A method and apparatus for purifying a Bayer process stream

Abstract

An apparatus and method for purifying a Bayer process stream includes a filtration stage comprising at least one filter configured to filter particulate matter from at least one ionic liquid stream from an extraction stage, a stripping stage, and a regeneration stage. Filtering particulate matter from the at least one ionic liquid stream reduces the amount of circulating particulate matter and reduces the likelihood of scale formation.

Description

Field of the Invention

[0001] The present invention generally relates to a method and apparatus for purifying a Bayer process stream.

[0002] In particular, although not exclusively, the present invention relates to a method and apparatus for purifying a Bayer process stream by using ionic liquids to remove impurities. Background of the Invention

[0004] The Bayer process is used to produce alumina from bauxite ore.

[0005] Bauxite ore typically contains organic and inorganic impurities, the contents of which are specific to the source of the bauxite.

[0006] Part of the process involves purifying the aluminate liquor to remove dissolved and undissolved impurities to form a purified filtrate. Alumina is then precipitated from the filtrate as alumina trihydrate crystals.

[0007] The purification step is important because alumina trihydrate containing high levels of organic impurities tends to produce a final product with undesirably high levels of color.

[0008] The remaining liquid phase, or spent liquor, may be concentrated to form "thick" liquor. The spent liquor stream is typically returned to the initial digestion step and, after reconstitution with additional caustic, used as a digester for additional ore.

[0009] Because the Bayer process is a closed loop, impurities that enter the process stream tend to accumulate with each cycle of the process. These impurities can have a negative impact on the process.

[0010] Ionic liquids can be used to remove impurities from the Bayer process, but such liquids are often expensive and toxic.

[0011] It would therefore be desirable to provide a method and apparatus for purifying Bayer process streams that would allow for the recycling of these ionic liquids.

[0012] The above description should not be taken as an admission of the common general knowledge in Australia or elsewhere. SUMMARY OF THE INVENTION

[0014] The present invention is a method and apparatus for purifying a Bayer process stream, which uses an ionic liquid as an extractant for impurities in a liquid / liquid extraction method and apparatus to remove impurities from the Bayer process stream.

[0015] In one embodiment, the Bayer process stream is a liquid stream produced during the Bayer process and can be one or more of a concentrator overflow, mother liquor, spent liquor, and a concentrate stream.

[0016] The term "impurities" is understood to mean compounds that may contaminate the Bayer process stream. Impurities include, but are not limited to, organic and / or inorganic substances. One class of impurities of particular interest is non-oxalate organic compounds (NOOCs), which are commonly and empirically represented as Na2C5O. However, it will be appreciated that customized selection of ionic liquids will allow for the removal of other classes of impurities from the Bayer process stream.

[0017] More specifically, the present invention is a method and apparatus for purifying a Bayer process stream using an ionic liquid that can reversibly associate with impurities from the Bayer process stream. The method / apparatus controls operating parameters such that the impurities can associate with the ionic liquid to remove the impurities from the Bayer process stream, and such that the impurities can dissociate from the ionic liquid to remove the impurities from the ionic liquid and regenerate the ionic liquid for recycling in the method / apparatus.

[0018] The present invention was developed following work by the applicant using ionic liquids in a small-scale pilot plant (referred to herein as a benchtop pilot or BTP) for the process / apparatus. The BTP work was conducted following successful small-scale laboratory trials of the process / apparatus.

[0019] During his work at BTP, the applicant encountered many problems that did not exist in small-scale laboratory experiments.

[0020] One such problem is the effect of particulate matter circulating in the ionic liquid recycle loop.

[0021] More specifically, applicants have discovered that when a threshold concentration of particulate matter in the loop is reached, an emulsion stabilized by the particulate matter forms between the ionic liquid and the aqueous solution, which renders the recirculation loop inoperable.

[0022] This is a surprising discovery as it was not previously known that particulate matter, particularly but not limited to particulate matter derived from Bayer liquor, would behave in such a deleterious manner when the method / apparatus was scaled up to operate as a substantially industrial process.

[0023] In order to find a solution to this problem, the applicant conducted a series of experiments to determine the properties of the particulate matter.

[0024] In one experiment, the particulate matter was separated and analyzed using XRD, and it was determined that the particulate matter consisted of:

[0025] ·Al(OH)3 (gibbsite)-main component

[0026] CaCO3-component

[0027] ·Al(OH)3(bayerite)-trace

[0028] ·Na3H(CO3)2.2H2O (natural alkali) - trace

[0029] ·Na2C2O4 (sodium oxalate) - trace

[0030] ·Ca3Al2(SiO4)(OH)-trace

[0031] Various other minor components.

[0032] Compositional analysis indicated that the particulate matter originated from Bayer liquor. However, it will be appreciated that the particulate matter is not limited to this source and may also originate from other sources, such as NaCl brine impurities, or may be externally derived particulate matter.

[0033] It was also determined that the particulate matter did not dissolve in any aqueous stream in the process / apparatus and remained locked in the ionic liquid.

[0034] Without wishing to be bound by theory, it is believed that the particulate matter stabilizes the emulsions formed between the ionic liquid used in the recycling process and any aqueous stream used. These stable emulsions are described herein as "cruds." It is also believed that the various ions present in the purified process water stream combine to form a precipitate, which, along with any captured foreign particles (such as dust), is described herein as particulate matter and is carried around the circuit in the ionic liquid.

[0035] Other analysis reveals that scale forms at the ionic liquid (organic) phase / aqueous phase interface and subsequently coalesces at this interface, separating the aqueous phase and the ionic liquid phase. The resulting coalesced layer of scale between the ionic liquid phase and the aqueous phase may hinder further separation of the freshly entered mixed phase from the mixer, resulting in loss of efficiency and loss of ionic liquid to the water flow leaving the settler. This makes the separation of the organic ionic liquid phase and the aqueous phase difficult. The scale in the organic phase also accumulates and concentrates in the process. This affects the efficiency of the liquid / liquid extraction that occurs at each stage. It should be noted that the settler can be completely filled with scale so that no additional process stream can be pumped into the settler, making the entire recirculation loop inoperable.

[0036] During the troubleshooting process, it was observed that the settler for the BTP became clogged with fouling after a period equivalent to approximately 35 hours to 40 hours of plant operation time.

[0037] It has also been found that scale can form independently in each of the aqueous and organic phases, and that scale formation can occur at all stages of the process.

[0038] It was observed that scale formation was more pronounced in the EXTRACT stage when the ionic liquid feed stream to this stage interacted with the Bayer process stream.

[0039] In some BTP operations, it was also observed that once the NaCl impurity-derived precipitate reached a threshold concentration, the focus of fouling formation shifted to the regeneration stage where it increased to such an extent that the entire settler became inoperable.

[0040] Applicant tested the following methods which Applicant believed would be successful in removing the scale from the circuit, but with no or limited success.

[0041] 1. Mixing or settling out the ionic liquid, heating the ionic liquid, dissolving it in water, and salting out the ionic liquid solution. This approach was unsuccessful. The salting-out process investigated by the applicant involves adding a salt solution, such as sodium hydroxide, to the ionic liquid solution and allowing the ionic liquid to separate from the salt solution, which allows for the recovery of the ionic liquid.

[0042] 2. Due to the rapid accumulation of scale, temporary removal of scale is not a viable solution.

[0043] 3. Filter the ionic liquid stream from one or more of the extraction stage, the STRIP stage, and the regeneration stage to determine if controlling the concentration of particulate matter in the regenerated ionic liquid affects scale formation. Initial filtration options tested by applicants were unsuccessful.

[0044] Ultimately, further testing work on filtration led to the development of the present invention.

[0045] As a result of further test work, the present invention provides an apparatus for purifying a Bayer process stream comprising:

[0046] an extraction stage comprising at least one contacting / separating device configured to receive and mix an impure Bayer process stream and an ionic liquid stream comprising a quaternary organic cation to form a purified Bayer process stream and an impurity-laden ionic liquid stream;

[0047] a stripping stage comprising at least one contacting / separating device configured to receive and mix the impurity-laden ionic liquid stream and the halide-containing salt stream to form a halide-containing ionic liquid stream and an impurity-laden salt stream;

[0048] a regeneration stage comprising at least one contacting / separating device configured to receive and mix the halide-containing ionic liquid stream and the caustic stream to form a regenerated ionic liquid stream and a halide-containing caustic effluent stream, wherein the extraction stage is configured to be in fluid communication with the regeneration stage via a recirculation loop to receive at least a portion of the regenerated ionic liquid stream to form the ionic liquid feed stream, and

[0049] A filter stage includes at least one filter configured to filter particulate matter from at least one ionic liquid stream from the extraction stage, the stripping stage, and the regeneration stage.

[0050] Filtering particulate matter from the at least one ionic liquid stream reduces the amount of circulating particulate matter and reduces the potential for scale formation.

[0051] The present invention also provides an apparatus for recycling an ionic liquid used to purify a Bayer process stream, comprising:

[0052] a stripping stage comprising at least one contacting / separating device configured to receive and mix the impurity-laden ionic liquid stream and the stripping solution stream to form an impurity-reduced ionic liquid stream and an impurity-laden stripping solution stream;

[0053] a regeneration stage comprising at least one contacting / separating device configured to receive and mix the impurity-reduced ionic liquid stream and the caustic solution stream to form a regenerated ionic liquid stream and a caustic effluent stream; wherein the at least one contacting / separating device from the regeneration stage is configured to recycle at least a portion of the regenerated ionic liquid stream and form the ionic liquid feed stream to purify the Bayer process stream, and

[0054] A filtration stage includes at least one filter configured to filter particulate matter from at least one ionic liquid stream from the extraction stage, the stripping stage, and the regeneration stage.

[0055] The term "particulate matter" is understood herein to mean any particulate matter in one of the ionic liquid streams. "Particulate matter" can be particulate matter in a Bayer process stream. "Particulate matter" can be any solid that interacts with ionic species in the circuit and forms material, such as "fouling," that interferes with the purification or recirculation circuit.

[0056] The term "filter" is understood herein as any suitable device for separating particulate material from an ionic liquid feed stream.

[0057] The contact / separation devices used in the extraction stage, stripping stage, and regeneration stage can be selected from mixer-settlers, columns, centrifuges, static mixers, reactors, or other devices suitable for mixing and separating two at least partially immiscible liquid streams. A preferred contact / separation device is a mixer-settler, such as is typically used in solvent extraction circuits.

[0058] The ionic liquid may be any suitable ionic liquid.

[0059] By way of example, an ionic liquid may include an alkylphosphonium salt in three forms, depending on the molecule to which the phosphonium ion is bonded. These forms are: - ), regenerated (OH - ) and loaded (NOOC - ). Transitions between these forms enable ionic liquids to reversibly associate with impurities.

[0060] At least one of the ionic liquid-containing operating units for the extraction stage, stripping stage, and regeneration stage may include a filter for the filtration stage to remove particulate matter, particularly colloidal solids, from the ionic liquid stream to control the concentration of particulate matter in the regenerated ionic liquid.

[0061] In other words, the filtration stage can be part of the extraction stage, the stripping stage and the regeneration stage.By way of example, the filtration stage can be part of a storage tank, a fluid conduit or a contact / separation device of the extraction stage, the stripping stage and the regeneration stage.

[0062] The filtration stage may also be an operating unit separate from the operating units forming the extraction stage, the stripping stage and the regeneration stage.

[0063] The filtration stage may be located after the stripping stage. In one embodiment, the filtration in the filtration stage is performed on the ionic liquid stream after the stripping stage.

[0064] It should be emphasized that the present invention is not limited to this embodiment.

[0065] As is apparent from the above, the ionic liquid stream diverted to the filtration stage is typically an ionic liquid containing particulate matter that may form scale.

[0066] The solids concentration, ie, the concentration of particulate matter, in the ionic liquid stream transferred to the filtration stage can be as high as 0.3 g / L solids.

[0067] Applicants have tested solids concentrations up to 5.5 g / L and the results of this testing have provided a basis for concluding that higher solids concentrations are possible.

[0068] Solids concentrations can be as high as 6 g / L.

[0069] Solids concentrations can be as high as 10 g / L.

[0070] Typically, the solids concentration in the ionic liquid stream transferred to the filtration stage is less than 3 g / L of the ionic liquid stream.

[0071] The ionic liquid stream may comprise a stable emulsion comprising an aqueous phase and an ionic liquid phase.

[0072] The aqueous phase may be up to 50 vol.% of the stable emulsion. More suitably, the aqueous phase of the stable emulsion is <10 vol.%.

[0073] Typically, filtration in the filtration stage breaks up the stable emulsion into an aqueous phase and an ionic liquid phase.

[0074] The filtration stage may be performed using any suitable filter capable of separating solid material, ie particulate matter, from the ionic liquid stream transferred to the filtration stage.

[0075] The filter may be configured to use differential pressure as the driving force for filtration.

[0076] The filter may be a positive pressure filter.

[0077] The filter may be a candle filter.

[0078] The filtration stage may include candle filters with perlite filter aid.

[0079] Any suitable filter media may be used in the filter.

[0080] Suitably, the filter medium is compatible with the ionic liquid.

[0081] Based on short term test work the applicant has found that polypropylene (PP) and polytetrafluoroethylene (PTFE) are suitable.

[0082] The filter media may have a multifilament construction or a monofilament construction.

[0083] The filter medium can have a 2 / min-200L / dm 2 The air permeability is between 100 and 150 nm.

[0084] The filtration stage may include the use of filter aids such as ceramic materials, tricalcium aluminate hexahydrate (TCA), and flocculants.

[0085] Filter aids can be selected for higher throughput and life of the filter media.

[0086] The filter aid material may be any suitable chemically resistant material that does not react with the ionic liquid.

[0087] The filter aid material may be expanded perlite.

[0088] The filter aid material may have a median particle size between 10 μm and 100 μm. Suitably, the filter aid has a median particle size between 50 μm and 85 μm. More suitably, a filter aid having a median particle size of 68 μm is used for filtration.

[0089] Filter aids may be introduced into the ionic liquid stream being transferred to the filtration stage by adding them directly to the ionic liquid stream.

[0090] More suitably, the filter aid is pre-batched with an aqueous solution at a temperature between 20°C and 80°C before being added to the ionic liquid stream. Most suitably, the filter aid is pre-batched with an aqueous solution at a temperature of 55°C.

[0091] The pre-batch filter aid solution may be prepared to a solids concentration between 10 g / L and 200 g / L. More preferably, the solids concentration is between 40 g / L and 100 g / L. More preferably, the solids concentration is 60 g / L.

[0092] The filter aid may be added to the ionic liquid stream transferred to the filtration stage at a solids ratio (solids in the feed stable emulsion: filter aid solids) between 1:0.1 and 1:5. More suitably, the addition ratio is between 1:1 and 1:2.

[0093] The filtration stage may be configured to operate in a temperature range of 20°C - 70°C. Most suitably, the filtration stage operates in a temperature range of 55°C - 60°C.

[0094] When operating with a pressure filter, the filter stage can operate within a pressure differential range of between 2 bar and 8 bar. More suitably, the pressure is between 4 bar and 6 bar. Most suitably, the operating pressure is 6 bar.

[0095] The filter stage can be configured to filter at 10L / m 2 / h-700L / m 2 More preferably, the filtration process is operated at a filtration flux rate of 50 L / m 2 / h-200L / m 2 / h. Optimally, the filtration process is operated at a flux rate of 100 L / m 2 / h-150L / m 2 Operates at flux rates between / h.

[0096] The filtration stage may include a cleaning process to remove filter aids and ionic liquid entrapped within the solid filter cake.

[0097] The cleaning process may include a filter cake washing step, typically wherein the recovered ionic liquid is returned to the process.

[0098] The washed and cleaned cake can then be discharged as a slurry or as a dry cake for disposal.

[0099] The filter may be a filter having a pore size ranging from 5 μm to 100 μm. Suitably, a filter having a pore size ranging from 10 μm to 100 μm is used for the filtration step. More suitably, a filter having a pore size of 10 μm to 30 μm is used for filtration. The filter may be any device capable of performing solid-liquid separation, such as a Buchner funnel or a centrifuge.

[0100] Filtration can be facilitated using a positive pressure filtration system, a vacuum filtration system, or a centrifuge.

[0101] The apparatus may include a controller to control parameters of the caustic stream, such as flow rate and concentration, to account for dilution of the halide-containing ionic liquid.

[0102] The apparatus may comprise at least three mixer-settlers. Suitably, the apparatus comprises ten mixer-settlers.

[0103] In the extraction stage, at least one mixer-settler may be configured to receive and mix the impure Bayer process stream and the ionic liquid feed stream to form a purified Bayer process stream and an impurity-laden ionic liquid stream, respectively. Suitably, the extraction stage comprises three mixer-settlers arranged in series.

[0104] In the stripping stage, at least one mixer-settler may be configured to receive and mix the impurity-laden ionic liquid stream with the halide-containing salt stream to form a halide-containing ionic liquid stream and an impurity-laden salt stream, respectively. Suitably, the stripping stage comprises three mixer-settlers arranged in series.

[0105] In the regeneration stage, at least one mixer-settler may be configured to receive and mix the halide-containing ionic liquid stream and the caustic stream to form a regenerated ionic liquid stream and a halide-containing caustic effluent stream, respectively. Suitably, the regeneration stage comprises four mixer-settlers arranged in series.

[0106] The first mixer-settler in the extraction stage can be configured to be in fluid communication with the end mixer-settler in the regeneration stage via a recirculation loop to receive at least a portion of the regenerated ionic liquid stream to form the ionic liquid feed stream.

[0107] In one embodiment, in use, in the mixer-settler of the extraction stage, hydroxide ions in the ionic liquid feed stream are replaced by NOOC ions in the impure Bayer process stream to form a purified Bayer process stream and an impurity-laden ionic liquid stream (NOOC-form). The impurity-laden ionic liquid stream exiting the mixer-settler of the third extraction stage then flows into the first mixer-settler of the stripping stage.

[0108] In one embodiment, in use, within the mixer-settler of the stripping stage, NOOC ions are transferred from the impurity-laden ionic liquid stream to the halide-containing salt stream. The NOOC ions in the impurity-laden ionic liquid stream are replaced by chloride ions from the halide-containing salt stream to form a halide-containing ionic liquid stream (Cl- form) and an impurity-laden salt stream. Mass transfer is driven by the high concentration of chloride ions in the aqueous phase.

[0109] The stripped ionic liquid exiting the mixer-settler of the third stripping stage then flows into the first mixer-settler of the regeneration stage.

[0110] In one embodiment, in use, within the mixer-settler of the regeneration stage, the stripped ionic liquid is converted to regenerated ionic liquid (OH-form) upon contact with the caustic stream to form a regenerated ionic liquid stream and a halide-containing caustic effluent stream. The regenerated ionic liquid stream exiting the mixer-settler of the fourth regeneration stage is then recycled to the first mixer-settler of the extraction stage. The halide-containing caustic effluent stream is pumped to the salt separation unit.

[0111] The equipment can be installed after the alumina trihydrate precipitation stage to treat spent Bayer liquor.

[0112] The filtration stage may be configured such that the concentration of particulate matter in the regenerated ionic liquid stream is below a predetermined threshold concentration before the regenerated ionic liquid is returned to the extraction stage as at least a portion of the ionic liquid feed stream.

[0113] The predetermined threshold concentration may be any suitable concentration taking into account any one or more of the following factors: the Bayer process liquor being processed, the particular ionic liquid, and the processing conditions.

[0114] Suitably, the filtrate solids are less than 3 g / L of particulate matter. More suitably, the filtrate solids are less than 0.5 g / L of particulate matter. Most suitably, the filtrate solids are less than 0.1 g / L of particulate matter.

[0115] The filter stage can provide multiple stages of filtration.

[0116] The present invention also provides a method for purifying a Bayer process stream, comprising:

[0117] providing an ionic liquid feed stream comprising a quaternary organic cation, wherein the ionic liquid feed stream is at least partially immiscible with the Bayer process stream;

[0118] mixing a Bayer process stream with an ionic liquid feed stream and forming an aqueous phase comprising purified Bayer process liquor and an organic phase comprising the impurity-laden ionic liquid, wherein the mixing reduces the concentration of the impurities in the Bayer process liquor;

[0119] at least partially separating the aqueous phase from the organic phase and forming a purified Bayer process stream and an impurity-laden ionic liquid stream;

[0120] mixing the impurity-laden ionic liquid stream and the halide-containing salt stream to form an aqueous phase comprising the impurity-laden salt and an organic phase comprising the halide-containing ionic liquid, wherein the mixing reduces the concentration of the impurity in the impurity-laden ionic liquid stream;

[0121] at least partially separating the aqueous phase from the organic phase and forming a halide-containing ionic liquid stream and an impurity-laden salt stream;

[0122] mixing a halide-containing ionic liquid stream and a caustic solution and forming an aqueous phase comprising the halide-containing caustic solution and an organic phase comprising regenerated ionic liquid, wherein the mixing replaces at least some of the halide groups in the halide-containing ionic liquid with hydroxyl groups from the caustic solution;

[0123] at least partially separating the aqueous phase from the organic phase and forming a halide-containing salt stream and a regenerated ionic liquid stream;

[0124] filtering at least one of the ionic liquid streams from the extraction stage, the stripping stage, and the regeneration stage and removing particulate matter; and

[0125] At least a portion of the regenerated ionic liquid stream is recycled and forms at least a portion of the ionic liquid feed stream.

[0126] The present invention also provides a method for recycling an ionic liquid used to purify a Bayer process stream, comprising:

[0127] combining the impurity-laden ionic liquid stream with the stripping solution stream and forming an aqueous phase comprising the impurity-laden stripping solution and an organic phase comprising the impurity-reduced ionic liquid;

[0128] at least partially separating the aqueous phase from the organic phase and forming an impurity-reduced ionic liquid stream and an impurity-laden stripping solution stream;

[0129] combining the impurity-reduced ionic liquid stream and the caustic solution stream and forming an aqueous phase comprising spent caustic solution and an organic phase comprising regenerated ionic liquid;

[0130] filtering at least one of the ionic liquid streams from the extraction stage, the stripping stage, and the regeneration stage and removing particulate matter; and

[0131] At least a portion of the regenerated ionic liquid stream is recycled to form the ionic liquid feed stream.

[0132] The filtering step may include removing particulate matter such that the concentration of particulate matter in the regenerated ionic liquid stream is below a predetermined threshold concentration.

[0133] In one embodiment, the ionic liquid comprises an alkylphosphonium salt that exists in three forms, depending on the molecule to which the phosphonium ion is bonded. These forms are: stripped (Cl-), regenerated (OH-), and supported (NOOC-). Transitions between these forms enable the ionic liquid to reversibly associate with impurities.

[0134] The method can include providing an ionic liquid feed stream that is at least partially immiscible with the Bayer process stream.The ionic liquid feed stream can include an ionic liquid comprising a quaternary organic cation.

[0135] Australian Patent 2010337293 in the name of Cytec Technology Corp. discloses ionic liquids comprising quaternary organic cations and methods and compositions for removing impurities from impurity-laden ionic liquids.

[0136] Reference to Cytec's Australian patent herein is not an admission that the disclosure in the patent is part of the common general knowledge in Australia or elsewhere.

[0137] The following description of quaternary organic cations is closely based on the description in the Cytec Australia patent.

[0138] As reported in the Cytec Australia patent, the quaternary organic cation may be selected from the group consisting of phosphonium, ammonium, sulfonium, pyridinium, pyridazinium, pyrimidinium, pyrazinium, pyrazolium, imidazolium, thiazolium, oxazolium, pyrrolidinium, quinolinium, isoquinolinium, guanidinium, piperidinium and methylmorpholinium.

[0139] Suitably, the quaternary organic cation is selected from the group consisting of:

[0140]

[0141]

[0142] where R a 、R b 、R c 、R d 、R e 、R f can be independently selected from hydrogen or substituted C1-C 50 An alkyl group wherein the substituents include one or more selected from the group consisting of alkyl, cycloalkyl, alkenyl, cycloalkynyl, alkynyl, alkoxy, alkoxyalkyl, aldehyde, ester, ether, ketone, carboxylic acid, alcohol, carboxylate, hydroxy, nitro, silyl, aryl, and halide functional groups.

[0143] R a to Rf may individually contain from about 1 to about 50 carbon atoms. It is understood that R a to R f Two or more of them can form a ring structure.

[0144] R1 to R7 can be independently selected from hydrogen, halogen or substituted C1-C 50 Alkyl groups wherein the substituents include one or more selected from the group consisting of alkyl, cycloalkyl, alkenyl, cycloalkynyl, alkynyl, alkoxy, alkoxyalkyl, aldehyde, ester, ether, ketone, carboxylic acid, alcohol, carboxylate, hydroxyl, nitro, silyl, aryl, and halogen functional groups. R1 to R7 may individually contain from about 1 to about 50 carbon atoms. It will be appreciated that two or more of R1 to R7 may form a ring structure.

[0145] Examples of quaternary organic cations include, but are not limited to, tributyloctylphosphonium, tetrabutyl(methyl)phosphonium, tributyl-8-hydroxyoctylphosphonium, tetrabutylphosphonium, tetrapentylphosphonium, tetrahexylphosphonium, tetraoctylphosphonium, octyl(tributyl)phosphonium, tetradecyl(tributyl)phosphonium, tetradecyl(trihexyl)phosphonium, tributyl(methyl)ammonium, tetrabutylammonium, tetrapentylammonium, tetrahexylammonium, tetraoctylammonium, tetradecyl(tributyl)ammonium, tetradecyl(trihexyl)phosphonium Onium, dimethylamino, 1-octyl-2,3-dimethylimidazolium, 1-butyl-3-methylimidazolium, sulfonium and guanidinium. The term "coco" refers to an alkyl group derived from the mixture of fatty acids found in cocoa butter, which are typically saturated fats having about 12 carbon atoms.

[0146] A preferred quaternary organic cation is tributyloctylphosphonium.

[0147] The quaternary organic cation is typically associated with an anionic counterion or anions. The anions may be chaotropic or kosmotropic.

[0148] Examples of suitable anions include, but are not limited to, halides (e.g., fluoride, chloride, bromide, iodide), hydroxide, alkyl sulfates (e.g., methyl sulfate, ethyl sulfate, octyl sulfate), dialkyl phosphates, sulfate, nitrate, phosphate, sulfite, phosphite, nitrite, hypochlorite, chlorite, chlorate, perchlorate, carbonate, bicarbonate, carboxylates (e.g., formate, acetate, propionate, butyrate, hexanoate, fumarate, maleate, lactate, oxalate, pyruvate), bis(trifluoromethyl)sulfonyl imide ([NTF2]), tetrafluoroborate, hexafluorophosphate, CN - 、SCN - and OCN.

[0149] Halides and halogen-containing compounds may include, but are not limited to: F - 、Cl - Br - , I - 、BF4 - 、ClO3 - 、ClO4 - BrO3 - BrO4 - IO3 - 、IO4-、PF6 - 、AlCl4 - 、Al2Cl - 、Al3Cl 10 - 、AlBr4 - 、FeCl4 - 、BCl4 - 、SbF6 - 、AsF6 - 、ZnCl3 - 、SnCl3 - 、CuCl2 - CF3SO3 - 、(CF3SO3)2N - CF3CO2 - and CCl3CO2 - .

[0150] A preferred class of anions are halides. A preferred anion is chloride.

[0151] Ionic liquids can include any pairing of any quaternary organic cation and anion.

[0152] The ionic liquid may be selected from the group consisting of tributyloctylphosphonium chloride, trihexyltetradecylphosphonium chloride, tetrabutylphosphonium chloride, tetradecyl(tributyl)phosphonium chloride, tributyl(8-hydroxyoctyl)phosphonium chloride, and octyl(tributyl)phosphonium chloride.

[0153] The ionic liquid may be selected from the group consisting of tetrabutylammonium hydroxide, tetrabutylammonium chloride, stearamidopropyl dimethyl-2-hydroxyethylammonium nitrate, ethyltetradecyldiundecylammonium chloride, tetrahexyl ammonium bromide, dodecyltrimethylammonium chloride, benzyldimethylcocoyl ammonium chloride, N,N-dimethyl-N-dodecylglycine betaine, Adogen HTA-1 and tallow alkyl trimethyl ammonium chloride.

[0154] Ionic liquids can be phosphonium salts that exist in three forms, depending on the molecule to which the phosphonium ion is bonded: stripped (Cl-), regenerated (OH-), and supported (NOOC-).

[0155] The ionic liquid may be tributyloctylphosphonium salt, which exists in three forms: stripped (Cl-), regenerated (OH-), and supported (NOOC-).

[0156] The ionic liquid feed stream may include a diluent. The diluent may be an alcohol (e.g., isopropyl alcohol), a polyol, and / or polyethylene oxide. Such a diluent may facilitate phase separation.

[0157] The ionic liquid feed stream may comprise at least 1 wt.% ionic liquid. Suitably, the ionic liquid feed stream comprises at least about 10% by weight ionic liquid. More suitably, the ionic liquid feed stream comprises at least about 50% by weight ionic liquid. Even more suitably, the ionic liquid feed stream comprises about 70% by weight ionic liquid.

[0158] The process involves mixing an ionic liquid feed stream with a Bayer process stream.

[0159] Although the ionic liquid stream and the Bayer process stream may be mutually soluble to some extent, typically the two phases are at least partially immiscible with each other to form a liquid / liquid mixture in the extraction stage.

[0160] The ionic liquid entering the extraction stage may be in its regenerated form. Suitably, the ionic liquid entering the extraction stage is tributyloctylphosphonium hydroxide.

[0161] In the extraction stage, the external O / A ratio may be in the range of 0.5 to 2. Suitably, the external O / A ratio is in the range of from 0.67 to 1. Most suitably, the external O / A ratio is in the range of from 0.75 to 0.85.

[0162] The external O / A ratio defines the O / A ratio for each stage. This is in contrast to the internal O / A ratio, which defines the O / A ratio for each mixer-settler within each stage.

[0163] During mixing, impurities, such as NOOC, are extracted from the spent liquor and transferred to the ionic liquid. This reduces the concentration of impurities in the Bayer process stream and forms an aqueous phase containing purified Bayer process liquor and an organic phase containing the impurity-laden ionic liquid.

[0164] The aqueous and organic phases are then at least partially separated to form a purified Bayer process stream and an impurity-laden ionic liquid stream.

[0165] The purified Bayer process stream from the extraction stage is sent for further processing, such as to a refinery, while the impurity-laden ionic liquid stream is directed to the stripping stage.

[0166] The ionic liquid entering the stripping stage may be in its supported form. Suitably, the ionic liquid entering the extraction stage is NOOC-associated tributyloctylphosphonium salt.

[0167] In the stripping stage, the external O / A ratio may be in the range of 0.5 to 3. Suitably, the external O / A ratio is in the range of from 0.67 to 2.5. Most suitably, the external O / A ratio is 1.89.

[0168] The internal O / A ratio may be in the range from 0.5 to 2. Suitably, the internal O / A ratio is in the range from 0.8 to 1.2.

[0169] In the stripping stage, the impurity-laden ionic liquid stream is mixed with a stripping solution. Suitably, the stripping solution is a halide-containing salt stream. More suitably, the halide-containing salt stream is a brine solution (sodium chloride).

[0170] During mixing, ion exchange occurs between the ionic liquid and the halide-containing salt, wherein anionic impurities from the ionic liquid are exchanged for halide groups from the salt to reduce the concentration of impurities in the impurity-laden ionic liquid stream. This forms a mixture comprising an aqueous phase containing the impurity-laden salt and an organic phase containing the halide-containing ionic liquid.

[0171] The aqueous and organic phases are then at least partially separated to form an impurity-laden salt stream and a halide-containing ionic liquid stream.

[0172] Prior to discharge to the environment, the impurity-laden salt stream is processed to remove residual ionic liquid. Due to the nature of the mixing / sedimentation process, a certain level of ionic liquid carryover is expected in the impurity-laden salt stream, typically in the range of 300-400 ppm. Therefore, the impurity-laden salt stream passes through a coalescer designed to aggregate and collect residual ionic liquid for recycling back into the loop.

[0173] The impurity-laden salt stream may also be passed through at least one activated carbon column to further reduce the final ionic liquid concentration before being discharged to the environment.At least a portion of the salt from the stream may be recycled back to the stripping stage.

[0174] The final ionic liquid concentration in the salt stream can be <1 ppm.

[0175] The halide-containing ionic liquid stream is directed to the regeneration stage.

[0176] The ionic liquid entering the regeneration stage may be in its stripped form. Suitably, the ionic liquid entering the regeneration stage is tributyloctylphosphonium chloride.

[0177] In this stage, the external O / A ratio may be in the range of 0.5 to 2. Suitably, the external O / A ratio is in the range of from 0.67 to 1.5. Most suitably, the external O / A ratio is 1.13.

[0178] The internal O / A ratio may be in the range from 0.5 to 2. Suitably, the internal O / A ratio is in the range from 0.8 to 1.2.

[0179] In the regeneration stage, a halide-containing ionic liquid stream is mixed with a caustic stream.

[0180] The caustic concentration may be less than 50 wt%. Suitably, the caustic concentration is less than 30 wt%. More suitably, the caustic concentration is less than 20 wt%. Most suitably, the caustic concentration is 10 wt%.

[0181] The caustic stream may comprise sodium hydroxide.

[0182] During mixing, halide groups from the halide-containing ionic liquid are replaced by hydroxyl groups from the caustic stream. This forms a liquid / liquid mixture comprising an aqueous phase containing the regenerated ionic liquid and the halide-containing caustic solution.

[0183] The aqueous and organic phases are then at least partially separated to form a regenerated ionic liquid stream and a halide-containing caustic stream.

[0184] The halide-containing caustic stream is processed for discharge to the environment.

[0185] At least a portion of the regenerated ionic liquid stream will be recycled to the extraction stage to form the ionic liquid feed stream.

[0186] The ionic liquid inventory gradually degrades or is lost in the circuit, particularly in the extraction and regeneration stages where high concentrations of caustic are present. To maintain the concentration of ionic liquid in the circuit, fresh ionic liquid may be added to the process, preferably in the regeneration stage. Suitably, the fresh ionic liquid is in its stripped form. More suitably, the fresh ionic liquid is tributyloctylphosphonium chloride.

[0187] Suitably, either or both the entering and exiting regenerated organic ionic liquid are filtered.

[0188] Because the viscosity of ionic liquids at ambient temperature is too high to effectively filter clean ionic liquids, the ionic liquid can be diluted before being filtered to facilitate the filtration process. Suitably, the ionic liquid is diluted with water at a ratio ranging from 0.5 (1:2) to 2 (2:1). Suitably, the ratio of ionic liquid to water is 1 (1:1).

[0189] Parameters of the caustic solution stream, such as flow rate and concentration, may be adjusted to account for dilution by the ionic liquid.

[0190] Dilution of the ionic liquid may occur on the stream entering the regeneration stage. Suitably, water is added to the stream entering the regeneration stage to dilute the ionic liquid stream.

[0191] Once the colloidal solids are filtered out, at least a portion of the resulting filtered stream can be recycled to the ionic liquid feed stream.

[0192] The filtered stream can be mixed with a metal halide salt and / or caustic solution to recover the ionic liquid. Suitably, the recovered ionic liquid is recycled back into the loop. The recovered ionic liquid can be decanted before being recycled back into the loop.

[0193] The regenerated ionic liquid stream may be diluted with water prior to the filtration step.

[0194] In each of the extraction, stripping, and regeneration stages, the water stream can flow countercurrent to the stream containing the organic ionic liquid. Operation in countercurrent mode enhances the transfer of impurities from the impurity-containing stream to the extractant stream by maintaining a nearly constant concentration gradient between the two streams throughout their contact length.

[0195] In each of the extraction stage, stripping stage and regeneration stage, the flow rate of each stream can be from 2m 3 / h-44m 3 / h range.

[0196] The organic ionic liquid flow in the extraction stage can have a flow rate from 10m 3 / h-26m 3 The flow rate is within the range of / h.

[0197] The water flow in the extraction stage may be any suitable flow rate.

[0198] The water flow in the stripping stage can have a flow rate from 4m 3 / h-14m 3 The flow rate is within the range of / h.

[0199] The water flow in the regeneration stage can have a flow rate from 6m 3 / h-23m 3 The flow rate is within the range of / h.

[0200] In each of the extraction stage, stripping stage and regeneration stage, the mixing step may be performed in a variety of ways, including by a batch process, a semi-continuous process or a continuous process. Suitably, the mixing step is a continuous process.

[0201] Each mixing step may comprise feeding the organic and aqueous streams into any suitable apparatus that can be used for mixing and phase separation or sedimentation. Examples of suitable mixing and phase separation or sedimentation apparatus include, but are not limited to, continuous mixer / settler units, static mixers, in-line mixers, towers, centrifuges, and hydrocyclones. A preferred apparatus is a mixer-settler.

[0202] In each of the extraction, stripping, and regeneration stages, the operating temperature may be as high as 100° C. The operating temperature may be varied to control the rate of phase separation.

[0203] The operating temperature of each of the extraction stage, stripping stage and regeneration stage may be in the range of from 50-80°C, suitably 65-75°C, more suitably 60-65°C.

[0204] The method can include controlling the internal O / A ratio and / or the external O / A ratio of each of the extraction stage, the stripping stage, and the regeneration stage. The O / A ratio can be in the range of 0.001 (1:1000) to 100 (100:1). In one embodiment, the O / A ratio is in the range of from 0.01 to 100. In another embodiment, the ratio is in the range of from 0.1 to 10. In another embodiment, the ratio is in the range of from 0.25 to 6.67. In yet another embodiment, the ratio is in the range of from 0.25 to 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0206] Embodiments of the invention are hereinafter described, by way of example only, with reference to the accompanying drawings, in which:

[0207] Figure 1 is a flow chart of an embodiment of a method for recycling an ionic liquid according to the present invention; and

[0208] Figure 2 is a diagram of an embodiment of an apparatus configured to recirculate an ionic liquid according to the present invention. DETAILED DESCRIPTION

[0209] The embodiments described herein are embodiments of methods and apparatus according to the present invention for purifying a Bayer process stream using ionic liquids to remove impurities from the Bayer process stream.

[0210] The examples described therein focus on the application of the invention to the removal of impurities from a spent Bayer liquor stream.As mentioned above, one class of impurities of particular relevance in spent Bayer liquor streams is NOOCs.

[0211] An embodiment of the method for purifying a Bayer process stream according to the invention is Figure 1 Marked with 10.

[0212] An embodiment of the apparatus according to the invention for purifying a Bayer process stream is Figure 2 Marked with 110.

[0213] Referring to the drawings, the basic unit operations for the apparatus are an extraction stage 16 , a stripping stage 18 , and a regeneration stage 20 .

[0214] The extraction stage 16 includes three mixer-settlers, including mixers 48A-48C and settlers 46A-46C ( Figure 2 ). The extractor mixer-settlers are arranged in series with a first extractor mixer-settler E1 comprising a mixer 48A and a settler 46A and a terminal extractor mixer-settler E3 comprising a mixer 48C and a settler 46C.

[0215] The peeling stage 18 includes three mixer-settlers, including mixers 52A-52C and settlers 50A-50C ( Figure 2 ). The peel mixer-settlers are arranged in series with a first peel mixer-settler S1 comprising a mixer 52A and a settler 50A and a terminal peel mixer-settler S3 comprising a mixer 52C and a settler 50C.

[0216] The regeneration stage 20 includes four mixer-settlers, including mixers 56A-56C and settlers 54A-54C arranged in series ( Figure 2 ).

[0217] The methods and apparatus of the present invention are characterized by a filtration stage comprising at least one filter configured to filter particulate matter from at least one ionic liquid stream from the extraction stage 16 , the stripping stage 18 , and the regeneration stage 20 .

[0218] An ionic liquid feed stream 12 comprising 70% by weight tributyloctylphosphonium hydroxide and 30% by weight water and a spent Bayer liquor stream 14 comprising NOOC as carbon at a concentration of 22.5 g / L are fed countercurrently to an extraction stage 16 ( Figure 1 The spent Bayer liquor stream 14 enters via the terminal extractor mixer-settler E3, while the ionic liquid feed stream 12 enters via the first extractor mixer-settler E1.

[0219] The temperature of the spent Bayer liquor stream 14 is in the range of from 60-80°C, while the temperature of the ionic liquid feed stream is in the range of from 20-30°C, preferably from 20-25°C.

[0220] An operating temperature in the range from 50-80°C, preferably 60-65°C is maintained in the extraction stage.

[0221] As mentioned above, the mixer-settlers of extraction stage 16 include mixers 48A-48C and settlers 46A-46C ( Figure 2 ).

[0222] The first mixer-settler E1 is in fluid communication via a recirculation loop with the terminal mixer-settler R4 comprising mixer 56C and settler 54C in the regeneration stage 20. E1 receives regenerated ionic liquid from the regeneration stage to form the ionic liquid feed stream 12, and the terminal extraction mixer-settler E3 is in fluid communication with the first mixer-settler S1 of the stripping stage 18 comprising mixer 52A and settler 50A.

[0223] During mixing in mixers 48A-C, NOOC is extracted from the spent Bayer liquor stream 14 and transferred to the ionic liquid feed stream 12. This reduces the concentration of NOOC in the spent Bayer liquor stream 14 and forms an aqueous purified spent Bayer liquor and an organic, NOOC-laden ionic liquid.

[0224] The aqueous and organic phases are then separated to form a purified spent Bayer process stream 24 having a lower NOOC concentration than spent Bayer liquor stream 14 (eg, 6.9 g / L or less) and a NOOC-laden ionic liquid stream 26 exiting the extraction stage.

[0225] The purified spent Bayer liquor stream 24 (exiting via the first extractor mixer-settler E1 ) is transferred for further processing in the refinery, while the NOOC-laden ionic liquid stream 26 is transferred to the stripping stage 18 .

[0226] As mentioned above, the stripping stage 18 includes three mixer-settlers, including mixers 52A-52C and settlers 50A-50C arranged in series ( Figure 2 ).

[0227] The first peel mixer-settler S1 is in fluid communication with the end mixer-settler E3 of the extraction stage 16 including the mixer 48C and the settler 46C, and the end peel mixer-settler S3 is in fluid communication with the first mixer-settler R1 of the regeneration stage 20 including the mixer 56A and the settler 54A.

[0228] In the stripping stage 18, the NOOC-loaded ionic liquid stream 26 flows countercurrently to the brine (sodium chloride) stream 28 at an external O / A ratio in the range of 0.67 to 2.5 and an internal O / A ratio in the range of 0.8 to 1.2 for mixing. The brine (sodium chloride) stream 28 is fed to the end stripping mixer-settler S3, while the NOOC-loaded ionic liquid stream 26 enters via the first stripping mixer-settler S1.

[0229] An operating temperature in the range of from 60°C to 80°C, preferably 70°C to 75°C is maintained in the stripping stage.

[0230] During mixing in 52A-52C, ion exchange occurs between the ionic liquid and the brine, wherein the anionic NOOC exchanges with chloride groups in the brine. This forms a mixture comprising an aqueous phase containing the NOOC-loaded brine and an organic phase containing the chloride-containing ionic liquid.

[0231] The aqueous and organic phases are then separated to form a NOOC-laden brine stream 30 having a NOOC concentration of typically at least 20 g / L and a chloride-containing ionic liquid stream 32 exiting the stripping stage.

[0232] The NOOC-laden brine stream 30 (exiting via the first peel mixer-settler S1 ) is diverted for further processing before discharge into the environment.

[0233] Additional processing includes passing the NOOC-laden brine stream 30 through a coalescer to aggregate and collect any entrained ionic liquid, typically in the range of from 300 ppm to 500 ppm, for recycling back into the loop.

[0234] Additional processing also includes passing the NOOC-laden brine stream 30 through a series of activated carbon columns to reduce the final ionic liquid concentration to <1 ppm before the clean brine stream is discharged to the environment.

[0235] A portion of the clean brine stream is recycled to the regeneration stage.

[0236] The chloride-containing ionic liquid stream 32 is directed to the regeneration stage 20 comprising four mixer-settlers.

[0237] As mentioned above, Figure 2 Four regenerative mixer-settlers are shown as mixers 56A-56C and settlers 54A-54C arranged in series.

[0238] The first mixer-settler R1 of the regeneration stage 20 is in fluid communication with the end mixer-settler S3 of the stripping stage 18 , and the end mixer-settler R4 of the regeneration stage 20 is in fluid communication with the first mixer-settler E1 of the extraction stage 16 to transfer the regenerated ionic liquid to the extraction stage 16 .

[0239] In the regeneration stage 20, the chloride-containing ionic liquid stream 32 is mixed with a caustic (sodium hydroxide) stream 35, which typically has a concentration of at least 10 wt%, at an external O / A ratio in the range of 0.67 to 1.5 and an internal O / A ratio in the range of 0.8 to 1.2. The caustic (sodium hydroxide) stream 35 is fed to the final regeneration mixer-settler R4, while the chloride-containing ionic liquid stream 32 is fed to the first regeneration mixer-settler R1.

[0240] The temperature of the caustic stream 35 is in the range of from 10-30°C, preferably 25°C.

[0241] An operating temperature in the range from 50°C to 80°C, preferably 60°C to 65°C is maintained in the regeneration stage.

[0242] During mixing in mixers 56A-56C, chloride groups from the ionic liquid are replaced by hydroxyl groups from the caustic solution. This forms an aqueous phase comprising regenerated ionic liquid and chloride-containing caustic solution.

[0243] The aqueous and organic phases are then separated to form a regenerated ionic liquid stream 12 and a chloride-containing caustic stream 36 that exits the regeneration stage 20 via a first regeneration mixer-settler R1.

[0244] The chloride-containing caustic stream 36 is further processed in a salt separation unit 40. The processed caustic stream produces a sodium chloride stream 42 that is at least partially fed to the brine stream 28, or a sodium hydroxide stream 44 that is at least partially fed to the caustic stream 35.

[0245] The ionic liquid inventory is gradually degraded or lost in the circuit.

[0246] To maintain the ionic liquid concentration, fresh ionic liquid 37 in the form of tributyloctylphosphonium chloride is added to the regeneration stage 20 .

[0247] As previously discussed, one problem encountered during BTP operation is that once a threshold concentration of particulate matter in the ionic liquid recirculation loop is reached, an emulsion stabilized by the particulate matter forms between the ionic liquid used and the aqueous solution (referred to above as "fouling") and renders the purification or recirculation loop inoperable.

[0248] To reduce scale formation, the exiting stripped organic ionic liquid stream is passed through a filtration device of appropriate size to maintain the solids concentration (i.e., particulate matter) below a threshold concentration in the filtered stream before being transferred to the regeneration stage as the chloride-containing ionic liquid stream 32.

[0249] In another embodiment, to reduce scale formation, the exiting regenerated organic ionic liquid stream is passed through a filtration device of appropriate size to maintain the solids concentration (i.e., particulate matter) below a threshold concentration in the filtered stream before being recycled as the ionic liquid feed stream 12.

[0250] Once the colloidal solids are filtered out, the resulting stream can be salted out using sodium chloride and / or caustic to recover the ionic liquid before it is decanted and recycled back into the loop.

[0251] As mentioned above, the present invention extends to filtering the organic ionic liquid stream before or after any one or more of the extraction, stripping and regeneration stages 16 , 18 , 20 .

[0252] To evaluate the present invention, the above-mentioned Bench-Top Pilot (BTP) was operated using methods and equipment similar to those described above, using the operating parameters summarized in Table 1 .

[0253] Table 1: BTP parameters

[0254]

[0255] The measured operating parameters are listed in the "Actual" column, while the set parameters are listed in the "Standard" column.

[0256] Table 2 provides a summary of the BTP analysis results.

[0257] Table 2: Summary of BTP analysis results

[0258]

[0259] Three samples were taken from each of the three feed water storage tanks (Extraction-DSL, Stripping-SA, Regeneration-RA) and each settler water overflow weir, for a total of 39 samples. Each sample was analyzed individually for phosphorus, chlorine, and total organic carbon. Once the sample results were received, the median of each set of three results was taken and presented in Table 2 above.

[0260] Phosphorus was chosen as a representative species for ionic liquids because the P background was expected and had been shown to be low enough not to interfere with the analysis, and because ionic liquids contain phosphorus.

[0261] All values ​​less than 20 ppm are reported as "<20 ppm". In the above table, where "<20 ppm" is reported for SA and RA, the value is entered as 0 in the above table since this is the pure solution before contact with any ionic liquid. In all other cases where a "<20 ppm" value is reported, a value of 10 ppm is entered instead as a working estimate of the P content of the sample.

[0262] Based on the results in Table 2, the following observations are made:

[0263] • Purification of the spent Bayer liquor stream 14 containing NOOCs occurs in the extraction stage. This is demonstrated by a reduction in the TOC content in the spent Bayer liquor stream 14 fed to E3 from 22,900 mg / L to 6,910 mg / L in the purified spent Bayer process stream 24 leaving E1.

[0264] NOOC is primarily removed in the stripping stage. This is demonstrated by an increase in TOC content from 6,880 mg / L in the brine (S3; SA) stream 28 fed into S3 to 21,700 mg / L in the NOOC-laden brine stream (S1; SSA) 30 exiting S1.

[0265] • Regeneration of the ionic liquid in the regeneration stage is demonstrated by increasing the Cl concentration in the caustic (R4; RA) stream 35 supplied to R4 from 14.4 ppm to 23,900 ppm in the chloride-containing caustic (R1; SRA) stream 36 exiting R1.

[0266] A small amount of ionic liquid is removed by the chloride-containing caustic stream (R1; SRA) 36 leaving the regeneration stage 20. This is demonstrated by increasing the P concentration in the caustic (R4; RA) stream 35 supplied to R4 from 0 mg / L to 10 mg / L in the chloride-containing caustic (SRA) stream 36 leaving R1.

[0267] The effectiveness of filtering organic ionic liquid streams is demonstrated by the following filtration experiments summarized in Examples 1-3 below.

[0268] Example 1

[0269] - Filter unit: DrM TSD filter in 316L stainless steel with 32 mm diameter candle filter.

[0270] - No filter aids or diluents

[0271] -Temperature: 51℃

[0272] -G11 M080 / 30 filter cloth (polypropylene)

[0273] -Feed solids 1.7g / L

[0274] -Maximum filtration pressure: 4 bar

[0275] - Filtrate solids after cake development, 0.43 g / kg.

[0276] -After 240 minutes, the total flux was 48 L / m 2 / h

[0277] Example 2

[0278] - Filter unit: DrM TSD filter in 316L stainless steel with 32 mm diameter candle filter.

[0279] - Coarse perlite AP 70, feed without water dilution

[0280] - Temperature: 57°C

[0281] -Filter aid main body feed ratio 1:1

[0282] -G11 M080 / 30 filter cloth (polypropylene)

[0283] -Feed solids 4.3g / L

[0284] -Maximum filtration pressure: 3 bar

[0285] -After 117 minutes, the total flux was 89 L / m 2 / h

[0286] - No visible filtrate solids observed (indicating <0.1 g / L based on visual correlation with measurements from previous testing)

[0287] Example 3

[0288] - Filter unit: DrM TSD filter in 316L stainless steel with 32 mm diameter candle filter.

[0289] - Coarse perlite AP 70, undiluted

[0290] - Temperature: 58°C

[0291] -Filter aid main body feed ratio 2:1

[0292] -G11 M080 / 30 filter cloth (polypropylene)

[0293] -Feed solids 0.7g / L

[0294] -Maximum filtration pressure: 3 bar

[0295] -After 23 minutes, the total flux was 378 L / m 2 / h

[0296] - No visible filtrate solids observed (indicating <0.1 g / L based on visual correlation with measurements from previous testing)

[0297] The above observations show that the filter installed in the device effectively removes circulating particulate matter to prevent scale formation and allow the device to function.

[0298] Many modifications may be made to the embodiments of the invention described above without departing from the spirit and scope of the invention.

[0299] By way of example, the mixers and settlers in the extraction stage 16, the stripping stage 18, and the regeneration stage 20 may be any suitable mixers and settlers.

[0300] In the appended claims and the foregoing description of the invention, unless the context requires otherwise due to express language or necessary meaning, the word "comprise" or variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of recited features in various embodiments of the invention, but not to exclude the presence or addition of further features.

[0301] Glossary

[0302]

[0303]

Claims

1. An apparatus for purifying a Bayer process stream comprising an ionic liquid recirculation loop, comprising: an extraction stage comprising at least one contacting / separating device configured to receive and mix an impure Bayer process stream and an ionic liquid stream comprising a quaternary organic cation to form a purified Bayer process stream and an impurity-laden ionic liquid stream; a stripping stage comprising at least one contacting / separating device configured to receive and mix the impurity-laden ionic liquid stream and the halide-containing salt stream to form a halide-containing ionic liquid stream and an impurity-laden salt stream; a regeneration stage comprising at least one contacting / separating device configured to receive and mix the halide-containing ionic liquid stream and the caustic stream to form a regenerated ionic liquid stream and a halide-containing caustic effluent stream, wherein the extraction stage is configured to be in fluid communication with the regeneration stage via a recirculation loop to receive at least a portion of the regenerated ionic liquid stream, and A filtration stage includes at least one filter configured to filter particulate matter from at least one of the ionic liquid streams from the extraction stage, the stripping stage, and the regeneration stage to control a concentration of the particulate matter in the ionic liquid stream.

2. The apparatus of claim 1 , wherein the filtration stage is configured such that the concentration of the particulate matter in the regenerated ionic liquid stream is below a predetermined threshold concentration before the regenerated ionic liquid is returned to the extraction stage.

3. The apparatus of claim 1 or claim 2, wherein at least one ionic liquid-containing operating unit for the extraction stage, the stripping stage, and the regeneration stage comprises the filter of the filtration stage to control the concentration of the particulate matter in the regenerated ionic liquid.

4. Apparatus according to claim 1 or claim 2, wherein the filtration stage is an operating unit separate from the operating units forming the extraction stage, the stripping stage and the regeneration stage.

5. Apparatus according to claim 1 or claim 2, wherein the filtration stage follows the stripping stage.

6. The apparatus according to claim 1 or claim 2, configured so that the filtration stage is at 10 L / m 2 / h-700L / m 2 Operate at filtration flux rates between / h.

7. The apparatus of claim 6, configured to dilute the at least one ionic liquid flow.

8. The apparatus of claim 1 or claim 2, wherein the filter is configured to use a pressure differential as a driving force for filtration.

9. The apparatus of claim 1 or claim 2, wherein the filter comprises a filter having a flow rate of 3 L / dm 2 / min-200L / dm 2 The air permeability of the filter medium is between 100 and 200 nm / min.

10. Apparatus according to claim 1 or claim 2, wherein the filtration stage comprises a filter aid and a flocculant.

11. Apparatus according to claim 1 or claim 2, wherein the filtration stage is configured to operate within a temperature range of 20°C to 70°C.

12. An apparatus for recycling an ionic liquid used to purify a Bayer process stream, comprising: a stripping stage comprising at least one contacting / separating device configured to receive and mix the impurity-laden ionic liquid stream and the stripping solution stream to form an impurity-reduced ionic liquid stream and an impurity-laden stripping solution stream; a regeneration stage comprising at least one contacting / separating device configured to receive and mix the impurity-reduced ionic liquid stream and a caustic solution stream to form a regenerated ionic liquid stream and a caustic effluent stream; wherein the at least one contacting / separating device from the regeneration stage is configured to recycle at least a portion of the regenerated ionic liquid stream and form an ionic liquid feed stream to purify a Bayer process stream, and A filtration stage includes at least one filter configured to filter particulate matter from at least one of the ionic liquid streams from the stripping stage and the regeneration stage to control a concentration of the particulate matter in the ionic liquid stream.

13. The apparatus according to claim 12, configured to generate a 2 / h-700L / m 2 The filtration stage is operated at a filtration flux rate of between 1 / 2 h and 1 / 4 h.

14. The apparatus of claim 13, configured to dilute at least one ionic liquid stream.

15. Apparatus according to any one of claims 12 to 14, wherein the filtration stage is configured to operate within a temperature range of 20°C - 70°C.

16. The apparatus of any one of claims 12 to 14, configured to operate at least one of the extraction stage, the stripping stage and the regeneration stage within a temperature range of from 50°C to 80°C.

17. A method for purifying a Bayer process stream using an ionic liquid, comprising: providing an ionic liquid feed stream comprising a quaternary organic cation, wherein the ionic liquid feed stream is at least partially immiscible with the Bayer process stream; mixing the Bayer process stream with the ionic liquid feed stream and forming an aqueous phase comprising purified Bayer process liquor and an organic phase comprising the impurity-laden ionic liquid, wherein the mixing reduces the concentration of impurities in the Bayer process liquor; at least partially separating the aqueous phase from the organic phase and forming a purified Bayer process stream and an impurity-laden ionic liquid stream; mixing the impurity-laden ionic liquid stream and the halide-containing salt stream to form an aqueous phase comprising the impurity-laden salt and an organic phase comprising the halide-containing ionic liquid, wherein the mixing reduces the concentration of impurities in the impurity-laden ionic liquid stream; at least partially separating the aqueous phase from the organic phase and forming a halide-containing ionic liquid stream and an impurity-laden salt stream; mixing the halide-containing ionic liquid stream and a caustic solution and forming an aqueous phase comprising the halide-containing caustic solution and an organic phase comprising regenerated ionic liquid, wherein the mixing replaces at least some of the halide groups in the halide-containing ionic liquid with hydroxyl groups from the caustic solution; at least partially separating the aqueous phase from the organic phase and forming a halide-containing salt stream and a regenerated ionic liquid stream; filtering at least one of the ionic liquid feed stream, the impurity-laden ionic liquid stream, the halide-containing ionic liquid stream, and the regenerated ionic liquid stream to remove particulate matter to control the concentration of the particulate matter in the ionic liquid stream; and At least a portion of the regenerated ionic liquid stream is recycled and forms at least a portion of the ionic liquid feed stream.

18. A method for recycling an ionic liquid used to purify a Bayer process stream, comprising: combining the impurity-laden ionic liquid stream with the stripping solution stream and forming an aqueous phase comprising the impurity-laden stripping solution and an organic phase comprising the impurity-reduced ionic liquid; at least partially separating the aqueous phase from the organic phase and forming an impurity-reduced ionic liquid stream and an impurity-laden stripping solution stream; combining the impurity-reduced ionic liquid stream and the caustic solution stream and forming an aqueous phase comprising the spent caustic solution and an organic phase comprising the regenerated ionic liquid stream; filtering at least one of the impurity-laden ionic liquid stream, the impurity-reduced ionic liquid stream, and the regenerated ionic liquid stream to remove particulate matter to control a concentration of the particulate matter in the ionic liquid stream; as well as At least a portion of the regenerated ionic liquid stream is recycled to form an ionic liquid feed stream to purify the Bayer process stream.

19. The method according to claim 17 or claim 18, comprising: 2 / h-700L / m 2 At least one of the ionic liquid streams is filtered at a filtration flux rate of between 1 / h and 2 / h.

20. A method according to claim 17 or claim 18 comprising diluting at least one of the ionic liquid streams.

21. A method according to claim 17 or claim 18, comprising diluting at least one of the ionic liquid streams prior to the filtering step.

22. The method of claim 21, wherein at least one of the ionic liquid streams is diluted with water at a ratio ranging from 0.5 (1:2) to 2 (2:1).

23. A method according to claim 17 or claim 18 comprising filtering at a temperature in the range 20°C to 70°C.

24. A method according to claim 17 or claim 18, comprising operating such that the temperature of at least one of the ionic liquid streams is in the range of from 50°C to 80°C.

25. The method of claim 17 or claim 18, wherein the filtering step comprises adding a filter aid directly to at least one of the ionic liquid streams.

26. The method of claim 25, comprising pre-batch treating the filter aid with an aqueous solution at a temperature between 20°C and 80°C prior to being added to at least one of the ionic liquid streams.

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