US2433751A - Separation of organic compounds - Google Patents

Description

Patented Dec. 30, 1947 SEPARATION or ORGANIC COMPOUNDS Bernard S. Friedman, Riverside, Ill., assignor to Universal Oil Products Company, Ch1cago,'Ill., a corporation of Delaware No Drawing. Application September 30, 1943, Serial No. 504,455

This invention relates to the separation of organic compounds having different degrees of saturation and more particularly to a novel solvent therefor and to a process using the same.

The invention is particularly applicable to the treatment of hydrocarbon fractions which, as usually recovered from various sources, contain saturated and unsaturated hydrocarbons. For example, normally liquid products of a cracking process contain olefins, aromatics, paraffins and naphthenes, Likewise, the products recovered by distillation of crude oil contain paraiiins, naphthenes, aromatics and, in most cases, a small amount of olefins. Likewise, normally gaseous products of a cracking process contain olefinic gases such as propylene and butylenes, and paraflinic gases such as propane and butanes.

In many cases, it is desirable to separate the unsaturated from the saturated hydrocarbons, but this cannot be accomplished by purely fractional distillation means in practical operations because of the similarity in boiling points of the various hydrocarbons.

Other organic compounds are likewise recov-.

ered from various sources including synthetic processes wherein the products contain organic compounds of difierent degrees of saturation. For example, saturated and unsaturated glycerides are frequently recovered in admixture and their separation cannot be effected purely by fractional distillation in practical operations.

In a broad aspect the present invention relates to a process for separating a mixture of organic compounds of different degrees of saturation which comprises treating said mixture with a solvent comprising a substituted aliphatic nitrile. In another aspect the present invention relates to the separation of a mixture of hydrocarbons having diiierent degrees of saturation and similar boiling points which comprises treating said mixture with a solvent comprising a substituted aliphatic nitrile, the substituent group being hydrophilic in nature.

In still another aspect the present invention 2 relates to a process for separating a mixture of hydrocarbons having different degrees of saturation and similar boiling points which cannot readily be separated by purely fractipnal distillation means which comprises treating said hydrocarbons with a solvent comprising a substituted aliphatic nitrile in which the aliphatic portion contains from 2 to '5 carbon atoms inclusive, and in which the substituent group comprises at least one group selected from the class consisting of CN, NO2, NRRi, NRCORi,

16 Claims. (01. 196-1435) OR, -OCOR, COOR, CONRR1, SOsR and -SO2NRR1, in which R and R1 represent at least one of the following: --H, CHs, CzHs, C3H'1, CHzOH, C2H4OH, CaHsOH, CHzNI-Iz, -C2H4NH2, and CaHsNHz.

The present invention is particularly applicable to the treatment of ither normally gaseous or normally liquid hydrocarbon fractions for the separation of the unsaturated from the Saturated hydrocarbons. As used in the present specifications and claims, the term saturated hydrocarbons is intended to include the parafiins and/or naphthenes, while the term unsaturated hydrocarbons is intended to include the olefins and/or aromatics. The oleflns include both the mono and polyolefinic hydrocarbons.

Thus, the invention may be utilized for the separation of olefiiis and/or aromatics from paraffins and/or naphthenes. Likewise, the invention may be utilized for the separation of mono-olenns from di-olefins, the mono-olefins being less unsaturated than the di-olefins. V

The present invention is characterized by a novel solvent which comprises a -substituted aliphatic nitrile and may be represented broadly by the formula NCCnHZnX, wherein n is 2 to 5 inclusive and X is selected from the class as heretofore mentioned and as will be hereinafter described in detail.

In accordance with the invention the aliphatic portion of the solvent contains from 2 to 5 carbon atoms inclusive. tion of the solven refers to that portion of the molecular structure as represented by CnH2n in the formula NCCnHZnX, and does not refer to the carbon atoms in. the radical group or groups as represented by R and R1. When the aliphatic portion of the solvent comprises a single CH2 group, the nitrile group (CN) and the substituent group are both attached to the same carbon atom. Such compounds are not desired since they will decompose on heating to their boiling point, which heating is required in order to separate the solute from the solvent in a subsequent step of the process. On the other hand, when the aliphatic portion of the solvent comprises more than 5 CH2- groups, the efiect of the polar groups is outweighed by the hydrocarbon portion of the molecules and the compound does not possess the desired selectivity.

It is a particular feature of the present invention that the substituent groups hereinbefore set forth be strongly hydrophilic; that is, they The term aliphatic nor-- greatly'increase the solubility in water of the compound to which it is attached. Thus, while halogens increase the solubility of the compounds in water, this effect is only very slight and therefore the halogens are definitely excluded from the present invention. These compounds have high solvent power (dissolving large amounts of hydrocarbons) and high selectivity (dissolving unsaturated hydrocarbons preferentially to saturated hydrocarbons) In accordance with the invention, the substituted aliphatic nitrile contains at least one substituent group (X) selected from the class consisting of -CN, --NO2, NRR1, -NRCOR1, OR, OCOR, COOR, CONRR1, SO3R and -SO2NRR1, in which R and R1 represent at least one of the following: --H, --CH3, --C2H5, --C3H7, CH2OH, C2H4OH, --C3HsOH, CH2NH2, -C2H4NH2, and C3H6NH2.

When the substituent group comprises a nitrile (CN) the solvent will be a dinitrile as represented by succinonitrile (CNCHeCI-IaCN), glutaronitrile (CNCH2CH2CH2CN) adiponitrile and pimelonitrile (CNCI-IcCHzCHzCHzCI-IzCN).

Other suitable solvents may comprise the dinitrile compounds in which one of the hydrogen atoms is replaced by one or more of the X or R groups, provided that no more than one X group be attached to the same carbon atom. Succinonitrile is one of the preferred solvents of the present invention and is particularly suitable for use in the separation of hydrocarbons as will be illustrated in one of the examples hereinafter set forth.

When the substituent group comprises a nitro (N02), the solvent will be a nitro-nitrile as exemplifled by 2-nitro-ethylcyanide or similar nitro-nitrile derivatives of propane, butane or pentane. Similarly, one or more of the hydrogen atoms may be replaced by one or more of the X or R groups as heretofore set forth.

When the substituent group comprises -NRR1, the solvent will be an amino-nitrile such as 2- amino-ethyl-cyanide (NH2CH2CH2CN) or the corresponding amino-substituted propyl, butyl and amyl cyanides. Likewise, one or more of the hydrocarbon hydrogen atoms may be replaced by one or more X or R groups as hereinbefore set forth. Thus, such compounds as are utilizable.

When the substituent group comprises --NRCOR, a suitable solvent may have the formula CNCHzCHzNHCOCH: or, when desired, one or more of the hydrocarbon hydrogen atoms may be replaced by an R group. as hereinbefore set forth.

When the substituent group comprises OR, the solvent may be a hydroxy-nitrile such as ,9- hydroxypropionitrile (HOCHzCHzCN) or the corresponding hydroxynitriles containing 3, 4 and 5 carbon atoms in the aliphatic portion of the molecule and in which one or more of the hydrocarbon hydrogen atoms may be replaced by one or more X or R groups as heretofore set forth. p-hydroxypropionitrile is one of the preferred 4 solvents of the present invention. Particularly suitable compounds include those in which the hydroxyl hydrogen is replaced by an R group, typical examples of which are cyanoethylether of ethyleneglycol (CNCH2CH2OCH2CH2OH) or the acetic acid ester of fl-hydroxypropionitrile (CHaCOOCI-IzCHzCN) I When the substituent group comprises a carboxyl, (COOR in which R is hydrogen) the solvent will be a cyano aliphatic acid having the formula CNCnHznCOOH in which n is 2 to 5 inclusive, and particularly CNCHzCHzCOOH or Likewise, one or more of the hydrocarbon hydrogen atoms may be replaced by one or more of the X or R groups as heretofore set forth.

When the substituent group comprises -CONRR1, the resulting compound may be called a cyano derivative of an aliphatic acid amide and may have the formula,

or if one of the hydrogen atoms attached to nitrogen is replaced by an alkyl radical such as methyl, it may have the formula CNCI-IzCHzCONHCI-Ia When the substituent group comprises SO3R, the resulting compound may be a sulfonic acid substituted aliphatic nitrile and may have the formula NCCHzCHzSOaH. Similarly, one or more of the hydrocarbon hydrogen atoms may be replaced by one of the X or R groups as heretofore set forth.

When the substituent group comprises SOONRRi. the resulting solvent will be a sulfonamide and may have the formula NCCI-IzCHzSOONHz Likewise, one or more of the hydrocarbon hydrogen atoms may be replaced by the X or R groups as heretofore set forth.

It is to be noted that there are a great number of solvents which may be satisfactorily employed in accordance with the present invention, the essential limitations being that the solvent contain one or' more hydrophilic groups in addition to the nitrile group, and that it will not decompose when heated to its boiling point at atmospheric pressure. It is preferred that the total number of carbon atoms in the solvent should not be' too great since the solvent then is less selective, the compound exhibiting more and more the properties of an aliphatic hydrocarbon as it increases in hydrocarbon content. Thus, when the number of carbon atoms in the alkyl group is 4 or 5, the radical group preferably contains not more than 1 or 2 carbon atoms, whereas when the number of carbon atoms in the alkyl group is 2 or 3, the number of carbon atoms substituted in the hydrogen atoms may be greater. In general, it may be stated that the hydrocarbon content in the solvent molecule should not exceed about 64% by weight.

It is understood that the various alternative compounds which may be employed in accordance with the present invention as heretofore set forth are not necessarily equivalent in their effectiveness as a selective solvent for the separation of organic compounds and particularly hydrocarbons, The choice as to the particular solvent to be employed with any given charging stock to be subjected to extraction will depend upon the characteristics of the charging stock and the type of separation to be effected.

is relatively simple and may comprise introducing the hydrocarbon mixture to be extracted into a suitable extraction zone. The extraction zone may or may not contain bafile plates, bubble decks, side to side pans, or the like. The extraction zone may be equipped with stirring or other contacting means in order to obtain eflicient contacting of the hydrocarbons and solvent. The solvent extraction is effected under conditions of temperature and pressure in order to form an extract phase containing a major portion of the solvent and a major portion of the unsaturated hydrocarbons, and a railinate phase containing a major portion of the saturated hydrocarbons.

The temperature employed is preferably atmospheric or Slightly superatmospheric but it should be high enough to maintain the solvent in liquid phase in case it is solid at ordinary temperatures, but must be below that at which decomposition of the solvent or hydrocarbons ocours. The pressure to be employed is usually atmospheric or moderately superatmospheric but likewise should be sufilcient in order to maintain the hydrocarbons and solvent in liquid phase. When treating normally gaseous hydrocarbons, a higher superatmospheric pressure is employed in order to maintain the hydrocarbons in substantially liquid phase.

It is within the scope of the invention to add water, glycol or similar material to the hydrocarbon and/or solvent in case the hydrocarbons are too soluble in the solvent. The addition of water in this case serves to decrease the solubility of the hydrocarbons and also to increase the selectivity of the solvent. Frequently it is necessary to add water especially to extract mixtures so rich in aromatics or olefins as to be mutually miscible with the solvent.

Usually more than one extraction is required in order to effect substantially complete separation of the unsaturated from the saturated hydrocarbons. In some cases, however; one extraction may be sufllcient when it is required only to slightly lower the concentration of the unsaturated hydrocarbons in the mixture or in case the charging stock originally contains only a small percentage of unsaturated hydrocarbons.

After formation of the extract and raffinate phases, the solvent may be separated from the hydrocarbons by various means including: 1) distillation at increased temperature and/or reduced pressure; (2) adding water or the like in order to decrease the solubility of the hydrocarbons in the solvent and (3) counter-extractin the hydrocarbons from the solvent by contacting the extract phase with a secondary solvent which is immiscible with the first solvent and may comprise, for example, a paraflinic or naphthenic hydrocarbon of higher or lower boiling point than the solute. The second solvent is then separated from the solute by ordinary fractional distillation means.

The following examples are introduced for the EmampleI A synthetic mixture of benzene and cyclohexane containing 17.5% by volume of benzene 6 was contacted with an equal amount by weight of succinonitrile (CNCHZCHZCN) at atmospheric temperature and atmospheric pressure. The extract and rafiinate phases were separately withdrawn from the extraction zone and the dissolved hydrocarbons were separated from the solvent by distillation. It was found that the concentration of benzene in the hydrocarbons recovered from the extract phase was 82%, While the concentration of benzene in the raffinate phase hydrocarbons was only 13.7%. It is thus shown that the concentration of benzene in the charge was reduced from 17.5% to 13.7% in the raflinate by one extraction. By additional extractions, it is possible to reduce the benzene content of the raffinate to a very low figure.

Example I I A synthetic mixture of benzene and normal heptane containing 17.5% of benzene was prepared and extracted with fi-hydroxypropionitrile (HOCH2CH2CN) at atmospheric temperature and atmospheric pressure. The extract phase and raffinate phase was separately withdrawn from the extraction zone and the hydrocarbons were separated from the solvent by water-wash-' ing. In this case, the volume of benzene in the extract hydrocarbons amounted to 67 while the volume of benzene in the raffinate was 13%. I

Here, again, one extraction reduced the volume of benzene from 17.5% in the charge to 13% in the rafiinate and continued extractions will reduce it to a still lower figure.

I claim as my invention:

1. A process for separating a mixture of organic compounds of difierent degrees of saturation which comprises treating said mixture with a solvent comprising a substituted aliphatic nitrile in which the nitrile and substituent groups are attached to different carbon atoms.

2. In a solvent extraction process for separating a mixture of hydrocarbons into fractions of differing degrees of saturation with respect to carbon-hydrogen ratio, the step of extracting said hydrocarbons with a substituted aliphatic nitrile in which the hydrocarbon content does not exceed about 64% by weight of the molecule and in which the nitrile and substituent groups are attached to difierent carbon atoms.

3. A process for separating a mixture of hydrocarbons of differing degrees of saturation which comprises treating said mixture with a selective solvent comprising a substituted aliphatic nitrile in which the nitrile and substituent groups are attached to different carbon atoms and in which the aliphatic portion of the solvent contains from 2 to 5 carbon atoms inclusive, the substituent group being strongly hydrophilic in nature.

-4. A process for separating unsaturated hydrocarbons from saturated hydrocarbons which comprises treating a mixture of unsaturated and saturated hydrocarbons with a selective solvent comprising a substituted aliphatic nitrile in which th nitrile and substituent groups are attached to diflerent carbon atoms and in which the aliphatic portion of the solvent contains from 2 to 5 carbon atoms inclusive, under conditions to form an extract phase and a rafiinate phase.

5. The process of claim 4 further characterized in that said unsaturated hydrocarbons comprise olefins and aromatics.

6. The process of claim 4 further characterized in 311:1; said unsaturated hydrocarbons comprise ole 7. The process 01' claim 4 further characterized in that said unsaturated hydrocarbons comprise aromatics.

8. A process for. separating an unsaturated hydrocarbon from a mixture thereof with a saturated hydrocarbon which comprises contacting the mixture with succinonitrile under conditions to form an extract phase and a rafiinate phase.

9. A process for separating an unsaturated hydrocarbon from a mixture thereof with a saturated hydrocarbon which comprises contacting the mixture with p-hydroxypropionitrile under conditions to form an extract phas and a rafiinate phase.

10. A process for separating a mixture of saturated and unsaturated hydrocarbons which comprises subjecting the mixture to solvent ex traction with a substituted aliphatic nitrile containing a strongly hydrophilic substituent group and an aliphatic group having from 2 to 5 carbon 20 atoms, said substituent group and the nitrile group being attached to different carbon atoms of the molecule.

11. A process for separating a mixture of saturated and unsaturated hydrocarbons which 25 characterized in that said substituent group 35 comprises the hydroxyl radical.

14. A process for separating a mixture of saturated and unsaturated hydrocarbons which comprises subjecting the mixtur to solvent extraction with a nitro-nitrile containing an allphatic group of from 2 to 5 carbon atoms, the nitro and nitrile groups of the compound being attached to different carbon atoms of said aliphatic group.

15. A process for separating a mixture of organic compounds of different degrees of saturation which comprises treating said mixture with a solvent comprising a'substituted aliphatic compound containing as substituents at least two nitrile groups attached to diiferent carbon atoms.

16. A process for separating a mixture of hydrocarbon compounds of different degrees of saturation which comprises treating said mixture with a solvent comprising a substituted aliphatic compound containing as substituents at least two nitrile groups attached to different carbon atoms.

BERNARD S. FRIEDMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 30 2,023,375 Van Dijck Dec. 3, 1935 2,114,852 McKittrick Apr. 19, 1938 2,128,958 Mueller-Cunradi et a1. Sept. 6, 1938 2,162,963 McKittrick June 20, 1939 2,092,739 Van Dijck Sept. 7, 1937 2,143,415 Hixson et al Jan. 10, 1939 2,160,607 Van Dijck May 30, 1939