Method for preparing methacrolein and methacrylic acid

Abstract

The present invention relates to the technical field of production of methacrolein and methacrylic acid, and discloses a method for preparing methacrolein and methacrylic acid. The method comprises: contacting a raw material containing isobutylene or tert-butyl alcohol with a first molybdenum bismuth catalyst and a second molybdenum bismuth catalyst in sequence; wherein the selectivity of the first molybdenum bismuth catalyst is higher than that of the second molybdenum bismuth catalyst, and the conversion rate of the second molybdenum bismuth catalyst is higher than that of the first molybdenum bismuth catalyst. The method of the present invention can improve the conversion rate of isobutylene or tert-butyl alcohol and the selectivity of methacrolein and methacrylic acid.

Description

Technical Field

[0001] The invention relates to the technical field of production of methacrolein and methacrylic acid, and in particular to a method for preparing methacrolein and methacrylic acid. Background Art

[0002] Methacrolein (MAL) and methacrylic acid (MAA) are basic organic chemical raw materials. As organic chemical intermediates, they are mainly used to produce organic glass. In addition, they can also be used in the manufacture of functional materials such as resins, coatings, adhesives and lubricants. They are widely used. Among them, methyl methacrylate (MMA) obtained by further reaction of methacrolein / methacrylic acid is an important acrylic resin monomer and an important organic chemical intermediate. It is a raw material for producing organic glass and synthesizing higher methacrylic acid esters. At present, the industrial production of MMA mainly adopts the acetone cyanohydrin method (ACH method), ethylene carbonylation method and isobutylene (tert-butyl alcohol) catalytic oxidation method. The raw material hydrocyanic acid of the ACH method is highly toxic and has low atomic utilization rate. Highly corrosive sulfuric acid and caustic soda are used in the reaction process, and the equipment is severely corroded; the production cost of the ethylene carbonylation method is high, and it needs to be combined with ethylene production to be competitive; the isobutylene (or tert-butyl alcohol) oxidation method has sufficient raw material sources, water as a by-product, high process atomic utilization rate, and can optimize the use of C4 resources. It has strong advantages in terms of economy, environmental protection and raw material utilization.

[0003] There are generally two process routes for producing MMA by isobutylene / tert-butyl alcohol oxidation: one is to oxidize isobutylene / tert-butyl alcohol to obtain MAL, then oxidize to obtain MAA, and finally esterify to produce MMA. The other is to oxidize isobutylene / tert-butyl alcohol to prepare MAL, and then directly oxidize and esterify with methanol to produce MMA. Regardless of the route, the conversion rate of isobutylene / tert-butyl alcohol and the selectivity of generating MAL / MAA directly affect the final yield of MMA.

[0004] At present, the catalyst used for the oxidation of isobutylene / tert-butyl alcohol to produce MAL mainly adopts molybdenum-bismuth composite metal oxides. Standard Oil Company, Mitsubishi of Japan, Asahi Kasei of Japan and other companies have successively promoted the application of this catalyst in the oxidation reaction of isobutylene. The catalyst system includes Mo-Bi-P system, Mo-Bi-Fe-Co system and Mo-Bi-W-Fe-Co system, and may also contain As, Sb, Sn, Te, Ce, Ni and other elements. The synergistic effect between the various metals can improve the performance of the catalyst. Since there are two identical methyl groups at the α position of isobutylene and the acidity is strong and side reactions are prone to occur, some alkali metals or alkaline earth metals Cs, Rb, K, Mg, etc. need to be added in the preparation of the catalyst to adjust the acidity of the catalyst and improve the selectivity of MAL. By adjusting the types and proportions of different metal additives, controlling the precipitation conditions of the catalyst preparation process and the conditions of the calcination activation process, the catalyst can finally form phase composition, particle size and specific surface area differences, thereby showing different performance in the oxidation reaction of isobutylene or tert-butyl alcohol.

[0005] The second step of the process of producing methyl methacrylate by oxidation and esterification of isobutylene or tert-butyl alcohol is to further oxidize methacrolein to methacrylic acid. The catalyst used in this reaction is mostly a heteropolyacid or heteropolyacid salt with Keggin structure containing P, Mo, and V. When a large amount of isobutylene remaining in the first oxidation reaction is adsorbed on the catalyst surface, it is easy to cause the catalyst to be deactivated, thereby affecting the final yield of methyl methacrylate. Therefore, in the isobutylene or tert-butyl alcohol oxidation process, the oxidation conversion rate of isobutylene or tert-butyl alcohol is generally required to be greater than 95%.

[0006] Since the selective oxidation reaction of isobutylene or tert-butanol is a typical selective oxidation reaction of low-carbon organic matter, a large amount of heat is released during the reaction process. During the scale-up of the reactor, it is impossible to quickly remove the heat in the reaction tube, resulting in a high catalyst surface temperature, which is not conducive to the long-term stability of the catalyst surface structure and composition. In addition, in a strongly exothermic reaction system, as the catalyst surface temperature increases, the catalyst activity increases, further leading to greater heat release and higher hot spot temperatures. The temperature increase in turn promotes excessive oxidation of isobutylene or tert-butanol methacrolein to generate CO and CO2, reducing the selectivity of the main product.

[0007] CN102211027B discloses a method for preparing a catalyst for the oxidation of isobutylene to methacrolein by simply mixing a catalyst active substance with a carrier or a catalyst with a heat-conducting diluent. The catalyst has no molding process, and the carrier powder and the active substance powder are simply mixed to play more of a role as a heat-conducting diluent. The catalyst activity is low, and it needs to be at a higher reaction temperature of 410-450°C and a space velocity of 800h / min. -1Under the condition of the above, the isobutylene conversion is greater than 95% and the methacrolein selectivity is between 85% and 92%.

[0008] CN101848883A provides a method for improving the yield of methacrolein and / or methacrylic acid. The method uses tert-butyl alcohol or isobutylene as a raw material, partially oxidizes the raw material in the presence of molecular oxygen, and uses an inert substance to dilute the catalyst layer on the raw material inlet side, thereby forming two exothermic peaks on the catalyst bed of the reaction tube, and the minimum value of the temperature between the two exothermic peaks of the oxidation catalyst layer is set to T m , the reaction bath temperature is set to T b , T m -T b ≥15℃, at airspeed 1000h -1 Under the present invention, the isobutylene conversion rate is greater than 99%, and the effective selectivity of methacrolein and methacrylic acid is 84-86%. However, the overall selectivity of methacrolein and methacrylic acid in this method is low. At the same time, since more inert substances are filled in the inlet section to dilute the catalyst layer, the processing capacity of the raw material isobutylene or tert-butanol is limited.

[0009] CN104781221A provides a method for improving the yield of methacrolein and methacrylic acid. In the reaction process, the method starts the reaction at a boundary temperature (TA) lower than the activation energy of the oxidation reaction, controls the conversion rate of the raw material to be constant while increasing the reaction temperature, and ends the reaction at a temperature exceeding TA. The heating rate A (℃ / hour) from the temperature rising to TA and the heating rate B (℃ / hour) from the temperature exceeding TA to the set reaction temperature are controlled, and the ratio of A to B is (A / B)=0.05-0.18. The catalyst can maintain a relatively good conversion rate and oxidation product selectivity under this control condition. The average conversion rate of the raw material is between 95-96%, the average selectivity of methacrolein is between 87-88%, and the average selectivity of methacrylic acid is between 5-6%. However, the process operation is relatively complicated, and the process needs to be controlled to ensure that the early activity of the catalyst does not decrease. At the same time, the conversion rate of the raw material is low, resulting in an overall yield of methacrolein and methacrylic acid of about 87-88%.

[0010] In order to make the final isobutylene or tert-butanol oxidation route to produce methyl methacrylate process more competitive, the catalyst needs to have both high conversion rate and high selectivity. Since there is no tail gas recycling unit in the production process, how to improve the selectivity of methacrolein and methacrylic acid while maximizing the isobutylene single-pass conversion rate is the key to catalyst development. Summary of the invention

[0011] In order to achieve the above object, the present invention provides a method for preparing methacrolein and methacrylic acid, the method comprising: contacting a raw material containing isobutylene or tert-butyl alcohol with a first catalyst and a second catalyst in sequence; wherein the selectivity of the first catalyst is higher than that of the second catalyst, and the conversion rate of the second catalyst is higher than that of the first catalyst;

[0012] The conversion rate is defined as the mole number of isobutylene or tert-butanol consumed divided by the mole number of isobutylene or tert-butanol fed × 100%, and the selectivity is defined as the mole number of methacrolein generated divided by the mole number of isobutylene or tert-butanol consumed × 100%; the conversion rate and selectivity are tested under the conditions of a temperature of 360°C, a pressure of 0.1 MPa, and a reaction time of 48 h.

[0013] Preferably, the first catalyst is a first molybdenum-bismuth catalyst, and the second catalyst is a second molybdenum-bismuth catalyst.

[0014] In the prior art, a single-composition catalyst is generally used to ensure the catalytic effect of the reaction. Due to the high activity of the catalyst, the conversion rate of the reaction raw material isobutylene or tert-butyl alcohol is generally above 95%. Further improving the conversion rate of the reaction will cause the total selectivity of methacrolein and methacrylic acid to be reduced to below 87%. The inventors have found that by contacting isobutylene or tert-butyl alcohol with catalysts of different compositions in succession, isobutylene or tert-butyl alcohol can have a higher conversion rate and improve the selectivity of methacrolein and methacrylic acid. At the same time, the use of a first molybdenum-bismuth catalyst with high selectivity and low activity in the inlet section can reduce the temperature of the upper section bed of the catalyst and ensure the long-term use of the catalyst in the inlet section. At the same time, the use of a second molybdenum-bismuth catalyst with higher activity in the outlet section can further process the unreacted reaction raw materials, give play to the role of the outlet section catalyst, and ensure the improvement of the selectivity of the overall conversion rate.

[0015] By adopting the method provided by the present invention, the selectivity of methacrolein can reach 86-90% and the selectivity of methacrylic acid can reach 2-5% when the conversion rate of isobutylene / tert-butyl alcohol is ensured to be 96-99.2%. Compared with the same catalyst treatment method, by adopting the method of the present invention, the conversion rate of isobutylene or tert-butyl alcohol can be increased by 5.4% at most, the selectivity of methacrolein can be increased by 4.6% at most, and the total selectivity of methacrolein and methacrylic acid can be increased by 4.9% at most. DETAILED DESCRIPTION

[0016] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0017] The present invention provides a method for preparing methacrolein and methacrylic acid, characterized in that the method comprises: contacting a raw material containing isobutylene or tert-butyl alcohol with a first catalyst and a second catalyst in sequence; wherein the selectivity of the first catalyst is higher than that of the second catalyst, and the conversion rate of the second catalyst is higher than that of the first catalyst;

[0018] The conversion rate is defined as the number of moles of isobutylene or tert-butanol consumed divided by the number of moles of isobutylene or tert-butanol fed × 100%, and the selectivity is defined as the number of moles of methacrolein generated divided by the number of moles of isobutylene or tert-butanol consumed × 100%; the conversion rate and selectivity of the first catalyst and the second catalyst are tested under the same conditions.

[0019] Preferably, the first catalyst is a first molybdenum-bismuth catalyst, and the second catalyst is a second molybdenum-bismuth catalyst.

[0020] According to the present invention, preferably, the selectivity of the first molybdenum-bismuth catalyst is 0.1-6.0% higher than the selectivity of the second molybdenum-bismuth catalyst.

[0021] According to the present invention, preferably, the conversion rate of the second molybdenum-bismuth catalyst is 2.0-6.0% higher than the conversion rate of the first molybdenum-bismuth catalyst.

[0022] According to the present invention, preferably, the first molybdenum-bismuth catalyst and the second molybdenum-bismuth catalyst are different; the active component of the first molybdenum-bismuth catalyst comprises the general formula shown in formula (1), and the active component of the second molybdenum-bismuth catalyst comprises the general formula shown in formula (2):

[0023] Mo a Bi b Fe c Co d Mg e A f B g C h Si i O x Formula (1);

[0024] Mo a Bi b’ Fe c Co d’ Mge’ A f B g C h Si i O x Formula (2);

[0025] Wherein, when a=12, b=1.5-4, c=2-10, d=2-4, e=0.5-1, f=0.1-3, g=0.1-3, h=1-4, i=0-2, b'=1-2, d'=4-8, e'=1-2, x is the number of oxygen atoms required to meet the atomic valence requirements of other elements present; A is selected from at least one of K, Rb and Cs, B is selected from B and / or P, and C is selected from at least one of Ni, Er, Nb, Sb, V, In and Ti.

[0026] It should be noted that in formula (1) and formula (2), a, b, c, d, e, f, g, h, i, x, b', d', and e' respectively represent the atomic ratios of the corresponding elements.

[0027] According to the present invention, preferably, the preparation method of the first molybdenum-bismuth catalyst comprises: adjusting the pH value of the mixture containing molybdenum salt, bismuth salt, iron salt, cobalt salt, magnesium salt and silicon source to 3-9, and then performing a first calcination and a second calcination.

[0028] According to the present invention, preferably, the preparation method of the first molybdenum-bismuth catalyst comprises: adding a dispersed phase containing a silicon source and an acid solution II containing a bismuth salt, an iron salt, a cobalt salt and a magnesium salt to a solution I containing a molybdenum salt to obtain a mixture, and adjusting the pH value of the mixture to 3-9, more preferably 3-7; and then performing a first calcination and a second calcination.

[0029] According to the present invention, in order to further improve the selectivity of methacrolein and methacrylic acid, preferably, when preparing the first molybdenum-bismuth catalyst, solution II also contains at least one of a nickel salt, a boron source, a phosphorus source, a cesium salt and a rubidium salt, and the dispersed phase also contains at least one of an antimony source, a titanium source and an erbium source.

[0030] According to the present invention, in order to better adjust the selectivity of the catalyst, preferably, the first calcination conditions include: temperature of 200-300°C, time of 2-4h; the second calcination conditions include: temperature of 400-600°C, time of 1-12h.

[0031] According to the present invention, preferably, the preparation method of the second molybdenum-bismuth catalyst comprises: controlling the pH value of a mixture containing molybdenum salt, bismuth salt, iron salt, cobalt salt, magnesium salt and silicon source to <4, and then performing a third calcination and a fourth calcination.

[0032] According to the present invention, preferably, the preparation method of the second molybdenum-bismuth catalyst comprises: adding a dispersed phase containing a silicon source and an acid solution II containing a bismuth salt, an iron salt, a cobalt salt and a magnesium salt to a solution I containing a molybdenum salt to obtain a mixture, and adjusting the pH value of the mixture to be controlled to <4, more preferably <3; and then performing a third calcination and a fourth calcination.

[0033] According to the present invention, preferably, when preparing the second molybdenum-bismuth catalyst, solution II also contains at least one of nickel salt, boron source, phosphorus source, cesium salt, vanadium salt, indium salt and niobium salt, and the dispersed phase also contains an antimony source.

[0034] According to the present invention, in order to better adjust the activity of the catalyst, preferably, the conditions of the third calcination include: temperature of 200-300°C, time of 2-4h; the conditions of the fourth calcination include: temperature of 400-600°C, time of 1-12h.

[0035] The inventors also found that when preparing the first molybdenum-bismuth catalyst and the second molybdenum-bismuth catalyst, limiting the pH value within different ranges can form different active crystalline phase crystallinity, thereby further affecting the catalyst activity and the selectivity of generating MAL and MAA.

[0036] According to the present invention, the type of acid in the acid solution II is not particularly limited. Preferably, the acid in the acid solution II is at least one of nitric acid, phosphoric acid, sulfuric acid, hydrochloric acid, tartaric acid, and oxalic acid, preferably nitric acid. Further preferably, the nitric acid is added in the form of a solution, and the mass fraction of the nitric acid solution is 10-30% by weight.

[0037] According to the present invention, the amount of nitric acid solution in the acid solution II can be selected within a wide range, but in order to completely dissolve the substances in the acid solution II and avoid precipitation, preferably, the amount of nitric acid solution is 90-200g relative to 100g of molybdenum salt.

[0038] According to the present invention, the molybdenum salt in the solution I containing the molybdenum salt can be obtained by directly dissolving the molybdenum salt in water, or by dissolving oxides or hydroxides containing metallic molybdenum elements in a nitric acid solution.

[0039] In the present invention, during the first calcination process, the nitrate begins to decompose in large quantities at 240-270°C, and the metal cations present therein react with MoO3 in a solid phase to form a β-CoMoO4 main crystal phase containing a small amount of α-Bi2Mo3O 12, β-Bi2Mo2O9, γ-Bi2Mo2O6 and other metal-substituted mixed phases such as Fe2(MoO4)3. The main crystal phase β-CoMoO4 can enhance the electron flow and redox efficiency, and rapidly improve the catalyst performance; Fe in the Fe2(MoO4)3 crystal phase 3+ / Fe 2+ The redox pair can accept electrons in the reaction process, effectively improving the conversion rate of isobutylene; in addition, the presence of other metals or through doping can adjust the acidity of the composite metal oxide catalyst, change the adsorption strength of isobutylene and products, so as to improve the selectivity of methacrolein, or stabilize the catalyst structure by forming molybdate compounds with Mo. After the second calcination stage, the crystallinity of the main crystal phase β-CoMoO4 is improved, and the crystallinity of some mixed phases is changed, thereby playing a role in adjusting the activity and selectivity of the catalyst.

[0040] According to a preferred embodiment of the present invention, when preparing the first molybdenum-bismuth catalyst or the second molybdenum-bismuth catalyst, if the acid solution II is first added to the solution I, the molybdenum salt will precipitate under acidic conditions to generate molybdenum trioxide, resulting in uneven distribution of molybdenum trioxide in the catalyst (solid solution). Therefore, when preparing the first molybdenum-bismuth catalyst or the second molybdenum-bismuth catalyst, the dispersed phase is first added to the solution I, and after the molybdenum salt and the dispersed phase are evenly mixed, the acid solution II is added.

[0041] According to the present invention, in order to make the distribution of each active component in the catalyst more uniform, preferably, the addition rate is 1-10 mL / min, preferably 4-6 mL / min.

[0042] According to the present invention, the pH adjusting agent used in the process of adjusting the pH value of the mixture is not particularly limited, and can be an alkaline substance commonly used in the art. Preferably, the pH adjusting agent used in the process of adjusting the pH value of the mixture is at least one of ammonia, urea, ammonium carbonate, ammonium bicarbonate, ammonium hydrogen phosphate, and ammonium dihydrogen phosphate. Further preferably, the pH adjusting agent is added in the form of an aqueous solution, more preferably ammonia water.

[0043] According to the present invention, the concentration of the ammonia water is not particularly limited. Preferably, the mass fraction of the ammonia water is 2-25% by weight.

[0044] According to the present invention, the amount of the aqueous ammonia used is not particularly limited, as long as it can ensure that the pH of the mixture is within a specified range.

[0045] According to the present invention, the solvent in the solution I containing a molybdenum salt is not particularly limited. Preferably, the solvent in the solution I containing a molybdenum salt is water.

[0046] According to the present invention, the solvent of the dispersed phase is not particularly limited. In order to improve the dispersibility of the silicon source, preferably, the solvent of the dispersed phase is a hydrophilic organic solvent. Further preferably, the solvent of the dispersed phase is at least one of methanol, ethanol, propanol, formamide, N,N-dimethylformamide, pyrrolidone, and dimethyl sulfoxide, more preferably ethanol.

[0047] According to the present invention, the type of the molybdenum salt is not particularly limited. Preferably, the molybdenum salt is at least one of ammonium molybdate, molybdenum nitrate, molybdenum sulfate, molybdenum chloride, molybdenum acetate, molybdenum oxalate, and sodium molybdate.

[0048] According to the present invention, the type of the bismuth salt is not particularly limited. Preferably, the bismuth salt is at least one of bismuth nitrate, bismuth sulfate, bismuth chloride, bismuth acetate, bismuth oxalate, and bismuth phosphate.

[0049] According to the present invention, the type of the iron salt is not particularly limited. Preferably, the iron salt is at least one of ferric nitrate, ferric sulfate, ferric chloride, ferric acetate, ferric oxalate, and ferric phosphate.

[0050] According to the present invention, the type of the cobalt salt is not particularly limited. Preferably, the cobalt salt is at least one of cobalt nitrate, cobalt sulfate, cobalt chloride, cobalt acetate, cobalt oxalate, cobalt phosphate, and cobalt carbonate.

[0051] According to the present invention, the type of the magnesium salt is not particularly limited. Preferably, the magnesium salt is at least one of magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium acetate, magnesium oxalate, magnesium phosphate, and magnesium carbonate.

[0052] According to the present invention, the type of the silicon source is not particularly limited. Preferably, the silicon source is soluble silicate and / or silicon dioxide.

[0053] According to the present invention, the type of silica is not particularly limited. Preferably, the silica is amorphous silica particles and / or silica microspheres. More preferably, the amorphous silica particles have a particle size of 50-200 μm, and the silica microspheres have a particle size of 200-1000 nm.

[0054] According to the present invention, the type of the soluble silicate is not particularly limited. Preferably, the soluble silicate is at least one of ethyl silicate, methyl silicate and propyl silicate.

[0055] According to the present invention, the type of the nickel salt is not particularly limited. Preferably, the nickel salt is at least one of nickel nitrate, nickel sulfate, nickel chloride, nickel acetate, nickel oxalate, nickel phosphate, and nickel carbonate.

[0056] According to the present invention, the type of the boron source is not particularly limited. Preferably, the boron source is at least one of boric acid, borate, and metaborate.

[0057] According to the present invention, the type of the antimony source is not particularly limited. Preferably, the antimony source is at least one of antimony trioxide, antimony acetate, and antimony meta-orthoate.

[0058] According to the present invention, the type of the phosphorus source is not particularly limited. Preferably, the phosphorus source is at least one of phosphorus pentoxide, orthophosphoric acid, and pyrophosphoric acid.

[0059] According to the present invention, the type of the cesium salt is not particularly limited. Preferably, the cesium salt is at least one of cesium nitrate, cesium sulfate, cesium chloride, cesium acetate, cesium oxalate, cesium phosphate, and cesium carbonate.

[0060] According to the present invention, the type of the rubidium salt is not particularly limited. Preferably, the rubidium salt is at least one of rubidium nitrate, rubidium sulfate, rubidium chloride, rubidium acetate, rubidium oxalate, rubidium phosphate, and rubidium carbonate.

[0061] According to the present invention, the type of the titanium source is not particularly limited. Preferably, the titanium source is at least one of titanium dioxide and tetrabutyl titanate.

[0062] According to the present invention, the type of the erbium source is not particularly limited. Preferably, the erbium source is at least one of erbium oxide and erbium hydroxide.

[0063] According to the present invention, the type of the vanadium salt is not particularly limited. Preferably, the vanadium salt is at least one of ammonium metavanadate, vanadoyl nitrate, vanadium chloride, vanadyl oxalate, and vanadate.

[0064] According to the present invention, the type of the indium salt is not particularly limited. Preferably, the indium salt is at least one of indium acetate, indium nitrate, indium sulfate, indium chloride, indium oxalate, and indium oxide.

[0065] According to the present invention, the type of the niobium salt is not particularly limited. Preferably, the niobium salt is at least one of niobium oxalate, niobium nitrate, niobium sulfate, niobium chloride and niobium acetate.

[0066] According to the present invention, in the preparation process of the first molybdenum-bismuth catalyst, the amount of each material can be selected in a wide range, but in order to improve the selectivity of methacrolein and methacrylic acid, preferably, the amount of each material is such that the first molybdenum-bismuth catalyst has the general formula shown in formula (1); further preferably, relative to 100g of molybdenum salt, the amount of the bismuth salt is 30-100g, the amount of the iron salt is 20-60g, the amount of the cobalt salt is 20-60g, the amount of the magnesium salt is 5-20g, the amount of the silicon source is 4-10g, the amount of the nickel salt is 10-20g, the amount of the boron source is 3-10g, the amount of the antimony source is 3-10g, the amount of the phosphorus source is 0-2g, the amount of the cesium salt is 0-6g, the amount of the rubidium salt is 0-3g, the amount of the titanium source is 0-1g, and the amount of the erbium source is 0-1g.

[0067] According to the present invention, in the preparation process of the second molybdenum-bismuth catalyst, the amount of each material can be selected in a wide range, but in order to improve the conversion rate of isobutylene or tert-butyl alcohol, preferably, the amount of each material is such that the second molybdenum-bismuth catalyst has the general formula shown in formula (2); further preferably, relative to 100g of molybdenum salt, the amount of the bismuth salt is 20-50g, the amount of the iron salt is 20-40g, and the amount of the cobalt salt is 50-110g, The amount of the magnesium salt is 14-25g, the amount of the silicon source is 4-15g, the amount of the nickel salt is 10-15g, the amount of the boron source is 4-10g, the amount of the antimony source is 4-7g, the amount of the phosphorus source is 0-1g, the amount of the cesium salt is 3-6g, the amount of the titanium source is 0-1g, the amount of the vanadium salt is 0-1.5g, the amount of the indium salt is 0-30g, and the amount of the niobium salt is 0-60g.

[0068] According to the present invention, preferably, the preparation method of the first molybdenum bismuth catalyst and / or the second molybdenum bismuth catalyst further comprises: drying before calcination; further preferably, the drying conditions comprise: temperature of 80-120°C and time of 12-24h.

[0069] According to the present invention, preferably, the preparation method of the first molybdenum bismuth catalyst and / or the second molybdenum bismuth catalyst further comprises: aging after adjusting the pH value of the mixture, and further preferably, the aging conditions include: temperature of 50-90°C and time of 0.5-12h.

[0070] In the present invention, the first molybdenum bismuth catalyst and / or the second molybdenum bismuth catalyst can be directly contacted with a raw material containing isobutylene or tert-butanol to prepare methacrolein and methacrylic acid, or the first molybdenum bismuth catalyst and / or the second molybdenum bismuth catalyst can be molded or loaded and then contacted with a raw material containing isobutylene or tert-butanol to prepare methacrolein and methacrylic acid.

[0071] According to the present invention, in order to improve the specific surface area, macropore ratio and strength of the catalyst, preferably, the preparation method of the first molybdenum bismuth catalyst or the second molybdenum bismuth catalyst also includes molding the catalyst: the calcined product is mixed with an inorganic compound and / or an organic binder.

[0072] According to the present invention, preferably, the amount of the inorganic compound used is 0-20 g relative to 100 g of the calcined product.

[0073] According to the present invention, preferably, the amount of the organic binder is 0-10 g relative to 100 g of the calcined product.

[0074] According to the present invention, preferably, the inorganic compound is at least one of graphite, diatomaceous earth and inorganic fiber; more preferably, the inorganic fiber is at least one of glass fiber, ceramic fiber and carbon fiber.

[0075] According to the present invention, preferably, the organic binder is at least one of methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose.

[0076] According to the present invention, the molding method can be selected within a wide range. Preferably, the molding method is tableting and / or extrusion molding. The shape of the catalyst after molding is not particularly limited, for example, it can be spherical, cylindrical, hollow cylindrical, etc.; further preferably, the particle size of the catalyst after molding is 3-6 mm.

[0077] According to the present invention, in order to further reduce the production cost of the catalyst and improve the utilization rate of the catalyst, preferably, the preparation method of the first molybdenum-bismuth catalyst or the second molybdenum-bismuth catalyst further includes loading of the catalyst: the calcined product is loaded on a carrier. There is no special requirement for the loading method, and it can be a loading method commonly used in the art. For example, an impregnation method, a coating method, or a rolling ball method can be used.

[0078] According to the present invention, the type of the carrier is not particularly limited, preferably, the carrier is at least one of silicon dioxide, aluminum oxide, magnesium oxide, titanium dioxide and silicon carbide. The shape of the carrier is not particularly limited, for example, it can be spherical, cylindrical, hollow cylindrical, etc.; further preferably, the particle size of the carrier is 3-6 mm.

[0079] According to the present invention, preferably, the method is carried out in a reactor, and the first molybdenum bismuth catalyst and the second molybdenum bismuth catalyst are loaded in the reactor in the following manner: the first molybdenum bismuth catalyst is loaded in the inlet section of the reactor, and the second molybdenum bismuth catalyst is loaded in the outlet section of the reactor.

[0080] According to the present invention, preferably, in the reactor, the ratio of the packing volume of the first molybdenum-bismuth catalyst to the packing volume of the second molybdenum-bismuth catalyst is 80-20:20-80.

[0081] According to the present invention, preferably, the raw material containing isobutylene or tert-butyl alcohol enters from the inlet section of the reactor. When the reactor is placed vertically, the inlet section can be arranged at the top of the reactor or at the bottom of the reactor.

[0082] According to the present invention, the inventors also found that under the premise of considering the economic efficiency of the synthetic catalyst, the bulk density of the catalyst in the fixed bed reactor directly affects the distribution of the fluid flow in the bed and the pressure drop when flowing through the bed. Maintaining an appropriate bulk density of the catalyst is conducive to the rapid diffusion of the reaction fluid on the catalyst surface, and can also ensure the compressive strength of the catalyst during use. Preferably, the bulk density of the first molybdenum bismuth oxygen catalyst and the second molybdenum bismuth oxygen catalyst after molding or loading is independently 0.7-1.7 g / cm 3 , for example, it can be 0.7 g / cm 3 , 0.75g / cm 3 、0.80g / cm 3 , 0.85g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.35g / cm 3 , 1.4g / cm 3 , 1.45g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 And any value therebetween, preferably 0.9-1.5 g / cm 3 .

[0083] According to the present invention, in order to reduce the overall bed temperature of the catalyst, improve product selectivity, and suppress the hot spot temperature of the bed, an appropriate amount of inorganic diluent can be added and mixed with the first molybdenum bismuth and / or the second molybdenum bismuth catalyst when loading the catalyst. Preferably, the inorganic diluent is at least one of silicon carbide, alumina, silicon dioxide, titanium dioxide and molecular sieves.

[0084] According to the present invention, the contact conditions can be selected within a wide range, but in order to further improve the selectivity of methacrolein and methacrylic acid, preferably, the contact conditions include: temperature of 300-550°C, pressure of 0.01-0.2MPa, reaction time of 1-48h, total volume space velocity of raw materials of 500-3000h -1 The molar ratio of isobutylene: oxygen: water in the raw material is 1: 1-5: 2-6. Alternatively, the contact conditions include: temperature of 300-550°C, pressure of 0.01-0.2 MPa, reaction time of 1-48h, total raw material volume space velocity of 500-3000h -1 The molar ratio of tert-butanol: oxygen: water in the raw material is 1: 1-5: 1-5.

[0085] The present invention will be described in detail below by way of examples. In the following examples,

[0086]

[0087]

[0088]

[0089] The composition of the catalytic product is determined by an online analysis method. The raw gas and tail gas in the reactor are taken out of a branch to the chromatograph for component analysis. The raw materials and products of the oxidation reaction are analyzed and detected by TCD and FID from different gas paths. The analytical instrument is an Agilent 7890b gas chromatograph equipped with three valves and four columns. Among them, the low-boiling point gas is analyzed and detected by TCD, and the reaction raw material hydrocarbon or alcohol enters a capillary chromatographic system and is detected by an FID detector. Standard gases containing N2, CO2, CO and methane are injected through a quantitative tube and analyzed by a TCD detector. The absolute correction factor measured by the methane standard gas is used as a reference, and the average value of the peak area of ​​each substance is obtained by multiple analysis to measure the relative molar correction factor of each substance to methane. Then, benzene is used as a standard substance, and a solution containing benzene and organic products such as acetaldehyde, acetic acid, acrolein and acrylic acid produced by the reaction is prepared. The solution is analyzed by an FID detector, and the average value of the peak area of ​​each substance is taken by multiple injections to calculate the relative correction factor of various organic products to benzene. By calculating the relative correction factor of benzene to methane, the relative correction factor of the side reaction product to benzene is converted into its relative correction factor to methane, all carbon-containing substances are associated with methane, the yield of each substance and the conversion rate of isobutylene / tert-butanol are calculated, and the carbon balance is calculated at the same time. The data used in the following discussion are all data with a carbon balance between 98-102%.

[0090] All raw materials are commercially available products, among which the raw materials containing crystal water have their molecular formulas given in Preparation Example 1, and the remaining raw materials do not contain crystal water.

[0091] Preparation Example 1

[0092] This preparation example is used to illustrate the preparation of the first molybdenum bismuth catalyst.

[0093] 100g of ammonium heptamolybdate ((NH4)6Mo7O 24·4H2O) was dissolved in 200g of deionized water (the temperature of the deionized water was 60°C) to obtain solution I. 34.3g of bismuth nitrate (Bi(NO3)3·5H2O), 38.1g of iron nitrate (Fe(NO3)3·9H2O), 54.9g of cobalt nitrate (Co(NO3)2·6H2O), 3.6g of cesium nitrate, 13.7g of nickel nitrate (Ni(NO3)2·6H2O), 9.7g of magnesium nitrate (Mg(NO3)2·6H2O) and 5.8g of boric acid were dissolved in 184g of dilute nitric acid aqueous solution (the temperature of the dilute nitric acid aqueous solution was 60°C and the mass fraction of nitric acid was 15% by weight) to obtain solution II. 6.9g of antimony pentoxide, 0.4g of titanium dioxide and 7.9g of ethyl silicate were dispersed in 100mL of ethanol to obtain a dispersed phase. Then, the dispersed phase and solution II were added dropwise to solution I in turn at a dropping speed of 5 mL / min to obtain a mixed solution. Then, the pH of the mixed solution was adjusted to 7 with an ammonia solution (the mass fraction of ammonia was 5% by weight), and stirred and aged at 60°C for 4 hours to obtain a slurry. The slurry was dried at 100°C for 24 hours, and the dried product was further calcined at 300°C for 3 hours and at 500°C for 5 hours. The general formula of the active component of the catalyst obtained according to the feed ratio is Mo 12 Bi 1.5 Fe2Co4Ni1Mg 0.8 Sb 0.9 Ti 0.1 Cs 0.4 B2Si 0.8 O x , numbered A1.

[0094] Preparation Example 2-12

[0095] The molybdenum-bismuth catalyst was prepared according to the method of Preparation Example 1, except for the composition and amount of raw materials and the pH value of the mixed solution, as shown in Table 1. The general formula of the active component of the catalyst prepared in Preparation Example 2-12 and the acid content of the catalyst are shown in Table 2.

[0096] Table 1

[0097]

[0098]

[0099] Table 2

[0100]

[0101] Example 1

[0102] Catalyst A1 was loaded at the upper part of the single tube reactor, and the loading height was 80% of the total height of the single tube reactor. Catalyst B1 was loaded at the lower part of the single tube reactor, and the loading height was 20% of the total height of the single tube reactor.

[0103] Example 2

[0104] Catalyst A2 is loaded at the upper part of the single tube reactor, and the loading height is 60% of the total height of the single tube reactor. Catalyst B2 is loaded at the lower part of the single tube reactor, and the loading height is 40% of the total height of the single tube reactor.

[0105] Example 3

[0106] Catalyst A3 is loaded at the upper part of the single tube reactor, and the loading height is 40% of the total height of the single tube reactor. Catalyst B3 is loaded at the lower part of the single tube reactor, and the loading height is 60% of the total height of the single tube reactor.

[0107] Example 4

[0108] Catalyst A4 is loaded at the upper part of the single tube reactor, and the loading height is 40% of the total height of the single tube reactor. Catalyst B4 is loaded at the lower part of the single tube reactor, and the loading height is 60% of the total height of the single tube reactor.

[0109] Example 5

[0110] Catalyst A5 was loaded at the upper part of the single tube reactor, and the loading height was 20% of the total height of the single tube reactor. Catalyst B5 was loaded at the lower part of the single tube reactor, and the loading height was 80% of the total height of the single tube reactor.

[0111] Example 6

[0112] Catalyst A6 was loaded into the upper part of the single tube reactor, and the loading height was 10% of the total height of the single tube reactor. Catalyst B6 was loaded into the lower part of the single tube reactor, and the loading height was 90% of the total height of the single tube reactor.

[0113] Comparative Example 1

[0114] Catalyst A1 was loaded into the upper and lower parts of the single tube reactor.

[0115] Comparative Examples 2-6

[0116] The catalyst was loaded according to the method of Comparative Example 1, except that the catalysts used were catalysts A2-A6 prepared in Preparation Examples 2-6, respectively.

[0117] Comparative Example 7

[0118] Catalyst B1 was loaded into the upper and lower parts of the single tube reactor.

[0119] Comparative Examples 8-12

[0120] The catalyst was loaded according to the method of Comparative Example 7, except that the catalysts used were catalysts B8-B12 prepared in Preparation Examples 8-12, respectively.

[0121] Comparative Example 13

[0122] The catalyst was loaded according to the method of Example 1, except that the catalyst B1 was loaded in the upper part of the single-tube reactor and the catalyst A1 was loaded in the lower part of the single-tube reactor.

[0123] Comparative Example 14

[0124] The catalyst was loaded according to the method of Example 2, except that the catalyst B2 was loaded in the upper part of the single-tube reactor and the catalyst A2 was loaded in the lower part of the single-tube reactor.

[0125] Comparative Example 15

[0126] The catalyst was loaded according to the method of Example 3, except that the catalyst B3 was loaded in the upper part of the single-tube reactor and the catalyst A3 was loaded in the lower part of the single-tube reactor.

[0127] Comparative Example 16

[0128] The catalyst was loaded according to the method of Example 4, except that the catalyst B4 was loaded in the upper part of the single-tube reactor and the catalyst A4 was loaded in the lower part of the single-tube reactor.

[0129] Comparative Example 17

[0130] The catalyst was loaded according to the method of Example 5, except that the catalyst B5 was loaded in the upper part of the single-tube reactor and the catalyst A5 was loaded in the lower part of the single-tube reactor.

[0131] Comparative Example 18

[0132] The catalyst was loaded according to the method of Example 6, except that the catalyst B6 was loaded in the upper part of the single-tube reactor and the catalyst A6 was loaded in the lower part of the single-tube reactor.

[0133] Test Case

[0134] The catalysts loaded in the above examples and comparative examples were evaluated, and the reaction conditions included: temperature of 360°C, pressure of 0.1 MPa, and reaction time of 48 hours. The reaction conditions and catalytic performance are shown in Tables 3 and 4.

[0135] Table 3 Catalytic performance of catalysts in selective oxidation of isobutylene

[0136]

[0137] Table 4 Catalytic performance of catalysts in the selective oxidation reaction of tert-butyl alcohol

[0138]

[0139] It can be seen from the results in Table 3 and Table 4 that the method of loading the first molybdenum bismuth catalyst and the second molybdenum bismuth catalyst in combination of the present invention can ensure that the isobutylene / tert-butyl alcohol conversion rate is 96-99.2%, the selectivity of methacrolein reaches 86-90%, and the selectivity of methacrylic acid reaches 2-5%. Compared with the same catalyst treatment method, the method of the present invention can increase the conversion rate of isobutylene or tert-butyl alcohol by up to 5.4%, the selectivity of methacrolein by up to 4.6%, and the total selectivity of methacrolein and methacrylic acid by up to 4.9%, which has a significantly better effect on improving the yield of isobutylene / tert-butyl alcohol selective oxidation products.

[0140] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing methacrolein and methacrylic acid, characterized in that: The method comprises: contacting a raw material containing isobutylene or tert-butyl alcohol with a first catalyst and a second catalyst in sequence; wherein the selectivity of the first catalyst is higher than that of the second catalyst, and the conversion rate of the second catalyst is higher than that of the first catalyst; The conversion rate is defined as the number of moles of isobutylene or tert-butanol consumed divided by the number of moles of isobutylene or tert-butanol fed × 100%, and the selectivity is defined as the number of moles of methacrolein generated divided by the number of moles of isobutylene or tert-butanol consumed × 100%; the conversion rate and selectivity of the first catalyst and the second catalyst are tested under the same conditions; The first catalyst is a first molybdenum-bismuth catalyst, and the second catalyst is a second molybdenum-bismuth catalyst; The first molybdenum-bismuth catalyst and the second molybdenum-bismuth catalyst are different; the active component of the first molybdenum-bismuth catalyst comprises the general formula shown in formula (1), and the active component of the second molybdenum-bismuth catalyst comprises the general formula shown in formula (2): Mo a Bi b Fe c Co d Mg e A f B g C h Si i O x Formula (1); Mo a Bi b’ Fe c Co d’ Mg e’ A f B g C h Si i O x Formula (2); Wherein, when a=12, b=1.5-4, c=2-10, d=2-4, e=0.5-1, f=0.1-3, g=0.1-3, h=1-4, i=0-2, b'=1-2, d'=4-8, e'=1-2, x is the number of oxygen atoms required to meet the atomic valence requirements of other elements present; A is selected from at least one of K, Rb and Cs, B is selected from B, and C is selected from at least one of Ni, Er, Nb, Sb, In and Ti; The method is carried out in a reactor, and the first molybdenum-bismuth catalyst and the second molybdenum-bismuth catalyst are loaded in the reactor in the following manner: the first molybdenum-bismuth catalyst is loaded in the inlet section of the reactor, and the second molybdenum-bismuth catalyst is loaded in the outlet section of the reactor; In the reactor, the ratio of the packing volume of the first molybdenum-bismuth catalyst to the packing volume of the second molybdenum-bismuth catalyst is 80-20:20-80.

2. The method according to claim 1, wherein: The selectivity of the first molybdenum-bismuth catalyst is 0.1-6.0% higher than the selectivity of the second molybdenum-bismuth catalyst; And / or, the conversion rate of the second molybdenum-bismuth catalyst is 2.0-6.0% higher than the conversion rate of the first molybdenum-bismuth catalyst.

3. The method according to claim 1 or 2, wherein: The preparation method of the first molybdenum-bismuth catalyst comprises: controlling the pH value of a mixture containing a molybdenum salt, a bismuth salt, an iron salt, a cobalt salt, a magnesium salt and a silicon source to be 3-9, and then performing a first calcination and a second calcination; And / or, the preparation method of the second molybdenum-bismuth catalyst comprises: controlling the pH value of a mixture containing molybdenum salt, bismuth salt, iron salt, cobalt salt, magnesium salt and silicon source to <4, and then performing a third calcination and a fourth calcination.

4. The method according to claim 1 or 2, wherein: The preparation method of the first molybdenum-bismuth catalyst comprises: adding a dispersed phase containing a silicon source and an acid solution II containing a bismuth salt, an iron salt, a cobalt salt and a magnesium salt to a solution I containing a molybdenum salt to obtain a mixture, and adjusting the pH value of the mixture to 3-9; and then performing a first calcination and a second calcination; And / or, the preparation method of the second molybdenum-bismuth catalyst comprises: adding a dispersed phase containing a silicon source and an acid solution II containing a bismuth salt, an iron salt, a cobalt salt and a magnesium salt to a solution I containing a molybdenum salt to obtain a mixture, and adjusting the pH value of the mixture to <4; and then performing a third calcination and a fourth calcination.

5. The method according to claim 4, wherein: When preparing the first molybdenum-bismuth catalyst, the solution II also contains at least one of a nickel salt, a boron source, a cesium salt and a rubidium salt, and the dispersed phase also contains at least one of an antimony source, a titanium source and an erbium source; And / or, when preparing the second molybdenum-bismuth catalyst, solution II also contains at least one of a nickel salt, a boron source, a cesium salt, an indium salt and a niobium salt, and the dispersed phase also contains an antimony source.

6. The method according to claim 5, wherein: The molybdenum salt is at least one of ammonium molybdate, molybdenum nitrate, molybdenum sulfate, molybdenum chloride, molybdenum acetate, molybdenum oxalate, and sodium molybdate; and / or the bismuth salt is at least one of bismuth nitrate, bismuth sulfate, bismuth chloride, bismuth acetate, bismuth oxalate, and bismuth phosphate; And / or, the iron salt is at least one of ferric nitrate, ferric sulfate, ferric chloride, ferric acetate, ferric oxalate, and ferric phosphate; and / or the cobalt salt is at least one of cobalt nitrate, cobalt sulfate, cobalt chloride, cobalt acetate, cobalt oxalate, cobalt phosphate and cobalt carbonate; And / or, the magnesium salt is at least one of magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium acetate, magnesium oxalate, magnesium carbonate, and magnesium phosphate; and / or, the silicon source is a soluble silicate and / or silicon dioxide; And / or, the nickel salt is at least one of nickel nitrate, nickel sulfate, nickel chloride, nickel acetate, nickel oxalate, nickel carbonate, and nickel phosphate; and / or, the boron source is at least one of boric acid, borate, and metaborate; And / or, the antimony source is at least one of antimony trioxide, antimony acetate, and antimony acid; and / or, the cesium salt is at least one of cesium nitrate, cesium sulfate, cesium chloride, cesium acetate, cesium oxalate, cesium carbonate, and cesium phosphate; and / or the rubidium salt is at least one of rubidium nitrate, rubidium sulfate, rubidium chloride, rubidium acetate, rubidium oxalate, rubidium carbonate, and rubidium phosphate; And / or, the titanium source is at least one of titanium dioxide and tetrabutyl titanate; and / or, the erbium source is at least one of erbium oxide and erbium hydroxide; And / or, the indium salt is at least one of indium acetate, indium nitrate, indium sulfate, indium chloride, indium oxalate, and indium oxide; And / or, the niobium salt is at least one of niobium oxalate, niobium nitrate, niobium sulfate, niobium chloride and niobium acetate.

7. The method according to claim 5, wherein: The silicon source is at least one of ethyl silicate, methyl silicate and propyl silicate.

8. The method according to claim 3, wherein: The first calcination conditions include: temperature of 200-300°C and time of 2-4h; And / or, the second calcination conditions include: temperature of 400-600° C., time of 1-12 h; And / or, the conditions of the third calcination include: temperature of 200-300° C., time of 2-4 h; And / or, the fourth calcination conditions include: temperature of 400-600° C. and time of 1-12 h.

9. The method according to claim 3, wherein: The preparation method of the first molybdenum-bismuth catalyst or the second molybdenum-bismuth catalyst further comprises forming the catalyst: mixing the calcined product with an inorganic compound and / or an organic binder; And / or, the preparation method of the first molybdenum-bismuth catalyst or the second molybdenum-bismuth catalyst further includes loading the catalyst: the calcined product is loaded on a carrier.

10. The method according to claim 9, wherein: The inorganic compound is at least one of graphite, diatomaceous earth and inorganic fiber; and / or, the organic binder is at least one of methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose; And / or, the carrier is at least one of silicon dioxide, aluminum oxide, magnesium oxide, titanium dioxide and silicon carbide.

11. The method according to claim 1 or 10, wherein: The contact conditions include: temperature of 300-550°C, pressure of 0.01-0.2MPa, reaction time of 1-48h, total volume space velocity of raw materials of 500-3000h -1 , the molar ratio of isobutylene: oxygen: water in the raw material is 1: 1-5: 2-6; Alternatively, the contact conditions include: temperature of 300-550°C, pressure of 0.01-0.2 MPa, reaction time of 1-48 h, total volume space velocity of raw materials of 500-3000 h -1 The molar ratio of tert-butanol: oxygen: water in the raw material is 1:1-5:1-5.

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