JPS61227537A - Production of high-purity cyclopentadiene - Google Patents

Abstract

PURPOSE:To obtain cyclopentadiene economically in high yield and purity, by carrying out the liquid-phase decomposition of dicyclopentadiene at a specific temperature in a solvent comprising an aromatic hydrocarbon having an initial boiling point or boiling point higher than a specific level. CONSTITUTION:A high-purity cyclopentadiene having low isoprene content and useful especially as a raw material of 5-vinyl-2-norbornene is produced by a series of continuous steps economically on an industrial scale, by carrying out the liquid-phase decomposition of dicyclopentadiene at 200-250 deg.C in a solvent comprising an aromatic hydrocarbon having an initial boiling point or boiling point of >=250 deg.C, e.g. diphenyl, diphenylmethane, diphenylethane or alkylbenzene mixture (e.g. a bottom residue in the production of ethylbenzene, cumene, cymene, etc.), especially an alkylbenzene mixture having an initial boiling point of >=250 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously producing cyclopentadiene by thermally decomposing synchropentadiene in the liquid phase. More specifically, when synchropentadiene is subjected to liquid phase decomposition, an aromatic hydrocarbon having an initial boiling point or boiling point of 250°C or higher is used as a solvent, and the temperature is 200°C.
The above relates to a method for producing 2 clopentadiene by decomposition at a temperature within a range of less than 250°C.

Cyclopentadiene is synchronopentadiene or 5
- It is a compound useful as a raw material for vinyl-2-norbornene and the like. When producing synchropentadiene by thermally polymerizing cyclopentadiene, if other diolefins are present, they will form a codimer with cyclopentadiene, reducing the purity of synchropentadiene. Furthermore, when producing 5-vinyl-2-norbornene by subjecting cyclopentadiene to a Diels-Alder reaction with 1,3-butadiene, if other diolefins such as isoprene are included, 5-isopropenyl- 2-norbornene is produced as a by-product, making separation and purification of the main product difficult. Furthermore, when unreacted raw materials are collected and reused, isoprene has lower reactivity than 1,8-butadiene, so it will be circulated and accumulated in the 5-vinyl-2-norbornene manufacturing equipment. The accumulation of isoprene reduces the concentration of butadiene in the circulating fluid,
The productivity of the main product, 5-vinyl-2-norbornene, is significantly inhibited. In order to prevent this, it is necessary to discharge isoprene from the system together with the active ingredient butadiene depending on the amount of isoprene generated, which is extremely disadvantageous economically. For example, although it depends on the setting of reaction conditions and the configuration of the circulation system in the Diels-Alder reaction process, if we consider a case where the amount of isoprene mixed into cyclopentadiene is approximately doubled, the amount of circulating l,3 - To keep the isoprene concentration in the butadiene the same, 3 to 1
It becomes necessary to discharge 0 times the amount of 1,3-butadiene out of the system. For these reasons, it is highly desirable to obtain high-purity cyclopentadiene that does not contain other diolefins. Conventionally, there is a known method for obtaining cyclopentadiene by fractionating IW of cyclopentadiene in a liquid phase system. There is. However, this method generally has the disadvantage that the decomposition product cyclopentadiene and the raw material synclopentadiene react to form a polycyclopentadiene compound, which causes clogging of the apparatus and that the yield of cyclopentadiene is low. ing.

Therefore, an improved method for liquid phase decomposition of synchropentadiene using a solvent has been proposed in order to reduce the loss of raw materials due to resinization.

U.S. Pat. No. 2,881,904 proposes a method in which paraffinic hydrocarbons having an initial boiling point of 250'C or more are used as a solvent and decomposed at a temperature within the range of 200 to 850'C. It is stated that hydrocarbons are not preferred as solvents. In fact, in Example 1, when a solvent containing an aromatic compound such as spindle oil was used, the yield of cyclopentadiene decreased. Further, even if the paraffinic hydrocarbon is used, the yield of cyclopentadiene is extremely low when the decomposition temperature is 250'C or lower.

Furthermore, in the specification of Japanese Patent Publication No. 50-1021, 250°
Using a hydrocarbon having an initial boiling point of C or higher as a solvent, 2
Methods have been proposed for decomposition at temperatures in the range of 50-850'C and for regulated residence times in condensers. However, this method also states that paraffinic hydrocarbons are a more preferable solvent, and in the examples, only examples using paraffinic hydrocarbons are described. suggests that cyclopentadiene can be obtained in good yield when decomposed at temperatures above 250'C.

The present inventors conducted intensive studies on a method for economically obtaining high-yield and high-purity cyclopentadiene in the decomposition of synchropentadiene. The inventors have now discovered that cyclopentadiene of high purity can be obtained without any loss in yield when decomposed at a temperature within a range of less than

That is, the present invention relates to a method for producing high-purity cyclopentadiene, which is characterized by using an aromatic hydrocarbon containing cyclopentadiene as a solvent and decomposing it at a temperature within a range of 200°C or more and less than 250°C. It is.

It is presumed that the aromatic hydrocarbon used in the present invention has some effect of promoting decomposition or some effect of suppressing the production of polymers, and its effect is greater at lower temperatures than the preferable decomposition temperature that has been proposed in the past. According to the method of the present invention, highly pure cyclopentadiene can be industrially advantageously produced from synchlopentadiene through a series of continuous processes.

The aromatic hydrocarbon used in the present invention may be one that has an initial boiling point or boiling point of 250°C or higher, is thermally and chemically stable under decomposition conditions, and does not react with cyclopentadiene or synclopentadiene. . Examples of aromatic hydrocarbons with a boiling point of 250°C or higher include diphenyl,
Diphenylmethane, diphenylethane, etc. cause vignetting.

Further, examples of aromatic hydrocarbons having an initial boiling point of 250'C or higher include alkylbenzene mixtures, ethylbenzene, cumene, cymene, etc., which are leftover from the production process.

Particularly preferred are alkylbenzene mixtures having an initial boiling point of 250° C. or higher, which are normally used only as fuels. Their use therefore also significantly reduces the costs that would otherwise be incurred by using solvents.

The decomposition temperature ranges from 200°C to 250°C. 5-impropenyl-2-norbornene, which is usually contained in a few percent of commercially available synclopentadiene, is thermally rearranged to methyltetrahydroindene or converted into isoprene and cyclopentadiene. The rate of this rearrangement and decomposition changes depending on the temperature, and the rate of decomposition is higher at high temperatures.Therefore, once isoprene is mixed in, the two are separated because their physical properties are similar, and highly pure cyclopentadiene is produced. It is very difficult to obtain. Therefore, in order to obtain highly pure cyclopentadiene, it is desirable to decompose it at a low temperature.

On the other hand, at low temperatures, the decomposition rate of cyclopentadiene is usually slowed down, resulting in a by-product of a terminating polymer and a decrease in the yield of cyclopentadiene. Therefore, in order to obtain cyclopentadiene in high yield, it is desirable to decompose it at a high temperature.

For this reason, although conventional decomposition reaction systems using paraffinic hydrocarbons as solvents have the disadvantage of contaminating isoprene, in order to ensure the decomposition yield, temperatures above 200°C and
High yields and high purity cyclopentadiene with low isoprene content can be obtained at temperatures in the range below 50°C.

Since the high-purity cyclopentadiene obtained by the method of the present invention has a low isoprene content, the yield of 5-clopentadiene is low, and at 250'C or higher, the isoprene content increases.

As the raw material synchropentadiene used in the present invention, in addition to commercially available synchropentadiene (M degree 93 to 97%), crude synchropentadiene may be used. However, the lower limit of the crude synchropentadiene is about 70 wt% of synchropentadiene. However, it is possible to obtain cyclopentadiene of higher purity by using relatively pure synchropentadiene, and the amount of hydrogen chloride used is in a steady state weight ratio of 1:1 to 20:1, preferably 4:1. :1 to 15:l, but it can be used with various changes. If the proportion of the solvent used is too large, the amount discharged from the decomposer to the outside of the system will also increase and the recovery rate of cyclopentadiene will decrease. On the other hand, if the proportion of the solvent is too small, the fluidity of the liquid in the decomposer will deteriorate, which will impede continuous operation, which is not appropriate.

The raw material synchropentadiene may be mixed with a solvent before being supplied to the decomposer, or each may be separately supplied to the decomposer. The feedstock may also be preheated to a temperature below the boiling point of the synchropentadiene.

In order to prevent the accumulation of cyclopentadiene polymers produced as by-products in the decomposer and high-boiling components contained in the raw materials, it is necessary to continuously or intermittently discharge a portion of the liquid from the decomposer to the outside of the system. The amount of discharge is determined by the amount of polymers produced and the amount of impurities in the raw material, but it is approximately 2 to 30% of the amount of liquid in the decomposer per hour.
25 vol% is preferred.

It is desirable to keep the amount of liquid in the decomposer constant by supplying new solvent according to the amount discharged outside the system.

The liquid temperature in the decomposer is heated to 200°C or more and less than 250°C, and heating is preferably performed using a forced circulation heat exchanger.

Generally, the method according to the invention is carried out as follows. Decomposition can be carried out using an apparatus equipped with a decomposer, a heater, a fractionator, a condenser, and a cooler. Synchropentadiene and a solvent are supplied to a decomposer, and the mixture of the solvent and synchropentadiene in the decomposer is heated to a predetermined temperature in a forced circulation heat exchanger. In order to keep the amount of liquid in the decomposer constant, a portion of it is discharged outside the system. The cracked gas generated in the decomposer passes through a fractionator, a condenser, and a cooler and is cooled to -1O to -50°.

The cyclopentadiene obtained according to the present invention is generally suitable for subsequent processing purposes, eliminating the difficulties involved in separating impurities from raw materials and products.

Example 1 The residue of an ethylbenzene production process kettle having an initial boiling point of 252°C and about 90% distilled out at 860°C was used as a solvent for decomposition. 8.000 m of solvent 650f
1 capacity decomposer and forced circulation heat exchanger to produce 280
``Heat to C.

At this temperature, a mixture of commercially available 96 wt% pure synchropentadiene and a solvent (90:10 quantitative ratio) is fed to the decomposer at a flow rate of 450 f/H. The generated cracked gas is condensed through a condenser. The flow rate is 881
y/H, and the cyclopentadiene concentration is 98.9wt.
%, and the isoprene concentration was 0.18 wt%. The liquid in the decomposer is discharged to the outside of the system at a flow rate of 69 g/)L, and the liquid capacity is maintained at 650 g. This operation was carried out continuously for 350 hours, and the overall average recovery rate of cyclopentadiene was 96.
．． It was 9%. After 350 hours of operation, the decomposer, fractionator,
The heater and condenser were inspected and found to be very clean with almost no polymeric substances observed.

Example 2 Decomposition was carried out using diphenylmethane having a boiling point of 264°C as a solvent. 600f of solvent was charged into a decomposer with a capacity of 8.000w/capacity and heated to 230°C using a forced circulation heat exchanger. At this temperature, a mixture of commercially available 96 wt% pure synchropentadiene and a solvent (88:12 weight ratio) was mixed with 4
Supplied to the decomposer at a flow rate of 6017H. The generated cracked gas is condensed through a condenser.

The flow rate is 882f/H, the cyclopentadiene concentration is 98.8wt%, and the isoprene concentration is 0.18wt%.
Met. The liquid in the decomposer is discharged to the outside of the system at a flow rate of 781/H, and the liquid capacity is maintained at 600f.

This operation was carried out continuously for 240 hours, and the overall average recovery rate of cyclopentadiene was 97.1%. 240
After some time, the device was clean with almost no polymeric substances observed.

Comparative Example 1 Decomposition was carried out using the residue from the ethylbenzene manufacturing process kettle, which had an initial boiling point of 252°C and about 90% distilled out at 360°C, as a solvent. 650g of solvent to 8.000 #l
/ capacity into a decomposer and heated to 180° using a forced circulation heat exchanger.
Heat to C.

At this temperature, a mixture of commercially available 96 wt% pure synchropentadiene and a solvent (90:10 weight ratio) was mixed with 45%
! Supplied to the decomposer at a flow rate of M/)1. The generated cracked gas is condensed through a condenser. Its flow rate is 84497
H, and the cyclopentadiene concentration is 98.6 Wt”%
, the isoprene concentration was 0.04 wt%. The liquid in the decomposer is discharged to the outside of the system at a flow rate of 11 t f/H, and the liquid capacity is maintained at 650y.

This operation was carried out continuously for 36 hours, and the average recovery rate of cyclopentadiene over the whole was 86.0%. After 36 hours, the device had a large amount of polymeric material attached to it.

Comparative Example 2 1. with a boiling point of 269°C. Decomposition was carried out using l-diphenylethane as a solvent. 650 tons of solvent is charged into a decomposer with a capacity of 8,000 and heated to 265°C using a forced circulation heat exchanger. At this temperature, a mixture of commercially available 96 wt % pure synchropentadiene and solvent (88:12 weight ratio) is fed to the decomposer at a flow rate of 458 g/H. The generated cracked gas is condensed through a condenser. The flow rate was 386 Da/H, the cyclopentadiene concentration was 9s,
twt%, and the isoprene concentration was 0.24wt%.

The liquid in the decomposer is discharged to the outside of the system at a flow rate of '12 f//H, and the liquid capacity is maintained at 6509.

This operation was carried out continuously for 92 hours, and the overall average recovery rate of cyclopentadiene was 97.8%.

Claims (1)

[Claims] In a method of obtaining cyclopentadiene by liquid phase decomposition of synchropentadiene, an aromatic hydrocarbon having an initial boiling point or boiling point of 250°C or higher is used as a solvent, and the decomposition is performed at a temperature within the range of 200°C or higher and lower than 250°C. A method for producing high purity cyclopentadiene, characterized by: