Investigation of co-pyrolysis mechanism of oil shale and rubber seed shell, product yield and optimization of pyrolysis parameter using response surface methodology

Abstract

The current work presents an inclusive study on the co-pyrolysis mechanism of oil shale (OS) and rubber seed shell (RSS). The OS and RSS were mixed in blending ratio of 1:1, 1:2, and 2:1 and subjected to thermogravimetric analysis (TG-DTG) to identify the organic matter decomposition zones. The TG-DTG data were considered for determination of kinetic parameters and establishing the thermal program for lab-scale pyrolysis. The kinetic parameters were identified using isoconversional methods. The mean apparent activation energy values of the co-pyrolysis process were determined to be 249.5 kJmol−1 for OS to RSS blend ratio of 1:2 and increased to 275 kJmol−1 for blend ratio of 2:1. The possible decomposition mechanisms were predominantly identified as F2 second order, and A3 Avrami Eroffev reaction model. However, with the increase of oil shale in the blend, D3 diffusion model occurred as an intermediate between F2 and A3 reaction model. The kinetic triplets were validated by reconstruction of thermogravimetric data. The lab-scale pyrolysis experiments were designed using Design of Experiments for optimization of pyrolysis parameters using response surface methodology (RSM) to maximize the oil yield. It was observed that pyrolysis temperature and blending ratio were the significant parameters for regulating the yield of pyrolytic products. Characterization of the pyrolytic products showed that with increase in concentration of OS in the blend, the percentage of –OH compounds decreased in the oil samples. It may be assumed that, the presence of clay minerals in the OS sample acted as a catalyst for deoxygenation of the produced oil samples by inhibiting the production of –OH compounds. Also, increase of OS in the blend, increased the generation of CO and CO2. GC–MS, and NMR analysis of the pyrolytic oil samples showed that increase in the percentage of oil shale in the blend from 1:2 to 2:1 led to an increase in concentration of aliphatics (19.2 % to 31.15%), and reduces the percentage of the oxygenated compounds (41.42% to 32.1%), therefore increasing the heating value of the obtained pyrolytic oils.