Study on the synergistic effect during co-pyrolysis of chlorella and polyvinyl chloride: Thermal behavior, kinetic and thermodynamic analysis

Chlorella vulgaris (CV), polyvinyl chloride (PVC) and their mixtures (1:3, 1:1 and 3:1) were used as the feedstock of co-pyrolysis experiments on thermogravimetric (TG) analyzer and tube furnace respectively, to investigated their synergistic effects. The TG curves indicate that the decomposition of mixtures can be divided into five stages. Among them, the decompositions of carbohydrate and protein in CV showed obvious synergistic effect with the dechlorination of PVC in the second and third stages of co-pyrolysis reaction (IIM and IIIM), while the coating effect of PVC on CV can inhibit the pyrolysis process in the four and five stages (IVM and VM). The kinetic and thermodynamic parameters also show that there is synergistic effect between CV and PVC. For example, the average activation energies of mixtures are all lower than the theoretical values in the stage IIM and IIIM, with CV1PVC3 having the maximum synergistic effect (average activation energy is 165.6 kJ/mol, 30.3 % less than the theoretical value). In addition, the average Delta H (162.9 kJ/mol) of CV1PVC3 also decrease by 29.6 % compared with the theoretical values. The fast pyrolysis experiments show that the co-pyrolysis of CV and PVC can improve the bio-oil yields, increase the proportion of monocyclic aromatics, and inhibit the production of nitrogen heterocyclic compounds. Therefore, a possible reaction network was proposed based on the synergistic effect of the CV and PVC in co-pyrolysis.