Co-pyrolysis of microalgae, sludge and lignocellulosic biomass for aromatic hydrocarbon production

Abstract

Co-pyrolysis, where a mixture of two or more different biomasses are subjected to pyrolysis, has gained attention over the years. Many studies have revealed that it leads to bio-oil production with desirable properties like reduced moisture content and enhanced caloric value. In the present study, blends of cedar wood (CW), algal biomass (AB), and digested sludge (DS) were subjected to co-pyrolysis in presence and absence of the catalyst ZSM-5. Differential Scanning Calorimetry (DSC) analysis was carried out for 18 different combinations of these biomasses to assess the total activation energy (Ea), change in enthalpy (ΔH), and change in Gibb’s free energy (ΔG) for these blends. The lowest value of Ea (87.28 kJ/mol) and ΔH (80.49 kJ/mol) were obtained for the 2:1 wt/wt catalyst to 1:1:1 wt/wt biomass blend of CW: AB: DS with ΔG value of 207.62 kJ/mol.

Statistical analysis of the DSC data resulted in significant response surface models (RSM) for Ea and ΔH, but could not model ΔG well. Additionally, it has demonstrated that the catalyst addition to blends reduced the energy requirement for pyrolysis. Therefore, based on the RSM models for Ea and ΔH, 2:1 wt/wt blend of ZSM– 5 to biomass: 57.14 wt % DS, 4.29 wt % AB and 38.57 wt % CW was chosen as the optimum combination (OC). The 2:1 wt/wt ZSM–5: biomass blend containing equal weight fractions of three biomasses produced a bio-oil with the highest aromatic hydrocarbon yield of 89.38 wt %. The aromatic hydrocarbon content of 83.12 wt % was obtained in the bio-oil produced from pyrolysis of OC. Naphthalene, anthracene and their methyl derivatives were the main aromatic hydrocarbons in the bio-oil.

ASPEN PLUS simulation of the AB, DS and CW co-pyrolysis system confirmed the findings obtained with the DSC experiments indicating that co-pyrolysis can reduce energy requirement and allowed both mass and energy balance calculations for the process.