A process for the hydrogenation of crude methyl acetate

Abstract

The present application belongs to the technical field of ester hydrogenation, and particularly relates to a method for hydrogenation of crude methyl acetate. The method comprises the following steps: S1, a pretreatment step: crude methyl acetate liquid phase containing methyl acetate and at least one hydrogenation catalyst poison is mixed with a first part of hydrogen and preheated, and is contacted with a pretreatment catalyst in a pretreatment reactor to cause hydrogenation conversion of the hydrogenation catalyst poison; S2, a hydrogenation step: the pretreated material obtained in S1 is mixed with a second part of hydrogen and heated to a reaction temperature, and is contacted with a hydrogenation catalyst in a hydrogenation reactor to obtain crude alcohol; and S3, a separation step: the crude alcohol is rectified to obtain an ethanol product. The present application significantly reduces the difficult-to-separate by-products such as azeotrope in industrial production by setting a preheating and then heating process for crude methyl acetate, matching the reactor, and setting a pre-preprocessing process for pressure conditions and liquid space velocity, and then performing a hydrogenation reaction, and has low rectification energy consumption, higher product purity, simple operation, and good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of ester hydrogenation technology, specifically relating to a method for hydrogenating crude methyl acetate. Background Technology

[0002] With the increasing demand for energy, the escalating tension in oil supply, and the growing global environmental pressures, fuel ethanol has gained widespread attention worldwide due to its clean and environmentally friendly properties. As an important clean energy source, ethanol blended with gasoline at a ratio of 10% is called ethanol gasoline (E10). Ethanol gasoline can reduce emissions of carbon monoxide and hydrocarbons from vehicle exhaust, which is of great significance for solving air pollution problems and achieving sustainable development.

[0003] Currently, fuel ethanol is mainly divided into three categories: grain ethanol, non-grain ethanol, and cellulosic ethanol. Grain ethanol uses grains such as corn and wheat as raw materials. Because the production of grain ethanol and non-grain ethanol will occupy more arable land and pose a competition for food with humans and livestock, they are gradually being restricted or prohibited by relevant policies of governments around the world. In recent years, researchers have explored an economical and environmentally friendly process route: "syngas → methanol → dimethyl ether → methyl acetate → ethanol". Currently, the total capacity of dimethyl ether plants in China has reached approximately 14 million tons, but the operating rate is only 38%. This route solves the problem of severe overcapacity of dimethyl ether.

[0004] Currently, researchers have developed a technical route of "dimethyl ether → methyl acetate → ethanol". In this route, dimethyl ether and carbon monoxide undergo a carbonylation reaction to produce methyl acetate, and methyl acetate and hydrogen undergo a hydrogenation reaction to produce ethanol. The technology of hydrogenating methyl acetate to produce ethanol is already mature and has been industrialized.

[0005] However, the hydrogenation of crude methyl acetate generated during the dimethyl ether carbonylation process affects the quality of the ethanol product, and increases energy consumption to separate impurities. Furthermore, unsaturated aldehydes / acids / ketone esters in the crude methyl acetate are prone to undergoing high-temperature hydrogenation reactions, such as aldol or aldol condensation, to form large molecular byproducts, or to form carbon precursors on the catalyst surface, leading to catalyst deactivation.

[0006] Chinese patent application number CN202111641495.2 proposes that acetic acid impurities in crude methyl acetate can cause deactivation of hydrogenation catalysts, and discloses a Cu-Zn-Al-B catalyst that is specifically resistant to acetic acid. Although this technical solution is aware of the impurity problem, the solution (such as developing a resistant catalyst) only solves the problem of acetic acid impurities. It cannot solve all the problems caused by impurities for other unsaturated aldehydes / ketones / acids / esters.

[0007] To address this issue, this patent proposes pretreating crude methyl acetate before hydrogenation to reduce impurities in the product and lower separation energy consumption.

[0008] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventors studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0009] This invention belongs to the field of ester hydrogenation technology, specifically relating to a method for hydrogenating crude methyl acetate.

[0010] To address the aforementioned technical problems, one objective of this invention is to provide a method for hydrogenating crude methyl acetate, comprising the following steps: S1 Pretreatment step: The crude methyl acetate liquid phase containing methyl acetate and at least one hydrogenation catalyst poison is mixed with the first part of hydrogen and preheated, and then contacted with the pretreatment catalyst in the pretreatment reactor to cause the hydrogenation catalyst poison to undergo hydrogenation conversion. S2 Hydrogenation step: The pretreated material obtained from S1 is mixed with the second part of hydrogen and heated to the reaction temperature. Then, it is contacted with the hydrogenation catalyst in the hydrogenation reactor to obtain crude alcohol. S3 Separation step: Distill the crude alcohol to obtain the ethanol product.

[0011] According to a preferred embodiment, in S1, the molar ratio of crude methyl acetate liquid to hydrogen is 1:0.01-50. Preferably, the molar ratio of crude methyl acetate liquid to hydrogen is 3:1. More preferably, the molar ratio of crude methyl acetate liquid to hydrogen is 8:1.

[0012] According to a preferred embodiment, in S1, the temperature of the crude ester is 5°C-180°C.

[0013] According to a preferred embodiment, in S1, the hydrogenation temperature is 50-180°C, and the pretreatment pressure is 1-10 MPa.

[0014] According to a preferred embodiment, in S1, the pretreatment reactor is an adiabatic bed reactor. The reactor is filled with a pretreatment catalyst, which is a supported catalyst of one or more metals selected from Pt, Pd, Ru, Cu, Zn, Cr, and Ni on a porous material such as silica, alumina, molecular sieve, or activated carbon. The pore size distribution of the porous material is >50% (2-15 nm).

[0015] According to a preferred embodiment, in S1, the pretreatment reactor is a fixed-bed reactor, and gas-phase pretreatment or liquid-phase pretreatment is used.

[0016] According to a preferred embodiment, in S1, the liquid hourly space velocity (LHSV) of crude methyl acetate is 0.2-10.0 h⁻¹. -1 .

[0017] According to a preferred embodiment, the molar ratio of hydrogen to crude methyl acetate in S1 is lower than the molar ratio of hydrogen to pretreated material in S2. Preferably, in S2, the molar ratio of crude methyl acetate to hydrogen before entering the hydrogenation reactor is 1:10-50.

[0018] According to a preferred embodiment, in S2, the hydrogen is either recycled gas from the hydrogenation reaction or a mixture of hydrogen and fresh hydrogen. The hydrogenation catalyst is an oxide catalyst composed of one or more of the following components: CuO, ZnO, Cr2O3, NiO, and Al2O3.

[0019] According to a preferred embodiment, the hydrogenation temperature in S2 is lower than that in S1. Preferably, in S2, the hydrogenation temperature is 200-280°C, and the pressure is 2.0-5.0 MPa.

[0020] According to a preferred embodiment, the crude methyl acetate contains 80.0%-99.99% methyl acetate and 0.01%-20.0% hydrogenation catalyst poison.

[0021] According to a preferred embodiment, the hydrogenation catalyst poison is at least one of a C2-C7 ester, ketone, acid, aldehyde, or alcohol. Preferably, the hydrogenation catalyst poison includes acetic acid, an unsaturated aldehyde, or an unsaturated ketone.

[0022] One of the objectives of this invention is to provide the use of the above-described method for hydrogenating crude methyl acetate in the preparation of ethanol.

[0023] One object of the present invention is to provide the use of the above-described method for hydrogenating crude methyl acetate in the preparation of products containing ethanol, such as industrial ethanol or disinfectants.

[0024] The beneficial effects of this technical solution are: This invention achieves significant advantages over existing technologies by preheating crude methyl acetate, using a reactor with a specific catalyst, and implementing pretreatment steps with controlled pressure and liquid hourly velocity before hydrogenation.

[0025] Specifically, by synergistically coupling the pretreatment step and the hydrogenation step, this invention overcomes the technical bias of prior art that requires "dependence on catalyst tolerance" or "direct high-temperature hydrogenation," resulting in unexpected technical effects: (1) Precise matching of temperature gradient and reaction stage Existing technologies typically involve directly heating crude methyl acetate to the hydrogenation reaction temperature (above 200°C) or performing hydrogenation at a single temperature throughout the entire process. This invention innovatively employs a temperature gradient reaction strategy: in a pretreatment stage at a lower temperature (50-180°C), a specific catalyst is used to selectively hydrogenate unsaturated aldehydes, ketones, acids, and other poisons into saturated compounds or volatile substances; subsequently, the material is heated to the main hydrogenation temperature (200-280°C). This temperature gradient design is based on the inventors' in-depth research into the kinetics of poison conversion and the main reaction—unsaturated poisons can be effectively converted at relatively low temperatures, while methyl acetate hydrogenation requires higher temperatures to proceed efficiently. Precise control of the temperature difference between the two stages avoids side reactions such as condensation and polymerization of poisons at high temperatures, preventing the formation of difficult-to-separate byproducts, while ensuring the efficient execution of the main reaction. This is a technical effect that cannot be achieved by simple high-temperature direct hydrogenation or low-temperature standalone treatment.

[0026] (2) Synergistic effect of phased hydrogen supply This invention employs a staged hydrogen supply strategy: the pretreatment stage requires only a low hydrogen-to-ester ratio (0.01-10:1) to complete the poison conversion, while the main hydrogenation stage supplements hydrogen to a higher ratio (10-50:1). By allocating hydrogen usage, the reaction mechanism is optimized: the poison hydrogenation in the pretreatment stage is a rapid reaction, efficiently completed with a small amount of hydrogen. However, if a large amount of hydrogen is introduced at once for pretreatment, it will exacerbate excessive hydrogenation of the poison, leading to the formation of alkane impurities, or result in uneven hydrogen distribution in the subsequent main reaction. Staged hydrogen supply combined with a temperature gradient achieves synergistic effects between the directional conversion of the poison and the deep hydrogenation of the main reaction, significantly reducing the energy consumption of subsequent distillation and separation.

[0027] (3) Differentiated division of labor and protection mechanism of catalyst function Unlike existing technologies that attempt to use a single catalyst to simultaneously withstand poisons and complete hydrogenation (such as the acid-resistant catalyst described in CN202111641495.2), this invention employs a catalyst functional differentiation strategy: a pretreatment catalyst is dedicated to poison conversion (using highly active metals such as Pt, Pd, and Ru), while the main hydrogenation catalyst is dedicated to methyl acetate hydrogenation (using selective catalysts such as Cu-based catalysts). This division of labor protects the main hydrogenation catalyst from poison attack, maintaining long-term stability; simultaneously, the pretreatment catalyst operates under low-harshness conditions and is less prone to carbon buildup and deactivation; furthermore, it addresses the issue of low efficiency in staged hydrogenation, making staged hydrogenation a viable treatment method. The synergistic effect of the two catalysts significantly extends the overall catalyst lifetime and eliminates the need to develop complex, specially resistant catalysts, thus reducing industrialization costs.

[0028] (4) Source control of impurities and reduction of energy consumption Comparative experiments (see Table 1) show that direct hydrogenation of untreated crude methyl acetate significantly increases the content of difficult-to-separate byproducts such as isopropanol and n-propanol in the crude alcohol. However, the content of these impurities is greatly reduced in the product after pretreatment according to this invention (Example 1: isopropanol 0.010%, n-propanol 0.033%). This reduction in impurities is not achieved through subsequent distillation separation, but rather by controlling the impurities at the source by inhibiting side reactions in the toxic substance conversion pathway during the pretreatment stage. Therefore, it significantly reduces the energy consumption and operational difficulty of the distillation section, and the purity of the product ethanol can reach over 99.5%, which can be directly adapted to fuel ethanol or high-purity industrial ethanol standards.

[0029] In summary, this invention forms an organically integrated technical solution through temperature coupling of "low-temperature pre-detoxification-high-temperature main hydrogenation," material coupling of "segmented hydrogen supply," and system coupling of "functional division of labor among dual catalysts." Through multi-step optimization and coordination, the treatment results produce a synergistic technical effect of 1+1>2, solving the long-standing technical problem in the field of balancing toxin removal and deep hydrogenation, and the contradiction between impurity control and energy consumption reduction. Compared with existing technologies, this invention has significant creative contributions and industrial application value.

[0030] This process is simple and can be seamlessly integrated with existing industrial hydrogenation units without large-scale modifications. It offers high operational flexibility and can be adapted to crude methyl acetate feedstocks from different sources and with varying impurity contents, thus broadening the sources of raw materials and reducing procurement costs. The entire process is continuous, with no additional auxiliary materials introduced, enabling the cascade utilization of reaction waste heat. Overall energy consumption and operating costs are significantly optimized, and the generation of waste gas, wastewater, and solid waste is greatly reduced. It combines excellent economic efficiency, safety, and promising prospects for industrial application. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] In the description of this invention, terminology is used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0033] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents or instruments used, unless otherwise specified by the manufacturer, are all commercially available reagents and materials; the conditions not specified in the examples are all carried out according to conventional conditions or conditions recommended by the manufacturer. At the same time, the present invention does not limit the source of the raw materials used. Unless otherwise specified, the raw materials used in the present invention are all commercially available products in this technical field.

[0034] Example 1 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (methyl acetate content 99.8%, acetic acid content 0.11%, acetaldehyde content 0.02%, methyl propionate content 0.04%, methyl butyrate content 0.02%, butyraldehyde content 0.01%) are preheated to 80°C and mixed, then fed into a fixed-bed reactor packed with 0.1% Pt / Al₂O₃ catalyst. The pretreatment pressure is 6 MPa, and the liquid hourly space velocity (LHSV) of the crude ester is 3.0 h⁻¹. -1 The molar ratio of hydrogen to crude ester is 3:1.

[0035] After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 230℃, the pressure is 5MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 25. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0036] The total conversion rate of methyl acetate and the impurities in crude ethanol after 300 h are shown in Table 1.

[0037] Example 2 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 99.5% methyl acetate, 0.42% acetic acid, 0.03% acetaldehyde, 0.02% methyl acrylate, 0.015% methyl butyrate, and 0.015% butyraldehyde) are preheated to 100°C and mixed, then fed into a fixed-bed reactor packed with a 0.05% Ru / C catalyst. The pretreatment pressure is 5 MPa, and the liquid hourly space velocity (LHSV) of the crude ester is 5.0 h⁻¹. -1 The molar ratio of hydrogen to crude ester is 8:1.

[0038] After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 225℃, the pressure is 4MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 15. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0039] The total conversion rate of methyl acetate and the impurities in crude ethanol after 300 h are shown in Table 1.

[0040] Example 3 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 98.5% methyl acetate, 0.93% acetic acid, 0.5% acetaldehyde, 0.034% methyl acrylate, 0.012% methyl butyrate, and 0.023% butyraldehyde) are preheated to 130°C and mixed, then fed into a CuCrO2-filled container. xA fixed-bed reactor with a catalyst was used, with a pretreatment pressure of 4.5 MPa and a liquid hourly space velocity (LHSV) of 6.0 h⁻¹ for the crude ester. -1 The molar ratio of hydrogen to crude ester is 10:1.

[0041] After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 230℃, the pressure is 4.5 MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 20. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0042] The total conversion rate of methyl acetate and the impurities in crude ethanol after 300 h are shown in Table 1.

[0043] Example 4 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 98.0% methyl acetate, 1.62% acetic acid, 0.26% acetaldehyde, 0.04% methyl propionate, 0.036% methyl butyrate, and 0.035% butyraldehyde) are preheated to 150°C and mixed before being introduced into a CuZnAlO4 filling chamber. x A fixed-bed reactor with a catalyst was used, with a pretreatment pressure of 5 MPa and a liquid hourly space velocity (LHSV) of 5.0 h⁻¹ for the crude ester. -1 The molar ratio of hydrogen to crude ester is 10:1.

[0044] After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 240℃, the pressure is 5MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 19. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0045] The total conversion rate of methyl acetate and the impurities in crude ethanol after 300 h are shown in Table 1.

[0046] Example 5 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 90.0% methyl acetate, 0.38% acetic acid, 3.1% acetaldehyde, 2.5% methyl acrylate, 2.2% methyl butyrate, and 1.82% butyraldehyde) are preheated to 150°C and mixed before being fed into a CuZnAlO4 filling chamber. x A fixed-bed reactor with a catalyst was used, with a pretreatment pressure of 5 MPa and a liquid hourly space velocity (LHSV) of 5.0 h⁻¹ for the crude ester. -1 The molar ratio of hydrogen to crude ester is 10:1.

[0047] After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 240℃, the pressure is 5MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 19. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0048] The total conversion rate of methyl acetate and the impurities in crude ethanol after 300 h are shown in Table 1.

[0049] Example 6 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (methyl acetate content 99.6%, acetic acid content 0.15%, acetaldehyde content 0.018%, methyl propionate content 0.03%, methyl butyrate content 0.025%, butyraldehyde content 0.012%) are preheated to 100°C and mixed, then fed into a fixed-bed reactor packed with 0.1% Pt / Al₂O₃ catalyst. The pretreatment pressure is 6 MPa, and the liquid hourly space velocity (LHSV) of the crude ester is 2.0 h⁻¹. -1 The molar ratio of hydrogen to crude ester is 0.5:1. After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 230℃, the pressure is 5MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 25. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0050] The total conversion rate of methyl acetate was measured to be 98.6% after 300 h. The crude ethanol contained 56.45% ethanol, 39.12% methanol, 0.014% isopropanol, and 0.038% n-propanol. The results indicate that even under extremely low hydrogen-to-ester ratio conditions, the pretreatment step can still effectively convert the toxin and significantly inhibit the formation of byproducts.

[0051] Example 7 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 99.3% methyl acetate, 0.35% acetic acid, 0.025% acetaldehyde, 0.028% methyl acrylate, 0.018% methyl butyrate, and 0.016% butyraldehyde) are preheated to 110°C and mixed, then fed into a fixed-bed reactor packed with a 0.05% Ru / C catalyst. The pretreatment pressure is 5 MPa, and the liquid hourly space velocity (LHSV) of the crude ester is 4.0 h⁻¹. -1 The molar ratio of hydrogen to crude ester is 40:1.

[0052] After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 235℃, the pressure is 4MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 45. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0053] The total conversion rate of methyl acetate was measured to be 99.3% after 300 h. The crude ethanol contained 56.92% ethanol, 39.85% methanol, 0.009% isopropanol, and 0.031% n-propanol. The results indicate that the conversion of the poison was more complete under the higher hydrogen ester ratio, the content of by-products was further reduced, and the product purity was higher.

[0054] Example 8 This embodiment provides a method for hydrogenating crude methyl acetate, focusing on verifying its applicability over a wide pressure range. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 98.8% methyl acetate, 0.65% acetic acid, 0.18% acetaldehyde, 0.032% methyl propionate, 0.022% methyl butyrate, and 0.028% butyraldehyde) are preheated to 90°C and mixed before being introduced into a CuZnAlO4 filling chamber. x A fixed-bed reactor with a catalyst was used, with a pretreatment pressure of 1.5 MPa and a liquid hourly space velocity (LHSV) of 3.0 h⁻¹ for the crude ester. -1 The molar ratio of hydrogen to crude ester is 5:1.

[0055] After pretreatment, the mixture is mixed with circulating hydrogen and superheated before entering the hydrogenation reactor. The hydrogenation temperature is 240℃, the pressure is 2.0 MPa, and the molar ratio of hydrogen to crude ester at the reactor inlet is 20. After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude ethanol is separated by distillation to obtain the product ethanol.

[0056] The total conversion rate of methyl acetate was 98.9% after 300 h. The crude ethanol contained 56.15% ethanol, 39.25% methanol, 0.016% isopropanol, and 0.041% n-propanol.

[0057] Comparative Example 1 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 98.0% methyl acetate, 1.83% acetic acid, 0.06% acetaldehyde, 0.04% methyl propionate, 0.036% methyl butyrate, and 0.035% butyraldehyde) are preheated and heated to 230°C respectively, then mixed and fed into a superheated hydrogenation reactor. The hydrogenation temperature is 230°C, the pressure is 5 MPa, and the molar ratio of hydrogen gas to crude methyl acetate at the reactor inlet is 25. After hydrogenation, the mixture undergoes condensation and gas-liquid separation, followed by gas recycling. The liquid phase crude ethanol is then separated by distillation to obtain the product ethanol.

[0058] The total conversion rate of methyl acetate and the impurities in crude ethanol after 300 h are shown in Table 1.

[0059] Comparative Example 2 This embodiment provides a method for hydrogenating crude methyl acetate. In this embodiment, fresh hydrogen gas and crude methyl acetate (containing 97.0% methyl acetate, 2.62% acetic acid, 0.26% acetaldehyde, 0.041% methyl propionate, 0.039% methyl butyrate, and 0.034% butyraldehyde) are preheated and heated to 230°C respectively, then mixed and fed into a superheated hydrogenation reactor. The hydrogenation catalyst is prepared according to the catalyst described in Example 1 of patent CN202111641495.2. The hydrogenation temperature is 230°C, the pressure is 5 MPa, and the molar ratio of hydrogen gas to crude ester at the reactor inlet is 25. After hydrogenation, the mixture is condensed, separated into gas and liquid phases, and the gas is recycled. The liquid phase crude ethanol is then separated by distillation to obtain the product ethanol.

[0060] The total conversion rate of methyl acetate and the impurities in crude ethanol after 300 h are shown in Table 1.

[0061] Comparative Example 3 This comparative example provides a method for hydrogenating crude methyl acetate. In this comparative example, fresh hydrogen gas and crude methyl acetate (methyl acetate content 99.6%, acetic acid content 0.15%, acetaldehyde content 0.018%, methyl propionate content 0.03%, methyl butyrate content 0.025%, butyraldehyde content 0.012%) are preheated and heated to 230°C respectively, mixed, and then directly introduced into the hydrogenation reactor. The hydrogenation temperature is 230°C, the pressure is 5 MPa, and the molar ratio of hydrogen gas to crude ester at the reactor inlet is 0.5:1.

[0062] After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude liquid ethanol is separated by distillation to obtain the product ethanol.

[0063] The total conversion rate of methyl acetate after 300 h was measured to be 71.3% (far lower than 98.6% in Example 6). The crude ethanol contained 41.25% ethanol, 28.16% methanol, 0.089% isopropanol, and 0.156% n-propanol.

[0064] Comparative Example 4 This comparative example provides a method for hydrogenating crude methyl acetate. In this comparative example, fresh hydrogen gas and crude methyl acetate (methyl acetate content 99.3%, acetic acid content 0.35%, acetaldehyde content 0.025%, methyl acrylate content 0.028%, methyl butyrate content 0.018%, butyraldehyde content 0.016%) are preheated and heated to 235°C respectively, and then mixed before being directly introduced into the hydrogenation reactor. The hydrogenation temperature is 235°C, the pressure is 4 MPa, and the molar ratio of hydrogen gas to crude ester at the reactor inlet is 40:1.

[0065] After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude liquid ethanol is separated by distillation to obtain the product ethanol.

[0066] The total conversion rate of methyl acetate was measured to be 96.8% after 300 h. The crude ethanol contained 54.12% ethanol, 37.85% methanol, 0.042% isopropanol, and 0.078% n-propanol.

[0067] Comparative Example 5 This comparative example provides a method for hydrogenating crude methyl acetate. In this comparative example, fresh hydrogen gas and crude methyl acetate (methyl acetate content 98.8%, acetic acid content 0.65%, acetaldehyde content 0.18%, methyl propionate content 0.032%, methyl butyrate content 0.022%, butyraldehyde content 0.028%) are preheated and heated to 240°C respectively, and then mixed before being directly introduced into the hydrogenation reactor. The hydrogenation temperature is 240°C, the pressure is 2.0 MPa, and the molar ratio of hydrogen gas to crude ester at the reactor inlet is 20.

[0068] After hydrogenation, the mixture is condensed and separated into gas and liquid phases. The gas is then recycled, and the crude liquid ethanol is separated by distillation to obtain the product ethanol.

[0069] The total conversion rate of methyl acetate was measured to be 68.5% after 300 h. The crude ethanol contained 39.82% ethanol, 26.45% methanol, 0.112% isopropanol, and 0.185% n-propanol.

[0070] Comparative Example 6 This comparative example provides a method for hydrogenating crude methyl acetate. In this comparative example, fresh hydrogen gas and crude methyl acetate (methyl acetate content 99.5%, acetic acid content 0.30%, acetaldehyde content 0.04%, methyl acrylate content 0.025%, methyl butyrate content 0.020%, butyraldehyde content 0.018%) were preheated to 220°C and mixed before entering a fixed-bed reactor packed with 0.1% Pt / Al₂O₃ catalyst. The pretreatment pressure was 5 MPa, and the liquid hourly space velocity (LHSV) of the crude ester was 3.0 h⁻¹. -1 The molar ratio of hydrogen to crude ester is 5:1.

[0071] After pretreatment, the material is cooled to 200°C and enters the hydrogenation reactor at a pressure of 4 MPa. The molar ratio of hydrogen to crude ester at the reactor inlet is 18.

[0072] The total conversion rate of methyl acetate was measured to be 82.4% after 300 h. The crude ethanol contained 47.35% ethanol, 32.18% methanol, 0.065% isopropanol, and 0.098% n-propanol.

[0073] The results showed that when the S1 pretreatment temperature was higher than the S2 main hydrogenation temperature, although the poison was partially converted during the pretreatment stage, the low main hydrogenation reaction temperature hindered the kinetics of the methyl acetate hydrogenation reaction, resulting in a significant decrease in the conversion rate. At the same time, the material after high-temperature pretreatment was cooled before entering the main reactor, causing energy waste and increased process complexity.

[0074] Table 1 Comparison of Ethanol and Impurity Content in Crude Alcohol

[0075] It should be noted that the specific embodiments described above are exemplary, and those skilled in the art can devise various solutions inspired by the disclosure of this invention. These solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents.

Claims

1. A method for hydrogenating crude methyl acetate, characterized in that, Includes the following steps: S1 Pretreatment step: The crude methyl acetate liquid phase containing methyl acetate and at least one hydrogenation catalyst poison is mixed with the first part of hydrogen and preheated, and then contacted with the pretreatment catalyst in the pretreatment reactor to cause the hydrogenation catalyst poison to undergo hydrogenation conversion. S2 Hydrogenation step: The pretreated material obtained from S1 is mixed with the second part of hydrogen and heated to the reaction temperature. Then, it is contacted with the hydrogenation catalyst in the hydrogenation reactor to obtain crude alcohol. S3 Separation step: Distill the crude alcohol to obtain the ethanol product.

2. The method according to claim 1, characterized in that, In S1, the molar ratio of crude methyl acetate liquid to hydrogen is 1:0.01-50.

3. The method according to claim 1, characterized in that, In S1, the hydrogenation temperature is 50-180℃, and the pretreatment pressure is 1-10 MPa.

4. The method according to claim 1, characterized in that, In S1, the pretreatment reactor is either an adiabatic bed reactor or a fixed bed reactor.

5. The method according to claim 1, characterized in that, In S1, the liquid hourly space velocity (LHSV) of crude methyl acetate is 0.2–10.0 h⁻¹. -1 .

6. The method according to claim 1, characterized in that, In S2, the molar ratio of the pretreated material to hydrogen before entering the hydrogenation reactor is 1:10-50.

7. The method according to claim 1, characterized in that, In S2, the hydrogenation catalyst is an oxide catalyst composed of one or more of the following components: CuO, ZnO, Cr2O3, NiO, and Al2O3.

8. The method according to claim 1, characterized in that, The hydrogenation temperature in S2 is higher than that in S1.

9. Use of the method for hydrogenating crude methyl acetate according to any one of claims 1-8 in the preparation of ethanol.

10. Use of the method for hydrogenating crude methyl acetate according to any one of claims 1-8 in the preparation of products containing ethanol.

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