A kind of decolorization method of crude styrene

Abstract

A method for decolorizing crude styrene, comprising: introducing the raw material after the reaction of crude styrene and a decolorizer into a decolorizing and refining tower, wherein a structured packing is filled above the feed port of the decolorizing and refining tower, and a tower plate is arranged below the feed port, wherein the theoretical number of stages of the tower plate is 0.3-6, and after vacuum distillation, refined styrene is distilled from the top of the decolorizing and refining tower, part of which is refluxed into the top of the decolorizing and refining tower, and the rest is discharged from the tower top product pipeline, and the liquid flowing out from the bottom layer of the tower plate of the decolorizing and refining tower is introduced into the heat exchange tube of the falling film evaporator located outside the tower kettle, flows from top to bottom, and is heated by the heating medium in the shell of the falling film evaporator, and then returns to the lower part of the tower kettle of the decolorizing and refining tower, a part of which is discharged from the bottom of the decolorizing and refining tower, and the rest is returned to the heat exchange tube of the falling film evaporator, wherein the decolorizer is a diene-philic compound. The method can extend the stable operation cycle of the crude styrene decolorizing and distillation device.

Description

Technical Field

[0001] The invention relates to a method for decolorizing crude styrene, in particular to a method for decolorizing crude styrene separated from pyrolysis gasoline by using a dienophilic compound. Background Art

[0002] A feasible method for recovering styrene from unhydrogenated pyrolysis gasoline is extractive distillation. 8 + fraction is used as raw material, firstly, the C 8 The product is then subjected to selective hydrogenation to remove phenylacetylene, followed by styrene extraction and distillation to obtain yellow crude styrene, and finally decolorization and refining to obtain polymer-grade styrene products. The specifications for premium products require a purity of ≥99.8% by mass and a platinum-cobalt color of ≤10. So far, the biggest challenge to the industrialization of the entire technology is to achieve no sewage discharge and long-term stable operation in the decolorization and refining process.

[0003] WO0031007 discloses a method for decolorizing and refining styrene obtained from pyrolysis gasoline, wherein the crude styrene obtained from pyrolysis gasoline is mixed with 0.5-3% by mass of a dienophilic compound such as maleic anhydride for decolorization reaction at a temperature of 50-140°C and a residence time of 0.5-1.5 hours, and 10-2500 ppm of 2-sec-butyl-4,6-dinitrophenol (DNBP) is added as a polymerization inhibitor to avoid polymerization, followed by alkali washing, drying and dehydration, and flash evaporation to obtain a refined styrene product with a platinum-cobalt chromaticity of less than 10. This method directly decolorizes the crude styrene with the decolorizing agent, and the styrene obtained after decolorization needs to be alkali washed, thereby also generating salt-containing wastewater with a very high COD (chemical oxygen demand) content.

[0004] CN101121633A discloses a method for recovering and purifying styrene by cracking gasoline C 8 Fraction cutting, selective hydrogenation of phenylacetylene, extractive distillation of styrene, desulfurization with oxidants such as hydrogen peroxide, decolorization with activated carbon, activated clay or molecular sieve, and then distillation to obtain colorless refined styrene products. This method has poor decolorization effect and is difficult to apply industrially.

[0005] CN101429090A discloses a decolorization method for recovering styrene from cracked gasoline, which comprises: crude styrene enters the middle part of a refined styrene tower, and pure styrene vapor is obtained at the top of the tower. After condensation, a part of the pure styrene is extracted as a pure styrene product, and its platinum-cobalt chromaticity is less than 10, and another part of the pure styrene enters a reflux tank and is mixed and dissolved with a decolorant and then enters the top of the tower for reflux, and a heavy component is obtained in the tower kettle, and the decolorant is selected from at least one of oxalic acid, maleic anhydride and acetic anhydride. The defect of this method is that the decolorization reaction is carried out in the reflux tank at the top of the tower, and the reflux flows into the top of the tower, and is evaporated from the top of the tower after only one-level equilibrium. Therefore, a lot of decolorants are inevitably carried in the gas phase, which not only affects the decolorization effect, but also contains decolorant impurities in the styrene product. In addition, since maleic anhydride accumulates at the bottom of the tower and needs to be removed, if it is concentrated, it is easy to cause the tower internals and the tower bottom reboiler to be blocked, making it difficult for the device to operate for a long period of time. If it is not concentrated, more styrene will remain in the bottom of the tower, causing a decrease in the recovery rate of styrene.

[0006] CN104276926A discloses a method for preparing a pyrolysis gasoline C 8 The decolorization method of crude styrene obtained by fraction extraction and distillation is to first evaporate and dehydrate the crude styrene, add a diene-philic compound as a decolorizing agent to the dehydrated crude styrene for a decolorization reaction, and then send it to a decolorization and refining tower for distillation, and obtain a product with a platinum-cobalt chromaticity of less than 10 at the top of the tower, and the heavy components are discharged from the bottom of the tower. This method uses a conventional decolorization and refining tower, so the generated polymer is particularly easy to clog the bottom reboiler and the packing of the refining tower, and the operation cycle is short.

[0007] CN109422615A discloses a decolorization method and device for separating crude styrene from cracked gasoline, comprising: mixing crude styrene with a dienophilic compound and reacting them thoroughly, and then passing them into a decolorization refining tower from the middle, and then undergoing vacuum distillation, styrene is discharged from the top of the decolorization refining tower, and refluxed into the upper part of the decolorization refining tower, and the product is discharged from the top of the tower or the upper side line, and the bottom of the refining tower adopts a falling film evaporator placed outside the tower as a reboiler, and the heated material flows in the falling film evaporator tube from top to bottom, and then returns to the tower kettle. This method solves the problem that the existing thermosyphon reboiler is easy to scale and has a short operating cycle when treating heat-sensitive systems, but the problem of using a conventional decolorization refining tower filled with regular fillers is that the filler in the lower section of the refining tower is easy to be blocked, and the operating cycle is still not long.

[0008] The crude styrene recovered from pyrolysis gasoline is yellow, which is caused by the trace amount of conjugated dienes in it. The use of maleic anhydride-type dienophilic compounds as decolorizers for crude styrene is mainly to utilize the Diels-Alder reaction between maleic anhydride and the conjugated dienes in the crude styrene to generate dyed heavy components, which are then removed through the subsequent distillation process. Since maleic anhydride is very easy to copolymerize with styrene to generate polymers that are difficult to dissolve in styrene, together with the autopolymers of styrene, it is easy to cause scaling and blockage of the refining tower and its reboiler used for distillation, resulting in a short operating cycle of the decolorizing refining tower system.

[0009] In order to reduce the bottom temperature of the decolorization and refining tower as much as possible, the existing technology uses a packed tower with structured packing above and below the feed port. In the early stage of operation, the pressure drop of this type of tower is very low, the operating temperature is also low, and the effect is very good. However, as the operation time increases, such as 4 to 6 months, the pressure drop of the lower section of the refining tower gradually increases due to the polymers and colloids produced by decolorization hanging on the packing, and the operating temperature is forced to increase. This vicious cycle often occurs in less than 10 months. The pressure drop of the decolorization and refining tower reaches more than 5kPa, and the bottom temperature is close to 90°C. Generally, it needs to be shut down for cleaning in less than a year, which seriously affects the economic benefits of the device. Summary of the invention

[0010] The purpose of the present invention is to provide a method for decolorizing crude styrene, which can prolong the stable operation period of a crude styrene decolorizing and distillation device.

[0011] The decolorization method of crude styrene provided by the present invention comprises the following steps: introducing the crude styrene and a decolorizing agent into a decolorizing and refining tower after a mixed reaction; the decolorizing and refining tower is filled with regular packing above a feed inlet; a tower plate is arranged below the feed inlet; the theoretical number of the tower plates is 0.3-6; after vacuum distillation, refined styrene is distilled out from the top of the decolorizing and refining tower, part of which is refluxed into the top of the decolorizing and refining tower, and the rest is discharged from a tower top product pipeline; the liquid flowing out from the bottom tower plate of the decolorizing and refining tower is introduced into a heat exchange tube of a falling film evaporator located outside the tower kettle, flows from top to bottom, and is heated by a heating medium in a shell of the falling film evaporator, and then returns to the lower part of the tower kettle of the decolorizing and refining tower; part of the liquid is discharged from the bottom of the decolorizing and refining tower, and the rest is returned to the heat exchange tube of the falling film evaporator; the decolorizing agent is a diene-philic compound.

[0012] The method of the present invention sets the part below the feed inlet of the decolorization and refining tower as a tower plate with a theoretical number of 0.3 to 6, and fills the part above the feed inlet with regular packing, which can effectively reduce the blockage of the packing of the lowest stage of the decolorization and refining tower caused by heavy components and polymers without affecting the effect of distillation separation and refining styrene, thereby extending the stable operation time of the device for one cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1The present invention is a schematic flow diagram of decolorizing crude styrene using a decolorizing refining tower with a tower plate at the lower part of the feed inlet, wherein a sealing plate is provided at the bottom of the downcomer of the lowest tower plate of the decolorizing refining tower, so that the downcomer becomes a sealing tank.

[0014] Figure 2 The present invention is a schematic diagram of the process of decolorizing crude styrene using a decolorizing and refining tower with a tower plate arranged at the lower part of the feed inlet, wherein a liquid collecting plate with grooves is arranged at the upper part of the tower kettle of the decolorizing and refining tower.

[0015] Figure 3 The present invention is a schematic diagram of the process of decolorizing crude styrene using a decolorizing refining tower with a tower plate at the lower part of the feed inlet, wherein a liquid collecting plate with grooves is arranged at the upper part of the tower kettle of the decolorizing refining tower, and a liquid sealing groove is arranged under the downcomer of the lowest tower plate.

[0016] Figure 4 The present invention is a schematic diagram of the process of decolorizing crude styrene using a decolorizing and refining tower fully filled with structured packing in the prior art. DETAILED DESCRIPTION

[0017] In order to reduce the pressure drop and bottom operating temperature of the decolorization refining tower, the prior art uses structured packing above and below the feed port, where the height of the lower packing is 4 to 6 meters, equivalent to 8 to 15 theoretical stages. The main purpose is to achieve the small amount of C contained in the crude styrene feed. 9 The partial separation between aromatics and styrene and the separation from other heavy components produced by decolorization ensure the quality and recovery rate of refined styrene. If a plate tower with better anti-blocking performance is used, 15 to 20 actual plates will be required, and the resulting tower pressure drop will be as large as 6 to 9 kPa, and the corresponding tower bottom temperature will exceed 90°C and cannot be operated for a long period of time.

[0018] The method of the present invention converts C 9 The aromatic content is controlled at a certain level, preferably below 0.2% by mass, and a dienophilic compound having a sufficient boiling point difference with styrene (>190°C) is selected as a decolorizing agent. The heavy components generated by the decolorization reaction have a higher boiling point. In this way, a few low-pressure-drop plate-type tower plates can be arranged in the lower section of the decolorization refining tower to replace the existing packing section, which does not affect the separation effect and greatly enhances the anti-clogging property of the tower plate, and better solves the problems of large pressure drop of the plate tower and easy clogging of the packed tower, which can effectively extend the stable operation time of the decolorization device and increase the operation cycle life.

[0019] In the method of the present invention, the concentration of the decolorant component of the lowest theoretical stage tray in the decolorizing and refining tower is the highest, and it is the place where the components in the tower are most likely to be blocked. It is preferred to make a special design for the downcomer of the lowest (or lowest) actual tray so that the liquid flowing out of the lowest tray flows into the heat exchange tube of the falling film evaporator, flows from top to bottom under the heating of the shell side heating medium, evaporates, and then enters the lower part of the kettle of the decolorizing and refining tower. The material entering the lower part of the kettle of the decolorizing and refining tower is deposited at the bottom of the decolorizing and refining tower, stays for a certain period of time, and then discharged from the bottom. Preferably, the bottom of the kettle of the decolorizing and refining tower adopts a reduced diameter design so that its diameter is smaller than the diameter of the kettle.

[0020] In the bleaching and refining tower, after vacuum distillation, refined styrene is distilled out from the top of the bleaching and refining tower, part of which is refluxed into the top of the bleaching and refining tower, and the rest is discharged from the bleaching and refining tower. Optionally, refined styrene is distilled out from the top of the bleaching and refining tower, part of which is refluxed into the top of the bleaching and refining tower, and the rest is discharged from the top product pipeline of the bleaching and refining tower, and the other part is discharged from the side line below the top reflux pipeline of the bleaching and refining tower.

[0021] The kettle of the decolorizing and refining tower is a space for storing materials and separating vapor and liquid at the bottom of the tower. The heating source of the kettle of the decolorizing and refining tower of the present invention is a falling film evaporator placed outside the tower and substantially at the same level as the kettle. The liquid flowing out of the lowest tray enters the heat exchange tube of the falling film evaporator (tube side) and is heated and vaporized by the heating medium in the shell (shell side), and then returns to the lower part of the kettle, deposits at the bottom for a certain period of time, and then a part is discharged, and the rest returns to the heat exchange tube of the falling film evaporator. Preferably, the arrangement of the kettle of the decolorizing and refining tower and the downcomer of the lowest tray has the following three ways.

[0022] In the first arrangement, a sealing plate is provided at the bottom of the downcomer of the lowest plate of the decolorization and refining tower, so that the downcomer becomes a sealing groove, and the liquid flowing out of the lowest plate of the decolorization and refining tower is introduced from the sealing groove into the heat exchange tube of the falling film evaporator located outside the tower kettle.

[0023] The second arrangement is to set a liquid collecting plate with grooves on the upper part of the tower kettle of the decolorization and refining tower, and the liquid flowing out of the lowest tower plate of the decolorization and refining tower is introduced into the heat exchange tube of the falling film evaporator located outside the tower kettle through the grooves of the liquid collecting plate.

[0024] The third arrangement is to set a liquid collecting plate with grooves on the upper part of the kettle of the decolorization and refining tower, and set a liquid sealing groove under the downcomer of the lowest tower plate. The liquid flowing out of the lowest tower plate of the decolorization and refining tower is introduced into the heat exchange tube of the falling film evaporator outside the kettle through the grooves of the liquid collecting plate.

[0025] The tray arranged below the feed port of the decolorizing and refining tower may be a sieve tray or a valve tray, and the theoretical number of stages of the tray may be 0.5 to 4, 0.5 to 3 or 0.5 to 2. The actual number of tray layers (or blocks) may be 1 to 6.

[0026] The sieve plate can be a large-hole sieve plate or an inclined-hole sieve plate, the diameter of the sieve holes of the sieve plate can be 6-20 mm, preferably 8-15 mm, the diameter of the hole of the float valve plate can be 30-50 mm, the ratio of the opening area of ​​the tower plate to the cross-sectional area of ​​the tower, that is, the opening rate is 5-20%, preferably 10-20%. The height of the tower plate outlet weir can be 5-50 mm, preferably 20.5-45 mm.

[0027] The theoretical number of stages of the structured packing loaded above the feed port of the decolorizing and refining tower is 5 to 20, preferably 8 to 16. The total height of the structured packing section is 2 to 9 m, preferably 3 to 8 m.

[0028] The crude styrene decolorizing agent is selected from maleic anhydride or cinnamaldehyde and its derivatives, preferably maleic anhydride. The mass ratio of the decolorizing agent to the crude styrene is 0.01-0.3%, preferably 0.03-0.1%.

[0029] In order to inhibit the polymerization of crude styrene during the refining process, the mixture of crude styrene and decolorizing agent also contains a styrene polymerization inhibitor (inhibitor), and the mass ratio of the styrene polymerization inhibitor to crude styrene is 0.001-0.1%, preferably 0.002-0.05%.

[0030] The styrene polymerization inhibitor is selected from 2-sec-butyl-4,6-dinitrophenol and / or nitroxide free radicals, and the nitroxide free radicals can be 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radicals.

[0031] The top temperature of the decolorization and refining tower is 50-75°C, the bottom temperature is 65-89°C, preferably 70-87°C, the top pressure is 4-12kPa, and the mass ratio of the top reflux to the distillate, i.e., the reflux ratio, is 0.3-1.5.

[0032] The liquid (heavy components, including decolorization reaction products and a small amount of polymer) flowing out from the decolorization and refining tower plate has a very low flow rate, and the average residence time at the bottom of the decolorization and refining tower is 2 to 8 hours, preferably 3 to 6 hours, so as to stabilize the operation of the falling film evaporator and prevent the heavy components from staying at the bottom of the tower for too long to cause the polymerization of styrene. The mass ratio of the amount of material returned from the bottom of the decolorization and refining tower to the amount of crude styrene fed into the falling film evaporator heat exchange tube is 1 to 8, preferably 2 to 6.

[0033] The crude styrene described in the present invention is pyrolysis gasoline C 8 The crude styrene obtained by extractive distillation of the fraction contains C 9 The aromatic content is not higher than 0.2% by mass, such as 0.02-0.2% by mass, preferably not higher than 0.1% by mass. 9Aromatic hydrocarbons are mainly isopropylbenzene, n-propylbenzene and methylethylbenzene. 9 The reduction of aromatic content can significantly reduce the number of theoretical stages required for separation in the lower section of the bleaching and refining tower, so that plate trays can be used instead of the packing section.

[0034] The present invention is described below in conjunction with the accompanying drawings.

[0035] Figure 1 In the process, the crude styrene obtained by extractive distillation of pyrolysis gasoline is fully mixed with the dienophilic compound in the decolorizing tank 1 for reaction, and then enters the decolorizing and refining tower 3 through the pipeline 2. The structured packing 16 is filled above the feed port of the decolorizing and refining tower 3, and a tower plate 17 is arranged below the feed port. The tower plate can be a sieve plate or a floating valve plate. The downcomer of the bottom tower plate is 18, and a sealing plate 21 is arranged at the bottom, so that the downcomer 18 becomes a sealing groove. In the decolorizing and refining tower 3, after vacuum distillation, the refined styrene is distilled out from the tower top pipeline 4, a part of which is refluxed into the upper part of the decolorizing and refining tower through the tower top reflux pipeline 5, and the rest is discharged from the tower top product pipeline 6 as a refined styrene product. The liquid flowing out of the plate of the decolorizing and refining tower (3) enters the feed head 23 of the falling film evaporator 10 through the pipeline 9 from the bottom of the sealing groove formed by the downcomer, and after being evenly distributed through the heat exchange tubes extending out of the tube sheet of the feed head 23, it flows into the heat exchange tube 24, flows from top to bottom, and then is discharged from the bottom of the falling film evaporator 10 and returns to the lower part of the tower kettle of the decolorizing and refining tower through the pipeline 11. The heating medium enters the shell of the falling film evaporator through the pipeline 13, and then is discharged through the lower pipeline 14, and the tube-side materials in the heat exchange tubes are heated by heat exchange. The heavy components returning to the lower part of the tower kettle of the decolorizing and refining tower from the pipeline 11 flow out from the bottom pipeline 7 of the tower, a part of which returns through the pipeline 8, and enters the heat exchange tube of the falling film evaporator 10 after mixing with the materials flowing out of the pipeline 9, and the rest is discharged through the bottom component discharge pipeline 12.

[0036] In the above method, most of the top effluent from the decolorization and refining tower 3 can also be refluxed into the upper part of the decolorization and refining tower via the top reflux pipeline 5, and then a small amount (approximately 5 to 20% by mass of the total top effluent) of topped styrene can be discharged through the top product pipeline 6, and the refined styrene product can be discharged from the side line 15 located below the top reflux pipeline 5.

[0037] from Figure 1 It can also be known that the falling film evaporator 10 is arranged outside the decolorization and refining tower 3 and is basically parallel to the tower kettle. The setting position should make the tube side material of the falling film evaporator flow into the lower part of the tower kettle of the decolorization and refining tower 3 only under the action of gravity.

[0038] Figure 2 and Figure 1The process shown is the same, except that a liquid collecting plate 20 with a groove 22 is provided on the upper part of the tower kettle of the decolorizing and refining tower 3, and the downcomer 18 of the lowest tower plate is preferably an inclined downcomer with a contraction at the bottom, or a straight downcomer, without a sealing plate at the bottom. The liquid flowing out of the tower plate of the decolorizing and refining tower 3 flows into the groove of the liquid collecting plate 20 through the downcomer 18, and then enters the feed head 23 of the falling film evaporator 10 through the pipeline 9 from the bottom of the groove, and then enters the heat exchange tube 24 of the falling film evaporator 10.

[0039] Figure 3 and Figure 2 The embodiments are basically the same, except that a liquid sealing tank 19 is arranged under the downcomer 18 of the lowest tray of the decolorizing and refining tower 3. The liquid flowing out of the tray of the decolorizing and refining tower 3 flows into the liquid sealing tank 19 through the downcomer 18, and then overflows from the liquid sealing tank 19, flows into the groove of the liquid collecting plate 20, and then enters the feed head 23 of the falling film evaporator 10 through the pipeline 9 from the bottom of the groove, and then enters the heat exchange tube 24 of the falling film evaporator 10.

[0040] Figure 4 The schematic diagram of the decolorization process of crude styrene in the prior art is as follows: Figure 2 The process is basically the same, except that the decolorization and refining tower 3 is filled entirely with structured packing, and the filling below the feed inlet is still structured packing, without tower plates.

[0041] exist Figure 2 , Figure 3 and Figure 4 In the decolorization and refining tower 3, the liquid collecting plate 20 arranged on the upper part of the tower bottom is provided with a gas lift 25 to facilitate the discharge of the tower bottom gas.

[0042] The present invention is further described in detail below by examples, but the present invention is not limited thereto.

[0043] Example 1

[0044] The crude styrene obtained by extractive distillation from pyrolysis gasoline is used as raw material. Figure 1 The method and apparatus shown are used to decolorize and purify crude styrene.

[0045] Crude styrene enters decolorization tank 1 at a flow rate of 3500 kg / h. 9The aromatic content is 0.05% by mass, the xylene content is 0.01% by mass, and the platinum cobalt chromaticity is 300. The decolorant maleic anhydride and the polymerization inhibitor are added to the decolorizing tank 1, the maleic anhydride addition amount is 3kg / h, and the mass ratio of the maleic anhydride to the crude styrene is 0.086%, the polymerization inhibitor is a mixture of DNBP and 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical, the polymerization inhibitor addition amount is 0.25kg / h, wherein the mass ratio of DNBP to the crude styrene is 0.005%, and the mass ratio of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical to the crude styrene is 0.002%. After the material in the decolorizing tank 1 is fully reacted, it enters the middle part of the decolorizing and refining tower 3 through the pipeline 2.

[0046] The diameter of the decolorization and refining tower 3 is 1600mm. A 7m high Y250 structured packing is arranged above the feed port, with 14 theoretical stages. Four layers of large-pore sieve plates are arranged below the feed port, with 2.4 theoretical stages. The diameter of the holes on the sieve plates is 13mm, the opening rate of the sieve plates is 12%, and the height of the tower plate outlet weir is 30mm. The downcomer 18 of the lowest tower plate of the decolorization and refining tower is provided with a sealing plate 21 at the bottom, so that the downcomer 18 becomes a sealing groove. The liquid flowing out of the tower plate of the decolorization and refining tower 3 enters the feed head 23 of the falling film evaporator 10 through the pipeline 9 from the bottom of the sealing groove formed by the downcomer, and then enters the heat exchange tube 24 of the falling film evaporator 10.

[0047] The outer diameter of the falling film evaporator used is 800 mm, the length of the heat exchange tube is 2.0 m (excluding the extension height for liquid distribution), the inner (straight) diameter of the heat exchange tube is 20 mm, a total of 467 heat exchange tubes are set, and the heat exchange area is 69.0 m 2 A liquid distributor is installed in the feed head of the falling film evaporator, which is a heat exchange tube extending out of the feed head 23 tube sheet with a height of 300mm. The temperature of the material flowing out of the bottom of the falling film evaporator is controlled to be 85°C. The heating medium used in the shell side of the falling film evaporator is 0.35MPa low-pressure water vapor.

[0048] The top pressure of the bleaching and refining tower is 8 kPa, the top reflux ratio is 0.8, and the top temperature is 71°C.

[0049] The flow rate of the bottom components returned from pipeline 8 to the falling film evaporator is 14000 kg / h, the mass ratio of the return amount to the crude styrene feed amount is 4.0, and the average residence time of the heavy components at the bottom of the decolorization and refining tower is 4 hours.

[0050] The flow rate of refined styrene extracted from pipeline 6 is 3465 kg / h, and the flow rate of heavy components extracted from the bottom pipeline 12 is about 38 kg / h. The number of trays in the decolorization refining tower 3 and the decolorization effect are shown in Table 1, the pressure drop at each stage of the decolorization refining tower 3 operation is shown in Table 2, and the bottom temperature is shown in Table 3.

[0051] Decolorization and refining operation results: As shown in Tables 1 to 3, after distillation and decolorization, the purity of refined styrene is 99.94% by mass, the platinum-cobalt chromaticity is less than 10, and no maleic anhydride is detected. The device has been running continuously for 24 months, and the styrene recovery rate is still maintained at a high level of 98.9% by mass. The pressure drop of the decolorization and refining tower has only increased by about 0.3 kPa, and the bottom temperature of the decolorization and refining tower has increased from 82 to 83°C, an increase of 1°C, indicating that the device can operate well and stably for a long period of time.

[0052] Example 2

[0053] The crude styrene was decolorized and purified according to the method of Example 1, except that a layer of F1 type float valve tray with 0.7 theoretical stage was set below the feed inlet of the decolorization and purification tower 3. The hole diameter of the opening on the float valve tray was 39 mm, the valve weight was 25 g, the opening rate of the float valve tray was 17%, and the height of the tray outlet weir was 40 mm.

[0054] The number of trays in the decolorizing and refining tower 3 and the decolorizing effect are shown in Table 1, the pressure drop at each operation stage of the decolorizing and refining tower 3 is shown in Table 2, and the tower bottom temperature is shown in Table 3.

[0055] Decolorization and refining operation results: the purity of refined styrene is 99.94% by mass, the platinum cobalt chromaticity is less than 10, and the content of maleic anhydride is 1 mg / kg, which can still meet the specifications of premium products. The device has been running continuously for 24 months, and the styrene recovery rate has been maintained at 98.7% by mass. The pressure drop of the decolorization and refining tower has not changed much, and the tower bottom temperature has increased from 79 to 82°C, an increase of 3°C, indicating that the device can operate well and stably for a long period of time.

[0056] Example 3

[0057] The crude styrene was decolorized and purified according to the method of Example 1, except that there were 6 layers of large-pore sieve plates arranged below the feed inlet of the decolorization and purification tower 3, with 3.6 theoretical stages, the diameter of the holes on the sieve plates was 10 mm, the porosity of the sieve plates was 12%, and the height of the tower plate outlet weir was 35 mm.

[0058] The number of trays in the decolorizing and refining tower 3 and the decolorizing effect are shown in Table 1, the pressure drop at each operation stage of the decolorizing and refining tower 3 is shown in Table 2, and the tower bottom temperature is shown in Table 3.

[0059] Decolorization and refining operation results: the purity of refined styrene is 99.94% by mass, the platinum cobalt chromaticity is less than 10, and no maleic anhydride is detected. The device has been running continuously for 24 months, and the styrene recovery rate has slightly decreased from 99.0% by mass to 98.1% by mass. The pressure drop of the decolorization and refining tower is 4.5kPa, and the tower bottom temperature has slightly increased from 85°C to 87°C, indicating that the device can operate well and stably for a long period of time.

[0060] Example 4

[0061] The crude styrene was decolorized and purified according to the method of Example 1, except that Figure 2 The process shown is that a liquid collecting plate 20 with a groove 22 is arranged at the upper part of the bottom of the decolorization and refining tower and the lower part of the 4th tower plate, and no sealing plate is arranged at the bottom of the downcomer of the 4th tower plate. The liquid flowing out from the tower plate 3 of the decolorization and refining tower flows into the groove of the liquid collecting plate 20 through the downcomer 18, and then enters the feed head 23 of the falling film evaporator 10 through the pipeline 9 from the bottom of the groove, and then enters the heat exchange tube 24 of the falling film evaporator 10.

[0062] The number of trays in the decolorizing and refining tower 3 and the decolorizing effect are shown in Table 1, the pressure drop at each operation stage of the decolorizing and refining tower 3 is shown in Table 2, and the tower bottom temperature is shown in Table 3.

[0063] Decolorization and refining operation results: the purity of refined styrene is 99.94% by mass, the platinum-cobalt chromaticity is <10, the device has been running continuously for 24 months, the styrene recovery rate has slightly decreased from 99.94% by mass to 98.9% by mass, the pressure drop of the decolorization and refining tower is 2.7 kPa, and the tower bottom temperature is 82°C.

[0064] Example 5

[0065] The crude styrene was decolorized and purified according to the method of Example 1, except that Figure 3 The process shown is that a liquid collecting plate 20 with a groove 22 is arranged at the upper part of the bottom of the decolorization and refining tower and the lower part of the 4th tower plate, and a liquid sealing groove 19 is arranged at the bottom of the downcomer of the 4th tower plate. The liquid flowing out from the tower plate 3 of the decolorization and refining tower flows into the groove of the liquid collecting plate 20 through the liquid sealing groove 19 arranged under the downcomer 18, and then enters the feed head 23 of the falling film evaporator 10 through the pipeline 9 from the bottom of the groove, and then enters the heat exchange tube 24 of the falling film evaporator 10.

[0066] The number of trays in the decolorizing and refining tower 3 and the decolorizing effect are shown in Table 1, the pressure drop at each operation stage of the decolorizing and refining tower 3 is shown in Table 2, and the tower bottom temperature is shown in Table 3.

[0067] Decolorization and refining operation results: the purity of refined styrene is 99.94% by mass, the platinum cobalt color is less than 10, and no maleic anhydride is detected. After 20 months of continuous operation, the styrene recovery rate is still as high as 99.0% by mass, and the tower pressure drop and tower bottom temperature are quite stable. However, as time goes by, in the 23rd month, the tower pressure drop and tower bottom temperature begin to increase. In the 24th month, the decolorization and refining tower pressure drop and tower bottom temperature rose to 5.1kPa and 89℃ respectively, and the styrene recovery rate dropped to 96.8% by mass.

[0068] Example 6

[0069] The crude styrene was decolorized and purified according to the method of Example 1, except that the C 9 The aromatic hydrocarbon content was 0.20 mass %.

[0070] The number of trays in the decolorizing and refining tower 3 and the decolorizing effect are shown in Table 1, the pressure drop at each operation stage of the decolorizing and refining tower 3 is shown in Table 2, and the tower bottom temperature is shown in Table 3.

[0071] Decolorization and refining operation results: The purity of refined styrene is 99.81% by mass, of which the main impurities are C 9 Aromatics, content is 0.18% by mass, purity meets the GB3915-2011 quality grade specification of not less than 99.80% by mass, styrene platinum cobalt chromaticity <10. The device has been running continuously for 24 months, styrene recovery rate is maintained at 98.8% by mass, and the pressure drop and bottom temperature of the decolorization refining tower have not changed much.

[0072] Comparative Example 1

[0073] The crude styrene was decolorized and purified according to the method of Example 1, except that Figure 4 The prior art process shown is that a 7m high Y250 structured packing is arranged above the feed inlet of the decolorization refining tower, and a 1.2m high Y250 structured packing is arranged below the feed inlet, with 2.4 theoretical stages.

[0074] The number of trays in the decolorizing and refining tower 3 and the decolorizing effect are shown in Table 1, the pressure drop at each operation stage of the decolorizing and refining tower 3 is shown in Table 2, and the tower bottom temperature is shown in Table 3.

[0075] Decolorization and refining operation results: the purity of refined styrene is 99.94% by mass, the platinum cobalt color is less than 10, and no maleic anhydride is detected. The method has a good effect in the initial operation, but as the operation time increases, the pressure drop of the whole tower gradually increases with the increase of the pressure drop of the lower section, and the temperature at the bottom of the tower increases. When it reaches 11 months, the pressure drop of the decolorization and refining tower increases from the initial 1.3kPa to 8.9kPa, and the temperature at the bottom of the tower also increases to 93℃, and the styrene recovery rate decreases to 96% by mass. It was forced to stop the operation for cleaning, and it was found that the filler at the bottom below the feed inlet of the decolorization and refining tower was seriously blocked.

[0076] Comparative Example 2

[0077] The crude styrene was decolorized and purified according to the method of Example 1, except that the C 9 The aromatics content was 0.26% by mass, and the top reflux ratio of the bleaching and refining tower was 1.0.

[0078] The number of trays in the decolorizing and refining tower 3 and the decolorizing effect are shown in Table 1, the pressure drop at each operation stage of the decolorizing and refining tower 3 is shown in Table 2, and the tower bottom temperature is shown in Table 3.

[0079] Decolorization and refining operation results: Due to the C 9The influence of aromatic content increased the bottom discharge to 140kg / h, the top extraction was about 3363kg / h, the purity of refined styrene was 99.80% by mass, basically reaching the 99.80% premium product quality index, platinum cobalt chromaticity <10, and no maleic anhydride. The device was operated continuously for 24 months, and the styrene recovery rate was maintained at 96.1% by mass. The pressure drop of the decolorization refining tower and the changes in the bottom temperature were the same as those in Example 1, indicating that the device can operate stably for a long period of time.

[0080] Table 1

[0081]

[0082] Table 2

[0083]

[0084] Table 3

[0085]

[0086] From the data in Tables 1 to 3, it can be seen that in Comparative Example 1, the styrene decolorization and refining tower can only run for 11 months using the prior art method, and is forced to stop and clean up due to excessive tower pressure drop, excessive tower bottom temperature, and styrene recovery rate reduced to 96% by mass. According to the method of the present invention, after running for 11 months, the pressure drop and tower bottom temperature of the decolorization and refining tower change very little, the purity of the refined styrene reaches the specification of superior grade, wherein the platinum cobalt chromaticity is less than 10, and the styrene recovery rate is as high as 98.3-99.0% by mass. After running for 24 months, the styrene recovery rate still reaches 96.6-98.9% by mass. When C in crude styrene 9 When the aromatic content is 0.05 mass%, the purity of refined styrene reaches 99.94 mass%. 9 When the aromatic content is as high as 0.2 mass%, the purity of refined styrene can reach 99.81 mass%, which is the premium grade specification.

[0087] The data of Comparative Example 2 show that when the C 9 When the aromatic content is 0.26 mass%, the purity of the refined styrene obtained basically meets the technical indicators of high-grade products due to the small number of tower plates below the feed inlet, but this is at the expense of increasing the loss of styrene at the bottom of the decolorization and refining tower, and the styrene recovery rate is low.

Claims

1. A method for decolorizing crude styrene, comprising: introducing the crude styrene and a decolorizing agent into a decolorizing and refining tower (3), wherein a structured packing is filled above the feed inlet of the decolorizing and refining tower, and a tower plate is arranged below the feed inlet, wherein the theoretical number of stages of the tower plate is 0.5 to 3.6; after vacuum distillation, refined styrene is distilled from the top of the decolorizing and refining tower (3), part of which is refluxed into the top of the decolorizing and refining tower, and the rest is discharged from the tower top product pipeline (6); and liquid flowing out from the bottom layer of the tower plate of the decolorizing and refining tower (3) is introduced into a decolorizing and refining tower located outside the tower kettle. The decolorizing agent is a diene-philic compound, the boiling point difference between the diene-philic compound and styrene is greater than 190° C., and the crude styrene is obtained by extractive distillation of the C8 fraction of pyrolysis gasoline, wherein the C9 aromatic hydrocarbon content is not higher than 0.2% by mass. A sealing plate is provided at the bottom of the downcomer (18) of the lowest tray of the decolorizing and refining tower (3), so that the downcomer becomes a sealing groove, and the liquid flowing out of the lowest tray of the decolorizing and refining tower (3) is introduced from the sealing groove into the heat exchange tube of the falling film evaporator (10) located outside the tower kettle, or A liquid collecting plate (20) with grooves is arranged on the upper part of the tower kettle of the decolorizing and refining tower (3), and the liquid flowing out of the bottom tray of the decolorizing and refining tower (3) is introduced into the heat exchange tube of the falling film evaporator (10) located outside the tower kettle through the grooves of the liquid collecting plate. The top temperature of the decolorizing and refining tower is 50-75°C, the bottom temperature is 65-89°C, the top pressure is 4-12 kPa, and the mass ratio of the top reflux to the distillate is 0.3-1.

5.

2. The method according to claim 1, characterized in that The decolorizing agent is selected from maleic anhydride or cinnamaldehyde.

3. The method according to claim 1, characterized in that The mass ratio of the decolorizing agent to the crude styrene is 0.01-0.3%.

4. The method according to claim 1, characterized in that The mixture of crude styrene and decolorizing agent also contains a styrene polymerization inhibitor, and the mass ratio of the styrene polymerization inhibitor to the crude styrene is 0.001-0.1%.

5. The method according to claim 4, characterized in that The styrene polymerization inhibitor is selected from 2-sec-butyl-4,6-dinitrophenol and / or nitroxide free radical.

6. The method according to claim 1, characterized in that The residence time of the liquid flowing out from the plates of the decolorizing and refining tower (3) at the bottom of the decolorizing and refining tower is 2 to 8 hours.

7. The method according to claim 1, characterized in that The mass ratio of the amount of material returned to the heat exchange tube of the falling film evaporator (10) to the amount of crude styrene fed is 1 to 8.

8. The method according to claim 1, characterized in that The tower plate arranged below the feed port is a sieve plate or a float valve plate, the sieve hole diameter of the sieve plate is 6-20 mm, the hole diameter of the float valve plate is 30-50 mm, and the ratio of the tower plate opening area to the tower cross-sectional area is 5-20%.

9. The method according to claim 1, characterized in that The theoretical number of stages of the structured packing loaded above the feed inlet is 5 to 20.

10. The method according to claim 1, characterized in that Refined styrene is distilled from the top of the decolorization and refining tower (3), part of which is refluxed into the top of the decolorization and refining tower, and the rest is discharged from the top product pipeline (6) of the decolorization and refining tower (3), and the other part is discharged from the side line (15) below the top reflux pipeline (5) of the decolorization and refining tower (3).

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