DE10243444A1 - Oligomerization of 4C-hydrocarbon mixtures containing 1-butene, 2-butene and butane comprises hydroisomerization of a portion of the olefins contained in the residue stream to cis-2-butene and recycle of a high b.p. fraction - Google Patents

Abstract

Oligomerization of 4C-hydrocarbon mixtures containing 1-butene, 2-butene and butane comprises oligomerization of portion of olefins contained in the 4C hydrocarbon mixture, fractionation of reaction mixture to form residue stream comprising 4C hydrocarbons, hydroisomerization of portion of olefins contained in the residue stream to cis-2-butene and recycle of high b.p. fraction. A process for the oligomerization of 4C-hydrocarbon mixtures containing 1-butene, 2-butene and butane comprises; (a) oligomerization of a portion of the olefins contained in the 4C hydrocarbon mixture; (b) fractionation of the reaction mixture to form a residue stream comprising 4C hydrocarbons and a product stream containing the oligomers; (c) hydroisomerization of a portion of the olefins contained in the residue stream to cis-2-butene; (d) separation of the reaction mixture from (C) into a low b. p. fraction, containing the largest portion of butane, 1-butene and trans-2-butene and a high b. p. fraction containing the largest portion of cis-2-butene and; (e) recycle of the high b. p. fraction from (D) to the oligomerization reaction step (A).

Description

The present invention relates to a process for the oligomerization of butenes with separation of the linear butenes from n-butane-containing residual streams, by hydroisomerization and distillation and recycling of the 2-butenes thus obtained.

For the production of plasticizer alcohols, ie alcohols with 8-16 carbon atoms, C ₃ - or C ₄ -hydrocarbons are widely used, for. B. from FCC crackers oligomerized to longer-chain olefins, then hydroformylated and hydrogenated. The hydrocarbons used are generally mixtures of isomers and / or contain large amounts of inert aliphatics. In the case of the C ₄ -hydrocarbons, these are as a rule previously freed of butadiene by a corresponding selective hydrogenation and isobutene by reaction with methanol or water to give MTBE or tert-butanol.

The oligomerization of olefins, in particular of the butenes, to the corresponding C ₈ olefins is known to the person skilled in the art and is carried out worldwide in three process steps:

Oligomerization has long been known on acidic catalysts (process A), with technical z. B. Zeolites or phosphoric acid on carrier be used. Here are mixtures of isomers of branched Obtain olefins, which are primarily dimethylhexenes (WO 92/13818). Another one practiced worldwide The process is known for oligomerization with soluble Ni complexes as DIMERSOL process (process B) (B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis with Organometallic Compounds, page 261-263, Verlag Chemie 1996). Finally the oligomerization on nickel fixed bed catalysts should be mentioned, such as. B. the procedure the OXENO GmbH. The process has entered the literature as the OCTOL process C) (Hydrocarbon Process., Int. Ed. (1986) 65 (2nd Sect. 1), page 31-33) found.

In all variants, the olefins react and the saturated C ₄ -hydrocarbons remain unchanged, ie the concentration of the olefins decreases sharply during the reaction.

Such syntheses are only economical if high space-time yields are achieved. For this reason, complete olefin conversion is generally not sought under technical conditions. This leaves C ₄ hydrocarbon mixtures in which the olefins are severely depleted.

The C ₄ residual streams from oligomerization plants typically contain approximately 70% n-butane and approximately 30% butenes, which are present in a molar ratio of 1: 3 to 1:10 as 1-butene and 2-butene (cis and trans).

From these mixtures, which mainly contain chemically inert butanes, the olefins 1-butene and 2-butene, the n-butane can be converted to trans-butene (owing to the small difference in boiling point). 2 ) are not separated by distillation. In principle, cis-butene ( 2 ) can be obtained as heavy boilers by distillation, but such a separation is not economical because of its low content in the C ₄ residual streams because of the chemical equilibrium with trans-butene.

These residual currents can currently pass through Hydrogenation of the olefins contained in the mixture processed further are or are used as a cracker feed. Isobutane and n-butane for example as liquid gas or blowing agents can be used. n-Butane can also be a starting material for maleic anhydride his.

However, the hydrogenation of the butenes to the corresponding saturated hydrocarbons represents a material devaluation, since C ₄ olefins generally achieve a higher price than the saturated C ₄ hydrocarbons.

The object was therefore to develop a process with which C ₄ olefins from oligomerization processes, ie from mixtures which contain saturated C ₄ hydrocarbons and linear C ₄ olefins, are separated off or better exploited.

It was found that the distillative Processing the residual flows oligomerization by hydroisomerization of trans-butenes to cis-butenes and their separation significantly simplified and thus can be designed economically.

The hydroisomerization of 1-butene to 2-butene is known per se and e.g. B. in GB 2 057 006 described. Here, a C ₄ stream, which contains isobutene, 1-butene and 2-butene in addition to the saturated butanes, is subjected to a hydroisomerization with subsequent polymerization. This process combination converts isobutenes to the corresponding C ₈ olefins (or higher), the 2-butenes contained remaining virtually unchanged. After separation from the polymer by distillation, the 2-butenes are reacted with isobutane to give alkylate gasoline. Oligomerization of n-butene with removal of the butanes, hydroisomerization and recycling of 2-butenes is not disclosed here.

Analog procedures are e.g. B. in US 5 113 023 or EP 0 900 773 disclosed. Hydroisomerization processes for isobutene-containing feed mixtures or hydrocarbon mixtures with a low n-butane content are disclosed here.

• a) Oligomerisierung eines Teils der im C₄-Kohlenwasserstoffgemisch enthaltenen Olefine
• b) Fraktionierung des Reaktionsgemisches in einen Reststrom, enthaltend C₄-Kohlenwasserstoffe und einen Produktstrom, enthaltend die Oligomeren
• c) Hydroisomerisierung eines Teils der im Reststrom enthaltenen Olefine zu cis-2-Buten
• d) Trennung des Reaktionsgemisches aus c) in eine Leichtsiederfraktion, enthaltend den größten Teil der Butane, 1-Buten und trans-2-Buten und eine Schwersiederfraktion, enthaltend den größten Teil des cis-2-Buten
• e) Rückführung der Schwersiederfraktion aus d) in die Oligomerisierungsreaktion gemäß a).

The present invention therefore relates to a process for the oligomerization of C ₄ carbons hydrogen mixtures containing 1-butene, 2-butene and butanes

• a) Oligomerization of part of the olefins contained in the C ₄ hydrocarbon mixture
• b) fractionation of the reaction mixture into a residual stream containing C ₄ hydrocarbons and a product stream containing the oligomers
• c) Hydroisomerization of part of the olefins contained in the residual stream to cis-2-butene
• d) separation of the reaction mixture from c) into a low boiler fraction containing the major part of the butanes, 1-butene and trans-2-butene and a high boiler fraction containing the major part of the cis-2-butene
• e) recycling the high boiler fraction from d) into the oligomerization reaction according to a).

The oligomerization in the process according to the invention is preferably carried out on C ₄ hydrocarbon streams with n-butene contents of 45-100%.

Hydroisomerization of olefins is preferably carried out up to thermodynamic equilibrium.

If the hydroisomerization according to c) as Reactive distillation carried out, so can also almost complete sales, d. H. a complete Hydroisomerization of the olefins can be achieved.

Block diagrams of plants in which the inventive method can be carried out are in the 1 to 4 shown. The internals containing the solid catalyst are marked with a cross. In a facility according to 1 the educt ( 1 ) together with hydrogen ( 2 ) in the reactive distillation column ( 3 ) fed. The rectifying section of this column contains internals with the hydroisomerization catalyst. As a bottom product ( 4 ) is a C ₄ hydrocarbon mixture with a higher concentration of cis-2-butenes and as a top product ( 5 ) a C ₄ hydrocarbon with a lower concentration of trans-2-butenes and a higher concentration of n-butane than in the starting material ( 1 ) deducted.

2 outlines a second embodiment variant of the method according to the invention. The educt ( 1 ) is placed in a distillation column ( 2 ) headed. The distillate ( 4 ) together with hydrogen ( 5 ) in the hydroisomerization reactor ( 6 ) fed. Part of the reaction mixture emerging from the hydroisomerization reactor ( 7 ) flows into the column ( 2 ) back. The other part ( 8th ) is used as a C ₄ hydrocarbon mixture with a lower concentration of trans-2-butenes and a higher concentration of n-butane than in the starting material ( 1 ) deducted. As a bottom product ( 3 ) a C ₄ -hydrocarbon mixture with a higher concentration of cis-2-butenes is obtained.

The 3 and 4 describe two further variants of the process according to the invention with two interconnected reactive distillation columns. In 3 the educt ( 1 ) together with hydrogen ( 2 ) in a first reactive distillation column ( 3 ) fed. The rectifying section of the column contains internals with the hydroisomerization catalyst. As a bottom product ( 4 ) a C ₄ -hydrocarbon mixture with a higher concentration of cis-2-butenes than in the starting material ( 1 ) deducted. The header product ( 5 ) is placed in a second reactive distillation column ( 6 ) passed, which is preferably provided with catalyst-containing internals over the entire column height. The bottom of the second reactive distillation is optionally hydrogen ( 9 ) fed. As a bottom product ( 7 ) falls a C ₄ -hydrocarbon mixture with a smaller content of trans-2-butenes and a higher content of n-butanes than in the starting material ( 1 ) on. The header product ( 8th ) of the second column ( 6 ), which consists essentially of unreacted 1-butene and n-butane, is returned to the first column. Hydrogen is used as electricity ( 10 ) removed.

In a further variant of the method according to the invention, shown in 4 , educt ( 1 ) into the distillation column ( 2 ) initiated. The brothers ( 4 ) the distillation column ( 2 ) together with hydrogen ( 5 ) in the external hydroisomerization reactor ( 6 ) fed. Part of the hydroisomerization reactor ( 6 ) emerging reaction mixture ( 7 ) flows into the column ( 2 ) back. The other part ( 8th ) is in the reactive distillation column ( 9 ), which is preferably carried out over the entire column height as a reaction distillation apparatus. As a bottom product ( 3 ) the distillation column ( 2 ) is a C ₄ hydrocarbon mixture with a higher concentration of cis-butenes than in the starting material ( 1 ) deducted. The bottom of the reaction column ( 9 ) is optionally hydrogen ( 12 ) fed. The header product ( 11 ) (essentially 1-butene and n-butane) of this column ( 9 ) is in the first column ( 2 ) returned. A partial stream ( 13 ) of the distillate ( 11 ) removed. (13) contains the hydrogen that has been removed. As a bottom product ( 10 ) of the second column ( 9 ) is a C ₄ hydrocarbon mixture with a smaller content of trans-butenes and a high concentration of n-butane than in the starting material ( 1 ) deducted.

• – Die Leichtsiederfraktion aus d) kann teilweise z. B. bis zu 50 – 70 % in die Hydroisomerisierung gemäß c) zurückgeführt werden.
• – Die Hydroisomerisierungsreaktion gemäß c) und eine Fraktionierung gemäß d) können gleichzeitig in einer oder mehreren Reaktivdestillationskolonnen durchgeführt werden.
• – Die Hydroisomerisierungsreaktion gemäß c) und eine Fraktionierung gemäß d) können in mehreren Reaktivdestillationskolonnen durchgefihrt werden, wobei die Leichtsiederfraktion der letzten Reaktivdestillationskolonne teilweise (z. B. bis zu 50 – 70 %) in die erste Reaktivdestillationskolonne zurückgeführt werden kann.
• – Vor der Hydroisomerisierungsreaktion gemäß c) kann eine Trennung des Reststroms aus b) in eine Leichtsiederfraktion enthaltend Butane, 1-Buten und frans-2-Buten und eine Schwersiederfraktion enthaltend den größten Teil des cis-2-Buten, d. h. 50 – 100 %, bevorzugt 70 – 80 % durchgeführt werden. Die Leichtsiederfraktion kann in die Hydroisomerisierung gemäß c) und die Schwersiederfraktion in die Oligomerisierung gemäß a) zurückgeführt werden.

Based on 1 to 4 the following variants of the method according to the invention are readily apparent:

• - The low boiler fraction from d) can partially z. B. up to 50 - 70% in the hydroisomerization according to c).
• - The hydroisomerization reaction according to c) and a fractionation according to d) can be carried out simultaneously in one or more reactive distillation columns.
• - The hydroisomerization reaction according to c) and a fractionation according to d) can be repeated in several active distillation columns can be carried out, the low boiler fraction of the last reactive distillation column being able to be partly (eg up to 50-70%) recycled into the first reactive distillation column.
• - Before the hydroisomerization reaction according to c), a separation of the residual stream from b) into a low boiler fraction containing butanes, 1-butene and frans-2-butene and a high boiler fraction containing most of the cis-2-butene, ie 50-100%, preferably 70-80%. The low boiler fraction can be returned to the hydroisomerization according to c) and the high boiler fraction to the oligomerization according to a).

The process according to the invention is suitable for working up C ₄ -hydrocarbon mixtures which contain linear butenes and butane, in which the butane content is between 40 and 95, in particular 50 to 95, particularly 75 to 95%. The proportion of frans-2-butene is 15 to 30%, cis-2-butene 5 to 15% and 1-butene 1 to 10%.

For the hydroisomerization, catalysts are used which contain at least one metal from the eighth subgroup of the Periodic Table of the Elements as an active component. A preferred metal is palladium. The metal concentrations are 0.1 to 2.0 mass% (based on the total mass of the catalyst), preferably 0.5 to 1.0 mass%. The catalysts are expediently applied to support materials, MgO, Al ₂ O ₃ , SiO ₂ , TiO ₂ , SiO ₂ / Al ₂ O ₃ , CaCO ₃ or activated carbon being used as support materials. Preferred carrier materials are Al ₂ O ₃ , SiO ₂ and SiO ₂ / Al ₂ O ₃ .

Is in the fresh catalyst material the active component mostly in the oxidic or salt-like Form before. Therefore, the catalyst must be used before or during the Starting up with hydrogen or hydrogen-containing gas mixtures be reduced. The reduction can be carried out in a separate reactor, in the hydroisomerization reactor or in the reactive distillation column respectively. The active component changes to the metallic state.

If no external reactors are used, the catalyst can be immobilized in reactive distillation columns, for example in structured packings, for example using KataMax ^® packs from Koch-Glitsch ( EP 0 428 265 ), Katapak ^® packs from Sulzer ( EP 0 396 650 ) or MultiPak ^® packs from Montz (utility model No. 298 07 007.3). An alternative to the use of structured catalytic packings are special internals that fix the catalyst for plate columns ( US 5026459 ).

The hydroisomerization takes place in Presence of hydrogen. The molar ratio between added Hydrogen and all of the olefins in the feed mixture in the range of 0.001 to 0.01, in particular in the range of 0.003 up to 0.004.

The hydroisomerization is in the temperature range from 30 to 150 ° C, especially 40 to 120 ° C, whole carried out particularly preferably at 80 to 100 ° C. If the hydroisomerization outside a distillation column, the isomerization and Distillation temperature independent chosen from each other become. Otherwise the temperature is in the catalyst layer specified by the temperature profile of the reactive distillation column.

In the process according to the invention, the material separation is preferably carried out in a ( 2 ) or in two interconnected reactive distillation columns ( 4 ) carried out.

When separating materials using a reactive distillation column ( 1 ) is the reaction distillation zones with the catalyst at the top of the column. The starting material is fed in together with hydrogen below the catalyst layer.

The distillation column or the distillative part of the reactive distillation column preferably has the following characteristics:
The stripping section has 0 to 100 theoretical plates, in particular 0 to 50, very particularly 0 to 30.

The amplifier section up to the catalytic converter has 50 to 250 theoretical plates, especially 80 to 200, especially 100 to 180.

The reflux ratio in the single column process (e.g. according to 1 or 2 ) is between 1 and 200, in particular between 80 and 150.

The distillation temperatures are between 50 and 150 ° C, preferably between 80 and 100 ° C. The Pressure is dependent from the distillation temperature.

When using two interconnected reactive distillation columns (e.g. according to 3 or 4 ) the top product or the hydroisomerized distillate withdrawn from the first column is passed into a second column which is completely filled with catalytic packings or internals with catalyst.

The first column has one Separation number from 80 to 160, especially one from 100 to 140. Das The starting material is in the first column between zero and tenth, in particular between zero and fifth, entirely especially between zero and first separation stage (each from below counted) fed.

The reflux ratio of the first column is between 40 to 120, in particular between 50 and 80th

The second column has one Separation number from 80 to 160, especially one from 100 to 140. Das Distillate from the first column is between in the second column 4th and 120th, in particular between 60th and 110th separation stage (each counted from above) fed.

The reflux ratio is in the second Column between 10 and 50, in particular between 20 and 40.

The distillation temperatures are in both columns between 50 and 150 ° C, preferably between 80 and 100 ° C.

The top product of the second column is fed into the first column below the catalyst layer, preferably to levels 40 to 120, very particularly preferably to levels 50 to 90 (each counted from the top).

In the catalyst zones of the columns, the LHSV (volume of distillate withdrawn per catalyst volume per hour) is 1 to 20 h ^-1 , in particular 4 to 12 h ^-1 . For external reactors, the LHSV is dimensioned so that the hydroisomerization equilibrium at the reactor outlet is adjusted to over 90%, in particular over 95%.

In principle, it is with the method according to the invention possible, Almost 100% pure butenes and practically 100% pure To separate the yield. One refrains from economic considerations however, as a rule, the butene concentration lies in the target product at over 50%, preferably to over 60%, very particularly preferably up to over 70%.

The following example is intended to illustrate the invention explain, without narrowing their scope.

Separation of linear butenes from n-butane-containing mixtures in a single-column process The separation of the C ₄ -hydrocarbon mixture into a butene-rich and a butene-less stream than the feed mixture was carried out as a single-column process in a technical test facility. Due to the structural conditions in the technical center, the desired column height or number of plates could not be achieved. The single-column process was therefore operated in two thermally coupled partial columns, which, from a process engineering point of view, represents the same situation as a single-column process. The block diagram of the test facility is in 5 shown. The sub-columns with 8th ) and ( 2 ) designated. The crosses represent the internals for the distillation.

Execution:

The mix of operations ( 1 ) was placed in the sub-column ( 2 ) fed. A C ₄ hydrocarbon stream ( 4 ) with a larger proportion of cis-2-butenes than in the feed mixture ( 1 ) deducted. The distillate ( 5 ) of the sub-column ( 2 ) was across the capacitor ( 6 ) and the evaporator ( 7 ) into the sub-column ( 8th ) hazards. The swamp product ( 9 ) of the sub-column ( 8th ) was placed on the top of the column ( 2 ) returned. The distillate ( 10 ) from the sub-column ( 8th ) after condensation in the heat exchanger ( 11 ) together with hydrogen ( 12 ) in the hydroisomerization reactor ( 13 ) headed. A part ( 14 ) of the hydroisomerate was applied to the top of the column ( 8th ) returned. The other part ( 15 ) was used as a product that had a lower content of trans-butenes and a higher content of n-butane than the feed mixture ( 1 ) had subtracted.

Construction of the apparatus and their operating parameters

Column ( 2 )

Diameter: 80 mm
Package height from Sulzer BX: 9.2m
Number of stages: 56
Inlet from (1), liquid, boiling: on the 36th separation stage from above, ie after 3.3 m packing from below
Evaporation ratio: = 150.98
Pressure: 10 bar (abs.)

Column ( 8th )

Diameter: 80 mm
Package height from Sulzer BX: 9.2 m
Number of stages: 56
Intake( 5 ), liquid boiling: at the lowest separation level
Return ratio: = 100
Pressure: 10 bar (abs.)

Description of the outside reactor:

• - more thermostatted Fixed bed reactor in isothermal operation
• - Catalyst type: 0.5 mass% Pd on Al ₂ O ₃
• - catalyst volume: 300 ml

Tabelle 1: Temperatur, Menge und Zusammensetzung der relevanten Ströme

Table 1: Temperature, quantity and composition of the relevant flows

This attempt shows that with the help of the method according to the invention linear butenes in 69.6% yield from an n-butane / n-butene mixture can be separated, being the n-butene concentration is brought from 40 to 70%. An n-butene mixture of this concentration can be used economically in organic synthesis.

Claims (9)

Process for the oligomerization of C ₄ -hydrocarbon mixtures containing 1-butene, 2-butene and butanes by a) oligomerizing part of the olefins contained in the C ₄ -hydrocarbon mixture b) fractionation of the reaction mixture into a residual stream containing C ₄ -hydrocarbons and a product stream, containing the oligomers c) hydroisomerization of part of the olefins contained in the residual stream to cis-2-butene d) separation of the reaction mixture from c) into a low boiler fraction, containing the majority of the butanes, 1-butene and trans-2-butene and a high boiler fraction , containing most of the cis-2-butene e) recycling the high boiler fraction from d) into the oligomerization reaction according to a). A method according to claim 1, characterized in that the hydroisomerization reaction according to c) and d) in one or more Reactive distillation columns is carried out. A method according to claim 1 or 2, characterized in that that the low boiler fraction from d) partially into the hydroisomerization is returned according to c). Method according to one of claims 1 to 3, characterized in that that the hydroisomerization reaction according to c) and the fractionation according to d) in several reactive distillation columns is carried out, the low boiler fraction the last reactive distillation column partially into the first reactive distillation column is returned. Method according to one of claims 1 to 4, characterized in that that before the hydroisomerization reaction according to c), a separation of the residual stream from b) into a low boiler fraction containing butanes, 1-butene and trans-2-butene and a high boiler fraction containing the biggest part of the cis-2-butene being, the low boiler fraction in the hydroisomerization reaction is performed according to c). Method according to one of claims 1 to 5, characterized in that that the hydroisomerization reaction according to c) on a heterogeneous catalyst the at least one metal of the eighth subgroup of the periodic table that contains elements carried out becomes. Method according to one of claims 1 to 6, characterized in that that the hydroisomerization reaction according to c) in the presence of hydrogen with a relationship of hydrogen to olefins from 0.001: 1 to 0.01: 1 is carried out. Method according to one of claims 1 to 7, characterized in that that the n-butane content in the residual stream according to b) is between 40 and 95%. Method according to one of claims 1 to 8, characterized in that that the high boiler fraction from d) at least 50% cis-2-butene contains.