Study on the sio2 supported ionic liquid phase (silp) catalysts for the hydroformylation of ethylene

LIST OF TABLE 1.4 Supported ionic liquid phase hydroformylation in ionic liquids 30 1.5 Supports used for SILP-catalysed hydroformylation of propene 32 2.2 Retention times of reactants a

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

STUDY ON THE SiO 2 SUPPORTED IONIC LIQUID PHASE

(SILP) CATALYSTS FOR THE HYDROFORMYLATION OF ETHYLENE

Speciality: Petrochemistry and catalysis for organic synthesis

Code: 62.44.35.01

CHEMISTRY DISSERTATION

A thesis submitted to Hanoi University of Science and Technology

for the degree of Doctor of Philosophy in Chemistry

By Nguyen Thi Ha Hanh

SUPERVISORS : Assoc.Prof Dr Vu Dao Thang

Assoc.Prof Dr Le Minh Thang INVITED SUPERVISOR: Prof Rasmus Fehrmann

HANOI - 2011

ACKNOWLEDGMENTS

I would like to thank my supervisors, Assoc Prof Vu Dao Thang, Assoc Prof Le Minh Thang, Prof Rasmus Ferhmann, and Assoc Prof Anders Rissager for their guidance, encouragement, and the academic and financial support in accomplishing this work

Many thanks to Dr Olivier Nguyen Van Buu for introducing me to the sensitive synthetic techniques, the hydroformylation reactor unit

air-I also would like to thank my college - Msc.Truong Duc Duc for all his help in the characterization of catalyst structures presented in this dissertation Very special thanks to my husband Quach and my daughter Minh Khue for their love, support, and encouragement And to my mom, and my dad– thanks for being always there for me

I would like to thank to my teachers at Department of Organic and Petrochemical Technology, my colleges at the Laboratory of Petrochemical Refining and Catalysis Materials for their supports, their commendation and their discussions

Acknowledgments are also extended to Danida Foundation for funding this research

CONTENTS

CHAPTER 1: LITERATURE REVIEW

1.1.1 The importance of hydroformylation products 5

1.1.4 Recent trends in the heterogeneous hydroformylation

2.2.3 Thermal analysis 44

2.2.5 Nuclear magnetic resonance spectroscopy –NMR 49

CHAPTER 3: RESULTS AND DISCUSSION

3.2.1 Catalytic activity of the catalysts using ligand

TPPTS-Cs3 for the hydroformylation of ethylene

3 2.1.5 Activation energy 93 3.2.2 Catalytic activity of the catalysts using sulfoxantphos

111

LIST OF TABLE

1.4 Supported ionic liquid phase hydroformylation in ionic liquids 30 1.5 Supports used for SILP-catalysed hydroformylation of propene 32

2.2 Retention times of reactants and products in the hydroformylation of

after hydroformyl reaction (used)

68

3.6 Element compositions of different points indicated in figure 3.23 77

LIST OF FIGURES

1.1 Global consumption of 2–ethylhexanol for various applications (wt %) 6 1.2 Global consumption of n–butanol and iso–butanol (wt %) 7

1.4 Region wise production statistics for oxo products (2008) 9

1.7 Production capacities for oxo products by worldwide known

industries

10

1.9 Coordinative anchoring of a metal complex to the support surface 18

2.3 Ways to obtain vibrational spectroscopy: Transmission infrared 44

2.5 Effects produced by electron bombardment of a material 46 2.6 Transmission electron microscope with all of its components 48

2.8 A description of the transition energy for a 31P nucleus 49

2.9 Scheme of the reactor set-up 52

3.1 Density of inonic liquid [BMIM][n-C8H17OSO3], at different

Temperature

58

3.2 Ab Viscosity of [BMIM][n-C8H17OSO3] at different temperature 58

3.5 TG-DSC profiles of [BMIM][n-C8H17OSO3] (nitrogen atmosphere,

heating rate: 5oC/min)

62

3.6 TG-DSC profile of ligand TPPTS-Cs3 (nitrogen atmosphere, heating

rate: 5oC/min)

63

3.7 TG-DSC profile of SILP -Cs-L/Rh10-IL10- Rh0.2 (nitrogen

atmosphere, heating rate: 5oC/min)

64

3.8 TG-DSC profile of SILP -Cs-L/Rh10-IL50- Rh0.2 (nitrogen

atmosphere, heating rate: 5oC/min)

64

3.9 TG-DSC profile of SILP -Cs-L/Rh10-IL30- Rh0.2 (nitrogen

atmosphere, heating rate: 5oC/min)

64

3.10 TG-DSC profile of SILP -SX-L/Rh10-IL10- Rh0.2 (nitrogen

atmosphere, heating rate: 5oC/min)

64

3.11 BJH desorption profiles of samples with different IL loading content

before (a) and after the reaction (used) (b)

3.16 FT-IR spectra of SILP catalysts with different IL loading before and

afer exposed to high temperatures of the reactions

73

3.17 FT-IR spectra of SILP catalysts with different Rh loading before and

afer exposed to high temperatures of the reactions

74

3.23 Positions for EDX measurement and EDX spectra of

SILP-Cs-L/Rh10-IL10-Rh0.2 catalyst:

a) position for EDX measurement, b) EDX spectrum at S1, c) EDX

spectrum at S2, d) EDX spectrum at S3

77

3.24 SEM images of SILP-Cs-L/Rh10-IL5-Rh0.2 before and afer exposed

to high temperatures of the reactions

78

3.25 SEM images of SILP-Cs-L/Rh10-IL10-Rh0.2 before and afer

exposed to high temperatures of the reactions

79

3.26 SEM images of SILP-Cs-L/Rh10-IL50-Rh0.2 before and afer

exposed to high temperatures of the reactions

79

3.27 TEM images of SiO2 support 80 3.28 TEM images of SILP-Cs-L/Rh10-IL5-Rh0.2 before and afer exposed

to high temperatures of the reactions

80

3.29 TEM images of SILP-Cs-L/Rh10-IL10-Rh0.2 before and afer

exposed to high temperatures of the reactions

81

3.30 TEM images of SILP-Cs-L/Rh10-IL10-Rh0.2 before and afer

exposed to high temperatures of the reactions

81

3.31 TEM images of SILP catalysts with different Rh loading 82 3.32 Catalytic activity of SILP catalysts with different IL loading 85 3.33 Influence of IL loading contents on the maximum temperature which

the catalysts still work stably

3.37 Influence of ligand/Rh ratios on the maximum temperature which the

catalysts still work stably

89

3.38 TOF at 90oC (except for the sample with 50%IL, which TOF is at

80oC since the catalyst start to loose activity from 90oC already) of

the catalysts with different IL loading contents before and after the

exposition to high temperatures

90

3.39 TOF at 90oC of the catalysts with different Rh loading contents

before and after the exposition to high temperatures

91

3.40 Activity at 90oC of the catalyst SILP-Cs-L/Rh10-IL10-Rh0.2 before

and afer cofeed 10%V propanal in the feed stock

92

3.41 Influence of evacuation on the activity of deactivated catalysts 93 3.42 Arrhenius plots of the samples with different IL loading content 94 3.43 Arrhenius plots of the samples with different Rh loading content 95 3.44 Arrhenius plots of the samples with different L/Rh ratios 96 3.45 Influence of ethylene partial pressure on the TOF of the catalyst 97 3.46 Influence of ethylene partial pressure on the ethylene conversion 98 3.47 Influence of ethylene partial pressure on propanal selectivity 99

3.48 Catalytic activity on stream of the catalyst

SILP-SX-L/Rh10-IL10-Rh0.2 at different ethylene pressures

100

3.49 Influence of residence time on ethylene conversion 101 3.50 Influence of residence time on propanal selectivity 101 3.51 Influence of residence time on turn over frequency 101

3.52 Arrhenius plots to calculate activation energy of the catalyst

SILP-SX-L/Rh10-IL10-Rh0.2 at different ethylene pressures

103

3.55 Arrhenius plot for Rh-SILP-catalyzed hydroformylation 105 3.56 Selectivity (n/iso ratio) at different temperatures 105

3.57 Arrhenius plot for hydroformylation of pentene on the catalyst

SILP-SX-L/Rh10-IL10-Rh0.2 10bar syngas (alkene:CO:H2 = 1:1:1),

residence time =17s

106

LIST OF SCHEME

1.1 Three stages of the catalyst development for the

hydroformylation reaction

13

1.3: Dissociative mechanism for hydroformylation cycle 22

1.7 Illustration of supported ionic liquid phase catalyst 27

LIST OF SYMBOLS AND ABBREVIATIONS

TPPTS-Cs3 Tri-cesium tris(m-sulfonatophenyl)phosphine

1

INTRODUCTION

Hydroformylation is one of the oldest and largest homogeneously catalyzed reactions of olefins

Hydroformylation is conducted in a mixture of reactants and products, and

as of 1984 in biphasic aqueous media to allow dissolution of Rh catalyst and reactants in a homogeneous liquid phase The catalysts used are homogeneous in nature, dissolved into the solvent or reactant/product mixture This poses significant challenges related to separation, which is simplified in the biphasic RCH/RP oxo-process This process is based on aqueous biphasic catalysis and uses tri(m-sulfonyl) triphenylphosphine (TPPTS), as the ligand and a water soluble Rh metal as the catalyst

Rhodium is more active than cobalt, but is also more expensive Rhodium

is the catalyst of choice for conversion of low molecular weight alkenes, while cobalt based catalysts are used for conversion of high molecular weight alkenes For example, Ruhrchemie/Rhone-Poulenc (RCH/RP) process has been applied for hydroformylation of propene by Rh based catalysts

Though, homogeneous catalysts give higher conversion and selectivity for desired product in short reaction time as compared to heterogeneous catalyst system, this have disadvantage in the separation of catalyst from the product mixture Thus, efforts are directed towards the heterogenization of rhodium complex on the inorganic solid supports for hydroformylation of alkenes In this concern, more attention in the present thesis has been paid on literature review related to the recent developments in the heterogenizaton of homogeneous catalysts on the inorganic solid supports for hydroformylation of alkenes

On the other hand, ethylene, propene, butene are light alkene, but only the hydroformylation of propene, butene reaction in biphasic medium very successfully

The main product - propanal derived from the hydroformylation of ethylene, however, bears a significant miscibility with water If the reaction could happen in aqueous- biphasic like propene reaction, there would be some problems:

- Water in the aldehyde cannot be removed by distillation, due to the formation of azeotropic mixtures,

Thus, if the hydroformyltion of ethylene reaction can be done by using SILP catalyst as heterogenous way, it will be a promising way to apply in industry scale

The goal of this research was to develop a solid catalyst for heterogeneous hydroformylation of ethylene Rhodium is the most active transition metal for hydroformylation and it was obvious choice for the catalytic metals in the preparation of the solid catalysts Silica was chosen, because it is an inert, available support material widely applied in catalysis

Ligands change the electronic and steric properties of the catalyst complex Two ligands (TPPTS-Cs3 and sulfoxantphos) were chosen to evaluate their activity in ethylene hydroformylation

The thesis includes three chapters The first chapter summarizes the aspects about the hydroformylation process, synthesis, the structure, the catalytic property of SILP catalyst in the literature The second chapter describes the catalysis synthesis and introduces basic principles of the physico-chemical methods used in the thesis

The chapter III is focused on the characterization of SILP, the catalytic activity of SILP with two above mentioned ligands

Final is the general conclusions of the performed work

3

CHAPTER 1: LITERATURE REVIEW

Development of green catalytic routes for the synthesis of commercially important chemicals is a rewarding endeavor from environment and economic point of view Green chemistry comprises designing, development and implementation of chemical products and processes to reduce or eliminate the use and generation of substances hazardous to the human health and environment It is an innovative, non–regulatory, economically driven approach toward sustainability Green technology is receiving significant attention as the awareness about environmental issues has increased The concept for the design

of environmentally benign products and processes is embodied in the 12 Principles of Green Chemistry as follow [11]

1 Waste prevention instead of remediation

2 Atom efficiency

3 Use of less hazardous/toxic chemicals

4 Design safer chemicals and products

5 Use innocuous solvents and reaction conditions

6 Design energy efficient processes

7 Preferably renewable raw materials

8 Shorter synthesis route and avoid derivatization

9 Use catalyst instead of stoichiometric reagents

10 Design products for degradation after use

11 Real time analytical methodologies for pollution prevention

12 Inherently safer processes to minimize the potentials for accidents

Catalysis plays a vital role in production of wide variety of products, which are having applications in drugs, plastics, agrochemicals, perfumery, detergents, food, clothing, fuels etc [90] In addition to, it plays an important role in the balance of ecology and environment by providing cleaner alternative routes to stoichiometric technologies Green catalytic process efficiently utilize all the atoms of raw materials, eliminates waste and avoids the use of toxic and/or

1.1 Hydroformylation of alkenes (Oxo Reaction)

Hydroformylation is one of the oldest and largest homogeneously catalyzed reactions of olefins The reaction was first discovered in 1938 by Roelen while working for Ruhrchemie in Germany Roelen investigated the effect of added olefins to cobalt catalysts and identified aldehydes as one of the oxygen containing components H2 and CO can add across the double bond of olefins to form aldehydes in the presence of a Co (or Rh) catalyst [42, 93]

The process is frequently referred to as the “Oxo” process, with Oxo being short for Oxonation, i.e the addition of oxygen to a molecule However, the term hydroformylation is descriptively more accurate and more useful in characterizing this type of reaction catalyzed by various transition metal complexes because during the reaction a hydrogen atom and a formyl group are added to the olefinic double bond

RCH2 = CH2 + CO + H2→RCH2CH2CHO + RCH(CH3)CHO (Eq.1.1)

“normal” “branched”

The relative amounts of normal- and branched-chain aldehydes produced depend on the identity of R and other constituents of the reaction mixture Normal-chain aldehydes, the more desirable products, usually are hydrogenated, affording straight-chain alcohols, or self-condensed, affording more complex aldehydes With a terminal alkene as substrate, the normal/branched ratio is an important parameter in the industrial hydroformylation process; generally speaking, the better catalytic performance, the higher the ratio, although significant markets have

5

developed for the branched aldehydes In addition to linear terminal olefins,

a wide variety of different olefins have been successfully hydroformylated, e.g linear internal olefins, unsaturated alcohols, phenols, ethers, and amides Hydroformylation, the reaction of an alkene with syngas (carbon monoxide and hydrogen) to form aldehydes and alcohols, is an homogeneously catalyzed reaction performed industrially on a large scale Rhodium and cobalt carbonyls have been used for a long time, but such a homogeneous process includes a difficult and expensive step of catalyst recovery Consequently it has been attempted to avoid this step by using heterogeneous catalysts

The first generation of hydroformylation catalysts was based on cobalt carbonyl without phosphine ligand [26, 42, 93] The conditions were harsh,

as activity of cobalt is low The process was used both for lower as for higher alkenes, and notably also internal alkenes give mainly linear product aldehyde Initially rhodium catalyzed reaction seemed slow, because the formation of rhodium hydrides requires high pressures of hydrogen

A nearly commercial application of phosphine-free rhodium was by Mitsubishifor the hydroformylation of higher 1-alkenes in 1970 Since Shell's report on the use of phosphines in this process [93], many industries started applying phosphine ligands in the rhodium process as well While alkylphosphines are the ligands of choice for cobalt, they lead to slow catalysis when applied in rhodium catalysis In the mid-sixties the work of Wilkinson showed that arylphosphines should be used for rhodium and that even at very mild conditions very active catalysts can be obtained [37, 114]

1.1.1 The Importance of Hydroformylation Products

World production and consumption of hydroformylation (oxo) chemicals is more than 8.8 million metric tons per year finding use in the manufacture of solvents, soaps, detergents, plasticizers and various intermediates for fine and perfumery chemical industry n–propanol and n–propyl acetate produced from ethylene hydroformylation are used in flexographic and gravure inks, which require volatile solvents to prevent spreading and ink accumulation on printing processes [32,59,104] n–propanol is also used as a solvent, pesticide intermediate, precursor for glycol ether, surface coating applications, grain and

6

food preservatives, herbicides, etc

Over 90% of world consumption of n–butanal, which is produced by hydroformylation of propylene, is for the production of 2–ethylhexanol (2–EH) and n–butanol The butanal is mainly applied as an intermediate for the production of plasticizers, rubber accelerators, synthetic resins, solvents and high molecular weight polymers The reason for high production and demand of C4

aldehydes is due to its use in the production of 2–ethylhexanol (2–EH) About 60% of the total C4aldehydes production amount (or about 70% of the n–butanal production capacity) is consumed for the synthesis of 2–ethylhexanol 2–Ethylhexanol is used for the production of dioctyl phthalate and other plasticizers, coatings, adhesives, stabilizers, low volatility solvent, perfumery and specialty chemicals (Figure 1.1) 2–ethylhexanol derivatives are used as an additive for diesel fuel to reduce engine emissions and for lube and mining oils

to improve their performance

Figure 1.1 Global consumption of 2–ethylhexanol for various applications

(wt %) [32]

n–Butanol is a versatile intermediate for chemical industry It reacts with acids to yield esters and with oxides to yield glycol ethers n–Butanol is an intermediate chemical for the synthesis of esters like butyl acetate, butyl acrylate, butyl methacrylate, etc and these esters are used as solvents for coating Other applications of n–butanol are solvent, cleaning fluids, herbicides, dyes, printing inks, personal care products, pharmaceuticals, plasticizers, textiles and lube additives The global consumption of the butanol is shown in Figure 1.2

7

Figure 1.2 Global consumption of n–butanol and iso–butanol (wt %)[32]

C5 valeraldehyde derivatives are used predominantly to make lube oil additives, automotive anti–wear applications, aeromotive synthetic lube formulation and refrigerant lubricants n–valeric acid, which is prepared from the hydroformylation of butene followed by oxidation, is used for the synthesis of lubricants, biodegradable solvents, plasticizers, perfumery and pharmaceutical chemicals C6-15 oxo alcohols are used in the fine chemicals and perfumery industry, for the synthesis of neopolyol esters plasticizers and detergent applications [105]

1.1.2 The role of Hydroformylation Reaction in Industry

The fast growing market for the oxo products plays an important role in the hydroformylation processes Figure 1.3 shows the growth in the production of oxo products around the world [32]

As seen from Figure 1.3 and 1.4, Asia, North America and Western Europe are contributing 32%, 23% and 30%, respectively to the world production capacity of oxo products and are major oxo producers today USA and Germany with 23% and 21% of world’s production are also leading producers Within Asia, Japan, South Korea and China are the major manufacturers with as many

as five other countries engaged in the production of oxo products (Figure 1.5)

Vietnam is still an imported country, production of oxo products has not been started yet, most of chemicals are imported Between 1998 and 2002,

to grow at an average annual rate of 2.0% during 2008–2013 Japanese consumption is forecast to experience 0.9% average annual growth during 2008–

2013 Other Asian consumption, excluding Japan, is expected to grow at 5.0% annually during the same period; China, India and Taiwan are the main growth markets in this region Middle Eastern consumption of oxo chemicals is forecast

to grow significantly at an average annual rate of 4.8% during 2008–2013, albeit from a small base, largely as a result of increased n-butanol demand for n-butyl acrylate by late 2010

These data show that Asia has been the main growth center for these chemicals during last five year with North America and Western Europe showing stagnancy It is estimated that in the coming five years too, Asia will witness the growth in oxo products with only a small increase in production capacities in other countries

9

Figure 1.3 Worldwide growth in the production of oxo products [32]

Figure 1.4 World concumption of oxo products (2008)[106] The worldwide oxo product derivatives distribution is shown in Figure 1.6 The production rate of 2–ethylhexanol is high among all oxo derivatives, which

is mostly consumed by the plastic industry, followed by production of butanol

10

Figure 1.5 Productions of oxo products in Asia region (2003) [32]

Figure 1.6 Worldwide oxo product derivatives distribution [32]

The detergent grade alcohols also have significant contribution in the world

market, which are produced by oxo reaction Figure 1.7 gives the estimated

production capacities for the oxo products via hydroformylation reaction by

worldwide known industries It is observed from these data that around 57% of

the oxo products are produced by seven big companies namely BASF, Exxon,

EON, Celanese, Dow, Eastman and Kyowo Hakko [32]

11

Figure 1.7 Production capacities for oxo products by worldwide known

industries [32]

1.1.3 Catalysts for Hydroformylation Reaction

The hydroformylation catalysts, typically, consist of a transition metal atom (M), especially from the platinum group metals These transition metal complexes interact with carbonmonoxide and hydrogen to form metal carbonyl hydride species, which is an active hydroformylation catalyst Typically, complexes containing carbonyl ligands are known as unmodified catalysts On the other hand, the introduction of tailor–made ligand to the transition metals are known as the modified catalysts

Three developmental stages for hydroformylation catalysts are reported in the literature The first stage of hydroformylation was exclusively based on cobalt (Co) containing catalyst The catalytic active species for hydroformylation reaction was the cobalt carbonyl hydrides in the pressure range of 240–300 bar at 150–200 °C temperature Separation of products from the reaction mixture, severe reaction conditions and low activities of catalysts were the main limitations of this stage’s processes The research efforts led phosphine replacing

12

carbonyl complexes as an electron donating ligand and this emerged as a fundamental step in metal carbonyl catalyzed reaction, which imparted ability to the scientists to tailor–make catalyst by modifying the electronic and steric properties of the ligand

The second stage of hydroformylation reaction was the combined development in ligand modification and replacement of cobalt rhodium (Rh) metal It took almost a decade of research before first rhodium catalyst based commercial process was launched in 1974 and the process was termed as Low Pressure Oxo (LPO) process Compared to cobalt based processes, many advances were made in the second developmental stage of hydroformylation, especially with respect to material and energy utilization Thus, second stage of hydroformylation was concluded with development of more effective Rh–phosphine catalyst However, the industrial problems of first stage such as, separation of products from reaction mixture, catalyst recovery, loss of costly metals, use of corrosive solvents, etc continued in the second stage too

The third stage, can be called a break-through in hydroformylation process - two-phase catalysis (biphasic or liquid multi-phase systems hydroformylation), because of finding a way of separating the catalyst and the reaction products under mild conditions that is ecologically as well as economically efficient The fundamental idea consisted in applying water–soluble catalysts by ligand modification and thus transferring the hydroformylation into aqueous phase With the help of such catalysts, separations of desired products have become an easy task The idea of applying water–soluble Rh–complex as a catalyst for the hydroformylation of propylene and 1–butene was taken up and commercialized by Ruhrchemie AG [29] The first plant was commissioned in 1984, only two years after the development on laboratory scale, followed by rapid further increases in capacity to more than 3 x

106tons/year An additional unit for the production of n–pentanal (n–valeraldehyde) from 1–butene [95] has been brought on stream in 1995 The developments of hydroformylation processes in different stages are shown in Table 1.1 and the catalysts used are presented in Scheme 1.1

13

Table 1.1 Developments in hydroformylation processes [26]

Catalyst

4 = Union Carbide process (LPO);

5 = Ruhrchemie–Rhone–Poulene process; LHSV = Liquid hourly space

velocity

Scheme 1.1 Three stages of the catalyst development for the

hydroformylation reaction [26]

14

Presently, most of the industrial plants are running successfully with rhodium and cobalt based catalysts Attempts had been made to compare the catalytic activity of group VIII and IX metals for hydroformylation of alkenes to understand the role of metal atom in hydroformylation reaction [38, 84] Ruthenium is attracting the attention of the researchers after rhodium and cobalt; nevertheless, it is yet to move from laboratory to pilot plant scale The ligand plays a significant role in the hydroformylation reaction from the catalytic activity, selectivity and regio–selectivity point of view Phosphines and phosphite based monodentate and bidentate ligands are most commonly used and accepted ligands for the hydroformylation reaction [38, 84] Nitrogen containing ligands showed lower reaction rates than phosphines due to their stronger coordination to the metal centers A comparative study of Ph

3R (where R= elements of main group V) were made for the hydroformylation of 1–dodecane [84] and showed following order; Ph3P > Ph3N > Ph3As > Ph3Sb > Ph3Bi In another study, the activity of the triphenylphosphine, triphenylarsine and triphenylantimony ligands were compared for hydroformylation of ethylene and 1–hexene using transition metal catalysts [58, 59, 84] Today, most of work in the homogeneous catalysis for hydroformylation is focused on the developments

of the bulky phosphorous/phosphite ligands, which include both monodentate, and more bulky bidentate ligands

Is there a forth stage of the catalyst development for the hydroformylation reaction? Rh-catalyzed hydroformylation can be carried using a wide variety of

ligands, allowing for extensive ligand variation and optimization A ligand

design has been being done with several objectives in mind; besides the normal

wish list of activity, selectivity, and stability (of Rh catalyst and free ligand) Besides, the successful applicability of supported ionic liquid phase catalyst (SILP) as heterogenous catalysts for hydroformylation of alkenes has recently appeared in the literature (thus will be discussed in the next section) Hopefully, the combination of the ligand design and applied SLIP catalyts can be realiable and soon become the forth of stage

1.1.4 Recent Trends in the Heterogeneous Hydroformylation Reaction

Commercial processes are using triphenylphosphine modified Rh–complex [HRhCO(PPh3)3] as a catalyst for the hydroformylation of lower carbon chain

15

length alkenes (C2 – C5) under milder reaction conditions This catalyst is limited upto the hydroformylation of lower carbon chain alkenes such as, ethylene and propylene due to separation problems of Rh–complex from the product mixture after completion of the reaction Conventionally, homogeneous catalyst is separated from the product mixture by stripping the products in vacuum (vacuum distillation) The thermal stress caused by the vacuum distillation process decomposes the expensive metal complex which is used as a catalyst for hydroformylation reaction Most homogenous hydroformylation catalysts are thermally sensitive and decompose below 150 °C This is the main reason, which limits the applicability of Rh–complex for hydroformylation of lower carbon chain length alkenes because in case of higher carbon chain length alkenes, decomposition of rhodium complex occurred during the separation of catalyst from higher boiling point product mixture As far as hydroformylation reaction is concerned, Rh–complexes as catalysts typically work under mild conditions (80–100 °C, 20–40 atm), giving good activity & selectivity (95–99%)

to the desired linear (n–) aldehyde

For the hydroformylation of higher alkenes, cobalt catalysts are widely used, which require drastic reaction conditions (200 °C, 200–250 atm) and yield poor selectivity for linear aldehyde The cobalt catalyst is recycled after vacuum distillation of the product mixture by the “decobalting” procedure In the decobalting process, regeneration of cobalt catalyst after reaction is carried out

by changing the oxidation state of cobalt either by hydrothermal treatment or by oxygen treatment in acidic medium Typically, cobalt is recovered in the form of cobalt formate or acetate by addition of the oxygen and formic or acetic acid [38] Although, cobalt catalyst is recycled for hydroformylation of alkenes, but still has drawbacks of higher temperature, pressure, longer reaction time and lower selectivity of the desired aldehyde as compared to rhodium based catalysts Solving the product separation problem for the rhodium catalyzed hydroformylation in an effective and economically acceptable way, would present a major step forward in homogeneous catalysis Therefore, development

of a heterogeneous catalyst for hydroformylation in today’s research scenario can

be broadly classified into two categories

+ In the first category, catalyst is anchored or supported on the surface of solid inorganic material, which is used as heterogeneous catalyst either in

16

continuous reactor (fixed bed) or in the high pressure batch reactor (autoclave)

This type of process is often referred to as heterogenization of homogeneous catalysts

+ Second category is the designing of a water–soluble ligand, which is insoluble in the product mixture, is often referred to as biphasic systems One of the most important developments in 1980-2000 in the area of homogeneous catalysis is the successful development of water-stable as well as highly water-soluble catalyst systems and the consecutive introduction of the aqueous two-phase technology The reaction in biphasic system involves aqueous and organic phases (Figure 1.8)

With the hydroformylation reaction in biphasic medium; reaction takes place at the interphase Catalyst is separated from the reaction mixture using phase separator [87] There are some reports presented in the literature on the development of cobalt and ruthenium biphasic systems for hydroformylation of alkenes [87] Application of biphasic catalyst is limited to hydroformylation of propene and butene due to lower solubility of higher carbon chain length alkenes

in aqueous medium (water)

Though, homogeneous catalysts give higher conversion and selectivity for desired product in short reaction time as compared to heterogeneous catalyst system The homogeneous catalysis has disadvantage in the separation of catalyst from the product mixture Thus, efforts are directed towards the heterogenization of rhodium complex on the inorganic solid supports for hydroformylation of alkenes In this concern, more attention in the present thesis has been paid on literature review related to the recent developments in the heterogenization of homogeneous catalysts on the inorganic solid supports for hydroformylation of alkenes

Impregnation is the common method for heterogenizaton of homogeneous catalyst In this method, inorganic solid support is mixed with the solution of homogeneous complex prepared by dissolving the complex in suitable solvent Then, the suspension is stirred for long time either at room temperature or at a particular desired temperature Ligands can also be anchored or impregnated onto solid inorganic materials, generally silica, zeolites or polymers The ligand

or complex anchored covalently to the solid support of high surface area ensures the reusability of the catalyst

17

Figure 1.8 Hydroformylation reaction in biphasic medium

Main problem in the heterogenization of homogeneous complex is the breaking of bonds between metal and ligand during the course of catalytic reaction and this is the cause of leaching of the active metal species responsible for the reaction This “leaching” process leads to the loss of catalytic activity in the reusability experiments The leaching problems can be solved upto certain extent by anchoring the homogeneous complex using some tethering agent or encapsulation inside the pores of the solid support used

1.1.5 Heterogeneous Catalysts for Vapor Phase Hydroformylation of Alkenes

Homogeneous catalysts are highly active and selective, but they have several disadvantages: problems with separation of the catalyst from reaction products, expensive metal losses, solubility limitations and corrosivity of catalytic solutions For rhodium catalysis, economical operation requires recovery at ppb level due to the high cost of rhodium Therefore, several

Table 1.2 Classification of immobilised metal complex catalysts [62] 1.Supported metal complex catalysts

Catalysts containing a dispersed phase of complex on a support

Supported liquid phase Catalysts (SLPC)

Supported Aquesous Phase catalysts (SAPC)

2 Anchored Metal complex catalysts (Chemical bonding)

19

Figure 1.9: Coordinative anchoring of a metal complex to the support

surface, A is a mononuclear complex, B is a polynuclear complex, L is a ligand

The supported metal catalysts are prepared by impregnating metal salts and

oxides on the support followed by reduction, or by decomposition of

organometallic compounds on the support For instance, active carbon, silica,

alumina or zeolites can be used as supports onto which e.g the metal nitrates are

impregnated

Both rhodium and cobalt (in inorganic form), separately and together, in

combination with other metals on various supports have been studied in the

hydroformylation of ethene [22, 23] and higher alkenes [24– 27]

Even though the heterogenisation of the homogeneous precursors often

results in a decrease in activity, it has also resulted in improved performance

In liquid-phase applications, leaching of the active metal into the liquid

phase [16, 29, 86] has prevented the commercial use of heterogenised catalysts

In gas-phase hydroformylation, the use of supported metal catalysts is more

feasible, since the operating conditions are mild: the reaction can be carried out

at low pressures (and below 150ºC) where the competing Fischer-Tropsch

reaction ceases

Most of the developments for rhodium based catalysts supported on various

inorganic materials were studied for vapor phase hydroformylation of ethylene

and propylene in a continuous flow (fixed bed) reactor Since, the lower carbon

number alkenes (ethylene and propylene) exist in gaseous form, it seems

20

appropriate to produce aldehydes under continuous flow conditions over batch mode In the 1980s, heterogenization of rhodium complex was performed by taking zeolites as solid supports The series of highly active catalysts were synthesized by rhodium entrapping in the framework of zeolite X and Y and used as catalysts for vapor phase hydroformylation of propylene and ethylene (Scheme 1.3) [56–58]

Scheme 1.2 Hydroformylation of ethylene and propylene

Detailed comparative study for hydroformylation of ethylene and propylene were made by Davis et al using Rh–Y and Rh–X as catalysts in the continuous flow reactor at an atmospheric pressure [85] Activity of catalysts for the formation of propanal and butanal did nofall for a period of one month’s continuous experimental run The results concluded that the active sites were formed either at the entrance of pore or external surface can effectively catalyze the hydroformylation of ethylene and propylene In another study, hydroformylation of propylene was investigated using palladium (Pd) trimethylphosphine carbonyl clusters entrapped in the cage of zeolite Na–Y The rate of reaction was reported to depend on calcination and reduction temperatures as well as concentration of trimethylphosphine Excess concentration of trimethylphosphine results into the drop of catalytic activity of the catalyst [59]

Due to large surface area of silica as compared to zeolites, the Rh–complex was also heterogenized on the surface of silica for hydroformylation Naito et al found the rhodium supported silica to be the most selective catalyst for the formation of butanal via hydroformylation of propylene in fixed bed reactor [60] There are some reports in which In–situ reduction of rhodium impregnated catalyst was claimed to convert it into nanocrystalline or amorphous metallic phase, which was very active for hydroformylation reaction Lenarda et al reduced the impregnated Rh on silica in a solution of tetrahydrofuran (THF) and

21

1 M lithium aluminum hydride at low temperature and obtained rhodium nanocrystals was used as a catalyst for propylene hydroformylation [69] Apparent activation energy for the propylene hydroformylation was found to be

26 kJ/mol Catalytic activity and selectivity of aldehyde could be improved by the addition of promoters or use of the bimetallic catalysts The bimetallic nanocrystalline Rh–Co based catalysts with varied Rh/Co ratio were synthesized

by the reduction of metal salts impregnated on silica with NaBH

4 in the nitrogen atmosphere [72] The obtained catalyst showed high regio– and chemo– selectivity for aldehyde and catalytic activity was observed to increase with increase in the Rh/Co ratio Effect of triphenylphosphine (PPh

3) on the rhodium impregnated silica (Rh/SiO

2) was also studied for hydroformylation of propylene using fixed bed reactor [74] and batch slurry reactor for hydroformylation of ethylene, 1–hexene and 1–octene [73] The obtained results were compared with the HRhCO(PPh3)3/SiO2 and PPh

3–Rh/SiO

2 systems The coordination of PPh

3

was retained in Rh/SiO

2 catalyst that was confirmed by solid state 31P–nuclear magnetic resonance (NMR) and in–situ Fourier transform infrared (FT–IR) spectroscopic analysis Excellent conversion of propylene with higher n/iso ratio

of aldehydes was obtained using PPh3–Rh/SiO2 as a catalyst and deactivation of catalyst was not observed over a period of 1000 h reaction time on stream The correlation of homogeneous and heterogeneous catalyst (Rh/SiO

2) for hydroformylation of ethylene was made based on the results obtained from the FT–IR spectroscopic study [65] Later on infrared spectroscopic studies were continued for the hydroformylation of ethylene and propylene and developed the reaction mechanism and kinetic models Chuang et al using immobilized rhodium catalysts studied the coordination and formation of the intermediate species during hydroformylation of ethylene, mainly Rh/SiO

2 and manganese modified Mn–Rh/SiO

2 Progress of ethylene and propylene hydroformylation, formation of intermediate active species, mechanistic aspects and reaction kinetics were studied from the analysis of transient response of the formed product obtained by isotopic methods combined with in–situ infrared spectroscopy [31,76,108,109]

Applicability of the supported ionic liquid phase (SILP) catalysts, prepared

by impregnation of the partly dehydroxylated silica support with an anhydrous

2] and bisphosphine ligand, was used as a effective catalyst for hydroformylation of propylene in a fixed bed reactor [13, 14, 16] Review articles for the applicability of supported ionic liquid as catalysts for hydroformylation of alkenes have recently appeared in the literature [15, 106] Except the applicability of Rh metal for hydroformylation of alkenes, the researchers also performed the experiments on the activity of ruthenium (Ru) exchanged pillared clay as a catalyst for hydroformylation of ethylene and propylene in a fixed bed reactor at atmospheric pressure in the temperature range

of 100 – 220°C The Ru–catalyst showed constant rate of reaction even at the end of 1week experimental run [88]

1.1.6 Mechanism of hydroformylation reaction

In the early 1960s Heck and Breslow [46-49] formulated the generally accepted hydroformylation cycle for cobalt catalysis that is also valid for unmodified rhodium catalysts The hydroformylation mechanism for phosphine-modified rhodium catalysts follows, with minor modifications, the Heck-Breslow cycle According to Wilkinson [34], two possible pathways are imaginable: the associative and the dissociative mechanisms (as depicted in Scheme 1.3 and Scheme 1.4)

23

Scheme 1.3 Dissociative mechanism for hydroformylation cycle [95]

The associative route begins with coordination of the alkene to the dicarbonyl species (Scheme 1.4, 1B) The dissociative route involves dissociation of one of the ligands (PPh3 or CO) and is similar to Heck-Breslow cycle After the initial steps, the following steps in the associative and dissociative mechanisms are similar; following alkene coordination, an alkyl species (Scheme 1.4, 1D, Scheme 1.3, 2D) is formed Alkyl migration to CO leads to acyl formation (Scheme 1.4, 1E, Scheme 1.3, 2F) Hydrogen addition produces dihydrido acyl species (Scheme 1.4, 1F, Scheme 1.3, 2G) Finally, elimination of the aldehyde and addition of CO regenerates the active catalytic species HRh(CO)2L2

24

Scheme 1.4 Associative mechanism for hydroformylation [95,117]

The associative mechanism involves 20-electron intermediates and is often rejected on the grounds that Rh should form 16 or 18 electron complexes It is accepted today that Wilkinson’s dissociative mechanism is the likely kinetic path for hydroformylation [95] In order to avoid referring to two figures depicting mechanism as the subsequent, literature review discussion will refer to scheme 1.5 as it is much simpler to follow

25

Scheme 1.5 Mechanism for ethylene hydroformylation, L=PPh3 [95,117]

The active species are 16-electron hydrides of the general formula HRh(CO)x(PPh3)3-x (x = 1, 2) formed by the dissociation of CO from the 18-electron carbonyl hydride The basic steps in the hydroformylation reaction after the initial formation of the hydrido metal carbonyl are: (1) dissociation of CO to form the unsaturated 16-electron species, (2) coordination of alkene, (3) formation of the alkylmetal carbonyl species, (4) coordination of CO, (5) insertion of CO to form the acylmetal carbonyl, (6) oxidative addition of hydrogen, and (7) cleavage of the acylmetal species by hydrogen to form the aldehyde and regeneration of the hydridometal carbonyl It is generally believed that the oxidative addition of hydrogen to the rhodium-acyl complex (step 6 in Scheme 1.5) is the rate determining step Leeuwen [95] has proposed that, roughly speaking, in phosphine catalyst systems the migratory insertion of the alkene into Rh-H (step 3 in Scheme 1.5) is the rate-determining step under standard industrial process conditions

The reaction mechanism on supported catalysts follows a similar mechanism Henrici- and Olivé [50] have suggested that the decisive difference between the homogeneous and the heterogeneous process is the availability of a

26

free, mobile, very reactive hydrido-metal species in solution According to them, the last step (steps 6 and 7 in Scheme 1.5), the transformation of the acyl-metal species to the aldehyde, proceeds through reaction with a second catalyst species

in homogeneous media, but in heterogeneous media the oxidative addition of molecular hydrogen to an acyl-metal species is the only means of formation of the aldehyde The hydrogenation of the acyl intermediate was identified as the rate determining step at 0.1 MPa on Rh/SiO2 [21]

In some studies, the CO insertion selectivity on supported unmodified metal catalysts, is related exclusively to the linearly adsorbed CO on isolated Rh sites [59], whereas other studies show that reaction rate and selectivity for hydroformylation increases in the presence of Rh+ sites [28] Thus, the dispersion of the catalytic metal and the extent of reduction are the main factors determining the CO insertion activity, and thereby, the selectivity towards aldehyde formation According to Sachtler and Ichikawa [102], two types of active sites are responsible for aldehyde formation: isolated, partially oxidised metal crystallites for the migratory CO insertion into metal alkyl bonds, and fairly large metal ensembles for the dissociation of hydrogen Hedrick et al [102, 104] noticed that on a Mn- Rh/SiO2 catalyst, spill-over hydrogen from the metal

to the silica surface plays a role in the hydrogenation of the acyl intermediate Thus, the hydrogenation of ethyl species to form ethane, and the hydrogenation

of adsorbed acyl species to form propanal, are involved with two different types hydrogen: metal adsorbed hydrogen and hydrogen from Si-OH

Besides the main reaction (hydroformylation reaction), the hydrogenation, and aldol condensation are unexpected reactions By-products can be aldehyde isomers, low – reactive alkene isomers, alcohols, aldkenes, and heavy ends [Scheme 1.6) The formation of heavy ends constitutes the biggest proplem Heavy-ends accumulation can cause serious process problems such as Rh leaching, diluted ionic liquid (in case catalyst is SILP)

27

Scheme 1.6 The formation of heavy products (by-product)[95] 1.2 SILP catalysts

1.2.1 Composition of SILP catalysts

A supported ionic liquid phase catalyst – SILP was a new concept, which was led by the pioneers are Mehnert and co-workers in 2002, they extended this methodology to support Rh(I) complexes for hydroformylation of hex-1-ene to heptanal in both IL and molecular solvents [85]

In these SILP systems, a thin film of ionic liquid containing the homogeneous catalyst is immobilised on the surface of a high-area, porous support material, as depicted in scheme 1.7 SILP catalysts appear as solids, the active species dissolved in the liquid phase on the support, maintaining the attractive properties of ionic liquid homogeneous catalysts such as good dispersion of molecular reactant, and high activity Thus, SILP belonged to the