Multi-tube parallel filler oxidizer and isobutyric acid preparation method

Abstract

The invention provides a multi-tube parallel filler oxidizer and a preparation method of isobutyric acid, and relates to the field of preparation of isobutyric acid. According to the multi-tube parallel filler oxidizer disclosed by the invention, oxygen and isobutyraldehyde are in countercurrent contact, so that the contact efficiency is improved, and the oxidation reaction is rapid; and an external circulation heat exchange system is additionally arranged on the basis of circulating cooling water, so that the temperature of reactants can be better controlled, side reactions are greatly reduced, and the product purity is improved.

Description

Technical Field

[0001] The invention relates to the field of preparation of isobutyric acid, and in particular to a multi-tube parallel-connected packed oxidizer and a method for preparing isobutyric acid. Background Art

[0002] Isobutyric acid is an important chemical that plays a key role in the chemical industry, food and pharmaceutical fields. In the chemical industry, isobutyric acid is widely used in the synthesis and reaction processes of the chemical industry; in the food industry, isobutyric acid is mainly used in acidity regulators and food flavors; in the pharmaceutical field, isobutyric acid can inhibit the growth and reproduction of bacteria in some cases, and has a certain control effect on infections and diseases caused by some bacteria.

[0003] The traditional method for preparing isobutyric acid is to directly oxidize isobutyraldehyde using air or oxygen, but the purity of the prepared isobutyric acid is low. Summary of the invention

[0004] The invention provides a multi-tube parallel-connected packed oxidizer and a method for preparing isobutyric acid. The prepared isobutyric acid has high purity.

[0005] The present invention provides a multi-tube parallel-connected packed oxidizer, comprising a shell;

[0006] A tube located inside the shell; the number of the tubes is ≥ 2;

[0007] The first plate and the second plate embedded in the tube block the space except the tube body in the horizontal direction; the first plate and the second plate are respectively located at the upper part and the lower part of the tube;

[0008] a cooling water inlet and a cooling water outlet located between the first plate and the second plate;

[0009] A first distributor located at the top of the tubes passes the reaction raw materials into each tube;

[0010] External circulation heat exchanger and second distributor;

[0011] The inlet of the external circulation heat exchanger is connected to the bottom of the shell, and the outlet of the external circulation heat exchanger is connected to the second distributor, so that the reactants passing through the external circulation heat exchanger are introduced into each tube;

[0012] The second distributor is located between the first plate and the second plate;

[0013] The third distributor located below the second plate introduces the oxidizing gas into each tube.

[0014] Preferably, it also includes: a compressor;

[0015] The inlet of the compressor is connected to the shell above the first plate, and the outlet of the compressor is connected to the inlet of the third distributor.

[0016] Preferably, the cooling water inlet is located at the bottom, and the cooling water outlet is located at the top.

[0017] Preferably, it further comprises: a preheater and a compression pump connected to the preheater;

[0018] The compression pump is also connected to the first distributor.

[0019] The present invention also provides a method for preparing isobutyric acid, which is carried out in the multi-tube parallel packed oxidizer described in the above technical solution, comprising the following steps:

[0020] Isobutyraldehyde is continuously introduced into each tube through a first distributor and oxygen is continuously introduced into each tube through a third distributor to carry out a first oxidation reaction. The continuously generated crude isobutyric acid is introduced into an external circulation heat exchanger for heat exchange and then continuously introduced into each tube through a second distributor to carry out a second oxidation reaction to obtain the isobutyric acid.

[0021] Preferably, the gas-liquid ratio of isobutyraldehyde to oxygen is 4 to 8:1.

[0022] Preferably, the sum of the time of the first oxidation reaction and the second oxidation reaction is 1 to 1.5 hours.

[0023] Preferably, the flow rate of the oxygen is 700-900 mL / min, and the flow rate of the isobutyraldehyde is 120-160 mL / min.

[0024] Preferably, the temperature of the crude isobutyric acid and the isobutyric acid is independently 25 to 55°C.

[0025] Preferably, the pressure of the first oxidation reaction and the second oxidation reaction is 0.3-0.5 MPa.

[0026] The present invention provides a multi-tube parallel-connected packed oxidizer, comprising a shell;

[0027] A tube located inside the shell; the number of the tubes is ≥ 2;

[0028] The first plate and the second plate embedded in the tube block the space except the tube body in the horizontal direction; the first plate and the second plate are respectively located at the upper part and the lower part of the tube;

[0029] a cooling water inlet and a cooling water outlet located between the first plate and the second plate;

[0030] A first distributor located at the top of the tubes passes the reaction raw materials into each tube;

[0031] External circulation heat exchanger and second distributor;

[0032] The inlet of the external circulation heat exchanger is connected to the bottom of the shell, and the outlet of the external circulation heat exchanger is connected to the second distributor, so that the reactants passing through the external circulation heat exchanger are introduced into each tube;

[0033] The second distributor is located between the first plate and the second plate;

[0034] The third distributor located below the second plate introduces the oxidizing gas into each tube.

[0035] The multi-tube parallel packed oxidizer of the present invention can make oxygen and isobutyraldehyde contact in countercurrent, improve the contact efficiency, and make the oxidation reaction react rapidly; and the installation of an external circulation heat exchange system on the basis of circulating cooling water can better control the temperature of the reactants, greatly reduce the occurrence of side reactions, and improve the purity of the product.

[0036] The multi-tube parallel-connected packed oxidizer of the present invention is easy to regulate.

[0037] Furthermore, the present invention further improves the purity of isobutyric acid by adjusting the gas-liquid ratio of oxygen and isobutyraldehyde, the temperature of crude isobutyric acid, the time and pressure of the oxidation reaction. The results of the examples show that the preparation method of the present invention enables the oxidation rate of isobutyraldehyde to reach about 95%, which exceeds the development level of the same period. Compared with the existing kettle type and tube type production processes, this method reduces the reaction time and improves the isobutyraldehyde conversion rate.

[0038] The temperature and pressure of the preparation method of the present invention are relatively mild, the process is highly safe and the product has good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a process flow chart of an embodiment of the present invention;

[0040] Figure 2 is the gas chromatogram of isobutyric acid when the oxygen flow rate is 500 mL / min in Example 1;

[0041] Figure 3 is the gas chromatogram of isobutyric acid when the oxygen flow rate is 700 mL / min in Example 1;

[0042] Figure 4 is the gas chromatogram of isobutyric acid when the oxygen flow rate is 900 mL / min in Example 1;

[0043] Figure 5 This is the gas chromatogram of isobutyric acid when the reaction time is 0.5h in Example 2;

[0044] Figure 6This is the gas chromatogram of isobutyric acid when the reaction time is 1 h in Example 2;

[0045] Figure 7 This is the gas chromatogram of isobutyric acid when the reaction time is 1.5 h in Example 2;

[0046] Figure 8 is the gas chromatogram of isobutyric acid of the conventional intermittent oxidizer in Example 3;

[0047] Fig. 9 The isobutyric acid gas chromatogram of the multi-tube parallel packed oxidizer of the present invention in Example 3;

[0048] Fig.10 is the gas chromatogram of isobutyric acid when the temperature of crude isobutyric acid in Example 4 is 30°C;

[0049] Fig.11 is the gas chromatogram of isobutyric acid when the temperature of crude isobutyric acid is 40° C. in Example 4;

[0050] Fig.12 This is the gas chromatogram of the crude isobutyric acid in Example 4 when the temperature is 50°C. DETAILED DESCRIPTION

[0051] The present invention provides a multi-tube parallel-connected packed oxidizer, comprising a shell;

[0052] A tube located inside the shell; the number of the tubes is ≥ 2;

[0053] The first plate and the second plate embedded in the tube block the space except the tube body in the horizontal direction; the first plate and the second plate are respectively located at the upper part and the lower part of the tube;

[0054] a cooling water inlet and a cooling water outlet located between the first plate and the second plate;

[0055] A first distributor located at the top of the tubes passes the reaction raw materials into each tube;

[0056] External circulation heat exchanger and second distributor;

[0057] The inlet of the external circulation heat exchanger is connected to the bottom of the shell, and the outlet of the external circulation heat exchanger is connected to the second distributor, so that the reactants passing through the external circulation heat exchanger are introduced into each tube;

[0058] The second distributor is located between the first plate and the second plate;

[0059] The third distributor located below the second plate introduces the oxidizing gas into each tube.

[0060] In the present invention, the multi-tube parallel packed oxidizer comprises a shell;

[0061] In one embodiment of the present invention, the inner diameter of the housing is 14 cm;

[0062] In the present invention, the multi-tube parallel packed oxidizer comprises tubes located inside the shell; the number of the tubes is ≥ 2;

[0063] In one embodiment of the present invention, the number of the tubes is 7, the inner diameter of the tubes is 2 cm, and the tubes are filled with ceramic fillers, which are preferably ceramic ball ring fillers with a specification of 25 mm*25 mm*3 mm.

[0064] In the present invention, the multi-tube parallel packed oxidizer includes a first plate and a second plate embedded in the tubes to block the space except the tube body in the horizontal direction; the first plate and the second plate are located at the upper part and the lower part of the tube respectively. Cooling water can be passed into the blocked space to cool the tube.

[0065] In the present invention, the multi-tube parallel packed oxidizer comprises a cooling water inlet and a cooling water outlet located between the first plate and the second plate;

[0066] In one embodiment of the present invention, the cooling water inlet is located at the bottom, and the cooling water outlet is located at the top.

[0067] In the present invention, the multi-tube parallel packed oxidizer includes a first distributor located at the top of the tube, which passes the reaction raw materials into each tube.

[0068] In the present invention, the multi-tube parallel packed oxidizer includes an external circulation heat exchanger; the inlet of the external circulation heat exchanger is connected to the bottom of the shell, and the outlet of the external circulation heat exchanger is connected to the second distributor, so that the reactants passing through the external circulation heat exchanger are introduced into each tube.

[0069] In the present invention, the multi-tube parallel packed oxidizer comprises an external circulation heat exchanger and a second distributor;

[0070] The inlet of the external circulation heat exchanger is connected to the bottom of the shell, and the outlet of the external circulation heat exchanger is connected to the second distributor, so that the reactants passing through the external circulation heat exchanger are introduced into each tube;

[0071] The second distributor is located between the first plate and the second plate.

[0072] In the present invention, the multi-tube parallel packed oxidizer includes a third distributor located below the second plate to introduce the oxidizing gas into each tube.

[0073] In one embodiment of the present invention, the multi-tube parallel packed oxidizer further comprises: a compressor;

[0074] The inlet of the compressor is connected to the shell above the first plate, and the outlet of the compressor is connected to the inlet of the third distributor. The excess oxygen at the top of the multi-tube parallel packed oxidizer is pressurized by the compressor and recycled, and the discharge port and the feed port are connected to achieve continuous reaction, avoiding the problems of high energy consumption, large pollution, long time consumption and harsh reaction conditions in the traditional production process.

[0075] The present invention also provides a method for preparing isobutyric acid, which is carried out in the multi-tube parallel packed oxidizer described in the above technical solution, comprising the following steps:

[0076] Isobutyraldehyde is continuously introduced into each tube through a first distributor and oxygen is continuously introduced into each tube through a third distributor to carry out a first oxidation reaction. The continuously generated crude isobutyric acid is introduced into an external circulation heat exchanger for heat exchange and then continuously introduced into each tube through a second distributor to carry out a second oxidation reaction to obtain the isobutyric acid.

[0077] Before isobutyraldehyde is continuously introduced into each tube via the first distributor and oxygen is continuously introduced into each tube via the third distributor, the present invention preferably further comprises: using oxygen to discharge the gas in the multi-tube parallel packed oxidizer and introducing circulating cooling water.

[0078] In the present invention, the pressure in the multi-tube parallel packed oxidizer after exhausting the gas is preferably 0.3-0.5 MPa; the temperature of the cooling water is preferably 15-20°C.

[0079] In the present invention, after exhausting the gas, the process preferably includes: passing the isobutyraldehyde into a third distributor via a preheater and a compression pump.

[0080] In the present invention, the temperature of the isobutyraldehyde after preheating is preferably 35°C.

[0081] In the present invention, the flow rate of the oxygen is preferably 700-900 mL / min, the flow rate of isobutyraldehyde is preferably 120-160 mL / min, more preferably 130-150 mL / min; the gas-liquid ratio of isobutyraldehyde to oxygen is preferably 4-8:1, more preferably 5-6:1.

[0082] In the present invention, the pressure of the first oxidation reaction and the second oxidation reaction is 0.3-0.5 MPa, more preferably 0.4-0.45 MPa. In the present invention, the temperature of the crude isobutyric acid and isobutyric acid without the external circulation heat exchanger is independently 35-55°C, preferably 40-45°C.

[0083] In the present invention, the sum of the time of the first oxidation reaction and the second oxidation reaction is preferably 1 to 1.5 hours.

[0084] The multi-tube parallel packed oxidizer and the method for preparing isobutyric acid provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0085] A multi-tube parallel packed oxidizer, comprising:

[0086] Shell: The inner diameter of the shell is 14 cm;

[0087] The tube is located inside the shell; the number of the tubes is 7; the inner diameter of the tube is 2 cm; the tube is fully filled with ceramic ball ring packing with a specification of 25 mm*25 mm*3 mm;

[0088] The first plate and the second plate embedded in the tube block the space except the tube body in the horizontal direction; the first plate and the second plate are respectively located at the upper part and the lower part of the tube;

[0089] A cooling water inlet and a cooling water outlet are located between the first plate and the second plate; the cooling water inlet is located at the bottom, and the cooling water outlet is located at the top.

[0090] A first distributor located at the top of the tubes passes the reaction raw materials into each tube;

[0091] External circulation heat exchanger and second distributor;

[0092] The inlet of the external circulation heat exchanger is connected to the bottom of the shell, and the outlet of the external circulation heat exchanger is connected to the second distributor, so that the reactants passing through the external circulation heat exchanger are introduced into each tube;

[0093] The second distributor is located between the first plate and the second plate;

[0094] a third distributor located below the second plate, for introducing oxidation gas into each tube;

[0095] compressor;

[0096] The inlet of the compressor is connected to the shell above the first plate, and the outlet of the compressor is connected to the inlet of the third distributor.

[0097] Figure 1 The process flow chart of an embodiment of the present invention.

[0098] Example 1

[0099] (1) First, use oxygen to discharge the gas in the multi-tube parallel packed oxidizer;

[0100] (2) In multiple experiments, the oxygen flow rates were controlled at 500, 700, and 900 mL / min, and the system pressure was raised to 0.4 MPa and then kept constant;

[0101] (3) The material circulation pump preheats the isobutyraldehyde to 35° C. and then continuously pumps it into the multi-tube parallel packed oxidizer at a rate of 140 mL / min;

[0102] (4) The external cooling water is set at 15°C to remove the reaction heat in time;

[0103] (5) the crude isobutyric acid at the bottom of the oxidizer is subjected to external circulation heat exchange and then re-enters the multi-tube parallel packed oxidizer, and the temperature of the crude isobutyric acid is controlled at 40° C.;

[0104] (6) Excess oxygen is discharged from the top of the oxidizer, and the oxygen is pressurized by a compressor and pumped back into the oxidizer for recycling;

[0105] (7) Continuously introduce oxygen to maintain a stable internal pressure of the device;

[0106] (8) Continue the reaction for 1 h. When the discharge temperature of the device stabilizes, take a sample from the bottom of the oxidizer and analyze the product composition.

[0107] The conversion rate of isobutyraldehyde at oxygen flow rates of 500, 700, and 900 mL / min was investigated, and the results were reflected by gas chromatography data. Figures 2 to 4 And as shown in Table 1. Among them, Figure 2 is the gas chromatogram of isobutyric acid when the oxygen flow rate is 500 mL / min; Figure 3 is the gas chromatogram of isobutyric acid when the oxygen flow rate is 700 mL / min; Figure 4 This is the gas chromatogram of isobutyric acid when the oxygen flow rate is 900 mL / min.

[0108] Table 1 Gas chromatography data of isobutyric acid in Example 1

[0109] serial number Retention time area Peak area% Figure 2 12.539 45203759 3079659 74.463 Figure 3 12.539 52664062 3561252 93.892 Figure 4 12.468 46989051 3063106 85.245

[0110] From Table 1, Figures 2 to 4 It can be seen that when the oxygen flow rate is 700mL / min, the isobutyric acid content in the product is the highest, which is 93.892%; when the oxygen flow rate is 700mL / min, the isobutyric acid content decreases due to the decrease in oxygen flow rate; when the oxygen flow rate is 700mL / min, the increase in oxygen intensifies the reaction, causing an increase in by-products, resulting in a decrease in the isobutyric acid content in the product.

[0111] Example 2

[0112] (1) First, use oxygen to discharge the gas in the multi-tube parallel packed oxidizer;

[0113] (2) The oxygen flow rate was controlled at 700 mL / min, and the system pressure was increased to 0.4 MPa and then kept constant;

[0114] (3) The material circulation pump preheats the isobutyraldehyde to 35° C. and then continuously pumps it into the multi-tube parallel packed oxidizer at a rate of 140 mL / min;

[0115] (4) The external cooling water is set at 15°C to remove the reaction heat in time;

[0116] (5) the crude isobutyric acid at the bottom of the oxidizer is subjected to external circulation heat exchange and then re-enters the multi-tube parallel packed oxidizer, and the temperature of the crude isobutyric acid is controlled at 40° C.;

[0117] (6) Excess oxygen is discharged from the top of the oxidizer, and the oxygen is pressurized by a compressor and pumped back into the oxidizer for recycling;

[0118] (7) Continuously introduce oxygen to maintain a stable internal pressure of the device;

[0119] (8) In multiple tests, the reaction time was controlled to be different at 0.5, 1, and 1.5 h. After the discharge temperature of the device was stable, samples were taken from the bottom of the oxidizer and the product composition was analyzed.

[0120] The conversion rate of isobutyraldehyde at different reaction times was investigated, and the results were reflected by gas chromatography data. Figures 5 to 7 And as shown in Table 2. Among them, Figure 5 It is the gas chromatogram of isobutyric acid when the reaction time is 0.5h;

[0121] Figure 6 It is the gas chromatogram of isobutyric acid when the reaction time is 1 h; Figure 7 This is the gas chromatogram of isobutyric acid when the reaction time is 1.5h.

[0122] Table 2 Isobutyric acid gas chromatography data of Example 2

[0123] serial number Retention time area Peak area% Figure 5 12.596 35057518 2716423 58.732 Figure 6 12.529 52308842 3550206 92.866 Figure 7 12.562 47955077 3377229 82.781

[0124] From Table 2, Figures 5 to 7 It can be seen that when the reaction time is 1h, the isobutyric acid content in the product is the highest, which is 92.866%; when the reaction time is 0.5h, due to the short reaction time, the reaction is incomplete and the isobutyric acid content drops significantly; when the reaction time is 1.5h, due to the long reaction time, the side reactions increase, resulting in an increase in by-products, which leads to a decrease in the isobutyric acid content in the product.

[0125] Example 3

[0126] Experiments were conducted using a conventional intermittent oxidizer (compared with the tube parallel packed oxidizer of the present invention: the conventional intermittent oxidizer does not contain a first plate, a second plate, a first distributor, a tube, an external circulation heat exchanger, a second distributor, and a third distributor) and a multi-tube parallel packed oxidizer:

[0127] When using a conventional intermittent oxidizer, add 2000mL of isobutyraldehyde to the oxidizer, which is 1 / 4 of the total volume, introduce oxygen to discharge the gas in the oxidizer, raise the system pressure to 0.4MPa and keep it constant, pass cooling water for circulation and heat exchange (the temperature of the condensed water is 15°C), control the oxygen flow rate at 700mL / min and introduce it from the top, stop after 1h, and take samples;

[0128] When using a multi-tube parallel packed oxidizer:

[0129] (1) introducing oxygen to discharge the gas in the oxidizer, controlling the oxygen flow rate at 700 mL / min, and raising the system pressure to 0.4 MPa and then keeping it constant;

[0130] (2) The material circulation pump preheats the isobutylaldehyde to 35° C. and then continuously pumps it into the multi-tube parallel packed oxidizer at a rate of 140 mL / min;

[0131] (3) The external circulating cooling water is set at 15°C (the cooling water flow rate is the same as that when using a conventional intermittent oxidizer) to remove the reaction heat in a timely manner;

[0132] (4) the crude isobutyric acid at the bottom of the oxidizer is subjected to external circulation heat exchange and then re-enters the multi-tube parallel packed oxidizer, and the temperature of the crude isobutyric acid is controlled at 40° C.;

[0133] (5) Excess oxygen is discharged from the top of the oxidizer, and the oxygen is pressurized by a compressor and pumped back into the oxidizer for recycling;

[0134] (6) Continuously introduce oxygen to maintain a stable internal pressure of the device;

[0135] (7) Continue the reaction for 1 h. When the discharge temperature of the device stabilizes, take a sample from the bottom of the oxidizer and analyze the product composition.

[0136] The conversion rate of isobutyraldehyde under different reaction devices was investigated, and the results were reflected by gas chromatography data, such as Figures 8-9 .in, Figure 8 This is the gas chromatogram of isobutyric acid from a conventional batch oxidizer; Fig. 9 It is the gas chromatogram of isobutyric acid of the multi-tube parallel packed oxidizer of the present invention.

[0137] Table 3 Isobutyric acid gas chromatography data of Example 3

[0138] serial number Retention time area Peak area% Figure 8 12.605 38741899 2888563 65.943 Fig. 9 12.538 53389331 3587107 93.594

[0139] From Table 3, Figures 8-9 It can be seen that when a conventional intermittent oxidizer is used, the content of isobutyric acid in the product is relatively low, at 65.943%. The intermittent reaction makes it difficult to control the reaction temperature in the oxidizer, resulting in violent side reactions and reduced isobutyric acid purity. When a multi-tube parallel packed oxidizer is used, the content of isobutyric acid in the product is relatively high, at 93.594%, which can better control the system temperature, remove the reaction heat in time, and inhibit the occurrence of side reactions.

[0140] Example 4

[0141] (1) First, use oxygen to discharge the gas in the multi-tube parallel packed oxidizer;

[0142] (2) The oxygen flow rate was controlled at 700 mL / min, and the system pressure was increased to 0.4 MPa and then kept constant;

[0143] (3) The material circulation pump preheats the isobutyraldehyde to 35° C. and then continuously pumps it into the multi-tube parallel packed oxidizer at a rate of 140 mL / min;

[0144] (4) The external cooling water is set at 15°C to remove the reaction heat in time;

[0145] (5) The crude isobutyric acid at the bottom of the oxidizer is subjected to external circulation heat exchange and then re-enters the multi-tube parallel packed oxidizer. The temperature of the crude isobutyric acid is controlled at 30°C, 40°C, and 50°C in multiple experiments;

[0146] (6) Excess oxygen is discharged from the top of the oxidizer, and the oxygen is pressurized by a compressor and pumped back into the oxidizer for recycling;

[0147] (7) Continuously introduce oxygen to maintain a stable internal pressure of the device;

[0148] (8) Continue the reaction for 1 h. When the discharge temperature of the device stabilizes, take a sample from the bottom of the oxidizer and analyze the product composition.

[0149] The conversion rate of isobutyraldehyde at different discharge temperatures was investigated, and the results were reflected by gas chromatography data, such as Figures 10-12 .in, Fig.10 This is the gas chromatogram of isobutyric acid when the temperature of crude isobutyric acid is 30°C; Fig.11 This is the gas chromatogram of isobutyric acid when the temperature of crude isobutyric acid is 40°C; Fig.12 This is the gas chromatogram of crude isobutyric acid when the temperature is 50°C.

[0150] Table 4 Isobutyric acid gas chromatography data of Example 4

[0151] serial number Retention time area Peak area% Fig.10 12.678 22172301 2024520 37.284 Fig.11 12.522 55997521 3736374 93.449 Fig.12 12.566 46876057 3325833 80.700

[0152] From Table 4, Figures 10-12 It can be seen that when the external circulation reflux temperature is controlled at 40°C, the isobutyric acid content in the product is the highest, which is 93.449%; when the external circulation reflux temperature is controlled at 30°C, the reaction is incomplete due to the low temperature, and the isobutyric acid content drops significantly; when the external circulation reflux temperature is controlled at 50°C, the reaction temperature is too high, which intensifies the side reactions, causes an increase in by-products, and leads to a decrease in the isobutyric acid content in the product.

[0153] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A multi-tube parallel packed oxidizer, characterized in that: including a housing; A tube located inside the shell; the number of the tubes is ≥ 2; The first plate and the second plate embedded in the tube block the space except the tube body in the horizontal direction; the first plate and the second plate are respectively located at the upper part and the lower part of the tube; a cooling water inlet and a cooling water outlet located between the first plate and the second plate; A first distributor located at the top of the tubes passes the reaction raw materials into each tube; External circulation heat exchanger and second distributor; The inlet of the external circulation heat exchanger is connected to the bottom of the shell, and the outlet of the external circulation heat exchanger is connected to the second distributor, so that the reactants passing through the external circulation heat exchanger are introduced into each tube; The second distributor is located between the first plate and the second plate; The third distributor located below the second plate introduces the oxidizing gas into each tube.

2. The multi-tube parallel packed oxidizer according to claim 1, characterized in that: Also includes: compressor; The inlet of the compressor is connected to the shell above the first plate, and the outlet of the compressor is connected to the inlet of the third distributor.

3. The multi-tube parallel packed oxidizer according to claim 1, characterized in that: The cooling water inlet is located at the bottom, and the cooling water outlet is located at the top.

4. The multi-tube parallel packed oxidizer according to claim 1, characterized in that: Also includes: A preheater and a compression pump connected to the preheater; The compression pump is also connected to the first distributor.

5. A method for preparing isobutyric acid, characterized in that: The method is carried out in the multi-tube parallel packed oxidizer according to any one of claims 1 to 4, comprising the following steps: Isobutyraldehyde is continuously introduced into each tube through a first distributor and oxygen is continuously introduced into each tube through a third distributor to carry out a first oxidation reaction. The continuously generated crude isobutyric acid is introduced into an external circulation heat exchanger for heat exchange and then continuously introduced into each tube through a second distributor to carry out a second oxidation reaction to obtain the isobutyric acid.

6. The preparation method according to claim 5, characterized in that: The gas-liquid ratio of the isobutyraldehyde to oxygen is 4 to 8:

1.

7. The preparation method according to claim 5, characterized in that: The sum of the time for the first oxidation reaction and the second oxidation reaction is 1 to 1.5 hours.

8. The preparation method according to claim 5, characterized in that: The flow rate of the oxygen is 700-900 mL / min, and the flow rate of the isobutyraldehyde is 120-160 mL / min.

9. The preparation method according to claim 5, characterized in that: The temperature of the crude isobutyric acid and the isobutyric acid is independently 25 to 55°C.

10. The preparation method according to claim 5, characterized in that: The pressure of the first oxidation reaction and the second oxidation reaction is 0.3-0.5 MPa.

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