GB2271575A

GB2271575A - Production of cycloalkanes

Info

Publication number: GB2271575A
Application number: GB9221795A
Authority: GB
Inventors: Orto Giovanni Battista Dall; Christian Francois Pardou; Andre Adrien Laurent Theyskens
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1992-10-16
Filing date: 1992-10-16
Publication date: 1994-04-20
Also published as: GB9221795D0

Abstract

Cycloalkane is added as a diluent in the manufacture of the same cycloalkane from the dicycloalkadiene by thermal depolymerization and catalytic hydrogenation of the resulting monomeric cycloalkadiene. The process is especially suited to the manufacture of cyclopentane. The catalytic hydrogenation of the cycloalkadiene is carried out in a closed loop batch reactor, the catalyst being circulated in the form of a slurry until it is removed from contact with the reactants and reaction product at the end of the reaction by filtration.

Description

"Cycloalkanes" This invention relates to the manufacture of cycloalkanes, more especially to the manufacture of cyclopentane.

For some years, and until very recently, favoured physical blowing agents for making many foamed polymers have been chlorofluorocarbons (CFCs). For example, in the manufacture of foamed polyurethane, there has been used monofluorotrichloromethane, or CFC-ll, b.p. 240C, which is conveniently mixed with the polyol reactant.

When this is contacted with the isocyanate, the exotherm associated with the urethane-forming reaction is sufficient to boil the CFC-ll, causing cell formation in the material.

CFCs have, however, been shown to damage the atmospheric ozone layer, and there is a need to replace them by other effective but less damaging products.

Certain hydrocarbon blowing agents were previously employed for this purpose, for example, propane, butane and pentane, but were superseded by the CFCs. They are now again under investigation, and interest has been shown in using cyclopentane. The low thermal conductivity of this material results in a foamed product with good insulation properties. The material, however, is at present obtained by fractionation of a petroleum feedstock and is not readily available in the necessary purity at competitive prices. There remains a need for a process whereby cyclopentane may be produced on a more economical commercial scale. There is a similar need for a commercially acceptable route to methylcyclopentane and other cycloalkanes from the corresponding dicycloalkadiene.

In British Specification No. 1,302,481, there is described a process in which dicyclopentadiene is depolymerized to cyclopentadiene in the presence of hydrogen, and subsequently partially reduced to cyclopentene with hydrogen in the presence of a catalyst. At the start of the reaction, substantial proportions of cyclopentane are produced and little of the desired cyclopentene but after start-up the proportion of cyclopentane produced is very small.

The present invention provides a process for the manufacture of a cycloalkane from the corresponding dicycloalkadiene, which comprises thermally depolymerizering the dicycloalkadiene to monomeric cycloalkadiene and catalytically hydrogenating the cycloalkadiene monomer, wherein the said cycloalkane is used as a diluent for the reactants entering at least the hydrogenation stage.

More especially the present invention provides a process for the manufacture of (methyl)cyclopentane from di (methyl) cyclopentadiene, which comprises thermally depolymerizing di (methyl) cyclopentadiene to (methyl) cyclopentadiene, and catalytically hydrogenating the (methyl) cyclopentadiene to (methyl) cyclopentane, wherein (methyl)cyclopentane is used as a diluent for the reactants entering at least the hydrogenation stage.

In the immediately preceding paragraph, the term (methyl)cyclopentane is used to refer to cyclopentane or to methylcyclopentane and the other similar terms have corresponding meanings. In the subsequent description, the invention will be described for simplicity with reference to cyclopentane manufacture only but it will be understood that the references to conditions and procedures advantageous and preferred for the manufacture of cyclopentane apply mutatis mutandis also to the manufacture of other cycloalkanes especially methylcyclopentane.

Advantageously, cyclopentane is used as a diluent in the depolymerization stage also. Conveniently the cyclopentane diluent is recycled cyclopentane product.

Advantageously, the depolymerization is carried out in the presence of hydrogen.

The process may conveniently be operated by mixing a dicyclopentadiene-containing feedstock with cyclopentane and hydrogen, and passing the reaction mixture to a heater (a heat exchanger or furnace) to depolymerize the dimer to monomeric cyclopentadiene. The monomercontaining feed is catalytically hydrogenated, and the hydrogenated product divided into two main streams; the first stream is removed as a cyclopentane-containing product, optionally being distilled and/or otherwise treated to provide a product of the desired purity, the second stream being recycled and mixed with the dicyclopentadiene feedstock and hydrogen and passed to the heater.

In the depolymerization or cracking stage, the following conditions may conveniently be employed.

A temperature within the range of from 200 to 4000C, advantageously from 200 to 3000C, and preferably from 200 to 2500C, may be used. Although higher temperatures favour depolymerization, cyclopentadiene and dicyclopentadiene also tend to form higher polymers that collect as gummy deposits in various parts of the plant, causing blockages, and this reaction is also favoured at higher temperatures. Although it has been observed that the process of the present invention, at least in certain embodiments, is less prone to cause polymerization than certain prior art processes, it has been found preferable to operate at the lower end of the temperature range, temperatures of 220 to 2400C having proved especially valuable.

Advantageously, superatmospheric pressure is employed; a pressure within the range of from 1 MPa to 5 MPa is typical, and a pressure in the range of from 1.5 to 3.5 MPa is preferred.

In the depolymerization stage, a space velocity in the range of from 0.5 to 50 v/hr/v may conveniently be used, a velocity in the range of 0.9 to 45 v/hr/v being found advantageous. Throughout this specification, space velocity values are based on diluted feedstock.

The proportion of dimer in the feedstock is advantageously from 10 to 50%, preferably from 20 to 30%, and most preferably about 25%, by weight. The feedstock is a mixture of recycled hydrogenated product and the raw dicyclopentadiene feed, which itself contains normally about 75% of the subject dimer, the remainder comprising methyl and dimethyl pentadiene dimers and trimers, and toluene. The recycled hydrogenated product comprises mainly cyclopentane and the fully saturated tetrahydrodicyclopentadiene. It is within the scope of the invention to use additional inert diluents, but the advantages of the invention are obtained most notably when cyclopentane forms a major proportion of the diluent.

The ratio of dicyclopentadiene to hydrogen, if present, in the feed to the cracking stage may vary widely, 0.5 to 20 moles of hydrogen per mole of dicyclopentadiene being advantageous; a preferred ratio range is from 0.75:1 to 10:1, for example about 5:1. Beneficial results are observed in the presence of molar proportions of hydrogen below the minimum levels required in the above-mentioned GB-A-1,302,481, where a ratio of at least 1:1, and preferably from 8:1 to 40:1, is needed to obtain a reduction in reactor fouling by gummy polymeric deposits.

In the hydrogenation stage, the following conditions may conveniently be employed: A temperature within the range of from 30"C from 1750C, advantageously from 50 to 1200C, is conveniently employed. The preferred temperature is dependent on, among other factors, the state of the catalyst, a fresh catalyst corresponding to a lower operating temperature and an old catalyst to a higher temperature.

A pressure within the range of from 1 MPa to 5 MPa, advantageously within 1.5 MPa to 3.5 MPa, may be employed.

A space velocity in the hydrogenation reactor of from 0.5 to 10 v/hr/v, advantageously from 1 to 5 v/hr/v, may be used.

The proportion of cyclopentadiene in the feedstream is advantageously from 10 to 40%, preferably from 15 to 25%, by weight.

It will be understood that, while the cyclopentane or other diluent is advantageously mixed with the fresh feedstock before it enters the depolymerization zone, it is also possible, though less preferred, to feed diluent into the hydrogenation zone to mix with the reactants there. It is also possible in either case, though less preferred, to feed diluent separately into a reaction zone rather than mix it with feed before the zone is entered.

The molar ratio of hydrogen to cyclopentadiene is advantageously from 1:1 to 20:1, and preferably from 4:1 to 8:1.

The catalyst may be a noble metal catalyst, advantageously nickel. A preferred catalyst is a supported nickel metal catalyst, for example, 50% nickel metal on alumina. Such a catalyst is commercially available as Ni 3288 from Engelhard Corporation. Other noble metals, e.g., Pt, are suitable provided the feedstock is substantially sulphur free.

The proportion of the product recycled as diluent to either the hydrogenation or, preferably, the cracking stage is selected to give the desired proportion of dicyclopentadiene in the feedstock and to control the exotherm of the hydrogenation reaction; in general, however, the ratio of recycled hydrogenated product to fresh feed is advantageously 2:1 to 10:1 by weight, depending on the heat control requirements of the reactor.

Although, as indicated above, the process of the present invention produces less gummy polymer than previously proposed processes, there may still be some polymer build-up in the reactor, especially that of the cracking stage. It has been found that it is desirable at intervals to flush the reactor system with a solvent for the polymer. Advantageously, the solvent is white spirit (petroleum spirit), or other solvent having a high naphthenic content. Any solvent used should preferably contain less than 5 ppm sulphur, to avoid hydrogenation catalyst poisoning.

Normally, the reactor used for the hydrogenation stage is advantageously a fixed-bed reactor. If fouling of the reactor by polymerization products is likely to prove a problem or if a the feedstock contains sulphur at a level (above about 10 ppm) that could cause rapid catalyst poisoning, a closed loop reactor may be used.

Accordingly, the invention also provides a process for the catalytic hydrogenation of a cycloalkadiene in which process a catalyst in powder form is used, and on completion of the reaction is removed from contact with the reactants by filtration. The invention further provides the use of a closed loop reactor in the catalytic hydrogenation of a cycloalkadiene.

More especially, the invention provides a closed loop batch reactor process for catalytic hydrogenation of a cycloalkadiene in which a catalyst powder is circulated in the form of a slurry and removed from contact with the reactants and reaction product at the end of the reaction by filtration. Advantageously, the operating conditions, especially temperature, are controlled by heating or cooling the circulating slurry.

The invention has been described in terms of a two stage process using a dicycloalkadiene, especially dicyclopentadiene, as starting material because of the instability of the monomer. It is, however, within the scope of the invention to use a cycloalkane as a diluent in hydrogenation of the corresponding cycloalkadiene whether obtained from the dimer or otherwise.

Accordingly, the invention also provides the use of a cycloalkane as a feed diluent in the hydrogenation of the corresponding cycloalkadiene to the cycloalkane. The invention is especially applicable to the use of a cyclopentane in such a process.

One form of process carried out in accordance with the invention will now be described by way of example only with reference to the accompanying drawing, in which the sole figure is a schematic flow diagram illustrating generally the type of apparatus that is used.

From a floating cover-equipped atmospheric storage tank 10, liquid dicyclopentadiene is fed through feed line 12 to a heat exchanger 14 to heat the feed/gas mixture to 220 to 2400C.

Hydrogen gas is added to the feed through a feed line 16, while recycled cyclopentane-rich hydrogenated product is supplied through a feed line 18, both joining the feed between the tank 10 and the heat exchanger 14.

The reaction product from the heat exchanger 14, comprising hydrogen, cyclopentadiene, unreacted starting material, and recycled cyclopentane-rich hydrogenated product is fed to a heat exchanger 20 where it is cooled to about 500C or other suitable temperature for the hydrogenation stage.

The cooled reaction mixture is fed through a line 22 to a catalytic hydrogenation reactor where cyclopentadiene is reduced to cyclopentane at a temperature of from 50 to 1200C. The resulting reaction mixture is fed by a line 26 to a gas/liquid flash drum separator 28 where hydrogen and other gaseous components are removed.

The resulting liquid product mixture is divided into two streams, a first being recycled through the line 18 to be mixed with feed dicyclopentadiene and a second being fed by a line 30 to a stabilizer distillation column 40 to remove the remaining hydrogen and other light gaseous components.

In the column 40, components lighter than cyclopentane are removed overhead by a line 42, the resulting concentrated product mixture being fed by a line 44 to a storage tank 50. From the tank 50 the product is fed to a fractionation column 52 where a concentrated cyclopentane-containing product is recovered as overhead via a line 54, and fed to a product storage tank 60.

The bottoms product from the column 52 may be used as a gasoline component or, with additional fractionation, the heavy bottoms product may be used as a source of tetrahydrodicyclopentadiene, obtainable at high purity by additional fractionation.

A similar process to that described above with reference to the drawing may be used to convert methylcyclopentadiene dimer to methyl cyclopentane, with a similar possibility of using the heavy bottoms product as a source of high purity tetrahydrodi(methylcyclopentadiene).

Examples Example 1 This example illustrates thermal decomposition of dicyclopentadiene in the presence of hydrogen and cyclopentane and cyclopentadiene. The dicyclopentadiene was of commercial grade, 73t by weight pure, S.G. 0.978.

A feedstock containing the components set out in Table 1 below was fed at a rate of 0.9 litre per hour together with hydrogen at a rate of 200 litres per hour to a catalyst-free reactor maintained at the temperature shown and a pressure of 2.9 MPa. The depolymerizing reactor had a volume of 0.025 litre and was externally heated by a sandbath. The conversion rate, in terms of weight percentage of dicyclopentadiene converted to cyclopentadiene, is calculated by subtracting the weight of cyclopentadiene in the feed from that in the product and dividing that value by the weight of dicyclopentadiene in the feed.

In the Tables Conv. represents conversion, NC5 represents normal pentane, (D)CPD represents (di)cyclopentadiene, TH-DCPD represents tetrahydrocyclopentadiene, CP cyclopentane, and CPE represents cyclopentene.

Table 1

Run Feed, wt% Product, wt% Temp, Conv.

DCFD CPD CP NC5 DsD CPD CP NC5 OC 1 17.6 12 54.2 3.7 12.4 17.4 52.3 3.4 220 31 2 17.6 12 54.2 3.7 12.5 18.8 54.1 3.5 220 39 3 13.8 15.1 56.5 4.1 6.1 23.7 54.8 3.9 240 62 4 13.8 15.1 56.5 4.1 6.6 23.0 57.9 5.0 240 57 5 14.4 15.3 56.4 4.1 6.1 25.4 55.6 4.1 250 70 The remaining components, about 10 wt%, in feed and product are inert impurities in the feed streams, each individual component being present at less than 1 wt%.

It will be seen from Table 1 that the conversion rate increases with temperature. This is, however, accompanied by an increase in reactor fouling. The weight dilution ratio of CP to DCPD was about 3.08:1 in Runs 1 and 2, 4.04:1 in Runs 3 and 4, and 3.92:1 in Run 5.

Example 2 Example 1 was repeated at 2200C, but with a feed rate of liquid reactant of 0.5 litre per hour, maintaining the other conditions the same. The result is shown in Table 2.

Table 2

Feed, wt% Product, wtt Conv.

DBD CPD CP NC5 DBD CPD CP NC5 % 18.6 12.3 55.1 4.0 11 21.6 56.3 3.9 50 Comparison of the result of this example with those of Runs 1 and 2 of Example 1 shows the increase in conversion rate at lower space velocities.

Example 3 This example describes the hydrogenation step of a stream containing cyclopentane, tetrahydrocyclopentadiene, cyclopentadiene and dicyclopentadiene over a nickel catalyst in an isothermal reactor at a temperature of 600C and a pressure of 2.6 MPa.

The reactor contained 0.165 litre of the commercial nickel catalyst Engelhard Ni 3288. The feedstock was fed to the reactor at a rate of 0.415 litre per hour together with hydrogen at a rate of 200 normal litres per hour.

The results are shown in Table 3 below, the values below the components representing percent by weight of the feed or product.

Table 3

Time TH-DD CPD CP CPE NC5 Hours Ebbed O 12 18.1 22.9 26.4 0 0.7 Product 4 0 31 0 44.7 0 0.7 Product 8 0 29.6 0 43.5 0 0.7 9 9 13.3 18.7 19.7 25.6 0 0.7 Product 15 0 31.4 0 42.9 0 0.7 Product 17 0 30.4 0 44.3 0 0.7 The remaining components (around 25 wt%) in the feed and in the product are impurities contained in the raw dicyclopentadiene and cyclopentane.In addition to these components some other components, not well identified and having boiling points close to dicyclopentadiene, were produced during hydrogenation. These new unknown components from the hydrogenation were completely saturated. All of these show a content about 1 wt% each.

Table 3 shows that the hydrogenation was complete to the saturated tetrahydrodicyclopentadiene and cyclopentane, and no intermediate unsaturated components were detected.

Example 4 Example 3 was repeated at 1000C, otherwise keeping the same operating conditions. This example was carried out to simulate the conditions required when the catalyst is almost deactivated. Table 4 shows the results.

Table 4

Time DCPD TH-DCPD CPD CP CPE NC5 Hours Feed O 12.6 19.4 19.3 26 0 0.7 Product 4 0 32.9 0 43.1 0 0.7 product 8 0 31.9 0 41.1 0 0.7 Feel 9 14.2 19.5 17.4 25 0 0.7 Product 13 0 35.4 0 39.2 0 0.7 Product 17 0 32.9 0 39.7 0 0.7 18 18 15.1 19.5 16.3 24.9 0 0.7 Product 22 0 37.2 0 36.4 0 0.7 product 26 0 34.4 0 38.3 0 0.7 Comparison between the results of this example with those of Example 3 shows that the higher operating temperature has no adverse effect on the product quality.

Claims

CLAIMS:

1. A process for the manufacture of a cycloalkane from the corresponding dicycloalkadiene, which comprises thermally depolymerizering the dicycloalkadiene to monomeric cycloalkadiene and catalytically hydrogenating the cycloalkadiene monomer, wherein the said cycloalkane is used as a diluent for the reactants entering at least the hydrogenation stage.

2. A process as claimed in claim 1, which is a process for the manufacture of cyclopentane.

3. A process as claimed in claim 1, which is a process for the manufacture of methylcyclopentane.

4. A process for the manufacture of cyclopentane, which comprises thermally depolymerizing dicyclopentadiene to cyclopentadiene and catalytically hydrogenating the cyclopentadiene to cyclopentane, wherein cyclopentane is fed as a diluent to the cyclopentadiene in the hydrogenation stage.

5. A process as claimed in any one of claims 1 to 4, wherein cycloalkane is fed as a diluent to the depolymerization stage.

6. A process as claimed in any one of claims 1 to 5, wherein the cycloalkane fed as a diluent is part of a cycloalkane-rich hydrogenated product produced by the hydrogenation reaction and recycled.

7. A process as claimed in any one of claims 1 to 6, wherein dicycloalkadiene is present in the feed to the depolymerization stage in a proportion of from 10 to 50% by weight.

8. A process as claimed in any one of claims 1 to 7, wherein the depolymerization is carried out in the presence of hydrogen.

9. A process as claimed in claim 8, wherein the molar ratio of hydrogen to dicycloalkadiene is from 0.5:1 to 20:1.

10. A process as claimed in claim 9, wherein the ratio is from 0.75 to 10:1.

11. A process as claimed in claim 9, wherein the ratio is about 5:1.

12. A process as claimed in any one of claims 1 to 11 wherein depolymerization is carried out at a temperature within the range of from 200 to 3000C.

13. A process as claimed in claim 12, wherein the temperature is within the range of from 200 to 2500C.

14. A process as claimed in claim 12, wherein the temperature is within the range of from 220 to 2400C.

15. A process as claimed in any one of claims 1 to 11, wherein hydrogenation is carried out at a temperature within the range of from 300C to 1750C.

16. A process as claimed in claim 15, wherein the temperature is within the range of from 50 to 1200C.

17. A process as claimed in any one of claims 1 to 16, wherein hydrogenation is carried out in the presence of a noble metal catalyst.

18. A process as claimed in any one of claims 1 to 16, wherein hydrogenation is carried out in the presence of a nickel catalyst.

19. A process as claimed in claim 18, wherein the catalyst is nickel metal supported on alumina.

20. A process as claimed in any one of claims 1 to 19, wherein any polymeric deposit building up in apparatus in which the process is carried out is removed by periodic flushing with a solvent for the deposit.

21. A process as claimed in claim 20, wherein the solvent is white spirit.

22. A process as claimed in claim 20, wherein the solvent has a substantial naphthenic content.

23. A process as claimed in any one of claims 1 to 22, wherein catalytic hydrogenation is carried out in a closed loop reactor.

24. A closed loop batch reactor process for catalytic hydrogenation of a cycloalkadiene in which a catalyst powder is circulated in the form of a slurry and removed from contact with the reactants and reaction product at the end of the reaction by filtration.

25. A process as claimed in any one of claims 1 to 24, wherein a heavy fraction of the hydrogenation product stream is used as a source of a saturated dimer product.

26. The use of a closed loop reactor in the catalytic hydrogenation of a cycloalkadiene to a cycloalkane.

27. The use of a cycloalkane as a feed diluent in the hydrogenation of the corresponding cycloalkadiene to the cycloalkane.

28. The use as claimed in claims 26 or claim 27, wherein the cycloalkane is cyclopentane.

29. Any new feature described herein or any new combination of hereindescribed features.