NL8800685A - Prepn. of 2,3-di:di:methyl-1-butene from mixt. of methyl:butene(s) - by isomerisation to 2,3-di:methyl-2-butene, sepn. and reversed isomerisation, opt.on zeolite - Google Patents

Abstract

(I) is prepd. from a hydrocarbon mixt. contg. (a) 2,3-dimethyl-1-butene and/or 2,3-dimethyl-2-butene and (b) methylpentene or methylpentenes and/or other 6C olefins with similar b.pt., by (i) treating the mixt. to isomerise any 2,3-dimethyl-1-butene in the mixt. to 2,3-dimethyl-2-butene, (ii) sepg. a prod. contg. conc. 2,3-dimethyl-2-butene, and (iii) carrying out reversed isomerisation of the 2,3-dimethyl-2-butene from step (ii), to 2,3-dimethyl-1-butene. (iv) (I) is recovered from the mixt. from step (iii) by reactive distn. Steps (i) and (iii) may be carried out on a molecular sieve based on Al and SiO2, with pore size above 0.4nm. Steps (iii) and (iv) can be combined by using in the distn. tower a catalyst bed based on a molecular sieve. The hydrocarbon mixt. has been obtd. by dimerisation of propylene. Step (iii) gives an equilibrium mixt. of 2,3-dimethyl-1-butene and 2,3-dimethyl-2-butene, and the process includes the step of recovering the conc. (I) from the equilibrium mixt., esp. by reactive distn.

Description

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Nw 1066

Process for preparing 2,3-dimethyl-1-butene.

The invention relates to a process for preparing 2,3-dimethyl-1-butene. The invention is especially useful for preparing 2,3-dimethyl-1-butene from a mixture of C 8 hydrocarbons obtained by the dimerization of propylene.

As known in the art, 2,3-dimethyl-1-butene is used as an intermediate in the preparation of various other compounds, and in particular compounds such as 7-acetyl-1,1,4,4,4,6-hexamethyl- 1,2,3,4-tetrahydro-10-dronaphthalene (also known as Tonalid), which are desirable for their odor properties. It is also well known that propylene can be dimerized to obtain a mixture of the 2f3-dimethylbutene isomers as the main component in a mixture of Cg-olefinic hydrocarbons, including methyl pentenes and other dimers and trimers of propylene. For this, reference may be made, for example, to U.S. Patents 3,390,201, 3,467,726, 3,482,001, 3,485,892, 3,622,649, 3,655,811, 3,686,352, 3,784,629, 3,897,512 and 4,209,653, as well as 20 to East German Patent 112,973. Other processes are also known for preparing mixtures of Cg olefinic hydrocarbons containing 2,3-dimethylbutenes. For example, reference may be made to U.S. Pat. Nos. 3,445,538, 3,538,182, 3,660,517, and 4,288,643, as well. to Bull. Soc. Chem.

Belgian. 60, 344-354 (1959).

The blends obtained by the above processes are then used for various applications where the 2,3-dimethyl-1-butene need not necessarily be the major component and / or significant amounts of 2,3-dimethyl-2-butene and / or methyl pentenes may be present. For example, by hydrogenating the mixture of <8800685 * -2- of isomers, 2,3-dimethylbutanes are obtained, which increase the octane number, while dehydrogenation yields 2,3-dimethylbutadiene, which can be used to prepare synthetic rubber materials. In fact, if desired, the recovery of substantially pure 2,3-dimethyl-1-butene from such blends is very difficult due to the similarity in boiling points between 2,3-dimethyl-1-butene and the methyl pentene compounds . When it is intended to obtain 2,3-dimethylbute-10s, this difficulty has been recognized in the art and attention has been focused on processes using expensive starting materials and / or complex techniques to obtain only the 2, 3-dimethylbutene isomers and to avoid the formation of methylpentene as much as possible. For this, reference may be made, for example, to U.S. Patents 4,288,643 and 4,579,992.

The present invention therefore relates to a process for preparing 2,3-dimethyl-20-1-butene from a hydrocarbon mixture composed of (a) 2,3-dimethyl-1-butene and / or 2,3- dimethyl-2-butene and (b) methylpentene or methylpentenes and / or various other Cg-olefins with similar boiling points, the process comprising the following steps: (a) treating the hydrocarbon mixture to each 2,3-dimethyl-1- isomerizing butene in the hydrocarbon mixture to 2,3-dimethyl-2-butene, (b) separating from the hydrocarbon mixture obtained in step (a) a product containing concentrated 2,3-dimethyl-2-butene, and ( c) reverse isomerizing the 2,3-dimethyl-2-butene obtained in step (b) to 2,3-dimethyl-1-butene.

According to a preferred embodiment of this invention, the hydrocarbon mixture used as starting material is prepared by dimerizing propylene. According to. 8806685 »-3- another preferred embodiment, the reverse isomerization is performed with an aluminum and silica molecular sieve having a pore size greater than 0.4 nm, and the 2,3-dimethyl-1-butene 5 is obtained from the reaction mixture recovered by a reactive distillation process.

As mentioned earlier, there are several known methods and catalysts for dimerizing propylene to obtain a mixture of C 8 olefin isomers. For example, in U.S. Patent 3,467,726, it is proposed to use nickel halide phosphine complexes in combination with a Lewis acid component to convert mono-olefins such as propylene into oligomers (mainly dimers). In general, this process and other known processes can be used to prepare hydrocarbon mixtures containing (a) 2,3-dimethyl-1-butene and / or 2,3-dimethyl-2-butene together with (b) the various methylpentene isomers. Such mixtures can also be the direct result of a fractional distillation of a crude hydrocarbon or of another chemical process, such as the metathesis of butene or the isomerization of neohexene.

Preferably, however, the starting mixture is a mixture comprising C 8 olefinic hydrocarbons prepared by dimerization of propylene. These mixtures typically comprise a significant amount of 2,3-dimethyl-1-butene together with amounts of 2,3-dimethyl-2-butene and methyl pentenes. Further purification or recovery of 2,3-dimethyl-1-butene from this mixture is particularly difficult because of the similarity in boiling points with the other components, especially the methyl pentenes.

According to the present invention, 2,3-dimethyl-1-butene isomer is selectively prepared from such mixtures of Cg monoolefins. In the first step of this process, the hydrocarbon mixture .880 0685 t Λ -4- is subjected to conditions under which the 2,3-dimethyl-1-butene (if any) is isomerized to 2,3-dimethyl-2-butene. Various thermal or catalytic double bond isomerization processes are known for isomerizing 1-olefins to 2-olefins wherein the olefin has a branched chain. The mechanism of the double bond isomerization is not critical.

It can take place via carbanion or carbonium ion or it can be thermally induced via radicals.

Typical methods that can be used are described in U.S. Pat. Nos. 3,236,909, 3,467,726, 3,482,001, 3,485,892, 3,636,125, 3,686,352, 3,920,765, 4,209,653, and 4,288,643. Known catalysts include acids, bases, metals, metal complexes and boron compounds.

Particularly suitable double bond isomerization techniques include the use of a sulfonated ion exchange resin as a catalyst, as described in U.S. Patent 3,920,765, and more preferably the use of an activated 5A molecular sieve, as described in U.S. Patent 3,636,125 . Generally, this isomerization can be carried out in a reactor vessel or in a continuous process using a fixed bed catalyst. It has been found preferable to use a 5A molecular sieve as a fixed bed catalyst in a continuous process for isomerizing 2,3-dimethyl-1-butene into 2,3-dimethyl-2-butene . Prior to isomerization, it is preferable to activate the molecular sieve by heating in nitrogen or dry air.

After the 2,3-dimethyl-1-butene has been converted into 2,3-dimethyl-2-butene by double bond isomerization, the 2-butene isomer is more easily separated or freed from the impurities which remain in the rest of the reaction mixture obtained (especially the methyl 8800685 * 1 * -5-pentene isomers). This can generally be done by distillation or extractive distillation. Because of the difference in boiling points between the 2-butene isomer (higher boiling) and the methyl pentenes (lower boiling), the methyl pentenes are preferably initially distilled off to obtain a concentrated 2,3-dimethyl-2-butene fraction.

The concentrated 2,3-dimethyl-2-butene fraction is then subjected to reverse isomerization to obtain the desired 2,3-dimethyl-1-butene.

This is sometimes referred to as counter-thermodynamic isomerization. Various known methods are suitable for this double bond isomerization. Generally, an acidic or basic catalyst is used for liquid phase counter-thermodynamic isomerization.

U.S. Pat. No. 3,236,909 shows that silica and aluminum based zeolites are suitable for isomerizing 2,3-dimethyl-2-butene to 2,3-dimethyl-20-butene with good yields under specified conditions. U.S. Patent 3,920,765 describes sulfonated ion exchange resins and process conditions for isomerizing 2-olefins to 1-olefins. It is also known to use acidic catalysts such as sulfuric acid or acetic anhydride / sulfuric acid to isomerize olefins.

According to the present invention, it has been found to be particularly effective to perform the reverse isomerization of the 2,3-dimethyl-2-butene using a molecular sieve type (zeolite) catalyst with a pore size greater than 0.4 nm. Examples of such materials are the 5A molecular sieves with a pore diameter of about 0.5 nm and the 13X type molecular sieves with pore diameters of about 1 nm. This zeolite-catalyzed reverse isomerization has been found to yield less unwanted high boiling products (tar products) than the acid-catalyzed process. To perform a reverse isomerization using such catalysts, the reaction temperature is in the range of 100-200 ° C, preferably in the range of 125-175 ° C. The residence time for the reaction is preferably greater than 5 minutes and is preferably in the range of 5-60 minutes, most preferably in the range of 5-20 minutes. The pressure conditions for carrying out the reverse isomerization are at least 400 kPa and are preferably in the range of 400-2000 kPa and most preferably in the range of 400-1500 kPa.

The 2,3-dimethyl-1-butene can then be recovered from the product obtained by the reverse isomerization according to known processes.

In a preferred mode of operation, the concentrated 2-butene isomer product obtained by the initial double bond isomerization step is continuously passed through a fixed bed molecular sieve catalyst to carry out the counter-thermodynamic double bond isomerization. -tie. The resulting stream, which contains the equilibrium mixture of 1 and 2-butene isomers, is then continuously fed to a distillation tower. The tower 25 operates under such conditions that the overhead fraction contains a considerably higher concentration of 2,3-dimethyl-1-butene than the equilibrium mixture. Typically, this overhead fraction contains at least 90% 1-butene isomer (the remainder is 2-butene isomer and other impurities); preferably the overhead fraction contains more than 95% 1-butene isomer and most preferably even more than 97% thereof.

At the bottom of these distillation tower, a stream containing mainly 2,3-dimethyl-2-butene is discharged and this stream is again fed to the molecular sieve catalyst bed 35 to carry out the reverse isomerization. The reverse isomerization 8800685-7 and distillation steps can also be combined by introducing a molecular sieve catalyst bed into the distillation tower. The concentrated 2-butene fraction is then fed to the tower and contacted with the catalyst bed. The lower boiling 1-butene isomer is then continuously removed from the bed (evaporated), thereby directing the reaction to a maximum production of 1-butene isomer.

The following experiment illustrates the present invention. The starting material was a mixture of Cg olefins as shown in Table A below.

This mixture was obtained by dimerization of propylene essentially according to the method described in U.S. Pat. No. 3,467,726. As can be seen from Table A 15, the starting material contains a substantial amount of the two 2,3-dimethylbutene isomers and minor amounts of the various methyl pentenes as impurities. These and other determinations of the compositions of the various hydrocarbon mixtures shown below were made by gas chromatography.

Table A also shows the composition of the product obtained by routine distillation of this dimerization product in an attempt to recover the 2,3-di-methyl-1-butene fraction. As can be seen from the table, due to the small difference between the boiling points of the methylpentene isomers and the desired 2,3-dimethyl-1-butene, it is very difficult to obtain the 1-butene isomer in a high purity.

30 .8800685

-8-TABLE A

Cg hydrocarbon mixture 5 ordinary dimerization distillation product product product 4-methyl-1-pentene 6.4 7.4 10 2,3-dimethyl-1-butene 70.8 75.5 cis-4-methyl-2-pentene 10, 6 10.5 trans-4-methyl-2-pentene 9.5 6.2 2-methyl-1-pentene 2.7 trace 2-methyl-2-pentene trace 0.4 15 2.3-dimethyl-2- buteen rail rail high-boiling products rail rail

The dimerization mixture described in Table A above was then fed to a reactor vessel containing a 5A molecular sieve as a catalyst to isomerize the 2,3-dimethyl-1-butene to 2,3-dimethyl-2-butene. The reaction mixture was fed in an amount of 10 parts. per 1 part by weight of catalyst. The 5A molecular sieve catalyst was a synthetic crystalline zeolite prepared from calcium, aluminum and silica and is commercially available from Baker Chemical. This catalyst was used in the form of pellets with a mesh size of 1.68-2.38 mm, which pellets were initially activated in dry air at a temperature of 250 ° C. The reaction time for carrying out the isomerization reaction was about 15 minutes.

The product mixture obtained by this isomerization process is designated "isomerization product" in Table B below. This isomerization product was then distilled to obtain a lake

__________________________, M'J

8800685-9-Concentrated 2,3-dimethyl-2-butene fraction, the composition of which is also shown in Table B below, and is designated "Distilled 2,3-dimethyl-2-butene".

5 TABLE · B

isomerization of distilled product 2,3-dimethyl-

Product (wt%) 2-butene (wt%) 10 4-methyl-1-pentene 5.6 trace 2.3-dimethyl-l-butene 8.3 trace cis-4 ~ methyl-2-pentene 9.4 trace trans-4-methyl-2-pentene 9.6 .0.2 15 2-methyl-1-pentene 0.6 0.3 2-methyl-2-pentene 3.1 4.0 2.3-dimethyl-2-butene 60.4 90.2 high-boiling products 3.0 5.3 20 For the counter-thermodynamic (reverse) isomerization, the intermediate distilled 2,3-dimethyl-2-butene fraction obtained was then continuously fed to a second catalyst bed from 5A molecular sieve containing the same catalyst material as had been used in the initial isomerization. The catalyst bed temperature was 150 ° C, the pressure was 1500 kPA, and the residence time was 10 minutes. The composition of the resulting reverse isomerization stream is designated "reverse isomerization" in Table C below. As can be seen, the 2,3-dimethyl-1-butene concentration has increased but is still somewhat on the low side.

The effluent from the reverse isomerization reactor was then continuously fed to a distillation column 35 for reactive distillation. A glass Vigreux distil-. latency column with 25 theoretical plates was used 880 0685 e -10- at atmospheric pressure and at a reflux ratio of 20: 1. In the reactive distillation process, the distillate fraction consisted of high purity 2,3-dimethyl-1-butene (due to its low boiling point), while a stream from the distillation tower rich in 2,3-dimethyl-2- butene isomer was continuously fed back to the reverse isomerization reactor. The composition of the high purity 2,3-dimethyl-1-butene fraction is shown in Table C below. For comparison, the composition obtained from carrying out ordinary distillation of the dimerization product of propylene shown in Table A is also shown again.

.8800685 -11- α> • Η Φ 4-> ζ,> C0 Ο 0) I — I ^ ι — I tS st CM Η Π Ο • Η ι_! g * 2 yy H · ο οο ο ο ο ο ο α.

ο ρ & ΟΝ α> co ω φ οι α) οβ Ρ Ό ^ ο <• Η C0 Οί ^ Ρ ί-4 η, α <f m m Ν ο <r ο ο

(D Η (0 ϊΐ “" "“ S S S

Π · Η Ρ · Ι ^ ιΠΟ ^ ΛΟΛΟ- Q4-) S Γ— «-! C CDC0 £ CO Ρ φ φ Ι) Ή to öO Τ3 D ^ to Φ Ο) ρ .ζ;

y 1) 4J

g Ό to tw Ρ “α) Η ^

_ φ p & -S Ο- * P5-J

C ^ ίφ · Οι — I Ο οοοιποοοο Φ φ β & 0 * 00 “* -“ U ω ΟΟΟ Φ αη nftocnvom -JJ geo ω and r-i co and r- J 3 Ο · η ^ Η ·?

co JL

<7 Η Λ

r C

4 = φ U C Φ c ο C φ 4-> Cm

S φ Φ C φ 4J

• 1-4 φ Ρ Φ φ ΐ • φ 3 Φ I Φ Φ 3 rrt Φ ^ οα, <ΝΦΦ-ο ^ “ρ ι ι I 4-> 3 ι ρ C> -) CM ^ -IC! CCMq. Φ ι ι> \ Φ Φ I ^ CU ι — ι ι — ι 42 ΛΛι — 1 «ι 1 ^ 44 I 1 trt Ρ 4: 43 Φ Η Ν £ gr Ρ 4-> β ι ι Ρ 3 I — I φ φ I ι — I ι — I φ>% Β Β'ί> - >> “> 0ο 4 = I 1 4 = 4 = · η Η PO <t-WJ-> POÏL φ! I d Φ Φ ι £ β en en co β β co g I - · Η Ο I I “g - <J- CM U Ρ Ν Ν Ν ^ .6800685 -12-

As can be seen from the above data, the product obtained by the process of the present invention, referred to above as "reactive distillation", has a much higher purity than the product obtained by "ordinary distillation" of the dimerization mixture of propylene (this is not according to the present invention).

8800635

Claims (7)

An improved process for preparing 2,3-dimethyl-1-butene from a hydrocarbon mixture composed of (a) 2,3-dimethyl-1-butene and / or 2,3-dimethyl-2-butene, And (b) methylpentene or methylpentenes and / or one or more other Cg-olefins with similar boiling points, the process being characterized in that it comprises the following steps: 10 (a) treating the hydrocarbon mixture to each 2,3-dimethyl- isomerizing 1-butene in the hydrocarbon mixture to 2,3-dimethyl-2-butene, (b) separating from the hydrocarbon mixture obtained in step (a) a product containing concentrated 2,3-dimethyl-2-butene, and (c) reverse isomerizing the 2,3-dimethyl-2-butene obtained in step (b) to 2,3-dimethyl-1-butene. 2. Process according to claim 1, characterized in that the hydrocarbon mixture is obtained by dimerisation of propylene. 3. Process according to claim 1, characterized in that the step (c) of the reverse isomerization is carried out with a molecular sieve based on aluminum and silica and with a pore size larger than 0.4 nm. Process according to claim 3, characterized in that the initial isomerization (a) is carried out with a molecular sieve based on aluminum and silica and with a pore size greater than 0.4 nm. Process according to claim 4, characterized in that step (c) gives an equilibrium mixture of 2,3-dimethyl-.8800685 -14-1-butene and 2,3-dimethyl-2-butene and the process further comprising the following step: (d) recovering concentrated 2,3-dimethyl-1-butene from the equilibrium mixture. Process according to claim 5f, characterized in that the 2,3-dimethyl-1-butene is recovered from the mixture obtained in step (c) by reverse isomerization by carrying out a reactive distillation. 7. Process according to claim 6, characterized in that the reverse isomerization and distillation steps are combined by using a molecular sieve catalyst bed in the distillation tower. 8800685