(424d) A Low Energy Separation Process to Isolate Xylose from Aqueous Hydrolyzate Streams

Water removal is a key process step in a majority of process industries including biomass conversion and biofuels industry. Unit operations such as evaporation, concentration, membrane filtration, etc., are widely used for water removal; however, they contribute significantly to the overall processing cost to produce biofuels primarily due to their high energy requirement. For example, it takes 9,274 BTU to remove 1 gal of water from 70 F via evaporation. Sugar extraction from biomass and its conversion to bioproducts via fermentation is typically a water based process – requiring large volumes of water removal to produce the products. Moreover, the products resulting from fermentation are typically low energy density fuel alcohols, organic acids, etc. If the sugars extracted can be made available in dry solid form, then the sugars can be converted to high energy density biofuels and bio-hydrocarbons via chemical synthesis. Conn Center at University of Louisville developed a highly energy efficient separation process for hemicellulose (C5) based sugars, specifically xylose, which is conducted under ambient conditions and delivers xylose in a dry form from an aqueous hydrolyzate stream containing xylose.

A boron chelation chemistry is used in this xylose isolation process. This chemistry and the associated methodology can be extended to the recovery of anhydrosugars. The current commercially practiced xylose separation process involves complex chromatographic separation and high-energy evaporation steps and generates large volumes of waste streams. The boron chelation chemistry can clearly lead to process intensification: it is done under ambient conditions, consists of fewer number of process steps, and leads to minimal waste generation. The isolation scheme also includes recovery of boron for reuse in the front end of the process.