Method and system for preparing maleic anhydride through selective oxidation of C4 hydrocarbons

Abstract

The invention discloses a method for preparing maleic anhydride through selective oxidation of C4 hydrocarbons, which is carried out in a first-stage reactor and a second-stage reactor which are connected in series, and one or more reaction tubes are independently arranged in each of the first-stage reactor and the second-stage reactor, the length-diameter ratio of the reaction tube in the first-stage reactor is smaller than that of the reaction tube in the second-stage reactor, and the (molten salt) temperature of the first-stage reactor is smaller than that of the second-stage reactor. According to the invention, the two stages of reactors are connected in series, the first-stage reactor adopts a reaction tube with a small length-diameter ratio, the molten salt reaction temperature is low, and a low-activity and high-selectivity catalyst is used, so that the n-butane conversion rate is kept at 40-60%, and the corresponding maleic anhydride selectivity is 60-80%; the second-stage reactor adopts a reaction tube with a large length-diameter ratio, the molten salt reaction temperature is high, and a high-activity catalyst is used, so that the unreacted n-butane is further converted.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical processes, and particularly relates to a method and a system for improving the process of selective oxidation reaction of C4 hydrocarbons. Background Art

[0002] Maleic anhydride (referred to as MA) is a very important organic chemical raw material. As an organic acid anhydride containing unsaturated double bonds, it has many uses and can be used to produce important organic chemicals such as unsaturated polyester resin (UPR), 1,4-butanediol, butyrolactone, and 1,4-butanedioic acid.

[0003] Industrially, a shell-and-tube molten salt reactor is used to produce MA. The main reason is that this reaction is a strongly exothermic reaction, and excessive reaction heat significantly reduces the selectivity of MA, resulting in a large amount of by-produced carbon oxides.

[0004] The existing process uses a single-stage reactor. That is, after the mixer of n-butane and air enters the oxidation reactor, the reaction products directly enter the subsequent separation stage. It is difficult to adjust and control the reaction process during the oxidation stage, which is not conducive to improving the selectivity of MA. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the present invention provides a method and a system for selectively oxidizing C4 hydrocarbons to produce MA. A two-stage reactor series reaction device and process are adopted, supplemented by a condensation separation process in the middle, which can further improve the overall yield of MA.

[0006] One of the purposes of the present invention is to provide a method for selectively oxidizing C4 hydrocarbons to produce MA, including: performing in a series of a first-stage reactor and a second-stage reactor, and one or more reaction tubes are independently arranged in the first-stage reactor and the second-stage reactor respectively. Among them, the aspect ratio of the reaction tubes in the first-stage reactor is less than that of the reaction tubes in the second-stage reactor, and the (molten salt) temperature of the first-stage reactor is less than the (molten salt) temperature of the second-stage reactor.

[0007] Among them, the temperature of the reactor is controlled by molten salt.

[0008] The method of the present invention is carried out in a series of two-stage reactors. However, when two-stage reactors are connected in series, there are the following problems that are difficult to solve:

[0009] One is to solve the matching of the first-stage reactor and the second-stage reactor. Setting two-stage reactors with a large throughput can further convert the n-butane in the first-stage reactor, but it will increase the energy consumption of the device, resulting in a large amount of energy and resource waste. If the throughput of the device is small, it cannot handle the unreacted raw materials in the first-stage reactor well, and the overall yield improvement of MA is not obvious;

[0010] Second, it is necessary to control the conversion rate of n-butane in the first-stage reactor. This conversion rate cannot be too low, otherwise it will be difficult to further convert in the second-stage reactor, resulting in a low overall maleic anhydride yield. Therefore, the catalyst in the first-stage reactor needs to have high reaction activity to achieve a suitable conversion rate at a relatively low molten salt temperature; if the conversion rate of n-butane is too high, carbon oxides will be produced as by-products, reducing the selectivity of maleic anhydride.

[0011] In a preferred embodiment, the aspect ratio of the reaction tubes in the first-stage reactor is 5-10, such as 5, 6, 7, 8, 9 or 10; and / or, the aspect ratio of the reaction tubes in the second-stage reactor is 10-20, such as 10, 12, 14, 16, 18 or 20.

[0012] In a further preferred embodiment, the inner diameter of the reaction tubes in the first-stage reactor is 20-50 mm, preferably 30-40 mm, and the reaction tube length is 10-40 cm, preferably 20-30 cm; and / or, the inner diameter of the reaction tubes in the second-stage reactor is 15-30 mm, preferably 20-25 mm, and the reaction tube length is 15-45 cm, preferably 20-40 cm.

[0013] For example, the inner diameter of the reaction tubes in the first-stage reactor is 20 mm, 30 mm, 40 mm or 50 mm, and the reaction tube length is 10 cm, 20 mm, 30 mm or 40 cm; the inner diameter of the reaction tubes in the second-stage reactor is 15 mm, 20 mm, 25 mm or 30 mm, and the reaction tube length is 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm or 45 cm.

[0014] In a preferred embodiment, one or more reaction tubes are independently arranged in each of the first-stage reactor and the second-stage reactor, preferably 1-10 reaction tubes are independently arranged, such as 1, 2, 4, 6, 8 or 10.

[0015] In a further preferred embodiment, the loading amount of the catalyst (i.e., the first vanadium phosphorus catalyst) in a single reaction tube of the first-stage reactor is 5-50 g, preferably 10-30 g; and / or, the loading amount of the catalyst (i.e., the second vanadium phosphorus catalyst) in a single reaction tube of the second-stage reactor is 5-50 g, preferably 10-30 g.

[0016] For example, the loading amount of the catalyst in a single reaction tube of the first-stage reactor is 10 g, 15 g, 20 g, 25 g or 30 g, and the loading amount in a single reaction tube of the second-stage reactor is 10 g, 15 g, 20 g, 25 g or 30 g.

[0017] In a preferred embodiment, the (molten salt) temperature of the first-stage reactor is 360 to 400 °C, the space velocity is 1000 to 1500 h -1 , and the n-butane concentration is 1.2 - 2% (volume fraction); and / or, the (molten salt) temperature of the second-stage reactor is 360 - 450 °C, and the n-butane concentration is 0.3 - 1.5% (volume fraction).

[0018] For example, the (molten salt) temperature of the first-stage reactor is 360 °C, 370 °C, 380 °C, 390 °C or 400 °C, and the space velocity is 1000 h -1 , 1100 h -1 , 1200 h -1 , 1300 h -1 , 1400 h -1 or 1500 h -1 , and the n-butane concentration is 1.2%, 1.4%, 1.6%, 1.8% or 2% (volume fraction); and / or, the molten salt temperature of the second-stage reactor is 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, 410 °C, 420 °C, 430 °C, 440 °C or 450 °C, and the n-butane concentration is 0.3%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 14% or 1.5% (volume fraction).

[0019] In a further preferred embodiment, the (molten salt) temperature of the first-stage reactor is 360 - 380 °C, and the n-butane concentration is 1.5 - 1.8% (volume fraction); and / or, the molten salt temperature of the second-stage reactor is 390 - 410 °C, and the n-butane concentration is 0.5 - 1.1% (volume fraction).

[0020] Wherein, in addition to n-butane, the reactor also contains air and / or oxygen.

[0021] In a preferred embodiment, the conversion rate of n-butane in the first-stage reactor is 40 - 70%, and the maleic anhydride selectivity is 55 - 85%; and / or, the conversion rate of n-butane in the second-stage reactor is 80 - 90%, and the maleic anhydride selectivity is 40 - 60%.

[0022] For example, the conversion rate of n-butane in the first-stage reactor is 40%, 45%, 50%, 55%, 60%, 65% or 70%, and the maleic anhydride selectivity is 55%, 60%, 65%, 70%, 72%, 74%, 76%, 78%, 80% or 85%; and / or, the conversion rate of n-butane in the second-stage reactor is 80%, 82%, 84%, 86%, 88% or 90%, and the maleic anhydride selectivity is 40%, 50%, 52%, 54%, 56%, 58% or 60%.

[0023] In a further preferred embodiment, the hot spot temperature of the first-stage reactor is 370 - 400 °C; and / or, the hot spot temperature of the second-stage reactor is 400 - 420 °C.

[0024] For example, the hot spot temperature of the first-stage reactor is 370 °C, 380 °C, 390 °C or 400 °C; and / or, the hot spot temperature of the second-stage reactor is 400 °C, 405 °C, 410 °C, 412 °C, 414 °C, 416 °C, 418 °C or 420 °C.

[0025] Wherein, the hot spot temperature refers to the highest temperature at a certain position in the catalyst bed.

[0026] In a preferred embodiment, an intermediate condenser is provided between the first-stage reactor and the second-stage reactor to condense the reaction gas of the first-stage reactor.

[0027] In a further preferred embodiment, cold brine is used for the condensation.

[0028] In a further preferred embodiment, the reaction gas of the first-stage reactor is condensed to 200 - 350 °C, preferably condensed to 250 - 300 °C, such as to 200 °C, 250 °C, 300 °C or 350 °C.

[0029] Among them, the intermediate condenser uses cold brine to condense the reaction gas, and there is an air passage in the middle, so that air can enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction. A gas chromatograph is provided downstream of the condenser to analyze the concentration at the outlet of the first-stage reactor, and then air or oxygen is added to increase the oxygen content (on the one hand, it can control the butane concentration, and on the other hand, it can provide sufficient oxygen for the second-stage reaction), which can better promote the conversion of n-butane.

[0030] In the present invention, two-stage reactors are connected in series. The first-stage reactor uses a reaction tube with a small length-diameter ratio, a low molten salt reaction temperature, and a low-activity, high-selectivity catalyst, so that the conversion rate of n-butane is maintained at 40 - 60%, and the corresponding selectivity of maleic anhydride is 60 - 80%; the second-stage reactor uses a reaction tube with a large length-diameter ratio, a high molten salt reaction temperature, and a high-activity catalyst to further convert the unreacted n-butane. A condensation heat exchange device is provided between the first-stage reactor and the second-stage reactor to condense and capture the maleic anhydride produced by the first-stage reactor and by-product steam. The separated butane gas is mixed with fresh air and enters the second-stage reactor for further conversion in the second-stage reactor. Using this reaction device and process to produce maleic anhydride, the conversion rate of n-butane can be 90 - 95%, and the corresponding selectivity of maleic anhydride is 50 - 60%; the overall weight yield of maleic anhydride is 96 - 105%.

[0031] In a preferred embodiment, a first vanadium phosphorus catalyst is loaded in the first-stage reactor, and a second vanadium phosphorus catalyst is loaded in the second-stage reactor.

[0032] The advantage of this method is that the first-stage reactor optimally controls the conversion rate to ensure high selectivity; the second-stage reactor maximizes the conversion rate as much as possible to convert n-butane as much as possible, and ensures a certain selectivity, disperses the hot spots, and reduces side reactions as much as possible. The difficulty lies in matching the reaction parameters of the first-stage and second-stage reactors and developing two types of catalysts with different performances. The first type of catalyst has the advantages of low activity and high selectivity and is suitable for use in the first-stage reactor to ensure very high selectivity in the first-stage reactor and to be able to convert a part of n-butane. Therefore, it is necessary to adjust the phosphorus-vanadium ratio on the surface and use a pore-forming agent to promote the formation of macropores, thereby improving the selectivity of the catalyst; the second type of catalyst has high activity and is suitable for use in the second-stage reactor to ensure very high conversion rate in the second-stage reactor and to convert most of the n-butane entering the second-stage reactor. It is a non-pore-forming catalyst, a high phosphorus-vanadium ratio catalyst, to ensure the overall yield of maleic anhydride.

[0033] In a further preferred embodiment, the phosphorus-vanadium ratio of the first vanadium phosphorus catalyst is greater than that of the second vanadium phosphorus catalyst; preferably, the phosphorus-vanadium ratio in the first vanadium phosphorus catalyst is 0.3 to 1.25 (preferably 0.3 to 0.67), and the phosphorus-vanadium ratio in the second vanadium phosphorus catalyst is 0.2 to 0.67 (preferably 0.25 to 0.5).

[0034] For example, the phosphorus-vanadium ratio in the first vanadium phosphorus catalyst is 0.3, 0.5, 0.7, 0.9, 1.1 or 1.25, and the phosphorus-vanadium ratio in the second vanadium phosphorus catalyst is 0.2, 0.3, 0.4, 0.5, 0.6 or 0.67.

[0035] In a still further preferred embodiment, the pore size of the first vanadium phosphorus catalyst is greater than that of the second vanadium phosphorus catalyst; preferably, the first vanadium phosphorus catalyst is a pore-forming catalyst with a pore size of 0.1 - 2 μm, and the second vanadium phosphorus catalyst is a non-pore-forming catalyst (i.e., not separately pore-forming), and its pore size is smaller than that of the first vanadium phosphorus catalyst, preferably 0.01 - 0.1 μm.

[0036] For example, the pore size of the first vanadium phosphorus catalyst is 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2 μm, and the pore size of the second vanadium phosphorus catalyst is 0.01 μm, 0.02 μm, 0.04 μm, 0.06 μm, 0.08 μm or 0.1 μm.

[0037] In a preferred embodiment, the first vanadium phosphorus catalyst is obtained as follows: Raw materials including a phosphorus source, a vanadium source, a solvent, a reducing agent, an auxiliary agent, and a cyclic polyol are mixed and processed, and after solid-liquid separation, washing, drying, and calcination, a catalyst precursor is obtained. The catalyst precursor is subjected to an activation treatment, and then a pore-forming agent is used for pore-forming treatment to obtain the first vanadium phosphorus catalyst.

[0038] In a further preferred embodiment, the first vanadium phosphorus catalyst is obtained as follows:

[0039] (1) Raw materials including a vanadium source, a solvent, a reducing agent, an auxiliary agent, and a cyclic polyol are mixed, heated, and then cooled to room temperature.

[0040] (2) The phosphorus source is added dropwise with stirring, and heated under reflux to obtain a catalyst slurry.

[0041] (3) The catalyst slurry is subjected to solid-liquid separation, washing, drying, and calcination to obtain a catalyst precursor.

[0042] Among them, when tableting and forming the catalyst precursor, 0.5-10 wt% of a lubricant (such as graphite, etc.) can be added.

[0043] (4) The catalyst precursor is subjected to an activation treatment, and then a pore-forming agent is used for pore-forming treatment to obtain the first vanadium phosphorus catalyst.

[0044] In an even more preferred embodiment, the treatment is preferably a heating under reflux treatment.

[0045] Among them, the pore-forming agent needs to be granulated to form particles with a mesh number of 60-100 (such as 60, 70, 80, 90, or 100 mesh), and then mixed with the precursor and pressed into a certain shape to form macropores.

[0046] In a preferred embodiment, the second vanadium phosphorus catalyst is obtained as follows: Raw materials including a phosphorus source, a vanadium source, a solvent, a reducing agent, an auxiliary agent, and a cyclic polyol are mixed and processed, and after solid-liquid separation, washing, drying, and calcination, a catalyst precursor is obtained; the catalyst precursor is subjected to an activation treatment to obtain the second vanadium phosphorus catalyst.

[0047] In a further preferred embodiment, the second vanadium phosphorus catalyst is obtained as follows:

[0048] (1) Raw materials including a vanadium source, a solvent, a reducing agent, an auxiliary agent, and a cyclic polyol are mixed, heated, and then cooled to room temperature.

[0049] (2) The phosphorus source is added dropwise with stirring, and heated under reflux to obtain a catalyst slurry.

[0050] (3) Carry out solid-liquid separation, washing, drying and calcination on the catalyst slurry to obtain a catalyst precursor;

[0051] (4) Carry out activation treatment on the catalyst precursor to obtain the second vanadium phosphorus catalyst.

[0052] In a further preferred embodiment, the treatment is preferably heat reflux treatment.

[0053] In a preferred embodiment, when preparing the first vanadium phosphorus catalyst and the second vanadium phosphorus catalyst: their respective phosphorus sources are independently selected from at least one of phosphoric acid (preferably 85% - 105% phosphoric acid, such as 85% phosphoric acid, 95% phosphoric acid or 105% phosphoric acid), phosphorus pentoxide, and PCl5; and / or, their respective vanadium sources are independently selected from at least one of vanadium pentoxide, ammonium metavanadate, and oxalic acid vanadyl; and / or, their respective solvents are selected from at least one of isobutanol, isopropanol, n-butanol, pentanol, and isopentanol; and / or, their respective reducing agents are independently selected from at least one of oxalic acid and benzyl alcohol; and / or, their respective promoters are independently selected from at least one of iron, nickel, cobalt, copper, zinc, potassium, rubidium, and cesium; and / or, their respective cyclic polyols are independently isosorbide.

[0054] Among them, the introduction of the cyclic polyhydroxy alcohol isosorbide into the catalyst of the present invention is beneficial to the formation of crystal nuclei, can adjust the low-temperature selectivity of the catalyst, and improves the low-temperature selectivity of the first-stage catalyst.

[0055] In a further preferred embodiment, when preparing the first vanadium phosphorus catalyst, the pore-forming agent is selected from conventional pore-forming agents, preferably but not limited to at least one of stearic acid, oxalic acid, and urea.

[0056] Among them, the pore-forming agent needs to be granulated to form particles of a certain mesh number, and then mixed with the precursor and pressed into a certain shape to form macropores.

[0057] In a preferred embodiment, when preparing the first vanadium phosphorus catalyst, the molar ratio of the phosphorus source to the vanadium source is (0.8 - 3):1, the molar ratio of the solvent to the vanadium source is (10 - 30):1, the molar ratio of the reducing agent to the vanadium source is (1 - 2):1, the molar ratio of the promoter to the vanadium source is (0.01 - 0.5):1, and the molar ratio of the cyclic polyol to the vanadium source is (0.01 - 0.8):1.

[0058] Among them, the above molar ratios are all based on the molar amounts of the molecules. For example, when preparing the first vanadium phosphorus catalyst, the molar ratio of the phosphorus source to the vanadium source is 0.8:1, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1; the molar ratio of the solvent to the vanadium source is 10:1, 15:1, 20:1, 25:1 or 30:1; the molar ratio of the reducing agent to the vanadium source is 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1 or 2:1; the molar ratio of the auxiliary agent to the vanadium source is 0.01, 0.05, 0.1, 0.2, 0.3, 0.4 or 0.5; the molar ratio of the cyclic polyol to the vanadium source is 0.01, 0.05, 0.1, 0.2, 0.4, 0.6 or 0.8.

[0059] In a further preferred embodiment, when preparing the first vanadium phosphorus catalyst, the molar ratio of the phosphorus source to the vanadium source is (1.5 - 3):1; the molar ratio of the solvent to the vanadium source is (15 - 25):1; the molar ratio of the reducing agent to the vanadium source is (1.2 - 1.8):1; the molar ratio of the auxiliary agent to the vanadium source is (0.05 - 0.3):1; the molar ratio of the cyclic polyol to the vanadium source is (0.1 - 0.5):1.

[0060] In a preferred embodiment, when preparing the second vanadium phosphorus catalyst, the molar ratio of the phosphorus source to the vanadium source is (1.5 - 5):1; the molar ratio of the solvent to the vanadium source is (10 - 30):1; the molar ratio of the reducing agent to the vanadium source is (1 - 2):1; the molar ratio of the auxiliary agent to the vanadium source is (0.05 - 0.3):1; the molar ratio of the cyclic polyol to the vanadium source is (0.01 - 0.5):1.

[0061] Among them, the above molar ratios are all based on the molar amounts of the molecules. For example, when preparing the second vanadium phosphorus catalyst: the molar ratio of the phosphorus source to the vanadium source is 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1; the molar ratio of the solvent to the vanadium source is 10:1, 15:1, 20:1, 25:1 or 30:1; the molar ratio of the reducing agent to the vanadium source is 1:1, 1.2:1, 1.4:1, 1.61:1, 1.8:1 or 2:1; the molar ratio of the auxiliary agent to the vanadium source is 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1; the molar ratio of the cyclic polyol to the vanadium source is 0.01, 0.05, 0.1, 0.2, 0.3, 0.4 or 0.5.

[0062] In a further preferred embodiment, when preparing the second vanadium phosphorus catalyst, the molar ratio of the phosphorus source to the vanadium source is (2-4):1, the molar ratio of the solvent to the vanadium source is (15-25):1, the molar ratio of the reducing agent to the vanadium source is (1.2-1.8):1, the molar ratio of the promoter to the vanadium source is (0.05-0.3):1, and the molar ratio of the cyclic polyol to the vanadium source is (0.1-0.3):1.

[0063] Preferably, the molar ratio of the phosphorus source to the vanadium source when preparing the first vanadium phosphorus catalyst is less than the molar ratio of the phosphorus source to the vanadium source when preparing the second vanadium phosphorus catalyst.

[0064] In a preferred embodiment, when preparing the first vanadium phosphorus catalyst and the second vanadium phosphorus catalyst, the activation treatment can adopt any activation treatment method disclosed in the prior art (such as CN111054409A). Preferably, the activation treatment is carried out independently as follows: heating the VPO catalyst precursor to 380-480 °C, and introducing a first active atmosphere when the temperature is raised to a temperature in the range of 120-270 °C, so that the catalyst precursor undergoes a first activation in the first active atmosphere, where the first active atmosphere can be "oxygen and / or nitrogen" and / or "a mixture of air and water vapor"; maintaining the VPO catalyst precursor treated in the above step in the first active atmosphere at 380-480 °C for a first time, and then maintaining it in a second active atmosphere at 380-480 °C for a second time to carry out a second activation, and the second active atmosphere is composed of water vapor and a protective gas.

[0065] In a further preferred embodiment, the protective gas is nitrogen.

[0066] In a preferred embodiment, when preparing the first vanadium phosphorus catalyst, the pore-forming treatment is carried out as follows: crushing the activated catalyst precursor and mixing it with a pore-forming agent and then pressing it into a mold, and then removing the pore-forming agent to obtain the first vanadium phosphorus catalyst.

[0067] In a further preferred embodiment, based on 100 wt% of the activated catalyst precursor and the pore-forming agent, the pore-forming agent accounts for 10-30 wt%, preferably 15-25 wt%, such as 10 wt%, 15 wt%, 20 wt%, 25 wt% or 30 wt%.

[0068] In a further preferred embodiment, the pore-forming agent is removed by heating and raising the temperature.

[0069] A second object of the present invention is to provide a system for carrying out the method described in the first object of the present invention. The system includes a first-stage reactor and a second-stage reactor connected in series. One or more reaction tubes are independently arranged in the first-stage reactor and the second-stage reactor respectively. A first catalyst zone is arranged in the reaction tubes of the first-stage reactor, and a second catalyst zone is arranged in the second reactor. The first vanadium phosphorus catalyst is filled in the first catalyst zone, and the second vanadium phosphorus catalyst is filled in the second catalyst zone.

[0070] In a preferred embodiment, the length-to-diameter ratio of the reaction tubes in the first-stage reactor is smaller than that of the reaction tubes in the second-stage reactor.

[0071] In a preferred embodiment, the length-to-diameter ratio of the reaction tubes in the first-stage reactor is 5-10, and / or the length-to-diameter ratio of the reaction tubes in the second-stage reactor is 10-20.

[0072] In a further preferred embodiment, the inner diameter of the reaction tubes in the first-stage reactor is 20-50 mm, preferably 30-40 mm, and the reaction tube length is 10-40 cm, preferably 20-30 cm; and / or the inner diameter of the reaction tubes in the second-stage reactor is 15-30 mm, preferably 20-25 mm, and the reaction tube length is 15-45 cm, preferably 20-40 cm.

[0073] In a preferred embodiment, one or more reaction tubes are independently arranged in the first-stage reactor and the second-stage reactor respectively, preferably 1-10 reaction tubes are independently arranged.

[0074] In a preferred embodiment, an intermediate condenser is arranged between the first-stage reactor and the second-stage reactor for condensing the reaction gas of the first-stage reactor.

[0075] In a further preferred embodiment, cold brine is used for the condensation.

[0076] In the ranges and any values disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article. In the following text, in principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed in this article.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] (1) The present invention adopts a two-stage reactor. Each stage of the reactor has a different length-diameter ratio and different filling amounts are controlled. The two-stage reactors are matched, the process flow is simple, the reaction device can withstand a low temperature, the risk coefficient is small, the service life is long, and the maleic anhydride weight yield is improved.

[0079] (2) The catalyst of the present invention introduces cyclic polyhydroxy alcohol isosorbide, which is beneficial to the formation of crystal nuclei, can adjust the catalyst activity and selectivity, and improves the selectivity of the first-stage catalyst and the conversion rate of the second-stage catalyst.

[0080] (3) The reaction device of the present invention and the prepared catalyst are coupled with each other, which better promotes the partial oxidation reaction of n-butane and has a very high maleic anhydride weight yield, which can reach 96-105% (calculated according to the weight yield, the obtained molar yield will be multiplied by 98 and then divided by 58, so there will be a situation where the yield exceeds 100%). Detailed Embodiments

[0081] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention according to the content of the present invention still fall within the protection scope of the present invention.

[0082] In addition, it should be noted that all the specific technical features described in the following specific embodiments can be combined in any suitable way without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0083] In addition, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention. The technical solutions formed thereby belong to a part of the original public content of this specification and also fall within the protection scope of the present invention.

[0084] If there is no special limitation on the raw materials used in the examples and comparative examples, they are all disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art. The phosphorus-vanadium ratio of the catalyst in the examples is calculated according to the molar usage ratio of the raw material phosphorus source and vanadium source.

[0085] In the present invention, the conversion rate of n-butane in the first reactor and the second reactor is determined by chromatographic calibration. The conversion rate is calculated based on the chromatographic peak areas of n-butane in the feed gas and the reaction tail gas. The weight yield of maleic anhydride is determined by the cumulative collection method. The cumulative yield is determined by titration with sodium hydroxide solution, and the molar yield and weight yield of maleic anhydride are calibrated. The concentrations of by-products carbon monoxide and carbon dioxide are calibrated by the TCD method, and the concentration of n-butane is calibrated by the FID method. The concentrations of both are calibrated by the external standard method, that is, using the standard gases of the above-mentioned gases, chromatographic analysis is carried out respectively, and the standard curves are fitted to calculate the concentration of n-butane in the feed and the concentrations of carbon monoxide and carbon dioxide in the reaction tail gas.

[0086]

Catalyst Preparation

[0087] (1) The preparation method of the first vanadium phosphorus catalyst A1 is as follows:

[0088] Precursor preparation: Place 100 g of V2O5, 60 g of oxalic acid, 10 g of Fe(NO3)3, and 7.2 g of Co(NO3)2 in a 3 L three-necked flask, then add 1000 mL of isobutanol and 30 g of isosorbide. Heat the above mixture to the reflux temperature, reflux for 1 hour, then cool to room temperature. Dropwise add 120 g of 105% phosphoric acid with stirring, heat to reflux for 16 hours to obtain a catalyst slurry. Centrifuge the slurry, wash it with anhydrous ethanol, then place it in an 80 °C oven and dry for 24 hours. Then transfer it to a muffle furnace and calcine at 240 °C for 5 hours. Mix the calcined catalyst powder with 4% graphite and press it into a certain shape to obtain the catalyst precursor.

[0089] Precursor activation: When the temperature is raised to 250 °C, a mixture of water vapor and air is introduced, where the ratio of water vapor to air is 10:88 and the space velocity is 1000 h -1 , when the temperature is raised to 425 °C, the air is replaced with nitrogen, and other ratios remain unchanged, and it is maintained at this temperature for 10 hours to obtain the activated catalyst.

[0090] Removal of pore-forming agent: Crush 100 g of the activated catalyst and mix it with 25 g of urea and press it into a shape, then remove the pore-forming agent at 90 °C to obtain the vanadium phosphorus oxygen catalyst.

[0091] The molar ratio of the phosphorus source to the vanadium source of the first vanadium phosphorus catalyst A1 obtained above is 2.33, and the pore diameter is 1.2 μm.

[0092] (2) The preparation method of the second vanadium phosphorus catalyst B1 is as follows:

[0093] The preparation of the second vanadium phosphorus catalyst is the same as that of the first vanadium phosphorus catalyst, except that: (a) the addition amount of phosphorus, where the addition amount of phosphoric acid is 140 g; (b) no pore formation is carried out after obtaining the activated catalyst.

[0094] The vanadium phosphorus ratio of the obtained second vanadium phosphorus catalyst B1 is 1:2.73, and the pore diameter is 0.05 μm.

[0095]

Example 1

[0096] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 360 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0097] An intermediate condenser is arranged between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas of the first-stage reactor to 280 °C. An air passage is arranged in the middle of the intermediate condenser so that air can enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0098] Place the second vanadium phosphorus catalyst B1 in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 400 °C, and the concentration of n-butane is 0.75% (volume fraction). The evaluation data of the catalyst are shown in Table 1-1.

[0099] Table 1-1 Evaluation data of the catalyst

[0100]

[0101]

Example 2

[0102] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 380 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0103] An intermediate condenser is provided between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas from the first-stage reactor to 280 °C. An air passage is provided in the middle of the intermediate condenser, enabling air to enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0104] The second vanadium phosphorus catalyst B1 is placed in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 400 °C, and the concentration of n-butane is 0.45% (volume fraction). The evaluation data of the catalyst are shown in Table 1-2.

[0105] Table 1-2 Evaluation data of the catalyst

[0106]

[0107]

Example 3

[0108] The first vanadium phosphorus catalyst A1 is placed in the first-stage reactor. There are 3 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 360 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0109] An intermediate condenser is provided between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas from the first-stage reactor to 280 °C. An air passage is provided in the middle of the intermediate condenser, enabling air to enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0110] The second vanadium phosphorus catalyst B1 is placed in the second-stage reactor. There are 3 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 25 mm, the length of the reaction tube is 25 cm, the reaction temperature using molten salt is 380 °C, and the concentration of n-butane is 0.75% (volume fraction). The evaluation data of the catalyst are shown in Table 1-3.

[0111] Table 1-3 Evaluation data of the catalyst

[0112]

[0113]

Example 4

[0114] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 4 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 360 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0115] An intermediate condenser is arranged between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas of the first-stage reactor to 290 °C. An air passage is arranged in the middle of the intermediate condenser so that air can enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0116] Place the second vanadium phosphorus catalyst B1 in the second-stage reactor. There are 4 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 25 mm, the length of the reaction tube is 25 cm, the reaction temperature using molten salt is 400 °C, and the concentration of n-butane is 0.75% (volume fraction). The evaluation data of the catalyst are shown in Table 1-4.

[0117] Table 1-4 Evaluation data of the catalyst

[0118]

[0119]

Example 5

[0120] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 380 °C, and the space velocity is 1500 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0121] An intermediate condenser is arranged between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas of the first-stage reactor to 280 °C. An air passage is arranged in the middle of the intermediate condenser so that air can enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0122] Place the second vanadium phosphorus catalyst B1 in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 400 °C, and the concentration of n-butane is 0.9% (volume fraction). The evaluation data of the catalyst are shown in Table 1-5.

[0123] Table 1-5 Evaluation data of the catalyst

[0124]

[0125]

Example 6

[0126] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 5 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 30 g. The inner diameter of the reactor is 40 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 370 °C, and the space velocity is 1300 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0127] An intermediate condenser is arranged between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas of the first-stage reactor to 290 °C. An air passage is arranged in the middle of the intermediate condenser so that air can enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0128] Place the second vanadium phosphorus catalyst B1 in the second-stage reactor. There are 5 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 400 °C, and the concentration of n-butane is 0.82% (volume fraction). The evaluation data of the catalyst are shown in Table 1-6.

[0129] Table 1-6 Evaluation data of the catalyst

[0130]

[0131]

Example 7

[0132] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 5 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 30 g. The inner diameter of the reactor is 40 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 380 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.7% (volume fraction).

[0133] An intermediate condenser is arranged between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas of the first-stage reactor to 290 °C. An air passage is arranged in the middle of the intermediate condenser so that air can enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0134] Place the second vanadium phosphorus catalyst B1 in the second-stage reactor. There are 5 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 400 °C, and the concentration of n-butane is 0.8% (volume fraction). The evaluation data of the catalyst are shown in Table 1-7.

[0135] Table 1-7 Evaluation Data of the Catalyst

[0136]

[0137]

Example 8

[0138] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 40 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 360 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.7% (volume fraction).

[0139] An intermediate condenser is arranged between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas of the first-stage reactor to 280 °C. An air passage is arranged in the middle of the intermediate condenser so that air can enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0140] Place the second vanadium phosphorus catalyst B1 in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 400 °C, and the concentration of n-butane is 0.97% (volume fraction). The evaluation data of the catalyst are shown in Table 1-8.

[0141] Table 1-8 Evaluation Data of the Catalyst

[0142]

[0143]

Comparative Example 1

[0144] Place the first vanadium phosphorus catalyst A1 in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 350 °C, and the space velocity is 1600 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0145] An intermediate condenser is provided between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas from the first-stage reactor to 280 °C. An air passage is provided in the middle of the intermediate condenser to allow air to enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0146] The second vanadium phosphorus catalyst B1 is placed in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 400 °C, and the concentration of n-butane is 1.0% (volume fraction). The evaluation data of the catalyst are shown in Table 1-9.

[0147] Table 1-9 Evaluation Data of the Catalyst

[0148]

[0149] In Comparative Example 1, after the space velocity was increased, there was a significant decrease in the conversion rate of n-butane. The concentration of butane entering the second stage was relatively high, so the overall yield decreased.

[0150]

Comparative Example 2

[0151] The first vanadium phosphorus catalyst A1 is placed in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 350 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0152] An intermediate condenser is provided between the first-stage reactor and the second-stage reactor. The intermediate condenser uses cold brine to condense the reaction gas from the first-stage reactor to 280 °C. An air passage is provided in the middle of the intermediate condenser to allow air to enter the condenser and mix with the unreacted butane gas, and then enter the second-stage reactor for reaction.

[0153] The second vanadium phosphorus catalyst B1 is placed in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 400 °C, and the concentration of n-butane is 0.825% (volume fraction). The evaluation data of the catalyst are shown in Table 1-10.

[0154] Table 1-10 Evaluation Data of the Catalyst

[0155]

[0156] In Comparative Example 2, the reaction temperature of the first-stage reactor was 350°C, which was relatively low, resulting in a low conversion rate in the first stage and affecting the overall yield. This also reflects the complexity and difficulty of process matching.

[0157]

Comparative Example 3

[0158] The first vanadium phosphorus catalyst A1 was placed in the first-stage reactor. There were 2 reaction tubes in the first-stage reactor, and the loading mass of the first vanadium phosphorus catalyst in each reaction tube was 20 g. The inner diameter of the reactor was 30 mm, the length of the reaction tube was 20 cm, the molten salt reaction temperature was 350°C, and the space velocity was 1000 h -1 , and the concentration of n-butane was 1.7% (volume fraction).

[0159] The second vanadium phosphorus catalyst B1 was placed in the second-stage reactor. There were 2 reaction tubes in the second-stage reactor, and the loading mass of the second vanadium phosphorus catalyst in each reaction tube was 15 g. The inner diameter of the reactor was 20 mm, the length of the reaction tube was 20 cm, the molten salt reaction temperature was 410°C, and the concentration of n-butane was 1.1% (volume fraction). The evaluation data of the catalyst are shown in Table 1-11.

[0160] Table 1-11 Evaluation data of the catalyst

[0161]

[0162] In this Comparative Example 3, the reaction temperature of the first-stage reactor was 350°C and the concentration of n-butane was increased. The overall result was a decrease in yield. It should be noted here that the operating parameters are relatively important for this process. If the conversion rate of the first-stage reactor is too low, it will affect the overall yield, thus also indicating the difficulty of connecting the two-stage reactors in series and the need to match the overall yield well.

[0163]

Comparative Example 4

[0164] The first vanadium phosphorus catalyst A1 was placed in the first-stage reactor. There were 2 reaction tubes in the first-stage reactor, and the loading mass of the first vanadium phosphorus catalyst in each reaction tube was 20 g. The inner diameter of the reactor was 30 mm, the length of the reaction tube was 20 cm, the molten salt reaction temperature was 350°C, and the space velocity was 1000 h -1 , and the concentration of n-butane was 1.7% (volume fraction).

[0165] The first vanadium phosphorus catalyst B1 was placed in the second-stage reactor. There were 2 reaction tubes in the second-stage reactor, and the loading mass of the second vanadium phosphorus catalyst in each reaction tube was 15 g. The inner diameter of the reactor was 20 mm, the length of the reaction tube was 20 cm, the molten salt reaction temperature was 420°C, and the concentration of n-butane was 1.1% (volume fraction). The evaluation data of the catalyst are shown in Table 1-12.

[0166] Table 1-12 Evaluation Data of Catalysts

[0167]

[0168]

Comparative Example 5

[0169] Repeat the preparation process of the first vanadium phosphorus catalyst A1 above, with the difference that isosorbide is not used, and other conditions remain unchanged, to obtain the first vanadium phosphorus catalyst A1'; repeat the preparation process of the second vanadium phosphorus catalyst B1 above, with the difference that isosorbide is not used, and other conditions remain unchanged, to obtain the second vanadium phosphorus catalyst B1'.

[0170] The evaluation method is the same as the conditions in Example 1. Place the first vanadium phosphorus catalyst A1' in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 360 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0171] Place the second vanadium phosphorus catalyst B1' in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 400 °C, and the concentration of n-butane is 0.9% (volume fraction). The evaluation data of the catalyst are shown in Table 1-13.

[0172] Table 1-13 Evaluation Data of Catalysts

[0173]

[0174]

Comparative Example 6

[0175] Repeat the preparation process of the first vanadium phosphorus catalyst A1 above, with the difference that glycerol of equal weight is used to replace isosorbide, and other conditions remain unchanged, to obtain the first vanadium phosphorus catalyst A1"; repeat the preparation process of the second vanadium phosphorus catalyst B1 above, with the difference that glycerol of equal weight is used to replace isosorbide, and other conditions remain unchanged, to obtain the second vanadium phosphorus catalyst B1".

[0176] The evaluation method is the same as the conditions in Example 1. Place the first vanadium phosphorus catalyst A1" in the first-stage reactor. There are 2 reaction tubes in the first-stage reactor. The loading mass of the first vanadium phosphorus catalyst in each reaction tube is 20 g. The inner diameter of the reactor is 30 mm, the length of the reaction tube is 20 cm, the molten salt reaction temperature is 360 °C, and the space velocity is 1000 h -1 , and the concentration of n-butane is 1.5% (volume fraction).

[0177] Place the second vanadium phosphorus catalyst B1” in the second-stage reactor. There are 2 reaction tubes in the second-stage reactor. The loading mass of the second vanadium phosphorus catalyst in each reaction tube is 15 g. The inner diameter of the reactor is 20 mm, the length of the reaction tube is 20 cm, the reaction temperature using molten salt is 400 °C, and the concentration of n-butane is 0.885% (volume fraction). The evaluation data of the catalyst are shown in Table 1-14.

[0178] Table 1-14 Evaluation Data of the Catalyst

[0179]

[0180]

Comparative Example 7

[0181] Repeat the process of Example 1, except that the settings and conditions of the second-stage reactor are the same as those of the first-stage reactor. Other conditions remain unchanged. The evaluation data of the catalyst are shown in Table 1-15.

[0182] Table 1-15 Evaluation Data of the Catalyst

[0183]

[0184]

Comparative Example 8

[0185] Repeat the process of Example 1, except that the settings and conditions of the first-stage reactor are the same as those of the second-stage reactor. Other conditions remain unchanged. The evaluation data of the catalyst are shown in Table 1-16.

[0186] Table 1-16 Evaluation Data of the Catalyst

[0187]

[0188]

Comparative Example 9

[0189] Repeat the process of Example 1, except that: use the first-stage reactor and its conditions in Example 1 as the second-stage reactor and its conditions in Comparative Example 9, and use the second-stage reactor and its conditions in Example 1 as the first-stage reactor and its conditions in Comparative Example 9. Other conditions remain unchanged. The evaluation data of the catalyst are shown in Table 1-17.

[0190] Table 1-17 Evaluation Data of the Catalyst

[0191]

[0192]

Comparative Example 10

[0193] Repeat the process of Example 1, except that: load the second vanadium phosphorus catalyst B1 (i.e., use a non-pore-forming catalyst) in the first-stage reactor. Other conditions remain unchanged. The evaluation data of the catalyst are shown in Table 1-18.

[0194] Table 1-18 Evaluation Data of Catalysts

[0195]

[0196]

Catalyst Preparation

[0197] (1) The preparation method of the first vanadium phosphorus catalyst A2 is as follows:

[0198] Preparation of precursor: Place 100 g of V2O5, 60 g of oxalic acid, 14 g of Cu(NO3)2, and 9.3 g of Bi(NO3)3 in a 3 L three-necked flask, then add 1000 mL of isobutanol and 40 g of isosorbide. Heat the above mixture to the reflux temperature, reflux for 1 hour, then cool to room temperature. While stirring, add 120 g of 105% phosphoric acid dropwise, and heat to reflux for 16 hours to obtain a catalyst slurry. Centrifuge the slurry and wash it with absolute ethanol, then place it in an 80°C oven and dry for 24 hours. Then transfer it to a muffle furnace and calcine at 240°C for 5 hours. Mix the calcined catalyst powder with 4% graphite and press it into a certain shape to obtain a catalyst precursor.

[0199] The processes of activation, shaping, and removal of pore-forming agent of the precursor are the same as those in Example 1.

[0200] The molar ratio of the phosphorus source to the vanadium source of the obtained first vanadium phosphorus catalyst A2 is 2.33:1, and the pore diameter is 1.1 μm.

[0201] (2) The preparation method of the second vanadium phosphorus catalyst B2 is as follows:

[0202] The preparation process of the catalyst is the same as that of the first vanadium phosphorus catalyst A2, except that: (a) 135 g of 105% phosphoric acid is added. (b) Pore formation is not carried out after obtaining the activated catalyst.

[0203] The molar ratio of the phosphorus source to the vanadium source of the obtained second vanadium phosphorus catalyst B2 is 2.63:1, and the pore diameter is 0.06 μm.

[0204]

Example 9

[0205] Repeat the process of Example 1, except that the above first vanadium phosphorus catalyst A2 is loaded in the first-stage reactor and the above second vanadium phosphorus catalyst B2 is loaded in the second-stage reactor. The evaluation data of the catalyst are shown in Table 1-19.

[0206] Table 1-19 Evaluation Data of Catalysts

[0207]

[0208]

Catalyst Preparation

[0209] (1) The preparation method of the first vanadium phosphorus catalyst A3 is as follows:

[0210] Preparation of precursor: Place 100 g of V2O5, 62 g of oxalic acid, 8.8 g of Fe(NO3)3, and 11.2 g of Bi(NO3)3 in a 3 L three-necked flask, then add 1000 mL of isobutanol and 40 g of isosorbide. Heat the above mixture to the reflux temperature, reflux for 1 hour, then cool to room temperature. While stirring, add 120 g of 105% phosphoric acid dropwise, heat to reflux for 16 hours to obtain a catalyst slurry. Centrifuge the slurry, wash it with absolute ethanol, then place it in an 80 °C oven and dry for 24 hours. Then transfer it to a muffle furnace and calcine at 240 °C for 5 hours. Mix the calcined catalyst powder with 4% graphite and press it into a certain shape to obtain the catalyst precursor.

[0211] The processes of activation, shaping, and removal of the pore-forming agent of the precursor are the same as those in Example 1.

[0212] The molar ratio of the phosphorus source to the vanadium source of the first vanadium phosphorus catalyst A3 obtained above is 2.33:1, and the pore size is 1.1 μm.

[0213] (2) The preparation method of the second vanadium phosphorus catalyst B3 is as follows:

[0214] The preparation process of the catalyst is the same as that of the first vanadium phosphorus catalyst A3, except that: (a) 140 g of 105% phosphoric acid is added; (b) no pore-forming is carried out after obtaining the activated catalyst.

[0215] The molar ratio of the phosphorus source to the vanadium source of the second vanadium phosphorus catalyst B3 obtained above is 2.73:1, and the pore size is 0.05 μm.

[0216]

Example 10

[0217] Repeat the process of Example 1, except that the above first vanadium phosphorus catalyst A3 is loaded in the first-stage reactor, and the above second vanadium phosphorus catalyst B3 is loaded in the second-stage reactor. The evaluation data of the catalyst are shown in Table 1-20.

[0218] Table 1-20 Evaluation data of the catalyst

[0219]

[0220] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for the selective oxidation of C4 hydrocarbons to prepare maleic anhydride, comprising: It is carried out in a series-connected first-stage reactor and second-stage reactor. One or more reaction tubes are independently arranged in the first-stage reactor and the second-stage reactor respectively. Among them, the length-diameter ratio of the reaction tubes in the first-stage reactor is smaller than that of the reaction tubes in the second-stage reactor, and the temperature of the first-stage reactor is lower than that of the second-stage reactor.

2. The method according to claim 1, wherein the length-diameter ratio of the reaction tubes in the first-stage reactor is 5-10; and / or, the length-diameter ratio of the reaction tubes in the second-stage reactor is 10-20.

3. The method according to claim 1, wherein one or more reaction tubes are independently arranged in the first-stage reactor and the second-stage reactor respectively, preferably 1 to 10 reaction tubes are independently arranged respectively; and / or, an intermediate condenser is arranged between the first-stage reactor and the second-stage reactor to condense the reaction gas of the first-stage reactor.

4. The method according to claim 1, wherein The temperature of the first-stage reactor is 360 to 400 °C, the space velocity is 1000 to 1500 h -1 , the concentration of n-butane is 1.2-2%; and / or, the temperature of the second-stage reactor is 360-450 °C, and the concentration of n-butane is 0.3-1.5%.

5. The method according to any one of claims 1 to 4, characterized in that, A first vanadium phosphorus catalyst is filled in the first-stage reactor, and a second vanadium phosphorus catalyst is filled in the second-stage reactor; wherein, the vanadium-phosphorus ratio of the first vanadium phosphorus catalyst is greater than that of the second vanadium phosphorus catalyst, and / or, the pore diameter of the first vanadium phosphorus catalyst is larger than that of the second vanadium phosphorus catalyst.

6. The method according to claim 5, wherein The vanadium-phosphorus ratio in the first vanadium phosphorus catalyst is 0.3-1.25, and / or, the vanadium-phosphorus ratio in the second vanadium phosphorus catalyst is 0.2-0.

67.

7. The method according to claim 5, wherein More preferably, the first vanadium phosphorus catalyst is a pore-forming catalyst, and / or, the second vanadium phosphorus catalyst is a non-pore-forming catalyst.

8. The method according to claim 5, wherein the first vanadium phosphorus catalyst is obtained as follows: Mix and process raw materials including a phosphorus source, a vanadium source, a solvent, a reducing agent, an auxiliary agent, and a cyclic polyol, perform solid-liquid separation, washing, drying and calcination to obtain a catalyst precursor, perform activation treatment on the catalyst precursor, and then perform pore-forming treatment with a pore-forming agent to obtain the first vanadium phosphorus catalyst; and / or, the second vanadium phosphorus catalyst is obtained as follows: Mix and process raw materials including a phosphorus source, a vanadium source, a solvent, a reducing agent, an auxiliary agent, and a cyclic polyol, perform solid-liquid separation, washing, drying and calcination to obtain a catalyst precursor; perform activation treatment on the catalyst precursor to obtain the second vanadium phosphorus catalyst.

9. The method according to claim 8, characterized in that, When preparing the first vanadium phosphorus catalyst and the second vanadium phosphorus catalyst: their respective phosphorus sources are independently selected from at least one of phosphoric acid, phosphorus pentoxide, and PCl5; and / or, their respective vanadium sources are independently selected from at least one of vanadium pentoxide, ammonium metavanadate, and oxovanadium oxalate; and / or, their respective solvents are independently selected from at least one of isobutanol, isopropanol, n-butanol, pentanol, and isopentanol; and / or, their respective reducing agents are independently selected from at least one of oxalic acid and benzyl alcohol; and / or, their respective promoters are independently selected from at least one of iron, nickel, cobalt, copper, zinc, potassium, rubidium, and cesium; and / or, their respective cyclic polyols are independently isosorbide.

10. The method according to claim 8, wherein When preparing the first vanadium phosphorus catalyst: the molar ratio of the phosphorus source to the vanadium source is (0.8 - 3):1, and / or, the molar ratio of the solvent to the vanadium source is (10 - 30):1, and / or, the molar ratio of the reducing agent to the vanadium source is (1 - 2):1, and / or, the molar ratio of the promoter to the vanadium source is (0.01 - 0.5):1, and / or, the molar ratio of the cyclic polyol to the vanadium source is (0.01 - 0.8):1; and / or, When preparing the second vanadium phosphorus catalyst: the molar ratio of the phosphorus source to the vanadium source is (1.5 - 5):1, and / or, the molar ratio of the solvent to the vanadium source is (10 - 30):1, and / or, the molar ratio of the reducing agent to the vanadium source is (1 - 2):1, and / or, the molar ratio of the promoter to the vanadium source is (0.05 - 0.3):1, and / or, the molar ratio of the cyclic polyol to the vanadium source is (0.01 - 0.5):

1.

11. A system for performing the method according to any one of claims 1 to 10, the system comprising a first-stage reactor and a second-stage reactor connected in series, and one or more reaction tubes are independently arranged in the first-stage reactor and the second-stage reactor. A first catalyst zone is arranged in the reaction tubes of the first-stage reactor, a second catalyst zone is arranged in the second reactor, the first vanadium phosphorus catalyst is loaded in the first catalyst zone, and the second vanadium phosphorus catalyst is loaded in the second catalyst zone; Preferably, the aspect ratio of the reaction tubes in the first-stage reactor is smaller than that of the reaction tubes in the second-stage reactor.

12. The system according to claim 11, wherein The aspect ratio of the reaction tubes in the first-stage reactor is 5 - 10, and / or, the aspect ratio of the reaction tubes in the second-stage reactor is 10 - 20; Preferably: the inner diameter of the reaction tubes in the first-stage reactor is 20 - 50 mm, preferably 30 - 40 mm, and the reaction tube length is 10 - 40 cm, preferably 20 - 30 cm; and / or, the inner diameter of the reaction tubes in the second-stage reactor is 15 - 30 mm, preferably 20 - 25 mm, and the reaction tube length is 15 - 45 cm, preferably 20 - 40 cm.

13. The system according to claim 11 or 12, wherein One or more reaction tubes are independently arranged in the first-stage reactor and the second-stage reactor respectively, preferably 1 to 10 reaction tubes are independently arranged respectively; and / or, An intermediate condenser is arranged between the first-stage reactor and the second-stage reactor for condensing the reaction gas of the first-stage reactor.

Images