RU2206557C1 - 1-hexene purification method - Google Patents

Abstract

FIELD: petrochemical processes. SUBSTANCE: 1- hexene containing more than 1 wt % 2-ethyl-1-butene is purified using selective isomerization of 2-ethyl-1-butene into 3-methyl-2-pentene at 50- 80 C and pressure 1-3 atm of inert atmosphere, volume flow rate of raw material being 1 to 10 h^-1. Isomerization is catalyzed by middle-acidity macroporous sulfocationite having total static volume capacity 3.5-4.5 mg*equ. H⁺/g. EFFECT: increased purity of product. 2 cl, 1 dwg, 3 tbl, 8 ex

Description

 The invention relates to the field of production of high purity α-olefins, in particular to the field of purification of hexene-1 containing a mixture of branched isomers.

One of the industrial methods for producing hexene-1 is the oligomerization of ethylene in the presence of an organoaluminum catalyst, for example triethylaluminum, at a temperature of 100-300 ^o C and a pressure of 10-250 atm. The resulting oligomerizate contains olefins having from 4 to 18 carbon atoms. Hexene-1 can be isolated from the oligomerizate by distillation [Higher olefins. Production and application. / Serebryakov B.R., Plaksunov T.K. Ansheles V.R., Dalin M.A. et al. Ed. M.A.Dalina. -L., Chemistry, 1984, p. 59].

 However, hexene-1 thus isolated contains a certain amount (up to 5 wt.%) Of reaction by-products, branched isomers, in particular 2-ethyl-butene-1, related to the so-called vinylidene olefins.

 For some applications, for example, when using hexene-1 as a comonomer in the production of linear low density polyethylene (LLDPE), the content of branched isomers (primarily 2-ethyl-butene-1) having increased reactivity should be minimal.

The separation of 2-ethyl-butene-1 from hexene-1 by conventional distillation is difficult due to the relatively close boiling points of 2-ethyl-butene-1 and hexene-1 (64.5 and 63.4 ^o C, respectively).

 Below are the structural formulas of hexene isomers used in the further description.

линейные внутренние изомеры гексена-1:
цис-гексен-2 (Т_кип.=69^oС)

транс-гексен-2 (Т_кип.=67,8^oС)

разветвленные винилиденовые изомеры:
2-этил-бутен-1 (Т_кип.=64,5^oС)

разветвленные внутренние изомеры гексена-1:
цис-3-метил-пентен-2 (Т_кип.=67,6^oС)

транс-3-метил-пентен-2 (Т_кип.=70,4^oС)

Известен способ очистки С₆-С₂₂ α-олефинов, содержащих винилиденовые изомеры, путем обработки указанных олефинов сероводородом или меркаптанами в присутствии кислот (патент США 4511753; С 07 С 7/17; заявл. 16.01.84, 570934; опубл. 16.04.85). Однако применение указанных агентов - сероводорода и меркаптанов, являющихся очень токсичными, делает процесс экологически опасным. Кроме того, указанный процесс включает стадию отмывки от сульфидов щелочными реагентами, что усложняет процесс.hexene-1 (T _{boiling point} = 63.4 ^o C)

linear internal isomers of hexene-1:
cis-hexene-2 (T _boiling. = 69 ^o C)

trans-hexene-2 (T _boiling. = 67.8 ^o C)

branched vinylidene isomers:
2-ethyl-butene-1 (T _boiling. = 64.5 ^o C)

branched internal isomers of hexene-1:
cis-3-methyl-penten-2 (T _bp = 67.6 ^° C)

trans-3-methyl-penten-2 (T _bp = 70.4 ^° C)

A known method of purification of C ₆ -C ₂₂ α-olefins containing vinylidene isomers by treating the indicated olefins with hydrogen sulfide or mercaptans in the presence of acids (US Pat. No. 4,511,753; C 07 C 7/17; claimed 16.01.84, 570934; publ. 16.04. 85). However, the use of these agents - hydrogen sulfide and mercaptans, which are very toxic, makes the process environmentally dangerous. In addition, this process includes the stage of washing from sulfides with alkaline reagents, which complicates the process.

 A known method of purification of α-olefins from vinylidene olefins by selective oligomerization of more reactive vinylidene olefins in the presence of a catalytic system based on boron trifluoride, water and an organic promoter, followed by separation of α-olefins from the obtained oligomers of vinylidene olefins by distillation (US patent 5095172 С 07; / 00; claimed 20.03.91, 672486; publ. 10.03.92).

 This method requires the use of highly toxic boron trifluoride and, in addition, corrosion-resistant equipment due to the formation of hydrogen fluoride during operation.

 Upon isomerization of the 2-alkyl substituted isomer of hexene-1 (2-ethyl-butene-1), a mixture of the cis and trans isomers of 3-methyl-pentene-2 (3-MP-2) is formed. At the same time, a less stable cis isomer is formed with greater speed [Report of the USSR Academy of Sciences, 1966, v. 166, 5, 1147-1150].

 According to the method described in the patent [US Patent 3424810, C 07 C 7/12, 11/00; declared 02/08/67, 614552, publ. January 28, 69], it is also seen that under ordinary conditions (temperature close to room temperature), the cis isomers of internal olefins are formed predominantly during the treatment of olefins with macroporous sulfocationionite. So, for example, the content (wt.%) Of trans isomers increases from 0.0 to 0.2, and cis isomers from 1.0 to 1.8.

Closest to the claimed is a method according to which medium-chain C ₅ -C ₈ α-olefins containing 2-alkyl substituted isomers of the corresponding olefins as impurities are purified by passing said olefin over an acid catalyst, for example, Amberlyst 15 sulfocationionite having a full static volumetric capacity (PSOE) 4.81 mg • equiv. N ⁺ / g, at a temperature of 20-30 ^o C, atmospheric pressure and a volumetric feed rate of 10-20 h ^-1 (US patent 5789646; C 07 C 7/00, application. 20.11.96, 752130; publ. 04.08. 98). As a result of the isomerization of the 2-alkyl substituted isomer of a C ₆ -C ₈ olefin into 3-alkyl substituted isomers of olefins, a mixture of cis and trans 3-alkyl substituted isomers of olefins is formed. The C ₅ olefin is also purified by this method, the 2-alkyl substituted isomer of which is 2-methyl-butene-1, when isomerized, gives only one internal isomer, 2-methyl-butene-2, which does not have geometric isomers (cis or trans).

 Thus, we can conclude that this method does not solve the problem of obtaining a certain type of geometric isomers of (cis-, trans-) 2-alkyl-substituted alpha-olefins.

Moreover, as noted above, in US patent 3424810, when isomerized at temperatures close to room temperature, mainly cis isomers are formed (in the case of 2-ethyl-butene-1 - cis-3-methyl-pentene-2), what also happens during the isomerization of 2-alkyl substituted isomers of the corresponding olefins under the conditions described in the prototype (temperature 20-30 ^o C, the volumetric feed rate of 10 h ^-1 , the catalyst - Amberlyst 15, with PSOE of 4.81 mg • equiv. H ⁺ / g), i.e. everywhere the predominant formation of cis isomers of 3-alkyl substituted olefin isomers takes place.

 This is also confirmed by comparative example 1 below.

The boiling point of the cis-isomer of 3-methyl-pentene-2 (67.6 ^o C), trans-isomer - (70.4 ^o C). Since the boiling point of hexene-1 is (63.4 ^{° C.} ), the formation of the trans isomer of 3-methyl-pentene-2 is preferable, which will allow it to be separated from hexene-1 by conventional distillation with the greatest efficiency.

 However, the selective isomerization of 2-ethyl-butene-1 in predominantly (more than 50%) trans-3-methyl-pentene-2, in the presence of hexene-1 and without its substantial isomerization to the internal isomers of hexene-1 and with the content of 2-ethyl- butene-1 in an amount of up to 5 wt.% in the prototype is not described.

 The disadvantages of the described method is that the method allows to purify alpha-olefins with an impurity content of vinylidene isomers of not more than 1 wt.% And a distillation column with a large number of theoretical plates is required for further isolation of hexene-1.

 The objective of the invention is to obtain hexene-1 of high purity.

The problem is solved by the method of purification of hexene-1 containing 2-ethyl-butene-1, including the stage of isomerization of 2-ethylbutene-1 in 3-methyl-pentene-2 on an acid catalyst and the stage of separation of hexene-1 of high purity, and the isomerization stage is carried out at a temperature of 50-80 ^o C, a pressure of 1-3 atmospheres in an inert atmosphere and a volumetric feed rate of 1-10 h ^-1 , and macroporous sulfonic cation exchanger medium acidity having a PSOE of 3.5-4.5 mg equiv . H ⁺ / g. The content of 2-ethyl-butene-1 in the starting mixture may be more than 1 wt.%.

The selective conversion of the 2-alkyl substituted isomer of hexene-1 2-ethyl-butene-1 with its content up to 5 wt.% From hexene-1 to the 3-alkyl substituted isomer - 3-methyl-pentene-2 transconfiguration is carried out without significant isomerization of hexene- 1 into the internal isomers of hexene-1, which makes it possible to separate the obtained fractions by conventional distillation using fewer theoretical plates and to obtain a high-purity vinylidene isomer of hexene-1 (not less than 99.5 wt.% Based on C ₆ olefins).

To maintain the activity of the catalyst, which falls at a low temperature, the selectivity of isomerization in the direction of obtaining trans-measurements and the implementation of the reaction in the liquid phase, the process is carried out at a temperature of 50-80 ^o C and a pressure of 1-3 ATM.

To prevent the formation of peroxide compounds during the implementation of isomerization at 50-80 ^o With the process is carried out in an inert gas. As an inert gas, nitrogen, argon, and the like can be used.

At high acidity of the catalyst (total static volumetric capacity (PSOE)> 4.5 mg • equiv H ⁺ / g), under these conditions, an increase in the content of internal linear isomers of hexene-1 (hexene-2, hexene-3) is observed, and at low acidity (PSOE <3.5 mg • equiv H ⁺ / g) - a decrease in the rate of isomerization of the vinylidene isomer (2-ethyl-butene-1) to 3-methyl-pentene-2 is observed.

 The volumetric feed rate of hexene-1 is determined by the rate of formation and stability of the 3-methyl-pentene-2 isomers (the cis-isomer of 3-methyl-pentene-2 is formed faster and is less stable than the trans-isomer of 3-methyl-pentene-2).

 With an increase in the temperature of isomerization, both isomerization of 2-ethyl-butene-1 into the trans isomer of 3-methyl-pentene-2, and the transition of the less stable cis-isomer of 3-methyl-pentene-2 to the more stable trans-isomer of 3-methyl pentene-2.

The difference in boiling points of the trans-isomer of 3-methyl-pentene-2 and hexene-1 (70.4 and 63.4 ^o C, respectively) allows the separation of hexene-1 from the trans-isomer of 3-methyl-pentene-2 with significantly lower rectification costs.

 In the table. 1 shows the calculated values of the number of theoretical plates required to obtain hexene-1 with a purity of 99.5% from a mixture containing 95 wt. % hexene-1 and 5 wt.% cis and trans isomers of 3-methyl-pentene-2 (3-MP-2), depending on the ratio of cis and trans isomers.

 From the data obtained, it is seen that with an increase in the ratio of isomers towards the trans-isomer 3-methyl-pentene-2, a smaller number of theoretical plates are required during rectification.

Thus, the proposed technical solution allows you to:
- increase the yield of hexene-1 in the target product due to the concentration of the main product;
- improve the technical and economic indicators of the process by simplifying the stage of rectification.

Distinctive features of the invention are:
- conducting the stage of isomerization at a temperature of 50-80 ^o C, a pressure of 1-3 ATM, in an inert atmosphere and a volumetric feed rate of 1-10 h ^-1 ,
- the use as a catalyst of macroporous sulfocationic acid of medium acidity, with PSOE 3.5-4.5 mg • equiv. H ⁺ / g;
leading to the selective conversion of more than 1 wt.% 2-ethyl-butene-1 to the trans-isomer of 3-methyl-pentene-2, which allows you to separate the impurity of 2-ethyl-butene-1 from hexene-1 by conventional distillation with maximum efficiency and significantly increase the concentration of hexene-1 in the target product.

 These signs are new and not described in the prototype, therefore, we can conclude that the proposed technical solution meets the criterion of "novelty."

 The introduction of new distinguishing features, which are not described in any similar method, in combination with the achieved effect (obtaining high-purity hexene-1 and simplification of the rectification stage), indicates the "inventive step" of the invention.

The invention meets the criterion of "industrial applicability", as it is confirmed by the following set of conditions:
the invention is intended for use in industry;
for the invention in the form described in the independent claim, the possibility of its implementation using the means and methods described in the application is confirmed, as shown in examples 2-7.

 Figure 1 shows a schematic diagram of a process.

 The initial mixture of hexene-1, containing isomer impurities, is introduced through line 1 into reactor 2, where it is in contact with sulfocationite 3. The reaction temperature is maintained by the coolant supplied through line 4 to the jacket 6 of the reactor and discharged through line 5. The product is further discharged from the reactor via line 7 and served in the column 8 for distillation. From column 8, the lower boiling hexene-1 is withdrawn through the top and discharged via pipeline 9, and the higher boiling isomers are discharged through a cube through pipeline 10.

 The method is carried out on a pilot installation of continuous operation, designed to operate at elevated pressures.

Sulfocathionite (Amberlyst 15) is pre-treated with a 1M NaOH solution (to obtain the necessary PSOE), washed with distilled water and dried at a temperature of 110 ^o C to constant weight, then washed with acetone and purged with nitrogen.

 The liquid fraction of α-olefins is fed to the bottom of the reactor, filled with sulfocathionite. In the reactor, nitrogen creates the excess pressure necessary to carry out the process in the liquid phase.

 From the reactor, the product is fed for distillation.

 The starting, intermediate and final products are analyzed by NMR on a Varian-300 spectrometer and gas-liquid chromatography on a PerkinElmer AutoSystem XL chromatograph using a 50 m capillary column coated with WAX-52 with an accuracy of 0.005%.

 The influence of the process temperature on the composition of the isomerization products is shown in table. 2.

 The method is illustrated by the following examples.

Example 1 (comparative, prototype)
The initial mixture of hexene-1, containing (wt.%): Hexene-1 - 95.12, cis-hexene-2 - 0.32; trans-hexene-2 - 0.10; 2-ethyl-butene-1 - 4.46 at a pressure of 1 ATM, a temperature of 30 ^o C and a space velocity of 10 h ^{-1 was} passed through sulfonic cation exchange resin Amberlyst 15, with a PSO of 4.81 mg · EQ. H ⁺ / g, and received the product (isomerizate) composition (wt.%): Hexene-1-94.01; cis-hexene-2 - 1.22; trans-hexene - 0.31; 2-ethyl-butene-1 0.43; cis-3-methyl-penten-2 - 2.97; trans-3-methyl-penten-2 - 1.06. Further distillation obtained the product (rectified) composition (wt.%): Hexene-1 - 98.39; cis-hexene-2 - 0.12; trans-hexene-2 0.14; 2-ethyl-butene-1 0.41; cis-3-methyl-penten-2 - 0.91; trans-3-methyl-penten-2 - 0.03.

Example 2
The initial mixture of the composition, as described in example 1, at a pressure of 1 ATM, a temperature of 50 ^o C and a space velocity of 10 h ^{-1 was} passed through Amberlyst 15 sulfocationite, having a PSOE of 4.5 mg · equiv. H ⁺ / g, and received the product (isomerizate) composition (wt.%): Hexene-1 - 93.89; cis-hexene-2 - 1.01; trans-hexene 0.64; 2-ethyl-butene-1 - 0.15; cis-3-methyl-penten-2 - 1.15; trans-3-methyl-penten-2 - 3.16. Further distillation obtained the product (rectified) composition (wt.%): Hexene-1-99.35; cis-hexene-2 - 0.12; trans-hexene-2 - 0.16; 2-ethyl-butene-1 - 0.12; cis-3-methyl-penten-2 - 0.21; trans-3-methyl-penten-2 - 0.04.

Examples 3-8
The method was carried out analogously to example 2. The conditions of the experiments in examples 1-8 and the results are shown in table. 3.

Thus, the inventive method allows to obtain hexene-1 of high purity when the content of the initial C ₆ olefin fraction of a significant amount of 2-ethyl-butene-1.0

Claims (2)

1. The method of purification of hexene-1 containing 2-ethylbutene-1, comprising the step of isomerizing 2-ethylbutene-1 to 3-methylpentene-2 on an acid catalyst and the step of isolating hexene-1 of high purity, characterized in that the isomerization step is carried out at a temperature 50-80 ^o C, a pressure of 1-3 atmospheres, in an inert atmosphere and a volumetric feed rate of 1-10 h ^-1 , and as a catalyst using macroporous sulfonic acid cation exchange medium acid having PSOE - full static volumetric capacity of 3.5-4, 5 mg • equiv. H ⁺ / g.  2. The method according to claim 1, characterized in that the content of 2-ethylbutene-1 in the initial mixture is more than 1%.

Images