Industrial grade multiwalled carbon nanotubes (IG-MWCNTs) were functionalized with polyethylenimines (PEIs) for CO2 capture from simulated flue gas. Ethylenediamine end-capped PEI (PEI-EC) impregnated IG-MWCNTs was found to exhibit a significantly higher adsorption capacity than other branched PEIs impregnated IG-MWCNTs. The PEI-EC impregnated IG-MWCNTs were characterized with various experimental methods including N2 adsorption/desorption isotherms, X-ray diffraction, and thermogravimetric analysis. The CO2 adsorption behavior of the PEI-EC impregnated IG-MWCNTs is influenced by PEI loading and adsorption temperature. The PEI-EC impregnated IG-MWCNTs exhibit a CO2 adsorption capacity as high as 2.538 mmol/g at 343 K, and can be completely regenerated higher than 403 K. The CO2 adsorption/desorption kinetics of the PEI-EC impregnated IG-MWCNTs was investigated with Avrami’s fractional order kinetic model. The activation energy of the CO2 adsorption/desorption was calculated from Arrhenius equation and used to evaluate the performance of the adsorbent.

A plasma driven catalyst reactor was applied to the degradation of gaseous xylene combined with the TiO2 catalyst processed by an acidized treatment, which promoted both Lewis and Bronsted acid sites on the surface of the catalyst. Results showed that the acidized TiO2 performed much better than untreated TiO2 in the degradation process. 92.48 % of 110 ppm xylene in air was decomposed by the acidized catalyst at 14 kV when the carrier gas was humid, meanwhile nearly all the destructed xylene was transformed to COx, with CO2 selectivity reaching 85.62 %. However, under the dry condition, besides the conversion ratio and selectivity of COx achieved by various catalysts all decreased, it was also found that the acidized TiO2 exhibited smaller advantage than untreated TiO2 in the degradation process. It may be concluded that water vapor was not only beneficial to the destruction of xylene but also positively related with the surface catalytic activation of acidized catalyst. Finally, catalytic mechanisms with the acidized catalyst were briefly discussed.

The major drawback of aqueous alkanolamine-based CO2 capture processes is the high energy penalty for regeneration. To overcome this weakness, we studied the absorption of CO2 with amines dissolved in nonaqueous solvents. It was observed that triethylenetetramine (TETA) dissolved in ethanol produces a solid precipitate after absorption, which can then be easily separated and regenerated. As a comparison, a TETA/water solution does not form any precipitate after absorbing CO2. The TETA/ethanol solution offers several advantages for CO2 capture in absorption rate, absorption capacity, and absorbent regenerability. Both the rate and capacity of CO2 absorption with the TETA/ethanol solution were significantly higher than with a TETA/water solution, because ethanol not only promotes the solubility of CO2 in the liquid phase but also facilitates the chemical reaction between TETA and CO2. This approach was able to capture 81.8% of the absorbed CO2 in the solid phase as TETA-carbamate. In addition, results show that the decomposition of TETA-carbamate can be completed at 90 °C. Moreover, the cycling absorption/regeneration runs of the TETA/ethanol solution display a relatively stable absorption performance.

The adsorption/desorption kinetics of carbon dioxide on tetraethylenepentamine (TEPA) impregnated industrial grade multiwalled carbon nanotubes (IG-MWCNTs) was investigated to obtain insight into the underlying mechanisms on the fixed bed. After evaluating four kinetic models for CO2 adsorption at various adsorption temperatures, CO2 partial pressure, and amine loadings, it was found that Avrami’s fractional-order kinetic model provided the best fitting for the adsorption behavior of CO2. In order to find the optimal regeneration method, three desorption methods were evaluated for the regeneration of solid sorbents. The activation energy Ea of CO2 adsorption/desorption was calculated from Arrhenius equation and used to evaluate the performance of the adsorbent. The Ea decreased with increasing CO2 concentration, indicating that CO2 adsorption of amine-functionalized IG-MWCNTs is possibly intraparticle controlled. Meanwhile, because of the energy input of a vacuum pump, Ea for the vacuum swing regeneration method was less than that for temperature swing regeneration.

The adsorption behavior of adsorbents for carbon dioxide can be significantly affected by flue gas contaminants. In this work, we examined the performance of tetraethylenepentamine (TEPA) impregnated industrial grade multiwalled carbon nanotubes (IG-MWCNTs) in trace amounts of flue gas contaminants such as H2O, NO, and SO2. It was observed that H2O and NO had a minimal impact on CO2 adsorption capacity, while the effect of SO2 on CO2 adsorption was influenced by adsorption temperature and SO2 concentration. Compared with silica-based adsorbents, i.e., TEPA-impregnated MCM-41, amine-functionalized IG-MWCNTs show significantly better tolerance to H2O and SO2. In addition, we examined the variation of CO2 adsorption with and without SO2 with various experimental methods (N2 adsorption/desorption isotherms, X-ray diffraction, and differential scanning calorimetry analysis) and molecular simulation. Experimental results show that irreversible sulfate/sulphite species deposited into the adsorbent contributes to the decrease on CO2 adsorption, while the results from simulation studies reveal that the enthalpy difference between the isolated TEPA with SO2 and TEPA···SO2 (ΔH(TEPA···SO2)) is larger than that of CO2 (ΔH(TEPA···CO2)), indicating that SO2 has a stronger reaction activity with TEPA than CO2. The increase of the ratio of ΔH(TEPA···SO2)/ΔH(TEPA···CO2) with increasing temperature illustrates that the difference of CO2 adsorption capacity with and without SO2 increases with elevated temperatures.

A solid amine adsorbent for CO2 was developed by carbon nanotubes (CNTs) impregnated with tetraethylenepentamine (TEPA). The adsorption behavior toward CO2 (2.0 vol %) was investigated in a fixed-bed column. After modification, the adsorption capacity of CNTs–TEPA reached 2.97 mmol g–1 at 298 K. Rising temperatures from 283 to 313 K enhanced the CO2 adsorption capacity. The maximum adsorption capacity was approximately 3.56 mmol g–1 at 313 K. The adsorption capacity was also influenced by moisture and reached as high as 3.87 mmol g–1 (2.0% H2O). In comparison to many other types of modified carbon or silica adsorbents in the literature, CNTs–TEPA had a higher adsorption capacity at the same temperature. The adsorption capacity for CO2 remained almost the same after cyclic regeneration experiments. A deactivation model, capable of describing the uptake of CO2, was applied under various conditions. In all cases, the experimental data agreed with the predicted breakthrough model.

A novel solid amine sorbent was prepared using KIT-6-type mesoporous silica modified with tetraethylenepentamine (TEPA). Its adsorption behavior toward CO2 from simulated flue gases is investigated using an adsorption column. The adsorption capacities at temperatures of 303, 313, 333, 343, and 353 K are 2.10, 2.29, 2.58, 2.85, and 2.71 mmol g–1, respectively. Experimental adsorption isotherms were obtained, and the average isosteric heat of adsorption was 43.8 kJ/mol. The adsorption capacity increases to 3.2 mmol g–1 when the relative humidity (RH) of the simulated flue gas reaches 37%. The adsorption capacity is inhibited slightly by the presence of SO2 at concentrations lower than 300 ppm but is not significantly influenced by NO at concentrations up to 400 ppm. The adsorbent is completely regenerated in 10 min at 393 K and a pressure of 5 KPa, with expected consumption energy of about 1.41 MJ kg–1 CO2. The adsorption capacity remains almost the same after 10 cycles of adsorption/regeneration with adsorption conditions of 10 vol % CO2, 100 ppm SO2, 200 ppm NO, 100% relative humidity, and a temperature of 393 K. The solid amine sorbent, KIT-6(TEPA), performs excellently for CO2 capture and its separation from flue gas.

The effect of iron addition to Ni/H-BEA on selective catalytic reduction of NOx with propane (C3H8–SCR) was investigated under a lean-burn condition. The addition of iron significantly lowered the optimum reaction temperature of Ni/H-BEA from 623 to 573 K. The 3Ni–1Fe/H-BEA catalyst had the highest activity among samples with different bimetal loading. NOx conversion of 100% was obtained at 573 K. Oxygen played an important role in activating NO and propane during the C3H8–SCR reaction. NOx conversion increased as the C3H8/NO molar ratio increased. A complete conversion of NOx was achieved with C3H8/NO = 1.25 at 573 K. The catalytic activity was inhibited slightly at a low SO2 concentration (100 ppm) but decreased dramatically at a high SO2 concentration (600 ppm) over different catalysts. The introduction of 10% water also exhibited a negative impact on the reduction of NOx. The catalytic activity of Ni–Fe/H-BEA represented only a slight drop in the presence of 100 ppm SO2 and 10% H2O. The addition of iron to Ni/H-BEA notably improved the tolerance of SO2 and H2O.

A promising adsorbent for CO2 removal from flue gas was prepared by introducing tetraethylenepentamine (TEPA) into KIT-6 type mesoporous silica using post-synthetic impregnation. The as-prepared adsorbents were characterized by X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), nitrogen adsorption/desorption as well as adsorption-column-breakthrough measurements. Surface area, pore size and pore volume of TEPA-loaded KIT-6 adsorbent decrease with the increasing of TEPA loading, while its fundamental pore structure is unchanged. The dynamic adsorption capacity increases from 1.5 mmol/g-adsorbent to 2.9 mmol/g-adsorbent when the amount of loaded TEPA increases from 10 wt.% to 50 wt.% at 333 K. The net adsorption capacity is about 72% of dynamic adsorption capacity. Regarding the regeneration performance of CO2 adsorbent, the suitable desorption temperature is nearly 373 K. The dynamic adsorption capacity drops slightly (about 5%) during forty cycles of adsorption/desorption. The adsorbent of KIT-6 modified by TEPA exhibits excellent CO2 adsorption/desorption performance.

Effects of adding manganese to Ag/H-BEA for selective catalytic reduction of NOx with propane (C3H8−SCR) were investigated under a lean-burn condition. Mn addition significantly promotes the catalytic performance of Ag/H-BEA below 673 K. A Ag−Mn/H-BEA catalyst with equal metal weight of 3 wt % has the highest activity for C3H8−SCR among samples with a different bimetal loading. Manganese is mainly present in the 3+ and 4+ oxidation states in Ag−Mn/H-BEA catalysts. The major contributions of manganese suggested by the data presented in this paper are to catalyze the NO oxidation and stabilize silver in a dispersed Ag+ state. The presence of silver enforces the transformation of a certain amount of Mn3+ ions to Mn4+ ions. The activity of Ag−Mn/H-BEA decreases slightly at low SO2 concentrations (0−200 ppm) but decreases significantly at high SO2 concentrations (400−800 ppm). In the presence of 10% H2O and 200 ppm SO2, the inhibition of C3H8−SCR below 673 K is more significant than that at high temperature above 673 K. Ag−Mn/H-BEA is a promising catalyst for the removal of NOx from diesel engine exhaust.

Decomposition of dimethyl sulfide (DMS) in air was investigated experimentally by using a wire-cylinder dielectric barrier discharge (DBD) reactor at room temperature and atmospheric pressure. A new type of high pulse voltage source with a thyratron switch and a Blumlein pulse-forming network (BPFN) was adopted in our experiments. The maximum power output of the pulse voltage source and the maximum peak voltage were 1 kW and 100 kV, respectively. The important parameters affecting odor decomposition, including peak voltage, pulse frequency, gas flow rate, initial concentration, and humidity, which influenced the removal efficiency, were investigated. The results showed that DMS could be treated effectively and almost a 100% removal efficiency was achieved at the conditions with an initial concentration of 832 mg/m3 and a gas flow rate of 1000 ml/min. Humidity boosts the removal efficiency and improves the energy yield (EY) greatly. The EY of 832 mg/m3 DMS was 2.87 mg/kJ when the relative humidity was above 30%. In the case of DMS removal, the ozone and nitrogen oxides were observed in the exhaust gas. The carbon and sulfur elements of DMS were mainly converted to carbon dioxide, carbon monoxide and sulfur dioxide. Moreover, sulfur was discovered in the reactor. According to the results, the optimization design for the reactor and the matching of high pulse voltage source can be reckoned.

The adsorption of CO2 on SBA-16 functionalized with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS) was investigated by DSC–TGA at 333 K. Hydrolysis of the calcined SBA-16 improved the adsorption performance. The functionalized samples prepared with hydrolyzed supports showed superior adsorption capacity and rate to those prepared with calcined supports. The adsorption capacity and rate increased with decrease in the particle size of samples. The samples with fine particle size exhibited good accessibility and high surface area for the grafting agent. The maximum adsorption capacity of CO2 at 333 K was 0.727 mmol g−1 for the functionalized SBA-16 (hydrolyzed SBA-16 as support) with the particle size range of 0.124–0.15 mm. The relationship between adsorption capacity and amine content is Y = 0.3855X−0.4397 where Y is adsorption capacity (mmol g−1) and X is amine content (mmol-N g−1).

A rigorous model for absorption of CO2 into aqueous 2-amino-2-methyl-1-propanol (AMP) was investigated at a temperature of 303 K using a double stirred-cell absorber with a planar gas–liquid interface. It was demonstrated that the kinetics region of absorption CO2 into aqueous AMP was the fast pseudo-first order reaction regime. The mass transfer-reaction kinetics equilibrium model according to the film theory is satisfactory to represent CO2 absorption into aqueous AMP. The model predictions had been found to be in good agreement with the experimental results. And the proposed model could handle the prediction much more effectively when CO2 loading was much smaller.

To improve the efficiency of the carbon dioxide cycling process and to reduce the regeneration energy consumption, a sterically hindered amine of 2-amino-2-methyl-1-propranol (AMP) was investigated to determine its regeneration behavior as a CO2 absorbent. The CO2 absorption and amine regeneration characteristics were experimentally examined under various operating conditions. The regeneration efficiency increased from 86.2% to 98.3% during the temperature range of 358 to 403 K. The most suitable regeneration temperature for AMP was 383 K, in this experiment condition, and the regeneration efficiency of absorption/regeneration runs descended from 98.3% to 94.0%. A number of heat-stable salts (HSS) could cause a reduction in CO2 absorption capacity and regeneration efficiency. The results indicated that aqueous AMP was easier to regenerate with less loss of absorption capacity than other amines, such as, monoethanolamine (MEA), diethanolamine (DEA), diethylenetriamine (DETA), and N-methyldiethanolamine (MDEA).

A rigorous model for absorption of CO2 into aqueous 2-amino-2-methyl-1-propanol (AMP) was investigated at a temperature of 303 K using a double stirred-cell absorber with a planar gas–liquid interface. It was demonstrated that the kinetics region of absorption CO2 into aqueous AMP was the fast pseudo-first order reaction regime. The mass transfer-reaction kinetics equilibrium model according to the film theory is satisfactory to represent CO2 absorption into aqueous AMP. The model predictions had been found to be in good agreement with the experimental results. And the proposed model could handle the prediction much more effectively when CO2 loading was much smaller.