557
prepared by three routes, by reacting glycerol with urea or dimethyl carbonate or by
directly reacting it with carbon dioxide under supercritical conditions [322].
Transesterification of glycerol with ethylene carbonate over basic oxide catalysts
(MgO, CaO) and mixed metal oxides of Al-Mg, Li-Al and Al-Ca-MO with hydrotalcite structure at 35 °C results in high conversion and >98% selectivity to GC
[347]. Ionic liquid catalysts like 1-n-butyl-3-methylimidazolium-2-carboxylate
could yield 93% GC in 5 h. With the ionic liquid 1-ethyl-3-methylimidazolium
acetate as catalyst, glycerol conversion of 93.5%, selectivity of 94.9% and GC yield
of 88.7% were obtained at optimum conditions of 120 °C, 0.5 mol.% catalyst loading, diethyl carbonate/glycerol molar ratio of 2 and reaction time of 2 h [348]. There
was no deactivation even after the catalyst was used three times, which was attributed to excellent interaction between the ionic liquid and the reactant.
1,3-Propane diol is a versatile chemical intermediate and highly useful monomer
for the production of polyesters (polytetramethylene terephthalate, PTT), polyethers, polyurethanes and many other value-added chemicals [322]. Hydrogenolysis
of C-O bond in glycerol results in the formation of 1,2-propane diol (1,2-PDO) and
1,3-propane diol (1,3-PDO), with the selectivity for specific diol determined by the
type of catalyst and the reaction conditions adopted. Hydrogenolysis, which involves
dehydration as the first step, can result in the formation of hydroxy acetone, which
on further hydrogenation leads to 1,2-PDO. If, on the other hand, the dehydration
leads to the formation of 3-hydroxy propanal, its further hydrogenation results in
1.3-PDO [349]. Since formation of hydroxy acetone is favoured thermodynamically, 1,2-PDO is formed with high selectivity on many types of catalysts, noble
metal, non-noble metal or noble metals in combination with acidic/basic components [98–102]. However, 1,3-PDO with high selectivity of 66% is observed only
with noble metal- mixed oxide catalysts, like Pt-WO x /AlOOH with moderated acidity [100]. Though a large number of other catalyst systems, mono- and bimetallic
catalysts with different supports, have been explored [322, 349], maximum 1,3PDO selectivity of 52% could be realized. On Ir-ReO x /SiO 2 catalyst, Nakagawa
et al. [349] could observe 1,3-PDO selectivity of 65% but at lower glycerol conversion of 22.6%. Thus, achieving high conversion of glycerol with high selectivity for
1,3-PDO on heterogeneous catalysts remains a challenge. Biochemical conversion
of glycerol to 1,3-PDO, using different microorganisms like Bacillus, Lactobacillus,
Klebsiella, Citrobacter, Ilyobacter, Enterobacter and Clostridium, in batch and
continuous mode processes, has been reported [350].
Glycerol as biochemical feedstock has gained prominence when it replaced glucose as the raw material for the enzymatic conversion to 1,3-PDO [21]. With glycerol as the feedstock, 1,3-PDO yields approaching to the theoretical yield (g of
1,3-PDO per g of feed) of 67% could be achieved with genetically modified
Clostridium acetobutylicum with concentrations of over 84 g L
−1
at a rate of
1.7 g L
−1
h
−1
. In contrast, with glucose as feedstock, the yield was 30–40% only
[351, 352]. Fermentation of crude glycerol with Clostridium acetobutylicum [353]
and Klebsiella pneumoniae [354] resulted in the same level of PDO concentration
and productivity realized with purified glycerol, thus paving way for the utilization
of crude glycol as economically viable bio-resource for the production of 1,3-PDO.
Catalytic Conversion of Alcohols into Value-Added Products
prepared by three routes, by reacting glycerol with urea or dimethyl carbonate or by
directly reacting it with carbon dioxide under supercritical conditions [322].
Transesterification of glycerol with ethylene carbonate over basic oxide catalysts
(MgO, CaO) and mixed metal oxides of Al-Mg, Li-Al and Al-Ca-MO with hydrotalcite structure at 35 °C results in high conversion and >98% selectivity to GC
[347]. Ionic liquid catalysts like 1-n-butyl-3-methylimidazolium-2-carboxylate
could yield 93% GC in 5 h. With the ionic liquid 1-ethyl-3-methylimidazolium
acetate as catalyst, glycerol conversion of 93.5%, selectivity of 94.9% and GC yield
of 88.7% were obtained at optimum conditions of 120 °C, 0.5 mol.% catalyst loading, diethyl carbonate/glycerol molar ratio of 2 and reaction time of 2 h [348]. There
was no deactivation even after the catalyst was used three times, which was attributed to excellent interaction between the ionic liquid and the reactant.
1,3-Propane diol is a versatile chemical intermediate and highly useful monomer
for the production of polyesters (polytetramethylene terephthalate, PTT), polyethers, polyurethanes and many other value-added chemicals [322]. Hydrogenolysis
of C-O bond in glycerol results in the formation of 1,2-propane diol (1,2-PDO) and
1,3-propane diol (1,3-PDO), with the selectivity for specific diol determined by the
type of catalyst and the reaction conditions adopted. Hydrogenolysis, which involves
dehydration as the first step, can result in the formation of hydroxy acetone, which
on further hydrogenation leads to 1,2-PDO. If, on the other hand, the dehydration
leads to the formation of 3-hydroxy propanal, its further hydrogenation results in
1.3-PDO [349]. Since formation of hydroxy acetone is favoured thermodynamically, 1,2-PDO is formed with high selectivity on many types of catalysts, noble
metal, non-noble metal or noble metals in combination with acidic/basic components [98–102]. However, 1,3-PDO with high selectivity of 66% is observed only
with noble metal- mixed oxide catalysts, like Pt-WO x /AlOOH with moderated acidity [100]. Though a large number of other catalyst systems, mono- and bimetallic
catalysts with different supports, have been explored [322, 349], maximum 1,3PDO selectivity of 52% could be realized. On Ir-ReO x /SiO 2 catalyst, Nakagawa
et al. [349] could observe 1,3-PDO selectivity of 65% but at lower glycerol conversion of 22.6%. Thus, achieving high conversion of glycerol with high selectivity for
1,3-PDO on heterogeneous catalysts remains a challenge. Biochemical conversion
of glycerol to 1,3-PDO, using different microorganisms like Bacillus, Lactobacillus,
Klebsiella, Citrobacter, Ilyobacter, Enterobacter and Clostridium, in batch and
continuous mode processes, has been reported [350].
Glycerol as biochemical feedstock has gained prominence when it replaced glucose as the raw material for the enzymatic conversion to 1,3-PDO [21]. With glycerol as the feedstock, 1,3-PDO yields approaching to the theoretical yield (g of
1,3-PDO per g of feed) of 67% could be achieved with genetically modified
Clostridium acetobutylicum with concentrations of over 84 g L
−1
at a rate of
1.7 g L
−1
h
−1
. In contrast, with glucose as feedstock, the yield was 30–40% only
[351, 352]. Fermentation of crude glycerol with Clostridium acetobutylicum [353]
and Klebsiella pneumoniae [354] resulted in the same level of PDO concentration
and productivity realized with purified glycerol, thus paving way for the utilization
of crude glycol as economically viable bio-resource for the production of 1,3-PDO.
Catalytic Conversion of Alcohols into Value-Added Products