US2398674A - Hydrocarbon conversion process - Google Patents

Description

April 16, 1946.

cg'Cq. HYDROCARBONS LIGHT GASOLENE W. A. SCHULZE HYDROCARBON CONVERSION PROCESS Filed July 6, 1943 VENT ' fl sz HYDROGEN -CONTAI NING GASES ABSORPTION UNIT LIGHT GASES STEAM P L'i AVIATION BLENDI NG STOCK HOLVNOILDVHJ FEED STOCK HEAVY GASOLINE HINGE LVBHHJSVM T k l WALTER A. SCHULZE ufactur-e of aviation gasoline blends.

Patented Apr. 16, 1946 HYDRQCARBON CONVERSION PROCESS Walter A. Schulze, Bartlesville, Ok1a., assignor to Phillips Petroleum Company, a corporation of Delaware Application July 6, 1943, Serial No. 493,669

1 Claim. (Cl. 196-50) This invention relates to the catalytic conversion'of hydrocarbon oils to produce gasoline of special characteristics including high octane number, predominantly aromatic composition and low contents of paraflin and olefin hydrocarbons. More specifically this invention relates to a catalytic conversion process wherein the said gasoline characteristics are obtained through a unique combination of feed stock composition and catalytic treating conditions.

The thermal or catalytic conversion of liquid or gaseous non-aromatic hydrocarbons to aromatic hydrocarbons has heretofore been of interest principally from-the standpoint of improving the octane rating of ordinary motor gasoline by inclusionof minor concentrations of aromatics. More recently, however, it has become essential to increase the selectivity and extent of conversion in processes yielding aromatic hydrocarbons in the gasoline boiling range in order to produce higher yields and concentrations of said aromatic hydrocarbons for various uses, some of which involve segregation of the pure compounds.

Another important use of said aromatic hydrocarbon concentrates has developed in the man- This particular utilization not only requires high concentrations of aromatics in the blending stocks,

but also limits to very low values the amounts of low octane parafiins, olefins or other undesirable hydrocarbon types. which may be tolerated without impairing the desired qualities of the aromatic gasolines stocks and their potency in aviation gasoline blends. These qualities include the octane ratings, rich mixture characteristics and blending values, and stability toward gum formation.

In previously proposed methods for the production of aromatic gasolines by catalytic cracking and other related processes, the desired aromatics have usually been produced in mixtures containing olefins and parafiins in proportions depending on the nature of the original feed and the extent of conversion permitted by mechanical or other limiting process features such as sirable hydrocarbon types to the exentdemanded by aviation gasoline specifications.

usually high aromatic content and low olefin and paraflln hydrocarbon content in a single catalytic conversion treatment.

Another object of the invention i to provide a catalytic process capable of producing the desired type and extent of conversion in substantially a single pass operation.

Still another object of this invention is the coordination of the composition of feed stocks with the conditions of the catalytic conversion in order to adjust the rate and extent of the convertive reactions and control the concentration of the various hydrocarbon types in the products.

Other objects and advantages of the invention such as the production of superior aviation gasoline stocks from conventional refinery gasolines will be apparent from the following disclosure.

We have now discovered that the production of predominantly aromatic gasolines through the catalytic conversion of hydrocarbon mixtures containing both cyclic and acyclic hydrocarbons may be accomplished by concomitant and/or sequential reactions in a catalytic treating zone. The desired promotion and extent of the arcmatization reactions are effected by the conditions imposed in the catalytic zone and the proportions of the dilferent hydrocarbon types in the feed stock. As a result "of the co-ordination of the treating conditions and the relative quantities of each type of hydrocarbon undergoing conversion, the various reactions are adjusted to accomplish greatly increased conversion of paraffin, olefin and naphthene hydrocarbons and correspondingly increased concentrations of are matic hydrocarbons.

In one specific embodiment of this invention a liquid hydrocarbon feed stock in the gasoline boiling range is treated in the presence of a catalyst capable of promoting aromatization under conditions favorable to a relatively complete degree of conversion of paraffins, olefins and naphthenes contained in the feed. This catalytic treatment is followed by fractionation of the products to segregate aromatic concentrates and/or gasoline blending stocks within substantially the same boiling range as the feed stock.

A simplified fiow diagram of the process steps involved is shown in the drawing. According to this arrangement, the fresh feed stock entering through a line I0 is preheated in a coil in a furnace H and passes through a transfer line 12 to the catalytic zone. Steam diluent from a line l3 is also preheated in furnace II and may be added It isvan object of the present invention to acl complish the production or aromatic concentrates and/or gasoline stocks suitable for the abovedescribed purposes.

It is a further object of the invention to accomplish the conversion of selected liquid hydrocarbon feed stocks to gasoline stocks of unto the feed vapors in the preheating coil and/or at one or more points in the transfer line and a catalytic reactor l5 through line H. v

The feed vapors from line l2 pass through catalytic reactor l5 under conditions promoting maximum eflicient conversion to aromatics and, thence, through a line I! to awaste heat boiler ill for reduction of temperature. The partially cooled eflluent stream passes through a line l9 to a separator 20. Further cooling may be applied to enable condensation -of the liquid hydrocarbons and separation of water through a line 2|. Light gases, e. g. C4 and lower boiling uncondensed material may be removed through a line 22 while the liquid products pass through a line 23 to a fractionator 24.

In column 24 the gasoline is fractionated to any desired end point with heavier bottoms passing through a line 26 to motor fuel or other uses, or possibly for recycling to the catalytic treatment. The overhead gasoline vapors are taken through a line 25 to further fraotionating equip ment illustrated by av column 21. In the subsequent fractionation steps, light gasoline, e. g., Cs and lighter may be taken overhead, while the aviation blending stock fraction passes through a line 29 to fractionation, clay treatment or other supplementary refining or blending treatment.

The light uncondensed gases removed through line 22 pass to an absorption unit 30 for recovery of the heavier components, e. g., (Ia-04 hydrocarbons, while the stripped gas stream containing hydrogen and methane is taken through line 32 to be vented or used as fuel. In some cases, depending on the catalyst, the source of the feed stock, and other operating conditions, it may be desirable to recycle a portion of this hydrogencontaining gas stream through line 33 to the fresh feed stream.

In the conversion of feed stocks containing paraflin, olefin and naphthene hydrocarbons in a single catalytic step to produce aromatics, several types of reactions are involved. These include the following: (1) dehydrogenation, (2) cracking, (3) isomerization, (4) dealkylatz'on, alkylation, (6) polymerization and (7) cyclization. While the sequence and extent of each of these types of' reaction are often obscure, the

overall heat balance for production of high concentrations of aromatics indicates more efficient conversion is obtained with a somewhat greater 'extent of exothermic reactions such as alkylation, polymerization and cyclization. This in turn indicates that under suitable conditions, the exothermic reactions are capable of supplying heat somewhat in excess of that required by the endothermic reactions when a feed stock of proper composition is employed,

At the same time, the presence of hydrocarbons undergoing endothermic conversion is desirable in order to absorb a portion of the exothermic heat and prevent the temperature in the catalytic zone from reaching undesirably high levels. However, since aromatic gasoline products of highest quality may contain only limited amounts of unconverted hydrocarbons of the type most apt to undergo endothermic conversion the proportions of said hydrocarbons in the feed stock must be correspondingly limited in order to achieve the desired completeness of conversion and also to prevent absorption of heat by endothermic reactions from lowering the temperature in the catalytic zone below the optimum aromatization level. In this respect, temperatures in the catalytic zone and the relative amounts of endothermic and exothermic reactions are critical from the standpoint of rate of reaction and completeness of conversion.

In view of the foregoing, I have found that improved results are obtained by a relatively critical selection of feed stock composition particularly with regard to the boiling range and also of importance.

quantities or parafiln and olefin hydrocarbons. In the case of cyclic components, such as naphthene and aromatic hydrocarbons which may be presentin the feed stocks, the concentrations are Thus, naphthenes are consldered as being rapidly and substantially completely converted to aromatics, although certain alkylation and dealkylation reactions may occur. Aromatic hydrocarbons present in the feed stock contribute to the aromatic concentration in the product and,,furthermore, apparently enter into alkylation reactions with olefins present or formed in the catalytic zone, Dealkylation and isomerization reactions may also occur, whereby the length, number and position of the alkyl side chains are changed, In addition, the proportions of cyclic hydrocarbons in the feed stock are an index of the refractoriness of the stock toward carbon formation and, hence, of the extent to which the catalyst temperature may be raised to increase the rate and extent of the aromatiza. tion reactions. 1

The conditions most favorable to eificient conversion in a process of the type described include (1) a catalyst of moderate and well-sustained activity, (2) temperatures substantially above about 1000 F., and (3) temperature-reaction time relationships which promote the desired depth of conversion of the selected feed stocks.

Catalysts suitable for the promotion of the various convertive reactions occurring in the catalytic reactor are usually alumina-base contact catalysts of natural or synthetic origin, In many applications the natural mineral ore-bauxite is employed and this catalyst exhibits satisfactory activity during relatively long conversion periods and is unusually resistant to the high temperatures during conversion and reactivation. Other catalysts of satisfactory activity comprise synthetic alumina, often modified by incorporation of minor amounts of magnesia and/or oxides or hydroxides of alkali and/or alkaline earth metals. The preferred catalysts are resistant to poisoning by water vapor, sulfur compounds and the like and undergo substantially no chemical or mechanical deterioration.

When these catalysts become temporarily deactivated because of accumulation of carbonaceous deposits, reactivation is efi'ectedby treatment with a gas stream of controlled oxygen content, whereby the carbonaceous deposits are burned off and the original activity is substantially restored. Temperatures during reactivation are ordinarily controlled below those causing deterioration of the catalyst or vessels, usually below about 1400 to 1500 F.

The conversion temperatures employed in treatment of the preferred feed stocks are ordinarily in the range of about 1000 to about 1300 F. Pressures in the catalytic zone are low superatmospheric pressures in the range of about zero to about 200 pounds gage. Flow rates are chosen to conform to the temperature and pressure of treatment and the desired depth of conversion and may vary from about 0.1 to about 10 liquid volumes of charge stock per volume of catalyst per hour.

Under the above-mentioned conversion conditions, the convertive reactions are most efilciently balanced and particularly valuable aromatic gasoline products are obtained with a relatively narrow boiling range charge stock containing anproximatelyv equal parts of acyclic and cyclic hydrocarbons. The cyclic hydrocarbons, aromatics and naphthenes, may be present in variable wise partially determined by the nature of previous operations producing the desired; charge stocks, although said proportions are more critical and, hence, are closely controlled. In general, a somewhat greater concentration of the more reactive olefinic types is preferred, or, conversely, the paraiiin concentration is ordinarily limited to an amount which can be substantially completely converted in the catalytic treatment to aromatics and/or the various intermediates leading to the formation of aromatics. Regulation of the olefin content is particularly important with respect to the boiling range, in order to obtain most efficient utilization of the intermediate reaction products. For example, light (C5-C6) olefinsmay be relatively refractory and, hence, difiicult to convert, while heavy oleflns (boiling above about 375 F.) may be associated with increased carbon formation.

In one specific embodiment of the invention, the charge stock for the production of aromatic concentrates in the gasoline'boiling range has the following approximate composition:

' Weight Hydrocarbon type per gent Oleflns.... ...l 28-30 Parafllna. 20-22 Aromatics 20-25 Naphthenes 20-25 cracking of the high boiling acyclic olefins and parafflns.

In the production of aromatic concentrates (benzene, toluene, xylenes, etc.) and/or aviation gasoline blending stocks with boiling ranges of about 150 to about 350 F. or somewhat higher.

the charge stock may be fractionated to the following approximate true boiling range:

Initial boiling point, "F 150-160 5% i 170 10% 190-195 20% ........L 200-205 50% 240-260 95% -4 350 End boiling point 3'15 The 'response of the various hydrocarbon types within this boiling ran e to the catalytic treatment is favorable to relatively high yields of aromatic compounds. Yields of aromatic gasoline i often amount to from about 60 to about 80 per cent based on the quantity of the charge stock within the corresponding boiling range.

The effect of the above-mentioned factors on the yield and quality of aromatic aviation gasoline stockswill be illustrated by the following said ratio may be higher if suitable stocks and/or pretreating processes are available.

This charge stock composition, moreover, is obtained within a critical boiling range chosen to conform to the nature of the convertive reactions,

the reactivity of the hydrocarbons in the charge stocks, and the desired boiling range of the products. The yield of aromatic concentrates in the gasoline boiling range is directly related to the proportions of charge hydrocarbons in the same boiling range, and to a certain extent, the inclusion'of charge hydrocarbons outside of the said product boiling range complicates the catalytic Such heavier components may be cracked to lower-boiling olefins within the gasoline range but in this intermediate form constitute less desirable components of the products. Higher boiling cyclics, however, may be charged and/or recycled in moderate amounts, since dealkylation reactions may produce additional aromatic gasoline without the carbon formation associated with the exemplary operations. However, no limitation to the source or previous treatment of the charge stocks or to the specific conditions of treatment are implied, except as defined by the terms of the foregoing disclosure.

Example Comparative tests were carried out on four the aviation gasoline range. A summary of the tests is given in the following table.

Operation Charge stock:

Composition, weight per cent- Oleflns eases I asses eases eases Total cyclics Boiling range characteristics- Aviation B. R. traction,

weight per cent Fraction above 375 F.,

weight per cent Fraction below F.,

weight per cent 7 Product yields: i Yields based on total charge,

weight per cent- Light gas and loss CrCt alkylation stock; Total gasoline Aviation gasoline yields- Weight per cent of total c arge... Weight per cent of charge fraction having corresponding boiling range Catalyst inlet temperature, F Aveli agc temperature rise in catalyst,

The charge stock for operation 89 was a 375 F.

end point polyform gasoline, but containing about 7 weight per cent or material boiling below 150 F. The charg stock for operation 95 was this same gasoline from which the low boiling material had been removed by fractionation. The fractionation also aiiected changes in the composition of the stock, increasing the total cyclics from 40 to 51 per cent and increasing the fraction in the aviation boiling range from73 to 85 per cent.

Improved operation and yields in operation 95 as compared to operation 89 are indicated by lowered production of light gases and carbon and substantially higher production of both total gasoline and the aviation gasoline fraction. The exothermic reaction heat in operation 95 was somewhat less than in operation 89 due in part to the lowered olefin content. In each operation the C3Cs alkylation stock contained about 70 to 80 per cent of oleiins.

In contrast to operation 95, in which the charge stock exemplified the preferred composition with regard to both boiling range and concentration of the hydrocarbon types, are operations 105 and 114. In these latter operations the charge stocks were cracked naphthas from two types of thermal cracking units. The charge stock to operation 105 contained only 32 per cent total cyclics, and 44 per cent boiled above 375 F. The parafllnolefin ratio was also above the preferred range. The charge stock to'operation 114 contained 30 per cent total cyclics and 50 per cent boiled above The efiects of the high boiling range and the feed composition are shown in the high production of light gases and C3-C5 stock together with relatively lower production of total gasoline. Aviation gasoline yields based on the quantity of charge stock in the corresponding boiling range are fairly high but did not reach the values obtained with the preferred hydrocarbon type composition of'operation 95. In both operations 105 and 114 the exothermic reaction heat was exaseae'ra cessive, causing a temperature rise in the catalyst of about 200 F. so that optimum conversion conditions could not' be maintained. Lowered catalyst inlet temperatures on the other hand, failed to initiate and promote aromatic forming reactions at a suitable rate.

From the foregoing, it is believed .that the method and apparatus forpracticing my instant invention wilrbe readily comprehended by persons skilled in theart. It is to be clearly understood, however, that various change in the apparatus herewith shown and described and in the method of practicing the invention, outlined above, may be resorted to without departing from the spirit of the invention as defined by the appended claim.

I claim:

A method of producing improved yields of aromatic hydrocarbons boiling in the gasoline range which cOmprises contacting a hydrocarbon feed mixture boiling within the temperature range of about 375 F. and comprising on a weight basis about 28-30 parts olefins, about 20-22 parts parafiins, about 20-25 parts of naphthenes, and about 20-25 parts aromatics, with a bauxite catalyst at a. temperature of about 10001300 F. and at a flow rate of about 0.1-10 liquid volumes. of feed per volume of catalyst per hour, whereby substantial conversion to aromatic hydrocarbons boiling in the gasoline range accompanied by exothermic and endothermic reactions concomitantly occurs,. the proportions of component in said hydrocarbon feed having been so selected that under the conditions of the reaction a net liberation of heat occurs somewhat in excess of that required by the endothermic reactions and the endothermic heat losses are compensated 01 with an accompanying rise in temperature, and fractionating the products of reaction to separate a highly aromatic fraction boiling in the gasoline range.

WALTER A. SCHULZE.

Images