Showing papers on "Phosphotungstic acid published in 2001"

Oxidation reactivities of dibenzothiophenes in polyoxometalate/H2O2 and formic acid/H2O2 systems

Abstract: Dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene are typical thiophenic sulfur compounds that exist in diesel fuels Using toluene solutions of the model compounds, experiments were carried out to compare the reactivity of the different dibenzothiophenes in oxidation reactions, a key step for oxidative desulfurizations A series of polyoxometalate/H2O2 systems were evaluated for dibenzothiophene oxidation The H2O2 solutions of phosphotungstic acid and its salt were very active catalyst systems for the model compound oxidation, while their molybdenum counterpart systems were much less active The H2O2 solutions of silicotungstic and silicomolybdic compounds were the least active catalyst systems for the reaction Oxidation reactivities decreased in the order of dibenzothiophene>4-methyldibenzothiophene>4,6-dimethyldibenzothiophene, the same reactivity trend that exists in HDS However, the oxidation of the dibenzothiophenes was achieved under mild reaction conditions and it was easy to increase reaction temperature or reaction time to achieve high oxidation conversions, even for the least reactive 4,6-dimethyldibenzothiophene Apparent activation energies of dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene oxidation were 538, 560, and 587 kJ/mol, respectively These activation energies indicated a decrease in reactivity of dibenzothiophenes as methyl substitutes increased at the 4 and 6 positions on dibenzothiophene rings Interestingly, in a formic acid/H2O2 system, the oxidation reactivity of the dibenzothiophenes showed the reverse trend, suggesting that steric hindrance might play a role when bulky polyoxoperoxo species, which likely form in a hydrogen peroxide solution, act as catalysts

Direct polymerization of sulfonated poly(arylene ether) random copolymers and poly(imide) sulfonated poly (arylene ether) segmented copolymers: new candidates for proton exchange membrane fuel cell material systems

Abstract: Commercially available 4,4’-dichlorodiphenylsulfone (DCDPS) was successfully disulfonated with fuming sulfuric acid to yield 3,3’-disodiumsulfonyl-4,4’dichlorodiphenylsulfone (SDCDPS). Subsequently, DCDPS and SDCDPS were systematically reacted with 4,4’-biphenol under nucleophilic step polymerization conditions to generate a series of high molecular weight, film-forming, ductile, ion conducting copolymers. These were converted to the acid form and investigated as proton exchange membranes for fuel cells. Hydrophilicity increased with the level of sulfonation. However, water sorption increased gradually until about 50 mole percent SDCDPS was incorporated, and thereafter showed a large increase to yield water soluble materials for the 100% SDCDPS system. Atomic force microscopy (AFM) confirmed that the morphology of the copolymers displayed continuity of the hydrophilic phase at 60 mole percent SDCDPS. Conductivity measurements in the 40-50 mole percent SDCDPS range, where excellent mechanical strength was maintained, produced values of 0.1 S/cm or higher which were comparable to the control, NafionTM. These compositions also show a high degree of compatibility with heteropolyacids such as phosphotungstic acid. These inorganic compounds provide a promising mechanism for obtaining conductivity at temperatures well above the boiling point of water and membrane compositions containing them are being actively pursued. The water soluble 100% SDCDPS system was further investigated by successfully functionalizing the endgroups to afford aromatic amines via appropriate endcapping with m-aminophenol. Oligomers and polymers from 5-30 kg/mole number average molecular weight were synthesized and well characterized by NMR spectroscopy, endgroup titrations and size exclusion chromatography. The diaminotelechelic sulfonated segment was reacted with several dianhydrides and diamines to produce multiblock, hydrophobic polyimide-hydrophilic sulfonated polyarylene ether copolymers. Both ester-acid and amic acid synthesis routes were utilized in combination with spin-casting and bulk imidization. A series of tough, film-forming segmented copolymers was prepared and characterized. AFM measurements demonstrated the generation of quite well defined, nanophase-separated morphologies which were dependent upon composition as well as aging in a humid environment. Characterizations of the segmented copolymers for conductivity, and water and methanol sorption were performed and comparisons to state-of-the-art perfluorinated NafionTM systems were made. It is concluded that the segmented or block systems have the potential to enhance certain desirable PEM characteristics in fuel cells, particularly those related to swelling, retention of mechanical strength at elevated temperatures, and critical adhesion issues in membrane electrode assemblies. To Sue and the Boys: Thank you all for the years of support and understanding in this long journey

Phosphotungstic Acid Eliminates Uranyl Nitrate as a Sensitizer Before the Silver Impregnation of Helicobacter pylori

Abstract: Five different oxidizers were tested as “sensitizers” for the silver impregnation used to screen for the presence of H. pylori in gastric biopsies. Only phosphotungstic acid (0.01% aqueous solution) proved to be as reliable as the conventional 1% aqueous solution of uranyl nitrate. The organisms stained deep black and could be detected in all the samples where present. This procedure reduces the health hazards existent in laboratories where the radioactive uranyl nitrate is used. (The J Histotechnol 24:113, 2001)Submitted: January 23, 2001; Accepted with revisions: March 6, 2001

Phosphonation process for heteropoly acid system

Abstract: A phosphonating technuqie features that the Keygin-type heteropoly acids with redox catalysis activity and surface activating function or its salts (phosphotungstic acid, phosphomolybdic acid, etc), or the transition metal (Cu, Cr, etc) substituted heteropoly acids are used as phosphonating promoter to speed up the phosphonation of ordinary carbon steel or rolled steel plate, which is phosphonated at 20-50 deg.C by dipping or showering. Its advantages are quickly filming, less dreg deposit, uniform film and high antirust performance.

ISOMERIZATION OF α-PINENE CATALYZED BY PHOSPHOTUNGSTIC ACID SUPPORTED ON ACTIVATED CARBON

Abstract: Isomerization of α pinene was studied over phosphotungstic acid and activated carbon supported phosphotungstic acid catalysts.Influences of the reaction condition on conversion and selectivity of products were investigated.The experimental results show that solvents and temperature have obvious influence on activity of the catalyst and that HPW catalyst has both high catalytic activity and selectivity even at lower temperature to produce the expected camphene and limonene isomers.After being supported on activated carbon, the catalytic activity and stability of phosphotungstic acid have been improved greatlty and the catalyst can be reused.