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

1. Mechanical Breakdown
2. Steam Explosion
3. Strong Acid Treatment
4. Strong Base Treatment

1. Enzymatic Breakdown

1. 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

1. Calcium ions poison the isomerization enzyme
2. Ca2 exchange with H on active sites
3. pH is significantly reduced due to addition of
   protons
4. Exchange capacity 1.8 eq/L
5. 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

Inlet Ca2 Concentration 100-500 ppm Predicted
Benchtop Column Diameter 0.75 inches Specified
Wet Resin Volume 25 mL Specified
Xylose Concentration 50-100 g/L Predicted
Effluent Ca2 Concentration lt 2.0 ppm ICP/API Calcium test kit
Effluent pH 4-7.5 Vernier Probe
Scale-up production 200 L/day Desired
Scale-up flow 10 L/hr Desired
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.