Jonathan De Vydt catalysts of the next generation of cooperative heterogeneous Green aldol ...

130 Pages·2015·5.53 MB·English

Green aldol condensation: synthesis, testing and design
of the next generation of cooperative heterogeneous
catalysts
Jonathan De Vydt
Supervisors: Prof. dr. ir. Joris Thybaut, Prof. Pascal Van Der Voort
Counsellor: Ir. Jeroen Lauwaert
Master's dissertation submitted in order to obtain the academic degree of
Master of Science in Chemical Engineering
Department of Chemical Engineering and Technical Chemistry
Chairman: Prof. dr. ir. Guy Marin
Vakgroep Anorganische en Fysische Chemie
Chairman: Prof. dr. Isabel Van Driessche
Faculty of Engineering and Architecture
Academic year 2014-2015
..
Green aldol condensation: synthesis, testing and design
of the next generation of cooperative heterogeneous
catalysts
Jonathan De Vydt
Supervisors: Prof. dr. ir. Joris Thybaut, Prof. Pascal Van Der Voort
Counsellor: Ir. Jeroen Lauwaert
Master's dissertation submitted in order to obtain the academic degree of
Master of Science in Chemical Engineering
Department of Chemical Engineering and Technical Chemistry
Chairman: Prof. dr. ir. Guy Marin
Vakgroep Anorganische en Fysische Chemie
Chairman: Prof. dr. Isabel Van Driessche
Faculty of Engineering and Architecture
Academic year 2014-2015
Acknowledgement

Nu deze opleiding op zijn einde loopt, wil ik graag even de tijd nemen om enkele mensen te
bedanken die me geholpen hebben tijdens deze periode. Deze thesis was een ware uitdaging.
Voornamelijk de vele arbeidsintensieve momenten in het labo, werden in het tweede semester
steeds langer. Maar wat eens zo veraf bleek, is nu binnen handbereik. Het studentenleven kan
met een goed, toch wel trots, gevoel afgesloten worden.
In de eerste plaats bedank ik prof. dr. ir. Guy B. Marin voor de mogelijkheid die ik heb gekregen
om mijn masterproef op het Laboratory for Chemical Technology uit te voeren.
Mijn promotor prof. dr. ir. Joris W. Thybaut wil ik bedanken voor de raad en de opvolging tijdens
deze thesis. Het was verrijkend om tijdelijk deel uit te maken van de CaRE-groep. Via de CaRE
lunch meetings kwam ik in contact met de ruime wereld van Catalytic Reaction Engineering. Een
interessante ervaring!
Daarnaast wens ik ook prof. dr. Pascal Van Der Voort te danken voor de gekregen kans om me
verder te verdiepen in het onderzoeksdomein van periodieke mesoporeuze organosilica’s.
Mijn begeleider, Jeroen Lauwaert, verdient een heel grote “dankuwel”. Hij was steeds
beschikbaar indien ik vragen had. Ook als er problemen waren in het labo, stond hij steeds
paraat. Onder zijn begeleiding heb ik veel bijgeleerd. Tevens wil ik hem bedanken voor het
geduld bij het nalezen van dit werk.
Er zijn nog zovelen die direct of indirect betrokken zijn bij de ontwikkeling van deze thesis.
Zo ook een woord van dank aan Els De Canck, Judith Ouwehand en Dolores Esquivel voor hun
hulp tijdens de functionalisatie en karakterisatie van de gesynthetiseerde materialen. Tom
Planckaert wil ik bedanken voor de vele elementaire analyses en XRD metingen. Ook de
technische staf van het LCT, in het bijzonder Erwin Turtelboom, bedank ik voor het in orde
brengen van de waterkoeling in het labo.
Ik wil ook mijn klasgenoten, en dan speciaal de mensen uit het thesislokaal, bedanken voor de
vele verhalen en discussies. Het was fijn deze momenten met hen te kunnen delen.
Ten slotte gaat een oprecht woord van dank uit naar mijn ouders voor de onophoudelijke steun
die ze geven. Dat ik deze masterproef en de daarbijhorende opleiding tot een goed einde heb
kunnen brengen, is zeker ook aan hen te danken!
FACULTY OF ENGINEERING AND ARCHITECTURE

Department of Chemical Engineering and Technical Chemistry
Laboratory for Chemical Technology
Director: Prof. Dr. Ir. Guy B. Marin

Laboratory for Chemical Technology

Declaration concerning the accessibility of the master thesis

Undersigned,

Jonathan De Vydt

Graduated from Ghent University, academic year 2014-2015 and is author of the
master thesis with title:

Green aldol condensation: synthesis, testing and design of the next generation of
cooperative heterogeneous catalysts

The author gives permission to make this master dissertation available for consultation
and to copy parts of this master dissertation for personal use.
In the case of any other use, the copyright terms have to be respected, in particular with
regard to the obligation to state expressly the source when quoting results from this master
dissertation.

(Date)
26/05/15

(Signature)

Laboratory for Chemical Technology • Technologiepark 914, B-9052 Gent • www.lct.ugent.be
Secretariat : T [phone] • F [phone] • [email protected]
Summary

Green aldol condensation: synthesis, testing and design of the next generation of cooperative
heterogeneous catalysts

Author: Jonathan De Vydt

Supervisors: Prof. dr. ir. Joris Thybaut, Prof. Pascal Van Der Voort
Coach: Ir. Jeroen Lauwaert

Faculty of Engineering and Architecture
Academic year 2014-2015

Abstract: In this work, the synthesis of a new type of Periodic Mesoporous Organosilica (PMO)
materials is described. These structured organosilicas have been synthesized by the acid-
catalyzed hydrolysis and condensation of bridged precursors. These materials are functionalized
with cysteine using a thiol-ene click reaction. Afterwards, the cooperative catalysts are tested in
the aldol condensation of 4-nitrobenzaldehyde with acetone. It was found that the materials
with ethane bridges are more active than the ones with benzene groups in the support. In the
second section of this work, the effect of silanol groups on the hydrophobicity of the material is
tuned by adding tetraethyl orthosilicate (TEOS) to the precursor mixture. Materials with both
hydrophobic and hydrophilic blocks are obtained. The effect of the support’s hydrophobicity is
assessed by determining the catalyst activity in the presence of water. The outcome of these
experiments is that the TE-materials have promising results. It is an interesting result to see
that, even in the presence of water, the most hydrophobic material (TE1-C) is able to preserve
its activity. This indicates that the hydrophobic pore walls impede the water molecules to enter
the pores.

Keywords: aldol condensation, cysteine, furfural, thiol-ene click reaction, effect of hydrophobicity

Green aldol condensation: synthesis, testing and
design of the next generation of cooperative
heterogeneous catalysts
Jonathan De Vydt
Coach: Ir. Jeroen Lauwaert
Supervisors: Prof. dr. Pascal Van Der Voort, Prof. dr. ir. Joris W. Thybaut
Abstract: In this work, the synthesis of a new type of Periodic Even with the shale gas boom in recent years, one cannot
Mesoporous Organosilica (PMO) materials is described. These deny that the diminishing reserves of these non-renewable
structured organosilicas have been synthesized by the acid- resources cause a lot of concerns. In this regard, biomass can
catalyzed hydrolysis and condensation of bridged precursors. serve as a sustainable source for our industrialized society.
These materials are functionalized with cysteine using a thiol-ene
Furfural is an important intermediate during the conversion of
click reaction. Afterwards, the cooperative catalysts are tested in
biomass and can be used as reactant in the aldol condensation
the aldol condensation of 4-nitrobenzaldehyde with acetone. It
with acetone, see Figure 1, to produce C and C alkanes
was found that the materials with ethane bridges are more active 8 13
which can be employed as biofuel [1, 2].
than the ones with benzene groups in the support. In the second
section of this work, the effect of silanol groups on the In industry, the product stream of furfural contains water.
hydrophobicity of the material is tuned by adding tetraethyl Therefore for an industrial application of the aldol
orthosilicate (TEOS) to the precursor mixture. Materials with condensation with furfural, it would be beneficial for the
both hydrophobic and hydrophilic blocks are obtained. The feasibility if the reaction can proceed at a significant rate even
effect of the support’s hydrophobicity is assessed by determining in the presence of water.
the catalyst activity in the presence of water. The outcome of
In this regard, Periodic Mesoporous Organosilicas can be a
these experiments is that the TE-materials have promising
good solution. Due to their large pore sizes and surface areas,
results. It is an interesting result to see that, even in the presence
these mesoporous silica materials provide sufficient space to
of water, the most hydrophobic material (TE1-C) is able to
incorporate multiple functional groups while the stability of
preserve its activity. This indicates that the hydrophobic pore
walls impede the water molecules to enter the pores. the matrix is ideal for many types of reaction. Thus, if one is
able to synthesize a material with hydrophobic pores, the
water could be excluded from entering, leading to a situation
Keywords: aldol condensation, cysteine, furfural, thiol-ene click
reaction, effect of hydrophobicity in which only the reactants are able to physisorb in the pores.

II. PROCEDURES
I. INTRODUCTION
A. Catalyst synthesis
The aldol condensation is an important reaction to create
new C-C bonds and yield larger and more complex molecules. An overview of the synthesis and functionalization of the
The aldol condensation might have a bright future in the Periodic Mesoporous Organosilica (PMO) materials is shown
discipline of green, renewable and sustainable energy, e.g. in in Figure 2.
the valorization of biocomponents such as glycerol and The co-condensation of 1,2-bis(triethoxysilyl)ethane
furfural. (BTEE) and 1,4-bis(triethoxysilyl)benzene (BTEB) with
vinyltriethoxysilane (VTES) is performed in the presence of a
structure directing agent, Brij 76. The synthesis mixture is
stirred at 50°C during 24 hours and subsequently aged at 90°C
for 24 hours. After filtration of the precipitate, the material is
refluxed three times with acidified ethanol at 80°C during 24
hours to remove the surfactant as much as possible.
B. Functionalization
After the synthesis of these PMO materials, the amino acid
is introduced into the pores via a post-functionalization. In a
UV reactor, cysteine is grafted onto the vinyl group of the
VTES precursor via a thiol-ene click reaction.
First 0.50 g photo-initiator (Irgacure 2959) is dissolved in
10 mL demineralized water and the long vertical Schlenk
flask is placed into a supersonic bath. Meanwhile 0.53 g
cysteine is added to a separate glass bottle with 10 mL
Figure 1: Aqueous-phase conversion of sugars and derivatives into
liquid hydrocarbon fuels [1] demineralized water. The mixture is heated using a heat gun
until a clear solution is obtained. Next, the cysteine and 0.50 g syringe needle and to transfer the sample to a vial. Afterwards
of the organosilica are brought together in the Schlenk flask. the catalyst was separated from the sample by means of
The stopcock is used to place the mixture under an inert centrifugation. Finally, the samples were analyzed using a
atmosphere with helium. After that, the mixture is placed in reversed-phase high-performance liquid chromatograph (RP-
the UV reactor and stirred during 24 hours for the thiol-ene HPLC). The components were identified using a UV-detector
click reaction to take place. with a variable wavelength. Quantification of the different
components in the reaction mixture was performed by relating
the peak surface areas to the amount of internal standard,
methyl 4-nitrobenzoate [3].
E. Vapour-Liquid equilibrium
Because the molar ratio of the reactants has an influence on
the reaction rate, it is important to know the exact composition
of the liquid phase after the vapour-liquid equilibrium has
been established. Thus, it is necessary to check how much of
each component has to be added to the Parr reactor, in order to
obtain the desired concentrations in the liquid phase. An
existing code based on the Non-Random Two-Liquid (NRTL)
and Hayden-O’Connell (HOC) methods has been modified
which allows for an initial estimation of the vapour-liquid
equilibrium. This code accounts for the thermodynamic non-

ideality of both the liquid as well as the gas phase via so-
Figure 2: Synthesis and functionalization of Periodic Mesoporous called activity coefficients and fugacity coefficients.
Organosilicas
III. EXPERIMENTAL RESULTS
C. Catalyst characterization
Nitrogen adsorption-desorption measurements are carried A. Valorization of furfural via the aldol condensation
out at 77K using a Tristar 3000 gas analyser of Micromeritics. In order to obtain higher conversions for the aldol
The specific surface area and pore volume are determined condensation of furfural with acetone, higher reaction
using the Brunauer–Emmett–Teller (BET) method. The temperatures were investigated. When higher temperatures
average pore size of the organosilica is obtained using the (>60°C) are applied, one has to consider the vapour-liquid
Broekhoff and de Boer (BdB-FHH) method, with the equilibria of the reactants. In particular for acetone, with a
modification of Frenkel, Halsey and Hill. boiling point of 56°C, one has to take into account that a
The amine loading is determined using elemental (CHNS) fraction of this reactant will be in the vapour phase.
analysis. These experiments are performed on a Thermo Flash The results from a simulation with the NRTL-HOC code
2000 elemental analyser using V2O5 as catalyst. indicate that this system deviates a few percentages from an
The structure of the mesoporous materials is determined ideal mixture. As was expected, only a fraction of the acetone
with the use of X-ray diffraction. The X-ray diffraction evaporates at higher temperatures. For toluene and furfural it
patterns were recorded on a ARL X'TRA Diffractometer of is correct to assume that everything remains in the liquid
Thermo Scientific which is equipped with a Cu Kα tube and a phase. If a reaction temperature of 90°C is considered, about
Peltier cooled lithium drifted silicon solid stage detector. 1.55 % of the acetone will evaporate, which corresponds with
The presence of amine groups after grafting is demonstrated a pressure increase up to a total pressure of 3.7 bar.
by means of Diffuse Reflectance Infrared Fourier Transform For the aldol condensation of furfural with acetone at 90°C,
(DRIFT) spectroscopy. These measurements are performed on the decline of the turnover frequency as a function of the
a Nicolet 6700 of Thermo Scientific with a nitrogen cooled volume percentage of water in the reaction mixture indicates
MCT-A detector. The spectra are obtained using a Graseby that a small amount of 1 vol% or 2 vol% water is already
Specac diffuse reflective cell, operating in vacuo at 120°C. sufficient to lower the catalytic activity with 23.43 %,
respectively 57.17 %.
D. Catalytic experiments
1.0
The experiments were performed in a 25 mL two-neck
round-bottom flask equipped with a condenser and a septum. 0.8
The reaction mixture was prepared separately by mixing the
desired amounts of acetone (50 vol%), n-hexane (co-solvent, 0.6
o
50 vol%), 4-nitrobenzaldehyde (0.03 mmol/mL) and methyl ita
4-nitrobenzoate (internal standard, 0.022 mmol/mL). r FO 0.4
Afterwards 8 mL of the reaction mixture was injected into the T
flask which contains the catalyst (4 mol% with respect to the
0.2
4-nitrobenzaldehyde concentration) and the flask was
immediately placed in an oil bath at 45°C. The moment the
0.0
flask was placed in the oil bath was taken as the start of the 0 2 4 6 8 10 12
Water (vol %)
reaction. The reaction was monitored for 4 hours by taking
a sample of the reaction mixture (about 100 µL) every 30 Figure 3: TOF ratio as a function of the volume % of water in the
minutes. Typically 0.9 mL of acetone was used to wash the reaction mixture
B. Catalyst characterization amine functionalities are too close to each other and are not
Characterization of the organosilicas affirmed the successful fully promoted by neighbouring silanol groups. Leading to
synthesis and functionalization of the materials. With nitrogen lower TOF-values than would be expected from linear
physisorption a type IV isotherm was obtained, indicating that interpolation.
the material is mesoporous. After functionalization, a small
decrease in surface area and total pore volume - resulting from 2.0E-04
the loss in free volume - was observed. 1.8E-04
X-ray diffraction patterns confirm that for most materials a 1.6E-04
hexagonal ordered mesoporous structure is maintained before 1.4E-04
and after the functionalization. However, from the X-ray 1.2E-04
diffractograms, it was found that the washing procedure at )s 1.0E-04
/
1
120°C is too harsh for the "modified SBA-15" materials (T1). ( F 8.0E-05
O
Adapting the washing procedure to a milder temperature of T 6.0E-05
40°C and a shorter time (2h - 3h) results in a material which 4.0E-05
properties are better preserved. Although, the mesoscopic 2.0E-05
ordering is still lost and an amorphous solid was obtained. 0.0E+00
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0
Elemental analysis determined the amine loading to be in
TEOS (mol %)
the range of 0.05 – 0.15 mmol/g.
Figure 4: Turnover frequency as a function of the molar % of TEOS
The DRIFT spectra demonstrated the presence of a primary
in the catalysts. Blue: TE-materials; Red: TB-materials. Dashed lines
amine after functionalization with cysteine.
indicate the theoretical TOF values in case of linear interpolation.
C. Aldol condensation of 4-nitrobenzaldehyde with acetone
D. Effect of water in the reaction mixture
The functionalized materials were used as catalyst in the
The influence of the hydrophobicity of the catalyst support
aldol condensation of 4-nitrobenzaldehyde with acetone at
on the catalytic activity in the presence of water is
45°C. To investigate the influence of the hydrophobicity of
investigated. This is an important property because for a
the catalyst support on the catalytic activity, the reaction was
possible application in industry, e.g. in the valorization of
performed both in the absence and presence of water.
biocomponents such as glycerol and furfural, the reactants
Although both catalyst have similar amine loadings, E1-C
will most likely be in an aqueous solution. Thus the activity of
(0.0592 mmol/g) and B10-C (0.0692 mmol/g) have very
these bifunctional catalysts in the presence of water will have
different reaction rates. The turnover frequency of E1-C is
a major impact on the potential feasibility of these materials.
about one order of magnitude higher than B10-C.
The turnover frequencies of the TE-materials both for the
For a possible explanation it is necessary to take into
reference reaction and the reaction in presence of 1 vol%
consideration that the concentration of reactants in the pores
water are compared in Table 1. For the most hydrophobic
may be different from the concentration of the reaction
material, TE1-C, the catalytic activity remains at the same
mixture. The properties of the pores play an important role on
level. It is an interesting result to see that, even in the presence
the physisorption of the reactants into the pores. It is not
of water, TE1-C is able to preserve its activity. This indicates
unlikely that for the material B10-C the environment of the
that the hydrophobic pore walls impede the water molecules
pores is more in favour of 4-nitrobenzaldehyde to enter due to
to enter the pores. Thus the reaction continues as it would in
some interactions with the benzene groups in the support. This
the situation without water. Interestingly, while in the
can be justified with the "like likes like" principle.
reference reaction the turnover frequency of TE1-C was still
As a consequence of the relative higher concentration of
lower than the one of T1-C-S2, this catalyst now becomes
4-nitrobenzaldehyde in the pores, this reactant reacts with the
more active in the presence of water. Materials with more
primary amine and may lead to the formation of a stable
TEOS in the pore wall are more susceptible to the water and
Schiff base, which eliminates active sites. This inhibition of
therefore the effect of water is more pronounced.
the reaction kinetics was also observed by Kandel et al. [4]

The turnover frequencies of the TB-materials in the absence
An overview of the turnover frequencies for the catalysts
or presence of water are shown in Table 2. In comparison to
comprising of both hydrophobic and hydrophilic blocks (TE-
the TE-materials, the presence of water has a much larger
and TB-materials) is given in Figure 4.
effect on the catalytic activity. The TOF values for the aldol

condensation in the presence of 1 vol% water drop
The lower turnover frequencies obtained from the catalytic
significantly. All TB-materials exhibit a turnover frequency
experiments indicate that no linear relationship applies for the
around 9 x 10-6 s-1.
activity of the catalysts. Adding three different precursors to
An explanation why the ratio of the TB-materials is much
the precursor mixture complicates the synthesis because every
lower than the TE-materials has to do with the Snyder polarity
precursor has its own hydrolysis and condensation rates.
index. Water is one the most polar solvents, and has a Snyder
When the difference between these rates is too large, the
polarity index of 9, while benzene has a lower value of 3. The
tendency towards homocondensation reactions increases. This
polarity of an ethane is in the range of 0.1 to 0.3. Comparing
will be a problem during the co-condensation because the
the polarity index of ethane and benzene, it can be expected
homogeneous distribution of the organic functionalities in the
that the ethane groups in the silica support have a stronger
framework cannot be guaranteed.
repulsive effect on water. Thus, the TE-materials are capable
As a consequence, it is possible that the different precursors
to exclude water to a greater extent from the pores than the
are clustered in the support. And after functionalization, the
TB-materials.