Reaction behavior of solid acid catalytic cellulose acetylation

Substituting solid acid for liquid acid to catalyze the cellulose acetylation can simplify the conventional production process and make it environmentally friendly, but the related technique remains at the research stage. The unclear reaction behavior of solid acid catalytic cellulose acetylation results in limited success of previous efforts and measures. In the present work, SO₄²⁻/TiO₂ solid acid was used as the research object in comparison with H₂SO₄. Various characterization results demonstrate that the reaction behavior of cellulose acetylation catalyzed by SO₄²⁻/TiO₂ is completely different from that by H₂SO₄. SO₄²⁻/TiO₂ is limited to the outer surface of cellulose for catalytic acetylation through solid-to-solid contact, while H₂SO₄ can penetrate into the cellulose interior for internal and external simultaneous acetylation. The superficial cellulose molecular chains undergo partial acetylation by SO₄²⁻/TiO₂ catalysis and subsequently dissolve in acetate acid, followed by being further catalytic acetylated. The subsurface cellulose molecular chains are exposed to interact with SO₄²⁻/TiO₂ for subsequent round of acetylation till the depletion of the celluloses. Based on the present research result of reaction behavior, it is clarified that the efficiency of solid acid catalytic cellulose acetylation is mainly determined by the micron-scale morphological limitation between solid acid and cellulose rather than the intrinsic catalytic activity of solid acid.