1. ALDOL CONDENSATION OF FURFURAL AND CYCLOHEXANONE
ON Mg-Al MIXED OXIDE AND RECONSTRUCTED HYDROTALCITE
David Kadlec, Oleg Kikhtyanin
UniCRE (Unipetrol Centre for Research and Education, Inc.), Areál Chempark 2838, Litvínov – Záluží 1, , Czech Republic
INTRODUCTION
EXPERIMENTAL
Aldol condensation of bio-derived compounds is an important reaction for the synthesis of compounds which, after their hydrodeoxygenation, can be used as second generation biofuels. Homogeneous catalysts (for example NaOH) are typically used for aldol condensation. Nevertheless, the use of liquid basic solution results in high operation costs and serious environmental problems. That is why heterogeneous basic catalysts, for example hydrotalcites, are intensively used as catalysts because of their easier recovery and recycling.
Mg-Al hydrotalcites (HTCs) are natural
or synthetic layered materials which are derived
from brucite [Mg(OH)2] by the partial substitution
of Mg2+ with Al3+. The generated positive charge
of HTC framework is compensated by interlayer
anions (CO32-). Water is situated in the free space
between the molecules of anions. The layered
HTC structure collapses under calcination
at 450°C forming Mg-Al mixed oxide which
contains Lewis basic sites. The rehydration
of this material results in the recovery of layered
HTC structure (memory effect) and the change
of Lewis to Brønsted basic sites (the presence
of OH- in interlayer). Both Mg-Al mixed oxides
produced by HTC calcination and reconstructed
HTC exhibit good catalytic performance
in different organic reactions.
Fig. 1. Structure of hydrotalcite
Rivers, W. at al. Layered double hydroxides Coordination Chemistry Reviews (1999)
a – as prepared Mg-Al HTC
b – calcined Mg-Al mixed oxide
c – rehydrated (reconstructed) Mg-Al HTC
Fig. 4. Physico-chemical characteristics of Mg-Al samples used in the present study
1: HTC
2: MO
3: RH
Fig. 5. XRD patterns of catalyst samples
Catalyst characterization: Catalytic experiment:
XRD • Batch stirred reactor
XRF • T = 25 – 90°C, t = 0 – 180 min.
TGA • Different CH/F molar ratio
DRIFT • GC-MS analysis of reaction products
N2 physisorption
TPD-CO2
Two reactions take place simultaneously:
Fig. 2. Cyclohexanone self-condensation D1: 1‘-Hydroxy-1,1‘-bi(cyclohexyl)-2-one
D2: 1,1‘-Bi(cyclohexan)-1‘-en-2-one
D3: 1,1‘-Bi(cyclohexyliden)-2-one
Fig. 3. Aldol condensation of furfural (F) and cyclohexanone (CH)
FCH-OH: 2-[2-furyl(hydroxy)methyl]cyclohexanone
FCH: (2E)-2-(2-furylmethylene)cyclohexanone
F2CH: (2E,6E)-2,6-Bis(2-furylmethylene)cyclohexanone
Fig. 6. Influence of the presence of water on CH conversion Fig. 9. Influence of CH/F molar ratio on F conversion
in cyclohexanone self-condensation (T = 90°C, RH catalyst) in aldol condensation
Fig. 7. Influence of reaction temperature on CH conversion Fig. 10. Influence of CH/F molar ratio on selectivity
in cyclohexanone self-condensation of reaction products in aldol condensation at 25°C
Fig. 8. Influence of reaction temperature on selectivity Fig. 11. Influence of CH/F molar ratio on selectivity
of reaction products in cyclohexanone self-condensation of reaction products in aldol condensation at 90°C
Fig. 12. Influence of reaction temperature on F conversion Fig. 13. Influence of reaction temperature on F conversion
in aldol condensation on HTC catalyst. in aldol condensation on RH catalyst.
RESULTS
Sample
Phase
composition
BET area
[m2/g]
Mg/Al in
synthesis gel
[mol/mol]
Mg/Al by XRF
Conc. of basic sites
by CO2-TPD
[mmol/g]
HTCa
HTC 64 3
3.1
MOb
MgO
180
1.54
RHc
CONCLUSIONS
1. The catalytic performance of Mg-Al mixed oxide and rehydrated HTC in CH self-condensation and aldol condensation of F with CH has been investigated.
2. The effect of different reaction parameters (including reaction temperature, CH/F molar ratio, Brønsted vs. Lewis basicity, water presence) on the performance of the catalysts has been evaluated.
3. The inhibiting effect of water on the activity of rehydrated catalyst in CH self-condensation has been found (Fig. 6). The presence of water introduces larger impact on CH conversion than reaction temperature.
4. Both Mg-Al mixed oxide and reconstructed HTC demonstrate good catalytic performance in aldol condensation of F and CH (Fig. 12, 13). The activity of the later catalyst is much higher proving that Brønsted basic sites are essential for this reaction.
5. In contrast to CH self-condensation, the growth of reaction temperature in aldol condensation of F and CH uniquely increases F conversion.
6. The growth of CH/F molar ratio in reaction mixture results in the increase of both F conversion and selectivity to FCH (Fig. 9, 10, 11).
48th Symposium on Catalysis 7-9 November 2016, Prague, Czech Republic
The presentation is a result of the project reg. no. GBP106/12/G015 which is financially supported by GA CR. The project has been integrated into the National Programme for Sustainability I of the Ministry of Education, Youth and Sports of the Czech Republic through the project Development of the UniCRE Centre, project code LO1606.