3.2. Effects of polyethylene proportion on product distribution in catalytic co-pyrolysis of black-liquor lignin and polyethylene
The effects of PE proportion on product carbon yields and selectivities are shown in Fig. 3. The experiments were conducted at 600 °C with spent FCC catalyst. As shown in Fig. 3(a), both aromatic and olefin yields increased with increasing PE proportion. Besides, aromatic yield is a little higher than olefin yield. These results indicated that the temperature of 600 °C favors aromatic formation. Catalytic pyrolysis of black-liquor lignin only produced 3.2% and 4.6% of olefins and aromatics, respectively, and near 45% yield of char and coke. When catalytically co-pyrolysis with PE, the aromatic and olefin yield increased rapidly. This can be attributed to the following reasons: (1) PE pyrolysis produces a lot of products with high H/Ceff ratio which can offer hydrogen to black-liquor lignin ( Carlson et al., 2009 and Zhang et al., 2012); (2) the pyrolysis oxygenates of black-liquor lignin with high activation favor PE degradation; (3) PE substitution effect. The CH4 carbon yield retains at around 5–7% with the maximum value of 7.3% at 0.33 PE proportion, while the yields of CO and CO2 decreased with increasing PE proportion.