Dehydration of alcohol fuels by pervaporation

481

Desalination,70 (1988) 481-485 Elsevier SciencePublishersB.V., Amsterdam-

DEHYDRATION

OF ALCOHOL

Printed in The Netherlands

FUELS

BY

PERVAPORATION

L. KRAETZ Department of Chemical Engineering, University D-67S0 Kaiserslautern (FRG)

of Kaiserslautern,

P.O. Box 3049,

SUMMARY Presented are experimental results of the dehydration of a liquid mixture with same composition as fuse1 oil, a by-product from fermentation of sugar cane to ethanol for use as fuel. Investigations on the pervaporative separation of water from the initial solution were performed with two different pervaporation membranes. Flux through the membranes depends strongly on the water concentration and on feed temperature.

INTRODUCTION The possibility substitutional

of using renewable

fuel interesting.

resources

makes biotechnological

production

of

Car engines typically run with a mixture of gasoline-

alcohol at a ratio 1:9, though pure alcohol use is possible. Liquid

mixtures

produced

generally

processed

traction.

Particularly

nomical

effort

downstream

processing

separation

-

fermentation

has almost

mostly

appearing

for their further separation

of

of

the same importance azeotrops

and its water

from

mixtures

-

Especially

of

of pro-

distillation

of com-

need special

fuse1 oil is obtained

concentration

from

efforts

mixture composed

a side stream

must be reduced before

of a rectifying

mixing it up with

of two phases. The concentration

fuse1

column

gasoline

in

of water in the dried

fuse1 oil shall be 0,s %-w or less. The mixture can be separated

Pervaporation

the technical/eco-

(ref. 2).

order to avoid the formation

a concentration

are

by ex-

as the development

resulting

at water-alcohol

resources

but also

so that the development

This paper deals with the dehydration of a alcohol-water oil. This co-called

vegetable

new processes

is very decisively

(ref. 1). Multicomponent

plex mixtures

of

methods, mostly by distillation

in the case of introduction

of product

duction itself

by means

by conventional

by distillation

up to

of water of 2%-w (ref. 3).

for the separation through

of water

a nonporous

from

alcohols

membrane

steps: sorption of permeating molecules,

diffusion

takes

pervaportion

place

in the

of these molecules

is very useful. following

three

and evaporation

from the permeate side of the membrane. Sorption separation

from

the liquid phase into the membrane

step. Therefore

tures, provided different

OOll-9164/88/$03.50

it is possible

solubilltles

to separate

phase is the most

close-boiling

are present.

0 1988Elsevier SciencePublishersB.V.

important

or azeotropic

mix-

482 The permeate phase

transformation

membrane. lower

From

than

mass

flux

the

the limited the feed

in connection

with

partial

saturation

or a carrier the

mass

pressure

pressure

gas

and

therefore

transport

through

has to be maintained

in order

to

achieve

a the

much

a sufficient

the membrane. depends

feed

high permeate

place

by a vacuum

the permeate-side

corresponding

flux

while

as vapor

takes

that,

through

The mass tion,

is removed

further

pressure

rates,

has

on temperature

only

pervaporatlon

temperature

temperature

shall

stability

cannot

a minor

of

and composition

effect

on

the

be carried

out

at high

the membrane

be higher

of

flux.

as well

the

feed

In order

solu-

to

achieve

temperatures.

as

the

sealing

Due to materials,

than 100 C.

EXPERIMENTAL The pervaporation circulation

loop

pressure

of

the

feed

on the permeate

the pump

was 5 mbar.

condensator respectively.

The

module

in the

were

performed

solution

side

through

is achieved

was

of

the

radial

The determination

in series

flow

from

the

a laboratory

membrane

over

with

the

the outer

of the flux

results

water

determined

to

vapor

of

membrane

with

reduced

pressure

is carried

the centre.

on the temporal

The

Absolute

temperatures

circular

edge

apparature

module.

pump.

of the permeate

trap connected

direction

with

by a vacuum

Safe condensation

and cooling

built kg/hr.

experiments

out

at

in one

25 C and -80, (area=100

Flow

variation

rate

of

crnzi was

2

the perme-

ate mass. The alcohol

mass

fraction

concentration

Two

different

According more

composite

for

higher

During

pure

acids

the experiments

concentrations

with both

alcohols

at 60 C with

and distilled

as they are solved

on. (Experiments

with

The composition

RESULTS

KARL-FISCHER-titration

used

in the

dehydration

FRGl the membrane and membrane

and

the

MY

experiments.

MX for

(our code)

a low

is

concen-

rishment

types

membrane This

liquid

concentrations

real fuse1 oil are still

the temperature

type MY. The feed mixture

does

in the real

fuse1

not oil

was maintained solution contain from

consists organic

fermentati-

in progress.)

(ref. 3, see Table

1).

AND DISCUSSION

fraction

mainly

water.

in low

membrane

of fuse1 oil was analyzed

The pervaporation mass

were

(GFT, Homburg,

water

by

by gaschromatography.

respectively.

at 90 C and additionally of

was

membranes

to the manufacturer

suitable

tration,

of

was analyzed

due of

of to

flux

water

the

influence

the mixture

of the desorption

shows

in the of

a marked liquid

reduced

(see

sweeling

on the permeation

resistance.

change

mixture

of

of

the curvature

Figs.

1,21. These

properties

water

as well

in the

depending variations case

of

as the higher

of

the

result impoveinfluence

483 TABLE

1

Mass fractions

of alcohols

and water, resp. of fuse1 oil.

Component

Mass fraction

Water 3-Methyl-I-butanol Isobutanol n-Butanol n-Propanol Ethanol

Membrane Temperature

0.131 0.641 0.125 0.0065 0.0084 0.0881

MX

Membrane

MY

m Temperature

90

8 Temperature

.A

2

0.001

Mass

fraction

of water

in feed

60

A

c

0.1

0.01

Mass fraction

of water

in feed

Figs. 1 and 2. Variation of pervaporation flux of water with mass fraction of water in feed. Temperatures of feed solution as indicated in the plot.

At a temperature

of 90 C membrane

type MX

shows

little

higher permeate

flux

compared with type MY with an increasing alcohol flux at the same time in the area of higher water transported

concentration

in the feed.

This is due to a flux

alcohol components with the preferred

absorpted

water.

coupling Mass

of

flux

co-

thro-

ugh the membrane drops with smaller feed temperature (see Fig. 2). A messure of selectivity is the separation factor defined as (w*/w&

S A’B =

(I)

(WA/WB)F

with the weight fractions

w, where index A denotes the species that is preferentially

separated, water, B the total alcohol fraction, F the feed and P the permeate side. Fig. 3 shows the variation of the separation with shows lower

the total

mass

a well-defined water

fraction

of

maximum.

concentration

-

alcohol

Selectivity

as already

factor

computed

in the feed of

seen

solution.

membrane (refs.

compared with membrane MY on much lower levels.

4,s)

MX -

according Membrane firstly

to eqn. (1) type

decreases

and secondly

arises

MY with but

484

50:

)I

, , , , , , , , , , I I

0.85

0.90

Total

mass

Fig. 3. Variation feed.

of

Temperatures

0) %

0.60

z )$

0.50

o

0.95

fraction

separation of liquid

1 .oo

alcohol

factor mixture

(eqn.

in feed 1) with

as indicated

total

mass

fraction

of alcohol

in

in the plot.

Membrane MY Membrane MY

A

a .s

0.40

z g a

0.30

*&

0.20

z :

0.10

z z

0.00

Total

mass

fraction

Fig. 4. Variation of total mass in feed. Operating temperatures

According

to ref.(b)

paring

different

way is to compare

identical

membrane

composition

alcohol in feed

fraction of alcohol in permeate as indicated in plot.

the use of

better

1 .oo

0.95

0.90

0.85

types the

of the feed

the separation as well

water

as

factor

for

concentrations

solution.

with

total

is no proper

lay-out

of

of

the

the

mass

value

technical

permeate

for

fraction

com-

plant.

measured

A at

485 Comparing for

mass

fractions higher

curves

fractions of

mass

step

of

alcohol

of

the greater mass

up to the highest

alcohol

are to

fractions

Dehydration

proximately

in Fig. 4, it is obviously

of water

fuse1 part

between

separate

oil

of

fraction tolerable

and

effective

membrane 0.997. with

MY is better

Mixtures

with

membrane

qualified

lower

MX

due

mass to

the

in the permeate.

can

be

the water of

0.88

more

that

0.02.

mass

performed is separated Pervaporation

fraction

by

a two-step

process.

by conventional can be

used

At

distillation for

further

the

first

to

a ap-

dehydration

of 0.00s.

REFERENCES 1

2 3 4 S

6

C.-M. Bell, F.J. Gerner, K. Kimmerle and H. Chmiel, Pervaporation. Einsatzmijglichkeiten eines neuen Membranverfahrens in der Biotechnologie, in: M.R. Kula (Ed.), Technische Membranen in der Biotechnologie, GBF Monographien Vol. 9, Verlag Chemie, Weinheim, 1986, pp. ISI-158. R.H. Perry and C.H. Chilton, Chemical engineer’s handbook, Sth edn., McGraw-Hill, New York, 1973. M.E. Minelli Figueira de Greco, Escola de Engenharia da U.F.M.G., Belo Horizonte, Brasil, personal communication. G.C. Tealdo, P. Canepa and S. Munari, Water-ethanol permeation through radiation grafted PTFE membranes, J. Memb. Sci 9(1981) 191-196. A. Takizawa, T. Kinoshita, M. Sasaki and Y. Tsajita, Solubility and diffusion of binary water-methylalcohol vapor mixtures in cellulose acetate membrane, J. Memb. Sci., 6(1980) 265-269. H.E.A. Briischke, Industrielle Anwendung der Pervaporation, in: GVC(ed.), Proc. Seminar on Membranverfahren in der Umwelttechnik - Prozesse, Anwendungen und Betriebserfahrungen, Aachen, December S-6, 198.9, VDI, Diisseldorf, 1985, pp. IBS-1%.