A recent article published in the journal Cleaner engineering and technology exhausted bleaching earth studied as an energy source while taking into account the economic viability of the various conversion methods. While previous studies suggest that SBE could be used in its solid form as a fuel, its high ash content and residual waste would still present some of the same SBE waste problems.
To study: Economic analysis of waste minimization and energy recovery from spent bleaching earth, cleaner engineering and technologythere. Image Credit: Low, A et al., Cleaner Engineering and Technology.
Spent bleaching earth (SBE) is a solid waste resulting from the bleaching process in the edible oil industry. Typically, this solid waste is disposed of directly in landfills without treatment, causing severe water and air pollution. SBE is the largest contributor to solid waste produced in edible oil refining processes.
Bleaching earths are typically used throughout the process of refining vegetable oils and animal fats to make them fit for human consumption. This compound is categorized as “montmorillonite,” which is a powdered form of clay known for its absorbency.
By removing impurities and unwanted materials, including soaps, proteins, coloring substances, etc., bleaching earth becomes unstable and tends to explode or burn easily. Therefore, not only is spent bleaching earth considered an environmental pollutant, it is classified as hazardous waste and therefore there is a lot of guesswork on how to dispose/reuse this volatile waste by-product. .
Extraction of residual oils for use as fuel is probably the most economically attractive option, as oil-free SBE could potentially be reclaimed and recycled in the oil bleaching process.
Rashid Shamsuddin, Department of Chemical Engineering, Teknologi Petronas University, Malaysia
Although the properties of SBE vary depending on its source and the type of oil it has been used to process, it generally contains high concentrations of residual oil. This residual oil could be considered a useful resource and is attracting the attention of researchers who wish to make the use of bleaching earth a more sustainable practice in the edible oil refining industry.
“The use of SBE or the residual oil in SBE for the production of biodiesel, biofertilizers, combustible briquettes and unfired wall tiles could reduce the waste generated by the edible oil refining industry and improve its sustainability. ,says Shamsuddin.
Extraction of residual oils
To recover the energy of the residual oils contained in the used bleaching earth, different methods were analyzed by the team. Among these, they assessed the potential for using the extracted oil as fuel converted to biodiesel.
Biodiesel could be used for power generation and presents an economically attractive option as oil-free SBE can also be reused later in petroleum refining processes, which in the long run creates better sustainability practices. .
Among the oil extraction options for conversion to biodiesel are pressure treatments using carbon dioxide or water, steam extraction, and solvent extraction:”Regenerated bleaching earth reported bleaching efficiencies between 90-100% compared to virgin bleaching earth,” said Shamsuddin.
Among the various extraction methods, the most economically viable was the use of solvents such as methanol, acetone and hexane. To extract the oil, the solvent is introduced into the SBE in a mixing tank and filtered to separate the oil-containing solvent mixture from the deoiled SBE.
The oil is then extracted from the solvent by distillation, and the solvent can then be reused. However, one of the main disadvantages of this process is that the solvents are also considered hazardous materials and are difficult to work with.
Yet, despite the hazardous nature of the solvents, separating oil from the solvent mixture by distillation shows promise if scaled up enough, as it is believed to be an efficient process.
While the researchers explain their methods in detail in the article, they reveal that acetone extraction was considered the most suitable for extracting residual oils from spent bleaching earth compared to hot water and in methanol. The process minimized waste and demonstrated good energy recovery.
The researchers also indicate that for the process to be economically viable, the operation must be carried out on a large scale, as the process might not justify the costs of an individual edible oil processing facility. “If larger quantities of SBE were generated or if a centralized dedicated facility was built to manage SBE from multiple facilities, this process could become more economically viable,” explains Shamsuddin.
Therefore, while it is possible to recover contaminated oil from spent bleaching earth to convert it into biofuels, more work and research is needed to make the process suitable for smaller scale operations or to provide solutions. alternatives such as centralized facilities to make it economically viable. .
Low, A., Shamsuddin, R., Siyal, AA, Economic Analysis of Waste Minimization and Energy Recovery from Spent Bleaching Earth, Cleaner Engineering and Technology (2022), doi: https:// www.sciencedirect.com/science/article/pii/S2666790822000234?via%3Dihub