Composite materials based on CaO obtained from egg shells and k-carrageenan, an anionic sulfated linear polysaccharide obtained from red seaweeds was used as an efficient, environmentally friendly heterogeneous catalyst for the transesterification of soybean oil with methanol at 60 degrees C. The different composite samples were produced through the dissolution of the biopolymer in an ionic liquid (IL) derived from imidazolium ion and by further addition of CaO. The samples were characterized by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM) and Termogravimetry (TGA). The materials exhibit an internal structure consisting of meso and macropores which widen with the addition of small amounts of Hexamethylene diisocyanate (HMDI) that acts as a crosslinker. The composite materials present a similar thermal behaviour to k-carrageenan, without loss of stability. The catalytic activity of the prepared composite materials was evaluated in the transesterification reaction of soybean oil with methanol through catalytic runs in batch conditions. It was found that both CaO loading and polymer cross-linking affect the sorption capacity and the transport properties of the prepared catalytic materials, with best results obtained for the intermediate CaO concentration in membrane and a lower crosslinking degree.