(174z) Experimental Proof-of Concept and Model-Based Analysis of an Autonomous Sabatier Reactor for Thermocatalytic Conversion of CO2

Introduction

Converting
CO₂ into synthetic fuels is an attractive pathway to decrease CO₂
emissions and to reduce our dependence on fossil fuels. Thermocatalytic
hydrogenation provides advantages of fast reaction rates and high conversion
efficiencies, thus allowing for compact, high-throughput operation [1]. The
required H₂ can be generated via water electrolysis using renewable
electricity (hydro, wind, and solar). Thermal management is a major problem, as
the overall process is highly exothermic, Eqs (1-3):

To address this issue, the Sabatier reactor should be designed
with a highly-efficient heat removal [2, 3]. In this study, the actively cooled
Sabatier reactor was designed and simulated by numerical simulations first, to
assess its feasibility. Based on the simulations results, a lab-scale prototype
was assembled and tested successfully.

Model
Formulation

The
reactor configuration is shown in Fig. 1a. The dynamic, pseudo-heterogeneous, non-isothermal
model was solved using the MATLAB PDE solver:

Result and Discussion

A
typical spatio-temporal temperature profile is shown in Fig. 1b. Initially, the
hot spot is formed at the reactor entrance. As a result of the elevated
temperature at this location, the catalyst starts to deactivate due to coke
formation, leading in turn to lower reaction rates and, therefore, lower heat
release. Under certain condition this phenomenon can results in the hot spot
propagation downstream the reactor, which can eventually lead to reactor
extinction. The proof-of-concept unit is shown in Fig. 1c (10 cm active length,
7 g of catalyst), with the corresponding performance presented in Fig. 1d.
After preheating and initial ignition, the reactor was operated as a standalone
unit without any external heating, with heat being removed by compressed air fed
through the inner tube. 100% selectivity and 90% CO₂ conversion was
achieved.

Figure 1: Reactor
configuration (a), simulated spatio-temporal temperature profile (b),
proof-of-concept unit (c), and lab-scale reactor performance (d).

Conclusions

The
Sabatier reactor was first investigated using the comprehensive mathematical model
and numerical simulations. The lab-scale proof-of-concept unit was successfully
tested. Further investigation is underway.

Acknowledgments

The
authors acknowledge funding support from the Canada Foundation for Innovation
and Ontario Research Fund through the Research Infrastructure program and from
the Natural Science and Engineering Research Council of Canada through the
NSERC Discovery Grant program.

References

Simakov, D. S. A. (2017). Renewable
Synthetic Fuels and Chemicals from Carbon Dioxide. Springer.

Sun, D., Simakov, D. S. A. (2017). Thermal management
of a Sabatier reactor for CO₂ conversion into CH4: Simulation-based
analysis. J. CO₂. Util., 21, 368.

Sun, D., Khan, F. M., Simakov, D. S. A. (2017). Heat
removal and catalyst deactivation in a Sabatier reactor for chemical fixation
of CO₂: Simulation-based analysis. Chem. Eng. J., 329,
165.