CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent

Application No. 62/204,427, filed August 12, 2015, which is hereby incorporated by reference.

FIELD

[0002] The present disclosure relates generally to recovery of solvents by removal of contaminants.

BACKGROUND

[0003] Power generation and other industrial processes generate flue gas and other greenhouse gases, including C0 ₂ and S0 ₂ . The gases are often captured by dissolution in solvents. The solvents may be costly to manufacture, purchase or license, and dispose of. The costs associated the solvents provide an incentive to recover the solvents. Solvent recovery may be undertaken by distillation or other known methods. In some cases contaminants are removed by precipitation or crystallization of contaminants from the solvent.

SUMMARY

[0004] It is an object of the present disclosure to obviate or mitigate at least one disadvantage of previous approaches to removing contaminants from solvents.

[0005] In a first aspect, the present disclosure provides a solvent recovery method and system. Contaminated solvent is alkalized to provide an alkalized contaminated solvent. Crystals including a component of the contaminant are formed from the alkalized

contaminated solvent, resulting in purified solvent. The purified solvent is filtered through the crystals, resulting in filtered solvent. The system includes a vessel with heat exchangers and other features for localizing crystal formation and filtering the purified solvent through the crystals.

[0006] In a further aspect, the present disclosure provides a method for recovering solvent comprising: providing a contaminated solvent; increasing a pH of the contaminated solvent, resulting in an alkalized contaminated solvent; forming crystals from the alkalized contaminated solvent, resulting in a purified solvent; and filtering the purified solvent through the crystals, resulting in a filtered solvent.

[0007] In some embodiments, the contaminated solvent comprises at least one amine species contaminated with at least one oxidized sulphur species. In some

embodiments, at least one amine species comprises a diamine. In some embodiments, the at least one amine species comprises a monoethanolamine (MEA), 2-amino-2-methyl-1- propanol (AMP), methyldiethanolamine (MDEA), piperazines, or a combination thereof. In some embodiments, the at least one oxidized sulphur species comprises S0 ₃ ^2" , S0 ₄ ^2" , S ₂ 0 ₃ ^2" , or a combination thereof.

[0008] In some embodiments, the contaminated solvent is contaminated with at least one species of halide, C0 ₃ ^"2 , HCO., or a combination thereof.

[0009] In some embodiments, increasing the pH of the contaminated solvent comprises adding a basic salt to the contaminated solvent. In some embodiments, the basic salt comprises NaOH. In some embodiments, the crystals comprise a complex of Na+ and at least one oxidized sulfur anion. In some embodiments, the basic salt to the contaminated solvent comprises adding sufficient basic salt to the contaminated solvent to provide a salt- saturated alkalized contaminated solvent. In some embodiments, adding the basic salt increases a temperature of the alkalized contaminated solvent to an elevated temperature. In some embodiments, forming the crystals from the alkalized contaminated solvent comprises lowering the temperature of the alkalized contaminated solvent from the elevated temperature to a crystallization temperature. In some embodiments, the elevated

temperature is a crystallization temperature. In some embodiments, the method includes, prior to adding the basic salt to the contaminated solvent, cooling the contaminated solvent to a lowered temperature to facilitate reaching the crystallization temperature as a result of adding the basic salt to the contaminated solvent. In some embodiments, the lowered temperature is between 2 and 10 °C above a freezing point of the contaminated solvent.

[0010] In some embodiments, increasing the pH of the contaminated solvent comprises increasing the pH of the contaminated solvent to a pH value above an

equivalence point of the contaminated solvent.

[0011] In some embodiments, forming the crystals from the alkalized contaminated solvent comprises forming the crystals on a surface positioned to oppose flow of the purified solvent with the crystals. In some embodiments, the surface is immobile relative to the flow of the purified solvent. In some embodiments, the surface is displaceable relative to the flow of the purified solvent. In some embodiments, the surface is in thermal communication with a temperature controller and forming the crystals comprises lowering a temperature of the surface. In some embodiments, the surface is removable and wherein dissolving the crystals comprises removing the surface from a tank in which forming the crystals takes place and dissolving the crystals separately from the tank. In some embodiments, rinsing the crystals comprises removing the surface from a tank in which forming the crystals takes place and rinsing the crystals separately from the tank.

[0012] In some embodiments, forming the crystals from the alkalized contaminated solvent comprises cooling the alkalized contaminated solvent to a lowered temperature at a first location relative to the alkalized contaminated solvent to induce crystallization at the first location. In some embodiments, the first location is on a surface positioned to oppose flow of the alkalized contaminated solvent with the crystals.

[0013] In some embodiments, forming the crystals from the alkalized contaminated solvent comprises, prior to increasing the pH of the contaminated solvent, cooling the contaminated solvent to a lowered temperature to facilitate forming the crystals. In some embodiments, the method includes cooling the alkalized contaminated solvent to a second lowered temperature at a first location relative to the alkalized contaminated solvent to induce crystallization at the first location. In some embodiments, the first location is on a surface positioned to oppose flow of the purified solvent with the crystals. In some embodiments, the first lowered temperature is equal to the second lowered temperature. In some embodiments, the first lowered temperature is lower than the second lowered temperature.

[0014] In some embodiments, filtering the purified solvent through the crystals comprises flowing the purified solvent downward through the crystals.

[0015] In some embodiments, filtering the purified solvent through the crystals comprises settling the crystals into a bed and flowing the purified solvent through the bed.

[0016] In some embodiments, filtering the purified solvent through the crystals comprises applying negative pressure to the purified solvent

[0017] In some embodiments, filtering the purified solvent through the crystals comprises rinsing the crystals with a rinse fluid to remove the purified solvent from the crystals. In some embodiments, the rinse fluid is at a lowered temperature to mitigate dissolution of the crystals in the rinse fluid. [0018] In some embodiments, increasing the pH of the contaminated solvent, forming the crystals, and filtering the purified solvent through the crystals take place in a single vessel.

[0019] In some embodiments, the method includes recovering the crystals. In some embodiments, recovering the crystals comprises dissolving the crystals in a dissolution fluid. In some embodiments, the dissolution fluid is at an elevated temperature to facilitate dissolution of the crystals in the dissolution rinse. In some embodiments, recovering the crystals comprises heating a surface upon which the crystals are formed.

[0020] In some embodiments, the method includes recovering a portion of the purified solvent. In some embodiments, recovering the portion of the purified solvent begins prior to filtering the purified solvent through the crystals.

[0021] In some embodiments, the method includes, prior to adding the basic salt to the contaminated solvent, dewatering the contaminated solvent.

[0022] In some embodiments, the method includes deionizing the filtered solvent.

[0023] In some embodiments, the method includes removing particulates from the filtered solvent.

[0024] In a further aspect, the present disclosure provides a system for recovering solvent comprising: a vessel defining a cavity therein for receiving a reaction mixture; a heat exchanger in communication with the vessel at a first portion of the cavity for originating a change in temperature within the cavity from the first portion; a crystallization location for localizing crystallization at a second portion of the cavity; and a recovery port defined by the vessel for providing external fluid communication with the cavity and recovering a fluid from the cavity.

[0025] In some embodiments, a length of the vessel is greater than a height of the vessel.

[0026] In some embodiments, the heat exchanger comprises at least one external heat exchange member located outside the cavity and wherein the crystallization location is located inside the cavity at a portion of the vessel corresponding with the external heat exchange member.

[0027] In some embodiments, the crystallization point comprises a rough surface for facilitating crystallization.

[0028] In some embodiments, the first portion and the second portion are

substantially coextensive. In some embodiments, the heat exchanger comprises at least one heat exchange member located in the cavity and wherein the crystallization location is located on the at least one heat exchange member. In some embodiments, the at least one heat exchange member is removable from the cavity. In some embodiments, the at least one heat exchange member is located proximate a wall of the vessel. In some

embodiments, the at least one heat exchange member is located distally into the cavity from a wall of the vessel. In some embodiments, the at least one heat exchange member comprises a plurality of segments, and the crystallization location is located along each of the segments. In some embodiments, the at least one heat exchange member is continuous along the segments. In some embodiments, the at least one heat exchange member comprises separate heat exchange zones, the heat exchange zones being thermally isolated from each other for independent control of fluid temperature in the at least one heat exchange member as between the zones. In some embodiments, the at least one heat exchange member comprises at least two heat exchange members and the heat exchange zones are located on separate heat exchange members. In some embodiments, the segments are spaced from each other to distribute the change in temperature throughout the cavity. In some embodiments, the segments are spaced from each other by vertical and horizontal separation. In some embodiments, the segments are angled with respect to each other inside the cavity. In some embodiments, at least a portion of the segments are oriented substantially vertically within the cavity and at least a portion of the segments are oriented substantially horizontally within the cavity.

[0029] In some embodiments, the crystallization location is on a releasable module in thermal communication with the heat exchanger and reversibly connected with the tank. In some embodiments, the releasable module is in fluid communication with the recovery port. In some embodiments, the releasable module comprises a module body comprising an intake for receiving a fluid, and wherein the crystallization location is on an inside diameter of the module body for receiving a fluid through the intake and filtering the fluid through a crystal formed on the crystallization location.

[0030] In some embodiments, the recovery port is located at a lower portion of the vessel for facilitating recovery of the fluid from the cavity by gravity-induced flow. In some embodiments, the system includes a source of negative pressure in communication with the recovery port at the lower portion of the vessel.

[0031] In some embodiments, the recovery port comprises a barrier to mitigate passage of particulates into the recovery port. [0032] In some embodiments, the recovery port is located at a bottom of the body for facilitating flow to the recovery port. In some embodiments, the crystallization location is located proximate the recovery port and the bottom of the body, and the second portion is defined in a lower portion of the cavity.

[0033] In some embodiments, the system includes a fluid delivery system for providing fluid into the cavity proximate the crystallization point.

[0034] In some embodiments, the fluid delivery system is selectably in

communication with a first source of fluid for rinsing the crystal and with a second source of fluid for dissolving the crystal.

[0035] In a further aspect, the present disclosure provides a method for recovering solvent comprising: providing a contaminated solvent comprising a diamine contaminated with at least one oxidized sulphur species; adding a basic salt to the contaminated solvent for increasing a pH of the contaminated solvent, resulting in an alkalized contaminated solvent; forming crystals comprising at least one oxidized sulfur anion from the alkalized

contaminated solvent, resulting in a purified solvent, the crystals being formed on a surface positioned to oppose flow of the purified solvent with the crystals; and filtering the purified solvent through the crystals, resulting in a filtered solvent.

[0036] In some embodiments , increasing the pH of the contaminated solvent comprises increasing the pH of the contaminated solvent to a pH value above an

equivalence point of the contaminated solvent.

[0037] In some embodiments, the method includes recovering the crystals.

[0038] In some embodiments, the method includes recovering a portion of the purified solvent.

[0039] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached figures, in which features sharing reference numerals with a common final two digits of a reference numeral correspond to similar features across multiple figures (e.g. the body 12, 1 12, 212, 312, 412, 512, 612, etc.). [0041] Fig. 1 is an end elevation view of a tank;

[0042] Fig. 2 is a side elevation view of the tank of Fig. 1 ;

[0043] Fig. 3 is a plan view of the tank of Fig. 1 ;

[0044] Fig. 4 shows the tank of Fig. 1 including a contaminated solvent;

[0045] Fig. 5 shows the tank of Fig. 4 during addition of a salt solution to the contaminated solvent, resulting in an alkalized contaminated solvent;

[0046] Fig. 6 shows the tank of Fig. 5 following formation of crystals from the alkalized contaminated solvent, resulting in a purified solvent;

[0047] Fig. 7 shows the tank of Fig. 6 following filtering the solvent by flowing the solvent over and through the crystals, resulting in a filtered solvent;

[0048] Fig. 8 shows the tank of Fig. 7 while rinsing the crystals to remove purified solvent trapped in the crystals;

[0049] Fig. 9 shows the tank of Fig. 8 while dissolving the crystals;

[0050] Fig. 10 is an end elevation view schematic of a tank;

[0051] Fig. 1 1 is a side elevation view schematic of the tank of Fig. 10;

[0052] Fig. 12 is a plan view schematic of the tank of Fig. 10;

[0053] Fig. 13 shows the tank of Fig. 10 including a contaminated solvent;

[0054] Fig. 14 shows the tank of Fig. 13 during addition of a salt solution to the contaminated solvent, resulting in an alkalized contaminated solvent;

[0055] Fig. 15 shows the tank of Fig. 14 following formation of crystals from the alkalized contaminated solvent, resulting in a purified solvent;

[0056] Fig. 16 shows the tank of Fig. 15 following filtering the solvent by flowing the solvent over and through the crystals, resulting in a filtered solvent;

[0057] Fig. 17 shows the tank of Fig. 16 while rinsing the crystals to remove purified solvent trapped in the crystals;

[0058] Fig. 18 shows the tank of Fig. 17 while dissolving the crystals;

[0059] Fig. 19 is a perspective view of a tank;

[0060] Fig. 20 is a perspective view of a tank;

[0061] Fig. 21 is a perspective view of a tank;

[0062] Fig. 22 is a schematic of a solvent recovery system;

[0063] Fig. 23 is a partial cross-sectional perspective view of a tank used in the system of claim 22;

[0064] Fig. 24 is a partial cross-sectional perspective view of the tank of Fig. 23; [0065] Fig. 25 is a cutaway plan view of the tank of Fig. 23;

[0066] Fig. 26 is an elevation view of a tank; and

[0067] Fig. 27 shows a crystallization and recovery unit used in the tank of Fig. 26. DETAILED DESCRIPTION

[0068] Generally, the present disclosure provides a method and system for solvent recovery and removal of contaminants from a solvent. The method and system may be applied to solvents that include a dissolved salt that may be crystallized from the solvents following changes in pH, temperature, or both. The changes in pH to induce crystallization would be determined with reference to the solubility of the salt in the solvent at different pH values. The method and system may be applied to solvents used in capture of pollutants from flue gas, such as S0 ₂ and C0 ₂ (e.g. amines, cyclic diamines, glycols, etc.). The solvents may include amines, diamines, monoethanolamine (MEA), 2-amino-2-methyl-1- propanol (AMP), methyl diethanolamine (MDEA), piperazines, or other solvents used in flue gas treatment, in traditional gas process treating facilities, or in other industrial applications. A particular example of a solvent used for scrubbing flue gas is Cansolv Absorbent DS™ solvent, the composition of which is described in United States publication no. 2014/0260979 to Infantino as including 54% w/w water, 27 % w/w of a 9: 1 mixture of Ν,Ν'- bis(hydroxyethyl)piperazine and N-(2-hydroxyethyl)piperazine, 1.06 % w/w sodium, and 12.9 % w/w sulfate. A similar composition for the Cansolv Absorbent DS™ solvent is disclosed in United States patent no. 8,097,068 to Campbell et. al.

[0069] The pH of a contaminated solvent is increased, resulting in an alkalized contaminated solvent. The alkalized contaminated solvent may have a pH equal to or greater than the equivalence point of the contaminated solvent. At a pH equal to or above the equivalence point of the contaminated solvent, formation of crystals from the alkalized contaminated solvent may be facilitated. The crystals may include at least one anion from the contaminant (e.g. S0 ₄ ^2" , S0 ₃ ^2" , S ₂ 0 ₃ ^2" , C0 ₃ ^2" , etc.). The crystals may include at least one cationic component present in the alkalized contaminated solvent (e.g. Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , etc.), which cationic component may be present in the contaminated solvent or in a basic salt added to the contaminated solvent to raise the pH of the contaminated solvent. Formation of crystals including at least one divalent cation may be facilitated where C0 ₃ ^2" is a

contaminant. For example, where the equivalence point of the contaminated solvent is about 9.0 and the contaminant includes S0 ₄ ^2" , the pH may be raised to between 9.5 and 13.5 to facilitate formation of Na ₂ S0 ₄ crystals from the alkalized contaminated solvent.

[0070] Increasing the pH of the contaminated solvent may be achieved by adding a basic salt (e.g. NaOH, KOH, K ₂ C0 ₃ , soda ash, etc.) to the contaminated solvent. Where increasing the pH of the contaminated solvent includes adding a base (e.g. OH ^" , C0 ₃ ^2" , HCO ^" , etc.) to the contaminated solvent, Na ⁺ or another cation may be included in the crystals complexed with the anion of the basic salt. Formation of the crystals removes at least a portion of the contaminant from the alkalized contaminated solvent, resulting in a purified solvent. The purified solvent includes a lower concentration of contaminants than the alkalized contaminated solvent. A portion of the purified solvent may be recovered after formation of the crystals without flowing the portion of the purified solvent through the crystals.

[0071] The crystals may be formed on an immobilized substrate or otherwise positioned to remain static relative to, or otherwise oppose, flow of the purified solvent. The crystals may be formed on a member extending into a reaction vessel containing the alkalized contaminated solvent. The crystals may be formed on a belt and the belt passed through the reaction vessel. The crystals may form freely in solution in the alkalized contaminated solvent. Any combination of approaches to opposing flow of the purified solvent with the crystals may also be applied during crystallization.

[0072] The purified solvent may be passed over and through the crystals anchored with the immobilized substrate or otherwise opposed with flow of the alkalized contaminated solvent. Flow of the alkalized contaminated solvent over and through the crystals facilitates filtering the purified solvent through the crystals, removing a portion of any remaining suspended particles including the contaminant in the purified solvent passing through the crystals and resulting in a filtered solvent. The suspended particulates may be of

substantially the same chemical composition as the crystals, may be different chemicals, or a combination thereof.

[0073] Increasing the pH may be associated with an increase in the temperature of the alkalized contaminated solvent. At a given pH and with other relevant conditions being constant, lower temperatures may facilitate crystallization in terms of a more rapid crystallization, greater crystal strength, a crystal matrix structure providing a selected permeability or other feature for a given solvent recovery application, or other advantages. To accommodate the increase in temperature, the contaminated solvent may be cooled before or after increasing the pH. Increasing the pH of the contaminated solvent by addition of NaOH results in a temperature increase of the alkalized contaminated solvent.

[0074] Any increase in temperature resulting from addition of the NaOH or other alkaline chemical to alkalize the contaminated solvent may be accounted for to maintain the alkalized contaminated solvent at a selected crystallization temperature. The crystallization temperature may be selected to facilitate more rapid crystallization, result in increased crystal strength, a crystal matrix structure providing a selected permeability or other feature for a given solvent recovery application, or other advantages. The increase in temperature from adding the NaOH or other basic salt may be accounted for by cooling the contaminated solvent prior to adding the basic salt, in which case the end point of the temperature increase following increasing the pH of the contaminated solvent is at or close to the selected crystallization temperature. The increase in temperature resulting from adding the high-pH chemical may also be accounted for by cooling the temperature of the alkalized

contaminated solvent to the selected crystallization temperature after addition of the basic salt to the contaminated solvent. In other cases, cooling may be applied before, after, or both, with respect to lowering the pH of the contaminated solvent. Lowering the temperature of the contaminated solvent too far may result in formation of ice crystals, which may interfere with crystallization of the contaminant and may plug equipment used for fluid transfer. For example, when crystallizing Na ₂ S0 ₄ from a cyclic diamine in aqueous solution, cooling the contaminated solvent to between about 2 °C and 10 °C above the freezing point of the cyclic diamine in aqueous solution may result in a temperature of the alkalized contaminated solvent that is close to the crystallization temperature. In this example, this approach may facilitate reaching a selected crystallization temperature of about 10 °C, which may facilitate formation of Na ₂ S0 ₄ crystals from the aqueous diamine solvent.

[0075] The contaminated solvent may be dewatered prior to having the basic salt added to the contaminated solvent. Where increasing the pH of the contaminated solvent is by addition of NaOH in solution (e.g. 50% w/w NaOH, etc.), additional liquid volume is added to the contaminated solvent, increasing the amount of water in the solvent. Dewatering the contaminated solvent before raising the pH may mitigate this effect. Dewatering may also facilitate crystallization by concentrating any contaminants present in the contaminated solvent and lowering the amount of basic salt necessary to achieve a selected pH in the alkalized solvent. [0076] The filtered solvent may include components of the basic salt, the contaminant, or both. For example, where the contaminant is S0 ₄ ^"2 and the basic salt is NaOH, the filtered solvent may include dissolved Na ⁺ , entrained Na ₂ S0 ₄ , or both. Dissolved ions and the suspended particles may each be undesirable for end-use of the filtered solvent. The filtered solvent may be deionized through any appropriate method (e.g. ion exchange media, electro dialysis, graphene filtration, etc.). Particles may be removed from the recovered solvent through any appropriate method (e.g. centrifugation, a hydrocylone, filtration, ultrafiltration, filter press, gravity separation, etc.).

[0077] Tithe dissolved ions and suspended particles may be undesirable during recovery of the filtered solvent (e.g. crystals form in a saturated solution during recovery, suspended salt particles may clog a conduit and burn out a pump motor, etc.). Control over concentration of the basic salt, crystallization conditions, and recovery conditions may mitigate facilitate limits on ionic strength. Physical barriers, application of upward flow during filtering of the purified solvent, and other approaches may exclude or sequester suspended particles during recovery. Where a portion of the purified solvent is recovered after formation of the crystals without flowing the portion of the purified solvent through the crystals, the portion of the purified solvent may have a greater density of suspended solids than the filtered solvent. Techniques to remove suspended particles may be applied to the portion of the purified solvent to address any such higher levels of suspended solids.

[0078] Figs. 1 to 3 show a tank 10 for providing a reaction vessel in which a solvent may be purified by formation of crystals from the solvent, and filtered by flowing the solvent through the crystals. The tank 10 includes a body 12 defining a cavity 14 therein. The bottom of the tank 10 includes plates 16 angled to define depressions 18 at the bottom of the cavity 14. Where four plates 16 are arranged as shown in the tank 10, a "W" shaped portion of the cavity 14 is defined by the depressions 18 and the plates 16.

[0079] Heat exchanger conduits 20 are positioned to control temperature within the cavity 14. The heat exchanger conduits 20 are located behind the plates 16. The location of the heat exchanger conduits 20 facilitates controlling a local temperature of the cavity 14 at a first portion 15 of the cavity. Heat exchanger conduits may also or alternatively be located at other positions relative to the body 12 and the cavity 14 to control temperature at other portions of the cavity 14. Some examples of other heat exchanger conduit arrangements are shown in the tank 1 10 (Figs. 10 to 18), the tank 210 (Fig. 19), the tank 310 (Fig. 20), the tank

410 (Fig. 21), the tank 510 (Figs. 23 to 25), and the tank 610 (Fig. 26). Water, glycol, or any suitable heat exchange material may be circulated through the heat exchanger conduits 20 to cool or heat the cavity 14 and any fluids included therein.

[0080] Recovery conduits 22 are defined within the depressions 18 to recover fluids from the cavity 14 at the depressions 18. The recovery conduits 22 may include a filter screen or other barrier to mitigate or prevent entry of crystals or precipitate into the recovery conduits 22. Where a pump or other source of negative pressure is applied to the recovery conduits 22, crystals entering the recovery conduits may result in plugging or damage to the pump or other source of negative pressure. The barrier may include a series of closely- spaced small apertures. Apertures in the barrier may for example have a major dimension no larger than 3 diameters of the smallest suspended particle being targeted for exclusion from the recovery conduits 22. The crystals may bridge the slots and be excluded from the recovery conduits 22. Apertures with a higher surface area may provide greater flow rate into the recovery conduits 22 at the expense of less effective filtering of solids from a fluid flowing through the apertures. Apertures with a lower surface area may provide slower flow rate into the recovery conduits 22 and more effective filtering of solids from a fluid flowing through the apertures.

[0081] A barrier similar to a well liner used in hydrocarbon production with 1/8" slots may be applied in some applications (e.g. a Variperm well liner, etc.). In other cases, slot sizes of between about 1/8" and about 1/32" may be applied. Wider slot size may provide greater flow rate into the recovery conduits 22 at the expense of less effective filtering of solids from a fluid flowing through the apertures. Narrower slot size may provide lower flow rate into the recovery conduits 22 with the benefit of more effective filtering of solids from a fluid flowing through the apertures.

[0082] Nozzles 24 provide a rinse fluid, a dissolution fluid, or both, to the cavity 14. As with the heat exchanger conduits 20, the rinse solutions provided through the nozzles 24 may have different temperatures and compositions depending on the application. Use of the nozzles 24 to provide a rinse fluid to rinse purified solvent from crystals and use of the nozzles 24 to provide a dissolution fluid to dissolve crystals are described herein.

[0083] Fig. 4 shows the tank 10 including contaminated solvent 50.

[0084] Fig. 5 shows the tank 10 with a basic salt 52 being added to the contaminated solvent 50, resulting in an alkalized contaminated solvent 54. The basic salt 52 may include NaOH and may be added as a solution (e.g. a 50% w/w NaOH solution in water, a 10 N NaOH solution in water, etc.), in dry form, or a combination thereof. A target caustic pH may be selected to crystallize out a contaminant. The target caustic pH may be selected to be at or above the equivalence point of the contaminated solvent 50. For example, where an aqueous diamine solvent with an equivalence point of about 9.0 is used and an oxidized sulphur-containing anion is present in the contaminant to be removed from the alkalized contaminated solvent 54, a target caustic pH above about 9 may be selected, such as 9.0, 9.5, 10.0, 10.5, 1 1.0, 1 1.5, 12.0, 12.5, 13.0, 13.5, any other pH value in the range of 9.0 to 13.5, or any suitable pH value. The target caustic pH may result in separation of an organic phase and a salt saturated aqueous phase within the alkalized contaminated solvent 54. The separate organic and salt saturated aqueous phases are not shown in the figures.

[0085] Fig. 6 shows formation of crystals 56 from the alkalized contaminated solvent

54, leaving behind a purified solvent 58. The crystals 56 include at least one ion from the basic salt 52. The crystals 56 may have a high entrainment of both the contaminant component and the solvent component of the alkalized contaminated solvent 54.

Crystallization may be facilitated by lowering the temperature in the cavity 14 at the first location 15. The temperature in the cavity 14 may be lowered by circulation of water, glycol, or other coolant through the heat exchanger conduits 20. The first location 15 is substantially coextensive with the heat exchanger tubes 20 behind the plates. The lowered temperature at the first location 15 and the plates 16 provide a crystallization location in the tank 10. The coolant may be circulated through the heat exchanger conduits 20 to cool the contaminated solvent 50 before addition of the basic salt 52 to the contaminated solvent 50. The coolant may be circulated through the heat exchanger conduits 20 to cool the alkalized contaminated solvent 54 after addition of the basic salt 52 to the contaminated solvent 50. The coolant may be circulated through the heat exchanger conduits 20 to cool the contaminated solvent 50 before addition of the basic salt 52 to the contaminated solvent 50 and to cool the alkalized contaminated solvent 54. In either case, the temperature of the alkalized contaminated solvent 54 may be controlled to be at a crystallization temperature selected for crystallization of a particular contaminant from a particular solvent.

[0086] In some applications, water at 4 °C may be circulated through the heat exchanger conduits 20 to cool the alkalized contaminated solvent 54. The lowered temperature accelerates growth of the crystals 56. Crystallization, which goes through a colloidal intermediate, provides a structure with good permeability for filtering the

contaminated solvent 50. Rapid or gradual precipitation of a compound including the ions from the basic salt 52 and from the contaminated solvent 50 found in the crystals 56 from alkalized contaminated solvent 54 may not provide the same permeability as a crystal structure.

[0087] When the pH is elevated by dissolution of NaOH, the temperature of the alkalized contaminated solvent 54 increases. The increase in temperature may inhibit crystallization of a sodium salt of the contaminant. Onset of crystallization may be at a temperature of between 14 and 27 °C (e.g. when crystallizing Na ₂ S0 ₄ , etc.), depending on conditions. In some cases, addition of NaOH results in an increase in the temperature of the alkalized contaminated solvent 54 from an ambient temperature to between about 23 and 33 °C. Circulation of coolant through the heat exchanger conduits 20 may precede or follow addition of NaOH or other salt to the contaminated solvent 54. Circulation of coolant through the heat exchanger conduits 20 or otherwise cooling the cavity 14 may facilitate

crystallization by accelerating crystallization, forming stronger crystals 56, or both. In cases where organic and aqueous phases are present in the contaminated solvent 50, cooling the cavity 14 may also result in faster separation, more complete separation, or both, of an organic phase from the contaminated solvent 50 (e.g. when using a cyclic diamine-based solvent including an aqueous component, etc.).

[0088] The heat exchanger conduits 20 define the crystallization location. The crystallization location may also be defined by materials and surface features used at the crystallization location. Rough or scored conductive material could be provided at the selected crystallization locations, which may overlap with the first portion 15 and the heat exchanger conduits 20. Material that is smooth to inhibit crystallization, which insulates heat transfer, or both, could be provided where crystallization is not desired, such as on the walls of the tank 10. Combined with cooling, rough textures, or both, in selected locations, crystal growth could be directed in terms of location both by facilitating cooling at the first portion 15 of the cavity 14 and by mitigating cooling at a second portion of the cavity 14, such as near an inside surface of a wall of the tank 10. Surface area provided for crystal formation can also be leveraged on a tank including a heat exchanger conduit (e.g. the tanks 110, 210, 310, 410, 510, and 610) by providing a fin tube in place of a standard pipe, or by other suitable extensions of the surface area of a heat exchange member to provide a

crystallization location.

[0089] Fig. 7 shows the tank 10 after filtration of the purified solvent 58 through the crystals 56 and recovery of the resulting filtered solvent 59 from the recovery conduits 22. The crystals 56 act as a filter and capture suspended contaminants remaining in the purified solvent 58. The contaminants remaining in the purified solvent 58 may include suspended crystals, precipitate, or both, and may include species similar to the species making up the crystals 56. The purified solvent 58 may be drawn through the crystal 56 by gravity. The purified solvent 58 may be drawn through the crystal 56 by application of negative pressure (e.g. suction from a pump, vacuum, etc.) to the purified solvent 58 to facilitate flow of the purified solvent 58 through the crystals 56 to the recovery conduits 22. The plates 16 and the "W shape of the body 12 at the bottom proximate the recovery conduits 22 together facilitate maintaining a level of liquid in the depressions 18 of the tank 10 to allow negative pressure to be applied to the liquid in the tank 10.

[0090] Drainage velocities may be primarily gravity-driven and directed in part by the location of the crystallization portions and the filter design. In the tank 10, the crystallization portions are at the first location 15, which is coextensive with the plates 16. A source of negative pressure (e.g. a vacuum line, a pump, etc.) may be in communication with the recovery conduits 22 to provide motive force to the purified solvent 58 passing through the crystals 56, and may be applied where the tank 10 is sealed from the outside atmosphere. Negative differential pressure may be induced downstream of the receiving vessel through any manner (e.g. pump, steam induction, temp differential, etc.). Applying differential pressure at a value selected to control flow rate of the purified solvent 58 through the crystals 56 may mitigate flow of mobilized crystals 56 through the recovery conduits 22, which may be caused by excessive liquid velocity. A low differential pressure may result in a higher quality separation, with a possible drawback of increasing the amount of time required to treat a batch of feedstock.

[0091] A portion of the purified solvent 58 may be decanted or otherwise recovered from the tank 10 without being filtered through the crystals 56. Recovery of the purified solvent 58 may take place prior to application of negative pressure or other driving force being applied to the purified solvent 58 to facilitate flowing the purified solvent 58 through the crystals 56. Recovery of the purified solvent 58 may also or alternatively take place while filtering the purified solvent 58 through the crystals 56. The portion of the purified solvent 58 that is recovered without filtering through the crystals 56 may have a greater suspended crystal and other particulate load than the filtered solvent 60.

[0092] Fig. 8 shows rinsing of the crystals 56 with a rinse fluid 60 from the nozzles

24. Some purified solvent 58 may remain entrained within the crystals 56. The rinse fluid 60 rinses a portion of the purified solvent 58 entrained within the crystals 56 and combines with the purified solvent 58 to provide a diluted filtered solvent 61. The diluted filtered solvent 61 is recovered at the recovery conduits 22. which includes at least a portion of the rinse fluid provided into the cavity 14 by the nozzles 24.

[0093] The rinse fluid 60 may be at a low temperature to minimize dissolution of the crystals 56 while rinsing out the purified solvent 58 entrained within the crystals 56. The amount and temperature of the rinse fluid 60 may be controlled to prevent redissolution of the crystals 56. In one example, when rinsing Na ₂ S0 ₄ crystals, the temperature of the rinse fluid 60 may be about 4 °C. In some cases, the low temperature of the rinse fluid may be selected to be sufficiently elevated to prevent any chance of crystal formation from the rinse fluid 60 itself. For example, where the rinse fluid 60 is water, keeping the temperature of the rinse water to between 2 and 4 °C may provide an effective rinse fluid for Na ₂ S0 crystals without dissolving the crystals while mitigating the chances of ice crystal formation in the rinse fluid 60.

[0094] When the pH is elevated by dissolution of NaOH in an aqueous solution, the amount of water in the purified solvent 58 increases. Water in the purified solvent can be removed downstream by any suitable method (e.g. distillation, vacuum distillation, etc.).

Similarly, the amount of Na ⁺ remaining in in the aqueous solution after crystallization may be removed downstream by any suitable method. Methods for removing dissolved Na ⁺ (e.g. distillation, vacuum distillation, etc.), methods for removing suspended crystal or precipitated Na ₂ S0 ₄ in solution (e.g. centrifugation, etc.), or both, may be applied to the filtered solvent

59.

[0095] Fig. 9 shows application of a dissolution fluid 62 from the nozzles 24 to the crystals 56. The dissolution fluid 62 dissolves the crystals 56, resulting in a salt solution 64. The salt solution 64 may be removed from the tank 10 and disposed of (e.g. deep well injection, etc.) or otherwise recovered and used as a subsequent rinse agent to minimize salt dissolution even further. The salt solution 64 may be recovered at the recovery ports 22. In one example, when dissolving Na ₂ S0 crystals, the dissolution fluid 62 may be at a temperature of between about 21 °C and 99 °C. The dissolution rinse 62 may include water. The water may include any suitable solvent, chelating agent, or other additive (e.g. Versene, Ethylenediaminetetraacetic acid [EDTA], ethylene glycol-bis^-aminoethyl ether)-N,N,N',N'- tetraacetic acid [EGTA], etc.).

[0096] In summary, the basic salt 52 is added to the tank 10 until a desired pH is reached, providing the alkalized contaminated solvent 54. The heat exchanger conduits 20 may be used to provide coolant to induce crystallization of the crystals 56 at the crystallization point along the first portion15 on the plates 16. Coolant may be applied to the heat exchanger conduit 20 before addition of the basic salt 52 to cool the contaminated solvent 50, after addition of the basic salt 52 to the contaminated solvent 50, or both. Once crystallization is complete, the purified solvent 58 is drawn through the crystals 56 and the recovery conduits 22 (including through any filters or other flow barriers therein). The crystals 56 may be rinsed with the rinse fluid 60 from the nozzles 24 to remove purified solvent 58 from the crystals 56 and recover the diluted filtered solvent 61. Once minimal residual purified solvent 58 is recovered with the diluted filtered solvent 61 , the dissolution fluid 62 may be applied to the crystals 56, dissolving the crystals 56 and providing the salt solution 64. The salt solution 64 may be circulated with additional dissolution fluid 62 until the crystals 56 are fully dissolved.

[0097] Centrifugation may also be applied to generate a filtered organic phase (not shown), provided that adequate temperature control is available. However, this approach may be limited where variable sized crystals (e.g. colloidal to well defined crystals, etc.) may cause the centrifuge to plug with solids as it is dewatered. This approach may be used where distinct crystals have formed and essentially no further transition from colloidal to crystal matrices remains. The approach using the tank 10 provides simplicity and allows formation of the crystals 56 during static residence time.

[0098] Figs. 10 to 12 show a tank 110 for providing a reaction vessel in which a solvent may be purified by formation of crystals from the solvent, and filtered by flowing the solvent through the crystals. The tank 1 10 includes the body 112 defining the cavity 114 therein. The bottom of the tank 110 includes the plates 1 16 angled to define the depressions 118 at the bottom of the cavity 114. Where four plates 1 16 are arranged as shown in the tank 1 10, a "W" shaped portion of the cavity 1 14 is defined by the depressions 118 and the plates 1 16.

[0099] The heat exchanger conduits 120 are positioned to control temperature within the cavity 114. The heat exchanger conduits 120 are located behind the plates 1 16, which are proximate the bottom of the body 1 12. The location of the heat exchanger conduits 120 facilitates controlling a local temperature of the cavity 1 14 at a first portion 115 of the cavity. An upper heat exchanger conduit 125 is located between the bottom of the body 1 12 and the nozzles 124. The upper heat exchanger conduit 125 includes a number of segments extending perpendicularly to each other inside the cavity 114. The arrangement of the segments of the upper heat exchanger conduit 125 is selected to distribute heating or cooling effects of the upper heat exchanger conduit 125 throughout the cavity 114. Water, glycol, or any suitable heat exchange material may be circulated through the heat exchanger conduits 120 and the upper heat exchanger conduit 125 to cool or heat the cavity 1 14 and any fluids included therein.

[00100] The recovery conduits 122 are defined within the depressions 118 to recover fluids from the cavity 114 at the depressions 118. The recovery conduits 22 may include a filter screen or other barrier to mitigate or prevent entry of crystals or precipitate into the recovery conduits 122 as described above with respect to the recovery conduits 22 of the tank 10. The nozzles 24 provide a rinse fluid, a dissolution fluid, or both, to the cavity 1 14 as described above with respect to the nozzle 24 of the tank 10.

[00101] Figs. 13 to 18 show the basic salt 152 added to the tank 110 until a desired pH is reached, providing the alkalized contaminated solvent 154. The heat exchanger conduits 120 may be used to provide coolant to induce crystallization of the crystals 156 at the crystallization point along the first portion 1 15 on the plates 1 16 and along the second portion 117 on the upper heat exchanger conduit 125. Coolant may be applied to the heat exchanger conduit 120 and the upper heat exchanger conduit 125 before addition of the basic salt 152 to cool the contaminated solvent 150, after addition of the basic salt 152 to the contaminated solvent 150, or both. Once crystallization is complete, the purified solvent 158 is drawn through the crystals 156 and the recovery conduits 122 (including through any filters or other flow barriers therein). The crystals 156 may be rinsed with the rinse fluid 160 from the nozzles 124 to remove purified solvent 158 from the crystals 156 and recover the diluted filtered solvent 161. Once minimal residual purified solvent 158 is recovered with the diluted filtered solvent 161 , the dissolution fluid 162 may be applied to the crystals 156, dissolving the crystals 156 and providing the salt solution 164. The salt solution 164 may be circulated with additional dissolution fluid 162 until the crystals 156 are fully dissolved.

[00102] Fig. 19 shows an exploded view of a tank 210 having an isolation cage 226. The isolation cage 226 includes a heat exchanger matrix 229 made up of heat exchanger conduits extending along the walls 211 of the tank 210 and separated from the walls 211. The heat exchanger matrix 229 provides a crystallization location extending from the heat exchanger matrix 229 toward the walls 211 and towards the interior of the cavity 214. A cage heat exchanger conduit 228 extends around the isolation cage 226 to provide additional temperature control, and may be used to increase crystallization at the crystallization location provided by the heat exchanger matrix 229. Similarly to the upper heat exchanger conduits 125 of Figs. 10 to 18, distribution of coolant throughout the cavity 214 is facilitated by the surface area of the isolation cage 226, allowing temperature control of the tank 210 more effectively than cooling or heating the entire bulk volume from the bottom of the tank 210, facilitating cooling or heating more quickly, with less energy, or both.

[00103] The isolation cage 226 may be prepared from extruded metal plates or any suitable material that provides a porous cage to be chilled when a cooling medium is pumped through the heat exchanger matrix 229, the cage heat exchanger conduit 228, or both.

Together, the cage heat exchanger conduit 228 and heat exchanger matrix 229 define the first portion 215 within the cavity 214 when the isolation cage 226 is located within the cavity 214. Crystals growing on the crystallization location provided heat exchanger matrix 229 and the cage heat exchanger conduit 228 may extend toward the first portion 215 (not shown in Fig. 19; analogous to the crystals 56 and 156 in Figs. 1 to 18).

[00104] The heat exchanger matrix 229 and the cage heat exchanger conduit 228 may be insulated on the sides facing the walls 21 1 to limit the crystallization location to a face of the heat exchanger matrix 229 and the cage heat exchanger conduit 228 extending into the interior of the cavity 214 and not towards the walls 211. Mitigating crystal growth between the isolation cage 226 and the walls 211 may mitigate formation of crystals on the walls 21 1 , which may facilitate cleaning crystals from the tank 210.

[00105] In use, the isolation cage 226 may be lowered to the bottom of the cavity 214. The heat exchanger matrix 229 and the cage heat exchanger conduit 228 would be applied and crystallization allowed to commence. Upon completion of crystal growth, the isolation cage 226 is covered with salt, and the isolation cage 226 may be raised out of the tank 210 to allow free drainage of filtered solvent (not shown; similar to the filtered solvent 58 and 158 of Figs. 1 to 18) through the crystals. The filtered solvent may then be recovered through the recovery conduits 222.

[00106] Chilled mats (not shown) may also be used to control chilling inside the tank similarly to the isolation cage 226 by localizing chilling to the mats. Glycol or another heat exchange material may be run through the mats.

[00107] A chilled filter cloth may be also be applied (not shown). The chilled filter cloth may be drawn out of the tank after crystals form on the filter cloth. As the filter cloth is drawn out of the tank, it may be rinsed of clarified solvent. The crystals could then be easily moved to a solids waste container. The chilled filter cloth may be run on a continuous belt running into and out of the tank, returning underneath the tank in an endless loop. Where the tank design has a significant length, the endless loop may allow longer operation times between having to completely clean out the tank by redissolution, which may facilitate operation with reduced water usage.

[00108] Fig. 20 shows a tank 310 having the isolation cage 326, the heat exchanger matrix 329 made up of heat exchanger conduits extending along the walls 31 1 of the tank 310 and separated from the walls 311 , and the cage heat exchanger conduit 328 extending around the isolation cage 326. The isolation cage 326 includes an inner heat exchanger conduit 327 extending across the cavity 314. The inner heat exchanger conduit 327 provides additional temperature control, and may be used to increase crystallization across the cavity 314. Similarly to the upper heat exchanger conduits 125 of Figs. 10 to 18, distribution of coolant throughout the cavity 314 is facilitated by the surface area of the isolation cage 326, including the inner heat exchanger conduit 327, the cage heat exchanger conduit 328, and the heat exchanger matrix 329, allowing temperature control of the tank 310 more effectively than cooling or heating the entire bulk volume from the bottom of the tank 310, facilitating cooling or heating more quickly, with less energy, or both.

[00109] Together, the cage heat exchanger conduit 328 and heat exchanger matrix 329 define the first portion 315 within the cavity 314 when the isolation cage 326 is located within the cavity 314. Crystals growing on the crystallization location provided heat exchanger matrix 329 and the cage heat exchanger conduit 328 may extend toward the first portion 315 (not shown in Fig. 19; analogous to the crystals 56 and 156 in Figs. 1 to 18). Similarly, the heat exchanger conduit 327 defines a second portion 317 of the cavity 314 at which temperature control is facilitated. Crystals growing on the crystallization location provided heat exchanger conduit 327 may extend toward the second portion 317.

[00110] Fig. 21 shows a tank 410 having the isolation cage 426, the heat exchanger matrix 429 made up of heat exchanger conduits extending along the walls 41 1 of the tank 410 and separated from the walls 411 , and the cage heat exchanger conduit 428 extending around the isolation cage 426. The isolation cage 426 includes the inner heat exchanger conduit 427 extending across the cavity 414. The inner heat exchanger conduit 427 provides additional temperature control, and may be used to increase crystallization across the cavity

414. Similarly to the upper heat exchanger conduits 125 of Figs. 10 to 18, distribution of coolant throughout the cavity 414 is facilitated by the surface area of the isolation cage 426, including the inner heat exchanger conduit 427, the cage heat exchanger conduit 428, and the heat exchanger matrix 429, allowing temperature control of the tank 410 more effectively than cooling or heating the entire bulk volume from the bottom of the tank 410, facilitating cooling or heating more quickly, with less energy, or both.

[00111] Together, the cage heat exchanger conduit 428 and heat exchanger matrix 429 define the first portion 415 within the cavity 414 when the isolation cage 426 is located within the cavity 414. Crystals growing on the crystallization location provided heat exchanger matrix 429 and the cage heat exchanger conduit 428 may extend toward the first portion 415 (not shown in Fig. 19; analogous to the crystals 56 and 156 in Figs. 1 to 18). Similarly, the heat exchanger conduit 427 defines the second portion 417 of the cavity 414 at which temperature control is facilitated. Crystals growing on the crystallization location provided heat exchanger conduit 427 may extend toward the second portion 417.

[00112] In use, the isolation cage 426 may be lowered to the bottom of the cavity 414 with a hydraulic ram system 430. The hydraulic ram system 430 may be attached to each corner of the isolation cage 426. The heat exchanger conduit 427, the heat exchanger matrix 429, and the cage heat exchanger conduit 428 would be used to cool the first portion 415 and the second portion 417 of the cavity 414, and crystallization allowed to commence on the isolation cage 426. Upon completion of crystal growth, the isolation cage 426 would be covered with crystals, and the isolation cage 426 may be raised out of the tank 410 to allow free drainage of filtered solvent (not shown; similar to the filtered solvent 58 and 158 of Figs. 1 to 18) through the crystals. The filtered solvent may then be recovered through the recovery conduits 422.

[00113] Once above the solvent level, rinse fluid from the nozzles 424 may remove residual purified solvent entrained within the pore spaces of the crystals as described above with respect to operation of the tanks 10 and 1 10 in Figs. 8 and 17. The rinse fluid may be combined with the filtered solvent below the raised isolation cage 426 and drawn off for recovery or further processing as required. Once the isolation cage 426 is empty of the solvent, the isolation cage 426 would be lowered into the cavity 414 and dissolution fluid may be is added to dissolve the crystals for disposal. After the salt solution has been removed from the cavity 414, a fresh batch of contaminated solvent may be introduced to the tank 410.

[00114] Figs. 22 to 25 show a system 505 including a tank 510 with a body 512 that has a greater height than length or width. In that sense, the body 512 is vertically oriented and has a smaller footprint than the tank 10, which has a greater length than its height. The height compared with cross sectional area may facilitate gravity drainage and provide net positive suction head for the discharge pump 582 described below. The tank 510 facilities automated operation, combining mixing of the basic salt with the contaminated solvent, crystallization of the crystals from the alkalized contaminated solvent, filtration of the purified solvent, and removal of the salt solution as described above in Figs. 4 to 9 and 13 to 18 in a single vessel. The tank 510 may have a volume in the cavity 514 for accommodating two B- trains of contaminated solvent with freeboard space above a liquid level within the tank 510, in which case the tank would have a volume of at least about 110 m ³ .

[00115] Cooling and heating may be provided with a heat exchanger 580 or other temperature controller in communication with an external heat exchanger conduit 521 and an internal heat exchanger conduit 530 through a pair of heat exchanger cycling tubes 519. The heat exchanger 580 receives hot or cold fluids from a fluid delivery pump 581. A

temperature control system 586 is in communication with the heat exchanger 580 for providing heating or cooling heat exchange fluid to the external heat exchanger conduit 521 and internal heat exchanger conduit 530. Cooling and heating may be facilitated by simultaneous cooling or heating by both the internal heat exchanger conduit 530 and the external heat exchanger conduit 521.

[00116] The external heat exchanger conduit 521 may be coiled around the body 512. The internal heat exchanger conduit 530 extends throughout the cavity 514 to provide uniform heat exchange and facilitate uniform crystallization throughout the tank 510, extending the first portion 515 throughout a large portion of the volume of the tank 510. The internal heat exchanger conduit 530 includes first segments 532, second segments 534 at an angle to the first segments 532, and third segments 536 at angles and vertically offset from the first segments 532 and the second segments 534.

[00117] The first segments 532, the second segments 534, and the third segments 536 may be in communication with each other along the continuous heat exchanger conduit 530, providing the same heat exchange throughout the first portion 515. Alternatively, some portions of the internal heat exchanger conduit 530 may be fed by separate fluid flows from the heat exchanger 580. In such a case, the first segments 532, the second segments 534, and the third segments 536 may be grouped into heat exchange zones that may be controlled independently to provide differing heat exchange fluids through different portions of the internal heat exchanger conduit 530. [00118] A discharge pump 582 provides negative pressure to drain fluids from the tank 510 through a barrier 540 similar to the filter described above over the recovery conduits 22. The barrier 540 is a conical barrier with apertures at the bottom of the tank 510 to provide a barrier to entry of the crystals into the discharge pump 582.

[00119] A recirculation pump 584 pumps fluid into the bottom 518 of the tank 512, which enters the cavity 514 through the barrier 540. The fluid may circulate through the tank for mixing by flowing out of the tank in a lower fluid outlet 588, an upper fluid outlet 589, or both. The lower fluid outlet 588 may be applied in cases where the volume of fluid in the tank does not provide a fluid surface level at the height of the upper fluid outlet 589. A back- pressure control device may be applied between the barrier 540 and the recirculation pump 584.

[00120] A caustic feed pump 585 provides the basic salt solution to the recirculation pump 584. After a contaminated solvent is added to the tank 510, the basic salt solution may be pumped through the caustic feed pump 585 and the recirculation pump 584 into the tank 510 to provide the alkalized contaminated solvent. The recirculation pump 584 may then be applied to cycle the alkalized contaminated solvent out of the tank 510 through the lower fluid outlet 588, the upper fluid outlet 589 if the volume is sufficient, and back into the tank 510 through hate barrier 540.

[00121] A portion of the purified solvent may be recovered through the lower fluid outlet 588 may be applied in cases where the volume of fluid in the tank does not provide a fluid surface level at the height of the upper fluid outlet 589. Rinsing may be carried out through a dense crystal matrix growing from the heat exchange conduit 530.

[00122] The purified solvent may be filtered through the crystals by applying negative pressure from the discharge pump 582. The purified solvent may be drawn through the crystals and the resulting filtered solvent may be recovered from the tank 510 through the barrier 540. The rinse fluid may be provided from the nozzles 524 to rinse the crystals and recover the diluted filtered solvent.

[00123] The dissolution fluid may be provided from the nozzles 524, the fluid delivery pump 581 and the recirculation pump 584, or a combination of both. Heat may be provided into the tank 510 by the external heat exchanger conduit 521 and the internal heat exchanger conduit 530 to heat the tank 510 and any crystals and purified solvent in the cavity 514 in the first portion 515. The dissolution fluid applied through the barrier 540, the nozzles 524, or both and heating of the tank walls with the external heat exchanger 521 facilitates dissolution of the crystals into the salt solution. After the crystals are dissolved, the discharge pump 582 may be applied to pump the salt solution out of the tank 510 for deep well or other disposal.

[00124] In the vertically oriented tank 510, gravity drainage is facilitated. Gravity drainage may be applied for emptying the bulk of the filtered solvent (e.g. into a pump transfer tank, etc.) before vacuum is applied. In addition, the height of the tank 510 may facilitate gravity draining of fluids in the tank 510 to a small pump tank (not shown), which may provide liquid head to a pump downstream of the discharge pump 582 (downstream pump not shown). A level control may be applied to turn the discharge pump 582 on or off as required when draining the tank 510. In some cases, additional cooling at the bottom of the tank 510 may facilitate stronger crystals at the bottom of the tank 510. The cooling zones described above that provide independent control of cooling at different portions of the heat exchanger conduit 530 (if the heat exchanger conduit 530 were prepared from separately supplied portions) would facilitate these features.

[00125] Sample ports 583 in the tank 510 allow data of crystal growth and fluid quality to be acquired during automated operation of the system 505. Once a selected recovery condition is observed, the crystals may be rinsed with chilled water from the nozzles 524 to recover any purified solvent entrained in the crystal. Sampling of the diluted filtered solvent recovered would provide information on when to begin applying dissolution fluid from the nozzles 524.

[00126] Fig. 26 shows a tank 610 including a plurality of crystallization and recovery units 660. The crystallization and recovery units 660 are removable modules. The crystallization and recovery units 660 are in fluid communication with the tank 610 at a recovery conduit 670. The crystallization and recovery units 660 are in thermal

communication a heat exchanger (not shown; similar to the heat exchanger 580 of Fig. 22) through the heat exchanger cycling tubes 619.

[00127] Fig. 27 shows the crystallization and recovery unit 660. The crystallization and recovery unit 660 includes a body 662. A heat exchanger conduit 664 is wrapped around the body 662. The heat exchanger conduit 664 is in communication with the heat exchanger cycling tubes 619. A plurality of inlets 666 are positioned around the body 662, providing fluid communication within the body 662. An outlet 668 of the body 662 provides communication with the recovery conduit 670.

[00128] In operation, the tank 610 is provided with the contaminated solvent, which is combined with the basic salt to provide the alkalized contaminated solvent in the tank 610, or the alkalized solvent is provided to the tank 610. Cycling of the heat exchange fluid through the heat exchanger cycling tubes 619 is applied to lower the temperature proximate the heat exchanger conduit 664. The low temperatures at the heat exchanger conduit 664 facilitate crystallization within the body 612. In the absence of insulation on the heat exchanger conduit 664 facing away from the body 612, crystals may also form on the outside of the heat exchanger conduit 664.

[00129] A negative pressure source may be applied to the outlet 668 at the recovery conduit 670 to induce flow of the alkalized contaminated solvent from the cavity 614 into the inlets 666. The negative pressure source is controlled in conjunction with the heat exchanger conduit 664 to draw the alkalized contaminated solvent into the body 662 and facilitate formation of the crystals in the body 662. Once the crystals are formed inside the body 662 and on the heat exchanger conduit 664, the purified solvent may be drawn into the inlets 666 and through the crystals, resulting in the filtered solvent.

[00130] When the interior of the body 662 and the exterior of the heat exchanger conduit 664 are both covered in crystals, a rinse fluid may be drawn through the crystals inside the body 662 and on the heat exchanger conduit 664 to provide the diluted filtered solvent. Alternatively, or prior to reaching a stage where the crystals and purified solvent are ready for rinsing, one or more of the crystallization and recovery units 660 may be

disconnected from the heat exchanger cycling tubes 619 and the recovery conduit 670, then removed for rinsing and then dissolving the crystals. The crystallization and recovery unit 660 may then be replaced by a fresh crystallization and recovery unit 660, which may facilitate a continuous or staggered batch process within the tank 610. The shape of the body 612 may be hexagonal or otherwise designed to more efficiently fill the space within the tank 610 with side-by-side crystallization and recovery units 660.

[00131] Example I

[00132] Samples of an aqueous diamine solvent that had been used to scrub S0 ₂ from power plant emissions were dewatered and alkalized by addition of NaOH. Five 500 g samples of the contaminated solvent were placed in separate beakers. In each sample, the pH was adjusted to the target to the pH by addition of 50% (w/w)/19.4 N NaOH and monitoring with an electrode to provide five samples of the alkalized contaminated solvent. A cooling coil pre-chilled to 4 °C was inserted into each of the alkalized contaminated solvent samples. Temperature values were monitored over time. In all samples, colloids were observed beginning within the first hour. In all samples, crystals were observed on the chilled coils within 15 hours.

[00133] Example II

[00134] A tank with a 20 m ³ capacity having the general features of the tank 110 described above was applied to carry out a method having the general steps as shown in Figs. 9 to 18. The contaminated solvent used in these trials was the same contaminated solvent used in Example I. The basic salt was 50% (w/w)/19.4 N NaOH in water. The basic salt was mixed with the contaminated solvent under agitation and the resulting alkalized contaminated solvent was added to the tank. The rinse fluid was water chilled to 2 °C. The dissolution fluid was water heated from about 21 °C to about 99 °C.

[00135] Thirteen trials were completed, all of which resulted in filtered solvent. Data of the trials is summarized in tables 2 to 4. In tables 2 to 4:

[00136] "Feedstock V" is the volume of the contaminated solvent prior to adding the basic salt (m ³ );

[00137] "Caustic V" is the volume (m ³ ) of 50% (w/w)/19.4 N NaOH added to the contaminated solvent; [00138] "Max T" is the maximum temperature after mixing the contaminated solvent with the basic salt (°C);

[00139] "Transfer pH" is the pH of the alkalized contaminated solvent at transfer into the tank;

[00140] "Transfer T" is the temperature of the alkalized contaminated solvent at transfer into the tank (°C);

[00141] "Cryst Onset pH" is the pH of the alkalized contaminated solvent at onset of crystallization;

[00142] "Avg Cryst T" is the average temperature of the alkalized contaminated solvent from the onset of crystallization until the onset of rinsing (°C); and

[00143] "Min Cryst T" is the minimum observed temperature of the alkalized contaminated solvent during crystallization (°C).

[00144] Not all of the above data is available for each of the 13 trials.

Table 2: Datasets 1 to 5 of Example II

6 7 8 9 10

Caustic V (m ³ ) 1.62 2.43 2.43 1.89 1.52

Max T (°C) 23.8 25.2 32.6 29 24.7

Transfer pH - 13.40 13.40 10.71 13.20

Transfer T (°C) - 25.2 - 25 -

Cryst Onset pH - - - - -

Avg Cryst T (°C) 16.0 - - 21.22 -

Min Cryst T (°C) 62 6.3 - 5.0 5.4

Table 4: Datasets 11 to 13 of Example II

[00145] In addition to the above data, the following data is available for some datasets. In dataset 3, the contaminated solvent was dewatered prior to being recovered. The temperature of the alkalized contaminated solvent at the onset of crystallization was also measured in dataset 3 at 27.7 °C. In dataset 8, the time from transferring the alkalized contaminated solvent into the tank until the onset of crystallization was recorded at 27.6 hours. In dataset 10, the temperature of the purified solvent when filtration and recovery began was measured at 5.4 °C. [00146] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details are not required.

[00147] The above-described embodiments are intended to be examples only.

Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.