Download Reactive Extraction of o-Aminophenol Using Trialkylphosphine Oxide

Chinese J. Chem. Eng., 14(1) 46—50 (2006)
Reactive Extraction of o-Aminophenol Using Trialkylphosphine Oxide*
LI Deliang(李德亮)**, LIU Xiaoqiang(刘小强) and CUI Jiehu(崔节虎)
Chemistry and Chemical Engineering College, Henan University, Kaifeng 475001, China
Abstract Extraction of o-aminophenol (OAP) using trialkylphosphine oxide (TRPO) was studied with different diluents.
The neutral OAP was extracted using TRPO under an equilibrium pH in the range of 6—7.5, and a maximum distribution
coefficient occurred. It was confirmed that the pH value and the TRPO concentration are the key factors that affect distribution coefficient. Nonpolar diluents could provide better extraction distribution coefficient for the extraction of OAP
and the order is: kerosene >n-octanol >chloroform.
Keywords reactive extraction, o-aminophenol, trialkylphosphine oxide, diluent
1
INTRODUCTION
Reversible reactive extraction is a new separation
technique that is composed of several chemical reactions between certain functional groups of the extracted species and the extractant. It is a useful method
to recover the organic species from the effluent with
high effectiveness and selectivity[1]. This technique is
now receiving increased attention. A number of successful researches have been done in the fields of extraction mechanism, chemical engineering separation,
and organic wastewater processing. It was found from
these numerous studies that the organic species separated from aqueous solutions through reactive extraction contain only one Lewis functional group, Lewis
acid, or Lewis base, for example, carboxylic acids[2―5],
phenols[6], or organic amine[7] solutions. However,
very few research works about the extraction of compounds with two functional groups based on Lewis
acidic and/or Lewis base have been reported.
Amino acid is an important biochemical compound. In the production process of amino acid, the
cost of separation and purification alone occupied
more than 80% of the total cost. To obtain a new and
excellent separation method, Liu et al. studied the extraction characteristics of phenylalanine[8], L-isoleucine[9],
and L-tryptophan[10], and discussed the effect of pH on
the extraction distribution coefficient. All these works
were based on a theoretical foundation for the separation and recovery of amino acid. Yoshinori et al.[11]
investigated the extraction of amino acid chelated with
Cu and Ni and got good experimental results. This
work proved to be useful in the exploration of the new
extractant.
Aminobenzene sulfonic acid, aminobenzoic acid
and aminophenol are important intermediates of dyes
and medicines. Li et al.[12, 13] carried out the determination of the distribution coefficient of aminobenzene
sulfonic acid solution by using Alamine 336 and Aliquat 336 in n-octanol, chloroform and benzene, respectively. Compared to Alamine 336, Aliquat 336
could be used in a wider pH range. Liu, Zhang et al.[14, 15]
investigated the extraction equilibrium and mechanism of o, p-aminobenzoic acid solution with trioctylamine (TOA), tributyl phosphate (TBP), and
di(2-ethylhexyl)-phosphoric acid (D2EHPA) as extractant. Li et al.[16] studied the effect of different diluents
and pH on the distribution coefficient of p-aminophenol
by using trialkylphosphine oxide (TRPO) as extractant.
Based on this research work, Qin et al.[17] attempted a
further study on the extraction of p-aminophenol by using the mixture of trialkylamine and D2EHPA as extractant with n-heptane as diluent. They found that there was
a synergistic effect when extracting p-aminophenol with
the mixed solvent. This method has broadened the application range of reactive extraction.
The research works referred to above give us a
foundation for the reactive extraction of diluted solution of organic compounds bearing both acid and basic
functional groups, but the theory of the extraction rule
is not yet perfected. There has not been a suitable extraction model like the extraction of carboxylic acids
with TOA[2], which can predict the reactive extraction
characteristics of amphoteric organic compounds.
o-Aminophenol (OAP), a white needle crystal, is
Received 2005-03-08, accepted 2005-11-20.
* Supported by the Educational Department of Henan Province (No.2004530001).
** To whom correspondence should be addressed. E-mail: [email protected]
Reactive Extraction of o-Aminophenol Using Trialkylphosphine Oxide
a typical amphoteric organic compound. It is commonly used in pesticides, printing, dye, and pharmaceutical industries as starting material. In this paper,
the reactive extraction characteristics of OAP with
TRPO were studied in n-octanol, kerosene, and chloroform diluents. The effects of TRPO concentration
and pH on the distribution coefficient were also investigated. These results will provide useful knowledge
and experience for further investigation of OAP
wastewater and the extraction of organic wastewater
containing other amphoteric compounds with TRPO.
47
finally two phases were available and separated. The
pH value of the aqueous phase was measured with a
pH meter (Hana pH HI 9321 model with a deviation
of ±0.01, Italy) and then the pH of aqueous phase
was adjusted to 1—1.5 by concentrated H2SO4. OAP
concentrations in the aqueous layers were analyzed at
271nm with a UV-250 spectrometer (Shimadzu, Japan). The solution concentrations in the organic phase
were calculated by a material balance. The deviation
of this method was less than 2%[17].
3
2 EXPERIMENTAL
2.1 Chemicals
o-Aminophenol was purchased from FLUKA
(German) with purity ≥99% (by mass). It is not stable
in an aqueous solution, so 0.1250g of OAP was dissolved in 500ml H2SO4 solution with the concentration
－
of 0.05mol·L 1 ; The concentration of the aqueous OAP
－
－
－
solution was 2.29×10 3mol·L 1 (250mg·L 1).
Kerosene was obtained from a local chemical
plant. After a fractional distillation, the collected
amount was in the range of 180℃ to 220℃. The distilled kerosene was washed with concentrated sulfuric
acid (98%) (VH2SO4︰Vkerosene =1︰5) twice and distilled water several times until the aqueous layer became neutral. The density of the sulfonated kerosene
－
was about 0.78g·cm 3.
TRPO was from CYTEC Canada Incorporation
with purity ≥93% (by mass) [The average molecular
－
weight of TRPO was 350, the density was 0.88g·cm 3
(25℃)]. TRPO contains a little acid and it will affect the
pH of the system greatly. So it needs to be washed with a
base before use. The TRPO solution was washed with
5% NaOH solution (VNaOH︰VTRPO=1︰5), then diluted
with H2SO4 (3%), and finally washed with distilled water
until the aqueous layer became neutral. All other reagents
were from the Beijing Chemical Reagent Plant with purity ＞99 % (by mass).
2.2
Experiments
All extraction experiments were conducted with
100ml conical flasks at 25℃. Unless otherwise noted,
25ml of OAP solution and 25ml of the mixture (different concentration of diluents and TRPO) were
added to each conical flask. Saturated NaOH and diluted H2SO4 were used to adjust the pH of the system.
The reaction mixture was shaken for about 1.5h in a
constant temperature shaker bath with a vibrating rate
－
of 180r·min 1 and then was left to equilibrate for 1—2h;
RESULTS AND DISCUSSION
OAP has one Lewis acid group, —OH, and one
Lewis base group, —NH2. This amphoteric compound
exists in three forms in aqueous solution: +H3NArOH (A+),
－
－
H2NArOH (A) and H2NArO (A ). Two dissociation
equilibria exist in aqueous solutions as follows:
Ka1
+
NH 2 ArOH+H +
NH 3 ArOH (1)
Ka2
NH 2 ArO − + H +
NH 2 ArOH (2)
with the dissociation balance constants of (1) and (2)
－
(mol·L 1):
+
K a1 =
[A] ⋅ [H ]
+
[A ]
−
K a2 =
+
[A ] ⋅ [H ]
[A]
(3)
(4)
where pKa1 and pKa2 are 4.72 and 9.72, respectively[18].
As can be seen from the above equations the pH of the
solution affects the existing forms of the solute greatly.
The cation of OAP exists at low pH (pH＜pKa1),
while the anion appears at high pH (pH＞pKa2), and
neutral OAP dominates at an intermediate pH (pKa1＜
pH＜pKa2). Fig.1 describes the molar fraction of the
different existing forms of OAP at different pH values.
It is apparent that the molar fractions of various forms
for OAP differs in different pH values. So the extraction behavior and mechanism are different in different
pH values.
3.1 The effect of pH on the distribution coefficient
A TRPO (R3P O) molecule has a phosphinyl
and a lone-pair electron, so it is a Lewis base. TRPO
reacts with neutral OAP by forming a hydrogen bond
with hydroxyl of OAP. So, the molar fraction of neutral OAP will reach the maximum with the increase of
the pH, and the distribution coefficient (D) also
greatly depends on the pH of the aqueous phase. As
Chinese J. Ch. E. 14(1) 46 (2006)
Chinese J. Ch. E. (Vol. 14, No.1)
48
fraction of various styles of o -aminophenol
indicated in Figs.2—4, the D value increased with the
increase of the pH value and then decreased. There is
a maximum D when the equilibrium pH value is between 6 and 7.5(initial pH value is between 6.5 and
8).Obviously, the variation trend of molar fraction
(Fig.1) has the same order as that of the D value. The
bigger the concentration of TRPO is，the more evident
is the departure of maximum D. As TRPO contains a
little phosphorous acid[19] (R2POH) and aliphatic acid[20],
its equilibrium solution pH tends to drop 0.5—2pH units
compared with the initial pH. According to reference[19], this kind of acid cannot be eliminated by base
washing completely. So, the acid will enter the aqueous phase and decrease the pH value in the aqueous
phase in the extraction process. To avoid this condition, the purity of TRPO and the optimization of pH
operation should be considered before extraction.
A
1.0
Figure 3
Extraction behavior of OAP with
TRPO+n-octanol
TRPO concentration, mol·L－1:
■ 0.266; ● 0.531; ▲ 0.797; ▼ 1.329; ◆ 2.338
A+
0.8
0.6
0.4
0.2
Figure 4
A
0
2
0
2
4
6
8
10
12
14
16
Extraction behavior of OAP with
TRPO+chloroform
TRPO concentration, mol·L－1:
■ 0.266; ● 0.531; ▲ 0.797; ▼ 1.329; ◆ 2.338
pH
Figure 1
Dependence of the fraction of o-aminophenol
styles on pH
A+ — o-aminophenol cation; A— neutral o-aminophenol;
A－ — o-aminophenol anion
Figure 2
Extraction behavior of OAP with
TRPO+kerosene
TRPO concentration, mol·L－1:
■ 0.266; ● 0.531; ▲ 0.797; ▼ 1.329; ◆ 2.338
February, 2006
3.2 The effect of extractant concentration on the
distribution coefficient
It can be seen from Figs.2—4 that D values increased
with the extractant concentrations. The increase of extractant concentration results in the increase of extractability.
Consequently, the extraction equilibrium moves toward
the direction of forming an extraction complex with the
increase of extractant concentration.
3.3 The effect of diluents on the distribution coefficient
From Fig.5, we can see that the physical extractability of n-octanol is greater than that of kerosene and
chloroform. From Figs.2—4 and Fig.6, it can be seen
that when the TRPO concentrations are the same,
TRPO/kerosene mixture has higher D values than that
of TRPO/n-octanol and TRPO/chloroform. This phenomenon is closely related to the following factors.
Reactive Extraction of o-Aminophenol Using Trialkylphosphine Oxide
49
This is owing to the fact that the acidity of OAP (pKa＝
4.74, pKb=4.74) is stronger than that of p-aminophenol
(pKa=5.29, pKb=3.70). This result conforms to the theory
of Lewis acid-base, which is the basis of reactive extraction.
5
Figure 5 Extraction behavior of OAP with diluent
■ kerosene; ▲ chloroform; ◆ n-octanol
Figure 6
Extraction behavior of OAP with different diluent
■0.797mol·L－1 TRPO＋ kerosene;
●0.797mol·L－1 TRPO＋ n-octanol;
▲0.797mol·L－1 TRPO＋ chloroform
Chloroform has a stronger acidity than that of
n-octanol and n-octanol in turn has a stronger acidity
than that of kerosene. The hydrogen bonds formed between TRPO and acid diluents (chloroform, n-octanol)
weaken the extractability of TRPO to OAP. So the extractability of TRPO /chloroform or TRPO/n-octanol is
weaker than that of TRPO/ kerosene.
CONCLUSIONS
(1) TRPO mainly reacts with neutral OAP. The
distribution coefficient increased with the increase of
undissociated neutral OAP in the aqueous phase. As
TRPO contains a little phosphorous acid and aliphatic
acid, the equilibrium solution pH is different from the
initial one. The distribution coefficient greatly depends on the pH of the aqueous phase.
(2) The experimental results show that polar
diluents are not favorable to the reactive extraction of
OAP with TRPO. Nonpolar diluents could provide
better extraction distribution coefficient and the order
is: kerosene＞ n-octanol>chloroform. The hydrogen
bonds formed between TRPO and acid diluents
weakened the extractability of TRPO to OAP. Kerosene will be a suitable choice as diluent when TRPO is
used to extract OAP in wastewater.
NOMENCLATURE
D
distribution coefficient
Ka1 the first dissociation constant of OAP, mol·L－1
Ka2 the second dissociation constant of OAP, mol·L－1
REFERENCES
1
2
3
4
COMPARISON WITH OTHER WORKS
We reported the extraction equilibrium of
p-aminophenol with TRPO[16]. As a little remnant phosphorous acid (R2POH) and aliphatic acid in TRPO were
not treated with alkali, it caused the emulsification phenomenon and therefore the peak value of extraction was
not obtained. In our present work, two systems, 20％
TRPO+PAP (p-aminophenol)+n-octanol (previous work)
－
and 0.531mol·L 1+PAP+n-octanol (present work), are
compared and it was found that the extraction capability
of TRPO is greater than that of PAP (both have the same
initial concentration of TRPO and the peak value D).
4
5
6
7
King, C.J., “Separation process based on reversible
chemical complexation ” , Handbook of Separation
Process Technology, Chapter15, John Wiley & Sons,
New York, 760—774 (1987).
Li, Z.Y., “Extraction mechanism of carboxylic acid by
tri-n-octylamine”, Ph. D. Thesis, Tsinghua Univ., Beijing
(2001). (in Chinese)
Hong, Y.K., Hong, W.H., “Reactive extraction of succinic
acid with tripropylamine (TPA) in various diluents”, Bioprocess Engineering, (22), 281—284(2000).
Maria, M., George, K., Joël, A., Jacques, M., Guy,
M.,“Separation of tartaric and lactic acids by means of solvent extraction”, Separation and Purification Technology,
(37), 199—207(2004).
Aynur, S., “Extraction equilibria of valeric acids using Alamine 308/diluent and conventional solvent systems. Modeling
considerations”, Chem. Eng. Proc., (41), 681—692(2002).
Li, G. Z., Zhao, H., “Study on extraction of
o-dihydroxybenzene with tributyl Phosphate”, Shanghai
Environmental Sciences, 22(3), 197 — 199(2003). (in
Chinese)
Cai, R., Guan, G.F., “Study on caprolactam waste water
Chinese J. Ch. E. 14(1) 46 (2006)
Chinese J. Ch. E. (Vol. 14, No.1)
50
8
9
10
11
12
13
treatment”, Journal of Nanjing University of Chemical
Technology, 22(5), 73—75(2000). (in Chinese)
Liu, Y. Sh., Dai, Y.Y., Wang, J.D., “Distribution behavior
of L-phenylalanine by extraction with di(2-ethylhexyl)
phosphoric acid”, Sep. Sci. Tech., 34(11), 2165 —
2176(1999).
Liu, Y. Sh., Zhang, J., Dai, Y.Y., “Study on extraction of
L-isoleucine with di(2-ethylhexyl)phosphoric acid”, J.
Chem. Eng. Chin. Univ., 14(5), 415—419(2000). (in
Chinese)
Liu, Y.Sh., Di, Y.Y., “Extraction of L-tryptophane with
di(2-ethylhexyl)phosphoric acid”, J. Chem. Ind. Eng.
(China), 52(3), 216—221(2001). (in Chinese)
Yoshinori, I., Kurose, S., Takashi, K., “Extraction of unprotected amino acids by mixed-ligand nickl (II) and
copper (II) chelates”, Monatshefte fÜr Chemie, 132,
1433—1438(2001).
Li, Zh. Y., Yang, Y.Y., Dai, Y.Y., “Extraction of
p-amionbenzen sulfonic acid with trialkylamine(7301)
based on chemical complexation”, J. Chem. Ind. Eng.
(China), 51(1), 85—89(2000). (in Chinese)
Li, Zh.Y., Qin, W., Yang, Y.Y., Dai, Y.Y., “Extraction
p-aminobenzene sulfonic acid from dilute solution by
chemical complexation with aliquat 336”, J. Chem. Eng.
Chin. Univ., 15(6), 578—582(2001). (in Chinese)
February, 2006
14
15
16
17
18
19
20
Zhang, J., Liu, Y. Sh., Liu, Z.Y., Dai, Y.Y., “A study on
extraction aminobenzoic acid based on chemical complexation”, Environmental Chemistry, 19(2), 131 —
135(2000). (in Chinese)
Zhang, J., Dai, Y.Y., “Distribution behavior of aminobenzoic acid by extraction with di(2-ethylhexyl)phosphoric acid”, Chinese J. Chem. Eng., 8(4), 300 —
303(2000).
Li, D.L., Qin, W., Dai, Y.Y., “Extraction equilibrium of
p-aminophenol with TRPO”, J. Chem. Ind. Eng. (China),
54(3), 339—342(2003). (in Chinese)
Qin, W., Li, D.L., Dai, Y.Y., “Liquid-liquid Equilibria of
p-aminophenol between water and trialkylamine, trialkylphosphine oxide, and di(2-ethylhexyl)phosphoric acid in
heptane”, J. Chem. Eng. Data, 48, 1606—1609(2003).
Dean, J.A., Lang’s Handbook of Chemistry,
McGraw-Hill, New York (1985).
Lu, X.Y., “Synthesis of phosphoric extractant”, Science
and Technology of Nuclear Energy, (6), 627—635(1964).
(in Chinese)
Xin, R.X., Wu, W., Jiao, J.X., “Determination of trace
fatty acids in tri-alkyphosphine oxide by pyrolysis methylation gas chromatography”, Chinese Journal of
Analysis Laboratory, 20(1), 8—11(2001). (in Chinese)