US2520715A - Method of separating organic - Google Patents

Description

Patented Aug. 29, 1950 UNITED STATES PATENT OFFICE METHOD OF SEPARATING ORGANIC COMPOUNDS BY MEANS OF UREA AND THIOUREA No Drawing. Application March 29, 1947, Serial No. 738,213

Claims. 1

This invention relates to a process for the extractive fractionation of organic compounds. More particularly, it relates to improvements in the process of fractionally extracting organic compounds from mixtures thereof by the use of such complex-forming agents as urea and thiourea.

The fractionation of mixtures of organic compounds presents numerous problems, both technical and economic. For example, the separation of mixtures of closely allied isomers, such as octane from iso-octane, is difficult by any of the more reasonably economic procedures such as alkylation, isomerization and cyclization is reduced if feed stocks are not of the correct composition, either during the primary feed state or in recycling operations.

In most of such conversion'reactions an equilibrium mixture is generally obtained comprising fixed ratios of unconverted feed stockand the desired product, such as from a previous cycle through the converter, the amount of conversion is correspondingly reduced.

The two principal means for fractionation of such mixtures on a commercial scale have been by fractional distillation and by solvent extraction. Recently, however, a new method has been shown to be suitable for large scale separations, namely extractive crystallization with urea. It was found that urea forms crystalline complexes with organic compounds of substantially normal structure, while it appears to be inert in this respect toward branched compounds such as the isoparafiins, or cyclic compounds such as most aromatics and naphthenes. The complexes so formed are of indeterminate structure, but appear to be unstable molecular complexes rather than true chemical reaction products. This is indicated by their unstable character and the consequent ease of the regeneration of their components, namely urea and the unaltered organic compound.

When thiourea is the complex-forming agent employed the complexes formed thereby are usually. of a substantially different character in that thiourea forms complexes with organic compounds having either a branched configuration zoo-s74) from mixtures containing other types of compounds usually in excess. This latter process is usually employed for the purification of aromatics such as benzene, toluene, etc.

These processes are particularly applicable to the refinement of petroleum or other hydrocarbon mixtures, especially those of unbranched structure (which may be suitably fractionated by complex formation with urea) or hydrocarbons of branched chain or saturated cyclic structure (which readily form complexes with thiourea). The general procedure known to the prior art comprised treatment of such mixtures with a solution of the complex-forming agent. Under these circumstances a mixture of complexes usually was formed. This was due to the characteristics of the complex-forming agents whereby under a given set of operating conditions certain classes of compounds formed complexes with the agents present. Thus, if both isoparafiins and naphthenes were present in a mixture of hydrocarbons, the treatment of such a mixture with thiourea resulted in the formation of complexes of both of these types of hydrocarbons with thiourea. For many purposes the presence of one or another type of compound in admixture with other types is undesirable. If, for example, this process were being used for the preparation of high'octane gasoline, the presence of naphthenes in the product would be undesirable. Therefore, an improvement upon the known process would comprise a revision thereof whereby the final product substantially excluded naphthenes and largely comprises isoparaifins.

In a number of instances a mixture of organic compounds contains a relatively minor fraction of material which will form crystalline complexes with one of the above agents. It has been noted that if only a minor amount of complexes are formed and thereafter separated from the mixture by filtration the thin layer of crystals tends to clog the filter cloth and thus to reduce the efiior a cycloaliphatic structure. Under normal operating conditions. thiourea forms only minor amounts of complexes with organic compounds normal parafpounds.

ciency of the filtration step.

Many mixtures of organic compounds, such as petroleum fractions, contain aromatics such as alkylated benzenes, as well as non-aromatics, including straight-chain compounds, branchedchain compounds, and saturated cyclic com- For many purposes it is advantageous to completely separate the aromatic fraction from other types of materials which may be present, 'Due to similarity of melting points such separations are often difiicult when attempted by fractional distillation. Furthermore, due to the unreactivity of the aromatics toward either of the complex-forming agents discussed above, it has heretofore been difficult to isolate or remove aromati fractions from mixtures to be treated by complex-forming agents or from the raflinate obtained in such operations. By raflinate" is meant that portion of the mixture of organic compounds which fails to form crystalline complexes in the presence of urea or thiourea.

It is an object of this invention to improve extractive crystallization processes, particularly those wherein the complex-forming agent is either urea or thiourea. It is another object of this invention to provide for the production of more highly fractionated materials than those theretofore possible by the subject extractive fractionation processes. It is a further object of this invention to effect the separation of aromatic compounds from other portions of a mixture during a complex forming treatment. Other objects will become apparent during the following discussion.

Now, in accordance with this invention, it has been found that the formation of complexes between urea or thiourea and organic compound mixtures containing both aromatic and nonaromatic fractions may be improved by conducting the complex formation in the presence of a solvent medium for the aromatic fraction, said medium being a non-solvent for the other components of the reaction mixture. By this improvement it is possible to simultaneously separate aromatic constituents from a mixture while other types of separation are being effected with the complex forming agent which is present. Still in accordance with this invention, it is possible thereby to remove the aromatic fraction either prior to or subsequent to complex formation or prior to or subsequent to the isolation of the complexes so formed.

In carrying out the process of the present invention, mixtures 01 organic compounds containing aromatic and non-aromatic fractions may be contacted with a complex-forming agent in the presence of a selective solvent for the aromatic fraction. The mixture may then be passed to a settling tank wherein phase separation occurs, the mixture settling into three or more phases, one of which is a solution of the aromatics. Two other phases which will be present are the crystalline complexes formed between the agent employed and at least a part of the non-aromatic constituents of the mixture of organic compounds as well as a raflinate phase immiscible with the solution of the aromatics, said raflinate being substantially free of any aromatic constituents. After phase separation the three phases may be individually recovered such as by filtration of the crystalline complexes and decanting of the solution of aromatics from the immiscible rafilnate phase.

The selective solvent for aromatic constituents should be substantially a non-solvent for the other components of the reaction mixture and especially for the non-aromatic constituents which may be present as well as for any com- .plexes which may be formed. Such selective solvents include especially alcohols, modified by the addition thereto of substances such as acetamide, phenols, nitrobenzenes, aniline or ethanolamines. Other suitable selective solvents include dimethyl sulfolane, furfural, ,e',p'-dichloroethyl ether, and liquid sulfur dioxide. The alcoholic solutions containing modifying agents such as the ethanolamines, should contain from about to about 50% of such modifiers.

Under these circumstances the alcoholic solutions become substantially non-solvents for nonaromatic constituents of organic compound mixtures.

The selective solvent described above may be added to the mixture of organic compounds prior to contacting with either urea or thiourea. In this case the phase separation may be effected prior to complex formation, the aromatics then never passing through the zone wherein complexes are formed. Alternatively, the phase containing the aromatic constituents may pass through the latter zone and may be separated from the reaction mixture in a subsequent operation.

Alternatively, the selective solvent may be added to the mixture of organic compounds during or after complex formation. It has been found that the presence of substantially inert selective solvents do not appreciably affect the complex formation.

The mixtures of organic compounds which may be treated with urea by the process of the present invention comprise compounds having substantially normal structure and/or compounds having a predominating substituent of substantially normal structure. Conditions may be employed whereby certain normal organic compounds are separated from other normal organic compounds, or from other organic compounds such as isoparafiins, aromatics, naphthenes, etc. The organic compounds of normal structure which may be formed into complexes by the process of the present invention include both saturated and unsaturated compounds, especially the paraffins, and olefins. The normal compounds may be of a number of types, such as hydrocarbons, alcohols, ketones, aldehydes,

esters, amines, amides, sulfides, disulfides, mercaptans, acids, halogenated compounds, ethers, nitro-compounds, silicones, carbohydrates, etc. The hydrocarbons respond especially well to the process of the present invention.

Suitable hydrocarbons which form crystalline complexes with urea include the parafiinic hydrocarbons such as butane, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, etc.

Olefin hydrocarbons which may be treated by the process of the present invention include 1- butene, 2-butene, l-pentene, 2-pentene, l-hexene, 2-hexene, 3-hexene, l-heptene, Z-heptene, B-heptene, l-octene, 2-octene, 3-octene, 4-octene, 2-nonene, 3-nonene, 4-nonene, l-decene, 2-decene, 3decene, 5-decene, l-undecene, 2-undecene, 5-undecene, l-dodecene, G-dodecene, l-tridecene, 6-tridecene, l-pentadecene, 8-heptadecene, 13-heptacosene, etc.

Another class of hydrocarbons which may be formed into complexes with urea, according to the process of the present invention are the normal diolefins such as 1,2-butadiene, 1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, 1,4- pentadiene, 1,2-hexadiene, 1,3-hexadiene, 1,4- hexadiene, 1,5-hexadiene, 2,3-hexadiene, 2,4- hexadiene, 1,3-heptadiene, 1,6-heptadiene, 2,4- heptadiene, 1,4-octadiene, 1,5-octadiene, 1,7- octadiene, 2,6-octadiene, 3,5-octadiene, 1,5-nonadiene, 1,8-nonadiene, 2,6-nonadiene, 1,3-decadiene, 1,4-decadiene, 1,9-decadiene, 2,8-decadiene, 3,7 decadiene, 2,6-dodecadiene, 1,17- octadecadiene, etc.

Normal hydrocarbons of a greater degree of unsaturation which form crystalline complexes with urea'by the process of the present invention include the triolefines, acetylenes, diacetylenes, olefin-acetylenes and the diolefln-acetylenes, including 1,3,5-hexatriene, 1,3,5-heptatriene, 2,3,6- octatriene, ethylacetylene, propylacetylene, butylacetylene, amylacetylene, caprylidene, 4- octyne, diacetylene, propyl-diacetylene, 1,8-nonadiyne, 1-hepten-3-yne, 1,5-hexadien-3-yne, etc. Normal alcohols, especially those having six or more 'carbon atoms, may be treated by the present process to form complexes with urea. These include the aliphatic monohydric alcohols such as hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, dodecyl alcohol, cetyl alcohol, carnaubyl alcohol, and the polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and hexitol.

Ethers of normal structure forming complexes with urea include acetal, dioxane, paraldehyde, crotonyl ether, etc. Aldehydes of normal structure also respond to the process of this invention, including butyraldehyde, valeraldehyde, caproaldehdye, palmitic aldehyde, citral adipaldehyde, etc. Ketones which form urea complexes are exemplified by 3-hexanone, palmitone, 2,3-pentanedione, etc. Acids also may be treated according to the subject process. Typical normal acids forming urea complexes are the normal fatty acids, especially those having four or more carbon atoms, such as butyric, valeric, caproic, enanthylic, caprylic, pelargonic, capric, undecylic, lauric, tridecoic, myristic, pentadecanoic, palmitic, margaric, stearic, etc., acid. Acrylic acids also respond, such as methacrylic acid, tiglic acid, oleic acid, etc. The acetylene acids form urea complexes. These include sorbic and linoleic acids.

Other types of normal-structured compounds which may be treated according to the process of the present invention includes esters, such as amyl acetate, ethyl stearate, etc.; amines such as n-decyl amine, dibutyl amine and triethyl amine; amides, such as stearamide; mercaptans, such as heptyl mercaptan: and other organic compounds of normal structure, including halogenated derivatives of the above compounds, thioalcohols, alkyl hydrazines, thioaldehydes, amino acids, nitroparaffins, etc.

Themixturescontainingtheorganiccompounds of normal structure may be composed solely of mixed normal compounds, or they may contain materials substantially inert toward urea, such as branched parafiins, isoolefins, aromatics, cycloparaffins, etc. Usually, especially when treat- .ing natural products such as petroleum, the inert ingredients are present as isomers of the normal structure compounds, and may occur therewith naturally or by reason of some treatment to which the organic material has been subjected, such as alkylation, cyclization, lsomerization, etc. However, active or inert diluents or solvents may be added to normal organic compounds in order to modify the type and degree of crystallization of the latter with urea. The reason for and use of diluents is discussed hereinafter.

Hydrocarbons which form complexes with thiourea are those having a predominating member which is a substantially branched radical or a naphthene radical, such as alkaryl hydrocarbons wherein at least one alkyl group, is an isoparaifin radical of about six or more carbon atoms.

.Isoparafllns which form complexes with thiourea include isobutane, isopentane, 2,2-dimethylpropane, isohexane, 2,3-dimethylbutane, 2- methylpentane, 3-methylpentane, 2-ethylbutane, 2 ethylpropane, 1,1 dimethylpentane, 1,2 dimethylpentane, 1,3 dimethylpentane, 1,4 dimethylpentane, 2-ethylpentane, 3-ethylpentane, 2-n-propylbutane, 2-isopropylbutane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3- dimethylpentane, 2,2,3-trimethylbutane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 3-ethylhexane, 2,2-dimethylhexane, 2,3-dimethylhexane, 2,4-dim'ethylhexane, 2,5-.dimethylhexane, 3,3 dimethylhexane, 3,4 dimethylhexane, 2,2,3-trimethylpentane, 2,2,4 trimethylpentane, 2,3,3-trimethylpentane, 2,3,4-trimethylpentane, 2,2,3,3,-tetramethylbutane, 2 methyl 3 ethylpentane, 3 methyl-3-ethylpentane, 2 methyloctane, 3-methyloctane, 4-methyloctane, 2,2-dimethylheptane, 2,3 dimethylheptane, 2,4 7 dimethylheptane, 2,5 dimethylheptane, 2,6 dimethylheptane, 3,3 dimethylheptane, 3,4 dimethylheptane, 3 ethylheptane, 4 ethylheptane, 2,2,3 trimethylhexane, 2,2,4 trimethylhexane, 2,2,5 trimethylhexane, 2,3,3 trimethylhexane, 2,3,5 trimethylhexane, 2,4,4 trimethylhexane, 3,3,4 trimethylhexane, 2 methyl 3 ethylhexane, 2 methyl 4 ethylhexane, 2,2,3,3- tetramethylpentane, 3,3 diethylpentane, 2,2- dimethyl 3 ethylpentane, 2,3 din'iethyl 3- ethylpentane, 2,4 dimethyl 3 ethylpentane, 2,2,3,4 tetramethylpentane, 2 methylnonane. 3 methylnonane, 4 methylnonane, 5 methylnonane, 2,2 dimethyloctane, 2,3 dimethyloctane, 2,4 dimethyloctane, 2,5 dimethyloctane, 2,6 dimethyloctane, 2,7 dimethyloctane, 3,3-dimethyloctane, 3,4-dimethyloctane, 3,6-dimethyloctane, 4,5-dimethyloctane, 3-ethyloctane, 2,2,3-trimethylheptane, 2,3,3 trimethylheptane, 2,2,6 trim'ethylheptane, 2,3,6-trimethylheptane, 2,4,4-trimethy1heptane, 2,4,6-trimethy1heptane, 3,3,5-trimethylheptane, 3-methy1 3 ethylheptane, 4 propylheptane, 4 isopropylheptane, 2,2,3,3-tetramethylhexane, 2,2,3,4 tetramethylhexane, 2,2,5,5-tetramethylhexane, 2,2-dimethyl- 4-ethylhexane, 3,3,4,4-tetramethylhexane, 3,3- diethylhexane, 3,4 diethylhexane, 2,2,4 trimethylheptane, 2,2,4,5 tetramethylhexane, 2- methyl 5 ethylheptane, 4-methyldecane, 5- methyldecane, 2,3-dimethylnonane, 2,4-dimethylnonane, 2,5 dimethylnonane, 2,6 dimethylnonane, 3,3-dimethylnonane, 4-ethylnonane, 5--

ethylnonane, 2,3,7 trimethyloctane, 2,4,7 trimethyloctane, 2,2,3,3-tetramethylheptane, 2,2,4- trimethyloctane, 2,2,4,6 tetramethylheptane, 2,2,4,5-tetramethylheptane, 3 methylundecane, 4-methylundecane, 2,3-dimethyldecane, 2,5-dimethyldecane, 2,6-dimethyldecane, 2,9-dimethyldecane, 3-ethyldecane, 5 propylnonane, 2,2,7,7- tetramethyloctane, 2,3,6,7 tetramethyloctane, 2,4,5,7-tetramethyloctane, 3,3,6,6-tetramethyloctane, 2-methyl 5 propyloctane, 3,6-diethyloctane,2,6-dimethyl-3-isopropylheptane,4,5-diethyloctane, 2,2,4,6,6-pentamethylheptane, 2,2,4,4- fi-pentamethylheptane, 5-methyldodecane, 2,10- dimethylundecane, 2,5,9-trimethyldecane, 4-propyldecane, 4-ethylundecane, 5-butylnonane, 2,11- dimethyldodecane, 4,5-diisopropyloctane, 2,7- dimethyl-4,5-diethyloctane, 4 propylundecane, 2,7-dimethyl-4-isobutyloctane, 2,6,l0-trimethyldodecane, 2,6,11-trimethyldodecane, 6-methyl-7- ethyldodecane, 5 propyldodecane, 6 propyldodecane, 4-methyl-G-propylundecane, 6,9-dimethyltetradecane, 7,8-dimethyltetradecane, 3-ethyltetradecane, 5,7-diethyldodecane, 2,6,7,11-tetrapylcyclobutane, 1,2-dimethyl-3,4-diethylcyclobu- 1 tane, 1,1,2,2-tetramethyl-3,4-diisopropylcyclobutane, cyclopentane, methylcyclopentane, 1,1-dimethylcyclopentane, 1,2-dimethylcyclopentane, 1,3 dimethylcyclopentane, ethylcyclopentane, propylcyclopentane, isopropylcyclopentane, 1,1,3- trimethylcyclopentane, l-methyl 2 ethylcyclopentane, 1-methyl-3-ethylcyclopentane, butylcyclopentane, isobutylcyclopentane, 1-methyl-2- propylcyclopentane, 1-methyl-3-propylcyclopen tane, 1,3-dimethyl-2 ethylcyclopentane, 1,3-dimethyl-5-ethylcyclopentane, 1,1-diethylcyclopentane, amylcyclopentane, isoamylcyclopentane. 2-cyclopentylpentane, 1-methyl-3-butylcyclopentane, 1-methyl-2,5-diethylcyclopentane, 1,2,3- trimethyl-4-isopropylcyclopentane, heptylcyclopentane, cyclohexane, methylcyclohexane, ethyl-- cyclohexane, 1,1-dimethylcyclohexane, 1,2-dimethylcyclohexane, 1,3 dimethylcyclohexane, 1,2,3-trimethylcyclohexane, 1,3,5-trimethylcyclohexane, butylcyclohexane, l-methyli-ethylcyclohexane, 1-methyl-3-propylcyclohexane, l-methyl-3-isopropyl-cyclohexane, 1,3-dimethyl-5-ethylcyclohexane, 1,3-diethylcyclohexane, amyloyclohexane, pentamethylcyclohexane, 1,2-dimethyl-3,G-diethylcyclohexane, 4-cyclohexylheptane, 3-cyclohexyl- 3 -ethylpentane, triisopropylcyclohexane, 2,8-dimethyl-5-ethy1- 5 -cyclohexylnonane, l-methyl-i-isopropyl 2 dodecyclohexane, octadecylcyclohexane, propylcycloheptane, etc.

The ratio of the complex-forming agent to active organic compounds will vary with the type of mixture to be treated and with the conditions of complex formation. For example,'the extractive fractionation may be carried out with the intention of removing from the mixture the maximum amount possible of the compounds of normal structures present. In this particular case, it is preferred practice to contact the mixture with urea employed in an amount in excess of that necessary for complete complex formation.

Complexes may be formed having varying amounts of the complex-forming agent combined with the active organic compound. When the temperature or other conditions during complex formation are such that about 3 mols of the agent combined with about every 4 carbon atoms of the active organic compound-it is preferred practice to contact the active organic compound with an amount of the agent somewhat in excess of this ratio.

The formation, separation and purification of the complexes having been accomplished as described hereinbefore, there remains the step of decomposing the complexes in order to recover the active organic compounds present therein.- While a number of methods have been found for effecting "such a decomposition or regeneration, the following methods have been found to be the most satisfactory for use when carrying out the process of the present invention:

A. Simple distillation.

3. Steam distillation.

0. Application of a solvent for the complexforming agent.

D. Heating.

E. Application of a solvent for aparticular fraction of the regenerated organic compounds.

The complexes, as has been pointed out hereinbefore, are relatively unstable formations which appear to be loose combinations involving hydrogen bonding or some form of molecular attraction, the exact nature of which has not been deduced. It has been found that due to their unstable character, splitting into the component parts of the complex may be readily accomplished, the complex-forming agent and the organic compounds in complex combination therewith separately recovered in their original state.

By subjecting the complexes to distillation. simultaneous destruction of the complex and fractionation or the organic compounds regenerated therefrom may be accomplished. The distillation may take place under normal or reduced pressures and the temperature and pressure are so adjusted that the complexes-are readily destroyed and the compounds regenerated therefrom are distilled into fractions which can be utilized for the purposes considered herein. For example, if it is desired to enrich the feed with low boiling normal hydrocarbons, complexes of urea and a mixture of normal hydrocarbons may be decomposed by distillation and the distillant may be recycled to the mixer.

Steam distillation is a refinement of the above process and the principle of regeneration and fractionation applies here as well. Steam distillation is preferable where the organic compounds to be regenerated are of such high boiling point that their distillation would be accomplished by substantial decomposition.

A further type of regeneration comprises addition of a solvent for the complex-forming agent such as water or alcohol to the complex and the application of heat to facilitate the regeneration. By this means the regenerated organic compounds separate from the solution of the complex-forming agent and subsequently may be fractionated by normal purification or fractionation procedures.

A more preferred type of regeneration comprises the addition of a solvent for one or more fractions of the organic compounds to be regenerated from the complexes. When such a mixture is heated the complex decomposes, thus regenerating the organic compounds and complexforming agents and, in presence of such a solvent, a solution of part of the regenerated organic compounds which form and may be readily separated from the insoluble fractions which are present. Hence, fractionation according to solubility may be readily accomplished.

Fractionation by simple heating is satisfactory for some purposes. Following the regeneration by such means it is usually necessary to purify or fractionate the regenerated compounds and the regenerated complex-forming agent for further use.

The process of the present invention is useful for the preparation of high octane gasoline for minutes the reaction mixture was allowedto settle into three phases. The crystalline complexes so formed were removed by filtration and the two liquid phases were separated by decantation. One of the liquid phases comprised the alcoholic solution of acetamide containing dissolved therein substantially all of the alkylated benzenes in the original gasoline. The other liquid'phase comprised the raifinate and contained substantially no aromatics but the entire quantity of iso-octane present in the original gasoline. The crystalline complexes were heated in the presence of water to about 75 C., at which temperature the complexes decomposed to yield the normal octane originally present in the gasoline and an aqueous solution of urea and two phases were separately recovered by decantation.

I claim as my invention:

1. In the process for the fractionation of a liquid mixture of hydrocarbons, wherein crystalline complexes are formed between a fraction thereof and an agent of the group consisting of urea and thiourea, said mixture also containing an aromatic fraction and a non-aromatic inert fraction not, forming complexes with the agent under the i'ractionating conditions, the improvement which comprises conducting said complex formation in the presence of a solvent, said solvent being a solvent for the aromatic fraction of the mixture and a non-solvent for the nonaromatic inert fraction and the crystalline complexes, thereby forming three phases, a liquid non-aromatic inert fraction phase, a liquid solvent phase containing the dissolved aromatic fraction and the solid crystalline complex phase, and separating said phases.

2. In the process for the fractionation of a mixture of petroleum hydrocarbons, wherein crystalline complexes are formed between a fraction thereof and urea, said mixture also containing an aromatic fraction and a non-aromatic inert fraction not forming complexes with urea under the fractionating conditions, the improvement which comprises conducting the complex formation in the presence of an alcoholic solution of acetamide, thereby forming three phases, a liquid non-aromatic inert phase, a liquid solvent phase containing the aromatic fraction dissolved in the alcoholic acetamide solution and the solid crystalline complex phase, and sepa- 10 rately recovering the complexes, the inert nonaromatic fraction and the alcoholic acetamide solution of urea, acetamide and aromatic fraction.

3. The process which comprises treating a mixture of petroleum hydrocarbons containing aromatic and substantially straight-chain hydrocarbons with urea, whereby complexes are formed between urea and at leastpart of said straight-chain hydrocarbons, in the presence of an alcoholic solution of acetamide which is a solvent for the aromatic fraction but a non-solvent for the remainder of the reaction mixture, whereby a solution of said aromatic fraction is formed, and separately recovering the complexes prior to separating the solution of aromatics from the remaining portion of the non-aromatic hydrocarbons.

4. The process which comprises treating a mixture of alkylated benzenes, iso-octane and normal octane with a saturated alcoholic solution of urea having 20% by weight of acetamide dissolved therein, whereby crystalline molecular complexes of urea and normal octane formed, and separately recovering said complexes, isooctane and alcoholic solution of urea, acetamide and alkylated benzenes.

5. In the process for the fractionation of a liquid mixture of petroleum hydrocarbons wherein crystalline complexes are formed between a fraction thereo fand thiourea, said mixture also containing an aromatic fraction and a non-aromatic-inert fraction not forming complexes with thiourea under the fractionating conditions, the improvement which comprises conducting said complex formation in the presence of an alcoholic solution of an ethanolamine which is a solvent for the aromatic fraction but a non-solvent for the remainder of the reaction mixture, thereby forming three phases, a liquid non-aromatic inert fraction phase, a liquid solvent phase containing the aromatic fraction dissolved in the alcoholic ethanolamine solution and the solid crystalline complex phase, and separating said phases.

' LLOYD C. FET'IERLY.

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

UNITED STATES PATENTS Number Name Date 2,081,524 Barnes May 25, 1937 2,396,303 Cummings et al. Mar. 12, 1946 FOREIGN PATENTS Number Country Date 459,189 Great Britain Jan. 4, 1937 466,980 Great Britain July 9, 1937 OTHER REFERENCES Beng'en, Tech. 011 Mission, Reel 143, 5 pages.

Claims (1)

1. IN THE PROCESS FOR THE FRACTINATION OF A LIQUID MIXTURE OF HYDROCARBONS, WHEREIN CRYSTALLINE COMPLEXES ARE FORMED BETWEEN A FRACTION THEREOF AND AN AGENT OF THE GROUP CONSISTING OF UREA AND THIOUREA, SAID MIXTURE ALSO CONTAINING AN AROMATIC FRACTION AND A NON-AROMATIC INERT FRACTION NOT FORMING COMPLEXES WITH THE AGENT UNDER THE FRACTIONATING CONDITIONS, THE IMPROVEMENT WHICH COMPRISES CONDUCTING SAID COMPLEX FORMATION IN THE PRESENCE OF A SOLVENT, SAID SOLVENT BEING A SOLVENT FOR THE AROMATIC FRACTION OF THE MIXTURE AND A NON-SOLVENT FOR THE NONAROMATIC INERT FRACTION AND THE CRYSTALLINE COMPLEXES, THEREBY FORMING THREE PHASES, A LIQUID NON-AROMATIC INERT, FRACTION PHASE, A LIQUID SOLVENT PHASE CONTAINING THE DISSOLVED AROMATIC FRACTION AND THE SOLID CRYSTALLINE COMPLEX PHASE, AND SEPARATING SAID PHASES.