Purification of hemicellulose hydrolysates by antisolvent precipitation in a spinning disc reactor

The hemicellulose (HMC) fraction of lignocellulosic biomass is a biorenewable precursor for platform molecules such as furfural and 5-hydroxymethylfurfural. However, this fraction is often not valorized. This study presents a novel method to produce high-purity HMC from industrial HMC hydrolysate streams utilizing antisolvent precipitation in a spinning disc reactor (SDR) for potential application in a biorefinery. Spinning disc reactors are ideal intensified precipitation technologies due to their continuous processing ability, high mixing rates, short residence times, and scalability potential. The effects of three different antisolvents (ethanol, acetone, and ammonium sulfate), disc speed, flow rate, and antisolvent (AS) : solvent (S) mass ratio on the yield, purity, and particle size of sugar precipitates were investigated. Ethanol was the preferred antisolvent, yielding the greatest average recovery of solid precipitate of 32% at a 10:1 AS:S ratio and high sugar purity of more than 97%. Acetone failed to produce a solid precipitate, and ammonium sulfate contaminated the product, rendering both antisolvents unsuitable. The SDR overcame mixing limitations at all hydrodynamic conditions tested so that only the AS:S ratio affected product yield significantly, increasing the ethanol AS:S from 1:1 to 10:1, enhancing average solid recovery from 4 to 32%. Optimal SDR operating conditions were 600 rpm disc rotation speed and 8 mL s⁻¹ total flow rate, maximizing product throughput and minimizing energy consumption, with a residence time less than 1 s. In a continuously operated scaled-up system, 485 L of HMC hydrolysate could be processed per day, demonstrating the SDR to be a promising method of intensifying HMC recovery at scale in a biorefinery.