Isobutyric anhydride cracking furnace and isobutyric anhydride cracking method

Abstract

The invention relates to an isobutyric anhydride cracking furnace and an isobutyric anhydride cracking method.The isobutyric anhydride cracking furnace is composed of two cracking furnace bodies which are used for heating raw material gas and providing heat for cracking reaction respectively, so that the occupied area of a heating area is reduced, a coking area is limited, different cracking furnaces can be independently subjected to temperature regulation and control, and the cracking efficiency is improved. The method has the advantages that the reverse reaction in the cracking process can be effectively inhibited, the side reaction caused by too high temperature can be inhibited to the greatest extent, the selectivity of the product is improved, the production cost is reduced and the economic benefit is obvious under the condition of ensuring the conversion rate of the isobutyric anhydride; meanwhile, by improving the material and the structure of the cracking furnace, the internal heat transfer effect is improved, and the operation cycle of the cracking furnace is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of chemical equipment, and in particular to an isobutyric anhydride cracking furnace and an isobutyric anhydride cracking method. Background Art

[0002] Ketene compounds are special unsaturated ketones containing ketone groups, in which the carbonyl group of the ketone molecule is connected to another carbon atom by a double bond. Since the molecular structure of such compounds is highly unsaturated, addition, decomposition and polymerization reactions can occur, and various compounds can be synthesized. There are many methods for preparing ketenes. One is the dehalogenation method of α-acyl halide compounds. This method has many side reactions, a long reaction time, and high cost for the treatment of three wastes. Another method is the high-temperature cracking method of fatty acids or fatty acid anhydrides. This method has low raw material cost and fast reaction rate, so the commonly used method in industry is the cracking method of fatty acids or fatty acid anhydrides.

[0003] Dimethyl ketone is an important intermediate for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, and is mainly obtained by cracking isobutyric anhydride in industry. The cracking furnace is the core equipment of the cracking process. However, there are few studies on cracking furnaces developed for isobutyric anhydride cracking process in industry. At the same time, during the cracking process, when the temperature in the furnace is too high, a large number of reverse reactions will occur, affecting the selectivity of dimethyl ketone. When the temperature in the furnace is too low, the cracking reaction occurs slowly, requiring a larger equipment volume, thus affecting the equipment investment. On the other hand, during the cooling process, a large number of cracking reverse reactions will occur, thereby reducing the conversion rate of the product.

[0004] CN118221508A discloses a method for preparing dimethyl ketone by cracking isobutyric anhydride. In this method, isobutyric anhydride is mixed with a catalyst and then vaporized, and then introduced into a cracking furnace. The cracked product is introduced into ammonia to quench the catalyst, and then rapidly condensed to obtain dimethyl ketone in the gas phase, while the liquid phase is mainly unreacted isobutyric anhydride and generated isobutyric acid. In this invention, the single-pass conversion rate of isobutyric acid and the selectivity of dimethyl ketone are high, but it does not involve improving the cracking furnace to improve the reaction effect.

[0005] CN117342934A discloses a method and device for preparing dimethyl ethylene ketone by two-stage thermal cracking coupling technology. The device comprises an acetic acid thermal cracking unit, an isobutyric acid absorption unit, and an isobutyric anhydride thermal cracking unit connected in series in sequence; the acetic acid thermal cracking unit comprises a cracking furnace I; the isobutyric acid absorption unit comprises an absorption device and a separation device connected in sequence, and the absorption device adopts at least one of a bubbling tower, a spray tower, and a stirring kettle; the separation device is used to separate isobutyric anhydride and acetic acid, and the acetic acid flow flowing out of the separation device returns to the acetic acid thermal cracking unit, and the separation device adopts a distillation tower; the isobutyric anhydride thermal cracking unit comprises a cracking furnace II. However, the cracking furnace used in the invention is a conventional general cracking furnace, which cannot effectively improve the product yield.

[0006] Therefore, in view of the shortcomings of the prior art, it is urgently necessary to provide a cracking furnace that can effectively inhibit the reverse reaction during the cracking process, ensure the conversion rate of isobutyric anhydride and improve the product selectivity. Summary of the invention

[0007] The object of the present invention is to provide an isobutyric anhydride cracking furnace and an isobutyric anhydride cracking method, which effectively solve the problems of difficult temperature control and low product conversion rate in the isobutyric anhydride cracking process.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides an isobutyric anhydride cracking furnace, the isobutyric anhydride cracking furnace comprising a first cracking furnace and a second cracking furnace, the first cracking furnace being provided with a material inlet, the second cracking furnace being provided with a material outlet, and a partition being provided between the first cracking furnace and the second cracking furnace;

[0010] The inner cavities of the first cracking furnace and the second cracking furnace are independently and transversely provided with furnace tubes, electric heaters are provided between the furnace tubes, and temperature sensors are provided on both sides of the inner cavities perpendicular to the furnace tubes; the number of furnace tubes and electric heaters in the second cracking furnace is greater than that in the first cracking furnace, and the volume of the second cracking furnace is greater than that of the first cracking furnace; the furnace tubes of the first cracking furnace and the second cracking furnace are independently connected by elbows, and the outlet end of the first cracking furnace is connected to the inlet end of the second cracking furnace by an elbow;

[0011] A sampling port is provided at the outlet end of the furnace tube of the first cracking furnace close to the material outlet side, and a sampling port is provided at the outlet end of each furnace tube of the second cracking furnace. The sampling port is located in the inner cavity and is connected to a detection instrument connector.

[0012] The isobutyric anhydride cracking furnace provided by the present invention consists of two cracking furnaces, which are respectively used for heating raw gas and providing heat for cracking reaction, thereby reducing the occupied area of ​​the heating area and limiting the coking area. Different cracking furnaces can be individually temperature-controlled, which can effectively inhibit the occurrence of reverse reaction in the cracking process and inhibit the side reaction caused by excessive temperature to the greatest extent. Under the condition of ensuring the conversion rate of isobutyric anhydride, the selectivity of the product is improved, the production cost is reduced, and obvious economic benefits are obtained. At the same time, by improving the material and structure of the cracking furnace, the internal heat transfer effect is improved and the operation cycle of the cracking furnace is extended.

[0013] Preferably, the first cracking furnace and the second cracking furnace are both steel structures, and are both provided with refractory layers inside.

[0014] Preferably, the bent pipe is a bent pipe obtained through heat preservation treatment.

[0015] Preferably, the furnace tube and the elbow are connected via a flange.

[0016] The furnace tube and the bent tube are connected by flanges, so that a single furnace tube can be replaced and then decoked, and the output can be subsequently regulated to a certain extent by increasing or decreasing the number of furnace tubes.

[0017] Preferably, the bending radius of the curved pipe is 200-1000 mm, for example, 200 mm, 400 mm, 600 mm, 800 mm or 1000 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] Preferably, the inner diameter of the curved pipe is 30-60 mm, for example, 30 mm, 35 mm, 40 mm, 50 mm or 60 mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] Preferably, the inner diameter of the furnace tube is 25-60 mm, and the inner diameter of the furnace tube is smaller than the inner diameter of the elbow, for example, it can be 25 mm, 36 mm, 40 mm, 58 mm or 60 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the spacing between the furnace tubes is 200-400 mm, for example, 200 mm, 250 mm, 300 mm, 350 mm or 400 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the material outlet is connected to a quench cooler.

[0022] Preferably, an air inlet pipe is provided between the material outlet and the quench cooler, and the air inlet pipe is used to introduce nitrogen or an inert gas.

[0023] The introduction of nitrogen or inert gas into the air inlet pipe can slow down the reverse reaction rate, shorten the residence time of the product in the subsequent quench cooler, and improve the conversion rate.

[0024] Preferably, the inner diameter of the air intake pipe is 10-30 mm, for example, 10 mm, 15 mm, 20 mm, 25 mm or 30 mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the detection instrument connector comprises a gas chromatograph connector.

[0026] Preferably, the materials used for the furnace tube and the bent tube independently include ferrochrome alloy or chromium-aluminum alloy.

[0027] Preferably, the inner walls of the furnace tube and the bent tube are pre-coated with coatings independently.

[0028] Preferably, the coating comprises any one or a combination of at least two of Al, Si, Cr, Mn or Ca. Typical but non-limiting combinations include a combination of Al and Si, a combination of Cr, Mn and Ca, or a combination of Al, Si, Cr, Mn and Ca.

[0029] Preferably, the thickness of the coating is 5-10 μm, for example, 5 μm, 6 μm, 8 μm, 9 μm or 10 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the furnace tube and the bent tube are heat treated at 700-900°C before use, for example, 700°C, 750°C, 800°C, 850°C or 900°C, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the heat treatment is carried out in an atmosphere with an oxygen partial pressure of ≤30Pa, for example, 30Pa, 20Pa, 10Pa, 5Pa or 1Pa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] The furnace tube and the elbow are made of alloy material, and heat treatment and pre-coating can inhibit the formation of coke in the tube. At the same time, the tube diameter is slightly increased at the elbow to avoid blockage of the furnace tube due to coking.

[0033] Preferably, the cross-sections of the furnace tube and the bent tube are both plum blossom holes, and the plum blossom holes are composed of four circular holes, and the radius of the circular holes is half of the tube diameter.

[0034] The cross-sections of the furnace tube and the bent tube are plum blossom holes, which effectively increases the turbulence of the fluid in the tube, improves the heat transfer effect, reduces the radial temperature difference, and retains a smooth contact surface, avoiding the situation where coke is difficult to clean after being generated at the edges and corners.

[0035] In a second aspect, the present invention provides a method for cracking isobutyric anhydride, the cracking method is carried out by the isobutyric anhydride cracking furnace described in the first aspect, and the cracking method comprises the following steps:

[0036] The isobutyric anhydride cracking gas enters the first cracking furnace from the material inlet, where it is heated up, enters the second cracking furnace through the elbow, undergoes cracking reaction, and is discharged from the material outlet.

[0037] Preferably, the flow rate of the material inlet is 4-20m 3 / h, for example, 4m 3 / h、7m 3 / h、10m 3 / h、15m 3 / h or 20m 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the temperature of the material inlet is 100-200°C, for example, 100°C, 120°C, 150°C, 180°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the set temperature of the first cracking furnace is 400-550°C, for example, it can be 400°C, 420°C, 450°C, 500°C or 550°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the set temperature of the second cracking furnace is 350-500°C, for example, it can be 350°C, 380°C, 400°C, 450°C or 500°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the internal pressure of the furnace tube in the second cracking furnace is 5-30 kPa, for example, it can be 5 kPa, 10 kPa, 15 kPa, 20 kPa or 30 kPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the product discharged from the material outlet is cooled and separated together with nitrogen or an inert gas.

[0043] Preferably, the outlet temperature of the quench cooler used for the cooling separation is 20-80°C, for example, 20°C, 35°C, 50°C, 65°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the blowing flow rate of the nitrogen or inert gas is 2-10m 3 / h, for example, it can be 2m 3 / h、4m 3 / h、6m 3 / h、8m 3 / h or 10m 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The isobutyric anhydride cracking furnace provided by the present invention uses electric heating instead of traditional gas heating, so that the furnace tube is heated more evenly and the temperature control is more precise, thereby reducing the occurrence of side reactions, ensuring the conversion rate and improving the selectivity of the product;

[0047] (2) The isobutyric anhydride cracking furnace provided by the present invention is composed of two cracking furnaces, which are respectively used to heat the raw gas and provide heat for the cracking reaction, thereby reducing the area occupied by the heating area and limiting the coking area. Different cracking furnaces can be individually temperature-controlled, which can not only effectively inhibit the occurrence of reverse reactions during the cracking process, but also inhibit the side reactions caused by excessive temperature to the greatest extent. Under the condition of ensuring the conversion rate of isobutyric anhydride, the selectivity of the product is improved, the production cost is reduced, and obvious economic benefits are achieved;

[0048] (3) In the present invention, the furnace tube and the elbow are connected by flanges, and a single furnace tube can be replaced and decoked. The output can be adjusted to a certain extent by increasing or decreasing the number of furnace tubes. The furnace tube and the elbow are made of alloy material, and heat treatment and pre-coating can inhibit the formation of coke in the tube. At the same time, the tube diameter is slightly increased at the elbow to avoid blockage of the furnace tube due to coking. The cross-section of the furnace tube and the elbow is a plum blossom hole, which effectively increases the turbulence of the fluid in the tube, improves the heat transfer effect, and reduces the radial temperature difference, while retaining a smooth contact surface, avoiding the situation where coke is difficult to clean after it is generated at the edges and corners.

[0049] (4) In the present invention, nitrogen or inert gas is introduced into the air inlet pipe to slow down the reverse reaction rate and shorten the residence time of the product in the subsequent quench cooler, thereby improving the conversion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1is a schematic diagram of the structure of the isobutyric anhydride cracking furnace provided in Example 1 of the present invention;

[0051] Figure 2 is a cross-sectional schematic diagram of a furnace tube and a bent tube provided in Example 1 of the present invention;

[0052] Among them: 1, the first cracking furnace; 2, the second cracking furnace; 3, the material inlet; 4, the material outlet; 5, the partition; 6, the furnace tube; 7, the electric heater; 8, the temperature sensor; 9, the elbow; 10, the sampling port; 11, the quench cooler; 12, the air inlet pipe. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0054] Example 1

[0055] This embodiment provides an isobutyric anhydride cracking furnace, the structural schematic diagram of which is shown in FIG. Figure 1 As shown, the isobutyric anhydride cracking furnace comprises a first cracking furnace 1 and a second cracking furnace 2, both of which are steel structures and are provided with refractory layers inside; the first cracking furnace 1 is provided with a material inlet 3, the second cracking furnace 2 is provided with a material outlet 4, and a partition 5 is provided between the first cracking furnace 1 and the second cracking furnace 2;

[0056] The inner cavities of the first cracking furnace 1 and the second cracking furnace 2 are independently and transversely provided with furnace tubes 6, electric heaters 7 are provided between the furnace tubes 6, and temperature sensors 8 are provided on both sides of the inner cavities perpendicular to the furnace tubes 6; the number of furnace tubes 6 and electric heaters 7 in the second cracking furnace 2 is greater than the number of furnace tubes 6 and electric heaters 7 in the first cracking furnace 1, and the volume of the second cracking furnace 2 is greater than the volume of the first cracking furnace 1; the furnace tubes 6 of the first cracking furnace 1 and the second cracking furnace 2 are independently connected by elbows 9, the outlet end of the first cracking furnace 1 and the inlet end of the second cracking furnace 2 are connected by elbows 9, and the furnace tubes 6 and the elbows 9 are connected by flanges;

[0057] A sampling port 10 is provided at the outlet end of the furnace tube 6 near the material outlet 4 of the first cracking furnace 1, and a sampling port 10 is provided at the outlet end of each furnace tube 6 of the second cracking furnace 2. The sampling port 10 is located in the inner cavity, and a gas chromatograph connector is connected to the sampling port 10; the material outlet 4 is connected to a quencher 11, and an air inlet pipe 12 with an inner diameter of 20 mm is provided between the material outlet 4 and the quencher 11, and the air inlet pipe 12 is used to introduce nitrogen;

[0058] The bending radius of the elbow 9 used between the furnace tubes 6 of the first cracking furnace 1 and the second cracking furnace 2 is 300mm, and the inner diameter is 40mm; the bending radius of the elbow 9 used between the outlet end of the first cracking furnace 1 and the inlet end of the second cracking furnace 2 is 600mm, and the inner diameter is 40mm; the inner diameter of the furnace tube 6 is 36mm, and the spacing is 300mm; the elbow 9 is an elbow 9 obtained after heat preservation treatment; the materials used for the furnace tube 6 and the elbow 9 are chromium-iron alloy respectively; the inner walls of the furnace tube 6 and the elbow 9 are pre-coated with a coating with a thickness of 6μm respectively; the coating contains substances including Al, Si, and Ca, wherein Si accounts for 25% by mass, Al accounts for 13% by mass, and Ca accounts for 7% by mass; the furnace tube 6 and the elbow 9 are heat treated at 800°C in an atmosphere with an oxygen partial pressure of 10Pa before use; the cross-sections of the furnace tube 6 and the elbow 9 are both plum blossom holes, and the cross-sectional schematic diagram is shown as follows Figure 2 As shown, the plum blossom hole is composed of four circular holes, and the radius of the circular hole is half of the tube diameter.

[0059] The method for cracking isobutyric anhydride using the isobutyric anhydride cracking furnace comprises the following steps:

[0060] The isobutyric anhydride cracking gas enters the first cracking furnace from the material inlet and is heated up, then enters the second cracking furnace through the elbow to undergo cracking reaction, and the product discharged from the material outlet is sent to the quench cooler together with nitrogen for cooling and separation;

[0061] The flow rate of the material inlet is 10m 3 / h, temperature 150℃, the set temperature of the first cracking furnace is 450℃, the set temperature of the second cracking furnace is 400℃, the internal pressure of the furnace tube in the second cracking furnace is 15kPa, the outlet temperature of the quench cooler is 50℃, and the nitrogen blowing flow rate is 6m 3 / h.

[0062] Example 2

[0063] This embodiment provides an isobutyric anhydride cracking furnace, which is different from the embodiment 1 in that the inner diameter of the air inlet pipe 12 is adjusted to 10 mm; the bending radius of the elbow 9 used between the furnace tubes 6 of the first cracking furnace 1 and the second cracking furnace 2 is adjusted to 200 mm, and the inner diameter is adjusted to 30 mm; the bending radius of the elbow 9 used between the outlet end of the first cracking furnace 1 and the inlet end of the second cracking furnace 2 is adjusted to 400 mm, and the inner diameter is adjusted to 30 mm; the inner diameter of the furnace tube 6 is adjusted to 25 mm, and the spacing is adjusted to 400 mm; the thickness of the coating is adjusted to 5 μm; the heat treatment temperature is adjusted to 700° C., and the oxygen partial pressure is 30 Pa;

[0064] In the method for isobutyric anhydride cracking using the isobutyric anhydride cracking furnace, the flow rate of the material inlet is 4m 3 / h, temperature 100℃, the set temperature of the first cracking furnace is 400℃, the set temperature of the second cracking furnace is 350℃, the internal pressure of the furnace tube in the second cracking furnace is 30kPa, the outlet temperature of the quench cooler is 20℃, and the nitrogen blowing flow rate is 10m 3 / h, and the rest are the same as in Example 1.

[0065] Example 3

[0066] This embodiment provides an isobutyric anhydride cracking furnace, which is different from the embodiment 1 in that the inner diameter of the air inlet pipe 12 is adjusted to 30 mm; the bending radius of the elbow 9 used between the furnace tubes 6 of the first cracking furnace 1 and the second cracking furnace 2 is adjusted to 500 mm, and the inner diameter is adjusted to 60 mm; the bending radius of the elbow 9 used between the outlet end of the first cracking furnace 1 and the inlet end of the second cracking furnace 2 is adjusted to 1000 mm, and the inner diameter is adjusted to 60 mm; the inner diameter of the furnace tube 6 is adjusted to 58 mm, and the spacing is adjusted to 200 mm; the material used for the furnace tube 6 and the elbow 9 is replaced with chromium-aluminum alloy; the thickness of the coating is adjusted to 10 μm; the heat treatment temperature is adjusted to 900° C., and the oxygen partial pressure is 1 Pa;

[0067] In the method for cracking isobutyric anhydride using the isobutyric anhydride cracking furnace: the flow rate of the material inlet is 20m 3 / h, temperature 200℃, the set temperature of the first cracking furnace is 550℃, the set temperature of the second cracking furnace is 500℃, the internal pressure of the furnace tube in the second cracking furnace is 5kPa, the outlet temperature of the quench cooler is 80℃, and the nitrogen blowing flow rate is 2m 3 / h, and the rest are the same as in Example 1.

[0068] Example 4

[0069] This embodiment provides an isobutyric anhydride cracking furnace, which is different from Embodiment 1 in that no air inlet pipe 12 is provided between the material outlet 4 and the quench cooler 11, and the rest is the same as Embodiment 1.

[0070] Example 5

[0071] This embodiment provides an isobutyric anhydride cracking furnace, which is different from Embodiment 1 in that the inner walls of the furnace tube 6 and the curved tube 9 are not pre-coated with a coating, and the furnace tube 6 and the curved tube 9 are not heat-treated before use. The rest is the same as Embodiment 1.

[0072] Example 6

[0073] This embodiment provides an isobutyric anhydride cracking furnace, which is different from Embodiment 1 in that the cross-sections of the furnace tube 6 and the curved tube 9 are adjusted to circular holes, and the rest are the same as Embodiment 1.

[0074] Comparative Example 1

[0075] This comparative example provides an isobutyric anhydride cracking furnace, which is different from Example 1 in that the isobutyric anhydride cracking furnace only includes a second pyrolysis furnace 2, and the rest is the same as Example 1.

[0076] The isobutyric anhydride cracking furnace provided in Examples 1-6 and Comparative Example 1 was used to carry out isobutyric anhydride cracking reaction, and the isobutyric anhydride conversion rate and dimethyl ketone selectivity at the outlet of the quench cooler and the cracking furnace operation period in which the conversion rate and selectivity remain relatively stable were calculated. The results are shown in Table 1.

[0077] Table 1

[0078]

[0079] It can be seen from Table 1 that the isobutyric anhydride cracking reaction is carried out by using the isobutyric anhydride cracking furnace provided by the present invention, which can ensure the conversion rate of isobutyric anhydride while improving the product selectivity;

[0080] By comparing Example 1 with Example 4, it can be seen that if nitrogen or inert gas is not introduced, the residence time of the cracking product in the quencher will be prolonged, so that a reverse reaction occurs and the conversion rate of isobutyric anhydride is reduced; by comparing Example 1 with Example 5, it can be seen that without heat treatment and pre-coating, it is difficult to suppress the formation of coke in the tube, thereby affecting the operation cycle of the cracking furnace; by comparing Example 1 with Example 6, it can be seen that the cross-section of the furnace tube and the elbow is a round hole, and compared with the plum blossom hole, the heat transfer effect is reduced, the turbulence of the fluid is reduced, and coke is easily generated at the edges and corners, which is difficult to clean;

[0081] By comparing Example 1 with Comparative Example 1, it can be seen that using a single furnace body for cracking reaction cannot reduce the area occupied by the heating area, and thus cannot limit the coking area.

[0082] In summary, the isobutyric anhydride cracking furnace provided by the present invention uses electric heating instead of traditional gas heating, so that the furnace tube is heated more evenly and the temperature control is more accurate, thereby reducing the occurrence of side reactions, ensuring the conversion rate and improving the selectivity of the product;

[0083] The isobutyric anhydride cracking furnace provided by the present invention is composed of two cracking furnaces, which are respectively used for heating the raw gas and providing heat for the cracking reaction, thereby reducing the area occupied by the heating area and limiting the coking area. Different cracking furnaces can be individually temperature-controlled, which can effectively inhibit the occurrence of reverse reactions in the cracking process and can also inhibit side reactions caused by excessively high temperatures to the greatest extent. Under the condition of ensuring the conversion rate of isobutyric anhydride, the selectivity of the product is improved, the production cost is reduced, and obvious economic benefits are achieved.

[0084] In the present invention, the furnace tube and the elbow are connected by flanges, and a single furnace tube can be replaced and then decoked. The output can be adjusted to a certain extent by increasing or decreasing the number of furnace tubes. The furnace tube and the elbow are made of alloy material, and heat treatment and pre-coating can inhibit the formation of coke in the tube. At the same time, the tube diameter is slightly increased at the elbow to avoid blockage of the furnace tube due to coking. The cross-sections of the furnace tube and the elbow are plum blossom holes, which effectively improves the turbulence of the fluid in the tube, improves the heat transfer effect, and reduces the radial temperature difference, while retaining a smooth contact surface, avoiding the situation where coke is difficult to clean after being generated at the edges and corners.

[0085] In the present invention, nitrogen or inert gas is introduced into the air inlet pipe to slow down the reverse reaction rate, shorten the residence time of the product in the subsequent quench cooler, and improve the conversion rate.

[0086] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. An isobutyric anhydride cracking furnace, characterized in that: The isobutyric anhydride cracking furnace comprises a first cracking furnace and a second cracking furnace, the first cracking furnace is provided with a material inlet, the second cracking furnace is provided with a material outlet, and a partition is provided between the first cracking furnace and the second cracking furnace; The inner cavities of the first cracking furnace and the second cracking furnace are independently and transversely provided with furnace tubes, electric heaters are provided between the furnace tubes, and temperature sensors are provided on both sides of the inner cavities perpendicular to the furnace tubes; the number of furnace tubes and electric heaters in the second cracking furnace is greater than that in the first cracking furnace, and the volume of the second cracking furnace is greater than that of the first cracking furnace; the furnace tubes of the first cracking furnace and the second cracking furnace are independently connected by elbows, and the outlet end of the first cracking furnace is connected to the inlet end of the second cracking furnace by an elbow; A sampling port is provided at the outlet end of the furnace tube of the first cracking furnace close to the material outlet side, and a sampling port is provided at the outlet end of each furnace tube of the second cracking furnace. The sampling port is located in the inner cavity and is connected to a detection instrument connector.

2. The isobutyric anhydride cracking furnace according to claim 1, characterized in that: The first cracking furnace and the second cracking furnace are both steel structures, and are both provided with refractory layers inside; Preferably, the bent pipe is a bent pipe obtained by heat preservation treatment; Preferably, the furnace tube and the elbow are connected via a flange.

3. The isobutyric anhydride cracking furnace according to claim 1 or 2, characterized in that: The bending radius of the elbow is 200-1000mm; Preferably, the inner diameter of the elbow is 30-60 mm; Preferably, the inner diameter of the furnace tube is 25-60 mm, and the inner diameter of the furnace tube is smaller than the inner diameter of the elbow; Preferably, the spacing between the furnace tubes is 200-400 mm.

4. The isobutyric anhydride cracking furnace according to any one of claims 1 to 3, characterized in that: The material outlet is connected with a quench cooler; Preferably, an air inlet pipe is provided between the material outlet and the quench cooler, and the air inlet pipe is used to introduce nitrogen or inert gas; Preferably, the inner diameter of the air inlet pipe is 10-30 mm; Preferably, the detection instrument connector comprises a gas chromatograph connector.

5. The isobutyric anhydride cracking furnace according to any one of claims 1 to 4, characterized in that: The materials used for the furnace tube and the bent tube include chromium-iron alloy or chromium-aluminum alloy respectively and independently.

6. The isobutyric anhydride cracking furnace according to any one of claims 1 to 5, characterized in that: The inner walls of the furnace tube and the bent tube are independently pre-coated with coatings; Preferably, the coating contains any one or a combination of at least two of Al, Si, Cr, Mn or Ca; Preferably, the coating has a thickness of 5-10 μm.

7. The isobutyric anhydride cracking furnace according to any one of claims 1 to 6, characterized in that: The furnace tube and the bent tube are heat treated at 700-900°C before use; Preferably, the heat treatment is performed in an atmosphere with an oxygen partial pressure of ≤30Pa.

8. The isobutyric anhydride cracking furnace according to any one of claims 1 to 7, characterized in that: The cross sections of the furnace tube and the bent tube are both plum blossom holes, which are composed of four circular holes, and the radius of the circular holes is half of the tube diameter.

9. A method for cracking isobutyric anhydride, characterized in that: The cracking method is carried out by the isobutyric anhydride cracking furnace according to any one of claims 1 to 8, and the cracking method comprises the following steps: The isobutyric anhydride cracking gas enters the first cracking furnace from the material inlet, where it is heated up, enters the second cracking furnace through the elbow, undergoes cracking reaction, and is discharged from the material outlet.

10. The cracking method according to claim 9, characterized in that: The flow rate of the material inlet is 4-20m 3 / h; Preferably, the temperature of the material inlet is 100-200°C; Preferably, the set temperature of the first cracking furnace is 400-550°C; Preferably, the set temperature of the second cracking furnace is 350-500°C; Preferably, the internal pressure of the furnace tube in the second cracking furnace is 5-30 kPa; Preferably, the product discharged from the material outlet is cooled and separated together with nitrogen or inert gas; Preferably, the outlet temperature of the quench cooler used for the cooling separation is 20-80°C; Preferably, the blowing flow rate of the nitrogen or inert gas is 2-10m 3 / h.

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