tained from run 1 a t 900" F. u s i n g r e c y c l e g a s for entrainment is t h e l e a s t aromatic. T h e o i l from run 2 a t t h e s a m e temperature but using a i r for entrainment is somewhat more aromatic. The a i r d e c r e a s e d t h e over-all o i l yield by 20 t o 25 % and t h i s d e c r e a s e may h a v e been differential according t o hydrocarbon type. T h e oil obtained a t t h e higher t e m p e r a t u r e of 950" F. and a l s o u s i n g air, is t h e most aromatic, showing t h e combined e f f e c t s of t h e s e two variables. T h e oil yield on t h i s last run w a s equivalent t o t h e run using rec y c l e gas. T h e aniline p o i n t s of t h e individual fractions obtained i n t h e vacuum d i s t i l l a t i o n s of t h e s e o i l s , plotted in F i g u r e 6, show t h a t t h e d i f f e r e n c e s in composition of t h e o i l s are a l s o evident i n the higher-boiling fractions where hydrocarbon group determinations could not b e made. Figure 6 i n c l u d e s a n i l i n e points for the entrained s o l i d s oil and a n average curve that is taken a s representative of o i l s produced in t h e F i s c h e r a s s a y , G a s Combustion, Union, and Otto retorts. T h e curve for the entrained s o l i d s oil approximates t h a t for t h e medium aromaticity oil from t h e P a r r y retort, although t h e entrained s o l i d s o i l w a s from a run having a nominal retorting temperature about 200' F. higher. Although retorting temperature i s an important variable t h a t may b e correlated with composition for a given retort, other factors s u c h a s residence time affect composition. O i l s from retorts in which t h e products a r e removed by a s w e e p g a s and from t h e F i s c h e r a s s a y retort h a v e much higher a n i l i n e points, as indicated by t h e upper curve i n F i g u r e 6. A s t h e Brazilian and Colorado s h a l e s differ with r e s p e c t t o nitrogen content, t h e hydrocarbon compositions of s e v e r a l oils were compared to see if differences were indicated. T h e F i s c h e r a s s a y , entrained s o l i d s , and G a s Combustion retorts were used on s h a l e s from both s o u r c e s . Hydrocarbon a n a l y s e s of t h e combined naphtha and light d i s t i l l a t e fractions after removal of tar a c i d s and tar b a s e s a r e shown in T a b l e 111. T h e s a t u r a t e s for t h e Colorado oils are c o n s i s t e n t l y higher and t h e aromatics correspondingly lower, with only small differences in t h e olefin c o n t e n t s . T h i s trend is apparent even if t h e t a r a c i d s and tar b a s e s , which are generally higher for the Colorado o i l s , are considered a s aromatics.
SUMMARY O i l s obtained from B r a z i l i a n and Colorado s h a l e by s e v e r a l different experimental retorting methods have been analyzed by t h e Bureau of Mines method for crude s h a l e oil. T h e proportion of lower-boiling d i s t i l l a t e s w a s primarily a function of the retorting method, but t h e Colorado o i l s a l w a y s contained larger amounts of residuum. T h e retorting method
c a u s e d a variation in t h e t o t a l nitrogen and sulfur c o n t e n t s of t h e o i l s . T h e average nitrogen content of t h e Colorado o i l s was about twice that of t h e Brazilian o i l s . T h i s difference apparently r e s u l t s from variations in structure of organic matter, as total nitrogen c o n t e n t s were about t h e same. Most of t h e Brazilian o i l s had a different distribution of nitrogen with respect to boiling range than t h e Colorado oils. O i l s produced from the two s h a l e s by the s a m e retorting method showed regular differences in hydrocarbon composition, the Colorado o i l s having a greater content of s a t u r a t e s and a lower content of aromatics.
ACKNOWLEDGMENT T h i s project w a s part of t h e Synthetic F u e l s Program of t h e Bureau of Mines, performed a t t h e Petroleum and OilShale Experiment Station, Laramie, Wyo. T h a n k s are extended t o R. A. Van Meter, I. A. J a c o b s o n , and L . G. Adams for analytical work. T h e s a m p l e s of Brazilian oil were analyzed under a cooperative agreement between t h e Brazilian and United S t a t e s Governments. T h e work w a s done under a cooperative agreement between t h e University of Wyoming and the U. S. Department of t h e Interior, Bureau of Mines.
LITERATURE CITED (1) Allbright, C. S , Dinneen, G. U., Ball, J. S , U. S. Bur. Mines, Rept I n v e s t 5286 (1956). (2) Cameron, R. J., Guthrie, R , Chem. Eng. Progr. 50, 336-41 (1954). (3) Guthrie, B., Klosky, S , U. S. Bur. Mines, Rept I n v e s t 4776 (1951). (4) Rlosky, S., U. S. Bur. Mines, Bull. 468, 588 (1949); Ger. Patent 717,737. (5) Kraemer, A. J., Thome, H. M , U. S Bur. Mines, Rept. Invest. 4796 (1951). (6) Parry, V. F., Landers, W. S , Wagner, E O., Goodman, J. R , Lammers, G. C,Ibid., 4954 (1953). (7) Reed, H . , Berg, C., Petroleum Processing 3, 1187-92 (1948). (8) Secretary of the Interior, Annual Report for 1950, Part IIOil from Oil Shale; U. S Bur. Mines, Rept. Invest. 4771 75 (1951). (9) Sohns, H. W., Jukkola, E E., Cox, R. J., Brantley, F. E., Collins, W. G., Murphy, W. I. R., Znd. Eng. Chem. 47, 461 (1955). . . (10) Stanfield, K. E,Frost, I. C., U. S Bur. Mines, Rept Invest. 4477 (1949). (11) Stevens, R. F.,Dinneen, G. U., Ball, J. S , Ibid., 4898 (1952). (12) Thorne, H. M., Kraemer, A. J., Ibid., A736 (1950). (13) Ibid., 5019 (1954). Received for review May 14, 1956. Accepted March 7, 1957. Division of Petroleum Chemistry, 129th Meeting, ACS, Dallas, T e x . , April 1956.
Distribution of Nitrogen Compounds in Wilmington, Calif. , Petroleum R. V. HELM, D. R. LATHAM,. C. R. FERRIN,' AND J. S. BALL P e t r o l e u m ond O i l - S h a l e E x p e r i m e n t Station, Bureau of Mines, Department of t h e Interior, L a t o m i e , Wyo.
U. S.
N itrogen compounds in petroleum are known to h a v e d e l e t e r i o u s e f f e c t s on cracking c a t a l y s t s i n refining operations (6, 8 , 22, 26) and on t h e s t a b i l i t y of petroleum products ( 5 , 25). Knowledge of t h e occurrence, types, and 'Present address, U. S . Air Force, San Antonio, Tex.
1957
properties of nitrogen compounds i n petroleum i s important in combating t h e s e undesirable e f f e c t s . To procure fundamental d a t a on t h e structure and properties of t h e s e compounds, t h e American Petroleum I n s t i t u t e R e s e a r c h Project 52 on nitrogen c o n s t i t u e n t s i n petroleum w a s e s t a b l i s h e d July 1, 1954. T h e initial s t u d i e s of one p h a s e of Project CHEMICAL AND ENGINEERING DATA SERIES
95
5 2 h a v e b e e n concerned with t h e nitrogen compounds i n a c.rude o i l from t h e Wilmington field i n California. A concentrate of nitrogen compounds w a s prepared by a combination of deasphaltening and adsorption techniques. T h e removal of a s p h a l t e n e s by pentane precipitation inc r e a s e s the fluidity of t h e oil, making i t more convenient t o handle. T h e nitrogen compounds were then segregated from t h e deasphaltened o i l by a n adsorption technique, using Florisil. Control t e s t s of t h e two procedures gave considerable information on t h e distribution of the nitrogen compounds i n the crude oil. T h i s report d e s c r i b e s t h e distribution of nitrogen i n t h e crude oil a s a function of molecular weight, d i v i d e s t h i s nitrogen into b a s i c and nonbasic categories, and d e s c r i b e s some of t h e precautions n e c e s s a r y t o prevent c h a n g e s in t h e nitrogen compounds during processing. T h e major portion of t h e nitrogen compounds present in Wilmington crude oil h a v e molecular weights a b o v e 320. T h e ratio of b a s i c t o total nitrogen is fairly constant throughout t h e crude oil with a value of 0.28. T h e nitrogen compounds h a v e high sensitivity toward oxygen, and careful blanketing of t h e material with oxygen-free nitrogen during t h e various p h a s e s of processing w a s employed. A procedure for obtaining a concentrate of nitrogen compounds for further separation work is a l s o given.
SELECTION OF CRUDE OIL Wilmington crude o i l w a s s e l e c t e d b e c a u s e i t represents a large source of production and h a s a high nitrogen content, which f a c i l i t a t e s t h e study of nitrogen compounds. For comparison, T a b l e I s h o w s t h e nitrogen contents of crude o i l s from t h e ten largest f i e l d s in t h e United S t a t e s in 1953. Table I.
Nitrogen Contents of Crude O i l s from T e n Largest Producing Fields in the United States
Field
State
Nitrogen, Wt. 70
East Texas Wilmington Ventura Avenue Coalinga Rangely Huntington Beach Wasson Hawkins Goldsmith Veha
Texas California California California Colorado California Texas Texas Texas Oklahoma
0.085 0.65 0.42 0.52
purification and drying, the nitrogen contained l e s s t h a n 2 p.p.m. of oxygen and up t o 150 p.p.m. of water. All equipment w a s No. 7740 Pyrex g l a s s or s t a i n l e s s s t e e l to minimize contamination or decomposition of t h e nitrogen compounds. Solutions and s o l v e n t s were transferred by s t a i n l e s s s t e e l microbellows pumps. T o t a l nitrogen w a s determined on t h e fractions from t h e s e s t u d i e s by t h e macro-Kjeldahl method using t h e modification of L a k e and others ( 4 ) . Basic nitrogen w a s determined o n t h e fractions by potentiometric titration using t h e method of Moore, McCutchan, and Young (10). No determination of total or b a s i c nitrogen w a s made below 0.001%. Molecular weights were calculated on t h e fractions from t h e distillations by t h e method of Mills, Hirschler, and Kurtz (9). Molecular weights of t h e residue from t h e distillation of t h e deasphaltened oil and of t h e a s p h a l t e n e s were determined by t h e ebullioscopic method (3, 7 ) . T h e crude oil w a s deasphaltened in Deasphaltening. s t a i n l e s s s t e e l pressure v e s s e l s by diluting with 15 volumes of n-pentane. T h e s e l e c t i o n of 1 5 volumes of n-pentane w a s b a s e d on r e s u l t s obtained in small-scale s t u d i e s , which indicated that fewer a s p h a l t e n e s were precipitated by either more or l e s s dilution with n-pentane. After precipitation of t h e asphaltenes, t h e pentane solution w a s separated from them by pressure filtration, and the a s p h a l t e n e s were washed with n-pentane. T h e n-pentane w a s removed from t h e o i l by isothermal stripping a t 50' in the Pyrex-glass apparatus shown in F i g u r e 1. T h i s isothermal stripping unit provides for evaporation of t h e solvent from a t h i n film of o i l while sweeping with a countercurrent stream of purified nitrogen gas. D i s t i l l a t i o n . Comparative fractions of t h e crude oil and deasphaltened oil were prepared by a distillation procedure similar t o that employed i n t h e Bureau of Mines routine a n a l y s i s method. T h e s e distillations yielded, for e a c h oil, U .
7 EXHPUST
9
0.063 0. a3
0.10 0.13 0.086
0.27
T h e California R e s e a r c h Corp. supplied a 21-barrel sample of crude oil from t h e Wilmington, Calif., field. T h i s sample w a s collected and stored under nitrogen in 1954. Twelve barrels of t h i s s a m p l e were received by API Research P r o j e c t 5 2 for s t u d i e s of nitrogen compounds, 8 barrels were received by A P I Research Project 4 8 for s t u d i e s of sulfur compounds, and 1 barrel w a s received by A. H. Corwin a t J o h n s Hopkins University for s t u d i e s of porphyrin content. T h e general properties of t h i s crude o i l , a s determined by t h e Bureau of Mines routine crude-oil a n a l y s i s (Id), a r e listed i n T a b l e 11.
EXPERIMENTAL A concentrate of nitrogen compounds w a s prepared by deasphaltening t h e crude oil with n-pentane and segregating t h e nitrogen compounds of t h e deasphaltened oil by Florisil adsorption. A s some organic nitrogen compounds a r e s e n s i t i v e to oxygen a s well a s to heat and light, materials were protected during a l l operations. T h e nitrogen u s e d a s a n inert blanket g a s w a s t h e commercial water-pumped grade subsequently purified by p a s s a g e with 5% hydrogen over a platinum c a t a l y s t in a Baker & Co. Puridryer unit. After 96
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 1. Isothermal stripping u n i t
VOL. 2, NO. I
T a b l e II. Analysis of Wilmington, Calif., Crude O i l
General Characteristics Pour point, OF. Below 5 Specific gravity, 0.939. A. P. I. gravity 19.2'. Sulfur, 70, 1.59. Nitrogen, 7'0 0.65. Color, brownish black Saybolt Universal v i s c o s i t y at IOO'F., 480 s e c . ; at 130'F., 190 s e c . Sp. Gg.,
Fraction Cut at OC.
Sum, 7'
%
60/60 F .
'A. P. I., 60 OF.
c. I.
Aniline Pzint, C.
s.
u.
Cloud Tzst, F.
Visc., 100°F.
Stage 1. Distillation at atmospheric pressure, 760 mm. Hg. First drop, 58 'C.
50 75 100 125 150 175 200 225 250 275
...
...
0.8 0.8 2.4 2.5 2.3 2.6 3.7 4.7 6.9
1.6 4.0 6.5 8.8 11.4 15.1 19.8 26.7
O.9
...
...
0.715 0.750 0.771 0.793 0.814 0.834 0.853 0.871
66.4 57.2 52.0 46.9 42.3 38.2 34.4 31.0
...
...
... ... ...
... ... 51.6 51.1 51.9 51.2 51.0 52.8 54.2 54.0
27 29 32 36 40 44 48
Stage 2. Distillation continued at 40 mm. Hg.
200 225 250 275 300
0.6 4.8 6.4 5.7 7.2 Residuum 47.2 Carbon residue of residuum, 12.77" Carbon residue of crude, 6.5%
...
38.5 44.2 51.4 98.6
0.902 0.914 0.933 0.947 1.013
...
25.4 23.3 20.2 17.9 8.2
... ... 57 63 66
...
55.2 56.2 56.8 58.2
... 51 72 145 450
...
Below 5
20 40 55
Too dark
Approximate Summary %
Light gasoline Total gasoline and naphtha Kerosine distillate Gas oil Nonviscous lubricating distillate Medium lubricating d i s t i l l a t e Viscous lubricating distillate Residuum Distillation loss
'A. P. I.
0.715 0.773
66.4 5 1. 6
17.7 8.5 4.8 9.0 47.2 1.4
0.862 0,902-0.922 0.922-0.935 0.935-0.955 1.013
32.7 25.4-22.0 22.0-19.8 19.8-16.7 8.2
...
nine fractions distilling u p t o 275" a t 760 m m . of mercury pressure, five fractions distilling up t o 300' a t 40 mm. of mercury pressure, and a residue. F l o r i s i l Adsorption. A concentrate of t h e nitrogen compounds w a s prepared from t h e deasphaltened oil, u s i n g F l o r i s i l (synthetic magnesium silicate), 30-60 mesh, a s t h e adsorbent. Smith, Smith, and Dinneen (23) h a v e shown t h i s material to b e superior t o other adsorbents i n t h e concentration of nitrogen compounds present in s h a l e oil. Small-scale s t u d i e s of t h e deasphaltened o i l in a l l - g l a s s s y s t e m s indicated that, i n eluting t h e hydrocarbon portion of t h e oil with pentane, optimum retention of t h e nitrogen compounds w a s obtained with a column height-to-diameter ratio of 60 and a ratio of 1 gram of F l o r i s i l t o 1 mg. of nitrogen. Methanol, acetone, benzene, a n d mixtures of t h e s e m a t e r i a l s w e r e t e s t e d for desorptive properties, and benzene followed by a c e t o n e w a s found t o give nearly quantitative recovery of t h e adsorbed nitrogen compounds. T h i s combination w a s used i n t h e s u b s e q u e n t s t u d i e s described below. T h e nitrogen compounds present i n t h e deasphaltened o i l were concentrated i n a s t a i n l e s s s t e e l column 1.75 x 105 inches, shown i n F i g u r e 2. T h e column w a s packed with 2 kg. of Florisi1;heated t o 150°, and purged 24 hours with purified nitrogen. T h e nitrogen flow w a s maintained while the column cooled t o room temperature. n - P e n t a n e w a s charged to t h e reservoir tank and t h e column w a s filled from t h e bottom with pentane t o d i s p l a c e t h e nitrogen. About 7 l i t e r s of pentane t h e n were p a s s e d downward 1957
Sp. Gr.
1.6 11.4
...
...
Viscosity
... 50-100 100-200 Above 200
...
through t h e F l o r i s i l to remove s o l u b l e materials from the adsorbent. Approximately 450 grams of t h e deasphaltened oil containing 0.53% of nitrogen were used. T h e deasphaltened oil w a s diluted with pentane, placed on t h e adsorbent, and eluted with approximately 15 l i t e r s of npentane t o remove t h e nonnitrogenous portion of t h e oil. T h e nitrogen compounds were removed by c o n s e c u t i v e application of approximately 15 l i t e r s e a c h of b e n z e n e and acetone. T h e s o l v e n t s were recovered for re-use by stripping in t h e isothermal unit previously described.
RESULTS N i t r o g e n D i s t r i b u t i o n from D e o s p h a l t e n i n g . Solvent extraction of t h e crude oil with 15 volumes of n-pentane g a v e two fractions-the a s p h a l t e n e s and t h e deasphaltened oil. T a b l e 111 l i s t s t h e distribution of t h e nitrogen in t h e s e materials, together with t h e ratio of b a s i c t o total nitrogen. T h e deasphaltened o i l c o n t a i n s three fourths of t h e nitrogen, and, a s i t contains t h e l o w e s t boiling materials, i s t h e most convenient and practicable for u s e in identification work. T h e a s p h a l t e n e s , which h a v e t h e highest molecular weights, represent approximately o n e fifteenth of t h e o i l , and contain about o n e fourth of t h e nitrogen. T h i s asphalt e n e material i s of s u c h complexity that detailed study of i t will b e postponed. Some consideration w a s given t o t h e stability of the a s p h a l t e n e s , from t h e standpoint of both crude-oil distillation and s t o r a g e of a s p h a l t e n e s . Separate s a m p l e s of t h e a s p h a l t e n e s heated a t 200' and 300" for 24 hours a t
CHEMICAL AND ENGINEERING DATA SERIES
97
atmospheric pressure showed only a slight i n c r e a s e i n basicity and were somewhat less s o l u b l e in benzene than the untreated a s p h a l t e n e s . No d i s t i l l a t e w a s obtained a t either temperature, although a small amount of hydrogen sulfide w a s formed a t 3 0 0 " . Exposure of the original a s p h a l t e n e s to a i r a t room temperature changed the N E / " , ratio from 0.24 t o 0.17, indicating that oxidation or polymerization reactions had occurred. T o compare propane deasphaltening with pentane deasphaltening, a sample of t h e n-pentane-deasphaltened o i l w a s deasphaltened further with propane by T h e T e x a s Co. T h i s treatment precipitated additional a s p h a l t e n e s equivalent t o 14% of the crude oil. T h e resultant oil and asphalt e n e s contained, respectively, 0.33% and 1.7% of total nitrogen. T h u s , deasphaltening with pentane followed by propane r e s u l t s in t h e removal of 21% of the crude oil or about three times a s much a s t h e pentane procedure alone. Nitrogen D i s t r i b u t i o n A c c o r d i n g t o B o i l i n g Range. T a b l e IV shows the nitrogen content of fractions from the distillation of both Wilmington crude oil and the deasphaltened oil. Nitrogen d o e s not reach t h e 0.001% level i n the d i s t i l l a t e s until the fraction d i s t i l l i n g a t a vapor temperature of 225" t o 250" is reached. Both o i l s have high N E / " , ratios in the boiling range of 250" t o 3 0 6 " (306" corresponds t o 225" a t 40 mm. of m e r c u r y pressure). High ratios in t h i s boiling range a l s o were observed by Richter and others (11). A somewhat higher N B / N T ratio o c c u r s in the crude oil fraction boiling i n the range of 250 " to 275 " than i n t h e corresponding fraction from t h e deasphaltened oil. T h e weight-per c e n t s of the distillation fractions of t h e two o i l s agree within t h e limits of experimental error, Table
Sample
Ill.
except for t h e fractions boiling a t 250" to 275". T h i s s u g g e s t s t h a t cracking of the crude oil occurs within t h i s temperature range, c a u s i n g the high N B / N T ratio. Above 275" t h e N B / N T r a t i o s are almost t h e same for both oils. T h e s e r a t i o s d e c r e a s e i n t h e higher boiling fractions t o e s s e n t i a l l y t h e s a m e r a t i o s observed i n the undistilled oils. T h e d i s t i l l a t i o n r e s i d u e s have lower ratios than t h e corresponding undistilled oils. Nitrogen D i s t r i b u t i o n from A d s o r p t i o n Separations. T h e n-pentane-deasphaltened o i l w a s subjected t o adsorption on Florisil t o produce a nitrogen-compound concentrate containing 1.5% of nitrogen. T h e concentrate, a s shown in T a b l e 111, i s approximately 25% of the crude oil, and h a s a N B / " T ratiq of 0.27. T h e pentane e l u a t e , or nonnitrogenous portion of the deasphaltened oil, contained only 0.01% of total nitrogen, and the b a s i c nitrogen w a s too low t o determine. The adsorption experiments revealed the s e n s i t i v i t y of the nitrogen compounds t o small amounts of oxygen. T a b l e V p r e s e n t s d a t a for a series of runs in which increasingly effective s t e p s were taken t o keep oxygen away from t h e oil. In run A , the F l o r i s i l column w a s washed with pentane by filling it from the top. T h e recovery of b a s i c nitrogen, a s shown i n t h e t a b l e , w a s only 88%. B a s i c nitrogen determinations were more useful, a s they show c h a n g e s in basicity of nitrogen compounds a s well a s recovery. In run B the column w a s filled with pentane from t h e bottom in order t o d i s p l a c e the a i r , and a recovery of 93% w a s obtained. Run C, which used the conditions finally adopted-namely, purging of the column with purified nitrogen a t 150" followed by filling the column from t h e
Results of Deasphaltening and Adsorption
Wt. 7 0 of Crude Oil
Per Cent of Total Nitrogen
Total Nitrogen, Wt. %
100
100
0.65
0.ia
0.288
7 93
26 74
2.28 0.53
0.54 0.16
0.24 0.30
Crude Oil
NT
NE
B a s i c Nitrogen, Wt. 70
NB/NT
Deasphaltening Asphaltenes Deasphaltened oil
Adsorption of Deasphaltened Oil
0.00 0.00 1 0.01 Florisil eluate 68 1.50 0.41 0.27 73 Florisil concentrate 25 *This ratio f a l l s in range of 0.30 k0.05 found for 14 crude o i l s by Richter and others (If). Ratio is higher for pentane-soluble material than for asphaltenes. Table IV. Nitrogen Distribution According to Roiling Range
Crude Oil Fraction Temp. "C.
Fraction, Wt. 70
Total nitrogen, 70
Deasphaltened Oil
NB/NT
Fractiona, Wt. 70
Total nitrogen, %
Distillation at 760 Mm. of Mercury u p to 75
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.013 0.038
75-100 100-125 125-150 150-175 175-200 200-225 225-250 250-275
0.3 0.a 2.0 2.2 2.0 2.4 3.4 5.2 9.6
u p to 200
0.6
0.084
4.7 6.1 5.9 8.4 46.4
0.114
... ... ... ... ... ... ... 0.21 0.60
NB/NT
... ... ... ... ... ...
0.4 0.7 1.7 1.9 2.1 2.5 3.1 4.a
a. 1
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.006 0.036
0.30 0.44
0.9 4.6 5.8 5.8 9.3 40.8
0.087 0.109 0.183 0.293 0.397 1.03
0.47 0.46 0.38 0.31 9.28 0.25
e..
Distillation Continued at 40 Mm. of Mercury
200-225 225-250 250-275 275-300 Residue aCnlculated
98
to
0.213 0.320 0.427 1.20
0.44 0.47 0.35 0.30 0.28 0.27
crude-oil b a s i s .
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 2, NO. I
T a b l e V.
Effect of Air in Concentrating Nitrogen Compounds on Florisil
Adsorption Run
C
A
B
14.2 0.13
76.4 0.32
88.7 0.27
Acetone fraction 70of N g N B /NT
74.0 0.55
16.6 0.35
14.1 0.23
Recovery % Of N g % Of N T
88.2 90
93.0 91
B e n z e n e fraction 7 ' of N g NB/NT
102.8 99
Run A. Column filled with p e n t a n e from t o p before introduction of oil. Run B. Column filled with p e n t a n e from bottom before introduction of oil. Run C. Column purged with purified nitrogen a t 150' and filled with p e n t a n e from bottom before introduction of oil.
bottom-gave quantitative recovery within experimental limits. T a b l e V a l s o s h o w s that t h e proportion of t h e b a s i c nitrogen removed from t h e F l o r i s i l by t h e benzene inc r e a s e d , and t h e amount removed by a c e t o n e d e c r e a s e d . To determine t h e heat stability of t h e nitrogen concentrate, s a m p l e s w e r e heated a t 2 0 0 " and 3 0 0 " for 24 hours under a n atmosphere of purified nitrogen. No c h a n g e s were noted a t t h e lower temperature, but a t 3 0 0 " a dec r e a s e in N B / N T occurred with some evolution of ammonia. Distillation of t h e nitrogen concentrate t o a temperature of 150' a t 0.1 mm. produced only 3% of distillate. T h e concentrate w a s s o l u b l e in pentane; however, on exposure of t h e pentane solution t o air, a granular precipitate w a s formed that w a s soluble i n benzene. ATY.)
N"
SIGHT GAGE-
QUICK CONNECTOR FOR FILLING WITH ADSORBENT
-
-
3 / 8 " TUBING
NOTE
~
Z,Z'ARE
VALVES FOR FILLING COLUMN BEFORE INTRODUCTION OF SAMPLE.
3-xx) WATT HEATING SECTIONS THERMALLY UWD
QUICK CONNECTORPYREX WOOLY Y P L l N G a M2 R R G E VALVE
0.
$
r- -7-
BLEEDlATYj
r=====f
ELUATE RESERVOIR 1 IGAL.)
Figure 2. Florisil adsorption column
1957
CRUDE OIL. WEIGHT r(RCEl1
Figure 3. Properties of fractions from Wilmington crude oil
DISCUSSION Figure 3 s h o w s s e l e c t e d properties of fractions of Wilmington crude oil, including t h e average molecular weights, b a s i c and total nitrogen contents, and mid-boiling points. T h e c u r v e s a r e derived from d a t a obtained for t h e distillate fractions of t h e deasphaltened oil, t h e residue from t h e same o i l , and t h e a s p h a l t e n e s from t h e crude oil. Inasmuch a s only two d a t a points a r e a v a i l a b l e for t h e residue and a s p h a l t e n e s , t h e c u r v e s a r e dotted i n t h e s e regions. Approximately 53% of t h e crude oil is distillable with t h e l a s t fraction having a mid-boiling point of 380" a t 760 mm. of mercury pressure. Calculation i n d i c a t e s t h a t t h e lowest boiling fraction i n which nitrogen compounds become appreciable h a s a n a v e r a g e molecular weight of 180. T h e nitrogen content i n c r e a s e s through t h e l a s t fraction t h a t contains 0.42% of nitrogen and h a s a n average molecular weight of 325. If i t i s a s s u m e d that t h o s e nitrogen compounds present contain only 1 atom of nitrogen per molecule, t h i s fraction c o n t a i n s about 10% of nitrogen compounds. F i g u r e 4, b a s e d on t h e above assumption, s h o w s per c e n t nitrogen compounds present in t h e fractions from Wilmington crude o i l . T h e distillate contains only 13% of t h e total nitrogen i n t h e crude oil and therefore represents only a small portion of t h e nitrogen compounds present in t h e crude oil. T h i s i s typical of nitrogencontaining crude o i l s as shown by t h e work of B a l l , Whisman, and Wenger (1, 2). T h e residue from t h e distillation of deasphaltened Wilmington crude o i l h a s a n a v e r a g e molecular weight of 475. T h e molecular weight c u r v e in Figure 3 i n d i c a t e s a molecular weight range of 320 t o 1100 for t h i s residue. T h e composition of t h e residue in terms of nitrogen compounds i s shown in F i g u r e 4 . B a s e d on the average molecular weight of 475, t h e residue contains 35% of nitrogen compounds, assuming one atom of nitrogen per molecule. T h i s r e s i d u e c o n t a i n s approximately 60% of t h e nitrogen present in t h e crude o i l . The a s p h a l t e n e s from t h e crude oil have a n average molecular weight of 1225. T h i s material contains 26% of the nitrogen present in t h e crude oil. T h e assumption of one atom of nitrogen per molecule l e a d s to t h e absurdity of 200% of nitrogen compounds, a s shown in Figure 4 . Consequently, most of t h e s e a s p h a l t e n e molecules must contain more than one nitrogen atom. CHEMICAL AND ENGINEERING D A T A SERIES
99
T h e relationship between b a s i c and total nitrogen i s shown in Figure 3. T h e differentiation between b a s i c and nanbasic nitrogen is probably significant in t h e lower molecular weight range a s a measure of t y p e s of nitrogen compounds present. In t h e higher molecular weight range, however, t h i s may not b e t h e c a s e . Substitution i n c r e a s e s t h e basicity of pyrroles ( I I), and tetramethylpyrazine i s only 50% titratable a s b a s i c nitrogen. R e s u l t s of t h e s t u d i e s on a s p h a l t e n e s indicate a dec r e a s e in t h e b a s i c nitrogen content of t h e s e materials when they a r e exposed t o a i r . T h e nitrogen concentrate from t h e deasphaltened o i l , while originally soluble i n pentane, will react when exposed to a i r to form a pentaneinsoluble material. F l o r i s i l adsorption s t u d i e s h a v e shown that small amounts of a i r present on t h e adsorbent will c a u s e low recovery of both total and b a s i c nitrogen. In addition, a difference in e a s e of removal of the nitrogen compounds from t h e adsorbent by benzene and acetone is indicated by runs where various quantities of oxygen a r e >resent on t h e Florisil. T h e adsorption r e s u l t s show that
nitrogen compounds from Wilmington crude o i l will react with small concentrations of oxygen a t room temperature. Both b a s i c and nonbasic t y p e s of compounds a r e reactive. A procedure b y which a concentrate of nitrogen compounds may b e obtained for future investigations of A P I Research P r o j e c t 52 c o n s i s t s of a preliminary deasphaltening s t e p followed by concentration of the nitrogen compounds by adsorption on Florisil. T h i s results in a concentrate with one fourth t h e volume and more than twice t h e nitrogen content of t h e original oil. T h e remainder of the nitrogen i s present in t h e high-molecular-weight asphaltenes. Calculations indicate t h a t the nitrogen-containing molecules (assuming one nitrogen atom t o t h e molecule and a molecular weight of 600) constitute about 65% of t h e concentrate. Further concentration and separation i s planned to identify t y p e s of compounds and some individual compounds.
ACKNOWLEDGMENT T h e authors wish t o thank W. J . Wenger for performing t h e crude oil a n a l y s i s , G. U. Dinneen and W . E. Haines for constructive criticism of t h e manuscript, and t h e entire Advisory Committee of Project 52 for encouragement.
LITERATURE CITED I
I
1
I I
I I
I
I I
I
I
I
1
I I I I I I 1 I
/
/
/
/
I I
B
CRUDE OIL, WEIGHT PERCENT
Figure 4. Quantity of nitrogen compounds in Wilrnington crude oil fractions
100
INDUSTRIAL AND ENGINEERING CHEMISTRY
i
I I
(1) Ball, J. S., VanderWerf, C. A., Waddington, Guy, L a k e , G. R., P r o c . Am. Petroleum I n s t . 34 (VI), 152 (1954). (2) Ball, J. S., Whisman, M. L., Wenger, W. J . , Ind. E n g . Chem. 43, 2577 (1951). (3) Ketcham, D . , Anal. Chem. 19, 504 (1947). (4) L a k e , G. R., McCutchan, P . , Van Meter, R., and Neel, J. C., Ibid., 23, 1634 (1951). (5) Mapstone, G. E., Petroleum Refiner 28, 111 (1949). (6) Maxted, E. B., J . SOC.Chem. Ind. (London) 67. 9 3 (1948). (7) Menzies, A. .W. C., Wright, S. L., J . Am. Chem. SOC. 43, 2314 (1921). (8) Mills, G. A., Boedeker, E. R., Oblad, A. G., Ibid., 72, 1554 (1950). (9) Mills, I. W., Hirschler, A. E., Kurtz, S. S., Jr., Ind. E n g . Chem. 38, 442 (1946). (10) Moore, R. T., McCutchan, P . , Young, D. A., Anal. Chem. 23, 1639 (1951). (11) Richter, F. P . , C a e s a r , P. D., Meisel, S. L., Offenhauer, R. D., Znd. Eng. Chem. 44, 2601, (1952). (12) Schall, J. W., Dart, J. C., Petroleum Refiner 31, 101 (1952). (13) Smith, J. R., Smith, C. R., Jr., Dinneen, G. U., Anal. Chem. 22, 867 (1950). (14) Smith, N. A. C., Smith, H. M., Blade, 0. C., Garton, E. L., “Bureau of Mines Routine Method for A n a l y s i s of Petroleum, I. Analytical Method,” Bur. Mines Bull. 490, (1951). (15) Thompson, R. B., Chenicek, J. A., Druge, L. W., Syman, T., Ind. Eng. Chem. 43, 935 (1951). (16) Voge, H. H., Good, G. M., Greensfelder, B. S., World P e t r o leum Congr., Proc., 3 r d Congr., Hague, 1951, Sect. IV, 131. Received for review November 12, 1956. Accepted January 28, 1957. Investigation performed a s part of the work of American Petroleum Institute R e s e a r c h P r o j e c t 52 on nitrogen c o n s t i t u e n t s in petroleum, conducted b y t h e Bureau of Mines in Laramie, Wyo., and Bartlesville, Okla., and t h e University of K a n s a s in Lawrence, Kan. Work done under cooperative agreements between the Bureau of Mines, U.S. Department of t h e Interior, American Petroleum I n s t i t u t e , and University of Wyoming.
VOL. 2, NO. I
