US2844520A - Catalytic cracking - Google Patents

Description

United States Patent 0.

CATALYTIC CRACKING Clare Kenneth Viland, Martinez, Calif., assignor to Tidewater Oil Company, a corporation of Delaware No Drawing. Application September 16, 1955 Serial No. 534,882 V 10 Claims. (Cl. 196-50) nitrogen compounds in the feed stocks to catalytic cracking operations has a detrimental effect on the yields and product distribution. It has been generally found that gasoline yields can be improved and coke production reduced by lowering the nitrogen content of the feed stocks. Methods generally recommended for reducing :It is now well recognized that the presence of organic f Patented July 22, 1958 tions. Consequently, basic nitrogen compounds should be removed as far as practical. Various methods are known in the art for the removal of basic nitrogen compounds, any one of which may be used, if needed, in conjunction with the present invention. Satisfactory results are generally obtained by extraction with dilute sulfuric acid such as H 80 for example. The removal of the basic nitrogen compounds may be efiected either before the addition of the non basic nitrogen compounds, or after the addition and before the catalytic cracking operation.

The amount of non-basic organic nitrogen compound to be added to the catalytic cracking charge stock in More'particularly, it pertains to the cata- An important object is the improv'e- 1' accordance with the invention preferably should be suflicient to result in a total non-basic nitrogen content in the charge stock of about 0.3%. However, substantial results may be obtained where the amount of added nonbasic nitrogen is 0.1%. Where the total non-basic nitrogen content of the charge is increased above about 0.4%

some gain in antiknock value of the cracked gasoline may be realized, but usually at the expense of lower yields.

In some instances this may be desirable.

The non-basic nitrogen compounds may be added to I the catalytic cracking charge stock at any time prior to the actual cracking opera-tion. For example, if readily soluble, it may be added to the charge stock while in storage, with whatever agitation is required for uniform the nitrogen content (such as dilute acid treating and the like) preferentially remove the more basic nitrogen com-' pounds (pyridines, 'quinolines, etc.) with lesser or no effect on the non-basic nitrogen compounds present (pyrroles, indoles and carbazoles).

in accordance with the present invention it has been found that, contrary to the general conception concerning j nitrogen compounds in catalytic cracking feed stocks, the presence of non-basic nitrogen compounds in the feed stock has a beneficial rather than a detrimental effect on the yield and, particularly, the anti-knock rating of the gasoline produced. The invention, therefore, broadly contemplates the enhancement of the catalytic cracking of stocks low in non-basic nitrogen content by the addition thereto of organic non-basic nitrogen compounds.

The non-basic organic nitrogen compounds preferred for this purpose are those having boiling points within the approximate boiling range of the charge stock. Since most catalytic cracking operations are conducted on stocks with boiling ranges above 400 F. and below about 1000 F., the nitrogen compound chosen should preferably have a boiling point above about 400 F. Indole, carbazole and their homologues have been identified as present in various nitrogen-containing gas oils, and these non-basic compounds are suitable for use in the invention. However, other high-boiling non-basic nitrogen compounds are suitable, such as, for example, quinoxaline, diphenylamine, phenazine, indazole and benzotriazole. Although the high-boiling non-basic nitrogen compounds are preferred, since they have the approximate volatility of the hydrocarbon charge stock, lower boiling non-basic nitrogen compounds such as pyrimidine, pyrazine, pyrrole, alkyl nitriles, and their homoloques, for example, may be found suitable.

The catalytic cracking charge stocks which are adaptable for improvement in accordance with the invention are those naturally containing less than about 0.1 weight percent of non basic nitrogen, although some improvement may be realized with stocks containing up to 0.3% of non-basic nitrogen. As stated above, basic nitrogen compounds are detrimental to catalytic cracking operadispersion. Alternately, a concentrate of the non-basic nitrogen compound may be made in a portion of the charge stock (which need not necessarily be identical to the remaining charge stock) or other suitable solvent,

-with the use of heat or whatever other aids are necessary to effect solution, and the concentrate blended into the catalytic charge stock in required proportions.

' In accordance with a specific embodiment of the invention, the non-basic nitrogen content of a catalytic cracking charge stock low in nitrogen content is in-- creased'to the desired amount of between 0.1% and 0.5% by blending therewith a suflicient amount of a suitable; hydrocarbon fraction naturally containing high amounts. of non-basic nitrogen. Since the said fraction would normally also contain large amounts of basic nitrogen compounds, it should first be treated (such as, for exam-- ple, by extraction with 25% sulfuric acid to remove the non-basic nitrogen compounds. Alternately, the blend of the low-nitrogen stock with the high-nitrogen fraction may be treated to remove the basic nitrogen compounds. As an example of catalytic cracking charge stock prepared in this manner, 60% by volume of a Minas (Sumatra) heavy gas oil having a boiling range of 500 to 1050 F., a non-basic nitrogen content of 0.04% and .a basic nitrogen content of 0.025% is blended with 40% by volume of a deasphaltized residuum representing 27% of Wilmington Crude oil, said residuum having a nonbasic nitrogen content of 0.70% and a basic nitrogen content of 0.30%. The resulting blend, having a nonbasic nitrogen content of 0.31% and a basic nitrogen content of 0.13%, after reduction of the basic nitrogen content to below 0.05% (by extraction with 25 H is an excellent charge stock for catalytic cracking capable of giving yields and octant numbers superior to that obtained from either stock alone.

The invention may further be illustrated by the following example comprising experimental runs in a catalytic pilot plant of the type described in Petroleum Processing, volume 6, No. 12, December 1951, pages 1370- 1373. This pilot plant has proven to be capable of accurate control and to correlate closely with the operations of a 30,000 barrel per day commercial fluid catalytic cracking plant. I

Four crackingruns in the pilot plant, at separate levels of conversion, were made on each of five charging stocks using for each run a separate portion of equilibrium catalyst withdrawn from'a'commercial fluid catalytic iibon lay-down is the critical parameter for comparison.) The accompanying'table shows the properties and recracking unit. The catalyst consisted of 21% synthetic suits-obtained (interpolated to a uniform carbon laysilica-alumina microspheres and 79% natural catalyst of down of 5% by weight of the charge) from each of the the sulfur resistant type manufactured from"halloysite. 5 five stocks described above.

TABLE Effect on catalytic cracking yields of adding basic and non-basic nitrogen Low Nitrogen Basie Nitrogen Non-Basic Nitrogen Content Charging Stock A B C D E Properties of Oil:

Basic Nitrogen, Wt. percent-.-" 0. 02 0. 80 0. 58 0.02 0. 02 Non -Basic Nitrogen, Wt. per- 514 446 488 475 494 698 696 624 687 636 836 836 i 744 833 746 90% 1, 010 1, 011 Cracked 995 Cracked Cracking Conditions:

Reactor Temperature, F 985 985 985 985 985 Carbon on Regenerated Catalyst, Avg. Wt. percent 0. 10 0.09 0. 10 0. 12 0. 14 Cracking Yields:

Carbon, Wt. percent 5.0 5.0 5.0 5. 0 5. 0 Conversion, Vol. percent Gas Oil Disappearance 63. 2 58.5 51. 7 64. 2 59. 2 Gas Cg'and lighter, C b1 Ch 277 435 430 352 318 Propane-Propylene, Vol. percent. 13. 9 9. 9 7. 2 15. 5 11. 8 Butanes-Butylenes, Vol. percent 16. 8 14 3 10. 0 18. 8 14. 5 Debutanized Gasoline, Vol. percent 390 F. 90% Distilled--. 40. 6 38. 9 35. 5 39.6 38. 8 Total Gasoline, C4 and heavier,

Vol. ercent 57. 4 53. 2 45. 5 58. 4 53. 3 Total esoline to Carbon ratio- 11.5 10.6 9.1 11.7 10.7 Gas Oil, Vol. percent 36.8 41. 5 48. 3 35. 8 40. 8

Octane Number, Debutanized gasoline, clear (ASTM D-908-53) 93. 5 90. 9 88.8 94. 8 95.1 Octane Number, Debutanized gasoline with 3.0 m1 TEL/gal 98. 3 97. 7 96. 0 99. 6 99. 7 .Average Volatility of Debutanized Gasoline, 50% Distilled, F 202 234 248 193 201 It had. a U. 0. P. activity of 21 at the start of each pilot run.

The five charging stocks were prepared as follows:

(A) A 500 to 1050 F. gas oil was distilled from Minas (Sumatra) crude oil.

(B) 29 parts by weight of the basic nitrogen compound, isoquinoline, were dissolved in 971 parts of the Minas gas oil as prepared in (A), to obtain a stock containing about 0.3% of basic nitrogen but low in nonbasie nitrogen.

(C) 59 parts by weight of isoquinoline were dissolved in 943 parts of the Minas gas oil to obtain a stock containing about 0.6% basic nitrogen but low in non-basic nitrogen.

(D) 27 parts by weight of the non-basic nitrogen compound, indole, were dissolved in 973 parts of the Minas gas oil to obtain a stock containing about 0.3% non-basic nitrogen but low in basic nitrogen.

(E) 52 parts by weight of indole were dissolved in 948 parts of the Mines gas oil to obtain a stock containing about 0.6% non-basic nitrogen but low in basic nitrogen.

All twenty cracking runs were conducted at the same The data summarized in the table show that when basic nitrogen is present in a catalytic cracking charge stock there is a marked detrimental effect on product distribution and on octane rating of the gasoline. The ratio of volume percent gasoline yield to weight percent of the charge burned as carbon in regenerating the catalyst decreases substantially when basic nitrogen is present. There is also a sharp drop in both the clear and leaded research octane ratings of the gasoline product. Likewise, there is a definite drop in the volatility of the debutanized gasoline when basic nitrogen is present. As stated prior, the art is generally aware of the detrimental eiiect of nitrogen compounds on catalytic cracking and their removal has been recommended. The data demonstrate that the detrimental effects recognized by the art are due principally to basic nitrogen compounds.

However, the data also show that, in contrast to the detrimental efiect which basic nitrogen has upon catalytic cracking, the presence of added non-basic nitrogen improves the antiknock quality of the cracked gasoline. Also, when present in amount of about 0.3% the nonbasic nitrogen in the charge stock improves the volatility and yield of the gasoline.

As used herein, the term catalyti cracking is used in the sense generally used by the art to denote the conversion of relatively heavy hydrocarbon fractions into relatively lighter products by vapor phase contact with silica, alumina, silica-alumina, silica-magnesia and the like catalysts at temperatures in excess of about 800 F. Although operations with the well known fluidized bed of catalyst are preferred, fixed bed and other types of moving bed are contemplated as equivalent for the purposes of the invention.

It is recognized that the various organic nitrogen compounds may difier in basicity throughout the range from strongly basic (such as pyridine) to definitely non-basic (such as carbazole). For the purposes of the invention, an organic nitrogen compound may be considered nonbasic if it cannot be extracted from solution in hydrocarbons by a dilute solution of a strong mineral acid (such as 25% aqueous solution of H 80 for example). Where used herein, the term non-basic nitrogen is used to denote the nitrogen contained in a non-basic organic nitrogen compound. Similarly, basic nitrogen is used to denote the nitrogen contained in the functional groups of a basic organic compound.

I claim:

1. In a process of catalytic cracking hydrocarbon oil wherein a hydrocarbon distillate having a boiling range between about 400 F., and 1050 F. and a non-basic nitrogen content not over about 0.1% by weight, is subjected to cracking in the presence of an active cracking catalyst to produce substantial amounts of gasoline components, the improvement which comprises adding to said distillate, prior to contact with said catalyst, a sulficient quantity of non-basic organic nitrogen compound to increase by at least 0.1% the non-basic nitrogen content of the distillate.

2. The process of claim 1 wherein the addition of the non-basic nitrogen compound to the distillate is accomplished by blending with said distillate an asphalt-free hydrocarbon fraction containing more than 0.6% non-basic nitrogen and less than 0.1% basic nitrogen.

3. The process of claim 1 wherein the non-basic nitrogen compound added is selected from the group consisting of benzotriazole, pyrimidine, indazole, phenazine, diphenylamine, quinoxaline, pyrazine, pyrrole, indole, alkyl nitriles, carbazole, and their non-basic homologues.

4. The process of claim 3 wherein the non-basic nitrogen compound has a boiling point above about 400 F.

5. The process of claim 4 wherein the non-basic nitrogen compound is indole.

6. The process of claim 4 wherein the non-basic nitrogen compound is carbazole.

7. The process of claim 1 wherein the total non-basic nitrogen content of the distillate after the addition of the non-basic nitrogen compound is between 0.2% and 0.4%.

8. The method of claim 1 wherein, as an additional step, a substantial amount of the basic nitrogen content normally present in the distillate is removed before contact with the catalyst.

9. An improved methodfor cracking hydocarbon oils which comprises blending a substantially asphalt-free hydrocarbon fraction containing less than 0.1% non-basic nitrogen with a substantially asphalt-free hydrocarbon I fraction containing more than 0.6% non-basic nitrogen in proportions sufiicient that the resulting blend contains between 0.2% and 0.4% non-basic nitrogen, then contacting the resulting blend with an active cracking catalyst under conditions of time and temperature sufiicient to convert a substantial proportion of said blend into gasoline components.

10. In the cracking of hydrocarbon oils, the combination of steps which comprises: contacting a substantially asphalt-free hydrocarbon fraction containing more than about 0.6% non-basic nitrogen and a detrimental amount of basic nitrogen with an aqueous solution of a strong acid under conditions to extract from said fraction a substantial amount of the basic nitrogen content, removing the resulting acid phase, blending the resulting hydrocarbon fraction with a substantially asphalt-free hydrocarbon fraction containing less than about 0.1% nonbasic nitrogen in proportions that the resulting blend contains between about 0.2% and 0.4% non-basic nitrogen, and then contacting the resulting blend with an active cracking catalyst under conditions of time and temperature sufficient to convert a substantial proportion of said blend into gasoline components.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN A PROCESS OF CATALYTIC CRACKING HYDROCARBON OIL WHEREIN A HYDROCARBON DISTILLATE HAVING A BOILING RANGE BETWEEN ABOUT 400* F., AND 1050* F. AND A NON-BASIC NITROGEN CONTENT NOT OVER ABOUT 0.1% BY WEIGHT, IS SUBJECTED TO CRACKING IN THE PRESENCE OF AN ACTIVE CRACKING CATALYST TO PRODUCE SUBSTANTIAL AMOUNTS OF GASOLINE COMPONENTS, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID DISTILLATE, PRIOR TO CONTACT WITH SAID CATALYST, A SUFFICIENT QUANTITY OF NON-BASIC ORGANIC NITROGEN COMPOUND TO INCREASE BY AT LEAST 0.1% THE NON-BASIC NITROGEN CONTENT OF THE DISTILLATE.