GB2292156A

GB2292156A - Method for separation of hydrocarbons

Info

Publication number: GB2292156A
Application number: GB9513373A
Authority: GB
Inventors: Stephen Robert Tennison; Richard Henry Weatherhead
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1994-08-12
Filing date: 1995-06-30
Publication date: 1996-02-14
Also published as: GB9513373D0

Abstract

A method for the selective complexation of alkanes and aromatics from a mixture of hydrocarbons which comprises contacting the mixture of hydrocarbons with an aqueous solution of a calixarene of formula (I> <IMAGE> where n is 4, 6 or 8 R is a component which renders the calixarene water soluble R<1> is OH, an ester or an ether. Compounds with R<1> = OH and R is 4-sulphonato benzez diazonium are claimed per se.

Description

METHOD FOR SEPARATION OF HYDROCARBONS The present invention relates to a method for separating selected hydrocarbons from hydrocarbon mixtures through the use of aqueous azocalixarenes.

During the refining of petroleum products, the recovery of benzene from other hydrocarbons may be achieved through a variety of techniques such as extractive or fractional distillation, solvent extraction or crystallisation. Complexation techniques in the liquid phase have also been used to separate aromatics from other hydrocarbons.

Such techniques employ countercurrent solvent extraction or facilitated transport membranes.

The study of complexation of macrocyclic molecules by acceptor ligands is important because of their potential as complexing materials. Typically, cyclodextrins,crown ethers and cyclophanes have all been studied for their complexation properties.

A different class of compounds also exhibiting complexation properties are calixarenes. These compounds are examples of a class of synthetic macrocyclic phenolic oligomers and are discussed in reviews entitled "Monographs in Supra Molecular Chemistry" by CD Gutsche, edited by J F Stoddart and published by the Royal Society of Chemistry, 1989, and "Calixarenes, a Versatile Class of Macro-cyclic Compounds" by J Vicens and V Böhmer, published by Kluwer, Dordrecht 1991.

Calixarenes have an advantage over the aforementioned cyclodextrins and crown ethers in that they are relatively simple to prepare. Calixarenes are known to complex with guest molecules, for example p-(diallyl aminomethyl) calixarenes and p (carboxyethyl)calixarenes ranging in size from calix[5]arenes to calix[8]arenes.

We have now found that aqueous calixarenes can be used to separate hydrocarbons.

Accordingly, the present invention provides a method for the selective complexation of alkanes and aromatics from a mixture of hydrocarbons which comprises contacting the mixture of hydrocarbons with an aqueous solution of a calixarene of general formula (I),

where n is 4, 6 or 8 R is a component which renders the calixarene water soluble R1 is OH, an ester or an ether.

The method of the present application is particularly suitable for the selective removal of benzene from a hydrocarbon mixture such as a reformate stream containing benzene. Equally applicable, the process may be used for the separation of a linear isomer with varying amounts of mono branched isomer from an isoformate stream or separation of alkanes and alkenes, either in the liquid or gaseous phase. The method may also be used for the removal of linear and mono branched alkanes from an isoformate stream containing mixtures of linear, mono and di-branched alkanes. The relative amounts of linear versus mono branched alkane may suitably be tuned by selection of the R component of the calixarene.

Typically, a hydrocarbon mixture may suitably comprise benzene, toluene, anthracene, hexane, cyclohexane, methyl alkanes such as 2-methyl pentane and the like.

Where it is desired to remove benzene from a hydrocarbon mixture, the nature of complexation of benzene with the calixarene is controlled by R of general formula I.

For the removal of benzene, it is preferred that R is planar with respect to the ring system. R may suitably be:

According to another aspect of the present invention, there is provided a novel calixarene having.the following formula

The method of the present application is particularly suitable for the selective adsoprtion of benzene using the aforementioned novel calixarene.

Where it is desired to remove isomers from an isoformate stream, R may be CH2CH2COOH or CH2N(CH2CH=CH2)2.

The selective complexation reaction of the present invention is suitably carried out by contacting the hydrocarbon mixture with an aqueous calixarene of general formula I under suitable pressure and temperature. Suitably, the complexation is carried out at a temperature as low as possible e.g. from 20 to 500C and under a pressure of typically atmospheric pressure or a pressure to ensure vapourisation of the hydrocarbon.

The complexed component may be separated by reducing the pressure or by temperature swing or through the use of an inert gas.

The calixarenes may be prepared by methods known to the person skilled in the art and as described in the aforementioned reviews. Typically, azocalixarenes may be prepared by diazocoupling of the respective calixarene in the presence of aniline.

The present invention will be further illustrated with reference to the following examples.

Example 1 - Prenaration of Calixarenes: R is SsulDhonatobenzene diazonium ion A calixarene according to general formula I where R is 4-sulphonato benzene diazonium ion, n is 4 and R1 is OH was prepared as follows: A solution of the calixarene (0.92mmol) in dimethylformamide was prepared.

6ml of pyridine were added to the solution. 0.81g (4.4mmol) ofthe 4sulphonatobenzene diazonium ion was added to the solution at 0-4"C and the resulting solution kept at this temperature for 36 hours.

The solution was then concentrated in vacuo, the product dissolved in water and precipitated by addition of NaBr. The product was purified by repeating the dissolution and precipitation steps once more.

Example 2 - Preparation of Calixarene: R=CB2CH,COOU A calixarene according to general formula I where R is CH2CH2COOH, n is 4 and R1 is OH was prepared as follows: A solution of 5mmol calix(4)arene in 80ml of DMSO and 1.9ml of CH3I (30mmol) was stirred for 30 minutes prior to the addition of sodium diethyl malonate in 28ml of ethanol; sodium diethyl malonate was prepared from 1.2g of Na and 7.28g of diethyl malonate. The resulting mixture was heated for 2 hours at 80"C under nitrogen. The solution was then cooled, poured into iced water (200ml), acidified with 2N HCL and the solid product filtered.The product was then dissolved in 1 100ml DMSO and 30ml concentrated HCl and the solution heated at 1200C for 10 hours under nitrogen. The mixture was then cooled, poured onto iced water (500ml), stirred for 10 minutes and filtered. The precipitate was recrystallised using acetone and ethyl acetate.

Example 3 - Preparation of Calixarene: R=CH,N(CH,Cll=CH2 A calixarene according to General formula I where R is CH2N(CH2CH=CH2)2, n is 4 and R1 is OH was prepared as follows.

A mixture of calix[4]arene (39.5mmol), tetrahydrofuran (360ml), acetic acid (45ml), diallylamine (0.2mol) and HCHO (37%aq, 0.2mol) was stirred for 24 hours at room temperature. The solvents were removed under vacuum, the residue dissolved in 250ml water and the aqueous solution extracted with ether (2x200ml) before being neutralised with 1 oO/o K2CO3 solution. The precipitate formed was filtered and the product dried and recrystallised from chloroform.

Example 4 - Complexation of Hedrocarbons The binding properties of the calixarenes prepared according to Examples 1, 2 and 3 were studied using UV/visible spectroscopy with a Perkin-Elmer Lambda 5 spectrophotometer.

(a) The azocalixarene prepared as detailed in Example 1 was added to various hydrocarbons as detailed in Table 1.

It can be seen from Table 1 that the calixarene is particularly suitable for complexation with benzene.

(b) The procedure of (a) above was repeated for the calixarene prepared as detailed in Example 2. The results are given in Table 2. It is evident that this calixarene is particularly suitable for complexation with hexane and 2-methylpentane.

(c) The procedure of (a) above was repeated for the calixarene prepared as detailed in Example 3. The results are given in Table 3. It is again evident that this calixarene is particularly suitable for complexation with hexane.

TABLE 1 Hydrocarbon K(xlo-3/M-1 Naphthalene No binding Benzene 10i2.0 Toluene < 0. 1 chloroform 1.9 l 0.6 2,3-Dimethyl-butane 0.4 # 0.1 2-Methyl pentane 0.4 # 0.1 Cyclobexane 0.3 # 0.15 Hex-l-ene 0.7 # 0.2 TABLE 2 Hydrocarbon K(xl o-3/M-1 Benzene No binding Toluene No binding Anthracene No binding Hexane 10.0 l 0.1 Cyclohexane No binding 2-Methylpentane 1.4 + 0.1 2,3-Dimethyl-butane No binding TABLE 3 Hvdrocarbon K(x10-3/M-1 Benzene No binding Toluene No binding Anthracene No binding Hexane 14.0i 1.0 Cyclohexane No binding 2-Methylpentane 8.0 # 0.8 2,3-Dimethyl-butane No binding

Claims

Claims: 1. A method for the selective complexation of alkanes and aromatics from a mixture of hydrocarbons which comprises contacting the mixture of hydrocarbons with an aqueous solution of a calixarene of formula (I)

where n is 4, 6 or 8 R is a component which renders the calixarene water soluble.

R1 is OH, an ester or an ether.
2. A method as claimed in claim 1 in which R is planar with respect to the ring system.
3. A method as claimed in claim 2 in which is selected from CH2CH2COOH, CH2N(CH2CH=CH2)2 or
4. A method as claimed in any one of claims 1 to 3 carried out at a temperature of from 20 to 500C..
5. A calixarene suitable for use in the method as claimed in any one of claims 1 to 4 of the formula