CN111545219A

CN111545219A - Catalyst for preparing acrolein by propylene oxidation and preparation method thereof

Info

Publication number: CN111545219A
Application number: CN202010368643.7A
Authority: CN
Inventors: 赵玉平
Original assignee: Individual
Current assignee: Shaanxi Yuanheng Pharmaceutical Technology Co ltd
Priority date: 2020-05-01
Filing date: 2020-05-01
Publication date: 2020-08-18
Anticipated expiration: 2040-05-01
Also published as: CN111545219B

Abstract

The catalyst has a blocky integral structure, has a good mass and heat transfer effect, has high conversion rate and selectivity on acrolein, and can effectively maintain the catalytic performance especially under the condition of high space velocity.

Description

Catalyst for preparing acrolein by propylene oxidation and preparation method thereof

Technical Field

The invention relates to a catalyst for preparing acrolein by propylene oxidation and a preparation method thereof, belonging to the field of preparation of propylene selective oxidation catalysts by an electrochemical method.

Technical Field

Acrolein is the simplest unsaturated aldehyde, since it contains C = C and C = O double bonds in the molecule

The chemical property is active, and the compound is an important organic chemical intermediate, for example, acrolein can be further oxidized to generate acrylic acid, so that the acrylic acid can be synthesized, and the compound can also be reduced to synthesize propanol and glycerol, and is an important raw material for synthesizing spices, preservatives and emulsifiers.

The propylene catalytic oxidation method is the most important synthesis method for producing acrolein in industry at present, and a plurality of patents have been reported for preparing the acrolein by propylene oxidation:

chinese patent CN200810235193, Hefei Haili scientific and technological development Limited, discloses a catalyst for producing acrolein by direct oxidation of propylene, which contains molybdenum (Mo), bismuth (Bi), iron (Fe), cobalt (Co) or/and nickel (Ni) and oxygen (O), and is different from the prior art in that the catalyst is prepared by mixing a cesium (Cs) -containing catalyst (I) and a potassium (K) -containing catalyst (II) according to the mass percent of 10-50% and 50-90%, kneading, molding, drying and roasting, wherein the catalysts (I) and (II) are as follows: moa, Wb, Bic, Fed, (Co or/and Ni) e, Sif, Csg, Ox (I), Moa, Wb, Bic, Fed, (Co or/and Ni) e, Sif, Kg, Ox (II), where the subscripts a, b, c, d, e, f, g, x are the atomic numbers of the respective elements, and a: 10-12; b: 0-2, a + b-12; c: 0.5-2, d: 0.5-2, e: 3-6, when Co and Ni are simultaneously contained, the relative quantity ratio is arbitrary; f: 1-3 min; g: 0.01-0.3, x is the sum of oxygen atom number in corresponding element oxide, namely physical mixing of different active components is adopted to improve the catalytic effect of the catalyst.

Chinese petrochemical company, china research institute for petrochemical industry, shanghai, CN201210412591, discloses an acrolein catalyst and a preparation method thereof, wherein the catalyst is prepared by mixing a powdery catalyst precursor, which takes at least one of SiO2 or Al2O3 as a carrier, with a binder and a molybdenum additive, molding, and finally roasting; the technical scheme that the molybdenum additive comprises 50-100% of ammonium heptamolybdate and 0-50% of molybdenum trioxide in mole percentage better solves the technical problem, can be used in industrial production of acrolein catalyst prepared by propylene oxidation, adopts a molybdenum-bismuth catalyst, and has a single-pass yield of acrolein of over 75%.

Chinese patent CN201210392989 is prepared by selecting from SiO₂Or Al₂O₃Is a carrier containing an active ingredient represented by the following general formula: mo12 BiaFebNicSbXeYfZgQqOx, wherein X is at least one selected from Mg, Co, Ca, Be, Cu, Zn, Pb or Mn; y is at least one selected from Zr, Th and Ti; z is at least one selected from K, Rb, Na, Li, Tl or Cs; q is at least one of La, Ce, Sm or Th, wherein the antimony starting material is selected from ammonium antimony tartrate, the problem is solved well, and the catalyst can be used in the industrial production of acrolein by propylene oxidation, namely, the yield of acrolein and acrylic acid can reach more than 92% through improvement of a molybdenum-bismuth catalyst.

It can be seen that the catalyst mainly used at present is Mo-Bi-Fe-O series composite oxide catalyst, the preparation method of the catalyst mainly adopts solution mixing precipitation method, i.e. the raw materials are made into solution, then mixed and stirred under a certain condition, and evaporated, dried and pulverized into fine powder with a certain grain size, the fine powder can be added with binder and powdered carrier to be kneaded and formed (extruded or pressed into sheets), the shape of the catalyst is basically solid cylinder and sheet in the early stage, and then developed into various abnormal bodies, mainly hollow cylinder, hollow sheet, ring body or fine powder is stuck on the falling macroporous ball, such as CNCN 105195166A, but it is known that the gas phase catalytic oxidation reaction of propylene to prepare acrolein and acrylic acid is strong exothermic reaction, a large amount of reaction heat is instantaneously accumulated in the reactor to form local hot spot, if the reaction heat can not be timely and effectively removed, the continuous accumulation of the heat accumulated instantaneously leads to the loss and falling off of the active components of the catalyst, so that the activity of the catalyst is reduced, the service life of the catalyst is shortened, and the formation of byproducts is accelerated due to over-oxidation reaction, thereby reducing the yield of acrolein and acrylic acid, even causing runaway reaction, and sintering the catalyst.

Namely, the following problems obviously exist in the prior art: (1) the loading of the active component is realized by coating the Mo-Bi-Fe-O series composite oxide catalyst on the surface of the carrier only through simple mixing, thereby causing great waste for the full utilization and the repeated use of the catalyst; (2) the carrier can only be used as a load, has limited effect in the aspects of mass and heat transfer, is generally spherical particles, and has great limitation on mass and heat transfer for high-space-velocity reaction; (3) the research of the Mo-Bi-Fe-O series composite oxide catalyst is over mature, the academic value of the basic research is limited, and the further research cannot be effectively carried out.

Before the advent of the Mo-Bi-Fe-O based composite oxide catalyst, the catalyst which was widely studied was a noble metal catalyst, such as a gold-copper bimetallic catalyst system of the present invention disclosed in US 3989674A published in 1976, the catalyst support being selected from the group consisting of silica, alumina, magnesia, thoria, zirconia and mixtures thereof, other support materials such as diatomaceous earth, asbestos, pumice and silicon carbide may also be used, the gold-copper bimetallic catalyst having a propylene conversion of 40.8% and an acrolein selectivity of 61.9%, i.e. the space that can be promoted for the above gold-copper catalyst is extremely large.

The current industrialized catalyst carrier is granular or powdered alumina or silica, and the loading and unloading of the granular catalyst are troublesome in the using process; is not easy to form and the mechanical strength can not meet the requirement; mass and heat transfer are greatly hindered, and the treatment efficiency is reduced; the pressure drop difference between the front and the back of the catalyst bed is large, and the energy consumption is increased. The integral catalyst integrates active components of the catalyst, a structured carrier and a reactor, the geometric surface area of a bed layer in unit volume is large, the integral catalyst has the advantages of high mass transfer and heat transfer efficiency, reduced bed lamination, high catalytic efficiency and the like, the adsorption of reactants on the surface of the catalyst, the desorption and release of products, the removal of heat and the like are facilitated, the chemical reaction process is enhanced, and the reactor is easy to assemble, maintain and disassemble and is considered to be one of the development directions with the most prospects in the field of heterogeneous catalysis at present, but the case of preparing the acrolein catalyst by oxidizing propylene into blocks is rare at present.

Based on the above, as a catalyst for the gas phase catalytic oxidation of propylene, improvement of its performance and method of use, many patents have been issued abroad, and studies on the composition of the catalyst have been advanced, but studies on the catalyst carrier, such as the mechanical strength of the carrier, are low; the carrier powder particles are not beneficial to high space velocity catalysis, namely, the contribution of the carrier pore channel structure to the catalytic performance should be fully exerted on the premise of ensuring that the catalyst has enough strength.

Disclosure of Invention

Based on the problems in the prior art, the catalyst for preparing acrolein by propylene oxidation and the preparation method thereof are provided, the catalyst is of an integral blocky structure, the carrier is a carbon nano tube-gamma-alumina mixture, the mechanical strength is high, the pore structure is rich, the catalyst has a macroporous structure and a mesoporous structure, the mass transfer effect is good, Au-Cu alloy is loaded on the surface of the catalyst by an electrochemical method, the active components of the Au-Cu alloy are highly dispersed on the outer wall of the carbon nano tube, and the Au-Cu alloy/carbon nano tube-alumina catalyst has obvious benefits on the improvement of the propylene oxidation reaction effect and the heat dissipation of a catalyst bed layer.

The preparation method of the catalyst for preparing the acrolein by oxidizing the propylene comprises the following steps:

(1) preparing carbon nanotube-doped polystyrene, wherein the volume porosity of the polystyrene is more than or equal to 75%: (a) washing the styrene and divinylbenzene reagent for many times by using NaOH solution and deionized water; (b) putting a proper amount of Span 80 and AIBN into a three-neck flask, adding washed styrene and divinylbenzene, gradually and slowly adding 60-80ml of deionized water into the three-neck flask by using a liquid conveying pipe with stirring, wherein the dropping time of the deionized water is 2-3h, adding carbon nano tubes after the dropping of the deionized water is finished, and continuously stirring for 3-4h to obtain an off-white emulsion; (c) filling the grey emulsion into a test tube with the caliber of 4-6cm, sealing, drying and polymerizing for 18h to obtain the grey rod-shaped polystyrene doped with the carbon nano tube, and then drying by cold air.

Carbon nanotube pre-passes 100^oC, refluxing with mixed acid for 5H, wherein the mixed acid is 98wt.% of H in a volume ratio of 2.5:1₂SO₄And 65% -67wt.% of HNO₃And (4) mixing acid.

(2) Filling alumina sol and drying: (a) weighing 2.5g of pseudoboehmite, adding the pseudoboehmite into 40mL of deionized water in batches under the stirring condition, stirring vigorously for 2 hours, and then adding 1.5 mol/LHNO₃Continuously stirring the generated semitransparent alumina hydrosol for 7 hours; (b) placing the carbon nanotube-doped polystyrene obtained in the step (1) in alumina hydrosol, vacuumizing and filling for 1.5h by using a vacuum water pump, and then 75^oAnd C, drying in an oven, repeatedly filling and drying for 5 times.

(3) Roasting: under the inert atmosphere condition of nitrogen protection at 600 DEG^oC, roasting for 24 hours.

(4) Preparing Au-Cu plating solution: 5-9g/L KCN, Au (CN)2K 0.5-1g/L, Cu (CN)2K, 1.5-3g/L, EDTA-2Na 3-7g/L, pH = 9.8. + -. 0.1 adjusted with ammonia.

(5) Bidirectional pulse electrodeposition of Au-Cu: forward pulse current density of 0.1-0.5A/dm²Duty ratio of 30%, negative pulse current density of 0.1-0.5A/dm2, duty ratio of 50%, and temperature of 40%^oC, time is 1-3min, magnetic stirring is 200-.

The catalyst is Au-Cu alloy/carbon nano tube-alumina catalyst, the catalyst is of a blocky structure, and the alumina is gamma-Al₂O₃The Au-Cu alloy exists in the form of one or more of AuCu3, AuCu or Au3Cu, and the active component of the Au-Cu alloy is only highly dispersed on the surface of the carbon nano tube.

The alloy Au-Cu alloy/carbon nano tube-alumina catalyst has the advantages that under 320 ℃ and at a space velocity of 30000mL.g-1h < -1 >, the conversion rate of propylene is 93.3%, the yield of acrolein is 86.0%, the selectivity of acrolein is 91.2%, the selectivity of acrylic acid is 4.7%, and the other selectivity is 4.1%.

The invention has the following points:

(1) regarding the carbon nanotube-polystyrene template: the polystyrene template is obtained by a reverse concentrated emulsion method, the preparation principle is briefly summarized as that deionized water (water phase) is dripped into styrene and divinylbenzene (oil phase) under the action of a surfactant span 80, extrusion is carried out between water droplets to force the liquid level of the oil phase to be thinned, and after the oil phase is subjected to polymerization reaction, water in the water phase is evaporated under a heating condition, so that the polystyrene template with a porous structure can be obtained. The macroporous structure utilizes mass transfer in the reaction process, in addition, the carbon nano tubes are uniformly dispersed in the matrix of the alumina, and finally, the volume porosity of the carbon nano tube-polystyrene can be effectively controlled by controlling the addition amount of the water phase, wherein the porosity is preferably more than or equal to 75 percent.

Secondly, adding carbon nanotubes into the polystyrene template, which mainly aims to improve the conductivity of the subsequent carrier so as to realize the subsequent operation of electrochemically depositing the active components, and in addition, the carbon nanotubes are commercially available carbon nanotubes which are previously subjected to 100 times^oC, refluxing with mixed acid for 5H, wherein the mixed acid is 98wt.% of H in a volume ratio of 2.5:1₂SO₄And 65% -67wt.% of HNO₃Mixed acid, via mixed acid H₂SO₄/HNO₃The treated carbon nanotube can effectively improve the solubility and the dispersibility in the process of preparing polystyrene, is favorable for improving the dispersity of the carbon nanotube in the polystyrene, and in addition, the carbon nanotube pair is considered to be reversedThe effect of the concentrated emulsion process and the problem of agglomeration are caused, the loading of carbon nanotubes is 10-20wt.%, preferably 15%.

(2) The prepared carbon nano tube-polystyrene has rich pore channels and high porosity, the pseudo-boehmite is hydrolyzed to obtain the alumina sol, the alumina sol is pumped by a vacuum pump to be fully filled on the surface of the graphene-polystyrene, and then the alumina sol is dried to obtain the alumina, because of the vacuum pumping, enough alumina sol can not be loaded on the surface of the carbon nano tube-polystyrene once, the alumina-carbon nano tube-polystyrene is subjected to multiple times of vacuum pumping filling-drying treatment once, the mechanical strength of the alumina-carbon nano tube-polystyrene is improved along with the increase of the filling times or the increase of the sol concentration, and the mechanical strength of a subsequent carrier can be effectively controlled, wherein the filling-drying times can be 4-6 times, preferably 5 times.

(3) Roasting: the roasting process mainly uses high-temperature treatment to effectively crack the polystyrene, and inert gas protection must be used in the high-temperature treatment process, which is mainly based on the following considerations: (a) with air, such as combustion in a muffle furnace, polystyrene can carbonize, introducing unwanted impurities, and the presence of carbon can significantly reduce the porosity and catalytic activity of the support; (b) the introduction of air can cause the combustion of the carbon nano tube and destroy the raw materials; as for the temperature of calcination, the cracking temperature of polystyrene is 450-600-^oC, so that the roasting temperature should not be lower than 450 DEG^oAnd C, in addition, the roasting temperature has obvious influence on the crystal form and the specific surface area of the alumina, and the crystal form and the specific surface area are shown in the table 1:

TABLE 1 Al calcined at different temperatures₂O₃Specific surface area and crystalline form of carbon nanotube-polystyrene support

Temperature of calcination	BET specific surface area/m²/g	Crystal form
			500	286	γ-Al₂O₃
600	293	δ-Al₂O₃
			950	93	δ-Al₂O₃
1250	15	α-Al₂O₃

Based on the consideration of the surface area and the crystal form, 600 is preferable^oAnd C, roasting by nitrogen.

With respect to electrodeposition: the bidirectional pulse plating is adopted, the pulse plating can increase the activation polarization of the cathode and reduce the concentration polarization of the cathode, and the working principle of the bidirectional pulse plating mainly utilizes the relaxation change of current pulse or voltage pulse. When the current is conducted, metal ions close to the cathode are fully reduced; when the current is turned off, the consumed discharge metal ions around the cathode are restored to the original concentration again. The current is periodically and repeatedly switched on and off, namely relaxation change of the pulse current is mainly used for reducing metal ions, particularly the surface of the carbon nano tube in the pore channel. CN < - > and EDTA in the electroplating solution are complexing agents, the main effect of the complexing agents is CN < - >, the complexing strength is moderate, Cu and Au ions can be complexed simultaneously, and the EDTA is auxiliary, but the indispensable complexing agents are not beneficial to the formation of alloys when being absent. The main pH value range should be kept in time during the electrodeposition process to prevent the metal ions from hydrolytic precipitation, and the pH is adjusted to be =9.8 +/-0.1 by using ammonia water.

Finally, as for the loading position of the active metal on the surface of the carrier, based on the understanding that the carbon nanotube is conductive and the alumina is not conductive, it can be obviously concluded that the active component will be dispersed on the surface of the carbon nanotube and rarely attached to the surface of the alumina through physical adsorption, as shown in fig. 1, the active component is mainly distributed on the carbon nanotube, and the particle size is 5-10 nm.

The scheme of the invention has the following beneficial effects:

(1) the catalyst is of a blocky structure, the mass and heat transfer effect is good, and the conversion rate and the selectivity of the catalyst to acrolein are high;

(2) the specific surface area of the catalyst is large, and the active component exists on the surface of the catalyst in an alloy state;

(3) by the electrochemical deposition method, the alloy components can be effectively and selectively controlled to be only loaded on the outer wall of the carbon nanotube, and the catalytic performance is loaded on the surface of the aluminum oxide.

(4) Under the condition of high space velocity, the catalytic performance can be effectively maintained.

Drawings

FIG. 1 is a TEM image of Au-Cu alloy of the present invention on the surface of carbon nanotube.

Detailed Description

Example 1:

(1) preparing carbon nanotube-doped polystyrene, wherein the volume porosity of the polystyrene is more than or equal to 75%: (a) washing the styrene and divinylbenzene reagent for many times by using NaOH solution and deionized water; (b) putting a proper amount of Span 80 and AIBN into a three-neck flask, adding washed styrene and divinylbenzene, gradually and slowly adding 70ml of deionized water into the three-neck flask by using a liquid conveying pipe while stirring, wherein the dripping time of the deionized water is 3 hours, adding carbon nano tubes after the dripping of the deionized water is finished, and continuously stirring for 3 hours to obtain an off-white emulsion; (c) filling the grey emulsion into a test tube with the caliber of 4-6cm, sealing, drying and polymerizing for 18h to obtain the grey rod-shaped polystyrene doped with the carbon nano tube, and then drying by cold air. Carbon nanotube is previously passed through100^oC, refluxing with mixed acid for 5H, wherein the mixed acid is 98wt.% of H in a volume ratio of 2.5:1₂SO₄And 65% -67wt.% of HNO₃And (4) mixing acid.

(4) Preparing Au-Cu plating solution: 5g/L KCN, 0.5g/L Au (CN)2K, 1.5g/L Cu (CN)2K, 3g/L EDTA-2Na, balance deionized water, and pH =9.8 was adjusted using ammonia. .

(5) Bidirectional pulse electrodeposition of Au-Cu: forward pulse current density 0.1A/dm²Duty cycle 30%, negative pulse current density 0.1A/dm2, duty cycle 50%, temperature 40^oC, the time is 1min, the magnetic stirring is carried out at 200-300rpm, and finally 10wt.% of the total mass of the carbon nano tube loaded catalyst in the catalyst carrier is obtained.

Example 2

(1) Preparing carbon nanotube-doped polystyrene, wherein the volume porosity of the polystyrene is more than or equal to 75%: (a) washing the styrene and divinylbenzene reagent for many times by using NaOH solution and deionized water; (b) putting a proper amount of Span 80 and AIBN into a three-neck flask, adding washed styrene and divinylbenzene, gradually and slowly adding 70ml of deionized water into the three-neck flask by using a liquid conveying pipe while stirring, wherein the dripping time of the deionized water is 3 hours, adding carbon nano tubes after the dripping of the deionized water is finished, and continuously stirring for 3 hours to obtain an off-white emulsion; (c) filling the grey emulsion into a test tube with the caliber of 4-6cm, sealing, drying and polymerizing for 18h to obtain the grey rod-shaped polystyrene doped with the carbon nano tube, and then drying by cold air. Carbon nanotube pre-passes 100^oC, refluxing with mixed acid for 5H, wherein the mixed acid is 98wt.% of H in a volume ratio of 2.5:1₂SO₄And 65% -67wt.% of HNO₃And (4) mixing acid.

(4) Preparing Au-Cu plating solution: 7g/L KCN, 0.75g/L Au (CN)2K, 2g/L Cu (CN)2K, 5g/L EDTA-2Na, the balance being deionized water, and pH =9.8 was adjusted using ammonia. .

(5) Bidirectional pulse electrodeposition of Au-Cu: forward pulse current density 0.13A/dm²Duty cycle 30%, negative pulse current density 0.3A/dm2, duty cycle 50%, temperature 40^oC, the time is 2min, the magnetic stirring is carried out at 250rpm, and finally 15wt.% of the total mass of the carbon nano tube loaded catalyst in the catalyst carrier is obtained and named as D-2.

Example 3

(1) Preparing carbon nanotube-doped polystyrene, wherein the volume porosity of the polystyrene is more than or equal to 75%: (a) washing the styrene and divinylbenzene reagent for many times by using NaOH solution and deionized water; (b) putting a proper amount of Span 80 and AIBN into a three-neck flask, adding washed styrene and divinylbenzene, gradually and slowly adding 70ml of deionized water into the three-neck flask by using a liquid conveying pipe while stirring, wherein the dripping time of the deionized water is 3 hours, adding carbon nano tubes after the dripping of the deionized water is finished, and continuously stirring for 3 hours to obtain an off-white emulsion; (c) filling the grey emulsion into a test tube with the caliber of 4-6cm, sealing, drying and polymerizing for 18h to obtain the grey rod-shaped polystyrene doped with the carbon nano tube, and then drying by cold air. Carbon nanotube pre-passes 100^oC mixed acid recoveryTreating the mixture for 5H, wherein the mixed acid is 98wt.% of H in a volume ratio of 2.5:1₂SO₄And 65% -67wt.% of HNO₃And (4) mixing acid.

(4) Preparing Au-Cu plating solution: 9g/L KCN, 1g/L Au (CN)2K, 3g/L Cu (CN)2K, 7g/L EDTA-2Na, and the balance deionized water, and pH =9.8 was adjusted using ammonia water.

(5) Bidirectional pulse electrodeposition of Au-Cu: forward pulse current density 0.5A/dm²Duty cycle 30%, negative pulse current density 0.5A/dm2, duty cycle 50%, temperature 40^oC, time 3min, magnetic stirring 200-. Finally, 20wt.% of the total mass of the carbon nanotube-loaded catalyst in the catalyst support was obtained.

Comparative example 1

Consistent with the preparation method of example 2, except that the catalyst was polished and sieved to 60-80 mesh after the preparation was completed, and named as D-1.

Comparative example 2

The preparation method is consistent with the preparation method of example 2, and is characterized in that the active component is loaded by an impregnation method, namely, the catalyst carrier is soaked in 5-9g/L KCN, Au (CN)2K 0.5-1g/L, Cu (CN)2K, 1.5-3g/L and EDTA-2Na 3-7g/L solution for 24h, then the catalyst carrier is placed into a refrigerator for freezing for 2h, and then the catalyst carrier is subjected to vacuum freeze drying to remove water, and the catalyst carrier is named as D-2.

Comparative example 3

The method is consistent with the preparation method of example 2, except that the carbon nanotubes are replaced by graphene, and the graphene is processed in a manner consistent with that of the carbon nanotubes and is named as D-3.

And (3) testing the activity of the catalyst:

raw material gas (propylene: air =1: 10), reaction temperature 320^oC, the space velocity of the reaction raw material is 30000mL^.g^-1h^-1FID online analysis was performed using gas chromatography.

TABLE 1 catalytic Activity test

Based on the catalytic activity test in table 1, it can be shown that (1) the catalytic performance of the bulk catalyst and the particle catalyst of the Au-Cu alloy/carbon nanotube-alumina catalyst prepared by the method is not obviously different at a low airspeed; (2) the method is suitable for electrochemical load of active components, the active components are selectively adsorbed on the surface of the carbon nano tube, the obtained active components are in an alloy state, and Au-Cu alloy is highly dispersed on the surface of the carbon nano tube, so that the influence on the conversion rate, the selectivity and the yield of propylene is particularly positive; (3) the graphene is not as good as a carbon nano tube in use, and the graphene is difficult to obtain a single-layer graphene which is uniformly dispersed by using a hummer method, the graphene is inevitably of a multilayer structure, in the electrochemical deposition process, a solution easily enters graphene sheet layers to be deposited, so that part of active components of a catalyst are loaded between the graphene sheet layers, the problem of active component embedding exists, finally, the active components cannot be contacted with propylene and cannot generate catalytic activity, and compared with the carbon nano tube, the active components are more selectively adsorbed on the surface of the carbon nano tube and are easily contacted with the propylene, and the acrolein is obtained by oxidation.

Effect of space velocities on catalyst conversion for S-2 and D-1 samples

TABLE 3 influence of space velocity on the catalytic Activity

From table 3, it can be seen that the catalytic performance of the powder catalyst is significantly reduced at a high space velocity, mainly the reaction gas cannot sufficiently contact with the catalyst, resulting in the reduction of the activity of the catalyst, but the space velocity of the catalyst with a block structure has a certain effect on the catalytic performance, but the effect is very low compared with the powder catalyst.

Although the present invention has been described above by way of examples of preferred embodiments, the present invention is not limited to the specific embodiments, and can be modified as appropriate within the scope of the invention.

Claims

1. A preparation method of a catalyst for preparing acrolein by propylene oxidation is characterized by comprising the following steps:

(1) preparing carbon nanotube-doped polystyrene, wherein the volume porosity of the polystyrene is more than or equal to 75%:

(2) filling alumina sol and drying:

(3) roasting:

(4) preparing Au-Cu plating solution:

(5) performing bidirectional pulse electrodeposition on Au-Cu,

the catalyst is Au-Cu alloy/carbon nano tube-alumina catalyst, the catalyst is of a blocky structure, and the alumina is gamma-Al₂O₃The Au-Cu alloy exists in one or more of AuCu3, AuCu or Au3Cu, and the loading amount of the carbon nano tubes in the catalyst is 10-20 wt.%.

2. The method according to claim 1, wherein the step (1) comprises the steps of: (a) washing the styrene and divinylbenzene reagent for many times by using NaOH solution and deionized water; (b) putting a proper amount of Span 80 and AIBN into a three-neck flask, adding washed styrene and divinylbenzene, gradually and slowly adding 60-80ml of deionized water into the three-neck flask by using a liquid conveying pipe with stirring, wherein the dropping time of the deionized water is 2-3h, adding carbon nano tubes after the dropping of the deionized water is finished, and continuously stirring for 3-4h to obtain an off-white emulsion; (c) filling the grey emulsion into a test tube with the caliber of 4-6cm, sealing, drying and polymerizing for 18h to obtain the grey rod-shaped polystyrene doped with the carbon nano tube, and then drying by cold air.

3. The method of claim 2, wherein the carbon nanotubes are previously passed through 100. ang^oC, refluxing with mixed acid for 5H, wherein the mixed acid is 98wt.% of H in a volume ratio of 2.5:1₂SO₄And 65% -67wt.% of HNO₃And (4) mixing acid.

4. The method according to claim 1, wherein the step (2) comprises the steps of: (a) weighing 2.5g of pseudoboehmite, adding the pseudoboehmite into 40mL of deionized water in batches under the stirring condition, stirring vigorously for 2 hours, and then adding 1.5 mol/LHNO₃Continuously stirring the generated semitransparent alumina hydrosol for 7 hours; (b) placing the carbon nanotube-doped polystyrene obtained in the step (1) in alumina hydrosol, vacuumizing and filling for 1.5h by using a vacuum water pump, and then 75^oAnd C, drying in an oven, repeatedly filling and drying for 5 times.

5. The method according to claim 1, wherein the step (3) comprises the steps of: under the inert atmosphere condition of nitrogen protection at 600 DEG^oC, roasting for 24 hours.

6. The method of claim 1, wherein the Au — Cu plating solution of the step (4) comprises: 5-9g/L KCN, 0.5-1g/L Au (CN)2K, 1.5-3g/L Cu (CN)2K, 3-7g/LEDTA-2Na and the balance of deionized water, and adjusting the pH to be 9.8 +/-0.1 by using ammonia water.

7. The method of claim 1, wherein the Au — Cu plating solution of the step (5) comprises: forward pulse current density of 0.1-0.5A/dm²Duty ratio of 30%, negative pulse current density of 0.1-0.5A/dm2, duty ratio of 50%, and temperature of 40%^oC, when1-3min, magnetic stirring at 200-.

8. The method of claim 1, wherein the alloy Au-Cu alloy/carbon nanotube-alumina catalyst is at 320%^oC, space velocity 30000mL^.g^-1h^-1The conversion of propylene was 93.3%, the yield of acrolein was 86.0%, the selectivity for acrolein was 91.2%, the selectivity for acrylic acid was 4.7%, and the other was 4.1%.

9. A catalyst for the preparation of acrolein by oxidation of propylene, characterized in that the catalyst is obtained by the preparation process according to any one of claims 1 to 8.

10. The catalyst for preparing acrolein through propylene oxidation according to claim 9, wherein the Au — Cu alloy active component in the catalyst is highly dispersed only in the outer wall of the carbon nanotube.