Extraction/impurity removal

Solvent extraction—purification of wet-process phosphoric acid is based on preferential extraction of H PO by an organic solvent vs the cationic impurities present in the acid. Because selectivity of acid over anionic impurities is usually not sufficient, precipitation or evaporation steps are included in the purification process for removal. Cmde wet-process acid is typically concentrated and clarified prior to extraction to remove post-precipitated sludge and improve partition of the acid into the solvent. Concentration also partially eliminates fluoride by evaporation of HF and/or SiF. Chemical precipitation of sulfate (as Ba or Ca salts), fluorosiUcates (as Na salt), and arsenic (as sulfides) may also be used as a prepurification step preceding solvent extraction. 

EDC from the oxychlorination process is less pure than EDC from direct chlorination and requires purification by distillation. It is usually first washed with water and then with caustic solution to remove chloral and other water-extractable impurities (103). Subsequently, water and low boiling impurities are taken overhead in a first (light ends or heads) distillation column, and finally, pure, dry EDC is taken overhead in a second (heavy ends or product) column (see Fig. 2). 

OSL Impurities. It was also of interest to determine the impurities removed from crude OSL by reslurry in aqueous sodium bicarbonate, which was done to improve its usefulness in phenolic resins (Cook, P. M., Eastman Kodak at Kingsport, TN, personal communications, 1987). Extraction and acetylation procedures, involving methylene chloride, acetic anhydride pyridine... 

Materials. To satisfy the requirements for models for pyrolysis studies, it was necessary to select compounds that were of high purity and well-defined structure which would produce carbonaceous residues when subjected to high temperatures. Commercially available organic dyestuffs proved to be a ready source of model compounds containing various heterocyclic structures. It was necessary to purify these dyes by recrystallization and extraction to remove small quantities of organic impurities and residual inorganic contaminants. The identity, structure, and chemical composition of the model compounds can be seen in Table I and Figure 1. 

This purification step is designed to remove impurities from the proanthocyanidin extract. It utilizes liquid-liquid extraction to remove lipophilic material and monomeric flavan-3-ols, and also adsorption chromatography to remove more hydrophilic material such as organic acids, sugars, and residual flavan-3-ol monomers. Following the steps in this protocol, purified and powdered proanthocyanidins are obtained. 

Depending on the impurities that are present, perform liquid-liquid extraction of the aqueous proanthocyanidin extract to remove impurities with different solubility properties. 

Various procedures for the purification of specific amine-boranes have been reported.12 Ethylenediamine-bisborane can be purified conveniently by aqueous extraction to remove water-soluble impurities. The crude product obtained from the tetrahydrofuran solution is ground to a fine powder in a mortar and added in small portions, with stirring, to about 75 ml. of water which has been cooled in an ice-water bath. Foaming may occur during this treatment. The white crystalline solid which does not dissolve is collected by filtration through a coarse-fritted-glass funnel and washed several times with small portions of cold water (about 5°C.). The final wash filtrate should be neutral toward pH paper. The product is dried by... 

Residual amounts of extracted impurities are removed from the loaded extractant by 7M HNOn washing. Three to five contacts are made using an A/0 = 0.2. Tne wash is either sent to feed acid adjustment or discarded depending upon americium content. 

Frozen or chilled to remove most of the co-extracted impurities. 

Frozen or chilled to remove most of the co-extracted impurities. 3 Linear gradient from 80 20 to 50 50 in 10 minutes. 

It has been found that catalytic naphthas contain about ten times as much cresylic acid as do thermal naphthas (32). The cresylic acid may easily be recovered by treatment with dilute caustic soda to give a product containing 20% phenol, 25% xylenols, 45% cresols, and 10% impurities. Removal of sulfur from this extract to give marketable cresylic acid is a problem, being solved by air blowing, partial neutralization, distillation, or a combination thereof. 

Non-Metallic Impurities Viscosity index (VI) improvers or polychlorinated biphenyls, PCBs, can be determined by dialysis or chlorine analysis, respectively. Indication of the presence of VI improver is given by unusually high viscosity indices. Solvent extraction can remove VI improvers or their fragments. 

Locust bean gum can be extracted from the European carob tree. As the extract, with impurities removed, it gives clear solutions. It shows significant synergy with carrageenan and xanthan, usually at about 50/50 levels, and this synergy tends to eliminate the syneresis often seen with carrageenan. Being insoluble in cold water, heat is required to obtain solutions. 

Backwashing is used with batch extractions. The combined phases of several extractions are washed to remove impurities. Because the D of the impurities is usually much less than that of the metal extracted, this removes impurities much the same as reprecipitation. 

Iodo-N-BOC-piperidine 42 was obtained by iodination of 4-hydroxy-Af-BOC-piperidine 41 with iodine/triphenylphosphine/imidazole in THE. An extractive workup removed the triphenylphos-phine oxide, allowing a direct crystallization of the pure iodide from ethanol/water that typically contained <1 mol% of triphenylphosphine oxide and other by-products. DMAC was later identified as a better solvent to avoid the formation of THF-polymer or dimer impurities resulting from the interaction of I2/THF. 

To purify anserine and carnosine contained in the chicken extract, impurities (mainly creatinine and sodium chloride) need to be removed. Molecular weights of these impurities are 113 and 58, respectively, while average molecular weight of anserine and carnosine is 234. Therefore, 13 different kinds of nanofiltration membranes that had NaCl rejection values of 10% to 60% or molecular weight cutoff values of 700 to 2,500 were chosen. Membranes tested in this study are listed in Table 22.1. 

The zinc-loaded organic solution is washed with acidified water to remove aqueous entrapment and traces of co-extracted impurities in a washing/scrubbing stage. The cleaned zinc-loaded organic is stripped using spent electrolyte to produce an extremely pure zinc-loaded electrolyte. 

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