Ceria‐coated diesel particulate filters for continuous regeneration

The potential of diesel particulate filters wash‐coated with highly dispersed nano‐metric ceria particles for continuous regeneration has been investigated. To this end, catalytic filters were prepared, soot‐loaded (avoiding the formation of the cake layer), and regenerated—under isothermal conditions—at temperature ranging from 200–600°C. Results have shown that catalytic oxidation of soot starts from 300°C and, at all temperatures, the selectivity to CO₂ is higher than 99%. 475°C is the minimum temperature at which the filter is regenerated via catalytic path. At this temperature, the catalytic filter maintains substantially the same performance over repeated cycles of soot loading and regeneration, indicating that the thermal stability of ceria is preserved. This has been further confirmed by comparison between the outcomes obtained from characterization (X‐ray powder diffraction, N₂ adsorption at 77 K, Hg intrusion porosimetry, and scanning electron microscope/energy dispersive X‐ray analysis) of fresh filter and filter subjected to repeated regeneration tests. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3442–3449, 2017     

Thermal regeneration of activated carbon saturated with p-nitrophenol

Water contamination by organic compounds is an important environmental problem. Activated carbon filters are widely used to eliminate these contaminants. After exhaustion, activated carbon must be regenerated or replaced by fresh carbon. In this study thermal regeneration of saturated carbon with p-nitrophenol has been analysed. Three thermal regeneration methods have been tested: (1) pyrolysis, (2) pyrolyis-gasification and (3) direct gasification, the gasifying agents being air and CO₂. The results show that the pyrolysis treatment does not completely eliminate the contaminant from the carbon and the recovery of the initial adsorption properties is rather limited. The effect of gasification depends on both the gasifying agent and the sample (pyrolysed or saturated with PNP). CO₂-gasification yields to a complete regeneration of the adsorption characteristics in both pyrolysis-gasification and direct gasification samples. In general, air-gasification produces lower regeneration properties, although direct air-gasification sample has 87% recovery of the PNP maximum adsorption capacity. These results suggest that thermal regeneration could be carried out in a single step, simplifying the process and reducing the operation cost. Moreover, although CO₂ seems to give better recovery of the initial carbon characteristics than air, it should be noted that air is cheaper and the regeneration time is shorter.     

Regeneration of Activated Carbon Loaded with Toluene by Supercritical Carbon Dioxide

Abstract

Activated carbon loaded with toluene was regenerated by supercritical carbon dioxide. The adsorptive capacities after several regeneration cycles were still close to that of virgin carbon and remained stable. The effects of temperature, pressure, and flow rate on regeneration efficiency were studied. It was found that the operations at higher pressures were more favorable for regeneration, but the optimal operating temperature depended on pressure. The interphase mass transfer resistance was insignificant during regeneration. A one-parameter mathematic model assuming linear desorption kinetics is proposed which agrees well with the experimental data. The adsorption rates of activated carbon regenerated by the supercritical regeneration method and the steam regeneration method are compared in this study. It was found that the supercritical regeneration method is superior to the steam regeneration method.     

Effect of H2SO4 concentration in washing solution on regeneration of commercial selective catalytic reduction catalyst

Commercial SCR catalysts used in a coal-fired power plant were regenerated by H₂SO₄ solution. The characterization study of the catalysts was carried out by using various analytical techniques. Major deactivating elements for the SCR catalyst were determined and the optimal condition for regeneration of the catalyst was investigated. The catalyst regenerated with 0.5 wt% H₂SO₄ solution showed a high catalytic activity due to an increase in the polymeric vanadates and acid sites by surface sulfates. A higher H₂SO₄ concentration than 2.5 wt% in the washing solution leads to a loss of active components out of the catalyst by dissolution and a dramatic decrease in the surface area.     

活性炭纤维吸附稀溶液中SCN-的电化学再生

为了研究电化学再生活性炭纤维（ACF）的效果,以SCN^-为模型物,通过测量再生后活性炭纤维对SCN^-的吸附容量的大小,考察了时间、吸附质浓度、再生循环次数等再生过程中的影响因素。结果表明,适宜的再生条件为0.8 mA正极化2 h,0.5 mol·L^-1的硫酸溶液,能使再生后ACF的吸附容量提高为原始ACF的3倍。5次电化学再生循环后,ACF的吸附容量没有明显降低,再生后ACF纤维表面也没有明显损伤。     

Pore size distribution model derived from a modified DR equation and simulated pore filling for nitrogen adsorption at 77 K

The Dubinin-Radushkevich (DR) equation has been used extensively to characterize microporous materials. However, it assumes a continuous pore filling mechanism and does not reduce to Henry’s law at low adsorptive pressures. In this study, we modify the DR equation by introducing adsorption density and the correlation between pore filling pressure and critical pore size for N₂ adsorption at 77 K. This modified DR equation is used as the local isotherm in the generalized adsorption isotherm (GAI) to interpret N₂ adsorption isotherm at 77 K. To solve the GAI, a modified normal distribution is developed and used as a distribution function of pore size on the domain [0, ∞). Pore size distribution (PSD) analyses of several adsorbent samples are carried out using this model. The results are found comparable with other popular PSD methods (e.g. MP, JC, HK and DFT).     

Study of SO2 adsorption and thermal regeneration over activated carbon-supported copper oxide catalysts

The mechanisms of SO₂ adsorption and regeneration over activated carbon-supported copper oxide sorbent/catalysts were analyzed. Studies were carried out in a fixed-bed reactor equipped with a non-dispersive infrared gas analyzer to detect the reaction products and by using X-ray powder diffraction (XRPD) and temperature-programmed desorption (TPD) experiments to characterize the nature of the sulfate species and surface oxygen complexes. The results indicate that SO₂ was catalytically oxidized to SO₃ over a copper phase in the presence of gaseous oxygen, and then reacted with a copper site to form a sulfate linked to copper without desorption into the gas phase. The activated carbon support did not participate in this sulfation reaction. After the adsorption of SO₂, the exhausted sorbent/catalysts could be regenerated by direct heat treatment in inert gas at temperatures between 260 and 480 °C, while the neighboring surface oxygen complexes on the carbon surface were acting as the reducing agents to reduce CuSO₄ to Cu. During the subsequent adsorption process, the copper is rapidly oxidized by oxygen in the flue gas.     

n-butane isomerization on sulfated zirconia. Deactivation and regeneration as studied by Raman,UV-VIS diffuse reflectance and ESR spectroscopy

n-butane isomerization on sulfated zirconia was studied in the temperature range 393–473 K. Rapid deactivation occurs, when the reaction is carried out in He carrier gas. In contrast, stable stationary activity was observed in H₂ carrier gas. In situ Raman and UV-VIS diffuse reflectance spectroscopy and ESR showed that the deactivation is caused by the formation of allylic and polyenylic cations and polycyclic aromatic compounds, the formation of which is largely prevented in the presence of H₂. Deactivated catalysts can be fully regenerated by treatment at 723–753 K in flowing O₂. The regeneration process was also followed by in situ spectroscopies.     

Usefulness of CO2 adsorption at 273 K for the characterization of porous carbons

Characterization of microporous solids (activated carbons and carbon molecular sieves) has been carried out by N₂ (subatmospheric pressures) and CO₂ adsorption (at subatmospheric and high pressures) at 77 and 273 K, respectively. Because the relative fugacity range covered by our CO₂ study is similar to the relative pressure range covered with N₂, a suitable comparison of both adsorptives can be made. The results of such comparison show that both adsorptives give the same micropore size distribution (MPSD) for open porosity activated carbons. This observation confirms that the adsorption mechanism of both adsorptives is similar. However, carbon molecular sieves, with very narrow microporosity, cannot be characterized by N₂ at 77 K, due to the existence of diffusional problems. This is also extensive to many other carbon materials, such as carbon fibers and activated carbons with low degree of activation. As a consequence, in this type of samples, N₂ adsorption at 77 K is useless to determine neither the micropore volumes of the narrowest porosity nor their micropore size distributions (MPSD). In this work, the usefulness of CO₂ for the characterization of carbon molecular sieves and activated carbons with different activation degrees is demonstrated. In addition, examples of applications that cannot be explained from N₂ adsorption but yes by CO₂ are presented. As a result, we strongly encourage the use of CO₂ (i.e. at 273 K) as a complement to N₂ adsorption at 77 K.     

Electrochemical regeneration of activated carbon loaded with p-nitrophenol in a fluidized electrochemical reactor

This paper described a novel electrochemical process for the regeneration of activated carbon (AC) loaded with p-nitrophenol (PNP), aiming to reduce regeneration time and improve cost-effectiveness of the process by adoption of a novel non-active anode of modified lead dioxide and operation of AC in a fluidized mode. The regeneration parameters such as current density, liquid flow rate, NaCl concentration, pH of the solution and regeneration time were systematically investigated. Under the optimum conditions, the regeneration efficiency of AC could reach 90% in 1.5 h, and no significant declination was observed after five-times continuous adsorption-regeneration cycles, confirming the reuse feasibility of the regenerated AC. The adsorption of organic pollutants was confirmed occurring in the micropore of AC, and AC regeneration was mainly due to the decomposition of organics by the attack of active species such as hydroxyl radical that were generated by electrochemical oxidation. The time-space production for AC regeneration has been greatly improved in the present modified process, indicating this regeneration process is much more potentially cost-effective for application.     

介质阻挡放电技术再生Pd/AC催化剂的机理探讨

利用介质阻挡放电对失活钯炭催化剂(Pd/AC)进行再生,并通过催化臭氧氧化硝基苯反应评价再生后催化剂的活性。运用扫描电镜(SEM)、比表面积测定(BET)、热重分析(TG)等测定手段对Pd/AC进行表征;并对放电过程进行臭氧产量测定和等离子体发射光谱诊断,分析了Pd/AC催化剂再生的机理。结果表明,催化剂经放电处理30 min后再生率为95%;利用在最优条件下再生的Pd/AC进行催化臭氧氧化反应,硝基苯的降解率为87%;再生过程中臭氧贡献率仅为25.6%,表明放电过程中产生的强氧化性自由基是促使催化剂再生的主要因素。     

Comparison between microwave and conventional thermal reactivations of spent activated carbon generated from vinyl acetate synthesis

Microwave and traditional thermal reactivations of activated carbon (AC) used as catalyst support in vinyl acetate synthesis have been investigated. Experiments have been carried out by using a single mode microwave device (MW) operating at 2450 MHz and a conventional electric furnace (CF) under steam and CO₂ atmosphere, respectively. The surface properties of the spent AC and the reactivated samples were characterized by means of N₂ adsorption and SEM, and compared the effects of different heating mechanisms and activating agents on the adsorption capacities and pore structures of the reactivated AC. These results indicated that the AC obtained by microwave irradiation showed higher adsorption capacities for iodine, methylene blue (MB) and acetate acid, higher BET surface areas and mesoporosity than those obtained by conventional thermal heating. The reactivated samples activated by steam had a narrower and more extensive microporosity as well as higher BET than those activated by carbon dioxide under the same heating equipment. From the results, it was concluded that microwave heating combined with steam as an activating agent could remarkably increase the reactivating efficiency compared to the traditional thermal heating.     

A study of the sulfidation and regeneration reaction cycles of Zn-Ti-based sorbents with different crystal structures

The reaction cycles of the sulfidation and regeneration of Zn-Ti-based sorbents prepared by a physical mixing method (ZT-700 and ZT-1000) or co-precipitation method (ZT-cp) were tested in a fixed bed micro-reactor at middle temperature (Sulfidation; 480 °C, regeneration; 580 °C). The ZnS produced during sulfidation from the Zn₂TiO₄ with a spinel structure (ZT-1000, ZT-cp) was easily regenerated even at 550 °C, while the ZnS produced from the ZnO with a hexagonal structure (ZT-700) needed a temperature higher than 610 °C. After regeneration, each sorbent was restored to its original crystal structure. The differences in the regeneration properties and the reaction cycles of the sorbents were related to the original crystal structures rather than to the physical properties such as pore volume and surface area. To study these differences further, FT-IR, FT-Raman, XRD and TPR were used, and their results including the reaction cycles of the sulfidation and regeneration on the Zn-Ti based sorbents with different crystal structures were discussed.     

Chemical and thermal regeneration of an activated carbon saturated with chlorophenols

An activated carbon obtained by activation of olive stones in carbon dioxide at 1113 K has been used in this study. This was saturated with o-chlorophenol and m-chlorophenol from their corresponding aqueous solutions. The spent activated carbon samples were regenerated by means of organic solvent treatments and subsequent heat treatments. The organic solvents used were: acetone, methanol, ethanol and benzene. The extent of the chemical regeneration in these systems is a function of the strength of the adsorbent–adsorbate interactions. When the systems are treated with organic solvents the adsorbate extracted mainly comes from the physisorbed fraction. When the samples extracted with organic solvents are thermally regenerated by heating at 1073 K in an inert flow, in most of the cases, the amount of adsorbate removed increased in comparison to treatments without solvents. A part of the physisorbed fraction remaining in these samples after the solvent treatments is released at lower temperatures than the chemisorbed fraction. During the heat treatment, part of the physisorbed fraction is transformed to a chemisorbed one which has a greater desorption energy than the former.     

Nano-sized carbon hollow spheres for abatement of ethylene

In this paper, the ethylene adsorption capacities of the nano-sized carbon hollow spheres (CNB) and active carbon (AC), the Pd (PdCl₂) impregnated CNB or AC (Pd/CNB, Pd/AC) and heat treatment under various conditions, were studied at different ethylene concentrations from 64 to 1060 ppm. The results indicated that AC had a good ethylene adsorption capacity at high ethylene concentration. Pd impregnation decreased the ethylene adsorption capacity of AC. Heat treatment and H₂ activation could increase the ethylene adsorption capacity, but also lowered than AC itself. CNB had lower ethylene adsorption capacity than AC, but heat treatment and H₂ activation could increase its ethylene adsorption capacity markedly. With activating condition from heat treatment in N₂ at 300 °C to activation in H₂/N₂ at 100 °C, to activation in H₂ at 200 °C, and to activation in H₂ at 300 °C, the ethylene adsorption capacity of Pd/CNB was increased regularly. At low ethylene concentration, viz., 64 ppm, the ethylene adsorption quantities (q _a) by Pd/CNB activated in H₂ at 200 or 300 °C were higher than any other adsorbents. So, activated in H₂ atmosphere at higher than 100 °C, Pd/CNB is particularly advantaged for adsorbing low concentration of ethylene. Amongst all the adsorbents used, Pd/CNB activated in H₂ atmosphere at 300 °C for 2 h has the highest ethylene adsorption capacity at lower concentration than 125 ppm. In addition, all the CNB, Pd/CNB, AC, and Pd/AC samples can be easily regenerated in airflow for more than 3 h.     

Catalyst deactivation and regeneration in low temperature ethanol steam reforming with Rh/CeO2–ZrO2 catalysts

Rh/CeO₂–ZrO₂ catalysts with various CeO₂/ZrO₂ ratios have been applied to H₂ production from ethanol steam reforming at low temperatures. The catalysts all deactivated with time on stream (TOS) at 350 °C. The addition of 0.5% K has a beneficial effect on catalyst stability, while 5% K has a negative effect on catalytic activity. The catalyst could be regenerated considerably even at ambient temperature and could recover its initial activity after regeneration above 200 °C with 1% O₂. The results are most consistent with catalyst deactivation due to carbonaceous deposition on the catalyst.     

Interaction of molten salts with a semianthracite char at 743-1173 K. Effects on chemical composition,textural properties,and reactivity in air

The effects of chemical heat treatments of a semi-anthracite char (AC) on the mass of sample and on the composition of the mineral fraction of the material, textural properties, and reactivity in air are investigated. The starting char was first treated with a mixture of LiCl/KCl or LiCl/KCl/CaO at 743, 873, or 1173 K in N₂ and the products obtained were then washed thoroughly with distilled water. The composition changes were studied by X-ray diffraction. Information on textural modifications was derived from the adsorption isotherms for CO₂ at 273 K. The reactivity tests were carried out at 808, 823, and 838 K. Major mineral components of AC were quartz, mullite, muscovite and/or kaolinite, and oldhamite. The mass loss produced in the preparation of the samples was markedly influenced by the composition of the reaction mixture and also by the heat treatment temperature. The treatments of AC resulted in significant changes in the mineral fraction of the material, in particular when LiCl/KCl/CaO was used. In this case, spurrite, γ-calcium orthosilicate, gehlenite, and lithium aluminum silicate were formed. Also, the microporosity developed and the reactivity in air increased. The former effect was stronger for the LiCl/KCl-treated samples and the latter one for a larger number of the LiCl/KCl/CaO-treated samples.     

The effect of impregnation of activated carbon with SnCl2.2H2O on its porosity, surface composition and CO gas adsorption

Activated carbon was impregnated with different concentrations of SnCl₂.2H₂O. Unimpregnated and impregnated activated carbons were analysed by means of physical adsorption and XPS and were tested for CO gas adsorption in a PSA system. The adsorption isotherms of N₂ at 77 K were measured and showed a Type I isotherm indicating microporous carbon for all the samples. The surface area, pore volume and pore size distribution were reduced with impregnation. XPS analysis showed an increase in the intensity of Sn3d peak with impregnation. The impregnated activated carbon showed a very good adsorption ability of CO gas compared to the unimpregnated sample. The adsorptive species responsible for CO gas adsorption was confirmed to be SnO₂ instead of SnO due to the former’s comparative thermodynamic stability.     

Interaction of molten salts with a semianthracite char at 743-1173 K. Effects on chemical composition,textural properties,and reactivity in air

The effects of chemical heat treatments of a semi-anthracite char (AC) on the mass of sample and on the composition of the mineral fraction of the material, textural properties, and reactivity in air are investigated. The starting char was first treated with a mixture of LiCl/KCl or LiCl/KCl/CaO at 743, 873, or 1173 K in N₂ and the products obtained were then washed thoroughly with distilled water. The composition changes were studied by X-ray diffraction. Information on textural modifications was derived from the adsorption isotherms for CO₂ at 273 K. The reactivity tests were carried out at 808, 823, and 838 K. Major mineral components of AC were quartz, mullite, muscovite and/or kaolinite, and oldhamite. The mass loss produced in the preparation of the samples was markedly influenced by the composition of the reaction mixture and also by the heat treatment temperature. The treatments of AC resulted in significant changes in the mineral fraction of the material, in particular when LiCl/KCl/CaO was used. In this case, spurrite, γ-calcium orthosilicate, gehlenite, and lithium aluminum silicate were formed. Also, the microporosity developed and the reactivity in air increased. The former effect was stronger for the LiCl/KCl-treated samples and the latter one for a larger number of the LiCl/KCl/CaO-treated samples.     

Influence of regeneration conditions on the cyclic performance of amine-grafted mesoporous silica for CO2 capture: An experimental and statistical study

This work deals with the behavior of amine-grafted mesoporous silica (referred to as TRI-PE-MCM-41) throughout adsorption–desorption cycles in the presence of 5% CO₂/N₂ using various regeneration conditions in batch experiments. The criteria proposed to determine the optimum regeneration conditions are the working adsorption capacity, the rate of desorption and the change of adsorption capacity between consecutive cycles. Using a 2³ factorial design of experiments, the impact on the performance of the adsorbent of different levels of temperature, pressure, and flow rate of purge gas during desorption was determined. It was found that all the parameters under study have a statistically significant influence on the working adsorption capacity, but only temperature is influential with respect to desorption rate. Regeneration using temperature swing was found to be attractive, as the highest CO₂ adsorption capacity (1.95 mmol g^?1) and the fastest desorption rate (9.82×10^?4 mmol g^?1 s^?1) occurred when desorption was carried out at 150 °C. However, if vacuum is applied, regeneration can be achieved at a temperature as low as 70 °C with only a 13% penalty in terms of working adsorption capacity. It was also demonstrated that under the proper regeneration conditions, TRI-PE-MCM-41 is stable over 100 adsorption–desorption cycles.