US2349826A - Method for the aromatization of aliphatic hydrocarbons - Google Patents

Description

May 30, 1944. l E; r LAYNG l 2,349,826

METHOD FOR THE AROMATIZATION OF ALIPHATIG HYDROGARBONS Filed Oct. 24, 1938 INV EN TOR.

ATTORNEY.

- ence of a catalyst.

processed.

l lysis.

tures of such A accompanied bons formed polymerize.

Patented May 3o, 1944 UNITI-:D STATE 'sf iurrau'r ortica n Ms'rnon non 'rim snoua'rrza'rron or urna 'ric Edwin r. M. w.

mnt, Jersey City. Keller: Company.

mmcsnons N. J.. sssirncr to 'rue New York, N. Y., a

corporation o! Delaware Application October 24, 1938, Serial No. 236,627

lClaim.

My inventonrelates toa method for the aromatization of aliphatic hydrocarbons and more particularly to a process for the catalytic aromatization of aliphatic hydrocarbons in a two stage process.

Currently, the is .carried on as a single operation in the pres- The operatins conditions the particular stock being In general. it has been found that temperatures in the vicinity of from 850 F. to 1000 Rand pressures varying from atmospheric to 100 pounds per square is vrecognised that the degreeof vary. depending upon charged to the volume of catalyst in the reaction chamber exercises considerable innuence: upon the reaction.' The catalysts suitable for the process are known as aromatizing" or dehydrogenatins-cyclizing catalysts, and as suitable cataoxides of metals of the third and sixth groups of the periodic table, sulphides of metals of the sixth group ofthe periodic table, or mixsulphides and oxides have been Aromatization; as now practiced at elevated temperatures in the by several side reactions. these side reactions is simple dehydrogenation of paraiiins. This' results in the formation of oleiinic hydrocarbons. The oleilnic hydrocarlOne of hydrocarbons which become catalyst rendering is pyrolytic conversion of the hydrocarbons into lower boiling hydrocarbons as cracking. Both these reactions are undesirable in an aromatization Dehydrolyst and ultimately render it inactive.

If the hydrocarbons chargedto a one stage aromatization process comprise principally naph the production of carbon and car' thenic stocks. bonaceous material is negligible when compared with that produced when the hydrocarbons being charged are predominantly of a saturated or paraflinlc nature. For example, I have found that the dehydrogenation or'aromatization of a typical naphthene like methyl cyclohexane can be carried out with great efilclency over a lons period of time without the formation of deleinch are satisfactory.v

presence of a catalyst. is'

aromatization of hydrocarbons drocarbon (Cl. 26o-413.5)

or dehydrogenation of a typical parailln hydroa carbon such as' normal heptane can be conducted emcienuy only for a relatively snort period of time.

It has been attempted to overcome the dim- 4culty of carbon deposits with resultant loss in catalyst activity by varying the operating conditions employed. Eor example, it is obvious that the use of lower temperatures will decrease the lrate of carbon formation.. Similarly, the use of` lower pressures and higher throughputs will achieve the same end. Uniorunately, however, all of these expedients lower the yield of the desired aromatic hydrocarbons, since it has been shown that the proportion of aromatic hydrocarbons in the products from such a reaction is increased within rather broad limits by raising the temperature and/or lowering the space velocity. Consequently, it has been necessary to strike a balance in the operating conditions where an optimum ratio of aromatic hydrocarbons and carbonaceous deposits is obtained. Such an ar rangement naturally limits the yield per pass to low level, since high material loss through carbon formation is not feasible.

Another means of varying the space velocity and 4therefore the extent to which the reactions occur is to add hydrogen gas to thehyllrllbon feed stock. This has results, although as will prior art is by no means It will also be shown that by my invention the. hydroen'is utilized in a most logical and eilicient manner so that a high yield of aromatic hyis obtainable from a wide variety of charging stocks with a minimum loss through be apparent later the the most eiii'cient one.

formation of carbonaceous materials.

One object of my invention is to provide a method for the catalytic aromatization of hydrocarbons in which the formation and deposit of carbonaceous material is substantially minimized.

Another object of my invention is to provide a method for the aromatization of hydrocarbons in which a static body of catalyst may be employed with efficiency.

Other and further objects of my invention will appear from the following description.

The accompanying drawing which forms part of the instant specification and is to be read in Y conjunction therewith, is a, diagrammatic view of one form of apparatus capable of carrying out the process of my invention.

- In general, my invention contemplates a methbeen found to give goodw"Vm Reaction (2) is much more vconversion of heptane od in which the aromatization is carried out in two-zones. The catalyst employed may be the same in both zones. If desired, one catalyst may be employed in one zone and a diierent catalyst in the other zone. In the first zone, I employ conditions of moderate pressure as for example in the vicinity of i) pounds per square inch and carry on the aromatization reaction in the presence of an excess of hydrogen. These operating conditions direct the reaction so that predominantly naphthenichydrocarbons'are formed. In the second zone, I employ a lower pressure and a lower hydrogen concentration. Lower pressures and lower hydrogen concentrations in the rsecond zone are adapted to convert naphthenic hydrocarbons produced in the rst zone into aromatic hydrocarbons. The carrying on of aromatization according to my method, minimizes the formation of undesirable products and prolongs the life of the catalyst.

In order that a more complete understanding of the nature of my method may be gained, let us review the reactions which ordinarily occur under the usual conditions for dehydrogenation.

'I'hey are as follows: (1) Paramn=olen+Hs (2) =naphthene+Hz (3) O1en=naphthene (4) Naphthene=aromatic+3H2 All of the foregoing are equilibrium reactions andare thermodynamically favorable to'varying degrees under the conditions of my process. By

way of example and not by Way of limitation, if, in reaction (1) normal heptane is the parafn hydrocarbon and heptene is the olen formed, calculations will show that, at equilibrium, 26 percent of the heptane is converted according to the reaction at a process temperature of 1000 F. and a. process pressure of one atmosphere.

v favorable in a forward direction. Calculations show that approximately 92 percent ofthe heptane is converted under the same equilibrium conditions. Similarly, in reaction (4), calculations show that essentially all of the naphthene is converted into the corresponding' aromatic. The calculations were checked in the laboratory, using heptane,

heptene, methyl cyclohexane and toluene.

fl'hetype ot calculations may be made for reaction (3), but as will hereinafter be shown more fully, these need not be considered in the instant process.

On the basis of equilibrium considerations, it will be readily apparent that the use of either` higher pressures or an excess ofhydrogen will force reactions (l), (2) and (4) in the reverse direction while reaction (3) will be unaiected. For example. a pressure of 100 pounds per square inch gauge decreases the conversion of heptane in reaction (1) from '26 percent to 9 percent. In other words, an increase in pressure from atmospheric to 100 pounds per square inch decreases the formation of oleilnic hydrocarbons about 581 percent. Similarly. the addition of 4 mols-of' hydrogen for each mol .of heptane reduces the from 26 percent to 7 percent or a reduction of 73 percent. The application of an increased pressure of 10() pounds, together with the addition of 4 mols of hydrogen reduces the conversion of heptane from 26 perof 96 percent.

ation of reaction (l).

In reaction (2) the application of an increased pressure of pounds, using heptane by Way oi example, reduces the conversion of heptane from 92 percent to SS percent or a reduction of about 28 percent. The addition of 4 mols of hydrogen reduces the conversion of heptane in reaction (2) from 92 percent to 87 percent or a reduction of about 51/2 percent. The simultaneous use of increased pressure and added hydrogen reduced the conversion of heptane only to 49 percent.

Reaction (4) is so favorable thermodynamically under all conditions that the conversion in all cases approaches 100 percent. t will be seen i the presence of 4 mols of hydrogen and 10() pounds pressure renders reaction (l) -virtually impossible. These conditions, too, reduce reaction (3) since substantially no olens will be produced in the reactions, under conditions of elevated pressure and an excess reverse of action (l), stances may be converted to naphthenes via reaction (3).

It follows that, if the process is so conducted, that is, in the presence of an excess of hydrogen and under elevated pressure, the formation of to the fact that at no time will there be an ap- Y ess, though oi' thenes to aromatics will take place in the iirst zone.

It will be' readily apparent to those skilled in the art that the process conditions will vary with a fresh charge, the acting as a reaction control.

More particularly -referring now to the drawing, the hydrocanbons to be aromatized are charged from any suitable source through pipe l, and pumped by pump 2 through pipe 3 through `mixtures thereof.

convection heated coil 4 and radiantly vheated tubes t of the heater `I which is fired by any suitable burner 1. The hydrocarbons are heated to vaporizing temperature and pass from the heater 6 through transfer line l into an evaporator 9 past valve It. In the evaporator t the heated hydrocarbons are ilashed into vapors and unvaporized oil. The unvaporized oil is withdrawn from the process through' pipe il controlled by valve I2. The vapors pass through pipe I3, through a heater il and are heated in convection heated coil i and radiantly heated tubes i6 to the desired temperature which may be between 850 F. and 1000 F. 'I'he superheated vapors enter a catalyst chamber l1 through a transfer pipe Il. The catalyst chamber contains a suitable catalyst l! which may be an oxide of a metal of the third or sixth group or a sulphide of a metal of the slx'thgroup, of Hydrogen from hydrogen storage tank is pumped by pump 2i through pipe 22 and passed through pipe 23 into the bottom of the catalyst chamber, it being understood that valve 24 is open. The catalyst chamber is maintained under a pressure of about 100 pounds per square inch. It is understood, of course, that the pressure may be varied within suitable limits, depending upon the charging stock being employed. Similarly, the quantity of hydrogen being passed into the catalyst chamber may be varied. r i

In the catalyst chamber l1 the paramn and olefin hydrocarbons will be converted chieiiy into naphthenic hydrocarbons. due to the use of increased pressure and added ludrogen. The products oi' the reaction are withdrawn from the chamber I1 through pipe 2l and passed through a condenser 26 which is supplied with a cooling medium through pipe 21. The condensate and uncondensed gases are withdrawn from the condenser through pipe 2l and pass into a separator 253. It desired, a portion ofthe liquid products may hewithdrawn through pipe Il controlled by a valve 3l and recycled. A back pressure controlled valve 32 maintains the desired elevated pressure upon the iirst catalyst zone. The gases withdrawn from the separator will be preponderantly hydrogen. These may be passed through pipe 33 and pumped by pump u through pipe 23 back to the catalyst chamber to supply the excess of hydrogendesired. A portion of the gases may be vented through pipe-3l by opening valve The hydrocarbons formed,

which are chieiiy hydrogen, are withdrawn from the separator through pipe II and past back preswhich will be principally naphthenic hydrocarbons, are withdrawn from the separator 2l through pipe 31 and pumped by pump' n through the heating coil ll. of heater Il. The heated hydrocarbons are withdrawn from heater 30 through transfer pipell andpassed into a second catalyst chamber 42 containing a suitable catalyst 4l. 'I'he temperature existing ln the second catalyst zone maybe between 850 F. and

1000 F. The prsure existing in the second catalyst zone is considerably lower and may be as low as atmospheric. In the second reaction zone, the naphthenes will be converted into aromatic hydrocarbons accompanied by the evolution of hydrogen. Thel reaction products are withdrawn from the catalyst chamber I2 through pipe M and passed through a condenser which is supplied with a cooling medium through pipe I6. The condensate land inccndensable gases leave the condenser through pipe l41 'and'pass into a separator 4I. The incondensable gases sure controlled valve Il into pipe 5I from which they are pumped by pump 52 through pipe t3 into the hydrogen storagetank 2li. Back pressure controlled valve il determines the pressure which existsin the second catalyst zone l2. The desired aromatic hydrocarbons are withdrawn from the separator through pipe 54, controlled by valve B5. Ii desired, a portion oi' the hydrocarbons may be withdrawn from the separator through pipe It, controlled by valve 51 and recycled either to the second heater I4 or the third heater It. If the conditions are such that an excess of hydrogen is desired in the second catalyst zone, valve Il may be opened and a portion of the hydrogen from pipe 22 may pass through pipe il along with the heated hydrocarbons entering the second catalyst zone through pipe 4l.

. It will be observed4 that I have accomplished the objects of my invention. I have provided an aromatization process-in which a static body of catalyst may be employed and long runs be obtained by minimizing vthe deposition of carbonaceous materials. Not only are long runs obtained, but the avoidance of the formation oi carbonaceous materials produces higher yields o! the desired aromatica. The employment oi such a two stage process will also lengthen the life and permit the reduction in rate of ow of a moving catalyst when used.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. It is obvious that various changes may be made in the operating conditions within the scopeof the claims without departing from the spirit oi the invention. It is therefore understood that the invention is not limited to the specic details shown and described.

Having thus described my invention, I claim:

In a method of producing aromatic hydrocarbons'and hydrogen by contacting aliphatic hydrocarbons oi' six or more carbon atoms in a straight chain at an elevated temperature within the range of about850 F. to 1000l F, with a dehydrogenating-cyclizing catalyst comprising a compound selected from the oxides and suliides of the metals included within the sixth group' of the periodic table, the improvement which consists in eiecting such contact in an initial stage by passing said hydrocarbons in contact with the catalyst at superatmospheric pressures of the order of about lbs. and in the presence of added hydrogen in amount such that the aliphatic compounds are converted largely to cyclic compounds with minimized formation of oleiinic compounds and consequent deposition of carbonaceousmaterial on the catalyst, cooling A and separating the reaction products into normally gaseous products and a condensate containing the liquid conversion, products, thereafter vaporizing and contacting said condensate in a second stage with the catalyst at a pressureand with a quantity oi added "hydrogen substantially lower with respect to the pressure and quantity of added hydrogen than that utilized in the initial stage, and recycling hydrogen produced ir. the process to supply said added hydrogen EDWIN T. LA YNG.

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