Liquid-phase purification

While these techniques are widely used, they do not provide sufficient purity. Liquid phase purification is not an environmentally friendly process and requires corrosion-resistant equipment, as well as costly waste disposal processes. Alternative dry chemistry approaches, such as catalyst-assisted oxidation or ozone-eiuiched air oxidation, also require the use of aggressive substances or supplementary catalysts, which result in an additional contamination. Moreover, in many previous studies trial and error rather than insight and theory approaches have been applied. As a result, a lack of understanding and limited process control often lead to extensive sample losses of up to 90%. Because oxidation in air would be a controllable and enviromnentaUy friendly process, selective purification of carbon nanomaterials, such as CNT and ND, in air is very attractive. In contrast to current purification techniques, air oxidation does not require the use of toxic or aggressive chemicals, catalysts, or inhibitors and opens avenues for numerous new applications of carbon nanomaterials. 

The interest that had been aroused by the publicity given to the use of carbon in gas masks in World War I extended to liquid-phase purification, and workers in many industries began to explore possible benefits from the use of activated carbon. Considerable enthusiasm also developed in the direction of additional facilities for manufacturing activated carbon. As a result the period following World War I was marked by intense competition. Of the hundred or more brands of commercial carbon developed during that period, only a few remain. The quest for survival led to continual advancement in the quality of activated carbon. Within a space of twelve years, the process based on black-ash went through four major changes in method of manufacture. 

The flexibility of the batch-contact unit makes it adaptable for many varied industrial applications, and this adaptability has done much to extend the use of carbon. Until recently the batch-contact unit operation was employed in all liquid-phase purifications that require a decolorizing type carbon. 

Activated carbon is a very important industrial adsorbent because it exhibits a well developed porosity (micro, meso and macroporosity) and this is coupled with a great thermal and chemical stability, a relatively large hydrophobicity (thus favouring the adsorption of non-polar substances in the presence of humidity), low production cost, etc. Additionally, the surface of activated carbon can be functionalised with different heteroatoms (but mainly oxygen), thus modifying the chemical nature. A large and accessible surface area is a necessary but not sufficient condition for the preparation of activated carbons to be used in industrial adsorption processes (gas and liquid phase purification, separation, environmental control, etc.), since the last few years has shown that the chemical composition of the carbons surface plays a very important role in the process. 

In liquid-phase purification, the pnrity with respect to metal impnrities initially present in the mixtnre is improved simnltaneonsly with that with respect to nondiamond carbon. The content of impnrities of chrominm componnds introduced with the purification decreases in the alkaline treatment based on a better solubility of the amphoteric chromium compounds in a weak alkaline solntion rather than in an acid, and also by the treatment with ion-exchange resins (in particular, cation-exchange resins). 

Miblimation The volatilization of a solid substance into the vapour phase without passing through the liquid phase. Also used to describe the process of purification in which the vapour is condensed directly from the vapour phase to a solid (on a cold-finger often cooled by refrigerant). In the latter case this substance may melt during the initial vaporization. Used for purification. 

Liquid-phase oxidation of lower hydrocarbons has for many years been an important route to acetic acid [64-19-7]. In the United States, butane has been the preferred feedstock, whereas ia Europe naphtha has been used. Formic acid is a coproduct of such processes. Between 0.05 and 0.25 tons of formic acid are produced for every ton of acetic acid. The reaction product is a highly complex mixture, and a number of distillation steps are required to isolate the products and to recycle the iatermediates. The purification of the formic acid requires the use of a2eotropiag agents (24). Siace the early 1980s hydrocarbon oxidation routes to acetic acid have decliaed somewhat ia importance owiag to the development of the rhodium-cataly2ed route from CO and methanol (see Acetic acid). 

The following are some of the typical industrial applications for liquid-phase carbon adsorption. Generally liquid-phase carbon adsorbents are used to decolorize or purify liquids, solutions, and liquefiable materials such as waxes. Specific industrial applications include the decolorization of sugar syrups the removal of sulfurous, phenolic, and hydrocarbon contaminants from wastewater the purification of various aqueous solutions of acids, alkalies, amines, glycols, salts, gelatin, vinegar, fruit juices, pectin, glycerol, and alcoholic spirits dechlorination the removal of... 

Activated Carbon for Process Water Treatment Activated Carbon from CPL Carbon Link - Activated carbon from CPL Carbon Link for liquid and gas phase purification by adsorption. Activated carbons for all applications including chemical, water, air, solvent recovery, gold recovery, food, automotive, industrial, catalysis.. http //www.activated-carbon.com. 

From the pioneering studies of Ito et al. [117], CCC has been mainly used for the separation and purification of natural products, where it has found a large number of applications [114, 116, 118, 119]. Moreover, the potential of this technique for preparative purposes can be also applied to chiral separations. The resolution of enantiomers can be simply envisaged by addition of a chiral selector to the stationary liquid phase. The mixture of enantiomers would come into contact with this liquid CSP, and enantiodiscrimination might be achieved. However, as yet few examples have been described in the literature. 

The novel approach finally taken was to conduct the reaction and purification steps in a reactor-distillation column in which methyl acetate could be made with no additional purification steps and with no unconverted reactant streams. Since the reaction is reversible and equilibrium-limited, high conversion of one reactant can be achieved only with a large excess of the other. However, if the reacting mixture is allowed to flash, the conversion is increased by removal of the methyl acetate from the liquid phase. With the reactants flowing countercurrently in a sequence of... 

Aluminum sulfate, AI2 (804)3 > widely used in water purification to remove finely divided particulate matter. When added to water, aluminum sulfate forms a precipitate of aluminum hydroxide that has a very open structure and large surface area. This precipitate, called a gel, traps dispersed particulate matter as it settles out of the liquid phase. 

ESI-MS has emerged as a powerful technique for the characterization of biomolecules, and is the most versatile ionization technique in existence today. This highly sensitive and soft ionization technique allows mass spectrometric analysis of thermolabile, non-volatile, and polar compounds and produces intact ions from large and complex species in solution. In addition, it has the ability to introduce liquid samples to a mass detector with minimum manipulation. Volatile acids (such as formic acid and acetic acid) are often added to the mobile phase as well to protonate anthocyanins. A chromatogram with only the base peak for every mass spectrum provides more readily interpretable data because of fewer interference peaks. Cleaner mass spectra are achieved if anthocyanins are isolated from other phenolics by the use of C18 solid phase purification. - ... 

Other purification methods include a liquid phase chromatography, electrophoretic separation by mass spectroscopy, separation using magnetic properties, and so on. These separation methods are limited only for the metal nanoparticles having a special property useful for these purification methods. 

Wu and Sun have presented a versatile procedure for the liquid-phase synthesis of 1,2, ,4-tctrahydro-/i-carbolines [77]. After successful esterification of the MeO-PEG-OH utilized with Fmoc-protected tryptophan, one-pot cyclocondensations with various ketones and aldehydes were performed under microwave irradiation (Scheme 7.68). The desired products were released from the soluble support in good yields and high purity. The interest in this particular scaffold is due to the fact that the l,2,3,4-tetrahydro-/f-carboline pharmacophore is known to be an important structural element in several natural alkaloids, and that the template possesses multiple sites for combinatorial modifications. The microwave-assisted liquid-phase protocol furnished purer products than homogeneous protocols and product isolation/ purification was certainly simplified. 

Initiator, water or benzene may be added so as to keep the initiator constant. The gas and liquid phases are removed continuously, the polymer gets separated and the ethylene is recycled after purification. 

The amorphous phase is not usually a desirable state for the API because the formation process is more random and difficult to control than a crystallization. A second dispersed liquid phase is usually formed just prior to freezing and may coalesce or disperse under the influence of hydrodynamic forces in the crystallizer, making the process sensitive to micro-mixing effects on scale up. Amorphous solids also have significantly lower thermodynamic stability than related crystalline material and may subsequently crystallize during formulation and storage. Because of the non-uniformity of the amorphous solid it can more easily incorporate molecules other than the API, making purification less effective. 

Volatile substances of which the vapours, on cooling, condense directly to crystals without passing through the liquid phase are sometimes advantageously purified by sublimation, particularly when solubility relations render recrystallisation difficult. The purification of iodine is a well-known case in point. In organic chemistry this process is particularly suitable for quinones. 

Industrial examples of adsorbent separations shown above are examples of bulk separation into two products. The basic principles behind trace impurity removal or purification by liquid phase adsorption are similar to the principles of bulk liquid phase adsorption in that both systems involve the interaction between the adsorbate (removed species) and the adsorbent. However, the interaction for bulk liquid separation involves more physical adsorption, while the trace impurity removal often involves chemical adsorption. The formation and breakages of the bonds between the adsorbate and adsorbent in bulk liquid adsorption is weak and reversible. This is indicated by the heat of adsorption which is <2-3 times the latent heat of evaporahon. This allows desorption or recovery of the adsorbate from the adsorbent after the adsorption step. The adsorbent selectivity between the two adsorbates to be separated can be as low as 1.2 for bulk Uquid adsorptive separation. In contrast, with trace impurity removal, the formation and breakages of the bonds between the adsorbate and the adsorbent is strong and occasionally irreversible because the heat of adsorption is >2-3 times the latent heat of evaporation. The adsorbent selectivity between the impurities to be removed and the bulk components in the feed is usually several times higher than the adsorbent selectivity for bulk Uquid adsorptive separation. 

Since the Sorbex process is a liquid-phase fixed-bed process, the selection of particle size is an important consideration for pressure drop and process hydraulics. The exact particle size is optimized for each particular Molex process to balance the liquid phase diffusion rates and adsorbent bed frictional pressure drop. The Sorbex process consists of a finite number of interconnected adsorbent beds. These beds are allocated between the following four Sorbex zones zone 1 is identified as the adsorption zone, zone 2 is identified as the purification zone, zone 3 is identified as the desorption and zone 4 is identified as the buffer zone. The total number of beds and their allocation between the different Sorbex zones is dependent on the desired performance of the particular Molex process. Molex process performance is defined by two parameters extract normal paraffin purity and degree of normal paraffin recovery from the corresponding feedstock. Details about the zone and the bed allocations for each Molex process are covered in subsequent discussions about each process. 

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