Vo l. 3 1 . N o . 2 ^ . Ja n u a r y 1 9 4 5 .
CLASSIFICATION OF CRUDE OILS.
B y K . G. Ma r g o s o h e s (Member).
' In t r o d u c t i o n.
Se v e r a l a tte m p ts to classify crude oils are recorded in th e lite ra tu re ,16 b u t only th e m ore recent developm ents will be described in th is review.
T he accuracy an d completeness of th e classifications depend on our knowledge of th e individual com pounds or groups of com pounds in th e petroleum and on th e accuracy of m ethods to detect an d determ ine them .
Some references have been selected to show th e progress m ade during recent years.
As to th e d eterm ination of groups of com pounds, besides referring th e reader to th e m ethods of various S tandardization Com m ittees, a few references m ay be q u oted.1
F o r th e purpose o f identification of th e com pounds them selves th e crude oils have first to be separated into fractions. A system 10 for th is fractio n a
tion, which m akes use of distillation, extraction, crystallization, and adsorption, has been chiefly developed b y A .P .I. R esearch P ro ject 6.
Of th e m any physico-chem ical properties of th e compounds, especially in th e petroleum fractions, electrom agnetic spectra 12' 13, 14' 15 are very helpful in throw ing light on th e question.
In connection w ith nam es o f com pounds 8 present in petroleum a n d its products, a tte n tio n is directed to a review by T ru sty ,9 an d also to some 2 3- 4' 5- 6' 7 of th e m any research papers of th e above-m entioned A .P .I. Research P ro ject 6.
Hi s t o r i c a l Re v i e w.
The earlier classifications consider geological d istrib u tio n ,16“’ *> chemical composition 1 or physical properties (e.g., optical a ctiv ity ,16*
solubility W i).
Re c e n t Cl a s s i f i c a t i o n s.
(A) U.S. Bureau of Mines Classifications.— Methods to Evaluate the
“ Baser
The B ureau of Mines of th e U n ited S tates has published reports on crude oils classifications, which distinguish various “ bases.”
I n 1927, N . A. C. S m ith 17 differentiated four “ base ’’-groups (see Table I . 18) and in a B ulletin published later 19 th e usefulness of this system is also tested.
W ith th e progress of th e science of petroleum it was found th a t th e num ber of groups was n o t su fficien t: three of th e four classes were retained and four interm ediate groups were added 20 (see Table II.). T he last two classes are possible according to this classification, b u t no exam ples of either of them have been found am ong th e m any h undred samples analysed b y th e B ureau of Mines (at least u n til 1939).21 I t m ay be m entioned th a t according to L ane and G arton,22 ab o u t 85 per cent, of 800 analysed crude
TableI (1927).
2 M A R G O S C H E S : C L A S S IF IC A T IO N O F C R U D E O IL S .
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* Fraction250-275°C. (482-527°F.)atatmosphericpressure, Bureau ofMines Hempel method, f Fraction275-300°C. (527-572°F.)at40mm. absolutepressure, Bureau ofMinesHempel method.
M A R G O S C H E S : C L A S S IF IC A T IO N O F C R U D E O IL S . 3
oils from th e producing fields throughout th e world fell definitely in one of th e th ree classes : paraffin, interm ediate, or n aphthene base.
N elson 23 gives a list of m ethods for judging th e base of an oil. A p art from considering th e properties indicated in th e reports by N. A. C. S m ith ,17 an d Lane an d G arton,20 there are several m ethods which m ake use of th e fact t h a t properties are a function of th e character of crude oils for th e purpose of evaluating th e “ base ” of stocks.
One can com pare th e properties of an unknow n oil w ith th e properties of know n stocks. This m ethod, however, has to be applied to a large num ber of sam ples.24
T he “ cast ” of lubricating oils gives to a certain e x te n t inform ation on th e base.25
T he gasoline content p lo tted against specific g rav ity of crude oils shows zones for th e th ree m ain bases of oils.26
Some of th e m any 27 m ethods which correlate two or more physical properties in order to o btain an “ average ” chemical constitution or th e
“ predom inating ” constituents in petroleum fractions are th e viscosity index, th e characterization factor, th e characterization gravity, and, quite recently, th e correlation index.
The viscosity index and th e viscosity g rav ity constant have been ex ten sively described in th e literatu re,28 an d only reference to this literatu re need be m ade here.
T he characterization factor has been developed by m em bers of th e staff of th e U niversal Oil P roducts Com pany,29’ 30> 31 and is defined as th e ratio of th e cube root of th e average boiling point (in degrees R ankine) to th e specific g rav ity a t 60°/60° F . F o r highly paraffinic crudes th is factor is 12-5-13-0, while for arom atic or naphthenic crude-oil fractions its value is 10 or below, a n d th e increase betw een 10 an d 12 indicates th e increase in paraffinicity. T he factor has also been related to m any other physico
chemical properties.30 I t is additive on a weight basis.32
T he S ta n d ard Oil Com pany of California has developed a te s t to classify heavy oils as to th e ir paraffinicity, th e characterization g rav ity ,33 which is defined as “ th e arithm etic average of th e instantaneous gravities of th e distillate boiling a t 350°, 450°, an d 550° F. vapour-line tem perature a t 25 mm. pressure in a true-boiling-point distillation.”
H . M. S m ith 34 states th a t his correlation index
“ cannot be com pared to a ‘ base ’ system of classification as it is not a m eans of grouping crude oils according to th e ir properties. I t provides a cross-sectional view of th e distillable portion of a crude oil, employing for th is purpose num bers or indexes th a t represent th e average boiling-point an d specific-gravity characteristics of th e distilled fractions.”
This m ethod of correlation of physical properties is therefore n o t m eant to evaluate th e “ base ” for th e “ base ” system , and th e system of correla
tio n indexes can w ith advantage be included in analyses 39 as a classification on its own or in addition to th e “ base ” system .
Sm ith 34 claims, th a t
“ th e defects of th e ‘ base ’ system are e lim in ated ; Differences are shown equally w ith sim ilarities, there are no border-line cases or
4 M A R G O S C H E S : C L A S S IF IC A T IO N O F C R U D E O IL S .
d ou b tfu l classifications, an d nam es are n o t used, hence th e danger of form ing m isconceptions due to th e nam e is elim in ated .”
I t will perhaps be interesting to give a sh o rt description of th e develop
m e n t a n d use o f th is te rm .34
S m ith considers first th e relationships betw een boilin g p o in ts an d specific gravities existing in 1940 : th e boiling point—g ra v ity co n stan t o f Ja c k so n for crude-oil fractions a n d th e characterization facto r 29 for pure h y d ro carbons. H e reaches th e conclusion t h a t an ideal relationship betw een boiling p o in t an d specific g ra v ity should show system atic differences betw een th e m em bers of th e homologous series of h y drocarbons a n d also betw een th e homologous series. This ideal case is n o t en tirely reached, b u t th e reciprocals of th e boiling points, in degrees K elvin, for th e norm al paraffins p lo tte d against th e ir specific gravities (a t 60° F .) “ G ” show a linear relation. This line is used as a reference base for th e in terp re ta tio n of th e o th er hydrocarbons and, because no h y d ro carb o n of a n y other series w ith th e same boiling p o in t has a fighter specific g ra v ity , th is lim iting b oundary has been assigned an index nu m b er C.I. of 0 . A fine parallel to it an d passing th ro u g h th e co-ordinates of th e h y d ro carb o n benzene has been given an index num ber C.I. = 100. These tw o fines enclose a n area w hich contains m ost of th e hydrocarbons, except polynuclear com ponents.
T he equation for th e stra ig h t fines is : = b — 9-7396 X 10“3 G, where b is th e in tercep t on th e ^ axis. 6 for th e fine th ro u g h th e n o rm al paraffins is 9-392 X 10'3, b for th e fine th ro u g h benzene is 11-448 X 1W3. The correlation index equation is :
4 8 6 4 0
C.I. = - + 473-7 G - 456-8.
XA
This equation m ay be applied to pure hydrocarbons, an d also to fractions of crude oils, in which la tte r case C.I. is only an average value for th e hydrocarbon m ixtures. A ccording to S m ith, fractions w ith C .I. 0 -15 are alm ost certainly predom inatingly paraflfinic; a C.I. above 50 indicates
“ t h a t arom atic rings pro b ab ly p red o m in ate,” a n d a C.I. 15-50 indicates
“ n aphthenes or different m ixtures of paraffins, n a p h th en es a n d aro m atics.”
Side-chains have a n influence on th e value.36 W hen applied to crude oil fractions, th e “ average boiling p o in t ” “ K ” is used. T here are several definitions for th is te rm .31 All can be o btained from th e volum etric average boiling p o in t b y applying a correction facto r b ased on th e slope of th e distillation curve. F o r sm all values o f th e slope th e correction is sm aller th a n th e errors of th e d istillatio n m ethod, a n d th e volum etric average boiling p o in t can be used w ith an accuracy o f w ith in one index n um ber.34 T he volum etric average boiling p o in t is d eterm in ed b y m easu r
ing w ith a planim eter th e average height of th e curve from th e te m p e ra tu re axis, or b y averaging th e te m p eratu res for th e in itial p o in t, end p o in t, an d tem p eratu res o f each 10 per cent, of th e distillation. S m ith 37 gives tw o tab les b y m eans of w hich one can rea d th e correlation index for an y given specific g ra v ity of th e H em pel fractions. T he correlation index is n o t ad d itiv e.40 I t seems useful in obtaining refining characteristics of crude
M A R G O S C H E S : C L A S S IF IC A T IO N O F C R U D E O IL S . 5
oils (see also under “ D ecim al System ” ), which subject Sm ith 38 discusses in a R e p o rt on Illinois crude oils, in which he proves th a t oils which had been shown to have a sim ilar correlation index h ad been used by refiners to m an u factu re a sim ilar series of products.
In a n o th er R e p o rt on Illinois crude oils, Rees, Henline, and Bell 39 give th e correlation indexes and characterization factors for each fraction of th e ir num erous H em pel M ethod D istillations.
(B) Decimal System.
A decim al system has been proposed by Voinov,41 and is being fu rth er developed. Voinov classifies th e crude oils into classes, sub-classes, and groups, according to th e ir properties, and so far has assigned 3-figure num bers. The figures in th e num bers so far consider th e content of resinous substances, sulphur, and paraffins.
Two m otives underlie th e work to develop m ethods for analysing, ch ar
acterizing, an d classifying crude oils ; th e one is th e purely scientific purpose of furthering th e progress of our knowledge, th e o th er is th e wish to o b tain characteristics of crude oils which are of use to th e refiner in selecting suitable crudes for m anufacturing desired products.42' 43, 44
W h atev er classification of crude oils has been adopted, based on either separate or com bined application of schemes w ith regard to geographical distribution, geological location, physical properties, chemical properties, chem ical composition, products, etc., num bers can be assigned to each item of th e adopted classification b y applying th e decim al classification of L. C. U r e n 45—which is a m odification of D ew ey’s system — an d /o r th e Bruxelles System 46' 47.
(C) Classification with Regard to Products.
A short explanation of w h at is m eant by classification “ w ith regard to products ” : Beiswenger 43 differentiates tw elve types of crudes (“ A ” to
“ L ” ), and shows th e differences in yiçld and q uality of various fractions.
Theoretically one can now adays produce an y ty p e of refined product from any crude oil ; however, th e selection of th e refiner will be influenced 43 by
1. Processing cost.
2. Yield o f products of desired characteristics.
3. Processing equipm ent available to him.
4. Price of products.
A lthough such a system will probably be very fluctuating, being a function of extrem ely variable factors, it se e m s47 w orthy of fu rth er developm ent.
Co n c l u s i o n.
H aving quoted a few selected references on th e present state of our knowledge of th e composition and properties of crude oils, some older classifications 16 have been nam ed and various more recent system s briefly reviewed.
T he more recent system s are th e classifications by N . A. C. Sm ith 17 and L ane and G arton,20 who distinguish groups of “ bases ” ; th e system by H . M.
S m ith,34 who introduces th e correlation index; th e scheme by Voinov,41
6 M A R G O S C H E S : C L A S S IF IC A T IO N O F C R U D E O IL S .
who applies a decim al s y s te m ; a n d th e arrangem ent b y Beiswenger,43 who classifies crude oils according to th e ir products.
F u rth e r, th e essential features of several m ethods have been m entioned, which enable one to evaluate th e “ base ” (Table I., T able I I .,24, 25 26' 28, 29,
3 0. 3 3)
L itera tu re which refers to geographical d istrib u tio n a n d geological location, or which relates to th e problem of origin of crude oils (e.g., classifies th e petroleum as carbonaceous m in e ra l48) has n o t been d e a lt w ith.
A lready to -d ay m an y organic com pounds can be d irectly se p arated from crude oils by fractio n atio n m ethods 10 or synthesized from th em b y applying various processes 43’ 44. I t will be interesting to see w hether, a n d if so how, (1) th e progress of our knowledge of th e com pounds p resen t in th e crude oils o f th e world, (2) th e progress in synthesizing new p ro d u c ts from petroleum as th e u ltim a te raw m aterial, will influence th e developm ent of classifications. I f th e classifications te n d to becom e m ore ex tended an d /o r subdivided, it is possible th a t, as o utlined above,47 an y adopted classification of crude oils will get assigned num bers to its item s, in order to aid th e refiner in choosing quickly th e ap p ro p ria te crude oil for his production.
B ib lio g ra p h y .
A . A . E . D u n sta n el a l., “ T h e S c ie n c e o f P e tr o le u m ,” V o l. I I , L o n d o n , 1938.
B . W . A . G ruse a n d D . R . S te v e n s, “ T h e C h em ica l T e c h n o lo g y o f P e tr o le u m ,” 2nd e d ., N e w Y o r k , 1942.
C. W . L . N e ls o n , “ P e tr o le u m R e fin e r y E n g in e e r in g ,” 2 n d e d ., N e w Y o r k , 1941.
la A . N . S a c h a n e n a n d M. D . T ilic h e y e v , “ C h em istry a n d T e c h n o lo g y o f C ra ck in g ,”
p p . 184^90, N e w Y o r k , 1932. S ta n d a r d m e th o d for t h e q u a n tit a tiv e d e te r m in a tio n o f th e c h e m ic a l c o m p o sitio n o f c ra ck ed g a so lin e .
s S ee a lso refs. 2 a n d 5.
c J . C. V lu g te r , H . I . W a te r m a n , a n d H . A . v a n W e s te n , “ I m p r o v e d M e th o d s o f E x a m in in g M in eral O ils, e s p e c ia lly t h e H ig h -b o ilin g C o m p o n e n ts ,” J . In st.
P etro l. T ech ., 1932, 18, 7 3 5 - 7 5 0 ; 1935, 2 1 , 6 6 1 -6 7 6 . “ T h e A p p lic a tio n o f
■ G rap h ical a n d S ta t is t ic a l M eth o d s o f H y d r o c a r b o n A n a ly s is t o D ie s e l F u e ls ,”
ib id ., 1939, 2 5 , 6 7 8 -6 8 3 .
d S. S. K u r tz a n d C. E . H e a d in g to n , “ A n a ly s is o f L ig h t P e tr o le u m F r a c tio n s ,”
I n d u s tr . E n g n g Chem . A n a l., 1937, 9 , 2 1 -2 5 .
e R . M. D e a n e s ly a n d L . T . C arleton , “ T y p e A n a ly s is o f H y d r o c a r b o n O ils,” I n d u s tr.
E n g n g Chem . A n a l., 1942, 14, 2 2 0 -2 2 6 .
1 S ee a lso in B ., p p . 5 3 -9 2 , “ H y d r o c a r b o n G r o u p s.” I n B ., p p . 9 3 - 1 1 8 , “ N o n - H y d r o c a r b o n C o n stitu e n ts .”
" H . A b ra h a m , “ A s p h a lts a n d A llie d S u b sta n c e s,” N e w Y o r k , 1938.
h O. G. S tr ieter , “ M eth o d for D e te r m in in g t h e C o m p o n e n ts o f A s p h a lts a n d Crude O ils,” J . R e s. N a t. B u r . S ta n d ., 1941, 2 6 , 4 1 5 -4 1 8 .
’ A . J . H o ib e r g a n d W . E . G arris, J r ., “ A n a ly tic a l F r a c tio n a tio n o f A s p h a lt s ,”
In d u s tr . E n g n g Chem . A n a l., 1 9 4 4 , 16, 294-302.''
2 F . D . R o ssin i, “ A D e c a d e o f R e se a r c h o n t h e C h em ica l C o n stitu tio n o f P e tr o le u m ,”
(1) P ro c . A . P . I . , 1937, 18, I I I , 3 6 - 5 9 ; (2) O il G as J . , 1937, 3 6 , (2 6 ), 1 9 3 -2 2 2 ; (3) R ef. N a t. G aso. M fr ., 1937, 1 6 , 5 4 5 -5 6 2 .
3 F . D . R o ssin i, B . J . M air, A . F . F o r z ia ti, A . R . G la sg o w , J r ., a n d C. B . W illin g h a m ,
“ M eth o d s for A n a ly sin g t h e G a so lin e F r a c tio n o f P e tr o le u m , w ith P r e lim in a r y R e s u lts on E a s t T e x a s a n d O k la h o m a C ru d es,” (1) P ro c . A . P . I . , 1942, 2 3 , I I I , 7 -1 4 ; (2) O il G a s J ., 1942, 4 1 , (27), 1 0 6 -1 1 4 ; (3) P e tro l. R efin er, 1942, 2 1 , 3 7 7 -3 8 2 . 4 A . F . F o r z ia ti, C. B . W illin g h a m , B . J . M air, a n d F . D . R o s s in i, “ H y d r o c a r b o n s in th e G a so lin e F r a c tio n o f S e v e n R e p r e s e n ta tiv e C rudes, in c lu d in g a ll th e D is t illa te to 102° C. a n d t h e A r o m a tic s t o 160° C .” , (1) P ro c . A . P . I . , 1943, 24, I I I , 34—4 8 ; (2) J . R e s. N a t. B u r . S ta n d ., 1944, 3 2 , 11—3 7 ; (3) P e tro l. R e fin er,
1943, 2 2 , 1 0 9 -1 1 9 .
5 F . D . R o s s in i, “ H y d r o c a r b o n s in t h e L u b r ic a n t F r a c tio n o f P e tr o le u m ,” (1) P ro c A . P . I . , 1938, 19, I I I , 9 9 - 1 1 3 ; (2) O il G as J . , 1938, 3 7 , (27), 1 4 1 - 1 5 3 ; (3) R e f N a t. G aso. M f r ., 1938, 17, 5 5 7 -5 6 7 .
xvAAxvvjfu'oc'jxxiio . xvjA T IO N O F C R U D E O IL S . 7 6 F . D . R o s sin i a n d B . J . M air, “ H y d ro ca rb o n s in th e K ero sen e F r a c tio n o f P e tr o
le u m ,” (1) P ro c. A . P . I . , 1941, 2 2 , I I I , 7 - 1 2 ; (2) O il O a s J . , 1941, 4 0 , (26), 1 2 9 - 1 3 2 ; (3) R e f. N a t. O aso. M fr ., 1941, 20, 4 9 4 -4 9 8 .
7 B . J . M air a n d S. T . S c h ic k ta n z , “ C o m p o sitio n o f P e tr o le u m W a x ,” I n d u s tr.
E n g n g C hem ., 1936, 2 8 , 1 0 5 6 -1 0 5 7 .
8 S ee a lso in B ., p p . 3 5 -5 2 , “ H y d ro ca rb o n s in Crude O ils.” In B ., p p . 9 3 -1 1 8 ,
“ N o n -H y d r o c a r b o n C o n stitu e n ts .”
9 A . W . T r u s ty , “ H y d ro ca rb o n S tru c tu re o f P e tr o le u m is C o m p le x ,” P etro l. R efiner, 1942, 2 1 , 2 5 7 -2 6 0 .
10 S ee ref. 2, O il G as J . , 1937, 36, (26), 1 9 4 -1 9 7 . 11 S ee ref. 2, O il G as J . , 1937, 36, (26), 1 9 7 -2 0 2 .
12 J . R . N ie ls e n , “ A p p lic a tio n o f S p e c tr o sc o p y in th e P e tr o le u m I n d u s tr y ,” O il Gas J . , 1942, 40, (37), 3 4 -3 9 .
O. L . R o b e r ts, “ Q u a n tita tiv e A n a ly sis b y M ass S p e c tr o m e tr y ,” P etro l. E n g r., M ay, 1943, 1 4 , 1 0 9 -1 1 1 .
C. H . S ch lesm a n a n d F . P . H o c h g e sa n g , “ R a d ia tio n : th e N e w P e tr o le u m A n a ly tic a l T o o l,” O il G as J . , 1944, 42, (2), 4 1 -4 4 , 69, 72, 7 5 -7 6 .
13 J . L e c o m te in A , p p . 1 1 9 6 -1 2 0 2 , “ T h e A p p lic a tio n o f t h e In fra -red A b so r p tio n S p ectra to th e S tu d y o f P e tr o le u m O ils a n d S p ir its .”
R . B . B a r n e s, U . L id d el, a n d V . Z. W illia m s, “ In fra -red S p e c tr o sc o p y In d u s tr ia l A p p lic a tio n s ,” In d u s tr. E n gn g Chem . A n a l., 1943, 15, 6 5 9 -7 0 9 ; in b o o k form b ib lio g r a p h y in clu d ed .
14 J . H . H ib b e n in A , p p . 1 2 0 6 -1 2 1 2 , “ T h e A p p lic a tio n o f t h e R a m a n E ffe c t to P e tr o le u m C h e m istr y .”
A . A n d a n t in A , p p . 1 2 1 3 -1 2 1 5 , “ A n a ly sis o f P e tr o le u m S p ir its u sin g th e R a m a n S p e c tr o g r a p h .”
G. G lock ler, “ T h e R a m a n E ffe c t,” R e v. M o d e rn P h y sic s , 1943, 15, 1 1 1 -1 7 3 , e s p e c i
a lly p p . 1 5 6 -1 5 9 .
15 F . F r a n c is a n d S. H . P ip e r , in A , p p . 1 2 0 3 -1 2 0 5 , “ T h e A p p lic a tio n o f th e X - R a y M eth o d t o th e S tu d y o f th e P araffin H y d r o c a r b o n s.”
16“ C. F . M ab ery, “ On th e C o m p o sitio n o f A m erica n P e tr o le u m ,” P ro c. A m e r . P h il.
S o c., 1897, 36, 1 2 6 -1 4 0 .
4 C. F . M ab ery, “ A R e su m e o f th e C o m p o sitio n a n d O ccurrence o f P e tr o le u m ,”
P ro c. A m e r . P h il. S oc., 1903, 4 2 , 3 6 -5 4 .
c S. F . P e c k h a m , “ F ir st I n te r n a tio n a l P e tr o le u m C ongress, P a r is, 19 0 0 ,” P etro l.
In d u s tr . T echn. R e v., L o n d o n , 1900, 3 , S u p pl. 3 9 -4 1 .
d K . W . C harichkoff, Z h u m . R u sskoe F iz ik i K h im ich esk o e ohshchestyo, S t. P e te r s bu rg, 1896, 29, 1 5 1 -1 7 1 ; Chem . Z tg ., 1896, 20, 1 0 33; 1897, 21, 7 ; Chem . Z en trb l., 1897, I I , 2 1 3 -2 1 4 .
" J . A . A k u n ja n z , T r u d y bak. otd. im p . ru ssk . techn. obshch., 1897, 12, 4 3 8 ; Chem . Z tg . R e p ., 1897, 2 1 , 311.
K . W . C harichkoff, V e stn ik sh irov. veshch., 1904, 5 , 1 50; Chem . Z tg . R e p ., 1904, 28 392
9 N a p h th a , 1903, 11, 2 4 -2 5 .
u M. A . R a k u sin , “ P o la r im e tr ie der E r d o e le ,” p . 38, B e r lin , 1910.
* A . R ic h e a n d G. H a lp h e n , J . de P h a rm , et de C h im ., 1894, 30, (5), 2 8 9 -3 0 0 ; D in g l.
p o ly t. J . , 1895, 2 9 6 , 9 4 -9 6 .
1 S .-A isin m a n n , D in g l. p o ly t. J ., 1895, 2 97, 4 4 -4 7 .
* H . v . H o efer, “ D a s E r d o e l u .s. V e r w e n d u n g ,” 3rd ed ., p . 107, B r a u n sch w eig , 1912.
1 C. E n g le r a n d H . v . H o efer, “ D a s E r d o e l,” V o l. 1, p p . 226, 2 2 9 -2 3 0 , L e ip z ig , 1913.
m R . F . B a c o n a n d W . A . H a m o r, “ T h e A m erica n P e tr o le u m I n d u s tr y ,” V o l. 2, p . 4 47, N e w Y o rk , 1916.
17 N . A . C. S m ith , “ T h e In te r p r e ta tio n o f C rude-O il A n a ly s e s ,” U .S . B u r. M ines, R e p . I n v . 2 8 0 6 , 1927, 20 p p .
18 S ee ref. 17, p . 33.
19 N . A . C. S m ith a n d E . C. L a n e , “ T a b u la te d A n a ly se s o f R e p r e s e n ta tiv e Crude P e tr o le u m s o f t h e U n ite d S ta t e s ,” U .S . B u r. M in es, B u i. 2 91, 1928, 69 pp . 20 E . C. L a n e a n d E . L . G arton , “ B a s e o f a Crude O il,” U .S . B u r. M in es, R e p . I n v .
3279, 1935, 12 pp .
21 A . J . K ra em er a n d G. W a d e , “ T a b u la te d A n a ly se s o f T e x a s Crude O ils,” U .S . B u r. M in es, T ech . P a p e r 607, 1939, p . 2.
22 See ref. 20, p . 10.
23 See in C, C hapter V I I , “ T h e E v a lu a tio n o f O il S to c k s ,” p p. 68 et seq.
S ee a lso for co m p a riso n : “ D e te r m in a tio n o f C om p oun d s-G rou p s,” e sp e c ia lly refs. le a n d le.
8 M A R G O S C H E S : C L A S S IE I C A tiu j n u i- < jn u u n u r n o . 24 S ee in C, p p . 7 1 -7 6 .
25‘ S ee in C, p . 77.
20 See in C, p p . 71, 72.
27 S ee ref. 2, O il G as J . , 1937, 36, (26), 202.
S ee a lso for co m p a riso n refs. lc a n d ls. ,,
28 P . D o c k s e y in A , p p . 1 0 9 1 -1 0 9 8 , “ V isc o sity I n d e x a n d V is c o s ity G r a v ity C o n sta n t.
S ee in B , p p . 2 2 6 -2 2 8 .
S ee in C, p p . 6 9 - 7 1 . „
J . C. C ragg a n d E . A . E v a n s , “ V is c o s ity M e a su rem en t a n d V is c o s it y I n d e x ,
J . I n s t. P e tro l., 1943, 29, 9 9 -1 0 9 . _ . .
29 K . M. W a tso n a n d E . F . N e lso n , “ Im p r o v e d M eth o d s for A p p r o x im a tin g C ritica l an d T h er m a l P r o p e r tie s o f P e tr o le u m F r a c tio n s ,” I n d u s tr . E n g n g C h em ., 1933, 25, 8 8 0 -8 8 7 .
30 K . M. W a tso n , E . F . N e lso n a n d G. B . M u rp h y, “ C h a r a c te r iz a tio n o f P e tr o le u m F r a c tio n s ,” In d u s tr . E n g n g Chem,., 1935, 2 7 , 1 4 6 0 -1 4 6 4 .
31 R . L . S m ith a n d K . M. W a tso n , “ B o ilin g P o in ts a n d C ritica l P r o p e r tie s o f H y d r o ca rb o n M ix tu r e s,” In d u s tr . E n g n g C h em ., 1937, 2 9 , 1 4 0 8 -1 4 1 4 .
32 R . M. D e a n e s ly a n d L . T . C arleton , “ A d d itiv e P h y s ic a l P r o p e r tie s in H y d r o c a r b o n M ix tu r e s,” J . P h y s . C h em ., 1942, 4 6 , 8 5 9 -8 7 0 , se e p p . 8 6 3 -8 6 5 .
33 R . C. M ith o ff, G. R . M acPh&rson, a n d F . S ip o s, “ C h a r a c te r istic s o f C alifornia C rude O ils,” P ro c . A . P . I . , 1941, 22, I I I , 2 5 -3 7 , se e p . 30.
34 H . M. S m ith , “ C orrelation I n d e x to A id in I n te r p r e tin g C rude O il A n a ly s e s ,” U .S . B u r. M in es, T e ch . P a p e r 6 10, 1940, 34 p p .
35 E . A . J a c k so n , “ B o ilin g P o in t — G r a v ity C o n sta n t is I n d e x o f L u b e O il C h aracter
is t ic s ,” O il G as J . , 1935, 33, (44), 16, 20.
36 See a lso ref. 10.
37 S ee ref. 34, p p . 4, 2 9 -3 1 .
38 H . M. S m ith , “ A n a ly se s o f S o m e I llin o is C rude O ils,” U .S . B u r. M in es, R e p . In v . 35 3 2 , 1940, 27 p p ., se e e s p e c ia lly p . 5.
39® o . W . R e e s, P . W . H e n lin e , a n d A . H . B e ll, “ C h em ica l C h a ra cteristics o f Illin o is Crude O ils, w it h a D isc u s sio n o f th e ir G e o lo g ic a l O ccu rren ce,” D iv . o f t h e S ta te G eol. S u r v e y , U rb a n a , 111., R e p . I n v . 88, 1943, 128 p p .
b S ee a lso v a lu e s o f C .I. in th e A n a ly se s in : B . G u th rie, “ A n a ly s e s o f C rude O ils from so m e W e st T e x a s F ie ld s ,” U .S . B u r. M in es, R e p . I n v . 3 7 4 4 , 1944, 45 p p.
40 S ee ref. 39«, p . 21.
41 B . P . V o in o v , “ In d e x in g o f P e tr o le u m s a n d th e ir C la ssific a tio n ,” V estn ik S ta n d a r d iz a ts ii, 1937, N o . 4, 4 3 - 4 4 ; K h im . R e fera t. Z h u m ., 1938, 1, 127; A m er.
Chem . A b s tr., 1939, 33, 7085.
42 H . D . W ild e , “ W h y C rudes D iffe r in V a lu e ,” B u i. A m e r . A s s . P e tro l. G eol., 1941, 25, 1 1 6 7 -1 1 7 4 .
43 G. A . B e isw e n g e r , “ F a c to r s A ffe c tin g th e R e fin e r ’s C hoice o f C ru d es,” A m e r . In s t.
M in. M et. E n g r s., T e ch . P u b l. 1155, 1940, .11 p p .
44 A . E . D u n sta n , “ C h e m istr y a n d t h e P e tr o le u m I n d u s tr y ,” J . I n s t. P e tro l., 1943, 29, 1 6 3 -1 8 9 .
15 L . C. U ren , “ D e c im a l I n d e x o f P e tr o le u m T e c h n o lo g y ,” C le v e la n d , 1928.
40 “ C la ssific a tio n D e c im a le U n iv e r s e lle ,” I n s t it u t I n t e r n a tio n a l d e B ib lio g r a p h ie , B r u x e lle s, 1 9 2 7 -1 9 3 3 .
47 R e m a r k o f th e w riter o f t h is r e v ie w .
48 H . B r ig g s, P ro c. R o y . S o c., E d in b u rg h , 1 9 3 0 -1 9 3 1 , 5 1 ,5 4 - 6 3 ; 1 9 3 3 -1 9 3 4 , 54, 1 1 5 -1 2 0 .
THE MICROBIOLOGICAL ASPECTS OF GASOLINE INHIBITORS.
B y Fr a s e r H. Al l e n.*
Ga s o l i n e s are stabilized against gum and colour form ation, and th e precipitation of T E L , by th e addition of suitable substances know n as inhibitors or anti-oxidants. The use of anti-oxidants to inhibit th e au toxidation of organic com pounds was reported by Moureu and Dufraisse in a series of over th irty publications starting in 1922.1 The stabilization of m otor fuels by th e addition of inhibitors was first introduced in E ngland in 1926, where tricresol was em ployed in m otor benzoles.2 Three years la te r th e first use of inhibitors by th e petroleum in d u stry was reported in papers by Egloff, Faragher, and M orrell.3 Since th a t tim e gasoline inhibitors have become regularly em ployed in stabilizing essentially all gasoline m otor fuels.
The chemical m echanism by which th e usual inhibitor concentrations of ab o u t 0-002 per cent.- by weight can successfully stabilize gasolines during storage periods of up to eighteen m onths has never been adequately explained. I t is know n th a t th e form ation of gum is represented by a chain of chemical reactions, an d th a t inhibiting or preventing any reaction in th e chain will consequently re ta rd or prevent th e production of gum as th e final product. H ydrocarbon peroxides are know n to represent th e first step in th e form ation of gum in gasolines. Gasoline inhibitors ap p aren tly exert th e ir effect by preventing this initial peroxidation.
This contention is supported by th e fact th a t peroxide concentrations are usually negligible in inhibited gasolines stored in th e dark.
Gasoline inhibitors are sometimes referred to as “ anti-o x id an ts.”
A nti-oxidants are generally assum ed to p rotect th e substance to which th e y are added by th e preferential oxidation of th e anti-oxidant mole
cules. The period of protection, or “ induction period,” continues u ntil th e anti-oxidant is com pletely oxidized. This concept requires th a t one molecule of an ti-oxidant be destroyed for each reaction chain which is broken or prevented from starting. The num ber of oxidation chains which are in itiated in th e absence of an anti-oxidant even during short periods of storage far exceeds th e num ber of molecules of inhibitor which are present. This phenom enon is usually explained by following th e original concept of Moureu an d Dufraisse.1 These workers postulated th a t th e oxidized an ti-oxidant molecule breaks down to yield inactive oxygen plus th e original anti-oxidant molecule which is ready to de
activ ate another activ ated oxygen molecule. Milas 4 points out th a t a mechanism of th is kind is therm odynam ically unsound, since no provision is m ade for th e energy whiqh m ust be liberated by th e breakdow n of th e oxidized anti-oxidant molecule.
R ecent studies in these laboratories 5 have shown conclusively th a t
* D e p a r tm e n t o f P etro leu m E n g in eerin g , T h e U n iv e r s ity o f T e x a s.
1 0 A L L E N : T H E M IC R O B IO L O G IC A L A S P E C T S OJb' G A SU LlJN Ji H'ijCLujJix'-'a.vo.
various m icro-organisms in th e w ater phase w hich is norm ally presen t below gasoline m otor fuels in storage m ay have a pronounced deterio ratin g effect on th e m otor fuel. This effect has also been produced b y certain gasoline-soluble bacterial ex tracts. The b acterial a c tiv ity was found to resu lt in m an y cases in th e greatly increased form ation of peroxides an d gum in m otor gasolines an d th e precipitation o f lead te tra e th y l from av iatio n gasolines. I n a few cases th e results of b acterial actio n were found to be actually beneficial to gasoline sta b ility . This s tu d y has also shown th a t all th e com pounds w hich are em ployed com m ercially as gasoline inhibitors contain a phenolic, or polyphenolic group, a n d th e re b y possess an tib acterial properties. A num ber of organic dyes also are know n to be reasonably good gasoline inhibitors. The b acterio static properties of such com pounds is well know n.6' 6,1 An incom plete list of some of th e b e tte r inhibitors and reference to th e bactericidal powers of th e inhibitors, or very closely related com pounds, is shown below.
Ta b l e I .
L ite ra tu re R eferences w h ich D escrib e the B a c te ric id a l P r o p e r tie s o f S e v e ra l C om m on O asolin e In h ib ito r s .
C om p oun d . In d u c tio n P e r io d .3
D e sc r ib e d a s I n h ib ito r b y -
D e s c r ib e d a s B a c te r ic id e b y —
a -N a p h th o l . 2 2 5 0 F isc h e r a n d G u sta fs o n 7 R a iz is s a n d C lem en ce 8 p -A m in o p h e n o ls 2 340 R o g e r s a n d V o o r h e e s 9 O str o m isle n s k y 10 H y d r o q u in o n e 85 L e w is a n d M ead 11 M a ed a 12 0-, m -, p -C reso ls 210 H o ffe r t a n d S o m e r v ille 2 K a n o a 13
P y r o g a llo l 2185 L e w is a n d M ead 11 M a ed a 12
C a tech o l 2400 H y m a n a n d A y r e s 14 M a ed a 12
6 -N a p h th o l . 330 P u r e O il C o .15 R a iz is s a n d C lem en ce 8
G u a ia co l 105 E g lo ff, e t a l l R e a d 16
This relationship betw een th e com m on gasoline inhibitors a n d their disinfectant properties, to g eth er w ith th e fa c t t h a t b a c teria are found to ex ert a p articu larly detrim e n tal effect u pon gasolines during storage over w ater, suggests th a t an im p o rta n t function of these in hibitors is their ab ility to minimize b acterial action. Since th e b acteria live in th e w ater phase an d use th e gasoline as th e ir carbon source, it is . logical to assum e th a t th e b acteria te n d to congregate on th e w ater side of th e gasoline- w ater interface. The im p o rta n t characteristics of a satisfacto ry gasoline inhibitor are th a t th e substance is soluble in gasoline a n d as n early insoluble in w ater as possible. To be effective as d isinfectants ag ain st Tm~p.ro- organism s below th e gasoline-w ater interface, it is necessary t h a t th e bactericidal group in th e chem ical stru c tu re o f th e d isin fectan t be located in th e w ater phase. I t is evident t h a t th e com m on gasoline inhibitors which are used comm ercially depend on th e ir phenolic groups for th e ir bactericidal properties. I t is also know n th a t phenol a n d o th e r arom atics w hich possess a highly polar radical have a strong ten d en cy to orient them selves a t th e interface betw een a non-polar organic solvent a n d w ater, so th a t th e polar radical is located in th e w ater phase an d th e benzene ring is in th e organic solvent. I n th is w ay a gasoline in h ib ito r w hich contains a phenolic group would orient itself a t th e interface in such a
w ay th a t th e toxic hydroxyl group is located below th e interface in th e p roxim ity of th e bacteria.
The efficiency of gasoline inhibitors as bactericides will depend on th e ir concentration a t th e gasoline-w ater interface. No direct m easure
m ent of th is concentration was possible. G ibbs’ rule states th a t if the interfacial tension of a solvent is reduced by increasing th e concentration of th e solute, th e n th e solute will be concentrated a t th a t interface. Thus a decrease in interfacial tension a t th e gasoline-w ater interface when an inhibitor is added would indicate th a t th e inhibitor is concentrated on th e gasoline side of th e interface. The following surface an d interfacial tension d a ta were obtained on a n unleaded aviation gasoline base stock w ith several commercial gasoline inhibitors and lecithin, which is added to gasolines to increase inhibitor efficiency. The concentration of th e inhibitors was approxim ately 0-0012 per cent, by weight an d of th e lecithin, 0-005 per cent, by weight. These interfacial tension m easurem ents were m ade w ith a ring ty p e tensim eter.
A L L E N : T H E M IC R O B IO L O G IC A L A S P E C T S O F G A S O L IN E IN H IB IT O R S . 1 1
Ta b l e I I .
S u rfa ce a n d In te r fa c ia l T en sio n R e la tio n sh ip s o f a n In h ib ite d A v ia tio n G asoline B a se Stock.
S y ste m . In te r fa c ia l T e n sio n .
G asolin e—air . . . . 28-0 d y n e s /c m .2
G a so lin e + le c itliin -a ir . . . . . . . 27-9
G a so lin e + A -n -b u ty l-p -a m in o p h e n o l-a ir . . . . 27-9 G a so lin e + 2 : 6 -d i-ie r i.-b u ty l-4 -m e th y l p h e n o l-a ir 27-9
G a so lin e -w a te r . . . . . . . . 36-0
G a so lin e + le c ith in -w a te r . . . . . . ni l ,,
G a so lin e -j- A -^ -b u ty l-p -a m in o p h e n o l-w a te r 20-8 G asolin e -j- 2 : 6 -d i-ieri.-b u ty l-4 = m eth y l p h e n o l-w a te r . 33-8 G asolin e -j- J V -iso b u ty l-p -a m in o p h en o l-w a ter 18-0 G asolin e -j- jV -n -b u ty l-p -a m in o p h en o l + le c ith in -w a te r 1-5
There is no question th a t th e inhibitors and lecithin are strongly adsorbed a t th e gasoline-w ater interface. Thus, according to G ibbs’ rule, these m aterials will be concentrated a t th e interface. The orientation concept th e n provides th a t th e phenolic hydroxyl group will be located in th e w ater phase a t th e interface where th e bacteria are also th o u g h t to con
centrate to gain easy access to th e gasoline hydrocarbons.
Fig. 1 shows th e orientation of several inhibitor molecules a t th e gasoline- w ater interface. I t would be expected th a t compounds such as catechol w ith tw o phenolic hydroxyl groups which can both be located in the w ater phase a t th e same tim e would be more effective th a n th e mono
hy droxy phenols. I t is ap p aren t th a t th e p-am inophenol ty p e of inhibitor which is used so widely in th e in d u stry consists essentially of a phenolic group, which is oriented w ith th e toxic hydroxyl group in th e w ater phase an d great enough m ass of hydrocarbon radicals to m ake th e molecule m ore soluble in gasoline th a n in w ater. Thus p-cresol is a b e tte r inhibitor th a n phenol, because phenol is too soluble in w ater and does n o t ten d to concentrate a t th e gasoline-w ater interface so readily. The cresols generally are also known to be more toxic th a n phenol, as their high
phenol coefficients indicate. U sually these hydrocarbon groups are tie d to th e phenol b y m eans of a n am ino-nitrogen atom . The alk y lated phenols, especially those which m ay occur n a tu ra lly in th e crude, are also know n to m ake excellent inhibitors. I t is easily observed from th e illustration th a t hydrocarbon groups which are su b stitu te d in th e para position to th e phenolic hydroxyl group are th e m ost effective in m ain taining th e desired orientation of th e hydroxyl group in th e w ater phase.
rO X O ' * Xro 0
1
1 2 A L L E N : T H E M IC R O B IO L O G IC A L A S P E C T S O F G A S O L IN E IN H IB IT O R S .
NH
o-Naphthol N -n -B u tyl-p-o m in op h en ol Ca techol
p-Creso l m - C re s o l
L e c ith in Fi g. i.
T H E O R IE N T A T I O N O P I N H I B I T O R M O L E C U L E S A T T H E G A S O L I N E - W A T E R I N T E R P A C E .
S u b stitu tio n in th e ortho an d meta positions should n o t be so effective in th is respect, since th e y w ould exert a m om ent on th e benzene ring w hich w ould te n d to pull th e phenolic hydroxyl group from th e w ater phase.
Two hydroxyl groups on th e same benzene ring are advantageous if th e y are ortho to one another so th a t th e y can b o th be located in th e w ater phase a t th e same tim e. More th a n one hydroxyl group lo cated in th e meta or para positions is a disadvantage, since th e benzene ring m u st he in th e interface, th ereb y reducing th e effectiveness of th e hy d ro x y l groups.
The p-am inophenol com pounds w hich are used so extensively as gasoline inhibitors in th e in d u stry are secondary amines, an d should serve as effective reducing agents capable of decomposing hydrocarbon peroxides.
T hus, in addition to th e toxic phenolic group, these com pounds also con
A L L E N : T H E M IC R O B IO L O G IC A L A S P E C T S O F G A S O L IN E IN H I B IT O R S . 1 3
ta in a reactive group which m ay destroy such hydrocarbon peroxides as are form ed. Fig. 1 shows th a t this amino group is oriented in th e gasoline phase som ew hat above th e gasoline-w ater interface. In this location it is available to reduce an y peroxides which m ay diffuse from th e interface tow ards th e m ain body of th e gasoline. I t appears th a t a gasoline inhibitor like A - n - butyl -p - a m inophenol serves in th e dual role of (1) inhibiting bacterial peroxidation by th e toxic phenolic group an d (2) reducing peroxidized hydrocarbons by th e oxidation of th e amino group.
According to th is concept of inhibitor action, a p articularly effective inhibitor for th e storage of gasoline over w ater m ight be a su b stitu ted catechol such as 1 : 2-dihydroxy-4 : 5-di-IV-alkyl am inobenzene, which would be insoluble in w ater and be capable o f orientation w ith tw o toxic phenolic hydroxyl groups below th e gasoline-w ater interface.
Le c i t h i n a s a n In h i b i t o r In t e n s i f i e r.
The use of soybean lecithin has been described in th e litera tu re to increase inhibitor efficiency.17’ 18> 19 The m echanisms by which this is accom plished are vaguely asserted to be “ b o th physical an d chem ical.” 17 I t has also been suggested th a t lecithin acts as a peptizing agent or as a protective colloid in preventing th e form ation of haze in leaded gasolines.19 L ecithin is found to be insoluble in w ater an d soluble in gasoline in w hat appears to be a tru e solution. Since th e choline an d oleic, palm itic and glyceryl phosphoric acid which are th e ap p aren t reactive com ponents of lecithin did n o t give th e same stabilizing effect as lecithin itself,17 it is concluded th a t it is th e physical size of th e non-polar molecule which accounts for this property. The fact th a t lecithin is so strongly adsorbed a t th e gasoline-w ater interface suggests th a t its actual function in increas
ing inhibitor efficiency w hen gasoline is stored over w ater m ay be an ability to facilitate th e orientation of th e phenolic inhibitors a t th e interface.
Previous work in these laboratories has shown th a t th e ra te o f gum form a
tion in gasolines stored over w ater is g reatly increased by th e presence of air or oxygen in th e w ater phase.20 I t was also concluded from th e same w ork th a t m ost of th e deterioration takes place a t th e gasoline- w ater interface.
Two possible explanations of th e m echanism by which lecithin is capable of inhibiting th e deterioration of gasolines in storage are suggested from th e foregoing discussion. These m ay be classified as physical ( la and 16) and bacteriological (2) as follows, (la) L ecithin is know n to be adsorbed on th e gasoline side of th e interface, where it m ay serve as an inert layer which retard s th e diffusion of oxygen an d /o r oxidation products from th e interface to th e m ain body o f th e gasoline. (16) I t is also possible th a t th e large molecules of lecithin m ay aid in orienting or stabilizing th e orientation of th e phenolic groups of th e inhibitors a t th e interface.
(2) Most of th e micro-organisms which are present in gasoline storage ta n k w aters are soil bacteria. Lecithin is easily hydrolysed by soil bacteria to produce glycerol, fa tty acids, phosphoric acid, a n d choline.21 I t is suggested th a t lecithin m ay have a beneficial effect on gasolines which w ould otherwise be subject to bacterial action by being preferentially attack ed , thereby sparing th e hydrocarbons from oxidation. I t is reported
th a t lecithin is also effective as a n inhibitor when gasolines are sto red d ry.
I t is general refinery practice to d iv ert finished m otor fuels to ta n k farm storage over w ater before th e y are m easured in to drum s for shipm ent.
D uring th is storage over w ater gasoline is subject to b acterial action.
The gasoline m ay also become contam in ated b y e x trac tin g d etrim en tal oxidative enzymes into th e gasoline phase. These enzym es w ould th e n be carried into th e d ry storage w ith th e gasoline. Since all b acterial action m ay be considered as being enzym atic a n d m an y o f th e enzym es produced by bacteria are gasoline-soluble, it is possible t h a t dissolved lecithin could ex ert a sim ilar beneficial effect on dissolved oxidative enzym es in contam inated gasolines stored dry.
Me t a l De a c t i v a t o r s.
The use of disalicylal ethylene for th e d eactiv atio n o f copper, iron, cobalt, an d vanadium has been described by Downing, Clarkson, and P eterson.22 Traces of these m etals, p articu larly copper, in gasolines have a very severe effect on its storage stab ility . A ny of th e m etals which these authors have nam ed m ay co n stitu te th e m etallic ato m in th e p o r
ph y rin enzymes. The porp h y rin enzym es are v e ry activ e biological oxidation an d reduction cataly sts w hich are form ed b y b acterial as well as other form s of life. The porphyrins are v ery widely d istrib u te d in n a tu re ,23 an d th e ir solution or dispersion in gasoline as a re su lt of bacterial action seems quite likely. I t appears possible t h a t these m etals m ay actually be present in th e gasoline in th e form of th e ir p o rp h y rin com pounds. D isalicylal ethylene m ig h t th e n d ea ctiv ate th ese several m etals b y some reaction w ith th e p o rp h y rin molecule w hich w ould reduce its a ctiv ity as an oxidation-reduction enzym e. This hypothesis presents an interesting topic for fu tu re research.
Su m m a r y.
A new th e o ry is presented to account for th e delay in th e d eterio ratio n of gasoline m otor an d aviation fuels w hich is produced b y th e ad d itio n of inhibitors. The bactericidal properties of th e com m ercial inhibitors are noted. D a ta are presented to show t h a t these inhibitors are strongly adsorbed a t th e gasoline-w ater interface w here th e y are able to ex ert th e ir greatest bactericidal ac tiv ity . The m icrobiological aspects of inhibitor intensifiers an d m etal d eactiv ato rs are also discussed. This biological concept of gasoline inhibitors is in ten d ed to supplem ent th e extensive chemical research which has been conducted on th e d eterio ratio n of gasoline m otor fuels in storage.
Ac k n o w l e d g e m e n t.
The au th o r wishes to express his a p p reciatio n to D r. Lewis F . H a tc h an d D r. H . J . Sawin of th is U niversity for th e ir help in th e p re p aratio n of th is paper.
L ite r a tu re C ited.
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