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Flame Retardants: Analytical Aspect of Brominated Flame Retardants
Published in Narendra Kumar, Vertika Shukla, Persistent Organic Pollutants in the Environment, 2021
Devendra Kumar Patel, Sandeep Kumar, Neha Gupta
Supercritical fluid extraction extracts the chemical compound from the matrices using supercritical carbon dioxide, which means it is in a stage between the gas and liquid phases. The supercritical phase is reached when a gas is heated to its critical temperature at its critical pressure. The solubility and selectivity for samples can be manipulated by changing the temperature and pressure. Samples are placed in an extraction vessel which is pressurized with carbon dioxide. The extraction vessel is then transferred into the fraction collector and the pressure is released. On depressurizing, carbon dioxide loses its solubility, which precipitates the desired material. The condensed carbon dioxide can be recycled, which makes the technique economical and environmentally friendly. PBDEs and PBBs, along with polychlorinated biphenyls (PCBs) and chlorinated benzenes, are extracted using solid-phase trapping (with carbon dioxide as the supercritical fluid) from sediment samples (Hartonen et al., 1997), which are mixed with copper powder and sodium sulfate before extraction for drying. The extraction efficiency can be enhanced using carbon dioxide and modifiers like methanol, diethyl amine, and acetone. The extract obtained is much cleaner for direct injection into the instrument, so the cleanup step can be avoided. The extraction efficiency of supercritical fluid extraction for PBDEs from plastic is more than 97% (Peng et al., 2014). Efficiency can be further enhanced by modifiers such as tetrahydrofuran, toluene, and acetonitrile (Altwaiq et al., 2003).
Sample Preparation Techniques
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
Explain why two smaller volume solvent extractions may be more efficient at removing an organic compound from water than one larger volume one.Why is a different apparatus needed for continuous extraction of a pesticide from water when the solvent is changed from methylene chloride to hexane.What are some of the advantages of supercritical fluid extraction over liquid solvent extraction.What are the two main purposes for the use of chelating agents in the preparation of aqueous samples for metal determinations?A sample of water contaminated with pesticide is extracted with methylene chloride for determination of the pesticide. In experiments with a standard solution, it is found that when a 100 mL water sample is extracted with 30 mL of methylene chloride, 75% of the pesticide is removed. What fraction of the pesticide would be removed if three extractions of 10 mL of methylene chloride each were done instead?LLE has long been a standard method for removing and concentrating organic compounds such as pesticides from water. Newer methods such as SPE are replacing LLE. Compare the two methods, discussing the advantages and disadvantages of each method.
Recovery of Precious Metals Using Precipitation, Adsorption, Electrowinning, Supercritical Fluids and Bio-mediated Approaches
Published in Sadia Ilyas, Hyunjung Kim, Rajiv Ranjan Srivastava, Sustainable Urban Mining of Precious Metals, 2021
Sadia Ilyas, Muhammad Ahmad Muhsan, Hyunjung Kim, Rajiv Ranjan Srivastava
Supercritical fluid extraction is a simple process, with good selectivity and low energy consumption. Supercritical fluids have low surface tension, are less toxic than other solvents, and are easily recycled. They are used in wide variety of reactions (Laintz et al., 1992; Eckert et al., 1996; Phelps et al., 1996). At controlled temperature and pressure, metal ions can be easily leached and efficiently extracted from supercritical fluids according to their size, boiling point, polarity, and molecular weight.
Large scale strategy for the extraction of oil from sesame seed: scalable approach
Published in Indian Chemical Engineer, 2023
Jayeshkumar S. Mevada, Yogeshsing N. Rajput, Shaziya Chowdhary, Shirley Kokane, Faith Dias, Ranjeet B. Doke, Ravindra D. Kulkarni, Amit P. Pratap, Aniruddha B. Pandit
In supercritical fluid extraction, it is difficult to maintain the lower temperature and high pressure throughout the process, giving rise to challenges against its scalability and feasibility issues. They have also not reported any significant rise in extraction efficiency compared to conventional methods [20]. In such conditions, ultrasound extraction has shown to be a much more effective extraction technology due to its very low time of operation and higher extraction yield. The cavitation phenomena involve nucleation, bubble growth, and bubble implosion, which results in the massive release of energy in the form of high pressure (100–5,000 bars) and temperature (1,000–10,000 K). Depending on the mode of generation, cavitation is generally classified into four types such as acoustic, hydrodynamic, optic, and particle cavitation. Among these, acoustic cavitation and hydrodynamic cavitation (HC) is widely used for cell disruption and process intensification for physical, chemical and biological processes [21]. The major challenge associated with ultrasound-assisted extraction is the energy consumption; hence it is not scalable. But certain advantages such as preservation of the nutritional quality, reduced processing time, and increased extraction efficiency make the cavitation process promising for large-scale operation [22–25]. The challenges associated with the higher energy requirement required bring prime focus on the scale-up of the process.
Mathematical modeling of supercritical CO2 extraction of Eugenia pyriformis Cambess. leaves
Published in Chemical Engineering Communications, 2021
Elissandro Jair Klein, Gracielle Johann, Edson Antônio da Silva, Melissa Gurgel Adeodato Vieira
Interest in the research and development of appropriate extraction methods has grown due to the wide range of potential applications of bioactive compounds occurring in natural sources. Extraction by hydrodistillation, maceration, and Soxhlet extractor are conventional extraction methods (Chemat et al. 2017). In contrast, unconventional extraction methods have been studied and developed to reduce the use of organic solvents, operational time, and improve the yields and quality of the obtained extracts (Azmir et al. 2013). Supercritical fluid extraction is as an interesting alternative because it exhibits characteristics that overcome the limitations of conventional extraction techniques, as it is a green extraction technology and can achieve better efficiency with reduced environmental impact (da Silva et al. 2016).
Valorization of selected fruit and vegetable wastes as bioactive compounds: Opportunities and challenges
Published in Critical Reviews in Environmental Science and Technology, 2020
Nerea Jiménez-Moreno, Irene Esparza, Fernando Bimbela, Luis M. Gandía, Carmen Ancín-Azpilicueta
The method followed for extracting bioactive compounds and nutraceuticals from FVW largely conditions the yield and selectivity obtained and thus production costs. In this review, the main conventional and emerging technologies available for obtaining these valuable products have been presented. Conventional techniques such as Soxhlet extraction, maceration, and hydrodistillation are well established but suffer from low extraction rates and selectivity as well as relatively high-energy costs associated to solvent evaporation for recovery and recycle. Alternative technologies such as MAE, ultrasound-assisted extraction, supercritical fluid extraction, pulsed electric field extraction, enzyme-assisted extraction, and PLE provide, in general, higher yields and selectivities compared to the conventional methods and they are well suited for extracting thermolabile compounds. However, the best developed one (i.e. supercritical fluid extraction) requires high investment and operating costs, whereas the remaining technologies are still immature and have difficulties for reaching the full industrial scale. Further research and development in this field is required in the short term to guarantee suitable progress in FVW valorization.