A copper-zinc-iron ternary catalyst for low-temperature hydrogenation and a preparation method and use method thereof

Abstract

The application discloses a copper-zinc-iron ternary catalyst for low-temperature hydrogenation, and the main chemical components of the catalyst are copper oxide, zinc oxide and iron oxide, wherein the copper oxide accounts for 5-15 wt.% of the weight of the catalyst, the zinc oxide accounts for 40-55 wt.% of the weight of the catalyst, and the iron oxide accounts for 30-50 wt.% of the weight of the catalyst. By changing the chemical composition of the catalyst, the catalytic performance of the oxalate hydrogenation reaction can be changed. The catalyst still exhibits excellent oxalate hydrogenation activity and ethanol selectivity under the conditions of a H2 / DMO feed molar ratio (100) and a reaction temperature (210 DEG C), the oxalate conversion is as high as 99%, and the ethanol selectivity is as high as 95%. The catalyst exhibits excellent thermal stability, and no obvious deactivation phenomenon is found within 350 h. The catalyst has the characteristics of easy availability of raw materials, low cost, simple synthesis process, stable structure, strong operability, good industrial application prospect and the like.

Description

Technical Field

[0001] This invention relates to the field of hydrogenation catalyst technology, and to a copper-zinc-iron ternary catalyst, particularly a copper-zinc-iron ternary catalyst for low-temperature hydrogenation, and its preparation and application methods. Background Technology

[0002] The process of producing dimethyl oxalate via carbon monoxide coupling from syngas, followed by hydrogenation of dimethyl oxalate to ethanol, is characterized by high atom economy and environmental friendliness, making it an important non-petroleum route for ethanol synthesis. The hydrogenation of dimethyl oxalate to ethanol is the core step in this process. Copper-based catalysts have achieved good activity and selectivity in this reaction system, but the required hydrogen-to-ester ratio (H2 / DMO) is high (greater than 200), and the reaction temperature is also high (280℃). An excessively high H2-to-ester ratio leads to a larger hydrogen circulation volume, increasing the requirements for compressor parameters and significantly raising the equipment and power costs of the process. The excessively high reaction temperature causes catalyst particles to sinter and grow, leading to deactivation and poor stability. Furthermore, the high temperature also results in the formation of large amounts of byproducts containing three or four carbon atoms, such as 1,2-butanediol and 1,2-propanediol, which further increases subsequent separation costs and energy consumption. Therefore, designing novel, highly active copper-based catalysts to achieve high conversion rates of oxalate esters and high selectivity for ethanol in the hydrogenation reaction of dimethyl oxalate under conditions of low hydrogen-to-ester ratio and low temperature is key to optimizing the syngas-to-ethanol process technology.

[0003] The hydrogenation of oxalate esters is a cascade reaction, where they are sequentially hydrogenated to methyl glycolate, ethylene glycol, and ethanol over a conventional copper-based catalyst. The hydrogenolysis of ethylene glycol to ethanol, in particular, requires a relatively high reaction temperature (path A, see...). Figure 1 Recent reports indicate that by changing the catalyst system to metal carbides (molybdenum carbide and iron carbide), the reaction pathway of oxalate hydrogenation can be altered. Specifically, the initial hydrogenation product, methyl glycolate, is hydrogenated to methyl acetate, which is then hydrogenated to ethanol (pathway B, see...). Figure 1 However, due to the weak hydrogenation ability of metal carbides, the hydrogenation of methyl acetate to ethanol still requires a relatively high reaction temperature (260℃) and a hydrogen-to-ester ratio (greater than 180). Considering that copper-based catalysts can activate and hydrogenate carbonyl groups at low temperatures, promoting the activation of hydroxyl groups on the reaction intermediate is key to achieving the low-temperature production of ethanol from oxalate. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and to propose a solution to the problems of poor catalyst stability and low product selectivity caused by the high hydrogen-ester ratio and high reaction temperature in the hydrogenation of oxalate to ethanol. The solution proposed in this invention is a simple and efficient method for preparing a copper-zinc-iron ternary catalyst, utilizing FeO... x The copper-zinc catalyst, due to its oxalate affinity, converts the initial hydrogenation product of oxalate, methyl glycolate, into methyl acetate. Since the copper-zinc catalyst is a highly efficient catalyst for the hydrogenation of methyl acetate to ethanol, the copper-zinc-iron catalyst obtained by this method has very high activity and stability for the hydrogenation of oxalate to ethanol at low temperature and low hydrogen-to-ester ratio.

[0005] This invention is achieved through the following technical solution:

[0006] The copper-zinc-iron catalyst for oxalate hydrogenation in this invention has the following main chemical components: copper oxide, zinc oxide, and iron oxide, wherein copper oxide accounts for 2-20 wt.% of the catalyst weight, zinc oxide accounts for 20-80 wt.% of the catalyst weight, and iron oxide accounts for 5-80 wt.% of the catalyst weight. A preferred embodiment is: copper oxide accounts for 5-15 wt.% of the catalyst weight, zinc oxide accounts for 40-55 wt.% of the catalyst weight, and iron oxide accounts for 30-50 wt.% of the catalyst weight. The catalyst has a specific surface area of ​​10-80 m². 2 / g, with an average pore volume of 0.04-0.5cm³. 3 / g, with an average pore size of 10-40nm; the preferred option is a catalyst with a specific surface area of ​​30-55m². 2 / g, with an average pore volume of 0.25-0.35cm³. 3 / g, with an average pore size of 15-25nm.

[0007] Another object of the present invention is to provide a method for preparing a copper-zinc-iron catalyst for oxalate hydrogenation, comprising the following steps:

[0008] (1) Add the precursor salts of copper, zinc and iron to deionized water, heat and maintain the temperature at 50-100℃, and stir for 0.5-2 hours to obtain a clear mixed solution. The preferred method is to heat to 70℃.

[0009] The precursor salts of copper, zinc, and iron are any one of the corresponding acetate, nitrate, chloride, or sulfate. Preferably, the precursor salts are copper nitrate, zinc nitrate, and iron nitrate.

[0010] (2) Add the alkaline agent dropwise to step (1) and stir at 50-100℃ for 15-40 hours.

[0011] The alkaline agent is a mixed solution composed of any two, any three, or all of ammonia, ammonium chloride, sodium carbonate, or sodium hydroxide.

[0012] A preferred embodiment is that the alkaline agent is a mixed solution of sodium carbonate and sodium hydroxide. The molar ratio of sodium carbonate to the iron precursor salt is 1-3. The ratio of the molar number of sodium hydroxide to the total molar number of all precursor salts of copper, zinc, and iron is 1-3.

[0013] Maintain the molar ratio of alkaline agent and metal ions (copper, zinc and iron) between 0.5 and 5.

[0014] (3) Wash the product from step (2) with deionized water, dry the washed product at 40-100℃ for 8-20h, and then calcine at 400-700℃ for 2-10h.

[0015] The washing method is either filtration washing or centrifugal washing, and the drying method is either conventional drying or vacuum drying. The preferred method is centrifugal washing and conventional drying.

[0016] The catalyst needs to be reduced online before use. Specifically, the reduction temperature is 150-400℃, the reduction atmosphere is hydrogen, and the hydrogen flow rate required for the reduction of each gram of catalyst is 40-200 mL / min.

[0017] The catalyst is used in the following manner: in the hydrogenation reaction of oxalate ester, the reaction pressure is 0.5-3.5 MPa, the reaction temperature is 160-250℃, the hydrogen-to-ester ratio is 20-140, and the liquid hourly space velocity is 0.05-0.5 h⁻¹. -1 The liquid hourly space velocity (LISH) refers to the LISH of oxalate ester.

[0018] The advantages and positive effects of this invention are:

[0019] 1. The catalyst developed in this invention exhibits excellent catalytic activity (up to 99% oxalate conversion and 95% ethanol selectivity) in the hydrogenation of oxalate to ethanol at a relatively low temperature (210°C) and a low hydrogen-to-ester ratio (H₂ / DMO = 100). This is the lowest reported reaction temperature for the hydrogenation of oxalate to ethanol. Furthermore, the lower hydrogen-to-ester ratio significantly reduces the amount of hydrogen recycled in industrial applications, saving power consumption of the gas compressor and increasing the processing capacity per unit volume of reactor. Simultaneously, the high ethanol selectivity greatly reduces the energy consumption and cost of subsequent product separation.

[0020] 2. The catalyst developed in this invention exhibits excellent stability at low temperature (210°C) in the hydrogenation of oxalate to ethanol reaction, and no obvious catalyst deactivation was observed within 350 h.

[0021] 3. This invention proposes a synergistic effect of copper and iron species in a series hydrogenation reaction. By changing the relative content of copper and iron, the relative rates of different reaction pathways can be flexibly controlled, thereby modulating the selectivity of the products.

[0022] 4. The catalyst developed in this invention has the advantages of readily available raw materials, low cost, simple and controllable synthesis process, stable structure, strong operability, and good industrial application prospects. Attached Figure Description

[0023] Figure 1 This is a diagram showing the different hydrogenation reaction pathways for oxalate esters.

[0024] Figure 2 This is the X-ray diffraction (XRD) pattern of the catalyst after reduction according to the present invention.

[0025] Figure 3 The attached diagram shows the N2 isothermal adsorption-desorption of the synthesized catalyst in this invention.

[0026] Figure 4 Catalyst lifetime observation diagram for the hydrogenation of dimethyl oxalate to ethanol.

[0027] Figure 5 X-ray diffraction (XRD) patterns of different catalysts: (a) samples after reduction and carbonization prepared according to reference 1, and (b) samples after stability evaluation of the catalyst of the present invention. Detailed Implementation

[0028] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in the manual, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified.

[0029] Example 1

[0030] Catalyst preparation

[0031] 0.96 g of copper nitrate trihydrate, 14 g of zinc nitrate hexahydrate, and 14 g of ferric nitrate nonahydrate were added to 150 ml of deionized water, and the mixture was stirred at 70 °C for 1 h. 8 g of sodium carbonate and 6 g of sodium hydroxide were dissolved in 100 ml of deionized water and added to the homogeneous solution formed above. The mixture was stirred at 70 °C for another 24 h. The resulting product was washed three times by centrifugation with deionized water, dried at 60 °C for 12 h, and calcined at 500 °C for 4 h to obtain the catalyst.

[0032] Catalyst evaluation:

[0033] In this invention, the gas-phase hydrogenation reaction of oxalate is carried out in a fixed-bed reactor. The calcined catalyst is pressed into tablets and sieved to a size of 40-60 mesh. 0.5 g of catalyst is loaded and reduced at 300°C in a 2.5 MPa H₂ atmosphere at a gas flow rate of 100 mL / min. The temperature is increased from room temperature to 300°C at a rate of 2°C / min and maintained for 4 hours. The temperature is then lowered to the reaction temperature of 210°C, and the oxalate is vaporized and mixed with hydrogen before entering the reaction tube. The hydrogen-to-ester ratio is 100, and the oxalate mass hourly space velocity (WHSV) is 0.1 h⁻¹. -1 The reaction was carried out at 2.5 MPa. Gas chromatography was used to analyze the products and obtain the components of dimethyl oxalate (DMO), methyl glycol (MG), ethylene glycol (EG), methyl acetate (MA), and ethanol (EtOH). The catalyst evaluation results are shown in Table 1. The X-ray diffraction (XRD) pattern of the catalyst of this invention is shown below. Figure 2 As shown, copper oxide is reduced to metallic copper, and the peak is weak, indicating that metallic copper is highly dispersed in the catalyst after reduction. Iron oxide is reduced to metallic iron and magnetite (Fe3O4), and a zinc oxide peak is also present, indicating that copper, zinc, and iron are successfully synthesized into the catalyst of this invention. The isothermal nitrogen adsorption-desorption curves and pore size distribution are shown in the figure. Figure 3 As can be seen from the display, the catalyst of the present invention has a distinct mesoporous structure.

[0034] Example 2

[0035] The catalyst preparation method and evaluation conditions were the same as in Example 1, except that the amounts of zinc nitrate hexahydrate and ferric nitrate nonahydrate were set to 22 g and 4 g, respectively, and the amount of sodium carbonate was changed to 2 g. The catalyst results are shown in Table 1.

[0036] Example 3

[0037] The catalyst preparation method and evaluation conditions were the same as in Example 1, except that the amounts of zinc nitrate hexahydrate and ferric nitrate nonahydrate were set to 18.5 g and 9 g, respectively, and the amount of sodium carbonate was changed to 4 g. The catalyst results are shown in Table 1.

[0038] Comparative Example 1

[0039] The catalyst preparation method and evaluation conditions were the same as in Example 1, except that the amount of zinc nitrate hexahydrate was set to 25 g, and ferric nitrate nonahydrate and sodium carbonate were not added. The catalyst results are shown in Table 1.

[0040] Comparative Example 2

[0041] The catalyst preparation method and evaluation conditions were the same as in Example 1, except that the amount of ferric nitrate nonahydrate was set to 35g, zinc nitrate hexahydrate was not added, and the amount of sodium carbonate was changed to 20g. The catalyst results are shown in Table 1.

[0042] Comparative Example 3

[0043] The catalyst preparation method and evaluation conditions were the same as in Example 1, except that the amount of ferric nitrate nonahydrate was set to 35g, copper nitrate trihydrate and zinc nitrate hexahydrate were not added, and the amount of sodium carbonate was changed to 20g. The catalyst results are shown in Table 1.

[0044]

[0045] Table 1: Performance Evaluation of Different Catalysts

[0046] As shown in Table 1, the copper-zinc catalyst (Comparative Example 1) exhibits the worst hydrogenation activity, with the main products being methyl glycolate (MG) and ethylene glycol (EG), and almost no ethanol (EtOH) produced. This indicates that the hydrogenolysis reaction of ethylene glycol is difficult to carry out under these low-temperature conditions (210°C). After the addition of iron (Examples 1-3), the selectivity of ethylene glycol decreased significantly, while the selectivity of methyl acetate (MA) and ethanol increased. Furthermore, the selectivity of ethanol gradually increased with increasing iron content during the preparation process. This suggests that the addition of iron can alter the reaction pathway of oxalate esters, converting the initial hydrogenation product methyl glycolate into methyl acetate instead of ethylene glycol. Methyl acetate can be rapidly hydrogenated to ethanol at low temperatures. Therefore, under low-temperature conditions of 210°C and a low hydrogen-to-ester ratio (H2 / DMO = 100), the catalyst of this invention can achieve a dimethyl oxalate conversion rate of up to 99% and an ethanol selectivity of up to 95% (Example 1). The catalytic activity of the copper-iron catalyst (Comparative Example 2) was better than that of the copper-zinc catalyst (Comparative Example 1), but lower than that of the copper-zinc-iron catalyst (Examples 1-3), indicating that the addition of zinc promotes the activation of reactants and intermediates. On catalysts without added copper and zinc, almost no DMO conversion occurred on the iron-only catalyst (Comparative Example 3). Unlike the product of Comparative Example 1, almost no ethylene glycol was produced; instead, methyl acetate and ethanol were produced. This indicates that the pure iron-based catalyst cannot effectively activate the reactant dimethyl oxalate, but it can effectively promote the hydrogenation of the initial hydrogenation product methyl glycolate to methyl acetate and ethanol.

[0047] The above results demonstrate that by introducing iron oxide into the copper-based catalyst and changing the mass ratio of copper to iron, the relative reaction rates of methyl glycolate to ethylene glycol (path A) on the copper species and methyl glycolate to methyl acetate (path B) on the iron oxide species can be adjusted, thereby reducing the overall reaction temperature and hydrogen-to-ester ratio of oxalate to ethanol. Simultaneously, the introduction of zinc species promotes the dispersion of copper and iron oxide species and modulates the intermetallic interactions, enhancing the activation ability of the reactants. Table 1 also presents the activities reported in two current publications. It can be seen that, under similar catalytic activities, the reaction temperature is much higher than 210℃ and the hydrogen-to-ester ratio is much greater than 100, indicating that the catalyst of this invention has great industrial application potential.

[0048] Furthermore, the stability of the catalyst of the present invention was evaluated, and the results are as follows: Figure 4As shown, no significant deactivation was observed within 350 hours, indicating that the catalyst of this invention possesses excellent stability. To further compare the catalyst of this invention with the iron carbide catalyst, we used the method in Reference 1 to reduce and carbonize the prepared Fe3O2 catalyst, and compared and analyzed the X-ray diffraction (XRD) patterns of the samples after stability evaluation with those of the catalyst of this invention. Figure 5 As can be seen, the sample prepared according to Reference 1 showed obvious Fe5C2 species (a), while the catalyst of the present invention showed almost no Fe5C2 species after 350 hours of evaluation, and mainly existed as metallic Fe and Fe3O4 species (b).

[0049] Document 1: X.Shang, HJHuang, Q.Han, Y.Xu, YJZhao, SPWang and XBMa, Preferential synthesis of ethanol from syngas via dimethyl oxalatehydrogenation over an integrated catalyst, Chemical Communications, 2019, 55, 5555-5558.

[0050] Document 2: Z.Du, Z.Li, S.Wang,

[0051] Examples 4-7

[0052] The catalyst preparation method was the same as in Example 1. The catalyst performance evaluation method was also the same as in Example 1, with the reaction temperatures set to 190, 200, 220, and 230 degrees Celsius, while other parameters remained unchanged. The catalyst performance evaluation results are shown in Table 2.

[0053] Examples 8-12

[0054] The catalyst preparation method was the same as in Example 1. The catalyst performance evaluation method was also the same as in Example 1, with the hydrogen-to-ester ratio set to 140, 80, 60, 40, and 20, while other parameters remained unchanged. The catalyst performance evaluation results are shown in Table 2.

[0055] Reaction temperature (°C) <![CDATA[H2 / DMO]]> DMO conversion rate (%) EtOH selectivity (%) Example 1 210 100 99 95.0 Example 4 190 100 66.8 51.7 Example 5 200 100 90.6 70.4 Example 6 220 100 99.9 97.6 Example 7 230 100 99.9 95.2 Example 8 210 140 99.5 97.4 Example 9 210 80 98.2 88.8 Example 10 210 60 97.6 79.2 Example 11 210 40 91.9 67.8 Example 12 210 20 77.8 52.8

[0056] Table 2: Catalyst performance evaluation at different reaction temperatures and hydrogen-to-ester ratios

[0057] As shown in Table 2, the conversion rate of oxalate ester (DMO) and the selectivity of ethanol (EtOH) gradually increase with increasing temperature. The highest conversion rates (99.9%) and selectivity (97.6%) of oxalate ester (EtOH) are achieved at 220℃. Meanwhile, as the hydrogen-to-ester ratio decreases, the conversion rate of oxalate ester decreases slowly, while the selectivity of ethanol decreases rapidly, indicating that the hydrogen-to-ester ratio has a significant impact on the catalytic performance of the oxalate hydrogenation reaction.

[0058] Examples 13-16

[0059] The catalyst preparation method was the same as in Example 1. The catalyst performance evaluation method was also the same as in Example 1, with the reaction pressures set to 1, 1.5, 2, and 3 MPa, while other parameters remained unchanged. The catalyst performance evaluation results are shown in Table 3.

[0060] Examples 17-20

[0061] The catalyst preparation method was the same as in Example 1. The catalyst performance evaluation method was also the same as in Example 1, with the mass hourly space velocity (HHSV) of oxalate set to 0.05, 0.2, 0.3, and 0.4 h⁻¹. -1 Everything else remains unchanged. The performance evaluation results of the catalyst are shown in Table 3.

[0062] Reaction pressure (MPa) <![CDATA[DMO mass hourly space velocity (h -1 )]]> DMO conversion rate (%) EtOH selectivity (%) Example 1 2.5 0.1 99 95.0 Example 13 1 0.1 92.3 82.7 Example 14 1.5 0.1 96.5 89.3 Example 15 2 0.1 98.5 92.5 Example 16 3 0.1 99.9 96.2 Example 17 2.5 0.05 99.5 97.4 Example 18 2.5 0.2 95.8 65.1 Example 19 2.5 0.3 91 40.3 Example 20 2.5 0.4 81.9 29.8

[0063] Table 3: Catalyst performance evaluation under different reaction pressures and oxalate mass hourly space velocities

[0064] As shown in Table 3, the conversion of oxalate (DMO) and the selectivity of ethanol (EtOH) gradually decrease with decreasing reaction pressure. The conversion of oxalate and the selectivity of ethanol decrease rapidly with increasing oxalate mass hourly space velocity (MHV), indicating that oxalate MHV has a significant impact on the catalytic performance of the hydrogenation reaction.

Claims

1. A copper-zinc-iron ternary catalyst for low-temperature hydrogenation, characterized in that: The catalyst comprises copper oxide, zinc oxide and iron oxide, the copper oxide accounts for 5-15 wt.% of the catalyst weight, the zinc oxide accounts for 40-55 wt.% of the catalyst weight, and the iron oxide accounts for 30-50 wt.% of the catalyst weight; The specific surface area of the catalyst is 30-55 m 2 / g, the average pore volume is 0.25-0.35 cm 3 / g, and the average pore diameter is 15-25 nm. Copper nitrate trihydrate, zinc nitrate hexahydrate and iron nitrate nonahydrate were added to deionized water, which was kept at 70 o C under stirring; Sodium carbonate and sodium hydroxide were dissolved in deionized water and added to the above formed homogeneous solution under stirring at 70 °C. o C under stirring; The obtained product was washed by centrifugation with deionized water three times, dried at 60 o C for 12 h, and calcined at 500 o C for 4 h to obtain the catalyst product. The use method of the copper-zinc-iron ternary catalyst: in the reaction of hydrogenating oxalate ester to prepare ethanol, the reaction pressure is 2.5 MPa, the reaction temperature is 210 DEG C or 220 DEG C, the hydrogen-ester ratio is 100, the liquid hourly space velocity is 0.05 h -1 or 0.1 h -1 , wherein the liquid hourly space velocity refers to the mass space velocity of oxalate ester.

Images