Chromatography in the Petroleum Industry

428 Pages·1995·8.43 MB·III-XVIII, 1-430\428

by  E.R. Adlard (Eds.)

JOURNAL OF CHROMATOGRAPHY LIBRARY-volume 56
chromatography in the
petroleum industry
edited by
E. R. Adlard
Burton, South Wirral, UK
ELSEVIER
Amsterdam-Lausanne-New York-Oxford-Shannon -Tokyo 1995
ELSEVIER SCIENCE B.V.
Sara Burgerhartstraat 25
P.O. Box 21 1,1000AE Amsterdam, The Netherlands
Library of Congress Cataloging-in-Publication Data
Chromatography in the petroleum industry / edited by E.R. Adlard.
p. cm. -- (Journal of chromatography library ; v. 56)
Includes bibliographical references and index.
ISBN 0-444-89776-3( acid-free)
1. Petroleum-Analysis. 2. Chromatographic analysis-Industrial
applications. I. Adlard, E.R. 11. Series.
TP691.C58 1995
665.5’028’7--dc?O 95-30628
CIP
ISBN 0-444-89776-3
0 1995 Elsevier Science B.V. All rights reserved.
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XV
Foreword
Although the spectacular development of gas chromatography in the 1950s
and 1960s is now a fading memory of a golden era, there are still advances being
made in apparatus, technique and applications. The petroleum industry makes
use of all the variants of chromatography as should be clear from the present
volume, but gas chromatography in particular is the most important analytical
technique in petroleum analysis and has been since its first announcement by
James and Martin in 1952. Indeed it is no exaggeration to claim that many of the
major advances in gas chromatography in that golden era emanated from the
laboratories of the petroleum industry.
This book is intended primarily for those concerned with the analysis of crude
oil and its products but many of the chapters have much broader applications. It
is hoped, therefore, that many outside the immediate sphere of petroleum analy-
sis will find sufficient of interest to make it a worthwhile purchase.
In multi-author books there will be inevitable variations in the style and con-
tent of each contribution. There is no reason why this should be regarded as a
weakness since as William Cowper pointed out “variety’s the very spice of life”.
Likewise a small amount of overlap between some chapters is not a drawback if
it allows each chapter to be a freestanding account of a particular topic.
It was interesting to reread the comments of the editors of the only other book
dedicated to the subject of petroleum analysis by chromatography published
15 years ago. These editors spent some time describing the reasons for the
choice of the title of their book. In this context, it is interesting that the original
title intended for their book was the one used here.
In concluding this foreword, I should like to thank all the contributors and El-
sevier for their efforts to make this both a useful and an interesting volume.
E. R.A dlard
XVII
List of Contributors
D.J. ABBOTT Esso Research Centre, Analytical Group, Abingdon, Oxford-
shire OX13 6AE, UK
A. BARKER Dussek Campbell Ltd, Thames Road, Crayford, Dartford, Kent
DAI 4Q.J UK
J. BEENS Koninklijke/ShelI-Laboratorium, Amsterdam {Shell Research
B. K), Badhuisweg 3, 1031 CMAmsterdam, The Netherlands
G. BONDOUX Waters Chromatography Division, Millipore S.A., 6 Rue Jean-
Pierre Timbaud, BP 307, 78054 St. Quentin-en- yvelines,
France
J. BOS Koninkl~~/SheII-LaboratoriumA, msterdam {Shell Research
B. K), Badhuisweg 3, 1031 CMAmsterdam, The Netherlands
C.J. COWER 84, West Grove, Walton on Thames, Surrey KT12 5PD, UK
A. DE WIT KoninklijkdShell-Laboratorium, Amsterdam (Shell Research
B. K), Badhuisweg 3, 1031 CMAmsterdam, The Netherlands
N. DYSON @son Instruments Ltd, Hatton Lyons Industrial Estate, Hatton,
Houghton-le-Spring, Tyne and Wear DH5 Om,U K
R.S. HUTTE Sievers Instruments Inc., 1930 Central Avenue, Suite C, Boul-
der, CO 80301, USA
T. JONES Waters Chromatography Division, MiIlipore (CK) Ltd, Winster
House, Heronsway, Chester Business Park, Wrexham Road,
Chester CH4 SQR, UK
T.P. LYNCH Analytical & Applied Science Division, BP Research & Engi-
neering Centre, Sunbury-on-Thames, Middlesex, TWI 6 7LN
UK
H. MAHLER Siemens AG, Abt AUT 35 CHR, Postfach 21 12 62, 76187
Karlsruhe, Germany
T. MAURER Siemens AG, Abt AUT 35 CHR, Postfach 21 12 62, 76187
Karlsruhe, Germany
F. MUELLER Siemens AG, Abt AUT 35 CHR, Postfach 21 12 62, 76187
Karlsruhe, Germany
A.C. NEAL Esso Research Centre, Milton Hill, Abingdon, Oxfordshire
OX13 6AE. UK
XVIII List of contributors
1. ROBERTS Analytical & Applied Science Division, BP Research & Engi-
neering Centre, Sunbury-on-Thames, Middlesex, TW16 7LN,
UK
A.T. REVILL CSIRO Division of Oceanography, Castray Esplanade, Hobart,
Tasmania, Australia
S.J. ROWLAND Petroleum and Environmental Geochemistry Group, Depart-
ment of Environmental Sciences, Universily of Plymouth, Drake
Circus, Plymouth, PL4 8AA, UK
A. SIRONI Fisons Instruments, Strada Rivoltana, 20090 Rodano (Milan),
Italy
R. TIJSSEN KoninklijkdShell-Laboratorium, Amsterdam (Shell Research
B. V.), Badhuisweg 3, I03 I CM Amsterdam, The Netherlands
G.R. VERGA Fisons instruments, Strada Rivoltana, 20090 Rodano (Milan),
Italy
E.R. Adlard (Ed.), Chromatography in the Petroleum Industry
Journal of Chromatography Library Series, Vol. 56
0 1995 Elsevier Science B.V. All rights reserved 1
CHAPTER 1
The analysis of hydrocarbon gases
C.J. Cowper”
British Gas pfc,L ondon Research Station, Michael Road, London SW6 ZAD, UK
“That man ... sat down to write a book, to tell the world what the world had all his life been
telling him.”
Boswell’s Life of Johnson
1.1 INTRODUCTION
Hydrocarbon gases can be categorized in a number of ways, one of which is to
define them as natural or man-made.
Natural gas is a major energy source for domestic, commercial and industrial
consumers, and is used, so far as possible, with minimum change to the compo-
sition found in the reservoir. It consists generally of methane and other saturated
hydrocarbons and some non-flammable gases. Man-made gases arise from refin-
ing operations on liquid hydrocarbon feedstocks, and their compositions vary
widely according to the process from which they are derived. Those components
found in natural gas are likely to be present, in addition to unsaturated hydrocar-
bons.
Gas chromatography is the principal analytical method used for hydrocarbon
gases. Particular components can be measured by spectroscopic or chemical
means, but for analysis of the bulk of components, the separating power of
chromatography is both essential and well developed.
Although gases are often considered to be simple mixtures, their analysis has
frequently tested the ability of gas chromatography, either because of the range
of components present (boiling range, or concentration spread, or both), or be-
cause of the need to use highly specific stationary phases to separate apparently
intractable pairs of components. The different separating requirements relating
to groups of components within the same gas mixture has led to the use of multi-
column systems, with columns being isolated or reversed, or their order changed
* Current address: 84, West Grove, Walton on Thames, Surrey KT12 SPD, UK.
References p. 40
2 Chapter I
by means of valves. This complexity, which is more daunting in prospect than in
use, has led to a number of ready-configured chromatographic systems for many
of the application areas.
The thermal conductivity detector (TCD) and flame ionization detector (FID)
are the two most commonly used for hydrocarbon gases in the petroleum indus-
try. Because many of the gases contain non-hydrocarbon components, the TCD,
as a universal detector, is essential. Its dynamic range allows it to be used also
for all the major and many of the minor components of most mixtures. The FID,
while the most commonly used detector in gas chromatography generally, can be
regarded as a specialist and specific detector in gas analysis. Process chroma-
tographs frequently use the TCD alone, to reduce the need for the extra facilities
needed for the use of the FID.
1.2 NATURAL GAS
Hydrocarbon gases arise naturally from a variety of sources. Bacterial fermen-
tation under anaerobic conditions produces methane or marsh gas in great pro-
fusion, about 109 tonnes per year worldwide. Small accumulations of this type of
gas can be found during tunnelling or other operations, and the same mecha-
nisms produce landfill gas from waste. Mine drainage gas is a methane-rich
mixture found where coal measures have been worked. However, the term natu-
ral gas is normally taken to refer to the fossil-based gaseous equivalent to oil and
coal, abstracted from ancient, large, deeply buried accumulations. This is the
sense in which the term is used in this chapter.
Natural gases can vary considerably in composition, from nearly pure nitrogen
to nearly pure carbon dioxide to nearly pure methane. Fortunately for the indus-
try and the consumer, most natural gases consist mainly of methane, with small
amounts of inert gases (helium, nitrogen and carbon dioxide) and ethane and
higher alkanes in concentrations which diminish as their carbon number in-
creases.
By far the largest use of natural gas is as a fuel, where its accessibility via
wide-ranging distribution systems and its cleanness in terms of handling and
combustion products make it a popular choice for both domestic and industrial/
commercial markets. Other uses are as a chemical feedstock, as a source of pure
single hydrocarbon gases or (if present in sufficient quantities) of helium, and as
a moderator in nuclear reactors.
Current estimates indicate that the world has more reserves of natural gas than
of oil at the present rate of consumption. Recent measures of worldwide produc-
tion give a figure of around lo9 tonnes per year, which is comparable to the bac-
terial production referred to earlier.
The analysis of hydrocarbon gases 3
Natural gas is part of a continuum of hydrocarbons, ranging from methane to
the heaviest ends of oil, which are found in geological accumulations. Pressure
and temperature conditions in the reservoir are such that there is no distinction
between what we regard as gases and liquids; this only occurs when the fluid has
been extracted and is subject to conditions at which this discrimination is possi-
ble. Whether an accumulation is regarded as a gas or oil field is only a matter of
the relative proportions of the hydrocarbons. Natural gas fields always contain
liquids, usually in the form of a lightish condensate, and oil fields always contain
associated gases.
Gas separated from a natural gas field will burn in that form, but is usually
treated to remove or to control the levels of particular components, for opera-
tional, or contractual, or legislative reasons. Hydrogen sulphide, being toxic and
corrosive, is invariably subject to very low (parts per million) specification lim-
its, and is typically removed in an amine plant. Carbon dioxide is less acidic, but
still potentially corrosive at the pressures used for gas transmission, and its con-
centration is also controlled, usually to low percentage levels. It can be removed
by an alkali scrubbing process. Water is removed by glycol scrubbing, since the
presence of liquid water increases the corrosive effect of acid gases, and because
it can form solid methane hydrate, a clathrate compound, under certain pressure
and temperature conditions. Potential hydrocarbon liquids are also removed,
usually by chilling, sometimes by adsorption. This is to prevent their condensa-
tion downstream of the processing plant.
The fact that natural gas, once processed at the wellhead or reception termi-
nal, is in the form which virtually every consumer can accept without modifica-
tion has given rise to very complex and detailed pipeline systems, which cross
international boundaries and finally enter the consumer’s premises. In Western
Europe, most countries have access to pipeline supplies from Holland, the North
Sea, Siberia and Algeria in addition to their own indigenous sources. In the
United States, which is the home of long-distance natural gas transmission,
pipeline systems include Canada and Mexico as well as extensive offshore net-
works.
Properties and behaviour of natural gas have been reviewed by Melvin [ 13. A
large number of papers on quality specifications, physical properties, sampling,
odorization and analysis of natural gas, and on calibration gases and standardi-
zation are collected in the proceedings of the 1986 Gas Quality Congress [2].
Analysis of natural gas is carried out for a range of purposes, and the choice
of analytical method is often dictated by the reason for the analysis being re-
quired. There are three basic purposes for analysis:
- identification of source,
- calculation of physical properties, and
- measurement of specific minor components because of their particular
characteristics.
References p. 40
4 Chapter I
For identification of source, the concentrations of the inert components and
the ratios of a small number of hydrocarbons are good indicators; the analysis
need not be detailed. An example of specific minor component analysis is the
measurement of odorants; the analysis is clearly targeted upon a few compo-
nents, probably using a selective detector, and the composition of the main com-
ponents is without interest, except insofar as they may interfere with the meas-
urement. Calculation of properties is the most common need for analysis, with
calorific value the most usual target.
The following is a list of some of the properties of natural gas which are cal-
culable from analysis. It is not comprehensive, but describes those most fre-
quently used. Most properties can be measured directly, but independently of
each other; a properly configured analytical method allows calculation of all.
1. Culorijic value (CV): Natural gas is bought and sold in units of volume, as
a source of energy, hence the importance of CV as energy per unit of volume.
2. Relative density (RD): This is the density of a gas relative to dry air
(= 1.000). It is used in metering calculations and for the Wobbe index (see be-
low).
3. Wobbe index (WI): Gases from different sources must be assessed for their
inter-changeability, which represents the effectiveness with which a gas of com-
position B will burn on an appliance designed for a gas of composition A. WI is
an empirical measure of the ability to supply heat to a burner, and is the most
important characteristic in determining interchangeability. It is calculated by di-
viding the CV by the square root of the RD.
4. Compression factor (Z): Compression factor appears in the modified ideal
gas equation PV= nZRT, and arises from gas phase interactions. For hydro-
carbon gases and their mixtures over normal temperature and pressure ranges, Z
is always less than 1, which means that a defined volume of gas at a defined
pressure will contain more moles than predicted from ideal behaviour by a factor
of 1/Z. At ambient conditions, Z for most natural gases is around 0.997, but the
correction is much more significant at higher pressures. At 70 bar, typical of
transmission pressures, Z is usually less than 0.9. Metering at high pressure is
therefore very dependent upon accurate measurement or calculation of Z.
5. Hydrocarbon dewpoint: Retrograde condensation is the phenomenon
whereby a liquid phase can separate from a hydrocarbon gas mixture as it is de-
pressurized at a constant temperature. It is another feature of gas phase interac-
tions, and may be regarded as a form of “gas phase solubility”, with components
coming out of solution as the pressure binding the molecules together is re-
leased.
6. .Joule-Thomson coefficient: This property influences the extent of cooling
as a gas is expanded. As the pressure of natural gas is reduced, the amount of
pre-heating necessary to avoid hydrocarbon condensation can be calculated.
The analysis of hydrocarbon gases 5
1.2.1 Analytical requirements
Although distributed natural gases consist mostly of methane, they are in fact
complex mixtures of a dominant major component (methane), a small number of
components in the range 0.1-15%, and a large number of trace components. Fig-
ure 1.1 shows the boiling points of both major and minor components from he-
lium to n-decane, indicating a boiling range of over 400°C. While gases are not
often considered in terms of their boiling points, it is a good illustration of the
potential chromatographic problem. As a simple rule of thumb, an isothermal
separation will handle components with a boiling range of about 100°C. The ap-
proach to natural gas analysis, therefore, can be to split it up into a series of
separations of groups of components, a temperature programming approach, or a
column switching method. Analytical needs are considered below in respect of
two important properties: CV and dewpoint calculation.
1.2.1.1 CVmeasurement
The CV of a gas mixture is an additive property, with inert gases contributing
zero, and flammable gases contributing in proportion to their concentration and
individual CV. A small correction is necessary for compression factor (2)a t
ambient conditions.
Figure 1.2 shows, for a typical North Sea gas, the component contributions in
terms of molar %, and of CV and RD as percentages of the total. Nitrogen, pres-
ent at 2.5%, contributes nothing to the CV, but 4% to the RD. The Y-axis of the
figure is limited to 6% so that component contributions can be clearly seen.
Methane, of course, contributes far more than the figure indicates.
B.R. deg C
200 I I
-300 I 1
He N2 02 C02 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10
Component
Fig. 1. I. Component boiling points.
References p. 40