Table Of ContentCONTENTS
Preface
Chapter 1 Catalytic Activity and Kjnetics of Liquid-Solid-Liquid
Phase-Transfer Catalysis l
Ha-Shing Wu
Chapter 2 Aerogels in Catalysis
Aleksandar M. Orlovic. Djordje T. Jana{:kovif: and Dejan U. Skala
Chapter3 Heterogeneous Catalysis on Basic Sites in Organic Synthesis 85
A. Marinos .1. M. Marinas M. A. Aramendia and F. J. Urbano
Chapter4 Organic Transfom1ations Through Supported Guanidines
Giovanni Sartori. Raimondo Maggi and Roffaella Sartorio
ChapterS Selective Catalytic Reduction of NOx with
Organic Compounds over Ag/AI203 Catalyst
Hong He and Yunbo Yu
Chapter 6 Behavior of Nitrogen in Molvbdcnum Nitride
Hydrodesulfurization Catalyst by X PS 1.83
Masatoshi Nagai. Takashi Omara. and Shinzo Omi
Chapter 7 Design of New Generation Vanadium Complex Catalysts
Offering New Possibilities for Controlled Olefin Polymerization
Korohim Nomura
Index
PREFACE
The chemical or biological process whereby the presence of an external compound, a
catalyst, serves as an agent to cause a chemical reaction to occur or to improve reaction
perfom1ance without altering the external compound. Catalysis is a very imponant process
from an industrial point of view since the production of most industrially important chemicals
involve catalysis. Research into catalysis is a major field in applied science, and involves
many fields of chemistry and physics. The new book brings together leading research in this
vibrant field.
'vtatenal chron1ony prawefll autorskun
In: New Developments in Catalysis Research lSBN: 1-59454-440-9
Editor: Lawrence P. Bevy, pp. 1-38 ~2005 Nova Science Publishers, Inc.
Chapter I
CATALYTIC ACTIVITY AND KINETICS OF LJQIDD
SOLJD-LJQUID PHASE-TRANSFER CATALYSIS
Ho-Shing wu·
Department of Chemical Engineering and Materiais Science, Yuan Ze University,
Chungli, Taoyuan, 32003, Taiwan
ABSTRACT
Phase-transfer ca.talysis (PTC) is the most widely synLhesized method for solving the
problem of the mutual insolubility of nonpolar and ionic compounds. The liquid-solid
liquid phase-transfer catalysis (LSLPTC) can overcome the purification of product and
the separation of reacl<lnt and catalyst in the liquid-liquid phase-transfer catalytic
reaction. The main structure of LSLPTC discussed in this study was focused the
quaternary ammonium poly(methylstyrene-co-styrcne) salt for membmne and resin
system. The reaction mechanism. catalytic activity. characterization of catalyst.
theoretical modeling, mass transfers of reactant and producL and reactor design of
LSLPTC were investigated.
INTRODUCTION
When chemical reactants in immiscible phases. the phase-transfer catalysts can carry one
of them to penetrate the interface into lhc other phase to conduct the reaction; thus giving a
high conversion and selectivity for the desired product under mild reaction conditions. This
fll-
type of reaction was tenned 'phase-transfer catalysis' ( PTC) by Starks Since tl1en. many
studied have investigated the applications. reaction mechanisms and kinetics of PTC.
Currently. PTC has become an imponam choice for organic synthesis: and it is widely
applied in the manufacruring processes of specialty chemicals. such as pharmaceuticals. dyes.
perfumes. additives for lubricants, pesticides. and monomers for polymer synthesis. The
•
Mate11al chroniony prawem autorskirn
2 Ho-Shing Wu
global usage of phase-transfer catalysts was estimated over mill ions pounds in 1996. and the
industrial utilization of PTC is continuously growing at an annual rate of I 0-20% [2]. Phase
transfer catalysis is a very effective tool in many types of reactions. e.g. alkylation, oxidation,
reduction, addition, hydrolysis, etherification, esterification, carbene. chiral reaction, etc [2,3].
Reaction Cvcle of PTC
•
The first reaction scheme presented by Starks [I) was for the reaction of aqueous sodium
cyanide and organic 1-chlorooctane as in Eqs (I) and (2). No apparent reaction occurred after
24 h in the absence of catalyst. However, the cyanide displacement reaction took place
rapidly with only I% of the quatemary ammonium salt (C ,H 4N-cr added, and achieving
1 13)
near I 00% yield of 1-cyanooctanc product in 2-3 h [I]. The reaction scheme for the phase
transfer catalyzed cyanide displacement reaction in aqueous-orgamc phases is shown as
follows:
OCI
NaCN (aq) + I·CRHnCI (org) ---'~-') l-CsH11CN (org) + NaCI (aq) (I)
NaCN + QCI QCN + NaCI
(2)
in which Q is quatemary ammonium cation. e.g. . (C,,H IJ).N'. In addition. the phase
tTansler catalyst QCI should first react with the aqueous reactant, cyanide anion to fom1 the
active intermediate QCN. which is then transferred into the organic phase to react with the
organic reactant 1-C~H 17CL and then is regenerated back to QCJ to conduct the next cycle of
reactions.
Classification of PTC Reactions
Typical PTC reactions can be classified into two types, the soluble PTC and the insoluble
PTC. Each reaction type can be further divided into several categories as shown in Figure I.
Insoluble PTC contains liquid-solid-liquid PTC (LSLPTC) and tri-liquid PTC (TLPTC). by
which the catalyst can be recovered and reused, showing. great potential in large-scale
production for industry. Tho: catalyst used in LSLPTC is immobilized in an organic or
u10rganic support. while in TLPTC it is concentrated withu1 a viscous layer located between
the organic and "queous phases. Soluble PTC includes liquid-liquid PTC (LLPTC). solid
liquid PTC (SLPTC) and gas-liquid PTC (GLPTCJ. There arc also typical PTC reactions
called irl\'crse PTC (IPTC) and reverse PTC (RPTC). which differ in catalyst type and
transfer route from normal PTC 12.3).
\llatenal chronrony prawe111 autorskrm
Catalytic Activity and Kinetics ... 3
Phase-Transfer Catalysis
c
] NSOLUBLE SOLUBLE J ....
PTC PTC RPTC
TLFTC SLYJC GLJTC
Figure I. Classification of phase-transfer catalytic reaction.
Commonly used phase-transfer catalysts arc quaternary onium salts (ammonium and
phosphonium), crown ethers, cryptands, and polyethylene glycols. The essential
characteristics of these phase-transfer catalysts are I) that they must have the ability to
transfer the reactive anion into the organic phase to conduct the nucleophilic attack on the
organic substrate, 2) and the cation-anion bonding is loose enough to enable a high reaction
rate in the organic phase. In addition, other factors in selecting a suitable catalyst include its
cost, its structure, low toxicity of catalyst and solvent, ease of separation of the catalyst from
the products, low energy requirement for reaction, high stability of catalyst in process
conditions. and easy treatment of the waste streams. Together. these lead to an efficient and
economical PTC process. Hence. this paper presents the catalytic activity and kinetic of
liquid-solid-liquid phase-transfer catalyst which is important since the industrial use of liquid
solid-liquid phase-transfer catalysis growing continuously.
LIQUID-SOLID-LIQUID PHASE-TRANSFER CATALYSIS
Phase-transfer catalysis is the most widely used method to solve the problem of the
mutual insolubility of nonpolar and ionic compounds (4-11), allowing two compounds in
immiscible phases arc able to react because of the phase transfer catalyst. However. processes
using a two-phase phase-transfer catalytic reaction always encounter the separation problem
of purifying the final product from the catalyst. Regen [ 12] was the first to use the solid-phase
catalyst ( triphase catalyst (TC) or polymer-support catalyst), in which the tertiary amine was
immobilized on a polymer support. in the reaction of ;m organic reactant and an aqueous
reactant. In terms of the industrial applications. the supported-catalyst can be easily separated
from the final product and the unreacted reactants simply by filtration or centrifugation. In
addition. either the plug now reactor (PFR) or the continuous stirred tank reactor (CSTR) can
be used to carry out this reaction. Most of the synthetic methods used for triphase catalysis
arc presented in Regen ct al. 112·16] and Tomoi ct al. 11 7-2 1]. Another advantage of triphase
catalysis is that it can be easily adapted to continuous processes [22-24), giving high potential
for industrial scale applications to synthesize organic chemicals from two immiscible
reactants.
Maknal chromony prawef"' autorskrm
4 Ho-Shing Wu
Quaternary onium salts, crown ethers. cryptands, and polyethylene glycol have all been
immobilized on various kinds of supports. including polymers (most commonly
poly(methylstyrene-co-styrcne) resin crosslinked with divinylbenzene), alumina, sil.ica gel,
clays, and zeolites. [ 12-31 ). The supports for immobilizing the triphase catalyst are generally
organic, e.g. copolymers of polystyrene. ln addition, Yadav and Naik [4] reported that clay
could be used as a support for the PT catalyst, describing the preparation of benzoic
anhydride from benzoyl chloride and sodium benzoate using clay-supported quaternary
ammonium salt at 30 "C. The polymer-supported catalysts arc less active than the clay
supported catalysts for this reaction system. Desikan and Doraiswamy (2000) [5) investigated
the enhanced activity of polymer-supported phase-transfer catalysts for the esterification of
benzyl chloride with aqueous sodium acetate. They found that the reactivity using triphase
catalyst is higher than that using the soluble catalyst, and hypothesized that the enhancement
was more due to increased lipophilicity of polymer-supported catalyst, than compensation
due to decreased diffusional resistances. Because of diffusional limitations and high cost, the
industrial applications of immobilized catalysis (triphase catalysis) are not fully utilized. This
unfortunate lack of technology for industrial scale-up of triphase catalysis is mainly due to a
lack of understanding of the complex interactions between the three phases involved in such a
system. In addition to the support macrostructure, the support microenvironment is also
crucial in a triphase catalytic reaction since it determines the interactions of the aqueous and
the organic phases with the phase-transfer catalyst immobilized on the support surface [32].
However, to date, there has been investigation of the microenvironment. The effect of the
internal molecular structure of the polymer support, which plays an important role in the
imbibed composition, which affects the reaction rate, has seldom been discussed. In addition
to the reactivity, a triphase catalyst in an organic and aqueous solution must consider the
volume swelling. ratios of imbibed dil1ercnl solvents, amount of active site, and mechanical
structure of the catalyst. Hence. these complex interactions in microenvironment must be
resolved in order to obtain a high reactivity of tripbase catalyst.
Mechanism of LSLPTC
In general, these are three reaction mechanism for the fluid-solid reactions: (i) mass
transfer of reactants from the bulk solution to the surlitcc of the catalyst pellet; (ii) diffusion
of reactant to the interior of the catalyst pellet (active site) through pores: and (iii) intrinsic
reaction of reactant with active sites. Triphase catalysis is more complicated than traditional
heterogeneous catalysis, because it involves not merely diffusion of a single gaseous or liquid
phase into the solid catalyst. but rather organic reactant and aqueous reactant together exist
within the pores of the polymer pellet. In step (iii), the substitution reaction in the organic
phase and ion exchange reaction in the aqueous phase occur. Diffusion of both the aqueous
and organic phases within the solid support is important step in achieving good reaction
ilfl
rate. Various mechanisms have been proposed to describe the reaction type for triphase
catalysis. Although each mechanism can explain only a single reaction system. as presented
by Naik and Doraiswamy 132) in their review paper. Tundo and Venturcllo (30.33) presented
a mechanism for TC system using silica gel as support to account for the active participation
1341
of the gel by adsorption of reagents. Telford et al. suggested an alternation shell model
that requires periodical changes in the li4uid phase filling the pores of the catalyst. Schlunt
Matenal chron1ony prawem autorskun
Catalytic Activity and Kinetics ... 5
and Chau (25) tried to validate this model using a novel cyclic slurry reactor. and indicated
that only the catalyst in a thin shell near the particle surface was umilized. Tomoi and Ford
[ 17] and Hradil et al. [35] reponed that a realjstic mechanism involves the collision of
droplets of the organic phase with solid catalyst panicles dispersed in a continuous aqueous
phase. Svec's model [36] for transport of the organic reagent form the bulk phase through
water to the catalyst panicle was developed in terms of emulsion polymerization.
Because the triphasc reaction involves not merely diffusion of a single phase into the
solid support. the organic reaction take places in the organic phase and the ion-exchange
reaction occurs in the aqueous phase. Thus, the catalyst suppon is usually lipophilic. The
organic phase and aqueous phase fill the catalyst pores to form the continuous phase and the
disperse phase, respectively. The interaction between quaternary salts. as well as the organic
phase and aqueous phase play a crucial role in promoting the triphasc reaction rate, although
the each mechanism is unclear.
The experimental results in our previous studies [37, 42) revealed that the imbibed ratio
of organic solvent to aqueous solution in the poly(methylstyrence-co-styrene) resin with
benzyltri-n-butylammonium group was slightly larger than I. That is, the resin shows both
lipophilic and hydrophilic behaviors. Hence, the resin was still remained at the interface
between organic solvent and aqueous solution when the organic chemicals were synthesized
using this resin as triphase catalyst in a liquid-solid-liquid triphase reaction. It is well known
that the triphase reaction rate increases with an increasing amoum of triphase catalyst.
However, it is not known whether the increase of the triphase catalyst is a good method for
increasing the product yield in a liquid-solid-liquid triphase reaction. If the catalyst cannot
remain at the interface between two phases during the course of reaction, then tbc reaction
rate is reduced. due to the following two reasons:
[i]. The resin was thrown on the reactor wall by centrifugal force and was separated
from the interface between both phases. This reaction phenomenon was particularly
clear at higher agitation rate or smaller ratios of the amount of camlyst to reactor
volume. In the past, the concentration (or density) of the catalyst was in the range
of 104- 10.2 mol/dm3 (or 104- 10.3 g/cm3 at the agitation rates below 1000 rpm for
)
a batch reactor. However, this depended on the geometry of the reactor. particle
size of the catalyst and viscosity of the solvent.
[ii). The cross-sectional area of the catalyst exceeds the limited interfacial area between
both phases. that is. the ratio of the coverage area of the catalyst to the interfacial
area is larger.
The effect of coverage of catalyst between organic solvent and aqueous solution on the
apparent reaction-rate constant at difTcrent interfacial areas and different particle sizes of
resins has been presented [87), showing that a multilayer of the catalyst was fonned at the
interface between two phases when the coverage of the catalyst was more than I 00%. The
reaction-rate constants have the optimum range of the coverage of the catalyst of 65- 77% and
around 85% for the resins of 60-80 and 80-150 mesh. respectively. The coverage of the
catalyst between the two phases is more than 65%: and this reaction rat.: may be reduced in a
liquid-solid-liquid triphase reaction system. The higher coverage of the catalyst reduces the
rotational freedom of the catalyst at the interface to decrease the reacrion rate. Hence. the
fixed-bed reactor applied in a Lriphase reaction may not be the best reactor. The calculation of
Matenal chron1ony prawem autorskun
6 Ho-Shing Wu
average weight for one dry particle and the average cross-sectional area for one wet particle
can be wri lien as
W = V ·p (3)
I.Jig 0\')t pf
and
(4)
where w denotes tbe swelling volume ratio of wet resin to dry resin; r,, and V arc the
"'"It
11
average rJdius and the average volume for dry particles, respectively; and ppr is the true
density of dry particles.
The maximum cross- sectional area of total resin is given as
w
A - A (5)
T
W
T.RrSin - a''8·
M'el
"'11
where W is the total amount of the resin. Hence, the coverage of the catalyst on the
1
interface between organic solvent and aqueous solution is defined and expressed as
coverage = Ar x I 00%,
.R<>in (6)
A,nlC"rf'ltt
in which is the interfacial area between the phases.
A,.ucrJ<n•
CATALYTIC A CT IVITY AND C HARACTERJZATION OF LSLPT C
Poly(styrcnc-cu-chloromethylstyrene) crosslinking with divinylbenzenc. which is
activated with quatemary ammonium salts. was investigated to synthesize the line chemicals
in our previous works [37-42). The microenvironment of the polymer support played a crucial
role in enhancing the reaction rmc. More information abolll characterization of the polymer
structure. the interaction among organic solvent, resin and aqueous solution. and the reuse of
the catalyst is required to facilitate industrial application
Wu and Lee (42] reported that 24 kinds of ion-exchange resins were conducted to clarify
the character of the resin, including 6 kinds of commercial ion-exchange micro-resin, 5 kinds
of lab-produced macro-resins, and 13 kinds of lab-produced micro-resins using the instntmcnt
analysis of TGA. EA. SEM-EDS. and reaction method. The densities of active site in the
resin titrated using the Volhard method for commercial anion exchangers were higher than
those f(lr lab-produced resins.
'vtatenal chron1ony prawefll autorskun
Catalytic Activity and Kinetics ... 7
?H2
- NI
c.H9 ~c.H9
cr
c R 1
4 9 (7)
Scanning electron microscopy (SEM) analyzes electrons that arc scattered from the
sample's surface to monitor the morphological observation of the polymer resin. The
elemental analysis is studied by means of energy dispersive X-ray spectrometer (EDS)
methods. The chloride density was well distributed on the resin surface by X-ray image of
chloride, which also demonstrated that the active sites ( in the resin were completely
-N~Cl)
dispersed. Other chemical compounds for synthesized the polymer resin were also detected.
Although the resin was conducted with washing water for pretreatment, NaOH solution and
acetone, as well as the salts (AI, Si, Ca) used as reaction agents by the suspension method.
were slightly retained in the resin.
The immobilized content of tri-n-butylamine in the resin can be determined by the TGA,
EA and Volhard methods. The polymer backbone decomposed in the temperarure range of
300 to 450 in TGA analysis. Figure 2 shows thennogravimetric curve of weight loss versus
operating temperarure for various resins. The immobilized resin (lab-produced resin, called
mi4-20) was formed in a two-stage degradations, where the ranges of decomposed
temperature for the rwo stage were 160 to 200"C and 350 to 450•c. Although it is tempting to
divide the two stages into two distinctive units, the correlation between quaternary salt
content and weight loss in the first was quantitative. The weight Joss in the first step is equal
to the immobilized amou.nt of the functional group of -N(C.H9h, and the accuracy of
analytical technique was within I 0%. However, the commercial ion-exchange resins ( eg.
Dowex I x2. Amerlite IRA-41O )were revealed in a three-stage process. The decomposed
compounds and temperatures for each decomposition step are: imbibed water (- 10 0 °C},
functional group ( 16Q-300 "C). and polymer backbone (35Q-450 °C).
In addition. the immobilized amount of the flmctional group of -N((.Hq)J in the resin
was determined from the mass fraction of nitrogen by elemental analysis (EA} for C, H. and
N. and from the chloride ion density titrated by the Volhard method. The sequence as
determined by the immobilized coment of tri-n-burylaminc in the resin was TGA > EA >
Volhard. Th.: analyz<·d re, ults of the TGA (or EA) method were based on the elemental
weight, and it reveals the real immobilized content However, the analyzed results of the
Volhard method determined the free chloride ion in the solution by the AgNO, titration
method. The immobilized content of tri-11-butylamine in the resin by the TGA (or EA)
method was independent of the of erosslinkage, and only dependent of the degree of
degre~
the ring substitution. Howc\W. the inunobilizcd content of tri-n-butylamine by the Volhard
method was dependent on both the degree of cross linkages and the degree of ring
substitutions. Titc immobilized contents for the Volhanl method arc about SQ-70% that for
TGA (or EA). The trend of the content variations for microrcsin is larger than that for
Mate11al chroniony prawem autorskirn
