US2197460A - Use of solvent liquids in cracking heavy residual oils - Google Patents

Description

Patented Apr. 16, 1940 UNITED STATES- USE OF SOLVENTLIQUIDS I'N CRACKING HEAVY RESIDUAL o Ls Gale L. Adams, Los Angeles, Calif., assignor to Socony-Vacuum Oil Company, Incorporated,

New York, N. Y., a corporation of New York No Drawing. Application May 21, 193s, Serial No. 209,378

4 Claims.

The invention pertains to the art of cracking the heavy, residual petroleum oils known generically as black oils and containing relatively large proportions of asphaltic substances and paraffin wax.

The primary object of the invention is to permit the cracking of residual oils which are of too great viscosity and too high a carbon content to Permit them to be cracked in the conventional manner.

A corollary object of the invention is to afford the maximum yield of uncracked (so-called virgin) gas oil by simple distillation of the black oil followed by the cutting back of the viscous reduced product with a highly refractory cracked product having superior viscosity cutting properties for the stock charged to the cracking furnace.

It is conventional practice to crack black'oils, either for the production of motor fuels and other volatile products or for the reduction of viscosity and pour test. It is also well known to separate from the products of the cracking operation a fraction boiling above the boiling range of gasoline and to return this fraction as recycle stock to the black oil feed, to be cracked with it.

In conventional operations such as this it is impossible to fit the cracking temperature to the Wide range of hydrocarbons present. If a sufiiciently hightemperature be used to appreciably crack the cycle stock, the run is of short duration due to overcracking of the contained pitch. 0n the other hand, if the temperature be lowered to the optimum pointfor the asphaltic constituents, the cycle stockis not materially altered. The process to ice described makes possible maximum yields from all products charged to the cracking furnace by providing selective cracking gonditions for the highly reduced asphaltic resiues. I

Heretofore it has been impossible to crack black oils having a viscosity much in excess of 300 seconds Saybolt furol at 122 F; without excessive carbon formation and the rapid choking of tubes. I have discovered that it is possible'to crack, without undue'carbon deposition, a straight run 'residual oil of much higherviscosity'up to as much as 4,000 seconds S; F. at 122 Fahr., by diluting the black oil feed with a relatively small proportion of a heavilycracked and refractory fraction I selected, enables me to. disre ard. t cracking temperature of the small quantity of recycled oil and to crack at the temperature most favorable to obtaining whatever results may be desired from the cracking of the black oil.

The first requirement in the oil selected as a solvent oil is that it shall have a low viscosity and a well. developed power of dissolving the bituminous constituents of the black oil, these charac-. teristics permitting a relatively small proportion of the solvent oil to effect a relativelylarge reduction in viscosity. The second is that it shall be so refractory as tobe substantially unchanged at the temperatur at which the black oil is to be cracked. The third is a boiling range which permits it to be vaporized at the preferred cracking temperature, thus aiding in purgingthe furnace tubes of carbon *as formed, the vapors subsequently being fractionated out of the cracked Gravity,:A. P. I .'degrees 19.0

Boiling range, I. B. P., 454 F., dry point degrees 598 Minimum appreciable .cracking temperature under conditions of test degrees 930 to 940 Viscosity, Saybolt Universal at 100 F 35.6

An oil having this relation of gravity to viscosity and boiling rangeis very deeply altered from its original constitution as a petroleum fraction and consists'to an important extent of ring hydrocarbons.

We recognize that a satisfactory oil of r this character can often be built up from the reaction products in a-normal viscosity breaking ycle and that it is not necessarily essential that an extraneous solvent oil be used.

In order to illustrate the working out ofthis processandits utility under certain commercial conditions, the following experimental runs were made. .These are all based on an initial quantity of'10,000 barrels of a 125' viscosity asphaltic and waxy residuum from light California crude (viscosities are in seconds, Saybolt furol at 122 F. unless otherwise stated).

In the operation recorded in column 1 the 125 viscosity residuum was passed through the cracking operation as is (without any further reduction) and in a once-through treatment (without recycle).

In the operation shown in column 2 this 125 viscosity residuum was reduced by further distillation to 1800se conds viscosity and this reduced stock was fed to a once-through cracking operation without any addition of solvent oil.

In the operation recorded in column 3 the 125 viscosity residuum was reduced by distillation to 312 seconds viscosity and this stock was-fed to the cracking operation without the addition of solvent oil but with recycle of the gas oil produced in the operation. The volume of the recycle was to the volume of the fresh feed as 0.9 is to 1.0.

In the operation shown in column 4 the 125 viscosity residuum was reduced by distillation to 1800 seconds viscosity and out back to 340 seconds viscosity by admixture with 13.0% of. its own volume of the reformer solvent oil described above. The cut-back stock was then passed through a once-through cracking operation. As this operation proceeded the unaltered solvent oil was fractionated out of the products of the operation and returned to the feed, this returned uncracked solvent oil constituting a recycle having the ratio to the fresh feed of 0131100.

The operation recorded in column 5 was the same as operation 4 except that the original stock was reduced to a viscosity of 3400 seconds and out back to 340 viscosity'by the addition of 15.7% of its volume of solvent oil, the recycle ratio being thus 0.157 2 1.000.

In the five cracking operations the conditions were intentionally adjusted to give, as nearly as possible, the same yield of gasoline figured back to the original 10,000 barrels of 125 second resid- .uum. In all of these operations a portion of the gas oil yielded by the cracking operation was used to cut back the cracked residuum to fuel oil viscosity and the 'net yield of gas oilstated is that remaining after this portion was so utilized.

All yields in the following table are based upon a total volurnetricyield of 100 per cent of liquid products on the 125 second straight run residuum charge.

0 per cent by weight of charge is produced. This is due to the change in specific gravity relationship from charge to products.

In addition a gasyield of from 2 to 4 No. 1 No. 2 N0. 3 No. 4 No. 5

CRACKING FURNACE YIELDS (excluding recycle) Gasoline l, 200 l, 380 l, 230 l, 290 1, 170 Cracked gas oil. 1, 360 0 4, 500 730 460 Residue before back 7, 440 5, 520 3, 120 4, 880 4, 620

DISTRIBUTION OF GAS OILS Straight run:

Gross yield 0 3, l00 1, 150 3, 100 3, 750 Used as cut-back for fuel 0 250 0 370 710 Net yield O 2, 850 l, 150 2, 730 3, 040 Cracked:

1 Gross yield 1,360 0 4, 500 730 460 Used as cut-back for l'uel .1 0 0 1,930 730 400 Net yielrl l, 360 0 2, 570 0 0 Total of net yields..." l, 360 2,850 3, 720 2,7 10 3, 040

FINAL YIELDS FROM TOTAL OPERATION Gasoline 1, 200 1, 380 l, 230 l, 290 l, 170 Straight run gas oil 0 2, 850 l, 150 2, 740 3, 040 Cracked gas oil 1. l, 300 0 2, 570 0 0 Cut-back fuel Oil. 7, 440 5, 770 5, 050 5, 980 5, 790

PROPERTIES or PRODUCTS I Gasoline:

End point. degrees. 380 380 380 380 380 Octane number. 64. 1 64. 7' 64. 3 68. 1 67. 8 Straight run gas oil:

Viscosity, S. U.

100 71.4 44. 7 71.4 80, 6 Pour point. degrees 20 55 55 Initial point. do 484 403 484 444 50% point. .do 656 580 656 008 End point do 765 044 765 780 Cracked gas oil:

,Viscosity, S. U.

100 35. 2 49. 4 32. (l 32. l) 45 -30 30 380 368 347 507 428 415 p d 770 500 498 Cut-back fuel oil:

Viscosity, S. F.

122 125 123 111 l25 125 Pour pointdegrees" 40 15 20 45 Sediment. percent. 0.03 0. 82 0. 04 0. 33 0. 23

The principal utility of this process is found in two of its aspects: the obtaining of large yields of straight-run gas oil, and a major increase in the capacity for producing low viscosity and low pour point fuel oil of any given piece of cracking equipment.

Regarding the first named, gas oils are in large and increasing demand as'Diesel engine fuel, and for this purpose the straight run gas oils are more desirable than those produced by cracking. Further, if the purpose of the operation be to produce the maximum quantity of gasoline rather than gas and fuel oils, the cleanest operation and the maximum economy are obtained by cracking the gas oils in a separate operation rather than in a recycling operation in which the asphaltic constituents of the crude are present.

The second named feature is, however, the major element of utility, the process lending itself a:

- great increase in the output capacity of any given cracking installation is produced by the method above described, as is shown by the following figures indicatingthe yields of products from a cracking installation having a throughput capacity of 10,000 barrels per day, assuming sufilcient distillation capacity to provide for the various degrees of reduction required to provide the 300, 1800, and 3400 vis. charging stocks.

Operation No. 1 gives a high yield of fuel oil,

which is defective as regards pour point. Operation No. 5 is also deficient in this regard and it is possible that the optimum point of reduction has been passed in this run.

Operation No. 2 gives the highest yield of all products but this operation, without the addition of the solvent, is merely the statement of a desideratum as the operation is commercially impracticable. The high figure for sediment shown in the figures for properties of products indicates the liability to coking, and in fact this run was not completed because of the rapid choking of the coil by carbon. It is the addition of the solvent oil which makes this operation practicable and substantially free from the carbon accumulation which has heretofore prevented the cracking of these heavy black oil residues.

It will be noted that the addition of the solvent oil in runs 4 and 5 reduces only slightly the output capacity of the apparatus and that it increases by approximately four the octane number of the gasoline produced over that yielded by runs in which the solvent was not present. The reason for this result is not known to me, but it was observed equally in other experiments in'which cracking temperatures were raised and lowered to produce more and less gasoline and appears to be the direct result of the addition of the solvent oil. 1

It may be pointed out that the once-through operation of run 1 is not commercially desirable because of the low yields of products and the high pour point or the fuel. Run 3, however,

is the normal type of commercial recycle operation. As a consequence, the real comparison of cracking unit capacity is between the 5,937 barrels of run 3 and the 12,840 and 13,969 barrels of runs 4 and 5 respectively.

It is recognized that the enhanced output or the cracking unit in runs 4 and 5 over that obtained in run 3 is dependent on the provision of additional distillation capacity sufiicient to care for the additional reduction required to bring the cracking still charging stocks down to a reduced bulk. It is well known, however, that distillation equipment and distillation operation are much less costly than the equipment and operation required in cracking, and that the cost of distillation thus by no means offsets the economy incident to increased production from the cracking unit. 1

I claim as my invention:

1. In the cracking of heavy petroleum residuum containing asphaltic substances, the steps of: reducing said residuum by a non-cracking distillation to a viscosity exceeding that at which said residuum may be cracked without excessive carbon formation, said viscosity being substantially greater than 300 seconds Saybolt furol at 122 Fahn; blending with said reduced resid um a solvent oil, characterized by low viscosity and high solvent power for asphaltic substances, in amount required to produce a blend having a viscosity of about 300 seconds Saybolt furol at 122 Fahn; and subjecting said blend to a temperature at which the constituents of said residuum are cracked and at which said solvent oil is substantially uncracked.

2. A process substantially as and for the purpose set forth in claim 1, in which said residuum is reduced to a viscosity not less than 1800 seconds Saybolt furol at 122 Fahr. prior to being blended with said solvent oil.

3. A process substantially as and for the purpose set forth in claim 1, in which said solvent oil consists predominantly of aromatic hydrocarbons.

4. A process substantially as and for the purpose set forth in claim 1, in which said solvent oil is a highly cracked and refractory petroleum product.

GALE L. ADAMS.