US3029300A

US3029300A - Separation of organic compounds

Info

Publication number: US3029300A
Application number: US26489A
Authority: US
Inventors: William D Schaeffer
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1960-05-03
Filing date: 1960-05-03
Publication date: 1962-04-10
Anticipated expiration: 1979-04-10

Description

3,029,300 SEPARATION F ORGANIC COMPOUNDS William D. Schaeffer, Pomona, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed May 3, 1960, Ser. No. 26,489 1S Claims. (Cl. 2611-674) rIhisinvention relates to methods for separating difficultly separable compounds such as isomers, e.g., xylenes and the like, by selective clathration with heterocyclic nitrogen base Werner complexes. More particularly, the invention is concerned with an improvement in those clathration systems which employ aqueous alkaline solvent media in the clathration and/or declathration steps, and especially wherein liquid-liquid phase separations are relied upon for recovering the respective clathrated and non-clathrated feed components from the aqueous alkaline media. In brief, it has been found that certain disadvantageous features of these aqueous alkaline clathration systems can be avoided or greatly mitigated by adding to the aqueous alkaline media a substituted or unsubstituted ammonium salt which is soluble in the alkaline medium. The addition of these ammonium salts is found to give several important advantages, principally, (l) an improvement in the coefficient of solubility of the 'Werner complex in the alkaline solvent media, (2) an improvement in the solvent selectivity of the alkaline solvent for the heterocyclic nitrogen base component of the Werner complex, thereby reducing the loss of heterocyclic base to the separated product streams, and (3) elimination of metal hydroxide precipitation in the alkaline system. To obtain all of these advantages to the maximum extent, the ammonium sait employed should be a salt of the same anion which occurs in the metal salt component of the Werner complex used, eg., where a Werner complex of nickel thiocyanate is employed, the preferred ammonium salt would be a thiocyanate.

More specifically, the process of this invention is an improvement over the basic processes described in my prior applications, Serial No. 862,223, filed December 28, 1959, and Serial No. 3,058, filed January 18, i960. Brieiiy, the process of Serial No. 862,223 involves carrying out the clathration and declathration steps in aqueous ammonia, or an aqueous volatile amine solution, while the process of Serial No. 3,058 involves carrying out the clathration in an aqueous alkanolarnine sorution. While both of these processes offer important advantages over previously known techniques, they have been found to entail certain diiiiculties. The clathration step is ordinarily effected by iirst dissolving the Werner complex in the alkaline solvent (hereinafter called the primary solvent), adding the feed mixture, and then either reducing the temperature or removing volatile nitrogen base from the solution, or both, to thereby effect precipitation of the clathrate. The declathration step is carried out by redissolving the separated clathrate in the alkaline solvent at a relatively higher temperature. Unless a large temperature differential is employed between the clathration and declathration steps, or unless substantially all of the ammonia or volatile amine is removed during clathration, some Werner complex will remain in solution throughout, and will not be eifectively utilized. By the process of this invention, a more complete precipitation of Werner complex is obtained during clathration at any given temperature and nitrogen base concentration, than can be obtained without the added ammonium salt. Hence, the efficiency of the Werner complex is materially increased in terms of pounds of Werner complex required in the system per pound of feed throughput.

A second difiiculty involved in the foregoing processes `revolves about the liquid-liquid recovery systems for separating non-clathrated feed components from the primary solvent, and for recovering the clathrated feed component by redissolving the clathrate in the primary solvent and effecting a liquid-liquid phase separation.. Ordinarily, in each of these phase separations, a secondary solvent is employed which is miscible with the feed components, immiscible with the primary solvent, and a relatively poor solvent for the heterocyclic base of the Werner complex. This materially reduces the loss of heterocyclic base to the product streams, Nevertheless, the heterocyclic-base component of the dissolved Werner complex will still distribute itself to some extent between the respective phases, and hence the raffinate and extract product streams will be contaminated to a greater or lesser extent with the heterocyclic base. The process of this invention provides a means for substantially increasing the selectivity of the primary solvent for the heterocyclic base, as opposed to the extract and/or raffinate product streams, and the secondary solvents. This materially decreases the expense and facilities required for recovering heterocyclic base from the extract and raliinate product streams.

The metal salt component of the Werner complexes is always a heavy metal salt which, in aqueous alkaline solutions, will precipitate insoluble metal hydroxide to a greater or lesser extent. This precipitated metal hydroxide tends to settle out at various points in the process and may clog valves, pumps, filters and the like. By adding ammonium salts as described herein, it is found that precipitation of metal hydroxide is substantially completely eliminated.

Eliminating or minimizing the foregoing ditiiculties therefore constitute the principal objectives of this invention, in addition to the overall objective of providing a Werner complex clathration system which operates with maximum efficiency and a minimum of expense.

Reference is now made to the accompanying drawing which is a iiowsheet illustrating more concretely the basic steps of the process. lIn the clathration step, (I) the feed mixture is introduced through line 2, and a recycle solution of Werner complex and ammonium salt dissolved in the primary solvent is introduced through line 4. `Small makeup quantities of ammonium salt, Werner complex and primary solvent may be admitted through lines 6, 8 and 1li respectively. Clathration is effected in this step by agitating the mixture, and either reducing the temperature or removing sufficient volatile nitrogen base therefrom, or both, to cause precipitation of the solid clathrate. lt is ordinarily preferred to effect the clathration at moderate temperatures of about 10"- |70 C., preferably between about 0 and 50 C. The solid clathrate contains the more readily clathrated components of the feed mixture, while the less readily clathratable components will remain dissolved or dispersed in the primary solvent phase. The resulting slurry is then transferred via line 12 .to clathrate separation step II. This may involve a simple filtration, settling, or centrifuging, or any other suitable method for separating a liquid phase from a crystalline solid phase. The liquid phase from step II is sometimes hereinafter referred to as mother liquor.

The resulting liquid phase filtrate is then transferred via line 14 to rafnate separation step III wherein the non-clathrated portion of the feed is allowed to stratify and separate. Normally, at this point, it is preferred to add (via line 16) the secondary solvent which preferentially dissolves the non-clat'nratable feed components, and has a relatively low selectivity for the heterocyclic nitrogen base. Where the feed is composed of aromatic hydrocarbons, the secondary solvent is preferably a paranic or naphthenic hydrocarbon such as pentane, heptane, octane, nonane, or mixed hydrocarbons such as alkylate fractions. The solution of non-clathrated feed components in the secondary solvent is then withdrawn via line I3 and sent to secondary solvent recovery step IV, which may be for example a fractional distillation wherein secondary solvent plus any dissolved heterocyclic base is distilled overhead and returned to step IV via line 16, and the non-clathrated feed components are recovered as bottoms via line Z0.

The stripped primary solvent phase from step III (sometimes hereinafter referred to as lean mother liquor) is then transferred via line 22 to clathrate dissolving step V, to which the solid clathrate from step II is also transferred via line 24. In this dissolving step, the solid clathrate is redissolved in the primary solvent phase, either by raising the temperature to e.g., 50-l50 C., or by adding more of the volatile amine or ammonia which was removed in step I, or both. Upon dissolution of the clathrate, the clathrated component of the feed ordinarily forms a separate liquid phase. This two-phase mixture is then transferred via line 26 to extract separation step VI, wherein the clathrated feed components are separated by settling and decanting, or any other desired method. Here again, the separation may be facilitated by adding a secondary solvent (via line 23), which is preferably the same as the secondary solvent ernployed in raffinate separation step III. The solution of clathrated feed components in the secondary solvent is removed via line 30 and sent to secondary solvent recovery step VII, which again may be a fractional distillation wherein secondary solvent plus dissolved heretocyclic base is distilled overhead and returned to step VI via line 2S, and the clathrated feed components are recovered as bo-ttoms via line 32.

It is the foregoing extract separation step VI that diffculty is most often encountered in recovering heterocyclic base from the extract product. Since the primary solvent is rich in dissolved Werner complex at this stage, the concentration of dissolved heterocyclic base is larger than was present in raffinate separation step III. Hence the product in line 30 is relatively rich in heterocyclic base. This heterocyclic base is ordinarily recovered by azeotropic distillation along with `the secondary solvent.

This is entirely feasible, but sometimes will entail the use r of excessively large volumes of secondary solvent in order to obtain complete recovery of heterocyclic base. This problem is greatly alleviated where an ammonium salt, preferably a thiocyanate, is dissolved in the primary solvent phase, since this tends to decrease the amount of heterocyclic base which is extracted by the secondary solvent.

The primary solvent phase separated in extract separation step VI contains substantially all of the original Werner complex and ammonium salt which was used in step I. cycled to clathration step I for reuse as above described.

The primary solvents employed herein are made up of water plus any suitable water-soluble organic or inorganic nitrogen base which is more strongly basic than the heterocyclic nitrogen base of the Werner complex. The ratio of nitrogen base/water will vary widely depending upon the Werner complex used and the particular nitrogen base.' Generally, the primary solvent will It is hence withdrawn via line 4 and re-V contain between about l0% and 90% by weight of nitrogen base. The ratio should be such as to provide the desired differential solubility of Werner complex therein, at the respective clathration and declathration temperatures. When using ammonia, suitable concentrations may range between about 10% and 30% by weight in the clathration step and about 0% to 20% in the declathration step. Operative ratios of ethanolamine (NHZCHgCHZoH) may range between about 10% and 70% by weight in both stages. In all cases, it is preferred to use sutcient water to render the feed mixture substantially insoluble in the primary solvent.

Other alkanolamines which may be used in place of mono-ethanolamine include for example, diethanolamine, triethanolamine, Z-amino-n-butanol, 2-amino-2-methyl-lpropanol, Z-methylamino ethanol, Z-ethylamino ethanol, 2-arnino-2-ethyl-L3propanediol, 2-amino-2-methyl-1,3 propanediol, and the like. In general any lower alkanolamine containing from two to about ten carbon atoms, from one to three amino groups, and from one to three hydroxyl groups may be employed, including primary, secondary, and tertiary amines. The operative ratios of alkanolamine in the primary solvent may vary widely, e.g., from about 2 percent to 75 percent by weight, the remainder being water. Preferred ratios generally fall Within the range of about l0 percent to 70 percent. The greater the concentration of alkanolamine in the solvent, the greater will be the solubility of Werner complex and feed mixture therein.

Other volatile bases (boiling below water) which may be used in place of ammonia include for example, methylarnine, dimethylamine, trimethylamine, methyl-ethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, iso- `amylamine, and the like.

In general, any water-soluble nitrogen base having a dissociation constant greater than about 10-5, and greater than the dissociation constant of the heterocyclic base used in the Werner complex, may be used as the alkaline component of the primary solvent.

The operative ammonium salts which may be used herein comprise both organic and inorganic s alts. Suitable inorganic salts include for example ammonium thiocyanate, ammonium chloride, ammonium sulfate, arnmonium nitrate, and the like. Suitable organic salts include ammonium acetate, ammonium citrate, ammonium'l oxalate, ammonium glycolate, ammonium succinate and the like. Suitable substituted ammonium salts include methyl ammonium thiocyanate, dimethyl ammonium' thiocyanate, ethyl ammonium chloride, ethyl ammonium sulfate, ethanolammonium thiocyanate, ethanolammonium chloride, ethanolammonium sulfate, ethanolammoni-V um cyanate, ethanolammonium cyanide, diethanolammonium thiocyanate, ethanolammonium acetate, and the like. These salts may be used in proportions ranging between about 1% and 40% by weight of the primary solvent, depending upon relative solubilities. Any amounts are effective in some degree, and the preferred ratios generally range between about 15% and 30% by weight.

As previously indicated, it is preferred to use an arnmonium salt, the anion of which is the same as the anion of the metal salt used in the Werner complex. Since the preferred salts in the Werner complexes are the thiocyanates, it is therefore preferred to use ammonium thiocyanates. It is further preferred to use an ammonium saltof the same nitrogen base used in the primary solvent. Thus, where ethanolamine is used in the primary solvent, the preferred salt would be ethanolammonium thiocyanate (ethanolammonium thiocyanate is conveniently prepared by simply boiling an aqueous solution of ammonium thiocyanate and ethanolamine, whereby ammonia is continuously volatilized from the mixture).

The Werner-type complexes employed herein are made up of at least three components. The fundamental unit is a water-soluble salt of a metal having an atomic number above l2 which is capable of form-ing coordinate complexes of the Werner type. This includes primarily the metals of groups iB, IIB, VEB, VHB, and VIH of the periodic table, such for example as iron, cobalt, nickel, copper, zinc, cadmium, silver, manganese, chromium, mercury, and molybdenum. Aluminum may also be used in some instances. The preferred metals lare those of atomic numbers to 28 inclusive, i.e., manganese, iron, cobalt and nickel. f

The anion of the metal salt may comprise any acidforming negative radical, the salts of which will form relatively water-insoluble Werner complexes with heterocyclic nitrogen bases. The preferred anions are polyatomic monovalent anions, such as thiocyanate, isothiocyanate, azide, cyanate, isocyanate and cyanide. Other operable anions include formate, acetate, propionate, and the like.

The second major component of the Werner complexes consists of one or more heterocyclic nitrogen base or bases, which Vare bound to the central metal atom through coordinate bonds. The operative complexes are mainly of the tetraand hexe-coordinate types, wherein the metal atom is coordinated with four or six atoms of basic nitrogen. The heterocyclic base should be selected so as to give a maximum selective absorption for the particular compound which is to be absorbed into the crystal lattice of the complex. For example, if it is desired to absorb p-xylene, a very suitable nitrogen base is gamma-picoline. Not all nitrogen bases are equally effective in forming complexes which will absorb the desired component. For example, the beta-picoline complex with nickel thiocyanate is not as effective as the gamma-picoline complex for absorbing para-xylene, presumably because of the steric eiects of the 3-methyl group. However, the betapicoline complex may be used advantageously for absorbing other compounds. The heterocyclic base should therefore be selected by a judicious combination of theoretical reasoning and actual testing of the complexes with the particular mixture to be separated. The over-all molecular dimensions of the heterocyclic base should preferably approximate the molecular size of the compound `to be absorbed in the complex.

In general, any heterocyclic nitrogen base may be employed which is sufficiently basic to form coordinate complexes with the abovedescribed salts, but is weaker as a base than the nitrogen base which is to be used in the primary solvent. This includes monocyclic and polycyclic compounds, wherein at least one of the heterocycles contains from one to three hetero-N atoms. ln overall size, the nitrogen base may contain from three to about thirty carbon atoms, preferably from four to fifteen. lnterfering functional groups such as COOH should be absent, but other more neutral, relatively non-coordinating functional groups may be present such as halogen, hydroxyl, nitro, alkoxy, aryloxy, amino, cyano, carboalkoxy, alkanoyl, acetyl, etc., provided such functional groups are compatible with any functional groups present in the mixture of compounds to be separated. Examples of suitable bases include pyridine, substituted pyridines, substituted pyrroles, piperidines, substituted piperidines, and the like.

A particularly preferred class of heterocyclic bases are the resonance-stabilized bases which contain one to three, but preferably one, hetero-N atoms. Suitable examples are pyridine, the picolines, pteridine, triazole, quinoline, the quinaldines, isoquinoline, pyrimidine, pyrazine, pyridazine, and substituted derivatives of such compounds. Of this preferred class, a sub-group which is particularly versatile and useful comprises the substituted pyridines, and especially the 4-substituted, the 3-substituted, and the 3,4 disubstituted pyridines. These compounds form rela tively stable Werner complexes capable of selectively forming clathrates stable at room temperatures with a 6 wide ,variety of aromatic compounds. tuted pyridines comprise the following:

4-methyl pyridine 4-n-propyl pyridine 4-isopropyl pyridine 4-n-butyl pyridine 4-n-hexyl pyridine 4-vinyl pyridine 4-fluoro pyridine 4-chloro pyridine 4-bromo pyridine 1f-hydroxy pyridine 4-hydroxymethyl pyridine 4-methoxy pyridine 4-amino pyridine Methyl isonicotinate 4-cyano pyridine 4-acetyl pyridine 4-chloromethyl pyridine S-methyl pyridine 3-ethyl pyridine 3-m-propyl pyridine 3isopropyl pyridine 3-nbutyl pyridine 3-vinyl pyridine 3-chloro pyridine 3hydroxy pyridine 3-methoxy pyridine 3-acetyl pyridine 3-cyano pyridine Ethyl nicotinate 3,4-dirnethyl pyridine 3,4-diet'nyl pyridine S-rnethyl, Ai--ethyl lpyridine 4-methyi, 3-ethyl pyridine 4-methyl, 3nhexyl pyridine 4-methyl, S-cyano pyridine 4-chloro, 3-methyl pyridine 1f-acetyl, 3-methyl pyridine Ll-methoxy, 3-ethyl pyridine Isoquinoline Many other similar examples could be cited, as will be apparent to those skilled in the `art, and the complexes may include only one such base, or a mixture of two or more may be employed, in which case a mixed com plex may be formed.

The preferred Werner complexes of monovalent anion salts of this invention may be designated by the following general formula:

wherein X is the metal -atoin as above defined, Z is the heterocyclic nitrogen base, A is the anion as above defined, y is a number from 2 to 6, and n is a number from l to 3.

Examples of suitable complexes which may be employed are as follows:

[Ni(y-picoline)4(SCN)2] [CoM-picoline) l,(SCN)2] [Mn('ypicoline)4(SCN)2] [Fe (fy-picoline)4(SCN)2] [Co (pyridine)4(OCN)2] [Fe(pyrr01e)4(SCN) 2] [Co(fy-picoline)4(CN) 2] [Ag(fy-picoline)2(NNN)] [Ni ('y-picoline 4 (NNN) 2] [Ni 4-n-propylpyridine 4( SCN 2] [Ni(isoquinoline) 4(SCN)2] [Ni(4ethylpyridine) l,(SCN)2] [lt/in(isoquinoline)4(SCN)2] Obviously, many other complexes similar to the above could be employed, not all or" which would give optimum separation of all mixtures but which should be selected to meet the specific peculiarities ofthe mixture concerned.

Suitable substi- Y The amount of complex to be employed, relative to the feed mixture, depends upon its specific capacity for absorbing the particular feed component concerned, and also upon the proportion of that component present in the original mixture, as Well as upon the temperature of clathration. The complexes are found in general to be capable of absorbing between about to 79% by weight of absorbable compounds. Optimum eiiciency may require that more or less than this stoichiomet'ric amount of complex be employed, depending upon its relative capacity for other components in the mixture to be resolved. In general, the amount of complex to be ernployed m-ay vary between about 0.25 and 20 parts by weight per part of the feed component to be clathrated. Smaller proportions of complex will generally yield a purer extract, while the larger proportions'result in more complete recovery of absorbable components from the feed mixture.

The term clathrating as used herein is intended to mean any absorption or adsorption by the herein described Werner complexes of a sorbable organic compound, regardless of the mechanism by which such sorption may take place. The terms absorbate or extract refer to the total feed component which is absorbed into the clathrate, thus excluding the nitrogen bases, which are bound by coordinate valences. The term aromatic is intended to include all resonance-stabilized, cyclic, unsaturated compounds, which exhibit predominantly substitution rather than addition reactions toward electrophilic reagents (cf. Remick A. E., Electronic Interpretations of Onganic Chemistry, lohn Wiley, N.Y. 1943).

A wide variety of feed, mixtures may be resolved by the methods described herein, i.e., substantially any mixture of organic compounds wherein the components differ in molecular configuration, and preferably wherein at least one component is substantially aromatic in character. By substantially aromatic is meant that at least about 20% of the carbon atoms in the molecules to be clathrated are present as digits of an aromatic ring, the term aromatic having the meaning hereinafter specified. Any remaining carbon atoms may be present as saturated or unsaturated aliphatic side-chains, or saturated or un saturated non-aromatic ring systems. Such compounds may contain a total of from 4 to 60 carbon atoms, preferably from 6 to 20.

A difference in molecular conliguration, as referred to herein, means a difference in molecular size or shape as a result of dilerences in (l) the number of atoms per molecule, and/or (2) the arrangement of atoms within the respective molecules, and/ or (3) the size of the atoms present in the respective molecules.

Any number and type of. functional groups may be present in the feed components, provided that such groups are compatible with the Werner complex employed, i.e., that such groups do not change the chemical character of the Werner complex. Generally excluded are those compounds which are either so acidic as to decompose the Werner complex, or so basic as to displace the heterocyclic base from the Werner complex. In general, the pH of an aqueous mixture of the compounds to be separated should fall between about 4 and the pH of an aqueous solution of the heterocyclic base employed in the Werner complex. When the compounds are too acidic or too basic, it is feasible to prepare neutral derivatives thereof, eg., salts, esters, ethers, amides, etc., and then effect separation of the neutral derivatives.

Whenever any mixture of compounds is so incompatible with the Werner complex that the normal clathration procedures herein described result primarily in chemical decomposition, change, or disruption of the Werner complex, as opposed to the desired clathration, the contacting of such lmixtures with the Werner complex is by delinition excluded from the temi clathration as used herein and in the claims. Functional groups which generally do not disrupt the normal clathration reaction, and

may hence be present inthe feed components are as fol -NCQ -COOR, -COR, CSO-metal, -SR, -CONH2, wherein R is a hydrocarbon radical. Many groups of a similar nature may be present.

Examples of mixtures which may be separated herein include the following, but these examples are by no meansy exhaustive:

(A) Hydrocarbon mixtures:

o-Ethyl toluene p-Ethyl toluene o-Ethyl toluene m-Ethyl toluene p-Ethyl toluene m-Ethyl toluene Mesitylene Pseudocumene Cumene Mesitylene Cumene Pseudocumene p-Cymene p-Diethylbenzene m-Cymene Mesitylene Prehnitene Durene Durene Isodurene Prehnitene Isodurene Cyclohexane Benzene Methyl-cyclohexane Toluene Benzene n-Heptane Benzene 2,3-dimethy1 pentane Methyl cyclopentane Benzene Picene Chrysene Picene l,2,5,6-dibenzanthracene Tetralin Naphthalene Tetralin Decaln Diphenyl Diphenyl methane Anthracene Phenanthrene (B) Hydrocarbon-1101141 ydrocarbon mixtures:

2,5 -dimethyl furan Benzene Anthraquinone Anthracene Benzene Thiophene Z-methyl thiophene Toluene o-Xylene Thiophene Naphthoquinone Naphthalene (C) Non-hydrocarbon mixtures.'

o'Methyl toluate p-Methyl toluate o-Methyl toluate m-Methyl toluate p-Methyl toluate m-Methyl toluate 1-nitro naphthalene 2-nitro naphthalene l-amino naphthalene Z-aminonaphthalene Aniline Nitro-benzene nate 2-naphthol-8-sodiurn sulfu- Hate p-Amino benzaldehyde o-Amino benzaldehyde Benzidine p-Semidine 2,4-dinitro-chloro-benzene 2,5dinitro-chlorobenzene Isosafrol Piperonal 9 o-Toluidine o-Vanillin p-Toluidine I sovanillin o-Nitrotoluene o-Vanillin p-Nitrotoluene Vanillin o-Dichlorobenzene p-Dichlorobenzene o`Phenylene diamine p-Phenylene diamine o-Chlortoluene p-P'nentidine p-Chlorotoluene Phenacetin o-Methyl anisole Isocugenol p-Methyl anisole Vanillin Coumarin p-Methyl thiophenol Vanillin m-Methyl thiophenol Furan Diazoaminobenzene Thiophene p-Aminoazobenzene mis-dimethyl @maine Aniline Methyl benzoate Ethyl benzoate Terephthalonitrile Isophthalonitrile Sodium p-cresylate Sodium m-cresylate Potassium terephthalate Potassium isophthalate Dimethyl isophthalate Dimethyl terephthalate Dimethyl isophthalate p-Tolunitrile Dimethyl orthophthalate m-Tolunitrile Sodium o-toluene sulfonate Methyl salicylate Sodium p-toluene sulfonate Methyl p-hydroxy bcnzoate Sodium-l-methyl3naphtha p-Methyl acetanilide lene sulfonate m-Methyl acetanilide Sodium-l-methyl-4-naphtha- P Aminobenzenesulfom lene sulfonate amide Estriol i m-Aminobenzenesulfon- Estrone amide Estriol Sodium anthranilate Estradiol Sodium phthalamate Picolinic acid Alpha-picoline Nicotinic acid Beta-picoline Thymol 2,4-lutidine Menthol 2,6-lutidine It will be noted that some of the foregoing compounds are fairly soluble in water, and thus in the primary clathration solvent. In general this does not affect the clathration step, but may necessitate using different techniques for recovering the rainate and extract products from aqueous solution. Conventional techniques such as solvent extraction, distillation, fractional crystallization, chemical scavenging, precipitation or the like may be utilized for this purpose, the choice of the particular 1 u EXAMPLE 1 This example illustrates the benecial effect of the added ammonium saltsl in preventing precipitation of metal hydroxide in the alkaline clathration system. Several diierent clathration solvent compositions containing dissolved Ni(4methylpyridine)4(SCN)2 were heated for various lengths of time and then examined for Ni(OH)2 precipitation. The results were as follows:

Substantially equivalent results are obtained when other aqueous nitrogen base solutions, eg., ammonia, are used in place of ethanolamine, and when other Werner com# plexes of transitional metal salts are used, e.g., the corresponding Werner complexes of cobalt, iron, manganese,

etc.

EXAMPLE H This example demonstrates the beneficial ettects of the added ammonium salts on clathration eiciency, and on selectivity of the primary solvent for the heterocyclic base component of the Werner complex. In each of the experiments reported in Table 2, the clathration technique consisted in dissolving the Werner complex in the primary solvent at a suitable elevated temperaure of 75-90 C., stirring in the feed mixture, and then cooling the mixture to 25 C. to precipitate the clathrate. About 2 volumes of isooctane per volume of xylenes extracted was then added to facilitate separation of the hydrocarbon phase, and the solid clathrate was filtered ot. The hydrocarbon phase of the filtrate (ratlinate) was then separated and analyzed for xylene isomers and 'y-picoline. The solid clathrate was then redissolved in the stripped primary solvent at 75-90 C., and the solution was extracted with isooctane. The resulting hydrocarbon extract phase was then analyzed for xylene isomers and 'y-picoline. The results were as follows:

Table 2 Hydro- 'y-Pico Xylene Isomer Distribution Run N o. Solvent Comp., Wt. carbon line, Wt. percent Phase percent para meta ortho Et Bz Feed 14.8 81.2 0.6 3. 4 1

FDI {Extraet 6. 5 52. 9 42.1 0.2 4.8 0 Raflinate.. 5 3 2.1 94. 5 0. 5 2. 9 56.1% 1120.... Feed 14. 8` 81.2 O. 6 3. 4 2 31.4% NIEA Extract. 4.3 57. 7 37.6 0. 3 4.4 12.5% RNHsCl lh--- Rnfnate.. 5.0 1, 8 95.2 0.5 2. 5 51.5% IT20 Feed 14.8 81.2 0.6 3. 4 3 MEA Extract--- 2. s 47. 2 47. 5 0.3 5.0 tNaHsoN asfaltate.. 2.1 1.0 sa s 0.6 2.1

MEA=n1onoethanolarnlne b RNHsCl=ethanolammonlum chloride RNHaS CN =ethanolamm0niun1 thiooyanate method depending upon the particular compounds in- Conditions:

Werner complex/p-xylene (wt. ratio)=l2.0 Solvent/Werner complex (wt. ratio)=3.0

It isY thus evident that the added ammonium salts have a definite effect of increasing the relative solubility of ly-picoline in the primary solvent, thus decreasing loss of picoline to the raffinate and extract hydrocarbon phases. There is also a definite improvement in clathration efiiciency, as indicated by the higher purity of the raffinate m-xylene streams in runs Nos. 2 and 3.l While the absolute differences in purity may seem small, they are relatively quite significant, for as compared to a resolution efficiency' (alpha) of 56.4 in run No. 1, the resolution efficiencies in runs 2 and l-3 were 81.0 and 95.4, respectively. Thisris a reiiecrtion of the lesser solubility of the Werner complex at 25 C. in the modified s01- vents of runs 2 and 3, and thus of its more complete precipitation and utilization as a clathrate-former.

EXAMPLE III Other Werner complexes and ammonium salts can be substituted for the ones used in Example II to obtain resolutions of similar eiiiciency, but wherein isomers other than the paraxyiene are sometimes selectively clathrated. For example, in treating a xylene mixture containing 20% p-xylene, 45.5 m-xylene, 19.3% o-xylene and 15.3% ethylbenzene, under conditions described in Example II, the isomers selectively clathrated are as follows:

The nickel tetra.=(4methyl pyridine) dithiocyanate complex of Example II can also be utilized for the separation of nonhydrocarbon di-substituted benzene isomers. For example, in utilizing this complex according to the procedure of Example II, the ortho, metaand paraisomers of mixed chloro-toluenes, dichloro benzenes, toluidines, nitro-toluenes and methyl anisoles are effectively resolved, in each case the para-isomer being selectively clathrated.

The complexes of the above examples may be employed for effecting separations of other mixtures, and may be interchanged in `the various examples, to effect varying degrees of resolution. Likewise, many similar complexes and primary solvents could be substituted for those set forth in the examples.

The foregoing disclosure of this invention is not to be considered as limiting since many variations may be m-ade by those skilled in the art without departing from the scope or spirit of the following claims.

Iclaim:

1. In a selective clathration process for the separation of organic compounds, wherein the feed mixture to be resolved is contacted lwith a solution of a heterocyclic nitrogen base Werner complex'dissolved in a primary solvent comprising an aqueous nitrogen base solution, wherein clathration is effected by altering the environment of said mixture to effect precipitation of solid Werner complex clathrate, the improvement which oomprises including in said primary solvent a minor proportion of an added water-soluble ammonium sal-t.

2. A process as defined in claim v1 wherein said ammonium salt is ammonium 'thiocyanate 3. A process as defined in claim 1 wherein said ammonium salt is ethanolammonium thiocyanate.

4. A process `as defined in claim 1 wherein said primary 12 solvent comprises ethanolamine, and said ammonium salt is ethanolammonium thiocyanate.

5. A process as definedV in claim 1 wherein said primary solvent is aqueous ammonia, and said ammonium salt is ammonium thiocyanate.

6. In a selective cla-thration process for resolving a feed mixture of organic compounds, the steps which comprise (1) forming a solution of a heterocyclic nitrogen base Werner complex in an aqueous solution of a lower alkanolamine and a water-soluble ammonium salt; (2) mixing the resulting solution with said feed mixture; (3) cooling the resulting mixture to effect precipitation of a solid clathrate of at least one component of said Vfeed mixture with said Werner complex; (4) separating said solid clathrate from the liquid phase; (5) recovering the clathratedV feed component from said clathrate, and (6) recovering the vnon-clathrated feed component from the mother liquor of said clathration step.

7. A process as defined in claim 6 wherein said nonclathrated feed component is recovered from said liquid phase by liquid-liquid phase separation, thereby leaving a lean mother liquor.

8. A process as defined in claim 7 wherein said clathrated feed component is recovered by dissolving said solid clathrate in said lean mother liquor and subjecting the resulting mixture to liquid-liquid phase separation.

9. A method as defined in claim 6 wherein said alkanolarnine is mono-ethanolamine.

10. A method as defined in claim 6 wherein said heterocyclic base is a pyridine ring compound, and wherein said metal salt is selected from the class consisting of Athe thiocyanates, isothiocyanates, cyanates, isocyanates, cyanides and azides of manganese, iron, cobalt and nickel, the yanion of said ammonium salt being the same as the anion of said metal salt.

11. A method as defined in claim 6 wherein said clathrated organic compound is a benzenoid hydrocarbon.

12. A method as defined in claim 6 wherein said clathrated compound is p-xylene.

13. A method for resolving a mixture of disubstituted benzene isomers including a para isomer which comprises (1) forming a solution of a lower 4-alkyl pyridine Werner complex of a metal salt in an aqueous solution of a lower alkanolamine and a water-soluble ammonium salt; (2) admixing the resulting solution with said isomer mixture; (3) cooling the resulting mixture to effect preipitation of a solid clathrate of said para-isomer with said Werner complex; (4)` separating unclathrated isomers from the resulting mixture; (5) redissolving said clathrate in lthe remaining aqueous alkanolamine solvent phase at ya relatively high temperature thereby liberating said para-isomer; and (6) separating the enriched para-isomer from the reconstituted Werner complex solution.

14. A method as defined in claim 13 wherein said alkanolamine is mono-ethanolamine.

15. A method as defined in claim 14 wherein said metal salt is a thiocyanat-e of a metal of atomic number 25 to 28, and said ammonium salt is ethanolammonium thiocyanate.

16. A process for resolving a xylene mixture including p-xylene, which comprises (l) forming a solution of a 4-methyl pyridine Werner complex of a metal salt in an aqueous solution of a lower alkanolamine and a water-soluble ammonium salt; (2) admixing and agitating the resulting solution with said xylene mixture while cooling the mixture to effect precipitation of a solid clathrate of p-xylene and said Werner complex; (3) adding to the resulting mixture a saturated hydrocarbon; (4) separating solid clathrate from the clathration mother liquor; (5) separating said mother liquor into a raiiinate hydrocarbon phase and an aqueous alkanolamine solto recover (a) an overhead fraction comprising 4-methyl pyridine and said saturated hydrocarbon and (b) a higher boiling fraction comprising rainate xylenes; (7) recycling said overhead fraction to said step (3); (8) redissolving said clathrate in said aqueous allranolamine solvent phase at a temperature of `from about 50 to about 150 C.; (9) adding to the resulting mixture a saturated hydrocarbon 'boiling between about 90 and 135 C.; (10) separating the resulting mixture into a Werner complex solution phase and an extract hydrocarbon phase; (l1) distilling said extract hydrocarbon phase to recover (a) an overhead fraction comprising 4- methyl pyridine and said saturated hydrocarbon and (b) a higher boiling fraction comprising enriched p-Xylene, and (12) recycling said last-named overhead fraction to said step (9).

17. A method as defined in claim 16 wherein said alkanolamine is mono-ethanolamine.

18. A method as dened in claim 17 wherein said metal salt is a thiocyanate of a metal selected from the class consisting of manganese, iron, cobalt and nickel, and said ammonium salt is ethanolammonium thiocyanate.

References Cited in the file of this patent UNITED STATES PATENTS 2,798,103 Schaeffer et al. July 2, 1957 2,798,891 Schaeier July 9, 1957 2,849,513 Schaeffer Aug. 26, 1958 2,876,227 Schaeffer Mar. 3, 1959

Claims

1. IN A SELECTIVE CLATHRATION PROCESS FOR THE SEPARATION OF ORGANIC COMPOUNDS, WHEREIN THE FEED MIXTURE TO BE RESOLVED IS CONTACTED WITH A SOLUTION OF A HETEROCYCLIC NITROGEN BASE WERNER COMPLEX DISSOLVED IN A PRIMARY SOLVENT COMPRISING AN AQUEOUS NITROGEN BASE SOLUTION, WHEREIN CLATHRATION IS EFFECTED BY ALTERING THE ENVIRONMENT OF SAID MIXTURE TO EFFECT PRECIPITATION OF SOLID WERNER COMPLEX CLATHRATE, THE IMPROVEMENT WHICH COMPRISES INCLUDING IN SAID PRIMARY SOLVENT A MINOR PROPORTION OF AN ADDED WATER-SOLUBLE AMMONIUM SALT.