14 Nickel and Vanadium
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Up
to several thousand parts per million of nickel and vanadium may be present i n crude petroleum as metal porphyrin and other complexes. Although most of it i n a crude oil remains i n the residual fractions and coke during refining, minute quantities have been observed i n distillate fractions (1). Since nickel and vanadium are the most widely analyzed trace metals i n petroleum, the Project addressed itself only to the sub part-per-million levels. Available Analytical Methods. The most commonly used colorimetric reagent for nickel—dimethylglyoxime—can be used to measure levels of nickel as low as 20 ppb after appropriate preconcentration (2). F o r vanadium, hematoxylin (3) and PAR-zephiramine (4) are sensitive colorimetric reagents that can be used to measure as little as 0.1 and 0.015 ppm, respectively. However, a number of elements interfere, and they must be removed prior to measurement. X-ray fluorescence spectroscopy has been used to determine 50 ppb of nickel and vanadium after they have been concentrated on ion exchange resins (5, 6). Emission spectroscopy has been used but is only semiquantitative at the nanogram/gram levels of interest to the Project. Nevertheless, the technique may be useful as a screening tool. T w o relatively new instrumental techniques—spark source mass spectrometry (7) and kinetics of metal-catalyzed reactions (8)—can measure extremely low levels of nickel and vanadium, but they have not been utilized to any appreciable extent. F l a m e a t o m i c a b s o r p t i o n is sensitive e n o u g h t o measure p a r t - p e r b i l l i o n levels of n i c k e l i n aqueous s o l u t i o n , b u t i t is n o t t h a t sensitive f o r vanadium.
H e a t e d vaporization atomic absorption
is m o r e
sensitive,
p e r m i t t i n g d e t e c t i o n o f v a n a d i u m d o w n to 2 0 n g / m l i n aqueous s o l u t i o n . T h e r e f o r e , f o r the p r a c t i c a l q u a n t i t a t i v e d e t e r m i n a t i o n of n a n o g r a m / g r a m concentrations of b o t h n i c k e l a n d v a n a d i u m i n p e t r o l e u m , t h e c o m b i n a t i o n of H V A A
w i t h a preconcentration
a s h i n g step w a s selected f o r
detailed study. Role of Neutron Activation. T h e r m a l n e u t r o n a c t i v a t i o n does n o t p r o d u c e a s u i t a b l e g a m m a - e m i t t i n g isotope f o r m e a s u r i n g n a n o g r a m / g r a m levels of n i c k e l . F o r v a n a d i u m , t h e
5 1
V (n/y)
5 2
V reaction, producing a
1 4 3 4 - K e V g a m m a - r a y p e a k , m a y b e u s e d t o measure 10 n g V / g a n d is n o t subject to a n y interferences.
H o w e v e r , t h e h a l f - l i f e of t h e
5 2
V isotope is
160
In Analysis of Petroleum for Trace Metals; Hofstader, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
Nickel
HOFSTADER E T A L .
14.
and
161
Vanadium
o n l y 3.8 m i n , so t h a t p n e u m a t i c s a m p l e transfer f r o m t h e r e a c t o r core to t h e c o u n t i n g f a c i l i t i e s is essential. Special Analytical Considerations.
L o s s of n i c k e l a n d v a n a d i u m
w h e n p e t r o l e u m samples are d r y a s h e d is w e l l k n o w n . occur if the H V A A fractions (9).
Similar
losses
t e c h n i q u e is a p p l i e d d i r e c t l y t o s o m e p e t r o l e u m
Losses of this t y p e are p a r t i c u l a r l y serious w i t h the d i s t i l
late m a t e r i a l s s t u d i e d b y t h e P r o j e c t s i n c e t h e v o l a t i l e p o r p h y r i n s are f o u n d i n these fractions. S u l f u r i c a c i d has b e e n r e c o m m e n d e d as a s u i t a b l e d e c o m p o s i t i o n p r o c e d u r e f o r samples c o n t a i n i n g v o l a t i l e n i c k e l a n d v a n a d i u m , a n d this a p p r o a c h w a s i n v e s t i g a t e d . H o w e v e r , other
decom
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p o s i t i o n p r o c e d u r e s d e s i g n e d t o p r e v e n t loss of n i c k e l or v a n a d i u m , i n w h i c h the s a m p l e is h e a t e d w i t h either b e n z e n e s u l f o n i c a c i d (10) (11)
9
or sulfur
w e r e not i n v e s t i g a t e d .
A l t h o u g h n o c o n t a m i n a t i o n f r o m a p p a r a t u s o r reagents w a s
found
f o r v a n a d i u m , s e v e r a l sources of c o n t a m i n a t i o n w e r e e n c o u n t e r e d nickel.
H i g h p u r i t y s u l f u r i c a c i d c o n t a i n e d 4-5
for
n g N i / m l w h i l e the
h y d r o c h l o r i c a c i d d i d n o t c o n t a i n a n y m e a s u r a b l e a m o u n t . V y c o r dishes w h i c h h a d b e e n u s e d p r e v i o u s l y r e t a i n e d traces of n i c k e l t h a t w e r e signifi cant w h e n nanogram quantities were
being determined.
Even
after
t h o r o u g h w a s h i n g , s u c h dishes c o u l d n o t b e u s e d c o n f i d e n t l y . N e w glass w a r e s h o u l d b e u s e d a n d p r e f e r a b l y d e d i c a t e d e x c l u s i v e l y f o r the tests at this l e v e l . N e w vessels m u s t b e c l e a n e d c a r e f u l l y b e f o r e use. T h e d a t a i n T a b l e 14.1 s h o w t h e n i c k e l c o n t a m i n a t i o n r e s u l t i n g f r o m t w o n e w dishes Table 14.1. N i c k e l i n Solution after Successive A c i d Washing of 800-ml V y c o r Dishes Nickel Treatment (1) (2) (3) (4) (5)
a
6
10 m l 1:1 HC1 o n l y 5 m l cone. H S 0 + 10 m l 1:1 HC1 (1) F i r s t repeat of (2) Second repeat of (2) T h i r d repeat of (2) 2
4
Content
(ng)
Dish 1
Dish 2
157 74
92 55
34 23 29
19 24 24
" B o i l e d , evaporated to dryness o n the steam b a t h , a n d the residue t a k e n u p i n 10 m l 1:19 H C 1 . T a k e n to fumes of cone. H 2 S O 4 , 1 : 1 H C 1 added, t h e n t r e a t m e n t (1). 6
t h a t h a d b e e n p r e v i o u s l y u s e d o n c e to d e c o m p o s e samples c o n t a i n i n g p a r t - p e r - m i l l i o n levels of n i c k e l . T h e n i c k e l c o n t a m i n a t i o n w a s e l i m i n a t e d o n l y after several 5 - m l p o r t i o n s of c o n c e n t r a t e d s u l f u r i c a c i d w e r e t a k e n d o w n to fumes i n the d i s h ; the 20-30 n g of r e m a i n i n g n i c k e l r e p r e s e n t e d the reagent b l a n k .
In Analysis of Petroleum for Trace Metals; Hofstader, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
162
ANALYSIS O F P E T R O L E U M
FOR TRACE
METALS
T o test t h e t r e a t i n g p r o c e d u r e , s e v e r a l fuels w e r e a n a l y z e d f o r n i c k e l b y our recommended method, using both (1) treated a n d (2)
washed
b u t u n t r e a t e d V y c o r dishes. T h e results, w h i c h are c o m p a r e d i n T a b l e 14.11, s h o w t h a t c o n t a m i n a t i o n is e l i m i n a t e d b y t h e consecutive
fumings
w i t h the acid. Table 14.11.
Nickel in Fuels by H V A A Nickel Concentration
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Untreated
Vycor
(ng/g)
Treated
Vycor
Sample Gasoline Jet Fuel N o . 2 heating o i l Sample Preparation. T h e p r o c e d u r e d e s c r i b e d b y M i l n e r et a l . ( 1 2 ) , based on wet ashing w i t h sulfuric acid a n d incineration i n a V y c o r dish, w a s a d o p t e d w i t h o u t m o d i f i c a t i o n f o r t h e d e c o m p o s i t i o n of m i d d l e a n d h e a v y distillates. F o r l i g h t distillates (i.e., gasolines) t h e d e c o m p o s i t i o n t i m e was shortened considerably b y evaporating the sample i n a stream o f n i t r o g e n after t h e s u l f u r i c a c i d a d d i t i o n b u t b e f o r e t h e i n c i n e r a t i o n . Measurement.
Optimum H V A A
parameters w e r e e s t a b l i s h e d e m
p i r i c a l l y f o r s t a n d a r d d i l u t e h y d r o c h l o r i c a c i d solutions of t h e metals. T h e heat r e t a i n e d b y t h e t u b e f u r n a c e b e t w e e n cycles affects t h e repeata b i l i t y of successive injections. A l t h o u g h injections w e r e m a d e o n a fixed t i m e schedule, m u l t i p l e injections w e r e u s u a l l y necessary t o o b t a i n r e l i able readings. I t is i m p o r t a n t t o e s t a b l i s h t h a t t h e a s h c y c l e settings u s e d d o n o t cause loss of n i c k e l b y p r e m a t u r e v o l a t i l i z a t i o n . C a m p b e l l a n d O t t a w a y (13)
r e p o r t e d t h a t w h e n aqueous n i c k e l sulfate solutions w e r e i n j e c t e d ,
12-26%
of t h e n i c k e l w a s lost at a n a s h i n g t e m p e r a t u r e of 7 5 0 ° C f o r
300 sec. A t t h e p o w e r a n d t i m e settings u s e d i n t h e Project, i t w a s demonstrated that no metal was v o l a t i l i z e d prematurely. T h e existence of b a c k g r o u n d ( n o n - a t o m i c )
a b s o r p t i o n at t h e a n a l y t i
c a l w a v e l e n g t h s f o r N i (232.0 n m ) a n d V (318.5 n m ) w a s i n v e s t i g a t e d using a hydrogen c o n t i n u u m lamp. U n d e r the conditions used, the back g r o u n d signals f o r t h e samples w e r e i n d i s t i n g u i s h a b l e f r o m t h e b a s e l i n e . C o n s e q u e n t l y , n o b a c k g r o u n d c o r r e c t i o n is r e q u i r e d i n t h e p r o c e d u r e . F u r t h e r m o r e , u n d e r t h e c o n d i t i o n s f o r a t o m i z a t i o n , t h e m a x i m u m response w a s o b t a i n e d w i t h n o " m e m o r y " f r o m one a t o m i z a t i o n t o t h e next. T h e h i g h t e m p e r a t u r e r e q u i r e d to a t o m i z e t h e v a n a d i u m l o w e r s t h e l i f e of t h e a t o m i z a t i o n furnaces, a n d i t is r e c o m m e n d e d t h a t t h e f u r n a c e b e r e p l a c e d after 2 0 - 2 5 injections. electrodes
G o o d contact b e t w e e n t h e s u p p o r t
a n d the furnace must be maintained.
c r i t i c a l f o r v a n a d i u m because m a x i m u m p o w e r
T h i s is p a r t i c u l a r l y
is r e q u i r e d to ensure
In Analysis of Petroleum for Trace Metals; Hofstader, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
14.
HOFSTADER
E TA L .
Nickel
and
163
Vanadium
c o m p l e t e a t o m i z a t i o n . E v e n a s m a l l loss of p o w e r b y p o o r contacts m a y substantially reduce the temperature inside the furnace. U n d e r t h e specified c o n d i t i o n s , t h e c a l c u l a t e d d e t e c t i o n l i m i t s ( S / N =
2 ) f o r n i c k e l a n d v a n a d i u m a r e 2 Χ 1 0 " g a n d 25 Χ 1 0 " g, respec 11
11
t i v e l y . W i t h these l i m i t s , i t w a s p o s s i b l e to m e a s u r e 2 n g N i / g , a n d 5 n g V / g i n a n o r i g i n a l 100-g p e t r o l e u m s a m p l e , u s i n g respective 1- a n d 5-μ1 a l i q u o t s of t h e final s o l u t i o n f o r i n j e c t i o n . Response w a s l i n e a r o v e r t h e range 0 - 1 n g N i a n d 0 - 1 0 n g V . M a t r i x effects w e r e e n c o u n t e r e d i n t h e H V A A m e a s u r e m e n t of n i c k e l a n d v a n a d i u m . T h e response w h e n a m i x t u r e of 14 metals w a s a d d e d i n
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v a r i o u s ratios to a constant c o n c e n t r a t i o n of n i c k e l a n d v a n a d i u m is s h o w n i n T a b l e 14.111. W h e n t h e c o n c e n t r a t i o n of e a c h i n t e r f e r i n g m e t a l w a s t h e same as n i c k e l , t h e c h a n g e i n t h e n i c k e l response w a s i n s i g n i f i c a n t . H o w e v e r , as t h e c o n c e n t r a t i o n of i n t e r f e r i n g m e t a l w a s i n c r e a s e d , t h e n i c k e l response w a s s i g n i f i c a n t l y e n h a n c e d .
F o r v a n a d i u m , t h e response
w a s s i g n i f i c a n t l y depressed, e v e n w h e n t h e c o n c e n t r a t i o n of e a c h i n t e r f e r i n g m e t a l w a s t h e same as t h e v a n a d i u m c o n c e n t r a t i o n . A l t h o u g h n o e x p l a n a t i o n f o r t h e b e h a v i o r of n i c k e l a n d v a n a d i u m i n t h e presence of other metals has b e e n f o u n d , t h e n i c k e l a n d v a n a d i u m c a l i b r a t i o n curves are l i n e a r , i n d i c a t i n g t h a t t h e m e t h o d of s t a n d a r d a d d i t i o n s c a n b e utilized. E v e n w i t h t h e p r e c a u t i o n s n o t e d above, response f r o m v a n a d i u m w a s often q u i t e v a r i a b l e . C o n s e q u e n t l y , t h e slope a n d i n t e r c e p t of response Table 14.111.
Effect of Other Metals on the Determination of N i c k e l and V a n a d i u m " ' 6
Vanadium
Nickel Concentration of Each Interfering Metal/ ^g/ml 0 0.5 5 50
Avg. Re sponse, mm 50 53 65 89
Std. Avg. Dev. of Re No. Re sponse, of Meas sponse, mm urements mm 5 2 3 10
9 3 3 3
36 29 20 19
Std. Dev. of Response, mm
No. of Measurements
4 4 4 3
12 8 8 6
C o n c e n t r a t i o n of N i or V i n s o l u t i o n : 0.5 μg/m\. A m o u n t injected : 2 μ\ for N i , 5 μ\ for V . I n t e r f e r i n g metals present : S i , A l , C r , C a , F e , M g , N a , M n , Z n , C u , C o , P b , M o , N i , or V . a
6 c
vs.
/Ag/ml
of s t a n d a r d a d d i t i o n w e r e c a l c u l a t e d b y t h e m e t h o d of least
squares. T h e s t a n d a r d d e v i a t i o n of t h e response a b o u t t h e regression l i n e w a s also c a l c u l a t e d , a n d a n y d a t a p o i n t s o u t s i d e 2σ of t h e regression l i n e w e r e rejected.
T h e slope a n d i n t e r c e p t w e r e t h e n r e c a l c u l a t e d , a n d t h e
In Analysis of Petroleum for Trace Metals; Hofstader, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
164
ANALYSIS OF P E T R O L E U M
FOR TRACE
METALS
c o n c e n t r a t i o n of v a n a d i u m i n t h e s a m p l e s o l u t i o n w a s o b t a i n e d
by
e x t r a p o l a t i n g t h e " r e f i n e d " regression U n e . I n a l l d e t e r m i n a t i o n s t h e regression l i n e w a s s t a t i s t i c a l l y tested f o r l i n e a r i t y . T h e response w h e n n i c k e l w a s a t o m i z e d v a r i e d less t h a n that of v a n a d i u m , so t h e n i c k e l c o n c e n t r a t i o n i n t h e s a m p l e s o l u t i o n c o u l d b e c a l c u l a t e d e i t h e r b y least squares o r t h e e q u a t i o n o n p . 170. Recommended Method. I n t h e r e c o m m e n d e d m e t h o d a 1 0 0 - g s a m p l e is d e c o m p o s e d w i t h c o n c e n t r a t e d s u l f u r i c a c i d , a s h e d at 500° C , d i s s o l v e d i n d i l u t e h y d r o c h l o r i c a c i d , a n d t h e c o n c e n t r a t i o n of n i c k e l o r v a n a d i u m m e a s u r e d b y H V A A u s i n g t h e m e t h o d of s t a n d a r d a d d i t i o n s . T h e results
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of a p p l y i n g this p r o c e d u r e t o several d i s t i l l a t e fuels are s h o w n i n T a b l e 1 4 . I V . E a c h m a t e r i a l w a s s p i k e d t o c o n t a i n different levels o f n i c k e l a n d v a n a d i u m , w h i c h w e r e a d d e d as t h e sulfonates.
Essentially quantitative
recoveries w e r e o b t a i n e d f o r b o t h n i c k e l a n d v a n a d i u m f r o m a l l m a t e r i a l s . T h e s t a n d a r d d e v i a t i o n f o r n i c k e l w a s ± . 6 o v e r t h e r a n g e 5 0 t o 100 n g N i / g , a n d for v a n a d i u m ± 8 n g V / g over the range 30-100 n g V / g . T h e f e w tests at t h e h i g h e r l e v e l i n d i c a t e d a c o m p a r a b l e p r e c i s i o n . S a m p l e s of gasoline, jet f u e l , a n d N o . 2 h e a t i n g o i l w e r e s p i k e d w i t h n i c k e l a n d v a n a d i u m sulfonates a n d , together w i t h u n s p i k e d samples, w e r e a n a l y z e d a t t h e i n i t i a t i n g l a b o r a t o r y a n d at o n e c o o p e r a t i n g l a b o r a tory.
T h e results o n t h e s p i k e d samples at t h e c o o p e r a t i n g
laboratory
w e r e , o n t h e w h o l e , l o w e r t h a n those o f t h e i n i t i a t i n g l a b o r a t o r y
(Table
14.V), although the precision was identical. T h e l o w e r r e c o v e r y at t h e c o o p e r a t i n g l a b o r a t o r y is a t t r i b u t e d t o a t i m e l a g i n t h e analysis. T h e c o o p e r a t i n g l a b o r a t o r y a n a l y z e d t h e samples a b o u t f o u r m o n t h s after t h e y w e r e p r e p a r e d , w h e r e a s t h e i n i t i a t i n g l a b o r a t o r y a n a l y z e d t h e samples i m m e d i a t e l y . A separate l o n g - t e r m s t a b i l i t y s t u d y d e m o n s t r a t e d t h a t n i c k e l a n d v a n a d i u m sulfonates i n kerosene w e r e g r a d u a l l y d e p l e t e d i n storage ( F i g u r e 1 4 . 1 ) , a n d t h e d e l a y i n p e r f o r m i n g Table 14.IV.
Recovery of N i c k e l and Vanadium in Distillate Fuels by H V A A Method Nickel
Sample
Added
Concentration (ng/g) Measured"
Vanadium
% Recovery
Added
Concentration (ng/g) Measured'
% Recovery
53 95
56 93
100 95
35 72
41 74
117 103
Kerosene
104
106
102
109
98
90
Gasoline
234
208
89
468
467
100
D i e s e l fuel
a
Average of triplicate determinations.
In Analysis of Petroleum for Trace Metals; Hofstader, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
14.
HOFSTADER
Nickel
ETAL.
and
165
Vanadium
Table 14.V. Interlaboratory Analysis for N i c k e l and Vanadium by Proposed Method Nickel
Concentration (ng/g)
Added
Measured
0
Sample
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Vanadium
Initi ating Labora tory
Cooper ating Labora tory
Concentration (ng/g)
Added
Measured* Initi ating Labora tory
Cooper ating Labora tory
Gasoline
0 34