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In this paper, a heterogeneous catalytic system consisting of Co/Mn/Br/activated carbon is used to catalyze 2-nitro-4-methylsulfonyl benzoic acid (NMSBA) production from the oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) by oxygen. The activated carbon (AC) is made from coconut shell with acetic acid as an activator. The experiments indicate that the best AC is made by immersing coconut shell in 12 mol L−1 HAc solution at 50 °C for 32 h with a liquid/solid ratio (mL/g) of 5:1 and then being heated in nitrogen at 800 °C for 6 h. Compared with the Co/Mn/Br/H3PMo12O40@CAC (CAC, commercial activated carbon originated from coconut shell) catalytic system, the Co/Mn/Br/AC catalytic system is able to gain much higher NMSBA selectivity. In spite of holding smaller surface and less acidic groups, the AC owns much more carboxyl than CAC, which is the main reason for its better performance in the preparation of NMSBA.

Microtopography of fiber of Discorea nipponica Makino before and after mechanical activated by AGO-2 planetary mill was observed by SEM, and they changed the thick floccules to fine particles (D50 particle sizes were 10.18μm). Discorea fiber powder after mechanical activation had a narrow size distribution. According to XRD, the granularity and structures of discorea fiber with and without mechanical activation significantly differed, and the crystalline of discorea fiber was significantly converted into amorphous state after mechanical activation. On the basis of TG–DSC analysis, the activity of discorea fiber was enhanced, and certain internal energy were stored, and complete decomposition in advance. According to FT-IR, none of the functional groups of the mechanically activated discorea fiber disappeared, and no new functional groups appeared, which indicate that mechanical activation does not induce a chemical transformation of discorea fiber. According to the activation energy analysis, the thermal activation energy of dioscorea fiber after mechanical activation was18.49 kJ•mol, and the mechanical transfer activation energy was 56.06 kJ•mol, indicating that about 1/3 of the mechanical transfer activation energy was stored in the activated dioscorea fiber fine powder in the form of surface energy and internal energy.

The production of IPA from the oxidation of MX is completed under the catalysis of H3PW12O40 (HPW) loaded on carbon and cobalt. Oxalic acid is tried to modify the carbon to upgrade the catalytic activity of HPW@C catalyst. The experiments show that the best carbon is acquired by carbonizing the carbon at 450 °C for 2 h in N2 after being soaked in a 0.20 mol l−1 oxalic acid solution for 16 h. The IPA produced by the HPW@C catalysts prepared with the carbon modified is 58.9% over that obtained by the catalysts prepared with the original carbon.

The production of isophthalic acid (IPA) from the oxidation of m-xylene (MX) by air is catalyzed by H3PW12O40 (HPW) loaded on carbon and cobalt. We used H2O2 solution to oxidize the carbon to improve the catalytic activity of HPW@C catalyst. Experiments reveal that the best carbon sample is obtained by calcining the carbon at 700 °C for 4 h after being impregnated in the 3.75% H2O2 solution at 40 °C for 7 h. The surface characterization displays that the H2O2 modification leads to an increase in the acidic groups and a reduction in the basic groups on the carbon surface. The catalytic capability of the HPW@C catalyst depends on its surface chemical characteristics and physical property. The acidic groups play a more important part than the physical property. The MX conversion after 180 min reaction acquired by the HPW@C catalysts prepared from the activated carbon modified in the best condition is 3.81% over that obtained by the HPW@C catalysts prepared from the original carbon. The IPA produced by the former is 46.2% over that produced by the latter.

Isophthalic acid produced from the oxidation of m-xylene by air is catalyzed by H3PW12O40 (HPW) loaded on carbon and cobalt. In this paper, acetic acid solution is used to treat the carbon to ameliorate the catalytic ability of HPW@C catalyst. The experiments indicate that the best supporter is obtained by immersing the carbon in 3.5 mol L–1 HOAc for 24 h followed by carbonized at 500 °C for 4 h. The surface characterization proves that the modification with HOAc augments acidic groups and amplifies specific surface area on the carbon surface. The surface chemistry plays a more vital role than the physical properties in determining the catalytic ability of HPW@C. We find that 76.7% more IPA is produced after 180 min reaction by the HPW@C made of the carbon modified in the best conditions than by the HPW@C made of the original carbon.

The simultaneous scrubbing of NO and SO2 can be finished with the Co(NH3)62+ ammonia solution. Activated carbon aids the regeneration of Co(NH3)62+ to retain the ability of absorbing NO. Acetic acid is tried to improve the catalytic capability of activated carbon. The best treatment condition is the carbon samples impregnated in 2.0 mol l−1 HAc solution for 20 h followed by being calcined at 600 °C for 4 h. The HAc modification increases surface area and acidic groups on the carbon surface. The experiments prove that the modified carbon can obtain a higher NO removal efficiency than the original carbon.

The commercial production of 2-nitro-4-methylsulphonylbenzoic acid (NMSBA) is oxidizing 2-nitro-4-methylsulphonyltoluene (NMST) by nitric acid catalyzed with V2O5. A heterogeneous catalytic system composed of phosphotungstic acid supported on activated carbon, Co, Mn, and Br is used to catalyze the production of NMSBA from NMST by oxygen in this paper. The experiments show that the heterogeneous catalytic system composed of HPW@C, Co, Mn, and Br is capable of speeding up the oxidation of NMST to NMSBA by oxygen and acquiring a higher NMST oxidation rate and NMSBA yield than the homogeneous H3PW12O40/Co/Mn/Br catalytic system. The best HPW@C catalyst is obtained by supporting 0.0125 g/g H3PW12O40 on carbon followed by being calcined at 220 °C for 4 h under nitrogen atmosphere. The best heterogeneous catalytic system consists of 2.38 × 10−3 g/g HPW@C, 925 ppm Br, 236 ppm cobalt, and a Mn/Co molar ratio of 2.5. The usage of phosphotungstic acid in the heterogeneous system is diminished substantially.

Tartaric acid solution is applied to change the surface characteristics of activated carbon to improve its catalytic capability in the regeneration of Co(NH3)62+ that is used to realize the simultaneous removal of NO and SO2. The experimental results show that the best treatment condition is impregnating the carbon samples in 1.5 mol l−1 tartaric acid solution for 18 h followed by being activated at 400°C for 4 h under nitrogen atmosphere. After being treated with tartaric acid solution, the surface area of activated carbon and the acidity on its surface increase. The experiments show that the modified carbon can obtain a much higher NO removal efficiency than the original carbon. © 2017 American Institute of Chemical Engineers Environ Prog, 2017

2-Nitro-4-methylsulfonylbenzoic acid (NMSBA) is usually manufactured from the partial oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) by nitric acid under the catalysis of vanadium pentoxide. This paper reports a novel method for the production of NMSBA from the oxidation of NMST by oxygen catalyzed with a homogeneous catalyst system consisting of H 3 PW 12 O 40 /Co(II)/Mn(II)/Br. The experiments prove that this catalytic system realizes the oxidation of NMST to NMSBA. The optimal phosphotungstic acid concentration is 2500 ppm. The optimum Co(II) concentration is 148 ppm. The highest NMSBA yield is obtained with a Mn/Co ratio of 2.1. The best Br concentration is 1163 ppm. Temperature has a strong effect on the reaction rates. Oxygen partial pressure influences the NMST conversion and NMSBA yield greatly. The kinetic parameters, such as activation energy and reaction orders, have been estimated.

The oxidation of m-xylene(MX) to isophthalic acid(IPA) catalyzed by phosphotungstic acid(HPW) supported on modified activated carbon was investigated. The activated carbon loading with HPW is modified by HNO3 solution to ameliorate its catalytic capability in the oxidation of MX to IPA. Experiments have been carried out to study the effects of modification conditions, such as HNO3 concentration, impregnation time, impregnation temperature, activation temperature and activation time, on the catalytic performance of activated carbon. The experimental results demonstrate that the carbon sample impregnated in 10%(vol) HNO3 solution at 45°C for 8 h followed by calcined at 700°C for 4 h has the best catalytic capability. The characterization results imply that the specific surface area and micropores of the carbon samples decrease after being treated with HNO3 solution. But the acidic functional groups on the activated carbon surface increase, which play a vital role in improving the catalytic ability of the HPW/C catalyst in the oxidization of m-xylene to IPA.

NO can be removed at the same time with SO2 by aqueous Co(NH3)62+ solution. The reduction of Co(NH3)63+ to Co(NH3)62+ is catalyzed by activated carbon to regain the NO absorption ability of the scrubbing solution. Oxalic acid solution is explored to change the carbon surface to ameliorate its catalytic capability. The experimental results suggest that the best catalyst is prepared by impregnating the carbon sample in 0.7 mol l-1 oxalic acid solution for 24 h followed by being activated at 600 °C for 5 h under nitrogen atmosphere. After being treated with oxalic acid solution, the surface area and the acidity on the carbon surface increase. The experiments show that the carbon modified with oxalic acid can get a much higher NO removal efficiency than the original carbon.

The combined elimination of NO and SO2 can be realized by hexamminecobalt(II) solution. Activated carbon is utilized to catalyze the reduction of hexamminecobalt(III) (Co(NH3)63+) to hexamminecobalt(II) (Co(NH3)62+), so as to maintain a high NO removal efficiency for a long time. K2S2O8 solution has been tried to modify coconut activated carbon to enhance its catalytic capability in the reduction of hexamminecobalt(III). The experiments have been performed in a stirred cell to investigate the effects of K2S2O8 concentration, impregnation temperature, and impregnation time on the catalytic ability of activated carbon. The results showed that the best K2S2O8 concentration for the improvement of activated carbon is 0.3 mol L−1. The optimal impregnation temperature was 40°C. The optimum impregnation duration was 9 h. After treated with K2S2O8 solution, the surface area of activated carbon decreased. But the acidity on its surface was enhanced, which played a crucial role in improving the catalytic capacity of activated carbon in the reduction of Co(NH3)63+. The experimental results showed that the modified carbon could obtain a higher NO removal efficiency than the original carbon. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 65–73, 2015

Isophthalic acid (IPA) is commercially produced from m-xylene oxidation with the catalysis of the homogeneous Co–Mn–Br catalyst system. In this study, a catalytic system consisting of HPW/C and Co(II) has been put forward to oxidize m-xylene (MX) to IPA. The experimental results prove that the HPW/C and Co catalytic system is capable of catalyzing the oxidation of MX to IPA, which can obtain a higher MX conversion and IPA concentration than the homogeneous H3PW12O40/Co(OAc)2/Mn(OAc)2 catalytic system. The heterogeneous catalytic system is also advantageous over the homogeneous catalytic system in the inhibition of the oxidation of acetic acid and IPA. The optimal amount of phosphotungstic acid supported on carbon is 7.5% (wt). The best dosage of HPW/C is 15 g l−1. The optimum Co(II) concentration in the catalytic system for IPA production is 0.064% (wt). The best HPW/C activation temperature is 220 °C.

The combined absorption of NO and SO2 into the Fe(II)-ethylenediamineteraacetate(EDTA) solution has been realized. Activated carbon is used to catalyze the reduction of FeIII-EDTA to FeII-EDTA to maintain the ability to remove NO with the Fe-EDTA solution. The reductant is the sulfite/bisulfite ions produced by SO2 dissolved into the aqueous solution. Experiments have been performed to determine the effects of activated carbon of coconut shell, pH value, temperature of absorption and regeneration, O2 partial pressure, sulfite/bisulfite and chloride concentration on the combined elimination of NO and SO2 with FeII-EDTA solution coupled with the FeII-EDTA regeneration catalyzed by activated carbon. The experimental results indicate that NO removal efficiency increases with activated carbon mass. There is an optimum pH of 7.5 for this process. The NO removal efficiency increases with the liquid flow rate but it is not necessary to increase the liquid flow rate beyond 25 ml min−1. The NO removal efficiency decreases with the absorption temperature as the temperature is over 35 °C. The Fe2+ regeneration rate may be speeded up with temperature. The NO removal efficiency decreases with O2 partial pressure in the gas streams. The NO removal efficiency is enhanced with the sulfite/bisulfite concentration. Chloride does not affect the NO removal. Ca(OH)2 and MgO slurries have little influence on NO removal. High NO and SO2 removal efficiencies can be maintained at a high level for a long period of time with this heterogeneous catalytic process.

NO and SO 2 can be eliminated simultaneously by [Fe(II)EDTA] 2− solution with a pH range of 5.6–8.0 at 25–80 °C. Activated carbon is used to catalyze the regeneration of [Fe(II)EDTA] 2− . In this paper, KOH solution has been utilized to modify the carbon to improve its catalytic capability. Experimental results show that the optimal modification factors are as follow: KOH concentration 6.0 mol l −1 , impregnation time 9 h, activation temperature 700 °C and activation time 4 h. After KOH modification, the surface area of activated carbon decreases. But its basicity is enhanced, which plays an important role in improving the catalytic characteristics of activated carbon in the reduction of [Fe(III)EDTA] − . The experimental results demonstrate that the activated carbon modified by concentrated KOH solution can get a higher NO removal efficiency than the original activated carbon.

NO and SO2 can be removed simultaneously by [Fe(II)EDTA]2− solution. Activated carbon is used to catalyze the regeneration of [Fe(II)EDTA]2− to maintain the NO removal efficiency at a high level for a long time. In this article, ammonia solution has been tried to modify the coconut activated carbon to ameliorate its catalytic capability in the regeneration of [Fe(II)EDTA]2−. Experiments have been made in a batch stirred cell to investigate the effects of modification conditions, such as ammonia concentration, impregnation time, activation temperature, and activation time, on the catalytic performance of activated carbon. The experimental results suggest that the optimal modification condition be illustrated as follow: ammonia concentration 9.0 mol L−1, impregnation time 11 h, activation temperature 700°C, and activation time 4 h. After ammonia modification, the surface area of activated carbon decreases. But the total basicity of activated carbon is enhanced, which plays a vital role in improving the catalytic capability of activated carbon in the reduction of [Fe(III)EDTA]−. The activated carbon modified by ammonia solution can get a higher NO removal efficiency than the original activated carbon. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 99–106, 2014

The simultaneous scrubbing of NO and SO 2 can be accomplished by hexamminecobalt(II) solution. Activated carbon acts as a catalyst to regenerate hexamminecobalt(II), Co(NH 3 ) 6 2+ , to sustain the NO removal efficiency. In this paper, ZnCl 2 solution has been used to ameliorate the catalytic performance of coconut activated carbon in the regeneration of Co(NH 3 ) 6 2+ . The effects of the modification condition on the catalytic performance of activated carbon have been investigated in a batch stirred cell. The change of the surface chemical characteristics of the activated carbon caused by ZnCl 2 treatment was measured by determining the concentrations of acidic and basic groups as well as their points of zero charge (pH pzc ) with Boehm titration and mass titration. The alteration of the surface physical characteristics of the carbons was determined with an ASAP2000 Surface Analyzer using N 2 as the adsorbate. The experiments demonstrate that the catalytic performance of the coconut activated carbon may be improved when the carbon is treated by ZnCl 2 solution with concentration above 0.30 mol l −1 . The best ZnCl 2 concentration may be 0.50 mol l −1 . The optimal impregnation duration is 9 h. High activation temperature is propitious for the amelioration of the catalytic capability of carbon. 4 h may be the best time for the activation of activated carbon. In our experiment, the NO removal efficiency is maintained at a level of 73% when the regeneration of Co(NH 3 ) 6 2+ is under the catalysis of modified carbon while that is 57% with the regeneration of Co(NH 3 ) 6 2+ catalyzed by original carbon. It can be concluded that such modification can improve the catalytic performance of coconut activated carbon in the simultaneous removal of SO 2 and NO with Co(NH 3 ) 6 2+ ammonia solution.

In this study, the adsorption of [Fe(III)–EDTA]− on coconut-activated carbon from aqueous solutions has been studied in a batch stirred cell. Experiments have been carried out to investigate the effects of temperature, [Fe(III)–EDTA]− concentration, pH, and activated carbon mass on [Fe(III)–EDTA]− adsorption. The experimental results manifest that high temperature is favorable to the adsorption of [Fe(III)–EDTA]− on the activated carbon. The [Fe(III)–EDTA]− adsorption on activated carbon increases with its concentration in the aqueous solutions. However, the [Fe(III)–EDTA]− adsorption on activated carbon decreases as the pH rises. The [Fe(III)–EDTA]− adsorption on per gram of activated carbon decreases as the activated carbon mass increases. The kinetic study shows that [Fe(III)–EDTA]− adsorption on the activated carbon is in good compliance with the pseudo-second-order kinetic model. The Langmuir and Freundlich equilibrium isotherm models are found to provide a good fitting of the adsorption data. Thermodynamic parameters such as Ea, ΔG0, ΔH0, and ΔS0 for adsorption reaction are estimated. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 470–479, 2013

The simultaneous control of SO2/NOX can be realized with the [Fe(II)-EDTA]2− aqueous solution. However, the [Fe(II)-EDTA]2− is easily oxidized to [Fe(III)-EDTA] − by oxygen, which has no ability to bind NO. The reduction of [Fe(III)-EDTA] − to [Fe(II)-EDTA]2− is a key to the maintenance of the NO removal efficiency with the [Fe(II)-EDTA]2− aqueous solution. The reduction of [Fe(III)-EDTA]− can be accomplished by sulfite produced by SO2 dissolving in the aqueous solution under the catalysis of activated carbon. The experiments were performed in a fixed-bed reactor to investigate the regeneration of [Fe(II)-EDTA]2− catalyzed by activated carbon. The influences of [Fe(III)-EDTA] − and sulfite concentrations, pH, liquid flow, temperature, on [Fe(III)-EDTA] − catalytic reduction have been tested. The experimental results indicate that the [Fe(III)-EDTA]− reduction increases with the [Fe(III)-EDTA]− and sulfite concentrations. Raising the temperature can increase the [Fe(III)-EDTA] − conversion. The optimal pH range for the reduction of [Fe(III)-EDTA] − is 5.7–7.5. The apparent activation energy determined from the experimental results is 35.2 ± 0.5 kJ mol−1. The continuous experiment manifests that simultaneous removal of NO and SO2 with the [Fe(II)-EDTA]2− solution coupled with the Fe(II) regeneration catalyzed by activated carbon can be maintained at a high NO removal efficiency for a long period of time. The kinetic equation of [Fe(III)-EDTA]- reduction by sulfite catalyzed with activated carbon can be described as r = k 2 k 1 KC[Fe(III)−EDTA]−1/n C H + C SO32− k − 1 C EDTA ( 1 + C H + / Kaθ ) + k 2 C SO32− · ρ b e © 2012 American Institute of Chemical Engineers Environ Prog, 32: 206-212, 2013

A novel method has been put forward to retrofit the wet ammonia desulfurization process to realize the combined removal of sulfur dioxide and nitric oxide by introducing soluble cobalt(II) salt into aqueous ammonia solution. The active constituent of scrubbing NO from the flue gases is the Co(NH 3 ) 2+ 6 produced by ammonia coordinating with Co 2+ . The regeneration of Co(NH 3 ) 2+ 6 can be realized under the catalysis of activated carbon so as to sustain a high NO removal efficiency for a long time. In this paper, the adsorption-reduction behavior of Co(NH 3 ) 2+ 6 on activated carbon has been researched using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. A conclusion can be drawn from the results that cobalt ions in the aqueous solution are adsorbed by activated carbon and most of them are reduced to Co 2+ ions, and some of the Co 2+ ions are further reduced into metallic cobalt. The results also demonstrate that the functional groups on the surface of carbon take part in this redox reaction. The C—H groups on the carbon surface are oxidized into C—OH, and then some of the hydroxyl groups are further oxidized into carbonyl or carboxyl groups.

The simultaneous removal of SO2 and NO from the flue gases with the [Fe(II)-EDTA]2– solution has not been put into commercial application because of the quick oxidation of [Fe(II)-EDTA]2– to [Fe(II...

Isophthalic acid (IPA) is usually produced by the Co–Mn–Br catalyst system. In this study, a bromine-free catalyst system consisting of H 3 PW 12 O 40 /Co(OAc) 2 /Mn(OAc) 2 has been put forward to oxidizing m-xylene (MX) to IPA. The experimental results proves that the homogeneous H 3 PW 12 O 40 /Co(OAc) 2 /Mn(OAc) 2 catalytic system is able to catalyze the oxidation of MX to IPA. The optimal phosphotungstic acid concentration is 0.52 wt%. The optimum Co(II) concentration for IPA production is between 0.044% and 0.088 wt%. The best Mn/Co ratio is found to be 2.46. Temperature has a strong effect on the reaction rates. Oxygen partial pressure influences on the IPA yield greatly. The kinetic parameters such as activation energies, reaction orders have been estimated.

In this study, the adsorption of EDTA on activated carbon from aqueous solutions has been investigated in a batch stirred cell. Experiments have been carried out to investigate the effects of temperature, EDTA concentration, pH, activated carbon mass and particle size on EDTA adsorption. The experimental results manifest that the EDTA adsorption rate increases with its concentration in the aqueous solutions. EDTA adsorption also increases with temperature. The EDTA removal from the solution increases as activated carbon mass increases. The Langmuir and Freundlich equilibrium isotherm models are found to provide a good fitting of the adsorption data, with R 2 = 0.9920 and 0.9982, respectively. The kinetic study shows that EDTA adsorption on the activated carbon is in good compliance with the pseudo-second-order kinetic model. The thermodynamic parameters ( E a , Δ G 0 , Δ H 0 , Δ S 0 ) obtained indicate the endothermic nature of EDTA adsorption on activated carbon.

The simultaneous removal of NO and SO 2 from flue gases can be realized with Fe(II)–ethylenediamineteraacetate(EDTA) solution. Activated carbon is used to catalyze the reduction of Fe III –EDTA to Fe II –EDTA to maintain the capability of removing NO of the Fe–EDTA solution. The reductant is the sulfite/bisulfite ions produced by SO 2 dissolving into the aqueous solution. Experiments have been performed to determine the effects of activated carbon of coconut shell, Fe II –EDTA concentration, Fe/EDTA molar ratio, SO 2 partial pressure, NO partial pressure and SO 4 2− concentration on the combined elimination of NO and SO 2 with Fe II –EDTA solution coupled with the Fe II –EDTA regeneration catalyzed by activated carbon. According to the experimental results, activated carbon not only catalyzes the reduction of Fe III –EDTA by sulfite/bisulfite greatly but also avoids the release of N 2 O. The NO removal efficiency increases with the initial Fe II –EDTA concentration and SO 2 partial pressure. The ratio of Fe/EDTA and the SO 4 2− concentration has little effect on the catalytic reduction of Fe III –EDTA. The optimal initial NO concentration range is from 600 ppm to 900 ppm. The experimental results manifest that the Fe II –EDTA solution coupled with catalytic regeneration of Fe II –EDTA can maintain high nitric oxide removal efficiency for a long period of time.

Ammonia solution can be used to scrub NO from the flue gases by adding soluble cobalt(II) salts into the aqueous ammonia solutions. The hexamminecobalt(II), Co(NH3)62+, formed by ammonia binding with Co2+ is the active constituent of eliminating NO from the flue gas streams. The hexamminecobalt(II) can combine with NO to form a complex. For the development of this process, the data of the equilibrium constants for the coordination between NO and Co(NH3)62+over a range of temperature is very important. Therefore, a series of experiments were performed in a bubble column to investigate the chemical equilibrium. The equilibrium constant was determined in the temperature range of 30.0–80.0 °C under atmospheric pressure at pH 9.14. All experimental data fit the following equation well: K p = ( 1.9051 ± 0.124 ) × 10 − 6 exp 5359.25 ± 280.13 T ( ba r − 1 ) where the enthalpy and entropy are ΔH° = −(44.559 ± 2.329) kJ mol−1 and ΔS° = −(109.50 ± 7.126) J K−1 mol−1, respectively.

The homogeneous catalytic removal of NO and SO 2 with the hexamminecoblt(II) (Co(NH 3 ) 6 2+ ) solution is a novel alternative to comply with the environmental emission standards. The mass transfer and kinetics of the absorption of NO and SO 2 into the aqueous Co(NH 3 ) 6 2+ solutions have been investigated in a double-stirred reactor. The experimental results indicate that the gas–liquid reaction between NO and Co(NH 3 ) 6 2+ with 5.2% oxygen coexisting in the gas phase becomes gas film controlling as Co(NH 3 ) 6 2+ concentration exceeds 0.03 mol l −1 when there is 1600 ppm SO 2 in the gas phase. NO absorption rate is proportional to its inlet concentration. Higher SO 2 concentration in the gas phase reduces the NO absorption rate into the Co(NH 3 ) 6 2+ solution. The NO absorption rate decreases with temperature as it is above 34 °C and the disadvantage of temperature is smaller in the presence of SO 2 than in the absence of SO 2 . Oxygen in the gas phase is of benefit to the NO absorption. A high oxygen partial pressure is more beneficial to the combined removal of NO and SO 2 with the Co(NH 3 ) 6 2+ solution. The NO absorption rate increases with pH of the Co(NH 3 ) 6 2+ solution. A high pH is especially favorable to the combined removal of NO and SO 2 . A kinetic equation for NO absorption under gas film controlling at 50 °C has been obtained as N NO = K NO , G p NO C Co ( N H 3 ) 6 2 + 2 p O 2 C N H 4 + C O H − / K N H 3 1.357 H S O 2 2 p S O 2 2 + C Co ( N H 3 ) 6 2 + 2 p O 2 C N H 4 + 2 C O H − / K N H 3 .

In this study, adsorption of ammonia on activated carbon from aqueous solutions has been studied in a batch stirred cell. Experiments have been carried out to investigate the effects of temperature, ammonia concentration, and activated carbon dose on ammonia adsorption. The experimental results manifest that the ammonia adsorption rate on activated carbon increases with its concentration in the aqueous solutions. Ammonia adsorption also increases with temperature. The ammonia removal from the solution increases as activated carbon mass increases. The Langmuir and Freundlich equilibrium isotherm models are found to provide a good fitting of the adsorption data, with r2 = 0.9749 and 0.9846, respectively. The adsorption capacity of ammonia obtained from the Langmuir equilibrium isotherm model is found to be 17.19 mg g−1. The kinetic study shows that ammonia adsorption on the activated carbon is in good compliance with the pseudo-second-order kinetic model. The thermodynamic parameters (▵G°, ▵H°, ▵S°) obtained indicate the endothermic nature of ammonia adsorption on activated carbon. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

NO can be removed from exhaust gas streams by using a basic solution of cobalt ethylenediamine (H 2 NCH 2 CH 2 NH 2 ). The cobalt ethylenediamine acts as a homogeneous catalyst to oxidize NO into soluble nitrogen dioxide and realize the oxidation and absorption of nitric oxide simultaneously. The dissolved oxygen in equilibrium with the residual oxygen in the exhaust gas stream acts as the oxidant. SO 2 can also be removed by the Co(en) 3 3+ (en stands for ethylenediamine) solution. A double-stirred reactor with a plane gas–liquid interface that was planar to close approximation was used to measure the absorption rates of NO into the Co(en) 3 3+ solutions. The experiments demonstrate that the gas–liquid reaction becomes gas film controlling as the cobalt ethylenediamine concentration exceeds 0.03 mol l −1 when there is 1200 ppm SO 2 in the gas phase. The NO absorption rate decreases as SO 2 concentration increases. Oxygen in the gas phase accelerates the NO absorption rate into the cobalt ethylenediamine solution. The optimal temperature for nitric oxide absorption is 50 °C. The NO absorption rate increases as the pH of the Co(en) 3 3+ solutions rises.

NO pollutant causes acid rain and urban smog. The removal of NO from exhausted gas streams is necessary to meet stringent effluent discharge limits. NO can be removed from exhausted gas streams by putting soluble cobalt salts and ethylenediamine (H 2 NCH 2 CH 2 NH 2 ) into basic solutions. The Co(en) 3 3+ (en stands for ethylenediamine) ion produced by ethylenediamine binding cobalt acts as a homogeneous catalyst to oxidize NO into soluble NO 2 and realize the oxidation and absorption of nitric oxide in the same reactor. The dissolved oxygen in equilibrium with the residual oxygen in the exhausted gas stream acts as the oxidant. The experiments manifest that this process is superior to the methods using Fe(II)–ethylenediaminetetraacetate (EDTA) solution and H 2 O 2 solution as absorbents in removing NO from the exhausted gas stream. NO removal efficiency decreases with the increase of the gas flow rate. NO removal efficiency increases with the Co(en) 3 3+ concentration. pH of the solution affects the NO removal efficiencies obviously. Under anaerobic condition, the NO removal efficiency decreases with pH when pH is over 7.73. Under aerobic condition, there is an optimal pH for NO absorption into the Co(en) 3 3+ concentration. More than 90% of NO in the feed gas can be removed by the Co(en) 3 3+ solution.

A homogeneous catalyst system made up of [Co(NH3)6]2+/I- has been put forward to catalyze the oxidation of concentrated ammonium sulfite. The experiments were performed in a packed column with sulfite concentrations above 2.5 mol l(-1), temperature range 20-65 degrees C, and oxygen partial pressure 0.052-0.21 atm. The experimental results indicate that the Co(NH3)6(2+)/I- homogeneous catalyst system can obviously accelerate the concentrated ammonium sulfite oxidation rate. After 2h reaction, the sulfite conversion is only 12.5% with no catalysts while 72.1% sulfite conversion can be obtained with 0.02 mol l(-1) Co(NH3)6(2+) and 0.005 mol l(-1) I- in the ammonium sulfite solution. The sulfite oxidation rate increases 284% as Co(NH3)6(2+) concentration increases from 0.01 to 0.02 mol l(-1). But there is little use increasing the Co(NH3)6(2+) concentration above 0.04 mol l(-1). The sulfite oxidation rate may increase 229% as the temperature increases from 20 to 65 degrees C. Sulfite oxidation rate is independent of the initial sulfite concentration. Increasing the oxygen partial pressure can increase the sulfite conversion. The reaction order with respect to oxygen is 1.2 and sulfite is zero. The apparent activation energy determined is 23.5 kJ mol(-1).

NO can be removed from exhaust gas streams by using a basic solution of cobalt ethylenediamine (en = H 2 NCH 2 CH 2 NH 2 ). The cobalt ethylenediamine acts as a homogeneous catalyst to oxidize NO into soluble nitric dioxide and realize the oxidation and absorption of nitric oxide simultaneously. The dissolved oxygen in equilibrium with the residual oxygen in the exhaust gas stream acts as the oxidant. A stirred vessel with a plane gas-liquid interface was used to measure the absorption rates of NO into Co(en) 3 3+ solutions under anaerobic conditions and under aerobic conditions. The experiments demonstrate that the nitric oxide absorption reaction can be regarded as instantaneous when nitric oxide concentration levels are at ppm levels. The gas-liquid reaction becomes gas film controlling as the cobalt ethylenediamine concentration exceeds 0.02 M. Oxygen in the gas phase is favorable for the absorption of nitric oxide. The optimal temperature for nitric oxide absorption is 60 °C under anaerobic conditions and 50 °C with 5.2% oxygen present in the gas phase. The kinetics equation of NO absorption into Co(en) 3 3+ solutions in the presence of oxygen can be written as N NO = [2K NO,G (p NO + γ C Co(en)3 3+ ,L )H O2 (k 2 D O2,L ) 1/2 p O2 ]/pk -1 + 2H O2 (k 2 D O2,L ) 1/2 p O2 ].

An innovative catalyst system has been developed to simultaneously remove NO and SO2 from combustion flue gas. Such catalyst system may be introduced to the scrubbing solution using ammonia solution to accomplish sequential absorption and catalytic oxidation of both NO and SO2 in the same reactor. When the catalyst system is utilized for removing NO and SO2 from the flue gas, Co ( NH 3 ) 6 2 + ions act as the catalyst and I− as the co-catalyst. Dissolved oxygen, in equilibrium with the residual oxygen in the flue gas, is the oxidant. The overall removal process is further enhanced by UV irradiation at 365 nm. More than 95% of NO is removed at a feed concentration of 250–900 ppm, and nearly 100% of SO2 is removed at a feed concentration of 800–2500 ppm. The sulfur dioxide co-existing in the flue gas is beneficial to NO absorption into hexamminecobalt(II)/iodide solution. NO and SO2 can be converted to ammonium sulfate and ammonium nitrate that can be used as fertilizer materials. The process described here demonstrates the feasibility of removing SO2 and NO simultaneously only by retrofitting the existing wet ammonia flue-gas-desulfurization (FGD) scrubbers.

NO can be removed from exhaust gas streams by placing soluble cobalt salts and ethylenediamine (H2NCH2CH2NH2) into basic solutions. The cobalt ethylenediamine acts as a homogeneous catalyst to oxid...

The wet ammonia desulfurization process can be retrofitted for combined removal of SO2 and NO from the flue gases by adding soluble cobalt(II) salt into the aqueous ammonia solution. Activated carbon is used to catalyze the reduction of hexamminecobalt(III) to hexamminecobalt(II) to maintain the capability of removing NO of the hexamminecobalt solution. The effects of temperature, pH, activated carbon particle size, and superficial liquid flow velocity on hexamminecobalt(III) conversion have been investigated. An apparent activation energy is obtained. According to the experimental results, the catalytic reduction reaction rate increases with temperature. The batch reactor experiments show that the best pH range lies in between 3.5 and 6.5. In a fixed-bed reactor, superficial liquid flow velocity obviously affects the reaction and a high yield of cobalt(II) is obtained at a pH value lower than 9.0. The experiments manifest that the hexamminecobalt solution coupled with catalytic regeneration of hexamminecobalt(II) can maintain a high nitric oxide removal efficiency during a period of time.

An innovative catalyst system has been developed to simultaneously remove NO and SO2 from combustion flue gas. Such a catalyst system may be introduced to the scrubbing solution using ammonia solution to accomplish sequential absorption and catalytic oxidation of both NO and SO2 in the same reactor. When the catalyst system is utilized for removing NO and SO2 from the flue gas, Co(NH3)62+ ions act as the catalyst and I- as the cocatalyst. Dissolved oxygen, in equilibrium with the residual oxygen in the flue gas, is the oxidant. The overall removal process is further enhanced by UV irradiation at 360 nm. More than 95% of NO is removed at a feed concentration of 250−900 ppm, and nearly 100% of SO2 is removed at 800−2500 ppm. Increasing SO2 concentration in the feed gas results in higher NO removal efficiency. The optimal temperature for the NO removal is found about 50 °C. The best treatment results are obtained at an optimal I-/Co2+ with a concentration ratio of 0.25. The NO removal rate also increases wit...

The combined elimination of NO and SO(2) can be realized by hexamminecobalt(II) solution which is formed by adding soluble cobalt(II) salt into the aqueous ammonia solution. Activated carbon is used as a catalyst to regenerate hexamminecobalt(II), Co(NH(3))(6)(2+), so that NO removal efficiency can be maintained at a high level for a long time. In this study, KOH solution has been explored to modify coconut activated carbon to meliorate its catalytic performance in the reduction of hexamminecobalt(III), Co(NH(3))(6)(3+). The experiments have been performed in a batch stirred cell to investigate the effects of KOH concentration, impregnation duration, activation temperature and activation duration on the performance of activated carbon. The results show that the best KOH concentration for the improvement of activated carbon is 0.5 mol l(-1). The optimal impregnation duration is 9h. High temperature is favorable to ameliorating the catalytic performance of activated carbon. The optimum activation duration is 4h.