Low-temperature synthesis of kerosene- and diesel-range fuels from waste plastics using natural potash catalyst

Abstract

The current study tested the hypothesis of whether the low-temperature catalytic cracking of waste plastics would generate carbon fules using high-density polyethylene (HDPE) polymer by potash as a novel catalyst for both energy recovery and carbon recycling. We applied a one-stage pyrolysis reactor system with a 75 min reaction time to observe the highest yield at a low temperature range of 70–170 °C. The effects of the potash and zeolite catalysts, temperature, and catalyst–polymer ratio on the pyrolysis liquid yield and hydrocarbon contents were determined. The mineral concentration of potash was analyzed semiquantitatively using an inductively coupled plasma-optical emission spectrophotometer (ICP-OES) and X-ray diffractometer (XRD). The ICP-OES demonstrated that nine metals, in the order of K > Na > Fe > Si > Mg > Al > Cu > Ca > Ni, were predominant in the potash. GC–MS analysis of the liquid products showed that major catalytic cracking molecules are C11 to C20 as kerosene- to diesel-range liquid. Potash catalyst produced an average liquid conversion of 34.7% at a catalyst ratio of 30 wt% over a distillate temperature range of 76–140 °C, whereas zeolite generated 19.5% at the same catalyst ratio over 90–120 °C. Although the two catalysts favored mainly olefinic products, a higher potash ratio promoted a smaller carbon products with a purer composition. Our experiments demonstrated that the new natural potash catalyst could convert waste plastics into kerosene to diesel range of valuable and recyclable liquid products as potential renewable fuel sources for carbon recycling.