Method for separating mixed light hydrocarbons from alkanes and olefins

Abstract

The present invention discloses a method for separating mixed light hydrocarbons from alkanes and alkenes, comprising: mixed light hydrocarbons enter an extractive distillation tower and countercurrently contact with a lean solvent from a decomposition tower, the rich solvent enters a decomposition tower for decomposition, a gas phase containing olefins is extracted from the top of the decomposition tower, the lean solvent after decomposition comes out of the tower kettle of the decomposition tower and then circulates from the upper part of the extractive distillation tower into the extractive distillation tower as an extraction solvent; the gas phase containing mixed olefins extracted from the top of the decomposition tower is first pressurized and heated by a gas phase compressor, and then condensed by a normal temperature circulating water decomposition tower condenser before extraction. The present invention can reduce the energy consumption of the entire system by pressurizing and heating the gas phase coming out of the decomposition tower and then condensing it with normal temperature circulating water. In addition, a relatively low pressure operation can be adopted in the decomposition tower, and the gas phase coming out of the decomposition tower is pressurized and heated, and then condensed with normal temperature circulating water, which not only reduces the energy consumption of the entire system, but also the recovery rate of olefins is higher than that of olefins of the same NMP method.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical process, and in particular relates to a method for separating mixed light hydrocarbon alkanes and alkenes. Background Art

[0002] With the deepening of oil conversion policy, the comprehensive utilization of C4 hydrocarbons has attracted more and more attention. A large number of C4 hydrocarbons urgently need to find new chemical utilization methods. C4 separation is an emerging way to solve this problem. The alkanes and olefins in C4 hydrocarbons are separated and reused to improve the comprehensive utilization rate of C4 hydrocarbons.

[0003] Mixed C4 hydrocarbons mainly contain C3, isobutane, n-butane, n-butene (including butene-1, cis-2-butene, trans-2-butene), isobutene and other components. The olefin content in cracked C4 is relatively high, and the alkane content in refinery C4 is relatively high. The boiling points of butane and butene components in mixed C4 hydrocarbons are close, and their volatility is very close. It is difficult to separate them by ordinary distillation, so special distillation methods are often used for separation.

[0004] The extractive distillation process is mainly used in China. The 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), cyclopentane, 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, the 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 production method and device for producing n-butane, isobutane and 2-butene from mixed C4, which contacts the mixed C4 with maleic anhydride in the presence of an initiator and an organic solvent, and performs copolymerization to achieve the purpose of separation; CN102344330A provides a mixed solvent that can improve the relative volatility between the components of C4 and improve the solvent selectivity, and the main components are: NMP, inorganic salt and water, but it adopts a common extraction distillation production process; CN106478341A provides a device and process for separating C4 fractions using a binary mixed solvent, but it adopts a common extraction distillation process. The above inventions have explored the separation of mixed C4 hydrocarbons, and the main content is the development of extractants. The process design is a common extraction distillation process. Energy-saving optimization is not considered in the process design, and all fail to achieve high efficiency and energy-saving effects. In particular, the alkane-ene separation process technology using N-methylpyrrolidone as an extractant has no application cases in China, and further research is needed in terms of separation effect and energy-saving technology. Summary of the invention

[0006] The present invention aims to provide a method for separating mixed light hydrocarbon alkanes and olefins, aiming at the technical problem of high system energy consumption in the separation process of the existing NMP method light hydrocarbon alkane olefin separation technology.

[0007] The mixed light hydrocarbon alkane-olefin separation method of the present invention comprises the following steps:

[0008] Step S1, the mixed light hydrocarbons enter the extractive distillation tower and are countercurrently contacted with the lean solvent from the analytical tower, and the heavy components containing olefins are dissolved in the solvent to form a rich solvent and enter the analytical tower;

[0009] Step S2, the rich solvent is decomposed in the decomposition tower, the gas phase containing olefins is extracted from the top of the decomposition tower, and the decomposed lean solvent comes out from the bottom of the decomposition tower and then circulates into the extractive distillation tower from the upper part of the extractive distillation tower as an extraction solvent;

[0010] Wherein, in step S2, the gas phase containing mixed olefins extracted from the top of the analysis tower is first pressurized by a gas phase compressor to increase the temperature, and then condensed by a normal temperature circulating water analysis tower condenser before being extracted.

[0011] Preferably,

[0012] 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.

[0013] Preferably, in step S2, the olefin-containing gas phase extracted from the top of the analysis 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 analysis tower for condensation. Preferably, the pressure range of the gas phase after pressurization by the compressor is 0.42MPaG-2.6MpaG, and more preferably, the pressure range of the gas phase after pressurization by the compressor is 0.42MPaG-1.8MpaG.

[0014] Preferably, in step S2, the olefin-containing gas phase extracted from the top of the analysis tower is first pressurized by a gas compressor to increase the temperature, and the heated gas phase is first heat-exchanged with a reboiler, and then enters a condenser of a normal temperature circulating water analysis tower for condensation.

[0015] Preferably, the reboiler is an intermediate reboiler of an extractive distillation tower, an intermediate reboiler of a desorption tower, or a kettle reboiler of a feed evaporation tower.

[0016] Preferably, before step S1, the method further includes:

[0017] 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.

[0018] Preferably, the extractive distillation tower comprises an upper tower and a lower tower;

[0019] Step S1 specifically includes:

[0020] The mixed light hydrocarbons after vaporization and de-heavy treatment enter the upper tower and are countercurrently contacted with the lean solvent from the analytical tower. The mixed light hydrocarbons are extracted and distilled 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 and enter the analytical tower.

[0021] Preferably, the mixed light hydrocarbons are mixed C4s, the light components include normal butane, isobutane, C3 and a small amount of butene-1, and the heavy components include butene-1, cis-2-butene and trans-2-butene.

[0022] Preferably,

[0023] The kettle of the analytical tower uses an analytical tower reboiler, and preferably, the analytical tower reboiler is heated by steam;

[0024] The lower tower of the extractive distillation tower is heated by the extractive distillation tower kettle reboiler and the extractive distillation tower intermediate reboiler;

[0025] The kettle of the feed evaporation tower is heated by the evaporation tower reboiler;

[0026] 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 into the extractive distillation tower from the upper part of the upper tower of the extractive distillation tower as the extraction solvent.

[0027] Preferably,

[0028] In step S1, the light component is extracted from the top of the upper tower of the extractive distillation tower, and after being condensed in the condenser of the extractive distillation tower, a part of it is refluxed to the upper tower of the extractive distillation tower, and the other part is extracted through the alkane extraction outlet;

[0029] In step S2, the gas phase mixed olefins are extracted from the top of the analysis tower, first pressurized and heated by the gas phase compressor, and then condensed by the normal temperature circulating water analysis tower condenser. A part of it flows back to the analysis tower, and the other part is extracted through the olefin extraction port.

[0030] Preferably,

[0031] 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 N-methylpyrrolidone solution, the water content of the N-methylpyrrolidone solution is 1wt% to 12wt%, preferably 3wt% to 10wt%;

[0032] The butene concentration in the mixed C4 is 10 wt% to 90 wt%, preferably 20 wt% to 80 wt%.

[0033] Another object of the present invention is to provide a mixed light hydrocarbon alkane olefin separation system, the mixed light hydrocarbon alkane olefin separation system comprising:

[0034] Extraction distillation tower;

[0035] An analytical tower, wherein the middle portion of the analytical tower is connected to the kettle of the extractive distillation tower, and the kettle of the analytical tower is connected to the upper portion of the extractive distillation tower;

[0036] A decomposition tower condenser is arranged at the top of the decomposition tower;

[0037] Characterized in that the mixed light hydrocarbon system also includes:

[0038] A gas phase compressor for pressurizing the analyzed gas phase olefins is arranged between the top of the desorption tower and the analysis tower condenser.

[0039] Preferably, the outlet of the gas phase compressor is directly connected to the inlet of the analytical tower condenser.

[0040] 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.

[0041] 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.

[0042] Preferably, the reboiler is an intermediate reboiler of an extractive distillation tower, an intermediate reboiler of a desorption tower, or a kettle reboiler of a feed evaporation tower.

[0043] Preferably, the mixed light hydrocarbon system further comprises:

[0044] 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.

[0045] Preferably, the extractive distillation tower comprises:

[0046] An upper tower, the top of the feed evaporation tower is connected to the inlet of the upper tower;

[0047] The lower tower, the tower top of the lower tower is connected to the tower bottom of the upper tower, and the tower bottom of the lower tower is connected to the upper part of the analytical tower.

[0048] Preferably,

[0049] The tower kettle of the analytical tower is provided with an analytical tower reboiler;

[0050] The lower tower of the extractive distillation tower has an extractive distillation tower kettle reboiler and an extractive distillation tower intermediate reboiler;

[0051] The tower kettle of the feed evaporation tower has an evaporation tower reboiler;

[0052] Preferably, the reboiler of the analytical tower is heated by steam.

[0053] Preferably,

[0054] 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;

[0055] The outlet end of the analytical tower condenser is provided with a reflux passage and an olefin extraction outlet which are communicated with the upper part of the analytical tower.

[0056] Preferably, the mixed light hydrocarbon alkane-olefin separation system also has a temperature-controlled heat exchanger, and 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.

[0057] The positive and progressive effects of the present invention are:

[0058] 1) In the process of separating mixed light hydrocarbon alkanes and alkenes, the present invention 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) Further, the analysis tower can be operated at a relatively low pressure, and the gas phase coming out of the analysis tower can be pressurized and heated, and then condensed using circulating water at room temperature. This can not only reduce the energy consumption of the entire system, but also increase the olefin recovery rate to a higher level than that of the similar NMP method, i.e., there is 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 This is a schematic diagram of the mixed light hydrocarbon alkane-olefin separation system of Comparative Example 1. DETAILED DESCRIPTION

[0063] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints 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 an analytical 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 an analytical tower reboiler E4, and also comprises an analytical 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 1As shown, there is a feed inlet on the feed evaporation tower T1, and the top of the feed evaporation tower T1 is connected to the inlet of the lower part 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, and the extractive distillation tower condenser E6 has an outlet end, which is connected to the upper part of the upper tower T2 through a reflux passage, and the outlet end is also provided with an alkane extraction outlet. The upper tower T2 is also connected in series with the lower tower T3, that is, the tower kettle of the upper tower T2 is connected to the top of the lower tower T3. At the same time, the tower kettle of the lower tower T3 is also connected to the middle part of the analytical tower T4. The top of the analytical tower T4 is also connected in sequence with a gas phase compressor K1 and an analytical tower condenser E5, wherein the gas phase compressor K1 is arranged between the top of the analytical tower T4 and the analytical tower condenser E5, that is, the outlet of the gas phase compressor K1 is connected to the inlet of the analytical tower condenser E5. And the analytical tower condenser E5 is a condenser for condensation of circulating water at normal temperature.

[0066] Continue as Figure 1 As shown, the outlet end of the analytical tower condenser E5 has a reflux passage and an olefin extraction port 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, and 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 tower condenser E5. The reboiler includes the intermediate reboiler E8 of the extractive distillation tower, the intermediate reboiler of the analytical tower (not shown) or the reboiler E1 of the feed evaporation tower. Preferably, as Figure 2 As shown, the reboiler is arranged in the middle of the lower tower T3 of the extractive distillation tower, namely, 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] Solution 1

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

[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%, to vaporize the feedstock and remove the heavy components therein, and the evaporation tower reboiler E1 in the kettle of the feed evaporation tower T1 provides heat energy for vaporization and deweighting.

[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, and the poor solvent extracted from the poor solvent outlet of the tower bottom of the analytical tower T4 is countercurrently contacted 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 extracted and distilled in the upper tower T2 of the extractive distillation tower and the lower tower T3 of the extractive distillation tower connected in series, and the extractive distillation tower kettle reboiler E2 of the lower tower T3 tower bottom and the extractive distillation tower intermediate reboiler E3 provide the heat energy required for extractive distillation. The extractive distillation tower kettle reboiler E2 is heated by medium-pressure steam for start-up and heat supplement. After extractive distillation, the heavy components of mixed light hydrocarbons including butene-1, cis-2-butene, and trans-2-butene are dissolved in the solvent to form a rich solvent, and are extracted from the kettle of the lower tower T3 and enter the analytical tower T4. Light components including normal butane, isobutane, carbon three and a small amount of butene-1 are extracted from the top of the upper tower T2. After condensation in the extractive distillation tower condenser E6, a part of it is refluxed to the upper tower T2 of the extractive distillation tower, and the other part is directly extracted from the alkane extraction port as a 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 starting and supplementing heat. 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 control heat exchanger E7 respectively, and finally enters the extractive distillation tower from the upper part of the upper tower T2 of the extractive distillation tower, and is recycled as an extraction solvent. The gas phase containing olefins is extracted from the top of the analysis tower T4, first pressurized and heated by the gas phase compressor K1, the pressure range after pressurization is 0.42MPaG-1.8MpaG, and then condensed by the normal temperature circulating water analysis tower condenser E5. Finally, part of the system refluxes to the analysis tower T4, and the other part is directly extracted from the olefin extraction port as a mixed butene product.

[0074] Solution 2

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

[0076] The implementation method of the preprocessing step S0 and step S1 is Figure 1 The method of the mixed light hydrocarbon alkane alkene separation system shown is the same, except that: in step S2, after the analysis in the analysis tower T4, the lean solvent forming the liquid phase is extracted from the tower kettle of the analysis tower T4, first passes through the intermediate reboiler E3 of the extraction distillation tower, the reboiler E1 of the evaporation tower and the temperature control heat exchanger E7, and finally enters the extraction distillation tower from the upper part of the upper tower T2 of the extraction distillation tower, and is recycled as an extraction solvent. The gas phase containing olefins is extracted from the top of the analysis tower T4, first pressurized and heated by the gas phase compressor K1, and the pressure range after pressurization is 0.42MPaG-2.6MpaG, and after heating, it is heat exchanged by the reboiler, for example, heat exchanged by the intermediate reboiler E8 of the extraction distillation tower, and then condensed by the condenser E5 of the normal temperature circulating water analysis tower, and finally, a part of the system is refluxed to the analysis tower T4, and the other part is directly extracted from the olefin extraction port as a mixed butene product.

[0077] Table 1 Composition and content of C4 in the raw material ether in the separation of mixed light hydrocarbons and alkanes of the present invention

[0078]

[0079]

[0080] Example 1

[0081] like Figure 1As shown, the etherified C4 with a temperature of 40°C and a flow rate of 34000kg / hr enters the feed evaporation tower T1, wherein the specific composition and content of the etherified C4 are shown in Table 1, the gas phase flow rate at the top of the tower is 33999kg / h, the temperature is 56.75°C, and the pressure is 0.57MPaG, and enters the lower part of the upper tower T2 of the extractive distillation tower. The NMP lean solvent with a water content of 8% from the kettle of the analytical tower T4 is heat-exchanged to 50°C by the temperature-controlled heat exchanger E7 and enters the upper part of the upper tower T2 of the extractive distillation tower. The raw material is subjected to extractive distillation in the upper tower T2 of the extractive distillation tower and the lower tower T3 of the extractive distillation tower. The top product of the upper tower T2 is condensed by circulating water in the extractive distillation tower condenser E6, and the temperature is 41.4°C and the pressure is 0.45MPaG. A part of it is refluxed to the upper part of the upper tower T2, and the other part is produced as a butane product, with a production volume of 21000kg / h. The concentration of isobutane and normal butane in the produced product is 98.5wt%.

[0082] The liquid phase in the bottom of the extractive distillation tower T3 is pumped to the analytical tower T4, where the feed temperature is 144°C and the feed pressure is 0.55MpaG. After desorption in the analytical tower, the temperature of the gas phase product at the top of the tower is 41°C and the gas phase pressure at the top of the tower is 0.12MPaG; it is compressed to 0.42MPaG and the temperature is 79.3°C by the gas phase compressor K1; then it is cooled to 70°C by the normal temperature circulating water analytical tower condenser E5, a part of it is decompressed to 0.12MPaG and then refluxed into the analytical tower T4, and the other part is extracted as the product butene, and the product extraction amount is 12968kg / h, where the total concentration of butene-1, cis-butene and trans-butene is 98.53wt%.

[0083] The lean solvent temperature 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 50°C. Then, the lean solvent enters the upper part of the upper tower T2 of the extractive distillation tower as the extraction solvent.

[0084] Example 2

[0085] like Figure 2As shown, the etherified C4 with a temperature of 45°C and a flow rate of 34000kg / hr enters the feed evaporation tower T1, wherein the specific composition and content of the etherified C4 are shown in Table 1, the gas phase flow rate at the top of the tower is 33999kg / h, the temperature is 56.75°C, and the pressure is 0.57MPaG, and enters the lower part of the upper tower T2 of the extractive distillation tower. The NMP lean solvent with a water content of 8% from the kettle of the analytical tower T4 is heat-exchanged to 50°C by the temperature-controlled heat exchanger E7 and enters the upper part of the upper tower T2 of the extractive distillation tower. The raw material is subjected to extractive distillation in the upper tower T2 of the extractive distillation tower and the lower tower T3 of the extractive distillation tower. The top product of the upper tower T2 of the extractive distillation tower is condensed by circulating water in the extractive distillation tower condenser E6, and the temperature is 41.4°C and the pressure is 0.45MPaG. A part of it is refluxed to the upper part of the upper tower T2 of the extractive distillation tower, and the other part is produced as a butane product, with a production volume of 21000kg / h. The concentration of isobutane and normal butane in the produced product is 98.5wt%.

[0086] The liquid phase in the bottom of the lower tower T3 of the extractive distillation tower is transported to the analytical tower T4 by a pump, wherein the feed temperature is 140°C and the feed pressure is 0.55MpaG. After being analyzed by the analytical tower, the temperature of the gas phase product at the top of the tower is 41°C and the gas phase pressure at the top of the tower is 0.12MPaG; it is compressed to 1.2MPaG and the temperature is 123°C by the gas phase compressor K1; then it is heat exchanged by the intermediate reboiler E8 of the extractive distillation tower, the temperature drops to 86°C, and then it is cooled to 70°C by the condenser E5 of the normal temperature circulating water analytical tower. A part of it is decompressed to 0.12MPaG and then refluxed to the analytical tower T4, and the other part is extracted as the product butene, and the product extraction amount is 12968kg / h, wherein the total concentration of butene-1, cis-butene and trans-butene is 98.53wt%.

[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 3As shown, the conventional alkane-olefin separation process of the NMP method includes: the etherified C4 with a temperature of 40°C and a flow rate of 34000 kg / hr enters the feed evaporation tower T1, wherein the specific composition and content of the etherified C4 are shown in Table 1, and the top gas phase flow rate is 33999 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 NMP lean solvent with a water content of 8% from the bottom of the analytical tower T4 is heated to 50°C by the temperature-controlled heat exchanger E7 and enters the upper part of the extractive distillation tower T2. The raw material is subjected to extractive distillation in the upper tower T2 of the extractive distillation tower and the lower tower T3 of the extractive distillation tower. The top product of the extractive distillation tower T2 is condensed by circulating water in the extractive distillation tower condenser E6, and the temperature is 41.4°C and the pressure is 0.45MPaG. A part of it is refluxed to the upper part of the extractive distillation tower T2, and the other part is produced as a butane product, and the production amount is 21000kg / h. The concentration of isobutane and normal butane in the produced product is 97.3wt%.

[0090] The liquid phase of the bottom of the extractive distillation tower T3 is pumped to the analytical tower T4, wherein the feed temperature is 144°C and the feed pressure is 0.55MPaG. After being analyzed by the analytical tower, the gas phase product at the top of the tower is condensed by the analytical tower condenser E5 with normal temperature circulating water, and the temperature is 52.2°C. Before being condensed by normal temperature circulating water, the operating pressure of the gas phase at the top of the tower is 0.45MpaG, and the pressure of the gas phase product after condensation is 0.43MPaG; part of the cooled logistics is refluxed to the analytical tower T4, and the other part is produced as the product butene, and the product production volume is 13078kg / h, wherein the total concentration of butene-1, cis-butene and trans-butene is 97.7wt%.

[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 50°C. Then the lean solvent enters the upper part of the upper tower T2 of the extraction distillation tower as the extraction solvent.

[0092] The desorption tower of the conventional alkane-olefin separation technology of the NMP method is operated at a relatively high pressure, and the top condenser is cooled by circulating water. At this time, the temperature of the bottom and top of the analytical tower is relatively high, which causes problems such as high energy consumption of the system and large product loss. The analytical tower of the present invention is operated at a relatively low pressure, and the top gas of the tower is cooled by circulating water after being pressurized and heated by a compressor, or the top gas of the analytical tower is pressurized and heated by a compressor, and then the heat is recovered by a reboiler and then water-cooled. This method not only achieves the purpose of energy saving of the system, but also has a higher recovery rate of olefins than similar devices. Under the same feed conditions, the effect comparison is shown in Table 1 below.

[0093] Table 2 Comparison between the method and system for separating alkanes and olefins in 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 present invention appropriately controls the operating pressure of the top gas phase of the analysis tower at low pressure, and then pressurizes and heats the gas phase coming out of the analysis tower, and then condenses it with normal temperature circulating water, so that the energy consumption of the entire system can be reduced from 97.6 kg standard oil / t raw material in comparative example 1 to 60.9 kg standard oil / t raw material. 2) Further, the low-pressure and low-temperature operation in the analysis tower can reduce the solvent NMP carried out from the top of the tower, reduce the amount of solvent in the product, and increase 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 in the similar NMP method. Therefore, there is a synergistic effect in reducing energy consumption and improving olefin recovery rate.

[0096] The present invention is described in detail above in conjunction with the embodiments of the accompanying drawings. A person skilled in the art can make various variations of the present invention according to the above description. Therefore, some details in the embodiments should not be construed as limiting the present invention, and the present invention shall be protected by the scope defined by the attached claims.

Claims

1. A method for separating mixed light hydrocarbons from alkanes and alkenes, the method comprising the following steps: Step S1, the mixed light hydrocarbons enter the extractive distillation tower and are countercurrently contacted with the lean solvent from the analytical tower, and the heavy components containing olefins are dissolved in the solvent to form a rich solvent and enter the analytical tower; Step S2, the rich solvent is decomposed in the decomposition tower, the gas phase containing olefins is extracted from the top of the decomposition tower, the decomposed lean solvent comes out from the bottom of the decomposition tower and then circulates into the extractive distillation tower from the upper part of the extractive distillation tower as an extraction solvent; The characteristic point is that in step S2, the gas phase containing mixed olefins extracted from the top of the analysis tower is first pressurized by a gas phase compressor to increase the temperature, and then condensed by a normal temperature circulating water analysis tower condenser before being extracted.

2. The method for separating mixed light hydrocarbons from alkanes and alkenes according to claim 1, characterized in that In step S2, the top operating pressure 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.

3. The method for separating mixed light hydrocarbons from alkanes and alkenes according to claim 1 or 2, characterized in that In step S2, the olefin-containing gas phase extracted from the top of the analysis 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 analysis tower for condensation. Preferably, the pressure range of the gas phase after pressurization by the compressor is 0.42MPaG-2.6MpaG, and more preferably, the pressure range of the gas phase after pressurization by the compressor is 0.42MPaG-1.8MpaG.

4. The method for separating mixed light hydrocarbons from alkanes and alkenes according to claim 1 or 2, characterized in that In step S2, the olefin-containing gas phase extracted from the top of the analysis tower is first pressurized by a gas compressor to increase the temperature. The heated gas phase is first heat-exchanged with a reboiler, and then enters a condenser of a normal temperature circulating water analysis tower for condensation.

5. The method for separating mixed light hydrocarbons from alkanes and alkenes as claimed in claim 4, characterized in that The reboiler is an intermediate reboiler of an extractive distillation tower, an intermediate reboiler of a desorption tower, or a kettle reboiler of a feed evaporation tower.

6. The method for separating mixed light hydrocarbons from alkanes and alkenes according to claim 1, characterized in that Before step S1, the method further includes: 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.

7. The method for separating mixed light hydrocarbons from alkanes and alkenes according to claim 6, characterized in that The extractive distillation tower comprises an upper tower and a lower tower; Step S1 specifically includes: The mixed light hydrocarbons after vaporization and de-heavy treatment enter the upper tower and are countercurrently contacted with the lean solvent from the analytical tower. The mixed light hydrocarbons are extracted and distilled 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 and enter the analytical tower. Preferably, the mixed light hydrocarbons are mixed C4s, the light components include normal butane, isobutane, C3 and a small amount of butene-1, and the heavy components include butene-1, cis-2-butene and trans-2-butene.

8. The method for separating mixed light hydrocarbons from alkanes and alkenes according to claim 7, characterized in that The kettle of the analytical tower is heated by a analytical tower reboiler, and preferably, the analytical tower reboiler is heated by steam; The lower tower of the extractive distillation tower is heated by the extractive distillation tower kettle reboiler and the extractive distillation tower intermediate reboiler; The kettle of the feed evaporation tower is heated by the evaporation tower reboiler; 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 into the extractive distillation tower from the upper part of the upper tower of the extractive distillation tower as the extraction solvent.

9. The method for separating mixed light hydrocarbons from alkanes and alkenes according to claim 7, characterized in that In step S1, the light component is extracted from the top of the upper tower of the extractive distillation tower, and after being condensed in the condenser of the extractive distillation tower, a part of it is refluxed to the upper tower of the extractive distillation tower, and the other part is extracted through the alkane extraction outlet; In step S2, the gas phase mixed olefins are extracted from the top of the analysis tower, first pressurized and heated by the gas phase compressor, and then condensed by the normal temperature circulating water analysis tower condenser. A part of it flows back to the analysis tower, and the other part is extracted through the olefin extraction port.

10. The method for separating mixed light hydrocarbon alkanes and alkenes according to claim 7, characterized in that The solvent is acetonitrile, sulfolane, N-methylpyrrolidone, a mixture of methyl ethyl ketone and N-formylmorpholine, or a mixture of morpholine and N-formylmorpholine, preferably N-methylpyrrolidone solution, the water content of the N-methylpyrrolidone solution is 1wt% to 12wt%, preferably 3wt% to 10wt%; The butene concentration in the mixed C4 is 10 wt% to 90 wt%, preferably 20 wt% to 80 wt%.

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