Method for reprocessing polytetramethylene ether glycol

Abstract

The disclosed process relates to a process for converting polytetramethylene ether glycol to tetrahydrofuran, the process comprising the steps of: a) introducing a stream comprising polytetramethylene ether glycol into a strong acid catalyst capable of converting polytetramethylene ether glycol to tetrahydrofuran and water; b) operating the process in a reactor under operating conditions sufficient to carry out acid catalyzed depolymerization of polytetramethylene ether glycol to tetrahydrofuran and water; and c) recovering the tetrahydrofuran.

Description

Related Applications

[0001] This International PCT Patent Application claims priority to U.S. Provisional Patent Application No. 63 / 426,794, filed on November 21, 2022, which is incorporated herein by reference in its entirety. Related fields

[0002] The disclosed process relates to a process for converting polytetramethylene ether glycol ("PTMEG") to tetrahydrofuran ("THF") in the presence of a strong acid catalyst. Background Art

[0003] Polytetramethylene ether glycol (PTMEG) is a major component in a variety of polyurethane, polyester, and polyamide elastomers. PTMEG also reacts with isocyanates or organic acids to form elastomers. Major end uses include spandex, castable polyurethanes, thermoplastic polyurethanes, polyurethane coatings and sealants. PTMEG is a polymer of tetrahydrofuran (THF) that is prepared via THF polymerization and methanolysis reactions.

[0004] Current processes for making THF use a reaction mixture containing 1,4-butanediol ("BDO") which is carried out in a distillation reaction zone in the presence of an acid catalyst (e.g., sulfuric acid) in liquid form. This acid catalyst is necessary to complete the dehydration and ring closure of the BDO. However, the presence of this acid catalyst has a destructive effect on process components.

[0005] As an alternative to the use of an acid catalyst such as sulfuric acid, US2016214952A1 in the name of the present applicant and its Chinese equivalent CN105531266B disclose an improved process for producing THF from a reaction mixture comprising BDO in the presence of a strong acid catalyst in a reaction vessel comprising a distillation reaction zone, wherein the acid catalyst is suspended in a steam-rich zone in the distillation reaction zone. This improved process advantageously allows for cheaper process vessels and significantly reduces tar formation.

[0006] In downstream processing reactions, THF can then be converted to polytetramethylene ether acetate ("PTMEA") by ring-opening polymerization with a superacid (generally an acid stronger than 100% sulfuric acid), allowing for low residence times. Figure 1B As shown in , product molecular weight is controlled by the addition of acetic anhydride, which together with low residence time allows rapid transitions between product grades. PTMEA is then converted to PTMEG by strong base transesterification in a methanolysis reaction in a reactive distillation column, as Figure 1C shown.

[0007] The resulting PTMEG polymer contains molecules of different chain lengths with a wide molecular weight distribution. Typical average molecular weight distributions are between 150 Daltons and 3000 Daltons. Different end uses of PTMEG require PTMEG with different average molecular weight distributions. For example, some applications require PTMEG with an average molecular weight distribution of only 250 Daltons (Mn~250), while other applications require PTMEG with an average molecular weight distribution of 2000 Daltons (Mn~2000). The process conditions can be varied to result in the synthesis of PTMEG with different defined average molecular weight distributions.

[0008] For a given PTMEG polymer having a particular average molecular weight distribution, the molecular weight of the oligomers therein can still vary significantly. If the polymer contains too high a percentage of short chain oligomers, this can have a deleterious and adverse effect on the properties of the final product.

[0009] In addition, sometimes the step of converting THF to PTMEA (see Figure 1B ) inadvertently results in the formation of PTMEA with an incorrect molecular weight (usually greater than the desired average molecular weight) so that the PTMEG derived from the PTMEA falls outside the narrow molecular weight distribution ideal for use in the targeted downstream spandex and polyurethane markets. Entire batches of PTMEG produced from the PTMEA are rarely reprocessed and are therefore wasted.

[0010] Therefore, according to current practice, there is a need for methods to reprocess PTMEG that falls outside of a desired average molecular weight distribution. Summary of the invention

[0011] Embodiments disclosed herein provide an improved process for converting polytetramethylene ether glycol to tetrahydrofuran. Disclosed herein is a process comprising introducing a stream comprising polytetramethylene ether glycol to a strong acid catalyst capable of converting the polytetramethylene ether glycol to tetrahydrofuran and water; operating the process in a reactor under operating conditions sufficient to effect acid-catalyzed depolymerization of the polytetramethylene ether glycol to tetrahydrofuran and water; and recovering the tetrahydrofuran.

[0012] There is a known problem that the step of converting THF to PTMEA sometimes inadvertently results in PTMEG of incorrect molecular weight, such that the PTMEG derived from the PTMEA falls outside the narrow molecular weight distribution required for use in the downstream spandex and polyurethane markets. It is desirable to provide a solution for reprocessing such PTMEG that falls outside the desired molecular weight distribution.

[0013] Embodiments herein provide solutions to overcome this problem by providing a strong acid catalyst that can be used to depolymerize PTMEG into THF and water under certain reaction conditions. Such strong acid catalysts are known to convert BDO into THF and water (see Vaidya et al., Applied Catalysis A: General 242 (2003), 321-328, and U.S. Patent Application Publication No. 2016 / 0214952A1 in the name of the present applicant and its Chinese equivalent CN105531266B, which discloses an improved process for making THF from a reaction mixture containing BDO in the presence of a strong acid catalyst). However, surprisingly, there is no suggestion or prior motivation for using a strong acid catalyst in an alternative reaction for converting polytetramethylene ether glycol into tetrahydrofuran and water.

[0014] In a first aspect of the present invention, there is provided a method for converting polytetramethylene ether glycol to tetrahydrofuran, the method comprising the steps of: a) introducing a stream comprising polytetramethylene ether glycol into a strong acid catalyst capable of converting the polytetramethylene ether glycol to tetrahydrofuran and water; b) operating the method in a reactor under operating conditions sufficient to carry out acid-catalyzed depolymerization of the polytetramethylene ether glycol to tetrahydrofuran and water; and c) recovering the tetrahydrofuran.

[0015] In one embodiment of the process, the strong acid catalyst is a solid catalyst.

[0016] In one embodiment of the method, the solid catalyst is selected from the group consisting of polymer-based acid resins, mineral-based supported acid catalysts, and combinations thereof.

[0017] In one embodiment of the process, the solid catalyst is an acidic resin catalyst.

[0018] In one embodiment of the process, the acidic resin catalyst has an acid equivalent weight between 1 and 10.

[0019] In one embodiment of the process, the strong acid catalyst has a residence time of between 5 minutes and 60 minutes, and preferably between 10 minutes and 30 minutes.

[0020] In one embodiment of the process, the strong acid catalyst is contained in a fixed bed or a fluidized bed within the reactor.

[0021] In one embodiment of the process, the strong acid catalyst is slurried.

[0022] In one embodiment of the process, the ratio of solid catalyst to reactor liquid inventory is from 5 wt% to 90 wt%, and preferably from 10 wt% to 30 wt%.

[0023] In one embodiment of the process, the reactor comprises one or more tubular vessels.

[0024] In one embodiment of the process, the reactor is operated at a temperature of 80°C to 150°C, and preferably at 90°C to 120°C.

[0025] In one embodiment of the process, the reactor is operated at 0.3 to 5 bar, preferably at atmospheric pressure.

[0026] In one embodiment of the process, tetrahydrofuran and water are produced at 90±10 / 99.9±0.1, weight / weight, tetrahydrofuran / water.

[0027] In one embodiment of the process, there is a further step (d) of recycling at least a portion of the tetrahydrofuran to an upstream process reaction for the synthesis of polytetramethylene ether glycol.

[0028] In one embodiment of the process, step (d) recycles at least a portion of the tetrahydrofuran as feed to the tetrahydrofuran polymerization stage for converting the tetrahydrofuran into polytetramethylene ether acetate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present application is illustrated by way of example and not limitation in the accompanying drawings, in which like reference numerals indicate similar elements and in which:

[0030] Figure 1 shows the conversion of BDO to THF ( Figure 1A ); THF is converted to PTMEA ( Figure 1B ), and the conversion of PTMEA to PTMEG ( Figure 1C )’s reaction.

[0031] Figure 2 Schematic diagram of the configuration for the distillation process.

[0032] Figure 3 : is a graphical representation of the THF / water evolution rate as a function of temperature at a specific catalyst weight fraction, wherein the PTMEG has an average molecular weight distribution of 2000 Daltons.

[0033] Figure 4 : is a graphical representation of the THF / water evolution rate as a function of temperature at a specific catalyst weight fraction, wherein the PTMEG has an average molecular weight distribution of 250 Daltons.

[0034] Figure 5 Figure 2 is a graphical representation of the THF / water evolution rate as a function of catalyst weight fraction temperature at a specific reaction temperature, wherein the PTMEG has an average molecular weight distribution of 2000 Daltons.

[0035] Figure 6 Figure 2 is a graphical representation of the THF / water evolution rate as a function of catalyst weight fraction temperature at a specific reaction temperature, wherein PTMEG has an average molecular weight distribution of 250 Daltons. DETAILED DESCRIPTION

[0036] The following specific embodiments describe exemplary embodiments, and the disclosed features are not intended to be limited to one or more combinations explicitly disclosed. Therefore, unless otherwise stated, the features disclosed herein may be combined together to form additional combinations that are not otherwise shown for the purpose of brevity. Unless otherwise defined, all scientific and technical terms used herein are intended to have the same meanings as those skilled in the art to which the present disclosure relates. Materials, methods, and examples are merely illustrative and are not intended to be limiting. The word "comprise" and variants such as "comprises" or "comprising" are understood to mean including the stated integer or integer group, but do not exclude any other integer or integer group.

[0037] Unless otherwise specifically stated or apparent from the context used herein, the terms "about" and "approximately" are to be understood as being within the normal tolerance range in the art, e.g., within 2 standard deviations of the mean. "About" and "approximately" may be understood as being within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless the context indicates otherwise, all numerical values ​​provided herein are modified with the term "about".

[0038] As used herein, the term "PTMEG" means polytetramethylene ether glycol (CAS No. 25190-06-1). PTMEG is also known as polyoxybutylene glycol or poly(tetramethylene glycol) or PTMG. PTMEG is represented by the following molecular formula; H(OCH2CH2CH2CH2)nOH((C4H8O)n), where n is a number between 1 and 100.

[0039] As used herein, the term "PTMEA" means diacetate of polytetramethylene ether glycol (CAS No. 26248-69-1), which is represented by the formula (C4H8O)n, also known as polytetramethylene ether acetate.

[0040] As used herein, the term "BDO" means 1,4-butanediol, also known as 1,4-butanediol, which has the formula HOCH2CH2CH2CH2OH (CAS No. 110-63-4).

[0041] As used herein, the term "THF" means tetrahydrofuran, which is also known as cyclotetramethylene oxide, represented by the formula C4H8O. Unless otherwise indicated, percentages used herein are expressed in weight %.

[0042] As used herein, the term "PBAT" means polybutylene adipate terephthalate (CAS No. 60961-73-1).

[0043] In a first aspect, the present disclosure provides a method for converting polytetramethylene ether glycol to tetrahydrofuran, the method comprising the steps of: a) introducing a stream comprising polytetramethylene ether glycol to a strong acid catalyst capable of converting the polytetramethylene ether glycol to tetrahydrofuran and water; b) operating the method in a reactor under operating conditions sufficient to effect acid-catalyzed depolymerization of the polytetramethylene ether glycol to tetrahydrofuran and water; and c) recovering the tetrahydrofuran.

[0044] In the upstream processing reaction for the synthesis of PTMEG, BDO is converted to THF in a ring-closing reaction ( Figure 1A ), followed by conversion of THF to PTMEA ( Figure 1B ) and eventually converted to PTMEG ( Figure 1C ).

[0045] Current processes for converting BDO to THF utilize an acid catalyst in liquid form, such as sulfuric acid, in the distillation reaction zone. This acid catalyst is necessary to complete the dehydration and ring closure of BDO. However, the presence of this acid catalyst necessitates the use of high-grade materials to avoid corrosion of process vessels due to the strong acidity of the hot process liquid. In addition, the process disadvantageously produces an accumulated high concentration of acidic black viscous tar, which represents a yield loss and operating problems.

[0046] However, the literature teaches that the same chemistry (i.e., dehydration and ring closure of BDO) can be performed with a solid acid catalyst (see Vaidya et al., Applied Catalysis A: General 242 (2003), 321-328), where the reaction occurs on the surface of the catalyst, rendering the mixture pH neutral.

[0047] U.S. Patent Application Publication No. 2016 / 0214952A1 in the name of the present applicant and its Chinese equivalent CN105531266B disclose an improved process for producing THF from a reaction mixture containing BDO in the presence of a strong acid catalyst in a reaction vessel containing a distillation reaction zone, wherein the acid catalyst is suspended in a steam-rich zone in the distillation reaction zone. This improved process advantageously allows for cheaper process vessels and significantly reduces tar formation.

[0048] There is no motivation or suggestion Figure 1B or Figure 1C This strong acid catalyst is used in any other reaction step (forward or reverse reaction step) as shown.

[0049] Once formed, THF is converted to polytetramethylene ether acetate ("PTMEA") by ring-opening polymerization with a superacid (generally an acid stronger than 100% sulfuric acid), allowing for low residence times (see Figure 1B ). Product molecular weight is controlled by the addition of acetic anhydride, which together with low residence time allows rapid transitions between product grades. PTMEA is then converted to PTMEG by strong base transesterification in a methanolysis reaction in a reactive distillation column.

[0050] PTMEG polymer contains molecules of different chain lengths with a wide molecular weight distribution. Typical average molecular weight distributions are between 150 Daltons and 3000 Daltons. Different end uses of PTMEG require PTMEG with different average molecular weight distributions. For example, some applications require PTMEG with an average molecular weight distribution of only 250 Daltons (Mn~250), while other applications require PTMEG with an average molecular weight distribution of 2000 Daltons (Mn~2000). Process conditions can be varied to result in the synthesis of PTMEG with different defined average molecular weight distributions.

[0051] For a given PTMEG polymer having a particular average molecular weight distribution, the molecular weight of the oligomers therein can still vary significantly. If the polymer contains too high a percentage of short chain oligomers, this can have a deleterious and adverse effect on the properties of the final product.

[0052] After the methanolysis catalyst is removed from the PTMEG, oligomers and low molecular weight fractions are removed from the product in a narrowing step utilizing at least one short path distillation evaporator (as previously reported, e.g., as described in U.S. Pat. No. 5,282,929A). The final product has a narrower molecular weight distribution that is more suitable for use in the downstream spandex and polyurethane markets. Typically, the BDO to THF ring closing reaction step (e.g., Figure 1A The low molecular weight fraction removed from the product in the narrowing step is retreated with sulfuric acid at about 5% by weight (based on BDO) in a reactor (shown).

[0053] Additionally, as in any continuous manufacturing process, occasionally off-spec material may be produced due to, for example, process upsets, instrument failure / drift, such that the color or molecular weight may be incorrect. Therefore, occasionally the THF conversion step to PTMEA (see Figure 1B) inadvertently results in the formation of PTMEA with an incorrect molecular weight (usually greater than the desired average molecular weight) so that the PTMEG derived from this PTMEA falls outside the narrow molecular weight distribution ideal for use in the targeted downstream spandex and polyurethane markets. Sometimes this material can be blended back into the process, but is generally considered waste.

[0054] In the present disclosure, it has unexpectedly been discovered that a strong acid catalyst useful in an improved process for converting BDO to THF in a reaction mixture can also be used to depolymerize PTMEG to THF (and water). Specifically, such a strong acid catalyst can be advantageously used in a reprocessing step to depolymerize (i) fractions of PTMEG that have been removed in one or more narrowing steps and (ii) fractions of off-spec PTMEG, typically having an average molecular weight greater than that desired for a particular end use; and convert these fractions of PTMEG to THF.

[0055] As mentioned previously, the PTMEG fraction that has been removed in one or more narrowing steps is currently subsequently reprocessed in a BDO to THF ring closing reaction step (e.g. Figure 1A This reduces or even eliminates the current waste of PTMEG that falls outside the desired molecular weight range.

[0056] However, for environmental reasons, the growing interest in the biodegradable polymer polybutylene terephthalate adipate ("PBAT") has led to an increase in the number of manufacturing plants producing PBAT. PBAT plants produce THF as a byproduct, and therefore, the amount of THF from sources other than BDO manufacturing plants has increased. This greater availability of THF has opened up the use of THF as a feed to the THF polymerization process (see Figure 1B ) to produce PTMEG streams instead of the traditional route of making PTMEG from BDO.

[0057] The fraction of PTMEG that has been removed in one or more narrowing steps and is currently being reprocessed in the BDO to THF ring closing reaction step (e.g. Figure 1A can be recycled back to the THF polymerization process (in Figure 1B As more THF is produced in PBAT plants, this shorter and therefore more economical route to produce PTMEG becomes increasingly desirable compared to the longer route starting from BDO.

[0058] In some embodiments, the acid catalyst may be in the form of a solid, semi-solid, slurry and / or gel consistency. In one embodiment, the acid catalyst is a solid catalyst. In one embodiment, the solid catalyst is a strongly acidic ion exchange resin. In other embodiments, the solid catalyst may be a mineral-based supported acid catalyst, such as a zeolite. In one embodiment, the solid resin catalyst may be selected from commercially available strongly acidic cationic polymer catalysts. Non-limiting examples of such solid acid resin catalysts include Amberlyst ™ 35. Amberlyst ™ 70. Puralite ™ CT and combinations thereof. In some embodiments, suitable solid acid resin catalysts have an acid equivalent weight of at least 1, such as at least 1 to 10, such as 3 to 10.

[0059] In one embodiment, the method for converting PTMEG into THF uses one or more tubular containers. Such one or more tubular containers can be arranged in a form similar to a heat exchanger. Examples of reaction vessels include, but are not limited to, those with fixed bed reactors, structured distillation tower packed beds or fluidized beds; or continuous stirred tank reactors, plug flow reactors or trickle reactors. In the embodiment where the reaction vessel is a plug flow reactor, the catalyst is constrained by the screen at the bottom of the tubular reactor and the screen at the top of the tubular reactor. The screen keeps the catalyst at the bottom of the reactor, but the screen prevents the catalyst from jumping from one tube in the reactor to another tube. In yet another embodiment, the reaction vessel is a trickle reactor, in which liquid flows downward and vapor flows upward. In another embodiment, the reactor vessel is a tank with external circulation through a pump.

[0060] See also Figure 2 , PTMEG is kept molten in a heated batch in a PTMEG reservoir 201 and fed continuously by gravity to a distillation reactor 202, the temperature of which is controlled by a heating block 203. Reactor 202 contains a strong acid catalyst. In this particular embodiment, the strong acid catalyst is in slurry form. The gas phase distillate 204 leaving reactor 202 is cooled in a condenser 205 and the products (THF and water) are collected in chamber 206.

[0061] The production rates of THF and water vary with temperature (Examples 1 and 2; Figure 3 and Figure 4 ) and catalyst weight fraction (Examples 3 and 4; Figure 5 and Figure 6 ) changes.

[0062] Example

[0063] The depolymerization of polytetramethylene ether glycol (PTMEG) into tetrahydrofuran (THF) and water was carried out in glassware at atmospheric pressure in the presence of a solid acid resin catalyst. The reaction was carried out at several different process temperatures and catalyst weight fractions as described below, and samples were subsequently collected from the gas phase distillate and the reactor liquid phase over time. The samples were subsequently analyzed by gas chromatography (GC).

[0064] Examples 1, 2, 3 and 4 Figure 2 The distillation process configuration shown schematically in FIG. 1 uses DuPont Amberlyst ™ 35 solid acid resin catalyst. PTMEG was kept molten in a heated batch and fed continuously to the distillation reactor by gravity. As the reaction proceeded with temperature (Examples 1 and 2) or catalyst weight fraction (Examples 3 and 4), THF and water vapor were released and condensed at the top of the column. The rate of THF and water evolution was measured periodically by graduated cylinders.

[0065] Example 1

[0066] 16 g of catalyst (DuPont Amberlyst ™ ) together with PTMEG with an average molecular weight distribution of 2000 Daltons (Mn ~ 2000) are added to Figure 2 The reactor scheme is shown. The liquid level in the reactor was maintained at 310 ml by gravity feed and by adjusting the reservoir height with a laboratory jack. Heat was applied via an appropriately sized heating block to achieve the desired reaction temperature, and the rates of THF and water evolution were recorded. Figure 3 The rate of THF / water evolution was recorded as a function of temperature for this particular catalyst weight fraction and PTMEG having an average molecular weight distribution (Mn~2000) of 2000 Daltons.

[0067] Example 2

[0068] 16 g of catalyst (DuPont Amberlyst ™ ) together with PTMEG with an average molecular weight distribution of 250 Daltons (Mn ~ 250) was added to Figure 2 The reactor scheme is shown. The liquid level in the reactor was maintained at 310 ml by gravity feed and by adjusting the reservoir height with a laboratory jack. Heat was applied via an appropriately sized heating block to achieve the desired reaction temperature, and the rates of THF and water evolution were recorded. Figure 4 The rate of THF / water evolution was recorded as a function of temperature for this particular catalyst weight fraction and PTMEG having an average molecular weight distribution of 250 Daltons (Mn~250).

[0069] Example 3

[0070] Different amounts of DuPont Amberlyst ™ Together with PTMEG with an average molecular weight distribution of 2000 Daltons (Mn ~ 2000), it is added to Figure 2 The reactor scheme is shown. The liquid level in the reactor was maintained at 310 ml by gravity feed and the reservoir height was adjusted by a laboratory jack. Heat was applied via an appropriately sized heating block to achieve a reaction temperature of 115°C and the rates of THF and water evolution were recorded. Figure 5 The rate of THF / water evolution was recorded as a function of catalyst weight fraction temperature at this particular reaction temperature and with an average molecular weight distribution of 2000 Daltons (Mn~2000).

[0071] Example 4

[0072] Different amounts of DuPont Amberlyst ™ Together with PTMEG with an average molecular weight distribution of 250 Daltons (Mn~250), it is added to Figure 2 The reactor scheme is shown. The liquid level in the reactor was maintained at 310 ml by gravity feed and the reservoir height was adjusted by a laboratory jack. Heat was applied via an appropriately sized heating block to achieve a reaction temperature of 115°C and the THF and water evolution rates were recorded. Figure 6 The rate of THF / water evolution was recorded as a function of catalyst weight fraction temperature at this particular reaction temperature and with an average molecular weight distribution of 250 Daltons (Mn~250).

[0073] The disclosure provided herein describes features according to preferred and exemplary embodiments thereof. Upon reading this disclosure, one of ordinary skill in the art will recognize many other embodiments, modifications and variations within the scope and spirit of the appended claims.

Claims

1. A method for converting polytetramethylene ether glycol into tetrahydrofuran, the method comprising the following steps: a) introducing a stream comprising polytetramethylene ether glycol to a strong acid catalyst capable of converting the polytetramethylene ether glycol into tetrahydrofuran and water; b) operating the process in a reactor under operating conditions sufficient to effect acid catalyzed depolymerization of polytetramethylene ether glycol to tetrahydrofuran and water; and c) recovering the tetrahydrofuran.

2. The method according to claim 1, wherein the strong acid catalyst is a solid catalyst.

3. The method of claim 2, wherein the solid catalyst is selected from the group consisting of polymer-based acid resins, mineral-based supported acid catalysts, and combinations thereof.

4. The method according to claim 2, wherein the solid catalyst is an acidic resin catalyst.

5. The process of claim 4, wherein the acidic resin catalyst has an acid equivalent weight between 1 and 10.

6. The process according to claim 1, wherein the strong acid catalyst has a residence time between 5 minutes and 60 minutes, and preferably between 10 minutes and 30 minutes.

7. The method of claim 1, wherein the strong acid catalyst is contained in a fixed bed or a fluidized bed within the reactor.

8. The process of claim 7, wherein the strong acid catalyst is slurried.

9. The process according to claim 2, wherein the ratio of solid catalyst to reactor liquid inventory is from 5 to 90 wt%, and preferably from 10 to 30 wt%.

10. The method of claim 1, wherein the reactor comprises one or more tubular vessels.

11. The process according to claim 1, wherein the reactor is operated at a temperature of 80 to 150°C, and preferably at 90 to 120°C.

12. The process according to claim 1, wherein the reactor is operated at 0.3 to 5 bar, preferably at atmospheric pressure.

13. The method of claim 1, wherein the tetrahydrofuran and water produced are 90±10 / 99.9±0.1, weight / weight, tetrahydrofuran / water.

14. The method according to claim 1, further comprising step (d): recycling at least a portion of the tetrahydrofuran to an upstream process reaction for synthesizing polytetramethylene ether glycol.

15. The process according to claim 14, wherein said step (d) recycles at least a portion of said tetrahydrofuran as feed to a tetrahydrofuran polymerization stage for converting tetrahydrofuran into polytetramethylene ether acetate.

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