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