Apparatus and method for separating a mixture of methyl chloride and isobutane

Abstract

The application provides a device and method for separating a mixture of chloromethane and isobutane, comprising an extractive rectification tower, a chloromethane and isobutane mixture feeding port, an extractant feeding port and a chloromethane gas phase outlet arranged on the extractive rectification tower; the extractant fed by the extractant feeding port comprises n-hexane and / or isohexane; a cooler connected with the bottom of the extractive rectification tower; an extractant recovery tower connected with the cooler; an isobutane recovery unit connected with the top of the extractant recovery tower; an extractant recovery tower tank reboiler connected with the bottom of the extractant recovery tower, and an extractant buffer tank connected by a pipeline. The application can separate chloromethane and isobutane and obtain high-purity chloromethane and isobutane by using the above device and a specific kind of extractant; in addition, the device uses energy coupling technology and has low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of separation technology, and particularly relates to an apparatus and method for separating a mixture of chloromethane and isobutane. Background Technology

[0002] Chloromethane is a colorless, odorless, and volatile organic compound. High-purity chloromethane is used as a solvent in the production of products such as rubber, pesticides, and organosilicon.

[0003] Isobutane is a colorless, flammable gas at room temperature and pressure. It is slightly soluble in water but soluble in ethanol, diethyl ether, etc. It is mainly used in the production of products such as isobutene, n-butane, and alkylated oils.

[0004] Chloromethane and isobutane mixtures are commonly found in the synthesis of rubber, organic solvents, and pesticides. Separating high-purity chloromethane and isobutane is beneficial for improving the quality of products such as rubber, pesticides, and alkylated oils. Analysis revealed that chloromethane and isobutane form an azeotropic system. A review of relevant domestic and international literature and patents did not uncover any effective methods or apparatus for separating mixtures of chloromethane and isobutane. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide an apparatus and method for separating a mixture of chloromethane and isobutane, the apparatus being capable of separating the chloromethane and isobutane components to obtain a high-purity chloromethane solution.

[0006] The present invention provides an apparatus for separating a mixture of chloromethane and isobutane, comprising an extractive distillation column, wherein the extractive distillation column is provided with an inlet for the mixture of chloromethane and isobutane, an extractant inlet, and a chloromethane gas phase outlet;

[0007] A cooler connected to the bottom of the extractive distillation column;

[0008] The extractant recovery tower is connected to the cooler;

[0009] An isobutane recovery unit connected to the top of the extractant recovery tower;

[0010] The extractant recovery tower reboiler is connected to the bottom of the extractant recovery tower, and the extractant buffer tank is connected by a pipeline.

[0011] Preferably, it also includes a buffer tank for the mixture of chloromethane and isobutane, which is connected to the inlet of the chloromethane and isobutane mixture via a mixture feed pump.

[0012] Preferably, the extractive distillation column top condenser, extractive distillation column top condenser tank, extractive distillation column top reflux pump, and chloromethane product buffer tank are connected in sequence to the chloromethane gas phase outlet.

[0013] Preferably, the bottom of the extractive distillation column is connected to a primary feed cooler for the extractant recovery column and a secondary feed cooler for the extractant recovery column;

[0014] The secondary feed cooler of the extractant recovery tower is connected to the extractant recovery tower.

[0015] Preferably, the isobutane recovery unit includes:

[0016] The extractant recovery tower is sequentially connected to the top of the tower by an extractant recovery tower top condenser, a tower top condenser tank, an extractant recovery tower top reflux pump, and an isobutane product buffer tank.

[0017] Preferably, it also includes an extractant product condenser that communicates with the bottom of the extractant recovery tower;

[0018] The extractant product condenser is connected to the extractant buffer tank via an extractant circulation pump.

[0019] This invention provides a method for separating a mixture of chloromethane and isobutane, comprising the following steps:

[0020] A mixture of chloromethane and isobutane is subjected to extractive distillation in the presence of an extractant to obtain chloromethane and the bottom liquid of the extractive distillation column;

[0021] After the bottom liquid of the extractive distillation column is cooled, the extractant is recovered and isobutane is collected.

[0022] Preferably, the extractant comprises isohexane and / or n-hexane.

[0023] Preferably, the pressure of the extractive distillation is 600–850 kPag;

[0024] The temperature for extractive distillation is 40–185℃.

[0025] Preferably, the theoretical plate number of the column during extractant recovery is 20–40;

[0026] The theoretical plate number of the extraction column is 60–80.

[0027] This invention provides an apparatus for separating a mixture of chloromethane and isobutane, comprising an extractive distillation column, wherein the extractive distillation column is provided with a chloromethane and isobutane mixture inlet, an extractant inlet, and a chloromethane gas phase outlet; the extractant supplied through the extractant inlet includes n-hexane and / or isohexane; a cooler connected to the bottom of the extractive distillation column; an extractant recovery column connected to the cooler; an isobutane recovery unit connected to the top of the extractant recovery column; a reboiler for the extractant recovery column connected to the bottom of the extractant recovery column; and an extractant buffer tank connected via pipeline. This invention, using a specific type of extractant in the above apparatus, can separate chloromethane and isobutane to obtain high-purity chloromethane and isobutane; furthermore, this apparatus utilizes energy coupling technology, resulting in low energy consumption. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the apparatus for separating a mixture of chloromethane and isobutane provided by the present invention. Detailed Implementation

[0029] The present invention provides an apparatus for separating a mixture of chloromethane and isobutane, comprising an extractive distillation column, wherein the extractive distillation column is provided with an inlet for the mixture of chloromethane and isobutane, an extractant inlet, and a chloromethane gas phase outlet;

[0030] A cooler connected to the bottom of the extractive distillation column;

[0031] The extractant recovery tower is connected to the cooler;

[0032] An isobutane recovery unit connected to the top of the extractant recovery tower;

[0033] The extractant recovery tower reboiler is connected to the bottom of the extractant recovery tower, and the extractant buffer tank is connected by a pipeline.

[0034] See Figure 1 , Figure 1 A schematic diagram of the apparatus for separating a mixture of chloromethane and isobutane provided by the present invention;

[0035] This includes an extractant mixer 1, an extractant buffer tank 2, an extractant feed pump 3, a chloromethane and isobutane mixture buffer tank 4, a mixture feed pump 5, an extractive distillation column 6, an extractive distillation column overhead condenser 7, an extractive distillation column overhead condenser 8, an extractive distillation column overhead reflux pump 9, a chloromethane product buffer tank 10, an extractive distillation column reboiler 11, an extractant recovery column primary feed cooler 12, an extractant recovery column secondary feed cooler 13, and an extractant recovery column 14. The extractant... The extraction solvent recovery tower has a top condenser 15, an extractant recovery tower top condenser 16, an extractant recovery tower top reflux pump 17, an isobutane product buffer tank 18, an extractant recovery tower bottom reboiler 19, an extractant product condenser 20, an extractant circulation pump 21, an extractant feed stream a into the extractive distillation tower, a mixed feed stream b into the extractive distillation tower, an extractive distillation tower top product stream c, an extractive distillation tower bottom product stream d, an extractant recovery tower top product stream e, and an extractant circulation pump outlet stream f.

[0036] The apparatus provided by the present invention includes an extractive distillation column 6, wherein the extractive distillation column 6 is provided with a chloromethane and isobutane mixture inlet, an extractant inlet, and a chloromethane gas phase outlet.

[0037] The present invention also includes a buffer tank 4 for a mixture of chloromethane and isobutane, wherein the mixture in the buffer tank 4 is connected to the inlet of the chloromethane and isobutane mixture via a mixture feed pump 5 and enters the lower part of the extractive distillation column 6.

[0038] The present invention also includes a mixer 1 and an extractant buffer tank 2 connected to the mixer 1. The extractant buffer tank 2 enters the upper part of the extractive distillation column 6 through the extractant inlet via an extractant feed pump 3.

[0039] The apparatus provided by this invention includes an extractive distillation column top condenser 7, an extractive distillation column top condenser tank 8, an extractive distillation column top reflux pump 9, and a chloromethane product buffer tank 10, all sequentially connected to the chloromethane gas phase outlet. The fluid in the condenser tank 8 is pumped by the extractive distillation column top reflux pump 9 into the extractive distillation column 6 and the chloromethane product buffer tank 10, respectively.

[0040] The apparatus provided by this invention includes a cooler connected to the bottom of the extractive distillation column; specifically, the bottom of the extractive distillation column 6 is sequentially connected to a primary feed cooler 12 for the extractant recovery column and a secondary feed cooler 13 for the extractant recovery column; the secondary feed cooler 13 for the extractant recovery column is connected to the extractant recovery column 14. This invention, by setting up the primary feed cooler 12 for the extractant recovery column, enables heat exchange between the bottom liquid of the extractive distillation column and the bottom liquid of the extractant recovery column, thereby recovering the heat load of the extractive distillation column and reducing the load on the extractant recovery column system.

[0041] The apparatus provided by the present invention includes an extractant recovery tower 14 and an isobutane recovery unit connected to the top of the extractant recovery tower;

[0042] The isobutane recovery unit specifically includes:

[0043] The extractant recovery tower is sequentially connected to the top of the tower by an extractant recovery tower top condenser 15, a top condenser tank 16, an extractant recovery tower top reflux pump 17, and an isobutane product buffer tank 18.

[0044] The apparatus provided by the present invention further includes an extractant recovery tower reboiler 19, which is connected to the primary feed cooler 12 of the extractant recovery tower and the extractant recovery tower 14, respectively. Part of the bottom liquid of the extractant recovery tower is heated by the primary feed cooler 12 and the reboiler 19 and then returned to the bottom of the extractant recovery tower.

[0045] The apparatus provided by the present invention further includes an extractant product condenser 20 that communicates with the bottom of the extractant recovery tower 14; the extractant product condenser 20 is connected to the extractant buffer tank 2 via an extractant circulation pump 21.

[0046] This invention provides a method for separating a mixture of chloromethane and isobutane, comprising the following steps:

[0047] A mixture of chloromethane and isobutane is subjected to extractive distillation in the presence of an extractant to obtain chloromethane and the bottom liquid of the extractive distillation column;

[0048] After the bottom liquid of the extractive distillation column is cooled, the extractant is recovered and isobutane is collected.

[0049] The extractant described in this invention includes isohexane and / or n-hexane;

[0050] In this invention, the chloromethane and isobutane mixture contains 70-99 wt% chloromethane and 1-30 wt% isobutane. In a specific embodiment, the mixture consists of 90 wt% chloromethane and 10 wt% isobutane.

[0051] If the extractant is a mixture, the mixture shall contain at least 50 to 85 wt% n-hexane; for example, the extractant may contain 62 wt% n-hexane, 34 wt% isohexane, and 4 wt% methylcyclopentane; or the extractant may contain 62.53 wt% n-hexane, 33.55 wt% isobutane, 3.91 wt% methylcyclopentane, and 0.01 wt% cyclohexane.

[0052] In this invention, the solvent ratio during extraction is 3.2–4.8, where the solvent ratio is the ratio of the mass flow rate of the extractant to the mass flow rate of the chloromethane and isobutane mixture feed; in specific embodiments, the solvent ratio is 3.7 or 4.3. The extractive distillation pressure is 600–850 kPag; the extractive distillation temperature is 40–185 °C; in specific embodiments, the extractive distillation pressure is 766 kPag; and the extractive distillation temperature is 105 °C.

[0053] The theoretical number of plates in the extraction column is 60-80; the extractant is preferably introduced into the 8th plate of the extractive distillation column, and the mixture is preferably introduced into the 72nd plate of the extractive distillation column.

[0054] A mixture of chloromethane and isobutane is fed into an extractive distillation column for extraction and separation. Isobutane is extracted into the extractant, while chloromethane is collected as a gaseous substance from the top of the extractive distillation column.

[0055] Chloromethane is discharged from the top of the column and cooled by the top condenser 7 of the extractive distillation column. The temperature after cooling is 40°C, and high-purity (99.9%) chloromethane product is collected.

[0056] The bottom material of the extractive distillation column 6 exchanges heat with the first-stage feed cooler 12 of the extractive recovery column, and the recovered heat is used as the heat source for the bottom of the extractant recovery column 14 (equivalent to the effect of multi-effect distillation). The bottom material after heat exchange exchanges heat with the second-stage feed cooler 13 of the extractant recovery column, and the remaining heat is recovered to generate low-pressure steam. The material after heat exchange is in the state of saturated liquid and enters the extractant recovery column 14.

[0057] The pressure in the extractant recovery tower is 300–650 kPag; the temperature in the extractant recovery tower is 40–155 °C; the theoretical number of plates in the extractant recovery tower is 20–40; in a specific embodiment, the theoretical number of plates in the extractant recovery tower is 30, and the saturated liquid preferably enters the 6th plate of the extractant recovery tower. After separation in the extractant recovery tower, the gaseous isobutane at the top of the tower is cooled by condenser 15, and high-purity isobutane product is collected at the top of the tower; the temperature after cooling is 40 °C.

[0058] The liquid in the bottom of the extractant recovery tower recovers some heat through the extractant product condenser 20 to generate low-pressure steam, and then enters the extractant buffer tank 2 for recycling.

[0059] Specifically, a method for separating a mixture of chloromethane and isobutane includes:

[0060] a) Mixer 1 is connected to extractant buffer tank 2. The extractant composition transported from the tank area is mixed by mixer 1 and then enters extractant buffer tank 2.

[0061] b) The extractant buffer tank 2 is connected to the extractant feed pump 3, the extractant feed pump 3 extracts the distillation column 6, and the extractant in the extractant buffer tank 2 enters the upper part of the distillation column 6 through the extractant feed pump 3.

[0062] c) The mixture of chloromethane and isobutane produced by the upstream unit enters the mixture buffer tank 4;

[0063] e) The mixture feed pump 5 is connected to the mixture buffer tank 4, and the mixture enters the lower part of the extractive distillation column 6 through the mixture feed pump 5;

[0064] f) The top condenser 7 of the extractive distillation column is connected to the extractive distillation column 6. The chloromethane gas stream at the top of the extractive distillation column is condensed into a liquid phase through the top condenser 7.

[0065] g) The top condenser 8 of the extractive distillation column is connected to the top condenser 7 of the extractive distillation column, and the condensed liquid chloromethane enters the top condenser 8 of the extractive distillation column.

[0066] h) The top reflux pump 9 of the extractive distillation column is connected to the chloromethane product buffer tank 10, the top condenser 8 of the extractive distillation column, and the extractive distillation column 6, respectively. The fluid in the condenser enters the extractive distillation column 6 and the chloromethane product buffer tank 10 through the top reflux pump 9 of the extractive distillation column.

[0067] i) The reboiler 11 of the extractive distillation column is connected to the extractive distillation column 6. Part of the bottom liquid of the extractive distillation column is heated by the reboiler 11 and then returned to the bottom of the extractive distillation column.

[0068] j) The primary feed cooler 12 of the extractant recovery tower is connected to the extractive distillation tower 6 and the secondary feed cooler 13 of the extractant recovery tower respectively. The bottom liquid of the extractive distillation tower is cooled to saturated liquid state through the primary and secondary feed coolers of the extractant recovery tower and then enters the extractant recovery tower 14.

[0069] k) The top condenser 15 of the extractant recovery tower is connected to the extractant recovery tower 14. The isobutane gas stream at the top of the extractant recovery tower 14 is condensed into a liquid phase through the condenser 15.

[0070] l) The condenser 16 at the top of the extractant recovery tower is connected to the condenser 15 at the top of the extractant recovery tower, and the condensed liquid isobutane enters the condenser 16.

[0071] m) The top reflux pump 17 of the extractant recovery tower is connected to the isobutane product buffer tank 18, the top condenser 16 of the extractant recovery tower and the extractant recovery tower 14 respectively. The fluid in the condenser enters the extractant recovery tower 14 and the isobutane product buffer tank 18 respectively through the top reflux pump 17 of the extractant recovery tower.

[0072] n) The reboiler 19 of the extractant recovery tower is connected to the primary feed cooler 12 of the extractant recovery tower and the extractant recovery tower 14 respectively. Part of the bottom liquid of the extractant recovery tower is heated by the primary feed cooler 12 and the reboiler 19 and then returned to the bottom of the extractant recovery tower.

[0073] o) The extractant product condenser 20 is connected to the extractant recovery tower 14, and the bottom liquid of the extractant recovery tower is cooled to a certain temperature through the extractant product condenser 20;

[0074] p) The extractant circulation pump 21 is connected to the extractant buffer tank 2, and the cooled extractant product enters the extractant buffer tank 2 through the extractant circulation pump 21.

[0075] To further illustrate the present invention, the apparatus and method for separating a mixture of chloromethane and isobutane provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0076] Example 1

[0077] Taking a mixture of 90 wt% chloromethane and 10 wt% isobutane as an example, with an extractant composition of 100% isohexane and an extractant mass flow rate of 13000 kg / h, the apparatus and process described in this invention are used.

[0078] The mixture generated from the upstream unit enters the mixture buffer tank 4 of the present invention. The above-mentioned mixed extractant is stored in the extractant buffer tank 2. The theoretical number of plates in the extractive distillation column is 75, and the top pressure is 766 kPag. The extractant enters the 8th plate of the extractive distillation column, and the mixture enters the 72nd plate of the extractive distillation column. The vapor phase at the top of the column is cooled by the condenser 7, and the temperature after cooling is 40°C. High-purity (99.9 wt%) chloromethane product is collected from the top of the column. The bottom material of the column exchanges heat with the first-stage feed cooler 12 of the extraction recovery column. The recovered heat is used as the heat source for the bottom of the extractant recovery column 14 (equivalent to the effect of multi-effect distillation). The bottom material after heat exchange... The material exchanges heat with the secondary feed cooler 13 of the extractant recovery tower to recover the remaining heat and generate low-pressure steam. After heat exchange, the material is in the state of saturated liquid and enters the 6th plate of the extractant recovery tower 14. The theoretical number of plates in the extractant recovery tower is 30, and the pressure at the top of the tower is 440 kPag. The vapor phase at the top of the tower is cooled by condenser 15 to a temperature of 40°C. High-purity isobutane product is collected from the top of the tower, and high-purity extractant is collected from the bottom of the tower. The liquid at the bottom of the tower passes through the extractant product condenser 20 to recover some heat and generate low-pressure steam before entering the extractant buffer tank for recycling. The total amount of extractant replenished in the entire process is 0.3 kg / h. The data results are shown in Table 1.

[0079] Comparative Example 1

[0080] The mixture consists of 90 wt% chloromethane and 10 wt% isobutane, the extractant consists of 100% isohexane, the extractant mass flow rate is 24000 kg / h, the theoretical number of plates in the extraction tower is 70, and the process flow is the same as that described in this invention except that the primary feed cooler 12 of the extractant recovery tower is not set. The main energy consumption comparison data with Example 1 is shown in Table 2.

[0081] Table 1

[0082]

[0083] Table 2 Comparison of Key Energy Consumption (per hour)

[0084]

[0085] In this embodiment, compared with the traditional separation method, (1) the present invention selects a suitable extractant with a solvent mass ratio of only 3.7, which realizes the effective separation of chloromethane and isobutane; (2) the present invention optimizes the extraction tower system, which reduces the load of the extraction tower system by 12978kw; and by using energy integration technology, the load of the extractant recovery tower system is reduced by 9121kw, which greatly reduces the operating cost of the entire extraction distillation unit.

[0086] Example 2

[0087] Example 2 uses the same apparatus and method as Example 1. Taking the mixture composition as 90 wt% chloromethane and 10 wt% isobutane, the extractant composition as 100 wt% n-hexane, and the extractant mass flow rate as 15000 kg / h, the apparatus and process method described in this invention are used, and the data results are shown in Table 3.

[0088] Comparative Example 2

[0089] The mixture consists of 90 wt% chloromethane and 10 wt% isobutane, the extractant consists of 100% isohexane, the extractant mass flow rate is 35,500 kg / h, the theoretical number of plates in the extraction tower is 65, and the process flow is the same as that described in this invention except that the primary feed cooler 12 of the extractant recovery tower is not set. The main energy consumption comparison data with Example 2 is shown in Table 4.

[0090] Table 3 Main Logistics Data Table

[0091]

[0092]

[0093] Table 4 Comparison of Main Energy Consumption (per Hour)

[0094]

[0095] In this embodiment, compared with the traditional separation method, (1) the present invention selects a suitable extractant with a solvent mass ratio of 4.3, and achieves effective separation of chloromethane and isobutane with low energy consumption; (2) the present invention optimizes the extraction tower system, achieving a reduction of 16912kw in the load of the extraction tower system; and by using energy integration technology, the load of the extractant recovery tower system is reduced by 570kw, which greatly reduces the operating cost of the entire extraction distillation unit.

[0096] Example 3

[0097] Example 3 uses the same apparatus and method as Example 1. Taking a mixture of 90 wt% chloromethane and 10 wt% isobutane as an example, and an extractant of 62.53 wt% n-hexane, 33.55 wt% isobutane, 3.91 wt% methylcyclopentane, and 0.01 wt% cyclohexane as an example, with an extractant mass flow rate of 14500 kg / h, the apparatus and process described in this invention are used, and the data results are shown in Table 5.

[0098] Comparative Example 3

[0099] The mixture consists of 90 wt% chloromethane and 10 wt% isobutane, the extractant consists of 100% isohexane, the extractant mass flow rate is 27000 kg / h, the theoretical number of plates in the extraction tower is 70, and the process flow is the same as that described in this invention except that the primary feed cooler 12 of the extractant recovery tower is not set. The main energy consumption comparison data with Example 3 is shown in Table 6.

[0100] Table 5 Main Logistics Data Table

[0101]

[0102]

[0103] Table 6 Comparison of Key Energy Consumption (per hour)

[0104]

[0105] In this embodiment, compared with traditional separation methods, (1) the extractant used in this invention has sufficient market supply and low price, and achieves effective separation of chloromethane and isobutane; (2) this invention optimizes the extraction tower system, achieving a reduction of 14,110 kW in the load of the extraction tower system; and by using energy integration technology, the load of the extractant recovery tower system is reduced by 925 kW, thus reducing operating costs.

[0106] Comparative Example 4:

[0107] Acetone is a commonly used extractant. The extractant of this invention is changed to 100wt% acetone. Similarly, the mixture of 90wt% chloromethane and 10wt% isobutane is separated. Using the device and process method described in this invention, when the theoretical plates of the extraction tower are increased to 95 and the flow rate of the extractant is increased to 30000 kg / h, the specific data results are shown in Tables 7 and 8.

[0108] Table 7 Main Logistics Data Table

[0109]

[0110]

[0111] Table 8 Comparison of Key Energy Consumption (per hour)

[0112]

[0113] Based on the above data and a comparison with Implementation Case 1, it can be seen that when acetone is used as the extractant: the number of theoretical plates in the extraction tower increases, leading to increased equipment investment costs; when the extractant usage increases to 30,000 kg / h, the separation requirements are not met; and the energy consumption of the device increases by 940 kW / h, leading to increased operating costs.

[0114] As can be seen from the above embodiments, the present invention provides an apparatus for separating a mixture of chloromethane and isobutane, comprising an extractive distillation column, wherein the extractive distillation column is provided with an inlet for the mixture of chloromethane and isobutane, an extractant inlet, and a chloromethane gas phase outlet; the extractant supplied through the extractant inlet includes n-hexane and / or isohexane; a cooler connected to the bottom of the extractive distillation column; an extractant recovery column connected to the cooler; an isobutane recovery unit connected to the top of the extractant recovery column; a reboiler for the extractant recovery column connected to the bottom of the extractant recovery column; and an extractant buffer tank connected by a pipeline. The present invention, using a specific type of extractant in the above apparatus, can separate chloromethane and isobutane to obtain high-purity chloromethane and isobutane; furthermore, the apparatus utilizes energy coupling technology, resulting in low energy consumption.

[0115] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An apparatus for separating a mixture of chloromethane and isobutane, comprising an extractive distillation column, wherein the extractive distillation column is provided with a chloromethane and isobutane mixture inlet, an extractant inlet, and a chloromethane gas phase outlet; the extractant conveyed by the extractant inlet includes n-hexane and / or isohexane; A cooler connected to the bottom of the extractive distillation column; The extractant recovery tower is connected to the cooler; An isobutane recovery unit connected to the top of the extractant recovery tower; The extractant recovery tower reboiler is connected to the bottom of the extractant recovery tower, and the extractant buffer tank is connected by a pipeline.

2. The apparatus according to claim 1, characterized in that, It also includes a buffer tank for a mixture of chloromethane and isobutane, which is connected to the inlet of the chloromethane and isobutane mixture via a mixture feed pump.

3. The apparatus according to claim 1, characterized in that, The extractive distillation column top condenser, extractive distillation column top condenser tank, extractive distillation column top reflux pump, and chloromethane product buffer tank are sequentially connected to the chloromethane gas phase outlet.

4. The apparatus according to claim 1, characterized in that, The bottom of the extractive distillation column is connected to the primary feed cooler of the extractant recovery column and the secondary feed cooler of the extractant recovery column; The secondary feed cooler of the extractant recovery tower is connected to the extractant recovery tower.

5. The apparatus according to claim 1, characterized in that, The isobutane recovery unit includes: The extractant recovery tower is sequentially connected to the top of the tower by an extractant recovery tower top condenser, an extractant recovery tower top condenser tank, an extractant recovery tower top reflux pump, and an isobutane product buffer tank.

6. The apparatus according to claim 1, characterized in that, It also includes an extractant product condenser that is connected to the bottom of the extractant recovery tower; The extractant product condenser is connected to the extractant buffer tank via an extractant circulation pump.

7. A method for separating a mixture of chloromethane and isobutane, comprising the following steps: A mixture of chloromethane and isobutane is subjected to extractive distillation in the presence of an extractant to obtain chloromethane and the bottom liquid of the extractive distillation column; The extractant includes isohexane and / or n-hexane; After the bottom liquid of the extractive distillation column is cooled, the extractant is recovered and isobutane is collected.

8. The method according to claim 7, characterized in that, The pressure for extractive distillation is 600~850 kPag; The temperature for extractive distillation is 80~125℃.

9. The method according to claim 7, characterized in that, The theoretical plate number of the column during extractant recovery is 20~40; The theoretical plate number of the extraction column is 60-80.

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