Forced-flow leaching

Forced-flow leaching. 74 3.4.6 Pressurised fluid extraction. 117... 

In liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently... 

Applications Mangani el al. [169] introduced forced-flow leaching for the direct extraction with hot toluene (at 100 °C) of low-MW PAHs from ashes. The method does not appear to have been used for poly-mer/additive analysis. 

Forced-flow leaching is an extraction technique that can provide a nearly quantitative recovery of many organic compounds. In this technique, the sample of interest is packed into a 20 cm x 4 mm stainless steel column. An extraction solvent is pumped under a gas pressure of 2.5 kg/cm through the column, which is heated close to the solvent s boding point. The results are comparable to Soxhlet extraction, but the extraction time is reduced from 24 to 0.5 hr using the forced-flow technique. An advantage of this method is that the sample is subjected continuously to fresh, hot solvent, and the effluent from the column can be collected easUy for further treatment. 

Principles and Characteristics Less well-characterised extraction methods include solvent leaching at high temperature with forced-solvent flow. In the... 

In some solid-bed leaching the solvent is volatile, necessitating the use of closed vessels operated under pressure. Pressure is also needed to force solvent through beds of some less permeable solids. A series of such pressure tanks operated with countercurrent solvent flow is known as a diffusion battery. 

There are two primary problems associated with the use of ILMs. Solvent loss can occur. This loss is caused by evaporation, dissolution, or large pressure differences forcing solvent out of the pore support structure. Also, carrier loss can occur. This loss can be due to irreversible side reactions or solvent condensation on one side of the membrane. Pressure differences can force the liquid to flow through the pore structure and leach out the carrier. 

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