KR20060009873A - Method including antisolvent crystallization process - Google Patents

Abstract

A method for preparing a salt composition using an antisolvent,

Comprising the following processes a), b), c), d) and e) or comprising the following processes a), b), c), d), e) and f), or the following processes a), b) , c), d), e) and g) or the following processes a), b), c), d), e), f) and g), preferably closed loop method loop process, the salt is sodium chloride, and preferably further includes a reverse osmosis process before the overflow of the crystalliser / settler is fed to the nanofiltration unit. It is characterized by:

a) supplying water to the inorganic salt source to form an aqueous solution comprising the inorganic salt;

b) feeding said aqueous solution to a crystallizer / settler;

c) contacting the aqueous solution with at least one antisolvent, wherein the antisolvent crystallizes some or all of the salt, and at least one of these antisolvents is crystal growth inhibiting property, scaling inhibiting property inhibiting property) or crystal growth inhibition property and scaling inhibition property, and if the anti-solvent does not exhibit effective crystal growth inhibition property, effective scaling inhibition property, or effective crystal growth inhibition property and effective scaling inhibition property, one kind The above crystal growth inhibitor is added to the antisolvent, the aqueous solution, or the antisolvent and the aqueous solution, or the at least one scaling inhibitor is added to the antisolvent, the aqueous solution, or the antisolvent and the aqueous solution, or the at least one crystal growth inhibitor and the at least one kind Scaling inhibitors can be added to an antisolvent, an aqueous solution, or an antisolvent and an aqueous solution. Also added;

d) supplying an overflow of a crystallizer / settler comprising at least one antisolvent and a salt aqueous solution to a nanofiltration device (the nanofiltration device having a membrane for separating at least one antisolvent from an aqueous salt solution) ;

e) removing the crystallized salt from the crystallizer / settler and sending it to an aqueous slurry;

f) recycling at least one kind of antisolvent to the crystallizer / settler;

g) recycling the water from the slurry to a first dissolution process, to a crystallizer / settler, or to a first dissolution process and to a crystallizer / settler.

Description

PROCESSES INVOLVING THE USE OF ANTISOLVENT CRYSTALLISATION

The present invention relates to a process for preparing an inorganic salt composition comprising a process for crystallizing salts from a crude aqueous solution using an antisolvent and to drinking and / or process water. It relates to a manufacturing method.

Many inorganic salts are industrially prepared from aqueous solutions prepared by dissolving the natural source of salts in water. Such salts are conventionally obtained by crystallizing the salts from an aqueous solution by evaporation of water, which is usually carried out using a multiple-effect or vapor recompression evaporator. Multiple effect systems typically contain three or more forced-circulation evaporating vessels connected in series. The steam produced in each evaporator is fed to the next evaporator in a multi-effect system to increase energy efficiency. The steam recompression forced circulation evaporator consists of a crystalliser, a compressor, and a vapor scrubber. The aqueous salt solution enters the crystallizer vessel where the salt is crystallized. The steam is recovered, scrubbed and compressed for reuse in the heater. Both recompression evaporators and multiple effect evaporators are energy intensive due to the water evaporation process involved. In addition, aqueous salt solutions are typically prepared by dissolving the natural source of the salt in water containing a large amount of contaminants. Therefore, further purification of the salt solution, additional washing of the prepared inorganic salts, and / or energy consuming drying processes must be applied prior to crystallization to reduce the level of contaminants.

Such contaminants in aqueous salt solutions from natural sources include potassium, magnesium, calcium and sulfate ions. In addition, small amounts of carbon dioxide, bicarbonate and carbonate are present in the crude aqueous solution. During evaporative crystallization in conventional evaporators (multi-effect or vapor recompression apparatus), which are usually operated at elevated temperatures, CaSO ₄ , CaSO ₄ .2H ₂ O and CaCO ₃ scaling are formed especially at the surface of the heat exchanger. The reason for this scale formation is due to the evaporation of water, the aqueous salt solution is more concentrated, resulting in supersaturation of CaSO ₄ and CaCO ₃ , and the solubility of anhydrite (CaCO ₄ ) and calcium carbonate decreases with increasing temperature. As a result of scaling, the manufacturing capacity of the salt plant decreases with time, as in the energy efficiency of the process. The availability of the salt plant is also reduced since the evaporation apparatus needs to be washed after the typical production period in the amount of contaminants in the aqueous solution and in the conventional process setup. The most common procedure for solving the above-mentioned problems is to purify the raw water before supplying it to the evaporation plant. Another technique is to recycle the hard gypsum crystals with a large specific surface in the evaporation plant to precipitate most of the CaCO ₄ in the crystal phase rather than on the heat exchanger. However, the extra method process results in extra purification costs, requires further manipulation, or produces salts of poor quality.

The problems mentioned above also appear in the conventional process for the preparation of the sodium chloride composition. Conventional methods for preparing sodium chloride and wet sodium chloride include preparing brine by dissolving a natural source of NaCl in water followed by evaporative crystallization of brine. Such brine will contain large amounts of dissolved K, Br, SO ₄ , Mg, Sr and / or Ca because these contaminants are typically present in natural NaCl sources. A disadvantage of this method is that of the mother liquor in the evaporative crystallization process, in which the crystal lattice of the obtained salt is imperfection and occludes, ie, in the cavity in the salt crystal. It contains a small pocket. Because of this imperfection and occlusion, not only the brine produced but also the (wet) salt is contaminated with the compound present in the mother liquor. In particular, the amount of K, Br, SO ₄ , Mg, Sr and / or Ca drawn in is quite large. Thus, additional cleaning processes are required to reduce as much contaminants as possible.

In addition to occlusion of the mother liquor in incomplete salt crystals, in the second mechanism contaminants are eventually present in the salts. Both potassium and bromide ions have physical properties and sizes similar to those of sodium and chloride ions, respectively. This means that these ions produce a salt crystal lattice. Depending on the number and nature of the imperfections in the crystal lattice, that is, on the ion scale, the process of the potassium ions or bromide ions becoming crystal lattice is enhanced or suppressed. Thus, the bromide partitioning coefficient, ie the bromide content [mg / kg] in the salts produced above the bromide concentration [mg / l] in the mother liquor, depends on the crystallization conditions. The same applies to the distribution constant of potassium. It should also be noted that the distribution constants for potassium and bromide increase with temperature, so that the conventional method performed at elevated temperatures is not a good method.

It is known that antisolvent crystallization can save energy as an alternative to the production of inorganic salts typically prepared by evaporative crystallization. In antisolvent crystallization, salts are obtained by adding an antisolvent to an aqueous solution of salt to induce crystallization of the salt, followed by a filtration process. Typically continuous and industrially useful methods are made possible by antisolvents. In view of the above, antisolvents that are partially miscible with water are suitable. These antisolvents are used in the mother liquor used by forming a two-phase system from two liquids, which can be easily separated from each other by raising or lowering their temperature to a low solubility of the antisolvent and water (partially Can be recovered. Crystallization can be carried out in either a single-phase system or in a two-phase system. Salts crystallize because incorporation of water in a single-phase system introduces antisolvents into the aqueous salt solution where the solubility of salts is reduced. In a two-phase system, three phases are present together in the crystallizer, the solid salt phase, the antisolvent rich phase and the water rich liquid phase. The driving force for crystallization here is produced by extracting water from the water phase into the organic antisolvent-rich phase and by antisolvent dissolution in the water phase.

Special antisolvent crystallization methods for inorganic salts are described in DA Weingaertner et al . in Ind. Eng. Res. , 1991, Vol. 30, pages 490-501. The antisolvent crystallization method is an extractable crystallization method which recovers special salts such as sodium chloride and sodium carbonate in their saturated aqueous solution by adding an organic solvent. Water migrates from the aqueous phase to the organic phase, resulting in direct shrinkage of the aqueous phase and / or solvent entering the aqueous phase, resulting in reduced solubility of the salt in the aqueous phase resulting in a solid salt. Either way, salts are removed after precipitation and crystal growth of the solid salt phase. The solvent is recovered by changing the temperature to two liquid phases, one of which is a solvent rich phase and the other of which forms a water rich phase. Separation of these two phases then yields a relatively dry solvent phase and aqueous phase.

Three major factors that determine the quality of the salt product are the size distribution of the particles formed, the purity of the product, and the shape of the particles. However, a common drawback of the antisolvent crystallization method is due to the contaminants that have a high related supersaturation and tend to precipitate with salts. Also, the occurrence of aggregates or morphological instability is often observed. This growth pattern increases the amount of mother liquor in the pores because the empty space inside the aggregate is filled with mother liquor. Thus, contaminants, such as antisolvent molecules, which do not pose a problem when using evaporative crystallization methods can also be a problem. Thus additional washing processes or recrystallizations are typically required to obtain salts with the desired purity. The primary mechanism for crystal formation is primary nucleation because of the high supersaturation typically seen in antisolvent crystallization. As a result, most antisolvent crystallization produces very small crystals and crystal aggregates. An important drawback of these crystal slurries is that they are difficult to separate from the mother liquor using conventional centrifuges in conventional multi-effect evaporation methods. As a result, it is a very expensive process to wash the salt slurry from the mother liquor and to separate the salt slurry from the mother liquor so that the water content of the commonly required slurry is 10% by weight or less.

It is an object of the present invention to provide an improved salt crystallization process with lower energy consumption and lower water consumption than conventional methods while obtaining the desired product quality.

Surprisingly, the inventors have found that the improved antisolvent crystallization method makes it possible to produce inorganic salt compositions with reduced levels of contaminants using methods that require less energy and consume less water than conventional evaporation or antisolvent crystallization methods. Found.

More specifically the method comprises the following processes a), b), c), d) and e), or comprises the following processes a), b), c), d), e) and f), or Comprising processes a), b), c), d), e) and g) or comprising the following processes a), b), c), d), e), f) and g) It relates to a process for preparing a high purity salt composition according to:

a) supplying water to the inorganic salt source to form an aqueous solution comprising the inorganic salt;

b) feeding said aqueous solution to a crystalliser / settler;

c) contacting the aqueous solution with at least one antisolvent, wherein the antisolvent crystallizes some or all of the salt, and at least one of these antisolvents is crystal growth inhibiting property, scaling inhibiting property one or more kinds of crystals unless the anti-solvent exhibits effective crystal growth inhibitory properties, effective scaling inhibitory properties, or effective crystal growth inhibitory properties and effective scaling inhibitory properties. A growth inhibitor is added to an antisolvent, an aqueous solution or an antisolvent and an aqueous solution, or one or more scaling inhibitors are added to an antisolvent, an aqueous solution or an antisolvent and an aqueous solution, or one or more crystal growth inhibitors and one or more scaling inhibitors To an antisolvent, an aqueous solution, or an antisolvent and an aqueous solution. Add;

d) Overflow of a crystallizer / settler comprising at least one antisolvent and a salt solution to a nanofiltration unit (a nanofiltration unit is a membrane for separating at least one kind of antisolvent from an aqueous salt solution). Supplying);

e) removing the crystallized salt from the crystallizer / settler and sending it to an aqueous slurry;

f) recycling at least one kind of antisolvent to the crystallizer / settler;

g) recycling the water from the slurry to a first dissolution process, to a crystallizer / settler, or to a first dissolution process and to a crystallizer / settler.

The term contact, as used throughout this specification, may dissolve the antisolvent (s) and the following aqueous solution in whole or in part, one in part, meaning partial by 0.5 weight of the antisolvent in a 1: 1 mixture of the antisolvent and water. Dissolving at least%, preferably at least 2% by weight in an aqueous solution, and / or dissolving at least 0.5% by weight of water, preferably at least 2% by weight in an antisolvent, and an antisolvent in an aqueous solution containing an inorganic salt. It is meant to include any prior art for adding (s). In addition, the term "membrane" placed inside a nanofiltration apparatus for separating one or more antisolvents from an aqueous salt solution used throughout this specification is 100 Da or more, preferably 150 Da or more, more preferably. Is a molecular weight cut-off of 200 Da or more, most preferably 250 Da or more and 100,000 Da or less, preferably 25,000 Da or less, more preferably 10,000 Da or less, most preferably 2,500 Da or less It means any conventional film having a point.

In a preferred embodiment the antisolvent crystallization process of the invention is suitable for preparing high purity salts. When antisolvents are used in the process according to the invention together with crystal growth inhibition properties and / or one or more crystal growth inhibitors, no further purification or recrystallization processes are usually required. This finally yields relatively coarse salt crystals (i.e. crystals having a diameter of about 300 microns) having a uniform crystal size distribution, which can be easily separated from the aqueous slurry, for example by using a centrifuge. Crystal growth inhibition antisolvent and / or crystal growth inhibitor (s) prevent primary nucleation of salt crystals. The narrow crystal size distribution also makes it possible to use conventional centrifuges at relatively small average particle sizes.

The method is usable for the crystallization of inorganic salts. The method is preferably used for the crystallization of inorganic salts typically produced by evaporative crystallization. It is also known that the method can be used to selectively remove contaminants from solution, for example, to remove calcium sulfate from brine by applying a specific antisolvent for calcium sulfate. In addition, the production of sodium sulfate from sulfate rich brine is possible by applying this technique. This method is preferably used for the crystallization of alkali or alkaline earth salts of halides, phosphates, carbonates, sulfates or nitrates. The method is most preferably used for the crystallization of sodium chloride. The sodium chloride used as the raw material is preferably rock salt and / or subterraneous salt deposits. Underground salt deposits are more preferably utilized as dissolution mining. This method may also be used for the purification and crystallization of sun salts (salts obtained by evaporating water from brine using solar heat or saturated brine), including sun salts typically obtained in seawater. The term "sodium chloride" as used throughout this specification should be understood to mean that at least 25% by weight of all forms of sodium chloride is NaCl. The sodium chloride preferably contains at least 50% by weight of NaCl. More preferably, sodium chloride contains at least 75 wt% NaCl, most preferably at least 90 wt% NaCl.

The present invention will now be described in more detail with respect to the preferred embodiment depicted in FIG. 1.

1 is a conceptual diagram of a preferred flow chart in the novel method disclosed above. Water (1) which dissolves some or all of the salt is fed to salt source (A). If the solution is from the source (2), it is preferably saturated with salts and will typically include contaminants such as dissolved K, Br, SO ₄ , Mg, Sr and / or Ca ions. The (saturated) solution is fed to a conventional crystallizer / settler (B) which preferably comprises an inlet pipe. One or more antisolvents 3 are also fed to the crystallizer / settler (B). The crystalline salt composition formed is removed from the crystallizer / settler (B) as an aqueous slurry (6) and is preferably fed to a centrifuge. The salt slurry (6) removed from the crystallizer / settler (B) by one or more outlets may still contain a significant amount of antisolvent so that the salt slurry is washed before being fed to the centrifuge Most preferably, it is fed to the washing leg. In particular, if the salt slurry is to be used for electrolysis purposes, it is important to wash the mother liquor attached, ie, the residual solution remaining after the crystal salt (s) are removed, and / or the antisolvent from the salt crystals.

This can be achieved by feeding the salt slurry to a conventional wash leg operated with an aqueous crude or purified aqueous salt solution as the wash medium. It is known that purified aqueous salt solutions can be prepared by washing the salt crystals with water on a centrifuge. In this method, the preparation of the wash brine is combined with a further washing process in the centrifuge, while the filtration of the centrifuge can be used as the wash brine.

Overflow of the crystallizer / settler comprising the combined antisolvent and salt aqueous solution (4) is fed to the nanofiltration device (C), which is capable of separating one or more antisolvent and salt aqueous solutions. Contains the membrane. The membrane preferably permeates contaminants present in salts and aqueous solutions but not persolvent. After separation from each other, aqueous solutions (5) and antisolvents (7) saturated with salts are removed in the nanofiltration apparatus. It is possible to remove traces of antisolvents in aqueous solutions in nanofiltration devices by adding adsorbents with high specific surface areas, such as clay minerals, or by using conventional ion exchangers. The recovered antisolvent 7 is preferably reused by recycling to a crystallizer / settler.

In a particularly preferred embodiment the process is a continuous, closed loop process wherein the aqueous solution filtered through the membrane while saturated with salt is reused as a salt source in the nanofiltration apparatus. More salts need to be dissolved to produce an aqueous solution, preferably a saturated aqueous solution, which can be fed to the crystallizer / settler. In an even more preferred embodiment the crystalline salt composition is removed in the crystallizer / settler (B) and the recycle of the centrifuge is recycled back to the crystallizer / settler after being fed to the centrifuge as a slurry and / or salt Reused as a source. The main advantage of this method (herein referred to as the closed loop antisolvent crystallization method) is that there is no need to drain the aqueous salt solution stream.

Suitable antisolvents for use in the process according to the invention are mixtures or liquid compounds of the liquid compounds in which the salt to be crystallized is less soluble in 20 ° C. water. The antisolvent can also be used as being an aqueous component or a solid component. More particularly, the term "antisolvent" as used throughout this specification refers to crystallization of at least 5 g of salt after addition of 500 g of antisolvent to 1,000 ml of saturated aqueous salt solution at a temperature of -10 ° C to 110 ° C. It is meant to include each component, liquid compound, or a mixture of components and / or liquid compounds, which leads to a likelihood. The exact temperature at which the crystallization is carried out depends on the salt, the liquid compound (s) and / or component (s) used, and on the desired process temperature. Preference is given to using at least one antisolvent which is fluid at 20 ° C. in the process according to the invention. Organic solvents. It is more preferable to use an ionic solvent or a liquid compound which is an organic or inorganic complex as an antisolvent. Most preferably, an organic solvent is used as the antisolvent. The temperature at which the crystallization according to the invention is carried out is the test temperature.

In a preferred embodiment the antisolvent is used in an amount of at least 1 g per liter of saturated aqueous salt solution. More preferably at least 50 g, most preferably at least 200 g per liter of saturated salt aqueous solution is used.

Particularly preferred antisolvents in the antisolvent crystallization method of the present invention are organic solvents that exhibit crystal growth inhibition properties and / or scale inhibition properties.

In order to determine whether the antisolvent has crystal growth inhibition properties, the following test can be used, preferably Test 3, more preferably Test 2, most preferably Test 1.

1) A 1 L aqueous saturated salt solution containing 200 mg / L bromide in a stirred glass beaker was heated to a boiling point under atmospheric conditions and evaporated until a volume of water of 800 ml was obtained. The precipitated salt was filtered off, washed with 500 ml of acidified saturated salt aqueous solution (0.1 M HCl), centrifuged and dried. Next, the amount of occluded water was measured by heating the sample to 700 ° C while passing nitrogen, and then conventional coulometric titration was performed. The amount of bromide (in Br mg per kg of dried salt) was also measured using conventional absorbance spectrophotometry. Finally, the diameter of d50, i.e. 50% by weight of the crystal, had a large crystal diameter and 50% by weight of the crystal had a small crystal diameter. Crystal size distributions can be measured using conventional techniques such as sieve analysis and (optical) microscopy. The partition coefficient is calculated from the salt crystals and the bromide content in the final mother liquor (about 200 / 0.8 = 250 mg / l). The partition coefficient is the Br content (mg / kg) in the salt crystals divided by the Br content (mg / L) in the mother liquor. The experiment is a control experiment.

The procedure described above was repeated with 10 g / l antisolvent and the values obtained in occluded water in the crystals, partition coefficient and d50 compared to the values obtained in the control experiment. Preference is given to using 50% by weight antisolvent based on the total weight of the reaction mixture. The antisolvent is considered to be a crystal growth inhibitor if the amount of occluded water is reduced by at least 5%, and / or the partition coefficient is reduced by at least 5%, and / or the d50 value is changed by at least 5%. If the analysis using a (optical) microscope also shows a crystal with a (111) face, the antisolvent is also considered to have crystal growth inhibition properties.

2) 1 L of saturated aqueous salt solution containing 200 mg / L bromide is heated to reflux in a stirred glass beaker. The boiling solution is then saturated again by adding extra salt. The saturated solution was then left in a hood at room temperature for 48 hours. The precipitated salt is then filtered off, washed with 500 ml of acid brine (0.1 M HCl), centrifuged and dried. Thereafter the amount of occluded water was measured as described in Method 1 above. In addition, the amount of bromide was measured in Br mg per kg of dried salt as described in Method 1. Finally, d50 was measured as described in Method 1. This is a control experiment.

The procedure described above was repeated using 10 g / l antisolvent. Preference is given to using 50% by weight antisolvent based on the total weight of the reaction mixture. The values obtained for occluded water in the crystals, partition coefficient and d50 values were compared with those in the control experiment. The antisolvent is considered to be a crystal growth inhibitor if the amount of occluded water is reduced by at least 5%, and / or the partition coefficient is reduced by at least 5%, and / or the d50 value is changed by at least 5%. In addition, if the analysis using a (optical) microscope shows a crystal having a (111) plane, the antisolvent is also considered to exhibit crystal growth inhibition properties.

3) 1 L of saturated salt aqueous solution containing 200 mg / L bromide in a stirred glass beaker was left in a hood at room temperature for 1 week. The precipitated salt is filtered off, washed with 500 ml of saturated aqueous acid salt solution (0.1 HCl), centrifuged and dried. The amount of water occluded again, the amount of bromide and the d50 value were measured as described in Method 1 above. This is a control experiment.

The procedure described above was repeated using 10 g / l antisolvent. Preference is given to using 50% by weight antisolvent based on the total weight of the reaction mixture. The values obtained for occluded water in the crystals, partition coefficient and d50 values were compared with those in the control experiment. The antisolvent is considered to be a crystal growth inhibitor if the amount of occluded water is reduced by at least 5%, and / or the partition coefficient is reduced by at least 5%, and / or the d50 value is changed by at least 5%. In addition, if the analysis using a (optical) microscope shows a crystal having a (111) plane, the antisolvent is also considered to exhibit crystal growth inhibition properties.

As used throughout this specification, the term “antisolvent which exhibits scaling inhibiting properties” means that the antisolvent inhibits both scaling and crystallization of calcium and / or strontium salts. The antisolvent preferably also inhibits scaling and crystallization of magnesium and / or potassium salts. This will greatly reduce the contamination of the membrane in the nanofiltration device, there is an advantage that can be omitted to purify the brine using chemicals. Whether the antisolvent exhibits scaling inhibition properties can be measured using one of the following three tests. In one of these tests, preferably in two of these tests, most preferably in all of these tests, the antisolvent is suitable for use in the method according to the invention if the antisolvent is considered to be a scaling inhibitor. Do.

1) Antisolvent testing in scaling and crystallization of SrCO ₃ and / or CaCO ₃ :

a) saturated salt comprising 360 meq / l SO ₄ , 2.0 meq / l Ca, 0.1 meq / l Sr, 10 meq / l CO ₃ , 6 meq / l OH and 120 meq / l Br One liter of aqueous solution is stirred and heated to a boiling point under atmospheric conditions. Evaporate the water until the volume is 500 ml. The reaction mixture was filtered with a 0.2 micron filter, and the amount of dissolved Ca, Sr and CO _{3 in} the mother liquor was measured using conventional ICP (Inductively Coupled Plasma) spectroscopy (for amounts of Ca and Sr ions) and titration (CO ₃ ). In order to measure the density, This is a control experiment. The procedure was repeated using 10 g / l antisolvent. The amounts of Ca, Sr and CO ₃ in the mother liquor were compared with the amounts of Ca, Sr and CO ₃ in the mother liquor observed in the control experiment. If the amount of dissolved Ca and / or Sr and / or CO ₃ increases by at least 5%, the antisolvent is considered to have scaling inhibitory properties.

b) saturated salt comprising 360 meq / l SO ₄ , 2.0 meq / l Ca, 0.1 meq / l Sr, 10 meq / l CO ₃ , 6 meq / l OH and 120 meq / l Br To 1 liter of aqueous solution, Socal P2 (trade name, Socal P2, manufactured by Solvay Chemicals), that is, 5 g of CaCO ₃ crystals was added. The mixture was heated with stirring to boiling point under atmospheric conditions. Evaporate the water until the volume is 500 ml. The reaction mixture was filtered through a 0.2 micron filter and the amounts of Ca, Sr and CO ₃ dissolved in the mother liquor were measured. This is a control experiment. The procedure was repeated using 10 g / l antisolvent. The amounts of Ca, Sr and CO ₃ in the mother liquor were compared with the amounts of Ca, Sr and CO ₃ in the mother liquor observed in the control experiment. If the amount of dissolved Ca and / or Sr and / or CO ₃ increases by at least 5%, the antisolvent is considered to have scaling inhibitory properties.

c) 10 l of an aqueous saturated salt solution containing 75 meq / l Ca, 2 meq / l Sr and 75 meq / l SO ₄ with a pH value of 7 and 0.1 mol of sodium carbonate were added to a 1 m 2 nanofiltration membrane. It was filtered for hours. The permeate was recycled back to the high pressure side of the membrane. After 15 hours, the transmission through the membrane at constant pressure was measured. This is a control experiment. The procedure was repeated with a saturated salt solution containing 1 g / l antisolvent. The permeate was recycled back to the high pressure side of the membrane with the antisolvent present. Anti-solvents are considered to have scaling inhibitory properties if the flux increases by at least 5% compared to the transmittance observed in the control experiment.

d) The test was carried out in the same manner as in Test 1a, except that 100 mg / l of Socal P2 seed from Solvay Chemicals was added to the aqueous salt solution. If the boiling point of the antisolvent-brain mixture was below 90 ° C., both the control test and the antisolvent test were carried out at the boiling point of the mixture.

e) The test was carried out in the same manner as in Test 1d, except that it was run at 20 ° C.

f) The test was performed in the same manner as in Test 1d, except that SO ₄ was not present in the saturated salt aqueous solution.

Test 1f, more preferably Test 1e, even more preferably 1d, even more preferably Test 1c, even more preferably 1b, most preferably to test whether the antisolvent has scaling inhibitory properties. Preference is given to using test 1a.

2) Antisolvent test to confirm scaling and crystallization inhibition of CaSO ₄ (anhydrite): 5 g / L of saturated salt aqueous solution containing 100 meq / L Ca and 100 meq / L SO ₄ It was heated to a temperature of 100 ° C. (or to the boiling point of the antisolvent-brain mixture) for 1 hour with stirring in the presence. The test was run under reflux conditions to prevent evaporation of the antisolvent. A sample was then taken to be filtered. The amount of dissolved Ca was then measured by ICP, and the amount of dissolved SO ₄ was measured using ion chromatography or titration. This is a control experiment. The procedure described above was repeated using 1 g / l antisolvent. Antisolvents are considered to have scaling inhibitory properties if the amount of Ca and / or SO ₄ dissolved in the mother liquor increases by at least 5% compared to the values in the control experiment. It is desirable to adjust the pH and add 10 meq / lOH.

3) Antisolvent test to confirm scaling and inhibition of crystallization of CaSO ₄ 2H ₂ O (gypsum, gypsum): Gypsum crystals with saturated aqueous solution containing 150 meq / l Ca and 150 meq / l SO ₄ Stirred at a temperature of 20 ° C. for 1 hour in the presence of g / l. A sample was then taken to be filtered. The amount of Ca and SO ₄ dissolved thereafter was measured as described immediately before in test 2. This is a control experiment. The procedure described above was repeated using 1 g / l antisolvent. If the amount of Ca and / or SO ₄ dissolved in the mother liquor increases above 5%, the antisolvent is considered to have scaling inhibitory properties. It is desirable to adjust the pH and add 10 meq / lOH.

If an antisolvent that does not exhibit crystal growth inhibition and / or scaling inhibition properties is present in either the antisolvent or the water phase in an effective amount of at least one crystal growth inhibitor and / or at least one scaling inhibitor, it is also in accordance with the invention Can be used in the method.

Whether the additive is a crystal growth inhibitor can be determined using one of the following three tests, preferably Test 3, more preferably Test 2, and most preferably Test 1.

1) A 1 L aqueous saturated salt solution containing 200 mg / L bromide in a stirred glass beaker was heated until a volume of water of 800 ml was obtained. The precipitated salt was filtered off, washed with 500 ml of acidified saturated salt aqueous solution (0.1 M HCl), centrifuged and dried. Subsequently, in order to determine whether the antisolvent exhibits crystal growth inhibitory properties, the amount of water and bromide occluded as the above-described method 1 was measured, and the d50 value was measured. Partition coefficients were calculated from the salt crystals and the amount of bromide in the final mother liquor. The partition coefficient is the Br content in the salt crystals divided by the Br content in the mother liquor. This is a control experiment.

The procedure described above was repeated with 200 L of additive and the values obtained in occluded water in the crystals, partition coefficient and d50 values were compared with those obtained in the control experiment. The additive is considered to be a crystal growth inhibitor if the amount of occluded water is reduced by at least 5%, and / or the partition coefficient is reduced by at least 5%, and / or the d50 value is changed by at least 5%. If the analysis using a (optical) microscope also shows a crystal with (111) plane, the additive is also considered to be a crystal growth inhibitor.

2) 1 L of saturated aqueous salt solution containing 200 mg / L bromide is heated to reflux in a stirred glass beaker. The boiling solution is then saturated again by adding extra salt. The saturated solution was left in a hood at room temperature for 48 hours. The precipitated salt is filtered off, washed with 500 ml of acidic saturated salt aqueous solution (0.1 M HCl), centrifuged and dried. In addition, the amount of occluded water, bromide amount, and d50 value were measured by Method 1 described above during the test to determine whether the antisolvent exhibited crystal growth inhibition properties. This is a control experiment.

The procedure described above was repeated with 200 mg / l additive. The values obtained for occluded water in the crystals, partition coefficient and d50 values were compared with those in the control experiment. The additive is considered to be a crystal growth inhibitor if the amount of occluded water is reduced by at least 5%, and / or the partition coefficient is reduced by at least 5%, and / or the d50 value is changed by at least 5%. If the analysis using a (optical) microscope also shows a crystal with a (111) face, the additive is also considered to be a crystal growth inhibitor.

3) 1 L of saturated salt aqueous solution containing 200 mg / L bromide in a stirred glass beaker was left in a hood at room temperature for 1 week. The precipitated salt is filtered off, washed with 500 ml of acidic saturated salt aqueous solution (0.1 HCl), centrifuged and dried. In addition, the amount of occluded water, bromide amount, and d50 value were measured by Method 1 described above during the test to determine whether the antisolvent exhibited crystal growth inhibition properties. This is a control experiment.

The procedure described above was repeated with 200 mg / l additive. The values obtained for occluded water in the crystals, partition coefficient and d50 values were compared with those in the control experiment. The additive is considered to be a crystal growth inhibitor if the amount of occluded water is reduced by at least 5%, and / or the partition coefficient is reduced by at least 5%, and / or the d50 value is changed by at least 5%. If the analysis using a (optical) microscope also shows a crystal with (111) plane, the additive is also considered to be a crystal growth inhibitor.

Whether the additive is a scaling inhibitor can be determined using one of the four tests below. In one of these tests, preferably in at least two of these tests, most preferably in all of these tests, the additive is suitable for use in the method according to the invention if the additive is considered to be a scaling inhibitor. .

1) Additive test to confirm the inhibition of scaling and crystallization of SrCO ₃ and / or CaCO ₃ :

a) saturated salt comprising 360 meq / l SO ₄ , 2.0 meq / l Ca, 0.1 meq / l Sr, 10 meq / l CO ₃ , 6 meq / l OH and 120 meq / l Br 1 L of the aqueous solution is heated to the boiling point under atmospheric conditions and the water is evaporated until the volume is 500 ml. The reaction mixture was filtered through a 0.2 micron filter and the amount of Ca, Sr and CO ₃ dissolved in the mother liquor was tested as described above to determine whether the antisolvent inhibited crystallization and scaling of SrCO ₃ and / or CaCO ₃ . It was measured by heavy method 1a. This is a control experiment. The amounts of Ca, Sr and CO ₃ in the mother liquor were compared with the amounts of Ca, Sr and CO ₃ in the mother liquor observed in the control experiment. The additive is considered to be a scaling inhibitor if the amount of dissolved Ca and / or Sr and / or CO ₃ increases by at least 5%.

b) saturated salt comprising 360 meq / l SO ₄ , 2.0 meq / l Ca, 0.1 meq / l Sr, 10 meq / l CO ₃ , 6 meq / l OH and 120 meq / l Br Sokal P2 (Solvay Chemicals agent) aqueous solution in 1 ℓ, i.e., the addition of CaCO ₃ was determined 5 g. The mixture is heated to boiling point under atmospheric conditions and water is evaporated until the volume is 500 ml. The reaction mixture was filtered through a 0.2 micron filter and the amounts of Ca, Sr and CO ₃ dissolved in the mother liquor were measured. This is a control experiment. The procedure was repeated with 10 ppm of additive. The amounts of Ca, Sr and CO ₃ in the mother liquor were compared with the amounts of Ca, Sr and CO ₃ in the mother liquor observed in the control experiment. The additive is considered to be a scaling inhibitor if the amount of dissolved Ca and / or Sr and / or CO ₃ increases by at least 5%.

c) 10 l of a saturated aqueous salt solution with 75 meq / l Ca, 2 meq / l Sr and 75 meq / l SO ₄ and a pH value of 7 and 1 having a Mw of about 600 g / mol in 0.1 mol of sodium carbonate Polyethylene glycol, acetone or ethanol was added. The salt solution was filtered through a nanofiltration membrane over 15 hours. The permeate was recycled to the side of the membrane with the antisolvent present. After 15 hours, the transmission through the membrane at constant pressure was measured. This is a control experiment. The procedure was repeated with saturated aqueous salt solution containing 10 ppm of additive. The additive is considered to be a scaling inhibitor if the transmittance increases by at least 5% compared to the transmittance observed in the control experiment.

d) tests for scaling and crystallization inhibition of Ca and / or Sr carbonate:

Under permeability conditions, the temperature was 90 ° C. and tested in the same manner as in test 1a except for 100 mg / l of Socal P2 seed from Solvay Chemicals.

e) was tested in the same manner as test 1d, except that the control experiment was run without Socal P2 seed.

Preference is given to using test 1e, even more preferably test 1d, even more preferably test 1c, even more preferably 1b and most preferably test 1a.

2) Additive test to confirm scaling and crystallization inhibition of CaSO ₄ (hard gypsum): Aqueous saturated salt solution containing 100 meq / l Ca and 100 meq / l SO ₄ was stirred in the presence of 5 g / l pumice crystal Heated to a temperature of 100 ° C. for 1 h. After this, a sample to be filtered was taken. The amount of Ca and SO ₄ dissolved was then measured by Method 2 of the test described above to determine whether the antisolvent inhibited the crystallization and scaling of CaSo ₄ . This is a control experiment. The procedure described above was repeated with 10 ppm of additive. The additive is considered to be a scaling inhibitor if the amount of Ca and / or SO ₄ dissolved in the mother liquor increases above 5%. It is desirable to adjust the pH and add 10 meq / lOH.

3) Additive test to confirm scaling and suppression of crystallization of CaSO ₄ 2H ₂ O (gypsum): 5 g / L of saturated salt solution containing 150 meq / L of Ca and 150 meq / L of SO ₄ Stirred at a temperature of 20 ° C. for 1 hour in the presence of. The sample was then taken to be filtered. Then, the amount of dissolved Ca and SO ₄ was measured. This is a control experiment. The procedure described above was repeated with 10 ppm of additive. The additive is considered to be a scaling inhibitor if the amount of Ca and / or SO ₄ dissolved in the mother liquor increases above 5%. It is desirable to adjust the pH and add 10 meq / lOH.

4) Additives are tested as described in S. Patel, MA Finon, Desalination 124 (1999) 63-74, with inhibition of at least 5%.

If a crystal growth inhibitor and / or a scaling inhibitor are added to the antisolvent (s), the crystal growth inhibitor and / or the scaling inhibitor are used in the method according to the invention in an effective amount. Without the addition of a crystal growth inhibitor, the occluded water in the salt crystals is reduced by at least 5% and / or the partition coefficient is reduced by at least 5% compared to salts prepared from the same salt solution under the same conditions, and / or the d50 value If this decreases by more than 5%, an effective amount of crystal growth inhibitor is present. Effective amount of scaling if the amount of dissolved Ca and / or Sr and / or SO ₄ and / or CO _{3 in} the mother liquor changed by at least 5% compared to the mother liquor produced from the same salt solution under the same conditions without the addition of a scaling inhibitor Inhibitors are present.

If a crystal growth inhibitor is used in the method according to the invention, the amount of said crystal growth inhibitor which is typically present in the mother liquor-antisolvent system is up to 5,000 mg per kg of mother liquor. It is preferable to use 1,500 mg / kg or less, more preferably 300 mg / kg. However, concentrations of more than 5,000 mg of crystal growth inhibitor per kg of mother liquor are also possible. Usually at least 10 mg, preferably at least 12.5 mg and most preferably at least 14 mg of crystal growth inhibitor is used per kg of mother liquor.

If a scaling inhibitor is used in the method according to the invention, the amount of said scaling inhibitor which is typically present in the mother liquor-antisolvent system is also up to 5,000 mg per kg of mother liquor. Preferably up to 1,500 mg / kg, more preferably up to 300 mg / kg is used. However, concentrations of scaling inhibitors above 5,000 mg per kg of mother liquor are also possible. Typically at least 1 mg, preferably at least 3 mg, most preferably at least 5 mg of scaling inhibitor is used per kg of mother liquor.

It is preferable to use only one antisolvent. More preferably, an antisolvent exhibiting crystal growth inhibition properties and / or scaling inhibition properties is optionally used in combination with one or more scaling inhibitors and / or crystal growth inhibitors. The antisolvent is not essential but can be miscible with (partly) pure water. It is also possible to use an antisolvent or antisolvent mixture in which an emulsion is formed after addition to an aqueous salt solution. The antisolvent or antisolvent mixture may be partially salted because the antisolvent (s) may be recovered by temperature induced liquid-liquid separation (these systems have two liquid phases below or above a certain threshold temperature). It is preferable to use those which are miscible with the aqueous solution. The phase separation of the water layer and the antisolvent can then be a temperature induced phase-separation method as is commonly known in the art. The antisolvent (s) used in the process according to the invention are most preferably environmentally friendly and preferably of edible grade. Preferred antisolvents are also inexpensive and readily available solvents.

The choice of one or more antisolvents depends on the solubility characteristics of the salts in the crystallized state. Anti-solvents exhibiting crystal growth inhibition and / or scaling inhibition properties in the brine crystallization method are aliphatic or aromatic alcohols, nitriloacetic acid, carboxylic acids or polycarboxylic acids, phosphonates, polyphosphonates, functionalized or pessimistic. Functionalized carboxymethyl cellulose, organic complexes of Fe (II) and Fe (III) ions, ethanol, acetone, isopropanol, quaternary ammonium salts, cyclodextrins, amino group containing polymers, quaternary ammonium group containing polymers, nitrogen-containing aliphatic rings It is preferable to select from the group which consists of a polymer, the sodium salt of an anion group containing polymer, and the chloride salt of a cationic group containing polymer. More preferably, polyvinyl alcohol, polyethylene glycol or choline chloride is used.

In a particularly preferred embodiment ionic liquids are used as antisolvent (s). Examples of ionic liquids suitable for use as antisolvents in the process according to the invention include, but are not limited to, choline chloride based ionic liquids such as choline chloride / urea, choline chloride / phenol or choline chloride / saccharides. . It is most preferable to use nitrogen free as the ionic liquid.

Suitable crystal growth inhibitors for use in the method of antisolvent crystallization of salts include all conventional crystal growth inhibitors. Preferably, the crystal growth inhibitor in the brine crystallization method comprises an oligopeptide, a polypeptide and at least two carboxylic acid groups or a carboxyalkyl group, or is selected from the group consisting of phosphate, phosphonate, phosphino, sulfate and sulfonate groups Polymers that may include those that are; Functional or nonfunctional monosaccharides, disaccharides and polysaccharides; Ferrocyanide salts; Lead chloride; Cadmium chloride; Magnesium sulfate; Quaternary ammonium salts; Cyclodextrins; Amino group-containing polymers; Quaternary ammonium group-containing polymers; Polymers comprising nitrogen-containing aliphatic rings; Sodium salts of anionic group-containing polymers; And chloride salts of the cationic group-containing polymer. Crystal growth inhibitors are most preferably selected from the group consisting of polymaleic acid, polyacrylates, glycos, saccharose and urea. In the preferred and closed loop antisolvent crystallization process according to the invention, it is preferred to use crystal growth inhibitors that do not pass through the membrane in the nanofiltration process. In fact it will remain in the antisolvent stream which will later be recycled to the crystallizer / settler.

It has also been found that addition of the crystal growth inhibitor according to the invention to the antisolvent during the salt preparation process can affect the crystal size distribution. It is clear that increasing the amount of crystal growth inhibitor in the antisolvent produces smaller crystals. d50 crystal diameters, i.e., 50% by weight of the crystals have a larger crystal diameter, and 50% by weight of the crystals have a smaller crystal diameter, the presence of a crystal growth inhibitor immediately after fitting the amount of crystal growth inhibitor in the antisolvent. It is desirable to be able to vary by more than 10% compared to the size of the crystals that are produced when not. The crystal size distribution can be measured using conventional techniques such as particle size analysis or using an optical microscope.

It has also been found that the deformation of the crystals obtained by using the antisolvent method according to the present invention (ie, the form of crystal lattice) can be more easily influenced.

Scaling inhibitors suitable for use in the method of antisolvent crystallization of salts include any conventional scaling inhibitor. The scaling inhibitor in the brine crystallization method may contain oligopeptides, polypeptides, two or more carboxylic acid groups or ester groups, or may include those selected from the group consisting of phosphate, phosphonate, phosphino, sulfate and sulfonate groups. Polymers, functional or non-functional monosaccharides, disaccharides, polysaccharides, polymers having one or more alcohol groups, humic acids, surfactants from natural sources (such as unbalanced rosin acid soaps), lactic acid, Phospholipids. Suspension of yeast cells, suspension of algae, N, N-diethyl-1,3-diaminopropane, ethylene diamine, polyisobutylene derivatives, N, N-dimethyl-1,3-diaminopropane, diethylene tri Amine, triethylene tetraamine, 1,6-diaminohexane, poly [oxy (methyl-1,2-ethanediol)], hexamethylene biguanide, maleic anhydride homopolymer, amylase, protease, sodium citrate, citric acid , N, N, N ', N'-tetraacetylethylene diamine, nonanoyloxybenzene sulfonate, polyepoxysuccinic acid, polyacrylamide, ethylenediamine tetramethylene phosphoric acid, sulfonated polyoxyethylene ether, quaternary ammonium salt, Cyclodextrins, amino group-containing polymers, quaternary ammonium group-containing polymers, polymers containing nitrogen-containing aliphatic rings, sodium salts of anionic group-containing polymers, chlorides of cationic group-containing polymers, fatty acids, orange juice, apple juice, polyethylenyl chloride Is selected from the imine, sodium dimethyl dithiocarbamate, and a scaling inhibitor and the group consisting of Fe (Ⅱ) or Fe (Ⅲ) ion complex described in one or more of the above are preferred. The scaling inhibitor is most preferably selected from the group consisting of polyacrylates, polyphosphates, sucrose and sodium gluconate.

For the water in the process, any water feed that can be used in conventional salt crystallization processes is commonly used. In the preferred and closed loop antisolvent crystallization process according to the invention only a small amount of water is required. First, water is needed to initiate the crystallization process by dissolving a portion of the salt source. The aqueous salt slurry is removed from the crystallizer / settler during the process. An amount of water, preferably equal to the amount of water lost via the aqueous salt slurry, is then added to the salt source to continue the process. The amount of water required to preserve the continuous crystallization process may be less if the centrifuge recycle is preferably recycled to the crystallizer / settler and / or salt source where the crystallized salt in the aqueous slurry is fed.

In a particularly preferred embodiment of the present invention, the salt source is a sodium chloride precipitate underground in the exposed holes used as a means of dissolution mining. Undersaturated salt aqueous solutions removed from the nanofiltration apparatus in a closed loop process and reused as sodium chloride precipitates will contain certain levels of contaminants such as K, Br, SO ₄ , Mg, Sr and / or Ca contaminants. When used with sodium chloride, not only will it be saturated with sodium chloride, but the contaminants present in the precipitate will also dissolve. In conclusion, the concentration of the contaminants in saturated aqueous salt solution leaving the sodium chloride precipitate will increase during the process until the solution is also saturated with these contaminants. In conclusion, the stationary phase will no longer require power for new contaminants present in sodium chloride deposits dissolved in aqueous solutions. In the preferred embodiment described, only water is added that will fill the pores formed when the natural salt source is dissolved.

The purity of the aqueous salt solution in the evaporation method can be increased by reducing the amount of contaminants, such as pumice, gypsum and polyhalide (and / or strontium analogs thereof) dissolved in the aqueous solution. This is commonly done by mixing these agents and salt sources prior to addition to the water or by adding certain agents to the water used in the process. Such agents are conventionally referred to as "retarding agents". Although such formulations are not required for the production of high purity salts via the process of the present invention, additives of this type may also be added as water feed if desired.

The nanofiltration device used in the process according to the invention may comprise any conventional membrane capable of separating one or more antisolvents and aqueous salt solution. Separation may be based on molecular dimension and / or electrostatic repulsion. Separation is preferably based only on molecular size. In a particularly preferred embodiment, the membrane uses those which can permeate the salts and contaminants present in the aqueous solution but not the antisolvent. The membrane is preferably 75% to 100% selective in antisolvent and salt aqueous solution. More preferably, the membrane is 85% to 100% selective, even more preferably 95% to 100% selective, most preferably 99.9% to 100 in order to limit the amount of antisolvent leaving the nanofiltration device with a low saturated salt aqueous solution. % Optional. The antisolvent passing through the membrane eventually becomes a low saturated salt aqueous solution stream that is removed from the system or reused as a salt source in a preferred embodiment. In the latter case, the low saturated salt aqueous solution containing any antisolvent is saturated again and returns to the crystallizer / settler as in saturated aqueous salt solution. Thus, the loss of antisolvent from the closed loop method will not be significant. The optimum process temperature will vary depending on the nature, shape of the antisolvent and the concentration of contaminants in the aqueous salt solution to be filtered and the nature of the membrane. Typical temperatures for separation of the antisolvent and salt aqueous solution range from -10 ° C to 110 ° C.

Suitable crystallizers / settlers for use in the process according to the invention can be any conventional crystallizers / settlers. Crystallizers containing a continuous phase in a crystallizer containing at least one antisolvent to continuously crystallize salts, equipped with a vertical feed hose system, and having no impeller or other moving parts Precipitator is preferred. The crystallizer / settler has at least a bottom wall, preferably a vertical wall having a cylindrical cross-sectional area, at least a first inlet, preferably a first inlet and a second inlet for feeding the first and second reactants to the reactor, and It is preferably a reactor for precipitation and / or crystallization substrates comprising an outlet. Such crystallizers / settlers are described, for example, in US Pat. No. 4,747.917. However, it is most preferred to use crystallizers / settlers in which one or more inlets comprise respective release holes arranged to direct the reactants to the surface and at the same time induce collisions, which is described, for example, in NL 7215309.

Crystallized salt is removed from the crystallizer / settler as an aqueous slurry. It is preferably supplied to a centrifuge to produce the wet salt. The term "wet salt" is used to denote salts containing large amounts of water. More preferred are water-containing salts in which at least 50% by weight consists of pure salts. The salt is preferably at least 90% by weight pure salt. It is more preferred that the salt is at least 92% by weight pure, but in practice it is most preferred that both salts are pure salt and water. The wet salt will contain at least 0.5% by weight, preferably at least 1.0% by weight, more preferably at least 1.5% by weight of water. It is preferred to contain up to 10% by weight, more preferably up to 6% by weight and most preferably up to 4% by weight of water. All weight percentages are based on total composition weight. If desired, the wet salt may be dried by conventional methods to obtain a dry salt comprising up to 0.5% by weight of water.

In a particularly preferred embodiment according to the invention the method further comprises a reverse osmosis process prior to feeding the nanofiltration device an overflow of the crystallizer / settler comprising antisolvent (s), water and salts. do. In the osmotic process, water is removed from the aqueous mixture comprising the salt and the antisolvent, resulting in a more concentrated aqueous component. As a result, many salts crystallize.

Osmotic processes are well known and will be defined in conventional terms as diffusion which proceeds through a semipermeable membrane that separates two solutions containing unequal concentrations of solutes. Diffusion of one of the solvents into the other solution will result in equal concentrations of the solutes in each solution. For example, in osmotic operation, pure water will diffuse the first aqueous solution with lower solute concentration into the second aqueous solution with higher solute concentration through the semipermeable membrane. The diffusion of water through the membrane is suppressed when the second aqueous solution is subjected to a high water pressure in proportion to the water pressure present in the first solution. The pressure at which diffusion into the second solution substantially stops is osmotic pressure. Reverse osmosis occurs if the water pressure applied to the second solution further increases in proportion to the water pressure of the first solution such that the osmotic pressure of the second solution is exceeded, ie water from the second aqueous solution diffuses through the membrane into the first aqueous solution. For example, the osmotic pressure of brine saturated in proportion to water is approximately 300 bar. This means that in reverse osmosis more than 300 bar water pressure is required to crystallize the salt. The high pressure requires special equipment. It also requires high energy costs. However, adding antisolvent to brine will reduce the solubility of the salt. In conclusion, osmotic pressure is also reduced, making it a more economical way. In this particularly preferred embodiment of the process according to the invention, a solution consisting essentially of water is used as the first solution, while in the second solution the overlying crystallizer / settler comprising antisolvent (s), water and salts. Use what consists of flows. The pressure applied to the second solution is the pressure at which water diffuses into the first solution. The pressure at which the reverse osmosis is carried out typically depends on the composition of the second solution. Usually a pressure of 1 bar to 250 bar, preferably 5 bar to 150 bar is required. More preferably, a pressure of 8 bar to 100 bar, more preferably 10 bar to 80 bar, most preferably 10 bar to 50 bar is applied. The first solution is preferably of high quality water, which can be used as drinking water and / or process water, or if desired can be safely released into streams, rivers, lakes and the like without further treatment. The antisolvent-membrane technique according to the invention is suitable for producing drinking water or process water in an aqueous solution comprising salt using one or more antisolvents. In areas where water is very scarce, reverse osmosis up to very high concentrations of the second solution is preferred.

The economic feasibility of the process according to the invention depends on the pressure required for filtration of the brine via nanofiltration or reverse osmosis. The pressure required for the reverse osmosis process can be greatly reduced when the first solution comprising water is combined with an alkaline and / or alkaline earth salt such as a waste stream comprising raw brine or an ion containing waste stream from another process. have. Preferably, the waste stream can be safely released to streams, rivers, lakes and the like without further treatment. Thus in a preferred embodiment according to the invention the process further comprises a reverse osmosis process, wherein the water from the second solution comprising some or all of the overflow of the crystallizer / settler is water and alkali and / or Diffuse into a first solution comprising a waste stream comprising alkaline earth salts.

After the reverse osmosis process 5% to 40% by weight, more preferably 10% to 25% by weight of the second solution is recycled to the crystallizer / settler, while 95 to 60% by weight, more preferably 90% to 75% by weight is preferably supplied to the nanofiltration device. The feed portion of the second solution to the crystallizer / settler has the advantage of reducing the amount of salts crystallized during the reverse osmosis process by reducing the level of supersaturation during the overflow of the crystallizer / settler. It is known that nucleation is inhibited if the antisolvent exhibits crystallization inhibitory properties and / or includes one or more crystal growth inhibitors, which will help to reduce the amount of salt crystallized during the reverse osmosis process.

The semipermeable membrane used in the reverse osmosis process according to the present invention may be any conventional semipermeable membrane which does not permeate contaminants present in the antisolvent and aqueous solution used but at the same time reliably permeates water. The semi-permeable membrane has a permeability of not more than 25% of the anti-solvent and contaminants, more preferably not more than 15%, even more preferably not more than 5%, most preferably not more than 0.1%. It is preferred that at least 10% by weight of water be removed in the reverse osmosis process based on the total weight of the aqueous solution comprising the salt. More preferably at least 50% by weight, even more preferably at least 75% by weight and most preferably at least 99% by weight of water are removed based on the total weight of the aqueous solution comprising the salt.

In a further optimal embodiment of the process described above according to the invention a slightly adapted crystallizer / settler is used. The method was also slightly modified. Refer to FIG. 2 for the conceptual diagram of the flowchart in the above embodiment.

In the optimization process according to the invention water (1) is fed to the salt source (A), which dissolves some or all of the salt. Preferably, the saturated salt solution is fed to the conventional crystallizer / settler (B) when it exits the salt source (2). One or more antisolvents 3 are also fed to the crystallizer / settler. The settler (B) comprises an inlet pipe (F), and the partition wall (E) has a cross section of a cylinder located on the lower wall surrounding the lower end of the inlet pipe (F). The partition wall (E) has the effect of creating a rising stream to whirl the slurry. The height of the partition wall is at most 60%, preferably at most 50%, of the effective height of the settler (B), in which the slurry on the partition wall (E) is swirled in the opposite direction to the flow in the partition wall (E) This is because it strengthens the settling of. The crystallization composition formed is sedimented and removed in the space between the partition wall E and the side wall of the settler in the form of a salt slurry via at least one outlet 6 at the bottom of the side wall. The salt slurry is preferably fed to a centrifuge. More preferably, the salt slurry removed from the crystallizer / settler with one or more outlets 6 will still contain a relatively large amount of antisolvent so that it is not processed before the salt slurry is fed to the centrifuge. Aqueous salt solution or purified aqueous salt solution is fed to the washing leg used as wash medium. It is particularly important to wash the attached mother liquor and / or antisolvent from salt crystals if salt slurries are used for the purpose of electrolysis. However, in a preferred embodiment the washing process is by supplying a solution (part of the solution) out of the source 2 to the bottom crystallizer / settler (B) in the space between the partition wall (E) and the side wall of the settler. It is run in crystallizer / settler (B). The slurry removed from the crystallizer / settler in this process is continuously washed with fresh, antisolvent-free, raw salt solution. In conclusion, the salt slurry removed from the crystallizer / settler by one or more outlets 6 is already free of antisolvent (s) before being sent to the centrifuge. It is known that the salt can be washed in an additional washing leg or centrifuge to remove contaminants dissolved in the solution leaving source (2).

The overflow (4) of the crystallizer / settler comprising antisolvent (s), water and salt is fed to a reverse osmosis device (D) in which part of the water dissolved in the antisolvent is removed. 0 to 50% by weight, preferably 5 to 40% by weight, more preferably in the concentrated antisolvent stream leaving the demineralized water (9) prepared in the reverse osmosis device (D) while leaving the reverse osmosis device Preferably from 10% to 25% by weight to the inlet pipe (F) of the settler (B) and from 100% to 50% by weight, preferably from 95% to 60% by weight, more preferably 90% by weight. % To 75% by weight is fed to a nanofiltration device (C) comprising a membrane separating one or more antisolvents from any salt and water present in the antisolvent stream. As described above, the membrane preferably permeates contaminants and salts present in the antisolvent stream but does not permeate the antisolvent. After separation, purge 11 and antisolvent 3 containing water, dissolved salts and contaminants are removed from the nanofiltration apparatus. The purge 11 preferably does not exceed 20% by weight, more preferably 10% by weight, of the total weight of the stream 2 fed to the crystallizer / settler. The antisolvent 3 removed in the nanofiltration device is preferably used again by recycling to the crystallizer / settler.

It is also preferred in one particular and optimal embodiment of the invention that at least one hydrophilic antisolvent is used to form the two-phase system with pure water. The term "hydrophilic antisolvent" means that it will absorb at least 5% by weight, more preferably at least 10% by weight and most preferably 20% by weight of water, based on the total weight of the antisolvent. It means the antisolvent described. The hydrophilic antisolvent preferably does not absorb at least 60% by weight, more preferably at least 50% by weight and most preferably at least 40% of water, based on the total weight of the antisolvent. The hydrophilic antisolvent will crystallize the salt by extracting water from an aqueous solution containing the salt. In a preferred embodiment the hydrophilic antisolvent is applied having a density of 1,200 kg / m 3 or less, more preferably 1,150 kg / m 3 or less, most preferably 1,125 kg / m 3 or less. In this case, the interior of the crystallizer / settler (b) will form as the two-phase system overflows the crystallizer / settler (B), which is mostly an antisolvent comprising water. As is known in the literature, only a small amount of salt will dissolve in the antisolvent / water phase. In this preferred method the overflow of the crystallizer / settler is fed to a nanofiltration device (C) in which the antisolvent (s) are separated from the aqueous solution. The recovered antisolvent (s) is recycled to the crystallizer / settler (B) while the recovered aqueous solution can be discharged slowly. Preferred hydrophilic antisolvents include, but are not limited to, choline chloride / phenolic ionic liquids and polypropylene glycols.

It is also possible to feed the overflow to reverse osmosis as described above. The reverse osmosis process will be more economical due to the fact that the anti-solvent / water osmotic pressure during overflow in proportion to water is currently very low.

Preferably, at least 10% by weight of the total amount of water dissolved in the antisolvent stream fed to the reverse osmosis device is removed in the reverse osmosis process. More preferably at least 50% by weight of the total amount of water and even more preferably at least 75% by weight of the total amount of water dissolved in the antisolvent stream fed to the reverse osmosis device are removed. Preferably up to 90% by weight of the total amount of dissolved water is removed in the reverse osmosis process to prevent crystallization of the salts present in the antisolvent stream.

It is known that any additive suitable for improving the permeability of the membrane in reverse osmosis membranes and / or nanofiltration devices by preventing the membrane from being contaminated can be added to the antisolvent (s) and / or aqueous salt solution. It is preferred that the surfactant be added to the antisolvent to increase the permeability of the membrane (s).

In a particularly preferred embodiment the salt is sodium chloride. The (wet) sodium chloride according to the invention is preferably used for producing brine in the electrolysis process and more preferably in the modern membrane electrolysis process. Sodium chloride prepared by the method described above can be used for consumption purposes. For example, table salt is suitable.

The invention has been described by way of example and not by way of limitation.

In the examples below raw raw brine samples in the brine field to Hengel, Netherlands were used as the source of sodium chloride.

Example 1

The following model experiments were performed for antisolvent crystallization of sodium chloride using polyethylene glycol.

For this purpose, the four saturated aqueous solutions in unpurified sodium chloride (Brine) will each contain 5%, 10%, 25% by weight of polyethylene glycol (PEG, hereinafter called PEG600) having a molecular weight of about 600, Prepared by addition in an amount of 50% by weight. Precipitated sodium chloride was filtered off and dried.

The amounts of dissolved Ca, Mg, SO ₄ , K and Br were measured in samples 3 and 4 using an inductively coupled plasma (ICP) spectrometer. The results are summarized in Table 2 and compared with the amount of contaminants present in the electrolysis (vacuum) salts.

As can be seen from Tables 1 and 2, polyethylene glycol not only functions as an antisolvent but also exhibits crystal growth inhibition properties. In particular, the concentrations of K and Br were significantly lower than in conventional electrolysis (vacuum) salts.

Example 2

The solution was prepared as follows:

21.55 kg of unrefined sodium chloride (75% by weight)

7.11 kg PEG600 (25 wt.%)

Crystallization of sodium chloride was observed after the addition of PEG600. Crystallized sodium chloride was filtered off and the mother liquor was fed to a nanofiltration device equipped with tubular nanofiltration membranes of type PCI AFC30 (manufactured by PCI).

The experiment was run under recycle conditions, i.e., feeding the total permeate stream back to the pressure side of the membrane. Thus CF, i.e., the concentration factor, is 1.

R, retention factor was calculated as follows:

In the experiment, PEG600 was found to be an antisolvent that can be retained in the nanofiltration membrane.

Claims (14)

A process for preparing a salt composition using an antisolvent, Comprising the following processes a), b), c), d) and e) or comprising the following processes a), b), c), d), e) and f), or the following processes a), b) , c), d), e) and g) or comprising the following processes a), b), c), d), e), f) and g): a) supplying water to the inorganic salt source to form an aqueous solution comprising the inorganic salt; b) feeding said aqueous solution to a crystalliser / settler; c) contacting the aqueous solution with at least one antisolvent, wherein the antisolvent crystallizes some or all of the salt, and at least one of these antisolvents is crystal growth inhibiting property, scaling inhibiting property one or more kinds of crystals unless the anti-solvent exhibits effective crystal growth inhibitory properties, effective scaling inhibitory properties, or effective crystal growth inhibitory properties and effective scaling inhibitory properties. A growth inhibitor is added to an antisolvent, an aqueous solution or an antisolvent and an aqueous solution, or one or more scaling inhibitors are added to an antisolvent, an aqueous solution or an antisolvent and an aqueous solution, or one or more crystal growth inhibitors and one or more scaling inhibitors To an antisolvent, an aqueous solution, or an antisolvent and an aqueous solution. Add; d) Overflow of a crystallizer / settler comprising at least one antisolvent and a salt solution is carried out by a nanofiltration unit (a nanofiltration unit is a membrane for separating at least one kind of antisolvent from an aqueous salt solution). Supplying); e) removing the crystallized salt from the crystallizer / settler and sending it to an aqueous slurry; f) recycling at least one kind of antisolvent to the crystallizer / settler; g) recycling the water from the slurry to a first dissolution process, to a crystallizer / settler, or to a first dissolution process and to a crystallizer / settler. The method of claim 1, And performing a reverse osmosis process before feeding some or all of the overflow of the crystallizer / settler to the nanofiltration device. The method of claim 2, Removing from 10% to 99% by weight of water, based on the total weight of the aqueous solution comprising salt in the reverse osmosis process. The method of claim 3, wherein The removed water is used as drinking water or process water. The method according to any one of claims 1 to 4, Wherein the aqueous salt solution from the nanofiltration device is a continuous closed loop process that is reused as a salt source. The method according to any one of claims 1 to 5, The crystalline salt in the aqueous slurry is fed to the centrifuge or to the centrifuge after being fed to the washing leg. The method of claim 6, The recycle of the centrifuge is fed to the crystallizer / settler, reused as a salt source, or fed to the crystallizer / settler and reused as a salt source. The method according to any one of claims 1 to 7, The salt source is selected from the group consisting of sodium chloride, sodium carbonate and sodium sulfate sources. The method of claim 8, The salt source is a subterraneous sodium chloride deposit. The method according to any one of claims 1 to 9, Antisolvents can be selected from aromatic alcohols, polyvinyl alcohols, polyethylene glycols, nitrilotriacetic acid, carboxylic acids or polycarboxylic acids, phosphonates, polyphosphonates, functional or nonfunctional carboxymethyl cellulose, Fe ( II) Organic complexes of ions and Fe (III) ions, ethanol, acetone, isopropanol, quaternary ammonium salts, cyclodextrins, amino group containing polymers, quaternary ammonium group containing polymers, nitrogen containing aliphatic rings, polymers containing anionic groups Sodium salt, chloride of a cationic group-containing polymer, choline chloride and choline chloride ionic liquids. The method according to any one of claims 1 to 10, Antisolvents include polymers, polypeptides and oligopeptides which contain two or more carboxylic acid groups or carboxyalkyl groups or which may contain one selected from the group consisting of phosphate, phosphonate, phosphino, sulfate and sulfonate groups; Functional or nonfunctional monosaccharides, disaccharides and polysaccharides; Potassium ferrocyanide; Lead chloride; Cadmium chloride; Magnesium sulfate; Quaternary ammonium salts; Cyclodextrins; Amino group-containing polymers; Quaternary ammonium group-containing polymers; Polymers comprising nitrogen-containing aliphatic rings; Sodium salts of anionic group-containing polymers; And at least one crystal growth inhibitor selected from the group consisting of chloride salts of cationic group-containing polymers. The method according to any one of claims 1 to 11, Antisolvents contain polymers, polypeptides and oligopeptides, functional or which may contain two or more carboxylic acid groups or ester groups or may contain one selected from the group consisting of phosphate, phosphonate, phosphino, sulfate and sulfonate groups Non-functional monosaccharides, disaccharides and polysaccharides, polymers having one or more alcohol groups, surfactants from natural sources such as humic acid, unbalanced rosin acid soaps, lactic acid, phospholipids, yeast cells , Suspensions of algae, N, N-diethyl-1,3-diaminopropane, ethylene diamine, polyisobutylene derivatives, N, N-dimethyl-1,3-diaminopropane, diethylene triamine, Triethylene tetramin, 1,6-diaminohexane, poly [oxy (methyl-1,2-ethanediyl)], hexamethylene biguanide, maleic anhydride homopolymer, amylase, protease, citric Sodium, citric acid, N, N, N ', N'-tetraacetylethylene diamine, nonanoyloxybenzene sulfonate, polyepoxysuccinic acid, polyacrylamide, ethylenediamine tetramethylene phosphoric acid, sulfonated polyoxyethylene ether, 4 Primary ammonium salts, cyclodextrins, amino group containing polymers, quaternary ammonium group containing polymers, polymers containing nitrogen-containing aliphatic rings, sodium salts of anionic group containing polymers, chloride salts of cationic group containing polymers, fatty acids, orange juice, cider juice , Polyethylene imine, sodium dimethyl dithiocarbamate, and a scaling inhibitor selected from the group consisting of at least one of the above-mentioned scaling inhibitors and Fe (II) ions or Fe (III) ion complexes. Characterized in that the method. The method according to any one of claims 1 to 12, At least one antisolvent or at least one crystal growth inhibitor has scaling inhibitory properties. The method according to any one of claims 1 to 13, A hydrophilic antisolvent is used which absorbs at least 5% by weight of water based on the total weight of the antisolvent.

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