GB2045797A - Process for producing oligomers or co-oligomers from butene-2 - Google Patents

Abstract

In a process for oligomerising or co-oligomerising butene-2 in which the catalyst is a nickel/alkyl aluminium halide system, the used catalyst is employed to isomerise butene-1 to butene-2 in a hydrocarbon mixture which also comprises isobutene. Butene-2 can be readily distilled from the treated mixture.

Description

SPECIFICATION Process for producing oligomers or co-oligomers from butene-2 Oligomers of n-butenes, especially dimers of butene-2, and co-dimers of butene-2 with propylene are desirable feedstocks for the manufacture of alcohols by hydroformylation processes. When such alcohols, preferably having 8 or 9 carbon atoms, are used in the form of their phthalate esters for plasticising polyvinylchloride compositions they should have as little chain branching as possible and it is desirable for this reason that the dimers or codimers of butenes used in their manufacture should be made using an n-butene. Butenes are readily available as products of cracking longer chain hydrocarbons for example heavy oil fractions to produce gasoline and especially in the cracking of naphtha to produce ethylene, propylene, butadiene and butenes.Normally ethylene, propylene and butadiene and also a mixture of butene-1, cis-and trans-butene-2 and isobutene normally together with n-and iso-butane are recovered from the product of such cracking processes. The separation of n-butenes from such mixtures is complicated by the fact that butene-1 is difficult to separate from iso-butene by distillation. Butene-2 may however be more easily separated from such mixtures.

In this invention butene-1 in a mixture containing also isobutene is isomerised to butene-2 which is then separated from the isobutene by distillation.

The isobutene is recovered as an overhead product.

It is known to isomerise butene-1 to butene-2 in the presence of hydrogen, but there is a tendency in such processes to convert butenes to butanes. It is an object of this invention to carry out such an isomerisation under conditions which do not lead to substantial hydrogenation of the butenes.

In our preferred oligomerisation reactions nickel aluminium alkylhalide catalysts are employed. It is a further object of this invention to carry out the isomerisation in a manner which does not involve the introduction into the isomerisation stage of catalysts which must be removed before the oligomerisation reaction may be performed.

The invention comprises oligomerising butene-2 optionally with a co-oligomerwhich is preferably a normal olefin and is more preferably propylene in the presence of a nickel/alkyl aluminium halide catalyst, in which the process the butene-2 which is fed to the oligomerisation stage is produced by isomerising butene-1 to butene-2 in the presence of isobutene by contacting a feedstock comprising butene-1 and iso-butene with a nickellalkyl aluminium halide catalyst which has been used in an oligomerisation reaction, preferably of butene-2 optionally with a co-monomer, which may be the oligomerisation reaction aforesaid, and separating isobutene from the isomerisate by distillation.

The nickel component of the catalyst may be supplied initially as a compound of nickel which is soluble in the reaction medium, for example a carboxylic acid salt of nickel, for example a salt of a carboxylic acid having 8 to 20 carbon atoms. The active catalyst is believed to be a complex of aluminium, nickel and olefin.

The feedstock may comprise butene-1, butene-2, isobutene and optionally paraffins. The aluminium alkyl halide component of the catalyst may be a mono-alkyl aluminium di-halide or alkyl aluminium sesquihalde for example ethyl aluminium dichloride or sesquichloride. The alkyl groups suitably have 1 to 10 carbon atoms and the halid is suitably chloride or bromide.We have found that although freshly prepared catalysts of this type cause polymerisation of isobutene and copolymerisation of isobutene with normal butenes catalyst which has already been used in an oligomerisation reaction is less active in this side reaction whilst being of acceptable activity in isomerising butene-1 to butene-2 and that the re-introduction of such catalysts to the oligomerisation reaction together with butene-2 recovered from the isomerisation stage has no unacceptable effect on the oligomerisation reaction.

It is preferred that the Briisted acidity of the catalyst should be as low as possible and for this reason the isomerisation is preferably carried out in the substantial absence of water; the feestock if it contains water, is preferably dried before the isomerisation is carried out. If desired a small amount of an aluminium alkyl for example triethyl aluminium may be introduced suitably before the isomerisation is begun, to remove protons; preferably both of these precautions are adopted as otherwise there is a tendency for additional polymerisation to occur.

The acidity may also be controlled by adding bases for example dimethylaniline, 1 ,8-bis(dimethylamino) naphthalene or other tertiary amines which are poor ligands for nickel. Alternatively co-ordinating phosphines may be used but the problem of catalyst removal renders them relatively less attractive.

It will be appreciated that some dimerisation or codimerisation of isobutene may occur during the isomerisation stage.

The isomerisation is suitably carried out at a temperature of -20 to +80"C and preferably 0-40"C.

The pressure is preferably sufficient to maintain the reactants in a liquid phase.

If desired a solvent or diluent may be present for example a paraffin or aromatic hydrocarbon or phenyl chloride may be present.

The catalyst concentration during isomerisation is preferably in the range 1-100 parts per million of nickel and preferably 2 -10 parts per million by weight and the atomic ratio of aluminium to nickel may be 4:1 to 100:1 for example 12:1 to 20:1. In general the use of higher concentrations of catalyst in the isomerisation stage assists in the removal of butadiene and other materials which inhibit the oligomerisation reaction but increases the tendency to polymerise isobutene and the optimum catalyst concentration depends on the concentration of dienes and isobutene.

Suitably the amount of any aluminium alkyl introduced, for example in a step of pretreatment of the feedstock represents at most 5 atoms of aluminium per atom of aluminium in the catalyst and suitably represents 0.1 to 1 atom of aluminium per atom of aluminium in the catalyst.

If a base is introduced it is preferred that at most an equivalent of base be introduced per atom of aluminium in the catalyst.

Example A continuously stirred reactor of 50 ml capacity provided with three inlets and one outlet was fed with separate streams of a mixture (23 ml per hour as liquid) of n-butenes (92.5% by weight) and n-butane (7.5% by weight), nickel decanoate dissolved in cyclohexane (1.75 ml per hour, 0.1% w/w of nickel decanoate expressed as nickel) and ethyl aluminium dichloride dissolved in methyl cylcohexane (0.6 ml per hour, 10% w/w ethyl aluminium dichloride) at a pressure of 3.5 bar. The reactor was maintained at a temperature of 38"C. The average residence time in the reactor was approximately 2 hours, the nickel content expressec as the element was 70 parts per million, and the aluminium to nickel atomic ratio was 15:1.

After 3 hours from the start of the reaction the effluent flowing from the reactor had the composition:- catalyst + solvent 14% w/w, C2s and heavier 12% w/w, and C4s74%w/w.This product was passed continuously into a second reactor contain ing 40 ml of dried mixed butenes, of composition isobutane 6.35%, n-butane 15.47% butene-1 10.26%, isobutene 47.39%, trans-butene-2 12.91% cis butene-2 7.61% by weight, stirred at 22"C and 3.5 bars pressure.After 15 minutes when 3.4 g of the productfrom reactor 1 had entered reactor2theflow was stopped and reactor 2 stirred for a further 30 minutes at which time the C4 composition in reactor 2 was isobutane 5.8%, n-butane 15.3%, butene-1 1.2%, isobutene 40.5% trans butene-2 26.2% and cis-butene-2 10.9% by weight.

Butenes and butanes, after separation by distillation from the solvent, catalyst and C8 and heavier products, may be distilled in a 75 theoretical plate still at a reflux ratio of 15:1 and a pressure of 6.5 bars at a head temperature of 50.5"C and a re-boiler temperature of 62"C to give an overhead fraction of 47.5% of the feed containing isobutene, 97.3% and butene-1 2.7% and a bottoms product of 52.5% of the feed containing isobutene 2%, n-butane 13.3% and butene-2 79.6%, all percentages being byweight.

Claims (18)

1. A process which comprises a stage of oli gomerising butene-2 optionally with a co-oligomer in the presence of a nickel/alkyl aluminium halide catalyst in which process butene-2 fed to the oligom erisation stage is produced by isomerising butene-1 to butene-2 in the presence of isobutene by contact ing afeedstockcomprising butene-1 and iso-butene with a nickellalkyl alminium halide catalyst which has been used in an oligomerisation reaction, and separating isobutene from the isomerisate by distillation.

2. A process as claimed in claim 1 in which in the oligomerisation stage propylene is present as a co-oligomer.

3. A process as claimed in claim 1 or 2 in which the nickellalkyl aluminium halide catalyst which is used in the isomerisation has been used in the oligomerisation of butene-2 optionally with comonomer.

4: A process as claimed in claim 1, 2 or 3 in which the alkyl groups of the alkyl aluminium halide component of the catalyst have 1 to 10 carbon atoms.

5. A process as claimed in any preceding claim in which the alkyl aluminium halide component of the catalyst is a chloride or bromide.

6. A process as claimed in any preceding claim in which the nickel component of the catalyst is a salt of a carboxylic acid having 8 to 20 carbon atoms.

7. A process as claimed in any preceding claim which is carried out in the substantial absence of water.

8. A process as claimed in any preceding claim in which an aluminium alkyl is present in the isomerisation stage.

9. A process as claimed in claim 8 in which the amount of aluminium alkyl introduced before the isomerisation stage represents 0.1 to 1 atom of aluminium per atom of aluminium in the catalyst.

10. A process as claimed in any preceding claims in which a compound which is a base and a poor ligand for nickel is present.

11. A process as claimed in claim 10 in which at most one equivalent of base is introduced per atom of aluminium in the catalyst.

12. A process as claimed in claim 9 in which the base is a tertiary amine.

13. A process as claimed in any preceding claim in which the isomerisation is carried out at a temperature of 0 to 40"C.

14. A process as claimed in any preceding claim in which the isomerisation is carried out at a pressure sufficient to maintain the reactants in a liquid phase.

15. A process as claimed in any preceding claim in which the catalyst concentration during the isomerisation is in the range 1-100 parts per million by weight of nickel and the atomic ratio of aluminium to nickel is 4:1 to 100:1.

16. A process for the production of oligomers of butene-2 when carried out substantially as described in the Example.

17. Oligomers whenever produced by a process as claimed in any preceding claim.

18. Isobutene whenever produced by a process as claimed in any preceding claim.