RESEARCH NOTES
Chinese Journal of Chemical Engineering, 20(5) 1034ü1038 (2012)
Effect of Polyethylene Glycol on the Properties of -Al2O3 Formation
by Polyaluminum Chloride*
ZHAO Changwei (ვЩฟ)1,**, WANG Xiaonian (ฆໍભ)2, HE Jingsong (‫࠱ۥ‬ഞ)1, WANG
Yuanyuan (ฆၓၓ)1 and LUAN Zhaokun (៥ი࣯)1
1
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences,
Chinese Academy of Sciences, Beijing 100085, China
2
The Equipment Research Institute of PLA’s Second Artillery, Beijing 100085, China
Abstract A polyaluminium chloride solution with high Al13 content self-prepared was used as material for preparing the spherical -Al2O3 by the sol-gel and oil-drop method. Polyethylene glycol with different molecular mass
was used as surfactant to investigate the effect on property of -Al2O3. The physical property was characterized by
27
Al NMR (nuclear magnetic resonance) spectra, X-ray diffraction, FT-IR (Fourier transform infrared spectroscopy)
and TG-DTA (thermogravimetric-differential thermal analysis). The results showed that surface area, pore volume
and pore size of -Al2O3 all increased with the increase of polyethylene glycol molecular mass in the experimental
research range, and polyethylene glycol 10000 was the most suitable pore forming additive. -Al2O3 with surface
area of 339 m2·g1, pore volume of 0.59 cm3·g1 and pore diameter of 6.9 nm were obtained at 450 °C.
Keywords -Al2O3, polyaluminum chloride, preparation, polyethylene glycol
1
INTRODUCTION
-Al2O3 is widely used as catalysts, adsorbents,
coatings and alumina derived materials in many processes [16]. Macro-mesostructured -Al2O3 support
with high BET surface area is important and useful for
the treatment of bulky molecules, such as petroleum
heavy cuts and residues. In order to prepare macromesostructured -Al2O3, using surfactant as pore forming additive is a feasible method to improve surface
area of alumina sample [710]. Different aluminum
sources and preparation methods lead to different
sample properties. It is significant to find new source
to prepare pseudo-boehmite and -Al2O3. Polyaluminium chloride (PAC) is an intermediate product in
the processes of hydrolysis, polymerization, gelation
and precipitation of aluminum species [1115]. Among
Al species in PAC, active species Al13 has an -Keggin
structure of the tridecameric polymer with a charge of
+7 and a size of 1.06 nm, and is now used in many
fields such as catalysis, material and environment
protection for its nano-sized and positively charged
characteristics [1619].
Previous study proved that PAC including Al13
species can be used as raw material to prepare
pseudo-boehmite and -Al2O3 [20, 21]. However, there
are few reports on surfactant effect on sample property
using new PAC including Al13 species as aluminum
source. The goal of this work is the study of the influence of polyethylene glycol (PEG) with different molecular mass on pseudo-boehmite and -Al2O3 when
high concentration PAC including high Al13 content is
as new aluminum source.
2
EXPERIMENTAL
2.1 Materials and method
In order to investigate the property and broaden
the application of a new high concentration PAC prepared from our laboratory, a 2.1 mol·L1 concentration
PAC solution self-made by chemical synthesis-membrane
distillation (MD) method: Firstly, a 0.2 mol·L1 PAC
was prepared by neutralizing 170 ml of 1 mol·L1
AlCl3 aqueous solution in a 1000-ml glass reactor kept
at 65 qC by adding 420 ml of 0.6 mol·L1 NaOH solution and reacting for 12 h at 65 qC. Then MD process
was applied to concentrate the 0.2 mol·L1 PAC solution in a membrane module equipped with flat-sheet
membrane having efficient area of 70 cm2. The membrane material is a hydrophobic microporous PVDF
(IPVH00010, Millipore) with 0.45 m pore size and is
placed between the two identical chambers. The temperature of the feed and the permeate were controlled
at 55 °C and 20 °C respectively. The permeate side was
flushed with tap water. After MD of 30 h, 480 ml of
2.1 mol·L1 concentration PAC solution was prepared
and used as raw material for preparing spherical -Al2O3.
NH3·H2O (purity>99%), nitric acid (purity>99%),
liquid paraffin (purity>99%), PEG 1000, 4000 and
10000 (purity>99%) were supplied from Beijing
Chemical Reagent Company, Beijing, China.
Ferron reagent (mixture reagent) was prepared as
follows [22]: 0.2% (by mass) Ferron (8-hydroxy-7iodoquinoline-5-sulfonic acid, Sigma Chemical Co.,
USA) solution, 20% NaAc solution, and 100 ml was
mixed with 900 ml of deionized water and 1Ή9 HCl
(using 37% hydrochloric acid) solution were prepared
Received 2011-07-11, accepted 2012-03-05.
* Supported by the National Natural Science Foundation of China (21076219), and the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry (ITLXHG2009071702).
** To whom correspondence should be addressed. E-mail: [email protected]
1035
Chin. J. Chem. Eng., Vol. 20, No. 5, October 2012
and filtered through pre-washed 0.45 m membranes
separately. The Ferron colorimetric solution was obtained by mixing 0.2% Ferron, 20% NaAc and 1Ή9
HCl at a ratio of 2.5Ή2Ή1.
2.2 Preparation of spherical pseudo-boehmite and
-Al2O3
Spherical pseudo-boehmite and its derivative
-Al2O3 were prepared by a combination of the sol-gel
method and oil-drop method. Pseudo-boehmite sol
was firstly prepared by sol-gel method as follows:
70 ml of 4% NH3·H2O solution was added into 250 ml
of 2.1 mol·L1 PAC solution in a bath temperature of
65 °C, then PEG 1000, 4000 or 10000 used as surfactant separately was added into solution up to the content range of 5%25% under mechanical stirring of 40
min at the same temperature. The resulted white slurry
was aged for 6 h to form alumina hydrate gel and then
washed with distilled water to pH value to 7. After that,
1 mol·L1 HNO3 was peptized into gel at the H+/Al3+
molar ratio of 0.12 under ultrasonic action for 20 min.
The resulted pseudo-alumina sol became viscous and
was transferred to a dropper for granulation process. The
droplets first fell through liquid paraffin layer (relative
density 0.8450.890 g·cm3, viscosity 30.4232.04
mPa·s) and partially formed spherical wet-gel granules
by the surface tension, and then the wet-gel granules
fell through an 8% (by mass) ammonia solution layer
with the 45 cm depth. The structure of the wet-gel
granules were consolidated after aging in the ammonia
solution for 4 h. The granules were then removed from
the ammonia solution, dried in an ambient oven at 60 °C
for 12 h, and finally calcined in the muffle furnace at
450 °C for 8 h.
2.3
Analytical methods
The Al species in solution was measured by the
Al-Ferron Assay [23] with a transient colorimetric reaction with Ferron reagent to provide Al species distribution based on chemical reactivity on a UV-Vis
spectrophotometer (DR/4000U, Hach, USA). Based
on the kinetic difference of the reactions between the
Al species and Ferron reagent, the hydrolyzed Al species can be divided into three types: monomeric species (Ala) (reacting with Ferron from 0 min to 1 min),
oligomeric and medium polymeric species (Alb) (reacting with Ferron from 1 min to 120 min), and colloidal hydroxides (Alc) (reacting with Ferron after 120
min and non-reacting with Ferron). 27Al solution nuclear magnetic resonance (NMR) spectroscopy was
used as another analytical tool to characterize the aluminum species distribution. 27Al NMR spectra were
generated at 70 °C on a Fast Fourier Transformation
spectrometer (JNM-ECA600, JOEL, Japan), which
was operated at a field strength of 14.09 T, single
pulse method, resonating frequency 156.39 MHz,
X-pulse of 6.4 s, X-acq-duration 0.20 s, repetition
time 0.50 s, relaxation delay 0.30 s, scans 2048.
Transmission electron microscopic (TEM) image was
obtained on a TECNOL 20 microscope (Philips, Dutch).
The crystalline phases of the samples were characterized by X-ray diffraction (Shimadzu XRD-6000, Japan) technique at 40 kV and 30 mA, with Cu K radiation, 0.15418 nm. Diffraction patterns were run
from 10°80° at a scan speed of 5°·min1. Nitrogen
adsorption-desorption isotherms (ASAP 2000, Micrometrics, USA) were determined and the surface areas
were calculated using the BET equation. The pore
volume and pore size distribution were determined by
mercury porosimetry (ASAP 2000, Micromeritics,
USA). The spectrum of the samples was obtained by
Fourier transform infrared spectroscopy (FT-IR) (Nexus
670, Nicolet, USA) at room temperature using KBr
pellets. Thermogravimetric-differential thermal analysis (TG-DTA) curves of the samples were carried out
using a TGA-Q50 (TA-Waters, USA) instrument at a
heating rate of 10 °C·min1.
3
3.1
RESULTS AND DISCUSSION
Al species distribution
The 2.1 mol·L1 PAC with high Al13 content of
81.5% (based on moles of Al) was prepared by chemical synthesis-membrane distillation method. The content of Al species in the solutions is shown in Table 1.
Table 1
Al species distribution of PAC
solutions by ferron assay
AlT/mol·L1
Ala/%
Alb/%
Alc/%
Al13
2.1
4.5
88.2
7.3
81.5
Note: AlT Total Al species concentration, Ala Al monomer
mole percentage, Alb Al oligomeric and medium polymer
mole percentage, Alc Al colloidal hydroxide mole percentage,
Al13 = Al13 polymerization percentage.
Figure 1 shows the 27Al NMR spectrum signals
of PAC solution sample with high Al13 content in
our laboratory. The peak at 63.0 ppm can be attributed
to central tetrahedral Al atom of the Keggin
[AlO4Al12(OH)24 (H2O)12]7+ ion Al13. Firstly, The 80
ppm resonance represented the standard sample, sodium aluminate, and was set as 1.0. Integrating 0 ppm
Figure 1
solution
27
Al NMR spectrum of a polyaluminum chloride
1036
Chin. J. Chem. Eng., Vol. 20, No. 5, October 2012
peak area, a standard curve was obtained regarding the
peak area as abscissa and Al concentration as the coordinate. The aluminum content was calculated according to the standard curve with the 80 ppm peak
area as the basis. The Al13 polymerization percentage
was obtained as central tetrahedral Al atom of the Keggin [AlO4Al12(OH)24 (H2O)12]7+ ion multiplied by 13.
Table 3
Content/%
BET surface area
/m2·g1
pore volume
/cm3·g1
pore size
/nm
3.2 Effect of PEG with different molecular mass
on -Al2O3 sample
In experiment, PEG 1000, 4000 and 10000 were
chosen as surfactant and added with the 15% content
to PAC solution. The effects of PEG with different
molecular mass on -Al2O3 sample were investigated.
The surface area, pore volume and pore size of
-Al2O3 after 450 °C calcination with different PEG as
surfactant are shown in Table 2.
Table 2
Surfactant
Pore volume
/cm3·g1
Pore diameter
/nm
no surfactant
282
0.41
4.5
PEG1000
298
0.44
4.9
PEG4000
314
0.49
5.6
PEG10000
339
0.59
6.9
ķ Experimental conditions: PEG addition is 15%, calcined at
450 °C.
From Table 2 we can see that surface area, pore
volume and pore size of -Al2O3 all increased with the
increase of PEG molecular mass in the experimental
range. PEG 10000 is most suitable for increasing surface area of -Al2O3. Based on PEG10000 as surfactant, Table 3 gives the effects of surfactant content on
-Al2O3 sample calcined at 450 °C. It can be seen that
the surface area, pore volume and pore size are the
biggest at PEG10000 15% in the experimental range.
Figure 2 shows the micro-structure of -Al2O3
after 450 °C calcination with different PEG as surfactant at 15% content. From TEM images it can be seen
FEG 1000
Figure 2
5
296
0.44
5.2
10
316
0.56
6.1
15
339
0.59
6.9
20
322
0.55
6.5
25
286
0.45
5.0
that the structure are porous for every sample, pore
diameter of the sample with PEG 10000 is the largest.
3.3 Effect of PEG with different molecular mass
on alumina sample phase
To further characterize alumina crystal morphology, the XRD patterns of alumina samples with different PEG as surfactants are shown in Fig. 3. The
diffraction pattern of every sample after 450 °C calcination shows the main strong diffraction peaks of
-Al2O3 at 2 19.27°, 37.43°, 39.66°, 46.02°, 66.73°.
It can be seen the sample can retain its structure although
surfactant added. The result indicated that PAC with
high Al13 content can be used as raw material to prepare the spherical -Al2O3 granules by sol-gel method.
Pore structure of -Al2O3 granules obtained
with different surfactantsķ
BET surface area
/m2·g1
Pore structure of -Al2O3 granules obtained
with different PEG10000 content
3.4 Pore forming mechanism of PEG with different molecular mass
To further investigate the pore forming mechanism of PEG 1000, 4000 and 10000 as surfactant, the
FT-IR spectra is characterized and shown in Fig. 4,
showing that the peaks at 1384 cm1, 1070 cm1 and
842420 cm1 can be attributed to the pseudo-boehmite.
The adsorption peak at 1633 cm1 is due to the complex peak of the residual water intercalated in the layers of pseudo-boehmite and OH groups on the surface of pseudo-boehmite. Compared to curve without
surfactant, the curve with surfactant shows distinct
peaks located around 2900 cm1 and 952 cm1. These
FEG 4000
FEG 10000
TEM images of -Al2O3 granules obtained with different surfactants
Chin. J. Chem. Eng., Vol. 20, No. 5, October 2012
1037
Figure 3 XRD patterns of -Al2O3 granules obtained with different surfactants
Figure 4
FT-IR spectra of spherical pseudo-boehmite granules with different surfactants
peaks are due to the vibration of OH group and
C O C group of PEG. The results illustrate that PEG
molecules are chemisorbed on the surface of the
products.
Figure 5 illustrates the TG-DTA results of samples
with and without PEG10000 surfactant. From Fig. 5 (a)
we can see that the DTA curve show that two endothermic peaks exist at around 132 °C and 418 °C. There is
also one broad exothermic peak corresponding to the
second mass loss process. An endothermic peak at 132
°C is due to desorption of the surface water. The endothermic peak at 418 °C is attributed to the release of
interlayer water. There is no distinct peak after 450 °C
in the range of experimental research temperature,
which indicates that pseudo-boehmite transformed
Figure 5 DTA curve of pseudo-boehmite granules (a) no
surfactant; (b) PEG 10000 surfactant
1038
Chin. J. Chem. Eng., Vol. 20, No. 5, October 2012
completely to -Al2O3. It is thus known that the excess
water molecules in the colloid were removed by calcination. As shown in Fig. 5 (b) with PEG 10000 surfactant, the DTA curve show that one endothermic
peak exists between 135 and 145 °C, which is result
of release of desorption of the surface water and PEG
evaporation. Around 262 °C there is one exothermic
peak corresponding to the second mass loss process,
which is result of decomposition of PEG 10000 surfactant. There is also no distinct peak after 450 °C in the
range of experimental research temperature, which indicates that pseudo-boehmite transformed to -Al2O3.
REFERENCES
1
2
3
4
5
6
7
8
9
Zhang, X., Zhang, F., Chan, K.Y., “The synthesis of large mesopores
alumina by microemulsion templating, their characterization and
properties as catalyst support”, Mater. Lett., 58, 28722877 (2004).
Cai, W.Q., Yu, X.F., “Preparation of macro-mesostructured pseudoboehmite and -Al2O3 with high surface area”, Progr. Chem., 19,
13221330 (2007). (in Chinese)
Ren, T.Z., Yuan, Z.Y., Su, B.L., “Microwave-assisted preparation of
hierarchical mesoporous-macroporous boehmite AlOOH and -Al2O3”,
Langmuir, 20, 15311534 (2004).
Rachiero, G.P., Demirci, U.B., Miele, P., “Facile systhesis by polyol
method of a ruthenium catalyst supported on -Al2O3 for hydrolytic
dehydrogenation of ammonia borane”, Catal. Today, 170, 8592 (2011).
Chen, R.Z., Du, Y., Xing, W.H., “Effect of alumina particle size on
Ni/Al2O3 catalysts for p-nitrophenol hydrogenation”, Chin. J. Chem.
Eng., 15 (6), 884888 (2007).
Dang, D., Ding, W.M., Ceng, A., “Isotherm equation study of F adsorbed from water solution by Fe2(SO4)3-modified granular activated
alumina”, Chin. J. Chem. Eng., 19 (4), 581585 (2011).
Liu, M.Z, Yang, H.M., “Large surface area mesoporous Al2O3 from
kaolin: Methodology and characterization”, Appl. Clay. Sci., 50,
554559 (2010).
Gonzalez-Pena, V., Diaz, I., Marquez-Alvarez, C., “Thermally stable
mesoporous alumina synthesized with non-ionic surfactants in the
presence of amines”, Micro. Mes. Mater., 44-45, 203210 (2001).
Zhang, Z.R., Pinnavaia, T.J., “Mesostructured -Al2O3 with a lathlike
framework morphology”, J. Am. Chem. Soc., 124, 1229412301 (2002).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Cai, W.Q., Li, H.Q., Zhang, Y., “Azeotropic distillation-assisted
preparation of macro-mesostructured -Al2O3 nanofibres of crumpled
sheet-like morphology”, Mater. Chem. Phys., 96, 136139 (2006).
Luan, Z.K., “Study on basic theory and application of inorganic
polymer flocculate polyaluminum chloride”, Ph.D. Thesis, Research
Center for Eco-Environmental Science, CAS, China (1997). (in
Chinese)
Qu, J.H., Liu, H.J., “Optimum conditions for Al13 polymer formation
in PACl preparation by electrolysis process”, Chemosphere, 55,
5156 (2004).
Hu, C.Z., Liu, H.J., Qu, J.H., “Coagulation behavior of aluminum
salts in eutrophic water: significance of Al13 species and pH control”,
Environ. Sci. Technol., 40, 325331 (2006).
Gao, B.Y., Chu, Y. B., Yue, Q.Y., “Characterization and coagulation
of a polyaluminum chloride (PAC) coagulant with high Al13 content”,
J. Environ. Sci., 21, 1822 (2005). (in Chinese)
Lin, J.L., Huang, C.H., Pan, J.R., “Effect of Al(III) speciation on
coagulation of highly turbid water”, Chemosphere, 72, 189196
(2008).
Sanabria, N.R., Centeno, M.A., Molina, R., “Pillared clays with
Al-Fe and Al-Ce-Fe in concentrated medium: Synthesis and catalytic
activity”, Appl. Catal. A Gen., 356, 243249 (2009).
Vicente, M.A., Belver, C., Trujillano, R., “Preparation and characterisation of vanadium catalysts supported over alumina-pillared clays”,
Catal. Today, 78, 181190 (2003).
Casey, W.H., “Large aqueous aluminum hydroxide molecules”,
Chem. Rev., 106, 116 (2006).
Qian, Z.S., Feng, H., Yang, W.J., “Theoretical investigation of water ex7
change on the nanorneter-sized polyoxocation AlO 4 Al12 (OH) 24 (H 2 O)12
(Keggin-Al13) in aqueous solution”, J. Am. Chem. Soc., 130,
1440214403 (2008).
Zhao, C.W., He, J.S., Ren, X.J., “Preparation and property of pseudoboehmite by polyaluminum chloride”, Chin. Inorg. Chem., 26,
521524 (2010). (in Chinese)
Zhao, C.W., Wang, X. N., Luan, Z.K., “Preparation and characterization of -Al2O3 by polyaluminum chloride with high Al13 content”,
Chin. J. Chem. Eng., 18 (2), 333336 (2010).
Feng, C.H., Shi, B.Y., Wang, D.S., “Characteristics of simplified
ferron colorimetric solution and its application in hydroxy-aluminum
speciation”, Colloids Surfaces A Physicochem. Eng. Aspects., 287,
203211 (2006).
Chen, Z.Y., Fan, B., Peng, X.J., “Evaluation of Al30 polynuclear species
in polyaluminum solutions as coagulant for water treatment”, Chemosphere, 64, 912918 (2006).