102
4.1 Bio-catalytic Routes to Methacrylic Acid
The biotechnological production of MAA has received significantly less attention
compared to the chemical routes. The first report of the biotechnological production
of MAA was published in 1990 [107]. In this report, nitrilase-rich Rhodococcus
rhodochrous J1 cells were used for the biotransformation of methacrylonitrile to
MAA. Under the optimized reaction conditions, 3.02 Mol. MAA was produced in
24 h with a 100% molar conversion yield from methacrylonitrile. A patent filed by
Burgard et al. disclosed the biosynthesis of MAA from renewable sugar feedstock
by metabolically engineered cells or organisms [108]. The optimum yield of MAA
was attained from succinyl-CoA, alpha-ketoglutarate, and acetyl-CoA precursors,
respectively, via 3-hydroxyisobutyrate pathway.
In 2012, Pyo et al. proposed an interesting route for the production of MAA from
2-methyl-1,3-propanediol (2 M1,3PD), an industrial by-product, by the combination of bio- and chemo-catalysis [109]. The oxidative biotransformation of
2 M1,3PD to 3-hydroxy-2-methylpropionic acid (3H2MPA) was investigated by
using resting cells of Gluconobacter oxydans in a bioreactor. After 3 h and at
25–30 °C using 5–10 g substrate and 2.6 g cell (dry weight) per liter, a selectivity of
95% 3H2MPA was obtained with 95–100% conversion of 2 M1,3PD. Gluconobacter
oxydans cells were active for the biotransformation of up to 20 g per L of substrate
in a continuous reactor. The chemical transformation of 3H2MPA to MAA was
achieved by a titanium dioxide catalyst. Over 95% conversion and 95% overall
yield of MAA were obtained at 210 °C. These results seem impressive, but the catalyst stability was not disclosed.
5 Styrene
ST is an industrially important commodity substance, widely used to produce polystyrene plastics, polyesters, protective coatings, resins, rubbers, and other copolymers The worldwide demand for ST has been witnessing high growth mainly in
packaging and construction industries. It was anticipated that most of ST is consumed in automotive and construction as an end-user application. The global market
of ST is expected to reach around 33 million in 2023, increasing around 2% per year
in the period 2017–2023 [110]. About 80% of the world’s ST capacity is based on
ethylbenzene technology. In 2017, over 98% of ethylbenzene was consumed for the
production of ST. About 35% of the total ST is used to produce polystyrene (PS).
The other main end uses of ST include ABS resins, unsaturated polyester resins, SB
latex, and SB rubber. ST is also the key ingredient for expandable polystyrene,
which is expected to grow in the future [111]. Expandable polystyrene has the largest market share in China and Central Europe. Northeast Asia remains the dominant
player. The fastest growing regions are the Middle East and Africa, with anticipated
yearly growth rates of 8% and more than 20%, respectively.
K. Avasthi et al.
4.1 Bio-catalytic Routes to Methacrylic Acid
The biotechnological production of MAA has received significantly less attention
compared to the chemical routes. The first report of the biotechnological production
of MAA was published in 1990 [107]. In this report, nitrilase-rich Rhodococcus
rhodochrous J1 cells were used for the biotransformation of methacrylonitrile to
MAA. Under the optimized reaction conditions, 3.02 Mol. MAA was produced in
24 h with a 100% molar conversion yield from methacrylonitrile. A patent filed by
Burgard et al. disclosed the biosynthesis of MAA from renewable sugar feedstock
by metabolically engineered cells or organisms [108]. The optimum yield of MAA
was attained from succinyl-CoA, alpha-ketoglutarate, and acetyl-CoA precursors,
respectively, via 3-hydroxyisobutyrate pathway.
In 2012, Pyo et al. proposed an interesting route for the production of MAA from
2-methyl-1,3-propanediol (2 M1,3PD), an industrial by-product, by the combination of bio- and chemo-catalysis [109]. The oxidative biotransformation of
2 M1,3PD to 3-hydroxy-2-methylpropionic acid (3H2MPA) was investigated by
using resting cells of Gluconobacter oxydans in a bioreactor. After 3 h and at
25–30 °C using 5–10 g substrate and 2.6 g cell (dry weight) per liter, a selectivity of
95% 3H2MPA was obtained with 95–100% conversion of 2 M1,3PD. Gluconobacter
oxydans cells were active for the biotransformation of up to 20 g per L of substrate
in a continuous reactor. The chemical transformation of 3H2MPA to MAA was
achieved by a titanium dioxide catalyst. Over 95% conversion and 95% overall
yield of MAA were obtained at 210 °C. These results seem impressive, but the catalyst stability was not disclosed.
5 Styrene
ST is an industrially important commodity substance, widely used to produce polystyrene plastics, polyesters, protective coatings, resins, rubbers, and other copolymers The worldwide demand for ST has been witnessing high growth mainly in
packaging and construction industries. It was anticipated that most of ST is consumed in automotive and construction as an end-user application. The global market
of ST is expected to reach around 33 million in 2023, increasing around 2% per year
in the period 2017–2023 [110]. About 80% of the world’s ST capacity is based on
ethylbenzene technology. In 2017, over 98% of ethylbenzene was consumed for the
production of ST. About 35% of the total ST is used to produce polystyrene (PS).
The other main end uses of ST include ABS resins, unsaturated polyester resins, SB
latex, and SB rubber. ST is also the key ingredient for expandable polystyrene,
which is expected to grow in the future [111]. Expandable polystyrene has the largest market share in China and Central Europe. Northeast Asia remains the dominant
player. The fastest growing regions are the Middle East and Africa, with anticipated
yearly growth rates of 8% and more than 20%, respectively.
K. Avasthi et al.