Direct Oxidation of Methane to Methanol

GROUP 7

JOEY SAAH, RICHARD GRAVER, SHEKHAR SHAH, JOSH CONDON

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

Reaction

ΔG reaction (KJ/mol)

298 650 700 750 800 1000

Direct CH4+1/2O2 è CH3OH -111 -93 -91 -88 -86 -76

SR CH4 + 1/2O2 è CO + 2H2 -86 -152 -162 -172 -182 -222

SR CH4 + H2O è 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

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

CH4 + ½ O2 CH3OH Direct Oxidation Reaction

References Khirsariya, P., Mewada, R. “Single Step Oxidation of Methane to Methanol – Towards Better Understanding”. Procedia Engineering 51 409-415. 2013.