3.3. Comparison of product distribution in catalytic co-pyrolysis of black-liquor lignin and PE with different catalysts
Fig. 4 shows the product distribution in catalytic co-pyrolysis of black-liquor lignin and PE with different catalysts. The PE to black-liquor lignin mass ratio is 1:1. The reaction temperature is 600 °C. As shown in Fig. 4(a), the aromatic and olefin yields increased significantly with catalysts compared to sand as bed materials. Catalytic co-pyrolysis of PE and black-liquor lignin with LOSA-1 produced the maximum yields of aromatics and olefins of 29.9% and 14%, respectively. The main component of LOSA-1 is ZSM-5. The pore size of ZSM-5 is 0.5–0.6 nm which favors the production of olefins and aromatics (Cheng et al., 2012). LOSA-1 produced much more aromatics compared to olefins due to its special pore selectivity and acid activity. The total petrochemical yield for catalytic co-pyrolysis of black-liquor lignin and PE with LOSA-1 is 43.9% which is more than two times of that without catalyst. The catalyst performance is in the following sequence: LOSA-1 > spent FCC > Gamma-Al2O3. Although the performance of spent FCC is not as good as that of LOSA-1, the spent FCC catalyst as a waste of FCC unit is very cheap. Biomass pyrolysis vapors are active, thus FCC catalyst still has better catalytic characteristics for biomass pyrolysis process. Co-pyrolysis with sand presents the minimum yield of char and coke (most of them is char) of 22.1%. Catalytic co-pyrolysis with Gamma-Al2O3 produced the maximum yield of char and coke and the minimum yield of CO. The selectivity of aromatics shows co-pyrolysis with sand gives the biggest benzene selectivity, while co-pyrolysis with Gamma-Al2O3 offers the biggest selectivity of naphthalene and its derivatives.