DODH by Molybdenum Innovation Introduction DODH by Rhenium

Comments

Transcription

DODH by Molybdenum Innovation Introduction DODH by Rhenium
Development of the Molybdenum-Catalyzed
Deoxydehydration of Polyols
Lasse B. Nielsen, Ayele T. Gorfo, Daniel B. Larsen, Allan R. Petersen, Johannes R. Dethlefsen, and Peter Fristrup*
Technical University of Denmark, Department of Chemistry, Kemitorvet 207, DK-2800 Kgs. Lyngby, Denmark, Email. [email protected]
To elucidate the mechanism a series of
experiments with variations in substrate,
reductant and catalyst were carried out.
To the right are shown the kinetic profiles
for the standard experiment (green), less
reductant (blue) and less catalyst (red),
figure 5. This kinetic behaviour can be
explained by a catalytic cycle driven by
the reduction of Re(VII) to Re(V) by
oxidation of a secondary alcohol with
reversible deactivation of the catalyst
through complexation with the substrate
diol (figure 6).5
alkene concentration / m
The exhaustion of fossil resources requires that alternative pathways to fuels and
materials are developed. Utilization of biomass is one of the more prominent
solutions but the development of new, sustainable chemical reactions (i.e.
catalysis) is necessary (figure 1).
Kinetics & Mechanism
alkene concentration / M
Introduction
0.40
0.30
0.20
entry 1
entry 4
entry 6
model
0.10
0.00
0
10
OH
Figure 1 A paradigm shift is necessary to allow for replacement of crude oil with
biomass.
DODH by Rhenium
The rhenium-catalyzed deoxydehydration
(DODH) was discovered in 1996 and
converts a vicinal diol into an alkene
(figure 3).1,2
OH
C12H25
OH
OH
+
C5H11
Et
CH3ReO3
dodecane
using deoxygenation (red arrows),
dehydration (blue arrows), and
deoxydehydration (green arrows).
R''
R'
O
r
O
O
R
60
70
80
90 100
CH3
Re
CH3
deactivating
pre -equilibrium
50
O
tion
c
u
d
e
R''
Re
O
O
CH3
xt
e
The chemical components of biomass are typically richer in oxygen than the
desired products, thus requiring chemical reactions capable of reducing the
oxygen content.
This is fundamentally different from
classical synthesis routes from oil which
is based upon introduction of oxygen.
Although traditional chemical routes
involving dehydration, oxidation and
hydrogenation have shown some promise
more efficient solutions are needed. One
promising solution is the deoxydehydration (DODH) which allows the
removal of two hydroxyl groups in a
single chemical transformation. To the
right is shown the changes in H/C and O/ Figure 2 Diagram illustrating the H/C vs.
C ratios upon dehydration, deoxygenation O/C ratios for various biomass-derived
compounds. They are transformed
or deoxydehydration (figure 2).
O
40
R
ru s
O
densation
con
CH3
O Re O
30
time // min
min
time
Figure 5 Alkene concentration as a
function of time. Standard experiment
(green), less sec. alcohol (blue), less
catalyst (red).
H2O +
R'
20
O Re
O
O
ion
OH
R
OH
H2O
R
Figure 6 Proposed mechanism for Rhenium-catalyzed DODH.
DODH by Molybdenum
The price on rhenium is very high (>3000 $/kg) and it is therefore desirable to
find cheaper alternatives. We have conducted open-system experiments on Mocatalyzed DODH and found the reaction to be efficient (Mo price: 22 $/kg), but
unlike Re it undergoes oxidative deformylation of the diols (figure 7).6
OH
2 HO
O
Mo Cat.
OH + HO
OH
O
+
+ 2 H 2O
H
H
Figure 7 Molybdenum-catalyzed DODH. The diol also serves as reductant.
The reaction was characterized by DFT calculations and the transition states for
extrusion and reduction was found (figure 8).7 Using the insight gathered during
the DFT study it was possible to adapt the reaction to the use of iso-propanol as
reductant.8 The experimental conditions are relatively harsh (250 °C, 80 bar) and
current effort are directed towards lowering the temperature of the reaction.
O
C12H25
+
+
C5H11
Et
2 H2O
Figure 3 Rhenium-catalyzed DODH. Reductants can be PPh3, H2 and secondary alcohols.
In the first examples PPh3 was the reductant but the scope has been expanded
to “greener” reductants such as hydrogen and secondary alcohols.3,4 To elucidate
the mechanism and possible improve the methodology we carried out an in situ
study of the Rhenium-catalyzed DODH reaction at 180 °C using a ReactIR
instrument (figure 4).
Figure 8 Left: TS for alkene extrusion with Mo. Right: TS for diol oxidation with Mo.
Innovation
Bio-diesel is produced by a trans-esterification of a tri-glyceride feedstock with
methanol yielding 10% (by weight) glycerol as byproduct. Annual production of
bio-diesel has increased to about 25 billion liters thus resulting in 2.5 mio. tons of
glycerol. We have shown that our technology can be used to convert glycerol to
allyl alcohol,9 which may then be further converted to plastic monomers such as
acrylic acid, 1,4-butane diol and propylene (see below).
OH
O
acrylic acid
OH
OH Mo-catalyst
HO
glycerol
OH
allyl alcohol
OH
HO
1,4-butanediol
Figure 4 ReactIR spectrophotometer (left), probe with mirror conduit (center) and probe
submerged in reaction mixture (right).
References
(1)  Cook, G. K.; Andrews, M. A. J. Am. Chem. Soc. 1996, 118, 9448.
(2)  Dethlefsen, J. R.; Fristrup, P., ChemSusChem, 2015, 8, 767 (review).
(3)  Ziegler, J. E.; Zdilla, M. J.; Evans, A. J.; Abu-Omar, M. M. Inorg. Chem. 2009, 48, 9998.
(4)  Arceo, E.; Ellman, J. A.; Bergman, R. G. J. Am. Chem. Soc. 2010, 132, 11408−11409.
http://www.kemi.dtu.dk/PeterFristrup
propylene
(5) Dethlefsen, J. R.; Fristrup, P., ChemCatChem 2015, 7, 1184.
(6) Dethlefsen, J. R.; Lupp, D.; Oh, B.-C.; Fristrup, P. ChemSusChem, 2014, 7, 425.
(7) Lupp, D.; Christensen, N. J.; Dethlefsen, J. R.; Fristrup, P. Chem. Eur. J. 2015, 21, 1.
(8) Dethlefsen, J. R.; Lupp, D.; Teshome, A.; Nielsen, L. B.; Fristrup, P. ChemSusChem, 2014, 7, 425.
(9) Dethlefsen, J. R.; Fristrup, P. WO 2015/028028 A1
ResearcherID: A-7211-2008
http://orcid.org/0000-0001-7175-3796

Similar documents