Journal of Geoscience and Environment Protection, 2014, 2, 68-76
Published Online April 2014 in SciRes. http://www.scirp.org/journal/gep
How to cite this paper: Zhang, T. et al. (2014). Preparation and Characterization of a New Desulfurizer and Its Performance
on Removal of SO2. Journal of Geoscience and Environment Protection, 2, 68-76. http://dx.doi.org/10.4236/gep.2014.22011
Preparation and Characterization of a New
Desulfurizer and Its Performance on
Removal of SO2
Ting Zhang, Jun qing Li, Shurong Yu*, Yi Wang
School of Petrol-Chemical Engineering, Lanzhou University of Technology, Lanzhou, China
Email: firstname.lastname@example.org, email@example.com, *firstname.lastname@example.org, email@example.com
Received January 2014
Sulfur dioxide is one of the major pollutants resulting from fuel combustion. In this study, CaO and
attapulgite were utilized as raw material for synthesizing CaO/attapulgite (CaO/ATP) desulfurizer.
The physicochemical characteristics of CaO/ATP desulfurizer were evaluated by various tech-
niques such as XRD, SEM, FT-IR. The performance of samples was studied in dynamic conditions.
Major factors affecting on desulfurization such as weight ratio of CaO to total, types of modifiers,
roasting time and temperature were investigated. The desulfurization agent synthesized under
optimal synthesis conditions with CaO content of 30 wt% and NaOH modifier, and the desulfuriza-
tion roasting time of 2 hours and roasting temperature of 600˚C, exhibit sulfur tolerance of 10.15
wt%. This desulfurizer with excellent absorbency and catalysis of desulfurization, economical and
environment-friendly, could be especially useful in industrial applications.
Attapulgite; CaO; Desul furi zation; SO2; Ad sor p tion
Sulfur dioxide (SO2) emission from coal-fired power plants and refinery operations is one of the most important
pollution among other pollutants. Discharge of SO2 from various sources can easily create air pollution and
cause harmful effects on living things and the environment. For instance, it causes acid rain affecting negatively
on plant and animals (Aytar , 2011; Cao, 1996; Chen, 2003).
It is noted that the dry processes are generally advantageous over the wet systems in terms of secondary
treatment of wastes produced during wet methods. So because of their simplicity and relatively low cost, dry
sorption technologies are applied more than the wet methods. Application of calcium-based sorbents, spray dry
flue gas desulfurization, metal oxides sorption and activated carbon or coke processes are the main dry sorption
processes used for SO2 and NOx removal (Che n, 2003).
Lime/gyp method is a conventional dry desulfurizing method, which uses CaO or Ca(OH)2 as desulfurizers.
T. Zhang et al.
The lime/gyp method is considered to be more effective and cheaper than other desulfurizing methods, such as
activate carbon adsorption and Claus recycle, etc. But the calcium-based desulfurizer has a big problem: It is
easy to scaling during the process of desulfurization, because CaSO4, whose molar volume is three times as much as
CaO, is generated, and the micro pore of desulfurizer would be soon jammed by CaSO4, which prevent the reaction
and decreased SO2 removal efficiency (Chen, 2004; Fro st, 1998; Görkem, 2006; Her ná nd e z -Maldonado, 2005).
In the field of dry and regenerable sorbents, considerable attention has been devoted to activated carbon or ac-
tivated coke due to their large adsorption capacity of SO2 at near room temperatures (Li, 2007; Li, 2008). Much
work has also been done on metal oxides such as CuO, Fe2O3, MnO, CaO, Co3O4, ZnO and CeO2 for H2S or
SO2 capture at higher temperatures (Li n, 1998). Despite that the metal oxides alone exhibit high sulfur sorption
capacity, their performance and life time are adversely affected by problems such as sintering, evaporation, and
mechanical disintegrations. To overcome these problems, Al2O3 and natural zeolites were added to metal oxides
or their mixtures as structure stabilizer (Liu, 2011; Ma, 20 03; P an, 2005). Jianrong Ma et al. (Cao, 1996) i nve s-
tigated a novel regenerable Fe/activated coke (AC) desulfurizer prepared by impregnation of Fe(NO3)3 on an ac-
tivated coke. Experiment results showed that at 200˚C the SO2 adsorption capacity of the Fe/AC was higher than
that of AC or Fe2O3.
Attapulgite (or palygorskite-as it often called) is a crystalline hydrated magnesium aluminum silicate with
unique three-dimensional structure and has a fibrous morphology. Attapulgite has the structural formula
Si8O20Mg5(Al)(OH)2(H2O)4∙4H2O. The distinguishing feature of its structure is that the Si-O tetrahedral form
long strips, each an amphibole unit wide, on alternate sides of the oxygen sheet in a manner which confers a
regular corrugated Si-O structure. The formulas are written as such to indicate the two types of water present;
magnesium coordinated water and adsorbed water. The structure of the mineral results in zeolite-like channels,
which are approximately 3.7×6.0 and 5.6×11.0Å wide, respectively. These channels may be filled with water or
organic molecules. The water is partly arranged in these channels and water molecules are also bound to the
magnesium cations of the Mg(Al, Fe) brucite-like ribbon edges that border the channels running along the length
of the crystals. Specific surface areas of about 200m2/g may, therefore, result form fine particle size rather than
significant contributions from internal channel surface (Perderiset, 1988; S he n, 2012; W a ng, 2005). Because of
its structural morphology, attapulgite has received considerable attention with regard to the adsorption of organ-
ics on the clay surface and to their use as support for catalysts (Wa ng, 2011; Wie c kowska , 1995; Yan, 2002).
In this study, CaO and attapulgite were utilized as raw material for synthesizing CaO/attapulgite (CaO/ATP)
desulfurizer. Major factors affecting on desulfurization such as weight ratio of CaO to total, types of modifiers,
roasting time and temperature were investigated.
2.1. Material and Equipment
Attapulgite clay came from Linze County, Gansu Province, China (60-mash sieve, specific surface area 110 ~
150 m2/g), with ATP content of 31% ~ 57%, illite and kaolinite content of 18% ~ 23%, quartz and feldspar con-
tent of 15% ~ 25%, dolomite and montmorillonite content of trace. Its chemical components (%) are as follows:
SiO2, 57.61; Al2O3, 14.06; MgO, 1.10; CaO, 5.26; Fe2O3, 4.96; K2O, 2.57; Na2O, 1.41; Ti, 0.3873; Mn, 0.0603;
P, 0.0585; Sr, 0.0451; Ba, 0.0424; Zr, 0.0197; V, 0.0093; Cr, 0.0071; Zn, 0.0067; La, 0.0041; Ni, 0.0032; Cu,
0.0030; Y, 0.0024; Pb, 0.0015; Th, 0.0014; Nb, 0.0013; Co, 0.0010. The other reagents supplied by their manu-
facturers was all analytical pure.
2.2. Preparation Method of the Desulfurizer
CaO, ATP and some water were mixed and well-distributed at a certain ratio. The mixture was aged for a day,
shaped, and dried in the oven at the temperature of 105˚C. The samples were roasted in the high temperature
oven at 600˚C for 2 hours, then cooled. The CaO/ATP desulfurizer samples were obtained.
2.3. Characterization and Analysis
SEM was utilized to determine the crystal morphology and chemical element composition. Measurements were
made on a JSM-5500 SEM instrument using a digital imaging process. FT-IR was used to confirm the chemical
groups in the prepared CaO/ATP desulfurizer. Measurements were made on a Nicolet AVTAR 360 FT-IR spec-
trometer after samples were mixed with 300 mg of spectroscopic grade KBr and ground in an agate mortar. The
T. Zhang et al.
crystalline form of the samples was identified by a Panalytical X’Pert PRO XRD instrument (Cu Ka radiation),
operating at 40 kV and 30 mA. Surface area, pore volume, and pore size distribution were obtained on a
ASAP2010 BET apparatus.
2.4. Determining the Properties of the CaO/ATP Desulfurizer
The ability of desulphurization of CaO/ATP desulfurizer was determined by the experiment equipment showed
in Figure 1. The experimental conditions can be seen in Table 1. SO2 gas went through the little desulfurizing
tower continuously and was absorbed and transferred by CaO/ATP desulfurizer. SO2 concentration both at the
inlet and at the outlet were determined ever few minutes until the desulfurizer was fully penetrated (SO2 con-
centration at the inlet equals to that at the outlet). Then the desulfurization efficiency curves (penetrating curves)
were obtained and the sulfur tolerance (S) was calculated by following formula:
Ga—the weight of the desulphurizer after desulphurization;
Gb—the weight of the desulphurizer before desulphurization.
3. Results and Discussion
3.1. Characterization of the Synthesized Samples
The phase structures of samples were investigated by XRD, and the obtained results are shown in Figure 2 and
Figure 3. XRD patterns of the samples prepared with different CaO content are contrasted with those of ATP.
Samples CaO/ATP with different CaO content showed the characteristic peaks (26.8˚, 29.9˚, 39.6˚, 43.3˚, 47.6˚,
Figure 1. Experimental equipment.
Table 1. Characteristics of experimental conditions.
Desu l f urizer C a O / ATP
Column length (m) 0.20
Column diameter (m) 0.02
Particle diameter (m) 0.003
Total porosity 0.34
Apparent density (kg/m3) 398.089
BET surface area (m2/g) 206.9
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Figure 2. XRD patterns of ATP and CaO/ATP samples with different CaO
Figure 3. XRD patterns of CaO/ATP samples with different modifier (□—
48.4˚) of cubic spinel structure known from bulk CaO phase. The intensity of some characteristic peaks of CaO
of CaO/ATP sample became stronger along with CaO content increasing.
Figure 3 showe d XRD patterns of CaO/ATP samples were disposed by H2SO4, NaOH respectively. From
Figure 3 we can see that the samples which were disposed by NaOH did not change remarkably compared with
the samples which were not disposed. The main reaction of that is ion exchange. But when H2SO4 was used as
modifier, CaO reacted with H2SO4 and generated CaSO4.
SEM micrographs were collected to illustrate the morphologies of ATP, CaO/ATP, modified samples by
MgCl 2, H2SO4 or NaOH, as depicted in Figure 4. Rod-shaped particles with lengths of 500 ~ 700 nm and widths
of 100 ~ 150 nm are visible (Figur e 2(a)). After the introduction of CaO species into ATP, rod-shaped crystal
still can be seen, but the surface area decreased (Figure 2(b)). Morphological observations of CaO/ATP mod-
ified by NaOH is shown in Figure 2(c), which we cannot see the rod-shaped particles because NaOH destroyed
three-dimensional space structure of ATP (Zhan g, 2005), the surface area increased instead. While the sample
modified by H2SO4, which can be seen in F igur e 2(d), its surface presented a chaotic condition.
The FT-IR results of CaO/ATP (different roasting temperature) can be seen in Figure 5. The strong wide ab-
sorption bands appeared at 3440 cm−1 associated with the surface hydroxyl groups. The weak sharp absorption
T. Zhang et al.
Figure 4. SEM micrographs of ATP, CaO/ATP, CaO/ATP modified samples by H2SO4 or NaOH. (a) ATP ;
(b) CaO/ATP; (c) CaO/ATP modified by NaOH; (d) CaO/ATP modified by H2SO4.
00 3000 2500 2000 1500 1000500
Figure 5. FT-IR results of CaO/ATP (different roasting temperature).
bands at 1630 cm−1 is flexural vibrations of water H-O-H. The strong wide absorption bands at 1020 cm−1 is dis-
symmetry stretching vibrations of Si-O-Si, and the absorption bands at 777 cm−1 and 476 cm−1 are symmetry
stretching and flexural vibrations of Si-O. The strong wide absorption bands appeared at 3440 cm−1 became
weak when increasing roasting temperature from 400˚C to 700˚C, for zeolitic water, crystal water and constitu-
tion water of ATP crystal will decrease when temperature increase. Crystal structure changed at high tempera-
ture. Over 600˚C, zeolitic duct was destroyed, and zeolitic water disappeared.
T. Zhang et al.
3.2. SO2 Desulfurizing Experiment by CaO/ATP Desulfurizer
Except ATP, CaO was another main component of the desulfurizer. Its content would influent sulfate efficiency.
The results were presented in Figure 6 and Figure 7. The SO2 removal efficiency represents the ratio of SO2
concentration at the inlet subtracting that at the outlet to that of inlet feed. Thus, the efficiency curves also indi-
cate the penetrating curves. With increasing content of CaO, the penetrating time and sulfur tolerance were
gradually increased. It was because CaO was basic oxide, which could react with acidic gas SO2 quickly. In fact,
the desulurizer has two effects on SO2, ATP adsorbed SO2 and CaO transferred it to sulfate. The higher CaO
content was, the more SO2 was transferred. Meanwhile, CaO content could not be too high, that would cause
mechanical intensity of the desulfurizer decreased. As a result, CaO content should be about 30 wt%, the effect
of desulfurization of the samples was better.
ATP is often modified by acid, such as sulfur acid and hydrochloric acid. When acid was dissociated in
aqueous solution, H+ was produced and exchanged with K+, Na+, Ca2+ of ATP to enlarge pore volume of that. In
this study, H2SO4 and NaOH were used for CaO/ATP modifying, and the result can be seen in Figure 8. Be-
cause ATP was corporated with CaO, H2SO4 reacted with CaO and generated CaSO4, which blocked the micro-
pore and reduced its activities. The samples modified by NaOH had higher surface area so that the higher sulfur
tolerance can be obtained.
Roasting temperature and time will influence the sulfur tolerance, as we saw from Figure 9 and Figure 10. At
Figure 6. Influences of CaO content on SO2 removal efficiency.
Figure 7. Influences of CaO content on sulfur tolerance.
010 20 30 40 50 60 70
SO2 removal efficiency/%
CaO-0% CaO-10% CaO-20% CaO-30%
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Figure 8. Influences of modifier on sulfur tolerance.
Figure 9. Influences of roasting temperature on sulfur tolerance.
Figure 10. Influences of roasting time on sulfur tolerance.
CaO/ATP CaO/ATP modified by H2SO4CaO/ATP modified by NaOH
300 400 500 600 700
1.0 1.5 2.0 2.5 3.0
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600˚C and roasting sample 2 hours, highest sulfur tolerance (10.15%) was achieved. It is known from Figure 5
that duct was destroyed when roasting over 600˚C, which will make the surface area of samples decrease.
Roasting time will also influence the sulfur tolerance. The CaO/ATP samples were roasted to clot gradually.
When roasted over 2 hours, the pore canal of samples would collapse because of losing water excessively.
A new CaO/attapulgite desulfurization agent was synthesized by mixing of CaO and attapulgite directly. The
optimum synthesizing and operating conditions were as follows: weight ratio of CaO to attapulgite, 3:7; types of
modifiers, NaOH (1 mol/L); roasting temperature and time, 600˚C and 2 hours; weight ratio of water to
CaO/ATP desufurizer, 20 - 30 wt%. The desufurizer synthesized and operated under optimal synthesis condi-
tions exhibited sulfur tolerance of 10.15 wt%.
This new approach showed promising in utilizing natural resource of Gansu, China, such as attapulgite in the
production of desulfurization agent, which could significantly reduce the production cost and make the tech-
nique quite environmental friendly.
This work was financially supported by the National Natural Science Foundation of China (Grant No.
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