Method for preparing 1, 4-butanediol through organic acid gas phase esterification hydrogenation one-step method

Abstract

The invention relates to a method for preparing 1, 4-butanediol through an organic acid gas phase esterification hydrogenation one-step method. The method comprises the following steps: mixing a raw material with a low-carbon alcohol solvent, preheating and gasifying the obtained mixture, feeding the preheated and gasified mixture into a fixed bed reactor filled with a Cu-based catalyst bed layer under hydrogen purging, and carrying out esterification-hydrogenation reaction at 180-240 DEG C and 4-12 MPa to generate 1, 4-butanediol, wherein the raw materials are maleic acid, maleic acid monoester, succinic acid, fumaric acid or fumaric acid monoester; the active component of the Cu-based catalyst is Cu, and the carrier of the Cu-based catalyst is ZnO or a ZnO-containing mixed solid oxide. The catalyst used in the method is cheap and easy to obtain, and the yield of the 1, 4-butanediol is far higher than that reported in the current literature.

Description

Technical Field

[0001] The invention belongs to the field of chemical synthesis and relates to a method for producing 1,4-butanediol. Background Art

[0002] 1,4-Butanediol, referred to as BDO, is an important chemical raw material. With the continuous implementation of national energy conservation and carbon reduction policies, the maleic anhydride method of preparing 1,4-butanediol using maleic anhydride as raw material is gradually replacing the high-pollution and high-carbon emission acetylene aldehyde method and becoming a new direction for the development of 1,4-butanediol projects.

[0003] The maleic anhydride method was first developed by Davy McKee of the United Kingdom (patent CA1246616A, 1988). This method uses maleic anhydride and low-carbon alcohol as raw materials, first esterifies to prepare dialkyl maleate, and then hydrogenates the dialkyl ester to obtain 1,4-butanediol. Patent CN1298381A (2001) optimized the maleic anhydride process, but the process still requires the esterification section and hydrogenation section. CN1182732A (1998) and CN1182639A (1998) developed catalysts for the hydrogenation section, which contain heavy metal Cr that pollutes the environment, and still require the esterification section and hydrogenation section. The maleic anhydride method of esterification followed by hydrogenation has the disadvantages of long process flow and high energy consumption in process operation.

[0004] The literature (Green Chemistry, 25, 2023, 627-638) explored the process of esterification followed by hydrogenation of succinic anhydride, and optimized the catalysts for the esterification of succinic anhydride to dimethyl succinate and the hydrogenation of dimethyl succinate, respectively. However, the overall process flow is not much different from the maleic anhydride method, and the two stages of esterification and hydrogenation are still required.

[0005] The literature (ACS Sustainable Chem. Eng., 7, 2019, 18483-18492) developed a Cu-Pd catalyst for catalytic hydrogenation of succinic acid to 1,4-butanediol at 200 °C, 8 MPa, and a mass space velocity of 0.01 h ﹣1 Under the reaction conditions, the selectivity of 1,4-butanediol can reach 82%. The catalyst of this type of direct hydrogenation of carboxylic acid to alcohol mainly uses precious metals as active components, which increases the process cost, and in order to ensure the conversion rate and selectivity, the reaction needs to be carried out at an extremely low space velocity.

[0006] The literature (Journal of Molecular Catalysis A: Chemical, 395, 2014, 234-242) used Re-Cu-MC to catalyze the esterification and hydrogenation of succinic acid and methanol in a batch reactor to prepare 1,4-butanediol in one step. ﹣1Under these conditions, the selectivity of 1,4-butanediol was low, only 19.4%. The literature (Journal of Catalysis, 433, 2024, 115469) used Re / CuZnZr catalyst in a fixed bed reactor to catalyze the hydrogenation of maleic anhydride dissolved in methanol to produce 1,4-butanediol at a mass space velocity of 0.2h ﹣1 Under the above conditions, the yield of 1,4-butanediol can reach 85%, the yield of n-butanol 5%, the yield of γ-butyrolactone 9%, and the yield of tetrahydrofuran 1%. However, the study did not explore the one-step esterification and hydrogenation of monomethyl maleate, monomethyl succinate, and succinic acid to produce 1,4-butanediol. In addition, in the 200h stability test of the study, a 5% n-butanol yield appeared in the product, indicating that the process has the phenomenon of deep hydrogenation and deoxygenation of 1,4-butanediol, which is not conducive to the industrial scale-up of 1,4-butanediol.

[0007] Among the above-mentioned publicly reported technologies, the closest to this technology are the references (Journal of Molecular Catalysis A: Chemical, 395, 2014, 234-242) and (Journal of Catalysis, 433, 2024, 115469). The reference (Journal of Molecular Catalysis A: Chemical, 395, 2014, 234-242) explored the one-step process of preparing BDO by esterification and hydrogenation of succinic acid and methanol, but its BDO yield was low, mainly due to its unreasonable selection of catalysts and reaction forms; the reference (Journal of Catalysis, 433, 2024, 115469) selected the form of gas phase reaction to explore the hydrogenation system of maleic anhydride, and at a relatively high mass space velocity (0.2h ﹣1 ), the BDO yield can reach 85% and run stably for 200h, but there is a 1,4-butanediol hydrodeoxygenation reaction in the system, resulting in a 5% n-butanol yield in the product, which is not conducive to the scale-up of the process. In addition, the process only discusses the hydrogenation reaction of maleic anhydride and succinic anhydride in methanol solvent to produce 1,4-butanediol, and lacks the exploration of the process of hydrogenating organic acids derived from C4 compounds to produce 1,4-butanediol. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing 1,4-butanediol by gas phase esterification hydrogenation of organic acid in one step in view of the limitations of the current technology. The method uses a Cu-ZnO catalyst, the reaction raw material is an organic acid, the solvent is a low-carbon alcohol, and the mixture of the raw material and the solvent is fed under high pressure and high hydrogen-ester ratio conditions before entering the bed to achieve the effect of gas phase esterification hydrogenation reaction. The 1,4-butanediol preparation process of the present invention does not need to set up an esterification section, and the organic acid can be catalytically converted to obtain 1,4-butanediol in a single reactor.

[0009] The present invention is achieved through the following technical solutions: A method for preparing 1,4-butanediol by one-step organic acid gas phase esterification hydrogenation, the method comprising the following steps: The raw material is mixed with a low-carbon alcohol solvent, and the resulting mixture is preheated, gasified, and then enters a fixed bed reactor equipped with a Cu-based catalyst bed under hydrogen purge, where an esterification-hydrogenation reaction occurs at 180-240°C and 4-12MPa to generate 1,4-butanediol (by-products are a small amount of γ-butyrolactone, tetrahydrofuran, methyl 4-hydroxybutyrate, succinic acid diester, and water); The molar ratio of hydrogen to raw material is in the range of 100-2000, and the mass space velocity of raw material in the reactor is 0.2-1.5h ﹣1 (mass of reactants g / mass of catalyst g / 1h); Wherein, the raw material is maleic acid, maleic acid monoester, succinic acid, fumaric acid or fumaric acid monoester, preferably maleic acid monoester or succinic acid; In the mixture of the raw material and the low-carbon alcohol, the mass fraction of the raw material is 10wt.%-80wt.%.

[0010] The active component of the Cu-based catalyst is Cu, and the carrier is ZnO or a mixed solid oxide containing ZnO; the loading amount of Cu is 20wt.%-60wt.%.

[0011] The mixed solid oxide containing ZnO is Al2O3-ZnO, CeO2-ZnO, ZrO2-ZnO, MgO-ZnO or CaO-ZnO; the mass of ZnO is 80-100% of the mixed solid oxide.

[0012] When the raw material is maleic acid monoester, after mixing with low-carbon alcohol and preheating and gasification, a small amount of maleic acid monoester is completely esterified to generate dimethyl maleate and water. Except for the solvent low-carbon alcohol and a trace amount of water, the remaining components of the obtained mixture are maleic acid monoester and a trace amount of maleic acid diester.

[0013] When the raw material is succinic acid, after being mixed with low-carbon alcohol and preheated and gasified, a small amount of succinic acid generates succinic acid monoester and water through esterification reaction, and a small amount of succinic acid monoester generates succinic acid diester and water through esterification reaction. Except for the solvent low-carbon alcohol and a trace amount of water, the remaining components of the obtained mixture are succinic acid, a trace amount of succinic acid monoester and a trace amount of succinic acid diester.

[0014] The preheating temperature of the mixture containing raw materials is 50-120°C, and the gasification temperature is 180-200°C.

[0015] The low-carbon alcohol is specifically methanol, ethanol, n-propanol or isopropanol.

[0016] The mixture after the reaction is passed through a high-pressure separation tank to recover the circulating hydrogen, and then separated through a distillation tower to obtain 1,4-butanediol product.

[0017] The essential features of the present invention are: The limitations of current technologies include: ① The process of preparing 1,4-butanediol by esterification followed by hydrogenation requires the establishment of two stages: esterification and hydrogenation. The process is too long and the operating energy consumption is high. ② The direct hydrogenation of maleic acid / succinic acid and the one-step esterification and hydrogenation process require the use of precious metal or rare metal catalysts to improve the catalyst reaction activity and selectivity for 1,4-butanediol. Hydrogenation and deoxygenation reactions are prone to occur during the reaction, and n-butanol is prone to appear in the product, which is not conducive to industrial scale-up production. ③: The yield of 1,4-butanediol produced by esterification and hydrogenation of organic acids is low.

[0018] The invention adopts a Cu-Zn catalyst for catalytic reaction, feeds an organic acid (succinic acid or monomethyl maleate) and a low-carbon alcohol simultaneously in a fixed bed reactor, and stably and efficiently prepares 1,4-butanediol by catalyzing a gas-phase esterification hydrogenation reaction of the organic acid (ZnO is both a carrier and an auxiliary agent in the catalyst). Byproducts are gamma-butyrolactone and dimethyl succinate which can be further hydrogenated to generate 1,4-butanediol. No hydrodeoxygenation reaction occurs in the system, and no n-butanol is generated.

[0019] The beneficial effects of the present invention are: The process for preparing 1,4-butanediol by the maleic anhydride method, i.e., the conventional ester hydrogenation process, requires the setting of an esterification reaction section and a hydrogenation reaction section in the process of converting an organic acid into 1,4-butanediol. The 1,4-butanediol preparation process of the present invention does not require the setting of an esterification section, and the catalytic conversion of the organic acid to prepare 1,4-butanediol can be completed in a single reactor, thereby greatly reducing the overall energy consumption and cost of the 1,4-butanediol preparation process.

[0020] Under the same reaction conditions, in the stability test of succinate esterification and hydrogenation for 40 hours in Example 9, the yield of the target product 1,4-butanediol did not show a continuous decline; while in the stability test of dimethyl succinate hydrogenation for 40 hours in Comparative Example 1, the yield of the target product 1,4-butanediol continued to decrease. The comparison of the above examples shows that the reaction stability of the process system developed by the present technology is much higher than the diester hydrogenation system in the maleic anhydride method of esterification followed by hydrogenation, and 1,4-butanediol can be stably and continuously prepared with a higher yield of 1,4-butanediol.

[0021] At present, the direct hydrogenation conversion technology of organic acid to 1,4-butanediol often requires the use of precious metals or rare metals as active components to improve the activity of the catalyst, but the introduction of precious metals and rare metals will lead to the hydrogenation and deoxygenation of part of the 1,4-butanediol in the reaction system to n-butanol. The main active component of the catalyst used in the present invention is Cu, and the carrier and auxiliary agent are ZnO, which are all cheap and readily available materials. The catalyst preparation cost is low and has no hydrogenation and deoxygenation activity under the reaction conditions. The n-butanol selectivity is 0, and the 1,4-butanediol output rate of the present technology (Example 9: 0.5h ﹣1 , BDO yield 72.86%, 0.2780 gBDO / h / g catalyst) is much higher than the system of carboxylic acid hydrogenation to 1,4-butanediol catalyzed by precious metal catalysts reported in the literature (ACSSustainable Chem. Eng., 7, 2019, 18483-18492: 0.01h ﹣1 , BDO yield 82%, 0.0063 gBDO / h / g catalyst). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a process flow chart for preparing 1,4-butanediol by esterification and hydrogenation of monomethyl maleate; Figure 2 The mass space velocity in Example 9 is 0.5 h ﹣1 Stability test of succinate esterification and hydrogenation for 40h; Figure 3 For comparison, the mass space velocity in Example 1 is 0.5 h ﹣1 Stability test of dimethyl succinate hydrogenation for 40h; DETAILED DESCRIPTION

[0023] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0024] Example 1 The method for preparing 1,4-butanediol by hydrogenation of monomethyl maleate in one step described in Example 1 comprises the following steps: ① The specific preparation process of the Cu-ZnO catalyst used is as follows: 11.08g Cu(NO3)2·3H2O and 16.1g Zn(NO3)2·6H2O are dissolved in 100ml deionized water to obtain a precursor solution containing copper nitrate and zinc nitrate; a sodium carbonate aqueous solution with a concentration of 1 mol / L is prepared and used as a precipitant; 100ml deionized water is added to a four-necked flask, and heated in a water bath. Under the conditions of a temperature of 70°C and a stirring paddle speed of 300rpm, the precursor solution and the precipitant are respectively dripped into the flask through two separating funnels (the dropping speed of the precursor solution is 1 drop / s), and the dropping speed of the precipitant is adjusted so that the pH of the liquid in the flask is 8; when the metal precursor solution When the liquid is exhausted, the mixture is aged at a temperature of 70°C and a stirring blade speed of 100 rpm for 1 hour, then filtered and washed with deionized water. The solid is dried at 90°C overnight and then sent to a muffle furnace for calcination at 417°C in an air atmosphere for 2 hours. The catalyst powder obtained after calcination is pressed and sieved to form particles with a size of 20-40 mesh. The Cu loading in the obtained catalyst is 40wt.%, and the remaining components are all ZnO. The catalyst reduction conditions are: in-situ reduction at 300°C for 4h in a hydrogen atmosphere in a fixed bed reactor, and the hydrogen flow rate is 80ml / min.

[0025] ② Mix monomethyl maleate and methanol in a mass ratio of 1.33:9. During the mixing process, the temperature is 50°C and the pressure is normal pressure. During the mixing process, a small amount of monomethyl maleate undergoes esterification reaction to convert into dimethyl maleate and water. In addition to methanol, the main components of the obtained mixture are monomethyl maleate and a small amount of dimethyl maleate. The molar ratio of the two substances is 99.8 / 0.2.

[0026] The mixture was sent to a hydrogenation fixed bed reactor through a transmission pipeline insulated at 120°C and a gasification chamber at 200°C. The reactor had an inner diameter of 1 cm and a length of 60 cm. The reactor was placed vertically. The raw materials and hydrogen were introduced from the upper end of the reactor. The fixed bed layer was composed of inert quartz sand of 40-60 mesh at both ends of the bed and catalyst particles of 20-40 mesh in the middle. The system pressure was 8 MPa, the reaction temperature was 200°C, the molar ratio of hydrogen entering the reactor to the raw material monomethyl maleate was 200, and the mass space velocity of the raw material monomethyl maleate was 0.33 h ﹣1 , the catalyst dosage was 0.25 g, and the reaction was catalyzed by Cu-ZnO catalyst prepared by co-precipitation method.

[0027] After catalysis in a fixed bed reactor, the conversion rate of raw material monomethyl maleate was 100%, the yield of target product 1,4-butanediol was 85.02%, the yield of dimethyl succinate in the by-product was 1.23%, the yield of γ-butyrolactone was 11.11%, the yield of tetrahydrofuran was 2.07%, the yield of methyl 4-hydroxybutyrate was 0.57%, the yield of n-butanol was 0, and the product composition was analyzed by gas chromatography. The gas chromatograph model was Anhui Chromatography GC 5190, and the chromatographic column model used was JN.PEG-20M.

[0028] ③ Hydrogen recovery and product separation, such as Figure 1 As shown, the mixture after the reaction is passed through a high-pressure separation tank to recover the circulating hydrogen, and the liquid mixture is separated through a distillation tower to obtain 1,4-butanediol product.

[0029] Embodiment 2-8 The other steps are the same as those in Example 1, except for the mass space velocity of monomethyl maleate, the molar ratio of hydrogen to raw material, the reaction temperature and the reaction pressure; the specific values ​​are shown in Table 1; Table 1 Esterification and hydrogenation results of monomethyl maleate

[0030] Example 9 The method for preparing 1,4-butanediol by one-step succinate esterification and hydrogenation described in Example 9 comprises the following steps: ① Succinic acid and methanol are mixed in a mass ratio of 1:9. The temperature during the mixing process is 50°C and the pressure is normal pressure. During the mixing process, a small amount of succinic acid undergoes esterification reaction to convert into monomethyl succinate and dimethyl succinate. In addition to methanol, the main components of the obtained mixture are succinic acid, monomethyl succinate, and dimethyl succinate. The molar ratio of the three substances is 99.70 / 0.28 / 0.02.

[0031] ② The mixture was fed into the reaction section. The catalyst, reaction conditions and method used were the same as those in Example 1, except that the molar ratio of hydrogen entering the reactor to the raw material succinic acid was 200, and the mass space velocity of succinic acid was 0.5 h ﹣1 The reaction results are shown in Table 2, and the stability test results are shown in Figure 2 As shown, the yield of 1,4-butanediol did not show a continuous decrease during the 40-h stability test, and the system had continuous operation stability.

[0032]

[0033] Comparative Example 1 The method for preparing 1,4-butanediol by hydrogenation of dimethyl succinate described in this comparative example 1, the dimethyl succinate used in the method can be obtained by complete esterification of succinic anhydride or succinic acid. By comparing the data of Example 9 with that of this example, the stability advantage of the esterification-hydrogenation one-step process can be demonstrated. Comparative example 1 comprises the following steps: ① Dimethyl succinate and methanol were mixed in a mass ratio of 1:9. The mixing conditions were the same as those in Example 9. The main component of the obtained mixture except methanol was dimethyl succinate.

[0034] ② The mixture was fed into the reaction section. The catalyst, reaction conditions and method used were the same as those in Example 9, except that the molar ratio of hydrogen entering the reactor to the raw material dimethyl succinate was 200, and the mass space velocity of dimethyl succinate was 0.5 h ﹣1 The stability test results are as follows: Figure 3 As shown, the conversion rate of the raw material dimethyl succinate and the yield of the target product 1,4-butanediol continued to decrease within 40 hours, indicating that the reaction system does not have the stability for continuous operation. In the reaction product of the 40th hour, the conversion rate of the raw material dimethyl succinate was 78.42%, the yield of 1,4-butanediol was 63.59%, the yield of 4-hydroxybutyric acid methyl ester was 1.13%, the yield of γ-butyrolactone was 12.55%, and the yield of tetrahydrofuran was 1.17%.

[0035] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing 1,4-butanediol by a one-step process of gas phase esterification and hydrogenation of an organic acid, the method comprising the following steps: The raw material is mixed with a low-carbon alcohol solvent, and the resulting mixture is preheated and gasified, and then enters a fixed bed reactor equipped with a Cu-based catalyst bed under hydrogen purge, and undergoes esterification-hydrogenation reaction at 180-240°C and 4-12MPa to obtain 1,4-butanediol; in, The molar ratio of hydrogen to raw material is in the range of 100-2000, and the mass space velocity of raw material in the reactor is 0.2-1.5 h ﹣1 ; The raw materials are maleic acid, maleic acid monoester, succinic acid, fumaric acid or fumaric acid monoester; In the mixture of the raw material and the low-carbon alcohol, the mass fraction of the raw material is 10wt.%-80wt.%; The active component of the Cu-based catalyst is Cu, and the carrier is ZnO or a mixed solid oxide containing ZnO; the loading amount of Cu is 20wt.%-60wt.%.

2. The method for preparing 1,4-butanediol by one-step organic acid gas phase esterification hydrogenation as claimed in claim 1, characterized in that the raw material is preferably maleic acid monoester or succinic acid.

3. The method for preparing 1,4-butanediol by one-step organic acid gas phase esterification hydrogenation as claimed in claim 1, characterized in that the mixed solid oxide containing ZnO is Al2O3-ZnO, CeO2-ZnO, ZrO2-ZnO, MgO-ZnO or CaO-ZnO; the mass of ZnO is 80-100% of the mixed solid oxide.

4. The method for preparing 1,4-butanediol by one-step organic acid gas phase esterification hydrogenation as claimed in claim 1, characterized in that The preheating temperature of the mixture containing raw materials is 50-120°C, and the gasification temperature is 180-200°C.

5. The method for preparing 1,4-butanediol by one-step organic acid gas phase esterification hydrogenation as claimed in claim 1, characterized in that The low-carbon alcohol is specifically methanol, ethanol, isopropanol or n-propanol.

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