Two-Stage Acetaldehyde Process from Ethylene

The two-stage process has been developed by the research group of Wacker s Consortium fiir elektrochemische Industrie. While this group worked on the development of a single-stage process, Wacker had to realize that at the time and the site of the scheduled first commercial plant, oxygen was not available at a reasonable price. So, Wacker was forced to develop another version using air as the oxidant. 

It has been mentioned in Section 4.1 that cupric chloride causes chlorination reactions. Thus, chlorinated aldehydes (see Eq. (9.26)) are the main by-products. Others include acetic acid and chlorinated acetic acids. Light ends are carbon dioxide, methyl, and ethyl chloride. By chlorination, oxidative, and hydrolytic reactions, oxalic acid is formed causing insoluble copper oxalate. In order to avoid an accumulation in the catalyst, it is continuously thermally decomposed by heating a small side stream in the regeneration step (reactor (i) in the one-stage, reactor (m) 

Through this, the content of copper oxalate in the catalyst can be kept constantly low. Thus, the catalyst shows a kind of self-cleaning behavior. 

As chlorinated by-products are formed during the process and subsequently removed from the catalyst solution, the deficit of chloride in the catalyst must be compensated by feeding the equivalent amount of hydrochloric acid into the catalyst solution. 

The subsequent purification of the product is carried out by a two-step distillation. At first (column k), the light ends, mainly carbon dioxide, methyl, and ethyl chloride, are removed overhead. In the second step (1), acetaldehyde goes overhead water, acetic acid, and some chlorinated products are removed as bottoms and chlorinated acetaldehydes as a side cut. 

---