1-step direct oxidative synthesis of methanol from methane

Report
Direct Oxidation
of Methane to
Methanol
GROUP 7
J O E Y S A A H , R I C H A R D G R AV E R , S H E K H A R S H A H , J O S H
CO N D O N
Methanol
Applications
◦ Solvent
◦ Gasoline additive
◦ Feedstock for many chemical processes
21 million tons produced per year
Primary component of natural gas
◦ Currently an abundant fuel source
◦ Difficult and uneconomical to transport
Simple and cost effective on-site process required
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Standard Methanol Synthesis
Conversion of natural gas into syngas
◦ Steam reforming reactor with catalyst
◦ Creates carbon monoxide and hydrogen from methane
Syngas to Methanol
◦ H2 and CO react in 2:1 ratio
to form methanol
◦ Catalyst selectively forms
methanol
Haldor Topsoe
One-Step Methanol Process
Advantages
◦
◦
◦
◦
Steam in steam reformer is expensive to produce
Less capital costs required to build one-step plant
May be created near more remote methanol sources
Remote methanol sources more profitable, attractive
Challenges
◦ Past one-step reactions showed low yield or selectivity with homogeneous
and heterogeneous catalysts
◦ Other methods did not produce methanol levels required for
commercialization
◦ Liquid phase or Supercritical reactor methods
History of Methanol
1661 – Methanol discovered by Robert Boyle
1834 – The chemical structure and identity of methanol was identified
by Dumas and Peligrot
Destructive distillation of wood was the first method to produce
methanol
◦ Pyrolysis in a distillation apparatus
History of Industrial Methanol
Production
First synthetic methanol production route discovered in 1905
BASF commercialized the process in 1934
◦ Zinc-Chromium Oxide Catalyst
◦ 300 °C and 200 atm
◦ This process was used until 1966 when a lower pressure, higher efficiency
method was discovered
History of Industrial Methanol
Production cont.
Imperial Chemical Industries, Ltd. discovered a new process in 1966
◦ Copper-Zinc Oxide catalyst
◦ 250-300 °C
◦ 50-100 atm
Poisoning of catalyst was a problem for this method
Lifetime of catalyst is about 4 years
◦ Only if there is good control of temperature and feedstock purity
Thermodynamic Analysis
ΔG
reaction
(KJ/mol)
Reaction
298
650
700
750
800
1000
Direct
CH4+1/2O2  CH3OH
-111
-93
-91
-88
-86
-76
SR
CH4 + 1/2O2  CO + 2H2
-86
-152
-162
-172
-182
-222
SR
CH4 + H2O  CO + 3H2
142
60
48
36
23
-27
Optimal Conditions
Traditional steam reforming requires 1000 K or higher
Direct oxidation (direct synthesis) favorable at lower temperatures
thermodynamically
Theoretically, 33% equilibrium conversion at 298 K for direct synthesis
Maximum of 5 % equilibrium conversion in direct synthesis actually
obtained due to high activation energy
Thermodynamic Requirements
Direct synthesis would be economically feasible (compared to
traditional method) if 5.5% conversion and 80% selectivity to methanol
is obtained in the reaction
Low conversion requirement is indicative of the high cost of current
methanol production
CO2 and CO are thermodynamically the most favorable products of
direct oxidation (selectivity to methanol is a challenge)
Why do we need a catalyst?
Methane is a more stable molecule than methanol
◦ Reaction equilibrium favors methane at operating conditions
◦ Low conversion
◦ Large activation energy
Complete oxidation to carbon monoxide and carbon dioxide is
thermodynamically favored
◦ Low selectivity for the partially oxidized product
Harsh operating conditions
◦ Requires 440 kJ/mol to break the first C—H bond
◦ 50-100 bar and 500-550 K
◦ Energy intensive step would be eliminated
Important Catalytic
Parameters
1.Temperature
2.Pressure
3.Oxygen concentration in the feed gas
4.Gas flow rate
5.Additives
These parameters are critical to optimizing the conversion of methane
and selectivity toward the methanol product.
Heterogeneous Catalytic Partial
Oxidation
Direct conversion of methane and oxygen to methanol
◦ Conversion of methane and selectivity to desired product are limiting factors
◦ Activation energy for the reaction is extremely large and limits the
conversion of methane to products
CH4 + ½ O2
CH3OH
Direct Oxidation Reaction
Involves the abstraction of a hydrogen from methane to create a methyl
radical followed by subsequent reaction to form methoxide ions
◦ Solid catalysts containing metal oxide catalysts have been effective at
removing hydrogen
References
Khirsariya, P., Mewada, R. “Single Step Oxidation of Methane to
Methanol – Towards Better Understanding”. Procedia Engineering 51
409-415. 2013.

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