| abstract |
Tarry residues often are formed in carbonylation reactions, such as those in which esters or ethers are carbonylated to produce ethylidene diacetate or carboxylic acid anhydrides, such as acetic anhydride. Such residues contain Group VIII noble metal catalysts, typically rhodium, which must be separated before the residues can be disposed of. In the process of the invention, the residues are extracted with solvents which preferentially dissolve the tars. Preferred solvents include alkanes, cycloalkanes, halogenated alkanes, and aromatic hydrocarbons, particularly cyclohexane, carbon tetrachloride, and toluene. Separation of the residues from the noble metal catalyst by solvent extraction makes possible the disposal of the residues and the return of the noble metals to the reaction for reuse. |