JP2001089399A - IMPROVED PROCESS FOR PRODUCTION OF LINEAR alpha-OLEFIN WITH SUPERCRITICAL ETHYLENE RECYCLE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably reduce the amount of compression required for unconverted ethylene by carrying out separation and recycle of supercritical ethylene in oligomerization of the ethylene. SOLUTION: A linear α-olefin is continuously produced by oligomerizing the ethylene in a polar phase containing a transition metal catalyst system under oligomerizing conditions including a temperature and a pressure greater than the critical temperature and pressure of ethylene. The resultant hydrocarbon phase containing hydrocarbons and unconverted ethylene is subjected to physical treatment which tends to render the ethylene a nonsolvent for oligomers to thereby produce a liquefied stream rich in supercritical ethylene which can be recycled to the oligomerization reactional zone by pumping.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to an improved process for producing linear alpha olefins comprising a supercritical ethylene reflux step.

[0002]

BACKGROUND OF THE INVENTION Linear olefins are one of the most useful hydrocarbons used as feedstocks in petrochemicals, among which linear alpha olefine-the double bond at the end of the chain. The-located forms an important part. Linear alpha-olefins can be converted to linear primary alcohols by hydroformylation (oxo synthesis); alcohols with 10 or less carbon atoms are used in the synthesis of plasticizers, whereas Number 11
The above are used in the synthesis of detergents. Hydroformylation can also be used to prepare aldehydes as major products, and these aldehydes can be used to oxidize to produce fatty acids; Useful as Linear alpha olefins are also used in the most useful types of detergents for home use, specifically the Friedel-Crafts reaction of benzene with linear olefins and sulfonation. Is a linear alkylbenzene sulfonate prepared by

Another important use of alpha olefins is the hydrobromide radical reaction, which can produce primary alkane bromides, which can be thiols, amines, It is an important intermediate in producing amine oxides and ammonium compounds. By directly sulfonating alpha olefins, a mixture of alpha olefin sulfonic acids, isomerized alkene sulfonic acids and isomerized alkane sulfonic acids can be obtained, which can be used as an effective detergent even in hard water and at low concentrations. Can be. Linear alpha olefins, especially those having up to eight hydrocarbons, are used as comonomers in producing high and low density polyethylene.

[0004] Linear olefins are the dehydrogenation products of linear alkanes, the major part of such products being internal olefins. The preparation of olefins is mostly based on the oligomerization of ethylene, and thus the olefins produced have an even number of carbon atoms. For example,
When a catalytically effective amount of triethylaluminum is used, the oligomerization of ethylene proceeds at temperatures below 200 ° C., resulting in a mixture of alpha-olefins whose carbon number follows a Schuifz-flory distribution. C
The proportion of the side chain alpha-olefin in the range of ₆ -C ₁₀ lower than 4%, but the degree of branching and chain length is extended to approximately 18 8
%. A modification process called the Ethyl Process allows for a controlled distribution of ethylene alpha
Although high conversions to olefins are obtained, the quality of the product is significantly affected, especially the content of branched olefins. Accordingly, in the range of C ₁₄ -C ₁₆ it is only about 76% of linear alpha-olefins products.

A remarkable advance in the art has involved the use of transition metals as catalysts to produce ethylene oligomers. For example, when using a nickel, cobalt, titanium, or zirconium catalyst, substantially
100% of mono-olefins were obtained, alpha-olefins above 97%, branched olefins below 2.5% and internal olefins below 2.5%. Owing to the fact that the catalyst is insoluble in hydrocarbons, the formation of oligomers, generally by means of catalyst systems based on transition metals, takes place in a polar solvent in which the catalyst is dissolved. Ethylene and its oligomers have a limited limit of solubility in the polar solvent used and can introduce ethylene into the polar phase and at the same time withdraw the oligomerization product as a hydrocarbon phase, thus providing a continuous oligomerization process. Becomes possible.

[0006]

Oligomerization of ethylene results in alpha olefins having a Schulz-Flory distribution, which is generally catalyst dependent, and at least the catalysts discussed herein. In the case of, the temperature dependence is very slight. Such catalysts having transition metal components that are particularly attractive as oligomerization catalysts are described in U.S. Patent Application No. 4,689,437, U.S. Patent Application No. 4,716,138, U.S. Patent Application No. 4,822,915 and U.S. Patent Application No. 4,668,823. I have. Schulz
The use of such a catalyst under the condition of a Flory distribution constant of 0.65 results in products which, from an economic point of view, have a particularly favorable distribution of alpha-olefins in the range C ₆ -C ₁₆ .
That is, the economic value of ethylene oligomers can be maximized when the Schulz-Flory distribution constant is about 0.65.
Under these operating conditions, the oligomerized reactor effluent contains oligomeric compounds and unreacted ethylene. This unreacted ethylene needs to be recovered and circulated to the oligomerization reaction zone. Conventionally, unreacted ethylene has been recovered by fractional distillation and then compressed before being refluxed in the oligomerization reaction zone. Since compression is expensive, it is desirable to introduce at least a portion of the reflux into the oligomerization reaction zone without compression. According to the present invention, this desirable goal is achieved.

It has been found that the amount of compression required for unreacted ethylene can be greatly reduced by separating and circulating supercritical ethylene. It is desirable to be able to recover up to 90% of ethylene from the reactor effluent under supercritical conditions and then to return to the reactor inlet by pumping rather than compression. Since supercritical separation under the preferred operating conditions is not a rapid and complete separation, 15 to 25 mole% of the material recovered and refluxed to the reactor is oligomer. However, one advantage of the separation here is that these oligomers can be used as an aid to dissolve the heavy wax produced in the oligomerization reaction zone.

During the oligomerization reaction, about 10% of the oligomers are solids at ambient temperature and have 20 or more carbon atoms (C ₂₀₊ ). _{C20 +} oligomers have a limited solubility in the hydrocarbon phase resulting from the oligomerization process described above, thus forming a separate solid wax phase. In that case, the oligomerization process is a system composed of four phases: a vapor phase of ethylene, a polar solvent phase with dissolved catalyst, a non-permeable liquid hydrocarbon phase, and a solid phase of _{C20 +} hydrocarbons. When solids are formed, reactors with current configurations tend to clog,
Thus, a continuous process may periodically interrupt reactor operation to clear clogs, and even during process operation, accumulation of solids may prevent liquid flow. Since these solids create problems, it is highly desirable to prevent the solids from depositing. This can be done by increasing the solubility of the heavy chain oligomers in the liquid hydrocarbon phase by simultaneously circulating a portion of the light oligomer fraction and refluxing ethylene through the oligomerization reaction zone.

No. 4,689,437 and US Pat. No. 5,523,508 disclose transition metal compounds, catalytic activators and catalysts in polar solvents such as sulfolane under preferred conditions including temperatures and pressures above the critical temperature and pressure of ethylene. Disclosed is a process for oligomerizing ethylene in the presence of a catalyst system comprising an oreganophosphorus sulfonate ligand. These patents do not disclose the separation of supercritical ethylene from the effluent of the oligomerization reaction zone according to the invention and the subsequent reflux of the supercritical ethylene.

It is an object of the present invention to produce linear alpha olefins from the oligomerization of ethylene using a solution of a transition metal catalyst system as a catalyst in a polar solvent while simultaneously allowing unreacted ethylene in the oligomerization reaction zone. Is to perform more economical separation for refluxing.
A hydrocarbon phase containing the oligomer and unreacted ethylene is removed from the oligomerization reaction zone, and the unreacted ethylene is subjected to a physical treatment to dissolve the oligomer in a non-solvent, thereby being returned to the oligomerization reaction zone by a pump operation. Is to produce a liquid phase containing supercritical ethylene.

[0011]

SUMMARY OF THE INVENTION One embodiment of the present invention is an improved process for the continuous oligomerization of ethylene to produce linear alpha olefins, comprising:
(A) In an oligomerization reaction zone 3 including a liquid polar phase composed of a solution of a transition metal catalyst system in a polar solvent under oligomerization conditions including a temperature and pressure above the critical temperature and pressure of ethylene. Introducing ethylene 2 and (b) oligomerizing the ethylene to form an oligomer having 5 or more carbon atoms in the liquid polar phase, separating the liquid polar phase from the liquid polar phase and containing unreacted ethylene. Forming a hydrogen phase; (c)
The liquid hydrocarbon phase is continuously withdrawn in the supercritical separation zone and subjected to a physical treatment to make ethylene a non-solvent for the oligomer, whereby the first liquid phase contains supercritical ethylene in a countercritical solvent state. Forming a two-phase system, wherein the second liquid phase comprises oligomers;
(D) circulating at least a portion of the first liquid phase produced in step (c) to provide at least a portion of the ethylene of step (a); and (e)
Recovering the second liquid phase 8 containing the oligomer produced in step (c).

Another embodiment of the present invention comprises an improved process featuring the first embodiment for continuous oligomerization of ethylene to produce linear alpha olefins. At least a portion of the second liquefied phase comprising oligomer and ethylene produced in step (c) is fractionated to produce a stream comprising ethylene and a stream comprising oligomer, and the ethylene recovered from the fractionation step is removed. Wherein at least a portion of the liquid stream comprising is recycled to provide at least a portion of the ethylene of step (a).

[0013] The present invention is a continuous oligomerization process of ethylene to produce linear alpha olefins. Using a solution of the transition metal catalyst system in a polar solvent, the oligomerization of ethylene proceeds with the formation of phase separated hydrocarbons consisting mostly of linear alpha olefins formed according to a Schulz-Flory distribution. If the Schulz-Flory distribution constant is greater than 0.60, significant amounts of _{C20 +} oligomers are formed that cannot be completely dissolved at the process temperature. The eluate from the oligomerization reaction zone contains unreacted ethylene, up to 90% of which is recovered from the eluate of the reactor under supercritical conditions and then pumped, rather than compressed, into the reaction inlet. Can be circulated.

Preferably, the oligomerization of ethylene is catalyzed by a transition metal catalyst system. Suitable metal catalyst systems are described in U.S. Patent Application No. 4,689,437. A preferred transition metal catalyst system is a reaction product composed of three components: a transition metal compound, a catalyst activator, and an organophosphorous sulfonate ligand. Transition metal catalyst systems for ethylene oligomerization are well known in the art and need not be described further herein.

The oligomerization of ethylene is a liquid phase reaction, and the catalyst may be dissolved in a solvent or suspended in a liquid medium. Of course, the solvent or medium must be inert to process components and equipment under process conditions. Solvents include ethanol, methanol, water, sulfolane (tetramethylene sulfone),
Examples include ethylene glycol, 1,4-butanediol, ethylene carbonate, and mixtures thereof. In what is described here and its variants, solvents which can easily phase-separate from the oligomer product are preferred in order to obtain a polar solvent phase and a hydrocarbon phase. The most preferred solvent for ethylene oligomerization is sulfolane, which completely dissolves the catalyst of the present invention but does not dissolve the oligomer.

The general catalyst concentration is 10 to 1,00
It is in the range of 0 ppm. Some of the more active catalysts are 40 ppm
At a very high reaction rate, with a broader catalyst concentration range between 0.1 and 1,000 ppm. In a more preferred embodiment for practicing the present invention, the range of the catalyst concentration is between 15 and 300 ppm.

According to the present invention, the oligomerization conditions include a temperature range of 5 to 200 ° C. (40 to 392 ° F.), preferably 20 to 14 ° C.
0 ° C (68-284 ° F) range, more preferably 30-80 ° C
(86-176 ° F). The pressure for oligomerization is preferably in the range of 6.2 to 34.6 mPa (885 to 5,000 psig), more preferably 6.2 to 13.9 mPa (885 to 2,000 ps).
ig). These pressures are those at which ethylene can be introduced into the reactor and maintained by the reactor. The critical temperature and pressure of ethylene are 5 ° C (40 ° F) and
6.2 mPa (885 psig), so the oligomerization reaction zone is operated at the above critical temperature and pressure conditions for ethylene.

The oligomerization process is a process for forming oligomers having a low solubility in polar solvents, mainly having from 4 to 20 or more carbon atoms, especially when the solvent of the transition metal catalyst system of the present invention is sulfolane. It is. As a result, oligomer formation always involves the formation of a separate phase, the hydrocarbon phase, at least a portion of which is continuously withdrawn. The constituents of the hydrocarbon phase are ethylene oligomers, the relative proportions of which follow a Schulz-Flory distribution. The practice of the present invention is particularly suitable when significant amounts of heavy oligomers are formed in a Schulz-Flory distribution function. "Heavy oligomers" means oligomers that are usually (wax) solids at the process temperature and can be considered _{C20 +} oligomers. These heavy oligomers have a temperature-dependent, limited solubility in the hydrocarbon phase. Increasing the reaction temperature to maintain homogeneity is not practical because temperature also affects the quality of the oligomer product via selectivity to linear alpha olefins. If the homogeneity of the hydrocarbon phase cannot be maintained, the reactor (or auxiliary equipment) becomes clogged, but the present invention solves this problem.

The process of the present invention does not supercritically recover at least a portion of unreacted ethylene from the eluate of the reaction zone, but uses it in a general method for oligomerization of ethylene. Thus, ethylene is continuously introduced into the reactor, which is placed under the oligomerization conditions as defined above. The transition metal catalyst system is in a polar solvent, preferably in sulfolane. Oligomerization involves the formation of a separate hydrocarbon phase due to the low solubility of the oligomer in sulfolane. The hydrocarbon phase containing oligomers and unreacted ethylene is continuously removed and subjected to physical treatment to reduce the solvent capacity of supercritical ethylene.

Reduction of the solvent capacity of supercritical ethylene can be achieved by lowering the pressure, increasing the temperature, or a combination thereof. The most important consideration in the separation and recycle of supercritical ethylene is that the ability of supercritical ethylene to extract heavier components is highly dependent on its density. The density of supercritical ethylene (pressure drop, temperature rise,
(Or by a combination thereof) decreases the amount of heavy substances, that is, the amount of oligomers remaining in supercritical ethylene. According to the present invention, it is preferred that the solvent capacity for the supercritical ethylene oligomer decreases with both a decrease in pressure and an increase in temperature. The pressure is 6.2-34.6m
Preferably, the pressure is reduced from Pa (850-1350 psig) to 850 psig and the temperature is increased to 80-205 ° C (175-400 ° F). After lowering the solvent capacity of the supercritical ethylene, the eluate from the oligomerization reaction zone is introduced into the supercritical separation zone, where a top liquid stream containing unreacted ethylene is generated and recovered, and then returned to the oligomerization reaction zone. Circulated. Because the separation of unreacted ethylene from the eluate from the reactor is not a rapid separation, about 15 to 25 mole percent of the material recovered and returned to the reactor is an oligomer with up to 14 carbon atoms. It is.
These oligomers, which are refluxed with supercritical ethylene, are used to dissolve the heavy wax formed in the oligomerization reaction zone.

The bottoms liquid stream containing oligomers and unreacted ethylene is removed from the supercritical separation zone and fractionated in a conventional manner to form a stream containing the product oligomers and unreacted ethylene which is also refluxed to the oligomerization reaction zone. Is recovered.

[0022]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show preferred embodiments of the present invention and are simple process drawings.

In this figure, a freshly supplied ethylene stream is introduced into the process equipment via line 1 and
And a second circulating liquid stream containing unreacted ethylene, which is sent via line 12, containing unreacted ethylene and oligomers. The resulting mixture is introduced into the oligomerization reaction zone 3 in line 2 and the resulting product stream comprising oligomers and unreacted ethylene is withdrawn from the oligomerization reaction zone 3 via line 4 and the heat exchanger 5 Introduced within. The heated eluate obtained from the heat exchanger 5 is sent via a line 6 and introduced into a supercritical separation zone 7. The overhead distillate stream containing unreacted ethylene and oligomers is
It is removed from the supercritical separation zone 7 via 13 and introduced into the heat exchanger 14. The resulting cooled eluate from heat exchanger 14 is sent via line 15 to provide the first circulating liquid stream described above. The bottom liquid stream is withdrawn from supercritical separation zone 7 via line 8 and introduced into fractionation zone 9. The overhead distillate stream containing unreacted ethylene is withdrawn from the overhead of fractionation zone 9 from the overhead of fractionation zone 9 and sent via line 12 to provide the second circulating liquid stream. . The bottoms liquid stream containing oligomers is withdrawn from fractionation zone 9 via line 10 and recovered.

The process according to the invention is further illustrated by the following embodiments.

[0025]

EXAMPLE A stream of fresh ethylene was introduced into the above process at a rate of 981 mol / h and was introduced into the process equipment and combined with the first circulating liquid stream from the supercritical separation zone 7 at 784 mol / h. Addition mix with ethylene, 213 mol / h butane, and a balance of heavy oligomers (157 mol / h), totaling 1154 mol / h.

A second recycle stream from the oligomer product fractionation zone of ethylene at a rate of 196 moles / hour is also circulated with fresh feed ethylene and the first recycle stream and admixed with fresh feed ethylene. , Introduced into the oligomerization reaction zone 3, which is maintained at a temperature of 60 ° C. (140 ° F.) and a pressure of 10.3 mPa (1500 psia). Table 1 shows the details of the mixed feed stream and the product stream from the oligomerization reaction zone sent to the reaction zone.

The pressure of the eluate from the oligomerization reaction zone was reduced to 9.2 mPa (1335 psia) and the temperature was increased to 185 ° C. (3
(65 ° F.) and introduced into the supercritical separation zone.
The overhead liquid stream from the supercritical separation zone is removed and
Pumped into the oligomerization reaction zone as a circulating liquid stream. Fractionating the bottom liquid stream from the supercritical separation zone,
An overhead distillate stream containing unreacted ethylene at a rate of 196 moles / hour is created, which is refluxed to the oligomerization reaction zone as a second recycle stream. The linear alpha olefin oligomer product stream is recovered from the fractionation zone at a rate of 256 moles / hour and has the characteristics shown in Table 1.

[0028]

[Table 1]

[0029]

The present invention is a process for producing a linear alpha-olefin in which unreacted ethylene is separated and circulated as supercritical ethylene, and the compressed amount of unreacted ethylene required for the conventional circulation is reduced. Significantly reduced.

[Brief description of the drawings]

FIG. 1 is a simplified process diagram of a preferred embodiment of the present invention.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Brian H. Johnson United States Illinois, Death Plains, East Argon Quinn Load 25 UOP LLC F-term (reference) 4H006 AA02 AC21 BA10 BA20 BA21 BA48 BB13 BB14 BB15 BB23 BB42 BC10 BC11 BD33 BD52 4H039 CA19 CF10 CL20

Claims (6)

[Claims] 1. An improved process for the continuous oligomerization of ethylene to produce linear alpha olefins, comprising: (a) under oligomerization conditions comprising temperatures and pressures above the critical temperature and pressure of ethylene. Introducing ethylene (2) into an oligomerization reaction zone (3) containing a liquid polar phase comprising a solution of a transition metal catalyst system in a polar solvent; and (b) 5 or more carbon atoms in the liquid polar phase. Oligomerizing ethylene to form oligomers with atoms to form a liquid hydrocarbon phase (4) separated from the liquid polar phase and containing unreacted ethylene; and (c) a supercritical separation zone (7). ), The liquid hydrocarbon phase (4) is continuously withdrawn and subjected to a physical treatment in which ethylene is used as a non-solvent for the oligomer, whereby the first liquid phase (13) is subjected to a critical solution. Forming a two-phase system wherein the second liquid phase (8) contains supercritical ethylene in the state and contains the oligomer; and (d) said first liquid phase (13) created in step (c) Circulating at least a portion of the second liquid phase (8) to provide at least a portion of the ethylene of step (a), and (e) the second liquid phase (8) comprising the oligomers formed in step (c). ) Recovering. 2. The method of claim 1, wherein the transition metal catalyst system comprises a transition metal compound, a catalyst activator, and an organophosphorous sulfonate ligand. 3. A polar solvent comprising ethanol, methanol, sulfolane, ethylene glycol, 1,4-butanediol, and ethylene carbonate.
Production method described in 1. 4. The method according to claim 1, wherein the oligomerization condition is a temperature of 5 to 200 ° C.
4. A process according to any one of the preceding claims, comprising a pressure in the range of 885 to 5,000 psig. 5. The method according to claim 1, wherein the critical solvent state in step (c) is 6.0.
~ 9.4 mPa (850-1350 psig) pressure and 80-205 ° C (175-4
5. A method according to claim 1, comprising a temperature in the range of 00 ° F.
Production method described in the section. 6. A stream (12) containing ethylene and a stream (12) containing oligomer and at least a part of the second liquid phase (8) containing oligomer and ethylene produced in step (c) are fractionated. A process wherein 10) is made and at least a portion of the ethylene-containing liquid stream (12) is circulated to provide at least a portion of the ethylene of step (a).