Purification of 2,5-furandicarboxylic acid dimethyl ester and other esterified products

Abstract

To provide a method for the purification by crystallization of crude compositions comprising 2,5-furandicarboxylic acid dimethyl ester (FDME) or other diester derivatives (for example, dialkyl ester derivatives) of 2,5-furandicarboxylic acid (FDCA).SOLUTION: A method for purifying a crude composition comprising 2,5-furandicarboxylic acid dimethyl ester (FDME), the method comprising: forming a biphasic solution of the crude composition in a solvent comprising an organic phase and a separate aqueous phase; separating the organic phase from the aqueous phase; and crystallizing, from the organic phase, a purified composition having an increased content of FDME relative to the crude composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a method for purifying bio-based monomers, particularly esterified monomers such as 2,5-furandicarboxylic acid dimethyl ester (FDME), which are useful in the production of bio-based polymers such as poly(alkylene terephthalate) polymers. [Background technology]

[0002] Background of the Invention The depletion of fossil fuels has created a major incentive to search for alternative feedstocks to petroleum-based carbon for synthesizing so-called "platform" molecules that can serve as building blocks for commercially important products. Although biomass is now considered a promising alternative feedstock from which many such high-value chemicals can be derived, the development of sustainable technologies for producing such chemicals from renewable resources remains a major challenge.

[0003] The biobased monomer 2,5-furandicarboxylic acid (FDCA) and its methyl ester derivative, 2,5-furandicarboxylic acid dimethyl ester (FDME), are recognized as important starting materials for the production of poly(alkylene furandicarboxylate) polymers, which can replace known, mass-produced petroleum-derived analogs, namely, poly(alkylene terephthalate) polymers such as polyethylene terephthalate (PET). A well-known example of a biobased poly(alkylene furandicarboxylate) polymer is poly(ethylene furandicarboxylate) (PEF), obtained by reacting FDCA or FDME with ethylene glycol. This biobased plastic exhibits many superior properties compared to its petroleum-derived analog, PET, particularly in the field of packaging. For example, blends of PEF with PET can improve CO2 and O2 barrier properties, extending shelf life over pure PET and providing containers suitable for products such as beer that are susceptible to oxidative degradation. Other packaging applications of PEF include films used to manufacture pouches, packaging materials, and heat-shrinkable materials with high mechanical strength and recyclability.

[0004] In general, FDCA and FDME are both useful platform molecules in the production of polyamides, polyurethanes, and polyesters, which have a variety of applications, including plastics, fibers, coatings, adhesives, personal care products, and lubricants. An important consideration for polymers produced from these monomers is their color and color stability, i.e., resistance to color degradation over time, particularly due to exposure to a combination of heat and oxygen (e.g., air). Color, or more appropriately, lack of color, is important for applications such as food packaging and particularly beverage bottle production, where a lack of transparency or even yellowing of the plastic is easily noticeable and often leads to rejection. For this purpose, it has been recognized that the use of the esterifying monomer, FDME, offers advantages over FDCA in that it not only improves the color of the final poly(alkylene furan dicarboxylate) polymer, but also makes it easier to handle and process. The improved color from esterification can be attributed, at least in part, to the improved stability of the esterified product, in that it prevents aldol condensation reactions that might otherwise occur.

[0005] There are known methods for converting FDCA to its dialkyl ester derivative (e.g., its dimethyl ester derivative, FDME) by reaction with an appropriate alcohol (e.g., methanol). Processes are disclosed, for example, in International Publication No. 2017 / 019431, including a post-reaction crystallization step to enhance the purity of FDME. U.S. Patent Application Publication No. 2019 / 0031634 discloses a reactive distillation process for the esterification of FDCA, in which distillation is combined with an esterification reaction to obtain an FDME product of improved purity. Meanwhile, U.S. Patent No. 9,169,229 describes a series of steps for obtaining purified FDME (referred to as "DMFD") and other esterified derivatives, including physical separation (e.g., distillation to drive off excess alcohol) and solid-liquid separation, with optional drying or crystallization. The disclosed compositions are alleged to have improved color and reduced levels of impurities, such as 0.8% by weight or less of 5-formyl-2-furancarboxylic acid methyl ester (referred to as "methyl 5-formylfuran-2-carboxylate").

[0006] Improving the quality of FDME and other diester derivatives of FDCA is key to the overall effort to establish poly(alkylene furan dicarboxylate) polymers as commercially viable alternatives to their petroleum-based counterparts. However, despite efforts to date, obtaining such diester derivatives in sufficient purity remains a significant challenge, especially for the production of biobased plastic end products with commercially acceptable color properties. Summary of the Invention [Means for solving the problem]

[0007] overview More specifically, the present invention was developed in consideration of the many practical difficulties encountered in purifying FDME and other diester derivatives of FDCA by distillation as suggested in the cited art. Such difficulties can include, inter alia, equipment contamination; color development and aggregation in the purified composition; low yields; loss of valuable unconverted and partially converted compounds; and the need for pre- and post-treatment steps.

[0008] Thus, the present invention provides an alternative method (instead of distillation) for the purification of crude compositions comprising 2,5-furandicarboxylic acid dimethyl ester (FDME) or one or more other diester derivatives (e.g., dialkyl ester derivatives) of 2,5-furandicarboxylic acid (FDCA), comprising crystallization from a solvent.

[0009] Advantageously, it has been discovered that certain solvents and classes of solvents promote selective crystallization of FDME relative to impurities that would be detrimental to the color and / or color stability of the purified composition.

[0010] This discovery further enables the use of purification methods, described in detail below, that do not subject crude compositions or solutions formed from these crude compositions to temperatures typically required for distillation of FDME, even under vacuum conditions, which can independently result in thermal decomposition and the formation of impurities that contribute directly to color or contribute to reducing the color stability of the desired FDME over time.

[0011] According to certain non-limiting embodiments that take advantage of this discovery, crystallization can be combined with an aqueous-organic (liquid-liquid) extraction performed on a solution of the crude composition (e.g., in the case of extractive crystallization) and / or with passing the solution through or contacting it with a solid treatment medium, such as to remove solids and / or improve color.

[0012] Thus, in this specification, one or more diesters of primarily FDME or more generally FDCA are used. Processes for purifying crude compositions comprising ester derivatives (e.g., diethyl ester derivatives of FDCA or diphenyl ester derivatives of FDCA) have been described, according to which specific solvents are used and / or one or both of a two-phase solution and a solid processing medium are employed. These processes can advantageously provide purified compositions, or optionally second-stage, third-stage, or higher-stage purified compositions (e.g., after multi-stage crystallization, optionally in combination with extraction and / or processing), which are superior in terms of purity, color properties (e.g., colorless appearance), rheological properties (e.g., free-flowing crystals), and color stability.

[0013] "Purity" in this context can be defined in terms of the presence (e.g., a high weight percent) of the compound of interest (FDME or other diester derivative of FDCA), or it can be meaningfully defined in terms of the absence (e.g., a low weight percent) of impurities resulting from the process used to produce FDME or other diester derivatives of FDCA, particularly impurities that result in undesirable initial and / or over-time color formation.

[0014] Color stability can be demonstrated, for example, by maintaining a colorless appearance even after extended storage periods, which can be up to several years, under ambient conditions (e.g., in air at about room temperature.) Further advantages of the methods described herein are the high yield or recovery of the target compound, as well as the overall simplicity, particularly compared to techniques involving distillation or other approaches requiring high temperatures, such as above 100°C. DETAILED DESCRIPTION OF THE INVENTION

[0015] Detailed Description of the Embodiments As used herein, the terms "wt. %" and "wt. ppm" are used to denote weight percent and parts per million by weight, respectively.

[0016] Throughout this disclosure, processes are described with respect to their use to purify 2,5-furandicarboxylic acid dimethyl ester (FDME) present in a solid crude composition obtained, for example, from the esterification reaction of 2,5-furandicarboxylic acid (FDCA) with methanol. It will be understood that such processes can be readily extended to other diester derivatives (e.g., dialkyl ester derivatives) obtained from the esterification of FDCA with other alcohols, such as ethanol, propanol, or phenol, whether or not such diester derivatives are explicitly mentioned with 2,5-furandicarboxylic acid dimethyl ester (FDME) being the primary (but not the only) target.

[0017] However, regardless of the specific esterification, some degree of inefficiency is observed in the esterification reaction, as evidenced by incomplete conversion and / or by-product formation. Reaction inefficiencies are also unavoidable in other processing steps that have been considered in the art to occur upstream of esterification, such as, for example, in the dehydration of carbohydrates (e.g., hexose sugars) to produce FDCA-forming furans, such as 5-hydroxymethylfurfural (HMF), among others, and in the oxidation of these FDCA-forming furans to produce crude compositions containing FDCA.

[0018] As a result, crude compositions containing FDME or another diester derivative of FDCA as the target compound will necessarily and unavoidably further contain impurities, such as (i) aldehyde derivatives and (ii) aldehyde-ester (e.g., aldehyde-alkyl ester) derivatives of FDCA, at least some of which may initially and / or over time cause color formation.

[0019] In the case of (i), one of the carboxylic acid groups of FDCA is replaced with an aldehyde group; In the case of (ii), one of the carboxylic acid groups of FDCA is replaced with an aldehyde group, and the other carboxylic acid group is an ester derivative of a carboxylic acid, which is the same type of ester derivative (e.g., a methyl ester derivative) as the target compound (e.g., a diester derivative of FDME or other FDCA). Other impurities may include (iii) partially esterified or partially converted compounds, such as a monoester derivative of FDCA, in which one of the carboxylic acid groups is an ester derivative of a carboxylic acid, which is the same type of ester derivative (e.g., a methyl ester derivative) as the target compound, and (iv) unconverted FDCA. Additional impurities may include metals and their metal salts, such as salts of metal cations Co, Ca, Mn, Sn, and Na, and / or salts of anions of Br, P, and fumaric acid, which may be derived from homogeneous or heterogeneous catalysts used to carry out the esterification reaction.

[0020] The above-mentioned impurities in the crude composition result from the process used to produce FDME or other diester derivatives of FDCA. Often, the crude composition exhibits poor color characteristics. This means that the color may be yellow, brown, or even black, which is significantly different from a white or colorless appearance. However, a crude composition with poor color characteristics may actually contain only trace amounts of a given impurity, or may contain only very small amounts of all impurities combined.

[0021] Thus, a representative crude composition containing FDME or other diester derivatives of FDCA may contain the target compound in an amount of at least 70 wt. % (e.g., 70 wt. % to 98 wt. %), such as at least 75 wt. % (e.g., 75 wt. % to 95 wt. %) or at least 80 wt. % (e.g., 80 wt. % to 90 wt. %) (i.e., providing a compound that can be further purified in accordance with the present invention). Such a composition may contain an impurity according to (i) above (e.g., 5-formyl-2-furandicarboxylic acid (FFCA)) in an amount of from 1 wt. % to as little as 0.01 wt. %, e.g., from 0.5 wt. % to 0.03 wt. %, or from 0.2 wt. % to 0.05 wt. Such a composition may independently or additionally contain an impurity according to (ii) above (e.g., 5-formyl-2-furandicarboxylic acid methyl ester (FFME)) in an amount of from 2 wt. % to 0.1 wt. %, e.g., from 1 wt. % to 0.2 wt. %, or from 0.8 wt. % to 0.3 wt. %. Such compositions may independently comprise, or may further comprise, an impurity according to (iii) above (e.g., 2,5-furandicarboxylic acid monomethyl ester (FDMME)) in an amount of from 20% to 3% by weight, e.g., from 15% to 5% by weight, or from 12% to 8% by weight. Such compositions may independently comprise, or may further comprise, an impurity according to (iv) above, i.e., FDCA, in an amount of from 2% to 0.05% by weight, e.g., from 1% to 0.1% by weight, or from 0.8% to 0.2% by weight. Such compositions may independently comprise, or may further comprise, other impurities, such as the above metals and / or their metal salts, in an amount of from 12% to 0.5% by weight, e.g., from 10% to 1% by weight, or from 8% to 3% by weight.

[0022] Advantageously, the processes described herein can include utilizing or recycling at least a portion of the partially converted and unconverted compounds (or impurities according to (iii) and / or (iv) above) back to the esterification reactor to improve overall esterification performance. For example, recycling can improve the overall conversion of FDCA and the overall yield of FDME or other diester derivatives of FDCA compared to the conversion and yield per pass achieved in the esterification reactor (i.e., a single pass of the reactants through the reactor). When esterification performance approaches the ideal case of recycling and eliminating the partially converted and unconverted compounds, the overall conversion in the esterification reactor approaches 100%, and the overall yield approaches the selectivity of the reaction.

[0023] In view of the above, according to certain embodiments in which the dialkyl ester derivative FDME is the target for recovery in the purified composition, specific color-forming impurities to be removed (or reduced in concentration relative to their concentration in the crude composition) in the purified composition are (i) 5-formyl-2-furandicarboxylic acid (FFCA) and (ii) 5-formyl-2-furandicarboxylic acid methyl ester (FFME). Other impurities are (iii) partially esterified or partially converted 2,5-furandicarboxylic acid monomethyl ester (FDMME), and (iv) unconverted FDCA, which are valuable intermediates and unconverted feed components, respectively, and therefore have the potential to improve overall esterification performance, as discussed above.

[0024] As previously mentioned, the alternative purification method (instead of distillation) to which this application pertains proceeds by identifying a specific solvent in which the target compound (FDME or other diester derivative of FDCA) is particularly soluble and which promotes the selective crystallization of this compound upon cooling. That is, crystallization allows the recovery of a purified solid composition having an increased content or weight percentage of the target compound relative to the crude composition.

[0025] An exemplary process for utilizing this discovery includes dissolving a crude FDCA ester composition in a solvent to form a solution of the crude composition, and crystallizing (or selectively crystallizing) from the solution of the crude composition a purified composition containing an increased content of FDME or other diester derivative of FDCA relative to the crude composition. According to such embodiments, the solvent differs from conventional solvents in that it is not the specific alcohol used to esterify FDCA in obtaining the target compound, or at least does not contain this alcohol in a significant amount (e.g., the alcohol is present in the solvent in an amount of less than 10 wt %, less than 5 wt %, or less than 1 wt %).

[0026] For example, if FDME is the target compound, resulting from the esterification of FDCA with methanol, the solvent may be referred to as a "non-methanol" solvent, which does not contain methanol, or at least does not contain significant amounts of methanol, as described above. Representative non-methanol solvents are organic solvents, such as those that form two distinct phases when combined with an equal volume of water. This type of solvent may be, more specifically, a non-alcoholic solvent that does not contain compounds with hydroxy (-OH) functional groups, such as alcohols, diols, polyols, and glycols, or at least does not contain significant amounts of such compounds, as described above. Alternatively, or in combination, in a preferred solvent, the target compound (FDME or other diester derivative of FDCA) has a solubility of at least 10% by weight (e.g., 10% to 45% by weight), at least 12% by weight (e.g., 12% to 40% by weight), or at least 15% by weight (e.g., 15% to 30% by weight) at 35°C. According to some embodiments, the solvent may include a halogenated hydrocarbon, a nitrile, an amide, a heterocycle-containing compound, an acetate, a ketone, or a sulfoxide. The solvent may, for example, comprise a major amount (e.g., at least 50% by weight, at least 75% by weight, at least 90% by weight, at least 95% by weight, or at least 99% by weight) of a particular compound from one of these classes. The solvent may comprise a mixture of compounds within these classes (thus, where the term acknowledges the possibility of both a single solvent type or multiple solvent types, it is expressly understood that "solvent" encompasses multiple chemically distinct solvent types in combination) and / or a mixture of compounds between these different classes, with such mixtures present in the solvent in such a major amount. Exemplary solvents may include one or more of methylene chloride; acetonitrile; N,N'-dimethylformamide; 1,4-dioxane; 1,1,2,2-tetrachloroethane; ethyl acetate; tetrahydrofuran; pyridine; acetone; and dimethyl sulfoxide, which may be present in the solvent in such a major amount, either alone or in combination. A particularly preferred solvent is methylene chloride due to its favorable combination of properties in terms of solubility of the target compound (e.g., FDME) and its selective crystallization from the impurities described herein. do.

[0027] The solution of the crude composition formed by dissolving the crude composition in a solvent (e.g., the non-methanol solvents described above for FDME) can be formed by dissolving the crude composition in the solvent at an elevated temperature, such as from 25°C to the normal boiling point of the solvent, or, if the solvent is a mixture, to the normal boiling point of the lowest boiling point compound in the mixture. For example, the elevated temperature can be from 25°C to 100°C, e.g., from 25°C to 80°C, or from 30°C to 50°C.

[0028] As noted above, purifying crude compositions according to the alternative processes to distillation described herein advantageously avoids the high temperatures to which crude compositions or solutions of such compositions would be subjected (if distillation, as proposed in the prior art, were used to purify these compositions). For example, the dissolution and crystallization steps can be carried out at temperatures below 130°C, below 100°C, below 80°C, below 60°C, or even below 40°C. Preferably, all dissolution and crystallization steps, in the case of certain processes utilizing two or more crystallization stages, are carried out at such temperatures. In more specific embodiments, in any process for purifying crude compositions described herein, the entire process is carried out at such temperatures; i.e., such temperatures are not exceeded at any point during the process. By limiting the maximum temperature, color formation and / or reduced color stability in the purified composition that may occur at higher temperatures can be reduced or entirely avoided.

[0029] Following the formation of a solution, such as by dissolving the crude composition in a solvent as described above, the crystallization step can be carried out by cooling the solution, optionally in combination with evaporating the solvent, for example, under vacuum. The cooling temperature profile can be selected to balance the objectives of processing efficiency with the objective of obtaining crystals of the desired size and / or size distribution. The solution can be cooled to a minimum temperature, for example, below 20°C, below 15°C, below 10°C, or below 5°C, which is reached in any of these cases after at least 1 hour, at least 2 hours, at least 3 hours, at least 4 hours, at least 6 hours, at least 8 hours, at least 10 hours, at least 20 hours, or at least 24 hours after cooling has begun. Cooling results in crystallization of the purified composition in solid form having an increased content or weight percent of the target compound (FDME or other diester derivative of FDCA), a decreased content or weight percent of one or more impurities, such as impurities (i), (ii), (iii), and (iv) above, and / or a decreased content or weight percent of the metals and / or their metal salts above.

[0030] After any crystallization step described herein, whether it involves crystallizing a composition purified in a first stage of crystallization, crystallizing a second-stage purified composition having an increased content or weight percentage of the target compound (e.g., FDME or other diester derivative of FDCA) relative to both the purified and crude compositions, or crystallizing a higher-stage purified composition, such a crystallization step is typically and preferably followed by recovery of such purified composition. This involves separating such purified composition as a solid from its respective mother liquor, such as when such purified composition is recovered as a solid residue in a filtration step. Recovery of such purified composition may include additional steps of rinsing (e.g., with additional washes of solvent) and / or drying. Thus, a process having two or more crystallization stages can include crystallizing the purified composition in each stage, with successive crystallization steps resulting in compositions with successively increasing purity or weight percent of the target compound. Recovery of such purified composition in all stages except the final stage can be followed by redissolving such purified composition in respective additional amounts of solvent, and then redissolving the solvent in each additional amount of solvent. The solvent may be referred to as a second stage solvent, a third stage solvent, etc. These additional amounts will typically have the same composition as the solvent used in the first stage to dissolve the crude composition. However, the use of solvents with different components, or different amounts of the same components, is also contemplated.

[0031] In another embodiment, a process for purifying a crude composition containing a target compound (e.g., a diester derivative of FDME or other FDCA) combines the use of liquid-liquid extraction of a solution of the crude composition with crystallization. An exemplary process involves forming a biphasic solution of the crude composition in a solvent containing an organic phase and a separate aqueous phase. Such a process further includes separating the organic phase from the aqueous phase and crystallizing a purified composition from the organic phase, which has the characteristics described herein (e.g., increased content or weight percent of FDME or other diester of FDCA). The organic phase as part of the biphasic solution can include or have the composition of any of the organic solvents described above. The organic phase is not limited by the exclusion of alcohols and, therefore, may include one or more compounds having at least one hydroxy (OH) functional group, such as alcohols (e.g., methanol), diols, polyols, and / or glycols (e.g., in the major component amounts described above). The biphasic solution can be formed, for example, by dissolving the crude composition in the organic phase to form a solution of the crude composition, followed by adding the aqueous phase to the solution. Alternatively, the components for forming the two-phase solution may be added in other orders, such as combining the aqueous phase with the crude composition before dissolving the crude composition in the organic phase, or combining the organic and aqueous phases before adding the crude composition. When a two-phase solution is formed, the organic phase can be easily separated from the aqueous phase, such as by removing the denser phase (e.g., the organic phase) through the bottom of a separation device, before crystallizing the purified composition from the organic phase. The crystallization step can be carried out as described above, for example, by following a cooling temperature profile having a minimum temperature achieved over a period of time within the parameters set forth above.

[0032] In such extraction or extractive crystallization processes, one or more impurities in the crude composition (e.g., one or more of impurities (i), (ii), (iii), and (iv) above) are selectively solubilized in the aqueous phase relative to the target compound (FDME or other diester of FDCA) in the crude composition. The target compound is selectively solubilized in the organic phase relative to one or more impurities in the crude composition. For a given compound to be selectively solubilized in a given phase, a greater proportion of that compound originally present in the crude composition is solubilized in that particular phase than in other phases. The aqueous phase can be water or, in preferred embodiments, an aqueous salt solution that aids in the selective solubilization of one or more impurities (e.g., FDMME and / or FDCA) in this phase, for example, by ionizing the carboxylic acid groups of these impurities. A preferred salt solution is sodium bicarbonate solution, however solutions of other salts such as salts of alkali and alkaline earth metals (e.g., Na, K, Mg, Ca, Sr, Ba) as well as salts of other metals, including carbonates, bicarbonates, nitrates, sulfates, halides (e.g., chlorides), phosphates, or other salts, can also be used as the aqueous phase, with such salts being present alone or in combination in the salt solution / aqueous phase.

[0033] Particularly for large-scale operations, the steps of forming a biphasic solution and separating the organic phase from the aqueous phase can be efficiently carried out as steps of a continuous liquid-liquid extraction or as steps of an overall continuous extractive crystallization process. The steps of forming a biphasic solution and separating the organic phase from the aqueous phase can also be carried out as steps of a multi-stage liquid-liquid extraction or as steps of an overall extractive crystallization process. Such extraction or extractive crystallization processes may further include one or more additional steps of extracting the aqueous phase with additional extract volumes of organic phase, e.g., with additional volumes of liquid having the composition of the organic phase but not originally used for the organic phase itself. The process may include extracting the aqueous phase by contacting it with each of such one or more respective additional extract volumes of organic phase in one or more extraction steps to extract (or selectively solubilize) one or more respective additional portions of the target compound (FDME or other diesters of FDCA originally present in the crude composition) from the aqueous phase. Following such an extraction step, one or more additional extraction steps may be carried out. A quantity of the organic phase can be combined with the organic phase originally used in forming the two-phase solution, and then the purified composition can be crystallized from the resulting combined organic phase. Thus, one or more additional steps of extracting the aqueous phase can serve to increase the yield of the target compound in the combined organic phase, and therefore the yield upon recovery after the subsequent crystallization step.

[0034] Alternatively, or in combination, such extraction or extractive crystallization processes may further include one or more additional steps of extracting the organic phase with an additional extract volume of aqueous phase, e.g., with an additional volume of liquid having the composition of the aqueous phase but not originally used in the aqueous phase itself. The process may include extracting the organic phase in one or more extraction steps by contacting the organic phase with each of such one or more additional extract volumes of aqueous phase to extract (or selectively solubilize) from the organic phase an additional portion of one or more of the impurities present in the crude composition (e.g., one or more of impurities (i), (ii), (iii), and (iv) described above). Following such an extraction step, the one or more additional extract volumes of aqueous phase may be combined with the aqueous phase originally used in forming the two-phase solution, and then the purified composition may be crystallized from the resulting combined aqueous phase. Thus, one or more additional steps of extracting the organic phase may serve to increase the yield of one or more impurities in the combined aqueous phase and / or increase the purity of the target compound after crystallization from the organic phase or the combined organic phase (when using an additional extract volume of organic phase as described above).

[0035] With regard to such processes in which impurities of the crude composition are extracted (selectively solubilized) into the aqueous phase or the combined aqueous phase (when using additional extraction amounts of aqueous phase as described above), either sequentially or using one or more extraction steps, removal of such impurities that would otherwise be present in the purified composition can improve its color and / or color stability, as in the case of removal of impurities according to (i) and / or (ii) above. Alternatively, or in combination, extraction of such impurities into the aqueous phase or the combined aqueous phase can concentrate certain impurities of value as partially converted and unconverted compounds in this phase, as in the case of concentrating impurities according to (iii) and / or (iv) above. This advantageously allows such partially converted and unconverted compounds to be recycled to the esterification reactor for their complete, or at least more complete, esterification.

[0036] In a typical process, for example, the aqueous phase may contain a greater proportion of impurities according to (iii) and / or (iv) above (e.g., partially esterified (partially converted) 2,5-furandicarboxylic acid monomethyl ester (FDMME) and / or unesterified (unconverted) 2,5-furandicarboxylic acid (FDCA) originally present in the crude composition) relative to the target compound (FDME or other diester of FDCA) than the organic phase. Similarly, or conversely, the aqueous phase may contain a greater amount of impurities according to (iii) and / or (iv) above (e.g., partially esterified (partially converted) 2,5-furandicarboxylic acid monomethyl ester (FDMME) and / or unesterified (unconverted) 2,5-furandicarboxylic acid (FDCA) originally present in the crude composition) than the organic phase. According to certain embodiments, the process may further include utilizing impurities according to (iii) and / or (iv) above (e.g., FDMME and / or FDCA) present in the aqueous phase in an esterification reactor to convert at least a portion of such impurities to the target compound (e.g., FDME). For example, one or more of such impurities can be recycled to the same esterification reactor from which the crude composition is obtained.

[0037] Whether or not the impurities from (iii) and / or (iv) above are ultimately utilized (e.g., recycled) in the esterification reactor, they can be recovered from the aqueous phase (or the combined aqueous phases) as valuable products, thereby improving the economics of the process. These impurities (e.g., FDMME and / or FDCA) can be removed from the esterification reactor. The step of utilizing the impurities for recycling to the purification reactor or for another purpose may include recovering at least a portion of these impurities present in the aqueous phase (or the combined aqueous phases) by separation from this phase. For example, the process may include recovering at least a portion of these impurities as a solid precipitate, more specifically recovering this precipitate by filtration. If valuable impurities are present in the aqueous phase (e.g., in the sodium bicarbonate solution), they can be precipitated from this phase by altering the properties of the aqueous phase that reduce their solubility, such as lowering the pH of the aqueous phase to reduce the proportion of carboxylic acid groups on these impurities that are ionized.

[0038] The step of forming a biphasic solution is not limited to the step of forming such a solution of the crude composition. For example, in a process using two or more crystallization stages, a second-stage biphasic solution of the purified composition may be formed, a third-stage biphasic solution of the second-stage purified composition may be formed, etc. In other embodiments, the step of forming a biphasic solution of the crude composition may be omitted, but one or more steps of forming a biphasic solution of the purified composition and / or a biphasic solution of a higher-stage purified composition may be used, whereby the associated higher-stage stage is an extractive crystallization stage.

[0039] The use of a solid processing medium to improve the quality of a solution of the crude composition is also contemplated, in various combinations with crystallization. One example involves dissolving the crude composition in a solvent to form a solution of the crude composition and contacting the solution of the crude composition with a solid processing medium to obtain a treated solution of the crude composition. The solvent may be any of those described above, but is not limited by the exclusion of alcohols. Thus, it may include one or more compounds having at least one hydroxy (—OH) functional group, such as alcohols, diols, polyols, and / or glycols (e.g., in major amounts as described above). A preferred solvent is methanol. The solid processing medium can remove insoluble impurities, such as the metals and their metal salts, from the solution of the crude composition, so that the treated solution contains a reduced content of insoluble impurities compared to the solution of the crude composition. For this purpose, a solid processing medium containing diatomaceous earth (DE) is effective. Similarly, or alternatively, the solid processing medium can improve the color of the solution of the crude composition, for example, so that the treated solution has a lighter color compared to the solution of the crude composition. For this purpose, a solid processing medium containing carbon, such as activated carbon (AC), is effective. Such treatments to reduce the content of insoluble impurities and / or to improve the color of solutions of crude compositions also extend to the same improvements in purified compositions and / or higher stage purified compositions.

[0040] Following its formation, the solution of the crude composition can be contacted with such a solid treatment medium either batchwise or continuously. For example, batch contacting can be accomplished by mixing the solution of the crude composition with particles of the solid treatment medium, agitating the mixture (e.g., shaking, stirring, vibrating), and then filtering the mixture to separate the solid treatment medium and recover the treated solution. Continuous contacting can be accomplished by passing (e.g., pumping) the solution of the crude composition through a fixed bed of the solid treatment medium, with the effluent from the bed corresponding to the treated solution.

[0041] Furthermore, the step of treating by contact with a solid treatment medium is not limited to treating a solution of a crude composition. For example, in processes using two or more stages of crystallization, such steps may include contacting a second-stage solution of a purified composition, a third-stage solution of a composition purified in the second stage, etc. In other embodiments, the step of treating by contacting a solution of a crude composition may be omitted, but one or more steps of contacting a solution of a purified composition and / or a solution of a higher stage of purified composition may be used. The steps of treating with a solid treatment medium to remove insoluble impurities and / or improve color, as described above, can be performed in any order and can be used independently at various stages of a process utilizing two or more stages of crystallization.

[0042] For example, according to certain embodiments, a representative process may include contacting a solution of the crude composition with a solid processing medium, such as diatomaceous earth (DE), to remove insoluble impurities and obtain a treated solution having a reduced content of insoluble impurities compared to the solution of the crude composition. When DE is used as the solid processing medium with which the solution of the crude composition is contacted, the subsequent stage of crystallization may omit the use of DE and instead use carbon (e.g., AC) to improve the color of the purified composition solution (recovered from the first stage) formed by dissolving the purified composition in a second-stage solvent (e.g., having the same or different composition as the solvent used to form the solution of the crude composition). Thus, a representative process may include recovering the purified composition (e.g., by filtration), as well as performing a second stage of purification (crystallization) that includes dissolving (or redissolving) the purified composition in a second-stage solvent to form a second-stage solution of the purified composition, and contacting the second-stage solution of the purified composition with a solid processing medium, such as carbon (e.g., AC), to obtain a second-stage treated solution having a lighter color compared to the second-stage solution. These processes may further include crystallizing a second-stage purified composition from the second-stage processed solution, which has an increased content or weight percent of the target compound (FDME or other diester of FDCA) compared to both the purified and crude compositions. Additional stages of crystallization are also contemplated, with or without contacting the solution formed in these stages with a solid processing medium. Similarly, any stage of crystallization may alternatively or in combination utilize a separate aqueous phase to form the two-phase solution described above, thereby making any such stage an extractive crystallization stage.

[0043] Advantageously, the crystallization process described herein, optionally in combination with the use of extraction and / or solid processing media described herein, provides an effective and straightforward solution for the purification of solid compositions of FDME and other diesters of FDCA, particularly when compared to distillation. This process provides a favorable combination of purity and recovery (yield) of the target compound based on the amount initially present in the crude composition. After one stage of crystallization, for example, the target compound (e.g., FDME) may be present in the purified composition at a purity of greater than 98%, greater than 99%, or even greater than 99.8% by weight. These purity levels, or even higher, are applicable to higher-stage purified compositions (e.g., second-stage purified compositions). Of further practical importance is the ability of the processes described herein to provide purified compositions having very low levels of impurities according to (i) and / or (ii) above, which, even in very small amounts, are deleterious in terms of their tendency to form color and / or reduce color stability in these compositions and in bio-based polymers produced by using these compositions in downstream polymerizations. For example, either or both of impurities according to (i) (e.g., 5-formyl-2-furandicarboxylic acid (FFCA)) and (ii) (e.g., 5-formyl-2-furandicarboxylic acid methyl ester (FFME)) may be present in the purified composition or higher-stage purified composition in amounts of less than 500 ppm by weight, less than 100 ppm by weight, less than 50 ppm by weight, or even less than 10 ppm by weight. Any of these purity characteristics of the purified composition or higher stage purified composition, with respect to the presence of the target compound and / or the presence of undesired impurities, can achieve a recovery of the target compound in the purified composition or higher stage purified composition of at least 60% by weight (e.g., 60% to 99% by weight), at least 70% by weight (e.g., 70% to 95% by weight), or at least 75% by weight (e.g., 75% to 92% by weight) of the target compound in the crude product.

[0044] The following examples are provided as representative of the present invention. These examples are illustrative and should not be construed as limiting the scope of the invention, which is defined by the appended claims. [Example]

[0045] Example 1 Solubility of crude compositions containing FDME in various solvents An impure solid FDME sample obtained by esterifying FDCA with methanol was found to contain 82.6 wt. % FDME (dimethyl ester) in addition to 10.4 wt. % FDMME, the monomethyl ester, resulting from incomplete esterification. The sample also contained 0.35 wt. % FDCA starting compound and 0.58 wt. % FFME, an aldehyde contaminant. In separate solubility studies using different solvents, various amounts of this sample were loaded into scintillation vials, and 10 ml of solvent was added in each case. The vials were then sonicated at 35°C for 15 minutes to determine the solubility of FDME. The results are shown in Table 1 below.

[0046] [Table 1]

[0047] From these results, it can be seen that the crude FDME composition exhibits good solubility in methylene chloride; acetonitrile; N,N'-dimethylformamide; 1,4-dioxane; 1,1,2,2-tetrachloroethane; ethyl acetate; tetrahydrofuran; pyridine; acetone; and dimethyl sulfoxide.

[0048] Example 2 Extractive crystallization of FDME from the crude composition using a biphasic solution with methylene chloride as the organic phase and sodium bicarbonate as the aqueous phase A 200 gram sample of the dried impure mixture (crude composition containing FDME) obtained from the esterification of FDCA to FDME with methanol was placed on a PTFE magnetic stir bar. The solid composition was determined by UPLC-PDA to be 80 wt% FDME, 18 wt% FDMME, and 2 wt% FDCA. Approximately 100 ml of methylene chloride was added to the flask, followed by 100 ml of 5 wt% sodium bicarbonate. The biphasic solution was vigorously stirred for 30 minutes and transferred to a 1-liter separatory flask, which was used to remove the lower organic phase. The upper aqueous phase was extracted twice with additional 30 ml methylene chloride extracts. These extracts were combined with the organic phase, and the combined liquid was transferred to a 500 ml Wheaton bottle and placed in the freezer overnight. The next morning, the storage bottle was removed from the freezer, revealing a large amount of long, shard-like crystals, which were filtered using a Buchner funnel. The retained crystals were dried under a stream of argon for 1 hour and determined to weigh 58.7 grams. They were then stored in a 250 ml Wheaton bottle. Crystal purity analysis of the purified composition was quantitative. 1 H NMR was performed and showed them to be 99.98% pure by weight. The crystals were stored in a tabletop bottle in ambient air. This extremely high purity was surprisingly maintained after 3.5 years, indicating the exceptional stability of the purified composition. Furthermore, the composition retained its characteristics over this period in that it contained free-flowing crystals with little to no off-white color development.

[0049] In this regard, the color of the purified FDME composition was quantitatively evaluated by determining its chromaticity coordinates in the L*a*b* color space, which refers to the specific color space of the different color systems of the CIE, or Commission Internationale de l'Echairage. These color systems were developed as a way to standardize color or to express color values ​​numerically, thereby eliminating the subjectivity of human observers. The CIE 1976 (L*a*b*) color space is based on the opponent color theory of color vision, which states that two colors cannot simultaneously be both green and red, or both blue and yellow. Therefore, a single value can be used to represent the red / green and yellow / blue attributes of a sample. In this regard, when a color is expressed using the La*b* color space, the L*, a*, and b* coordinates represent lightness, red / green value, and yellow / blue value, respectively, and these coordinates range from -100 to +100. With respect to yellow, for purposes of characterizing the compositions described herein, the b* value is particularly relevant. Evaluation of the L*, a*, and b* coordinates of purified FDME compositions was performed using a commercially available colorimeter, Model CM-5, manufactured by Konica Minolta, Inc.

[0050] Another color measurement, called APHA color, was also determined for the purified FDME composition according to ASTM D1209. APHA color is also known as the Hazen scale and the platinum-cobalt (Pt / Co) scale. APHA is a color standard named after the American Public Health Association, originally intended to describe the color of wastewater, but its use has expanded to include other applications. APHA color is a color scale sometimes called the "yellowness index" used to evaluate the quality of clear to yellowish liquids.

[0051] To prepare the first sample (Sample #1) of purified FDME composition for color analysis, a 0.597 gram portion of the composition was dissolved in 9.414 grams of a 1:1 (v / v) acetonitrile / isopropanol solvent mixture. As a result, Sample #1 contained 5.96% dissolved composition by weight. A second sample, Sample #2, was prepared by dissolving a 0.592 gram portion of the composition in 9.406 grams of this solvent, such that Sample #2 contained 5.92% dissolved composition by weight. Two CIE 1976 (L*a*b*) colorimetric measurements and two APHA measurements were performed on each sample, with a target concentration of 6% dissolved solids by weight. The samples and results are summarized in Tables 2 and 3 below.

[0052] [Table 2]

[0053] [Table 3]

[0054] The above results demonstrate that the purified FDME composition (crystallized from methylene chloride) has excellent color stability when stored for more than three years without special handling, i.e., exposed to ambient air. Even after the passage of time, the colorimetric results met the purified FDME specifications of L*>99, a*<0.5, and b*<0.5.

[0055] Example 3 Crystallization of FDME from crude compositions using DE as a solid processing medium The combination of diatomaceous earth filtration and crystallization was investigated for its effectiveness in purifying a crude FDME composition having the weight percent proportions of individual compounds described in Example 1. A 105-gram sample of this crude composition was ground and dissolved in 700 ml of methanol to obtain a 15 wt. % stock solution of the crude composition, which was maintained at 55°C with shaking in a water bath. A 300-gram portion of this stock solution was removed, diluted to 2 wt. % dissolved solids, or approximately its solubility at room temperature, and filtered through a 2-inch diatomaceous earth (DE) filter using a Buchner funnel. Following this DE filtration, a vacuum pump was used to concentrate the solution back to 20 wt. % in the crystallizer, and the methanol solvent was distilled off. Starting at a temperature of 50°C, cooling crystallization was performed without the need for seeding, as primary nucleation occurred rapidly upon cooling. Agitation at 100 rpm was maintained during cooling, and particle size distribution was measured in real time. A programmed cooling profile was used to achieve a solution temperature of 10°C over 20 hours, with varying residence times at different temperatures. It was determined that a 2-hour residence time at 35°C followed by cooling to 30°C resulted in significant nucleation. After a 2-hour residence time at 30°C, crystal growth became evident, with the number of fine crystals decreasing at approximately the same rate as the number of large (>100 micron) crystals increased. The initial fine crystal growth was evidenced by the total crystal number remaining stable. This growth continued at 1.7°C / hr over a period that resulted in a 25% increase in crystal weight. As crystallization progressed, the average crystal size increased and the crystal size distribution narrowed.

[0056] The solids from the crystallization were emptied onto a Buchner funnel filter, and the crystals were sprayed with room-temperature methanol. The mother liquor from the filtration contained approximately 2 wt. % FDME, corresponding to its room-temperature solubility in methanol. However, warming the 10 °C crystallized solid / methanol mixture to room temperature redissolved only fine crystals, making crystal growth a key factor for achieving high yields and recovery rates. Methanol spraying was discontinued when the color of the wash methanol lightened, indicating that no more impurities were being removed. After this one-stage crystallization, 67% of the FDME from the crude composition was recovered in the purified composition, which was determined to be 99.05 wt. % FDME and 0.86 wt. It was also possible to capture the remaining 2-4 wt. % FDME in the mother liquor / wash methanol. In any case, favorable purity and recovery characteristics were obtained.

[0057] Example 4 Crystallization of FDME from crude composition using DE as solid processing medium, followed by rapid cooling Additional experiments were performed as described in Example 3, except that cooling from 65°C to 15°C was performed more rapidly over 6 and 2 hours. These experiments resulted in the recovery of crystals with greater than 99% wt. FDME purity, but also with smaller average sizes resulting in lower yields (higher losses in the wash methanol, as explained in Example 3). The purified composition obtained after 6 hours was 99.20% wt. FDME and 0.76% wt. FDMME, while the composition obtained after 2 hours was 99.06% wt. FDME and 0.90% wt. FDMME. Again, high purity was achieved in a single step, and additional experiments demonstrated the trade-off between cooling time and recovery rate.

[0058] Example 5 Crystallization of FDME from crude compositions using AC as a solid processing medium Additional experiments were conducted as described in Example 3, but using AC rather than DE as the solid treatment medium. Specifically, a methanol solution of the crude composition described in this example was treated with 5 wt. % AC, followed by cooling, crystallization, and methanol washes as described in this example. Importantly, the yield or recovery of FDME from the crude composition after this single stage of crystallization was 84.1%, and the crystals were significantly whiter in color compared to those recovered in Example 3. The purity of these crystals was determined to be 99.56 wt. %. Another important result of this experiment is that no FDME was lost in the activated carbon treatment step; 100% was recovered, despite the fact that an isothermal carbon study of pure FDME indicated loss of some furan rings. Without being bound by theory, it is believed that competing impurities in the crude FDME composition mitigated this effect. This single stage of crystallization with activated carbon pretreatment advantageously provided a beneficial combination of product purity, recovery, and appearance.

[0059] The specific embodiments and examples described herein are for illustrative purposes only and do not limit the invention as defined by the appended claims. Practice of the invention further relates to all beneficial effects inherent therein. Those skilled in the art, armed with the knowledge gained from this disclosure, will recognize that various modifications may be made to the disclosed processes to achieve these and other advantages without departing from the scope of the present disclosure.

[0060] Terms: 1. A method for purifying a crude composition containing 2,5-furandicarboxylic acid dimethyl ester (FDME), comprising: dissolving the crude composition in a non-methanol solvent to form a solution of the crude composition; and crystallizing a purified composition from the solution of the crude composition, the purified composition having an increased content of FDME compared to the crude composition; A method comprising: 2. The method of claim 1, wherein the crude composition comprises FDME in an amount of 75% to 95% by weight. 3. The method of clause 1, wherein the non-methanol solvent is an organic solvent. 4. The method of clause 1, wherein the non-methanol solvent is a non-alcohol solvent. 5. The method of any one of clauses 1 to 4, wherein a non-methanol solvent is used in which FDME has a solubility of at least 12% by weight at 35°C. 6. The method of clause 1, wherein the non-methanol solvent comprises a halogenated hydrocarbon, a nitrile, an amide, a heterocycle-containing compound, an acetate, a ketone, or a sulfoxide. 7. The method of clause 1, wherein the non-methanol solvent comprises a compound selected from the group consisting of methylene chloride; acetonitrile; N,N'-dimethylformamide; 1,4-dioxane; 1,1,2,2-tetrachloroethane; ethyl acetate; tetrahydrofuran; pyridine; acetone; and dimethyl sulfoxide. 8. The method of any one of clauses 1 to 7, wherein the solution of the crude composition is formed at an elevated temperature from 25° C. to the normal boiling point of the non-methanol solvent. 9. The method according to clause 8, wherein the dissolving and crystallizing steps are carried out at a temperature below 100°C. 10. The method of any one of clauses 1-9, wherein the step of crystallization comprises cooling a solution of the crude composition. 11. The method of claim 1, wherein the purified composition contains a reduced content of one or more impurities selected from the group consisting of 2,5-furandicarboxylic acid monomethyl ester (FDMME); 2,5-furandicarboxylic acid (FDCA); 5-formyl-2-furancarboxylic acid methyl ester (FFME); 5-formyl-2-furancarboxylic acid (FFCA); and methyl 2-furoate (MF) compared to the crude composition. 12. A method for purifying a crude composition containing 2,5-furandicarboxylic acid dimethyl ester (FDME), comprising: forming a biphasic solution of the crude composition in a solvent comprising an organic phase and a separate aqueous phase; Separating the organic phase from the aqueous phase; and crystallizing a purified composition from the organic phase, the purified composition having an increased content of FDME compared to the crude composition; A method comprising: 13. The method of clause 12, wherein the steps of forming a biphasic solution and separating the organic phase from the aqueous phase are steps of continuous liquid-liquid extraction, wherein one or more impurities in the crude composition are selectively solubilized in the aqueous phase relative to FDME in the crude composition, and wherein FDME is selectively solubilized in the organic phase relative to one or more impurities in the crude composition. 14. The steps of forming a two-phase solution and separating the organic phase from the aqueous phase are steps of multi-stage liquid-liquid extraction; extracting the aqueous phase in one or more extraction steps by contacting the aqueous phase with one or more respective additional extract amounts of the organic phase to extract one or more respective additional portions of FDME from the aqueous phase; and combining one or more additional extract amounts of organic phase containing one or more respective additional portions of FDME with the organic phase, and then crystallizing the purified composition from the combined organic phase; 13. The method of clause 12, further comprising: 15. The aqueous phase contains a greater ratio of partially esterified 2,5-furandicarboxylic acid monomethyl ester (FDMME) and / or non-esterified 2,5-furandicarboxylic acid (FDCA) to FDME than the organic phase; utilizing the FDMME and / or FDCA present in the aqueous phase in an esterification reactor to convert at least a portion of the FDMME and / or FDCA to FDME; 13. The method of clause 12, further comprising: 16. The process utilizing FDMME and / or FDCA is 16. The method of claim 15, comprising recovering at least a portion of the FDCA and / or FDCA as a solid precipitate. 17. A method for purifying a crude composition containing 2,5-furandicarboxylic acid dimethyl ester (FDME), comprising: dissolving the crude composition in a solvent to form a solution of the crude composition; contacting the solution of the crude composition with a solid treatment medium to obtain a treated solution; and crystallizing a purified composition from the treated solution of the crude composition, the purified composition comprising an increased content of FDME compared to the crude composition; A method comprising: 18. The method of claim 17, wherein the solid processing medium removes insoluble impurities from the solution of the crude composition. 19. The method of claim 17, wherein the solid processing medium improves the color of the solution of the crude composition. 20. The method further comprising recovering the purified composition and performing a second stage of purification, wherein the second stage of purification comprises: dissolving the purified composition in a second-stage solvent to form a second-stage solution of the purified composition; contacting the second-stage solution of the purified composition with a solid treatment medium to obtain a second-stage treated solution having a lighter color than the second-stage solution; and crystallizing a second-stage purified composition from the second-stage treated solution, the second-stage purified composition having an increased content of FDME compared to both the purified composition and the crude composition; 18. The method according to clause 17, comprising:

Claims

1. 1. A method for purifying a crude composition comprising 2,5-furandicarboxylic acid dimethyl ester (FDME), comprising: dissolving the crude composition in a non-methanol solvent to form a solution of the crude composition; and crystallizing from said solution of said crude composition a purified composition comprising an increased content of FDME compared to said crude composition; A method comprising:

2. 10. The method of claim 1, wherein the crude composition comprises FDME in an amount of 75% to 95% by weight.

3. 10. The method of claim 1, wherein the non-methanol solvent is an organic solvent.

4. 10. The method of claim 1, wherein the non-methanol solvent is a non-alcohol solvent.

5. 10. The method of claim 1, wherein a non-methanol solvent is used in which FDME has a solubility of at least 12% by weight at 35°C.

6. 10. The method of claim 1, wherein the non-methanol solvent comprises a halogenated hydrocarbon, a nitrile, an amide, a heterocycle-containing compound, an acetate, a ketone, or a sulfoxide.

7. 10. The method of claim 1, wherein the non-methanol solvent comprises a compound selected from the group consisting of methylene chloride; acetonitrile; N,N'-dimethylformamide; 1,4-dioxane; 1,1,2,2-tetrachloroethane; ethyl acetate; tetrahydrofuran; pyridine; acetone; and dimethyl sulfoxide.

8. 8. The method of any one of claims 1 to 7, wherein the solution of the crude composition is formed at an elevated temperature from 25°C to the normal boiling point of the non-methanol solvent.

9. 9. The method of claim 8, wherein the steps of dissolving and crystallizing are carried out at a temperature below 100°C.

10. 10. The method of claim 1, wherein the step of crystallizing comprises cooling the solution of the crude composition.

11. 1. A method for purifying a crude composition comprising 2,5-furandicarboxylic acid dimethyl ester (FDME), comprising: forming a biphasic solution of said crude composition in a solvent comprising an organic phase and a separate aqueous phase; separating the organic phase from the aqueous phase; and crystallizing from said organic phase a purified composition comprising an increased content of FDME compared to said crude composition; A method comprising:

12. 12. The method of claim 11, wherein said steps of forming a two-phase solution and separating said organic phase from said aqueous phase are steps of continuous liquid-liquid extraction, wherein one or more impurities in said crude composition are selectively solubilized in said aqueous phase relative to FDME in said crude composition, and wherein FDME is selectively solubilized in said organic phase relative to one or more impurities in said crude composition.

13. said steps of forming a two-phase solution and separating said organic phase from said aqueous phase are steps of multi-stage liquid-liquid extraction; The method comprises: extracting the aqueous phase in one or more extraction stages by contacting the aqueous phase with one or more respective additional extract amounts of the organic phase to extract one or more respective additional portions of FDME from the aqueous phase; and combining the one or more additional extraction amounts of the organic phase containing the one or more respective additional portions of FDME with the organic phase, and then crystallizing the purified composition from the combined organic phase; The method of claim 12 further comprising:

14. the aqueous phase contains a greater ratio of partially esterified 2,5-furandicarboxylic acid monomethyl ester (FDMME) and / or unesterified 2,5-furandicarboxylic acid (FDCA) to FDME than the organic phase; utilizing the FDMME and / or FDCA present in said aqueous phase in an esterification reactor to convert at least a portion of said FDMME and / or FDCA to FDME; The method of claim 12 further comprising:

15. 15. The method of claim 14, wherein the step of utilizing FDMME and / or FDCA comprises recovering at least a portion of the FDMME and / or FDCA present in the aqueous phase as a solid precipitate.

16. 1. A method for purifying a crude composition comprising 2,5-furandicarboxylic acid dimethyl ester (FDME), comprising: dissolving the crude composition in a solvent to form a solution of the crude composition; contacting said solution of said crude composition with a solid processing medium to obtain a treated solution; and crystallizing from the treated solution of the crude composition a purified composition comprising an increased content of FDME compared to the crude composition; A method comprising:

17. recovering the purified composition and performing a second stage of purification, the second stage of purification comprising: dissolving the purified composition in a second-stage solvent to form a second-stage solution of the purified composition; contacting the second-stage solution of the purified composition with a solid treatment medium to obtain a second-stage treated solution having a lighter color than the second-stage solution; and 17. The method of claim 16, comprising crystallizing from the second-stage treated solution a second-stage purified composition comprising an increased content of FDME compared to both the purified composition and the crude composition.

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