"A raw material of feedstock should
be renewable rather depleting wherever technically and economically
practicable" (Green Chemistry
Principles, Dr. Paul Anastas et al)
eliminate our contribution
to systematic increases in concentrations of substances from the
Earth's crust. This means substituting certain minerals that are
scarce in nature with others that are more abundant, using all
mined materials efficiently, and systematically reducing dependence
on fossil fuels." (The
Natural Step, Promoters of Sustainable Development)
Every living organism must take material
from the surrounding environment in order to survive. In some
cases considerable changes in the environment may take place as
a result, but these are normally part of renewable cycles.
Continued extraction of minerals, oil and gas from the Earth's
crust, however, will result in steady depletion, as these resources
are finite. In addition, "new" material is continually
being added to the biosphere, affecting the on-going cycles. This
is part of the problem the chemical industry is faced with.
Much of the chemical industry uses a relatively
limited range of raw materials. The fossil fuels, coal oil and
natural gas, are used to make fuels, but also form the basis for
the manufacture of many bulk chemicals. An enormous number of
common products are therefore ultimately petrochemical in origin.
Some common bulk chemicals manufactured
from oil and gas:
Fossil reserves will continue to be important
resources for many years to come, but much research and development
has focussed on more efficient use, and recycling of the end products.
The recycling of nylon
is a good example of this.
If a resource is renewable, it will be replenished
over a relatively short timescale. Plants have the potential to
be more or less infinitely renewable as feedstock. Plant material,
when used in this context, is usually referred to as biomass.
Chemicals, including many pharmaceuticals, have been made successfully
from plant extracts for many years.
Ethanol, primarily a petrochemical product
in the UK, is produced by fermentation link to ethanol production
at production methods summary, p4 in most of the rest of the world.
Starch and Cellulose are important renewable
resources for chemical production.
Click here to find out more about these.
A general-purpose oil ("Bio Oil")
from fast pyrolysis, already in use as a substitute for fuel oils,
could become the basis for a future bio-refinery, similar to current
petrochemical refineries in function. For
more details on bio oil, click here
Glucose, the main building block of starch,
is relatively easy to obtain from plant material, and can be used
to synthesise a wide
range of existing chemicals.
There are problems, however, with relying
on plants to produce chemicals:
- Apart from cellulose, plants themselves
rarely contain individual chemicals in large amounts, so a lot
of plant material is needed for simple extraction, with a consequent
high volume of waste. This may be acceptable with products only
needed in small quantities (eg specialised medicines), but not
for high volume manufacture. This underlines the importance
of synthetic routes from cellulose and glucose, materials present
in substantial amounts.
- Plants usually contain many complex
materials, whereas the chemical industry works best with a more
limited range of simpler substances.
- Setting aside land for dedicated feedstock
crops is not always desirable. In many cases the local population
may gain little benefit, and valuable agricultural land may
be used. Chemical manufacture from agricultural waste, where
feasible, is a better alternative. Phenolic
resins can be made using timber waste.
- Traditional methods of production from
biomass can be inefficient, as they cannot utilise enough all
of the feedstock. Higher chemical yields may require genetically
modified bacteria, as in the case of new
methods for ethanol production.