Treballs Finals de Grau d'Enginyeria Química, Facultat de Química, Universitat de Barcelona, Curs: 2014-2015, Tutors: Eliana Ramírez Rangel i Fidel Cunill GarcíaLactose is a disaccharide contained in milk, in a 5% of its volume. The existence of this carbohydrate causes serious crystallization difficulties in the dairy industry, in addition to environmental problems. Moreover, it has to be taken into consideration that a 70% of the population is lactose intolerant. The present document shows the results of a study carried out in order to determine the current condition of the lactose hydrolysis process to produce free-lactose milk. The study will base on the process variables and the optimal conditions of the enzymatic hydrolysis, always taking into account the extent of reaction. The reaction presents inhibition by product which should have to be minimized in order to reach an efficiency of the process higher than an 80%. Moreover, it will be determined economic and social factors involved in the selection of this kind of process, that make more suitable the use of soluble enzyme instead of the immobilized one. On the other hand, a literature search has been done to study the different thermal treatments applicable to raw milk in order to deactivate the soluble enzyme that causes the lactose hydrolysis. It will be develop the mathematic modeling of a thermal treatment which will allow inactivating the enzymes and the micro-organisms presents in free-lactose milk for human consumption. In this case, HTST pasteurization (High Temperature Short Time) avoids a meaningful change of the flavor of milk and the loss of its nutritional components as calcium and vitamins source. The modeling will be done with a plate heat exchanger of four sections to treat a flow of 6.500 L/h and a pasteurization temperature of 84ºC. The model will be validated by software simulation and compared to real data provided by the industry.