A method to exploit the glycerin obtained as a by-product of the industrial process to produce biodiesel inside or out of the industrial production unit, providing a reduction in the environmental liability that may be caused by an excess in the production of glycerin that cannot be exploited for industrial use. The referenced method uses recycling of the glycerin obtained through industrial process to produce biodiesel, using a process basically consisting of four stages: a) extracting glycerin produced as a by-product of the industrial process for producing biodiesel; b) hydrogenation of said n-propanol glycerin, c) recycling of the n-propanol thus obtained to be added to a mixture of alcohols; and d) transesterfication of the n-propanol mixture added to the alcohol mixture, together with raw material triglycerides from renewable sources in order to obtain biodiesel. The referenced recycling of the n-propanol stream provides a reduction in the amount of the alcohol mixture necessary for the industrial process to produce biodiesel, consequently reducing operational costs.