JPH0631105A - Multi-stage recrystallization of crystallizable substance for super purification - Google Patents

Abstract

PURPOSE: To execute superrefining of a crystallizable material at an extremely high level by executing plural stages of recrystallization by imparting a metering means for controlling the amounts of a crystal and mother liquor feedback material and controlling feedback ratio conditions. CONSTITUTION: A fresh solution is introduced from respective stages collectors 21 to a crystallizer 22 where crystallization is effected by procedures including cooling. Next, the crystal slurry is divided to the dehydrated crystal and the mother liquor in a separator 23 downstream of the crystallizer 22. The crystal is transferred to a receiver 24 and the mother liquor to a receiver 25. The volume and weight of the mother liquor are metered by a metering feedback receiver 26. The mother liquor above the adjusted amount is discharged from an overflow pipe 27. The crystal is thus executed to >=1 stage of the recrystallization. The mother liquor is subjected to washing of the crystal below one stage. The final crystal product has purity of about 99.999%.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to multi-step recrystallization, and more particularly to crystallization which purifies a crystallizable material to a very high level of purity, typically 99.999 percent order. It relates to a multistage recrystallization method and device for the ultrapurification of possible substances. The reflux ratio conditions are strictly controlled, preferably in connection with establishing and maintaining a steady state at each stage of the system (multi-stage recrystallization method and apparatus),
Thereby facilitating totally automatic control of the reflux ratio conditions by closely monitoring and metering selected mass transfer, charge and / or yield of each stage of the system.

[0002]

BACKGROUND OF THE INVENTION Purification of crystallizable materials by recrystallization techniques is known and has been practiced for many years. Generally speaking, removal of trace impurities from crystallizable materials is extremely difficult by recrystallisation of crystals from saturated solutions or by other techniques including fractional crystallization and fractional freezing procedures. A zone purification procedure that increases the product purity by adding a recrystallization step can be included as a typical purification method, but this method is the last or most purified recrystallization step. The yield% of product formed is sacrificed. For example, dozens of separate evaporation dishes, or crystallizers.
The use of fractional crystallization is well known for the separation of radium chloride from barium chloride by the classical separation procedure using a (crystallizer) elaborate grid pattern.
In this procedure, the crystal crop of each crystallizer is transferred to the adjacent crystallizer in one direction, while the mother liquor is transferred in the opposite direction. The concentration of radium chloride increases to follow the movement of the crystal crop from one crystallizer to the next, but a large number of crystallizers are required and the operating costs for this type of equipment. Is very high.

Generally speaking, currently available fractional crystallization applications recognize the desirability of operating at optimal reflux ratios, but are not necessarily suitable for carrying out this desired approach. Not providing details effectively.

Multi-stage recrystallization techniques include multi-stage recrystallization systems for separating fluid materials having two or more different components. For example, US Reissue Patent 32,241 discloses that a substance containing a component
It is described that the components crystallize on the cooling surface as it flows down. In this patent, the solution of a given stage is used to wash the crystals formed at that stage before they are transferred to the next higher purity stage. The wash solution is a solution that is in the stage just before any substance crystallizes from the wash solution. In the embodiment of this patent, the crystals are transferred to the one-stage high-purity stage as long as a suitable valve does not allow the liquid of the one-stage high-purity stage to come into contact with and dissolve the crystals. The wash solution is used to wash the crystal harvest of a given stage, but before any material from the given stage is crystallized, most of the solution present at that given stage is It's a pure part.

Publications such as US Pat. No. 4,666,456 describe what is essentially a single stage crystallization system. This particular patent shows the continuous partial crystallization of a compound from a liquid mixture, where the mixture can be charged through a plurality of stepped cooling sections. These cooling sections are connected in series,
The temperature of the section following the stepped cooling section is lower than the temperature of the previous section.

[0006]

Through a multi-step recrystallization procedure that achieves a purification level of the order of 99.999 percent, which is exceptional for the multi-step recrystallization procedure. It has been found that by removing certain impurities from the crystallizable material, ultra-purification of the crystallizable material can be achieved by proceeding according to the invention. This includes an effective way of controlling the reflux ratio condition while achieving and maintaining steady state operating conditions.

[0007] In summary, the present invention comprises a multi-step recrystallization process which comprises controlling the reflux ratio conditions by providing a metering procedure which controls the amount of crystals and mother liquor reflux material transferred according to the method and apparatus of the present invention. A method and apparatus for the ultra-purification of a crystallizable substance by a procedure. At each stage, the crystallizable material is dissolved in a solvent or unsaturated solution to form a new solution and then recrystallized from the new solution. The crystals are then separated from the mother liquor.
A metered amount of mother liquor is metered, which metering may include transfer to a reflux receiver at that stage. At the lowest purity stage,
This metered mother liquor gives a controlled amount of by-products. The weighed mother liquor of the other stage is the crystal slurry of the one lower purity stage.
To crystals separated from it in order to wash it.
The crystals collected in the highest purity stage provide the expected amount of crystalline product. A predetermined amount of crystallizable material is charged to the minimum purity stage and another cycle is run.
If desired, an additional similar step of concentrating the by-products is provided to form a purified material of relatively high percentage and a highly impure material of lower percent. obtain. This purified material can be used as a feed for a multi-stage recrystallization system.

A general object of the present invention is to provide an improved method and apparatus for ultrapurifying crystallizable material.

Another object of the present invention is to make the reflux ratio condition effective.
It is an object of the invention to provide an improved ultra-purification system that uses efficient and very tightly controlled multi-step recrystallization.

Another object of the present invention is to provide an improvement in multi-step recrystallization which is able to achieve and maintain a steady state.

Another object of the present invention is improved by near-automatic metering of feed and product discharges to the system and between stages maintaining gradients of different purification levels. To provide ultra-purification of crystallizable material.

Another object of the present invention is to provide an improved multi-stage recrystallization system which achieves very high purification with particularly high yields.

Another object of the invention is to provide a reflux of the wash liquor from one stage of a multi-stage recrystallization system adjacent to the stage where the wash liquor reflux occurs and at a lower purity level than that stage. It is an object of the invention to provide an improved ultra-purification device and method for crystallizable substances, which involves using the design used to replace the residual mother liquor from the crystals formed.

Another object of the present invention is to provide a multi-stage recrystallization system in which minor constituents are separated from major constituents in a particularly efficient and thorough manner.

Another object of the invention is to utilize multiple stages,
It is an object of the present invention to provide an improved apparatus and method comprising forming a new crystal crop at each stage from a mother liquor which is a saturated solution of the components to be purified.

Another object of the present invention is an improved multi-stage fractional crystallization with controlled reflux ratio so that the proper reflux ratio can be used to separate minor components having a given separation factor. It is to provide a system.

Another object of the invention is that the reflux leaving a stage of a multi-stage system is as impure as possible, and the crystalline material leaving the stage is as free of its mother liquor as it is. To provide an improved method and apparatus which maximizes the separation efficiency of each stage.

These and other objects, features and advantages of the present invention will be clearly understood in view of the following detailed description.

[0019]

DESCRIPTION OF SPECIFIC EMBODIMENTS Reference will now be made to the accompanying drawings in the course of this description. In the design illustrated in FIG. 1, a multi-stage recrystallization system has four
It is shown as comprising two different steps, each step processing substantially equal amounts of the various components, while maintaining different purification levels. In the embodiment illustrated, stage L is the stage in which the crystallizable material has the lowest purification level of the stages illustrated in FIG. Step P is the highest level of purification, and steps I1 and I2 have an intermediate degree of purification,
That means that these stages are both purer than stage L but less than stage P, while stage I2 is purer than stage I1. These intermediate stages can be omitted or additional intermediate stages can be added without significantly reducing the yield of the multi-stage crystallization system. 99.99 in a typical situation
Ultra-purification levels of 9 percent order purity can be achieved in four intermediate stages. If higher purity or ultra-purification is desired, 6-8 or more intermediate stages can be used, but it should be recognized that the greater the number of intermediate stages, the greater the processing cost and time. I have to. The flow rates during these various steps are substantially the same, and flow rates are developed to ensure that there is sufficient solvent within each cycle to dissolve the crystals.

Each stage has collectors 21a, 21b, 21
c and 21d are included. These collector-regions or vessels typically function, including heating, to dissolve the crystalline material in the solvent used in the system, but with a separate crystal dissolver or heating device (not shown). It can be provided if desired. The collector-vessel is typically a vessel in which the mother liquor and crystal charge are sufficiently heated to dissolve the crystals to form a new solution, which in some cases is the solution in Can be used to evaporate a controlled weight of solvent from a batch of. A new solution was added from each stage collector to crystallizers 22a, 22b, 2
Means such as the illustrated pumps or other suitable type of equipment can be used to transfer 2c, 22d, and crystallization in the crystallizer is typically carried out by a procedure involving cooling. The crystallizer at each stage is a cooled container for crystallizing a suitable proportion of crystallizable material.

Separators 23a, 23b, 23c and 23d are provided downstream of the crystallizer at each stage in order to separate the crystal slurry into dehydrated crystals and mother liquor.
Each separator can take any suitable form, such as those that utilize gravity separation, those that include centrifugation procedures, and the like, as well as combinations thereof. The crystals in the dehydrated separator can be transferred to crystal receivers 24a, 24b, 24c, 24d, while the mother liquor present in the separator is transferred to suitable mother liquor receivers 25a, 25b, 25c, 25d.

Means are then provided for metering a controlled amount of mother liquor from each mother liquor receiver. Such means at this location, or elsewhere in the cycle, may be synchronized, proportioning, to carry a controlled volume and / or weight of each substance to each stage during the appropriate time of the cycle. It can take the form of a pump or the like (not shown).
Other suitable devices or methods can be used.

In the design illustrated in FIG. 1, this metering function is accomplished using metering reflux receivers 26a, 26b, 26c, 26d, which receive and store the measured volume or weight of mother liquor. Can be any suitable container. Each reflux receiver can be used in combination with a suitable design to ensure that a predetermined volume and / or weight of mother liquor is transferred to it. One design is to provide a suitable metering device that can monitor and control the flow to the metering reflux receiver. Another design could be to provide a liquid level response probe in the metering reflux receiver that detects when a volume of mother liquor is present. Yet another method is that excess or residual mother liquor in each mother liquor receiver is thereby removed, so that a controlled amount of mother liquor from mother liquor receivers 25a, 25b, 25c, 25d to metered reflux wash receivers 26a, 26b, 26c, 26d over
The flow tubes 27a, 27b, 27c and 27d are provided. Regardless of what design is used, there is a regulation function in the metering or control means so that this device can be used to achieve different reflux ratios and / or to process different crystallizable substances. Incorporation is typically preferred.

In this way further means are provided for transferring metered or regulated volumes and / or weights of mother liquor from each reflux wash liquid receiver. In stage L, this means provides a by-product from stage L, which by-product may be further added upstream of stage L or simply treated by-product later, in suitable multi-stage recrystallization. It can be further processed by a chemical concentrator. Each stage of such an enrichment system is similar to that shown in FIG. 1, and FIG.
In more detail.

Other quantities of the mother liquor or otherwise adjusted amounts are crystallized in the mother liquor having a higher purity than the mother liquor remaining with the crystals after the separators 23a, 23b, 23c, 23d are operated. In order to carry out the washing of, the crystals are transferred to the crystals of one lower purity stage. Typically, the transfer is done by washing the mother liquor through the crystals, which can be easily accomplished by flowing the mother liquor through a separator. More specifically, the metered mother liquor from stage I1 is transferred to the separator 23a and the metered mother liquor from stage I2 is separated into the separator 23d.
And the weighed mother liquor from stage P is separated into the separator 23c.
Moved to. Preferably the predetermined amount and temperature of the solvent,
Enter separator 23d or crystal receiver 24d to replenish the required amount of Stage P reflux solution to dissolve these crystals well, and also to wash Stage P crystalline product.

The crystalline material is transferred from each crystal receiver or the like to a collector in the higher purity stage or its equivalent. In the case of crystal receiver 24d, the crystals removed therefrom constitute the ultra-purified crystal product according to the invention. In a preferred embodiment, the amount of this product is metered or adjusted by any suitable means, such as those described above for metering or controlling the mother liquor reflux operation. The drawings show excess or residual crystal transfer tubes 28a, 28b, 28c, 28d.
Where the reflux ratio and steady state of the system are not disturbed and these crystals are recrystallized and not lost, all of the excess crystals in the crystal receiver are at the same stage collector. -Transferred to etc. For example, transfer tube 28a transfers excess crystal from crystal receiver 24a to collector-21a, and substantially the same transfer can be performed at each of the other stages of the system.

Depending on the particular metering means used, the transfer of excess crystal out of the crystal receiver can take place before or after the transfer of the metered amount of crystal. Transferring a weighed weight and / or volume of crystals is to the location where further crystal recrystallization and purification of the higher purity stage is done. In the embodiment illustrated in FIG. 1, this transfer involves transferring metered crystals from crystal receiver 24a to collector-21b, crystal receiver 24b to collector-21c, and crystal receiver 24c to collector-21d. It includes that.

Whatever substance is then present in each collector, it is then combined with fresh solution,
It is then transferred to the same stage crystallizer in order to carry out recrystallization of each collector from a fresh solution. For the lowest purity stage collector-21a, some of what comes in is a charge of recrystallizable material, which is also metered as needed to maintain the system's reflux ratio and steady state. sell. Collector-21
The material then present in a is transferred to crystallizer 22a by any suitable means, such as the illustrated pump.
Similarly, the material inside the collector-21b is crystallizer-2.
2b, and so on for each stage of the system.

Preferably, withdrawing the mother liquor reflux from the crystallization vessel in which the mother liquor is produced is carried out after completion of a given amount of crystallization. This results in the greatest possible difference in purity between crystals at any given stage and reflux withdrawn. This maximizes the separation efficiency of each step.

FIG. 2 illustrates another embodiment of the present invention, which identifies other ways of accomplishing the objects of the invention.
Again, there are four stages: stage L, stage I1, stage I
2 and stage P are shown. Each of these stages
It has substantially the same implications as discussed herein with respect to the embodiment of FIG. Each stage has collectors 31a, 3
1b, 31c, 31d, crystallizer-32a, 32
b, 32c, 32d and separators 33a, 33b, 33
c, 33d, each of which operates in much the same manner as the similarly named components of the embodiment of FIG.

Instead of providing a separate crystal receiver as described in FIG. 1, the required amount of crystal is passed from the single stage separator through tubes 34a, 34b, 34c to a higher purity stage collector. -Moved to. The flow of such crystals is generally discussed here, and as outlined in Figure 2,
It can be facilitated by pumps and / or metering devices. These crystals are passed from separator 33a to collector-31b, while the crystals from separator 33b are passed to collector-31c and the crystals from collector-33c are passed to collector-31c.
Passed to 31d. In the embodiment described, one crystal receiver 29 is included. The desired product is then transferred via tube 46 to another location.

Excess crystalline material from each stage is preferably passed along with the cleaning material discussed above to the collector of the same stage for subsequent recrystallization in the crystallizer of that stage. . In stage L, stage I1 and stage I2, this transfer is respectively the separator 33 of that stage.
a, 33b, 33c through tubes 38a, 38b, 38c directly to collectors 31a, 31b, 31c. In stage P, this transfer is performed by the crystal receiver 2
9 through tube 38d to collector-31b. Each collector-31a, 31b, 31c, 31d
The material within is transferred to a respective crystallizer for each stage as shown. In this embodiment, the mother liquor from the mother liquor receiver 35d is discharged as a by-product, while the mother liquor reflux cleaning liquid receiver 36 from the receivers 35b, 35c, 35d.
a, 36b, 36c. Substantially pure solvent can optionally be introduced to the reflux wash receiver 36d. Metering means, such as valves, pumps, etc., can be located at 49a, 49b, 49c to allow the draining of the reflux wash solution from the crystals being washed in the separators 33a, 33b, 33c, 33d.

The operation of the embodiment shown in FIG. 2 will be described in more detail. In order to control the reflux cleaning liquid discharge rate from the reflux cleaning liquid receiver at each stage to the crystallizer at that stage, the valve 4 is controlled.
1a, 41b, 41c, 41d, etc. may be provided.
Valves 42a, 42b, 42c, 42d, etc. may be provided to regulate mother liquor discharge from each stage separator to its mother liquor receiver. Generally, as discussed above, valves 43a, 43b, 4 are provided to allow for controlled transfer of crystals from each stage of separator to the collector of one higher purity stage.
3c or other suitable weighing means is provided, and the weighing means 3
In the case of 4d, it is installed so that the crystal can be transferred to the crystal receiver 29. Valves or other metering means 44a, 44
b, 44c, 44d can be provided to control the discharge of mother liquor from the mother liquor receiver to the same stage collector. Means 45 transfer excess crystalline material to the highest purity stage collector, and means 46 transfer product out of the multi-stage system illustrated in FIG. Metering means 47 may be provided to control the flow of by-products out of the system, in this case from the mother liquor receiver 35a. The system can be charged through the transfer means 48, which is the lowest purity stage collector-31a.
Open mouth to.

Overflow tubes 51a, 51b, 51
Means such as c, 51d, etc. are provided so that excess or overflow mother liquor can be transferred from each stage mother liquor receiver to the same stage collector. Overflow tube 3
8d can be used to transfer the overflow crystals from the crystal receiver 29 to the highest purity stage collector 31d. These overflow means can function to determine the stagnant volume to be retained in the mother liquor or crystal receiver by the level in such receiver.

Referring to FIG. 3, an impurity concentration system having two stages is illustrated. Again, additional steps can be added as desired. Details of the components of each step generally follow those shown in FIGS. 1 and 2 or their equivalents. In general, the impurity enrichment section is suitable for providing impurities in the by-product from Stage L to provide a small portion of new, highly impure by-product and some of the charge to Stage L. Can be provided for the purpose of concentrating to a large proportion of the substance. This typically improves the overall system yield, especially when the impurity enrichment section is returned to Stage L as the feed. This can be facilitated by making the product from the impurity concentration section substantially the same purity as the charge of crystallizable material into Stage L. Generally speaking, the by-products of the impurity enrichment section make up a small volume percent of the charge there and will have a much higher impurity concentration than the charge material that is the Stage L by-product.

The difference between the operation of the impurity concentrating system and the main system of the type described in FIGS. 1 and 2 is that, as illustrated in FIG. It means that the impurity concentration system is charged for each stage.

Stage B, the stage in which the more impure or the most impure substance is treated, communicates with Stage A in substantially the same manner as the adjacent stage in FIGS. The mother liquor is transferred from the more pure stage A to the less pure stage B by means of transfer 6
Transferred through 1. The crystalline material from stage B moves to stage A through transfer means 62. The desired amount of product exits Stage A while the recycled crystalline material is transferred 63.
Go to step A again. The desired amount of by-products are removed from stage B, while mother liquor recycle is performed by transfer means 64.

To elaborate on the various control and / or metering functions and means discussed in connection with the various stages and transfers between stages, the following control and / or metering schemes are preferred. During each cycle, substantially the same volume of reflux mother liquor should be transferred from each stage to the next lower numbered stage. During each cycle, substantially the same volume of recrystallized crystalline material should be transferred from each stage to the next higher numbered stage. During each cycle, a controlled volume of recrystallized crystalline material should be discharged from the highest purity stage as the product of the purification system. During each cycle, a controlled volume of mother liquor should be discharged from the lowest purity stage as a byproduct from the purification system. During each cycle, the volume of feed material that is substantially the same as the sum of the volumes of product and by-products passed out of the system is at the lowest purity stage of the primary system and / or higher than the by-product enrichment system. It should be introduced into the purity or highest purity stage.

During each cycle, a sufficient amount to provide at least sufficient crystalline material to allow an appropriate volume of material to be transferred from each stage to one higher purity stage during each operating cycle. , And typically some excess of material must be recrystallized. During each cycle
There should be sufficient volume of mother liquor remaining in each crystallizer to allow the proper volume of mother liquor reflux to be transferred from each stage to the next lower numbered stage during each operating cycle. Conditions within the crystallizer, including crystallization time, should be limited or otherwise controlled.

The reflux ratio of a given section is the ratio of the cycle weight of the reflux solute to the cycle weight of the crystalline product discharged from the same stage (reflux solute is discharged from each stage of the system). Which is monitored at the highest purity stage, for example). The reflux ratio of the impurity concentration system can be different than that of the primary recrystallization system, and the duration of each cycle of each of these systems can also be different. The reflux ratio can be controlled by adjusting the volume of product removed from the system per cycle and the volume of reflux transferred from stage to stage. The% yield of ultra-purified product recovered from the crystallizable material charged to the system can be controlled by adjusting the volume per cycle of product and by-products removed from the purification system. Generally speaking, the higher the reflux ratio (eg 1: 1) the greater the difference in purity per stage from one stage to the purer stage and the lower the reflux ratio (eg 0: 1). .5:
1), a higher amount of product occurs each cycle.

In more detail about controlling the reflux ratio, this is done by controlling the weight of reflux solute transferred from each stage to one lower purity stage per unit time and from each stage to one higher purity stage. This can be achieved by controlling the weight of crystalline product from each stage transferred per hour. Furthermore, the weight of the crystalline product generated per unit time is controlled by controlling the weight per unit time of the crystal entering the highest purity stage, and controlling the weight per unit time of the reflux solute leaving the stage. Can be indirectly controlled by the difference between these incoming crystals and the leaving reflux solute is the weight of the crystalline product. More specifically, two main factors that determine the reflux ratio of the system are controlled. These factors are the net weight of crystalline product produced per cycle by the highest purity stage, and the weight of mother liquor reflux solute transferred from this stage to the next lower purity stage per cycle.

Depending on the indirect weighing method, the operator can weigh the correct weight of the reflux condensate by withdrawing the appropriate volume of mother liquor to be used as reflux. The percentage of solute in the reflux is a function of its specific gravity,
Monitoring it can be useful to provide the proper volume of reflux needed to transfer the correct weight of solute as reflux. It is also possible to monitor and control the specific gravity of the new solution formed during each stage, or to combine all the crystals and the mother liquor therein added to the crystallizer of that stage to make a new solution. In some cases, this can be desirable and preferred. Specific gravity is the addition of pure solvent to a new solution,
Alternatively, it can be adjusted as needed by either evaporating the solvent from the fresh solution. Adjustment of the specific gravity can be done in the crystallizer at any stage, either by adding pure solvent or by evaporating the solvent.

It is important to maintain the desired steady state throughout the system. When this steady state is achieved, the system exhibits the following characteristics. The same weight of crystallizable material (or major component) to be purified is present in the crystallizer at each stage during the crystallization process.
This same weight is present in the crystallizer at each stage during the crystallization period of each cycle. Each stage yields the same weight of crystalline product during each cycle, which weight is substantially the same as the weight of charge introduced into the system. Equal weight of product crystals are made during each cycle. The same weight of byproduct solute is created during each cycle. The weight of product per cycle is the same as the weight of charge introduced per cycle minus the weight of byproduct solute produced per cycle. Each cycle has substantially the same reflux ratio.

Such a steady state is achieved and maintained according to the present invention by the following steps. Add the same weight of charge during each cycle of this cycle. The same weight of pure solvent was added to the highest purity stage during each cycle of the system, this weight being just enough weight to produce the required amount of reflux that must be discharged from this stage during each cycle. Should be. Monitor the specific gravity of the new solution in the crystallizer or collector so that the specific gravity of each solution to be crystallized is the same at each stage.
Then adjust. The temperature of the solution to be crystallized and separated is monitored and adjusted to ensure that the crystallization temperature and the specific gravity of the mother liquor at each stage are the same during each cycle.
All of the crystalline product that is recrystallized in each stage is transferred to the crystal dissolver in one high purity stage during each cycle. The same volume of mother liquor reflux from each stage is then transferred to one lower purity stage (or transferred elsewhere from the lowest purity stage as a byproduct).
During each cycle, the crystalline product is removed from the highest purity stage after the pure solvent is added to the highest purity stage to form a new reflux for the crystalline product.

When these conditions are maintained, the weight of crystals produced in each stage is the same per cycle as the weight of charge introduced into the lowest purity stage during each cycle. Also, when such a steady state is maintained, the reflux ratio of the system remains substantially the same during one running series.

A sufficient amount of mother liquor retention should be maintained in each stage to allow the production of a suitable weight of crystals per cycle in each stage. This required weight is at least equal or greater than the weight of charge introduced during each cycle.

When controlling the reflux ratio according to the invention, it is necessary to adjust both the weight of product per cycle as well as the amount of reflux transferred. Three controllable variables are considered for adjusting the weight of the crystalline product. These are the charge introduced during each cycle, the by-products discharged in each cycle, and the crystalline products discharged in each cycle. By introducing the same weight and / or volume of material for each stage of crystallizer at the beginning of the crystallization period, control of any two of these variables automatically sets the third variable. Control. In all situations, the weight and / or volume of charge introduced per cycle is equal to the sum of the weight and / or volume of product and by-products discharged per cycle. Further reflux transfer can be maintained by metering the mother liquor reflux transferred from each stage to one lower purity stage or by measuring the recrystallized crystalline material transferred from each stage to one higher purity stage. .

Control of the reflux ratio condition can therefore be achieved according to the invention by metering three different transfers. In the first case, the charge of crystallizable material, the mother liquor byproduct and the mother liquor reflux are each metered. In the second case, the recrystallized product, the charge and the reflux are weighed. In the third case, product, by-products and reflux are metered in. In the fourth case, the charge, by-products and crystalline material transferred from one stage to another are weighed. In the fifth case, the product,
The transfer of charge and crystalline material is metered. In the sixth case, the transfer of product, by-product and crystalline material are each metered.

The procedure and apparatus according to the invention are suitable for ultrapurifying various crystallizable salts in solvents such as water, alcohols, ethers, ketones and the like. Examples of recrystallizable substances in this respect are sodium chloride, potassium chloride, cesium chloride, barium nitrate, copper nitrate, sodium iodide, barium chloride, copper sulphate, nickel sulphate, alum (ammonium, aluminum sulphate). ), Ammonium molybdate, etc. are included. The following examples illustrate some specific procedures suitable for this type of material.

[0050]

【Example】

Example 1 An impurity stripping apparatus of the type outlined in FIG. 1 but containing 6 stages instead of the 4 stages described in the drawing, 12.5 kg per cycle
Was operated to produce 8.46 kg of ultra-purified cesium chloride crystals and 4.23 kg of impure cesium chloride solute by-product from an industrial grade cesium chloride crystal feed. The solvent used is water. The operator of this system can maintain or change the reflux ratio depending on the particular purpose of each cycle.

First, an initial scale determination cycle or start cycle was performed. Prior to the start of the first cycle of the calibrating run, 35.86 kg of technical grade cesium chloride charge and 13.26 liters of distilled water were added to each stage collector. The device was then operated at a reflux ratio of 1 to 0 for 12 cycles in order to achieve a normal operating distribution of impurities in the device before normal operation began. The reflux ratio was then changed to 1-0.5 for each cycle.

During the beginning of the 1-0 reflux ratio cycle, the crystal dissolver vessel or collector was heated to boiling, 118 ° C. until all the crystals had dissolved. Distilled water is added to reduce the specific gravity at the stage where the specific gravity must be adjusted, or additional evaporation is performed to increase the specific gravity so that the crystallization temperature of the solution at each stage is as close to 100 ° C as possible. Was done either. Crystallization was then carried out for 2 hours, during which the temperature was lowered to 10 ° C., forming cesium chloride crystals very close to 12.7 kg in each stage. After separating these crystals from the mother liquor, 19.9
7 kg of mother liquor was transferred from each stage mother liquor receiver to the same stage metering reflux receiver. This transferred mother liquor was 12.
It contained 7 kg of cesium chloride.

The separated crystals were then washed while undergoing centrifugal rotation of the separator in each stage, the washing being carried out by the reflux mother liquor from the reflux receiver in the one-high purity stage. In addition to washing the crystals, this step also transferred the reflux from each step to the next lower purity step. Crystals at that stage were not washed because there was no reflux entering the highest numbered stage. The result of this washing step is that the composition of any mother liquor still moistening the crystals after the washing step of any given stage is the composition of the mother liquor of the next higher purity stage to which these crystals are transferred. Had substantially the same composition as.

The transfer of crystals was then carried out and 12.7 kg of washed crystals were transferred to the crystal melting vessel or collector of the higher purity stage except in the highest purity stage. Since these early cycles are of a starting or calibrating nature and have a reflux ratio of 1 to 0, the recrystallized crystals of the highest purity stage will be used in the same stage of the crystal dissolver or collector. And 7.27 kg of water was added thereto so that all the crystals could be dissolved.

The mother liquor retentate in the mother liquor receiver of each stage is returned to the collector of each stage until the specific gravity of the solution is increased to the point of achieving a crystallization temperature of 100 ° C., the crystallizer or collector of minimum purity. The water was evaporated from.

This procedure was carried out over 12 consecutive cycles. For all subsequent cycles,
The reflux ratio was modified to a ratio determined to be an advantageous reflux ratio of 1-0.5. Cesium chloride charge 1 to be ultra-refined
2.7 kg were introduced into the crystallizer or collector of the lowest purity stage and 8.46 kg of ultra-purified product with a purity of 99.999% was taken from the highest purity stage during each cycle, and 4 .23 kg of byproduct quality was withdrawn from the lowest purity stage during each cycle.

The procedure followed by each cycle is similar to that performed during the scale determination cycle, but with the following modifications. 6.65 kg of mother liquor was withdrawn from the mother liquor receiver and transferred to a metered reflux receiver at each stage. This known amount of mother liquor reflux had a crystallization temperature of 10 ° C. and contained 4.23 kg of cesium chloride content and 2.42 kg of water solvent. The contents of the lowest purity stage reflux receiver were discarded as by-products. For the other steps, 6.65 kg of reflux was transferred to wash the recrystallized crystals of the one lower purity step. The highest purity stage recrystallized crystals were washed with 2.42 kg of warm distilled water and these crystals were removed from the system as 8.46 kg of product. The recrystallized crystals of the other stage were transferred to the crystal dissolver or collector of the one higher purity stage. It is not necessary to boil down the lowest purity stage. Instead, another 12.7 kg of cesium chloride charge was added. Steady-state was established and maintained at each stage during these non-scaled determinations, ie operating cycles. These steady states involved having 35.56 kg of the same residence weight of cesium chloride in each crystal dissolver or collector at the end of each cycle of each experiment. Cesium chloride crystals of the same weight, i.e. 12.7 kg, were formed in each stage of the crystallizer during each cycle of each experiment. The same weight, ie 8.46 kg of cesium chloride product was purified during each cycle.

The reflux ratio was between 1 and 0.5 during each cycle of the experiment.
This control is possible by establishing their steady state and by directly controlling the weight of charge introduced per cycle and the rate of reflux transfer from stage to stage in the system. Was done. This control also controls the weight of product produced per cycle.

Example 2 An impurity concentrating apparatus as outlined in FIG. 3 was carried out except that it was modified into a three-stage one. This system was used to treat the cesium chloride byproduct solution made according to Example 1. The impurity concentrating system recovered 75% of the qualities as a crystalline product having substantially the same purity as the charged material fed into the apparatus of Example 1. The remaining 25% of this quality is
It was converted to a very impure content containing virtually all the impurities present in the charge. The by-product solution from Example 1, which was the charge to this impurity concentration system, had a crystallization temperature of 10 ° C. and contained approximately 63.6 wt% cesium chloride content. In this regard, a typical quality also contained by weight about 500 ppm sodium chloride and about 5000 ppm rubidium chloride.

The crystal dissolver at each stage of the impurity concentrating system was charged with 33.3 kg of charge, thus 21.19 kg of cesium chloride content and 12.12 kg of water. 10
Adjusting the specific gravity to exhibit a crystallization temperature of 0 ° C required evaporation of water to 7.83 kg.

7.5 kg of cesium chloride crystals were made by crystallization at each stage and the mother liquor and crystals were separated as described in Example 1. 7.47 kg of mother liquor was transferred from the highest purity stage mother liquor receiver to the reflux receiver and 4.37 kg of lowest purity mother liquor was transferred to the reflux receiver. The crystals were washed and 7.5 kg of washed crystals in the highest purity (concentration) stage were removed as the product of the impurity concentration section. 7.5 kg of washed crystals from the lowest purity (concentration) stage were transferred to the next higher purity (concentration) stage.

Boiling was carried out in a minimum purity crystal dissolver, the dissolver containing 33.3 kg of solution,
The solution was 21.17 kg cesium chloride and 12.1 kg.
It contained 2 kg of water and was reduced to 7.83 kg. After boiling, there was 29 kg of fresh solution with a crystallization temperature of approximately 100 ° C. The crystals that dissolved in the higher purity stage provided 33.3 kg of a new solution, which contained 21.17 kg of cesium chloride and 12.1 kg.
It contained 2 kg of water.

An additional cycle, identical to this first, was performed with 7.5 kg of crystalline product per cycle and 2.
It was carried out to continue the production of 5 kg of impure cesium chloride. After several cycles, the impurity distribution at this stage of the impurity enrichment section reached equilibrium.
The by-product contained when equilibrium was reached contained almost four times the concentration of impurities in the charge.
The reflux ratio of the impurity concentration section was 1 to 0.75.

It should be understood that the embodiments of the invention described describe some of the applications of the principles of the invention. Many modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention.

[Brief description of drawings]

FIG. 1 is a general sketch of a flow chart of a multi-stage ultra-purification system according to the present invention, and FIG. 2 is a schematic diagram of another embodiment flow chart for carrying out the multi-stage recrystallization ultra-purification according to the present invention. And, FIG. 3 is an illustration of an example of a multi-step impurity concentration system as referred to in the present invention.

Claims (22)

[Claims] 1. A method for ultra-purifying a crystallizable substance by a multi-step recrystallization procedure comprising controlling a reflux ratio condition, wherein the crystallizable substance of each step is dissolved and recrystallized in each step. Through a plurality of substantially overlapping cycles that are performed at substantially the same time during each step, providing a plurality of steps (hereinafter a group of steps) having a container containing a crystallizable substance, The step group is carried out by cyclically advancing a series of steps, and one of the step group is that a controlled amount of a crystallizable substance to be ultrapurified as a feed is a minimum purity step container. Is a minimum purity step that is added from outside the step group, and another one of the step groups is that a solvent that does not contain the crystallizable substance and is different from the crystallizable substance is added from outside the step group. It is the highest purity stage and each stage The sequence of steps of step (a) ~
(J), ie (a) dissolving the crystallizable material to be recrystallized in a collector-vessel, provided that the crystallizable material for the lowest purity stage is crystallizable to be ultrapurified The above charge of material, and for the remaining steps, the crystallizable material is the material that has been recrystallized in one less pure step and is subjected to this dissolution step from the crystallizable material and primarily the solvent. The mother liquor from the stage made up is combined in the stage, thereby dissolving the crystallizable material in the solvent and forming another saturated fresh solution in the collector-vessel, Dissolving is accomplished by making the saturated fresh solution a solution in which all crystallizable material is dissolved in the solvent, and (b) adding another saturated fresh solution of each step from the collector-vessel to the crystallizer-vessel. Moved to (C) recrystallizing the crystallizable material in the crystallizer-vessel at each stage, wherein the recrystallizing step comprises re-crystallizing the temperature of the another saturated fresh solution. Crystallizing, thereby lowering to a selected temperature, forming in each stage an amount of crystalline slurry containing recrystallized crystals, (d) bringing the crystalline slurry of that stage Transfer to a separation vessel, (e) separate the crystal slurry into recrystallized crystals and mother liquor in the separation vessel, and (f) adjust the amount of the mother liquor separated in step (e) to that stage. Of the separated mother liquor to the collector-vessel of the stage, thereby leaving only the recrystallized and separated crystals in the separation vessel, (g) When the step is the minimum purity step, the step (f) The adjusted amount of the separated mother liquor is a by-product transferred to the outside of the step group, and when the step (h) is other than the minimum purity step, the adjusted amount of the mother liquor provided to the reflux vessel in the step (f) is Transferring to a lower-purity stage separation vessel, whereby the recrystallized separated crystals in the lower-purity stage separation vessel are washed with a mother liquor that is purer than the one-purity stage mother liquor, (i) Transfer a controlled amount of the recrystallized crystals separated in step (e) to the collector vessel of the one higher purity step,
However, the term "recrystallized crystal" as used herein means that a controlled amount of the recrystallized crystal in the step (i) of the highest purity step is outside the step group as an ultra-purified recrystallized crystal product. Except in the case of transfer, it corresponds to the crystallizable material of step (a) of the one-stage high-purity stage, and all the remaining recrystallized crystals separated in step (e) are stored in the collector-vessel of that stage. And (j) the reflux ratio of the multi-step recrystallization procedure was changed to step (f)
Controlling by adjusting said adjusted amount of mother liquor transferred during step (i) and adjusting the amount of recrystallized crystalline product transferred from the highest purity stage during step (i) How to be. 2. The method of claim 1, wherein the crystalline product has a purity of about 99.999 percent. 3. The method of claim 1, wherein the temperature conditions are substantially the same within each step. 4. The method of claim 1, wherein the system comprises a number of stages between about 2 and about 10. 5. The method of claim 1, wherein the adjusted amounts of mother liquor and crystals transferred between the steps are substantially the same regardless of the steps transferred to or about to be transferred. . 6. The method of claim 1, further comprising transferring the crystals separated in step (e) to a crystal receiver for carrying out step (i). 7. Each collector prior to step (c)
The method of claim 1, further comprising adjusting the specific gravity of the fresh solution therein. 8. The step of controlling the reflux ratio comprises charging crystals of a crystallizable substance, mother liquor, by-products at each stage of the system (stage group) and throughout each cycle thereof.
2. The method of claim 1, comprising adding the same amount of wash liquid and product, removing and / or transferring, and maintaining the same temperature conditions at each step and each cycle. 9. A crystallizable material charge, wherein said adjustment of product discharged from the system (stages) is introduced in each cycle, by-products discharged in each cycle, and products discharged in each cycle. 2. The method of claim 1, comprising adjusting any two of 10. A step (j) of metering an adjusted amount of said mother liquor
The method of claim 1 wherein is controlled indirectly by metering the recrystallizable crystalline material that is transferred from each step to a higher purity step. 11. The above control of the product discharged from the system (stages) is such that the charge of crystallizable material introduced in each cycle, the by-product discharged in each cycle, and the product discharged in each cycle. A step of controlling the adjusted amount of mother liquor, wherein step (j) is transferred from each step to a higher purity step. The method of claim 1, wherein the method is indirectly controlled by: 12. The method further comprises an impurity concentration system having a plurality of concentration steps for treating the by-product of step (g), the impurity concentration system including a highest purity concentration step and a lowest purity concentration step. Therefore, the impurity concentration system is not charged to the highest purity concentration step, the by-product from the impurity concentration device is from the lowest purity concentration step, and the concentrated product from the impurity concentration device is from the highest purity concentration step. The concentrated product is purer than the stage (g) by-product, each said concentration step dissolving the crystallizable material, recrystallizing it, separating it into crystals and mother liquor, The method of claim 1, wherein the mother liquor is transferred to one lower purity stage and the crystals are transferred to one higher purity stage. 13. A step of providing a controlled amount of mother liquor for washing crystals of a single lower purity stage, the step of transferring the controlled amount of mother liquor, moving the mother liquor to the reflux receiver of that stage prior to said step. The method according to 1. 14. An apparatus for ultra-purifying a crystallizable material by a cyclic multi-step recrystallization procedure, wherein the steps are performed through substantially overlapping cycles that occur substantially simultaneously within each step, and a minimum purity step. And a plurality of stages (hereinafter referred to as stages) having constituents including collector means for each stage, and a controlled amount of crystallizable material at a minimum purity stage. Means for adding a solvent for the crystallizable substance, which is different from the crystallizable substance and does not contain the crystallizable substance, to the highest purity step, Means for dissolving the crystallizable substance in the mother liquor containing the solvent to form a saturated new solution, the temperature of the saturated new solution at each step to crystallize the crystallizable substance from the new solution. By lowering the selected temperature,
Means for recrystallizing substantially all of the crystallizable material in the saturated fresh solution to form an amount of crystal slurry containing recrystallized crystals at each stage, the crystal slurry at each stage Means for separating the recrystallized crystals and mother liquor, and transferring the separated mother liquor to the mother liquor receiver at each stage, and adjusting the amount of mother liquor from the mother liquor receiver downstream of the mother liquor receiver at that stage. Refluxing means at each stage to provide a controlled amount of mother liquor by metering, with the exception of the lowest purity stage, transferring the controlled amount of mother liquor at each stage to one lower purity stage and recrystallizing one lower purity stage. Means for washing the crystals with the mother liquor from the more pure stage, means for giving a controlled amount of the mother liquor from the lowest purity stage to give a controlled amount of by-products, with the exception of the highest purity stage, The recrystallized crystal is collected in a high purity stage collector. Means for collecting the adjusted amount of recrystallized crystals from the separating means of the highest purity step as an adjusted amount of ultra-purified crystalline product, an excess over the adjusted amount of mother liquor measured by the reflux means. Minutes of residual mother liquor from each of the mother liquor receivers of each stage to the collector of the same stage, the reflux means and the means for collecting a controlled amount of ultra-purified product. An apparatus comprising means for controlling the reflux ratio of a multi-stage apparatus, further comprising means for maintaining a steady state within and between stages. 15. The means for transferring the adjusted amount of the mother liquor to the one-step low-purity stage separates the adjusted amount of the mother liquor passed to the mother-liquor receiver at a stage other than the minimum-purity stage into the one-step low-purity stage. 15. An apparatus according to claim 14 which is a means for cleaning transfer to the means. 16. The apparatus of claim 14, further comprising means for maintaining substantially equal temperature conditions within each constituent of each stage. 17. The device of claim 14, wherein the device comprises a number of stages between 2 and about 10. 18. The apparatus of claim 14 wherein the means for transferring crystals comprises a crystal receiver separate from the separating means. 19. A fresh solution slurry in each collector means.
15. The apparatus of claim 14 including means for adjusting the specific gravity of the. 20. The steady state maintaining means comprises means for controlling the means for transferring the mother liquor, the means for washing and transferring, the means for transferring the crystals, and the means for collecting the crystals, whereby these 16. The apparatus of claim 15, wherein each means controls the transfer of substantially equal amounts of the respective substance between each of the plurality of stages (groups of stages). 21. The method further comprises an impurity concentrator having a plurality of concentrating stages for further processing the by-products from the lowest purity stage, the impurity concentrating device comprising at least a highest purity concentration stage and a lowest purity concentration stage. A charging means for passing the by-products from the lowest purity stage to the highest purity concentration step, a discharge means for removing by-products from the lowest purity concentration step, and a concentrated product removed from the highest purity concentration step. Product overflow means for purifying the concentrated product, wherein the concentrated product is purer than the by-product from the lowest purity step, and each of the concentration steps is a by-product from the lowest purity step. Means to dissolve organisms, means to recrystallize it, means to separate it into crystals and mother liquor, means to transfer a controlled amount of mother liquor to one lower purity concentration step, and means to transfer crystals to one higher purity concentration step Including 15. The device of claim 14, which is: 22. The apparatus of claim 14, wherein the means for transferring the mother liquor comprises a reflux receiver separate from the mother liquor receiver.