paper istadi jnatgaschem 2005 thermo
Journal of Natural Gas Chemistry 14(2005)140–150
Co-Generation of C2 Hydrocarbons and Synthesis
Gases from Methane and Carbon Dioxide:
a Thermodynamic Analysis
Istadi1) ,
Nor Aishah Saidina Amin∗
Chemical Reaction Engineering Group (CREG), Faculty of Chemical and Natural Resources Engineering,
Universiti Teknologi Malaysia, UTM Skudai, Johor, 81310 Malaysia
[Manuscript received August 01, 2005; revised September 08, 2005]
Abstract: This paper deals with thermodynamic chemical equilibrium analysis using the method of
direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2 /CH4
feed ratio, reaction temperature, and system pressure on equilibrium composition, conversion, selectivity
and yield were studied. In addition, carbon and no carbon formation regions were also considered at
various reaction temperatures and CO2 /CH4 feed ratios in the reaction system at equilibrium. It was
found that the reaction temperature above 1100 K and CO2 /CH4 ratio=1 were favourable for synthesis
gas production with H2 /CO ratio unity, while carbon dioxide oxidative coupling of methane (CO2 OCM)
reaction to produce ethane and ethylene is less favourable thermodynamically. Numerical results indicated
that the no carbon formation region was at temperatures above 1000 K and CO2 /CH4 ratio larger than 1.
Key words: thermodynamic chemical equilibrium, co-generation, synthesis gas, C2 hydrocarbons, Gibbs
free energy, CH4 , CO2 , carbon
1. Introduction
The simultaneous utilization of CH4 and CO2 for
conversion to important chemicals provides several
advantages from the environmental and energy perspectives. Natural gas is a fuel consisting of methane,
ethane, carbon dioxide, H2 S, and trace amounts of
other compounds. It is highly desirable to utilize
and to convert both methane and carbon dioxide, two
typical components in acidic natural gas, into higher
value-added chemicals and also liquid fuels [3] without having to separate the carbon dioxide first. The
composition of natural gas varies widely from location to location. For example, the CO2 /CH4 ratio of
natural gas in Natuna’s [1] and Arun’s [2] fields are
71/28 and 15/75, respectively.
The co-generation of synthesis gas and C2 hydro-
carbons from CH4 and CO2 is important in the utilization of CO2 -contented natural gas. The process
yields lower H2 /CO molar ratio synthesis gas and
light hydrocarbons (C2 hydrocarbons). The synthesis gas (H2 and CO) can be converted to liquid fuels by the Fischer-Tropsch process and also to various value-added chemicals, especially methanol and
gasoline via the methanol-to-gasoline (MTG) process.
The synthesis gas is also the main source of hydrogen for refinery processes and ammonia synthesis.
The use of CO2 as an oxidant for the selective oxidation of methane may also be beneficial, because it
is expected that the replacement of O2 with CO2 inhibits the gas-phase non-selective oxidation and thus
increases the selectivity to higher hydrocarbons. Previously, the thermodynamic calculation on equilibrium conversion of CH4 to C2 hydrocarbons (C2 H6
Corresponding author. Tel. +607-5535588; Fax. +607-5581463; E-mail: [email protected].
1) Permanent address: Chemical Reaction Engineering & Catalysis Group, Dept. of Chemical Engineering, Diponegoro
University, Semarang, Indonesia. E-mail: [email protected]
∗
Co-Generation of C2 Hydrocarbons and Synthesis
Gases from Methane and Carbon Dioxide:
a Thermodynamic Analysis
Istadi1) ,
Nor Aishah Saidina Amin∗
Chemical Reaction Engineering Group (CREG), Faculty of Chemical and Natural Resources Engineering,
Universiti Teknologi Malaysia, UTM Skudai, Johor, 81310 Malaysia
[Manuscript received August 01, 2005; revised September 08, 2005]
Abstract: This paper deals with thermodynamic chemical equilibrium analysis using the method of
direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2 /CH4
feed ratio, reaction temperature, and system pressure on equilibrium composition, conversion, selectivity
and yield were studied. In addition, carbon and no carbon formation regions were also considered at
various reaction temperatures and CO2 /CH4 feed ratios in the reaction system at equilibrium. It was
found that the reaction temperature above 1100 K and CO2 /CH4 ratio=1 were favourable for synthesis
gas production with H2 /CO ratio unity, while carbon dioxide oxidative coupling of methane (CO2 OCM)
reaction to produce ethane and ethylene is less favourable thermodynamically. Numerical results indicated
that the no carbon formation region was at temperatures above 1000 K and CO2 /CH4 ratio larger than 1.
Key words: thermodynamic chemical equilibrium, co-generation, synthesis gas, C2 hydrocarbons, Gibbs
free energy, CH4 , CO2 , carbon
1. Introduction
The simultaneous utilization of CH4 and CO2 for
conversion to important chemicals provides several
advantages from the environmental and energy perspectives. Natural gas is a fuel consisting of methane,
ethane, carbon dioxide, H2 S, and trace amounts of
other compounds. It is highly desirable to utilize
and to convert both methane and carbon dioxide, two
typical components in acidic natural gas, into higher
value-added chemicals and also liquid fuels [3] without having to separate the carbon dioxide first. The
composition of natural gas varies widely from location to location. For example, the CO2 /CH4 ratio of
natural gas in Natuna’s [1] and Arun’s [2] fields are
71/28 and 15/75, respectively.
The co-generation of synthesis gas and C2 hydro-
carbons from CH4 and CO2 is important in the utilization of CO2 -contented natural gas. The process
yields lower H2 /CO molar ratio synthesis gas and
light hydrocarbons (C2 hydrocarbons). The synthesis gas (H2 and CO) can be converted to liquid fuels by the Fischer-Tropsch process and also to various value-added chemicals, especially methanol and
gasoline via the methanol-to-gasoline (MTG) process.
The synthesis gas is also the main source of hydrogen for refinery processes and ammonia synthesis.
The use of CO2 as an oxidant for the selective oxidation of methane may also be beneficial, because it
is expected that the replacement of O2 with CO2 inhibits the gas-phase non-selective oxidation and thus
increases the selectivity to higher hydrocarbons. Previously, the thermodynamic calculation on equilibrium conversion of CH4 to C2 hydrocarbons (C2 H6
Corresponding author. Tel. +607-5535588; Fax. +607-5581463; E-mail: [email protected].
1) Permanent address: Chemical Reaction Engineering & Catalysis Group, Dept. of Chemical Engineering, Diponegoro
University, Semarang, Indonesia. E-mail: [email protected]
∗