Preparation method and application of Cu-based catalyst for preparing 1, 2-propylene glycol through selective hydrogenation of glycerol

Abstract

The invention discloses a Cu-based catalyst for preparing 1, 2-propylene glycol through selective hydrogenation of glycerol, and belongs to the technical field of biomass energy and chemical industry. The catalyst comprises the following components in percentage by weight: 20 to 40 percent of Cu, 5 to 15 percent of Mg and 40 to 60 percent of AlO. According to the research, firstly, a Cu / Al2O3 precursor is synthesized, then metal Mg is introduced, and the Cu / MgAlO catalyst is prepared. The synthesis method of the catalyst is simple, the production cost is low, the catalyst is suitable for batch production, the catalyst has excellent reaction activity in a reaction for preparing 1, 2-propylene glycol through hydrogenolysis of glycerin, the glycerin conversion rate is 100%, and the selectivity of 1, 2-propylene glycol reaches up to 95%.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass energy and chemical engineering, and particularly relates to a preparation method and application of a Cu-based catalyst for the selective hydrogenation of glycerol to prepare 1,2-propanediol. Background Art

[0002] In the past century, due to the extreme shortage of traditional fossil fuel resources, clean and renewable energy sources such as biodiesel have received extensive attention, which has promoted the rapid development of the biodiesel industry. However, this has also led to a large surplus of by-product glycerol in biodiesel production, and effective measures are urgently needed to add value to the surplus glycerol. In fact, as an important biomass-derived platform molecule, glycerol can be converted into high-value-added C1-C3 molecules, including glyceric acid, glycolic acid, formic acid, etc.

[0003] In recent years, many researchers have been dedicated to finding efficient catalytic pathways for converting glycerol into value-added chemicals. The hydrogenolysis of glycerol is essentially a reduction reaction, and it is generally desired to achieve the controlled cleavage of the C–O bond in the presence of a catalyst to convert it into 1,2-propanediol. The effective hydrogenolysis of the primary hydroxyl C–O bond of glycerol is achieved through a bifunctional catalyst. First, acidic sites on the catalyst are required to dehydrate glycerol to form hydroxyacetone (HA), which is further hydrogenated to 1,2-propanediol. Currently, it can be summarized into two main catalytic systems: (1) noble metal catalyst systems (such as Pt, Ru, Rh, Pd, and Re); (2) transition metal catalyst systems (Cu, Co, Ni). The high cost and scarcity of noble metals, as well as the excessive cleavage of the C–C bond in glycerol, make it difficult to be industrially applied on a large scale. As a cheap and abundant alternative, transition metals not only have a low C–C bond cleavage ability but also show high activity in the selective catalytic hydrogenation of olefins, aldehydes, and ketones. These favorable properties have promoted extensive research on the catalytic conversion of glycerol to 1,2-propanediol. It was found in the published literature (Appl. Catal. B Environ. 2016, 181, 47-57) that the addition of the second metal Ce can significantly inhibit the crystal growth of CuO, increase the specific surface area of the catalyst, and the Cu / Ce / Mg sample exhibits a higher acid site concentration and stronger acidic sites, making this catalyst have excellent performance. Basic sites also play an important role in the glycerol hydrogenolysis reaction. The published literature (ACS Sustain. Chem. Eng. 2021, 9(5), 2246-2259) doped Ca(II) into Co-Al hydrotalcite to obtain the CoCa-Al catalyst. The generated CaO-CoAl2O4 mixed metal oxide serves as basic sites and can selectively promote the dehydrogenation of glycerol to 1,2-propanediol. However, the above catalysts are usually limited to the regulation of a single variable of acidic or basic sites and do not involve the study of factors such as the influence on the valence state of the active metal. At the same time, they have the disadvantages of complex preparation processes and high synthesis costs. Summary of the Invention

[0004] To solve the problems of complex synthesis, high synthesis cost, low glycerol conversion rate, and poor selectivity of 1,2-propanediol in the glycerol hydrogenolysis reaction of existing catalysts, the present invention utilizes the high activity and stability of Cu / MgAlO. With copper as the active site, a promoter metal magnesium is innovatively introduced to regulate the electron distribution of Cu and the number of acidic and basic sites of the catalyst, thereby providing a new efficient and green pathway for the high-quality conversion of glycerol and achieving high conversion of glycerol hydrogenolysis and high selectivity of 1,2-propanediol. The copper-based catalyst obtained in the present invention has the advantages of low cost, rich reserves, simple synthesis, and environmental friendliness, and at the same time has a high glycerol conversion rate and high selectivity of 1,2-propanediol.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a Cu-based catalyst for the selective hydrogenation of glycerol to prepare 1,2-propanediol, comprising the following steps: (1) Preparation of Cu / Al2O3 precursor Step 1: Add 1.0 - 3.5 parts of copper source and 1.0 - 5.0 parts of aluminum source into 150 - 200 parts of deionized water, stir for 10 - 30 min until completely dissolved to obtain solution A, and the stirring speed is 200 - 600 rad / min.

[0006] Step 2: Dropwise add 3 - 8 parts of alkaline salt solution into solution A, adjust the pH value to 8 - 12, age at 60 - 100 °C for 6 - 24 h, and then stand for 3 - 8 h to obtain material X. Preferably, the pH value is 10 - 12 and the aging temperature is 80 - 90 °C.

[0007] Step 3: Wash material X with deionized water, remove soluble salts in the solvent, replace with absolute ethanol, filter, and obtain filter cake Y.

[0008] Step 4: Place filter cake Y in a vacuum oven at 60 - 100 °C and dry for 4 - 12 h, grind to obtain the Cu / Al2O3 precursor.

[0009] (1) Preparation of Cu / MgAlO catalyst Step 5: Add 1 - 2 parts of Cu / Al2O3 precursor and 40 - 90 parts of deionized water into a beaker, transfer to a constant temperature water bath, heat to 40 - 80 °C, and activate for 5 - 30 min to obtain a suspension.

[0010] Step 6: Subsequently, fully dissolve 1.0 - 3.5 parts of magnesium source in 10 - 30 parts of deionized water to prepare solution B, dropwise add solution B into the suspension, transfer to a hydrothermal autoclave, rotate and age at 80 - 150 °C for 18 - 30 h, take out and stand to obtain material Z. Preferably, the temperature is 100 - 120 °C and the time is 20 - 24 h.

[0011] Step 7: Wash, filter, and dry material Z with deionized water, fully grind and mix evenly, then place in a muffle furnace and calcine at 400 - 700 °C for 3 - 8 h, with a heating rate of 1 - 10 °C / min, to obtain the catalyst precursor. Preferably, the calcination temperature is 500 - 600 °C, the time is 5 - 6 h, and the heating rate is 2 - 4 °C / min.

[0012] Step 8: Place the catalyst precursor in a tubular furnace and calcine it under a H2 / Ar mixed gas. Before heating up, first introduce nitrogen into the tubular furnace at a flow rate of 20 - 40 mL / min to expel the air inside. After 10 - 30 min of passing, switch the gas to the H2 / Ar mixed gas and adjust the flow rate to 40 - 80 mL / min. Heat it up to the range of 300 - 600 °C at a heating rate of 1 - 4 °C / min and hold for 2 - 6 h; during this process, the H2 / Ar mixed gas is continuously introduced until the temperature of the tubular furnace naturally drops to room temperature. Then open the tubular furnace to take out the sample to obtain the Cu / MgAlO catalyst. Preferably, the hydrogen reduction temperature is 400 - 500 °C and the time is 3 - 4 h.

[0013] Further, the copper source in Step 1 is at least one of copper nitrate, copper chloride, and copper sulfate; the aluminum source is any one of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum silicate. Further, the alkaline salt solution in Step 2 is any one of sodium carbonate, sodium bicarbonate, ammonium chloride, sodium chloride, sodium hydroxide, potassium carbonate, potassium bicarbonate, etc. Further, the magnesium source in Step 6 is any one of magnesium chloride, magnesium nitrate, and magnesium sulfate.

[0014] For the above Cu / MgAlO catalyst, based on the total mass of the catalyst, the Cu element content is 10 - 50 wt%, the Mg element content is 5 - 20 wt.%, and the AlO content is 20 - 80 wt.%.

[0015] Further, the Cu element content is 20 - 40 wt%, the Mg element content is 5 - 15 wt.%, and the AlO content is 40 - 60 wt.%.

[0016] The copper-based catalyst prepared by the above method can be used for the catalytic hydrogenolysis of glycerol to prepare 1,2-propanediol. The specific application method is as follows: Dissolve glycerol in a solvent, add the copper-based catalyst, and carry out a hydrogenation reaction for 0.5 - 6 h under the conditions of 190 - 300 °C, a hydrogen pressure of 1.5 - 6.5 MPa, and a stirring rate of 600 - 800 rpm. Then cool it to room temperature and centrifuge. Cool the reaction solution obtained to room temperature and centrifuge.

[0017] The mass ratio of the catalyst used to glycerol is 0.1 - 1:1, and the solvent is one or several of water, methanol, ethanol, and formic acid.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The synthesis method is simple and suitable for batch production. It has strong reaction activity and 1,2-propanediol selectivity, can catalyze the cleavage of the C–O bond in the hydrogenation process of small molecule structures such as glycerol under suitable conditions, and at the same time, the active components are not easily lost.

[0019] (2) The introduction of metal in the present invention endows the catalyst with three synergistic regulation methods, which can simultaneously adjust the acid-base sites of the catalyst and optimize the electronic structure of the active metal site copper, thereby regulating the selectivity of the hydrogenation products of the catalyst.

[0020] (3) The conditions for preparing the catalyst in the present invention are mild, and the cost of the catalyst is relatively low. When it is applied to the glycerol hydrogenolysis reaction, it has excellent performance and can achieve complete conversion of glycerol and high selectivity of 1,2-propanediol. Description of the Drawings

[0021] Figure 1 It is the X-ray powder diffraction (XRD) pattern of the catalysts prepared in Examples 1-2 and Comparative Example 1.

[0022] Figure 2 It is the X-ray photoelectron spectroscopy (XPS) pattern of the catalysts prepared in Examples 1-2 and Comparative Example 1; among them, (a) is the XPS pattern of the Al 2p orbital; (b) is the XPS pattern of the Mg 2p orbital.

[0023] Figure 3 It is the XPS pattern of the Cu LMM orbital.

[0024] Figure 4 It is the ammonia adsorption-desorption (NH3-TPD) pattern of the catalysts prepared in Examples 1-2 and Comparative Example 1.

[0025] Figure 5 It is the carbon dioxide adsorption-desorption (CO2-TPD) pattern of the catalysts prepared in Examples 1-2 and Comparative Example 1. Detailed Embodiments

[0026] To make the above features and advantages of the present invention more obvious and understandable, the following examples are specifically given for detailed description. Unless otherwise specified, the methods of the present invention are all conventional methods in the art.

[0027] The parts in the following examples refer to parts by weight.

[0028] Example 1 (1) Preparation of Cu 0.3 / Al2O3 Precursor Step 1: Add 1.9 parts of Cu(NO3)2·3H2O and 1.5 parts of Al(NO3)3·9H2O to 150 parts of deionized water, and stir vigorously until completely dissolved to obtain solution A, and the stirring speed is 450 rad / min.

[0029] Step 2: Gradually add 3 portions of NaOH solution (1.0 mol / L) dropwise into solution A, adjust the pH value to about 10, age at 90 °C for 18 h, and then let it stand for 6 h to obtain material X.

[0030] Step 3: Wash material X with deionized water to remove soluble salts in the solvent until the conductivity of the filtrate is lower than 0.1 S / m. Then displace it with absolute ethanol and filter to obtain filter cake Y.

[0031] Step 4: Place filter cake Y in a vacuum oven at 60 °C and dry for 12 h, and then grind to obtain the Cu 0.3 / Al2O3 precursor.

[0032] (2) Preparation of Cu 0.3 / Mg 0.1 AlO-500 catalyst Step 5: Add 1.5 portions of the Cu 0.3 / Al2O3 precursor prepared in step (1) and 80 portions of deionized water into a beaker, transfer it to a constant temperature water bath and heat to 60 °C for 20 min of activation to obtain a suspension.

[0033] Step 6: Subsequently, fully dissolve 1.8 portions of Mg(NO3)2·6H2O (Mg 10 wt.%) in 10 portions of deionized water to prepare solution B. Dropwise add solution B into the suspension, transfer it to a hydrothermal autoclave, rotate and age at 120 °C for 24 h, take it out and let it stand to obtain material Z.

[0034] Step 7: Wash, filter and dry material Z with deionized water, fully grind it evenly, and then place it in a muffle furnace and calcine at 500 °C for 4 h to obtain the catalyst precursor.

[0035] Step 8: Place the catalyst precursor in a tubular furnace and calcine it under a 10% H2 / Ar mixed gas. Before heating up, first pass nitrogen into the tubular furnace at a flow rate of 30 mL / min to exhaust the air in the furnace. After 20 min, switch the gas to a 10% H2 / Ar mixed gas and adjust the flow rate to 60 mL / min. Heat it at a heating rate of 2 °C / min to the range of 450 °C and hold for 4 h; during this process, the 10% H2 / Ar mixed gas is continuously passed until the temperature of the tubular furnace naturally drops to room temperature, open the tubular furnace and take out the sample. The obtained catalyst is denoted as catalyst 1, and the content of Cu:Mg:AlO in the catalyst is 30:10:60 wt.%.

[0036] Example 2 Except for changing the addition amounts of Cu(NO3)2·3H2O (1.09 parts, 3.04 parts, 2.77 parts, 3.38 parts) and Mg(NO3)2·6H2O (1.51 parts, 2.01 parts, 0.96 parts, 3.52 parts), other operation steps are the same as those in Example 1. Catalysts with Cu:Mg:AlO contents of 20:10:70 wt.%, 40:10:50 wt.%, 40:5:55 wt.%, and 40:15:45 wt.% are respectively prepared and denoted as Catalyst 2, Catalyst 3, Catalyst 4, and Catalyst 5.

[0037] Example 3 Except that the calcination temperatures in Step 7 are respectively set to 400 °C, 600 °C, and 700 °C, other operation steps are the same as those in Example 1. The obtained catalysts are denoted as Catalyst 6, Catalyst 7, and Catalyst 8, and their component contents are the same as those in Example 1.

[0038] Comparative Example 1 Except for changing the addition amount of Cu(NO3)2·3H2O to 2.52 parts and without the operation of adding Mg(NO3)2·6H2O in Step 6, directly performing high-temperature calcination and hydrogen temperature-raising reduction, other operation steps are the same as those in Example 1. The obtained catalyst is denoted as Catalyst 9, and its Cu:AlO content is 40:60 wt.%.

[0039] Comparative Example 2 In Step 1, Cu(NO3)2·3H2O is not added, and other operation steps are the same as those in Example 1. The obtained catalyst is denoted as Catalyst 10, and its Mg:AlO content is 14:76 wt.%.

[0040] Performance evaluation of glycerol hydrocracking reaction: Weigh 1 part of glycerol, dissolve it in 10 parts of methanol solvent, and then add the obtained solution and 0.2 part of catalyst into a high-pressure reactor. Perform hydrogenation reaction for 4 h under the conditions of 250 °C, hydrogen pressure of 3.5 MPa, and stirring rate of 700 rpm. Cool the reaction solution to room temperature and centrifuge it. Use a gas chromatography-mass spectrometry (GC-MS) to analyze the conversion rate of glycerol and the selectivity of the target product 1,2-propanediol by the catalyst under this condition. The results are shown in Table 1.

[0041] Table 1 Hydrogenation performance results of the catalysts described in the examples and comparative examples It can be seen from the above results that the catalysts in each example of the present invention can completely convert glycerol and have a high selectivity for 1,2-propanediol. In Comparative Example 1, the selectivity significantly decreases when the co-metal Mg is not added. In Comparative Example 2 without the active metal Cu, due to poor reaction activity, both the glycerol conversion rate and the selectivity of 1,2-propanediol are extremely low.

[0042] It can be seen from Figure 1 that a high Cu loading leads to a higher degree of crystallization and is prone to agglomeration during the calcination process. It can be seen from Figure 2 and Figure 3 that different Cu / Mg ratios can cause an electronic interaction between Mg and Cu to varying degrees, stabilizing Cu in the catalyst + , and improving the catalyst activity; at the same time, it shows that Mg in the catalyst exists in three forms: acidic Mg–O–Al, basic Mg–OH, and Mg–O. Figure 4 It shows that the introduction of metallic Mg increases the number of acidic sites in the catalyst and can provide active sites for the dehydration step in the reaction path of glycerol dehydration followed by hydrogenation. Figure 5 It shows that the introduction of metallic Mg increases the number of basic sites in the catalyst and can provide active sites for the dehydration step in the reaction path of glycerol hydrogenation followed by dehydration and then hydrogenation.

[0043] The specific embodiments described above can further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. However, it should be understood that the above description is only for the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a Cu-based catalyst for selective hydrogenation of glycerol to produce 1,2-propylene glycol, characterized in that: The following steps are involved: Preparation of Cu / Al2O3 Precursor Step 1: dissolving 1.0-3.5 parts of a copper source and 1.0-5.0 parts of an aluminum source in 150-200 parts of deionized water to obtain a solution A; Step 2: Add 3 to 8 parts of alkaline salt solution dropwise into solution A, adjust the pH value, and let stand after aging to obtain material X; Step 3: Wash material X, remove soluble salts, replace with anhydrous ethanol, and obtain filter cake Y after filtering; Step 4: drying and grinding the filter cake Y to obtain a Cu / Al2O3 precursor; Preparation of Cu / MgAlO catalyst Step 5: Place 1-2 parts of Cu / Al2O3 precursor and 40-90 parts of deionized water in a beaker and heat to activate to obtain a suspension; Step 6: Dissolve 1-3.5 parts of magnesium source in 10-30 parts of deionized water to prepare solution B, add solution B dropwise into the suspension, transfer it to a hydrothermal autoclave for rotational aging, and then stand to obtain material Z; Step 7: Washing, filtering, drying and calcining the material Z to obtain a catalyst precursor; Step 8: placing the catalyst precursor in a tubular furnace and calcining it under a H2 / Ar mixed gas to obtain a Cu / MgAlO catalyst.

2. The preparation method according to claim 1, characterized in that: The copper source is any one of copper nitrate, copper chloride and copper sulfate; the aluminum source is any one of aluminum nitrate, aluminum chloride, aluminum sulfate and aluminum silicate; the magnesium source is any one of magnesium chloride, magnesium nitrate and magnesium sulfate.

3. The preparation method according to claim 1, characterized in that: The alkaline salt solution is any one of an aqueous solution of sodium carbonate, sodium bicarbonate, ammonium chloride, sodium chloride, sodium hydroxide, potassium carbonate, and potassium bicarbonate, and the concentration of the alkaline salt solution is 1.0 mol / L.

4. The preparation method according to claim 1, characterized in that: The pH value in step 2 is 8-12, the aging temperature is 60-100 °C, the aging time is 6-24 h, and the standing time is 3-8 h.

5. The preparation method according to claim 1, characterized in that: The temperature of rotary aging is 80~150 °C, the aging time is 18~30 h, the calcination temperature is 400~700 °C, the calcination time is 3~8 h, and the heating rate is 1~10 °C / min; the temperature of hydrogen reduction is 300~600 °C, and the time is 2~6 h.

6. A Cu / MgAlO catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that: Based on the total mass of the catalyst, the Cu element content is 10~50 wt.%, the Mg element content is 5~20 wt.%, and the AlO content is 20~80wt.%.

7. The Cu / MgAlO catalyst according to claim 6, characterized in that: The Cu element content is 20~40 wt.%, the Mg element content is 5~15 wt.%, and the AlO content is 40~60 wt.%.

8. Use of the Cu / MgAlO catalyst as claimed in any one of claims 6 to 7 in catalyzing the hydrogenolysis of glycerol to produce 1,2-propylene glycol.

9. The use according to claim 8, characterized in that: Glycerol was dissolved in a solvent, a catalyst was added, and hydrogenation reaction was carried out at 190-300 °C, a hydrogen pressure of 1.5-6.5 MPa, and a stirring rate of 600-800 rpm for 0.5-6 h. The mixture was cooled to room temperature and centrifuged to obtain 1,2-propylene glycol.

10. The use according to claim 9, characterized in that: The mass ratio of the catalyst to glycerol is 0.1-1:1; the solvent is one or more of water, methanol, ethanol and formic acid.

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