Abstract: Traditional non-polar oil collectors cannot achieve high recovery of low-rank coal because of the presence ofoxygen-containing groups at coal surface. Compared with the traditional diesel collector, the collector containing carboxylic acid functional groups was further synthesized to enhance the flotation of low rank coal based on the alcoholysis of waste oil into biodiesel. The mechanism of collector promoting flotation was further analyzed by infrared spectroscopy, nuclear magnetic hydrogen spectroscopy, X-ray photoelectron spectroscopy and contact angle measurement. Carboxylic acid collector, 0^# diesel oil and biodiesel were used to carry out flotation tests on a low-level extremely difficult coal sample. The results showed that the carboxylic acid collector had the best flotation effect on clean coal. Compared with diesel collector, the yield of clean coal increased by 14.63%, and the ash content decreased by 12.06%.