The Study Of Industry Catalysts For The Dehydrogenation Of Methanol To Water-free Formaldehyde

Catalytic methanol dehydrogenation to produce water -free formaldehyde presents an attractive alternative to the current method since water formation is avoided.The catalytic system and process for methanol dehydrogenation have attracting many researchers attention since 1960' s. Many materials are active and selective catalysts. Howe- ver,most are subject to fast deactivation due to reduction of the oxides and vaporization of the elements, so it have not realized industry production. Among them, sodium carbonate was shown to exhibit highly activity, high selectivity for formaldehyde, and good stability at high temperature.Therefore, sodium carbonate catalyst was employed in the present work. Several aspects, including the moulding of sodium carbonate, carrier and additives , preparation methods,reaction parameters, different kinds of promoters,had been studied systematically in a broad range of condition. The effects of methanol conversion and formaldehyde selectivity have been studied earnestly.1. The capability of methanol dehydrogenation by sodium carbonate was studied. It was found that the sodium carbonate as catalysts show constant selectivity up to 50-60% conversion. At high methanol conversion, the selectivity of formaldehyde formation depends on conversion and falls to zero at complete onversion.2. Sodium carbonate has been moulded so as to use in industry. In this process, sodium silicate acts as bond, active carbon as additives and bentonite as carrier, we have prepared industry catalysts. These catalysts can catalysis methanol to formaldehyde in long time and its capability is very stabilization, and with high activity. In addtion, these catalysts can regenerate after it been used long time. The activity of regenerated catalysts is preferably.3. The effects of dehydrogenation reaction condition were studied. The experimental results indicated that the optimum reaction condtion is: temperature 700℃, mass space velocity 1.5ml/g.s, press 0.1MPa, methanol/feed gas ratio 10%. In this condition, corresponding methanol conversion was 63.14%, formaldehyde selectivity 71.53%. The yield of formaldehyde is 45.16%. This result indicated that the moulding catalyst of carbon sodium is viable on using in industry.4. Sodium carbonate catalyst was mixed with active carbones and carrier.The additives promoted the reaction rate without modifying formaldehyde selectivity.This effect increases with increasing carbon content in the carbon-carbonate mixture.It is suggested that actomic hydrogen produced on sodium carbonate during methanol dehydrogenation spills over onto active carbons or metals and recombines to form hydrogen gas.Hydrogen desorption from sodium carbonate the rate-determining step,is thus accelerated. At same time, the carrier separated active center and prohibited co-reactions.5. Thermodynamic analyse shows that the purification of formaldehyde is dificullty. A piont of view is proposed after theoretic analysis. When the methanol-formaldehyde aqueoue solution is separated, methanol is comparatively easier to volatilize. We want to use the method of distillation. The sequence steps are: (a) removal of methanol, for which the bottom product is foemodehyde-water and (b) removal of formaldehyde, for which the bottom product is pure water.