Method for preparing phthalic anhydride, ex-situ activation method and application

Abstract

The invention relates to the technical field of phthalic anhydride, and discloses a method for preparing phthalic anhydride, an ex-situ activation method and application. The method comprises the following steps: activating a catalyst in an oxygen-containing atmosphere under the condition that the pressure is greater than or equal to 0.2 bar, and then contacting feed gas containing o-xylene and / or naphthalene and air with the activated catalyst. By adopting the method provided by the invention to activate the catalyst, o-xylene and / or naphthalene in the feed gas can be rapidly increased to the highest concentration from the initial concentration, the load extraction period of the catalyst is obviously reduced by about 30-40 days, the operation cost of enterprises is reduced, and the cost of manufacturers is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of phthalic anhydride, and particularly relates to a method for preparing phthalic anhydride, a method for out-of-vessel activation, and an application thereof. Background Art

[0002] Phthalic anhydride (PA) is an important organic chemical raw material and is considered one of the top ten organic chemical raw materials. As an intermediate, PA is mainly used in the production of plasticizers, alkyd resins, and unsaturated polyester resins (UPR). Among them, plasticizers are mainly used in PVC compounds, accounting for about 57% of the global PA consumption; alkyd resins account for about 19% of the global PA consumption and are widely used in the production of solvent-based coatings and agricultural cover films. Unsaturated polyester resins (UPR) account for about 15% of the global PA consumption and are mainly used in the construction and transportation industries. Other uses include applications in dyes and various specialty chemicals.

[0003] Phthalic anhydride (phthalic anhydride) is prepared by gasifying o-xylene and / or naphthalene and then subjecting it to fixed-bed catalytic oxidation. Generally, a V-Ti system catalyst is used, with TiO2 and V2O5 as the main active substances, and one or several compounds of potassium, rubidium, cerium, cesium, niobium, chromium, tungsten, iron, silver, cobalt, gold, gallium, indium, antimony, bismuth, zirconium, erbium, tungsten, and tin as promoters. The above-mentioned active substances are sprayed on an inert annular carrier with a specific thickness to prepare catalysts with different performances.

[0004] Currently, patents for the oxidation of phthalic anhydride mainly focus on the screening of promoters and the optimization of formulations. BASF Corporation has disclosed a method for gas-phase oxidation, in which a gas stream comprising at least one hydrocarbon and molecular oxygen is passed through a catalyst produced using antimony trioxide containing a significant proportion of valentinite.

[0005] Southern Chemical Corporation has developed a multi-layer catalyst for the preparation of phthalic anhydride. The catalyst is arranged as follows: the catalyst arrangement has a first catalyst layer on the gas inlet side and at least one second catalyst layer with different catalytic activities downstream of the first catalyst layer along the gas flow direction.

[0006] Since the oxidation of phthalic anhydride is an exothermic reaction, in the initial stage of the reaction, the concentration of o-xylene and / or naphthalene in the raw material gas should not be too high. If the concentration is too high, it will cause instantaneous temperature runaway, even deactivate the catalyst, and may even cause an explosion in more serious cases. Therefore, in the prior art, the concentration of o-xylene and / or naphthalene in the raw material gas is usually controlled at a low level in the initial stage of the reaction, and then the salt temperature is gradually reduced while synchronously increasing the concentration of o-xylene and / or naphthalene in the raw material gas. However, the catalyst prepared by the existing method takes a long time to increase the concentration of o-xylene and / or naphthalene in the raw material gas from the initial concentration to the highest load (highest concentration), usually taking 2-3 months. The long activation period increases the production cost of enterprises. Summary of the Invention

[0007] The object of the present invention is to overcome the problem of the relatively long activation period of the catalyst existing in the prior art, and to provide a method for preparing phthalic anhydride, an ex-situ activation method and its application. This method can effectively shorten the time required for the initial concentration of o-xylene and / or naphthalene in the raw material gas to increase to the maximum load (maximum concentration), and can significantly improve the economic benefits of enterprises.

[0008] The inventors of the present invention unexpectedly found that the performance of the catalyst prepared by activating the catalyst under the condition of a pressure ≥ 0.2 bar is stable, and it can be directly heated to the production operation temperature, fed at a higher load, and shorten the time required for the initial concentration of o-xylene and / or naphthalene in the raw material gas to increase to the maximum load. To achieve the above object, in a first aspect of the present invention, there is provided a method for preparing phthalic anhydride, which includes activating the catalyst in an oxygen-containing atmosphere under the condition of a pressure ≥ 0.2 bar, and then contacting the raw material gas containing o-xylene and / or naphthalene and air with the activated catalyst.

[0009] In a second aspect of the present invention, there is provided a method for activating a catalyst, which includes placing the catalyst in an oxygen-containing atmosphere and activating it under the condition of a pressure ≥ 0.2 bar.

[0010] In a third aspect of the present invention, there is provided an application of the method for increasing the activation pressure of the catalyst in shortening the load-raising period of the raw material gas containing o-xylene and / or naphthalene in the preparation of phthalic anhydride.

[0011] By using the method of the present invention to activate the catalyst, the initial concentration of o-xylene and / or naphthalene in the raw material gas can be increased, and feeding can be carried out at a higher load. The initial concentration of o-xylene and / or naphthalene in the raw material gas is 55 - 70 g / m 3 or more.

[0012] By using the method of the present invention to activate the catalyst, the o-xylene and / or naphthalene in the raw material gas can be quickly increased from the initial concentration to the maximum concentration, the catalyst load-raising period can be significantly reduced by about 30 - 40 days, the operation cost of the enterprise can be reduced, the cost of the manufacturer can be saved, and at the same time, the performance of the catalyst is improved, and the weight yield of the product phthalic anhydride is increased by 0.4% - 1.7%. Brief Description of the Drawings

[0013] Figure 1 is a top view of the activator of the present invention;

[0014] Figure 2 is a sectional view of the activator of the present invention.

[0015] Description of the Reference Numerals

[0016] 1. Intake port, 2. Outlet port, 3. Flange, 4. Heat preservation and heating, 5. Bottom support, 6. Mesh sieve Detailed implementation manner

[0017] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and 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 herein.

[0018] In the present invention, "o-xylene" is abbreviated as "o-phthalic".

[0019] The "pressure" in the present invention refers to "relative pressure (i.e., gauge pressure)".

[0020] The first aspect of the present invention provides a method for preparing phthalic anhydride, which includes activating the catalyst in an oxygen-containing atmosphere under the condition of pressure ≥ 0.2 bar, and then contacting the raw material gas containing o-xylene and / or naphthalene and air with the activated catalyst.

[0021] According to the present invention, the oxygen-containing atmosphere can be an oxygen-containing atmosphere commonly used in the art. Preferably, the oxygen content in the oxygen-containing atmosphere is 10-50% by volume, preferably 20-40% by volume.

[0022] According to the present invention, preferably, the activation method includes:

[0023] S1. Heating the catalyst to the first temperature T1 at the first heating rate in an oxygen-containing atmosphere;

[0024] S2. Then heating to the second temperature T2 at the second heating rate in an oxygen-containing atmosphere;

[0025] S3. Then heating to the third temperature T3 at the third heating rate in an oxygen-containing atmosphere, then raising the pressure to 0.2-2 bar (preferably 0.5-1.5 bar), and maintaining for 8-72 h under the conditions of this temperature and this pressure.

[0026] The pressure in step S3 can be 0.2 bar, 0.4 bar, 0.6 bar, 0.8 bar, 1 bar, 1.2 bar, 1.4 bar, 1.6 bar, 1.8 bar, 2 bar, and the ranges composed of any two of the above point values, preferably 1-1.5 bar, more preferably 1.2-1.5 bar.

[0027] The holding time in step S3 can be 8h, 12h, 16h, 20h, 24h, 30h, 36h, 40h, 48h, 52h, 56h, 60h, 64h, 70h, 72h, and the ranges formed by any two of the above values. Preferably, it is 24 - 48h, and more preferably 40 - 48h.

[0028] According to the present invention, preferably, in step S1, the oxygen-containing atmosphere is provided by a gas mixture including oxygen and an inert gas. Preferably, the volumetric space velocity of the gas mixture is 100 - 500 h -1 (preferably 200 - 400 h -1 ), and the oxygen content in the gas mixture is 20 - 25 vol%.

[0029] In the present invention, without special instructions, the inert gas can be an inert gas and / or nitrogen, preferably nitrogen. In the present invention, the oxygen-containing atmosphere can generally be prepared by mixing air with oxygen or air with an inert gas.

[0030] According to the present invention, preferably, in step S1, the first heating rate is 20 - 40 °C / h (preferably 25 - 35 °C / h), and the first temperature T1 is 90 - 110 °C (preferably 95 - 105 °C).

[0031] According to the present invention, preferably, in step S2, the oxygen-containing atmosphere is provided by a gas mixture including oxygen and an inert gas. Preferably, the volumetric space velocity of the gas mixture is 3000 - 5000 h -1 (preferably 3500 - 4500 h -1 ), and the oxygen content in the gas mixture is 25 - 40 vol% (preferably 28 - 30 vol%).

[0032] According to the present invention, preferably, in step S2, the second heating rate is 30 - 50 °C / h (preferably 35 - 45 °C / h), and the second temperature T2 is 240 - 260 °C.

[0033] According to the present invention, preferably, in step S3, the oxygen-containing atmosphere is provided by a gas mixture including oxygen and an inert gas. Preferably, the volumetric space velocity of the gas mixture is 100 - 500 h -1 (preferably 200 - 400 h -1 ), and the oxygen content in the gas mixture is 30 - 40 vol% (preferably 34 - 37 vol%).

[0034] According to the present invention, preferably, in step S3, the third heating rate is 20 - 40 °C / h (preferably 15 - 25 °C / h), and the third temperature T3 is 400 - 500 °C, more preferably 410 - 460 °C, and further preferably 430 - 450 °C.

[0035] According to the present invention, the contact conditions can be the contact conditions commonly used in the art. Preferably, the contact conditions include: the temperature is 300 - 450 °C, the space velocity of air in the feed gas is 2000 - 4000 h -1 , and the initial concentration of o-xylene and / or naphthalene in the feed gas is 55 - 70 g / Nm 3 .

[0036] According to the present invention, preferably, the method further includes: during the contact process, gradually increasing the concentration of o-xylene and / or naphthalene in the feed gas from the initial concentration to the highest concentration, where the highest concentration is 80 - 100 g / Nm 3 . The definition of the highest concentration is the concentration that o-xylene and / or naphthalene in the feed gas can reach when ensuring stable operation of the reaction, the salt temperature is not lower than 345 °C, the hot spot is not higher than 455 °C, and the weight yield of phthalic anhydride is not lower than 113%.

[0037] According to the present invention, preferably, the gradual increase is carried out to reach the highest concentration within 30 days.

[0038] According to the present invention, preferably, the operation of increasing the concentration of o-xylene and / or naphthalene in the feed gas from the initial concentration to the highest concentration includes: under the conditions of the initial load and the initial salt temperature (360 °C - 370 °C), controlling the salt temperature drop rate not to exceed 0.5 - 2 °C / day and the hot spot temperature not to be higher than 455 °C, controlling the load increase rate to be 0.5 g / Nm in 30 minutes or longer 3 , and the daily load increase rate not to exceed 2 g / Nm 3 ; no load is increased when the hot spot is higher than 450 °C.

[0039] According to the present invention, the loading method of the catalyst is not particularly limited and can be the loading methods commonly used in the art. Preferably, the catalyst is loaded in a segmented manner. More preferably, the catalyst is loaded in 3 - 6 segments, and different catalysts (different element compositions or ratios are regarded as different) are loaded in each segment.

[0040] According to the present invention, the types of the catalyst can be the catalysts commonly used in the art. For example, the catalyst is prepared according to the method of patent CN101422727B. Preferably, the catalyst is a V-Ti based phthalic anhydride catalyst. More preferably, the catalyst includes a carrier and an active component supported on the carrier, and the active component includes V, Cs, Nb, Ti, Sb, and optionally P.

[0041] According to the present invention, preferably, the content ratio of V, Cs, Nb, Ti, Sb, and P in the catalyst is 0.05 - 0.2:0.001 - 0.02:0.001 - 0.1:1:0.01 - 0.1:0 - 0.01.

[0042] According to the present invention, preferably, the loading heights ratio of the catalysts in the first to sixth sections is 1:0.5 - 0.8:0.5 - 0.8:0.3 - 0.6:0 - 1:0 - 1. The raw material gas contacts the catalysts in the first to sixth sections in sequence, that is, the raw material gas enters the reactor from the first section catalyst. The contents of V and Sb in the catalysts of the first to sixth sections increase in sequence.

[0043] The second aspect of the present invention provides a method for activating a catalyst, which includes placing the catalyst in an oxygen-containing atmosphere and activating it under the condition of pressure ≥ 0.2 bar.

[0044] In the present invention, the type of the activator is not particularly limited as long as it can provide the activation conditions. Preferably, as Figure 2 shown, the activator includes an air inlet 1, an air outlet 2, a flange 3, a heat preservation and heating layer 4, a bottom support 5, and a mesh sieve 6, wherein the catalyst is loaded in the mesh sieve 6. Valves are respectively arranged on the air inlet 1 and the air outlet 2. When the activator needs to maintain pressure, first close the valve on the air outlet 2, and when the pressure in the activator reaches the set value (pressure ≥ 0.2 bar), then close the valve on the air inlet 1 to activate the catalyst under the condition of the set pressure value.

[0045] According to the present invention, the number of the mesh sieves 6 can be selected according to the amount of the catalyst to be activated. More preferably, the number of the mesh sieves 6 is 4 - 30.

[0046] According to the present invention, the mesh aperture of the mesh sieve 6 is not particularly limited as long as it can fix the catalyst. Preferably, the mesh aperture of the mesh sieve 6 is 150 - 1700 μm.

[0047] The activator of the present invention can be cylindrical, or other shaped activators that can meet the activation conditions are also acceptable. Preferably, the inner diameter of the activator used in the present invention is 200 - 800 mm, the height is 500 - 1000 mm; the diameter of the mesh sieve 6 is 150 - 750 mm, the single-layer height is 30 - 50 mm; the total stacked height of the mesh sieves 6 is 120 - 950 mm; the heat preservation and heating layer 4 includes heating furnace wires and an asbestos cloth heat preservation layer. When activating, the catalyst is laid flat on the mesh of the mesh sieve 6, and the laying height is not higher than 20 - 40 mm. After the mesh sieves are stacked to the stacked height, seal the top cover flange. Under the heating of the heating furnace wires, the catalyst placed in the mesh sieve 6 is uniformly heated, and the pressure can be controlled.

[0048] In the present invention, the type of the reactor is not particularly limited and can be a reactor commonly used in the art. Preferably, the reactor is a single-tube evaluation device.

[0049] The method for out-of-reactor activation according to the present invention, wherein the activation conditions, the contact conditions, the type of catalyst, and the loading method are the same as those described in the first aspect, and will not be elaborated herein.

[0050] The third aspect of the present invention provides an application of a method for increasing the activation pressure of a catalyst in shortening the stripping load cycle of a raw material gas containing o-xylene and / or naphthalene in the preparation of phthalic anhydride.

[0051] According to the application of increasing the activation pressure in shortening the stripping load cycle of a raw material gas containing o-xylene and / or naphthalene in the preparation of phthalic anhydride, wherein the activation conditions, the contact conditions, the type of catalyst, and the loading method are the same as those described in the first aspect, and will not be elaborated herein.

[0052] According to the application of increasing the activation pressure in shortening the stripping load cycle of a raw material gas containing o-xylene and / or naphthalene in the preparation of phthalic anhydride. Wherein, the activator is the same as the conditions described in the second aspect, and will not be elaborated herein. Definition of the stripping load cycle of the raw material gas The time experienced by o-xylene and / or naphthalene in the raw material gas from the initial concentration to the highest concentration.

[0053] The present invention will be described in detail below through examples. In the following examples,

[0054] The calculation formula for the weight yield of phthalic anhydride is

[0055]

[0056] Catalyst 1 was prepared according to the method of Example 1 of Patent CN101422727B and denoted as Catalyst A; Catalyst 2 was prepared according to the method of Example 2 of Patent CN101422727B and denoted as Catalyst B; Catalyst 3 was prepared according to the method of Example 3 of Patent CN101422727B and denoted as Catalyst C; Catalyst 4 was prepared according to the method of Example 4 of Patent CN101422727B and denoted as Catalyst D.

[0057] Example 1

[0058] Activation was carried out in an activator. The activator (such as Figure 1-2As shown in the figure, it includes an air inlet 1, an air outlet 2, a flange 3, a heat-insulating and heating layer 4, a bottom support 5, and a mesh sieve 6. Among them, the catalyst is filled in the mesh sieve 6. Valves are respectively arranged on the air inlet 1 and the air outlet 2. When airtight pressure retention is required, first close the valve on the air outlet 2. When the pressure in the activator reaches the set value, then close the valve on the air inlet 1, so that the catalyst is activated under the condition of the set pressure value. The inner diameter of the activator is 500 mm and the height is 800 mm; the diameter of the mesh sieve 6 is 400 mm, and the single-layer height is 40 mm; the total stacked height of the mesh sieve 6 is 160 mm, the number of the mesh sieve 6 is 4, and the aperture of the sieve mesh of the mesh sieve 6 is 550 μm; the heat-insulating and heating layer 4 includes heating furnace wires and an asbestos cloth heat-insulating layer.

[0059] Weigh 600 g each of catalyst A, catalyst B, catalyst C, and catalyst D, and respectively load them into the mesh sieve 6 of the activator. Seal the top cover flange 3, and then start the activation. During activation, spread the catalyst flat on the mesh sieve of the mesh sieve 6, and the spreading height is about 20 mm.

[0060] S1. Start heating at a rate of 20 °C / h, and at the same time, pass air into the activator through the air inlet 1. The volumetric air velocity of the air is 300 h -1 ;

[0061] S2. When the temperature reaches 100 °C, heat at a rate of 40 °C / h, and at the same time, pass a mixed gas containing oxygen (the oxygen content in the mixed gas is about 28 vol%) into the activator through the air inlet 1, and increase the volumetric air velocity of the mixed gas to 4000 h -1 ;

[0062] S3. When the temperature reaches 250 °C, heat at a rate of 20 °C / h, and at the same time, pass a mixed gas containing oxygen (the oxygen content in the mixed gas containing oxygen is about 35 vol%) into the activator through the air inlet 1, and reduce the volumetric air velocity of the mixed gas to 300 h -1 ; When the temperature reaches 440 °C, keep this atmosphere unchanged, carry out airtight pressurization and heat preservation on the activator, control the pressure to be 0.5 bar, and the activation time is 12 h. Then naturally cool down to room temperature (about 25 °C) to obtain the activated catalyst A, the activated catalyst B, the activated catalyst C, and the activated catalyst D respectively.

[0063] Take out the activated catalyst A, activated catalyst B, activated catalyst C, and activated catalyst D in sequence, and then load the activated catalyst D, activated catalyst C, activated catalyst B, and activated catalyst A into a 4400 mm single-tube evaluation device in the order from bottom to top. The total loading height is 3400 mm. Among them, the loading heights of the activated catalyst D, activated catalyst C, activated catalyst B, and activated catalyst A are 600 mm, 800 mm, 800 mm, and 1200 mm respectively. When the molten salt temperature (hereinafter referred to as salt temperature) is heated to 365 °C, start to introduce the raw gas containing air and o-xylene above the single-tube evaluation device to start the evaluation reaction. The initial space velocity of air and the initial concentration of o-xylene in the raw gas are shown in Table 1. The operation of increasing the initial concentration of o-xylene in the raw gas to the highest concentration includes: under the conditions of the initial load and initial salt temperature, controlling the salt temperature decrease rate not exceeding 0.5 - 2 °C / day and the hot spot temperature not higher than 455 °C, and controlling the load increase rate to be 0.5 g / Nm in 30 minutes or more 3 , and the daily load increase rate does not exceed 2 g / Nm 3 ; do not increase the load when the hot spot is higher than 450 °C. The evaluation results are shown in Table 1.

[0064] Example 2

[0065] Perform activation and catalyst evaluation according to the method of Example 1. The difference is that in step S3, the activation time is 18 h. The evaluation results are shown in Table 1.

[0066] Example 3

[0067] Perform activation and catalyst evaluation according to the method of Example 1. The difference is that in step S3, the controlled pressure is 1 bar and the activation time is 24 h. The evaluation results are shown in Table 1.

[0068] Example 4

[0069] Perform activation and catalyst evaluation according to the method of Example 1. The difference is that in step S3, the controlled pressure is 1.5 bar and the activation time is 48 h. The evaluation results are shown in Table 1.

[0070] Example 5

[0071] The activation is carried out in the activator in Example 1

[0072] Weigh 600 g of each of catalyst A, catalyst B, catalyst C, and catalyst D, and load them into the mesh sieve 6 of the activator respectively. Seal the top cover flange 3, and then start the activation. When activating, spread the catalyst evenly on the mesh sieve of the mesh sieve 6, and the spreading height is about 20 mm.

[0073] S1. Start heating up at a rate of 30 °C / h. Meanwhile, pass a mixed gas containing oxygen (the oxygen content in the mixed gas is about 20 vol%) into the activator through the air inlet 1. The volume space velocity of the mixed gas is 100 h -1 ;

[0074] S2. When the temperature reaches 90 °C, continue heating up at a rate of 30 °C / h. Meanwhile, pass a mixed gas containing oxygen (the oxygen content in the mixed gas is about 25 vol%) into the activator through the air inlet 1, and increase the volume space velocity of the air to 3000 h -1 ;

[0075] S3. When the temperature reaches 250 °C, continue heating up at a rate of 30 °C / h. Meanwhile, pass a mixed gas containing oxygen (the oxygen content in the mixed gas is about 30 vol%) into the activator through the air inlet 1, and reduce the volume space velocity of the air to 500 h -1 , when the temperature reaches 410 °C, keep this atmosphere unchanged, seal and pressurize the activator for heat preservation, control the pressure at 2 bar, and the activation time is 8 h. Then naturally cool down to room temperature (about 25 °C) to obtain activated catalyst A, activated catalyst B, activated catalyst C, and activated catalyst D respectively.

[0076] Then conduct catalyst evaluation according to the method of Example 1. The evaluation results are shown in Table 1.

[0077] Example 6

[0078] Activation is carried out in the activator in Example 1

[0079] Weigh 600 g of each of catalyst A, catalyst B, catalyst C, and catalyst D, and separately load them into the mesh sieve 6 of the activator. Seal the top cover flange 3, and then start activation. When activating, spread the catalyst evenly on the mesh of the mesh sieve 6, and the spreading height is about 20 mm.

[0080] S1. Start heating up at a rate of 40 °C / h. Meanwhile, pass a mixed gas containing oxygen (the oxygen content in the mixed gas is about 25 vol%) into the activator through the air inlet 1. The volume space velocity of the mixed gas is 500 h -1 ;

[0081] S2. When the temperature reaches 110 °C, continue heating up at a rate of 50 °C / h. Meanwhile, pass a mixed gas containing oxygen (the oxygen content in the mixed gas is about 40 vol%) into the activator through the air inlet 1, and increase the volume space velocity of the air to 5000 h -1 ;

[0082] S3. When the temperature reaches 250 °C, raise the temperature at a rate of 40 °C / h. At the same time, introduce a mixed gas containing oxygen (the oxygen content in the mixed gas is about 40 vol%, and the remaining gas is nitrogen) into the activator through the air inlet 1, and reduce the volumetric air velocity of the air to 100 h -1 . When the temperature reaches 460 °C, keep this atmosphere unchanged, seal and pressurize the activator for heat preservation, control the pressure to be 0.2 bar, and the activation time to be 72 h. Then naturally cool down to room temperature (about 25 °C) to obtain the activated catalyst A, the activated catalyst B, the activated catalyst C, and the activated catalyst D respectively.

[0083] Then, conduct the catalyst evaluation according to the method of Example 1. The evaluation results are shown in Table 1.

[0084] Comparative Example 1

[0085] The activation process is carried out in a single-tube evaluation device.

[0086] Load the catalyst D, catalyst C, catalyst B, and catalyst A into the 4400 mm single-tube evaluation device in the order from bottom to top. The total loading height is 3400 mm. Among them, the loading heights of the catalyst D, catalyst C, catalyst B, and catalyst A are 600 mm, 800 mm, 800 mm, and 1200 mm respectively, and then start the activation.

[0087] S1. Start to raise the temperature at a rate of 20 °C / h. At the same time, introduce air into the single-tube evaluation device, and the volumetric air velocity of the air is 300 h -1 ;

[0088] S2. When the temperature reaches 100 °C, raise the temperature at a rate of 40 °C / h, keep this atmosphere unchanged, and increase the volumetric air velocity of the air to 4000 h -1 ;

[0089] S3. When the temperature reaches 250 °C, raise the temperature at a rate of 20 °C / h, keep this atmosphere unchanged, and reduce the volumetric air velocity of the air to 300 h -1 . When the temperature reaches 440 °C, keep this atmosphere unchanged and conduct heat preservation (keep the volumetric air velocity of the air unchanged during the heat preservation process), and the heat preservation time is 48 h. Then, when it naturally cools down to 25 °C and the salt temperature is heated to 365 °C, start to introduce the raw material gas containing air and o-xylene above the single-tube evaluation device to start the evaluation reaction. The operation of increasing the o-xylene in the raw material gas from the initial concentration to the highest concentration is the same as that in Example 1. The evaluation results are shown in Table 1.

[0090] Comparative Example 2

[0091] Activation and catalyst evaluation were carried out according to the method of Comparative Example 1, except that in step S3, when the temperature was naturally cooled to 395 °C, the evaluation reaction was started by introducing a raw material gas containing air and o-xylene into the single-tube evaluation device. The o-xylene in the raw material gas was increased from the initial concentration to the highest concentration according to the existing industrial operation steps. The specific process is as follows:

[0092] (1) Feed air volume: 3.0 Nm 3 / h·tube; Initial load: 25.5 g / Nm 3 .

[0093] (2) Salt temperature of the supplied air: 400 ± 5 °C; Salt temperature was controlled at 380 °C after feeding.

[0094] (3) On the first day of starting up: Increase by 1 g / Nm per hour 3 (in multiple steps). When the hot spot temperature rises to about 425 °C, stop increasing the load; when the hot spot temperature rises to 440 °C, reduce the load.

[0095] (4) On the second day of starting up: Increase by 1 g / Nm per hour 3 (in multiple steps). When the hot spot temperature reaches about 435 °C, stop increasing the load. When the hot spot temperature rises to 440 °C, reduce the load.

[0096] (5) On the third day of starting up: Increase by 0.05 Nm every 30 minutes 3 / h·tube to 3.5 Nm 3 / h·tube. Keep the load constant during the process of increasing the air volume.

[0097] (6) On the fourth day of starting up: Increase by 0.05 Nm every 30 minutes 3 / h·tube to 4.0 Nm 3 / h·tube. Keep the load constant during the process of increasing the air volume.

[0098] During the process of increasing the air volume, control the hot spot temperature at 435 - 440 °C. If it exceeds 440 °C, reduce the load. After the air volume reaches 4.0 Nm 3 / h·tube, maintain it on the same day. If the hot spot exceeds 440 °C, reduce the salt temperature, but the reduction amplitude does not exceed 2 °C per day.

[0099] (7) After the air volume reaches 4.0 Nm 3 / h·tube, the rate of reducing the salt temperature:

[0100] ≥365 °C: It does not exceed 0.5 °C in 30 minutes or more, and does not exceed 2 °C per day;

[0101] 365 - 355 °C: It does not exceed 0.3 °C in 60 minutes or more, and does not exceed 1 °C per day;

[0102] 355~350℃: Not exceeding 0.2℃ in 60 minutes or longer, not exceeding 0.5℃ per day; continue to reduce the salt temperature not exceeding 0.3℃ per day or every two days.

[0103] (8) Load increasing rate: Increase 0.5 g / Nm in 30 minutes or longer 3 , the load increasing rate does not exceed 3 g / Nm per day 3 . When the load reaches 58 g / Nm 3 after that, the load increasing rate does not exceed 2 g / Nm per day 3 . Do not increase the load when the hot spot is greater than 445℃, control the hot spot to be less than 448℃. When increasing the load, if the hot spot is greater than 445℃ during the process, reduce the salt temperature with reference to step (7).

[0104] The evaluation results are shown in Table 1.

[0105] Table 1

[0106]

[0107] It can be seen from the results in Table 1 that compared with Comparative Examples 1-2 (the catalyst activation methods adopted in the existing industry), Examples 1-6 of the present invention can significantly reduce the load increasing period of the catalyst, reduce the enterprise operation cost, save the cost of the manufacturer, and at the same time improve the catalyst performance and increase the weight yield of the product phthalic anhydride.

[0108] Particularly preferably, adopting the catalyst activation method of Example 4 of the present invention can further shorten the load increasing period to 20 days.

[0109] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing phthalic anhydride, characterized in that, The method includes activating the catalyst in an oxygen-containing atmosphere under the condition of a pressure ≥ 0.2 bar, and then bringing a feed gas containing o-xylene and / or naphthalene and air into contact with the activated catalyst.

2. The method according to claim 1, wherein, The content of oxygen in the oxygen-containing atmosphere is 10 - 50 vol%, preferably 20 - 40 vol%.

3. The method according to claim 1 or 2, wherein, The activation method includes: S1. Heating the catalyst to a first temperature T1 at a first heating rate in an oxygen-containing atmosphere; S2. Then heating to a second temperature T2 at a second heating rate in the oxygen-containing atmosphere; S3. Then heating to a third temperature T3 at a third heating rate in the oxygen-containing atmosphere, raising the pressure to 0.2 - 2 bar, and maintaining for 8 - 72 h under this temperature and this pressure condition.

4. The method according to claim 3, wherein, In step S1, the oxygen-containing atmosphere is provided by a gas mixture including oxygen and an inert gas. Preferably, the volumetric space velocity of the gas mixture is 100 - 500 h -1 , and the oxygen content in the gas mixture is 20 - 25 vol%; And / or, in step S1, the first heating rate is 20 - 40 °C / h, and the first temperature T1 is 90 - 110 °C.

5. The method according to claim 3, wherein, In step S2, the oxygen-containing atmosphere is provided by a gas mixture including oxygen and an inert gas. Preferably, the volumetric space velocity of the gas mixture is 3000-5000 h -1 , and the oxygen content in the gas mixture is 25-40 vol%; And / or, in step S2, the second heating rate is 30 - 50 °C / h, and the second temperature T2 is 240 - 260 °C.

6. The method according to claim 3, wherein, In step S3, the oxygen-containing atmosphere is provided by a gas mixture including oxygen and an inert gas. Preferably, the volumetric space velocity of the gas mixture is 100 - 500 h -1 , and the oxygen content in the gas mixture is 30 - 40 vol%; And / or, in step S3, the third heating rate is 20 - 40 °C / h, and the third temperature T3 is 400 - 500 °C.

7. The method according to claim 3, wherein The conditions for contact include: the temperature is 300 - 450 °C, the space velocity of air in the raw material gas is 2000 - 4000 h -1 , and the initial concentration of o-xylene and / or naphthalene in the raw material gas is 55 - 70 g / Nm 3 .

8. The method according to claim 7, wherein The method further includes: during the contact process, gradually increasing the concentration of o-xylene and / or naphthalene in the raw material gas from an initial concentration to a maximum concentration, where the maximum concentration is 80 - 100 g / Nm 3 ; Preferably, the stepwise increasing manner is to increase to the highest concentration within 30 days.

9. A method for activating a catalyst, characterized in that, The method includes placing the catalyst in an oxygen-containing atmosphere and activating it under the condition of a pressure ≥ 0.2 bar.

10. Application of a method for increasing the activation pressure of a catalyst in shortening the feed gas stripping load cycle of o-xylene and / or naphthalene in phthalic anhydride preparation.

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