US2352755A - Hydrocarbon conversion - Google Patents

Description

Julyr4, 1944. J. McAFEE HYDRocARBoN CONVERSION` Filed oct. 27, 1941 y QQ V 1 @WR Patented. July 4,A 1944 nYnnocARBoN coNvsasxoN 4Jerry McAfee, Chicago, Ill., asslgnor to Universal OiLProducts Company tion of Delaware Chicago, Ill., a corpora- Application October 2 7, i941, Serial No. 416,622

(cl. 19e-49) 5 Claims.

'I'his invention relates to a process for the pro duction of motor fuel'from residual hydrocarbon oils. More specifically, it is concerned with a topped crude or reduced crude may be converted to high yields of gasoline bya combination catalytic and thermal crackingoperation.

In the catalytic cracking of hydrocarbons carbonaceous substances are deposited on the catalyst which tend to impair its activity and which vtherefore must be removed at frequent intervals to maintain the activity lof the catalyst at a practical level. It has been observed that extremely high boiling hydrocarbons such as, for example, those present in reduced crudes tend to form carbonaceous catalyst deposits more rapidly than the lower boiling hydrocarbons and for this reason residual stocks have not ordinarily been employed directly as catalytic cracking charging stocks. However, various combinations vof catalytic and thermal cracking havebeen proverted to gas, gasoline, and residuum. l

I have found that the overall gasoline yield which may be obtained from a given reduced or topped crude may be substantially increased over process whereby a heavy charging oil such as may be employed in'some instances, 'and these variations will be discussed presently.

In one speciilc embodiment the present invention comprises subjecting a residual hydrocar bon oil to a. mild thermal cracking operation,-v

separating `the resultant reaction products into a iight 'fraction and a. heavy fraction, subjecting said light fraction together with other hydrocarbon'o'ils formed ais-hereinafter set forth to a catalytic cracking operation, |'recovering gasolineV fromthe resultant products, subjecting the insufficiently converted hydrocarbons separated from the catalyticproducts together with the aforesaid heavy fraction .to thermal cracking treat-v ment, separating the reaction products into a a heavy fraction, supplying said intermediate "fraction to said 'catalytic cracking treatment,

that obtained in processes of the above type by employing a particular sequence of steps on the charging oil.

To be more speclflc,. this sequence may be briefly described as follows: 'I'he charging oil is subjected to a mild thermal cracking treatment such that the production of material boiling'below the initial boiling point of the chargedoes not exceed 20%. The resultant products are then treated to separate a vaporous overhead from a non-vaporous residue. The vaporous overhead is subjected to catalytic cracking, the products therefrom fractionated to separate gasoline and gas from the reflux condensate, and the latter, together with the v non-vapor'ous residue from the flashing operation, if desired, is subjected to a separate thermal cracking treatment to produce substantial yields of gasoline. Light and heavy fractions separated from, the products of this second thermal cracking treatment are supplied to the catalytic. and separate thermal cracking treatments, respectively. l

In addition, several variations of this sequehce drocarbons.

and returning said heavy fraction to said thermal cracking treatment.

The accompanying diagrammatic drawing shows in side elevation one specic form of apparatus that may beemployed to accomplish the object of this invention.

Referring now to the drawing, a residual hydrocarbon oil charge such as topped or reduced crude, containing high boiling hydrocarbons, is directed through line l, valve 2, pump 3, line 4, and valve 5, whereafter it is commingled, if desired, with a diluting medium such as steam or gases formed in the process introducedthrough line 8 and valve 1. The composite material is then heated in coil 8 at a relatively lowsuperatmospheric pressure, usually less than 50 pounds per square inch gauge and in some cases at a subatmospheric pressure, to a temperature of from 700 to 1000 F. to eifect a mild cracking, heat being supplied by means of furnace 9. The products from coil 8 are directed through line I0 containing valve ll to separating chamber I2 wherein a separation is effected between the non-volatile residual hydrocarbons and the vaporized hy- Chamber' l2 is preferably operated I at al slightly lower temperature and pressure than that maintained at the -outlet of coil 8 and is ordinarily' insulated to reduce heat losses tion of material boiling below the initial boiling point of the charge, will not exceed 20%.

The vapors from chamber I2 are withdrawn through line lland may be thereafter supplied without condensation'"through valve I4 and line 26 to heating coil 2l 0r may be directed through line I5 and valve I6 and cooled and substantially condensed in condenser I1. The resulting condensate is then directed through line Il and valve I9 to receiver 20 wherein. a separation may be effected between the condensed hydrocarbons and whatever small amounts of non-condensable materials may be present. The non-condensables may be vented through line 2| and valve 22 while the condensate is directed through line 23, valve 24, pump 255, line 26, and valve 21. In most cases it may be preferable to supply the vapors from chamber I2 directly to coil 28 without condensation, since this procedure eliminates the necessity for the condensing and collecting equipment previously mentioned. It should also be noted at this point that instead -of being merely a separating chamber in which a liquid condensate is separated from vapors, chamber I2 may also be, under some circumstances, a coking chamber, in which case it is desirable that several such chambers be employed in order that the operation may be continuous.

Continuing nowl with the flow, the vapor or condensate, as the case may be, in line 28 is commingled with a light fraction formed as hereinafter set forth and supplied through line 10, and the resulting mixture is supplied to heating coil 28 as previously noted, wherein it is heated to a temperature of from 800 to 1100 F., preferably oi from 900 to 1000 F. at a pressure ordinarily in the range of from atmospheric to 100 pounds per square inch, heat beingv supplied by means of furnace 29. It is necessary, of course, that if the vapors are supplied directly from chamber I2 through line I3 and valve I4 that the pressure in coil 28 be less than that employed in chamber I2. The substantially vaporized hydrocarbons from coil 28 are then directed through line 30 and valve 3I to catalytic reaction chamber 82 wherein they are contacted with a cracking catalyst.

In the case here illustrated, reactor 32 preferably comprises a cylindrical vessel containing one or more beds of catalytic material, said vessel being suilciently insulated to reduce radiation losses therefrom, so that the reaction may be accomplished substantially adiabatica y. If desired, however, the reactor maybe f the heat exchanger type wherein the' catalyst is maintained in indirect heat exchange relationship with a heat exchange'fiuid adapted to supply heat to or remove heat from the catalytic mass.

Among the catalysts which have been found to be effective in the cracking of hydrocarbons are silica'or other siliceous and refractory materials composited with compounds selected from the group consisting of alumina and zirconia. Natural catalysts of this type oompriseffor example, hydrosilicates of alumina, either untreated or treated. These catalysts maybe synthetically prepared by precipitating hydrated alumina and/or hydrated zirconia from suitable compounds thereof on a hydrated silica base followed by washing, pelleting, and calcining at temperatures of irom800 to 1500 F. Although the catalysts above recited are generally considered to be the preferred ones, their use is not to be construed as a vlimiting feature, for other catalysts wellknown to those in the artmay be employed.

As previously stated, the carbonaceous deposit formed in the catalyst during the cracking reaction is removed' at frequent intervals so thatit is desirable to employ two reactors and in some cases more than two, so that at least one reactor Imay be processing at any one time, thereby per- It mitting the processing to be continuous. Regeneration of the used catalytic material may be accomplished in several ways, perhaps the most convenient of which is the method of passing 5 -oxygen-containing regenerating gases in contact with the used catalyst, thereby burning the carbonaceous deposit from the surface of the catalyst.

Although the drawing and accompanying dem scription have been directed specifically toward catalytic operations of the type in which a hydrocarbon vapor is passed through a xed bed of catalytic material, it is entirely within the scope of this invention to employ any other well known type of operation. For example, the catalytic cracking step may be of the type in which a powdered catalyst is injected into a stream of hydrocarbon vapors and the resulting mixture supplied to a reactor in which the mixture has an upward velocity component. In this way, a

greater concentration of catalyst may be maintained in the reactor than is present in the en-v tering stream, since the net upward velocity of the hydrocarbon vapors is greater than that of the powdered catalyst. The catalyst may then tion in which the catalyst is suspended in the oil and the resulting slurry supplied to a cracking coil and, if desired, to a reaction chamber. In

this particular variation, any suitable means such as cyclone separators and the like may be utilized for the separation of reactant vapors from the spent powdered catalyst. In both of these powdered cracking operations the catalyst may be regenerated and recirculated, thereby providing for a continuous process.

o Returning again to the drawing, reaction products from reactorz are withdrawn through line 33 containing valve 34 and are thereafter supe plied to fractionator 35 wherein a separation is effected betweeman overhead product of the desired end point and""a bottoms fractionl comprising insufficiently converted hydrocarbons. The overhead product consisting of gasoline and gas y is withdrawn through line 36 containing valve 31 and may thereafter be cooled to condense the gasoline present therein, and the resulting two-phase mixture separated in a suitable Y receiver. A portion of the condensed gasoline may be returned to the top of fractionator Il to serve as a reflux.v The-remaining portion together with the gases is recovered as a product of the process.

Turning now to the thermal cracking section of the combination process, the combined feed to this section ordinarily comprises the bottoms from column 35 supplied through line II', valve o u', pump n, une as, and va1ve u; me bottoms from fractionator 4I supplied through line Il,

valve pump 4I, line 4l, and valve ll; and the bottoms from chamber I2 supplied through line 41, valve I8, pump 49, line lill, and valve II. In 55 the event that chamber 'I 2 is employed to produce coke rather than liquid bottoms, the last named fraction will not, of course, be employed as part ,of the thermal combined feedbut will be removed as solid coke. lIn-any event, the combined feed is supplied through line 52 to heating coil Il wherein it is raised to 'a cracking temperature ordinarilyin the range of from 800 to 1100 l". and at a superatmospheric pressure usually less Y than 500 pounds per square inch to effect substantial conversion thereof to lighter hydrocarbons,

assfcfnssl c heat being supplied by means of furnace ll. The reaction'productsfrom coil I3 are passed through line l containing valve 5l into reaction chamber l1 where further cracking is effected at a slightly lowertemperature and pressure.V Chamber l1 is ordinarily insulated to prevent excessive loss cf heat by radiation therefrom,although no insulation appears in the drawing.

-I'he products from chamber I1 are directedthrough line 58 containing valve 59 ini-n vaporizing and separating chamber 00, ordinarily operated at a pressure or from 30 to 150 pounds per square inch and at a temperature of from '100 to 850 F. to eil'ect a separation between liquid residue and vaporous conversion products. The liquid residue is withdrawn through line 6I containing valve B2 and may thereafter, if de sired, be cooled and returned tothe top of chamber 8l or to line 58 to serve as a'quenching rnedium. The vapors from chamber Il are withdrawn through line- 63 containing valve Il and' s are thereafter directed to Iractionator Il wherein the vapors are fractionated into a distillate fraction of the desired end point, 'an intermediate boiling range-fraction ordinarily having an 2 end point not in excess -of 650 F., anda heavy fraction. The distillate fraction comprising gasoline and gas is withdrawn through line G8 Acontaining valve '86 and may thereafter be cooled. etc. in a manner similar to that employed on the overhead from fractlonator It. The intermediate fraction from fractionator il is directed through line 8l, valve 88, pump 89, line 10, and valve 1I to line 2B wherein -it forms a part of the feed to the catalytic section as hereinbei'ore set forth. The heavy fraction separated in.

chamber Il is returned tothe thermal section by way of line 42, etc.. as previously noted.

The following example is given to demonstrate the advantages of this invention, although the invention is not intended to-be limited thereby. In a semi-commercial size plant a series of tests were madein which a residual charging oil was heated, flashed to separate' a vaporous i'ra.c.`

tion from a non-vaporous traction, and the vaporous fraction condensed, reheated, and supplied to the catalytic cracking chamber. The bottoms obtained from fractionation of the products yof .Il summary of the data so obtained as well as ,the conditions of operation of the tests is presented below:

v Test number Percentage oi charge taken overhead from ilashin o tion and supplied to the catalytic crgckieperationn A lproximate percentage of products of flashing loperation boiling below the initial boiling point of the charging oil (55d F.)

Gasoline yieldvolume percent of charge: Catalytic Total Operating conditions flashing section:

chamber pressure, pounds gauge.

- The abovetects show the benecial -eiIect of mild thermal cracking in the flashing operation inasmuch as a higher gasoline yield may be obtained thereby.

I claim as my invention: i

1A-process for the conversion of l'llydrocarbonl i oil which comprises subjecting said oil to a relatively mild thermal cracking, separating the resuitant conversion products into vapors and resi'- due, subjecting said vapors. including all of those catalytic cracking were combined with the nonthermal cracking'step while the light fraction was supplied to the catalytic cracking operation.

Gasoline was recovered from-both of the crackingsteps.

These tests were made at slightly different temperatures and times of reaction in the nashing step and resulted therefore in varying degrecs of thermal cracking in the iiashingoper-v ation. 'In each test, however, approximately the same percentage of the charge was taken overhead from the dashing' operation so that the effect of varying'degrees of thermal cracking in a.

boiling below the initial Iboiling point of said oil. to catalytic cracking, fractionating resultant vaporous conversion products independently of said vapors to condense and separate fractions higher boiling than gasoline, subjecting resultant reflux condensate to thermal cracking independently of said oil, independently fractionating resultant thermally cracked vaporous conversion products to condense and separate a light reflux condensate and a heavier reflux condensate, supplying the latter to the last mentioned thermal crackingv step and supplying light reflux condashing operation could be determined. The o densate to the catalytic cracking step.

2. The process of claim 1 further characterized in that said oil is subjected to cracking under conditions such that substantially no more than 20% is converted to material boiling below the initial boiling point of the oil. .l Y

8. The process of claim 1 further characterized in that a vaporous diluent is added to said oil prior to cracking.

4. The process of claim 1 further characterized in that a vaporous diluent comprising hydrocarbon gases is combined with said oil prior to cracking.-

5. The process of claim 1 further characterized in that vsaid residue is subjected -to lthermal cracking'in the last mentioned thermal cracking MP. f

. JERRY MCAFEE.

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