A low-energy propylene oligomer separation system and separation method

Abstract

The present invention provides a low-energy propylene oligomer separation system and separation method, comprising a first separation tower, a second separation tower, a third separation tower and a fourth separation tower, wherein the tower bottom discharge port of the first separation tower is connected to the middle feed port of the second separation tower, a first tower top condenser is provided at the top of the first separation tower, a first middle reboiler is provided at the middle of the first separation tower, a fourth tower top condenser is provided at the top of the fourth separation tower, and the first middle reboiler is connected to the fourth tower top condenser through a pipeline. The low-energy propylene oligomer separation system and separation method of the present invention optimizes the four-tower process of propylene oligomer separation, reduces the energy consumption of the device, reduces the steam and circulating water consumption, and reduces the operating cost while ensuring the product yield.

Description

Technical Field

[0001] The invention belongs to the technical field of distillation, and in particular relates to a propylene oligomer separation system and a separation method with low energy consumption. Background Art

[0002] Propylene oligomers are important chemical raw materials with a wide range of uses, mainly including propylene dimers, trimers and tetramers. Propylene dimer (4-methyl-1-pentene) can be used to produce isoprene; propylene trimer (nonene) can be used as an additive component for high-octane gasoline, and can also be used to prepare chemical raw materials such as nonylphenol, tertiary carbonic acid, and surfactants; propylene tetramer (1-dodecene) can be used to prepare calcium dodecylphenol sulfide, which is widely used in the production of lubricant additives and polymer molecular regulators. The traditional propylene oligomer separation process mainly includes the main processes of depropanization, de-crude dimer, dimer refining, trimer refining, etc.

[0003] According to the literature report "Progress in Propylene Oligomerization Technology", the conventional separation process of propylene oligomers is as follows: Figure 3 As shown, the crude propylene oligomer obtained by propylene polymerization first enters the first separation tower to separate propylene and propane fractions at the top of the tower, a part of which is sent to the liquefied gas storage tank, and the rest is circulated to the reactor. The saturated liquid obtained in the tower bottom is pumped to the second separation tower, and the crude dimer fraction is extracted from the tower top and pumped to the third separation tower through the discharge pump. The qualified propylene dimer product is obtained at the top of the tower and sent to the outside, and the gasoline fraction is obtained in the tower bottom and pumped to the gasoline fraction storage tank; the crude trimer fraction in the tower bottom of the second separation tower is pumped to the fourth separation tower for trimer and tetramer separation, and a qualified propylene trimer product is obtained at the top of the tower, and a propylene tetramer product is obtained in the tower bottom. This separation process has the following problems:

[0004] (1) The top temperature of the first separation tower is 15-20°C, and the bottom temperature is 170-185°C. The temperature difference between the top and bottom of the tower is large, which consumes a large amount of high-grade steam;

[0005] (2) Propylene dimers are condensed and re-vaporized in the second and third separation towers, which consumes a lot of energy;

[0006] (3) The temperature of the fourth separation tower kettle reaches above 200°C. At high temperatures, propylene tetramers will cause coking problems. Summary of the invention

[0007] In view of this, the present invention aims to provide a low-energy consumption propylene oligomer separation system to reduce the energy consumption of the device and reduce the consumption of steam and circulating water.

[0008] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0009] A low-energy propylene oligomer separation system comprises a first separation tower, a second separation tower, a third separation tower and a fourth separation tower, wherein the tower bottom discharge port of the first separation tower is connected with the middle feed port of the second separation tower, a first tower top condenser is arranged at the top of the first separation tower, a first middle reboiler is arranged at the middle of the first separation tower, a fourth tower top condenser is arranged at the top of the fourth separation tower, and the first middle reboiler is connected with the fourth tower top condenser through a pipeline.

[0010] The top discharge port of the second separation tower is connected to the middle feed port of the third separation tower, and the bottom discharge port of the second separation tower is connected to the middle feed port of the fourth separation tower;

[0011] Alternatively, the bottom discharge port of the second separation tower is communicated with the middle feed port of the third separation tower, and the bottom discharge port of the third separation tower is communicated with the middle feed port of the fourth separation tower.

[0012] Furthermore, the operating pressure of the first separation tower is 0.6-1MpaG, the tower top temperature is 10-20°C, the tower bottom temperature is 160-180°C, the reflux ratio is 0.1-5, and the number of theoretical plates is 13-18.

[0013] Furthermore, the first middle reboiler is arranged between the 9th to 11th theoretical plates of the first separation tower.

[0014] Furthermore, the operating pressure of the fourth separation tower is 0-80 kPaA, the tower top temperature is 120-140° C., the tower bottom temperature is 160-180° C., the reflux ratio is 0.5-5, and the number of theoretical plates is 30-40.

[0015] Another object of the present invention is to provide a low-energy propylene oligomer separation method to optimize the four-tower process for propylene oligomer separation, thereby ensuring product yield and reducing operating costs.

[0016] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0017] A low-energy propylene oligomer separation method, using the propylene oligomer separation system as described above, comprises the following steps:

[0018] S1, crude propylene oligomers enter the first separation tower, the gas phase separated from the top of the first separation tower enters the first top condenser, the gas phase produced by the first top condenser is produced as fuel gas, and the bottom liquid of the first separation tower enters the second separation tower;

[0019] S2, the gas phase separated from the top of the second separation tower enters the third separation tower, and the bottom liquid of the second separation tower enters the fourth separation tower;

[0020] S3: The gas phase separated from the top of the third separation tower is condensed to obtain propylene dimer, and the bottom liquid of the third separation tower is extracted as a gasoline fraction;

[0021] S4. The gas phase separated from the top of the fourth separation tower is used as a heat source to heat the first middle reboiler and then enters the fourth top condenser for condensation to obtain propylene trimer, and the bottom liquid of the fourth separation tower is produced as propylene tetramer.

[0022] Furthermore, the operating pressure of the second separation tower is 20-70 kPaG, the tower top temperature is 50-80°C, the tower bottom temperature is 130-170°C, the reflux ratio is 0.5-5, and the number of theoretical plates is 20-30.

[0023] Furthermore, the operating pressure of the third separation tower is 5-10 kPaG, the tower top temperature is 40-80°C, the tower bottom temperature is 90-120°C, the reflux ratio is 0.5-5, and the number of theoretical plates is 10-20.

[0024] A low-energy propylene oligomer separation method, using the propylene oligomer separation system as described above, comprises the following steps:

[0025] S1, crude propylene oligomers enter the first separation tower, the gas phase separated from the top of the first separation tower enters the first top condenser, the gas phase produced by the first top condenser is produced as fuel gas, and the bottom liquid of the first separation tower enters the second separation tower;

[0026] S2, the gas phase separated from the top of the second separation tower is condensed to obtain propylene dimer, and the bottom liquid of the second separation tower enters the third separation tower;

[0027] S3: The gas phase separated from the top of the third separation tower is condensed and taken out as the gasoline fraction, and the bottom liquid of the third separation tower enters the fourth separation tower;

[0028] S4. The gas phase separated from the top of the fourth separation tower is used as a heat source to heat the first middle reboiler and then enters the fourth top condenser for condensation to obtain propylene trimer, and the bottom liquid of the fourth separation tower is produced as propylene tetramer.

[0029] Furthermore, the operating pressure of the second separation tower is 5-30 kPaG, the tower top temperature is 50-80°C, the tower bottom temperature is 130-170°C, the reflux ratio is 0.5-5, and the number of theoretical plates is 20-30.

[0030] Furthermore, the operating pressure of the third separation tower is 5-30 kPaG, the tower top temperature is 90-120° C., the tower bottom temperature is 140-160° C., the reflux ratio is 0.5-5, and the number of theoretical plates is 30-40.

[0031] Compared with the prior art, the low-energy propylene oligomer separation system and separation method of the present invention have the following advantages:

[0032] (1) The low-energy propylene oligomer separation system and separation method of the present invention arranges a first middle reboiler in the middle of the first separation tower, thereby reducing the heat load of the first tower bottom reboiler and effectively reducing the high-grade steam consumption in the tower bottom. The first middle reboiler is connected to the fourth tower top reboiler through a pipeline for heat coupling, thereby effectively saving the consumption of steam and circulating water.

[0033] (2) The low-energy propylene oligomer separation system and separation method of the present invention optimizes the operating pressure, top and bottom temperatures of the separation tower, and reasonably sets the temperature difference, which is beneficial to improving product quality and reducing the probability of coking;

[0034] (3) The low-energy propylene oligomer separation system and separation method described in the present invention provide a new type of distillation sequence, in which the second separation tower obtains the dimer product, the third separation tower removes the remaining light components, and the fourth separation tower obtains the trimer and tetramer products. The dimer product does not need to be condensed and vaporized again, which further saves steam and circulating water consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 This is a schematic diagram of the connection structure of the low-energy propylene oligomer separation system according to Example 1 of the present invention;

[0037] Figure 2 This is a schematic diagram of the connection structure of the low-energy propylene oligomer separation system according to Example 2 of the present invention;

[0038] Figure 3 The figure is a schematic diagram of the connection structure of the propylene oligomer separation system in the prior art.

[0039] Description of reference numerals:

[0040] 1. First separation tower; 2. Second separation tower; 3. Third separation tower; 4. Fourth separation tower; 5. First middle reboiler; 6. First bottom reboiler; 7. First top condenser; 8. Second bottom reboiler; 9. Second top condenser; 10. Third bottom reboiler; 11. Third top condenser; 12. Fourth bottom reboiler; 13. Fourth top condenser. DETAILED DESCRIPTION

[0041] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0042] The present invention will be described in detail below with reference to the embodiments and the accompanying drawings.

[0043] Example 1

[0044] The low-energy propylene oligomer separation system in this embodiment includes a first separation tower 1, a second separation tower 2, a third separation tower 3 and a fourth separation tower 4. The bottom discharge port of the first separation tower 1 is connected to the middle feed port of the second separation tower 2. The first separation tower 1 is provided with a first bottom reboiler 6 at the bottom, the first separation tower 1 is provided with a first top condenser 7 at the top, the first separation tower 1 is provided with a first middle reboiler 5 in the middle, the second separation tower 2 is provided with a second bottom reboiler 8 at the bottom, and the second separation tower 2 is provided with a second top condenser 7 at the top. A condenser 9, a top discharge port of the second separation tower 2 is connected to a middle feed port of the third separation tower 3, a bottom discharge port of the second separation tower 2 is connected to a middle feed port of the fourth separation tower 4, a third bottom reboiler 10 is provided at the bottom of the third separation tower 3, a third top condenser 11 is provided at the top of the third separation tower 3, a fourth bottom reboiler 12 is provided at the bottom of the fourth separation tower 4, a fourth top condenser 13 is provided at the top of the fourth separation tower 4, and the first middle reboiler 5 is connected to the fourth top condenser 13 through a pipeline.

[0045] The low-energy propylene oligomer separation method in this embodiment comprises the following steps:

[0046] S1, crude propylene oligomers from the reactor enter the first separation tower 1 to separate unreacted propylene and propane, the gas phase separated from the top of the first separation tower 1 enters the first top condenser 7, the gas phase produced by the first top condenser 7 is produced as fuel gas, the liquid phase is circulated back to the reactor for reaction, and the bottom liquid of the first separation tower 1 is pumped into the second separation tower 2;

[0047] S2, the gas phase separated from the top of the second separation tower 2 passes through the second top condenser 9, the uncondensed crude dimer gas phase enters the third separation tower 3, and the bottom liquid of the second separation tower 2 enters the fourth separation tower 4 to separate trimers and tetramers;

[0048] S3: The gas phase separated from the top of the third separation tower 3 is condensed by the third top condenser 11 to obtain propylene dimer, which is pumped out, and the bottom liquid of the third separation tower 3 is extracted as a gasoline fraction;

[0049] S4. Before the high-temperature gas phase separated from the top of the fourth separation tower 4 enters the fourth top condenser 13, it is first used as a heat source to heat the first middle reboiler 5 to recover the heat therein, and then enters the fourth top condenser 13 for condensation, part of which is used as reflux, and the rest is extracted as a propylene trimer product through a pump, and the bottom liquid of the fourth separation tower 4 is extracted as a propylene tetramer.

[0050] The operating parameters of the four separation towers are shown in Table 1.

[0051] Table 1 Example 1 Separation tower operating parameters

[0052]

[0053] The top condensers, bottom reboilers and product purity of this embodiment are compared with the prior art as shown in Table 2-4.

[0054] Table 2 Comparison of energy consumption of top condenser

[0055]

[0056] Table 3 Comparison of energy consumption of bottom reboiler

[0057]

[0058] Table 4 Product Purity Comparison

[0059]

[0060] It can be seen from Tables 2 and 3 that, with a propylene trimer scale of 50,000 tons / year, the separation system and separation method of the present invention are used, and the optimized process reduces the cooling load by 24.6% and the heat load by 40.6% compared with the conventional process, and the total steam consumption is saved by 2518.8kW, which can save 4.6t / h of steam (measured at a pressure of 1.2MPaG steam); the total circulating water consumption is saved by 1401.4kW, and the circulating water (measured at a temperature difference of 10°C) is saved by 120.7t / h; the total chilled water consumption is saved by 30kW, and the chilled water (measured at a temperature difference of 5°C) is saved by 5.1t / h, and the energy-saving effect is significant. At the same time, it can be seen from Table 4 that the purity of the optimized process products propylene dimer, trimer and tetramer is improved compared with the traditional process, and the quality purity reaches more than 99.5%.

[0061] Example 2

[0062] The low-energy propylene oligomer separation system in this embodiment includes a first separation tower 1, a second separation tower 2, a third separation tower 3 and a fourth separation tower 4. The bottom discharge port of the first separation tower 1 is connected to the middle feed port of the second separation tower 2. The first separation tower 1 is provided with a first bottom reboiler 6 at the bottom, the first separation tower 1 is provided with a first top condenser 7 at the top, the first separation tower 1 is provided with a first middle reboiler 5 in the middle, the second separation tower 2 is provided with a second bottom reboiler 8 at the bottom, and the second separation tower 2 is provided with a second top condenser 7 at the top. Condenser 9, the bottom discharge port of the second separation tower 2 is connected with the middle feed port of the third separation tower 3, a third bottom reboiler 10 is provided at the bottom of the third separation tower 3, a third top condenser 11 is provided at the top of the third separation tower 3, the bottom discharge port of the third separation tower 3 is connected with the middle feed port of the fourth separation tower 4, a fourth bottom reboiler 12 is provided at the bottom of the fourth separation tower 4, a fourth top condenser 13 is provided at the top of the fourth separation tower 4, and the first middle reboiler 5 and the fourth top condenser 13 are connected by a pipeline.

[0063] The low-energy propylene oligomer separation method in this embodiment comprises the following steps:

[0064] S1, crude propylene oligomers from the reactor enter the first separation tower 1 to separate unreacted propylene and propane, the gas phase separated from the top of the first separation tower 1 enters the first top condenser 7, the gas phase produced by the first top condenser 7 is produced as fuel gas, the liquid phase is circulated back to the reactor, and the bottom liquid of the first separation tower 1 enters the second separation tower 2;

[0065] S2, the gas phase separated from the top of the second separation tower 2 is condensed by the second top condenser 9 to obtain propylene dimer, which is pumped out of the boundary, and the bottom liquid of the second separation tower 2 is pumped into the third separation tower 3 to separate the C7-C8 fraction and the trimer fraction;

[0066] S3: The gas phase separated from the top of the third separation tower 3 is condensed by the third top condenser 11 and part of it is used as reflux, and the rest is pumped out as a gasoline fraction, and the bottom liquid of the third separation tower 3 is pumped into the fourth separation tower 4 to separate trimers and tetramers;

[0067] S4. Before the high-temperature gas phase separated from the top of the fourth separation tower 4 enters the fourth top condenser 13, it is first used as a heat source to heat the first middle reboiler 5 to recover the heat therein, and then enters the fourth top condenser 13 for condensation, part of which is used as reflux, and the rest is extracted as a propylene trimer product through a pump, and the bottom liquid of the fourth separation tower 4 is extracted as a propylene tetramer.

[0068] The operating parameters of the four separation towers are shown in Table 5.

[0069] Table 5 Example 2 Separation Tower Operating Parameters

[0070]

[0071] The top condensers, bottom reboilers and product purities in this embodiment are compared with the prior art as shown in Tables 6-8.

[0072] Table 6 Comparison of energy consumption of top condenser

[0073]

[0074]

[0075] Table 7 Comparison of energy consumption of bottom reboiler

[0076]

[0077] Table 8 Product Purity Comparison

[0078]

[0079] It can be seen from Tables 5 and 6 that, with a propylene trimer scale of 50,000 tons / year, the separation system and separation method of the present invention are used, and the optimized process reduces the cooling load by 24.4% and the heat load by 40.6% compared with the conventional process, and the total steam consumption is saved by 2517.1kW, which can save 4.6t / h of steam (measured at a pressure of 1.2MPaG steam); the total circulating water consumption is saved by 1387kW, and the circulating water (measured at a temperature difference of 10°C) is saved by 119.5t / h; the total chilled water consumption is saved by 30kW, and the chilled water (measured at a temperature difference of 5°C) is saved by 5.1t / h, and the energy-saving effect is significant. At the same time, it can be seen from Table 8 that the purity of the propylene dimer, trimer and tetramer products of the optimized process is improved compared with the traditional process, and the quality purity reaches more than 99.5%.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low energy consumption propylene oligomer separation system, characterized in that: The method comprises a first separation tower, a second separation tower, a third separation tower and a fourth separation tower, wherein the tower kettle discharge port of the first separation tower is connected with the middle feed port of the second separation tower, a first tower top condenser is arranged at the top of the first separation tower, a first middle reboiler is arranged at the middle of the first separation tower, a fourth tower top condenser is arranged at the top of the fourth separation tower, and the first middle reboiler is connected with the fourth tower top condenser through a pipeline, The second separation tower is provided with a second top condenser at the top, the top discharge port of the second separation tower is connected with the middle feed port of the third separation tower, the gas phase separated from the top of the second separation tower passes through the second top condenser, and the uncondensed crude dimer gas phase enters the third separation tower; the gas phase separated from the top of the third separation tower is condensed to obtain propylene dimer; the bottom discharge port of the second separation tower is connected with the middle feed port of the fourth separation tower; The operating pressure of the first separation tower is 0.6-1MpaG, the top temperature is 10-20°C, the bottom temperature is 160-180°C, the reflux ratio is 0.1-5, and the number of theoretical plates is 13-18; The operating pressure of the third separation tower is 5-10 kPaG, the tower top temperature is 40-80°C, the tower bottom temperature is 90-120°C, and the reflux ratio is 0.5-5; The operating pressure of the fourth separation tower is 0-80kPaA, the top temperature is 120-140 ℃, the bottom temperature is 160-180 ℃, the reflux ratio is 0.5-5; The first middle reboiler is disposed between the 9th and 11th theoretical plates of the first separation tower; The fourth separation tower has 30-40 theoretical plates.

2. A low energy consumption propylene oligomer separation method, using the propylene oligomer separation system according to claim 1, characterized in that: The following steps are involved: S1, crude propylene oligomers enter the first separation tower, the gas phase separated from the top of the first separation tower enters the first top condenser, the gas phase produced by the first top condenser is produced as fuel gas, and the bottom liquid of the first separation tower enters the second separation tower; S2, the gas phase separated from the top of the second separation tower enters the third separation tower, and the bottom liquid of the second separation tower enters the fourth separation tower; S3: The gas phase separated from the top of the third separation tower is condensed to obtain propylene dimer, and the bottom liquid of the third separation tower is extracted as a gasoline fraction; S4. The gas phase separated from the top of the fourth separation tower is used as a heat source to heat the first middle reboiler and then enters the fourth top condenser for condensation to obtain propylene trimer, and the bottom liquid of the fourth separation tower is produced as propylene tetramer.

3. The low energy consumption propylene oligomer separation method according to claim 2, characterized in that: The operating pressure of the second separation tower is 20-70 kPaG, the tower top temperature is 50-80°C, the tower bottom temperature is 130-170°C, the reflux ratio is 0.5-5, and the number of theoretical plates is 20-30.

4. The low-energy propylene oligomer separation method according to claim 2, characterized in that: The operating pressure of the third separation tower is 5-10 kPaG, the tower top temperature is 40-80°C, the tower bottom temperature is 90-120°C, the reflux ratio is 0.5-5, and the number of theoretical plates is 10-20.

5. A low energy consumption propylene oligomer separation system, characterized in that: The method comprises a first separation tower, a second separation tower, a third separation tower and a fourth separation tower, wherein the tower kettle discharge port of the first separation tower is connected with the middle feed port of the second separation tower, a first tower top condenser is arranged at the top of the first separation tower, a first middle reboiler is arranged at the middle of the first separation tower, a fourth tower top condenser is arranged at the top of the fourth separation tower, and the first middle reboiler is connected with the fourth tower top condenser through a pipeline, The bottom discharge port of the second separation tower is connected to the middle feed port of the third separation tower, and the gas phase separated from the top of the second separation tower is condensed to obtain propylene dimer; the bottom discharge port of the third separation tower is connected to the middle feed port of the fourth separation tower; The operating pressure of the first separation tower is 0.6-1MpaG, the top temperature is 10-20°C, the bottom temperature is 160-180°C, the reflux ratio is 0.1-5, and the number of theoretical plates is 13-18; The operating pressure of the third separation tower is 5-30 kPaG, the tower top temperature is 90-120°C, the tower bottom temperature is 140-160°C, the reflux ratio is 0.5-5, and the number of theoretical plates is 30-40; The operating pressure of the fourth separation tower is 0-80kPaA, the top temperature is 120-140 ℃, the bottom temperature is 160-180 ℃, the reflux ratio is 0.5-5; The first middle reboiler is disposed between the 9th and 11th theoretical plates of the first separation tower; The fourth separation tower has 30-40 theoretical plates.

6. A low energy consumption propylene oligomer separation method, using the propylene oligomer separation system according to claim 5, characterized in that: The following steps are involved: S1, crude propylene oligomers enter the first separation tower, the gas phase separated from the top of the first separation tower enters the first top condenser, the gas phase produced by the first top condenser is produced as fuel gas, and the bottom liquid of the first separation tower enters the second separation tower; S2, the gas phase separated from the top of the second separation tower is condensed to obtain propylene dimer, and the bottom liquid of the second separation tower enters the third separation tower; S3: The gas phase separated at the top of the third separation tower is condensed and taken out as the gasoline fraction, and the bottom liquid of the third separation tower enters the fourth separation tower; S4. The gas phase separated from the top of the fourth separation tower is used as a heat source to heat the first middle reboiler and then enters the fourth top condenser for condensation to obtain propylene trimer, and the bottom liquid of the fourth separation tower is produced as propylene tetramer.

7. The low energy consumption propylene oligomer separation method according to claim 6, characterized in that: The operating pressure of the second separation tower is 5-30 kPaG, the tower top temperature is 50-80°C, the tower bottom temperature is 130-170°C, the reflux ratio is 0.5-5, and the number of theoretical plates is 20-30.

8. The low energy consumption propylene oligomer separation method according to claim 6, characterized in that: The operating pressure of the third separation tower is 5-30 kPaG, the tower top temperature is 90-120° C., the tower bottom temperature is 140-160° C., the reflux ratio is 0.5-5, and the number of theoretical plates is 30-40.

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