Liquefaction and Gasification of Cellulose with Na₂CO₃ and Ni in Subcritical Water at 350 °C

Abstract

Cellulose decomposition without catalyst, liquefaction with Na2CO3, and gasification with Ni were studied in an autoclave and in a 50-nL microreactor (diamond anvil cell; DAC) coupled with optical and infrared microcopy in subcritical water up to 350 °C. Solid residue was the main product for noncatalytic decomposition of cellulose, which took place mostly under heterogeneous conditions at slow heating rates (0.18 °C/s). Homogeneous conditions could be achieved at a high heating rate of 2.2 °C/s, and solid residue was still the main product, but with different structure and reaction pathways. When Na2CO3 and Ni were used, however, oil and gas were the main products, with little residue being formed. In both catalytic cases, liquefaction and gasification seemed to occur in the aqueous phase after cellulose dissolution. Different reaction mechanisms for homogeneous and heterogeneous environments are proposed. It is expected that by using a high heating rate (e.g., 2.2 °C/s), a homogeneous phase can be achieved and more oil and gas can be produced to avoid solid residue formation.

Understanding the Mechanism of Cypress Liquefaction in Hot-Compressed Water through Characterization of Solid Residues

“…Previous researchers reported that one of the most important types of compounds present in bio-oil obtained from hydrothermal liquefaction of biomass were weak acids such as acetic acid, formic acid, and levulinic acid [5,6,9]. The acids were mainly produced from the decomposition of hemicelluloses and cellulose.…”

“…However, the use of environmentally friendly and low energy-intensive approaches is highly desired. Hot-compressed and super/subcritical water have been widely studied and developed as technologies for the conversion of biomass to clean fuel and valuable chemicals [6,7]. The main advantage of these technologies is that drying process is not required for the conversion of wet biomass, because the water contained in biomass served as solvent as well as reactant [7].…”

“…In recent years, although bio-oils have been analyzed by GC-MS, FT-IR, and NMR in many reports [5,6,8], the degradation of biomass cannot be easily described by detailed chemical reaction pathways with well-defined single reaction steps. This is mainly due to the complexity of the bio-oil components, which include acids, alcohols, aldehydes, ketones, esters, heterocyclic derivatives, and phenolic compounds as products of the degradation of biomass [9].…”

Current and Foreseeable Applications of Supercritical Water for Energy and the Environment

“…The main product was then a solid residue (57 %) without any catalyst. [40] The reaction mechanisms for cellulose under homogeneous and heterogeneous conditions are quite different, and the scheme for these mechanisms proposed in the study by Kozinski and co-workers [40] is reported in Figure 9.…”

“…Mechanisms of cellulose decomposition carried out in a homogeneous or a heterogeneous medium in subcritical water (adapted from Ref. [40]). …”