Glycerol acetalization using water-tolerant catalyst

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Glycerol acetalization using water-tolerant catalyst

Thèse

Lin Chen

Doctorat en génie chimique

Philosophiae Doctor (Ph.D.)

Québec, Canada

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Glycerol acetalization using water-tolerant catalyst

Thèse

Lin Chen

Sous la direction de

:

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Résumé

L'application commerciale du glycérol a attiré l'attention de la communauté scientifique ces dernières années. Le glycérol formal, qui est produit par l'acétalisation du glycérol, est bénéfique en tant qu'additif pour carburant, en particulier pour les propriétés d’écoulement du biodiesel à basse température. Cependant, le processus réversible d'acétalisation est ralenti par la formation d'eau qui cause aussi une désactivation des catalyseurs acides.

Dans ce travail une étude comparative de differents catalyseurs résistants à l’eau et incluant, Cs2.5H0.5PW12O40, AS-MES (acide arène sulfonique éthane-silice), zéolithe

ZSM-5, H3PW12O40 en tant que modèle homogène et le catalyseur commercial

Amberlyst -15 a été effectuée. De plus, une étude cinétique préliminaire a été réalisée dans un réacteur discontinu agité, étudiant l'influence de différents paramètres, tels que la température, la composition de l'alimentation et la charge de catalyseur. Un des isomères du glycérol formal, le 1,3 dioxan-5ol pourrait être transformé en 1,3-propanediol. Par conséquent, la distribution des deux isomères d'acétal de glycérol a été étudiée systématiquement.

Pour améliorer d’avantage l'activité du Cs2.5H0.5PW12O40 non-supporté dans

l'acétalisation du glycérol, il a été déposé sur de la silice mésoporeuse par une méthode d'imprégnation pour augmenter la surface de contact des réactifs et des sites

acides. En outre, le Cs2.5H0.5PW12O40 supporté sur des silice mésoporeuse 2D

(SBA-15) et 3D (KIT-6 et SBA-16) ont été comparées puisque le réseau poreux topologiques de le silice mésoporeuse avec une structure 3D facilite l'accès aux sites acides, tandis que les canaux longs 2D de SBA-15 peuvent entraîner des limitations au transport aux points de connexion des particules élémentaires. L'impact du volume de mésopores a également été étudié.

Trouver une source d'aldéhyde appropriée est également crucial pour améliorer l'activité du catalyseur employé. Comme la solution de formaldéhyde contient de grandes quantités d'eau qui désactiveraient le catalyseur et favoriserait la réaction

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inverse, le paraformaldéhyde (une source solide de formaldéhyde sans eau) et l'acétone ont été étudiés afin de remplacer la solution de formaldéhyde.

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Abstract

The commercial application of glycerol has attracted attention of the scientific community in recent years. Glycerol formal, which is produced from glycerol acetalization, is beneficial as fuel additive especially for the low temperature properties of biodiesel. However, the acetalization process is hampered by formation of water which will reverse the reaction and deactivate the acid catalysts. Using water-resistant heterogeneous acid catalyst will be favorable for acetalization of glycerol.

In this research work, a comparative study has been carried out using the water-tolerant Cs2.5H0.5PW12O40, AS-MES (arene sulfonic acid ethane-silica), zeolite

ZSM-5, H3PW12O40 as a homogeneous model and the commercial catalyst

Amberlyst-15. In addition, a preliminary kinetic study was performed in a batch stirred tank reactor, studying the influence of different process parameters including temperature, feed composition and catalyst loading. One of glycerol formal isomers, 1,3 dioxan-5ol may be postsynthetically modified into important chemical products such as 1,3-propanediol. Therefore, the distribution of the two glycerol acetal isomers has also been studied systematically.

To further enhance the activity of bulk Cs2.5H0.5PW12O40 for glycerol acetalization, it

was supported on mesoporous silica by incipient impregnation method to increase the contact area of reactants and acid sites. Besides, supported Cs2.5H0.5PW12O40

supported on 2D (SBA-15) and 3D (KIT-6 and SBA-16) pore lattice mesoporous silicas have been compared since the topological curvatures of mesoporous silica with 3D structure would reasonably provide good transportation channels to get facilitated access to acid sites, while 2D long channels of SBA-15 may yield transport limitations at the points of connections of elemental particles. The impact of mesopore volume on activity has also been studied.

Finding an appropriate aldehyde source is also crucial to improve the activity of the catalyst used. Since formaldehyde solution contains large amount of water which

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would deactivate the catalyst and favor the reversibility of the reaction, paraformaldehyde (a solid water-free source of formaldehyde) and acetone were studied to replace formaldehyde solution.

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List of Tables

Table 2.1 Hydrolysis of Phenyloxirane with Some Solid Acid Catalysts ... 15 Table 2.2 Properties of methyl esters of ESG oil in comparison with other esters ... 29

Table 4.1 Properties of the various catalysts ... 52

Table 5.1 Physical properties of supported Cs2.5 mesoporous silicas with various Cs2.5 loadings and structure ... 85 Table 5.2 Quantitative data of NH3-TPD characterization for the acidity of supported Cs2.5

mesoporous silicas with various Cs2.5 loadings and structure ... 87 Table 5.3 Physical properties of supports and supported Cs2.5 mesoporous silicas with various aging temperature ... 95 Table 5.4 Physical properties of supported Cs2.5 mesoporous silicas after each cycle ... 98

Table 6.1 Optimization of reaction conditions for glycerol acetalization with acetone on non supported Cs2.5 ... 107 Table 6.2 Physical properties and acidities of Cs2.5 and supported Cs2.5/KIT-6 ... 108 Table 6.3 Comparison of activity of different catalysts for glycerol acetalization with acetone

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List of Figures

Figure 2.1 Amounts of water, methanol, benzene, and n-hexane adsorbed on H-ZSM-5 as a function of SiO2/AlO3 ratio: (●) water; (▲) methanol; (□) benzene; (○) n-hexane. 32_{... 7}

Figure 2.2 Initial heat of NH3 adsorption as a function of Si/Al ratio of various zeolites.17 ... 8

Figure 2.3 (a) Representative plots of the first-order kinetics over various catalysts. X: conversion of ethyl acetate (reaction temperature: 60℃). (b) The effect of the Si/Al atomic ratio on the activity of H-ZSM-5 (reaction temperature: 60 ℃) 35_{... 9}

Figure 2.4 Catalytic hydrolysis of cellulose over Thermal, H-ZSM-5, and Bimodal-HZ-5 at process parameters of microcrystalline cellulose = 0.25 g, water = 10 mL, catalyst = 0.25 g, reaction temperature = 443K, and reaction time = 4 h. 40_{... 11}

Figure 2.5 (a) 29_{Si MAS NMR and (b)}13_{C CP MAS NMR spectra of the mesoporous material}

with 2D-hexagonal symmetry. (c) Chemical reaction path for the formation of the organic-inorganic hybrid network structure with peak assignments of the NMR spectra.42_{... 12}

Figure 2.6 Structures of heteropoly and isopolyanions. (a) Keggin structure, α-XM12O40n-; (b)

Keggin structure, β-XM12O40n-; (c) lacunary Keggin anion; (d) Dawson structure,

XM12O40n-; (e) Anderson structure, XM6O24n- (shaded tetrahedron indicates the

heteroatom site); (f) XM9O34n-; (g) isopolyanions, W10O324-. 26 ... 17

Figure 2.7 Primary structure, Secondary structure, Tertiary Structure of heteropoly compounds 56_{... 18}

Figure 2.8 (a) Acid strength of liquid and solid super acids. (b) TPD profile of NH3 over

various solid acids, (a) Cs2.5H0.5PW12O40, (b) H3PW12O40, (c) SO42-/ZrO2, (d) SiO2-Al2O3, (e)

H-ZSM-5. Solid line: NH3 (m/e = 17); dotted line: N2 (m/e = 28). 57 ... 19

Figure 2.9 The hydrophobicity of solid acids evaluated from adsorption of benzene and water: △ H-ZSM-5 (Si/Al=628), □ Cs3, ◇H-ZSM-5(Si/Al=40), ○ Cs2.5, ▲ SiO2-Al2O3,

■Al2O3. Sw and SB are adsorption areas of pure H2O and benzene, respectively. 58 ... 20

Figure 2.10 Surface area and surface acidity of CsxH3-XPW12O40 as a function of Cs content,

x.61_{... 22}

Figure 2.11 Isotherms of N2 adsorption on CsxH3-xPW12O40 at 77K. The catalysts were

pretreated at 573K in vacuum. →:Adsorption branch,←：Desorption branch.61_{... 23}

Figure 2.12 Variation of the catalytic activity as a function of the Na or Cs content in MxH3-xW12O40. (a) M=Na; ○ : Dehydration of 2-propanol. □ : Conversion of methanol. (b) M=Cs; ■ conversion of dimethyl ether. ▲ : alkylation of 1,3,5- trimethylbenzene with cyclohexene. 62_{... 24}

Figure 2.13 Three types of catalysis by heteropoly compounds 63_{... 24}

Figure 2.14 Relationship between catalytic activity and bulk acidity. (a): (○)Dehydration of 2-propanol, (△) decomposition of formic acid, (□)conversion of methanol. (b): ( ■ )isomerization of cis-2-butene after treatment at 423K, ( ● )isomerization of cis-2-butene after treatment at 573K. 26_{... 25}

Figure 2.15 Catalytic activities of solid acids for reaction of liquids: Alkylation of 1,3,5-trimethylbenzene with cyclohexene (373K); alkylation of phenol with 1-dodecene; rearrangement of benzopinacol. 26_{... 26}

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Figure 2.16 Compilation of the main glycerol derivatisation routes 10_{... 27}

Figure 2.17 Transesterification of oil to produce biodiesel 66_{... 28}

Figure 2.18 Glycerol esterification with acetic acid ... 29

Figure 2.19 Dehydration of glycerol over solid acid catalysts ... 30

Figure 3.1 2D-hexagonal structure, 3D hexagonal structure, and bicontinuous cubic 3D structure of mesoporous silicas. ... 36

Figure 3.2 SEM images of: a) SBA-15; b) MM-SBA15-1; c) MM-SBA15-2 and d) MM-SBA15-4 hierarchical macroporous–mesoporous silicas. ... 38

Figure 3.3 SEM image of activated carbon (left) and carbon nanofibres (right). ... 39

Figure 3.4 TEM images of carbon nanotubes 98_{... 40}

Figure 3.5 Polythermic catalytic tests: ethanol conversion to diethyl ether on different catalysts. 98_{... 40}

Figure 3.6 FE-SEM images of a N-SC support and b its surface. 99_{... 41}

Figure 3.7 Effect of catalysts : guaiacol 0.005 mol; vinyl acetate 0.03 mol; catalyst loading 0.009 g/cm3_{; speed of agitation 1000 rpm; temperature 170 °C; solvent 1,4-dioxane.}102 ... 42

Figure 4.1 Small angle XRD pattern of sample AS-MES ... 52

Figure 4.2 High resolution SEM and TEM images of AS-MES sample ... 52

Figure 4.3 TPD profile of NH3 from HPW and Cs2.5H0.5PW12O40 ... 53

Figure 4.4 GC chromatogram of sample at 10 min ... 56

Figure 4.5 Evolution of glycerol conversion (a) and yield of glycerol formal (b) over various acid catalysts ... 58

Figure 4.6 Evolution of glycerol conversion, yield of glycerol formal and yield of hemiacetal over Cs2.5 catalyst. ... 58

Figure 4.7 Evolution of glycerol conversion, yield of glycerol formal and yield of hemiacetal over HPW catalyst. ... 59

Figure 4.8 Evolution of glycerol conversion, yield of glycerol formal and yield of hemiacetal over AS-MES catalyst. ... 59

Figure 4.9 Evolution of glycerol conversion, yield of glycerol formal and yield of hemiacetal over Amberlyst-15 catalysts. ... 60

Figure 4.10 Molar Ratio of glycerol formal isomers over various acid catalysts (solid points : 5R isomer, hollow points :6R isomer) ; same conditions as in Figure 4.5. ... 61

Figure 4.11 Stability studies on Cs2.5 and AS-MES ... 62

Figure 4.12 Evolution of glycerol conversion and yield of glycerol formal with time at varying catalyst weight ... 63

Figure 4.13 Molar Ratio of formed glycerol formal isomers as a function of the reaction time with 1.33g (a), 0.79g (b), 0.25g (c) of Cs2.5.Same reaction conditions as Figure 4.12. .. 64

Figure 4.14 Evolution of glycerol conversion and yield of glycerol formal with time at varying molar ratio. ... 65

Figure 4.15 Molar Ratio of formed glycerol formal isomers as a function of reaction time with glycerol/formaldehyde molar ratio: 1:1.2 (a), 1.5:1 (b), 2:1 (c), same reaction conditions as Figure 4.14. ... 66

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Figure 4.16 Evolution of glycerol conversion and yield of glycerol formal with time at varying molar ratio when formaldehyde was in excess. ... 67 Figure 4.17 Effect of mole ratio on acetalization of glycerol over Cs2.5. Same reaction condition as Figure 4.14 and Figure 4.16. ... 67 Figure 4.18 Evolution of glycerol conversion and glycerol formal yield with time at varying temperature. ... 68 Figure 4.19 Evolution of mol of isomers as a function of glycerol conversion at 90℃, Reaction conditions are same as in Figure 4.18. ... 69 Figure 4.20 Molar Ratio of formed glycerol formal isomers over the reaction time with t=70℃(a),80℃(b),90℃(c).Reaction conditions are same as Figure 4.18. ... 70 Figure 4.21 Molar ratio of formed glycerol formal isomers as a function of time with 1.33 g Cs2.5 ... 71

Figure 5.1 XRD pattern of bulk and supported Cs2.5/KIT-6 with different loadings a) bulk, b) 40% Cs2.5/KIT-6, c) 30% Cs2.5/KIT-6, d) 20% Cs2.5/KIT-6, e) 10% Cs2.5/KIT-6 ... 81 Figure 5.2 FTIR spectra of bulk and supported Cs2.5/KIT-6 with different loadings ... 82 Figure 5.3 29_{Si MAS NMR spectra of KIT-6 SiO}

2 support, HPW/KIT-6 and Cs2.5/KIT-6 ... 83

Figure 5.4 31_{P MAS NMR spectra of KIT-6 SiO}

2 support and Cs2.5/KIT-6 ... 83

Figure 5.5 Relationship between (a) mesopore surface area and mesopore volume of supported catalysts (b) Cs2.5 loading percentages and volume of Cs2.5 that occupies mesopores ... 84 Figure 5.6 (a) High resolution TEM image (b) small angle X-ray scattering of 40% loading Cs2.5/KIT-6 ... 85 Figure 5.7 (a) Nitrogen adsorption-desorption isotherms (b) Pore size distribution with various loadings of supported Cs2.5 with various loadings ... 86 Figure 5.8 TPD profiles of NH3 from supported Cs2.5/KIT-6 with various loadings ... 87

Figure 5.9 Evolution of glycerol conversion (a) and yield of glycerol formal (b) with time at varying loading (c) Molar fraction of glycerol formal isomers over supported catalysts with various loadings (solid points: fraction of 5R isomer, hollow points: fraction of 6R isomer); Reaction conditions: bath temperature 70℃, formaldehyde/glycerol molar ratio: 1.2:1, stirring speed: 400rmp, amount of Cs2.5 was kept constant at 0.25g/batch. ... 89 Figure 5.10 Evolution of glycerol conversion, yield of glycerol formal and yield of hemiacetal over Cs2.5/KIT-6 ... 90 Figure 5.11 Evolution of glycerol conversion (a) and yield of glycerol formal (b) with time at varying Cs2.5/KIT-6 catalysts weight. ... 91 Figure 5.12 Nitrogen adsorption desorption isotherms of (a) parent SBA-15, SBA-16, KIT-6 mesoporous silicas and (b) 30% supported Cs2.5 with corresponding 2D and 3D structures ... 93 Figure 5.13 Evolution of glycerol conversion and yield of glycerol formal with time using supported Cs2.5 on mesostructured silica catalysts ... 94 Figure 5.14 (a) NLDFT pore size distributions of KIT-6 with different aging temperatures (b) Nitrogen adsorption desorption isotherms of KIT-6 mesoporous silicas ... 95 Figure 5.15 Evolution of glycerol conversion (a) and yield of glycerol formal (b) with time

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using supports prepared at different aging temperatures. ... 96 Figure 5.16 Evolution of glycerol conversion with time using supports prepared at 30% Cs2.5/KIT-6 for three cycles. ... 97

Figure 6.1 Evolution of glycerol conversion (left) and yield of solketal (right) over supported Cs2.5 and bulk Cs2.5. Reaction conditions: bath temperature 25o_{C, acetone/glycerol}

molar ratio: 6:1, stirring speed: 400 rpm, the amount of Cs2.5 was kept constant at 0.25g/batch ... 107 Figure 6.2 Evolution of glycerol conversion (left) and yield of solketal (right) over bulk Cs2.5 separated at 3 min. Reaction conditions: bath temperature 25o_{C, acetone/glycerol}

molar ratio: 6:1, stirring speed: 400 rpm, the amount of Cs2.5 was kept constant at 0.25g/batch ... 109 Figure 6.3 Stability study on Cs2.5 for glycerol acetalization with acetone. Reaction conditions: bath temperature 25o_{C, acetone/glycerol molar ratio: 6:1, stirring speed:}

400 rpm, the amount of Cs2.5 was kept constant at 0.5g/batch ... 111 Figure 6.4 Stability study on Cs2.5/KIT-6 for glycerol acetalization with acetone. Reaction conditions: bath temperature 25o_{C, acetone/glycerol molar ratio: 6:1, stirring speed:}

400 rpm, the amount of Cs2.5 was kept constant at 0.5g/batch ... 112 Figure 6.5 Evolution of glycerol conversion (left) and yield of glycerol formal (right) over bulk Cs2.5. Reaction conditions: bath temperature 70o_{C, glycerol/formaldehyde molar ratio:}

1:1.2, stirring speed: 400 rpm, the amount of Cs2.5 was kept constant at 0.25g/batch ... 113 Figure 6.6 Evolution of glycerol conversion (left) and yield of glycerol formal (right) over bulk Cs2.5.Reaction conditions: bath temperature 70o_{C, glycerol/formaldehyde molar ratio:}

1:1.2, stirring speed: 400 rpm, the amount of Cs2.5 was kept constant at 0.25g/batch ... 114 Figure 6.7 Evolution of glycerol conversion (left) and yield of GF (right) for glycerol acetalization with paraformaldehyde over bulk Cs2.5.Reaction conditions: glycerol/formaldehyde molar ratio: 1:1.2, stirring speed: 400 rpm. ... 116 Figure 6.8 Evolution of glycerol conversion (left) and yield of GF (right) for glycerol acetalization with paraformaldehyde over supported Cs2.5/KIT-6 and bulk Cs2.5. Reaction conditions: bath temperature 70o_{C, glycerol/formaldehyde molar ratio: 1:1.2,}

stirring speed: 400 rpm, the amount of Cs2.5 was kept constant at 0.25g/batch ... 117 Figure 6.9 Stability study on bulk Cs2.5 (left) and Cs2.5/KIT-6 (right) for glycerol acetalization with paraformaldehyde. Reaction conditions: bath temperature 70o_{C, acetone/glycerol}

molar ratio: 6:1, stirring speed: 400 rpm, the amount of Cs2.5 was at 0.5g/batch (left) and 0.25g/batch (right) ... 117

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Acknowledgments

It has been a long journey for me to study and live in Québec City, a lovely and beautiful city that I would never forget. I put a lot of effort and time on my PhD project. It was a really challenging but fun experience for me to accomplish this research project. I would like to thanks everyone that helped me during my whole PhD journey.

First, I would like to express my respect and appreciation to my supervisor Prof. Kaliaguine. Thanks for providing me the opportunity to work on this interesting project. I have learned a lot from the discussions we had during the research. Compared to the knowledge I learned from this project, how to think and write like a scientist is more important and valuable to me for my future academic career. Thanks for his inspiration, encouragement and support during my whole PhD study.

I would also like to thank my previous supervisor Prof. Haolin Tang and my classmate Prof. Junsheng Li from Wuhan University of Technology. Thanks for their help in material characterization. And thank Prof. Dongyuan Zhao from Fudan University for the help in characterization and the review for my paper.

I am grateful for the kind help in my life from Madame Guoying Xu since I came to Quebec City. And thank our former technician Mr. Gilles Lemay for helping me with experimental procedures.

I really appreciated the generous help from all my colleagues in Prof. Kaliaguine’s research group: Dr. Bendaoud Nohair, Dr. Vinh Thang Hoang, Dr.Zhen Kun Sun, Dr. Foroughazam Afsahi, Dr. Arsia Afshar Taromi, Dr. Kiran Shinde, and Mr. Dominique Jean, Luc Charbonneau, Tien Binh Nguyen, Chi Cong Tran, Gloire Justesse Adolphe Mbou, Madame Chenfeng He and Thanh Binh Nguyen. It was my pleasure to work with these colleagues.

I am also grateful to China Scholarship Council (CSC) and the Natural Sciences and Engineering Research Council (NSERC) of Canada for project funding and resources

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Lastly, I would like also thank for my family, no matter where I am, I know they will always be there to support me.

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Foreword

This dissertation is composed of seven chapters. The first chapter is a brief introduction of glycerol utilization and objectives of the thesis. The second chapter provides a review of water tolerant catalysts to target an appropriate one for glycerol acetalization. The third chapter focuses on the support for one of the water tolerant catalyst, heteropoly compound, to further improve its activity. Chapters four, five, six report the results of this dissertation in the form of three scientific articles as follows: Chapter four:

Glycerol acetalization with formaldehyde using water-tolerant solid

acids

Lin Chen, Bendaoud Nohair, Serge Kaliaguine*

Department of Chemical Engineering, Laval University, Quebec (Quebec), Canada G1V0A6

Published in Journal of Applied Catalysis A-Gen, 2016, 509, 143-152.

Three types of water-tolerant heterogeneous catalysts namely acid functionalized periodic mesoporous organosilicas (PMOs), zeolite ZSM-5 and a heteropoly compound Cs2.5H0.5PW12O40 as well as commercial catalyst Amberlyst-15 were used

for glycerol acetalization. The activity of Cs2.5H0.5PW12O40 was found superior to that

of the other catalysts and the glycerol conversion was over 70% within 60 min of reaction time.

Chapter five:

Glycerol acetalization with formaldehyde using heteropolyacid salts

supported on mesostructured silica

Lin Chena_{, Bendaoud Nohair}a_{, Dongyuan Zhao}b_{，Serge Kaliaguine*}a

a _{Department of Chemical Engineering, Laval University, Quebec (Quebec), Canada}

G1V0A6

b _{Laboratory of Advanced Materials, Department of Chemistry & Shanghai Key}

Laboratory of Molecular Catalysis and Innovative Materials Fudan University, Shanghai 200433, China

Published in Journal of Applied Catalysis A-Gen, 2018, 549, 207-215

Mesoporous silica supported heteropolyacid salts were studied systematically for glycerol acetalization with formaldehyde. Attention was focused on finding an appropriate loading of Cs2.5H0.5PW12O40 (Cs2.5) on mesoporous silica supports and

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studying the influence of the architecture of mesoporous silica on activity. Supported Cs2.5H0.5PW12O40 on 2D (SBA-15) and 3D (KIT-6 and SBA-16) pore lattice

mesoporous silicas have been compared. The activity of all supported Cs2.5 catalysts

was found superior to that of bulk Cs2.5 owing to the high surface area of the

mesoporous supports. Chapter six,

Highly efficient glycerol acetalization over supported heteropolyacid

catalysts

Lin Chena_{, Bendaoud Nohair}a_{, Dongyuan Zhao}b_{，Serge Kaliaguine*}a

a _{Department of Chemical Engineering, Laval University, Quebec (Quebec), Canada}

G1V0A6

b _{Laboratory of Advanced Materials, Department of Chemistry & Shanghai Key}

Laboratory of Molecular Catalysis and Innovative Materials Fudan University, Shanghai 200433, China

Accepted by Chem.Cat.Chem. DOI: 10.1002/cctc.201701656R1

The acetalization of glycerol with acetone to yield solketal was catalyzed by Cs2.5H0.5PW12O40 (Cs2.5) supported on mesoporous silica, under mild conditions. It

gave high glycerol conversion and selectivity to targeted product even at room temperature (23o_{C). Another highly efficient glycerol acetalization reaction with}

paraformaldehyde using both bulk and supported Cs2.5 as catalysts was studied, which

gave much higher activity compared with formaldehyde solution.

Lastly, chapter seven completes this dissertation by providing overall conclusions along with some prospects for future work.

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Chapter 1 Introduction

1.1 General Introduction

Fossil energy is the main energy source which meets over 80% of the energy needs 1_.

The combustion of fossil fuels also emits green house gases such as CO2,

concentration of which was around 399 ppm in 2015, approaching serious climate change point. Thus finding new sustainable energy source to replace fossil energy and cut CO2 emissions is a focus for the scientific community. Biofuels stand out as

interesting alternative fuels as they are compatible with commercial engines, have enhanced biodegradability, are free of sulfur and emit less harmful particulates and gases compared to traditional fuels 2_{. One of the interests is focused on biodiesel. It is}

produced from natural triglycerides (for example: vegetable oil, waste cooking oil or animal fats) reacting with methanol 3_{. Glycerol is a by-product representing 10 wt%}

of total biodiesel production. In 2016, the global glycerol production was as high as 37 billion gallons owing to the increasing production of biodiesel 4_{. Thus glycerol has}

saturated the commercial market, resulting in low prices of glycerol and disposal of crude glycerol waste, which also has a negative impact on environment 5_{. One route to}

utilize over produced crude glycerol is producing pure glycerol, which is already widely used in the food industry, cosmetics and pharmaceticals. The other route is converting glycerol to value-added chemicals. The latter would not require high cost purification procedure and have more extensive applications in industry.

1.2 Glycerol utilization

Recently, there are extensive studies about glycerol valorization to value-added chemical products, such as acrolein obtained by glycerol dehydration 6, 7_{, which is an}

important intermediate to acrylic acid. Glycerol hydrogenolysis (glycerol reduction process) to obtain 1,2-propanediol and 1,3-propanediol, which are not only useful chemical compounds but also valuable starting materials for polymer productions; Esterification of glycerol including glycerol carboxylation to glycerol carbonate,

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glycerol nitration to glycerol nitrate and esterification with carboxylic acids 8_;

glycerol etherification such as the polymerization to obtain polyglycerols and polyglycerol esters, as stabilization agents in water-in-gasoline microemulsions 9_;

glycerol oxidation to obtain dihydroxyacetone 10_{, which is an active substance in}

sunless tanning lotions; Glycerol conversion to synthesis gas and glycerol acetalization to acetals or ketals. Among all these applications, glycerol acetalization with aldehydes or ketones which produce acetals or ketals attracts much attention recently. The acetalization reaction cannot only protect carbonyl groups in presence of other functional groups, the products of the reaction (acetals and ketals) could also be used as scent 11_{, flavor}12_{, basis for surfactants}13_{, disinfectant, solvent for medical and}

cosmetic uses and fuel additive 14_{. Acetals or ketals as fuel additive could be added up}

to 10 vol% of the fuel, which doesn’t only improve the cold properties but also help to meet the requirements of the European and American Standards for diesel and biodiesel fuels (European Standard EN 14214. Automotive fuels fatty acid methylesters (FAME) for diesel engines. Requirements and test methods, 2003; American Society for Testing and Materials (ASTM) Standard D6751. Standard specification for biodiesel fuel blend stock (B100) for middle distillate fuels), such as oxidation stability and flash point 3_{. Biodiesel with 5% glycerol formal as fuel additive has a melting point of -21} o_{C which is much lower than biodiesel without fuel additive (melting point : -7}o_C)3_.

Thus glycerol acetals or ketones as fuel additive are very useful for reducing the melting point, which is necessary for fuels having freezing problems during cold winters.

1.3 Objectives of the thesis

Glycerol acetalization reaction is normally acid catalyzed. Bronsted acid and Lewis acid catalysts are both proved to be very active and selective for this reaction. Bronsted acid catalysts including homogeneous sulfuric acid, p-toluenesulfonic acid, hydrochloric acid, heterogeneous catalysts such as zeolites , heteropoly acids, oxides and phosphates, organic-inorganic composites, Lewis acid catalysts such as metal and metal salts Au, Ag, Al, Zn, AuCl3 or tropylium salts have been studied for various

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acid catalyzed reactions 15-17_{. Conventional homogeneous strong acid catalysts present}

problems of separation and reusability, which is not environment friendly. Lewis acid catalysts metal salts also present issues during purification process. Thus Bronsted acidic heterogeneous catalysts play significant role for acetalization reaction. Hydrophobicity is considered to be a more determinant property for glycerol acetalization compared to acid strength and density of acid sites, since water is produced during the reaction which could deactivate the catalyst and favor the reverse reaction. Thus, hydrophobic acidic catalysts with moderate acid strength sometimes can give higher activity than hydrophilic catalysts with high acid strength for glycerol acetalization 17_{. Therefore the first objective of the work is to find an appropriate}

water tolerant catalyst for glycerol acetalization and optimized reaction conditions to reach ideal glycerol conversion and high yield of the targeted products, glycerol acetals. Activity of typical water-tolerant heterogeneous catalysts such as zeolites, heteropoly acid, organic-inorganic composites will be compared with commercial catalyst Amberlyst under optimized reaction conditions.

After targeting the suitable water tolerant catalyst, we will consider how to further improve its activity. Supported catalysts are widely applied for various catalytic reactions, since the active species could be well dispersed on a support in order to increase the surface contact with reactants. Mesoporous silica such as SBAs and MCMs family normally have large surface area (600-1000 m2_{/g), feasibility of tuning}

pore structure geometries and wall composition, suitable pore size (2-50 nm) for reactions with large molecule reactants and high thermal stability. These features are very attractive for support of active species. Thus, the second part of the work is to support the water tolerant catalyst on mesoporous silica materials and explore the effect of geometries (2D and 3D) and pore size.

The last objective is to explore the effect of reactant with different types of aldehydes or ketones. Glycerol acetalization has been studied with various kinds of aldehydes or ketones. The most studied aldehydes are formaldehyde 18_{, acetaldehyde} 19_,

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different kinds of hydrocarbon chains has shown that the glycerol conversion was affected by the the length of aldehyde alkyl chain, and decreased as the size of the aldehyde chain increased 14_{. Thus, it is interesting to explore the effect of different}

aldehydes and ketones for acetalization reaction and product distribution with our best water tolerant catalyst which will be done in the last part of the thesis.

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Chapter 2 Review of water-tolerant heterogeneous catalysts

Reactions such as esterification, glycerol acetalization, hydrolysis and hydration 22_{, in}

which water participates as reactant or product, need solid catalysts that are stable, insoluble and active in aqueous solutions. The acid sites of most solid acid catalysts could however be poisoned by water, leading to low activity. Most of catalysts used in industry for those water-producing or water involving reactions are conventional homogeneous acids such as H2SO4 or AlCl3, which may present problems of toxicity,

corrosion and difficult separation and recovery. Thus, development of promising new water-tolerant solid acid catalysts is desirable. In this chapter, the state of the art of water-tolerant solid catalysts including zeolites 16_{, organic-inorganic composites}23_,

oxides 24_{and heteropoly compounds}25_{will be reviewed respectively for various}

water-involving reactions.

2.1 Zeolites

Zeolites crystals have been used widely as heterogeneous catalysts for petrochemical industry owing to their strong Brønsted and Lewis acidity, high activity and selectivity, high thermal stability because of the crystalline inorganic frameworks 26_.

Zeolites are crystalline aluminosilicates composed of connected framework of AlO4

and SiO4 tetrahedra with micropores, the pore size of which is below 2 nm according

to the IUPAC 27_{. The smallest building unit of zeolites, the tetrahedron, could be}

combined by oxygen groups in various ways, leading to a large number of different zeolites structures such as Zeolite-A, ZSM-5, Zeolite-X, Zeolite-Y and Zeolite-β. Zeolites are classified into types of small (Zeolites A with pore diameter of around 4.1 Å), medium (ZSM-5 with straight channel of 5.3×5.6 Å) and large pore zeolites (Zeolites X and Y with ports entrance of around 7Å in diameter) 28_{. Microporosity}

and high surface area are significant features of zeolites. The microporous system would allow small molecule reactants diffusing inside the zeolite crystal, making the internal acid sites accessible. In addition, another important feature of zeolites,

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namely shape-selectivity due to this microporous system is useful for various industrial applications. Micropore channels could not only allow small molecule reactants diffusing inside zeolite crystals, but also restricting the formation of large size unwanted products, which leads to high selectivity and yield of valuable and desired chemicals. For example, zeolites could convert methanol to high-octane gasoline selectively and also remove wax molecules from petroleum fractions 29, 30_.

2.1.1 Hydrophobicity of zeolites

Highly siliceous zeolites such as HZSM-5 are hydrophobic due to the non-polar Si-O-Si groups 31, 32_{. The pores of siliceous zeolites are mainly consisting of silica,}

which are tetrahedra SiO4, so that the pores without defects which would be silanol

groups should also be hydrophobic. When Si4+_{is substituted by Al}3+_{, a negative}

charge would be present on AlO4, counter ions such as alkaline ions as well as protons

could compensate for the charge and give the zeolites affinity for water and polar solvents 33_{. Therefore, the ratio of Si/Al is an important parameter to control the}

adsorption properties, including the property of hydrophobicity.

The hydrophobic nature of ZSM-5 was studied as early as 1982 31_{. Its hydrophobicity}

increases linearly with the increase of Si/Al ratio. As shown in Figure 2.1, the adsorbed amounts of water and polar solvent methanol, gradually decrease with an increase in Si/Al ratio. However, the adsorbed amount of non-polar n-hexane and benzene changes slightly when the ratio is raised beyond 160. These facts suggest that the highly siliceous HZSM-5 are hydrophobic and thus have strong affinity to hydrocarbons.

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Figure 2.1 Amounts of water, methanol, benzene, and n-hexane adsorbed on H-ZSM-5 as a function of SiO2/AlO3 ratio: (●) water; (▲) methanol; (□) benzene; (○)

n-hexane. 31

2.1.2 Acidity of zeolites

Regarding the acid properties of zeolites, what types of acid sites are desired? Either Brønsted or Lewis? How is the acid strength and what is the number of acid sites? Those questions are important for acid-catalyzed reactions 16_{. Brønsted acid sites are}

generated by substitution of Si4+_{by Al}3+_{, which creates a negative charge in the lattice}

and would be compensated by a proton. The proton is attached to oxygen atom, forming a hydroxyl group which is responsible for the Brønsted acid sites of zeolites. The acid strength of zeolites could be measured by a titration method; Temperature-Programmed Desorption (TPD) of base molecules; Vibrational spectroscopy methods including infrared (IR) and Raman spectroscopy 16_{. The IR}

spectroscopy allows to detect directly the hydroxyl group by interacting with basic molecules such as pyridines and therefore to know which present Brønsted acidity and which present Lewis acidity. The Si/Al ratio also plays a significant role in determining the acid strength. Nishimiya and Tsutsumi studied the influence of Si/Al ratio on the acid strength. Results are shown in Figure 2.2, the initial heat of adsorption of ammonia increased with the increase of Si/Al ratio.

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Figure 2.2 Initial heat of NH3 adsorption as a function of Si/Al ratio of various

zeolites.16

2.1.3 Applications of zeolites for organic reactions in water

Hydrolysis of ethyl acetate is a typical reaction in aqueous solution. Namba et.al 34

compared the activity of high-silica zeolites (H-ZSM-5, dealuminated H-mordenite) for hydrolysis reaction. As shown in Figure 2.3, H-ZSM-5 (Si/Al=46.6) showed a higher activity than H-M (Si/Al=8.7 and 5.5) probably owing to the higher Si/Al ratio which lead to more hydrophobic surface, possessing stronger affinity to ethyl acetate. For ZSM-5 zeolites, the highest activity was achieved when the Si/Al ratio was at 47 (Figure 2.3 (b)). Higher Si/Al ratio could provide a more hydrophobic environment to adsorb organic reactants, leading to higher specific activity. However, when the ratio is too high, the activity will decrease owing to the decrease in number of acid sites.

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Figure 2.3 (a) Representative plots of the first-order kinetics over various catalysts. X: conversion of ethyl acetate (reaction temperature: 60℃). (b) The effect of the Si/Al atomic ratio on the activity of H-ZSM-5 (reaction temperature: 60 ℃) 34

Formalin (aqueous formaldehyde) could be converted to a raw material namely trioxane which is used for polyacetal copolymer 35_{. The activities of various zeolites}

for trioxane synthesis using formaldehyde solution (65%w/w) were compared. The activity of Mordenite zeolite with Si/Al ratio of 33, is higher than that with ratio of 10. For zeolite-Y with relatively low Si/Al ratio of 5, there is no apparent formation of trioxane, indicating that acid strength and hydrophobicity have a profound impact on the catalytic activity for this reaction.

Esterification is one of the most significant and widely studied reactions catalyzed by acids in industry 36_{. In the liquid phase esterification, water is produced as a product}

and will therefore deactivate common water soluble solid acid catalysts. For the reaction of esterification of acetic acid with n-butanol at 313K 36_{, the activity of cation}

exchange resin Amberlite 200C was higher than HZSM-5 with Si/Al ratio of 49. However, when a small amount of water was added to the reaction system, the reaction rate of Amberlite 200C was reduced to 35% of the original value, while it was only reduced to 82% of the original one using zeolite HZSM-5. Therefore, the cation exchange resin was more severely deactivated by water than hydrophobic HZSM-5.

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2.1.4 Recent development of zeolites for water involving reactions

Hydrophobic zeolites with high Si/Al ratio have been applied widely for water sensitive reactions as discussed above. However, the narrow pore sizes of some zeolites such as ZSM-5 limited the applications that deal with reactions with bulky organic reactants and products. Mesopore-micropore zeolites have attracted much attention recently since they have the advantages of both microporous and mesoporous materials 37_{, such as improved diffusion of reactants by mesoporous}

channels, high acidity provided by microporous zeolites, which can be used in biodiesel production.

There are many synthesis routes to obtain micro-mesoporous zeolites materials including post synthetic dealumination or desilication which produce mesopores or macropores as defects inside the zeolite crystal within the range of 5-100 nm; hard templating which uses hard template (mesoporous carbon, nonporous nanobeads and nanofibers) as mesopore structure directing agent; soft templating that creates mesopores via supramolecular self-assembly. The last synthesis method is nanomorphic zeolites obtained by surfactant equipped with zeolites structure directing agent 38_{. Among these synthesis routes, the methodology of alkaline treatment in}

NaOH solution has been recently applied for the synthesis of bimodal-HZ-5 (micro-mesoporous zeolite ZSM-5), which is used for hydrolysis of cellulose to glucose and other value-added products such as 5- 5-hydroxymethylfurfural (5-HMF)

39_{. The performance of the bimodal-HZ-5 was compared with H-ZSM-5 (Figure 2.4)}

under the same reaction conditions. The cellulose conversion followed Bimodal-HZ-5 (26%) > H-ZSM- 5 (11%) > Thermal (6%). The yields of 5-HMF and glucose over Bimodal-HZ-5 were also higher than those of ZSM-5.

Micro-mesoporous zeolites material is a remarkable milestone in zeolite science. Except for the traditional alkaline or acidic treatment, the most promising method is the use of surfactant equipped with zeolite structure directing agent. This approach allows controlling the morphology of both mesopores and micropores. These kinds of nanomorphic zeolites have great potential in heterogeneous catalysis.

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Figure 2.4 Catalytic hydrolysis of cellulose over Thermal, H-ZSM-5, and Bimodal-HZ-5 at process parameters of microcrystalline cellulose = 0.25 g, water = 10 mL, catalyst = 0.25 g, reaction temperature = 443K, and reaction time = 4 h. levulinic acid (LA), formic acid (FA) 39

2.2 Organic-Inorganic composites 2.2.1 PMO

PMO (periodic mesostructured organosilicas) have shown potential in fields ranging from catalysis, adsorption and sensing technology to nanoelectronics 40_{. Unlike}

microporous zeolites, mesostructured silicas materials have pore diameters in the range of 2-50 nm which allow large molecules to diffuse inside pores and show broad applications in catalysis. Organic groups such as methane, ethane, ethylene, benzene as a part of mesostructured framework yield materials with a wider range of properties including hydrophobicity which is useful in the applications as water-tolerant catalysts. As seen in Figure 2.5, organosilane monomer containing two trialkoxysilyl groups (BTME, 1,2-bis(trimethoxysilyl)ethane) could be used as the starting material to prepare ordered mesoporous materials in the present of a surfactant. The organic groups could be homogeneously distributed in the mesoporous frameworks, creating organic−inorganic hybrid mesoporous materials with a highly ordered structure. Acid functional groups can be directly incorporated in PMO’s structure so as to create acid sites in a hydrophobic organic environment.

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Figure 2.5 (a) 29_{Si MAS NMR and (b)}13_{C CP MAS NMR spectra of the mesoporous}

material with 2D-hexagonal symmetry. (c) Chemical reaction path for the formation of the organic-inorganic hybrid network structure with peak assignments of the NMR spectra.41

AS-MES (arene sulfonic acid ethane-silica), PS-MES (propyl sulfonic acid ethane-silica) and AS-SBA-15 (arene sulfonic acid SBA-15) were prepared in our group for acetalization of heptanal with 1-butanol 42_{. The activities of AS-MES and}

AS-SBA-15 at 75℃ were compared under the same reaction conditions. The results show that the AS-MES material is more efficient than AS-SBA-15, which indicates that the higher hydrophobicity plays a more crucial role than the acid strength for acetalization reaction. Another work in our group is about the synthesis of a novel PMO using ethylene bridges followed by alkylation of ethylene sites with benzene and sulfonation in H2SO443. This work provided a new preparation procedure to form

the arene sulfonic group functionalized PMO compared to AS-MES. Likewise, the activity of this ethylene bridged PMO and AS-MES are higher than those of catalysts supported on polar samples such as SBA-15 and Amberlyst-15. Overall, PMO is

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currently one of the most advanced hydrophobic organic-inorganic nano composite owing to the homogeneous distribution of organic groups within the inorganic framework and shows unprecedented properties as adsorbents, separation materials and heterogeneous catalysts.

2.2.2 Organic grafting on mesoporous silica

Surface modification techniques allowed organic or inorganic hybrid functional groups to be anchored on MCM (Mobil Composition of Mater), HMS (Hexagonal mesoporous silica) or SBA (Santa Barbara Amorphous type) structures mesoporous materials 44_{. MCM-41 silica containing grafted organic groups was active for glycerol}

esterification with lauric acid 45_{. For example, alkylthiols could be grafted over}

mesoporous silica using 3-mercaptopropyltrimethoxysilane (MPTMS) by co-condensation with a silica source and surfactant, followed by oxidization of the thiol groups into sulfonic acid in H2O2. Not only by co-condensation, organic

functional groups could also be grafted onto silica surface by post-synthesis silylation or coating over calcined mesoporous materials 46_{. The resulting MCM-SO}₃_H

materials possess both high acid strength and hydrophobic nature owing to the propyl group connected to the SH group. The activity of MCM-41-SO3H prepared by

co-condensation of MPTMS and TEOS in the presence of a neutral surfactant is higher than the commercial catalyst Amberlyst-15 for glycerol esterification with lauric acid 47_{. In addition, other alkyl and sulfonic acid functionalized MCM-41 silicas}

were also active for esterification reaction of glycerol with lauric acids. Methyl or propyl groups functionalized sulfonic MCM-41 were prepared by one-step hydrothermal treatment of gels 48_{. The acid conversion using catalysts with organic}

methyl group is higher than that which only uses MPTMS without adding any methyl or propyl groups 45_{. This means that the methylation of catalysts shows not only better}

acid conversion but also desirable selectivity to monoester in this esterification reaction.

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Nafion resin is a super acidic catalyst which possesses a terminal-CF2CF2SO3H group

with a strong Hammett acidity similar to 100% sulfuric acid. It is an ideal replacement for hazardous and corrosive homogeneous acid catalysts. However, the surface area of Nafion is very low (around 0.02 m2_{/g or less), which makes most of the acid sites}

poorly accessible, leading to poor reaction activity. A nanocomposite of Nafion resin entrapped within a porous silica network combined excellent solid acid catalyst properties and desirable characteristics of porous silica support 49_{. These new porous}

nanocomposites are prepared using an in situ sol-gel technique: first Nafion resin solutions are mixed with silicon sources and then the formed gel is dried to a clear glass-like material. In an esterification reaction of dicyclopentadiene with acrylic acid

50_{, Nafion, Amberlyst-15 and 13 wt% Nafion in silica nanocomposites were used as}

catalyst, the nanocomposites gave an esterified products at 91% level which is higher than Amberlyst-15. Increasing the acid loading and operating at high temperature (100℃) could narrow the activity gap of Nafion silica nanocomposites and Amberlyst-15, whereas the selectivity using Amberlyst-15 was still lower than Nafion silica nanocomposites (90% for the composites vs 70% for Amberlyst-15). In the case of activity comparison between Nafion resin and Nafion resin silica composites for nitration reaction of benzene with nitric acid, the average nitric acid conversion using Nafion resin and Nafion resin silica is 64% and 82% respectively and the selectivity of which is 98.8% and 99.6%. Therefore, in some cases, the activity of Nafion silica nonacomposites is better than those of Nafion resin and Amberlyst-15. A novel silica composite of perfluorocarbonsulfonic acid resin, namely Aciplex-SiO2, was also

found to be active for reactions involving water 51_{. Aciplex-SiO}₂_{nanocomposites}

possess an ion-exchange capacity of 0.46 meq.g-1 which is higher than 13 wt% Nafion-SiO2 (0.12 meq.g-1). In addition, the activity of Aciplex-SiO2 is superior to

Nafion-SiO2 for hydrolysis of ethyl acetate in excess water and esterification of

acrylic acid with 1-1butanol.

2.3 Oxides 2.3.1 Niobic acid

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Niobic acid (hydrated niobium oxide Nb2O5.nH2O) showed an acidic character (H0<

-5.6) when calcined at moderate temperature (373-573K) 52_{. While at the higher}

temperature of 873K, Nb2O5.nH2O will lose all the acidity and become neutral. In

addition, niobium oxide is a water-tolerant catalyst which is useful for reactions such as hydrolysis and esterification 53_{. As shown in Table 2.1, typical strong solid acids}

such as H-Nafion, H-ZSM-5 exhibited less activity than niobic acid for hydrolysis of phenyloxirane with solid acid catalysts. The selectivity to diol was also higher using niobic acid compared to others. Niobic acid could also be used for esterification reaction of acrylic acid with methanol 54_{, the conversion of acrylic acid reached a}

level of more than 90% and the selectivity to methyl acrylate was nearly 100%. Table 2.1Hydrolysis of Phenyloxirane with Some Solid Acid Catalysts

2.3.2 Zirconia-supported molybdenum oxide catalysts

MoO3-ZrO2, which was calcined at 873K-1073K, possesses a catalytic activity

comparable to that of H-ZSM-5 (Si/Al=40) 24_{. The acid amount and the surface area}

decreased at increasing calcination temperature. The surface hydrophobicity tested from the amount of water adsorbed was enhanced with an increase of calcination temperature. It was reported that MoO3-ZrO2 was very active for water sensitive

reactions such as hydrolysis of ethyl acetate and esterification of acetic acid with ethanol. Even though the density of acid sites and catalytic activity of MoO3-ZrO2

were comparable to other solid acidic catalysts, its acid strength is extremely low as tested by NH3 desorption (desorption peak 473K).

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2.4 Heteropolyacids

This part intends to introduce important properties of heteropoly compound catalysts, such as strong Brønsted acidity, hydrophobicity, and thermal stability, especially focusing on their mesoporous and microporous structure which directly impacts on the activity and selectivity of heteropoly compounds. Moreover, supported heteropoly compound catalysts attract much attention recently owing to their larger surface area and higher activity compared to bulk ones. Various carbons, silicas, polymer resins, zeolites, clays are used as supports for heteropoly compounds, which will be introduced respectively. As a general goal, this part intends to provide enough information to give an overview of heteropoly compound catalysts that can help future works develop more sustainable and eco-friendly chemicals from biomass derived glycerol utilization reactions.

Heteropolyanions are formed by more than two different acidic elements such as Mo, W, V, Nb and Ta with a Keggin structure (eg: PW12O403-) which is shown in Figure

2.6. A central PO4 tetrahedron is surrounded by 12 WO6octahedra. The centre atom

could be P, As, Si, Ge, B, etc. and the other addenda atoms could be W or Mo, V, Co. In addition, there are other types of polyanions structure such as Dawson (X2Ml8O6),

Waugh (XMgO32), Silverton (XM12O42) and Anderson (XM6O24) structures. Among

those structures, Keggin structure is the most widely studied and reviewed as it is easily obtained and thermally stable. Heteropoly anions have high molecular weight of 2000-4000. The salts with small metal cations such as Na+_{are soluble in water and}

polar solvents, and salts with large cations such as NH4+, Cs+, Ag+ are insoluble or

slightly soluble. The solubility of heteropoly compounds is related to the water content of compounds. Besides, heteropolyanions are stable in aqueous solution at low pH value, but tend to be hydrolyzed at high pH. Acids of heteropolyanions are usually strong acids. Heteropoly anions are multielectron oxidants, especially for those having Mo and V polyatoms, which are strong oxidants.

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Figure 2.6 Structures of heteropoly and isopolyanions. (a) Keggin structure, α-XM12O40n-; (b) Keggin structure, β-XM12O40n-; (c) lacunary Keggin anion; (d)

Dawson structure, XM12O40n-; (e) Anderson structure, XM6O24n- (shaded tetrahedron

indicates the heteroatom site); (f) XM9O34n-; (g) isopolyanions, W10O324-. 25

There are many advantages of using heteropoly compounds as acid or redox catalysts. Heteropoly compounds could be applied in various phases, such as homogeneous liquid phase, two-phase liquid, liquid-solid phase and gas-solid phase. Acidic and redox properties can be controlled by choosing appropriate constituent elements (types of polyanion, addenda atom, heteroatom. countercation, etc.). Heteropoly compounds are multi functional and possess properties of acid-redox, acid-base, multi-electron transfer, photosensitivity, etc. Applications of heteropoly compounds have a long history, as they have been used for industrial processes such as hydration of propene, isobutene, and 1-butene. The industrial process of direct oxidation of ethylene to acetic acid was started in Japan in 1997 using palladium plus HPA (100000 ton/year). It is evident that finding proper industrial applications using heteropoly compounds is desirable and promising.

2.4.1 Structure

It is therefore important to investigate the structure of heteropoly compounds aiming to understand heterogeneous catalytic properties of heteropoly compounds. The

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structure of heteropolyanions is called primary structure (Figure 2.7) which was discussed in the introduction part. Crystallization water, cations, polyanions and other molecules form a three-dimensional secondary structure. IR spectra present the primary structure which is very stable and the XRD patterns reflect the secondary structure which is variable depending on the countercations and environmental conditions. The tertiary structure means particle size, surface area, pore structure. Counter-cation has a great impact on the tertiary structure which is influential on catalytic performance, as described later.

Figure 2.7 Primary structure, Secondary structure, Tertiary Structure of heteropoly compounds 55

2.4.2. Properties

2.4.2.1 High acid strength properties Acid form

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illustrating acid properties. In the case of heteropoly compounds acids (abbreviated as HPAs) , HPAs such as H3PW12O40 and H3PMo12O40 are purely Brønsted strong

acids, the order of HPAs solid acid strength is H3PW12O40 > H3SiW12O40 >

H6P2W21O71(H2O3) > H6P2W18O62 25 . The acid strength of H3PW12O40 is measured by

Hammett indicators with pKa values ranging from -5.6 to -14.5. H3PW12O40 makes

the indicator p-nitrochlorobenzene (pKa= -13.6) show acidic color, which means the H0 of H3PW12O40 is smaller than -13.6. Compared to other solid acids, the strength of

H3PW12O40 is higher than Nafion and liquid H2SO4 (Figure 2.8(a)). From results of

NH3-TPD (Figure 2.8(b)) 56, the order of acid strength should be (SO42-/ZrO2) >

H3PW12O40 > H-ZSM-5 > SiO2-Al2O3.

Figure 2.8 (a) Acid strength of liquid and solid super acids. (b) TPD profile of NH3

over various solid acids, (a) Cs2.5H0.5PW12O40, (b) H3PW12O40, (c) SO42-/ZrO2, (d)

SiO2-Al2O3, (e) H-ZSM-5. Solid line: NH3 (m/e = 17); dotted line: N2 (m/e = 28). 56

Acid salts

The heteropoly acid salts are classified into two groups, one is group A salts with small metal cations (eg. Na, Mg), the other one is group B salts with large cations (Cs, NH4, Ag). Acidic properties of heteropolyacid salts depend on countercations,

constituent elements of polyanions and tertiary structure. There are several types of origins of acidity.

Cu1.5PW12O40 possesses Lewis acidity which was established by IR spectrum of

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pyridine due to Lewis acidity of metal ions. Acidity of CsxH3-XPW12O40 is from

protons present in the acidic salts. Proton was also observed if Ag3PW12O40 is treated

with hydrogen at 573K (Ag+_{+ 1/2 H}₂_Ag0_{+ H}+_{) using IR spectrum of pyridine. For}

group A salts, the number of protons exceeds the amount of protons expected in formula NaHPW12O40 due to the partial hydrolysis during neutralization. (PW12O40

PW11O397- + WO42- + 6H+).

2.4.2.2 Water tolerant catalysis

Water-tolerant solid acids are essential for eco-friendly catalytic reaction 54_{. However,}

some solid acids are severely deactivated by water and easily lose their catalytic activities in aqueous solution. The only commercial catalyst for liquid-phase hydration process was H-ZSM-5 zeolite.

Cs2.5H0.5PW12O40 is a well studied water tolerant catalysis 57, which is active for

hydrolysis of esters in water and used several times without apparent deactivation 58_.

The hydrophobicity of Cs2.5 has been estimated from the ratio of the adsorption

capacity of benzene to that of water (Figure 2.9).

Figure 2.9 The hydrophobicity of solid acids evaluated from adsorption of benzene and water: △H-ZSM-5 (Si/Al=628), □Cs3, ◇H-ZSM-5(Si/Al=40), ○Cs2.5,

▲SiO2-Al2O3, ■Al2O3. SH2O and SC6H6 are adsorption areas of pure H2O and benzene,

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The ratio of adsorbed amount of water to that of hydrocarbon is a good measurement for evaluating hydrophobicity of the surface. Choosing benzene as a hydrocarbon is due to its non polar property and weak interaction with solid surface. Figure 2.9 shows the ratio of the adsorption area of benzene to that of water as a function of the relative pressure of the adsorbate. The adsorption area is the product of the adsorbed amount and molecular cross-sectional area of benzene and water. The order of hydrophobicity is H-ZSM-5 (Si/Al =628) > Cs3PW12O40 (Cs3) > H-ZSM-5 (Si/Al

=40) > Cs2.5H0.5PW12O40 (Cs2.5) > SiO2-Al2O3 > Al2O3. In conclusion, the surface of

Cs2.5H0.5PW12O40 has a hydrophobic nature close to that of H-ZSM-5 (Si/Al = 40)

which is already commercially used as a water-tolerant catalyst.

2.4.2.3 Thermal stability, surface area and pore structure Thermal stability

Thermal stability of heteropoly compounds could be monitored by X-ray diffraction (XRD), thermal gravimetric analysis and different thermal analyses (TG-DTA). Herve et al. 59_{reported that there were two types of water in heteropoly compound, one is}

crystallization water, the other one is called “constitutional water molecules” (acidic protons connected to oxygen of polyanion). Crystallization water will be lost below 473K, while constitutional water molecules are lost over 543K for H3PMo12O40 or

623K for H3PW12O40.

It was proven that the thermolysis of H3PMo12O40 proceeds in two steps. The first step

is the loss of crystallization water at temperature of 473-623K. Constitutional water was lost at temperature over 658K. Above 723K, the Keggin structure of H3PMo12O40

was destroyed. Thermal stability of mixed-addenda heteropolyanions is low in general. The polyanion structure of H3+_XPM_12-X_VO₄₀_{will be destroyed on thermal treatment}

above 463K.

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Figure 2.10 Surface area and surface acidity of CsxH3-XPW12O40 as a function of Cs

content, x.60

H-form HPA and group A salts have low surface area (1-15 m2_{/g). On the other hand,}

the surface areas of group B salts are much higher than those of group A (50-200 m2_{/g). For Cs salts, the content of Cs controlled the pore size and surface area (Figure}

2.10). When x is below 2, the surface area will decrease from x=0, (6 m2_{/g) as x}

increase to x=2. When value of x is between 2 to 3, the surface area will increase dramatically from x=2 (1 m2_{/g) to x=3 (156 m}2_{/g). It is also interesting to notice that}

the surface acidity of Csx reaches a maximum at x=2.5. The high surface area is probably due to the small size of primary particles, rather than to the presence of micropores in the crystal structure.

2.4.2.5 Effect of x (2<x<3) in CsxH3-xW12O40 for pore size distribution

Pore size of CsxH3-xPW12O40 could also be controlled by Cs content. x=2.5,

Cs2.5H0.5PW12O40 possesses both mesopores and micropores 60. Cs2.1 and Cs2.2 salts

have only micropores which was proven by N2 adsorption-desorption (Figure 2.11),

showing Type I isotherms. Furthermore, Cs 2.3, Cs 2.7 and Cs 2.9 show the Type IV isotherms, indicating that these have mesopores and micropores similar to Cs2.5.

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Figure 2.11 Isotherms of N2 adsorption on CsxH3-xPW12O40 at 77K. The catalysts were

pretreated at 573K in vacuum. →:Adsorption branch,←：Desorption branch.60

2.4.2.6. Effect of x in CsxH3-xW12O40 for reaction activity

Reaction activities of group B salts have been reported. The activities of CsxH3-xW12O40 in two different reactions are shown in Figure 2.12. It is important to

notice that the activity reached a maximum at x=0 and x=2.5. The reason is that in the range of 0<x<2, CsxH3-xW12O40 was actually a mixture of H3PW12O40 and

Cs2HPW12O40, the fraction of active HPW will decrease from unity to zero as x

increase from 0 to 2. Therefore the activity of CsxH3-xW12O40 will decrease as x

increase. On the other hand, when x is in the range of 2<x<3, the precipitates CsxH3-xW12O40 was a mixture of Cs2HPW12O40 and Cs3PW12O40 , heat treatment at

573K will homogenize the mixture and increase the concentration of protons near the surface. High surface area of CsxH3-xW12O40 (2<x<3) also contributes to the high

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Figure 2.12 Variation of the catalytic activity as a function of the Na or Cs content in MxH3-xW12O40. (a) M=Na; ○: Dehydration of 2-propanol. □: Conversion of methanol.

(b) M=Cs; ■ conversion of dimethyl ether. ▲: alkylation of 1,3,5- trimethylbenzene with cyclohexene. 61

2.4.3 Surface and bulk type reactions

The catalytic activity of heteropoly compounds could be classified into “bulk type” including bulk type Ⅰand bulk type Ⅱ and “surface-type” reactions (Figure 2.13).

Figure 2.13 Three types of catalysis by heteropoly compounds 62

Surface type catalysis is heterogeneous catalysis, the reaction of which takes place on 2D surface (outer surface and pore walls). The reaction rate is related to the catalyst

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surface area. For example, the activity of NaxH3-xPW12O40 for butane isomerization is

only related to catalysts surface. Butene is non-polar and can’t be absorbed in the catalyst, thus it only reacts on the surface of NaxH3-xPW12O40, the activity of which

changed related to Na content and pretreatment temperature.

On the contrary, the pretreatment temperature has little impact on bulk type catalysis (bulk type Ⅰ), as shown in Figure 2.14, the relative activity of NaxH3-xPW12O40

increased monotonically with the Na content in salts. All the reactants are polar molecules, leading to the activities of reactions related well with the bulk acidities. In bulk type Ⅱ reduction, the whole catalyst is reduced. The major difference between the noncatalytic surface and bulk type Ⅱ reaction is that catalytic oxidations proceed via redox mechanism. Catalytic oxidation proceeds by the cyclic reduction and reoxidation of the catalyst, called a redox mechanism, the reaction rate of catalytic oxidation and the rates of reduction and reoxidation of the catalyst must be consistent with each other if they are measured in the stationary state of catalytic oxidation. For example, the oxidation of H2 catalyzed by H3PMo12O40 with different

specific surface areas was tested. While the degree of reduction in the stationary state is different among the catalysts, the rates of reduction of the catalysts by H2, the rates

of reoxidation, and the rates of catalytic oxidation coincide quite well. This agreement indicates that the catalytic oxidation of H2 proceeds by a redox mechanism.

Glycerol acetalization using water-tolerant catalyst

Glycerol acetalization using water-tolerant catalyst

Thèse

Lin Chen

Doctorat en génie chimique

Philosophiae Doctor (Ph.D.)

Québec, Canada

Glycerol acetalization using water-tolerant catalyst

Thèse

Lin Chen

Sous la direction de

:

Résumé

Abstract

Table of Contents

List of Tables

List of Figures

Acknowledgments

Foreword

Glycerol acetalization with formaldehyde using water-tolerant solid

acids

Glycerol acetalization with formaldehyde using heteropolyacid salts

supported on mesostructured silica

Highly efficient glycerol acetalization over supported heteropolyacid

catalysts

Chapter 1 Introduction

Chapter 2 Review of water-tolerant heterogeneous catalysts