Multi-stage washing production process and system for high-concentration p-xylene

Abstract

The invention provides a multi-stage washing production process of high-concentration p-xylene, which comprises the following steps: cooling and crystallizing a raw material under a first temperature condition to obtain first crystal mush; carrying out solid-liquid separation on the first crystal mush, washing raw materials and part of products to obtain first crystals, first filtered mother liquor and first eluate, and melting the first crystals to obtain a first p-xylene product; sending part of the first filtered mother liquor to a second temperature condition for cooling crystallization to obtain second crystal mush; repeating the steps on the second crystal mush to obtain a second p-xylene product; and cooling and crystallizing part of the second filtered mother liquor under a third temperature condition to obtain third crystal mush, and repeating the steps on the third crystal mush to obtain a third p-xylene product. The problems that the crystal transfer amount is large and difficult and the crystal particle circulation amount is large during p-xylene production can be solved.

Description

Technical Field

[0001] The present application relates to a multi-stage washing production process and system for high-concentration paraxylene. Background Art

[0002] Paraxylene (PX) is mainly used as a raw material for the production of purified terephthalic acid (PTA) and dimethyl terephthalate (DMT), while purified terephthalic acid (PTA) is used to manufacture polyester products such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). When the upstream paraxylene (PX) production is insufficient, the downstream terephthalic acid (PTA) factories can only choose to import from neighboring countries. Therefore, the shortage of paraxylene (PX) raw materials has become the biggest constraint on the development of my country's polyester industry.

[0003] At present, p-xylene is mainly obtained by separating mixed xylene, and mixed xylene mainly comes from petroleum aromatics. Limited by the carbon distribution and thermodynamic equilibrium in petroleum aromatics, the p-xylene content in C8 aromatics obtained from different aromatic production processes is very low, but the aromatics combined unit can be used to convert between aromatics, thereby increasing the production of p-xylene. Mixed xylene is mainly composed of p-xylene, m-xylene, o-xylene and ethylbenzene. The boiling points of the components are very small. It is almost impossible to obtain high-purity p-xylene products using distillation methods, which makes the production of high-purity products energy-intensive. However, the melting points of these components are quite different. Generally speaking, the freezing point of p-xylene is about 13.2°C. Compared with other xylenes, the production conditions are milder and the energy consumption is lower. Therefore, the melt crystallization method has obvious technical advantages in separating and purifying p-xylene.

[0004] During the crystallization separation process, the main component paraxylene is precipitated from the solution, while other xylenes are present in the solution. High-purity paraxylene can be obtained by completely separating the paraxylene crystals from the xylene solution. However, since it is difficult to completely separate the solid-liquid phases, and the purity of paraxylene is generally required to be >99.7%, many post-processing processes are required to obtain high-purity paraxylene. Summary of the invention

[0005] In order to solve the problems of large and difficult crystal transfer and large crystal particle circulation in the existing production process when producing paraxylene, the present application discloses a multi-stage washing production process and system for high-concentration paraxylene, and adopts the following technical solutions:

[0006] In a first aspect, the present application discloses a multi-stage washing production process for high-concentration paraxylene, comprising:

[0007] Cooling and crystallizing the raw material containing para-xylene under a first temperature condition to obtain a first slurry;

[0008] Performing solid-liquid separation on the first slurry to obtain first crystals and a first filtered mother liquor;

[0009] returning part of the first filtered mother liquor to the first temperature condition for further cooling and crystallization, and cooling and crystallizing the remaining first filtered mother liquor at a second temperature condition to obtain a second crystal slurry;

[0010] Using the raw material and the para-xylene product as washing liquids to wash the first crystals in sequence;

[0011] Melting the first crystals after being washed with the raw material and the para-xylene product to obtain a first para-xylene product;

[0012] Performing solid-liquid separation on the second crystal slurry to obtain second crystals and a second filtered mother liquor;

[0013] returning part of the second filtered mother liquor to the second temperature condition for further cooling and crystallization, and cooling and crystallizing the remaining second filtered mother liquor at a third temperature condition to obtain a third crystal slurry;

[0014] Using the raw material and the para-xylene product as washing liquids to wash the second crystals in sequence;

[0015] Melting the second crystals washed with the raw material and the p-xylene product to obtain a second p-xylene product;

[0016] Performing solid-liquid separation on the third slurry to obtain third crystals and a third filtered mother liquor;

[0017] returning part of the third filtered mother liquor to the third temperature condition to continue cooling and crystallizing, and discharging the remaining third filtered mother liquor out of the system;

[0018] Using the raw material and the paraxylene product as washing liquids to wash the third crystals in sequence;

[0019] Melting the third crystals washed with the raw material and the p-xylene product to obtain a third p-xylene product;

[0020] The operating temperatures of the first temperature condition, the second temperature condition and the third temperature condition decrease in sequence.

[0021] Optionally, after obtaining the first p-xylene product, a portion of the first p-xylene product is returned to the first crystals in the previous step as a washing liquid to wash the first crystals;

[0022] After obtaining the second p-xylene product, returning part of the second p-xylene product as washing liquid to the second crystals in the previous step to wash the second crystals;

[0023] After obtaining the third p-xylene product, part of the third p-xylene product is returned to the third crystals in the previous step as washing liquid to wash the third crystals.

[0024] Optionally, 10% to 30% of the first para-xylene product is returned to the first crystals of the previous step as washing liquid to wash the first crystals;

[0025] returning 10% to 30% of the second para-xylene product as washing liquid to the second crystals in the previous step to wash the second crystals;

[0026] 10% to 30% of the third para-xylene product is returned to the third crystals of the previous step as washing liquid to wash the third crystals.

[0027] Optionally, the raw material and the para-xylene product are used as washing liquids to wash the first crystals in sequence to obtain a first eluate;

[0028] Using the raw material and the para-xylene product as washing liquids to wash the second crystals in sequence to obtain a second eluate;

[0029] The raw material and the paraxylene product are used as washing liquids to wash the third crystals in sequence to obtain a third eluate, and the first eluate, the second eluate and the third eluate are all returned to the first temperature condition to continue cooling and crystallizing.

[0030] Optionally, a C8 mixture with a paraxylene concentration ranging from 95% to 98% is used as a raw material and cooled and crystallized under the first temperature condition.

[0031] Optionally, the operating temperature range of the first temperature condition is 8°C to 12°C, the operating temperature range of the second temperature condition is 4°C to 9°C, and the preferred operating temperature of the third temperature condition is 0°C to 6°C.

[0032] Optionally, 5% to 20% of the first filtered mother liquor is returned to the first temperature condition to continue cooling and crystallization, 5% to 20% of the second filtered mother liquor is returned to the second temperature condition to continue cooling and crystallization, and 5% to 20% of the third filtered mother liquor is returned to the third temperature condition to continue cooling and crystallization.

[0033] In a second aspect, the present application further discloses a multi-stage washing production system for high-concentration para-xylene, based on the multi-stage washing production process for high-concentration para-xylene as described in the first aspect, comprising a primary crystallization device, a secondary crystallization device and a tertiary crystallization device;

[0034] The primary crystallization device comprises a first crystallizer, a first solid-liquid separator and a first melter, the secondary crystallization device comprises a second crystallizer, a second solid-liquid separator and a second melter, and the tertiary crystallization device comprises a third crystallizer, a third solid-liquid separator and a third melter;

[0035] The operating temperatures of the first crystallizer, the second crystallizer and the third crystallizer are sequentially reduced;

[0036] The first crystallizer is used to cool and crystallize the raw material containing para-xylene under a first temperature condition to obtain a first crystal slurry;

[0037] The first crystallizer outlet is communicated with the first solid-liquid separator inlet, and the first solid-liquid separator is used to perform solid-liquid separation on the first crystal slurry and wash the first crystals;

[0038] The first solid-liquid separator outlet is communicated with the first melter inlet, and the first melter is used to melt the first crystals to obtain a first paraxylene product;

[0039] The first solid-liquid separator outlet is also connected to the first crystallizer inlet and the second crystallizer inlet;

[0040] The outlet of the second crystallizer is connected to the inlet of the second solid-liquid separator, and the second crystallizer is used to cool and crystallize part of the first filtered mother liquor under a second temperature condition to obtain a second crystal slurry;

[0041] The second solid-liquid separator is used for performing solid-liquid separation on the second crystal slurry and washing the second crystals;

[0042] The outlet of the second solid-liquid separator is communicated with the inlet of the second melter, and the second melter is used to melt the second crystals to obtain a second paraxylene product;

[0043] The second solid-liquid separator outlet is also connected to the second crystallizer inlet and the third crystallizer inlet;

[0044] The outlet of the third crystallizer is connected to the inlet of the third solid-liquid separator, and the third crystallizer is used to cool and crystallize part of the first filtered mother liquor under a third temperature condition to obtain a third slurry;

[0045] The third solid-liquid separator is used to perform solid-liquid separation on the third crystal slurry and wash the third crystals;

[0046] The outlet of the third solid-liquid separator is communicated with the inlet of the third melter, and the third melter is used to melt the third crystal to obtain a third paraxylene product;

[0047] The third solid-liquid separator outlet is also connected to the third crystallizer inlet.

[0048] Optionally, the first melter outlet is communicated with the first solid-liquid separator inlet, and is used to return part of the first para-xylene product as washing liquid to the first crystals in the previous step to wash the first crystals;

[0049] The first solid-liquid separator outlet is connected to the first crystallizer inlet, and is used to return the first product eluate to the first temperature condition for cooling and crystallization.

[0050] Optionally, the second melter outlet is communicated with the second solid-liquid separator inlet, and is used to return part of the second para-xylene product as washing liquid to the second crystals in the previous step to wash the second crystals;

[0051] The outlet of the second solid-liquid separator is connected to the inlet of the first crystallizer, so as to return the second product eluate to the first temperature condition for cooling and crystallization.

[0052] Optionally, the third melter outlet is communicated with the third solid-liquid separator inlet, so as to return part of the third para-xylene product as washing liquid to the third crystals in the previous step to wash the third crystals;

[0053] The outlet of the third solid-liquid separator is connected to the inlet of the first crystallizer, and is used to return the third product eluate to the first temperature condition for cooling and crystallization.

[0054] Based on the above technical solution, the beneficial effects of this application compared with the prior art are as follows:

[0055] The embodiment of the present application adopts step-by-step cooling crystallization, and the slurry of the three crystallization levels can directly produce products after the raw materials and products are washed. This process is suitable for raw materials with a paraxylene concentration range of 95% to 98%, and the three crystallization levels can produce products that meet the purity requirements. It has the characteristics of simple process and high production efficiency. After filtering the crystal slurry, the filtered mother liquor is first discharged from the solid-liquid separator, and then the crystals are washed in the solid-liquid separator, that is, the filtering and separation of the crystal slurry and the washing process of the crystals are integrated in a solid-liquid separator, which greatly reduces the overall production energy consumption.

[0056] Among them, the raw materials enter the system in the form of divided feed, part of the raw materials directly enter the first temperature condition, part of the raw materials enter the first crystallizer 1 in the form of the first filtered mother liquor, part of the raw materials enter the second crystallizer 4 in the form of the second filtered mother liquor, and part of the raw materials enter the third crystallizer 7 in the form of the third filtered mother liquor. Thereby, the solid content of the first solid-liquid separator 2 can be reduced. The design of the three-stage crystallization makes the operating temperature difference between each stage decrease step by step, effectively reducing the explosive nucleation, thereby obtaining larger crystal particles, so that the crystals obtained in the three crystallization stages can meet the product purity requirements, reduce the overall transfer and circulation of crystals, and improve production efficiency. The solid-liquid separator divides the filtered mother liquor and the product eluate, and treats the relatively high-concentration product eluate and the relatively low-concentration filtered mother liquor separately. The filtered mother liquor poor in paraxylene goes to the next stage, and the product eluate rich in paraxylene returns to the first temperature condition to stabilize the product purity and output and reduce the loss of paraxylene.

[0057] In addition, using raw material washing slurry can also increase the crystal temperature, reduce the impurity inclusion caused by explosive nucleation in the crystal during the product washing stage, and discharge some impurities first, which can improve the product washing efficiency and reduce the amount of product washing liquid used, thereby greatly improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 1 is a schematic flow chart of a multi-stage washing production process for high-concentration paraxylene in an embodiment of the present application;

[0059] Figure 2 It is a schematic diagram of a multi-stage washing production system for high-concentration paraxylene in an embodiment of the present application.

[0060] Description of reference numerals:

[0061] a, raw material; b, first slurry; c, first filtered mother liquor; d, first crystal; e, first para-xylene product; f, first product eluate; g, second slurry; h, second filtered mother liquor; i, second crystal; j, second para-xylene product; k, second product eluate; m, third slurry; n, third filtered mother liquor; o, third crystal; p, third para-xylene product; q, third product eluate;

[0062] 1. First crystallizer; 2. First solid-liquid separator; 3. First melter; 4. Second crystallizer; 5. Second solid-liquid separator; 6. Second melter; 7. Third crystallizer; 8. Third solid-liquid separator; 9. Third melter. DETAILED DESCRIPTION

[0063] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0064] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0065] In the description of the present disclosure, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0066] In the description of the present disclosure, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0067] The inventors found that in the related art, when producing paraxylene by melt crystallization, the purity of the paraxylene product is required, and in the cooling crystallization process of some later levels, due to the lower crystallization temperature, the resulting crystal particles are smaller and not easy to filter and wash. Therefore, usually this part of the crystals will continue to enter the reslurry tank for reslurrying to continue growing, but this easily makes the circulation volume of the entire process logistics too large, reducing production efficiency. Therefore, how to ensure product purity and reduce the loss of paraxylene while minimizing the material circulation volume is a problem that technicians in this field have long hoped to solve.

[0068] Based on the above problems, the embodiments of the present application disclose a multi-stage washing production process and system for high-concentration para-xylene, which solves the problem of large circulation volume of logistics in the system when producing para-xylene in the existing production process. The following is a detailed description of various specific implementation methods of the multi-stage production system and production method of para-xylene provided in the embodiments of the present disclosure.

[0069] In the first aspect, the present application embodiment provides a multi-stage washing production process for high-concentration paraxylene, referring to Figure 1 ,include:

[0070] S101. Cooling and crystallizing the para-xylene-containing raw material a under a first temperature condition to obtain a first slurry b;

[0071] S102. performing solid-liquid separation on the first slurry b to obtain first crystals d and a first filtered mother liquor c;

[0072] S103. returning part of the first filtered mother liquor c to the first temperature condition for further cooling and crystallization, and cooling and crystallizing the remaining first filtered mother liquor c at the second temperature condition to obtain a second slurry g;

[0073] S104. Using the raw material a and the para-xylene product as washing liquids, sequentially washing the first crystal d;

[0074] S105. Melting the first crystal d after washing with the raw material a and the para-xylene product to obtain a first para-xylene product e;

[0075] S106. performing solid-liquid separation on the second slurry g to obtain second crystals i and a second filtered mother liquor h;

[0076] S107. returning part of the second filtered mother liquor h to the second temperature condition to continue cooling and crystallizing, and the remaining second filtered mother liquor h;

[0077] S108. Using the raw material a and the para-xylene product as washing liquids, sequentially washing the second crystal i;

[0078] S109. Melting the second crystal i after washing with the raw material a and the para-xylene product to obtain a second para-xylene product j;

[0079] S110. performing solid-liquid separation on the third slurry to obtain third crystals and a third filtered mother liquor;

[0080] S111. returning part of the third filtered mother liquor to the third temperature condition to continue cooling and crystallizing, and discharging the remaining third filtered mother liquor out of the system;

[0081] S112. Using the raw material and the paraxylene product as washing liquids to sequentially wash the third crystal;

[0082] S113. Melt the third crystal after washing with the raw material and the para-xylene product to obtain a third para-xylene product.

[0083] Among them, the operating temperatures of the first temperature condition, the second temperature condition and the third temperature condition decrease successively, and the purity of the first paraxylene product e, the second paraxylene product j and the third paraxylene product o is not less than 99.8%.

[0084] Specifically, in an optional embodiment, in step S101, a C8 mixture with a paraxylene concentration range of 95% to 98% is used as raw material a for cooling crystallization under a first temperature condition, the operating temperature range of the first temperature condition is 8°C to 12°C, the operating temperature range of the second crystallizer 4 is 4°C to 9°C, and the operating temperature of the third temperature condition is 0°C to 6°C.

[0085] In an optional embodiment, the first crystal slurry b is first separated from the solid and liquid to obtain the first filtered mother liquor c and the first crystal d. After the first filtered mother liquor c is discharged, the first crystal d is washed with raw material a and the paraxylene product in sequence. Using raw material a for washing can increase the crystal temperature and reduce the impurity inclusion caused by explosive nucleation during the product washing stage. At the same time, the washing of raw material a can first discharge some impurities and reduce the amount of product washing liquid, thereby greatly improving production efficiency. In addition, the solid-liquid separation of the crystal slurry and the washing operation of the crystal can be integrated into one device, which greatly reduces energy consumption.

[0086] In an optional embodiment, in step S103, 5% to 20% of the first filtered mother liquor c is returned to the first temperature condition, which is conducive to promoting the continued growth of crystals in the first temperature condition and improving the subsequent separation efficiency. The remaining first filtered mother liquor c enters the second temperature condition for cooling and crystallization.

[0087] Further, in step S105, after the first crystal d is melted to obtain the first p-xylene product e, part of the first p-xylene product e is returned to the first crystal d in the previous step as a washing liquid to wash the first crystal d to obtain the first product eluate f, and the first product eluate f is returned to the first temperature condition to continue cooling and crystallization. Among them, the first p-xylene product e returned to the first temperature condition accounts for about 10% to 30%. Using the first p-xylene product e to wash the first crystal slurry b can improve the purity of the obtained first crystal d and reduce other impurities attached to the surface of the first crystal d.

[0088] Correspondingly, in steps S106 to S109, the second crystal slurry g is first separated from the solid and liquid to obtain the second crystal i and the second filtered mother liquor h. After the second filtered mother liquor h is discharged, the raw material a and the para-xylene product are used as washing liquids to continue washing the second crystal i in sequence to obtain the second eluate k. The second product eluate k is also returned to the first temperature condition to continue cooling and crystallizing.

[0089] In an optional embodiment, in step S107, 5% to 20% of the second filtered mother liquor h is returned to the second temperature condition for continued cooling and crystallization, which is conducive to promoting the continued growth of crystals at the second temperature condition and improving subsequent separation efficiency. The remaining second filtered mother liquor h enters the third temperature condition for the next stage of cooling and crystallization.

[0090] Similarly, 10% to 30% of the second para-xylene product j is returned as washing liquid to the second crystal i in the previous step to wash the second crystal i.

[0091] Finally, in steps S110 to S113, the third slurry m is firstly subjected to solid-liquid separation and washing of the raw material a and part of the product p to obtain the third crystal o, the third filtered mother liquor n and the third eluate q, 5% to 20% of the third filtered mother liquor n is returned to the third temperature condition to continue cooling and crystallizing, and the remaining third filtered mother liquor n is discharged from the system. The third eluate q is also returned to the first temperature condition to continue cooling and crystallizing.

[0092] At the same time, since the concentration of paraxylene in the raw material a is relatively high, the third crystal o obtained in the third stage cooling crystallization process can meet the product purity. After the third crystal o is melted to obtain the third paraxylene product p, 10% to 30% of the third paraxylene product p is used as washing liquid to wash the third crystal o.

[0093] It should be noted that in the actual production process, in the initial state, a pure p-xylene product can be used to wash the crystals, and after the corresponding product is generated, the corresponding p-xylene product is used for washing. For example, in the embodiment of the present application, in the middle and late stages of production, after the corresponding first p-xylene product and the second p-xylene product are generated, the first p-xylene product is used as a washing liquid to wash the first crystals, and the second p-xylene product is used as a washing liquid to wash the second crystals.

[0094] In the second aspect, the present application embodiment discloses a multi-stage washing production system for high-concentration p-xylene, which is used to implement the multi-stage washing production process for high-concentration p-xylene in the first aspect, referring to Figure 2The multi-stage washing production system of paraxylene includes a primary crystallization device, a secondary crystallization device and a tertiary crystallization device. The primary crystallization device includes a first crystallizer 1, a first solid-liquid separator 2 and a first melter 3. The secondary crystallization device includes a second crystallizer 4, a second solid-liquid separator 5 and a second melter 6. The tertiary crystallization device includes a third crystallizer 7, a third solid-liquid separator 8 and a third melter 9.

[0095] It should be noted that the operating temperatures of the first crystallizer 1, the second crystallizer 4 and the third crystallizer 7 are successively reduced. Specifically, the temperature range of the first crystallizer 1 is 8°C to 12°C, the temperature range of the second crystallizer 4 is 4°C to 9°C, and the temperature range of the third crystallizer 7 is 0°C to 6°C. Thus, under the premise of meeting the purity of the product, the overall crystallization energy consumption is lowered by the step-by-step cooling and crystallization method.

[0096] It should be noted that in this embodiment, the first solid-liquid separator and the second solid-liquid separator are integrated devices that can not only achieve solid-liquid separation of the slurry, but also further wash and filter the separated crystals, which is beneficial to reducing overall energy consumption.

[0097] Specifically, refer to Figure 2 The outlet of the first crystallizer 1 is connected to the inlet of the first solid-liquid separator 2, and the outlet of the first solid-liquid separator 2 is further connected to the inlet of the first melter 3. The first crystallizer 1 is used to cool and crystallize the raw material a containing paraxylene under a first temperature condition to obtain a first crystal slurry b, the first solid-liquid separator 2 is used to perform solid-liquid separation on the first crystal slurry b, and wash the first crystal d, and the first melter 3 is used to melt the first crystal d to obtain a first paraxylene product e.

[0098] In an alternative embodiment, referring to Figure 2 The outlet of the first solid-liquid separator 2 is also connected to the inlet of the first crystallizer 1 and the inlet of the second crystallizer 4, so as to return a part of the first filtered mother liquor c to the first crystallizer 1, and send the remaining part to the second crystallizer 4 for cooling and crystallization.

[0099] In an alternative embodiment, referring to Figure 2 The outlet of the first melter 3 is also connected to the inlet of the first solid-liquid separator 2, so as to return part of the first para-xylene product e to the first solid-liquid separator 2 to wash the first crystal slurry b and obtain the first product eluate f. The outlet of the first solid-liquid separator 2 is also connected to the inlet of the first crystallizer 1, so as to return the first product eluate f to the first crystallizer 1.

[0100] Further, in an optional embodiment, referring to Figure 2The outlet of the second crystallizer 4 is connected to the inlet of the second solid-liquid separator 5, and the outlet of the second solid-liquid separator 5 is connected to the inlet of the second melter 6. The second crystallizer 4 is used to cool and crystallize part of the first filtered mother liquor c under the second temperature condition to obtain the second crystal slurry g; the second solid-liquid separator 5 is used to perform solid-liquid separation on the second crystal slurry g and wash the second crystal i.

[0101] In an alternative embodiment, referring to Figure 2 The outlet of the second solid-liquid separator 5 is also connected to the second crystallizer 4 and the third crystallizer 7, so as to return a part of the second filtered mother liquor h to the second crystallizer 4, and send the remaining part to the third crystallizer 7 for cooling and crystallization.

[0102] In an alternative embodiment, referring to Figure 2 The outlet of the second melter 6 is connected to the inlet of the second solid-liquid separator 5, so as to return part of the second para-xylene product j to the second solid-liquid separator 5 to wash the second crystal slurry g, thereby obtaining the second product eluate k. The outlet of the second solid-liquid separator 5 is connected to the first crystallizer 1, so as to return the second product eluate k to the first temperature condition.

[0103] In an alternative embodiment, referring to Figure 2 The outlet of the third crystallizer 7 is connected to the inlet of the third solid-liquid separator 8, and the outlet of the third solid-liquid separator 8 is connected to the inlet of the third melter 9. The third crystallizer 7 is used to cool and crystallize part of the second filtered mother liquor h under the third temperature condition to obtain the third crystal slurry m; the third solid-liquid separator 8 is used to perform solid-liquid separation on the third crystal slurry m and wash the third crystal o; the third melter 9 is used to melt the third crystal o to obtain the third para-xylene product p.

[0104] In an alternative embodiment, referring to Figure 2 The outlet of the third solid-liquid separator 8 is also connected to the third crystallizer 7, so as to return part of the third filtered mother liquor n to the third temperature condition for further cooling and crystallization.

[0105] In an alternative embodiment, referring to Figure 2 The outlet of the third melter 9 is also connected to the inlet of the third solid-liquid separator 8, so as to return part of the third para-xylene product p to the third solid-liquid separator 8 to wash the third crystal slurry m, thereby obtaining the third product eluate q. The outlet of the third solid-liquid separator 8 is also connected to the first crystallizer 1, so as to return the third product eluate q to the first temperature condition for further cooling and crystallization.

[0106] In summary, the embodiment of the present application adopts step-by-step cooling crystallization, and the slurry of the three crystallization levels can directly produce products after washing the raw materials and products. This process is suitable for raw materials with a concentration range of 95% to 98% of p-xylene, and the three crystallization levels can produce products that meet the purity requirements, with the characteristics of simple process and high production efficiency. After filtering the slurry, the filtered mother liquor is first discharged from the solid-liquid separator, and then the crystals are washed in the solid-liquid separator, that is, the filtering and separation of the slurry and the washing process of the crystals are integrated in a solid-liquid separator, which greatly reduces the overall production energy consumption. Among them, the raw materials enter the system in the form of divided feeds, part of the raw materials directly enter the first temperature condition, part of the raw materials enter the first crystallizer 1 in the form of the first filtered mother liquor, part of the raw materials enter the second crystallizer 4 in the form of the second filtered mother liquor, and part of the raw materials enter the third crystallizer 7 in the form of the third filtered mother liquor. Thereby, the solid content of the first solid-liquid separator 2 can be reduced, so that the crystals obtained in the three crystallization levels can meet the product purity requirements, reduce the overall transfer amount and circulation amount of the crystals, and improve production efficiency. The solid-liquid separator separates the filtrate mother liquor and the product eluate, and processes the relatively high-concentration product eluate and the relatively low-concentration filtrate mother liquor separately. The filtrate mother liquor lean in paraxylene goes to the next stage, and the product eluate rich in paraxylene returns to the first temperature condition to stabilize the product purity and output and reduce the loss of paraxylene. In addition, using raw material washing slurry can also increase the crystal temperature, reduce the impurity inclusion caused by the explosive nucleation of the crystal in the product washing stage, and discharge some impurities first, which can improve the product washing efficiency and reduce the amount of product washing liquid, so as to greatly improve the production efficiency.

[0107] Below, a specific example is used to explain in detail the multi-stage washing production process and system of high-concentration paraxylene in the embodiment of the present application:

[0108] A C8 mixture with a paraxylene content of 95% is added as raw material a (flow rate of 1560 kg / h) to the first crystallizer 1 for cooling and crystallization. The crystallization temperature is 9°C. The obtained first crystal slurry b enters the first solid-liquid separator 2 for separation to obtain a first filtered mother liquor c and a first crystal d. 20% by weight of the first filtered mother liquor c returns to the first crystallizer 1, and the remaining part enters the second crystallizer 4 for cooling and crystallization. The first crystal d is washed with raw material a (flow rate of 240 kg / h) and a paraxylene product (flow rate of 240 kg / h) to obtain a first eluate f, which is returned to the first crystallizer 1 for recrystallization. The washed first crystal d is melted in the first melter 3 to obtain a first paraxylene product e. 15% by weight of the first paraxylene product e is returned to the first solid-liquid separator 2 as a washing liquid to wash the first crystal d, and the remaining first paraxylene product e leaves the crystallization system as a product.

[0109] About 80% by weight of the first filtered mother liquor c enters the second crystallizer 4 for cooling and crystallization, and the crystallization temperature is 6°C. The obtained second crystal slurry g enters the second solid-liquid separator 5, and after solid-liquid separation, the second filtered mother liquor h and the second crystal i are obtained. The second filtered mother liquor h, which accounts for 5% by weight, returns to the second crystallizer 4, and the remaining part enters the third crystallizer 7 for cooling and crystallization. The second crystal i is washed in the second solid-liquid separator 5 with the raw material a (flow rate of 108 kg / h) and the para-xylene product (flow rate of 240 kg / h) to obtain the second eluate k, and the second product eluate k is returned to the first crystallizer 1 for recrystallization. The washed second crystal i is melted in the second melter 6 to obtain the second para-xylene product j. 20% of the second para-xylene product j is returned to the second solid-liquid separator 5 as a washing liquid to wash the second crystal i, and the remaining part leaves the crystallization system as a product.

[0110] About 95% by weight of the second filtered mother liquor h enters the third crystallizer 7 for cooling and crystallization, and the crystallization temperature is 0°C. The obtained third crystal slurry m enters the third solid-liquid separator 8, and after solid-liquid separation, the third filtered mother liquor n and the third crystal o are obtained. The third filtered mother liquor n, which accounts for 10% by weight, is returned to the third crystallizer 7, and the remaining part is discharged from the crystallization system. The third crystal o is washed with raw material a (flow rate of 92 kg / h) and para-xylene product (flow rate of 92 kg / h) in the third solid-liquid separator 8 to obtain the third product eluate q, and the third product eluate q is returned to the first crystallizer 1 for recrystallization. The washed third crystal o is melted in the third melter 9 to obtain the second para-xylene product o. The second para-xylene product o, which accounts for 30%, is returned to the third solid-liquid separator 8 as a washing liquid to wash the third crystal o, and the remaining part leaves the crystallization system as a product.

[0111] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", as explained by "including" used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A multi-stage washing production process for high-concentration p-xylene, characterized in that: include: Cooling and crystallizing the raw material containing para-xylene under a first temperature condition to obtain a first slurry; Performing solid-liquid separation on the first slurry to obtain first crystals and a first filtered mother liquor; returning part of the first filtered mother liquor to the first temperature condition for further cooling and crystallization, and cooling and crystallizing the remaining first filtered mother liquor at a second temperature condition to obtain a second crystal slurry; Using the raw material and the para-xylene product as washing liquids to wash the first crystals in sequence; Melting the washed first crystals to obtain a first p-xylene product; Performing solid-liquid separation on the second crystal slurry to obtain second crystals and a second filtered mother liquor; returning part of the second filtered mother liquor to the second temperature condition for further cooling and crystallization, and cooling and crystallizing the remaining second filtered mother liquor at a third temperature condition to obtain a third crystal slurry; Using the raw material and the para-xylene product as washing liquids to wash the second crystals in sequence; Melting the washed second crystals to obtain a second p-xylene product; Performing solid-liquid separation on the third slurry to obtain third crystals and a third filtered mother liquor; returning part of the third filtered mother liquor to the third temperature condition to continue cooling and crystallizing, and discharging the remaining third filtered mother liquor out of the system; Using the raw material and the paraxylene product as washing liquids to wash the third crystals in sequence; Melting the washed third crystals to obtain a third p-xylene product; The operating temperatures of the first temperature condition, the second temperature condition and the third temperature condition decrease in sequence.

2. The multi-stage washing production process of high-concentration p-xylene according to claim 1, characterized in that: After obtaining the first p-xylene product, returning part of the first p-xylene product as washing liquid to the first crystals in the previous step to wash the first crystals; After obtaining the second p-xylene product, returning part of the second p-xylene product as washing liquid to the second crystals in the previous step to wash the second crystals; After obtaining the third p-xylene product, part of the third p-xylene product is returned to the third crystals in the previous step as washing liquid to wash the third crystals.

3. The multi-stage washing production process of high-concentration p-xylene according to claim 2 is characterized in that: returning 10% to 30% of the first para-xylene product as washing liquid to the first crystals in the previous step to wash the first crystals; returning 10% to 30% of the second para-xylene product as washing liquid to the second crystals in the previous step to wash the second crystals; 10% to 30% of the third para-xylene product is returned to the third crystals of the previous step as washing liquid to wash the third crystals.

4. The multi-stage washing production process of high-concentration p-xylene according to claim 2, characterized in that: Using the raw material and the para-xylene product as washing liquids to wash the first crystals in sequence to obtain a first eluate; Using the raw material and the para-xylene product as washing liquids to wash the second crystals in sequence to obtain a second eluate; The raw material and the paraxylene product are used as washing liquids to wash the third crystals in sequence to obtain a third eluate, and the first eluate, the second eluate and the third eluate are all returned to the first temperature condition to continue cooling and crystallizing.

5. The multi-stage washing production process of high-concentration p-xylene according to claim 1, characterized in that: A C8 mixture with a paraxylene concentration ranging from 95 to 98% is used as a raw material and subjected to cooling crystallization under a first temperature condition.

6. The multi-stage washing production process of high-concentration p-xylene according to claim 1, characterized in that: The operating temperature range of the first temperature condition is 8°C to 12°C, the operating temperature range of the second temperature condition is 4°C to 9°C, and the operating temperature of the third temperature condition is 0°C to 6°C.

7. The multi-stage washing production process of high-concentration p-xylene according to claim 1, characterized in that: 5% to 20% of the first filtered mother liquor is returned to the first temperature condition to continue cooling and crystallizing, 5% to 20% of the second filtered mother liquor is returned to the second temperature condition to continue cooling and crystallizing, and 5% to 20% of the third filtered mother liquor is returned to the third temperature condition to continue cooling and crystallizing.

8. A multi-stage washing production system for high-concentration p-xylene, used for implementing the multi-stage washing production process for high-concentration p-xylene according to any one of claims 1 to 7, characterized in that: It includes a primary crystallization device, a secondary crystallization device and a tertiary crystallization device; The primary crystallization device comprises a first crystallizer, a first solid-liquid separator and a first melter, the secondary crystallization device comprises a second crystallizer, a second solid-liquid separator and a second melter, and the tertiary crystallization device comprises a third crystallizer, a third solid-liquid separator and a third melter; The operating temperatures of the first crystallizer, the second crystallizer and the third crystallizer are sequentially reduced; The first crystallizer is used to cool and crystallize the raw material containing para-xylene under a first temperature condition to obtain a first crystal slurry; The first crystallizer outlet is communicated with the first solid-liquid separator inlet, and the first solid-liquid separator is used to perform solid-liquid separation on the first crystal slurry and wash the first crystals; The first solid-liquid separator outlet is communicated with the first melter inlet, and the first melter is used to melt the first crystals to obtain a first paraxylene product; The first solid-liquid separator outlet is also connected to the first crystallizer inlet and the second crystallizer inlet; The outlet of the second crystallizer is connected to the inlet of the second solid-liquid separator, and the second crystallizer is used to cool and crystallize part of the first filtered mother liquor under a second temperature condition to obtain a second crystal slurry; The second solid-liquid separator is used for performing solid-liquid separation on the second crystal slurry and washing the second crystals; The outlet of the second solid-liquid separator is communicated with the inlet of the second melter, and the second melter is used to melt the second crystals to obtain a second paraxylene product; The second solid-liquid separator outlet is also connected to the second crystallizer inlet and the third crystallizer inlet; The outlet of the third crystallizer is connected to the inlet of the third solid-liquid separator, and the third crystallizer is used to cool and crystallize part of the first filtered mother liquor under a third temperature condition to obtain a third slurry; The third solid-liquid separator is used to perform solid-liquid separation on the third crystal slurry and wash the third crystals; The outlet of the third solid-liquid separator is communicated with the inlet of the third melter, and the third melter is used to melt the third crystal to obtain a third paraxylene product; The third solid-liquid separator outlet is also connected to the third crystallizer inlet.

9. The multi-stage washing production system of high concentration paraxylene according to claim 8, characterized in that: The first melter outlet is in communication with the first solid-liquid separator inlet, and is used to return part of the first para-xylene product as washing liquid to the first crystals in the previous step to wash the first crystals; The first solid-liquid separator outlet is connected to the first crystallizer inlet, and is used to return the first product eluate to the first temperature condition for cooling and crystallization.

10. The multi-stage washing production system of high concentration paraxylene according to claim 8, characterized in that: The second melter outlet is in communication with the second solid-liquid separator inlet, and is used to return part of the second para-xylene product as washing liquid to the second crystals in the previous step to wash the second crystals; The outlet of the second solid-liquid separator is connected to the inlet of the first crystallizer, so as to return the second product eluate to the first temperature condition for cooling and crystallization.

11. The multi-stage washing production system of high concentration paraxylene according to claim 8, characterized in that: The third melter outlet is in communication with the third solid-liquid separator inlet, and is used to return part of the third paraxylene product as washing liquid to the third crystals in the previous step to wash the third crystals; The outlet of the third solid-liquid separator is connected to the inlet of the first crystallizer, and is used to return the third product eluate to the first temperature condition for cooling and crystallization.

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