WO2018126175A1

WO2018126175A1 - Removal of aldehydes from solvents using reactive separation via amines

Info

Publication number: WO2018126175A1
Application number: PCT/US2017/069017
Authority: WO
Inventors: Aaron ROYER; Roy Ray Odle
Original assignee: Sabic Global Technologies B.V.
Priority date: 2016-12-30
Filing date: 2017-12-29
Publication date: 2018-07-05

Abstract

A method for purifying a crude solvent comprising an aldehyde impurity includes adding an amine, and optionally an acid catalyst, to the crude solvent to form a reaction product with the aldehyde impurity; and separating the reaction product from the crude solvent to provide a purified solvent wherein the aldehyde impurity is present in the purified solvent in an amount of less than 100 parts per million, preferably less than 75 parts per million, more preferably less than 50 parts per million, even more preferably less than 25 parts per million.

Description

REMOVAL OF ALDEHYDES FROM SOLVENTS USING

REACTIVE SEPARATION VIA AMINES

BACKGROUND

[0001] Aromatic solvents are useful for a variety of commercial chemical applications. For example, halogenated aromatic solvents have a high boiling point, provide good solubility for organic chemicals, are non-flammable, are not miscible in water, and are generally unreactive. Dichlorobenzenes such as meta- and ortho-dichlorobenzenes are colorless liquids with boiling points around 172 to 180°C. They are both insoluble in water and denser than water. Dichlorobenzenes are used across a range of industries and are used as organic solvents, in insecticides, as chemical intermediates, in degreasing agents, in metal polishes, as odor controllers, in wood preservatives, in lubricants, in paints, as coolants, as dielectric fluids, and in motor oils.

[0002] Aromatic solvents such as dichlorobenzenes are often used as a solvent in the synthesis of polymers. For example, dichlorobenzenes are used as solvents for the preparation of polyetherimides and polycarbonates. These solvents must be exceptionally free of impurities, and in particular colored impurities, otherwise the synthesized polymers will have undesirable color characteristics and an overall low quality appearance. These solvents must also be free of reactive impurities that could prematurely terminate the polymerization processes and result in polymers of insufficient molecular weight. The impurities can arise during the synthesis of the polymers or can be introduced from the use of contaminated reagents. Due to the physical and chemical properties of the impurities, known purification and separation processes such as recrystallization, distillation, and sublimation are generally ineffective for purifying the solvents.

[0003] There has been an active interest in overcoming the above-described technical limitations for purifying some solvents. Accordingly, there remains a need for an improved purification process for some solvents.

BRIEF DESCRIPTION

[0004] A method for purifying a crude solvent comprising an aldehyde impurity includes adding an amine, and optionally an acid catalyst, to the crude solvent to form a reaction product with the aldehyde impurity; and separating the reaction product from the crude solvent to provide a purified solvent wherein the aldehyde impurity is present in the purified solvent in an amount of less than 100, preferably less than 75, more preferably less than 50 parts per million, even more preferably less than 25 parts per million.

[0005] A purified solvent is provided by the method for purifying a crude solvent. [0006] A method for purifying a crude solvent comprising an aldehyde impurity includes adding a monoamine and an acid catalyst to the crude solvent to form a reaction product with the aldehyde impurity; and separating the reaction product from the crude solvent to provide a purified solvent wherein the aldehyde impurity is present in the purified solvent in an amount of less than 100 parts per million, preferably less than 75 parts per million, more preferably less than 50 parts per million, even more preferably less than 25 parts per million.

[0007] The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] A description of the figures, which are meant to be exemplary and not limiting, is provided in which:

[0009] FIG. 1 is a graph of concentration (M) versus time (sec) showing the change in aldehyde concentration during the course of a reaction with an amine according to an embodiment;

[0010] FIG. 2 is a graph concentration (ln[M]) versus time (sec) showing data from a first-order kinetic analysis for a reaction according to an embodiment;

[0011] FIG. 3 is a graph of concentration (ppm) versus time (min) showing the change in aldehyde concentration during the course of a reaction with an amine according to an embodiment;

[0012] FIG. 4 is a graph of concentration (ln[M]) versus time (sec) showing data from a first-order kinetic analysis for a reaction according to an embodiment; and

[0013] FIG. 5 is a graph of inverse concentration (1/[M]) versus time (sec) showing from a second-order kinetic analysis for a reaction according to an embodiment.

[0014] The above described and other features are exemplified by the following detailed description and Examples.

DETAILED DESCRIPTION

[0015] An aldehyde impurity can be difficult to remove, for example by distillation, from a high boiling point solvent. This is especially true when the solvent and the aldehyde impurity have similar boiling points. Described herein is a method for removing an aldehyde impurity from high boiling point solvents. The inventors surprisingly discovered that an aldehyde impurity could be reacted with a primary amine to form a corresponding imine, and the imine could then be removed from the solvent using physical methods. For example, an imine formed by this reaction can have a boiling point that is dissimilar to the boiling point of the solvent, such that the imine can be removed by distillation. Scheme 1 shows a general scheme for the reaction of an aldehyde (R= alkyl, aryl) with a primary amine (R'=alkyl, aryl) to form an imine with the removal of water.

Scheme 1.

[0016] The method disclosed herein provides an aromatic solvent at high purity, for example 95 to 99+%. The method further provides for the removal of an aldehyde impurity from an aromatic solvent in a solvent recovery system of a reactor, wherein the purified solvent can then be reintroduced into the reactor for further use. Use of the solvents for the synthesis of polymers such as polyetherimides can provide polymers of low color and high molecular weights.

[0017] Accordingly, a method for purifying a crude solvent comprising an aldehyde impurity can include adding an amine, and optionally an acid catalyst, to the crude solvent to form a reaction product with the aldehyde impurity. The method further includes separating the reaction product from the crude solvent to provide a purified solvent. The purified solvent has less aldehyde impurity compared to the crude solvent. The aldehyde impurity can be present in the crude solvent in amount of 50 to 8,000 parts per million (ppm), 100 to 7,500 ppm, 100 to 5,000 ppm, 250 to 5,000 ppm, 250 to 2,500 ppm, 250 to 1,500 ppm, 250 to 1,000 ppm, or 500 to 1,000 ppm.

[0018] The aldehyde impurity can be present in the purified solvent in an amount of less than 100 ppm, preferably less than 75 ppm, more preferably less than 50 ppm, even more preferably less than 25 ppm. For example, the aldehyde impurity can be present in the purified solvent in an amount of less than 90 ppm, 80 ppm, 70 ppm, 60 ppm, 40 ppm, 30 ppm, 20 ppm, 15 ppm, 10 ppm, or 5 ppm.

[0019] The crude solvent can be an aromatic solvent, for example a substituted or unsubstituted C6-C20 aromatic solvent. Non-limiting examples include benzene, toluene, ortho- xylene, meta-xylene, para-xylene, chlorobenzene, ortho-dichlorobenzene, meta-dichlorobenzene, para-dichlorobenzene, 2-chloro-l,4-dimethylbenzene, 3-chloro-l,2-dimethylbenzene, 2-chloro- 1,3-dimethylbenzene, 4-chloro-l,2-dimethylbenzene, 1,2,3-trichlorobenzene, 1,2,4- trichlorobenzene, 1,3,5-trichlorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5- trifluorobenzene, 1,2,4,5-tetrachlorobenzene, 1,2,3,5-tetrachlorobenzene, 1,2,3,4- tetrachlorobenzene, 1,2,4,5-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,3,4- tetrafluorobenzene, pentachlorobenzene, pentafluorobenzene, 2,3,4, 5,6-pentafluorotoluene hexafluorobenzene, octafluorotoluene, 2,3,5,6-tetrafluorotoluene, 2-chlorotoluene, 3- chlorotoluene, 4-chlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 3,4-dichlorotoluene, 2,3-dichlorotoluene, 2,6-dichlorotoluene, bromobenzene, 1,2-dibromobenzene, anisole, mesitylene, veratrole, phenetole, diphenylether, nitrobenzene, benzonitrile, and the like.

[0020] The crude solvent can have a boiling point of 80 to 250°C, 80 to 220°C, 80 to 210°C, 80 to 200°C, 80 to 190°C, 80 to 180°C, 80 to 170°C, 80 to 160°C, 80 to 150°C, 80 to 140°C, 80 to 130°C, 80 to 120°C, 80 to 120°C, 80 to 110°C, 80 to 100°C, or 80 to 90°C. For example, the crude solvent can have a boiling point of 90 to 250°C, 100 to 250°C, 110 to 250°C, 120 to 250°C, 130 to 250°C, 140 to 250°C, 150 to 250°C, 160 to 250°C, 160 to 250°C, 160 to 250°C, 160 to 200°C, 160 to 190°C, 170 to 190°C.

[0021] The boiling point of the aldehyde impurity and the crude solvent can be similar to each other. The difference between the boiling point of the aldehyde impurity and the boiling point of the crude solvent is less than 75°C, less than 50°C, or less than 25°C. For example, a difference between the boiling point of the aldehyde impurity and the boiling point of the crude solvent is less than 60°C, less than 55°C, less than 50°C, less than 45°C, less than 40°C, less than 35°C, less than 30°C, less than 25°C, less than 20°C, less than 15°C, less than 10°C, or less than 5°C. Without being bound to theory, the proximity of the boiling points hinders and limits the amount of the aldehyde impurity that can be removed efficiently from the crude solvent by a physical method, for example by distillation.

[0022] In an embodiment, the aldehyde impurity is one that is not substantially removed from the crude solvent by distillation. For example, the aldehyde impurity can be present in the crude solvent in an amount of 100 to 8,000 ppm, 100 to 5,000 ppm, 100 to 2,500 ppm, 100 to 2,000 ppm, or 100 to 1,000 ppm after distillation of the crude solvent.

[0023] The crude solvent includes an aldehyde impurity, which can be expressed by the formula RC(=0)H. Non-limiting examples R include a substituted or unsubstituted CMS alkyl, a substituted or unsubstituted C2-18 alkenyl, a substituted or unsubstituted C2-18 alkynyl, or a substituted or unsubstituted C₆-i8 aryl. For example, the aldehyde impurity can be dodecyl aldehyde, lauric aldehyde, tridecanal, 2-tridecenal, decanal, octanal, nonanal, undecanal, tiglic aldehyde, 2-methyl-2-butenal, 3-methyl-2-butenal, 2-methyl-2-pentenal, 2-ethyl-2-butenal, cinnamaldehyde, 2-phenyl-2-pentenal, 2-methyl-2-pentenal, or 2-[(4-methoxybenzyl)oxy]-4- pentenal, benzaldehyde, 4-(dimethylamino)benzaldehyde, 4-methylbenzaldehyde, 2-methyl-p- anisaldehyde, p-anisaldehyde, o-anisaldehyde, and the like. In a specific embodiment, the aldehyde impurity is 2-methyl-2-pentenal.

[0024] In an embodiment, the aldehyde impurity can be a dialdehyde expressed by the formula H(0=)C-Z-C(=0)H. Non-limiting examples of Z include a substituted or unsubstituted Ci-18 alkylene, a substituted or unsubstituted C3-18 cycloalkenyl, or a substituted or unsubstituted C6-18 arylene. For example, the aldehyde impurity can be glutaric dialdehyde, 2- bromoisophthalaldehyde, ortho-phthalaldehyde, 2,5-thiophenedicarboxaldehyde, 2,5- dimethoxybenzene-l,4-dicarboxaldehyde, isophthalaldehyde, terephthalaldehyde, 4-(4- formylphenoxy)benzaldehyde, and the like.

[0025] The amine can be a primary amine, for example a monoamine of the formula R¹- NH2, wherein R¹ is a monovalent organic group. For example, R¹ can be a substituted or unsubstituted Cs-40 alkyl, a substituted or unsubstituted C3-40 cycloalkyl, a substituted or unsubstituted Cs-40 alkenyl, a substituted or unsubstituted Cs-₄o alkynyl, or a substituted or unsubstituted C₆-40 aryl. For example, the amine can be octadecylamine, hexadecylamine, dodecylamine, tetradecylamine, pentadecylamine, tridecylamine, nonylamine, heptylamine, undecylamine, 3-amino-3-phenyl-l-propanol, 3-amino-l-phenyl-propan-l-ol, 4-isobutoxy- phenylamine, or N-(3-aminopropyl)-N-ethyl-N-phenylamine. In a specific embodiment, the amine is octadecylamine (oDA).

[0026] The amine can also be a primary diamine of the formula H₂N-R²-NH2, wherein R² is a divalent organic group. For example, R² is a substituted or unsubstituted C₆-20 arylene, a substituted or unsubstituted C2-20 alkylene, a substituted or unsubstituted C3-8 cycloalkylene, or a substituted or unsubstituted C3-8 cycloalkenyl. For example, the diamine can be

hexamethylenediamine, polymethylated 1,6-n-hexanediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 1,12-dodecanediamine, 1 , 18-octadecanediamine, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 4-methylnonamethylenediamine, 5-methylnonamethylenediamine, 2,5- dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 2, 2- dimethylpropylenediamine, N-methyl-bis (3-aminopropyl) amine, 3- methoxyhexamethylenediamine, l,2-bis(3-aminopropoxy) ethane, bis(3-aminopropyl) sulfide, 1,4-cyclohexanediamine, bis-(4-aminocyclohexyl) methane, m-phenylenediamine, p- phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, m-xylylenediamine, p- xylylenediamine, 2-methyl-4,6-diethyl-l,3-phenylene-diamine, 5-methyl-4,6-diethyl-l,3- phenylene-diamine, benzidine, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 1,5- diaminonaphthalene, bis(4-aminophenyl) methane, bis(2-chloro-4-amino-3,5-diethylphenyl) methane, bis(4-aminophenyl) propane, 2,4-bis(p-amino-t-butyl) toluene, bis(p-amino-t- butylphenyl) ether, bis(p-methyl-o-aminophenyl) benzene, bis(p-methyl-o-aminopentyl) benzene, 1, 3-diamino-4-isopropylbenzene, bis(4-aminophenyl) sulfide, bis-(4-aminophenyl) sulfone, or bis(4-aminophenyl) ether. Any regioisomer of the foregoing compounds can be used. Combinations of these compounds can also be used. In a specific embodiment, the amine is meta-phenylenediamine or para-phenylenediamine.

[0027] Without being bound by theory, the group R¹ and R² in the monoamine and diamine, respectively, is selected such that the imine product produced by the reaction between the amine and the aldehyde impurity has a boiling point that is sufficiently dissimilar from the boiling point of the crude solvent to allow for removal of the imine from the crude solvent. For example, the imine can be removed from the crude solvent by a physical method such as recrystallization, distillation, precipitation, sublimation, or a combination thereof.

[0028] In the method for purifying the crude solvent comprising the aldehyde impurity, the amine is added to the crude solvent to form a reaction product with the aldehyde impurity. The amount of amine that is added is determined from the amount of aldehyde impurity that is present in the crude solvent. In the method, a molar ratio of the amine to the aldehyde impurity can be 1: 1 to 10: 1, 1: 1 to 9: 1, 1: 1 to 8: 1, 1: 1 to 7: 1, 1: 1 to 6: 1, 1: 1 to 5: 1, 1: 1 to 4: 1, 1: 1 to 3: 1, or 1 : 1 to 2: 1. In a specific embodiment, the molar ratio of the amine to the aldehyde impurity is 1 : 1 to 2: 1.

[0029] The method can also include an optional acid catalyst, and in an embodiment, the acid catalyst is a carboxylic acid catalyst of the formula R³-COOH, wherein R³ is a monovalent organic group. For example, R³ can be a substituted or unsubstituted Cs-40 alkyl, a substituted or unsubstituted C3-40 cycloalkyl, a substituted or unsubstituted Cs-₄o alkenyl, a substituted or unsubstituted Cs-40 alkynyl, or a substituted or unsubstituted C₆^o aryl. Specific examples of the acid catalyst include salicylic acid, stearic acid, sorbic acid, palmitic acid, myristic acid, lauric acid, palmitoleic acid, linolenic acid, benzoic acid, 2-chlorobenzoic acid, 3-chlorobenzoic acid, 4-chlorobenzoic acid, 2-bromobenzoic acid, 3-bromobenzoic acid, 2-nitrobenzoic acid, 3- nitrobenzoic acid, 4-nitrobenzoic acid, 2-fluorobenzoic acid, 2,6-difluorobenzoic acid, diphenylacetic acid, or diaminobenzoic acid. A combination of different acids can be used. In a specific embodiment, the acid catalyst is (e.g., at least one of) stearic acid, salicylic acid, or a combination comprising at least of the foregoing.

[0030] The acid catalyst is optionally added to the crude solvent, together with the amine, to form a reaction product with the aldehyde impurity. The amount of acid catalyst that is added is determined from the amount of amine that is added. In the method, a molar ratio of the amine to the acid catalyst is 1: 1 to 20: 1, 2: 1 to 20:1, 4: 1 to 20: 1, 1: 1 to 10: 1, 2: 1 to 10: 1, 4: 1 to 10:1, 6: 1 to 10: 1, 8: 1 to 10: 1. In a specific embodiment, the molar ratio of the amine to the acid catalyst is 4: 1 to 6: 1. [0031] After the amine and the optional acid catalyst are added to the crude solvent, the combination can be heated to provide the reaction product. For example, the combination can be heated at a temperature of 30 to 150°C, 30 to 120°C, 30 to 90°C, or 30 to 60°C to provide the reaction product.

[0032] This disclosure is further illustrated by the following examples, which are non- limiting.

EXAMPLES

[0033] The materials shown in Table 1 were used in the following examples.

Table 1.

[0034] For the examples below, gas chromatography (GC) was used to determine the concentration of 2-methyl-2-pentenal (2M2P) based on external calibration standards. Calibration standards were prepared at concentrations of 1,000 ppm, 500 ppm, 100 ppm, and 50 ppm of 2M2P in oDCB. The samples were transferred from the reaction vessels to a vial for sampling. If the sample contained particulates, it was first filtered using a 0.45 micrometer

polytetrafluoroethylene (PTFE) syringe filter.

[0035] GC analysis was performed using a Thermo TR-WAX column (30 meter x 0.53 millimeter x 1 micrometer; Fisher Cat No. 03-150-143) to separate the analytes of interest. The injection volume was 1 and injections were performed with an autosampler. The injection inlet liner was a Restek #22406: Gooseneck liner (4 mm x 6.5 mm x 78.5 mm). The injector mode was a 1: 10 split and the split vent was 20 mL/min at 2.0 min. The carrier gas was He, the injector temperature 250°C, and the constant carrier gas flow was 5.0 mL/min. Signals were identified and quantified with a flame ionization detector at a temperature of 250°C, hydrogen flow rate of 40 mL/min, airflow rate of 450 mL/min, and 20 mL/min of a helium makeup gas.

[0036] The oven heating program is shown in Table 2. Total run time was 14.00 minutes

(min).

Table 2. Time (min) Rate (°C/min) Temperature (°C) Hold Time (min)

0 - 40 2.00

2.0 10 70 0.00

5.0 20 250 0.00

[0037] A first-order calibration curve was established in the data analysis software (Chemstation) using the three calibration standards (10 ppm, 50 ppm, 500 ppm). No dilution factor is required when analyzing a sample. Analysis of the 50 ppm standard was performed periodically to verify the limit of quantitation. If the check standard was less than 45 ppm or higher than 55 ppm, a new calibration was performed by GC analysis of the three calibration standards and updating the calibration curve.

[0038] Reactions were performed to determine if 2M2P could be effectively removed from oDCB by reacting 2M2P with oDA and an acid catalyst. The change in concentration for 2M2P was monitored over the course of each reaction and plotted against time to evaluate the rate at which 2M2P was removed from the oDCB. The overall reaction is shown in Scheme 2.

Scheme 2.

Example 1. Removal of Aldehyde with oDA and SA at 60°C

[0039] To a clean, oven-dried test tube (Corning Pyrex 9825-25, 55 mL capacity) were added 50 g of a 1000 ppm 2M2P oDCB stock solution, 0.0435 g of SA (0.000153 mol, 10% loading), and 0.4119 g of oDA (0.001528 mol, 3 molar equivalents). A small magnetic stir bar was added to the test tube, which was then capped and positioned upright in an oil bath at 60°C. The time at which the solution was set in the bath to heat and stir was recorded as the starting point for the reaction (t = 0 min). If any solids were stuck on the inner walls of the test tube, the cap was secured and the tube was shaken briefly.

[0040] After 15 to 30 minutes, the test tube was uncapped and a 2 mL sample was removed via plastic transfer pipet. The sample was delivered to a scintillation vial, which was then placed in a shallow, cool water bath. After the sample cooled for 2 to 3 minutes, it was syringe-filtered into an LC vial for GC analysis. If the sample could not be analyzed

immediately, it was stored in a refrigerator or freezer until ready. Samples stored overnight would continue to react and would not be representative of the solution at the time the sample was pulled. Additional samples were collected at 30-minute intervals, or as necessary. Example 2. Removal of Aldehyde with oDA and SA at 30°C

[0041] Reagents were added to a Pyrex 9825 55 mL test tube and heated to 60°C, as described for Example 1. After 5 minutes in the 60°C oil bath, the tube was quickly wiped down and transferred to a 30°C water bath. After stirring for an additional 5 minutes, a sample was removed, as described for Example 1, and the time was recorded as the starting point (t = 0 min) for the reaction. Additional samples were collected at 30-minute intervals, or as necessary.

Example 3. Other Amines and Acid Catalysts

[0042] Using methods similar to those described in Examples 1 and 2, analyses were performed using amines other than oDA (e.g., mPD) or an acid catalyst other than SA (e.g., SAA). In each case, the reagent quantities were adjusted to preserve the stoichiometric ratios as defined in Example 1. The reactions were prepared and run as previously described in Example 1 (60°C) or Example 2 (30°C).

Example 4. Comparison of oDA and mPD as Amines

[0043] oDA and mPD were compared for their ability to remove 2M2P from crude oDCB, followed by distillation of the purified oDCB. The reactions of amines with 2M2P were evaluated at 120°C using 3 molar equivalents of oDA or mPD, and the reaction time was 1 hour. The oDA was effective in reducing the concentration 2M2P in the oDCB from 160 ppm to an effective non-detect level of less than 10 ppm. In contrast, mPD was not effective under these conditions.

Example 5. Removal of Aldehyde with oDA and SA at 60°C

[0044] The reactivity of 2M2P with oDA in the presence of SA was evaluated and the kinetics of imine formation in oDCB was determined. FIG. 1 shows the decrease in the concentration of 2M2P over the course of reaction with oDA. For each reaction plotted in FIG. 1, the reaction followed the method of Example 1 and each was performed at 60°C using 2M2P, 2 molar equivalents of oDA, and 10 mole-percent (mol%) of SA (based on the number of moles of oDA). As seen in FIG. 1, oDA effectively reacted with 2M2P to completion, including in water-saturated oDCB. In view of the results in the presence of water, it was apparent that the equilibrium in Scheme 2 lay to the right.

[0045] Furthermore, it is clear from FIG. 1 that doubling the concentration of oDA had little effect on the reaction rate, whereas doubling the concentration of 2M2P in the oDCB nearly doubled the rate of reaction. Assuming that the effect of the concentration on the reaction rate is negligible, and the rate of the reverse reaction is negligible (based on the reactivity in wet oDCB), the reaction rate can be evaluated by equation 1 :

Rate = k[2M2P] (equation 1)

wherein k is the rate constant and [2M2P] is the concentration of 2M2P in oDCB.

[0046] The kinetic experiments suggested that the overall reaction was first-order and dependent on the concentration of 2M2P. To confirm this, the natural logarithm of the concentration of 2M2P, ln[2M2P], was calculated for each data point and plotted against time. The results are depicted in FIG. 2. As can be seen in FIG. 2, a graph of ln[2M2P] versus time (seconds) showed a linear decay and confirmed the first-order kinetics.

[0047] A value of k for each reaction was then calculated from the slopes of each reaction in FIG. 2. For example, k = 0.00047 s^"1 for the reaction using laboratory-grade oDCB with 3 equivalents of oDA and 10 mol% SA. The value of k was then used to calculate the half- life (tm) of 2M2P in the reactions using equation 2:

ti 2 = ln(2)/k (equation 2)

[0048] From this equation, a k of 0.00051 s^"1 translated to a half-life of approximately 23 minutes. For subsequent Examples, the tm for each reaction was calculated and used as the primary tool for judging the speed of the reactions of oDA with 2M2P under varying conditions. It is noted that a half-life of 20 minutes and a residence time of 2 hours corresponds to 6 half- lives over the course of a reaction, which would be sufficient to reduce aldehyde concentration from 1,000 ppm to roughly 16 ppm.

Example 6. Effect of SA Loading

[0049] The reaction of oDA with 2M2P was evaluated at 60°C using 0 to 100 mole percent (mol%) of an SA acid catalyst, and 3 equivalents of oDA. The procedure followed the method of Example 1. The effect of SA loading on the kinetics of the reaction of oDA and 2M2P was evaluated and the data is shown in Table 3.

Table 3.

^Reaction performed at 60°C

[0050] As seen in Table 3, without the addition of SA, the reaction proceeded slowly with a ti 2 of 115.8 minutes (min). At a 10% loading of SA the reaction was nearly 5-fold faster with a ti/2 of 22.7 minutes. The fastest reaction was at 100% loading of SA, with a half-life of 10.4 minutes. Additionally, the solubility of oDA in oDCB at 30°C was found to decrease as the loading of SA increased, as shown in Table 3.

[0051] Although the reaction with a 100% loading of SA had the shortest half-life, the reaction with a 50% loading of SA was the most effective overall. FIG. 3 is a graph of the reaction at 100% loading of SA. As can be seen, the concentration of 2M2P (ppm) at 100% loading of SA initially decreased rapidly for -30 minutes, but then the concentration of 2M2P was observed to increase significantly for the next 1 to 2 hours (from -200 ppm to nearly 400 ppm). This result was reproducible and suggested that higher loading of the acid catalyst should be avoided, possibly due to the formation of protonated ammonium salts.

[0052] It was possible that an effective loading of SA that exceeds 100% had a negative effect on the reaction rate, and possibly changed the reaction equilibrium shown in Scheme 2 to favor the reverse reaction. It is theorized that as 2M2P reacted with oDA and the concentration of oDA is decreased relative to SA, the amount of SA increased above a 100% loading. Thus, after one-third of the oDA had reacted, the SA loading relative to amine became 160%.

Example 7. Acid Catalysts

[0053] The reaction of oDA with 2M2P was evaluated at 60°C using 10 mol% of an acid catalyst, and 3 equivalents of oDA. The procedure followed the method of Example 1. The acids evaluated were sulfuric acid, benzoic acid (BA), stearic acid (SA), salicylic acid (SAA), and 2-chlorobenzoic acid (2-ClBA). The pKa, reaction half-life, and solubility for each acid catalyst are shown in Table 4.

Table 4.

^Reaction performed at 60°C

[0054] Sulfuric acid was ineffective as an acid catalyst for the reaction of oDA with 2M2P, and 2M2P had a half-life of 161.4 minutes for the reaction with oDA. Additionally, in the presence of the sulfuric acid catalyst, oDA was insoluble in oDCB at both 30°C and 60°C. The half-life of 2M2P using the benzoic acid catalyst was 18 minutes and the oDA was soluble in oDCB at 30°C. The half-life of 2M2P using the 2-chlorobenzoic acid catalyst was 26.4 minutes and the oDA was soluble in oDCB at 30°C. There was an outstanding improvement realized by using salicylic acid, both in terms of half-life and solubility. The half-life of 2M2P using SAA was 6.2 minutes and the oDA was soluble in oDCB at 30°C.

Example 8. Amines

[0055] The reaction of an amine other than oDA was evaluated. Meta-phenylenediamine (mPD) was reacted with 2M2P in oDCB using SA as an acid catalyst following the procedure described in Example 1. The results showed mPD to be ineffective under these conditions, as the half-life of 2M2P was 349 minutes. However, mPD had better solubility in oDCB compared with oDA.

Example 9. Comparison of SA and SAA as Acid Catalyst at 30°C

[0056] The reaction of oDA with 2M2P was evaluated at 30°C using either SA or SAA as the acid catalyst. The procedure followed the method of Example 2, with 3 equivalents of oDA and a 10 mol% acid catalyst loading (based on the number of moles of oDA). The results are shown in Table 5.

Table 5.

[0057] The results in Table 5 show that the half-life of 2M2P when individually using SA and SAA as an acid catalyst at 30°C was 346.6 minutes and 39.5 minutes, respectively. From this, it was determined that SAA was the superior acid catalyst. Additionally, oDA was soluble in oDCB when using the SAA acid catalyst at 30°C.

Example 10. Comparison of SA and SAA as Acid Catalyst at 60°C

[0058] The reaction of oDA with 2M2P was evaluated at 60°C using either SA or SAA as the acid catalyst, and 3 equivalents of oDA. The procedure followed the method of Example 1. The acid catalyst loading, in mol% based on the number of moles of oDA, was varied as shown in Table 6. Table 6.

^Reaction performed at 60°C

[0059] As shown in Table 6, the reaction half-life with 100 mol% of SA was 10.4 minutes, which was slower than the reaction of half-life with 10 mol% of SAA (6.2 minutes). The reaction half-life with 10 mol% of SA was 22.7 minutes, which was also slower than the reaction half-life with 1 mol% of SAA. At 60°C, SAA was more effective than SA, even when acid loading was an order of magnitude less.

Example 11. Other Contaminants in oDCB

[0060] The reaction of oDA with 2M2P was evaluated at 30°C and 60°C using 10 mol% of either SA or SAA as the acid catalyst (based on the number of moles of oDA), and using 3 equivalents of oDA. The procedure followed the method of Example 1 (60°C) or Example 2 (30°C). The source of the oDCB, the acid catalyst, and the temperature were varied as shown in Table 7.

Table 7.

[0061] As shown in Table 7, the reaction half-life was lower when SAA was used as the acid catalyst. Additionally, the reaction half-life was comparable when the solvent source was varied between laboratory grade oDCB (oDCB) and plant recycled oDCB (Plant oDCB) that contained up to 3 wt% siloxanes. The results of these experiments suggested that the methods could be used effectively for oDCB that was contaminated with siloxanes with little impact on reaction rate.

Example 12. High Concentration of Aldehyde

[0062] The reaction of oDA with 2M2P was evaluated at 60°C using 10 mol% of either SA or SAA as the acid catalyst (based on the number of moles of oDA), and using 3 equivalents of oDA. The procedure followed the method of Example 1. The oDCB included 5,846 ppm of aldehyde impurity, 2M2P. The results are shown in Table 8.

Table 8.

^Reaction performed at 60°C

[0063] As shown in Table 8, the higher concentration of 2M2P increased the reaction rate, consistent with the observed first order kinetics where the reaction rate was dependent on the concentration of 2M2P. The results suggested that the method was sufficiently robust to accommodate for high (ca. 5,000+ ppm) contamination levels of aldehyde in oDCB using either SA or SAA as the acid catalyst.

Example 13. Optimization of SAA and oDA Loadings

[0064] The acid catalyst loading when using SAA was optimization following the procedure outlined in Example 1. Reactions were prepared by varying either the amount of oDA or the amount of SAA in oDCB, and the reactions with 2M2P were performed at 60°C. The results are shown in FIG. 4, which shows a graph of the natural logarithm of the concentration of 2M2P versus time for reactions at 60°C with oDA loadings ranging from 1.1 to 3. Using 2 equivalents of oDA with 15 mol% of SAA (based on the number of moles of oDA) was virtually equivalent to the same reaction using 3 equivalents of oDA and 10 mol% of SAA (based on the number of moles of oDA). The plot in FIG. 4 also demonstrated that first-order reaction kinetics was maintained when the oDA loading is altered.

Example 14. High Acid Catalyst Loading

[0065] The loading of acid catalyst was evaluated, in particular the use of very high levels of acid catalyst relative to the oDA. The reaction of oDA with 2M2P was evaluated at 30°C using 50 mol% of SAA as the acid catalyst (based on the number of moles of oDA), and either 2 or 3 equivalents of oDA were reacted with 2M2P. The procedure followed the method of Example 2 (30°C).

[0066] Increasing the loading of the acid catalyst to 50 mol% was evaluated to determine the effect on reaction kinetics, yet avoiding the situation where greater than 100 mol% of SAA could be present in the oDCB during the course of reaction. The SAA catalyst was used at a 50% loading level with either 2 or 3 equivalents of oDA. The resulting kinetics study showed that the high catalyst mixture had 2nd order kinetics, which was as good for high concentrations of 2M2P, but was not as efficient at lower concentrations of 2M2P. FIG. 5 shows the kinetics plots derived the reactions using 2 equivalents of oDA/50 mol% SAA and 3 equivalent of oDA/50 mol% SAA, where both reactions were found to have 2nd order rate dependence on the concentration of 2M2P ([2M2P]).

Example 15. Large Batch Processing

[0067] The method of Example 4 was scaled for use in a manufacturing plant using 1,500 gallons of oDCB. In a series of reactions, 1 to 4 molar equivalents of oDA were added to the crude oDCB based on the measured amount of 2M2P impurity in the crude oDCB.

[0068] The resulting mixture was stirred at 120°C for 1 hour and then allowed to cool to 25 °C. The mixture was fed to a distillation column where the purified oDCB went overhead and a waste mixture of oDCB (boiling point 179°C), oDA, and a portion of oDCB were collected in the column bottoms as waste. The solvent overheads were condensed into another vessel, the purified oDCB was collected, and the concentrations of oDA and 2M2P in the purified oDCB were each measured to be less than 10 ppm.

[0069] The following aspects of the disclosure are not intended to be limiting.

[0070] Aspect 1. A method for purifying a crude solvent comprising an aldehyde impurity includes adding an amine, and optionally an acid catalyst, to the crude solvent to form a reaction product with the aldehyde impurity; and separating the reaction product from the crude solvent to provide a purified solvent wherein the aldehyde impurity is present in the purified solvent in an amount of less than 100 parts per million, preferably less than 75 parts per million, more preferably less than 50 parts per million, even more preferably less than 25 parts per million.

[0071] Aspect 2. The method of Aspect 1, wherein the crude solvent is an aromatic solvent, preferably wherein the crude solvent is ortho-dichlorobenzene.

[0072] Aspect 3. The method of Aspect 1 or Aspect 2, wherein the aldehyde impurity is present in the crude solvent in an amount of 50 to 8,000 parts per million, preferably 100 to 5,000 parts per million, more preferably 250 to 5,000 parts per million, even more preferably 250 to 2,500 parts per million.

[0073] Aspect 4. The method of any one or more of Aspects 1 to 3, wherein the aldehyde impurity cannot be removed from the crude solvent by distillation.

[0074] Aspect 5. The method of any one or more of Aspects 1 to 4, wherein the aldehyde impurity is present in the crude solvent in an amount of 100 to 8,000 parts per million after distillation of the crude solvent. [0075] Aspect 6. The method of any one or more of Aspects 1 to 5, wherein a difference between a boiling point of the aldehyde impurity and a boiling point of the crude solvent is less than 75°C, less than 50°C, or less than 25°C.

[0076] Aspect 7. The method of any one or more of Aspects 1 to 6, wherein the aldehyde impurity is of the formula R-C(=0)H, wherein R is a substituted or unsubstituted CMS alkyl, a substituted or unsubstituted C2-18 alkenyl, a substituted or unsubstituted C2-18 alkynyl, or a substituted or unsubstituted C6-18 aryl.

[0077] Aspect 8. The method of any one or more of Aspects 1 to 7, wherein the aldehyde impurity is 2-methyl-2-pentenal.

[0078] Aspect 9. The method of any one or more of Aspects 1 to 8, wherein the amine is a monoamine of the formula R^Nf , wherein R¹ is a substituted or unsubstituted Cs^o alkyl, a substituted or unsubstituted C3-40 cycloalkyl, a substituted or unsubstituted Cs-40 alkenyl, a substituted or unsubstituted Cs-40 alkynyl, or a substituted or unsubstituted C₆-40 aryl.

[0079] Aspect 10. The method of any one or more of Aspects 1 to 9, wherein the amine is octadecylamine.

[0080] Aspect 11. The method of any one or more of Aspects 1 to 9, wherein the amine is a diamine of the formula H₂N-R²-NH2, wherein R² is a substituted or unsubstituted C₆-20 arylene, a substituted or unsubstituted C2-20 alkylene, a substituted or unsubstituted C3-8 cycloalkylene, or a substituted or unsubstituted C3-8 cycloalkenyl.

[0081] Aspect 12. The method of any one or more of Aspects 1 to 11, wherein the acid catalyst has the formula R³-COOH, wherein R³ is a substituted or unsubstituted Cs-40 alkyl, a substituted or unsubstituted C3-40 cycloalkyl, a substituted or unsubstituted Cs-40 alkenyl, a substituted or unsubstituted Cs-40 alkynyl, or a substituted or unsubstituted C₆-40 aryl.

[0082] Aspect 13. The method of any one or more of Aspects 1 to 12, wherein the acid catalyst is stearic acid, salicylic acid, or a combination comprising at least one of the foregoing.

[0083] Aspect 14. The method of any one or more of Aspects 1 to 13, wherein a molar ratio of the amine to the aldehyde impurity is 1: 1 to 10: 1, preferably 1: 1 to 6: 1, more preferably 1: 1 to 4: 1 , even more preferably 2: 1.

[0084] Aspect 15. The method of any one or more of Aspects 1 to 14, wherein a molar ratio of the amine to the acid catalyst is 1: 1 to 20: 1, preferably 2: 1 to 20: 1, more preferably 4: 1 to 10: 1, even more preferably 17:3.

[0085] Aspect 16. The method of any one or more of Aspects 1 to 15, further comprising heating the crude solvent, the amine, and optionally the acid catalyst at a temperature of 30 to 150°C to provide the reaction product. [0086] Aspect 17. A purified solvent provided by the method of any one or more of Aspects 1 to 16.

[0087] Aspect 18. The purified solvent of Aspect 17, wherein the purified solvent comprises less than 100 parts per million, preferably less than 50 parts per million, more preferably less than 25 parts per million of 2-methyl-2-pentenal.

[0088] Aspect 19. A method for purifying a crude solvent comprising an aldehyde impurity, the method comprising: adding an amine and an acid catalyst to the crude solvent to form a reaction product with the aldehyde impurity; and separating the reaction product from the crude solvent to provide a purified solvent wherein the aldehyde impurity is present in the purified solvent in an amount of less than 100 parts per million, preferably less than 75 parts per million, more preferably less than 50 parts per million, even more preferably less than 25 parts per million.

[0089] Aspect 20: The method of Aspect 19, wherein the crude solvent is ortho- dichlorobenzene; the amine is a monoamine of the formula R^-Nf , wherein R¹ is a substituted or unsubstituted Cs^o alkyl; and the acid catalyst is stearic acid, salicylic acid, or a combination comprising at least one of the foregoing.

[0090] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate components or steps herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any steps, components, materials, ingredients, adjuvants, or species that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0091] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. "Or" means "and/or" unless clearly indicated otherwise by context. "Optional" or "optionally" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not.

[0092] The endpoints of all ranges directed to the same component or property are inclusive and independently combinable (e.g., ranges of "less than or equal to 25 wt%, or 5 wt% to 20 wt%," is inclusive of the endpoints and all intermediate values of the ranges of "5 wt% to 25 wt%," etc.). Disclosure of a narrower range or more specific group in addition to a broader range is not a disclaimer of the broader range or larger group.

[0093] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this disclosure belongs. A "combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash ("-") that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -C(=0)H is attached through carbon of the carbonyl group.

[0094] As used herein, the term "hydrocarbyl" and "hydrocarbon" refers broadly to a substituent comprising carbon and hydrogen, optionally with 1 to 3 heteroatoms, for example, oxygen, nitrogen, halogen, silicon, sulfur, or a combination thereof; "alkyl" refers to a straight or branched chain, saturated monovalent hydrocarbon group; "alkylene" refers to a straight or branched chain, saturated, divalent hydrocarbon group; "alkylidene" refers to a straight or branched chain, saturated divalent hydrocarbon group, with both valences on a single common carbon atom; "alkenyl" refers to a straight or branched chain monovalent hydrocarbon group having at least two carbons joined by a carbon-carbon double bond; "cycloalkyl" refers to a non- aromatic monovalent monocyclic or multicylic hydrocarbon group having at least three carbon atoms, "cycloalkylene" refers to a non-aromatic divalent monocyclic or multicylic hydrocarbon group having at least three carbon atoms, "cycloalkenyl" refers to a non-aromatic cyclic divalent hydrocarbon group having at least three carbon atoms, with at least one degree of unsaturation; "aryl" refers to an aromatic monovalent group containing only carbon in the aromatic ring or rings; "arylene" refers to an aromatic divalent group containing only carbon in the aromatic ring or rings; "alkylarylene" refers to an aryl group that has been substituted with an alkyl group as defined above, with 4-methylphenyl being an exemplary alkylarylene group; "arylalkylene" refers to an alkyl group that has been substituted with an aryl group as defined above, with benzyl being an exemplary arylalkylene group; "acyl" refers to an alkyl group as defined above with the indicated number of carbon atoms attached through a carbonyl carbon bridge (-C(=0)-); "alkoxy" refers to an alkyl group as defined above with the indicated number of carbon atoms attached through an oxygen bridge (-0-); "aryloxy" refers to an aryl group as defined above with the indicated number of carbon atoms attached through an oxygen bridge (-0-), and

"arylalkoxy" refers to an alkoxy group as defined above that has been substituted with an aryl group as defined above, with benzyloxy being an exemplary arylalkoxy group. A "siloxane" refers to one or more compounds having repeating diorganosiloxane units of the formula - (R2S1O)- wherein each R is the same or different, and is a Ci-13 monovalent organic group. The siloxane can contain 40 repeating units or less. [0095] Unless otherwise indicated, each of the foregoing groups can be unsubstituted or substituted, provided that the substitution does not significantly adversely affect synthesis, stability, or use of the compound. The term "substituted" as used herein means that at least one hydrogen on the designated atom or group is replaced with another group, provided that the designated atom's normal valence is not exceeded. When the substituent is oxo (i.e., =0), then two hydrogens on the atom are replaced. Combinations of substituents or variables are permissible provided that the substitutions do not significantly adversely affect synthesis or use of the compound. Exemplary groups that can be present on a "substituted" position include, but are not limited to, cyano; hydroxyl; nitro; alkanoyl (such as a C2-6 alkanoyl group such as acyl); carboxamido; Ci-β or C1-3 alkyl, cycloalkyl, alkenyl, and alkynyl (including groups having at least one unsaturated linkages and from 2 to 8, or 2 to 6 carbon atoms); Ci-6 or C1-3 alkoxys; C₆- 10 aryloxy such as phenoxy; Ci-6 alkylthio; Ci-6 or C1-3 alkylsulfinyl; Ci-6 or C1-3 alkylsulfonyl; aminodi(Ci-6 or Ci-3)alkyl; C₆-i2 aryl having at least one aromatic rings (e.g., phenyl, biphenyl, naphthyl, or the like, each ring either substituted or unsubstituted aromatic); C7-19 arylalkylene having 1 to 3 separate or fused rings and from 6 to 18 ring carbon atoms; or arylalkoxy having 1 to 3 separate or fused rings and from 6 to 18 ring carbon atoms, with benzyloxy being an exemplary arylalkoxy.

[0096] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0097] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

CLAIMS What is claimed is:

1. A method for purifying a crude solvent comprising an aldehyde impurity, the method comprising:

adding an amine, and optionally an acid catalyst, to the crude solvent to form a reaction product with the aldehyde impurity; and

separating the reaction product from the crude solvent to provide a purified solvent wherein the aldehyde impurity is present in the purified solvent in an amount of less than 100 parts per million, preferably less than 75 parts per million, more preferably less than 50 parts per million, even more preferably less than 25 parts per million.

2. The method of claim 1, wherein the crude solvent is an aromatic solvent, preferably wherein the crude solvent is ortho-dichlorobenzene.

3. The method of claim 1 or claim 2, wherein the aldehyde impurity is present in the crude solvent in an amount of 50 to 8,000 parts per million, preferably 100 to 5,000 parts per million, more preferably 250 to 5,000 parts per million, even more preferably 250 to 2,500 parts per million.

4. The method of any one or more of claims 1 to 3, wherein the aldehyde impurity cannot be removed from the crude solvent by distillation.

5. The method of any one or more of claims 1 to 4, wherein the aldehyde impurity is present in the crude solvent in an amount of 100 to 8,000 parts per million after distillation of the crude solvent.

6. The method of any one or more of claims 1 to 5, wherein a difference between a boiling point of the aldehyde impurity and a boiling point of the crude solvent is less than 75°C, less than 50°C, or less than 25°C.

7. The method of any one or more of claims 1 to 6, wherein the aldehyde impurity is of the formula R-C(=0)H, wherein R is a substituted or unsubstituted CMS alkyl, a substituted or unsubstituted C2-18 alkenyl, a substituted or unsubstituted C2-18 alkynyl, or a substituted or unsubstituted C6-18 aryl.

8. The method of any one or more of claims 1 to 7, wherein the aldehyde impurity is 2- methyl-2-pentenal.

9. The method of any one or more of claims 1 to 8, wherein the amine is a monoamine of the formula R^-Nfh, wherein R¹ is a substituted or unsubstituted Cs-40 alkyl, a substituted or unsubstituted C3-40 cycloalkyl, a substituted or unsubstituted Cs-₄o alkenyl, a substituted or unsubstituted Cs-40 alkynyl, or a substituted or unsubstituted C₆^o aryl.

10. The method of any one or more of claims 1 to 9, wherein the amine is octadecylamine.

11. The method of any one or more of claims 1 to 9, wherein the amine is a diamine of the formula H₂N-R²-NH2, wherein R² is a substituted or unsubstituted C₆-20 arylene, a substituted or unsubstituted C2-20 alkylene, a substituted or unsubstituted C3-8 cycloalkylene, or a substituted or unsubstituted C3-8 cycloalkenyl.

12. The method of any one or more of claims 1 to 11, wherein the acid catalyst has the formula R³-COOH, wherein R³ is a substituted or unsubstituted Cs-40 alkyl, a substituted or unsubstituted C3-40 cycloalkyl, a substituted or unsubstituted Cs-40 alkenyl, a substituted or unsubstituted Cs-40 alkynyl, or a substituted or unsubstituted C₆^o aryl.

13. The method of any one or more of claims 1 to 12, wherein the acid catalyst is stearic acid, salicylic acid, or a combination comprising at least one of the foregoing.

14. The method of any one or more of claims 1 to 13, wherein a molar ratio of the amine to the aldehyde impurity is 1: 1 to 10: 1, preferably 1: 1 to 6: 1, more preferably 1: 1 to 4: 1, even more preferably 2: 1.

15. The method of any one or more of claims 1 to 14, wherein a molar ratio of the amine to the acid catalyst is 1: 1 to 20: 1, preferably 2: 1 to 20: 1, more preferably 4: 1 to 10: 1, even more preferably 17:3.

16. The method of any one or more of claims 1 to 15, further comprising heating the crude solvent, the amine, and optionally the acid catalyst at a temperature of 30 to 150°C to provide the reaction product.

17. A purified solvent provided by the method of any one or more of claims 1 to 16.

18. The purified solvent of claim 17, wherein the purified solvent comprises less than 100 parts per million, preferably less than 50 parts per million, more preferably less than 25 parts per million of 2-methyl-2-pentenal.

19. A method for purifying a crude solvent comprising an aldehyde impurity, the method comprising:

adding a monoamine and an acid catalyst to the crude solvent to form a reaction product with the aldehyde impurity; and

20. The method of claim 19, wherein

the crude solvent is ortho-dichlorobenzene;

the monoamine is of the formula R^-Nf , wherein R¹ is a substituted or unsubstituted Cs- 40 alkyl; and

the acid catalyst is stearic acid, salicylic acid, or a combination comprising at least one of the foregoing.