Energy density enhancement via pyrolysis of paper mill sludge using CO₂

Paper manufacture is a very energy-intensive industry and generates a large amount of waste such as paper mill sludge (PMS). Given that the current PMS disposal ways (e.g., incineration and landfilling) are not eco-friendly and costly, establishing an appropriate PMS disposal platform including energy recovery is crucial to making more environmentally benign and economically viable industrial paper manufacturing process. In this respect, this study places a great emphasis on investigating the influence of CO₂ on pyrolysis of PMS by systematical analysis of major three-phase pyrolytic products, such as gases and tar, under N2 and CO₂ atmospheres. It was validated that using CO₂ as a reaction medium in pyrolysis of PMS not only increased the production of CO (a major constituent of syngas) by ∼1000% but also decreased the amount of tar by 23%. The increase in CO production and decrease in tar formation likely resulted from reactions between CO₂ and volatile organic compounds (VOCs) generated from thermal decomposition of PMS, which could be expedited by catalytic effects of minerals contained in PMS. The results shown in this paper could be applied to design green paper manufacturing processes efficiently utilizing a potent greenhouse gas, CO₂. Copyright © 2017 Elsevier B.V.