a lipase from aspergillus niger immobilized by adsorption on microporous, polypropylene hollow fibers was used to effect the hydrolysis of the glycerides of melted butterfat at 40 $degree$ c and ph 7.0. mcilvane buffer was pumped through the lumen and melted butterfat was pumped concurrently through the shell side of a shell-and-tube reactor. nonlinear regression methods were employed to determine the kinetic parameters of three nested rate expressions derived from a ping pong bi bi enzymatic mechanism coupled with three nested rate expressions for the thermal deactivation of the enzyme for the reaction conditions used in this research, a four-parameter rate expression (which includes a two-parameter deactivation rate expression and a two-parameter hydrolysis rate expression) is sufficient to model the overall release of free fatty acids from the triglycerides of butterfat as a function of space time and time elapsed after immobilization. at a space time of 3.7 h immediately after immobilization of lipase, 50 of the fatty acid residues esterified in the sn-1,3 positions of the triglycerides can be released in the hollow-fiber reactor. (author abstract) 51 refs