US2560511A - Catalytic cracking of heavy hydrocarbons in two stages - Google Patents

Description

muy 10, 1951 G. l. JENKINS CATALYTIC CRACKING oF HEAVY HYDRocARoNs 1N Two STAGES Filed July 29, 1948 XUDN WQWWIK MM ws. n.

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CATALYTC CRACKING OF HEAVY HYDRO- CATtBONS IN TWO STAGES Gwilym Islwyn Jenkins, Sunbury-onJihames,

England, assigner to Anglo-Iranian Oil Company Limited, London stock corporationl England, a British joint- @pplication July 29, 1948, Serial No. 41,268 In Great Britain August 9, 1947 The invention relates to the catalytic crack- 6 Claims. (Cl. 196--49) ing of heavy hydrocarbons, such as wax disn tillates. l

The reaction products obtained by the catalytic cracking of heavy hydrocarbons, such as Wax distillate, may conveniently be divided into three fractions, viz. gaseous hydrocarbons, cracked motor gasoline and cracked gas oil, all three fractions boiling belowthe boiling range of the feedstock. We Ahave found that the conditions under which the cracking reaction is carried out may be varied to obtain on the one hand a cracked motor gasoline having a high octane number,'and of commercial value, without re-treating or blending, in which case the cracked gas oil is of poor quality and is of doubtful value, particularly as a Diesel fuel, or on the other handl a gas oil of much better quality, and a -lower yield ofv motor gasoline of lower Octane number. Thus, for example, if a high severity cracking process resulting in approximately 75 to 80% feedstock destruction is employed, there is a yield of 33% gasolineof 81 octane number and a yield of 18% gas oil having a Diesel index of only 7. Such a gas oil can only be utilised as a blending stock for thel improvement of the pour-point of a fuel oil. Ifa low severity cracking process be employed, forA example, a process `'carried out under conditions of high feed ratev and relatively low catalyst circulation rate such that the feedstock destruction amounts to 40 to x by 3% and Vfurthermore such small decrease is more than compensated for by the increased feed-rate permissible at the lower .feed-stock del struction; The low ,severity cracking process suffers from the disadvantage, however, that there is alarge residue amounting to 55% to 60% of the feedstock and having substantially the same boiling range asgthe. feedstock. y

lThe inventionI has ,amongl its objects' to .pro-

vide a process which embodies the advantages of f both the high severity vandjow'severity cracking Lprocesses so as to obtain the maximum yields of gasoline, gas oil vand fuel oil having the optimum octane number,

u Diesel index and pourpointy respectively.

According to; theinv'entionthvere is provided a two-stage process for the catalytic cracking ofA y a heavy hydro'carbon'vf'eedstock, such yfalsgigzai; dis-f tillate, in which in the rst stage the feedstock is cracked under conditions resulting in rela-' tively low feedstock destruction to give a high yield of gas oil suitable for use as a Diesel fuel, while in the second stage the residue from the first stage is cracked under conditions resulting in relatively high feedstock destruction to give a high yield of good quality motor gasoline and a residue constituting a source of fuel oil having `a low pour-point due to the presencevin the residue of cracked gas oil.

The process of the invention may be carried into effect in various Ways according to refinery as overhead through line I4, and a gas oil havx ing a high Diesel index as side stream through line I5. A residue boiling above the gas oil range is 'separated as bottoms through line i6. The overhead product is passed to a second fractionator Il where the gas is separated overhead ,through line I8 and the stabilised gasoline as a bottoms product through line I9, the residue' from fractionator I3 being passed to a second reactor 2li where it is cracked under high severity conditions resulting in the production of a gasoline of high octane number. The re.-

`action products from the second reactor are' passed through line 2i to a third fractionator 22 Where the gasoline and lighter hydrocarbons are separated as overhead through line 23 and a bottoms product withdrawn through line 24 consisting of residual material containing cracked gas oil produced in the second reactor.

The overhead products from the third fractionator 22 may be passed through line 25 to the second fractionator Il in conjunction with the overhead products from the first fractionator, so that the gasoline produced in the first reactor is improved in octane number by the addition of the gasoline of higher octane number produced in the second reactor. If desired, however, the

overhead product from the third fractionatol` 22 i may be passed through line 2li to a separate stabiliser 2l so as to provide a gasoline of high octane number as compared with the gasoline of low octane number separated from the second' fractionator, the gasoline ibeing removed as a bottoms product through line 28 and the gas overhead through line 29.

The two-stage process of the invention may be carried into effect according to any of the Wellknown operating principles. Thus, for example, both loivrconversion and high-conversion operations may be carried out in reactors, both of -which are operated on the normal downow or bottom catalyst draw-off, uidised bed principle. Alternatively, it is particularly satisfactory to use a first reactor operating on the well-known uplow fluidised principle, in order to deal conveniently with the high linear velocities often necessary for low conversion, while the second reactor is operated on the normal downflow principle. Where both reactors are of the uidised or moving bed type, it is possible to utilise either a single regenerator serving both reactors, or a separate regenerator for each reactor.

The improvement obtained by means of the process according to the invention is clearly brought out in the following tables.

' Table I gives the experimental results obtained when processing a wax distillate of Iranian origin on a synthetic silica-alumina catalyst under conditions of high and of low cracking severity. The reactor temperature, pressure and dilution were identical in both cases, but the oil throughput, expressed as weight of oil per hour per unit of weight of catalyst in the reactor Wo/H/Wc, was more than twelve times as great in the low severity operation as in the high severity operation. In order to provide direct assessments of the two modes of operation the experimental data provided in Table I have been transferred to comparative bases and the results are given in Tables II and III. In Table II the high and low severity operations are compared on the basis of equal oil feed rate, a value of 10,000 barrels per stream day being chosen as the basis for comparison. In Table III the two operations are compared on the basis of equal quantities of catalyst i. e. approximately equal reactor dimensions. Table IV gives the results of operating the two-stage piocess according to the invention, while Table V gives a comparison between the two-stage process and the normal single stage process.

In the following tables andk throughout this speciiication the feedstock conversion is dened as 100 minus the volume percentage of material, in they reaction product, boiling above a true boiling point temperature of 430 F.

Table I Feedstockfwax distillate of Iranian origin. Catalyst-synthetic silica-alumina.

High Low Severity Severity Reactor Conditions:

Temperature'.... F.. 900 900 Outlet Pressure. ...p. s. i. g-. 10.0 10. Space. Velocity Wo/H/Wc.- 0.81 10.3 Dilution (as steam) weight per cent on feed.. l2. 7 13.1 Product Yields:

Ca and lighter....weiglit per cent oii feed.. 8. 26 2. 31 Total O4 -.do.... 10.3 1.98 Debutginised Gasoline ..do.-.. 33.1 17. 2 GasOil ..do.... 18. 2 14.6 Residue -do.- 24.1 60.3 Coke hydrogen) `.do.... 5.0 Feedstock Conversion: 1130" Basis Volume per cent.. 60.0 24. 5 Product Properties:

Gasoline End-point C.. 208 209 Gasoline O. N 81 76. 5 Sulphur .weight per cent.- 0.09 0.19 Gas Oil Diesel Index.- 7 20 Gas Oil Pour Point.-. F.. -5 +5 Gas Oil Sulphur weight per cent.. 2. 26 2.14

Table JI Feedstock and catalyst-as in Table I.

60% 25.5% Couver- Conversion sion Oil Feed-rate .B. P. S. D-. 10,000 10,000 Catalyst in reactor lbS.. 163, 700 12, 870

Products C3 and lighter.. .SCF/bbl.. 251 75 T al Cl .B. S. D.. 1,630 316 Gasoline (400 F. E. P.):

' 77 O. S. D 2, 040 (b) 81 O. N B. P. S. D-- 4,090 Gas Oil (0 F. Pour):

` (a) 20 D.v IL .B. P. S. D 1, 450 (b) 7 D. I.... S. D.. 1,730 Residue above Gas oil.. Y S. D.. 2,330 6,080

Table III Feedstock and catalyst-as in Table I.

@ 60% 24.5% Oonver- Conversion sion Oil Feed-rate. 10,000 Catalyst in rea l 12,870

C3 and lighter. 75 T al C S. 316 Gasoline (400 (l) 77 2.040 (2) 8i Gas Oil (0 (l) 20 1,450 (2) 7 D. iso Residue above G 183 6, 080

Tabl@ IV Catalyst and feedstock-as in Table I.

Process A-reactor operating at low conversion (24.5%) with fresh'feed'.

Process -reactor operating at high conversion on residue from process A..

Process A+B"-net result ou operating A and 13" in series with segregation of gasolines and gas oils.

Process .A'fnet result on operating A" and YB in series with combination of gasoline's and gas oilsvirito single streams.

Process Ref.

A+B AB Oil Feed Rate-Fresh B. P. s. D-- io, 000 Nili 10,000 Oil Feed Rate-Residue B. P. S. D.. Nil Catalyst iny Reactor(s) .-...1bs.. 12, 870 Feed'stock Conversion LevelY i Basie igesh reed.

Table V Catalyst and feedstock-as in Table I. Process S"si11gle reactor operating at 60% conversion level. Process A+B-dual system with segregation of gasolines and Process Ref.

S A+B AB Oil Feed Rate-Fresh- B. P. S. D-- 10,000 10,000 10,000 Catalyst 111 total system lbs.- 163, 700 111, 600 111, G00

Products O3 and lighter sGF/BbLL- 251 22s 228 Total C4 B. P. S. D.. 1,630 1, 310 1,310 Gasoline (400 77 O B. S. D. 2,040

(b) 81 O. N B. P S. D-- 4,090 4, 530

(c) 79 O. N B. P S. D.. 4,530 Gas Oil (0 F. Pour):

(il) 20 D. I B. P. S. D-- 1,450

c approx Residue 2, 330 1, 420 l, 420

1 Basic fresh feed.

It will be seen from a consideration of Table II that although the reaction space required for processing 10,000 B. P. S. D. at a conversion of 24.5% is less than one-tenth of that required for the same quantity of feed at 60% conversion, the gas oil yield is only 280 B. P. S. D. less at the lower conversion while the Diesel index is 13 units higher. It will be seen from a consideration of Table III that the low conversion operation yields 1450 B. P. S. D. of gas oil of 20 Diesel index as compared with only 136 B. P. S. D. of 7 Diesel index in the high conversion operation.

It is also clear from Tables IV and V that the two-stage process is advantageous as compared with the single stage process in many respects and particularly with regard to gas oil yield and quality. Thus, the tota1 catalyst requirement in the two-stage process is 52,000 lbs. less than in the single stage process. The single stage process gives more gas and volatiles, thus requiring a larger gas-handling plant, and some 900 B. P. S. D. more cracked residue. The total quantity of gas oil in the two-stage process, is 2,500 B. P. S. D. of which 1450 B. P. S. D. is at 20 Diesel index and the remainder is at 7 Diesel index. The Diesel index of the combined material is estimated as being 15. With the single stage process, the gas oil yield is only 1730 B. P. S. D. and the Diesel index is 7. The single stage process gives 4090 B. P. S. D. of gasoline of 81 octane number, while by combining the two gasolines from the two-stage process there is a total yield of 4530 B. P. S. D. at an estimated octane number of 79, or, on an alternative basis, the two-stage process yields 358,000 barrel-octane numbers as compared with 331,000 BON from the single stage process.

I claim:

1. A two-stage process for the catalytic cracking of a hydrocarbon feedstock boiling above the gas oil range, comprising passing the feedstock to a reactor wherein it is cracked at a relatively high space velocity resulting in approximately iO-45% feedstock destruction, passing the reaction products from the reactor to a fractionator s. 6 Where gasoline having an octane number about 77 and lower hydrocarbons are separated as overhead, a gas oil having a Diesel index of approximately 20 as a side stream and a residue boiling above the gas oil range as bottoms, removing the gas oil from the system, passing the overhead product to a second fractionator where the gas is separated overhead and the stabilized gasoline as a bottoms product, passing the residue boiling above the gas oil range to a second reactor where it is cracked at a relatively low space velocity resulting in approximately 7 5-80% feedstock destruction, and passing the reaction products from the second reactor to a third fractionator where gasoline having an octane number about 81 and lighter hydrocarbons are separated as overhead, and a bottoms product is withdrawn consisting of residual material containing cracked gas oil having a Diesel. index about 7 produced in the second reactor and constituting a source of fuel oil.

2. A two-stage process according to claim 1, in which the overhead products from the third fractionator are passed to the second fractionator in conjunction With the overhead products from the first fractionator and gasoline is separated from the second fractionator, the yield of gasoline so produced having a greater total barrel octane number than the yield of gasoline which could be obtained by cracking the original feedstock in a single stage.

3. A process according to claim 1, in which the overhead product from the third fractionator is passed to a separate stabilizer where the gas is separated overhead and the gasoline of octane number approximately 81 is separated as a bottoms product.

4. A process according to claim 1, wherein the first reactor operates on the up-ow fluidized principle, while the second reactor is operated on the down-flow principle.

5. A process according to claim 1, wherein cracking in the first reactor is carried out at a temperature of 900 F., a pressure at the outlet of the reactor of 10 lbs/sq. in., and a space velocity of 10.3 Wo/H/Wc.

6. A process according to claim 1, wherein the cracking in the second reactor is carried out at a temperature of 900 F.; a pressure at the outlet of the reactor of 10 lbs/sq. in., and a space velocity of 0.81 Wo/H/Wc.

GW ILYM ISLWYN JENKINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,271,670 Thomas Feb. 3, 1942 2,326,705 Thiele et al Aug. 10, 1943 2,339,874 Nysewander Jan. 25, 1944 2,353,731 Kanhofer July 18, 1944 2,444,131 Seguy June 29, 1948 2,444,545 Thomas July 6, 1948 OTHER REFERENCES Production of Premium Diesel Fuels, George M. Woods, part 2, The Petroleum Engineer. Dec. 1936, pages 58, 60, 62, 64.

Certificate of Correction Patent No. 2,560,511 u July 10, 1951 GWILYM ISLWYN JENKINS It is hereby certified that error appears inthe printed specification of the above numbered patent requiring correction as follows:

Column 4, Table II, in the heading to the third column thereof, for 25.5% read 24.5%

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oiiice. Signed and sealed this 25th day of September, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Claims (1)

1. A TWO-STAGE PROCESS FOR THE CATALYTIC CRACKING OF A HYDROCARBON FEEDSTOCK BOILING ABOVE THE GAS OIL RANGE, COMPRISING PASSING THE FEEDSTOCK TO A REACTOR WHEREIN IT IS CRACKED AT A RELATIVELY HIGH SPACE VELOCITY RESULTING IN APPROXIMATELY 40-45% FEEDSTOCK DESTRUCTION, PASSING THE REACTION PRODUCTS FROM THE REACTOR TO A FRACTIONATOR WHERE GASOLINE HAVING AN OCTANE NUMBER ABOUT 77 AND LOWER HYDROCARBONS ARE SEPARATED AS OVERHEAD, A GAS OIL HAVING DIESEL INDEX OF APPROXIMATELY 20 AS A SIDE STREAM AND A RESIDUE BOILING ABOVE THE GAS OIL RANGE AS BOTTOMS, REMOVING THE GAS OIL FROM THE SYSTEM, PASSING THE OVERHEAD PRODUCT TO A SECOND FRACTIONATOR WHERE THE GAS IS SEPARATED OVERHEAD AND THE STABILIZED GASOLINE AS A BOTTOMS PRODUCT, PASSING THE RESIDUE BOILING ABOVE THE GAS OIL RANGE TO A SEOND REACTOR WHERE IT IS CRACKED AT A RELATIVELY LOW SPACE VELOCITY RESULTING IN APPROXIMATELY 75-80% FEED-

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