US2911354A - Preparation of aromatic petroleum concentrate of reduced sulfur content - Google Patents

Description

Nov. 3, 1959 c, HOLDER ET AL 2,911,354

' PREPARATION OF AROMATIC PETROLEUM CONCENTRATE OF REDUCED SULFUR CONTENT Filed Dec. 21, 1954 CRUDE STILL OIL H Clinton H. Holder Chester L. Read By @f/fi d/ Attorney CRUDE Inventors PREPARATION OF AROMATIC PETROLEUM {oN- CENTRATE F REDUCED SULFUR CONTENT Clinton H. Holder and Chester L. Read, Westfield, NJ., assignors to Esso Research and Engineering Company,- a corporation of Delaware Application December 21, 1954, Serial No. 476,776

. 1 Claim. (e1. 208-96) This invention relates to the preparation of condensed ring aromatic petroleum concentrates andv particularly to the preparation of such concentrates which have a moderately low sulfur content, i.e., about 0.8% or less sulfur content by weight. g

Condensed ring aromatic concentrates are'particularly useful as a flux oil for coal tar burned as fuel in open hearth furnaces and the like. A highly aromatic material is particularly desirable for such applications in that the luminosity of the flame produced increases with aromatic content. Highly luminous 'fiames are very desirable in reverberating furnaces or the like. f In addition, such materials may be employed in making electrode coke for the aluminumindustry and-as intermediates in themanufac- ,ture of various chemicals such as acids. derived from condensed ring aromatic compounds. They may. also be used as heat exchange media. In the'past thepr'eparation of such materials from petroleum distillates has been made difiicult due to the fact that. the requirements of the steel and aluminum industries necessitate the production of material having a fairly low sulfur content. This is necessary to avoid absorption of sulfur by the metallic charge in the furnace. While numerous processes exist for the reduction'of sulfur content in variouspetroleum distillates to, a satisfactory level, mostof theseprocesses involve a hydrogenation reaction which converts the sulfur to hydrogen sulfide and at the same time results in the hydrogenation of the aromatic compounds. In addition, sulfur is very often associated with aromatic rings so that highly aromatic concentrates generally contain large amounts of sulfur. It has been possible, therefore, to produce an aromatic concentrate of low sulfur content only where the concentration of aromatics was relatively low.

It is an object of this invention to provide a process whereby a condensed ringaromatic concentrate derived from petroleum and having both a low sulfur content and.

a high concentration of aromatics may be produced."

It is a further object of this invention to provide a process whereby catalytically crackedcycle stock may 'be converted to a relatively low sulfur-contentaromatic concentrate without hydrogenationof the aromatic content thereof.

These and other objects, whichwill be in part apparent and in part specifically pointed out in the ensuing description, are attained by distillingia' crude oil to produce a fraction boiling above aboutf600? F., subjecting this fraction to catalytic cracking, segregating the cracked products to form a fraction boiling in thesame range as the original distillate, subjecting this cracked stock to a solvent extraction process in orderv to segregate aromatic compounds, and then contacting the aromatic concentrate produced by this extraction process with hydrogen in the presence of a catalyst in order to reduce the sulfur content. of the concentrate.

Ithas been found that in order toproduce a satisfac- 2,911,354 I Patented Nov. .3, 1959 distilled from the crude oil be subjected to catalytic cracking. Prior to cracking the gasoil fraction normally contains less than 25% by weight of aromatics. This step is believed to cause the dehydrogenation of naphthenes so that the aromatics in the catalytica'lly cracked cycle stock are in a form relatively easily separable by conventional solvent extraction processes such as extraction with phenol, liquid' sulfur dioxide, or furfural. Most of the sulfur in the feed stock tends to concentrate'itself in the aromatic phase so that the feed for thehydrodesulfurization step isof substantially higher sulfur content than the original' crude. The hydrodesulfurization step of the process must becarried out under sufiiciently severe conditions to materially reduce the sulfur content of the aromatic concentrate, but the reaction conditions must not figure of drawings, which is a diagrammatic representation of a processembodying the present invention.

The drawing shows a conventional crude still v10 into which crude oil is introduced through line 11. Heavy residualpro'ducts are removed from the bottom of the still at 12, while light fractions are taken off overhead through line 13. Thepresent invention is concerned with the processing of that fraction boiling in' the range; of about 600 F. to about 1200 P. which is removed from the still through line 14and passesto thecatalyt-ic cracking unit 15. In the catalytic cracking unit-the feedstock is cracked under conditions well known to the art and forms a hydrocarbon mixture containing a substantial concentration of aromatic compounds. As previously stated; these aromatic compounds areparticularly-well adapted .to solvent separation from, the aliphatic C Ol'l-- stituents of the cracking stock and are peculiar 'tocatalytic as opposed to thermal cracking. For this reason the cracking operation: carried out in unit 15 must be of a catalytic nature. Any conventional catalytic cracking system adapted to convert hydrocarbons into materials of a lower boiling range may be employed. The process may beof a continuousor batch operation. in fixed bed, moving bed, fluid or suspensoid systems. Heat required for cracking may besupplied. as preheat of the distillate and/or as sensible heat of exothermically regenerated catalyst,.or in any other conventional. manner. Modified natural orsynthetic clay or gel type catalysts such as silica-alumina composites or other conventional cracking catalysts may be employed at temperatures of about 800.-1000 F. and at pressures of from about atmospheric to about 25 p.s.i.g., all in a manner well known to the art.

The cracked cycle stock is passed from the cracker 15 via line 16 to the still 17. There the cracked hydro- 7 carbon mixture is separated into a light. fraction taken off overhead at 18, a heavy residual fraction taken oif'at 19, and a fraction. boiling in approximately the same range as the feed stock for the catalytic cracking operation, namely, 600l200 F; This fraction,.referred to as catalytically cracked cycle stock, is taken off via line 20 and passed to the extraction tower 21. For purposes of illustration it will be assumed that the extraction operationcarried out in tower 21 utilizes phenol as a solvent for the aromatics in the feed stock. However, it is to be understood that phenol is specified only for the purpose .of illustration and thatother. solvents exhibiting .i- 3 similar selectivity for aromatics, such as liquid sulfur dioxide, nitrobenzene, aniline, cresol, and furfural, may be employed with equal facility. The phenol extracts thearomatic contentof the catalytically cracked cycle stock in a manner well known to the art, forming an extract phase in which the aromatics are concentrated and a raffinate phase relatively poor in aromatics, which 4 the original crude oil. In order to prepare a concentrate suitable for use as flux oil or the like, it is necessary to effect a substantial reduction in the sulfur content of this aromatic extract, i.e., to reduce the sulfur content to a level not higher than about 0.8% by weight. It is well known in the petroleum refining art to reduce the sulfur content of various hydrocarbon fractions by contacting them with hydrogen under suitable conditions in latter is taken off through line 22 and passed to a suitable solvent recovery system not shown. The extract containing the aromatics passes via line 23 to the stripper 24, wherein solvent is separated from the aromatic hydrocarbon concentrate, the solvent being removed overhead through line 25 while the aromatic concentrate is removed via line 26. 7

As pointed out above, the aromatics produced during catalytic cracking are particularly adapted to separation by solvent extraction. In addition to this, the operation of catalytic cracking itself increases the content of condensed ring aromatic compounds. A comparison is set forth below, illustrating'the concentration by weight of compounds containing aromatic rings in various extraction cuts madelby the phenol extraction of a typical cracked cycle stock and a typical virgin lube distillate. From this comparison it is seen that the concentration of aromatics is considerably greater for the same yield when extracting cycle stock than when extracting the virgin distillate.

The efficiency of the extraction process may be con-.

' trolled by varying temperature, amount of solvent employed, etc. For example, at extraction temperatures of 125 l90 F. using phenol modified by 1-10% of water, the following relation exists between extract yield and amount of phenol employed.

Percent Extract Yield, Percent Solvent on Feed by Volume It will be appreciated from the above that extracts of order to convert the sulfur to hydrogen sulfide. In some cases the hydrogen is supplied by the dehydrogenation of various constituents of the hydrocarbon fraction. Such a hydrodesulfurization method is unsuitable for the treatment of highly aromatic stocks, however, and it has been found necessary to utilize a hydrodesulfurization step in which the hydrogen is supplied from an external source rather than by dehydrogenation of the hydrocarbon constituents being treated.

Accordingly, the hydrodesulfurization of the aromatic concentrate is carried out in reactor 27, into which hydrogen is introduced via line 28. The hydrogen and the aromatic concentrate must be contacted in the presence of a catalyst in order to produce the desired reaction. Numerous catalysts which will effect this result are known to the refining art, and any of these wellknown methods may be employed in reactor 27 in accordance. with the present invention. It has been found, however, that most beneficial results, from the standpoint of reducing sulfur content and of retaining a relatively high level of aromaticity, are obtained when a cobalt molybdate catalyst is employed. Catalysts made up of from 324% by weight of cobalt molybdate supported on A1 0 and preferably containing about 15% by weight of cobalt molybdate, are particularly suitable. Mixtures of cobalt and molybdenum oxides may be employed instead of cobalt molybdate. Other desulfurizing catalysts that may be employed include platinum (up to about 2%) supported on alumina and molybdenum oxide-alumina compositions. The contacting may be carried out utilizing a fixed bed technique,

or in any other conventional manner.

In order to minimize or substantially prevent the hydrogenation of the aromatic compounds in the concentrate while the hydrodesulfurization reaction is taking place, it is necessary to carefully control the conditions existing within the hydrodesulfurization unit 27. In general, the hydrodesulfurization conditions must be kept relatively mild, that is, factors which would tend to cause hydrogenation of the aromatics must be maintained near theirminimum limits. These factors are temperature,

sufiiciently high aromatics concentration can be pre pared using from about 75% to about 200% by volume of phenol based on feed.

The above comparison illustrates the advantages of using catalytically cracked cycle stock as a feed material to the hydrodesulfurization process and also that more highly concentrated aromatic feeds may be obtained when operating the extraction process at relatively low Although the concentrate leaving the stripper through line 26 is rich in condensed ring aromatics and there-1v;

fore of potential value as aflux oil, etc., it may have a sulfur concentration as great as or greater than thatof pressure, and ratio of hydrogen to aromatic concentrate employed. A suitable temperature range has been found to be from about 600 F. to 800 F., and preferably from 650 F. to 750 F- Pressures in the hydrodesulfurization unit should be kept at about 50 to 500 psig, with a preferred range of 300-500 p.s.i.g., and the gas rate from about 400 to about 4000 cubic feet of hydrogen per barrel of feed.

The concentrate is withdrawn from the hydrodesulfurization unit 27 via line 29. This concentrate, in addition to being'useful as a flux oil for coal tar or other reverberatoryfurnace fuels, may also serve as a starting material for the manufacture of various condensed aromatic ring compounds. Specific aromatic compounds or types of compounds may be isolated from this stream and used for any desired purpose.

The hydrodesulfurization catalyst may become coated with carbon after an extended period of use. Such a deposit may be removcd by a suitable oxidizing procedure, and the catalyst may then be regenerated according to any technique known to the prior art.

As a specific example of the operation of the process of the present invention, an'aromatic concentrate having the following inspections obtainedfrom phenol extraction of catalytically cracked cycle stock was employed as a starting material.

Gravity, API 1.5 Viscosity at 100 F., S.S.U. 957.0 Viscosity at 210 F., S.S.U. 50.3 Sulfur, weight percent 1.83 Conradson carbon, weight percent 5.0 Tag Robinson color Mt Pour point, F. 45 Refractive index at 75 C. 1.6434 Aniline point, F. -1 43 Aromatics by silica gel, wt. percent 92 Initial boiling point, F.

Using this feed stock, two hydrodesulfurization runs were carried out using a 15% cobalt molybdate catalyst supported on A1 0 and externally supplied hydrogen. The conditions of these hydrodesulfurization runs areset forth in Table I below.

Table 1 Run 1 Run 2 Oil rate, volumes per volume of catalyst per hour 1. 0 2. 0 Temperature, F 700 700 Total Gas Rate, Standard Cubic Feet per Barrel 3, 500 3, 500 Fresh Hydrogen Rate, Standard Cubic Feet per Barrel 1, 000 1, 000 Pressure, p.s.i.g 400 400 In both cases the hydrofined liquid was lemon yellow in color and had the following inspections set forth in Table II below.

Table 11 Run 1 Run 2 Gravity, API 1. 2 0. 8 Viscosity at 100 F. S.S.U 597 Viscosity at 210 F; S.S.U 47. 4 47. 6 Sulfur, Weight Percent 0.5 0. 8 Conradson Carbon, Weight Percent 3.0 3.1 Pour Point, 30 35 Refractive Index at 75 C- 1. 6210 1. 6241 ine Point, --22 --22 Aromatics by Silica Gel, Weight Percent" 92 90 Initial Boiling Point, F 514 439 From the above data it will be seen that the aromatic content of the feed stock, which is expressed here in terms of the percentage of compounds containing an aromatic ring, was not lowered appreciably or at all under the conditions of hydrodesulfurization employed, while the sulfur content was reduced very substantially to an acceptable level in each of the runs. The low sulfur content aromatic, concentrate thus produced is useful as a flux oil for the burning of coal tar in open hearth furnaces, as pointed out previously, and also as the starting material for the preparation of various forms of carbon such as coke for the aluminum industry and carbon black.

While the invention has been described in terms of a specific embodiment employing a particular solvent extraction method for concentrating the condensed ring aromatic compounds and a specific hydrodesulfurization method, it is to be understood that the invention is not limited to the utilization of these specific means, but that equivalent steps known to those skilled in the art may be substituted therefor. therefore not to be limited except by What is claimed is:

The process of preparing a condensed ring aromatic petroleum concentrate useful as a flux oil for burning coal tar in open hearth furnaces, said concentrate containing at least about weight percent aromatic compounds and having a reduced sulfur content of less than about 0.8 weight percent, which comprises the steps of distilling a crude petroleum oil containing sulfur to form a gas oil fraction boiling above about 600 F. and containing at least about 1 weight percent sulfur, catalytically cracking said fraction to form a cracked hydrocarbon product, distilling said cracked hydrocarbon product to segregate a cracked fraction boiling above about 600 F., subjecting said cracked hydrocarbon fraction to a solvent extraction to produce an extract phase rich in aromatic compounds, recovering an aromatic hydrocarbon concentrate containing at least about 90 weight percent of aromatic hydrocarbons from said extract phase, and contacting said aromatic concentrate at a liquid oil space velocity rate of 1 to 2 volumes per volume of catalyst per hour with supported cobalt molybdate catalyst at 700 to 750 F. under a pressure of 200 to 400 psig. in the presence of hydrogen gas flowing at a rate of 1000 to about 3500 standard cubic feet per barrel of the aromatic concentrate, said gas'containing fresh free hydrogen supplied from an external source in an amount of at least about 1000 standard cubic feet per barrel ofthe aromatic concentrate treated to reduce the sulfur content of the thus treated aromatic concentrate to less than about 0.8 weight percent without appreciably lowering its aromatic content.

the appended claim.

References Cited in the file of this patent UNITED STATES PATENTS The scope of the invention is

Images