L5 Flashcards
1
Q
CO Methanation reaction
A
- Methanation is a chemical process to generate methane from a mixture of various gases such as syngas or biogas
- Used for generation of bio-based natural gas substitutes
- CO + 3H2 -> CH4 + H2O
- Exothermic and catalysts (nickel etc)
- Reverse reaction of steam methane reforming
- Need to consider side reactions (WGS and Boudouard)
2
Q
CO2 methanation reaction
A
- Reaction of H2 with CO (exothermic)
- High P
- 300-400 Celsius
- Produces CH4 and H2O
- CO2 + 4H2 -> CH4 + 2H2O
- Sum of WGS and CO methanation
3
Q
Steam reforming reaction
A
- Producing H2, CO or other products (syngas) from hydrocarbon fuels as such methane. (SMR)
- Reverse CO methanation reaction
- 700 - 1100 Celcius, with nickel based catalyst
- CH4 + H2O -> CO + 3H2
- Side reactions
- — WGS
- — Reverse CO2 methanation reaction
- Endothermic
4
Q
Water gas shift reaction
A
- reaction of CO and water vapour to form CO2 and H2
- CO + H2O -> CO2 + H2
- Integrated with biomass gasification to generate renewable hydrogen
- Exothermic
5
Q
Heat transfer considerations
A
- Try to minimise thickness of gas film at tube wall
- Smaller catalyst particles improve heat transfer form wall to bulk gas
- Smaller particles increases pressure drop
- Catalyst shape needs to be optimised for HT and pressure drop
6
Q
Carbon formation and prevention
A
- Carbon formation is unwanted
- Will cause catalyst breakage and deactivation
- Over heating to tubes
- Carbon formation occurs when:
- — Steam to carbon ratio is low
- — Catalyst not active enough
- — Higher hydrocarbons are present
Use a potash doped catalyst to reduce carbon formation
7
Q
Fischer Tropsch process
A
- (2n+1) H2 + nCO -> CnH(2n+2) + nH2O
- Iron, cobalt or nickel catalyst
- Selectivity of products dependant on T, P and gas composition
8
Q
High temperature FT
A
- 320 - 350 Celsius
- reactants and products all in gaseous phase
- Need heat exchanger to condense
- Circulating fluidised bed reactor
9
Q
Low temperature FT
A
- 220 - 250 Celsius
- Products are in liquid phase
- Fixed bed reactor and slurry reactor
10
Q
FT Tubular slurry reactor advantages
A
- High heat capacity = good temperature control
- Easy heat recovery
- High reaction rate per unit volume is catalyst is active
- Small particles can be used
- Used for batch or flow processing
11
Q
FT Tubular slurry reactor disadvantages
A
- Generation of fine particles
- Catalyst removal may cause increased capital costs due to operational issues
