Upgrading Furfurals to Drop-in Biofuels: An Overview

Biomass is a promising feedstock for the next generation drop-in liquid fuels and renewable chemicals, and hence the development of economically viable technologies for the production of commodity and specialty chemicals from sustainable biomass have received significant attention in recent years. Although biomass transformation into drop-in biofuels involves multiple processing steps in which biomass is first depolymerized and converted to furfurals (5-hydroxymethylfurfural, furfural), catalytic upgrading of furfurals is the most important step in achieving end products of the desired fuel properties. Several research papers have been published in the past decade reporting homogeneous and heterogeneous catalytic processes for upgrading furfurals to relevant drop-in fuel candidates such as, 2,5-dimethylfuran (DMF), 2-methylfuran (2-MF), 5-ethoxymethylfurfural (EMF), γ-valerolactone (GVL), ethyl levulinate and long chain hydrocarbon alkanes. Although process technologies for the production and upgrading of some of these fuel compounds have been reviewed, a concise overview on production methodologies for all relevant furan based fuel compounds, including long chain hydrocarbon alkanes, from furfurals is worth publishing for further advancement. This perspective article is aimed at presenting an up to date analysis of the reported catalytic technologies for upgrading furfurals into long chain hydrocarbons with special emphasis on the condensation reactions for producing high carbon chain precursors and catalytic systems for their subsequent deoxygenation to achieve high yield and selectivity in fuel grade hydrocarbons. The current state-of-the-art on upgrading furfurals to DMF, 2-MF and EMF are also analyzed.