US2924569A - Hydrodealkylation of hydrocarbons - Google Patents

Description

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United. .States Parent" 2,924,555) HYDRODEALKYLATION oF HYnRocARBoNs Armand M. Souby, Chambers County, Tex., assignor, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, NJ., a corporation of Delaware Application August 1, 1956, Serial No. 601,556

8 Claims. (Cl. 208-107) The present invention is directed to a method' for dea'lkylating alkylated aromatic hydrocarbons. More particularly, the invention is directed'to vthe`thermaldealkylatin of alkylated :aromatic hydrocarbons. In its r'nore'speciic aspects, theinvention is directed to the thermal dealkylation of alkylated aromatic hydrocarbons atan elevated temperature in the presence. of hydrogen. .The present invention may'bebrieiiy` describedxas a method for thermally dealkylatin'g. analkylated aromatic hydrocarbonin `which the formation of coke is controlled and suppressed. .1' l z i The alkylated aromatic hydrocarbon feed is heated in athermal dealkylation zone in the presence of hydrogen to a temperature withinthe'range betweenA about 1l00 and about 1600 F. and at a pressure within the range between about-400 and4 about 1000 pounds per square inch gauge for a time within the range `of about 2 and about 120 seconds in the presence of a-uidized bed of catalytically' inert :linelyfdivided solids in vwhich a liquid product and a residue-gas are produced. .In the present invention theresidue gas is flowedthrough a sensing zone to obtain a signal `which `is a function of the methane to hydrogen ratio in the*residue gas."This Asignal is-then employed to vary the ratioof hydrogen and alkylated aromatic hydrocarbon feed in the thermal reaction zone to provide a methane to lhydrogen ratio in the residue gas such that 'the ratiofof the equilibrium methane concentration to the actual methane concentration is above about 1.7 times the thermodynamic equilibrium ratio.

Y The nely divided solid employed in the bed may have a'particle size inthe range from about 100 to about 400 meshand suitably may bejalpha alumina, quartz, Carmullitewhich is a silica-alumina, and the The amountof hydrogen employed may'be within the range of 6000 to 12,000 standard cubic feet per barrel of alkylated aromatic hydrocarbonfeed, `depending upon the hydrogen purity` and operating. severity. While pure hydrogen-may be employed, a hydrogen-containing gas such asa catalytic reformertail gas may also be used in suitable amount. Preferred ranges may Abe from 7000 to 8000 standard cubic feet Aof pure hydrogen per. barrel of `.alltylated aromatic feed, or from 311,000 to 13,000 standard cubic feed of reformeritail gas containing ,75 percent hydrogen per barrel of alkylated aromatic feed.

' The presentinvention, asstated,is suitably conducted ata'temperaturewithinthe. range .from about 1100 to ICC 2 invention may be any alkylated aromatic hydrocarbon boiling within the range from about 200 to about 750"v F., alkylated hydrocarbons such as alkyl benzenes such as illustrated by toluene, xylenes, ethyl benzene, mesitylene, and the like,'and alkyl naphthalenes are illustrative desirable feed stocks. The alkyl naphthalenes maybe illustrated by methyl naphthalenes, dimethylnaphthalenes, ethylnaphthalenes, trimethylnaphthalenes, methyl-ethylnaphthalenes and higher molecular weight homologues but other alkylated aromatic hydrocarbons may be used. For example, the present invention may suitably be practiced with alkylated aromatic hydrocarbons in the gasoline and kerosene `boiling ranges. f i

The sensing zone employed in the presentinvention to obtain a signal which is a function of methane to hydrogen ratio may be any sensing zone which will indicate the relative amounts of hydrogen and methane. For example, the sensing zone may suitably be a mass spectrometer or may be an indicating or recordingr gasl gravitometer. Other sensing zones such as a 4gas adsorption chromatographic apparatus, a thermal conductivity cell, or an el'fusiometer 'may be employed.. A signal is obtained from the sensing zone which is a function o the methane to hydrogen ratio. i.

The present invention will be further illustrated -by reference to the drawing in which the single ligure is a llow diagram of a preferred mode.

Referring now to the drawing, a feed aromatic hydrocarbon of the nature illustrated is introduced into the system by line 11 controlled by valve 12 and ahydrogenrich gas is introduced intoline 11 by line 2'1 controlled by valve 22. `The aromatic hydrocarbon andthe hydro-` gen-rich gas are mixed in line 11 and introduced into a heat exchanger 13 wherein the temperature of the total feed is raised to a temperature within the range between about 400 F. and 800 F. The total Vfeed at this temi perature is withdrawn from theA heat exchanger 13 by line' 14 and may be introduced thereby into a heater or. furnace 15 and llows through coil 16 wherein it is heated to a temperature within the range between about 4700 F. and 900 F. by means 'of heat provided by burners 17.

' The heated feed in a vaporized condition is withdrawn by way of line 18 from furnace 15 and introduced into a reaction zone 20. In the reaction zone 20, the preferred reaction temperature of l250 F. to 1350 F. 'ismaintained by the highly exothermic reactions of hydrodealkylation and hydrocracking. Alternatively, `the feed aromatic hydrocarbon and the hydrogen-rich gas maybel preheated separately and combined before being:.intro duced at the proper temperatureinto the reaction zone.

-A"lluidized bed 23 is maintained inreaction zone 20 i" of nely divided catalytically inert solids of the type mentioned before. The bed 23 ismaintained abov'e a reactor grid 24. In reaction zone 20.the reaction takes place wherein in accordanceiwith the present invention the alkylatedv aromatic hydrocarbons are dealkylated vto form substantially only the desired aromatic hydrocarbons aboutl 1600` F. with a preferred temperature within the and hydrogen and methane. The products of'the der alkylation reaction are withdrawn from reaction zone 20 by way of line 25 and are' quenched in line 25 by means of a quench oil-introduced byline 26. This' quench Voil may suitablyV bean oil such as the bottoms stream-lev ing fractionator 34 through line 40. vThe quenchedproduct in line 25 at a temperature within therange of about 700 F. to 1000 F. is then passed through heat exchanger 13 in heat exchange with the feed which further reduces the temperature toapproximately 300 F. The cooled'` The feed. stocksemployedia-the.practicasfffhs Prater.

product `is then introduced by way of line 27 `into`a scrubbingzone 28 wherein the quenched and cooled product is `scrubbed with a heavy4 oil, lsuch asrecycled slurry,oil from line 30.11eaving scrubber 28,-in'troduc'ed..

to remove any finely divided catalytically inert solids carried over with the reaction product. The oil and the solids are discharged by way of line 30 from scrubber 28. The excessl slurry' oil from. line. 30 maybe ltered in a lten'zone not shown and introduced into line 31 ahead `of separator 32 in `order to recover all of' the desired product, whilel the catalytically inert solids'recoveredby filtration may be discarded. 'The reaction products are from zone 20 by line 60 controlled by valve 61. Line 60 withdrawn from scrubber 28 by Way of line 31 into a separation` zone 32 in'which a separation is made between the gaseous products and the liquid products. The liquid products are withdrawn from separator 32 by way of line 33 and introduced thereby into a fractional distillation zone 34. Fractional distillation tower 34 is shown as a single fractionaldistillation tower which suitably may include a plurality of fractional distillation towers, each equipped-With internal vapor-liquid contacting means, such asl bell cap trays andthe like, means for inducing reux and means for condensingr and cooling the fractionated products. In short, zone 34 will include all auxiliary equipment necessarily found in the modern distillation tower.

- In zone 34,. temperature and pressure conditions are adjusted'v byV heating means illustrated by steam coil 35 such4 that light hydrocarbons are removed from zone 34 by line 36 and the dealkylated-hydroearbons are withdrawn by lines 37, 38, and 39. Heavier products are discharged'V byline 40.

Thegaseous products. from separator 32 arewithdrawn therefrom by line 41 and'introduced by line 42 into an absorption zone 43 into which absorber oil is introduced by lline 44 to contact countercurrently the residue gas introduced by line 42. The absorber oil may suitably be a stream fromvfractionator 34 such as one of thefproduct streamsv from lines 37, 38, 39, or 40.

The absorption zone 43 is operated under suitable conditions of temperature and pressure to absorb hydrocarbons such as propane, propylene, butanes, butylenes and heavier hydrocarbons While ethane and lighter hydrocarbons including hydrogen are not absorbed. The enriched absorption oil is discharged from zone 43 by line 44a for recovery of the absorbed hydrocarbons and for stripping' of the absorber oil for re-use in the process. The enriched absorption oil from line 44a may conveniently be` introduced into line 33y ahead of fractionator 34 wherein it will be stripped for re-'use and the absorbed hydrocarbons recovered.

Line 45 controlled by valve 46 connects to line 41 and to a sensing means or an analyzer 47 to allow the residue gas in line 41 to pass therethrough and be discharged by way of line 48 controlled by valve 49 back into line. 42'.

Provision of analyzer or sensing means 47 allows a portion` of the residue gas in line 41 to be routed through thefanalyzer 47 and back into line 42.

The unabsorbed residue gas from absorption zone 43 is discharged therefrom by way of line 50 andpmay be discarded or recycled to the process as a hydrogen-con taining gas.

Connected to line 50 is line 51 controlled by valve 52 'whichA leads to an analyzer or sensing means 53 of the type described. Line 54l controlled by valve 55 connects the analyzer 53 back into line 50 such that' the residue gas may be circulated through the analyzer 53.

The analyzers 47 and'` S3 suitably connectby electrical leads 54a, 55a, 56, and 57 to valve 22 in line 21, valve 12 in line 11 and to valve 58 in line 59.

The loperation of the reaction zone 20 is such that the heated feed' is introduced by means of line 18 in admixture with hydrogen from line 21 into the bed 23 of nely divided catalytically inert solids in reaction zone 20. From time to time the catalytically inert solids' may become fouled with carbonaceous deposits and itis desiralxleu to replace a portion ofthe catalyticallyinert' solids. To end; a portion' of? the: inert solids-*is withdrawn leads into the zone 20 and connects into an annular section 62 dened by the walls 63.

The inert solids in line 60 are carried to a regeneration zone 64 by way of line 65 connected thereto into which air is introduced by Way of line 66 to support a combustion operation in zone '64 above the grid plate 67.

The combustion operationburns olf the' carbonaceous matter from the catalytically inert solids at a temperature in the range from 900 to 1500 F. and a combustion product ue gas is withdrawn from zone 64 by line 68.

The burned off catalytically inert solids are withdrawn from zone 64 through a zone 69 of zone 64 defined by an annular Wall 70. Line 71 controlled by valve 72 connects into zone 69. Line 71 also connects into a hopper for catalytically inert solids 73 which is connected to line 76 by way of line 74. controlled by valve 75,

In operating the present invention, any withdrawn catalytically inert solids containing carbonaceous material may be replaced by fresh or regenerated catalytically inert solids from hopper 73 by Way of line 74 controlled byvalue 75,. .When catalytically inert solids are added, hydrogen is introduced by line 59 controlled by valve 58 to carry'the catalytically inert solids through line 76 to thebed 23. Hopper 73 is capable of being operated at the. pressure ofthe reaetionzone 20l while catalytically inert solids are being added.

Hydrogen is admixed Withthe feed stock as has been described during the operation but1 hydrogen is added to line 76 only when it is desired to add catalytically inert solids from-hoppen73. r

It is to beemphasized that catalytically inert solids may be withdrawn fromi zone 20 and added to zone 20 only at relatively long intervals as carbonaceous' deposits accumulate on the catalyticallyr inert solids. The amount withdrawn and the amount added may comprise only about 5% by weight of the amount of catalytically inert solids' in the bed 23. `The' interval of time at which catalytically inert solids are Withdrawn and added may rangefrom about 1 to 20 days. In short,the withdrawal and addition of -catalytically, inert solids is only at infrequent intervals. The Withdrawn catalytically inert solids containing carbonaceous material may be cooled and discarded ratherl than` regenerated if desired.

In accordance withv the present invention formation of carbon and coke in the-reaction zone 20 and in the transfer` line 2S yis controlled and suppressed bymaintaining a ratio of the :thermodynamic equilibrium concentration of methane (calculated on the basis of the concentration of hydrogen present) to the actual concentration of methane inthe residue gas above a Value of about 1.7, under the conditions of reaction zone 20.

In order to illustrate the invention further, hydrodealkylation operations were conducted on a Vfraction boilingy above` 400 F. of kerosene sulfur dioxide extract which containedabout 86% of' alkylated aromatics. Thiskeroseneextract was heated to about 800 F. and introduced into a reaction' zone containingY a uidized bed of silica sand. The exothermic heat of reaction inv the reaction zone maintained the temperature of reaction at about 1300 F. Hydrogen-rich gas was introduced with hydrocarbon feed to provide the required amount of hydrogen. Runs were conducted at 1270" to 1345 F., 600 pounds per squarel inch gauge and at 50 to 60 seconds residence time VWith vfrom 6600 to 9800 standard cubic feet of hydrogenper barrel of feed being employed. The hydrogen employed contained between about 70 and about 79% H2, the other components being methane and heavier hydrocarbons.'

In these operations, coking was experienced in the reaction zone. In one of the runs at 1320" F. and 600 pounds per square inch gauge, it was found that the concentration of hydrogeninfthe' residue gas was 32.3 mole .fatwa-M99 r percent- A'Ihenthermodynamic equilibrium concentration corresponding to the actual'hydr'ogen concentration was 45.1 mole percent.= Theratio of the equilibrium methane concentrationto theactual methane concentration was 0.95. In this run the operation had to be terminated after hours due to coking.-' l

In another run with the same feed stock and 600 pounds per squareinchgauge, the residue gas contained 35.6 mole percentnhydrogen and 44.7 mole percent of methane. The thermodynamic equilibrium concentration of the 'methanecorresponding `to thehydrogen was 56.5 mole percent.y The ratio of equilibrium methane concentration to the actual methane concentration was .1.26. This run hadtobeV terminated after 12 hours due to :coking.` 1

It has been observed that the only hydrocarbon in the product under conditions existing at the reaction zone outlet which may be thermodynamically stable is methane. In the presence of sufficient hydrogen to make methane thermodynamically stable, the heavier hydrocarbons decompose and result in the formation of methane. In the presence of smaller quantities of hydrogen than are necessary to make methane thermodynamically stable, the decomposition reaction results in the formation of carbon and hydrogen. This carbon deposits on the walls, lines and in the reaction zone and makes the operation inoperable if allowed to continue. A measure of the ability of hydrogen to prevent coking is the degree of approach of the partial pressure of methane actually present to the partial pressure of methane that exists in thermodynamic equilibrium to the hydrogen under the conditions existing in the reaction zone. The equilibrium concentration of methane corresponding to the hydrogen concentration at reaction zone conditions may be determined by calculation based on the thermodynamic data published by the Carnegie Press for American Petroleum Institute Research Project 44, Selected Values of Physical and Thermodynamic Properties of Hydrocarbons and Related Compounds. y

It has been found that, if the ratio of equilibrium methane concentration to the actual methane concentration in the reaction zone is maintained above about 1.7 times the thermodynamic equilibrium ratio, the formation of coke may be suppressed or controlled. This operation may be effected by controlling the amount of hydrogen added to the feed or by varying the amount of hydrogen with respect to the feed. In short, either increasing or decreasing the hydrogen or increasing or decreasing the feed aromatic hydrocarbon may allow the formation of carbon in the reaction zone to be controlled.

To illustrate the present invention a number of runs were conducted with the same sulfur dioxide kerosene extract, employed in previous runs, wherein the ratio was varied in accordance with the present invention.

These operatlons are summarized in the following table:

Table I Run Period, Hours 14-26 26-38 38-50 50-62 Reactor Temperature, F 1, 290 1, 290 1, 295 1, 295 Reactor Pressure, p.s.i.g. 600 600 600 600 Charge Gas:

S.c.f./bb1. Feed 11, 250 11,510 10, 330 10,090 H2, Mol Percent 76.1 77. 5 76. 4 76.1 Residue Gas:

Specific Gravity (Referred to Air 0. 428 0. 430 0. 460 0. 465 H2, Mol Percent.. 43. 4 43. 0 38. 3 37. 5 01:14, Mol Percent 37. 4 37. 8 42. 1 42. 9 Calc. Equil. CH4, Mol Percent.. 97. 7 95. 9 73.8 70. 8 Ratio Equil. (BH4/Actual CH4.- 2. 61 2. 54 1. 75 1. 65

It will be seen that during the series of yield periods, the ratio of the calculated equilibrium concentration of methane to the actual concentration decreased continuously during the yield periods. After 62 hours, the ratio had dropped to a value of 1.65, and the run was terminated by coking.

.6 In; anothertrun the concentrationothydrogen and 'methane in ,the Iresidue 'gas werel controlled.- 4by varying the. quantity of rthecharged gas so that the specific grav'- ity, with referenceto ain, of the residue gas remained within the limits of 0.43 to 0.45. The results of consecutive yield periods 4for this run are shown in Table Il:

Table llf Run Period, Hours- 9-21 21-57 57-69 'G9-103 Reactor Temperature, F.- 1, 315 1,315 1,320 1,325 Reactor Pressure, p.s.i.g r 600 600 600 600 Charge Gas: l

S.c.f./bb1. Feed---- 13,080 11, 770 12, 440 12, 550 H2, Mol Percent y 75.2 `76.4 76.3 73.6 Residue Ges:

. Specific Gravity I.

A-ir .436. 0.442 0.432 0. 446 Hq, Mol Percent. -`42. 1 41. 2 42. 7 40. 5 CHI, Mol Percent..-- 38. 6 39.4 38.1 40. l Calc. Equll. CHI. Mol Percent.. 79. 1 75. 7 78.8 69. 0 Ratio Equil. CB14/Actual CHL.. 2. 05 1. 92 2. 07 1. 72

It will be seen from these data that by maintaining the ratio of equlibrium concentration of methane to the actual concentration above about 1.7 that coking is substantially eliminated and further that the operation may be controlled by varying the concentrations of hydrogen and methane in the residue gas.

The present invention is quite advantageous and useful in that coking in hydrodealkylation of aromatic hydrocarbons may be suppressed, controlled or entirely eliminated.

The nature and objects of the present invention having been completely described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for controlling and suppressing the formation of coke in a thermal dealkylation zone in which an alkylated aromatic hydrocarbon feed is heated in said dealkylation zone in the presence of hydrogen to4 a temperature within the range between about l and about 1600 F. and at a pressure within the range between about 400 and about 1000 pounds per square inch gauge for a time within the range between about 2 and about 120 seconds in the presence of a fluidized bed of catalytically inert finely divided solids in which a liquid product and a residue gas are produced which comprises the steps of analyzing said residue gas to obtain a signal which is a function of the methane to hydrogen ratio in the residue gas, and employing said signal to vary the ratio of hydrogen and alkylated aromatic hydrocarbon feed in said thermal reaction zone to provide a methane to hydrogen ratio in said residue gas such that the ratio of the thermodynamic equilibrium methane concentration to the actual methane concentration is above about 1.7.

2. A method in accordance with claim 1 in which the amount of hydrogen and alkylated aromatic hydrocarbon feed is varied by varying the amount of hydrogen.

3. A method in accordance with claim l in which the amount of hydrogen and alkylated aromatic hydrocarbon feed is varied by varying the amount of alkylated aromatic hydrocarbon.

4. A method for controlling and suppressing the formation of coke in a thermal dealkylation zone in which an alkylated aromatic hydrocarbon feed is heated in said dealkylation zone in the presence of hydrogen to a temperature within the range between about 1100 and about 1600 F. and at a pressure within the range between about 400 and about 1000 pounds per square inch gauge for a time within the range between about 2 and about 120 seconds in the presence of a liuidized bed of catalytically inert finely divided solids in which a liquid product and a residue gas are produced which comprises the steps of owing said residue gas through a sensing zone to obtain a signal which is a function of the methane to hydrogen ratio @in Athe residue gas, 'and employing `said signal such :that .the ratio o'f the thermodynamic equilibrium methane concentration to the `actual methane Aconcentration ris above about 1.7.. .y A

5. A method in accordance with claim 4 in which the alkylated aromatic hydrocarbon boils within the range from about 200 to about 750 F.

6. A method in accordance with claim 4 in which the amount of `hydrogen and alkylated aromatic hydrocarbon feed is varied by varying theamount of hydrogen.

7. A method in accordance with claim 4 in which the amount ofhydrogen and alkylated aromatic hydro l15 2,853,433k

carbon feed is varied by varying the amount of alkylated aromatic hydrocarbon. f

8. A method in `accordance'with claim 4 in lwhich the hydrogen is present in, 1an amount within the range of labout 6,000 to about y'12,000 standard ycubic feet per barrel of aromatic hydrocarbon feed.4 K l References Cited 1in the file of this 'patent UNITED `STATES PATENTS 2,261,498 AKarcher -a ;....r. Nov. 4, 1941 2,414,889 Murphree v Jan. 28, 1947 2,738,307 Beckberger Mar. 13, 1956 2,780,661 Hemminger etal. a Feb. 5, 1957 Y KeithA Sept. 23, 1958

Claims (1)

1. A METHOD FOR CONTROLLING AND SUPPRESSING THE FORMATION OF COKE IN A THERMAL DEALKYLATION ZONE IN WHICH AN ALKYLATED AROMATIC HYDROCARBON FEED IS HEATED IN SAID DEALKYLATION ZONE IN THE PRESENCE OF HYDROGEN TO A TEMPERATURE WITHIN THE RANGE BETWEEN ABOUT 1100* AND ABOUT 1600*F. AND AT A PRESSURE WITHIN THE RANGE BETWEEN ABOUT 400 AND ABOUT 1000 POUNDS PER SQUARE INCH GAUGE FOR A TIME WITHIN THE RANGE BETWEEN ABOUT 2 AND ABOUT 120 SECONDS IN THE PRESENCE OF A FLUIDIZED BED OF CATALYTICALLY INERT FINELY DIVED SOLIDS IN WHICH A LIQUID PRODUCT AND A RESIDUE GAS ARE PRODUCED WHICH COMPRISES THE STEPS OF ANALYZING SAID RESIDUE GAS TO OBTAIN A SIGNAL WHICH IS A FUNCTION OF THE METHANE TO HYDROGEN RATIO IN THE RESIDUE GAS, AND EMPLOYING AND SIGNAL TO VARY THE RATIO OF HYDROGEN AND ALKYLATED AROMATIC HYDROCARBON FEED IN SAID THERMAL REACTION ZONE TO PROVIDE A METHANE TO HYDROGEN RATIO IN SAID RESIDUE GAS SUCH THAT THE RATIO OF THE THERMODYNAMIC EQUILIBRIUM METHANE CONCENTRATION TO THE ACTUAL METHANE CONCENTRATION IS ABOVE ABOUT 1.7.

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