Table XI.
Cost Estimate for Methyl Mercaptan from Methanol
(5,000,000 pounds per year) Capital cost
$644,000 Pounds per Year
Products Methyl mercaptan Dimethyl sulfide Direct costs Operating labor Supervision and maintenance Methanol at 29 cents/gal. Hydrogen sulfide at 0.142 cent/lb. Catalyst and miscellaneous supplies Utilities Total
5,000,000 98,000 Cen ts/Lb . CHISH
1.63 0.56 3.55 0.13 0.48 0.44 6.79
costs are somewhat less with dimethyl ether, because of a simpler recovery section. However, this is to a large degree nullified by lower mercaptan yields per pass and the need for pressure storage to accommodate the ether. Thus the over-all cost of the process is about the same for either reactant. literature Cited (1) Bell, R. T. (to Pure Oil Go.), U. S. Patent 2,685,605 (1954). (2) Binder, J. L., J . Chem. Phys. 18, 78 (1950). (3) Folkins, H. 0. (to Pure Oil Co.), U. S. Patent 2,786,079 (1957). (4)' Folkins, H. O., Miller, E. L. (to Pure Oil Co.), Ibid., 2,820,060 (1958).
\
Gulf Coast location (Table XI). Total direct operating costs have been estimated a t 6.79 cents per pound for producing methyl mercaptan from methanol as the reactant. The capital cost will be dependent upon the specific conditions under consideration, such as tankage, H2S recovery facilities available, etc. Since availability of H2S will be governed by the location of the plant, its cost may vary from that included here. Because some chemical companies may have a supply of by-product dimethyl ether, estimates have been made also on the basis of the ether as a n alternative reactant. Investment
,
trand, New'York, 1947. ' (8) Hennig, H. (to Pure Oil Co.), U. S. Patent 2,819,313 (1958). (9) Kelley, K. K., "Thermodynamic Properties of Sulfur and Its Inorganic Compounds," Bur. Mines Bull. 406 (1937). (10) Kistiakowsky, G. B., Rice, W. W., J . Chem. Phys. 8, 618 (1940). (11) Kramer, R. L., Reid, E. E., J . A m . Chem. Soc. 43, 880 (1921). (12) Natl. Bur. Standards, "Tables of Selected Values of Thermodynamic Properties," Circ. 500 (1952). (13) Sabatier, P., Comfit. rend. 150, 1217 (1910). (14) West, J. R., Chem. Eng. Progr. 44, 287 (1948). RECEIVED for review September 14, 1961 ACCEPTEDMarch 19, 1962 Division of Petroleum Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961.
P R E P A R A T ION OF LOW FREEZING JET FUELS B Y ISOCRACKI NG R. H. KOZLOWSKI, H . F. MASON,AND J . W . SCOTT California Research Gorp., Richmond, Calif.
Gas oils boiling in the range of 550" to 850" F. were lsocracked in the laboratory to evaluate the products as jet fuel components. Processing at 60% per pass conversion and 500" to 525" F. recycle cut point gave about a 20 to 40% yield of kerosine-type jet fuel with freezing points below -60" F. Produced in addition to the jet fuel were butanes, high octane light gasoline, and naphthenic reformer feed giving a total C4+ liquid yield of about 1 17%. Neither the yields nor the low freezing points of the synthetic jet fuels produced appear to be significantly affected by feed properties. The very low freezing points are attributed to very low normal paraffin content. Low freezing kerosine-type jet fuel components of high quality can be produced from heavy, lower value distillates by Isocracking. HE fastest growing major petroleum product today is Tkerosine-type jet engine fuel. If forecasts of continuing growth are correct, the demand for these fuels will exceed the petroleum industry's ability to supply them from straight-run fractions. Specifications (3) rather than volume of kerosine distillates will limit production. I n general, the freezing point and smoke point specifications represent the most important limits. Problems arising from high freezing points are the most difficult to overcome. Present solvent or urea dewaxing processes are effective for this purpose but Are not a t present economical. Molecular Sieve treatment or isomerization processes are possibly applicable, but their commercial feasibility has not been proved. O n the other hand, solvent extraction, acid treatment, and hydrofining have been used to correct
276
I & E C PROCESS D E S I G N A N D D E V E L O P M E N T
smoke point, as well as polynuclear aromatic content, sulfur content, and stability. Such processes cannot correct both freezing point and smoke point problems in one step, however. I n addition, these processes use relatively valuable stocks already in the jet fuel boiling range. Isocracking can be used to produce kerosine-type jet fuel fractions from heavy distillates of lower value (75). Isocracking (72-74, 77) is a commercial low temperature hydrocracking process-a method of cracking in the presence of hydrogen and a catalyst. The jet fractions produced possess very low freezing points even when produced from paraffinic feed stocks. I n addition, they possess low total aromatic content and are substantially free of polynuclear aromatics, nitrogen and sulfur compounds, and other impurities. High quality gasoline is produced simultaneously.
LOW PRESSURE HlOROFIUEO
SEPARATOI
'-?FRESH
GAS
(25 RECYCLE
FEED
r
PUMP
STRIPPER
fELD
F
uon PUMP
ILllED
_______ Figure 1 .
PUMP
I
D
I
STRIPPED P R O D U C T 10 ISOCRACKIMP
P I 00 U C 1 TRIMSFER
ONCE-THROUGH BOTTOYS
Figure 2.
lsocracking
This paper presents the results of Isocracking three different 550' to 850' F. boiling range feeds to produce kerosine-type fuels, evaluates these products as jet fuel components, and discusses their properties in relation to their composition. The effects of recycle splitter cut point, once-through operation, and feed properties are also discussed. Experimental Equipment and Procedures
The pilot plant results presented here were obtained in continuous flow, bench-scale units. Figure 1 shows the schematic flow diagram for the Isocracking experiments. T h e unit contained 120 cc. of catalyst in a vertical reactor of 13/16inch inside diameter. Isothermal operation was maintained by control of multiple electrical heaters arranged along the axis of the reactor. T h e reactor effluent was continuously fractionated, as shown, with efficiencies comparable to high quality TBP-type distillations. Cut point was monitored in these columns by temperature-programmed vapor phase chromatographic analyses of the overhead and bottoms streams. Cut point is defined as that temperature on the composite true boiling point curve which gives the same overhead and bottoms yields as those actually observed. The cut point in the splitter column was controlled a t 500' or 525' F. The stabilization column was controlled to give a split between CS'Sand (26)s. This resulted in a hydrogen to C S gas stream and a C 6 to cut point liquid stream. T h e gas stream was analyzed by mass spectrometer. The liquid stream was usually fractionated prior to analysis to give a Ce to 180' F. fraction (light gasoline), a 180" to 400' F. fraction (reformer feed), and a 400' F. to cut point fraction (jet fuel component). Mass spectrometer group-type analyses were obtained on the reformer feeds. Estimates of reforming yields and octane numbers for these reformer feeds were based on operating a reformer a t 500 p.s.i.g. with liquid hourly space velocity of 2. Distribution of hydrocarbons in the jet fuel fractions was determined by mass spectrometric techniques ( 9 , 7 7 ) . Product quality tests on these fractions included the conventional freezing point (70), naphthalene content (7), total aromatic content (7), and smoke point (2). Reaction conditions for each experiment (given in the tables) were 1200 p.s.i.g., 6500 standard cubic feet of gas recycle per barrel of total liquid feed, and catalyst temperatures from 525' to 650' F. T h e experiments were run consecutively over the same catalyst charge, although not necessarily in the order given. T h e catalyst used in this study was nickel sulfide on a commercial silica-alumina. Hydrofining of the raw feeds was performed in a reactor containing 9.9 liters of catalyst and having 25/*-inch inside
Hydrofining
diameter. T h e flow scheme (Figure 2) was that conventionally employed for catalytic hydrofining with provisions for gas recycle and adiabatic temperature control. Also, water was injected into the reactor effluent. Liquid yields ranged from 102 to 104%. T h e catalysts used for hydrofining were cobalt and molybdenum on alumina. Reaction conditions were 1200 p.s.i.g., 6000 standard cubic feet of gas recycle per barrel of liquid feed, and average reactor catalyst temperatures of 640' to 730' F. Three stocks from different sources with boiling ranges of about 550" to 850' F. were processed-(1) a heavy heart cut catalytic cycle oil obtained from commercial processing of predominantly California crudes, (2) a heavy cycle oil from commercial catalytic cracking of charge stocks made while running 85% Arabian crudes, and (3) a gas oil fraction from an Arabian crude. Table I gives properties of hydrofined stocks. In the following discussion, per pass conversion is the conversion of total reactor feed (fresh feed plus liquid recycle) to products boiling below the recycle splitter cut point in a single pass through the reactor. I n extinction recycle operation, per pass conversion varies with the amount of liquid recycle and is calculated as the rate of fresh feed make-up divided by the total reactor feed rate. Thus, in extinction recycle operation the over-all conversion of fresh feed is 100%. For once-through operation, conversion is 100 minus the volume per cent yield of reactor effluent boiling above the cut point. Results
Extinction Recycle Operation. The results of Isocracking the hydrofined feeds a t extinction recycle conditions with about 60% per pass conversion to products boiling below Table 1.
Description
Gravity, API Aniline point, O F. Composition, vol. % Paraffins Naphthenes Aromatics ASTM distillation, F. St/5
10/30 ?0/90
95/EP Pour point,
O
Feed Properties Cal$ornia Arabian Heaay Heavy Cycle O i l Cycle Oil
31.9 155.0
31.2 180.0
35.2 195.0
24 55 22 D 1160 3271440 479/545 585 624/689 722/771 30
28 57 16 D 1160 4271536 572/643 690 7301780 801 /845
35 49 16 D 1160 357/541 587/666 696 722/749 763 /799 +55
+
F.
VOL.
1
Arabian Gas 011
NO. 4
+60
OCTOBER 1 9 6 2
277
500 " F. are given in Table 11. I n all cases? the freezing point of the 400 " to 500 F. jet fuel fraction was below - 70 " F. and, in two cases, below - 76 O F. These freezing points were much lower than the proposed specification maximum ( - 58 F.). Smoke points of the jet fractions were generally acceptable (approximately 20 mm.) and were found to increase with increasing paraffin content. T h e low naphthalene content of these fuels makes them especially interesting. Because of their low freezing points and high purity, these products are particularly useful as jet fuel blending stocks. 'Thus? if a product is obtained with too low a smoke point, it can be blended with higher freeze point straight-run stocks to give the desired aromatic content. Less than 2 weight % of C1-C3 gases were produced, most of which was propane. Total yield of liquid products obtained was about 117 volume Fh, This comprised about 11% butanes, 19y0Cb to 180' F. light gasoline. and 67% cf a 180' to 400" F. naphthenic reformer feed along with about 20% cf the 400" to 500" F. jet fuel fraction. T h e butanes produced were about 74% isobutane. 'The Cj- 1803 F. light gasoline had a n F-1 octane number of 100 \\-it11 3 nil. of T E L per gallon. T h e 180' to 400" F. fraction can be reformed to 100 octane number (F-1 plus 3 ml. of T E L per gallon) a t Cj+ gasoline yields of about 84 to 89 volume %, depending on the feed source.
Table II. lsocracking at 500" F. Recycle Cut Point Arabian California Heaoy Cycle Oil Heavy Cycle Oil
Feed Designation
Catalyst temp., F. Conversion, vol. 70per pass Hydrogen consumption, SCF/Bn Yields6 CP C:, iC1 nCr (2-180 F. 180-500 F. Reformer feed and jet product properties Gasoline cut point, ' F. Jet fraction (gasoline cut point to 500" F.) Yield, vol. lo Gravity, API Aniline point, O F. Composition, vol. yo Paraffins Naphthenes Aromatics Freezing point, F. O
Jet fuel was increased by decreasing the end point of the gasoline produced. Thus, for example, the yield of jet fuel \vas increased from about 20% to about 407, by decreasing the gasoline cut point from 400" to 320" F., as shown in Table 11. In addition to the increased yield, a lower freezing point product was obtained. T h e smoke point increased as the initial boiling point of the jet fuel was decreased. As expected? lowering the boiling range gave a less dense jet fuel. .Also, the refcrmer feeds which tvere prepared at the lower gasoline cut points can be rrformed to a higher octane number at the same yield. Even with large variations in feed source, the yields and the freezing points of the jet fractions \.\.ere similar. Relativr proportions of paraffins and aromatics in the feeds are reflected in the paraffins and aromatics of the jet fuel and reformer feed fractions of the products-that is, the higher the paraffin and aromatic content of the feed, the higher the paraffin and aromatic content of the products. 'The consistency of the properties of these products is due to specific Isocracking reactions which take place, resulting in a product distribution governed by mechanistic factors (6! 76, 78). Group-type analyses of these jet fuel fractions are also given in Table 11. T h e freezing points \212
40.7
13.3 40.0
180-400° F. Product
400-500" F. Product
51.5 124.5
39.9 144.5
35.2 52.7 12.1
45 26
+
500 F. Bottoms
41.4 >212
32 46 22
58 6
Below - 76 16 0.35
D 1160 582/617 625/663 691 722/764 785,4330 f85
Standard cubic feet per barrel of fresh feed to Isocracker.
cracker feed component. I n the same regard, partial recycle operation can be used advantageously for versatility in fuel production. Once-through operation also gave a lower paraffin content reformer feed than did extinction recycle operation. This, too, reflects the lower paraffin content of the reactor feed during once-through operation. As a consequence, higher quality reformer feeds were obtained from once-through operation than from recycle operation. Thus: the 180' to 400' F. fractions from once-through operation with the -4rabian heavy cycle oil and the Arabian gas oil can be reformed to 100 octane (F-1 plus 3 ml. of TEL per gallon) at CS+ gasoline yields of about 91 and 8870, respectively. The ratio of jet fuel to Csf gasoline produced was higher during once-through operation than during extinction recycle operation. T h e yields of jet fuel were increased even further by decreasing the end point of the gasoline. T h e very low freezing point and high purity of these fractions make them especially attractive as jet fuel blending stocks. Conclusions Kerosine-type jet fuels with freezing points below -60' F. can be prepared by Isocracking 550' to 850' F.boiling range straight-run gas oils and catalytic cycle oils. Processing at 60% per pass conversion and 500" to 525' F. recycle cut point gives abcut 20 to 40% yield of stable, synthetic jet fuel of very low freezing point. I n addition, butanes, high octane light gasoline, and naphthenic reformer feeds are produced, giving a total C4+ liquid yield of about 117'%. Neither the yields nor the low freezing points of the synthetic jet fuels produced appear to be significantly affected by feed properties. However, aromatic contents and smoke points are influenced by feed type. T h e very low freezing points of these synthetic jet fuels are attributed to very low normal paraffin contents. 280
VOl. 7%
0 9
29
D 158 418/431 433/440 437 459/479 487/520
See experimental part.
Wt. yo 0.001 0.02 0 8 2 9
2.6 1.2 8.8 38.6 19.4 39.8
O
a
500 570 60.0 5 40 VOl. %
0.8
Ca- 1800 1 180-400 F. 400-cut point, ' F. Bottoms, cut point,
Arabian G a s Oil
525 600 60.2 670
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
D 158 41 7/429 430/435 440
447/461 471 /500 Below -76 21 c
D 1160 537/568 592/635 671 696/729 734/775 +65
0.60 Based on fresh feed to Isocracker
Acknowledgment The authors express their appreciation to the California Research Corp. for permission to publish this paper. T h e valuable contributions and assistance of H. A. Frumkin and our many other associates are also greatly appreciated. Literature Cited (1) Am. SOC. Testing Materials, Philadelphia, Pa., "ASTM Standards on Petroleum Products and Lubricants." ASTM D 1319, 1959. (2) Ibid., ASTM D 1322. (3) Ibid., ASTM D 1655-59T. (4) Beverly, J. B., Marschner, R. F., Division of Petroleum Chemistry, 135th Meeting, ACS, Boston, Mass., April 1959. ( 5 ) Chem. W e e k 86, 54 (Feb. 27, 1960). (6) Egan, C. J., Langlois? G. E., White, R. J., Division of Petroleum Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961. (7) Federal Test Method Standard 791, Method 3704T. (8) Gollis, M. H . , Belenyessy, L. I., Gudzinowich, B. J., Koch. S. O., Smith, J. O., \Vineman, R. J., Division of Petroleum Chemistry, 138th Meeting, ACS, New York. September 1960. (9) Hastings, S. H., Johnson, B. H., Lumpkin, H. E.: Anal. C/zem. 28, 1243 (1956). (10) Institute of Petroleum, London, Method I.P. 16B. (11) Lumpkin, H. E., Anal. Chem. 28, 1946 (1956). (12) Oil G a s J . 57, 48 (Oct. 26, 1959). (13) Ibid., 58, 127 (March 28, 1960). (14) Petrol. Refiner 38, 376 (Xovember 1959). (15) Robbers, J. A , , Paterson, N. J., Lane, \V. T., Hydrocarbon Processing and Petrol. Refiner 40, 147 (June 1961). (16) Scott, J. TY., Mason, H. F., Kozlowski, R. H . ? Petrol. Refiner 39, 155 (April 1960). (17) Scott, J. h'., Robbers, J. .A., Paterson, N. J., Lavender. H. M., Ibid., 39, 161 (May 1960). (18) Sullivan, R. F., Egan, C. J., Langlois, G. E., Sieg: R. P.. J . .4m. Chem. SOC. 83, 1156 (1961). RECEIVED for review September 29, 1961 ACCEPTED February 12, 1962 Division of Petroleum Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961. Isocracking is the proprietary name of the California Research Corp.
