The sulfonation of solid acrylonitrile‐butadiene‐styrene, a feedstock that is often used in the 3D printing process of fused filament fabrication, and its application in characterizing liquid‐solid mass transfer is reported. The ion‐exchange capacity was assessed experimentally, and intraparticle diffusion coupled with extraparticle liquid‐solid mass transfer was simulated. Tubular reactors and spherical particles were fabricated by 3D printing, modified by sulfonation, and used to determine mass transfer coefficients for laminar flow in a tubular reactor and a fixed bed of spherical particles. The results show good agreement with published correlations and demonstrate the applicability of this cost‐effective, accurate, and reliable method.