Co-pyrolysis between microalgae and textile dyeing sludge by TG–FTIR: Kinetics and products

• The pyrolysis of textile dyeing sludge could be improved by blending microalgae.
• There existed synergistic interaction between microalgae and textile dyeing sludge.
• The yields of gaseous products did not monotonically change by blending microalgae.
• The low average activation energy was obtained by blending 80% microalgae.
• The high yield of desired products was obtained by blending 80% microalgae.

In this work, the kinetic behavior and evolution characteristics of the gaseous products of microalgae (MA) and textile dyeing sludge (TDS) blends during co-pyrolysis were investigated using TG–FTIR. The TDS was blended with MA in the range of 10–90 wt.%, and then heated from 105 °C to 900 °C at 10, 20 and 40 °C/min under N2 atmosphere with a flow rate of 80 ml/min. The initial decomposition temperature of TDS was lower than MA, but the pyrolysis intensity of MA was higher than TDS. The co-pyrolysis of MA and TDS could avoid the drawbacks with each other and improve their pyrolysis performance. The synergistic interaction between MA and TDS was mainly due to the flowing and sticky bio-oil and alkali metals catalytic effect. Two iso-conversional methods of Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS) were used to calculate the activation energy, and low average activation energy was obtained when the blending ratio of MA was 80%. CO2, H2O, CH4, CO, HNCO, NH3, HCN, SO2, CH, CO and CO groups were the main gaseous products observed from the FTIR spectrums during co-pyrolysis. The origin of CO2, H2O, CH4, CO, HNCO, NH3, HCN, SO2, CH, CO and CO groups was analyzed combined with the decomposition order of the components in MA and TDS. The evolution of the gaseous products was consistent with the weight loss of the blends during co-pyrolysis. The yields of CO2, CH, CO, CO, CO, HNCO, NH3, HCN and SO2 did not monotonically change with the increasing blending ratio of MA, attributed to the synergistic interaction between MA and TDS. The blending ratio of MA reached 80% would obtain the highest yield of desired products. In order to get the low average activation energy and more desired products, the potential global optimum blending ratio of MA for co-pyrolysis of the blends was 80%.