etc., often contain other inorganic salts as a mineral component, and if the amount is sufficient, particularly add other inorganic salts. No need.

Usually, in order to obtain a sufficient effect, it is desirable that the ratio of other inorganic salts in the raw material salt is 5% or more. In addition, an increase in the proportion of other inorganic salts in the raw material salt also means that the amount of impurities increases, which may cause a reduction in quality value. You need to be careful not to do this.

[0007] The recrystallization conditions themselves are not special.
For example, inorganic salts can be heated to a relatively high temperature (for example, 80 to 100 ° C).
), And cooled to a relatively low temperature (for example, 20 ° C or lower, preferably 0 to 10 ° C) to precipitate crystals. The cooling time depends on the amount of liquid, but may be 20 minutes or more, preferably 20 minutes to 3 hours.

In the method of the present invention, during the cooling,
Irradiate ultrasonic waves. Here, the term “during cooling” means a period during which the precipitation of crystals progresses, and includes not only a time during which the temperature is lowered but also a time during which the supersaturated state is maintained. Irradiation of ultrasonic waves may be performed continuously,
In the case of continuous irradiation, since the temperature of the liquid rises, it is preferable to perform pulse irradiation (for example, irradiation for 1 minute and repetition of pause for 1 minute) at appropriate intervals. The output of the ultrasonic wave to be irradiated differs depending on the size of the reactor, the amount of liquid, and the like, and may be appropriately set according to each condition. For a liquid amount of about 300 ml, about 100 μV is sufficient. Further, the frequency is preferably in the range of 20 to 50 kHz.

After cooling to a predetermined temperature, the crystal is filtered and dried to obtain a deliquescent inorganic crystal whose deliquescent has been suppressed (deliquesce has been delayed). In this case, the crystals may be filtered off immediately after cooling, but by further aging by holding at the same temperature to room temperature for an appropriate time,
The crystal state is gradually improved, and the deliquescence suppressing effect is further increased. However, in the normal case, the improvement effect by aging is moderate, and since the crystallization water may be entrapped in some cases, it is preferable to set the maximum to about 24 hours in consideration of industrial applicability. .

[0010] The mechanism by which the method of the present invention produces a crystal with a slow deliquescence has not been completely elucidated, but it is presumed as follows at this stage. By irradiating ultrasonic waves while slowly cooling a mixture containing a supersaturated deliquescent inorganic salt and other inorganic salts, a mechanochemical reaction occurs between the deliquescent inorganic salt and the other inorganic salts, and the nuclide is generated. A large amount of fine crystals are generated, and the fine particles are activated. It is considered that the crystal grows further and forms a composite crystal of the deliquescent inorganic salt and a small amount of another inorganic salt, and becomes a crystal with a slow deliquescent. Here, the mechanochemical reaction refers to a reaction in which the particles irradiated with ultrasonic waves locally become high temperature and high pressure, and the particles are instantaneously bonded to each other. The crystal thus formed is less likely to deliquesce than a crystal obtained by simple recrystallization.

In the method of the present invention, it is necessary to irradiate the entire reactor with ultrasonic waves at the time of ultrasonic irradiation. Therefore, it is preferable that the shape of the reaction vessel is such that the ultrasonic waves radiated therein are irregularly reflected and the energy of the ultrasonic waves can be effectively used. As a specific example, a round-shaped flask, such as an eggplant-shaped flask, the wall surface is formed with a curved surface that is convex outward, and a container with a shape in which the upper portion is squeezed is preferable,
Even a shape like an Erlenmeyer flask is effective. The ultrasonic irradiation reaction device of the present invention has an ultrasonic oscillator attached to the upper part of such a reaction vessel. With such a configuration, it is possible to manufacture a deliquescent inorganic salt crystal in which deliquescing is delayed by the method of the present invention without separately providing an ultrasonic wave reflecting device such as a stirrer or a reflecting plate. As an example of the reaction apparatus of the present invention, an apparatus having a configuration in which an ultrasonic oscillator 2 is mounted on an upper part in an eggplant type container 1 is shown in FIG.
With such a configuration, the ultrasonic waves radiated from the ultrasonic oscillator mounted on the upper part go straight and collide with the bottom member of the reactor. The colliding ultrasonic wave travels in a straight line by reflection and spreads over the entire reaction vessel, so that the entire inside of the reaction vessel can be efficiently irradiated.

[0012]

The present invention will be described more specifically with reference to the following examples. Using a magnesium chloride hexahydrate (MgCl ₂ .6H ₂ O) as a deliquescent inorganic salt, a deliquescent evaluation test was performed on samples treated under various conditions. As the magnesium chloride hexahydrate, a commercially available food additive (produced by boiling and concentrating) and a special-grade reagent were used. The composition of this commercial product is as shown in Table 1, and the content of other inorganic salts in the component (magnesium chloride + other inorganic salts) excluding water containing crystal water is about 6% by weight. is there. The components of the special-grade reagent were 98% by weight or more as MgCl ₂ .6H ₂ O, and the balance was water, and no other mineral components were detected.

[0013]

[Table 1]

(Preparation of Sample) A sample was prepared by the ultrasonic irradiation method of the present invention as follows. 250 g of a commercially available product or a special-grade reagent, magnesium chloride, was placed in a reactor having an internal volume of 300 ml having the structure shown in FIG. 1, and 100 ml of water was added thereto and dissolved by heating to 80 to 90 ° C. Next, the crystal was precipitated by cooling to 2 to 4 ° C. for a predetermined period of time while irradiating with ultrasonic waves of 20 kHz and 100 μV at intervals of one minute and repeating pulse irradiation for one minute at a time. Immediately after cooling, or after being aged for a predetermined time at the same temperature for aging, crystals were separated by suction filtration and dried under predetermined conditions to obtain a sample. In addition, as a comparative sample, a sample that was subjected to recrystallization (i.e., a conventional recrystallization method) without irradiation with ultrasonic waves and in exactly the same manner under the other conditions was produced. In the following examples, a sample recrystallized without performing ultrasonic irradiation is a recrystallized product, and a sample recrystallized while irradiating ultrasonic waves for a predetermined time by the above method is irradiated with ultrasonic waves for a predetermined time, and is irradiated with ultrasonic waves for a predetermined time. A sample obtained by recrystallizing while aging for a predetermined time is referred to as a product irradiated for a predetermined time and aged for a predetermined time.
For example, a one-hour irradiation product is one in which irradiation for one minute is repeated at one-minute intervals for one hour, and the net irradiation time is 30 hours.
Minutes.

(Evaluation Test) For a certain amount of dried sample,
The hygroscopic rate (evaluation of deliquescence) was evaluated by determining the hygroscopic rate from the relationship between the elapsed time and the weight increased by the hygroscopicity. Since the relationship between the elapsed time and the weight change is not linear, the vertical axis represents the weight change rate and the horizontal axis represents the elapsed time. The gradient in the figure is the moisture absorption rate. Since the degree of deliquescence does not always coincide with the amount of absorbed moisture, the degree of deliquescence was visually observed at regular intervals. The end of the deliquescence was visually determined in two stages, the first stage was when moisture was confirmed on the sample surface, and the second stage was the time when no crystals were present. The degree of deliquescence was determined by weight change and visual observation. As a specific evaluation method, 5 g of a sample was weighed in an evaporating dish, and the evaporating dish was allowed to stand in a desiccator filled with water, and the weight increase of the dish was taken as the moisture absorption. The deliquescent evaluation test was performed at normal temperature and normal pressure. Unless otherwise specified, the average temperature during the test was 0 to 15 ° C and the humidity was about 45 to 55%.

(Test Results) [A. Influence of Sample Drying State on Hygroscopicity Evaluation] First, the effect of the degree of drying after sample preparation on hygroscopicity evaluation was examined. A moisture absorption test was performed on four types of samples: a sample obtained by drying a commercially available recrystallized product, a sample obtained by drying a commercially available product irradiated for 20 minutes, a sample obtained by drying a commercial product, and a sample obtained as it is. In addition, all drying was 105
° C for 2 hours, the temperature during the moisture absorption test was 7 ° C on average, and the humidity was 7 ° C.
It was 0%. The results are as shown in FIG. 2, and the result is that the commercially available product that has not been dried has the lowest moisture absorption. This is probably because a considerable amount of moisture had already been absorbed at the start of the test.

[B. Relationship between drying time and evaporation rate]
The results show that some deliquescence has already occurred when drying is not sufficient. Therefore, it is necessary to keep the amount of water at the start of the moisture absorption test constant for all the samples. Therefore, a commercial product, a commercially available ultrasonic (100 μ
V) For the irradiated product and the commercially available ultrasonic (200 μV) irradiated product, the drying time was changed to 1 day, 2 days, 6 days, and 12 days at 105 ° C. using a natural convection dryer. After drying, twelve types of samples (1) to (12) in Table 2 were prepared, and the moisture content was measured to examine the relationship between the drying time and the free moisture content in the crystal. The free water content was measured by further drying these samples at 105 ° C. for 1 day using a natural convection dryer, and measuring the weight loss (evaporation amount) at that time. FIG. 3 shows, as the evaporation rate, the free water content at this time, that is, the ratio of the evaporation amount to the sample weight before drying. As can be seen from FIG. 3, the weight of each sample was stable after 2 days of drying. Therefore, in the following tests, the degree of drying was standardized to drying at 105 ° C. for 2 days using a natural convection type dryer. In the following description, a dried product is dried under these conditions. Although the drying time is long in this drying method, the drying time can be shortened by the forced convection method.

[0018]

[Table 2]

[C. Effect of Ultrasonic Irradiation] Deliquescent by changes in water absorption and visual observation of three types of samples: dried commercially available products, dried commercially available recrystallized products, and dried commercially available samples for 1 hour Were compared. FIG. 4 shows the relationship between the water absorption and the number of elapsed days. From FIG. 4 and the result of the visual observation, the sample was 10 days and the sample was 2 days.
On day 0, the sample deliquesced in 26 days. This was the time when the second stage was reached by visual observation, and the moisture absorption at that time was about 220%. In FIG. 4, n in MgCl ₂ .nH ₂ O was less than 6 in the first rapid portion (up to 2 days), and it seems that n became 6 in just about 2 days. Subsequent increases correspond to the increase in free moisture that directly causes deliquescence. It can be seen that the effect of delaying deliquescence was obtained by recrystallization while irradiating ultrasonic waves.

[D. Influence of Ultrasonic Wave Irradiation Time] Since it was found from the above C that ultrasonic irradiation had an effect of delaying deliquescence, the time change of the moisture absorption rate due to the difference in ultrasonic wave irradiation time was examined. All samples were made from commercial products and dried recrystallized products, dried samples for 20 minutes, dried samples for 1 hour, dried samples for 3 hours, and dried samples for 3 hours. did. Although there was no significant difference in the particle size of the crystal observed by visual observation, the crystal was the smallest after 3 hours of ultrasonic irradiation, followed by 1 hour and then 20 minutes. However, FIG.
As shown in Table 2, the moisture absorption rate was highest in the case of irradiation for 1 hour, then in order of 20 minutes and then for 3 hours, but no significant difference was observed. From this, it is understood that such a difference in particle diameter does not necessarily cause a reduction in deliquescence. Further, it is considered that irradiation time of 20 minutes or more is sufficient.

[E. Effect of Crystal Aging Time] Next, the effect of the crystal aging time after ultrasonic irradiation was examined. All samples were obtained by drying the irradiated product for 20 minutes using commercial products as raw materials,
There were four types of samples: a sample obtained by drying a product aged for 1 day irradiated for 20 minutes, a sample obtained by drying a product irradiated for 1 hour, and a sample obtained by drying a product aged for 1 hour. The change in the moisture absorption was as shown in FIG. 6. In both cases of the irradiation for 20 minutes and the irradiation for 1 hour, the one aged for 1 day gave better results. Therefore, one of the reasons for the difference in the moisture absorption rate may be due to the difference in the crystal structure. Also, irradiation for 20 minutes is less likely to absorb moisture than products irradiated for 1 hour, and good results are obtained. This is because, in the case of irradiation for one hour, the irradiation of the ultrasonic wave continues even after the generation of the crystal is completed, and the diameter of the crystal generated by the vibration of the ultrasonic wave is reduced. Good balance between the ultrasonic wave irradiation time and the crystal precipitation time, the obtained crystal is not broken by the vibration of the ultrasonic wave, the aging proceeds more than the one-hour irradiation product, and a large crystal is obtained, and the effect is increased. it is conceivable that.

[F. Influence of Other Inorganic Salts] In order to confirm the effect of coexistence of other inorganic salts, a moisture absorption test was performed using a special grade reagent close to a pure substance. The samples used were of three types: a sample obtained by drying a recrystallized product, a sample obtained by drying an irradiated product for 20 minutes, and a sample obtained by drying an irradiated product for 20 minutes. The results are as shown in FIG. 7, and no effect due to the irradiation of the ultrasonic wave was observed.

As described above, by irradiating ultrasonic waves during crystal precipitation, the crystal structure is improved, deliquescence can be reduced, and the effect of ultrasonic irradiation requires the coexistence of other inorganic salts. It can be seen that it is. That is, it is presumed that a complex salt of a deliquescent inorganic salt such as magnesium chloride and other inorganic salts is generated in the case of ultrasonic irradiation, which contributes to the reduction of the deliquescent. Further, it is considered that such a complex salt is not formed only by recrystallization.

The mechanism of the formation of crystals by the conventional recrystallization method and the formation of the composite crystals having a low moisture absorption rate according to the present invention, which are summarized based on the above results, will be described by taking magnesium chloride containing trace amounts of iron chloride and calcium chloride as an example. FIG. 8 shows a schematic diagram. Considering the crystal formation reaction in two stages, a nuclide generation reaction stage and a growth reaction stage, in the nuclide generation reaction stage, a strong ultrasonic force acts, a large amount of fine nuclides are generated, and fine particles are activated. . In the crystal growth reaction stage, since the fine particles are activated, a deliquescent inorganic salt and a small amount of other inorganic salts grow as a composite crystal during crystal growth. In contrast, recrystallization alone produces crystals containing a large amount of free water between the crystals, and at the same time, traces of other salts crystallize independently of the deliquescent inorganic salt.

[0025]

According to the method of the present invention, deliquescent inorganic salt crystals which can be easily handled with delayed deliquescence can be easily produced. The deliquescent inorganic salt cannot be deliquescent due to its chemical properties, but according to the method of the present invention, a small amount of other inorganic salts that do not originally crystallize are mixed with the deliquescent inorganic salt as a main component to form a composite crystal. As a result, a crystal having a slow deliquescence rate and a long life as a crystal can be obtained. Further, the ultrasonic irradiation reaction apparatus of the present invention is suitable as an apparatus for performing the above method.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of an ultrasonic irradiation reaction apparatus of the present invention and the progress of ultrasonic waves.

FIG. 2 is a diagram showing a relationship between a moisture absorption rate and elapsed time for samples in different dry states.

FIG. 3 is a diagram showing a relationship between a drying time and a water evaporation rate.

FIG. 4 is a diagram showing the relationship between water absorption and elapsed time for samples without and without ultrasonic irradiation.

FIG. 5 is a diagram showing the relationship between the water absorption and the elapsed time for a sample with different ultrasonic irradiation times.

FIG. 6 is a graph showing the relationship between water absorption and elapsed time for samples without and after aging after ultrasonic irradiation.

FIG. 7 is a diagram showing the relationship between water absorption and elapsed time for samples with and without ultrasonic irradiation using a special grade reagent.

FIG. 8 is a schematic diagram illustrating the mechanism of crystal formation by a conventional recrystallization method and formation of a composite crystal having a low moisture absorption rate.

Claims (4)

[Claims] 1. A deliquescent inorganic salt is dissolved in relatively high-temperature water in the presence of other inorganic salts, and then gradually cooled to a relatively low temperature while irradiating ultrasonic waves to precipitate crystals. A method for producing a deliquescent inorganic salt crystal having a slow deliquesce, characterized by drying. 2. The method for producing a deliquescent inorganic salt crystal according to claim 1, wherein the ultrasonic irradiation is performed by pulse irradiation. 3. The method for producing a deliquescent inorganic salt crystal with a slow deliquescence according to claim 1, wherein after the crystal is precipitated, the ripening is performed while maintaining the same temperature. 4. An ultrasonic irradiation reactor in which an ultrasonic oscillator is mounted on an upper portion of a reaction vessel, wherein the reaction vessel has a structure in which ultrasonic waves are irregularly reflected inside. An ultrasonic irradiation reactor for performing any one of the methods.