Removal of Hg0 from simulated coal-fired flue gas by using activated spent FCC catalysts

Hua-sheng WANG Yan-jun REN Shuang DENG Jia-yu HUANG Feng-yan GUO Gang TIAN

Citation:  WANG Hua-sheng, REN Yan-jun, DENG Shuang, HUANG Jia-yu, GUO Feng-yan, TIAN Gang. Removal of Hg0 from simulated coal-fired flue gas by using activated spent FCC catalysts[J]. Journal of Fuel Chemistry and Technology, 2020, 48(12): 1466-1475. shu

活化废FCC催化剂用于模拟烟气中汞的脱除

    通讯作者: 邓双, dengshuang@craes.org.cn
摘要: 采用有机溶剂内部瞬间沸腾法活化废流体催化裂化(SFCC)催化剂,通过固定床反应器考察了吸附温度、烟气成分及活化条件等多种变量对SFCC催化剂脱汞性能的影响。结果表明,SFCC催化剂经甲醇和乙醇活化后脱汞(Hg0)效果良好,焙烧温度也会影响催化剂活性。烟气中O2的存在有利于汞的脱除。含O2气氛下,NO在FCC-E催化剂表面形成含N活性位点,促进汞的脱除。SO2因浓度差异对Hg0的脱除表现出吸附催化和竞争吸附。在6% O2、12% CO2、0.06% NO烟气组分,120 ℃吸附温度,120 ℃活化温度,乙醇活化条件下,SFCC催化剂的脱汞效率接近100%。采用X射线荧光光谱(XRF)、扫描电镜(SEM)、X射线衍射(XRD)、热重(TG)和X射线光电子能谱(XPS)表征活化和未活化SFCC催化剂,探究与其脱汞性能关联。

English

  • Mercury (Hg) pollution with high toxicity, biological accumulation, migration capacity, and durability has drawn increasing global attention[1]. The stationary combustion of fossil fuels and biomass is responsible for approximately 24% of global Hg emissions, with coal as the largest contributor[2]. In China, coal combusted in the power plants accounts for approximately 50% of total coal consumption[3]. With the announcement of Minamata Convention, the control of Hg emissions in the coal-fired power plants has become a serious concern in China[4]. In 2011, the Chinese Ministry of Ecological Environment set the emission limit of Hg as 0.03 mg/m3[5], which exacts the development of cost-effective and highly efficient technical scheme for Hg removal.

    Hg in coal-fired flue gas occurs mainly in the form of elemental (Hg0), particulate (Hgp), and oxidation state (Hg2+) mercury[6]. Current air pollution control devices (APCDs), such as selective catalytic reduction system, dust collectors, and desulfurization devices can synergistically remove most Hgp and Hg2+, but have negligible effects on Hg0 removal[7]. Accordingly, a number of sorbents developed for the removal of gaseous Hg from coal flue gas aimed at converting Hg0 to Hg2+ or Hgp; Hg2+ and Hgp could then be removed by the existing air pollution control devices[8-12]. Among these sorbents, activated carbon is the most widely used trapper for Hg capture and corresponding activated carbon injection (ACI) technology has been commercially used in coal power plants. Nonetheless, ACI is expensive and has adverse effects on the further reutilization of fly ash due to the high carbon contents[13]. In contrast, non-carbon-based adsorbents have many advantages including large surface area, high mercury removal efficiency[14, 15], high thermal stability[16], numerous sources[17], and little adverse effects on the fly ash products.

    The fluid catalytic cracking (FCC) catalyst has been widely used in oil refineries. In 2018, the global demand for refining catalysts was 831 kiloton, of which the FCC catalyst accounts for 65% and the residual FCC catalysts, i.e. the so-called spent fluid catalytic cracking (SFCC) catalyst, holds for 16%[18]. The disposal of huge amounts of waste solid FCC catalyst generated from the oil refineries is still a great challenge[19, 20]. Ferella et al[21] found that the modified spent FCC catalysts were efficient in metal adsorption in a synthetic wastewater solution. Yuan et al[22] reported that Fe3O4-modified spent catalyst was a suitable adsorbent for phosphate removal. The SFCC catalyst is similar to zeolite in the structure, containing silicon-oxygen and aluminum-oxygen tetrahedrons that are bridged by oxygen atoms in the center. Some void cages formed in three dimensions create the zeolite pore channel system, whilst the exchangeable cations in the framework play the roles for charge neutrality. The high porosity and large surface area of zeolite provide the FCC catalyst with the capacity in adsorption and catalysis[23]. All these features make the FCC catalyst a potential sorbent to capture gaseous Hg in the flue gas of industrial boilers[24].

    In this work, the spent fluid catalytic cracking (SFCC) catalysts were activated by an internal instant vaporization (IIV) method[25]. The blocked catalyst channels can be effectively unchoked by the IIV method with low boiling organic solvent without impairing the internal channel structure and the activated SFCC catalysts were then used in the removal of Hg0 from a simulated flue gas in a fixed bed reactor. The effect of various operation parameters such as the SFCC activation conditions, adsorption temperature, and flue gas components on the Hg0 removal efficiency was investigated and a possible mechanism of mercury adsorption on the activated SFCC catalysts was then proposed. This should be rather meaningful as an idea of waste control by waste.

    About 10 g of the SFCC catalyst samples provided by Guangxi Tiandong Oil Chemical Factory Co. LTD. of China was calcined at 25, 120, 240, 360, 480 and 600 ℃ for 4 h, cooled to 25 ℃, and then ground into 140 mesh for the activity test. Depending on the calcination temperature, corresponding activated SFCC catalyst samples are labeled as SFCC, FCC-120, FCC-240, FCC-360, FCC-480 and FCC-600, respectively.

    To activate the SFCC catalyst by the internal instant vaporization (IIV) method with organic solvents, 10 g of the FCC-120 sample was placed in a 250 mL beaker containing 10 mL of methanol, ethanol, acetone, or petroleum ether. The beaker was then sealed with a membrane and kept at 25 ℃ and atmospheric pressure for 2 h. Subsequently, 50 mL of boiling deionized water was poured into the beaker, kept at 100 ℃ for 5 min. After that, the beaker was placed in a drying oven at 120 ℃ until a constant weight was achieved; the samples were then cooled to room temperature, and grounded into 140 mesh. Depending on the solvent used for IIV, the activated SFCC catalysts obtained with the solvent of methanol, ethanol, acetone, and petroleum ether are labeled as FCC-M, FCC-E, FCC-A and FCC-P, respectively.

    The surface area and pore diameter distribution of the activated and non-activated SFCC catalysts were measured on an ASAP2020 surface area analyzer of the Micromeritics Company, United States. The specific surface area and pore volume were calculated through the Brunauer-Emmett-Teller (BET) method and the Barrett, Joyner, and Halenda (BJH) model, respectively. Powder X-ray diffraction patterns (PXRDs) were measured on a Bruker AXS/ D8 ADVANCE powder diffractometer using Cu Kα radiation (40 kV and 20 mA), in the range of 10° to 80°. The microstructure was analyzed by Zeiss SUPRATM55 scanning electron microscopy (SEM). Thermogravimetric analysis (TG) was carried out on a Shimadzu DTG-60 AH instrument up to 850 ℃ with a heating rate of 10 ℃/min in air. X-ray photoelectron spectroscopy (XPS) was performed on a PHI Quantera II (Ulvac-Phi) spectrometer with Al Kα as the excitation source, transmission power of 150 W, and photoelectron energy of 200 eV; the C 1s line at 284.6 eV was taken as the reference for the binding energy calibration.

    The Hg0 adsorption test over the activated and non-activated SFCC catalysts was performed in a bench-scale fixed-bed adsorption test system, which included mainly an elemental mercury generator, a simulated flue gas generator, an adsorption fixed-bed reactor, a flue gas on-line analysis system, and an exhaust gas treatment system, as illustrated in Figure 1.

    Figure 1

    Figure 1.  Schematic diagram of the fixed-bed adsorption evaluation device

    The simulated flue gas consists of N2, CO2, O2, SO2 and NO, regulated by several mass flow controllers. The overall gas flow rate is 1 L/min and detailed composition of the mixed gas is given in Table 1. The reactor was heated with a tubular furnace. The Hg0 generator included mainly an elemental mercury permeation tube (VICI Metronics Inc.), a U-shaped quartz tube, and a super thermostat. To yield a stable concentration of Hg0 (20.00±1.00) μg/m3, N2 was used as the carrier gas. Before the test, the mercury permeation tube was bypassed to calibrate the signal baseline. After that, the carrier gas was then diverted into the mercury permeation tube to generate a stable mercury concentration. Subsequently, the gaseous stream with a stable concentration of Hg0 was diverted into the packed fixed-bed reactor and the breakthrough curves were monitored online using a mercury analyzer (Lumex RA-915M, Russia). The reactor was packed with 1 g of SFCC catalyst and the adsorption was performed at a space velocity of 75000 h-1 and lasted for 2 h. Quartz wool was used as a support to prevent the loss of SFCC catalyst. Potassium dichromate solution and sodium hydroxide solution were used to address the exhaust gas emissions.

    Table 1

    Table 1.  Experimental conditions for the Hg0 adsorption tests
    下载: 导出CSV
    Set Adsorbent Activation conditions Flue gas composition Adsorption temp t/℃
    calc. temp /℃ solvent
    I SFCC, activated SFCC 120-600 - 6% O2, 12% CO2, N2 120
    II activated SFCC 120 methanol, ethanol, acetone, petroleum ether 6% O2, 12% CO2, N2 120
    III activated SFCC 120 ethanol 6% O2, 12% CO2, N2 80-300
    IV activated SFCC 120 ethanol 0-10%O2, 12% CO2, N2 120
    V activated SFCC 120 ethanol 6% O2, 12% CO2, 0.06%-0.1% SO2, N2 120
    VI activated SFCC 120 ethanol 6% O2, 12% CO2, 0.01%-0.06% NO, N2 120

    Several preliminary tests were conducted to investigate the effect of activation and adsorption conditions on the removal efficiency of Hg0. The detailed operation conditions of the six sets of adsorption tests are summarized in Table 1. The removal efficiency of Hg0 from the flue gas was calculated as follows:

    $ \eta=\left(\left[\mathrm{Hg}^{0}\right]_{\mathrm{in}}-\left[\mathrm{Hg}^{0}\right]_{\mathrm{out}}\right) /\left[\mathrm{Hg}^{0}\right]_{\mathrm{in}} \times 100 \% $

    (1)

    where [Hg0]in and [Hg0]out represent the Hg0 concentrations in the stream at the inlet and outlet of the adsorption bed, respectively.

    As shown by the SEM images in Figure 2, the SFCC catalysts have a spherical appearance with a rough surface with some bumps and collapses as well as porous structure, which facilitate the adsorption of gaseous mercury. High temperature and organic solvent activation have insignificant influence on the morphology of the SFCC catalysts.

    Figure 2

    Figure 2.  SEM images of the activated and non-activated SFCC catalysts: ((a), (b)) SFCC; ((c), (d)) FCC-360; and ((e), (f)) FCC-M

    As given in Table 2, the surface area and average pore diameter of the SFCC catalysts are approximately 74.9 m2/g and 3.181 nm, respectively. However, the surface areas of the activated SFCC catalysts are in the range of 76.5-101.2 m2/g and the pore diameter in the range of 3.382-4.862 nm, both are larger than those of the original SFCC catalysts. Moreover, it seems that the surface area of the activated SFCC catalysts increases with the increase of the activation temperature, probably attributing to the removal of more physically adsorbed water and other volatile matters at higher temperature. Furthermore, the carbonaceous matters deposited on the catalyst surface can also be burned out at high temperature, as confirmed by the results of thermogravimetric/differential thermal analysis (TG/DTA) analysis. As shown in Figure 3, the weight loss of the SFCC catalysts during the calcination can be divided into three stages, viz., 2.116% at 36.00-135.09 ℃, 2.615% at 135.09-474.52 ℃, and 0.491% at 762.5-840.00 ℃, which are probably ascribed to the removal of the physically adsorbed water, combustion of the deposited carbon, and aluminum stripping on the skeleton of the molecular sieves, respectively[26].

    Table 2

    Table 2.  Textural properties of the activated and non-activated SFCC catalysts
    下载: 导出CSV
    Adsorbent Surface area A/(m2·g-1) Pore volume v/(cm3·g-1) Pore diameter d/nm
    SFCC 74.9 0.09 3.181
    FCC-120 78.5 0.11 3.382
    FCC-360 90.4 0.11 3.795
    FCC-600 101.2 0.11 4.862
    FCC-M 87.3 0.10 3.804
    FCC-E 83.7 0.10 3.396
    FCC-A 77.9 0.09 3.400
    FCC-P 76.5 0.09 3.389

    Figure 3

    Figure 3.  TG/DTA curves of the SFCC catalyst in the air atmosphere (a) and N2 atmosphere (b)

    Table 3 illustrates that the SFCC catalyst consists of O, Al, Si, Ca, as well as a small amount of transition metals such as Ni, Fe, Ce and V. Meanwhile, XPS was also employed to analyze the states of surface elements on FCC-120, in order to probe the active species and the reaction pathways for mercury adsorption on the SFCC catalysts, as shown in Figure 4. The XPS survey indicates that O, Al, Si, C, Ca, Ni, Fe and Ce are present on the surface of FCC-120 (Figure 4(a)). The peaks in the Fe 2p region at 711.0 and 709.9 eV are attributed to Fe3+ (Figure 4(b)), whereas the peaks at 712.8, 719.1 and 724.8 eV correspond to FeIII-OH, Fe3+ cations and Fe2+, respectively[27, 28]. It indicates that iron mainly appears in the form of Fe3+ on surface of FCC-120. The peaks of u′ for Ce 3d3/2 and v′ for Ce 3d5/2 can be attributed to Ce3+, whereas other peaks in the Ce 3d region to Ce4+ (Figure 4(c))[29]. In contrast, the peak at 529.6 eV for O 1s is ascribed to lattice oxygen, whereas the peak at 532.6 eV to surface oxygen (Figure 4(d))[30].

    Table 3

    Table 3.  Chemical composition of the SFCC catalysts determined by XRF
    下载: 导出CSV
    Component Percentage Component Percentage Component Percentage
    Al2O3 46.397 Cs2O 1.115 V2O5 0.169
    SiO2 43.147 Na2O 0.782 CeO2 0.166
    CaO 2.012 P2O5 0.714 Sb2O3 0.121
    SO3 1.546 TiO2 0.302 ZnO 0.093
    NiO 1.416 MgO 0.254 La2O3 0.089
    Fe2O3 1.330 K2O 0.177 else 0.163

    Figure 4

    Figure 4.  XPS spectra of the FCC-120 catalyst: (a) survey of elements; (b) Fe 2p; (c) Ce 3d; and (d) O 1s

    The crystal structure and phase of the SFCC catalysts were characterized by XRD, as shown in Figure 5. Obviously, the activation process has little influence on the crystal structure of the SFCC catalysts; the activated SFCC catalysts still display the characteristic diffraction peaks of Y zeolite, Al2O3 and ZSM-5 zeolite[10, 31].

    Figure 5

    Figure 5.  XRD patterns of various catalyst samples: a: SFCC; b: FCC-360; c: FCC-600; d: FCC-M; e: FCC-E; f: FCC-A; g: FCC-P
    2.2.1   Impact of activation conditions

    As shown in Figure 6, the initial Hg0 removal efficiency of the SFCC catalysts is in the range of 17.77%-48.97% after the activation at high temperature. However, the Hg0 removal efficiency decreases with the adsorption time, as more active sites on the catalyst surface were covered by Hg with the extension of adsorption time, which may reduce the adsorption capacity of the SFCC catalyst[32].

    Figure 6

    Figure 6.  Effect of the calcination temperature on the Hg0 removal efficiency of activated SFCC catalysts; the operation conditions of set I specified in Table 1 are used

    Figure 6 also indicates that the initial Hg0 removal efficiency of the SFCC catalysts increases first and then decreases with the increase of the activation temperature. The SFCC catalyst activated at 360 ℃ displays the highest Hg0 removal efficiency (48.97%), whereas the Hg0 removal efficiency is only 17.77% over the catalyst activated at 600 ℃, probably due to the aluminum stripping at high temperature from the skeleton of the molecular sieve in the SFCC catalysts[25].

    Meanwhile, the solvent used to activate the SFCC adsorbents by IIV also has a significant influence on the Hg0 removal efficiency, as shown in Figure 7. Methanol and ethanol as the solvent for activation give a higher initial Hg0 removal efficiency, 53.06% and 46.65%, respectively. The Hg0 removal efficiency over the FCC-E and FCC-M catalysts decreases with the adsorption time and becomes stable after the adsorption for 120 min. Although the SFCC adsorbents show higher adsorption efficiency for Hg0 after the treatment with either methanol or ethanol, ethanol is probably more popular as an organic solvent to activate the SFCC catalysts due to its less toxicity.

    Figure 7

    Figure 7.  Effect of the activation organic solvent on the Hg0 removal efficiency of the activated SFCC catalysts; the operation conditions of Set II specified in Table 1 are used
    2.2.2   Impact of adsorption temperature

    As shown in Figure 8, the initial Hg0 removal efficiency on FCC-E is 47.35% at 80 ℃, decreases to 18% after adsorption for 30 min and keeps at the level of about 15% after adsorption for 90 min. In contrast, the initial Hg0 removal efficiency at 120-300 ℃ increases with the extension of the adsorption time. After adsorption for 15 min, the adsorption of Hg0 reaches equilibrium and the Hg0 removal efficiency on FCC-E then becomes stable with the adsorption time. Meanwhile, it seems that the Hg0 equilibrium removal efficiency over FCC-E increases with an increase in the adsorption temperature, indicating that the removal of Hg0 from the simulated flue gas by the SFCC catalysts is mainly contributed by chemical adsorption at high temperature, in comparison to that by the physical adsorption at low temperature.

    Figure 8

    Figure 8.  Effect of different adsorption temperature on the Hg0 removal efficiency of FCC-E; the operation conditions of Set III specified in Table 1 are used
    2.2.3   Impact of flue gas composition

    A stable Hg0 removal efficiency of FCC-E is achieved after adsorption for about 90 min, as shown in Figure 9; however, the stable Hg0 removal efficiency increases with the increase of O2 concentration in the flue gas. In the absence of O2, the Hg0 removal efficiency of FCC-E is 5.34%; it increases to 33.25% in the presence of 10% O2, about 6 times of that under anaerobic adsorption condition. That is, the adsorption of Hg0 on the activated SFCC catalysts can be greatly promoted by O2 in the flue gas, as O2 in the flue gas can be adsorbed on the activated SFCC catalysts to supplement the lattice oxygen[12, 33, 34].

    Figure 9

    Figure 9.  Effect of O2 concentration in the flue gas on the Hg0 removal efficiency of FCC-E; the operation conditions of Set IV specified in Table 1 are used

    Figure 10 shows that the Hg0 removal efficiency of FCC-E is only 15% when the flue gas contains 0.06% SO2 but no O2, higher than that (5.34%) in the inert atmosphere. It means that SO2 may also promote the removal of Hg0 from the flue gas in the absence of oxygen. In the presence of O2, the stable Hg0 removal efficiency of FCC-E increases with the increase of SO2 concentration from 0.06% to 0.10%, possibly due to the fact that SO2 is oxidized to SO3 by O2 and SO3 reacts with Hg0 to form mercury sulfate and mercurous sulfate[6]. However, when the SO2 concentration increases to 0.18%, the stable Hg0 removal efficiency of FCC-E does not increase anymore with the rise in the SO2 concentration. It was reported that there is a competitive adsorption between SO2 and Hg0[27, 35, 36], which brings on a balance point for the effect of SO2 concentration; that is, the promoting effect by mercury oxidation with SO3 originated from SO2 is counteracted by the inhibitive effect by the competitive adsorption of SO2 with mercury and subsequent mercury oxidation[37].

    Figure 10

    Figure 10.  Effect of SO2 concentration in the flue gas on the Hg0 removal efficiency of FCC-E; the operation conditions of Set V specified in Table 1 are used

    The effect of NO concentration in the flue gas on the Hg0 removal efficiency of FCC-E NO was also inspected, as shown in Figure 11. Obviously, NO has an evident promoting effect on the mercury removal. In the presence of NO, the mercury removal efficiency decreases first and then increases with the operation time, suggesting that the physical adsorption of mercury is changed to chemical adsorption with the extension of adsorption time, as more NO is adsorbed on the surface of the SFCC, forming more active sites conducive to mercury removal. Moreover, Figure 11 also shows that when the NO concentration is 0.03%, the initial Hg0 removal efficiency of the FCC-E in the absence of O2 is lower than that in the presence of O2 and the Hg0 removal efficiency increases significantly with the rise of NO concentration in the presence of oxygen. This is probably ascribed to the numerous hydroxyl radicals on the surface of the activated SFCC catalysts, which can oxidize NO into NO2* and then react with adsorbed Hg0 (ads) and O2 into Hg(NO3)2, leading to a significant increase of the Hg0 removal efficiency[33, 38-41]. This further demonstrates that Hg0 adsorption on the spent FCC catalysts is mainly contributed by the chemical adsorption.

    Figure 11

    Figure 11.  Effect of NO concentration in the flue gas on the Hg0 removal efficiency of FCC-E; the operation conditions of Set VI specified in Table 1 are used

    To confirm the mechanism of oxidation-promoted mercury removal, a temperature program desorption (TPD) test was conducted to observe the mercury compounds on the adsorbent after the adsorption test in the presence of NO. N2 was chosen here as the carrier gas and the adsorbent was heated from 50 to 600 ℃ at the heating rate of 5 ℃/min. The Hg0-TPD profile is shown in Figure 12. The release of Hg0 appears at approximately 145 and 240 ℃. The peak at 145 ℃ corresponds to the physically adsorbed Hg0. The boiling point of the pure Hg(NO3)2 is approximately 180 ℃; it decomposes to HgO and further to Hg0, with the increase of the temperature[42]. In addition, the mercury species, heating rate, vapor pressure etc. can also influence the decomposition characteristics of the mercury-containing compounds. According to literature, the single peak at 240 ℃ could be assigned to the desorption of Hg from Hg(NO3)2.

    Figure 12

    Figure 12.  TPD profile of the SFCC-E adsorbent under N2 after mercury adsorption in the presence of NO and O2 at 120 ℃

    In the presence of NO and O2, the NO2* species is formed between NO and the surface or lattice oxygen over the FCC-E catalyst. The mechanism can be summarized as:

    $ \begin{array}{l} \mathrm{NO}(\mathrm{g})+\mathrm{O}^{*}(\mathrm{ads}) \rightarrow \mathrm{NO}_{2}{ }^{*}(\mathrm{ads}) \end{array} $

    (2)

    $ \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{O}^{*}(\text { ads }) $

    (3)

    $ \mathrm{Hg}(\mathrm{g}) \rightarrow \mathrm{Hg}^{*}(\text { ads }) $

    (4)

    $ \mathrm{Hg}^{*}(\mathrm{ads})+\mathrm{O}^{*}(\mathrm{ads})+\mathrm{NO}_{2}^{*}(\mathrm{ads}) \rightarrow \\ \mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{ads}) $

    (5)

    Current results illustrate that the Hg0 removal efficiency of the activated SFCC catalysts, prepared with ethanol as solvent and calcined at 120 ℃, is close to 100% in the presence of 0.06% NO, 12% CO2, 6% oxygen and balanced N2. The Hg0 removal efficiency remains stable after adsorption for 120 min. This indicates that the SFCC catalysts are suitable for the removal of Hg0 by adsorption from the coal-fired flue gas after proper activation.

    The spent fluid catalytic cracking (SFCC) catalysts were activated by an "internal instant vaporization (IIV)" method and used in the removal of Hg0 from a simulated flue gas in a fixed bed reactor; the effect of various operation parameters such as the SFCC activation conditions, adsorption temperature, and flue gas components on the Hg0 removal efficiency was investigated.

    The results indicate that the blocked catalyst channels can be effectively unchoked by the IIV method with the organic solvent without impairing the internal channel structure. The SFCC catalyst activated with methanol or ethanol performs adequately in terms of Hg0 removal, whilst the calcination temperature also has a great influence on the activation of the SFCC catalyst. O2 in the flue gas favors the Hg0 removal, whilst NO facilitates the oxidation of mercury and displays a positive effect for mercury removal in the presence of O2, accompanying with the formation of N-containing active species on the FCC-E surface. A relatively higher adsorption temperature is beneficial to the Hg0 removal on the activated SFCC catalyst, indicating that the chemical adsorption plays an important role. The presence of O2 and NO promote the Hg0 adsorption on the activated SFCC catalyst, suggesting that the Hg0 adsorption on the spent FCC catalysts is contributed mainly by the catalytic oxidation. SO2 in the flue gas, depending on its concentration, may exert the effect of catalytic adsorption or competitive adsorption on the Hg0 removal. Approximately 100% Hg0 can be removed in the stream of 6% O2, 12% CO2 and 0.06% NO at 120 ℃ by using the activated SFCC catalyst with ethanol as an organic solvent and calcined at 120 ℃. It suggests that the SFCC catalysts after proper activation are potential adsorbents for the removal of Hg0 from the coal-fired flue gas.


    本文的英文电子版由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18725813).
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  • Figure 1  Schematic diagram of the fixed-bed adsorption evaluation device

    Figure 2  SEM images of the activated and non-activated SFCC catalysts: ((a), (b)) SFCC; ((c), (d)) FCC-360; and ((e), (f)) FCC-M

    Figure 3  TG/DTA curves of the SFCC catalyst in the air atmosphere (a) and N2 atmosphere (b)

    Figure 4  XPS spectra of the FCC-120 catalyst: (a) survey of elements; (b) Fe 2p; (c) Ce 3d; and (d) O 1s

    Figure 5  XRD patterns of various catalyst samples: a: SFCC; b: FCC-360; c: FCC-600; d: FCC-M; e: FCC-E; f: FCC-A; g: FCC-P

    Figure 6  Effect of the calcination temperature on the Hg0 removal efficiency of activated SFCC catalysts; the operation conditions of set I specified in Table 1 are used

    Figure 7  Effect of the activation organic solvent on the Hg0 removal efficiency of the activated SFCC catalysts; the operation conditions of Set II specified in Table 1 are used

    Figure 8  Effect of different adsorption temperature on the Hg0 removal efficiency of FCC-E; the operation conditions of Set III specified in Table 1 are used

    Figure 9  Effect of O2 concentration in the flue gas on the Hg0 removal efficiency of FCC-E; the operation conditions of Set IV specified in Table 1 are used

    Figure 10  Effect of SO2 concentration in the flue gas on the Hg0 removal efficiency of FCC-E; the operation conditions of Set V specified in Table 1 are used

    Figure 11  Effect of NO concentration in the flue gas on the Hg0 removal efficiency of FCC-E; the operation conditions of Set VI specified in Table 1 are used

    Figure 12  TPD profile of the SFCC-E adsorbent under N2 after mercury adsorption in the presence of NO and O2 at 120 ℃

    Table 1.  Experimental conditions for the Hg0 adsorption tests

    Set Adsorbent Activation conditions Flue gas composition Adsorption temp t/℃
    calc. temp /℃ solvent
    I SFCC, activated SFCC 120-600 - 6% O2, 12% CO2, N2 120
    II activated SFCC 120 methanol, ethanol, acetone, petroleum ether 6% O2, 12% CO2, N2 120
    III activated SFCC 120 ethanol 6% O2, 12% CO2, N2 80-300
    IV activated SFCC 120 ethanol 0-10%O2, 12% CO2, N2 120
    V activated SFCC 120 ethanol 6% O2, 12% CO2, 0.06%-0.1% SO2, N2 120
    VI activated SFCC 120 ethanol 6% O2, 12% CO2, 0.01%-0.06% NO, N2 120
    下载: 导出CSV

    Table 2.  Textural properties of the activated and non-activated SFCC catalysts

    Adsorbent Surface area A/(m2·g-1) Pore volume v/(cm3·g-1) Pore diameter d/nm
    SFCC 74.9 0.09 3.181
    FCC-120 78.5 0.11 3.382
    FCC-360 90.4 0.11 3.795
    FCC-600 101.2 0.11 4.862
    FCC-M 87.3 0.10 3.804
    FCC-E 83.7 0.10 3.396
    FCC-A 77.9 0.09 3.400
    FCC-P 76.5 0.09 3.389
    下载: 导出CSV

    Table 3.  Chemical composition of the SFCC catalysts determined by XRF

    Component Percentage Component Percentage Component Percentage
    Al2O3 46.397 Cs2O 1.115 V2O5 0.169
    SiO2 43.147 Na2O 0.782 CeO2 0.166
    CaO 2.012 P2O5 0.714 Sb2O3 0.121
    SO3 1.546 TiO2 0.302 ZnO 0.093
    NiO 1.416 MgO 0.254 La2O3 0.089
    Fe2O3 1.330 K2O 0.177 else 0.163
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  • 发布日期:  2020-12-01
  • 收稿日期:  2020-09-02
  • 修回日期:  2020-10-20
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