US2463873A - Separation of pentene-1 from its mixtures with other c5 olefins - Google Patents

Description

March 8, 1949. R. L. HEINRICH SEPARATION OF' PENTENE-l FROM ITS MIXTURES WITH OTHER C5 OLEFINS Filed Oct. 3, 1947 I atented Mar. 8, 1949 SEPARATION OF PENTENEJ FROM ITS MIX- TURES WITH OTHER Cs OLEFINS Raymond L. Heinrich, Baytown. Tex., assignor,

by mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware Application October 3, 1947, Serial No. 777,702

6 Claims. (Cl. 260-67'1) The present invention relates to the separation of straight chain alpha oleflns from mixtures with branched chain olens. More particularly, the invention is directed to the separation of pentene-l from its mixtures with other oleflns having ve carbon atoms in the molecule.

The production of synthetic lubricants and other polymers from oletlnic hydrocarbons generally requires a feed stock comprising substantially olens having a double bond in the alpha position and having all of the carbon atoms arranged in a straight chain. If the double bond is in the beta position or if the carbon atoms are not arranged in a straight chain, the quality of the polymer, when used as a synthetic lubricating oil, will be seriously impaired. Now that the supplies of crude petroleums from which high quality lubricating oil is produced is decreasing, it becomes increasingly important to produce synthetic lubricating oils of high quality to supply the deficiency in the natural lubricating oils which is becoming more and more apparent.

Unfortunately, pentene-l is not obtained from petroleum hydrocarbons as a pure compound. It is usually produced as a result of cracking and other conversion operations or dehydrogenation operations and, besides pentene-l, there may be produced cis and trans pentene-2, 2-methylbutene-l, 3methylbutene1, and 2methylbu tene-2. The boiling points of the several olenic hydrocarbons having iive carbon atoms in a molecule are such that a separation of pentene-l may be made from pentene-2 by distillation. Similarly, B-methylbutene-l may be separated from the Cs oleiinic mixture by distillation. Similarly, it is possible, by modern fractionating techniques, to separate 2methylbutene2 from its mixtures with other hydrocarbons. However, the separation between pentene-l and 2-methylbutene-l is quite diiilcult due to the proximity of the boiling points of the olenic hydrocarbons. The following table gives the boiling points of the olefinic hydrocarbons having five carbon atoms in the molecule:

2methylbutene2 101.3

Y Separation among the olefinic hydrocarbons by isomerization is also difilcult because, according to the prior art methods, pentene-l has the tendency to isomerlze to pentene-2 and 2-methylbutene-2. Thus, instead of obtaining the pure pentene-l as desired, all one would obtain would be pentene-2, which is an undesirable feed stock for the production of synthetic lubricating oils.

Therefore, it is the main object of the present invention to provide a method for separating straight chain alpha oleilns from branched chain oleflns.

Another object of the present invention is to separate pentene-l from its mixtures with other Ct carbon atom olens.

A further object of the present invention is to provide a process wherein an oleflnic mixture, including oleflns having five carbon atoms, may be separated into pure compounds.

The objects of the present invention are achieved by isomerizing a mixture including pentene-l and 2methylbutene1 under controlled conditions such that the pentene-l is substantially unaiiected while the 2-methylbutene-1 is isomerized to Z-methylbutene-Z.

In accordance with the present invention, a. mixture of C5 olefins, including pentene-l and Z-methylbutene-l, is subjected to contact with sulfuric acid having a concentration in the range from about 40% to 70% H2804 at a temperature in the range from about 40 to 100 F. for a contact time ranging from about 5 to about 60 minutes. Under these conditions, the pentene-l and the pentene-Z in the mixture are unaffected and the 2-methylbutene-1 is largely isomerized to 2- methy1butene-2. Reference to the foregoing table will show that the separation among the oleilns may then be accomplished by simple distillation employing modern fractionating techniques which allow separation among compounds having boiling points within 2 or 3 degrees.

The invention will now be illustrated by reference to the drawing in which the sole gure presents a preferred mode of practicing the invention.

Referring now to the drawing, numeral Il designates a charge line through which a C5 hy drocarbon fraction may be introduced into the system. This fraction includes olefinic hydrocarbons having five carbon atoms in a molecule and contains pentene-l in admixture with 2- methylbutene-l. The feed stock may also include paramnic hydrocarbons, but for purpose of simplifying the description, it is assumed that the hydrocarbon fraction flowing into the system through line IlA is substantially free of parainic hydrocarbons. The oleflnic fraction in line Il is admixed with sulfuric acid, having a strength 3. in the range given, which is introduced into the system by way of line I2, controlled by valve I3. The mixture of oleflnic hydrocarbon and sulfuric acid may be contacted in a reaction vessel I4 which may be provided with suitable internal equipment which allows intimate contact between the Ct olenic fraction and the sulfuric acid. The temperature conditions in reactor I4 are maintained within the critical range and reactor I4 is of sufficient size to allow a residence time sufficient for the isomerization of 2-methylbutene-1 to 2methylbutene2 to go to completion.

Since olens in the presence of sulfuric acid have a tendency to polymerize, it may be necessary to provide a cooling system for the reactor I4. Therefore, reactor I4 may be provided with a Jacket I5 through which a cooling uid may be circulated around the reactor through inlet pipe I6 and outwardly through outlet pipe I'I. This cooling fluid may be a low-boiling hydrocarbon fraction or other refrigerant.

As mentioned before, reactor I4 may be equipped with internal contacting equipment which may include baffle plates, bell cap plates, and the like and as a result, the hydrocarbons and oleflns may issue from the reactor I4 by line I8 as an emulsion which is discharged thereby into a settler I9 where, under the infiuence of gravity, a separation betwen the hydrocarbon constituents and the acid constituents of the emulsion may be effected. The sulfuric acid separated from the emulsion in separator I9 discharges therefrom by line 20 and may be recycled to the reactor by line 2l, controlled by valve 22, which connects into line I2. From time to time it may be desirable to withdraw a portion of the acid separated from the emulsion in separator I9 and under these conditions, valve 23 in line 20 may be opened allowing the acid to discharge to a recovery system not shown. When acid is withdrawn from the system, it may be desirable to replace it by an equivalent amount of fresh acid and this may be done provided the fractionationtowers are of sufficient l efficiency to allow the desired separation. For purposes of illustration, it wil be assumed that fractionating tower 30 is a single, highly efficient fractionating tower which will allow separation among the Cs olens remaining in the mixture. Pentene-l, which boils at about 86 F., is removed overhead from fractionating tower 30 by line 32, a mixture of cis and trans pentene-2, boiling at about 97 F., is removed as a side stream by line 33, and 2methlybutene2, boiling at about 101 F., is removed as a bottoms fraction by line 34. It will thus be seen from the foregoing description taken with the drawing that a. method has been provided for separating the various oleflns ordinarily contained ln a C5 olenic mixture.

If it is desired to obtain the 2-methylbutene-1, then the 2methylbutene2 may be subjected to a separate treatment with sulfuric acid since the isomerization of the 2-methylbutene-1 to 2- methylbutene-Z is an equilibrium reaction.

In order to illustrate further the practice of the present invention, a number of runs were made in which hydrocarbon mixtures, including pentanes and the several C5 oleflnic hydrocarbons, were subjected to treatment in accordance with the present invention. In the rst run, a Cs hydrocarbon fraction, including pentanes and the 40 every volume of 70% sulfuric acid. In the secby opening valve I3 connecting line I2 to a .I

source of fresh sulfuric acid not shown.

The hydrocarbon phase separated in separator I9 may be discharged therefrom by line 25 into a.

several C5 olens, was contacted with 70% H2804 at a temperature in the range between '70 and 80 F. for 30 minutes at atmospheric pressure. Five volumes of hydrocarbon were employed for ond run, a temperature in the range between 78 and 83 F. was employed for contact time of 30 minutes at atmospheric pressure with five volumes of hydrocarbon being employed with every volume of '70% sulfuric acid.'

The third run comprised a feed stock including only the C5 olelns. Atmospheric pressures were used and a temperature in the range between and '70 F. was maintained with the acid contacting the hydrocarbon for 30 minutes. this run 2 volumes of hydrocarbon were contacted with every volume of 70% sulfuric acid.

Run No. 1 Run N o. 2 Run No. 3 Composition, Mol Percent Charge Product Charge Product Charge Product Pentanes 80. 0 80. 9 84. 3 84. 3 0. 0 0. 0 3-Methylbutene- 3. 2 0. 9 0. 7 0. 0 0. 2 0. 4 Pentenc-l 10. 2 l1. 7 6. 8 5. 8 48. 3 5l. 5 2Methy1butenel 5. 7 0. 9 7. 2 3. 4 51. 1 2. 0 Pentenes-2 0. 0 0. 8 0. 2 0. 8 0. 4 0. 5 2-Methylbutene-2 0. 0 3. 8 0. 7 4. 7 0. 0 5. 6 Olefin Absorbed by HgSO4 1. 0 0. 9 40. 0

Total 100. 0 100. 0 100.0 100.0 100.0 100. 0

head fraction comprising substantially S-methylbutene-l by line 28. The boiling point of 3- methylbutene-l is such that it may be easily separated from the other olefinic hydrocarbonshaving five carbon atoms in a molecule by distillation. The remaining C5 olefins in the mixture discharge from fractionating tower 26 by line 29 into a second fractionation tower 30 which, similar to fractionation tower 26, is equipped with a heating means illustrated by a coil 3|. Differing from fractionating tower 26, fractionatlng tower butene-l was isomerized to 2-methylbutene-2. It y will be further observed that the pentene-l concentration did not change significantly, while the j pentene-Z concentration rose to 0.8%, indicating that only a small amount of pentene-l was isomerized to pentene-2.

accaeve In run No. 2 the pentene-l concentration was reduced by only 1.0% while the pentene-2 concentration increased by 0.6%. On the other hand, the 2-methylbutene-1 concentration decreased 3.8% and the 2-methylbutene-2 concentration increased from nothing to 4.7%. The decrease in 3-methylbutene-l concentration in both runs indicates that this olefin is isomerized to some extent to 2-methylbutene-2 at about the same rate as 2-methylbutene-1 is isomerized to Z-methylbutene-Z. In run No. 3, in which a substantially oleiinic hydrocarbon feed stock was employed, the 2-methylbutene-1 concentration was reduced from 51.1% to 2.0% while the 2methyl butene-2 concentration increased from nothing to 5.6%. The pentene-l concentration was not appreciably changed and the pentene-2 concentration increased only 0.1%. It is apparent that a large amount of the 2-methylbutene-1 has been absorbed in the acid. However, the 2-methy1- butene-l may be recovered therefrom by wellknown means. It is apparent from the foregoing runs that satisfactory isomerization of 2- methylbutene-l to 2-methylbutene-2 may be obtained. It is also apparent from the data that the presence of pentanes as a diluent in the reaction may be beneficial in the practice of the present invention in the mode illustrated with respect to the drawing. When pentanes are present, it may be desired to remove, as described, the 3- methylbutene-l by line 28, the pentanes by line 32, pentene-l by line 33, and to separate pentene-2 from 2-methylbutene-2 in a third fractionation tower, not shown. In any event, the separation of parafilns from olefins may be easily accomplished.

In practicing the present invention, it may be desirable to obtain from a petroleum fraction containing olens a fraction boiling in the range from about 55 to 95 F. including pentane and the C5 olens. This mixture may be subjected to contact with 40-'70% sulfuric acid at a temperature in the range from 40 to 100 F. for a time up to about 60 minutes. The amount of acid employed of the strength given may vary from about volumes of hydrocarbon to 1 volume of acid to about 1 volume of hydrocarbon to 1 volurne of acid. Under these conditions, the pentene-l is not appreciably isomerized and the 2- methylbutene-l is substantially isomerized to 2- methylbutene-2.

It is important that the temperature and the strength of the acid be carefully controlled. If the temperature should be allowed to rise appreciably, the pentene-l may be isomerized to pentene-2 thus defeating the whole purpose of the invention. If the strength of the acid is allowed to increase appreciably, the olens may be polymerized and undesirable products obtained.

Under the conditions where a mixture of pentenes and C5 olens are employed, the pentene-l may be separated from the pentanes by solvent extraction or azeotropic or extractive distillation if the fraction should include substantial quantity of isopentane, which boils at the boiling of pentene-l.

The nature and objects of the present invention, having been fully described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for separating pentene-l from its mixtures with other C5 oleiins which comprises contacting an olefnic mixture containing pentene-l and 2-methylb'utene-1 with sulfuric acid 75 t0 having a strength in the range from 40% to '10% H3804 at a temperature in the range from 40 to F. for a time in the range between 5 and 60 minutes to form a reaction product and to cause isomerization of Z-methylbutene-1 to 2-methylbutene-Z, separating sulfuric acid from the reaction product, and subjecting the reaction product ttg disltillation to recover substantially pure pen- 2. A method for separating pentene1 from a hydrocarbon fraction including paramn hydrocarbons having 5 carbon atoms in the molecule and containing'pentene-l and 2-methylbutene1 which comprises contacting said hydrocarbon fraction with sulfuric acid having a strength in the range from 40% to 70% H2804 at a temperature in the range from 40 to 100 F. for about 30 minutes to form a reaction product, separating the reaction product from the sulfuric acid and subjecting the reaction product to a separation treatment to recover substantialy pure pentene-l therefrom.

3. A method for recovering substantially pure olens from a C5 oleflnic hydrocarbon fraction containing pentene-l, pentenes-Z, 2-methylbutene-1, 2-methylbutene-1, and 2-methylbutene-2 which comprises contacting said olenic fraction with sulfuric acid having a strength in the range from 40% to '70% HzSO4 at a temperature in the range from 40 to 100 F. for about 30 minutes to form a reaction product and to cause selective isomerization of 2-methylbutene-1 to 2-methylbutene-Z, separating sulfuric acid from the reaction product, subjecting the reaction product to distillation and separately recovering by distillation S-methylbutene-l, pentene-l, pentenes-Z,

and 2-methy1butene-2.

4. A method for separating pentene-l from its mixtures with other C5 olefins which comprises contacting an olefinic mixture containing pentene-l and 2-methylbutene-1 with '70% sulfuric acid at a temperature in the range between 60 and 85 F. for about 30 minutes to form a reaction product and to cause isomerization of 2-methylbutene-1 to 2-methylbutene-2, separating sulfuric acid from the reaction product, and subjecting the reaction product to distillation to recover substantially pure pentene-l.

5. A method for separating pentene-l from its mixtures with other C5 olens which comprises contacting an oleilnic mixture containing pentene-1, pentenes2, 2methylbutene1, 3-methylbutene-l, and 2-methylbutene-2 with sulfuric acid having a strength in the range from 40% to '70%, said olenic mixture being employed in an amount in the range between 1 volume and 10 volumes for every volume of sulfuric acid, at a temperature in the range from 40 to 100 F. for about 30 minutes to form a reaction product and to cause isomerization of 2-methy1butene-1 to 2methy1butene2, separating sulfuric acid from the reaction product, and subjecting the reaction product to distillation to recover substantially pure pentene-l.

6.' A method for separating pentene-l which comprises contacting an oleiinic mixture including substantial amounts of pentene-l and 2-methylbutene-1 with sulfuric acid having a strength in the range between 40% and r10% H1SO4 at a temperature in the range between 40 and 100 F. for a time in the range between 5 and 60 minutes to form a reaction product and to cause isomerization of 2-methylbutene-1 2-methy1butene-2 while the pentene-l is subpure pentene-l.

RAYMOND L. HEINRICH.

REFERENCES Crum The following references are of record 1n the le of this patent:

Number UNITED STATES PATENTS Name Date Davis et al. Feb. 9, 1932 Clark et al July 2,1935 Cramer Oct. 16, 1945 Marsh A'ug. 6, 1946

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