GB2273107A - Production of cycloalkanes - Google Patents

Abstract

A cycloalkane is manufactured from a corresponding dicycloalkadiene by cracking the dimer and catalytically hydrogenating the monomer at a temperature below 175 DEG C in the presence of an inert diluent. The process is especially applicable to the manufacture of cyclopentane. The catalytic hydrogenation is carried out in a closed loop batch reactor. Catalyst powder is circulated in the reaction zone in slurry form until it is removed by filtration from contact with the reaction mixture upon completion of the reaction. The inert diluent comprises at least in part the cycloalkane being manufactured.

Description

"Cvoloalkanes" 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-11, 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blowing agents were previously employed for this purpose, for example, propane, butane and pentane, but were superseded by the CFCs.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 an at least molar proportion of hydrogen and an inert hydrocarbon diluent at a temperature within the range of from 2000C to 4000C, preferably 250"C to 3500C, and subsequently partially reduced to cyclopentene with hydrogen in the presence of a catalyst at a temperature within the range of from 1750C to 3500C. 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 a corresponding dicycloalkadiene, which comprises thermally depolymerizing the dicycloalkadiene to monomeric cycloalkadiene in the presence of an inert diluent, and catalytically hydrogenating the cycloalkadiene to cycloalkane at a temperature below 1750C.

The invention is especially applicable to the manufacture of cyclopentane or methylcyclopentane from dicyclopentadiene or di(methylcyclopentadiene).

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

For clarity, the invention will be further described with reference to the manufacture of cyclopentane but it will be understood that similar procedures and conditions may be used for other cycloalkanes.

As diluent there may be used any inert fluid which, with one exception, must be readily removable from the desired reaction product, the exception being when cyclopentane is itself used as diluent. By "inert" is meant inert to conditions both in the depolymerization (cracking) and hydrogenation (saturation) zones.

Advantageously, the diluent either has a substantial heat of vaporization if it is to assist in controlling the hydrogenation exotherm by vaporizing or is sufficiently high boiling to remain as a liquid to act as a heat sink for the hydrogenation exotherm.

To be economically removable from the reaction product, its volatility should be substantially different from the reaction product, and may be either higher or lower. Hydrocarbons, either aromatic or saturated, are preferred, mixtures and single species being suitable.

If the diluent is wholly aromatic, it should be removed before proceeding to the hydrogenation stage to avoid its being saturated and accordingly contributing to, rather than mitigating, the hydrogenation exotherm. A mixture of aromatic and saturated hydrocarbons containing up to about 30% by weight aromatics may be used. Examples of more volatile hydrocarbons are alkanes up to C5, e.g., pentane and isopentane. Less volatile hydrocarbons include C6 to Cg alkanes, cycloalkanes, and aromatics, and hydrocarbon mixtures boiling in the same boiling range as such hydrocarbon. A mixture of about 30% aromatic hydrocarbons and about 70% linear alkanes has proved suitable. Other diluents are listed in British Specification No. 1,302,481, the disclosure of which is incorporated by reference herein.

The process may conveniently be operated by mixing a dicyclopentadiene-containing feedstock with diluent and hydrogen, and passing the reaction mixture to a heat exchanger or furnace to depolymerize the dimer to monomeric cyclopentadiene. The monomer-containing feed is catalytically hydrogenated, and the hydrogenated product recovered.

Product recovery differs depending on whether the diluent is cyclopentane or not. If cyclopentane is the diluent, the reaction mixture from the hydrogenation reactor is 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.

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 diluent in the feedstock.

If the diluent is other than cyclopentane then the reaction mixture from the hydrogen reactor is fractionated to separate product cyclopentane from diluent, and the diluent is recycled. It is within the scope of the invention, though not presently preferred, to use as a diluent a mixture of cyclopentane and another diluent, in which case fractionation is carried out so as to separate only part of the cyclopentane as product.

Diluent, whether cyclopentane or otherwise, may be employed in different proportions in different stages of reaction, in which event diluent may be recycled to the cracking stage feed or to the hydrogenation stage feed, or to a point, e.g., an intermediate cooling stage, between. Additional diluent may similarly be applied at any stage.

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 300, 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, a pressure in the range of from 1.5 to 3.5 MPa is preferred.

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 diluent 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 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 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 300C to below 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 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 diluent is advantageously mixed with reactants before they enter either reaction zone, it is also possible, though less preferred, to feed diluent separately into a reaction zone to mix with the reactants there. The proportion of diluent is selected to give the desired proportion of dicyclopentadiene in the feedstock; this in turn is dependent on the desirability of controlling the exotherm of the hydrogenation reaction from within the reaction mixture. The ratio of recycled product or other diluent is, however, preferably in the range of from 2:1 to 10:1.

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 if the feedstock is substantially sulphur-free.

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 have a sulphur content less than 5 ppm to avoid catalyst poisoning in the hydrogenation stage.

The invention has been described in terms of a two stage process using a dicycloalkadiene as starting material because of the instability of the monomer. It is, however, within the scope of the invention to use a diluent in hydrogenation of a cycloalkadiene at temperatures below 175"C whether obtained from the dimer or otherwise. Accordingly, the invention also provides the catalytic hydrogenation of an alkadiene, especially cyclopentadiene or methylcyclopentadiene, to the corresponding cycloalkane at a temperature below 1750C in the presence of an inert diluent.

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 the feedstock contains sulphur at a level, above about 10 ppm, that causes rapid catalyst poisoning, a closed loop reactor may be used.

Accordingly, the invention also provides a process for the catalytic hydrogenation of a cycloalkadiene, especially cyclopentadiene, at a temperature below 1750C in the presence of an inert diluent 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 a "closed loop" batch reactor process for the catalytic hydrogenation of a cycloalkadiene below 1750C wherein a catalyst powder is circulated in the reaction zone in slurry form and removed from contact with the reactants and reaction products by filtration after completion of the reaction.

Advantageously, the operating conditions, especially the temperature, are controlled by heating or cooling the circulating slurry.

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 to 220 to 2400C. Hydrogen is added to the feed through a feed line 16, while recycled diluent (which may be cyclopentanerich hydrogenated product) is supplied through a feed line 18, both being added to the feed before it reaches the heat exchanger 14. The reaction product from the exchanger 14, comprising cyclopentadiene, unreacted starting material, recycled diluent, and hydrogen, is fed to a heat exchanger 20 where it is cooled to about 500C or other appropriate hydrogenation reactor inlet temperature.

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.

When the diluent is cyclopentane, 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 distillation column 40, components lighter than cyclopentane are removed overhead by line 42, the resulting concentrated product mixture being fed by a line 44 to a storage tank 50. When the diluent is other than cyclopentane and, for the purposes of illustration, is lower boiling than cyclopentane, the liquid product from the separator 28 is all passed to the stabilizer distillation column 40, and diluent is removed as a sidestream from the column 40 through line 43 and recycled to the feed line 12.

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, the bottoms being used as a gasoline component or, after further fractionation, as a source of high purity tetrahydrodicyclopentadiene.

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, 73% 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

pun Feed, wt% Product, wtt Temp, Conv.

DD CPD CP NC5 DCPD 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 wtt.

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, wt% Conv.

CPD CPD CP NC5 DCPD CPD CP NC5 % 18.6 12.3 55.1 4.0 g 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 illustrates the thermal decomposition of dicyclopentadiene in the presence of hydrogen and a commercially available hydrocarbon solvent containing about 30% aromatic components and about 70% linear alkanes by weight. The dicyclopentadiene was the same grade as used in Example 1.

A feedstock containing 30% by weight of the raw dicyclopentadiene and 70% by weight of the solvent was fed at a rate of 0.3 litre per hour together with hydrogen at the rate shown in Table 3 below to a reactor maintained at a temperature of 2400C at a pressure of about 2.4 MPa. The space velocity was 1 v/hr/v. No fouling was observed in the reactor.

Table 3

H? - normal Product, wtt litre/hour CPD DCPD 60 9.7 4.45 150 16.5 4.01 224 21.1 2.90 255 19.4 3.37 267 21.1 2.90 280 19.9 2.79 289 21.1 2.79 Example 4 The procedure of Example 3 was repeated, but the feedstock was passed through the reactor at a rate of 1.2 litres per hour, corresponding to a space velocity of 4 v/hr/v, and the temperature and pressure were varied.

Although in one run no hydrogen at all was used no fouling was observed. The results are shown in Table 4.

Table 4

H? - normal Temp. Pressure Product litre/hour OC MPa CPD DCPD 0 240 1.5 6.6 10.4 260 240 1.7 14.3 8.7 310 240 2.2 16.0 8.0 260 220 2.15 11.1 13.1 260 220 2.37 11.8 13.9 260 220 2.38 11.8 12.6 290 220 2.37 12.6 12.1 Example 5 Example 3 was repeated, but using a mixture of equal weights of raw dicyclopentadiene and the solvent. The results are shown in Table 5. No reactor fouling was observed.

Table 5

H? - normal Product, wt% litre/hour CPD DCPD 0 10.-9 15.4 265 35.8 4.2 278 36.0 4.1 320 35.9 4.1 382 37.5 2.5 Example 6 Example 5 was repeated but operating at 2400C and a flow rate of 0.6 litre/hour - space velocity 2 v/hr/v, with pressures as shown in Table 6. Fouling of the reactor took place, the inert spheres filling the reactor being stuck together.

Table 6

H2 - normal 7 Pressure Product, wt% litre/hour- MPa CPD DCPD 73 1.24 13.49 10.54 85 1.85 14.54 10.33 250 1.13 25.56 10.36 255 2.18 31.99 11.68 305 1.68 36.30 3.73 Example 7 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 7 below, the values below the components representing percent by weight of the feed or product.

Table 7

TIDe DUD TH-DCPD) CpD CP CPE NC5 Hours Ebbed 0 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 Peeed 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 7 shows that the hydrogenation was complete to the saturated tetrahydrodicyclopentadiene and cyclopentane, and no intermediate unsaturated components were detected.

Example 8 Example 7 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 8 shows the results.

Table 8

Time DD 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 9 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 Feed 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 7 shows that the higher operating temperature has no adverse effect on the product quality.

Claims (27)

CLAIMS:

1. A process for the manufacture of a cycloalkane, which comprises thermally depolymerizing a corresponding dicycloalkadiene in the presence of an inert diluent, and catalytically hydrogenating the resulting cycloalkadiene monomer to cycloalkane at a temperature below 1750C.

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 in the presence of an inert diluent, and catalytically hydrogenating the cyclopentadiene to cyclopentane at a temperature below 1750C.

5. A process as claimed in claim 4, wherein cyclopentane is a diluent in the depolymerization stage.

6. A process as claimed in claim 4 or claim 5, wherein the diluent is a recycled cyclopentane-rich hydrogenated product of the hydrogenation reaction.

7. A process as claimed in any one of claims 1 to 6, wherein the diluent is present in the feed in a proportion of from 50 to 90% 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 50:1.

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 240"C.

15. A process as claimed in any one of claims 1 to 14, wherein hydrogenation is carried out at a temperature within the range of from 400C to below 1750C.

16. A process as claimed in claim 15, wherein the temperature is within the range of from 50 to 1500C.

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 17, wherein hydrogenation is carried out in the presence of a nickel catalyst.

19. A process as claimed in claim 14, wherein the catalyst is nickel metal supported on alumina.

20. A process as claimed in any one of claims 1 to 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 a high naphthenic content solvent is used.

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 process as claimed in any one of claims 1 to 23, wherein a heavy fraction of the hydrogenation product is used as a source of saturated dimer.

25. A closed loop batch reactor process for the catalytic hydrogenation of a cycloalkadiene below 1750C, wherein a catalyst powder is circulated in the reaction zone in slurry form and removed from contact with the reaction mixture after completion of reaction by filtration.

26. A process for the manufacture of a cycloalkane which comprises catalytically hydrogenating a cycloalkadiene at a temperature of less than 1750C in the presence of an inert diluent.

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