Study Of Formaldehyde Prepared By Using Semifinished Methanol As Raw Material

Formaldehyde is an important basic organic chemical material which is very useful. There are several ways of formaldehyde production like air oxidation of methanol, methyl acetal oxidation. The main production process of formaldehyde is the"silver method"in china, which is oxidation and dehydrogenation reaction of methanol under the action of the silver catalyst. Using semifinished methanol as the raw material directly to produce formaldehyde, the new technique could save energy of distillation, simplify operations, reduce production costs, improve the economic efficiency."silver method"is not good enough to produce formaldehyde by semifinished methanol as the raw material. Because impurities in the semifinished methanol can make electrolytic silver catalyst poison.There is a determination of semifinished methanol. The experiment results obtained that semifinished methanol in this experiment have the content of methanol, iron impurity, sulfur impurity, water, and wax which respectively is 56.40% (mass fraction), 0.01258μg/mL, 0.1739μg/mL, 42.18% (mass fraction), 1.1% (mass fraction).The effects of impurities of Fe²⁺ and S^2- in methanol about the activation of the electrolytic silver, Fe-Mo and composite catalyst by catalytic oxidation producing formaldehyde has been investigated on gas-solid catalytic device. Experiment results showed that electrolytic silver catalyst and Fe-Mo catalyst had little effect when the impurities of Fe²⁺ S^2- in methanol lowing. When the methanol concentration of Fe2 + impurity less than 1.258×10-2 g/L, the Fe-Mo catalyst and electrolytic silver catalyst activity is not affected in a relatively short time, Fe-Mo catalyst activity keep longer activation than the electrolytic silver catalyst. The two catalysts are inactivated when the impurity concentration of Fe²⁺ is 3.774×10-2 g/L in methanol, electrolytic silver catalyst is more susceptible to the impact of Fe²⁺ impurity in fast inactivation than Fe-Mo catalysts. When S^2- impurity concentration less than 1.699×10-2 g/L, it can not be affected by the Fe-Mo catalyst activity, while the electrolytic silver catalyst will be deactivated. When the S^2- impurity concentration is 5.097×10-2 g/L, the S^2- impurity must be removed. Fe²⁺ impuritiy concentration less than 1.258×10-2 g/L, S^2- impurity concentration less than 1.699×10-2 g/L in the methanol, Molybdenum oxide and Ag composite catalyst is best of the composite catalyst, Molybdenum oxide and Ag composite catalyst productivity in a certain period of time basically unchanged, indicating that this composite catalyst had no effect by semifinished methanol, Molybdenum oxide and Ag composite catalyst can product formaldehyde by using semifinished methanol as raw material.There is a determination of the optimum conditions about electrolytic silver and composite catalysts in catalytic oxidation preparing formaldehyde by semifinished methanol. The obtained optimum conditions of electrolytic silver were reaction temperature 540℃, ratio of water and methanol 60%, ratio of oxygen and methanol 0.38, reaction time 9 hours. The optimum conditions of Molybdenum oxide and Ag composite catalyst were reaction temperature 480℃, ratio of water and methanol 58%, ratio of oxygen and methanol 0.44, reaction time 8 hours. The optimum conditions of Aluminum oxide and Ag composite catalyst were reaction temperature 480℃, ratio of water and methanol 58%, ratio of oxygen and methanol 0.44, reaction time 8 hours.