OCTOBER 1947
767
of different design and mznufacture, grating instruments as well as prism instruments, differ widely in their ability to transmit t h e two kinds of plane polarized light. These transmission characteristics of spectrographs for polarized light are largely responsible for much of the variation in intensity measurements quoted in the literature. The author ( 2 ) has shown how true relative intensities can be measured in Raman spectra. For the convenience of the reader, the derivation of the equation for the true intensity in terms of p n , the depolarization factor for natural unpolarized exciting light, and T , the transmission factor of the spectrograph for the two kinds of plane polarized light, are given beloly.
The transmission of an instrument, T ,for natural unpolarized light is
T
=
So’Po [unpolarized]
(1)
where So is the intensity measured for the perpendicular ( I ) component, the electric vector vibrating in the vertical plane, and P o the intensity for the parallel (11) component, or electric vector vibrating in the horizontal plane. Then p,,, the depolarization factor for a polarized line, will be given by
If I t represents the true intensity of the line in question and IO represents the observed natural intensity of the spectrum line, the following relationships result:
+ Io = Po (1 + It = Po (1
Pn)
(3)
PnT)
( 4)
from which is obtained
The scattering coefficient K Oreferred to in the previous paper is defined as
where Io is the observed intensity of the line in question and IO. is the A V = 459 cm.-’ line of carbon tetrachloride-Le., the standard line. The true scattering coefficient, as would be observed by means of a n instrument which did not preferentially transmit one kind
of plane polarized light, we shall call K1. means of the following equation.
K Ois related’to K , by
where superscripts I and s on the pn’s refer to the line in question and the standard line, respectively. The part of the fraction involving only p: and T is a constant for all lines observed under a given set of experimental conditions. Then Equation 7a becomes, for the purposes of transforming the data of the preceding paper ( 1 ):
Let us call the right-hand side of Equation 7af(p,, T ) . I n Figure 1f(p,, T ) !s plotted against pn, using a value of T = 0.90 as was observed in ( I ) .I n order to find K t it is only necessarv to multiply thej(p,, T ) value for a giyen p a by the K Oobserved by Fenske and his collaborators. I n Figure l f ( p n , T ) is also plotted against p n for various values of T ranging from T = 0.3 t o T = 1.0. If a Kt value is known from the data of Fenske et al. the K Ovalue can be obtained for a given instrument bv dividing the value of f(p,, T ) (for a given T appropriate to the instrument in question) into K,. The treatment given above is applicable only to experimental conditions where true t’heoretical depolarization factors are experiment,ally achieved. The method of excitation used by the author and his collaborators (3, 4)has been shown to fulfill these conditions. A recent paper of the author’s has shown that the cylindrical lens method of excitation yields. quantitatively theoretically correct values of p., pe, and p p . Two additional observations concerning the excitation of Raman spectra might be pertinent. The cylindrical lens method of excit,ation, properly used, is the most powerful method of excitation with Tvhich the author is acquainted. The original Wood’s light furnace method of escitation does not yield theoretically correct depolarization values when used in the ordinary manner. LITERATURE CITED
(1) Fenske, M.R., Braun, W.G., Wiegand, R. V.,Quiggle, D., >ICCormick, R. H., and Rank, D. H., .%SAL. CHEM.,19, 700 (1947). ( 2 ) Rank, D. H., J . Optical SOC.S m . ( t o be published October 1947). (3) Rank, D . H., Pfister, R. J., and Grimm, H. H., I b i d . , 33, 31 (1943). (4) Rank, D. H., and Wiegand, R . V., I b i d . , 36,32.5 (1946). RECEIVED ,June 1, 1917
System for Rapid Evaluation of Catalysts for Production of Butadiene from Ethanol SI. H. WHITLOCK’, G. J. H.kDD.ID, ‘ Mellon
AND E. E. STAHLY Znstitute of Industrial Research, Pittsburgh, Pa.
T
HE great number of chemical combinations that must be investigated in a catalyst development program make the use of some type of screening test essential. This program was based on the testing of five hundred catalysts per year, with each material evaluated a t five different condit,ions. I n order to meet t,hese requirements, it, was necessary to be equipped to handle a t least ten catalysts per week, plus a control; it was also desirable t,o be able to do special work on a t least one mat,erial. Laboratory production of large batches of cat,alysts is a slow time-consuming procedure; it is very much easier and quicker to prepare a small quantity of most catalysts. These factors were the 1 Present address, Reeonstruction Finance Corp., Office of Rubber Re‘serve, Washington 25, D. C.
guides which led to the design of an apparatus to evaluate simultaneously twelve materials using only 20 cc. of each catalyst per test. S\IhLL-SCALE TESTIXG UNIT
h small-scale testing unit was designed, which consists essentially of the feed system, reactor, separation and collection system for C, and lighter hydrocarbons, and sampling system. The main requirements of such a unit are: (1) constant, feed rate for very small rates of f l o for ~ the alcohol feed mixtures, ( 2 ) accurate control of reactor temperature, (3) continuous separation and collection of a C, and lighter fraction. free from traces of acetaldehyde (and other osygen-containing compounds which might
V O L U M E 19, N O , 1 0
768
Inorder to evaluatein a short time a large number of new catalysts for the production of butadiene from alcohol, a multiple-test apparatus has been developed t h a t appraises twelve catalysts sirnultaneously. As only 20 m. of catalyst are required for each test, the apparatus permits the evaluation of catalysts which are difficult or time-consuming to prepare i n large quantities. A feeder enables liquid addition a t rates as low as 6 eo. per hour w i t h an accuracy of *lo%. Gaseous products are scrubbed
interfere with subsequent, bul.adiene analysis), and (4) all curate measure of the C6fraction collected. A flow diagram for a single unit. developrd tu fill t,hr?sr nmds is shomn in Figure 1. Feed is supplied from a constant-rate buret, 1, l o the reaction tube, 2, which consists of a 95-cm. (3Ginch) length of 13-mm. outside diameter Pyrex tubing, includinga preheat seet,ionpacked with glass beads followed by the bed section containing 20 cc. of catalyst. The side an the top of the reaction tube is connected nitrogen supply, 5, and to a water manom 6. The nitrogen is used for flushing out system a t the beginning and end of each Manometer 6 measures the difference in pressure between the reactor and the atmosphere. It was found necessary to insert the trap, 4, in the side-arm connection in order to prevent the manometer liquid from being drawn into the reactor in ease of a pressure drop in t.he system. The reactor. 2. is heated bv a n electric furnace, 3. fitanhard-taper 12/36gmund joints,
to remove d u h l e components stid ,wlleeted by displacing a salt. solution in a eonst,ant-pressure system. Gas samples are taken by Imercury displacement for analysis by chemical or physical methods. This apparatus is applicablie to catalyst -"A "F studies in which the feed is i n a liquid suoh a nature that it may be separated fmm the lowboiling products by countercurrent scrubbing. Soluble products may be separated by the use of aF
-.
7;md 7-iIlin. k'yrex tubing are U S P ~t,o cotivey the product to Llw separation train. Separat,ion of the water-solublr and higher-boiling components is by of a 9, fractionation column 3G0 mm. long and 15 mm. in diameter packed with 0.3-cm. (0.125-inch) Pyrex helices, 10. Water for scrubbing is supplied from a constant-head reservoir, 8. Liquid iractionx ape collected in a flask, 11, which is kept a t a gentle hoil hy a hont,ev, 12; t,he hoiling drives nbsorhed or dissolved
Figure 2. General View of Multiple,-Test Assembly
gases back uu the fractionation coluinn.
Figure 1. Flowmiagram of Single-Catalyst Test Unit
Gaseous products come
present in t,he gas,'the indicator chan kes color ?from blue co vellow). The gas from the bubbler is ,rollected in bottles, 14,"by displacement of a sodium sulfate sobution. The pressure of the whole system is controlled by adjust,ing the height of outlet B with resneet, to eas inlct A . At the
