OA18414A - Oil-free crystal growth modifiers for alumina recovery. - Google Patents

Abstract

Disclosed herein is a method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream wherein an aqueous emulsion comprising an alkyl or alkenyl succinic anhydride is added to the alumina trihydrate recovery process stream, wherein the aqueous emulsion is substantially free of mineral oils. The method provides a decrease in percentage of alumina trihydrate crystals having a volume average diameter of less than about 45 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous emulsion of an alkyl or alkenyl succinic anhydride.

Description

OIL-FREE CRYSTAL GROWTH MODIFIERS FOR ALUMINA RECOVERY

This application claims priority to pending US patent application 62/131,460 filed March 11, 2015 incorporated herein in its entirety.

BACKGROUND OFTHE INVENTION [0001] The présent invention is directed towards a method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream.

[0002] Production by the Bayer process involves the digestion of bauxite at high températures and pressures in caustic soda liquor, producing a saturated sodium aluminate solution (prégnant liquor) containing an insoluble ferruginous residue called “red mud”. In the Sinter process, bauxite is combined with lime and heated to about 1200°C prior to leaching with caustic soda liquor to generate a sodium aluminate liquor containing insoluble “sinter mud”. Mud slurries generated in the above processes are treated with flocculants to flocculate and separate the muds from the prégnant liquor by gravity settling in thickener vessels (settlers). After settling, the clarified liquor (overflow) is removed from the top of the settler. At this point, the Sinter process often requires another step wherein a desilication additive such as lime is added to the overflow liquor to remove soluble silica from the liquor. This slurry is treated with flocculants and fed to a desilication settler to remove insoluble desilication products. The liquor is then further purified in a filtration process in order to remove suspended fine solids and other impurities.

[0003] The purified prégnant liquor - an example of an alumina trihydrate recovery process stream - is then cooled and seeded with fine alumina trihydrate crystals or neutralized with CO2 gas in a précipitation process to produce alumina trihydrate as gibbsite crystals, followed by calcination to produce the final alumina product. In the Bayer process, précipitation of alumina trihydrate from supersaturated caustic aluminate solutions is the rate limiting step, taking up over half of the résidence time in an alumina refinery. Précipitation does not take place under idéal conditions because the digestion of bauxite ore in refinery “spent” liquor results in a solution supersaturated in alumina, and which also contains significant amounts of organic and inorganic impurities. Précipitation is accelerated by the use of seed alumina trihydrate crystals.

I [0004] Bayer process operators optimize précipitation to maximize yield while still obtaining high quality product having a target crystal size distribution. It is désirable to produce relatively large crystals as this facilitâtes subséquent processing steps. A large percentage of fine crystals (i.e., below 45 micrometers) are undesirable. However the presence of some fine crystals may be désirable for seeding purposes. The yield and properties of the alumina trihydrate crystals can be significantly affected by the process conditions used, such as température, résidence time, and the nature of the seed crystal used, and these conditions can vary from plant to plant.

[0005] A crystal growth modifier (CGM) can be added to the alumina trihydrate recovery process stream to impose a deliberate modification of the alumina trihydrate crystals. A modification generally used is a réduction in the proportion of fines, and therefore, an increase in the average alumina trihydrate particle size. Crystal growth modifiers can be used to control particle size and strength. Not only must product quality crystals (> 45 micrometers) be produced, but sufficient seed crystals (< 45 micrometers) are also needed to promote précipitation. Crystal growth modifiers can also enhance agglomération by combining and cementing smaller particles. Crystal growth modifiers can also suppress or control primary nucléation (génération of new particles) and secondary nucléation (génération of new particles on surfaces of existing particles). A crystal growth modifier can modify the crystal particle size distribution, allowing the user to use a lower fill température and higher seed charge. Crystal growth modifiers can also be used to affect the morphology of oxalate crystals that often co-precipitate in the alumina trihydrate précipitation circuit.

[0006] Extensive efforts hâve been invested into finding effective crystal growth modifiers and methods of their use in optimizing crystal particle size. Many crystal growth modifiers (e.g., C18-fatty acids) require the addition of an oil or secondary surfactant to aid in dispersion of the CGM into prégnant liquor. Added oil or surfactant increases the impurity load in the liquor, negatively impacting précipitation yield, and may cause discoloration of the alumina trihydrate, which is highly undesirable.

[0007] Because of the organic content of Bayer liquor (predominantly humic substances), it has a natural tendency to foam. Foaming of the liquor is aggravated by the mixing steps in the Bayer process. Foaming is especially a problem after clarification (séparation of the red mud) and during précipitation. The amount of prégnant liquor cannot be maximized in vessels partly filled with foam, and therefore maximum product throughput cannot be obtained. Foam also poses a safety hazard in that overflow can expose workers to high levels of caustic, which can cause severe chemical bums. Since foam is an insulator, réduction in foam can improve heat transfer efficiency. Réduction of foam can reduce sealing in precipitators and improve operation of alumina trihydrate classification Systems due to reduced alumina trihydrate rétention in foam.

[0008] In view of these factors, a way to economically reduce the génération of fine particles in the précipitation of alumina trihydrate is désirable. In particular, the method should provide a decrease in percentage of crystals having a volume average diameter of less than about 45 micrometers. The crystal growth modifier employed should be effective at low doses (i.e., less than about 100 milligrams per liter of prégnant liquor), and should be substantially free of ancillary oils or surfactants, thereby minimizing contamination and discoloration of the alumina trihydrate crystals. Moreover, foam génération in the method should also be minimized.

BREF DESCRIPTION OF THE INVENTION [0009] An improved method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream is provided. The method comprises adding an aqueous émulsion comprising an alkyl or alkenyl succinic anhydride to the alumina trihydrate recovery process stream, wherein the aqueous émulsion is substantially free of minerai oils (e.g., paraffinic oil, naphthenic oil) and fuel oils. The alumina trihydrate crystals are crystallized from the alumina trihydrate recovery process stream, thereby providing a decrease in percentage of alumina trihydrate crystals having a volume average diameter of less than about 45 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous émulsion of an alkyl or alkenyl succinic anhydride.

DETAILED DESCRIPTION OF THE INVENTION [0010] A method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream provides a decrease in percentage of crystals having a volume average diameter of less than 45 micrometers. The method employs a crystal growth modifier which is effective at low doses (less than 100 milligrams per liter of prégnant liquor). Advantageously, the crystal growth modifier is provided neat (100% active ingrédients) and is substantially free of ancillary oils or surfactants to minimize discoloration of the alumina trihydrate crystals. The effective amount of alkyl or alkenyl succinic anhydride is low enough to be economical and to minimize contamination of the alumina trihydrate crystals. The crystal growth modifier is added to alumina trihydrate recovery process streams as an aqueous émulsion. Moreover, foam génération in the method can be reduced with a defoamer.

[0011] The improved method of producing alumina trihydrate crystals in an alumina recovery process stream comprises: adding an aqueous émulsion comprising an alkyl or alkenyl succinic anhydride to the alumina trihydrate recovery process stream, wherein the aqueous émulsion is substantially free of minerai oils and fuel oils; and crystallizing the alumina trihydrate crystals from the alumina trihydrate recovery process stream, thereby providing a decrease in percentage of alumina trihydrate crystals having a volume average diameter of less than about 45 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous émulsion of an alkyl or alkenyl succinic anhydride collectively abbreviated herein as ASA.

[0012] The alkyl or alkenyl succinic anhydride can hâve the structure:

wherein x is from 1 to 30, and y is 2x-l or 2x+l. Within this range, x can be from 6 to 24, 12 to 24, or 14 to 20. The alkyl and alkenyl groups can be branched or unbranched. Examples of alkyl or alkenyl succinic anhydrides include tetracocenyl succinic anhydride (C-24 ASA), eicosenyl succinic anhydride (C-20 ASA), n-octadecenyl succinic anhydride, (C-18 ASA), iso-octadecenyl succinic anhydride, n-hexadecenyl succinic anhydride (C-16 ASA), dodecenyl succinic anhydride (C-12 ASA), octenyl succinic anhydride, triisobutenyl succinic anhydride, tetrapropenyl succinic anhydride, and combinations thereof. Alkyl or alkenyl succinic anhydrides can be provided as mixtures, for example mixtures of one or more of C14-ASA, C-16 ASA, C18-ASA, and C-20 ASA can be used. In some embodiments, the alkyl or alkenyl succinic anhydride is a C14-C20 alkenyl succinic anhydride.

[0013] Alkenyl succinic anhydrides are produced by the reaction of internai alkenes with maleic anhydride at températures of about 200°C. Alkyl succinic anhydride can be produced by hydrogénation of alkenyl succinic anhydrides. The internai olefins can be produced by isomerization of alpha-olefins under thermodynamic conditions, or by acid-catalyzed oligomérization of alpha-olefins (e.g., triisobutene, tetrapropene). Alkyl or alkenyl succinic anhydrides can also be produced from vegetable oils (triglycérides) having a high content of mono-unsaturated fatty acid groups, for example oleic acid groups or esters produced during estérification of fatty acid or triglycérides. These alkenyl succinic anhydrides are referred to as “maleated triglycérides”.

[0014] The aqueous émulsion is substantially free of minerai oils and fuel oils, including paraffinic oils and naphthenic oils, based on total weight of the aqueous émulsion. As used herein, “substantially free of ’ means less than about 5,4, 3, 2, 1, or 0.1 weight percent of the indicated material. In some embodiments “substantially free of ’ means that there is no measureable amount of the material. The minerai oil and fuel oil can hâve a boiling point of greater than about 93°C (200°F). Advantageously, the absence of minerai oils and fuel oils minimizes contamination and discoloration of the alumina trihydrate with organic material.

[0015] In some embodiments, the aqueous émulsion is substantially free of distillation bottoms from the production of alkyl alcohols by the oxo process (hydroformylation). The distillation bottoms are sometimes referred to as “heavy oxo fraction”. The distillation bottoms can be high boiling, and can contain a mixture of alkyl alcohols, hydroformylation reactants (olefins), as weil as ether and ester by-products.

[0016] In some embodiments, the aqueous émulsion is substantially free of surfactants. Surfactants are organic compounds that are amphiphilic, meaning they contain both hydrophobie groups (“tails”) and hydrophilic groups (“heads”). The hydrophobie groups can comprise, for example, aliphatic, branched aliphatic, or alkylaromatic hydrophobes of about 8 to about 24 carbon atoms. In some embodiments, the aqueous émulsion is substantially free of polyalkoxylated non-ionic surfactants, fatty acids, fatty acid salts, or combinations thereof. Polyalkoxylated non-ionic surfactants are composed of ethylene oxide (EO) repeat units, propylene oxide (PO) repeat units, butylène oxide (BO) repeat units, and combinations thereof. The polyalkoxylated non-ionic surfactant can be a homopolymer, a random copolymer, an altemating copolymer, a periodic copolymer, a block copolymer, a graft copolymer, or a branched copolymer of EO, PO, B O, and combinations thereof. The polyalkoxylated non-ionic surfactant can be, for example, a poly(ethylene oxide-propylene oxide) block copolymer, commercially available under the trade names PLURONIC™, SYNPERONIC™ PE, DOWFAX™, and MONOLAN™.

[0017] The polyalkoxylated non-ionic surfactant can be an ethylene oxide, propylene oxide, and butylène oxide polymers and copolymers formed with alcohol, phenolic, or amine initiators. The alcohol can be, for example, a mono-, di-, tri- or tetrol. The alcohol can be, for example, a fatty alcohol. Polyalkoxylated non-ionic surfactants of this type are commercially available under the trade name PLURAFAC™. The diol can be ethylene glycol or propylene glycol and the triol can be glycerol or trimethylol propane. Polyalkoxylated non-ionic surfactants of this type are commercially available under the trade names UKANIL™ and DOWFAX™. The tetrols can be pentaerythritol. Polyalkoxylated non-ionic surfactants based on ethylene diamine are available under the trade name TETRONICS™. In polyalkoxylated non-ionic surfactants having ethylene oxide, propylene oxide, and butylène oxide repeat units, the amount of butylène oxide is about 1 to about 40 weight percent. The polyalkoxylated non-ionic surfactant can hâve a molecular weight of the EO/PO (and optionally B O) chain of about 600 Daltons or greater, specifically about 2,000 to about 5,000 Daltons.

[0018] Fatty acids are carboxylic acids (head) having a long alkyl or alkenyl chain (tail). Most naturally occurring fatty acids hâve an even number chain of from about 4 to about 28 carbon atoms. The fatty acid can be a mixture of fatty acids having different even carbon chain lengths. For example, the fatty acid can be a mixture of Ce, Ce, Cio and C12 fatty acids, or it can be tall oil, which is mainly composed of oleic acid. The fatty acid can be présent as its conjugate base (e.g., as métal or ammonium carboxylate salts), which are formed in situ in the presence of alkali.

[0019] As described above, production of alumina from bauxite is done by the Bayer process, S inter process, or various combinations of the two. Production by the Bayer process involves the digestion of bauxite at high températures and pressures in a caustic soda solution to produce a caustic saturated sodium aluminate solution containing an insoluble ferruginous residue called “red mud”. A caustic sodium aluminate solution - “prégnant liquor” - is obtained after removal of the red mud, fine suspended solids and other impurities. Caustic prégnant liquor from the Bayer process is an example of an alumina trihydrate recovery process stream. Thus, in some embodiments, the alumina trihydrate recovery process stream is a caustic Bayer process stream. Alumina trihydrate crystals are precipitated from the resulting caustic sodium aluminate solution (prégnant liquor). Thus, in some embodiments, the aqueous émulsion of alkyl or alkenyl succinic anhydride is added after red mud séparation and prior to isolation of alumina trihydrate crystals.

[0020] Alkyl or alkenyl succinic anhydrides are crystal growth modifiers (CGM) which can be added to alumina trihydrate recovery process streams to modify alumina trihydrate crystals. Crystal growth modifiers can be used to control particle size and strength. A modification generally used is a réduction in the proportion of fines, and therefore, an increase in the average alumina trihydrate particle size. An overall increase in average alumina trihydrate crystal size is désirable as it reduces energy consumption and makes the process more economical. For example, an increase in alumina trihydrate crystal size can facilitate isolation of the crystals from the alumina trihydrate recovery process stream. Volume average diameters of less than about 45 micrometers and less than about 20 micrometers are useful parameters. Advantageously, the method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream provides a decrease in percentage of alumina trihydrate crystals having a volume average diameter of less than about 45 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous émulsion of an alkyl or alkenyl succinic anhydride. The method can also provide a decrease in percentage of alumina trihydrate crystals having a volume average diameter of less than 20 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous émulsion of an alkyl or alkenyl succinic anhydride.

[0021] Alkyl or alkenyl succinic anhydrides can be added to the alumina trihydrate recovery process stream as an aqueous émulsion. The aqueous émulsion can be an oil-in-water émulsion, where the oil in this case is the active ingrédient (i.e., an alkyl or alkenyl succinic anhydride). Advantageously, the aqueous émulsion can be formed in the absence of minerai oil and fuel oil as co-solvents or diluents, thereby minimizing organic contamination of the alumina trihydrate crystals. In some embodiments, alkyl or alkenyl succinic anhydride droplets in the aqueous émulsion hâve a volume average particle diameter of about 1 to about 100 micrometers ('pm'), about 1 to about 50 pm, or about 10 to about 50 pm.

[0022] In some embodiments, the aqueous émulsion is prepared with a high shear mixer. For example, on a laboratory scale, the aqueous émulsion can be prepared using a Polytron PT2100 homogenizer, equipped with a 12-millimeter aggregate stirring shaft and operating at 11,000,19,000, and 26,000 révolutions per minute ('rpm').

[0023] Aqueous émulsions of alkyl or alkenyl succinic anhydride can be prepared at convenient concentrations. For example, the amount of alkyl or alkenyl succinic anhydride can be from about 0.1 to about 25 grams per 100 milliliters, or about 1 to about 10 grams per 100 milliliters. Thus in some embodiments, the aqueous émulsion comprises from about 0.1 to about 20 grams per 100 milliliters of alkyl or alkenyl succinic anhydride.

[0024] The aqueous émulsion of alkyl or alkenyl succinic anhydride can be added to an alumina trihydrate recovery process stream in an amount effective to decrease the percentage of alumina trihydrate crystals having a volume average diameter of less than about 45 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous émulsion of an alkyl or alkenyl succinic anhydride. Advantageously, the effective amount of alkyl or alkenyl succinic anhydride is small enough to be economical and minimize contamination of the alumina trihydrate crystals.

[0025] As used herein, the amount of alkyl or alkenyl succinic anhydride added to the alumina trihydrate recovery process stream is defined as the dose, which is expressed in units of milligrams alkyl or alkenyl succinic anhydride per liter of alumina trihydrate recovery process stream. The alkyl or alkenyl succinic anhydride can be added at a dose of from about 0.1 to about 100 milligrams per liter of alumina trihydrate recovery process stream, from about 1 to about 50 milligrams per liter of alumina trihydrate recovery process stream, or from about 2 to about 20 milligrams per liter of alumina trihydrate recovery process stream.

[0026] Advantageously, the alkyl or alkenyl succinic anhydride provides the bénéficiai effect of increasing average alumina trihydrate particle size without adversely affecting the yield of alumina trihydrate crystals. The alkyl or alkenyl succinic anhydride can hâve its greatest effect in the early stages of précipitation of alumina trihydrate crystals form the alumina trihydrate recovery process stream. Thus in some embodiments, the alumina trihydrate yield after about 5 hours crystallizing time is not decreased by addition of the aqueous émulsion to the alumina trihydrate recovery process stream. Total crystallizing time in the Bayer process can be greater than 24 hours in a refînery.

[0027] Foam can occur in the crystallizing step in alumina trihydrate production, wherein the alumina trihydrate recovery process stream is agitated. Foam is a stable dispersion of air in a liquid (here, a stable dispersion of air in the alumina trihydrate recovery process stream).

Foam is generated by the introduction of air into the alumina trihydrate recovery process stream by agitation. The bubbles produced tend to assume a spherical shape, and since they are lighter than the liquid phase, rise to the liquid-air interface. Foam reduces the effective volume of crystallizing vessels by occupying head space above the liquid. Foam can also interfère with liquid transfer operations (e.g., pumping).

[0028] Defoamers can be added to the alumina trihydrate recovery process stream to reduce the formation of foam. Suitable defoamers include polypropylene oxide (also known as polypropylene glycol), polypropylene oxide mono-Cl-C6 alkyl ethers (also known as polypropylene glycol mono-Cl-C6 alkyl ethers), polyethylene oxide (also known as polyethylene glycol), polyethylene oxide mono-Cl-C6 alkyl ethers (also known as polyethylene glycol mono-Cl-C6 alkyl ethers), polysiloxanes, organic-modified polysiloxanes, hydrophobie silica particles, distillation bottoms from the oxo process, or combinations thereof. The defoamer can be added to the alumina trihydrate recovery process stream together with the alkyl or alkenyl succinic anhydride.

[0029] The defoamer can be combined with the alkyl or alkenyl succinic anhydride in the aqueous émulsion. Thus, in some embodiments, the aqueous émulsion further comprises a defoamer chosen from polypropylene oxide, polypropylene oxide mono-Cl-C6 alkyl ethers, polyethylene oxide, polyethylene oxide mono-Cl-C6 alkyl ethers, polysiloxanes, organicmodified polysiloxanes, hydrophobie silica particles, distillation bottoms from the oxo process, or combinations thereof. While the alkyl or alkenyl succinic anhydride can be added in an amount effective to increase the average size of the alumina trihydrate crystals, the defoamer can be added in an amount effective to reduce foam in the aqueous émulsion and/or alumina trihydrate recovery process stream. In some embodiments, the weight ratio of the alkyl or alkenyl succinic anhydride to defoamer is from about 100:1 to about 1:1. Within this range, the weight ratio of alkyl or alkenyl succinic anhydride to defoamer can be from about 20:1 to about 1:1, about 10:1 to about 1:1, about 5:1 to about 1:1, or about 3:1 to about 1:1.

[0030] The method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream provides a decrease in percentage of crystals having a volume average diameter of less than about 45 micrometers. The method employs a crystal growth modifier which is effective at low doses (i.e., less than about 100 milligrams per liter of prégnant liquor). Advantageously, the crystal growth modifier is provided neat (100% active ingrédients) and is substantially free of ancillary oils or surfactants to minimize discoloration of the alumina trihydrate crystals. The effective amount of alkyl or alkenyl succinic anhydride is low enough to be economical and to minimize contamination of the alumina trihydrate crystals. The crystal growth modifier can be added to alumina trihydrate recovery process streams as an aqueous émulsion. Moreover, foam in the alumina trihydrate recovery process stream can be reduced with a defoamer.

[0031] This invention includes at least the following embodiments.

[0032] In general, the présent invention is directed towards a method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream. This method includes the steps of adding an aqueous émulsion comprising alkyl or alkenyl succinic anhydride to the alumina trihydrate recovery process stream, wherein the aqueous émulsion is substantially free of minerai oils (e.g., paraffinic oil, naphthenic oil) and fuel oils; and crystallizing the alumina trihydrate crystals from the alumina trihydrate recovery process stream. This provides a decrease in the percentage of alumina trihydrate crystals having a volume average diameter of less than about 45 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous émulsion of alkyl or alkenyl succinic anhydride.

[0033] In one embodiment, the aqueous émulsion is substantially free of surfactants.

[0034] In another embodiment, the aqueous émulsion is substantially free of polyalkoxylated non-ionic surfactants, fatty acids, fatty acid salts, and a combination thereof.

[0035] In one embodiment, the aqueous émulsion has a volume average particle diameter of about 1 to about 100 micrometers. Preferably, the aqueous émulsion has a volume average particle diameter of about 1 to about 50 micrometers. In another embodiment, the aqueous émulsion has a volume average particle diameter of about 10 to about 50 micrometers.

[0036] In one embodiment, the alkyl or alkenyl succinic anhydride used in the method described above has the structure:

O wherein x is from 1 to 30, and y is 2x-l or 2x+l.

[0037] In one embodiment, the alkyl or alkenyl succinic anhydride is a C14-C24 alkenyl succinic anhydride.

[0038] In one embodiment, the aqueous émulsion is substantially free of distillation bottoms from the oxo process (hydroformylation).

[0039] The aqueous émulsion used in the method described above can further include a defoamer. The defoamer can be polypropylene oxide, polypropylene oxide mono-Ci-Cô alkyl ethers, polyethylene oxide, polyethylene oxide mono-Ci-Cô alkyl ethers, polysiloxanes, organic-modified polysiloxanes, hydrophobie silica particles, distillation bottoms from the oxo process, or combinations thereof.

[0040] In the embodiment wherein a defoamer is added to the aqueous émulsion, the weight ratio of alkyl or alkenyl succinic anhydride to defoamer is from 100:1 to 1:1.

[0041] In one embodiment, the alumina trihydrate recovery process stream is a caustic Bayer process stream.

[0042] In one embodiment, the aqueous émulsion is added after red mud séparation and prior to isolation of alumina trihydrate crystals.

[0043] In one embodiment, the aqueous émulsion is prepared with a high shear mixer.

[0044] In one embodiment, the alkyl or alkenyl succinic anhydride is added at a dose from about 0.1 to about 100 milligrams per liter of alumina trihydrate recovery process stream.

[0045] In one embodiment, the aqueous émulsion comprises from about 1 to about 20 milligrams per 100 milliliters of alkyl or alkenyl succinic anhydride.

[0046] In one embodiment, the alumina trihydrate yield after about 5 hours crystallizing time is not decreased by addition of the aqueous émulsion to the alumina trihydrate recovery process stream.

[0047] This invention is further illustrated by the following non-limiting examples.

EXAMPLES [0048] Materials used in Examples 1-8 are described in Table 1.

Table 1 - Description of Materials Used in Examples 1-8.

Substance	Chemical Description and Source
C18-ASA	Ci8 alkenyl succinic anhydride, or dihydro-3-(octadecenyl)2,5-furandione, available from Dixie Chemicals.
C18-ASA Emulsion	5 g/100 mL C18-ASA in deionized water at pH 3.5.
C18-FA	Ci8 fatty acid, available from Arizona Chemical as SYLFAT™ FAI.
DF225	Alumina trihydrate, available from R.J. Marshall as DF225, having 60% fines (< 45 pm) (Alcoa C-31 équivalent).
Commercial Product A	Ci8 fatty acid, 15 g/100 mL in oil.
Commercial Product B	Ci8 fatty acid, 15 g/100 mL in oil.
Defoamer	Liquid, glycol ether-based defoaming reagent, available from Cytec Industries as CYBREAK™ 632.

[0049] Each test was run using spent liquor samples A or B (obtained from two different alumina plants) reconstituted to prégnant liquor by adding alumina and dissolving it at 145 °C. The prégnant liquor comprised 165 g/L ± 10 g/L alumina (A, expressed as AI2O3), 230 g/L ± lOg/L caustic soda (C, expressed as Na2CÜ3), and 320 g/L ± lOg/L total soda (S, expressed as Na2CÜ3), wherein the A/C ratio was 0.72. (A/C ratios in prégnant liquor are generally in the range of 0.68 to 0.72.) [0050] C18-ASA Emulsions were prepared by weighing out the required amounts of deionized water (adjusted to a pH of 3.5 with sulfuric acid) and C18-ASA or Cl 8-AS A and defoamer. The amounts used were calculated to give a 5 g/100 mL C18-ASA émulsion. The water was added first, and then the Cl 8-AS A. The mixture was then homogenized for 1 minute (min.) at 19,000 révolutions per minute (19k rpm) using a Polytron PT-2100 homogenizer, equipped with a 12-millimeter aggregate stirring shaft, unless otherwise stated.

[0051] Précipitation tests were performed in 250-mL NALGENE™ bottles rotated end-over15 end at approximately 15 rpm in a température controlled water bath (Thomton Engineering) at either 50°C or 70°C. In the tests, 200 mL of prégnant liquor was added to the bottles. CGM was then mixed into the prégnant liquor. Ail the bottles were tightly sealed and placed into the water bath for 15-20 minutes at 50°C or 70°C to allow the samples to corne to equilibrium. After equilibrium, the bottles were removed and charged with the designated quantity of seed alumina trihydrate and retumed to the water bath. The bottles were rotated for 5 hours (hr.) or 18 hr. at the desired température.

[0052] After précipitation of alumina trihydrate for 5 or 18 hr., the bottles were removed from the water bath one at a time, and a 15 mL sample was removed for liquor analysis. 2-3 drops of sodium gluconate solution (400 g/L) were added to this sub-sample to prevent further précipitation from the liquor. The remaining slurry sample was immediately filtered and the solids were collected by vacuum filtration, and then thoroughly washed with hot deionized water and dried at 105°C. Volume average diameter was determined on a Horiba LA 920 light scattering instrument using a laser diffraction method that is well known in the art. The effect of the CGM on particle size distribution was determined by comparing the amounts (%) of particles below 45 pm (fines) and below 20 pm (super-fines) in the precipitated product from CGM-treated prégnant liquor versus commercially available crystal growth modifier-treated prégnant liquors and untreated control prégnant liquor.

EXAMPLE 1 AND COMPARATIVE EXAMPLES 1-3 [0053] Alumina trihydrate crystal growth from prégnant liquor reconstituted from spent liquor A was evaluated in the presence of Cl 8-AS A, C18-FA, and C18-ASA émulsion at doses of 5, 10, and 15 parts per million (ppm) real each. Units of parts per million (ppm) are on a mg/L basis. 50 g/L of DF225 was added as seed crystal. Précipitation was conducted at 70°C for 5 hrs. The results are summarized in Table 2.

Table 2 - Comparative effect of ASA émulsion against ASA neat

	Crystal Growth Modifier	Dose, ppm (real)	% Fines (< 45 pm)	% Super fines (< 20 pm)
C. Ex. 1	None	0	62.1	12.3
C. Ex. 2	C18-ASA Neat	5	62.85	11.45
10	64.35	13.1
15	64.3	14.15
C. Ex. 3	C18-FANeat	5	62.05	14.35
10	63.1	15.1
15	62.8	15.2
Ex. 1	C18-ASA Emulsion	5	61.55	11.9
10	61.15	12.15
15	59.8	12

[0054] As can be seen from Table 2, adding neat CGM as in Comparative Examples 2 (neat Cl 8-AS A) and 3 (neat C18-FA) resulted in increased levels of fines (négative resuit) as compared to emulsified Cl 8-AS A, Example 1, which lowered the amount of fines (positive 5 resuit).

EXAMPLE 2 AND COMPARATIVE EXAMPLES 4-6 [0055] Alumina trihydrate crystal growth from prégnant liquor reconstituted from spent liquor A was evaluated in the presence of Commercial Product A, Commercial Product B, and C18-ASA émulsion at doses of 1.5, 3, 4.5, 6, and 7.5 ppm real each. 50 g/L of DF225 10 was added as seed crystal. Précipitation was conducted at 50°C for 5 hrs. The results are summarized in Table 3.

Table 3 - Comparative effect of ASA émulsion against ASA in oil

	Crystal Growth Modifier	Dose ppm (real)	% Fines (< 45 pm)	% Super fines (< 20 pm)	Yield (g/L)
C. Ex. 4	None	0	52.95	4.7	40.15
Ex. 2	C18-ASA Emulsion	1.5	47.7	3.05	41.20
3	42.95	2.3	40.83
4.5	42.05	2.3	41.26
6	39.4	2.15	41.27
7.5	38.3	1.9	40.76
C. Ex. 5	Commercial Product A	1.5	51.45	3.55	40.03
3	48.65	3.2	39.99
4.5	46.8	2.85	39.97
6	41.75	2.25	40.03
7.5	38	1.85	40.46
C. Ex. 6	Commercial Product B	1.5	48.75	3.2	37.94
3	43.1	2.3	38.28
4.5	39.7	2	37.44
6	37.9	1.85	37.99
7.5	38.45	1.85	38.19

[0056] Yield was calculated from the différence in the A/C values before and after précipitation, multiplied by C after précipitation:

Yield — (ΔΑ/C) — ([A/C]initial-[A/C]fînal) X Cfmal [0057] As can be seen from Table 3, Cl 8-AS A Emulsion can hâve a positive effect on yield, while Commercial Products A and B tend to decrease yield. These data demonstrate that on a real or active component basis, C18-ASA Emulsion performance is equal or better than commercial CGM’s. An advantage of Cl 8-AS A is its much higher solids content (neat), and 10 thus lower dosage requîrements, than Commercial Products A and B, having only 15 g/100 mLCGM.

EXAMPLES 3-5 AND COMPARATIVE EXAMPLE 7 [0058] Alumina trihydrate crystal growth from prégnant liquor reconstituted from spent liquor A was evaluated in the presence of a C18-ASA/defoamer émulsion at the Cl 8-AS A 15 doses indicated in Table 4 below. C18-ASA and defoamer (CYBREAK™ 632) in a 90:10 weight ratio were emulsified in deionized water adjusted to pH 3.5 with sulfuric acid to give an émulsion having 5 g/100 mL C18-ASA and 0.56 g/100 mL defoamer. Emulsification conditions are provided in Table 4. 50 g/L of DF225 was added to the prégnant liquor as seed crystal, and précipitation was conducted at 50 °C for 18 hrs. The results are summarized in Table 4.

Table 4 - Effect of Defoamer on AS A Emulsion performance.

	Emulsification Conditions	Volume Avg. Particle Diam. of Emulsion (gm)	C-18ASA Dose (ppm real)	% Fines <45 pm	% Super Fines < 20 pm
C. Ex. 7	None	-	0	50.15	1.25
Ex. 3	1 lk rpm, 1 min.	48.8	2.7	46.25	1.1
5.4	44.7	1
8.1	34.9	0.85
Ex. 4	19k rpm, 1 min.	29.4	2.7	34.05	0.8
5.4	34.6	0.9
8.1	41.6	0.95
Ex. 5	26k rpm, 1 min.	14.4	2.7	42.2	0.95
5.4	42.75	0.95
8.1	35.75	0.8

[0059] These data show that C18-ASA/defoamer émulsions with émulsion droplet sizes in the range of about 14 to 50 micrometers (volume average particle diameter) are effective in reducing the percentage of fines compared to untreated prégnant liquor.

EXAMPLES 6-8 AND COMPARATIVE EXAMPLE 8 [0060] The C18-ASA can resuit in increased foam during agitation with prégnant liquor. The effect of C18-ASA and defoamers on foam génération was evaluated in the presence of C18ASA at a dose of 3 ppm (Examples 6-8). C18-ASA was added as a 5 g/100 mL émulsion. In Example 7, C18-ASA was added in a 90:10 weight/weight mixture with defoamer (CYBREAK™ 632) to give a defoamer dose of 0.33 ppm; and in Example 8, C18-ASA was added in a 75/25 weight/weight mixture with defoamer to give a defoamer dose of 1 ppm.

[0061] Spent liquor B was reconstituted to prégnant liquor by adding alumina trihydrate and dissolving (as above). The prégnant liquor composition was also the same. 125 g/L of fine alumina trihydrate seed was added to 400 mL of hot prégnant liquor (90°C), and the resulting mixture was shook. The resulting slurry was poured into a 1-L graduated cylinder placed in a water bath at 70°C. The slurry température was allowed to equilibrate to 70°C and checked intemally with a thermometer at approximately 30 minutes. The slurry was kept in suspension by means of a magnetic stir bar placed in the bottom of the graduated cylinder. The dose of CGM/defoamer was placed on the end of a stainless steel rod and immersed into the hot slurry with agitation. CGM/defoamer blends were prepared as 5% ASA émulsions as described above. The treated slurry was then allowed to mix and corne to equilibrium for 2 min. (conditioning step). A gas dispersion tube (sparger) was then immersed in the slurry to a depth of ~1 inch from the bottom of the cylinder. Air was introduced into the prégnant liquor via the sparger, generating air bubbles in the prégnant liquor. The height of the resulting foam head was then monitored as a function of time. B y comparing the rate of foam génération of the chemically treated slurry to untreated slurry, the efficacy of the treatment to reduce foam was evaluated. The results are summarized in Table 5.

Table 5 - Effect of Defoamer

	Crystal Growth Modifier	Rate of Foam Génération (mL/s)
C. Ex. 8	None	2.23
Ex. 6	Cl 8-AS A Emulsion	2.59
Ex. 7	C18-ASA Emulsion +10% Defoamer	1.47
Ex. 8	C18-ASA Emulsion + 25% Defoamer	1.38

[0062] As can be seen from Table 5, defoamer can reduce the rate of foam generated in the presence of C18-ASA émulsion and also relative to untreated prégnant liquor.

EXAMPLES 9-17 and Comparative Examples 9 and 10 [0063] Each test was run using spent liquor obtained from an aluminum plant and reconstituted to prégnant liquor by adding alumina trihydrate to the plant spent liquor and dissolving at 145°C. Typical starting A/C ratio for the prégnant liquors used was in the range of 0.68-0.72.

[0064] The précipitation tests were performed in 250 mL Nalgene bottles rotated end-overend at ~ 15rpm in a température controlled water bath (Thomton Engineering) at 50°C. 200 mL of prégnant liquor was added to the bottles. The CGM was then dosed to the appropriate bottles and then ail the bottles were tightly sealed and placed into the water bath for 15-20 minutes to allow the samples to corne to equilibrium. After equilibrium, the bottles were removed and charged with the required quantity of seed and retumed to the water bath. The bottles were rotated 18 hrs at the stated température.

[0065] The CGM was prepared by weighing out the required amounts of deionized water (adjusted to a pH of 3.5 with sulfuric acid) and ASA or ASA/defoamer/anti-foam blend. The amounts used are calculated to give a 5% ASA émulsion. The water was added first, and then the ASA. The mixture was then homogenized for 1 minute at 19K rpm, unless otherwise stated.

[0066] After the précipitation time was complété, the bottles were removed from the water bath, one at a time, and a 15 mL sample was removed for liquor analysis. 2-3 drops of sodium gluconate solution (400g/L) was added to this sub-sample to prevent further précipitation of the liquor. The remaining slurry sample was immediately filtered and the solids were collected by vacuum filtration and then thoroughly washed with hot deionized water, finally dried at 105°C. The particle size distribution of the solids was determined on a Horiba LA 920 light scattering instrument using a laser diffraction method that is well known in the art. The effect of the CGM on the particle size distribution is determined by comparing the amount (%) of particles below 45pm (the fines) in the new CGM treated precipitated product vs. an un-dosed control sample and/or commercially available products.

[0067] Typical Prégnant liquor composition:

A: 165 g/L ± lOg/L (as AI2O3)

C: 230 g/L ± lOg/L (as Na₂CO₃)

S: 320 g/L ± lOg/L (as Na₂CO₃)

A/C: 0.72

Table 6 below describes the ASA’s used in EXAMPLES 9-17:

Product	Supplier	Composition
ASAA	Dixie, ASA 100	C16 -ASA, 3(hexadecenyl)dihydro-2,5Furandione
ASAB	Dixie, ASA 2024	C20/C24 mixture, n-eicosane succinic anhydride/ntetracosane succinic anhydride
ASAC	Electron Microscopy Sciences (EMS), DDSA	C12 ASA, dihydro-3(tetrapropenyl)-2,5-Furandione
ASAD	Aldrich	C9-ASA, (2-nonen-l-yl) succinic anhydride
ASAE	Electron Microscopy Sciences (EMS)	Mainly C9-ASA, (2-nonen-lyl) succinic anhydride
ASAF	Tokyo Chemical Ind. (TCI)	C8-ASA, dihydro-3-(octenyl)- 2,5 Furandione
AS A F	Tokyo Chemical Ind. (TCI)	C8-ASA, dihydro-3-(octenyl)- 2,5 Furandione

[0068] Conditions used for EXAMPLES 9-12 and Comparative example 9:

Température = 50°C

Précipitation time = 18h

Liquor: Reconstituted prégnant liquor using plant spent liquor A

Seed: DF225 from RJ Marshall & Co. (60% fines, Alcoa-C31 équivalent) Seed charge: 50 g/L [0069] The results for EXAMPLES 9-12 and Comparative example 9 are shown in Table 7 below.

Table 7:

Example	Crystal Growth Modifier	Dose, ppm (real)	%Fines (·45μ)	%Super fines (·20μ)
C. Ex. 9	None	0	58.28	11.41
EXAMPLE 9	C18-	1.5	56.0	10.6
	ASA	3	53.9	9.4
	Emulsion	4.5	50.2	8.1
EXAMPLE 10	ASA A Emulsion	1.5 3 4.5	51.1 50.4 52.7	8.6 8.4 8.4
EXAMPLE 11	ASA B	1.5 O	51.9 50 48.7	7.7 9.0 9.9
	Emulsion	J 4.5
EXAMPLE 12	ASAC Emulsion	1.5 3 4.5	52.3 47.9 52.9	9.6 7.9 9.6

[0070] Conditions used for EXAMPLE 13-17 and Comparative example 10:

Température = 50°C

Précipitation time=18h

Liquor: Reconstituted prégnant liquor using plant spent liquor A

Seed: DF225 from RJ Marshall & Co. (60% fines, Alcoa-C31 équivalent) Seed charge: 50 g/L [0071] The results are shown in Table 8.

Table 8:

Example	Crystal Growth Modifier	Dose, ppm (real)	%Fines (·45μ)	%Super fines (-20μ)
CEx.10	None	0	67.6	5.8
EXAMPLE	C18-	1.5	63.7	4.55
13	ASA	3	64.9	5.1
	Emulsion	4.5	61.7	4.6
EXAMPLE 14	ASAC Emulsion	1.5 3 4.5	63.8 60.6 64.8	5.4 4.5 5.5
EXAMPLE 15	ASAD Emulsion	1.5 3 4.5	68.6 70.8 64.3	6.3 7.5 5.4
EXAMPLE 16	ASAE	1.5	67.7	6.5
	Emulsion	3	65.1	5.7
		4.5	62.3	• 5.2
EXAMPLE 17	ASA F	1.5	65.7	5.6
	Emulsion	3	62.6	5.2
		4.5	62	5.0

[0072] The results shown in Tables 7 and 8 show that ASA's containing a range of 5 alkyl/alkenyl chain lengths can be used in the process of the invention.

[0073] Unless indicated otherwise, concentrations of crystal growth modifier and defoamer in émulsions and doses in prégnant liquor are expressed on a “real” basis (i.e., the concentrations reflect the amount of active ingrédient in solution). Unless indicated 10 otherwise, concentration units are on a weight/volume basis (i.e., percent (%) is on a g/100 mL basis, and parts per million (ppm) is on a mg/L basis).

[0074] The defoamers described herein can hâve both anti-foam and defoaming properties (i.e., they canprevent foam and can reduce foam that is already formed).

[0075] As used herein, the terms “a” and “an” do not dénoté a limitation of quantity, but 15 rather the presence of at least one of the referenced items. “Or” means “and/or” unless clearly indicated to the contrary by the context. Recitation of ranges of values are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, and each separate value is incorporated into this spécification as if it were individually recited. Thus each range disclosed herein constitutes a dîsclosure of any 5 sub-range falling within the disclosed range. Dîsclosure of a narrower range or more spécifie group in addition to a broader range or larger group is not a disclaimer of the broader range or larger group. Ail ranges disclosed herein are inclusive of the endpoints, and the endpoints are independentiy combinable with each other. “Comprises” as used herein includes embodiments “consisting essentially of ’ or “consisting of ’ the listed éléments.

[0076] While typical embodiments hâve been set forth for the purpose of illustration, the foregoing descriptions should not be deemed to be a limitation on the scope herein. Accordingly, various modifications, adaptations, and alternatives can occur to one skilled in the art without departing from the spirit and scope herein.

Claims (17)

1. We claim:

   1. A method of producing alumina trihydrate crystals from an alumina trihydrate recovery process stream, the method comprising:

   adding an aqueous émulsion comprising an alkyl or alkenyl succinic anhydride to the alumina trihydrate recovery process stream, wherein the aqueous émulsion is substantially free of minerai oils and fuel oils; and crystallizing the alumina trihydrate crystals from the alumina trihydrate recovery process stream, thereby providing a decrease in percentage of alumina trihydrate crystals having a volume average diameter of less than about 45 micrometers compared to the percentage of alumina trihydrate crystals produced in the absence of the aqueous émulsion of an alkyl or alkenyl succinic anhydride.
2. 2. The method according to claim 1 wherein the aqueous émulsion is substantially free of surfactants.
3. 3. The method according to claim 1 wherein the aqueous émulsion is substantially free of polyalkoxylated non-ionic surfactants, fatty acids, fatty acid salts or combinations thereof.
4. 4. The method according to claim 1 wherein the aqueous émulsion has a volume average particle diameter of about 1 to about 100 micrometers.
5. 5. The method according to claim 1 wherein the aqueous émulsion has a volume average particle diameter of about 1 to about 50 micrometers.
6. 6. The method according to claim 1 wherein the alkyl or alkenyl succinic anhydride has the structure:

   O wherein x is from 1 to 30, and y is 2x-l or 2x+l.
7. 7. The method according to claim 1 wherein the alkyl or alkenyl succinic anhydride is a C14C24 alkenyl succinic anhydride.
8. 8. The method according to claim 1 wherein the aqueous émulsion is substantially free of distillation bottoms from an oxo process.
9. 9. The method according to claim 1 wherein the aqueous émulsion further comprises a defoamer.
10. 10. The method according to claim 9 wherein the defoamer is chosen from polypropylene oxide, polypropylene oxide mono-Ci-Cô alkyl ethers, polyethylene oxide, polyethylene oxide mono-Ci-Cô alkyl ethers, polysiloxanes, organic-modified polysiloxanes, hydrophobie silica particles, distillation bottoms from an oxo process, or combinations thereof.
11. 11. The method according to claim 9 wherein the weight ratio of alkyl or alkenyl succinic anhydride to defoamer is from 100:1 to 1:1.
12. 12. The method according to claim 1 wherein the alumina trihydrate recovery process stream is a caustic Bayer process stream.
13. 13. The method according to claim 1 wherein the aqueous émulsion is added after red mud séparation and prior to isolation of alumina trihydrate crystals.
14. 14. The method according to claim 1 wherein the aqueous émulsion is prepared with a high shear mixer.
15. 15. The method according to claim 1 wherein the alkyl or alkenyl succinic anhydride is added at a dose of from about 0.1 to about 100 milligrams per liter of alumina trihydrate recovery process stream.
16. 16. The method according to claim 1 wherein the aqueous émulsion comprises from about 1 to about 20 milligrams per 100 milliliters of alkyl or alkenyl succinic anhydride.

    t
17. 17. The method according to claim 1 wherein alumina trihydrate yield after about 5 hours crystallizing time is not decreased by addition of the aqueous émulsion to the alumina trihydrate recovery process stream.