PROSPECTS ON PHOTOBIOREFINERY

Very recently, Prof. Dr. K. Faungnawakij and his research group have summarized a mini review report on an emerging renewable technique of Photobiorefinery. This is one of the beyond technique of Artificial Photosynthesis (AP) [1].

Despite great promises, AP technologies for solar H2 production and CO2 reduction are far uncompetitive to other promising technologies at the current stage.

However, despite an enormous effort, time, and budget paid on AP-related researches throughout several decades, AP technologies have struggled to strive beyond laboratory demonstration except a very few exceptions [2]. This bitter reality makes the translation of this excellent science to practical application questionable [3].

Technoeconomic analysis shows that without achieving the aggressive technology targets, this technology will not be commercially viable. This has directed the research community towards the development of highly efficient yet expensive devices.

While tremendous progress has been demonstrated, the poor profitability prospect originating from low profit margins, high energy requirement, and impractical engineering remains unaddressed. It is time to step back and redefine the alternative targets which are closer to profitable investment, rather than a specific locking-in technology with insignificant returns.

Recently, photocatalytic biorefinery, herein defined as photobiorefinery, has emerged as a promising approach to apply the recently-advanced AP knowledge for near practical or industrial applications.

Biorefinery, an analog to petroleum refinery, is the processing of biomass into a multitude of commercializable bio-based chemicals, materials, fuels and energy [4].

Photobiorefinery has emerged as one of the most promising approaches to apply the AP knowledge for near practical industrial applications.

Figure 1. Photobiorefinery concept for the conversion of biomass to sustainable chemicals. Starting with plants, the lignocellulosic biomass (lignin, cellulose, and hemicellulose) and triglyceride are obtained as raw materials for photocatalytic conversion to produce renewable chemicals and fuels. The chemicals can be recycled or undergone combustion or decomposition processes to CO2. The CO2 can be utilized directly via artificial photosynthesis (AP) or returned to plants via natural photosynthesis [1].

If we could use the ubiquitous sunlight to convert this renewable resource into fuels or value-added chemicals and reduce the biomass waste burnt and greenhouse gases, the energy and environmental problems could be simultaneously solved, similar to the ultimate goals of AP. The concept of photobiorefinery depicted in Figure 1 shows that the typical feedstocks for this process consist of lignocellulosic biomass (lignin, cellulose, and hemicellulose) and triglyceride. Lignin can be converted to valuable aromatic compounds.

 The Following Merits of Photobiorefinery:

Photobiorefinery requires much less activation energy than photocatalytic water splitting even though both processes are endergonic (ΔG_RT>0) [5].

The oxidation potential of biomass and its derivatives is −0.2–0.26 V vs reversible hydrogen electrode (RHE), much more facile compared to 1.23 V vs RHE of water oxidation [6].

Thus, biomass and its derivatives can serve as scavengers for low energy photogenerated holes, reducing the overall potential requirement for solar H₂ production or CO₂ reduction, and producing valuable chemicals simultaneously [7].

Under the same reaction condition, photobiorefinery generally has higher quantum yield (QY) compared to the classical AP approach.

The greatest challenge lies in the mechanistic understanding of this complex chemistry and overcoming the slow kinetics. Using model molecules and utilizing systematic investigations similar to the approach inspired from CO₂ reduction literature, as well as establishing a standardized protocol similar to those done in solar water splitting field likely accelerate the progress in photocatalytic biomass valorization towards commercialization.

References

[1]. T. Butburee, P. Chakthranont, C. Phawa, K. Faungnawakij, ChemCatChem 2020, 12, 1873–1890

[2]. Y. Goto, T. Hisatomi, Q. Wang, T. Higashi, K. Ishikiriyama, T. Maeda, Y. Sakata, S. Okunaka, H. Tokudome, M. Katayama, S. Akiyama, H. Nishiyama, Y. Inoue, T. Takewaki, T. Setoyama, T. Minegishi, T. Takata, T. Yamada, K. Domen, Joule 2018, 2, 509.

[3]. M. Antonietti, A. Savateev, Chem. Rec. 2018, 18, 969.

[4]. E. de Jong, A. Higson, P. Walsh, M. Wellisch, IEA Bioenergy, Task42 Biorefinery 2012, 34.

[5]. T. P. A. Ruberu, N. C. Nelson, I. I. Slowing, J. Vela, J. Phy. Chem. Lett. 2012, 3, 2798.

[6]. Z. Wu, J. Wang, Z. Zhou, G. Zhao, J. Mater. Chem. A 2017, 5, 12407.

[7]. X. Lu, S. Xie, H. Yang, Y. Tong, H. Ji, Chem. Soc. Rev. 2014, 43, 7581.

 Blog Written By

Dr. A. S. GANESHRAJA

National College

Thiruchirappalli, Tamilnadu, India

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