membrane separations: opportunities in bioenergy...
TRANSCRIPT
Andrew ZydneyDepartment Head and
Walter L. Robb Family Endowed ChairDepartment of Chemical Engineering
Membrane Separations: Opportunities in Bioenergy
Production
Presented at CrossOver 2007Bioenergy: From Fields to Wheels
Cellulose-to-Ethanol
Pretreatment Hydrolysis
Fermentation
Ethanol+
Other biofuels
Cellulose-to-Ethanol
Pretreatment Hydrolysis
Fermentation
Ethanol+
Other biofuels
Recovery of Enzymes
Continuous Removal ofEthanol + By-Products
EthanolPurification
Removal ofInhibitors
Membrane Research• Membrane Fundamentals
– Membrane transport / characterization– Membrane fouling phenomena– Novel membrane devices
• Nanoporous carbon membranes
• Bioprocessing / protein purification
Nanoporous Carbon• Nanoporous carbon has exceptional thermal and
mechanical stability, potentially providing membranes with very long lifetimes
• Previous work in our group has demonstrated feasibility of making nanoporous carbon membranes using polyethylene glycol (PEG) as a pore-forming agent
• Performance characteristics of early nanoporous carbon membranes were inadequate for commercial applications
Membrane Formation
• Pyrolysis of polyfurfuryl alcohol (PFA)• Polyethylene glycol (PEG) as pore forming agent• Macroporous stainless steel support
Hypothesis• Poor performance of prior nanoporous carbon
membranes related to large amount of carbon needed to insure integral membrane layer
• Effective membranes could be made by significantly reducing mass of carbon
• Approach -- Slip-casting of sub-micron sized silica particles within stainless steel support, reducing size of macropores and matching thermal and mechanical properties of support and carbon
Slip-Casting Silica
• Monodisperse silica particles with average diameter of200-250 nm synthesized by standard sol-gel process
• Sol diluted in methanol (5:1 MeOH by volume)
• Sol filtered through stainless steel support to deposit particles
Rajagopalan et al. (Carbon, 2006)
1 µm
Slip-Casting Silica
20 µm
Stainless Steel Support Silica-Modified Support
10 µm
Nanoporous Carbon Membrane
20 µm
Membrane after 3 coats
Dextran Sieving Curves
Permeability - Selectivity Tradeoff
• Key factors governing performance are the permeability (related to filtrate flux) and the selectivity or separation factor
`
Permeability: L p =Q filtrate
A∆P
α =Flux of ImpurityFlux of Product
=1
SproteinSelectivity:
0
50
100
150
200
0 10 20 30 40 50 60
Time (min)
Filtr
ate
Flux
(L m-2 h-1
)
0
50
100
150
0 10 20 30 40 50 60
Biomax
back pulse for 60 s (Every 5 min, Carbon)
Carbon
Pressure Pulsing5 g/L BSA, ∆P = 40 psi, Backpulse = 7.5 psii
No Pulsing
Nanoporous Carbon - Summary• Thin nanoporous carbon ultrafiltration membranes
can be made by slip-casting of silica particles in stainless steel supports
• Membranes have outstanding stability- Compatible with 3 N NaOH- Stable with repeated pressure-pulsing- Steam sterilizable
• Nanoporous carbon membranes have significant potential in a wide range of new applications
Fouling - Pore Geometry
Slotted Pore Circular Pore
• Membrane fouling is critical issue in yeast cell filtration
• Effect of pore geometry on fouling behavior is largely uncertain due to difficulties inaccurately controlling pore morphology
Micro-machined Membranes
6 µm Slotted Pore 6 µm Circular Pore
200 µm
100 µm
• Micro-machined nickel membranes made by MicroPore Technologies Ltd
• Yeast grown in our laboratory
Submerged Membranes
Fermentation
Biomass Ethanol + Water +Fermentation By-Products
• Hollow fiber MF membranes placed directly in fermentor• Continuous liquid removal using small vacuum• Critical issues are membrane fouling and flux
SubmergedHollow Fiber
Module
Pervaporation• Use of hydrophobic membranes for continuous
removal of ethanol• Ethanol withdrawn as vapor under vacuum• Need to develop new materials with enhanced
flux and fouling characteristics
feed
permeate
Summary• Membrane technology can play an important role
in the cost-effective conversion of biomass to energy
- Continuous fermentation with yeast separation- Pervaporation for ethanol recovery- Purification of biodiesel from renewable oils / fats
• Fundamental understanding of membrane transport phenomena and fouling is critical to the successful development of high performance membrane systems for bioenergy applications