Dehydration with silica pervaporation membranes

Dehydration with silica pervaporation membranes By Nick Wynn, Snlzer Chemtech GmbH, Membrantechnik, Neunkirchen, Germany The October

2000 issue of Membrane

i’2cbnoZog-y reported on a new type of

past three

pervaporation membrane which has been introduced by German company Sulzer

testing

Chemtech GmbH.

solvents

These microporous

silica membranes, launched at Achema

2000, can operate at high temperatures and are stable in acidic conditions. Here we provide further details of the technology. In

the

chemical

pervaporation process

for

especially Sulzer

and

removing from

pervaporation Membrane

called

System

the

(SMS),

molecules

new

Pervap making

for a wider

range

composite active

plants

polymer

layer

polyvinyl

membranes

is a thin

alcohol,

film

supported

Although

membranes

are acid-resistant,

operating

below

1) today

(Figure

substrate. and

zeolite-A The

of

membranes

the

robust.

on a microporous

normal

polymer

membranes

membranes

used

industrial

reactions

acidic conditions The

like

(Figure

of microporous 2).

These

and

water

from

new

chemically stable in a

they can even be condensation where

strongly

and

durability

have been measured

tested are an order of magnitude rates

typically

temperatures

with

of ECN’s over the

achieved

However,

membranes

can operate

as 24O”C, by operating

at

even-higher

higher

the

conventional

membranes.

same

polymer

because

the

silica

at temperatures

as high

flux rates can be reached

at elevated

temperatures.

Housed in isothermal ‘hi-flux’ modules In all membrane housed and

installations,

in modules required

distributed surface,

membranes

(Figure

seal the membrane

difference

4). These

against over

and the retentate

are

support

the pressure

to drive the process.

uniformly

the

Feed is

membrane

and permeate

streams

are kept separate. Special performance

predominate.

of exhaustive flux rates for the

of the

modules,

Pervap

membranes

tailored

membranes, SMS

to

the

are an important technology.

are externally

coated

The

highpart actual

on ceramic

Membrat ie

Much effort has been devoted

to development for pervaporation.

suitable

Centre

Research

a range

in a programme 3). The water

in ceramic

ceramic

membranes

Energy

esterifications,

performance

silica membranes

Developments membranes

to even

environment,

remove

are restricted

110°C.

Unfortunately,

are very sensitive

are mechanically

fluxes are modest to

for water

but not molecules

Not only are the membranes to

(see

page S),

acidity.

has developed

silica

cross-linked

composite

temperatures

use

where

2000,

and isopropanol.

Netherlands

(ECN)

of the

to pass through,

such as ethanol the slightest

of

dehydrations. Most

membranes

which have pores that are small enough

iso-Rropanol. a

focus was zeolite-A

Membrane i’kbnology November

organics,

introduced

competitive

An initial

preferred

from

and

has

technology

pervaporation

industries, the

water

ethanol

Chemtech

Silica

allied

is increasingly

than

years

(Figure

of

Membrane Technology No. 129

Removing reaction water

materials

The

regenerated.

features

expand

of the

the

field

pervaporation. removing

water

reactions

are normally yield,

of

application

directly

such These

equilibrium-limited, water

so

is important

throughput

and

absorbents

for

product

quality, because dehydration

the

Pervap

silica

at temperatures

condensation

from water removal reaction

can

allows

polymer

efficient

using

now

can

adding

and environmentally

pharmaceutical dedicated

Removing

plants

are typically

entrainers

of

better more

benign.

solvents.

companies solvent

Most

non-polar

and,

until

candidates however, down

organics

are nominally now,

have

for drying

not

as hexane

been

considered

as

They are,

where water removal

per million

(ppm)

critical. Traces of water can, for example,

industries,

which Captive

for a limited

without

can

to be able to treat Because

are resistant

now

restrictions

whatever the Pervap

to both acids and

so called ‘aprotic’ use

range

solvent-recycling

such as dimethylfor-mamide recyclers

and by

of sources.

designed

solvents -

in the

(DMF) pervaporation

solvents, -

solvent plants

on the feed.

or

with water

by pervaporation.

used in situations

to the parts

such

immiscible

need

in

companies

contrast,

mix is sent to them.

SMS membranes

Continuous drying of nonpolar organics

a number

In

for reuse

typical

and chemical

feed from

are both

are recovered

solvent-recycling

aggressive

propylene

or

in product

is continuous.

facilities,

collect

to make

which

solvents captive

benefit

organic

manufacturers processes

poly-

also

by pervaporation.

water without

products,

membranes

up to 240°C

reactions

sieves or

discarded

General-purpose membranes for recycling both

Because

be

There are no fluctuations

Industrial

purity. operate

No molecular need

is

from

as ester&cations.

of co-product

maximising

technology

applications

important

reaction

removal

SMS

of

An

condensation reactions

Pervap

continuously.

other

level is

For more information, contact: Nick Wynn, Sulzer Chemtech GmbH, Membrantechnik,

Friedrichsthaler

Strasse 19, D-66540 Neunkirchen, Germany. Tel: +49 6821 79234, Fax +49 6821-79250,

Email:

nick.wynn@sulzermembranes,com

consume

expensive catalysts. Silica membranes non-polar

organics

-

remove water very fast from

This feature is based on an article with the same

the less polar the faster -

title, which appears in SuLzer~ Technical Review,

so Pervap SMS technology

tubes which unit

are installed

like

(Figure annular

5).

When

passage

the ceramic

flows

water

of a

exchanger through

the module is sucked

by the vacuum

the ceramic

the tubes heat

feed

between

tube,

membrane The

inside

a shell-and-tube

the

tube and

through

maintained

the inside

tube.

SMS

geometry

includes

two

key

features:

l

By connecting the annular high

the annular flow-rate

fluid

passages

in series,

is very high and creates This

turbulence.

prevents

concentration

polarisation

-

the permeating

component

at the membrane

surface

when

depletion

one component

permeates

membrane

very fast -

so the driving

maintained,

even

very

under

of a

force is

high

flux

situations. l

By feeding

steam

heat of evaporation the membrane

to the module

shell,

the

of the water permeating

is supplied

directly

to the

is ideal for drying

these

No. 3, 2000.