Alcoholysis of waste PLA-based plastics to methyl lactate over sulfated ZrO2/SiO2 catalyst

Polylactic acid (PLA) is popularly used to replace some petroleum-based polymers due to its biodegradability. However, biodegradation of waste PLA requires specific bacteria, stringent conditions and long time. Catalytic recycling of waste PLA to valuable added products rather than composting is a sustainable green routine. In this work, catalytic alcoholysis of waste PLA to methyl lactate (MLA) was carried out over a SiO2 @UiO-66 derived solid acid (SO2–4/ZrO2/SiO2). Characterizations indicated that SO2–4/ZrO2/SiO2 processed large surface area and homogenously dispersed acid sites, and it exhibited excellent performance for the alcoholysis of waste PLA under mild conditions. At 140 oC, the yield of MLA is 92.7% within 5 h, and SO2–4/ZrO2/SiO2 could be recycled at least five times without obvious loss of activity. The specific yield of MLA over SO2–4/ZrO2/SiO2 reached 2678 mg-MLA/g-cat/h, which was higher than that of H3PW12O40, Amberlyst-45, Hβ, HZSM-5 and α-ZrP. At the same time, SO2–4/ZrO2/SiO2 was also capable of the alcoholysis of waste PLA-based products. A possible pathway of PLA alcoholysis over SO2–4/ZrO2/SiO2 catalyst was proposed.