US2254555A - Catalytic treatment of hydrocarbons - Google Patents

Description

Sept. 2, 1941. c. THOMAS CATALYTIC TREATMENT OF` HYDROCARBONS Filed Feb. 9, 1959 Patented Sept. 2, 1941 1 CATALYTIC TREATMENT F HYDRO- CARBON S Charles L. Thomas, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application February 9, 1939, Serial No. 255,481

12 Claims.

This invention relates particularly to a process for converting straightrun hydrocarbon oils or paraiiinic hydrocarbon oils boiling substantially in the range of gasoline which have a relatively low antiknock value into gasoline of relatively high antiknock value and/or normally gaseous hydrocarbons relatively rich in polymerizable olens.

It has been previously found that straightrun gasolines or hydrocarbon oils predominately parailinic in nature and boiling in the range of gasoline may be converted into oils containing substantial quantities of liquid olefinic hydrocarbons by subjecting them to contact with a dehydrogenating catalyst under selected conditions of temperature and pressure. Investigations have further shown that when the charging stock to-a catalytic cracking process contains substantial quantities of oleflnic hydrocarbons the yields of gasoline obtained approximate those obtained when running a stock predominately paraiinic and that the gases produced in the prcess contain higher percentages of oleilns and particularly more isobutene. In addition, it has been found that lower cracking temperatures may be employed when the catalytic cracking stock contains substantial quantities of olefins, resulting in less deposition of carbonaceous materials on the catalysts and, therefore, longer catalyst life, because fewer reactivations are necessary to keep the catalysts in an active state. Furthermore, the lower temperatures employed in the catalytic cracking reaction conform more closely to the desired conditions for obtaining a greater degree of isomerization of the cracked products.

The present process is not limited to any particular type of charging stock, except with respect to those hydrocarbons boiling in the range of gasoline. It may, for example, be employed as a `means for substantially completely gasifying the hydrocarbon oil charging stock. This particular feature is especially applicable when the charging stock consists of normal straight-chain parafiinic hydrocarbons containing l0 carbon atoms, or less, to the molecule, such as, for example, normal octanes or decanes which have a relatively low antiknock value. Hydrocarbons in this particular class of compounds, such as, for ex- `ample, normal octane, when subjected to dehydrogenation yields a normal octane. A normal octane when subjected to contact with a cracking catalyst under selected'conditions of temperature and pressure yields normal and iso-butene.y The (ci. 19e- 49) polymerization to yield an iso-octane which after hydrogenation finds wide application as an aviation fuel.

Within the broad concepts of this invention 5 dehydrogenation refers to the breaking of carbonto-hydrogen bonds resulting in the splitting off of hydrogen from the molecule-and the formation "of a molecule containing a double bond, otherwise known as an oleilnic hydrocarbon, whereas catalytic cracking refers to the breaking of carbon-to-carbon bonds resulting in the formation of two or more molecules of lighter hydrocarbons than the original.

In -one specific embodiment the present invention comprises catalytically dehydrogenating hyv condensate to thecracked products, fractionating the mixture of cracked products and cooling oil to produce gases, vapors of gasolineboiling range which are condensed and collected, light reux condensates used partly `as said cooling oil and as recycle material to said vapor phase cracking and heavy residual materials which are removed from the process.

The outline ofthe process given in the preceding paragraph will be amplified in the following description to indicate its important features in greater detail by describing characteristic operations in connection with the attached diagrammatic drawing. The drawing illustrates one specific form of apparatus in which the process of the invention may be conducted. It is not drawn to any absolute or relative scale and the design and relative sizes of the individual units may be varied within reasonably wide ranges without departing from the broad scope of the invention.

through line land valve 2 to pump 3 which discharges through lined containing valve 5 into heating coil 6. The hydrocarbon oil in passing through heating coil 6 is substantially completely vaporized therein and raised to the desired temperature without any substantial pyrolytic cracking,thereof by means of heat supplied from furnace 1. The vaporized hydrocarbony oil discharged from heating coil 6 is directed through line 8 and valve 9 into catalytic reactor Ill and is normal and iso-butene may then be subjected to contacted therein with a dehydrogenating catalyst under substantially the same conditions of temperature andpressure as were employed on the outlet of the aforementioned heating coil.

Preferably and in .the case here illustrated. catalytic reaction I comprises a pluralityof small diameter reactor tubes II connected in parallel between upper and lower headers I2 and I3 and is disposed within a heating or cooling sone I4. In order to obtain the bestv results when dehydrogenating, which is an endothermic reaction (requiring heat). some form of heating must be employed in zone I4. It has been found that best results are usually obtained when employing fluid heating means, preferably comprising hot combustion gases, which may be introduced to zone I4 through duct I5, passed in indirect heat exchange relationship with the vapors in reactor tubes i i and later discharged from the upper portion of zone I4 through duct I6. 1

In catalytic dehydrogenatiom carbon deposits upon the catalysts as long as the vapors are in contact with it, and after a prolonged time the carbon deposition reaches such a point that the active surface of the catalyst exposed to the vapors is materially reduced. Frequent reactivatlons. after relatively short periods of operation, are therefore necessary in order to maintain the catalyst in an active state. Because of this, a plurality of reactors are preferably employed, each disposed within a separate heating or cooling zone, and in order to make the operation continuous, with respect to the balance-of the equipment, the catalysts may be reactivated in some of the reactors while the catalysts in others are contacted with the process vapors.f Although the assauts ties of oxygen are introduced to reactor I0 by way of line I'vl, valve Il, and line l. The reactivating gases pass through reactor tubes Ii and due to oxidation the carbon deposited upon the catalysts disposed therein is caused to burn and/the resulting gases are discharged from reactor I0 by way of line Il, line 20, and valvej'2l and may be recirculated or discharged to the atmosphere as de- A sired. When reactivating, the reaction that type of reactor described above has been found v to have many advantages when employed in this particular process, various other kinds of reactors may be employed without departing from the broad scope of the invention.

Catalysts are preferably employed which have been found to be highly emcient in the catalytic dehydrogenation of hydrocarbon oil lvapors to produce optimum yields of oleflnic liquid hydrocarbons. `The preferred catalysts for effecting dehydrogenation are the catalysts consisting of activated aluminum oxide supporting chromium sesquioxide. Such catalysts are preferably produced by the deposition of chromium trioxide or Y its salt or salts of trlvalent chromium, such as chromium nitrate, Cr(NOs) s, or by the precipitation of chromium trihydroxide. CNDH): alumina granules.

While the present process has been found to operate very effectively in dehydrogenating hydrocarbon oils when employing an aluminachromla catalyst, the process is not limited to this particular composition of catalyst but may employ other composite catalysts of a more or less refractory character. such as, for example,y

alumina or silica or an inert refractory material composited with compounds, and preferably the oxides selected from the groupcomprising compounds and oxides of the elements in the left hand columns of groupe 4, 5, and 6 in the periodic table. The catalysts which are alternately-utilizable are not exactly equivalent in their reaction and are not to be considered as absolute substitutes one for the other, which fact will be more or less apparent' to those conversant with the practical aspects of catalysis.

In the case here illustrated, whenthe catalyst is reactivated the flow of hydrocarbon vapors is stopped and suitable reactivating gases at an elevated temperature containing regulated quantiupon l takes place is ``exothermic, and, therefore,y a suitable means must be employed to dissipate the heat. This may be accomplished by directing cooled combustion gases into reactor I4 by way of duct I5, passing the same in indirect heat exchange relationship with the reactivating gases in reactor tubes Il and discharging them by way of duct I5.

The products of dehydrogenation from reactor I0 are directed through line I8 andvalve 22 into cooler 23 wherein they are cooled to a temperature substantially below that at which pyrolytic cracking is effected. 'I'he cooled products of dehydrogenation from cooler 23 are directed through line 24 and valve 25 into separator and absorber 25. Fixed gases produced in the dehydrogenation reaction are preferably separated from the liquid products in separator and absorber 25. Provision is made for introducing cooled reflux condensate, produced as subsequently described, to the upper portion of separator and absorber 26 by way of line I3 as a cooling and refluxing medium therein and as an absorber oil for the lighter normally liquid hydrocarbons. Provision is also made for reboiling the bottoms of separator and absorber 25 by passing a suitable heating medium through closed coil 21.

Although separator and absorber 2l is preferably operated to remove all of the normally gaseous hydrocarbons, it may be desirable at times to separate only hydrogen and methane, in which case the balance of the normally gaseous hydrocarbons would be contained in the liquid recovered as bottoms in this step. In any case, the

fixed gases separated in separator and absorber 26 are directed from the Aupper portion thereof through line 28 and valve 29 to cooling and storage or elsewhere as desired. The liquid products of dehydrogenation collected in the lower portion of separator and absorber 26, comprising normally liquid hydrocarbons and. when desired. condensed and dissolved normally gaseous hydrocarbons, are vdirected from the lower portion thereof through line 30 and valve 3i to pump 32 which discharged through line 33 and valve 34 into heating coll 35.

The products of dehydrogenation introduced to heating coil 35 are vaporized therein and raised to the desired reaction temperature, without substantial pyrolytio cracking thereof, by means of heat supplied from furnace 35. The heated vapors from heating coil 35 are directed through line $1 and valve 38 into catalytic reactor 39 and is contacted' with a cracking Vcatalyst 4suitably disposed therein.

Preferably and in the case here-illustrated, reactor 30 comprises an apparatus of like design to reactor Ill consisting essentially of reactor tubes 40. upper and lower heaters 4I and 42, and disposed within heating or cooling zone 43.l Catalytic cracking is also an endothermic reaction and, therefore, provision is made for the introduction and withdrawal of hot combustion gases to zone 43 during the processing cycle and for the introduction and withdrawal of cooler combustion gases during the reactivating cycle, ducts M and 45 being supplied for this purpose.

When desired, steam may be 'introduced with the charge to reactorv 39 in order to assist in vaporizing the charge and in reducing the effective pressure on the hydrocarbon vapors. Steam may be introduced to the products of dehydrogenation prior to'their introduction to heating coil 35 by way of line 46 and valve 41, or after they have been vaporized in heating coil 35 by way of line 48 and valve 49.

Catalysts which have been found to be highly efficient in the catalytic cracking of hydrocarbon vapors consist in general of uniform size pellets of specially prepared silica composited with alumina. the amount of the alumina being varied tovsuit requirements depending upon the stock to be treated and the operating conditions employed. As a rough average, good results are usually obtained, for example, when employing silica composited with alumina. This alumina percentage is varied for best results under specific conditions `over a relatively wide range, for example, from 2% to 50%, or alumina may be employed as the major ingredient and the silica varied over substantially the same range as the alumina, i. e., 2% to 50%. Catalysts of this character may be initially prepared in any of several different manners and subsequently dried. The preferred catalyst is prepared by precipitating silica hydrogel from a solution of sodium silicate by acidifying with an acid, such as hydrochloric acid, for example, subsequently treating and washing the silica hydrogel to remove substantially all of the alkali metal ions, suspending the purified silica hydrogel in a solution of aluminum salts and depositing the alumina hydrogel upon the suspended silica by the addition of volatile basic precipitants, such as, for example, ammonium hydroxide, ammonium carbonate, or ammonium sulfide. After the alumina hydrogel has been deposited upon the purified silica hydrogel the material is dried,` formed into pellets and calcined at a temperature of approximately 850 to 1000o F. The process, how.

ever, is not limited to this particular composition of cracking catalyst but may employ other composite catalysts of a refractory character, such as, for example, silica composited with com-1y pounds selected from the group consisting of zirconia, vanadia, alumina-zirconia or aluminathoria, and other catalysts such as acid treated clays may be employed. The catalysts referred to above are not exactly equivalent in their reaction and are not to be considered as absolute substitutes one for the other, which fact will be more or less apparent to those conversant with the practical aspects of catalysis.

In catalytic cracking, as in dehydrogenation,

I the deposition of carbon on the active surface of 4 the catalyst lowers its activity and, therefore, -in

order to obtai.. best results frequent reactivation of the catalyst is desirable. In order that this operation maybe made continuous along with the rest of the process, a plurality of'reactors The conversion products from reactor 39 are directed through line 52 and valve 53, preferably cooled to a temperature below that at which substantial pyrolytic cracking is effected by commingling with the same a suitable cooling medium, introduced as subsequently described, and the conversion products, together with the cooling oil, are introduced to separating zone 51 within combined fractionator and separator 58. As illustrated in the accompanying drawing, vessel 55 comprises a separating zone 51 in its lower portion and a fractionatlng/zone 58Aseparated from said separating zone by means of reflux trapout tray 59. However, other means .may be employed to accomplish the same purpose, such as, for example, separate vessels.

In separating zone 51, tlre-1yaporous componentsaraseparated from thecnvaporous liquid residue which is directed through the lower porton'thereof through line 50 and valve 5| to cooling and storage or elsewhere as desired. The vaporous components are subjected to fractionation in fractionatlng zone 58 to separate fractionated vapors inthe gasoline boiling range from the higher boiling hydrocarbons.

Fractionated vapors of the desired end boiling point are directed from the upper portion of fractionating zone 58 through line 52 and valve 63 to cooler and condenser 64. The resulting gas-containing distillate, together with undissolved and uncondensed gases discharged from condenser 54, are directed through line 65 and valve 55 to receiver 61. 1

Undissolved and uncondensed gases collected and separated in receiver 61 are directed from the upper portion thereof through line 58 and valve 69 to collection and storage or elsewhere as desired. Regulated portions of the distillate collected and separated in receiver 61 are directed through line 10 and valve 1l to pump 12 which discharges through line 13 and valvel 14 into theupper portion of fractionatlng zone 58 for reiluxing 4and cooling therein. The remaining distillate collected and separated in receiver 61 is directed from the lower portion thereof through line 15 and valve 16 to stabilization and subsequent storage or elsewhere as desired. Water collected in the lower portion of receiver 61 resulting from the condensation of steam employed in the .process is directed from the lower portion thereof through line 11 and valve 18 to waste.

The higher boiling hydrocarbons separated from the fractionated vapors, comprising a Ifraction whose average boiling point is `above that of said fractionated vapors, are condensed as reflux condensate in fractionatlng zone 58 and collected on trapout tray 59. This reflux condensate withdrawn from the lower portion of fractionatlng zone 58 through line 19 may be directed through line containing valve 8l to cooling and storage as a product of the process. Preferably, however, the reflux condensate is supplied to the catalytic cracking step to obtain substantial further conversion thereof. This may be accomplished by directing the reflux condensate in line 19 through valve 82 to pump 83. Pump 83 discharges through line 84 and a portion of the reflux condensate is directed through line 85 and valve 86 into line 52, commingling therein with the conversion products discharged from reactor 39 in order to cool said conversion products, as previously described. The balance of the reflux condensate in line 84 may be directed all vor in part through line 93 land valve l1 to sub-cooler 88. The cooled reflux condensate is discharged from sub-cooler It through line Il containing valve 80 into the upper portion of separator and absorber 2l to act as a cooling and absorption medium, as pre`- the oil into a predominantly olennic product, and subjecting said olenic product in a second stage to cracking in the presence of a cracking catalyst of different composition than said dehydrogenating catalyst and which is selective in the breaking of carbon-'to-carbon bonds.

2. A process for increasing the anti-knock l value of parafilnic gasoline fractions which commingled state with the liquid products of dehydrogenation or a portion may be returned to the dehydrogenation step by directing it through valve OI into line 4.

vThe preferred range of operating conditions which may beemployed in an apparatus such as illustrated and above described to accomplish the desired results is approximately' as follows:

The heater to which the charging stock is supplied may employ an outlet temperature ranging, for example, from 800 to 1200 F. and a superatmospheric pressure of from approximately to 100 pounds or more per square inch. Subtantially the same conditions of temperature and pressure are maintained on the process vapors introduced to the catalytic dehydrogenation reactor as are employed on the outlet of the heating coil to which the charging stock is supplied. The separator and absorber may employ a superatmospheric pressure substantially the same as that on the outlet of the catalytic dehydrogenation reactor. The furnace to which the dehydrogenated products are' introduced may employ an outlet temperature' ranging, for example, from 800 to 1200 F. and a superatmospheric pressure of from 20 to 100 pounds or more per square inch. However, this process permits the' utilization of lower temperaturesatha'n would otherwise b'e em ployed if the cracking step was not preceded by the dehydrogenation step. Substantially the same conditions of temperature and pressure may b utilized on the processvapors introduced to the catalytic cracking reactor as are employed on the outlet of the heating coil to which the dehydrogenated products are supplied. The conversion products discharged from the catalytic cracking reactor are preferably cooled to a tem perature ranging, for example, from 600 to 800 or at least to a temperature below that at which substantial pyrolytic cracking is effected. The combined fractionator and separator may utilize a pressure substantially the same as that employed at the outlet of the catalytic cracking reactor.

I claim as my invention:

1. A process for treating paraiiinic gasoline fractions which comprises contacting the parafnic oil in a first stage with a dehydrogenating catalyst under dehydrogenating conditions, said catalyst and conditions being such as to convert prises dehydrogenating the paraiilnic oil in a first stage in the presence of a dehydrogenating catalyst and under dehydrogenating conditions such as to convert the oil into a predominantly olefinic product, and subjecting said oleiinic product in a second stage to catalytic cracking in the presence of a cracking catalyst of different composition than said dehydrogenating catalyst.

3. The process as deiined in claim 1 further characterized in that said dehydrogenating catalyst comprises an alumina-chromia composite and said cracking catalyst predominates in silica.

4. The process as dened in claim 1 further characterized in that said cracking catalyst com' -prises a silica-alumina composite.

5. The process as denned in claim 1 further characterized in that said cracking catalyst com- -y prises a silica-zirconia composite.v

6. The process as defined in claim 2 further characterized in that said dehydrogenating catalyst comprises an alumina-chromia composite and said cracking catalyst predorninates in silica.

'7. The processes defined in claim 2 further characterized in that said cracking catalyst comprises a silica-alumina composite.

8. The process as defined in claim 2 further characterized in that said cracking catalyst comprises a silica-zirconia composite.' T

9.(1A process for Vincreasing the anti-knock value ofparainic gasoline fractions which comprises dehydrogenating the parafilnic oil in a lfirst stage in the presence of an alumina-chromia catalyst under dehydrogenating conditions such as to convert the oil into a predominantly olenic product, and subjecting said olen product in a second stage to catalytic cracking in the presence of a silica-alumina composite.

10. A process for increasing the anti-knock value of paramnic gasoline fractions which comprises dehydrogenating the paraiiinic oil in a first stage in the presence of an alumina-chromia catalyst under dehydrogenating conditions such as to convert the oil into a predominantly oletlnic product, and subjecting said olefin product in a second stage ence of asilica-zirconia composite.

11. The process as defined' in claim l further characterized in that said cracking catalyst cornprises silica, alumina and zirconia.

l2. The process as defined in claim 9 further characterized in that said composite contains zirconia in addition to the silica and alumina.

CHARLES L. THOMAS.

to catalytic cracking in the pres-

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