The invention relates to methods and systems for preparing macrocyclic polyester oligomer (MPO) directly from monomer via heterogeneous catalysis, rather than by depolymerizing a polyester. For example, in an exemplary embodiment, cyclic poly(butylene terephthalate) (cPBT) is produced by reacting butanediol (BDO) and dimethylterephthalate (DMT) in an organic solvent—for example, ortho-dichlorobenzene (oDCB). The mixture flows over (or otherwise contacts) the catalyst-coated fiberglass or silica gel, e.g., which is packed in a column or bed. MPO is produced in the reaction mixture, while residual linears and catalyst residue remain in the column/bed.