Fossil hydrocarbons: chemistry and technology

348 Pages·1997·5.046 MB·English

by  N Berkowitz

PREFACE
The decade of 1973-1983, in which most of the Western world moved from
economic turmoil and panic created by an oil crisis to blissfully "putting it all
behind us", illustrates how easily we persuade ourselves to forget what should
have taught us a profound lesson~and how cavalierly we face the need to
secure long-term supplies of liquid fuels.
The oil crisis abated not because of how we responded to it, but because
the major Middle East oil producers raised output in expectation of recouping
revenues that had fallen victim to the Iraq-Iran war. This generated an oil
glut that halved crude oil prices and allowed us to return to the status quo
ante. Laissez-faire economic policies once again allowed profligate use and/or
export of diminishing indigenous reserves of gas and conventional oil. Alterna-
tive sources~the heavy fossil hydrocarbons that could help us to attain reason-
able energy self-sufficiency~were once again consigned to the dim recesses
of our collective minds. Research and development, which outlined and some-
times defined the new technologies through which self-sufficiency could be
achieved, was abruptly discontinued. And development of future crude oil
supplies once again became centered on distant sources over which we have
little, if any, control. All this occurred, despite the demonstration by major
commercial ventures (in particular, South Africa's coal-based SASOL complexes
and production of "synthetic" light crudes from Alberta's oil sands) of what
is technically possible and could be competitively accomplished.
It is difficult to understand a mindset that allows such energy "policies"~
and, not coincidentally, reflects a deplorable disregard for macroeconomics on
which all national well-being ultimately depends~as anything other than an
attitude of apres mois la deluge.
Even academia is not immune to that malaise. Instruction in petroleum
engineering at universities and technical colleges is rarely augmented by the
study of heavy fossil hydrocarbons, the existence of which is, as a rule, acknowl-
xi
xii Preface
edged only when deemed to be relevant to instruction in rock mechanics,
mining engineering, and mineral preparation. And between petroleum devotees
who generally don't much care about these "other" resources and a dwindling
band of professionals who do, we have thus promoted two solitudes--each
sustained by a technical jargon that suggests differences where few exist, and
each side seemingly incapable of speaking to the other.
In these circumstances, it seemed to me pertinent to draw attention to the
fact that the entrenched dichotomy between petroleum hydrocarbons and coal,
which in no small measure shaped popular attitudes about energy, is technically
inadmissable and to observe that the heavy fossil hydrocarbonsmall much
more abundant than natural gas and conventional crudes and distributed more
equitably across the globemoffer attractive sources of synthetic gas and light
oils even though the required conversion technologies are sometimes, as in
the matter of coal liquefaction, still far from fully developed.
The format of this book, which discusses the fossil hydrocarbons under
common topic headings rather than by type, reflects my objectives. The first
section (Chapters 1-7) thus opens with a review of indicators that support
the underlying concept and then considers source materials, biosources, meta-
morphic histories, host rock geology and geochemistry, classification, and
molecular structure. Chapters 8-10 focus on preparation, processing, and
conversion technologies. Finally, Chapter 11 examines some of the environ-
mental issues that arise from production, processing, and use of fossil hydrocar-
bons. Each topic is augmented by end-of-chapter notes that I deemed to be
helpful, but did not want to insert into the main text (where they might have
proved disruptive), and for each topic I have sought to provide a reasonably
detailed bibliography for the interested reader to consult. To assist such refer-
ence, I have, wherever possible, made use of English-language literature--even
though this might, at first glance, distort the scene and not give proper recogni-
tion to the outstanding contributions made in many other countries and re-
ported in other languages. Because I wanted to retain some historical flavor
that traced the development of the relevant science and technologies as well
as give credit where due, I have also, as far as possible, stayed with the original
literature rather than cite more recent sources that added little to what had
long been known.
The use of the term fossil snobracordyh in the title and throughout the text
does, of course, take liberties with chemical nomenclature. But as muelortep
snobracordyh include bitumens and kerogens whose oxygen contents are no
lower than those of some coals, I make no apology for such indiscretion. Nor
do I apologize for overtly differentiating between preparation and processing,
because the former is generally concerned with physically modifying the raw
hydrocarbon and the latter changes it chemically.
Preface xiii
In preparing the text, I have drawn on open literature, on my lecture notes,
and on what I have learned over the years from discussions with friends and
colleagues. I must in this connection acknowledge my particular indebtedness
to Dr. E. J. Wiggins, who served as Director of the Alberta Research Council
and (later) as Board Member of AOSTRA (Alberta's Oil Sands Technology &
Research Authority), as well as to colleagues at the University of AlbertamDr.
.A E. Mather, Professor of Chemical Engineering; the late Dr. .L G. Hepler,
Professor of Chemistry; Drs. .R G. Bentson and .S M. Farouq Ali, Professors
of Petroleum Engineering; and Dr. J. M. Whiting, Professor of Mining Engi-
neering.
I must also thank the publisher, Academic Press, who encouraged me to
undertake the writing of this book, and the Alberta Research Council's librarian,
Ms. Nancy .R Aikman, who steered me to much helpful literature and thereby
made my task so much easier.
I would, however, be terribly remiss if I did not here also specifically express
my deep gratitude to my wife for her unfailing love, support, and endurance
during the many months I devoted to writing. To her I dedicate this volume.
1
CHAPTER
Introduction: ehT Family
of Fossil Hydrocarbons
Flawed classifications of living and inanimate matter are not uncommon and
are usually of little concern except to the specialist. Sometimes, however, the
flaws are "validated" by common usage and, in time, become counterproductive
fallacies. So in the case of "petroleum": this term has come to be progressively
expanded to "petroleum hydrocarbons," which include natural products as
diverse as natural gas, light crudes, heavy oils, all bituminous substances, and
oil-shale kerogens--but which, be definition, exclude all types of coal and
thereby create an untenable distinction. The venerable role that coal has played
as a primary fuel since the late 12th century 111; as sources of metallurgical
coke since the early 1700s; and in the mid-1700s as the trigger of an industrial
revolution that changed the very course of human society--all this may provide
a historical perspective for sometimes setting it apart from the "petroleum
hydrocarbons." But as the record also makes clear, there is little technically
legitimated warrant for such dichotomy 2.
Taken for what it is popularly assumed to mean, "petroleum hydrocarbons"
is a semantically questionable term even though it may be sanctioned by some
dictionaries: for, although kerogens are indeed oil precursors, and bi-
tuminous substances--notably bitumen in oil sands2mmay represent mi-
crobially and/or oxidatively altered oil residues 3, neither they nor other
bituminous materials (such as tars and asphaltics) are oils, as "petroleum"
implies and is commonly understood to mean 4. However, more to the point
here is the untenable implicit technical meaning of the term. Designating
natural gas--a variable mix of C1-C 6 alkanes--as a petroleum hydrocarbon
is certainly warranted by its composition, its common association with crude
oil, and its descent from residual oily matter in late stages of kerogen catagene-
sis. But adoption of bituminous substances and kerogens into the petroleum
hydrocarbon family can only be justified if they are deemed to be, or to be
chemically directly related to, oil precursors. And if so, one might ask why
srebmuN ni erauqs stekcarb refer ot retpahc-fo-dne .seton
2 liO sands era osla ylnommoc derrefer ot sa suonimutib sdnas ro rat .sdnas
1 :noitcudortnI ehT ylimaF fo lissoF snobracordyH
hydrogen-rich boghead and cannel coals, which meet this criterion by closely
resembling sapropelic kerogens in their origin, developmental history, and
chemistry, are excluded from an otherwise all-embracing clan; and if, on
reflection, they are admitted, why orphan the equally closely related and much
more abundant, albeit less H-rich, humic coals?
Differentiation between fossil hydrocarbons and choices among them are,
of course, often necessitated by economic and/or supply constraints. But it is
significant that where such need exists, choices almost always require resort
to one or another of the heavy hydrocarbons, to bitumens, oil shales, or coals.
In practice, differentiation is, in short, between these and what are properly
termed "petroleum hydrocarbons"mi.e., natural gas and light crude oils; and
where circumstances actually force resort to the "heavies," choices are always
based on consideration of availability and costs 5.
Nor can it be otherwise, because fossil hydrocarbons stem from the same
source materials~the entities that make up the basic fabric of living organ-
isms~and consequently form a continuum of chemically related substances
that extend from methane to anthracite. What differentiated the assemblages
of source materials that over time developed into different hydrocarbon forms
were primarily the relative proportions of the source materials; and these were
determined by when and in what environments they accumulated 6. In
one form or another, organic carbon was continuously deposited from late
Precambrian times, when primitive biota first appeared in ocean waters; and
from early Devonian times, when terrestrial vegetation made its appearance,
the locales in which organic carbon accumulated ranged therefore from alpine
meadows, woodlands, and oxic swamps to disoxic lacustrine regions, paralic
environments, and deep anoxic seas.
Qualitatively, a hydrocarbon continuum is indicated by general connections
between different hydrocarbon forms (Table 1.1). But more convincing chemi-
cal linkages between them emerge when they are broadly arranged in order
of increasing gravity, as in
natural gasmlight oils--heavy oilsmbituminous substances--
kerogensmsapropels~humic coals
In such serial order, the continuum is mirrored in an uninterrupted, progres-
sive fall of the H/C ratio from 4 in the case of methane, the principal component
of natural gas, to ---0.7, an average value for mature bituminous coals; and
because that indicates increasing carbon aromaticity from progressive internal
cyclization and dehydrogenation, it defines the nature of the transitions from
gaseous to liquid, semisolid, and solid hydrocarbons.
But the continuity of the fossil hydrocarbon series is also convincingly
shown in other features.
There is, for example, a remarkable similarity between constructs that pur-
1 Introduction: The Family of Fossil Hydrocarbons
TABLE 1.1 Connections among "Petroleum Hydrocarbons" and Coals a
Gaseous marsh gas (CH4)
natural gas
Bituminous fluid petroleum natural gas liquids
hydrocarbons crude oils
viscous asphalts
bitumens
tars
solid kerogens
sapropels cannel coals
boghead coals
humic coals lignites
subbituminous coals
bituminous coals
anthracites
Waxy mineral waxes
a Adapted from .R .R F. Kinghorn, An Introduction ot the Physics and Chemistry of Petroleum,
Wiley & Sons, New York, 1983.
port to depict average molecular structures of bituminous substances, kerogens,
and coals and to show macromolecular, pseudo-crystallographic ordering in
them 7.
There are pronounced behavioral similaritiesmfor instance, a close parallel
between thermal degradation of kerogen (during catagenesis) and coal (during
carbonization), with both yielding H-rich liquids (oils or tars) in amounts
determined by their H/C ratios or hydrogen contents 8, and both leaving
correspondingly H-depleted solid residues.
And although the behavior of coal is profoundly influenced by its solidity
and rank-dependent porosity, its responses to chemical processing--to thermal
cracking and hydrogenationmare much the same as those of other heavy
fossil hydrocarbons.
sA might indeed be expected, these similarities make for interchangeability
between bituminous substances, kerogen-rich oil shales and coal, and allow
virtually identical processing techniques to transform any one of them into
more useful, lighter members of the series. Regardless of whether the feed is
a heavy oil, oil residuum, bitumen, oil shale, or coal, such transformation
always entails some particular form of carbon rejection or H-additionmin one
case increasing the H/C ratio by pyrolytically abstracting carbon as "coke,"
CO, and/or CO2, and in the other raising it by inserting externally sources H
into the feed 9.
These procedures, summarized in Chapters 9 and ,01 make it technically
feasible to convert natural gas into an almost pure form of carbon 10 and,
1 Introduction: The Family of Fossil Hydrocarbons
more important, to convert heavy oils, bituminous substances, oil shale kero-
gens, or coals into light transportation fuels. They also allow transforming
heavy hydrocarbons into a "substitute" or "synthetic" natural gas (SNG), or
into a syngas from which an extraordinarily wide range of hydrocarbon liquids
and industrial chemicals can be produced by Fischer-Tropsch techniques (see
Chapter 10). The aromaticity of the feed will, as a rule, only determine the
severity of processingmthat is, the extent of carbon rejection or H-addition,
and in practice, this rarely means much more than selecting suitable processing
regimes 11.
This given, questions of whether or when any of these options might be
exercised can generally only be answered in light of prevailing economic
circumstances.
NOTES
1 Authentic documentary evidence places the first use of coal as a heating fuel in late 12th-
century England, but there are indications that it was occasionally also used as such by the
Roman legions in Britain during the 1st century.
2 Episodal uses of coal other than as primary fuel are a matter of record. In the mid-1800s,
it began to be gasified and thereby converted into a domestic fuel gas. In the 1920s, it
commenced service as a source of syngas needed for production of gasolines and diesel and
aviation fuels. And by the early 1930s, it had established itself as a hydrogenation feedstock
for manufacturing transportation fuels, heating oils, and high-purity carbon electrodes. These
activities were mostly abandoned in the early 1950s, when abundant supplies of cheap oil
and natural gas almost entirely displaced coal as anything other than a primary fuel and source
of metallurgical coke, and sometimes displaced it even there. Since then, coal conversion
has only attracted attention in perceived crises: in the 1960s and 1970s, coal gasification
commanded wide but transient interest because projections, later proven wide of the mark,
anticipated serious shortages of acceptably priced natural gas; and intensive work on trans-
forming coal into liquid hydrocarbons lasted no longer than the crippling economic disloca-
tions that followed the 1973 oil crisis, but were soon "remedied" by such events as the
Iraq-Iran warna conflict that, by the convoluted economic policies of an international oil
cartel (OPEC), caused an oversupply of oil and a consequent oil-price collapse that is likely
to continue until well into the 21st century. That coal conversion can neverthelsss remain
attractive is demonstrated by some 20 commercial plants in Europe and Asia that currently
produce ammonia (for fertilizer use) from coal-based syngas.
Parenthetically it is also worth observing that oft-repeated "technical" justifications for
the dichotomy between "petroleum hydrocarbons" and coal are more contentious than real.
Arguments that coal cannot meet the multifaceted needs of modern societies, or meet them
as easily or conveniently as natural gas and/or petroleum, seem to ignore advances in coal
processing since the mid-1940s. And the contention that coal is so much dirtier than oil
and gas, and therefore environmentally "unfriendly," discounts what is required to prepare
oil and gas for environmentally acceptable use, and ignores impressive advances in coal
preparation (and combustion) over the past 40 or so years.
3 Although the relevant literature seems to regard all bitumens to be microbially oxidized
and water-washed (see Chapter 3) and designates most heavy oils in like terms, the evidence
Notes 5
for this view is not entirely satisfactory. There are, as suggested in Chapter 3, other possible
mechanisms that could explain the their origins.
4 Oils are generated by thermal degradation of kerogen much as tars are thermally generated
from coal, and bituminous substances are widely (but not necessarily correctly) assumed
to have been microbially altered much as weathered coals were abiotically altered. In neither
case can a reaction product be properly classified with its precursor.
5 That availability should often force the decision is due to a natural inequity--the fact that
the so-called advanced societies tend to be well endowed with heavy fossil hydrocarbons
(mainly coal), but lack the abundant natural gas and crude oils that, for the most part,
occur in less developed jurisdictions.
6 Particularly important in this context is that prior to Devonian times, ligninman important
constituent of higher terrestrial plants that then made their first massive appearancem
contributed very little to the precursor masses of fossil hydrocarbons.
7 sA illustrated in Chapter ,7 these constructs differ primarily in their carbon aromaticities,
which increase steadily from the lighter to the heavier members of the series at the expense
of aliphatic and, later, naphthenic moieties.
8 Because of the overriding importance of H for generation of hydrocarbon liquids (see Chapter
3), their yields and compositions depend on the concentration of lipids (or lipid-like matter)
in the precursor; and this implies that oily matter increases and tends to become the lighter
the farther its origin from an inland location. In other words, light oils originate in deep or
moderately deep marine conditions, kerogens and sapropelic coals in paralic and/or lacustrine
environments, and humic coals on land.
9 The many seemingly different (or differently named) processing methods turn out, on closer
inspection, to be versions of basic techniques that differ in little more than operating minutiae;
the rich vocabulary that characterizes petroleum preparation and processing (see Chapters
8 and 9) merely reflects the wide range of products that technical development and stimulated
market demands allowed to be made from crude oil. yB the same token, the much more
limited process terminology relating to oil shale and coal mirrors the limited utilization of
these resources. Oil shale, from which substantial quantities of (shale) oil were produced
in the 19th century, is now little more than an occasional subject of a "hard look", and coal,
long used as primary fuel and source of metallurgical coke, continues to be restrictively
viewed as such.
10 This is, in fact, done in production of carbon blacks, which are used as pigments in printing
inks, fillers for rubber tires, etc. Such carbons are characterized by small (10-1000 nm),
nearly spherical particles and bulk densities as low as 0.06 g/cm .3
11 For carbon rejection, the primary components of an "appropriate" regime are temperature,
pressure, time, and, in some versions, catalysts. For hydrogenation, they are mainly tempera-
ture, pressure, and a suitable catalyst.
2
CHAPTER
snigirO
1. THE CHEMICAL PRECURSORS
All biota, even the most primitive algae and bacteria that contributed their
substance to the source materials of fossil hydrocarbons in early Paleozoic
times, construct their fabric by selectively drawing on a pool of four chemically
well-defined classes of matter: lipids, amino acids, carbohydrates, and lignins.
Of these, particularly important for eventual formation of oils are lipids, a
group of closely related aliphatic hydrocarbons that include water-insoluble
neutral fats, fatty acids, waxes, terpenes, and steroids. In living organisms,
lipids serve primarily as sources of energy; however, during putrefaction they
are hydrolyzed to long-chain carboxy acids and subsequently decarboxylated
to form alkanes.
The fats of the group, mixed triglycerides, illustrate this reaction, first
being saponified by aqueous NaOH to yield glycerol and the Na salts of the
corresponding fatty acids, as in
H3C~ (CH2)nmC(O) ~O~CH2 HOOCH2
I I
H3C~(CH2)n~C(O)~OmCH ~ HOOCH + H3Cm(CH2)n~C(O)~O~,
I I
HBC~ (CH2)nmC (O) ~O~CH2 HOOCH2
and the fatty acidsmwhich can exist in saturated forms exemplified by palmitic
)2023H61C( and stearic )2063H81C( acids or unsaturated versions such as oleic
,)2043H81C( linoleic ,)2023H81C( and linolenic )2003H81C( acids--then losing
mCOOH and yielding straight-chain alkanes 1.
However, waxes, terpenes, and steroids belonging to the group are structur-
ally more complex and undergo correspondingly more complex changes when
they decompose.
The waxes are esters of alcohols other than glycerol, contain as a rule only
one mOH group, and present themselves either as sterols such as cholesterol
2 snigirO
%C3H A ~C3H
H3~I~~CH3
L__II c,..r L_fl
3HC 3HC
~--~"*J~ 5H2C 5H20_
HO" -v v HO" "~ v-
I 2
C3H
I 3HC
HC 3
"OH v v OH HO
H
3 4
FIGURE 2.1.1 Some important natural sterols. (1)/3-Sitosterol, (2) stigmasterol, (3) fungisterol,
(4) cholic acid.
(Fig. 2.1.1) or as straight-chain 63C-61C aliphatic alcohols such as cetyl alcohol,
.HO2HC41)2HC(3HC
The terpenes are polymeric forms of isoprene (or 2-methyl-l,3-butadiene;
see Chapter 5),
H2C~C ~CH---CH2,
I
3HC
a basic building block of chlorophyll 2 and of the natural gums of higher
plants. In nature, they are encountered :sa
.1 monoterpenes ;01C( Fig. 2.1.2), i.e., isoprene dimers that abound in al-
gae and in the essential oils 3 of many higher plants;
.2 sesquiterpenes ;51C( Fig. 2.1.3) and diterpenes ;02C( Fig. 2.1.4), respec-
tively comprising three and four isoprene units and, combined with
phenylpropane derivatives such coniferyl alcohol, representing major
components of conifer resins;
3. triterpenes ;)03C( Fig. 2.1.5), made up of six isoprene units, often de-
veloping from squalene ;05H03C( see Fig. 2.1.5) and believed to be di-
rect precursors of petroleum hydrocarbons;
4. tetraterpenes ,)04C( a group of carotenoid pigments represented by,
and commonly present as, carotene (Fig. 2.1.6).