10.1002/cctc.201601678
ChemCatChem
FULL PAPER
Catalyst recycle test for nonanone reduction to nonanol. To test the
recyclability of the catalysts (specifically. Pd/Al2O3, Pd/C, & Ni/SiO2.Al2O3)
the reduction of 5-nonanone was carried out under identical conditions as
described above for a reaction period of 1 hour. The catalyst was then
removed from the reaction mixture via centrifugation. The reaction mixture
was decanted and fresh nonanone (and hexadecane solvent) was added
in the same amounts. This was agitated to produce a suspension of the
used catalyst and fresh reaction mixture, which was transferred to a 50
cm3 stainless steel reactor and the reduction repeated under identical
conditions. This was repeated a further 3 times, for a total of 5 runs per
catalyst.
Dehydration of nonanol to nonene To a ~20 ml sample vial, 5-nonanol
(0.50 ml, 0.411g, 2.84 mmol), hexadecane (4.45 ml, 3.43g, 15.1 mmol),
benzene (internal standard, 0.05 ml, 0.044 g, 0.56 mmol) and solid acid
catalyst (300 mg) were added. This was sealed, heated to desired
temperature by placing into a pre-heated aluminum block and stirred at
500 rpm for the desired reaction period. After the reaction period, the
vessel was removed and allowed to cool to room temperature. The
reaction mixture was filtered through a glass-wool plug to remove the
catalyst and analyzed by NMR (using benzene as an internal standard)
and GC-MS.
Combining these catalysts, a multifunctional catalyst system
(Ni/SiO2.Al2O3, HZSM-5) was able to fully convert 5-nonanone to
nonane with 97% selectivity at 200 °C, 1.38 MPa H2 for an hour.
The conversion of 2,5-hexanedione was more challenging due to
the tendency of the intermediates to ring close and produce DM-
THF. While our initial hypothesis was to proceed via 2,5-
hexanediol, which could be readily produced in H2O, the
subsequent dehydration could only be performed neat which
would be a challenge in an integrated system.
By studying this reaction stepwise we discovered that the key
intermediate in this process was DM-THF and we found
conditions that were effective at ring-opening and
defunctionalizing what we initially believed to be
a highly
undesirable product. However, by implementing a two-step
catalytic system, using DM-THF as the intermediate we could
produce hexane from 2,5-hexanedione rapidly under milder
conditions than had been previously reported. We also improved
our own prior processes to eliminate the need for acetic acid and
to move to a fully heterogeneous system which performs the
reaction via a different mechanism. This new catalytic system
should provide greater improvements as we translate these
results to a continuous flow reactor. Upon optimization and
validation of this as a biomass-derived molecule conversion
technology, these catalyst systems will be assessed for their
capabilities of converting real biomass derived feedstocks from
thermochemical processes[22] and hydrolysate.[23]
Reduction of 2,5-hexanedione For
a typical reaction protocol, 2,5-
hexanedione (0.117 ml, 0.120 g, 1.05 mmol), 5 mol % reduction catalyst
(Pd/Al2O3, Pd/C, Ni/SiO2.Al2O3) and, if stated, 4 ml solvent (water, MeOH,
IPA) was added to a 50 cm3 stainless steel reactor. This was then sealed
and pressurized with hydrogen to 2.76 MPa, flushing the reactor three
times. The reactor was then heated to the desired reaction temperature
by placing in a pre-heated aluminum block and stirred at 500 rpm for the
desired reaction period. After the reaction period, the reactor was
submerged in a bath of room-temperature water to cool. After ~15 minutes
(i.e. once the reactor had reached room temperature), the pressure was
released. The reaction mixture was centrifuged and filtered through a
glass-wool plug to remove the catalyst and analyzed by GC-MS.
Experimental Section
HDO of 2,5-hexanedione / 2,5-hexanediol / DM-THF to hexane For a
General experimental All chemicals and reagent grade solvents were
obtained from Fisher Scientific or Sigma Aldrich and used without further
purification, unless otherwise stated. Amberlyst-15, Amberlyst-36, Nafion,
ZrO2, Al2O3 were obtained from commercial vendors, and HZSM-5
(SiO2/Al2O3 = 80) was obtained from Zeolyst. All solid acids were dried at
110 °C under atmosphere for 24 hours before use. Pd/Al2O3, Pd/C,
Ni/SiO2.Al2O3 and Ci/SiO2 were obtained from Sigma Aldrich and used
without further purification. 1H NMR spectra were obtained at room
temperature on a Bruker AV400 MHz spectrometer, with chemical shifts
(δ) referenced to the residual solvent signal (1H). GC–MS analysis was
carried out using an Agilent 7820A GC system equipped with a CP-Sil 5
column (100% dimethylpolysiloxane [30m x 0.25 mm x 0.25 µm]), coupled
with an Agilent 5975 MS detector.
Reduction of nonanone to nonanol To a 50 cm3 stainless steel reactor, 5-
nonanone (0.50 ml, 0.413 g, 2.90 mmol), hexadecane (4.50 ml, 3.48 g,
15.4 mmol) and 4.6 mol% metal loading with respect to 5-nonanone (Pd/C
-140 mg of 10 wt% Pd/C, 14 mg Pd, 0.132 mmol Pd; Pd/Al2O3 - 140 mg of
10 wt% Pd/Al2O3, 14 mg Pd, 0.132 mmol Pd; Ni/SiO2.Al2O3 - 12 mg of 65
wt% Ni/SiO2.Al2O3, 7.7 mg Ni, 0.132 mmol Ni; CuO/Al2O3 - 87 mg of 13
wt% CuO/Al2O3, 8.4 mg Cu, 0.132 mmol Cu) was added. This was then
sealed and pressurized with H2 to 1.38 MPa, flushing the reactor three
times. The reactor was then heated to the desired reaction temperature by
placing in a pre-heated aluminum block and stirred at 500 rpm for the
desired reaction period. After the reaction period, the reactor was
submerged in a bath of room-temperature water to cool. After ~15 minutes
(i.e. once the reactor had reached room temperature), the pressure was
released. The reaction mixture was filtered through a glass-wool plug to
remove the catalyst and analyzed by NMR and GC-MS for conversion and
product elucidation. Further quantification information is produced in the
supplementary information.
typical reaction protocol,
1 mL of reactant (2,5 hexanedione, 2,5
hexanediol or DM-THF) was added with 5 mol% reduction catalyst
(Pd/Al2O3, Pd/C, Ni/SiO2.Al2O3) and 15 wt% HZSM-5 (unless otherwise
stated) was added to a 50 cm3 stainless steel reactor. This was then sealed
and pressurized with H2 to the desired pressure, flushing the reactor three
times. The reactor was then heated to the desired reaction temperature by
placing in a pre-heated aluminum block and stirred at 500 rpm for the
desired reaction period. After the reaction period, the reactor was
submerged in a bath of room-temperature water to cool. Once the reactor
had reached room temperature, the pressure was released. The reaction
mixture was centrifuged and filtered through a glass-wool plug to remove
the catalyst and analyzed by GC-MS. For GC-MS sample preparation, a
known amount of reaction mixture was diluted to 10ml using a suitable
solvent (pentane and/or MeOH). 10 ul of this mixture was then added to a
GC vial, along with 1.5 mL of a suitable solvent (pentane and/or MeOH).
For reactions carried out in water, a second analyses was carried out by
extracting potentially insoluble organic products into pentane (1 mL). A
known amount of the organic layer was diluted to 10ml, 10ul of this mixture
was added to a GC vial along with 1.5 mL of pentane and analyzed by GC-
MS.
Acknowledgements
We thank the LANL Laboratory Directed Research and
Development (LDRD) program (LDRD20160095ER) and the
Office of Energy Efficiency
Bioenergy Technology Office (BETO) for financial support.
Additionally we thank the LANL LDRD program for a Director's
& Renewable Energy (EERE)
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