DE1568895A1 - Process for the production of isoprene in high purity - Google Patents

Description

PATENT LAWYERS

DIPL.-ING. GÜNTHER KOCH DR, TINO HAI BACH

8 MUNICH 2, 1 6, NOV, 1966

: 10601 - Dr.R / Ele

Japan Gas — Chemical Company Tokyo (Japan)

Process for the production of isoprene in high purity

The invention relates to an improved process for the separation of diolefins from hydrocarbon _{mixtures, in particular from C c} fractions of a cracking residue of petroleum. The invention further relates to a process for separating diolefins from these Cc fractions, in which an extractive distillation is carried out using β-methoxypropiononitrile as the selective solvent; in particular, it relates to a process for the recovery of isoprene with high purity from C ^ fractions.

In recent years, the thermal cracking of petroleum, particularly naphtha, is used on a large scale for the extraction of gaseous olefins such as ethylene, propylene and the like. Performed. The cracking residue obtained from this thermal cracking contains various Cc hydrocarbons with different degrees of saturation. The typical

009837/2128

Statute of the crack residue and the boiling points of these Hydrocarbons are given in column A of Table I. Table I shows that this CL fraction is a large amount Contains isoprene, and it is highly desirable that the isoprene recover and use.

When separating isoprene from a hydrocarbon mixture with this composition, however, occur Difficulties arise, for example, a small amount of acetylenic hydrocarbons, especially lower as isoprene-boiling hydrocarbons, present in the cracking residue that was formed by thermal cleavage of naphtha), there are also components with boiling points close to the boiling points of the C ^ diolefins in a mixture of C, - paraffins and C, - monoolefins etc. These substances behave similarly to isoprene, and it is difficult to get isoprene in high purity with a good one Gain efficiency.

A method is already known in which the cracking residue is removed with the aid of a selective solvent, e.g. ammoniacal copper (l) acetate solution, sulfolanes, etc. is separated into groups with different degrees of saturation, those based on the different degrees of saturation Differences in the chemical and physicochemical properties are exploited, whereupon the desired

009837/2128 ^{# / #}

pure hydrocarbon is obtained by rectification. Furthermore, a method is known in which an extractive distillation is carried out with a selective solvent will} here the different degrees of saturation are simultaneously and the different boiling points are used to determine the concentration of the desired hydrocarbon to bring to the desired value, whereupon the pure hydrocarbon is obtained by rectification. Other procedures work similarly.

The C, fractions become one by thermal cleavage If the cracking residue obtained from naphtha is separated off by these known processes, the isoprene obtained usually contains small amounts of monoolefins, mainly 2-methylbutene-2, and acetylene compounds such as butyne-2, isopropyl acetylene and isopropenyl acetylene, while the paraffinic Hydrocarbons are practically completely separated from the isoprene.

Several processes have already been proposed for the production of isoprene from complex C, mixtures by steam cracking or by other high temperature hydrocarbon conversion processes. Once in a while a two-stage, extractive distillation is used to remove the acetylene compounds. Will continue a combination of direct distillation and extractive distillation to remove the acetylene compounds.

009837/2128 /

leads. However, these processes have not proven entirely satisfactory because very small amounts of acetylene compounds remain in the isoprene. In order to clean the product to a solvent suitable for the polymerization of isoprene, an additional operation is required to remove the impurities Thereby, complicated procedures and difficult, and the yield decreases. It is therefore difficult to obtain isoprene suitable for polymerization.

One purpose of the invention is to provide a process for the recovery of isoprene using one suitable for polymerization Degree of purity at which the acetylene compounds are removed prior to the extractive distillation, which means that the previously common methods characteristic disadvantages are eliminated.

Another purpose of the invention is to provide a Process for the separation of diolefins, in which an extractive distillation irit ß-Methoxypropyonenitril as selective solvent is carried out.

These and ar.ofire !, arouse result from the following Description and claims.

It was gefur.con that from the C ¹ C-KoI enwasferstoffgerrischen given in Table I, the acetylenes completely through

009837/2128 ■ »

Direct distillation can be distilled off after the Cyclopentadiene has been dimerized; in this way isoprene can be obtained with high purity,

To explain the invention, reference is made to the accompanying drawing, which shows a schematic flow diagram of the method according to the invention _o

According to the drawing, the feedstock, namely a C, --- fraction, which has a large amount of cyclopentadiene with a degree of saturation as well as chemical and physical properties comparable to those of isoprene and which behaves in a complicated manner during distillation and makes it difficult to obtain pure isoprene, * treated in a first ⁿ eiKkessel e at 80120 ^0C. As a result of this heating, the cyclopentadiene is easily ^{dimerized to dicyclopentadiene with a higher boiling point (170 °} C.), which greatly simplifies the subsequent work steps. The treated C ^ fraction is introduced into a separating column T ^ for the higher boiling components, in which the diir.ere and the components boiling higher than the C ^ fraction are drawn off at the bottom. The mixture drawn off at the top, which consists of components with a boiling point of not more than 55 ^° C., is introduced into a column, separating column T ", for the lower-boiling components, in which the lower-boiling components than isoprene, which mainly consist of isopentane exist, are distilled off at about 28 ⁰ C (atmospheric pressure) at the top. BAD OBlGlNAt

0U3837 / 2128 /

This feed contains about 30 # · hydrocarbons, which boil lower than isoprene. It is possible to distill off acetylene hydrocarbons at temperatures which are lower than the boiling points of the pure substances, but it is impossible to distill off all fractions boiling below isoprene with practically no isoprene losses. Acetylene hydrocarbons can be almost completely distilled off, some of the monoolefin hydrocarbons remaining in the residue. The Kenge the drawn off at the top fraction and the lost of isoprene are directly dependent on the number of floors of the fractionation column and the Riickflußverhältnis. When carrying out the invention, the loss of isoprene can be up to 5%, preferably up to 2%, based on the total isoprene content, while the amount of the fraction withdrawn at the top can be up to 30%, preferably up to 25 % t in relation to the total amount of the input material. The acetylenic hydrocarbons were analyzed; it was found there /? they contain 3utin-2, Pentin-1, isopropyl acetylene and isopropenyl acetylene. It is most advantageous to remove these substances at this point, as they act as inhibitors in the polymerization of isoprene. The fraction withdrawn at the bottom is a C _c fraction with a narrow boiling range and consists mainly of paraffinic, monoolefinic and diolefinic hydrocarbons.

00983 7/2128

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BATH ORIGINAL

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The C, fraction obtained in this way is then transferred to a column T, initiated in which the diolefin hydrocarbons through be separated extractive distillation. As a selective solvent can be used at this stage, for example Acetone, acetonitrile, dimethylformamide, dimethylacetamide, Use furfural, etc .; however, ß-methoxypropionitrile becomes particularly preferred. It is possible to make the diolefins by distilling the mixture with such a solvent to be selectively separated from the hydrocarbon mixtures with a narrow boiling range.

Used as a selective solvent, it becomes a low-boiling solvent used, part of the solvent in the top fraction of the distillation column is in the form of an azeotropic Contain a mixture, and it is then necessary that the solvent is removed from the distillate. This The method also has the disadvantage that you need colder cooling water or must work under pressure, because the temperature at the top of the column is low, and that additional trays are required to remove the hydrocarbons from the Extract, which consists of a mixture of the solvent and the hydrocarbons from the column, is to be separated off.

If, on the other hand, a high-boiling solvent is used, so the above-mentioned disadvantages are avoided), however, the solvent should be chemically resistant, since this

009837/2128 ^ ₀ ORIGINAL

Work step necessarily at high temperatures
is made. Although some of the known high-boiling solvents can be well suited as solvents, since, for example, the relative volatilities of various hydrocarbons compared to those of diolefins in these solvents are favorable, their chemical resistance at higher temperatures is inadequate

It has been found that β-methoxypropionitrile meets all of the claims mentioned. A comparison of the relative volatilities of hydrocarbons and isoprene in this solvent
and known solvents are given in Table II.

Table I l

Influence of the solvent on the relative
Volatilities of hydrocarbons

solvent n-pentane 2-methy! -Butene-? no solvent |
acetone
I acetonitrile
Dimethylformamide
ß-methoxypropio
nitrile 0.92
1.80
2.36
2.44
2.37 0.88
1.16
1.29
1.30
1.37

009837/2128

BATH

The feed used at this stage is obtained by removing a Cv fraction from a cracked naphtha residue is subjected to a heat treatment in which the cyclopentadiene is removed; it has the one in column X of Composition given in Table HI. The ratio /, wipe Solvent and hydrocarbons is 2: 1.

Table ITE

Composition of the Cv parliamentary group

Composition Y (G Z I. , 11 X 23.4 Isopentane 15.2 40.0 , 91 η-pentane 23.6 0.4 Cyclopentane 0.75 7.21 8th Pentene-1 4.96 5.28 Cis-pentene-2 3.66 4.28 0 , 87 Trans pentene 2 3.41 - 3-methylbutene-1 0.19 11.1 , 9 2-methflbutene-1 7.03 3.90 , 64 2-methylbutene-2 4.05 3 , 3 Cyclopentene 2.76 , 32 Isoprene 17.9 55 Cis-piperylene 3.43 9 Trans-Pipetylen 6.70 19th Cyclopentadiene 0.94 2

009837/2128

BAD ORIQINAt

Ί568895

As already said, this is β-methoxypropionitrile in terms of its solvent properties are comparable to those up to now known solvents and with regard to 2-methylbutene-2, the was previously difficult to separate, much more advantageous than the known solvent. Furthermore, the ß-! £ ethoxypropionitril the advantage that the above-mentioned disadvantages of the low-boiling solvents are avoided and that ^ u chemically resistant at high temperatures as well is easily accessible and cheap.

In an extractive distillation, the acetylenic hydrocarbons column accumulate in the feedstock at the oden or Sunpf together with the diolefins, even if their boiling points are lower than that of the isoprene to _c contrast, according to: the invention, the acetylenic hydrocarbons method according virtually not in contain the biolefins, since they were previously removed in the column T ". The small amount of the selective solvent introduced into the distillation column is preferably one to five times the volume of the hydrocarbons admitted to the tray to which the solvent is directed. The oil fraction withdrawn at the bottom of the column is then: n a column of t / ar 'iede: - »" »only / of the solvent, in which the solvent is completely separated from this fraction. will.

BATH ORIGINAL

009837/2128

The treated diolefin fraction is then washed in a column TV with Waaser and in a fractionation column Tg passed, in which the isoprene is separated. The parliamentary group consists of diolefins and a small amount of monoolefins, there is no fraction lower than isoprene. Therefore, an isoprene can easily be added to this fraction high purity can be obtained-

The work steps specified above can be carried out either at atmospheric pressure or at overpressure? however, it must be avoided to bring the temperature to more than 90 ° C. at a higher isoprene concentration in order to avoid the polymerization of the isoprene.

The following examples illustrate the invention.

example 1

A C "fraction with the addition given in column A of Table I was heated to 110 ° in an attoclave for 4 hours, wc! ei a product with the composition given in column B of Table J was obtained. This I-roduct wurae then subjected to a direct distillation, the lower boiling fractions with boiling points up to 5b ⁰ C zv remove. The distillate, the composition of which is given in column C of Table I, was then

009837/2128 _BAD original

.at a speed of 150 cm-yh. into a FuIL - body color (T _o in the drawing) with an inner: iurehi: etiser of 20 mm, a packing height of 1500 mm and a ti your tisehen number of trays of 70 J .: 44. Bottom enters from above. The Column 7 / was operated at a reflux ratio of 25 * 20% by weight of the hydrocarbon mixture used ;, were drawn off at the top of the column, while the remainder was sucked off at the bottom of the column. The temperature at the top be 't-ug at atmospheric pressure 27 ⁰ C. The top distillate and the bottom product had indicated in column D and E composition. The acetylene hydrocarbons in this working batch were for the most part removed at the top of the column; they were practically non-existent in the lower part of the column, ie from the 44th tray from the top). In 'FabelLe I the columns F urin G show the composition -im 44. n .- :, w. 52. floor. About 5 % isoprene is lost in this operation

The bottom residue obtained in this way was then at a rate of 120 cnr / hour. in the middle of a packed column (T-, in the drawing) with an inside diameter of 20 mm, a packing height of 1300 mm and a theoretical Eödent'.ahl of 60, while acetonitrile irit 2 fo water on the 12th tray from above with a Speed of 550 cm per hour was initiated. The column was operated at a reflux ratio of 6. 55 wt. 5 * the

BAD ORIGINAL ^ ^

009837/2128

C ^ fraction used were drawn off at the top of the column, while the remainder was drawn off at the bottom of the column. The temperature at the top was 32 ⁰ C. The bottom fraction mainly au was "a mixture of diolefins, acetonitrile and Wasaer, was in a column for '.Vie lergewinrmng of Lösungsmittel3 (T ^ in the drawing) having an inner diameter of? 0 mni and a Piil 1 height of 1000 mn; passed, in which the hydrocarbons were separated from the acetonitrile. The diolefins obtained in this way were then washed with water and placed in a packed column (T- in the drawing) with an internal diameter of 20 mm: a column height of ISO0 mm. and a theoretical plate number of 80 distilled. Here y / urde an isoprene with; of a purity sufficient for polymerization (Spulte J from Table J) air. Preserved the head of the column.

Example ?

The Sunp fraction obtained according to "Example 1 with the in The composition given in column E of Table I was taken at a speed of 50 cm / hour. in the hut a packed column with a diameter of 20 mm and a packing height of 1200 mm, while ß-methoxypropionitrile at a point 100 mm below the Head at a speed of 500 cc ^ / hour. initiated became. The extractive distillation was carried out with a reflux

009837/2128 BAD

ratio of 8.5 carried out., with a diolefin-free Fraction similar to that given in column L of Table I. Composition was obtained at the top of the column. One Fraction containing the solvent and the hydrocarbons contained, was at the bottom of the column with a speed speed of 520 cm ^ / hour peeled off and then in the middle a scraper with a diameter of? 0 mrc and a Height of 500 mn; initiated. In this way became a Fraction which mainly contained diolefins and which had the composition given in column T »'of Table I, with a 'reading speed of 20 cnr / hrc ^ m head of the Column received.

Example 3

A charge with the combination specified in column X of Tatelle IJI. t ^j zung was carried out at a speed of 50 cm ^ / hour. : η the putty of an Ijllköri l column with a diameter ve ·. 20 me, and a height of 120C nrri initiated, while ii-l- et'uoxypropioni tri 1 at one point 100 tr.ir. juterr.a] Ί of the head, = the column n: with a speed of 500 o! ir / 3td. was introduced into the column. The column was frozen at a reflux ratio of 8.5 'refluxing pressure (approx. 60 cm / hour) and a head temperature of 35 ^{° C. The} distillate was frozen at a rate of

BAD ORiG _iNAL 009837/2128

33 cirVh. removed at the top of the column. Here was a diolefin-free fraction with that in column Y of Table III given composition obtained.

Contained a fraction solvent] and hydrocarbons, was <_': m floor or bottom of the · column at a rate of 520 cni-yStd "withdrawn and then in the middle of ABBL Reifers with a diameter of 0 mm and a height? initiated by LOO mm. Here, a fraction which mainly contained diolefins, with the composition indicated in column Z in Talelle II1, was at the top of the column at a rate of 20 cnr / hour. obtain.

Example A.

Dienes ^p eir _; } i (·] shows the results of an experiment carried out with overpressure.

A C ₁ -Fral 'ti on rri ♦ of the ', ■ ''; through there :; ι '110 ⁰ C held Hehr H ₁ passed, wherein the C ₁ -Fr-JkIi (I:. was heated and dimerized Cl The thus treated was d-nn at a rate of 10.0 kg / hr in a read illierkolonne. The column was not operated at a reflux ratio of 0.35. The C _c fraction was removed at a rate of

009837/212 8 ₀ aD ORIGINAL

7.82 kg / hour withdrawn at the top of the column. The temperature at the head was 60 ⁰ G and the pressure 2.2 ata «

The fraction from which the high-boiling components were removed in this way had the composition given in column 0 of Table IV. The fraction was then passed into a rectifying column with 130 plates at a rate of 7.82 kg / hour. The column was operated at a reflux ratio of 18. The lower boiling than the C _r fraction, which mainly contained isopentane, was at the top of the column at a rate of 1.99 kg / hour. sucked off. The acetylenic hydrocarbons contained in the feed were practically completely enriched in this fraction. A practically acetylene-free fraction with the composition given in column E of Table IV was obtained at the bottom of the column. The temperature at the head was 58 ⁰ O and the DiHick 2.8 ata.

The fraction obtained in the preliminary stage with the composition indicated in column E of Table Iv was at a rate of 02 kg / h. in the middle of a column T, introduced for extractive distillation with 94 plates and a reflux ratio of 5, while acetonitrile, which contained 5 wt .- # water, at a rate of 39.5 kg / hour. was introduced into the column at the 10th tray from the top. The temperature at the head was 60 ^° C. and the pressure

2.66 ata « _8A D ORiGSMAL

009837/2128

The composition of the Cc fraction in the distillate withdrawn at the top is given in column H of Table IV. A mixture of acetonitrile and a C _c fraction, which consisted essentially of diolefins, was at the bottom of the column at a rate of 41.0 kg / Stri. obtain. This mixture was then introduced into a solvent recovery column T. with 20 plates, which was operated at a reflux ratio of / S ία .. The temperature was CO ⁰ C and the pressure was 2.16 ata.

The diolefin fraction obtained was washed with water in a washing machine in order to separate the solvent from the fraction. After the aqueous layer had been separated off, the fraction was returned to the hectification stage for the isoprene. This working step was carried out at a: reflux ratio of 11 using a column TV with 1D6 trays. At a feed rate of 2.29 kg / hour. isoprene was fed at the top of the column with a purity of not less than $ 99.8 and a rate of 1.05 kg / hour. obtain. The composition of the stream withdrawn at the bottom is given in column K of Table IV. The temperature at the top was 50 ⁰ G and the pressure 1.72 ata.

009837/2128 ORIGINAL BATHROOM

IV

Component cn of the Πρ-Fraktjon

Lower air Oi faction

j κ ο pen ι ·
n-pentane

" ¹ Y ■>!

V-Yfithyll: -iteii-1

¹ O "JH-FeIUr-. -,

\ _i: * - *! <■ thy j butene "ο ^ v ^ lonenien

\ '\'. ".. po ν ran
ω _t "r-iTis-Pi ι eryl en ο ['i G-Pi pe τ.', v leu 'yelopentaü: en

Ο »rl '<ί 4 ·> I.

· <■ - Acetylene "composition (weight-? ')

öijfr old? Uf ₁ -I rnk t: ά on ⁰ J ca en per cont. "

Pat ent ans rrü 3 h e:

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0 0 9 8 3 7 2 12 8

Claims (5)

Patent claims: 1. A process for the production of isoprene with high purity, characterized in that a Cc-Kohlenw.'isseratoffraktion, the Cr-paruffins, C ^ monoolefins, Cc-diolefins, C, - acetylenes and a higher than the Cc- Fraction contains boiling traction, heated, the cyclopentadiene contained in the C ^ -r hydrocarbon fraction is diraerized and in 1 the remainder is distilled for the purpose of removing a fraction boiling lower than isoprene, whereupon the residual oil is used to separate the diols contained therein 'Infraklion subjected to extractive distillation. 2. The method according to claim 1, characterized in that that a C ^ fraction is used as the ^ - hydrocarbon fraction J t ^ erriii see ■> turns that by! splitting of petroleum, in particular of Naphtha. 3. The method according to claim 1-2, characterized gekennzei without t, there? the fraction lower boiling than isoprene contains mainly isopentane. 4. The method according to claim 1-3, characterized in that ia2 rran as a selective solvent for the extractive Distillati oi. ß- "ethoj <ypropionitril used. 0098 37/2 128 BAD ORIGINAL 5. The method according to claim 1-4 »characterized in that that one can choose selective solutions; toi for the exfcrakbi ve distillation in 1 - 5 times the volume ^ e issr at the bottom, at which the release agent is introduced, return Introduced hydrocarbons BATH ORIGINAL 009837/2128 L eersei \ e