Malic acid production

Abstract

A method for producing malic acid includes treating a first intermediate product to form a second intermediate product. The treating includes: substantially removing impurities from the first intermediate product by gas stripping crude maleic anhydride, or subjecting a mixture of one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization to obtain a treated intermediate product; passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; obtaining a feed comprising the second intermediate product, and subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid.

Description

Technical Field

[0001] The present subject matter generally relates to the production of malic acid and in particular to the production of malic acid from different raw materials starting from butane, benzene, o-xylene, naphthalene or from intermediate products obtained by processing butane, benzene, o-xylene, naphthalene. Background Art

[0002] Malic acid is usually prepared by hydrating maleic acid prepared by dissolving maleic anhydride in demineralized water, or using a mixture of maleic acid and fumaric acid under conditions of high pressure and temperature. The time taken to reach equilibrium (i.e., to form an equilibrium mixture of malic acid, fumaric acid and trace amounts of unreacted maleic acid) (which is considered to be the time to reach reaction completion for a given amount of maleic acid or its isomer fumaric acid or mixture thereof) varies between 4 hours and 8 hours.

[0003] It has been found that in the aqueous hydration of maleic acid, catalysts increase the productivity of malic acid.In a typical hydration reaction, maleic acid is hydrated in the presence of various catalysts, including sulfuric acid.

[0004] U.S. Patent No. 3,379,756 describes a process for synthesizing malic acid from maleic acid, fumaric acid, and mixtures thereof in an aqueous reaction mixture at elevated temperature and pressure, wherein the process is carried out in a reactor zone whose surface exposed to the reaction mixture is composed of at least one material selected from the group consisting of titanium, zirconium, tantalum, and alloys containing at least one of said materials.

[0005] US Patent No. 5,210,295 discloses a method for hydrating an acid selected from maleic acid, fumaric acid, etc., wherein a high temperature reaction is performed in the presence of sodium ions in a specific molar ratio.

[0006] In European Patent No. EP 0515345, "New Catalysts for Hydration of Maleic Acid" by NABzhasso and MPPyatnitskii, Zhur.Priklandnoi Khim., Vol. 42, No. 7, pp. 1610-1614 (1969) is mentioned, which reports that when the hydroxides of aluminum and chromium are added to the aqueous maleic acid solution, the conversion of maleic acid to malic acid is increased. The fumaric acid of the equilibrium amount is also found in the hydrated product. It is also pointed out that the published Russian patents of the authors, i.e. USSR Patent No. 208706 and No. 218874, have disclosed that maleic acid is hydrated to malic acid by dissolving maleic acid in water and adding aluminum hydroxide, chromium sulfate or aluminum chloride as a reaction catalyst. The use of aluminum chloride and sulfate results in the formation of acid, i.e. hydrochloric acid and sulfuric acid, respectively. Because these acids contact with metal surfaces, especially in the downstream of the reactor, this leads to severe corrosion in the reactor vessel, thereby contaminating the product. In addition, these ions (i.e., aluminum chlorides and sulfates) are highly soluble and must be removed by ion exchange or by other expensive methods. In addition to imparting color to the mother liquor, the use of chromium hydroxide also results in the formation of toxic chromium malate. Chromium malate concentrates in the mother liquor over a period of time and can precipitate with and contaminate the product.

[0007] U.S. Patent No. 3,379,757 discloses a method for preparing malic acid from an aqueous maleic acid solution obtained by gas-phase catalytic oxidation of an organic compound such as benzene, which comprises aging the obtained maleic acid solution in the presence of air, filtering the aged solution and heating the filtrate under superatmospheric pressure in a closed system to convert the maleic acid into malic acid. The aging process is carried out in a rubber-lined steel tower.

[0008] However, conventional methods for producing malic acid have several disadvantages. The reaction requires very high temperatures and pressures; it takes a long time for the reaction to reach equilibrium; the reaction products are corrosive and toxic, leading to corrosion of the reactor vessel; and additional processes are required to remove contaminants from the product, leading to higher capital and operating costs. Therefore, an alternative method for preparing malic acid is needed. Summary of the invention

[0009] Disclosed herein is a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, a vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) gas stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and a vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization, and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (a) obtaining a feed comprising the second intermediate product; and (b) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid.

[0010] In some embodiments, the feedstock may be reacted in the presence of a catalyst. In some embodiments, the catalyst may be selected from aluminum metal, aluminum borates, and aluminum carbonates.

[0011] In some embodiments, the concentration of the catalyst may be in the range of about 50 mg / L to about 500 mg / L relative to the crude maleic anhydride or equivalent in the feed.

[0012] In some embodiments, the catalyst particles may range in size from about 10 microns to about 800 microns.

[0013] In some embodiments, the ratio of feed to catalyst may be in the range of about 1:0.00005 to about 1:0.0005.

[0014] In some embodiments, the methods disclosed herein include obtaining a raw material selected from butane, benzene, o-xylene, naphthalene, and combinations thereof. In some embodiments, the raw material may be processed to obtain a first intermediate product.

[0015] In some embodiments, stripping the crude maleic anhydride may include one of: passing nitrogen through the heated crude maleic anhydride under vacuum to substantially remove impurities; or passing air through the heated crude maleic anhydride to substantially remove impurities. In some embodiments, the step of passing air through the heated crude maleic anhydride to substantially remove impurities may be performed in a tower. In other embodiments, stripping the crude maleic anhydride may include passing carbon dioxide through the heated crude maleic anhydride under vacuum to substantially remove impurities. In some embodiments, the flow rate of air may be about 0.5 Nm 3 / hour to about 20Nm3 / hour, or 0.5Nm 3 / hour to about 10Nm 3 / hour, or 1Nm 3 / hour to 5Nm 3 / hour, for example 3Nm 3 In some embodiments, the temperature of the tower may be from about 70°C to about 100°C, such as from about 75°C to about 95°C, or about 90°C.

[0016] In some embodiments, subjecting the mixture to crystallization may include: cooling the mixture in multiple stages to a temperature below about 30°C, below about 25°C, or below about 15°C, for example, about 10 degrees Celsius, to obtain maleic acid crystals; and filtering out the maleic acid crystals as a treated intermediate product.

[0017] In some embodiments, obtaining the feed may include mixing the second intermediate product with one or more of water, maleic acid, maleic anhydride, and fumaric acid.

[0018] In some embodiments, subjecting the feed to a hydration reaction may include passing the feed in a tubular reactor at a Reynolds number of about 2,900 to about 10,000, preferably about 5,000 to about 7,000. In some embodiments, the feed may be reacted at a temperature of about 135° C. to 195° C. and a pressure of about 11 bar to 15 bar for about 1 hour to 2 hours. In some embodiments, the tubular reactor may be operated in one of a batch mode, a semi-continuous mode, or a continuous mode.

[0019] In some embodiments, in batch mode, the solution containing the product can be completely discharged after the reaction is complete.

[0020] In some embodiments, in semi-continuous mode, a portion of the solution containing the product may be removed after a predetermined period of time, and an equal amount of feed may be fed to the tubular reactor.

[0021] In some embodiments, in continuous mode, a portion of the solution containing the product may be continuously removed and at the same time the same amount of feed may be fed into the tubular reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The detailed description is described with reference to the accompanying drawings. In the drawings, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Wherever possible, the same reference numbers are used throughout the drawings to refer to similar features and components.

[0023] Figure 1 A flow chart of a process for producing malic acid according to one embodiment of the present disclosure is illustrated.

[0024] Figure 2 is a schematic diagram of a continuous tubular reactor system for producing malic acid according to one embodiment of the present disclosure.

[0025] Figure 3 is a schematic diagram of a semi-continuous tubular reactor system for producing malic acid according to one embodiment of the present disclosure.

[0026] Figure 4 is a schematic diagram of a batch tubular reactor system for producing malic acid according to one embodiment of the present disclosure.

[0027] Figure 5 is a schematic diagram of a stirred tank reactor for producing malic acid according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present subject matter relates to the production of malic acid from different raw materials or raw materials and mixtures thereof in different operating modes with and without the use of catalysts.

[0030] Usually, malic acid is to use the pure maleic anhydride obtained by distilling crude maleic anhydride or to be produced commercially by pure fumaric acid.Crude maleic anhydride or crude fumaric acid are obtained by vapor phase oxidation / gas phase oxidation of organic compounds such as butane, benzene, furans, furfural, etc.The gaseous mixture mainly of maleic anhydride released from the reactor outlet is cooled in a condenser to obtain a solid material, which is referred to as crude maleic anhydride.This crude maleic anhydride is subjected to distillation to produce pure maleic anhydride.The uncondensed gas leaving the condenser is washed in water to produce crude maleic acid, which is referred to as scrubber solution.This maleic acid scrubber solution is further subjected to dehydration and azeotropic distillation with o-xylene, and then vacuum distilled to produce pure maleic anhydride.Then pure maleic anhydride is used to produce malic acid.

[0031] However, the purification of maleic anhydride is very expensive, and the use of maleic anhydride in pure form causes the cost of malic acid production to increase greatly. In addition, this also increases the time required for producing malic acid. The production of pure maleic anhydride also involves a large amount of loss of maleic anhydride during the purification process. The malic acid production method of the present disclosure overcomes the problems and shortcomings associated with conventional malic acid production methods. The present disclosure relates to a method for producing malic acid and co-producing fumaric acid by butane, benzene, o-xylene (raw material) or by any other intermediate product formed during the production of maleic anhydride or phthalic anhydride in an integrated production method. In addition to using the pure form of these products as raw materials, the crude product formed during the production of maleic anhydride, phthalic anhydride, maleic acid, fumaric acid and other similar compounds can also be used, as well as the uncondensed exhaust gas (commonly referred to as scrubber solution) recovered by dissolving in water. In an example, in order to purify the intermediate product, any one or more of the following processes known to those skilled in the art can be carried out: adsorption, absorption, spray drying technology, falling film evaporation. The malic acid production method of the present disclosure includes simple processing of raw materials, which eliminates the need for the less environmentally friendly and more expensive dehydration and distillation steps commonly used in the purification of raw materials or intermediates. Production can be carried out in a continuous mode, a semi-continuous mode, a batch mode or any combination thereof. In one embodiment, the reactor used is a tubular reactor operated in a continuous, semi-continuous or batch mode. The method of the present disclosure can be carried out in a suitably designed tubular reactor to prevent clogging and promote high conversion by maintaining a turbulent flow with a Reynolds number in the range of 5000 to 7000. In the method of the present disclosure, there is no back mixing in the solution flow in the tubular reactor. This improves the reaction rate to achieve faster equilibrium conditions. Therefore, in the method of the present disclosure, the cost, energy and duration (reaction hours) of achieving equilibrium are greatly reduced, resulting in an increase in productivity. In some embodiments, the stream in the reactor can have a Reynolds number of about 2900 to about 10000, about 3000 to about 9000, about 4000 to about 8000, about 5000 to about 8000, about 5000 to about 7000, about 5500 to about 7000, or about 6500 to about 7000. In some embodiments, the Reynolds number can be, for example, at least 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, or in a range defined by any two of the foregoing Reynolds numbers.

[0032] In another embodiment, the reactor is a stirred tank reactor. The reaction is carried out in the presence of an aluminum borate catalyst, which results in less time required to achieve equilibrium compared to conventional methods and thus increases productivity. However, in many embodiments described herein, a catalyst is not required.

[0033] In addition, the method does not require pure raw materials as required in the conventional method, thereby significantly reducing costs. The method also reduces the amount of effluent to be treated during the production of pure maleic anhydride or pure maleic acid or fumaric acid. The method also reduces the reaction time to 1 hour to 2 hours. The time reduction reduces the energy consumed during operation, and therefore reduces operating costs. In some embodiments, impurities can be present in 0.1% weight / weight, 0.2% weight / weight, 0.3% weight / weight, 0.4% weight / weight, 0.5% weight / weight, 0.6% weight / weight, 0.7% weight / weight, 0.8% weight / weight, 0.9% weight / weight, 1% weight / weight or more of raw materials. In some embodiments, impurities can be acetic acid, acrylic acid or a combination thereof.

[0034] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid.

[0035] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor to produce malic acid.

[0036] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) gas stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a continuous stirred tank reactor to produce malic acid.

[0037] In another embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) obtaining a raw material selected from butane, benzene, o-xylene, naphthalene and combinations thereof; (b) processing the raw material to obtain a first intermediate product; (c) treating the first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by stripping the crude maleic anhydride to obtain a treated intermediate product; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (d) obtaining a feed comprising the second intermediate product; and (e) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid.

[0038] In yet another embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) obtaining a raw material selected from the group consisting of butane, benzene, o-xylene, naphthalene, and combinations thereof; (b) processing the raw material to obtain a first intermediate product; (c) treating the first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization to obtain a treated intermediate product; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (d) obtaining a feed comprising the second intermediate product; and (e) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid.

[0039] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) obtaining a raw material selected from butane, benzene, o-xylene, naphthalene and combinations thereof; (b) processing the raw material to obtain a first intermediate product; (c) treating the first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by stripping the crude maleic anhydride to obtain a treated intermediate product; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (d) obtaining a feed comprising the second intermediate product; and (e) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid.

[0040] In yet another embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) stripping the crude maleic anhydride, comprising passing nitrogen under vacuum through heated crude maleic anhydride to substantially remove impurities from the first intermediate product to obtain a treated intermediate product; (a) removing impurities from the raw material, or passing air through heated crude maleic anhydride to substantially remove impurities, or (ii) subjecting a mixture comprising crude maleic acid, crude fumaric acid, and one or more of an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid. Passing air through heated crude maleic anhydride to substantially remove impurities can be carried out in a tower, wherein the flow rate of air is about 0.5 Nm 3 / hour to about 20Nm 3 / hour, preferably about 0.5 Nm 3 / hour to about 10Nm 3 / hour. The temperature of the column may be from about 70°C to about 100°C, such as from about 75°C to about 95°C, or about 90°C. In other embodiments, stripping the crude maleic anhydride may include passing carbon dioxide through the heated crude maleic anhydride under vacuum to substantially remove impurities.

[0041] In another embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by (i) stripping the crude maleic anhydride, or (ii) subjecting the first intermediate product to a treated intermediate product comprising crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof A mixture of one or more of the exhaust gas scrubber solutions obtained in the formic anhydride production process or the maleic anhydride production process is subjected to crystallization, which includes: cooling the mixture to a temperature of less than about 15 degrees Celsius in multiple stages to obtain maleic acid crystals; and filtering out the maleic acid crystals as a treated intermediate product; and passing the aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid. In another embodiment, the mixture can be cooled to a temperature of less than about 10 degrees Celsius in multiple stages to obtain maleic acid crystals.

[0042] In one embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by (i) stripping the crude maleic anhydride, or (ii) subjecting a first intermediate product comprising crude maleic acid, crude fumaric acid, or a phthalic anhydride production process to obtain a treated intermediate product. (a) subjecting a mixture of fumaric acid, and one or more of an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product, which comprises mixing the second intermediate product with one or more of water, maleic acid, maleic anhydride and fumaric acid; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid.

[0043] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by: (i) stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor at a Reynolds number of about 2,900 to about 10,000 to produce malic acid.

[0044] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by: (i) stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor at a Reynolds of about 5000 to about 7000 to produce malic acid.

[0045] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by: (i) stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor in the presence of a catalyst at a Reynolds number of about 2,900 to about 10,000 to produce malic acid.

[0046] In one embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by (i) stripping the crude maleic anhydride, or (ii) subjecting the first intermediate product to a treated intermediate product comprising crude maleic acid, crude fumaric acid, and a phthalic anhydride production process. (a) subjecting the mixture of one or more of the effluent gas scrubber solutions obtained from the phthalic anhydride production process or the maleic anhydride production process to crystallization; and passing the aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor in the presence of a catalyst at a Reynolds number of about 2,900 to about 10,000 to produce malic acid, wherein the catalyst is selected from metallic aluminum, aluminum borates and aluminum carbonates.

[0047] In one embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by (i) stripping the crude maleic anhydride, or (ii) subjecting an exhaust gas scrubber solution comprising crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to obtain a treated intermediate product. (a) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor in the presence of a catalyst at a Reynolds number of about 2,900 to about 10,000 to produce malic acid, wherein the catalyst is selected from metallic aluminum, aluminum borates and aluminum carbonates, wherein the concentration of the catalyst is in the range of about 50 mg / L to about 500 mg / L relative to the crude maleic anhydride or equivalent in the feed.

[0048] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor in the presence of a catalyst to produce malic acid, wherein the average diameter of the catalyst particles is in the range of about 10 microns to about 800 microns.

[0049] In one embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by (i) stripping the crude maleic anhydride, or (ii) subjecting a first intermediate product comprising crude maleic acid, crude fumaric acid, and a mixture of one or more of a vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process subjecting the mixture to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor in the presence of a catalyst to produce malic acid, wherein the ratio of the feed to the catalyst is in the range of about 1:0.00005 to about 1:0.0005.

[0050] In one embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by (i) stripping the crude maleic anhydride, or (ii) subjecting a first intermediate product comprising crude maleic acid, (a) subjecting a mixture of crude fumaric acid and one or more of an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor at a temperature of about 135°C to 195°C and a pressure of about 11 bar to 15 bar for about 1 hour to 2 hours to produce malic acid.

[0051] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by: (i) stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor to produce malic acid, wherein the tubular reactor is operated in one of a batch, semi-continuous, or continuous mode.

[0052] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) gas stripping crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor to produce malic acid, wherein the tubular reactor is operated in a batch mode, and a solution comprising the product is completely discharged after the reaction is complete.

[0053] In one embodiment, the subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by (i) stripping the crude maleic anhydride, or (ii) subjecting the first intermediate product to a treated intermediate product comprising crude maleic acid, crude fumaric acid, and a phthalic anhydride production process. (a) subjecting a mixture of one or more of the effluent gas scrubber solutions obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor to produce malic acid, wherein the tubular reactor is operated in a semi-continuous mode, wherein a portion of the solution comprising the product is removed after a predetermined period of time, and an equal amount of the feed is fed to the tubular reactor.

[0054] In one embodiment, the present subject matter includes a method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product by: (i) stripping the crude maleic anhydride, or (ii) subjecting a mixture comprising one or more of crude maleic acid, crude fumaric acid, and an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor to produce malic acid, wherein the tubular reactor is operated in a continuous mode, continuously removing a portion of the solution comprising the product, and simultaneously feeding the same amount of feed into the tubular reactor.

[0055] Aspects of the present disclosure are further described in conjunction with the accompanying drawings. It should be noted that the description and the accompanying drawings merely illustrate the principles of the present subject matter. Therefore, it should be understood that various arrangements that implement the principles of the present subject matter can be designed from the description and are included within the scope thereof, although not explicitly described or shown herein.

[0056] Figure 1 A flow diagram of a method for producing malic acid according to one embodiment of the present subject matter is shown. Figure 1110 of them are raw materials; Figure 1 116, 118, 132a and 132b are first intermediate products; Figure 1 122, 126 and 138a are processed intermediates. Figure 1 138b is the second intermediate product of this theme. In one embodiment, the starting raw material 110 is butane or benzene. In another embodiment, the starting raw material 110 is o-xylene or naphthalene. In one embodiment, butane or benzene reacts with a catalyst in the gas phase to produce maleic anhydride gas 114. Maleic anhydride gas 114 is condensed to produce crude maleic anhydride 116. Crude maleic anhydride 116 (first intermediate product) can be processed in a variety of ways to form pure maleic anhydride 122 (treated intermediate product), or pure maleic acid, or a mixture 126 of pure maleic acid and pure fumaric acid (treated intermediate product). Crude maleic anhydride 116 can produce crude maleic acid 118 when hydrolyzed. Crude maleic acid 118 can be isomerized, and therefore 118 can be a mixture of maleic acid and its isomer fumaric acid. Crude maleic acid or a mixture of crude maleic acid and fumaric acid 118 can be purified by conventional processes to form pure maleic acid or a mixture of pure maleic acid and pure fumaric acid 126. Crude maleic anhydride 116 can also be purified by conventional processes to form pure maleic anhydride 122. Although conventional processes can be used to obtain pure maleic anhydride 122 or a mixture of pure maleic acid or pure maleic acid and pure fumaric acid 126 (processed intermediate products), the preferred treatments of crude maleic anhydride 116 and crude maleic acid 118 are gas stripping 136 and crystallization 134, respectively, followed by carbon treatment 138 in a carbon tower to substantially remove residual impurities, thereby forming a second intermediate product 138b. Together with crude maleic anhydride 116, uncondensed exhaust gas is produced. Uncondensed exhaust gas passes through a scrubber to form a solution, referred to herein as exhaust gas scrubber solution 132a. The vent gas scrubber solution 132a comprises maleic anhydride, maleic acid, any unreacted starting material 110, and any other impurities.

[0057] In another embodiment, the raw material 110 is o-xylene or naphthalene. The raw materials are reacted to produce phthalic anhydride 128. The uncondensed product gas is passed through water to form another exhaust gas scrubber solution 132b, which typically contains any unreacted raw material 110, phthalic anhydride 128, and any other impurities.

[0058] In one embodiment, crude maleic anhydride 116 can be subjected to simple treatment before reaction. Maleic anhydride 116 can be subjected to gas stripping 136, and then subjected to carbon treatment in carbon tower 138 to remove impurities. Gas stripping 136 can be carried out in nitrogen or air or carbon dioxide, under vacuum or without vacuum. In one example, crude maleic anhydride 116 is heated and nitrogen is bubbled through. The temperature can be maintained at 80°C to 85°C. Then, a vacuum is applied to remove impurities such as acetic acid and acrylic acid. The removal can be carried out for about 5 hours. In another embodiment, gas stripping 136 can be carried out for about 5 hours using air at a temperature of about 90°C. In another example, crude maleic anhydride 116 is heated and carbon dioxide is bubbled through. The temperature can be maintained at 80°C to 85°C. Then, a vacuum is applied to remove impurities such as acetic acid and acrylic acid. The removal can be carried out for about 5 hours. In another embodiment, gas stripping 136 can be carried out for about 5 hours using air at a temperature of about 90°C.

[0059] The treated crude maleic anhydride 116 may be dissolved in demineralized water and subjected to carbon treatment 138. The carbon treatment 138 may be performed by passing the dissolved maleic anhydride 116 through a carbon tower to remove color-imparting organic impurities such as chromophores.

[0060] In another embodiment, crude maleic acid or crude fumaric acid 118 and exhaust gas scrubber solutions 132a and 132b can be subjected to controlled crystallization 134 to remove impurities. Crude maleic acid or fumaric acid 118 and exhaust gas scrubber solutions 132a and 132b can be slowly cooled to obtain crystals. Cooling can be performed using a coolant such as cold water or frozen water at 5°C to 10°C. The temperature of the solution can be carefully reduced from, for example, 25°C to 20°C within 60 minutes and maintained for another 60 minutes. Then, the temperature can be reduced to 15°C within a duration of 90 minutes, then reduced to 10°C within a time period of 120 minutes, and maintained at this temperature for about 120 minutes. The maleic acid crystals thus obtained can be filtered, dried, dissolved in water and subjected to carbon treatment 138 to further remove impurities. The maleic acid obtained can contain impurities less than 100ppm each. This simple process of crystallization or gas stripping and subsequent carbon treatment is less energy and labor intensive and therefore cheaper than widely employed conventional purification techniques such as dehydration and distillation.

[0061] The feed 140 for producing malic acid can be selected from: crude maleic anhydride, pure maleic anhydride, crude maleic acid, crude fumaric acid, pure maleic acid, pure fumaric acid, exhaust gas scrubber solution from producing maleic anhydride from organic compounds (e.g., butane, benzene), exhaust gas scrubber solution from producing phthalic anhydride from organic compounds (e.g., o-xylene or naphthalene), and any combination thereof. Water can be added to the above raw materials as needed to form a slurry or solution for passing through the reactor. Crude fumaric acid can be obtained from any one of maleic anhydride, maleic acid, as a byproduct of phthalic anhydride production, or by biotechnology approaches known in the art.

[0062] In one embodiment, feed 142 undergoes reaction in the absence of a catalyst. In another embodiment, feed 144 undergoes reaction in the presence of a catalyst. Feed 140 undergoes reaction to produce a mixture of malic acid and fumaric acid at a temperature range of 135° C. to 195° C. and a suitable pressure. The reaction can be carried out in the presence of a catalyst or in the absence of a catalyst. The catalyst is selected from aluminum metal or its borate or carbonate in its micronized form so that the use of the catalyst does not cause corrosion of the inner surface of the reactor vessel, thereby ensuring that the catalytic process is corrosion-free. In some specific embodiments, the catalyst is aluminum borate. Using an alternative aluminum borate solution results in the formation of boric acid. Since boric acid is a weak acid, it does not corrode the reactor. In addition, using aluminum borate as a catalyst results in reaching reaction equilibrium faster than any other catalyst.

[0063] When used in the reaction, the presence and concentration of the catalyst affects the process time, the reaction rate to reach equilibrium, and the need for additional purification steps for removing the used catalyst. However, in the catalytic process, the concentration of aluminum metal or aluminum borate or aluminum carbonate in its micronized form is in the range of 50 mg / L to 500 mg / L relative to the crude maleic anhydride solution in the feed. 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500 mg / L, or in a range defined by any two of the foregoing concentrations, relative to the crude maleic anhydride solution in the feed. For example, the concentration of the catalyst relative to the crude maleic anhydride solution in the feed can be 50 mg / L to 100 mg / L, 60 mg / L to 100 mg / L, 70 mg / L to 100 mg / L, 50 mg / L to 500 mg / L, 100 mg / L to 200 mg / L, 300 mg / L to 500 mg / L, or 50 mg / L to 200 mg / L.

[0064] The particle size of the micronized aluminum metal or borate or carbonate thereof in the form of powder or granules thereof is in the range of 10 microns to 800 microns. In some embodiments, the particle size of the catalyst may be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340 , 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 650, 700, 750, 800 microns, or within the range defined by any two of the foregoing particle sizes. For example, in some embodiments, the particle size of the catalyst can be about 10 microns to 50 microns, 10 microns to 100 microns, 10 microns to 200 microns, 50 microns to 200 microns, 100 microns to 500 microns, 100 microns to 300 microns, 300 microns to 800 microns, or 150 microns to 300 microns.

[0065] Preferably, the catalyst used is aluminum metal in the form of its powder or particles. Aluminum metal or its borate or carbonate dissolved in the feed solution 140 significantly accelerates the reaction to reach equilibrium. In an example, when aluminum borate is used as a catalyst, the reaction reaches equilibrium faster than when any other catalyst is used. In one embodiment, in the resulting solution, the mass ratio of crude maleic acid to catalyst is 1:0.0001. In some embodiments, the mass ratio of crude maleic acid to catalyst can be 1:0.00005, 1:0.0001, 1:0.0002, 1:0.0003, 1:0.0004, 1:0.0005 or in the range defined by any two of the aforementioned ratios. For example, the ratio of crude maleic acid to catalyst may be 1:0.00005 to 1:0.0001, 1:0.0001 to 1:0.0002, 1:0.0002 to 1:0.0003, 1:0.0003 to 1:0004, 1:0004 to 1:0005, 1:0.0001 to 1:0.0005.

[0066] The feed 140 may be reacted in a reactor 150. The reactor 150 may be a tubular reactor 152, which may be configured to operate in any of a continuous mode, a semi-continuous mode, a batch mode, or any combination thereof.

[0067] The tubular reactor 152 for producing malic acid by the feed solution is appropriately designed to prevent clogging and promote high-speed conversion, made of suitable construction materials including but not limited to titanium, tantalum, Hastelloy, aluminum bronze or zirconium, with a high-pressure circulation pump. The feed end of the tubular reactor 152 is connected to the pump, and the other end is connected back to the pump suction through a bypass valve to circulate continuously under pressure. Alternatively, there is a bypass in the pipeline after the tubular reactor 152, for removing all or some materials into a flash tank or a discharge tank. The flash tank can also be connected back to the circulation pump suction. By making the feed mixture or solution circulate a certain number of batches at high temperature, then completely discharge or partially discharge and remove the stream, it is achieved to produce malic acid and fumaric acid semi-continuously or continuously or batchwise with a flexible ratio as required.

[0068] Tubular reactor can have the arrangement of pipe such as loop reactor, circular or spherical pipe arrangement, it can improve reaction rate and therefore reduce processing hours to realize producing malic acid with stoichiometric yield.The tube bank in tubular reactor is so arranged and interconnected, and is provided with twister and cyclone, to provide the flow velocity of about 1.5 m / sec, this causes feed material to be almost completely converted to final balance in the process time of reduction.In some embodiments, the flow velocity in tubular reactor can be about 1.0,1.1,1.2,1.3,1.4,1.5,1.6,1.7,1.8,1.9 or 2.0 m / sec.

[0069] In some embodiments, the solution in the reactor can be heated to 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or more, or within the range defined by any two of the foregoing temperatures. For example, in some embodiments, the solution in the reactor can be heated to 135°C to 195°C, 145°C to 195°C, 135°C to 150°C, 135°C to 180°C, 150°C to 195°C, or 145°C to 185°C.

[0070] In some embodiments, the solution in the reactor can be pressurized to 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14.0, 14.5, 15.0 or more pressures, or within the range defined by any two of the foregoing pressures. For example, in some embodiments, the solution in the reactor can be pressurized to 5 to 15 bar, 5 to 10 bar, 10 to 15 bar, 11 to 15 bar, or 12 to 15 bar.

[0071] In some embodiments, the solution in the reactor can be subjected to heat and / or pressure for 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 1 hour, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours or longer, or within the range defined by any two of the foregoing times. For example, in some embodiments, the solution in the reactor can be subjected to heat and / or pressure for 30 minutes to 2 hours, 1 hour to 2 hours, 1.5 hours to 2 hours, or 1 hour to 3 hours.

[0072] In one embodiment, the crude feed solution is pumped into the tubular reactor assembly at a high speed. The solution is circulated continuously in the reactor. The solution is heated to a temperature of 135° C. to 195° C. at a pressure of 11 to 15 bars for about 1 to 2 hours. In another embodiment, when the process is carried out in the presence of a catalyst, a solution of aluminum metal or a borate or carbonate thereof is added to the crude feed solution before being pumped into the tubular reactor, so that the mass ratio of crude feed solution to catalyst in the resulting solution is 1:0.0001 (100 ppm catalyst).

[0073] In some embodiments, the malic acid production method can be carried out with any one of a batch process, a semi-continuous process or a continuous process. In a batch process, after the above-mentioned operation, the solution is completely discharged in a holding tank and used for further processing. In a semi-continuous process, after the above-mentioned operation, a portion of solution is discharged after a fixed time period and an equal amount of a feed solution containing a catalyst is fed to the pipe, recycled, another fixed amount is discharged again after a fixed time period, and the process is repeated. In a continuous process, after the above-mentioned operation, a very small amount of solution is continuously discharged in a flash tank, and the same amount of a feed solution containing a catalyst is fed to the pipe simultaneously.

[0074] The reaction product obtained is a mixture of fumaric acid and malic acid. The two acids are separated from the mixture by filtration or other conventional means. The volatile impurities and the compounds causing color derived from crude maleic anhydride 116 and scrubber solution 132a are removed by conventional purification methods. The mother liquor containing malic acid is concentrated to reclaim malic acid, which is further purified. The purification of the gained malic acid can be carried out by various means, including but not limited to using ion exchanger, activated carbon in powder form or making malic acid pass through a series of carbon towers.

[0075] The boric acid formed when aluminum borate is used as catalyst is removed from the mixture by methods known in the art.

[0076] The method of the present disclosure is carried out in a tubular reactor of suitable design to prevent clogging and promote high conversion by maintaining turbulence with a Reynolds number in the range of 5000 to 7000. The turbulence in the tubular reactor is achieved and maintained by optimizing the following parameters that affect the solution flow rate: the diameter (size) and speed of the reactor. In the method of the present disclosure, there is no back mixing in the solution flow in the tubular reactor. This increases the reaction rate to achieve faster equilibrium conditions. Therefore, in the method of the present disclosure, the cost and energy to achieve equilibrium are greatly reduced, and the duration (reaction hours) to achieve equilibrium is reduced, resulting in an increase in productivity.

[0077] In one example, with turbulence in the tubular reactor 152, the Reynolds number calculated using the size and flow rate of the reactor using known methods is 6700. In another example, when there is no turbulence in the tubular reactor 152, the Reynolds number is calculated to be 2400. In the method of the present disclosure, there is no back mixing in the solution flow in the tubular reactor. This increases the reaction rate to achieve faster equilibrium conditions. Therefore, in the method of the present disclosure, the cost, energy, and duration (reaction hours) of achieving equilibrium are significantly reduced, resulting in increased productivity.

[0078] In another embodiment, the reaction is carried out in the presence of an aluminum borate catalyst in a stirred tank reactor 156 in a feed 146. Any of the aforementioned feed compositions can be used. For example, the feed 146 for producing malic acid in a stirred tank reactor 156 can be selected from: crude maleic anhydride, pure maleic anhydride, crude maleic acid, crude fumaric acid, pure maleic acid, pure fumaric acid, exhaust gas scrubber solutions from the production of maleic anhydride by butane, benzene, exhaust gas scrubber solutions from the production of phthalic anhydride by o-xylene or naphthalene, and any combination thereof. The use of a catalyst can reduce the reaction time by up to 3 times compared to conventional methods. This increases the efficiency of the operating process, reduces costs and improves productivity.

[0079] Figure 2 is a schematic diagram of a continuous tubular reactor system for producing malic acid according to one embodiment of the present subject matter. The reactor system includes a tubular reactor 210. The feed from the feed tank 220 is fed to the tubular reactor 210 via a circulation pump 230. The reaction to form malic acid occurs in the tubular reactor 210. The tubular reactor 210 is designed so that the feed has a sufficiently long residence time for the reaction to reach equilibrium, and the feed is no longer circulated back to the tubular reactor 210. The solution-slurry with the reaction product is discharged into a flash tank 240, and the product 250 from the flash tank 240 can be sent for further processing, such as purification, etc.

[0080] Figure 3 is a schematic diagram of a semi-continuous tubular reactor system for producing malic acid according to one embodiment of the present subject matter. The feed from feed tank 220 is fed to tubular reactor 210 via circulation pump 230. During processing, a portion of the product stream is discharged into flash tank 240, and a portion is recycled back to tubular reactor 210 via circulation pump 230, forming a semi-continuous process. Recycling of a portion of the product stream can be performed several times until the desired conversion to produce product 250 is achieved.

[0081] In another embodiment, the reactor system comprises a plurality of such tubular reactor subsystems, each having a pump, a flash tank and a recirculation line, wherein each subsystem is connected in series, resulting in a stepwise increase in the conversion of each subsystem, and ultimately, once the total residence time-conversion time is ensured to reach a final equilibrium conversion, the resulting final effluent from the entire system is discharged to undergo further separation and purification processes.

[0082] Figure 42 is a schematic diagram of a batch tubular reactor system for producing malic acid according to one embodiment of the present subject matter. Tubular reactor 210 is part of a closed loop system in which the feed is circulated for a sufficient number of cycles until nearly complete conversion of the reactants is obtained. After the reaction is complete, the process is stopped and the product 250 is discharged to undergo further separation and purification.

[0083] Figure 5 It is a schematic diagram of a stirred tank reactor for producing malic acid according to an embodiment of the present theme. The reactor system includes a tank 510 with an agitator 520. Feed is added to the tank 510 via a feed inlet 530, and steam is fed to the tank 510 via a steam inlet 540. The feed is continuously stirred in the tank 510 by the agitator 520 for a desired time period to ensure that the reactant is almost completely converted into product. The product is removed via an outlet 550, any condensate is removed via a condensate outlet 560, and the gas is removed via a steam outlet 570. The feed can be any raw material described above or any combination thereof. The reaction is carried out in the presence of an aluminum borate catalyst. Compared with conventional methods, the presence of a catalyst reduces the reaction time by about three times, thereby improving productivity. Example

[0084] The disclosure will now be illustrated with working examples, which are intended to illustrate the work of the disclosure, and are not intended to restrictively imply any limitation to the scope of the disclosure. Unless otherwise defined, all technical terms and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the disclosure belongs that are generally understood. Although methods and materials similar or equivalent to those described herein can be used in the practice of disclosed methods and compositions, exemplary methods, devices and materials are described herein. It should be understood that the disclosure is not limited to the described ad hoc methods and experimental conditions (because such methods and conditions can be applicable).

[0085] The examples show raw materials 1, 2 and 3. However, any combination thereof may also be used.

[0086] Mode 1A: Tubular batch, semi-continuous and continuous processes with catalyst

[0087] Using aluminum borate as a catalyst

[0088] Experimental details:

[0089] Maleic acid solution: 17 liters, (or) fumaric acid solution: 17 liters

[0090] Concentration of maleic acid aqueous solution: 45% weight / volume

[0091] Reaction temperature: 185℃

[0092] Reactor pressure: 12 bar.

[0093] Raw material details:

[0094] The following are three different raw material compositions in Table 1:

[0095] Table 1: Different raw material compositions

[0096]

[0097] The raw materials in these experiments can be defined as any of the following:

[0098] 1. Dissolve 6.46 kg of maleic anhydride in 13.12 liters of demineralized water so that the amount of maleic acid is 7.65 kg.

[0099] 2. 7.65kg pure fumaric acid.

[0100] 3. A mixture of items 1 and 2 in any proportion or combination, wherein the amount of the mixture is equivalent to 7.65 kg of maleic acid.

[0101] Experimental steps:

[0102] The raw materials were dissolved in 13.12 liters of demineralized water in a feed tank. Aluminum-based catalyst was added to the vessel and stirred thoroughly so that the final solution contained 100 mg / L (ppm) of aluminum borate or aluminum powder catalyst relative to the incoming feed. The ratio of raw materials to catalyst was 1:0.0001. Some heating was applied to dissolve the catalyst if necessary. The solution was loaded into a tubular reactor and circulated thoroughly.

[0103] The temperature of the solution in the reactor was gradually increased to 135° C. to 195° C., and the pressure in the reactor reached about 12 bar. This condition was maintained until the solution was continuously circulated in the reactor to complete the reaction.

[0104] In the case of a batch process, after the reaction is complete, the heating is discontinued. The reactor system is carefully depressurized by controlled venting of steam. When the temperature of the reactor reaches about 80° C. to 90° C., the entire liquid slurry mass from the reactor vessel is completely drained into a separate container. The solution is cooled to ambient temperature.

[0105] The fumaric acid is separated and the mother liquor comprising malic acid, some dissolved fumaric acid and small amounts of unreacted maleic acid is used for further separation and purification stages.

[0106] In the semi-continuous method, after the reaction is completed, 1000 mL of solution is discharged into a flash tank, the reactor pressure is reduced to about 10 bar, the same amount of maleic acid feed solution is fed into a titanium tube assembly, and the reaction is carried out for another 20 minutes, and then 1000 mL of solution is discharged into a flash tank. This process lasts for several hours and is called a semi-continuous method. All liquid slurry materials from the reactor vessel are completely discharged into a separate container. The solution is cooled to ambient temperature. After this, the method follows the same steps as the batch method.

[0107] In the continuous process, after the reaction duration is completed, the solution in the reactor is discharged into a flash tank at a rate of 50 mL / min. At the same time, an equal amount of maleic acid feed solution is fed into a titanium tube. This process lasts for several hours, and all liquid slurry materials from the reactor vessel are completely discharged into a separate container. The solution is then cooled to ambient temperature. Thereafter, the method follows the same steps as the batch method.

[0108] The same experiments were performed using aluminum hydroxide and aluminum carbonate catalysts instead of aluminum borate. The results of these experiments are shown in Table 2.

[0109] Mode 1B: Catalyst-free tubular batch, semi-continuous and continuous processes

[0110] The same process was performed without catalyst in all three operating modes: tubular batch, tubular semi-continuous, and tubular continuous.

[0111] Turbulent state

[0112] The time taken to reach equilibrium depends on the turbulence achieved, and the two operating regimes characterized by turbulence are given below:

[0113] 1) In the case of turbulent flow, the Reynolds number is equal to 6700 (calculated by known methods).

[0114] 2) In the absence of turbulence, the Reynolds number is equal to 2400 (calculated by known methods)

[0115] Mode 2A: Stirred Tank Reactor - Batch Process with Catalyst

[0116] Using aluminum borate as a catalyst

[0117] Experimental details

[0118] Maleic acid solution: 50L, (or) fumaric acid solution: 50L

[0119] Concentration of maleic acid aqueous solution: 45% weight / volume

[0120] Catalyst (aluminum borate) - 100 mg / L (100 ppm) relative to maleic acid

[0121] Reaction temperature: 185℃

[0122] Reactor pressure: 12 bar.

[0123] Reaction duration: 120 minutes

[0124] The feed compositions are the same as those used in the tubular reactor process.

[0125] Raw material details:

[0126] The raw materials used in these experiments were defined as any of the following:

[0127] 1. Dissolve 21.12 kg of maleic anhydride in 43 liters of demineralized water so that the amount of maleic acid is 25 kg.

[0128] 2. 25kg fumaric acid.

[0129] 3. A mixture of items 1 and 2 in any ratio or combination, wherein the amount of the mixture is equivalent to 25 kg of maleic acid.

[0130] 4. Catalyst concentration: 100 ppm of aluminum-based catalyst.

[0131] Experimental steps:

[0132] 21.12kg maleic anhydride (or 25kg fumaric acid) is dissolved in 43 liters of demineralized water in a separate container. Pure aluminum borate is added thereto and stirred thoroughly so that the final solution contains 100mg / liter of aluminum borate relative to maleic acid (i.e., the mass ratio of maleic acid: aluminum borate is 1:0.0001). If necessary, some heating is provided to dissolve the aluminum borate. The solution is loaded into a stirred tank reactor and stirred thoroughly. The temperature of the solution in the closed reactor is slowly raised to 135°C to 195°C, and the pressure in the reactor rises to about 12 bar while continuing to stir. This condition is maintained until the solution completes the reaction in the reactor. After the reaction is completed, heating is interrupted. The reactor is carefully decompressed by controlled discharge of steam. A cooling water circulation can be provided by the jacket of the reactor to reduce the temperature of the solution to 80°C to 90°C. All liquid slurry materials from the reactor container are completely discharged into a separate container. Here, the solution is cooled to ambient temperature in about 6 to 8 hours. Thereafter, the process follows the same steps as the other tubular reactor processes described above.

[0133] The same experiment was performed using aluminum hydroxide and aluminum carbonate catalysts instead of aluminum borate. The results are shown in Table 2.

[0134] Mode 2B: Stirred Tank Reactor Batch Process - No Catalyst

[0135] The same experiment as above was carried out in a stirred tank reactor without using a catalyst. The results are included in a combined table (Table 2).

[0136] Given below is a combined table (Table 2) that includes different feedstock compositions, operating modes, turbulence, and presence / absence of catalyst, as well as the time taken to achieve equilibrium (reaction duration) for different combinations of these parameters.

[0137] Table 2: Different feedstock compositions, operating modes, turbulence, and presence / absence of catalyst, and the time taken to achieve equilibrium (reaction duration) for different combinations of these parameters.

[0138]

[0139]

[0140] As shown in Table 2, the use of turbulence alone, the use of a catalyst alone, or the use of a combination of turbulence and a catalyst reduces the reaction time required to reach equilibrium in a tubular reactor in batch, semi-continuous, or continuous mode. The use of aluminum borate as a catalyst and turbulence showed the least time required to reach equilibrium. For a stirred tank reactor, the use of aluminum borate as a catalyst showed the least reaction time to reach equilibrium compared to the use of no catalyst or the use of aluminum hydroxide as a catalyst.

[0141] The exact amounts of malic acid, fumaric acid and unreacted maleic acid in all these processes were measured from the amounts obtained and the stoichiometric conversions calculated.

[0142] The stoichiometric conversions (Table 3) of the raw materials obtained by all these processes as described above are shown in the table below. Assuming that the total acid amount before the reaction is 100% maleic acid or 100% fumaric acid or 100% malic acid (expressed as maleic acid), these are almost the same as those obtained in any batch process.

[0143] Table 3: Stoichiometric conversions of the starting materials obtained.

[0144] Serial number Compound Name Stoichiometric conversion of raw materials 1. Malic Acid 57% to 58% 2. Fumaric Acid 37 to 38 percent 3. Maleic acid 1.2% to 1.5% 4. <![CDATA[Loss / Not Specified (CO, CO2, etc.)]]> 2% to 3%

[0145] Thus, as shown in Table 3, the stoichiometric conversion of the feedstock is comparable to any other batch process. However, as previously mentioned, the time required to reach equilibrium is significantly reduced, thus allowing an increase in productivity.

[0146] Example: Maleic Acid and Exhaust Gas Scrubber Treatment

[0147] Any or all of the treatment process can be performed on crude maleic acid or fumaric acid 118, or an exhaust gas scrubber solution 132a after partial condensation of gaseous maleic anhydride prepared from maleic anhydride, or an exhaust gas scrubber solution 132b after condensation and separation of gaseous phthalic anhydride prepared from phthalic anhydride 132a. 1 liter of maleic acid scrubber solution containing about 46% weight / volume maleic acid, about 0.7% acetic acid and about 0.4% acrylic acid is placed in a glass beaker. The beaker is provided with an agitator and the speed is maintained at 25 rpm. Chilled water or cold water is circulated through the jacket device in the beaker. The contents of the beaker are at room temperature (about 25°C).

[0148] The temperature was gradually reduced to 20°C over a period of 60 minutes. The temperature was then maintained for a further 60 minutes. Some crystallization could be observed. By adjusting the cooling water flow, the temperature was further reduced to 15°C over a period of 90 minutes. Similarly, the temperature of the maleic acid solution was further reduced to 10°C over a period of 2 hours. The temperature was maintained for 120 minutes.

[0149] In this way, crystallization is carefully controlled. The maleic acid crystals thus obtained are filtered and dried and subjected to further treatment to remove color by carbon treatment. The mother liquor is recycled. The impurity analysis of the maleic acid crystals on a dry basis is provided in Table 4.

[0150] Table 4. Impurity concentrations before and after treatment

[0151] Serial number Impurities Before processing After treatment 1 Acetic acid(impurity) 0.7% (approx.) Less than 0.01% 2 Acrylic acid (impurity) 0.3% to 0.4% (approximately) Less than 0.01%

[0152] Table 4 shows that the impurities in the crude maleic acid solution after crystallization and passing through the carbon tower are less than 0.01%.

[0153] Example: Crude Maleic Anhydride Treatment

[0154] 1 kg of crude maleic anhydride is placed in a 2.0 liter 3-neck round bottom flask. Crude maleic anhydride generally contains about 0.1% acetic acid and 0.1% acrylic acid as impurities. Together with a nitrogen bubbling configuration and a vacuum configuration, the flask is equipped with an agitator and the rotation speed is maintained at 100. The flask is heated by a heating jacket and the temperature of the flask is maintained in the optimal range of 80°C to 85°C. Once the temperature is within this range, a vacuum of 20 torr is generated with a suitable device and under an inert atmosphere. The temperature is maintained under these conditions for a period of more than 3 hours.

[0155] The two major impurities, namely acetic acid and acrylic acid, were almost completely stripped from the crude maleic anhydride, so that the quality of the treated maleic anhydride was as shown in Table 5. The maleic anhydride was further subjected to carbon treatment for color removal.

[0156] Table 5: Impurity analysis of crude maleic anhydride before and after treatment

[0157] Serial number Impurities Before processing After treatment 1 Acetic acid(impurity) 0.1% (by weight) Less than 0.01% 2 Acrylic acid (impurity) 0.1% (by weight) Less than 0.01%

[0158] Table 5 shows that after treatment with maleic anhydride, the impurities were reduced to less than 0.01%.

[0159] Example: Crude Maleic Anhydride Treatment

[0160] About 25 kg of crude maleic anhydride was placed in a 35 liter capacity stainless steel feed tank with a jacket arrangement. Heating was provided by low pressure steam. The feed typically contained about 0.1% acetic acid and 0.1% acrylic acid as impurities.

[0161] The feed tank discharge outlet is connected to a stainless steel column of about 3 meters in height and 50 mm in diameter and is packed with structured packing material. The regulated flow rate of crude maleic anhydride is about 5 kg / hour at an operating temperature of 90°C. The air flow rate from the bottom is about 3 Nm 3 The temperature of the column was maintained at about 90° C. over a duration of 5 hours.

[0162] The treatment can be described as a continuous countercurrent operation to remove impurities (i.e. acetic acid and acrylic acid) in crude maleic anhydride by air stripping. The two major impurities (i.e. acetic acid and acrylic acid) were almost completely stripped from the crude maleic anhydride, so that the quality of the treated maleic anhydride is shown in Table 6.

[0163] Table 6: Impurity analysis of crude maleic anhydride before and after treatment

[0164] Serial number Impurities Before processing After treatment 1 Acetic acid(impurity) 0.1% (by weight) Less than 0.01% 2 Acrylic acid (impurity) 0.1% (by weight) Less than 0.01%

[0165] The treated crude maleic anhydride is dissolved in demineralized water to prepare a crude maleic acid solution. The maleic anhydride is further subjected to carbon treatment for color removal.

[0166] Although embodiments for producing malic acid are described in language specific to structural features, it is to be understood that these specific features and methods are disclosed as exemplary embodiments for implementing the claimed subject matter.

Claims

1. A method for producing malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from the group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, an exhaust gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: Removing impurities from the first intermediate product by the following process to obtain a treated intermediate product: (i) stripping the crude maleic anhydride; or (ii) subjecting a mixture comprising one or more of the crude maleic acid, the crude fumaric acid, and the vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing the aqueous solution of the treated intermediate product through a carbon tower to remove residual impurities, thereby forming the second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) subjecting the feed to a hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid, wherein the hydration reaction of the feed is carried out in the presence of a catalyst, and wherein the catalyst is an aluminum borate. 2 . The method according to claim 1 , wherein the concentration of the catalyst is in the range of 50 mg / L to 500 mg / L relative to the second intermediate product in the feed.

3. The method of claim 1, wherein the average diameter of the catalyst particles is in the range of 10 microns to 800 microns.

4. The method of claim 1, wherein the weight ratio of the feed to the catalyst is in the range of 1:0.00005 to 1:0.0005.

5. The method of claim 1, wherein the first intermediate product is a product of processing a raw material selected from the group consisting of butane, benzene, o-xylene, naphthalene, and combinations thereof.

6. The process of claim 1, wherein stripping the crude maleic anhydride comprises one of: Passing nitrogen through the heated crude maleic anhydride under vacuum to remove impurities; or Air or carbon dioxide is passed through the heated crude maleic anhydride to remove impurities.

7. A process according to claim 6, wherein passing air over the heated crude maleic anhydride to remove impurities is carried out in a column.

8. The method according to claim 7, wherein the air flow rate is 0.5 Nm 3 / hour to 20Nm 3 / Hour.

9. The method according to claim 7, wherein the temperature of the tower is 70°C to 100°C.

10. The method of claim 1, wherein subjecting the mixture to crystallization comprises: Cooling the mixture to a temperature below 15 degrees Celsius in multiple stages to obtain maleic acid crystals; as well as The maleic acid crystals were filtered off as the treated intermediate product.

11. The method of claim 1, wherein obtaining the feed comprises mixing the second intermediate product with one or more of water, maleic acid, maleic anhydride, and fumaric acid.

12. The method of claim 1, wherein subjecting the feed to a hydration reaction comprises passing the feed in the tubular reactor at a Reynolds number of 2,900 to 10,000.

13. The method of claim 1, wherein the feed is reacted at a temperature of 135 to 195°C and a pressure of 11 to 15 bar for 1 to 2 hours.

14. The process of claim 1, wherein the tubular reactor is operated in one of a batch mode, a semi-continuous mode, or a continuous mode.

15. The method according to claim 14, wherein in the batch mode, the solution containing the product is completely discharged after the reaction is completed.

16. The process of claim 14, wherein in the semi-continuous mode, a portion of the solution containing the product is removed after a predetermined period of time and an equal amount of feed is fed into the tubular reactor.

17. The process according to claim 14, wherein in the continuous mode, a portion of the solution containing the product is continuously removed and simultaneously the same amount of feed is fed into the tubular reactor.

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