Producing Liquid Fuels from Wood: An Introduction

Producing a proper wood-derived biofuel follows a three-step recipe. One, grow trees. Two, break down wood from the trees into its components. Three, use these components to produce biofuels. Unfortunately, this simple recipe does not equate to “technologically doable and economically viable” in the current market place. That said, dozens of firms are pursuing projects in the US to produce liquid transportation fuels from wood raw materials. Forisk teamed with the Schiamberg Group to evaluate all US-based projects and technology pathways under consideration. Below we share an introductory overview from this research:

Three general routes exist for converting wood biomass to transportation fuels. The first involves exposing wood to high heat in the presence of limited amounts of oxygen or steam – in a process called gasification – to produce a gas mixture called synthesis gas (commonly known as “syngas”) which can be converted to liquid fuels such as ethanol or diesel. The second route involves breaking down cellulose and hemicellulose to constituent sugars using acids and enzymes and then using microbes to ferment the sugars to ethanol. The third route involves heating wood in the absence of oxygen – in a process called pyrolysis – to produce a complex liquid called bio-oil. The bio-oil can then be stabilized before upgrading and refining to diesel, gasoline or associated blend products.

Complications arise because the chemical properties of wood differ from other feedstock types under development or in use for liquid fuels production. Wood bears a biochemical resemblance to other lignocellulosic feedstock types such as switchgrass or corn stover.  However, woody biomass has a higher density, lower ash content, higher lignin content, and lower pentose content. The density and ash content are advantages for transportation when comparing woody biomass to agricultural biomass. However, the higher levels of lignin in woody biomass compared to agricultural biomass make breakdown of woody biomass by microbes or enzymes more difficult than for agricultural biomass.  These challenges have encouraged wood biofuel firms to pursue multiple end product markets.