A halogen-modified nickel-aluminum hydrotalcite, its preparation method and application in the catalytic hydrogenation of lignin

Abstract

The present invention discloses a halogen-modified nickel-aluminum hydrotalcite, a preparation method thereof, and an application thereof in the catalytic hydrogenation of lignin. A water-soluble nickel salt, a water-soluble aluminum salt, an alkali precipitating agent and water are mixed and then subjected to a hydrothermal reaction. The hydrothermal reaction product is first calcined in an air atmosphere and then calcined in a reducing atmosphere to obtain a nickel-aluminum hydrotalcite. The nickel-aluminum hydrotalcite is mixed with a halogenated aromatic hydrocarbon and an organic solvent and then subjected to a solvothermal reaction to obtain the halogen-modified nickel-aluminum hydrotalcite. The halogen-modified nickel-aluminum hydrotalcite is applied to the catalytic hydrodeoxygenation reaction of lignin compounds and / or aryl ether compounds to synthesize phenolic compounds, showing high catalytic selectivity and high yield. Moreover, the halogen-modified nickel-aluminum hydrotalcite can be recovered and separated by magnetic separation and can be reused multiple times, greatly reducing its use cost.

Description

Technical Field

[0001] The present invention relates to a catalytic material, specifically to a halogen-modified nickel-aluminum hydrotalcite, and also relates to a preparation method of the halogen-modified nickel-aluminum hydrotalcite, as well as the application of the halogen-modified nickel-aluminum hydrotalcite as a catalyst in the hydrodeoxygenation reaction of lignin-based compounds and / or aryl ether compounds to synthesize phenol, belonging to the field of catalytic technology. Background Art

[0002] As the only renewable aromatic hydrocarbon resource in nature, efficiently catalytically converting biomass lignin into the bulk chemical phenol to replace the increasingly depleted fossil resources to prepare renewable bio-based phenol has important research significance.

[0003] As is well known, the lignin structure is complex, and there are great challenges in the directional and efficient cleavage of ether bonds in lignin. The bond energy of the 4-O-5 bond in the lignin structure is the highest at 314 KJ / mol, higher than the bond energies of β-O-4 and α-O-4, which are 296 and 245 KJ / mol. Efficiently cleaving the 4-O-5 bond is of great significance for the high-value utilization of biomass lignin. Therefore, 4-O-5 bond-type lignin and its model compounds have been widely studied. For example, Chinese Patent (authorized publication number CN112028728B) discloses a method for catalytic hydrogenation of diphenyl ether to cyclohexanol and cyclohexane, using a nickel-cobalt bimetallic catalyst to obtain the fully hydrogenated products cyclohexane and cyclohexanol in the diphenyl ether system. However, in this system, the aromatic ring is over-hydrogenated, and no more valuable aromatic hydrocarbon products are obtained. This is mainly because the hydrogenation activity of the catalyst active center is relatively high, resulting in over-hydrogenation of the benzene ring. Summary of the Invention

[0004] Aiming at the defects existing in the prior art, the first object of the present invention is to provide a halogen-modified nickel-aluminum hydrotalcite, which has high selectivity and catalytic activity for the hydrogenolysis of aryl ether bonds, is suitable for catalyzing the hydrodeoxygenation reaction of lignin-based compounds and / or aryl ether compounds to synthesize phenol, and at the same time has magnetism and is easy to recover.

[0005] The second object of the present invention is to provide a preparation method of the halogen-modified nickel-aluminum hydrotalcite, which has simple operation, low cost, and is conducive to large-scale production.

[0006] The third object of the present invention is to provide an application of the halogen-modified nickel-aluminum hydrotalcite. When it is applied to catalyze the hydrodeoxygenation reaction of lignin-based compounds and / or aryl ether compounds to synthesize phenolic compounds, it shows high catalytic selectivity and high yield, and the catalyst can be recovered and separated by magnetic separation and can be reused multiple times, greatly reducing the use cost of the catalyst.

[0007] To achieve the above technical objectives, the present invention provides a preparation method of halogen-modified nickel-aluminum hydrotalcite. In this preparation method, a water-soluble nickel salt, a water-soluble aluminum salt, an alkali precipitating agent, and water are mixed and then subjected to a hydrothermal reaction. The obtained hydrothermal reaction product is first calcined in an air atmosphere and then in a reducing atmosphere to obtain nickel-aluminum hydrotalcite. The nickel-aluminum hydrotalcite is mixed with a haloarene and an organic solvent and then subjected to a solvothermal reaction to obtain the halogen-modified nickel-aluminum hydrotalcite.

[0008] In the technical solution of the present invention, nickel-aluminum hydrotalcite is first synthesized. Nickel-aluminum hydrotalcite has relatively high catalytic activity, and the catalytic active centers are relatively concentrated, and it has a relatively strong adsorption capacity for benzene rings, resulting in a relatively low catalytic selectivity for the hydrodeoxygenation of lignin-like compounds and / or aryl ether compounds. The key to the technical solution of the present invention lies in using a haloarene to modify the nickel-aluminum hydrotalcite, using the haloarene to change the charge structure and adsorption configuration of the nickel-aluminum hydrotalcite. The provided halogen element can cause the nickel metal to lose electrons and achieve its electron transfer, so that part of the active centers of the nickel-aluminum hydrotalcite are deactivated, reducing its hydrogenation catalytic activity, and indirectly improving the dispersion degree of the active centers. Moreover, the aromatic ring can modify and fill the spatial structure of the nickel-aluminum hydrotalcite, reducing its adsorption of benzene rings. Therefore, the halogen-modified nickel-aluminum hydrotalcite can highly selectively promote the cleavage of C-O bonds and obtain phenol in high yield.

[0009] As a preferred embodiment, the water-soluble nickel salt and the water-soluble aluminum salt are metered according to a molar ratio of nickel to aluminum of 1:1 to 4:1. As the nickel-aluminum molar ratio increases, the particle size of elemental Ni gradually becomes smaller, and small-size and highly dispersed Ni metal active sites can be obtained. However, when the nickel-aluminum molar ratio further increases, the elemental nickel particles with too small a size are prone to agglomeration. Therefore, the nickel-aluminum molar ratio is preferably controlled within the preferred range.

[0010] As a preferred embodiment, the water-soluble nickel salt can be common organic or inorganic nickel salts. The nickel salt mainly provides nickel ions. In theory, nickel salts with better hydrolysis performance all meet the usage requirements. Specifically, for example, Ni(NO 3 ) 2 ·6H 2 O, NiCl 2 , Ni(OH) 2 etc. or any combination thereof.

[0011] As a preferred embodiment, the water-soluble aluminum salt can be common organic or inorganic aluminum salts. The aluminum salt mainly provides aluminum ions. In theory, aluminum salts with better hydrolysis performance all meet the usage requirements. Specifically, for example, Al(NO 3 ) 3 ·9H 2 O.

[0012] As a preferred solution, the alkaline precipitant includes at least one of urea, sodium carbonate and KOH. The alkaline precipitant is generally in excess relative to the water-soluble nickel salt and the water-soluble aluminum salt, which is 1 to 3 times the theoretical molar amount required to convert nickel and aluminum into precipitates. The preferred alkaline precipitant is urea.

[0013] As a preferred solution, the conditions of the hydrothermal reaction are: temperature of 100-180°C and reaction time of 6-12h. Too low a hydrothermal reaction temperature will affect the dissolution of the reactants and the crystallization of the products, which is not conducive to the growth and formation of the hydrotalcite structure. Too high a hydrothermal reaction temperature will increase the catalyst particle size and affect the catalytic activity.

[0014] As a preferred solution, the calcination temperature in air atmosphere is 400-600°C and the time is 3-7 hours, and the calcination temperature in reducing atmosphere is 500-700°C and the time is 0.5-3 hours. The calcination process in air can form a metal oxide with a stable structure, and further in reducing atmosphere (H 2 ) The purpose of heat treatment is to reduce the metal oxide to a metal element, and the metal element plays an active role in the hydrogenation and deoxidation process.

[0015] As a preferred solution, the halogenated aromatic hydrocarbon includes at least one of bromobenzene, iodobenzene and chlorobenzene. Halogenated aromatic hydrocarbons are preferably used as modifiers, mainly because the halogen elements on the halogenated aromatic hydrocarbons are active and easy to remove from the benzene ring, thereby achieving the modification of nickel-aluminum hydrotalcite, and the benzene ring can be used to modify the structure of nickel-aluminum hydrotalcite, while the structure of halogenated alkanes is stable and the halogen is not easy to remove. The preferred halogenated aromatic hydrocarbon is bromobenzene.

[0016] As a preferred solution, the mass of the halogenated aromatic hydrocarbon is 0.5% to 20% of the mass of the nickel-aluminum hydrotalcite. As the mass ratio of the halogenated aromatic hydrocarbon increases, the total catalytic activity of the halogen-modified nickel-aluminum hydrotalcite will decrease to a certain extent, but the selectivity for converting lignin compounds and aryl ether compounds into phenolic compounds will increase significantly. However, when the mass ratio of the halogenated aromatic hydrocarbon increases to a certain extent, the selectivity for converting lignin compounds and aryl ether compounds into phenolic compounds will no longer increase significantly, so the mass of the halogenated aromatic hydrocarbon is further preferably 7.5% to 20% of the mass of the nickel-aluminum hydrotalcite.

[0017] As a preferred solution, the conditions of the solvent thermal reaction are: temperature of 90-150° C. and time of 2-6 hours. Too high or too low temperature is not conducive to the removal of halogen from the benzene ring, affecting the catalyst modification effect.

[0018] The invention also provides a halogen-modified nickel-aluminum hydrotalcite, which is obtained by the preparation method.

[0019] The mass percentage content of nickel metal in the preferred halogen-modified nickel-aluminum hydrotalcite is 5-20 wt%.

[0020] The present invention also provides an application of the halogen-modified nickel-aluminum hydrotalcite, which is used as a catalyst in the hydrogenation and deoxygenation reaction of lignin compounds and / or aryl ether compounds to synthesize phenolic compounds. The aryl ether compounds include diphenyl ether and diphenyl ether derivatives, benzyl phenyl ether and benzyl phenyl ether derivatives. The lignin compounds include alkali lignin, organic solvent lignin, etc. The diphenyl ether derivatives and benzyl phenyl ether derivatives mainly refer to those with conventional substituents on the benzene ring, such as alkyl groups, hydroxyl groups, etc.

[0021] As a preferred scheme, the conditions for the hydrogenation and deoxygenation reaction are as follows: the mass ratio of the halogen-modified nickel-aluminum hydrotalcite to the lignin compound and / or aryl ether compound is 6:1-1:2, the hydrogen pressure is 0.1-3 MPa, the temperature is 120-180 °C, and the time is 1-6 h.

[0022] As a preferred scheme, the hydrogenation and deoxygenation reaction uses alcohols as solvents, specifically at least one of methanol, ethanol, and isopropanol.

[0023] Compared with the prior art, the technical solution of the present invention brings beneficial technical effects:

[0024] 1) The halogen-modified nickel-aluminum hydrotalcite provided by the present invention has high catalytic activity and selectivity for the cleavage of C-O bonds in the catalytic reaction system of the hydrogenation and deoxygenation of lignin compounds and aryl ether compounds to synthesize phenolic compounds, reduces the adsorption of the benzene ring and the generation of ring hydrogenation products, and increases the yield of phenolic monomers.

[0025] 2) The halogen-modified nickel-aluminum hydrotalcite of the present invention has magnetism, can realize the recycling of the catalyst, does not deactivate after repeated use for many times, reduces its use cost, has a good application prospect, and is suitable for large-scale production.

[0026] 3) The halogen-modified nickel-aluminum hydrotalcite of the present invention uses cheap transition metals as catalyst raw materials, and the preparation method is simple and the cost is low, which is beneficial to large-scale production. Description of the Drawings

[0027] Figure 1 XRD diagrams of catalysts with different amounts of bromobenzene modifiers in Examples 7-10.

[0028] Figure 2 XPS diagrams of the catalyst before and after bromobenzene modification.

[0029] Figure 3 CO-FTIR diagrams of the catalyst before and after bromobenzene modification.

[0030] Figure 4 Effect of catalysts with different dosages of bromobenzene modifiers on the conversion rate of diphenyl ether and the selectivity of phenol.

[0031] Figure 5 For Br in Example 8 10mg Reusability of -NiAl-LDH catalyst in the reaction. Specific embodiments

[0032] The technical solutions of the present invention will be further described below in conjunction with specific embodiments of the present invention. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; these embodiments are only for better understanding of the present invention, rather than limiting the scope protected by the present invention.

[0033] Examples 1-5

[0034] A certain amount of Ni(NO 3 ) 2 ·6H 2 O, 0.01 mol Al(NO 3 ) 3 ·9H 2 O, an excessive amount of alkali precipitant (2 times the theoretical molar amount) and 50 ml of water were mixed and added to a hydrothermal reactor, and hydrothermal reaction was carried out at 140 °C for 9 h. The obtained hydrothermal reaction product was first calcined at 500 °C in an air atmosphere for 6 h, and then treated at 700 °C in an H 2 atmosphere for 2 h to obtain nickel-aluminum hydrotalcite, and its physical property parameters are shown in Table 1.

[0035] Table 1 Nickel-aluminum hydrotalcite synthesized under different reaction conditions

[0036] Example Molar ratio of nickel to aluminum Alkali precipitant Ni particle size (nm) <![CDATA[Specific surface area / m 2 ·g -1 > 1 1:1 Urea 12.01 131.47 2 2:1 Urea 10.85 130.43 3 3:1 Urea 9.07 136.21 4 3:1 KOH 10.34 90.54 5 3:1 <![CDATA[Sodium 2 CO 3 > 9.81 128.08

[0037] The nickel-aluminum hydrotalcite of Example 3 has the smallest nickel particle diameter and the largest specific surface area. Therefore, the nickel-aluminum hydrotalcite prepared in this example is used for subsequent halogen modification.

[0038] Examples 6-12

[0039] 200 mg of nickel-aluminum hydrotalcite, 10 ml of methanol and 1-20 mg of halogen modifier (bromobenzene, iodobenzene or chlorobenzene) were added to a high-pressure reactor, and solvothermal reaction was carried out at 120 °C for 8 h. The obtained product was washed with methanol and dried overnight at 80 °C to obtain halogen-modified nickel-aluminum hydrotalcite.

[0040] Add 10 mg of diphenyl ether, 20 mg of halogen-modified nickel-aluminum hydrotalcite, and 3 ml of methanol into a reaction kettle, heat it under the conditions of 2 MPa of hydrogen and 150 °C for 3 h. After the reaction is completed, use gas chromatography for product analysis, and calculate the phenol yield by the internal standard method of tridecane. The results are shown in Table 2.

[0041] Table 2 Catalytic reaction effects of nickel-aluminum hydrotalcite catalysts modified with different halogen dosages

[0042] Example Dosage of bromobenzene modifier Diphenyl ether conversion rate / % Phenol selectivity / % 6 <![CDATA[Br 1mg -NiAl-LDH]]> 99.00 9.80 7 <![CDATA[Br 5mg -NiAl-LDH]]> 97.18 12.9 8 <![CDATA[Br 10mg -NiAl-LDH]]> 58.59 29.94 9 <![CDATA[Br 15mg -NiAl-LDH]]> 43.59 38.38 10 <![CDATA[Br 20mg -NiAl-LDH]]> 26.74 39.07 11 <![CDATA[I 10mg -NiAl-LDH]]> 2.80 / 12 <![CDATA[Cl 10mg -NiAl-LDH]]> 10.80 /

[0043] Examples 13 - 18

[0044] Add 10 mg of diphenyl ether, 20 mg of Br 10mg -NiAl-LDH catalyst, and 3 ml of methanol into a reaction kettle, heat it under the conditions of 2 MPa of hydrogen and 150 °C for a certain time. After the reaction is completed, use gas chromatography for product analysis, and calculate the phenol yield by the internal standard method of tridecane. The results are shown in Table 3.

[0045] Table 3 Influence of different catalytic reaction conditions on the reaction effect

[0046] Example Reaction time / h Diphenyl ether conversion rate / % Phenol selectivity / % 13 1 7.17 35.99 14 2 18.13 34.50 15 3 58.59 29.94 16 4 79.69 26.19 17 5 90.36 24.39 18 6 92.01 16.62

[0047] Examples 19 - 22

[0048] Add 10 mg of substrate, 20 mg of Br 10mg -NiAl-LDH catalyst, and 3 ml of methanol into a reaction kettle, heat it under the conditions of 2 MPa of hydrogen and 150 °C for 3 h. After the reaction is completed, use gas chromatography for product analysis, and calculate the phenol yield by the internal standard method of tridecane. The results are shown in Table 4.

[0049] Table 4 Hydrodeoxygenation reaction effects of different aryl ether compounds

[0050] Example Substrate type Conversion rate / % Phenolic monomer selectivity / % 19 Diphenyl ether 58.59 29.94 20 Benzyl phenyl ether 99.99 9.08 21 Alkali lignin 23.15 7.69

[0051] Result detection:

[0052] As can be seen from Table 1, as the nickel-aluminum molar ratio increases, the particle size of elemental Ni in nickel-aluminum hydrotalcite becomes smaller. When the nickel-aluminum molar ratio is 3:1, the particle size of elemental Ni is 9.07 nm. Using different precipitants has a greater impact on the structure of nickel-aluminum hydrotalcite. When using urea and Na 2 CO 3 a layered hydrotalcite structure is obtained, which has a relatively large specific surface area. When using KOH as the precipitant, a spherical structure is obtained, and the specific surface area is 90.54 m 2 ·g -1As can be seen from Table 2, with the increase in the amount of bromobenzene, the activity of the halogen-modified nickel-aluminum hydrotalcite decreases. This is because of the poisoning effect of bromobenzene, which causes partial inactivation of the halogen-modified nickel-aluminum hydrotalcite. However, the selectivity for phenol is improved. This is because the presence of Br inactivates some of the Ni active sites and simultaneously changes its adsorption configuration, hindering the adsorption of large phenol molecules and benzene ring hydrogenation, thus improving the selectivity for phenol. When the amount of bromobenzene is 10 mg, the conversion of diphenyl ether is 58.59% and the selectivity for phenol is 29.94%. This shows that the modified nickel-aluminum hydrotalcite has high activity and phenol selectivity for the catalytic hydrogenation of diphenyl ether to prepare phenol. When using iodobenzene and chlorobenzene to modify the NiAl-LDH catalyst, due to the high toxicity of iodobenzene, the catalyst is completely inactivated. As can be seen from Table 3, with the extension of time, the conversion of diphenyl ether continuously increases, while the selectivity for phenol decreases. This is because excessive hydrogenation of the benzene ring occurs due to the extended time. When the reaction time is 3 h, the conversion of DPE is 58.59% and the selectivity for phenol is 29.94%, taking into account both the appropriate conversion of diphenyl ether and the selectivity for phenol. As can be seen from Table 4, the halogen-modified nickel-aluminum hydrotalcite catalyst has high activity and phenol selectivity for lignin and other model compounds.

[0053] As Figure 1 shown, the characteristic peaks of Ni in the unmodified NiAl-LDH catalyst are obvious. The peaks at 2θ of 44.3°, 51.7° and 76.3° correspond to the (111), (200) and (220) crystal planes of Ni respectively. The crystallite size of Ni in the NiAl-LDH catalyst is calculated to be 9.07 nm by the Scherrer formula, with a small Ni particle size, which ensures the high activity of the catalyst. The characteristic peaks of Ni in the modified Br-NiAl-LDH catalyst are well retained. Figure 2 Fig. shows the XPS spectra of the NiAl-LDH catalyst before and after modification. The NiAl-LDH and the bromobenzene-modified catalyst are composed of Ni, Al and O elements. After modification, the characteristic peak of the Br element appears. The peak position of the modified catalyst at Ni 2p1 / 2 shifts by 0.2 eV, showing a red shift phenomenon, which may be caused by the transfer of electrons from Ni to Br. Figure 3 Fig. shows the CO-FTIR spectra of the NiAl-LDH catalyst before and after modification. The positions of the peaks in the figure are attributed to the binding of CO at the bridging site (1956 cm -1 ) and the linear site (2057, 2086 cm -1 ). Compared with the unmodified catalyst, the Bridging site (1956 cm -1 ) appears after the introduction of Br, and at the same time, the linear sites at the step edges and defects are enhanced (2057 cm -1 ). The enhancement of the linear site reduces the adsorption of the benzene ring, resulting in a higher yield of aromatic hydrocarbons.Figure 4 The influence of bromobenzene content on the conversion rate and phenol selectivity of diphenyl ether cracking reaction. When the dosage of bromobenzene is 10 mg, the conversion rate of diphenyl ether is 58.59%, and the phenol selectivity is 29.94%. With the increase of the dosage of bromobenzene, the conversion rate of diphenyl ether decreases, but the phenol selectivity is improved. This is because the presence of Br inactivates some Ni active sites, hinders the adsorption of phenol macromolecules and the hydrogenation of benzene rings, and improves the phenol selectivity. Figure 5 For Br in Example 8 10mg The reuse of the -NiAl-LDH catalyst in the reaction.

[0054] The above embodiments are only for better explaining the principle and practical application of the present invention, so that those skilled in the relevant technical fields can better understand and utilize the present invention. It does not limit the patent scope of the present invention. Any equivalent transformation made by using the content of the present invention is within the patent protection scope of the present invention.

Claims

1. A preparation method of halogen-modified nickel-aluminum hydrotalcite, characterized in that: A water-soluble nickel salt, a water-soluble aluminum salt, an alkali precipitating agent and water are mixed and then subjected to hydrothermal reaction. The obtained hydrothermal reaction product is first calcined in an air atmosphere and then calcined in a reducing atmosphere to obtain nickel-aluminum hydrotalcite; the nickel-aluminum hydrotalcite is mixed with a halogenated aromatic hydrocarbon and an organic solvent and then subjected to solvothermal reaction to obtain halogen-modified nickel-aluminum hydrotalcite; wherein, the calcination temperature in the air atmosphere is 400-600 °C, the time is 3-7 h, and the reduction calcination temperature in the reducing atmosphere is 500-700 °C, the time is 0.5-3 h; The halogenated aromatic hydrocarbon is bromobenzene; The mass of the halogenated aromatic hydrocarbon is 5%-10% of the mass of the nickel-aluminum hydrotalcite.

2. The preparation method of a halogen-modified nickel-aluminum hydrotalcite according to claim 1, characterized in that: The water-soluble nickel salt and the water-soluble aluminum salt are measured according to the molar ratio of nickel to aluminum of 1:1-4:

1.

3. The preparation method of a halogen-modified nickel-aluminum hydrotalcite according to claim 1 or 2, characterized in that: The water-soluble nickel salt includes at least one of Ni(NO 3 ) 2 ∙6H 2 O, NiCl 2 ; The water-soluble aluminum salt includes aluminum nitrate; The alkali precipitating agent includes at least one of urea, sodium carbonate, and KOH.

4. The preparation method of a halogen-modified nickel-aluminum hydrotalcite according to claim 1 or 2, characterized in that: The conditions of the hydrothermal reaction are: the temperature is 100-180 °C, and the reaction time is 6-12 h.

5. The preparation method of a halogen-modified nickel-aluminum hydrotalcite according to claim 1, characterized in that: The conditions of the solvothermal reaction are: the temperature is 90-150 °C, and the time is 2-6 h.

6. A halogen-modified nickel-aluminum hydrotalcite, characterized in that: It is obtained by the preparation method described in any one of claims 1-5.

7. The application of the halogen-modified nickel-aluminum hydrotalcite described in claim 6, characterized in that: It is used as a catalyst in the hydrodeoxygenation reaction of lignin-based compounds and / or aryl ether compounds to synthesize phenolic compounds.

8. The application of the halogen-modified nickel-aluminum hydrotalcite described in claim 7, characterized in that: The conditions of the hydrodeoxygenation reaction are: the mass ratio of the halogen-modified nickel-aluminum hydrotalcite to the lignin-based compounds and / or aryl ether compounds is 6:1-1:2, the hydrogen pressure is 0.1-3 MPa, the temperature is 120-180 °C, and the time is 1-6 h.

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