Acetals are considered as an important bio-based diesel additives. Generally, the catalytic production of these compounds from an alcohol and an aldehyde suffers from a low conversion because of thermodynamic limitations. These limitations can be overcome through the in situ removal of the by-product water using, for example, a water selective membrane. A critical evaluation on the membrane performance, catalyst activity, optimal configuration, and feed composition leads to the conclusion that a combined reaction and separation is unlikely to be advantageous. The water permeance of the selected membrane was assessed to be too low in relation with the catalyst activity. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 18621868, 2012