Journal of Natural Gas Chemistry 14(2005)140–150
Co-Generation of C
2Hydrocarbons and Synthesis
Gases from Methane and Carbon Dioxide:
a Thermodynamic Analysis
Istadi
1),
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/CH4ratio larger than 1.
Key words: thermodynamic chemical equilibrium, co-generation, synthesis gas, C2hydrocarbons, Gibbs
free energy, CH4, CO2, carbon
1. Introduction
The simultaneous utilization of CH4and CO2 for
conversion to important chemicals provides several advantages from the environmental and energy per-spectives. Natural gas is a fuel consisting of methane, ethane, carbon dioxide, H2S, 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] with-out having to separate the carbon dioxide first. The composition of natural gas varies widely from loca-tion to localoca-tion. 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
uti-lization of CO2-contented natural gas. The process
yields lower H2/CO molar ratio synthesis gas and
light hydrocarbons (C2 hydrocarbons). The
synthe-sis gas (H2 and CO) can be converted to liquid
fu-els by the Fischer-Tropsch process and also to var-ious value-added chemicals, especially methanol and gasolineviathe methanol-to-gasoline (MTG) process.
The synthesis gas is also the main source of hydro-gen for refinery processes and ammonia synthesis. The use of CO2 as an oxidant for the selective
oxi-dation of methane may also be beneficial, because it is expected that the replacement of O2 with CO2
in-hibits the gas-phase non-selective oxidation and thus increases the selectivity to higher hydrocarbons. Pre-viously, the thermodynamic calculation on equilib-rium conversion of CH4 to C2 hydrocarbons (C2H6
∗Corresponding author. Tel. +607-5535588; Fax. +607-5581463; E-mail: noraishah@fkkksa.utm.my.
