Process for producing acid anhydrides

Abstract

Provided herein is a method of producing an anhydride of an organic monoacid, the method comprising contacting an organic monoacid with a thermally renewable anhydride to produce an anhydride of the organic monoacid, as well as a diacid of the renewable anhydride, a partially hydrolyzed renewable anhydride, or both. In particular embodiments, acetic acid and glutaric anhydride may react to form acetic anhydride.

Description

[0001] Cross - reference to related applications

[0002] This application is a divisional application of a Chinese patent application with application number 202180034015.8, filing date May 7, 2021, and invention title "Method for Producing Acid Anhydrides". The original application is the Chinese national phase application of an international application with international application number PCT / US2021 / 031252, which claims the priority of a US provisional patent application 63 / 022,075 filed on May 8, 2020, and the said US provisional patent application is incorporated herein by reference. Background Art

[0003] Acid anhydrides are useful reactive substances that are often used as water scavengers or acylating agents in chemical processes. The direct condensation of acids to form acid anhydrides is an energetically unfavorable reaction, especially for monoacid substances. So the synthesis of these acid anhydrides is usually energy-intensive, carried out at high temperatures and pressures, and / or with poor selectivity in terms of product formation.

[0004] Acetic anhydride is commercially produced by three routes: the ketene reaction, the carbonylation of methyl acetate, and the direct oxidation of acetaldehyde. The ketene route is the most widely practiced industrial acetic anhydride process and involves pyrolyzing acetic acid or acetone to form ketene under reduced pressure and very high temperatures, followed by reacting with acetic acid in a compressor at near ambient temperature (see, for example, US Patent 3,111,548). The carbonylation process involves the esterification of acetic acid with methanol to form methyl acetate at moderate temperatures. Then, methyl acetate reacts with carbon monoxide at high temperatures and pressures (see, for example, US Patent 4,002,677). Water is also added to the reactor to control the ratio of acetic acid to acetic anhydride. Although carried out at low temperatures and pressures, the direct oxidation route of acetaldehyde has lower selectivity (about 80 mol%, while the selectivity of the other routes is greater than 90 mol%), so it is economically unattractive. Although a common technique is to use an excess of acetic anhydride to produce other desired acid anhydrides, similar versions of the above routes are known to be used to produce other acid anhydrides.

[0005] The production of acetic anhydride by reacting acetic acid with cyclic anhydrides has been described in the literature (Haddadin et al., Journal of Pharmaceutical Sciences, 1975, 64(11), 1759-1765). However, these experiments relied on the presence of a large excess of acetic acid and a strong acid catalyst (e.g., perchloric acid) to obtain <10% acetic anhydride (relative to acetic acid). Since this equilibrium strongly favors the glutaric anhydride side, an efficient and practical industrial method for producing glutaric anhydride involves treating glutaric acid and its derivatives with a small excess of acetic anhydride to quantitatively produce glutaric anhydride (Cason, Organic Syntheses, 1958, 38, 52; and Besrat et al., Journal of Biological Chemistry, 1969, 244(6), 1461-1467). However, in practice, this reaction is considered virtually irreversible, no process has described utilizing this reverse reaction to produce acetic anhydride, and no method utilizing a low acetic / glutaric anhydride ratio has been described to date. Additionally, coupling this type of non-thermally renewable anhydride production reaction with a thermally renewable anhydride reaction (e.g., glutaric acid to glutaric anhydride and water) to produce a continuous process has not been described.

[0006] Accordingly, there remains a need for alternative syntheses for producing anhydrides under less demanding conditions while still maintaining high selectivity. SUMMARY OF THE INVENTION

[0007] The present invention provides a method for producing an anhydride of an organic monoacid, the method comprising contacting the organic monoacid with a thermally renewable anhydride to produce the anhydride of the organic monoacid and the diacid of the renewable anhydride, a partially hydrolyzed renewable anhydride, or both the diacid of the renewable anhydride and the partially hydrolyzed renewable anhydride. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Containing two different general schematic diagrams showing the following two-step process: 1) converting an organic monoacid and a renewable anhydride into an anhydride of the organic monoacid or a mixed anhydride of the organic monoacid and a hydrolyzed renewable anhydride (transanhydridization reaction); and 2) regeneration of the renewable anhydride that has lost water (anhydride regeneration reaction).

[0009] Figure 2 Shows a series of reactions using, for example, polyphosphoric acid and pyromellitic dianhydride to hydrolyze an anhydride to form a partially hydrolyzed anhydride.

[0010] Figure 3 Is a schematic diagram showing the feeding of acetic acid (AcOH) and glutaric anhydride to produce acetic anhydride (Ac2O).

[0011] Figure 4 It is a reaction schematic diagram showing the reaction of acetic acid (organic monoacid) with glutaric anhydride (renewable anhydride) to form acetic anhydride (anhydride of organic monoacid) and glutaric acid (dioic acid of anhydride), and the glutaric acid is subsequently dehydrated to reform glutaric anhydride (renewable anhydride). Detailed Description

[0012] The present invention provides an anhydride synthesis that occurs at ambient or near-ambient pressure and moderate temperature (e.g., a temperature of about 200 °C or lower). Additionally, although a catalyst can be added, the process does not require a catalyst to produce highly selective anhydrides. The process can use relatively inexpensive dehydrating agents, including industrial by-products (e.g., glutaric anhydride) and / or low-cost materials (e.g., polyphosphoric acid). An additional advantage is that the process of the present invention does not require the addition of a third component (e.g., water) to the system to control the acid / anhydride ratio required in standard carbonylation processes. Instead, the residence time and / or relative flow rate of the starting acid and the renewable anhydride can be manipulated to adjust the ratio.

[0013] Specifically, the present invention provides a method for producing an anhydride of an organic monoacid, the method comprising contacting the organic monoacid with a hot renewable anhydride to produce the anhydride of the organic monoacid and the dioic acid of the hot renewable anhydride, a partially hydrolyzed anhydride, or both the dioic acid of the renewable anhydride and the partially hydrolyzed anhydride. Figure 1 This transesterification reaction is shown. Figure 2 The formation of the partially hydrolyzed anhydride is shown. Generally, a stream containing at least one organic monoacid ("organic monoacid" or "organic acid") is reacted with a stream containing at least one regenerable anhydride ("hot renewable anhydride" or "renewable anhydride"). The reaction produces a stream containing one or more desired anhydrides and the acid in the form of the renewable anhydride, as well as unreacted acid and unreacted renewable anhydride. The reaction can be carried out to completion or to partial completion at different reactant ratios.

[0014] After the reaction is completed, the residual reactants and products are separated into various streams in one or more steps. For example, the method includes a separation step that includes forming a first stream and forming a second stream, the first stream containing the anhydride of the organic monoacid (desired product) and any unreacted organic monoacid, and the second stream containing the dioic acid of the renewable anhydride, the partially hydrolyzed anhydride, and / or the unreacted anhydride. In some embodiments, the residual unreacted renewable anhydride is extracted from its acid form to drive the regeneration reaction forward.

[0015] The separation steps described herein can use any suitable physical separation method, including distillation (e.g., simple, molecular, evaporation, short path, batch, continuous, flash, steam, vacuum, cryogenic, fractional, azeotropic, extractive, or combinations thereof). In some embodiments, depending on the reactants, the separation step is carried out by fractional distillation, azeotropic distillation, and / or extractive distillation.

[0016] In azeotropic distillation or distillation of two or more compounds with a close boiling point difference, a new component (e.g., an entrainer) is typically added to the azeotrope or other inseparable mixture. The new component is used to form two or more immiscible liquid phases that can be separated. Additionally, a third component, such as a solid dehydrating agent, e.g., molecular sieve, silica gel, alumina, other thermally renewable solid desiccants, and combinations thereof, can also be added.

[0017] Azeotropic distillation can be carried out as homogeneous azeotropic distillation, heterogeneous azeotropic distillation, reactive distillation, and salt addition distillation. In homogeneous azeotropic distillation, an entrainer miscible with the original mixture is added. In heterogeneous azeotropic distillation, an entrainer that forms a heterogeneous azeotrope with one or more components in the original mixture is added. In reactive distillation, an entrainer that reacts with one or more components in the original mixture is added. The non-reacting components are produced as distillate, and the entrainer is recovered from the reverse reaction. Salt addition distillation is a type of extractive distillation that changes the relative volatility by adding salt as an entrainer.

[0018] In certain embodiments, the unreacted organic monoacid is separated from the acid anhydride of the organic monoacid. If desired, the separated unreacted organic monoacid can be recovered as a starting material for reuse. In some cases, a portion of the unreacted organic monoacid is transferred to a container containing a second stream. In such cases, it is believed that during the regeneration of the renewable acid anhydride, the recovered organic monoacid can act as an entrainer or azeotropic agent to remove water.

[0019] The renewable acid anhydride is regenerated by removing water from the polyacid form of the renewable acid anhydride. In any of the foregoing embodiments, to regenerate the acid anhydride, the second stream can optionally be heated and distilled (e.g., azeotropically distilled) in the presence or absence of a catalyst. Preferably, the renewable acid anhydride is regenerated in the separation step of the reaction to form the acid anhydride of the organic monoacid. In some preferred embodiments, the regenerated acid anhydride can be recovered as a starting material for reuse.

[0020] The reactants and products of the method of the present invention can be separated and / or concentrated by many different unit operations. The reaction and separation steps can be combined or integrated. Similarly, the separation and regeneration steps can be combined or integrated. Unit operations include, for example, distillation, extractive distillation, reactive distillation, extraction, reactive extraction, mixer-settler, pervaporation, membrane separation, evaporation, condensation, flash distillation, fractionation, electro-treatment, flotation, phase separation, coalescence, hydrocyclone, decantation, parametric pumping, sublimation, ion exchange, adsorption, absorption, and / or crystallization.

[0021] In the method, the anhydride starting material is any suitable renewable anhydride. In some cases, the renewable anhydride is cyclic or can form a cyclic structure. It has been observed that anhydrides having a cyclic structure or capable of forming a cyclic structure are more readily regenerated thermally. In some embodiments, the thermally renewable anhydrides are selected from carboxylic anhydrides, sulfonic anhydrides, phosphinic anhydrides, phosphonic anhydrides, phosphoric anhydrides, and mixed anhydrides. In some embodiments, the mixed anhydrides contain combinations of different acid moieties. In some embodiments, the backbone structure of the mixed anhydrides is different (e.g., mixed anhydrides resulting from the condensation of an organic monoacid in the feed with another acidic moiety). Preferably, at least a portion of the structure of the mixed anhydride is cyclic or capable of forming a cyclic structure.

[0022] Generally, renewable carboxylic anhydrides can have a cyclic structure of the formula R 1 -C(O)-O-C(O)-R 2 wherein R 1 and R 2 are joined together to form an alkylene, arylene, or mixed alkylene / arylene having 1 or 2 optional double bonds. The mixed alkylene / arylene can form a dianhydride or trianhydride in some cases. The alkylene, arylene, and mixed alkylene / arylene having 1 or 2 optional double bonds are optionally substituted with one or more (e.g., 1, 2, 3, 4, 5, 6, etc.) substituents selected from: alkyl (including alkylene), halogen, alkoxy, trialkylsiloxy, nitro, aryl, and carboxy-substituted phenyl. Examples of carboxylic anhydrides include, for example, tetrafluorosuccinic anhydride, maleic anhydride, itaconic anhydride, succinic anhydride, glutaric anhydride, 2,7-epoxyhexanedione (adipic anhydride), azelaic anhydride, suberic acid, sebacic anhydride, 3-methylglutaric anhydride, methylsuccinic anhydride, 3-(tert-butyldimethylsiloxy)glutaric anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,3-cyclohexanedicarboxylic anhydride, camphoric anhydride, homophthalic anhydride, phthalic anhydride, isophthalic anhydride, trimellitic anhydride, pyromellitic dianhydride, mellitic trianhydride, and 3-fluorophthalic anhydride or 4-fluorophthalic anhydride.

[0023] Generally, renewable sulfonic anhydrides have the formula R 3-S(O)2-O-S(O)2-R 4 , wherein R 3 and R 4 are the same or different and each is C 1-12 alkyl or aryl (e.g., phenyl), or R 3 and R 4 are joined together to form alkylene, arylene and mixed alkylene / arylene. Each C 1-12 alkyl, aryl, alkylene, arylene and mixed alkylene / arylene are optionally substituted by one or more (e.g., 1, 2, 3, 4 or 5) substituents selected from: alkyl, halo, alkoxy, trialkylsiloxy, nitro and aryl. Examples of sulfonic anhydrides include, for example, methanesulfonic anhydride, 1,2-ethanedisulfonic anhydride, nonafluorobutanesulfonic anhydride and p-toluenesulfonic anhydride.

[0024] The renewable phosphinic anhydride has the formula R 5 -P(O)(R 6 )-O-P(O)(R 7 )-R 8 , wherein R 5 、 R 6 , R 7 and R 8 are the same or different and each is H, C 1-12 alkyl or aryl (e.g., phenyl), or R 5 and R 8 are joined together to form alkylene, arylene and mixed alkylene / arylene. Each C 1-12 alkyl, aryl, alkylene, arylene and mixed alkylene / arylene are optionally substituted by one or more (e.g., 1, 2, 3, 4 or 5) substituents selected from: alkyl, halo, alkoxy, trialkylsiloxy, nitro and aryl. Examples of phosphinic anhydrides include, for example, propane-1,3-bis(methylphosphinic acid) anhydride, butane-1,4-bis(methylphosphinic acid) anhydride, hexane-1,6-di(methylphosphinic acid) anhydride and decane-(1,10-dimethylphosphinic acid) anhydride.

[0025] The renewable phosphonic anhydride has the formula R 9 -P(O)(OH)-O-P(O)(OH)-R 10 , R 9 -P(O)(OH)-[O-P(O)(R 10 )] n -O-P(O)(OH)-R 11 or wherein R 9 , R 10 and R 11The same or different, and each is C 1-12 alkyl or aryl (e.g., phenyl), or R 9 and R 10 are linked together to form alkylene, arylene and mixed alkylene / arylene groups. Each C 1-12 Alkyl, aryl, alkylene, arylene and mixed alkylene / arylene groups are optionally substituted with one or more (e.g., 1, 2, 3, 4 or 5) substituents selected from alkyl, halide, alkoxy, trialkylsiloxy, nitro and aryl. Examples of phosphonic anhydrides include, for example, propane-phosphonic anhydride, butane-phosphonic anhydride, hexane-phosphonic anhydride, octane-phosphonic anhydride, decane-phosphonic anhydride, methane-pyrophosphoric anhydride and propane-pyrophosphoric anhydride.

[0026] Renewable phosphoric anhydrides include, for example, phosphorus pentoxide, pyrophosphoric acid, trimetaphosphoric acid, polyphosphates, cyclic polyphosphates, and polyphosphoric acid.

[0027] In some embodiments, the regenerable anhydride forms a polymer structure. Typically, an alkane with more than 5 carbons (e.g., C6, C7, C8, C9, C10, etc.) is used to form the polymer structure. It is believed that when the end of one molecule is combined with the end of a second molecule, a polymer structure is formed, and so on. The diacid that forms the polyanhydride can have the formula HO2C-(CH2) m -C(O)-OC(O)-(CH2) n -CO2H, wherein m and n are the same or different and each is an integer from 6 to 12 (i.e., 6, 7, 8, 9, 10, 11 or 12). In some embodiments, the polyanhydride may have the formula:

[0028]

[0029] Where R 12 is a C optionally containing one or more double bonds 6-12 Alkylene, arylene or its mixture.Alkylene and arylene can be substituted as described herein.Subscript "p" is the number of repeating units, and is an integer of at least 2 (e.g., 5 or more, 10 or more, 15 or more, etc.).The example of the dianhydride that can form the polyanhydride includes, for example, adipic anhydride, azelaic anhydride, suberic anhydride, sebacic anhydride, decanic anhydride, dodecanoic anhydride, 1,6-bis (p-carboxyphenoxy) hexane anhydride, 1,3-bis (p-carboxyphenoxy) propane anhydride, p-carboxyphenoxymethane anhydride, p-carboxyphenoxypropane anhydride, p-carboxyphenoxyvaleric anhydride, p-carboxyphenoxyacetic anhydride, p-carboxyphenoxy caprylic anhydride, phenylene dipropionic anhydride and its combination. The polymer anhydrides can also be mixed together, that is, two different acids are condensed, such as sebacic acid copolymerized with 1,3-bis(p-carboxyphenoxy)propane or 1,6-bis(p-carboxyphenoxy)hexane.

[0030] In some cases, the renewable anhydride is a mixture of anhydrides that are in cyclic form, capable of forming cyclic structures, and / or in polymeric form.

[0031] The renewable anhydride can also be a mixed anhydride, which includes different organic groups of a single type of anhydride (e.g., benzoic acid-trifluoroacetic anhydride) and anhydrides of both carboxylic acid and sulfonic acid (e.g., o-sulfobenzoic anhydride / m-sulfobenzoic anhydride / p-sulfobenzoic anhydride, including mixtures thereof), anhydrides of both carboxylic acid and phosphoric acid, or anhydrides of both sulfonic acid and phosphoric acid. In some cases, the mixed anhydride is produced by the condensation of an organic monoacid and another acidic moiety present in the reaction.

[0032] In a preferred embodiment, the renewable anhydride is succinic anhydride, glutaric anhydride, nitrophthalic anhydride, homophthalic anhydride, 1,2-ethanedisulfonic anhydride, polyphosphoric acid, pyromellitic dianhydride, propanephosphonic anhydride, o-sulfobenzoic anhydride, mixed benzoic acid-trifluoroacetic anhydride, or any combination thereof. More preferably, the anhydride is glutaric anhydride.

[0033] The renewable anhydride can be added to the reaction in any suitable manner.

[0034] The organic monoacid is a carboxylic acid, sulfonic acid, sulfinic acid, phosphonic acid, or phosphinic acid. Generally, a carboxylic acid has the formula R-C(O)OH; a sulfonic acid has the formula R-S(O)2OH; a sulfinic acid has the formula R-S(O)OH; a phosphonic acid has the formula R-P(O)(OH)2; and a phosphinic acid has the formula R-P(R')(O)OH. In any of the foregoing formulas, R is C 1-18 alkyl or aryl. R' is H, C 1-18 alkyl or aryl. The C of R and R' 1-18 alkyl and aryl can optionally be substituted with one or more (e.g., 1, 2, 3, 4, 5, or 6) substituents selected from: alkyl, halogen, alkoxy, trialkylsiloxy, nitro, and aryl.

[0035] In some cases, the organic monoacid is C 1-18 monocarboxylic acid, halogen-substituted C 1-18 monocarboxylic acid (e.g., chloroacetic acid or trifluoroacetic acid), aryl-containing acid (e.g., benzoic acid or cinnamic acid), methanesulfonic acid, or a combination thereof.

[0036] In some cases, the organic monoacid is C 1-18Monocarboxylic acids, such as formic acid, acetic acid, propionic acid, butanoic acid / butyric acid, isobutyric acid, pentanoic acid / valeric acid, hexanoic acid / hexanoic acid / caproic acid, heptanoic acid, octanoic acid / octanoic acid / caprylic acid, nonanoic acid / nonaic acid / pelargonic acid, decanoic acid / decanoic acid / capric acid, undecanoic acid / undecanoic acid / undecylic acid, dodecanoic acid / dodecanoic acid / lauric acid, tridecanoic acid / tridecanoic acid / tridecylic acid, tetradecanoic acid / tetradecanoic acid / myristic acid, pentadecanoic acid / pentadecanoic acid / pentadecylic acid, hexadecanoic acid / hexadecanoic acid / palmitic acid, heptadecanoic acid / heptadecanoic acid / margaric acid, octadecanoic acid / octadecanoic acid / stearic acid, or combinations thereof. In a preferred embodiment, the organic monoacid is acetic acid.

[0037] If desired, the organic monoacid can be added in the form of a salt. While not wishing to be bound by any theory, it is believed that the salt facilitates the formation of a non-volatile mixed anhydride intermediate, which is kinetically more favorable for the formation of the desired anhydride product from the organic monoacid (e.g., monocarboxylic acid) than the anhydride alone (e.g., cyclic anhydride). The organic monoacid can be, for example, a salt of an alkali metal (e.g., Group 1 cations such as lithium, sodium, or potassium), an alkaline earth metal (e.g., Group 2 cations such as calcium, magnesium, and barium), a transition metal (e.g., Group 3 to 12 cations such as Fe(II), Zn(II), Cu(I), Cu(II), Cr(II), Al(III), Mn(II), or Ni(II)), or ammonium. In any of the foregoing formulas of the organic monoacid, one or more hydrogens can be replaced by a cation (X + ), such as R-C(O)-O-X + . Examples of salts of organic monoacids include, for example, lithium acetate and potassium isobutyrate.

[0038] The organic monoacid can be present in the reactor and / or added to the reaction in a single stage or in more than one stage (e.g., 2 or more stages, 3 or more stages, 4 or more stages, 5 or more stages, 6 or more stages, etc.). Additionally, the amount of the organic monoacid added can be added in an amount less than, equal to, or in excess of the stoichiometry of the renewable acid anhydride. In certain embodiments, the organic monoacid is present in the reactor in an amount in excess of the renewable acid anhydride. In such cases, the ratio of the organic monoacid to the renewable acid anhydride ranges from 1:1 to 10:1 or is 1:1 or greater (e.g., 2:1 or greater, 3:1 or greater, 4:1 or greater, 5:1 or greater, 6:1 or greater, 7:1 or greater, 8:1 or greater, or 9:1 or greater) and / or 10:1 or less (e.g., 9:1 or less, 8:1 or less, 7:1 or less, 6:1 or less, 5:1 or less, 4:1 or less, 3:1 or less, or 2:1 or less). Any two of the above endpoints can be used to define a closed range, or a single endpoint can be used to define an open range.

[0039] In any of the above embodiments, the term "alkyl" means a straight-chain or branched-chain alkyl substituent containing, for example, from about 1 to about 18 carbon atoms, such as, for example, from about 1 to about 14 carbon atoms, from about 1 to about 12 carbon atoms, from about 1 to about 10 carbon atoms, from about 1 to about 8 carbon atoms, from about 1 to about 6 carbon atoms, or from about 1 to about 4 carbon atoms. Examples of alkyls include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-dodecyl, etc. As described herein, the alkyl can be substituted or unsubstituted.

[0040] The term "alkylene" refers to a divalent alkyl, such as methylene (-CH2-), ethylene (-CH2CH2-), propylene (-CH2CH2CH2-), etc., where the alkyl is as described above. The alkylene can optionally include 1 or 2 double bonds, such as (-CH=CH-), (-CH=CHCH2-), or (-CH2CH=CH-). Preferably, the alkylene contains from about 1 to about 6 carbon atoms, from about 1 to about 4 carbon atoms, or from about 1 to about 3 carbon atoms. The alkylene can be substituted as described herein.

[0041] In any of the above embodiments, the term "aryl" refers to a monocyclic, bicyclic or tricyclic carbocyclic system having one, two or three aromatic rings, e.g., phenyl, naphthyl, anthryl or biphenyl. The term "aryl" refers to an unsubstituted or substituted aromatic carbocyclic moiety as commonly understood in the art, and includes monocyclic and polycyclic aromatic compounds, e.g., phenyl, biphenyl, naphthyl, anthryl, pyrenyl, etc. Preferably, the aryl is phenyl. The aryl moiety typically contains, for example, from 6 to 30 carbon atoms, from 6 to 18 carbon atoms, from 6 to 14 carbon atoms or from 6 to 10 carbon atoms. It should be understood that according to Hückel's Rule, the term aryl includes a planar carbocyclic moiety containing 4n + 2 π electrons, where n = 1, 2 or 3. As described herein, the aryl can be substituted or unsubstituted.

[0042] The term "arylene" refers to a divalent aryl, such as divalent phenylene, etc., where the aryl is as described above. The arylene can be substituted as described herein.

[0043] In any of the above embodiments, the term "halo" refers to a halogen moiety selected from fluorine, chlorine, bromine and iodine.

[0044] In any of the above embodiments, the term "alkoxy" encompasses a straight-chain or branched-chain alkyl group attached to a divalent oxygen. As described herein, the alkyl group is the same.

[0045] The term "at least one" means 1 or more, 2 or more, 3 or more or 4 or more, including 1, 2, 3, 4, etc.

[0046] In any of the above embodiments, the method may further include a suitable solvent. One purpose of the solvent may be to increase the anhydride production rate of the reaction by manipulating the dielectric constant and / or solubility characteristics of the mixture. Without wishing to be bound by theory, it is believed that conducting the reaction in a high dielectric solvent, such as sulfolane or dimethyl sulfoxide (DMSO), allows for a more efficient reaction with organic monoacids, such as polyphosphoric acid and low dielectric carboxylic acids. Another purpose of the solvent may be to act as an entrainer or azeotropic agent to facilitate the separation of compounds in the system, particularly the separation of the product from the starting materials. A variable temperature or variable pressure distillation system may be used to facilitate further separation of the bottoms, distillate, or both. The solvent may be, for example, protic or aprotic and preferably has a dielectric constant (ε) of 15 or greater (e.g., ε is 20 or greater, 25 or greater, 30 or greater, 35 or greater, 40 or greater, etc.). The higher the dielectric constant, the higher the polarity of the solvent. Examples of suitable solvents include acetone, acetonitrile, N,N-dimethylacetamide, N,N-dimethylformamide (DMF), formamide, hexamethylphosphoramide, dimethyl sulfoxide (DMSO), sulfolane, methanol, ethanol, isopropanol, nitrobenzene, nitromethane, cyclohexanone, methyl ethyl ketone, methyl cyclohexane, toluene, m-xylene, o-xylene, p-xylene, and any combination thereof. Preferred solvents include DMSO, sulfolane, or a combination thereof. In some embodiments, no solvent is used.

[0047] Although not generally necessary, one or more catalysts may be used. In some embodiments of the method of the present invention, the catalyst may be used to facilitate the regeneration of the anhydride (e.g., cyclic anhydride), increase the yield of the product, or both. Suitable catalysts may be homogeneous, insoluble but flowable (e.g., slurry), or heterogeneous. Examples of catalysts include perchloric acid, magnesium chloride, ion exchange resins (e.g., macroporous (macroporous) polystyrene-based ion exchange resins having strong acidic sulfonic groups, such as AMBERLYST TM ), perfluorinated resins (e.g., sulfonated tetrafluoroethylene-based fluoropolymer-copolymers, such as NAFION TM ), and combinations thereof.

[0048] The transanhydration reaction ( Figure 2) It can be carried out at any suitable temperature. Generally, the temperature of the transesterification reaction is moderate, such as 200 °C or lower temperatures, including 180 °C or lower temperatures, 160 °C or lower temperatures, 150 °C or lower temperatures, 145 °C or lower temperatures, 140 °C or lower temperatures, 135 °C or lower temperatures, 130 °C or lower temperatures, 125 °C or lower temperatures, 120 °C or lower temperatures, 115 °C or lower temperatures, 110 °C or lower temperatures, 105 °C or lower temperatures, 100 °C or lower temperatures, 95 °C or lower temperatures, 90 °C or lower temperatures, 85 °C or lower temperatures, 80 °C or lower temperatures, 75 °C or lower temperatures, 70 °C or lower temperatures, 65 °C or lower temperatures, 60 °C or lower temperatures, 55 °C or lower temperatures or 50 °C or lower temperatures. Generally, the transesterification reaction is carried out at a temperature of 45 °C or higher (for example, 50 °C or higher, 60 °C or higher, 70 °C or higher, 80 °C or higher, 90 °C or higher, 100 °C or higher, 110 °C or higher, 120 °C or higher, 130 °C or higher or 140 °C or higher). Any two of the above endpoints can be used to define a closed range, or a single endpoint can be used to define an open range. In some preferred embodiments, the reaction temperature is about 170 °C or lower, more preferably 150 °C or lower, 120 °C or lower, 115 °C or lower, 110 °C or lower or 80 °C or lower.

[0049] The transanhydration reaction can be carried out at any suitable pressure, and is typically carried out at ambient pressure (e.g., atmospheric pressure of 1 atm) or near ambient pressure (e.g., 1 atm ± 10%, 1 atm ± 5%, 1 atm ± 2% or 1 atm ± 1%). In some embodiments, the transanhydration reaction is carried out at a slight pressure, such as 15 atm or less (e.g., 10 atm or less, 8 atm or less, 6 atm or less, 5 atm or less, 4 atm or less, 3 atm or less or 2 atm or less). In such embodiments, the reaction pressure is typically 1 atm or greater (e.g., 2 atm or greater, 3 atm or greater, 4 atm or greater, 5 atm or greater, 6 atm or greater, 7 atm or greater, 8 atm or greater, 9 atm or greater, 10 atm or greater or 12 atm or greater). For the separation step (e.g., the pressure in the stripping column), the pressure is typically lower to help prevent the reverse reaction from occurring, such as 0.05 atm or greater (e.g., 0.1 atm or greater, 0.2 atm or greater, 0.5 atm or greater, 0.8 atm or greater, 1 atm or greater and / or 5 atm or less, 2 atm or less, 1 atm or less, 0.8 atm or less, 0.5 atm or less, 0.2 atm or less or 0.1 atm or less). Any two of the above endpoints can be used to define a closed range, or a single endpoint can be used to define an open range.

[0050] The transanhydration reaction can be carried out for any suitable length of time. The reaction time can be 0.01 hours or longer (e.g., 0.05 hours or longer, 0.1 hours or longer, 0.15 hours or longer, 0.02 hours or longer, 0.25 hours or longer, 0.5 hours or longer, 0.75 hours or longer, 1 hour or longer, 1.5 hours or longer, 2 hours or longer, 3 hours or longer, 4 hours or longer or 5 hours or longer). Generally, the reaction will be completed within 4 days or less (e.g., 3.5 days or less, 3 days or less, 2.5 days or less, 2 days or less, 1 day or less, 20 hours or less, 15 hours or less, 10 hours or less, 8 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less, 2 hours or less or 1 hour or less). Any two of the above endpoints can be used to define a closed range, or a single endpoint can be used to define an open range.

[0051] The acid anhydride regeneration reaction ( Figure 2) It can be carried out at any suitable temperature for regenerating the acid anhydride (for example, a temperature of 350 °C or lower, 325 °C or lower, 300 °C or lower, 275 °C or lower, 250 °C or lower, 225 °C or lower, 200 °C or lower, 175 °C or lower, 150 °C or lower, 125 °C or lower, 100 °C or lower, 90 °C or lower, 85 °C or lower, 80 °C or lower, 75 °C or lower, 70 °C or lower, 65 °C or lower, 60 °C or lower, 55 °C or lower, or 50 °C or lower). Generally, the acid anhydride regeneration reaction temperature is at a temperature of 30 °C or higher (for example, 40 °C or higher, 50 °C or higher, 60 °C or higher, 70 °C or higher, 75 °C or higher, 80 °C or higher, 85 °C or higher, 90 °C or higher, 100 °C or higher, 110 °C or higher, 115 °C or higher, 125 °C or higher, 130 °C or higher, 135 °C or higher, 140 °C or higher, 145 °C or higher, 150 °C or higher, 175 °C or higher, or 200 °C or higher). Any two of the above endpoints can be used to define a closed range, or a single endpoint can be used to define an open range.

[0052] The acid anhydride regeneration reaction can be carried out at any suitable pressure and is generally carried out at atmospheric pressure (about 1 atm) or under reduced pressure.

[0053] The method has high selectivity because the by-products detected outside the expected product are minimal. For example, the term "high selectivity" means that 85 mol% or more (for example, 87 mol% or more, 89 mol% or more, 90 mol% or more, 92 mol% or more, 94 mol% or more, 95 mol% or more, 96 mol% or more, 97 mol% or more, 98 mol% or more, or 99 mol% or more) of the desired product is formed in any conversion observed.

[0054] In a preferred embodiment of the method of the present invention, the acid anhydride is glutaric anhydride, the organic monoacid is acetic acid, and the acid anhydride of the monocarboxylic acid is acetic anhydride.

[0055] The method of the present invention can be used to produce acid anhydrides in subsequent on-site processing steps (e.g., cellulose acetate manufacture) or to produce acid anhydrides in a solvent for ease of shipment. The process can be used in combination with other processes, such as using the glutaric acid by-product steam in adipic acid manufacture, to produce a more valuable acetic anhydride product stream. The process can be closely integrated with other processes. For example, in cellulose acetate production, considering the thermal integration of unit operations, the acetic acid by-product stream can be converted into acetic anhydride raw materials.

[0056] In any of the methods described herein, the intrinsic capital intensity per ton of installed annual capacity in 2020 is less than $5,000 (e.g., less than $4,500, less than $4,000, less than $3,500, less than $3,000, less than $2,500, less than $2,000, less than $1,500 or less than $1,000). In some embodiments, the intrinsic capital intensity per ton of installed annual capacity in 2020 is $1,000 or more (e.g., $1,000 or more, $1,500 or more, $2,000 or more, $2,500 or more, $3,000 or more, $3,500 or more, $4,000 or more or $4,500 or more). Any two of the above endpoints can be used to define a closed range, or a single endpoint can be used to define an open range. The installed annual capacity refers to the capacity of a plant with a scale of less than 36 thousand metric tons per year (kmta) (e.g., less than 34 kmta, less than 30 kmta, less than 30 kmta, less than 28 kmta, less than 25 kmta, less than 22 kmta, less than 20 kmta, less than 18 kmta, less than 16 kmta, less than 15 kmta, less than 14 kmta, less than 12 kmta, less than 10 kmta, less than 8 kmta, less than 6 kmta or less than 5 kmta).

[0057] In any of the methods described herein, at the same plant scale, the inherent capital intensity of the overall process is more than 5% lower than the inherent capital intensity of the ketene-based acetic acid to acetic anhydride process. For example, at the same plant scale, the inherent capital intensity of the overall process is preferably more than 10% lower (e.g., more than 15% lower, more than 20% lower, more than 25% lower, more than 30% lower, more than 35% lower, more than 40% lower) than the inherent capital intensity of the ketene-based acetic acid to acetic anhydride process. In any of these embodiments, the plant scale is less than 50 kmta (e.g., less than 45 kmta, less than 40 kmta, less than 35 kmta, less than 30 kmta, less than 25 kmta, less than 20 kmta, less than 15 kmta, less than 10 kmta or less than 5 kmta) capacity.

[0058] In any of the methods described herein, at the same plant scale, the inherent capital intensity of the ISBL (inside battery limits) of the overall process is more than 5% lower than the inherent capital intensity of the ISBL equipment of the ketene-based acetic acid to acetic anhydride process. For example, at the same plant scale, the inherent capital intensity of the ISBL equipment of the overall process is preferably more than 10% lower (e.g., more than 15% lower, more than 20% lower, more than 25% lower, more than 30% lower, more than 35% lower, more than 40% lower) than the inherent capital intensity of the ISBL equipment of the ketene-based acetic acid to acetic anhydride process. In any of these embodiments, the plant scale is less than 50 kmta (e.g., less than 45 kmta, less than 40 kmta, less than 35 kmta, less than 30 kmta, less than 25 kmta, less than 20 kmta, less than 15 kmta, less than 10 kmta or less than 5 kmta) capacity.

[0059] In any of the methods described herein, at the same plant scale, the inherent capital intensity of the ISBL (inside battery limits) and OSBL (outside battery limits) of the overall process is more than 5% lower than the inherent capital intensity of the ISBL and OSBL equipment of the ketene-based acetic acid to acetic anhydride process. For example, at the same plant scale, the inherent capital intensity of the ISBL and OSBL equipment of the overall process is preferably more than 10% lower (e.g., more than 15% lower, more than 20% lower, more than 25% lower, more than 30% lower, more than 35% lower, more than 40% lower) than the inherent capital intensity of the ISBL and OSBL equipment of the ketene-based acetic acid to acetic anhydride process. In any of these embodiments, the plant scale is less than 50 kmta (e.g., less than 45 kmta, less than 40 kmta, less than 35 kmta, less than 30 kmta, less than 25 kmta, less than 20 kmta, less than 15 kmta, less than 10 kmta or less than 5 kmta) capacity.

[0060] As used herein, the term "inherent capital intensity" means the capital cost in dollars divided by the annual installed capacity of a chemical plant to perform a specific process or chemical conversion. The inherent capital intensity of a process can be defined as the ISBL (inside battery limit) equipment or the ISBL plus OSBL (outside battery limit) equipment (based on installed cost), or the total plant project cost.

[0061] The present invention is further illustrated in the following aspects.

[0062] Aspect (1) A method for producing an anhydride of an organic monoacid, the method comprising contacting the organic monoacid with a thermally renewable anhydride to produce the anhydride of the organic monoacid and the diacid or partially hydrolyzed anhydride of the renewable anhydride.

[0063] Aspect (2) The method according to aspect (1), wherein the anhydride of the organic monoacid and the diacid or the partially hydrolyzed anhydride of the renewable anhydride are separated.

[0064] Aspect (3) The method according to aspect (2), wherein the separation step comprises forming a first stream and a second stream, the first stream comprising the anhydride of the organic monoacid and unreacted organic monoacid, and the second stream comprising the diacid or partially hydrolyzed anhydride of the renewable anhydride and unreacted anhydride.

[0065] Aspect (4) The method according to any one of aspects (1) to (3), wherein the separation step is carried out by distillation.

[0066] Aspect (5) The method according to aspect (3) or (4), wherein the unreacted organic monoacid is separated from the anhydride of the organic monoacid.

[0067] Aspect (6) The method according to aspect (5), wherein the separated unreacted organic monoacid is recycled.

[0068] Aspect (7) The method according to any one of aspects (3) to (6), wherein the second stream is heated to regenerate the renewable anhydride.

[0069] Aspect (8) The method according to aspect (7), wherein azeotropic distillation is used to regenerate the renewable anhydride.

[0070] Aspect (9) The method according to aspect (7) or aspect (8), wherein the renewable anhydride is recycled.

[0071] Aspect (10) The method according to any one of aspects (1) to (9), wherein the renewable anhydride is cyclic or can form a cyclic structure.

[0072] Aspect (11) The method according to any one of aspects (1) to (10), wherein the renewable acid anhydride is selected from carboxylic anhydrides, sulfonic anhydrides, hypophosphorous anhydrides, phosphonic anhydrides, and mixed acid anhydrides containing a combination of different acid moieties or different main chain structures.

[0073] Aspect (12) The method according to any one of aspects (1) to (11), wherein the renewable acid anhydride is selected from succinic anhydride, glutaric anhydride, nitrophthalic anhydride, homophthalic anhydride, 1,2-ethanedisulfonic acid, polyphosphoric acid, phthalic anhydride sulfonic acid, and mixed benzoic acid-trifluoroacetic anhydride.

[0074] Aspect (13) The method according to any one of aspects (1) to (12), wherein the renewable acid anhydride is glutaric anhydride.

[0075] Aspect (14) The method according to any one of aspects (1) to (13), wherein the organic monoacid is a carboxylic acid, a sulfonic acid, a sulfinic acid, a phosphonic acid, or a hypophosphorous acid.

[0076] Aspect (15) The method according to aspect (14), wherein the carboxylic acid is a C 1-12 monocarboxylic acid.

[0077] Aspect (16) The method according to aspect (15), wherein the C 1-12 monocarboxylic acid is selected from formic acid, acetic acid, propionic acid, butanoic acid / butyric acid, isobutyric acid, pentanoic acid / valeric acid, hexanoic acid / caproic acid, heptanoic acid, octanoic acid / caprylic acid, decanoic acid, and dodecanoic acid.

[0078] Aspect (17) The method according to any one of aspects (1) to (16), wherein the organic monoacid is acetic acid.

[0079] Aspect (18) The method according to any one of aspects (1) to (17), wherein the acid anhydride of the monocarboxylic acid is acetic anhydride.

[0080] Aspect (19) The method according to any one of aspects (1) to (18), wherein the addition amount of the organic monoacid exceeds that of the acid anhydride.

[0081] Aspect (20) The method according to any one of aspects (1) to (19), wherein the organic monoacid is added in multiple stages.

[0082] Aspect (21) The method according to any one of aspects (1) to (20), further comprising adding a salt of the organic monoacid.

[0083] Aspect (22) The method according to any one of aspects (1) to (21) further includes a solvent.

[0084] Aspect (23) The method according to any one of aspects (1) to (22) further includes a catalyst.

[0085] Aspect (24) The method according to any one of aspects (3) to (23), wherein a portion of the monocarboxylic acid is transferred to a container containing the second stream.

[0086] The present invention provides the following non-limiting embodiments.

[0087] Embodiment 1. A method for producing an anhydride of an organic monocarboxylic acid, the method comprising contacting the organic monocarboxylic acid with a thermally renewable anhydride to produce the anhydride of the organic monocarboxylic acid and the diacid of the renewable anhydride or a partially hydrolyzed renewable anhydride.

[0088] Embodiment 2. The method according to Embodiment 1, wherein the anhydride of the organic monocarboxylic acid and the diacid of the renewable anhydride or the partially hydrolyzed renewable anhydride are separated.

[0089] Embodiment 3. The method according to Embodiment 2, wherein the separation step is carried out by distillation.

[0090] Embodiment 4. The method according to Embodiment 2, wherein the separation step includes forming a first stream and a second stream, the first stream containing the anhydride of the organic monocarboxylic acid and unreacted organic monocarboxylic acid, and the second stream containing the diacid of the renewable anhydride or a partially hydrolyzed renewable anhydride and unreacted renewable anhydride.

[0091] Embodiment 5. The method according to Embodiment 4, wherein the unreacted organic monocarboxylic acid is separated from the anhydride of the organic monocarboxylic acid.

[0092] Embodiment 6. The method according to Embodiment 5, wherein the separated unreacted organic monocarboxylic acid is recycled.

[0093] Embodiment 7. The method according to Embodiment 4, wherein the second stream is heated to regenerate the renewable anhydride. Embodiment 8. The method according to Embodiment 7, wherein azeotropic distillation is used to regenerate the renewable anhydride.

[0094] Embodiment 9. The method according to Embodiment 7, wherein the renewable anhydride is recycled.

[0095] Embodiment 10. The method according to Embodiment 1, wherein the renewable anhydride is cyclic or capable of forming a cyclic structure.

[0096] Embodiment 11. The method according to Embodiment 1, wherein the renewable anhydride is selected from carboxylic anhydrides, sulfonic anhydrides, phosphinic anhydrides, phosphonic anhydrides, and mixed anhydrides containing combinations of different acid moieties or different backbone structures.

[0097] Embodiment 12. The method according to Embodiment 1, wherein the renewable anhydride is selected from succinic anhydride, glutaric anhydride, nitrophthalic anhydride, homophthalic anhydride, 1,2-ethanedisulfonic acid, polyphosphoric acid, pyromellitic dianhydride, propanephosphonic anhydride, o-sulfobenzoic anhydride, mixed benzoic-trifluoroacetic anhydride, and any combination thereof.

[0098] Embodiment 13. The method according to Embodiment 12, wherein the renewable anhydride is glutaric anhydride.

[0099] Embodiment 14. The method according to Embodiment 1, wherein the organic monoacid is a carboxylic acid, sulfonic acid, sulfinic acid, phosphonic acid, or phosphinic acid.

[0100] Embodiment 15. The method according to Embodiment 14, wherein the carboxylic acid is a C 1-18 monocarboxylic acid.

[0101] Embodiment 16. The method according to Embodiment 15, wherein the C 1-18 monocarboxylic acid is selected from formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, and combinations thereof.

[0102] Embodiment 17. The method according to Embodiment 1, wherein the organic monoacid is acetic acid.

[0103] Embodiment 18. The method according to Embodiment 1, wherein the anhydride of the monocarboxylic acid is acetic anhydride.

[0104] Embodiment 19. The method according to Embodiment 1, wherein the amount of the organic monoacid added exceeds that of the renewable anhydride.

[0105] Embodiment 20. The method according to Embodiment 1, wherein the organic monoacid is added in multiple stages.

[0106] Embodiment 21. The method according to Embodiment 1, which further comprises adding a salt of the organic monoacid.

[0107] Embodiment 22. The method according to Embodiment 1 further includes a solvent.

[0108] Embodiment 23. The method according to Embodiment 1 further includes a catalyst.

[0109] Embodiment 24. The method according to Embodiment 4, wherein a portion of the monocarboxylic acid is transferred to a container containing the second stream.

[0110] The following examples further illustrate the present invention, but should of course not be construed as limiting its scope in any way.

[0111] Example 1

[0112] This example demonstrates a general method for producing an anhydride of an organic monocarboxylic acid by reacting the organic monocarboxylic acid with a renewable anhydride.

[0113] A low-boiling monocarboxylic acid (such as acetic acid, propionic acid, or isobutyric acid) is fed into a reactor and reacted with a higher-boiling renewable cyclic anhydride (such as succinic anhydride, glutaric anhydride, 1,2-ethanedisulfonic anhydride, or phthalic anhydride) to produce the anhydride of the monocarboxylic acid and the diacid form of the renewable cyclic anhydride.

[0114] The mixture of the product and the starting materials is separated in a series of flash stages or distillations to produce a first stream and a second stream. The first stream mainly contains the produced anhydride and the residual monocarboxylic acid, and the second stream mainly contains the residual renewable cyclic anhydride and the produced diacid of the renewable cyclic anhydride. Then, the stream containing the anhydride product is further concentrated in the anhydride product by partial condensation, flash evaporation, or distillation, and most of the residual monocarboxylic acid is recycled to the initial reactor. The stream containing the residual renewable cyclic anhydride is thermally regenerated to remove the produced water, and the renewable cyclic anhydride is recycled to the reactor. Figure 3 is a schematic diagram showing the feed of acetic acid (AcOH) and glutaric anhydride to produce acetic anhydride (Ac2O). Figure 4 Shows a reaction schematic of this process. Acetic acid (organic monocarboxylic acid) reacts with glutaric anhydride (renewable anhydride) to form acetic anhydride (anhydride of the organic monocarboxylic acid) and glutaric acid (diacid of the renewable anhydride). Glutaric acid is dehydrated to regenerate glutaric anhydride (renewable anhydride).

[0115] Example 2

[0116] This example demonstrates a method for producing various anhydrides using a renewable anhydride and an organic monocarboxylic acid in one embodiment of the present invention.

[0117] Following the procedure shown in Example 1, a solution of a renewable anhydride in an organic monoacid was heated in a batch reactor at 50 °C or 100 °C for a specified time. No solvent or catalyst was used. The product was analyzed by nuclear magnetic resonance (NMR) spectroscopy. No by-products were detected by NMR, indicating a high selectivity. The results of these experiments are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] * Based on the calculated molar concentration, 84 wt% P2O5 equivalent as the anhydride equivalent, balancing H3PO4.

[0122] Example 3

[0123] This example demonstrates a method for producing various anhydrides using a renewable anhydride and an organic monoacid under various reaction conditions in one embodiment of the present invention.

[0124] Solids and / or liquids were added to 2-dram vials with PTFE caps or 2 - 5 ml microwave vials with crimp caps, and each vial was equipped with a stir bar. In some trials, a corresponding cosolvent was added to the corresponding vial and sealed. The sealed vials were placed in a preheated (75 °C to 150 °C) aluminum block, and the reaction was stirred at 800 rpm for 1 hour. The vials were removed from the heat source and cooled on an aluminum block at room temperature. If the reaction mixture was homogeneous at room temperature, dichloromethane (DCM) standard was added, and an NMR sample was prepared. If the reaction mixture was solid at room temperature, an appropriate amount of DMSO or DMF was added to the reaction mixture to dissolve the solid. DCM standard was added to the reaction mixture, and an NMR sample was prepared. The solution was added to an NMR tube with a capillary containing C6D6, and NMR was performed with a long relaxation delay to ensure quantitative NMR. The reaction conditions are shown in Table 2, and the products are shown in Table 3.

[0125] Table 2

[0126]

[0127]

[0128]

[0129] Table 3

[0130]

[0131]

[0132] N / D: Not Determined

[0133] Example 4

[0134] This example demonstrates the staged addition of an organic monoacid to a renewable anhydride in one embodiment of the present invention.

[0135] To test the potential of a multi-stage reaction, glutaric anhydride (10 g) was heated to 100 °C in a 50 ml round bottom flask. Acetic acid (5.25 g) was added and the flask was sealed. After 1 hour, a vacuum (10 torr (0.013 atm)) was applied to most of the acetic acid and acetic anhydride for 15 minutes, the system was repressurized to atmospheric pressure, and acetic acid was added again for another cycle. The results of the cycling experiment are shown in Table 4 and demonstrate that changing the local concentration of the starting materials (e.g., in reactive distillation) results in a higher yield than the equilibrium product yield allowed in a single-stage batch process.

[0136] Table 4

[0137] Cycle Conversion rate of glutaric anhydride (mol%) 1 5.8 2 10.1 3 14.0 4 17.2 5 20.0 6 23.1

[0138] All references cited herein (including publications, patent applications, and patents) are hereby incorporated by reference herein to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and set forth in its entirety herein.

[0139] Unless otherwise indicated herein or otherwise clearly contradicted by context, in the context of describing the present invention (especially in the context of the following claims), the terms "a", "an", "the", "at least one", and similar designations shall be construed to cover both the singular and the plural. Unless otherwise indicated herein or otherwise clearly contradicted by context, the term "at least one" (e.g., "at least one of A and B") used after a list of one or more items shall be construed to mean either an item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B). Unless otherwise specified, the terms "comprising", "having", "including", and "containing" shall be construed as open-ended terms (i.e., meaning "including but not limited to"). Unless otherwise indicated herein, the recitation of numerical ranges herein is merely intended to serve as a shorthand method for individually referring to each separate numerical value falling within the range, and each separate numerical value is incorporated into the specification as if it were individually recited herein. Unless otherwise specified herein or otherwise clearly contradicted by context, all methods described herein may be performed in any suitable order. The use of any and all examples or exemplary language (e.g., "such as") provided herein is merely intended to better describe the invention and does not limit the scope of the invention unless otherwise indicated. No language in this specification should be construed as indicating any non-claimed element as essential to practicing the invention.

[0140] Preferred embodiments of the invention are described herein, including the best mode known to the inventors for practicing the invention. After reading the foregoing description, variations of those preferred embodiments may become apparent to those of ordinary skill in the art. The inventors expect those skilled in the art to adopt these variations where appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, to the extent permitted by applicable law, the invention includes all modifications and equivalents of the subject matter recited in the appended claims. In addition, unless otherwise indicated herein or otherwise clearly contradicted by the context, the invention covers any combination of the above elements in all possible variations thereof.

Claims

1. A system for producing an anhydride of acetic acid by a method, the method comprising: contacting acetic acid with glutaric anhydride to produce the anhydride of acetic acid and the diacid of glutaric anhydride or partially hydrolyzed glutaric anhydride; separating the anhydride of acetic acid and the diacid of glutaric anhydride or the partially hydrolyzed glutaric anhydride by distillation, wherein the distillation includes forming a first stream and a second stream, the first stream comprising the anhydride of acetic acid and unreacted acetic acid, and the second stream comprising the diacid of glutaric anhydride or partially hydrolyzed glutaric anhydride and unreacted glutaric anhydride; separating the unreacted acetic acid from the anhydride of acetic acid; recycling the separated unreacted acetic acid; heating the second stream to regenerate the glutaric anhydride; and recycling the glutaric anhydride.

2. The system according to claim 1, wherein a portion of the acetic acid is transferred to a container containing the second stream.

3. The system according to claim 1, wherein azeotropic distillation is used to regenerate the glutaric anhydride.

4. The system according to claim 1, wherein the amount of acetic acid added exceeds that of glutaric anhydride.

5. The system according to claim 1, wherein the acetic acid is added in multiple stages.

6. The system according to claim 1, wherein the method further comprises adding a salt of acetic acid.

7. The system according to claim 2, wherein the amount of acetic acid added exceeds that of glutaric anhydride.

8. The system according to claim 3, wherein the amount of acetic acid added exceeds that of glutaric anhydride.

9. The system according to claim 2, wherein the acetic acid is added in multiple stages.

10. The system according to claim 3, wherein the acetic acid is added in multiple stages.

11. The system according to claim 4, wherein the acetic acid is added in multiple stages.

12. The system according to claim 2, wherein the method further comprises adding a salt of acetic acid.

13. The system according to claim 3, wherein the method further comprises adding a salt of acetic acid.

14. The system according to claim 4, wherein the method further comprises adding a salt of acetic acid.

15. The system according to claim 5, wherein the method further comprises adding a salt of acetic acid.

16. A method for producing an anhydride of an organic monoacid, the method comprising contacting the organic monoacid with glutaric anhydride to produce the anhydride of the organic monoacid and the diacid of glutaric anhydride or partially hydrolyzed glutaric anhydride.

17. The method according to claim 16, wherein the anhydride of the organic monoacid and the diacid of glutaric anhydride or the partially hydrolyzed glutaric anhydride are separated.

18. The method according to claim 17, wherein the separation step is carried out by distillation.

19. The method according to claim 17, wherein the separating step comprises forming a first stream and a second stream, the first stream comprising the anhydride of the organic monoacid and unreacted organic monoacid, and the second stream comprising the diacid of glutaric anhydride or partially hydrolyzed glutaric anhydride and unreacted glutaric anhydride.

20. The method according to claim 19, wherein the unreacted organic monoacid is separated from the anhydride of the organic monoacid.

21. The method according to claim 20, wherein the separated unreacted organic monoacid is recycled.

22. The method according to claim 19, wherein the second stream is heated to regenerate the glutaric anhydride.

23. The method according to claim 22, wherein azeotropic distillation is used to regenerate the glutaric anhydride.

24. The method according to claim 22, wherein the glutaric anhydride is recycled.

25. The method according to claim 16, wherein the organic monoacid is a carboxylic acid, a sulfonic acid, a sulfinic acid, a phosphonic acid or a phosphinic acid.

26. The method according to claim 25, wherein the carboxylic acid is a C 1-18 monocarboxylic acid.

27. The method according to claim 26, wherein said C 1-18 monocarboxylic acid is selected from formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, and combinations thereof.

28. The method according to claim 16, wherein the organic monoacid is acetic acid.

29. The method according to claim 16, wherein the anhydride of the monocarboxylic acid is acetic anhydride.

30. The method according to claim 16, wherein the amount of the organic monoacid added exceeds that of the glutaric anhydride.

31. The method according to claim 16, wherein the organic monoacid is added in a plurality of stages.

32. The method according to claim 16, further comprising adding a salt of the organic monoacid.

33. The method according to claim 16, further comprising a solvent.

34. The method according to claim 16, further comprising a catalyst.

35. The method according to claim 19, wherein a portion of the monocarboxylic acid is transferred to a container containing the second stream.

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