180
In the last several years, tremendous efforts have been made for developing propane ammoxidation catalyst system and various multicomponent catalyst systems
[128–130] have been explored. Mitsubishi/Asahi catalyst system based on
MoV(Nb,Ta)(Te,Sb)O can give about 65% acrylonitrile yield. The catalytic system
contains two distinct phases, M1- the paraffin-activating phase and M2- the propylene mop-up phase which acts synergistically. The active sites are isolated from each
other by Nb- or Ta-containing pentagonal bipyramids and different elements offer
unique catalytic functions to synergistically promote selectivity for desired product.
The olefin- and paraffin-based ammoxidation reactions although relatively mature
still present challenges to the physical, inorganic, and synthetic chemist, to further
explore the development of new materials. It is also of scientific curiosity to investigate the nature of the catalytic active sites capable of the complex molecular transformations required for the ammoxidation process. It would be also interesting to
discover new and still more effective compositions for making acetonitrile production with 100% yield as per the maximum theoretical thermodynamic limit [104].
Fe-Bi/SiO 2 -based catalyst system is examined at 500 °C for propane ammoxidation
reaction which showed 49% yield of acrylonitrile at 36% propane conversion [131].
However, such acrylonitrile yield is not sufficient to replace propylene ammoxidation method as far as techno-commercial feasibility is concerned.
Very recently, a novel method of acrylonitrile production from renewable feedstock such as 3-hydroxypropanoate (ethyl 3-HP), which can be made from
3-hydroxypropionic acid (3-HP), has been established [132]. 3-HP can be produced
from sugars catalyzed by the selective microbes. The process is based on two steps
first being the dehydration of ethyl 3-HP (at 260 °C) over TiO 2 catalyst to ethyl
acrylate followed by nitrilation with ammonia to ACN over TiO 2 catalyst at
315 °C. Another promising renewable route is based on glycerol dehydration to
propylene followed by ammoxidation of propylene to ACN. Thrust for renewable
acrylonitrile from bio-based alternative sources will increase to avoid petroleumbased propylene price volatility and also for reducing the carbon footprint of the
existing ACN process.
4.3 Acrylic Acid
4.3.1 Chemical and Technical Aspects of Acrylic Acid
Acrylic acid (CH 2 =CHCOOH) is one of the simplest unsaturated carboxylic acids.
It has a unique chemical structure comprising of a vinyl group connected to a carboxylic acid. Due to the presence of C=C and C=O bond conjugation, acrylic acid
can undergo both electrophilic addition and nucleophilic substitution reactions.
Such a conjugated C–C double bond can stabilize free radical and thus undergo free
radical polymerization reactions in presence of a suitable initiator. The carboxyl
group later can allow nucleophilic displacement reactions as well as esterification
reactions to incorporate the desired functional group into the polymer moiety. Crude
C. Samanta and R. K. Das
In the last several years, tremendous efforts have been made for developing propane ammoxidation catalyst system and various multicomponent catalyst systems
[128–130] have been explored. Mitsubishi/Asahi catalyst system based on
MoV(Nb,Ta)(Te,Sb)O can give about 65% acrylonitrile yield. The catalytic system
contains two distinct phases, M1- the paraffin-activating phase and M2- the propylene mop-up phase which acts synergistically. The active sites are isolated from each
other by Nb- or Ta-containing pentagonal bipyramids and different elements offer
unique catalytic functions to synergistically promote selectivity for desired product.
The olefin- and paraffin-based ammoxidation reactions although relatively mature
still present challenges to the physical, inorganic, and synthetic chemist, to further
explore the development of new materials. It is also of scientific curiosity to investigate the nature of the catalytic active sites capable of the complex molecular transformations required for the ammoxidation process. It would be also interesting to
discover new and still more effective compositions for making acetonitrile production with 100% yield as per the maximum theoretical thermodynamic limit [104].
Fe-Bi/SiO 2 -based catalyst system is examined at 500 °C for propane ammoxidation
reaction which showed 49% yield of acrylonitrile at 36% propane conversion [131].
However, such acrylonitrile yield is not sufficient to replace propylene ammoxidation method as far as techno-commercial feasibility is concerned.
Very recently, a novel method of acrylonitrile production from renewable feedstock such as 3-hydroxypropanoate (ethyl 3-HP), which can be made from
3-hydroxypropionic acid (3-HP), has been established [132]. 3-HP can be produced
from sugars catalyzed by the selective microbes. The process is based on two steps
first being the dehydration of ethyl 3-HP (at 260 °C) over TiO 2 catalyst to ethyl
acrylate followed by nitrilation with ammonia to ACN over TiO 2 catalyst at
315 °C. Another promising renewable route is based on glycerol dehydration to
propylene followed by ammoxidation of propylene to ACN. Thrust for renewable
acrylonitrile from bio-based alternative sources will increase to avoid petroleumbased propylene price volatility and also for reducing the carbon footprint of the
existing ACN process.
4.3 Acrylic Acid
4.3.1 Chemical and Technical Aspects of Acrylic Acid
Acrylic acid (CH 2 =CHCOOH) is one of the simplest unsaturated carboxylic acids.
It has a unique chemical structure comprising of a vinyl group connected to a carboxylic acid. Due to the presence of C=C and C=O bond conjugation, acrylic acid
can undergo both electrophilic addition and nucleophilic substitution reactions.
Such a conjugated C–C double bond can stabilize free radical and thus undergo free
radical polymerization reactions in presence of a suitable initiator. The carboxyl
group later can allow nucleophilic displacement reactions as well as esterification
reactions to incorporate the desired functional group into the polymer moiety. Crude
C. Samanta and R. K. Das