(617gy) Methanol Synthesis from CO2 in Slurry Bubble Column Reactors: A Modelling/ Experimental Approach

Methanol Synthesis from CO2 in Slurry Bubble Column Reactors: A
Modelling/ Experimental Approach

Methanol is a common feedstock in
the production of many industrial products and is the main reactant in the
production of dimethyl ether (DME), which itself can be transformed into
olefins and other commodity chemicals. DME is also being considered as a clean
fuel for LPG based engines.  Methanol is usually
produced in fixed bed catalytic reactors (ICI, Mitsubishi, Lurgi). The reaction is highly exothermic, leading to
hot spots in the reactor and catalyst sintering in the fixed beds. This work is
part of a wider study investigating the production of methanol from CO₂
in bubble column reactors (employing colloidal catalysts), where heat may be
better distributed throughout the reactor. To this effect two slurry bubble
column reactors have been designed and commissioned (1m and 2m tall with a
volume of 1L and 2L, respectively) to investigate CO₂ hydrogenation
in such systems. The focus of this work is to develop a calibrated model that
accounts for the residence time distribution of gas in the reactor and allows
mass transfer coefficients as well as Henry’s constants to be determined.

The reactor system (Figure 1) is
operated in semi-batch mode, whereby reactant gases (CO₂ and
hydrogen) and product vapour (methanol and water) interact with a colloidal
catalyst suspended in an inert solvent (squalane). A
gas circulation loop recycles permanent (reactant) gases whereas product is
condensed and collected. The slurry bubble column reactors can be operated up
to 300°C and 100bar.   

Figure 2 shows the exit tracer
signal of an Argon pulse from the 1L reactor system. It was found that the
residence time distribution is a strong function of the carrier flow rate. We
postulate that recirculation currents within the solvent become appreciable above
200mL/min. At 400mL/min the distribution is almost bimodal, suggesting that
appreciable amounts of gas are entrained in the liquid. Above 500mL/min
flooding occurs and solvent is carried out of the column. A model capturing
these observations and allowing for the subsequent determination of mass
transfer coefficients and Henry’s constants of reactive gases into a number
solvents is proposed.

Figure  SEQ Figure \* ARABIC 1: Reactor System

Figure  SEQ Figure \* ARABIC 2: Exit Tracer Signal of Argon Pulse In response to a
30s Input Pulse (max. concentration = 2.5%)