Chlorinated compounds emitted into the atmosphere are responsible for the current thinning and shrinking of the ozone layer in the stratosphere. Two main potential methods have been suggested for their transformation: oxidative destruction to form environmentally safe products or hydrodechlorination to form potentially valuable chemical compounds. In this review, performances of halogenated compounds over the zeolites and the noble metal-containing zeolite catalysts are characterized by different spectroscopic methods (IR, NMR, etc.) to clarify the reaction mechanism of hydrodechlorination over the catalysts. NMR studies provided evidence that chlorofluorocarbon reacts more aggressively with zeolites at elevated temperatures. The extent and nature of reaction depended on the zeolite type and the exchanged cation. Infrared spectra of the gas phase showed that HCl, CO2 and COCl2 were detected as the reaction products in the hydrodechlorination reaction of CCl2F2 over HY. The phosgene intermediate is believed to be the key to the structural damage of the zeolite. Pt-containing zeolite catalyst was more active in the hydrodechlorination of carbon tetrachloride than the Pd-containing catalyst, and beside the main products (methane and HCl) chloroform as intermediate product was formed. On Pd-containing zeolite no chloroform, but high amounts of ethane as final products together with methane were formed. The activity and selectivity of the hydrodechlorination reaction of various chlorine-containing compounds (C1, C2, with and without fluorine content) on different metal-containing zeolites of various types is summarized.
Effects of the carrier characteristics were studied on the catalytic properties of Pt-Pd-supported USY zeolites in the hydrogenation of tetralin and the hydrodesulfurization of 4,6-dimethyldibenzothiophene. The dispersion of Pt-Pd on USY zeolite increased with the ratio of SiO2/Al2O3 in the range of 5 to 150, but was independent on the crystal size of the zeolite. The increment of the Pt-Pd dispersion may affect the enhancement of catalytic hydrogenation and hydrodesulfurization activities. Catalysts on carriers with smaller crystals exhibited higher activities in both catalytic hydrogenation and hydrodesulfurization. Higher catalytic activities of the catalyst prepared from carriers with small zeolite crystals probably resulted from the high external surface area, which contributes to efficient diffusion of the reactant in the liquid phase reaction.
To improve the antioxidative effect of polyolefin (PP or PE) resin, two types of antioxidants with structures similar to vitamin E (S-13 and S-19) were synthesized. The antioxidative activity of the compounds added to polypropylene as 0.005 wt% was examined by the melt-index and yellow index methods. The compounds had only antioxidative activity. The antioxidative activity significantly increased mixing with phenolic and phosphoric antioxidants. Investigation of the mechanism of the antioxidative activity revealed that hydrocarbon radicals produced by the thermal decomposition of polypropylene or polyethylene immediately reacted with the antioxidant to form stable product. The S-13 or S-19 antioxidants were regenerated by the reaction between the antioxidant radicals, and phenolic and phosphoric antioxidants.
ZSM-5 supported Mo catalysts for the dehydroaromatization reaction of methane were characterized by Mo K-edge EXAFS, NH3-TPD, and XPS techniques. Mo/ZSM-5 catalysts showed the maximum activity for benzene formation at 5 wt% Mo. The activity of the catalysts was related to the particle size of Mo2C supported on ZSM-5 estimated by Mo K-edge EXAFS. The addition of a second metal did not increase the activity for benzene formation. These results are ascribed to the weakening of the interaction between the acid sites of ZSM-5 and Mo oxide precursors due to competitive consumption of zeolite protons by added metal atoms, resulting in the formation of less dispersed Mo carbide particles and the decreased number of acid sites.
The use of chemicals and waste materials from petroleum refineries for the solubilization of activated sludge was investigated. "Refinery spent caustic" and sodium sulfate had similar solubilization activities to sodium hydroxide. Solubilization of activated sludge reached 30-34% after 10-30 min at 25°C, and was relatively rapid compared to that of activated sludge from sewage waste. Solubilization reached 45-50% after 10-30 min at 60°C. The flora of microorganisms in the sludge from a petroleum refinery, which mainly consists of bacteria in contrast to the various microorganisms in sewage sludge, could possibly be responsible for this rapid solubilization.
Solubilization of activated sludge using alkaline waste refinery spent caustic is feasible. Stimulatory solubilization of activated sludge with combinations of a high-speed mixer and alkaline treatment was investigated. A high-speed mixer operated at 12,000 rpm (liquid linear velocity, 15 m/s) containing 0.05 mol/l alkaline solution enabled solubilization of 40% and 50% solubilization after 30 min and 1 h, respectively, or 1.3-1.4 times greater compared with solubilization with only alkaline treatment. Higher temperature (50°C) stimulated solubilization up to 55% after 1 h. A pilot-scale solubilization reactor (1 m3) was constructed. Under the optimum conditions obtained in laboratory scale experiments, about 50% solubilization with "refinery spent caustic" was achieved, similar to that of laboratory experiments, in 1 h, suggesting that such combinations are practically possible.
This paper presents a genetic simulated annealing algorithm (GSAA)-based inverse algorithm for reconstructing the shape of a two-dimensional defect from the magnetic flux leakage (MFL) signals. In the algorithm, the GSAA formulated by incorporating the simulated annealing technique into the mutation operator of the standard genetic algorithm (GA) is employed to solve the optimization problem in the inverse problem, and a radial-basis function neural network (RBFNN) is utilized as the forward model. Experimental results demonstrated that the GSAA-based inverse algorithm is more accurate and is more robust to noise than the GA-based inverse algorithm.
A rapid quantitative analysis method for the oxidation products of propylene was established. The analysis system consists of a gas chromatograph equipped with two detectors. Many products from the oxidation reaction of propylene, such as propylene oxide, propionaldehyde, acetone, acrolein, hydrocarbon, carbon monoxide, carbon dioxide, and oxygen, can be simultaneously analyzed within 30 min. Actual catalytic activity tests under various temperature conditions confirmed that the analytical method was useful for the rapid screening of propylene oxidation catalysts.