2.1
Process Comparison and Selection Criteria
Today about all of the world's commercial formaldehyde is manufactured from methanol and air by using metal or metal oxide catalyst but a portion is produced by the partial oxidation of lower petroleum hydrocarbons. The former procedure gives essentially pure formaldehyde containing methanol and traces of formic acid as a primary product, where as the later gives a mixture of lower aliphatic aldehydes, alcohols and acids which on refining yield an excessive group of petro-chemicals. Although there are, other mcellaneous methods for producing formaldehyde including the hydration of carbon oxides, the pyrolytic decomposition of formates etc... But they do not appear to have achieved commercial importance.
2.1.1 Natural Gas Process Normally three methods are used for the manufacturing of formaldehyde from natural gas: 1) Oxidation in gaseous phase by passing mixture of gas and air over catalyst. 2) Oxidation of natural gas by ozone. 3) Iodination of subsequent hydrolysis. Formaldehyde is also synthesized by cracking of methane in electric discharge. Many types of catalyst e.g. copper, nickel, cobalt, chromium, manganese, gold and silver are used for production of formaldehyde. Maximum conversion of 60% to 70of methane to formaldehyde occurs in this process.
2.1.2 Methanol Process Formaldehyde is produced by vapor phase oxidation of methanol in excess of air followed by absorption of water liquid methanol is vaporized in vaporizer then it is mixed with compressed air. These mixed streams are then introduce into tubular reactor, filled with silver catalyst Heat is generated by oxidation of Methanol. In this process, 87.4% conversion of methanol to formaldehyde takes place. In natural gas process, the conversion of low molecular weight hydrocarbons in the oxidation step together with a complex separation system, results in energy-intensive plant, that, with increasing fuel .costs, suffers economically when competing with newer, 21