Light-Driven Depolymerization of Cellulosic Biomass into Hydrocarbons

Abstract

Cellulose and hemicellulose are the main constituents of lignocellulosic biomass. Chemical derivatization of lignocellulosic biomass leads to a range of C5 and C6 organic compounds. These C5 and C6 compounds are valuable precursors (or fine chemicals) for developing sustainable chemical processes. Therefore, depolymerization of cellulose and hemicellulose is essential, leading to the development of various materials that have applications in biomaterial industries. However, most depolymerized processes for cellulose have limited success because of its structural quality: crystallinity, high hydrogen-bond networking, and mild solubility in organic and water. As a result, various chemical treatments, acidic (mineral or solid acids) and photocatalysis, have developed. One of the significant shortcomings of acidic treatment is that the requirement for high temperatures increases the commercial end cost (energy) and hampers product selectivity. For example, a catalyst with prolonged exposure to high temperatures damages the catalyst surface over time; therefore, it cannot be used for iterative cycles. Photocatalysts provide ample application to overcome such flaws as they do not require high temperatures to perform efficient catalysis. Various photocatalysts have shown efficient cellulosic biomass conversion into its C6 and C5 hydrocarbons and the production of hydrogen (as a green energy component). For example, TiO2-based photocatalysts are the most studied for biomass valorization. Herein, we discussed the feasibility of a photocatalyst with application to cellulosic biomass hydrolysis.

Cellulose Functionalization Using N-Heterocyclic-Based Leaving Group Chemistry

“…1 H, 13 C NMR spectroscopy, and two-dimensional (COSY, HSQC, and HMBC) experiments were recorded using a Bruker NMR Spectrometer AV III 400 MHz equipped with a 5 mm liquid-state probe. The chemical shifts were recorded in ppm relative to SiMe 4 .…”

“…The chemical shifts were recorded in ppm relative to SiMe 4 . The 1 H and 13 C NMR data were collected at 400 MHz and 100 MHz for all the compounds, respectively. Deuterated solvents (CDCl 3 , CD 3 OD, (CD 3 ) 2 SO, D 2 O) were used for the NMR spectroscopy.…”

“…1 H NMR (400 MHz, DMSO-d 6 , ppm) δ 8.91-8.87 (m, 6H, 2-pyridinyl H-2 and H-6; 4-pyridinyl H-2 and H-6; 6-pyridinyl H-2 and H-6), 8.50 (m, 3H, 2-pyridinyl H-4; 4-pyridinyl H-4; 6-pyridinyl H-4), 8.05-7.92 (m, 6H, 2-pyridinyl H-3 and H-5; 4-pyridinyl H-3 and H-5; 6-pyridinyl H-3 and H-5). 13…”

“…1 H NMR (400 MHz, CD 3 OD, ppm) δ 7.58 (dt, J = 13.4, 1.7 Hz, 6H, H-4 ′ and H-5 ′ of N-methyl imidazole ring; H-4 ′ and H-2 ′ of imidazole ring), 3.97 (s, 9H, CH 3 -groups of N-methyl imidazole). 13 C NMR (101 MHz, CD 3 OD, ppm) δ 150.16 (triazine, C-2, C-4 and C-6), To the solution of cyanuric chloride (0.5 g, 2.71 mM, 1 equivalent) in acetone solvent (20 mL) in a three-necked 25 mL round bottom flask, nicotinic acid (0.996 g, 8.10 mM, 3 equivalent) was added gradually over a period of 2-3 min, and a less exothermic reaction was observed compared to the pyridine and N-methyl imidazole reactions. After stirring at room temperature overnight, a light-yellow compound precipitated, which was washed with fresh acetone (2 × 10 mL) (m.p.…”

“…The hydrogen bond network and molecular packing impart high crystallinity in cellulosic materials, making them chemically less penetrable. Therefore, cellulose functionalization requires preactivation, either with the help of reactive chemicals (surface-modifying chemicals, such as epoxides, azides, and amines) [ 5 , 6 , 7 , 8 ] or by enforcing other energy-consuming processes (such as photoactivation, hydrothermal, thermomechanical) [ 9 , 10 , 11 , 12 , 13 ]. Due to the availability of a wide range of reactive chemical auxiliaries for cellulose material processing, various commercial-grade cellulose forms have been discovered, including nitrocellulose, sulpho-cellulose, cellulose acetate, and cellulose phosphate.…”