ENGINEERING, DESIGN, A N D PROCESS DEVELOPMENT At the present no signs of deactivation have been detected. This is shown in Figure 7 where the first reactor temperature profile is plotted for the beginning of the commercial operation and after 4 months on stream. T h e very minor differences in these two profiles result from the higher inlet temperature for the profile taken after 4 months on stream and the slightly different charge stock composition. The one discrepancy between the pilot unit and commercial operation is that of a longer catalyst life in the commercial plant than would be predicted from pilot plant operation. Thus, the experience with the commercial Houdriforming unit has indicated that the catalyst deactivation shown in t h e pilot unit for this type operation is most likely one of trace contaminants introduced in small scale preparation and handling of charge stocks. At the time of writing the predicted catalyst life of 6 months has been exceeded with no detectable deactivation.
pilot unit operation and commercial plant operation is that catalyst life is considerably longer in the commercial plant than was predicted from pilot plant data. This is most likely a result of trace contaminants introduced to the pilot plant charge stock during the preparation and handling. The predicted catalyst life of 6 months has a t the present been exceeded in the Sun Oil plant with no signs of catalyst deactivation of any type.
Acknowledgment The authors wish to express their appreciation t o the Sun Oil Technical Service Division for providing commercial Houdriforming data. Acknowledgment is also extended to members of the pilot plant groups of the Houdry Process Corp. and the Sun Oil Co. for their help in obtaining the pilot plant information.
Literature Cited Conclusion
(1) Heinemann, H., Mills, G. A., Hattman, J. B., Kirsch, F. W., IND.ENG.CKEM.,45, 130-4 (1953). (2) Heinemann, H., Schall, J. W., and Stevenson, D. H., Petroleum Refiner, 30, No. 11, 107-10 (1951). ( 3 ) Kirkbride, C. G., Ibid., 30, No. 6, 95-8 (1951).
The operation of the first commercial Houdriforming unit for production of aromatics has been as predicted from pilot unit studies in most respects. Xylene yields in excess of 100% of the theoretical amount that can be produced from the naphthenes in the charge are being obtained. Operation for benzene and toluene production results in aromatics yields of 87y0 of the amount possible from complete conversion of the naphthenes in the charge. T h e only significant difference existing betwren
(4) Rossini, F. D., Pitzer, K. S., Amett, R. L., Braun, R. M., and Pimeiital, G. C., “Selected Values of Physical and Thermodynamic Properties of Hydrocarbons and Related Compounds,” American Petroleum Institute Project No. 44, Carnegie Institute of Technology (1953). RECEIVED for review August 27, 1954.
ACCEPTED January 6 , 1983.
Selective Hydrotreating over Tungsten Nickel Su1fid.e Catalyst Treatment of Cracked Gasolines R. M. CASAGRANDE, W. K. MEERBOTT, A. F. SARTOR, Shell Oil Co.,
P. 0.Box 2527,
Houston
AND
R. P. TRAINER‘
I , rex.
A selective hydrotreating process using tungsten nickel sulfide catalyst has been developed to desulfurize and improve stability of cracked gasolines. At optimum conditions, 50 to 60% sulfur reduction, 90% conjugated diolefin removal, and 10 to 2070 mono-olefin saturation are obtained with a processing period of 10 to 15 barrels of feed per pound of catalyst before regeneration is necessary. Isomerization of the olefins over the tungsten nickel sulfide catalyst produces sufficient upgrading of the olefin fraction to compensate for the octane loss due to saturation. Improved lead susceptibility of the product is realized through the sulfur reduction. A marked reduction in inhibitor requirements results from the removal of conjugated diolefins.
THE
greater utilization of sour crude oils t o meet consumer demand for petroleum products has considerably accentuated the refiner’s treating problems. The increased sulfur content of gasoline fractions appears to contribute to engine dirtiness and may be responsible for greater engine wear, especially under lowtemperature driving conditions. Moreover, sulfur compounds have a n adverse effect on the susceptibility of fuels to improvement by addition of tetraethyllead (TEL); therefore, high sulfur gasolines consequently require greater TEL concentrations per unit octane number improvement. Thus, the problem of meeting 1
744
Present address, Shell Oil Co., 50 West 50th St., New York, N. Y .
sulfur specifications and controlling the deleterious effects of sulfur compounds is becoming increasingly important. The problem of treating high sulfur straight run gasoline fractions has been extensively discussed in the literature ( 2 , 3, 6, 7 , 9, 10, 13). Processing cracked gasolines by these methods, however, presents considerable difficulty arising from poor catalyst life and loss in product yield or octane number. In some instances, where sulfur concentrations are extremely high-e.g., some California stocks-the loss in octane number from olefin saturation is compensated b y the greater lead response of the desulfurized product (3). Xormally, however, olefin saturation
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 4
GASOLINE PROCESSING during desulfurization leads to a n octane number loss despite wme improvement in lead susceptibilit) of the product. Ipatieff, ?rlonroe, and Schaad (8) treated cracked gasolines with hydrogen over nickel thiomolybdate catalyst and obtained 60 to 80% sulfur removal and improved color stability but reduced the octane number 4 to 8 units. It appears necessary, therefore, in treating cracked gasolines, t o develop a process which will selectively hydrodesulfurize without severe mono-olefin saturation. &loreover, cracked gasolines, particularly thermally cracked, contain
made in which the hydrogen stream u as diluted with light hydrocarbon gases to simulate recycle gas operation. I n the process flow, the hydrogen and oil feed were combined prior t o entering the reactor system. The oil was pumped from a calibrated tank through A preheater to the top of the reactor. Additional preheating was provided in the upper section of the reactor. After passing through the catalyst bed, the reactor effluent was cooled and routed to the high pressure receiver in n hich the gas and liquid phases were separated. The gas s t r p a m , a f t e r p r e s s u r e reduction, was metered and sampled for analyses. The I Hydrogen compressor liquid product \%aspassed through a pres2 Surge tank 3 Pressure regulators eure-reducing valve and collected in a cali4 Rotameter 5 High pressure wet test meter brated tank. In addition t o the pilot plant 6 Charge tank 7 Hills-McCanna pump operations, several runs were made on a 8 Preheater 9 Reactor semicommercial scale in a refinery hydro10 Water cwler genation unit t o check the pilot plant reIt High pressure receiver 12 Liquid level controller sults. The flow scheme of the plant unit 13 Product tank 14 Caustic scrubber was similar t o the system presented in Fig15 Wet test meter ure 1. Feed Stock. The principal feed used in this investigation was pressure distillate tops (P.D. Tops) produced from thermal cracking of Mixed East-West Texas straightrun residue Table I presents typical inspection properties of the pressure distillate tops as well as properties of several other feed stocks which were hydrotreated. Catalyst. Most of the experiments in this study were carried out over regenerated tungsten nickel sulfide catalyst, which had Figure 1. Hydrogenation pilot plant flow diagram been used previously for 5700 hours in a commercial dehydrogenation plant and 700 appreciable quantities of diolefins Partial saturation of the hours in a catalytic desulfurization unit. Before use in the presdiolefins t o mono-olefins is desirable for improving gasoline staent experiments, the catalyst was regenerated by burning in an bilitg and reducing gum formation. It has been shown by air-steam mixture at 800" F. and resulfiding with hydrogen Anderson and coworkers ( I ) and Young and coworkers ( 1 4 ) that sulfide a t the same temperature. The unsupported catalyst was butadiene can be selectively hydrogenated to butene in the originally prepared by co-precipitation of the metal components presence of low pressure catalysts, such as supported nickel sulfide. t o result in 40 nt. % tungsten and 25 wt.. % nickel in the finished The objective of the work to be reported was t o develop a catalyst. process which would selectively desulfurize cracked gasoline and partially saturate diolefins without loss in unleaded octane Experimental Results number of the treated product. This paper presents a summary of the pilot plant development of a process which achieved these Hydrodesulfurization of catalytically cracked gasoline fractions objectives and permitted reasonably long processing periods &-asused during World War I1 t o supplement aviation gasoline with the hydrotreating catalyst. base stocks ( 4 , I d ) . As reported by Cole and Davidson ( 4 ) ,
Experimental The hydrotreating experiments were carried out in pilot plant fixed-bed catalytic reactors using a tungsten nickel sulf i d e c a t a l y s t . A schematic flow diagram of the pilot unit is shown in Figure 1. Oncethrough hydrogen produced by Shell Chemical from isopropyl alcohol dehydrogenation (98+% HO purity) was used in these experiments. Since little or no cracking occurred while processing, and hydrogen sulfide can be removed effectively by caustic or amine scrubbing, the need for recycle operation was not considered essential in these experiments. Several runs weIe April 1955
Table 1.
i l P I gravity Total sulfur, wt. '3% Mercaptan sulfur, wt. '3% Bromine No. Maleic anhydride value Induction period, clear, hr F-2 clear octane number Lead susceptibilityb ASTM distillation Initial b.p., ' F. 10% 50 %
90% End point Recovery. % Composition
Typical Inspection Properties of Feed Stocks 1 Pressure Distillate Tops 56.0 0.340 0.080 80 30 0.5 68.0 0.45 135 195 260 330 385 98.2
2 Catalytioally Cracked Gasoline 44.0 0.225
...
58
11 5 f 81.9 0 29
136 192 286 373 418 98.4
3 Thermally Cracked and Reformed Debutanised Bottoms 81.6
0.195 0.120 110 13 0.6 76.1 0.36 98 104 114 167 257 97.0
4
Low E n d Point TOW
75.2 0.096 0.054 4 0
%1 .$0 0 100 130 154 192 285 96.0
Blend" 60.4 0.226 0.013 79 11 3 75.3 0.35 116 146 204 332 397 98 8
Vol. %
1 26.5 2 29.0 3 18.0 4 2G.5 b As defined by Ryan ( 1 1 ) .
INDUSTRIAL AND ENGINEERING CHEMISTRY
745
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT the cracked gasolines were hydrogenated over tungsten nickel eulfide catalyst for sulfur and olefin removal a t 720 pounds per square inch gage, 650" F., 7 hydrogen: oil mole ratio, and a liquid hourly space velocity (LHSV) of 10. From this work it is apparent that moderate pressures (-50 atmospheres) lead to extensive olefin saturation. Consequently, it would appear that for high selectivity (low mono-olefin saturation) low pressure opI W
,
'
I
/
'
I
'
Cr BOJF a t 0 4 HolOLL
I
75
I
100
I
125
I
IM
I
175
PRESSURE, wlg
Figure 3.
c 0
Unit: pilot plant Catalyst: regenerated tungsten nickel sulfide Charge pressure distillate tops Conditions: 600' F., 2H2:oil mole ratio, 10 LHSV
-I 1
20
'lo
w
80
Effect of pressure in hydrotreating pressure distillate tops
IOJ
hydrogen: oil mole ratio, 600" F., and 75 pounds per square inch gage. The experimental results, summarized in Figure 4 and Table 111, indicate a sharp decrease in mono-olefin saturation as the space velocity approached 10. The effect of contact time upon selectivity is presented in another manner in Figure 5 , Unit: pilot plant which shows the relationship between depth of desulfurization Charge: pressure distillate tops and clear F-2 octane number. This graph shows that, for pressure distillate tops gasoline, about 60% desulfurization can be obtained without loss in octane number. eration is necessary. The results of a study of the effect of presSuch operating variables a s tempersture and hydrogen: oil sure on selectivity are shown in Figure 2, which confirms the mole ratio may be rapidly dealt with by a summary of the exnecessity for low pressure processing. Additional experiments perimental work. Increasing temperature t o 700" F. or higher a t in the low pressure range were carried out and these results are 75 pounds per square inch gage resulted in rapid catalyst activity presented in Figure 3 and Table 11. These data indicate that decline. Increasing hydrogen:oil ratios beyond 2 to 3 showed 75 pounds per square inch gage is probably optimum pressure. little advantage for the higher ratios, whereas lower ratios seriBelow this range diolefin reduction [as measured by decrease in ously reduced desulfurization and diolefin removal. maleic anhydride value (MAV)] (6)falls off sharply, whereas Since the pilot plant did not include hydrogen recycle facilities, increasing the pressure from 75 to 150 pounds per square inch natural gas was injected into the hydrogen stream t o approximate gage results in a serious loss in clear F-2 octane number. This recycle operation. Dilution was made by adding natural gas loss in octane number is far in excess of any advantage which (90 t o 95% CH,) while maintaining constant liquid hourly space might be derived from the small increase in sulfur removal. velocity and Hz:oil mole ratio. As a result, oil contact times The effect of pressure on the several reactions above indicates were decreased with increased dilution. The effect of dilution that reaction contact time plays a n important role in selective was considerably more pronounced than would be expected hydrotreating of cracked gasolines. The role of contact time from a comparable increase in space velocity. The results of the was also studied by varying the oil space velocity a t constant dilution studies and a comparison a t constant contact time are shown in Figure 6. Table II. Effect of Pressure on Stability and Octane Number Catalyst Life. The utilization of any fixed-bed process Unit: pilot plant Catalyst: regenerated tungsten nickel sulfide depends on first, the ability of Feed: pressure distillate tops Conditions: 600° F., 2Hz:oil mole ratio, 10 LHSV the catalyst t o retain activity Pressure, lb./sq. inch gage 5 25 75 150 for a reasonable processing Chg. Prod. Chg. Prod. Chg. Prod. Chg. Prod. period without regeneration F-2 octane number and, secondly, the ease of re68.2 66.2 62.9 67.2 65.7 68.7 66.3 66.9 Clear g e n e r a t i o n . I n t e r e s t was, 72.4 69.9 67.5 69.2 73.2 71.2 70.7 71.3 $ 1 co. TEL 71.7 71.2 75.8 71.8 75 7 73.4 72.8 72.2 f 2 cc. TEL t h e r e f o r e , c e n t e r e d on t h e 0.40 0.76 0.49 0.80 Lead susceptibility 0.58 0.64 0.37 0.58 ability of the tungsten nickel F-1octane number sulfide catalyst t o maintain 7 1 . 0 6 7 . 0 7 3 . 5 7 2 . 6 7 6 . 9 7 7 . 5 75.6 76.1 Clear 78.2 79.2 75.2 73.0 activity under low pressure 82.7 81.2 79.7 78.0 + 1 cc. TEL 75.9 82.5 78.7 76.3 85.0 82.4 82.1 84.1 +2 00. TEL conditions. The activity deInduction period, clear, hr. ... 2 ... 2 1.5 8.5 , . . >20 cline data presented in Figure Reduction, % 7 are for processing pressure 66 70 45 35 Sulfur 89 97 distillate tops a t 600" F., 75 21 52 Conjugated diolefin 21 34 0 Mono-olefino pounds per square inch gage, = Brz No. of charge - Brz No. of product 10 liquid hour space velocity x 100, a Mono-olefin, % Bm No. of charge and 3Hz:oil mole ratio. The where Bre No. has been corrected for diolefins. run was terminated a t about PERCENT SULFUR REWCTDN
Figure 2. Effect of pressure on desulfurization selectivity over tungsten nickel sulfide catalyst
,
~~
. I
746
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 47, No. 4
.
GASOLINE PROCESSING
Table 111.
Unit: pilot plant Catalyst: regenerated tungsten nickel sulfide Feed: pressure distillate tops Conditions: 75 lb./sq. inch gage, 600' F., 2Hz:oil mole ratio 2 5 10 Chg. Prod. Chg. Prod. Chg. Prod.
LHSVa
conditions generally confirmed the pilot plant data. The catalyst from the life tests was regenerated satisfactorily and the only limitation on the number of regenerations was the mechanical strength of the catalyst.
Effect of Space Velocity on Stability and Octane Number
20 Chg.
Prod.
F-2 octane number Clear + I ml. T E L +!2 ml. T E L
66.6 70.8 73.0
62.3 69.0 73.4
69.4 71.9 73.4
67.0 72.3 75.0
67.8 70.8 73.7
66.6 71.3 75.3
67.5 70.2 72.7
68.2 72.5 73.6
Lead susceptibilit,y
0.68
1.14
0.38
0.77
0.55
0.86
0.46
0.55
78.2 81.6 83.3
74.2 74.0 77.1
77.6 83.1
...
73.2 79.6 83.6
76.4 79.6 82.0
73.0 78.9 82.2
76.9 80.5 82.9
76.5 82.0 84.0
0.9
10
F-1 octane number Clear + I ml. T E L + 2 ml. TEL
Induction period, clear, hr.
0.7
Reduction, yo Sulfur Conjugated diolefin Mono-olefin a LHSV = Volume of oil/hour/volume
24
69 97 35
86 97 65 of catalyst.
600 hours ( w l l barrels of feed per pound of catalyst) because product quality was approaching a n unsatisfactory level. The improved product stability is shown in Figure 7 , which indicates the clear induction period for the product to be 6 hours or longer, for the entire run; induction period for the charge averaged about 1.25 hours. If the space velocity had been reduced to 5 at 600 hours on-stream, an additional 700 hours of processing with satisfactory product could be expected. Operations on a refinery hydrogenation unit a t comparable
Analysis of Hydrotreated Product
Fairly complete analyses of the pressure distillate tops charge and hydrotreated prod1.1 8.3 0.7 2.0 uct (prepared at 75 pounds per 65 45 square inch gage, 600" F., 10 93 62 liquid hour space velocity, and 25 11 2H2:oil) were made by fractionating these materials into 50" F. boiling range cuts. The distillations were carried out in an Oldershaw column of approximately 45 theoretical plates a t a 2 4 : l reflux ratio. A group sulfur analysis was
14
t
T
1
-12
-16
4-
L
b
I b
b
I
I2
I6
,h
b ,
o;
I
Figure 5. Effect of depth of desulfurization on clear F-2 octane number
LHSV
Figure 4.
Effect of LHSV in hydrotreating pressure distillate tops
Unit: pilot plant Catalyst: regenerated tungsten nickel sulfide Conditions: 75 Ib./sq. inch gage, 600" F., 2Hz:oil mole ratio
Unit: pilot plant Catalyst: regenerated tungsten nickel sulfide Charge: pressure distillate tops Conditions: 75 Ib./sq. inch gage, 600' F., 2-3 ratio, 2-20 LHSV
0
5
I 10
I 15
I 20
MOLEPERCENT DILUENT IN
Figure 6.
I 25
x)
35
ne STREAM
Effect of diluent in hydrogen stream Diluent consists 90+Ye CHa
April. 1955
1
1
I
I
I
I
0
100
Figure 7.
0
j
H2:oil mole
1
I
I
I
600
700
0 0
, 4
300 4w HOURS ON STREAM
0
10 500
Catalyst life study
Unit: pilot plant Catalyst: regenerated tungsten nickel sulfide Charge: pressure distillate tops Conditionr: 75 Ib./sq. inch gage, 600' F., 3Hz:oil mole ratio, 10 LHSV
INDUSTRIAL AND ENGINEERING CHEMISTRY
747
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Table IV.
Hydrotreating Various High Sulfur Gasoline Components Unit: hydrogenation pilot plant Catalyst: regenerated tungsten nickel sulfide Conditions: 75 lb./sq. inch gage, 600' F., 2Hz:oil
Total sulfur wt. % Mercaptan6ulfur, wt. % Bromine No. Maleic anhydride value F-2 octane number Clear +1 ml. T E L + 2 ml. T E L
Catalytically Cracked Gasoline= Prod. Clig. L H S V 1 0 LHSV.5 0.225 0.150 0.109 0.0 0.006 0.004 58 47 48
11
5
81.9 83.0 83.9
82.0 83.8 84.8
Lead susceptibility 0.29 Reduction, % Sulfur Conjugated diolefin Mono-olefin Pilot plant product from West Texas and 40 to 60,% conversion level. b Composition as listed in Table I.
0.34
Thermally Cracked and Reformed Debutanixed Bottoms Prod Chg. LHSV 10 LHSV.5 0.195 0.033 0.030 0.120 0.011 0 008 110 74 . . ,
13
3 81.5 83.6 84.7
76.1
..,
79.0
0.37
2
7G.0 81.3 83.1
0.36
1
70.2 81.2 83.3
0.80
0.87
Low E n d Point Tops Prod. Chg. LHSVlO L H S V 5 0.09Il 0.011 0,007 0.064 0.004 0.002 4 3 2
Chg. 0.226 0.053 79
0
15
69.6 76.0 79.0 1.00
0
70.0 80.0 83.8 1.82
0 69.2 79.6 84.2
75.3 78.9 78.7
2.00
0.35
52 83 8.5 89 93 73 88 92 .. , . 18 16 31 .. .. .. straight-run flashed distillate oYer aged silica-alumina (.Jrnerican Cyanamid hIS.4-1)cracking 33 5.5
-
Blend b Prod.
LHSV9
LHSV5
0.089 0,009 48
0.059 0.006 43
1
3 75.0 79.0 81.1
74.1 80.0 80.8
0.69
0.76
61 74 80 93 38 43 catalyst a t 9 2 5 O F.
Although consumption was relatively low, the greater part of the hydrogen was consumed in unavoidable mono-olefin saturation. At a desulfurization level of 65%, 90 to 95% diolefin reduction, and 25% saturs tion of mono-olefins, the theoreticalconsumption was 181 cu. ft. per barrel of feed. Actual measured consumption was 161 cu. f t . per barrel. The breakdown of the theoretical consumption into quantities used for each of the three reactions is
Y
20
-
Sulfura Diolefin Mono-olefin
MLUME
10 ISP-M
150-203
200-250
250-300 BOILING RANGC,*F.
322-JIQ
-
7
24 64 100
-
Includes saturation of free carbon bonds remaining from sulfur removal.
Comparison of 50' F. cuts of charge and product from hydrotreating pilot plant
obtained for each 50' F. fraction, as well as total sulfur, bromine number, and maleic anhydride value. It was noted from the distillations of the charge and product that there was no significant volume change in any of the 50' F. fractions. The greater part of the gasoline (-55 vol. yo) boiled in the 200' to 300" F. range. A comparison of the total sulfur, monoolefin content, and maleic anhydride value for the 50' F. fractions is presented in Figure 8. Diolefins were effectively removed from all fractions; mono-olefins were seriously removed only from the light fractions; and the removal of sulfur from the lighter fractions was more nearly complete than from the heavier cuts. A comparison of sulfur types in the charge and product is presented in Figure 9. These data show t h a t , by this treatment, aliphatic sulfur types are removed extensively from all fractions. Moreover, mild hydrotreating removes approximately 50% of the residual-type sulfur from all of the fractions analyzed. Although 10 t o 2001, olefin saturation occurred during the process (for 50-60% sulfur removal), no loss in octane number of the product was observed. This effect cannot be attributed to desulfurization alone but appears also to involve olefin isomerization. Data were obtained by infrared analyses that showed considerable double-bond shift of the a-olefins in pressure distillate tops. It is this olefin isomerization with the attendant octane number appreciation over tungsten nickel sulfide catalyst that offsets any loss in octane number due to olefin saturation. 248
13 52 116 181
RESWE
a
Figure 8.
Hydrogen Consumption Std. % of cu. ft./bbl. total
Removal
HYOROGEN SULFIDE, MERCAPTANS, M I D DISULFlDES
$
5
BOILING FANGE, 'F
Figure 9. Comparison of 50' F. cuts of charge and product from hydrotreating pilot plant
Gasoline componcnts other than pressure distillate tops were also treated over tungsten nickel sulfide catalyst under low pressure conditions. The data from processing several of these materials are shown in Table IV. Effective treatment can be obtained from processing the various feeds. In addition to effective desulfurization and improvement in lead susceptibility, substantial benefit was obtained in induction period tests for gasoline stability.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 4
GASOLINE PROCESSING Acknowledgment
(6) Helmers, C. J., and Brooner, G. M., Petroleum Processing, 3 , 133 _ _ _ I1 948). (7) Hoog, H.. Klinkert, H. G., Schaafsma, A., Petroleum Refiner, \ - - - - I
The authors wish to thank J. Crocoll, S. W.Kapranos, E. C. Mertz, and R. G. Walton for their participation in the work reported here. We would also like t o express our gratitude t o t h e Shell Oil Co. for permitting publication of this work.
Literature Cited Anderson, J., Mchllister, S. H., Derr, E. L., and Peterson, W. H., IND.ENG.CHEM.,40, 2295 (1948). (2) Berg, C., Bradley, W. E., Stirton, R. I., Fairfield, R. G., Leffert, C. B., and Ballard, J. H., C h e m . Eng. Progr., 1, 1-12 (1947). (3) Byrns, A. C., Bradley, W. E., and Lee, M. W., IXD.ENG. CHEW,35, I160 (1943). (4) Cole, R. M., and Davidson, D. D., Ibid.,41, 2711 (1949). (5) Groennings, S.,IND. EKQ.CHEM.,ANAL.ED., 17, 361 (1945). (1)
32, Ao. 5, 137-41 (1953). (8) Ipatieff, V. N., Monroe, G. S., and Schaad, R. E., Division of Petroleum Chemistry, 115th Meeting ACS, San Francisco, March, 1949. (9) Kalichevsky, V. A., Petroleum Re$ner, 30, No. 5, 117-22 (1951). (10) Petroleum Processing, 7, 467-9 (1952). (11) Ryan, J. G., IND.ENG.CHEM.,34, 824 (1942). (12) Voorhies, A., Jr., Smith, W. M., Hemminger, C. E., Ibid., 33, 1104 (1947). (13) Yabroff, D. L., and Border, L. E., Refiner A'atural Gasoline M f r . , 18, 171-6, 203 (1939). (14) Young, W. G., Meier, R. L., Tinograd, J . , Bollinger, H., Kaplan, L.. and Linden, S.L., J . Ant. Chem. SOC.,69,2046 (1947). R E C E I + E fDo i review Derember 8, 1954
ACCEPTED
January 28, 1955
(SELECTIVE HYDROTREATING OVERTUNGSTEN NICKEL SULFIDE CATALYST)
Studies with Mixtures of Pure Compounds W. K. MEERBOTT
AND
G. P. HINDS, JR.
Shell Oil Co., P. 0.Box 2527, Houston 7 , rex.
Studies of hydrotreating of cracked gasolines for desulfurization and stability improvement indicated that olefin isomerization also occurred: In order to establish the nature of this isomerization as well as the other reactions involved in the process, experiments were carried out with mixtures of pure compounds. At optimum hydrotreating conditions, only isomerization via double-bond shifting occurs over regenerated tungsten nickel sulfide. At the longer contact times required for skeletal isomerization, extensive olefin saturation results. The presence of sulfur compounds in the feed inhibits mono-olefin saturation but not diolefin hydrogenation. Qualitative evidence was obtained which indicates that n-olefins saturate faster than branched olefins.
I
K THE previous paper (4)the prsctical aspects of selective hydrotreating of cracked gasolines were discussed. The questions of reaction mechanism and reaction rates were not taken into consideration. However, it was shown earlier that as much as 20% olefin saturation occurred during the process with no loss in product octane number, while achieving 60% desulfurization and 90% conjugated diolefin removal. Data were presented indicating that isomerization of olefins off sets the octane number loss due to saturation. Ilon-ever, because of the coniplexity of the feed stock, i t was uncertain whether olefin isomerization involved more than double-bond shifts. Several investigators ( 2 , 5, 6, 6) have shown that n-olefins can be isomerized to branched-chain olefins. However, all these instances of olefin isomerization occurred over acid treated or acidic catalysts with low activity for the competing saturation reaction. Tungsten nickel sulfide (W/Ni/S) catalyst is a n active hydrogenation catalyst which has not been considered acidic, nor does it have the large surface area generally associated with aluminas and cracking catalysts. T o understand more clearly the isomerization reaction, as well as the other reactions involved in hgdrotreating, a series of experiments was made with mixtures of pure compounds over regenerated tungsten nickel sulfide catalyst. This paper presents the results of this investigation with synthetic feeds and offers a qualitative comparison of the several reactions involved in hydrotreating. The experimental work was carried out in a laboratory unit with essentially the same flow scheme as that presented in the previous paper (4). Operating conditions for these experiments April 1955
were similar to those used in the selective hydrotreating of thermally cracked gasoline: namely, 600" F., 75 pounds per square inch gage, 2I-L:oil mole ratio, and varying space velocities from 1.4 to 8.3. The catalyst was regenerated tungsten nickel sulfide. The liquid charge was a mixture of equal weights of n-heptane and I-octene to which other compounds were added. This standard blend, with about a 70 bromine number, was used in practically all experiments. The sulfur compounds were generally blended one part by weight of n-butyl mercaptan t o two parts of thiophene t o produce the desired sulfur concentration. The liquid products were not caustic washed for hydrogen sulfide removal t o avoid removing mercaptans along with the hydrogen sulfide. Potentiometric titration was used t o analyze for hydrogen sulfide, and the total sulfur was corrected for this amount of reaction product. Liquid recoveries in all the experiments were 99 t o 100 wt. yo of the charge. Practically no cracking or gas make occurred during the process. The materials used in these experiments, their sources, and purities were:' I-Octene n-Heptane n-Octane Thiophene n-Butyl mercaptan tert-Butylphenol Z-MethyI-l,3-pentadiene
99 % 99 % 99 % c P. C.P.
Practical C.P
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
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749
