Environmental Engineering Reference
In-Depth Information
2.
Formaldehyde
is produced by oxidation of methanol.
a.
Methanol is manufactured from methane obtained from natural gas.
3.
Sodium cyanide
is from the combination of sodium hydroxide with hydrogen cyanide.
a. Sodium hydroxide is generated by electrolysis of sodium chloride.
b. Hydrogen cyanide is synthesized by making methane react with ammonia over a
catalyst.
This simplified version of EDTA production is a representative example of the complexity of
ingredients produced by synthesis. The precursors that create the intermediates are ultimately
natural gas, which is a nonrenewable resource, and sodium hydroxide that is mined from con-
centrated deposits in the ground or by evaporation of seawater. Every step involved in this
synthesis has cumulative effects of:
1.
Consumption of nonrenewable energy in the form of electricity and heat with the conse-
quent emission of greenhouse gases and other gases (NOx and SOx) that produce regional
impacts as acid rain.
2.
Depletion of natural resources.
3.
Air and water pollution at global and regional levels.
Phosphate compounds are all made from phosphoric acid that is obtained from phosphate
rock. Phosphate rock is present in the earth crust in limited deposits so its consumption has a
high impact on this resource. See discussion on phosphate in a previous section of this chapter.
Case of sugar, wheat flour, and oil
These ingredients are all made from dedicated crops. Sugar comes either from sugar cane in
warm climates or sugar beets in colder areas. Wheat flour is from milling wheat kernels pro-
duced in temperate climates in different parts of the world. Most cooking oils are obtained via
extraction with solvents of oilseeds such as soybean, sunflower, safflower, peanuts, and can-
ola.
Although all three of these products come from different crops and are made using dis-
similar processes, they all share similar impacts at different stages of production. The agricul-
tural stage requires water, fertilizers, pesticides, and diesel to run the machinery. Then the raw
materials need transportation to the processing plant with all the emissions associated with
burning fossil transportation fuels. Electricity, heat, and water are used during processing to
transform the raw materials into finished products with the collateral production of solid
waste, wastewater, and gas emissions.
Table 3.7 displays the impacts for five categories for the production of 1 kilogram of sugar
(from beets), 1 kilogram of wheat flour, and 1 kilogram of vegetable oil (soybean or rapeseed)
Table 3.7
Cradle-to-factory-gate environmental impacts for the production of 1 kilogram of selected food
ingredients.
Impact category
Units
Sugar (from sugar beets)
Wheat flour
Vegetable oil
Global warming
g CO
2
eq.
840
1010
3510
Acidification
g SO
2
eq.
5.5
6.5
31
Nutrient enrichment
g NO
3
eq.
−12.8
83
438
Photochemical smog
g ethene eq.
0.73
0.23
2.0
Land use
m
2
year
0.45
1.4
4.5
Adapted from Nielsen et al., 2003.
