A method for producing paraxylene

Abstract

The present invention relates to the field of separation and purification, and discloses a method for producing paraxylene, which includes (1) subjecting a raw material containing paraxylene to cooling crystallization, wherein the crystallization temperature is 70°C to 10°C, to obtain a magma I containing paraxylene crystals; 2) feeding the magma I into a rotary pressure filter for filtration, wherein the rotary pressure filter is provided with a feed zone, at least one drying zone, at least one washing zone, a discharge zone, a cleaning zone, and a pre-cooling zone, wherein the magma I enters the feed zone, and filter cake I and mother liquor I are obtained by filtration. The filter cake I is then dried and washed in sequence, and then fed into the discharge zone, and the rotary pressure filter is discharged to obtain a paraxylene product. The method provided by the present invention shortens the process flow, reduces equipment investment, and reduces energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of separation and purification, and in particular to a method for producing p-xylene. Background Art

[0002] Paraxylene is an important bulk chemical product, primarily used in the production of purified terephthalic acid (PTA), which is then used to produce polyester. Industrial methods for separating paraxylene include adsorption and crystallization.

[0003] CN111655655A discloses a method for recovering a paraxylene product from a mixture of C8 aromatic hydrocarbons, the method comprising: feeding the C8 aromatic hydrocarbon mixture to a first crystallization stage; separating the effluent of the first crystallization stage in a first solid / liquid separator to form a first paraxylene-depleted stream and a first paraxylene filter cake; feeding at least a portion of the first paraxylene-depleted stream to a second crystallization stage; separating the effluent from the second crystallization stage in a second solid / liquid separator to form a second paraxylene-depleted stream and a second paraxylene filter cake; feeding the first paraxylene filter cake to a first repulping zone and a second repulping zone; at least one of the second repulping zones; feeding the second p-xylene filter cake to the first repulping zone and repulping the p-xylene with a first repulping fluid; separating the first repulped effluent in a third solid / liquid separator to produce a third p-xylene-depleted stream and a third p-xylene filter cake; feeding the third p-xylene filter cake to the second repulping zone and repulping the p-xylene with a second repulping fluid; separating the second repulped effluent in a fourth solid / liquid separator to form a fourth p-xylene-depleted stream and a fourth p-xylene filter cake; and recovering at least a portion of the fourth p-xylene filter cake as a p-xylene product.

[0004] CN1938247A discloses a method for separating p-xylene from low-concentration raw materials through multi-stage crystallization. This method uses ammonia absorption refrigeration to reduce refrigeration energy consumption, but the p-xylene crystals obtained by deep-crystallization still need to be melted and then recrystallized, so the energy consumption is still very high.

[0005] The crystallization method disclosed in the prior art requires multiple steps of beating, washing and solid-liquid separation, which not only has a long process flow, many production equipments and a large investment, but also has high energy consumption. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a method for producing paraxylene, which shortens the process flow, reduces equipment investment and lowers energy consumption.

[0007] In order to achieve the above object, the present invention provides a method for producing paraxylene, comprising the following steps:

[0008] (1) cooling and crystallizing the raw material containing p-xylene to obtain a slurry I containing p-xylene crystals;

[0009] (2) feeding the slurry I into a rotary pressure filter for filtration, wherein the rotary pressure filter is provided with a feeding area, at least one drying area, at least one washing area, a discharge area, a cleaning area, and a pre-cooling area. The slurry I enters the feeding area and is filtered to obtain a filter cake I and a mother liquor I;

[0010] (3) sending the filter cake I into the drying zone I, and drying the filter cake I with the drying gas I to obtain the filter cake II;

[0011] (4) sending the filter cake II to the washing zone I, washing the filter cake II with the washing liquid I to obtain the filter cake III;

[0012] (5) the filter cake III is optionally subjected to n drying-washing cycles as described in step (3) to step (4) in the rotary pressure filter;

[0013] (6) optionally drying the filter cake obtained in step (5) in a drying zone, and then sending it to a discharge zone and discharging it from a rotary pressure filter to obtain paraxylene;

[0014] (7) The drum of the rotary pressure filter continues to rotate to the cleaning area, and the filter cloth and the corresponding drum are cleaned with cleaning liquid;

[0015] (8) The drum of the rotary pressure filter continues to rotate to the pre-cooling zone, and the filter cloth and the corresponding drum are pre-cooled with a pre-cooling liquid. Then, the drum continues to rotate to the feeding zone to receive the slurry I.

[0016] Preferably, the temperature difference between the drying gas and the dried filter cake is 0-10°C, more preferably 0.5-5°C.

[0017] Preferably, the temperature difference between the washing liquid and the washed filter cake is 0.5-120°C, more preferably 10-105°C.

[0018] The method for producing paraxylene provided by the present invention adopts a rotary pressure filter for solid-liquid separation. By setting different areas, such as a drying area and a washing area arranged at intervals, pre-cooling the feed area, etc., and supplemented by drying gas, washing liquid, cleaning liquid and pre-cooling liquid, it is ensured that the functions of filtering, washing and drying can be smoothly achieved in one device. It can replace the existing multi-stage pulping and washing process, shorten the process, reduce equipment, reduce energy consumption, and achieve good technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of the method for producing p-xylene according to the present invention;

[0020] Figure 2is a schematic diagram of an existing method for producing p-xylene;

[0021] Figure 3 is a schematic diagram of an existing method for producing p-xylene;

[0022] Figure 4 It is a schematic diagram of the existing method for producing p-xylene.

[0023] Description of Reference Numerals

[0024] 1 Crystallizer 2 Rotary Pressure Filter

[0025] 3 Melting tank 4 Refrigeration system DETAILED DESCRIPTION

[0026] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0027] In the present invention, unless otherwise stated, the concentration and purity are percentage by weight.

[0028] The present invention provides a method for producing p-xylene, such as Figure 1 As shown, the following steps are included:

[0029] (1) cooling and crystallizing the raw material containing para-xylene (for example, in a crystallizer 1) to obtain a slurry I containing para-xylene crystals;

[0030] (2) feeding the slurry I into a rotary pressure filter 2 for filtration, wherein the rotary pressure filter is provided with a feeding area, at least one drying area, at least one washing area, a discharge area, a cleaning area, and a pre-cooling area. The slurry I enters the feeding area, and the para-xylene crystals are intercepted by the filter cloth to form a filter cake I. The mother liquor passes through the filter cloth to obtain mother liquor I;

[0031] (3) The filter cake I rotates with the drum and reaches the drying zone I, where it is dried by the drying gas I to obtain the filter cake II. The drying gas I and the mother liquid II separated from the filter cake are discharged from the rotary pressure filter together, separated in the gas-liquid separation tank, and collected separately;

[0032] (4) Filter cake II rotates with the drum and reaches the washing zone I, where it is washed with washing liquid I to obtain filter cake III. The washing filtrate III is discharged from the rotary pressure filter and collected separately;

[0033] (5) the filter cake III is optionally subjected to n drying-washing cycles as described in step (3) to step (4) in the rotary pressure filter;

[0034] (6) optionally drying the filter cake obtained in step (5) in a drying zone, and then sending it to a discharge zone and discharging it from a rotary pressure filter to obtain paraxylene, preferably after melting to obtain a paraxylene product;

[0035] (7) The drum of the rotary pressure filter continues to rotate to the cleaning area, and the filter cloth and the corresponding drum are cleaned with a cleaning liquid. The cleaning liquid cleans the filter cloth and the corresponding drum, and the cleaning liquid is discharged from the rotary pressure filter and collected separately;

[0036] (8) The drum of the rotary pressure filter continues to rotate to the pre-cooling zone, and the filter cloth and the corresponding drum are pre-cooled with a pre-cooling liquid. The pre-cooling liquid is discharged from the rotary pressure filter and collected separately, and then the drum continues to rotate to the feeding zone to receive the slurry I.

[0037] The present invention provides a wide range of options for the para-xylene-containing raw material, which can be any conventional raw material requiring purification. Preferably, the para-xylene-containing raw material has a para-xylene content of 17-98% by weight. The method provided by the present invention is applicable to the treatment of both high-concentration and low-concentration para-xylene-containing raw materials.

[0038] In the present invention, the raw material containing paraxylene contains at least one of metaxylene, o-xylene and ethylbenzene in addition to paraxylene.

[0039] The cooling crystallization in step (1) of the present invention can be a conventional operation in the art, and the present invention has no particular limitation thereto. The cooling crystallization can be completed in a crystallizer.

[0040] like Figure 1 As shown, the crystallizer may also be equipped with a refrigeration system 4. The refrigeration system may be any refrigeration system conventionally used in the art, preferably employing evaporative refrigeration of a liquid refrigerant (e.g., liquid ethylene) in the crystallizer jacket or evaporative refrigeration in which the liquid refrigerant directly contacts the material in the crystallizer.

[0041] The present invention has a wide range of temperature selection for the cooling crystallization in step (1), preferably -70 to 10°C.

[0042] The rotary pressure filter of the present invention has n independent zones on its drum. Based on their different functions, the rotary pressure filter can be divided into a feeding zone, a drying zone, a washing zone, a discharge zone, a cleaning zone, and a pre-cooling zone. There is no particular limitation on the number of drying and washing zones. Preferably, the number of drying and washing zones provided in the rotary pressure filter is independently 1-8, and more preferably 3-6. Preferably, the number of drying zones in the rotary pressure filter is one greater than the number of washing zones.

[0043] According to the present invention, there is no particular limitation on the location of specific areas in the rotary pressure filter, and those skilled in the art can make appropriate selections based on the flow direction of materials in specific steps. Specifically, the drying area and the washing area are spaced apart.

[0044] According to the present invention, the drying gases used in the drying zones may differ in type, concentration, and temperature. More preferably, the drying gases used in the different drying zones are of the same type but at different temperatures. More preferably, the temperature of the drying gas used in the subsequent drying zone is higher than that used in the preceding drying zone, with the temperature difference preferably being 5-30°C. This preferred embodiment is more conducive to improving product purity without causing product loss.

[0045] According to a preferred embodiment of the present invention, it is more preferred that different washing zones use different washing liquids.

[0046] According to the present invention, the different washing liquids used in the washing zones may be different in type, concentration and temperature. More preferably, the washing liquids used in the different washing zones are of the same type but at different temperatures, more preferably at different concentrations.

[0047] More preferably, according to the flow direction, the temperature of the washing liquid used in the post-washing zone is higher than that of the washing liquid used in the pre-washing zone, and further preferably the temperature difference is 5-20° C. This preferred embodiment is more conducive to improving product purity without causing product loss.

[0048] More preferably, according to the flow direction, the concentration of the washing liquid used in the post-washing zone is greater than that used in the pre-washing zone, and further preferably the concentration difference is 5-20%. This preferred embodiment is more conducive to improving product purity without causing product loss.

[0049] According to the present invention, preferably, the drying gas used in the drying zone is selected from an inert gas. The inert gas is a gas that does not participate in the reaction in the method. Preferably, the inert gas is selected from at least one of nitrogen, ethylene, propylene, propane, carbon dioxide and the low-temperature evaporated gas after evaporative refrigeration in the cooling crystallization refrigeration system in step (1). Specifically, a mixture of one or more of the refrigerant (for example, ethylene) gas obtained after evaporative refrigeration of the liquid refrigerant (for example, ethylene) in the crystallizer jacket, the refrigeration machine obtained after direct evaporative refrigeration in the crystallizer, and the refrigerant (for example, ethylene) gas in the compression refrigeration system can provide at least part of the drying gas.

[0050] Preferably, the temperature difference between the filter cake before and after drying is 0-10° C., more preferably 0.1-5° C., and even more preferably 0.5-2° C. This preferred embodiment is more conducive to improving product purity without causing product loss.

[0051] Preferably, the temperature difference between the drying gas and the dried filter cake is 0-10°C, more preferably 0.5-5°C.

[0052] According to a preferred embodiment A of the present invention, the washing liquid used in the washing zone is a liquid aromatic hydrocarbon containing p-xylene, more preferably mixed xylene. Preferably, the p-xylene content in the washing liquid is 60-99.99% by weight.

[0053] Preferably, the temperature difference between the filter cake before and after washing is 0.1-30° C., more preferably 1.5-25° C. This preferred embodiment is more conducive to improving product purity without causing product loss.

[0054] Preferably, the temperature difference between the washing liquid and the washed filter cake is 0.5-120°C, more preferably 10-105°C.

[0055] More preferably, the concentration of p-xylene in the washing liquid of the last washing is not less than 99.8%, and the temperature of the washing liquid is 15-30° C. This preferred embodiment is more conducive to improving product purity without causing product loss.

[0056] According to a preferred embodiment of the present invention, different crystallization and washing methods are adopted according to different para-xylene concentrations in the para-xylene-containing raw materials.

[0057] According to a preferred embodiment of the present invention, the para-xylene concentration in the para-xylene-containing feedstock is ≤24% by weight, the crystallization temperature is between -68°C and -60°C, the number of washing zones is 4-6, the para-xylene concentration in the washing liquid is between 75% and 99.95%, and the temperature of the filter cake after washing is between -50°C and 8°C. This preferred embodiment is more conducive to ensuring a smooth filter cake washing process, thereby achieving a purification effect and guaranteeing product purity and yield.

[0058] According to a preferred embodiment of the present invention, the para-xylene concentration in the para-xylene-containing feedstock is 50-90% by weight, the crystallization temperature is between -30°C and 5°C, and the number of washing zones is 3-5. The para-xylene concentration in the washing liquid is 88%-99.95%, and the temperature of the filter cake after washing is between -25°C and 10°C. This preferred embodiment is more conducive to ensuring a smooth filter cake washing process, thereby achieving a purification effect and guaranteeing product purity and yield.

[0059] According to a preferred embodiment of the present invention, the para-xylene concentration in the para-xylene-containing feedstock is ≥90% by weight, the crystallization temperature is between -20°C and 10°C, and the number of washing zones is 3-5. The para-xylene concentration in the washing liquid is between 90% and 99.98%, and the temperature of the filter cake after washing is between -15°C and 10°C. This preferred embodiment is more conducive to ensuring a smooth filter cake washing process, thereby achieving a purification effect and guaranteeing product purity and yield.

[0060] According to a preferred embodiment B of the present invention, the washing liquid used in the washing zone is at least one of liquid alkanes with low boiling points and low freezing points, liquid aromatic hydrocarbons and liquid alcohols.

[0061] In the present invention, the low boiling point refers to the boiling point of liquid aromatic hydrocarbons not higher than 120°C; the low freezing point refers to the freezing point of liquid aromatic hydrocarbons not higher than -70°C.

[0062] In the present invention, the low boiling point refers to the boiling point of the liquid alkane being no higher than 100°C; the low freezing point refers to the freezing point of the liquid alkane being no higher than 10°C.

[0063] In the present invention, the low boiling point refers to that the boiling point of the low-carbon alcohol is not higher than 100°C; the low freezing point refers to that the freezing point of the low-carbon alcohol is not higher than -70°C.

[0064] Preferably, the liquid alkane is at least one selected from n-hexane, cyclohexane and pentane.

[0065] Preferably, the liquid aromatic hydrocarbon is toluene.

[0066] Preferably, the liquid alcohol is methanol.

[0067] According to the present invention, preferably, the washing liquid used in the washing zone is at least one of n-hexane, cyclohexane, pentane, toluene and methanol.

[0068] Preferably, according to the flow direction of the logistics, the temperature of the washing liquid used in the subsequent washing zone is not lower than the temperature of the washing liquid used in the previous washing zone.

[0069] Preferably, the temperature difference between the filter cake before and after washing is 0.1-5° C., more preferably 0.1-1° C. This preferred embodiment is more conducive to improving product purity without causing product loss.

[0070] According to the method provided by the present invention, more preferably, the method further comprises melting the p-xylene obtained in step (6) in a melting tank 3, wherein the liquid in the melting tank enters a distillation tower for separation, a washing liquid is obtained at the top of the tower for further reuse, and the p-xylene product is obtained in the bottom of the tower. This preferred embodiment is more conducive to improving the purity of the p-xylene product.

[0071] In the present invention, the "optionally" in step (5) means that the filter cake III may undergo n times of the drying-washing cycle as described in step (3) to step (4), or may not undergo n times of the drying-washing cycle as described in step (3) to step (4), preferably undergoes n times of the drying-washing cycle.

[0072] The n may be, for example, an integer of 1-8, preferably an integer of 3-6.

[0073] In the present invention, the "optionally" in step (6) means that the filter cake may or may not be dried before being sent to the unloading area, preferably after being dried.

[0074] In the present invention, there is no particular limitation on the drying time, as long as the filter cake can be dried. Preferably, the filter cake is dried so that the moisture content is ≤5%.

[0075] In the present invention, there is no particular limitation on the washing time and the amount of washing liquid used, and it is preferred that the temperature difference between the filter cake before and after washing is satisfied.

[0076] The present invention has a wide range of selection for the type of the cleaning liquid. Preferably, the cleaning liquid is the same as the washing liquid or is a raw material containing para-xylene. Preferably, the cleaning liquid is a raw material containing para-xylene.

[0077] According to a preferred embodiment of the present invention, the temperature of the cleaning liquid is ≥15°C, more preferably 20-80°C.

[0078] In the method provided by the present invention, precooling the filter cloth and the corresponding drum in step (8) can achieve rapid separation of the filtrate and reduce product loss.

[0079] According to the present invention, preferably, the precooling liquid is the same as the washing liquid or is a raw material containing paraxylene, and more preferably the precooling liquid is a raw material containing paraxylene.

[0080] According to a preferred embodiment of the present invention, the temperature difference between the drum area after being cooled by the pre-cooling liquid and the temperature of the slurry I is 0.5-5° C. This preferred embodiment is more conducive to rapid separation of the filtrate and reduced product loss.

[0081] The present invention has no particular limitation on the method of unloading the filter cake in the unloading zone. Preferably, the filter cake in the unloading zone is scraped off by a scraper or blown off by back-blowing gas. Preferably, the back-blowing gas is the drying gas used in the drying zone.

[0082] According to another preferred embodiment of the present invention, the filter cake in the discharge zone is washed off by the liquid paraxylene product, and more preferably, the temperature of the liquid paraxylene product used for washing the filter cake is 20-80°C.

[0083] Preferably, the purity of the p-xylene product obtained by the method provided by the present invention is ≥99.8%, more preferably ≥99.9%.

[0084] The present invention will be described in detail below through examples.

[0085] Example 1:

[0086] The method for producing p-xylene according to the present invention

[0087] like Figure 1As shown, a raw material containing p-xylene, with a p-xylene concentration of 22%, m-xylene of 51%, o-xylene of 21%, ethylbenzene of 2%, and others of 4%, enters a crystallizer for cooling crystallization, and the crystallization temperature is -65°C to obtain a slurry I containing p-xylene crystals; the slurry I enters a rotary pressure filter, and the slurry I first enters the feed zone, and solid-liquid separation is performed in the pre-cooled drum, and the p-xylene crystals are intercepted by the filter cloth to form a filter cake I, and the mother liquor passes through the filter cloth to obtain mother liquor I; the filter cake I rotates with the drum and reaches the drying zone I, and is dried by a drying gas I, which is dry nitrogen with a water content of ≤10ppm and a temperature of -63°C to obtain a filter cake II, with a temperature of -64°C and a drying gas I The filter cake II is discharged from the rotary pressure filter together with the mother liquor II separated from the filter cake, and is separated in the gas-liquid separation tank and collected separately; the filter cake II rotates with the drum and reaches the washing zone I, where the filter cake II is washed with the washing liquid I. The washing liquid I is a mixed xylene containing p-xylene, which can be a mixture of the mother liquor discharged from the rotary pressure filter and one or more streams of the filtrate, wherein the p-xylene concentration in the washing liquid I is 75% and its temperature is 20°C, to obtain the filter cake III, the temperature of which is -42°C. The washing filtrate III is discharged from the rotary pressure filter and collected separately; the filter cake III rotates with the drum and reaches the drying zone II, where the filter cake III is dried with the dry gas II. The drying gas II is dry nitrogen with a water content of ≤ 10ppm, temperature is -40℃, filter cake IV is obtained, temperature is -41℃, dry gas II and mother liquor IV separated from the filter cake are discharged from the rotary pressure filter together, separated in the gas-liquid separation tank and collected separately; filter cake IV rotates with the drum and reaches washing zone II, where it is washed with washing liquid II, which is a mixed xylene containing p-xylene, which can be a mixture of one or more streams of the mother liquor discharged from the rotary pressure filter and the filtrate, wherein the p-xylene concentration of washing liquid II is 87%, and its temperature is 20℃, to obtain filter cake V, temperature is -25.4℃, and washing filtrate V is discharged from the rotary pressure filter and collected separately; filter cake V rotates with the drum and reaches drying zone III The filter cake is dried using dry gas III, which is dry nitrogen with a water content of ≤10ppm and a temperature of -23°C, to obtain filter cake VI at a temperature of -24°C. Dry gas III and mother liquor VI separated from the filter cake are discharged from the rotary pressure filter together, separated in a gas-liquid separator, and then collected separately. Filter cake VI rotates with the drum and reaches washing zone III, where it is washed using washing liquid III, which is a mixed xylene containing paraxylene. The washing liquid III can be a mixture of one or more streams of the mother liquor discharged from the rotary pressure filter and the filtrate. The paraxylene concentration of washing liquid III is 93%, and the temperature is 20°C. Filter cake VII is obtained at a temperature of -13.8℃, the washing filtrate VII is discharged from the rotary pressure filter and collected separately; the filter cake VII rotates with the drum and reaches the drying zone IV, where the filter cake VII is dried by dry gas IV, which is dry nitrogen with a water content of ≤10ppm and a temperature of -11℃, to obtain filter cake VIII with a temperature of -12℃. The dry gas IV and the mother liquor VIII separated from the filter cake are discharged from the rotary pressure filter together, separated in a gas-liquid separation tank and collected separately; the filter cake VIII rotates with the drum and reaches the washing zone IV, where the filter cake VIII is washed with washing liquid IV. The washing liquid IV is a mixed xylene containing p-xylene, which can be obtained by mixing one or more streams of the mother liquor and the filtrate discharged from the rotary pressure filter, wherein the p-xylene concentration in the washing liquid IV is 97%, and its temperature is 20°C, to obtain a filter cake IX at a temperature of -6.6°C. The washing filtrate IX is discharged from the rotary pressure filter and collected separately; the filter cake IX rotates with the drum and reaches the drying zone V, where it is dried by dry gas V, which is dry nitrogen with a water content of ≤10ppm and a temperature of -5°C, to obtain a filter cake X at a temperature of -6°C. The dry gas V and the filter cake are separated and separated. The mother liquor X separated from the rotary pressure filter is discharged together with the mother liquor X, separated in the gas-liquid separation tank and collected separately; the filter cake X rotates with the drum and reaches the washing zone V, where it is washed with a washing liquid V. The washing liquid V is a mixed xylene containing p-xylene, which can be a mixture of the mother liquor discharged from the rotary pressure filter and one or more streams of the filtrate, wherein the p-xylene concentration of the washing liquid V is 99% and the temperature is 25°C, to obtain a filter cake XI with a temperature of 0.4°C. The washing filtrate XI is discharged from the rotary pressure filter and collected separately; the filter cake XI rotates with the drum and reaches the drying zone VI, where it is dried using a drying method. The filter cake XI is dried by the dry gas VI, which is dry nitrogen with a water content of ≤10ppm and a temperature of 2°C, to obtain the filter cake XII at a temperature of 1°C. The dry gas VI and the mother liquor XII separated from the filter cake are discharged from the rotary pressure filter together, separated in a gas-liquid separation tank, and collected separately; the filter cake XII rotates with the drum and reaches the washing zone V, where it is washed with the washing liquid VI, which is a paraxylene product with a paraxylene concentration of 99.95% and a temperature of 30°C, to obtain the filter cake XIII at a temperature of 5.7℃, the washing filtrate XIII is discharged from the rotary pressure filter and collected separately; the filter cake XIII rotates with the drum and reaches the drying area VII, where the filter cake XIII is dried by the dry gas VII, which is dry nitrogen with a water content of ≤10ppm and a temperature of 7℃, to obtain the filter cake XIV with a temperature of 6℃. The dry gas VII and the crystallization mother liquor XIV separated from the filter cake are discharged from the rotary pressure filter together, separated in the gas-liquid separation tank and collected separately; the dried filter cake XIV continues to rotate with the drum and finally reaches the unloading area, where it is backflushed with dry nitrogen and discharged from the rotary pressure filter. The liquid enters the melting tank through a pressure filter, where it is melted to produce paraxylene, with a purity of 99.95%. The drum continues to rotate to the cleaning area, where the filter cloth and the corresponding drum are cleaned with a cleaning liquid. The cleaning liquid is the raw material containing paraxylene and its temperature is 80°C. The cleaning liquid is discharged from the rotary pressure filter and collected separately. The drum continues to rotate to the pre-cooling area, where the filter cloth and the corresponding drum are pre-cooled with a pre-cooling liquid. The pre-cooling liquid is the crystallization mother liquor I, with a temperature of -65°C. The pre-cooling liquid is discharged from the rotary pressure filter and collected separately. The temperature of the pre-cooled drum area is -63°C. The drum continues to rotate to the feed area, where it receives the crystal slurry I.

[0088] Compared with Comparative Example 1, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 60%, and the production energy consumption is greatly reduced by 66%.

[0089] Example 2:

[0090] The method for producing p-xylene according to the present invention

[0091] like Figure 1 As shown, with reference to the production method described in Example 1, wherein the filter cake I is washed 5 times with a washing liquid in a rotary pressure filter and dried 6 times with a drying gas, and the drying gases I to VI are all ethylene gas, ethylene gas obtained after evaporation and refrigeration of liquid ethylene in the crystallizer jacket and ethylene gas in the compression refrigeration system, wherein the water content is ≤10ppm, and the temperatures are respectively -63°C, -37°C, -19°C, -9°C, 0°C, and 6°C, and the temperatures of the filter cakes after drying are respectively -64°C, -38°C, -20°C, -9.5°C, -0.5°C, and 5°C, and the washing liquids I to VI are all mixed xylenes containing p-xylene, wherein the p-xylene concentrations are 75.6%, 75%, 87%, 98%, and 99.91%, respectively, and the washing liquid temperatures are all 30°C. The temperatures of the filter cakes after washing are respectively -39°C, -20.8°C, -9.9°C, -0.98°C, and 4.6°C, and the final p-xylene product purity is 99.91%.

[0092] Compared with Comparative Example 1, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 58%, and the production energy consumption is greatly reduced by 63%.

[0093] Example 3:

[0094] The method for producing p-xylene according to the present invention

[0095] like Figure 1 As shown, with reference to the production method described in Example 1, wherein the filter cake I is washed 4 times with a washing liquid in a rotary pressure filter and dried 5 times with a drying gas, and the drying gases I to V are all carbon dioxide gas, the carbon dioxide gas obtained after evaporation and refrigeration of liquid carbon dioxide inside the crystallizer and the carbon dioxide gas in the compression refrigeration system, the water content of which is ≤10ppm, the temperature is -60°C, -33°C, -17°C, -4°C, 5°C, respectively, the temperature of the filter cake after drying is -61°C, -35°C, -18°C, -5°C, 3°C, respectively, the washing liquids I to IV are all mixed xylene containing p-xylene, wherein the p-xylene concentration is 75%, 90%, 96.5%, 99.83%, respectively, the washing liquid temperatures are 40°C, 40°C, 40°C, 30°C, respectively, the temperatures of the filter cake after washing are -36°C, -19°C, -5.7°C, 2.68°C, respectively, and the final p-xylene product purity is 99.83%.

[0096] Compared with Comparative Example 1, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 56%, and the production energy consumption is greatly reduced by 60%.

[0097] Example 4:

[0098] The method for producing p-xylene according to the present invention

[0099] like Figure 1 As shown, with reference to the production method described in Example 1, wherein the filter cake I is washed 3 times with a washing liquid in a rotary pressure filter and dried 4 times with a drying gas, the drying gases I to IV are all nitrogen, the water content of which is ≤10ppm, and the temperatures are -63°C, -38°C, -22°C, and -12°C, respectively. The temperatures of the filter cakes after drying are -64°C, -24.5°C, -14.2°C, and -13°C, respectively. The washing liquids I to III are all mixed xylenes containing p-xylene, wherein the p-xylene concentrations are 76.2%, 91.5%, and 99.57%, respectively. The washing liquid temperatures are 25°C, 30°C, and 30°C, respectively. The temperatures of the filter cakes after washing are -40.3°C, -24.5°C, and -14.2°C, respectively. The final p-xylene product purity is 99.57%.

[0100] Example 5:

[0101] The method for producing p-xylene according to the present invention

[0102] like Figure 1As shown, with reference to the production method described in Example 4, wherein the filter cake I is washed 3 times with a washing liquid in a rotary pressure filter and dried 4 times with a drying gas, the drying gases I to IV are all nitrogen, the water content of which is ≤10ppm, and the temperatures are -63°C, -38°C, -22°C, and -12°C, respectively. The temperatures of the filter cakes after drying are -63.5°C, -25°C, -14.5°C, and -13.2°C, respectively. The washing liquids I to III are all toluene (purity 99.9%), and their temperatures are 25°C, 30°C, and 30°C, respectively. The temperatures of the filter cakes after washing are -40°C, -25°C, and -14°C, respectively. The filter cakes are finally backflushed with dry nitrogen and enter a melting tank. After melting, they enter a distillation tower, and toluene is obtained at the top of the tower for further reuse. The bottom of the tower obtains a paraxylene product with a purity of 99.85%.

[0103] Compared with Comparative Example 1, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 40%, and the production energy consumption is greatly reduced by 35%.

[0104] Example 6:

[0105] The method for producing p-xylene according to the present invention

[0106] like Figure 1 As shown, with reference to the production method described in Example 4, wherein the filter cake I is washed 3 times by a washing liquid in a rotary pressure filter and dried 4 times by a drying gas, the drying gases I to IV are all nitrogen, the water content of which is ≤10ppm, and the temperatures are -63°C, -38°C, -22°C, and -12°C, respectively. The temperatures of the filter cakes after drying are -63.8°C, -24.7°C, -14.3°C, and -12.8°C, respectively. The washing liquids I to III are all n-hexane (purity 99.9%), and their temperatures are 25°C, 30°C, and 30°C, respectively. The temperatures of the filter cakes after washing are -42°C, -26°C, and -12°C, respectively. The filter cakes are finally backflushed by dry nitrogen and enter a melting tank. After melting, they enter a distillation tower, and toluene is obtained at the top of the tower for further reuse, and para-xylene product is obtained in the bottom of the tower with a purity of 99.87%.

[0107] Compared with Comparative Example 1, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 50%, and the production energy consumption is greatly reduced by 45%.

[0108] Example 7:

[0109] The method for producing p-xylene according to the present invention

[0110] like Figure 1As shown, with reference to the production method described in Example 4, wherein the filter cake I is washed 3 times with a washing liquid in a rotary pressure filter and dried 4 times with a drying gas, the drying gases I to IV are all nitrogen, the water content of which is ≤10ppm, and the temperatures are -63°C, -38°C, -22°C, and -12°C, respectively. The temperatures of the filter cakes after drying are -63.4°C, -24.6°C, -14.7°C, and -13.2°C, respectively. The washing liquids I to III are all methanol (purity 99.9%), and the temperatures are 25°C, 30°C, and 30°C, respectively. The temperatures of the filter cakes after washing are -41°C, -23°C, and -15°C, respectively. The filter cakes are finally backflushed with dry nitrogen and enter the melting tank. After melting, they enter the distillation tower, and toluene is obtained at the top of the tower for further reuse, and para-xylene product is obtained in the bottom of the tower with a purity of 99.82%.

[0111] Compared with Comparative Example 1, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 45%, and the production energy consumption is greatly reduced by 50%.

[0112] Example 8:

[0113] The method for producing p-xylene according to the present invention

[0114] like Figure 1 As shown, a raw material containing p-xylene, wherein the concentration of p-xylene is 84.5%, the concentration of m-xylene is 7.2%, the concentration of o-xylene is 1.1%, and the others are 7.2%, enters a crystallizer for cooling crystallization, the crystallization temperature is -30°C, and a slurry I containing p-xylene crystals is obtained; the slurry I enters a rotary pressure filter, is washed 5 times by a washing liquid, and is dried 6 times by a drying gas, wherein the drying gases I to VI are all nitrogen, and the water content thereof is ≤10ppm, and the temperatures are -28°C, -16°C, -8°C, -2°C, 3°C, and 8°C, respectively. The temperatures of the filter cakes after drying are respectively The temperatures of the washing liquids are -29°C, -17°C, -9°C, -3°C, 2°C and 7°C, and the washing liquids I to V are all mixed xylenes containing p-xylene, wherein the concentrations of p-xylene are 88%, 95.3%, 98.2%, 99.3% and 99.93% respectively, and the temperatures of the washing liquids are 20°C, 20°C, 20°C, 20°C and 30°C respectively. The temperatures of the filter cakes after washing are -18.4°C, -9.8°C, -3.2°C, 1.9°C and 6.9°C respectively. The filter cakes are finally backflushed with dry nitrogen and enter the melting tank, and the p-xylene product is obtained after melting with a purity of 99.93%.

[0115] Compared with Comparative Example 2, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 55%, and the production energy consumption is greatly reduced by 50%.

[0116] Example 9:

[0117] The method for producing p-xylene according to the present invention

[0118] like Figure 1 As shown, according to the operating conditions of Example 8, the slurry I enters the rotary pressure filter, is washed 4 times by the washing liquid, and is dried 5 times by the drying gas. The drying gases I to V are all nitrogen, and their water content is ≤10ppm. The temperatures are -28°C, -10°C, -1°C, 6°C, and 10°C, respectively. The temperatures of the filter cakes after drying are -29°C, -11°C, -2°C, 5°C, and 9°C, respectively. The washing liquids I to IV are all mixed xylene containing p-xylene, wherein the p-xylene concentrations are 89.5%, 95.9%, 98.5%, and 99.84%, respectively. The washing liquid temperatures are all 30°C, and the temperatures of the filter cakes after washing are -12.4°C, -2.9°C, 4.33°C, and 8.9°C, respectively. The filter cakes are finally backflushed by dry nitrogen and enter the melting tank. After melting, the p-xylene product is obtained with a purity of 99.84%.

[0119] Compared with Comparative Example 2, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 52%, and the production energy consumption is greatly reduced by 48%.

[0120] Example 10:

[0121] The method for producing p-xylene according to the present invention

[0122] like Figure 1 As shown, according to the operating conditions of Example 8, the slurry I enters the rotary pressure filter, is washed 3 times by the washing liquid, and is dried 4 times by the drying gas. The drying gases I to IV are all nitrogen, and their water content is ≤10ppm. The temperatures are -28°C, -11°C, -2°C, and 5°C, respectively. The temperatures of the filter cakes after drying are -29.5°C, -12°C, -2.5°C, and 3.5°C, respectively. The washing liquids I to III are all mixed xylene containing p-xylene, wherein the p-xylene concentrations are 90%, 96.4%, and 99.82%, respectively. The washing liquid temperatures are all 30°C, and the temperatures of the filter cakes after washing are -12.7°C, -3.2°C, and 3.04°C, respectively. The filter cakes are finally backflushed by dry nitrogen and enter the melting tank. After melting, the p-xylene product is obtained with a purity of 99.82%.

[0123] Compared with Comparative Example 2, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 50%, and the production energy consumption is greatly reduced by 46%.

[0124] Example 11:

[0125] The method for producing p-xylene according to the present invention

[0126] like Figure 1As shown, according to the operating conditions of Example 8, the slurry I enters the rotary pressure filter, is washed twice by the washing liquid, and is dried three times by the drying gas. The drying gases I to III are all nitrogen, and their water content is ≤10ppm. The temperatures are -28°C, -11°C, and -2°C, respectively. The temperatures of the filter cakes after drying are -28.5°C, -11.5°C, and -3°C, respectively. The washing liquids I to II are all mixed xylene containing p-xylene, wherein the p-xylene concentrations are 91.1% and 99.56%, respectively. The washing liquid temperatures are all 30°C, and the temperatures of the filter cakes after washing are -12.6°C and -4.6°C, respectively. The filter cakes are finally backflushed by dry nitrogen and enter the melting tank. After melting, the p-xylene product is obtained with a purity of 99.56%.

[0127] Example 12:

[0128] The method for producing p-xylene according to the present invention

[0129] like Figure 1 As shown, the raw material containing p-xylene, with a p-xylene concentration of 94.51%, an m-xylene concentration of 1.76%, an o-xylene concentration of 0.86%, and the others of 2.57%, enters the crystallizer for cooling crystallization, and the crystallization temperature is -15°C to obtain a slurry I containing p-xylene crystals; the slurry I enters the rotary pressure filter, is washed 5 times by the washing liquid, and is dried 6 times by the drying gas, wherein the drying gases I to VI are all nitrogen, and the water content thereof is ≤10ppm, and the temperatures are respectively -13°C, -7°C, -3°C, 0°C, 2°C, and 8°C, and the temperatures of the filter cakes after drying are respectively -14°C, -8℃, -4℃, -1℃, 1℃, 6.5℃, washing liquids I~V are all mixed xylene containing p-xylene, wherein the p-xylene concentrations are 91.89%, 96.72%, 98.72%, 99.54%, 99.98%, respectively, the washing liquid temperatures are 10℃, 10℃, 10℃, 10℃, 30℃, respectively, the temperatures of the filter cake after washing are -9.39℃, -5.09℃, -1.77℃, 0.8℃, 6.05℃, respectively, the filter cake is finally backflushed with dry nitrogen and enters the melting tank, and the p-xylene product is obtained after melting with a purity of 99.98%.

[0130] Compared with Comparative Example 3, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 65%, and the production energy consumption is greatly reduced by 56%.

[0131] Example 13:

[0132] The method for producing p-xylene according to the present invention

[0133] like Figure 1As shown, according to the operating conditions of Example 12, the slurry I enters the rotary pressure filter, is washed 4 times by the washing liquid, and is dried 5 times by the drying gas. The drying gases I to V are all nitrogen, whose water content is ≤10ppm, and the temperatures are respectively -12°C, -8°C, -4°C, -1°C, and 5°C. The temperatures of the filter cakes after drying are respectively -13.5°C, -9°C, -4.8°C, -1.2°C, and 4.2°C. The washing liquids I to IV are all mixed xylenes containing p-xylene, wherein the p-xylene concentrations are respectively 92.03%, 96.88%, 98.89%, and 99.94%. The temperatures of the washing liquids are respectively 10°C, 10°C, 10°C, and 30°C. The temperatures of the filter cakes after washing are respectively -9.4°C, -5.09°C, -1.77°C, and 3.96°C. The filter cakes are finally backflushed by dry nitrogen and enter the melting tank. After melting, the p-xylene product is obtained with a purity of 99.94%.

[0134] Compared with Comparative Example 2, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 60%, and the production energy consumption is greatly reduced by 55%.

[0135] Example 14:

[0136] The method for producing p-xylene according to the present invention

[0137] like Figure 1 As shown, according to the operating conditions of Example 12, the slurry I enters the rotary pressure filter, is washed 3 times by the washing liquid, and is dried 4 times by the drying gas. The drying gases I to IV are all nitrogen, whose water content is ≤10ppm, and the temperatures are respectively -13°C, -8°C, -4°C, and 3°C. The temperatures of the filter cakes after drying are respectively -14.5°C, -8.6°C, -4.6°C, and 1.5°C. The washing liquids I to III are all mixed xylene containing p-xylene, wherein the p-xylene concentrations are 92.4%, 97.3%, and 99.86%, respectively. The temperatures of the washing liquids are respectively 10°C, 10°C, and 30°C, respectively. The temperatures of the filter cakes after washing are respectively -9.4°C, -5.1°C, and 1.3°C. The filter cakes are finally backflushed by dry nitrogen and enter the melting tank. After melting, the p-xylene product is obtained with a purity of 99.86%.

[0138] Compared with Comparative Example 2, the process flow of this embodiment is greatly shortened, the production equipment is greatly reduced, the investment is saved by 56%, and the production energy consumption is greatly reduced by 50%.

[0139] Example 15:

[0140] The method for producing p-xylene according to the present invention

[0141] like Figure 1As shown, according to the operating conditions of Example 12, the slurry I enters the rotary pressure filter, is washed twice by the washing liquid, and is dried 3 times by the drying gas. The drying gases I to III are all nitrogen, whose water content is ≤10ppm, and the temperatures are -12°C, -11°C, and -1°C, respectively. The temperatures of the filter cakes after drying are -14.6°C, -11°C, and -2°C, respectively. The washing liquids I to II are all mixed xylenes containing p-xylene, wherein the p-xylene concentrations are 93.3% and 99.66%, respectively. The washing liquid temperatures are 10°C and 30°C, respectively. The temperatures of the filter cakes after washing are -12.4°C and -2.2°C, respectively. The filter cakes are finally backflushed by dry nitrogen and enter the melting tank. After melting, the p-xylene product is obtained with a purity of 99.66%.

[0142] Comparative Example 1:

[0143] Existing methods for producing p-xylene

[0144] like Figure 2 As shown, a raw material containing p-xylene, with a p-xylene concentration of 22%, m-xylene of 51%, o-xylene of 21%, ethylbenzene of 2%, and others of 4%, enters a crystallizer for cooling crystallization, and the crystallization temperature is -65°C to obtain a slurry I containing p-xylene crystals; the slurry I enters a centrifuge I for solid-liquid separation to obtain a filter cake I and a mother liquor I, which is discharged from the centrifuge; the filter cake I enters a washing tank I and is pulped and washed with a washing liquid I, which is a C8 aromatic hydrocarbon containing p-xylene and can be mixed with one or more streams of the mother liquor discharged from the centrifuge and the washing filtrate, wherein the p-xylene concentration in the washing liquid I is 78%, and its temperature is 20°C to obtain a slurry II at a temperature of -15°C; the slurry II enters a centrifuge II for solid-liquid separation to obtain a filter cake II and a mother liquor II, which is discharged from the centrifuge. ; The filter cake II enters the washing tank II and is pulped and washed with the washing liquid II. The washing liquid II is a C8 aromatic hydrocarbon containing p-xylene, which can be mixed by one or more streams of the mother liquor discharged from the centrifuge and the washing filtrate, wherein the p-xylene concentration in the washing liquid II is 95%, and its temperature is 20°C, and the crystal slurry III is obtained at a temperature of 5°C; the crystal slurry III enters the centrifuge III for solid-liquid separation to obtain filter cake III and mother liquor III. The mother liquor III is discharged from the centrifuge and the filter cake III is washed with the washing liquid III. The washing liquid III is a p-xylene product, wherein the p-xylene concentration in the washing liquid III is 99.81%, and its temperature is 20°C. The washing filtrate is discharged from the centrifuge, and the washed filter cake enters the melting tank and is melted to obtain the p-xylene product, wherein the p-xylene purity is 99.81%.

[0145] Comparative Example 2:

[0146] Existing methods for producing p-xylene

[0147] like Figure 3 As shown, a raw material containing p-xylene, with a p-xylene concentration of 84.5%, an m-xylene concentration of 7.2%, an o-xylene concentration of 1.1%, and the others of 7.2%, enters a crystallizer for cooling crystallization at a crystallization temperature of -30°C to obtain a slurry I containing p-xylene crystals; the slurry I enters a centrifuge I for solid-liquid separation, the p-xylene crystals are intercepted by a filter cloth to form a filter cake I, and the mother liquor passes through the filter cloth to obtain a mother liquor I; the filter cake I enters a washing tank and is pulped and washed with a washing liquid I, which is a C8 aromatic hydrocarbon containing p-xylene, which can be obtained by the mother liquor discharged from the centrifuge and a stream of the washing filtrate. or multiple streams are mixed, wherein the concentration of p-xylene in the washing liquid I is 89%, and its temperature is 20°C, to obtain slurry II with a temperature of 4.6°C; the slurry II enters the centrifuge II for solid-liquid separation to obtain filter cake II and mother liquor II, the mother liquor II is discharged from the centrifuge, and the filter cake II is washed with washing liquid II, the washing liquid II is a p-xylene product, wherein the concentration of p-xylene in the washing liquid II is 99.82%, and its temperature is 20°C, the washing filtrate is discharged from the centrifuge, the washed filter cake enters the melting tank, and after melting, a p-xylene product is obtained, wherein the purity of p-xylene is 99.82%.

[0148] Comparative Example 3:

[0149] Existing methods for producing p-xylene

[0150] like Figure 4 As shown, the raw material containing p-xylene, with a p-xylene concentration of 94.51%, an m-xylene concentration of 1.76%, an o-xylene concentration of 0.86%, and the others of 2.57%, enters a crystallizer for cooling crystallization at a crystallization temperature of -15°C to obtain a slurry I containing p-xylene crystals; the slurry I enters a centrifuge I for solid-liquid separation, the p-xylene crystals are intercepted by a filter cloth to form a filter cake I, and the mother liquor passes through the filter cloth to obtain a mother liquor I; the filter cake I enters a washing tank and is pulped and washed with a washing liquid I, which is a C8 aromatic hydrocarbon containing p-xylene, which can be obtained from the mother liquor discharged from the centrifuge and the washing filtrate. The invention discloses a method for preparing a crystalline powder of the present invention, comprising mixing one or more streams, wherein the concentration of p-xylene in the washing liquid I is 92% and the temperature is 20°C, obtaining a crystalline powder II with a temperature of 6.7°C; the crystalline powder II enters a centrifuge II for solid-liquid separation to obtain a filter cake II and a mother liquor II, the mother liquor II is discharged from the centrifuge, and the filter cake II is washed with the washing liquid II, the washing liquid II being a p-xylene product, wherein the concentration of p-xylene in the washing liquid II is 99.85% and the temperature is 20°C, the washing filtrate is discharged from the centrifuge, the washed filter cake enters a melting tank, and is melted to obtain a p-xylene product, wherein the purity of p-xylene is 99.85%.

[0151] Comparative Example 4:

[0152] like Figure 1As described above, according to the operating conditions of Example 1, the rotary pressure filter has no pre-cooling zone, the rotary pressure filter cannot achieve continuous solid-liquid separation, and the filter cake cannot be formed in the feed zone.

[0153] Comparative Example 5:

[0154] like Figure 1 As described above, according to the operating conditions of Example 1, the rotary pressure filter has 6 washing zones and only 1 drying zone. The filter cake is washed 6 times with the washing liquid and dried only once. The rotary pressure filter cannot obtain qualified products, and the purity of the paraxylene product is 99.1%.

[0155] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for producing paraxylene, comprising the following steps: (1) cooling and crystallizing the raw material containing para-xylene at a crystallization temperature of -70°C to 10°C to obtain a slurry I containing para-xylene crystals; (2) feeding the slurry I into a rotary pressure filter for filtration, wherein the rotary pressure filter is provided with a feeding area, at least one drying area, at least one washing area, a discharge area, a cleaning area, and a pre-cooling area. The slurry I enters the feeding area and is filtered to obtain a filter cake I and a mother liquor I; (3) Sending filter cake I into drying zone I, drying filter cake I with drying gas I to obtain filter cake II; (4) Sending filter cake II to washing zone I, washing filter cake II with washing liquid I to obtain filter cake III; (5) The filter cake III continues to undergo the drying-washing cycle described in step (3) to step (4) in the rotary pressure filter for n times; wherein n is an integer from 1 to 8; (6) drying the filter cake obtained in step (5) in a drying area, and then sending it to a discharge area and discharging it from a rotary pressure filter to obtain a paraxylene product; (7) The drum of the rotary pressure filter continues to rotate to the cleaning area, and the filter cloth and the corresponding drum are cleaned with cleaning liquid; (8) The drum of the rotary pressure filter continues to rotate to the pre-cooling zone, and the filter cloth and the corresponding drum are pre-cooled with a pre-cooling liquid. Then the drum continues to rotate to the feeding zone to receive the slurry I; Wherein, according to the flow direction of the logistics, the temperature of the drying gas used in the rear drying zone is higher than the temperature of the drying gas used in the front drying zone; According to the flow direction of the logistics, the temperature of the washing liquid used in the subsequent washing area shall not be lower than the temperature of the washing liquid used in the previous washing area; The temperature difference between the drum area after being cooled by the pre-cooling liquid and the temperature of the slurry I is 0.5-5°C.

2. The method according to claim 1, wherein The drying gas used in the drying zone is selected from at least one of nitrogen, ethylene, propylene, propane, carbon dioxide and the low-temperature evaporation gas after evaporation refrigeration in the cooling crystallization refrigeration system in step (1).

3. The method according to claim 1, wherein The temperature difference between the filter cake after drying and before drying is 0-10°C.

4. The method according to claim 3, wherein: The temperature difference between the filter cake after drying and before drying is 0.1-5°C.

5. The method according to claim 2, wherein: The temperature difference between the drying gas and the dried filter cake is 0-10°C.

6. The method according to claim 5, wherein: The temperature difference between the drying gas and the dried filter cake is 0.5-5°C.

7. The method according to any one of claims 1 to 6, wherein: The washing liquid used in the washing zone is liquid aromatic hydrocarbon containing paraxylene.

8. The method according to claim 7, wherein: The washing liquid used in the washing zone is mixed xylene.

9. The method according to claim 7, wherein: According to the flow direction of the logistics, the concentration of the washing liquid used in the post-washing zone is higher than the concentration of the washing liquid used in the pre-washing zone.

10. The method according to claim 7, wherein: The temperature difference between the filter cake before and after washing is 0.1-30°C.

11. The method according to claim 10, wherein: The temperature difference between the filter cake before and after washing is 1.5-25°C.

12. The method according to claim 7, wherein: The temperature difference between the washing liquid and the washed filter cake is 0.5-120°C.

13. The method according to claim 12, wherein: The temperature difference between the washing liquid and the washed filter cake is 10-105°C.

14. The method according to claim 7, wherein: The concentration of p-xylene in the washing liquid of the last washing is not less than 99.8%, and the temperature of the washing liquid is 15-30°C.

15. The method according to claim 7, wherein: The paraxylene concentration in the paraxylene-containing raw material is ≤24% by weight, the crystallization temperature is -68°C to -60°C; there are 4-6 washing zones; the paraxylene concentration in the washing liquid is 75%-99.95%, and the temperature of the filter cake after washing is -50°C to 8°C; and / or, The paraxylene concentration in the paraxylene-containing feedstock is 50-90% by weight, the crystallization temperature is -30°C to 5°C, the number of washing zones is 3-5, the paraxylene concentration in the washing liquid is 88%-99.95%, and the temperature of the filter cake after washing is -25°C to 10°C; and / or, The concentration of p-xylene in the raw material containing p-xylene is ≥90% by weight, the crystallization temperature is -20°C to 10°C, and there are 3-5 washing zones; the concentration of p-xylene in the washing liquid is 90%-99.98%, and the temperature of the filter cake after washing is -15°C to 10°C.

16. The method according to any one of claims 1 to 6, wherein: The washing liquid used in the washing zone is at least one of liquid alkanes with low boiling points and low freezing points, liquid aromatic hydrocarbons and liquid alcohols.

17. The method according to claim 16, wherein The washing liquid used in the washing zone is at least one of n-hexane, cyclohexane, pentane, toluene and methanol.

18. The method according to claim 16, wherein The temperature difference between the filter cake before and after washing is 0.1-5°C.

19. The method according to claim 18, wherein The temperature difference between the filter cake before and after washing is 0.1-1°C.

20. The method according to any one of claims 1 to 6, wherein: The method further comprises melting the p-xylene obtained in step (6) in a melting tank, wherein the liquid in the melting tank enters a distillation tower for separation, the washing liquid obtained at the top of the tower is continuously recycled, and the p-xylene product is obtained at the bottom of the tower.

21. The method according to any one of claims 1 to 6, wherein: The cleaning liquid is the same as the washing liquid or is a raw material containing p-xylene.

22. The method according to claim 21, wherein The cleaning liquid is a raw material containing p-xylene.

23. The method according to claim 21, wherein The temperature of the cleaning solution is ≥15°C.

24. The method according to any one of claims 1 to 6, wherein: The precooling liquid is mixed xylene containing p-xylene.

25. The method according to claim 24, wherein The pre-cooling liquid is the crystallization mother liquor containing para-xylene obtained in step (1).

26. The method according to any one of claims 1 to 6, wherein: The filter cake in the discharge area is scraped off by a scraper or blown off by back-flushing gas; and / or, The filter cake in the discharge area is washed down by the liquid paraxylene product.

27. The method according to claim 26, wherein The back-flushing gas is the drying gas used in the drying area.

28. The method according to claim 26, wherein The temperature of the liquid paraxylene product used to flush the filter cake is 20-80°C.

29. The method according to any one of claims 1 to 6, wherein: The p-xylene product obtained by the method has a purity of ≥99.8%.

30. The method according to claim 29, wherein The p-xylene product obtained by the method has a purity of ≥99.9%.

Images