Separation method of mixed C4 alkene with heat pump system

Abstract

The invention discloses a method for separating mixed C4 alkene with a heat pump system. The method comprises the following steps: vaporizing to remove heavy components of a C4 raw material; then entering an extractive distillation tower to be in countercurrent contact with a lean solvent entering from the upper part of the extractive distillation tower, extracting gas-phase C4 alkane from the top of the extractive distillation tower, extracting a rich solvent from a tower kettle, entering a desorption tower for desorption, extracting gas-phase C4 olefin from the top of the desorption tower, and extracting the lean solvent from the tower kettle as an extracting agent to be circulated back to the extractive distillation tower; wherein the low-grade heat energy of the gas-phase C4 alkane extracted from the top of the extractive distillation tower is improved into high-grade heat energy through an open heat pump system, and then the high-grade heat energy is transferred to a process material in the extractive distillation tower; and the low-grade heat energy of the lean solvent extracted from the tower kettle of the desorption tower is improved into high-grade heat energy through the closed heat pump system after passing through the multi-stage heat exchanger, and then the high-grade heat energy is exchanged to a process material in the extractive distillation tower. The method provided by the invention can fully realize efficient recycling of low-grade heat energy of gas-phase steam at the top of the extractive distillation tower and low-grade heat energy of a lean solvent.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry and relates to a mixed carbon tetraalkene separation method with a heat pump system. Background Art

[0002] Mixed C4 is primarily a byproduct of ethylene steam cracking, refinery catalytic cracking (FCC), and methanol to olefins (MTO) units. It contains small amounts of C3, n-butane, isobutane, butene-1, isobutylene, cis- and trans-2-butene, and a small amount of C5. Currently, extractive distillation is the primary method used to separate mixed C4, both domestically and internationally. Extractants used include acetonitrile, a mixture of morpholine and N-formylmorpholine, a mixture of methyl ethyl ketone and N-formylmorpholine, sulfolane, and N-methylpyrrolidone. The use of N-methylpyrrolidone for the separation of mixed C4 alkanes has not yet been applied in China, and research is needed on how to utilize this technology in an energy-efficient and efficient manner.

[0003] Heat pump distillation is a highly efficient separation technology that utilizes heat pumps to recover low-grade heat energy from the distillation system and significantly reduce distillation energy consumption. Applying heat pump distillation to the separation of mixed C4-alkanes is of great significance for improving the economic benefits of the separation process.

[0004] Patent CN103502188A proposes to use a mixture of N-methylpyrrolidone and water as a solvent, and to separate C4 alkanes and C4 olefins by extractive distillation, without considering energy recovery. Patent CN104812725A uses the N-methylpyrrolidone method to separate C4 alkanes and C4 olefins, taking into account solvent heat recovery. Patent CN116670101A uses the N-methylpyrrolidone method to separate C4 alkanes and C4 olefins, taking into account solvent energy recovery and steam heat recovery. The above inventions studied the separation of mixed C4 alkanes and C4 olefins by the N-methylpyrrolidone method, but only considered the recovery of solvent or steam energy, and did not fully achieve energy saving and high efficiency. Therefore, it is necessary to conduct in-depth research on the use of heat pump distillation technology to further improve the energy efficiency level of the separation of mixed C4 alkanes by the N-methylpyrrolidone method. Summary of the Invention

[0005] The present invention adopts N-methylpyrrolidone solution as an extractant and provides a mixed carbon tetraalkene separation method with a heat pump system, aiming to fully realize efficient energy recycling.

[0006] The method for separating mixed carbon tetraalkanes with a heat pump system of the present invention comprises the following steps:

[0007] Step S1, the mixed C4 raw materials enter the C4 evaporation tower or tank for vaporization to remove heavy components;

[0008] Step S2, the vaporized mixed C4 enters the extractive distillation tower, and is countercurrently contacted with the lean solvent circulating from the upper part of the extractive distillation tower. The gaseous C4 alkanes are extracted from the top of the extractive distillation tower, and the rich solvent containing C4 olefins is extracted from the bottom of the extractive distillation tower and enters the desorption tower;

[0009] Step S3, the rich solvent is heated and decomposed in the decomposition tower, the gaseous C4 olefins are extracted from the top of the decomposition tower, and the lean solvent is extracted from the bottom of the decomposition tower and circulated back to the extractive distillation tower as an extractant;

[0010] Among them, the low-grade thermal energy of the gaseous carbon tetraalkanes extracted from the top of the extractive distillation tower is increased to high-grade thermal energy through an open heat pump system and then exchanged to the process materials in the middle of the extractive distillation tower, and / or the low-grade thermal energy of the lean solvent extracted from the kettle of the analytical tower after passing through a multi-stage heat exchanger is increased to high-grade thermal energy through a closed heat pump system and then exchanged to the process materials in the middle of the extractive distillation tower.

[0011] Preferably, in step S3, the gaseous C4 olefins extracted from the top of the analysis tower are condensed in a chilled water condenser at the top of the analysis tower, and a portion is extracted as the product, and the other portion is refluxed into the analysis tower from the upper part; preferably, the temperature of the condensed C4 olefins is 0°C to 20°C, more preferably 5°C to 15°C; the top pressure of the analysis tower is 0.01MPaG to 0.5MPaG, preferably 0.04MPaG to 0.1MPaG.

[0012] Preferably, the method includes a gas phase carbon tetraalkane low-grade thermal energy utilization step S2A or a gas phase carbon tetraalkane condensation step S2B,

[0013] The low-grade thermal energy utilization step S2A of gaseous tetraalkane specifically includes:

[0014] In step S2A1, the gaseous C4 alkanes extracted from the top of the extraction distillation tower are pressurized and heated by the C4 alkanes compressor of the open heat pump system;

[0015] In step S2A2, the pressurized and heated C4 alkanes exchange heat with the process material in the extractive distillation column via the first intermediate reboiler of the extractive distillation column;

[0016] In step S2A3, the C4 alkanes after heat exchange enter the C4 alkanes reflux tank. Preferably, the C4 alkanes after heat exchange are decompressed and cooled by a throttle valve and condensed before entering the C4 alkanes reflux tank. More preferably, the C4 alkanes after decompressed and cooled by the throttle valve and condensed before entering the C4 alkanes reflux tank are temperature-controlled by a circulating cooling water condenser. A portion of the liquid C4 alkanes are refluxed from the upper portion of the extractive distillation tower into the extractive distillation tower, another portion of the liquid C4 alkanes are extracted as a product, and the gaseous C4 alkanes in the C4 alkanes reflux tank are returned to the C4 alkanes compressor.

[0017] The gaseous phase tetraalkane condensation step S2B specifically comprises:

[0018] In step S2B1, the gaseous C4 alkanes extracted from the top of the extractive distillation tower are directly condensed by the circulating cooling water condenser at the top of the extractive distillation tower;

[0019] In step S2B2, the condensed C4 alkanes enter the reflux tank at the top of the extractive distillation tower, a portion of the C4 alkanes reflux into the extractive distillation tower through the upper part of the extractive distillation tower, and the other portion is extracted as a product.

[0020] Preferably, the method further comprises a lean solvent low-grade thermal energy utilization step S3A, wherein step S3A specifically comprises:

[0021] In step S3A1, the working fluid flowing out of the outlet of the working fluid storage tank of the closed heat pump system passes through the working fluid evaporator to absorb low-grade thermal energy of the lean solvent after heat exchange in the multi-stage heat exchanger;

[0022] In step S3A2, the gas phase working medium that absorbs the low-grade thermal energy is pressurized and heated by the working medium compressor of the closed heat pump system;

[0023] In step S3A3, the pressurized and heated gaseous working medium exchanges heat energy with the process material in the extractive distillation tower through the second intermediate reboiler of the extractive distillation tower, and then enters the working medium storage tank. Preferably, the working medium after heat exchange is decompressed and cooled by a throttle valve and condensed before entering the working medium storage tank.

[0024] Preferably, the method includes: a heat exchange step S3B for analyzing the heat energy of the lean solvent extracted from the tower kettle, and step S3B specifically includes:

[0025] In step S3B1, the lean solvent extracted from the reactor of the desorption tower is first passed through the rich solvent heater at the inlet of the desorption tower to transfer heat energy to the rich solvent;

[0026] In step S3B2, the lean solvent then passes through the third reboiler in the middle of the extractive distillation column to exchange heat energy for the process material in the extractive distillation column;

[0027] In step S3B3, the lean solvent is again passed through the C4 evaporation tower or the C4 evaporation reboiler at the bottom of the tank to exchange heat energy for the mixed C4 raw material;

[0028] In step S3B4, the lean solvent then passes through the working fluid evaporator to exchange low-grade heat energy for the working fluid exiting the outlet of the working fluid storage tank;

[0029] In step S3B5, the lean solvent finally passes through the lean solvent cooler to control the temperature and then enters the extractive distillation tower from the upper part of the extractive distillation tower.

[0030] Preferably,

[0031] In step S2, the kettle of the extractive distillation tower is heated by a kettle reboiler of the extractive distillation tower, preferably using steam as a heat medium;

[0032] In step S3, the kettle of the desorption tower is heated by a kettle reboiler of the desorption tower, preferably using steam as a heat medium;

[0033] The C4 evaporation tower or tank is a C4 evaporation tower or a C4 evaporation tank.

[0034] Preferably, the low-grade heat energy of the top gas phase of the extractive distillation tower is exchanged with an open heat pump system of the process material in the extractive distillation tower whose temperature differs from that of the top gas phase by 0°C to 30°C, preferably with a temperature difference of 0°C to 15°C, and / or the low-grade heat energy of the lean solvent after analysis in the analysis tower after heat exchange through a multi-stage heat exchanger is exchanged with a closed heat pump system of the process material in the extractive distillation tower whose temperature differs from that of the lean solvent after heat exchange by 0°C to 30°C, preferably with a temperature difference of 0°C to 30°C, preferably with a temperature difference of 0°C to 15°C, from that of the lean solvent after heat exchange in the multi-stage heat exchange device.

[0035] Preferably, in step S2, the operating pressure of the extractive distillation tower is 0.35 MPaG to 0.75 MPaG, preferably 0.45 MPaG to 0.55 MPaG.

[0036] Preferably,

[0037] In step S2, the pressure range of the gaseous carbon tetraalkane in the open heat pump system after pressurization by the compressor is 0.45 MPaG to 2.5 MPaG, preferably 1.2 MPaG to 1.8 MPaG; the pressure range of the carbon tetraalkane after decompression is 0.35 MPaG to 0.75 MPaG, preferably 0.45 MPaG to 0.55 MPaG;

[0038] and / or,

[0039] In step S3, the pressure range of the gas phase working medium in the closed heat pump system after pressurization by the compressor is 0.45MPaG~2.5MPaG, preferably 1.2MPaG~1.8MPaG; the pressure range of the working medium after decompression by the throttle valve is 0.2MPaG~0.6MPaG, preferably 0.25MPaG~0.35MPaG.

[0040] Preferably,

[0041] The gas phase working fluid in the closed heat pump system is preferably butane or tetrafluoroethane, more preferably n-butane;

[0042] The C4 olefin content in the mixed C4 is 10 wt% to 90 wt%, preferably 20 wt% to 80 wt%;

[0043] The extractant includes acetonitrile series solvents, morpholine and N-formylmorpholine series solvents, methyl ethyl ketone series solvents, sulfolane series solvents, N-methylpyrrolidone series solvents, etc., preferably an N-methylpyrrolidone solution with a water content of 1wt% to 12wt%, preferably 8wt% water content.

[0044] Another object of the present invention is to provide a mixed C4O-alkene separation device with a heat pump system, the mixed C4O-alkene separation device comprising:

[0045] The C4 evaporation tower or tank has a mixed C4 feed port;

[0046] An extractive distillation tower for separating alkanes and alkenes, wherein the inlet of the extractive distillation tower is connected to the top outlet of the C4 evaporation tower or tank;

[0047] An analytical tower, the analytical tower being connected to the kettle of the extractive distillation tower;

[0048] Wherein, the extractive distillation tower is also connected to a heat pump system. Preferably, the heat pump system includes an open heat pump system that exchanges the low-grade heat energy of the top gas phase of the extractive distillation tower to the process material in the extractive distillation tower, and / or a closed heat pump system that exchanges the low-grade heat energy of the lean solvent after analysis by the analysis tower through a multi-stage heat exchanger to the process material in the extractive distillation tower.

[0049] Preferably, the open heat pump system includes: a C4 alkane compressor, the top of the extractive distillation tower is connected to the inlet of the C4 alkane compressor, the outlet of the C4 alkane compressor is connected to the inlet of the C4 alkane reflux tank after heat exchange connection with the first intermediate reboiler of the extractive distillation tower, and the gas phase of the C4 alkane reflux tank is connected to the upper gas phase of the C4 alkane compressor for gas supply.

[0050] Preferably, the reflux branch at the outlet of the C4 alkane reflux tank is connected to the upper part of the extractive distillation tower, and the outlet of the C4 alkane reflux tank is also connected to an alkane production branch.

[0051] Preferably, the closed heat pump system includes: a working fluid evaporator for exchanging low-grade thermal energy of the lean solvent after multi-stage heat exchange, a working fluid compressor and a working fluid storage tank, the outlet of the working fluid evaporator is connected to the inlet of the working fluid compressor, the outlet of the working fluid compressor is connected to the second intermediate reboiler of the extractive distillation tower for heat exchange and then connected to the inlet of the working fluid storage tank, and the outlet of the working fluid storage tank is connected to the inlet of the working fluid evaporator; preferably, the gas phase of the working fluid storage tank is connected to the upper gas phase of the working fluid compressor for gas replenishment.

[0052] Preferably, the top of the extractive distillation tower is connected to the inlet of the C4 alkane reflux tank, the reflux branch of the outlet of the C4 alkane reflux tank is connected to the upper part of the extractive distillation tower, and the outlet of the C4 alkane reflux tank is also connected to the alkane production branch; preferably, a circulating cooling water system for cooling the C4 alkanes after separation and before reflux is connected between the top of the extractive distillation tower and the inlet of the C4 alkane reflux tank, and preferably the circulating cooling water system is a circulating cooling water condenser.

[0053] Preferably, the top of the analysis tower is connected to the inlet of the C4 olefin reflux tank, wherein a chilled water system is also connected between the top of the analysis tower and the inlet of the C4 olefin reflux tank for cooling the C4 olefins after analysis and before reflux; preferably, the chilled water system is a chilled water condenser with a temperature range of -10°C to 10°C; more preferably, it is a chilled water condenser with a temperature range of -5°C to 5°C; more preferably, the top of the analysis tower is a normal pressure or micro-pressure top, and more preferably, the operating pressure of the top of the analysis tower is 0.01 to 0.5 MPaG, preferably 0.04 to 0.1 PaG.

[0054] Preferably,

[0055] The extractive distillation tower further comprises a third intermediate reboiler of the extractive distillation tower and a tower kettle reboiler of the extractive distillation tower;

[0056] The bottom of the C4 evaporation tower or tank is provided with a C4 evaporation reboiler;

[0057] The bottom of the analytical tower is connected to the upper part of the extractive distillation tower, wherein the bottom of the analytical tower is first heat-exchanged with the rich solvent heater at the inlet of the analytical tower, and then heat-exchanged with the third intermediate reboiler of the extractive distillation tower, and then heat-exchanged with the C4 evaporator reboiler, and finally temperature-controlled with the upper part of the extractive distillation tower by a lean solvent cooler; preferably, in a mixed C4 alkane-olefin separation system with a closed heat pump system, after heat-exchanged with the C4 evaporator reboiler, it is also heat-exchanged with the working fluid evaporator in the closed heat pump system, and finally temperature-controlled with the lean solvent cooler, it is connected to the upper part of the extractive distillation tower.

[0058] Preferably, the reflux branch at the outlet of the C4 olefin reflux tank is connected to the upper part of the analytical tower, and the outlet of the C4 olefin reflux tank is also connected to an olefin production branch.

[0059] Preferably,

[0060] The low-grade heat energy of the top gas phase of the extractive distillation tower is exchanged with an open heat pump system of the process material in the extractive distillation tower, whose temperature difference with the top gas phase is 0°C to 30°C, preferably the temperature difference is 0°C to 15°C, and / or the low-grade heat energy of the lean solvent after analysis in the analysis tower is exchanged with the closed heat pump system of the process material in the extractive distillation tower, whose temperature difference with the lean solvent after heat exchange is 0°C to 30°C, preferably the temperature difference with the lean solvent after heat exchange in the multi-stage heat exchange device is 0°C to 30°C, preferably 0°C to 15°C.

[0061] Preferably,

[0062] The tower kettle of the analytical tower is provided with a reboiler for the analytical tower;

[0063] The extractive distillation tower kettle is provided with an extractive distillation tower kettle reboiler;

[0064] A lean solvent cooler is provided before the solvent inlet at the upper portion of the extractive distillation tower;

[0065] The tower kettle of the analytical tower is provided with a lean solvent circulation pump;

[0066] The C4 evaporation tower or tank is a C4 evaporation tank or a C4 evaporation tower.

[0067] The positive progress effect of the present invention is:

[0068] 1) The mixed C4 alkane-alkene separation process of the present invention has a heat pump system, which can fully realize the efficient recycling of low-grade thermal energy of the overhead gas phase steam and low-grade thermal energy of the lean solvent, greatly reduce the carbon emissions of the device, and strongly promote the comprehensive utilization of mixed C4.

[0069] 2) The present invention utilizes a heat pump system to heat the process materials within the tower, partially vaporizing them and enhancing the gas-liquid separation within the tower. The concentration of the resulting C4 alkanes increases from 98.2 to 98.5 wt%. This enhanced separation efficiency of the extractive distillation tower also improves the desorption efficiency of the C4 olefins in the rich solvent by the desorption tower, raising the C4 olefin concentration from 98.0 to 98.2 wt%. Simultaneously, the total amount of gaseous products remains unchanged, and the recovery rate of the resulting C4 alkanes and C4 olefins is higher than that of the conventional N-methylpyrrolidone method. This improves both the recovery rate and purity of the C4 alkanes and C4 olefins.

[0070] 3) The present invention installs a chilled water system on the top of the desorption tower, so that the desorption tower can operate at a lower pressure, lowering the desorption temperature in the entire desorption tower, thereby reducing the amount of steam used for heating the desorption tower kettle, that is, further reducing the energy consumption of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1Schematic diagram of the mixed carbon tetraalkene separation device with an open heat pump system of Example 1;

[0072] Figure 2 Schematic diagram of a mixed carbon tetraalkene separation device with a closed heat pump system according to Example 2;

[0073] Figure 3 This is a schematic diagram of the mixed carbon tetraalkene separation device of Comparative Example 1 without a heat pump system. DETAILED DESCRIPTION

[0074] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different perspectives and applications without departing from the spirit of the present invention.

[0075] like Figure 1 and Figure 2 As shown, the mixed C4-alkane-olefin separation device with a heat pump system of the present invention includes an open heat pump system that exchanges low-grade heat energy from the top gas phase of the extractive distillation tower T2 with the process material in the extractive distillation tower T2, and / or a closed heat pump system that exchanges low-grade heat energy from the lean solvent after desorption in the desorption tower T3 through a multi-stage heat exchanger with the process material in the extractive distillation tower T3.

[0076] like Figure 1 The apparatus for separating mixed C4 alkanes and alkenes with an open heat pump system according to the present invention comprises a C4 evaporation tower or tank V1, an extractive distillation tower T2, a desorption tower T3, a C4 alkane reflux tank V2, a C4 olefin reflux tank V3, a C4 evaporator-reboiler E1, an extractive distillation tower kettle reboiler E2, a third intermediate reboiler E3 in the extractive distillation tower, a desorption tower reboiler E4, a chilled water condenser E5, a rich solvent heater E6, a lean solvent cooler E7, a first intermediate reboiler E8 in the extractive distillation tower, a lean solvent circulation pump P1, and a C4 alkane compressor C1. The C4 evaporation tower or tank V1 has a mixed C4 feed port, through which the mixed C4 feed enters the C4 evaporation tower or tank V1 for vaporization to remove heavy components. The C4 evaporation tower or tank V1 is heated by the C4 evaporator-reboiler E1 at the bottom. Of course, the C4 evaporation tower or tank V1 can be a C4 evaporation tank or a C4 evaporation tower. When the heavy components in the mixed C4 raw materials are easy to separate, the C4 evaporation tank is used; when the heavy components in the mixed C4 raw materials are difficult to separate, the C4 evaporation tower is preferably used. Figure 1As shown, the vaporized mixed C4 enters extractive distillation tower T2, where it countercurrently contacts the lean solvent circulating from the top of extractive distillation tower T2. Extractive distillation tower T2 heats the process materials within the tower using the extractive distillation tower kettle reboiler E2. The gaseous C4 alkanes extracted from the top of extractive distillation tower T2 are first pressurized and heated by the C4 alkane compressor C1 of the open heat pump system. The pressurized and heated C4 alkanes then pass through the first intermediate reboiler E8 of the extractive distillation tower to exchange heat with the process materials within extractive distillation tower T2, whose temperature differs by 0°C to 30°C from the gas phase temperature at the top of the tower, preferably by 0°C to 15°C. This allows full utilization of the low-grade thermal energy of the gaseous alkanes extracted from the top of the tower, achieving efficient recycling of low-grade energy. After heat exchange in the open heat pump system, the C4 alkanes are condensed by reducing pressure and cooling through a throttle valve, and then enter the C4 alkanes reflux tank V2 after temperature control through a circulating cooling water condenser. Then, part of the C4 alkanes in the tank are refluxed to the upper part of the extractive distillation tower T2 through the reflux branch, and the other part is directly extracted from the alkane extraction branch as a product. The operating pressure of the extractive distillation tower T2 is 0.35MPaG~0.75MPaG, preferably 0.5MPaG~0.55MPaG.

[0077] Continue as Figure 1 As shown, after extractive distillation in the extractive distillation tower T2, a rich solvent containing C4 olefins is formed in the tower bottom. The rich solvent is heated by the rich solvent heater E6 from the tower bottom of the extractive distillation tower T2 and then enters the desorption tower T3. The desorption tower reboiler E4 in the tower bottom of the desorption tower T3 desorbs and heats the process materials in the tower, wherein the extractive distillation tower tower bottom reboiler E2 and the desorption tower reboiler E4 both use steam as the heat medium. Figure 1As shown, the rich solvent is heated and decomposed in the decomposition tower T3, and the gaseous olefins are extracted from the top of the tower. They are first cooled and cooled by the chilled water condenser E5 before entering the C4 olefin reflux tank V3. Part of the C4 olefins in the tank are refluxed to the upper part of the decomposition tower T3 through the reflux branch, and the other part is directly extracted from the olefin extraction branch as the product. Among them, the chilled water system is a chilled water condenser E5 with a temperature of -10℃ to 10℃, preferably a chilled water condenser with a temperature of -5℃ to 5℃, which can cool the gaseous olefins extracted from the top of the tower to a low temperature of 0℃ to 20℃ or 5℃ to 15℃. The chilled water condenser uses a circulating coolant available in the factory or device, which includes a calcium chloride aqueous solution, a propylene glycol aqueous solution, an ethylene glycol aqueous solution, etc., preferably a propylene glycol aqueous solution or an ethylene glycol aqueous solution. Since the top of the analysis tower T3 uses the chilled water condenser E5 to cool the C4 olefins extracted by analysis to a temperature lower than that of the prior art, the top of the analysis tower T3 can be at normal pressure or micro-pressure. The specific operating pressure of the top of the analysis tower T3 is 0.01MPaG~0.4MPaG, preferably 0.05MPaG~0.1MPaG, which further reduces the analysis temperature in the entire analysis tower T3, thereby reducing the amount of steam used for heating in the bottom of the analysis tower T3, that is, reducing the energy consumption of the entire device, and the separation effect of the olefins cooled to a low temperature by chilled water at low pressure is better, thereby improving the recovery rate and purity of the C4 olefins. At the same time, since N-methylpyrrolidone solution is used as the extraction solvent, the extraction distillation tower and the analysis tower can both use a single tower to meet the separation of mixed C4 alkanes, further optimizing the process flow and simplifying the number of equipment. Continue as Figure 1 As shown, the lean solvent in the bottom of the decomposition tower T3 is transported by the lean solvent circulation pump P1 of the bottom of the decomposition tower T3, and then circulated back to the extraction distillation tower T2 after heat exchange through a multi-stage heat exchange device and temperature control by the lean solvent cooler E7 at the entrance of the upper part of the extraction distillation tower T2. The multi-stage heat exchange device includes, in sequence, a rich solvent heater E6 at the entrance of the decomposition tower T3, a third intermediate reboiler E3 of the extraction distillation tower located in the extraction distillation tower T2, and a C4 evaporation reboiler E1 located at the bottom of the C4 evaporation tower or tank V1. Of course, the lean solvent can also pass through the intermediate reboiler of the decomposition tower, the reboiler of the bottom of the extraction distillation tower, etc. (not shown) to fully utilize the thermal energy of the lean solvent. The above-mentioned lean solvents include acetonitrile series solvents, morpholine and N-formylmorpholine series solvents, methyl ethyl ketone series solvents, sulfolane series solvents, and N-methylpyrrolidone series solvents, preferably an N-methylpyrrolidone solution with a water content of 1wt% to 12wt%.

[0078] like Figure 2The apparatus for separating mixed C4-alkanes from olefins with a closed heat pump system according to the present invention comprises a C4 evaporation tower or tank V1, an extractive distillation tower T2, a desorption tower T3, a C4 alkane reflux tank V2, a C4 olefin reflux tank V3, a C4 evaporation reboiler E1, an extractive distillation tower kettle reboiler E2, a third intermediate reboiler E3 of the extractive distillation tower, a desorption tower reboiler E4, a chilled water condenser E5, a rich solvent heater E6, a lean solvent cooler E7, a lean solvent circulation pump P1, a working fluid storage tank V4, a working fluid compressor C2, a second intermediate reboiler E9 of the extractive distillation tower, a circulating cooling water system comprising a circulating cooling water condenser E10, a working fluid evaporator E11, and a lean solvent circulation pump P1. The C4 evaporation tower or tank V1 has a mixed C4 feed port, through which the mixed C4 feed enters the C4 evaporation tower or tank V1 for vaporization to remove heavy components. The C4 evaporation tower or tank V1 is heated by the C4 evaporation reboiler E1 at the bottom. Of course, the C4 evaporation tower or tank V1 can be a C4 evaporation tank or a C4 evaporation tower. When the heavy components in the mixed C4 raw materials are easy to separate, the C4 evaporation tank is used; when the heavy components in the mixed C4 raw materials are difficult to separate, the C4 evaporation tower is preferably used. Figure 2 As shown, the vaporized mixed C4 enters the extractive distillation tower T2 and is countercurrently contacted with the lean solvent circulating in from the upper part of the extractive distillation tower T2. The extractive distillation tower T2 heats the process materials in the tower by the extractive distillation tower kettle reboiler E2 in the tower kettle. After extractive distillation in the extractive distillation tower T2, gaseous alkanes are extracted from the top of the tower. The extracted gaseous alkanes are directly cooled by the circulating cooling water condenser E3 and enter the C4 alkane reflux tank V2. Then, part of the C4 alkanes in the tank are refluxed to the extractive distillation tower T2 through the reflux branch, and the other part is directly extracted from the alkane extraction branch as a product. Among them, the operating pressure of the extractive distillation tower T2 is 0.35MPaG

[0079] ~0.75MPaG, preferably 0.5MPaG~0.55MPaG.

[0080] Continue as Figure 2As shown, the bottom of extractive distillation tower T2 forms a rich solvent containing C4 olefins. This olefin-containing rich solvent enters desorption tower T3 from the bottom of extractive distillation tower T2. The desorption tower reboiler E4 in the bottom of desorption tower T3 desorbs and heats the process materials in desorption tower T3. Both extractive distillation tower reboiler E2 and desorption tower reboiler E4 utilize steam as the heat medium. The rich solvent is heated and desorbed in desorption tower T3, and gaseous olefins are extracted from the top of the tower. The extracted gaseous olefins are first cooled by chilled water condenser E5 before entering the C4 olefin reflux tank V3. A portion of the C4 olefins in the tank are refluxed back to desorption tower T3 via the reflux branch, while the remaining portion is directly extracted as product from the olefin extraction branch. The chilled water system is a chilled water condenser E5 with a temperature of -10℃~10℃, preferably a chilled water condenser E5 with a temperature of -5℃~5℃, which can cool the gaseous olefins extracted from the top of the tower to a low temperature of 0℃~20℃, preferably 5℃~15℃. The chilled water condenser uses a circulating coolant available in the factory or device, and the circulating coolant includes calcium chloride aqueous solution, propylene glycol aqueous solution, ethylene glycol aqueous solution, etc., preferably propylene glycol aqueous solution or ethylene glycol aqueous solution. Since the top of the analysis tower T3 uses the chilled water condenser E5 to cool the C4 olefins extracted by analysis to a lower temperature than the existing technology, the top of the analysis tower T3 can be operated at normal pressure or micro-pressure. The specific operating pressure of the top of the analysis tower T3 is 0.01MPaG

[0081] ~0.4MPaG, preferably 0.05MPaG~0.1MPaG, thereby further reducing the decomposition temperature in the entire decomposition tower T3, reducing the amount of steam used for heating the bottom of the decomposition tower T3, that is, reducing the energy consumption of the entire device, and the separation effect of olefins cooled to low temperature by chilled water at low pressure is better, thereby improving the recovery rate and purity of C4 alkanes and C4 olefins. At the same time, since N-methylpyrrolidone solution is used as the extraction solvent, the extraction distillation tower and the decomposition tower can both use a single tower to meet the separation of mixed C4 alkanes and olefins, further optimizing the process flow and simplifying the number of equipment. Continue as Figure 2As shown, the lean solvent in the bottom of the desorption tower T3 is transported by the lean solvent circulation pump P1 at the bottom of the desorption tower T3, and then successively passes through a multi-stage heat exchange device, a closed heat pump system, and a lean solvent cooler E7 for temperature control before entering the upper part of the extractive distillation tower T2, fully utilizing the thermal energy and low-grade thermal energy of the lean solvent. The multi-stage heat exchange device includes, in sequence, a rich solvent heater E6 at the inlet of the desorption tower T3, a third intermediate reboiler E3 of the extractive distillation tower in the extractive distillation tower T2, and a C4 evaporation reboiler E1 at the bottom of the C4 evaporation tower or tank V1. Of course, the lean solvent can also pass through the intermediate reboiler of the desorption tower, the bottom reboiler of the extractive distillation tower, etc. (not shown) to fully utilize the thermal energy of the lean solvent. The above-mentioned lean solvents include acetonitrile series solvents, morpholine and N-formylmorpholine series solvents, methyl ethyl ketone series solvents, sulfolane series solvents, and N-methylpyrrolidone series solvents, preferably an N-methylpyrrolidone solution with a water content of 1wt% to 12wt%.

[0082] Continue as Figure 2 As shown, the low-grade thermal energy of the lean solvent after desorption in desorption tower T3 is converted to high-grade heat energy through a closed heat pump system. This heat energy is then transferred to the process material in the extractive distillation tower, which has a temperature difference of 0°C to 30°C (preferably 0°C to 15°C) from the lean solvent after heat exchange in the multi-stage heat exchanger. This fully utilizes the low-grade thermal energy of the lean solvent and achieves efficient energy recovery. The closed heat pump system includes a working fluid evaporator E11, a working fluid compressor C2, and a working fluid storage tank V4. Specifically, the working fluid exiting the outlet of the closed heat pump system's working fluid storage tank V4 passes through the working fluid evaporator E11, absorbing the low-grade thermal energy of the lean solvent after heat exchange in the multi-stage heat exchanger. The gaseous working fluid is preferably butane, tetrafluoroethane, or n-butane. The gaseous working fluid, having absorbed low-grade thermal energy, is then pressurized and heated by the closed-loop heat pump system's working fluid compressor C2. The pressurized and heated gaseous working fluid converts its thermal energy into high-grade heat energy, which is then transferred through the extractive distillation column's second intermediate reboiler E9 to the process material in extractive distillation column T2, which has a temperature difference of 0°C to 30°C (preferably 0°C to 15°C) from the lean solvent after heat exchange with the multi-stage heat exchanger. The process material then passes through a throttle valve, reducing pressure and cooling, condensing, and entering working fluid storage tank V4. Simultaneously, the gaseous working fluid condenses into a liquid phase. The liquid working fluid at the outlet of working fluid storage tank V4 is recirculated into the working fluid evaporator E11, where it exchanges heat with the lean solvent after heat exchange and vaporizes. A portion of the gaseous working fluid is then supplied to the working fluid compressor C2 through the tank's top outlet.

[0083] Table 1 Components and contents of mixed C4 raw materials in the separation of mixed C4 alkanes of the present invention

[0084]

[0085]

[0086] Example 1

[0087] according to Figure 1 As shown, the mixed C4 raw material 1 with a temperature of 40°C, a pressure of 0.6MPaG and a flow rate of 19200kg / hr enters the C4 evaporator V1, wherein the components and content of the mixed C4 raw material are shown in Table 1, and the flow rate of the mixed C4 2 in the top gas phase is 19200kg / h, the temperature is 64.2°C, and the pressure is 0.6MPaG, and enters the extractive distillation tower T2; the circulating lean solvent 14 (8wt% water + 92wt% N-methylpyrrolidone) is temperature-controlled to 40°C by the lean solvent cooler E7, and then enters the upper part of the extractive distillation tower T2, and the lean solvent inlet is above the mixed C4 raw material inlet; the gaseous C4 alkane 3 with a top temperature of 59.2°C in the extractive distillation tower T2 is pressurized and heated in the C4 alkane compressor C1, and the temperature of the compressed C4 alkane is 100.6°C and the pressure is 1.5MPaG; the compressed C4 alkane 4 enters the first intermediate of the extractive distillation tower and is then In the boiler E8, the process material is heated to 72℃. After the heat exchange, the temperature of the C4 alkane is 97℃. Then the gaseous C4 alkane is condensed into liquid phase. The liquid C4 alkane 5 is decompressed and cooled before entering the C4 alkane reflux tank V2. The temperature in the tank is 58.9℃ and the pressure is 0.55MPaG. The gaseous C4 alkane 8 in the tank is returned to the compressor C1. A part of the liquid C4 alkane 6 is refluxed to the upper part of the extractive distillation tower T2, and the other part is refluxed to the upper part of the extractive distillation tower T2. The product 7 is extracted as a liquid phase tetra-alkane product 7 at a production rate of 7120 kg / h, and the concentration of n-butane and isobutane in the tetra-alkane product is 98.5 wt%; the temperature of the rich solvent 9 in the bottom of the extractive distillation tower T2 is 101.6°C, the pressure is 0.61 MPaG, and the flow rate is 149000 kg / hr. After heat exchange through the rich solvent heater E6 by pressure difference, it is transported to the decomposition tower T3, and the temperature of the rich solvent after heat exchange is 121.3°C.

[0088] After the rich solvent is analyzed by the analysis tower T3, the gaseous C4 olefins 10 at the top of the tower are condensed by circulating chilled water in the top chilled water condenser E5, and the temperature is 11.3°C and the pressure is 0.045MPaG. A part of the C4 olefins 11 is refluxed to the upper part of the analysis tower T3, and the other part is produced as the C4 olefin product 12, with a production volume of 12080kg / h. The concentration of butene-1, isobutylene, cis-2-butene and trans-2-butene in the C4 olefin product is 98.2wt%; the temperature of the poor solvent 13 in the bottom of the analysis tower T3 is 151.8°C, the pressure is 0.09MpaG, and the flow rate is 136920kg / hr.

[0089] The lean solvent is delivered to the rich solvent heater E6 by the lean solvent delivery pump P1, and after heat exchange with the rich solvent, the temperature drops to 125°C; then it enters the third intermediate reboiler E3 of the extractive distillation tower, and after heat exchange with the process material in the tower, the temperature drops to 103°C; then it exchanges heat with the evaporator reboiler E1, and the temperature drops to 78°C; then it enters the lean solvent cooler E7, and after heat exchange with the circulating cooling water, the temperature drops to 40°C; finally, the lean solvent 14 enters the extractive distillation tower T2 as an extractant for recycling.

[0090] Example 2

[0091] according to Figure 2 As shown, the mixed C4 raw material 1 with a temperature of 40°C, a pressure of 0.6MPaG and a flow rate of 19200kg / hr enters the C4 evaporator V1, wherein the components and content of the mixed C4 raw material are shown in Table 1, and the flow rate of the mixed C4 2 in the top gas phase of the tank is 19200kg / h, the temperature is 64.2°C, and the pressure is 0.6MPaG, and enters the extractive distillation tower T2; the circulating lean solvent 11 (8wt% water + 92wt% N-methylpyrrolidone) is temperature-controlled to 40°C by the lean solvent cooler E7, and then enters the upper part of the extractive distillation tower T2, and the lean solvent inlet is above the mixed C4 raw material inlet; the C4 alkane in the gas phase of the top gas phase of the extractive distillation tower T2 is cooled to 40°C by the lean solvent cooler E7. After the circulating cooling water is condensed in the circulating cooling water condenser E10, the temperature is 58.9°C and the pressure is 0.55 MPaG. Subsequently, a portion of the liquid C4 alkanes 4 is refluxed to the upper part of the extractive distillation tower T2, and the other portion is extracted as the liquid C4 alkanes product 5 with an extraction rate of 7120 kg / h. The concentration of n-butane and isobutane in the C4 alkanes product is 98.5 wt%. The temperature of the rich solvent 6 in the bottom of the extractive distillation tower T2 is 101.6°C, the pressure is 0.61 MPaG, and the flow rate is 149,000 kg / hr. After heat exchange through the rich solvent heater E6 by pressure difference, it is transported to the decomposition tower T3. The temperature of the rich solvent after heat exchange is 121.3°C.

[0092] After the rich solvent is analyzed by the analysis tower T3, the gaseous C4 olefins 7 at the top of the tower are condensed by circulating chilled water in the top chilled water condenser E5, and the temperature is 11.3°C and the pressure is 0.045MPaG. A part of the C4 olefins 8 is refluxed to the upper part of the analysis tower T3, and the other part is produced as the C4 olefin product 9, with a production volume of 12080kg / h. The concentration of butene-1, isobutylene, cis-2-butene and trans-2-butene in the C4 olefin product is 98.2wt%; the temperature of the poor solvent 10 in the bottom of the analysis tower T3 is 151.8°C, the pressure is 0.09MpaG, and the flow rate is 136920kg / hr.

[0093] The lean solvent is delivered to the rich solvent heater E6 by the lean solvent delivery pump P1, and after heat exchange with the rich solvent, the temperature drops to 125°C; then it enters the third intermediate reboiler E3 of the extractive distillation tower, and after heat exchange with the process material in the tower, the temperature drops to 103°C; then it exchanges heat with the evaporator reboiler E1, and the temperature drops to 78°C; then it exchanges heat with the working fluid evaporator E11, and the temperature drops to 48°C; then it enters the lean solvent cooler E7 and exchanges heat with the circulating cooling water, and the temperature drops to 40°C; finally, the lean solvent 11 enters the extractive distillation tower T2 as an extractant for recycling.

[0094] The gaseous working fluid 12 (the working fluid is n-butane, the same below) is pressurized and heated in the working fluid compressor C2. After compression, the working fluid temperature is 91°C and the pressure is 1.2 MPaG. The compressed working fluid 13 enters the second intermediate reboiler E9 of the extractive distillation tower, where the process material with a temperature of 72°C in the tower is heated. After heat exchange, the temperature of the gaseous working fluid is 91°C, and the gaseous working fluid is condensed into a liquid phase. After being decompressed and cooled, the liquid working fluid 14 enters the working fluid storage tank V4. The temperature in the tank is 42°C and the pressure is 0.3 MPaG. The liquid working fluid 15 at the outlet of the working fluid storage tank V4 enters the working fluid evaporator E11, where it is vaporized after heat exchange with the low-grade lean solvent after heat exchange. The gaseous working fluid 16 at the outlet of the tank is returned to the working fluid compressor C2.

[0095] Comparative Example 1

[0096] like Figure 3 As shown, the process of separating mixed C4 alkanes with N-methylpyrrolidone solution includes: a mixed C4 raw material 1 with a temperature of 40°C, a pressure of 0.6 MPaG, and a flow rate of 19200 kg / hr enters a C4 evaporator V1, wherein the components and content of the mixed C4 raw material are shown in Table 1; the mixed C4 2 in the top gas phase has a flow rate of 19200 kg / h, a temperature of 64.2°C, and a pressure of 0.6 MPaG, and enters an extractive distillation tower T2; a circulating lean solvent 11 (8 wt% water + 92 wt% N-methylpyrrolidone) is temperature-controlled to 40°C by a lean solvent cooler E7, and then enters the upper part of the extractive distillation tower T2, with the lean solvent inlet being above the mixed C4 raw material inlet; the extractive distillation tower The gaseous C4 alkanes 3 at the top of tower T2 are condensed in the circulating cooling water condenser E3 at the top of the tower. After condensation by circulating cooling water, the temperature is 58.9°C and the pressure is 0.55 MPaG. A portion of the C4 alkanes 4 are refluxed to the upper part of the extractive distillation tower T2, and the other portion is extracted as the C4 alkanes product 5 at a production rate of 7120 kg / h. The concentrations of n-butane and isobutane in the C4 alkanes product are 98.2 wt%. The rich solvent 6 in the bottom of the extractive distillation tower T2 has a temperature of 101.6°C, a pressure of 0.61 MPaG, and a flow rate of 149,000 kg / hr. After heat exchange through the rich solvent heater E6 by pressure difference, it is transported to the decomposition tower T3. The temperature of the rich solvent after heat exchange is 121.3°C.

[0097] After the rich solvent is analyzed by the analysis tower T3, the gaseous C4 olefins 7 at the top of the tower are condensed by circulating chilled water in the top chilled water condenser E5, and the temperature is 11.3°C and the pressure is 0.045MPaG. A part of the C4 olefins 8 is refluxed to the upper part of the analysis tower T3, and the other part is produced as the C4 olefin product 9, with a production volume of 12080kg / h. The concentration of butene-1, isobutylene, cis-2-butene and trans-2-butene in the C4 olefin product is 98.0wt%; the temperature of the poor solvent 10 in the bottom of the analysis tower T3 is 151.8°C, the pressure is 0.09MpaG, and the flow rate is 136920kg / hr.

[0098] The lean solvent is transported to the rich solvent heater E6 by the lean solvent delivery pump P1, and after heat exchange with the rich solvent, the temperature drops to 125°C; then it enters the third intermediate reboiler E3 of the extractive distillation tower, and after heat exchange with the process material in the tower, the temperature drops to 103°C; then it exchanges heat with the evaporator reboiler E1, and the temperature drops to 78°C; then it goes to the lean solvent cooler E7, and after heat exchange with the circulating cooling water, the temperature drops to 40°C; finally, the lean solvent 11 enters the extractive distillation tower T2 as an extractant for recycling.

[0099] The separation of mixed C4-alkanes using an N-methylpyrrolidone solution method only considers solvent or steam energy recovery, failing to fully achieve energy conservation and high efficiency. The present invention utilizes a mixed C4-alkanes separation method with a heat pump system to further improve the energy efficiency of the N-methylpyrrolidone method for separating mixed C4-alkanes. Simultaneously, the separation of mixed C4-alkanes is significantly effective, meeting requirements for high recovery and high purity of C4-alkanes and C4-alkenes. A comparison of these results under the same feed conditions is shown in Table 2 below.

[0100] Table 2 Comparison of different process flows for separation of mixed carbon tetraalkenes using N-methylpyrrolidone solution

[0101]

[0102] Conclusion: 1) In the process of separating mixed C4 alkanes, the present invention adds an open heat pump system in Example 1 to enhance the recycling of low-grade heat energy of C4 alkanes, which can reduce the energy consumption of the entire system from 69.5 kg standard oil / t raw material in Comparative Example 1 to 57.0 kg standard oil / t raw material; and adds a closed heat pump system in Example 2 to enhance the recycling of low-grade heat energy of lean solvent, which can reduce the energy consumption of the entire system from 69.5 kg standard oil / t raw material in Comparative Example 1 to 56.5 kg standard oil / t raw material. 2) In the heat pump system, the process materials in the extractive distillation tower are heated in the first intermediate reboiler and / or the second intermediate reboiler of the extractive distillation tower, and the process materials are partially vaporized, thereby enhancing the gas-liquid separation effect in the tower, and the concentration of the product C4 alkanes is increased from 98.2 to 98.5 wt%; after the separation effect of the extractive distillation tower is enhanced, the decomposition effect of the rich solvent by the decomposition tower is improved, and the concentration of the product C4 olefins is increased from 98.0 wt% to 98.2 wt%. At the same time, the total amount of gas phase products did not change significantly, and the recovery rates of the products C4 alkanes and C4 olefins were higher than those of the conventional N-methylpyrrolidone method.

[0103] The present invention has been described in detail above with reference to the embodiments of the accompanying drawings. A person skilled in the art can make various modifications to the present invention based on the above description. Therefore, certain details in the embodiments should not be construed as limiting the present invention. The scope of protection of the present invention shall be determined by the scope defined by the appended claims.

Claims

1. A method for separating mixed carbon tetraalkanes using a heat pump system, comprising the following steps: Step S1, the mixed C4 raw materials enter the C4 evaporation tower or tank for vaporization to remove heavy components; Step S2, the vaporized mixed C4 enters the extractive distillation tower, and is countercurrently contacted with the lean solvent circulating from the upper part of the extractive distillation tower. The gaseous C4 alkanes are extracted from the top of the extractive distillation tower, and the rich solvent containing C4 olefins is extracted from the bottom of the extractive distillation tower and enters the desorption tower; Step S3, the rich solvent is heated and decomposed in the decomposition tower, the gaseous C4 olefins are extracted from the top of the decomposition tower, and the lean solvent is extracted from the bottom of the decomposition tower and circulated back to the extractive distillation tower as an extractant; It is characterized in that The low-grade thermal energy of the gaseous C4 alkanes extracted from the top of the extractive distillation tower is increased to high-grade thermal energy by an open heat pump system and then exchanged to the process materials in the middle of the extractive distillation tower; and / or the low-grade thermal energy of the lean solvent extracted from the kettle of the analytical tower is increased to high-grade thermal energy by a closed heat pump system after passing through a multi-stage heat exchanger and then exchanged to the process materials in the middle of the extractive distillation tower.

2. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1, wherein: In step S3, the gaseous C4 olefins extracted from the top of the analysis tower are condensed in a chilled water condenser at the top of the analysis tower, and a portion is extracted as the product, and the other portion is refluxed from the upper part of the analysis tower into the analysis tower; preferably, the temperature of the condensed C4 olefins is 0°C to 20°C, more preferably 5°C to 15°C; the top pressure of the analysis tower is 0.01MPaG to 0.5MPaG, preferably 0.04MPaG to 0.1MPaG.

3. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1 or 2, wherein: The method includes a gas-phase carbon tetraalkane low-grade thermal energy utilization step S2A or a gas-phase carbon tetraalkane condensation step S2B, The low-grade thermal energy utilization step S2A of gaseous tetraalkane specifically includes: In step S2A1, the gaseous C4 alkanes extracted from the top of the extraction distillation tower are pressurized and heated by the C4 alkanes compressor of the open heat pump system; In step S2A2, the pressurized and heated C4 alkanes exchange heat with the process material in the extractive distillation column via the first intermediate reboiler of the extractive distillation column; In step S2A3, the C4 alkanes after heat exchange enter the C4 alkanes reflux tank. Preferably, the C4 alkanes after heat exchange are decompressed and cooled by a throttle valve and condensed before entering the C4 alkanes reflux tank. More preferably, the C4 alkanes after decompressed and cooled by the throttle valve and condensed before entering the C4 alkanes reflux tank are temperature-controlled by a circulating cooling water condenser. A portion of the liquid C4 alkanes are refluxed from the upper portion of the extractive distillation tower into the extractive distillation tower, another portion of the liquid C4 alkanes are extracted as a product, and the gaseous C4 alkanes in the C4 alkanes reflux tank are returned to the C4 alkanes compressor. The gaseous phase tetraalkane condensation step S2B specifically comprises: In step S2B1, the gaseous C4 alkanes extracted from the top of the extractive distillation tower are directly condensed by the circulating cooling water condenser at the top of the extractive distillation tower; In step S2B2, the condensed C4 alkanes enter the reflux tank at the top of the extractive distillation tower, a portion of the C4 alkanes reflux into the extractive distillation tower through the upper part of the extractive distillation tower, and the other portion is extracted as a product.

4. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1 or 2, wherein: The method further includes a lean solvent low-grade thermal energy utilization step S3A, wherein step S3A specifically includes: In step S3A1, the working fluid flowing out of the outlet of the working fluid storage tank of the closed heat pump system passes through the working fluid evaporator to absorb low-grade thermal energy of the lean solvent after heat exchange in the multi-stage heat exchanger; In step S3A2, the gas phase working medium that absorbs the low-grade thermal energy is pressurized and heated by the working medium compressor of the closed heat pump system; In step S3A3, the pressurized and heated gaseous working medium exchanges heat energy with the process material in the extractive distillation tower through the second intermediate reboiler of the extractive distillation tower, and then enters the working medium storage tank. Preferably, the working medium after heat exchange is decompressed and cooled by a throttle valve and condensed before entering the working medium storage tank.

5. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1 or 2, characterized in that The method includes: analyzing the heat energy of the lean solvent extracted from the tower kettle and exchanging the heat energy in step S3B. Step S3B specifically includes: In step S3B1, the lean solvent extracted from the kettle of the desorption tower exchanges heat energy with the rich solvent through the rich solvent heater at the inlet of the desorption tower; preferably, the lean solvent extracted from the kettle of the desorption tower is preliminarily heat-exchanged with the process material in the desorption tower through the intermediate reboiler of the desorption tower, and then the heat energy is exchanged with the rich solvent through the rich solvent heater at the inlet of the desorption tower; In step S3B2, the lean solvent then exchanges heat energy with the process material in the extractive distillation column through the third reboiler in the middle of the extractive distillation column; preferably, the lean solvent first exchanges heat with the process material in the extractive distillation column through the reboiler in the kettle of the extractive distillation column, and then exchanges heat energy with the process material in the extractive distillation column through the third reboiler in the middle of the extractive distillation column; In step S3B3, the lean solvent is again passed through the C4 evaporation tower or the C4 evaporation reboiler at the bottom of the tank to exchange heat energy for the mixed C4 raw material; In step S3B4, the lean solvent then passes through the working fluid evaporator to exchange low-grade heat energy for the working fluid exiting the outlet of the working fluid storage tank; In step S3B5, the lean solvent finally passes through the lean solvent cooler to control the temperature and then enters the extractive distillation tower from the upper part of the extractive distillation tower.

6. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1 or 2, characterized in that In step S2, the kettle of the extractive distillation tower is heated by a kettle reboiler of the extractive distillation tower, preferably using steam as a heat medium; In step S3, the kettle of the desorption tower is heated by a kettle reboiler of the desorption tower, preferably using steam as a heat medium; The C4 evaporation tower or tank is a C4 evaporation tower or a C4 evaporation tank.

7. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1, wherein The low-grade heat energy of the top gas phase of the extractive distillation tower is exchanged with an open heat pump system of the process material in the extractive distillation tower, whose temperature difference with the top gas phase is 0°C to 30°C, preferably the temperature difference is 0°C to 15°C, and / or the low-grade heat energy of the lean solvent after analysis in the analysis tower is exchanged with the closed heat pump system of the process material in the extractive distillation tower, whose temperature difference with the lean solvent after heat exchange is 0°C to 30°C, preferably the temperature difference with the lean solvent after heat exchange in the multi-stage heat exchange device is 0°C to 30°C, preferably 0°C to 15°C.

8. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1, wherein: In step S2, the operating pressure of the extractive distillation tower is 0.35 MPaG to 0.75 MPaG, preferably 0.45 MPaG to 0.55 MPaG.

9. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1, wherein: In step S2, the pressure range of the gaseous carbon tetraalkane in the open heat pump system after pressurization by the compressor is 0.45 MPaG to 2.5 MPaG, preferably 1.2 MPaG to 1.8 MPaG; the pressure range of the carbon tetraalkane after decompression is 0.35 MPaG to 0.75 MPaG, preferably 0.45 MPaG to 0.55 MPaG; and / or, In step S3, the pressure range of the gas phase working medium in the closed heat pump system after pressurization by the compressor is 0.45MPaG~2.5MPaG, preferably 1.2MPaG~1.8MPaG; the pressure range of the working medium after decompression by the throttle valve is 0.2MPaG~0.6MPaG, preferably 0.25MPaG~0.35MPaG.

10. The method for separating mixed carbon tetraalkanes with a heat pump system according to claim 1, wherein: The gas phase working fluid in the closed heat pump system is preferably butane or tetrafluoroethane, more preferably n-butane; The C4 olefin content in the mixed C4 is 10 wt% to 90 wt%, preferably 20 wt% to 80 wt%; The extractant includes acetonitrile series solvents, morpholine and N-formylmorpholine series solvents, methyl ethyl ketone series solvents, sulfolane series solvents, N-methylpyrrolidone series solvents, etc., preferably an N-methylpyrrolidone solution with a water content of 1wt% to 12wt%, preferably 8wt% water content.

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