共查询到20条相似文献,搜索用时 46 毫秒
1.
The kinetics of methane steam reforming were studied on a Ni/Mg/K/Al2O3 catalyst that was developed for conditioning of biomass-derived syngas. Reactions were conducted in a packed-bed reactor while the concentrations of reactants (methane and steam) and products (hydrogen, carbon monoxide, and carbon dioxide) were varied at atmospheric pressure, with the effects of temperature (525–700 °C) and residence time also being investigated. A power law rate model was developed using nonlinear regression to provide a predictive capability for the rate of methane conversion over this catalyst, to be used for reactor design and technoeconomic analysis of process designs. In order to provide some mechanistic insight, and to compare this catalyst to other non-promoted Ni/Al2O3 catalysts reported in the literature, a reaction mechanism consisting of five elementary steps, using a Langmuir–Hinshelwood type approach, was also considered. These five steps included: (i) CH4 adsorption, (ii) H2O adsorption, (iii) surface reaction of adsorbed CH4 and H2O to form CO and H2, (iv) CO desorption, and (v) H2 desorption. Nonlinear regression was then used to fit each of the rate laws to the experimental data. From these results, the model that assumed CH4 adsorption to be the rate determining step provided the best fit of the experimental data. This finding is consistent with literature studies on non-promoted Ni/Al2O3 catalysts, in which methane adsorption has been proposed to be the rate determining step during catalytic methane steam reforming. Both the power rate laws and the rate law assuming CH4 adsorption to be the rate determining step can be used as predictive tools for determining methane conversion for a given set of process conditions. Additionally, a rate expression that assumed the rate was only a function of methane partial pressure was considered, namely, $rate = k*P_{{CH_{4} }}$ rate = k ? P CH 4 , where $k = k_{0} *e^{{^{{ - {\text{Ea}}/{\text{RT}}}} }}$ k = k 0 ? e ? Ea / RT , with PCH4 in units of Torr. This first-order-methane rate expression fit the data well, yielding an apparent activation energy over this catalyst of Ea = 93 kJ/mol and the pre-exponential rate constant of k0 = 7.67 × 105 mol/(g-cat s Torr CH4). 相似文献
2.
Sheng Cui Shuwen Yu Benlan Lin Xiaodong Shen Xin Zhang Danming Gu 《Journal of Porous Materials》2017,24(2):455-461
Amine-modified SiO2 aerogel was prepared using 3-(aminopropyl)triethoxysilane (APTES) as the modification agent and rice husk ash as silicon source, its CO2 adsorption performance was investigated. The amine-modified SiO2 aerogel remains porous, the specific surface area is 654.24 m2/g, the pore volume is 2.72 cm3/g and the pore diameter is 12.38 nm. The amine-modified aerogel, whose N content is up to 3.02 mmol/g, can stay stable below the temperature of 300 °C. In the static adsorption experiment, amine-modified SiO2 aerogel (AMSA) showed the highest CO2 adsorption capacity of 52.40 cm3/g. A simulation was promoted to distinguish the adsorption between the physical process and chemical process. It is observed that the chemical adsorption mainly occurs at the beginning, while the physical adsorption affects the entire adsorption process. Meanwhile, AMSA also exhibits excellent CO2 adsorption–desorption performance. The CO2 adsorption capacity dropped less than 10 % after ten times of adsorption–desorption cycles. As a result, AMSA with rice husk ash as raw material is a promising CO2 sorbent with high adsorption capacity and stable recycle performance and will have a broad application prospect for exhaust emission in higher temperature. 相似文献
3.
Xianglan Li Jing Ma Yunjun Yao Shunlin Liang Guangbin Zhang Hua Xu Kazuyuki Yagi 《Nutrient Cycling in Agroecosystems》2014,100(1):65-76
Straw application and midseason drainage play role in controlling methane (CH4) and nitrous oxide (N2O) emissions from rice paddy fields, but little information is available on their integrative effect on CH4 and N2O emissions. A two-year field experiment was conducted to study the combined effect of timing and duration of midseason aeration and wheat straw incorporation on mitigation of global warming potential (GWP) of CH4 and N2O emissions from irrigated lowland rice paddy fields. Results showed that incorporation of wheat straw increased CH4 by a factor of 5–9 under various water regimes, but simultaneously decreased N2O emission by 19–42 % during the rice growing season. Without straw incorporation, prolonged aeration significantly reduced the net 100-year GWP of CH4 and N2O emissions by 6 %, but also decreased rice production when compared with normal aeration. With straw incorporation, the lowest GWP was found by early aeration, which reduced GWP by 7 and 20 % in 2007 and 2008, respectively. Estimation of net GWPs of CH4 and N2O emissions indicated that early midseason drainage with straw incorporation offered the potential to mitigate CH4 and N2O emissions from irrigated lowland rice paddies in China. 相似文献
4.
S. Bhuvaneshwari 《Chemical Engineering Communications》2013,200(6):834-854
Wastewater containing low levels of pollutants can be effectively treated by the adsorption technique. In the present work, an adsorption study was carried out using chitosan as adsorbent in a fixed-bed column for the removal of Cr(VI) from wastewater solutions. The column performance of Cr(VI) adsorption onto chitosan was studied at different bed heights (3–9 cm), flow rates (50–200 mL/min), initial metal concentrations (2–10 mg/L), pH values (2–7), and temperatures (30°–60°C). The equilibrium data for the batch adsorption of Cr(VI) on chitosan were tested using the Langmuir, Freundlich, and BET isotherm models. The Langmuir model was found to be the most suitable, with a maximum adsorption capacity of 35.7 mg/g and a correlation coefficient (R 2) = 0.952. The experimental data were found to fit well with the pseudo-second-order kinetic model, with R 2 = 0.999. The dynamics of the adsorption process was modeled using the Adams-Bohart, Thomas, and mass transfer models. The models were used to predict the breakthrough curves of adsorption systems and to determine the characteristic design parameters of the column. The adsorption data were observed to fit well with all three models. The model parameters were derived using MATLAB software. In order to compare quantitatively the applicability of adsorption dynamic models in fitting to experimental data, the percentage relative deviation (P) was calculated and found to be less than 5, confirming that the fit is good for all three models. 相似文献
5.
《分离科学与技术》2012,47(2):491-505
Abstract This paper describes the extraction of uranium from aqueous phosphoric acid medium using 2-ethyl hexyl hydrogen 2-ethyl hexyl phosphonate (PC88A) and octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) individually as well as their synergistic mixture in different diluents. The extraction parameters such as variation in concentration of either of the extractants, concentration of H3PO4 and uranium in the aqueous phase are investigated to optimize the extraction conditions. Results indicate that the synergistic mixture, 0.9 M PC88A + 0.1 M CMPO in xylene, can be used for the extraction of uranium from the phosphoric acid medium. The loaded uranium from the synergistic organic phase can be stripped using 0.5 M solution of (NH4)2CO3. This synergistic mixture is used to recover uranium from a typical wet process phosphoric acid sample and the recovery is found to be better than 90%. 相似文献
6.
Zhu Shengdong Wu Yuanxin Zhao Yufeng Tu Shaoyong Xue Yongping Yu Ziniu 《Chemical Engineering Communications》2013,200(5):639-648
The batch simultaneous saccharification and fermentation (SSF) of microwave/acid/alkali/H2O2 pretreated rice straw to ethanol was optimized using cellulase from Trichoderma reesei and Saccharomyces cerevisiae YC-097 cells prior to the fed-batch SSF studies. The batch SSF optima were 10% w/v substrate, 40°C, 15 mg cellulase/g substrate, initial pH 5.3, and 72 hours. Under the optimum conditions the ethanol concentration and its yield were 29.1 g/L and 61.3% respectively. Based on the optimal batch SSF, the fed-batch SSF was investigated and its operation parameters were optimized. Under its optimal conditions the ethanol concentration reached 57.3 g/L, while its productivity and yield were only slightly less than those in the batch SSF. This suggests that fed-batch SSF is a potential operation mode for effective ethanol production from microwave/acid/alkali/H2O2 pretreated rice straw. 相似文献
7.
《分离科学与技术》2012,47(8):1251-1258
Fusarium sp. #ZZF51, marine-derived mangrove endophytic fungus, was chemically modified by poly(amic acid) to enhance its potential of uranium(VI) biosorption in aqueous solution. Compared with uranium(VI) removal of the pristine biomass, the maximum uranium(VI) adsorption capacity of the modified biomass increased 9.5-fold under the optimal condition of pH 5.0, S/L 0.4, and equilibrium time 180 min. Kinetic study showed that the process follows the pseudo-second-order kinetic model, which indicates that chemical reaction controls the adsorption rate. The thermodynamic experimental data fit well with Langumir, Freundlich, and Temkin isotherms, and their R 2 values are 0.954, 0.963, and 0.986, respectively. FTIR spectroscopic analysis of the native, modified, and uranium-loaded biomass demonstrated the involvement of carboxyl, amide, and hydroxyl groups on the surface of fungus Fusarium sp. #ZZF51 cell wall in the adsorption of uranium(VI). 相似文献
8.
The ZnO/ZnMn2O4 nanocomposite (ZnMn) was used as adsorbent for the removal of cationic dye Basic Yellow 28 (BY28) from aqueous solutions. The adsorbent was characterized by X-ray diffraction, scanning electron microscope, TEM, Fourier transform infrared ray, BET, particle size distribution and zeta potential measurements. The adsorption parameters, such as temperature, pH and initial dye concentration, were studied. Kinetic adsorption data were analyzed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The Langmuir and Freundlich isotherm models were applied to fit the equilibrium data. The maximum adsorption capacity of BY28 was 48.8 mg g?1. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were calculated. 相似文献
9.
《分离科学与技术》2012,47(3):681-711
Abstract A timber industry waste was transformed to activated carbon by a one-step chemical activation process using H3PO4 (H). The used activated carbon (SDH) was characterized by N2 adsorption, FTIR, density, pH, point of zero charge pHpzc, moisture and ash content. Methylene blue (MB) and the iodine number were calculated by adsorption from the solution. The applicability of the different activated carbon produced was carried out to treatment of aqueous waste contaminated with iodine-labeled prolactin (I-PRL) Treatment processes were performed under the varying conditions; contact time, temperature, carbon type, carbon dosage, and different particle size of the activated carbon (SDH). The results indicated that 5 hours are sufficient to reach a plateau, and the amount of I-PRL adsorbed on SDH activated carbons increase with the solution temperature with thermodynamic parameter of ΔG° = ?7.962 (kJ/mol), ΔH° = 28.869 (kJ/mol) and ΔS° = 109.94 (J/mol K). The optimum adsorption results were reached using carbon dose of 0.1 gm with particle size of <0.25 mm, and a batch factor (V/M) of 7.14 mlg?1. First- and second-order equations, intraparticle diffusion equation, and the Elovich equation have been used to test experimental data. The experimental data was found to fit the second-order model and a chemisorptions mechanism. 0.7 M NaOH can be used for regeneration of spent SDH activated carbon with the efficiency of 99.6% and the regenerated carbon can be reused for five cycles effectively. 相似文献
10.
《分离科学与技术》2012,47(6):824-831
This paper deals with studies on the extraction of uranium(VI) from phosphoric acid medium using (2-ethylhexyl)phosphonic acid mono 2-ethylhexyl ester and tri-n-octylphosphine oxide individually as well as from their synergistic mixture. Different extraction parameters were investigated. With an increase in phosphoric acid concentration in the aqueous phase, the distribution ratio (Du) was found to decrease in all the cases. Synergism was observed when a mixture of PC-88A and TOPO was used. The synergistic mixture in the mole ratio of 4:1 (1.80 M PC-88A: 0.45 M TOPO) in xylene was found to be most suitable for uranium extraction. Among the various strip liquors used, 5% (w/v) solution of (NH4)2CO3 was found to be the most suitable. Using a mixture of 1.8 M PC-88A and 0.45 M TOPO as the extractant system and 0.5 M ammonium carbonate as the stripping agent, uranium recovery was found to be better than 97% ± 3% in multiple contacts, (n = 2) from actual Davies Gray Waste while in case of wet phosphoric acid more than 52% ± 3% (n = 3) only could be recovered where n is the number of contacts. 相似文献
11.
The corrosion inhibition behavior of mild steel in 0.1 M H2SO4 in the presence of polyvinyl alcohol (PVA) was investigated using weight loss and potentiodynamic polarization measurements in the temperature range of 30°–60°C. The inhibition efficiency (IE) increased with increasing PVA concentration, showing a maximum IE of 81.41% at 30°C at 100 mg/L and decreased with increasing temperature. The inhibiting action of PVA is synergistically enhanced on addition of very small amounts of surfactants sodium dodecyl sulfate (SDS) and cetyl pyridinium chloride (CPC). The adsorption of PVA alone or in combination with surfactants on the metal surface is found to obey the Langmuir adsorption isotherm from the fit of the experimental data of all concentrations and temperatures studied. The synergism parameter evaluated is found to be greater than unity, indicating that the enhanced IE of PVA caused by addition of surfactants is due only to synergism. The phenomenon of physical adsorption is proposed from the trend of the IE with temperature as well as the values of Ea, ΔHads, and ΔGads obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. The results obtained by weight loss measurements are consistent with the results of the potentiodynamic polarization measurements. The surface morphology of the corroded steel samples in the presence and absence of inhibitors was also evaluated using scanning electron microscopy (SEM). 相似文献
12.
Magnetically separable mesoporous TiO2 modified with γ-Fe2O3 was prepared and characterized by X–ray diffraction, N2 adsorption–desorption measurements, scanning electron microscopy, UV–vis absorption and magnetic measurements. The adsorptive removal of Congo red using the binary system was performed under various experimental conditions to examine the effects of contact time, solution pH, and initial concentration of Congo red. The results show that the removal abilities and separability of mesoporous TiO2 adsorbent for Congo red can be significantly improved by modification with γ-Fe2O3. The adsorption of Congo red on the γ-Fe2O3–TiO2 reaches the maximum percentage removal of ca. 97 % within 60 min, showing that most of Congo red can be removed in a short time. When the pH of solution is varied from 3.4 to 10.3, the percentage removal of Congo red decreases from ca. 97 to ca. 15 %, showing that the adsorption is strongly dependent on solution pH. The adsorption kinetics of Congo red fit well with pseudo-second-order kinetic model, and the equilibrium data is best described by Langmuir adsorption model. The maximum adsorption capacity of the γ-Fe2O3–TiO2 for Congo red is estimated to be 125.0 mg/g. 相似文献
13.
《分离科学与技术》2012,47(18):2983-2992
ABSTRACTThis communication provides the eliminating of heavy metals from water resources using Ag-Mg/TiO2 nanoparticles. The nanoparticles with a size of 15 nm were prepared using sol-gel technique and used for the removal of Cr(VI) and Cu(II) from waste waters. Batch sorption studies were carried out to investigate the adsorption of the above metal ions for a concentration range of 0.1–10 mg/L. The maximum sorption capacity values were found to be 2.42 mg/g for Cr(VI) and 2.03 mg/g for Cu(II) at a concentration of 0.1 ppm. The mechanism of adsorption was also investigated. The results showed that both Freundlich and Dubinin–Radushkevitch isotherms were found to be the best fit for the adsorption of metals. The results from kinetic data reveal that the pseudo-second-order and Reichenberg film diffusion models were found to be well fit for the experimental data. The value of the thermodynamic parameter ΔH° revealed the endothermic adsorption process and negative value of ΔG° shows the feasibility and spontaneity of material–anion interaction. In addition, the method is considered to be simple and cost-effective, and shows excellent adsorption removal properties on heavy metals for industrial applications. 相似文献
14.
Marcel Riegel 《溶剂提取与离子交换》2017,35(5):363-375
The effects of the sorption of naturally occurring uranium on weakly basic anion exchangers (WBA) have been investigated. Systematic investigations on the effects of various parameters show in general three important factors influencing the adsorption equilibrium. First, the sorption depends on the presence of competing anions, with sulfates showing the greatest influence. Second, the speciation of uranium (VI), which in carbonate-containing waters in a pH range between 6.5 and 9 exists mainly as anionic complexes UO2(CO3)22- and UO2(CO3)34-, is changed by calcium and bicarbonates. Calcium forms neutral complexes with uranium and carbonate, and with these complexes no ion exchange occurs. On the other hand, increasing concentrations of carbonate species support the formation of anionic uranyl complexes of higher charge, and an increased uranium uptake arises. Third, the effective capacity of WBA depends on the pH. With increasing pH, the amount of protonated functional groups decreases and the sorption capacity decreases.
It has been demonstrated that WBA sorb uranium very selectively out of drinking water. WBA Amberlite IRA 67 reached the uranium loading of 10 mg/g at the uranium concentration of 10 µg/L by sorption out of tap water at pH 7. 相似文献
15.
Precipitation of magnesium silicate from sodium silicate and MgCl2 and MgSO4 solutions was investigated at four different reactant feed rates and two temperatures (25 °C and 50 °C). Sodium silicate solutions were produced from rice hull ash silica. The final product was characterized by scanning electron microscopy, X‐ray diffraction, thermogravimetric analysis/differential thermal analysis, crystal size distribution, and filtration rate measurements. Physical characteristics of the studied magnesium silicates were determined by the Brauner‐Emmett‐Teller method and their adsorption capacities were compared to commercial magnesium silicate (Florisil). The adsorption was spontaneous and endothermic. The best fit of the kinetic results was achieved by a pseudo‐second‐order equation. The equilibrium data were found to be well represented by the Freundlich isotherm equation. 相似文献
16.
Mitchell M. Johns Wayne E. Marshall Christopher A. Toles 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1998,71(2):131-140
Surplus, low value agricultural by-products can be made into granular activated carbons (GACs) which are used in environmental remediation. This study characterized and evaluated GACs, made from these feedstocks, as effective removers of organics and metals from water. The by-products included soft lignocellulosics such as rice straw, soybean hull, sugarcane bagasse, peanut shell, and harder materials such as pecan and walnut shells. The softer materials were combined with a binder, molasses, to produce briquettes and pellets. The precursors were CO2- or steam-activated, and subsequent treatments included oxidation to enhance metal adsorption. Many of the GACs had acceptable physical GAC attributes, such as durability, for commercial usage. GACs made from pecan and walnut shells adsorbed higher levels of benzene, toluene, methanol, acetonitrile, acetone, and 1,4-dioxane from an aqueous mixture than commercial GACs. Neither CO2 nor steam activation was particularly advantageous in enhancing metal adsorption. Oxidation using O2–N2 gas increased metal adsorption while (NH4)S2O8 solution did not. In a copper solution, oxidized GACs made from soybean hull had three to four times the Cu(II) adsorption capacity of metal-adsorbing, commercial GACs. Oxidized GACs made from soybean hull, sugarcane bagasse, peanut shell, and rice straw adsorbed from a mixture higher amounts of Pb(II), Cu(II), Ni(II), Cd(II) and Zn(II) than any commercial GACs. Commercial GACs adsorbed only Pb(II), Cu(II) and Cd(II). The GACs made from the agricultural by-products have considerable potential for adsorption of organics and metals of environmental concern. © 1998 SCI. 相似文献
17.
《分离科学与技术》2012,47(12):1793-1801
The sorption behavior of silver ions on rice husk has been investigated in detail. Various physico-chemical parameters were optimized to simulate the best conditions in which this material can be used as an adsorbent. Maximum adsorption was observed at 0.001 mol L?1 of acid solutions (HNO3, H2SO4 and HClO4) using 0.5 g of adsorbent for 9.27 × 10?5 mol L?1 silver concentration in fifteen minutes equilibration time. The adsorption of silver was decreased with the increase in the concentrations of all the acids used. The kinetic data indicated an intraparticle diffusion process with sorption being pseudo-second order. The determined rate constant k2 was 14.707 ± 1.832 mol g?1 min?1. The adsorption data obeyed the Freundlich, Langmuir, and Dubinin-Radushkevich isotherms over the silver concentration range of 1.85 × 10?4 to 1.16 × 10?3 mol L?1. The characteristic Freundlich constants, that is, 1/n = 0.38 ± 0.033 and K = 0.271 ± 0.104 m mol g?1 whereas the Langmuir constants Q = (1.504 ± 0.054) × 10?2 m mol g?1 and b = (16.582 ± 2.227) × 103 dm3 mol?1 have been computed for the sorption system. The sorption mean free energy from the Dubinin-Radushkevich isotherm is 12.16 ± 0.82 kJ mol?1 indicating ion-exchange mechanism of chemisorption. The uptake of silver increases with the rise in temperature (283–333 K). Thermodynamic quantities, namely, ΔG, ΔS, and ΔH have also been calculated for the system. The sorption process was found to be endothermic. The effect of other cations and anions on the adsorption of silver has also been studied. 相似文献
18.
The biosorbent used for removal of Pb2+, Hg2+, and Cd2+ from aqueous solutions was rice straw fermented by Aspergillus niger (ARS), and raw rice straw (RRS) was used as a control. When inoculum size, material–water ratio, and temperature were 106, 100%, and 303K, respectively, the optimized spore number was 109. The ARS exhibited a lager pore biosorption, which was better than RRS. The biosorption mechanism was involved in chelation with functional groups such as C-H, C = O, C-O, and C = C, and the biosorption data obtained were well described by the pseudo-second-order kinetic equation and the Freundlich isotherm model. 相似文献
19.
Duangdao Channei Auppatham Nakaruk Wilawan Khanitchaidecha Panatda Jannoey Sukon Phanichphant 《International Journal of Applied Ceramic Technology》2019,16(3):1060-1068
In this work, the coupling of BiVO4 nanoparticles with a highly porous material derived from rice straw (BiVO4/RS composites) and the photocatalytic degradation of 2-chlorophenol (2-CP) in an aqueous solution was studied. The results indicated that BiVO4/RS composites possessed a monoclinic structure. The morphologies of BiVO4/RS composites consisted of spherical shapes of BiVO4 particles coated on the RS adsorbent. The specific surface area of BiVO4 increased from 1.9024 to 31.1153 m2/g after coating with RS adsorbent. A shift occurred in adsorption edge from 510 to 525 nm, corresponding to a reduction in band gap energy from 2.43 to 2.35 eV. The change in the optical adsorption edge and band gap of BiVO4/RS composites may simultaneously result to the duplication of a structure caused by silicon species in rice straw, which was expected to be self-doped into the BiVO4 crystal lattice during synthesis. The photocatalytic performance of 2-chlorophenol under visible irradiation clearly showed that BiVO4/RS composites displayed the highest photocatalytic activities in comparison with other pure samples, which were 2 times higher than that of BiVO4. 相似文献
20.
《分离科学与技术》2012,47(3):434-451
The adsorption equilibrium data of CO2 and N2 at (303, 333, 363, 393, 423) K ranging 0-1 bar on zeolite 5A is reported. The pressure and temperature range covers the operating pressure in adsorption units for CO2 capture from power plants. Experimental data were fitted by the multi-site Langmuir model. The adsorbent is much more selective to CO2: loading at 303 K and 100 kPa is 3.38 mol/kg while loading of N2 at the same pressure is 0.22 mol/kg. The Clausius-Clapeyron equation was employed to calculate the isosteric enthalpy of adsorption. The fixed-bed adsorption and desorption of carbon dioxide and nitrogen on zeolite 5A pellets has been studied. A model based on the bi-LDF approximation for the mass transfer, taking into account the energy and momentum balances, had been used to describe the adsorption kinetics of carbon dioxide and nitrogen. The model predicted satisfactorily the breakthrough curves obtained with carbon dioxide–nitrogen mixtures. Desorption process (consisting of depressurization, blowdown, and purge) was also performed. Following the feasibility of concentration and capture of carbon dioxide from flue gases by Pressure Swing Adsorption (PSA) process was simulated. A CO2 recovery of 91.0% with 53.9% purity was obtained using a five-step Skarstrom-type PSA cycle. 相似文献