ANALYTICAL CHEMISTRY
426
films having a n extremely high permeability or having pinholes, a tube with a large diameter may be used to increase the accuracy. However, a maximum and a minimum diameter of the capillary exist. The maximum diameter is observed when the mercury will no longer fill the capillary (when mercury is used, approximately 0.3 cm.). A tube with a diameter that is too small will give excessive sticking of the mercury and thus accuracy will be impaired. When films containeven relatively large amounts of plasticizers, no inaccuracies are observed due to evaporation, as is the case when a vacuum system is employed. This is because the time required per run is much less and the apparatus is a t atmospheric pressure. The required accuracy is not too high for measurements of materials where permeability values change a great deal from sample to sample. Hotrever, on samples where the permeability is nearly constant from sample t o sample and from sheet to sheet, a high degree of accuracy is desired. On duplicate samples having the same thickness, the accuracy obtained using this apparatus was approximately 4%. A more detailed discussion of the accuracy which can be expected with this type of equipment has been given (3). EXAMPLES
The following examples will serve to typify the data which may be obtained with this apparatus and also give a n indication of the time required per run.
I. Helium Transmission for a Sample of Polyethylene Film Sample area. 314 sq. cm. Average diameter of capillary. 0.1428 em. Upstream pressure. 54 pounds per square inch Barometric pressure. 748.0 mm. Hg Temperature. 25" C. Sample 1
2 3
4
Thickness, Cm.
0.00254 0.00763 0.01320 0.08870
Time, Permeability Constant, S e c . Cc.-Cm./Sec.-Sq. Cm.-Cm.Hg
21.0 62.0 103.0
725.0
0.692 0.691 0.689 0.691
X 10-9
X 10-9 X 10 - 9 X 10-9
11. Hydrogen Transmission for a Sample of Trithene Film Sample area. 314 sq. cm. Average diameter of capillary. 0.0457 cm. Upstream pressure. 50.6 pounds per square inch
Barometric pressure. 741.4 mm. Hg Temperature. 25' C. Sample 1
2
Thickness, Cm.
0.00254 0.00508
Time, Permeability Constant, Sec. Cc.-Cm./Sec.-Sq. Cm.-Cm. Hg 190 0.0165 X 10-9 0.0167 X 10-9 370
111. Hydrogen Transmission for a Sample of Polyvinyl Chloride Film Sample area. 314 sq. cm. Average diameter of capillary. 0.0965 cm. Upstream pressure. SO_.? pounds per square inch Barometric pressure. i o 1 mm. Hg Temperature. 25" C. Film thickness. 0.0304 em. Time. I057 see 111 Is Permeability constant. 0.290 X 10-9 cc.-cm./sec.-sq.cni. -cm. Hg IV. Hydrogen Transmission for a Sample of Polyvinyl Chloride Film Sample area. 314 sq. cm. Average diameter of capillary. 0.108 cm. Upstream pressure. 25.5 inches Hg Barometric pressure. 750 mm. Hg Temperature. 25" C. Film thickness. 0.00304 cm. Time. 6.3 seconds Permeability constant. 1.50 X 1 0 - g cc.-cm , /sec.-sq. cni .-em. Hg ACKNOWLEDGMENT
The authors are indebted to General Mills, Inc., for having built the initial model. Inquiries concerning the availability of this apparatus should be directed t o General Mills, Inc., Minneapolis, Minn. LITERATURE CITED
dmerongen, van, G. J., J . Polvlnw Sci., 5, 307-32 (1950). Barrer, R. M.,"Diffusion in and through Solids," New York, Macmillan Co., 1941. Brubaker, D. TT., and Kammermeyer, K., Ind. Eiig. Chenz., 44, 1465 (1952). Cartwright, L. C., ANAL.CHEM.,19, 393 (1947). Davis, D. IT., Paper Trade J . , 123,No. 9, 33-40 (1946). Sarge, T. IT., Modern Packaging, 23, 127 (1939). Shuman, A. C., IXD.ENG.CHEM.,ANAL.ED., 16, 58 (1944). Todd, H. R., P a p e r Trade J . , 118, S o . 10, 32-5 (1944). RECEIVED for review .kiigust 27, lY52. Accepted Soveniber 26. 1952.
Determination of Basic Nitrogen in Oils VIRGINIA Z. DEAL, F R E D T. WEISS, AND THEODORE T. W H I T E ' Shell Development Co., Emerpille, Calif.
A
LTHOUGH the presence of basic nitrogen compounds in coal tars, petroleum, and shale oils has been known for nearly a century, recent emphasis on the utilization of shale and residual oils has heightened the need for methods to characterize nitrogen compounds or groups in oils. I n the past few years numerous publications have discussed the effect of nitrogen compounds on cracking catalysts and on the stability of oils in storage and have pointed up the value of a knowledge of types of nitrogen compounds in oils. Many basic nitrogen compounds have been reported to have an adverse effect on cracking catalysts, reducing the efficiency of the cracking operation seriously (6, 4 9 ) by inactivating the catalyst to varying degrees depending upon the particular type of nitrogen compound involved (51, 78). The determination of basic nitrogen allows prediction of the ex1
Present address, 145 ACNW Squadron, Fort Miley, Calif.
tent to which an oil i d 1 inactivate a cracking catalyst and may also be used as a control analysis of the effectiveness of hydrogenation. I t allows prediction of the amount of nitrogen which will be removed by acid extraction ( 4 7 ) and shows the tendency of the oil toward gum formation (6, 14,48, 71, 75, 76). Finally, it is important in the selection of an oil as a source of potentially valuable nitrogen compounds (50, 75). During the past century a great amount of work has been accomplished in the isolation and identification of nitrogen compounds in petroleum fractions, shale oils, and coal tar distillates. A detailed survey of the literature on the identification of specific nitrogen compounds in petroleum, shale oil, and coal tar is given in Table I. The majority of materials identified have been the so-called "nitrogen bases," homologs of pyridine, quinoline, and isoquinoline. Several pyrrole derivatives, such as methvl indole,
V O L U M E 25, NO. 3, M A R C H 1 9 5 3
427
Recent emphasis on the utilization of shale and residual oils has increased the need for methods to characterize nitrogen compounds or groups in oils. Two potentiometric titration methods are described for the determination and differentiation of organic bases in crudes, distillates, and residues. Total basic nitrogen can be determined by titration with perchloric acid in acetic acid-chlorobenzene solvent. ritrogen compounds of moderately strong basicity such as piperidines or alkyl amines may be distinguished from this total by titration with hydrochloric acid in chlorobenzene solvent. Neil her method determines nitrogen compounds of the pyrrole, indole, carbazole, or diphenylamine type. The basicity of the petroleum distillates, residues, and crude oils tested indicated that 20 to 4070 of the total nitrogen was present in the form of pyridine-quinoline-acridine types, whereas shale oils had from 50 to 7070 of total nitrogen in this form. No bases as strong as piperidine were found in any oils.
carbazole, and porphyrins, have likewise been isolated or identified. Apparently no saturated nitrogen compounds such as thp piperidines or alkyl amines have been definitely identified as constituents of these oils, although traces of primary and secondary amines have been reported (P8,47, 5 5 , 7 0 ) . t200 /SODIUM
HYDROXIDE
i
piperidine, alkyl amine, and quinoline types. As there appeared t o be very little difference in the titration curves of piperidine and pyridine by the perchloric acid method despite their large difference in basic strength in water, an additional method was necessary to obtain a more definite distinction between materials of such different basicity. In this second method, involving titration in chlorobenzene solution n.ith alcoholic hydrochloric acid, materials generally equivalent in basicity to piperidine or the aliphatic amines are easily differentiated from the weaker bases. The nonbasic nitrogen group is obtained as the difference between total nitrogen and total basic nitrogen. In general, this represents pyrrole or diphenylamine types; however, some substituted pyrroles and porphyrins have been reported to be moderately basic (53, 62) and may appear as basic nitrogen. The perchloric acid method for titration of weak bases was initially studied by Conant and Hall (11) and has been applied subsequently to a wide variety of amino compounds, including the determination of nitrogen bases in petroleum distillates, shale oils, and coal hydrogenation products (62,80, 81). METHODS FOR DETERMINATIOV OF BASIC XITROGEY
Total Basic Nitrogen (Perchloric Acid Alethod). The procedure employed was essentially as described by Moore, MeCutchan, and Young (62),except that the sample 1yas initially dissolved in 50 ml. of chlorobenzene and the mixture diluted with 50 ml. of acetic acid. d 1 to 1 mixture of chlorobenzene and acetic acid was used as solvent, as many of the samples tested, particularly asphalts, m-vere insoluble in acetic acid alone. The choice of chlorobenzene over benzene, also an excellent solvent for asphalts, was determined by the fact that a satisfactory potentiometric titration could not be made without special shielding devices when the cell solution contained over benzene or 50% chlorobenzene in glacial acetic acid. -%lthough the weak nitrogen base inflection covers a larger millivolt range in chlorobenzene than in acetic acid-chlorobenzpne mixtures, the advantage of extending the scope of the method somen hat by use of chlorobenzene alone did not outweigh the disadvantage of the resulting instability of the electrodes.
{
CRUDE PETHOLEURl
$%%E:c&T
Y
m{f-
---I
DISTILLATES AND R E S I D U E S
.%:FZr:HYDROXIDE n-BUTYLAMINE A 3 ,C5R- D I DI M I NEET H Y L P Y R I D I N E
3 -METHYLPYRIDINE QUINOLINE
-400 VOLUME PF H Y D R O C H L O R I C A C I D -300
Figure 1. Interpretation of Titration Curves in Hydrochloric Acid Method for Moderately Strong h'itrogen Bases Consider as moderately strong nitrogen bases only those with plateau mid-points above dashed line
Differences in the basic strength of nitrogen cornpounds suggest the possibility of analytical differentiation of nitrogen conipounds into three groups according to basicity, as illustrated in Table 11. A differentiation into three groups !vas made by 11apstone ( 4 7 ) on the basis of extractability with acid, and Moore (5E) has suggested separation into two groups by use of a perchloric acid titration similar to that described below. In this investigation, it has been found possible to achieve analytical differentiation into three nitrogen groups by use of t v o potentiometric titration methods requiring a glass-calomel electrode system. I n the first method, involving titration in a chlorobenzene-acetic acid solution with perchloric acid, total basic nitrogen is determined, including compounds of the pyridine,
-400
u
-7001
'CARBAZOLE.
INDOLE
1
Iml.
1
V O L U M E OF 0 . 1 N P E R C H L O R I C A C I D
Figure 2.
Perchloric Acid Method
Illustrative titration ourves for pure materials and oil samples
428 The total basicity of the sample, as weight per cent nitrogen, is calculated from the equation: Total basic nitrogen, %w. = ml. of perchloric acid (corrected for blank) X N X 14 grams of sample X 10
ANALYTICAL CHEMISTRY _ _ ~~
Table I.
Pyridines
Nitrogen Compounds Found in Oils.
/?"
Summary of L i t e r a t u r e S u r v e y
Source and Reference Siimber California Petroleum Cracked pressure distillate from gas Straighr. oil and run crude Crnde Shale xtru-enr residuum petroleuni oi 1
Coal tar
Moderately Strong Nitrogen Bases (Hydrochloric Acid Pyridine Method). APPARATUS. bfeter, .., ... glass electrode, calomel refer2-hlethylpyridine ... ' 5 , 24) ence electrode, stirrer, buret, Z-hlethyl-4-ethylpyridine and stand (45). Prepare, ... 5->I ethyl-5-ethylpyi idine ... maintain, and test electrodes as described by Lykken et 2-Methyl-6-ethylpyridine ,.. (24) 3-hlethylpyridine al. ( 4 5 ) . ... 184) 4-Methylpyridine ... ( 0 , 24) R EA G E s T s . P i p e r i d i n e , 2-Ethyl-4-methylpyridine . . ... (24) 0.05 N in chlorobenzene. 3-Ethyl-5-methylpyridine T e i g h accurately about 0.21 ' 65) 4-Ethylpyridine ... Li4) ... gram of piperidine (Eastman 2,3-Dimethylpyridine ... (2.4) Kodak practical) into a 502,3-Dimethyl-6-isopropylpyridine '4.2 ... .,. nil. volumetric flask and make 2,4-Dimethylpyridine ... (9,2.41 to volume with chlorobenzene. Hydrochloric acid, stand2 ,.%Dime thylpyridine .. . .. ( 0 %$4) P,6-Dimethylpyridine ard alcoholic, 0.1 .\-. Mix 0 ... ( 0 . 24) ml. of C.P. hydrochloric acid 2,6-Diniethyl-4-ethylpyridine ,.. ... with 1000 ml. of C.P. an3,4-Dimethylpyridine hydrous isopropyl alcohol. ... ,241 3.5-Dimethylpyridine ... 10, 24) APPARATUS STAXDARDIZ.42,3,4-Triniethylpyridine . . . ... TION. To ensure proper se5.3.5-Trimethylpyridine .. ... ... lection of titration end points ... ... (24) when only material with a ... basicity generally equivalent is, 'e4) ... to piperidine and the aliphatic amines is to be considered, ?,3.4,6-Tetramethylpyridine ... ... determine for the particular electrode-meter combination, ... ... ... ... at the temperature a t which titrations are to be made, the ... ... potential a t the mid-point of ... ... the titration plateau (see Fig4-Cyclopentylpyridine ... ure 1) of a standard piperidine 5-Phenylpyridine ... ... solution. Standardize once a 2-rllkenylpyridine ... ... 5-Alkylpyridine-2-methylethyl disulfide . . . . . ... week and whenever the glass electrode is changed, using a Quinolines 10-nil. portion of the freshly prepared pipeiidine qolution and titrating as described 3-7 Quinoline t)elow. .,. ' 6 , 0 , $4) ZMethylquinuline (6. 0 , 84) ... PROCEDURE. Into :t 250-ml. 2-Methyl-8-ethylquinoline 22 1 ... ... tall-form titration beaker con3-Methylqiiinoline ... (24) taining about 100 ml. of 4-hlethylquinoline ... ' 24) chlorobenzene, introduce a 5-Methylquinoline ... ... quantity of sample containing 6-SIethylquinoline ... about 0.5 meq. of base. M-arrn to dissolve if necessary. Cool t o room temperature, surround the cell completely with :I braes shield grounded to t,he instrument, and tisatisfactor! for many of the residuitl oil fractions studied in this , ' hydrochloric arid. Disregard any inflections trntr with 0.1 % investigation Potentiometric titration in benzene containing with plateau mid-points falling more than 150 mv. below that of small amounts of alcohol or no alcohol n-as not satisfactory piperidine. An arbitrary dividing line in the basicity range because of the very high resistance of the solution. Chlorotletrcted by this method is rhosen a t I50 mv. below the pil~eridineplateau mid-point, h ' b (water) = 1.6 X w3,and benzene, an excellent solvent for repidual oils, a as chosen is illustrated in Figure 1. Select, the end point from the approbecause it preqrnted fen-cr electrical difficulties than other solvents priate inflection in t,he titration curvp. Make a blank dete-ted. trimination carrying out the analysis in an identical manner but omitting the sample. Calculate in weight per cent nitrogen that, portion of the RESULTS OBTAINED WITH PURE XIATERIALS sample with a basicity generally equivalent to piperidine or the aliphatic amines: Perchloric Acid Method. T h e use of the mixed acetic acidchlorobenzene solvent has given titration curves similar t o those Moderately strong nit,rogen bases, as S , yaw. = o h t a i n d t)y Hall ( 2 5 )with glacial acetic acid alone. Illustrative nil. of hydrochloric acid (corrected for blank) X N X 14 bands rrjmsenting groups of titration curves for pure materials grams of sample X 10 are compared with those for typical oil samples in Figure 2. Titration curves for piperidine, pyridine, and similar compounds Lykken et al. (46) illustrate considerable differentiation befell in a iiarrom band despite the wide range of their aqueous tween bases in benzene-isopropyl alcohol titration solvent, and basic tlirwwiation constants. The response of a number of nitrotheir potentiometric method m-as considered ; however, the solt i ~ other materials examined is shon-n in Table gen c o m ~ ~ a u r iand vent (equal parts of benzene and isopropyl alcohol) is not
i$
I . .
t . .
of) b k
V O L U M E 25, NO. 3, M A R C H 1 9 5 3 ~
Table 1.
429
~
Nitrogen Compounds Found in Oils.
Quinolines, Contd
Summaryof Literature Survey ( C o n t d . )
Source a n d Reference S u m b e r California Petroleum Cracked pregsure distlllate from gas oil and Shale crude Crude oil petroleum residuum
...
... ... ... ...
,..
.
...
...
7-hlethylquinoline 8-Methylquinoline ?,3-Dimethylquinolinr 2.3-Dimethyl-ðylqriirioline 2.3-Dimethyl-&n-propyl~~riinoline
(24)
?.3-Diniethyl-4,8-diethylquinoline 2.3-Dimethyl-4-ethsl-8-n-r~rop?lquinoline 2,3-Dimethylbenzoih) qiiinoline 2,4-Diinethylquinoline
(24)
...
,..
...
... , . .
... . . ..
I
.
I . .
... ..
. , .
...
..
.. ...
... ... ...
..
... ...
... ..
...
..
2,8-Dlmethylqriinoline ti 8-Dimethylquinoline 2'3 4-Trimethyl-8-ethylquinoline 2~3~4-Triinethyl-8-n-propyl~uinoIine
1274)
...
, . .
...
...
.. .. ... ..
2,3,4-Triniethyl-8-isoprogylyuinol ine 2,3,8-Trimethylquinoline 2.3.8-Trimethyl-4-ethylquinoline 2,4,6-Trimetbylquinoline
... ... ...
... ...
... ...
...
... ...
.. ...
2.4.bTriinethvlauinoline
...
...
...
... ...
...
...
...
(24)
(24) (24)
... ...
... ... ...
... ...
2,4-Dimethylbenzoih)quinoline
...
...
I
.
.
...
Isoquinoline 1-Methylisoquinoline 3-Methylisoquinoline 1.3-Dimethylis0 uinoline CpHsNS (probabcty thioisoquinoline) C,aHeN (5-, 6-,or 7-methylisoquinoline) Miscellany Aniline Indole Methyl indole Pyrroles
... ...
...
...
... ...
... ... ... ...
...
... ... ,..
... ...
... ...
in Table 111, only those materials which had titration plateau mid-points above this dividing line 13-ereconsidered as reacting in the method. -in attempt was made to utilize the titration curve obtained hy the hydrochloric acid method for the determination of total basic nitrogen. This did not prove satisfactory because of the comparatively poor inflections obtained in the titration curves for the weaker bases, such as pyridine (see Figures 2 and 3). Titrat.ion a-ith stronger acid (1 .V) did not improve the pyridine end poiiit sufficiently. To determine how sharl) a differentiat,ion might be espected with oil samples, a shale oil, to n-hich piperidine had. been added, was titrated by this method. The titration curve showed a distinct inflection for the piperidine separate from t h a t of the shale oil and quantitative recovery of the added piperidine waa obtained. The basicity attributed to the shale oil was of considerably lower strength than that of the piperidine. RESULTS OBTAINED W I T H OILS
Suinerous oil samples including distillates, residues, ... asphalts, crude oils, and shale ... ... (96.38) Carbazoles (69) oils have been titrated by the ... ... ... (13. SS,361 Acridines ... lI7) ... 5,6-Dihydropyrindine (pyrindane) ... perchloric acid and the hydro... Ci1His.N (probably tl.iinethylpyrindane) (24) chloric acid methods. IYith ... ... 7-Azaindole no sample did the hydrochloric ... ... 4-Azafluorene ... ,.. 2-Azafluoranthene acid method indicate a basicity 7-Xl~thylcarbostyril ... ... corresponding in strength to ... Sitriles ... Diphenylrirethans piperidine or the alkyl amines. (2s; i.4) Pori>liyrin~. It is concluded that nitrogen compounds corresponding or analogous to these structures 111. As may be seen, neither diphenylamine (Ka = 7 X were absent from the materials tested or present only in trace nor any compound less basic is determined in this procedure. amounts. The basicity found by the peichloric acid method Thus, pyrrole, indole, carbazole, and similar materials were not for all the oil samples tested may be presumed to represent comdetermined. Salts of carboxylic acids Tvere determined quantitapounds of the pyridine, quinoline, anti act idine types. tively as bases in the titration. The basic nitrogen in shale oils determined by the perchloi ic Hydrochloric Acid Method. Titration curves for a number of acid method was found t o range from 50 to 70% of the total inaterials varying in basic strength from potassium hydroxide nitrogen content. D a t a for a series of shale oil distillation f i Nt o the essentially nonbasic carbazole are illustrated in Figure 3 tions are listed in Table IV. The propoi tion of basic nitrogen a n d compared with a band representing curves of typical oil remained of the same order of magnitude Kith the fractions of swmples. The position and differentiation of the titration curves increasing boiling range. The locations of titration rurves for corresponded approxiniatcly to the basic strength of the comtypical shale oils are shown in Figures 2 and 3. pounds in water and corresponded also with titration curves The basic nitrogen contents of petroleum distillates, residues, described by Lykken and coworkers (@) using benzene-isopropyl and asphalts (Table V) accounted for 20 t o 50% of the total alcohol solvent. The considerable difference between the titranitrogen but were lese than those of the shale oils examined, both tion curves of piperidine and the aliphatic amines and the titrain total basicity measured and in percentage of the total nitrogen. tion curves for the alkyl pyridines allows the placement of an The locations of titration curves for typical distillates, residues, arbitrary dividing line 150 niv. below the piperidine plateau and asphalts are given in Figures 2 and 3. Use of the solvents mid-point for differentiation of the basic nitrogen compounds of chosen for this investigation permitted rapid solution of the these types. I n obtaining t,he data on pure materials listed (69)
...
ANALYTICAL CHEMISTRY
430 Table IJ,
Group
Basicity of Representative Nitrogen Componnds
Same
Stiuctiire
Table 111. Results Obtained in Titration of Nitrogen Bases and Other Compounds
70 Reaction b y HC1 HClOi method for method moderately for strong S total basic N bases 9t.b at. st. st. st. st. ... st.
Dissociation Constanta, Kb (in Water a t 25' C.) Kba
(25' C.) 1 . 6 X 10-8 (41) 1 . 3 X 10-3 ( 4 2 ) 5 . 7 x 10-4 (41)
Name
I
Piperidine
Diethylamine
C2H6
\J
czir6
x
1.3
10-3
Pentamethvlhexa-
H Triethylamine
C2Ha
\d
...
CzHj 5,7
x
CZHK
CHs
I1
2 . 1 X 10-7
Trimethylpyridine
Pyridine
Quinoline
111
6 3 X 10-10
Diphenylamine
-
Pyrrole
7 X
10-14
x
10-14
2 S
...
10-4 (collidine) 3,S-Dimethylpyridine (lutidine) 3-Methylpyridine (picoline) Pyridine Quinoline 2-Methylquinoline (quinaldine) Isoquinoline Acridine Diphenylamine Py r r o1e N-Butylpyrrole Urea 2,4-Dimethyl-3,5diearbethoxypyrrole Cetylpyridinium bromide Indole Carbazole Benzotriazole Phenothiazine Benzoxazole Thiophenol 1,4-Dioxan Tetrahydrofuran Thiophene Kb = dissociation constant Stoichiometric.
2 1
7 2.5 1.5
x
10-7 ( 2 7 )
x x
'10-14 ($0)
x
'10-14 (41)
10-1' (26)
st.
st.
nt. st.
st. st.
...
st.
10.1
st.
