Preparation for industrial pellet production from blends of eucalyptus sawdust and hydrolysis lignin: the optimal variable combinations of co-pelletization

The technology of co-pelletization was adopted to improve the performance of eucalyptus sawdust pellets, and hydrolysis lignin was treated as an effective binder. The main objective of this work was to obtain the optimal variable combinations of co-pelletization for preparation of industrial production. Response surface methodology using a central composite design with five-factor and five-level was employed to design and obtain the optimal variable combinations. Single pellet-making experiments were carried out using a uniaxial piston-cylinder densification apparatus. The effect of variables on responses was analyzed in detail. The selected optimal models for responses are all modified quadratic expressed in the form of regression equations. By setting the desired values of the responses, the optimized variable combinations are 26% hydrolysis lignin adding amount, 11% moisture content, 107-°C temperature, 5500-N pressure, and 3-mm particle size. The validation experiments were performed using the same apparatus according to the optimal variable combinations, and the response values are 24.83 kJ kg⁻¹ for specific energy consumption, 1048.91 kg m⁻³ for relaxed density, and 31.44 N mm⁻² for Meyer hardness. The relative percentage errors between the response predicted values and validation experiment results are all less than 10%.