Energy-Saving-Targeted Solar Photothermal Dehydration and Confined Catalytic Pyrolysis of Oily Sludge Using Wood Sponge Loaded with Carbon Dots

Pyrolysis of oily sludge (OS) faces two significant challenges, dehydration in emulsion and coke formation, which cause extra energy consumption. Targeting energy saving, this paper first reported on solar photothermal dehydration and confined catalytic pyrolysis of OS using a single material. A wood sponge loaded with carbon dots (CM-CDs) can generate heat by absorbing solar energy and promote rapid phase separation and water transport via capillary action of oil–water emulsion in OS under sunlight. Almost all free water in OS with varied content can be removed after 3 h. Hydrocarbons entered the internal space of CM-CDs instead of contacting with soil minerals, contributed to the subsequent confined catalytic pyrolysis, led to a reduction in Ea (35.61 kJ/mol), inhibited coking and caking, and yielded higher oil recovery efficiency. In addition, CDs can form hotspots to enhance pyrolytic behaviors in local regions. When the ratio of OS to CM-CDs reached 10:0.6, the recovery rate of the oil fraction through combined pyrolysis was as high as 89%, which was 17% higher than that of OS pyrolysis alone. This discovery provides a new way to solve the bottleneck problems of OS pyrolysis in the industry.