Alkane-alkene separation system for mixed light hydrocarbon

Abstract

The utility model discloses a mixed light hydrocarbon alkane-olefin separation system which comprises an extractive distillation tower, a desorption tower and a desorption tower condenser arranged at the top of the desorption tower, the middle part of the desorption tower is communicated with a tower kettle of the extractive distillation tower, and the tower kettle of the desorption tower is communicated with the upper part of the extractive distillation tower; and a gas-phase compressor for pressurizing the desorbed gas-phase olefin is also arranged between the top of the desorption tower and the desorption tower condenser. The energy consumption of the whole system can be reduced by pressurizing and heating the gas phase from the desorption tower and then condensing the gas phase by using normal-temperature circulating water. Low-pressure operation can be adopted in the desorption tower, a gas phase from the desorption tower is pressurized and heated, and then normal-temperature circulating water is adopted for condensation, so that the energy consumption of the whole system can be reduced, and meanwhile, the recovery rate of olefin is higher than that of olefin in similar NMP (N-Methyl Pyrrolidone) methods.

Description

Technical Field

[0001] The utility model belongs to the technical field of chemical process, and in particular relates to a mixed light hydrocarbon alkane-alkene separation system. Background Art

[0002] With the continuous deepening of oil conversion policies, the comprehensive utilization of C4 hydrocarbons has attracted increasing attention. The large amount of C4 hydrocarbons urgently needs to find new chemical utilization pathways. C4 separation has become an emerging approach to solve this problem. It separates the alkanes and olefins in C4 hydrocarbons and reuses them to improve the comprehensive utilization rate of C4 hydrocarbons.

[0003] Mixed C4 hydrocarbons primarily contain C3, isobutane, n-butane, n-butene (including butene-1, cis-2-butene, and trans-2-butene), and isobutene. Cracked C4 contains a high olefin content, while refinery C4 contains a high alkane content. The butane and butene components of mixed C4 hydrocarbons have similar boiling points and very similar volatility, making them difficult to separate using conventional distillation. Therefore, specialized distillation methods are often used for separation.

[0004] The extractive distillation process is mainly adopted in China. Its process is to add a suitable solvent to the mixed hydrocarbon of butane and butene, which can change the relative volatility between butane and butene, so that alkanes and olefins are separated. The solvent can be a mixture of one or more solvents, such as acetonitrile (ACN), sulfolane, nitrogen-methyl pyrrolidone (NMP), a mixture of methyl ethyl ketone (MEK) and N-formylmorpholine (NFM), a mixture of morpholine (MOR) and N-formylmorpholine (NFM), etc. According to the different solvents used for extractive distillation separation of alkanes and olefins in mixed C4 hydrocarbons, more typical extractive distillation separation processes include acetonitrile (ACN) process, morpholine (MOR) and N-formylmorpholine (NFM) process, methyl ethyl ketone (MEK) process, etc.

[0005] Patent CN107879882A discloses a method and apparatus for producing n-butane, isobutane, and 2-butene from mixed C4. In the presence of an initiator and an organic solvent, the mixed C4 is contacted with maleic anhydride to undergo a copolymerization reaction to achieve separation. CN102344330A provides a mixed solvent that can increase the relative volatility of the C4 components and improve solvent selectivity. The main components are NMP, an inorganic salt, and water, but it uses a conventional extractive distillation production process. CN106478341A provides an apparatus and process for separating C4 fractions using a binary mixed solvent, but it uses a conventional extractive distillation process. The above inventions all explore the separation of mixed C4 hydrocarbons. The main content is the development of extractants. The process designs are all conventional extractive distillation processes. Energy-saving optimization is not considered in the process designs, and none of them can achieve high efficiency and energy-saving effects. In particular, the alkane-ene separation process technology using N-methylpyrrolidone as the extractant has no application cases in China, and further research is needed in terms of separation effect and energy-saving technology. Utility Model Content

[0006] The utility model aims to provide a mixed light hydrocarbon alkane alkene separation system in view of the technical problem of high system energy consumption during the separation process of the existing NMP method light hydrocarbon alkane alkene separation technology.

[0007] The mixed light hydrocarbon alkane alkene separation system of the utility model comprises:

[0008] Extractive distillation tower;

[0009] a decomposition tower, wherein the middle portion of the decomposition tower is connected to the kettle of the extractive distillation tower, and the kettle of the decomposition tower is connected to the upper portion of the extractive distillation tower;

[0010] A decomposition tower condenser is provided at the top of the decomposition tower;

[0011] Characterized in that, the mixed light hydrocarbon system further comprises:

[0012] A gas phase compressor for pressurizing the gas phase olefins after desorption is arranged between the top of the desorption tower and the desorption tower condenser.

[0013] Preferably, the outlet of the gas phase compressor is directly connected to the inlet of the analytical tower condenser.

[0014] Preferably, the outlet of the gas phase compressor is first connected to the reboiler for heat exchange, and then connected to the inlet of the analytical tower condenser.

[0015] Preferably, the analytical tower condenser adopts a chilled water condenser or a normal temperature circulating water condenser, and preferably a normal temperature circulating water condenser.

[0016] Preferably, the reboiler is an intermediate reboiler in an extractive distillation tower, an intermediate reboiler in a decomposition tower, or a kettle reboiler in a feed evaporation tower.

[0017] Preferably, the mixed light hydrocarbon system further comprises:

[0018] The feed evaporation tower has a feed inlet, and the top of the feed evaporation tower is connected to the inlet of the extraction distillation tower.

[0019] Preferably, the extractive distillation column comprises:

[0020] an upper tower, wherein the top of the feed evaporation tower is connected to the inlet of the upper tower;

[0021] The top of the lower tower is connected to the kettle of the upper tower, and the kettle of the lower tower is connected to the upper part of the analytical tower.

[0022] Preferably,

[0023] The tower kettle of the analytical tower is provided with an analytical tower reboiler;

[0024] The lower tower of the extractive distillation tower has an extractive distillation tower kettle reboiler and an extractive distillation tower intermediate reboiler;

[0025] The tower kettle of the feed evaporation tower has an evaporation tower reboiler;

[0026] Preferably, the reboiler of the analytical column is heated by steam.

[0027] Preferably,

[0028] The top of the upper tower of the extractive distillation tower is connected to an extractive distillation tower condenser, and the outlet end of the extractive distillation tower condenser has a reflux passage and an alkane production outlet communicated with the upper part of the upper tower;

[0029] The outlet end of the analytical tower condenser is provided with a reflux passage and an olefin production outlet communicated with the upper portion of the analytical tower.

[0030] Preferably, the mixed light hydrocarbon alkane-olefin separation system also has a temperature-controlled heat exchanger. The lean solvent outlet of the kettle of the analysis tower is connected to the intermediate reboiler of the extractive distillation tower for heat exchange, and then connected to the reboiler of the evaporation tower for heat exchange, and finally connected to the temperature-controlled heat exchanger for heat exchange, and then connected to the upper part of the upper tower of the extractive distillation tower.

[0031] The utility model adopts a mixed light hydrocarbon alkane alkene separation method, which comprises the following steps:

[0032] Step S1, mixed light hydrocarbons enter the extractive distillation tower and are countercurrently contacted with the lean solvent from the desorption tower, and the heavy components containing olefins are dissolved in the solvent to form a rich solvent and enter the desorption tower;

[0033] Step S2, the rich solvent is decomposed in the decomposition tower, and the olefin-containing gas phase is extracted from the top of the decomposition tower. The decomposed lean solvent comes out of the bottom of the decomposition tower and then circulates from the upper part of the extractive distillation tower into the extractive distillation tower as the extraction solvent;

[0034] In step S2, the gas phase containing mixed olefins extracted from the top of the desorption tower is first pressurized by a gas phase compressor to increase the temperature, and then condensed by a normal temperature circulating water desorption tower condenser before being extracted.

[0035] Preferably,

[0036] In step S2, the operating pressure at the top of the analytical tower is 0.01 MPaG to 0.4 MPaG, preferably 0.1 MPaG to 0.4 MPaG, and more preferably 0.12 MPaG.

[0037] Preferably, in step S2, the olefin-containing gas phase extracted from the top of the decomposition tower is first pressurized and heated by a gas phase compressor, and the heated gas phase directly enters the condenser of the normal temperature circulating water decomposition tower for condensation. Preferably, the pressure range of the gas phase after pressurization by the compressor is 0.42 MPaG-2.6 MPaG, and more preferably, the pressure range of the gas phase after pressurization by the compressor is 0.42 MPaG-1.8 MPaG.

[0038] Preferably, in step S2, the olefin-containing gas phase extracted from the top of the desorption tower is first pressurized by a gas phase compressor to increase the temperature, and the heated gas phase is first heat-exchanged with a reboiler, and then enters the condenser of the normal temperature circulating water desorption tower for condensation.

[0039] Preferably, the reboiler is an intermediate reboiler in an extractive distillation tower, an intermediate reboiler in a decomposition tower, or a kettle reboiler in a feed evaporation tower.

[0040] Preferably, before step S1, the method further includes:

[0041] In the pretreatment step S0, the mixed light hydrocarbons first enter the feed evaporation tower for vaporization to remove the heavy components in the feed.

[0042] Preferably, the extractive distillation tower comprises an upper tower and a lower tower;

[0043] Step S1 specifically includes:

[0044] The mixed light hydrocarbons after vaporization and de-heavy treatment enter the upper tower and come into countercurrent contact with the lean solvent from the desorption tower. The mixed light hydrocarbons undergo extractive distillation in the upper and lower towers. The light components are extracted from the top of the upper tower, and the heavy components are dissolved in the solvent and extracted from the bottom of the lower tower to enter the desorption tower.

[0045] Preferably, the mixed light hydrocarbons are mixed C4s, the light components include n-butane, isobutane, C3s and a small amount of butene-1, and the heavy components include butene-1, cis-2-butene and trans-2-butene.

[0046] Preferably,

[0047] The kettle of the analytical tower uses an analytical tower reboiler, and preferably, the analytical tower reboiler is heated by steam;

[0048] The lower tower of the extractive distillation tower is heated by the extractive distillation tower kettle reboiler and the extractive distillation tower intermediate reboiler;

[0049] The kettle of the feed evaporation tower is heated by the evaporation tower reboiler;

[0050] Preferably, the parsed lean solvent comes out of the kettle of the parsing tower, passes through the intermediate reboiler of the extractive distillation tower, the reboiler of the evaporation tower and the temperature-controlled heat exchanger, and then circulates from the upper part of the extractive distillation tower into the extractive distillation tower as the extraction solvent.

[0051] Preferably,

[0052] In step S1, the light component is extracted from the top of the extractive distillation tower, condensed in the extractive distillation tower condenser, and a portion of it is refluxed to the extractive distillation tower, and the other portion is extracted through the alkane extraction port;

[0053] In step S2, the gaseous mixed olefins are extracted from the top of the desorption tower, first pressurized and heated by a gas phase compressor, and then condensed by a normal temperature circulating water desorption tower condenser. A portion of the mixed olefins is refluxed to the desorption tower, and the other portion is extracted through the olefin extraction port.

[0054] Preferably,

[0055] The solvent is acetonitrile (ACN), sulfolane, N-methylpyrrolidone (NMP), a mixture of methyl ethyl ketone (MEK) and N-formylmorpholine (NFM), or a mixture of morpholine (MOR) and N-formylmorpholine (NFM), preferably an N-methylpyrrolidone solution, and the water content of the N-methylpyrrolidone solution is 1 wt% to 12 wt%, preferably 3 wt% to 10 wt%;

[0056] The concentration of butene in the mixed C4 is 10 wt% to 90 wt%, preferably 20 wt% to 80 wt%.

[0057] The positive progress effect of this utility model is:

[0058] 1) In the process of separating mixed light hydrocarbons from alkanes and alkenes, the utility model can reduce the energy consumption of the entire system by pressurizing and heating the gas phase coming out of the analytical tower and then condensing it with normal temperature circulating water.

[0059] 2) Furthermore, the desorption tower can be operated at a lower pressure, the gas phase exiting the desorption tower is pressurized and heated, and then condensed using circulating water at room temperature. This not only reduces the energy consumption of the entire system, but also increases the olefin recovery rate compared to that of a similar NMP process, thus achieving a synergistic effect in terms of energy consumption and olefin recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Schematic diagram of the mixed light hydrocarbon alkane-olefin separation system of Example 1;

[0061] Figure 2 Schematic diagram of the mixed light hydrocarbon alkane-olefin separation system of Example 2;

[0062] Figure 3 Schematic diagram of the mixed light hydrocarbon alkane-olefin separation system of Comparative Example 1. DETAILED DESCRIPTION

[0063] The following describes the implementation 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 specific implementations, 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.

[0064] like Figure 1 As shown, the mixed C4 light hydrocarbon alkane-olefin separation system of the present invention comprises a feed evaporation tower T1, an extractive distillation tower (upper tower T2 and lower tower T3) and a decomposition tower T4, as well as an evaporation tower reboiler E1, an extractive distillation tower kettle reboiler E2, an extractive distillation tower intermediate reboiler E3 and a decomposition tower reboiler E4, and also includes a decomposition tower condenser E5, an extractive distillation tower condenser E6, a temperature control heat exchanger E7 and a gas phase compressor K1.

[0065] Continue as Figure 1 As shown, the feed evaporation tower T1 has a feed inlet, and the top of the feed evaporation tower T1 is connected to the inlet at the bottom of the upper tower T2 of the extractive distillation tower. The top of the upper tower T2 is connected to the extractive distillation tower condenser E6, which has an outlet end that is connected to the top of the upper tower T2 via a reflux passage and is also equipped with an alkane extraction outlet. The upper tower T2 is also connected in series with the lower tower T3, that is, the bottom of the upper tower T2 is connected to the top of the lower tower T3. The bottom of the lower tower T3 is also connected to the middle of the desorption tower T4. The top of the desorption tower T4 is also connected in sequence to the gas phase compressor K1 and the desorption tower condenser E5. The gas phase compressor K1 is located between the top of the desorption tower T4 and the desorption tower condenser E5, that is, the outlet of the gas phase compressor K1 is connected to the inlet of the desorption tower condenser E5. The desorption tower condenser E5 is a condenser that uses ambient temperature circulating water.

[0066] Continue as Figure 1 As shown, the outlet end of the analytical tower condenser E5 has a reflux passage and an olefin extraction outlet connected to the upper part of the analytical tower T4. In addition, the bottom of the analytical tower T4 is also provided with a lean solvent outlet, and the feed evaporation tower T1, the lower tower T3 of the extractive distillation tower and the bottom of the analytical tower T4 are also provided with an evaporation tower reboiler E1, an extractive distillation tower bottom reboiler E2 and an analytical tower reboiler E4 respectively. The middle part of the lower tower T3 of the extractive distillation tower is also provided with an extractive distillation tower intermediate reboiler E3. Figure 1 As shown, the lean solvent outlet at the bottom of the analytical tower T4 is first connected to the intermediate reboiler E3 of the extractive distillation tower for heat exchange, then connected to the intermediate reboiler E3 of the extractive distillation tower for heat exchange, then connected to the reboiler E1 of the evaporation tower for heat exchange, and finally connected to the temperature control heat exchanger E7 for heat exchange, and finally connected to the upper part of the upper tower T2 of the extractive distillation tower.

[0067] As another example, Figure 2 As shown. Figure 1 The difference is that, in order to improve the heat utilization rate after pressurization and temperature increase, the outlet of the gas phase compressor K1 is first connected to the reboiler for heat exchange, and then connected to the inlet of the analytical column condenser E5. The reboiler includes the intermediate reboiler E8 of the extractive distillation column, the intermediate reboiler of the analytical column (not shown) or the reboiler E1 of the feed evaporation column. Preferably, as Figure 2 As shown, the reboiler is located in the middle of the lower tower T3 of the extractive distillation tower, i.e., the intermediate reboiler E8 of the extractive distillation tower. The other components and their connection relationships are the same as Figure 1 shown.

[0068] The following scheme will further illustrate the method of separating alkanes and alkenes in mixed light hydrocarbons using the above-mentioned mixed light hydrocarbon alkane and alkene separation system.

[0069] Option 1

[0070] use Figure 1 The mixed light hydrocarbon alkane-alkene separation system shown comprises the following steps for separating alkanes and alkenes:

[0071] In the pretreatment step S0, a mixed C4 hydrocarbon feedstock from different sources (etherified C4, residual C4, FCC C4, residual C4 or mixed C4 hydrocarbons from other sources) is fed into a feed evaporation tower T1 from a feed port with a butene concentration of 10 wt% to 90 wt%, preferably a butene concentration of 20% to 80%. The feedstock is vaporized and the heavy components in the feedstock are removed. The evaporation tower reboiler E1 in the kettle of the feed evaporation tower T1 provides heat energy for vaporization and weight removal.

[0072] Step S1, the vaporized raw material mixed light hydrocarbons are extracted from the top of the feed evaporation tower T1 and enter the upper tower T2 of the extractive distillation tower. The mixed light hydrocarbons are countercurrently contacted with the lean solvent extracted from the lean solvent outlet of the decomposition tower T4 tower bottom in the extractive distillation tower. The solvent is selected from acetonitrile (ACN), sulfolane, N-methylpyrrolidone (NMP), a mixture of methyl ethyl ketone (MEK) and N-formylmorpholine (NFM), a mixture of morpholine (MOR) and N-formylmorpholine (NFM), preferably N-methylpyrrolidone, and the water content of the N-methylpyrrolidone solution is 1wt% to 12wt%, preferably 3wt% to 10wt%. The mixed light hydrocarbons are extractively distilled in the upper tower T2 of the extractive distillation tower and the lower tower T3 of the extractive distillation tower connected in series therewith. The extractive distillation tower bottom reboiler E2 of the lower tower T3 tower bottom and the extractive distillation tower intermediate reboiler E3 provide the heat energy required for the extractive distillation. The extractive distillation column's kettle reboiler E2 is heated with medium-pressure steam for startup and heat replenishment. After extractive distillation, the heavy components of the mixed light hydrocarbons, including butene-1, cis-2-butene, and trans-2-butene, are dissolved in a solvent to form a rich solvent. This is withdrawn from the kettle of lower tower T3 and fed to desorption tower T4. Light components, including n-butane, isobutane, C3, and a small amount of butene-1, are withdrawn from the top of upper tower T2. After condensation in extractive distillation condenser E6, a portion is refluxed to upper extractive distillation tower T2, while the remaining portion is directly withdrawn from the alkane extraction port as mixed butane product.

[0073] Step S2, the rich solvent is parsed in the parsing tower T4, and the pressure range of the top of the parsing tower T4 is 0.01MpaG to 0.4MpaG, preferably 0.1MpaG to 0.4MpaG, more preferably 0.12MPaG. The parsing tower reboiler E4 of the tower kettle of the parsing tower T4 provides the heat energy required for parsing. The parsing tower reboiler E4 is heated by medium-pressure steam for start-up and heat supplement. After parsing, the lean solvent forming the liquid phase is extracted from the tower kettle of the parsing tower T4, first passes through the intermediate reboiler E3 of the extractive distillation tower, the evaporation tower reboiler E1 and the temperature-controlled heat exchanger E7 respectively, and finally enters the extractive distillation tower from the upper part of the extractive distillation tower T2 and is recycled as an extraction solvent. The olefin-containing gas phase is extracted from the top of the decomposition tower T4, first pressurized and heated by the gas phase compressor K1, with the pressure range after pressurization being 0.42MPaG-1.8MpaG, and then condensed by the normal temperature circulating water decomposition tower condenser E5. Finally, part of the system refluxes into the decomposition tower T4, and the other part is directly extracted from the olefin extraction port as a mixed butene product.

[0074] Option 2

[0075] use Figure 2 The mixed light hydrocarbon alkane-olefin separation system shown.

[0076] The implementation method of the pre-processing step S0 and step S1 is the same as Figure 1 The method of the mixed light hydrocarbon alkane-olefin separation system shown is the same, except that: in step S2, after desorption in desorption tower T4, the lean solvent forming the liquid phase is extracted from the bottom of desorption tower T4, first passing through the intermediate reboiler E3 of the extractive distillation tower, the reboiler E1 of the evaporation tower, and the temperature-controlled heat exchanger E7, and finally entering the extractive distillation tower from the upper part of the extractive distillation tower T2 and being recycled as the extraction solvent. The olefin-containing gas phase is extracted from the top of desorption tower T4, first pressurized and heated by the gas phase compressor K1, with the pressure range of 0.42MPaG-2.6MPaG after pressurization, and then heat exchanged in a reboiler, such as the intermediate reboiler E8 of the extractive distillation tower, and then condensed by the normal temperature circulating water desorption tower condenser E5. Finally, a portion of the system is refluxed to the desorption tower T4, and the other portion is directly extracted from the olefin extraction port as a mixed butene product.

[0077] Table 1 Composition and content of C4 after ether in the separation of mixed light hydrocarbons and alkanes in the utility model

[0078]

[0079]

[0080] Example 1

[0081] like Figure 1 As shown, etherified C4 at a temperature of 40°C and a flow rate of 34,000 kg / hr enters feed evaporation tower T1. The specific composition and content of etherified C4 are shown in Table 1. The overhead gas phase has a flow rate of 33,999 kg / h, a temperature of 56.75°C, and a pressure of 0.57 MPaG, entering the lower portion of upper tower T2 of the extractive distillation tower. NMP lean solvent with an 8% water content from the bottom of desorption tower T4 is heated to 50°C in temperature-controlled heat exchanger E7 and enters the upper portion of upper tower T2 of the extractive distillation tower. Extractive distillation is completed in upper tower T2 and lower tower T3 of the extractive distillation tower. The overhead product of upper tower T2 is condensed with recycled water in extractive distillation tower condenser E6, reaching a temperature of 41.4°C and a pressure of 0.45 MPaG. A portion is refluxed to the upper portion of upper tower T2, and the remaining portion is withdrawn as butane product at a rate of 21,000 kg / h. The concentration of isobutane and normal butane in the produced product is 98.5 wt%.

[0082] The liquid phase from the bottom of extractive distillation tower T3 was pumped to desorption tower T4 at a feed temperature of 144°C and a pressure of 0.55 MPaG. After desorption in the desorption tower, the top gaseous product had a temperature of 41°C and a pressure of 0.12 MPaG. It was compressed to 0.42 MPaG and a temperature of 79.3°C by gas compressor K1. The liquid was then cooled to 70°C in desorption tower condenser E5 using ambient temperature circulating water. A portion of the liquid was depressurized to 0.12 MPaG and refluxed into desorption tower T4. The remaining portion was extracted as butene product at a rate of 12,968 kg / h, with a combined concentration of 98.53 wt% for butene-1, cis-butene, and trans-butene.

[0083] The temperature of the lean solvent in the bottom of the analytical tower T4 is 155.4°C. After heat exchange with the analytical tower reboiler E4, the temperature drops to 91°C. After heat exchange with the evaporation tower reboiler E1, the temperature is 71°C. Then, after heat exchange with circulating water in the temperature-controlled heat exchanger E7, the temperature is reduced to 50°C. Then, the lean solvent enters the upper part of the extractive distillation tower T2 as the extraction solvent.

[0084] Example 2

[0085] like Figure 2 As shown, etherified C4 at a temperature of 45°C and a flow rate of 34,000 kg / hr enters feed evaporation tower T1. The specific composition and content of etherified C4 are shown in Table 1. The overhead gaseous phase has a flow rate of 33,999 kg / h, a temperature of 56.75°C, and a pressure of 0.57 MPaG, and enters the lower portion of upper extractive distillation tower T2. Lean NMP solvent with an 8% water content from the bottom of desorption tower T4 is heated to 50°C in temperature-controlled heat exchanger E7 and enters the upper portion of upper extractive distillation tower T2. Extractive distillation is completed in upper extractive distillation tower T2 and lower extractive distillation tower T3. The overhead product of upper extractive distillation tower T2 is condensed in extractive distillation tower condenser E6 with recycled water, reaching a temperature of 41.4°C and a pressure of 0.45 MPaG. A portion of the product is refluxed to the upper portion of upper extractive distillation tower T2, and the remaining portion is withdrawn as butane product at a rate of 21,000 kg / h. The concentration of isobutane and normal butane in the produced product is 98.5 wt%.

[0086] The liquid phase from the bottom of extractive distillation tower T3 was pumped to desorption tower T4, where the feed temperature was 140°C and the feed pressure was 0.55 MPaG. After desorption in the desorption tower, the top gaseous product had a temperature of 41°C and a pressure of 0.12 MPaG. It was compressed to 1.2 MPaG and a temperature of 123°C by gas compressor K1. The product then passed through reboiler E8 in the extractive distillation tower, where its temperature dropped to 86°C. The product was then cooled to 70°C by condenser E5 in the desorption tower using ambient temperature circulating water. A portion of the product was depressurized to 0.12 MPaG and refluxed to desorption tower T4, while the remaining portion was extracted as butene product at a rate of 12,968 kg / h. The combined concentration of butene-1, cis-butene, and trans-butene was 98.53 wt%.

[0087] The temperature of the lean solvent in the bottom of the analytical tower T4 is 155.4°C. After heat exchange with the intermediate reboiler E3 of the extractive distillation tower, the temperature drops to 91°C. After heat exchange with the reboiler E1 of the evaporation tower, the temperature is 71°C. Then, after heat exchange with circulating water in the temperature-controlled heat exchanger E7, the temperature is reduced to 50°C. Then, the lean solvent enters the upper part of the upper tower T2 of the extractive distillation tower as the extraction solvent.

[0088] Comparative Example 1

[0089] like Figure 3 As shown, the conventional alkane-olefin separation process of the NMP method includes: etherified C4 at a temperature of 40°C and a flow rate of 34,000 kg / hr enters the feed evaporation tower T1, wherein the specific composition and content of the etherified C4 are shown in Table 1; the top gas phase flow rate is 33,999 kg / h, the temperature is 56.75°C, and the pressure is 0.57 MPaG, and enters the lower part of the upper tower T2 of the extractive distillation tower. The 8% water-containing NMP lean solvent from the bottom of desorption tower T4 is heated to 50°C in temperature-controlled heat exchanger E7 and then fed into the upper portion of extractive distillation tower T2. Extractive distillation is then completed in upper extractive distillation tower T2 and lower extractive distillation tower T3. The overhead product from upper extractive distillation tower T2 is condensed in extractive distillation tower condenser E6 with recycled water to a temperature of 41.4°C and a pressure of 0.45 MPaG. A portion of the product is refluxed to the upper portion of upper extractive distillation tower T2, while the remaining portion is extracted as butane product at a rate of 21,000 kg / h. The isobutane and n-butane concentrations in the extracted product are 97.3 wt%.

[0090] The liquid phase from the bottom of extractive distillation tower T3 was pumped to desorption tower T4, where the feed temperature was 144°C and the feed pressure was 0.55 MPaG. After desorption in the desorption tower, the overhead gaseous product was condensed in desorption tower condenser E5 using ambient temperature circulating water to a temperature of 52.2°C. Prior to condensation with ambient temperature circulating water, the overhead gaseous product pressure was 0.45 MPaG, and the pressure of the condensed gaseous product was 0.43 MPaG. A portion of the cooled stream was refluxed to desorption tower T4, while the remainder was extracted as butene product at a rate of 13,078 kg / h, with a combined concentration of 97.7 wt% for butene-1, cis-butene, and trans-butene.

[0091] The temperature of the lean solvent in the bottom of the analytical tower T4 is 188.4°C. After being heated by the reboiler E1 of the evaporation tower and then heat exchanged with the temperature-controlled heat exchanger E7 through circulating water, the temperature is reduced to 50°C. Then the lean solvent enters the upper part of the upper tower T2 of the extractive distillation tower as the extraction solvent.

[0092] Conventional NMP-based alkane-olefin separation technologies operate their desorption tower at relatively high pressures, with the overhead condenser cooled by circulating water. This results in high temperatures at the bottom and top of the desorption tower, leading to high system energy consumption and significant product losses. The present utility model operates the desorption tower at a lower pressure, with the overhead gas either pressurized and heated by a compressor followed by circulating water cooling, or pressurized and heated by a compressor followed by heat recovery in a reboiler before water cooling. This not only achieves energy savings for the system, but also achieves higher olefin recovery rates than comparable systems. A comparison of these performances under the same feed conditions is shown in Table 1.

[0093] Table 2 Comparison between the method and system for separating alkanes and alkenes from mixed C4 by the NMP method of the present invention and the existing NMP method

[0094]

[0095] Conclusion: 1) In the process of separating mixed light hydrocarbon alkanes and alkenes, the utility model can reduce the energy consumption of the entire system from 97.6 kg standard oil / t raw material in Comparative Example 1 to 60.9 kg standard oil / t raw material by appropriately controlling the operating pressure of the gas phase at the top of the analysis tower at low pressure, and then pressurizing and heating the gas phase coming out of the analysis tower and then condensing it with normal temperature circulating water. 2) Furthermore, the low-pressure and low-temperature operation in the analysis tower can reduce the amount of solvent NMP carried out from the top of the tower, reducing the amount of solvent in the product, and increasing the concentration of olefins in the gas phase product from 97.7% to 98.6%, thereby improving the product quality. When the total amount of gas phase products is equivalent, the recovery rate of olefins is higher than that of olefins of the same NMP method. Therefore, there is a synergistic effect in reducing energy consumption and improving the recovery rate of olefins.

[0096] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. 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, and the present invention shall be protected within the scope of the appended claims.

Claims

1. A mixed light hydrocarbon alkane olefin separation system, comprising: Extractive distillation tower; a decomposition tower, wherein the middle portion of the decomposition tower is connected to the kettle of the extractive distillation tower, and the kettle of the decomposition tower is connected to the upper portion of the extractive distillation tower; A decomposition tower condenser is provided at the top of the decomposition tower; Characterized in that, the mixed light hydrocarbon system further comprises: A gas phase compressor for pressurizing the gas phase olefins after desorption is arranged between the top of the desorption tower and the desorption tower condenser.

2. The mixed light hydrocarbon alkane-olefin separation system according to claim 1, characterized in that The outlet of the gas phase compressor is directly connected to the inlet of the analytical tower condenser.

3. The mixed light hydrocarbon alkane-olefin separation system according to claim 1, characterized in that The outlet of the gas phase compressor is first connected to the reboiler for heat exchange, and then connected to the inlet of the analytical tower condenser.

4. The mixed light hydrocarbon alkane-olefin separation system according to claim 1, characterized in that The analytical tower condenser adopts a chilled water condenser or a normal temperature circulating water condenser, and preferably uses a normal temperature circulating water condenser.

5. The mixed light hydrocarbon alkane-olefin separation system according to claim 3, characterized in that The reboiler is an intermediate reboiler in an extractive distillation tower, an intermediate reboiler in a decomposition tower, or a kettle reboiler in a feed evaporation tower.

6. The mixed light hydrocarbon alkane-olefin separation system according to claim 1, characterized in that The mixed light hydrocarbon system also includes: The feed evaporation tower has a feed inlet, and the top of the feed evaporation tower is connected to the inlet of the extraction distillation tower.

7. The mixed light hydrocarbon alkane-olefin separation system according to claim 6, characterized in that The extractive distillation column comprises: an upper tower, wherein the top of the feed evaporation tower is connected to the inlet of the upper tower; The top of the lower tower is connected to the kettle of the upper tower, and the kettle of the lower tower is connected to the upper part of the analytical tower.

8. The mixed light hydrocarbon alkane-olefin separation system according to claim 7, characterized in that The kettle of the decomposition tower is provided with a decomposition tower reboiler, and preferably, the decomposition tower reboiler is heated by steam; The lower tower of the extractive distillation tower has an extractive distillation tower kettle reboiler and an extractive distillation tower intermediate reboiler; The tower bottom of the feed evaporation tower is provided with an evaporation tower reboiler.

9. The mixed light hydrocarbon alkane-olefin separation system according to claim 7, characterized in that The top of the upper tower of the extractive distillation tower is connected to an extractive distillation tower condenser, and the outlet end of the extractive distillation tower condenser has a reflux passage and an alkane production outlet communicated with the upper part of the upper tower; The outlet end of the analytical tower condenser is provided with a reflux passage and an olefin production outlet communicated with the upper portion of the analytical tower.

10. The mixed light hydrocarbon alkane-olefin separation system according to claim 8, characterized in that The mixed light hydrocarbon alkane alkene separation system also has a temperature-controlled heat exchanger. The lean solvent outlet of the kettle of the analytical tower is connected to the intermediate reboiler of the extractive distillation tower for heat exchange, and then connected to the reboiler of the evaporation tower for heat exchange, and finally connected to the temperature-controlled heat exchanger for heat exchange, and then connected to the upper part of the upper tower of the extractive distillation tower.

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