US2799627A - Process for obtaining concentrated aromatic hydrocarbons - Google Patents

Description

v. HAEVNSEL July 16, 1957 PROCESS FOR OBTAINING CONCENTRATED AROMATIC HYDROCARBQNS Filed Aug. 1'7, 1953 RN YN IN VE N TOR:

Vladimir Haense/ A T TOR/VEYS:

United States Patent PROCESS FOR @iSTAINING CONCENTRATED ARQMATHC HYDRQCARBONS Vladimir Haensel, Hinsdale, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware This invention relates to a process for obtaining a highly concentrated aromatic hydrocarbon fraction and in particular to a combination of mutually relate-d steps including treating a contaminated and unsaturated hydrocarbon fraction and subsequently subjecting the treated fraction to solvent extraction to obtain a highly concentrated aromatic hydrocarbon fraction.

As is well known, light liquid hydrocarbon fractions may be obtained by straight run distillation of a crude oil, or by destructive reactions such as cracking, which may be either catalytic or thermal, coking etc. The light liquid fractions obtained by destructive reactions are characterized by a certain degree of unsaturation. This degree of unsaturation is higher or lower depending upon the conditions used to effect the cracking. Therefore a highly cracked stock, that is one that has been subjected to severe destruction reactions, is more unsaturated than a mildly cracked stock which is one subjected to a lesser degree of reaction. A thermally cracked stock is more unsatnrated than a catalytically cracked stock. Straight run stocks are virtually saturated, as are the products of alkylation processes.

The present invention is directed towards obtaining highly concentrated aromatic hydrocarbon fractions preferably from a stock of petroleum origin comprising the lower boiling range, such as the gasoline fraction, naphthas, kerosene fraction, and the gas oil fraction. It is particularly desirable to obtain aromatic hydrocarbons from cracked stock as well as from straight run stock since the cracked stock is more highly aromatic in nature than the straight run stock, and is very abundant due to the widespread use of cracking processes.

The highly concentrated aromatic fraction is obtained in accordance with the present invention by subjecting a petroleum fraction containing aromatic hydrocarbons to a solvent extraction process subsequent to being suitably treated to improve its characteristics as a charge stock for the solvent extraction process. Solvent extraction processes are used to separate certain components in a mixture from other components thereof by a separation process based upon a difference in solubility of the components in aparticular solvent. It is frequently desirable to separate various substances by solvent extraction when the substances to be separated have similar boiling points, are unstable at temperatures at'which fractionation is effected, form constant boiling mixtures, etc. It is particularly desirable to separate aromatic hydrocarbons from a petroleum fraction containing these aromatic hydrocarbons by solvent extraction because a petroleum fraction is normally a continuous mixture of hydrocarbons whose boiling points are extremely close together and because the petroleum fraction contains numerous cyclic compounds which tend to form constant boiling or' azeotropic mixtures. As hereinbefore stated, the basis of a solvent extraction separation is the difference in solubility in a given solvent of one of the substances to be separated from the other. A It may therefore be seen that the more extreme this difference, the easier the separation-will be,

and an easier separation reflects itself, process-wise, in less extensive equipment and greater yields per pass in the use of processing equipment as well as in higher purity of product.

A particularly preferred solvent for separating aromatic hydrocarbons from non-aromatic hydrocarbons is a mixture of water and a hydrophilic organic solvent. Such a; solvent may have its solubility regulated by adding more or less water. Thus, by adding more water to the solvent, the solubility of all components in the hydrocarbon mix ture are reduced, but the solubility diiference between the components is increased. This effect is reflected processwise in less contacting stages required to' obtain a given purity of product, however, a greater throughput of solvent must be used in order to obtain the same amount of material dissolved.

In classifying hydrocarbon and hydrocarbon type compounds according to increasing solubility in such a solvent, it is found that the solubility of the various classes increases in the following manner: the least soluble are the paraffins followed in increasing order of solubility by naphthenes, olefins, di-olefins, acetylenes, sulfur, nitrogen, and oxygen-containing compounds and aromatic hydrocarbons. It may thus be seen that a cracked stock will present a greater problem in solvent extraction than a straight run stock since the cracked stock is rich in unsaturated compounds. A further difiiculty in having unsaturated compounds in the feed is that they tend to polymerize at higher temperatures to form sludges and otherundesirablematerial which causes great difliculty in processing equipment. It may be seen that an ideal charge to solvent extract is one containing parafiinic and aromatic hydrocarbons exclusively.

It is an object of the present invention to obtain a highly concentrated aromatic fraction from a petroleum fraction containing aromaic and unsaturated components by a novel combination of mutually interdependent steps.

In one embodiment the present invention relates to a process for obtaining a highly concentrated aromatic fraction from an aromatic-containing fraction by a series of inter-related steps which comprises catalytically treating said last mentioned fraction at selected conditions in the presence of a catalyst containing platinum and/or pal ladiur'n, removing normally gaseous components from the resultanttreated fraction, and separately recovering a highly concentrated aromatic fraction therefrom by solvent extraction.

In a specific embodiment, the present invention relates to a process obtaining a highly concentrated aromatic fraction which comprises treating an aromatic-containing fraction with a platinum-containing catalyst at a tempera ture of from about 300 F. to about 600 F. in the pres ence of hydrogen, separating normally gaseous products from the treated fraction, containing the resultant liquid product with a selective solvent, and separately recovering 7 said solvent;

a highly concentrated aromatic fraction from V The catalyst to' be used in the present invention for treating the charge stock priorto solvent extraction must be onehaving specific characteristics that make it par ti'cularly Suitable for the processfof the present invenf tion'. The catalyst must effect the desired rea'ctions' at temperatures which are low enough so that the desired hydrogenation is, effected without unde's-ira-bledehydro geriationl The catalyst must 'also'be sulfur resistantlarid able to promote the severance of carbonto sulfur and carbon to nitrogen bonds i-n'order to facilitate the form-a-j tion of H28 and NH: from the sulfur andfnitrogen bear It is of ririr'iiary ing molecules contained in the charge; I importance that the" treating step be at low temperatures for theVreasons vent undesired thermalzreactions from occurring.

Suitable platinum-containing catalysts may: include" hereinbefore set forth, as wellias to pre-" platinum composited with synthetically prepared inorganic oxides such as alumina, silica, boria, magnesia, zirconia, etc., or mixtures thereof, including silica-alumina, silicaalumina-magnesia, silica-zirconia, "titania-zirconia, etc. Catalystsmay also be prepared by compositing platinum with an inorganic oxide which is promoted with an acid acting substance such :as a halogen, phosphate, etc. Other catalysts may include platinum composited with naturally occurring material which may or may not be activated by acid-treatment, steam treatment, etc., such as bauxite, kieselguhr, diatomaceous earth, clay, pumice, etc., or mixtures thereof. A particularly suitable catalyst for effecting the desired treating reactions, and the preferred catalyst of this invention has been found to be a composite of from about 0.01% to about 10% by weight of platinum composited with alumina and having combined therewith a halogen which is preferably chlorine and/or fluorine in a concentration of from about 0.1% to about 5.0% by weight. The catalyst may be prepared in the form of spheres, pellets or a powder, depending upon the type of process in which it is used. Catalysts of palladium, which may be made in the same manner as the platinum catalysts, may also be used in the present process since they are sulfur resistant and have high hydrogena'ting activity, however, the results at the same opera-ting conditions are not necessarily equivalent.

The treating step of the present invention may be effected in any suit-able manner such as in a fixed bed, a fluidized process, moving bed process, slurry process, etc. It is preferable, however, that the process be effected in a fixed bed since this type of process requires the least amount of equipment and may be operated substantially without catalyst losses. Since the treating process is essentially non-regenerative, the fixed bed process is preferred. Although the preferred catalyst has a long active life, it may from time to time, require regeneration-after long periods of use.

Regardless of the particular type of operating equipment employed, the conditions of processing must be such that the unsaturated compounds which include olefins, conjugated diolefins, acetylenes, etc., which may be straight chain or cyclic in nature, will be saturated, however, .the, valuable and desirable aromatic compounds must not be hydrogenated. Processing conditions must also 'be such that the sulfur and nitrogen bearing molecules contained in the fraction .are hydrogenated to form the corresponding hydrocarbon molecules and hydrogen sulfide or ammonia. The desired results are obtained at the selected operating conditions herein set forth. The temperature to be employed is within the range of from about 300 F. to about 600 F. and preferably of from about 400 F. to 500 F. and the pressure from about 100 p. s. i. to about 1000 p. s. i. or more in the presence of hydrogen. The process is effected at any suitable liquid hourly space velocity, however, the space velocity is.

usually in the range of from about 5 to about 20 volumes of charge per volume of catalyst per hour depending upon the other process variables. When extremely low sulfur concentrations are present in the charge stock, it is desirable to effect the process at lower temperatures and/ or higher space velocities inasmuch as the saturation of olefins, acetylenes and diolefins proceeds rapidly and completely at low temperatures since the equilibrium towards saturation is more favorable as the temperature of the operation decreases. When a substantial concentration of sulfur and nitrogen compounds are present in the charge stock, the temperature maintained in the treating zone will be determined by the temperature at which the'desired degree of purification is effected. Since the treating process includes primarily hydrogenation, the partialpressure of hydrogen can be maintained at a high level, but not sufliciently high to effect substantial conversion of aromatics to cyclohexane derivatives. Thus, when' operating at higher temperatures the pressure may be diminished in order to prevent excessive hydrogenation of aromatic hydrocarbons.

The hydrogen-containing gas present "in the reaction zone may be obtained from a reforming process or other refinery sources and need not be extremely pure. The hydrogen-containing gas may be partially or totally recycled within the process of the present invention and it is contemplated that purification means may be introduced into the flow scheme to remove contaminants from the gas before recycling the latter to the treating zone. The eifluent from the treating zone is passed to a stabilizer which effects separation of the normally gaseous material, which comprises hydrogen, hydrogen sulfide, ammonia and hydrocarbons containing from 1 to 4 carbon atoms, from the normally liquid hydrocarbons.

As hereinbefore stated, the solvent to be used in this invention is preferably a mixture of a hydrophilic organic solvent and water, wherein the amount of watercontained in the mixture is selected to regulate the solubility in the solvent of the materials to be separated. Suitable hydrophilic organic solvents include alcohols, glycols, aldehydes, etc. Particularly preferred solvents are diethylene glycol, dipropylene glycol, and mixtures thereof containing from about 2% to about 30% by weight of water.

The accompanying drawing is presented to illustrate one embodiment of the present invention and is not intended to unduly limit the invention to the particular embodiment illustrated.

An aromatic hydrocarbon containing feed stock passes through line 1 and is commingled in line 4 with hydrogencontaining gas entering line 4 through line 2. Line 3 also enters line 4 and may pass hydrogen-containing gas in addition to that from line 2 into line 4. Line 4 passes into the upper portion of reactor 5 which contains a bed of treating catalyst and is maintained at a temperature of from about 300 F. to about 600 F. and at a pressure of from about p. s. i. to about 1000 p. s. i. In reactor 5 the desired reactions of saturating the unsaturated hydrocarbons and hydrogenating the combined sulfur and nitrogen to form hydrogen sulfide and ammonia are afhydrocarbon liquid comprising substantially aromatic hydrocarbons and paraflinic hydrocarbons. The gaseous material passes overhead through line 9 into cooler 10, wherein a portion of the material is condensed, and the entire stream passes through line 11 into receiver 12. In receiver 12 the liquid phase and the gaseous phase of the overhead material separate, the gaseous phase passing through line 13, from which it may be vented to the atmosphere through line 14 and valve 15 or passed through line 16 and compressor 17 which discharges into the before mentioned line 3 at the inlet of reactor 5. The liquefied portion of the overhead stream is passed through line 30 into the upper portion of stabilizer 8 as reflux, and a portion may be withdrawn from the flow through line 31. It is contemplated that the receiver will operate at suflicient pressure to liquefy at least a portion of the overhead material so that a liqud reflux stream may be available to improve the separation in stabilizer 8. It is also contemplated, but not shown, that either line 16 or line 3 passing from receiver 12 to the inlet of reactor 5 may contain suitable means for purifying the gas stream to remove undesirable contaminants such as hydrogen sulfide and ammonia therefrom.

The stabilizer bottoms which, as hereinbefore stated, comprises substantially paraflinic and aromatic hydrocarbons, are passed through line 18 and valve 19 into the lower'portion of extractor 20. In extractor 20 the hydroit from the broad scope of this invention.

with a descending stream of selective solvent entering the upperportion of extractor 20 through line 28. As a result of the countercurrent contact of the selective solvent and hydrocarbon charge stock, the aromatic hydrocarbons contained in the charge stock are selectively dissolved in the solvent, thereby forming an extract stream containing the solvent and aromatic hydrocarbons, and a, railinate stream containing the paraffinic hydrocarbons. The raffinate stream passes from the upper portion of extractor 20 through line 21 and valve 22, while the extract stream passes from the lower portion of extractor 20 through line 23 and valve 24. Line 23 passes to an intermediate portion of stripper 25, wherein the dissolved aromatic hydrocarbons are separated from the selective solvent. This separation is not diflicult in that the aromatic hydrocarbons are substantially diiferent in nature from the selective solvent as well as having a substantially different boiling point. The aromatic hydrocarbon stream passes overhead through line 26 and valve 27, while the solvent stream is taken from the bottom of stripper 25 through line 28 and valve 29 and passes through the before mentioned line 28 into the upper portion of extractor 20.

A portion of the overheadmaterial from stripper 25, which is substantially pure aromatic hydrocarbon, may be passed into the lower portion of extractor 20 as a reflux stream to improve the separation effected in extractor 20. When this is done the reflux stream will always enter colurnn 20 at a point below that which line 18 carrying the extractor charge enters column 20. Both the extraction zone and the stripper will contain means of promoting intimate contact between two substantially immiscible fluid streams, such as packing, perforated decks, bubble caps, trays, etc.

It is, of course, understood that many modifications of the described process may be made without removing Some of the modifications may include the interchanging of pumps for valves to be consistent with the pressure levels maintained at various portions of the plants, the use of various heat exchange schemes to effect energy savings, etc. Another modification may be to pass a portion of the raflinate stream from line 21 into treating zone to dilute an extremely unsaturated charge stock thereby reducing the temperature rise in this zone by dilution of reactants as well as by adding heat capacity to the charge.

Following are several examples to illustrate specific applications of the invention, without the intention of unduly limiting the same.

EXAMPLE I A fraction boiling within the gasoline range and obtained by the severe vapor phase thermal cracking of gas oil was catalytically treated, stabilized, and solvent extracted by the method of this invention. The charge stock was contacted with a catalyst comprising alumina, 0.4% by weight of platinum and 1.2% by weight of combined fluorine. The extracted stock contacted the catalyst at a temperature of'423 F., a pressure of 700 p. s. i., a liquid hourly space velocity of and a hydrogen to hydrocarbon molal ratio of 10. The purity of the hydrogen in the gas stream to the treating zone was 90%. The resultant product was stabilized and passed into an extraction zone, wherein it was countercurrently contacted with a mixture of diethylene glycol and water containing 8% water by weight, said contact being effected at a temperature of 275 F. and a pressure suificient to main tain the material in the liquid phase.

Another portion of the same charge stock was subjected to solvent extraction without the initial hydrogenation treatment, the extraction being effected with the same solvent and under the same conditions as that of the treated stock. An analysis of the various streams appears in Table 1 below:

Table 1 Without Hy- With Hydrogenation drogenation Charge Stabi- Ex- Ratfinlizer Ex- Railintract ate Bottract ate toms Density, API- 46 39. 3 69. 5 46.1 37. 4 71. 5 Initial Boiling Point, F 134 156 End Boiling Point,

237 248 Sulfur, Wt. percent. 0.10 0. 13 0 Dr. 0 0

Sweet Yields, Vol. percent Based on chit-gig: 75 25 104 70 34 Para s..- Naphthenes 15 0 00 33 0 99. 6 fins 5 1.0 17.0 0 0 0 Conjugated Diolesv l0 9. 5 11.0 0 0 0 Aromatics 70 89. 5 l2. 0 67 99. 9 0. 4

It may be seen from this example that the process of the present invention aflords a method of obtaining substantially pure aromatic hydrocarbons from a charge stock which is extremely poorly suited for solvent extraction. The charge stock comprising substantially aromatic hydrocarbon and unsaturated hydrocarbons, represents about as difficult a charge stock as could be found for separation by solvent extraction as is illustrated by the attempted solvent extraction of the charge stock without the pretreatment step. Through the present invention a process is provided for eflecting the separation on a commercial scale which heretofore would be difficult to efiect even on a laboratory scale. The present process starts with highly unstable material and produces a valuable aromatic concentrate, which may be of nitration grade, as Well as stable paraffinic materials suitable for use as a solvent or in motor fuel. Solvent extracting the charge stock without using the inter-related step of this process results in a fraction that is enriched in aromatics, but contains substantial proportions of non-aromatic compounds. The desired separation of aromatic compounds is not accomplished except by using the complete process.

EXAMPLE II A highly olefinic and sulfur-containing charge, obtained from a catalytic cracking unit, is passed into contact with a silica-alumina-platinum catalyst which contains about 13% alumina, 87% silica and 0.47% platinum by weight. The charge is contacted with the above described catalyst at a temperature of 530 F., a pressure of 750 p. s. i. in the presence of hydrogen, and the normally liquid portion of the resultant eflluent from the process is substantially saturated and sulfur free. The effluent is stabilized to remove the normally gaeous constituents therefrom and then is passed into countercurrent contact with a selective solvent comprising a mixture of diethylene glycol, dipropylene gylocol and water, resulting in the production of a raflinate stream and an extract stream, the rafiiinate stream containing parafiinic hydrocarbons and the extract stream containing the above described solvent and aromatic hydrocarbons. Upon separation of the extract stream into an aromatic stream and a solvent stream, the aromatic stream is found to comprise substantially pure aromatics.

I claim as my invention:

1. The method of obtaining a highly concentrated aromatic fraction from a mixture of aromatic and um saturated hydrocarbons which comprises treating said mixture with a catalyst comprising platinum, alumina, and combined halogen at a temperature of from about 300 F. to about 600 F. and at a pressure of from about 100 p. s. i. to about 1000 p. s. i. in the presence of hydrogen and hydrogenating substantially all of the unsaturated hydrocarbons at said temperature, removing the normally gaseous material from the resultant product, contacting the normally liquid material of said resultant product with a selective solvent comprising a hydrophilic organic solvent and water, and separately recovering a highly concentrated aromatic fraction and a highly concentrated aliphatic fraction.

' 2. The process of claim 1 further characterized in that said hydrophilic organic solvent comprises diethylene glycol.

3. The process of claim 1 further characterize'din that said hydrophilic organic solvent comprises dipropylene glycol.

' 4. The process of claim 1 further characterized inthat said hydrophilic organic solvent comprises a mixture of diethylene glycol and dipropylene glycol.

5. The process of claim 1 further characterized in that said catalyst contains from about 0.01% to about 10% platinum.

6. The process of claim 1 further characterized in that said catalyst contains from about 0.1% to about 5.0% halogen.

7. The method of obtaining a highly concentrated aromatic fraction from a mixture of aromatic and unsaturated hydrocarbons which comprises treating said mixture with a catalyst comprising alumina, platinum in a concentration of from about 0.01% to about 10% by weight and combined halogen at a concentration of from about 0.1%

to about 5.0% by weight, at a temperature ofjfrom about 300.F. to about 600 F., and a pressure of [from about 100 p. 5. i. to about 1000 p. s. i. in the presence of hydrogen and hydrogenating substantially all of the unsaturated hy-' highly concentrated aliphatic fraction from said selective solvent.

References Cited in the file of this patent UNITED STATES PATENTS 2,246,297 Duncan et a1. June 17, 1941 2,423,176 Cole July 1, 1947 2,444,582 Smith July 6, 1948 2,479,109 Haensel Aug. 16, 1949 2,534,025 Howes et al Dec. 12, 1950' 2,542,970 Jones Feb. 27, 19 51

Claims (1)

1. THE METHOD OF OBTAINING A HIGHLY CONCENTRATED AROMATIC FRACTION FROM A MIXTURE OF AROMATIC AND UNSATURATED HYDROCARBONS WHICH COMPRISES TREATING SAID MIXTURE WITH A CATALYST COMPRISING PLATINUM, ALUMINA, AND COMBINED HALOGEN AT A TEMPERATURE OF FROM ABOUT 300*F. TO ABOUT 600*F. AND AT A PRESSURE OF FROM ABOUT 100 P.S.I TO ABOUT 1000 P.S.I. IN THE PRESENCE OF HYDROGEN AND HYDROGENATING SUBSTANTIALLY ALL OF THE UNSATURATED HYDROCARBONS AT SAID TEMPERATURE, REMOVING THE NORMALLY GASEOUS MATERIAL FROM THE RESULTANT PRODUCT,

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