high speed mass spectrometer as a gas chromatography detector
TRANSCRIPT
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Section
V
Paper 16
u. c
A
HIGH SPEED M SS SPECTROMETER
S G S
CHROM TOGR PHY DETECTOR
IN THE DETERMIN TION
O
CRUDE OIL COMPOSITION
V. F Gaylor
-
C.
N.
Jones
**
-
J.H.Landerl
***
-
E.
C. Hughes
****
Abstract,
A
rapid crude oi l analysis procedure providing
boiling range data to 725 F and naphtha composition
in less than two hours has been devised. Whole crude is
charged to a gas chromatography unit comprising a strip -
per column and an analytical column.
A
t ime-of-f l ight mass spectrometer is used as an auxi l iary
detector for a conventional gas chromatography appa-
ratus. Continuous spectral monitoring of the column ef-
f luent permits identi f ication of single chromatographic
peaks. The spectrometers
1
microsecond scan rate is
particu larly valuable for studying distribu tion of indiv idual
compounds in non-homogeneous multicom pone nt chrom-
atographic peaks.
The mass spectrometer detector is used to characterize
chromatographic separations of virgin naphthas boi l ing
to 400 . Detailed spectra l analyses pro ve that the poor-
ly resolved peaks and shoulders obtained fro m a packed
chromatographic column could be related to hydrocarbon
type composition.
A
simple analyt ical procedure for estimating cycloparaf-
f in content from chromatograms of crude oi l and reform-
ing feed results in a method that is suitable for routine
refine ry use.
Rsum.
Larticle dcrit une nouvelle mthode danalyse
rapide du ptrole brut, indiquant les points dbullition
jusqu 725
F
et la composit ion des naphtas en moins
de deux heures. On introduit le brut entier dans une
unit de chromatographie gazeuse comprenant une co-
lonne de sparation et une colonne danalyse.
On monte un spectromtre de masse
temps de rponse
ultra rapide uti l is comme dtecteur auxi l iaire, sur un
appareil classique de chromatographie gazeuse, Le con-
trle spectral continu de l eff luent de la colonne permet
diden tifier chaque pic chroma tographique simple et, grce
l
vitesse de balayage du spectromtre
100
micro-
secondes),
l
est possible de dist inguer la rp art i t ion des
diffrents individus dans les pics complexes non homo-
gnes.
On uti l ise le dtecteur de spectromtrie de masse pour
caractriser les fractions de naphtas vierges ayant jus
qu
400
o F 205 C) de po int dbu llition initialemen t
spares par chromatographie. Des analyses spectrales
dtai l les montrent qu i l est possible de rel ier les pics
mdiocrement
rsolus
et les sai l l ies peu diffrencies
fournis par une colonne chromatographique garnissage
une composition type dhydrocarbure.
Une mthode danalyse sim ple perm ettant dvaluer la
teneur en cycloparaffines des bruts et des charges de
reforming, partir de leurs chromatogrammes, offre un
outi l appropri aux besoins usuels des raff ineries.
Introduction
The numerous applications of gas chromatography
to analysis of petroleum streams are well known.
Widespread, routine us s have, however, been
gener ally limited to the rel atively simple Ci through
C hydrocarbons. Outstanding successes in analyz-
ing more complex mixtures have been achieved,
using specialized techniques and equipment, but
often involve increased costs and analysis time.
* Authors Biographies v ide las t page
Methods which retain the speed and simplicity
features of the original chromatographic technique
may require a new approach to interpretation of
complex chromatograms. This paper describes such
an approach t o crude oil analysis, based
on
research
with a mass spectrometer used as a chromatographic
detector.
Previously reported applications of gas chromato-
graphy to quantitative crude oil analyses were
limited in scope. WebbI3 injected whole cr ude oil
directly into an analytical column and measured
Ci
through S hydr,ocarbons. Martin and WintersQ
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and Rysse1berget2) used a short precolumn to retain
heavy ends and quantitatively determined Cz
through C7 and C2 through C5 hydrocarbons, respec-
tively. A temperature-programmed gas chromato-
graphy column was used by Barras and Boyle') for
predicting jet fuel freezing point from crude oil
analysis.
The temperature programming technique vastly
extends the useful molecular weight range of a single
chromatographic analysis. Calculation of crude oil
boiling range distribution from a temperature-pro-
grammed chromatogram seemed feasible. Eggertsen,
Groennings and Holst5) conver ted programmed
chromatographic analyses of petrole um fractions to
distillation-type curves which closely approximated
a 60-plate distillation; Barras and Boyle1) used
analysis on an uncoated Chromosorb column to
predict yield points on a l-plate distillation column.
While distillation-type curves we re of obvious
value, determination of chemical composition from
crude oil chromatograms was equally desirable.
Chromatographic procedures were designed to
optimize both molecular weight range and s epara tion
efficiency in a single analy sis. Normal tricosane was
eluted in abou t 35 minutes while cons iderab le resolu-
tion of low molecular weight hydrocarbons was
retained.
As
many as 50 distinct peaks and shoulders
were obtained in th e C3 through Cii range, constit ut-
ing a fingerprint profile qualitatively useful for
characterizing crude oil. Quantitative interpretation
in terms of single compounds or over-all hydrocar-
bon type distribution require d some knowleld,ge of
composition of each single peak.
Identificationof the C3 through C7 peaks presen ted
no particular problems. Identification and determina-
tion of single compounds in the Cs-Cii range is more
difficult because of increasing complexity of composi-
tion. Desty, Goldup and Swanton3) identified more
than half of 122 peaks resolved from the C3-Cn
portion of the American Petroleum Institute 's Ponca
City crude in a 20-hour run on a coated capillary
column. Polgar, Holst and Groennings ) accom-
plished complete analys is Of C7 and CS alkanes, cyclo-
pentanes and cyclohexanes with two successive an-
alyses on a 300-feet capillary column totalling about
3 hours;
80
O o
of the possible compounds were quanti-
tative ly accounted for a s individuals. Lindeman and
Anni@) use'd a magne tic-type mass spe ctrometer
for complete qualitati ve and quanti tative analys is of
chromatographic pea ks of a
440
F
end-point naphtha
on a packed column; over 60 single compounds were
identified and general structure assignments wer
report ed for many Ci0 and Cii compounds.
It was unrealistic to expec t that single compoun
ana lyses could be achieved chromatographically from
the
30
poorly separated peaks representing th
hundreds of
c
through Cii compounds likely presen
in crude oil. Consistency of the peak patt ern, how
ever, and large variations in pea k size distribution
from sample to sample suggested that gross hydro
carbon -type distribution a nalyses might be compute
direc tly from the chromatogram. Peak height measu
rements were preferred for this purpose since appa
rent separation even between discrete peaks wa
usually poor. Qualitative composition analysis a
each peak maximum was thus desired. Time-O
Flight mass spectromete r, which produces 10,00
spectra per second, had the required speed an
sensitivity for monitoring chromatographic colum
effluent )
4
6 .
Photographic recording of spe ctr
permits qualita tive composition determination at an
single instant during elution of the chromatographi
peak. Mass spectra obtained in this way we re use
to estimate rela tive hydrocarbon-type distribution a
each peak maximum.
quipment and Procedures
A commercial gas chromatography unit (Mod
K-2 Kromo-Tog) employing a filament-type therma
conductivity detector,and equipped with temperatur
programmer, flow controller and precolumn assembly
was used (Burrell Corporation, Pittsburgh, Pennsyl
vania) . Primary elements of t he chromatographi
equipment ar e adequately described in the manufac
turer's literature. Details of the conventional flow
system are depicted in Figure 1 and are largely self
explanatory. The hairpin-shaped analytical colum
was 250 cm. long and 5 cm. I.D. The V4-inch I.D. pre
column was one foot long and contained packin
identical
to
the analytical column. Primary helium
carrier was directed through the precolumn durin
sample injection and maintained until desired por
tions of crude oil had been flushed into the analytic a
column. Carr ier flow was th en switched to precolum
by-pass position. Crude oil heav y ends trapped in th
precolumn were backflushed and vented to atmos
phere at the flash vaporizer inlet port.
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FIGUR
FLOW
S Y S T M
FIGUR
FLOW
S Y S T M
Two di fferent column packings an'd corresponding
experim ental parameters wer e used, Table I. Highest
molecular weight range w as achieved with Procedure
II while Procedure I was p refe rred for resolu tion of
low molecular weight hydrocarbons. Resolution of
Ci-Cs hydrocarbons was optimized in either proce-
dure by holding column temperature a t 25' C until
n-C5 was eluted.
Column packings w ere tempera ture stabilized be-
fore use b y heating for 24 hours under helium flow.
Columns I and II were programmed to 250'C and
300' C, respec tively, without detectable liquid phase
bleeding. Maximum molecular weight determined
was Cis for Procedure I and Ce3 for Procedure II.
Chromatograms were recorde d on a 1.0 millivolt
Potentiometer recoilder (Minneapolis-Honeywell Reg.
Co., Philadelphia, Pennsylvania), equipped with Disc
integrator (Disc Instrument Company, Santa Ana,
California) for peak area dete rmination .
The Time-Of-Flight mass ~pectrometer'~)
5)
Model 12-100 (The Bendix Corporation, Cincinnati,
Ohio), was attached to the chromatographic equip-
TABLE I
CHROMATOGRAPHIC OPERATING PAR-TERS
Procedure I Procedure
II
Column Packing
Analytical Column Temperature:
Initial Temperature.
.........................
Initial Temperature Hold.
Heating Ra te .. .............................
Final Temperature ..........................
Precolumn Temperature.
Precolumn
Flush
Time
.........................
Flow
Rate.. .................................
Sample Size
5.0 wt. yoApiezon L
on
30-60
mesh ChromosorbP
25
C
3.0
minutes
7 C p r
min
250
C
200 c
3 minutes
5 OB per
min
.o12 ml.
1.0 wt. yo D.C. 710 Fluid
and 3.0 wt. Apiezon
L
on 40 50 mesh
Chromosorb
P
25
C
2.0 minutes
11
C
per min.
300 c
300
c
1
minute
230
cc
per min.
.O24 ml.
ment at the detector vent (Figure
1).
The variable
leak (Model 9101-M, Granville-Phillips Company,
Pullman, Washington) was adjus ted to raise internal
spectrometer pressure to 2X 10 mm. mercury with
pure helium effluent. Temperature of the
2 5 VE
I.D.
line connecting the leak to the spectrometer inlet
port was maintained at 170' C and the spectrom eter
source chamber was hea ted to about 175OC. The
ionizing source was ope rated at
2.5
amperes filament
current, .125 microamperes trap current and O e.v.
energy level.
Spectra were viewed on th e screen of a Type 541
A
oscilloscope, equipped with Type CA Preamplifier
(Tektronix, Incorporated, Cleveland, Ohio) and pho-
tographe8dwith a Polaroid camera. Relative mass line
intensities were
estimated by use of a Microcard
Reader (Microcard Reader Corporation, Wes t Salem,
Wisconsin).
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Discussion
boilin,g range yield point calibration. The columns
described separated paraffins essentially by boiling
point and exhibited only slight selectivity for naph-
thenes and aromatics. Naphthenes were retarded,
Normal paraffin peaks in the crude oil chromato- relative to paraffins, by about one peak width and
grams were readily identified by either relative size aromatic selectivity was only slightly greater.
or elution time (Figure 2) and were employed for
Chromatographic analyses of carefully fractionated
Boiling Range Distribution Analysis
FIGURE
CR UDE
O I L
C H R O M A T O G R A M P R O C E D U R E
distillates of both highly aromatic and naphthenic
crude oils showe d that error due to column selectivi ty
was negligible. Consequently, norm al paraffin boiling
point-elution time plots were used for yield point
calibration.
Liquid volume per cent distillation yields were
oalculated .directly from summed peak areas. Mess-
nerlO)showed that thermal conductivity molar area
response for hydrocarbons is a function of both
molecular weight effects. Normal paraffin area
for single compounds thus requires accurate know-
ledge of re lat ive response of each compound. Aver-
aging structure effects seemed permissible, however,
when summing >areas of peaks composed of many
hydrocarbons likely including most possible struc-
tures.
Quantitative oalibration with normal paraffin
standa rds was a rea dy means of compensating for
molecular weight and structure. Quantitative analysis
response per un it liquid volume sampled also tended
to average out structure effects at each carbon
number level (Figure 3 . Liquid volume per cent
yields were therefore calculated from arealvolume
constants experime ntally de termined for each C5-
C 3 normal paraffin. Cons tants for C4 and lighter
NORMAL PARAFFINS
OIS
FWUFFINS
xNAPHTHENES
AROMATICS
FIGURE
EFFECT OF H Y D R O C A R B O N T Y P E O N
LIQUID
V O L U M E R ES P O N S E
paraffins were obtained by extrapolating linear
molar response curves.
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Composition o f
L i gh t N a p h t h a a nd O f f - G a s
Rresolution of low boiling hydrocarbons was suffi-
cient to obtain considerable composition information
from the crude oil chromatogram (Figure
4 .
Complete
separa tion of propane, isobutane and normal butane
was not achieved; resolution was, howeve r, adequate
for estimating concentration s with reasonable
degree of accuracy.
Octane number of light naphtha boiling 55-220
F
was estimated from relative concentratio ns of normal
paraffins and summed isoparaffins, naphthenes and
benzene. Weighted averag e blending octane numbers
of 45.0 for normal paraffins and 79.5 for isoparaffins,
naphthenes and benzene, calculated from pure
compound octane numbers determined by the Ameri-
can Petroleum Institute s Projec t 45, were used for
octane numbers prediction. Values estimated in this
way were at least
as
accurate a s values calculated
similarly from single compound analyse s.
FIGURE
P A R T I A L C R UD E O I L C H R O M A T O G R A M
P R O C ED U R
E
LE G E N D : 1 M E T H A N E N O N - C O N D . G A S E S
2.
E T H A N E
3
P R O P A N E
4
I S O - B U T A N E
5 N - B U T A N E
6 . I S O - P E N T A N E
7. N - P E N T A N E
Peak Label l ing
As many as 30 major peak s and shoulders were
obtained i n the n-CI to n-Ci1 portion of the chromato-
gram. Peak pattern could be considerably altered by
relatively small changes in column packing, as, for
example, Column I
vs
Column II (Figures 2 and 4 .
However, with identical ana lytical procedures, the
over-all peak patte rn was consisten t for many differ-
ent crude oil types. Most of the composition analyses
wer e obtained from Column though the same pro-
cedure s and principles w ere also effective for Column
II.
Chromatographic peaks eluted between n-Cs and
n-Ci1 w ere labelled for da ta hand lingpurposes. Major
group numbers were assigned to each series of pe aks
eluted between successive normal paraffins. Group
8
peaks included all peaks eluted between n-C7 and
n-CS, Group 9 peaks were eluted between n-Cs and
n-Cg, etc. (Figure
4 .
ingle peaks in each group were
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further identified by elution order with in the group.
A partia l relative retention time PRRT wa s calculat-
ed for each peak:
I
where Peak X is eluted between n-Pi and n-Pn.
The peak number identification included both group
number and PRRT anmdhus .defined exact location on
the chromatogram. For example Peak 8-50 was
eluted exact ly halfway between n-C7 and n-Ca.
Group number does not necessarily define carbon
number. The peaks immediately preceding a normal
paraffin of ca rbon number N usually contained both
and N 1 naphthenes and aromatics and isoparaf-
fins largely of N carbon number.
i l l
a s s
Spectrometer
nalyses
1
Useful mass spectr a
of
single peaks were achieved
only by minimizing lag time between chromatogra-
phic and spectrometer units. Careful attention to
length and temperature of
low
pressure inlet lines
produced virtually simultaneous response from both
ddtection systems. Over-all spectrometer speed and
sensitivity were sufficient to permit qualitative
characterization of small shoulders immediately fol-
lowing or preceding major peaks. For example
spectra of Peak 9-.69 show ed the peak like ly
contained a large amount of 3-methyl octane while
the 9-.75 shou lder wa s largely composed
of
ethyl
benzene and one or more Cg naphthenes Figure 5.
m
98
m e
n
I
t
z
39
4
43 55 57 67 69 7 81
8
9 97 1 6 126
mie
m
e
FIGURE
M A S S S P EC T RA L C H A R A C T E R I Z A T I O N
OF
A D J A C E N T
P E A K S
Contribution of 3-methyl octane to spectra of t he
9-.75 shou lder was small. Similarly the naphthe nic
character of the 10 .45 shoulder was not obscured
by paraffincontribution from the larger
10 .61
peak.
Spectral comparisons of most poorly separated
peaks showed chromatographic column efficiency to
be a good deal better than was superficially apparent.
Expected non-homogenity was detected and often
explained occasional anomalous peaks resulting from
large variations in single compound concentration.
Xylene and Cg naphthe ne for example wer e often
detec ted spectr ally in the leading edge of n-Cg peaks
Figure 6 through not evident chromatographically
A
shoulder on the n-Cg peak sometimes observed in
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consistent with boiling point relations between
branched and normal paraffins of the sam e carbon
Identification of single compounds, though possible
in many instances, was not a primary aim. Mass
spectra were used semi-quantitatively to estimate
hydrocarbon-typedistribution-ateach pea k and shoul-
number.
h
SAMPLE A n Cg
PEAK
FIGURE
der maximum. Repeatability was about rf
3
O o and
accuracy was largely unknown. Spectral analysis
could not necessarily define absence
of either naph-
thenic or paraffinic hydrocarbon, as was the cace for
aromatics. Apparent detection of small amounts of
paraffin in a predominantly naphthenic peak, or con-
versely, could have resulted from spectral inaccura-
cy, contamination from an adjacent poorly separa ted
peak, or could have been real. Hydrocarbon-type
distribution est imates were used only for qualita-
\
J
SAMPLE
B
n C9
tive guidance an,d inaccu racy was of no particu lar
concern.
PEAK
X Y L E N E D E T E C T I O N I N
TWO
CRUDE OI LS
M J O R X Y L E N E ml LI NES =
91
92 105
106 107
chromatograms of more aromatic crude oils, was
largely composed of xy lene wi th smaller amounts
o normal nonane and g naphthene.
Mass spect ra of compara ble chromatographic
peaks were qualitatively identical from sample to
sample. Comparative spectra contained the same
mass lines though relative intensities varied some-
what with differences in single compound or com-
pound-type distribution within a peak. Spectra of
the 9-.12 peak in paraffinic crude oils, for example,
indicated approximately equal concentrations
of
paraffinic (isoalkanes) and naphthenic (cycloalkanes)
compounds while naphthenes predominated in the
same peak in naphthen ic crudes, Figure 7.
Many
of
the chromatographic peaks were, how-
eve r, consist ently pure in hydrocarbon-type com-
position. Mass spectra of 9-.62 peaks were predo-
minantly paraffinic and 10-.10 shoulder spectra
were highly naphthenic in both paraffinic and na ph-
thenic-type crude oils, Figure
7.
In ge neral, isoparaf-
fin s were concentrated in the chromatographic PRRT
ranges of
.6
to
7
and
.2
to
3
in each peak group.
Conversely, in the PRRT ranges 1 to
.2 .4
to 5 and
.8
to
.9,
isoparaff in levels w ere minimum and naph-
thenic spectra were usually observed. This PRRT
distribution of isoparaffins in each peak group is
Quantit ative Hydroc arbon-Type Distribution
Accurate naphthene contents of peak group frac-
tions, collected from a p repa rative scale ga s chroma-
tography unit, were determined by conventional
mass spect rometry. Direct comparisons of composit-
ed a nalytica l ,data showed tha t th e chromatographic
peak profile could be related to gross hydrocarbon-
type distribution. Relative heights of predominantly
naphthenic peaks were directly proportional to total
naphthene content in each group, Figure 8. The major
naphthenic peak was larger tha n the major isoparaf-
fin peak in each group fraction of the Illinois crude
oil; specifically, 7-.27
>
7-.74
8 .30
>
6 . 6 4
9-.47
>
9-42 10-.45 > 10-.61 and 11--48
>
11-62. The reverse was true for the more paraffinic
East Texas crude;
7-.27
7-.74 8-.30