Chemistry Reference
In-Depth Information
supply of crude oil, and there is every reason to
anticipate an extraction and use pattern more or less
as shown in Fig. 4.2. Because crude oil is replenished
on time scales of many millions of years, because
current rates of use are clearly unsustainable and
because the decline in supply is so close in time,
it does not appear possible to construct a scenario
in which petroleum feedstocks can be made
sustainable.
Experience and theory in green chemistry indicate
that there are many potential paths from starting
materials to products, and, for many products, alter-
native potential starting materials [7]. In the case
of petrochemicals, the obvious potential alternatives
are feedstocks based on biotechnology and derived
from agricultural approaches [8,9]. As shown in Fig.
4.2, this means that development of biotechnologi-
cal feedstocks needs to be brought on line rapidly,
because they will probably need to overtake feed-
stocks based on petroleum within about 30-40 years
and become the dominant feedstock in about 60-
70 years, as shown in Table 4.1. The time window
within which the feedstock transition must begin to
occur if the chemical industry is to be sustainable
thus is almost upon us, and no chemical corporation
can legitimately call itself sustainable unless it is
planning and acting so as to become part of the feed-
stock transition.
Unlike petrochemical feedstocks, which are drawn
from below the Earth's surface by oil rigs having
rather small surface footprints, feedstocks based on
biotechnology inherently become part of the activi-
ties of global agriculture. The central goal of agricul-
ture, of course, is to provide food for people and
animals; biotechnological feedstocks will never be
more than a tiny fraction of that activity. As with
petroleum feedstocks and petroleum, biotechnologi-
cal feedstocks seem destined to ride on the back of
the world's approach to agriculture, for better or
worse. We are therefore brought to considerations of
the sustainability of agriculture. In this connection,
Ruttan [10] suggests that sufficient agricultural land
is not a long-term limitation, especially for the high-
value commodities one can expect chemical feed-
stocks to be. In some fragile resource areas there may
be limitations, but they are most likely to manifest
themselves for low-value crops.
The discussion above relates to feedstock sustain-
ability from a source standpoint but not from a
magnitude of use standpoint. Although using smaller
10
10
Sun dies
Life ends
Continents
shift position
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10
8
10
7
10
6
10
5
The next
ice age
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4
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3
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2
Target time
for sustainability
All resources
and planetary
systems sustainable
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1
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0
Fig. 4.1
Temporal projections of future events in Earth history,
including the target interval for sustainability planning.
capable of receiving whatever residues are
dissipated.
If it is agreed that these are reasonable targets for
sustainability in the green chemistry sector, the next
step is to determine what levels of use are sustain-
able in each regard. This is the discussion that
follows.
2.1 Sustainable use of chemical feedstocks
It is, of course, impossible to make synthetic chemi-
cals without chemical feedstock starting materials.
Most of those materials traditionally have been inor-
ganic materials or petrochemicals. In the case of the
former (calcium carbonate, phosphates, etc.), known
stocks are generally high enough so that sustainabil-
ity over a 50-year time span is not a serious concern
[3]. For petrochemical feedstocks, however, supply
concerns are more relevant. There is general agree-
ment among petroleum geologists that the all-time
production peak in crude oil production will occur
within the 2010-2020 period, declining thereafter
[4,5].
Almost all petroleum is processed and used as fuel,
with only about 3% serving as petrochemical feed-
stock [6]. Petrochemical use thus will not control the
