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Biodata of Christopher J. Rhodes, author of “Biofuel from Algae: Salvation from
Professor Chris J. Rhodes is currently a visiting professor at the University of Reading and Director of Fresh-Lands consulting. He was awarded a D.Phil from the
University of Sussex in 1985 and a D.Sc in 2003. He has wide scientific interests (www.fresh-lands.com) which cover radiation chemistry, catalysis, zeolites,
radioisotopes, free radicals, and electron spin resonance spectroscopy, and more
recently have developed into aspects of environmental decontamination and the
production of artificial fuels. He has published more than 200 peer-reviewed
papers and three books.
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DOI 10.1007/978-90-481-8569-6_14, © Springer Science+Business Media B.V. 2010
BIOFUEL FROM ALGAE: SALVATION FROM PEAK OIL?
CHRISTOPHER J. RHODES
Fresh-Lands, P.O. Box 2074, Reading, Berkshire, RG4 5ZQ,
There is practically nothing in the modern world that does not depend on the
resource of plentiful, cheap oil. The majority of crude oil is refined into fuel for
transportation, but it also provides a feedstock for a myriad of industries, producing products ranging from plastics to pharmaceuticals. In total, it is reckoned that
worldwide some 86 million barrels of oil are consumed daily, which amounts to just
over 31 billion barrels a year. Around one quarter of all oil is used in the USA, which
was formerly the world’s main oil-producing nation. Now that accolade is with
Saudi Arabia, which delivers an almost ten million barrel daily aliquot to the world
oil markets, while Russia exhumes an almost equal quantity. In 1999, the price of a
barrel of oil was $12, but reached almost $150 in the summer of 2008 preceding a
world stock market crash and a fallback to $25 a barrel (Rhodes, 2008). The price
rose during the following year and, writing in August 2009, it is now around $70 a
barrel. There are many factors held culpable for such frenetic activity in the marketplace, including a seemingly inexorable demand for oil (and indeed all kinds of
energy resources) from rising economies such as China and India, a weakening US
dollar, and that oil is becoming harder to produce, as a general principle. Over all
of this looms the specter of peak oil, which is the point at which production meets a
geological maximum, and beyond which it must relentlessly fall. The combination
of these factors must culminate in a gap between rising demand and ultimately falling supply. Within a decade or less, the world economies will no longer be able to
depend on some limitless growth in oil output. For these reasons, attention is being
turned toward “Alternatives,” which ideally are also “Renewables,” but the issue of
biofuels is more complex than is generally realized, and it is at best a partial solution bearing its own attendant environmental costs (Rhodes, 2005).
In addition to the simple fact that growing fuel crops must inevitably
compete eventually for limited arable land on which food-crops are to be grown,
there are vital differences in the properties of biofuels, e.g., biodiesel and bioethanol,
from conventional hydrocarbon fuels such as petrol and diesel, which will necessitate
the adaptation of engine designs to use them; for example, in regard to viscosity
at low temperatures, e.g., in planes flying in the frigidity of the troposphere. Raw
CHRISTOPHER J. RHODES
ethanol needs to be burned in a specially adapted engine to recover more of its
energy in terms of tank to wheels miles, otherwise it could deliver only about 70%
of the energy content of petrol, pound for pound in accordance with its lower
enthalpy of combustion (29 MJ/kg) than is typical for an oil-based fuel like petrol
(gasoline) or diesel (42 MJ/kg) (Rhodes, 2005).
Of the various means that are being considered, at least in terms of growing our way out of the oil crunch, is making biofuel from algae. There are many
advantages claimed as we shall see, but in particular, the quoted yields of oil
that might be derived from algae per hectare are high, even when compared with
those from high-oil-yielding plants such as jatropha and palm, which translate
to around 6 t of diesel per hectare (see Section 6). Most biofuel in Europe is
biodiesel and is made, for example, from rapeseed oil, which yields perhaps 1 t
of diesel per hectare. In contrast, it is reckoned that some species of high-oilyielding algae might furnish more than 100 t of diesel per hectare – an attractive
prognosis indeed, since an area, say the size of the southern UK, could fuel the
entire world (Rhodes, 2005). Algae offer further advantages that they can be
used to absorb CO2 from smokestacks at fossil-fuel-fired power stations, they
can be grown on saline waters or wastewaters (cleaning the latter in the process),
and furthermore there is no necessity to use arable land for algae production
since the tanks they are grown in can be placed anywhere, including brownfield
land or on the open ocean. Thus, the competition between fuel and food production is avoided.
The author attempts an overview of some specific aspects of a subject that
is, however, not quite as straightforward as it first appears.
2. The Peak Oil Problem
The prediction of peak oil was made in 1956 by Marion King Hubbert (Hubbert,
1956), a geophysicist working for the Shell Development Corporation. Hubbert predicted that the lower 48 states in the USA would peak (hit maximum production)
during 1965–1970, depending on his estimate of the total volume of the reserve.
At that time, the USA was awash with oil and his prediction was not taken seriously.
Hubbert’s analysis is based on the logistic function, the first derivative of which
gives a peak. Mathematically, this kind of curve can be represented by the logistic
differential equation (1).
dQ/dt = P = k(1 – Q/Qt )Q
In Eq. (1), P is the production rate, as shown by its equality to the rate of change
of cumulative production Q (i.e., the sum quantity of oil recovered from a given
source to date), Qt is the total amount of oil that will ever be recovered from it,
and k is the logistic growth rate (a sort of % compound interest). In Hubbert’s
original paper (Hubbert, 1956), he assumed two scenarios for the lower 48 states
in the USA: (1) there were 150 billion barrels worth of oil and (2) there were 200
BIOFUEL FROM ALGAE: SALVATION FROM PEAK OIL?
billion barrels as a total recoverable reserve, Qt. In those days before computers,
he simply reckoned the amount of oil represented by each square on his sheet of
graph paper, and drew a curve by hand that enclosed an area equal to the estimated volume of the reserve. For case (1), he predicted that the peak in production
would arrive in 1965 and for (2) around 1970. Thus, the method was not predictive
of the volume of oil that would be recovered in total; this had to be reckoned first.
In fact, US production peaked in 1971, so establishing both his fame and credibility in the basic method. In a later paper (Hubbert, 1982), Hubbert surveyed
the mathematics behind all this, from which an alternative and predictive method
coined the Hubbert Linearization (Deffeyes, 2005) was derived. The basis of this is
that Eq. (1), which is a quadratic, can be rewritten in the form of Eq. (2), which is
a linear equation of familiar form y = mx + c.
P/Q = k(1 – Q/Qt )
By plotting annual production divided by cumulative production (i.e., P/Q) versus
cumulative production alone (Q), a straight-line plot is obtained, with a y-axis
intercept equal to k and a slope of −k/Qt. Thus, both essential parameters of the
logistic peak, k and Qt, may be estimated without prior assumptions, an improvement
on the original approach (Hubbert, 1956). The method is still used extensively in
the oil industry, although now with modern PCs, it is easy to fit directly logistic
and all other kinds of functions to oil production data using programs like Origin.
Having established values for k and Qt, they can be used to construct the logistic
curve with considerable accuracy. Because of the symmetry of the curve, when
the peak is reached, half the reserve has been extracted, beyond which production
falls inexorably. For the entire world, a value for Qt of around two trillion barrels
is estimated, of which we have used close to half. It is expected that once the
peak is reached, there will be a decline in world oil production by 3% per annum.
This approach is not without its critics, however. Some maintain that it is an
oversimplification, and does not allow for future discoveries of oil or the production of unconventional oil and that it is more likely that the postpeak outcome
will be a more steady plateau followed by a gradual depletion in supply rather
than a mirror-fall of the growth phase. The oil industry actually uses a number of
methods of geophysics, e.g., seismic measurements, to estimate the volume of a
reserve, and their final predictions are often based on a combination of physical data
and various kinds of mathematical and numerical modeling procedures, including
Various estimates have been given for the time of arrival of peak oil. If all
production, ignoring tar sands and natural gas liquids (NGL), is considered, the
peak famously reckoned by Kenneth Deffeyes (2005) to arrive on November 24,
2005 (thanksgiving day!), is predicted. If all production including NGL is
included, the peak shifts forward to mid-2006. All studies that place peak oil in
2010 and beyond use other methods, but generally consider the rates of depletion
of existing oil fields and projections about developing fields. Such studies are
termed “bottom-up analysis.” Chris Skrebowski, a researcher for the Energy