A method for preparing propylene tetramer

Abstract

The application provides a preparation method of propylene tetramer, comprising the following steps: S1, carrying out oligomerization reaction in a reactor to obtain a mixed product by taking propylene as a raw material; S2, after the mixed product in S1 is subjected to flash evaporation, the liquid phase enters a light-removing tower, and the mass ratio of the liquid phase C6, C9 components at the top of the light-removing tower to the raw material propylene is 5-15:1, and the liquid phase C6, C9 components at the top of the light-removing tower are returned to the reactor to continue the reaction; S3, the propylene tetramer at the bottom of the light-removing tower in S2 is refined and purified to obtain a finished product. By controlling the mass ratio of the liquid phase C6, C9 components at the top of the light-removing tower to the raw material propylene returned to the reactor, the propylene conversion rate and the propylene tetramer yield are improved, meanwhile, a special three-section reactor is adopted, so that the oligomer generated in the oligomerization reaction can be reacted with propylene again in the reactor; the propylene conversion rate in the preparation method of the propylene tetramer provided by the application is more than 90%, and the propylene tetramer yield is more than 60%.

Description

Technical Field

[0001] The present invention relates to the field of propylene oligomerization production, and in particular to a method for preparing propylene tetramer. Background Art

[0002] Olefin oligomerization refers to the reaction process in which a certain olefin monomer (C2-C14) is polymerized to generate a compound in which one or more structural units are repeatedly connected under the action of a catalyst. This catalytic reaction has been widely used in chemical fields such as petroleum refining since the 1930s. Existing propylene oligomerization is produced, and the main product is propylene trimer-nonene. The nonene yield can reach up to 70%, while the propylene tetramer yield is generally on the low side, and the yield of propylene tetramer is generally 5-25%. Simultaneously, the propylene conversion is also generally on the low side, and the propylene conversion is generally less than 80%. For example, patent CN1285241A, a propylene oligomerization solid phosphoric acid catalyst, has a propylene conversion less than 80%, and the nonene selectivity conversion reaches up to 78%, corresponding to a dodecene selectivity conversion of 12%. The propylene tetramer yield is low, causing propylene tetramer to be in short supply on the market and unable to meet the demand of propylene tetramer downstream products, such as the production of tert-dodecyl mercaptan. In existing propylene tetramer production processes, various catalyst improvements have been made to improve propylene tetramer conversion. However, no research has examined whether and how the C6 and C9 components produced during the production process affect propylene tetramer conversion. Therefore, addressing the shortcomings and challenges of existing technologies, it is imperative to develop a high-conversion, high-selectivity propylene tetramer production process. Summary of the Invention

[0003] The present invention provides a method for preparing propylene tetramer, and the specific technical scheme is as follows:

[0004] A method for preparing propylene tetramer comprises the following steps: S1, using propylene as a raw material, performing an oligomerization reaction in a reactor to obtain a mixed product; S2, flashing the mixed product in S1, and then the liquid phase enters a lightness removal tower, and the mass ratio of C6 and C9 components in the liquid phase at the top of the lightness removal tower to the raw material propylene is 5-15:1 and returned to the reactor for further reaction; S3, refining and purifying the propylene tetramer at the bottom of the lightness removal tower in S2 to obtain a finished product;

[0005] Furthermore, the liquid phase of C6 and C9 components in the light removal tower in S2 is returned to the reactor to continue the reaction at a mass ratio of 6:1, 8:1, 10:1 or 12:1 to propylene;

[0006] Furthermore, when the oligomerization reaction is carried out using propylene as a raw material in S1, a phosphoric acid-supported catalyst is added as an oligomerization catalyst and propane is used as a diluent;

[0007] Further, the carrier of the phosphoric acid loaded catalyst is diatomite, kaolin, silicon dioxide or aluminum trioxide;

[0008] Further, the mass ratio of propylene to diluent is 1:1.

[0009] Further, the water injection amount of the propylene raw material in S1 is 0.1-0.2% of the mass of propylene.

[0010] Further, the reactor in S1 is a three-stage reactor, which includes a first-stage reactor, a second-stage reactor and a third-stage reactor, the discharge port of the first-stage reactor is connected to the feed inlet of the second-stage reactor, the discharge port of the second-stage reactor is connected to the feed inlet of the third-stage reactor, and the raw material propylene enters the feed inlets of the three-stage reactors respectively and is discharged from the discharge port of the third-stage reactor for flash evaporation.

[0011] Further, the raw material propylene is fed into the feed inlets of the first-stage reactor, the second-stage reactor and the third-stage reactor in the same amount.

[0012] Further, the temperature of the feed inlet of the first-stage reactor is 235-275℃, the temperature of the second-stage reactor is 235-275℃, and the temperature of the feed inlet of the third-stage reactor is 235-275℃.

[0013] Further, the pressure of the feed inlet of the first-stage reactor is 3.0-4.5MPa, the pressure of the feed inlet of the second-stage reactor is 3.0-4.5MPa, and the pressure of the feed inlet of the third-stage reactor is 3.0-4.5MPa.

[0014] Further, the temperature of the discharge port of the first-stage reactor is 265-305℃, the temperature of the discharge port of the second-stage reactor is 265-305℃, and the temperature of the discharge port of the third-stage reactor is 265-305℃.

[0015] Further, in S2, the mixed product is subjected to flash evaporation through a gas-liquid flash evaporation tank, and after flash evaporation, the product is subjected to gas phase cooling and pressurization and then recycled to the feed inlet of the first-stage reactor.

[0016] Further, in S2, the flash evaporation temperature is 120℃ and the flash evaporation pressure is 2.0MPa.

[0017] Further, in S3, the propylene tetramer is subjected to purification through a refining tower, and the propylene tetramer enters the refining tower from the bottom of a light removal tower.

[0018] Due to the adoption of the above technical solutions, the present application has the following beneficial technical effects:

[0019] 1. The present invention develops a new approach to improving the conversion and yield of propylene tetramer. The existing methods for improving propylene tetramer generally start with catalyst improvement. This application overcomes industry prejudice and considers the liquid phase C6 and C9 components at the top of the intermediate light product removal tower, thereby simply and effectively improving the conversion and yield of propylene tetramer.

[0020] 2. The present invention improves the propylene conversion rate and the yield of propylene tetramer by controlling the mass ratio of the liquid C6 and C9 components returned to the reactor from the top of the lightness removal column to the mass ratio of the raw propylene. At the same time, the present invention uses a specially designed three-stage reactor so that the oligomers generated by the oligomerization reaction can react with propylene again in the reactor. The single-pass conversion rate of propylene reaches over 90%, and the yield of propylene tetramer reaches over 60%; compared to the propylene conversion rate of less than 80% in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flow chart for the preparation of propylene tetramer.

[0022] In the figure: 1. Raw material feed port; 2. Raw material heating vaporizer; 3. Three-stage reactor; 31. First-stage reactor; 32. Second-stage reactor; 33. Third-stage reactor; 4. Gas-liquid flash tank; 5. Light-removal tower; 6. Light-removal tower bottom pump; 7. Light-removal tower reflux pump; 8. Light-removal tower top cooler; 9. Light-removal tower reflux tank; 10. Gas cooler; 11. Circulating compressor; 12. Refining tower; 13. Propylene tetramer collection tank. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] A method for preparing propylene tetramer comprises the following steps:

[0025] S1, using propylene as a raw material to carry out oligomerization reaction in a reactor to obtain a mixed product;

[0026] The mixed product in S2 and S1 is flashed and the liquid phase enters the light removal tower. The liquid phase C6 and C9 components at the top of the light removal tower are returned to the reactor to continue the reaction at a mass ratio of 5-15:1 to the raw material propylene.

[0027] S3, refining and purifying the propylene tetramer at the bottom of the lightness removal tower in S2 to obtain a finished product.

[0028] The general formula of the oligomerization product can be expressed as:

[0029]

[0030] Wherein n is 2-5, R is CmH2m+1, and m is 0-10.

[0031] Olefin oligomerization reaction is very complex, including polymerization reaction and disproportionation reaction. The carbon atom number in the reaction products is mainly C6, C9, C12, and C15 polymerization products.

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038] The present invention improves the propylene conversion rate and the yield of propylene tetramer by controlling the mass ratio of the C6 and C9 components returned to the reactor from the top of the lightness removal tower to the raw material propylene, so that the oligomers generated by the oligomerization reaction can react with propylene again in the reactor. Taking into account the reaction of the intermediate products C6 and C9 components with propylene, the optimal mass ratio is selected, thereby simply and effectively improving the conversion rate and yield of the propylene tetramer.

[0039] The raw material propylene needs to be mixed with the diluent propane, with the propylene to propane mass ratio generally being 1:1. Water needs to be injected into the raw material, with the water injection amount being 0.1-0.2% of the propylene mass. The mixture of raw material propylene and propane is evenly divided and then sent to three-stage reactors.

[0040] The three-stage reactor adopts a cold-wall tubular trickle flow reactor. The polymerization reaction is an exothermic reaction. The heat extraction from the reactor can adopt the existing heat exchange technology to ensure that the temperature difference between the reactor inlet and outlet is less than 10°C.

[0041] like Figure 1As shown, the preparation of propylene tetramer is as follows: the raw material propylene and diluent propane are fed from the raw material feed port 1 at a ratio of 1:1, the water injection amount in the raw material is the saturated water amount of the raw material propylene and diluent propane, the raw material is heated and vaporized by the raw material heating vaporizer 2, and then is evenly divided into three paths and is fed into the gas phase inlet of the first reactor 31, the second reactor 32 and the third reactor 33 of the three-stage reactor 3, the column tubes of the three-stage reactor 3 are filled with phosphoric acid supported catalyst, the reaction product is discharged from the third reactor 33 into the gas-liquid flash tank 4, the gas in the gas-liquid flash tank 4 is cooled by the gas cooler 10, and then is returned to the raw material heating vaporizer 2 through the circulating compressor 11, the liquid phase in the gas-liquid flash tank 4 is discharged to the light-removing tower 5, the gas phase at the top of the light-removing tower 5 is cooled by the light-removing tower top cooler 8, and then is returned to the raw material heating vaporizer 2 through the light-removing tower reflux tank 9, the gas cooler 10 and the circulating compressor 11 in turn, the liquid phase at the top of the light-removing tower 5 containing C6 and C9 components is transported back to the inlet of the first reactor 31 by the light-removing tower reflux pump 7 when the proportion reaches a certain value, and the oil at the bottom of the light-removing tower 5 is transported to the refining tower 12 of the propylene tetramer by the light-removing tower bottom pump 6, the propylene tetramer with a purity up to standard is obtained at the top of the refining tower 12, and the propylene tetramer is collected.

[0042] Example 1

[0043] A propylene tetramer preparation method comprises the following steps: 175ml of a propylene and 175ml of propane mixture is pressurized to 3.0MPa by the raw material heating vaporizer 2, heated to 235℃, and then evenly divided into three paths and fed into the inlet of the three-stage reactor 3, the column tubes of the reactor are filled with phosphoric acid supported catalyst, the carrier of the catalyst is silicon dioxide, the reaction product is discharged from the third reactor 33 into the gas-liquid flash tank 4, the temperature of the third reactor 33 outlet is 265℃, the gas phase of the reaction product in the gas-liquid flash tank 4 is cooled by the gas cooler 10, and then is returned to the raw material heating vaporizer 2 through the circulating compressor 11, the liquid phase of the gas-liquid flash tank 4 is fed into the light-removing tower 5, the gas phase at the top of the light-removing tower 5 is cooled by the light-removing tower top cooler 8, and then is returned to the raw material heating vaporizer 2 through the light-removing tower reflux tank 9, the gas cooler 10 and the circulating compressor 11 in turn, the mass ratio of the C6 and C9 components in the liquid phase at the top of the light-removing tower 5 to the mass of the raw material propylene is 6:1, which is transported back to the inlet of the first reactor 31 by the light-removing tower reflux pump 7, the oil at the bottom of the light-removing tower 5 is transported to the refining tower 12 of the propylene tetramer by the light-removing tower bottom pump 6, the propylene tetramer with a purity up to standard is obtained at the top of the refining tower 12, the propylene tetramer is collected from the outlet of the refining tower 12 into the propylene tetramer collection tank 13, the propylene conversion rate is 90%, and the propylene tetramer yield is 61%.

[0044] Example 2

[0045] A method for preparing propylene tetramer, comprising the following steps: 175ml propylene and 175ml propane mixture is pressurized to 6.0MPa by a raw material heating vaporizer 2, heated to 255℃, and then evenly divided into three paths to the inlet of a three-stage reactor 3, the column tube of the reactor is filled with phosphoric acid supported catalyst, the carrier of the catalyst is kaolin, the reaction product is discharged from the outlet of the third-stage reactor 33 into a gas-liquid flash tank 4, the temperature of the outlet of the third-stage reactor 33 is 285℃, the gas phase of the reaction product in the gas-liquid flash tank 4 is cooled by a gas cooler 10, and then returned to the raw material heating vaporizer 2 through a circulating compressor 11, the liquid phase of the gas-liquid flash tank 4 enters a light-removing column 5, the gas phase of the light-removing column 5 is cooled by a light-removing column top cooler 8, and then sequentially passes through a light-removing column reflux tank 9, the gas cooler 10, and the circulating compressor 11 to return to the raw material heating vaporizer 2, the C6 and C9 components of the liquid phase of the light-removing column 5 are transported back to the inlet of the first-stage reactor 31 by a light-removing column reflux pump 7 at a mass ratio of 8:1 to the raw material propylene, the bottom oil of the light-removing column 5 is transported to a propylene tetramer refining column 12 by a light-removing column bottom pump 6, the purity of the propylene tetramer obtained from the top of the propylene tetramer refining column 12 reaches the standard, the propylene tetramer is collected from the outlet of the propylene tetramer refining column 12 into a propylene tetramer collection tank 13, the propylene conversion rate is 93%, and the propylene tetramer yield is 65%.

[0046] Example 3

[0047] A method for preparing propylene tetramer, comprising the following steps: 175ml propylene and 175ml propane mixture is pressurized to 4.0MPa by a raw material heating vaporizer 2, heated to 275℃, and then evenly divided into three paths to the inlet of a three-stage reactor 3, the column tube of the reactor is filled with phosphoric acid supported catalyst, the carrier of the catalyst is diatomite, the reaction product is discharged from the outlet of the third-stage reactor 33 into a gas-liquid flash tank 4, the temperature of the outlet of the third-stage reactor 33 is 305℃, the gas phase of the reaction product in the gas-liquid flash tank 4 is cooled by a gas cooler 10, and then returned to the raw material heating vaporizer 2 through a circulating compressor 11, the liquid phase of the gas-liquid flash tank 4 enters a light-removing column 5, the gas phase of the light-removing column 5 is cooled by a light-removing column top cooler 8, and then sequentially passes through a light-removing column reflux tank 9, the gas cooler 10, and the circulating compressor 11 to return to the raw material heating vaporizer 2, the C6 and C9 components of the liquid phase of the light-removing column 5 are transported back to the inlet of the first-stage reactor 31 by a light-removing column reflux pump 7 at a mass ratio of 10:1 to the raw material propylene, the bottom oil of the light-removing column 5 is transported to a propylene tetramer refining column 12 by a light-removing column bottom pump 6, the purity of the propylene tetramer obtained from the top of the propylene tetramer refining column 12 reaches the standard, the propylene tetramer is collected from the outlet of the propylene tetramer refining column 12 into a propylene tetramer collection tank 13, the propylene conversion rate is 93.5%, and the propylene tetramer yield is 70%.

[0048] Example 4

[0049] A method for preparing a propylene tetramer comprises the following steps: a mixture of 175 ml of propylene and 175 ml of propane is pressurized to 4.0 MPa in a raw material heating vaporizer 2, heated to 275° C., and then evenly divided into three paths to feed the feed port of a three-stage reactor 3; the reactor tubes are filled with a phosphoric acid-supported catalyst, the catalyst carrier being aluminum oxide; the reaction product enters a gas-liquid flash tank 4 from the discharge port of the third stage reactor 33; the discharge port temperature of the third stage reactor 33 is 305° C.; the gas phase of the reaction product in the gas-liquid flash tank is cooled by a gas cooler 10, and then returned to the raw material heating vaporizer 2 via a circulation compressor 11; the liquid phase of the gas-liquid flash tank 4 enters a degassing tank; Light tower 5, the gas phase at the top of the light tower 5 is cooled by the light tower top cooler 8 and then returns to the raw material heating vaporizer 2 through the light tower reflux tank 9, the gas cooler 10, and the circulating compressor 11 in sequence. The C6 and C9 components in the liquid phase at the top of the light tower 5 are transported to the feed inlet of the first-stage reactor 31 through the light tower reflux pump 7 at a mass ratio of 5:1 to the raw material propylene. The bottom oil of the light tower 5 is transported to the propylene tetramer refining tower 12 by the light tower bottom pump 6. Propylene tetramer with purity meeting the standard is obtained at the top of the tower. The propylene tetramer enters the propylene tetramer collecting tank 13 from the discharge port of the refining tower 12 for collection. The propylene conversion rate is 95.4%, and the propylene tetramer yield is 61%.

[0050] Example 5

[0051] A method for preparing a propylene tetramer comprises the following steps: a mixture of 175 ml of propylene and 175 ml of propane is pressurized to 4.0 MPa in a raw material heating vaporizer 2, heated to 275° C., and then evenly divided into three paths to feed the feed port of a three-stage reactor 3; the tubes are filled with a phosphoric acid-supported catalyst, the catalyst carrier being diatomaceous earth; the reaction product enters a gas-liquid flash tank 4 through the discharge port of the third-stage reactor 33; the discharge port temperature of the third-stage reactor 33 is 305° C.; the gas phase of the reaction product in the gas-liquid flash tank 4 is cooled by a gas cooler 10, and then returned to the raw material heating vaporizer 2 via a circulation compressor 11; the liquid phase of the gas-liquid flash tank 4 enters a lightness removal column 5; The gas phase at the top of the lightness removal tower 5 is cooled by the lightness removal tower top cooler 8 and then returns to the raw material heating vaporizer 2 through the lightness removal tower reflux tank 9, the gas cooler 10, and the circulating compressor 11 in sequence. The C6 and C9 components in the liquid phase at the top of the lightness removal tower 5 are transported back to the feed inlet of the first-stage reactor 31 via the lightness removal tower reflux pump 7 at a mass ratio of 15:1 to the raw material propylene. The bottom oil of the lightness removal tower 5 is transported to the propylene tetramer refining tower 12 by the lightness removal tower bottom pump 6. Propylene tetramer with purity meeting the standard is obtained at the top of the tower. The propylene tetramer enters the propylene tetramer collecting tank 13 from the discharge port of the refining tower 12 for collection. The propylene conversion rate is 94.2%, and the propylene tetramer yield is 60.1%.

[0052] Example 6

[0053] A method for preparing a tetramer of propylene, comprising the following steps: a mixture of 175 ml of propylene and 175 ml of propane is pressurized to 4.0 MPa by a raw material heating vaporizer 2, heated to 275 DEG C, and then evenly divided into three paths to the inlet of a three-stage reactor 3, the column tube of which is filled with a phosphoric acid supported catalyst, the carrier of which is diatomite, the reaction product is discharged from the outlet of the third-stage reactor 33 into a gas-liquid flash tank 4, the temperature of the outlet of the third-stage reactor 33 is 305 DEG C, the gas phase of the reaction product in the gas-liquid flash tank 4 is cooled by a gas cooler 10, and then returned to the raw material heating vaporizer 2 through a circulating compressor 11, the liquid phase of the gas-liquid flash tank 4 is fed into a light-removing column 5, the gas phase of the light-removing column top is cooled by a light-removing column top cooler 8, and then returned to the raw material heating vaporizer 2 through a light-removing column reflux tank 9, a gas cooler 10 and a circulating compressor 11 in turn, the C6 and C9 components in the liquid phase of the light-removing column top are fed back to the inlet of the first-stage reactor 31 by a light-removing column reflux pump 7 when the mass ratio of the C6 and C9 components to the raw material propylene is 12:1, the bottom oil of the light-removing column 5 is fed to a propylene tetramer refining column 12 by a light-removing column bottom pump 6, the propylene tetramer with a purity up to standard is obtained from the top of the column, the propylene tetramer is collected in a propylene tetramer collecting tank 13 from the outlet of the refining column 12, the propylene conversion rate is 94.7%, and the propylene tetramer yield is 62.3%.

[0054] Comparative Example 1

[0055] Compared with Example 3, the C6 and C9 components in the light-removing column are not fed back to the first-stage reactor, and other steps are the same, the propylene conversion rate is 93%, and the propylene tetramer yield is 28%.

[0056] Comparative Example 2

[0057] Compared with Example 3, when the mass ratio of the C6 and C9 components to the raw material propylene in the light-removing column reaches 2:1, the C6 and C9 components are fed back to the first-stage reactor to continue reacting with propylene, the propylene conversion rate is 93.2%, and the propylene tetramer yield is 55%.

[0058] Comparative Example 3

[0059] Compared with Example 3, when the mass ratio of the C6 and C9 components to the raw material propylene in the light-removing column reaches 20:1, the C6 and C9 components are fed back to the first-stage reactor to continue reacting with propylene, the propylene conversion rate is 95%, and the propylene tetramer yield is 57%.

[0060] Table 1: Propylene conversion rate and propylene tetramer yield of Examples 1-6 and Comparative Examples 1-3

[0061] Propylene conversion (%) Propylene tetramer yield (%) Example 1 90 61 Example 2 93 65 Example 3 93.5 70 Example 4 95.4 61 Example 5 94.2 60.1 Example 6 94.7 62.3 Comparative Example 1 93 28 Comparative Example 2 93.2 55 Comparative Example 3 95 57

[0062] As can be seen from Table 1, by controlling the mass ratio of the liquid phase C6 and C9 components returned to the reactor from the top of the light-removal tower to the mass ratio of the raw propylene, and considering the liquid phase C6 and C9 components at the top of the intermediate product light-removal tower, the conversion rate and yield of propylene tetramer can be simply and effectively improved.

[0063] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing propylene tetramer, characterized in that: The following steps are involved: S1, using propylene as a raw material to carry out oligomerization reaction in a reactor to obtain a mixed product; The mixed product in S2 and S1 is flashed and the liquid phase enters the lightness removal tower. The mass ratio of the liquid phase C6 and C9 components at the top of the lightness removal tower to the raw material propylene is 5-15:1 and returned to the reactor to continue the reaction. S3, refining and purifying the propylene tetramer at the bottom of the lightness removal tower in S2 to obtain a finished product; The reactor in S1 is a three-stage reactor, which includes a first-stage reactor, a second-stage reactor, and a third-stage reactor. The discharge port of the first-stage reactor is connected to the feed port of the second-stage reactor, and the discharge port of the second-stage reactor is connected to the feed port of the third-stage reactor. The raw material propylene enters from the feed ports of the three-stage reactors respectively and is discharged from the discharge port of the third-stage reactor for flash evaporation. When the oligomerization reaction is carried out with propylene as the raw material in S1, a phosphoric acid-supported catalyst is added as a polymerization catalyst and propane is used as a diluent. The water injection rate of the propylene raw material in S1 is 0.1-0.2% of the mass of propylene. The temperature of the feed port of the first-stage reactor is 235°C to 275°C, the temperature of the second-stage reactor is 235°C to 275°C, and the temperature of the feed port of the third-stage reactor is 235°C to 275°C. In S2, the liquid phase C6 and C9 components at the top of the light removal tower are returned to the reactor to continue the reaction at a mass ratio of 6:1, 8:1, 10:1 or 12:1 to propylene; The inlet pressure of the first stage reactor is 3.0MPa-4.5MPa, the inlet pressure of the second stage reactor is 3.0MPa-4.5MPa, and the inlet pressure of the third stage reactor is 3.0MPa-4.5MPa; The discharge port temperature of the first stage reactor is 265°C-305°C, the discharge port temperature of the second stage reactor is 265°C-305°C, and the discharge port temperature of the third stage reactor is 265°C-305°C.

2. The method for preparing propylene tetramer according to claim 1, wherein: The carrier of the phosphoric acid supported catalyst is diatomaceous earth, kaolin, silicon dioxide or aluminum oxide.

3. The method for preparing propylene tetramer according to claim 1, wherein: The mass ratio of propylene to diluent is 1:

1.

4. The method for preparing propylene tetramer according to claim 1, wherein: The amount of raw material propylene entering the feed inlets of the first stage reactor, the second stage reactor and the third stage reactor is the same.

5. The method for preparing propylene tetramer according to claim 1, wherein: In S2, the mixed product is flashed through a gas-liquid flash tank, and after flashing, it is cooled in the gas phase, pressurized, and then circulated to the feed port of the first-stage reactor.

6. The method for preparing propylene tetramer according to claim 1, wherein: The flash temperature in S2 is 120°C and the flash pressure is 2.0 MPa.

7. The method for preparing propylene tetramer according to claim 1, wherein: The propylene tetramer in S3 is refined and purified by a refining tower, and the propylene tetramer enters the refining tower from the bottom of the lightness removal tower.

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