IiVDUSTRIdL 9-2TD ENGI.VEERIh-G CHE-IIISTRY
September, 1925
971
Preparation of Fused Iron Oxide for Use as a Catalyst’ By A. T. Larson and C. N. Richardson FIXEDNITROGEN RESEAHCH LABORATORY, WASHINGTON, D . C.
T
HE manufacture of iron catalysts for the direct synthesis of ammonia usually involves the preparation of an iron oxide admixed with certain other metallic oxides which act as “promoters.” For technical purposes a fused iron oxide, essentially an artificial magnetite, has been most frequently employed. To melt iron oxide, however, under conditions which permit the ready incorporation of desirable constituents and a t the same time the complete exclusion of all other substances has been a difficult problem. Fusion in heated crucibles has invariably added some of the crucible material to the melt. For example, crucibles made from refractory oxides and compounds such as alumina,
Fleure
1-Top
Received June 6, 1925.
Apparatus
The semiworks apparatus consisted of an iron pot (60 cm. i. d., 35 cm. deep), three water-cooled electrodes, and a source of electrical power,having a range of 10 to 110 volts. A top view of the pot with the electrodes in place is shown in Figure 1, and a side elevation is given in Figure 2 . The details of the water-cooled electrode are shown in Figure 3. These merp made of standard “3-inch” pipe about 60 cm. long, the furnace end of the pipe being welded shut and the other end capped. A standard “1/2-inch” pipe fitted into the cap and extending nearly to the bottom of the electrode provided means for water cooling. Leads from the furnace were attached to the pipe by means of copper bands, as shown in the figure. The electrodes were usually placed 30 to 40 cm. apart. However, with the electrodes a t this distance from one another practically no current flowed through the cold granular magnetite, even when the highest voltage available (110 volts) was employed. An auxiliary electrode was therefore provided, which could be attached to any one of the main electrodes by means of a flexible conductor. With this electrode the effective distance between any pair of electrodes could be varied a t will. When this electrode was placed approximately 1 cm. distant from one of the other electrodes enough current flowed to melt a small portion of the oxide. By proper manipulation of the auxiliary electrode a narrow bridge of hot oxide could be drawn between any pair of electrodes. As soon as all the phases had been connected in this
View of F u r n a r e
rnagnebia, and zircon, and alloys such as ferrotungsten, pure tungsten, and carborundum, have been found to react with molten iron oxide. In the preparation of some catalysts contamination by such crucible materials may not be serious but even in such cases the method does not commend itself because of its lack of quantitative control. It is the purpose of this paper to describe a method for manufacturing fused iron oxide catalysts of any desired chemical composition. The method of fusing iron oxide described in this paper consists essentially in. melting iron oxide together with the desired promoter ingredients upon a protecting bed having practically the same composition as the catalyst material. The fusion of the oxide under these conditions has been effected in various ways. By one method an electric furnace of the radiating arc type was employed. This was quite satisfactor); so far as the fusion was concerned, but had the disadvantage that it was difficult to prevent ash from the electrodes from dropping into the molten oxide. For small laboratory batches (0.5 to 1 kg.) the oxide was melted by means of an oxyhydrogen blow-torch. When this method was employed it was found advantageous to burn pure iron in oxygen, collecting the oxide drippings on a bed of oxide fines, and then adding the promoters during the subsequent fusion of the hot oxide. The essential details of this pro1
cedure have already been described.2 By a third method which has been particularly useful in the manufacture of large batches of catalyst material, the oxide is melted between water-cooled iron electrodes.
F i g u r e 2--Side View of A p p a r a t u s
way the current input increased rapidly so that fusion of the oxide mixture included between the main electrodes was readily accomplished. The electrical equipment consisted of a transformer, a switchboard, and the necessary leads. The transformer was 180K.V. A., 220 or 440 volts high tension, 10 to 110 volts low tension. The furnace was usually run three-phase, as indicated in Figure 2. The electromagnetic reactions of the polyphase 1 “Report on the Fixation and Utili-ation of Nitrogen,” Nitrate Division, Ordnance, War Department, in cooperation with the Fixed Nitrogen Laboratory, Document 1041.
Vol. 17, KO.9
I,VD USTRIAL A S D ESGINEERI-VG CHE.1fISTRY
972
currents produced a beneficial stirring effect, which was much more pronounced than with single-phase operation.
from the sizing being saved for use in making another batch of the same composition. Water
Procedure
In making a batch of catalyst, the proper proportions of iron oxide and the desired promoter (14 mesh or even smaller)
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A-ote-Iron oxide suitable for the manufacture of ammonia catalysts may be prepared by burning pure iron Iron rods (‘/4 t o 3/a inch) have been found to burn readily in d curent of oxygen.
Rere first weighed out and thoroughly mixed on a clean iron plate. The mixed batch was then shoveled into the furnace and the electrodes spaced and inserted a few inches into the batch. The material was hollowed out in the center and heaped around the edges so that the melt would stay in the center. Water was started running through the electrodes and the power switched on a t the maximum voltage. The three electrodes were then connected with a narrow bridge of hot oxide. When the maximum allowable current a t the starting voltage had been reached the next lower voltage was applied. This was repeated until the lowest voltage, highest current tap was reached (9-25”, 4O0Oa,3-phase). When the oxide included between the electrodes became fluid the power was shut off. After the mass had cooled the electrodes were withdrawn and the fused oxide crushed and sized, the fines
Elec+rode
Figure 3-Main
Electrode
Melts up to 400 pounds each have been made in this apparatus. The total time required was usually about one hour for each 100 pounds of batch. Energy consumption was never very accurately determined, but varied from one-half to three-fourths of a kilowatt-hour per pound of melt.
The Evaluation of Barium Dioxide’ By E. C. Wagner U N I V E R S I T Y OF PENNSYLVAXI.4,
PHILADPLPHIA, P A .
HE eyaluation of barium dioxide depends upon decomposition by an acid and determination of the hydrogen dioxide produced. The latter is commonly accomplished by titration with permanganate, or the decomposition by acid may be effected in presence of pota,.:’ wum iodide and the liberated iodine titrat’ed with iodine. This paper deals only with these two methods from among the limited number that have been d e v e l ~ p e d . ~ A decision as to the actual accuracy of any method is difficult, for so far as the writer knows there is no way to determine the barium dioxide content of a sample with certainty. For present purposes it seems permissible, because of the comparative instability of hydrogen dioxide solutions in presence of traces of common impurities, finely divided solids such as dust, or even rough glass surfaces, and the consequent tendency toward low results, to assume the superiority of that method which yields the highest consistent resuits when precautions are taken to prevent positive error.
hydrochloric acid by the dioxide or by the permanganate, that the use of >In-- was without advantage, and that solutions of hydrogen dioxide obtained from barium dioxide could be allowed to stand for 15 minutes without apparent decomposition. Chemists who have assayed barium dioxide will probably question the last finding, as it must be connnon experience that the permanganate method is very likely to give low and irregular results, especially in warm weather. It mas found by R. E. Beard that the procedure given by Treadwell and Hall yielded concordant results only when decomposition and titration were conducted a t 5’ to 10’ C.; a t higher temperatures, including all ordinary laboratory temperatures, results were low and less regular. The directions of Treadwell-Hall are satisfactory only when the words “cold water” are interpreted to mean water very nearly a t the freezing point. The 2 iV hydrochloric acid used should be similarly chilled, and in hot weather it is advisable to cool the beaker externally during the analysis. In order to eliminate these inconveniences a means v a s Permanganate Method sought by which the hydrogen dioxide solution could be A typical form of this familiar method is described by stabilized long enough to permit titration a t ordinary temperatures. Acids in general are said to have a preservative Treadwell and H a L 3 The method was proposed by who found that’ hydrochloric acid was preferable to sulfuric action, and it is well known that phosphoric acid is very for decomposition, that with a 0.5 N concentration of hydro- effective. The possible usefulness of this acid came to the chloric acid there was no irregularity due t o oxidation of writer’s attention as a suggestion from E. H. Korton, with whom some trials were carried out jointly in 1918. I t was 1 Received February 14, 1925. found later that the use of phosphoric acid, and also of ice2 Kassner, Arch. P h a t m . , 228, 432 (1890); Quincke, Z . anal. Chem., cold water, are described by Schimpf.6 The convenience S1,23 (1892); Raumann, Z . angew. Chem., 6, 116 (1892); Rupp, Arch. Phorm., and also probably the accuracy of Schimpf’s procedure are 240, 437 (1902); also see Merck, “Chemical Reagents,” 2nd ed., 1914, p . 52; Lob, Chem. Ztg., SO, 1275 (1906); Chwala, Z . angew, Chens., 21, 589 (1906). diminished by the operation of diluting the solution of hy-
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“Analytical Chemistry,” Vol. 11, 6th ed., 1924, p. 534. Lac. c i t .
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“Manual of Volumetric Analysis,” 5th ed., 1909, p. 161.
