WO1995002568A1

WO1995002568A1 - Process for the purification of olefins

Info

Publication number: WO1995002568A1
Application number: PCT/GB1994/001393
Authority: WO
Inventors: Arthur Gough; Derek John Irvine; Edmund Hugh Stitt
Original assignee: Imperial Chemical Industries Plc
Priority date: 1993-07-13
Filing date: 1994-06-28
Publication date: 1995-01-26
Also published as: GB9314514D0; AU7040294A; ZA944789B

Abstract

Highly insaturated compounds such as acetylenes are removed from an olefin stream by catalytic reaction with a reagent comprising a hydrogen-containing compound, other than a hydrocarbon, to form an addition product which is then separated. Suitable reagents include water, methanol, acetic acid, ammonia, hydrogen chloride, and methyl formate. A solvent such as acetone or dimethyl formamide may be used to assist extraction of the highly unsaturated compounds into a liquid phase for contact with the catalyst.

Description

PROCESS FOR THE PURIFICATION OF OLEFINS

This invention relates to hydrocarbon processing and in particular to the purification of olefins.

Olefins are often produced by reforming or cracking a hydrocarbon feedstock such as naphtha: as a result of the production process small proportions of more highly unsaturated compounds such as acetylenes and dienes are often formed. It is normally desirable to remove such more highly unsaturated compounds before further processing of the olefin product. While it is often possible to effect partial separation by fractionation, removal of the more highly unsaturated compounds to very low levels by fractionation is often difficult. One technique commonly employed for removal of the more highly unsaturated compounds is selective hydrogenation, for example using a supported palladium catalyst as described in EP-A-29321. However with the so-called "front-end" hydrogenation process where a substantial excess of hydrogen over that required to effect hydrogenation of the more highly unsaturated compounds is present, there is a risk of runaway reactions and hydrogenation of the olefins present. Consequently "front-end" selective hydrogenation is often undesirable on safety grounds. With the so-called "tail-end" process, where the olefin stream is subjected to fractionation into a C fraction and a C3 fraction, prior to the selective hydrogenation, there is a tendency for de-activation of the catalyst and for the formation of polymers from the ethyne in the C2 fraction and from propyne and propadiene in the C3 fraction. In the hydrogenation of the C2 stream it is not possible to hydrogenate the ethyne exclusively to ethene and some ethane is formed. Some operators extract the ethyne from the C£ stream and purify it for further use. This has the disadvantage of the hazards of handling pure ethyne.

We have devised an alternative process for the removal of the more highly unsaturated compounds. In the present invention they are selectively reacted with a hydrogen-containing compound, other than a hydrocarbon, rather than with hydrogen itself, under conditions wherein little or no reaction of the olefin with the hydrogen-containing compound takes place. The resulting addition product of the reagent and the more highly unsaturated compound is normally readily separated from the olefin by physical methods.

Accordingly the present invention provides a process for the removal of compounds that are more highly unsaturated than olefins from an olefin stream comprising mixing the olefin stream with a hydrogen-containing compound, other than a hydrocarbon, contacting the mixture with a catalyst effective under the conditions employed to catalyse the addition of the hydrogen-containing compound to the more highly unsaturated compounds, and thereafter separating the addition product of the more highly unsaturated compound and the hydrogen-containing compound, and any unreacted hydrogen-containing compound, from the olefin stream.

Hereinafter the hydrogen-containing compound will be referred to as the reagent.

The invention is of particular utility in the treatment of hydrocarbon streams consisting essentially of hydrocarbons containing 2 or 3 carbon atoms: particularly it is of utility in the treatment of C2 streams, which generally contain ethyne and ethane in addition to ethene; and in the treatment of C3 streams which generally contain propyne, propadiene and propane as well as propene. However the process is also applicable to other olefin streams and is not limited to the treatment of streams wherein essentially all the hydrocarbons contain the same number of carbon atoms.

Reagents that may be employed for the selective reaction include water, methanol, acetic acid, hydrogen cyanide, hydrogen bromide, and hydrogen chloride. The addition compounds formed by reaction of these reagents with ethyne are respectively acetaldehyde, methyl vinyl ether, vinyl acetate, acrylonitrile, vinyl bromide, and vinyl chloride, all of which are of considerable commercial importance. Hence the process of the invention may provide a source of useful chemical compounds as well as providing a method of purifying olefin streams. Generally the reagent should contain at least one polar H-X bond where X is an atom other than hydrogen. The reagent should of course be one that will react with the more highly unsaturated compounds present that it is desired to remove. Thus whereas ethyne and propyne react with both methanol and water, propadiene will react readily with methanol but less readily than methyl acetylene with water. Thus, by selection of an appropriate reagent, it may be possible to selectively remove some more highly unsaturated compounds but not others.

Other reagents that may be employed include ammonia and methyl formate. The latter is of interest as the reaction with ethyne has been found to give 2,2 methoxy-propane and a small proportion of methyl methacrylate. One route to the production of methyl methacrylate involves the catalytic reaction of propyne with methanol and carbon monoxide: unfortunately the catalyst employed in that reaction is poisoned by propadiene, thereby requiring that the propyne is first separated from any propadiene present: however by using methyl formate as the reagent in the process of the present invention, separation of the propadiene from the propyne is not necessary.

The catalyst employed will depend on the nature of the reagent employed and the reaction conditions. The catalysts may be homogeneous, eg a metal salt in solution in which phase the reaction is effected or heterogeneous. Particularly suitable are bivalent metal ions in a suitable form, eg disposed in a suitable ion exchange resin or on a suitable support, eg an oxidic material or carbon. Particularly suitable bivalent metals are those of Groups IB and IIB of the Periodic Table, ie copper, silver, gold, zinc, cadmium and mercury. Group IIB metals are preferred.

The olefin stream may be subjected to fractionation to produce a stream having an increased concentration of the more highly unsaturated compounds: this decreases the amount of hydrocarbon that has to be passed through the catalyst. Alternatively, or additionally, the more highly unsaturated compounds may be extracted with a suitable solvent to give a stream which is then contacted with the catalyst. Potential solvents include those known for the extraction of such hydrocarbons and may be, for example, N-methyl pyrrolidone, sulpholane, tetra-ethylene glycol, acetone, N-formyl morpholine, di-methyl sulphoxide, and di-methyl formamide. For ethyne extraction, acetone, di-methyl formamide, or N-methyl pyrrolidone are particularly suitable.

The time of addition of the reagent is largely a matter of process convenience, although if such fractionation and/or extraction steps are employed, it will be appreciated that the reagent may be added before the extraction or fractionation provided the reagent is fractionated, or extracted, into the same stream as the more highly unsaturated hydrocarbons.

In a preferred process, extraction, and at least part of the reaction, are effected simultaneously by contacting the olefin stream with the reagent and a suitable solvent in the presence of the catalyst.

Fractionation and/or extraction steps may decrease the amount of hydrocarbon stream that has to be passed through the catalyst. Preferably the more highly unsaturated hydrocarbons form 0.5 to 50Z by weight of the total hydrocarbons in the stream that is passed through the catalyst. The amount of reagent employed should generally be near, or in an excess of, the stoichiometric amount for reaction with the more highly unsaturated compounds. Generally we have found that the greater the excess of reagent over stoichiometric, the less selective and the less rapid is the reaction. Preferably there are 1 to 100 moles of the reagent for each mole of more highly unsaturated compounds.

The reaction temperature may be in the range 0 to 200°C and the pressure 1 to 30 bar abs. After contact of the reactants with the catalyst, unreacted reagent and the addition compound can be separated by physical means. The type of process adopted for the separation will depend on the nature of the reagent employed: in general it will be much higher boiling than the hydrocarbon stream and easily recoverable by simple distillation. Alternatively scrubbing with a suitable medium could be employed in many cases. The addition product may be separated from unreacted reagent and the latter recycled if desired. In a preferred embodiment of the invention, the catalyst is disposed as a bed in a column. The hydrocarbon stream to be treated is fed, in the liquid, or preferably gaseous, state to a lower part of the column and passes up through the bed, and exits the column at the upper end as purified product. A liquid stream, containing the reagent, eg an aqueous stream where the reagent is water, together with a suitable solvent if desired, is fed to the upper part of the column, flows down through the catalyst bed, and leaves the column at the bottom. The liquid effluent from the bottom of the column contains the addition product of the more highly unsaturated compound or compounds, eg acetylenes, and the reagent and, if desired, this addition product may be separated from the liquid medium. If desired, the residual liquid medium remaining after separation of the addition product may be recycled to the upper part of the column where, after addition of an appropriate amount of fresh reagent, it is re-used. In some cases it may be desirable to recycle the bulk of the liquid effluent from the bottom of the column without separation of the addition compound, and only take a part stream of the liquid effluent for further processing and/or recovery of the addition compound.

Preferred arrangements for treating a C2 stream from an olefins plant using water as the reagent are further described with reference to the accompanying drawings which are diagrammatic flowsheets of alternative processes. Referring to the embodiment of Figure 1, the process is effected using a packed column 10 having three packed regions: an upper physical absorption region 12 containing a catalyst-free packing, an intermediate reactive absorption region 14 containing a packing supporting a catalyst for the reaction of water (ie the reagent) and ethyne, and a lower reservoir reaction region 16 containing a bed of a catalyst for the reaction of water and ethyne. A mixture of water and a water-miscible solvent is fed via line 18 to a distributor 20 disposed above the upper packed region 12 so that it flows down through the packed regions 12 and 14 and into the reservoir region 16. The C2 stream, in the gaseous state, typically at a temperature in the range -20°C to +5°C, and at an elevated pressure, typically in the range 15 to 40 bar abs. , is fed via line 22 to a space 24 above the reservoir region 16 and below the intermediate packed region 14 and then flows upwards through the column in counter-current flow to the water/solvent liquor flowing down the packings in regions 12 and 14. The water/solvent liquor scrubs ethyne, and some ethene, from the C2 stream. The C2 stream then leaves the top of the column via line 26, and is then cooled and fed to a separator 28 to separate water and solvent therefrom as a liquid stream 30, leaving a purified gaseous C2 stream 32. After drying, for example in a molecular sieve drier (not shown), this C2 stream can be processed as required, eg separated into ethene and ethane streams.

As the gas passes up through the intermediate reactive absorption region 14, ethyne is stripped from the gas into the liquid phase wherein it reacts with the water in the presence of the catalyst on the packing to form the addition product, acetaldehyde. As a result of the reaction occurring in region

14, the absorption equilibrium is shifted to favour absorption of the ethyne, and so a shorter column is need than if the ethyne were simply absorbed into the liquid phase without reaction. The upper region 12 is free from catalyst so that there is simply physical absorption of the residual ethyne into the liquid phase; the absence of catalyst in this region ensures that any addition product, ie acetaldehyde, formed in the reactive region 14 and entrained in the upward flowing gas stream is scrubbed therefrom, thus avoiding the presence of acetaldehyde in the treated C2 stream.

The liquor loaded with ethyne and addition product flows down the packing from the intermediate region 14 into the reservoir region 16, containing a bed of catalyst immersed in liquid, wherein the reaction of the ethyne and water is completed.

Liquor, ie water plus solvent having dissolved therein the addition product, ie acetaldehyde, together with some olefins, is taken from the reservoir via line 34 and fed to a stripping column 36 wherein olefins are separated, leaving a liquid stream 38 containing addition product, water and solvent. The separated olefins are recycled to column 10 via line 40. The liquid stream 38 is then fed to a solvent recovery column 42 wherein it is separated into a stream 44 comprising the addition product, ie acetaldehyde, and a stream 46 comprising the solvent and water. The separated solvent and water stream 46 is recycled and added to the water/solvent stream 30 to form, with make-up solvent and water supplied via line 48, the water/solvent mixture fed via line 18 to the top of column 10.

This embodiment is suitable where the solvent, and addition product, are less volatile than the olefins. The separation stage 42 is typically a distillation column: which stream is separated as overheads and which as bottoms, will depend on the relative volatilities of the solvent, addition product, and reagent. Where the reagent is relatively volatile, eg where hydrogen cyanide is used as the reagent (giving acrylonitrile as the addition product with ethyne), some or all of the residual reagent in stream 34 may be separated into the recycle olefins stream 40, so that the separation stage 42 primarily serves to separate the addition product from the solvent. In Figure 2 a modification of the Figure 1 flowsheet is shown. In this case, in the first separation stage 36, the dissolved ethene and acetaldehyde are flashed off from stream 34 as a gas stream 38 leaving a water/solvent stream for recycle via line 50 which is added to the water/solvent stream 30 to form, with make-up solvent and water supplied via line 48, the water/solvent mixture fed via line 18 to the top of column 10. The gas stream 38 from the first separation stage 36 is then compressed and cooled and fed to the second separation stage 42 to give a liquid acetaldehyde product stream 44 and an ethene stream 52. This ethene stream 52 can be added to the treated C2 stream 32. As an alternative, the ethene stream 52 may be added to the C2 stream 22 fed to the column 10.

The following Table 1 shows the calculated flow rates, temperatures (T) and pressures (P) of a typical process of the Figure 2 flowsheet using water as the reagent and dimethyl formamide (DMF) as the solvent.

Table 1

Flow rate (te/h) for stream

22 48 18 16 in 34 26 52

CH 0.02 0.00 0.00 0.00 0.00 0.02 0.00

C₂H₂ 2.09 0.00 0.00 0.24 0.00 0.00 0.00

C₂H₄ 90.42 0.00 0.00 5.72 5.72 84.70 5.72

C₂H₆ 15.53 0.00 0.00 0.82 0.82 14.71 0.82

C₃H₆ 0.16 0.00 0.00 0.01 0.01 0.15 0.01

CH3CHO 0.00 0.00 0.04 3.17 3.58 0.00 0.00

H₂0 0.00 1.53 58.94 57.43 57.26 0.23 0.00

DMF 0.00 0.01 26.57 26.55 26.55 0.02 0.00

T (°C) -11.8 25.0 40.5 31.9 35.5 41.2 147.2

P (bara) 28.0 5.0 28.0 27.9 27.6 27.8 22.3

"16 in" is the liquor entering the reservoir from the intermediate region 14.

In a modification of the Figure 2 flowsheet, the amount of reagent employed for the reaction with the more highly unsaturated compounds is minimised so that the mixture of solvent and reagent recovered in the separation stage 36 contains little or no reagent. The recycled solvent stream 50 may be fed to the column 10 above the upper absorption region 12 and a stream of the reagent is fed to a distributor (not shown) between the upper and intermediate absorption regions 12 and 14. In this way the amount of reagent that is entrained in the C2 stream 26 from the top of the column may be minimised.

The invention is illustrated by the following examples in which all percentages are by weight. In the examples the catalysts employed were various metals on various supports as follows: Catalyst Active Metal Support

A 3.1Z Hg "Amberlyst" 15 ion exchange resin

B 4.0Z Hg Clinoptilolite zeolite

C 3.2Z Hg "Silicalite" zeolite

D 2.3Z Hg Alumina

E 2.4Z Hg Activated carbon

F 9.1Z Cd "Amberlyst" 15 ion exchange resin

G 4.3Z Cd Clinoptilolite zeolite

H 4.1Z Cd "Silicalite" zeolite

II 88..99ZZ ZZnn "Amberlyst" 15 ion exchange resin

J 7.2Z Fe "Amberlyst" 15 ion exchange resin,

K (aqual weiglits 0 atalysts A and J. "Amberlyst" 15 is an ion exchange resin supplied by Rohm & Haas; "Silicalite" is a zeolite supplied by Union Carbide Corporation.

Example 1 A pressure vessel of capacity 40-50 ml was charged with 35 ml of a solution containing 95Z acetone as solvent and 5Z water as the reagent. A C2 stream containing about 90Z ethylene, about 8Z ethane, and about 2Z acetylene, was continuously fed to the head space of the vessel for 1 hour at ambient temperature with frequent agitation to maintain the pressure in the vessel at 10 bar abs. About 1-1.5 g of the hydrocarbons dissolved in the solvent solution. The resultant solution was passed at 20 bar abs and 40°C over about 1-1.5 g of catalyst A at a flow rate of about 8 ml/h. The additional pressure was provided by means of helium as a "pusher" gas. The reaction products were identified by gas chromatography.

Analysis of the effluent showed that about 90Z of the acetylene had reacted to form acetaldehyde, but no ethanol, which would result from the addition of water to ethylene, was detected in the effluent.

Example 2 Example 1 was repeated using solvent solution containing 95.5Z acetone and 0.5Z water as the hydrogen- containing reactant, and a variety of catalysts. Samples of the effluent were taken at intervals of approximately 20-25 min. over a period of about 4 hours for analysis by gas chromatography. Since the composition of the hydrocarbon mixture was not constant for all the experiments, the ethene/ethane and ethyne/ethane ratios of the effluent were determined to enable comparison of the experiments, and for each batch of hydrocarbon the ratios for the solution before treatment was determined to give a "standard", ie where there was no reaction. From this data the proportion of ethene and ethyne reacted was calculated, and these results, together with the ratio of ethyne to ethene in the effluent, are set out in Table 2. ["ethyne conv" and "ethene conv" are respectively the proportions of ethyne and ethene reacted, expressed as percentages; likewise "ethyne/ethene" is the ratio of ethyne to ethene in the effluent, expressed as a percentage]. The samples were taken in numerical sequence; thus Sample 1 was the first sample taken and Sample 7 the last. In the original solution before treatment the amount of ethyne was about 2.4-2.5Z of the amount of ethene. From the results in Table 2 it is seen that in all cases the proportion of ethene reacted was small: no ethanol, which would result from the addition of water to ethene, was detected in the effluent. However the activity of the catalysts towards ethyne varied, depending on both the nature of the active metal and the support. Mercury and mercury plus iron are generally superior to cadmium and zinc and "Amberlyst" and "Silicalite" appear to give superior results than the other supports. Table 2

Sample

Cat (Z) 1 2 3 4 5 6 7 ethene conv 3 2 2 2 1 1 1

A ethyne conv 84 96 99 >99 >99 >99 >99 ethyne/ethene 0.4 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 ethene conv 1 1 2 1 1 1 0

B ethyne conv 39 62 31 24 24 27 22 ethyne/ethene 1.5 0.9 1.7 1.9 1.9 1.8 1.9 ethene conv 2 2 2 2 2 2 1

C ethyne conv 95 95 97 97 96 96 97 ethyne/ethene 0.1 0.1 <0.1 <0.1 0.1 0.1 <0.1 ethene conv 2 2 2 3 3 2 1

D ethyne conv 73 74 82 57 26 23 19 ethyne/ethene 0.7 0.6 0.5 1.1 1.9 1.9 2.0 ethene conv 2 2 2 2 3 1 1

E ethyne conv 60 68 70 67 63 28 11 ethyne/ethene 1.0 0.8 0.8 0.8 0.9 1.8 2.2 ethene conv 1 3 2 2 2 1 2

F ethyne conv 11 17 19 17 18 15 13 ethyne/ethene 2.2 2.1 2.0 2.1 2.1 2.1 2.2 ethene conv 8 2 2 2 2 2 2

G ethyne conv 35 14 18 18 18 17 14 ethyne/ethene 1.7 2.1 2.0 2.0 2.0 2.1 2.1 ethene conv 0 1 1 1 2 1 2

H ethyne conv 17 18 16 15 11 11 11 ethyne/ethene 2.0 2.0 2.1 2.1 2.2 2.2 2.2 ethene conv 4 3 3 _ 2 2 2

I ethyne conv 23 29 30 - 25 18 16 ethyne/ethene 2.0 1.8 1.8 - 1.9 2.1 2.1 ethene conv 3 3 3 2 2 3 2

K ethyne conv 83 89 99 >99 >99 >99 >99 ethyne/ethene 0.4 0.3 <0.1 <0.1 <0.1 <0.1 <0.1

Example 3 The procedure of Example 2 was repeated but using other hydrogen compounds in place of water as the reactant. The amount of hydrogen compound was approximately 0.5Z of the solvent, except in the case where the hydrogen compound was hydrogen chloride where the hydrogen chloride was about 5Z of the solvent. In each case, in the original solution before treatment the amount of ethyne was about 2.0-2.2Z of the amount of ethene. The results are shown in Table 3: the catalyst employed is indicated in parenthesis under the reactant.

Table 3

Sample

Reactant (Z)

1 2 3 4 5 6 methanol ethene conv 2 1 3 <1 _— <1

(A) ethyne conv 57 94 78 65 - 86 ethyne/ethene 1.0 0.1 0.5 0.8 - 0.3 acetic ethene conv <1 <1 1 <1 <1 <1 acid ethyne conv 99 >99 >99 99 99 99

(A) ethyne/ethene <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 ammonia ethene conv 1 <1 <1 <1 <1 <1

(A) ethyne conv 96 97 97 97 97 99 ethyne/ethene <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 hydrogen ethene conv 2 <1 <1 <1 <1 <1 chloride ethyne conv 24 19 17 17 17 18

(A) ethyne/ethene 1.7 1.8 1.8 1.8 1.8 1.8 methanol ethene conv <1 <1 <1 <1

(C) ethyne conv 93 78 86 90 ethyne/ethene 0.1 0.5 0.3 0.2

It is seen that little ethene was reacted in each case, and the proportion of ethyne reacted depended on the reactant employed. Ammonia and acetic acid were particularly effective reactants.

Example 4

The procedure of Example 3 was repeated using catalyst A, various hydrogen-containing compounds as the reactant in an amount of 0.5Z, and a C3 hydrocarbon stream in place of the C2 stream. The C3 stream contained propene and small proportions of propyne and allene (propadiene). In the following tables the allene/propene and propyne/propene ratios are quoted (expressed as percentages).

In a first set of experiments, using 0.5Z of methanol or acetic acid as the hydrogen-containing compounds, the ratios of allene and propyne to propene in the solution before treatment were relatively low, viz 1.2 and 2.0Z respectively. The results are shown in Table 4a.

Table 4a

methanol acetic acid sample allene/ propyne/ allene/ propyne/ propene propene propene propene

(Z) (Z) (Z) (Z)

1 <0.1 <0.1 0.1 0.1

2 <0.1 <0.1 0.4 0.4

3 <0.1 <0.1 0.2 0.2

4 <0.1 <0.1 <0.1 <0.1

5 <0.1 <0.1 <0.1 <0.1

6 <0.1 <0.1 <0.1 <0.1

7 <0.1 <0.1 <0.1 <0.1

8 - - <0.1 <0.1

This demonstrates that both methanol and acetic acid are particularly effective for the selective reaction of both allene and propyne in the presence of propene.

To demonstrate that little reaction of propene was occurring, the above experiment using methanol was repeated with the addition of a small proportion of a mixture of ethane and ethene to the C3 mixture: since the ethane is inert, the proportion of propene reacting can be calculated from the observed ratio of ethane to propene in the effluent. In the following Table 4b, the proportions of ethene, propene, allene, and propyne reacted are quoted as percentages, together with the allene/propene and propyne/propene ratios of the effluent, again expressed as percentages. The solution, before passage over the catalyst, had the above components in the weight ratio propene:ethane:propyne:allene:ethene of 100:3.3:2.0:1.2:0.3. Table 4b

conversion (Z) allene/ propyne/ sample propene propene ethene propene allene propyne (Z) (Z)

1 <1 4 85 96 0.2 <0.1

2 <1 2 91 98 0.1 <0.1

3 <1 <1 91 98 0.1 <0.1

4 1 <1 96 99 <0.1 <0.1

5 <1 <1 81 93 0.2 0.1

6 <1 <1 93 98 <0.1 <0.1

7 <1 <1 94 99 <0.1 <0.1

8 <1 <1 95 99 <0.1 <0.1

It is seen that essentially all of the propyne and allene were removed with essentially no reaction of the olefins.

The experiment was repeated using a C3 stream free of C2 hydrocarbons but containing greater proportions of propyne and allene and using water, or a mixture of equal weights of methanol and water, as the hydrogen-containing reactant, in each case with 0.5Z of the hydrogen-containing reactant. The weight ratios of allene/propene and propyne/propene of the solution before treatment with the catalyst were 5.0Z and 21.0Z respectively. The allene/propene and propyne/propene ratios, expressed as percentages, of the effluent are set out in Table 4c below.

Table 4c

water water/methanol sample allene/ propyne/ allene/ propyne/ propene propene propene propene

(Z) (Z) (Z) (Z)

1 0.7 0.6 <0.1 0.2

2 1.1 0.1 <0.1 <0.1

3 1.1 0.2 <0.1 <0.1

4 1.0 0.1 <0.1 <0.1

5 1.0 <0.1 <0.1 <0.1

6 0.7 0.1 <0.1 <0.1

7 0.7 <0.1 <0.1 0.1

8 1.1 0.1 <0.1 0.4 This shows that both water and a methanol/water mixture are effective at removing allene and propyne, with the methanol/water mixture being the more effective.

Example 5

The procedure of Example 4 was repeated using 0.5Z of water as the hydrogen containing reactant and a C stream as the hydrocarbon. The C4 stream contained n-butane, butene-1, i-butene, t-butene-2, c-butene-2, 1,3-butadiene, 1,2-butadiene, vinyl acetylene, and ethyl acetylene. Before treatment with the catalyst, the solution contained these components in the weight ratios: i-butene 100 1,3-butadiene 9 butene-1 69 vinyl acetylene 3 butane 40 ethyl acetylene 0.7 t-butene- -2 32 1,2-butadiene 0.6 c-butene- ^■2 15

No 1,2-butadiene, vinyl acetylene or ethyl acetylene was found in the treated effluent indicating that there had been complete reaction of those components: the proportions of the other components converted (expressed as percentages) were as set in Table 5a.

Table 5a

conversion (Z) sample butene-1 i-butene t-butene-2 c-butene-2 1,3-butadiene

1 11 71 9 -1 7

2 10 53 11 3 -2

3 9 57 7 -1 -1

4 9 60 8 0 0

5 8 61 7 -1 1

6 1 64 2 2 -2

7 0 65 0 -1 -1

This shows that a large proportion of the i-butene and a significant proportion of the butene-1 reacted.

In an attempt to reduce the proportion of i-butene and butene-1 reacting, the experiment was repeated, using a different C stream and using a proportion of water which would be approximately stoichiometric for reaction with the acetylenes present. The solution before treatment with the catalyst had a butane/i-butene ratio of 50.3Z and an ethyl acetylene/butane ratio of 17.2Z. The proportions of i-butene and ethyl acetylene reacted were as set out in Table 5b.

Table 5b

conversion (Z) sample i-butene ethyl acetylene

1 4 85 2 3 86 3 3 87 4 3 86

This demonstrates that by restricting the amount of hydrogen-containing reactant, the amount of reaction of the i-butene can be decreased while still reacting a large proportion of the acetylenes. In a similar manner it can be concluded that by restricting the amount of hydrogen-containing reactant, the amount of butene-1 reacting will also be decreased.

Example 6

The procedure of Example 1 was repeated using methyl formate as the reagent in place of water. Analysis of the effluent showed that essentially all of the acetylene had reacted, mainly producing 2,2-dimethoxypropane.

Claims

Claims .

1. A process for the removal of compounds that are more highly unsaturated than olefins from an olefin stream comprising mixing the olefin stream with a hydrogen-containing compound, other than a hydrocarbon, contacting the mixture with a catalyst effective under the conditions employed to catalyse the addition of the hydrogen-containing compound to the more highly unsaturated compounds, and thereafter separating the addition product of the more highly unsaturated compound and the hydrogen-containing compound, and any unreacted hydrogen-containing compound, from the olefin stream.

2. A process according to claim 2 wherein the olefin stream consists essentially of hydrocarbons containing 2 or 3 carbon atoms.

3. A process according to claim 1 or claim 2 wherein the hydrogen-containing compound contains at least one polar H-X bond where X is an atom other than hydrogen and is selected from water, methanol, acetic acid, hydrogen cyanide, hydrogen bromide, hydrogen chloride, ammonia and methyl formate.

4. A process according to any one of claims 1 to 3 wherein there are 1 to 100 moles of the hydrogen-containing compound for each mole of highly unsaturated compound in the mixture contacted with the catalyst.

5. A process according to any one of claims 1 to 4 wherein the more highly unsaturated compounds are extracted from the olefin stream by a solvent.

6. A process according to claim 5 wherein the solvent is selected from N-methyl pyrrolidone, sulpholane, tetra-ethylene glycol, acetone, N-formyl morpholine, di-methyl sulphoxide, and di-methyl formamide.

7. A process according to claim 5 or claim 6 wherein the olefin stream is contacted with the hydrogen-containing compound and the solvent in the presence of the catalyst.

8. A process according to any one of claims 1 to 7 wherein at least part of the catalyst is disposed as a bed in a column, and the olefin stream is fed, in the gaseous state, to a lower part of the column and passed up through the bed while a liquid stream containing the hydrogen-containing compound is fed to an upper part of the column and flows down through the catalyst bed, whereby the olefin stream exit the column at the upper end thereof as purified product, and a liquid stream containing the addition compound leaves the column at the lower end thereof.

9. A process according to claim 8 wherein part of the catalyst is disposed as a bed in the column through which the olefin stream passes and the remainder of the catalyst is disposed as a bed in a reservoir region at the lower end of the column below the location of the column to which the olefin stream is fed.

10. A process according to claim 8 or claim 9 wherein at least part of the liquid stream from the bottom of the column is recycled to the upper part of the column, and the addition product separated from the liquid stream before recycle.

11. A process according to any one of claims 8 to 10 wherein the column is provided, above the catalyst bed, with a catalyst- free packed region through which the olefin stream and the liquid stream fed to the upper part of the column pass.