Hydrogen Chloride Activation of Alumina and Pla tinu m-Alumina John W. Myers Research and Deuelopment Department, Phillips Petroleum Co., Bartlesuille, Okla. 74003 Activation of alumina and platinum-alumina with anhydrous hydrogen chloride a t 900" to 1400" F resulted in very active catalysts that isomerized butane a t 150°F. Activity was a maximum after activation at about 1200" F. Incorporation of platinum in the alumina increased activity considerably. Poisoning of activated catalysts with hydrogen sulfide indicated that platinum participates directly in the isomerization. Hydrogen pretreatment of platinum-alumina before activation markedly increased isomerization activity. The action of hydrogen was one of minimizing adsorption of poisons during chloriding rather than simple reduction only. X-Ray diffraction measurements showed a strong pattern of platinum crystallities when platinum-alumina was dried at 1200" F in nitrogen before activation, but the crystallites were too small to give a measurable pattern when the heating was in hydrogen. However, these differences in crystallite growth appeared unrelated t o isomerization activity.
A c t i v a t i o n of alumina and alumina containing hydrogenation promoters by heating in anhydrous hydrogen chloride a t high temperature gives catalysts sufficiently active to isomerize paraffins a t low temperature (Myers, 1969). Reduction of platinum-alumina before activation as well as activation with hydrogen-hydrogen chloride mixture is beneficial (Myers, 1969). I n the present work, hydrogen chloride activation of eta-alumina and platinum on eta-alumina was studied further t o learn more about the nature of these catalysts. Since these were very active catalysts, they were tested in the isomerization of normal butane a t the low temperature of 150" F. Experimental
Materials. Phillips pure grade normal butane, predried over activated alumina or molecular sieve, was used. Prepurified nitrogen, analytical and ultrahigh-purity grade helium, and electronic grade anhydrous hydrogen chloride were used without further purification. Electrolytic grade hydrogen was passed over palladium on alumina, Drierite, and activated alumina to remove traces of oxygen and water. Air was also dried over activated alumina. Eta-alumina was obtained from the Davison Chemical Go. I t was used in 14- t o 20-mesh granules. The B.E.T. surface area was 240 meters' per gram. The maximum concentration of total impurities is estimated as less than 0.1 wt 5.Impurities found were iron, magnesium, silicon, and carbon. Because of their very low concentrations, the impurities are believed to have had no significant effect on the catalysts. Platinum was added to the alumina by impregnation with an aqueous solution of chloroplatinic acid. Impregnated catalysts were dried at 220°F and calcined by heating in air to 800°F and maintaining at 800°F for two hours. Calcined catalysts contained 0.45% platinum and O.5OCc chloride. Apparatus and Procedure. All catalyst treatments and activity tests were conducted in a vertical-flow reactor system at atmospheric pressure. The reactor was a 22-mm quartz tube, 40 cm in length. Twenty-gram portions of 200
Ind. Eng. Chern. Prod. Res. Develop., Vol. 10, No. 2, 1971
catalyst were used in all tests. The catalyst was supported on a quartz grid in a 9-cm section in the center portion of the tube, which was heated in a three-section electrical furnace. A 3-mm thermowell extended axially through the catalyst bed. Gases passed downward through the reactor. All tests were a t a butane flow rate of approximately 40 gas hourly space velocity (0.18 LHSV), 15OoF, and atmospheric pressure. Reaction gases were sampled during the last 15 min of an hour period. Products were analyzed by chromatography. The chromatograph column, which was 4.6 meters in length and 0.6 cm in diam, was packed with 17 wt % ' Dow Silicone 703 on 35- to 80-mesh Chromosorb P and operated a t room temperature. Alumina was activated by heating in hydrogen chloride at 1200"F. The effects of preheating the alumina in hydrogen and nitrogen before activation were compared. Platinum-alumina was activated by heating in hydrogen chloride or a mixture of hydrogen and hydrogen chloride a t temperatures from 900" to 1400°F. The effects of preheating in hydrogen, helium, and nitrogen were studied. With both alumina and platinum-alumina, a hot spot of 50" to 100°F rapidly passed through the bed when the hydrogen chloride was started. After activation, catalysts were normally cooled in flowing activating gas-hydrogen chloride alone or hydrogen-hydrogen chloride mixture-to 400" F in about 10 min. In one case, activated catalyst was maintained a t 800OF in flowing hydrogen for one hour before further cooling. Usually after cooling to 400°F, the hydrogen chloride was stopped and hydrogen or nitrogen passed over the catalyst while cooling t o room temperature. In a few tests, activated catalysts were maintained a t 400" F and purged for one to two hours with H 2 , He, or air before cooling to room temperature. Heating before activation was for 14 to 17 hr a t gas rates of 20 to 21 liters per hr a t STP. During activation, hydrogen chloride flow rate was 8 liters per hr; and when used with the hydrogen chloride, hydrogen was at a rate of 6 liters per hr. Activation time was 0.5 to 3 hr. Purging rates a t 400" F were 15 to 20 liters per hr.
Table I . Effect of Heating Alumina and Platinum-Alumina in Hydrogen and Nitrogen Before HCI Activation Platinum-alumino
Alumina
Catalyst treatment Heating before chloridmg Atmosphere Temperature, F Chlonde activation Gas Temperature, F Chloride in catalyst, wt L> Isomerization activitya Conversion, wt CC Selectivity t o isobutane, wt Product composition, wt '7 Propane Isobutane n-Butane Pentane
LC
N1"
N , then H1" 1200
H," 1200
N; 1200
H; 1200
1200
HC1 1200 3.44
HC1 1200
HCl 1200 3.34
HC1 1200 3.38
HCI 1200
29.8 98.7
30.4 98.4
56.4 97.0
33.5 98.5
56.5 97.9
0.3 29.4 70.2 0.1
0.2 29.9 69.6 0.3
0.5 54.7 43.6 1.2
0.4 33.0 66.5 0.1 -
0.4 55.3 43.5 0.8
~
100.0 100.0 Total 100.0 100.0 100.0 'Heating time, 14 to 17 hr. 'Heating time. 19 hr in N ? and then 16 hr in Hi. ' Activation time, 1.5 hr. At 150" F, atmospheric pressure, and 40 GHSV (0.18 LHSVi
In studying promotion by platinum, pulses of H,S were added to nitrogen and contacted with activated alumina and platinum-alumina at 400" F. The sulfur atoms added were the equivalent of 1.8 times the platinum atoms in the activated platinum-alumina; the same size pulse was added to the activated alumina. The catalysts were then purged at 400" F for one hour before testing. Catalysts were examined for platinum crystallite growth by X-ray diffraction line broadening as has been done previously (Herrmann et al., 1961; Spenadel and Boudart, 1960; Van Nordstrand et al., 1964). Chloride contents were determined by using a potentiometric titration procedure after the catalyst was leached with hot sulfuric acid and chloroplatinic acid, if present. reduced.
Table II. X-Ray Diffraction Examination of Activated Platinum-Alumina Catalyst treatment Heating before chloriding Atmosphere Temperature, F Chloride activation' Gas Temperature, F X-Ray diffraction examinationd
H: 1200
N," 1200
N 2 then Hzb
HC1 1200
HC1 1200
HC1 1200
I
i
1200
Discussion
"Heating time, 15 hr. hHeating time, 19 hr in N t and then 16 hr in H,. ' Activation time, 1.5 hr. X-Ray diffraction measureme!ts are applicable with platinum crystallites larger than about 50 A. "Eta-Al,Oj, P t crystallites too small t o give measurable pattern. 'Eta-Al& P t crystallites large enough t o give a strong pattern.
Activation of Alumina. Isomerization data comparing the effect of heating alumina at 1200"F in hydrogen and nitrogen before activating with HC1 a t 1200°F are presented in Table I . Both types of preheating gave similar results; butane conversion was about 3070 and isomerization selectivity to isobutane 99 wt % a t the 150" F test temperature. The chloride content of activated catalyst was 3.44 wt 52. After drying at 1200°F for 16 hr, this eta-alumina contained 0.56 wt 'Z water, which, if replaced by HC1, would be equivalent t o only about 1.1% chloride. Thus, HC1 apparently reacted with both hydroxyl groups and oxygen in the alumina. A similar conclusion was reached by Peri (1966) from infrared and gravimetric measurements. Activation of Platinum-Alumina. Heating platinumalumina a t 1200°F in hydrogen before HC1 activation a t 1200"F gave a much more active catalyst than heating in nitrogen. Butane conversion was 56.4% when heated in hydrogen compared t o 33.5% when heated in nitrogen. These catalysts had almost identical chloride contents; 3.34% after heating in hydrogen and 3.38% after nitrogen. X-Ray diffraction examination showed a strong pattern of platinum crystallites after heating in nitrogen and activating with HCl but the crystallites were too small to give a measurable pattern when heated in hydrogen before activation. T o determine whether this crystallite growth was responsible for the lower activity, a portion of catalyst was heated in nitrogen and then in hydrogen
before activation. This catalyst, heated in nitrogen and then hydrogen, showed a strong pattern of platinum crystallites but gave identical butane conversion t o t h a t of catalyst heated only in hydrogen before activation. Thus, crystallite growth was evidently not responsible for the lower activity after heating in nitrogen. Giannetti and Sebulsky (1969) found variation in platinum content in the range of about 0.3 to 0.6% to have little effect on normal butane isomerization activity with platinumalumina heated in both hydrogen chloride and thionyl chloride. Results from X-ray examination are presented in Table I1 and activity data are shown in Table I. T o gain insight into whether platinum merely promoted chloriding of the alumina in a beneficial manner or actually participated catalytically during the reaction, pulses of H S were contacted with activated catalysts. Contacting activated platinum-alumina with a pulse of H2S reduced conversion markedly, 56 t o 385. When alumina that had been activated similarly was contacted with H2S, conversion decreased only from 30 t o 28%. Inasmuch as platinum is poisoned by sulfur, it appears that platinum functions as a part of the catalyst. The higher activity when catalysts were reduced in hydrogen before HC1 activation might be owing to hydrogen adsorbing reversibly on platinum or to a lower reactivity of reduced platinum with poisons. I n examining these possibilities, a portion of platinum-alumina was Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
201
~~~~
~
~
~
~
Table Ill. Effect of HCI Activation Temperature with Platinum-Alumina Catalyst treatment Heating before chloriding' Atmosphere Temperature, F Chloride activation" Gas Temperature, F Chloride in catalyst, wt ' c Surface area, m'; g Isomerization activity' Conversion, wt ['c Selectivity to isobutane, wt Product composition, wt (-r Propane Isobutane n-Butane Pentane
('c
Total
H1 1000
H? 1000
H? 1000
H1 1000
H, 1000
H, HCI '300 4.36 1'36
HJ-HC1 1100 3.90 165
HT-HCl 1200 3.62 133
H!-HC1 1300 2.80 94
Hj-HCl 1400 1.62 56
18.5 '37.3
55.1 97.5
67.5 97.5
64.4 97.5
47.6 98.3
0.3 18.0 81.5 0.2
0.4 53.7 44.9 1.o
0.5 65.8 32.5 1.2
0.4 62.8 35.6 1.2
0.3 46.8 52.4 0.5
100.0
100.0
100.0
100.0
-.
100.0
'Heating time before chloriding. 14 to 16 hr; chloride activation time, 1.5 hr. 'At 150"F, atmospheric pressure, and 40 GHSV (0.18 LHSV).
Table
IV. Purging of
Activated Platinum-Alumina
Preheated in nitrogenu
Catalyst purging Gas Temperature, F Time, hr Chloride in catalyst, wt ';C Isomerization activityd Conversion, wt '2 Selectivity to isobutane, wt 5%
Xone
H, 400 1.0
3.38 33.5 98.5
66.1 98.6
Preheated in hydrogeno
He 400 1.0 3.01 63.8 98.7
None
H, 400 1.o
H 2 then air' 400 1.o
63.8 97.5
68.9 98.0
71.6 97.6
"Pt-alumina heated at 1200" F in N, for 15 to 17 hr and chlorided with HC1 at 1200O F for 1.5 hr. ' Pt-alumina heated a t 1200" F in H2 for 15 hr and chlorided with HI-HC1 mixture a t 1200OF for 1.5 hr. 'Purged with H 2 for one hour and then air for one hour, He used for a short time before and after the air. At 1503F, atmospheric pressure, and 40 GHSV (0.18 LHSV).
1 4 0 1 0 LL
/
w
L
10 I
900
I
I
I
I
1000
1100
1200
1300
I
1400
HCI ACTIVATION TEMPERATURE, 'F Figure 1. Effect of HCI activation temperature on conversion with platinum-alumina Pt-alumina heated at 1000°F in H2 for 16 hr and chlorided with H2HCI mixture o t indicated temperature for 1.5 hr. Test conditions: 15OCF, atmospheric pressure, 40 GHSV
202
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
l 900
1000
y 1100
2 1200
5 1300
1400
HCI ACTIVATION TEMPERATURE, 'F Figure 2 . Effect of HCI activation temperature on chloride content and surface area of platinum-alumina
heated in hydrogen at 1000°F for 15 hr and then in helium for 0.8 hr while heating from 1000" to 1200°F for HC1 activation. This catalyst gave only 36% butane conversion compared to 59% when all of the heating before activation was in hydrogen. Apparently, adsorbed hydrogen prevented adsorption of poisons. Activation of Platinum-Alumina with H2-HCI Mixture. Since heating platinum-alumina in hydrogen before activation with HC1 resulted in more active catalyst than heating in nitrogen, activating with H,-HCl mixture might be expected to give more active catalyst than HC1 alone. This was the case. After heating in hydrogen at 1200°F and activation with H2-HC1, butane conversion was 63.8% compared to 56.4% when activated with HC1 alone. I n considering the effect of activation temperature, portions of platipum-alumina were heated in hydrogen a t 1000°F and then activated by heating with H2-HC1 a t 9000, 1100", 1200°, 1300°, and 1400°F. Results of this work are presented in Table I11 and Figures 1 and 2 . The most active catalyst was prepared by activation at 1200" F; conversion was 67.5% and selectivity 97.5%. This catalyst was somewhat' more active than those preheated in hydrogen a t 1200" rather than 1000"F before activation. Catalyst analyses showed that platinum was not lost during these activations. Chloride content of the catalysts decreased from 4.36 to 1.62 wt % and surface area decreased from 196 to 56 meters' per gram as activation temperature was increased from 900" to 1400" F. Evidently isomerization activity is very dependent on how the chloride is incorporated in the catalyst as well as the amount added. Activation times of 1.0, 1.5, and 3.0 hr a t 1200°F were compared. Catalyst activated for 1.5 hr was the most active. Activation time, hr Butane conversion, Yo 1.0 1.5 3.0
61.8 67.5 64.7
Purging of Catalysts after Activation. Portions of platinum-alumina that had been activated in various atmospheres a t 1200°F were purged with H P , He, and air for one hour a t 400°F before testing at 150°F. I n all cases, this purging increased isomerization activity. Upon purging with H z , catalyst that had been activated by heating in N P and then HC1 gave 66.1% conversion compared to 33.5% without purging. Purging catalyst activated in the same manner with He gave a similar increase in activity, conversion was 63.8%. Data for these tests are presented in Table IV. Platinum-alumina heated in H z and activated with HzHC1 gave 68.9% conversion after purging with Hz and 63.8% when not purged. I n one case, after purging with H2, the activated catalyst was purged for an additional hour with air (He was used for a short time before and after the air). This catalyst gave 71.6% conversion. Results from these tests are given in Table IV. Alumina alone that had been activated by heating in H z and then HC1 at 1200°F did not change in activity when purged with
HP. The increase in activity upon purging activated platinum-alumina and the lack of effect with activated alumina alone indicate that poison, probably chloride, is reversibly adsorbed on the platinum during activation. Heating platinum-alumina in H z and adding H z with the HCl during activation decreased but did not entirely elimi-
nate adsorption of poison. During activation with HrHC1 mixture, approximately equal volumes of H2 and HC1 were used. Heating of Activated Catalyst at High Temperature. The high activity of these catalysts is surprising in view of reports by Peri (1966) and Giannetti and Sebulsky (1969) that HC1-activated alumina and platinum-alumina were inactive for isomerizing pentane and butane. I t may be that the catalysts of these workers were deactivated by removal of chloride by being maintained a t high temperature in the absence of HC1. In the current work, catalysts were usually cooled from the activation temperature to 400°F in about 10 min. Normally, activating gas (HC1 or Hz-HC1) was passed over the catalyst during this time. In one case, after activation with Hz-HC1 a t 1200"F, H Z alone was passed over activated platinum-alumina a t 800° F for one hour. This catalyst contained 2.24% chloride and gave only 11.2% conversion compared to 3.62% chloride and 67.5% conversion when the heating a t 800° F was omitted. After heating activated catalyst at 800" F, another reactivation at 1200°F restored activity almost to that of onceactivated catalyst not heated at 800" F . Conclusions
Activation of platinum-alumina with anhydrous HC1 at 900" to 1400°F resulted in very active catalysts. With the more active catalysts, conversion of normal butane was 65 to 70% and isomerization selectivity t o isobutane 97 to 98% at 150"F, atmospheric pressure, and 40 GHSV (0.18 LHSV). Activity did not correlate directly with chloride content thus indicating that the high activity was dependent on the way chloride was incorporated in the catalyst. Prolonged heating a t high temperature in the absence of HC1 reduced activity but it could be restored by another activation. Platinum-alumina gave much more active catalyst than alumina alone. Poisoning of activated catalysts with HIS indicated that platinum participates directly in the isomerization. Hydrogen decreased adsorption of poisons on platinum-alumina during chloriding. These poisons were reversibly adsorbed and could be purged from the catalyst at 400" F . X-Ray diffraction measurements showed a strong pattern of platinum crystallites when platinum-alumina was heated at 1200"F in nitrogen before activation, but the crystallites were too small to give a measurable pattern when the heating was in hydrogen. However, these differences in crystallite growth appeared unrelated to activity. literature Cited
Giannetti, J. P., Sebulsky, R. T., Ind. Eng. Chem. Prod. Res. Dewlop., 8 (4), 356 (1969). Herrmann, R. A., Adler, S. F., Goldstein, M. S., DeBaun, R. M., J . Phys. Chem., 65, 2189 (1961). Myers, J. W. (to Phillips Petroleum Co.), U.S. Patent 3,449,264 (June 10, 1969). Peri, J. B., J . Phys. Chem., 70, 1482 (1966). Spenadel, L., Boudart, M., ibid., 64, 204 (1960). Van Nordstrand, R. A., Lincoln, A. J., Carnevale, A., Anal. Chem., 36, 819 (1964). RECEIVED for review October 28, 1970 ACCEPTED March 1, 1971 Presented a t the Division of Petroleum Chemistry, 160th Meeting, ACS, Chicago, Illinois, September 1970.
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971 203
