Relevance of Filtration Processes
in Solid-Liquid Separation
Dr Abdoulaye DOUCOURE, “Ablo”
Senior Scientist, Hollingsworth & Vose
[email protected]
FILTRATION 2012 LIQUID TUTORIAL
November 13th - Philadelphia
Solid-liquid separation via liquid filtration
Market perspective (USA)
FILTRATION 2012 CAN’T DO WITHOUT “LIQUIDS”!
% Sales by filter type in 2010
(total: $8.9 billion in the US)
2010 - 2015
$ 3.4 B
$ 2.9 B
33%
38%
Liquid filters
ICE filters
29%
Industrial Combustion Engine “ICE”
Data from “2011 Freedonia Group”
$ 2.6 B
% sales increase/yr
~ 7% per filter type
Application areas & market analysis
US MARKET VALUE FOR MEMBRANE MODULES BY APPLICATION
900
SALES OF MEMBRANES IN 2010 AND 2015 IN $ MILLIONS
800
700
600
500
400
300
200
100
0
Source : BCC Research
2010
2015
Solid/Liquid Separation
Separation (nofilter)
Filtration
Straining (= sieving capture)
Cake (surface) & Depth Filters
Gravity settling
Centrifugal settling
Flotation
Others (magnetic, electrostatic)
Flotation: Lighter particles float to liquid top and are separated.
Gravitation, centrifugation: particles are drawn to liquid bottom
(higher density than liquid phase) and are separated.
Driving Forces in Liquid Filtration
q Gravity - small scale, laboratory (e.g.: particle capture on filter paper)
q Vacuum – small & large scales
Driving forces
q Pressure – small & large scales
Note:
Liquid filtration involves size-based particle separation. The particle
of interest can either pass through or be retained by the filter.
The liquid properties (pH, viscosity, polarity, surface tension)
play a key role in liquid filtration performance.
Blood transfusion imperatives
BLOOD : 55% plasma + 45% blood cells
a Platelet : 2-4 um (clotting factor)
a RBC: 6- 8um (O2, CO2 transport)
a WBC: 10-25 um (immune response)
a WBC (leukocytes) need to be removed from blood
prior to transfusion: Universal Leukocyte reduction
Blood filters for leukocyte reduction
Blood flows by gravity
Into transfer bag
Filter media = polymeric non-woven
Leukocytes are retained (size exclusion)
RBC, platelet and plasma pass through
Membranes for municipal water
Conventional Process (solid-liquid separation)
Raw
Water
Coagulation
and Mixing
Clarification
Filtration
(sand)
Disinfection
Distribution
System
Backwash
Low Pressure Filtration Alternative (Membrane)
Raw
Water
Disinfection
Distribution
System
Liquid filtration (synthetic media) only demands 1 step prior disinfection!
2 Modes of Filtration
Feed
DEAD-END
FILTATION
Feed
CROSSFLOW
FILTRATION
Retentate
Permeate
Permeate
Crossflow mode:
Less fouling but the feed
stream is not fully recovered in
the permeate
Dead-end flow:
More fouling & flux decline
but the feed stream
is 100% filtered
Designs and configurations
Pleated filter
Bundle of hollow fibers
Spiral wound
Disc tube
•
Pleated filter
•
Hollow Fiber
•
Spiral Wound
•
Plate and Frame, cassette
•
Capillary
•
Tubular
•
Disc tube
Capillary filter
Tubular filter
Single hollow fiber
Plate and frame
Liquid Filtration Processes
Liquid filtration System
Microfiltration & Ultrafiltration
Nanofiltration & Reverse Osmosis
Filtration System & Process Parameters
FEED
Qf: feed flow rate
Qc: concentrate flow rate
Permeate stream
Qp: permeate flow rate
Qp
Feed stream
Qf
Pf
Pp
Prefiltration
Concentrate stream
Qc
Process Parameters
Membranes
Pressure (DP), Temperature (feed)
Recovery (%)
Feed stream quality
Flow rates (feed, concentrate)
Pf: upstream pressure (feed)
Pp :downstream pressure (permeate)
DP = Pf – Pp = Differential pressure
Recovery = Qp / Qf x100 (Percent)
System performance
Permeate quality
Throughput, filter fouling
Specific energy (KWH/volume permeate)
Filter service life, and cleaning cycles
Downtime (maintenance)
Pressure driven filtration processes
>40 Bar 10 Bar
High Pressure
Membranes
Reverse
Osmosis
< 1 Bar
Low Pressure Membranes
Ultrafiltration
Filters
Nanofiltration
0,0001
Microfiltration
0,001
0,01
Organic
Compound
s
Salts
0,1
1
10
100 µm
Colloids
Organic
Macromolecules
Virus
Yeasts
Algae
Pollens
Bacteria
Protozoa
Polio Virus
Smallest
Bacteria
Red Cell
Hair
Microfiltration (MF) & Ultrafiltration (UF)
 MF, UF separates contaminants with a size of 0.1 – 10um
 MF, UF are the most widely used membrane filtration processes.
 MF, UF operate at a recovery rate ~ 90-100% (almost no waste)
 MF, UF require moderate operating pressure, ranging 1 to 6 bars
Plate and frame
Pleated filter
Tubular filter
Hollow fibers
MF prime use is dead-end configuration, for fluid clarification or recovery purposes.
UF operates in cross flow mode. Function : concentrate or separate dissolved molecules.
Reverse Osmosis (RO) & Nanofiltration (NF)




RO, NF target the removal of small organics, ions in solvents, often water.
RO, NF separation mechanism is based on size and charge exclusion.
RO operational pressure is > 40 bars, while NF operates at 10-15 bars.
RO recovery is ~30-50% (seawater desalination). NF recovery ~ 80-90%.
Disc tube module
Spiral wound filter
NF/RO membrane (side view)
RO and NF operate in cross flow mode configuration.
RO filters reject >95% monovalent ions (Na+, Cl-) and only the solvent can pass through
NF pore size varies in the 0.4- 1.5 kDa range. It rejects particles, polyvalent ions over 90% but let
most mono-valent ions and the solvent pass through.
Filtering Media and prefilters
Fibrous materials
Membranes
Prefiltration media
Fibrous Media
*Abbreviations: PP: polypropylene - PE: polyester
Wet laid
uFiber glass, cellulose
DEPTH,
SURFACE
Meltblown,
*PP, *PE,
Nylon
Nanofibers
fiber size~ 50-300 nm
(PE, PP, nylon etc)
DEPTH ,
SURFACE
Coarse prefiltration, MF
pores ~ 1-10 um
Dry laid,
Spunbond
Substrates
(for membranes)
Pore
1-200 um
Porosity
40 -95 %
Basis weight
0.5-300 gsm
SURFACE,
DEPTH
Fine prefiltration & MF
Pores ~ 0.3-1.0 um
Nanofiber Media
q Nanofiber size varies in the 50 nm to 1,000 nm range – typical size < 500 nm.
q Nanofibers have found more applications in gas filtration so far (enhanced efficiency).
q In liquid filtration, nanofiber mats can be leveraged as membrane-like surface filters
(pore < 1um), while exhibiting a low hydraulic resistance and interconnected porous
structure similar to depth non-woven filters.
Surface filter
Depth filter
(Meltblown polypropylene)
(Polypropylene membrane)
Nanofibers create a stronger bond
between these 2 platforms
Finer pore size than standard depth media
ENHANCED EFFICIENCY
Higher specific area than standard depth media
HIIGHER RETENTION CAPACITY
More Interconnected pores higher porosity
to membranes
INCREASED PERMEABILITY
compared
Nanofibers for liquid filtration
ELECTROSPUN NANOFIBERS
TECHNOLOGY
1300 ×
H&V NANOWEB®
10 µm
PROPERTIES
Fiber size (nm)
Pore size (nm)
Open porosity (%)
Fine pore size distribution
than meltblown media
Increased surface area over
meltblown media
Basis weight (g/m^2)
Thickness (um)
Nanofiber chemistries
Solvent leaching, extracts
Shedding
Unsupported mat
Surface smoothness
(macroscopic)
Pleatability
50 – 800
200 – 800
70-90
Yes
120 - 1,000
400 – 9,000
50 - 90
Can be controlled
Yes
Yes
0.5 – 20
Up to 75
Polymers, ceramics,
Hybrids, additives
Achievable
Can be controlled
Not always
Achievable
5 - 150
60 - 250
Polyolefins, polyester, nylon
Challenging
Yes
No
No
Yes
Yes
Membrane types
(MF, UF, NF & RO)
SEM Top view
Polymer, Ceramic, Metal
Porous
Symmetric
Dense
Asymmetric
Composites
Standard polymeric membranes
Polyethersulfone (PES), polysulfone,
Polyvinydene fluoride, PVDF
Cellulose
Nylon
Polypropylene, PP
Polytetrafluoroethylene, PTFE
Polyacrylonitrile (PAN)
SEM Cross sections of PES membranes
Membranes, fibrous media, & nanofibers
.
Nanofibers
Pre-filtration media
Prefilter types
(water sector)
Granular media
(sand filter)
Cut-off rating ~ 20 um
Life cycle = 1-5 years
Back-washable
Depth cartridges,
bag filters
(nonwoven, wound
yarn, meltblown)
Cut-off rating ~ 1um
~weeks
Disposable
MF/UF membranes
(hollow fiber)
Cut-off rating~ 0.05um
Life cycle 5- 10 years
Back-washable
Membranes in Biotech/Biopharmaceuticals
Biopharm separations
(a “filter-loving” sector!)
Large scale
processes
(drug production)
Upstream
processing =
Cell culture
*Downstream
processing =
purification of
biomolecules
Lab scale processes
(drug development)
Syringe filters, X-flow filtration
Biomolec. concentration/purification
Peptide, protein recovery
*DP need numerous reusable and single-use MF/UF capsules, cartridges, cassettes
*DP recent trends: Disposable filters; virus removal filters
Separation steps in Downstream Bioprocessing
Major steps
{1.Capture + 2.Purification + 3.Polishing} of bio-product
Merits/limitations in liquid filtration
Merits
Limitations
High consistency in filtrate quality
Membrane fouling
High consistency in filter performance
Filter compatibility, stability issues
Highly selective processes
Capital cost of large installations
Broad application coverage
Abundance of commercial products can be
overwhelming
Modular technology
Membrane plant design can be complex
Competitive product offering
Reduced foot print & energy consumption
Ease of operation
ACKNOWLEDGEMENT
• FILTRATION 2012 PARTICIPANTS
• TUTORIALS’S HOSTS & SPONSORS
• HOLLINGSWORTH & VOSE
References
•
R.H. Perry, D.W. Green, Perry’s Chemical Engineer’s Handbook, 8th ed. , Mcgraw-Hill,
N.Y., 2007
•
L. Svarovsky, Solid-Liquid Separation, 3rd ed., Butterworths, 1990
•
D. Purchas and K.Sutherland, Handbook of Filter Media, 2nd ed., Elsevier Advanced
Technology, 2002.
•
D. Purchas, Solid-Liquid Separation Technology, Uplands Press, Croydon, 1981
•
K.Sutherland, Filtration + Separation, “A closer look at depth filtration”,3-23-2009
•
W.S. Winston Ho & K.K. Sirkar, Membrane Handbook, Chapman and Hall, N.Y., 1992
•
S. P. Nunes & K.V. Peinemann, Membrane Technology in the Chemical Industry, 2nd ed.,
2006
•
M. Mulder, Basic Principles of Membrane Technology, Springer, 1996
Porous Structure of Virtual Media
60
GSM=0.5; T=10 micron; d=75 nm
GSM=0.5; T=10 micron; d=150 nm
GSM=0.5; T=10 micron; d=300 nm
50
Volume %
40
30
20
10
0
0
2
4
Pore Diameter (micron)
6
Picture of virtual nanofiber media
(fiber diam. 300 nm, solidity 8.7%, and thickness 40 um)
Obtained using Full Morpholgy image Analysis Technique
Comparison of Empirical Equation
with Experimental results
Power law relationship between pore size and l
l relates to media {b. weight / thick., fiber diam., fiber density}
Specific length l = 8 w/ [p.T.d.r]
3.5
Simulation
Experiment
3
Good agreement between empirical
Data derived from virtual media design
&
Experimental data collected on glass
fibers
Mean Pore Diameter
Specific length l (1/um)
2.5
2
1.5
1
1E+11
1.5E+11
Specific Length
2E+11
2.5E+11 3E+11
Membrane technologies &
removal of contaminants
Removal of water contaminants by membranes
Filter Characterization
Basic terminologies (fluid transport)
Pore size determination
Wetting properties of membranes
Fluid transport
 Definitions
Flow rate “Q” = Volume / time
Flux “J” = Volume / (time x area) = Q/area
Permeability “Pe” = Volume / (time x area x pressure) = J/pressure
 Flow – DP profiles (3 different liquid cartridges)
DP (Pressure drop)
Filter 3 - smallest pores
Filter 2 – medium pores
Filter 1 – largest pores
Flow rate (liter per minute, Q)
Filter pore size
 Pore size : largest media opening that lets a contaminant pass through.
 No universal method of size determination. It dependents on the function,
such as “non-bio” clarification (suspended solids), biological treatment (microorganisms), or
high purity fluid processing (total particle removal).
 Common techniques used to measure pore size:
Visual method : SEM imaging (surface pores)
Porometry & Porosimetry (Mean Pore, Max Pore sizes)
Particle challenge (monodisperse spheres of latex, silica)
 When Pore size is less ~ 50 nm (UF, NF and RO membranes)
Membrane rejection is expressed as Molecular Weight Cut off (MWCO) in Dalton “Da”
If MWCO of a membrane is 70 kDa (proteins, small organics)
90% of 70 kDa molecules are retained, while 10% pass through.
Wettability and Extractables
q Wettability affects the amount of pressure needed to force the solvent through
the pores. Thus, liquid penetration is made easier with a wettable filter.
Hydrophobic polymers are widely used to filter aqueous solutions due to their good
stability (PTFE, PVDF, PP etc). But they need to be chemically modified to be rendered
water wettable, i.e. hydrophilic.
We can check the wetting properties of a
Hydrophilic PVDF membrane by pouring
a water droplet on its surface.
Water wettability (through-pore) is verified
when the membrane becomes transluscent!