June 23, 2020
Towards a green future: Efficient laser technique can convert cellulose into biofuel
With the imminent threat of a climate crisis hanging over our heads, it has become crucial to develop efficient alternatives to fossil fuels. One option is to use clean sources of fuels called biofuels, which can be produced from natural sources such as biomass. The plant-based polymer cellulose is the most abundant form of biomass globally and can be converted into raw materials such as glucose and xylose for the production of bioethanol (a type of biofuel). But this process is challenging owing to the molecule's rigid and dense structure, which makes it insoluble in water. Chemists and biotechnologists globally have used conventional techniques like microwave radiation, hydrolysis, and ultrasonication to degrade this polymer, but these processes require extreme conditions and are thus unsustainable.
To this end, in a new study published in Energy & Fuels, a research team in Japan, including Dr. Takayasu Kawasaki (Tokyo University of Science), Dr. Heishun Zen (Institute of Advanced Energy, Kyoto University), Prof Yasushi Hayakawa (Laboratory of Electron Beam Research and Application, Institute of Quantum Science, Nihon University), Prof Toshiaki Ohta (SR Center, Ritsumeikan University), and Prof Koichi Tsukiyama (Tokyo University of Science), developed a novel technique for cellulose degradation. This technique was based on a type of laser called the infrared-free electron laser (IR-FEL), whose wavelength is tunable in the range of 3 to 20 μm. This new method is a promising green technology for the zero-emission degradation of cellulose. Dr. Kawasaki says, "One of the unique features of the IR-FEL is that it can induce a multiphoton absorption for a molecule and can modify the structure of a substance. So far, this technology has been used in the basic fields of physics, chemistry, and medicine, but we wanted to use it to spur advances in environmental technology."
The scientists knew that IR-FEL could be used to perform dissociation reactions on various biomolecules. Cellulose is a biopolymer composed of carbon, oxygen, and hydrogen molecules, which form covalent bonds of varying lengths and angles with each other. The polymer has three infrared bands at the wavelengths of 9.1, 7.2, and 3.5 μm, which correspond to three different bonds: the C-O stretching mode, H-C-O bending mode, and C-H stretching mode, respectively. Based on this, the scientists irradiated powdered cellulose by tuning the wavelength of the IR-FEL to these three wavelengths. Then, they analyzed the products using techniques such as electrospray ionization mass spectrometry and synchrotron radiation infrared microscopy, which revealed that the cellulose molecules had successfully decomposed into glucose and cellobiose (precursor molecules for bioethanol production). Not just this, their products were obtained at high yields, making this process extremely efficient. Dr. Kawasaki explains, "This was the first method in the world to efficiently obtain glucose from cellulose by using an IR-FEL. Because this method does not require harsh reaction conditions such as harmful organic solvents, high temperature, and high pressure, it is superior to other conventional methods."
Apart from generating biofuels, cellulose has several applications—for example, as functional biomaterials in biocompatible cell membranes, antibacterial sheets, and hybrid paper materials. Thus, the new method developed in this study shows promise for various industries, such as healthcare, technology, and engineering. Moreover, Dr. Kawasaki is optimistic that their method is useful to process not only cellulose but also other wood constituents and can prove to be an innovative method for recycling forest biomass. He concludes, "We hope that this study will contribute to the development of an 'oil-free' society."