ANTIFOULING PAINTS Inactivation of Highly Pigmented Antifouling Films Applied to Steel Although the Falue of copper pigments a5 actite ingredients for antifouling paints has been recognized for a long time, metallic copper pigments ha\e been aioided generally in favor of cuprous oxide where the paint is intended for application to steel hulls. Recent shortages of high grade cuprous oxide stimulated intestigations of the use of copper flake and copper powder with a tiew to adapting them for use o\er metal, while eliminating simultaneou*l! the accompanying danger of accelerated corrosion of the steel to which they were applied. The current stud) reports the behaFior of such metallic pigments when dispersed in a typical antifouling matrix and applied to steel under ~aryingconditions. Limitations ha\e been estahlished between which metallic copper may be used safe]? as an antifouling pigment for application to steel. E\idence is pesented to indicate that, abate definite limits, inactivation of the paint will occur, and corrosion of the -tee1 will be accelerated. The maximum limit of pignientation is well aboFe that required for prolonged protection from the attachment of fouling organisms.
I
ALLES L. =ILEXANDER AND ROBERT L. BENEMELISl .\hval
S THE study of iiiitifouling compositions for application t o thc
stcel hulls of ships, significant data have been obtained on thr. optimum pigment-volumt, rt.lation that retard the attaclimc~nt.01' marinc, fouling and siiiiultanc,ously inhibit eseessive corrosion, iii cases where the toxic pigment consists of metallic copper in thca form of flake or pon-der. l-oung and Schneider (3)reported that antifouling efficiency is directly a function of the copper conttxit of the paint, with a stipulated minimum toxic loading for coniplctr protection. T h e studies reported here indicate t h a t toxic loadings above a n established minimum do not improve the dayiiy-day performance, although no consideration is given to tht, total rffective life of such compositions beyond a period of 8 niimths. The galvanic corrosion of steel hulls induced by contact \vith metallic copper is well known. T h e rate of corrosion uf s r w l in contact, with paint containing metallic copper indicates riiat some paints rich in copper flake perform somewhat as a mc~talconductor. I n view of the possibility of accelerated corro,-ion due to presence of metallic copper in paints for steel, most :illtifouling compositions have depended on cuprous oxide as 1111xctive ingredient. I n experiments in vyhich it was hoprd t o cbitablish the efficiency of metallic copper, there n-as evidencts to iiidieatr t h a t loss of fouling resistance resulted in antifouling ],:hints containing high volumes of metallic coppcr when placwl i n rontact with steel. It has been shown (2) that step1 strip. holted t o either primed steel or wooden panels painted with coplxxr flake antifouling formulations reduce markedly the antifouling properties of the film. This phenomenon is analogous t o tht. performance of a sheet of metallic copper employcd in a like role. .idditional evidence ( 2 , 4)indicates t h a t this effect can extend for a distance of several feet from the point of metallic contact, thc. distance and intensity being proportional to the ratio of metallicvopper to the resinous constituents of the formulation. LaQur (1 j reported on experiments at Kure Beach showing that copp(1r paints increase the corrosion of tiare stcel areas above that, mused I y control paints containing no copper. It, was observc.d aiao that intense fouling orcurs near the edges of the bare arcas. Sonic effort, has been made (4)to investigate the elt.etricd cotitluctancc of metallic copper paints on the assumption that tht,y 1
Present address, 1-nirersity of Ciiirinunri, Cincinnati, Ohio
Research Laboratory, Washington, D. C .
possess sufficicritly low reaiitancr t u support galvanic action. The rrported results indicated that, although accc~lcratetlcorrosion does occur and fouling resistance is impaired, thc conductivity of the film iy so low t h a t accurate measurements have twen difficult. The foregoing results indicate t h a t some type of (,I(+ trical contact exists between the pigment particles of highly pigmented antifouling paints and steel areas adjacent to them. T h e effects of Yuch contacts have been observed and reported, and several thcorics have been propovcd a s to the mechanism of this phenonienon. Young (.$) suggested that copper, whether present, in the paint film as oxide or metal, passes into solution, from which it subsequently plates out in the form of metallic copper OII the surface of the metal directly beneath the paint film. This iminediately s e w up a galvanic couple, the nature of which is ncll knovin. This paper presents the results of studies on thc conductivity i i f highly pigmented films and antifouling efficiency when applied to panels of strel and nonconducting media, such as wood and Lucitc. JIEASUREMERTS OF F I L M CONDUCTIVITY
1:arlier published data ( 4 ) indicated the difficulty involved in nieasuring the resistance of pigmented films in the plane of the film, arid no evidence was presented of any extremely low resist,an(-(', such as would be demanded if the antifouling pamt were to cathode in a galvanic couple with the substrate metal to was applied. T o explore such a possibility more thoroughly, a series of antifouling paints was prepared with varying the pigment tieing a highpigment-volume ratios from 5 to -GPO, purity copper flake dispersed in a vehicle consisting of a rosinPliolite-Ilercolyn blend. TWO.spray coats of the paints were inch masked inch applied to Lucite sheets size 3 X 3 X along each edge. After drying, the masking tape [van removed and left a 2-inch square of paint film exactly in the ccintcr of the panel. \Then thoroughly dry, two opposite edges w r e covered with colloidal silver conducting paint, which possesses a resistance of only 0.5 ohm vihen measured longitudinally across 2 X 8 inch strips at a thickness of 2 t o 3 mils. The finished panel is ahown in Figure 1 (rightj. Five sets of identical panels were prepared and permitted t o reach equilibrium in a constant temperaturehumidity room at 25" C. and relative humidity 50%. Duplicates \$-ereprrpared for each paint, and conductivities were determinc*d daily until a constant value was reached b y mcaiis of a mtBgohm Iiridge.. The hridgr is operated with alternating current which is capable of mrwuring resistances from 87,000 ohms to 1,000,000 megohms with an impressed voltage across the unknown resistance of 100 volts. The average resisthnces of duplicate deterniinations art' listed in Table I. .In average period of 1 t o 2 w'vks was required before the values 13 iiie constant. After reaching d i n artificial sua water, ~ v h c ~ r e rquilibrium the panels were imni they w-ero removed at t,he intervals indicated in Table I. Vpon removal, the panels were thoroughly mashed with distilled ivater t o dislodgr any loosely adhcring 5alt particles and roturned to the
1028
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
August 1947
TABLEI. SURFACE RESISTASCE PigmentVol. Ratio, %
10
45 hr.
I
96 hr.
5 10 15 20 25 30 35 40 45
Infinite Infinite Infinite 1.3 x 1010 8 . 0 x 108 3.0 X 108 5.0 X 107 2.4 x 105 1.0 x 108
Infinite 1.25 X 10" 7 5 x 10'0 1.0 x 10'0 1 1 X 109 2 6 X 108 3 0 x 108 8 6 X 108 5 25 X 108
Infinite Infinite Infinite 7 . 0 X 109 2.0 x 100 3.75 x 108 4 . 0 X 107 1.5 x 109 4.0 X 106
1.50 X 10" 1.0 x 10" 3 . 0 X 10'0 5.5 x 100 1.5 X loQ 3.3 x 108 4.0 X 108 9 . 0 X lo6 7.5 X loa
Set 1
" Average resistance of
IS OHMS O F COPPER FLAKE .kSTIFOULISQ PAINT
Set 2
Set 3
I
Couple h-0.
'&
70
Current in .\Iillianips a i t e r Sonking iur 6 hr. 23 h r . 28hr. 45 hr.
N o current aiter 114 hours.
TABLE111. R E S I ~ T A S C O FE P A I N T FILMS C O L P L E D IYITH STEEL I'ignlr n t Resistance, Ohnis Panel or Yol. r o u p l e So. Ratio, OiC Original After suahiny 1"
2 3 45 5 6 70
8 9 100 11 12 130 14 15 '1
15 15 15 20 20 20 25 25 25 30 30 30 35 35 35
Set 4
144 hr.
I Infinite Infinite Infinite 1.7 x 1.5 X 4 5 X 9.5 X 2.5 X 2.0 X
168 hr. 1 . 5 X 101' 1.5 X 10" 2.8 X 10'0 10'0 1 . 1 x l0lQ 100 1.5 X 109 10' 8.0 X 108 10' 4.1 X 108 108 1.7 X 100 108 1.4 X 109
___ Set 5 216 hx--I
Infinite Infinite Infinite 1.5 x 10'0 9 . 0 x 108 3.1 x 10' 7.1 x 107 1.8 x 108 2.0 x 108
1.75 X 10'1 1.25 x 10" 1 7 x 10'" 1 0 x 10'0 7.0 X 108 6 3 X 108 1.95 X 108 1.35 x 109 1 00 x 10'
duplicate determinations.
C OF I'AIST-STEELC(OL-PLEF T A B L E11. G . ~ L V A X ICVRREST PignientTal. Ratio,
1029
Infinite In filii t e Infinite
1 x 1010 1 . 1 x 10'0 7.8 x 109 1.75 X 10' 1.90 x 108 2.00 x 10' 6 . 0 x 107 6.0 X 10' 6.5 X 10: 4.7 x 107 6 . 8 X 107 5 . 4 x 10'
1.5 2 0
x
x
2.8 x 2 2 x 1 35 x 1.25 x 1 2 x 1 45 x 1.20 x 1.2 x 9.0
2 5 8 5 60 3
x x
10" 101' IO"
109 109
10"
10; 10
10s l01D ins in7
rncoupled controls.
1 (left). The silver-copper paint junction is entirely local, and any galvanic effect resulting from it n-ould not appear in the measurement of the value of the large cell. Five sets of copper paint-steel couples wcre prepared and imnwrscd in sea Twter along with the uncoupled control. All couples were prepared in duplicate for each paint and connected through a IO-ohm resietor. Currents resulting from the couples were dcte~minedprriodically by measuring the voltage drop across the knov-n resistance. Ueasurements Jyere made over a tot,al intc~rvalof 114 hours, at which time no couple prepared from a paint having n pignientvolume ratio beloTv 30Y0 showed any indication of pmducing iueasurable current. The two sets of couples prepared Frmn paints of 30 and 35qc pigment-volume ratio, respwtivr~ly.wacted as indicated in Table 11. i l t the end of 114 hours all panels were removed from tlir >(sa Ivater bath, and adhering salt particles m-ashed from the paiiit films n-ith distilled water. The panels xere returned t o cwritiilions of constant temperature and humidity, where they n t'rc ailowed to remain until constant resistance values wer? obTaincti. These values are shown in the last, column of Table 111. Figurw 4 o w i n g the original resistance before immersirin arc included f o r reference. Tliv dataof Table 111indicate that only the cc*mpositionsi)fhigh to hphavt piglll?nT-VolUme ratio display a n y tr~niit~nt.y
constant temperature-humidity room, where they were permitted to come to equilbirium; resistance measurements were then rvpeated until constant values were obtained. The data of Table I showing the initial resistance values along with values obtained after soaking for varying periods in artificial sea water appear t o confirm earlier conclusions ( 4 ) t h a t even highly pigmented films do not possess sufficiently low resistances in the dry state t o perform as a cathode when coupled t o steel. GALVANIC CURRENT AND COSDUCTIVITY
PIGMENTED FILMS COUPLED WITH STEEL. I n order to determine any current values resulting from coupling heavily pigmented copper antifouling paints with steel, a series of antifouling paints, as described, was prepared with varying pigmentvolume ratios ranging from 15 to 35Tc. Lucite panels size 5 X 5 X ' 1 4 inch were masked '12 inch on three sides and given twcs spray coats of antifouling paint. After thorough drying tht, masking tape was removed and a copper strip I/? inch in n-idtl~ Kas bolted carefully along the edge of the panel which had IIOI been masked. A copper rod had been soldered to the copper strip to serve &s a means of support as xell as a conductor. Biter final assembly all metal parts n-ere covered thoroughly n-ith t\yo coat.. of aluminized spar varnish and then a thick coat of heavy v a s to ensure against any electrical contact hetn-een metal parts and the sea water. A film of the silver conducting paint was applied to the edge of the panel opposite the copper strip to serve as another contact for measuring the resistance across the 4-inch square of paint. The aswmhlerl panc.1 is illustrated in Figurt-,
Figure 1.
Conductivity Panels
1030
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 39, No. 8
\
u\
0 '
I
25
M
15
100
125
i ----
150
175 HOURS
I
I
W T H AGITATION ANO A E R A T I O N
203
225
2%
215
303
325
3M
3I5
IMMERSED
Figure 2. Galvanic Current from Copper-Steel Couple ( t o p )and Copper Paint-Steel Couple (bottont)
cathodes. 111 the casc i~i the couples producing nicwurak)lt currents, the resistancct in the plaiic of the film was reduccd during the course of the experiment to a value characteristic of a good conductor. S o such change occurred in similar pancld uncouplcd with steel. Such behavior could be explained by the, th(bory (4, mentioned earlier that.sonie physical change in the dispositioii o t the copper within the film oceurs during the first fen. hours (11 immersion. STASUARU XNTIFOL-LINGPAIKTCOUPLEUD I I W ~ ~ WLI TYH BARE STEEL. Since the experinleiits described indicatr that highly pigmented films may behave as rathodcs when c~iupledto steel, an experiment was designed in which the amount of tlie current devtAlopcd was folloiwd. Lucite paric~ls 1 foot squaw were given two spray coats of a standard antifouling paint ( I ~ u reau of Ships .2F-23) containing copptlr flalcr dispersed in Vinylit c, a t a pigment-volume ratio of 377;;;. .\iter thorough drying a w p per strip inch in width was bolted across the top of each panel, cart: being taken t o ensure good electrical contact with the paint. A copper rod \vas soldered to the copper strip; after that all metal parts of the sytem were covered with one coat of aluminizid spar varnish and heavily waxed to seal completely all metal p a r k from contact with the sea water. The painted panels along with bare copper controls were coupled to steel panels 1 inch squaw through a 10-ohm resistor. The galvanic current of the couple. was determined by mcasuririg the voltage drop across the resistance, from which the current was calculated readily. The current produced by the couples was measured periodically. The results of a typical experiment are plotted in Figure 2. The current measurements were made under tiTo sets of coiiditions. The sea water was contained in a tank 60 X 30 X 18 inchcs l i n d with cured neoprene and filled n-ith approxinuit i . 1 ~ .
A gear pump having a capacity of 20 gallons per niiiiutc. auka Light itin mixer \vas used to circulate thc \ratt.r fIYJll1 inentcd oue end of the tank to thc othrr. At a point just behind thcx output end of the circulator tern, a stream of air was iiijoctcd i n t o the xvater to enwi'c. a itiuous supply of dissolved o s y y e n Tlic, circulating 5yhtc.m \vas allowed to run continuously during on(. set of c~sperinientsand was discontinued during this othczr. Th~lcuiipliltcb setup is illustrated in Figure 3. Figure 2 s h o w tlic, current produccd by the coppoi~-~t et4 couplcxs a n d the eopprSi' paint-steel couples with and witliiiut agitation of the sea watci'. Thr data for ertch couple trends, r>xcopt a tinw lapst, up t the painted Lucitc hcfow an a This indicates that wiiic penet is necessary hefor(, tht. ri ?aiice betwcen individual particles 01' coppcr i- reduced t o a point !Thew a measurable current ('an tw produced. It is d s o significant that, i n the case of the film 01' copper paint, 1ai.gc:i~currcnt v a l u t ~~ v e r eobtained than with the, copper-steel couple: this might he explained by the fact that H larger effective surfacta ai'ca \vas available becausc of th(, flaky charactcr of the eoppc'r pigmcxnt. The, assumption that individual pignic,nt partick- i n the dry film are in contact, and thus ~ I Y I vide straight-line contluctoi,?;throughout the plane of thcb 1i:iitit film, would providis aii immrdiate explanation for the product i i i r i d magnitude. EIowever, such a hypothesis does not explain thts tinic lapse required prior to thc. produc.tion of an appreviabli. currcnt, nor ran it be reconciled with t h t . data oi' Table I. Again t h e theory (/i) that paints contaiiting coppcr suhinergd i n w a \v2tt(ir produce copper ion, which s u h i ~ -
Figure 3.
(:otidiictivity 4pparatu.s
August 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
gueutly plates out in or beneath the paint film in the form of metallic copper, offcrs a n explanation of the time lapse before the paint film assumes the role of a good conductor. Films of low pigment-volume ratio which showed high resistance t o the passage of current developed the characteristic green or brownish color normally associated with films of this type immerwd in sea water. Upon removal the films were firmly adhering and were removed in the form of a powder n-hen scraped with a knife edge. On the other hand, film?; showing l o x electrical rcssistance, and which developed appreciable currents \Then coupkid with steel, retained a bright metallic appearance, blisi c i r t d , and thereby lost their adhesion to the Lucite. Cncouplcd cvntmls of high pigment-volume ratio behaved in rxactly the same nianiic~ras did the coupled films of lower pigment concentration.
.
STEEL
2
PERFORRIAXCE O F .4RTIFOULIRG PAISTS
1031
3
4
5
6
7
8
111 order to establish the extent to which the observed data apply in a practical demonstration, a series of experimental paints \vas exposed a t Miami Reach to determine the rate and extcnt of fouling which might show sonie correlation with conductivity data. For this study four pigments were selected as ~(JIIows: (a)a high purity cuprous oxide (pyrochemical), ( b ) a proprietary copper pigment consisting of 85-87Tc metallic copper powder, the remainder heing cuprous oxide, (c) a high purity copper flake, and ( d ) a copprr ponder analyzing above 99‘; metallic copper. Each sample of pigment was taken from a production hatch. The pigments were dispersrd i n three matrices a t pigment volume ratios of 12 and 36$. T h e composition of the matrices i n nvight ri is shown in the following tablr:
12
B 75 20
1
R
.I FV. 13.. Rosin M e t h y l abietate Pliolite S-1
87
C
-,a
5 20
Tht~c.t~ coats of each foriiiulation \ \ e r e sprayed on panels of ( u ) i v o d , ( b ) steel primed ivith two coats of fast-dry anticorrosivc. prit1it.r ( S a v y Specification 52-P-18), and (c) primed steel on which a txire window 1-inch square as provided in the center of one tide of the panel. The panels were exposed a t the marine station of the Woods Hole Oceanographic Institution a t l l i s m i Reach, Fla. After 3 months the paints of 12cd pigment-volume displayed no appreciable differences in their ability to prevent attachment of fouling (Table IY). Thcse data describe the behavior of the pigments in matrix ,4. Corroborative evidence was ribtained for matrices B and C but is not reproduced in this paper. .It the end of 3 months the panels of 12% pigment-volume were rtbmoved because of poor phj-sical condition as manifested by sicavrre checking and “alligatoring,” shown subsrquently to have rcsulted from the c:xtremely low pigmentation. During thc expo.GurcJ of the samples inspections were made monthly; the paints \~ic~w rated in terms of percentage of total surface area remaining f r w from fouling attachment. T h e efficiency of ,each pigment disl)ersed in matrix A a t 36% pigment-volume is shown in Figure 4. Cuprous oxide demonstrates the highest degree of protection, all panels remaining perfectly clean (1005 fouling resistance) for rhc. full 8 months, whether applied to steel or wood. Figure 4 (top) s h o w t h a t the copper pigment containing u p to 15?, cuprous oxide performs more efficiently over wood than over primed steel. Figure 4 (center and bottom) a k o demonstrates that a 4 o r t life at high pigment-volume ratios may be expected for copper metal pigments applied to stec.1. This is in direct, rontrast to their behavior on wood, for which good performance is obtained oyer the total period of the rsxperiment. Additional widcnce substantially duplicating matrix A was obtained for the same pigments dispersed in matricw R and C (Table IV). CONC LUSIONS
T h e d a t a indicate t h a t , under certain conditions, matrices pigmented with copper flake and copper powder a t reasonably high
EXPOSURE TIME - MONTHS
Figure 4. Antifouling Efficiency of Copper Pigments ( t o p ) , Copper Flake (center), and Copper J’ow-der ( b o t t o m ) Dispersed in RIatriv .4
Foiiling Ke.&tanre by Months,
Panel 40.
2 ”3
Pignierit Cuprous oxide
24
3
24
Copper pigment
25
5
26 47 6 27
48
Copperflnke Copper powder
Panel XIateriiil Steel n’induu TVond Steel l\indou R-ood Steel 15indov Wood Steel Windou Wood
_ _ _ _ ~ 5;. Protection 2
~
1 100
91
100
91
3 100 100
100
91
100
inn 100 ion ion
88 85
100 92
89
100 100
100 100 100 100 100
1 on
100
100
100
ion
100 93 100
in0 100
ion
1032
Vol. 39, No. 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
pignient volunitrs may l>respectec! t o peifonii coupled n-itli stcvl and immersed in thc sea, a (al~ovc,23$ pigment-volume ratios) retain resistance valuv stic of extremely poor conductors nlien uncoupled a n Klien placed in t h e role of a cathode, an initial time c.c;uiied in ivhich the copper particlea u i i t cliange in their relative position t o each othei,, oitbLei breakdo1r-n occurs in tlie resistance of iritervciiiiig t); lators iornietl by envelopes of the matiis. or c o p i ) ~ ~j i solution ant1 redeposits according to a theory (4)p r t ~ p o . > tt>:irlirr. ~l In tht, cast’ of l o x pigmentation the distancc bctn-ccn the iiiqjority of pigment particles is so great that, the insul:iting p i i ) i of thc, organic matris are not disturlird by the intensity applicd pot t,iJtial, and no significant change o c ~ u r sin tlie ~ I < the ~ Q film. a n w ] ) V I ~ I L ~ ~ uf Therefore, it seems obvious t h a t a tl valiir for pigmentation with ic copper pigments somrn-here tJetneen 25 and 30 ent-volume for nixof the type listed here. Abo crititzal value nullificiition of antifouling properties of the paint ni n-lien t h r paint is coupled with steel. -1.3 a ri couple, a corresponding acceleration in the rate of corwsion 01 the steel should follow. T h e d a t a do not indii.:ite that similar behavior niay bc espected of cuprous oyide. The quantitative d a t a obtained from specific paint-steel couples [vas substantiated experimentally by tlie behavior of paints rsposed in the sea t o a n environment of high fouling intensity. Theoretically, films containing a high volume of metallic pigment and performing as a cathode should foul readily. This as t h e case among t h e samples exposed a t lfiaiiii 13each.
Similarly, i e s highly pigniente(1 foiniulxtioris (vitii metallic copper) [>eI’f~Jrlii equally \ d i \rhcttlicir applied to stwI or wood. Finally, cuprous oside paints are apparently etlually effective whether used over wood or metal, irrespctctive of pigment concentration. t c i i \ ow LE u(; \I E \ -r
,l.;ton anti Scott Ewing of n ~ s,iggestious i in the course
LITE:R.\TLRF: C I T E D
1) LaQ1.ie. l:. L., Interiiatioiial Sickel C o . Kept. on Specimens Reinox-ed f r o m K n r e Beach. \-. C. (AIay 1941). ( 2 ) Koa?, Hole Oceanographic Institutioti’s h I o n t h l > ~Rcpt. t o Bur. of Ships (Sept. 1, 1914.) ‘3) ITourtg. 12.H., and Schneider, W.K , , ISO.ESG. CHEM.,35, 438 (1943). (4) l-ouiig. G . €I., Seagren, G . IT.,and Zehner, *J. C.. Ihid., 37, 461 (1915). ’
PRESENTED before t h e Di\.i\ion of Paint. Vnrni.sh, a n d Plastics Chemistry at the 110th LIeeting of t h e .-\MERICAN CHEMICAL SOCIETY.Chicago, Ill.
Catalytic Cracking ot Pure Hydrocarbons T
(:RACKI;NG OF STRUCTURAL ISOMERS
HE catalytic cracking of fiitp-siu pure hydrocarbons a n d a comparison of hydrocarbon classes have been reported in the first five papers of this series (1, b, 3 , 4 6 1 . No detailed study was G. 31. m a d r of the influence of structural isomerism upon the extent of cracking and product composition. However, a large difference was observed in the extent of cracking of normal and isopropylbenzenes and but a small difference in the case of n-dodecane and highly branched isododecane. These data and other observations made previously led us to further experimeuts and study designed to show the effect of structural isomerism on the cracking behavior of certain hydrocarbons. This n-ork esaniines and comp a r e the behavior of (a) the five isomeric hesanes, ( b ) cyclohexane and methylcyclopentane, (c) n-octane and 2,2,4-trimcthylpentane, ( d ) a-propylbenzene and isopropylbenzenc,. ( e ) three isomeric butylbenzenes reported earlier ( d ) , (f)n-dodecyrir and isododecane reported in the first paper (Ij, and ( g Decalin and 2,7-dimethyloctane, a naphthene and paraffin of 10 rarhon atonis each. ~
~~
EXPERISIENTA L P R O C E D U R E
Ikfinitions and terminology are the same as given i n the first paper ( 1 ) except for the “percentage dccomposcil” o r “estent of cracking” which now includes the hydrogen in thc coke, as \vel1 as carbon, gas, and liquid boiling below the origiuiil, all sumnietf on a no-loss weight basis. EIydrogm and c u b o n weic determined by the hurning of the catalyst deposit iii a n osygcn-nitrogen atmogphere, conversion of carbon monoxidc fornicd to carbon dioxide over copper oside, and absorption anti weighing of tht, i different lot of U.O.P. Rater anti carbon dioxide produced. ; cracking catalyst, type B, of slightly higher activity was used. This catalyst gives results similar to those obtained with the synthetic silica-alumina catalysts currently employed on a la.rgP scale in the petroleum industry.
GOOD, H. H. YOGE, ATD B. S. GREESSFELDER Shell Development C o m p a n y , Emerycille, Calif.
1Iodifications in the original procedure (1) follow: Reactiou products from the vertical catalyst, tube were led directly t o a still kettle cooled by solid carbon dioside. Cncondensed gases passed through a meter to a 255-liter holder containing saturated magnesium sulfate brine. -kt the end of each process period the system was purged directly with 2.8 liters of nitrogen into t h e gas holder. For the experiments with Decalin and 2,7-dimethyloctane, 57 cc. of catalyst \Yere used in a type 302 steel tube with a n inside diameter of 1.58 a n . , a. described previously ( 2 ) . Hexanes and octanes were cracked in a steel tube of 2.66 cm. i.d., with ‘200 and 90 cc. of catalyst, respectively. Xethylcyclopentane and cyclohexane were cracked in a steel tube of -1.08 cni. i.d., with 200 cc. of catalyst. In the larger tubes silira chips
Crachitig of six sets of isomeric hydrocarbons ober a silica-zirconia-alumina catalyst was studied, with emphasis on the behabior of the hexanes. Some large differences in rate of cracking arid product composition were observed within these sets, which can be correlated with the carbon atom groupings of the isomers. In particular, tertiary carbons enhance the crackability markedly, and quaternary carbons act in the opposite way. Comparison of a paraffin and naphthene of selected C,, structure pro5 ideb added information on cracking behavior.
