Functional Coating of NPK Granules with Pyrolysis Oils for Enhanced Slow-Release Performance

This study focused on developing slow-release fertilizers (SRFs) by coating pyrolysis oil on the fertilizer. The oils used included tire pyrolysis oil (TPO), wheat straw pyrolysis oil (WSPO), poplar wood pyrolysis oil (PWPO), and low-density polyethylene pyrolysis oil (LDPEPO). Coatings were created on fertilizer granules by co-pyrolysis at 200 °C in a fixed-bed pyrolysis reactor under nitrogen gas. The prepared SRFs included TPO-coated fertilizer (TPOCF), WSPO-coated fertilizer (WSPOCF), PWPO-coated fertilizer (PWPOCF), and LDPEPO-coated fertilizer (LDPEPOCF). Carboxylic, carbonyl, and hydroxyl compounds and functional groups in pyrolysis oils played an essential role by forming bonds and complexing with ions in NPK fertilizer. For uniform coverage of NPK fertilizer granules, maintaining a high nitrogen content in the fertilizer structure, and slower release of ions in a distilled water environment, WSPO and poplar wood were suitable.