Development of PBIL low pressure brackish-water reverse osmosis membranes

Development of PBIL low pressure brackish-water reverse osmosis membranes

Desaka~n.22(1977)311-333 0 EXsevierScientihcPublishing Company. - Rhted Net&dads inThe DEVELOPMENT OF PBIL LOW PRESSURE BRACKISH-MATER REVERSE OS...

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Desaka~n.22(1977)311-333 0 EXsevierScientihcPublishing Company.

- Rhted

Net&dads

inThe

DEVELOPMENT OF PBIL LOW PRESSURE BRACKISH-MATER

REVERSE OSKOSIS MEHBRAHES

ROBERT L. GOLOSMITHAND BARRY A. UIXXISLER Walden Division (U.S.A.),

of Abcor,

SW.,

850 Main Street,

Wilmington,

Massachusetts.

01887

and

SHIGEYOSHIHAM, KOH MORI, AND YUTAKA TAMiANI Limited, Iino Building. t-t s Uchisaiwai-Cho, Tokyo 100 (Japan) Teijin

2-Chome,

Ch+yada-Ku,

INTRODLJCTION AND SUMMARY

This paper describes were cast

(PBIL),

and was initially casting

brackish-water

in a phase fntiersion

benzimidazolone membrane.

the development of flat

low pressure

menbrar.es for

sheet reverse

process fron a novel aromatic

This polymer

demonstrated

was developed

to have potential

in

Japan

and curing

on membrane performance

conditions

for application

membranes

polymer,

poly-

by Teijin,

Ltd.

as a seawater desalting

The approach adopted here was to investigate

the membrane characteristics

osmosis

Asmetric

desalination.

the effects in

order

in brackish-water

of

to

tallor

desalting

at law pressure (250 psi). studjes

Preliminary concenrration temperature

fn Japan showed the major variables

of inorganic and time:

additive

ir;mersion bath temperature These parameters

annealing

time and tmperature.

at

Inc.,

Abcor,

The objective

where

in the casting

mre

water

flux

while

curing

and composition; were

than 200 membrane sheets

was to rrz&mire

to be the

solution; further

(-6”

and

evaluated

x 10”) were cast. a salt

maintaining

rejection

of 90% or greater. Immersion tests

were performed

membranes to oxidative

chlorine

membranes nere subjected including

operation

feedwater. Optimization and curing

to life

to evaluate

the resistance

and extremes of pH. tests

lasting

finally,

of nemhrane performance resulted

characteristics

In the fotrratian

several

more than 1100 hours, and

at 100, 200, and 300 psig with a simulated

conditions

of PBIL

Yuma plant

by varying

of m8nbranes wfth

casting

fnitfal

fluxes

of

15-16

and rejections

gfd

HaCl feed solution

tests with

In life

occurred during

in the range of 90-9%

(with

a 0.5%

250 psig and 25OC).

at

simulated

the initial

Yuma water,

some membrane compaction

testing

at 200 psig (for 267 hours). Observed However, during subsequent testing to -0.097.

compaction s! apes were -0.066

with fluxes

at 300 psig (for

629 hours) nil

rejection

stable

at maximum values of about 12 gfd and 99%, respectively.

Annealing

and/or

pre-compaction

somewhat effective

PBIL membranes exhibited level

compaction. excellent

resistance

to extremes

by exposure to sodium hypochlorite

of 100 ppm) in tests

at pH’s of 2 and 7 resulted

membrane embrittlment

and

at high pressure may be

of mtiranes

in reducing

and were unaffected chlorine

compaction was observed,

tasting

7 days.

and in certain

in reduced flux,

and mechanical

of

pH (Z-12)

at pH 12 (equivalent Exposure to chlorine

instanres,

failure.

These data suggest that PBIL is a suitable membrane material for application

in

low pressure

brackish-water

desalting.

EXPERIMENTALPROCEDURES MEMi3RA.ECASTING PROCEDURES Oope Preparation

The cast!ng solution (dope) was prepared by adding PBIL resin a solution

of

tic1

in

added to the RMP in a sealed

flask

dissolved. Pondered PBIL resin temperature. followed casting

This mixture

by continued

in a Millipare sealed

flasks

at

Lithium

cooling

an additional

to room 24 hours*

24 hours.

through a double layer

The viscosity

at room tmperature,

to was

completely

at room teryerature for

at 50-60°C for module.

chloride

at -35OC until

was then added after

under pressure

142 mn filter

was measured

and stirred

was stirred

stirring

dope was filtered

solution

(RHP).

Nmethylpytrolidone

The

of cloth

of the filtered dopes were stored

and the

in

-4T.

Membrane Format I on Procedures Mmbranes

were

cast on clean

(mounted on glass plates) using appl icator . following with

glass

Casting dopes uere raised

I;lembrane casting,

controlled

afr

velacity

the

plates

a Gardner

glass

after

cooling

for

was placed

and temperature.

one minute,

other tickIng rriterials adjustable

to 50°C before plate

specified period of time, the glass plate oven and,

or

6a wtde

After

film

casting.

Lmnediately

Cn a curjng curing

for

oven

the

was removed from the curing

was Immersed

fn the

gel&fan

bath,

This

consSsted

temperature.

of either The

water or water-methanol

base

Plate

upon which

oven was exchangeable.

curing Kawever,

superior

its higher rate gelation

hours.

of

prior

to

testing. sheets

in

plates

an asbestos

rested

sheet

was found to be beneficial

fn

the

was used.

in

producing

This was believed to be due to to the overlying glass and membrane film.

transfer

heat

then

backing

characteristics.

deionized water for at least

membranes were leached nith

They were

membrane

glass

some cases,

an aluminum plate

use of

mmbranes with After

In

at raom

mixtures

stored

in

deionized

water

As desired,

annealing

an agitated

hot water bath,

were 50, 60, 67, 80, and 90°C,

baths

was carried

at

24

raam temperature

out

by placing

Annealing

the

temperatures

menbtanes were held at tmperature

and all

10 minutes.

for

PERFORMANCE TESTING Membrane

flux arid

steel

stainless system.

flow-through

The system

concentrate

characteristics

test

tests

tests

was 20-24

the permeate

from

cc/mjn was then converted conversion of

to gal/day-ft* of

conductivity

percent

Robert

Riley

of

Universal

Oil

feed

test

The feed

The duration

of

were measured by collecting cylinder.

The flux

bY applying

m2dSUred

In most tests, a sample

This sample was provided (San

in

the necessary

and permeate were

rejection.

Products

solution

Tests were

25OC.

rates (gfd)

membrane was run as a control.

PA-300

Rr.

the

of

a graduated

in

The canductivities

factor.

to determine

temperature

cell

steel

mode, with both

to the feed tank.

Membrane flux

test

stainless

recycle

was a 0.5% NaCl solution.

hours.

each

measured using six

were

in an all

in a total

and permeate being returned

conducted at 250 psig and a feed most

cells

was operated

membrane screening

for

rejection

Diego,

by

CA).

ENVIRONMENTALRESISTA!XE TESTS Imnersion membranes chlorine times

to at

were

tests were performed to evaluate and extremes

chtorine levels

1 day,

3 days,

chlorite, desired

acid

and solutions

Additional

solutions.

were tested

sodrun hypochlorite

chlorine

levels.

pH.

resistance

Mmbranes pH 2.

7,

were

of

exposed

and 12.

PBIL to

Irrmersion

and 7 days, and both annealed and unannealed

The pH buffers

membranes were tested. phosphate-phosphoric

of

10, and 100 ppm at

of 0,

the

consisted Chlorine

daily

of 0.1 M potdsslum was added

to determine

was added ds necessary

as sodium

chlorine to majntain

hypo-

content. the

314 performance characteristics of both PBIL and

After imersion, me&ram PA-300 membranes were measured psig

with

0.5% NaCl at

investigated, LIFE

in 2-3 hour reverse

2VC.

For

membrane discs

were

each cut

from

the

of

at 250

pH and chlorine

level

same sheet.

TESTS

Five PBIL membranes and one PA-300 of

osmosis tests

combination

It29

hours

of

ccntinuous

membrane were This

operatfon.

included

tested

followed by 267 hours at 200 psig and 629 hours at 300 psig. solution was a synthetic Yma

Plant

brine

for a total

233 hours at

100

psig

The feed

approximately the following

having

composition: cmlstituent Calcium

Concentration 145

Magnesium

85

Sodium Potassium Chloride Sulfate Alkalinity

739

9 870 1071 16 (as CaC03) 23 7.8

Silica PH

This solution deionized

(mq/fi)

was prepared by dissolving

the following

constituents

in

water:

Constituent Na 2S04

Concentrztian 1495

;z!G; 2g 6H20

711

2

402

KC1

17

NaCl

588

Na2Si03-9H20

111

(ms/fi)

pH was adjusted to 7.8 by adding HCl . The feed tmperature ws 25OC. The mmbranes tested included four membranes imersed in water-methanol baths (195-2, 195-3, 195-60-S. 208-80-S) and one imersed in pure water (171-l). Of the four membranes immersed in watewzethanol, one was annealed at 60°C (195-60-S) and one at 80°C (208-80-S). In addition, one each of the annealed and unannealed membranes (195-60-S. 195-2) were pre-

The

The MS

100 psig

t;t?st was begun using

replaced by synthetic Ymra wter

0.5s

HaCl as the feed

at:hmr 67.5,

solution,

whSch mf continued

This until

hmr 571. A second batch af syntfietic Yuma water was prepared and used after hour 575 far the remainder of the test. The membranes were c'ieanecl three

times with

during

the first

continwd,

dilute hydroch'twic acid and mce

575 hours of testSng.

Subsequently.

but the membranes were rinsed

feed solution

with oxalk

acid

($4 2)

acid washing uas c!fs-

with dcionited

water and fresh

was substituted at weekly intervals,

RATA AHD ANALYSIS

Membrane pwfumtance fawn-s

characteristics

are affected

by a variety

of

involving

parameters

fcmratf on artd treatment pmc:PduPes + Among the majar investigated during this pragram were the fo’llcrwing: - LiCl

toncentratfon

- curing

in

the castSrrg dope

time and tmperature

- imers$x~

bath temperature and cmymsitfon

- anneal irtgfime

an;d tmperature

Ffrst number (171, 195, 203) indicates mmbrane sheet. taat nmber indfcates indfvidual disc cut from mtzbrana sheet. 6Q-S and 80-S indfcaze annealing cmditr’ons (60 and [email protected], ~4th water rais4 to annealing tmpcr*ature, bath initfally at raam temperature. and heid lkr 10 min.).

316

Chloride

Lithium

Concentration

In preliminary casting

Figure

dope nas evaluated.

characteristics

the effect

experiments,

as a function

of LiCl

concentratjon

1 shows membrane flux

of LiCl

concentration

in the

and rejection

and a range of curing

times. A concentrat$on of 45% by weight (relative to the weight of polymer) was found to be optimum and was used for most of the membranes described herein . Curing Time and Temperature The effects

darionstrated (80,

of curing

by Figures

115, and 13F’C) shorter

rejection

curing

decrease

higher

temperatures

samewhat better

resulted

In general,

time. flux

tested

flux/lower in a

rmbranes

and rejection

character-

than did those cured at 80°C. Replacfng

also

curing

temperatures

three

times yielded

in the optimum curing

cured at 115 and 135*C yielded istics

At each of the

Use of Mgher

membranes.

concomitant

on membrane performance are

time and temperature

2 and 3.

insulator

plate rested

the base on which the glass casting

had a significant

effect

(asbestos)

on mtirane

to a hfghly

effect comparable to increasing due to the increased

rate

properties.

conductive

heat sink (aluminum)had an

the curing

of solvent

during curing

Changing from an

temperatire.

evaporation

This was apparently

from a rare

rapidly

heated

membrane film. For any particular flux/low

rejection

these formation readtly

conditions,

controlled

were difficult general, procedures

temperature in

study.

higher curing

use of an aluminum base plate performance.

3ath

These conditions

Tmperature

250 psig)

flux

were

rejection,

control

shorter

but

In

region.

of

the bench-scale

continuous casting

high

Under

under conditfons

improved

temperature,

apparently

from

formation

of membrane

pracesses. curing

oven yielded

tkte,

preferred

lead to formation

and the membrane

of a thinner

process,

an4 Cmpositfon

The effect of fmersIon also studied

time for

However,

In the curing

skin during the phase inversion Inmersion

(at

was better

and longer curing this

transition

and 9%9fX

in a lower rejection/higher

may be expected for

In conclusion,

the

membranes was abrupt.

of 8-10 gfd flux

of membrane perfwxance

utilized

characteristics

conditions,

rejection

membrane characteristics

in the region

to control

control

lower curing

set of curing

to low flux/high

in a preliminary

bath temperature ntanrter. >

on mnbrane

As the flwc-rejection

perfomtance

ms

titatfonship

25

20

15

10

5

80

70

60

50

5.2 40

16 wt. % polymer i n dope 115°C Curing Tmperature No Annealing

30

20

._

4.5

Different

min 6

Symbols

10 _

LiCl

Fig.

Indicate

Curing Times (nin)

1.

Effect

Concentration

OF L$thium

on HabFane

(‘d of

Chloride

Perfomdnce.

polymer

weight)

Concentration

318

100

Slit Thickness: 17 mils Air Velocity: 5 m/set Curing Tcmp:

1 Open symbols denote use of asbestos base plate in oven Solid symbols denote use of aluminum base plate in Oven

I

I 10

20

I Curing

Fig.

2.

Effect

of

Curing

L

30

Cond5fions

40 Tine

I 50

(min]

on Membrane Perfo~ance,

I 60

Refer for

5

10 Water

Fig,

3.

15 Flux

20

to Figure Legend

30

(gfd)

Relationship Betueen Conductivity Rejectron and Kater Flux far Different Curing Con4ftions.

40

50

2

in

Figure 4 shows.

increasing

temperature

but only with a significant the

membranes

evaluated

Membrane

were

performance

presence

of

methanol

(by volume)

loss

methanol

in

curing

times

higher

are

flux

rejectfon

do those

than

in the short-term significant

at 115°C.

for

membranes

(typfcally

gain

5,

5 m/set

air

in water

in pure water,

25Z,

flux

and 75X

and rejection

velocity,

at

most of

by the

3X,

and a range - 50%

and 50% Hater

bath have

similar

flu noticeable

rejection).

flux,

bath.

in the methanol-water

imersed

in

affected

with

Xn Figure

imersion

imnersed

93-952

Baths

levels

of

difference

compaction slopes for membranes imersed Use of zt 75’1: methanol-25%

methanol baths. 50:50

compared

be strongly

to

bath.

were investigated.

Clearly,

methanol.

found

imnerslon

(at 1 hour) for mEntbranes cured of

a small

Based on these data,

in a roam temperature

gelled

was also the

can yield

in rejection.

in water or water-

bath did not yield

water

improvement in m8nbrane characteristics

salt

was found

over those for

a the

mixture.

Anneal i nq Conditions The effect dmnstrated

of annealing

by comparing

temperature

flux,

for

membranes annealed at several

(at

2 hours) decreased with

was variable. improved

Short-term

as a result

increasing

the

and compaction

temperatures

(Figure

annealing

is

characteristics

6).

In general,

temperature

slopes (-24-hr,

compaction

of

on membrane performance

rejection,

tests)

while were

flux

rejection

somewhat

anneal fng.

ENVIROWERTAL RESISTAHCE

Irmersion tests were performed to evaluate mmbranes to chlorfne Jn Figures

7 - 9.

was found at pH 2.

and extremes

No significant 7, or 12 with

ppm chlorfne

pH 2 within

and 3 days.

At

exposure period. (67OC) rapidly

pH 12,

in

Results

present.

nas found for

PA-300 mabranes

10 and I(30 ppnr chlorine

or

at

all

the

pH 2 after stable behavior

were found

pH levels.

salt

are

shown

rejection

Water flux of at pH 2 and pH 7.

and In 100 ppn chlorine,

PBIL membranes remained

of PBIL

of these tests flux

exposure to chlorine

in 10 ppm chlorine,

No difference

and unannealed PBIL.

the resistance

on water

no chlorine

one day; all

pH.

effect

PBIL membranes decreased fallowing These membranes hecame brittle

of

3 days; 100

pH 7 between

1

through the 7-day of

annealed

to deteriorate

32f 80

85

90

Increase f Temperature f i

I 95

Casti ng Solution: 16 wt. 30 wt. Curing

5 PBIL % LiCt

Condjtions:

130°C 14 mins

e

98

I

I

I

I

I

3

4

5 (gfd)

6

7

Water

Fig.

4.

Flux-Rejection Function

of

Flux

Relationship

Imersion

as a

Bath Temperature

1 8

.

322

-

II111

I

I Gelation

I

Bath: 0

l water

-

1

0

0 water

‘*

I

+ methanol

(1: 1)

0

Conditions:

Curing

115°C 5 m/six

0

fig.

5.

Effect of on Initial

Gelation Bath Composition Flux and Rejection Characteristics

1 0

I

323

-0.20 aJ g -0.15 z

0

100

z

95

-

c

0

CI

ki -2 az

90 85 I

80

I

I

I

15

13

5

0

fig.

6.

Effect of Perfommce

Anneal!ng Temperature Characteristks of

on Three

Membranes

-+-F--k

WaterFlux (gfd) E

Conductivity

RejectIon (%) g

325

ib-__

Imrsfan Fig. 8.

.

- -100

The

(days)

Effect of Exposure to Chlorine at pH 7. Nu&ers indicate chlorine level (ppd. H.T. indicates annealed meniirane.

,

‘I’’ ’ ’ ’ ’ ’ H .T.-10

3

kimersicn The f ‘ig. 9.

(days)

Effect of Exposure to Chlorjne at pH 12. Nuxhers indicate chlorine level (p~)~ H.T, indicates annealed membrane.

327 LIFE TESTS Five

PBIL membranes

of continuous rejection

testing,

10 - 12.

for

tinezr

Yuma Plant

fekkater.

100, 200, and 300 psig

the

regression

analyses

Flux

tests

are

and

plotted

in

where an equation

the

of

form was assumed: log Flux

The values

to 1129 hours

were performed to determine

compaction slopes of the membranes at each pressure, the following

subjected

membrane were

using simulated

measurements

Figures

and one PA-300

of the

= b log

compaction

time

slope,

+ log

b,

k.

correlation

and the

coefficients

for

the fits are given in Table 1, At 100 psig, correlation

compaction was negligible

coefficients

in

two cases,

instabilities

was of

slopes

derived

indicate

for

that

greater

coefficient

of -0.88.

from the regression instability

in the test

check valves,

The data for in all

cases.

analysis:

The

(a)

were affect& psig);

hour 236.5,

-0.049,

Only

with

a correlation

119 and 171 were

witted

problem,

by pressure

caused by maTfunctIoning

are indicative

of compaction

data it

points

were

coefficients omitted

appears that

the

from

the

membranes

(b) hours 119 and 141.5,

acid wash at hour 92 (325.5

slopes

in

were obtained regression

had not

because they

from start

at 100

because the membranes may have been affected

by foul ing .

that

these

level.

Fluxes

membranes

r&ucing At the

statistical

the lowest

However, if

and compaction

at

hours

High correlation

because

by the oxalic

A preliminary

in

1.

or other

membrane compactfan.

were

subsequently

recovered

by washing

HCl.

suggests for

to -0.097. following

hour

and (c)

signfficantly with

This

at the new pressure;

equilibrated

at

error

positive

at hour 187.

the 200 psig test

range of -0.066

the

points

The low

as the

because they may have been affected

system.

was corrected

than

crjmpaction slope,

The data

analyses

as well

fits,

random experimental

importance

membrane 195-Z had a significant

for most membranes.

these

300

treatment

(-0.066)

may not

be statistically

the differences

treatment

of the 200 ps$g results

and highest

given

(-0.097) different

are real,

membrane

195-60-S

it

(t-test)

slopes determined at

suggests

the

95Z confidence

that

the annealing

may be somewhat

effective

cOmp.Zcti0n.

psig.

beginning

caorpaction was near zero for most membranes. of the 300 psig test,

hours 1 and 16.8,

Data points

appear dfstinctly

I

329

.

to.009

II

1

I to.32 5 -0,081

+0.003* -0.99

+0.05

-0.97

-0.97

7

6

6

6

i

-0.015

-0.047

-0.007

-0.025

to.003

-0.006

Sl0pfZ

Table1, Resultsof RcgressIon Analysesfor LiftTestOata

*Thesedatamay be affectedby leaksIn test cells.

171-l

PA-300

I

-0.079

5

fO.24

208-00-S +0,007 mm

-0.097*

-0.030*

5

195-3

-0.56

7

-0.97

-0.066

5

-0.25

195-60-S -0.006

7

-0.97

-0.090

5

-0.88

-0.049

195-2

200 psig Correlation Coefficient # of pts.

Slope

100 psig

I Correlation Membrane Number Sl OPE Coefficient # of pts.

-0.86

-0.83

-0.63

-O.Si

to.26

-0.49

IO

6

10

6

10

10

300 prig Correlation I Coefficient_# OF pts,

332

law in flux

and were omitted

coefficients of

the

for

three

variability

the

highest

are

based

must

syste;ns of these

considered,

This

could

decl Inc.

although

the

membranes

Bench-scale

initial

90-952

high,

250

tests

0.5%

suggest

to that

Flux

of

favorable

for

a thinner

from

1~

the

solvent

in

are

off,

tested

of

also

limited to

the led

of

and repro-

more than

by varying

the

mfxture,

range

curfng

However,

in

Membranes

the

concurrently.

as a result

membranes

asymnetric

performance

and shorter

leachfng

times.

and after

can be controlled

flux

the

retatively

probably

solvent

to

period,

of

easily

evaporation.

rejection/high

a water-methanol

been

is

decline

desalting.

to deliver

can be well-controlled

Kore rapid

use of

membrane

temperature

performance,

several

slopes

may level

which

this

development

have

Also,

permeate

contributed during

water

the

continued

characteristics

during

in

the

Thus, the

foul ing

much

test data are

brackish-water

25°C)

compaction

High

in

the

performed

compaction

control

and PA-309,

and sat t rejection

at

membranes

a ?A-300

improved skin

gfd

feed

of

deionized

resulted

short-term

conditions_

f 1 ux membranes. from

KaCl

that

membrane characteristics transition

have

part

were

with

195-3

that

compaction.

when leaks

mmbrane

low pressure

PBIL

and rejection

membrane curing of

rinsed

as 15-16

Al though

1100 hours of testing, superior

that

than

were sealed.

latter

washes

as high

psig,

the

Correlation

indicating

other

175,

cells

test

low,

membranes hour

indicate

for

effects

for to

Ko acid

experiments

formed. life

&o

were

suitable

flux

(at

ducibly

were

when only

flux

PBIL membranes

to

subsequent

may be greater

analyses.

membranes are quite

slopes

on data

observed

with

from the regression

the

be ascribed

compaction only

wfthdrawal in flux

of

the

in which abrupt

rejection/lower

immersion to

are

formation

region by the

high

the

times

bath,

resulting

a significant

increase

in membrane flux. Although

the

is

not definitive,

at

high

pressure

Compaction the

range

moderate,

testing

analysis it

of

at

-0.066

becoming

at 300 psjg.

200 psig to

life

doubtful

significantly

slopes of

is

-0.097.

essentially

test that

improves (following

data

the

determine

annealing canpaction

-234

Subsequently, negligible

to

either

hours

slopes

pre-compaction

characteristics. at

compaction

during

ccmpactfon or

100 psig)

were

was found

more than

600

In

to

hours

of

PBIL nembrartes and were

unaffected

level

100 ppm) for

of

perfomance

This Office Dr.

of

exhibit&

up to

was adversely

project Hater

to project

also

by Drs.

Hisayuki

7 days.

affected

At

by exposure

by the U.S.

and Technology,

direction. Leon Mir

Honda of Teijin,

Ltd.

pH 12

of pH (Z-12) chlorine

however, rr;Gbrane

to chlorine.

Departnent

under

Yal uable

and Steve

to extrmes (equivalent

pH 7 and below,

as the OHR&TProject

K.C. CRannabasappa,

significantly

provided

to NaOCl at

was sponsored Research

resistance

excellent

by exposure

Contract

Officer,

the

No.

Interior,

14-34-0001-7509.

contributed

technical

Jakabhazy

of

of

consul tation Abcor.

Inc.

uas

and Mr.