Method for determining total aldehydes in one or more of crude 2,5-furan dicarboxylic acid (FDCA), crude terephthalic acid (TPA) and esters thereof

Abstract

A method for determining soluble aldehydes in a composition comprising one or more of (a) 2,5-furan dicarboxylic acid (FDCA), (b) terephthalic acid (TPA), (c) an ester of 2,5-furan dicarboxylic acid, and (d) an ester of terephthalic acid is described. The method can indicate even very low levels of soluble aldehydes associated with unacceptable color development in a) the composition, b) a portion of the composition, or c) a prepolymer, oligomer, or polymer at least partially prepared directly or indirectly from the composition or a portion of the composition, so that mitigating or improving measures can be taken in response.

Description

Technical Field

[0001] From one perspective, the present invention relates to methods for preparing 2,5-furandicarboxylic acid (FDCA) and its esters (e.g., its dimethyl ester derivatives (FDME)), and polymers that can be made from these materials. From another perspective, the present invention relates to conventional petroleum-based terephthalic acid (TPA), for which FDCA is proposed as a plant-based, renewable alternative, and polymers that can be prepared therefrom. Background Technology

[0002] The depletion of fossil fuels has greatly spurred the search for alternative resources of petroleum-based carbon for the synthesis of so-called "platform" molecules that can serve as building blocks for commercially valuable products. Biomass is currently considered a potential alternative from which many such high-value chemicals can be derived, but the development of sustainable technologies for producing such chemicals from renewable resources remains a significant challenge.

[0003] Bio-based monomers 2,5-furandicarboxylic acid (FDCA) and its dimethyl ester derivatives, including dimethyl 2,5-furandicarboxylate (FDME), are considered important starting materials for the production of poly(alkylfurandicarboxylate) polymers, which can replace their known, mass-produced petroleum-derived analogs, namely poly(alkyl terephthalate) polymers (e.g., polyethylene terephthalate (PET)). Prominent examples of poly(alkylfurandicarboxylate) polymers are polyethylene terephthalate (PEF), obtained through the reaction of FDCA or FDME with ethylene glycol. Bio-based polymers (bioplastics) such as PEF exhibit superior performance in many respects compared to their petroleum-derived analogs, particularly in the packaging field. For example, blends of PEF and PET can provide improved barrier properties against CO2 and O2, thus extending shelf life (compared to that obtained using pure PET) and providing acceptable containers for products susceptible to oxidative degradation, such as beer. Other packaging applications for PEF include films used to manufacture bags, wrapping materials, and heat-shrinkable materials with high mechanical strength and recyclability.

[0004] In summary, both FDCA and FDME are useful platform molecules for the production of polyamides, polyurethanes, and polyesters with a wide range of applications in plastics, fibers, coatings, adhesives, personal care products, and lubricants. The commercial significance of these molecules has been proven; for example, in a 2004 study by the US Department of Energy, FDCA was identified as one of twelve priority chemicals for building a future “green” chemistry. Due to its structural similarity to terephthalic acid (TPA), the potential of FDCA as an alternative monomer for synthetic polyesters has been recognized at least as early as 1946, for example in GB 621971 A, and numerous groups have devoted considerable effort over the years to achieving commercially viable methods for the preparation of FDCA.

[0005] Regarding the synthesis of FDCA from bio-based starting materials, progress is described in US 10,538,499, which describes an integrated treatment process for a feed containing hexose units (e.g., fructose), the first step of which is a dehydration step to provide 5-hydroxymethylfurfural (HMF) and / or certain HMF derivatives (e.g., their esters or ether derivatives). Then, based on a medieval-style oxidation similar to that used in the oxidation of p-xylene to prepare TPA, the dehydrated product containing such materials is oxidized to the desired FDCA using a homogeneous catalyst system containing cobalt, manganese, and bromine components.

[0006] US 9,029,580 discloses a method for producing a dried, purified carboxylic acid product containing furan-2,5-dicarboxylic acid (FDCA). The method comprises oxidizing at least one oxidizable compound (e.g., 5-(hydroxymethyl)furfural (5-HMF)) to produce a product having a small amount of 5-formylfuran-2-carboxylic acid (FFCA).

[0007] US Publication No. 20190352784 discloses a method for treating furan-2,5-dicarboxylic acid compositions by electrochemically reducing carbonyl groups, such as aldehyde groups, in the same impurity 5-formylfuran-2-carboxylic acid (FFCA) using an electrochemical cell.

[0008] Tachibana et al.'s "Plant-based Poly(Schiff-Base) Composed of Bifurfural" ACS Omega, May 18, 2018, 3(5): 5336-45, discloses the formation of a poly(Schiff-Base) composed of bisfurfural and a diamine as a desired polymer product.

[0009] A method for the quantitative determination of aldehydes in oxidized oils based on the reaction of N,N-dimethyl-p-phenylenediamine (DPPD) with aldehydes in the presence of acetic acid was disclosed by Miyashita et al. in the Journal of the American Institute of Petroleum Chemists (JAOCS), Volume 68, Issue 10, pp. 748-751 (October 1991). This method uses benzene as the solvent for the aldehyde solution, and the lowest detectable amount of aldehyde is 39 ppm.

[0010] WO 2019 / 014382 discloses a method for producing purified 2,5-furandicarboxylic acid (FDCA) pathway product. The method comprises: contacting an FDCA pathway product containing FDCA and 5-formylfuran-2-carboxylic acid (FFCA) with hydrogen gas in the presence of a heterogeneous reduction catalyst and a solvent, under conditions sufficient to form a reaction mixture for reducing FFCA to hydroxymethylfurancarboxylic acid (HMFCA), to produce a purified FDCA pathway product; wherein the purified FDCA pathway product comprises FDCA, HMFCA, less than 10 mol% of residual FFCA impurities, less than 10 mol% of 5-methyl-2-furfuric acid (MFA), and less than 10 mol% of... mol% tetrahydrofuran-2,5-dicarboxylic acid (THFDCA); wherein the solvent is a multi-component solvent comprising water and a water-miscible aprotic organic solvent; and wherein the heterogeneous reduction catalyst comprises a solid support and a metal selected from the group consisting of Cu, Ni, Co, Pd, Pt, Ru, Ag, Au, Rh, Os, Ir and any combination thereof.

[0011] Despite extensive attempts, commercial production of FDCA has not yet been achieved, and efforts are ongoing to improve the biosynthetic routes of FDCA and its derivatives in order to establish economic viability on a commercial scale. Summary of the Invention

[0012] In a first aspect, the present invention relates to a method for determining soluble aldehydes in a composition, wherein the composition comprises one or more of (a) 2,5-furandicarboxylic acid (FDCA), (b) terephthalic acid (TPA), (c) an ester of 2,5-furandicarboxylic acid, and (d) an ester of terephthalic acid, and wherein the method itself comprises combining one or more diamine salts with the composition under conditions suitable for reacting the soluble aldehydes present in the composition with the added diamine to form one or more imines, and then analyzing the imines in the composition.

[0013] On the other hand, the present invention relates to the use of such an analytical method for monitoring the amount of soluble aldehydes present in a composition whose color development exceeds a certain threshold related to an unacceptable color in a) the composition, b) a portion of the composition, or c) a prepolymer, oligomer, or polymer prepared directly or indirectly from the composition or a portion of the composition, and when the threshold is exceeded, the manner in which the composition or a portion of the composition is formed is altered, the composition or a portion of the composition is treated, or both the manner in which the composition or a portion of the composition is formed and the treatment of the composition or a portion of the composition are altered to prevent the development of the unacceptable color. In some embodiments, these improvements may include one or more of the following: altering the manner in which one or more oxidizing precursors of FDCA or TPA are oxidized to form FDCA or TPA, treating the composition or a portion thereof by introducing one or more color-stabilizing additives therein, and hydrogenating the composition or a portion thereof.

[0014] In this regard, it has long been known that methods for producing TPA or TPA esters necessitate conditions favorable for the formation of problematic byproducts, including unstable aldehydes, well-known chromophores. A prime known example of such chromophores that must be treated in the production of TPA or TPA esters is 4-carboxybenzaldehyde (hereinafter, 4-CBA). However, unstable aldehydes are also a problem for the production of FDCA or FDCA esters. For example, an aldehyde, particularly methyl 5-formyl-2-furanate (FFME), can be present in crude mixtures of medieval-style oxidation of one or more furan precursors of FDCA obtained from the acid-catalyzed dehydration of hexoses (e.g., fructose) in amounts up to 1 wt.%, and possesses almost identical physical properties to FDME, thus posing a purification challenge. Furthermore, in control experiments (where FFME is incorporated into the FDME mixture at low ppm levels), a distinct color was observed over short time intervals at temperatures just above the melting point of FDME. Instrumental methods (e.g., GC-FID, GC / MS, LC-PDA, and LC / MS) can certainly quantify known organic compounds, including aldehydes, at low ppm levels, but these methods cannot accurately account for all the various unknown molecular species produced with 5-formyl-2-furandicarboxylic acid in recent efforts to develop commercially viable methods for producing monomeric pure FDCA and / or FDME; therefore, the present invention can be broadly understood in its first aspect to provide a method that can rapidly account for trace amounts of known and unknown aldehydes present in compositions consisting of one or more of FDCA, FDCA esters with alcohols, TPA, and TPA esters with alcohols, and in its second aspect to efficiently and effectively take such improvements when the analytical methods of the present invention indicate the need for improvements to prevent undesirable color development (or eventual color development) in the composition or in materials or articles made from the composition.

[0015] In the examples, the composition thus analyzed or monitored is a crude FDCA product derived from the oxidation of one or more furan precursors of FDCA.

[0016] In another embodiment, the composition thus analyzed or monitored is a crude TPA product derived from the oxidation of p-xylene.

[0017] In yet another embodiment, the composition so analyzed or monitored is a mixed monomer composition comprising both FDCA and TPA, derived from the oxidation of one or more furan precursors of FDCA and p-xylene in the same or different reactors. In a particular embodiment, the mixed monomer composition is formed by the simultaneous oxidation of one or more furan precursors of FDCA and p-xylene in the same reactor under a single set of reaction conditions, as described in co-assigned Patent Cooperation Treaty Application Serial No. PCT / US 21 / 31969, "Co-production of monomers comprising at least one bio-based monomer" ("969 PCT Application"), filed May 12, 2021, and claims priority from U.S. Provisional Patent Application Serial No. 63 / 025,345, filed May 15, 2020, and European Patent Application No. 20196216.4, filed September 15, 2020.

[0018] In other embodiments, the composition so analyzed or monitored is produced by esterification of crude FDCA product from the oxidation of one or more furan precursors of FDCA, crude TPA product from the oxidation of p-xylene, or a combination of FDCA and TPA from the oxidation of one or more furan precursors of FDCA and p-xylene in the same or different reactors, using one or more alcohols. In the esterification of such a combination of FDCA and TPA, in certain embodiments, the combination to be esterified is a mixed monomer composition formed by the simultaneous oxidation of one or more furan precursors of FDCA and p-xylene in the same reactor under a single set of reaction conditions, as described in "969 PCT application".

[0019] In some embodiments, materials are analyzed or monitored in real time during the synthesis of one or more of FDCA, TPA, esters of one or more FDCA, and esters of one or more TPA.

[0020] In some embodiments, the materials in the process are analyzed or monitored in real time, and changes in the manner in which the composition or a part of the composition is formed, the composition or a part of the composition is processed, or both the manner in which the composition or a part of the composition is formed and the composition or a part of the composition are processed occur in real time in response to the results of the analysis or monitoring.

[0021] These and other aspects, embodiments, and related advantages will become apparent from the following detailed description. Detailed Implementation

[0022] As used herein, the terms “wt-%”, “wt-ppm”, and “wt-ppb” are used to specify weight percentage, parts per million (wt%), and parts per billion (wt%), respectively. The term “mol-%” is used to specify molar percentage. Unless otherwise specified, in various embodiments, the phrase “substantially free” may mean “having less than 5 wt-%”, “having less than 3 wt-%”, or “having less than 1 wt-%”. When referring to “byproducts” such as aldehyde byproducts and coloring byproducts, these are typically alternatively referred to as “contaminants” or “impurities,” for example, in the subject matter incorporated by reference.

[0023] The term "FDCA" refers to 2,5-furandicarboxylic acid (FDCA). "Esterified derivatives" of FDCA refer to derivatives of this compound in which one or both carboxylic acid groups are replaced by ester groups (e.g., alkyl or aryl ester groups, specifically methyl, ethyl, or phenyl ester groups). In the case of methyl ester groups, the desired FDCA esterified derivative for forming polyesters (e.g., with ethylene glycol (PEF)) is dimethyl 2,5-furandicarboxylic acid (FDME).

[0024] As will be apparent from the above description of the invention and the following specification, although the terms “soluble aldehyde,” “aldehyde,” “unstable aldehyde,” “aldehyde derivative,” etc. are used herein, those skilled in the art will understand that these essentially refer to those compounds (or in fact, to the aldehyde functional group itself) that contain at least one aldehyde group to react with the diamine salt in the method of the present invention to provide at least one corresponding imine group that can be analytically found as described herein.

[0025] For example, the term "aldehyde derivative" in FDCA refers to a derivative in which one of the formic acid groups is replaced by an aldehyde group (e.g., a formyl group directly bonded to the furan ring or a formylalkyl group bonded via an intermediate alkyl group, specifically examples being a formyl group, a formylmethyl group, or a formylethyl group). In the case of a formyl group, the aldehyde derivative of FDCA of most particular and primary interest in this invention is 5-formyl-2-furancarboxylic acid (FFCA), although other lower aldehyde derivatives that may not be identified (to the practitioner) are certainly of interest due to the formation of undesirable colors (as described above) by aldol condensation methods.

[0026] Therefore, the term "aldehyde derivative" for esterified derivatives of FDCA correspondingly means esterified derivatives of FDCA as defined above, wherein one of the ester groups of this derivative is replaced by an aldehyde group (e.g., a formyl group directly bonded to the furan ring or a formylalkyl group bonded via an intermediate alkyl group, specific examples being formyl, formylmethyl, or formylethyl). In the case of the formyl group and the esterified derivative of FDCA being FDME, the aldehyde derivative of FDME of particular and primary interest for the purposes of this invention is methyl 5-formyl-2-furanose (FFME), again although other, possibly unidentified, aldehyde derivatives of other esterified derivatives of FDCA are also certainly of interest due to the formation of undesirable colors through aldol condensation.

[0027] As outlined above, the present invention primarily relates to methods for preparing 2,5-furandicarboxylic acid (FDCA), although in some embodiments, FDCA is prepared in combination with other monomers, such as terephthalic acid (TPA). Some of these methods further explicitly include “esterifying” FDCA or a combination of dicarboxylic acids (FDCA and TPA) to form FDCA ester derivatives or ester derivatives of FDCA and TPA, wherein one or preferably both carboxylic acid groups of these dicarboxylic acids are replaced by ester groups (e.g., alkyl ester groups (in the case of monoalkyl or dialkyl ester derivatives) or aryl ester groups (in the case of monoaryl or diaryl ester derivatives), specific examples being methyl, ethyl, or phenyl ester groups). In the case of methyl ester groups, the preferred ester derivative of FDCA is dimethyl 2,5-furandicarboxylic acid (FDME), and the ester derivative of TPA is dimethyl terephthalate (DMT), which can be formed by reacting FDCA and TPA with sufficient methanol, respectively.

[0028] Real-time quantification of aldehydes and aldehyde derivatives

[0029] When considering the use of these materials to prepare various polymers, color—or more precisely, the absence of color—is a key attribute for the commercial acceptability of these materials and the polymers prepared from them in many applications, as previously noted. For example, PET is widely used in the manufacture of carbonated soft drink bottles, and it should be understood that bottles prepared at least partially from PEF will need to be substantially colorless to be an acceptable, at least partially plant-based, alternative to the PET bottles they are accustomed to purchasing. As coloration has been addressed above, we have found very small amounts of various aldehyde-containing materials (and combinations of these materials formed by aldol condensation, including dimers, trimers, etc.), including but not limited to FFCA / FFME prepared in the various methods described in the art for the preparation of FDCA (or FDME), which may contribute to unacceptable colors in FDCA / FDME and the polymers prepared from them (e.g., PEF). Therefore, in one aspect of the invention, a novel method has been developed and is disclosed herein, which enables the quantitative calculation of, for example, all such aldehydes and aldehyde derivative byproducts in FDCA-containing compositions oxidized from one or more oxidized precursors of FDCA, FDCA-containing compositions subsequently esterified from the same FDCA-containing composition, TPA-containing compositions oxidized from p-xylene, TPA-containing ester compositions subsequently esterified from the same TPA-containing composition, mixed monomer compositions containing both FDCA and TPA, or compositions containing ester products esterified from a mixture of mixed monomers.

[0030] The method provided herein includes a highly sensitive protocol that uses a diamine (e.g., N,N'-dimethylphenylenediamine (DPPD)) as a reagent to derivatize virtually all aldehydes into stable, long-wavelength-absorbing imines that can be analyzed by UV-Vis and detected in sub-ppm (millimole) amounts. This protocol can be performed rapidly enough to provide quantitative results, enabling real-time and online method control or real-time mitigation of excess aldehydes (as color-forming precursors, where "aldehyde" is again broadly understood to include, for example, FDCA, esters of FDCA, TPA, and esters of TPA) found in the analyzed or monitored composition. In one particular embodiment, the method disclosed herein can be used to determine the presence of more than 30 ppm of total aldehydes in crude 2,5-furandicarboxylic acid compositions, wherein the compositions are formed by oxidizing one or more furan precursors of 2,5-dicarboxylic acid. In another embodiment, the method can be used to determine the presence of more than 10 ppm of total aldehydes in crude 2,5-furandicarboxylic acid compositions. In yet another embodiment, the method can be used to determine the presence of more than 30 ppb of total aldehydes in a crude 2,5-furandicarboxylic acid composition.

[0031] The following chemical reaction formula illustrates the imine adduct formed from N,N'-dimethyl-p-phenylenediamine (DPPD) in the composition according to the method of the present invention, which is produced together with the aldehyde:

[0032]

[0033] The adduct is a highly colored Schiff base salt and exhibits strong absorption at long wavelengths.

[0034] The following are also diamine salts (formulas i to x) that can be used according to the present invention to provide UV-Vis detectable imines:

[0035]

[0036] N,N'-Dimethyl-p-phenylenediamine sulfate (DPPD sulfate);

[0037]

[0038] N,N'-Dimethyl-p-phenylenediamine dihydrochloride (DPPD dihydrochloride);

[0039]

[0040] N,N'-Dimethyl-p-phenylenediamine oxalate (DPPD oxalate);

[0041]

[0042] N,N'-Dimethyl-p-phenylenediamine hydrochloride (DPPD hydrochloride);

[0043]

[0044] N,N'-Dimethyl-o-phenylenediamine dihydrochloride (DOPD dihydrochloride);

[0045]

[0046] N,N'-Dimethyl-o-phenylenediamine sulfate (DOPD sulfate);

[0047]

[0048] N,N'-Dimethyl-o-phenylenediamine hydrochloride (DOPD hydrochloride);

[0049]

[0050] DPBD dihydrochloride;

[0051]

[0052] DPBD hydrochloride;

[0053]

[0054] DPBD sulfate.

[0055] Diamine salts i-vii are commercially available. Diamine salts viii, ix, and x can be readily prepared. Exemplary, non-limiting methods for preparing diamine salts viii, ix, and x are provided below, along with comments regarding their subsequent iminolation with aldehydes that may be present in compositions analyzed quantitatively according to the present invention.

[0056] This subsequent UV-Vis-detectable derivatization of imines can be conveniently performed at room temperature. We found that certain solvents should be particularly preferred for the reaction, rather than other commonly used industrial solvents, namely benzene, toluene (producing a pale green color), xylene, ethyl acetate, acetone, THF (producing a purple color), acetonitrile, methanol, and ethanol. Specifically, dichloromethane and chloroform appear to work very well.

[0057] Preparation of diamine salts from DPBD (viii) - DPBD dihydrochloride

[0058]

[0059] Procedure: Convert DPBD to DPBD dihydrochloride as follows.

[0060] A 50 mL round-bottom flask equipped with a PTFE-coated magnetic stir bar was filled with 1 g of N,N'-dimethyl-p-phenylenediamine (4.70 mmol) and 100 mL of 0.1 mol ethanol in HCl. The resulting mixture was stirred vigorously overnight, and then excess solvent was removed under pressure, first by rotary evaporation (50°C, 25 Torr) and then under high vacuum (< 1 Torr) for two days, to give 1.3 g of DPBD dihydrochloride as a crystalline solid.

[0061] Imine reaction with FFME: When FFME and DPBD dihydrochloride are mixed, a rapid reaction occurs to form the following adduct (formula xi). This substance will exhibit λ. max > 500 nm (Spectroscopy Letters (1998), 31(5), 1107-1122), because it has a λ of close to 400 nm in the mixture. max Any soluble furan oligomer (approaching DPPD adduct) is significantly different and advantageous.

[0062]

[0063] Preparation of diamine salts (ix) from DPBD - DPBD hydrochloride

[0064]

[0065] Procedure: Convert DPBD to DPBD hydrochloride as follows.

[0066] A 50 mL round-bottom flask equipped with a PTFE-coated magnetic stir bar was filled with 1 g of N,N'-dimethyl-p-phenylenediamine (4.70 mmol) and 100 mL of 0.047 mol ethanol in HCl. The resulting mixture was stirred vigorously overnight, and then excess solvent was removed under pressure, first by rotary evaporation (50°C, 25 Torr) and then under high vacuum (< 1 Torr) for two days, to give 1.2 g of DPBD hydrochloride as a crystalline solid.

[0067] Imine reaction with FFME: When FFME and DPBD hydrochloride are mixed, a rapid reaction occurs to form the following adduct (formula xii). This substance will exhibit λ. max > 500 nm (Spectroscopy Letters (1998), 31(5), 1107-1122), because it has a λ of close to 400 nm in the mixture. max Any soluble furan oligomer (approaching DPPD adduct) is significantly different and advantageous.

[0068]

[0069] Preparation of diamine salts (x)-DPBD sulfate from DPBD

[0070]

[0071] Procedure: Convert DPBD to DPBD sulfate as follows.

[0072] A solution of 1 g of N,N'-dimethyl-p-phenylenediamine (4.70 mmol) and 100 mL of 0.047 mol ethanol in H2SO4 was added to a 50 mL round-bottom flask equipped with a PTFE-coated magnetic stir bar. The resulting mixture was stirred vigorously overnight, and then excess solvent was removed under pressure, first by rotary evaporation (50°C, 25 Torr), and then under high vacuum (< 1 Torr) for two days, to give 1.5 g of crystalline solid DPBD sulfate.

[0073] Imine reaction with FFME: When FFME and DPBD sulfate are mixed, a rapid reaction occurs to form the following adduct (formula xiii). This substance will exhibit λ. max> 500 nm (Spectroscopy Letters (1998), 31(5), 1107-1122), because it has a λ of close to 400 nm in the mixture. max Any soluble furan oligomer (approaching DPPD adduct) is significantly different and advantageous.

[0074]

[0075] Those skilled in the art who benefit from this disclosure will recognize that other diamine salts can be prepared and used in the methods disclosed herein. These other diamine salts will differ only in the type and position of the substituents, while maintaining the two amino groups in the ortho and para positions relative to each other.

[0076] The following are the chemical formulas for FDCA and FDME.

[0077]

[0078] 2,5-Furfurandicarboxylic acid (FDCA)

[0079]

[0080] Dimethyl furanate (FDME)

[0081] Undesirable coloring carbonyl compounds (aldehydes) in FDCA and FFME compositions are shown in the following formula.

[0082]

[0083] 5-Formyl-2-furanoic acid (FFCA)

[0084]

[0085] Methyl-5-formyl-2-furanose ester (FFME)

[0086]

[0087] 2,5-Dicarboxyfuran (DFF)

[0088] The following are the chemical formulas for TPA and DMT.

[0089]

[0090] Terephthalic acid (TPA)

[0091]

[0092] Dimethyl terephthalate (DMT)

[0093] Undesirable coloring aldehydes in TPA and DMT compositions are shown in the following formula.

[0094]

[0095] 4-Carboxybenzaldehyde (4-CBA)

[0096]

[0097] terephthalaldehyde (also known as 1,4-formylbenzene)

[0098]

[0099] Methyl-4-formylbenzoate (also known as 4-methyl ester benzaldehyde)

[0100] This article discloses a feasible and rapid technique for determining ultra-low levels of such problematic aldehydes; in some examples using dichloromethane or chloroform, the presence of carbonyl compounds exceeding 30 ppb can be identified. Without being bound by theory, since the reaction to prepare imines is a rapid reaction, the total time for diamine (e.g., DPPD) derivatization is expected to be significantly shorter in practice than the time shown in the above illustrative procedure only.

[0101] After determining the total aldehydes in the subject composition, appropriate methods can be employed to mitigate color formation and / or improve color stability in the subject composition.

[0102] Attenuation of aldehydes in response to quantitative reactions above a threshold

[0103] As noted above, when excessively high levels of aldehydes in TPA or its esters and FDCA or its esters are found in compositions for monitoring or analyzing the formation and quantification of imines by UV-Vis spectroscopy, the present invention considers responsive initiation and the use of mitigation measures, such as hydrogenation or other derivatization of the aldehydes in the composition, to prevent chromophore formation by aldol condensation and / or the use of stabilizing additives in the composition, although a specific objective of the present invention in some embodiments is to provide adequate real-time determination of total aldehydes in compositions (e.g., compositions comprising FDCA, esters of FDCA, TPA, esters of TPA, both FDCA and TPA, or esters of both FDCA and TPA), so that the accumulation of lower aldehydes in the composition being produced can be reduced by changing the method of producing the composition, and thereby reducing the frequency and / or duration (and associated additional costs) of these mitigation measures. In one embodiment, the method change involves altering the manner in which the oxidation of FDCA, TPA, or a combination of FDCA and TPA is performed. In another embodiment, the subject composition is further or additionally oxidized to oxidize additional portions of the aldehydes. Such additional oxidation can be performed in a secondary oxidation zone.

[0104] When the aldehydes determined by this invention, whether in quantity and / or properties (e.g., having a larger proportion of condensed aldehydes, whose size is close to the proven color in the composition, oligomers or polymers prepared from the composition), make it necessary to take mitigation measures to prevent the development of undesirable colors in monomers, mixed monomer compositions or polymers made from monomers involved in this invention or combinations of such monomers, one mitigation measure that can be taken would involve low-temperature hydrogenation of the composition to be mitigated.

[0105] We have found that by using certain catalysts described herein for such low-temperature hydrogenation, the problematic aldehyde derivatives involved in this invention can be selectively hydrogenated even when present in small concentrations, such that the desired monomers in the composition (e.g., FDCA, esters of FDCA, TPA, and esters of TPA) remain largely to almost completely unreacted. This is surprising, at least considering monomers with unsaturated furan rings (FDCA and its esters), as these unsaturated furan rings are expected to be readily hydrogenated and thus form undesirable byproducts (e.g., tetrahydrofuran derivatives) that are no longer economically viable for the production of bio-based polymers. Without being bound by theory, favorable results have been obtained using the hydrogenation conditions and catalysts described herein, as they efficiently convert not only small amounts of aldehyde derivatives but also small amounts of degradation products that may also have aldehyde groups and / or conjugated double bonds. These aldehyde derivatives and their degradation products may contribute to initial color and reduced color stability.

[0106] Selective hydrogenation results in the conversion of these aldehyde groups to hydroxyalkyl groups. For example, in the case of any aldehyde derivative or esterified derivative of FDCA as described above, the formyl group directly bonded to the furan ring can be converted to a hydroxymethyl group directly bonded to the furan ring, the formylmethyl group can be converted to a hydroxyethyl group, or the formylethyl group can be converted to a hydroxypropyl group. In the case of contaminants that are aldehyde derivatives or esterified derivatives of FDCA, where the aldehyde group is a formyl group, such contaminants can be selectively hydrogenated to their hydroxymethyl derivatives. For example, in the case of FFCA (an aldehyde derivative of FDCA), such contaminants can be selectively hydrogenated to their hydroxymethyl derivative 5-hydroxymethyl-2-furanoic acid (HMFCA). In the case of FFME (an aldehyde derivative of FDME, which is an esterified derivative of FDCA), the contaminant can be selectively hydrogenated to its hydroxymethyl derivative methyl 5-hydroxymethyl-2-furanoic acid (HMFME).

[0107] A typical hydrogenation method involves contacting the monomer composition requiring mitigation with hydrogen in the presence of a catalyst and under sufficiently mild hydrogenation conditions (especially at sufficiently low temperatures), such that contaminants associated with color formation or color instability are selectively hydrogenated, and in the case of compositions comprising FDCA or FDCA esters, not simultaneously reducing the unsaturated furan rings in the FDCA or FDCA esterified derivatives to any substantial extent, for example, at least 99.5% of the FDCA or FDCA esterified derivatives originally found in the composition, and in other embodiments, at least 99.6%, 99.7%, 99.8%, and 99.9% of the FDCA or FDCA esterified derivatives remain intact in the hydrogenated composition.

[0108] The hydrogenation catalyst is typically in solid form and in some embodiments will contain at least a first noble metal, and in other embodiments may preferably contain both a first noble metal and a second noble metal. However, in all embodiments, the type of catalyst is such that it has sufficient activity under mild hydrogenation conditions (typically meaning 120 degrees Celsius or lower) to hydrogenate aldehyde derivatives found in untreated compositions, but its activity is insufficient to simultaneously reduce the unsaturated furan ring in those compositions containing FDCA or esterified derivatives of FDCA to any substantial extent.

[0109] Noble metals are understood in this context to refer to a class of metal elements resistant to oxidation. In representative embodiments, the first noble metal, and preferably both the first and second noble metals, can be selected from the group consisting of: platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), and gold (Au). According to specific embodiments, the term "composed of" is used only to indicate the selection of members of the group of noble metals, but does not exclude the addition of other noble metals and / or other metals. Therefore, hydrogenation catalysts containing noble metals include catalysts containing at least two noble metals, catalysts containing at least three noble metals, and catalysts also containing two noble metals and a third non-noble metal such as a metal promoter (e.g., a transition metal). Representative metal promoters can be selected from groups 12-14 of the periodic table, such as group 13 or 14. Preferred metal promoters are selected from the group consisting of: zinc (Zn), gallium (Ga), germanium (Ge), indium (In), and tin (Sn), with Sn being particularly preferred. Based on the weight of the catalyst, one or more metal promoters are typically present in amounts or combinations ranging from 0.3 wt% to 10 wt%, and typically from 0.5 wt% to 3 wt%.

[0110] According to a preferred embodiment, one or more noble metals and / or one or more metal promoters are present, typically in amounts or combinations ranging from 0.1 wt% to 10 wt%, and typically from 0.5 wt% to 5 wt%, based on the weight of the catalyst. Regardless of the amount, the hydrogenation catalyst can be a noble metal-containing catalyst on a solid support, meaning that one or more noble metals and optionally one or more metal promoters are disposed on a solid support that can be substantially refractory (inert) under hydrogenation conditions, or that the solid support itself can be functional (e.g., in providing acidic or basic sites to provide or promote catalytic activity). Carbon, including activated carbon, is an exemplary solid support. In the presence of at least two or only two noble metals, they can each be present independently, in amounts ranging from 0.05 wt% to 5 wt%, or from 0.3 wt% to 3 wt%, based on the weight of the catalyst. For example, a representative hydrogenation catalyst may comprise two noble metals, Pt and Ru, which can be present independently in amounts within these ranges (e.g., from 0.05 wt% to 5 wt%). In other words, Pt can be present in this amount, Ru can be present in this amount, or both Pt and Ru can be present in this amount. The hydrogenation catalyst can contain one or both of these noble metals, or other noble metals, in the amounts or combinations described above.

[0111] Particularly preferred hydrogenation catalysts will comprise the noble metals Pt and Ru, as well as the metal promoter Sn, in the amounts described above. According to a specific embodiment, the hydrogenation catalyst comprises from 0.1 wt% to 1 wt% (more preferably from 0.3 wt% to 1 wt%) of Pt, from 0.5 wt% to 5 wt% (more preferably from 1 wt% to 3 wt%) of Ru, and from 0.5 wt% to 5 wt% (more preferably from 1 wt% to 3 wt%) of Sn.

[0112] In representative embodiments, a single noble metal (e.g., Pt or Ru) or two other noble metals (e.g., both Pt and Ru) may be substantially the only noble metal present in the hydrogenation catalyst, such that, for example, based on the weight of the hydrogenation catalyst, any other one or more noble metals are present in an amount or combination of less than 0.1 wt% or less than 0.05 wt% in amounts or combinations. In other representative embodiments, in addition to metals that may be present in the solid support (e.g., aluminum present as alumina in the solid support), a single noble metal (e.g., Pt) or two noble metals (e.g., both Pt and Ru) and an optional single metal promoter (e.g., Sn) are substantially the only metal present in the hydrogenation catalyst. Thus, in the case of a support comprising substantially all carbon, a single noble metal or two noble metals and an optional one or more metal promoters may be substantially the only metal present. For example, based on the weight of the hydrogenation catalyst, any other one or more metals other than a single noble metal or two noble metals, an optional metal promoter, and the metal of the solid support (if any) may be present in an amount or combination of less than 0.1 wt% or less than 0.05 wt% in amounts or combinations. Any metal present in the catalyst, including one or more noble metals and optionally one or more metal promoters, may have a metal particle size typically ranging from 0.3 nanometers (nm) to 20 nm, typically from 0.5 nm to 10 nm, and often from 1 nm to 5 nm.

[0113] One or more noble metals and optionally one or more metal promoters of a representative hydrogenation catalyst may be disposed or deposited on a solid support. This is intended to include one or more noble metals and optionally one or more metal promoters on the surface of the support and / or within the porous internal structure of the support. Therefore, in addition to these one or more noble metals and optionally one or more metal promoters, the representative hydrogenation catalyst may further comprise a solid support, wherein an exemplary solid support comprises carbon and / or one or more metal oxides. Exemplary metal oxides are selected from the group consisting of alumina, silica, titanium dioxide, zirconium oxide, magnesium oxide, strontium oxide, tin oxide, etc. The solid support may comprise all or substantially all of one or more of these metal oxides, for example, such that the one or more metal oxides are present in an amount or combination of at least 95% by weight of the solid support. Alternatively, carbon such as activated carbon may be present in an amount of at least 95% by weight or at least 99% by weight of the solid support. Activated carbon refers to the form of carbon after any of a variety of possible treatments (e.g., high-temperature steaming) to increase porosity. Activated carbon also refers to the form obtained by chemical treatments (e.g., acids or bases) that alter properties such as acid site concentration.

[0114] One or more noble metals, along with optional metal promoters, can be incorporated into a solid support using known techniques for catalyst preparation, including sublimation, impregnation, or dry mixing. In the case of impregnation, preferably under an inert atmosphere, one or more soluble compounds of the noble metal and optional metal promoters can be contacted with the solid support in an impregnation solution in a polar (aqueous) or non-polar (e.g., organic) solvent. For example, this contact can preferably be carried out under stirring in an atmosphere of nitrogen, argon, and / or helium, or otherwise in a non-inert atmosphere such as air. The solvent can then be evaporated from the solid support, for example using heating, flowing gas, and / or vacuum conditions, leaving a dry support impregnated with the noble metal and optional metal promoters. One or more noble metals and optional metal promoters can be impregnated into the solid support, for example, when both noble metals and metal promoters are impregnated simultaneously (both dissolved in the same impregnation solution), or in other ways, impregnated separately using different impregnation solutions and contact steps. In any case, the carrier impregnated with precious metals and optional metal additives can be subjected to further preparation steps, such as washing with solvents to remove excess of one or more precious metals, one or more optional metal additives and impurities, further drying, calcination, etc., to provide a hydrogenation catalyst.

[0115] The solid support itself can be prepared according to known methods, such as extrusion to form cylindrical particles (extrudate), or dripping or spray drying to form spherical particles. Regardless of the specific shape of the solid support and the resulting catalyst particles, the amount of one or more noble metals and optionally one or more metal promoters present in the hydrogenation catalyst as described above refers to the average weight of such one or more noble metals and optionally one or more metal promoters in a given catalyst particle (e.g., having any shape, such as cylindrical or spherical), independent of the specific distribution of one or more noble metals and optionally one or more metal promoters within the particle. In this regard, it can be understood that different preparation methods can provide different distributions, such as depositing one or more noble metals and optionally one or more metal promoters primarily on or near the surface of the solid support, or uniformly distributing one or more noble metals and optionally one or more metal promoters throughout the solid support. Generally, the weight percentages described herein, based on the weight of the solid support or otherwise on the weight of the hydrogenation catalyst, may refer to the weight percentage in a single catalyst particle, but more typically to the average weight percentage over a larger number of catalyst particles, such as those in a hydrogenation reactor forming a catalyst bed used in the stabilization method described herein.

[0116] Typical hydrogenation conditions involve elevated hydrogen partial pressures, such as at least 2 MPa (291 psi), for example, from 2 MPa (291 psi) to 18 MPa (2611 psi), and more typically from 2.5 MPa (363 psi) to 10 MPa (1450 psi). The pressure in the hydrogenation reactor can be generated primarily or substantially by hydrogen, such that these hydrogen partial pressure ranges can substantially correspond to the total pressure. However, the presence of other gaseous substances vaporized from the reaction mixture (e.g., evaporated solvent) can cause the hydrogen partial pressures to decrease relative to these total pressures, such that, for example, the total hydrogenation reactor pressure can range, for example, from 2.5 MPa (363 psi) to 20 MPa (2900 psi), and more typically from 3 MPa (435 psi) to 12 MPa (1740 psi).

[0117] Typically, reaction temperatures below 120 degrees Celsius are preferred for hydrogenation, and as demonstrated in the following working examples, using the illustrated hydrogenation catalyst and supplying sufficient hydrogen to reduce substantially all aldehyde derivatives in the tested compositions containing FDCA and FDCA esters, a temperature of approximately 50 or 60 degrees Celsius was found to be sufficient while maintaining the integrity of the furan ring.

[0118] The reaction time, i.e., the time to maintain the reaction mixture at any target value or target sub-range of pressure and temperature within any range of the pressure and temperature given above (e.g., a target total pressure of 4.1 MPa (600 psi) and a target temperature of 80°C (176°F),) ranges from 0.1 h to 24 h, and preferably from 0.5 h to 5 h, in the case of batch reactions. For continuous methods, these reaction times correspond to reactor residence times. An additional parameter associated with continuous methods is the weight hourly space velocity (WHSV), which is understood in the art as the weight flow rate of feed (e.g., monomer composition) entering the reactor per hour divided by the weight of the hydrogenation catalyst. Thus, this parameter represents the equivalent catalyst bed weight of feed processed per hour, and it is related to the reciprocal of the reactor residence time. According to representative embodiments, hydrogenation conditions include WHSV (typically from 0.01 hr) -1 Up to 20 hr -1 And typically from 0.05 hr -1 up to 5 hours -1 ).

[0119] Such mild hydrogenation conditions, combined with a carefully selected, less active hydrogenation catalyst, allow for the selective hydrogenation of problematic aldehyde derivatives to their corresponding hydroxyalkyl derivatives. Compositions containing these aldehyde derivatives can be dissolved in a suitable solvent (e.g., an organic solvent containing methanol or other alcohols, or an organic solvent composed of methanol or other alcohols) when introduced into a hydrogenation reactor for contacting the feed with hydrogen in the presence of the hydrogenation catalyst. The untreated composition, optionally along with the solvent and hydrogen, can be added to the hydrogenation reactor in batches or continuously. For example, in continuous operation, hydrogen can be present in the circulating gas stream and added in a molar excess relative to the aldehyde derivative present in the monomer composition. In both continuous and batch operations, the reaction mixture containing the composition and solvent can be maintained under the hydrogenation conditions described herein to prepare aldehyde-reduced compositions for further processing or use.

[0120] Therefore, a continuous hydrogenation method can be carried out by continuously feeding the composition to be reduced (e.g., in the form of a dissolved composition dissolved in a solvent) and hydrogen into a hydrogenation reactor containing a catalyst (e.g., as a fixed bed) and optionally continuously extracting the resulting hydrogenated / aldehyde-reduced composition from the reactor after it has been separated from excess (unreacted) hydrogen.

[0121] According to some embodiments, the composition may undergo one or more purification steps prior to hydrogenation to reduce the amount of aldehyde present, thereby reducing the requirements (e.g., hydrogen consumption, hydrogen partial pressure, and / or temperature) for achieving aldehyde levels below a given color-related threshold in a given composition. For example, a representative method may further include crystallizing the crude composition containing FDCA or one or more esterified derivatives of FDCA prior to contact with hydrogen (e.g., upstream of contact with hydrogen) to improve the purity of the composition in FDCA or one or more esterified derivatives of FDCA prior to the hydrogenation step (relative to the crude composition).

[0122] Therefore, and incidentally, "hydrogenating the composition" as a specific means of mitigating the presence of aldehydes in the composition should not be construed as implying other means of mitigating aldehydes by removing a portion of the aldehydes from the composition, or in any other way. also It cannot be used; instead, a combination of mitigation measures, including but not limited to the exemplary methods described herein, can be used.

[0123] Crystallization may include dissolving the crude composition in a suitable solvent (e.g., an organic solvent containing methanol or other alcohols) and then cooling the crude composition / solvent system to crystallize the composition. In certain embodiments, the desired purity of the product from the crude composition of the preceding oxidation step is typically 85 wt% or lower (e.g., from 70 wt% to 85 wt%). As a result of crystallization, the purity of the hydrogenated composition can be increased to 99 wt% or higher. For example, in some embodiments, crystallization of the crude composition can achieve a purity specification of at least 99.5 wt%, in all cases with a reduced content of aldehyde derivatives.

[0124] In some embodiments, although some further mitigation measures would generally be desirable, such as hydrogenation of compositions of the type described above, it can be found that crystallization alone is sufficient as a mitigation measure, without the need for further measures. For example, the crystallization step can reduce the chromaticity coordinate b* from a value greater than 5 or greater than 10 to a value less than 5. Typically, crystallizing a crude composition containing FDCA or its esterified derivatives yields monomer-containing compositions with chromaticity coordinates b* less than 5, less than 3, or even less than 1. All or most of the color improvements associated with crystallization are likely due to a reduction in the amount of aldehyde present in the monomer-containing composition. For example, crystallization of crude FDCA or crude FDME compositions can reduce the amount of the associated FFCA or FFME from the values ​​described above (e.g., from 0.3 wt% to 10 wt% FFCA in the case of FDCA compositions, or from 0.1 wt% to 3 wt% FFME in FDME compositions), or optionally from other starting amounts of a given crude composition containing FDCA or its esterified derivatives, to less than 1 wt%, less than 0.5 wt%, or even less than 0.2 wt% of the corresponding aldehyde derivative.

[0125] Therefore, although it can be understood from the above that removing at least a portion of the aldehyde in the initial purification of crude compositions containing FDCA or its esterified derivatives (e.g., by crystallization) can itself significantly and beneficially improve the color and / or color stability of the resulting monomer-containing compositions and can provide high-purity materials with a significantly reduced concentration of the present aldehyde (color precursor), it will be recalled that even very small amounts of residual aldehyde and / or other chromatophores can cause the resulting compositions to fail to meet given color specifications, such as chromaticity coordinates b* less than 0.5. Therefore, some further mitigation will usually be employed, for example by hydrogenation as described herein.

[0126] As described above, the hydrogenation method envisioned herein is selective, enabling the aldehyde groups present in the composition to be effectively neutralized as a source of final color development through molecular weight buildup of aldol condensation. In representative embodiments, whether by converting the aldehyde groups to other groups (through selective hydrogenation or some other derivatization), removing aldehyde functional groups from the composition using crystallization or some other means, or by a combination of removing and converting aldehyde functional groups in the composition, in any case, the total amount of aldehydes combined in the composition will be reduced to less than 500 wt-ppm, less than 200 wt-ppm, or even less than 100 wt-ppm.

[0127] When the quantitative analytical method of the present invention indicates the presence of an excess level of aldehyde in the composition, other mitigation measures are considered, involving the addition of one or more color-stabilizing additive compounds to the composition, as described in the commonly assigned WO2019 / 246034 "Color Stabilization of Monomers and Other Reactants for the Formation of Bio-based Polymers" ("WO'034" application). These color-stabilizing additive compounds have been shown, for example, in WO'034 and the following examples reproduced from WO'034, to be effective in mitigating color development in compositions containing FDCA and FDCA esters resulting from medieval oxidation of one or more furan precursors derived from the dehydration of autosaccharides (fructose).

[0128] Representative color-stabilizing additive compounds taught in WO'034 include substituted phenols, which refer to compounds having at least one phenolic moiety, but possibly two or more, wherein the benzene ring of this one or more moiety has at least one substituent other than a hydroxyl substituent. Specific examples of such substituents are alkoxy and alkyl substituents, preferably methoxy and tert-butyl substituents. Thus, examples of substituted phenols include alkoxy-substituted (e.g., methoxy-substituted) and alkyl-substituted (e.g., tert-butyl-substituted) phenols, which are compounds having at least one phenolic moiety, but possibly two or more, each having one or more alkoxy (e.g., methoxy) and alkyl (e.g., tert-butyl) substituents. In the case of tert-butyl-substituted phenols, these compounds are often referred to as "hindered phenols" due to the steric hindrance caused by the geometry of these substituents.

[0129] Substituted phenols include butylated hydroxyanisole (BHA); 2,6-dimethoxyphenol (DMP); 2,6-di-tert-butyl-4-methoxyphenol (DTMP); pentaerythritol tetrakis[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate] (PETC); 2-tert-butylhydroquinone (TBHQ); triethylene glycol bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate); and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate. In these compounds, (i) BHA, DMP, and DTMP are methoxy-substituted phenols, and (ii) DTMP, PETC, TBHQ, triethylene glycol bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate; and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate are tert-butyl-substituted phenols. Other color-stabilizing additive compounds include phenyl-substituted amines (e.g., 4,4′-bis(α,α-dimethylbenzyl)diphenylamine (XDPA)), phosphites (e.g., tris(2,4-di-tert-butylphenyl)phosphite), and antioxidant vitamins (e.g., ascorbic acid). Compound PETC is used as Irganox. ® 1010 (BASF) or Dovernox ® 10 (commercially available from Dover Chemical Corp.); compound triethylene glycol bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate) is used as Irganox ® 245 (BASF) is commercially available; compound tris(2,4-di-tert-butylphenyl) phosphite is used as Irgafos ® 168 (BASF) is commercially available; and the compound octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate is used as Irganox. ® 1076 (BASF) or Dovernox ® 76 (Daohua Chemical Company) is available for commercial purchase.

[0130] The compounds and / or certain combinations of the above-mentioned compounds and / or classes of compounds are commercially available and readily usable if desired. For example, a combination of 50 wt% PETC and 50 wt% tris(2,4-di-tert-butylphenyl) phosphite is used as Irganox. ® B255 (BASF) is commercially available. A combination of 20 wt% octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and 80 wt% tris(2,4-di-tert-butylphenyl)phosphite is used as Irganox. ®B900 (BASF) is commercially available. A combination of 50 wt% PETC and 50 wt% tris(2,4-di-tert-butylphenyl) phosphite is used as Irganox. ® B225 (BASF) is commercially available.

[0131] Color-stabilizing additive compounds can be used in compositions requiring light reduction, either in a specific amount or in combination, typically from 10 parts per million (wt-ppm) to 1 wt% (wt-%), typically from 50 wt-ppm to 2000 wt-ppm, and generally from 50 wt-ppm to 1500 wt-ppm. According to preferred embodiments, additive BHA can be present in the composition in amounts from 100 wt-ppm to 500 wt-ppm, or additive Irganox... ® 245 can be present in the composition in amounts ranging from 800 wt-ppm to 1200 wt-ppm.

[0132] In other preferred embodiments, the additive BHA may be present in the composition in an amount from 50 wt-ppm to 800 wt-ppm, or more preferably from 50 wt-ppm to 500 wt-ppm. In other preferred embodiments, the additive DMP may be present in the composition in an amount from 200 wt-ppm to 1500 wt-ppm, or more preferably from 400 wt-ppm to 600 wt-ppm. In other preferred embodiments, the additive DTMP may be present in the composition in an amount from 50 wt-ppm to 100 wt-ppm. In other preferred embodiments, the additive XDPA may be present in the composition in an amount from 100 wt-ppm to 1500 wt-ppm. In other preferred embodiments, the additive PETC may be present in the composition in an amount from 200 wt-ppm to 1500 wt-ppm. In other preferred embodiments, the additive Irganox... ® 245 may be present in the composition in amounts from 50 wt-ppm to 1500 wt-ppm, or more preferably from 50 wt-ppm to 100 wt-ppm. In other preferred embodiments, the additive Irganox... ® B900 may be present in the composition in amounts from 50 wt-ppm to 1500 wt-ppm, or more preferably from 50 wt-ppm to 500 wt-ppm. In other preferred embodiments, the additive Irganox is included. ® B225 may be present in the composition in amounts from 50 wt-ppm to 1500 wt-ppm, or more preferably from 50 wt-ppm to 500 wt-ppm.

[0133] The following examples illustrate and support various aspects of the invention as just disclosed:

[0134] Example

[0135] Examples 1-4

[0136] For these embodiments, multiple aldehyde derivative solutions were prepared in dichloromethane using predetermined amounts of known aldehyde derivative impurities associated with FDME (FFME), TPA (4-formylbenzoic acid (or 4-carboxybenzaldehyde (4-CBA)) and terephthalaldehyde), and DMT (methyl-4-formylbenzaldehyde), and various dilution volumes of other dichloromethane. Appropriate amounts of DPPD sulfate were then added to each of these solutions as a solution of DPPD sulfate in a solvent consisting of 0.3% by weight acetic acid in methanol. After stirring for 30 minutes to form the desired imine adduct, each solution was then analyzed by UV-Vis spectroscopy to verify the instrumental method's ability to show absorbance proportional to the amount of the relevant aldehyde derivative impurity present in a given solution, typically in the wavelength range from 410 nm to 460 nm. Analysis shows that UV-Vis spectroscopy can effectively and accurately quantify FFME at levels as low as 900 parts per billion (wt%), 4-CBA at levels as low as 495 wt%, terephthalaldehyde at levels as low as 443 wt%, and methyl-4-carboxybenzoate at levels as low as 540 wt%.

[0137] Example 5

[0138] For an initial example demonstrating hydrogenation as an effective mitigation measure in the determination of excess aldehydes (particularly in compositions containing FDCA or FDCA esters) (given that hydrogenation / reduction was previously known for addressing 4-CBA in TPA), a mixture of 3 g FDME and 0.5 g FFME dissolved in 20 ml methanol was added to a 75 ml high-pressure reactor (Parr Instrument Company). 0.5 g of solid hydrogenation catalyst particles containing 2 wt% Ru / 2 wt% Sn / 0.5 wt% Pt supported on carbon was added to this solution. The reactor was pressurized and purged with hydrogen (three times at 500 psi) while the reaction mixture was continuously stirred at 800 rpm. The vessel was then pressurized to 600 psi with hydrogen, and the reaction contents were heated to 50°C and maintained at this temperature for 1 hour. The reaction mixture was then cooled to room temperature and filtered under vacuum to remove the catalyst. The filtrate was then rotary evaporated to remove the solvent and obtain a white solid. The solid was analyzed by nuclear magnetic resonance (NMR) to determine the composition of the product mixture. The mixture was found to contain 84.9 wt% FDME, or almost the same amount as in the initial mixture of FDME and FFME, in addition to only 3.1 wt% FFME. Hydroxymethyl derivatives and hydrogenated product HMFME were also present. Therefore, the results indicate that a significant portion of the FFME was converted or partially converted to HMFME, but not to FDME.

[0139] Example 6

[0140] The experiment of Example 5 was repeated, except that the reaction temperature was 60°C instead of 50°C. In this case, the product mixture contained 84.9 wt% FDME, or almost the same amount as in the starting mixture of FDME and FFME, plus only 4.2 wt% FFME. Hydroxymethyl derivatives and hydrogenated products HMFME were also present, as well as trace amounts (less than 1000 wt-ppm) of hydrogenated products with a tetrahydrofuran (saturated) ring. Again, these results indicate that even at temperatures higher than those used in Example 5 above, a considerable proportion of FFME is converted or partially reduced to HMFME, rather than converted to FDME.

[0141] Example 7

[0142] The experiment of Example 5 was repeated, except that the reaction pressure was 1200 psi instead of 600 psi. In this case, the product mixture contained 84.8 wt-% FDME, or almost the same amount as in the starting mixture of FDME and FFME, plus only 0.3 wt-% FFME. Hydroxymethyl derivatives and the hydrogenated product HMFME were also present, as well as trace amounts (less than 1000 wt-ppm) of the hydrogenated product with a tetrahydrofuran (saturated) ring. By increasing the severity of the reaction, in this case by increasing the hydrogen pressure, almost complete conversion of FFME was observed, and still no significant loss of FDME due to ring saturation was observed.

[0143] Comparison Example 1

[0144] The experiment of Example 5 was repeated, except that the reaction temperature was 80°C instead of 50°C and the pressure was 500 psi instead of 600 psi. Furthermore, the catalyst contained 2 wt% Ru and 1 wt% sulfur (S) supported on carbon. Using this catalyst composition, essentially all the furan rings in the starting mixture were hydrogenated to the corresponding tetrahydrofuran rings, resulting in the loss of the desired FDME.

[0145] Comparison Example 2

[0146] The experiment of Comparative Example 1 was repeated, except that the catalyst contained 2% wt% Ru supported on carbon. Using this catalyst composition, essentially all the furan rings in the starting mixture were hydrogenated to the corresponding tetrahydrofuran rings, resulting in the loss of the desired FDME.

[0147] Example 8

[0148] Partial hydrogenation of 5-hydroxymethylfurfural (HMF) to produce 2,5-dihydroxymethylfuran was investigated. 10 g of HMF sample dissolved in 90 g of methanol was added to a 300 mL high-pressure Pal reactor (Pal Instruments). 1.5 g of solid hydrogenation catalyst particles containing 5 wt% Ru supported on carbon were added to the solution. The reactor was pressurized and purged with hydrogen (three times at 500 psi) while the reaction mixture was continuously stirred at 600 rpm. The vessel was then pressurized to 1000 psi with hydrogen, and the reaction contents were heated to 100°C and maintained at this temperature for 1 hour. The reaction mixture was then cooled to room temperature and filtered under vacuum to remove the catalyst. The filtrate was then rotary evaporated to remove the solvent, yielding a light brown oil. The oil was analyzed by nuclear magnetic resonance (NMR) to resolve the components of the product mixture, which contained 2,5-dihydroxymethylfuran.

[0149] Example 9

[0150] Partial hydrogenation of 5-acetylmethylfurfural (AcMF) to produce 2-hydroxymethyl,5-acetylmethylfuran was investigated. 20 g of AcMF sample dissolved in 80 g of methanol was added to a 300 mL high-pressure Pal reactor (Pal Instruments). 3 g of solid hydrogenation catalyst particles containing 5 wt% Ru supported on carbon were added to the solution. The reactor was pressurized and purged with hydrogen (three times at 500 psi) while the reaction mixture was continuously stirred at 600 rpm. The vessel was then pressurized to 1000 psi with hydrogen, and the reaction contents were heated to 100°C and maintained at this temperature for 1 hour. The reaction mixture was then cooled to room temperature and filtered under vacuum to remove the catalyst. The filtrate was then rotary evaporated to remove the solvent, yielding a light brown oil. The oil was analyzed by nuclear magnetic resonance (NMR) to resolve the composition of the product mixture, which contained >95 wt% 2-hydroxymethyl,5-acetylmethylfuran.

[0151] Example 10

[0152] The color and color stability of samples containing FDME (with FFCA ranging from 100 wt-ppm to 10,000 wt-ppm) were investigated. To prepare the samples, 20 g of FDME (with a specified proportion of FFCA) for each case was placed in 25 ml headspace vials, each equipped with a magnetic stir bar. The vials were then placed in a heating block preheated to a specified temperature. Complete melting of the sample was observed between 5 and 10 minutes, with the stirring speed set to 500 rpm. After the specified time, the samples were removed, cooled to room temperature, and then the color, particularly the L*a*b* chromaticity coordinates and APHA color index, was analyzed. Samples used for color analysis contained 6 wt-% FDME / FFCA in a 1:1 acetonitrile / isopropanol solvent mixture. Each measurement was performed three times and the average was taken. The contaminant concentrations, except for the temperature, time, and atmospheric conditions used for stability testing, are shown in Table 1 below along with the results for each sample and a commercial reference specimen (Sarchem). If we assume the color specifications are L* > 99, a* < 0.5, b* < 0.5 and APHA < 10, then the table also includes an indication of whether the sample meets the specifications.

[0153] Table 1 - FFCA in FDME, Color Stability Test

[0154]

[0155] This example highlights how FFCA leads to color formation, particularly under high-temperature conditions, similar to those encountered during esterification. The most likely point of violation is the chromaticity coordinate b*, which is < 0.5. Importantly, even relatively low FFCA levels of 100 ppm can result in failure to meet this standard.

[0156] Example 11

[0157] Following the protocol used in Example 10, the color and color stability of samples containing FDME were investigated, except that FFME ranging from 100 wt-ppm to 10,000 wt-ppm was used as the colorant / contaminant in these samples. In addition to the temperature, time, and atmospheric conditions used for stability testing, the contaminant concentrations are presented in Table 2 below along with the results for each sample and a commercial reference specimen (Sarchem). Using the same assumed color specifications of L* > 99, a* < 0.5, b* < 0.5, and APHA < 10, the table also includes an indication of whether the sample meets the specifications.

[0158] Table 2 - FFME in FDME, color stability test

[0159]

[0160] This example highlights how FFME causes color formation, particularly under high-temperature conditions, similar to those encountered during esterification. As in Example 10, the most likely violation of the specification is the chromaticity coordinate b*, which is < 0.5. Importantly, even relatively low FFME levels of 100 ppm can lead to failure to meet this standard.

[0161] Example 12

[0162] As shown in Table 3 below, samples containing FDME and different levels of FFME were prepared according to the protocol used in Example 10, and then the colors, particularly the L*a*b* chromaticity coordinates and APHA color index, were analyzed. The samples used for color analysis contained 6 wt% FDME / FFME in a 1:1 acetonitrile / isopropanol solvent mixture. These samples were then subjected to a hydrogenation step to stabilize them. Color results before and after hydrogenation are also shown.

[0163] Table 3 - FFME in FDME, hydrogenated color test

[0164]

[0165] The results showed a strong correlation between the amount of FFME contaminants initially present in FDME and the final color of the sample. However, more importantly, hydrogenation had a significant impact on improving the color, and in fact, this improvement was evident even when visually comparing samples before and after hydrogenation.

[0166] Example 13

[0167] As shown in Table 4 below, samples containing FDCA and different levels of FFCA were prepared according to the protocol used in Example 10, and then the colors, particularly the L*a*b* chromaticity coordinates and APHA color index, were analyzed. The samples used for color analysis contained 1 wt% FDCA / FFCA in a solvent mixture of TEGMME. These samples were then subjected to a hydrogenation (reduction) step to stabilize them. The color results before and after hydrogenation (reduction) are also shown in Table 4.

[0168] Table 4 - FFCA in FDCA, hydrogenated color test

[0169]

[0170] As shown in Example 12, these results also demonstrate a strong correlation between the amount of contaminants initially present in FDCA (FFCA in this case) and the final color of the sample. Hydrogenation has a significant impact on improving color, and this improvement is evident even when visually comparing samples before and after hydrogenation. FDCA in the samples was essentially preserved intact; 99.7% of the hydrogenated FDCA was retained in samples 1 and 3, 99.8% in sample 4, and 99.9% in sample 2.

[0171] Example 14

[0172] An FDME sample was crystallized from the mother liquor of the esterification reaction step and determined to contain 82.6 wt% FDME (dimethyl ester), of which 16.0 wt% monomethyl ester (FDMME) was generated from incomplete esterification. The sample also contained 0.36 wt% FDCA starting compound and 0.58 wt% aldehyde derivative contaminant FFME. The solid material was dissolved in a solvent mixture, and the color was analyzed according to the procedure in Example 6. The chromaticity coordinates L*, a*, and b* were 69.38, 7.02, and 59.12, respectively, showing a significant color change, especially relative to b*. The analyzed sample was then subjected to a hydrogenation step for stability. Analysis of the hydrogenated sample showed that, on a solvent-free basis, it contained 82.9 wt% FDME, 16.1 wt% FDMME, and 0.45 wt% FDCA, and therefore hydrogenation had little effect on the conversion of these desired monomers. However, the sample lacked detectable FFME, further indicating that hydrogenation is highly selective for aldehyde derivatives. Consistent with this analytical result, the chromaticity coordinates L*, a*, and b* of the hydrogenated sample were significantly improved to 99.26, -0.53, and 1.34, respectively.

[0173] Examples 15-26

[0174] For the following examples related to the use of color-stabilizing additives as a mitigation measure, the color development in FDME was determined during accelerated degradation testing. In each test, 10 g of FDME sample was placed in a vial with a 20 ml gas headspace. The vial was then placed in a heating block, and the temperature was set to the temperature for measuring color stability. Once the solid melted and reached the desired temperature, a timer was started, and after a predetermined time period of testing, the vial was removed and allowed to cool to ambient conditions. Approximately 240 mg of the solid was then dissolved in a 1:1 (w / w) mixture of 3.76 g isopropanol (IPA) and acetonitrile, hereinafter referred to as the “matrix”. The solid and matrix were sonicated until completely dissolved, and the color of the solution was determined using a Konica Minolta CM-5 colorimeter.

[0175] Tables 5-7 below show the test results for the reference compositions in the absence of color-stabilizing additive compounds. The APHA chromaticity values ​​and chromaticity coordinates L*a*b* were determined for (i) the initial matrix, (ii) the initial FDME, and (iii) the FDME samples after heating at 120°C (248°F) for 15 hours (Table 5), or at 150°C (302°F) for 15 hours (Table 6), or at 120°F (248°C) for 48 hours (Table 7).

[0176] Table 5 - Matrix and FDME color data, 120°C, 15 h

[0177]

[0178] Table 6 - Matrix and FDME color data, 150°C, 15 h

[0179]

[0180] Table 7 - Matrix and FDME color data, 120°C, 48 h

[0181]

[0182] The initial FDME samples were obtained from a highly pure source, as can be clearly seen from the values ​​in the second row of Table 5-7 above. However, after exposure to the temperatures of all tests over the various testing periods, the APHA color exceeded 10, and the chromaticity coordinate b* exceeded 0.5.

[0183] Then, during accelerated degradation testing, the ability of the color-stabilizing additive compound to prevent discoloration of the FDME samples was tested. The test was conducted as described above, except that, prior to heating, the measured amount of additive was added to each 10 g FDME sample vial. In the table below, the APHA color values ​​and chromaticity coordinates L*a*b* are shown as determined for (i) the initial matrix, (ii) the initial FDME, and (iii) the FDME samples after heating with different wt-ppm levels of the color-stabilizing additive compound. In particular, the results obtained using BHA for 15 hours at 120°C (248°F) are shown in Table 8.

[0184] Table 8 - FDME with BHA additive, 120°C, 15 h

[0185]

[0186] Based on these results, BHA has a color-stabilizing effect on FDME, especially considering the decrease in APHA chromaticity (chromaticity coordinate b*) values ​​relative to the reference composition in the third row of the table above. When the BHA addition dose is 50-1500 ppm, the APHA color decreases to less than 10. When the BHA addition dose is 50-300 ppm, b* decreases to less than 0.5.

[0187] The results obtained by using BHA for 6 hours at 130°C (266°F) are shown in Table 9.

[0188] Table 9 - FDME with BHA additive, 130°C, 6 h

[0189]

[0190] These results further illustrate that BHA has a color stabilizing effect on FDME, especially considering that the APHA color (chromaticity coordinate b*) value is lower than the value of the reference composition in the third row of the table above.

[0191] The results obtained by using BHA for 6 hours at 150°C (302°F) are shown in Table 10.

[0192] Table 10 - FDME with BHA additive, 150°C, 6 h

[0193]

[0194] These results further demonstrate the color-stabilizing effect of BHA on FDME, particularly considering the decrease in APHA color (chromaticity coordinate b*) values ​​relative to the reference composition in the third row of the table above. When the BHA addition dose is 50–800 ppm, b* decreases to less than 0.5. Furthermore, when the BHA addition dose is 50–500 ppm, the APHA chromaticity also decreases to less than 10.

[0195] The results obtained by using TBHQ for 6 hours at 150°C (302°F) are shown in Table 11.

[0196] Table 11 - FDME using TBHQ additive, 150°C, 6 h

[0197]

[0198] The results obtained by using DMP for 6 hours at 150°C (302°F) are shown in Table 12.

[0199] Table 12 - FDME with DMP additive, 150°C, 6 h

[0200]

[0201] These results indicate that DMP has a color-stabilizing effect on FDME. When the DMP addition dose is 200–1500 ppm, the chromaticity coordinate b* decreases to less than 0.5. At a DMP addition dose of about 500 ppm (e.g., from about 400 ppm to about 600 ppm), the APHA chromaticity also decreases to less than 10.

[0202] The results obtained by using DTMP to conduct a 6-hour test at 150°C (302°F) are shown in Table 13.

[0203] Table 13 - FDME with DTMP additive, 150°C, 6 h

[0204]

[0205] These results indicate that DTMP has a color-stabilizing effect on FDME. When the dosage of DTMP is 50-100 ppm, the chromaticity coordinate b* decreases to less than 0.5.

[0206] The results obtained by using XDPA for 6 hours at 150°C (302°F) are shown in Table 14.

[0207] Table 14 - FDME with XDPA additive, 150°C, 6 h

[0208]

[0209] These results demonstrate that XDPA has a color-stabilizing effect on FDME, especially considering the decrease in APHA chromaticity (chromaticity coordinate b*) values ​​relative to the reference composition in the third row of the table above. When the XDPA addition dose is 100-1500 ppm, b* decreases to less than 0.5.

[0210] The results obtained by using PETC for 6 hours at 150°C (302°F) are shown in Table 15.

[0211] Table 15 - FDME with PETC additives, 150°C, 6 h

[0212]

[0213] These results indicate that PETC has a color stabilizing effect on FDME. When the dosage of PETC is 200-1500 ppm, the chromaticity coordinate b* decreases to less than 0.5.

[0214] Using Irganox ® The results of the 6-hour test at 150°C (302°F) are shown in Table 16.

[0215] Table 16 - Using Irganox ® FDME of additive 245, 150°C, 6 h

[0216]

[0217] These results indicate that Irganox ® 245 has a color-stabilizing effect on FDME. When Irganox... ®When the dosage of 245 is 50-1500 ppm, the chromaticity coordinate b* decreases to less than 0.5. When Irganox... ® When the dosage of 245 added is about 50 ppm (for example, about 50 ppm to about 100 ppm), the APHA color also decreases to 10.

[0218] Using Irganox ® The results of the B900 test at 150°C (302°F) for 6 hours are shown in Table 17.

[0219] Table 17 - Using Irganox ® FDME of B900 additive, 150°C, 6 h

[0220]

[0221] These results indicate that Irganox ® B900 has a color stabilizing effect on FDME, especially considering that the APHA color (chromaticity coordinate b*) value is lower than the reference composition value in the third row of the table above. When Irganox ® When B900 is added at a dose of 50-1500 ppm, b* decreases to less than 0.5. Furthermore, when Irganox... ® When B900 is added at a dosage of 50-500 ppm, the APHA color also decreases to 10 or lower.

[0222] Using Irganox ® The results of the 6-hour test at 150°C (302°F) for B225 are shown in Table 18.

[0223] Table 18 - Using Irganox ® FDME of B225 additive, 150°C, 6 h

[0224]

[0225] These results indicate that Irganox ® B225 has a color stabilizing effect on FDME, especially considering that the APHA color (chromaticity coordinate b*) value is lower than the reference composition value in the third row of the table above. When Irganox ® When B225 is added at doses of 50-1500 ppm, b* decreases to less than 0.5. Furthermore, when Irganox... ® When the dosage of B225 is 50-500 ppm, the APHA color also decreases to less than 10.

[0226] During accelerated degradation testing, the ability of the color-stabilizing additive compounds to prevent discoloration of the FDCA samples was also tested. In the first set of tests, 300 mg of FDCA sample was dissolved in 9700 mg of triethylene glycol monomethyl ether (TEGMME) to provide a 3 wt% solution. An FDCA reference composition without any additives was heated to 100°C (212°F) in air for 2 hours, and then cooled to ambient conditions. Compositions using various color-stabilizing additive compounds alone, namely BHA, Irganox... ® 245. Irganox ® B900, Irganox ® B225, Dovernox ® 10 and Dovernox ® 76. These heating conditions were applied. Furthermore, each of these additives was combined at an addition level of 100 ppm with a composition containing 3 wt% FDCA solution as described above, and the resulting stable composition was also subjected to these heating conditions.

[0227] The colors of the reference composition, individual additives, and stable FDCA compositions containing 100 ppm of these additives were determined using a Konica Minolta CM-5 colorimeter. Table 19 below shows the APHA color values ​​and chromaticity coordinates L*a*b* determined for the samples.

[0228] Table 19 - FDCA in TEGMME is 3 wt-%, stabilized with various additives at 100°C for 2 hours.

[0229]

[0230] These results demonstrate that all tested additives have a color-stabilizing effect on FDCA, especially considering the decrease in APHA color (chromaticity coordinate b*) values ​​relative to the reference composition in the third row of the table above.

[0231] Additional tests were performed according to the above procedure, but by dissolving 100 mg of FDCA sample in 9900 mg of propylene glycol (PG) to provide a 1 wt% solution. Different amounts of the additive were tested for color stability of FDCA, and the APHA color values ​​and chromaticity coordinates L*a*b* were determined, as shown in Table 20 below.

[0232] Table 20 - FDCA in PG is 1 wt-%, stabilized with various additives at 100°C for 2 hours.

[0233]

[0234] When the dosage of BHA is 100-500 ppm and Irganox is added ® When the dosage of 245 is about 1000 ppm (e.g., from about 800 ppm to about 1200 ppm), the chromaticity coordinate b* decreases to less than 0.5.

[0235] project:

[0236] 1. A method for determining soluble aldehydes in a composition, wherein the composition comprises one or more of (a) 2,5-furandicarboxylic acid (FDCA), (b) terephthalic acid (TPA), (c) an ester of 2,5-furandicarboxylic acid and (d) an ester of terephthalic acid, and wherein the method comprises combining one or more diamine salts with the composition under conditions suitable for reacting the added one or more diamine salts with a soluble aldehyde present in the composition to form one or more imines, and then analyzing the imines in the composition.

[0237] 2. The method as described in Project 1, wherein the analytical step includes ultraviolet-visible spectroscopy.

[0238] 3. The method of any one of items 1 or 2, wherein any soluble aldehyde present in the composition reacts with the added one or more diamine salts to such an extent that it can be determined whether there are more than 30 parts by weight of soluble aldehydes in the composition prior to reaction with the added one or more diamine salts.

[0239] 4. The method as described in Project 3, wherein any soluble aldehyde present in the composition reacts with the added one or more diamine salts to such an extent that it can be determined whether there are more than 10 parts by weight of soluble aldehydes in the composition prior to reaction with the added one or more diamine salts.

[0240] 5. The method of Project 4, wherein any soluble aldehyde present in the composition reacts with the added one or more diamine salts to such an extent that it can be determined whether there are more than 30 parts by weight of soluble aldehydes in the composition prior to reaction with the added one or more diamine salts.

[0241] 6. The method of any one of items 1-5, wherein the composition is a material sampled during the process of forming one or more of the oxidative steps of FDCA and TPA in a method for preparing one or more of the FDCA, TPA, esters of FDCA and esters of TPA.

[0242] 7. The method of Project 6, further comprising dehydrating a hexose to obtain one or more furan oxidation precursors of FDCA, oxidizing one or more of these furan oxidation precursors of FDCA to form a crude oxidation product containing FDCA, sampling the crude oxidation product in real time during the formation of the crude oxidation product, and analyzing the sampled crude oxidation product by any one of Projects 1-5.

[0243] 8. The method of Item 6, further comprising oxidizing a feed composition containing para-xylene to form a crude oxidation product containing TPA, sampling the crude oxidation product in real time during the formation of the crude oxidation product, and then analyzing the sampled crude oxidation product by any one of Items 1-5.

[0244] 9. The method of Project 6, further comprising dehydrating a hexose to obtain one or more furan oxidation precursors of FDCA, combining one or more of these furan oxidation precursors of FDCA with p-xylene, oxidizing the combination of one or more of the furan oxidation precursors of FDCA with p-xylene to form a crude oxidation product comprising both FDCA and TPA, sampling the crude oxidation product in real time during the formation of the crude oxidation product, and then analyzing the sampled crude oxidation product by any one of Projects 1 to 5.

[0245] 10. The method of any one of items 6-9, further comprising, in response to the results of the analytical step, altering one or more of the methods used to prepare the FDCA, TPA, FDCA esters and TPA esters by selectively hydrogenating a soluble aldehyde in the composition and / or by adding one or more color-stabilizing additives to the composition, or altering both the methods used to prepare one or more of the FDCA, TPA, FDCA esters and TPA esters and treating the composition.

[0246] 11. A method for monitoring soluble aldehydes in a composition comprising (a) crude 2,5-furandicarboxylic acid (FDCA) oxidized from one or more furan precursors of FDCA, (b) crude terephthalic acid (TPA) oxidized from p-xylene, (c) both 2,5-furandicarboxylic acid and terephthalic acid, (d) an ester of 2,5-furandicarboxylic acid, (e) an ester of terephthalic acid, or (f) an ester of both 2,5-furandicarboxylic acid and terephthalic acid, the method comprising the steps of:

[0247] Provide a diamine salt and combine the diamine salt with the composition under conditions suitable for reacting the diamine with a soluble aldehyde present in the composition to form one or more imines; and

[0248] The presence of an excess level of soluble aldehyde in the composition was determined by ultraviolet-visible spectroscopy; and

[0249] In response to the detection of an excess level of soluble aldehyde in the composition, the method for preparing the composition is changed or the composition is treated by selectively hydrogenating the soluble aldehyde in the composition and / or by adding one or more color-stabilizing additives to the composition, or both the method for preparing the composition and the treatment of the composition are changed.

[0250] 12. The method of Item 11, wherein the excess level of the soluble aldehyde is 30 parts by weight per million.

[0251] 13. The method of Item 12, wherein the excess level of the soluble aldehyde is 10 parts by weight per million.

[0252] 14. The method of Item 13, wherein the excess level of the soluble aldehyde is 30 parts by weight.

[0253] 15. The method of any one of items 1 to 14, wherein the composition is combined with a solvent selected from dichloromethane and chloroform before or during combination with the diamine salt.

[0254] 16. The method of item 15, wherein the solvent is dichloromethane.

[0255] 17. The method of any one of items 1-16, wherein the diamine salt is selected from at least one of the following:

[0256] N,N'-Dimethyl-p-phenylenediamine sulfate (DPPD sulfate);

[0257] N,N'-Dimethyl-p-phenylenediamine dihydrochloride (DPPD dihydrochloride);

[0258] N,N'-Dimethyl-p-phenylenediamine oxalate (DPPD oxalate);

[0259] N,N'-Dimethyl-p-phenylenediamine hydrochloride (DPPD hydrochloride);

[0260] N,N'-Dimethyl-o-phenylenediamine dihydrochloride (DOPD dihydrochloride);

[0261] N,N'-Dimethyl-o-phenylenediamine sulfate (DOPD sulfate);

[0262] N,N'-Dimethyl-o-phenylenediamine hydrochloride (DOPD hydrochloride);

[0263] (DPBD dihydrochloride);

[0264] (DPBD hydrochloride); and

[0265] (DPBD sulfate).

[0266] 18. The method of claim 17, wherein the diamine salt is selected from at least one of the following:

[0267] N,N'-Dimethyl-p-phenylenediamine sulfate (DPPD sulfate);

[0268] (DPBD dihydrochloride);

[0269] (DPBD hydrochloride); and

[0270] (DPBD sulfate).

[0271] 19. The method of Item 18, wherein the diamine salt is N,N'-dimethyl-p-phenylenediamine sulfate (DPPD sulfate).

[0272] 20. The method of any one of items 11-19, wherein the composition is treated by reacting it with hydrogen in the presence of a hydrogenation catalyst comprising at least a first noble metal to selectively hydrogenate the soluble aldehyde in the composition.

[0273] 21. The method of Project 20, wherein the hydrogenation catalyst comprises both the first noble metal and the second noble metal.

[0274] 22. The method of claim 21, wherein the hydrogenation catalyst further comprises a metal promoter.

[0275] 23. The method of Item 22, wherein the hydrogenation catalyst comprises 0.5 wt% to 5 wt% ruthenium (Ru), 0.5 wt% to 5 wt% tin (Sn), and 0.1 wt% to 1 wt% platinum (Pt) on a carbon-containing solid support.

[0276] 24. The method of any one of items 11-19, wherein the composition is treated by adding a color-stabilizing additive in the form of a substituted phenol.

[0277] 25. The method of item 24, wherein the substituted phenol is a methoxy-substituted phenol or a tert-butyl-substituted phenol.

[0278] 26. The method of any one of items 11-19, wherein the composition is treated by adding one or more color-stabilizing additives selected from the group consisting of: butylated hydroxyanisole (BHA); 2,6-dimethoxyphenol (DMP); 2,6-di-tert-butyl-4-methoxyphenol (DTMP); pentaerythritol tetrakis[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate] (PETC); 2-tert-butylhydroquinone (TBHQ); 4,4′-bis(α,α-dimethylbenzyl)diphenylamine (XDPA); triethylene glycol bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate); tris(2,4-di-tert-butylphenyl) phosphite; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and ascorbic acid.

[0279] 27. The method of item 26, wherein the one or more color stabilizing additives are added to the composition in an amount of 50 to 2000 parts per million (wt-ppm) of the whole composition.

Claims

1. A method for determining soluble aldehydes in a composition, wherein, The composition comprises one or more of (a) 2,5-furandicarboxylic acid (FDCA), (b) terephthalic acid (TPA), (c) an ester of 2,5-furandicarboxylic acid, and (d) an ester of terephthalic acid, and wherein the method comprises: One or more diamine salts are combined with the composition under conditions suitable for reacting the soluble aldehydes present in the composition with the added one or more diamine salts to form one or more imines. The imine in the composition was then analyzed, and In response to the results of the analytical steps, the method used to prepare one or more of the 2,5-furandicarboxylic acid, terephthalic acid, esters of 2,5-furandicarboxylic acid and esters of terephthalic acid may be modified, or the composition may be treated by selectively hydrogenating the soluble aldehyde in the composition and / or by adding one or more color-stabilizing additives to the composition, or both the method used to prepare one or more of the 2,5-furandicarboxylic acid, terephthalic acid, esters of 2,5-furandicarboxylic acid and esters of terephthalic acid and the treatment of the composition may be modified.

2. The method as described in claim 1, wherein, The analytical steps include ultraviolet-visible spectroscopy.

3. The method as described in claim 1, wherein, Any soluble aldehyde present in the composition reacts with the added one or more diamine salts to such an extent that it can be determined whether there are more than 30 parts by weight of soluble aldehydes in the composition prior to the reaction with the added one or more diamine salts.

4. The method of claim 3, wherein, Any soluble aldehyde present in the composition reacts with the added one or more diamine salts to such an extent that it can be determined whether more than 10 parts by weight of soluble aldehydes are present in the composition prior to reaction with the added one or more diamine salts.

5. The method of claim 4, wherein, Any soluble aldehyde present in the composition reacts with the added one or more diamine salts to such an extent that it can be determined whether there are more than 30 parts by weight of soluble aldehydes in the composition prior to the reaction with the added one or more diamine salts.

6. The method according to any one of claims 1-5, wherein, The composition is a material sampled during a process following an oxidation step in the formation of one or more of the following: 2,5-furandicarboxylic acid, terephthalic acid, esters of 2,5-furandicarboxylic acid and esters of terephthalic acid, in a method for preparing one or more of the following: 2,5-furandicarboxylic acid and terephthalic acid.

7. The method of claim 6, further comprising dehydrating a hexose to obtain one or more furan oxidation precursors of 2,5-furandicarboxylic acid, oxidizing one or more of these furan oxidation precursors of 2,5-furandicarboxylic acid to form a crude oxidation product containing 2,5-furandicarboxylic acid, sampling the crude oxidation product in real time during the formation of the crude oxidation product, and analyzing the sampled crude oxidation product.

8. The method of claim 6, further comprising oxidizing a feed composition containing p-xylene to form a crude oxidation product containing terephthalic acid, sampling the crude oxidation product in real time during the formation of the crude oxidation product, and then analyzing the sampled crude oxidation product.

9. The method of claim 6, further comprising dehydrating a hexose to obtain one or more furan oxidation precursors of 2,5-furandicarboxylic acid, combining one or more of these furan oxidation precursors of 2,5-furandicarboxylic acid with p-xylene, oxidizing the combination of one or more of the furan oxidation precursors of 2,5-furandicarboxylic acid with p-xylene to form a crude oxidation product comprising both 2,5-furandicarboxylic acid and terephthalic acid, sampling the crude oxidation product in real time during the formation of the crude oxidation product, and then analyzing the sampled crude oxidation product.

10. The method according to any one of claims 1-5, wherein, The composition is combined with a solvent selected from dichloromethane and chloroform before or during combination with the diamine salt.

11. The method of claim 10, wherein, The solvent is dichloromethane.

12. The method according to any one of claims 1-5, wherein, The diamine salt is selected from at least one of the following: N,N'-Dimethyl-p-phenylenediamine sulfate (DPPD sulfate); N,N'-Dimethyl-p-phenylenediamine dihydrochloride (DPPD dihydrochloride); N,N'-Dimethyl-p-phenylenediamine oxalate (DPPD oxalate); N,N'-Dimethyl-p-phenylenediamine hydrochloride (DPPD hydrochloride); N,N'-Dimethyl-o-phenylenediamine dihydrochloride (DOPD dihydrochloride); N,N'-Dimethyl-o-phenylenediamine sulfate (DOPD sulfate); N,N'-Dimethyl-o-phenylenediamine hydrochloride (DOPD hydrochloride); (DPBD dihydrochloride); (DPBD hydrochloride); and (DPBD sulfate).

13. The method of claim 12, wherein, The diamine salt is selected from at least one of the following: N,N'-Dimethyl-p-phenylenediamine sulfate (DPPD sulfate); (DPBD dihydrochloride); (DPBD hydrochloride); and (DPBD sulfate).

14. The method of claim 13, wherein, The diamine salt is N,N'-dimethyl-p-phenylenediamine sulfate (DPPD sulfate).

15. A method for monitoring soluble aldehydes in a composition comprising (a) crude 2,5-furandicarboxylic acid (FDCA) oxidized from one or more furan precursors of 2,5-furandicarboxylic acid, (b) crude terephthalic acid (TPA) oxidized from p-xylene, (c) both 2,5-furandicarboxylic acid and terephthalic acid, (d) an ester of 2,5-furandicarboxylic acid, (e) an ester of terephthalic acid, or (f) an ester of both 2,5-furandicarboxylic acid and terephthalic acid, the method comprising the steps of: Provide a diamine salt and combine the diamine salt with the composition under conditions suitable for reacting the diamine with a soluble aldehyde present in the composition to form one or more imines; and The presence of an excess level of soluble aldehydes in the composition was determined by ultraviolet-visible spectroscopy. as well as In response to the detection of an excess level of soluble aldehyde in the composition, the method for preparing the composition is changed or the composition is treated by selectively hydrogenating the soluble aldehyde in the composition and / or by adding one or more color-stabilizing additives to the composition, or both the method for preparing the composition and the treatment of the composition are changed.

16. The method of claim 15, wherein, The excess level of the soluble aldehyde is 30 parts by weight.

17. The method of claim 16, wherein, The excess level of the soluble aldehyde is 10 parts by weight per million.

18. The method of claim 17, wherein, The excess level of the soluble aldehyde is 30 parts by weight.

19. The method according to any one of claims 15-18, wherein, The composition is combined with a solvent selected from dichloromethane and chloroform before or during combination with the diamine salt.

20. The method of claim 19, wherein, The solvent is dichloromethane.

21. The method according to any one of claims 15-18, wherein, The diamine salt is selected from at least one of the following: N,N'-Dimethyl-p-phenylenediamine sulfate (DPPD sulfate); N,N'-Dimethyl-p-phenylenediamine dihydrochloride (DPPD dihydrochloride); N,N'-Dimethyl-p-phenylenediamine oxalate (DPPD oxalate); N,N'-Dimethyl-p-phenylenediamine hydrochloride (DPPD hydrochloride); N,N'-Dimethyl-o-phenylenediamine dihydrochloride (DOPD dihydrochloride); N,N'-Dimethyl-o-phenylenediamine sulfate (DOPD sulfate); N,N'-Dimethyl-o-phenylenediamine hydrochloride (DOPD hydrochloride); (DPBD dihydrochloride); (DPBD hydrochloride); and (DPBD sulfate).

22. The method of claim 21, wherein, The diamine salt is selected from at least one of the following: N,N'-Dimethyl-p-phenylenediamine sulfate (DPPD sulfate); (DPBD dihydrochloride); (DPBD hydrochloride); and (DPBD sulfate).

23. The method of claim 22, wherein, The diamine salt is N,N'-dimethyl-p-phenylenediamine sulfate (DPPD sulfate).

24. The method according to any one of claims 15-18, wherein, The composition is treated by reacting it with hydrogen in the presence of a hydrogenation catalyst containing at least a first noble metal, thereby selectively hydrogenating the soluble aldehydes in the composition.

25. The method of claim 24, wherein, The hydrogenation catalyst comprises both the first noble metal and the second noble metal.

26. The method of claim 25, wherein, The hydrogenation catalyst further comprises a metal promoter.

27. The method of claim 26, wherein, The hydrogenation catalyst comprises 0.5 wt% to 5 wt% ruthenium (Ru), 0.5 wt% to 5 wt% tin (Sn), and 0.1 wt% to 1 wt% platinum (Pt) on a carbon-containing solid support.

28. The method according to any one of claims 15-18, wherein, The composition is treated by adding a color-stabilizing additive in the form of a substituted phenol.

29. The method of claim 28, wherein, The substituted phenol is a methoxy-substituted phenol or a tert-butyl-substituted phenol.

30. The method according to any one of claims 15-18, wherein, The composition is treated by adding one or more color-stabilizing additives selected from the group consisting of: butylated hydroxyanisole (BHA); 2,6-dimethoxyphenol (DMP); 2,6-di-tert-butyl-4-methoxyphenol (DTMP); pentaerythritol tetrakis[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate] (PETC); 2-tert-butylhydroquinone (TBHQ); 4,4′-bis(α,α-dimethylbenzyl)diphenylamine (XDPA); triethylene glycol bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate); tris(2,4-di-tert-butylphenyl) phosphite; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and ascorbic acid.

31. The method of claim 30, wherein, One or more color stabilizing additives are added to the composition in an amount of 50 to 2000 parts per million (wt-ppm) of the whole composition.

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