IL31684A - Method for producing a solvent for edible oils - Google Patents

Description

Method for od cing a solve& for edible oils TOIVliRSAL OIL PRODUCES CQEBPAOT C§ 30011 This invention relates to a method for separating aromatic hydrocarbons from non-aromatic hydrocarbons. It particularly relates to a method for applying selective catalytic hydrogenation to purify a contaminated raffinate stream from an extraction process and thereby produce a solvent for edible oils.

The art of separating aromatic and non-aromatic hydrocarbons is well known. Generally, these hydrocarbons are separated via liquid-liquid extraction using a solvent which is selective for aromatic hydrocarbons under extraction conditions which produce an extract stream comprising solvent having aromatic hydrocarbons dissolved therein and a raffinate stream comprising non-aromatic hydrocarbons contaminated with solvent and aromatic hydrocarbons. The extract phase is sub-sequently sent to distillation means for further purification of the aromatic hydrocarbons and recovery and/or reuse of the solvent in the extraction process. The raffinate stream is conventionally subjected to treatment to recover dissolved and entrained solvent therefrom. The treatment of the raffinate stream is essentially a secondary extraction operation, wherein the contaminated raffinate is subjected to a water-wash treatment to remove the dissolved and entrained solvent from the hydrocarbon phase. The water-containing solvent may then be processed in the same distillation facility that is used for recovering the solvent from the aromatic extract phase. In any event the raffinate phase, even after this treatment, may still contain a significant quantity of solvent, e.g. more than 500 ppm. It will also contain the residual aromatic hydrocarbons which were It is the object of this invention to provide a method for separating aromatic hydrocarbons, including the aforesaid residual aromatics, from non-aromatic hydrocarbons, and thereby produce a substantially aromatic-free product which is especially suited as a solvent for edible oils.

Accordingly, the present invention provides a method for producing a solvent, which comprises (a) subjecting a hydrocarbon feed stock, which contains at least one aromatic hydro-: carbon and at least one non-aromatic hydrocarbon having from 6 to 9 carbon atoms per molecule, to contact in a first extraction zone with a primary solvent selective for aromatic hydrocarbons; (b) separately withdrawing from said first extraction zone a first extract stream comprising primary solvent and aromatic hydrocarbons and a first raffinate stream comprising non-aromatic hydrocarbons and contaminated with primary solvent and with more than 1% by volume of aromatic hydrocarbons; (c) recovering aromatic hydrocarbons in high purity. from said first extract stream; (d) subjecting said contaminated first raffinate stream to contact in a second extraction zone with a secondary solvent comprising water; (e) separately withdrawing from said second extraction zone a second raffinate stream comprising non-aromatic hydrocarbons of reduced solvent contenL, and a second extract stream containing water and primary solvent; (f) introducing said second raffinate stream into a hydrogenation zone and re-acting the same therein with hydrogen in the presence of a hydrogenation catalyst, thereby converting aromatic hydrocarbons into naphthenes; and (g) recovering from the effluent of said hydrogenation zone a fraction comprising at least one non-aromatic hydrocarbon having from six to nine carbon atoms per molecule, containing less than 1% by volume aromatic hydrocarbon, and containing less than 10 ppm. of primary solvent.

In a preferred embodiment of the invention, the primary solvent comprises sulfolane.

In the food processing industry it is known to extract oil from raw materials, such as soya beans, by contacting the pulverized material with a solvent such as hexane and subsequently recovering the solvent from the oil by distillation means. The extracted oil may be subjected to further purification treatments, including, for example, contacting with caustic soda (to remove free fatty acids) to produce an oil suitable for human consumption. Such a purified oil is commonly called an "edible oil." Typical requirements for a satisfactory edible oil solvent include an aromatic hydrocarbon content of less than 1% by volume, preferably from 0.05% to 0.5% by volume, and a content of less than 10 parts per million of sulfolane (or other solvent material used to extract aromatic hydrocarbons) , and preferably from 0.1 to 1.0 part per million. It is extremely difficult to produce such a highly purified hydrocarbon product via conventional processing schemes. Highly purified hexane is one of the best known solvents for extraction of edible oils.

The solvent extraction operation for aromatic hydrocarbon separation is suitably conducted by introducing feed stock containing hexane and benzene into the lower portion of an elongated column while solvent is introduced into the upper portion thereof. The feed stock and solvent move counter-currently through the column wherein effective contact is generally achieved by distributing or contacting means such as trays, contacting masses, distributing plates, perforated plates, rotating disks, and the like. Temperature and pressure conditions are suitably maintained in the column to assure the formation of an extract phase and a raffinate phase. The solvents used in the solvent extraction step have a preferential selectivity for the relatively more aromatic-type constituents as compared to the relatively more-paraffinic type constituents. Solvents which may be used are, for example, phenol, furfural, sulfurdioxide, cresol, aniline, nitrobenzene, sulfolane, the polyethylene glycols, and the like, sulfolane being preferred. Such solvents may be further modified with regard to selectivity and solvent power by the addition of inert solvents, for example, water.

In accordance with the present invention, the preferred solvent is of the sulfolane type and possesses a five-membered ring containing one atom of sulfur and 4 atoms of carbon with 2 oxygen atoms bonded to the sulfur atom of the ring. Generically, the sulfolane type solvents have the following structural formulas wherein R^, R2, and R4 are independently selected from the group comprising hydrogen, an alkyl group having from 1 to 10 carbon atoms, an alkoxy radical having from 1 to 8 carbon atoms, and an arylalkyl radical having from 1 to 12 carbon atoms.

Other suitable solvents of the preferred type are the sulfolenes, such as 2-sulfolene or 3-sulfolene. The distinctly preferred sulfolane has the following structural formula: Because the solvents typically utilized in aromatic extraction are water soluble, it is the usual practice to extract residual solvent from the raffinate stream by contact with an aqueous stream in a subsequent extraction means as previously mentioned. This extraction of the solvent from the raffinate with water may be effected in any suitable liquid-liquid contacting means, the solvent being readily recovered from the resulting aqueous solution by distillation. The raffinate, now substantially free of solvent, is further processed in accordance with the present invention. The hydro-genating operation of the present invention may utilize any of the catalysts which are known to those skilled in the art.

Typically, the hydrogenation step is conducted with a high nickel content catalyst such as one containing about 65% nickel on kieselguhr, Group VIII metals in ε.Ί ementary forms or the oxides thereof may be used satisfactorily. As examples thereof, but not limited thereto, these metals include nickel, palladium, platinum and rhodium. Specific examples include nickel on kieselguhr . and platinum on alumina. Operating conditions for the hydrogenation step include a temperature from 200°C. to 480°C, preferably from 230°C. to 370°C, a pressure from 14 to 136 atmospheres gauge, preferably from 41 to 68 atmospheres gauge, a liquid hourly space velocity from 0.1 to 2.0 (volume liquid feed per volume of catalyst per hour), preferably from 0.05 to 1.0, and hydrogen in the amount of from 36 to 3600 standard liters per liter of hydrocarbon, preferably from 53 to 1,780 standard liters per liter. In conjunction with the preferred operating conditions, it is distinctly preferred to utilize the catalyst which contains nickel as hydrogenating component.

It has been found that when hydrogenating a treated raffinate containing from 6 to 9 carbon atoms per molecule under the conditions described herein, a non-aromatic hydrocarbon stream containing less than 1% by volume aromatic hydrocarbons and less than 10 parts per million of solvent will result.

The present invention thus provides a method for separating aromatic from non-aromatic hydrocarbons to form a non-aromatic hydrocarbon product of such purity that it is suitable for use as a solvent for edible oils.

EXAMPLE A paraffinic raffinate stream containing sulfolane solvent in solution leaves an aromatics extraction zone at a temperature of from 65°C. to 120°C. and normally at a temperature of 93° C. to 99° C. The raffinate stream is then contacted with an aqueous stream and cooled to about 38°C. or less, whereby about two-thirds of the dissolved sulfolane is removed from the hydrocarbon solution. The cooled stream then passes into a mixer wherein additional aqueous phase is intimately contacted with the hydrocarbon phase under turbulence and with a reduced ratio of hydrocarbon phase to non-hydrocarbon phase which provides a haze-free raffinate fraction. The mixed stream of raffinate phase and sulfolane-containing aqueous phase enters an aqueous extractor means wherein the raffinate is contacted with still further water derived either from fresh water or as stripping steam condensate from the aromatics extraction process unit. The conditioned raffinate is extracted in this extractor to produce a raffinate stream substantially free of sulfolane. The aqueous stream containing extracted sulfolane leaves the extractor and is sent back into the aromatics process unit for recovery of the sulfolane solvent contained therein.

The treated raffinate stream, now substantially free of sulfolane, is passed into a hydrogenation zone in the presence of hydrogen and in contact with a nickel-containing catalyst.

The conditions in the hydrogenation zone include a temperature of about 290°C, a pressure of about 47.5 atmospheres gauge, and a liquid hourly space velocity of about 0.8. Hydrogen is mixed with the hydrocarbon phase at a rate of about 890 standard liters per liter of hydrocarbon. A raffinate stream comprising non-aromatic hydrocarbons substantially free of aromatic hydrocarbons and solvent is recovered. Such a product may contain about 0.1 volume percent aromatic hydrocarbons and about 0.5 ppm. of solvent.

Claims (7)

THE INVENTION CLAIMED; for edible oils

1. Method for producing a solvent/ which comprises (a) subjecting a hydrocarbon feed stock, which contains at least one aromatic hydrocarbon and at least one non-aromatic hydrocarbon having from 6 to 9 carbon atoms per molecule, to contact in a first extraction zone with a primary solvent selective for aromatic hydrocarbons? (b) separately withdrawing from said first extraction zone a first extract stream comprising primary solvent and aromatic hydrocarbons and a first raffinate stream comprising non-aromatic hydrocarbons and contaminated with primary solvent and with more than 1% by volume of aromatic hydrocarbons (c) recovering aromatic hydrocarbons in high purity from said first extract stream? (d) subjecting said contaminated first raffinate stream to contact in a second extraction zone with a secondary solvent comprising water? (e) separately withdrawing from said second extraction zone a second raffinate stream comprising non-aromatic hydrocarbons of reduced solvent content, and a second extract stream containing water and primary solvent? (f) introducing said second raffinate stream into a hydrogenation zone and reacting the same therein with hydrogen in the presence of a hydrogenation catalyst, thereby converting aromatic hydrocarbons into naphthenes? (g) recovering from the effluent of said hydrogenation zone a fraction comprising at least one non-aromatic hydrocarbon having from six to nine carbon atoms per molecule,

2. Method according to Claim 1, Wherein the feed stock consists largely of hexane and benzene, and the fraction recovered from the hydrogenation zone effluent comprises hexane.

3. Method according to Claims 1 or 2, wherein the primary solvent comprises sulfolane.

4. Method according to any of the Claims 1 to 3, wherein the second raffinate stream is reacted with hydrogen at a temperature from 200°C. to 480°C, a pressure from 14 to 136 atmospheres gauge, a liquid hourly space velocity from 0.05 to 1.0, and a hydrogen-to-hydrocarbon ratio from 36 to 3600 standard liters per liter of hydrocarbon.

5. Method according to any of the Claims 1 to 4, wherein the hydrogenation catalyst contains nickel.

6. Method for producing a solvent, substantially as hereinbefore described.

7. A solvent for edible oils, whenever produced by the process of any of the preceding claims.