KR100458361B1 - Process for Separation of Isoprene from C5 fraction of Cracked Naphtha by Extractive Distillation - Google Patents

Abstract

The present invention relates to a method for separating isoprene by extractive distillation from a C5 fraction obtained from a naphtha cracker, and an object thereof is to provide a method for minimizing energy consumption of an entire process.

(1) a primary extraction distillation step of extracting and distilling isoprene from the C5 fraction by contacting the C5 fraction with the extractant; and (2) recovering the extractant by distilling the mixture of isoprene and the extractant; 3) distilling isoprene separated in step (2) to remove high boiling point components to prepare crude isoprene, and (4) extractive distillation of crude isoprene to remove triple bond components; (5) recovering the extractant used to remove the triple bond components in step (4), and (6) removing high boiling point components from isoprene from which the triple bond components were removed in step (4) to produce high purity isoprene. In the step of separating the isoprene from the C5 fraction consisting of

In step (2), the operating conditions of the extractant recovery tower are set to normal pressure or higher so that the temperature of the extractant recovered to the column bottom is 150 ° C or higher, and in step (3), the high boiling point component is separated to obtain crude isoprene. With the operating conditions of 3 to 5 atm, the sensible heat of the extractant recovered in step (2) is supplied to the reboiler in step (3) while maintaining the operating temperature of the reboiler at 90 to 125 ° C, and extraction in step (5). The operating conditions of the second recovery column are set to at least normal pressure, so that the temperature of the extractant recovered to the column bottom is 150 ° C or higher, and in step (6), the operating conditions of the distillation column to obtain high-purity isoprene by separating low boiling point components are 2.7 to 4.5 atm The sensible heat of the extractant recovered in step (5) is supplied to the reboiler in step (6) while maintaining the operating temperature of the reboiler at 70 to 120 ° C.

Description

Process for Separation of Isoprene from C5 fraction of Cracked Naphtha by Extractive Distillation

The present invention relates to a method for separating isoprene from a C5 fraction, and more particularly, to a method for separating isoprene from a C5 fraction obtained from a naphtha cracker by extractive distillation.

Isoprene was first manufactured by C. E. Williams by pyrolysing natural rubber in 1860, and in 1955 began to be used as a raw material for synthetic rubber. It was mainly produced by synthetic methods before the 1970s, but after 1975, it is mainly separated from the C5 fraction obtained from naphtha crackers.

By the way, since the C5 fraction contains many similar boiling point components, it cannot be separated with high purity by conventional distillation. Therefore, methods such as multi-stage distillation, extractive distillation, liquid-liquid extraction, and heat treatment have been attempted (Chem. Eng., London, 1971, 315). Currently, commercial distillation using a specific extractant has been mainly adopted. . As the extractant, N-methylpyrrolidone, N-methylpyrrolidone, dimethylformamide (DMF), acetonitrile and the like are used.

As a method of separating isoprene by extractive distillation, British Patent No. 1,195,648 to Zeon discloses a two-stage extractive distillation process using dimethylformamide (DMF) as an extractant, which is based on a C5 fraction of isoprene content of 12%. It is possible to produce isoprene having a purity of 99% or more.

Referring to Figure 1 in more detail as follows.

When supplying the C5 fraction (1) to the central portion while supplying the extractant to the first extraction distillation tower (A) at the top, the C5 fraction is in contact with the extractant flowing into the upper portion and isoprene is absorbed by the extractant and discharged to the bottom, Pentane, isopentane, and pentenes 2 are discharged to the top. When the extractant containing isoprene discharged to the bottom of the first extraction distillation tower is introduced into the first extraction recovery column (B), C5 components including isoprene are discharged to the top, and the extractant (3) is discharged to the bottom. do. Subsequently, when the C5 component including isoprene discharged to the upper portion of the primary extractant recovery tower is introduced into the high boiling point separation tower (C), crude isoprene (4) from which high boiling point components such as piperylene are removed is removed. Is obtained. Subsequently, when the isoprene (4) is supplied to the center while supplying the extractant to the secondary extraction distillation column (D), the prepared isoprene is brought into contact with the extractant introduced into the upper part, and the cyclopentadiene (CPD) or acetylene 3 is extracted. After the heavy binding material is removed, it is discharged to the column top, and the triple binding material of cyclopentadiene (CPD) or acetylene is discharged to the column bottom together with the extractant. If isoprene discharged from the top of the second extraction distillation column is fed to the low boiling point separation tower (F) to remove low-boiling trace impurities such as isopropenyl-acetylene and 2-butyne, High purity isoprene 8 is obtained. On the other hand, the mixture (extractant containing impurities such as CPD) discharged to the bottom of the secondary extraction distillation column is supplied to the secondary extractant recovery tower (E) to recover the extractant. (The mixture 5 containing a large amount of impurities such as CPD is discharged from the top, and the extractant 6 is discharged from the bottom.)

In a similar process to Nippon Petrochemicals, U.S. Patent No. 1,225,549 uses acetonitrile as an extractant, and SNAM Progetti U.S. Patent No. 4,009,084 describes N-formyl morpholine (N). -formyl morpholine) is disclosed, and several patents, including another patent WO 98/40448 from Zeon of Japan, use a mixture of water and furfural as extractant or add various polymerization inhibitors. Methods and the like are disclosed.

However, these processes do not take into account the energy consumption, which is the most important factor in determining the economics of the distillation process, has a disadvantage in that a lot of energy is consumed.

In general, heat exchange may be considered as a method of recovering energy. That is, the extractant is cooled and supplied to the upper portion of the tower (primary extraction distillation tower and secondary extraction distillation tower) by heat-exchanging the extractant having a high temperature with the raw material (C5 fraction or prepared isoprene). It is supplied in the middle, but only part of the heat can be recovered.

It is an object of the present invention to provide a method for minimizing the energy consumption of the whole process in the process of separating isoprene by extractive distillation from a C5 fraction.

1 is a process chart of a general extraction distillation process.

2 is a flowchart of an extractive distillation process according to the present invention.

** Explanation of symbols for main parts of drawings **

A: 1st extraction distillation tower B: 1st extraction recovery tower

C: refinery tower (high boiling point separation tower) D: secondary extraction distillation tower

E: 2nd extractant recovery tower F: Refining tower (low boiling point separation tower)

G1, G2: Circulation Pump

Separation of isoprene from the C5 fraction by extraction distillation, as described above, is used in the extraction distillation column to recover and reuse the extractant used in the first, second, and two recovery towers through two extraction distillation steps. The amount of extractant used is about four times the amount of C5 fraction in the first extraction distillation column, and up to about eight times the amount of crude isoprene in the second extraction distillation column.

In addition, the recovered extractant is generally stored in a storage tank and reused. Some of the extractant is directly re-introduced into the first and second extraction distillation towers to remove high-boiling components such as dicyclopentadiene (DCPD). For this purpose (although not shown in Figure 1) is generally reused after a purification process such as distillation under reduced pressure.

In the conventional process, the amount of extractant used is 134,000 kg / hr and 39,000 kg / hr in primary and secondary extraction distillation towers, respectively, based on an annual scale of 30,000 tons (3,750 kg per hour). The temperature of is recovered to 150 ° C or more (when the extractant recovery tower is operated at atmospheric pressure), cooled to 120 ° C or less and stored in a storage tank.

The inventors of the present invention make the assumption that by optimizing the operating conditions from the operating conditions of the prior art, that is, the amount of extractant used for extractive distillation and the temperature of the extracted extractant, the heat of the recovered extractant can be effectively used. The present invention was completed through a series of experiments and sophisticated simulation.

The present invention for achieving the above object, (1) the first extraction distillation step of separating the isoprene from the C5 fraction by extractive distillation while contacting the C5 fraction and the extractant, and (2) the separation of isoprene and extractant previously separated Distilling the mixture to recover the extract, (3) distilling the isoprene separated in step (2) to remove high boiling point components to prepare crude isoprene, and (4) extracting and distilling the crude isoprene. Recovering the secondary extractive distillation step of removing the heavy binding component, and (5) extractant used to remove the triple binding component in step (4), and (3) removing the triple binding component in step (4). In the step of separating the isoprene from the C5 fraction, which is a step of removing the low boiling point component from the isoprene to produce a high purity isoprene, in step (2), the operating conditions of the extractant recovery tower are returned to the bottom of the column under normal pressure. The temperature of the extraction extractant is 150 ° C or higher, and the operating temperature of the distillation column for separating the high boiling point component in step (3) to obtain the prepared isoprene is 3 to 5 atm. The sensible heat of the extractant recovered in step (2) is supplied to the reboiler in step (3), and the temperature of the extractant recovered at the bottom of the extractor recovery tower in step (5) above normal pressure (5) while maintaining the operation temperature of the reboiler at 70-120 ° C. by setting the operating conditions of the distillation column to obtain high purity isoprene by separating low boiling point components in step (6). It characterized in that the sensible heat of the extractant recovered in the step (6) is supplied to the reboiler.

However, as can be seen in the examples described later, the larger the temperature difference between the temperature of the extractant recovered in step (2) and the fluid temperature of the reboiler of step (3), the more the temperature of the extractant recovered in step (5) The greater the temperature difference between the reboiler and the fluid temperature of step (6), the greater the amount of heat transferred and neither the temperature of the recovered extractant nor the fluid temperature of the reboiler can be arbitrarily adjusted.

In order to optimally control the temperature of the extractant supplied to the heat source of the reboiler and the fluid temperature of the reboiler, the extractant supplied to the reboiler is mixed with the extractant discharged from the reboiler to recover the extractant recovered in step (2). Keeping the difference between the temperature and the fluid temperature in the reboiler in step (3) and the temperature of the extractant recovered in step (5) and the fluid temperature in the reboiler in step (6) is within 25 ° C. desirable.

The process of the present invention is described in detail with reference to FIG.

In FIG. 2, the C5 fraction 1 is introduced into the first extraction distillation tower A, and isoprene is discharged to the bottom of the first extraction distillation column together with the extractant, and the pentane, isopentane, and pentenes 2 are formed in the top of the extraction column. Discharged. The mixture (extractant containing isoprene) discharged to the bottom of the primary extraction distillation column is separated in the primary extraction recovery column (B), and C5 components including isoprene are used at the top, and the extractant (3) is at the bottom. It is recovered.

In the high boiling point separation tower (C) for separating high boiling point from isoprene discharged to the top of the first extraction and recovery tower (C), the prepared isoprene (4) is obtained as a top top product, and at this time, the heat source necessary for reboiling the high boiling point separation tower. By using the extractant (3) recovered in the first extractant recovery tower.

At this time, the temperature difference between the fluid temperature in the reboiler and the extractant used as the heat source should be adjusted to the optimum conditions for boiling, and the circulation pump G1 is used to realize this. A part of the extractant used as a heat source by the circulation pump is mixed with the newly supplied extractant, adjusted to an appropriate temperature, and then supplied to the reboiler. As described in Figure 1, the prepared isoprene is once again extracted and distilled (secondary extraction distillation tower-D, secondary extraction and recovery tower-E, using a low boiling point separation tower-F) to be purified into high purity isoprene (8) and low boiling point separation. When the low boiling point component is separated from the tower (F) to obtain high purity isoprene (8) as the bottom product, the extractant (6) recovered from the secondary extractant recovery tower (E) is used as a heat source for reboiling of the low boiling point separation tower. Will be used.

The present inventors construct a distillation experiment apparatus for separating isoprene from C5 fraction by extractive distillation as in the following examples and experimentally confirm the operating conditions (temperature, pressure, reflux ratio, extractant usage, etc.) and separation performance of each distillation column. It was.

In addition, an experiment was also conducted to use the sensible heat of the extractant as a reboiler heat source for the high boiling point separation tower and the low boiling point separation tower.

<Example>

After preparing isoprene from C5 fraction using three distillation towers of extraction distillation tower, extractant recovery tower, and purification tower (high boiling point separation tower), three distillation towers (extraction distillation tower, extraction recovery column, and low boiling point separation tower) were added. To obtain high purity isoprene.

A. Experiment

1) Extraction distillation column: packed column of 2 inches in diameter x 6 meters in height with 2 kW reboiler (6 inches in diameter, 50 cm in height) and condenser. The filling is structured packing ( Sulzer's DX packing, which is structured packing, has 80 actual stages.

2) Extractor recovery tower: 2 inch diameter × 4m high packed tower with 2kW reboiler (8 inch diameter, 50 cm high) and condenser. The filling is 1/4 inch Raschig ring. , The actual number is 20.

3) Refining tower (high boiling point separation tower or low boiling point separation tower): A filling tower of 3 inches in diameter x 7 meters in height is equipped with a 2 kW reboiler (6 inches in diameter and 40 cm in height) and a condenser. Sulzer's DX packing, the actual number is more than 100 steps.

B. Experiment

1) Preparation of Crude Isoprene

The extraction distillation tower (1st) and extractant recovery tower (1st) were introduced with a C5 fraction containing 17% isoprene at a flow rate of 1.2 kg per hour (total amount: 42.8 kg) and DMF at a flow rate of 4.76 kg per hour as an extractant. Operation yielded 0.33 kg per hour of a mixture containing 38% isoprene. 42.8 kg of the mixture containing 38% isoprene was added to a purification tower (high boiling point separation tower) to obtain 19.1 kg of prepared isoprene having a purity of 98%. At this time, the operating conditions of each distillation column were as follows.

a) Extraction distillation column: The pressure was 2 atm, the temperature was 38 ℃ and 80 ℃ at the top and bottom, respectively, and the extractant / C5 raw material ratio was 3.97.

b) Extraction recovery column: The pressure was at atmospheric pressure and the top and bottom temperatures were 40 ° C and 154 ° C, respectively.

c) Refining tower (high boiling point separation tower): when the reflux ratio was 15 or more and the operating pressure was 1.6 atm, the tower top and tower bottoms had temperatures of 53 ° C, 60 ° C, and 3.5 atm. Column bottom temperature was 125 ° C.

When the pressure of the purification column is 5 atm or less, the bottom temperature is 125 ° C. or less, so it can be seen that reboiling using the extractant (154 ° C.) recovered from the extractant recovery tower is possible.

2) Reboiling experiment of the purification tower by the recovered extractant

The following experiment was carried out to confirm the boiling point of the purification column bottom effluent due to the sensible heat of the extractant.

The high-boiling mixture discharged from the bottom of the refinery tower was filled in a jacketed 15L tank (8 inches in diameter, 50 in height) about 8L, and the jacket was circulated with a heated extractant. When the temperature of the extractant circulated to the jacket was 110 ° C or higher, the boiling point of the high boiling point mixture in the tank was confirmed. When the temperature difference between the extractant and the tank was maintained at 25 ° C, the amount of heat transferred was about 1900 Kcal / hr. It was about. Even if the temperature difference became 25 degreeC or more, heat quantity did not increase significantly.

3) Preparation of Purified Isoprene

0.7 kg of isoprene was obtained with an purity of 99% or more by operating an extraction distillation tower and an extractor recovery tower with 1.22 kg of prepared isoprene and 6.73 kg of extractant (DMF) per hour. Since 99% pure isoprene contains a small amount of low-boiling impurities (2-butyne, etc.), it was put into a purification tower to remove low-boiling matters from the top of the column under conversion flow conditions, and then high-purity (99.5% or more) of isoprene was obtained at the bottom of the column. . At this time, the operating conditions of each distillation column were as follows.

a) Extraction distillation column: pressure was atmospheric pressure, temperature was 35 ℃ and 155 ℃ at the top and bottom, respectively, and the ratio of extractant / prepared isoprene was 5.52.

b) Extraction recovery column: The pressure was at atmospheric pressure, and the top and bottom temperatures were 35 ° C and 155 ° C, respectively.

c) Refining tower (low boiling point separation tower): The operating conditions of the refining tower (low boiling point separation tower) under conversion flow conditions are that the operating temperature of 1.6 atm is 50 ° C, 62 ° C, 2.6 atm and 4.5 atm, respectively. The temperature of the tower bottom became 69 degreeC and 125 degreeC.

When the pressure of the purification column is 4.5 atm or less, the bottom temperature is 125 ° C. or less, so it can be seen that re-use using the extractant (150 ° C. or more) recovered from the extraction recovery column is possible. That is, the sensible heat of the extractant can be used as a heat source for the reboiler.

4) Re-experimental experiment of the purification column with the recovered extractant

Experiment using the same device as 2). As in 2), the heat transfer amount increased up to 25 ℃ and the effect did not increase significantly.

According to the present invention, the amount of heat recoverable from an isoprene separation plant of 30,000 tons per year, which is an economic unit of production, is based on the operating conditions (reflux ratio and extractant usage) identified in the experiment, and the high boiling point separation tower and the low boiling point separation are separated. The tower reaches 2.4 x 10 ⁶ Kcal / hr and 1.4 x 10 ⁶ Kcal / hr, respectively. This calorie is equivalent to about 12% of the calorie used in the whole distillation process, which can reduce the production cost of isoprene by energy saving.

Claims (5)

(1) a primary extractive distillation step of extracting and distilling isoprene from the C5 fraction by contacting the C5 fraction with the extractant; (2) distilling the mixture of isoprene and extractant to recover the extractant; (3) distilling isoprene separated in step (2) to remove high boiling point components to prepare crude isoprene, (4) a second extraction distillation step of extracting and distilling the prepared isoprene to remove the triple bond component; (5) recovering the extractant used to remove the triple bond components in step (4), (6) a step of separating isoprene from a C5 fraction comprising the step of removing the low boiling point component from the isoprene from which the triple bond component is removed in (4) to produce high purity isoprene; In step (2), the operating conditions of the extractant recovery tower are set to normal pressure or higher so that the temperature of the extractant recovered to the column bottom is 150 ° C or higher, and in step (3), the high boiling point component is separated to obtain crude isoprene. With the operating conditions of 3 to 5 atm, the sensible heat of the extractant recovered in step (2) is supplied to the reboiler in step (3) while maintaining the operating temperature of the reboiler at 90 to 125 ° C, and extraction in step (5). The operating conditions of the second recovery column are set to at least normal pressure, so that the temperature of the extractant recovered to the column bottom is 150 ° C or higher, and in step (6), the operating conditions of the distillation column to obtain high-purity isoprene by separating low boiling point components are 2.7 to 4.5 atm By separating the isoprene from the C5 fraction, the sensible heat of the extractant recovered in step (5) is supplied to the reboiler in step (6) while maintaining the operating temperature of the reboiler at 70 to 120 ° C. Way. delete delete The method according to claim 1, wherein the extractant supplied to the reboiler is re-boiled to maintain a constant difference between the temperature of the extractant recovered in step (2) and the fluid temperature in the reboiler in step (3) within 25 ° C. A method for separating isoprene from a C5 fraction, characterized in that it can be mixed with the extractant discharged from. The method according to claim 1, wherein the extractant supplied to the reboiler is reboiled to maintain a constant difference between the temperature of the extractant recovered in step (5) and the fluid temperature in the reboiler in step (6) within 25 ° C. A method for separating isoprene from a C5 fraction, characterized in that it can be mixed with the extractant discharged from.