A plate type methanol decomposition catalyst which has higher heat conductivity was prepared based on anodic oxidation of aluminum. In order to reduce the formation of dimethyl ether as a by-product at the acid site of alumina, silica was coated on the anodized alumina plate. By the measurement of ammonia TPD, it was found that the acidity of the silica coated catalyst was lower than that of the plate without coating. As for the silica coated plate, the profile of methanol TPD also showed that the formation of dimethyl ether was smaller and peak temperature was higher, although those without silica coating indicated a large amount of dimethyl ether formation. After Pd was loaded on the plate, the catalytic activity of methanol decomposition to hydrogen and carbon monoxide and the formation of dimethyl ether as a by-product were evaluated at 200 and 250°C by a continuous fixed bed reactor. The content and dispersion of Pd of silica coated catalysts were smaller than that of the hydrated catalyst without silica coating and the formation rate of carbon monoxide was increased with increasing metal surface area of Pd. The formation rate of dimethyl ether over the silica coated catalyst was approximately 1/20 of that of the catalyst without silica coating and it was independent of silica contents.
Metal alkoxides are hydrolyzed and the hydrolysates are modified with a coupling agent containing alkyl chains. The modified uni-hydrolysates, prepared using each of the alkoxides of Ti, Fe, Al, and Zr, and the modified bi-hydrolysates, prepared using two alkoxides consisting of a given alkoxide as one and Ti or Al alkoxide as the other, are dispersible homogeneously into organic solvents. Organic solutions of the modified bi-hydrolysates show spectral changes with light irradiation when they are prepared using Ti alkoxide. The spectral changes are due to intra- and/or inter-particulate electron transfer from photogenerated Ti3+ to other metal atoms in the hydrolysates. The electron transfer is efficient, which can be explained in terms of extremely fine particle size of the modified hydrolysates.
Zirconium was introduced to MCM-41 and MCM-48 in order to improve the resistance to alkaline solution. In this research, zirconium-containing mesoporous silicas (Zr-MCM-41 and Zr-MCM-48) were synthesized from tetraethylorthosilicate (TEOS), zirconium(IV)propoxide (ZrPr), sodium hydroxide (NaOH), the quaternary ammonium surfactant (cetyltrimethylammoniumbromide: CTAB) and deionized water. The XRD, TEM and nitrogen adsorption measurements show that zirconium-containing products have high quality of ordered structure of MCM-41 and MCM-48. The pore volume and the specific surface area of Zr-MCM-41 and Zr-MCM-48 are similar to those of pure silica samples. These materials show high stability in the alkaline solutions.
Condensed tannins are ubiquitous plant polyphenols and have many potential applications. A novel tannin gel adsorbent was synthesized from natural condensed tannin and its adsorption mechanisms and properties for lead (Pb) removal from aqueous solutions were investigated. It was found that lead could be removed through three adsorption mechanisms, i.e., ion exchange, hydrolytic adsorption and surface precipitation. When the initial concentration of lead was varied from 20 mg/l to 80 mg/l, ion exchange took place preferentially in the low pH range of 3.0 to 6.0, and the stoichiometric equation could be described as 2RH + Pb2+ = R2Pb + 2H+. On the other hand, when pH > 6.0, surface precipitation and hydrolytic adsorption took the predominant parts in the adsorption. The adsorption was notably affected by pH of solutions. The adsorption isotherm corresponding to the ion exchange predominating stage was correlated well to Langmuir Equation and the maximum removal capacity in the stage was 0.15-0.19 mmol Pb/g dry tannin gel adsorbent (30-40 mg Pb/g dry adsorbent). This study has the potential to develop an effective natural adsorbent for removal and recovery of heavy metals.
In polyelectrolyte precipitation of lysozyme, the combination mechanism between lysozyme and polyacrylic acid (PAA) at various experimental conditions was investigated from the stoichiometric coefficient at equilibrium in a batch reactor. At the underdosed condition of PAA to lysozyme, the lysozyme-PAA combination was performed by the electric charge neutralization and polymer bridging between lysozyme and PAA. As the PAA dosage decreased and its molecular weight increased, the bridging effect of PAA became more significant in the lysozyme-PAA combination because the more lysozyme was captured by the polymer bridging of PAA. The stoichiometric coefficient of the lysozyme-PAA combination, which was estimated from the lysozyme separation, was affected by both the PAA dosage and its molecular weight, but the effect of agitation was not observed. The linear equations were derived from the relationship between the stoichiometric coefficient and the dosage at three different PAA molecular weights of 2.0 × 103, 4.5 × 105 and 4.0 × 106, and well consistent with the experimental data.
In lysozyme precipitation by polyacrylic acid (PAA) with different molecular weights, the lysozyme separation was predicted using Smoluchowski's collision theory and the micromixing limitation model, plus the model predictions were compared with the experimental data from an MSMPR reactor. Since, in Smoluchowski's theory, ideal mixing was assumed in the solution, the lysozyme separation was only predicted to depend on the PAA properties, such as the PAA dosage and its molecular weights. However, in the micromixing limitation model, the lysozyme separation was represented as being affected by the operational conditions, including the mean residence time and the mixing intensity, in addition to the PAA properties. The difference between the lysozyme separations predicted by each model significantly increased at short residence time and low agitation speed. When compared with the experimental data obtained with various PAA properties and operational conditions, the degree of the lysozyme separation predicted by the micromixing limitation model was found to be in better consistency with the experimental data than that done by Smoluchowski's theory because the operational conditions as well as the PAA properties were included in describing the lysozyme-PAA combination in the reactor.
The temperature-swing column adsorption of nonionic surfactant Triton X-100 with poly-(vinylmethylether) gel (PVMEG) was investigated. The adsorption rate and adsorbed amount of Triton on the regenerated PVMEG were almost the same as those on the virgin gel. The PVMEG was regenerated simply by shifting temperature below the transition temperature followed by flushing out the desorbed Triton with a small amount of Triton-free solution. Because of this unique regeneration feature, the concentration of adsorbate was possible. The maximum Triton concentration in the desorption process was more than 7 time larger than the Triton concentration fed to the column in the preceding adsorption process.
Batch experimental work on the fluidization hydrodynamic and entrainment phenomena of cohesive starch powders was studied. Results show that fluidization can be realized as vibration break particleparticle bond in the bed. The higher Umf values compared to predictions indicate the formation of agglomerates in the bed. This has increased the residence time of fines to reduce material loss by entrainment. It was found that using starch powders as feed materials, entrainment was only in the range of 0.5-1.7% of the total fines (should be entrained) in the bed. As has also been found by other workers, the entrainment rate constants of group C decrease as particle size decreases. By adapting the criterion proposed by Rietema (1984) as well as Ma and Kato (1998), it was found in this case that the critical cohesion number, Ncoh* is 19.
This paper describes the investigation of the generation of spherical silica particles, which could potentially be used as alternative calibration aerosol for substituting DOP (dioctylphthalate) particles. Silica particles were generated by a spray drying method using a nanometer-sized colloidal silica suspension as the starting material. The generated silica particles have a spherical morphology, are nearly monodispersed and their size can be controlled at submicron order. The smoothness of the particle surface is greatly affected by the size of the colloidal silica particles used. Silica aerosol particles were also generated by the spray pyrolysis of an aqueous solution of tetraethylorthosilicate (TEOS), in order to compare their properties with those of silica particles obtained by spray drying method. The electrical mobility equivalent diameter of silica particles generated by spray drying method is in good agreement with the diameter determined by SEM observation. The light scattering characteristics of the silica aerosol particles were also measured using a laser particle counter and compared with a polystyrene latex (PSL) aerosol. By increasing the drying temperature of the silica sol droplets to 1200°C, the change of scattered light intensity with particle diameter shows a tendency similar to that of spherical PSL particles. Consequently, the spherical submicron silica particles generated by the present spray drying method appear to be applicable to the test of air filters.
The effect of pressure and temperature on the axial dispersion of gas was examined in a fluidized bed of 10 cm I.D. × 100 cm height. The employed particle was zinc titanate catalyst and particle size was 150 μm. The stimulus-response method was employed in order to determine the axial dispersion coefficient of gas in a bubbling fluidized bed. The hydrogen was used as the trace gas. The experimental results showed that the increase of pressure and temperature did not significantly change the axial dispersion coefficient in spite of significant increase of minimum fluidization velocity.
In this paper a new monitoring algorithm utilizing a change in time-series distribution of process data is presented since the distribution reflects the corresponding operating condition. In order to quantitatively evaluate the difference between two data sets, a modified dissimilarity index is defined. It represents the degree of dissimilarity between data-sets. In training step the confidence interval of each eigenvalue is obtained from the data taken in normal operation. Then, current operating condition is monitored by checking whether dissimilarity index abruptly changes and whether each eigenvalue is contained within its confidence interval. This approach is used to identify various internal and external disturbances in the data from the simulated activated sludge process. Simulation results have clearly shown that the detection performance of the proposed method can detect the various faults and disturbances, and can automatically discriminate between serious and minor anomalies of faults. That is, it can detect not only the disturbances, but isolate the sources of them. These results confirm that the proposed method is a proper monitoring technique for the wastewater treatment process which has nonstationary property and various disturbances.
An efficient scheduling of pipeless plants is proposed as mixed integer linear programming models. As previous models based on uniform time discretization methods or two-coordinate time representation methods cause a large number of binary variables, a continuous time representation model based on conventional multipurpose/multiproduct formulations is proposed. It is composed of three formulations, which are the production-restricted scheduling, the vessel-restricted scheduling, and the waiting-station-restricted scheduling. When the number of products increases, the size of a proposed formulation exponentially increases. Therefore, periodic scheduling is considered and an iterative solution procedure is proposed. The performance of the proposed models and the solution procedures are illustrated with several examples.
A new type of waste gas treatment was previously proposed in the packed column containing the immobilized activated sludge gel beads of 5 mm in diameter together with the hollow plastic balls of 10 mm in the optimal diameter with their optimal volume ratio of 1 to 2 to avoid compaction of the gel beads. The same type of biofilter is employed and analyzed for removal of acetaldehyde or propionaldehyde as a model of toxic and malodorant pollutants under a wide range of the inlet aldehyde concentrations. The same spherical gel beads as prepared previously by the PVA-boric acid method are stable and durable during storage as well as use in the removal operation. The biofilter gives a very low pressure drop to the waste gas stream through the packed bed. The acetaldehyde or propionaldehyde removal in the column decreases with an increase in the inlet aldehyde concentration. The kinetics data on the gel beads suspended in an air-tight batch reactor reveal that the Michaelis-Menten type rate equation is applicable to both respiration and pollutant biodegradation by the gel beads with negligible mass transfer effect. A model for removal of a single pollutant is developed assuming that the Henry's law constant determines the dissolved pollutant concentration in the gel bead, the pollutant is biodegraded according to the above rate equation and the contact efficiency of gel beads with waste gas has the same value of 0.24 as determined previously. The observed removals agree well with those calculated from the design equation developed. As a result the observed decrease in removal of aldehyde with its inlet concentration is due to the fact that the biodegradation rate itself approaches asymptotically the maximum one with the aldehyde concentration.
Total organic carbon (TOC) removals of two synthetic wastewaters which contain diethylene glycol mono-n-hexyl ether (DGME) and 1,4-butanediol diglycidyl ether (1,4-BDE) respectively as a main component, have been carried out by using hydrogen peroxide and ultraviolet irradiation (H2O2/UV). Experiments were carried out in a batch reactor with a low pressure UV lamp (500 W) irradiating ultraviolet at 254 nm and at 185 nm (5% of energy). The following results were obtained. (1) The complete TOC removals of the two synthetic wastewaters have been obtained. TOC removals of the two synthetic wastewaters are pseudo-first-order processes. (2) The removal rates of TOC of the two synthetic wastewaters were governed by the concentration of hydrogen peroxide added initially and the maximum pseudo-first-order rate constant and the optimum initial hydrogen peroxide concentration existed both in the two synthetic wastewaters. (3) The relation between the initial TOC concentration and the optimum initial hydrogen peroxide concentration exhibited linear in both synthetic wastewaters. The optimum initial hydrogen peroxide concentration in the TOC removal of the 1,4-BDE synthetic wastewater is higher than that of the DGME synthetic wastewater at the given initial TOC concentration. (4) The maximum pseudo-first-order rate constant increases with the decrease in the initial TOC concentration in both synthetic wastewaters. The maximum pseudo-first-order rate constant for the DGME synthetic wastewater is higher than that for the 1,4-BDE synthetic wastewater at the given initial TOC concentration. (5) The experimental results agree well with the theoretical consideration which has been previously proposed by authors (Hou et al., 2001c) while hydrogen peroxide concentration and TOC concentration in the wastewater were very high.
This study is a starting point for the creation of a new plastic recycling process. The process consists of two successive pyrolyzing reactors, for which a spouted bed type seems to be most appropriate for the time being. In the first reactor, plastic chips are fed and instantaneously pyrolyzed into lower hydrocarbons (gas or vapor). In the second reactor, the hydrocarbons are further pyrolyzed into hydrogen and carbon. Hydrogen is a useful and clean fuel (no carbon dioxide evolution) and a chemical raw material. Carbon can be utilized as carbon black, activated carbon, and so forth. In this study, flash pyrolysis of plastics was investigated to obtain basic data for the first reactor of the process. Six types of plastics, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET), were flash-pyrolyzed by putting them into a pre-heated batch reactor (873 K, 5 × 10-5 m3), which was made from stainless steel and contained 5 mm-diameter non-porous α-alumina balls as a thermal medium. The products (gas, condensate and solid residue) were collected and analyzed. In most cases, solid residue (in the reactor) yield was less than 3%. Gas yield was 1 to 30%. Condensate yield was 10 to 90%. These results show that in the first reactor of the proposed process most of the fed plastics can be pyrolyzed into gas and vapor, which will move to the second reactor as a fluid.
The real-time gas mass filter system consisting of a mass filter and a capillary sampling tube was developed for the analysis of products during electron beam (EB) irradiation of trichloroethylene (TCE)-air mixture. Interesting trace substances in gases are analyzed by this gas mass filter system in real time. The gases at atmospheric pressure are introduced to the mass filter under vacuum through a capillary tube without packing. The system was calibrated with three different standard mono-gases which contain known concentrations of sulfur dioxide, benzene and chlorobenzene for each. And its detectable limits for each gas were in the range of 0.7-1 ppmv. Products of irradiated TCE-air mixture were analyzed with the system in real time. The concentrations of dichloroacetyl chloride and carbonyl chloride (COCl2) increased by low dose irradiation when TCE was decomposed. These products decreased by higher dose irradiation and were identified as primary products. Trichloroethylene and these primary products were oxidized into CO2, Cl2, and HCl at 15 kGy. Carbonyl chloride was dissolved in NaOH aq for natural-oxidation into CO32- and Cl-. The doses for the complete oxidation of TCE and the products were decreased from 15 to 7 kGy by the combination of the irradiation and the dissolution of the irradiated gas. The decomposition mechanism of TCE, especially formation of COCl2, was clarified from the change of the products as a function of dose.
The chemical characteristics of methanol soluble lignin separated from Eucalyptus globulus by steam explosion were clarified by measurement of number-averaged molecular weight, weight-averaged molecular weight, and phenolic hydroxyl group. It was found that the methanol soluble lignin separated from the exploded wood at a steam pressure of 3.5 MPa and a steaming time of 5 min was the most adequate raw material for the synthesis of epoxidized lignin, i.e. lignin epoxy resin. The thermosetting behavior of epoxidized lignin was almost the same as that of commercial bisphenol A resin. According to E-Screen assay, the methanol soluble lignin, a raw material of epoxidized lignin, did not show estrogenic activity. Since the methanol soluble lignin was easily degraded by the lignin-degrading enzymes, the epoxidized lignin seems to be a biodegradable resin in waste treatment after its use.
The association behavior of hydrophobically-modified poly(vinyl alcohols), HMPVAs, bearing a single hydrophobic modifier (dodecyl group) located at one end of the polymer chain, was investigated in aqueous solution using the techniques of pulsed gradient spin echo nuclear magnetic resonance (PGSE NMR) spectroscopy and viscometry. In comparison to control polymers lacking hydrophobic modification, at concentrations above 2.5 wt% HMPVAs exhibited slower diffusion, as measured using PGSE NMR, and higher viscosity, as measured using viscometry. The results are consistent with the formation of intermolecular association structures consisting of approximately 9 polymer chains. The finding that singly chainend HMPVAs form intermolecular hydrophobic associations suggests that such polymers may prove useful as latex rheology modifiers.