Method for removing organic chlorine through catalytic hydrogenation

Abstract

The invention discloses a method for removing organic chlorine through catalytic hydrogenation, which comprises the following step: under the reaction condition of liquid-phase catalytic hydrogenation dechlorination, carrying out contact reaction on chlorine-containing organic matters, hydrogen and a catalyst, the catalyst is a composite material of carbon-coated nickel-palladium alloy nanoparticles. According to the method, the dechlorination activity is high, the catalyst has intrinsic chlorine poisoning resistance and active metal loss resistance, and the catalyst is convenient to separate when the reaction is finished.

Description

Technical Field

[0001] The present invention belongs to the field of catalysis, and particularly relates to a method for catalytic hydrodechlorination of organic chlorine. Background Art

[0002] Catalytic hydrodechlorination is an important type of reaction, which is not only used in organic synthesis involving partial or complete dechlorination, but also used in the treatment of chlorinated organic wastes. Wastewater and waste residues generated in chemical processes usually contain chlorinated organic compounds, which are highly toxic and difficult-to-degrade pollutants. For example, chlorophenol is listed as one of the most priority pollutants to be treated by the US Environmental Protection Agency and must be completely removed. In addition, chlorine-containing additives are often used in the processes of crude oil extraction, storage, and transportation, resulting in an increase in the chlorine content of crude oil. The organic chlorine in crude oil can not only cause corrosion and leakage of refining units, but also cause irreversible poisoning of the entire catalyst bed, posing a serious threat to the safe and stable production of refining units. Therefore, it is necessary to perform dechlorination pretreatment on such crude oil. In addition, polyhalides are often by-produced in chlorination processes, and it is also necessary to recycle and reuse this part of by-products. In summary, catalytic hydrodechlorination can play an important role in organic synthesis, environmental protection treatment, and waste recycling and utilization.

[0003] Catalytic hydrodechlorination can be carried out in the gas phase or in the liquid phase. Generally, chlorine on aliphatic carbon is easy to remove, while chlorine on aromatic carbon is difficult to remove. At present, a large number of reports have disclosed the application of catalysts such as platinum, palladium, rhodium, ruthenium, and nickel in hydrodechlorination reactions. Among them, palladium has the highest catalytic activity, but the price of palladium is expensive, and issues such as the loss and recycling of palladium need to be considered. Moreover, a large amount of HCl is generated during catalytic hydrodechlorination, which is likely to cause catalyst poisoning. The prior art generally adds alkaline substances to protect the active sites of the catalyst.

[0004] There have been literature reports on composites of graphitized carbon layer-coated nickel nanoparticles. This kind of composite material with a core-shell structure can efficiently catalyze the hydrogenation of unsaturated groups, but generally does not dechlorinate. Although many composites of graphitized carbon layer-coated nickel nanoparticles have been disclosed in the prior art, literature on graphitized carbon layer-coated palladium is relatively rare, and there is still a lack of a simple and effective method for manufacturing graphitized carbon layer-coated palladium in the prior art. How to utilize the advantages of high catalytic activity of palladium nanomaterials while overcoming the weaknesses of easy aggregation and deactivation due to poisoning is a technical problem that has not been well solved in the prior art. Summary of the Invention

[0005] The object of the present invention is to provide a method capable of effectively removing chlorine atoms from saturated or aromatic organic compounds under mild liquid-phase conditions, which can at least solve one or all of the following technical problems: ① having high catalytic dechlorination ability with or without adding water; ② having intrinsic chlorine poisoning resistance and inhibiting the loss of active metals; ③ reducing the palladium content of the catalyst and / or reducing catalyst loss; ④ being easily separated from the reaction system.

[0006] The present invention provides a method for catalytic hydrogenation dechlorination of organic chlorine, comprising: contacting a chlorine-containing saturated or aromatic organic compound with hydrogen and a catalyst under the reaction conditions of liquid-phase catalytic hydrogenation dechlorination; the catalyst is a composite material of carbon-coated nickel-palladium alloy nanoparticles, the composite material has a core-shell structure with a shell layer and a core, the shell layer is a graphitized carbon layer, and the core is nickel-palladium alloy nanoparticles; in the composite material, the mass ratio of nickel to palladium is 3:1 to 10:1; based on the mass of the composite material, the total mass fraction of nickel and palladium is 20% to 80%.

[0007] According to the present invention, the reaction conditions of the liquid-phase catalytic hydrogenation dechlorination are: the temperature range is 40°C to 120°C, preferably 60°C to 100°C, and the hydrogen pressure range is 0.1 MPa to 3 MPa, preferably 1 MPa to 2 MPa.

[0008] According to the present invention, the chlorine-containing aromatic organic compound preferably has a chlorine atom directly connected to the aromatic ring. More preferably, it is selected from one or more of monochlorophenol, dichlorophenol, trichlorophenol, chlorinated aromatic hydrocarbons, 2,4-dichlorophenoxyacetic acid, and chloronitrobenzene.

[0009] According to the present invention, a solvent may or may not be used in the method. Whether to use a solvent depends on whether the reaction substrate itself is in a suitable liquid state under hydrogenation conditions and the needs of those skilled in the art; the choice of solvent depends on ensuring the solubility of the reaction substrate, which are all known in the art. If used to treat dissolved organic chlorides in wastewater, water itself is the solvent. Optional solvents include, but are not limited to: one or more of isopropanol, ethanol, acetone, tetrahydrofuran, cyclohexane, and water. If the organic chloride is soluble in alcohol but not in water, a mixed solvent of alcohol and water is preferably used, and the volume ratio of alcohol to water is preferably 10:1 to 5:1.

[0010] According to the present invention, the ratio of the catalyst to the reaction substrate is 0.05 to 0.8:1, preferably 0.1 to 0.3:1.

[0011] According to the present invention, the catalyst of the present invention has strong magnetism, and magnetic separation can be used when separating the catalyst.

[0012] According to the present invention, the composite material described in the dechlorination method is composed of nickel, palladium, carbon and oxygen. It should be understood that the composite material is mainly composed of zero-valent nickel, palladium and carbon. Since the carbon source in the synthesis raw materials contains oxygen, a small amount of oxygen will inevitably be incorporated into the surface carbon of the composite material; the surface of the composite material will also adsorb oxygen when stored in air, and a small amount or trace amount of nickel and palladium may exist in the oxidized state, and impurities in the synthesis raw materials may also cause the presence of a small amount or trace amount of other elements, but these factors have no obvious effect on the performance of the composite material; the present invention believes that it is not necessary to specify these.

[0013] According to the foregoing composite material, the mass ratio of nickel to palladium is 3:1 to 10:1, preferably 3:1 to 8:1, more preferably 3:1 to 6:1. Within the above ratio range, there is only a diffraction peak of the fcc NiPd alloy in the XRD pattern of the composite material, and there is no diffraction peak of elemental palladium; while when the palladium content is higher, characteristic peaks of elemental palladium appear, and these elemental palladium are difficult to be tightly coated by carbon and do not have the ability to resist coalescence and poisoning inactivation.

[0014] According to the foregoing composite material, its XRD pattern satisfies the following:

[0015] There is only one diffraction peak in the range of 2θ from 40.1° to 44.5°; and / or

[0016] There is a diffraction peak in the range of 2θ from 24° to 26°; and / or

[0017] There are diffraction peaks in the ranges of 2θ from 43° to 45°, 50° to 54°, and 75° to 80°; and / or

[0018] There is no diffraction peak in the range of 40.0° ± 0.2°.

[0019] According to the foregoing composite material, based on the composite material, the total mass fraction of nickel and palladium is 20% to 80%, preferably 30% to 80%, more preferably 50% to 80%. The present invention has found that even when a small amount of palladium is doped in nickel, the catalytic hydrogenation ability of the composite material is significantly improved. In some preparation examples of the present invention, even after acid treatment, the total mass fraction of nickel and palladium in the composite material can still reach about 75%.

[0020] According to the foregoing composite material, it is a mesoporous and / or macroporous material, and the sum of the mesoporous and macroporous volumes accounts for more than 50% of the total pore volume. The composite material has a mesoporous structure or a mesoporous and macroporous structure. As is well known in the art, the pore structure is a macroscopic property of the catalytic material.

[0021] The composite material and its characterization are described in detail in CN202310602919.7. The present invention hereby incorporates the content of this patent application in its entirety and will not repeat it here.

[0022] According to the present invention, in order to ensure the dechlorination efficiency, there are no sulfur-containing compounds in the reaction system.

[0023] According to the present invention, the dechlorination method can be used in the fields of sewage dechlorination treatment, crude oil dechlorination pretreatment, dechlorination recovery of organic by-products, and organic synthesis.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects.

[0025] First, the present invention utilizes the ability of nickel to promote carbon layer deposition and graphitization, combines the specific complexing and reducing abilities of polycarboxylic acids, and realizes the encapsulation of palladium metal into the carbon layer by a simple method with a relatively tight encapsulation, thereby obtaining a composite material of carbon-coated nickel-palladium alloy nanoparticles. This composite material combines the stability of nanocarbon materials and the catalytic characteristics of palladium metal nanoparticles. It has intrinsic safety, and theoretically there are no problems of metal nanoparticle coalescence deactivation and loss. Moreover, it exhibits the catalytic characteristics of palladium metal in the catalytic hydrodechlorination reaction. Specifically, when using the aforementioned composite material for catalytic hydrodechlorination, it has the following characteristics and advantages: the catalyst has intrinsic chlorine poisoning resistance and resistance to the loss of active metals; the catalytic active component is an alloy with a relatively low palladium content, but still has the ability of palladium to catalyze hydrodechlorination; no base is used in the reaction, but it still has a high dechlorination activity; the dechlorination activity is high whether the solvent contains water or not, so the application range is wider; since the alloy mainly contains nickel, it has strong ferromagnetism, and the catalyst can be conveniently separated by magnetic separation, avoiding the cost increase caused by catalyst loss. Detailed Embodiments

[0026] The present invention is described in detail below in conjunction with specific embodiments. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments and theoretical explanations, but is determined by the claims.

[0027] In the present invention, first, the directly recorded content shall prevail; second, the content recorded by way of introduction shall prevail. For any other matters or things not mentioned, those known in the art shall be directly applied without any change. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein. The technical solutions or technical ideas formed thereby shall be regarded as part of the original disclosure or record of the present invention, and shall not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider that the combination is obviously unreasonable.

[0028] All features disclosed by the present invention can be combined arbitrarily, and these combinations should be understood as the content disclosed or recorded by the present invention. Unless those skilled in the art consider such combinations to be obviously unreasonable, they should all be regarded as specifically disclosed and recorded by the present invention. The numerical points disclosed in this specification, unless otherwise specified, not only include the specific numerical points disclosed in the embodiments, but also include the endpoints of each numerical range in the specification. The ranges formed by any combination of these numerical points should be regarded as the ranges disclosed or recorded by the present invention.

[0029] For the technical and scientific terms in the present invention, those with definitions shall be subject to their definitions, and those without definitions shall be understood according to the common meanings in the art.

[0030] The term "graphitized carbon layer" refers to a layered carbon structure that can be clearly observed under a high-resolution transmission electron microscope, rather than an amorphous structure.

[0031] The term "mesopore" is defined as a pore with a pore diameter in the range of 2 nm to 50 nm. Pores with a pore diameter less than 2 nm are defined as micropores, and pores with a pore diameter greater than 50 nm are defined as macropores.

[0032] The term "acid treatment" refers to the operation of pickling the product generated after the high-temperature pyrolysis step at a temperature close to the boiling temperature of the acid solution when preparing the composite material of carbon-coated nickel-palladium alloy nanoparticles.

[0033] The term "inert gas" is defined as a gas that has no perceivable impact on the catalytic hydrogenation performance of the composite material. For example, it includes but is not limited to nitrogen, helium, argon, etc.

[0034] The term "soluble" means soluble in the solvent used.

[0035] The symbol "PPMw" represents parts per million by weight.

[0036] The term "optional" means can have or not have. For example, A and optional B means "having A and not having B" or "having both A and B".

[0037] The surface morphology of the material was characterized by high-resolution transmission electron microscopy (HRTEM, JEOL Ltd., JEM-2100), and the acceleration voltage was 200 kV.

[0038] The elemental distribution in the material was characterized by spherical aberration electron microscopy (STEM). The model of the spherical aberration electron microscopy used was JEM-ARM200F (JEOL Ltd.), and the test conditions were: the acceleration voltage was 200 kV.

[0039] The composition of the material, the structure or morphology of atoms or molecules inside the material, etc. are obtained by XRD. The XRD diffractometer used is the X-ray diffractometer of model X’Pert Pro purchased from PANalytical of the Netherlands. The test conditions are: Cu target, Kα ray, tube voltage of 40 kV, tube current of 40 mA, and 2θ scanning range of 5° to 80°.

[0040] The elements on the surface of the material are detected by X-ray photoelectron spectroscopy analyzer (XPS). The X-ray photoelectron spectroscopy analyzer used is the ESCALab220i-XL type ray electron energy spectrometer produced by VG Scientifc company and equipped with Avantage V5.926 software. The test conditions for X-ray photoelectron spectroscopy analysis are: the excitation source is monochromatic A1Kα X-ray, the power is 330 W, and the base vacuum is 3×10 -9 mbar when analyzing and testing.

[0041] The specific surface area and pore size distribution of the material are determined by the Brunauer-Emmett-Taller method (BET, Quantachrome AS-6B type analyzer).

[0042] The content test of carbon, hydrogen, oxygen, nitrogen, and sulfur elements is carried out on an Elementar Vario EL Cube elemental analyzer. The specific operation method is as follows: Weigh about 5 mg of the sample in a tin cup, put it into the automatic sampling tray, and enter the combustion tube through the ball valve for combustion. The combustion temperature is 1000 °C (to exclude the interference of the atmosphere during sampling, helium purging is used). The C, H, N, and S in the sample are respectively converted into carbon dioxide, water, nitrogen, and sulfur dioxide. The mixed gas is separated by a chromatographic column and finally detected by a thermal conductivity cell. When determining oxygen elements, the sample is pyrolyzed in a high-temperature pyrolysis tube filled with carbon powder. The oxygen in the sample is converted into carbon monoxide. The carrier gas carries the pyrolysis products into a series of scrubbers to remove acid gas and water vapor, and finally enters an infrared detector for detection.

[0043] The content determination of nickel and palladium elements adopts inductively coupled plasma optical emission spectrometry (ICP-OES). The specific method is as follows: (1) Nitrolysis: Measure 10 mg of the catalyst sample and put it into a flask, add 16 mL of freshly prepared aqua regia, add a magnetic stir bar, put the flask into an oil bath at 120 °C for 12 h of condensation reflux. After cooling to room temperature, suck the solution with a glass syringe and filter it with a disposable filter head with a pore size of 0.22 μm. The filtrate is added to a 500 mL volumetric flask and made up to the mark with ultrapure water. (2) Content test: Take 10 mL of the solution after nitrolysis and volume determination, and use the instrument Agilent 5110 to test the metal content.

[0044] Preparation Examples 1-2 are used to illustrate the composite materials of the present invention and their preparation methods.

[0045] Preparation Example 1

[0046] 1) Weigh 0.411 g of palladium acetate and measure 30 mL of glacial acetic acid, add them to 170 mL of deionized water, and stir to dissolve at 50 °C. According to the mass ratio of nickel source to palladium source of 9:1 (calculated by metal element) and the molar ratio of the total nickel and palladium amount to the complexing agent of 1:1, weigh citric acid monohydrate and nickel acetate tetrahydrate and add them to the above solution. Stir at 70 °C to obtain a homogeneous solution, and continue heating to dryness. Grind the solid to obtain a precursor.

[0047] 2) Place the precursor obtained in step 1) in a porcelain boat, then place the porcelain boat in the constant temperature zone of a tube furnace, introduce nitrogen with a flow rate of 150 mL / min, and heat up to 600 °C at a rate of 2.5 °C / min. After maintaining the temperature for 2 h, stop heating and cool to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0048] 3) Add the pyrolysis product obtained in step 2) to 200 mL of 1 mol / L HCl solution, stir and reflux at 90 °C for 4 h, then filter the solution by suction, wash with deionized water until neutral, and place the powder in an oven at 100 °C to dry for 2 h to obtain a carbon-coated nickel-palladium alloy nanocomposite.

[0049] Preparation Example 2

[0050] According to the method of Preparation Example 1, except that in step 1), weigh 0.943 g of palladium acetate and measure 60 mL of glacial acetic acid, add them to 170 mL of deionized water, and stir to dissolve at 50 °C. According to the mass ratio of nickel source to palladium source of 4:1 (calculated by metal element) and the molar ratio of the total nickel and palladium amount to the complexing agent of 1:1, weigh citric acid monohydrate and nickel acetate tetrahydrate and add them to the above solution. Stir at 70 °C to obtain a homogeneous solution, and continue heating to dryness. Grind the solid to obtain a precursor, and the rest are the same as Preparation Example 1, to obtain a carbon-coated nickel-palladium alloy nanocomposite.

[0051] Examples 1-2 illustrate the catalytic hydrodechlorination method using the composite material of the present invention as a catalyst

[0052] Add 100 mg of the carbon-coated nickel-palladium alloy nanocomposite prepared according to the methods of Preparation Examples 1-2, 315 mg of p-chloronitrobenzene, 27 mL of isopropanol, and 3 mL of water into a reaction kettle respectively, and introduce H 2 After replacing the reaction kettle 4 times, stir and heat up under low pressure, heat up to the predetermined reaction temperature of 60 °C, and introduce H again 2 Make the pressure in the reaction kettle 1.0 MPa, continue the reaction until the pressure does not change for 10 minutes, cool to room temperature, release the pressure, open the reaction kettle, take out the product, and perform chromatographic analysis.

[0053] After analysis of the product of Example 1, the conversion rate of p-chloronitrobenzene was 100%, and the dechlorination rate (i.e., the aniline yield) was 93.0%.

[0054] After analysis of the product of Example 2, the conversion rate of p-chloronitrobenzene was 100%, and the aniline yield was 97.9%.

[0055] Example 3

[0056] 100 mg of the composite material prepared in Preparation Example 2, 129 mg of 4-chlorophenol, and 30 ml of ethanol were added to the reaction kettle, and H 2 After replacing the reaction kettle 4 times, the temperature was raised with stirring under low pressure to the predetermined reaction temperature of 80 °C, and H 2 was introduced again to make the pressure in the reaction kettle 1.0 MPa. The reaction was continued until the pressure did not change for 10 minutes (about 60 min), then cooled to room temperature, the pressure was released, and the reaction kettle was opened to take out the product for chromatographic analysis. The results showed that the conversion rate of 4-chlorophenol was 100%, and the dechlorination rate was 100%.

[0057] Table 1 Mass fractions of nickel and palladium and the mass ratio of nickel to palladium in the composite material of the present invention

[0058] Ni mass fraction Pd mass fraction Mass ratio of Ni / Pd Preparation Example 1 65.90％ 8.38％ 7.86 Preparation Example 2 56.80％ 17.56％ 3.23

[0059] As can be seen from Table 1, despite the long-time pickling, the metal content in the composite materials of Preparation Examples 1-2 was about 75%, indicating that the metal content in the composite materials of the present invention can be very high, and it has the ability to resist acid corrosion, which can avoid the loss of active metals when applied in an acidic environment.

[0060] It can be seen from Examples 1-3 that although the composite materials of Preparation Examples 1-2 were pickled with hydrochloric acid at a higher temperature for a long time, they still had a very high catalytic hydrodechlorination ability, indicating that the composite materials of the present invention have good anti-chlorine poisoning ability.

[0061] It can be seen from Example 3 that although only organic solvents were used, the method of the present invention still had a very high catalytic hydrodechlorination ability.

Claims

1. A method for removing organic chlorine by catalytic hydrogenation, comprising: Under the reaction conditions of liquid-phase catalytic hydrogenation dechlorination, a chlorine-containing saturated or aromatic organic compound is contacted with hydrogen and a catalyst for reaction; the catalyst is a composite material of carbon-coated nickel-palladium alloy nanoparticles, the composite material contains a core-shell structure with a shell layer and a core, the shell layer is a graphitized carbon layer, and the core is a nickel-palladium alloy nanoparticle; in the composite material, the mass ratio of nickel to palladium is 3:1 to 10:1; based on the mass of the composite material, the total mass fraction of nickel and palladium is 20% to 80%; and no sulfur-containing compounds exist in the reaction system.

2. The dechlorination method according to claim 1, characterized in that: The reaction conditions of the liquid phase catalytic hydrodechlorination are: temperature range 40°C to 120°C, preferably 60°C to 100°C, and hydrogen pressure range 0.1MPa to 3MPa, preferably 1MPa to 2MPa.

3. The dechlorination method according to claim 1, characterized in that: The chlorine-containing aromatic organic compound is selected from one or more of monochlorophenol, dichlorophenol, trichlorophenol, chlorinated aromatic hydrocarbons, 2,4-dichlorophenoxyacetic acid and chloronitrobenzene.

4. The dechlorination method according to claim 1, characterized in that: The chlorine-containing saturated organic compound is selected from one or more chlorinated saturated aliphatic hydrocarbons.

5. The dechlorination method according to claim 1, characterized in that: A solvent is used in the method; the solvent is selected from one or more of isopropanol, ethanol, acetone, tetrahydrofuran, cyclohexane and water.

6. The dechlorination method according to claim 1, characterized in that: The mass ratio of the catalyst to the reaction substrate is 0.05 to 0.8:1, preferably 0.1 to 0.3:

1.

7. The dechlorination method according to claim 1, characterized in that: Magnetic separation is used to separate the catalyst.

8. The dechlorination method according to claim 1, characterized in that: In the composite material, the mass ratio of nickel to palladium is 3:1 to 6:

1.

9. The dechlorination method according to claim 1, characterized in that: Taking the composite material as a benchmark, the total mass fraction of nickel and palladium is 50% to 80%.

10. The dechlorination method according to claim 1, characterized in that: The composite material is a mesoporous and / or macroporous material, and the volume of the mesopores and macropores accounts for more than 50% of the total pore volume.