Provided is a zeolite-based adsorbent in the form of agglomerates, where the adsorbent having a tortuosity factor, calculated from the pore distribution determined by mercury intrusion porosimetry, of greater than 1 and less than 3. The adsorbent also has a porosity as determined by mercury intrusion porosimetry of between 25% and 35%. The adsorbent is useful in the field of separations in particular in a process for separating para-xylene from aromatic hydrocarbon isomer fractions containing 8 carbon atoms.