Application of Inductively Coupled Plasma Atomic Emission

7 Application of Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) to Metal Quantitation and Speciation in Synfuels R. S. BROWN, D. W. HAUSLER , J. W. H E L L G E T H , and L . T . T A Y L O R 1

Downloaded by CORNELL UNIV on October 15, 2016 | http://pubs.acs.org Publication Date: November 12, 1982 | doi: 10.1021/bk-1982-0205.ch007

Virginia Polytechnic Institute and State University, Department of Chemistry, Blacksburg, V A 24061

Metal analysis in coal derived products has typically been a laborious, time consuming process. Even with multielement emission techniques, typical sample preparations involving destruction of the sample matrix has limited sample throughput while not allowing any subsequent speciation. The direct analysis of coal derived products via inductively coupled plasma atomic emission spectrometry (ICP-AES) in organic solvents without pre-treatment is reported. Several solvents which can be employed with ICP are tabulated along with specific element detection limits. Subsequent analysis by liquid chromatography coupled with ICP detection in several modes is described for model organometallic systems as well as for several coal derived products as a first step toward speciation of organically bound metals in coal derived products. Highly s p e c i f i c information concerning the chemical nature and concentration of each moiety i n coal and coal conversion products i s d e s i r a b l e i f extensive coal u t i l i z a t i o n i s t o be achieved.(1_) Considering the high complexity and heterogeneous nature of each sample, m u l t i p l e , i n f o r m a t i o n - s p e c i f i c , chromatographic-spectroscopic a n a l y t i c a l methods are r e q u i r e d . In s o l u t i o n , where the maximum information i s achieveable the a n a l y s i s problem i s f u r t h e r complicated by the f a c t that most conventional s p e c t r o s c o p i c and chromatographic solvents have l i t t l e a f f i n i t y f o r coal and coal l i q u i d s . Within t h i s context, the q u a n t i t a t i o n and s p e c i a t i o n of o r g a n i c a l l y bound t r a c e metals i n coal l i q u e f a c t i o n s o l u b l e products presents a r e a l c h a l l e n g e . Quantitative t r a c e element methods i n the s o l i d s t a t e on l i q u e f a c t i o n Current address: Phillips Petroleum Company, Research and Development Laboratory, Bartlesville, OK 74005 1

0097-6156/82/0205-0163$06.25/0 © 1982 American Chemical Society

Fuller; Coal and Coal Products: Analytical Characterization Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


164

COAL AND

COAL

PRODUCTS

products have been p r e l i m i n a r i l y e x p l o r e d . Spark source mass spectrometry has been used to survey the d i s t r i b u t i o n and general l e v e l of about s i x t y elements in the feed coal (West V i r g i n i a ) and products from a s i n g l e batch of a long-term l i q u e f a c t i o n run on the 400 l b coal/day PDU at the Pittsburgh Energy Technology Center.(2) Atomic absorption spectrometry (AAS) was employed f o r p r e c i s e a n a l y s i s of s p e c i f i c elements. In each case, samples were ashed p r i o r t o a n a l y s i s to destroy the organic m a t e r i a l . Neutron a c t i v a t i o n a n a l y s i s (NAA) has been r e c e n t l y used t o obtain information on p o s s i b l e t r a c e element species present in s o l i d SRC I and l i q u i d SRC II products derived from a Western Kentucky c o a l . ( 2 » £) Although the d e t e c t i o n l i m i t s , multielement c a p a b i l i t y and r e l a t i v e lack of matrix i n t e r f e r e n c e s make NAA an a t t r a c t i v e a n a l y t i c a l procedure, long i r r a d i a t i o n times (10 minutes to 8 hours) and counting times (up t o 3 weeks) are major undesirable f e a t u r e s . Furthermore, " o n - l i n e " a n a l y s i s of separated components i s t o t a l l y i m p r a c t i c a l from a t i m e / e f f o r t point of view. Quantitation methods in s o l u t i o n have a l s o been minimal and have involved e i t h e r s i n g l e element (continuous n e b u l i z a t i o n ) a n a l y s i s v i a atomic absorption spectrometry^) (AAS) or m u l t i element a n a l y s i s v i a i n d u c t i v e l y coupled plasma atomic emission spectrometry (ICP-AES) both on acid digested aqueous-based matrices.(6) These methods have not proven h i g h l y s a t i s f a c t o r y because acTd d i g e s t i o n r i s k s the loss of v o l a t i l e elements and i n t r o d u c e s , in some cases, a s u b s t a n t i a l blank v a l u e , r e q u i r e s a great amount of time and labor and, in the AAS c a s e , provides f o r only s i n g l e element determinations with mandatory background correction. An a n a l y t i c a l method which e l i m i n a t e s the sample preparation step and provides f o r multi-element q u a n t i t a t i v e a n a l y s i s in the low ppm range seems h i g h l y a t t r a c t i v e f o r coal l i q u e f a c t i o n products. In t h i s regard ICP-AES a n a l y s i s in a p y r i d i n e matrix w i l l be reported here. For comparison, the simultaneous determination of 15 d i f f e r e n t wear metals in l u b r i c a t i n g o i l s d i s s o l v e d in 4-methyl-2-pentanone appears t o be the only p r e v i o u s l y reported e f f o r t at q u a n t i t a t i o n v i a ICP-AES in a t o t a l l y organic m a t r i x . ( 7 ) The need f o r sample d i g e s t i o n , in most of these r e p o r t s , in order t o achieve a metal a n a l y s i s r e s u l t s in m o d i f i c a t i o n of the chemical nature of the metals in these complex mixtures. Direct a n a l y s i s in p y r i d i n e or any other organic solvent may allow f o r information regarding the chemical nature of s p e c i f i c e n t i t i e s to be e s t a b l i s h e d . Information regarding s p e c i a t i o n , however, i s not r e a d i l y a s c e r t a i n e d . While c e r t a i n spectroscopic techniques such as x-ray photoelectron spectroscopy and heavy metal nuclear magnetic resonance spectrometry, are capable of y i e l d i n g s p e c i a t i o n i n f o r m a t i o n , these methods normally r e q u i r e a r e l a t i v e l y large concentration of i n d i v i d u a l metal s p e c i e s . A c e r t a i n degree of success in t h i s area has been r e c e n t l y achieved. EXAFS has been used to c h a r a c t e r i z e t i t a n i u m species in s o l i d SRC



7.

BROWN ET

AL.

Metal Analysis Using

ICP-AES

165

I and l i q u i d SRC II products and t o probe the chemical and s t r u c t u r a l environment of vanadium in coal and coal l i q u e f a c t i o n products,(8) Q u a n t i t a t i v e aspects of these s t u d i e s were not considered. In the same v e i n , an extensive e x t r a c t i o n ( a c i d i c methanol) and chromatographic procedure has been applied t o Daw M i l l coal (92 Kg) with the r e s u l t that 17.8 mg of a mixture of gallium complexes of homologous porphyrins (C27-C32) has been i s o l a t e d f o r the f i r s t time. I d e n t i f i c a t i o n was based upon a combination of s p e c t r o s c o p i c techniques.(9) In a n t i c i p a t i o n of experiments designed t o y i e l d q u a n t i t a t i v e s p e c i a t i o n i n f o r m a t i o n , we have r e c e n t l y e s t a b l i s h e d the c a p a b i l i t y f o r multi-element detection in toluene and p y r i d i n e matrices.(1Ό, 11) The development of a s i z e e x c l u s i o n chromatographyTTCP-AES i n t e r f a c e designed to handle h i g h l y v o l a t i l e organic solvents was reported and t e s t e d with mixtures of model organometallies. Multi-dimensional chromatographic f r a c t i o n s c o n t a i n i n g o r g a n i c a l l y bound metals from a SRC (Wyoming subbituminous coal) have r e c e n t l y been isolated(12) employing t h i s technique as a f i r s t step toward metal s p e c i a t i o n . The present work which we b e l i e v e r e l a t e s to both q u a n t i t a t i o n and s p e c i a t i o n w i l l (1) extend the number of solvents and chromatographic methods which can be employed using t h i s technique, (2) present metal detection l i m i t s in a v a r i e t y of solvents f o r both d i r e c t a s p i r a t i o n and pumped d e l i v e r y , (3) d i s c u s s t r a c e metal q u a n t i t a t i v e a n a l y s i s data obtained on p y r i d i n e s o l u t i o n s of several SRC's as a f u n c t i o n of processing c o n d i t i o n s and coal source and (4) d e s c r i b e the i s o l a t i o n of o r g a n i c a l l y bound metal f r a c t i o n s in a SRC process s o l v e n t . Experimental The ICP-AES used in t h i s work was an ARL (Sunland, CA) model 137000. The LC i n t e r f a c e and instrumental parameters have been described p r e v i o u s l y ( l O ) . An ice bath was used t o thermostat the i n t e r f a c e with a l l s o l v e n t s . Chromatographic equipment consisted of a Waters 6000A ( M i l f o r d , MA) pump with a Valco (50 and 200 yl loop) i n j e c t i o n valve f o r i s o c r a t i c s e p a r a t i o n s . Columns were purchased commercially and included a Waters μ - P o r a s i l s i l i c a column (3.9mm χ 30cm), a Waters normal phase μ-Bondapak CN (3.9 mm χ 30 cm) column, a Whatman Polar Amino Cyano column (4.6mm χ 75cm) and a Waters 100 A μ-Styragel s i z e e x c l u s i o n column (3.9 mm χ 30 cm). Solvents were chromatographic grade from F i s h e r S c i e n t i f i c . Model organometallie compounds were from "in-house" stocks or were purchased from chemical warehouses. Organo-metal q u a n t i t a t i o n standards in an o i l matrix were obtained from Conostan (Ponca C i t y , 0K) at 300 ppm concentration of each element. C a l i b r a t i o n standards in the range 0-25 ppm were prepared on a w/w basis in p y r i d i n e . C a l i b r a t i o n curves were generated from these standards f o r subsequent metal a n a l y s i s . T y p i c a l root mean square (RMS) concentration e r r o r f o r t h i s curve



166

COAL AND

COAL

PRODUCTS

was -2% or b e t t e r f o r most elements. P y r i d i n e s o l u t i o n s of coal derived material were -5-7% w/w. In order t o provide continuous d e l i v e r y of p y r i d i n e t o the n e b u l i z e r spray chamber, a standard l i q u i d chromatographic pump in conjunction with an i n j e c t o r equipped with a 3 ml sample loop was employed. To avoid d i l u t i o n of t h i s sample " p l u g " , a i r bubbles were placed in f r o n t and back of the sample. Flow r a t e s of 0.5 ml/min were employed with s i g n a l i n t e g r a t i o n times of 10-30 seconds. With chloroform and heptane as s o l v e n t s , d i r e c t a s p i r a t i o n of standard s o l u t i o n s was employed and d e t e c t i o n l i m i t s f o r a l l solvents were determined f o r each element by c a l c u l a t i n g the concentration of analyte necessary t o give a s i g n a l equal t o twice the standard d e v i a t i o n of the background emission at each wavelength. It should be noted that a l l d e t e c t i o n l i m i t s reported here are those at the i n t e r f a c e and represent the l i m i t s f o r both t o t a l unseparated metal and chromatographically separated and detected metal as each comes o f f the column. We have observed f o r i n j e c t e d known amounts onto a s i z e e x c l u s i o n column that a 10-20 f o l d increase i n d e t e c t i o n l i m i t due t o chromatographic d i l u t i o n i s r e a l i z e d at the interface. Six SRC samples derived from Kentucky No. 9 c o a l were obtained from the Southern S e r v i c e s , I n c . , W i l s o n v i l l e , AL p i l o t plant funded by the E l e c t r i c Power Research I n s t i t u t e and the U.S. Department of Energy and operated by C a t a l y t i c Inc. Information on processing c o n d i t i o n s was k i n d l y supplied by Mr. B i l l Weber. A process r e c y c l e solvent (92-03-035) o r i g i n a t i n g at the SRC-I p i l o t plant in W i l s o n v i l l e , AL. was obtained from Mobil Research and Development Corporation Central Research D i v i s i o n , P r i n c e t o n , NJ. Results and Discussion Metal A n a l y s i s of Solvent Refined C o a l s . I n i t i a l l y elemental d e t e c t i o n l i m i t s were determined in a v a r i e t y of organic s o l v e n t s . Chloroform and heptane were chosen because of t h e i r d e s i r a b i l i t y as chromatographic s o l v e n t s . Toluene and p y r i d i n e were s e l e c t e d f o r t h e i r tendency to s o l u b i l i z e coal derived products. Detection l i m i t s f o r each metal in chloroform, toluene and heptane were measured by d i r e c t a s p i r a t i o n using the n e b u l i z e r and spray chamber chromatographic i n t e r f a c e described in reference ( 1 1 ) , while a pumped d e l i v e r y system was employed f o r p y r i d i n e . Individual element d e t e c t i o n l i m i t s are shown in Table I f o r these solvents along with the a n a l y t i c a l wavelengths monitored. These represent compromise emission l i n e s f o r our polychromator system i n order t o minimize i n t e r f e r e n c e s while maintaining reasonably good d e t e c t i o n l i m i t s . Background l e v e l s f o r blanks although higher than those of aqueous s o l u t i o n s showed l i t t l e i n t e r f e r e n c e problems from organic emission. Detection l i m i t s f o r each metal are, in g e n e r a l , s i m i l a r in each organic solvent as well as in MIBK which has been p r e v i o u s l y i n v e s t i g a t e d . ( 7 ) An examination of Table I i n d i c a t e s that water continues t o be The s u p e r i o r matrix


Fuller; Coal and Coal Products: Analytical Characterization Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982. 0.015 0.060 0.007 0.003 0.067 0.004 0.011 0.006 0.009 0.003 0.002 0.074 0.038 0.079 0.126 0.055 0.006 0.016 0.015

c

Direct

aspiration

^Pumped d e l i v e r y

5

PYRIDINE*

a A l l concentrations

Ag Al Β Ba Ca Cd Cr Cu Fe Mg Mn Mo Ni Pb Si Sn Ti V Zn

ELEMENT

in ppm

0.034 0.091 0.197 0.041 0.003 0.040 0.005

—

0.017 0.070 0.005 0.002

—

0.005

0.003

—

0.025 0.014

TOLUENE 0

0.013 0.025 0.012 0.003 0.673 0.003 0.005 0.009 0.006 0.001 0.001 0.025 0.026 0.124 0.378 0.086 0.004 0.025 0.142

0

CHLOROFORM 0.004 0.025 0.007 0.004 0.249 0.005 0.009 0.018 0.008 0.001 0.001 0.043 0.096 0.258 0.044 0.064 0.005 0.012 0.009

HEPTANE°

—

0.1 0.3 0.07 0.03 0.03 0.03 0.04

—

0.006 0.04 0.007 0.01

—

—

15

0.015 0.042 0.027 0.025 0.0038 0.0075 0.0040

—

0.0054 0.0062 0.00015 0.0014

—

0.0034

0.0013

—

—

—

WATER 0.007 0.045

8

0.02 0.09

MIBK

3280.7 3082.2 2497.7 4554.0 3179.3 2265.0 2677.2 3247.5 2599.4 2795.5 2576.1 3132.6 2316.0 2203.5 2881.6 1899.8 3349.4 2924.0 2025.5

WAVELENGTH (A)

ELEMENTAL DETECTION LIMITS AND EMISSION LINES MONITORED IN VARIOUS SOLVENTS*

TABLE I


COAL AND COAL PRODUCTS


168

f o r metal a n a l y s i s provided there are no other experimental difficulties. Detection l i m i t s v i a e i t h e r d i r e c t a s p i r a t i o n or pumped d e l i v e r y are s i m i l a r f o r the same solvent ( t o l u e n e - p y r i d i n e ) , since n e b u l i z e r and spray chamber are i d e n t i c a l . P r e c i s i o n of a n a l y s i s , however, i s c o n s i d e r a b l y improved in the l a t t e r c a s e . This observation was most pronounced when p y r i d i n e s o l u t i o n s of coal derived m a t e r i a l were being examined r a t h e r than s o l u t i o n s of elemental standards. The r e l a t i v e l y high v i s c o s i t y of the concentrated coal derived s o l u t i o n s (-5-7% w/w) no doubt leads to i n c o n s i s t e n c y in a s p i r a t e d sample d e l i v e r y . R e l a t i v e standard d e v i a t i o n s (RSD) were a l s o improved on going from 10 second t o 30 second i n t e g r a t i o n t i m e s . Table II compares d e t e c t i o n l i m i t s and RSD's in p y r i d i n e employing d i r e c t a s p i r a t i o n (10 second i n t e g r a t i o n s ) and pumped d e l i v e r y (30 second i n t e g r a t i o n s ) . The RSD s f o r most elements were l e s s than 10% f o r the pumped delivery. 1

The above f o r c e d flow procedure was employed t o determine t r a c e element content in s i x a d d i t i o n a l p y r i d i n e s o l u b l e SRC's. Each SRC d i f f e r s from another i n e i t h e r raw coal source, conversion s e v e r i t y ( i . e . pressure-temperature), added Na£C03 content or method of residue removal. Table III o u t l i n e s the various processing parameters and the assigned run number. The measured elemental concentrations are l i s t e d in Table IV. R e l a t i v e standard d e v i a t i o n s f o r each a n a l y s i s were, in g e n e r a l , l e s s than 10%. This of course was higher f o r elements near t h e i r detection l i m i t . Runs #1636* and #166B ( L a f a y e t t e coal) d i f f e r only in the amount of Na2C03 added to the b a t c h . The concentration of each metal f o r the two runs i s remarkably s i m i l a r . Na2C03 a d d i t i o n i s supposed to i n h i b i t c o r r o s i o n . This o p e r a t i o n , no doubt, has been e f f e c t i v e s i n c e #166B c o n s i s t e n t l y has equal or lower metal concentrations than #163B. The decrease in Si and Fe concentration i s most n o t a b l e . On the other hand, the s i t u a t i o n i s d i f f e r e n t f o r Runs #210 and #220 ( F i e s c o a l ) . Few metals (Si and Sn) show concentration decreases upon a d d i t i o n of 25 lbs Na2C03/ b a t c h . Runs #210 and #220 were made at both higher temperature and p r e s s u r e , however, metal content comparisons with s i m i l a r runs (#163B, 166B) at lower temperature did not reveal any significant trends. Runs #198 and #199 employed a more convent i o n a l f i l t r a t i o n method. V a l i d comparisons would be #163B vs #198 and #166B vs # 199. In most every case the metal concent r a t i o n i s higher f o r the f i l t e r e d method (#199 vs #166B). This was not true f o r the other pairwise comparison (#198 vs #163B). It i s conceiveable that c o l l o i d a l mineral matter may have escaped the f i l t e r process. For c e r t a i n of the t r a n s i t i o n metals concentration remained e s s e n t i a l l y constant as one might suspect i f they are t r u l y s o l u b l e o r g a n i c a l l y bound s p e c i e s . Runs #217 and #220 enables one again t o observe i f processing s e v e r i t y i n f l u e n c e s metal content. For t h i s coal and these c o n d i t i o n s there s u r p r i s i n g l y i s e s s e n t i a l l y no change in metal content.


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169

ICP-AES

TABLE II TRACE ELEMENT ANALYSIS OF A SOLVENT REFINED COAL MEASURED IN PYRIDINE AS A FUNCTION OF SAMPLE DELIVERY Downloaded by CORNELL UNIV on October 15, 2016 | http://pubs.acs.org Publication Date: November 12, 1982 | doi: 10.1021/bk-1982-0205.ch007

3

Element

Direct Aspiration pg of element g of SRC RSD

Pumped D e l i v e r y uq of element g of S R C RSD

Ag AT Β Ba Ca Cd Cr Cu Fe Mg Mn Mo Ni Pb Si Sn Ti V Zn

b ND 325.8 121.4 1.7 789.9 ND 18.5 3.0 38.4 17.9 3.1 8.8 ND ND 1074 171.5 1217.0 13.7 8.4

2.7 152.3 87.7 1.5 601.5 4.4 13.3 15.2 29.9 12.6 1.1 6.0 21.7 59.6 737.6 122.5 466.8 6.5 33.8

a

Wilsonville,

6.8 2.5 43.3 55.0

-

15.3 235.0 28.3 3.9 13.1 225.6

-

6.3 36.2 10.3 6.4 32.9

AL, Run 199 (See Table I I I )

ND = elemental concentration i s less than ten times the d e t e c t i o n l i m i t as determined in p y r i d i n e

b


16.8 1.8 14.4 5.1 3.0 19.3 2.1 86.9 4.5 7.1 11.9 5.8 58.1 11.4 7.3 4.5 3.2 7.5 6.6


Solvent

Critical

40

Ο

40

1700/825

1700/825

1700/825

2100/840

2000/785

2100/840

166B

198

199

210

217

220

Lafayette

Lafayette

Lafayette

FIES

FIES

FIES

Solvent

Solvent

Solvent

Critical

Critical

Critical

25

25

Filter

Filter

Solvent

Critical

Ο

1700/825

163B

Residue Removal

Lafayette

e

Severity PSI/ F

Mine

Run Number

Na?C03 LB/Batch

PROCESSING CONDITIONS FOR KENTUCKY NO. 9 SOLVENT REFINED COAL

TABLE III


Deashing

Deashing

Deashing

Deashing

Deashing

Fuller; Coal and Coal Products: Analytical Characterization Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982. ND 35.9 36.3 ND 133.7 ND 2.2 7.2 14.8 4.8 0.2 ND ND ND 6.7 ND 136.0 5.2 7.8

ND 120.4 47.4 0.5 134.3 0.2 1.3 0.7 268.2 10.6 5.0 ND 1.1 4.0 270.6 ND 235.9 6.4 15.2

Ag Al Β Ba Ca Cd Cr Cu Fe Mg Mn Mo Ni Pb Si Sn Ti V Zn

ND 28.9 45.9 ND 85.8 0.5 0.2 ND 27.9 1.0 0.7 ND 8.7 ND 11.7 48.0 52.7 5.0 4.2

ND 133.8 70.3 ND 65.7 0.4 8.9 ND 167.1 9.7 9.2 ND ND 2.7 8.1 ND 591.0 9.4 10.9

ND = Elemental concentration i s

ND 43.3 47.9 ND 133.4 ND 1.3 ND 7.1 5.6 0.3 ND ND ND ND ND 97.2 4.8 3.5

RUN 217

as determined in

6.4 95.8 66.3 0.7 82.8 0.7 0.7 ND 27.7 3.2 1.4 ND ND ND ND ND 99.3 11.7 1.3

RUN 220

p l a n t ; data obtained by NAA

l e s s than ten times the d e t e c t i o n l i m i t

R e p o r t e d in Reference 9; SRC obtained from Tacoma, WA p i l o t

b

c

RUN 210

Run 198

Concentration expressed in ug of element per gram of SRC

RUN 166B

RUN 163B

ELEMENT —

pyridine

223.0 6.1 ND

-

-

ND

-

16.6

-

3.9

-

2.8

-

73

-

102.0

-

Run X

°

ta

CO

1'

55*

f

!

M H > r

z

g

TRACE ELEMENT ANALYSIS OF SRC AS A FUNCTION OF SOURCE AND PROCESSING CONDITIONS**

0

H

TABLE IV


COAL AND


172

COAL

PRODUCTS

A number of general observations can be made but not r e a d i l y explained given the l i m i t e d h i s t o r y a v a i l a b l e on each SRC. First, Lafayette and F i e s mines produce SRC of s i m i l a r metal content with a few e x c e p t i o n s . Second, those metals which are expected to be most s t r o n g l y organo-bound (mainly t r a n s i t i o n metals) do not s i g n i f i c a n t l y change concentrations as a f u n c t i o n of these processing parameters; whereas, " m i n e r a l - r e l a t e d " elements appear t o f l u t u a t e with processing c o n d i t i o n s . It i s r e a d i l y apparent that s p e c i a t i o n data i s d e s i r a b l e . A r e l a t e d study has been r e c e n t l y reported(4, 8) on one SRC. While the samples were drawn from a d i f f e r e n t piTot plant and the mine source i s unknown, i t i s i n t e r e s t i n g to note that our measured concentrations v i a ICP-AES and Weiss' concentrations v i a NAA are comparable. The absence of data in Table IV i n d i c a t e s that the element's concentration was not monitored by Weiss. Metal Detection In Coal Derived Process Solvent Chromatography. ICP-AES alone w i l l not suggest s p e c i a t i o n ; however, coupled with chromatography some knowledge of the nature of metal species can be obtained. Size e x c l u s i o n chromatography (SEC) of a SRC process solvent (92-03-035) with ICP-AES d e t e c t i o n has been performed. The solvent was d i l u t e d with p y r i d i n e (1:1) and i n j e c t e d (200 y l ) on the column. P r i o r to SEC, the process s o l v e n t , which had a b o i l i n g range defined as i n i t i a l b o i l i n g point ( I B P ) - 8 0 0 F , was r e - d i s t i l l e d to y i e l d 400-600 F and 600-800 F c u t s . Figure 1 shows s e l e c t metallograms f o r these three d i s t i l l a t e s . At the o u t s e t , i t should be noted that m e t a l l i c species have g e n e r a l l y not been thought to r e s i d e in process s o l v e n t s . Since the 400-600 F and 600-800 F f r a c t i o n s were taken from the IBP-800 F d i s t i l l a t e , a d d i t i o n of the former two metallograms should y i e l d the l a t t e r . Indeed, i f one looks at the Fe 400-600 F metallogram one sees a bimodal d i s t r i b u t i o n with the prominent f r a c t i o n being of smaller molecular s i z e . The 600-800 F Fe metallogram i s l i k e w i s e bimodal but the predominant f r a c t i o n i s of l a r g e r molecular s i z e . The IBP-800 F Fe metallogram e x h i b i t s an equal d i s t r i b u t i o n of small and large s i z e d molecules. S i m i l a r type r e s u l t s are noted f o r Cu and Zn although Zn appears t o be concentrated i n the lower temperature d i s t i l l a t e and the higher temperature f r a c t i o n s u r p r i s i n g l y has the smaller s i z e Zn compounds. One explanation f o r t h i s i s that these compounds may be more polar and intermolecular associaton causes the higher d i s t i l l a t i o n temperature. A d d i t i o n a l elements (Mg, Ca, T i , Cr, Mo, Mn, Co, N i , Cd, Hg and A l ) were monitored but not detected except f o r the t r a c e of Mn found in the IBP-800°F f r a c t i o n . e

e

e

e

e

e

e

e

e

These experiments suggest (1) m e t a l l i c m a t e r i a l s are found i n process s o l v e n t s , (2) metals are o r g a n i c a l l y bound s i n c e they have survived both d i s t i l l a t i o n and chromatographic separation and (3) a large number of d i f f e r e n t molecular s i z e d species c o - e x i s t . The exact nature of these metal components remains a mystery p r i m a r i l y because (1) the separation behavior of metal complexes v i a s i z e



600°-800° F

400°-600

e

F

Mn

Figure 1. Separation of process solvent 92-03-035 boiling cuts diluted 1:1 with pyridine with specific metal detection. Conditions: 100Â μ-Styragel column; eluent, pyridine;flowrate, 0.5 mL/ min; injection, 200 μΣ.

IBP-800° F



174

COAL AND COAL

PRODUCTS

e x c l u s i o n chromatography i s not c l e a r l y e s t a b l i s h e d , (2) adequate, s o l u b l e models are not forthcoming and (3) SEC does not e f f e c t i v e l y concentrate a p a r t i c u l a r metal type f o r i s o l a t i o n and examination by other a d d i t i o n a l spectroscopic methods. SEC-ICP-AES, i n other words, may never y i e l d d e t a i l s as to the exact environment about the metal i o n . M u l t i p l e peaks may represent d i f f e r e n t o x i d a t i o n s t a t e s or v a r i o u s l y i n t e r m o l e c u l a r l y associated or solvent associated metal-containing s p e c i e s . Broad peaks may suggest information regarding h i g h l y r e a c t i v e metal species. C l e a r l y a b e t t e r understanding of the chromatography of m e t a l l i c species i s needed here. In order t o employ more s p e c i f i c , "chemical c l a s s " separations and t o gain more d e t a i l e d s p e c i a t i o n i n f o r m a t i o n , normal phase chromatography of metal compounds with ICP-AES d e t e c t i o n has been e x p l o r e d . Normal phase l i q u i d chromatography with ICP d e t e c t i o n should provide a b e t t e r means f o r eventual s p e c i a t i o n of o r g a n i c a l l y bound metals in coal derived products. Its advantage l i e s in the a b i l i t y to separate compounds by p o l a r i t y and allows use of solvents which have a reasonable s o l u b i l i t y f o r coal derived products. Through extensive modeling work and the f u r t h e r development of separation schemes, i t should be p o s s i b l e t o more f u l l y understand the nature of the o r g a n i c a l l y bound metals present in coal derived products. One drawback t o normal phase LC i s that r e t e n t i o n and i r r e v e r s i b l e adsorption of l a b i l e species such as c o o r d i n a t i o n complexes may occur. The question of whether the solvent system employed i s strong enough to remove the more polar m a t e r i a l s i s always subject t o conjecture. Both normal phase and reverse phase gradient e l u t i o n should solve the l a t t e r problem; whereas, the former appears t o be most r e a d i l y approached by using r e l a t i v e l y mild i n t e r a c t i n g reverse phase m a t e r i a l s (~Cis) with aqueous/methanol solvent systems. Only one b r i e f report(14) has mentioned adsorption LC-ICP-AES i n a t o t a l l y organic pfîase; t h e r e f o r e , some p r e l i m i n a r y modeling has been performed in order t o show f e a s i b i l i t y of t h i s approach. Organometal 1ic systems i n c o r p o r a t i n g e i t h e r Fe or Si served as r e p r e s e n t a t i v e model mixtures. Figure 2 i l l u s t r a t e s a simple i s o c r a t i c separation of a mixture of s i x organo-iron compounds. The mixture i s composed of four organometallie compounds and two c o o r d i n a t i o n compounds (see f i g u r e 3 ) . The cyano-amino bonded phase s i l i c a (PAC) column used was s u f f i c i e n t l y r e t e n t i v e t o allow the employment of a good s o l u b i l i z i n g solvent (CHCI3) while also o b t a i n i n g a reasonably good s e p a r a t i o n . While a separation v i a p o l a r i t y i s envisioned here, nevertheless the only i o n i c compound in the mixture, i r o n c l a t h r o c h e l a t e , (15) was not the most retentive. I n t e r a c t i o n of the bonded pïïâse with the f r e e acetyl groups in acetyl ferrocene and d i a c e t y l ferrocene must be comparable to the above in that each of these compounds f l a n k s the i o n i c chelate in r e t e n t i o n time. Fe3(C0)i2 and CpFe(C0)2l are obviously q u i t e non-polar being neutral compounds with h i g h l y



7.

BROWN


ET AL.

175

ICP-AES

_l

2

3

4

5

6

TIMS (rain)

7

8

I

2

3

4

5

I

I

I

6

7

8

ΎΏΈ. (rain)

Figure 2. Separation of iron model compounds with Fe and Β detection. Condi tions: Polar amino cyano column; flow rate, 1 mL/min; eluent, CHCl /0.5% C H OH. Key: 1, triirondodecacarbonyl; 2, (Cp)Fe(CO) I; 3, acetyl ferrocene; 4, iron clathro chelate; 5, diacetyl ferrocene; and 6, Fe[B(PZ)J . Iron compounds are illustrated in Figure 3. s

t

s

g

t



CO

3

CH3

-R

/

roi

N—N

Ν—Ν

Ν—Ν

r£i

ÊLÎ-CH,

\/ \

I

O C - F E - C O

φ)

COLL.,

9

F/gwre J. Molecular structures of iron model compounds. Key: i , triirondodecacarbonyl; 2, (Cp)Fe(CO),I; 3, acetyl ferrocene; 4, iron clathro chelate; 5, diacetyl ferrocene; and 6, Fe[B(PZ)J .

4

3

— < / II ff-0

V

c H R-Bf-O-N

1

(CO)Î,FE—>FE(C0)

(CO^FE



7.

BROWN ET

AL.


177

ICP-AES

covalent i r o n - l i g a n d bonding. The higher symmetry of the former no doubt accounts f o r i t s e a r l i e r e l u t i o n p a t t e r n . The e a r l y e l u t i o n of iron t e t r a k i s ( l - p y r a z o y l ) - b o r a t e (16) i s somewhat puzzling. The uncoordinated pyrazoyl group apparently has l i t t l e a f f i n i t y f o r the column. The high symmetry of the complex and i t s zero charge probably operate to lower the a f f i n i t y a l s o . This separation a l s o demonstrates the multielement c a p a b i l i t y of ICP-AES d e t e c t i o n . The two c o o r d i n a t i o n compounds contain both Fe and B. Upon monitoring both Fe and Β emissions, p a i r s of peaks are observed at the same r e t e n t i o n time. The second mixture studied was composed of several o r g a n o - s i l i c o n compounds. Their separation was examined as a f u n c t i o n of column packing and s o l v e n t . Optimized separations are shown in Figure 4 f o r each column with the corresponding solvent system employed. By using stronger r e t e n t i v e packings ( i . e . s i l i c a ) b e t t e r solvents f o r s o l u b i l i t y ( i . e . heptane, heptane/2% 2-propanol, CHC13/5% 2-propanol) may be employed while again achieving s u i t a b l e s e p a r a t i o n s . The general e l u t i o n pattern f o r t h i s group of s i l i c o n compounds i s explained in terms of varying p o l a r i t y analogous to the s i m i l a r carbon c o n t a i n i n g components. An increase in r e t e n t i o n time i s observed from compound 1, the e a r l i e s t e l u t i n g and hence l e a s t p o l a r , through compound 6, the most s t r o n g l y r e t a i n e d and most p o l a r . The i n c l u s i o n of heteroatoms accounts f o r t h i s change in p o l a r i t y . The separation of compounds 1, 2 and 3 on PAC with non-polar heptane shows the separation of these weakly polar components. The acetylene group i s l e s s polar than the ether group which i s l e s s polar than the carbonyl group. Compounds 4, 5 and 6 do not e l u t e under these conditions. By changing t o a weaker r e t a i n i n g support (CN) and adding a polar m o d i f i e r in small amounts to heptane (2% 2-propanol), the most polar components are now e l u t e d , however, the e a r l y e l u t i n g weakly polar components now c o - e l u t e . The f r e e hydrogen on the nitrogen of compound 5 makes i t more r e t e n t i v e than the d i e t h y l groups on compound 4, while the dihydroxy groups are most r e t e n t i v e . S i m i l a r l y , by going to the strongest r e t a i n i n g support, s i l i c a , and a much stronger mobile phase, an intermediate separation i s achieved with r e s o l u t i o n of four of the s i x components. Gradient e l u t i o n should provide s i g n i f i c a n t improvement and should allow these components to be f u l l y separated. This w i l l be examined in f u t u r e work. The p r e l i m i n a r y modeling work on a v a r i e t y of chromatographically s t a b l e metal systems e s t a b l i s h e d a basis to separate and detect metal components in the process r e c y c l e solvent. P r e l i m i n a r y q u a n t i t a t i v e t o t a l metal a n a l y s i s showed only small amounts of a few m e t a l s . For t h i s reason, neat i n j e c t i o n s of the sample were performed. Large amounts of chromium, iron and s i l i c o n species were observed by normal phase separation with chloroform. Figure 5 shows the SEC of iron species in 400-600°F and 600-800 F b o i l i n g fractions. It i s i n t e r e s t i n g to note the large amount of iron e


178

COAL AND COAL PRODUCTS

SILICA


1

CONDITIONS Detector: Si Channel ICP-AES PAC: 2 ml/min Heptane CN: 1 ml/min Heptane/2% 2-propanol Silica: 1 ml/min CHCl3/5% 2-propanol

PAC

CN

ι .

0

2

4

6

8

1 2

10

TIME (min.)

3

4

5

6

2

7

3

4

5

6

7

TIME (min.)

TIME (min.)

Figure 4. Separation of silicon model compounds with silicon detection (Si chan nel ICP-AES) as a function of column packing. Key to packing: left, polar amino cyano (PAC); middle, cyano (CN); and right, silica. Key to compounds: 1, d j ^ i C s CSi ; 2, (C H ) Si(OC H ) ; 3, Si(OOCCH ) ; 4, 4> Si(NC H ); 5, Hexamethyldisilazane; and 6, Si(OH) . s

6

s

t

g

5

g

s

k

s

t

g

s

g


7.

BROWN ET A L .


179

ICP-AES


600-800

-800

I

318

I

4 21

I

5.24

I

6 27

1

1

7.31

8.34

1

9.37

1

10.40

RETENTION TIME

Figure 5. Separation of process solvent 92-03-035 boiling cuts with Fe detection. Conditions: column, PAC; eluent, CHCl ; flow rate, 1 mL/min; and injection, 200 pL. s


180

COAL AND

COAL

PRODUCTS

species present in the 400-800 F f r a c t i o n as compared to the higher b o i l i n g f r a c t i o n . This i n d i c a t e s that most of the iron species are v o l a t i l e below 6 0 0 F . It should also be noted that subsequent a n a l y s i s showed a very l a t e e l u t i n g F e - c o n t a i n i n g peak in the 400-800°F f r a c t i o n . The same two b o i l i n g f r a c t i o n s monitored simultaneously in the chromium channel ( F i g u r e 6) showed j u s t the reverse behavior. Chromium appears t o be concentrated in the 600-800°F f r a c t i o n while being absent or below the d e t e c t i o n l i m i t s in the o v e r a l l 400-800°F f r a c t i o n . S i m i l a r l y , in Figure 7, s i l i c o n species are more prevalent in the 600-800°F f r a c t i o n while appearing t o a much smaller degree i n the 400-800°F f r a c t i o n . Other metals are e i t h e r not present at measurable q u a n t i t i e s or they are i r r e v e r s i b l y r e t a i n e d on the column. The low concentration of metal species in these samples r e q u i r e d overloading of the column with organic c o n s t i t u e n t s and t h i s accounts f o r the broadness of the observed peaks. It should be noted that the c o n d i t i o n s employed f o r these separations were the same as those used f o r the separation of the i r o n models. The absence of several metals which were observed in SEC of the same process solvent i n d i c a t e that a l t e r n a t e separations w i l l have to be developed. e


e

Conclusions Work t o present has demonstrated both the existence of o r g a n i c a l l y bound metals in coal derived products as well as the f e a s i b i l i t y f o r d i r e c t d e t e c t i o n and q u a n t i t a t i o n in organic solvents by ICP-AES. Before r e l i a b l e s p e c i a t i o n can be accomplished, b e t t e r chromatographic separations need to be developed. These include p r e l i m i n a r y separation i n t o various f r a c t i o n s by p o l a r i t y followed by subsequent a n a l y s i s by HPLC. Work t o better separate a wide range of p o l a r i t i e s v i a gradient e l u t i o n i s d e s i r a b l e . A l s o , those m a t e r i a l s which are l a b i l e enough t o react with the normal phase packings need t o be examined by reverse phase chromatography both i s o c r a t i c a l l y and v i a gradient e l u t i o n . A d d i t i o n a l work on modeling of various o r g a n i c a l l y bound metal systems needs to be accomplished e s p e c i a l l y with those l a b i l e systems which up to now have been d i f f i c u l t to separate except by SEC. Work to developed methods of q u a n t i t a t i o n f o r chromatographically separated components i s necessary. Comparison of t o t a l metal content t o separated metal content should be made t o insure that a l l metal species have been removed from the column. From t h i s work, the r o l e of o r g a n i c a l l y bound metals in the SRC p r o c e s s , as well as other processes, can be b e t t e r understood. The a b i l i t y to track metals throughout a process as well as to i d e n t i f y p o s s i b l e species should g r e a t l y aid i n determining the e f f e c t of s p e c i f i c metals as p o s s i b l e c a t a l y s t s and/or poisons t o the c o n v e r s i o n .



BROWN ET AL.


181

ICP-AES

l.25mv

IBP-800

3.18

5.24

6.27

RETENTION

Figure 6.

7.30

833

TIME

Separation of process solvent 92-03-035 boiling cuts with Cr detection. Conditions are the same as in Figure 5.



400-600

ι

2 16

1 3 18

ι

420

ι

521

I

6 23

ι

ι

7 35

847

—ι

948

RETENTION TIME

Figure 7. Separation of process solvent 92-03-035 boiling cuts with Si detec tion. Conditions are the same as in Figure 5.


7.

BROWN ET AL.


ICP-AES

183

Acknowledgement - Support by the Commonwealth of V i r g i n i a , the Department of Energy under Grant EF-77-01-2696 and the E l e c t r i c Power Research I n s t i t u t e i s g r a t e f u l l y appreciated.

Literature Cited


1.

Gorbaty, M. L . , F. J. Wright, R. K. Lyon, R. B. Long, R. H. Schlosberg, Z. Baset, R. Liotta, B. G. Silvernagel and D. R. Neskora, Science, 1979, 206, 1029. 2. Lett, R. G., J. W. Adkins, R. R. DeSantis and F. R. Brown, "Trace and Minor Element Analysis of Coal Liquefaction Products", PETC/TR-79/3, August, 1979. 3. Filby, R. H. and S. R. Khalil, "Synthetic Fuel Technology", Κ. E. Cowser and C. R. Richmond, eds., Ann Arbor, MI, Ann Arbor Science, p. 102 (1980). 4. Weiss, C. S., "The Detection of Trace Element Species in Solvent Refined Coal", Ph.D. Dissertation, Washington State University, 1980. 5. Coleman, W. M., P. Perfetti, H. C. Dorn and L. T. Taylor, Fuel, 1978, 57, 612 and references therein. 6. Hausler, D. W. and L. T. Taylor, Fuel, 1981, 60, 41. 7. Fassel, V. Α., C. A. Peterson, F. N. Abercrombie and R. N. Kniseley, Anal. Chem., 1976, 48, 516. 8. Filby, R. H., D. R. Sandstrom, F. W. Lytle, R. B. Greegor, S. R. Khalil, V. Ekambaram, C. S. Weiss and C. A. Grimm, Proceedings DOE/NBS Workshop on "Environmental Speciation and Monitoring Needs for Trace Metal-Containing Substances from Energy Related Projects", F. E. Brinckman and R. H. Fish, eds., NBS Special Publication 618, 1981, p. 21. 9. Maylotte, D. H., J. Wong, R. L. St. Peters, F. W. Lytle and R. B. Greegor, Science, 1981, 214, 554. 10. Bonnett, R. and F. Czechowski, Phil. Trans. R. Soc. Lond. A, 1981, 300, 51. 11. Hausler, D. W. and L. T. Taylor, Anal. Chem., 1981, 53, 1227. 12.

Hausler, D. W. and L. T. Taylor, Anal. Chem., 1981, 53, 1221.

13.

Taylor, L. T., D. W. Hausler and A. M. Squires, Science, 1981, 213, 644. 14. Winge, R. K. Peterson, V. J. Fassel, V. A. "Inductively Coupled Plasma-Atomic Emission Spectroscopy: Prominent Lines", EPA-600/4-79-017, March, 1979. 15. Gast, C. H., J. C. Kraak, H. K. Poppe and F.J.M.J. Maessen, J. Chromatoqr., 1979, 185, 549. 16. Boston, D. R. and N. J. Rose, J. Amer. Chem. Soc., 1968, 90, 6859. 17. Trofimenko, S., J. Amer. Chem. Soc., 1968, 89, 3170. —

RECEIVED May 17,

1982


Application of Inductively Coupled Plasma Atomic Emission

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