High-efficiency co-liquefaction of low-rank coal and PAEs-rich PVC waste in supercritical water: Products upgrading and dechlorination.

With the extensive use of phthalates (PAEs)-rich polyvinyl chloride (PVC) plastic products, the recycling of PAEs-rich PVC waste has become a great challenge. Meanwhile, the efficient utilization of low-rank coal is important in China due to the abundant reserves. In this study, a high-efficiency co-liquefaction treatment of PAEs-rich PVC waste and low-rank coal (Inner Mongolia lignite) was developed by using supercritical water (SCW) process based on the interaction between the two kinds of waste. The effects of temperature, time, solid-to-liquid ratio (M Coal+PVC :M H2O), and mass ratio of coal-to-PVC (M Coal :M PVC) on the co-liquefaction conversion, composition of liquefied oil and dechlorination of PVC waste were investigated. The co-liquefaction of low-rank coal and PAEs-rich PVC waste had a significant positive synergistic effect with a maximum synergistic efficiency of 7.53% in the temperature range of 350–450 °C. The conversion ratio of low-rank coal and PAEs-rich PVC waste by SCW co-liquefaction increased from 59.71% to 74.92% with the increase of reaction temperature from 350 to 450 °C. PAEs-rich PVC waste could be almost completely dechlorinated (>98%) by the SCW co-liquefaction process, and more than 90% of the DEHP could be decomposed. The addition of PAEs-rich PVC waste resulted in a significant decrease of the percentage of heteroatom-containing compounds in the oil products by the co-liquefaction. At 450 °C, the co-liquefaction oil contained 69.16% of hydrocarbons and 6.14% of phenolic compounds. Different from supercritical water gasification, the purpose of SCW co-liquefaction in this study is to improve the coal liquefaction conversion ratio and oil quality by introducing the PAEs-rich PVC waste. The synergistic SCW treatment of PAEs-rich PVC waste and low-rank coal has good application prospects in products upgrading of low-rank coal and safe recycling of PAEs-rich PVC waste plastics. [Display omitted] • A co-liquefaction of low-rank coal and PAEs-rich PVC waste by SCW was reported. • Products upgrading and efficient dechlorination were found in the co-liquefaction. • A maximum synergistic efficiency of 7.53% could be obtained for the co-liquefaction. • Conversion efficiency was enhanced and high value-added hydrocarbons were recovered. • The co-liquefaction mechanism was proposed. [ABSTRACT FROM AUTHOR]