Influence of acid and thermal treatment on regeneration of spent bleaching clay and conversion of residual oil to biodiesel

Spent bleaching clay (SBC) is a hazardous waste produced by vegetable oil refining industries. SBC contains a residual oil (RO) with a lot of organic and inorganic impurities and its disposal leads to severe environmental consequences. In this study, SBC regeneration by extraction, acid modification and pyrolysis under various conditions and biodiesel production were studied. The GC-MS of the extracted RO shows that the fatty acid content is in conformity with crude oil and is appropriate for biodiesel production. FTIR was recorded in order to evaluate the main functional groups of fresh-, spent-, regenerated bleaching clay. The specific surface area (SSA) of fresh bleaching clay (FBC) (166.1 ± 1.7 m²/g) was lower than regenerated bleaching clay (RBC) one. The highest SSA (252.1 ± 1.7 m²/g) was revealed by pyrolysis at 550°C and activation with 10% sulfuric acid. Subsequent increase in the acid concentration and temperature of pyrolysis caused a decrease in the SSA. The heavy metals concentration in RBC was lower than the limits for activated bleaching clay in the National Food Safety Standard. Hence, RBC effectively copes with heavy metal removal. The peroxide, anisidine, acid values and oxidation stability of oil bleached with RBC are comparable to the FBC.Implications: The disposal of spent bleaching clay from vegetable oil refining industries has been recognized as a significant environmental issue. After adsorbing the impurities, spent bleaching clay becomes contaminated with a high concentration of organic and inorganic substances, including residual oils, fatty acids, phospholipids, and potentially toxic heavy metals. This makes spent bleaching clay a hazardous waste and improper disposal can lead to severe environmental consequences. Due to the potential environmental harm caused by spent bleaching clay disposal, it is crucial for vegetable oil refining industries to adopt proper waste management practices. Overall, the proper management and disposal of spent bleaching clay is essential to prevent environmental contamination and safeguard human health.