Catalytic Fast Co-Pyrolysis of Waste Greenhouse Plastic Films and Rice Husk over an HZSM-5/MCM-41 Catalyst

We performed catalytic fast co-pyrolysis of waste greenhouse plastic films and rice husk over a hierarchical HZSM-5/MCM-41 catalyst in an analytical Py-GC/MS. We evaluated the effect of pyrolysis temperature and the ratio of rice husk to waste greenhouse plastic films on the total peak area of condensable organic products and CO₂. Separated experiments with rice husk and waste greenhouse plastic films confirmed the existence of synergy between the two feedstocks. In addition, we report results for the catalytic fast co-pyrolysis of the mixture rice husk and waste greenhouse plastic films. The maximum relative content of hydrocarbons from catalytic fast co-pyrolysis of rice husk and waste greenhouse plastic films is obtained at 600 °C. When the mass ratio of rice husk to waste greenhouse plastic films is 1:1.5, the relative content of hydrocarbons reaches a maximum (71.1%).

Based the on results, we propose an overall pathway for the catalytic fast pyrolysis over the hierarchical HZSM-5/MCM-41 catalyst. The waste greenhouse plastic films serve as a hydrogen donor for the hydrocarbon pool. The pyrolysis of the mixture of feedstocks produces primary vapors, which interact with MCM-41 mesoporous structures, leading to cracking of large molecular weight oxygenated chemicals. Next, the cracked oxygenates move through the HZSM-5 catalyst. The pore diameter of HZSM-5 catalyst is similar to the dynamic diameters of some hydrocarbons ,causing it to have a significant shape-selective effect on the aromatic hydrocarbons products. The vapors diffuse into the internal pores of HZSM-5 catalyst and form aromatic hydrocarbons through a common intermediate in the HZSM-5 framework. The composite molecular sieve has higher catalytic activity then HZSM-5 alone. Therefore, co-catalytic fast pyrolysis of rice husk and waste greenhouse plastic films over HZSM-5/MCM-41 may be a viable option to increase production of hydrocarbons from pyrolysis.