Environmental Engineering Reference
In-Depth Information
O
OH
O
O
OH
H
2
O
H
2
O
O
HMF
O
Aldol condensation
Aldol condensation
OH
O
OH
O
O
7 H
2
Hydrogenation
(metals)
OH
O
OH
7 H
2
5 H
2
O
O
O
Hydrogenolysis
C15 alkane
FIGURE 18.7
Conversion of HMF to diesel-range compounds.
ethers, which is done in a process developed by Avantium (Gruter and De Jong,
2009), and which leads to higher yields and selectivities (see Figure 18.6). The
production of both methyl methoxyfurfural (MMF) and ethyl methoxyfurfural
(EMF) has been reported. Typically, flow processes with low residence times are
used. Starting with glucose, dissolved in water/ethanol/10% H
2
SO
4
, at 195
C, a
selectivity of >90% for HMF plus EMF has been reported (Gruter and De Jong,
2007). Especially, the amounts of by-products in the form of humins seem to be lower,
thereby significantly lowering the E-factor for these processes.
The transformation of HMF into DMF or aldol condensates also can be questioned
from a green chemistry standpoint. Conversion of HMF into DMF is carried out over
heterogeneous catalysts in modest yields of 60
79%, and there is an additional need
for external hydrogen (Roman-Leshkov et al., 2007).
For the production of diesel-range fuels, HMF needs to undergo chain lengthening
(see Figure 18.7). An essential reaction to achieve this is the aldol condensation. A C
−
-
C bond reaction of HMF with a ketone, e.g., acetone, over a base catalyst (NaOH) at
25
C produces a C9 derivative (when acetone is used), which can react with a second
molecule of HMF to produce a C15 intermediate. Condensation products can then
undergo hydrogenation/dehydration over bifunctional catalysts with metal and acid
sites (e.g., Pd/
140
C and 25
52 bar) to produce linear C9 or
C15 alkanes that are hydrophobic and separate spontaneously from water, reducing
the cost of purification.
A combination of aldol condensation, dehydration, hydrogenation, and hydroge-
nolysis is thus required to produce the desired end molecules. Especially, aldol
condensations are reputed for modest selectivities and massive by-product formation.
γ
Al
2
O
3
at 100
−
−
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