INDUSTRIAL AND ENGINEERING CHEMISTRY
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ACKNOWLEDGMENT
(6)
This investigation was supported by the Institute for Atomic Research a t Iowa State College. The valuable aid of -4dobh F. Voigt of the Institute for Atomic Research in developing the radioactive tracer techniques used is gratefully acknowledged. LITERATURE CITED
Association of Official Agricultural Chemists, “Slethods of Analysis,” 7th ed., Washington, D. C., 1950. Bridger, G. L., T.V.A. Chem. E w .R e p i . 5, C. S. Governnient Printing Office, Washington, D. C., 1949. Bridger, G. L., Boylan, D. R., and Markey, J. W., Anal. Chem., in press. Bridger, G. L., and Kapusta, E. c., I K D . EXG.CHEM., 44, 1540-6 ( 1 9 5 2 ) .
Hill, W. L., and Beeson, K.
c.,
Assoc.
ofic. Am-. Chemists,
19, 328-38 (1936).
Vol. 45, No. 2
Hill, W , L., Fox, E. J., and Slullins, J. F., IND.EXG.CHEM.,41, 1328-34 (1949).
(7) Hill, L., and Hendricks, s. B., Ibid., 28, 440-7 (1936). (8) MacIntire, W. H., Hardin, L. J.. and Johnson, H. S . , Jr., Ibid., 41, 1079-81 (1949). (9) MacIntire, W. H., Hardin, L. J.. Oldham, F. D , , and Hammond. J. W., Ibid., 29, 758-66 (1937). (10) MacKenzie, A. J., and Borland, J. IT.,Anal. Chem., 24, 176-9 (1952). (11) Sauchelli, v., “3tanual on ~ ~ ~production,^^ ~ i l naltimore, i ~ ~ Md., The Davison Chemical Corp., 1946. (12) \Yright, E. H,, and Tongue, T. o., u, s. patent 2,504,546
(April 18, 1950). RECEIVEDfor review J u l y 18, 1952. ACCEPTED October 3 , 1952. Presented before the Division’of Fertilizer Chemistry a t the 122nd Meeting of the AMERICAN CHEMICAL SOCIBTY, -4tlantic City, N. J. Contribution 200 from the Department of Chemical and RIining Engineering and the Institute f o r Atomic Research,
Activity of an Iron Oxide-Chromium Oxide Water-GaB Shift Catalvst J
EFFECT OF ADDED CONSTITUENTS KENTON ATWOOD AND &I. R . ARNOLD The Girdler Corp., Louisville, Icy.
T
HE more widely employed commercial water-gas shift
catalysts consist of iron and chromium oxides, either alone or mixed with a suitable support (3, 4). Although the principal active constituents are the same, there is a wide variation in the activities of the commercial catalysts, which might result from differences either in the method of preparation or in catalyst composition. This paper deals with the effect on catalyst activity of small amounts of other constituents added to a commercial water-gas shift catalyst. These constituents might come from the materials of construction or from the gas stream being treated in a commercial unit, or might be added deliberately as promotors for the water-gas shift reaction. The commercial catalyst selected for this study may be used a t temperatures as low as 700” F., the lowest temperature which is normally employed with any industrial catalysts of this type (C), unless elevated pressures are used ( 2 ) . The lowest possible operating temperature is desirable since the water-gas shift reaction (CO HzO = COZ HZ) proceeds further to the right as the temperature is lowered, while plant operating costs may be reduced by operating a t a low temperature. The catalyst employed in this investigation is not used a t temperatures above 1000” F., since inactivation may take place a t more elevated temperatures.
+
+
EXPERIMEIVTAL
Catalysts were prepared by precipitation of iron and chromium hydroxides from alkaline solutions. Six types of catalyst were tested: 1. A catalyst prepared commercially from technical grade chemicals. 2. A catalyst prepared in the laboratory from C.P. chemicals by approximately the same procedure as that used commercially. 3. Catalysts prepared by the preceding method, except that the hydroxide of an added constituent was coprecipitated with the iron and chromium hydroxides. 4. Catalysts prepared by the preceding method, except that the added constituent was precipitated immediately after the iron and chromium hydroxides. 5. Catalysts prepared by the second method (laboratory)
exept that an added constituent was ground into the dried mixture of iron and chromium oxides. 6. Catalysts prepared by grinding added constituents into the commercial catalyst (Type 1). Activity tests were conducted in reactors constructed of 8mm. borosilicate glass tubing and immersed in a solder bath maintained a t the desired temperature by means of electric heaters. The reactant gases flowed upwards through the tube over approximately 1 cc. of catalyst (weighing slightly less than 1 gram) in the form of cylindrical pellets, 7 / 3 2 inch in diameter and 3/le inch long. The hydrogen-arbon monoxide mixture ~ - a 3 metered from a gas cylinder to the unit by means of a calibrated flowmeter and steam was introduced into the reactant mixture by the gas saturation method. A schematic diagram of the apparatus is shown in Figure 1. Catalyst samples were reduced for 18 hours a t 750” F. xith a gas mixture consisting of 1 volume of hydrogen, 10 volumes of steam, and 9 volumes of nitrogen at a space velocity of 1500. After reduction, activity tests first were made a t 750” F. and a space velocity of 1900, using a gas mixture consisting of 1 volume of steam per volume of dry gas containing 26% carbon monoxide and 74’% hydrogen. The product gas was sampled for analysis a t 1- to 4-hour intervals subsequent t o the reduction period. Orsat analyses for carbon monoxide, using the cuprous sulfate-2naphthol absorption method, mere made on the initial dry gas mixtures. Carbon dioxide in the dried product gas samplcs v a s absorbed in Ascarite and weighed, and the residual gas as analyzed for carbon monoxide. After the activity measurements were completed a t 750” F., the temperature was lowered to 650” F. and, without change of catalyst, inlet gas composition, or flow rate, additional gas samples were taken for analysis. Tests under the above conditions on empty reactors shorn-ed no dctectable reaction of carbon monoxide with steam. Space velocity as used in this paper is defined as the volumes of dry inlet gas measured a t 60’ F. and 1 atmosphere passed per hour per volume of catalyst. The catalyst volume used in the calculation of the space velocities was based on the apparent volume of the catalyst, which w-as determined by measuring the volume
~
February 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
425
and weight of a large number of catalyst pellets. I n large conventional bench-scale reactors about 40% of this apparent volume is free space, whereas in the small-type reactor employed in this investigation about 58% of the apparent volume is free space. The contact time under the standard test conditions a t 750' F. and 1 atmosphere is, therefore, 0.33 second, based on the free space associated with 1cc. of catalyst.
with the standard catalyst and the theoretical conversion a t 750" F. (90.3%) and 650' F. (94.4%). A degree of conversion considerably under theoretical is required if reliable comparisons of catalyst activities are t o be obtained. This space velocity is considerably higher than t h a t used in commercial operations, but it is probable that comparisons of catalyst activities valid for large reactors can be obtained with apparatus and conditions greatly different from those employed in plant-size reactors (6). Several catalysts containing 95 parts by weight of iron and copper to 5 parts of chromium were studied. These preparations were of particular interest, since catalysts containing copper have been disclosed as effective low temperature water-gas shift catalysts (1, 6). Reproducible results with catalysts containing copper were not obtained, however, and ranged erratically between 36 to 80% actual conversion at 750' F. VENT Some refinements of the preparation and test methods are probably required before these catalysts can be tested. WHYDRONE ASCAFIITE The effect on catalyst activity of variTRAP CYLINDER CONSTANT TEMPERATURE SOLDER BATH TUBE TUBE ous constituents added t o preparations BATH containing 95 parts of ironto parts o f . Figure 1. Schematic Diagram of Apparatus chromium is shown in Table I. The amount of constituent added in each case was 1 or 5 parts by weight of the indicated element per 100 The reproducibility of the results obtained by the test method parts of iron and chromium. The per cent of actual conversion was determined on 18 different charges from the same batch of of carbon monoxide in the test gas at a space velocity of 1900 commercial catalyst. The actual conversion for 18 samples and temperatures of 750' and 650' F. is shown for each catalyst ranged from 68 to 76% at 750' F. and from 40 to 46% at 650' F. composition; the values are averages from tests made on two The reproducibility of the laboratory catalyst preparation method charges of each catalyst. The conversions obtained with most was tested on five different batches of catalyst containing 95 of the catalysts were no greater than the maximum conversion parts by weight of iron to 5 parts of chromium. The actual with the standard preparation. Higher conversions were obconversion ranged from 74 t o SO'% and between 48 to 58% at tained with six catalysts, those containing mercury, graphite, 750' and 650' F., respectively. The range of results is about titanium, molybdenum, and cobalt. Since the high result with the same as t h a t found in successive tests on a single catalyst the catalyst containing molybdenum was apparently without sample. The space velocity of 1900 was selected since there is significance, as shown by the data of Table 11, no significantly a considerable difference between the actual conversion obtained high activity is indicated for any of the catalysts b y these tests. I n several of the preparations tested, the added constituent (95 PARTS IRON-5PARTS acted as an inhibitor rather than a promoter. Catalysts conTABLE I. ACTIVITIESOF CATALYSTS taining boron, aluminum, and phosphorus have activities conCHROMIUM) CONTAINING VARIOUSADDEDCONSTITUENTS siderably below normal. The effect of aluminum is only noticeActual Conversion of Carbon Monoxide a t able a t the higher concentration, however, and in this case i t Constituent Added, T~~~ of 1900 Space Velocity, % can hardly be considered a minor constituent. Parts Catalyst 750' F. 650° F. 2 74-80a 48-58O Boron appears to be the most efficacious inhibitor of this group. 39 67 Results of further tests on the activity of boron-containing cata45 74 41 68 5 lysts are given in Table 111. Boron compounds greatly reduced 36 71 5 45 the activities of both plant and laboratory preparations. 73 3 35 3 70 Boron is unlikely to be introduced into a water-gas shift cata42 5 76 52 5 76 lyst, b u t the possibility of contamination with phosphorus is 52 4 73 much greater. I n one commercial installation where phosphorus 49 4 78 48 4 76 was introduced into an iron oxide-chromiun oxide water-gas 67 37 3 5 a2 57 shift catalyst during operations, the catalyst was almost com2 5 12
5
s
4 4 3 5 5 3 4 5
3 5 5
5
5
5 5 5 3 3 3 3 3 a
Range for five preparations.
74 54 73 80 81 79 71 79 75 79 75 80 59 77 84 72 78 77 78 81 75
48 24 49 61 56 55 40 54 49 52 46 56 24 48 51 43 51 49 55 63 54
TABLE 11. ACTIVITIESOF LABORATORY-PREPARED CATALYST (95 PARTSIRON-5 PARTSCHROMIUM)AND COMMERCIAL CATALYST WITH AND WITHOUT MOLYBDENUM ADDED Actual Conversion of Carbon Monoxide at 1900 Space-Velocity C atal yet Preparation A
Type of Catalyst 2 5
Constituent Added, Parts None Mo, 1 , as HzMo01
Preparation B
2 5
None Mo, 1 , as HzMoOa
79 76
59
Commercial
1 6
None Mo, 1, as HzMo04
71 74
42 43
70
750' F. 650' F. 78 48 84 51 58
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 45, No. 2
The effect of additives on catalyst life has not been studied in TABLE 111. EFFECT OF BORON O N ACTIVITIES OF A LABORATORY- this investigation. Since the commercial catalyst is known to PREPARED CATALYST (95 PARTS IRON-5 PARTS CHROMIUM) AND have an effective life of a t least 9 years, it appears unlikely that A COXMERCIAL CATALYST any of the additives considered in the present study ~vouldgive Actual Conversion of significant improvement in this respect. Carbon Monoxide a t 1900 Space Velocity, No effective promotors for the iron oxide-chromium oxide T y p e of % water-gas shift catalyst were found in a group of 33 elements Catalyst Catalyst P a r t s of Boron 750’ F. 650° F. considered. The majority of the additives had no significant Normal 2 h‘one 74-80a 48-580 effect on initial catalyst activity. Boron and phosphorus reduced Prep. C J 1 as HsBOs 12 2 1 a s N~.zBa07 24 11 catalyst activity to a considerable extent. Although other lighter elements may be inhibitors. it is known that sulfur comCommercial 1 None 70 41 6 1 as HJBOS 33 11 pounds do not have a very great effect on this type of catalyst ( 3 ) . a Range for five preparations. I n view of the relatively small effect of added constituents 011 catalyst activity, it appears probable that variations in the method of preparation are more important in producing differences pletely inactivated a t the end of 6 months. An analysis of this between commercial catalysts (4)than are minor changes in catalyst before use showed a negligible amount of phosphate, composition. It is indicated that contaminations either in while after 6 months of use analysis for phosphate shou-ed 3.5 manufacture or use would be unlikely to cause difficulties in the parts of phosphorus per 100 parts of iron and chromium on the commercial application of the catalyst. discarded catalyst. Activity tests were made on this catalyst before and after use, and on the commercial catalyst of this LITERATURE CITED investigation before and after impregnation with phosphoric (1) Armstrong, E. F., and Hiiditch, T. P., Proc. R o y . SOC.( L o n d o n ) , acid. These tests were made by the method described by Chris9 7 A , 265-73 (1920). .tian and Boyd (a), using 75-cc. samples a t 750’ F. and 400 space (2) Atwood, Kenton, &mold, M. R., and Appel, E. G., 1x0. ENG. velocity. The commercial catalyst which was inactivated during CHEM.,42, 1600-2 (1950). plant operations, Christian and Boyd’s catalyst “D,” gave 7270 (3) Bridger, G. L., Gernes, D. C., and Thompson, H.L., Chem. Eng. actual conversion before use and 21% conversion after use. -4 Progr., 44, 363-82 (1948). normal sample of the other catalyst showed 90% conversion, (4) C h r i s t i a n , D. C., and Boyd, P. B., Chem. Eng., 56, 148 (1949). ( 5 ) Laupichler, F. G., IND. ENG.CHEM.,30, 578-86 (1938). while a sample impregnated with phosphoric acid, to provide (6) Storch, H. H., and P i n k e l , I . I., Ibid., 29, 715 (1937). 2.7 parts of phosphorus per 100 parts of iron and chromium, showed only 24% actual conversion. RECEIVED for review June 9, 1952. A C C E P T E D September 17, 1952,
Porosity of Paint Films d
WATER VAPOR ADSORPTION AND PERMEABILITY SIGMUND ECKHAUS, IRVIN WOLOCK, AND B. L. HARRIS T h e Johns Hopkins University, Baltimore 18, M d .
T
HE exact nature of the physical structure of paint films is of
great interest in determining the mechanism of permeation of water vapor through a film. Recent studies (4)indicated that unpigmented linseed oil films are nonporous-i.e., there is no appreciable quantity of discrete fine pores in these films. An investigation of the nature of pigmented oil films by Asbeck and Van Loo ( I ) indicated that, for any given pigment-binder system, there is a “critical” pigment volume concentration (CPVC), in the region of which substantial changes are noted in the physical appearance and behavior of a film. They demonstrated that the permeability rises sharply a t the critical pigment volume concentration and postulated that a t this point there is just sufficient binder completely to fill the voids between the pigment particles in the film after evaporation of the thinner. Above this point, therefore, a dried film should be physically porous. Such pores should be easily detected by the technique used in previous studies of unpigmented linseed oil films-i.e., measurement of the total surface area of unsupported films of known geometrical area. The transition from a nonporous t o a porous film would then be noted by an increase in the total surface area of the film samples. These measurements would logically follow the work on unpigmented films and serve to give a more complete picture of the nature of pigmented oil films. It was believed that comparisons on similar films of the roughness factor (ratio of total surface area t o apparent or geometric film area) and of the water
vapor permeability would be of interest. studies are reported here.
The results of such
EXPERIMENTAL MEASUREMENTS
Surface area and mater vapor permeability were measured o n unsupported films of the four pigment-binder systems used by Asbeck and Van Loo ( 1 ) : titanium dioxide and magnesium eilicate in raw linseed oil and in bodied linseed oil. The pigment volume concentrations for each system ranged from 25 to 6570in 5 % intervals. All samplee contained 0.57, lead drier, 0.01570 manganese drier, and O.O15v, cobalt drier, in the form of naphthenate added on the basis of vehicle solids, as ne11 as varying amounts of mineral spiiits thinner. The films were prepared by uniformly coating tin-plate panels, using a Boston-Bradley adjustable blade with a 6-mil gate opening. The panels were held flat during the coating operation by a magnetic chuck. The films were allowed to air-dry at room temperature for 48 hours and were then stripped by amalgamation with mercury. The average thickness of each film was determined with an Ames dial gage (illode1 412 J, light pressure, calibrated in 0.0001 inch, and accurate to 0.0001 inch). Fifteen readings were taken on each film and the arithmetic average was calculated as the thickness. Variations were small, and the permeability samples were cut from the most uniform sections of the films. The thicknesses were 1.5 to 3.0 mils (1 mil = 0.001 inch). The geometric areas used for the study varied, owing to the desirability of always using a sample of the same total area as measured by adsorption. Films of low roughness factor required the order of 1000 sq. em. geometric area, while the others required less, down t o 20 sq. em.
