TITLE: USE OF GELS FOR ADSORPTION OF NAPHTHENIC ACIDS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of priority from copending U.S. provisional application no. 62/575,641 filed on October 23, 2017, the contents of which are incorporated herein by reference in their entirety.

FIELD

[0002] The present application relates to methods for removing naphthenic acids from an aqueous solution such as oil sands process water.

BACKGROUND

[0003] Oil sands bitumen extraction processes produce water that is contaminated with a class of chemicals known as naphthenic acids (NAs), which may be toxic to mammals, fish, insects and/or bacteria. In addition, naphthenic acid contaminated oil sands process water (OSPW) may not be reused as the presence of naphthenic acids may, for example, decrease extraction efficiency upon further use and/or corrode the equipment such as refinery units and/or pipelines. Therefore technologies to remove naphthenic acids from contaminated oils sands process water (sometimes referred to as water polishing) are desirable.

[0004] Naphthenic acids have the general formula C _n H2n+z02, wherein n is the number of carbons, and z is the hydrogen deficiency. Exemplary naphthenic acid structures are shown in Scheme 1 , where R ^a is H or alkyl and the carboxylic acid functionality is optionally linked to the ring system via an alkylene functionality. For the acyclic case, z = 0 and the structure is simply R ^a -COOH. The molecular weight range for naphthenic acids is typically from 1 15-1500 amu. The main fractions have backbones with 10-16 carbon atoms but can have up to 80 carbons.

Scheme 1

Monocyclic Bicyclic Tricyclic Tetracyclic

z = 2 z = 4 z = 6 z = 8

[0005] Technologies used for the removal of naphthenic acids from oil sands process water have included the use of adsorption, membrane filtration, biological treatment, oxidation treatment and coagulation/flocculation. For adsorption, adsorbents such as activated carbon, clays, carbonaceous materials, peat, walnut media, as well as synthetic polymers and polymer composites have been used.

[0006] Current technologies for removal of naphthenic acids are not 100% effective on their own. Complete and efficient removal of naphthenic acids from contaminated water will likely involve a combination of different technologies.

[0007] Debnath et al. ¹ disclose the use of dipeptide-based organogelators for adsorbing dyes such as crystal violet and rhodamine 6G. Okesola and Smith ² review supramolecular gels formed by self-assembling low molecular weight building blocks as materials for environmental remediation including the use of certain gels for immobilization of oil spills by selective gelling of the oil-phase. Ran et al. ³ disclose removal of toxic dyes from aqueous solution using low molecularweight organogelator N-(3,4,5-tributoxyphenyl)-N'- 4-[(4-hydroxyphenyl)azophenyl] benzohydrazide. US Patent Application Publication No. 2012/0136074 discloses the use of certain low molecularweight gelators to form gels that can comprise a crude oil and/or a petroleum product. US Patent Application No. 2013/0153508 discloses that its phase selective gelation processes (which include the use of alkylated aromatic acid organogelators) have a number of applications which can include environmental remediation processes such as remediation of oil spills.

[0008] US Patent No. 9,017,701 discloses organogels comprising an alkylated benzimidazolone organogelator compound and an organic liquid. US Patent No. 9,067,878 discloses organogels comprising an alkylated aromatic acid organogelator compound and an organic liquid. US Patent No. 9,623,345 discloses a process which comprises mixing an alkylated aromatic acid with a mixture comprising a first liquid and a second liquid, thereby causing formation of an organogel comprising the alkylated aromatic acid and the first liquid.

[0009] Although a significant number of such organogelator compounds are known, the rational design and synthesis of new organogelators for specific liquids of interest for commercial applications remains a significant challenge.

SUMMARY

[0010] Aerogels prepared from organogels comprising the low molecular weight organogelator 5-(2'-decyltetradecanamido)isophthalic acid were used as adsorbents for the removal of the model naphthenic acid 4-cyclohexane butyric acid (4CBA) from aqueous solutions. The naphthenic acid-loaded gels were analyzed and it was found that 39-90% of the 4CBA was removed. Such gels may therefore be useful, for example, as adsorbents for the removal of naphthenic acids from wastewater such as oils sands process water.

[0011] Accordingly, the present application includes a method for removing naphthenic acids from an aqueous solution comprising the naphthenic acids, the method comprising:

(a) contacting the aqueous solution with a gel to adsorb the naphthenic acids and obtain a naphthenic acid-loaded gel; and optionally

(b) separating the naphthenic acid-loaded gel from the aqueous solution.

[0012] In an embodiment, the gel comprises a compound of Formula I:

wherein

R ¹ and R ² are each independently COOR ⁴ ; R ³ is Cio-3oalkyl; and

R ⁴ is H or Ci- alkyl.

[0013] Otherfeatures and advantages of the present application will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating embodiments of the application are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present application will now be described in greater detail with reference to the drawings in which:

[0015] Figure 1 is a schematic of a method for removing naphthenic acids from an aqueous solution according to exemplary embodiments of the application.

[0016] Figure 2 shows digital photographs of an organogel comprising 5- (2'-decyltetradecanamido)isophthalic acid (ISA24) in cyclohexane (left, 2 wt %) and a freeze-dried gel prepared from the ISA24 in cyclohexane organogel (right, 2 wt %) according to exemplary embodiments of the application.

[0017] Figure 3 is a scanning electron microscopy (SEM) image of a freeze-dried gel prepared from an ISA24 in cyclohexane organogel (2 wt %) according to an exemplary embodiment of the application. Scale bar shows 50.0 μΐη.

DETAILED DESCRIPTION

I. Definitions

[0018] Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the present application herein described for which they are suitable as would be understood by a person skilled in the art.

[0019] In understanding the scope of the present application, the term "comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives. The term "consisting" and its derivatives, as used herein, are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The term "consisting essentially of", as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and/or steps as well as those that do not materially affect the basic and novel characteristic(s) of features, elements, components, groups, integers, and/or steps.

[0020] Terms of degree such as "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

[0021] The term "and/or" as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that "at least one of" or "one or more" of the listed items is used or present.

[0022] As used in this application, the singular forms "a", "an" and "the" include plural references unless the content clearly dictates otherwise. For example, an embodiment including "a compound" should be understood to present certain aspects with one compound or two or more additional compounds. In embodiments comprising an "additional" or "second" component, such as an additional or second compound, the second component as used herein is chemically different from the other components or first component. A "third" component is different from the other, first, and second components, and further enumerated or "additional" components are similarly different. [0023] The term "suitable" as used herein means that the selection of specific reagents or conditions will depend on the reaction being performed and the desired results, but none-the-less, can generally be made by a person skilled in the art once all relevant information is known.

[0024] The term "naphthenic acids" and the abbreviation "NAs" as used herein refer to a class of water soluble weak acids with the general formula C _n H2n+z02, wherein n is the number of carbons, and z is the hydrogen deficiency, a negative even integer representing the number of hydrogen atoms that are lost as the number of rings in the naphthenic acid increases.

[0025] The abbreviation "ISA24" as used herein refers to 5-(2'- decyltetradecanamido)isophthalic acid which has the following structure:

[0026] The abbreviation "4CBA" as used herein refers to 4-cyclohexane butyric acid, which has the following structure:

[0027] The term "organogel" as used herein refers to a semi-solid system in which an organic solvent liquid phase is immobilized within a three-dimensional network composed of self-assembled compounds of the application.

[0028] The term "aerogel" as used herein refers to a microporous solid prepared from an organogel under conditions to prevent collapse of the three- dimensional network formed by the compounds comprised therein such that the organic solvent liquid phase is replaced by a gas such as air; i.e. the network of the aerogel is substantially the same as the network in the organogel. [0029] The term "xerogel" as used herein refers to an open network solid prepared from an organogel under conditions to remove the organic solvent liquid phase, for example, by drying with unhindered shrinkage.

[0030] The term "alkyl" as used herein, whether it is used alone or as part of another group, means straight or branched chain, saturated alkyl groups. The number of carbon atoms that are possible in the referenced alkyl group are indicated by the numerical prefix "CniV. For example, the term Ci- alkyl means an alkyl group having 1 , 2, 3 or 4 carbon atoms.

[0031] The term "removing naphthenic acids from an aqueous solution comprising the naphthenic acids" as used herein in reference to the methods of the present application refers to a reduction in the total amount of naphthenic acids in the aqueous solution in comparison to the total amount of naphthenic acids in the aqueous solution prior to adsorption of the naphthenic acids by the gel. The term "reduction" in reference to the total amount of naphthenic acids in the aqueous solution includes embodiments in which the naphthenic acid- loaded gel remains in the aqueous solution (wherein the naphthenic acids are adsorbed to the gel rather than free in the aqueous solution) as well as embodiments wherein the naphthenic acid-loaded gel is separated from the aqueous solution.

II . Methods

[0032] Aerogels prepared from organogels comprising the low molecular weight organogelator 5-(2'-decyltetradecanamido)isophthalic acid were used as adsorbents for the removal of the model naphthenic acid 4-cyclohexane butyric acid (4CBA) from aqueous solutions. The naphthenic acid-loaded gels were analyzed and it was found that 39-90% of the 4CBA was removed. Such gels may therefore be useful, for example, as adsorbents for the removal of naphthenic acids from wastewater such as oils sands process water.

[0033] Accordingly, the present application includes a method for removing naphthenic acids from an aqueous solution comprising the naphthenic acids, the method comprising: (a) contacting the aqueous solution with a gel to adsorb the naphthenic acids and obtain a naphthenic acid-loaded gel; and optionally

(b) separating the naphthenic acid-loaded gel from the aqueous solution.

[0034] The gel is any suitable gel. In an embodiment, the gel comprises a compound of Formula I :

wherein

R ¹ and R ² are each independently COOR ⁴ ;

R ³ is Cio-3oalkyl; and

R ⁴ is H or Ci- alkyl.

[0035] Accordingly, the present application also includes a method for removing naphthenic acids from an aqueous solution comprising the naphthenic acids, the method comprising:

(a) contacting the aqueous solution with a gel comprising a compound of Formula I:

wherein

R ¹ and R ² are each independently COOR ⁴ ;

R ³ is Cio-3oalkyl; and

R ⁴ is H or Ci- alkyl,

to adsorb the naphthenic acids and obtain a naphthenic acid-loaded gel; and optionally

(b) separating the naphthenic acid-loaded gel from the aqueous solution. [0036] I n some embodiments, the compound of Formula I is a compound of Formula l(i):

wherein R ¹ , R ² and R ³ are as defined for the compound of Formula I .

[0037] I n some embodiments, R ¹ and R ² are each COOR ⁴ , wherein R ⁴ is Ci- alkyl. In another embodiment, R ⁴ is Ci-2alkyl. In a further embodiment, R ⁴ is methyl. In other embodiments, R ¹ and R ² are each COOH .

[0038] I n some embodiments, R ³ is selected from :

R ^5a H

j— CH |— CH

R ⁵ and R ^e ,

wherein

R ^5a and R ^5b are each independently C3- ₂ oalkyl; and

R ⁶ is Cio-2oalkyl.

_R 5a

i /

i—CH

[0039] I n some embodiments, R ³ is ^R5b , wherein R ^5a and R ^5b are each independently C3-2oalkyl.

[0040] In some embodiments, R ^5a is linear Ce-i6alkyl. In some embodiments, R ^5a is linear Cio-i alkyl. In some embodiments, R ^5a is n-dodecyl.

[0041 ] I n some embodiments, R ^5b is linear C6-i alkyl. In some embodiments, R ^5b is linear Ce-i2alkyl. In some embodiments, R ^5b is n-decyl.

H

I— CH

[0042] I n some embodiments, R ³ is ^r6 , wherein R ⁶ is Cio-2oalkyl.

(CH ₂ )i iCH ₃

I— CH

[0043] I n some embodiments, R ³ is (CH ₂ ) ₉ CH ₃ [0044] In some embodiments, the compound of Formula I is:

[0045] In some embodiments, the aqueous solution comprising naphthenic acids is wastewater. In some embodiments of the present application, the wastewater is oil sands process water (OSPW).

[0046] In an embodiment, the gel is an organogel, aerogel or xerogel.

[0047] In some embodiments, the gel comprises an organogel comprising a compound of Formula I and an organic solvent.

[0048] In some embodiments, the organogel is prepared by a method comprising heating a suspension of the compound in the organic solvent under conditions to obtain a clear solution or homogeneous dispersion, for example, under reflux conditions, cooling the clear solution or homogeneous dispersion, as the case may be, for example, to a suitable temperature (e.g. ambient temperature; i.e. about 18°C to about 25°C or about 21 °C) and allowing the cooled mixture to stand for a suitable period of time, for example, about 30 minutes to about 3 days for gelation to occur. In some embodiments, gelation has occurred if the mixture does not fall when the vessel containing it is inverted.

[0049] The organic solvent is any suitable organic solvent. For example, suitable solvents for preparing organogels comprising the compound of Formula I are disclosed in US Patent No. 9,067,878. In an embodiment, the organic solvent is selected from ethanol, 1-hexanol, ethyl acetate, chloroform, tetrahydrofuran, cyclohexane, decalin, benzene, toluene, xylenes, mesitylene, chlorobenzene, styrene, dodecane, hexadecane, paraffin oil and 1 ,2- dimethyoxy ethane. In some embodiments, the organic solvent is selected from a suitable hydrocarbon, halocarbon, alcohol, ester, ether and mixtures thereof.

[0050] In an embodiment, the hydrocarbon is a suitable linear aliphatic hydrocarbon, branched aliphatic hydrocarbon, cyclic aliphatic hydrocarbon or mixtures thereof. In another embodiment, the hydrocarbon is selected from a linear, branched or cyclic pentane or mixtures thereof; a linear, branched or cyclic hexane or mixtures thereof; a linear, branched or cyclic heptane or mixtures thereof; a linear, branched or cyclic octane or mixtures thereof; a linear, branched or cyclic nonane or mixtures thereof, a linear, branched or cyclic decane or mixtures thereof; a linear, branched or cyclic undecane or mixtures thereof; a linear, branched or cyclic dodecane or mixtures thereof; a linear, branched or cyclic tridecane or mixtures thereof; a linear, branched or cyclic tetradecane or mixtures thereof; a linear, branched or cyclic pentadecane or mixtures thereof; a linear, branched or cyclic hexadecane or mixtures thereof; a linear, branched or cyclic heptadecane or mixtures thereof; a linear, branched or cyclic octadecane or mixtures thereof; a linear, branched or cyclic nonadecane or mixtures thereof; a linear, branched or cyclic eicosane or mixtures thereof; naphthenes or mixtures thereof; and paraffin oil. In a further embodiment, the hydrocarbon is selected from n-dodecane, n-hexadecane, cyclohexane, decalin and paraffin oil. In another embodiment of the present application, the hydrocarbon is cyclohexane. In another embodiment, the hydrocarbon is an aromatic hydrocarbon. In a further embodiment, the hydrocarbon is selected from benzene, toluene, xylenes, mesitylene and styrene.

[0051] In an embodiment, the halocarbon is a suitable chlorocarbon. In another embodiment, the halocarbon is a suitable linear, branched or cyclic pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane or mixtures thereof, in which one or more hydrogen atoms has been replaced by halo. In another embodiment, halo is chloro. In a further embodiment, the halocarbon is chloroform (CHC ). In another embodiment, the halocarbon is an aromatic hydrocarbon in which one or more hydrogen atoms has been replaced by halo. In another embodiment, halo is chloro. In a further embodiment, the aromatic halocarbon is chlorobenzene.

[0052] In an embodiment, the alcohol is methanol, ethanol, propanol or a suitable linear, branched or cyclic butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol or mixtures thereof. In another embodiment, the alcohol is ethanol or 1 -hexanol.

[0053] In an embodiment, the ether is a suitable linear, branched or cyclic butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane or mixtures thereof in which one or more carbon atoms has been replaced with -0-. In another embodiment, the ether is a cyclic ether. In a further embodiment, the cyclic ether is tetrahydrofuran. In a another embodiment, the ether is 1 ,2-dimethoxyethane.

[0054] In an embodiment, the ester is a suitable linear, branched or cyclic butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane or mixtures thereof in which two consecutive carbon atoms have been replaced with a -C(0)0- moiety. In another embodiment, the ester is ethyl acetate.

[0055] In some embodiments, the compound of Formula I is present in an amount of from about 1 wt% to about 10 wt%, based on the total weight of the organogel comprising the compound of Formula I.

[0056] In some embodiments, the gel is an aerogel comprising a compound of Formula I. In some embodiments, the aerogel is prepared by a method comprising freezing an organogel comprising a compound of Formula I using liquid nitrogen then drying the frozen gel under vacuum for a time to obtain the aerogel, for example, about 1 day to about 4 days or about 3 days.

[0057] In some embodiments, about 1 g of aerogel is used per every about 1 mg to about 200 mg of naphthenic acids in the aqueous solution. In some embodiments, about 1 g of aerogel is used per every about 3 mg to about 50 mg or about 3 mg to about 30 mg of naphthenic acids in the aqueous solution.

[0058] In some embodiments, the gel is a xerogel comprising a compound of Formula I. In some embodiments, the xerogel is prepared by a method comprising drying an organogel comprising a compound of Formula I at a temperature of from about 4°C to about 30°C, about 15°C to about 25°C or about 23°C and at a pressure of from about 10 ^"5 atm to about 1 atm for a time to remove the solvent and thereby obtain the xerogel. In another embodiment of the present application, the pressure is ambient pressure (i.e. about 1 atm).

[0059] In some embodiments, at least 39 % of the naphthenic acids in the solution are adsorbed by the gel. In some embodiments, from about 39 % to about 90 % of the naphthenic acids in the solution are adsorbed by the gel.

[0060] In some embodiments, the method comprises separating the naphthenic acid-loaded gel from the aqueous solution. The means for separation can be any suitable means, the selection of which can be made by a person skilled in the art. In an embodiment, the separation comprises filtration.

[0061] In some embodiments, the method further comprises repeating steps (a) and (b) to remove a further portion of naphthenic acids from the aqueous solution comprising the naphthenic acids.

[0062] In some embodiments, the method further comprises desorbing the naphthenic acids from the naphthenic acid-loaded gel and recycling the naphthenic acid-loaded gel for further use in step (a) of the method.

[0063] In some embodiments, the method is for use in combination with an additional method for removing naphthenic acids. Additional methods for removing naphthenic acids are known and can be selected by a person skilled in the art. In some embodiments, the additional method for removing naphthenic acids comprises one or more of adsorption, membrane filtration, biological treatment, oxidation treatment and coagulation/flocculation.

[0064] The following non-limiting examples are illustrative of the present application:

EXAMPLES

Example 1 : Gel Adsorbents for the Removal of Naphthenic Acids from Contaminated Water

I. Materials and Methods

[0065] ISA24 was prepared as described in US Patent No. 9,067,878. (a) Procedure for preparation of ISA24 organogels

[0066] Cyclohexane (10 mL) was added to a carefully weighed amount of ISA24 gelator powder (199.3 mg, 2 wt %) in a sealed vessel and sonicated until a fine suspension was achieved. The suspension was then heated to reflux until a clear solution was obtained. The mixture was then allowed to slowly cool to 21 °C and allowed to stand for 48 h to allow gelation to occur. The mixture was confirmed to be a gel as the mixture did not fall when the vessel was turned upside down.

(b) General procedure for preparation of freeze-dried gels (aerogels)

[0067] A gel sample was immersed in liquid nitrogen for 30 min. The frozen gel was then freeze-dried in vacuo for 3 days to give a dried gel sample as a monolith solid.

(c) General procedure for preparation of xerogsels

[0068] The solvent from a gel sample is evaporated in air at 23°C and 1 atm or at 23°C and between 10 ^"5 to 1 atm to give a xerogel solid.

(d) Model Naphthenic Acid Adsorption Analysis. Adsorption of 4- Cyclohexane butyric acid by ISA24 aerogels (freeze-dried) gels.

[0069] 4-cyclohexane butyric acid (4CBA, 0.1 16 mg, 0.681 mmol) was dissolved in 0.1 M aqueous NaOH (10 mL). The pH was adjusted to about 8 with 0.1 M HCI (16 mL) and then diluted 50-fold to give 0.75 μΜ 4CBA (127 Mg mL).

[0070] The desired amount of freeze-dried gel powder was carefully weighed into a vial containing 1 mL of 0.75 μΜ 4CBA. After 1 .5 h, an aliquot (100 μί) was removed by syringe for 4CBA analysis. Analysis by LCMS in negative ion mode was used to determine the amount of the 4CBA that had been removed.

II. Results and Discussion

[0071] A schematic of an exemplary method 10 for adsorption of naphthenic acids is shown in Figure 1 . In the exemplified method, an exemplary insoluble gel 12 such as an aerogel is added to naphthenic acid (NA) contaminated water 14 under conditions to result in the adsorption 16 of the NA by the gel 12 to give an insoluble naphthenic acid-loaded gel 18. The naphthenic acid loaded gel 18 is then optionally separated 20 from the water 22. Analysis of the water may then optionally be carried out by liquid chromatography-mass spectrometry (LCMS) to determine how much of the NA is remaining in solution after the adsorption.

[0072] Figure 2 shows digital photographs of an organogel prepared from 2 wt% ISA24 in cyclohexane (left) and the freeze-dried gel prepared from organogel (right). Figure 3 is a scanning electron microscopy (SEM) image of the freeze-dried gel prepared from the ISA24 organogel.

[0073] Table 1 shows the results of adsorption of the model naphthenic acid 4CBAfrom water by aerogels from the low molecular weight gelators (LMWG) ISA24 and stearamide. Adsorption was tested using varying amounts of gel (mg of gel per mL of 4CBA solution) over different lengths of time, as detailed in Table 1 . The percentage of 4CBA adsorbed was measured by LCMS.

[0074] As can be seen from the results in Table 1 , a significant amount of the model naphthenic acid 4CBA was adsorbed by aerogels comprising the LMWG ISA24 which were placed in an aqueous solution containing the 4CBA. In contrast, the aerogel comprising stearamide did not adsorb 4CBA.

[0075] Accordingly, materials such as aerogels comprising compounds such as ISA24 may be useful for the removal of naphthenic acid contaminants from water such as oil sands process water. Such materials may, for example, be inexpensive, have high surface area and porosity, tunable surface properties, have fast, effective adsorption, a high adsorption capacity and/or be facile to break down for reuse or disposal and may be of interest for water treatment in oil refineries and the petrochemical industry and/or oil sands industries.

[0076] While the present application has been described with reference to what are presently considered to be the preferred examples, it is to be understood that the application is not limited to the disclosed examples. To the contrary, the present application is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0077] All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be in∞rporated by reference in its entirety. Where a term in the present application is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.

FULL CITATIONS FOR DOCUMENTS REFERRED TO IN THE DESCRIPTION

¹ S. Debnath, A. Shome, S. Dutta and P.K. Das, "Dipeptide-Based Low- Molecular-Weight Efficient Organogelators and Their Application in Water Purification" Chem. Eur. J. 2008, 14, 6870-6881 .

² B.O. Okesola and D.K. Smith, "Applying low-molecularweight supramolecular gelators in an environmental setting - self-assembled gels as smart materials for pollutant removal" Chem. Soc. Rev. , 2016, 45, 4226-4251 .

³ X. Ran, Y. Li, Q. Gao, W. Qiu and L. Guo, "A Smart Phase-Selective Gelator for Recycling Aromatic Solvents, the Removal of Toxic Dyes, and Molecular Delivery" Asian J. Org. Chem. 2017, 6, 95-101 .

Table 1

a Freeze-dried gel formed from ISA24 in cyclohexanes (2 wt %). ^b Freeze-dried gel formed from stearamide in cyclohexanes (2 wt %).