Using a methodology based on the element concept instead of the usual molar concept, a calculation procedure and meaning of the reactive residue curves are described. Through two well known industrial production processes (MTBE and methyl acetate), characteristics and advantages of the residue curve maps are depicted in order to analyse and design reactive distillation processes. Based on this, a new case is examined: esterification of lactic acid and ethanol to ethyl lactate, a biodegradable and non-toxic solvent that has been studied and obtained by reaction/pervaporation. Some alternatives via reactive distillation are discussed. (c) 2006 Elsevier B.V. All rights reserved.