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WO2006045795A2 - Procedes consistant a utiliser la cristallisation par effet antisolvant - Google Patents

Procedes consistant a utiliser la cristallisation par effet antisolvant Download PDF

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Publication number
WO2006045795A2
WO2006045795A2 PCT/EP2005/055527 EP2005055527W WO2006045795A2 WO 2006045795 A2 WO2006045795 A2 WO 2006045795A2 EP 2005055527 W EP2005055527 W EP 2005055527W WO 2006045795 A2 WO2006045795 A2 WO 2006045795A2
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Prior art keywords
salt
antisolvent
aqueous
settler
crystallizer
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WO2006045795A3 (fr
Inventor
Gerrald Bargeman
René Lodewijk Maria DEMMER
Antoon Ten Kate
Boris Kuzmanovic
Cornelis Elizabeth Johannus Van Lare
Mateo Jozef Jacques Mayer
Maarten André Irène SCHUTYSER
Cornelis Johannes Govardus Van Strien
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Akzo Nobel NV
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Akzo Nobel NV
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Publication of WO2006045795A3 publication Critical patent/WO2006045795A3/fr
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D3/00—Halides of sodium, potassium or alkali metals in general
    • C01D3/14—Purification
    • C01D3/16—Purification by precipitation or adsorption
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D3/00—Halides of sodium, potassium or alkali metals in general
    • C01D3/04—Chlorides
    • C01D3/06—Preparation by working up brines; seawater or spent lyes

Definitions

  • the present invention relates to a process to make inorganic salt compositions comprising the crystallization of said salt from a crude aqueous salt solution using an antisolvent, and to a process for the preparation of drinking and/or process water from a crude aqueous salt solution.
  • inorganic salts are made industrially from aqueous salt solutions produced by dissolving a natural source of the salt in water.
  • the salt is usually obtained by crystallizing it from the aqueous solution by evaporation of the water, which is generally accomplished using multiple-effect or vapour recompression evaporators.
  • 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 one in the multiple-effect system to increase energy efficiency.
  • Vapour recompression forced-circulation evaporators consist of a crystallizer, a compressor, and a vapour scrubber. The aqueous salt solution enters the crystallizer vessel, where salt is crystallized.
  • Vapour is withdrawn, scrubbed, and compressed for reuse in the heater.
  • Both recompression evaporators and multiple-effect evaporators are energy- intensive because of the water evaporation step involved.
  • aqueous salt solutions produced by dissolving a natural source of said salt in water normally contain a quantity of contaminations. Therefore, additional purification steps of the salt solution prior to crystallization, additional washing of the inorganic salt produced, and/or energy-consuming drying steps have to be employed to reduce the levels of contaminants.
  • the conventional process to make sodium chloride and wet sodium chloride involves producing a brine by dissolving a natural source of NaCI in water and subsequent evaporative crystallization of said brine.
  • the brine will contain quantities of dissolved K, Br, SO 4 , Mg, Sr, and/or Ca, since these contaminations are typically present in natural NaCI sources.
  • a disadvantage of such a process is that the salt obtained has imperfections in the crystal lattice and contains occlusions, i.e. small pockets of mother liquor of the evaporative crystallization process, which are present in cavities in the salt crystals.
  • the (wet) salt, as well as the brine produced therefrom is contaminated with compounds present in the mother liquor.
  • the quantities of K, Br, SO 4 , Mg, Sr, and/or Ca that are carried over are quite high. Therefore, additional washing steps are required to reduce the quantities of contaminants.
  • Potassium and bromide ions both have physical properties and dimensions that are close to those of sodium and chloride ions, respectively. This means that these ions are built into the salt crystal lattice.
  • the partitioning coefficient of bromide i.e. the content of bromide in the salt produced [mg/kg] over the concentration of bromide in the mother liquor [mg/l] depends on the crystallization conditions. The same applies for the partitioning coefficient of potassium. It is also noted that the partitioning coefficients for potassium and bromide increase with temperature, which makes the conventional processes performed at elevated temperature less attractive.
  • antisolvent crystallization can be an energy-saving alternative for the production of inorganic salts normally produced by evaporative crystallization.
  • the salt is obtained by the addition of an antisolvent to an aqueous salt solution, which induces crystallization of the salt, followed by a filtration step.
  • the antisolvent is usually recovered to allow the creation of a continuous, industrially useful process.
  • a special antisolvent crystallization process for inorganic salts is described by D.A. Weingaertner et al. in Ind. Eng. Res., 1991 , Vol. 30, pages 490-501.
  • Said antisolvent crystallization process is an extractive crystallization process wherein particular salts, such as sodium chloride and sodium carbonate, are recovered from their purified concentrated aqueous solutions by the addition of an organic solvent. Solid salt is formed because water is transferred from the aqueous phase to the organic phase, resulting in direct shrinkage of the aqueous phase, and/or because of solvent entering the aqueous phase, resulting in a diminished solubility of salt in that phase.
  • the process to make the high-purity salt compositions according to the present invention comprises the steps of
  • the term "contacting" as used throughout this specification is meant to comprise any conventional technique for adding the antisolvent(s) to the aqueous solution comprising the inorganic salt.
  • the antisolvent(s) is/are preferably contacted with the aqueous solution such that the antisolvent(s) and said aqueous solution are able to at least partially dissolve in one another, partially meaning that in a 1 :1 mixture of an antisolvent and water, at least 0.5 wt%, preferably at least 2 wt% of the antisolvent will dissolve in the aqueous solution, and/or that at least 0.5 wt%, preferably at least 2 wt% of water will dissolve in the antisolvent.
  • additional purification steps or recrystallization steps are not necessary when using at least one crystal growth inhibitor in the process according to the present invention.
  • the crystal growth inhibitor(s) prevent(s) primary nucleation of the salt crystals, which finally results in relatively coarse salt crystals (i.e. crystals with a diameter of about 300 microns) with reduced impurity levels and having a uniform crystal size distribution.
  • these crystals can be easily separated from the aqueous slurry, e.g. by use of a centrifuge.
  • the narrow crystal size distribution makes it possible to also apply conventional centrifuges at relatively small average crystal sizes.
  • the process according to the present invention is applicable for the crystallization of inorganic salts.
  • said process is used for the crystallization of inorganic salts usually produced by evaporative crystallization.
  • the process can also be used to selectively remove contaminations from a solution, for example the removal of calcium sulfate from brine by application of an antisolvent specific for calcium sulfate.
  • the production of sodium sulfate from a sulfate-rich brine is possible by application of this technology.
  • the process is used for the crystallization of alkali or alkaline earth salts of halides, phosphates, carbonates, sulfates, (per)chlorates, ammonium salts, or nitrates.
  • the process is not used for the crystallization of Ca or Sr salts.
  • the antisolvent or the aqueous solution preferably does not comprise one or more scaling inhibitors for these salts.
  • the process is used for the crystallization of MgSO 4 , Na 2 CO 3 or Na 2 SO 4 , and most preferably, the process is used for the crystallization of sodium chloride.
  • the sodium chloride used as raw material is rock salt and/or a subterraneous salt deposit. More preferably, it is a subterraneous salt deposit exploited by means of dissolution mining.
  • the process may also be used for the crystallization and purification of solar salt (sodium chloride or saturated brine obtained by evaporating water from brine using solar heat), including solar sea salt, which is typically obtained from sea water. In that case, the sea water, optionally after a concentration step, can be fed directly to the crystallizer/settler.
  • the salt source is a solid salt source.
  • sodium chloride as used throughout this document is meant to denominate all types of sodium chloride of which more than 25 wt% is NaCI.
  • such sodium chloride contains more than 50 wt% of NaCI.
  • the sodium chloride contains more than 75 wt% of NaCI, while a sodium chloride containing more than 90 wt% of NaCI is most preferred.
  • Fig. 1 is a schematic depiction of a preferred flow chart for the above-disclosed novel process.
  • Water (1 ) is fed to a salt source (A), where it dissolves at least part of the salt.
  • A salt source
  • the (saturated) aqueous 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), with one or more crystal growth inhibitors being present in the antisolvent(s) and/or one or more scaling inhibitors being present in the antisolvent(s).
  • the one or more crystal growth inhibitors and/or one or more scaling inhibitors may also be present in the (saturated) aqueous solution.
  • the crystalline salt composition formed is removed from the crystallizer/settler (B) as an aqueous slurry (6) and preferably fed to a centrifuge. Since said salt slurry (6) removed from the crystallizer/settler (B) by one or more outlets may still contain relatively large quantities of antisolvent, preferably, before said salt slurry is fed to a centrifuge, it is fed to a washing leg. For example, if the salt slurry is to be used for electrolysis purposes, it may be desirable to wash the adhered mother liquor, i.e.
  • the residual solution which remains after the crystallized salt(s) has/have been removed, and/or the antisolvent from the salt crystals can be realized by feeding said salt slurry to a conventional washing leg operated with a raw aqueous salt solution or a purified aqueous salt solution as washing medium.
  • a purified aqueous salt solution can be produced by washing the salt crystals with water on a centrifuge. In this way, the production of such a purified brine is combined with an additional washing step of the salt crystals on the centrifuge.
  • the overflow (4) of the crystallizer/settler which comprises the combined antisolvent and aqueous salt solution is subjected to a separation step in a separation unit (C), where the one or more antisolvents are separated from the aqueous salt solution by one or more techniques selected from the group consisting of adsorption, ion-exchange, a temperature change induced phase split, a pH change induced phase split, a complexation induced phase split, pressure reduction, evaporation, and extraction.
  • This separation unit (C) can be any conventionally used unit capable of handling solids and/or liquids and allowing their separation.
  • the separation unit is a unit selected from the group consisting of settlers such as stirred vessels, conventional separation columns, centrifuges, and heat-exchangers.
  • the aqueous solution (5), which is undersaturated with salt, and the antisolvent (7) are removed from the separation unit.
  • the recovered antisolvent (7) is reused by being recycled to the crystallizer/settler.
  • the process is a continuous, closed loop process wherein the aqueous salt solution, being undersaturated for salt after being separated from the one or more antisolvents, is recycled to the salt source. There it is used to dissolve more salt, thus producing a, preferably saturated, aqueous solution which can be fed to the crystallizer/settler.
  • the crystalline salt composition is removed from the crystallizer/settler (B) and fed to a centrifuge as a slurry, after which the liquid effluent of the centrifuge (also denoted as mother liquor) is recycled back to the crystallizer/settler and/or to the salt source.
  • a centrifuge as a slurry
  • mother liquor also denoted as mother liquor
  • An antisolvent suitable for use in the process according to the present invention is a liquid compound or mixture of liquid compounds in which the salt to be crystallized is less soluble than in water at 20°C and which differs in chemical composition from the employed crystal growth inhibitor(s) and scaling inhibitor(s).
  • an antisolvent can be employed which is a gaseous or solid component. More particularly, the term "antisolvent" as used throughout this application is meant to include each component, liquid compound, or mixture of components and/or liquid compounds which leads to the crystallization of 5 g or more of salt after the addition of 500 g of the antisolvent to 1 ,000 ml of saturated aqueous salt solution at a temperature between -10 and 110°C.
  • the exact temperature at which said crystallization is performed depends on the salt, the liquid compound(s), and/or component(s) used, and on the desired processing temperature.
  • one or more antisolvents which are fluid at 20°C are used in the process according to the present invention. More preferably, a liquid compound which is an organic solvent, an ionic solvent, or an organic or inorganic complex is used as the antisolvent. Most preferably, an organic solvent is used as the antisolvent.
  • the testing temperature is the temperature at which the crystallization according to the invention is conducted.
  • the antisolvent(s) is/are used in a total amount of at least 10 g per litre of aqueous salt solution. More preferably, at least 50 g and most preferably, at least 200 g of antisolvent(s) is used per litre of aqueous salt solution.
  • the total amount of antisolvent(s) used in the present process is no more than 10,000 g, more preferably no more than 5,000 g, even more preferably no more than 2,500 g, and most preferably no more than 1 ,000 g per litre of aqueous salt solution.
  • At least an effective quantity of one or more crystal growth inhibitors and/or one or more scaling inhibitors should be present either in the antisolvent(s) or in the aqueous solution before said aqueous solution is contacted with the antisolvent(s).
  • an additive is suitable for use as a crystal growth inhibitor according to the invention can be determined using the following tests. It is noted that it is sufficient if the additive is considered to be a crystal growth inhibitor according to one of these tests.
  • the quantity of bromide is determined (in mg Br per kg of dried salt) by conventional spectrophotometry measurements. From the bromide content in the salt crystals and in the final mother liquor the partition coefficient is calculated. Said partition coefficient is the Br content in the salt crystals divided by the Br content in the mother liquor. This is the blank experiment. The above-described procedure is repeated using additionally 200 mg/l of an additive, and the obtained values for occluded water in the crystals and the partition coefficient are compared to the ones obtained in the blank experiment.
  • An additive is considered to be a crystal growth inhibitor if at least one of the following observations is made: the quantity of occluded water decreases by more than 5%, the partition coefficient decreases by more than 5%, or analysis by means of a (light) microscope shows crystals with (111 ) faces.
  • An additive is considered to be a crystal growth inhibitor if at least one of the following observations is made: the quantity of occluded water decreases by more than 5%, the partition coefficient decreases by more than 5%, or analysis by means of a (light) microscope shows crystals with (111 ) faces.
  • the obtained values for occluded water in the crystals and the partition coefficient are compared to the ones obtained in the blank experiment.
  • An additive is considered to be a crystal growth inhibitor if at least one of the following observations is made: the quantity of occluded water decreases by more than 5%, the partition coefficient decreases by more than 5%, or analysis by means of a (light) microscope shows crystals with (111 ) faces.
  • an additive is suitable for use as a scaling inhibitor according to the present invention can be determined using the following four tests. It is noted that it is sufficient if the additive is considered to be a scaling inhibitor according to one of these tests.
  • ICP Inductively Coupled Plasma
  • spectrometry for the quantity of Ca and Sr ions
  • titrimetry for the quantity of CO 3
  • the procedure is repeated using additionally 10 ppm of additive.
  • the quantities of Ca, Sr, and CO 3 in the mother liquor are now compared to the quantities of Ca, Sr, and CO 3 in the mother liquor as observed for the blank experiment.
  • An additive is considered to have scale inhibiting properties if at least one of the dissolved quantities of Ca, Sr, and CO 3 increases by more than 5%.
  • tests 2b-e, 3, and 4 can also be used: b) In a stirred glass beaker, 360 meq/l of SO 4 (added as Na 2 SO 4 ), 2.0 meq/l of Ca (added as CaCI 2 ), 0.1 meq/l of Sr (added as SrCI 2 ), 10 meq/l of CO 3 (added as Na 2 CO 3 ), 6 meq/l of OH (added as NaOH), and 120 mg/l of Br (added as NaBr) are dissolved in 1 I of distilled water.
  • the salt to be crystallized is added in such an amount as to produce a saturated salt solution.
  • This solution is heated to boiling point under atmospheric conditions and water is evaporated until a volume of 500 ml is obtained.
  • the reaction mixture is filtered over a 0.2 micron filter and the quantity of dissolved Ca, Sr, and CO 3 in the mother liquor is determined by means of conventional ICP (Inductively Coupled Plasma) spectrometry (for the quantity of Ca and Sr ions) and titrimetry (for the quantity of CO 3 ). This is the blank experiment. The procedure is repeated using additionally 10 ppm of an additive.
  • the salt to be crystallized is added in such an amount as to produce a saturated salt solution.
  • a saturated salt solution 5 g of Socal ® P2 ex Solvay Chemicals (i.e. CaCO 3 crystals).
  • Socal ® P2 ex Solvay Chemicals i.e. CaCO 3 crystals.
  • the mixture is heated to boiling point under atmospheric conditions and water is evaporated until a volume of 500 ml is obtained.
  • the reaction mixture is filtered over a
  • test 2b The same test as test 2b, but at reflux conditions and a temperature of 90°C and with 100 mg/l Socal ® P2 seeds ex Solvay Chemicals.
  • test 2d The same test as test 2d, but without the addition of Socal ® P2 seeds in the blank experiment.
  • an additive is considered to be a scaling inhibitor if the quantity of Ca and/or SO 4 dissolved in the mother liquor increases by more than 5%.
  • the pH is controlled and 10 meq/l OH is added.
  • An additive is considered to be a scaling inhibitor if the quantity of Ca and/or SO4 dissolved in the mother liquor increases by more than 5%.
  • the pH is controlled and 10 meq/l OH is added.
  • one or more crystal growth inhibitors are used in the process according to the present invention, they have to be present in an effective quantity.
  • An effective quantity of crystal growth inhibitor is present if at least one of the following observations is made: the quantity of occluded water decreases by more than 5%, the partition coefficient decreases by more than 5%, or analysis by means of a (light) microscope shows crystals with (111 ) faces, compared to salt produced from the same salt solution under the same conditions, but without the addition of a crystal growth inhibitor.
  • one or more scaling inhibitors are employed in the process according to the present invention, they have to be present in an effective quantity.
  • An effective quantity of scaling inhibitor is present if at least one of the dissolved quantities of Ca, Sr, and CO 3 in the mother liquor increases by more than 5%, compared to mother liquor produced from the same salt solution under the same conditions, but without the addition of a scaling inhibitor.
  • high-purity salt as used throughout the specification is meant to denote salt which is crystallized according to the process of the present invention using an effective quantity of crystal growth inhibitor and/or scaling inhibitor.
  • the total quantity of said crystal growth inhibitors present in the mother liquor is less than 5,000 mg per kg of mother liquor.
  • the total quantity of said crystal growth inhibitors present in the mother liquor i.e. the combination of antisolvent(s) and aqueous solution minus the precipitated salt
  • the total quantity of said crystal growth inhibitors present in the mother liquor is less than 5,000 mg per kg of mother liquor.
  • less than 1 ,500 mg/kg and more preferably less than 300 mg/kg is used.
  • a total concentration of crystal growth inhibitors higher than 5,000 mg per kg mother liquor is also possible as long as it is lower than the total concentration of antisolvent.
  • more than 10 mg, preferably more than 12.5 mg, and most preferably more than 14 mg of crystal growth inhibitors is used per kg of mother liquor.
  • the total quantity of said scaling inhibitors present in the mother liquor-antisolvent system is less than 5,000 mg per kg of mother liquor as well.
  • the total quantity of said scaling inhibitors present in the mother liquor-antisolvent system is less than 5,000 mg per kg of mother liquor as well.
  • less than 1 ,500 mg/kg and more preferably less than 300 mg/kg is used.
  • a total concentration of scaling inhibitors higher than 5,000 mg per kg mother liquor is also possible as long as it is lower than the total concentration of antisolvent.
  • more than 1 mg, preferably more than 3 mg, and most preferably more than 5 mg of scaling inhibitors is used per kg of mother liquor.
  • the antisolvent may be, but is not necessarily, (partially) miscible with pure water. It is also possible to use an antisolvent or a mixture of antisolvents which will result in the formation of an emulsion after it/they is/are added to the aqueous salt solution.
  • the antisolvent(s) used in the process according to the present invention is/are environmentally friendly, and more preferably it/they is/are also food grade.
  • the preferred antisolvents are solvents which are inexpensive and readily available. The choice of the one or more antisolvents depends on the solubility characteristics of the salt being crystallized.
  • Preferred antisolvents are selected from the group consisting of alcohols such as methanol, ethanol, propanol, butanediol; ketones such as acetone, butanone; amines, such as diisopropylamine, ethylamine, ethylene diamine, butylamine, diethylene triamine, polyethylene imine; quaternary ammonium salts, preferably with chloride as counterion, such as polydimethyldiallyl ammonium chloride (known as Polyquat ® , ex Katpol-Chemie); phosphonium salts, preferably with chloride as counterion; sulfonium salts, preferably with chloride as counterion; acetonitrile; formic acid; acetic acid; polyethylene glycol; polyoxyethers; polypropylene glycol; 1 -methyl pyrrolidone; polyvinyl pyrrolidone; the sodium salt of ethylenediamine tetraacetic acid (EDTA),
  • ionic liquids are employed as the antisolvent(s).
  • ionic liquids suitable for use as an antisolvent in the process according to the present invention include but are not limited to choline chloride based ionic liquids such as choline chloride/urea, choline chloride/phenol, or choline chloride/saccharide.
  • the antisolvent is selected from the group consisting of ethanol, acetone, acetic acid, choline chloride, polyethylene glycol, and Polyquat ® .
  • Crystal growth inhibitors suitable for use in the present process of antisolvent crystallization of a salt include all conventional crystal growth inhibitors for said salt.
  • the crystal growth inhibitor for a sodium chloride crystallization process is selected from the group consisting of (poly)phosphates, polycarboxylic acids, phophinocarboxylic acids, oligopeptides, polypeptides, polymaleic acids, polyacrylates, polymers comprising sulfate and/or sulfonate groups, (functionalized) saccharides, cyclodextrines, ferrocyanide salts, humic acids, and ureas.
  • the crystal growth inhibitor is selected from the group consisting of phosphinocarboxylic acids, humic acids, and saccharose.
  • a crystal growth inhibitor is used which during the separation step to separate the antisolvent(s) from the aqueous salt solution will remain in the antisolvent stream subsequently recycled to the crystallizer/settler.
  • the crystal size distribution could be influenced. It appeared that increasing quantities of crystal growth inhibitor in the antisolvent resulted in the production of crystals with a narrower size distribution. It was also found that the d50 crystal diameter, i.e. the diameter at which 50 wt% of the crystals have a larger crystal diameter and 50 wt% of the crystals have a smaller crystal diameter, could be shifted by more than 10% compared to the size of crystals grown in the absence of a crystal growth inhibitor just by adapting the quantities of crystal growth inhibitor in the antisolvent.
  • the crystal size distribution can be determined by means of conventional techniques such as sieve analysis or using a light microscope.
  • Scaling inhibitors suitable for use in the process of antisolvent crystallization of a salt include any conventional scaling inhibitor.
  • the scaling inhibitor for a brine crystallization process is selected from the group consisting of polycarboxylic acids, oligopeptides, polypeptides, (poly)phosphates, polyacrylates, phosphinocarboxylic acids, polymaleic acids, polymers comprising sulfate and/or sulfonate groups, (functionalized) saccharides, cyclodextrines, sodium citrate, sodium gluconate, citric acid, humic acids, surfactants from a natural source such as disproportionated rosin acid soap, lactic acid, phospholipids, a suspension of yeast cells, a suspension of algae, amylase, protease, polyepoxysuccinic acid, polyacrylamide, fatty acids, orange juice, and apple juice.
  • the scaling inhibitor is selected from the group consisting of (poly)phosphates, polyacrylates, polymaleic aicds, phosphinocarboxylic acids, and sucrose.
  • a scaling inhibitor is used which during the separation step to separate the antisolvent(s) from the aqueous salt solution will remain in the antisolvent stream subsequently recycled to the crystallizer/settler.
  • any water supply normally used in conventional salt crystallization processes can be employed.
  • closed loop antisolvent crystallization process according to the present invention only small quantities of water are needed.
  • water is needed to start the crystallization process by dissolving part of the salt source.
  • an aqueous salt slurry is removed from the crystallizer/settler.
  • a quantity of water which preferably equals the quantity of water lost via the aqueous salt slurry is then added to the salt source in order to allow continuation of the process.
  • the quantity of water needed in order to preserve a continuous crystallization process can be lowered even further if the recycle of the centrifuge, to which the crystallized salt in an aqueous slurry is preferably fed, is at least partially fed into the crystallizer/settler and/or to the salt source.
  • the salt source is a subterraneous sodium chloride deposit in a well exploited by means of dissolution mining.
  • the undersaturated aqueous salt solution which is removed from the separation unit and recycled to the sodium chloride deposit will contain certain levels of contaminants, such as K, Br, SO 4 , Mg, Sr, and/or Ca contaminations.
  • contaminants such as K, Br, SO 4 , Mg, Sr, and/or Ca contaminations.
  • the concentrations of said contaminations in the saturated aqueous salt solution leaving the sodium chloride deposit will increase during the process until said solution is also saturated with these contaminations.
  • a stationary phase will be reached in which there is no driving force anymore for new contaminations present in the sodium chloride deposit to dissolve in the aqueous solution.
  • addition of water is only needed to fill the cavity which is formed upon dissolution of the natural salt source.
  • a specific volume of the mother liquor is purged in order to avoid unacceptable accumulation of contaminants in the aqueous salt solution because of the recycle.
  • aqueous salt solutions in evaporation processes can be increased by reducing the quantity of the contaminations, such as anhydrite, gypsum, and polyhalite (and/or their strontium analogues) that dissolve in said aqueous solutions.
  • This is typically done by adding certain agents to the water used in the process, or by mixing such agents with the salt source before adding the water.
  • agents are conventionally called "retarding agents.” Although such agents are not required for the production of high-purity salt via the process of the present invention, if desired, these types of additives may be added to the water supply.
  • the one or more antisolvents and the aqueous salt solution making up the overflow of the crystallizer/settler can be separated from each other by one or more techniques selected from the group consisting of adsorption, ion- exchange, a temperature change induced phase split, a pH change induced phase split, a complexation induced phase split, a pressure induced phase split, evaporation, and extraction, optionally in combination with a nanofiltration step as disclosed in co-pending international application EP2004/004383.
  • adsorption, ion- exchange a temperature change induced phase split
  • a pH change induced phase split a pH change induced phase split
  • a complexation induced phase split a pressure induced phase split
  • evaporation evaporation
  • This technique involves the adsorption of antisolvent(s) onto the surface of one or more solid adsorbents suitable for adsorbing the specific antisolvent(s) used in the process.
  • one or more adsorbents are employed selected from the group consisting of natural or treated clays, zeolites, activated carbon, carbon molecular sieves, adsorbing resins, and adsorbing polymers.
  • Contacting the solid absorbent(s) with the overflow of the crystallizer/settler that contains the antisolvent(s) is preferably done by flowing the overflow through a fixed bed of adsorbent(s), by moving adsorbent(s) preferably in a countercurrent manner through the overflow or by a simulated moving action in a conventional simulated moving bed system (SMB).
  • SMB simulated moving bed system
  • Desorption of the adsorbed antisolvent for its reuse can be achieved by contacting the solids with water or an aqueous salt solution at increased temperature; by washing with water or an aqueous salt solution at an adequate pH value; by applying centrifugal force during a wash with water or an aqueous salt solution; with the aid of ultrasound; by washing with a supercritical fluid such as CO 2 , after which said supercritical fluid and antisolvent can be separated from each other; or by washing with an organic solvent or an ionic liquid, followed by separation of the antisolvent(s) from the organic solvent or ionic liquid by, for example, evaporation or distillation.
  • the adsorption step has functioned either as a concentration step or as a separation step for the antisolvent.
  • This technique is suitable for separating an antisolvent which is composed of cations and anions from the aqueous salt solution. Furthermore, this technique is preferably used when the efficiency of the antisolvent is such that at least 70 wt%, and more preferably at least 85 wt% of the salt present in the aqueous solution is forced to crystallize in the crystallizer/settler before being contacted with the antisolvent.
  • the overflow of the crystallizer/settler is contacted with a combination of a weakly basic ion exchanger and a weakly acidic ion exchanger.
  • the acidic resin will adsorb the cation of the salt, whereas the basic resin, being protonated, will adsorb the anion.
  • These two types of ion exchangers can be applied as two separate materials, but can also be present in one and the same material, commonly known as an amphoteric ion exchanger.
  • contacting the ion exchangers and the overflow comprising the antisolvent(s) is preferably done by flowing the overflow through a fixed bed comprising one or more ion exchangers or by moving one or more ion exchangers, preferably in a countercurrent manner, through the overflow.
  • the process runs in a semi-continuous manner, whereas in the second it is usually operated as a continuous process.
  • the recovery of the adsorbed antisolvent(s) on the ion exchangers can be achieved by washing the ion exchangers with water or with a diluted aqueous salt solution, preferably by increasing or decreasing the temperature such that the antisolvent(s) is/are released from the ion-exchanger.
  • a two-step system is created which allows easy separation of the antisolvent(s) from the aqueous solution.
  • the ion-exchange step has functioned as a concentration step for the antisolvent.
  • This separation technique is preferably used if one or more antisolvents are employed which form a one-phase system with an aqueous salt solution at the crystallizing temperature, but which are immiscible or only slightly miscible with said aqueous salt solution at a temperature higher or lower than this temperature.
  • the antisolvent(s) can be recovered by increasing or decreasing the temperature of the overflow to a value where the mutual solubilities of the antisolvent and the aqueous salt solution are low, thus creating a two-phase system with an antisolvent-rich phase and a water-rich phase. These two liquid phases can be easily separated from each other by conventional methods, such as by decanting the antisolvent-rich phase.
  • This technique can also be employed if the one or more antisolvents precipitate from the overflow upon increasing or decreasing the temperature thereof to form a solid antisolvent-phase and a liquid water-rich phase instead of two liquid phases.
  • the antisolvent can be recovered from the aqueous salt solution in solid form, for example by conventional filtration methods. It is noted that this technique is a less preferred embodiment according to the present invention.
  • This separation technique is preferably used if one or more antisolvents are employed which form a one-phase system with an aqueous salt solution at the pH value during crystallization, but which are immiscible or only slightly miscible with an aqueous salt solution at a pH value higher or lower than this pH value.
  • the antisolvent(s) can be recovered by adding either acid or base to the overflow such that a pH value is reached where the mutual solubilities of the antisolvent and the aqueous salt solution are low, thus creating a two-phase system with a liquid antisolvent-rich phase and a liquid water-rich phase.
  • HCI or NaOH is used for this purpose.
  • the one or more antisolvents precipitate from the overflow upon the addition of either acid or base thereto to form a solid antisolvent-phase and a liquid water-rich phase instead of two liquid phases.
  • the antisolvent can be recovered from the aqueous salt solution in solid form, for example by conventional filtration methods or by decantation.
  • the thus recovered antisolvent is treated with acid or base such that it recovers its original form and subsequently it is recycled.
  • This separation technique is preferably used if one or more antisolvents forming a one-phase system with an aqueous salt solution are employed which are capable of forming a complex with one or more complexing agents to subsequently form either a two-phase liquid-liquid system or a two-phase solid- liquid system with the aqueous salt solution. Preferably, the formation of such a complex is reversible.
  • one or more complexing agents are added to the overflow, upon which two phases are formed consisting of an antisolvent-rich phase where the antisolvent(s) is/are complexed, and a water-rich phase.
  • the antisolvent-rich phase can be either a liquid phase or a solid phase.
  • the two phases can be easily separated from each other by conventional methods, such as by decanting the antisolvent- rich phase. If it forms a solid phase, the two phases can be separated from each other by, for example, a conventional filtration method.
  • the antisolvent-rich phase is subsequently treated to decomplex the antisolvent and obtain it in its pure form in order to allow reuse of the antisolvent(s).
  • the antisolvent(s) is/are decomplexed by a temperature change induced decomplexation, or a pH change induced decomplexation, preferably by using HCI, CO 2 or NaOH.
  • An example of preferred complexing agents are cyclodextrins, since they form inclusion complexes with the antisolvent(s).
  • This separation technique is preferably used if one or more antisolvents are used which are gaseous at atmospheric pressure. These antisolvents are preferably contacted with the aqueous solution at a pressure of at least 1.5 bar, more preferably at least 10 bar, and most preferably at least 15 bar. Preferably, no pressures higher than 120 bar, more preferably 100 bar, and most preferably 90 bar are employed. Under these conditions, part of the antisolvent will be dissolved in the aqueous salt solution and the salt will be forced to crystallize. What pressure range will give the best results depends on the properties of the antisolvent and can be easily determined by those skilled in the art by routine experimentation.
  • Said antisolvent(s) can be recovered by reducing the pressure, upon which the antisolvent concentration in the aqueous salt solution will decrease.
  • the recovery of antisolvent is performed at a pressure which is far below the pressure employed during the crystallization, in order to achieve maximum recovery.
  • the pressure is not reduced below atmospheric pressure.
  • Preferred gaseous antisolvents which can be separated from the aqueous phase include but are not limited to carbon dioxide, dimethylether, ammonia, dimethylamine, and trimethylamine.
  • one or more antisolvents having a boiling point lower than water they can be recovered from the overflow of the crystallizer/settler by evaporation thereof from the aqueous solution.
  • this technique is used when antisolvent(s) is/are used of which the boiling point is below 85°C at atmospheric pressure.
  • it is also possible to evaporate the water. Any evaporative technique conventionally used can be employed, such as evaporation by heating and/or pressure reduction, distillation or pervaporation.
  • the evaporated antisolvent(s) is/are condensed, whereupon they are preferably recycled in the process.
  • Preferred antisolvents which can be separated from the aqueous phase include but are not limited to acetone, methyl acetate, ethanol, and propanal.
  • a further method to separate the one or more antisolvents in the overflow of the crystallizer/settler from the aqueous salt solution involves contacting a suitable extraction solvent in which the antisolvent(s) will dissolve with the overflow of the crystallizer/settler, during which process a two-phase liquid-liquid system with the aqueous salt solution is generated.
  • a suitable extraction solvent in which the antisolvent(s) will dissolve with the overflow of the crystallizer/settler, during which process a two-phase liquid-liquid system with the aqueous salt solution is generated.
  • contacting the overflow with the extraction solvent is performed in an extraction column.
  • the extraction solvent and the one or more antisolvents can subsequently be separated from each other using one of the previously discussed separation techniques such as distillation, adsorption, ion-exchange, a temperature change induced phase split, a pH change induced phase split, complexation using one or more complexing agents, or evaporation.
  • the recovered extraction solvent and/or antisolvent(s) is/are recycled in the process.
  • an extraction solvent which forms a two-phase system with the aqueous salt solution.
  • an extraction solvent selected from the group consisting of toluene, diethyl ether, hexane, cyclohexane, and an ionic liquid is used.
  • the crystallizer/settler suitable for use in the process according to the present invention may be any conventional crystallizer/settler.
  • it is a crystallizer/settler with a vertical feed hose system and no impeller or other moving parts, which comprises a continuous phase in the crystallizer containing the one or more antisolvents so that the salt will crystallize continuously.
  • the crystallizer/settler is a reactor for precipitating and/or crystallizing a substance comprising at least a bottom wall, a vertical wall preferably having a cylindrical cross-section, at least a first inlet, preferably at least first and second inlets for feeding first and second reactants to the reactor, and an outlet.
  • Such a crystallizer/settler is for example described in US 4,747,917. However, most preferably, a crystallizer/settler is used wherein the one or more inlets comprise respective discharge openings arranged to direct the reactants to a surface and cause them to collide with the same, which is for example disclosed in NL 7215309.
  • the crystallized salt is removed from the crystallizer/settler as an aqueous slurry. Preferably, it is fed to a centrifuge, where a wet salt is produced.
  • the term "wet salt” is used to denominate salt containing a substantial quantity of water. More particularly, it is water-containing salt of which more than 50 wt% consists of the pure salt. Preferably, such salt contains more than 90 wt% of the pure salt. More preferably, the salt contains more than 92 wt% of the pure salt, while a salt of essentially the pure salt and water is most preferred.
  • the wet salt will contain more than 0.5, preferably more than 1.0, more preferably more than 1.5 wt% of water.
  • the wet salt may be dried in a conventional manner to obtain dried salt comprising less than 0.5 wt% of water.
  • the process further comprises a reverse osmosis step before the overflow of the crystallizer/settler comprising antisolvent(s), water, and salt is fed to a separation unit.
  • a reverse osmosis step before the overflow of the crystallizer/settler comprising antisolvent(s), water, and salt is fed to a separation unit.
  • the overflow has an osmotic pressure of less than 60 bar, more preferably less than 40 bar, and most preferably less than 20 bar.
  • water is removed from the mixture of the aqueous solution comprising the salt and the antisolvent(s), thus resulting in a more concentrated aqueous solution. As a consequence, more of the salt will be forced to crystallize out.
  • the process of osmosis is well-known and may be defined in general terms as the diffusion which proceeds through a semipermeable membrane separating two solutions comprising a solute in unequal concentrations.
  • concentration of the solute in each solution will be equalized.
  • pure water will diffuse from a first aqueous solution having a lower solute concentration through the semipermeable membrane into a second aqueous solution having a higher solute concentration.
  • the second aqueous solution is subjected to an elevated hydraulic pressure relative to the hydraulic pressure existing in the first solution, diffusion of the water through the membrane is restrained.
  • the pressure at which diffusion into the second solution is substantially halted is called the osmotic pressure.
  • reverse osmosis occurs, i.e. water from the second aqueous solution is transported through the membrane into the first aqueous solution.
  • the osmotic pressure of saturated brine relative to water is approximately 300 bar. This means that for reverse osmosis, hydraulic pressures higher than 300 bar are required to crystallize salt. Such high pressures require special equipment. Moreover, high energy costs are involved. However, when an antisolvent is added to the brine, the solubility of the salt will decrease.
  • a solution which essentially consists of water is used as a first solution, whereas for the second solution use is made of the overflow of the crystallizer/settler comprising antisolvent(s), water, and salt.
  • the pressure applied to the second solution preferably is such that water will be transported into the first solution.
  • the pressure at which said reverse osmosis takes place is generally dependent upon the composition of the second solution. Normally, pressures between 1-250 bar, preferably 5-150 bar are required. More preferably, pressures between 8-100 bar are applied, even more preferably pressures between 10-80 bar, and most preferably pressures between 10-50 bar are applied.
  • the first solution preferably is water of high quality which can be used as drinking water and/or process water or, if so desired, may be safely discharged into streams, rivers, lakes, and the like, without additional treatments.
  • the antisolvent-membrane technology according to the invention is suitable for the production of drinking water or process water from aqueous solutions comprising salt, using one or more antisolvents. Especially in regions where water is very scarce, reverse osmosis up to very high concentrations of the second solution is desired.
  • the economic feasibility of this process according to the present invention depends on the pressure required to filter the brine through the reverse osmosis unit. It is noted that the pressure required for the reverse osmosis step can be reduced when the first solution, which comprises water, is combined with an aqueous waste stream comprising alkali and/or alkaline earth salts, such as raw brine or an ion-comprising waste stream of a different process.
  • Feeding part of said second solution to the crystallizer/settler has the advantage that the supersaturation level in the overflow of the crystallizer/settler will decrease, so that the quantity of salt which crystallizes during the reverse osmosis step will be lowered. It is noted that if the antisolvent and/or the aqueous solution comprises one or more crystal growth inhibitors, nucleation will be inhibited, which will also help to reduce the quantity of salt which crystallizes during the reverse osmosis step.
  • the semipermeable membrane to be used in the reverse osmosis step according to the invention can be any conventional semipermeable membrane which has a definite permeability to water, while at the same time it is practically impermeable to the contaminants present in the aqueous solution and the antisolvents used.
  • the semipermeable membrane has a permeability of less than 25% to antisolvent and contaminants, more preferably less than 15%, even more preferably less than 5%, and most preferably less than 0.1%.
  • at least 10 wt% of water, based on the total weight of the aqueous solution comprising the salt is removed. More preferably, at least 50 wt% of water, even more preferably at least 75 wt%, and most preferably at least 99 wt% of water, based on the total weight of the aqueous solution comprising the salt, is removed.
  • hydrophilic antisolvent preferably an antisolvent as defined above which will take up at least 5 wt% of water, more preferably at least 10 wt% of water, and most preferably at least 20 wt% of water, based on the total weight of the antisolvent.
  • the hydrophilic antisolvent preferably does not take up more than 60 wt% of water, more preferably 50 wt% of water, and most preferably 40 wt% of water, based on the total weight of the antisolvent.
  • Such a hydrophilic antisolvent will extract water from the aqueous solution comprising the salt, thus forcing said salt to crystallize.
  • a hydrophilic antisolvent is applied which has a density of less than 1 ,200 kg/m 3 , even more preferably of less than 1 ,150 kg/m 3 , and most preferably of less than 1 ,125 kg/m 3 .
  • a two-phase system will be formed inside the crystal I izer/settler (B), with the overflow of the crystal I izer/- settler (B) being mostly antisolvent comprising water.
  • the salt will dissolve in said antisolvent/water phase.
  • the overflow of the crystallizer/settler is fed to the separation unit (C) wherein the antisolvent(s) are separated from the aqueous solution.
  • the recovered antisolvent(s) is/are recycled to the crystallizer/settler (B), whereas the recovered aqueous solution can be drained off.
  • Preferred hydrophilic antisolvents include but are not limited to choline chloride/phenol ionic liquid and polypropylene glycol. It is furthermore possible to feed said overflow to the reverse osmosis unit as described above. Due to the fact that the osmotic pressure of the antisolvent/water mixture in the overflow relative to water is now lowered, such a reverse osmosis step will be more economic.
  • said reverse osmosis step preferably at least 10 wt% of the total quantity of water dissolved in the antisolvent stream fed to the reverse osmosis unit is removed. More preferably, at least 50 wt% of the total quantity of water, even more preferably at least 75 wt% of the total quantity of water dissolved in the antisolvent stream fed to the reverse osmosis unit is removed. Preferably, to prevent crystallization of the salt present in said antisolvent stream, at most 90 wt% of the total quantity of dissolved water is removed in the reverse osmosis step.
  • any additive suitable for improving the flux of the membrane in the reverse osmosis membrane by preventing the membrane from fouling may be added to the antisolvent(s) and/or the aqueous salt solution.
  • surfactants are added to the antisolvent in order to increase the flux of the membrane.
  • the salt is sodium chloride.
  • (Wet) sodium chloride according to the present invention is preferably used to prepare brine for electrolysis processes and most preferably for the modern membrane electrolysis processes.
  • the sodium chloride produced in the above-described manner can also be used for consumption purposes. It is for instance suitable as table salt.
  • the present invention is elucidated by means of the following non-limiting Examples.
  • Examples Example 1 a raw brine sample from the brine field in Hengelo, The Netherlands, was used as the sodium chloride source.
  • the adsorbents Ambersorb ® 563 (ex Rohm and Haas), Amberlite ® XAD-4 (ex Rohm and Haas), Norit ROX ® (ex Norit) or sodium montmorillonite (ex Southern Clay Products) were applied for the separation of the antisolvents choline chloride (ex Acros), polydimethyldiallyl ammonium chloride (known as Polyquat ® , ex Katpol-Chemie), polyoxyalkylene amine (known as Jeffamine XTJ-500, ex Huntsman), and polyglycol A1100 (ex Clariant) from water.
  • Example 2 Sodium hexanoate, which is miscible with brine under the crystallizing conditions, was recovered by means of a pH change induced phase split.
  • carbonic acid i.e. carbon dioxide under pressure
  • 300 ml of an aqueous solution containing 130 g/l of sodium hexanoate, 30 g/l of sodium chloride, and 20 ppm of polymaleic acid (added as a 50wt% aqueous solution, i.e. Drewsperse ® 747A, ex Ashland) were introduced into a pressure vessel in which they were contacted with CO 2 at pressures between 5 and 35 bar.
  • a two-phase system comprising a hexanoic acid-rich top layer and a water-rich bottom layer. These two liquid phases were separated from each other by decanting the antisolvent-rich phase.
  • the hexanoic acid-rich layer By contacting the hexanoic acid-rich layer with a saturated solution of sodium hydrogen carbonate, the conversion of hexanoic acid back into the original sodium hexanoate was achieved.
  • the precipitated sodium chloride was filtered off, washed with 500 ml of PEG, and dried.
  • the quantity of occluded water was measured by heating the samples up to 700 0 C and subsequently performing conventional gravimetric measurements.
  • bromide and chloride quantities were determined by ion chromatography and titration, respectively.
  • the Br and Cl quantities in the mother liquors were also measured. These were the blank experiments.

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Abstract

Cette invention concerne un procédé qui consiste à utiliser un antisolvant, lequel procédé comprend les étapes consistant (a) à ajouter de l'eau à une source saline afin de former une solution aqueuse qui contient ledit sel, si la source saline ne se présente pas déjà sous forme de solution saline aqueuse, (b) à verser cette solution aqueuse dans un cristalliseur/décanteur, (c) à mettre en contact ladite solution aqueuse avec un ou plusieurs antisolvants entraînant ainsi la cristallisation au moins partielle du sel; un ou plusieurs inhibiteurs de croissance cristalline étant contenus dans les antisolvants et/ou dans la solution aqueuse, et/ou un ou plusieurs inhibiteurs de l'écaillage étant contenus dans les antisolvants et/ou dans la solution aqueuse, (d) à soumettre un trop-plein du cristalliseur/décanteur comprenant un ou plusieurs antisolvants et une solution saline aqueuse, à une étape de séparation au cours de laquelle un ou plusieurs antisolvants sont séparés de la solution saline aqueuse selon une ou plusieurs techniques choisies dans le groupe comprenant l'adsorption, l'échange ionique, la séparation de phase induite par un changement de température, la séparation de phase induite par un changement de pH, la séparation de phase induite par la complexation, la séparation de phase induite par la pression, l'évaporation et l'extraction, éventuellement conjointement avec une étape de nanofiltration, (e) à retirer le sel cristallisé du cristalliseur/décanteur dans une boue aqueuse, (f) éventuellement, à recycler le ou les antisolvants dans le cristalliseur/décanteur, et (g) éventuellement, à recycler la solution mère provenant de la boue dans une première étape de dissolution et/ou dans le cristalliseur/décanteur. De préférence, le procédé est un processus en boucle fermé et le sel est du chlorure de sodium. De préférence, le procédé décrit dans cette invention comprend une étape d'osmose inverse avant que le trop-plein du cristalliseur/décanteur ne soit soumis à l'étape de séparation.
PCT/EP2005/055527 2004-10-29 2005-10-25 Procedes consistant a utiliser la cristallisation par effet antisolvant Ceased WO2006045795A2 (fr)

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WO2009015286A3 (fr) * 2007-07-24 2009-06-25 Nexbio Inc Technologie pour la préparation de microparticules
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US20130165694A1 (en) * 2009-12-21 2013-06-27 E I Du Pont De Nemours And Company Process for the synthesis of choline salts
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US10881123B2 (en) 2017-10-27 2021-01-05 Frito-Lay North America, Inc. Crystal morphology for sodium reduction
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NL2000640C2 (nl) * 2007-03-05 2008-09-08 Stichting Wetsus Ct Of Excelle Werkwijze en systeem voor het zuiveren van een vloeistof.
WO2008108636A1 (fr) * 2007-03-05 2008-09-12 Stichting Wetsus Centre Of Excellence For Sustainable Water Technology Procédé et système pour purifier un liquide comprenant la récupération d'un inhibiteur de croissance cristalline
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US20130165694A1 (en) * 2009-12-21 2013-06-27 E I Du Pont De Nemours And Company Process for the synthesis of choline salts
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