MECHANOCHEMICAL SYNTHESIS OF CHROMIUM (III) MOLYBDATES ON THE BASIS OF VARIOUS PRECURSORS

Проведен анализ влияния прекурсоров (оксид молибдена (VI) и парамолибдат аммония) на физико-химические и каталитические свойства синтезированных образцов молибдатов хрома (III). Исследован фазовый состав и удельная поверхность данных образцов. Методами рентгенофазового, рентгеноструктурного, синхронного термического анализов, газовой хроматографии изучен процесс механохимического синтеза молибдатов хрома. Установлено, что в зависимости от источника молибдена, образуется молибдат хрома (III) различной структуры. Показана каталитическая активность и селективность молибдатов хрома (III) в реакции окислительного дегидрирования метанола. Установлены побочные продукты, образующиеся в ходе данной реакции. Степень конверсии для всех образцов составила более 80 %. Показано, что селективность молибдата хрома (III), полученного с использованием парамолибдата аммония значительно превосходит данный показатель у образца, полученного из оксида молибдена (VI), и достигает ~80%. The influence of precursors (molybdenum (VI) oxide and ammonium paramolybdate) on the physicochemical and catalytic properties of the synthesized samples of chromium (III) molybdates is analyzed. The phase composition and specific surface of these samples were studied. The process of mechanochemical synthesis of chromium molybdates. studied by methods of X-ray phase, X-ray diffraction, thermal synchronous analysis, gas chromatography. It was demonstrated that depending on the source of molybdenum, chromium (III) molybdate of various structures is formed. The catalytic activity and selectivity of chromium (III) molybdates in the oxidative dehydrogenation of methanol is shown. The by-products formed during this reaction have been identified. The degree of conversion for all samples was more than 80%. It was shown that the selectivity of chromium (III) molybdate obtained using ammonium paramolybdate significantly exceeds that of a sample obtained from molybdenum (VI) oxide and reaches ~ 80%.

Alkali Control for Gas Turbines by a Combined Hot Gas Clean-Up Approach

Gas turbines require very clean fuels if they are to avoid high temperature corrosion due to alkali sulfates and chlorides. Indications are that the alkali (sodium and potassium) salt levels need to be well below parts per million by volume in the hot gases and probably no more than 50 parts per billion by volume (0.01 mg/m3) for maintenance free operation. Moreover, it is the alkali that is the dominant factor and the actual concentrations of sulfur or chlorine are of minor relevance. Recently, numerous studies have shown that by using inexpensive absorbent type clay materials such as kaolin, bentonite, emathlite, or even bauxite and boehmite that these can reduce the alkali content very significantly (≥ 90%) in the hot gases. Coupled now to a final polishing method to remove the remainder, a new viable two step approach appears technically and economically feasible. This polishing method involves adding traces of either ammonium paramolybdate or ammonium metatungstate, both of which are water soluble, as a dilute aerosol into the hot gases. The ratio of molybdenum, or tungsten, to alkali needs to be in a ratio of about two to one on an atomic basis. This modifies the deposition process and alkali polymolybdate or polytungstate bronzes are preferentially produced. These are low melting point molecules that are benign and create with any remaining alkali a protective coating on the blades. They are thermodynamically more stable and rank above the sulfates and chlorides for formation. Also, being added in quantities of only parts per million or less there are no repercussions on NOX emissions or performance and remain cost effective at these levels. This coupling of the two complimentary approaches now appears feasible for final developmental testing to permit the use of alternate fuels without a need for cool-down cleaning cycles.

Pathomorphologic and histochemical changes in organs of rats subjected to chronic destroy by ammonium paramolybdate and sodium tungstate and their mixture

Pathomorphologic and histochemical studies of organs of rats subjected to chronic destroy by ammonium paramolibdate and sodium tungstate and their mixture are performed. Significant disorders in rats which inhale these agents in the concentration of 4,09, 0,51 mg/m3 and 1,05 mg/m3, respectively, are revealed.