天然沸石处理含铅、镉废水的试验研究

天然沸石经改性后对铅、镉有较好的吸附能力，当铅的浓度为2mg／L，沸石用量30g，动态变换3小时，吸附效率达90％以上，吸附容量达5mg／g；当镉的浓度为l00mg／L，沸石用量l0g，动态交换24小时，吸附效率可达99．8％以上。在450℃时处理的沸石吸附效果最佳，改性后的沸石对铜的吸附具有较好的选择性。     

SELECTIVITY STUDIES IN THE PHOTOCHLORINATION OF METHANE II: EFFECT OF THE RADIATION SOURCE OUTPUT POWER AND OUTPUT SPECTRAL DISTRIBUTION

The effect of the output power and output spectral distribution of the radiation energy fed to a photoreactor upon the reaction yield and selectivities is studied both theoretically and experimentally. The study aims at the analysis of these influences in a series reaction such as the photochlorination of methane where methylene chloride and eventually chloroform are the most valuable products. The computational model employed has been verified for a group of selected conditions by means of bench-sale experiments.

It is found that the chlorine conversion shows the expected square root dependence with respect to the Local Volumetric Rate of Energy Absorption (LVREA). This dependence, in a first approximation, can also be assigned to the effect of the radiation source output power upon yield. It is also found that by manipulating the amount of radiation power fed to the reactor it is possible to ascertain the operating conditions favoring the production of predetermined intermediate products (e.g., methylene chloride or chloroform).

It is concluded that the use of customized lamps especially designed for each particular product on the basis of feasible changes in the characteristics of the existing radiation sources will favor a selective and more economical production of some of the stable intermediates, i.e., lamp design is an important feature in any optimal process design.     

Gas transport properties of 6FDA-TAPOB hyperbranched polyimide membrane

Physical and gas transport properties of the hyperbranched polyimide prepared from a triamine, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and a dianhydride, 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), were investigated and compared with those of linear-type polyimides with similar chemical structures prepared from diamines, 1,4-bis(4-aminophenoxy)benzene (TPEQ) or 1,3-bis(4-aminophenoxy)benzene (TPER), and 6FDA. 6FDA-TAPOB hyperbranched polyimide exhibited a good thermal stability as well as linear-type analogues. Fractional free volume (FFV) value of 6FDA-TAPOB was higher than those of the linear-type analogues, indicating looser packing of molecular chains attributed to the characteristic hyperbranched structure. It was found that increased resistance to the segmental mobility decreases the gas diffusivity of 6FDA-TAPOB, in spite of the higher FFV value. However, 6FDA-TAPOB exhibited considerably high gas solubility, resulting in high gas permeability. It was suggested that low segmental mobility and unique size and distribution of free volume holes arising from the characteristic hyperbranched structure of 6FDA-TAPOB provide effective O₂/N₂ selectivity. It is concluded that the 6FDA-TAPOB hyperbranched polyimide has relatively high permeability and O₂/N₂ selectivity, and is expected to apply to a high-performance gas separation membrane.     

SEPARATION AND ENRICHMENT OF WEAK ORGANIC ACIDS OR BASES BY IMMOBILIZED LIQUID MEMBRANES

A new and effective liquid membrane process to achieve both separation and enrichment simultaneously of weak organic acids or bases was developed. The process utilizes effectively the difference in the apparent partition coefficient of the constituent species between the aqueous and organic phases, and uses the change of the apparent partition coefficients with the hydrogen ion concentration of the aqueous phase. For such a fundamental model apparatus as a diaphragm diffusion cell being operated batch wise, the effects of pK value of solutes, permeability of solutes through the membrane, volume ratio of liquids in two aqueous phases, and pH value of aqueous phase on enrichment factor and selectivity for the solute to be concentrated were discussed analytically. Separation and enrichment were demonstrated using aqueous mixed solutions of fumaric acid and L-malic acid. The results were in good agreement with the theoretical predictions.     

Separation of Polyvinyl Chloride from Plastic Mixture by Froth Flotation after Surface Modification with Ozone

Selective modification by ozonation for the surface of polyvinyl chloride (PVC) was evaluated to separate PVC from the other plastics, polyethylene terephthalate (PET), polycarbonate (PC) and polymethyl methacrylate (PMMA), with almost the same density as PVC by the froth flotation process. Ozonation could selectively decrease the contact angles of flexible PVC from 87.5 degrees to 68.4 degrees and rigid PVC from 90.3 degrees to 66.9 degrees, whereas little decreases in the contact angle were observed for other plastics. This would be due to the replacement of the chloride group on the surface of PVC, into hydrophilic functional groups; carbonyl, carboxyl and ester group. The PVC was successfully separated from the other plastics by the froth flotation process after the selective surface modification by ozonation.     

Evaluation of nucleation activation energy in metal CVD processes

A new approach to evaluate activation energy for nucleation in metal chemical vapor deposition (CVD) is presented. Deposition is performed by laser induced chemical vapor deposition (LCVD) using a low laser power and a high scan speed, so that only discrete particles in the initial nucleation stage are formed. The nucleation activation energy is then obtained from a relationship between the laser-induced surface temperature distribution and the particle distribution. The activation energy is directly related to the nucleation barrier, and hence the difference in the nucleation activation energies on different substrates may be used to explain the chemical selectivity which is often observed during metal CVD processes. This approach is experimentally applied to aluminum CVD using dimethylethylamine alane (DMEAA) precursor, and its nucleation activation energy is found to be 25kcal/mol on silicon surface.     

Simulation of reverse flow operation for manipulation of catalyst surface coverage in the selective oxidation of ammonia

A mathematical model has been developed for the simulation of the ammonia oxidation in a reverse flow reactor. Computer simulations were carried out with a kinetic scheme, based upon elementary reaction steps. Aim was to explore the potential of a reverse flow reactor for selective oxidation of NH₃ to produce either N₂, NO, or N₂O via a dedicated operation procedure. Therefore, the conversion of NH₃ and the selectivity toward N₂, NO, or N₂O, were compared for a reverse flow operation and a steady state, once-through operation.A new operation concept of reverse flow operation in combination with a periodically lower feed concentration is proposed. The novel reactor concept shows a better performance compared to normal reverse flow operation and to steady state, once-through operation. The results indicate that reverse flow operation can be applied for manipulation of conversion and selectivity. A periodically lower feed concentration may increase the conversion, even up to levels that exceed the steady state value.     

Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt:Sn ratio

Novel carbon supported Pt/SnO_x/C catalysts with Pt:Sn atomic ratios of 5:5, 6:4, 7:3 and 8:2 were prepared by a modified polyol method and characterized with respect to their structural properties (X-ray diffraction (XRD) and transmission electron microscopy (TEM)), chemical composition (XPS), their electrochemical properties (base voltammetry, CO_ad stripping) and their electrocatalytic activity and selectivity for ethanol oxidation (ethanol oxidation reaction (EOR)). The data show that the Pt/SnO_x/C catalysts are composed of Pt and tin oxide nanoparticles with an average Pt particle diameter of about 2 nm. The steady-state activity of the Pt/SnO_x/C catalysts towards the EOR decreases with tin content at room temperature, but increases at 80 °C. On all Pt/SnO_x/C catalysts, acetic acid and acetaldehyde represent dominant products, CO₂ formation contributes 1-3% for both potentiostatic and potentiodynamic reaction conditions. With increasing potential, the acetaldehyde yield decreases and the acetic acid yield increases. The apparent activation energies of the EOR increase with tin content (19-29 kJ mol⁻¹), but are lower than on Pt/C (32 kJ mol⁻¹). The somewhat better performance of the Pt/SnO_x/C catalysts compared to alloyed PtSn_x/C catalysts is attributed to the presence of both sufficiently large Pt ensembles for ethanol dehydrogenation and C-C bond splitting and of tin oxide for OH generation. Fuel cell measurements performed for comparison largely confirm the results obtained in model studies.     

The role of lanthana loading on the catalytic properties of Pd/Al2O3-La2O3 in the NO reduction with H2

The role of La₂O₃ loading in Pd/Al₂O₃-La₂O₃ prepared by sol–gel on the catalytic properties in the NO reduction with H₂ was studied. The catalysts were characterized by N₂ physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO.

The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La₂O₃ inclusion. The selectivity depends on the NO/H₂ molar ratio (GHSV = 72,000 h⁻¹) and the extent of interaction between Pd and La₂O₃. At NO/H₂ = 0.5, the catalysts show high N₂ selectivity (60–75%) at temperatures lower than 250 °C. For NO/H₂ = 1, the N₂ selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H₂O vapor. The high N₂ selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdO_x phase interacting with La₂O₃. The formation of this phase is favored by the spreading of PdO promoted by La₂O₃. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al₂O₃ the O₂ uptake is consistent with the oxidation of PdO to PdO₂, and when La₂O₃ is present the O₂ uptake exceeds that amount (1.5 times). La₂O₃ in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N₂.     

基于螺旋型铂铱合金电极的植入式葡萄糖生物传感器

采用螺旋型铂铱合金电极设计,旨在提高植入式葡萄糖生物传感器的葡萄糖氧化酶担载量并增大工作电极的电化学活性面积.以扫描电镜(SEM)观察聚氨酯(Polyurethane,PU)半透膜的形貌,采用循环伏安法(CV)和计时电流法(I-T)考察PU涂覆厚度、PU含量以及酶含量等参数对传感器电化学性能的影响,结果表明:所制备的螺旋型传感器灵敏度在20 nA/(mmol/L)~30 nA/(mmol/L),可在人体生理条件范围内线性检测(2 mmol/L~30 mmol/L)葡萄糖浓度,并且具有良好的重现性、稳定性和选择性,符合电极长期植入式需求,有望作为今后糖尿病患者血糖连续监测的关键器件.