| 摘要 |
<p>Formaldehyde is separated from a gaseous mixture containing formaldehyde, water vapour and gases, such as oxygen and nitrogen, by passing the gaseous mixture in indirect heat exchange with a coolant to condense and solidify the major proportion of the formaldehyde as paraformaldehyde and to condense a portion of the water vapour, separating the depleted gaseous mixture from the paraformaldehyde and condensed water, and then heating the paraformaldehyde and water together by indirect heat exchange to form an aqueous solution of formaldehyde. The formaldehydebearing gaseous mixture may be produced by a vapour-phase methanol oxidation plant employing air as oxidizing agent and a ferric oxide catalyst. The process may be carried out in an apparatus comprising two heat-exchangers associated with a system of valves whereby the flow of gaseous mixture may be switched from one heat-exchanger to the other so that the condensation of formaldehyde and water may take plac in one heat-exchanger while the paraformaldehyde and condensed water (formed in the previous cycle) are heated together in the other heat-exchanger (see Division B1). The depleted gaseous mixture may be scrubbed with water to recover residual formaldehyde.</p> |
