Through the study of the kinetics of dimethyl ether steam reforming reaction, a two-dimensional model of the reactor is established. At the same time, rate equations of simplified elementary reactions of DME steam reforming reaction are deduced by the mechanism of Langmuir-Hinshel-wood, and the rate constants are obtained by correcting the pre-exponential factor of Arrhenius equation. Finally, the analog data of DME steam reforming reaction under a variety of conditions are obtained, and making a simulation diagram. The two-dimensional model is substantially correct because of the analog data more in line with a variety of knowledge.
Dimethyl ether has the advantage of economy, security, and the sources of diversity, bound from the research stage to the industrial stage [
DME is an ideal vehicle fuel, but also has capability of chemical hydrogen storage. Therefore, many scholars have been studied to the DME reforming processes [
During the whole experiment, the space velocity of DME steam reforming reactor is 0.3 m/s. The molar ratio of water and DME is 1 to 3. The feed mole fraction of dimethyl ether is between 5 and 15. The flow rate of DME is
The kinetic model of DME steam reforming reactor applies to a two-dimensional model. Although the kinetic parameters of the reactor are difficult to be determined in the process of reaction, it can improve the accuracy of the change of amount of substance and energy conversion. The two-dimensional model is non-continuous, axial symmetry, similar to the two-dimensional reactor of Groppi, G. et al. [
Because the reactants are gas and in the high-speed motion in the reactor, and so axial diffusion of the gas mass is negligible. Because the heat exchanger conduit wall can isolate gas, so the radial diffusion of the gas mass in the reactor is also negligible. Then the above equation can be simplified to as follows:
Further, on the catalyst coating layer of the reactor, the mass conservation equation of each element in the course of the reaction and diffusion is as follows:
In this reactor, if the catalyst coating layer is a uniformly thickness, the boundary conditions are shown in
Similar to the gas phase mass balance of (2), axial and radial dispersions were neglected in the gas-phase heat balance:
Position | Boundary conditions |
---|---|
x = 0 (Catalyst coating surface) | |
z = 0 (Inlet) | |
z = L (outlet) | |
r = 0 (monolith center) | |
r = R (monolith outer edge) |
External energy transfers to DME and water using of the heat conduction manner of the axial and radial through the reactor wall and the catalyst coating layer, using the equation:
Wherein,
There are three major reactions in the process of DME steam reforming [
Arrhenius equation is used to solve the rate constants, and the expression is:
Due to the range of experimental temperature is 200˚C to 400˚C, so temperature variation range is small, and the pre-exponential factor A is corrected and the activation energy not, then Arrhenius equation:
where,
Then, the activation energy
The fitting parameter of Adsorption equilibrium constant
The main elementary reaction rate constant can be obtained by Equation (8) and (9) using ofrate constant
The legend of all graphics is the same with the legend of
Reaction Name | Chemical equation | The reaction rate |
---|---|---|
DME oxidation reaction | ||
DME hydrolysis | ||
CH3OH decomposition | ||
Water-gas shift |
Reaction type | Parameters | The value | Confidence intervals | Unit |
---|---|---|---|---|
DME oxidation reaction | 53.5 | ±6 | ||
104.1 | ±5 | |||
DME hydrolysis | 60.00 | ±14.03 | ||
173.53 | ±24.01 | |||
CH3OH decomposition | 135.42 | ±29.75 | ||
107.36 | ±44.5 | |||
Water-gas shift | 356.19 | ±170.4 | ||
180.84 | ±25.3 | |||
Adsorption reaction water | 3.88 | 1.15 | ||
−31.71 | 0.72 |
and H2 to temperature is the maximum, indicating that their speed of response here has a jump, which can be proven from
The two-dimensional model is substantially correct because of the analog data more in line with a variety of knowledge. For example, the ratio of water-DME and the ratio of oxygen-DME are important step of controlling the hydrogen yield. Finally, this article can provide important theoretical references to the kinetics of dimethyl ether steam reforming reaction.