Harmless Treatment of Sulfuryl Fluoride by Chemical Absorption

Abstract

Chemical absorption was employed for the harmless treatment of sulfuryl fluoride (SO₂F₂) in the simulated residual fumigant. SO₂F₂ was absorbed by sodium hydroxide (NaOH) solution in a packed column. Effects of spray density, gas flow rate, concentration of NaOH solution, and inlet SO₂F₂ volume concentration on SO₂F₂ removal efficiency were investigated at room temperature. It was found that SO₂F₂ could be removed completely when inlet SO₂F₂ volume concentration, spray density, gas flow rate, and NaOH concentration were 0.50%, 12 m³/(m² · h), 0.12 m³/h, and 0.68 mol/L, respectively. According to the two-film theory, a mathematical model based on Onda correlations was developed to describe the removal efficiency of SO₂F₂. Comparison between the experimental data and the calculated data proved that the predictability of the proposed model was within the maximum deviation of 8.0%. Aqueous NaOH solution after absorption was analyzed. It was found that the SO₂F₂ was fixed and converted to NaF, NaSO₃F, and Na₂SO₄.

Introduction

Sulfuryl fluoride (SO₂F₂), an odorless, colorless, generally nonreactive chemical, was developed by Dow Chemical Company in the 1950s (Derrick et al., 1990). It has been widely used to fumigate the timber, buildings, construction materials, soils, vehicles, foods, and so on (Athanassiou et al., 2012; Chayaprasert et al., 2012; Bonifácio et al., 2014; Cao et al., 2014), owing to its several advantages, including easy dispersal on a structure, rapid penetration into materials, almost no residue formation, and ready dissipation after aeration (Meikle and Stewart, 1962). Especially, SO₂F₂ is also being used as an alternative fumigant to methyl bromide, due to its zero ozone loss (Fields and White, 2002).

However, the toxicity and greenhouse effect of SO₂F₂ have recently aroused much attention. SO₂F₂ gas is considered as an inhalation hazardous material, which can cause damage to the human central nervous system and inhalation system after long-term exposure, and its occupational exposure limit is 5 ppm (Tsai, 2010). In addition, the atmospheric lifetime and global warming potentials (100-year time horizon, relative to carbon dioxide) for SO₂F₂ are ∼36 years and 4,780, respectively (Papadimitriou et al., 2008). Since 1978, SO₂F₂ has been accumulated in the global atmosphere with a growth rate of 5% ± 1% per year (Mühle et al., 2009). To date, SO₂F₂ has been registered for fumigation use in the United States, Canada, the Caribbean, Japan, the European Union, and so forth (Papadimitriou et al., 2008). However, almost 100% of SO₂F₂ is emitted to the atmosphere after use. Consequently, it is urgent to develop an effective method to remove SO₂F₂ after fumigation.

To solve this problem, in 2013, a two-step method was developed based on the dielectric barrier discharge (DBD) plasma followed by a chemical absorption (Nie et al., 2013b). However, the high energy consumption of the DBD plasma process limited its industrial application. Recently, a new approach for the removal of SO₂F₂ has been developed using chemical absorption alone, and aqueous sodium hydroxide (NaOH) solution was used as an absorbent (Nie et al., 2013a). SO₂F₂ is nearly insoluble in water in neutral conditions; however, SO₂F₂ can be rapidly hydrolyzed in aqueous NaOH solution due to the fact that nucleophilic hydroxyl ions will attack the S atom and replace one of the F ions (Cady and Misra, 1974). In 2014, the mass transfer and reaction kinetics of SO₂F₂ absorption with aqueous NaOH solution in an experimental double-stirred cell have been investigated, results showed that SO₂F₂ absorption by the aqueous NaOH solution was a fast pseudofirst-order reaction, and the liquid-phase mass transfer was the rate-determining step; moreover, the enhancement factors were also determined in the experimental double-stirred cell (Nie et al., 2014). The aforementioned research has provided the fundamental data for further treatment of SO₂F₂ by chemical absorption.

In this article, chemical absorption in a packed column was used for the harmless treatment of SO₂F₂ in the simulated residual fumigant. The effects of gas flow rate, spray density (defined as the ratio of liquid flow rate to the cross-sectional area of packed column), NaOH concentration, and inlet SO₂F₂ volume concentration on the removal efficiency of SO₂F₂ were investigated, respectively. According to the two-film theory, a mathematical model based on Onda correlations to describe the removal efficiency of SO₂F₂ was developed (Onda et al., 1968b; Tan et al., 1990). A comparison between the experimental data and the results calculated by the proposed model was performed. Moreover, products in NaOH solution after absorption were analyzed by an ion chromatogram.

Experimental Protocols

Materials

SO₂F₂ (99.9%) stored in a cylinder was purchased from Hangzhou Maoyu Electronic Chemicals Co., Ltd. Sodium hydroxide (96%), potassium biphthalate (99.9%), potassium fluorosulfonate (99.9%), sodium fluoride (99.5%), and sodium sulfate (99.5%) were purchased from Sinopharm Chemical Reagent Co., Ltd.

Apparatus and procedure

The schematic diagram of the experimental apparatus is shown in Fig. 1. The well-mixed air from a fan and SO₂F₂ from a cylinder were fed into the bottom of the packed column for chemical absorption. The SO₂F₂ flow rate was controlled by a rotameter, and the volume concentration of SO₂F₂ ranged from 0.10% to 0.54%, in which the volume concentration of 0.50% was equivalent to a regular SO₂F₂ application rate of 20 g/m³ used in container fumigation. The flow rate of mixed air and SO₂F₂ was measured with an orifice plate flow meter.

FIG. 1.

Schematic diagram of experimental apparatus.

The column was packed with a 12-mm ceramic Rasching ring, and the total height was 85 cm. The aqueous NaOH solution was used as the chemical absorbent, which was circulated between the column and solution tank by the pump. The flow rate of aqueous NaOH solution was measured by a rotameter, and the temperature was controlled at room temperature (25°C) by thermostatic bath. The operating pressure was controlled at atmospheric pressure.

Analysis

Inlet and outlet concentrations of SO₂F₂ were analyzed by a gas chromatography (GC), equipped with a Gaspro plot column and a flame photometric detector (Agilent 7890A). The sensitivity of the GC for SO₂F₂ analysis was 0.5 ppm. The analytical conditions of GC were described as follows: N₂, H₂, and air flow rate were 10, 30, and 300 mL/min, respectively; the temperature of the inlet, column, and detector was 80°C, 80°C, and 250°C, respectively. The concentration of NaOH solution was calibrated using the potassium biphthalate solution, and the components in the aqueous NaOH solution after chemical absorption were determined by ion chromatography (IC), equipped with a Supp4-250 anion-exchanged column and an electrical conductivity detector (Metrohm 883 Basic IC plus). The mobile phase of IC was the buffer solution of NaHCO₃ and Na₂CO₃, and the flow rate was 1 mL/min. The temperature of the IC detector was 40°C. Thus, the removal efficiency could be evaluated using the following equation: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}\eta = \frac { C_ { { \rm Ain } } - C_ { { \rm Aout } } } { C_ { { \rm Ain } } } \times 100 , \tag { 1 } \end{align*} \end{document}

where η (%) is the removal efficiency of SO₂F₂, and C_Ain and C_Aout are the inlet and outlet volume concentrations of SO₂F₂ in the packed column, respectively.

Mathematical Model

According to the two-film theory, a mathematical model based on Onda correlations was developed to describe the removal efficiency of SO₂F₂. In the Mass Balance of SO₂F₂ in the Packed Column section, the relationship of the removal efficiency of SO₂F₂ with structure parameters of the column, operating parameters, and overall gas-phase mass transfer coefficient was obtained. To calculate the earlier mass transfer coefficient, the correlations of overall gas-phase mass transfer coefficient and effective interfacial area are listed in the Overall Gas-Phase Mass Transfer Coefficient section, and the corresponding physical properties of the system are listed in the Physical Properties of the System section.

Mass balance of SO₂F₂ in packed column

Based on a previous study, the chemical absorption of SO₂F₂ by aqueous NaOH solution is a fast pseudofirst-order reaction. Since the equilibrium partial pressure of SO₂F₂ in liquid bulk is zero, mass transfer rate N_A can be described as follows (Tan et al., 1990): \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}N_{{\rm A}} = K_{{\rm G}} P_{{\rm A}} = K_{{\rm G}} Py_{{\rm A}} , \tag{2}\end{align*} \end{document}

where K_G is the overall gas-phase mass transfer coefficient, P_A is the partial pressure of SO₂F₂ in the gas bulk, P is the atmospheric pressure, and y_A is the molar fraction of SO₂F₂ in the gas bulk.

In the packed column, the cross section, molar gas flow rate, and the differential volume in height dZ are denoted as S, Q, and SdZ, respectively. Thus, the amount of SO₂F₂ absorbed in section dZ can be denoted as −Qdy_A, in which dy_A is the differential change of y_A, and the change of Q is neglected for the absorption of dilute gases. The corresponding mass balance can be described as follows (Tan et al., 1990): \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}N_{{\rm A}} aSdZ = - Qdy_{{\rm A}} , \tag{3}\end{align*} \end{document}

where a is the effective interfacial area per unit packed volume.

Since the SO₂F₂ concentration in the gas mixture is quite low and the concentration of NaOH solution remains almost constant in the column, K_G is independent to SO₂F₂ concentration (Tan et al., 1990). Integrating Equation (2) into Equation (3) can yield the following equation: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}K_ { { \rm G } } aPSZ = Q { \rm ln } \left( \frac { y_ { { \rm Ain } } } { y_ { { \rm Aout } } } \right) , \tag { 4 } \end{align*} \end{document}

where y_Ain and y_Aout are SO₂F₂ molar fractions at the inlet and outlet of the packed column, respectively, and Z is the height of the packing column. In this case, SO₂F₂ removal efficiency η can be also described as follows: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}\eta = \left( \frac { y_ { { \rm Ain } } - y_ { { \rm Aout } } } { y_ { \rm Ain } } \right) \times 100. \tag { 5 } \end{align*} \end{document}

Combining Equation (4) with Equation (5) yields the following equation after rearrangement: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}\eta = \left[ 1 - { \rm exp } \left( - \frac { PK_ { \rm G } aSZ } { Q } \right) \right] \times 100. \tag { 6 } \end{align*} \end{document}

Overall gas-phase mass transfer coefficient

Based on the two-film theory, the overall gas-film mass transfer coefficient K_G of SO₂F₂ can be described as follows: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} \frac { 1 } { K_ { \rm G } } = \frac { 1 } { k_ { \rm G } } + \frac { 1 } { HEk_ { \rm L } } , \tag { 7 } \end{align*} \end{document}

where k_G and k_L are the mass transfer coefficients of gas and liquid phases, respectively, and H is the Henry's constant of SO₂F₂, while E is the enhancement factor.

The correlations developed by Onda were employed to calculate the gas-side mass transfer coefficient k_G and liquid-side mass transfer coefficient k_L, as well as the effective interfacial area per unit packed volume a (Onda et al., 1968a, 1968b). \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}k_ { \rm G } = 2 \left( \frac { G } { a_ { \rm t } \mu_ { \rm G } } \right) ^ { 0.7 } \left( \frac { \mu_ { \rm G } } { \rho_ { \rm G } D_ { \rm G } } \right)^ { 1 / 3 } ( a_ { \rm t } D_ { \rm p } ) ^ { - 2 } \left( \frac { a_ { \rm t } D_ { \rm G } } { RT } \right) , \tag { 8 } \end{align*} \end{document}

where G is the superficial mass velocity; a_t is the total surface area per unit packed volume; μ_G is the viscosity of gas phase; ρ_G is the density of gas phase; D_G is the diffusivity of gas phase for the absorbed gas; D_P is the diameter of packing; R is the gas constant; and T is the absolute temperature. \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}k_ { \rm L } = 0.0051 \left( \frac { L } { a \mu_ { \rm L } } \right)^ { 2 / 3 } \left( \frac { \mu_ { \rm L } } { \rho_ { \rm L } D_ { \rm L } } \right)^ { - 1 / 2 } ( a_ { \rm t } D_ { \rm p } ) ^ { 0.4 } \left( \frac { \rho_ { \rm L } } { \mu_ { \rm L } g } \right) ^ { - 1 / 3 } , \tag { 9 } \end{align*} \end{document}

where L is the superficial mass velocity of liquid; a is the effective interfacial area per unit packed volume; μ_L is the viscosity of liquid phase; ρ_L is the density of liquid phase; D_L is the diffusivity of liquid phase for the absorbed gas; and g is the gravitational constant. \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} a =& a_{\rm t} \left( 1 -{\rm exp} \left( - 1.45 \left( \frac {\sigma_c} {\sigma_{\rm L}} \right)^{0.75} \left( \frac {L} {a_{\rm t} \mu_{\rm L}} \right)^{0.1} \right.\right.\\ &\quad \left.\left.\left( \frac {L^2a_{\rm t}} {\rho_{\rm L^2g}} \right) ^ {- 0.05} \left( \frac {L^2 } {\rho_{\rm L} \sigma_{\rm L}a_{\rm t}} \right)^{0.2} \right) \right) , \tag{10} \end{align*} \end{document}

where σ_c and σ_L are the critical surface tension of packing material and surface tension of liquid phase, respectively.

The enhancement factor E at 298.15 K can be calculated as follows (Nie et al., 2014): \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}E = 68.08C_{\rm NaOH}^{1 / 2} , \tag{11}\end{align*} \end{document}

where C_NaOH is the concentration of NaOH solution.

Physical properties of the system

The diffusivity D_L of SO₂F₂ in the water can be estimated using the equation developed by Tyn and Calus (Poling et al., 2000). The diffusivity D_G of SO₂F₂ in the air can be estimated using the equation developed by Fuller et al. (Poling et al., 2000). The solubility of SO₂F₂ in water can be calculated based on the previous studies at 298.15 K (Derrick et al., 1990; Tsai, 2010). The modified Stokes–Einstein equation (12) is used to estimate the diffusivity of the solute SO₂F₂ in aqueous NaOH solution (Onda et al., 1968a). \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}D_{\rm L} \mu_{\rm L}^{0.9} = {\rm const}. \tag{12}\end{align*} \end{document}

The Van Krevelen method is used to estimate the saturated concentration of SO₂F₂ in aqueous NaOH solution (Onda et al., 1970). Diffusivities, Henry's law constant of SO₂F₂, and properties of NaOH solution used in this study are given in Table 1. Properties of the packed column are given in Table 2.

Table 1.

Properties of NaOH Solution, Diffusivities, Surface Tension, and Henry's Law Constant of SO₂F₂ in Aqueous NaOH Solutions at 298.15K

C_NaOH (mol/L)	ρ_L (kg/m³)	μ_L × 10⁴ (Pa · s)	σ_L × 10² (N/m)	D_L × 10⁹ (m²/s)	H × 10⁵ [kmol/(m³ · kPa)]
0	997	8.94	7.20	1.56	7.27
0.11	1,003	9.06	7.22	1.54	7.01
0.21	1,008	9.22	7.23	1.51	6.77
0.41	1,016	9.56	7.26	1.46	6.32
0.58	1,023	9.84	7.28	1.43	5.95
0.68	1,027	10.02	7.30	1.40	5.74
0.78	1,031	10.17	7.31	1.39	5.56
0.95	1,038	10.45	7.33	1.35	5.25

Table 2.

Properties of Packed Column

Column diameter (cm)	10.40
Column height (m)	0.85
Type of packing	Rasching ring (12 mm)
Material	Ceramic
Packing surface (m²/m³)	390
Void fraction	0.70

Results and Discussion

Effect of gas flow rate

Effect of gas flow rate on the removal efficiency of SO₂F₂ was investigated with constant spray density, NaOH concentration, and inlet SO₂F₂ volume concentration. As can be seen from Fig. 2, the values calculated from the model were in good agreement with those from experiments. The removal efficiency of SO₂F₂ decreased with the increase of gas flow rate. This is because the mass transfer rate of SO₂F₂ (mol/s) mainly depends on the liquid-side film resistance. According to Equations (2) and (10), when the gas flow rate increases, the mass transfer rate N_A and effective interfacial area per unit packed volume a change slightly; thus, the mass transfer rate of SO₂F₂ (mol/s) remains almost constant, while the feeding rate of SO₂F₂ (mol/s) increases dramatically, as a result, the removal efficiency η decreases. In addition, as shown in Fig. 2, the removal efficiency of SO₂F₂ could reach 100% when the initial SO₂F₂ volume concentration, spray density, gas flow rate, and NaOH concentration were 0.50%, 12 m³/m²/h, 0.12 m³/h, and 0.68 mol/L, respectively.

FIG. 2.

Effect of gas flow rate on removal efficiency of SO₂F₂. Initial SO₂F₂ concentration: 0.50%; spray density: 12 m³/(m² · h); sodium hydroxide (NaOH) concentration: 0.68 mol/L; and gas flow rate ranged from 0.12 to 0.48 m³/h.

Effect of spray density

The effect of spray density on the removal efficiency of SO₂F₂ was investigated with the constant gas flow rate, NaOH concentration, and inlet SO₂F₂ volume concentration. As can be seen from Fig. 3, the removal efficiency of SO₂F₂ increased with the increase of spray density. The reason is that spray density affects the effective interfacial area, as shown in Equation (10). Larger spray density results in a larger effective interfacial area, and hence, a higher mass transfer rate of SO₂F₂ (mol/s), as shown in Equations (10) and (4). As a result, the removal efficiency η increases as shown in Equations (10) and (6). A similar trend for calculated data is observed in Fig. 3.

FIG. 3.

Effect of spray density on removal efficiency of SO₂F₂. Gas flow rate: 0.36 m³/h; initial SO₂F₂ volume concentration: 0.50%; NaOH concentration: 0.68 mol/L; and spray density ranged from 9 to 21 m³/(m² · h).

Effect of NaOH concentration

Effect of NaOH concentration on the removal efficiency of SO₂F₂ was investigated with the constant gas flow rate, spray density, and inlet SO₂F₂ volume concentration. As can be seen from Fig. 4, the tendency of the calculated data coincided well with the experimental data. It was also noted that the removal efficiency of SO₂F₂ increased with the increase of NaOH concentration; however, the increase rate was lower when the NaOH concentration was high. The reason is that NaOH concentration influences the enhancement factor E, as shown in Equation (11). With the increase of NaOH concentration, the enhancement factor E increases, and hence, the mass transfer rate of SO₂F₂ (mol/s) increases, as shown in Equations (7) and (4), contributing to the increase of removal efficiency η, as shown in Equations (7) and (6). However, with the increase of NaOH concentration, the solution is more viscous, and hence, the diffusivity coefficient and Henry's law constant of SO₂F₂ become smaller. As a result, the increase rate of removal efficiency η decreases.

FIG. 4.

Effect of NaOH concentration on removal efficiency of SO₂F₂. Gas flow rate: 0.36 m³/h; spray density: 12 m³/(m² · h); initial SO₂F₂ volume concentration: 0.50%; and NaOH concentration ranged from 0.11 to 0.96 mol/L.

Effect of inlet SO₂F₂ volume concentration

The effect of inlet SO₂F₂ volume concentration on the removal efficiency of SO₂F₂ was investigated with the constant gas flow rate, spray density, and NaOH concentration. As can be seen from Fig. 5, the inlet SO₂F₂ volume concentration had almost no influence on the removal efficiency of SO₂F₂. There was good agreement between the calculated and experimental data. The behavior can be explained by the fact that the chemical absorption of SO₂F₂ is a fast pseudofirst-order reaction, and NaOH concentration remains almost constant in the absorption process of dilute SO₂F₂. According to the mass balance [Eq. (6)], inlet SO₂F₂ volume concentration is unrelated to the removal efficiency η. Meanwhile, it is confirmed that the enhancement factor E is unrelated to the gas concentration in this case.

FIG. 5.

Effect of inlet SO₂F₂ volume concentration on removal efficiency of SO₂F₂. Gas flow rate: 0.36 m³/h; spray density: 12 m³/(m² · h); NaOH concentration: 0.68 mol/L; and initial SO₂F₂ volume concentration ranged from 0.10% to 0.54%.

Comparison of experimental and calculated data

As shown in Fig. 6, the proposed model expression based on Onda correlations gives a good agreement with the experimental data, since the average relative deviation is 1.9%, and the maximum relative deviation is 8.0%. Thus, the proposed model expression could be used to predict the removal efficiency of SO₂F₂ in the packed column.

FIG. 6.

Comparison of experimental and calculated data for removal efficiency of SO₂F₂.

Products analysis after chemical absorption of SO₂F₂

Aqueous NaOH solution after chemical absorption of SO₂F₂ was analyzed using an ion chromatogram, as illustrated in Fig. 7; fluoride ion (F⁻), sulfate ion (SO₄²⁻), and fluorosulfate ion (SO₃F⁻) were detected in the aqueous NaOH solution. The result shows that the overall process for this chemical absorption can be described as follows (Cady and Misra, 1974): \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{\rm SO}_2 {\rm F}_2 + {\rm NaOH} \rightarrow {\rm HOSO}_2{\rm F} + {\rm NaF} \tag{13}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{\rm HOSO}_2{\rm F} + {\rm NaOH} \rightarrow {\rm NaSO}_3{\rm F} + {\rm H}_2{\rm O} \tag{14}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{\rm NaSO}_3{\rm F} + 2{\rm NaOH} \rightarrow {\rm Na}_2{\rm SO}_4 + {\rm NaF} + {\rm H}_2{\rm O} \tag{15}\end{align*} \end{document}

By means of chemical absorption, SO₂F₂ was removed through Equations (13 )–(15) and finally converted to NaF, NaSO₃F, and Na₂SO₄. The salts in the solution could be further recycled by the crystallization method.

FIG. 7.

Ion chromatogram spectrum of aqueous NaOH solution after absorption.

Conclusions

(1) At 298.15 K, SO₂F₂ can be removed with alkaline absorption when inlet SO₂F₂ volume concentration, spray density, gas flow rate, and NaOH concentration were 0.50%, 12 m³/(m² · h), 0.12 m³/h, and 0.68 mol/L, respectively.

(2) According to the two-film theory, a mathematical model based on Onda correlations to describe the removal efficiency of SO₂F₂ was developed. The comparison between the calculated and experimental results showed a good agreement regarding the removal efficiency of SO₂F₂. The maximum relative deviation is 8.0%.

(3) Results from experiments and the proposed model show that the liquid spray density and NaOH concentration had a positive influence on removal efficiency of SO₂F₂. However, the gas flow rate had a negative influence on removal efficiency of SO₂F₂. The inlet SO₂F₂ volume concentration had almost no influence on the removal efficiency of SO₂F₂.

Footnotes

Acknowledgments

The financial support from the Natural Science Foundation of China (NSFC) (Grant No. 51107118) and Science and Technology Plan of General Administration of Quality Supervision of the P.R.C. (Grant No. 201010256651.9) are gratefully acknowledged.

Author Disclosure Statement

No competing financial interest exists.

Nomenclature

Greek letters

Subscripts

References

Athanassiou

C.G.

, Phillips

T.W.

, Aikins

M.J.

, Hasan

M.M.

, and Throne

J.E.

(2012). Effectiveness of sulfuryl fluoride for control of different life stages of stored-product psocids (Psocoptera). J. Econ. Entomol., 105, 282.

Bonifácio

L.F.

, Sousa

, Naves

, Inácio

M.L.

, Henriques

, Mota

, and Buckley

(2014). Efficacy of sulfuryl fluoride against the pinewood nematode, Bursaphelenchus xylophilus (Nematoda: Aphelenchidae), in Pinus pinaster boards. Pest Manage. Sci., 70, 6.

Cady

G.H.

, and Misra

(1974). Hydrolysis of sulfuryl fluoride. Inorg. Chem., 13, 837.

Cao

, Guo

, Yan

, Mao

, Wang

, Li

, and Wang

(2014). Evaluation of sulfuryl fluoride as a soil fumigant in China. Pest Manage. Sci., 70, 219.

Chayaprasert

, Maier

D.E.

, Subramanyam

, and Hartzer

(2012). Gas leakage and distribution characteristics of methyl bromide and sulfuryl fluoride during fumigations in a pilot flour mill. J. Stor. Prod. Res., 50, 1.

Derrick

M.R.

, Burgess

H.D.

, Baker

M.T.

, and Binnie

N.E.

(1990). Sulfuryl fluoride (Vikane): A review of its use as a fumigant. J. Am. Inst. Conserv., 29, 77.

Fields

P.G.

, and White

N.D.G.

(2002). Alternatives to methyl bromide treatments for stored-product and quarantine insects. Annu. Rev. Entomol., 47, 331.

Meikle

R.W.

, and Stewart

(1962). Structural fumigants, the residue potential of sulfuryl fluoride, methyl bromide, and methanesulfonyl fluoride in structural fumigations. J. Agric. Food Chem., 10, 393.

Mühle

, Huang

, Weiss

R.F.

, Prinn

R.G.

, Miller

B.R.

, Salameh

P.K.

, and Simmonds

P.G.

(2009). Sulfuryl fluoride in the global atmosphere. J. Geophys. Res., 114, D05306.

10.

Nie

, Ji

, Liang

, Lu

, and Yu

(2013a). An appratus for removing sulfur fluoride based on chemical absorption. China Patent No. 201320395223.

11.

Nie

, Liang

, Lu

, Yu

, Gu

, Min

, and Ji

(2014). Mass transfer and reaction kinetics of sulfuryl fluoride absorption with aqueous sodium hydroxide solutions. J. Zhejiang Univ. Sci. A., 15, 540.

12.

Nie

, Zheng

, Liang

, Gu

, Lu

, Min

, and Ji

(2013b). Decomposition treatment of SO₂F₂ using packed bed DBD plasma followed by chemical absorption. Environ. Sci.Technol., 47, 7934.

13.

Onda

, Sada

, Kobayashi

, Kito

, and Ito

(1970). Salting-out parameters of gas solubility in aqueous salt solutions. J. Chem. Eng. Jpn., 3, 18.

14.

Onda

, Sada

, and Takeuchi

(1968a). Gas absorption with chemical reaction in packed columns. J. Chem. Eng. Jpn., 1, 62.

15.

Onda

, Takeuchi

, and Okumoto

(1968b). Mass transfer coefficients between gas and liquid phases in packed columns. J. Chem. Eng. Jpn., 1, 56.

16.

Papadimitriou

V.C.

, Portmann

R.W.

, Fahey

D.W.

, Mühle

, Weiss

R.F.

, and Burkholder

J.B.

(2008). Experimental and theoretical study of the atmospheric chemistry and global warming potential of SO₂F₂. J. Phys. Chem. A, 112, 12657.

17.

Poling

B.E.

, Prausnitz

J.M.

, and O'Connell

J.P.

(2000). The Properties of Gases and Liquids (fifth edition). New York: McGraw-Hill.

18.

Tan

T.N.

, Jin

Y.Z.

, and Luo

Y.S.

(1990). The Process of Mass Transfer and Reaction. Hangzhou: Zhejiang University.

19.

Tsai

W.T.

(2010). Environmental and health risks of sulfuryl fluoride, a fumigant replacement for methyl bromide. J. Environ. Sci. Health. Part C, 28, 125.

Harmless Treatment of Sulfuryl Fluoride by Chemical Absorption

Abstract

Abstract

Introduction

Experimental Protocols

Materials

Apparatus and procedure

Analysis

Mathematical Model

Mass balance of SO2F2 in packed column

Overall gas-phase mass transfer coefficient

Physical properties of the system

Results and Discussion

Effect of gas flow rate

Effect of spray density

Effect of NaOH concentration

Effect of inlet SO2F2 volume concentration

Comparison of experimental and calculated data

Products analysis after chemical absorption of SO2F2

Conclusions

Footnotes

Acknowledgments

Author Disclosure Statement

Nomenclature

Greek letters

Subscripts

References

Mass balance of SO₂F₂ in packed column

Effect of inlet SO₂F₂ volume concentration

Products analysis after chemical absorption of SO₂F₂