2 Industrial processes

Importance of equilibrium to industrial processes Common examples Haber process T= 450oC, P= 200 – 1000 atm, catalyst = iron Low temp gives good yield but slow rate: compromise temp used High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure N2 + 3H2 2NH3 H = -ve exo Contact process Stage 1 S (s) + O2 (g)  SO2 (g) Stage 2 SO2 (g) + ½ O2 (g) SO3 (g) H = -98 kJ mol-1 T= 450oC, P= 10 atm, catalyst = V2O5 Low temp gives good yield but slow rate: compromise moderate temp used High pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure Hydration of ethene to produce ethanol CH2=CH2 (g) + H2O (g) CH3CH2OH(l) H = -ve T= 300oC, P= 70 atm, catalyst = conc H3PO4 Low temp gives good yield but slow rate: compromise temp used High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure High pressure also leads to unwanted polymerisation of ethene to poly(ethene) Production of methanol from CO CO (g) + 2H2(g) CH3OH (g) H = -ve exo T= 400oC, P= 50 atm, catalyst = chromium and zinc oxides Low temp gives good yield but slow rate: compromise temp used High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure Both methanol and ethanol can be used as fuels If the carbon monoxide used to make methanol in the above reaction was extracted from the atmosphere then it could be classed as carbon neutral The term carbon neutral refers to “an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere” It would only be carbon neutral, however, if the energy required to carry out the reaction was not made by combustion of fossil fuels Learn the equations for the production of methanol and ethanol below Recycling unreacted reactants back into the reactor can improve the overall yields of all these processes In all cases high pressure leads to too high energy costs for pumps to produce the pressure and too high equipment costs to have equipment that can withstand high pressures. In all cases catalysts speeds up the rate allowing lower temp to be used (and hence lower energy costs) but have no effect on equilibrium