CAT-4LTTIC ACTIVITY OF LEAD BY F. A . JIADEh*W.lLD, C. 0 . HENBE AXD 0.W. B R O W h
Introduction Finely divided lead prepared from commercial oxides was previously used as catalyst’, and it has been shown to be excellent for the hydrogenation of nitrobenzene. It produces not only aniline, but is also one of the three catalysts that produces azolxnzene in considerable amounts. I n this paper results are given of an extensive study of the behavior of lead catalysts made from carefully purified materials. Experimental Details The apparatus and general proceedure used in this work were the same as those described in an earlier paper?, with slight modifications as noted in Jour. Phys. Chem.. 26, 3 2 3 ( 1 9 2 2 ) . In each experiment 2 cc. of nitrobenzene ( 2 . 3 2 2 g.) was used, its rate of flow being 4 g. per hour. The rate of flow of hydrogen was 13 liters per hour, giving an excess of j30% of the amount necessary t o reduce the nitrobenzene. Preparation of the Catalysts The lead nitrate used in the preparation of the catalysts contained the folloiving impurities: insoluble substances 0.009‘;;, copper 0.002jyc, iron O.OOI%, and earths and alkalis o.IC;,. This product was dissolved in hot water, filtered, and allowed t o crystallize. The crystals were filtered on a Buechner funnel, washed, and then dried by drawing air through them. The lead prepared in this way was the material from which all catalysts were prepared. Lead carbonate was prepared by adding a solution of 600 g. of sodium carbonate in 4 j o o cc. water to a solution of the recrystallized lead nitrate containing 2,000 g. in j,ooo cc. of \%-ater. The sodium carbonate was made by heating Baker’s C. P. sodium bicarbonate for several hours a t 180°C. The precipitated lead carbonate was washed well with distilled water by decantation, t o remove soluble salts. It was then filtered on a Buechner funnel and further washed three times with distilled water. The lead carbonate was dried in a vacuum drier and then ground and passed through a 60 mesh sieve. All but 50 g. of the carbonate was converted t o red lead by roasting it for 102hours a t 430°C. in an electric muffle. The apparent density of the resulting red lead was determined by means of Dr. Schaeffer’s modification3 of the Scott Volumeter and found t o be 11.7 g. per cu. in. An analysis cf the red lead showed that it contained 3 3 . I % lead peroxide. Henke and Brown: 3. Phys. Chem., 26, 324 ( 1 9 2 2 ) . Brown and Henke: J. Phys. Chem., 26, 161, 631 (1922). 3 Schaeffer, Khite, and Calbeck: “Chemica! Analysis of Lead and Its Compounds”, p. 148 (1922).
CATALYTIC ACTIVITY O F LEAD
863
A second red lead was made by roasting 600 g. of the recrystallized lead nitrate. The nitrate was put in a covered dish and then placed in a mume. During the first two hours of heating, the dish was kept covered but when the sputtering, due t o the decomposition of the lead nitrate had ceased, the cover was removed. After I O hours roasting at 43oOC. the material was passed through a 60 mesh sieve. Then it mas heated, with frequent stirring, for 30: hours more at 430'C. The apparent density of this red lead was 23.3 g. per cu. in. Litharge was then made, one from each of the above red leads, and these were put into the electric muffle and heated t o a temperature of j jo°C. and 6oo0C., a current of air passing over them. The red lead prepared from the carbonate was heated for I O hours a t 5j03C., and for 1 2 hours a t 6oo0C., giving the product a peculiar brown color. I t contained zyc lead peroxide and its apparent density \vas 16.j g. per cu. in. The red lead from the nitrate was heated for 18 hours at j j o " C . and for I Z hours at 6ooOC. The color of the product was black; it contained only 8% of peroxide, and had an apparent density of 2 j.4 g . per. cu. in. Experimental Results The activity of the lead catalysts made from the carbonate, the light red lead ( 1 I . j g. per cu. in.), the heavy red lead (23.3 g. per cu. in.), the heavy litharge ( 2 j . 4 g. per cu. in.)>and the light litharge (16.j g. per cu. in.) mas studied. The same amounts of each catalyst by volume were put into a catalytic furnace and treated alike. They were each reduced for one hour a t 308OC. with the rate of f l o ~ of hydrogen a t 14 liters per hour. Xitrcbenzene and hydrogen were then introduced. It, was found that these lead catalysts act the same as copper catalysts, concerning the increase in activity with use. However, in the case of lead catalysts the increase is slower, requiring 60 t o 70 experiments t o obtain a constant yield; in the case of copper 6 t o 8 experiments were sufficient. There were usually 8 experiments carried out each day. On the first day the actihity of the catalysts was poor. The yields of aniline and azobenzene with the different catalysts were as follows: catalyst from light red lead (11.7 g. per cu. in.) 1 0 . 2 % aniline, no azobenzene; heavy red lead (23.3 g. per cu. in.) aniline 45.7%, azobenzene 14%; heavy litharge ( 2 j . 4 g. per cu. in.) aniline 4 1 . 4 5 ; , azobenzene I I . o ~ % ;light litharge (16.5 g. per cu. in.) aniline 73.4%, azobenzene 1 2 7 ~ and ; lead carbonate, aniline 29.1Yc>azobenzene 95". Upon use the activity of the catalysts gradually increased until they reached a constant yield of 9jc to 96YGof aniline on the eighth day. HOWever, the azobenzene yield decreased with use of the catalyst, none being produced a t the end of the third day. The catalyst from light litharge (16.5 g. per cu. in.) which gave the highest yield on the first day's run, seems to he the best. After using it in nearly 2 0 0 experiments sometimes a t a temperature 16'C. above the melting point of lead, it was still a loose mass of black powder containing no pellets of massive lead.
F. A. MADENWALD, C. 0. HENKE AND 0. W. BROWN
864
The effect of temperature on the activity of this catalyst was studied. Each result is the average of about eight experiments performed. The results are given in Table I.
TABLE I Rate of flow of hydrogen-14 liters per hour. Rate of flow of nitrobenzene-4 g. per hour. Excess of hydrogen-4500jc. Temperature
Per cent aniline
290 C.
82.5 70.7
212
Total
Per cent arobenrene 2.3
84.8
11.5
82.2
255
30.0
30.0
308 327 3 46 308
97.1 95.5 92.6 96.6
97.1 95 ' 5 92.6 96.6
From the results given in Table I it seems that the twst temperature for the production of aniline is 3 0 8 ° C . Experiments were carried out t o compare the efficiency of the catalysts used in a glass tube with those used in an iron tube. The light litharge (16.5 g. per cu. in.) was again used in making this T.4BLE
11
Catalyst--Light litharge (16.5 g. per cu. in.). Rate of flow of hydrogen-14 liters per hour. Rate of flow of nitrobenzene-4 g. per hour. Temperature-3 0 8 ° C . Excess of hydrogen-4507~. Unground material compreesed 29 grams
hlaterial ground 54 hrs.
hlaterial ground 108 hrs.
Material ground 2 0 0 hrs.
33.3 grams
35.1 grams
40.0 grams
B B
4
Daily average, material yield in per cent theory. 5 5 . 1 3 0 . 0 85.1 3 6 . 0
6 . 6 29.0 28.1 1 4 . 4 42.5 39.8 16.0 55.8 60.7 23.0 83. j 64.2 25.3 89.5 7 7 . 7 13.0 90.7 9 3 . 6 9 0 . 2 __ 9 0 . 2 93.6 9 5 . 5 9 4 . 2 -- 9 4 . 2 95.5 95.8 96.2 96.2 958 96. I 96.1 __ __ - _ _ ~ _ _ 22.4
~
~
81.8 10.3 92.1 45,6 0.6 46.2 67.8 12.6 80.4 8j.2 - 85.2 9 2 . 4 __ 9 2 . 4 9 5 . 9 -- 9 5 . 9 _ _ _ _
23.1 59.1 8 . 1 84.6 - 87.0 __ 9 0 ' 4 - 92'9 - 94.7 75.7 - 75'7 9 6~ . 3 __ 9 6 ' 3 __ 9 7 . 6 j6.5 87.0 90.4 92.9 94.7
CATALYTIC ACTIVITY O F LEAD
66.5
comparison, and it was found that it became active sooner when put in an iron tube than when put in a glass tube, Kinety-seven percent yield of aniline was secured on the fifth day, using an iron tube. When a glass tube was used a 93.5% yield was obtained on the fifth day, and a 96.5% yield on the eighth day. A study was undertaken t o determine what the effect of grinding would be upon the activity of the catalyst. A quantity of red lead ( I I.; par cu. in.) was ground in a ball mill. Samples were taken from the mill after j 4 , 108, and 2 0 0 hours of grinding. The apparent density of these red lead samples was 17.4, 2 1 . 7 , and 30 g. per cu. in., respectively. In order t o aid the grinding somewhat, the red lead was loosened from the sides of the ball mill every 1 2 hours. The data are given in Table 11. Although the catalyst from the ground material gave low Sields on the first day, they were higher than those obtained from the unground material. But similar t o the unground catalysts, the activity increases with use. The effect of grinding, however, was only important to the extent of increasing the apparent density of the catalyst so that more could be packed in the catalyst tube. The catalyst made from the material ground 108 hours was on the third day's run heated for a short time by mistake to 443OC., which is I 16 degrees above the melting point of massive lead. This overheating killed its activity, giving on the next day's run only a n average of 45.6Yc yield of aniline, as compared with the previous average yield of 8 1 . 8 7 ~ . However, this loss in activity was only temporary, and on the seventh day t,he yield reached 95.9% of aniline. This behavior of lead catalysts after heating to a high temperature in hydrogen is different from that of copper and nickel catalysts.' In continuing the study of the increase in activity with use, two catalysts were prepared from the material ground 108 hours. They were both reduced for one hour a t 308OC. Hydrogen was passed over one of them a t this teniperature for 48 hours, which time was equivalent t o four days use. The following day seven experiments were carried out with this catalyst, the average yield being 4.4Yc aniline and no azobenzene. This shows that hydrogen alone kills the activity of the catalyst as it causes its physical condition to be changed. It becomes agglomerated into pellets of massive lead of various sizes, with only slight traces of active, loose catalyst. Through the other catalyst from the same material, 80 cc. of nitrobenzene was passed a t the rate of 4 g. per hour. It was passed continuously stopping only at night, each day corresponding to a five day run with the other catalyst. The object in view was t o determine whether or not this would cause the same increase in activity of the catalyst as when used in z cc. portions, with intervals of 30 minutes required to remove the products from the furnace. After feeding 80 cc. of nitrobenzene continuously, experiments were made as in Table 11. The average yield on the first day was 9 4 . 6 7 ~aniline, with no azobenzene, and on the second day 94.7Tc aniline, with no azobenzene. Brown and Henke: J. Phys. Chem., 26, 161-190(1922).
866
F. A . M A D E S W A L D , C . 0 . HENKE A N D 0 . W. BROWii
These two days would correspond to the sixth and seventh days use, as figured from the amount of nitrobenzene passed over the catalyst. Comparing these yields with those obtained when used intermittently, (Table I1 catalyst ground 108 hours) it will he seen t,hat on the seventh day 9 j . 0 7 ~ yields of aniline were secured, while they were only 94.;7c in this case. This indicates that there was practically no difference between the intermittent and continuous use of a catalyst a t 308'c. for bringing it up to its maximum activity. Hydrogen alone kills the activity. The >ield of azobenzene were obtained with both the ground and unground catalyst only on the first few days as has been shown, the highest yield being 25.3%. Lead, bismuth, and thallium are the only catalysts that giv3 high yields of azobenzene.' Copper and nickel, although in many cases are very active catalysts, gave no azobenzene. The factors which determine whether or not a catalyst may give azohenzene are: first, the metal which constitutes the catalyst; second, the activity of the particular catalyst; and third, the temperature. All the previous experiments were carried out wi:h the rate of flow of hydrogen 1 4 liters per hour and the rate of flow of nitrobenzene 4 g . per hour. Experiments were also made with different rates of flow of both hydrogen and nitrobenzene a t the same temperature of 308'c.. The catalysts used were light red lead (11.7 g. per cu. in.j and light litharge (16.5 g. per cu. in.). The yields a t different rates varied from 65yc to 977c of aniline, the two catalysts giving about the same yields a t different rates. The best results were obtained with the rate of 1 4 liters of hydrogen and 4 g. of nitrobenzene per hour, while both higher and lower rates gave poorer results.
Conclusion Lead catalysts prepared by different methods were compared. The activity of lead catalysts increases slowly with use. 2. 3 . Different lead catalysts showed greater difference in activity on the first day's run, but by the eighth day their activities were practically the same. 4. A catalyst made from heavy litharge was used for nearly zoo experiments, maintaining about 97YGyield of aniline. 5 . Hydrogen alone kills the activity of the catalyst. 6. Activity of the catalyst increases more rapidly in an iron tube than in a glass tube. 7. Lead catalyst works best for the reduction of nitrobenzene a t 308OC. 8 . The grinding of the material in order t o increase its apparent density had no permanent effect on the activity of the catalyst produced. 9. The activity of the catalyst was only temporarily destroyed by heating it at 450°C. in hydrogen. I.
Laboratory o j Physical Chemistry, Indiana Cniaersily, Indiana.
Henke and Brown: J. Phys. Chem., 26, 324
(1922).
