Acetone hydrogenation in exothermic reactor of an isopropanol–acetone–hydrogen chemical heat pump: effect of intra-particle mass and heat transfer

Abstract

Intra-particle mass and heat transfer plays an important role in performance of the exothermic fixed-bed reactor for an isopropanol–acetone–hydrogen chemical heat pump. In this work, an exothermic fixed-bed reactor model, taking into account the actual packing structure, is established in the commercial software Fluent. A 120° segment of a tube with tube-to-particle diameter ratio (n) of 4, where realistic particles are packed and set to porous media, is used to simulate the 3D external flow, concentration and temperature fields in the exothermic packed-bed reactor. The influence of catalyst particle diameter (d _p) and micropore diameter (d ₀) on the intra-particle temperature, species distribution, reaction rate and selectivity is discussed. The appropriate d _p and d ₀ are obtained. Simulation results showed that intra-particle temperature gradient is not obvious. Large d _p and small d ₀ lead to remarkable gradient of reaction rate inside the catalyst particle and the decrease in the catalyst efficiency and reduce the acetone conversion and the selectivity in isopropanol. The optimal results reveal that the spherical catalyst with d _p of 1 mm and d _pore of 10 nm is appropriate for high-temperature acetone hydrogenation.

Appendix

C :

Mole concentration

D :

Integrated diffusion coefficient (m² s⁻¹)

d :

Diameter of catalyst particle (m)

∆H :

Reaction heat (kJ mol⁻¹)

I :

Identity matrix

J-:

Diffusive mass flux (kg m⁻² s⁻¹)

k :

Thermal conductivity (W m⁻¹ K⁻¹)

M :

Molecular weight (kg kmol⁻¹)

n :

Tube-to-particle diameter ratio

N :

Number of moles (mol)

p :

Pressure (Pa)

R :

Gas constant (J mol⁻¹ K⁻¹)

r :

Reaction rate in kinetic equations (mol m⁻³ s⁻¹)

R :

Mass reaction rate (kg m⁻³ s⁻¹)

S _i :

Selectivity of species i

S :

Gas–solid momentum exchange rate

T :

Temperature (K)

v :

Velocity (m s⁻¹)

V :

Molecule diffusion volume (m³ mol⁻¹)

X :

Conversion

Y :

Mass fraction

ε :

Porosity

η :

Rate exponent

μ :

Viscosity (Pa s)

ν :

Stoichiometric coefficient

ρ :

Density (kg m⁻³)

τ :

Tortuosity factor

τ− :

Stress tensor (Pa)

0:

Micropore

A:

Acetone

CO:

Carbon monoxide

e:

Effective diffusion

g:

Gas

H:

Hydrogen

I:

Isopropanol

i, j :

Chemical species

in:

Inlet condition

k:

Knudson diffusion

m:

Mixture

p:

Catalyst particle

‘:

Initial condition

“:

Final condition