GB2432164A

GB2432164A - Production of linear alpha olefins

Info

Publication number: GB2432164A
Application number: GB0705164A
Authority: GB
Inventors: Bryce A Williams; Andrew Lindsay Burns
Original assignee: Ineos USA LLC
Current assignee: Ineos USA LLC
Priority date: 2007-03-17
Filing date: 2007-03-17
Publication date: 2007-05-16
Also published as: GB0705164D0

Abstract

A process for the production of linear alpha-olefins, comprising the steps of autothermally cracking a hydrocarbon stream to produce a reaction product stream at a temperature of at least 900{C; and using a hydrocarbon quench stream, said hydrocarbon quench stream comprising at least 80% by weight of linear hydrocarbons with at least 6 carbon atoms, to quench the reaction product stream to less than 800{C. The hydrocarbon quench stream is preferably derived from the product stream of a Fischer-Tropsch process, or of an ethylene oligomerisation process. The hydrocarbon stream to be cracked may contain one or more gaseous paraffinic hydrocarbons, such as ethane, propane and butane.

Description

1 2432164

PROCESS

The present invention relates to a process for the production of linear aipha-olefins.

In particular, the present invention relates to a process for the production of linear alpha-olefins in an autothermal cracking process.

Linear alpha-olefins (LAO's) may be generally produced by the oligomerisation of ethylene, as described, for example, in US 2004/0122271 A. The products formed generally comprise a distribution of LAO's of general formula C2H(4 l)CH=CH2, where n is 1, 2, 3, etc., i.e. 1-butene, 1-hexene, 1-octene etc. LAO's may be used as surfactants and lubricants, but the most valuable uses of the "lower" LAO's, especially 1-butene, 1-hexene and l-octene, if they can be obtained in high enough purity, are as co-monomers for polymer production.

The "higher" LAO's are generally less valuable.

("Lower" LAO and "higher" LAO as used herein refer to the relative number of carbon atoms in the respective LAO's.) It is, however, difficult to target specific LAO's by ethylene oligomerisation due to the inherent product distribution obtained, and hence, significant proportions of higher LAO's are obtained. A typical product distribution may contain approximately 70% ClO and lower LAO's, 20% C12 and C14, 5% C16 and C18 and 5% C20 and above.

It is desired therefore to find a process by which the more valuable LAO's may be obtained.

Autothermal cracking (ATC) is a route to olefins in which a hydrocarbon feed is mixed with oxygen and passed over an autothermal cracking catalyst. The autothermal cracking catalyst is capable of supporting combustion beyond the fuel rich limit of flammability. In autothermal cracking, combustion is initiated on the catalyst surface and the heat required to raise the reactants to the process temperature and to carry out the endothermic cracking process is generated in situ. The autothermal cracking of paraffinic hydrocarbons is described in EP-332289B; EP-529793B; EP-709446A and WO 00/14035.

The ATC product stream is quenched as it emerges from the reaction zone to avoid further reactions taking place. Usually the product stream is cooled by contacting with a suitable quench liquid immediately downstream of the reaction zone.

It has now been found that LAO's may be advantageously obtained by using a selected hydrocarbon stream as a quench liquid for the autothermal cracking process.

Hence, the present invention provides a process for the production of linear alpha-olefins, which process comprises (i) autothermally cracking a hydrocarbon stream to produce a reaction product stream at a temperature of at least 900 C, and (ii) using a hydrocarbon quench stream, said hydrocarbon quench stream compnsing at least 80% by weight of linear hydrocarbons with at least 6 carbon atoms, to quench the reaction product stream to less than 800 C.

When being used as a quench, the linear hydrocarbons in the selected hydrocarbon quench stream have been found to undergo cracking reactions to yield linear alpha olefins (LAO's).

Preferably, the hydrocarbon quench stream comprises at least 90% by weight of linear hydrocarbons having at least 6 carbon atoms, most preferably at least 95% by weight.

Preferably, the hydrocarbon quench stream comprises at least 80% by weight (preferably at least 90% by weight and most preferably at least 95% by weight) of linear hydrocarbons having at least N carbon atoms, where N is at least 9, cracking of which hydrocarbons occurs to produce linear alpha-olefms having M or less carbon atoms, where M is less than N. In a further preferred embodiment, the hydrocarbon quench stream comprises essentially no hydrocarbons with less than N carbon atoms, for example less than lmol% of hydrocarbons with less than N carbon atoms. Use of a hydrocarbon quench stream comprising essentially no hydrocarbons with less than N carbon atoms has the advantage that the produced LAO's (having M or less carbon atoms), can be relatively easily separated from unreacted hydrocarbons in the quench, for example by distillation.

Unreacted hydrocarbons, and any other products which may be present in the ATC product stream after quenching having N or more carbon atoms can be recycled to the quench step.

Alternatively, some or all of the unreacted hydrocarbons, and any olefins which may be present in the ATC product stream after quenching having N or more carbon atoms, can be recycled the autothermal cracking step.

For example, when used as a quench, linear hydrocarbons with at least 9 carbon atoms can be cracked to yield linear alpha olefins (LAO's) having 8 or less carbon atoms, such as 1 -octene and I -hexene, and said linear alpha-olefins may be easily separated from * 3 the hydrocarbons used as the quench liquid because of the different numbers of carbon atoms, for example by distillation.

Selection of the hydrocarbon stream to the autothermal cracking reaction of step (i) can also be used to ease of separation of the desired LAO's from the products of the autothermal cracking reaction, allowing the desired LAO's to be produced with high purity using relatively simple separation steps, such as distillation.

In one preferred embodiment, the hydrocarbon quench stream of step (ii) has been derived from the product stream of a Fischer-Tropsch process.

The Fischer-Tropsch process produces hydrocarbons from carbon monoxide and hydrogen (synthesis gas). Typically the product stream from a Fischer-Tropsch reactor includes C4 to C20+ hydrocarbons. The hydrocarbons are generally highly linear.

Depending on the catalyst and process used, the product stream may be highly paraffinic or may comprise a substantial proportion of olefins.

The FT product stream (comprising C4 to C20+ hydrocarbons) may be treated by any suitable technique, to form the hydrocarbon quench stream for use as the quench liquid according to the present mvention. For example, where a hydrocarbon quench stream comprising essentially no hydrocarbons with less than N carbon atoms, where N is at least 9 is required as the quench liquid, the FT product stream (comprising C4 to C20+ hydrocarbons) may be treated by any suitable separations technique, for example by distillation, to remove hydrocarbons with less than N carbon atoms.

An added advantage of use of an FT-derived quench is that the quench need not be treated to reduce the olefin content, for example by hydrotreatment or hydrocracking, prior to being used. In contrast, it is conventional to treat FT-derived streams to reduce the olefins content therein prior to steam cracking because of the propensity of the olefins to cause coking in the steam cracker.

Thus, an FT reactor effluent comprising C4 to C20+ hydrocarbons may be treated, for example by distillation, to remove hydrocarbons with less than N carbon atoms, where N is at least 9, to give a liquid hydrocarbon stream which is used without treatment to reduce the olefin content as the hydrocarbon quench stream of step (ii). As an example, where I -octene is the desired product, an FT reactor effluent comprising C4 to C20+ hydrocarbons is treated, for example by distillation, to remove C4 to C8 hydrocarbons, preferably to remove C4 to C9 hydrocarbons (generally referred to as a naphtha fraction), * 4 and to give a liquid hydrocarbon stream comprising linear hydrocarbons with at least 9 carbon atoms, preferably at least 10 carbon atoms, which may be passed without treatment to reduce the olefin content as a hydrocarbon quench stream for an autothermal cracking stream. The C9+ (C 10+) hydrocarbon quench stream obtained will autothermally crack to produce 1-octene and lower LAO's. The 1-octene and lower LAO's will be easily separable from the higher hydrocarbons in the ATC product stream which comprise unreacted components of the hydrocarbon quench stream and cracked components which still have more than 8 carbon atoms.

In an alternative preferred embodiment, the hydrocarbon quench stream has been derived from the product stream of an ethylene oligomerisation process. It has been found that cracking of LAO's in the product stream occurs to produce LAO's with a lower number of carbon atoms than the LAO's used as the quench. Hence, the lower value, higher LAO's produced from a conventional LAO process may be upgraded to produce more valuable LAO's.

The product stream of the ethylene oligomerisation process (as it leaves the process) comprises LAO's with even numbers of carbon atoms.

Preferably, the product stream of the ethylene oligomerisation process is treated, for example by distillation, to remove LAO's (and any other hydrocarbons) with less than N carbon atoms, where N is at least 9, to give a liquid hydrocarbon stream for use as the hydrocarbon quench stream of step (ii) i.e. as the quench liquid. (N in the hydrocarbon quench stream for use as the quench liquid will then practically be at least 10, since the ethylene oligomerisation produces even numbered LAO's).

As well as easing subsequent separations, as described previously, the separation of the lower LAO's prior to use as a quench liquid prevents their cracking in the quench step.

In general, the most desired LAO product, and hence the preferred quench liquid may be determined based on the relative values of the LAO monomers, which may vary with market conditions.

For example, when using an FT-derived quench liquid, if it is desired to produce 1-decene (C 10, M= 10), the preferred hydrocarbon quench stream will comprise linear hydrocarbons having at least 11 carbon atoms (Cil, N1 1). As well as 1-decene, "lower" LAO's, such as 1-octene (C8), 1-hexene (C6) and 1-butene (C4) may also be produced. * 5

Alternatively, where 1 -octene is the most valuable/desired LAO from an FT-derived quench liquid, the preferred hydrocarbon quench stream will comprise linear hydrocarbons having at least 9 carbon atoms.

Although the above describe use of a hydrocarbon quench stream derived from an FT process comprising linear hydrocarbons having at least N carbon atoms to ease the subsequent separation of LAO products having M or less carbon atoms, where N = M + 1, it may be preferred to use a hydrocarbon quench stream comprising linear hydrocarbons having at least N carbon atoms, wherein N > M + 1, for example, N = M + 2, since this will further ease the subsequent separation of the product LAO's from unreacted linear hydrocarbons.

This embodiment of the process of the present invention also has the advantage that linear alpha-olefins with odd numbers of carbon atoms may be formed, such as 1 -pentene and 1 -heptene. In contrast, conventional LAO production by ethylene oligomerisation processes generally produces only the even numbered LAO's.

As an alternative example, when using an LAO derived stream as quench liquid, if it is desired to produce l-decene (C 10, M=lO), an LAO reactor effluent comprising LAO's having at least 12 carbon atoms (C 12, N=12) will preferably form the quench. As well as 1-decene, "lower" LAO's, such as 1-octene (C8), 1-hexene (C6) and 1-butene (C4) may also be produced.

Alternatively, where I -octene is the most valuable/desired LAO product, an LAO reactor effluent also compnsing I -decene may be suitable, although an LAO reactor effluent compnsing LAO's having at least 12 carbon atoms may still be preferred. Thus, in this embodiment the LAO reactor effluent comprises LAO's having at least 10 carbon atoms and the ATC product stream will comprise C8 and lower LAO's.

In step (i) of the process of the present invention, any suitable hydrocarbon stream may be autothermally cracked.

For example, one or more gaseous paraf[inic hydrocarbons, such as ethane, propane and butane may be fed and will crack to produce C2 to C4 olefins, such as ethylene.

Liquid hydrocarbons, especially liquid paraffinic hydrocarbons, may also be used.

When a liquid hydrocarbon is used as the hydrocarbon stream to the autothermal cracker and a second liquid hydrocarbon comprising linear hydrocarbons having at least N carbon atoms, where N is at least 9, is used as the quench liquid (hydrocarbon quench stream), it is * 6 preferred that the liquid hydrocarbon used as the hydrocarbon Stream to the autothermal cracker also comprise at least N carbon atoms, where N is at least 9, since this will further ease LAO product separation from the quenched ATC product stream.

In a further aspect, the hydrocarbon stream to be autothermally cracked in the ATC reaction zone and the hydrocarbon quench stream may be derived from the same source.

Thus, a hydrocarbon stream from a single source may be treated to produce a hydrocarbon quench stream comprising linear hydrocarbons for use as a quench and a second hydrocarbon stream for use as the hydrocarbon stream to be autothermally cracked.

In one example of this embodiment, an FT reactor effluent comprising C4 to C20+ hydrocarbons is treated, for example by distillation, to remove hydrocarbons with less than N carbon atoms, where N is at least 9, to give a liquid hydrocarbon stream comprising linear hydrocarbons with at least 9 carbon atoms which is used without treatment to reduce the olefin content as the hydrocarbon quench stream of step (ii), and the hydrocarbons with less than N carbon atoms, where N is at least 9 removed are passed as the hydrocarbon stream to the autothermal cracking step of step (i), for example, to produce ethylene.

In an alternative example of this embodiment, a portion of a hydrocarbon stream which is a liquid and has at least 80% by weight of linear hydrocarbons is simply separated to produce a liquid hydrocarbon stream for use as the hydrocarbon quench stream and the remainder of the hydrocarbon stream is passed as the hydrocarbon stream to the autothermal cracking step of step (i). Thus, in this embodiment the same liquid hydrocarbon is used as the hydrocarbon stream to be cracked and as a quench liquid.

This aspect of the present invention allows significant versatility in the product distribution from the overall autothermal cracking process. For example, by selection of the amount of liquid hydrocarbon passed to the quench and suitable conditions in the ATC reactor, the quenched ATC product stream may be tailored to maximise different products.

Thus, where it is desired to produce predominantly ethylene, with only a limited amount of LAO, the reactor conditions are run to optiniise ethylene and only a small proportion of the hydrocarbon stream is used for the quench liquid. The remainder of the quench liquid may be made up, for example, by water or other hydrocarbon, such as ethane.

Where it is desired to produce an increased amount of LAO's, a larger portion of the hydrocarbon stream may be diverted to the quench (in place of a water or ethane quench, for example) leading to increased LAO production.

The hydrocarbon stream is autothermally cracked in step (i) by contacting said stream with an autothermal cracking catalyst in the presence of an oxygen-containing gas.

The catalyst is a catalyst capable of supporting combustion beyond the fuel rich limit of flammability.

The oxygen-containing gas may be provided as any suitable molecular oxygen containing gas, such as molecular oxygen itself or air.

Preferably, hydrogen is co-fed to the autothermal cracking step (i). Hydrogen co-feeds are advantageous because, in the presence of the catalyst, the hydrogen combusts preferentially relative to the hydrocarbon stream, thereby increasing the selectivity of the overall process. The amount of hydrogen combusted may be used to control the amount of heat generated and hence the severity of cracking. Thus, the molar ratio of hydrogen to oxygen can vary over any operable range provided that the desired reaction product stream is produced. Suitably, the molar ratio of hydrogen to oxygen is in the range 0.2 to 4, preferably, in the range 0.2 to 3.

The hydrocarbon to be cracked and molecular oxygen-containing gas may be contacted with the catalyst capable of supporting combustion in any suitable molar ratio, provided that the desired reaction product stream is produced. The preferred stoichiometric ratio of hydrocarbon to oxygen-containing gas is 5 to 16, preferably, 5 to 13.5 times, preferably, 6 to 10 times the stoichiometric ratio of hydrocarbon to oxygencontaining gas required for complete combustion of the hydrocarbon to carbon dioxide and water.

The hydrocarbon is passed over the catalyst at a gas hourly space velocity of greater than 10,000 h, preferably above 20,000 h and most preferably, greater than 100,000 h It will be understood, however, that the optimum gas hourly space velocity will depend upon the pressure.

The autothermal cracking step may suitably be carried out at a catalyst exit temperature in the range 900 C to 1200 C, preferably, in the range 900 C to 1050 C and, most preferably, in the range 900 C to 1000 C.

The ATC reaction product stream exits the autothermal cracking step (exits the reaction zone) at a temperature of at least 900 C in step (i). In step (ii) of the process of the * 8 present invention the reaction product stream is quenched to below 800 C using a hydrocarbon quench stream, said hydrocarbon quench stream comprising at least 80% by weight of linear hydrocarbons with at least 6 carbon atoms.

In general, the reaction product stream is usually cooled by using sufficient hydrocarbon quench stream to quench to between 750-600 C within less than I OOmilliseconds of formation, preferably within 5Omilliseconds of formation and most prefcrably within 20milliseconds of formation e.g. within l0milhseconds of formation. As described above, the heat from the reaction product stream, on quenching, causes cracking of the hydrocarbon quench stream. Any residual heat in the mixed quenched stream may be used to generate high-pressure steam or heat exchanged with other streams, which can be used to provide power for those parts of the overall process requiring it.

The hydrocarbon quench stream is a liquid at room temperature and pressure. The hydrocarbon quench stream may be vaporised and used as a quench in a gaseous state, but is normally used in a liquid state.

The hydrocarbon quench stream may be contacted with the reaction product stream in any suitable manner, typically by injection from one of more nozzles located in the reactor immediately downstream of the catalyst.

The autothermal cracking step is usually operated at a pressure of greater than 0.5barg. Preferably the autothermal cracking process is operated at a pressure of between 0.5-4Obarg.

The catalyst capable of supporting combustion beyond the fuel rich limit of flammability usually comprises a Group VIII metal as its catalytic component. Suitable Group VIII metals include platinum, palladium, ruthenium, rhodium, osmium and iridium.

Rhodium, and more particularly, platinum and palladium are preferred. Typical Group VIII metal loadings range from 0.01 to lOOwt %, preferably, between 0.01 to 20 wt %, and more preferably, from 0.01 to 10 wt % based on the total dry weight of the catalyst.

Where a Group VIII catalyst is employed, it is preferably employed in combination with a catalyst promoter. The promoter may be a Group lilA, WA, andlor VA metal.

Alternatively, the promoter may be a transition metal; the transition metal promoter being a different metal to that which may be employed as the Group VIII transition metal catalytic component. Preferred promoters are selected from the group consisting of Ga, In, Sn, Ge, --9 Ag, Au or Cu. The atomic ratio of Group VIII B metal to the catalyst promoter may be 1: 0.1 -50.0, preferably, 1: 0.1 -12.0.

Preferred examples of promoted catalysts include Pt/Ga, Pt/In, Pt/Sn, Pt/Ge, Pt/Cu, Pd/Sn, Pd/Ge, Pd/Cu, RhJSn, Pt/Pd/Cu and PtJPdISn catalysts.

For the avoidance of doubt, the Group VIII metal and promoter in the catalyst may be present in any form, for example, as a metal, or in the form of a metal compound, such as an oxide.

The catalyst may be unsupported, such as in the form of a metal gauze, but is preferably supported. Any suitable support may be used such as ceramic or metal supports, but ceramic supports are generally preferred. Where ceramic supports are used, the composition of the ceramic support may be any oxide or combination of oxides that is stable at high temperatures of, for example, between 600 C and 1200 C. The support matenal preferably has a low thermal expansion co-efficient, and is resistant to phase separation at high temperatures.

Suitable ceramic supports include corderite, lithium aluminium silicate (LAS), alumina (a-Al203), yttria stabilised zirconia, alumina titanate, niascon, and calcium zirconyl phosphate. The ceramic supports may be wash-coated, for example, with y-A1203.

The catalyst may be prepared by any method known in the art. For example, gel methods and wet-impregnation techniques may be employed. Typically, the support is impregnated with one or more solutions comprising the metals, dried and then calcined in air. The support may be impregnated in one or more steps. Preferably, multiple impregnation steps are employed. The support is preferably dried and calcined between each impregnation, and then subjected to a final calcination, preferably, in air. The calcined support may then be reduced, for example, by heat treatment in a hydrogen atmosphere.

Although the catalyst has been described above in terms of a single catalyst bed, the catalyst may alternatively be present as a sequential catalyst bed, as described, for example, in WO 02/04389.

In addition to olefins, the autothermal cracking reaction produces hydrogen, carbon monoxide, methane, and small amounts of acetylenes, aromatics and carbon dioxide.

Separation of the desired products from the cooled product stream may be achieved by any suitable technique or series of techniques. For example, an amine wash may be used to remove carbon dioxide and water from the ATC product stream, a demethaniser to remove hydrogen, carbon monoxide and methane, and hydrogenation to remove acetylenic compounds and dienes.

Any suitable treatments to separate the respective olefinic products may be used depending on the respective products themselves, but generally, for example, any ethylene will be separated using a deethaniser, and any propylene using a depropaniser. Distillation is a particularly suitable technique for separation of the LAO's in the product stream. * 11

Claims

Claims I. A process for the production of linear alpha-olefins, which

process comprises (i) autothermally cracking a hydrocarbon stream to produce a reaction product stream at a temperature of at least 900 C, and (ii) using a hydrocarbon quench stream, said hydrocarbon quench stream comprising at least 80% by weight of linear hydrocarbons with at least 6 carbon atoms, to quench the reaction product stream to less than 800 C.

2. A process as claimed in claim 1, wherein the hydrocarbon quench stream comprises at least 90% by weight of linear hydrocarbons having at least 6 carbon atoms, most preferably at least 95% by weight.

3. A process as claimed in claim I or claim 2, wherein the hydrocarbon quench stream comprises at least 80% by weight (preferably at least 90% by weight and most preferably at least 95% by weight) of linear hydrocarbons having at least N carbon atoms, where N is at least 9.

4. A process as claimed in claim 3, wherein the hydrocarbon quench stream comprises less than 1 mol% of hydrocarbons with less than N carbon atoms.

5. A process as claimed in any one of the preceding claims, wherein the hydrocarbon quench stream has been derived from the product stream of a Fischer-Tropsch process.

6. A process as claimed in claim 5 wherein an FT reactor effluent comprising C4 to C20+ hydrocarbons is treated, for example by distillation, to remove hydrocarbons with less than N carbon atoms, where N is at least 9, to give a liquid hydrocarbon stream which is used without treatment to reduce the olefin content as the hydrocarbon quench stream of step (ii).

7. A process as claimed in any one of claims 1 to 5, wherein the hydrocarbon quench stream has been derived from the product stream of an ethylene oligomerisation process.

8. A process as claimed in claim 7 wherein the product stream of the ethylene oligomerisation process is treated, for example by distillation, to remove LAO's (and any other hydrocarbons) with less than N carbon atoms, where N is at least 9, to give a liquid hydrocarbon stream which is used as the hydrocarbon quench stream of step (ii).

9. A process as claimed in any one of the preceding claims wherein the hydrocarbon stream of step (i) is one or more gaseous paraffinic hydrocarbons, such as ethane, propane and butane.

10. A process as claimed in any one of the preceding claims wherein the hydrocarbon S stream to be cracked in step (i) and the hydrocarbon quench stream in step (ii) are derived from the same source.

11. A process as claimed in claim 10, wherein an FT reactor effluent comprising C4 to C20-i-hydrocarbons is treated, for example by distillation, to remove hydrocarbons with less than N carbon atoms, where N is at least 9, to give a liquid hydrocarbon stream comprising linear hydrocarbons with at least 9 carbon atoms which is used without treatment to reduce the olefin content as the hydrocarbon quench stream of step (ii), and the hydrocarbons with less than N carbon atoms, where N is at least 9 removed are passed as the hydrocarbon stream to the autothermal cracking step of step (i).

12. A process as claimed in claim 10 wherein the same liquid hydrocarbon is used as the hydrocarbon stream to be cracked in step (i) and as the hydrocarbon quench stream in step (ii).