A continuous process for the production of an alkyl ester product is described. The process includes the steps of carbonylating ethylene with carbon monoxide in the presence of C1-6 alkanol co-reactant to form the alkyl ester product. The carbonylation takes place in the presence of a catalyst system that includes (a) a bidentate ligand, (b) a catalytic metal selected from a group 8, 9 or 10 metal or a compound thereof, and (c) a sulphonic acid capable of forming an acid alkyl ester with the C1-6 alkanol. The process includes the step of separating the alkyl ester product from a carbonylated crude product stream by treatment effective to vaporizing the alkyl ester product in a single stage flash distillation column and providing a purified alkyl ester product stream separated from the bidentate ligand and catalytic metal.