(414d) Tandem Reaction for CO2 Hydrogenation to Methanol At Low Temperature
AIChE Annual Meeting
2013
2013 AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Catalysis for CO2 Conversion
Wednesday, November 6, 2013 - 9:30am to 9:50am
Carbon dioxide has
attracted much attention as a promising abundant and sustainable feedstock for
the synthesis of fuels and commodity chemicals. The hydrogenation of CO2
has the potential to become a carbon-neutral process, if hydrogen is obtained
from renewable energy resources (e.g. H2O). Methanol is an
interesting first product, because it can be utilized as a fuel or precursor
for other chemicals. State-of-the-art catalysts for CO2
hydrogenation usually requires high operating temperatures (> 200 ºC),
limiting the single-pass yield to methanol, which is thermodynamically favored
at low temperatures [1].
An alternative route
to produce methanol from CO2 via tandem reactions has recently been
reported, with the promise of improving the methanol yield at milder
temperatures (100-150 ºC) [2,3]. Methanol is synthesized via three sub-steps in
tandem: i) Hydrogenation of CO2 to formic acid; ii) esterification of
formic acid to alkyl formate; iii) hydrogenolysis of alkyl formate to methanol. (Reaction scheme is shown in
Figure 1.) An all-homogeneous cascade catalyst, consisting of viable catalyst
for each single step, has recently been developed and demonstrated for this tandem,
one-pot reaction [2]. However, the overall turnover number (TON) appeared to be
limited by hydrogenolysis catalyst, due to its incompatability with step ii
catalyst. This tandem reaction was also achievable using a single heterogenous
catalyst, with hydrogenolysis being the rate-determining step [3]. Therefore,
identifying more viable catalyst for the final step is crucial to enhance the overall
TON of this triple-tandem reaction.
This
talk will demonstrate ethyl formate hydrogenolysis over a series of
copper-based catalysts in a slurry-phase batch reactor. Several process
parameters, including H2 partial pressure and catalyst pretreatment
protocol, were studied to identify favorable conditions for methanol formation.
Figure 2 shows the reactant consumption and products formation profiles over a barium
promoted-copper chromite catalyst. A total yield of 45.3% methanol was achieved
at an ethyl formate conversion of 87.4% (8 hr, 135 ºC, 30 bar H2). We
also evaluated this catalyst for CO2 hydrogenation under similar
conditions; with just the Cu-based heterogeneous catalyst, an overall yield of
35.8% was achieved at a conversion of 41.4% (20 hr, 135 ºC, 10 bar CO2,
30 bar H2). The rates are likely to be improved when the appropriate
homogenous catalysts are combined with this heterogneneous catalyst.
Figure 1: Tandem reaction scheme for CO2
hydrogenation to methanol
Figure 2: Reactant consumption and products
formation profiles of ethyl formate hydrogenolysis over barium promoted-copper
chromite. 135 ºC, 30 bar, 200 rpm, 200 mg catalyst, 37.5 ml p-Dioxane, 0.55
mmole formate, 4.66 mmole H2 (based on solubility in p-Dioxane).
References
1. S. Natesakhawat, J. Lekse, J.
Baltrus, P. Ohodnicki, Jr. B. Howard, X. Deng, C. Matranga, ACS. Catal. 2
(2012) 1667.
2. C. Huff, M. Sanford, J. Am.
Chem. Soc. 133 (2011) 18122.
3. L. Fan, Y. Sakaiya, K. Fujimoto, Appl.
Catal. A: Gen. 180 (1999) L11.