US2908628A - Hydrocarbon conversion - Google Patents

Description

2,908,628'v HYDRocARBoN CoNvnRsIoN brahaxnS'chneider, Overbrook Hills;A and Conard K.

`Donnell, Springfield,` Par, assignors to Sun Oil Company, Philadelphia', Pa., a corporation of New Jersey Application .time 2s, 1956, serial Ne; I594,653 2 claims. (cr. zosgas) ICC Patented Oct. 13, 1959 I octane gasoline components also takes'place. The products are then fractionated to vrecover gasoline boiling range-hydrocarbons, and a fraction boiling above 400 F., which is recycled toA the aromatics separation step. It has ,been found that removal of the aromatics, particularly the bicyclicsv such as indenes,` prior to the hydrocracking step, 'reduces'th'e coke-forming characteristics of the feed to such an 'extent that the process may be carried out non-rcgeneratively even at moderate partial pressures of hydrogen. Since only monocyclic aromatics are formed as a result of dehydrocyclization, bicyclics will never be present t'o form coke on the catalyst.

The aromatics recoyeredfin the aromatics separation step are catalytically cracked to removeor shorten alkyl substituents so" as to lower the boiling/range of the monocyclic aromatics toi the gasoline boiling range, and the boiling above'500` F. can bereadil'y catalytically cracked to yield a gasoline fraction having an octane number in the n'ei'ghborhood of 94' to 96. The straight run fraction boiling' up to about 375 'F. to 400 F. maybereformed by contact with a hydrogenation-dehydrogenation catalyst in the presence of added hydrogen to increase the aromatic content thereof and yield a gasoline with an octane num'- b'er in excess of 95. The utilization of the V400 to 500 E'. fraction for the manufacture of gasoline'has, however, been `a problem for many years. This fraction is highly resistant' to' catalytic cracking` at theconditions `used' for cracking the 500 F plus fraction, so that if it is included as a component of the feed to the cracking operation, it will pass through largely unchanged. If it isV separately cracked under sever-e conditions, the yields, .per passthrough the reactor, of gasoline-boiling hydrocarbons are low, and the losses to coke and Vuncond'ensible gases are hg'h Y Attempts have been made to hydrocrack this fraction contacting it "with a` hydrogenation-dehydrogenation catalyst vinthe presence of added hydrogen. It has been foilndV thatthehigh partialpressure of hydrogen necessary toI prevent deactivation of the catalyst by coking.(l500 psi. and upward)` inhibits the dehydrogenation of naphthenes, so that the octane number of a gasoline produced in this manner is limited to` about 88. In addition, high yields of hutane Yand dry gas result, and the ultimate prof duction' of gasoline is low.

It is an' object of this invention to' provide an improved process for the production of a high-octane gasoline in good yields from a straight-run petroleum fraction boilin the range of 400 F. to 500` F. l A' further objectof the invention is to recover as a by-produ'ct a hydrocarbon fraction boiling above 400 F. which' is lich in bicyclio aromatic hydrocarbons, and which is suitable asa feed stock to a de-alkylation process for the" production of naphthalene. l

' We' have found that the foregoing objects maybe attained by iirst contacting the feed with a platinum catalyst having a low acidity in'theupresence ofV added hydrogen and under such relatively -rnild process conditions that little or no hydrocracking takes place.V In' this first step essentially' the lonly reactionv which takes place is the deh'ydogenation4 of naphthenes` to the corresponding arcnnatics.YA The vproduct; `re ':over`(=,d from the lirst stepnlis cracked product is fractionated :to recover gasoline aromatics which are blended' with the` gasoline hydrocarbons recovered 'from' the hydrcracking step'. A fraction boilingV aboye 400 recovered from the fractionation. This' fractiohfisrich' naphtlilene and alkylated naphl thalenes, and maybe dealkylat'ed by known processes for the productionA of 'naphthalene In order that -those skilled in the art may more fully understand' the nature: of our invention and the method of carrying it out, it will be more particularly described y inuconnectionlwiththe accompanying drawing, which is then treated` to-,separate aromatics from saturated-hydro cracked to gasoline boiling range products, and con i siderable dehydrocyclization and .isomerization toV high a diagrammatic flow sheet, of our new process.

A straight-run petroleum fraction which comprises hy drocarbons 'boiling between 400` FL and k500 F. is introduced `through li'neill and is mixed witlif recycle hydrogen from line 2, in' the ratioA of fromV 5 to lO'mols of hydrogen per mol of, feed.' The'frnixedA feed is then passed to reactor 3'in whichit iscont'acted with a catalyst comprising platinum distended on alumina. The 'catalyst is one which has a' low' acid"func'ztion- By low acid function we `lmean that the titratable" acidity ofvlthe catalyst, rwhen titratedpin anv aqueous medium, is less than aboutlLSO milliecjuivalents of KOH pe'rggrarnof catalyst. A coni inercially available catalyst'of this type comprises 0.46% platinum on an' alumina' support,2and has a titratable acidity of 1.20; f Process conditionsinV reactor 3 are: liquid hourly space velocity 5 to 20, pressure 200 to 1000 p.s.i,lg'.',lpreferably 300 to 600`.p`.s.i.g., `and temperature 830 F. to 900 F. Severityiof the conditions is main. tained at a value. such; that little or no hydrocra'ckng takes place, but extensive dehydrogenation of naphthenes to aromatics will occur. That is, when operating at the upper limitV of they allowable temperature-range, the space velocity should be high, to limit the timev of contact f the feed with the catalyst, while-when operating atthe lower limit of the temperature range, thespace velocity should be correspondingly decreased to maintain the re` quired conditionV of severity.

From reactor 3, the dehydrogenated products are taken through line 4 to high pressure separator 5, from which hydrogen is removed through line Z'for -recycletov reactor 3, excess "hydrogen produced in the reaction being vented throughV line 6. Y

Y Liquid products are taken through line 7 to aromatics separation zone 8, in which the products are separated into an' aromatics fraction and fa saturate fraction. 1 Such Vseparation may be accomplished by solvent extraction with sulfur dioxide or any other solvent which preferentially dissolves aromatics, but s ince itis' important Athat the saturate fraction recoveredfinrthi's stepl contain a mininilimA of 'aromatics;l and: essentially" no fbicyclic aromatics, it is preferred to separate the aromatics by a silica gel adsorption process, such as the Arosorb process matics, and, since the bicyclic aromatics are more strongly adsorbed on the gel than monocyclic aromatics, the fraction will be essentially free of bicyclics.

.T he saturate fraction recovered from aromatics separation zone 8 is taken through line 9, mixed with hydrogen from recycle line 10, and is passed to reactor 11, the mol ratio of hydrogen to saturates being from about :1 to about 10: 1. Reactor 11 is packed with a catalyst comprising platinum distended on alumina. In this case, however, the catalyst should have a titratable acidity in excess of 1.5 milliequivalents of KOH per gram and preferably in excess of 2. A commercially available catalyst of this type comprises 0.6% platinum and has a titratable acidity of 2.60. Such high acid catalysts promote extensive hydrocracking and dehydrocyclization of saturates at temperatures low enough to minimize coke formation. Process conditions in reactor 11 are: liquid hourly space velocity 2 to 5, pressure 300 to 600 p.s.i.g., and temperature 870 F. to 920 F. The conditions are adjusted within the foregoing limits to give maximum hydrocracking and dehydrocyclization while avoiding coke formation. When operating at lower pressures, the temperature should also be kept low, or the space rate should be at the upper end of the range, while when operating at the higher end of the pressure range the severity of the temperature and space velocity variables may be increased.

The efuent from reactor 11 is passed through line 12 to high pressure separator 13, from which hydrogen and other uncondensible gases are taken overhead through line 10 for recycle, excess gases produced in the reaction being vented through line 14. The C3 and heavier product are then taken through line 15 to debutanizer 16, from which C4 and lower hydrocarbons are taken overhead through line 17, while the C5 plus product is taken through line 18 to fractionator 19. A gasoline boiling range fraction is taken overhead through line 20, and a fraction boiling above about 400 F. is returned to aromatics separation zone through line 21.

The aromatics recovered in aromatics separation zone 8 are taken through line 22 to catalytic cracking unit 23 where they are catalytically cracked in the presence of a cracking catalyst such as acid treated clay, bauxite, or synthetic silica-alumina. In cracking unit 23, the longer alkyl groups attached to the mononuclear aromatics are cracked to yield aromatics in the gasoline boiling range, together with low molecular weight olens suitable as a feed stock for a catalytic polymerization unit to yield polymer gasoline. Some vdealkylation of bicyclic aromatics will also take place, but there Will be little or no ring rupture.

The products of catalytic cracking are taken through line 24 to fractionator 25 in which C4 and lower hydrocarbons are taken overhead for further processing, while a C5 and higher fraction is recovered as bottoms and is passed through line 26 to fractionator 27, from which a fraction boiling under 400 F. is recovered overhead for blending with the gasoline product recovered through line 20, and a bicyclic concentrate is recovered as bottoms through line 29 for further processing to naphthalene.

By proceeding in the foregoing manner, we have found that a high yield of gasoline with an octane number in the vicinity of 100 may be obtained from the hitherto troublesome 40G-500 F. straight-run petroleum fraction. The process is non-regenerative except in the catalytic cracking step, thus eliminating the need for any catalyst regeneration facilities in either the dehydrogeneation or the hydrocracking step. There are three essential elements in our new process which enable us to achieve these results. First, the catalyst in the dehydrogenation step must be of low acidity in order to minimize hydrocracking of bicyclic compounds, with the accompanying formation of coke; second, the saturate product recovered in the aromatics separation step must be esentially free of bicyclic aromatics; and third, the catalyst in the hydrocracking step must be of high acidity in order to promote extensive hydrocracking, dehydrocycliza-tion, and isomerization at process conditions mild enough to avoid the formation of coke. By combining these essential elements we are able to produce a high octane gasoline with a minimum of losses to coke and uncondensible gases, and to recover a gasoline product in far higher yield than has been heretofore obtainable from the 40G-500 F. straightrun fraction.

yIt should be understood that while the foregoing description has been concerned with the processing of a feed substantially all of which boils between 400 F. and 500 F., the process is also useful in processing wider cut fractions, for example, a fraction boiling between 260 F. and 500 F., and the appended claims should be construed as covering such feeds.

We claim:

1. A process for the conversion of hydrocarbons which includes passing a feed stock comprising straight run petroleum fraction boiling between 400 F. and 500 F. in the presence of added hydrogen, to a dehydrogenation zone; contacting it therein with a platinum-containing catalyst having a titratable acidity less than 1.5 milliequivalents of KOH per grain of catalyst, at a temperature between 830 F. and 900 F., at a pressure of from 200 p.s.i.g. to 1000 p.s.i.g., and at a liquid hourly space velocity of from 5 to 20, said conditions of temperature, pressure and space velocity being co-ordinated to promote dehydrogenation of naphthenes contained in the feed while minimizing hydrocracking; recovering an intermediate product more aromatic than the feed; separating said intermediate product into an aromatic-rich fraction and a saturate-rich fraction essentially free of bicyclic aromatics; passing said saturate-rich fraction to a hydrocracking zone and contacting it therein, in the presence of added hydrogen, with a platinum containing catalyst having a titratable acidity in excess of 1.5 milliequivalents of KOH per gram of catalyst, at a temperature of from about 870 F. to about 920 F., at a pressure of from about 300 to about 600 p.s.i.g., and at a liquid hourly space velocity of from about 2 to about 5, said conditions of temperature, pressure and space velocity being coordinated to promote hydrocracking while minimizing coke formation; recovering a hydrocarbon fraction boiling in the gasoline boiling range, and a hydrocarbon fraction boiling above 400 F.; and recycling the hydrocarbon fraction boiling above 400 F. to the aromatics separation step.

2. The process according to claim 1 including catalytically cracking the aromatic-rich fraction recovered from the aromatics recovery step, recovering from the cracked products a normally liquid fraction boiling below about 400 F. and a fraction rich in bicyclic aromatics boiling above about 400 F., and blending the fraction boiling below 400 F. with the hydrocarbon fraction boiling in the gasoline boiling range recovered from the' hydrocracking step.

References Cited in the lile of this patent

Claims (1)

1. A PROCESS FOR THE CONVERSION OF HYDROCARBONS WHICH INCLUDES PASSING A FEED STOCK COMPRISING STRAIGHT RUN PETROLEUM FRACTIONS BOILING BETWEEN 400*F. AND 500* F. IN THE PRESENCE OF ADDED HYDROGEN TO A DEHYDROGENATION ZONE; CONTACTING IT THEREIN WITH A PLATINUM-CONTAINING CATALYST HAVING A TITRATABLE ACIDITY LESS THAN 1.5 MILLIEQUIVALENTS OF KOH PER GRAM OF CATALYST, AT A TEMPERATURE BETWEEN 830*F. AND 900*F., AT A PRESSURE OF FROM 200 P.S.I.G. TO 1000 P.S.I.G. AND AT A LIQUID HOURLY SPACE VELOCITY OF FROM 5 TO 20, SAID CONDITIONS OF TEMPERATURE, PRESSURE AND SPACE VELOCITY BEING CO-ORDINATED TO PROMOTE DEHYDROGENATIONOF NAPHTHENES CONTAINED IN THE FEED WHILE MINIMIZING HYDROCRACKING; RECOVERING AN INTERMEDIATE PRODUCT MORE AROMATIC THAN THE FEED; SEPARATING SAID INTERMEDIATE PRODUCT INTO AN AROMATIC-RICH FRACTION AND A SATURATE-RICH FRACTION ESSENTIALLY FREE OF BICYCLIC AROMATICS; PASSING SAID SATURATE-RICH FRACTION TO A HYDROCRACKING ZONE AND CONTACTING IT THEREIN, IN THE PRESENCE OF ADDED HYDROGEN, WITH A PLATINUM CONTAINING CATALYST HAVING A TITRATABLE ACIDITY IN EXCESS OF 1.5 MILLIEQUIVALENTS OF KOH PER GRAM OF CATALYST, AT A TEMPERATURE OF FROM ABOUT 870*F. TO ABOUT 920*F., AT A PRESSURE OF FROM ABOUT 300 TO ABOUT 600 P.S.I.G. AND AT A LIQUID HOURLY SPACE VELOCITY OF FROM ABOUT 2 TO ABOUT 5, SAID CONDITIONS OF TEMPERATURE, PRESSURE AND SPACE VELOCITY BEING COORDINATED TO PROMOTE HYDROCARACKING WHILE MINIMIZING COKE FORMATION; RECOVERING A HYROCARBON FRACTION BOILING IN THE GASOLINE BOILING RANGE, AND A HYDROCARBON FRACTION BOILING ABOVE 400*F.; AND RECYCLING THE HYDROCARBON FRACTION BOILING ABOVE 400*F. TO THE AROMATICS SEPARATION STEP.

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