7 54
T H E J O U R h T A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Great differences will be noted in t h e results. For instance, a t ordinary temperature, 1 7 . j" C., t h e vapor pressure of cleaners' naphtha is 4 0 mm. of mercury; of 61' BC. gasoline, 8 2 m m . ; of 69' Bi..gasoline, I I O mm.; and of 73' Bi.., 2 1 2 mm. When these vapor pressures are expressed in terms of t h e percentage by volume of gasoline vapor t h a t will mix with air a t the temperatures given, t h e results become: Cleaners' naphtha, 6 4 O Be. gasoline,
69' BC. gasoline, 73' Be. gasoline,
401760 X 100 = 5 . 0 per 8 2 / 7 6 0 X 100 = 1 1 , O per 11OIi60 X 100 = 15.0 per 212/760 X 100 = 2 8 . 0 per
cent cent ce,nt cent
I n other words, air will uniformly mix with almost 6 times as much vapor from 73' B4. gasoline as from cleaners' naphtha a t a temperature of I 7 . j O C . Gasoline is not a definite compound and the specific gravity test is a poor criterion of t h e nature of a particular distillate; hence, t h e above figures are only approximate t o what t h e vapor pressure of different distillates from gasoline of the specific gravities given must be, b u t they indicate t h e relative danger of explosions due t o dumping into a sewer gasoline of different grades. S L- M M A R Y
One barrel ( 5 j gallons) of gasoline dumped into the sewer, all a t once, resulted in t h e formation of a n explosive mixture for a few minutes only a t any one particular point. This condition existed close t o t h e surface of t h e sewer water and did not extend very far into t h e upper sewer air. When one barrel ( j j gallons) of gasoline was dumped into t h e sewer a t t h e rate of j gallons per minute, t h e highest percentage of gasoline vapor z feet above the sewer water was 0 . 7 0 per cent. The gasoline vapor was practically all swept past the manholes in Under these same conditicns from 18 t o 30 minutes. of test, except with t h e velocity of the sewer mater much less, dangerous atmospheres existed in t h e sewer 5 hours after the gasoline was poured in. A C K Ii0 W L E D G M E N T S
T h e authors wish t o acknowledge the valuable assistance rendered t h e m in conducting these tests, b y hIr. W. H. Coster, Superintendent of t h e Board of Fire Prevention, Dept. of Public Safety, hIr. XI. S. Evans, Chief of the Bureau of Tests, and hlr. J. Chas. Palmer, Division Engineer, Bureau of Highways and Sewers, all of the staff of the Department of Public m'orks, City of Pittsburgh. They were present at all tests, made numerous suggestions and helped in many ways. XIr. X. S. Sprague, Superintendent of t h e Bureau of Engineering, City of Pittsburgh. also rendered valuable assistance. 1;.
s.
BUREAZ:O F MIXES. PITTSBURGH
THE ANALYTICAL DISTILLATION OF PETROLEUM-11' By W. F. RITTMANA N D E. W. DEAN Received June 26, 1915
I n a previous paper2 attention was called t o the need in t h e scientific and in t h e commercial petroleum world of an accurate and satisfactory method for the quantitative distillation of crude oil and its products. 1
2
Published with the permission of the Director of the Bureau of Rlincs. Rittman and Dean, THISJOURNAL, 7 (1915), 185.
Vol. 7 , No. 9
T h e results of a series of redistillation experiments showed t h a t a method of efficient separation, involving the use of a Hempel column of moderate dimensions, attained a degree of separation of 56 per cent, on t h e arbitrary and empirical scale fixed by experimental conditions. The Ubbelohde-Engler method, representing moderate separation, was rated a t 26 per cent on the same scale. T h e Allen-Jacobs method of minimum separation obtained a degree of separation of 14 per cent. I t was shown also t h a t a single Hempel distillation was more efficient t h a n t w o successive open flask distillations. SCOPE O F THE P R E S E N T P A P E R
The experiments described in the present paper deal chiefly with a comparison of results attained by t h e use of various types of fractionating apparatus. Crude oil distillations have been made with representatives of nearly all types of still-heads nov.7 in use and figures are given which should be readily intelligible t o t h e petroleum technologist. Attention has been given in the experiments both t o degree of efficiency attained and t o mechanical details. I n the earlier paper no attempt was made t o determine t h e relative advantages of various specific methods. I t mas, however, clearly indicated t h a t the class involving efficient fractionation seemed most promising, as they attained most nearly the desired end, which is the separation of the oil into its constituents. The method of minimum separation seems t o have advantages for t h e examination of emulsified or difficultly distillable oils b u t i t involves rather tedious manipulation, and for t h a t reason a s well as o n account of its inherently inefficient fractionation, it is not t o be recommended for general use. The whole problem, except for the matter of "cracking," seems t o resolve itself into applying t h e principle of efficient fractionation in some way which will be satisfactory t o t'he laboratory worker. A further series of experiments has been outlined which should furnish definite and conclusive evidence v-ith regard t o the matter of cracking. I t seems improbable, however, t h a t the results obtained will alter in any way the conclusions drawn from t h e present investigation. With Pennsylvania crude oil there is strong evidence t h a t no cracking occurs a t temperatures up t o a t least 3 0 0 ' C. and in addition it has been shown t h a t the possibility of cracking is b u t slightly greater with efficient t h a n with moderate separation. G E S E R A L OTJTLISE O F PROCEDURE
I t was decided t o make first a comparison of stills from as comprehensive a list as would in any possibility be available to the petrole\um chemist. Stills were not. however, purchased indiscriminately but consideration was given in most cases t o t h e possibility of too efficient condensation. At temperatures ranging betxl-een . 2 j o o and 300' C. any moderately long tube mill act as an air condenser and, on this account, few still-heads of excessive length were secured. Still-heads of all types listed in t h e catalogues of chemical supply houses were purchased and. i n
S e p t . . 191 j
T H E J O I ' R N A L O F I S D C S T R I A L & 4 N DE N G I N E E R I N G C H E M I S T R Y
addition, several not in common use, b u t of theoretical importance, were made t o order.' A Io-gallon sample of Pennsylvania crude petroleum was obtained a n d portions were used for all distillations of t h e series. Efficiency of separation was not measured b y t h e rather tedious method outlined in t h e previous paper, as results sufficiently explicit for present purposes could be more easily obtained. T h e
75 5
E X PE RIME X T A L DETAILS
KO modifications were made in t h e procedure outlined for the earlier series' of experiments except in the matter of rate of distillation. This was increased somewhat and kept approximately the same as t h e standard among petroleum technologists. which is z t o 2 . 5 cc. per minute. A11 results are recorded in terms of percentage by
f "-bulb Wurtz
a ?-bulb pear
i
Ile K o u i n k
Sorton & Otto
1.e Bel tienningev
FIG.
I-TYPES
OF
magnitude of the first c u t was taken as an indication of relative degree of efficiency and it was found possible t o differentiate t h e various stills with entire clearness on this basis. Experimental work was divided into three general sectioTs: I---Comparisons were made of the 1-arious types of still-heads. From the results of these experiments one t y p e n-as selected which was clearly indicated as most desirable. II---Ai careful s t u d y mas macle of the results obtained h y various modifications of t h e selected type. 111- Some experiments were performed t o s t u d y possible cracking effects in t h e particular still which the earlier experiments had indicated as most a d vant ageou s. I Special glass apparatus a a b constructed by hlr. F. E. Donath, glass blower in t h e Pittsburgh laboratory of t h e Bureau of Mines. Metal apparatus was made by I f r . XV. F. Hausstein, chief instrument maker in the Pittsburgh laboratory of the Bureau of Mines, and b y M r . 11'. F a r n h a m of the Industrial Department. Havemeyer Chemical Laboratories of Columhia l'niversity.
APPARATUSSTUDIED
%-eight. Unless otherwise specified, initial charges of zoo grams were employed. Several of t h e distilling \-essels were made with bulb and fractionating column in one piece. Most of t h e still-heads were, however. detachable and were employed in connection with a z j o cc. copper Kjeldnhl flask which had been modified (see Fig. I) so as to permit the easy measurement of tcmperntures of the liquid oil. The cork joints between distilling bulb and fractionating column proved troublesome b u t it was found t h a t b y thc exercise of sufficient care t h e y could be made tight with a paste of litharge a n d glycerine. The results obtained by the intli\-idual stills are shown in Table I. These are of little interest in detail unless it is desired t o learn the charactcristic behavior of a n y special type. Specific grai-ity figures have been obtitined in all cases b u t do not w e m t o be particularly instructive. Of more importance are 1
Rittman and Dean, LOG.izt
v01. 7 , NO. 9
T H E J O C R L Y , l L O F I A V D C S T R I A L AaVD EAVGINEERIiVG C H E M I S T R Y
756
TABLEI-RESULTS
DISTILLATIOKS MADE WITH VARIOUSC O L U M N S SHOWN IN F I G . 1 Z-Retort(a) (250 cc.) Thermometer bulb I-Allen and Jacobs Immersed Just below At middle 3-Lunge T a r Flask(a) Percentages Specific gravities in liquid outlet of outlet Percentages Specific gravities T e m p --a_-T e m p Per Sp. Pet Sp. Per Sp. T,emp. C. A B C Av. A B C Av. ' C . cent gr. cent gr. cent gr. C. A B C Av. A B C Av. 125 0 . 9 1 . 0 1 . 0 1 . 0 . . . . . . . . . . . . . . . . . . . . 100 0 . 0 . . . . . 0 . 5 . . . . . 2 . 1 0.689 100 0 . 8 0 . 7 1 . 6 1 . 0 . . . . . . . . . . , , ; . , ..... 150 4 . 9 5 . 2 4 . 9 5 . 0 0.708 0 , 7 0 9 0.707 0.708 125 0 . 8 . . . . . 2 . 5 0 . 6 9 1 4 . 5 0.729 125 3 . 8 3 . 9 4.2 4 . 0 0.699 0 . 6 9 6 0 . t 0 6 0.700 175 7 . i 7 . 5 7 . 8 7 . 6 0.732 0 , 7 3 4 0 , 7 3 3 0 . 7 3 3 150 4 . 1 0.701 8 . 7 0 . 7 2 4 7 . 6 0.733 150 7 . 7 7.7 7.1 7 . 4 U.727 0.727 0 . 7 3 0 0 . 7 2 8 200 7 . 7 7 . 9 7 . 8 7 . 8 0 . 7 5 3 0.754 0.752 0.753 175 z . 0 0.729 8 . 3 0.747 1 0 . 0 0.756 175 7 . 8 9 . 1 8 . 4 8 . 4 0 . 7 4 8 0 , 7 4 7 0.751 0.749 200 8 . 4 6.8 7 . 8 7 . 6 0.765 0.763 0.767 0.765 225 7 . 6 7 . 4 7 . 5 7 . 5 0 . 7 6 6 0.767 0.768 0.767 200 1 . 3 0 , 7 4 7 8 . 3 0.764 1 1 . 0 0.773 250 7 . 1 7 . 1 6 . 8 7 . 0 0.778 0.779 0 . 7 8 0 0 , 7 7 9 225 7 . 0 0.762 8 . 3 0.780 6 . 7 0.789 225 5 . 8 7 . 8 7 . 4 7 . 0 0.777 0.777 0 . ! 8 0 0 . 7 7 8 275 6 . 5 6 . 7 7 . 0 6 . 7 0 , 7 8 9 0.790 0.789 0 . 7 8 9 250 6 . 5 0 . 7 7 3 6 . 8 0.792 8 . 0 0.798 250 7 . 3 6 . 2 6 . 1 6 . 5 0 . 7 8 7 0.789 0 . , 9 3 0.790 275 6 . 0 0 , 7 8 4 6 . 5 0 , 8 0 4 9 . 1 0.816 275 6 . 1 6 . 3 6 . 5 6 . 3 0.797 0.799 0 , 8 0 2 0.799 300 6 . 5 6 . 3 5 . 9 6 . 2 0.799 0 , 8 0 0 0 . 8 0 0 0 , 8 0 0 3 2 5 6 . 2 6 . 6 6 . 9 6 . 6 0.809 0.811 0.811 0 . 8 1 0 300 8 . 1 0.797 7 . 4 0 . 8 1 3 , . 3 0.827 300 7 . 4 7 . 3 7 . 5 7 . 4 0.810 0 . 8 1 1 0.814 0 . 8 1 2 Averaee variation. 2.1 oer cent Averaee variation..~5.9 Der cent 4-Ubbelohde-Engler (Modified) ( b ) 5-Plain Distilling Tube(a) 6-Two-bulb Wiirrz(a) Height, flask t o outlet, 6 inches Percentages Specific gravities Height, flask t o outlet, 3 inches Temp. Percentages Specific gravities Temp-.Per Specific Temp. C. cent gravity "C. A B C DAv. A B C D Av 'C. A B CAv. A B C Av. 100 4.4 0.680 100 2 . 6 2 . 7 3 0 3 . 0 2 . 8 0.678 0.683 0.683 0.683 0.682 100 3 . 2 2 . 8 3 . 2 3 . 1 0.683 0 . 6 8 8 0 . 6 8 5 0 685 0.715 0.715 125 5 . 3 0.718 0.714 0 , 1 1 5 125 5 . 1 5 . 7 5 . 3 5 . 5 5 . 4 0.712 0.713 0.715 0 . 7 1 4 0.713 125 4 . 8 4 . 9 4 . 8 4 . 8 150 7.0 0.i41 150 7 . 9 7 . 7 7 . 6 7 . 8 7 . 7 0 , 7 3 7 0 . 7 3 8 0.738 0.739 0.738 150 ~5 7 . 3 1 . 3 7 . 4 0.738 0 . , 3 7 0.737 0.737 I75 7 . 2 7 . 9 2 . 6 7 . 0 7 . 4 0.755 0.257 0.756 0 . 7 5 7 0.756 175 8 . 0 8 . 0 8 . 4 8 . 1 0 , 7 5 7 0.755 0 . 7 5 6 0 . 7 5 6 Column flooded, due to 200 7 . 9 7 . 5 7 . 2 7 . 5 0 , 7 7 1 0 , 7 6 9 0 , 7 7 0 0 , 7 7 0 small bore of tube from 200 2 . 8 6 . 9 f . 4 7 . 5 7 . 1 0 . 2 6 9 0 . , 7 0 0 , 7 7 1 0 , 7 7 2 0.771 225 / . I 6 . 9 6 7 7 . 1 7 . 0 0 . / 8 2 0 . 7 8 3 0.782 0.783 0 , 7 8 2 225 6 . 6 6 . 9 7 . 3 6 . 9 0.782 0.781 0.782 0 . i 8 2 flask t o first bulb. 250 7 . 0 7.5 6 . 6 7 . 0 0.795 0 , 7 9 3 0.794 0 . 7 9 4 250 6 . 8 7 . 3 6 . 7 6 . 8 6 . 9 0 . 7 9 4 0.795 0.794 0 . 7 9 4 0.794 275 6 . 7 7 . 1 6 . 5 7 . 1 6 . 8 0 , 8 0 4 0 . 8 0 6 0 . 8 0 5 0 . 8 0 5 0 , 8 0 5 275 7 . 2 7 . 3 7 . 1 7 . 2 0.806 0 . 8 0 4 0 . 8 0 6 0 , 8 0 5 Average variation. 3.3 per cent Average variation, 2.5 per cent 7-Four-bulb Pear(a) 8-De Konink(a) 9-Sorton and Otto(a) Height, flask t o outlet, 9 inches Height, flask t o outlet, 8 inches T,emp. Height, flask Pert o outlet, Specific 9 inches Percentages Specific gravities Tzmp. Percentages Specific gravities A B C Av. A B C Av. C A B C Av. A B C Av. C. cent gravities 100 4 . 5 4 . 9 4 . 9 4 . 8 0.682 0.682 0.682 0 , 6 8 2 100 4.9 0,683 100 4 . 3 4 . 3 4 . 5 4 . 4 0.681 0.681 0 . 6 8 0 0.681 125 5 . 6 5 . 5 5 . 7 5 . 6 0 , 7 2 2 0.727 0.721 0 . 7 2 3 I25 5.7 0,726 125 5 . 7 5 . 1 5 . 8 5 . 5 0.722 0 . 7 2 2 0 . 7 2 2 0.722 150 7 . 1 6 . 7 7 . 0 6 . 9 0.744 0 , 7 4 5 0 . 7 4 4 0.744 150 6.7 0.744 150 8 . 5 9 . 2 8 . 0 8 . 5 0.745 0 . 7 4 4 0 . 7 4 3 0.744 175 6 . 4 7 . 0 6 8 6 . 7 0 . 7 5 9 0.759 0 , 7 5 8 0.759 ii5 6.8 0 760 175 / . 0 7 . 0 7 . 3 7 . 1 0.761 0.764 0.760 0 . 7 6 2 200 ,.2 0.773 200 6 . 9 7 . 5 6 , ) 7 . 0 0 , 7 7 0 0.771 0 , 7 7 2 0 . 7 7 1 200 6 . 1 6 . 7 6 . 6 6 . 5 0.773 0.775 0.773 0 . 7 7 4 Column flooded, due t o narrow225 6 . 9 6 . 3 6 5 6 . 6 0.782 0.782 0.782 0.782 225 6 . 2 6 . 2 5 . 8 6 . 1 0.784 0 . 7 8 6 0.783 0.784 ness of tubes 250 6 . 5 6 . 5 7 . 0 6 . 6 0.792 0.793 0.793 0 . 7 9 3 250 7 . 2 6 . 2 6 . 7 6 . 7 0.794 0.795 0.793 0 . 7 9 4 275 7 . 0 7 . 1 6 . 8 7 . 0 0.805 0 , 8 0 6 0.805 0.805 275 7 . 2 6 . 6 7 . 3 7 . 0 0 . 8 0 7 0.806 0.805 0 . 8 0 6 Averaee variation. 3.8 Der cent Average variation. 2.9 Der cent 10-Glinsky, with Glass Valves(a) 11-Young and Thomas Dephlegmator(c) 12-Twelve-Bulb 13-Le Bel14--Golodetz(c) Pear(a) Henninger(a) (copper) 18 inches 12 inches 8 inches Height, flask t o outlet. 9 inches Height. flask t o outlet. 10 inches T e m p . Percentages Specific gravities TEmp. Percentages Specific gravity Temp. Per Specific Per Specific Per Specific C. A B C Av. A B C Xv. C. A B C Av. A B C Av. C. cent gravity cent gravity cent gravity 6.2 0.682 0.682 0 . 6 8 3 100 5 . z 0.682 5 . 9 0.684 100 5 . 6 5 . 9 5 . 2 5 . 6 0.686 0 . 2 8 8 0.681 0.685 0.730 0.730 125 6 . t 0 . 7 3 1 5 . 8 0.730 5.7 0.732 125 5 . 9 6 . 1 5 . 4 5 . 8 0 . 7 2 5 0 . , 2 6 0.723 0.725 6.4 0.748 0 . 7 4 7 0.747 150 6 . 1 0.749 7 . 0 0.749 150 6 . 8 7 . 7 8 . 2 7 . 6 0.746 0 . 7 4 8 0.746 0.747 8.0 0.765 0.763 0.763 175 7 . 1 0 , 7 6 4 6 . 1 0 . 7 6 3 175 6 . 9 7 . 1 7 . 3 7 . 1 0.759 0.762 0.761 0 . 7 6 1 n 7. . .9 0.772 0.772 200 7 . 0 0 , 7 7 6 6 . 7 0.775 - . 7. 7. 7 200 5 . 8 6 . 3 6 . 6 6 . 2 0.772 0 . 7 7 5 0.774 0 . 7 7 4 0 . 7 8 3 0 , 7 8 3 225 6 . 1 0 , 7 8 5 co.lumn. . . 8.5 0.792 225 6 . 8 6 . 7 6 . 8 6 . 8 0.783 0.785 0.785 0 . 7 8 4 8 . 0 0 ,804 0.795 0 . 7 9 5 0 . 7 9 4 0 , 7 9 4 T h e column 0 . 7 9 3 0.797 250 6 . 2 7 . 4 6 . 2 6 . 6 0 . 8 0 5 0 . 8 0 5 flooded, due t o flooded and Results abnormal. 275 6 . 6 6 . 7 7 . 2 6 . 8 0 . 8 0 5 0 . 8 1 0 0.808 0.808 excessive reflux stopped dis- Strong indications of Averaee variation. 4.1 Der cent condensation. tillation. cracking (see p. 757). Ij-Hempel(c) (Diam.: 1 in. Beads: 5 in.) 16-Rod and Disk(a) 17-Three-Section Evaporator(c) Height, flask t o outlet, Height, flask t o outlet, 10 inches Height, flask t o outlet. 6 inches Percentages Specific gravities 18 inches Percentages Specific gravities Temp.Per Specific Temp. o C . A B C D E F . 4 v . A B C D E F Av. cent gravity C. A B C D 4 v . A B C D Av. 6.5 0.685 100 6.2 6.9 6.5 6.7 6.6 0.684 0.687 0.687 0.$87 0.686 100 6.2 6 5 5.9 5.9 0.732 125 5.4 6.8 6.0 6.0 6.0 0.729 0.734 0.731 0 . < 3 20.731 125 6.4 6.0 6.5 6.4 0.749 150 6.7 6.3 7.4 6.5 6.7 0.749 0.752 0.751 0,750 0.751 150 5.6 6.2 5.9 7.0 0.764 175 7.2 7.0 7.1 7.1 7.1 0.761 0.766 0.765 0.763 0.764 175 7 . 0 6.9 6.7 200 6.4 5.6 6.9 6.5 6.3 0,774 0.775 0.776 n 77.5 0.775 6.3 0.775 200 6.2 6.2 6.3 2.5 0.785 225 6.4 6.4 5.1 6.6 6.1 0.783 0.784 0.783 6 7 8 s 0 784 225 6.5 6 . 4 6.4 ,.I 0.797 250 6.7 6.6 6.9 6.4 6.7 0.795 0.792 0.792 0 792 0.793 250 6.9 6.1 6.5 Distillation stopped 275 7.1 6.9 6.5 7.1 6.9 0.807 0.808 0.808 0 806 0.807 275 15,517.0 6.9 b y excessive refllx Average variation, 4.3 per cent 'Average vatiation. 2.2 per cent. condensation. (b)Rittman and Dean, Loc. cil. ( c ) Made t o special order (a)Purchased from Chemical Supply House OF
--
.
---
-
I
2 ''
-
~
t h e figures for variations among t h e cuts of duplicate distillations, which are indicative, i n a general way, of t h e readiness with which checks may be obtained b y t h e laboratory worker. These figures have, of course, t o o limited a basis t o be regarded as a n y sort of a n exact measure b u t t h e y are of some weight as t h e distillations were all conducted b y one operator a n d with a n equal degree of care in manipulation. A s t u d y of Table I1 a n d of Fig. I1 shows t h a t when
comparisons are made on t h e basis of t h e magnit u d e of t h e first cut, a number of t h e still-heads are shown t o be practically equal in efficiency. Stillheads represented by Sections I O t o 17 of Table I1 are sufficiently alike so t h a t choice may b: m a d e among t h e m by considering other factors t h a n t h e degree of efficiency attained. T h e 12-bulb pear, t h e rod a n d disk, a n d t h e Le Bel-Henninger are immediately eliminated for petroleum because t h e y fail t o permit
TABLE11-SUMMARY OF TABLE I 5 6 7 8 9 10 11 12 13 Plain distillNorton Young Le BelAllen- Retort Ubbeing 2-Bulb 4-Bulb De and and 12-Bulb HenTemp Jacobs (B) Lunge lohde tube Wurtz Pear Konink O t t o Glinsky Thomas Pear ninger c. 4.4 4.8 4.9 5.6 5.7 5.7 5.9 3.1 4.4 0.5 1.0 2.8 100 . . . . . . . . . . . . 0 . 0 6.7 5.8 5.5 5.6 5.7 5.8 5.8 4.8 5.3 5.4 2.5 4.0 125 . . . . . . . . . . . . 1 . 0 6.1 7.0 6.9 6.7 7.6 6.2 7.0 8.5 150 . . . . . . . . . . . . 5 . 0 8.7 7.4 7.7 7.4 . . . . 7.6 8.3 8.4 7.4 8.1 ... 7.1 6.7 6.8 7.1 6.7 7.1 6.1 7.8 8.3 7.6 !.I 7.5 . . . 6.5 7.0 7.2 6.2 6.7 7.0 6.7 7.5 8.3 7.0 1.0 6.9 ... 6.1 6.6 ... 6.8 6.4 6.1 ... 7.0 6.8 6.5 6.9 7.0 ... 6.7 6.6 . . . 6.6 6.2 . . . . . . 6.7 6.5 6.3 6.8 7.2 ... 7.0 7.0 ... 6.8 6.9 . . . . . . 300 . . . . . . . . . . . . 6 . 2 7.4 7.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325.. . . . . . . . . . .6 . 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z J p t o 150 . . . . . . 6 . 0 11.7 12.4 15.9 15.3 16.7 18.4 17.3 17.3 19.0 17.7 18.5 18.7
No.
1
2
3
4
16
17
Golo- 6-Inch detz Hempel 6.2 6.3 5.7 6.3 6.4 6.0 8.0 6.8 7.9 6.3 6.4 8.5 8.0 6.5 7.0
Rod disk 6.5 5.9 6.4 7.0 6.3 6.5 7.1
Evaporator 6.6 6.0 6.7 7.1 6.3 6.1 6.7 6.9
18.3
18.8
19.3
14
15
... ... . . . . . . . . . . . . . . . . . . 18.6
... ...
T H E J O L 7 R N A L O F I A V D r S T R I d L A S D EATGIAYEERI:VGC H E M I S T R Y
S e p t . , 1 9 1j
t h e passage of vapor when higher temperatures are reached. T h e Golodetz, which on theoretical grounds seems t h e most desirable still-head of all, behaves in I
TYPE OF STILI.
PEKCLSTAGE UIJTILLISG BELOU . O U T
FIG.1 1 - R E L A T I V E
~ I A G S I T V DOEFSCVTS TO 100' OBTAINEDBY USE OF V A R I O U STYPES OF STILLS Both the Allen-Jacobs and Uhbelohde Methods Involve the Use of a n Engler Flask
IInfluence of height of column. n-Influence of diameter of column. 3-Influence of mechanical details. IKFLCESCE O F HEIGHT-Three Hempel columns were obtained, respectively 4, 6 and I O inches in height from constriction t o outlet tube. They were I inch in diameter and held columns of aluminum beads respectively 3, j and 9 inches in height. T h e stillheads were used in connection with the copper flask described in a n earlier connection. Results of distillations with these columns appear in Table 111. The last column in Table I11 brings out t h e fact t h a t when vapors from crude petroleum pass through a fractionating column of t h e Hempel t y p e a t t h e moderate rate a t which laboratory distillations are conducted t h e y come very nearly t o equilibrium with the condensed liquid after passing through a comparatively short length of t h e filling material. Increasing t h e length of t h e column as much as zoo per cent does not materially affect t h e results obtained. This is made evident when it is noted t h a t the Io-in.
an abnormal manner' with regard t o t h e size of cuts above 17j o . 1Iuch work was done with this still, using another sample of oil, a n d reliable results seemed t o be unobtainable. The four still-heads whose merits remain t o be discussed are t h e Glinsky, Young and Thomas, Hempel, and evaporator. The Young and Thomas, and evaporator are; perhaps, best in many ways b u t t h e y are not available on the market and in addition are rather fragile and complicated. The Glinsky is a little less efficient and while it can be easily purchased is subject t o objection on t h e grounds of fragility and costliness. A11 indications seem t o point t o the Hempel as most promising and f r o m the results of the present experiments it seems t o be in a class b y itself. I t s one inherent disadvantage is t h e amount of phlegm or condensed vapor held u p by t h e fractionating column. This has not, horn-ever, been found t o interfere seriously in distillations involving an initial charge of roo grams or more. Some of t h e numerous advantages of the Hempel still-head m a y be mentioned. T h e apparatus is efficient, cheap, readily available or improvisable, easy to manipulate and clean, and in addition it permits the elimination of t h e troublesome cork joint between distilling bulb and fractionating column. None of t h e other types possess this advantage except the pear and the rod and disk: both of these, however. fail t o attain the necessary degree of efficiency unless they are of excessive length, in which case t o o much condensation occurs and t h e stills fail t o work through the necessary range of temperature.
Coppel
S T U D Y O P T H E HERIPEL COLCMINS
Heyipel
The possibilities of the Hempel column u-ere studied in considerable detail and with regard t o the following factors (see Fig. 111): T h e only logical explanation of this action which has occurred to t h e writers is t h a t , o n account oE some details of construction, pressure i s developed in t h e still and crackine caused.
i57
I ti+"
n
W
FIG. 111-HEMPEI, C O L U X N STISTED
column mas merely of the same order of efficiency as t h e 4-in. For mechanical reasons t h e 6-in. height seemed t o be a n optimum. T h e Io-in. was unwieldy
T H E JOC'RYAL OF I N D U S T R I A L A N D ENGINEERI-VG C H E M I S T R Y
758
a n d produced too much condensation a t higher temperatures; t h e 4-in. tended t o be unreliable in producing checks unless t h e rate of distillation was regulated with much care. TABLE 111-RESULTS
HEMPELCOLUMNSOF VARIOUSHEIGHTS (DIAMETER,1 INCH) Temp. Percentages Specific gravities Av. O C . A B C D E F A B C D E F A v . % FOUR-INCHCOLUMN 100 5.7 5.9 5.9[7.015.6 . . . 0.690 0.692 0.691 0.687 0.687 . . . . . 0.689 5.8 125 6.1 6.2 6.4 6.3 5.8 . . . 0 730 0.730 0.730 0.733 0.731 . . . . . 0.731 6.2 150 6.2 6.5 7 . 0 6.4 6.1 . . . 0.748 0.747 0.746 0.748 0.747 . . . . . 0,747 6.4 175 7 . 0 6.6 6.6 6.7 6.9 . . . 0.761 0.762 0.762 0.762 0.761 . . . . . 0.762 6.8 200 6.2 6.4 6.3 6.4 6.2 . . . 0.773 0.772 0.772 0.773 0.772 ..... 0.772 6.3 225 6.3 6.7 6.2 6.2 6.7 . . . 0.783 0.782 0.783 0.783 0.782 . . . . . 0.783 6.4 250 6.5 6.3 6.4 6.5 6.2 . . . 0.792 0.794 0.794 0.793 0.793 . . . . . 0.793 6.4 275 7.3 7.3 7.2 6.7 7.1 . . . 0.806 0.805 0.805 0.806 0.805 . . . . . 0.805 7 . 1 Average variation, 2.4 Der cent S I X - INCHCOLUMN 100 6.2 6.5 5.9 6.1 6.5 6.3 0.698 0.695 0.696 0.694 0.689 0.684 0.693 6.3 125 6.4 6.0 6.5 6.4 6.2 6.1 0.733 0.732 0.732 0.732 0.73! 0.730 0.732 6.3 150 5.6 6.2 5.9 5.9 6.2 6.3 0.751 0.748 0.747 0.747 0.741 0.746 0.747 6.0 175 7.0 6.9 6 . 7 7.0 6.7 6.7 0.764 0.762 0.762 0.762 0.762 0.761 0.762 6.8 200 6.2 6.2 6.3 6.4 6.4 6.5 0.775 0.773 0.773 0.772 0.772 0.774 0.773 6.3 22s 6.5 6.4 6.4 6.0 6.5 6.4 0.785 0.783 0.783 0.782 0.783 0.783 0.783 6.4 250 6.9 6.1 6.5 6 . 4 6.5 6.5 0.796 0.793 0.794 0.794 0.794 0.793 0.794 6.5 275 [5.5]7.0 6.9 7.1 7.2 6.8 0.806 0.804 0.806 0.806 0.805 0.805 0.805 7 . 0 Average variation. 2.2 per cent TEN-INCH COLUMN 100 6.3 6.3 7.0 6.9 7.3 6.7 0.688 0.692 0.687 0.685 . . . . . 0.684 0.687 6.7 125 5.9 6.3 6.3 6.3 6.3 5.8 0.732 0.733 0.732 0.731 . . . . . 0,728 0.231 6.2 150 6.1 5.8 6.3 6.8 6.2 6.0 0.746 0.749 0.748 0.748 ..... 0.745 0.t47 6.2 175 6.7 6.5 6.8 6.9 6.9 6.9 0.762 0.762 0.763 0.762 . . . . . 0.759 0.762 6.8 200 6.1 6.2 6.1 6.2 6.5 6.3 0.272 0.772 0.772 0.773 ..... 0,772 0.772 6.2 225 6.4 6.5 6.5 6.5 . . . . . . 0.,82 0.782 0.783 0.783 . . . . . . . . . . 0.783 6.5 250 6.8 6.6 6.8 6.4 . . . . . . 0,793 0.794 0.794 0.793 . . . . . . . . . . 0.793 6.6 275 7.1 7.3 7.1 7.4 . . . . . . 0.804 0.806 0.806 0.807 . . . . . . . . . . 0.806 7.2 Average variation, 2.4 per cent WITH
INFLUEKCE O F DIAMETER-Having demonstrated t h a t a 6-in. column with 5 in. of beads seemed t o be a n optimum as far as t h e factor of height was concerned, t h e next experiments were concerned with t h e m a t t e r of diameter. Distillations were run with three 6-in. columns, respectively, 5 / ~in., 13/16 in. a n d I in. in diameter. These columns were sealed directly on glass bulbs a n d were made without a n y constriction a t t h e base of t h e column. Reasons for this will be set forth in t h e subsequent section on mechanical advantages a n d possibilities. Results, shown in Table I P , indicate t h a t t h e influence of diameter on t h e efficiency of a Henipel column used in petroleum distillation, is slight. Differences are of about t h e same order as those among figures for columns of different heights. I i i F L U E N C E O F M E C H A N I C A L DETAILS-After having demonstrated t h a t for petroleum distillation t h e effects
Vol. 7. No. 9
tilling bulb, series of experiments were performed in which similar Hempel columns were used in connection with different types of vessels. Comparisons were made between effects produced b y glass bulbs of caDistillapacities respectively 500 cc. a n d 300 cc. tions were made in 300 cc. bulbs with a n d without a constriction a t t h e base of t h e fractionating column. I n addition a copper distilling flask %-asused in connection with one of t h e s t a n d a r d 6-in. columns. The results are given in t h e first four columns of Table V. TABLE11'-RESULTS
WITH HEMPEL COLUMNSOF VARIOUS DIAMETERS WITH 5 INCHES OF BEADS) (HEIGHT, 6 INCHES, Temp Percentages Specific gravities Av. 'C. A B C D E A B C D E Av. 70 DIAMETER,= / E INCH 100 5.9 6.0 5.9 . . . . . . 0.681 0.685 0.685 . . . . . . . . . 0.684 5.9 125 6.4 6.1 5.7 . . . . . . 0.729 0.730 0.731 . . . . . . . . . . 0.730 6.1 6.6 150 6.9 6.7 6.4 . . . . . . 0.744 0.747 0.748 . . . . . . . . . . 0.747 0.758 0.761 0.762 . . . . . . . . . . 0.760 7.1 175 6.9 7.2 7.3 200 6.6 6.7 6.6 0.771 0.775 0.772 . . . . . . . . . . 0,773 6.6 225 6.0 6.2 6.2 . . . . . . 0.781 0.785 0.784 . . . . . . . . . . 0,783 6.2 6.9 250 7.0 6.9 6.7 . . . . . . 0.792 0.795 0.794 . . . . . . . . . . 0,794 275 . . . . . . 7.0 . . . . . . . . . . . . . . . . 0.809 . . . . . . . . . 0.809 7.0 Average cut, 6.3 per cent Average variation, 1.9 per cent
...... ......
0.684 0.682 0.683 0.684 . . . . . 0.683 0.730 0.730 0.728 0.730 . . . . . 0.730 0.749 0.i48 0.145 0.746 . . . . . 0.747 0.762 0.762 0 . / 6 2 0.761 . . . . . 0.762 . . . 0.774 0.773 0.772 0.772 . . . . . 0.773 . . . 0.784 0.783 0.782 0.783 ..... 0.783 . . . 0.795 0.795 0.793 0.794 . . . . . 0.794 . . . 0.806 0.805 0.804 0.804 ..... 0.805 . . . 0.815 0.816 . . . . . 0.815 . . . . . 0.815 Average cut, 6.3 per cent Average variation, 2.1 per cent
... ... ...
...
0.687 0.683 0.685 0.683 0.733 0.731 0.734 0.730 0.749 0.747 0.747 0.747 0.763 0.763 0.763 0.762 0.773 0.773 0.774 0.772 0.783 0.784 0.784 0.782 0.795 0.794 0.795 0.793 0.805 0.806 0.80: 0.804 0.816 0.816 0.81, 0.816 Average variation, 2.2
0.683 0.684 0.731 0.732 0.747 0.747 0.763 0.763 0.772 0.773 0.784 0.783 0.795 0.794 0.805 0.805 0.816 0.816 per cent
5.8 6.2 6.1 6.8 6.5 6.2 6.6 6.1 6.5 5.9 6.2 6.2 6.5 6.6 6.2 6.4 6.2 6.6
I t appears t h a t b y using Hempel columns of approximately equal dimensions like results are obtained, whether t h e distilling bulb is smaller or larger, constricted or unconstricted, glass or copper. Distillations made in a n apparatus with both column and bulb of copper (Table V, No. 8) proved t o be b u t slightly different from t h e ones employing a glass column. Distillations were made, using glass instead of aluminum beads as filling material, a n d it was learned
TABLE\'-SHOWING CLOSEAGREEMENTAMONG RESULTS (PERCENTAGES) OF DIFFERENTHEMPEL DISTILLATIONS Hempel column FL.4SK
6 X 1 in. Col. with 5 in. of Beads
_-__-___ Copper
Temperature
C.
1
Bur. of For. Creosote Regular Small bulb 2 3 6.2 6.2 6.5 6.1 6.4 6.4 6.6 6.7 6.5 6.6 6.5 6.4 6.5 6.6 6.1 5.9
... ...
...
...
---
Slender column (See Glass beads Table IV) 5 6 5.9 6.2 6.1 6.1 6.6 6.2 7.1 6.6 6.6 6.7 6.2 6.3 6.9 6.4 v.01 L6.81
Flask in Fig. I11
A1 beads 4 5.9 6.2 6.2 6.5 6.6 6.2 6.4 6.2
...
...
[ ] Bracketed results omitted from average.
Same as 4 Medium Copper b u t with column Hempel 100 g. (See Diam.: 1 in. charge Table I V ) Beads: 5 in. of oil Average 1-5 Average 1-9 9 7 8 6.2 5.8 6.2 6.5 6.1 6.2 5.8 6.1 5.8 6.2 6.7 6.1 6.2 6.1 6.3 7.0 6.6 6.8 6.8 6.8 6.5 6.6 6.5 6.1 6.5 6.4 6.2 6.2 6.3 6.2 6.5 6.6 6.5 6.2 6.6 6.1 6.2 6.1 6.0 6.1 6.34 6.3 ... ... 1.6 2.3 ... ...
T h e y include drainage of condenser a t end of distillation.
attained b y Hempel columns of widely varying dimensions differ b u t slightly it was deemed advisable t o s t u d y t h e influence of various mechanical details. T h e following were given consideration: a-Shape, size a n d material of distilling bulb. 6- Material of column. c-Filling material in column. d-Size of charge. T o determine t h e degree of importance of t h e dis-
t h a t this factor is of little influence as far as t h e numerical results of a n analysis are concerned. Finally distillations were run with a n initial charge of I O O grams of oil a n d here there was a tendency for t h e cuts a t higher temperatures t o be consistently a little low. This effect was undoubtedly due t o the influence of t h e lag of the distilled oil in t h e condenser tube. Table V summarizes t h e effects of all t h e types of
S e p t . . 1915
T H E JOl.RAV.4L O F I , V D U S T R I A L A N D E - V G I N E E R I N G C H E i M I S T R Y
&in. Hempel columns which h a v e been employed a n d shows t h a t t h e average variation among c u t s ( 2 . 3 per cent) is practically t h e s a m e a m o n g t h e different methods a s a m o n g duplicate distillations b y a n y one m e t h o d . T h e agreement is even more impressive %.hen comparisons are limited t o glass columns 6 in. long a n d I in. in diameter. Here t h e average variation is only 1.6 per cent. T h e figures i n T a b l e T' clearly d e m o n s t r a t e t h e fact t h a t b y using efficient fractionating columns of a p proximately equal dimensions t h e m a j o r i t y of t h e other factors which control results of distillation a r e rendered of negligible influence. IIECHASICAL
ADVAKTAGES
OF
DIFFEREST
TYPES
OF
A P P A R A T US
759
ing column has seemed desirable for t h e following reasons: i t permits t h e use of a shorter a n d less unwieldy flask, tends t o lessen t h e possibility of flooding a n d in addition makes easier t h e cleaning of t h e distilling vessel. There are numerous simple mechanical devices b y which t h e column of beads m a y be easily a n d conveniently supported. One which has been used is a copper wire, shaped i n t o a spiral a t one e n d a n d with a hook at t h e o t h e r . which can be pushed i n t o t h e outlet t u b e of t h e flask. Aluminum beads seem b e t t e r t h a n glass t h o u g h there is no marked difference in t h e degree of efficiency a t tained (see Table IT, KO. 4 ) . Glass beads fit together more closely a n d on t h a t account are more liable t o flood. CR A C K I SG
I n t h e absence of trials in t h e h a n d s of a considerable n u m b e r of operators i t is difficult t o arrive at final conclusions regarding t h e mechanical a d v a n t a g e s of different t y p e s of a p p a r a t u s . O n t h e basis of present experience, however, i t h a s appeared t h a t t h e simple *-f.
1
-n
! I
I
'I
Flti. 11'-HEMPBL F L A S K
O F OPTIhIUN D I > % B b S I O b ; BF O R
DISTILLATIOW
PSTROLELM
Bask with a n unconstricted column I in. i n diameter a n d holding j in. of a l u m i n u m beads is most satisfactory (see Fig. IV). T h e r e seems t o be little question a s t o t h e desirability of employing a fractionating column of approximately t h e size indicated. T h e details of material a n d m e t h o d of construction are a little less definitely established b u t i t is believed t h a t t h e flask selected approaches a n o p t i m u m with regard t o simplicity a n d convenience of operation. It mas a t one t i m e t h o u g h t t h a t a n a p p a r a t u s entirely of copper m i g h t b e best b u t objections developed after some use. +4n inherent disadvantage is t h e impossibility of w a t c h i n g t h e behavior of t h e boiling oil during t h e course of a distillation. A column of large bore is b e t t e r t h a n one of small as i t minimizes t h e possibility of flooding a n d also reduces t h e danger of variations caused b y air curr e n t s a n d atmospheric t e m p e r a t u r e changes. Dispensing with a constriction at t h e base of t h e fractionat-
T h e minimization or elimination of cracking is desirable in t h e analytical distillation of petroleum and on t h a t account consideration has been given t o i t in t h e present connection. T h e importance of t h i s fact o r of cracking seems t o h a r e been considerably 01-erestimated, a n d a n idea is prevalent t h a t i t is caused b y t h e superheating incident t o t h e running back of condensed vapors i n t o t h e h o t liquid in t h e bulb of a distilling flask. T h e folloying s t a t e m e n t s , which would be accepted as axiomatic b y a n y modern chemist, serve t o indicate t h e erroneousness of t h e above explanation of t h e mechanism of cracking. "The cracking of heavy hydrocarbons by heat is to be regarded as simply an instance of the general rule that organic compounds are decomposed by heat. It is well known that the simpler petroleum hydrocarbons are stable a t much higher temperatures than those of higher molecular weight."' W i t h t h i s point of view i t is obvious t h a t cracking is d u e t o t h e superheating of t h e h e a v y hydrocarbons of t h e boiling liquid in t h e distilling vessel a n d riot t o t h e Superheating of t h e products of reflux condensation in t h e fractionating column. T h e r e a r e t w o t e m p e r a t u r e factors of importance, one t h a t of t h e boiling liquid a n d t h e other t h a t a t which h e a t is t r a n s m i t t e d t o i t . I t does not seem t h a t with a system of external heating t h e l a t t e r factor can be of much influence in distilling systems of t h e size employed i n t h e laboratory. T h e problem seems t o resolve itself i n t o one of determining t h e t e m p e r a t u r e of t h e liquid i n t h e bulb. Approximate measurements of liquid t e m p e r a t u r e s ' were made in a n u m b e r of t h e distillations a n d i t was found t h a t with t h e 6 in. Hempel a p p a r a t u s t h e liquid was a b o u t 7 j oh o t t e r t h a n t h e vapor a t t h e beginning of a distillation a n d 40' h o t t e r a t t h e e n d when t h e t e m p e r a t u r e of t h e vapor was a b o u t 3 0 0 ' . The ' final difference in t h e open flask method was a b o u t 10' so t h a t a distillation of t h i s sort could be carried u p t h e t e m p e r a t u r e scale only a b o u t 30' farther t h a n one involving efficient fractionation, with t h e possibility of cracking t h e s a m e in b o t h cases. I n addition t o t h e above comparative evidence some of a more direct n a t u r e was secured b y distillation experiments which, however, dealt only with Pennsylvania crude oil. Cracking is a t i m e reaction a n d t h e . a m o u n t of decomposition should be proportional t o t h e 1
Brooks, Bacon, P a d g e t t a n d H umphrey, THIS J O U R N A L . 7 ( 1 9 1 5 ) . 180.
760
T H E J O U R N A L O F I N D U S T R I A L A N D EIVGINEERIAVGC H E M I S T R Y
t i m e during which t h e oil is kept a t a given temperat u r e capable of producing t h e "cracking" effect. It is, therefore, obvious t h a t if there is a n y cracking i n t h e course of a distillation t h e r e should be twice a s much in t h e course of two, a n d t h a t successive distillations of t h e s a m e sample of petroleum should cause a progressive increase i n t h e percentage of constituents distilling below some given temperature. On t h i s basis t h e following procedure was a d o p t e d : A sample of oil was distilled i n t h e usual manner u p t o a given t e m p e r a t u r e , all t h e distillate being collected in a single t a r e d receiver. After stopping t h e distillation a n d letting t h e condenser drain, t h e a m o u n t distilled was determined b y weighing. I t was t h e n poured back i n t o t h e cooled distilling flask a n d another distillation conducted u p t o t h e same temperature. If cracking occurred i n t h e first distillation i t should also TABLEV I - E X P E R I M E S T S
TO
TESTF O R
"CRACKING"
GLASS Large bore GLASS UnconMedium bore stricted APPARATUS ( H E M P E L ) COPPERConstricted neck neck T e m p . OF vapor a t end of distillation 289' C. 312O C. 312' C. 325' C. a 57.0 65.0 64.8 70.1 64.8 69.6 P e r cent by weight ' h 56.z 64.5 65'3 70.0 of repeated distillations: 56.' 66.1 I d .... 66.7 66.2 .... e , ... .... 66.3 .. .. Residue (per c e n t ) . . . . . . . . . , . . . . . I . . 4 2 . 0 33.0 32.5 28.6 S u m of residue a n d last distillate.. . . . 9 8 . 7 99.7 98.8 98.6 Per cent loss . . . , . . . , , , , .. , , , . . . , . , , 1 . 3 0.3 1.2 1.4
h a v e occurred i n t h e second a n d t h e cut up t o t h e given t e m p e r a t u r e would be greater i n t h e second instance. T h e results of several of these experiments are given i n Table IrI. I t is obvious t h a t even u p t o 3 2 j 0 C. (uncorrected) there is n o appreciable a m o u n t of cracking with t h e sample of Pennsylvania crude oil employed. It is proposed in a later connection t o experiment furt h e r i n t h i s direction a n d learn t h e behavior of other typical crude oils. For t h e present, however, it seems sufficiently clear t h a t t h e reflux condensation in\-olved in t h e \-arious methods of efficient fractionation is not a source of danger in t h e production of cracking. CONCLUSIOIiS
A former paper shorn-ed t h e fundamental advantages of a method of efficient fractionation for t h e analytical distillation of petroleum. T h e present series of experiments has brought o u t t h e following facts: I-Comparisons of a large number of t y p e s of distilling a p p a r a t u s showed t h a t several (Glinsky, Young a n d T h o m a s , long pear, Le Bel-Henninger, Golodetz, Hempel, long rod a n d disk a n d evaporator) produce approximately equal results. 11-Of t h e several, t h e Hempel is easily first on t h e basis of mechanical a d v a n t a g e , t h e Glinsky, Young a n d T h o m a s a n d evaporator being t h e only ones comparable t o i t . 111-With t h e moderate r a t e of distillation employed for t h e fractionation of petroleum t h e dimensions of Hempel columns may v a r y widely, b o t h i n length a n d bore, with b u t slight effect on t h e results produced. 117-With columns of equal dimensions other mechanical factors are of minor importance. T h e size, shape a n d material of t h e distilling bulb h a v e no ap-. preciable influence. Glass beads are not as good me-
T'ol. 7 , S o . 9
chanically a s aluminum b u t t h e y a t t a i n t h e same degree of fractionation. T h e size of t h e initial charge of oil is of some slight importance on account of t h e introduction of variation t h r o u g h t h e lag of t h e liquid i n t h e condenser t u b e . T-Mechanical advantages seem t o be greatest for t h e one-piece glass a p p a r a t u s with unconstricted neck of I-in. bore a n d 6-in. length f r o m bulb t o outlet. CHEJllCAL S E C T I O S O F P E T R O L E L M DIVISION
u. s
BUREAUO F h1VIIKES.
PITTSBURGH
A COMPARISON OF METHODS FOR DETERMINING
PUTRESCIBILITY OR OXYGEN DEMAND By FRANK E. HALEA N D THOMAS W. MELIA
Received April 7 , 1915
T h e experiments described in t h i s paper were carried o u t a' year ago in connection with t h e work of t h e committee, headed b y D r . A r t h u r Lederer, appointed t o establish s t a n d a r d methods for Putrescibility or Oxygen D e m a n d of Sen-age,' etc. Pressure of routine work has prevented further experiments which we hoped t o make t o sustain t h e conclusions here presented. N o results are reliable as representative of p a r t s per million of oxygen required t o prevent putrescibility unless such results can be consistently obtained a n d are supported b y t h e results of different methods. This laboratory has for several years used 'the Dilution Method as described b y Jackson a n d Horton.' T h e essential features are dilution with aerated distilled water of known oxygen c o n t e n t , employment of methylene green, zinc double salt ( t h e q u a n t i t y originally specified corresponds t o t h e a m o u n t of methylene blue recently recommended b y Ledere? a s yielding best results a n d least antiseptic power), dilutions differing b y t w o volumes sufficient t o obtain one bottle remaining colored, use of medicine droppers inserted t h r o u g h one-hole rubber stoppers, incubation for four t o five d a y s , a n d noting t h e days a t which different dilutions become colorless. T h e original oxygen of t h e distilled water multiplied b y (one plus t h e highest dilution becoming colorless) equals t h e p . p. m. oxygen required t o prevent putrescibility. Our dilutions ha\-e been made in cylinders without preventing aeration of t h e sewage. I n t h e present work comparison was made betlyeen t h e above method, using b o t h distilled water a n d Brooklyn t a p water, t h e English Excess Oxygen Dilution Method with some modifications, a n d t h e Lederer S i t r a t e Method using excess nitrate. T h e bottles used in each case were of 3 0 0 cc. capacity. For t h e English method t h e bottles were filled with aerated distilled water through a funnel, keeping t h e funnel full, a n d overflowed t o half their volume t o , displace air a n d t h e first water coming in contact with air. T h e n 3 cc. of sewage were introduced undern e a t h b y pipette forcing out some distilled water. Afedicine droppers inserted through rubber s t o p p e r s were filled with t h e distilled water a n d inserted collapsed 2 3
T H I S JOCRKIL, 6 (1914). 8 8 i . I h i d . . 1 (1909), 328. i l m . J o u r . Pub. Health, 4 (1914). 241
