KIESELGUHRS Suitability as Carriers in Catalysts ROBERT B. .iSDERSOS. J-iAIES T. hZcCARTSEY, V.KEITH HALL, AND L. J. E. HOFER Ceiitrul Experiment S t a t i o n , C7. S . Bureau of Mines, P i t t s b u r g h , Pa.
T h e properties of a number of kieselguhrs used as supports i n cobalt Fischer-Tropsch catalysts h a l e been studied. Data o n chemical analysis, x-ray diffraction, surface areas, and pore volumes, together with electron micrographs at a magnification of 2000 and 20,000 diameters, are presented and correlated.
N THE search for a suitable carrier for cobalt Fischer-Tropsch
I
catalysts the properties of a number of kieselguhrs were determined. Since these data may be of general interest t o chemists as well as of specific interest to those preparing catalysts, they are presented here; in later papers the influence of these kieselguhrs on the properties and activity of Fischei-Tropsch
a
e-
d. The data include clic~riiictilanalyses of rcpresentative samples, x-ray diffraction patterns, electron micrographs, surface areas by nitrogcm adsorptioii, :and porevolume studies. There is not a great, deal of infomiation i r i thc litcrature that may enable one t o determine the suitability of a given kieselguhr as a carrier in catalyst,s. The propertiw and uses of kieselguhrs have been summarized by Calvert ( 4 ) , Skiiiiicr (12),aiid others. Only a few papers havc appeared on the applictitioii of the electron microscope t o catalysts or constituents of cat,alysta. Ilics (9) has discussed electron microscope and atlsorptioii studies of a typical commercially available kieselguhr. Turlwvicli (14) has clrscribed electron micrographs of a number of catalysts, and Shekter, Roginskii, and Isaev ( 1 2 ) have published electroil micrographs of catalysts prepared with asbestos as a carrier. Kieselguhrs are composed rhiefly of diatoms. (In this C ristobalite country the names ciiatomaceous earth or diatomite are more common, but iii F,ischerTropsch literature the name J.M.Hyflo Super Cel kieselguhr is gencrally used.) Kieselguhrs may t x of either marine or fresh n.ttter origin but, they are always comDicalite Speedf low posed of aniorplious silica p l u s s m a l l a ~ u o u u I s of alumina, iron oxide, and t r a c e s of o t h e r oxides. J.M.Type 4: ICieselgulir particlw exhibit a variety of int,eresf,irig forms that reflect t o SOIW extent t,he source of the material. Kieselguhrs formed in Portuguese K.G. swamps eometimcs contain rather high perceiitages of r a r b o n a c e o u s 11111.1 e r i a1 , J.M.Filter G e l a c i d which is usually ' removed by calcinatioii. In preparex t roc t e d ing commercial kirselguhre the crude mnterid is crushed and then wparated into D i c a l i t e 637 T
German K.G.
Quartz
Figure 1. X-Ray- Diffraction Patterns of Kieselguhrs, Quartz, and Cristobalite
1618
ill water, air separation, or combiiiatiolls oC these. Some conniicrcinl kieselguhrs have been heat-treated (calcined) arid filltali-heattreated ( f ius-cialci lied) to produce varying, dcgrees Of sintering to improve their properties as filter aids, ctc.
i N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
December 1947
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ANGSTROMS
samples were dried in an oven a t 100" C. for 1 hour and then evacuated for 1 hour a t 100" C. before the isotherms were determined. ~Crlrtobalits I I l l Pore-volume studies were made by determining the bulk density, and . J.M Hvflo Super Gel. . ! I ! I / I I1 l I ! I I densities by the displacement of helium D i c a l i t e Speedflow l\ll I 1 I I I I I I and mercury. Bulk densities were determined on samples dried at, looo C. JM.TvDe E I I I I I / I I , for 1 hour by measuring the volume I Portuguese K 0. I 1 I I I I I 1 I , occupied in a 100-cc. graduate after it J . M Filtercel was tapped on a table 100 timed. acid extracted ! I l l I k l I I , I , I I Helium density m e a s u r e m e n t s a t Dicalite 637 T I I I1 I I 30" C. by the method of Smith and Rossman ( I S ) were made on dried German K . G L I I II I l l I I / samples pumped Tor 1 hour a t 100° C. Quartz I 1 , I I Ill Id 1111 h t I ! l l I f L11 I1111 I l l The accuracy of this niet,hod, as apt plied in this study, was only about I I1 I I I I I I I I I I I I I I I 50 30 20 10 *1.5% because of the small volumes ANGSTROMS of helium displaced by fairly large v o l u m e s of k i e s e l g u h r . JIercury Figure 2. X-Ray Diffraction Data for Kieselguhrs, Quartz, and Cristobalite densities were determined hy introducing mercury a t an absolute pressure of EXPERIJIENTAL 1140 n m . into samples which were dried and pumped as in the helium density method. Mercury-density measurements on a Specimens of each type of kieselguhr tvere prepared for obserfinely divided material may be uncertain because (a) particles vation n-ith the electron microscope by the follon-ing technique. may pack so closely under t h e pressure of the mercury that A supporting film i m s obtained by dipping a clean nlicroscope mercury cannot penetrate betrvceii the puticles, and ( b ) the slide into :t O . j C 2 solution of Fornivar (polyvinyl formal) in dioxmercury may require a long time t o penetrate all the pores availane. The lciesclgulir particles were dusted onto the dried film able t o it. If the first effect, is pronounced, the mercui'y density and dispersed by exposure t o a high-frequency, high-voltage spark discharge from a Tcsla coil (an ordinary vacuum-leak tester). should vary considerably in repeated determinations, especially The film as scored around the edges of t,he slide and crosstvise if t,he eize of bulb is changed. Significant variations did not iuto 0.25-inch squares, then moistened by the breath, and the occur in experiments Kith Dicalite 911 in n-hich the mercury slide mas lon-(,red obliquely into water so t h a t the film floated density n-as 0.371 and 0.375 ou repeated determinations in the off onto the water siirface. -1square of film n-ith adhering kieselguhr particles was picked up on a loop and lowered onto a 200same bulb and 0.378 in a bulb 50% larger than the first. The mesh scrccn placcd on the specimen holder. When dry, the effect of time of contact of the mercury mas not pronounced, as mount \vas ready for observation in the electron microscope. indicated by deterininations on Dicnlite, Grade 1, in which the mercury density after several minutes of contact was 0.348 The electron micrographs shor\.n here n-ere made in a n R . C h . compared with 0.361 after 6 days. At atmosplit.ric pressure Type B microscope. Those in Figures 5 to 9, which were selected mercury \vi11 penetrate only pores (cylindrical) n-hose openings by six or more persons as most representative of eight or more micrographs of each sample, were made at, a magnification of 2000. This was sufficiently high to reveal the structure of larger 870' C. 1,470' C. p CRISTOBALITE p QUARTZ e 7 TRIDYMITE pores, and thc larger field that could be viewed a t this magni575oc. 141OC. 220'C fication permitted study of the external shape of the part,iclcs. U CRISTOBALITE p TRlOYMlTE a QUARTZ However, finer detail of possible significance is revealed by enIOO'C. largement to 20,000 as illustrated in Figure 10. a TRIDYMITE T h e x-ray diffraction studies were made by the powder method. Figure 3. Transitions of Silica (7) All the samples m r e sufficiently fine to be used wlthout further grinding. Each specimen was prepared by packing the powder into small 20-nim. lengths of stainless steel tubing 0.7 mm. in inare larger than 5 microns ( I O ) . The macropore volume (pores side diameter; it as then partly extruded t o a length of about 5 larger than 5 microns) is the difference of the reciprocals of thc mm. by pushing a closely fitting stainless steel wire through the bulk and mercury densities, mhile the micropore volume (pore9 bore. S o hinder such as collodion n-as used t o increase the strength of the sample; compacting alone gave the specimen smaller than 5 microns) is the difference of i.hc reciprocals of the, sufficicxnt cohesion to withstand all subsequent treatment. The mercury and helium densities. The macropore volume probably use of biiiders, even if amorphous and of low scattering poiver, is consists almost erit,irely of spaces Letmen the particles of kicsclundesirable in smdying amorphous or semiamorphous catalyst guhr, and the micropore volume consists of volume between and materials. The tube with the extruded cylinder of compacted powder n-as mounted in a Debye-Scherrer camera of 71.6-nim. within the particles. -1sealed off x-ray tube of the Coolidge type equipped llium windows and a n iron target was used. Ks radiDESCRIPTION O F SAMPLES ation ma6 yemoved with a manganese dioxide filter. Exposures were for 3 hours a t 48 kilovolts and 7 milliamperes. P h J o H s ~ - ~ I A S V I L L E SAMPLES. .ill are from the Lompoc, Calif., identification v a s effected by means of the Hanax-alt index car deposit, n-hich is of marine origin. Filter-Ckl and Hyflo Superof x-ray reflections ( 1 ) and by comparison Kith patterns from Cel are examples of filter aids, the Filter-Cel being a natural authentic samples of cristobalite, tridymite, and quartz. material, rvhile Hyflo Super-Cel is a flux calcined product. Snow Floss is a natural kieselguhr characterized by a very small Nitrogen adsorption isotherms were determined on the kieselparticle size. Samples I t o IV are described as catalyst supports; I11 and IV are natural kieselguhrs, I1 is a calcined material, and I guhr samples, k)j-a volunietric method described by Emmett ( 5 ) . is flux-calcined. At the bureau, a sample of Filter-Cel was The surface areas were estimated by the use of the simple Bruntreated with hot nitric acid for 6 hours to reduce the percentages of auer, Emmett, and Teller equation (3),Khere the cross-s:ctional materials other than silica, then filtered and Idrid a t 120' C., and area of the nitrogen molecule is assumed t o be 16.2 Ae, All finally heated a t 650' C. for 2 hours.
I
I
I
20
30
50
I
I
I
l
1.0
l
l
l
l
l
l
I
I
I
1
I
1
I
3
11
11 11
=
11
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 39, No. 12
c
I
I A
I1,&-
6'I'able I .
Figure 1.
E l c n i r r l t n Other ~I'hariSilica i t i I i i e ~ e l g i i h r s
Aclsorption of Uitrogen 0 1 1 Kieselguhrs a t -195" C.
0. Shasta Count)
_.
kiesplguhr
Filter-Cel , II>flo Super-Ccl Solid points represent desorption A .
DiciLmE SaxrLcs. S:tnipl(Ts 911 and Grade 1 arc natural materials of the fresh-water deposit at Terrcbonne, Ore. Sninp1t.s S.15 and 637T are fresh-water kirwlgulirs from Ker:tda, \rhilc, GjST is a fresh-water material from the state of Kashingtoii. Speedflow and PS filler are flux-calcined materials, probaljly from the Lonipoc deposit in California. SHASTACOUSTY. CALIF., SAMPLE.This snni1)le from this fresh-n-atcr deposit in Shasta County was furnished by Iieiiiiet 11 Skinner, arid is a part of the sample "California 2a" mciitioned b y Skinner (MI. In 1940 there \vas no comniercial source of this niilterial. This samplc from Portugal aiid of PORTL-GL-ESI: IhsELGL-HR. ii,csh-ivater origin was sent t o the bureau b!- ('. C. Hall of the 13ritish Fuels Ilesearch Board, n-ho used it in cobalt FiseherTropsch catalysts. GERMAN KIESELGUHR.This n-as taken from tlie catalyst f w tory, Kuhrchcmie A,-G., Sterkrade, on -1pril 19, 1945. Probably this is the German Rostguhr. It is thought, t,o have come from a fresh-water deposit near Hannover and t o have been calcined f ( J 700" C. or higher, possibly t o remove carbonaceous material. Another sample of kieselguhr was obtained by ext,racting with hot nitric acid constituents other t h a n kieselguhr from a Gcrniaii cobalt Fischer-Tropsch catalyst.
IYeight 1 . 0 ~ son
~
~
~
I'erceutages ~ i ~ Computed i ~ ~as I~:lemrnts , Fe P Ti Ca J
~
AI
C,cI
Joliii~-3Inn~iIle IiyfloSuper-Cel
Filter-Cel
Filter-Cel (acidextracted) Dicalite 911 Phasta Couuty I'ortuguese (; er in n n 0
0.33 3.47
1 90 0 87 0 07 1 . 8 7 0 8.5 0.10
000 4.28 6.42 1 58 1 66
0 2 4 2 0
9 39 85 06 38
0 87 3.8G
a
0 01 0 02 0 006 0.01
0.03 0.03
a
0.46 0.28 0.49 0 08 0 . 0 3 0.05 0.27 0.10
a
0.09 0.31 0.0.5 0.19
Not determined.
X-R \Y DIFFRACTION STUDIES O F KIESELGL~III(S
15)- incxiiis 111' I-riiy diffraction pat terns of kieselguhr the crJ.st u1lint. p1i:isos ni:iy be identified, and morcovcr the width or diffuseti('..- of' tile diffraction lines gives a11 incliention of crystallite size. The reactivity of 1;ieselgulirs-for example, the solubility in solutions from which catalysts art' 1)reciI)itated-del)c.iitls among ot licr things upon the crystalline ph
Table 11. 4 - R a y Diffraction Data
011
Iiieselgiihrs
Diffuseness
CHEMICAL ASALYSES O F KIESELGUHRS
I n the preparation of some types of catalysts small pcrcentages of certain elements are undesirable. I n addition t o hytlratcd silica, kieselguhrs contain small amounts of ot,her compounds, aluminum and iron oxides being the chief impurities. Skinner ( I d ) presented analyses of a number of kieselguhrs from Washington and Oregon. I n this bulletin Skinner assumed that a n y aluminum came from clay present as a n impurity. Calvert (4) has given analyses of a number of kieselguhrs from the United States a n d Germany. I n the tables of Skinner and Calvert the amounts of silica varied from 70 to 90%, r i t , h m-eight losses upon ignition of 3 t o 12%. From 0.5 t o 10% of alumina a n d of iron oxide were reported.
04Y 1.49 2 24
0 12 0 10 0 . 1 3 0 31
Phase C'rxtobalite Cristobalite hmorphous Amorphous Amorphous, Amorphous, Cristobalite Cristobalite, Amorphous Amorphous Amorphous Amorphous Amorphous Cnstobalite hmorphous, Amorphous, Quartz
quartz, u n k n o a n quartz
I 3 quartz Ilicalite SF s 637T 658T X SA5 911 Grade 1 CPS Cunknown Shasta County quartz C Portuguese C German A . Sharp. B . Somenhat diffuse. C. Diffuse C-. Diffuse t o the point n-here phases are d i 5 c u l t t o ascertain X. Amorphous.
x x x
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1947
a
b
d
e
1621
C
f
.
I
h
I Figure 5 .
io p-
I
Elertrori 3Iicrographs of Vncalciried Kieselguhrs from Johiis-\Ian~ille( : o r p o r u t i o t i (2000 X ) a, b . c. d.e.
Filter-Cel Filter-Crl acid-extracted Snow Floss
f, 6. J.\f-lIl It, I . JN-1%
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INDUSTRIAL AND ENGINEERING CHEMISTRY
a
b
C
d
fI
e 4.
, Figure 6. a, b .
'Or-
,
Electron AIicrographs of Calcined Kieselguhrs from JohnsAIaiirille Corporation (ZOO0 x) I I ~ f l o wSuper-Cel
c, < I .
,111-1
e.f.
J1I-11
Vol. 39, No. 12
Crystallographically natural kieselguhr normally consists of hydrous amorphous silica. I n addition, impurities such a8 clay, and crystalline quartz often are found in perceptible quantit,ies. I n the series of samples st,udied, Johns-Manville Type 111, Johns-3Ianville Type IV, Johns-Manville Filter-Cel, both raw and acid-extracted, Dicalite 637T, Dicalite MST, Dicalite Sh.5,Dicalite 911, Diealite Grade 1, Shasta County, and the Portuguese kieselguhr all belong essentially t o this normal group. I n spite of the low water content, the Portuguese kieselguhr showed no cryst'allization, such as one might expect from calcination. X-ray diffraction patterns of various kieselguhrs and samples of cristobalite arid quartz are given in Figures 1 and 2, and these patterns are described in Table 11. Slight differences among these kieselguhrs occurred with respect to the quantity of crystalline matter-for example, a number of faint lines occurred in the Filter-Cel patterns, some of which disappeared on acid extraction. Those lines rrhich remained seem t o be those of quartz. The pattern of the Port,uguese kieselguhr, as far as the faint, lines were concerned, \vas very similar t o the acidestracted Filter-Cel. The'p:Lt,t,erii of the Shastn. County kieselguhr contairird faint linrs which cannot, be a or any other crystalline amount of impurities 8.0% as compared with 2.9% for Filter-Cel arid 1.4% for acid-extracted Filter-Cel, suggest that the strange lines were due to crgst,alline impurities. The other amorphous kieaelgiihrs gave vrry fev- fw,int, lines. The x-ray diffraction analysis of tlie heattreated silicas was much more satisfactory, since t h e diffraction p:ttrcrns irere much sharper in every case. Silica exists in a t least st forms, which may he nat,urally classified into a quartz series, a tridgmito series, and a cristobaliteseries. Transitions from one series t o another are sluggish, whereas aithin each series transitions are in general very rapid. At room temperature only one member of each series usually exists: a-quartz, a-t'ridymite, and a-cristohalite. Thelnst two o\ve their existence t o t h r slonmm of the transition from onc wyics to anothw. The only forms of silica which h:~v(' an accessible region of thermodynamic slability are a-quartz, @-quartz. :-triclymitc, and pcristohalitr. The various forms and their relations arc shown in Figure 3. Johns-1\Ianville T ~ - p cI, Johns-11anville Type IT, Hyflo SuprrCcl,Dicdite Speedflow, and Dicalitc I'd fi1l1.r all contsinctl cristobalite. In addition, Dicalite Speedflow contaiiietl a-qutwt z, indicating inconipIctc conversion from quartz to cristobalite. Sormally one might ex-
1623
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1947
0
A U
b
C
e
f
h
A
Y
Figure 7.
. t Electron 3Iicrographs of Kieselguhrs from Dicalite Company (2000 X) a, b . c,d.
Grade1
911
e, f.
SA-5
g, h. 637T
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 39, No. 12
C
f
h
a, 1,. r. d .
658T Speedflow
December 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
1625
b
'0r-
Figure 9.
Electron llic-rograph* of Foreign liir-clg~rhrs(2000
x)
n , b . German near IInnnorw r From G e r m a n cobalt catal3si [ I . e. i'ortupuese
pect direct t ranuitioii fi,oni tile lon.-tc~nipcraturc staljle form, quartz, t o t h e form stnblr alxive tlie tranaitioii p:~iiit,tridyniitc. It is douhtful if m)- of Ihc clticiiicd iiicwiguiirs were hc:itcd above 1470" C., rvlierc cristoba this irould require escccdingly expensiw cristohalite wa5 prot)nbl?- formed uritlcTi, coil different from those d ibcd by Sliiniicr ( 1 2 ) . Tile cau+e of t,he formntioii of crist,ob:rlite in :t tumperaturc range where it is h i o w n t o be nii able lies in tile kinetics 11 870" atid 1-170' C., thc stability of the transition. Ik region of tridymite, quartz changes t o cristobnlite much inore rapidlj- than t o tridyniitr, and c
Table 111.
Surface Areas and Pore Yolumes of Kieselguhrs
~
~
1628
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 39, No. 12
natural s:implcs.. 111 micrographs of flus-rcilciiid saniplw, s:~iiiph~s thc: calculated pore radii n v r era1 fold larger than I-Iyflo Super-Cel and J3I I, there ~ a ‘ no : eviclcnce of fine struetlit(~. tliose o t w s r v t d iii the micrographs. The sample appewed sintered, as indicated by drop-sli:ipt*d ACI(NOWLEDG>\IEST portions arid smooth outlinw of all particles. Sonic larger p o r w ~ w r erroded :ind erilargrd until they merged with acljaceiit IIOIYT I l i t ’ :it11 !1~>1~5 gratefully scknoivletlge the a and all ~ n i u l lpores had disappeared. Speedflon- and 1’s fillcr Sc,lviy ailti 1.’. 11. Gibson for the aiialytical ~ h o n - i ~more ! fiiie structure than the samplcs j List descrilrc.il, fiir I I ~ I ’ r:iiry-rlcnsit>I tleterniinations, 1Ii-s. IT. C. Peehlcs for anti thcl degree of sintering and croiion TT:E less. Cnlciucstl tiit, x-r:ty cliffriictinn patternq. a n d IIarlaii IIen-let8tfur prcparatiori ;.;implt: J l I I1 shc?\\-edslightly more structure th:in Speedflo\v o r ~1 saiuples. .icknowlctlgmcnt is given t o A. It. BolPS fillvr. The surface :mas, fine structure of clcctron niiwo1:tIii t OF t l i c 1)ic:ilite Company, 1%. L. King, J r . , of Johns-llsngraphs, m d diffuscncss of x-ray diffraction p x t t r r n s :ire iii qua lit:^villt. fi)r lic~lpfuldiscussions, anti Herman E. Rics, Jr., for contivc :igrccment for these calcined saniplcs. stru(ai ive criticism of tlie m:inuscript. Adsorption isotherms of naturnl kiesrlguhrs sho\vcd hysi t,rc>his ahovth ri-.l:itive pressures of 0.4, but the isotherm of Ilyflo SuperL I T E R A T L ~ R ECITED (:el s h o i r c d litt IP, if any, hysteresis in this range. Since p o i w fl) . \ i n . SO(.. for Tc,titig SIaterials. “Data Cards for ILleiitification thle in these micrographs (100 h.)~ c r found c iri o n Crysrailine hIatc=rids,” Philadelphia, Pa. guhrs but not in the flus-calcined samples, i t ( 2 ) lii.unauer, Deming, Deming, and Teller, J . Am. Chem. SOC., 62, may bc inferred that natural kieselguhrs also contain pows 1723 (1940); Brunauer, p. 150, “Adsorption of Cases and Vnlmrs,” Plinceton University Press, 1913. sniallc~than 100 .i. in diameter and flus-calcined mstct,i (3’1 Bi~unnuer,T n i n i e t t , and Teller, 6 .Am. Chem. SOC.,60, 309 not. This agrees with the current be$f that the hj-atci (1935). associated with pores smaller than 100 A. in diametcr. i$ 1 Calvcl t. “Diatomaceous Earth,” X e w Tork, Chemical Catalog I n many eases the avcrage pore diameters from the r:itio of co., 1930. ( 3 ) Ettirnett, “Xdrances in Colloid Science,” ed. by Krnemer, porv volunie t o surface area (Tahle 111) were of thc s ~ m ortlcr c Vol. I, pp. 1-36, Xew York, Interscience Publishers, 1942; of magnitude as those estimated from the larger pores of ttir Emmett, ISD. EXG.CHEK, 37, 639 (1945). micrographs, and for t,he high-area kieselguhrs tlie agrcenitnt (ii) I. In the more seiere soil burial test, cloth impregnated with ieroteu ga,e the best performance. Whereas the untreated cloth lost all of its tensile strength i n less than 7 dajs, a n impregnated cloth containing 5.9% icroteu \I-3 retained all of its strength for t h e duration of the test of 1L days. ilthough the preliminary experiments presented do not si1 e any indications as to the effectiFeiiess of resin-inipregnation relati3e to other antimildewing treatments, they
. 5’..Irrrij Qtcartermuster
Corps., Philadelphia, P a .
sLigge3t another purpose to which the many Taried re-in
Iweparations can be directed.
P
LL~~LI~IIS.iltY histological investigations ori the pent!tr:ttion of cotton fibers by fungi and Ijaeteria. (3, 4)indicate th:tt tlie orgmisiiis artark fi.r)m the outer surface iii\varcis in a n : t I ) i ) : L w i i t ly highly localized iiianncr. .LccordingIy, it seeins li,yicul to a s u m e t h a t any inert physical barrier preventing the i’uiigi 31111bacteria from coming into intimate contact u i t h the c ~ ~ l l u l i may w protect the cotton fabric against t h e microbio11 altacli. It ~ ~ thought s s that such a microbiologically ant cimtiiig can be applied ill the form of a resin inipregThe prvseiit paper describes preliminary studies in the ii:ition. niildew resist ancc of resin-impregnated clot,hs.
