A method and system for ultrasonic enhanced crystallization separation of C8 aromatics

Abstract

The application discloses a kind of ultrasonic reinforced C8 aromatic hydrocarbon crystallization separation method and system, belong to C8 aromatic hydrocarbon separation technical field.The system of the present application mainly includes primary crystallizer, centrifugal filter, melting tank, ultrasonic generator and the like device.According to the different separation requirements of raw material, different process flow and process system are used in the present application, two-stage filtration process and the combination process of fine filtration are first proposed in C8 aromatic hydrocarbon separation, and the separation of ethylbenzene and xylene can be realized through primary crystallization and filtration, with high separation purity;At the same time, the present application can select coarse separation or fine separation according to the purity requirement of process product, and the raw material has wide adaptability and flexible process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of C8 aromatic hydrocarbon separation, and particularly relates to a method and system for ultrasonic enhanced C8 aromatic hydrocarbon crystallization separation. BACKGROUND

[0002] C8 aromatic hydrocarbon, namely C8 aromatic hydrocarbon, refers to an aromatic hydrocarbon mixture containing eight carbon atoms in industry. In C8 aromatic hydrocarbons from different sources, the contents of each component are different, and the main components are o-xylene, p-xylene, m-xylene and ethylbenzene, and sometimes benzylstyrene is also contained. C8 aromatic hydrocarbon is a colorless and transparent liquid at room temperature, has an aromatic odor, and is an important organic chemical raw material (especially p-xylene and o-xylene).

[0003] Due to the need for a large amount of high-octane gasoline, a catalytic reforming process was developed, and benzene, toluene and xylene (commonly known as BTX) were obtained from reforming gasoline, so that the main source of xylene was shifted to petroleum. After the 1960s, the ethylene industry developed rapidly, and the byproduct cracking gasoline (containing a large amount of aromatic hydrocarbons) became another source of C8 aromatic hydrocarbons. In 1969, the Japanese company built a toluene disproportionation device to produce benzene and xylene, which provided another industrial production method for increasing the production of C8 aromatic hydrocarbons.

[0004] At present, the main methods to obtain C8aromatics are: (1) extraction from reforming gasoline or cracking gasoline, the total yield of aromatic hydrocarbons in reforming gasoline is about 55%, and the yield of xylene is about 18%, and xylene is obtained by aromatic extraction and fractionation. The total amount of aromatic hydrocarbons in cracking gasoline is about 70%, and the amount of xylene is 4-5%. Because it contains olefins and dienes, it needs to be hydrogenated first, and then xylene is obtained by aromatic extraction. (2) Toluene disproportionation and transalkylation. There are three kinds of processes that have been industrialized in the world: Tatoray method developed by Japan Toray Company and US Universal Oil Products Company, Xylene-plus method developed by US Atlantic Richfield Company and LTD method developed by US Mobil Company. Tatoray method is the most widely used process, which uses molecular sieve catalyst based on mordenite, the reactor is an adiabatic fixed bed, and the reaction is carried out under hydrogen condition, so the catalyst regeneration cycle is longer, and the activity can be maintained for half a year. Xylene-plus method uses Y-type molecular sieve exchanged with rare earth elements, and its process characteristics are that the proportion of toluene and C9aromatics in the feed can be adjusted to adjust the proportion of disproportionation reaction and transalkylation reaction, so as to achieve greater operation flexibility; it does not need hydrogen, and the catalyst is cheap; the disadvantage is that the structure of the moving bed reactor is complex, and the catalyst consumption is large due to mechanical wear. LTD method uses ZSM type zeolite catalyst (see molecular sieve catalyst), which can not only catalyze liquid phase reaction at low temperature (260-310℃), but also catalyze gas phase reaction at high temperature (370-538℃), which is a relatively late developed process and is not widely used. (3) By-product of coking, the crude benzene obtained in the coal coking process contains about 6% of xylene, which can be separated by distillation method to obtain C8aromatics.

[0005] At present, the separation of C8aromatics has been studied, mainly including adsorption separation method, crystallization method, etc.; such as patent document CN104513118A provides a method for separating ethylene and xylene by pressure swing adsorption; patent document CN100577618C provides a method for separating C8aromatics by adsorption-crystallization to obtain p-xylene and ethylbenzene. In general, the current method for separating xylene and ethylbenzene from C8still has the problems of complex process flow and low purity.

[0006] The ultrasonic enhanced crystallization has certain effect on mixed solution separation, and the application of ultrasonic to the crystallization separation of paraxylene is first proposed by the inventor in the patent CN202011213151.7, and a new process is developed in combination with the characteristics of ultrasonic crystallization and the PX system. The patent CN202210946311.1 proposes to use a low-power variable cross-section ultrasonic generator to enhance crystallization, avoid the thermal effect of ultrasonic, and develop a low-power variable cross-section ultrasonic generator and a double-enhanced paraxylene crystallization separation process by introducing crystal seeds to induce crystallization.

[0007] In view of this, the present application provides an ultrasonic enhanced C8 aromatic hydrocarbon crystallization separation method and system. SUMMARY

[0008] In view of the deficiencies of the prior art, one of the purposes of the present application is to provide an ultrasonic enhanced C8 aromatic hydrocarbon crystallization separation method, which proposes two different separation methods of rough separation and fine separation according to different process requirements, and has simple process and high purity.

[0009] Another purpose of the present application is to provide a system for the ultrasonic enhanced C8 aromatic hydrocarbon crystallization separation method.

[0010] In order to achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0011] In the first aspect, an ultrasonic enhanced C8 aromatic hydrocarbon crystallization separation method comprises the following steps:

[0012] The C8 aromatic hydrocarbon raw material is sent into a primary crystallizer for crystallization, and the obtained product after crystallization is sent into a one-stage centrifuge to separate ethylbenzene solution and filter cake; the ethylbenzene solution is sent out, and the filter cake is sent into a melting tank for treatment to obtain mixed xylene solution;

[0013] Alternatively, the obtained product after crystallization is sent into a two-stage centrifuge, the ethylbenzene solution obtained from the front stage of the centrifugal filter is fine filtered to obtain ethylbenzene solution and ethylbenzene crude liquid; the ethylbenzene solution is sent out; the ethylbenzene crude liquid is returned to the C8 aromatic hydrocarbon raw material; the filter cake obtained from the rear stage of the centrifugal filter is sent into the melting tank for treatment to obtain mixed xylene solution; a part of the mixed xylene solution is returned to the rear stage of the centrifugal filter as washing liquid; the mixed xylene solution after washing in the rear stage of the centrifugal filter is returned to the primary crystallizer.

[0014] As a preferred technical solution of the present application, when a one-stage centrifuge is used, the purity of the obtained mixed xylene solution is not less than 97%; when a two-stage centrifuge is used, the purity of the obtained mixed xylene solution is not less than 99.9%.

[0015] As a preferred technical scheme of the present application, when a two-stage centrifuge is used, the reflux ratio of the mixed xylene solution as the reflux liquid of the washing liquid of the rear stage of the centrifugal filter is 0.05-0.2.

[0016] In a second aspect, the present application provides a system for realizing the above separation method, comprising a primary crystallizer, a refrigeration system, a centrifugal filter, and a melting tank, wherein the primary crystallizer is externally provided with a refrigeration system for refrigerating the primary crystallizer; the centrifugal filter is arranged between the primary crystallizer and the melting tank.

[0017] The centrifugal filter is a one-stage centrifuge, the primary crystallizer is communicated with the inlet of the centrifugal filter through a pipeline, and the solid outlet of the centrifugal filter is communicated with the melting tank through a pipeline.

[0018] Alternatively, the centrifugal filter is a two-stage centrifuge, the two-stage centrifuge comprises a centrifugal filter front stage and a centrifugal filter rear stage which are communicated with each other; the primary crystallizer is communicated with the centrifugal filter front stage through a pipeline, the centrifugal filter front stage is further communicated with a fine filter through a pipeline; the outlet of the fine filter is communicated with the primary crystallizer through a pipeline; the centrifugal filter rear stage is communicated with the melting tank through a pipeline; and the outlet of the melting tank is further communicated with the centrifugal filter rear stage through a pipeline.

[0019] As a preferred technical scheme of the present application, the system further comprises an ultrasonic generator, which is installed in the interior of the primary crystallizer.

[0020] As a preferred technical scheme of the present application, the ultrasonic generator is a variable cross-section ultrasonic generator.

[0021] As a preferred technical scheme of the present application, the variable cross-section ultrasonic generator comprises a generator main body and a variable cross-section section, the diameter of the minimum cross-section of the variable cross-section section is 1 / 2 of the diameter of the maximum cross-section, the angle corresponding to the arc length of the variable cross-section section is 20-45°, and the arc length radius of the variable cross-section section is 3-8 times of the diameter of the maximum cross-section.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) The present application proposes a method and system for ultrasonic strengthening of C8 aromatic hydrocarbon crystallization separation, for the first time proposes a two-stage filtration process and a combination process of fine filtration in C8 aromatic hydrocarbon separation, and can realize the separation of ethylbenzene and xylene through one-time crystallization and filtration, with high separation purity.

[0024] (2) The application provides a method and system for ultrasonic reinforced C8 aromatic hydrocarbon crystallization separation, which can be used for rough separation or fine separation according to the purity requirement of process products, and is suitable for a wide range of raw materials and flexible process.

[0025] (3) The application further optimizes the structure of the ultrasonic generator, and provides a variable cross-section ultrasonic generator, which can form three-dimensional (axial and radial) ultrasonic waves in a large range, and can meet the needs of the whole crystallizer under the action of small size and low power, and the ultrasonic power can be reduced by 30-70%. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Figure 1 is a process flow diagram of ultrasonic reinforced C8 aromatic hydrocarbon crystallization separation in the embodiment 1 of the application;

[0027] Figure 2 Figure 2 is a process flow diagram of ultrasonic reinforced C8 aromatic hydrocarbon crystallization separation in the embodiment 2 of the application;

[0028] Figure 3 Figure 3 is a structure diagram of the variable cross-section ultrasonic generator in the application.

[0029] 1, primary crystallizer; 2, centrifugal filter; 21, front section of the centrifugal filter; 22, rear section of the centrifugal filter; 3, melting tank; 4, refrigeration system; 5, ultrasonic generator; 51, generator main body; 52, variable cross-section section; 6, fine filter. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0031] Please refer to Figure 1 and Figure 2 In the application, a method for ultrasonic reinforced C8 aromatic hydrocarbon crystallization separation comprises the following steps:

[0032] The C8 aromatic hydrocarbon raw material is sent into a primary crystallizer for crystallization, and the obtained product after crystallization is sent into a one-stage centrifugal machine to separate ethylbenzene solution and filter cake; the ethylbenzene solution is sent out, and the filter cake is sent into a melting tank to obtain mixed xylene solution after treatment;

[0033] Or, the product obtained after crystallization is sent to a two-stage centrifuge, the ethylbenzene solution obtained in the front stage of the centrifugal filter is fine filtered to obtain an ethylbenzene solution and an ethylbenzene crude liquid; the ethylbenzene solution is sent out; the ethylbenzene crude liquid is returned to the C8 aromatic hydrocarbon raw material; the filter cake obtained in the rear stage of the centrifugal filter is sent to a melting tank for treatment to obtain a mixed xylene solution; a part of the mixed xylene solution is returned to the rear stage of the centrifugal filter as a washing liquid; the mixed xylene solution after washing in the rear stage of the centrifugal filter is returned to the primary crystallizer.

[0034] In the technical solution, the C8 aromatic hydrocarbon is first separated into ethylbenzene and xylene by low-temperature crystallization, and after ultrasonic strengthening, the crystal is fine and uniform, and basically does not wrap the mother liquor, so that the primary crystallization basically meets the needs. If the purity requirement is high, the washing process needs to be increased; if the purity requirement is low, simple solid-liquid separation can be used. Specifically:

[0035] If the purity requirement is low, after low-temperature crystallization, the slurry in the crystallizer is transported into a one-stage rotary filter, and the xylene particles are separated into the melting tank; the ethylbenzene liquid is directly discharged.

[0036] If the purity requirement is high, after low-temperature crystallization, the slurry in the crystallizer is transported into a rotary filter, and a two-stage rotary filter is used; the ethylbenzene liquid is separated in the front stage, passes through a fine filter, and the ethylbenzene liquid is discharged as a product; after the solid in the rear stage is washed by the xylene solution, the xylene particles are separated into the melting tank, a part is used as a washing liquid, and a part is discharged as a xylene product.

[0037] The effects of ultrasonic strengthening crystallization in the above process are as follows:

[0038] (1) The crystallization speed is accelerated, so that the treatment capacity of the crystallizer can be improved, and the energy consumption of the crystallizer can be greatly reduced;

[0039] (2) The crystalline particles become fine and uniform, and are not easy to include the mother liquor, so that the crystallization purity of the system can be greatly improved after pure material washing.

[0040] After ultrasonic strengthening crystallization, if the purity requirement is high, it basically meets the requirement of more than 99.9%, and if the purity requirement is not high, it basically meets the requirement of more than 97%.

[0041] It needs to be particularly emphasized that the C8 aromatic hydrocarbon crystallization separation provided by the present application first solves the separation of ethylbenzene and xylene, does not change the existing main process of xylene crystallization separation, increases an ultrasonic generator in the crystallizer, improves the purity, reduces the energy consumption, is suitable for new construction and existing technology transformation. The basic concept and design idea of the present application give full play to the effects of ultrasonic waves, washing and filtration in the crystallization and separation process, are not simple physical combinations, fully exert the advantages of each other, and can be applied to the process flow of various crystallizers.

[0042] In some embodiments, when a two-stage centrifuge is used, the reflux ratio of the mixed xylene solution backflowing to the rear section of the centrifugal filter as the washing liquid is 0.05-0.2, i.e. 5%-20% wt of the mixed xylene solution backflows as the washing liquid; it can be understood that the reflux ratio can be 5%, 10%, 15%, 20% or any value within the range of 5%-20%, which can be flexibly adjusted according to the actual working conditions.

[0043] In the present application, a system suitable for the above-mentioned crystallization separation method comprises a primary crystallizer 1, a refrigeration system 4, a centrifugal filter 2, and a melting tank 3, wherein the primary crystallizer 1 is externally provided with the refrigeration system 4 for refrigerating the primary crystallizer; the centrifugal filter 2 is arranged between the primary crystallizer 1 and the melting tank 3.

[0044] The centrifugal filter 2 is a one-stage centrifuge, the primary crystallizer 1 is connected to the inlet of the centrifugal filter through a pipeline, and the solid outlet of the centrifugal filter 2 is connected to the melting tank 3 through a pipeline.

[0045] Alternatively, the centrifugal filter 2 is a two-stage centrifuge, which comprises a centrifugal filter front section 21 and a centrifugal filter rear section 22 that are connected to each other; the primary crystallizer 1 is connected to the centrifugal filter front section 21 through a pipeline, and the centrifugal filter front section 21 is further connected to a fine filter 6 through a pipeline; the outlet of the fine filter 6 is connected to the primary crystallizer 1 through a pipeline; the centrifugal filter rear section 22 is connected to the melting tank 3 through a pipeline; and the outlet of the melting tank 3 is further connected to the centrifugal filter rear section 22 through a pipeline.

[0046] In the above system, different structural forms are adopted according to different coarse separation and fine separation; when coarse separation is performed, the centrifugal filter 2 is arranged as a one-stage centrifuge; and when fine separation is performed, the centrifugal filter 2 is arranged as a two-stage centrifuge. It should be particularly emphasized that the one-stage centrifuge is a commonly used device in actual production; if a one-stage centrifuge is used, the mother liquor and the washing liquid are mixed together, and the separation effect is greatly reduced; the two-stage centrifuge is actually a simple improvement of the one-stage centrifuge, see Figure 1 and Figure 2It can be seen that, in fact, a baffle is arranged at the cyclone passage, which divides the one-stage cyclone passage into the front section 21 of the centrifugal filter and the rear section 22 of the centrifugal filter and adds a corresponding material leakage port. In the front section 21 of the centrifugal filter, the ethylbenzene solution containing a small amount of xylene crystals is separated out and will not be brought into the subsequent separation process. After the separation of most of the ethylbenzene solution, the material enters the rear section 22 of the centrifugal filter and then the filter cake can be separated. The refluxing mixed xylene washing liquid refluxes into the rear section 22 of the centrifugal filter and will not contact the material in the front section 21 of the centrifugal filter, thereby improving the separation efficiency. Obviously, compared with the one-stage centrifugal filter, the two-stage centrifugal filter has a cost advantage in separation effect. The application of this structure in the separation of C8 aromatic hydrocarbons is first proposed by the applicant. It needs to be particularly emphasized that, as described above, the two-stage centrifugal filter is actually an improvement of the one-stage centrifugal filter structure. The centrifugal separation process is divided into two parts. The improvement of the structure also belongs to basic improvement, which can be easily realized by the person skilled in the art and is a routine means of the person skilled in the art. The structure of the one-stage centrifugal filter belongs to a common centrifugal filter form in the prior art, and the specific structure thereof is not limited or described in the present application, as long as it can be realized by the person skilled in the art. Similarly, the crystallizer, the refrigeration system, the melting tank and the precision filter all belong to common device structures in the art, and they are also not specifically limited or described in the present embodiment.

[0047] In some embodiments, the ultrasonic generator 5 is installed inside the primary crystallizer 1. More preferably, the ultrasonic generator 5 is a variable cross-section ultrasonic generator, both of which are built-in. Compared with the prior art, the present application limits the specific setting form of the ultrasonic generator to be built-in. The advantage is that the effect of ultrasonic intensification of crystallization can be maximized.

[0048] Further referring to Figure 3 In some embodiments, the ultrasonic generator 5 includes a generator body 51 and a variable cross-section section 52. It can be understood that the variable cross-section section 52 can be provided in an outwardly convex or inwardly concave form. Preferably, it is in an inwardly concave form.

[0049] Further referring to Figure 3 The left part (A) shows that the ultrasonic generator 5 is provided in an inwardly concave form. The diameter of the smallest cross-section of the variable cross-section section 52 is 1 / 2 of the diameter of the largest cross-section (i.e. the diameter of the cross-section corresponding to the deepest concave part). The angle corresponding to the arc length of the variable cross-section section 52 is 20-45°. The radius of the arc length of the variable cross-section section 52 is 3-8 times the diameter of the largest cross-section. The specific setting form of the above variable cross-section section 52 can be determined according to the ultrasonic coverage area.

[0050] It can be understood that the setting form of the ultrasonic generator 5 is similar, and includes a generator main body 51 and a variable cross-section section 52. The specific specifications of the generator main body 51 and the variable cross-section section 52 can be flexibly set according to actual production needs, and the specifications can be completely the same or different. The generator main body 51 mainly includes an ultrasonic host and other related auxiliary components, and the variable cross-section section 52 is mainly an ultrasonic vibrator. The variable cross-section ultrasonic generator defined in the embodiment is essentially the same as other existing ultrasonic generators, except that the ultrasonic vibrator is set to a specific variable cross-section form. In the embodiment, the ultrasonic generator is selected to be in the form of a variable cross-section. The reason is that it is difficult to form a three-dimensional (axial and radial) ultrasonic wave in a large range using an ultrasonic generator with the same cross-section (equal cross-section). A variable cross-section generator can use a very small and low-power ultrasonic generator to meet the needs of the entire crystallizer and improve the crystallization effect. Actual test research shows that, to achieve the same crystallization effect (equal processing capacity and equal purification purity), the power of the ultrasonic wave of the combination process of the variable cross-section ultrasonic generator and the reflux crystal induced crystallization can be reduced by 30-70% compared with the combination process of the same cross-section ultrasonic generator and the reflux crystal induced crystallization, greatly reducing energy consumption.

[0051] In some embodiments, the number of ultrasonic generators 5 can be one or more; preferably, two.

[0052] Further referring to Figures 1 to 3 The process flow in the present application is specifically explained as follows:

[0053] Referring to Figure 1 When the purity of ethylbenzene and mixed xylene is high, an ultrasonic generator is arranged in the crystallizer, and xylene product washing and reflux are added to the centrifugal filter, and a precision filter is added to the ethylbenzene solution to improve the purity.

[0054] The C8 aromatic hydrocarbon mixture raw material, the refluxed xylene washing liquid, and the filtered remaining ethylbenzene solution enter the crystallizer 1 through the cold zone system, and are coupled by the refrigeration system 4 and the ultrasonic generator 5. The xylene is quickly crystallized, the crystallization particles are uniform and small, and almost no mother liquor is included, and the purity is high.

[0055] The slurry enters the centrifugal filter 2 for liquid-solid separation.

[0056] In the first stage, the crystallization mother liquor (ethylbenzene) is removed in the front section 21 of the centrifugal filter, discharged to the precision filter 6, and the filtered ethylbenzene solution is discharged outside the device. The remaining ethylbenzene solution is refluxed to the crystallizer 1.

[0057] In the second stage, the xylene particles are washed by the refluxed xylene washing liquid in the rear section 22 of the centrifugal filter, and the solid-liquid separation is discharged to the melting tank 3, and the washed xylene liquid is returned to the primary crystallizer 1. The solid xylene particles enter the melting tank 3, and after melting, part of them is discharged outside the device, and part of them is refluxed to wash the xylene particles.

[0058] Through the coupling effect of the refrigeration system 4 and the ultrasonic generator 5, the xylene is quickly crystallized, the crystalline particles are uniform and small, almost no mother liquor is included, and the purity is very high, and at this time, the purity can reach more than 99.9%.

[0059] The primary crystallizer 1 adopts an internal ultrasonic generator 5, which does not affect the original crystallization function and can also improve the original crystallization function. Although the ultrasonic generator 5 changes the crystallization conditions on the basis of the original, due to the induction of the crystal seed, the interfacial stability region is reduced, the influence of the supersaturation degree is avoided, and the crystallization process is stable, so the ultrasonic power is generally small, and the power is in the order of hundreds of watts or kilowatts. The main function is to change the morphology of the crystal and avoid the inclusion of mother liquor.

[0060] Further referring to Figure 2 When the purity requirements of ethylbenzene and mixed xylene are not high, the ultrasonic generator is arranged in the crystallizer, the fine filtration of the ethylbenzene solution and the reflux washing of the xylene are cancelled, the process is relatively simple, the energy consumption is low, but the purity is slightly lower, which can reach more than 97%.

[0061] Because the crystallization speed of xylene is increased under the action of ultrasonic waves, the crystallization temperature does not need to be too low, the morphology of the crystalline particles is more uniform, the purity of the crystal is improved after washing and filtering, and the market competitiveness of the ethylbenzene and xylene crystallization separation technology is greatly improved.

[0062] The ultrasonic enhanced C8 aromatic hydrocarbon crystallization separation method and system of the present application are further described below in combination with specific embodiments.

[0063] Embodiment 1

[0064] An ultrasonic enhanced C8 aromatic hydrocarbon crystallization separation system, comprising a primary crystallizer 1, a refrigeration system 4, a centrifugal filter 2, and a melting tank 3, wherein the primary crystallizer 1 is externally provided with a refrigeration system 4 for refrigerating the primary crystallizer; the centrifugal filter 2 is arranged between the primary crystallizer 1 and the melting tank 3; the primary crystallizer 1 is internally provided with an ultrasonic generator 5, and the ultrasonic generator 5 is a variable cross-section ultrasonic generator, comprising a generator main body 51 and a variable cross-section section 52.

[0065] The centrifugal filter 2 is a two-stage centrifugal machine, which comprises a centrifugal filter front stage 21 and a centrifugal filter rear stage 22 in communication with each other; the primary crystallizer 1 is communicated with the centrifugal filter front stage through a pipeline, and the centrifugal filter front stage 21 is further communicated with the fine filter 6 through a pipeline; the outlet of the fine filter 6 is communicated with the primary crystallizer 1 through a pipeline; the centrifugal filter rear stage 22 is communicated with the melting tank 3 through a pipeline; and the outlet of the melting tank 3 is further communicated with the centrifugal filter rear stage 22 through a pipeline.

[0066] In the embodiment, the ultrasonic generators 5 are built-in variable cross-section ultrasonic generators with the same specifications. The diameter of the minimum cross section of the variable cross-section section 52 is 1 / 2 of the diameter of the maximum cross section, the angle corresponding to the arc length of the variable cross-section section is 25°, and the arc length radius of the variable cross-section section 52 is 4 times the diameter of the maximum cross section.

[0067] In the embodiment, the number of the ultrasonic generators 5 is 2.

[0068] In the embodiment, a method for ultrasonic enhanced crystallization and separation of C8 aromatic hydrocarbons by using the above system is also provided, which comprises the following steps:

[0069] The C8 aromatic hydrocarbon raw material is sent into the primary crystallizer for ultrasonic enhanced crystallization, and the obtained product after crystallization is sent into the two-stage centrifugal machine; the ethylbenzene solution obtained from the centrifugal filter front stage is fine filtered to obtain an ethylbenzene solution and an ethylbenzene crude liquid; the ethylbenzene solution is sent out; the ethylbenzene crude liquid is returned to the C8 aromatic hydrocarbon raw material; the filter cake obtained from the centrifugal filter rear stage is sent into the melting tank for treatment to obtain a mixed xylene solution; a part of the mixed xylene solution is refluxed to the centrifugal filter rear stage as a washing liquid; and the mixed xylene solution after washing in the centrifugal filter rear stage is returned to the primary crystallizer.

[0070] In the embodiment, the reflux ratio of the mixed xylene solution refluxed to the centrifugal filter rear stage as the washing liquid is 0.1.

[0071] Embodiment 2

[0072] An ultrasonic enhanced crystallization and separation system for C8 aromatic hydrocarbons comprises a primary crystallizer 1, a refrigeration system 4, a centrifugal filter 2, and a melting tank 3; the primary crystallizer 1 is externally provided with the refrigeration system 4 for refrigerating the primary crystallizer; the centrifugal filter 2 is arranged between the primary crystallizer 1 and the melting tank 3; and the primary crystallizer 1 is internally provided with an ultrasonic generator 5, which is a variable cross-section ultrasonic generator and comprises a generator main body 51 and a variable cross-section section 52.

[0073] The centrifugal filter is a single-stage centrifugal machine, the primary crystallizer is communicated with the inlet of the centrifugal filter through a pipeline, and the solid outlet of the centrifugal filter is communicated with the melting tank through a pipeline.

[0074] In the embodiment, the ultrasonic generators 5 are built-in variable cross-section ultrasonic generators and have the same specifications. The diameter of the minimum cross section of the variable cross-section section 52 is 1 / 2 of the diameter of the maximum cross section, the angle corresponding to the arc length of the variable cross-section section is 25°, and the arc length radius of the variable cross-section section 52 is 4 times the diameter of the maximum cross section.

[0075] In the embodiment, the number of the ultrasonic generators 5 is 2.

[0076] In the embodiment, a method for ultrasonic strengthening of C8 aromatic hydrocarbon crystallization and separation by using the system is also provided, which includes the following steps:

[0077] The C8 aromatic hydrocarbon raw material is sent into the primary crystallizer for ultrasonic strengthening crystallization, and the product obtained after crystallization is sent into the single-stage centrifugal machine to separate ethylbenzene solution and filter cake; the ethylbenzene solution is sent out, and the filter cake is sent into the melting tank for treatment to obtain mixed xylene solution.

[0078] The above embodiments are used to illustrate the technical concept of the present application, but the present application is not limited to the above embodiments, that is, the present application does not mean that the present application must rely on the above embodiments to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of individual raw materials of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for ultrasonically enhanced crystallization separation of C8 aromatics, characterized in that, The process includes the following steps: C8 aromatic raw material is fed into a primary crystallizer for crystallization, and the product obtained after crystallization is fed into a two-stage centrifuge. The ethylbenzene solution obtained in the first stage of the centrifuge is finely filtered to obtain ethylbenzene solution and crude ethylbenzene liquid. The ethylbenzene solution is sent out; the crude ethylbenzene solution is returned to the C8 aromatics feedstock; the filter cake obtained from the downstream section of the centrifugal filter is sent to a melting tank for processing to obtain a mixed xylene solution; A portion of the mixed xylene solution is refluxed to the downstream section of the centrifuge as washing liquid; the washed mixed xylene solution in the downstream section of the centrifuge is returned to the primary crystallizer; When using a two-stage centrifuge, the purity of the resulting mixed xylene solution shall not be less than 99.9%. When using a two-stage centrifuge, the reflux ratio of the mixed xylene solution refluxed to the downstream section of the centrifuge filter as washing liquid is 0.05 to 0.

2. The first-stage crystallizer is equipped with an ultrasonic generator.

2. A system for the crystallization separation method of claim 1, characterized in that, It includes a primary crystallizer, a refrigeration system, a centrifugal filter, and a melting tank. The primary crystallizer is externally equipped with a refrigeration system for cooling the primary crystallizer. The centrifugal filter is installed between the primary crystallizer and the melting tank; The centrifugal filter is a two-stage centrifuge, comprising a front section and a rear section of the centrifugal filter that are interconnected. The primary crystallizer is connected to the front section of the centrifugal filter via a pipeline, and the front section of the centrifugal filter is also connected to a fine filter via a pipeline. The outlet of the fine filter is connected to the primary crystallizer via a pipeline. The rear section of the centrifugal filter is connected to the melting tank via a pipeline. The outlet of the melting tank is also connected to the rear section of the centrifugal filter via a pipeline.

3. The system of the crystallization separation method according to claim 2, characterized in that, The ultrasonic generator is a variable cross-section ultrasonic generator.

4. The system of the crystallization separation method according to claim 3, characterized in that, The variable cross-section ultrasonic generator includes a generator body and a variable cross-section section. The diameter of the minimum cross-section of the variable cross-section section is half of the diameter of the maximum cross-section. The angle corresponding to the arc length of the variable cross-section section is 20 to 45°. The radius of the arc length of the variable cross-section section is 3 to 8 times the diameter of the maximum cross-section.

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