Bond et al.
Article
Figure 2. Reaction pathways for ring-opening of γ-valerolactone to pentenoic acids and subsequent decarboxylation to butene, or
hydrogenation to pentanoic acid. ΔG° and ΔH° (in brackets) are included in kJ/mol for each reaction illustrated at standard conditions.
97%), 2-hexenoic acid (2HEA) (Sigma-Aldrich, >98%), penta-
noic acid (PAA) (Sigma-Aldrich >99%), propanoic acid (Sigma-
Aldrich >99.5%), acrylic acid (Sigma-Aldrich, 99%), 5,6-dihydro-
2H-pyran-2-one (DHP) (Sigma-Aldrich, tech. grade), R-angelica
lactone (AAL) (Sigma-Aldrich, 98%), and decane (Sigma-aldrich,
>99%) were used as purchased without further purification.
2.2. Computational Studies. Gaussian 0322 software was
used for simulation of the thermodynamic properties of the
molecules illustrated in Figure 2. Geometry optimizations and
subsequent frequency calculations were performed using B3LYP/
6-311þG(2d,p). Frequency calculations provided estimates for
standard changes of enthalpy, entropy, and Gibbs free energy,
which were used in estimating thermodynamic properties over the
range of temperatures relevant to experimental studies.
reactor was controlled using Brooks mass flow controllers (model
5850S). Upon reaching the desired reaction conditions, an aqu-
eous solution of GVL (10 wt %) was prepared and fed to the
packed-bed tubular reactor using a HPLC pump (Lab Alliance
SeriesI). The liquideffluent wascollected for quantitative analysis
in a separator (Jerguson Gage and Valve) at ambient temp-
erature and analyzed by GC (Shimadzu GC-2010 with FID
detector). Unknown product peaks were identified using GC-
MS (Shimadzu GCMS-QP2010S). CO and CO2 inthe gas effluent
were quantified using a Shimadzu GC-8A instrument equipped
with a TCD detector, and gas phase alkenes and alkanes were
quantified using a Varian GC (Star 3400 CX) apparatus equipped
with an FID detector. Butene carbon yield is reported as a percent
of theoretical yield of butene (C4) from GVL (C5). A continuous
hydrogen sweep was adjusted to keep the partial pressure of all
species inthe reactor constant equal to0.016, 0.164, and 0.820 atm
for GVL, H2, and water, respectively, for all temperatures and
weight-hourly space velocities (WHSV, defined as the mass of
GVL per mass of catalyst per hour). The hydrogen flow was
chosen such that the molar ratio of H2/GVL was equal to 10.
Total carbon balances typically closed to within 10%.
2.3. GVL Ring-Opening and Hydrogenation/Decarboxy-
lation Studies. Ring-opening of GVL and subsequent hydro-
genation or decarboxylation were studied in an up-flow reactor at
atmospheric pressure and temperatures from 498 to 623 K. The
catalyst (SiO2/Al2O3 or a physical mixture of SiO2/Al2O3 and Pd/
C) was loaded into a 1/4” tubular stainless steel reactor. When
necessary, the catalyst was mixed with crushed granules of fused
silica (Sigma-Aldrich) to fill the reactor volume. The catalyst bed
was held in place by two plugs of quartz wool, and the reactor was
mounted inside an aluminum block within a well insulated
furnace (Applied Test Systems). Reactor pressure was controlled
with a backpressureregulator (GOBP-60). Reactiontemperature
was monitored at the reactor wall by a Type K thermocouple
(Omega) mounted within the aluminum block and controlled by
using a Series 16 temperature controller (Love Controls). Prior to
introduction of feed, the desired reaction temperature and pres-
sure were achieved under flowing inert gas (He). Gas flow to the
2.4. Decarboxylation Studies of Various Lactone/Acid
Feedstocks. The production of alkenes from aqueous solutions
of alcohols, organic acids, and lactones through acid catalysis was
investigated in a tubular, fixed bed catalytic reactor identical to
that described above. Commercial SiO2/Al2O3 was used for each
of the experiments, and it was conditioned by calcination (4 h at
723 K inflowing air at 50 cm3(STP)/min) prior to the introduction
of a new feed. In the case of highly water-soluble species (GVL,
DVL, ECL, GCL, BEA, acrylic acid, propanoic acid), the feed was
introduced to the reactor as a 20 wt % solution using an HPLC
pump (Lab Alliance, Series I). For sparingly soluble reagents
(organic acids, AAL, DHP), the organic feed was delivered using
a syringe pump (Harvard Apparatus) and diluted to 20 wt % by
cofeeding deionized water using a HPLC pump (Lab Alliance,
Series I). Because hexenoic acid is a solid at room temperature, it
was dissolved in decane and introduced using a syringe pump
(Harvard Apparatus) and diluted as described above. The value of
WHSVfortheseexperimentsisdefinedasthemassoffeedmolecule
per mass of catalyst per hour. The liquid effluent was collected for
quantitative analysis in a separator (Jerguson Gage and Valve) at
ambient temperature and analyzed by GC (Shimadzu GC-2010
with FID detector). Unknown product peaks were identified using
GC-MS (Shimadzu GCMS-QP2010S). Gas phase products were
purged from the separator by flowing He at 50 cm3 (STP) min-1
using a mass flow controller (Brooks model 5850). CO and CO2 in
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Langmuir 2010, 26(21), 16291–16298
DOI: 10.1021/la101424a 16293