Topics in Current Chemistry (2019) 377:1
1 3
and the process was then translated to continuous flow conditions. The flow reactor
appeared to be more efficient than the batch system for performing the single‑ or
double‑condensation reaction, as reaction times were reduced from 2–4 h to 20 min,
and yet yields of 87–91% were obtained. The catalyst could be removed down‑
stream via straightforward liquid–liquid extraction. The scope of the methodology
was finally extended to single and double aldol condensation with acyclic symmetri‑
cal and unsymmetrical ketones as well as cyclic ketones, giving the corresponding
enones 68 and 69 in yields of 72–92% [118].
5 Conclusion and Perspectives
Intense research is currently being directed into assessing continuous‑flow technol‑
ogy for the upgrading of biobased platforms. Given the steady increase in relevant
reports in both the primary and the patent literature, we can foresee that this field of
research will grow rapidly in the near future. Future developments will most likely
rely on two of the main aspects of flow chemistry: the ability to explore new pro‑
cess windows and the goal of facilitating seamless scalability while maintaining a
small global footprint for the process. There are, however, still major challenges that
must be dealt with in this research area. These challenges concern both the specific
chemistry utilized to upgrade biobased platforms and the development of appropri‑
ate continuous flow technologies for these processes. Upgrading biobased platforms
at the industrial level is economically attractive as long as the process conditions are
robust enough to sustain long periods of operation with minimal maintenance and
the process ensures low waste generation and straightforward downstream purifica‑
tion. Robust process conditions rely on the development of cheap, readily available,
and selective catalysts that are employed at lower temperatures to prevent coking
and/or deactivation. Also, since biobased platforms inherently suffer from variable
quality, processes to upgrade them must be relatively accommodating. Low waste
generation not only relates to the use of additives and the reaction selectivity but
also to the use of solvents. Since most biobased platform molecules are either vis‑
cous liquids or solids, successfully using them for commercial applications under
continuous conditions requires the inclusion of solvents and/or additives to improve
processability in most instances, thus negatively impacting the overall footprint of
the process. Recent developments in the integration of innovative downstream tech‑
nologies such as membrane separation or pervaporation will likely support the fur‑
ther development of this research area.
Acknowledgements The authors acknowledge the European Regional Development Fund (ERDF)
and Wallonia for their financial support within the framework of the program “Wallonie‑2020.EU”
(INTENSE4CHEM, project no. 699993‑152208).
References
1. Werpy T, Petersen G (2004) Top value added chemicals from biomass, vol I. Results of screening
for potential candidates from sugars and synthesis gas. US Department of Energy, Oak Ridge
140
Reprinted from the journal
1 3
and the process was then translated to continuous flow conditions. The flow reactor
appeared to be more efficient than the batch system for performing the single‑ or
double‑condensation reaction, as reaction times were reduced from 2–4 h to 20 min,
and yet yields of 87–91% were obtained. The catalyst could be removed down‑
stream via straightforward liquid–liquid extraction. The scope of the methodology
was finally extended to single and double aldol condensation with acyclic symmetri‑
cal and unsymmetrical ketones as well as cyclic ketones, giving the corresponding
enones 68 and 69 in yields of 72–92% [118].
5 Conclusion and Perspectives
Intense research is currently being directed into assessing continuous‑flow technol‑
ogy for the upgrading of biobased platforms. Given the steady increase in relevant
reports in both the primary and the patent literature, we can foresee that this field of
research will grow rapidly in the near future. Future developments will most likely
rely on two of the main aspects of flow chemistry: the ability to explore new pro‑
cess windows and the goal of facilitating seamless scalability while maintaining a
small global footprint for the process. There are, however, still major challenges that
must be dealt with in this research area. These challenges concern both the specific
chemistry utilized to upgrade biobased platforms and the development of appropri‑
ate continuous flow technologies for these processes. Upgrading biobased platforms
at the industrial level is economically attractive as long as the process conditions are
robust enough to sustain long periods of operation with minimal maintenance and
the process ensures low waste generation and straightforward downstream purifica‑
tion. Robust process conditions rely on the development of cheap, readily available,
and selective catalysts that are employed at lower temperatures to prevent coking
and/or deactivation. Also, since biobased platforms inherently suffer from variable
quality, processes to upgrade them must be relatively accommodating. Low waste
generation not only relates to the use of additives and the reaction selectivity but
also to the use of solvents. Since most biobased platform molecules are either vis‑
cous liquids or solids, successfully using them for commercial applications under
continuous conditions requires the inclusion of solvents and/or additives to improve
processability in most instances, thus negatively impacting the overall footprint of
the process. Recent developments in the integration of innovative downstream tech‑
nologies such as membrane separation or pervaporation will likely support the fur‑
ther development of this research area.
Acknowledgements The authors acknowledge the European Regional Development Fund (ERDF)
and Wallonia for their financial support within the framework of the program “Wallonie‑2020.EU”
(INTENSE4CHEM, project no. 699993‑152208).
References
1. Werpy T, Petersen G (2004) Top value added chemicals from biomass, vol I. Results of screening
for potential candidates from sugars and synthesis gas. US Department of Energy, Oak Ridge
140
Reprinted from the journal