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Chemical Reactors and their Applications
Norges teknisk-naturvitenskapelige universitet
Chemical Reactorsand their
Applications
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Chemical Reactors and their Applications
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Chemical Reactors and their Applications
Outline
– Reactor concepts
– Natural gas reforming concepts
– Downstream processes
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Chemical Reactors and their Applications
Outline
– Reactor concepts
– Natural gas reforming concepts
– Downstream processes
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Chemical Reactors and their Applications
Reactor Concepts
– Fixed bed reactors
– Fluidized bed reactors
– Stirred tank reactors
– Slurry loop reactors
– Bubble columns
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Chemical Reactors and their Applications
Reactor Concepts
– Fixed bed reactors
– Fluidized bed reactors
– Stirred tank reactors
– Slurry loop reactors
– Bubble columns
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Chemical Reactors and their Applications
Fixed Bed ReactorsConcept– Collection of fixed solid
particles.– The particles may serve as a
catalyst or an adsorbent.– Continuous gas flow– (Trickling liquid)
Applications– Synthesis gas production
– Methanol synthesis
– Ammonia synthesis
– Fischer-Tropsch synthesis
– Gas cleaning (adsorption)
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Chemical Reactors and their Applications
Fixed Bed Reactors
Challenges/Limitations
– Temperature control
– Pressure drop
– Catalyst deactivation
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Chemical Reactors and their Applications
Fixed Bed Reactors
Challenges/Limitations
– Temperature control
– Pressure drop
– Catalyst deactivation
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Chemical Reactors and their Applications
Fixed Bed Reactors
Temperature control
– Endothermic reactions may die out
– Exothermic reactions may damage the reactor
– Selectivity control
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Chemical Reactors and their Applications
Fixed Bed Reactors
Single-Bed Reactor– All the particles are located
in a single vessel
Advantages/Disadvantages– Easy to construct
– Inexpensive
– Applicable when the reactions are not very exo-/endothermic
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Chemical Reactors and their Applications
Fixed Bed Reactors
Multi-Bed Reactor– Several serial beds with
intermediate cooling/heating stages
Advantages/Disadvantages– Applicable for exo-/endothermic
reactions
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Chemical Reactors and their Applications
Fixed Bed ReactorsSO3 reactor
NH3 reactor
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Chemical Reactors and their Applications
Fixed Bed Reactors
Multi-Tube Reactor– Several tubes of small
diameter filled with particles.
Advantages/Disadvantages– Expensive
– High surface area for heat exchange Very good very temperature control
– Applicable for very exo-/endothermic reactions
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Chemical Reactors and their Applications
Fixed Bed ReactorsSteam reformer
Reactor height: 30 m
Number of tubes: 40-10000
Tube length: 6-12 m
Tube diameter: 70-160 mm
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Chemical Reactors and their Applications
Fixed Bed Reactors
Challenges/Limitations
– Temperature control
– Pressure drop
– Catalyst deactivation
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Chemical Reactors and their Applications
Fixed Bed Reactors
Pressure drop– Friction between the gas and particle phase results in a
pressure drop.
– High pressure drop high compression costs
– Some systems have low tolerance for pressure drop.
– The pressure drop is mainly dependent on reactor length, particle diameter, void fraction and gas velocity.
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Chemical Reactors and their Applications
Fixed Bed Reactors
Large particles has to be used (dp>1mm).
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Chemical Reactors and their Applications
Fixed Bed ReactorsPorous catalyst particle– The particles are porous to increase
the surface area of the catalyst.– Reactants are transported inside
the pores by means of molecular diffusion and adsorb to the active sites where the reaction occurs.
– Products desorb and diffuse back to the bulk.
– Heat is transported by conduction.
Intra-particle diffusion/conductionmay be rate determining for largeparticles ( egg-shell particles).
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Chemical Reactors and their Applications
Fixed Bed Reactors
Challenges/Limitations
– Temperature control
– Pressure drop
– Catalyst deactivation
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Chemical Reactors and their Applications
Fixed Bed Reactors
Catalyst deactivation– The catalyst gets deactivated if the active sites get
contaminated.
– Sulfur compounds deactivate Ni-catalysts– Desulfurization is often necessary prior to reforming.
– Formation of carbon deposits deactivate the catalysts.– Large carbon deposits may clog the tubes, causing hot-
spots that damage the reactor.
– Catalyst regeneration is necessary.
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Chemical Reactors and their Applications
Fixed Bed Reactors
Summary Advantages/Disadvantages
– High conversion is possible
– Large temperature gradients may occur
– Inefficient heat-exchange
– Suitable for slow- or non-deactivating processes
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Chemical Reactors and their Applications
Reactor Concepts
– Fixed bed reactors
– Fluidized bed reactors
– Stirred tank reactors
– Slurry loop reactors
– Bubble columns
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Chemical Reactors and their Applications
Fluidized Bed Reactors
Concept– Collection of solid particles dispersed
in a continuous phase.– The particles may serve as a
catalyst, adsorbent or a heat carrier.– Continuous flow of gas or liquid
Applications– Catalytic cracking processes– Fischer-Tropsch synthesis– Polymerization– Waste combustion– Drying
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Chemical Reactors and their Applications
Fluidized Bed Reactors
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Chemical Reactors and their Applications
Fluidized Bed Reactors
A fluidized bed exhibits liquidlike behavior
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Chemical Reactors and their Applications
Fluidized Bed Reactors
Continuous regeneration
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Chemical Reactors and their Applications
Fluidized Bed Reactors
Summary Advantages/Disadvantages
– Conversion may be poor if gas is bypassing.
– Erosion of vessel and pipe lines.
– Uniform temperature
– Efficient heat-exchange
– Can handle rapid deactivating processes.
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Chemical Reactors and their Applications
Reactor Concepts
– Fixed bed reactors
– Fluidized bed reactors
– Stirred tank reactors
– Slurry loop reactors
– Bubble columns
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Chemical Reactors and their Applications
Stirred tank ReactorsConcept– Forced mixing by use of impeller.– Applied in reactive systems when
mixing is the rate determining step.– Single phase: liquid mixing.– Two phases: liquid/gas, liquid/particle– Three phases: liquid/particle/gas
Typical applications– Chemical component and phase
mixing– Fermentation reactor– Food and paper industry– Natural gas
conversion/polymerization
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Chemical Reactors and their Applications
Stirred tank ReactorsThe mixing is influenced by:
– stirring rate and pumping capacity
– liquid height
– baffle design– (baffles reduces solid body rotation)
– size and geometry of the tank
– size and geometry of heat equipment
– size and type of impeller
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Chemical Reactors and their Applications
Stirred tank ReactorsImpellers– Radial flow impellers are suitable
for dispersion of gas in liquid.
– Axial flow impellers are suitable to blend liquids and suspend solids in liquids.
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Chemical Reactors and their Applications
Stirred tank Reactors
Summary Advantages/Disadvantages
– Uniform temperature
– Efficient heat-exchange– Exception: slurries with high concentrations of large particles
(difficult mixing).
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Chemical Reactors and their Applications
Reactor Concepts
– Fixed bed reactors
– Fluidized bed reactors
– Stirred tank reactors
– Slurry loop reactors
– Bubble columns
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Chemical Reactors and their Applications
Slurry loop ReactorsConcept– Collection of solid catalyst particles
dispersed in a liquid phase (slurry).– The slurry is circulating at a high
velocity impelled by an axial pump.– The mixing pattern is very intensive
and well defined.
Typical application– Polymerization
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Chemical Reactors and their Applications
Slurry loop Reactors
Summary Advantages/Disadvantages
– Uniform temperature
– Very efficient heat-exchange
– Can operate at high polymer concentrations
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Chemical Reactors and their Applications
Reactor Concepts
– Fixed bed reactors
– Fluidized bed reactors
– Stirred tank reactors
– Slurry loop reactors
– Bubble columns
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Chemical Reactors and their Applications
Bubble ColumnsConcept– Gas dispersed in a continuous
liquid phase.– Two phases: liquid/gas.– Three phases: slurry/gas
Typical applications– Natural gas conversion
– Waste water treatment
– Bio-processes
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Chemical Reactors and their Applications
Bubble Columns
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Chemical Reactors and their Applications
Bubble Columns
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Chemical Reactors and their Applications
Bubble Columns
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Chemical Reactors and their Applications
Bubble Columns
Summary Advantages/Disadvantages
– Non-uniform product if bubble size distribution is heterogeneous
– Uniform temperature
– Efficient heat-exchange
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Chemical Reactors and their Applications
Outline
– Reactor concepts
– Natural gas reforming concepts
– Downstream processes
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Chemical Reactors and their Applications
Natural gas
– Vital component of the world's supply of energy (approx. 20%).
– Fuel
– Most common feedstock for hydrogen production or synthesis gas production.
– Production of base chemicals (methanol, ammonia)
Typical composition
CH4 70-90%
C2H6-C4H10 0-20%
CO2 0-8%
N2 0-5%
H2S 0-5%
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Chemical Reactors and their Applications
Natural gas reforming concepts
– Steam reforming (SR)
– Partial oxidation (POX)
– Autothermal reforming (ATR)
– New reforming concepts
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Chemical Reactors and their Applications
Natural gas reforming concepts
– Steam reforming (SR)
– Partial oxidation (POX)
– Autothermal reforming (ATR)
– New reforming concepts
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Chemical Reactors and their Applications
Steam reforming
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Chemical Reactors and their Applications
Steam reforming
Primary reformerCH4 + H2O CO + 3H2 ΔHr=206 kJ/mol
CO + H2O CO2 + H2 ΔHr= -41 kJ/mol (Water gas shift)
– Overall heat of reaction is endothermic multi-tube reformer
– Reactions are catalyzed over Ni-catalyst. Temperature 1100-1200K
Pressure 15-30 bar
H2/CO >3
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Chemical Reactors and their Applications
Steam reformingBurner configurations
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Chemical Reactors and their Applications
Steam reforming
Better temperature control with side fired burners
Catalyst deactivates
Retaining productivity by increasing temperature
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Chemical Reactors and their Applications
Steam reforming
Carbon formation2CO C + CO2 ΔHr= -173 kJ/mol (The Boudouard reaction)
CH4 C + 2H2 ΔHr= 75 kJ/mol (Decomposition of methane)
CO + H2 C + H2O ΔHr= -132 kJ/mol (Heterogeneous water gas reaction)
– Carbon deposits deactivates the catalyst.
Actions to reduce carbon formation– High steam/carbon (S/C) ratio reduces carbon formation.
– Expensive to produce steam.
– Addition of CO2 reduces carbon formation
– Pre-reformer if higher hydrocarbons are present– Common S/C-ratio is 2.5–4.5
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Chemical Reactors and their Applications
Steam reforming
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Chemical Reactors and their Applications
Steam reforming
Adiabatic Pre-reformer
CnHm + nH2O → nCO + (n+m/2)H2 ΔHr>0
CO + 3H2 CH4 + H2O ΔHr= -206 kJ/mol
– Overall heat of reaction is exothermic or thermoneutral.
– Reactions are catalyzed over Ni-catalyst.
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Chemical Reactors and their Applications
Steam reforming
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Chemical Reactors and their Applications
Steam reforming
Hydro-desulfurizer (HDS)– Sulfur compounds are present in practically all gas feedstocks.– Ni-catalysts are poisoned by sulfur compounds desulfurization
– Cyclic organic sulfur compounds are hydrogenated to H2S over Co-Mo or Ni-Mo catalysts.
– H2S and other sulfur species are adsorbed over a bed of zinc-oxide.
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Chemical Reactors and their Applications
Steam reforming
Advantages/Disadvantages– No need for expensive oxygen plant.
– Material limitations on temperature limited conversion.
– High H2/CO ratio, suitable for hydrogen production with CO2 capture, not for methanol- or FT-synthesis.
– Carbon formation
– Steam corrosion problems.
– Costs in handling excess H2O.
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Chemical Reactors and their Applications
Natural gas reforming concepts
– Steam reforming (SR)
– Partial oxidation (POX)
– Autothermal reforming (ATR)
– New reforming concepts
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Chemical Reactors and their Applications
Partial oxidation
CH4 + ½O2 → CO + 2H2 ΔHr= -36 kJ/mol
CH4 + 2O2 → CO2 + 2H2O ΔHr= -803 kJ/mol
CO + ½O2 → CO2 ΔHr= -284 kJ/mol
H2 + ½O2 → H2O ΔHr= -242 kJ/mol
– Overall heat of reaction is slightly exothermic.
– No catalyst (burners)
Temperature 1600-1900K
Pressure →150 bar
H2/CO <2
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Chemical Reactors and their Applications
Catalytic partial oxidationReactions are catalyzed to:– improve selectivities
– eliminate the need for burners
– eliminate soot formation
– lower reaction temperatures
Drawbacks– CH4/O2 mixtures can be explosive.
– Problems with selectivities at high pressures(above 20 bars).
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Chemical Reactors and their Applications
Partial oxidation
Advantages/Disadvantages– Less expensive than SR-plants.
– H2/CO ratio suitable for methanol- or FT-synthesis
– Soot problems (POX)
– Needs expensive oxygen plant.– (dependent on downstream process)
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Chemical Reactors and their Applications
Natural gas reforming concepts
– Steam reforming (SR)
– Partial oxidation (POX)
– Autothermal reforming (ATR)
– New reforming concepts
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Chemical Reactors and their Applications
Autothermal reforming
Temperature 1200-1400K
Pressure 20-100 bar
H2/CO 2-3
Catalytic/non-catalytic partial oxidation provides heat for steam reforming
More energy efficient
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Chemical Reactors and their Applications
Autothermal reforming
Advantages/Disadvantages– Less expensive than SR-plants.
– Higher conversion than SR (higher operating temperature).
– No soot problems
– Needs expensive oxygen plant.– (dependent on downstream process)
– Often used as a secondary reformer downstream an SR.
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Chemical Reactors and their Applications
Natural gas reforming concepts
– Steam reforming (SR)
– Partial oxidation (POX)
– Autothermal reforming (ATR)
– New reforming concepts
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Chemical Reactors and their Applications
Multifunctional reactors
Membrane reactors– Combine air separation and partial oxidation in one unit by
introduce oxygen permeable membranes.
– Remove H2 in the reactor by using membranes and thereby avoid equilibrium limitations
– Lower reaction temperatures can be used.
Chemical looping reforming– Continuous circulation of metal particles which serve as oxygen-
and heat carrier (metal oxide) for partial oxidation of methane. Two reactors are required: Air reactor and fuel reactor.
– Simple separation of oxygen.– No explosive mixtures.
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Chemical Reactors and their Applications
Multifunctional reactors
Sorption enhanced reaction process (SERP)
– Remove CO2 in the SR-process by using adsorbents mixed with the catalyst particles and thereby avoid equilibrium limitations. The adsorbent is regenerated by either increasing the temperature or reducing the pressure (temperature- or pressure swing).
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Chemical Reactors and their Applications
Outline
– Reactor concepts
– Natural gas reforming concepts
– Downstream processes
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Chemical Reactors and their Applications
Downstream processes
– Ammonia synthesis
– Methanol synthesis
– Fischer-Tropsch synthesis
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Chemical Reactors and their Applications
Ammonia synthesis
Ammonia– Base chemical for:
– Nitrogen fertilizers (CaNO3,KNO3)
– Explosive industry
Production history
– 1905; Birkeland/Eyde succeeded in producing CaNO3 from air.
– 1913; The Haber/Bosch-process was developed.
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Chemical Reactors and their Applications
Ammonia synthesis
N2 + 3H2 2NH3 ΔHr = -91.4 kJ/mol
– Ideal H2/N2-ratio is 3.
– Steam reforming is suitable reforming process due to high H2/CO-ratio. It is combined with an air-blown ATR that introduces N2.
– Equilibrium limited High pressure (100-250 bar) and low temperature (675-770K).
– Low single-pass conversion Recycling necessary.
– CO and CO2 has to be removed prior to the
ammonia synthesis several extra process units.
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Chemical Reactors and their Applications
Ammonia synthesis
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Chemical Reactors and their Applications
Ammonia synthesis
ICI quench reactor
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Chemical Reactors and their Applications
Ammonia synthesis
Haldor Topsøe radial flow reactor Kellogg vertical reactor Kellogg horizontal reactor
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Chemical Reactors and their Applications
Ammonia synthesis
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Chemical Reactors and their Applications
Methanol synthesis
Methanol– Base chemical for:
– Formaldehyde– Acetic acid
– Automobile fuel and fuel additive (MTBE)
Production history– 1923; BASF was the first to synthesize methanol from syngas.– 1960s; New catalysts were developed for low-pressure
production.
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Chemical Reactors and their Applications
Methanol synthesisCO + 2H2 CH3OH ΔHr = -90.8 kJ/mol
CO2 + 3H2 CH3OH + H2O ΔHr = -49.6 kJ/mol
CO + H2O CO2 + H2 ΔHr = -41 kJ/mol
– Ideal H2/CO-ratio is 2.– Low single-pass conversion Recycling necessary.
– Equilibrium limited High pressure (50-100 bar) and low temperature (500-550K).
– T < 570K due to catalyst sintering.
– The catalyst has to be very selective since methanol is thermodynamically less stabile than i.e. CH4. Cu/ZnO/Al2O3
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Chemical Reactors and their Applications
Methanol synthesis
Distillation– Column 1: Gases and light
impurities are removed.
– Column 2: Methanol is separated from heavy alcohols and water.
Reactor (ICI)– 40% of the feed enters the reactor– 60% of the feed is used as quench.
Separator– Gas and liquid are separated
after several cooling steps.
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Chemical Reactors and their Applications
Methanol synthesis
Lurgi reactor Haldor Topsøe reactor concept
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Chemical Reactors and their Applications
Methanol synthesis
Slurry reactor (fluidized bed)– Inert hydrocarbon liquid (absorbs heat, uniform temp.)– Solid catalyst.– Higher single-pass conversion less compression costs.
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Chemical Reactors and their Applications
Methanol synthesis
Direct conversion of methane
CH4+ ½O2 CH3OH ΔHr = -126 kJ/mol
– Significant efficiency increase.
– No CO2 production.
– Low yields.
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Chemical Reactors and their Applications
Fischer-Tropsch synthesis
Applicability– Fuels– Waxes
History– 1923; Fischer/Tropsch converted synthesis gas into a wide range
of hydrocarbons and/or alcohols.– WW II; Germany applied FT-synthesis to make fuels.– 1950s→; South Africa started to make fuels and base chemicals
in FT-plants to reduce the dependence on imported oil.
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Chemical Reactors and their Applications
Fischer-Tropsch synthesis
CO + 2H2 -CH2- + H2O ΔHr = -165 kJ/mol
– Chain growth.
– High exothermicity.– Effective heat removal is a major consideration in reactor design.
– Converted over Fe- or Co-based catalysts.
– Selective productivity is not possible product ranges.
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Chemical Reactors and their Applications
Fischer-Tropsch synthesis
T<530 K due to carbon deposition T>570 K to avoid heavy wax formation T<570 K due to hydrocracking