Extraction processes liquid-solid

EXTRACTION I Liquid-Solid). Many substances used in modem processing industries occur in a mixture of components dispersed through a solid material, To separate the desired solute constituent or to remove an unwanted component from the solid phase, the solid is contacted with a liquid phase in Ihe process called liquid-solid extraction, or simply leaching In leaching, when an undesirable component is removed from a solid with water, the process is called washing. 

Sample preparation represents a formidable challenge in the chemical analysis of the real-world samples. Not only is the majority of total analysis time spent in sample preparation, but also it is the most error-prone, least glamorous, and the most labor-intensive task in the laboratory. The components to be separated from the matrix are usually taken up with an auxiliary substance such as a carrier gas, an organic solvent, or an adsorbent. These separation processes can be regarded as extraction procedures [i.e., liquid-liquid extraction (LLE), liquid-solid extraction (LSE), Soxhlet extraction (SE), solid-phase extraction (SPE), supercritical fluid extraction (SEE), solid-phase microextraction (SPME), etc.]. 

The solid samples must be air-dried, frozen, sometimes with liquid nitrogen or freeze-dried [9-12], to remove the moisture that can significantly influence the extraction process. To improve the extraction process, the solid must be grounded and reduced to small particles to increase the contact surface between the raw material and the solvent and to reduce the extraction time because, theoretically, extraction time varies inversely with the square of the characteristic dimension of the solid particles. 

See Liquid-solid Metallurgy, extractive Mineral recovery and processing. 

Figure 1.9. Modelling concepts for the packed bed solid-liquid extraction. Process of coffee percolation.

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... 

The most common (off-line) sample preparation procedures after protein precipitation are solid phase extraction and liquid-liquid extraction. Multiple vendors and available chemistries utilize 96-well plates for solid phase extraction systems and liquid-liquid extraction procedures. Both extraction process can prepare samples for HPLC/MS/MS assay. Jemal et al.110 compared liquid-liquid extraction in a 96-well plate to semi-automated solid phase extraction in a 96-well plate for a carboxylic acid containing analyte in a human plasma matrix and reported that both clean-up procedures worked well. Yang et al.111 112 described two validated methods for compounds in plasma using semi-automated 96-well plate solid phase extraction procedures. Zimmer et al.113 compared solid phase extraction and liquid-liquid extraction to a turbulent flow chromatography clean-up for two test compounds in plasma all three clean-up approaches led to HPLC/MS/MS assays that met GLP requirements. 

Due to the predicted and previously detected low concentrations of pesticides in environmental samples (usually around the nanogram per liter level), a preconcentration step of the water samples is necessary prior to measurement. In this way, a preconcentration factor of several orders of magnitude (200-1,000-fold) is mandatory to reach the low detection limits necessary for the identification of pesticides, especially in complex wastewater samples. Also, the use of surrogate standards (e.g., triphenyl phosphate) added before the extraction step is a common practice in order to account for possible errors during the extraction process and for quantitative purposes. The commonly used extraction methods for polar compounds from water matrices involve isolation using liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which are commented on below. Other methods such as semipermeable membrane devices (SPMD) are also mentioned. 

Chemical separations are often either a question of equilibrium established in two immiscible phases across the contact between the two phases. In the case of true distillation, the equilibrium is established in the reflux process where the condensed material returning to the pot is in contact with the vapor rising from the pot. It is a gas-liquid interface. In an extraction, the equilibrium is established by motion of the solute molecules across the interface between the immiscible layers. It is a liquid-liquid, interface. If one adds a finely divided solid to a liquid phase and molecules are then distributed in equilibrium between the solid surface and the liquid, it is a liquid-solid interface (Table 1). 

This model of liquid extraction is symmetrical to fractional crystallization and has attracted renewed interest after the demonstration by Johnson et al. (1990) that REE distributions in abyssal peridotite clinopyroxene cannot be accounted for by equilibrium melting processes. The solid is supposed to maintain its chemical homogeneity while liquid is continuously extracted. Only the last drop of liquid is supposed to be in equilibrium with the residue. 

Mangani et al. [13] used Carbopack B columns to recover chlorinated insecticides in soil samples. These workers noted that, although the principles governing the adsorption and extraction process in the extraction in soil analysis are the same as those that govern liquid-solid chromatography, the main feature of a chromatographic column, i.e. separation efficiency, is almost completely absent. 

In simple experiments, particulate silica-supported CSPs having various cin-chonan carbamate selectors immobilized to the surface were employed in an enantioselective liquid-solid batch extraction process for the enantioselective enrichment of the weak binding enantiomer of amino acid derivatives in the liquid phase (methanol-0.1M ammonium acetate buffer pH 6) and the stronger binding enantiomer in the solid phase [64]. For example, when a CSP with the 6>-9-(tcrt-butylcarbamoyl)-6 -neopentoxy-cinchonidine selector was employed at an about 10-fold molar excess as related to the DNB-Leu selectand which was dissolved as a racemate in the liquid phase specified earlier, an enantiomeric excess of 89% could be measured in the supernatant after a single extraction step (i.e., a single equilibration step). This corresponds to an enantioselectivity factor of 17.7 (a-value in HPLC amounted to 31.7). Such a batch extraction method could serve as enrichment technique in hybrid processes such as in combination with, for example, crystallization. In the presented study, it was however used for screening of the enantiomer separation power of a series of CSPs. 

In liquid phase adsorption, some particular components of the feed steam are selectively adsorbed or extracted by a solid zeoUtic adsorbent. At the same time, other components of the feed stream are rejected by the adsorbent. At equilibrium, the liquid composition within the zeolite pores differs from that of the liquid surrounding the zeolite. In the process, a second liquid component, the desorbent, is also introduced into the system. The function of the desorbent is to desorb and recover the extracted feed components from the adsorbent In order for the desorbent to perform well in the process, a suitable interactive force between the desorbent and the extracted components to the adsorbent is required. If the selectivity is too high, it requires high desorbent volume to desorb the extracted components from the adsorbent. If the selectivity is too low, the desorbent tends to compete with extracted components for capacity of adsorbent. 

The three main separation processes between solid, gas, and liquid have long been known, while solvent extraction is a relatively new separation technique, as is described in the brief historical review in next two sections. Nevertheless, because all solutes (organic as well as inorganic) can be made more or less soluble in aqueous and organic phases, the number of applications of solvent extraction is almost limitless. Since large-scale industrial solvent extraction is a continnons process (in contrast to laboratory batch processes) and can be... 

Many industrial processes begin with a leaching step, yielding a slurry that must be clarified before solvent extraction. The solid-liquid separation is a costly step. The solvent extraction of unclarified liquids ( solvent-in-pulp ) has been proposed to eliminate solid-liquid separation. The increased revenue and reduced energy cost make this an attractive process, but many problems remain to be solved loss of metals and extractants to the solid phase, optimization of equipment design, effluent disposal, etc. 

A butoxylcarbonylation reaction was conducted in a liquid-liquid biphasic system under process conditions, but the removal of the product was conducted in a liquid-solid biphasic system at a lower temperature (84). lodobenzene or 4-bromoacetophenone reacted with CO at a pressure of 1-8 atm in the presence of a palladium-benzothiazole complex catalyst in the ionic liquid [TBA]Br (m.p. = 110°C) in the presence of Et3N base. The catalyst/ionic liquid system was recycled by extractive removal of the butyl ester product with diethyl ether. The solid residue, containing the catalyst, [TBA]Br, and Et3N.HBr, remained effective in subsequent carbonylation tests. After each cycle, the yields were still close to the initial value. A slight decrease in yield was attributed to a loss of catalyst during handling. 

The Biothemi Process uses the patented C-G Process approach for drying and solvent extraction to separate oil-soluble contaminants from liquid, solid, or slurry wastes. The C-G Process has been used extensively over the last 30 years to dry and extract compounds from a variety of wet, oily solids (D105453, pp. 1, 23). The C-G Process has been evaluated on the demonstration level by the U. S. Environmental Protection Agency (EPA) for treating petroleum-contaminated drilling mud from a Superfund site. 

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