1: Case Nitrogen Fixation
In 1900, the world was struggling to feed 1.5 billion people that is ever growing, and crops need fixed nitrogen. Chile fought a war against Peru to control the saltpeter mine, as the only supplemental source of fertilizer. How do we feed 5.5 billion people in 1997 easily, with no increase in the acres of farms cultivated? How do we get four times as much food from the same acre of farm?
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Living matter are made of C, H, O, (from air and water) Also N, P, K, (from the soil) Free N2 in air must be fixed before it could be utilized
Men Animals Plants Soil, Water, Air, Sunshine Food Chain
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Nitrogen Cycle
Free Nitrogen in Air
Lightning, soil bacteria in legume, 100 million tons/year
Soil bacteria
Fixed nitrogen in soil and water
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subsistence farming
N,P,K in food
N, P, K return in wastes
commercial farming N,P,K in food N, P, K in fertilizer
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Need for Fixed Nitrogen
Daily protein need per person is 1 g/kg, or 70 g protein for 70 kg man, or 10 g of N Today, world need 20 million tons fixed N per year for direct human food, much more needed for plants and animals
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Feeding a Hungry World
Wheat productivity per hectare-year varies from 550 kg in Burma to 2310 in Japan High yield agriculture depends on
Irrigation High yield plants Fertilizers
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Another Need for Nitrogen!!
Black gunpowder is based on charcoal, sulfur and saltpeter Dynamite is nitro-glycerine TNT is tri-nitro-toluene Guncotton is nitro-cellulose ALL DEPEND ON FIXED NITROGEN !
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The Electric Arc Process N 2 + O2 2 NO
This reaction requires a great deal of heat input and high temperature (1800 C). The conversion is very low, i.e. the reaction product contains very little (0.6%) NO. Therefore, it is very expensive.
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Ammonia Synthesis
N2 + 3H2 2 NH3
This was invented by Fritz Haber and Carl Bosch. It produces heat. The conversion is very low until the pressure is increased to several hundred atmospheres.
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The Ammonia Synthesis
Fritz Haber defined the required temperature (600 C) and pressure (200 atmospheres) for the synthesis (8% yield) Carl Bosch found the appropriate catalyst, iron oxide, and built the pressure reactors Germany built many ammonia synthesis plants just before World War I, in time to replace the cutoff of saltpeter from Chile
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Fritz Haber
1868 Born in Breslau, Prussia 1898 Professor of chemistry, Karlsruhe 1909 Established condition for ammonia synthesis 1911 Director of Kaiser Wilhelm Institute, Berlin 1914 Chemical warfare research 1918 Nobel in chemistry 1933 Forced to resign by Hitler 1934 Death at Basel
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Raw Material for Ammonia
N is from air, after you burn off the 21% oxygen. H is from water H2O, after you get rid of O. In either case, you need a fuel: Coal Natural gas Petroleum Biomass, charcoal CH4 + O2 --> CO + H2O + H2 CO + H2O --> CO2 + H2
Making Fertilizers
Direct injection of ammonia into soil
very alkaline and irritating acts too quickly, needs repeated applications
React to form water-soluble solids such as urea (NH2)2.CO or ammonia nitrate
less N per pound, as C and O are diluents less precaution in shipping and application slowly released over a period of time
Consequences of the Invention
Feed the hungry of the world, better nutrition, better health, longer lives, more children Enable the world population to grow to 5.5 billion in 1996
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Supply war efforts with gunpowder Deconstruction on world population, fertilizer runoff, ecosystem change
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Agriculture Trends Jesse Ausubel
Since mid-century, global use of land for agriculture has remained stable, and may decrease further. Since 1940, US wheat yield tripled, corn yield quintupled. Average Iowa farm grows twice the corn per hectare as world average, and top Iowa farmer grows twice the Iowa average. India in last four decades have raised wheat yields fivefold, spared cropland area equal to state of California Large amounts of land in Europe and North America are reverting from farm to woodland.
1997 Debates on whether to Grow more food in Africa?
Feeding the hungry is humanitarian More food per means acre more land for wildlife and ecology (Norman Borlaug, Nobel in Peace)
The poor needs discipline to control family size More food would mean less discipline, and retard progress (Ford Foundation, World Bank)
Science and Engineering Issues
Chemical reactions involve a change of matter and energy Stoichiometry studies matter (elements) and energy (calories) balance Input - Output = Accumulation
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Input
Accumulation
Output
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Stoichiometry: material and energy balance
CH4 + 2O2 --> CO2 + 2H2O + 800 kJ/mol
Atomic weights: H=1; C=12; O=16 Molecular Weights: CH4 = 1x12 + 4x1 = 16 H2O = 18 CO2 = 44 O2 = 32 It takes 16 grams methane to make 44 grams of CO2
Some Forms of Energy
Primary bond energy, holds atoms together to form molecules Secondary bond energy, holds molecules together as in liquids and solids Thermal energy, random motion Kinetic energy, velocity Potential energy, elevation, spring, etc. Enthalpy, H=U + PV Gibbs Free Energy, G = H - TS
CH4 + 2O2 --> CO2 + 2H2O + 800 kJ/mol
input: 16 g 64 0 0 output: 16(1-x) 64(1-x) 44x 36x x is the conversion, let us say x=0.1 output: 14.4 g 57.6 4.4 3.6 25 C 800xJ 25 C + 80J
if we burn 10% of the methane and oxygen mixture, what is the temperature rise in the mixture? that depends on the heat capacity of the mixture.
Heat Properties
molecule M. W. Cp, J/K.m Cp, J/K.g )H, kJ/g CO2 H2 CH4 N2 O2 H2O (g) 44 2 16 28 32 18 37.1 28.8 35.7 29.2 29.4 33.6 0.84 14.4 2.23 1.04 0.92 1.87 -151 -50
1 calorie is the heat needed to raise 1 g of water by 1oC. 1 Joule = 0.239 calorie.
Energy balance:
E = constant ) E=0
Chemical energy: Burning 10% of the methane produces 800,000 x 0.1 = 80,000 J of heat = 19,120 calories Thermal energy: The heat capacity of the exit mixture is: 14.4 x 2.23 + 57.6 x 0.92 + 4.4 x 0.84 + 3.6 x 1.87 = 95.4 J/K. Thermal energy required to raise the mixture by )T is 95.4 x )T Energy balance: 95.4 x )T = 19,120; or )T = 200 K If we burn methane in air, what is temperature rise?
Reversible Reaction Equilibrium
N2 + O2 2 NO
p p(1-x) p p(1-x) 0 2px
start: end:
x is the degree of conversion
There is a forward reaction, as well as a backward reaction. So this is called a Reversible Reaction.
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Thermodynamic Equilibrium
N
2
+O
2
2NO
When the forward reaction is equal in speed to the backward reaction, we have reached the equilibrium. This requires that the equilibrium constant K equals the ratio: ( NO )2 (2 px ) 2 K= = ( N 2 )( O 2 ) p (1 x ) p (1 x )
=
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(2 x ) (1 x ) 2
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2
Solution by Interpolation
x 0.01 0.02 0.03 0.0...