Process for condensing and recovering phthalic anhydride

Abstract

The invention discloses a process for condensing and recovering phthalic anhydride, and relates to the technical field of phthalic anhydride refining. The phthalic anhydride condensation and recovery process comprises the following steps: (1) enabling reaction gas to sequentially pass through a first condensation system and a second condensation system, and desublimating phthalic anhydride gas in the reaction gas into a solid; (2) transferring heat to enable the phthalic anhydride solid in the condensation system to become crude phthalic anhydride liquid, and separating the crude phthalic anhydride liquid in a separation tank to obtain refined phthalic anhydride; in the step (2), the treatment pressure of the separation tank is-1-2kpa, and the treatment temperature is 240-280 DEG C; in the separation process, a Na2CO3 aqueous solution with the mass percentage concentration of 28-40% is added into the separation tank, and the mass of the Na2CO3 aqueous solution is 0.01-0.02% of the mass of the crude phthalic anhydride liquid. The concentration of the sodium carbonate aqueous solution is limited to be 28%-40%, so that the phthalic anhydride content in the refined phthalic anhydride is increased, and the phthalic anhydride content in the refined phthalic anhydride is larger than or equal to 85%.

Description

Technical Field

[0001] The invention relates to the technical field of phthalic anhydride refining, and in particular to a condensation recovery process for phthalic anhydride. Background Art

[0002] Phthalic anhydride, whose full name is phthalic anhydride (PA), is a cyclic anhydride formed by dehydration of phthalic acid molecules. There are two production methods for phthalic anhydride: the naphthalene method and the ortho-method.

[0003] The naphthalene process of phthalic anhydride is based on the principle that naphthalene and air are oxidized in the gas phase under the action of a catalyst to generate phthalic anhydride. The specific production process is as follows: the process is that the air is purified, compressed and preheated, and then enters the bottom of the fluidized bed reactor, where liquid naphthalene is sprayed in. After naphthalene is vaporized, it mixes with air and passes through the fluidized catalyst layer to generate phthalic anhydride through an exothermic reaction. The reactor is equipped with a tube-and-tube cooler, and water is used as a heat carrier to remove the heat of reaction. The reaction gas passes through a three-stage cyclone separator to separate the catalyst carried by the gas, and then enters a liquid condenser, where 40%-60% of the crude phthalic anhydride is condensed in liquid form. The gas then enters a switching condenser to further separate the crude phthalic anhydride. The crude phthalic anhydride is pre-decomposed and distilled to obtain the finished phthalic anhydride. The tail gas is discharged after washing, and the washing liquid is diluted with water and discharged or sent for catalytic incineration.

[0004] The reaction principle of o-phthalic anhydride is that o-xylene and air are oxidized in the gas phase under the action of a catalyst to generate phthalic anhydride. The specific process flow is as follows: the filtered and purified air is compressed, preheated, mixed with vaporized o-xylene and enters a fixed bed reactor for an exothermic reaction, and a circulating molten salt is used outside the reaction tube to remove the reaction heat and maintain the reaction temperature. The reaction heat brought by the molten salt is used to produce high-pressure steam. The gas coming out of the reactor enters the switching condenser with cold oil passing through the fin tube through the precooler, condensing the phthalic anhydride on the fins, and then hot oil is regularly passed to melt the phthalic anhydride. After heat treatment, it is sent to a continuous distillation system to remove low-boiling point and high-rising point impurities to obtain the phthalic anhydride product. The tail gas coming out of the switching condenser is discharged into the atmosphere after two-stage high-efficiency washing. The circulating liquid containing an organic acid concentration of 30% is sent to a maleic anhydride recovery device or an incineration device, and can also be recycled to produce fumaric acid.

[0005] German patent DE2711289A1 discloses a process for optimizing the production of phthalic anhydride, including a step of gas-phase oxidation of o-xylene over a catalyst containing vanadium oxide and titanium oxide at a temperature of 300°C to 500°C. The patent also discloses a purification step of phthalic anhydride: the crude product obtained in the fin tube separator is purified, and the purification consists only of countercurrent crystallization, or a combination of pretreatment and countercurrent crystallization purification steps, and the pretreatment of the crude product is to add 0.01% by weight of sodium carbonate to the crude product, boil the crude product under reflux for 6 to 15 hours, and then distill it into a receiver at 200-400Torr. The purification step disclosed in the patent does not disclose the form of sodium carbonate, and the distillation process consumes a lot of energy, which is not economical and environmentally friendly.

[0006] In view of this, in order to solve the deficiencies of the prior art, the present invention provides a condensation recovery process for phthalic anhydride. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings existing in previous studies and provide a condensation recovery process for phthalic anhydride, which can increase the recovery amount of phthalic anhydride on the basis of energy saving.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a condensation recovery process for phthalic anhydride, comprising the following steps:

[0010] (1) passing the reaction gas through a first condensation system and a second condensation system in sequence to condense phthalic anhydride gas in the reaction gas into a solid;

[0011] (2) transferring heat to convert the phthalic anhydride solid in the condensation system into crude phthalic anhydride liquid, which then flows into a separation tank for separation to obtain refined phthalic anhydride;

[0012] In step (2), the treatment pressure of the separation tank is -1 to 2 kPa, and the treatment temperature is 240-280°C;

[0013] During the separation process, a Na2CO3 aqueous solution with a mass percentage concentration of 28-40% is added to the separation tank, and the mass of the Na2CO3 aqueous solution is 0.01-0.02% of the mass of the crude phthalic anhydride liquid.

[0014] Preferably, in step (1), the first condensation system comprises five U-shaped fin-tube switching condensers.

[0015] Further preferably, in step (1), four U-shaped fin-tube switching condensers in the first condensation system perform condensation; and one U-shaped fin-tube switching condenser in the first condensation system performs hot melting or condensation.

[0016] Preferably, in step (1), the second condensation system comprises two U-shaped fin-tube switching condensers.

[0017] Further preferably, in step (1), a U-shaped fin-tube switching condenser in the second condensation system performs condensation; and a U-shaped fin-tube switching condenser in the second condensation system performs hot melting or condensation.

[0018] Preferably, in step (1), the temperature of the heat transfer oil for condensation in the condensation system is 50-60°C.

[0019] Preferably, in step (1), the temperature of the heat transfer oil for hot melting in the condensation system is 180-190°C.

[0020] Preferably, in step (2), the treatment temperature of the separation tank is 245-265°C.

[0021] Further preferably, in step (2), the treatment temperature of the separation tank is 250-260°C.

[0022] More preferably, in step (2), the treatment temperature of the separation tank is 255°C.

[0023] Preferably, in step (2), the mass percentage concentration of the Na2CO3 aqueous solution is 32%.

[0024] Preferably, in step (1), the reaction gas is a gas generated by gas-phase oxidation of naphthalene and air in the presence of a catalyst.

[0025] Further preferably, in step (1), the temperature of the reaction gas is 170-180°C.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention increases the phthalic anhydride content in the refined phthalic anhydride by limiting the concentration of the sodium carbonate aqueous solution to 28%-40%, so that the phthalic anhydride content in the refined phthalic anhydride is ≥85%.

[0028] (2) The present invention limits the processing temperature of the crude phthalic anhydride separation tank to 240-280° C., so that the phthalic anhydride content in the refined phthalic anhydride is ≥85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the process flow diagram of the oxidation reaction.

[0030] Figure 2 This is the process flow chart for condensation recovery. DETAILED DESCRIPTION

[0031] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, which should also fall within the scope of the present invention.

[0032] The present invention is further described below by way of specific examples. Unless otherwise specified, the various drugs used in the examples of the present invention are obtained through conventional commercial channels.

[0033] Example 1

[0034] The process flow of phthalic anhydride preparation by naphthalene is as follows:

[0035] 1. Raw material supply

[0036] Industrial naphthalene is transported to the unloading area by tank trucks and then transported to the naphthalene tank T-2101A / B / C in the industrial naphthalene tank area by naphthalene unloading pump G-13 for storage. During the production process, naphthalene pump G-12A / B is used to extract the industrial naphthalene in T-2101A / B / C and send it to the oxidation unit.

[0037] 2. Oxidation reaction

[0038] The required air is filtered by air filter FIL-01, compressed to 0.05MPaG by air blower G-11, heated to 195℃ by steam in air preheater E-11, and then enters gasifier F-14.

[0039] The industrial naphthalene from G-12A / B first enters the preheater E-211 and is heated to 190°C before entering the top of the industrial naphthalene vaporization tower T-211 as reflux liquid. The gas phase at the top of the naphthalene vaporization tower is then heated to 250°C by the superheater E-214 using high-pressure steam and then enters the vaporizer F-14 to be completely mixed with air. Two reboilers are set in the tower kettle of the naphthalene vaporization tower T-211. The steam reboiler is indirectly heated by high-pressure steam; the heat transfer oil reboiler is indirectly heated by high-temperature heat transfer oil (used during start-up). The tower kettle liquid is forced to circulate between the tower kettle and the two reboilers through the kettle liquid pump P-212A / B.

[0040] The mixed gas enters from the top of the reactor D-14, and industrial naphthalene is oxidized by air on the surface of the V-Ti catalyst to generate phthalic anhydride. This reaction is a highly exothermic reaction. Part of the reaction heat heats the reaction gas to 360-450°C, and most of the reaction heat is removed through the molten salt circulating in the molten salt cooler E-14, and generates 4.6MPaG high-pressure saturated steam through the high-pressure drum F-15.

[0041] The 360-450℃ reaction gas is discharged from the bottom of the reactor D-14 and cooled to 175℃ by the gas cooler E-16, and then enters the phthalic anhydride condensation recovery process. The process flow of the oxidation reaction is as follows: Figure 1 shown.

[0042] The gas cooler E-16 is divided into two sections. The first section is used to heat the condensate from the high-pressure drum to produce 4.6MPaG high-pressure saturated steam, and the second section is used to preheat the boiler feed water.

[0043] The heat of reaction in the reactor D-14 is removed by the molten salt flowing through the reaction tubes. The molten salt is circulated through two molten salt pumps G-14A / B. Part of the hot molten salt flows through the molten salt cooler E-14 outside the reactor D-14, where the molten salt is cooled and 4.6MPaG high-pressure saturated steam is generated through the high-pressure drum F-15. This high-pressure saturated steam is sent to the plant network after removing the phthalic anhydride unit. The molten salt regulating valve V-14A regulates the flow of molten salt flowing through the molten salt cooler E-14 to keep the molten salt temperature constant. The electric heater C-14 provides heat to the molten salt when starting and maintains a sufficient salt bath temperature when stopping.

[0044] During the initial start-up, the molten salt is melted by electric heating in the molten salt tank F-16 equipped with a heating tube and then pumped into the reactor D-14 by the molten salt filling pump G-18.

[0045] 3. Condensate recovery

[0046] The reaction gas at about 170-180°C from the oxidation reaction process enters the U-shaped fin-tube switching condenser E-21A / B / C / D / E for further cooling to the desublimation temperature, and the phthalic anhydride is condensed into a solid. The switching condenser is loaded and unloaded periodically in a certain order (four condensers are fed with reaction gas for condensation, and one is in hot melting or condensation. The temperature of the heat transfer oil for condensation is 50-60°C; the temperature of the heat transfer oil for hot melting is 180-190°C). The switching operation steps are realized by the DCS system control program. The phthalic anhydride-containing gas coming out of the outlet of the condenser E-21A / B / C / D / E enters the U-shaped fin-tube switching condenser E22A / B again to be cooled to the desublimation temperature. The switching operation steps are realized by the DCS system control program, so that all phthalic anhydride is condensed into a solid, and the main by-product is the residual gas after desublimation. The optimal temperature of the gas leaving E-22 is 60-65°C. After condensation, the tail gas containing trace products and most of the by-products is sent to the gas incineration device V-01. Here, the organic matter is incinerated and the tail gas is discharged from the tail gas chimney.

[0047] The switchable E-22 condenser is composed of a horizontally installed finned tube bundle. The post-reaction gas flows around it from top to bottom. When the heat transfer oil flows through the finned tube at a temperature of 50-60℃, it takes away the heat of phthalic anhydride sublimation, causing the phthalic anhydride to be desublimated and separated, and precipitated on the finned tube in the form of crystals. When unloading, the phthalic anhydride is melted by the switched 180-190℃ heat transfer oil and enters the crude phthalic anhydride separation tank for separation.

[0048] The separation in the crude phthalic anhydride separation tank is carried out under a slight negative pressure (-1 to 2 kPa) and the processing temperature is 255°C.

[0049] While the crude phthalic anhydride separation tank is separating, a 32% Na2CO3 aqueous solution is added to the bottom of the crude phthalic anhydride separation tank. The mass of the Na2CO3 aqueous solution is 0.01-0.02% of the mass of the crude anhydride to polymerize the aldehydes. The low-boiling point components are separated and discharged to the tail gas treatment through the vacuum system. The obtained polymer is separated from the crude phthalic anhydride as a high-boiling point component and enters the crude phthalic anhydride tank. The process flow of condensation recovery is as follows: Figure 2 shown.

[0050] Example 2

[0051] Add Na2CO3 with a mass percentage concentration of 28% at the bottom of the crude phthalic anhydride separation tank, and the rest of the process is the same as in Example 1.

[0052] Example 3

[0053] Add Na2CO3 with a mass percentage concentration of 40% at the bottom of the crude phthalic anhydride separation tank, and the rest of the process is the same as in Example 1.

[0054] Example 4

[0055] The treatment temperature of the crude phthalic anhydride separation tank is 240° C., and the rest of the process is the same as in Example 1.

[0056] Example 5

[0057] The treatment temperature of the crude phthalic anhydride separation tank is 245° C., and the rest of the process is the same as in Example 1.

[0058] Example 6

[0059] The treatment temperature of the crude phthalic anhydride separation tank is 250° C., and the rest of the process is the same as in Example 1.

[0060] Example 7

[0061] The treatment temperature of the crude phthalic anhydride separation tank is 260° C., and the rest of the process is the same as in Example 1.

[0062] Example 8

[0063] The treatment temperature of the crude phthalic anhydride separation tank is 265° C., and the rest of the process is the same as in Example 1.

[0064] Example 9

[0065] The treatment temperature of the crude phthalic anhydride separation tank is 270° C., and the rest of the process is the same as in Example 1.

[0066] Example 10

[0067] The treatment temperature of the crude phthalic anhydride separation tank is 275° C., and the rest of the process is the same as in Example 1.

[0068] Embodiment 11

[0069] The treatment temperature of the crude phthalic anhydride separation tank is 280° C., and the rest of the process is the same as in Example 1.

[0070] Comparative Example 1

[0071] Add Na2CO3 with a mass percentage concentration of 10% at the bottom of the crude phthalic anhydride separation tank, and the rest of the process is the same as in Example 1.

[0072] Comparative Example 2

[0073] Add Na2CO3 with a mass percentage concentration of 20% at the bottom of the crude phthalic anhydride separation tank, and the rest of the process is the same as in Example 1.

[0074] Results

[0075] 1. Determination of phthalic anhydride content in refined phthalic anhydride

[0076] 1.1. Determination method

[0077] (1) Measurement principle

[0078] The samples were separated by capillary column and detected by flame ionization detector, and the quantification was performed by peak area normalization method.

[0079] (2) Instruments and equipment

[0080] Gas chromatograph GC-2014C with hydrogen flame ionization detector;

[0081] Chromatographic column: 30m long, 0.32mm inner diameter, stationary phase OV-17, 0.25μm film thickness capillary column;

[0082] Split ratio: 10:1;

[0083] Vaporization chamber temperature: 300℃;

[0084] Detector temperature: 300°C;

[0085] Carrier gas: nitrogen;

[0086] Column temperature: programmed temperature, initially at 160°C for 1 min, then increased to 200°C at a rate of 10°C / min;

[0087] Micro-injector: 10 μL.

[0088] (3) Analysis steps

[0089] Weigh 1.5 g (accurate to 0.2 g) of the finely ground sample into a 100 mL beaker, add 50 mL of acetone to make the sample concentration 30 mg / mL, and put the beaker containing the sample into an ultrasonic cleaner for 10 minutes to dissolve the sample completely for later use.

[0090] Turn on the chromatograph and wait for the programmed temperature to stabilize, record the sample and wait for injection, use a microinjector to draw 1.0 μL of sample and inject it into the chromatographic column for analysis.

[0091] (4) Calculation of results

[0092] The purity of phthalic anhydride (C8H4O3) is expressed in ω i The value is expressed in (%) and is calculated as follows:

[0093] ω i =A1 / A i ×100%

[0094] Where:

[0095] A1——Peak area value of phthalic anhydride;

[0096] A i ——The sum of the peak area values ​​of each component i in the sample;

[0097] The calculation result is rounded to two decimal places.

[0098] (5) Allowable difference

[0099] The difference between the parallel determination results of phthalic anhydride purity should not be greater than 0.20%, and the arithmetic mean value is taken as the determination result.

[0100] 1.2. Measurement results

[0101] Table 1

[0102]

[0103] From the results of the phthalic anhydride content determination of Comparative Examples 1-2 and Examples 1-3, it can be seen that the present invention increases the phthalic anhydride content in the refined phthalic anhydride by limiting the concentration of the sodium carbonate aqueous solution to 28%-40%, so that the phthalic anhydride content in the refined phthalic anhydride is ≥85%.

[0104] From the results of the phthalic anhydride content determination in Example 1 and Examples 4-11, it can be seen that the present invention increases the phthalic anhydride content in the refined phthalic anhydride by adjusting the treatment temperature of the separation tank. When the concentration of the sodium carbonate aqueous solution is 32% and the treatment temperature of the separation tank is 245-265°C, the phthalic anhydride content in the refined phthalic anhydride is ≥90%.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A condensation recovery process for phthalic anhydride, characterized in that: The steps include: (1) passing the reaction gas through a first condensation system and a second condensation system in sequence to condense phthalic anhydride gas in the reaction gas into a solid; (2) transferring heat to convert the phthalic anhydride solid in the condensation system into crude phthalic anhydride liquid, which then flows into a separation tank for separation to obtain refined phthalic anhydride; In step (2), the treatment pressure of the separation tank is -1 to 2 kPa, and the treatment temperature is 240-280°C; During the separation process, a Na2CO3 aqueous solution with a mass percentage concentration of 28-40% is added to the separation tank, and the mass of the Na2CO3 aqueous solution is 0.01-0.02% of the mass of the crude phthalic anhydride liquid.

2. The condensation recovery process for phthalic anhydride according to claim 1, characterized in that: In step (1), the first condensing system includes five U-shaped fin-tube switching condensers; and the second condensing system includes two U-shaped fin-tube switching condensers.

3. The condensation recovery process for phthalic anhydride according to claim 2, characterized in that: In step (1), four U-shaped fin-tube switching condensers in the first condensation system perform condensation; and one U-shaped fin-tube switching condenser in the first condensation system performs hot melting or condensation.

4. The condensation recovery process for phthalic anhydride according to claim 2, characterized in that: In step (1), a U-shaped fin-tube switching condenser in the second condensation system performs condensation; and a U-shaped fin-tube switching condenser in the second condensation system performs hot melting or condensation.

5. The condensation recovery process for phthalic anhydride according to any one of claims 3 to 4, characterized in that: In step (1), the temperature of the heat transfer oil for condensation in the condensation system is 50-60°C; the temperature of the heat transfer oil for hot melting in the condensation system is 180-190°C.

6. The condensation recovery process for phthalic anhydride according to claim 1, characterized in that: In step (2), the treatment temperature of the separation tank is 245-265°C.

7. The condensation recovery process for phthalic anhydride according to claim 6, characterized in that: In step (2), the treatment temperature of the separation tank is 250-260°C.

8. The condensation recovery process for phthalic anhydride according to claim 7, characterized in that: In step (2), the treatment temperature of the separation tank is 255°C.

9. The condensation recovery process for phthalic anhydride according to claim 1, characterized in that: In step (2), the mass percentage concentration of the Na2CO3 aqueous solution is 32%.

10. The condensation recovery process of phthalic anhydride according to claim 1, characterized in that: In step (1), the reaction gas is a gas generated by gas phase oxidation of naphthalene and air under the action of a catalyst.

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