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Concentration of acetic acid in sulfite pulp evaporation drain by reverse osmosis
(1978) 89-97 0 ElsevierscientificPublishingCompany,Amsterdam- Printedin “TheNetherlands
Desalination, 25
CONCENTRATION
OF ACETIC ACID IN SULFITE PULP EVAPORATION
DRAIN BY REVERSE OSMOSIS HITOSHI MA!?JJDA, C&II%-GSHI KAMIZAWA, TOM00 S&LAP AND MmmRcl SATO**
KUNIO
HATA*,
KING0
YOKOTA’,
IVational Chemical Laboratory for Indmtry, Non-machi, Shibuyu-ku, Tukyo 151 (Japan) (Received
April 25, 1977)
SUMMARY
The evaporation drain of sulfite pulp spent liquor contains few volatife fatty acids, most of which is acetic acid. The main objective of this study is to recover acetic acid as the concentrated solution (about 4%), which could be used as a culture medium of the yeast. As acetic acid can easily pass through the celIulose acetate membrane, SP drains neutralized by NaOH, NHaOH and Ca(OH), were used as the feed solutions. In all cases, concentration by reverse osmosis was successfully carried out provided the appropriate pretreatment was employed_ The recovery of acetic acid was 95.6,90.5 and 98.2% for Na-, NH,-, and Ca-drain, respectively. In addition, the recovered (permeated) water may be used as an
industrial one. INTRODUCTEON
Spent liquor produced in sufite
pulp prucessing contains not only lignin
and some kinds of sugar but also volatile fatty acids such its acetic acid and formic acid (I). Spent liquor is usually concentrated to such an extent that the solid content reaches SO”A by evaporation and then is subjected to combustion. In the concentration process of spent liquor, a large amount of water is
produced as the distillate, which contains fatty acids, mostly acetic acid, as azeotropic mixtures. The basic flow diagram for SP pulp processing is shown in Fig- 1. It is impossible, at least in Japan, to discharge the distillate without treatment, nor to reuse it as the industrial water for its high value of BOD. The distikte is, in most cases, treated by an activated sludge process, which requires much space and high costs. In addition, usefuf fatty acids arc discharged to water bodies without making use of them. The main objective of this study is to recover the
* Research Laboratory, JuJo Paper Co., Oji 5-chtne, Kitrr-ku, Tokyo II4 (Japan] ++ Lie Kyotu Prefecturul Cumprehensive Guidance Center for Small and Medim Nishishichijyc, Shrinogyo-ku, Kyoto 600 (Jupun)
Enterprises,
ET. MASUDA
Wood
Chip
Acid
Sulfite
Cooking
et
ai.
Liquor
(Ca-base)
I
I
I
Cooking
Pulp
Spent
7 kg/c&
fpIi 2, 14OT.
Liquor Evaporation
I I
I
Concentrate
Condensate
(Evaporation
Drain)
Fig, 1. Basic flow diagram for sulfite pulp processing.
fatty acids as the concentrated solution
also involves
solution
by reverse osmosis.
The concentrated
of the yeast. This process which could be utiIized for industry.
may be used as a culture medium
obtained
the recovery
of water,
EXPEIUMEIWAL Reverse osmosis experiment
Analytical data of SP drain used in this study is shown in Table I. The SP drain was neutralized by NaOH, NH,OH or Ca(OH), to approximately pH 6. The neutralized solution was filtered with a 0.45 p-microfilter (FM-45, Fuji Film Co. Ltd.) to avoid the fouling of the reverse osmosis membrane. The solution was introduced to a batch-type apparatus with an effective membrane area of 12.6 cm2. The experiment was carried out at the operating pressure of 50 atm, and at 25°C. To reduce concentration polarization, the impeller was rotated over the membrane
at 300 rpm by magnetic
induced force. The solution was concentrated
to about one-fourth of its original volume. The membrane the method
reported
by Loeb and Manjikian
used was prepared by
(2). The casting solution
was com-
posed of 25 wt%cellulose acetate, 65 wt % acetone and 10 wt % phosphoric acid. The evaporation temperature was 20” &- 1 “C and the evaporation time was 40 TABLE I ANALYTICAL
. DATA
OFSPEVAPORATXONDRALN
PH Spe&ic conductivity so2 Li@iXl Acetic acid COD
1.80 6,250 &XII 0.038% 380 ppm 1.35% 3422 mm
RO ACEI-IC ACID
CONC IZNTRATION
iI-4 SllD3TE
PULP
Fig. 2. Titration curve of SP drain_ Volume of SF drain: 5 ml.
seconds for aU Loeb-type membranes.
The membranes were pressurized use at 50 atm for a day to avoid compaction during the experiment.
prior to
The properties of the membrane were shown by water flux (m3/m2 and salt rejection. The salt rejection is shown by: Re = (1 -
q/q-)
l
day)
x 100
where Cp and Cf are the salt concentration of the product and feed solutions respectiveiy. Acetic acid in the feed and permeated solution was analyzed by titration, conductivity and gas chromatography. Preliminary experiments reveaIed that among three analytical methods, analytical data by titration were most reliable_ Therefore analysis was conducted mainly by titration (see titration curve of SP
drain as shown in Fig. 2), and the data were sometimes verified by gas chromatography and/or conductivity. Preparatory experiment for pretreatmart In the concentration process of SP drain, the most troublesome problem is the fouling of the membrane which causes the drop in water flux and rejection and shortens the life of the membrane. Therefore it was very important to study pretreatment processes. (I) T&t for the eflectiveness of pretreatment The time required when 500 ml of treated SP drain passed through the membrane was measured with a 0.45 p-miUipore f!ilter under reduced pressure of 500 mmHg as the criteria of the effectiveness of pretreatment.
non-treatment
nemralizatim by Ca(CH)2 or lGH#X
to
pH
sedimentat
ion
#,5,6, or 7
2
measurement of turbidity at 550 np
I I
centrifugal separation
2P.w I
I
permeation test 0.4Spmillipore filter
f [permeation test!
fig.
3. Three types of preparation of SP drain.
The pH of the original SP drain was 1.8 0, and the three types of preparation were carried out as follows (Fig. 3): (a) In the non-treatment section, the duct of lignin on the permeability of the membrane was studied. Comparing the time required to f&r 500 ml of a nontreated solution with that for a treated one, there seems little effect of lignin on the membrane performance. (b) When the SP drain was neutralized by NE&OH, the color became light brown with the increase of pH in spite of no precipitate being found. The efkct of pH change on the time required to filter SP drain was not obsrved.
RO
AC-C
ACSD CON cxNTRAmoN
I-N SuLFrrE
PULP
93
Fig. 4. Variation of CaS& and Ca!Xh precipitate with eIapsed time.
process, the solution separated with centrifugation was transparent. The white precipitate, however, was deposited after the solution was permitted to stand for at feast half a day. Considering the fact that the solution had a smell of S02, the precipitate seemed to be C&O, or CaSO& The permeation test of the solution after re-centrifugation gave a good result_ (d) In the case when SP drain was neutralized by Ca(OE&, the opticai density (at 550 mp) of the solution was varied peculiarly with the elapse of the time according to the pH of the solution as is shown in Fig. 4. Thus, it took much time for CaSO, or CaSOa to precipitate perfectly. The permeation test after centrifugation gave better resufts for the solutions treated at pH 6 and 7. X-ray diffraction revealed that the white precipitate was a mixture involving equivalent weights of CaSO, and CaS04. (c)
In the sedimentation
(3) Remowl
of SO2 by aeration
To remove free SO, in the drain, aeration was carried out under the following reduced pressure 40 mmHg, volume of SF drain 4 1. The conteot of SO2 in the solution was changed from 0.031% to OAXM%
conditions: temperature 3&38”C,
after two hours. Then three samples, with the aeration time of 30 min, 60 min, and 120 min, were neutralized by Ca(OH), and the turbidity of each sample was measured. The volumes of Ca(OH)2 solution required to neutralize CpH 7) three drains were almost same. There appeared a milky turbidity in each solution in a short time. Judging from the above mentioned fact, aeration was not effective on the removal of SOz, and SO2 was transformed to SO, only by the oxidizing effect of aeration.
H. AMSUDA (4) Study on sulubiriry of CuSU3 und CaS04 Taking note of the diEerence in solubility of CaSO, 1OOgand 0.2Og/lOOg at 20°C, respectively),
the following
and CaS04
et
Ql.
(O.O04g/
experiment w& carried
out. The SP drain was neutralized by Ca(OH), and permitted to stand for three hours. The solution became turbid and then 0.25 ml, 1.00 ml and 5.00 ml of H202 solution (30 %) were added to 500 ml of the solution individually. 0.25 ml of H,Oz was almost an equivalent amount of SO2 in the drain. After the addition of H202, the solution was allowed to stand for 12 hours. Though the precipitate disappeared and the solution became transparent, some precipitate was deposited again at the four-fold concentration even if 5.0 ml of H20, had been added to the solution. Thus, it is possible to prevent the precipitation of calcium salt by the addition of an excess amount of H,Or_ However, it is probable that some trouble should occur for reverse osmosis membranes. Therefore we are of the opinion that it is better to use NH,OH or NaOH instead of Ca(OH)2. RESULT
AND
DISCUSSION
Permeation behavior of each s&t of acetic acid It is well known that acetic acid can pass through membranes easily, but its salt such as sodium acetate can hardIy do so (3). In addition, the cellulose acetate membrane is deteriorated rapidly, with a ioss of performance, by acidic solution (4). Therefore the solutions used in this study were neutralized by NaOH, NH,OH or Ca(OH),. As the dissociation constant KHAc is expressed as
K HAc
=
[CH,COO -] p+-J [CH,COOH]
the amount of undissociated species can be calculated as a function of pH as shown in Fig. 5. As far as the cellulose acetate membrane is concerned, the rejection of undissociated species of acetic acid is appoximately zero. Therefore the rejection of acetic acid at pH 6 may be at most 94.6°A for the best membrane in view to NaCl rejection, for the percentage of undissociated species is 5.4%. Similarly, at
pH 5.5, the rejection is considered to be 84.7% at most. In this experiment, we took into consideration the deterioration of the membrane due to hydrolysis, and the experiment was carried out at about pH 6.4, though with a view to the recovery of acetic acid, the pH range at which acetic acid dissociates almost compIetely was desirable.
The results obtained with SP drains neutralized by NaOH, NH40H or Ca(OH), are shown in Table II. The change of water flux and rejection in concentration process with the elapsed time is shown in Fig. 6.
RO ACETIC
ACID CONCENIXATION
Fig. 5. Efkt
95
IN SULFITE PULP
of pH on the dissociationof acetic acid.
TABLE IC EtEsLJLTs oBTAINED
l-N THE
REVERSE OShfOSIS EXPERZMENT Acetic acid
pH
I%) Evaporation drain Ev. drain-NaOH Ev. drain-NJ&OH Ev. drain-C21(OH)z
Cont. soln. @R&drain)
1.8 6.4 6.4 6.4 6.7 6.4
cont.
4.90
6.4
SOIU. (ca-drain)
Concentration
VO/V
Cmn)
1.35 1.31 1.30 1.30 4.73 4.63
Cone. soln. (Na-drain)
Cuductivi~
Recover, of acetic acid (%o)
6.25 15.0 19.4 11.6 40.5
3.85
95.6
52.0 26.8
3.76 3.81
90s 98.2
*
of SP drain
The concentration of about 4% as acetic acid is desirable for the culture medium of a yeast. Therefore about three-fold concentration of drain was required. All the experiments were carried out with the same membrane, and the change in the membrane before and after a series of experiments was verified by water flux and NaCl rejectionwith an 0.1 M NaCl solution at an operating pressure of 50 atm. It took approximately IO0 hours for one process of concentration. The permeated solution was collected at the determined intelyal. Fig. 6 inc!icates that in the case of SP drain neutralized by NaOH or NH,OH, water flux decreased with the increase in the concentition of the feed, while the rejection remained approximately 97-6 and 94.4%, respectively, though a slight decrease appeared in the last stage of concentration.
H.
Total Vc4ume of Permixted
MASUDA
et al.
Sdutm[t-d]
Fig, 6, Variation of fluxes and rejections in the concentration drains Initial volume of neutralized SP drain: 21.
process of
neutraIizd
SP
In the case of Ca-base drain, the rejection remained higher than those of the former two. In this case, however, the hard scale, which seemed to be CaSO, and/or C&O,, was observed over the surface of the membrane after the experiment. But, judging from the fact that water flux and NaCl rejection with O-1 M NaCl
were restored to the original values after several hours, the membrane was not considered to be deteriorated badly by the state. The rejection shown in
solution
Fig. 6 was calcuIated from anaIytical data of acetic acid by titration and the estimated value of residual volume, and verified by the analytical data of acetic acid with gas chromatography. When the rejection remains constant, the extent of the concentration can be calculated from the following
equation
(5):
where C is the concentration of the feed and V is the residual volume of the feed. C, and V0 indicate the initial concentration and the voIume of the feed. From Table II, the values of VO/ V of Na-base, NH.+-base and Ca-base SP drain were found to be 3.85, 3.76 and 3.81, respectively. If their rejections were
assumed to be 97.6 %, 94.6 7; and 98.7 %, the calculated values of C/CO of Na-base, NH,-base and Ca-base drain were expected to be 3.73,3.50 and 3.74, respectively. The calculated values were in ftir agreement with the observed ones. During the experiment, the membrane performance seemed to be getting worse. This may be because the membrane was softened due to the presence of acetic acid and other organics and the structure of the softened membrane was changed by the applied pressure. Based on above-mentioned discussion, we come to the following conclusions:
RO
ACETIC ACID CQNC
ENJTRATION
IF4 SULETE
97
PULP
(1) Much attention should be paid to pH control would be appropriate. (2) At kst
of SP drain, About pH 6.5
60 atm is considered to he advisable
as the applied pressure to from 1-ELS*k to 4-5%. (3) Concentration of SP drain with polyamide or other new membranes as well as that with CA membranes which have little resistance to chemicals should be studied. _
concentrate
CH,COOH
REWRENCES AXESSON
2.
7-11.1973, p. 201. S. MANSIKUN, S.
LOEB AND J. W. MCCUTCHAN. Proc. first Intern. Symposium on Water Desaiimtiorz. Washington,D. C. (I965), 2 (1967) 159.
3. 4.
c.
5.
E. S. PEECRY,Ed., Progress in Separationand Purification,Intmcience,
AND
S_ E.
Proc. of the XV EUCEPA Conference held in Rome, May
0.
-WA
AND
~i%SSON,
1.
s.
I SHIUKA,
Kogyo
lthg&u
Zussfi,
72 (1969) 1227.
U. MERTEN,Ed., Des&ration by Reverse Osmsis, The MlT Press,Cambridge. Mass., 1966,
p. 151. 1968, p. 323.
New York, N.Y.,
Desalination, 25
CONCENTRATION
OF ACETIC ACID IN SULFITE PULP EVAPORATION
DRAIN BY REVERSE OSMOSIS HITOSHI MA!?JJDA, C&II%-GSHI KAMIZAWA, TOM00 S&LAP AND MmmRcl SATO**
KUNIO
HATA*,
KING0
YOKOTA’,
IVational Chemical Laboratory for Indmtry, Non-machi, Shibuyu-ku, Tukyo 151 (Japan) (Received
April 25, 1977)
SUMMARY
The evaporation drain of sulfite pulp spent liquor contains few volatife fatty acids, most of which is acetic acid. The main objective of this study is to recover acetic acid as the concentrated solution (about 4%), which could be used as a culture medium of the yeast. As acetic acid can easily pass through the celIulose acetate membrane, SP drains neutralized by NaOH, NHaOH and Ca(OH), were used as the feed solutions. In all cases, concentration by reverse osmosis was successfully carried out provided the appropriate pretreatment was employed_ The recovery of acetic acid was 95.6,90.5 and 98.2% for Na-, NH,-, and Ca-drain, respectively. In addition, the recovered (permeated) water may be used as an
industrial one. INTRODUCTEON
Spent liquor produced in sufite
pulp prucessing contains not only lignin
and some kinds of sugar but also volatile fatty acids such its acetic acid and formic acid (I). Spent liquor is usually concentrated to such an extent that the solid content reaches SO”A by evaporation and then is subjected to combustion. In the concentration process of spent liquor, a large amount of water is
produced as the distillate, which contains fatty acids, mostly acetic acid, as azeotropic mixtures. The basic flow diagram for SP pulp processing is shown in Fig- 1. It is impossible, at least in Japan, to discharge the distillate without treatment, nor to reuse it as the industrial water for its high value of BOD. The distikte is, in most cases, treated by an activated sludge process, which requires much space and high costs. In addition, usefuf fatty acids arc discharged to water bodies without making use of them. The main objective of this study is to recover the
* Research Laboratory, JuJo Paper Co., Oji 5-chtne, Kitrr-ku, Tokyo II4 (Japan] ++ Lie Kyotu Prefecturul Cumprehensive Guidance Center for Small and Medim Nishishichijyc, Shrinogyo-ku, Kyoto 600 (Jupun)
Enterprises,
ET. MASUDA
Wood
Chip
Acid
Sulfite
Cooking
et
ai.
Liquor
(Ca-base)
I
I
I
Cooking
Pulp
Spent
7 kg/c&
fpIi 2, 14OT.
Liquor Evaporation
I I
I
Concentrate
Condensate
(Evaporation
Drain)
Fig, 1. Basic flow diagram for sulfite pulp processing.
fatty acids as the concentrated solution
also involves
solution
by reverse osmosis.
The concentrated
of the yeast. This process which could be utiIized for industry.
may be used as a culture medium
obtained
the recovery
of water,
EXPEIUMEIWAL Reverse osmosis experiment
Analytical data of SP drain used in this study is shown in Table I. The SP drain was neutralized by NaOH, NH,OH or Ca(OH), to approximately pH 6. The neutralized solution was filtered with a 0.45 p-microfilter (FM-45, Fuji Film Co. Ltd.) to avoid the fouling of the reverse osmosis membrane. The solution was introduced to a batch-type apparatus with an effective membrane area of 12.6 cm2. The experiment was carried out at the operating pressure of 50 atm, and at 25°C. To reduce concentration polarization, the impeller was rotated over the membrane
at 300 rpm by magnetic
induced force. The solution was concentrated
to about one-fourth of its original volume. The membrane the method
reported
by Loeb and Manjikian
used was prepared by
(2). The casting solution
was com-
posed of 25 wt%cellulose acetate, 65 wt % acetone and 10 wt % phosphoric acid. The evaporation temperature was 20” &- 1 “C and the evaporation time was 40 TABLE I ANALYTICAL
. DATA
OFSPEVAPORATXONDRALN
PH Spe&ic conductivity so2 Li@iXl Acetic acid COD
1.80 6,250 &XII 0.038% 380 ppm 1.35% 3422 mm
RO ACEI-IC ACID
CONC IZNTRATION
iI-4 SllD3TE
PULP
Fig. 2. Titration curve of SP drain_ Volume of SF drain: 5 ml.
seconds for aU Loeb-type membranes.
The membranes were pressurized use at 50 atm for a day to avoid compaction during the experiment.
prior to
The properties of the membrane were shown by water flux (m3/m2 and salt rejection. The salt rejection is shown by: Re = (1 -
q/q-)
l
day)
x 100
where Cp and Cf are the salt concentration of the product and feed solutions respectiveiy. Acetic acid in the feed and permeated solution was analyzed by titration, conductivity and gas chromatography. Preliminary experiments reveaIed that among three analytical methods, analytical data by titration were most reliable_ Therefore analysis was conducted mainly by titration (see titration curve of SP
drain as shown in Fig. 2), and the data were sometimes verified by gas chromatography and/or conductivity. Preparatory experiment for pretreatmart In the concentration process of SP drain, the most troublesome problem is the fouling of the membrane which causes the drop in water flux and rejection and shortens the life of the membrane. Therefore it was very important to study pretreatment processes. (I) T&t for the eflectiveness of pretreatment The time required when 500 ml of treated SP drain passed through the membrane was measured with a 0.45 p-miUipore f!ilter under reduced pressure of 500 mmHg as the criteria of the effectiveness of pretreatment.
non-treatment
nemralizatim by Ca(CH)2 or lGH#X
to
pH
sedimentat
ion
#,5,6, or 7
2
measurement of turbidity at 550 np
I I
centrifugal separation
2P.w I
I
permeation test 0.4Spmillipore filter
f [permeation test!
fig.
3. Three types of preparation of SP drain.
The pH of the original SP drain was 1.8 0, and the three types of preparation were carried out as follows (Fig. 3): (a) In the non-treatment section, the duct of lignin on the permeability of the membrane was studied. Comparing the time required to f&r 500 ml of a nontreated solution with that for a treated one, there seems little effect of lignin on the membrane performance. (b) When the SP drain was neutralized by NE&OH, the color became light brown with the increase of pH in spite of no precipitate being found. The efkct of pH change on the time required to filter SP drain was not obsrved.
RO
AC-C
ACSD CON cxNTRAmoN
I-N SuLFrrE
PULP
93
Fig. 4. Variation of CaS& and Ca!Xh precipitate with eIapsed time.
process, the solution separated with centrifugation was transparent. The white precipitate, however, was deposited after the solution was permitted to stand for at feast half a day. Considering the fact that the solution had a smell of S02, the precipitate seemed to be C&O, or CaSO& The permeation test of the solution after re-centrifugation gave a good result_ (d) In the case when SP drain was neutralized by Ca(OE&, the opticai density (at 550 mp) of the solution was varied peculiarly with the elapse of the time according to the pH of the solution as is shown in Fig. 4. Thus, it took much time for CaSO, or CaSOa to precipitate perfectly. The permeation test after centrifugation gave better resufts for the solutions treated at pH 6 and 7. X-ray diffraction revealed that the white precipitate was a mixture involving equivalent weights of CaSO, and CaS04. (c)
In the sedimentation
(3) Remowl
of SO2 by aeration
To remove free SO, in the drain, aeration was carried out under the following reduced pressure 40 mmHg, volume of SF drain 4 1. The conteot of SO2 in the solution was changed from 0.031% to OAXM%
conditions: temperature 3&38”C,
after two hours. Then three samples, with the aeration time of 30 min, 60 min, and 120 min, were neutralized by Ca(OH), and the turbidity of each sample was measured. The volumes of Ca(OH)2 solution required to neutralize CpH 7) three drains were almost same. There appeared a milky turbidity in each solution in a short time. Judging from the above mentioned fact, aeration was not effective on the removal of SOz, and SO2 was transformed to SO, only by the oxidizing effect of aeration.
H. AMSUDA (4) Study on sulubiriry of CuSU3 und CaS04 Taking note of the diEerence in solubility of CaSO, 1OOgand 0.2Og/lOOg at 20°C, respectively),
the following
and CaS04
et
Ql.
(O.O04g/
experiment w& carried
out. The SP drain was neutralized by Ca(OH), and permitted to stand for three hours. The solution became turbid and then 0.25 ml, 1.00 ml and 5.00 ml of H202 solution (30 %) were added to 500 ml of the solution individually. 0.25 ml of H,Oz was almost an equivalent amount of SO2 in the drain. After the addition of H202, the solution was allowed to stand for 12 hours. Though the precipitate disappeared and the solution became transparent, some precipitate was deposited again at the four-fold concentration even if 5.0 ml of H20, had been added to the solution. Thus, it is possible to prevent the precipitation of calcium salt by the addition of an excess amount of H,Or_ However, it is probable that some trouble should occur for reverse osmosis membranes. Therefore we are of the opinion that it is better to use NH,OH or NaOH instead of Ca(OH)2. RESULT
AND
DISCUSSION
Permeation behavior of each s&t of acetic acid It is well known that acetic acid can pass through membranes easily, but its salt such as sodium acetate can hardIy do so (3). In addition, the cellulose acetate membrane is deteriorated rapidly, with a ioss of performance, by acidic solution (4). Therefore the solutions used in this study were neutralized by NaOH, NH,OH or Ca(OH),. As the dissociation constant KHAc is expressed as
K HAc
=
[CH,COO -] p+-J [CH,COOH]
the amount of undissociated species can be calculated as a function of pH as shown in Fig. 5. As far as the cellulose acetate membrane is concerned, the rejection of undissociated species of acetic acid is appoximately zero. Therefore the rejection of acetic acid at pH 6 may be at most 94.6°A for the best membrane in view to NaCl rejection, for the percentage of undissociated species is 5.4%. Similarly, at
pH 5.5, the rejection is considered to be 84.7% at most. In this experiment, we took into consideration the deterioration of the membrane due to hydrolysis, and the experiment was carried out at about pH 6.4, though with a view to the recovery of acetic acid, the pH range at which acetic acid dissociates almost compIetely was desirable.
The results obtained with SP drains neutralized by NaOH, NH40H or Ca(OH), are shown in Table II. The change of water flux and rejection in concentration process with the elapsed time is shown in Fig. 6.
RO ACETIC
ACID CONCENIXATION
Fig. 5. Efkt
95
IN SULFITE PULP
of pH on the dissociationof acetic acid.
TABLE IC EtEsLJLTs oBTAINED
l-N THE
REVERSE OShfOSIS EXPERZMENT Acetic acid
pH
I%) Evaporation drain Ev. drain-NaOH Ev. drain-NJ&OH Ev. drain-C21(OH)z
Cont. soln. @R&drain)
1.8 6.4 6.4 6.4 6.7 6.4
cont.
4.90
6.4
SOIU. (ca-drain)
Concentration
VO/V
Cmn)
1.35 1.31 1.30 1.30 4.73 4.63
Cone. soln. (Na-drain)
Cuductivi~
Recover, of acetic acid (%o)
6.25 15.0 19.4 11.6 40.5
3.85
95.6
52.0 26.8
3.76 3.81
90s 98.2
*
of SP drain
The concentration of about 4% as acetic acid is desirable for the culture medium of a yeast. Therefore about three-fold concentration of drain was required. All the experiments were carried out with the same membrane, and the change in the membrane before and after a series of experiments was verified by water flux and NaCl rejectionwith an 0.1 M NaCl solution at an operating pressure of 50 atm. It took approximately IO0 hours for one process of concentration. The permeated solution was collected at the determined intelyal. Fig. 6 inc!icates that in the case of SP drain neutralized by NaOH or NH,OH, water flux decreased with the increase in the concentition of the feed, while the rejection remained approximately 97-6 and 94.4%, respectively, though a slight decrease appeared in the last stage of concentration.
H.
Total Vc4ume of Permixted
MASUDA
et al.
Sdutm[t-d]
Fig, 6, Variation of fluxes and rejections in the concentration drains Initial volume of neutralized SP drain: 21.
process of
neutraIizd
SP
In the case of Ca-base drain, the rejection remained higher than those of the former two. In this case, however, the hard scale, which seemed to be CaSO, and/or C&O,, was observed over the surface of the membrane after the experiment. But, judging from the fact that water flux and NaCl rejection with O-1 M NaCl
were restored to the original values after several hours, the membrane was not considered to be deteriorated badly by the state. The rejection shown in
solution
Fig. 6 was calcuIated from anaIytical data of acetic acid by titration and the estimated value of residual volume, and verified by the analytical data of acetic acid with gas chromatography. When the rejection remains constant, the extent of the concentration can be calculated from the following
equation
(5):
where C is the concentration of the feed and V is the residual volume of the feed. C, and V0 indicate the initial concentration and the voIume of the feed. From Table II, the values of VO/ V of Na-base, NH.+-base and Ca-base SP drain were found to be 3.85, 3.76 and 3.81, respectively. If their rejections were
assumed to be 97.6 %, 94.6 7; and 98.7 %, the calculated values of C/CO of Na-base, NH,-base and Ca-base drain were expected to be 3.73,3.50 and 3.74, respectively. The calculated values were in ftir agreement with the observed ones. During the experiment, the membrane performance seemed to be getting worse. This may be because the membrane was softened due to the presence of acetic acid and other organics and the structure of the softened membrane was changed by the applied pressure. Based on above-mentioned discussion, we come to the following conclusions:
RO
ACETIC ACID CQNC
ENJTRATION
IF4 SULETE
97
PULP
(1) Much attention should be paid to pH control would be appropriate. (2) At kst
of SP drain, About pH 6.5
60 atm is considered to he advisable
as the applied pressure to from 1-ELS*k to 4-5%. (3) Concentration of SP drain with polyamide or other new membranes as well as that with CA membranes which have little resistance to chemicals should be studied. _
concentrate
CH,COOH
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