Co-pyrolysis characteristic and dynamic analysis of alkali lignin and oil shale

Abstract: Use of different heating rates (30, 50, 80 K/min) for lignin alkaline and oil shale mixed sample (lignin alkaline dosage 20%, 50%, 80%) in co-pyrolysis combined with TG-FTIR technique, we analyzed pyrolysis products and cumulative production trends at different heating rates. After that we fit data in two model free kinetic analysis methods (FWO method, Starink method). The results showed that due to differences in the rate of heat transfer, the amount of heat a sample received determined the quantity of weight loss from a tested sample. Weight loss increase in five specimens was observed with the increase of heating rate at the high temperature region. When lignin alkaline was added to oil shale, DTG curves changed significantly at 400-500 ℃. After 600 ℃, both oil shale and lignin in co-pyrolysis had an overlapped peak. Based on TGA data collected and the data in the pyrolysis product precipitated at the initial temperature and the temperature corresponding to the termination of weight loss, both samples obtained separate pyrolysis product yields when co-pyrolysis solution was in the same mixed sample heating rate. The 50% lignin alkaline product yields were the highest in contrast to that with mixed different heating rates and different mixing ratio of lignin alkaline and oil shale. It was possible that at the heating rate of 80 K/min, lignin alkaline dosage product yielded 50% of the maximum. According to FTIR detection, in the mixed sample, cumulative production curve of pyrolysis products under different mixing ratio showed that 50% of lignin alkaline added in the mixed sample with respect to the separate production of the two pyrolysis products can reduce aromatic ring structure compounds, phenolic compounds, H2O. For different heating rate and yield curve of accumulated pyrolysis products, it showed that the aromatic ring structure compounds, and CO2, CH4 cumulative production in response to increase of heating rates and temperature increased proportionally. Cumulative production of H2O over heating rate and temperature was proportionally related for pyrolysis temperature of 200-600 ℃. Only after 700 ℃, CO cumulative production and its relationship with the heating rate was proportionally related to temperature rise. For phenolic compounds, cumulative production at 50 K/min reached the highest for 250-800 ℃. In this temperature range heating rate and cumulative production of phenolic compounds was proportionally related to temperature. But beyond 800 ℃, at heating rate of 30 or 50 K/min, output began to fall. To choose proper lignin alkaline and oil shale content under a 50% of the mixed sample with a heating rate of 30, 50, 80 K/min we calculated the activation energy E for conversion rate for both lignin alkaline and the oil. The activation energy of both fit a linear function with a correlation coefficient of 0.95 and they were approximately parallel each other. The activation energy at the same conversion rate of maximum error was only 10 kJ/mol. In the model free methods, the conversion rate 0.45, 0.7, 0.85 have emerged during the activation energy decreases. By fitting the result, the two methods can show the complexity of the reaction mechanisms.