Hello,
Yes, there is a way to simulate this in a PFR within Aspen Plus.
I. What i understood about the problem is described in the following lines:
1. The reactor is of plug flow type and it is filled with solid catalyst particles.
2. The equilibrium reaction mentioned above describes the overall reaction.
3. The inlet stream is fully defined, except flow rate (but which is irelevant for this topic).
4. The process rate, rp [kmol/kg_cat-Pa-s], within reactor should respect this simple law:
rp = k * (P_CH4 - P_CH4,ch_eq) equivalent to rp = k * P *(y_CH4 - y_CH4,ch_eq)
, where:
k = k0 * exp(-Ea/RT);
k0 = 90.2 mol/kg_cat-Pa-s;
Ea = 63.5 kJ/mol;
y_CH4,ch_eq is the methane mole fr. @ chemical equilibrium of overall reaction;
y_CH4,ch_eq = 0,00052935 => partial pres. of CH4 @ ch_eq is 265 Pa (considering total pressure constant & equal to 5 bar(a) ).
II. Possible solution in A+:
Use a reaction type 'general' class 'powerlaw' with checked box for reversible.
Specify the kinetic factor :
k is k0, n=0, E is Ea, T0 to be empty (because it is not considered inn kinetic factor expression);
Specify the proper basis and units (i.e. partial pressure in Pa, catalyst wt, rate in kmol/kg_cat-s, reacting phase: vapor).
Specify the driving force, i.e. (in our case) : (P_CH4^1 - P_CH4_ch_Eq).
It's general form is : K1 * Prod(P_i ^ expon_i) - K2 * Prod(P_i ^ expon_j).
For forward reaction rate:
K1 is 1 => A, B, C, D are zero.
exponents are 1, 0 // 0, 0.
So, the first term becomes 1 * P_CH4 * 1.
For reverse reaction rate:
K2 is 265 Pa => A=ln(265)=5.5785
exponents are 0, 0 // 0, 0
So, the 2nd term is 265 Pa * 1
III. Observations and suggestions:
1. The mass of catalyst is very important for the reactor performance therefore it should be defined correctly acc reactor geometry and catalyst bulk density.
2. The process rate, r, law is very rigid, i.e. for a different feed P or/and composition, the driving force reverse reaction rate param. A must be changed based on new yCH4_ch_eq and feed P, otherwise the law would not be respected.
3. A calculator block for the calculation from points (1) & (2) would solve this issue.
I hope this answers your question.