US2423328A - Process for cyclizing hydrocarbons - Google Patents

Description

July l, 1947. E. T. LAYNG PROCESS FOR CYCLIZING HYDROCARBONS Filed Feb. 24. 1941 50W/1v 7. AY/v6.

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av ArroRNEY Patented July 1, 1947 F FCE 2,423,328 PROCESS FOR CYCLIZING HYDROCARBONS Edwin T. Layng, Jersey City, N. J., assignor to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Application February 24, 1941, Serial No.. 380,297

Claims. l

This invention relates generally to the catalytic dehydrogenation of hydrocarbons, and particularly to the conversion of paraflinic hydrocarbons into cyclic hydrocarbons by the action of a catalyst.

.'I'heoretically, it should be possible to convert paraflinic hydrocarbons into naphthenic and aromatic hydrocarbons catalytically without forming any by-products other than hydrogen. In practice, however, this ideal is never attained; solid carbonaceous matter is invariably deposited upon the catalyst and in time accumulates to such an extent that the activity of the catalyst is impaired. Removal of the contaminating deposit restores the catalyst to its initial activity or very nearly so, but in continuous large-scale operations such removal is by all methods now known quite expensive, entailing investment and operating costs which are frequently greater than those associated with the conversion step itself.

One of the objects or my invention is to provide a method of decreasing the amount of solid carbonaceous matter formed during the catalytic conversion of paraffin hydrocarbons 'into cyclic hydrocarbons. A

Another object of my invention is to provide an improved catalytic parailin cyclization wherein' contamination of the catalyst takes place more slowly, and wherein regeneration of the catalyst is necessary less frequently than in prior known processes. Other objects of the invention will be apparent during the course of the following description.

When vaporized parainic hydrocarbons are contacted with a cyclization catalyst in accordance with known methods of cyclization, the paramns are apparently converted successively to compounds having lower and lower hydrogencarbon ratios until, if the treatment is suiciently severe, aromatics are formed. At least some of the parallins are rst converted into olens before being sufliciently dehydrogenated to form cyclic compounds. Supposedly becauseof differences in the rates of the parailin-to-oleiin and olento-cyclic reactions, the olefin content of a mixture undergoing cyclization buildsup during the early stages of conversion, and is-not entirely depleted even after a major portion of the parafns have been cyclized.

I have discovered that a substantial if not a major proportion of the carbonaceous matter deposited upon catalysts during paraffin cyclization is derived in some way from transitory olefins, and that the greatest amounts of carbonaceous matter are laid down during those stages of the cyclization in which the olefin content of the reactants is greatest. This may be due to polymerization of the oleflns to high molecular weight solid compounds, or to thermal cracking accelerated by the instability or reactivity of hydrocarbons containing oleflnic double bonds.

vThe present invention contemplates the contacting of parallinic hydrocarbons with a cyclization catalyst undercyclizing conditions, the interruption of the ensuing conversion at an intermediate stage thereof. and the elimination of oleflns which have been formed. The invention further contemplates starting anew with the partially cyclized material of reduced olefin content and continuing the cyclization reaction.

It is within the scope of my invention to eliminate olens from a partially-cyclized mixture by simple removal, for example by treating the mixture either in the liquid or vapor phase with a substance such as sulfuric acid having a selective affinity for oleins. However, I prefer to eliminate olens by preferential catalytic hydron genation, converting them back into paraflins so that they may be cyclized in a subsequent stage of treatment. This method has the advantage of involving the least departure from cyclization conditions intermediate the cyclization stages.

The type of hydrogenation I employ is a mild one, involving only the saturation of olenic double bonds.A In general this is a comporatively low-pressure process and is not to be confused with the so-called destructive hydrogenation process which is' conducted ordinarily at very high pressures. The mild type of hydrogenation does not produce signicant changes in the average number of carbon atoms per molecule with an accompanying increase in volatility, which apparently is characteristic of destructive hydrogenation.

In further cyclizing material which has been subjected to the intermediate olefin-eliminating step, additional olens will be formed, but the average olefin content and hence the total degradation to carbonaceous material will, for the process as a whole, be substantially reduced. In some tarded catalyst contamination associated therewith, enables an increased amount of-hydrocar-` bons to be converted before regeneration of the catalyst is necessary. The catalyst then need be out of service for regeneration during a smaller percentage of the time, and cyclization may be accomplished more cheaply and efficiently.

-A more detailed description of my invention will now be given with reference to the annexed drawing, which is a, diagrammatic flow sheet illustrating one form of the invention. In the drawing, re'ctangles are used to designate successive zones of hydrocarbon treatment, and lines are used to show the paths of materials entering and leaving the zones.

As illustrated by linel of the drawing, a vaporized paraifinic hydrocarbon fraction is introduced into the presence of a cyclization catalyst in a zone 2 maintained under conditions favorable to cyclization. The time of residence of the reactant material in the zone is such that the conversion occurring` therein will bepreferably not lessy than about nor more than about 60% of that desired in the nal product.

Partially converted reactants pass from zone 2, as indicated by line 3, into zone 4 in which are maintained conditions favorable to olefin hydrogenation but not suiiiciently severe to hydrogenate the cyclic compounds produced in zone 2. The cyclization occurring in zone 2 may produce greater or less amounts of hydrogen depending upon the type of feed stock and the extent of conversion. In the event that olefin hydrogenation is desired to be effected in the presenceof a, greater or less amount of hydrogen than that produced in zone 2 the excess or the deciency is corrected by the respective withdrawal or addition of hydrogen as indicated by dotted line 5, any added hydrogen being obtained from the final products of .the-process as hereinafter described. Hydrogen may be separated from the partially cyclized hydrocarbon reactants by con- .As indicated by line I I, I may introduce .by-product hydrogen into the material entering zone 2, or via line I2 into the olefin-free material entering zonev 1. In the event that more hydrogen remains after the hydrogenation step than is desired in zone '1, transfer in the reverse direction along line l2 may be adopted, in which case condensation of hydrocarbons is again necessary to effect separation of the excess hydrogen. The introduction of by-product hydrogen into line 3 has already been referred to, and any excess hydrogen withdrawn through lines 5 or I2 into line Il may augment that obtained from line 8 in building up higher hydrogen content wherever necessary.

None of the various stages of treatment contemplated by my invention require to be carried out in any special type of apparatus, and any' which is suitable to the contacting of reactant vapors with a catalyst at an elevated temperature and superatmospheric pressure may be employed. Catalyst may remain static in a containing vessel and be subjected alternately to conversion and regeneration, or it may move continuously and alternately through a conversion l zone and a regeneration zone.

Y usually characterized by lower temperature than densing them to liquids, after which revaporization of the latter will be necessary before proceeding with olefin elimination.

After contacting a suitable hydrogenation catalystI in 'zone 4 and being freed of oleilns the reactants pass as indicated by line `6 into a second cyclization zone 1 wherein they are subjected to further cyclization in a, manner similar to that described with reference to zone 2, except that the treatment is made sufficiently severe and prolonged -to complete the desired conversion. Thereafter, as indicated by lines 8, 9 and I0, byproduct hydrogen (in admixture with other normally gaseous by-products) lis separated in any suitable manner from the cyclized product and rejected from the process via line 9.

It has been found that the contamination of dehydrogenation catalysts during cyclization is retarded appreciably by the presence of hydrogen, or a gas mixture containing hydrogen, added to reactants before conversion commences. I may take advantage of this fact to yenhance the efficacy of my tinvention by recirculatin'g by-product hydrogen-containing gas and admixing it with material about to entera vcyclization zone.

' Patent Number 2,320,147.

cyclization conditions, and I may employ any suitable heat-transferring devices such as heat exchangers in altering the temperature of reactants between a hydrogenation stage and a cyclization stage. In the event that hydrogen is to .be added to reactants between any two stages, I may introduce the hydrogen relatively hot or cold to alter the temperature of the reactants as desired.- Heating or cooling reactants in the conversion zones vthemselves may be accomplished by locating heat-transferring surfaces therein. I

My invention'may be applied, with particular advantage, to the manufacture of superior motor fuel from'paraiilnic naphtha, by conversion of straight chain hydrocarbons of poor anti-)mock characteristics into naphthenic and aromatic `compounds having high octane numbers. When my invention is so applied I prefer to operate pursuant to the teachings of my co-pending application (with L. C. Rubin) Serial No. 294,784, now In such operation I employ two cyclizing stages maintained under a pressure between about 30 and about 450 pounds per square inch, and at a temperature between about 8"'5" and i025. F.; I may use any ysuitable cyclization catalyst, of which chromium oxide and molybdenum oxide supported on activated alumina are exemplary. il prefer that the second cyclizationstage shall be characterized by theA greater severity factor, as defined in my co-pending application above referred to. That is to say,

I prefer'that a greater proportion of the desired conversion shall take place in the second stage than in the first, as may be insured by contacting the reactants with a greater quantity of catalyst in the second stage than in the first. Optionally,

4I may use the same amount of catalyst in 'both stages while maintaining a higher reaction temperature in the second stage than in the first.

It vappears that vthe olefin content of a mixtureI undergoing cyclization increases to a maximum during the initial portion of the conversion, and then declines slowly, A lower average olefin content is therefore obtained by interposing olefin elimination approximately at that point where the olefin content has ceased to increase. With operating conditions and catalysts different from those preferred by me, however, it may be desirable to put the olefin-eliminating step later or earlier in thecyclization. l

I prefer to conduct the cyclization reaction in the presence of hydrogen added to the reactant mixture in amounts as disclosed in my co-pending application, namely 0.5 to 8.0 mols of hydrogen per mole of fresh feed hydrocarbons. I may, however, use different amounts of hydrogen in the different-, cyclization stages.

In m'otor fuel vmanufacture as above described, suiiicient hydrogen for the olefin hydrogenation will usually be produced by the initial cyclization stage. I prefer that there shall be two .to-four times as much hydrogen present as is required to saturate the olenic compounds present. In

the treatment of straight-run parafnic naphtha,

from 0.25 to 1.5 mols of hydrogen per mol of naphtha will usually satisfy the latter preference. 'I'his hydrogen need not be in the pure state, but may be admixed with relatively inert gases such as methane and ethane.

For the olefin hydrogenation I preferably employ the same catalysts as in the cyclizing stages, catalytic dehydrogenation of paraflins to olens being a reversible reaction. Alternatively, I may use a nickel catalyst for the hydrogenating step. The catalyst in the preceding cyclization is then advantageously molybdenum oxide, which will protect nickel from contact with any poisonous sulfur compounds in the feed by reacting with them to form molybdenum sulfide.

When one of the -hydrogenation-dehydrocyclization catalysts such as chromium or molybdenum oxide is used in the hydrogenation stage, that stage may be maintainedv at a relatively high temperature below the cyclization range, for example between 600 and 750 F. lSuch high temperatures are not essential to the hydrogenation reaction, but they minimize the amount of cooling necessary subsequent to the preceding cyclizing stage and the amount of reheating prior to the succeeding cyclizing stage. If a nickel catalyst is used a somewhat lower temperature, in the vicinity'of 200 F., is required.

The hydrogenating stage is suitably maintained at a pressure, in the range specified for the cyclizing stages and preferably at the same pressure as actually used in said stages. Generally speaking, the higher hydrogenation pressures will be used with the higher temperatures, and vice versa, in order to insure that only the oleiins, which are the most readily hydrogenated compound encountered in the partially converted products, will be hydrogenated.

In the event that a stock to be cyclized already contains an appreciable amount of olens, I may interpose a hydrogenation stage preceding the i-lrst cyclization stage, so that the latter may enjoy the benefits of an olefin-free feed.

Also cracked naphtha from a thermal conversion operation, or other highly olefinic material, may be introduced directly into zone 4 of the drawing, and the severity of conversion in zone 1 made suiiicient to produce a desired product in the absence of the preliminary conversion normally afforded by zone 2 when non-olefinic feed is to be treated.

f It has been proposed, by L. C. Rubin in his copending application Ser. No. 330,315 to combine or overlap a cyclization stage with an olen hydrogenation stage by establishing a downward temperature gradient through a zone containing a hydrogenation-dehydrogenation catalyst.

It is within the scope of my invention to substitute suchV a zone in place of any two consecutive cyclization and hydrogenation zones, and such substitution may be advantageous when relatively small amounts of olens are to be eliminated.

While reference 4has been made in the foregoing description to the' cyclization of paranins, it will be understood that in treating` in accordance with my invention a feed stock containing naphthenes as well as paraiiin, the naphthenes will be further cyclized by dehydrogenation to aromatics. My invention is therefore notllmitelli to the treatment of purely paramnic materia s.

While 'various modications have been referred to, it is to be understood that my invention is not limited thereby, but onlylin and by the following claims, wherein I wish to claim all novel features of my invention.

1. In a process for the production of hydrogen and aromatic hydrocarbons from paraiiinic hydrocarbonswithin the gasoline vboiling range, by

contacting such parai'inic hydrocarbons with a dehydrogenating and cyclicizing catalyst at a temperature and space velocity adapted to effect dehydrogenation and cyclization thereof, the improvement which consists in effecting said contact in a plurality of successive stages and treating the reaction products from the first of said stages in an intervening stage to eliminate olens therefrom by catalytically hydrogenating them to paraflins prior to their passage to the second stage.

2. A process as defined in claim -1 wherein said dehydrogenation and cyclization reaction .is effected at a pressure between about 30 and 450 pounds per square inch, at a temperature of about 875 to 1025 F., and in the presence of between 0.5 to 8 mols of added hydrogen per mol'of hydrocarbon.

3.' In a process 'for the conversion of parafnic hydrocarbons within the gasoline boiling range to hydrogen and aromatic hydrocarbons by a catalytic dehydrogenation and cyclization reaction, the improvement which consists in effecting said conversion by passing the reactants in the vapor phase through at least three catalytic stages without intervening condensation and separation of products, the rst and third stages being effected under reaction conditions including a relatively high temperature adapted. to promote dehydrogenation and cyclization of the paraiflnic hydrocarbons and the intervening stage being eifected under reaction conditions including a relatively low temperature adapted to selectively hydrogenate olenic constituents produced in the rst stage.

4. A process as defined in claim 3 wherein hydrogen 'produced in the process is separated from the last stage reaction products and recycled to the reactants entering one of said stages.

5. In a process for the conversion of a low octane paraflinic naphtha to a, high octane highly aromatic motor fuel by a catalytic dehydrogenation and cyclization reaction, the improvement which consists in electing said conversion by vaporizing the naphtha and passing the vapors through at least three catalytic stages without intervening condensation and separation of products, 'the rst and third stage being effected under reaction conditions including a relatively high temperature adapted to promote dehydrogenation and cyclization of the paraflnic hydrocarbons and the intervening stage being effected under reaction conditions including a `relatively low temper- 1 7 s ature adapted `izo selectively hydrosenate olenlo Number v Name v Date constituents produced inthe nrst stage. 2,184,930 Ruys et aL 1--- Dec. 26, 1939 EDWIN T. LAYNG. 2,212,112 Clausen Aug. 20, 1940 2,249,337 Visser et al Ju1y15, 1941 'REFERENCES CITED 5 2,289,716 Marschner July 14, 1942 The following references are of record in the 21320147 Lyng et al May 25, 1943 le 0f this patent; i' FOREIGN PATENTS UNITED STATES' PATENTS Number Country Date Number Name Date 10 413,926 Great Britain ...l Nov. 2, 1934 i 2,045,795 P181 et al Juneo, 1936 OTPIER REFERENCES 2 24 566 G Jul 26, 938 i 251714 Flots Aug. 2, 33 Taylor et al.. article in Transl lFabradaamy Soc.,

1939, vol..35, pages 921-934.

2,183,591 Schulze Dec. 19, 1939 2,202,401 Rosen May 28, 1940. 15

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