Environmental Engineering Reference
In-Depth Information
fragrance additive for many household products and a 'green' solvent, e.g. for
cleaning electronics where it replaces atmospherically harmful halogenated
solvents) is increasing.
The production of chemical products from wet orange peel has had very limited
commercial success: limonene and other oils are extracted and sold but only for a
small proportion of the peel, while pectin is generally sourced from other fruit
(apples and lemons). The current methods for the production of pectin requires a
two-stage process involving the use of mineral acids, which generates large
amounts of contaminated wastewaters (from neutralising the waste acid) adding
to the cost of the final product, although there is a high demand for pectin for food
and non-food applications.
One way to improve the economics of this process of is to employ an integrated
technology that yields multiple products. Recent work has demonstrated that low-
temperature microwave processing of citrus peel such as orange yields limonene
and pectin as well as porous cellulose and other products in one process, thus
offering the real possibility of developing a microwave biorefinery that could be
employed wherever citrus waste is concentrated [21]. New uses for limonene have
also been reported recently, notably as a solvent for organic chemical manufactur-
ing processes where there is growing pressure to reduce the process environmen-
tal footprint and use more renewable compounds [22].
1.4 Green Chemistry
Green chemistry emerged in the 1990s as a movement dedicated to the develop-
ment of more environmentally benign alternatives to hazardous and wasteful
chemical processes as a result of the increased awareness in industry of the costs
of waste and of government regulations requiring cleaner chemical manufactur-
ing. Through a combination of meetings, research funding, awards for best prac-
tice and tougher legislation, the green chemistry movement gained momentum
through the 1990s and into the twenty-first century. New technologies which
addressed key process chemistry issues such as wasteful separations (e.g. through
the use of easy-to-separate supercritical CO
2
), atmospherically damaging volatile
organic solvents (e.g. through the use of involatile ionic liquids), hazardous and
difficult-to-separate process auxiliaries (e.g. by using heterogeneous reagents and
catalysts) and poor energy utilisation (e.g. through alternative reactors such as
microwave heating) were developed and promoted. The importance of metrics for
measuring process greenness also became recognised and was championed by the
pharmaceutical industry as well as by academics [23]. The pharmaceutical indus-
try has led the way in many examples of green chemistry metrics in practice,
including solvent selection guides and assessment of the environmental impacts
of different processes [24].
The legislative, economic and social drivers for change impact all of the
main chemical product life-cycle stages, resources, production and products.
