Reaction of natural gas reforming is catalytic reaction between natural gas and steam by uses nickel catalyst that is supported by alumina (NI/Al

_{2}O_{4}). Overall equilibrium reaction of natural gas reforming is endothermic. In industrial world, reaction of natural gas reformation with steam is main process to produce synthesis gas which consists of CO and H_{2}. If natural gas is represented by CH_{4}, so main reactions of natural gas reforming can be written in equations as follow:Equation 1:

CH

Equation 2:

_{4}+ H_{2}O ↔ CO + 3H_{2}ΔH_{298 K}= +206.2 kJ/molEquation 2:

CO + H

Equation 3:

_{2}O ↔ CO_{2}+ H_{2}ΔH_{298 K}= -41.1 kJ/molEquation 3:

CH

_{4}+ 2H_{2}O ↔ CO + 4H_{2}ΔH_{298 K}= +165 kJ/molAt high temperature and low pressure, conversion of CH

_{4}based on Equation 1 and Equation 3 thermodynamically will increase. Equilibrium reaction of equation 2 is known as*water-gas shift reaction*which has exothermic properties and does not depend on operating pressure.The new study of reforming reaction is CO

_{2}reforming as shown in Equation 4. The reaction is endothermic and conversion of CH_{4}thermodynamically will increase at high temperature and low pressure.Equation 4:

CH

CH

_{4}+ CO ↔ 2CO + 2H_{2 }ΔH_{298 K}= +247.4 kJ/molThis last reaction is utilized to get synthesis gas with low ratio of H

_{2}/CO by replace some or all steam with CO_{2}in feed gas process. High content of CO_{2}can increase carbon forming.Equilibrium composition in reaction of natural gas reforming, free Gibbs energy thermodynamically can be estimated as shown in Equation 5. For ideal gas, fugacity coefficient (Фi) can be assumed as one, so Equation 5 can be written as Equation 6. Equilibrium composition is reached at minimum free Gibbs energy is mathematically shown in Equation 7.

Where:

a

_{i}: activity of component iG

_{i}^{o}: free Gibbs energy in forming component in

_{t}: total moln

_{io}: initial mol of component in

_{i}: mol of component iy

_{i}: fraction of component iɛ : extent of reaction

Фi : fugacity coefficient of component i

Finally, equation of equilibrium reaction can be written as following equations:

K = exp (-ΔG / RT)

K = Π C

_{i}^{vi}K = P

^{Δv }Π (y_{i})^{vi}Where:

C

_{i}= equilibrium concentration of component iK = constant equilibrium reaction

P = total pressure

Δv = difference coefficient of product and reactant

Constant equilibrium reaction (Ki) can be calculated from empirical equation as function of temperature in following equations:

Where: T in Kelvin unit.

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