464
pyruvaldehyde, pyruvic acid, lactic acid, acrylic acid, tartronic acid and mesoxalic
acid [15–18]. Usual glycerol oxidation typically initiates with two types of reactions: dehydration (i.e. cleavages of C-H and C-O bonds) succeeded by additional
dehydrogenation and oxidation (i.e. formation of C-H and C-O bonds) and dehydrogenation (i.e. cleavages of C-H and O-H bonds). The pathway of C-O bond cleavage
differentiates the initial dehydration and dehydrogenation. The C-O bond cleavage
requires reaction temperature 300–400 °C for dehydration [19, 20] and <100 °C for
dehydrogenation [21, 22].
2.1 Glycerol Oxidation via Dehydration
In an economic viewpoint, glycerol conversion via dehydration becomes more
attractive since more than 60% oxygen content of glycerol can be simply removed
without hydrogen consumption under mild condition [23]. The existence of primary
and secondary hydroxyl groups with different reactivity induces the selectivity
problems in glycerol conversion. Commercial oxidation processes of glycerol using
hydrogen peroxide as an oxidant produce dihydroxyacetone and glycerol aldehyde
[24, 25] as an intermediate for serine and glyceric acid [26, 27] in liquid phase. To
conquer the reactivity/selectivity problem, it is better to synthesize glycerol derivatives, e.g. esters or acetals, which allow the subsequent oxidation of a particular type
of carbon atom only [28].
Acrylic acid, the simplest unsaturated carboxylic acid, is a monomer for polyacrylic acid which is widely used for production of hygiene products like diaper,
elastomers, plastics, paints, adhesives and coatings [29]. Using biomass resources
like glycerol for production of acrylic acid (via gas phase or liquid phase) has been
extensively investigated. A wide category of solid acid catalysts, such as zeolites,
metal oxides, phosphates and heteropolyacids, have been extensively evaluated for
glycerol dehydration [30]. Those acid catalysts failed to meet the industry demands
since they suffered from heavy coke deposition leading to fast deactivation.
2.2 Glycerol Oxidation into Acrylic Acid via Allyl Alcohol
as an Intermediate
Recently, some reports claimed that acrylic acid can be prepared from glycerol via
two steps: deoxydehydration (DODH) of glycerol to allyl alcohol followed by
selective oxidation of obtained allyl alcohol into acrylic acid. Recently, Lee’s group
reported that a high yield of ~87% of acrylic acid can be synthesized from glycerol
by using Au-deposited CeO 2 [31, 32]. They studied the effects of different morphologies of CeO 2 (like rods, cubes and octahedra) as support as well as the particle
size of the Au as active phase. The liquid phase DODH of glycerol is carried out
K. Bhaduri et al.
pyruvaldehyde, pyruvic acid, lactic acid, acrylic acid, tartronic acid and mesoxalic
acid [15–18]. Usual glycerol oxidation typically initiates with two types of reactions: dehydration (i.e. cleavages of C-H and C-O bonds) succeeded by additional
dehydrogenation and oxidation (i.e. formation of C-H and C-O bonds) and dehydrogenation (i.e. cleavages of C-H and O-H bonds). The pathway of C-O bond cleavage
differentiates the initial dehydration and dehydrogenation. The C-O bond cleavage
requires reaction temperature 300–400 °C for dehydration [19, 20] and <100 °C for
dehydrogenation [21, 22].
2.1 Glycerol Oxidation via Dehydration
In an economic viewpoint, glycerol conversion via dehydration becomes more
attractive since more than 60% oxygen content of glycerol can be simply removed
without hydrogen consumption under mild condition [23]. The existence of primary
and secondary hydroxyl groups with different reactivity induces the selectivity
problems in glycerol conversion. Commercial oxidation processes of glycerol using
hydrogen peroxide as an oxidant produce dihydroxyacetone and glycerol aldehyde
[24, 25] as an intermediate for serine and glyceric acid [26, 27] in liquid phase. To
conquer the reactivity/selectivity problem, it is better to synthesize glycerol derivatives, e.g. esters or acetals, which allow the subsequent oxidation of a particular type
of carbon atom only [28].
Acrylic acid, the simplest unsaturated carboxylic acid, is a monomer for polyacrylic acid which is widely used for production of hygiene products like diaper,
elastomers, plastics, paints, adhesives and coatings [29]. Using biomass resources
like glycerol for production of acrylic acid (via gas phase or liquid phase) has been
extensively investigated. A wide category of solid acid catalysts, such as zeolites,
metal oxides, phosphates and heteropolyacids, have been extensively evaluated for
glycerol dehydration [30]. Those acid catalysts failed to meet the industry demands
since they suffered from heavy coke deposition leading to fast deactivation.
2.2 Glycerol Oxidation into Acrylic Acid via Allyl Alcohol
as an Intermediate
Recently, some reports claimed that acrylic acid can be prepared from glycerol via
two steps: deoxydehydration (DODH) of glycerol to allyl alcohol followed by
selective oxidation of obtained allyl alcohol into acrylic acid. Recently, Lee’s group
reported that a high yield of ~87% of acrylic acid can be synthesized from glycerol
by using Au-deposited CeO 2 [31, 32]. They studied the effects of different morphologies of CeO 2 (like rods, cubes and octahedra) as support as well as the particle
size of the Au as active phase. The liquid phase DODH of glycerol is carried out
K. Bhaduri et al.