Ion Exchange for the Production of Cellulosic Ethanol

1. Ion Exchange for the Production of Cellulosic Ethanol • Hammervold, C. Cochran, J. Belsher, K. Childress • Sponsored by Trillium FiberFuels, Inc. Introduction Project Focus Column Design Column Design • Biomass contains a multitude of ions such as calcium and magnesium • Isomerization enzyme works most efficiently at a neutral pH • Cellulosic ethanol is ethanol derived from straw and wood biomass • Previous system modeling was done with a xylose-calcium solution • Xylose must be isomerized prior to fermentation • Calcium ions are known to poison the enzyme used for isomerization • Ion exchange is an effective means of Ca2+ removal • The project focuses on the design and scale-up of two ion exchange columns • Cation resin exchanges calcium and sodium ions for protons, therefore significantly decreasing the effluent pH • Anion resin is required to increase the pH to above 4.0 • The production of cellulosic ethanol requires less energy than starch based ethanol Acid Hydrolysate • Acid hydrolysate was used for a more accurate process model • Acid hydrolysate has proton concentrations that are much greater than Ca2+ concentrations • High cation concentration pushes Ca2+ off the resin bead, causing simultaneous treatment and regeneration • The team could not obtain a feasible column design using acid hydrolysate Production Breakdown into simple sugars Resin Specifications Fermentation Pretreatment • Mechanical Breakdown • Steam Explosion • Strong Acid Treatment • Strong Base Treatment • Enzymatic Breakdown • Yeast Fermentation Cation Exchange Anion Exchange Figure 1: Benchtop ion exchange column designed and built for the removal of Ca2+ from straw hydrolysate Theoretical Scale-Up • Team was asked to scale up for 50 L of a 400 ppm Na+, 400 ppm Ca2+, and 400 ppm K+ solution • Cation column will need to have 4.5 L of resin and the anion column will need to have 5.5 L of resin • Cation resin volume was verified by benchtop model • Calcium ions poison the isomerization enzyme • Ca2+ exchange with H+ on active sites • pH is significantly reduced due to addition of protons • Exchange capacity :1.8 eq/L • Regenerant: 7% HCl • Xylose isomerization requires neutral pH for highest efficiency • No actual ion exchange takes place – organics and acids absorb to the resin • Exchange capacity: 1.6 eq/L • Regenerant: 4% NaOH Wood Structure Operating Parameters Flow Rate and Breakpoint • Government grant specifies Trillium FiberFuels, Inc. to be able to process 200 L/day of straw hydrolysate • Ca2+ must be removed to a concentration below 2.0 ppm • Changing the flow rate of the feed solution alters the shape of the breakthrough curve • Two different test solutions were created: one using DI-water and one using tap water. • Lignin physically inhibits enzyme access to sugar polymers • Traditionally, cellulosic ethanol production is focused on the breakdown of cellulose to glucose Figure 4: Column design using theoretical values for resin capacities. All dimensions are in inches. The flow rate is 225 ml/min or 0.05 cm/s. Pumps will need to be rated for a 14.7 psi pressure drop. Trillium FiberFuels, Inc. Process Acknowledgements • Steve Potochnik and all the others at Trillium FiberFuels, Inc. • Dr. Azizian for ICP use • Dr. Harding • Increased demands require a more efficient means of ethanol production • Breakdown of hemicellulose to xylose could increase ethanol yields by 20-40% depending on biomass • Trillium FiberFuels is using agricultural residue (i.e. rye grass straw) as their feedstock Figure 3: ICP data shows that there is a significant difference in resin capacity between Trillium tap water and DI water. The process goal is to maintain a calcium ion concentration below 2 ppm, represented by the black line. Data also shows that the superficial velocity has a large influence over capacity.