568
catalysts with higher selectivity and stability and improvements in overall process efficiency.
• Though the process for the conversion of ethanol to 1,3-butadiene (BD) has successfully met all the criteria for sustainability, the process economics is not
favourable since BD production rate (grams of BD produced per hour per unit
weight of the catalyst) is to be improved, which requires the development of
superior catalysts [200, 205, 207, 229]. In this respect, 90% conversion of ethanol with 70% selectivity and high productivity rate of 0.4 g BD/g of catalyst/hr.
on Ag/ZrO 2 -SiO 2 reported by Dagle et al. [400] is noteworthy.
• Development of single-pot conversion processes, especially for versatile chemicals like levulinic acid/alkyl levulinates [364, 365], GVL and other furan derivatives, fuels and fuel additives [357], which utilize biomass intermediates and neat
platform chemicals as raw materials, is the right approach. Synthesis of these
chemicals directly from lignocellulosic biomass, though challenging, would be
desirable. Designing multi-functional catalysts with appropriate active sites and
a re-look on separation and purification steps are the key issues.
• Processes based on aldol condensation of alcohols with aldehydes and ketones
and self- and cross-aldol condensation of alcohols (Guerbet alcohols) are highly
important steps in C-C bond formation [27, 241] and synthesis of highly useful
fuels and chemicals and, in general, in many biomass conversion processes. Dual
functional catalysts involving metal (for dehydrogenation and hydrogenation)
and acid-base sites (for aldol condensation) are required. There are still questions
regarding the role of the key intermediates in these reactions, and the exact nature
of the acid-base sites responsible for generation of critical intermediates is yet to
be established. Various supports like hydroxyapatite, hydrotalcites, γ-Al 2 O 3 and
MgO with several modifiers and reducible of the metal ions (Ni. Cu, Ru, Pd)
have been explored for the conversion of ethanol to butanol [73–78]. However,
the mode of functioning of the catalysts is not clear, though the general consensus is that low ratio of acid-base sites of the support may favour this reaction.
Similarly, the criterion to be used for identifying the ease of reducibility of metal
ions is yet to specified [401].
• Several promising processes have been developed for the conversion of alcohols
to jet fuels and middle distillates/diesel [241, 282]. As the demand for these types
of fuels is set to increase, the future research focus in this area would be towards
a better understanding of oligomerization and aldolization chemistries that constitute the backbone for these routes. Studies in these and related areas would be
helpful in improving the process efficiency.
11 Summary and Conclusions
Tremendous potential of biomass as feedstock for fuels and chemicals was visualized as early as 1981 by Lipinsky [392], when the biomass conversion processes
were at primitive stage.
R. Vinayagamoorthi et al.
catalysts with higher selectivity and stability and improvements in overall process efficiency.
• Though the process for the conversion of ethanol to 1,3-butadiene (BD) has successfully met all the criteria for sustainability, the process economics is not
favourable since BD production rate (grams of BD produced per hour per unit
weight of the catalyst) is to be improved, which requires the development of
superior catalysts [200, 205, 207, 229]. In this respect, 90% conversion of ethanol with 70% selectivity and high productivity rate of 0.4 g BD/g of catalyst/hr.
on Ag/ZrO 2 -SiO 2 reported by Dagle et al. [400] is noteworthy.
• Development of single-pot conversion processes, especially for versatile chemicals like levulinic acid/alkyl levulinates [364, 365], GVL and other furan derivatives, fuels and fuel additives [357], which utilize biomass intermediates and neat
platform chemicals as raw materials, is the right approach. Synthesis of these
chemicals directly from lignocellulosic biomass, though challenging, would be
desirable. Designing multi-functional catalysts with appropriate active sites and
a re-look on separation and purification steps are the key issues.
• Processes based on aldol condensation of alcohols with aldehydes and ketones
and self- and cross-aldol condensation of alcohols (Guerbet alcohols) are highly
important steps in C-C bond formation [27, 241] and synthesis of highly useful
fuels and chemicals and, in general, in many biomass conversion processes. Dual
functional catalysts involving metal (for dehydrogenation and hydrogenation)
and acid-base sites (for aldol condensation) are required. There are still questions
regarding the role of the key intermediates in these reactions, and the exact nature
of the acid-base sites responsible for generation of critical intermediates is yet to
be established. Various supports like hydroxyapatite, hydrotalcites, γ-Al 2 O 3 and
MgO with several modifiers and reducible of the metal ions (Ni. Cu, Ru, Pd)
have been explored for the conversion of ethanol to butanol [73–78]. However,
the mode of functioning of the catalysts is not clear, though the general consensus is that low ratio of acid-base sites of the support may favour this reaction.
Similarly, the criterion to be used for identifying the ease of reducibility of metal
ions is yet to specified [401].
• Several promising processes have been developed for the conversion of alcohols
to jet fuels and middle distillates/diesel [241, 282]. As the demand for these types
of fuels is set to increase, the future research focus in this area would be towards
a better understanding of oligomerization and aldolization chemistries that constitute the backbone for these routes. Studies in these and related areas would be
helpful in improving the process efficiency.
11 Summary and Conclusions
Tremendous potential of biomass as feedstock for fuels and chemicals was visualized as early as 1981 by Lipinsky [392], when the biomass conversion processes
were at primitive stage.
R. Vinayagamoorthi et al.