A catalyst for preparing isoprene in gas phase and preparation method thereof

Abstract

The present invention provides a catalyst for preparing isoprene in gas phase and a preparation method thereof, and belongs to the technical field of catalysts for preparing isoprene in gas phase. The catalyst provided by the present invention comprises a carrier and an active component loaded on the carrier; the active component comprises a Cr element, a Ni element and a P element. The novel CrNiP catalyst with a specific composition and structure designed by the present invention simultaneously adjusts the valence state of the main catalyst and the co-catalyst and performs in-situ modification. The addition of Ni adjusts the valence state of Cr and the acidity of the overall catalyst, improves the catalytic performance of the catalyst, and also reduces the carbon deposition formation of the catalyst under reaction conditions. During use, high conversion rate, selectivity and long service life are taken into account, and the added auxiliary Ni is also environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts for preparing isoprene in gas phase, and relates to a catalyst for preparing isoprene in gas phase and a preparation method thereof, and a method for preparing isoprene in gas phase. Background Art

[0002] Isoprene, also known as 2-methyl-1,3-butadiene, has a conjugated diene structure and is prone to homopolymerization and copolymerization. High-purity isoprene is mainly used to produce isoprene rubber, butyl rubber, thermoplastic elastomer SIS (styrene-isoprene-styrene copolymer), etc. It is also used as an important raw material for the production of fine chemicals, such as spices, vitamins and pesticide intermediates. At present, the acquisition of isoprene in my country's industry mainly relies on fractionation extraction. The advantage of this method is that the raw material cost is low, but due to its extremely low yield, long separation process, and high production cost, as demand increases, the impact of the shale gas revolution on the ethylene industry, the shortage of petroleum resources, and the shortage of materials will become the bottleneck of industrial production of isoprene. Therefore, the research and development of new processes for the synthesis of isoprene monomers is imperative. At present, there are three main methods for the chemical synthesis of isoprene: acetylene-acetone method, isobutylene-formaldehyde two-step method, and isobutylene-formaldehyde one-step method. The acetylene-acetone method uses natural gas as a raw material to crack and produce acetylene, which is then reacted with acetone to produce methyl butenol, which is further dehydrated to produce isoprene. This method has high cost and a long process route, and requires catalytic hydrogenation using precious metals as catalysts. In the isobutylene-formaldehyde two-step method, isobutylene and formaldehyde Prins condense in the presence of an acidic catalyst to produce 4,4-dimethyl-1,3-dioxane (DMD), which is further cracked to produce isoprene, formaldehyde and water. The advantage of this method is that the purity of the isoprene product is high, but due to the many reaction steps and long process, the energy consumption is high, there are many by-products, and the pollution is serious. Therefore, the one-step synthesis of isoprene from isobutylene and formaldehyde is very attractive. This method has a short process, low cost, easy separation, good selectivity, and is considered to be the technology with the most industrial prospects.

[0003] The one-step method of preparing isoprene from olefins is a typical acid-catalyzed reaction, which requires appropriate acidity for catalytic reaction. Generally, weak acid or medium-strong acid is used. Strong acid will cause olefin polymerization and make the reaction difficult to proceed. Therefore, most of the research on catalysts for this reaction is focused on solid acid systems, such as molecular sieves, heteropoly acids, phosphates, etc. VL Sushkevich used Cs to exchange silicotungstic acid catalysts, and 2.5Cs-STA had the best activity, with an isoprene yield of 68.3% and a selectivity of 71.3%; they also used amorphous silica as a carrier, H3PW 12 O 40The catalyst with a content of 20% had the best catalytic effect, with an isoprene yield of 48% and a selectivity of 63%. However, the active components of the heteropolyacid catalyst will continue to be lost during the reaction, and the catalyst life is short. Dang Zhongyuan et al. studied Sb x O y / SiO2 catalyst was used in the one-step preparation of isoprene from enal. It was found that when the Sb loading was 3%, the optimal yield of isoprene was 45.8% and the selectivity was 71%. VLSushkevich's research team prepared a series of BP, AlP, TiP, ZrP, and NbP phosphate catalysts by different methods. When the reaction temperature was 573K and the enal ratio was 7, the selectivity of isoprene was 62.6% and the conversion rate of formaldehyde was 91.1% using NbP catalyst. The by-products of the reaction are mainly carbon monoxide and hydrogen produced by the decomposition of formaldehyde, and the preparation process may cause pollution to the environment. The transition metal phosphate system is represented by chromium-phosphorus catalysts, which are relatively early catalysts and the research is relatively comprehensive and complete. Chromium-phosphorus catalysts have good stability, but the side reactions are fierce and the selectivity is relatively poor.

[0004] Among the various catalysts used in existing research, although some catalysts have obvious effects, there are still the following problems: either the catalyst life is short, or the catalyst is difficult to achieve both high conversion rate and high selectivity, or the process flow is relatively complicated.

[0005] Therefore, how to find a more suitable catalyst for the gas-phase preparation of isoprene and solve the above-mentioned problems of existing catalysts has become one of the focuses of widespread attention of forward-looking researchers in the industry. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a catalyst for preparing isoprene in gas phase and a preparation method thereof, and a method for preparing isoprene in gas phase. The present invention provides a novel CrNiP catalyst, the addition of Ni adjusts the valence state of Cr and the acidity of the overall catalyst, improves the catalytic performance of the catalyst, and the preparation method is simple, the operability is strong, and there is a prospect for large-scale synthesis.

[0007] The present invention provides a catalyst for preparing isoprene in gas phase, the catalyst comprising a carrier and an active component loaded on the carrier;

[0008] The active components include Cr element, Ni element and P element.

[0009] Preferably, the valence state of the Cr element is +3 and +6;

[0010] The active component loading of the catalyst is 35% to 50%.

[0011] Preferably, the molar ratio of the Ni element to the Cr element is (0.01-0.06):1;

[0012] Among the Cr elements, the molar content of +3 valence Cr is 32% to 38%;

[0013] In the Cr element, the molar content of Cr with a valence of +6 is 62% to 68%;

[0014] The molar ratio of the P element to the Cr element is 16:(7-10).

[0015] Preferably, the valence state of the P element includes +5;

[0016] The catalyst includes pyrophosphate metal salt and metaphosphate metal salt;

[0017] The support includes silica.

[0018] The present invention also provides a method for preparing a catalyst for gas-phase preparation of isoprene as described in any one of the above technical solutions, comprising the following steps:

[0019] 1) heat-treating the impurity-removed carrier to obtain a pretreated carrier;

[0020] Mixing a Cr source, a P source, a Ni source and water to obtain an active solution;

[0021] 2) mixing the active solution obtained in the above step and the pretreated carrier again and letting it stand to obtain a mixture;

[0022] 3) The catalyst mixture obtained in the above steps is dried and calcined to obtain a catalyst.

[0023] Preferably, the particle size of the carrier is 40-80 mesh;

[0024] The impurity removal step includes pickling and water washing;

[0025] The temperature of the heat treatment is 500-550°C;

[0026] The heat treatment time is 3 to 5 hours.

[0027] Preferably, the Cr source includes CrO3;

[0028] The P source includes H3PO4;

[0029] The Ni source includes Ni(NO3)2·6H2O;

[0030] The re-mixing method includes dropwise addition.

[0031] Preferably, the standing time is 6 to 12 hours;

[0032] The drying is specifically carried out by a two-stage temperature method;

[0033] The calcination temperature is 500-550°C;

[0034] The calcination time is 3 to 5 hours.

[0035] The present invention also provides a method for preparing isoprene by a gas phase process, comprising the following steps:

[0036] Under the action of a catalyst, formaldehyde and isobutylene react to obtain isoprene;

[0037] The catalyst is the catalyst described in any one of the above technical solutions or a catalyst prepared by the preparation method described in any one of the above technical solutions.

[0038] Preferably, the reaction is specifically carried out in a fixed bed continuous reactor, using an inert gas as a reaction carrier gas, and the olefinic ratio of formaldehyde to isobutylene is 4 to 7;

[0039] The reaction temperature is 260-380°C.

[0040] The present invention provides a catalyst for preparing isoprene in gas phase, the catalyst comprising a carrier and an active component loaded on the carrier; the active component comprises Cr element, Ni element and P element. Compared with the prior art, the traditional Cr-P catalyst has good stability, but rapid deactivation, poor cycle performance, and defects such as low formaldehyde conversion rate and isobutylene selectivity when used, and high cost of rare earth element modification. The present invention is based on the Cr-P catalyst with the best stability, relatively complete research and clear mechanism, and adds a new catalyst to improve the problems of poor selectivity and rapid deactivation of the chromium-phosphorus catalyst.

[0041] The present invention particularly designs a novel CrNiP catalyst with a specific composition and structure, and simultaneously adjusts the valence state of the main catalyst and the co-catalyst and performs in-situ modification. The addition of Ni adjusts the valence state of Cr and the acidity of the overall catalyst, improves the catalytic performance of the catalyst, and reduces the carbon deposition of the catalyst under reaction conditions. During use, high conversion rate, selectivity and long service life are taken into account, and the added auxiliary Ni is also environmentally friendly. Moreover, the corresponding preparation method provided by the present invention has simple process, mild conditions, strong operability, and is more convenient for industrial promotion and application.

[0042] Experimental results show that when the CrNiP catalyst (Cr-Ni-P-SiO2) provided by the present invention is used for preparing isoprene by a gas phase method, the reaction yield reaches 70%, while the formaldehyde conversion rate and isobutylene selectivity are higher than 90%, and after 12 regenerations, the reaction yield can still be maintained above 67%. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 XRD diffraction comparison diagram of the CrNiP catalyst prepared by the present invention;

[0044] Figure 2 This is a comparison diagram of the BJH pore size distribution of the CrNiP catalyst prepared in the present invention;

[0045] Figure 3 A comparison diagram of N2 adsorption and desorption curves of the CrNiP catalyst prepared in the present invention;

[0046] Figure 4 This is a NH3-TPD comparison diagram of the CrNiP catalyst prepared by the present invention;

[0047] Figure 5 The Cr 2p XPS broad spectrum comparison diagram of the catalyst prepared in the present invention; wherein, (a) is the Cr 2p XPS broad spectrum diagram of CrP-SiO2, and (b) is the Cr 2p XPS broad spectrum diagram of CrNiP-SiO2 (Ni / Cr=0.03).

[0048] Figure 6 The P 2p XPS broad spectrum comparison diagrams of the catalysts prepared in the present invention; wherein (c) is the P 2p XPS broad spectrum diagram of CrP-SiO2, and (d) is the P 2p XPS broad spectrum diagram of CrNiP-SiO2 (Ni / Cr=0.03). DETAILED DESCRIPTION

[0049] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

[0050] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0051] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure raw materials or raw materials with purity requirements conventional in the field of synthesizing isoprene by the enal liquid phase method.

[0052] All raw materials and process steps of the present invention, their brands or abbreviations are conventional brands or abbreviations in the art, and each brand or abbreviation is clear and definite in the field of its related use. Those skilled in the art can purchase them from the market or prepare them by conventional methods, or implement them with corresponding equipment according to the brands, abbreviations and corresponding uses.

[0053] The present invention provides a catalyst for preparing isoprene in gas phase, the catalyst comprising a carrier and an active component loaded on the carrier;

[0054] The active components include Cr element, Ni element and P element.

[0055] In the present invention, the valence state of the Cr element is preferably +3 and +6.

[0056] In the present invention, the active component loading of the catalyst is preferably 35% to 50%, more preferably 37% to 48%, and more preferably 40% to 45%.

[0057] In the present invention, the molar ratio of the Ni element to the Cr element is preferably (0.01-0.06):1, more preferably (0.02-0.05):1, and more preferably (0.03-0.04):1. Specifically, the optimal ratio is 0.03:1.

[0058] In the present invention, the molar content of Cr with a valence of +3 in the Cr element is preferably 32% to 38%, more preferably 33% to 37%, and more preferably 34% to 36%.

[0059] In the present invention, the molar content of Cr with a valence of +6 in the Cr element is preferably 62% to 68%, more preferably 63% to 67%, and more preferably 64% to 66%. Specifically, the Cr with a valence of +6 plays a major catalytic role in the Cr element.

[0060] In the present invention, the molar ratio of the P element to the Cr element is preferably 16:(7-10), more preferably 16:(7.5-9.5), and more preferably 16:(8-9). Specifically, the optimal molar ratio is 16:9.

[0061] In the present invention, the valence state of the P element preferably includes +5.

[0062] In the present invention, the catalyst preferably includes a pyrophosphate metal salt and a metaphosphate metal salt.

[0063] In the present invention, the carrier preferably comprises silicon dioxide. Specifically, the catalyst may be Cr-Ni-P-SiO2.

[0064] The present invention provides a method for preparing a catalyst for gas-phase preparation of isoprene as described in any one of the above technical solutions, comprising the following steps:

[0065] 1) heat-treating the impurity-removed carrier to obtain a pretreated carrier;

[0066] Mixing a Cr source, a P source, a Ni source and water to obtain an active solution;

[0067] 2) mixing the active solution obtained in the above step and the pretreated carrier again and letting it stand to obtain a mixture;

[0068] 3) The catalyst mixture obtained in the above steps is dried and calcined to obtain a catalyst.

[0069] The present invention firstly heat-treats the impurity-removed carrier to obtain a pretreated carrier;

[0070] The Cr source, the P source, the Ni source and water are mixed to obtain an active solution.

[0071] In the present invention, the particle size of the carrier is preferably 40-80 mesh, more preferably 45-75 mesh, more preferably 50-70 mesh, and more preferably 55-65 mesh.

[0072] In the present invention, the impurity removal step preferably includes acid washing and water washing.

[0073] In the present invention, the temperature of the heat treatment is preferably 500-550°C, more preferably 510-540°C, and more preferably 520-530°C.

[0074] In the present invention, the heat treatment time is preferably 3 to 5 hours, more preferably 3.5 to 4.5 hours, or 4 to 5 hours.

[0075] In the present invention, the Cr source preferably includes CrO3.

[0076] In the present invention, the P source preferably includes H3PO4.

[0077] In the present invention, the Ni source preferably includes Ni(NO3)2, and specifically may be Ni(NO3)2·6H2O.

[0078] In the present invention, the active solution obtained in the above step and the pretreated carrier are mixed again and allowed to stand to obtain a mixture.

[0079] In the present invention, the re-mixing method preferably includes dropping.

[0080] In the present invention, the standing time is preferably 6 to 12 hours, more preferably 8 to 12 hours, more preferably 10 to 12 hours, and specifically may be 12 hours (standing overnight).

[0081] In the present invention, the catalyst mixture obtained in the above steps is finally dried and calcined to obtain a catalyst.

[0082] In the present invention, the drying is preferably carried out by a two-stage temperature method.

[0083] In the present invention, the calcination temperature is preferably 500-550°C, more preferably 500-540°C, more preferably 500-530°C, and more preferably 500-520°C.

[0084] In the present invention, the calcination time is preferably 3 to 5 hours, more preferably 3.4 to 4.6 hours, more preferably 3.8 to 4.2 hours, and specifically may be 4 hours.

[0085] The present invention provides a method for preparing isoprene by a gas phase process, comprising the following steps:

[0086] Under the action of a catalyst, formaldehyde and isobutylene react to obtain isoprene;

[0087] The catalyst is the catalyst described in any one of the above technical solutions or a catalyst prepared by the preparation method described in any one of the above technical solutions.

[0088] In the present invention, the reaction is preferably carried out in a fixed bed continuous reactor with an inert gas as a reaction carrier gas, and the olefinic ratio of formaldehyde to isobutylene is preferably 4-7, more preferably 4.5-6.5, and more preferably 5-6.

[0089] In the present invention, the reaction temperature is preferably 260-380°C, more preferably 280-360°C, and more preferably 300-340°C.

[0090] The present invention is to complete and refine the overall technical solution, better ensure the composition and structure of the catalyst, and further improve the catalytic performance of the catalyst. The above-mentioned catalyst for preparing isoprene in gas phase and its preparation method, and a method for preparing isoprene in gas phase may specifically include the following contents:

[0091] a) Soak the carrier SiO2 (40-80 mesh) particles in dilute nitric acid for 24 hours to remove acid-soluble impurities, then wash with water, dry at 100°C after suction filtration, and calcine at 500°C to obtain the pretreated carrier;

[0092] b) mixing a Cr source, a P source, water and a Ni source to obtain an active solution;

[0093] c) mixing the active solution and dropping it onto the pretreated carrier, and letting it stand for a certain period of time;

[0094] d) Dry the catalyst at 80℃ for 2h, raise the temperature to 120℃ and keep for 3h, and calcine at 500~550℃ for 4h when the catalyst turns dark reddish brown.

[0095] The above content of the present invention provides a catalyst for preparing isoprene in gas phase and a preparation method thereof, and a method for preparing isoprene in gas phase. The present invention particularly designs a novel CrNiP catalyst with a specific composition and structure, and simultaneously adjusts the valence state of the main catalyst and the co-catalyst and in-situ modification. The addition of Ni adjusts the valence state of Cr and the acidity of the overall catalyst, improves the catalytic performance of the catalyst, and also reduces the carbon deposition formation of the catalyst under reaction conditions. During use, high conversion rate and selectivity and a long service life are taken into account, and the added auxiliary Ni is also environmentally friendly. Moreover, the corresponding preparation method provided by the present invention has simple process, mild conditions, strong operability, and is more convenient for industrial promotion and application.

[0096] Experimental results show that when the CrNiP catalyst (Cr-Ni-P-SiO2) provided by the present invention is used for preparing isoprene by a gas phase method, the reaction yield reaches 70%, while the formaldehyde conversion rate and isobutylene selectivity are higher than 90%, and after 12 regenerations, the reaction yield can still be maintained above 67%.

[0097] To further illustrate the present invention, a catalyst for preparing isoprene in gas phase, application of the catalyst for preparing isoprene in gas phase in synthesizing isoprene by enal liquid phase method, and a method for synthesizing isoprene by enal liquid phase method provided by the present invention are described in detail below in conjunction with the examples. However, it should be understood that these examples are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operation processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

[0098] Example 1

[0099] The carrier SiO2 (40-80 mesh) particles were soaked in dilute nitric acid for 24 hours, then washed with water, dried at 100℃ after filtration, and calcined at 500℃ to obtain the pretreated carrier. 14ml H2O was added to a 50ml beaker, 1.2g CrO3 was weighed, and 1.5ml H3PO4 (85%) and 0.1047g Ni(NO3)2·6H2O (Ni:Cr molar ratio = 0.03) were added in sequence after dissolution; then ultrasonic treatment was performed and mixed evenly to obtain an active solution. The above active solution was added dropwise to 10.0g of the pretreated carrier and stirred thoroughly to obtain a catalyst slurry. The catalyst slurry was allowed to stand at room temperature (25℃) for 12h, then dried at 80℃ for 2h, dried at 120h for 3h, and then naturally cooled to room temperature. Then it was transferred to a muffle furnace and heated to 500℃ at 2℃ / min to obtain the catalyst CrNiP-SiO2.

[0100] 1. Characterize and detect the CrNiP-SiO2 catalyst prepared by the present invention.

[0101] 1. XRD analysis of catalyst:

[0102] See also Figure 1 , Figure 1 The XRD diffraction comparison diagram of the CrNiP catalyst prepared by the present invention is shown in the figure. In the XRD diagram, there are CrP-SiO2, NiP-SiO2 and CrNiP-SiO2 (Ni / Cr=0.03).

[0103] Depend on Figure 1 It can be seen that the XRD patterns of the three catalysts are mainly the same, and all have a wide and short SiO2 characteristic diffraction peak package near 2θ = 21.98°. This shows that Cr and Ni in the catalyst prepared by the present invention are evenly distributed on the carrier.

[0104] 2. Specific surface area, pore volume and pore size test of catalyst:

[0105] The catalyst obtained in the example was subjected to a BET test to measure characteristics such as the specific surface area and pore size of the catalyst.

[0106] See also Figure 2 , Figure 2 This is a comparison diagram of the BJH pore size distribution of the CrNiP catalyst prepared in the present invention. Figure 2 Figure 3 is the BJH pore size distribution diagram of CrP-SiO2 and CrNiP-SiO2 (Ni / Cr=0.03).

[0107] See also Figure 3 , Figure 3 It is a comparison diagram of N2 adsorption and desorption curves of the CrNiP catalyst prepared in the present invention. Figure 3The following are the N2 adsorption-desorption curves of CrP-SiO2 and CrNiP-SiO2 (Ni / Cr=0.03).

[0108] See Table 1.

[0109] Table 1 Specific surface area, pore volume and pore diameter of catalysts

[0110]

[0111] It can be seen that after adding Ni, the specific surface area and pore volume of the catalyst did not change significantly. The addition of Ni did not change the structure of the CrP catalyst itself and maintained the original pore properties.

[0112] 3. TPD test of catalyst acidity:

[0113] The catalysts obtained in the examples were subjected to TPD tests (NH3-TPD) to characterize the surface acidity of the catalysts (indicating information such as the surface acidity, acid strength, and acidity of the catalysts). The results are as follows: Figure 4 As shown, Figure 4 This is a NH3-TPD comparison chart of the CrNiP catalyst prepared in the present invention. Figure 4 Figure 3 shows the NH3-TPD diagram of CrP-SiO2 and CrNiP-SiO2 (Ni / Cr=0.03).

[0114] Depend on Figure 4 It can be seen that the addition of additive Ni can significantly change the acid amount, acid strength and acid distribution of the catalyst. After adding Ni, the strong acid sites are significantly reduced, and the medium-strong acid sites are increased.

[0115] 4. XPS test of catalyst:

[0116] See also Figure 5 , Figure 5 This is a comparison chart of Cr 2p XPS broad spectra of the catalysts prepared in the present invention. Figure 5 (a) is the Cr 2p XPS broad spectrum of CrP-SiO2, and (b) is the Cr 2p XPS broad spectrum of CrNiP-SiO2 (Ni / Cr=0.03).

[0117] See also Figure 6 , Figure 6 This is a comparison chart of the P 2p XPS broad spectra of the catalysts prepared in the present invention. Figure 6 (c) is the P 2p XPS broad spectrum of CrP-SiO2, and (d) is the P 2p XPS broad spectrum of CrNiP-SiO2 (Ni / Cr=0.03).

[0118] Figure 5 and Figure 6In the graph, hexavalent Cr is at I, trivalent Cr is at II, and the main forms of P are pentavalent pyrophosphate and metaphosphate.

[0119] 2. Catalyst evaluation:

[0120] Reaction temperature 300~340℃, olefinic aldehyde molar ratio = 6:1, catalyst loading = 1.5 g, contact time = 0.6 s, reaction cycle = 120 min. The gas phase product isoprene is quantified using a TCD detector.

[0121] Example 2

[0122] The carrier SiO2 (40-80 mesh) particles were soaked in dilute nitric acid for 24 hours, then washed with water, dried at 100°C after filtration, and calcined at 500°C to obtain a pretreated carrier. 14ml H2O was added to a 50ml beaker, 1.2g CrO3 was weighed, and 1.5ml H3PO4 (85%) and 0.1047g Ni(NO3)2·6H2O (Ni:Cr molar ratio = 0.03) were added in sequence after dissolution; then ultrasonic treatment was performed and mixed evenly to obtain an active solution. The above active solution was added dropwise to 10.0g of the pretreated carrier and stirred thoroughly to obtain a catalyst slurry. The catalyst slurry was allowed to stand at room temperature (25°C) for 12h, then dried at 80°C for 2h, dried at 120h for 3h, and then naturally cooled to room temperature. Then it was transferred to a muffle furnace and heated to 500°C at 2°C / min to obtain the catalyst CrNiP.

[0123] Catalyst evaluation: reaction temperature = 300 °C, olefinic aldehyde molar ratio = 6:1, catalyst loading = 1.5 g, contact time = 0.6 s, reaction period 120 min.

[0124] Example 3

[0125] The carrier SiO2 (40-80 mesh) particles were soaked in dilute nitric acid for 24 hours, then washed with water, dried at 100℃ after filtration, and calcined at 500℃ to obtain the pretreated carrier. 14ml H2O was added to a 50ml beaker, 1.2g CrO3 was weighed, and 1.5ml H3PO4 (85%) and 0.1047g Ni(NO3)2·6H2O (Ni:Cr molar ratio = 0.03) were added in sequence after dissolution; then ultrasonic treatment was performed and mixed evenly to obtain an active solution. The above active solution was added dropwise to 10.0g of the pretreated carrier and stirred thoroughly to obtain a catalyst slurry. The catalyst slurry was allowed to stand at room temperature (25℃) for 12h, then dried at 80℃ for 2h, dried at 120h for 3h, and then naturally cooled to room temperature. Then it was transferred to a muffle furnace, heated to 500℃ at 2℃ / min, and calcined for 4h to obtain the catalyst CrNiP.

[0126] Catalyst evaluation: reaction temperature = 310 °C, olefinic aldehyde molar ratio = 6:1, catalyst loading = 1.5 g, contact time = 0.6 s, reaction period = 120 min.

[0127] Example 4

[0128] The carrier SiO2 (40-80 mesh) particles were soaked in dilute nitric acid for 24 hours, then washed with water, dried at 100℃ after filtration, and calcined at 500℃ to obtain the pretreated carrier. 14ml H2O was added to a 50ml beaker, 1.2g CrO3 was weighed, and 1.5ml H3PO4 (85%) and 0.1047g Ni(NO3)2·6H2O (Ni:Cr molar ratio = 0.03) were added in sequence after dissolution; then ultrasonic treatment was performed and mixed evenly to obtain an active solution. The above active solution was added dropwise to 10.0g of the pretreated carrier and stirred thoroughly to obtain a catalyst slurry. The catalyst slurry was allowed to stand at room temperature (25℃) for 12h, then dried at 80℃ for 2h, dried at 120h for 3h, and then naturally cooled to room temperature. Then it was transferred to a muffle furnace, heated to 500℃ at 2℃ / min, and calcined for 4h to obtain the catalyst CrNiP.

[0129] Catalyst evaluation: reaction temperature = 320 °C, olefinic aldehyde molar ratio = 6:1, catalyst loading = 1.5 g, contact time = 0.6 s, reaction period = 120 min.

[0130] Example 5

[0131] The carrier SiO2 (40-80 mesh) particles were soaked in dilute nitric acid for 24 hours, then washed with water, dried at 100℃ after filtration, and calcined at 500℃ to obtain the pretreated carrier. 14ml H2O was added to a 50ml beaker, 1.2g CrO3 was weighed, and 1.5ml H3PO4 (85%) and 0.1047g Ni(NO3)2·6H2O (Ni:Cr molar ratio = 0.03) were added in sequence after dissolution; then ultrasonic treatment was performed and mixed evenly to obtain an active solution. The above active solution was added dropwise to 10.0g of the pretreated carrier and stirred thoroughly to obtain a catalyst slurry. The catalyst slurry was allowed to stand at room temperature (25℃) for 12h, then dried at 80℃ for 2h, dried at 120h for 3h, and then naturally cooled to room temperature. Then it was transferred to a muffle furnace, heated to 500℃ at 2℃ / min, and calcined for 4h to obtain the catalyst CrNiP.

[0132] Catalyst evaluation: reaction temperature = 330 °C, olefinic aldehyde molar ratio = 6:1, catalyst loading = 1.5 g, contact time = 0.6 s, reaction period = 120 min.

[0133] Example 6

[0134] The carrier SiO2 (40-80 mesh) particles were soaked in dilute nitric acid for 24 hours, then washed with water, dried at 100℃ after filtration, and calcined at 500℃ to obtain the pretreated carrier. 14ml H2O was added to a 50ml beaker, 1.2g CrO3 was weighed, and 1.5ml H3PO4 (85%) and 0.1047g Ni(NO3)2·6H2O (Ni:Cr molar ratio = 0.03) were added in sequence after dissolution; then ultrasonic treatment was performed and mixed evenly to obtain an active solution. The above active solution was added dropwise to 10.0g of the pretreated carrier and stirred thoroughly to obtain a catalyst slurry. The catalyst slurry was allowed to stand at room temperature (25℃) for 12h, then dried at 80℃ for 2h, dried at 120h for 3h, and then naturally cooled to room temperature. Then it was transferred to a muffle furnace, heated to 500℃ at 2℃ / min, and calcined for 4h to obtain the catalyst CrNiP.

[0135] Catalyst evaluation: reaction temperature = 340 °C, olefinic aldehyde molar ratio = 6:1, catalyst loading = 1.5 g, contact time = 0.6 s, reaction period = 120 min.

[0136] Example 7

[0137] Catalytic effect test

[0138] Catalytic synthesis experiment: 1.5g of catalyst was weighed and placed in the catalyst bed of a normal pressure continuous flow fixed bed reactor, the temperature inside the tube was 320℃, and the N2 flow rate was maintained at 20mL / min for catalyst activation for 2h. Isobutylene gas and formaldehyde aqueous solution (mass concentration 37%) were introduced separately, the isobutylene feed rate was 90mL / min, the olefinic aldehyde molar ratio was maintained at 6, and the reaction temperature was maintained at 320℃ to catalyze the synthesis of isoprene. After the above catalytic reaction was completed, the conversion rate, selectivity and yield of product isoprene based on formaldehyde of the two raw materials were tested.

[0139] The catalysts obtained in Examples 2 to 6 were subjected to the above catalytic synthesis experiments, and the results are shown in Table 2.

[0140] Table 2 Catalytic effects of the catalysts obtained in Examples 2 to 6 of the present invention

[0141]

[0142] Catalyst regeneration stability test

[0143] The catalyst of Example 2 was subjected to a catalytic synthesis experiment according to the second item of the preceding text, and the experiment was continued for 120 min. During the experiment, the product yield (product yield in terms of formaldehyde) was monitored, which was recorded as the first use effect (Fresh). Afterwards, the used catalyst was regenerated (regeneration method: placed in a muffle furnace, heated to 500 ° C at 2 ° C / min, and roasted for 4 h), and the catalytic synthesis experiment was performed again, and the experiment was continued for 120 min. During the experiment, the product yield was monitored, which was recorded as the first cycle use effect (1st). Then, the catalyst was regenerated in situ, and the catalytic synthesis experiment was performed again, and the experiment was continued for 120 min. During the experiment, the product yield was monitored, which was recorded as the second cycle use effect (2nd). The test results of the 12 cycles are shown in Table 3.

[0144] Table 3 Catalyst regeneration stability test results

[0145]

[0146] Example 8

[0147] Catalyst comparison experiment

[0148] The catalytic synthesis experimental conditions were the same as those in Example 7, and the catalyst evaluation conditions were the evaluation conditions in Example 4, T=320°C, and the olefinic aldehyde molar ratio was 6:1.

[0149] In the following table, FA is formaldehyde, IB is isobutylene, C is conversion, S is selectivity, and Y is yield.

[0150] See Table 4.

[0151] Table 4 Catalytic performance data of single metal phosphate active component

[0152]

[0153] See Table 5.

[0154] Table 5 Catalytic performance data of polymetallic phosphate active components

[0155]

[0156] Adjust the olefinic aldehyde ratio to compare the catalyst activity:

[0157] See Table 6.

[0158] Table 6 Comparative experimental data of the specific activity of olefins of the catalysts prepared by the present invention

[0159]

[0160] Test conditions: T = 320 ° C, the test catalyst is CrNiP-SiO2 (Ni / Cr molar ratio is 0.03).

[0161] Comparison of catalyst temperature activity:

[0162] See Table 7.

[0163] Table 7 Experimental data of temperature activity of the catalyst prepared by the present invention

[0164]

[0165] Comparison of Ni / Cr specific activity of catalysts:

[0166] See Table 8.

[0167] Table 8 Comparative experimental data of Ni / Cr specific activity of catalysts prepared by the present invention

[0168]

[0169] Among them, 1 represents the Ni / Cr molar ratio of 0.01:1, 2 represents the Ni / Cr molar ratio of 0.02:1, and so on.

[0170] Compared with existing catalysts:

[0171] See Table 9.

[0172] Table 9 Comparative experimental data of catalytic performance of the catalyst prepared by the present invention and the existing catalyst

[0173]

[0174] Among them, the temperature and olefin aldehyde molar ratio in 1 to 14 are the optimal temperature and olefin aldehyde molar ratio in the corresponding literature, and 15 is the catalyst prepared by the present invention. The above data are selected as the maximum value in the experimental process.

[0175] Catalysts 1 to 14 are catalysts in the current research progress in the field of catalysts for preparing isoprene by one-step gas phase enal process, as shown below:

[0176] Catalyst 1: Work by Xu Shan et al.: Study on heteropolyacid-based catalysts with high activity and reusability for isoprene synthesis from formaldehyde andisobutene.

[0177] Catalysts 2, 3: Work by VL Sushkevich et al.: Synthesis of isoprene from formaldehyde and isobutene over phosphate catalysts.

[0178] Catalyst 4: Work by Qi Yanlong et al.: Assembly line synthesis of isoprene from formaldehyde and isobutene over SiO2-supported MoP catalysts with active deposited carbon.

[0179] Catalyst 5: Work by Xu Shan et al.: The dimensions of different copper species on Cu / SiO2 catalysts in the one-step condensation of isoprene via formaldehyde andisobutene.

[0180] Catalyst 6: M. Ai et al. work: The formation of isoprene by means of a vapor-phase Prins reaction between formaldehyde and isobutene.

[0181] Catalyst 7: I. Ivanova et al.: Catalysis by coke deposits: Synthesis of isoprene over solid catalysts.

[0182] Catalyst 8: Work by Xu Shan et al.: Insight into the Efect of Acid Sites on the Catalytic Performance of HZSM-5 During the One-Step Preparation of Isoprene by Formaldehyde and Isobutene.

[0183] Catalyst 9, 10: Dang Zhongyuan et al.: Vapor-phase synthesis of isoprene from formaldehyde and isobutylene over CuSO4−MO x / SiO2 catalysts.

[0184] Catalyst 11: VL Sushkevich et al.: Prins condensation for the synthesis of isoprene from isobutylene and formaldehyde over sillicasupported H3SiW 12 O 40 catalysts.

[0185] Catalyst 12: Work by Yu Xue et al.: Isoprene synthesis from formaldehyde andisobutene over Keggin-type heteropolyacids supported on silica.

[0186] Catalyst 13: Yu Xue et al.’s work: Effect of Si / Al ratio of high-silica HZSM-5catalysts on the prins condensation of isobutylene and formaldehyde toisoprene.

[0187] Catalyst 14: Work by Yu Xue et al.: Effect of Phosphoric Acid on HZSM-5 Catalystsfor Prins Condensation to Isoprene from Isobutylene and Formaldehyde.

[0188] The above is a detailed introduction to a catalyst for preparing isoprene in gas phase, an application of the catalyst for preparing isoprene in gas phase in synthesizing isoprene by olefinic aldehyde liquid phase method, and a method for synthesizing isoprene by olefinic aldehyde liquid phase method provided by the present invention. Specific examples are used herein to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present invention, including the best mode, and also enables any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims, and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements that are not different from the textual expression of the claims, or if they include equivalent structural elements that are not substantially different from the textual expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A catalyst for preparing isoprene in the gas phase, characterized in that: The catalyst comprises a carrier and an active component loaded on the carrier; The active components include Cr element, Ni element and P element; The molar ratio of the Ni element to the Cr element is (0.02-0.04):1; The valence state of the Cr element is +3 and +6; Among the Cr elements, the molar content of +3 valence Cr is 32% to 38%; In the Cr element, the molar content of Cr with a valence of +6 is 62% to 68%; The molar ratio of the P element to the Cr element is 16:(7-10); The valence state of the P element includes +5; The catalyst includes pyrophosphate metal salt and metaphosphate metal salt; The carrier comprises silicon dioxide; The method for preparing the catalyst comprises the following steps: 1) heat-treating the impurity-removed carrier to obtain a pretreated carrier; Mixing a Cr source, a P source, a Ni source and water to obtain an active solution; 2) mixing the active solution obtained in the above step and the pretreated carrier again and letting it stand to obtain a mixture; 3) drying and calcining the catalyst mixture obtained in the above steps to obtain a catalyst; The calcination temperature is 500-550°C.

2. The catalyst according to claim 1, characterized in that The active component loading of the catalyst is 35% to 50%.

3. The catalyst according to claim 1, characterized in that The particle size of the carrier is 40-80 meshes.

4. The catalyst according to claim 1, characterized in that The impurity removal step includes acid washing and water washing.

5. The catalyst according to claim 1, characterized in that The temperature of the heat treatment is 500-550°C; The heat treatment time is 3 to 5 hours.

6. The catalyst according to claim 1, characterized in that The Cr source includes CrO3; The P source includes H3PO4.

7. The catalyst according to claim 1, characterized in that The Ni source includes Ni(NO3)2·6H2O; The re-mixing method includes dropwise addition.

8. The catalyst according to claim 1, characterized in that The standing time is 6 to 12 hours; The drying is specifically carried out by a two-stage temperature method; The calcination time is 3 to 5 hours.

9. A method for preparing isoprene by a gas phase process, characterized in that: The following steps are involved: Under the action of a catalyst, formaldehyde and isobutylene react to obtain isoprene; The catalyst is the catalyst according to any one of claims 1 to 8.

10. The method according to claim 9, characterized in that The reaction is specifically carried out in a fixed bed continuous reactor, using an inert gas as a reaction carrier gas, and the olefinic aldehyde ratio of formaldehyde to isobutylene is 4 to 7; The reaction temperature is 260-380°C.

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