Processos de Separação com Membranas

Processos de

Separação com

Membranas

UNIVERSIDADE FEDERAL DO RIO DE JANEIRO

EQB737 – TECNOLOGIAS VERDES PARA BIOPRODUTOS

Prof Bernardo DiasProf Bernardo Dias

[email protected]

mailto:[email protected]

Introdução

MEMBRANA: “Interface fina e discreta que modera (controla) a permeação das espécies

químicas em contato com ela”

Pode ser homogênea → completamente uniforme em sua composição e estrutura;

Ou heterogênea → possuindo poros ou estruturadas com diferentes camadas

Poros: 0.01–10 µm

in diameter→MF/UFSeparation = f(molecular size

and pore size distribution)

PG/PV/OISeparation =

f(diffusivity and

solubility in membrane)

Introdução









f(diffusivity and


Introdução









f(diffusivity and


Introdução

PROCESSOS DE SEPARAÇÃO COM MEMBRANAS

energéticamente favorável

operação em condições brandas (p e T)

modular

acoplamento simples com processos convencionais

Limitações:

seletividade (massa molar, difusão e troca iônica) e fluxos reduzidos

incrustações

condições de operação brandas (p, T)

resistência química

Introdução

PROCESSOS DE SEPARAÇÃO COM MEMBRANAS

energéticamente favorável

operação em condições brandas (p e T)

modular

acoplamento simples com processos convencionais

Limitações:

seletividade (massa molar, difusão e troca iônica) e fluxos reduzidos

incrustações

condições de operação brandas (p, T)

resistência química

Micro-

Organismos

Macromoléculas

e Vírus

Moléculas de

médio PM

Moléculas de

baixo PM e

Íons

Átomos

- 5

- 6

- 9

- 10

10

10

10

10

10

10

Técnica de SeparaçãoFiltração

1 m

Dimensões

das Partículas

e Moléculas (m)

1 Ao

- 7

- 8

Microfiltração

Água Sais Macromoléculas

Células / ColóidesMateriais em Suspensão

Membrana

P

Moléculasde médio PM

Ultrafiltração

Água Sais

Macromoléculas

Membrana

P

Água Sais

Nanofiltração

Membrana

P

Osmose Inversa

Água

Sais

Membrana

P



Principais Características dos Processos que Utilizam Diferença de Pressão como Força Motriz

R = 1-C

C

p

0

• REJEIÇÃO

ALIMENTAÇÃO

C 0

CONCENTRADO

PERMEADOMEMBRANA

C p

MF, UF, NF, OI

PROCESSO MEDIDA DE SELETIVIDADE

MEDIDAS DE SELETIVIDADE EM PSM

• FATOR DE SEPARAÇÃO

Y BY A

AX BX A B =

PV E PG

ALIMENTAÇÃO

NÃO PERMEADO

PERMEADO

MEMBRANA

AY BY,

X A X B,

FILTRAÇÃO CONVENCIONAL

“DEAD END FILTRATION”

FILTRAÇÃO COM ESCOAMENTO

TANGENCIAL

“CROSS FLOW FILTRATION”

FLUXO

TEMPO

TEMPO

FLUXO

FILTRAÇÃO CONVENCIONAL X FILTRAÇÃO TANGENCIAL

Parâmetros

Membrane porosity (ε) → fraction of the total membrane volume that is porous.

Typical microporous membranes have average porosities in the range 0.3–0.7.

This number can be obtained easily by weighing the membrane before and after filling the

pores with an inert liquid. The average porosity obtained this way must be treated

with caution, however, because the porosity of a membrane can vary from place to

place. For example, anisotropic membranes, such as the Loeb-Sourirajan phase separation

membrane, often have an average porosity of 0.7–0.8, but the porosity of the skin layer that

performs the actual separation may be as low as 0.05.

Parâmetros

Membrane tortuosity (τ ) → length of the average pore compared to the membrane thickness.

Simple cylindrical pores at right angles to the membrane surface have a tortuosity of 1, that

is, the average length of the pore is the membrane thickness. Usually pores take a more

meandering path through the membrane, so typical tortuosities are in the range 1.5–2.5.

pore diameter → most membranes actually contain a range of pore sizes. In ultrafiltration, the

pore diameter quoted is usually an average value, but to confuse the issue, the pore diameter

in microfiltration is usually defined in terms of the largest particle able to penetrate the

membrane. This nominal pore diameter can be 5–10 times smaller than the apparent pore

diameter based on direct microscopic examination of the membrane.

Parâmetros

Filtração superficial (Screen filtration) →

membranes with surface pores smaller than

the particles to be removed. These membranes

are usually anisotropic, with a relatively

finely microporous surface layer on a more

open microporous support. Particles in the

permeating fluid are captured and accumulate

on the surface of the membrane. Particles

small enough to pass through the surface

pores are not normally captured in the interior

of the membrane. Ex. UF

Filtração em profundidade → captures

the particles to be removed in the interior

of the membrane. The average pore

diameter of a depth filter is often 10 times

the diameter of the smallest particle able

to permeate the membrane. Some particles

are captured at small constrictions within

the membrane, others by adsorption as

they permeate the membrane by a tortuous

path. Depth filters are usually isotropic,

with a similar pore structure throughout

the membrane. Ex. MF

Filtração superficial x Filtração em profundidade

Módulos

Plana

Cilíndrica

Tubular

Capilares

Fibras-ocas

Espiral

Placa-quadro

Geometria da Membrana Tipo de Módulo

MódulosPlaca-Quadro (plate-and-frame) → consisted of flat sheets of membrane held in a type of

filter press. Membrane, feed spacers, and product spacers are layered together between two

end plates. The feed mixture is forced across the surface of the membrane. A portion passes

through the membrane, enters the permeate channel, and makes its way to a central permeate

collection manifold.

Plate-and-frame units have been developed for

some small-scale applications, but these units

are expensive compared to the alternatives, and

leaks through the gaskets required for each

plate are a problem. Plate-and-frame modules

are now only used in electrodialysis and

pervaporation systems and in a limited number

of reverse osmosis and ultrafiltration

applications with highly fouling feeds.

MódulosPlaca-Quadro (plate-and-frame) → consisted of flat sheets of membrane held in a type of

filter press. Membrane, feed spacers, and product spacers are layered together between two

end plates. The feed mixture is forced across the surface of the membrane. A portion passes

through the membrane, enters the permeate channel, and makes its way to a central permeate

collection manifold.

Plate-and-frame units have been developed for some small-scale applications, but these units

are expensive compared to the alternatives, and leaks through the gaskets required for each

plate are a problem. Plate-and-frame modules are now only used in electrodialysis and

pervaporation systems and in a limited number of reverse osmosis and ultrafiltration

applications with highly fouling feeds.

MódulosTubular→ the tubes consist of a porous paper or fiberglass support with the membrane

formed on the inside of the tubes. Modules are now generally limited to ultrafiltration

applications, for which the benefit of resistance to membrane fouling due to good fluid

hydrodynamics outweighs their high cost.

The first tubular membranes were between 2 and 3 cm in diameter, but more recently, as many

as five to seven smaller tubes, each 0.5–1.0 cm in diameter, are nested inside a single, larger

tube that serves as the pressure vessel. This produces a larger membrane area in the same size

module housing. In a typical tubular membrane system, many tubes are manifolded in series.

The permeate is removed from each tube and sent to a permeate collection header.

MódulosTubular → the tubes consist of a porous paper or fiberglass support with the membrane formed

on the inside of the tubes. Modules are now generally limited to ultrafiltration applications, for

which the benefit of resistance to membrane fouling due to good fluid hydrodynamics

outweighs their high cost.

The first tubular membranes were between 2 and 3 cm in diameter, but more recently, as many

as five to seven smaller tubes, each 0.5–1.0 cm in diameter, are nested inside a single, larger

tube that serves as the pressure vessel. This produces a larger membrane area in the same size

module housing. In a typical tubular membrane system, many tubes are manifolded in series.

The permeate is removed from each tube and sent to a permeate collection header.

MódulosEspirais (Spiral-wound) → consisting of a

membrane envelope of spacers and membrane

wound around a perforated central collection

tube; the module is placed inside a tubular

pressure vessel. Feed passes axially down the

module across the membrane envelope. A

portion of the feed permeates into the

membrane envelope, where it spirals toward the

center and exits through the collection tube.

Small laboratory spiral-wound modules consist

of a single membrane envelope wrapped

around the collection tube. The membrane area

of these modules is typically 0.2–1.0 m². This

type of module is widely used in “under-the-

sink” nanofiltration modules to remove calcium

and other divalent ions from hard drinking

water.

MódulosEspirais (Spiral-wound)

Industrial-scale modules contain many membrane envelopes, each with an area of 1–2 m²,

wrapped around the central collection pipe. Multi-envelope designs minimize the pressure

drop encountered by the permeate fluid traveling toward the central pipe. If a single membrane

envelope were used in a large-membrane-area module, the path taken by the permeate to reach

the central collection pipe would be several meters long. Such a long permeate path would

result in a large pressure drop in the permeate collection channel. By using multiple short

envelopes, the pressure drop in any one envelope is kept at a manageable level. For many

years, the standard industrial reverse osmosis/gas separation spiral-wound module had an 8-in.

diameter and was 40 in. long. However, there is a trend toward increasing the module

diameter, and large reverse osmosis plants now use 16-in. diameter modules.

MódulosFibras ocas (Hollow fiber)

Shellside feed design.

In such a module, a loop or a closed bundle of fibers is

contained in a pressure vessel. The system is pressurized

from the shell side; permeate passes through the fiber wall

and exits through the open fiber ends. This design is easy

to make and allows very large membrane areas to be

contained in an economical system. Because the fiber wall

must support considerable hydrostatic pressure, the fibers

usually have small diameters and thick walls, typically 50

µm internal diameter and 100–200 µm outer diameter.

The greatest single advantage is the ability to pack a very large

membrane area into a single module. Example: membrane area

contained in an 8-in. diameter, 40-in. long module; a spiral-

wound module about 20–40 m², while hollow fiber module,

filled with fibers with a diameter of 100 µm, will contain

approximately 300 m² of membrane area.

MódulosFibras ocas (Hollow fiber)Bore-side feed type.

The fibers in this type of unit are open at both ends, and the feed fluid is circulated through

the bore of the fibers. To minimize pressure drop inside the fibers, the diameters are larger

than those of the fine fibers used in the shell-side feed system and are generally made by

solution spinning. These so-called capillary fibers are used in ultrafiltration, pervaporation,

and some low- to medium-pressure gas applications. Feed pressures are usually limited to

below 150 psig in this type of module. In bore-side feed modules, it is important to ensure

that all of the fibers have identical fiber diameters and permeances. Even fiber variation as

small as ±10% from the average fiber can lead to large variations in module performance.

MÓDULOS DE MEMBRANA

Relação

Área de Membrana / Volume do Módulo

Tipo de Módulo m2/m3

Tubular 30

Placa/Quadro 500

Cartucho 600

Espiral 900

Capilar 1.000

Fibra Ôca 10.000

Módulos

Modos de OperaçãoSISTEMAS COM UMA ÚNICA PASSAGEM

Sistema Simples

Alimentação Permeado Concentrado

Esquema de Operação em Semi - Batelada

Piloto

Concentrado

Permeado

Alimentação

Sistema em Cascata ou Tipo “Árvore de Natal”

Alimentação

Permeado 3

Permeado 2

Permeado 1

Concentrado

Permeado

Sistema em dois estágios com reciclo

SISTEMAS COM RECIRCULAÇÃO

AlimentaçãoConcentrado

Permeado 1 Permeado 2

Permeado

( Reciclo do Concentrado)

Operação em dois estagios com reciclo do concentrado

Operação em dois estagios com reciclo do permeado

OPERAÇÃO EM CASCATA

Permeado

ConcentradoAlimentação

Permeado

ConcentradoAlimentação

OPERAÇÃO EM CASCATA

Operação em três estagios com reciclo do permeado

AlimentaçãoConcentrado

Permeado

Sistema misto com três estágios

Alimentação Concentrado

Permeado

SISTEMAS MISTOS DE OPERAÇÃO

Microfiltração

FORÇA MOTRIZ P ( < 2 bar )

TRANSPORTE CONVECTIVO

ALIMENTAÇÃO

PERMEADOMEMBRANA

CONCENTRADO

MACROMOLÉCULAS PEQUENAS MOLÉCULASSUSPENSÃO

( líquida )

( líquido )

APLICAÇÕES

• Esterilização de Águas

• Filtração de Mostos Fermentados

• Filtração de Vinhos e Cervejas R.Nobrega

COPPE/UFRJ

Membranas para MFOrganic membranes are made using a diverse range of polymers, including cellulose acetate, polysulfone, polyvinylidene fluoride (PVDF), polyethersulfone (PES) and polyamide. These are most commonly used due to their flexibility and chemical properties. Inorganic membranes are usually composed of sintered metal or porous alumina.

Plate-and-Frame Module

Membrane modules for dead-end flow MF are mainly plate-and-frame configurations. They possess a flat and thin-film composite sheet where the plate is asymmetric. A thin selective skin is supported on a thicker layer that has larger pores. These systems are compact and possess a sturdy design. Compared with crossflow filtration, plate-and-frame configurations possess a reduced capital expenditure; however, the operating costs will be higher. The uses of plate-and-frame modules are most applicable for smaller and simpler scale applications (laboratory) which filter dilute solutions.

Spiral-Wound Module

This particular design is used for crossflow filtration. The design involves a pleated membrane which is folded around a perforated permeate core, akin to a spiral, that is usually placed within a pressure vessel. This particular design is preferred when the solutions handled are heavily concentrated and in conditions of high temperatures and extreme pH.This particular configuration is generally used in more large-scale industrial applications of MF.

Membranas para MF

Ultrafiltração

ALIMENTAÇÃO CONCENTRADO

PERMEADO MEMBRANA

SUSPENSÃO MACROMOLÉCULAS PEQUENAS MOLÉCULAS

( líquida )

( líquido )

FORÇA MOTRIZ P ( < 10 bar )

TRANSPORTE CONVECTIVO

APLICAÇÕES

• Concentração de Leite e de Soro de Leite

• Concentração e Purificação de Proteinas e Enzimas

• Recuperação de Corantes e Pigmentos

Caracterização do tamanho de poro: Exclusão nominal “cut off”

A - distribuição estreita de poros

B - distribuição espalhada de poros A

B

101

102

103

104

105

100

Massa molar

0,0

1,0

0,5

R R=0,95

Retenção nominal

A B


B - distribuição espalhada de poros


B - distribuição espalhada de poros A

B

101

101

102

102

103

103

104

104

105

105

100

Massa molar

0,0

1,0

0,5

R R=0,95

Retenção nominal

A B

Cut off → number and average size

of the pores created during the

production of the membrane.

Typically refers to the smallest

average MM of a standard molecule

that will not effectively diffuse across

the membrane. Thus, a membrane

with a 10kDa cut-off will generally

retain >90% of a protein having a

molecular mass of at least 10 kDa.

Pore sizes typically range from

~10 to 100 Å for 1k to 50kDa

membranes. In order for a

molecule to rapidly diffuse

across a membrane it typically

needs to be at least 20–50

times smaller than the cut-off

Membranas para UFThere are two kinds of organic membranes used: polymers (regenerated cellulose, cellulose acetate (CA), cellulose nitrate, polyacrylonitrile,poly(vinylidene fluoride) polyimide, polysulfone, polyethersulfone) and inorganic membranes using inorganic materials represented by ceramics.

Because they are lighter than inorganic membranes, they are easy to handle, are generally cheap and it is easy to prepare various module membranes, but their usable temperature range is small and their chemical resistance is weak.

Inorganic membrane has a pore size distribution that is sharper than an organic thin membrane, and can be used at elevated temperature and pressure. After mixing it with binders, and having moulded ceramic particles such as alumina, mullite and titania, it is easy to form a porous structure with high ratio surface area by hardening it at a high temperature. A tubular shape with coarse particles is formed, and asymmetric ceramic separation membranes can be prepared by coating several layers with fine particles on this tubular support. Inorganic membranes are relatively expensive and not high in strength.

Membranas para UF

Módulos para UFDepending on the shape and material of the membrane, different modules can be used for the UF process. Commercially available designs in UF modules vary according to the required hydrodynamic and economic constraints, as well as the mechanical stability of the system under particular operating pressures.

Plate-and-Frame Module

This module uses a membrane placed on a flat plate separated by a mesh-like material. The feed is passed through the system from which permeate is separated and collected from the edge of the plate. Channel length can range from 10 to 60 cm and channel heights from 0.5 to 1mm. This module provides low volume hold-up, relatively easy replacement of

the membrane and the ability to feed viscous solutions because of the low channel

height, unique to this particular design.

Spiral-Wound Module

Spiral-wound modules are a compact and cheap alternative in UF design, offer a

high volumetric throughput and can also be easily cleaned. However, they are

limited by the thin channels, where feed solutions with suspended solids can result

in partial blockage of the membrane pores.

Módulos para UFTubular Module

The tubular module design uses polymeric membranes cast on the inside of plastic

or porous paper components with diameters typically in the range of 5–25mm with

lengths from 0.6 to 6.4m. Multiple tubes are housed in a PVC or steel shell. The

feed of the module is passed through the tubes, accommodating radial transfer of

permeate to the shell side. This design allows for easy cleaning; however, the main

drawbacks are its low permeability, high volume hold-up within themembrane and

low packing density.

Hollow-Fibre Module

This module is conceptually similar to the tubular module with a shell and tube

arrangement. A single module can consist of 50 to thousands of hollow fibres and

therefore is self-supporting, unlike the tubular design. The diameter of each fibre

ranges from 0.2 to 3 mm, with the feed flowing in the tube and the product permeate

collected radially on the outside. The advantage of having self-supporting

membranes is the ease with which they can be cleaned owing to their ability to be

backflushed. However, replacement costs are high, as one faulty fibre will require

the whole bundle to be replaced. Considering the tubes are of small diameter, using

this design also makes the system prone to blockage.

Módulos para UF

Diálise

P = 0 FORÇA MOTRIZ CTRANSPORTE DIFUSIVO DO SOLUTO

APLICAÇÕES HEMODIÁLISE ( RIM ARTIFICIAL )

DiáliseIn dialysis, solute separation is induced by the difference in solute diffusion transport within a membrane matrix. A diffusible small solute such as an electrolyte or acid is passed through a membrane and dialysed from a solution containing non-diffusable large molecules.

Membranes: film of regenerated cellulose (Cuprophane, Nephrophane) or cellulose

benzoyl ester (laboratory); polyethersulfone (PES), etched polycarbonate or

collagen (specific medical, food or water treatment applications); chitin, chitosan and

its derivatives, polyacrylonitrile, poly (methyl methacrylate), polysulfone (PS),

polyamide, polyethylene, polypropylene, and poly(vinylidene fluoride).

Solução de

diafiltração

PermeadoSolução contendo

Soluto a ser Purificado

Módulo de

Membrana

Diálise

Nanofiltração

For NF membranes, cut-off between 150 and 1000 (but often in the range 150–

300), this concept should be used with care:

- hydrophobic molecules larger than the MWCO, for example, often have a low

rejection;

- the pH of the solution might change the membrane’s surface charge as well as

the charge of the solute, so that the rejection of this solute can be higher or lower

than expected.

- The third important parameter is the recovery or yield. This is a parameter for the

design of an industrial application rather than a membrane characteristic. The

recovery is the ratio of the permeate stream to the feed stream; its value ranges

from 40 to 90%.

Most NF membranes are hydrophilic, except

some used for solvent applications.

The rejection in NF is mainly determined by

molecular size, hydrophobicity and charge,

but effects of, for example, molecular shape

and dipole moment might play a role as well.

Nanofiltração

Membranes

NF membranes have pore sizes from 1 to 10 Å, smaller than that used in

microfiltration and UF, but just larger than that in RO. Membranes used are

predominantly created from thin polymer and porous inorganic membranes.

Materials that are commonly used include polyethylene terephthalate or metal

oxides such as alumina, titania, zirconia and silica–zirconia. Pore dimensions are

controlled by pH, temperature and time during development, with pore densities

ranging from 1 to 106 pores/cm².

Other materials are cellulose acetate or poly (ether sulfone) (PES) (homogeneous

and asymmetric), and (aromatic) polyamides, polysulfone (PS)/PES/sulfonated PS,

polyimide and poly(piperazine amide) (heterogeneous, thin-film composite layer on

top of a substrate UF layer).

Most NF membranes are packed into spiral-wound elements; however, tubular,

hollow-fibre and flat-sheet or plate-and-frame modules are also available. Tubular

membranes with diameter around 1mm, denoted as capillary membranes, are

interesting in view of fouling control.

Membranas de NF

Poliamida aromática, Dupont (Permasep B15 HF)

Inversão de Fases: policarbonato, PVC, Polisulfona, polietersulfona

poli(óxido de fenileno), PVDF, poliacrilonitrila

PAN/PVC, poliacrilatos, poli(álcool vinílico)

Hidrofóbico → baixo fluxo Hidrofílico → prop. Mecânica

Introdução de grupos iônicos: sulfonação, carboxilação (balanço difícil)

Polímeros especiais: polibenzimidazol, polibenzoxazindiona

(alto custo)

Membranas de NF

Polisulfona sulfonada e PVA substituída (Nitto/Hydranautics)

-Maior resistência a cloro

-Exclusão eletrostática (Exclusão de Donnan)

Osmose InversaFORÇA MOTRIZ P ( < 80 bar )

TRANSPORTE “DIFUSIVO”

APLICAÇÕES

ALIMENTAÇÃO

PERMEADO MEMBRANA

CONCENTRADO

MACROMOLÉCULAS PEQUENAS MOLÉCULAS SUSPENSÃO

( líquida )

( líquido )

• Dessalinização de Águas Marinhas e Salobras

• Concentração de Suco de Frutas

• Produção de Água Ultra Pura

• Concentração de Antibióticos

Osmose Inversa

Osmose Inversa

PervaporaçãoFORÇA MOTRIZ a i P i( )

TRANSPORTE : SOLUÇÃO / DIFUSÃO

APLICAÇÕES

• Desidratação de Solventes Orgânicos

• Recuperação de Solventes de Soluções Aquosas

• Recuperação de Aromas

ALIMENTAÇÃOPERMEADO

FASE LÍQUIDA

FASE VAPOR

CONDENSADO

BOMBA DE

VÁCUO

NÃO PERMEADO Sorção Dessorção

1m,v

membrana

DifusãoFase VaporFase Líquida

1L

LC1

m,V1C

m,L1C

L1C 1

V

1

m,v

m,L

Pervaporação

Pervaporação

PervaporaçãoFORÇA MOTRIZ a i P i( )

TRANSPORTE : SOLUÇÃO / DIFUSÃO

APLICAÇÕES

• Desidratação de Solventes Orgânicos

• Recuperação de Solventes de Soluções Aquosas

• Recuperação de Aromas

ALIMENTAÇÃOPERMEADO

FASE LÍQUIDA

FASE VAPOR

CONDENSADO

BOMBA DE

VÁCUO

NÃO PERMEADO Sorção Dessorção

1m,v

membrana

DifusãoFase VaporFase Líquida

1L

LC1

m,V1C

m,L1C

L1C 1

V

1

m,v

m,L

Eletrodiálise

APLICAÇÕES

FORÇA MOTRIZ ETRANSPORTE DIFUSIVO DOS IONS

• Dessalinização de Águas

• Recuperação de Ions Metálicos Valiosos

• Concentração de Soluções Salínas

concentrado

anodo catodo

C A C Aalimentação

diluído

+

+

+ ++ +

+

+

Eletrodiálise

In ion exchange membranes, charged groups

are attached to the polymer backbone of the

membrane material. These fixed charge groups

partially or completely exclude ions of the

same charge from the membrane. This means

that an anionic membrane with fixed positive

groups excludes positive ions but is freely

permeable to negatively charged anions.

Similarly, a cationic membrane with fixed

negative groups excludes negative ions but

is freely permeable to positively charged

cations

EletrodiáliseIon exchange membranes contain a high concentration of fixed ionic groups, typically 3–4

meq/g or more. When placed in water, these ionic groups tend to absorb water; charge

repulsion of the ionic groups can then cause the membrane to swell excessively. This is why

most ion exchange membranes are highly crosslinked to limit swelling.

However, high crosslinking densities make polymers brittle, so the membranes are usually

stored and handled wet to allow absorbed water to plasticize the membrane. Most ion

exchange membranes are produced as homogenous films 50–200 μm thick. The membrane is

often reinforced by casting onto a net or fabric to maintain the shape and to minimize

swelling.

Ion exchange membranes fall into two broad categories: homogeneous and heterogeneous.

In homogeneous membranes, the charged groups are uniformly distributed through the

membrane matrix. These membranes swell relatively uniformly when exposed to water, the

extent of swelling being controlled by their crosslinking density. A number of early

homogeneous membranes were made by simple condensation reactions of suitable

monomers, such as phenol–formaldehyde condensation reactions. Other important category

is the perfluorocarbon type made by DuPont (trade name NafionR). The base polymer is

made by polymerization of a sulfinol fluoride vinyl ether with tetrafluoroethylene. The

copolymer formed is extruded as films about 120 μm thick, after which the sulfinol fluoride

groups are hydrolyzed to form sulfonic acid groups.

Eletrodiálise

crosslinked base membrane, which can

then be converted to a charged form in a

subsequent reaction.

Eletrodiálise

Eletrodiálise

In heterogeneous membranes, the ion exchange groups are contained in small domains

distributed throughout an inert support matrix, which provides mechanical strength.

Heterogeneous membranes can be made, for example, by dispersing finely ground ion

exchange particles in a polymer support matrix. In recent years, finely dispersed

heterogeneous membranes have been made by casting membrane films from ABA block

copolymers. The membrane film is then chemically treated to introduce fixed charges into

one of the phase separated domains. This domain forms the ion conducting path through the

membrane. Because of the difference in the degree of swelling between the ion exchange

portion and the inert portion of heterogeneous membranes, mechanical failure, leading to

leaks at the boundary between the two domains, can be a problem. For example, very finely

powdered cation or anion exchange particles uniformly dispersed in polypropylene.

A much finer heterogeneous dispersion of ion exchange particles, and consequently a more

stable membrane, can be made with a poly(vinyl chloride) (PVC) plastisol. A plastisol of

approximately equal parts PVC, styrene monomer, and crosslinking agent in a dioctyl

phthalate plasticizing solvent is prepared. The mixture is then cast and polymerized as a film.

The PVC and polystyrene polymers form an interconnected domain structure. The styrene

groups are then sulfonated by treatment with concentrated sulfuric acid or sulfur trioxide to

form a very finely dispersed but heterogeneous structure of sulfonated polystyrene in a PVC

matrix, which provides toughness and strength.

EletrodiáliseBipolar membranes

consist of an anionic and a cationic

membrane laminated together. When

placed between two electrodes, the

interface between the anionic and cationic

membranes becomes depleted of ions. The

only way a current can then be carried is by

the water splitting reaction, which liberates

hydrogen ions that migrate to the cathode

and hydroxyl ions that migrate to the

anode.

EletrodiáliseThe phenomenon can be utilized in an electrodialysis stack composed of a number of sets of

three-chamber cells between two electrodes. Salt solution flows into the middle chamber;

cations migrate to the chamber on the left and anions to the chamber on the right. Electrical

neutrality is maintained in these chambers by hydroxyl and hydrogen ions provided by water

splitting in the bipolar membranes that bound each set of three chambers.

Osmose Direta

DS: Glucose, Ammonium bicarbonate, NaCl, MgCl2

Osmose Direta

On the other hand, when an aqueous salt solution such as MgCl2 is used as a DS in FO, a driving force of 1000 atm is provided by an aqueous solute of 5 M MgCl2 [1]. Thus, water conversion is possible with a high recovery of more than 80% from highly concentrated salt water solution such as the seawater under atmospheric pressure without using a high-pressure pump in FO. In addition, as with RO, one of the problems in the water processingsystem with the separation membrane includes a drop in processing capacity as a result of membrane fouling. However, even when the same water permeability is provided, because hydraulic pressure is not applied in FO there are less collisions of molecules with the membrane wall than in RO, and the adsorption characteristics of the membrane pollutant at the film surface are lower than for an RO membrane. Therefore, detachment of the membrane pollutant is possible by physical washing.

The fundamental performances which are demanded for FO membranes are follows: (1) high water permeability through the active layer, (2) low salt permeability through the active layer and (3) structure of the support layer with low internal concentration polarization (ICP).

Generally, any dense, nonporous, selectively permeable material can be used. Membranes in flat sheet and capillary configurations have been tested for various applications of FO.

Extração por MembranasIntroduction

❑These membrane processes are generally referred to as membrane contactor.

(other names: pertraction, gas adsorption, membrane based solvent extraction, liquid-liquid

extraction, hollow-fiber contained liquid membrane, etc.)

In membrane contactors, the membrane functions as an interface between two phases but does

not control the rate of passage of permeants across the membrane.

❑In general, it is not the enhanced mass transfer but rather the large area per volume as can

found in hollow fiber and capillary modules, that makes this process more attractive than

convectional dispersed-phase contactor

Membrane contactors are often shell-and-tube devices containing microporous capillary hollow

fiber membranes. They are made of ceramic, alumina, Flat-sheet nonporous asymmetricpoly(vinyltrimethylsilane) membranes and composite membranes comprising a dense layer ofpolydimethylsiloxane/polyphenylsilsesquioxane block copolymer, poly[1-(trimethylsilyl)-1-propyne](PTMSP), cross-linked PTMSP and cross-linked nanofilled PTMSP

Extração por MembranasIntroduction

❑These membrane processes are generally referred to as membrane contactor.

(other names: pertraction, gas adsorption, membrane based solvent extraction, liquid-liquid

extraction, hollow-fiber contained liquid membrane, etc.)

In membrane contactors, the membrane functions as an interface between two phases but does

not control the rate of passage of permeants across the membrane.

❑In general, it is not the enhanced mass transfer but rather the large area per volume as can

found in hollow fiber and capillary modules, that makes this process more attractive than

convectional dispersed-phase contactor

Membrane contactors are often shell-and-tube devices containing microporous capillary hollow

fiber membranes. The air-filled membrane pores are sufficiently small that capillary forces

prevent direct mixing of the liquid phases on either side of the membrane.

The membrane contactor shown in Figure 13.8 separates a liquid and a gas phase: this is

a liquid/gas contactor. Membrane contactors can also be used to separate two immiscible

liquids (liquid/liquid contactors) or two miscible liquids (usually called membrane distillation)

[23]. Contactors can also be used to selectively absorb one component from a gas

mixture into a liquid (gas/liquid contactors).

Destilação por MembranaIntroduction

❑Most membrane transport processes are isothermal processes with either concentration

pressure or electrical potential difference as the driving force.In this case we have a thermal

process.

❑When a membrane separates two phases held at different temperatures, heat will flow from

the high-temperature side to the low-temperature side. This transport of heat can be described

by Fourier’s equation, where the heat flow is related to the corresponding driving force, the

temperature difference.

dx

dTJh −=

fluxheatJh :

tyconductivithermal:

diferenceetemperatur:dx

dT

(1)

Figure 1. Temperature profile across a

homogeneous membrane

Feed

side

Membrane Permeat

e side

To

TL

x = 0 x = L

Destilação por MembranaType of liquid/liquid membrane contactors.

The hydrophobic microporous membrane is not wetted by either solution and forms a vapor

gap between the two solutions. Because the solutions are at different temperatures, their

vapor pressures are different; as a result, water vapor diffuses across the membrane. The

latent heat required to vaporize the water is removed from the feed solution, and is carried to

the permeate solution when the vapor condenses. Consequently, the feed solution cools, and

the permeate warms.

Membrane distillation offers a number of advantages over alternative pressure-driven

processes such as reverse osmosis. Because the process is driven by temperature gradients,

low-grade waste heat can be used and expensive high-pressure pumps are not required.

Membrane fluxes are comparable to reverse osmosis fluxes, so membrane areas are not

excessive. Finally, the process is still effective with slightly reduced fluxes even for

concentrated salt solutions. This is an advantage over reverse osmosis, in which the

feed solution osmotic pressure places a practical limit on the concentration of a salt in

the solution to be processed.

The principal application proposed for the technique is the separation of water from salt

solutions. In the 1980s, a research group at Enka, then a division of Akzo, developed

membrane distillation to the commercial scale using microporous polypropylene capillary

membrane modules.

Destilação por Membrana

Destilação por Membrana

Sweep gas MD

direct contact MD

vacuum MD air-gap MD ThermostaticSweep gas MD

Liquid gap direct contact MD

Destilação por MembranaA large variety of membranes, including both polymeric and inorganic membranes of hydrophobic nature, can be used in the MD process; however, polymeric membranes have attracted much more attention owing to their possibility to modulate the intrinsic properties. PTFE (polytetrafluroethylene), polypropylene and polyvinylidenefluoride(PVDF) are the most commonly used polymeric membranes owing to their low surface tension values. The useful materials should be selected according to criteria that include compatibility with the liquids involved, cost, ease of fabrication and assembly, useful operating temperatures and thermal conductivity. Among them, PTFE membranes are the most hydrophobic ones, showing outstanding thermal stability and chemical resistance properties (they are not dissolved in all common solvents). The main disadvantage of PTFE membranes is the difficulty of processing. Polypropylene exhibits excellent solvent-resistant properties and high crystallinity. PVDF membranes exhibit good thermal and chemical resistance; however, this polymer easily dissolves at room temperature in a variety of solvents, including DMF and triethylphosphate.

There are two major MD module configurations, which are the plate-and-frame module (packing density is about 100 – 400 m²m-3) and the tubular module (3000 m²m-3).

Destilação OsmóticaAlso known as osmotic evaporation, membrane evaporation, or isothermal membrane distillation, is a

separation process in which a liquid mixture containing a volatile component is contacted with a

microporous, nonwettable membrane whose opposite surface is exposed to a second liquid phase

capable of absorbing that component. This technique can be used to extract selectively the water from

aqueous solutions under atmospheric pressure and at room temperature, thus avoiding thermal

degradation of the solutions. The process can also enable the selective removal of a single volatile

solute from aqueous solution (for instance, ethanol from wine and other ferments) using water as the

extracting solvent.

Brine Channel

Figure 5. In osmotic distillation, a semipermeable membrane acts as a vapor

gap that allows migration of volatiles in a single direction.

Semipermeable

Membrane

Dilute Feed In

Diluted Brine

Out

Feed Channel

Concentrated

Feed Out

Concentrated

Brine In

Destilação Osmótica

Transport mechanism (solute concentration)

Figure 6. Mechanism of osmotic distillation through a

microporous hydrophobic membrane

Concentrated

Brine In

Increasing Water Vapor pressure

Decreasing Water Vapor pressure

Dilute

Feed In Concentrated Feed

Out

Membrane

Diluted

Brine Out

The driving potential for such

transport is the difference in vapor

pressure of each component over

each of the contacting liquid

phases.

If the sole or primary volatile

component in solution is the

solvent, then evaporation of

solvent from the solution of higher

vapor pressure into that of lower

vapor pressure will result in

concentration of the former and

dilution of the latter.

If the solvent vapor pressure over

the liquid being concentrated drops

to a value equal to that over

receiving phase, no further

transport will occur.

Destilação Osmótica

Transport Mechanism (Alcohol removal )

Figure 8. Mechanism of selective alcohol removal by evaporative pertraction

Water In

Water

Alcohol

Increasing alcohol partial pressure

Decreasing alcohol partial pressure

Wine InDealcoholized Wine

Out

Membrane

Dilute Alcohol

Solution Out

In this case, the solute of interest is

evaporated from the feed at the

membrane surface, transported by

vapor diffusion through the

membrane pores, and condensed

into a strip liquid on the opposite

face of the membrane. Most

commonly, the stripping liquid is

pure water or an aqueous solution

containing a lesser concentration of

the solute being transferred.

Destilação OsmóticaThe most suitable materials for OD membranes are apolar polymers with low surface free

energies. These include the polyolefins, particularly PE and PP, and the perfluorocarbons,

especially PTFE and PVDF. Microporous membranes fabricated from these materials are

available with pore sizes and pore size distributions in acceptable ranges for this application.

The maximum tolerable pore radius to prevent liquid penetration is about 250 nm—

corresponding to a pore diameter of about 0.5 micron. Commercially available microporous

membranes fall well within this range of pore dimensions. Membranes of smaller pore size

than this, of course, will withstand higher hydrostatic pressures without liquid intrusion.

The selection of an osmotic agent for use on an industrial scale should preferably be in

accordance with several basic requirements. It should be thermally stable, nonvolatile, and

have a steep positive temperature coefficient of solubility. These properties allow the diluted

strip solution to be reconcentrated to high levels (through thermal evaporation) for reuse in

the OD process without loss or danger of crystallization in the evaporator. Also, the osmotic

agent should be biocidal, nontoxic, low cost and of food-grade quality.

For the osmotic distillation process, mostly salt solutions (NaCl, CaCl2, K2HPO4, potassium

acetate) or some kind of organic solutions (polyethylene glycol, glycerol, etc.) are used as an

osmotic agent.

Aplicações

Aplicações

Aplicações

Aplicações

Aplicações

Aplicações

Problemas

internal fouling

Concentration polarization is the accumulation of solutes (particles) at the membrane surface as a result of the transmembrane pressure. This phenomenon is reversible and causes the flux to decline in the first seconds of the filtration process. As a result of accumulation near the membrane, particles (solutes) might precipitate onto the membrane surface to cause membrane fouling, which is a collective term for phenomena that cause a long-term flux decline. Some of these phenomena are cake layer formation on top of the membrane, pore blocking, pore narrowing, adsorption, particle deposition, and so on, which are often irreversible phenomena. Fouling results in irreversible drop in performance due to increased hydraulic resistance and fouling-enhanced polarization.Fouling may be colloidal, inorganic (scaling by sparingly soluble salts, silica) and organic (e.g. by natural organic matter or dissolved organic matter) for each pressure-driven membrane process.

dynamic membrane complete poreblocking

partial poreblocking

Problemas

Solvente puro

Solução

Tempo

Fluxo do Permeado

Polarização de concentração

Polarização e incrustações

Incrustações orgânicas -“Fouling”Incrustações biológicas –“Biofouling”Precipitação de sais e coagulação de colóides -”scaling”

Deposições(incrustações)

Filtração Frontal X Filtração Tangencial

Solução(polarização + “fouling”)

3Solução (só polarização)

2Solvente1

Flu

xo

Pe

rme

ado

Tempo

1

2

3

Tempo

Flu

xo

P

erm

ea

do 1

2

3

(“DEAD END FILTRATION”) (“CROSS FLOW FILTRATION”)

Ocorrência de bioincrustações (“biofouling”)

-Depósito de microrganismos, fragmentos celulares e

produtos metabólitos

-Crescimento biológico na superfície da membrana e nos

interstícios dos módulos

Bioincrustações:

Microrganismos → concentração → polisacarídeos (EPS)

baixa de biocidas (biofilme)

Proteção contra biocidas

Ocorrência de bioincrustações (“biofouling”)

- Redução do fluxo e rejeição

- Aumento de DP

- Degradação da membranaEPS

membrana

permeado

Adesão

reversível

Síntese de EPS

crescimento hidrogel

Mecanismo:

Potencial: Cultura, Contagem de microorganismos (MF), taxas de crescimento

Ocorrência de “biofouling”

Membrana OI

(500 h operação)

colônias

Limpeza “mecânica” da membrana

biofilme

Membrana

s/ biofilme

Ocorrência de “biofouling”

Superfície de uma

Membrana de AC

(3 dias de uso)

Biofilme desenvolvido

Membrana (AC)

Suporte (poliéster)

Retrolavagem

Flu

xo

Pe

rme

ad

o

Tempo

Solução:Sem “backflushing”

Solução:Com “backflushing”

Solvente Puro

Suspensão

ou Solução

Permeado

Permeado

Operação normal Operanção em“Backflushing”

Permeado

Permeado

Permeação (UF/MF): Limpeza -- retrolavagem

Permeação (UF/MF): Limpeza -- química

1. Lavagem com água quente, maior velocidade de escoamento;

2. Solução acida ou alcalina (depende do depósito);

3. Solução aquecida com detergente.

4. Lavagem do sistema;

5. Medida do fluxo de água (condições pré-estabelecidas).

Geral:

Documents

Processos de Separação com Membranas