Recovery of phenolic acids

Generally, extraction is carried out at warm temperatures to increase the recovery of phenolic acids. The incubation temperature should not exceed the boiling point of the extraction solvent. Incubation time is variable from 1 hour to overnight and depends on the characteristics of the sample. During incubation, the extraction solution should be agitated frequently to increase contact between the solvent and sample. After extraction, the next step is to separate the extraction solvent from the sample solid residue. Either a centrifugation or filtration method can be applied in this step. The method selection usually depends on the... 

Recovery of phenolic acids by NaOH from amended soil samples was equal to or greater than those recovered from non-amended soil samples. The difference (minus approximately 0.01 p,mol/g soil) in recovery between amended and non-amended phenolic acid soils represented a portion of the amended phenolic acids (i.e., 1 M NaOH extractable) that had been irreversibly sorbed during the equilibration and/or incubation periods. Values for 1 M NaOH extractable phenolic acids from non-amended soils were < 0.0017 xmol/g soil for Cecil B (0.2% organic matter) soil samples and ranged from 0.013 xmol/g soil for ferulic acid to 0.073 p,mol/g soil for p-coumaric acid in the Cecil A (3.7% organic matter) soil samples. Differences between amended and non-amended soils ranged from 0 xmol/g soil for p-coumaric acid to 0.024 p,mol/g soil for ferulic acid in Cecil A soil samples and 0.013 p,mol/g... 

Dalton et al. (1989b) utilizing Mehlich 111, a mild chelating extractant, also observed that the recovery of available phenolic acids (femlic acid, vanillic acid, p-coumaric acid, p-hydroxybenzoic acid) from sterile soil (Cecil, Portsmouth and White Store) varied with soil type, horizon, time, and the type of phenolic acid added. When they allowed phenolic acids added to soil to equilibrate for 2 min before extraction, they noted a significant reduction in recovery of phenolic acids. Recovery declined with time up to 32 days. The decline was most rapid over the first 2 days. The presence of methoxy groups and acrylic side chains increased... 

Other Organic Processes. Solvent extraction has found appHcation in the coal-tar industry for many years, as for example in the recovery of phenols from coal-tar distillates by washing with caustic soda solution. Solvent extraction of fatty and resimic acid from tall oil has been reported (250). Dissociation extraction is used to separate y -cresol fromT -cresol (251) and 2,4-x5lenol from 2,5-x5lenol (252). Solvent extraction can play a role in the direct manufacture of chemicals from coal (253) (see Eeedstocks, coal chemicals). 

The aqueous sodium naphthenate phase is decanted from the hydrocarbon phase and treated with acid to regenerate the cmde naphthenic acids. Sulfuric acid is used almost exclusively, for economic reasons. The wet cmde naphthenic acid phase separates and is decanted from the sodium sulfate brine. The volume of sodium sulfate brine produced from dilute sodium naphthenate solutions is significant, on the order of 10 L per L of cmde naphthenic acid. The brine contains some phenolic compounds and must be treated or disposed of in an environmentally sound manner. Sodium phenolates can be selectively neutralized using carbon dioxide and recovered before the sodium naphthenate is finally acidified with mineral acid (29). Recovery of naphthenic acid from aqueous sodium naphthenate solutions using ion-exchange resins has also been reported (30). 

Several examples of cost-effective liquid-hquid extraction processes include the recovery of acetic acid from water (Fig. 15-1), using ethyl ether or ethyl acetate as described by Brown [Chem. Eng. Prog., 59(10), 6.5 (1963)], or the recoveiy of phenolics from water as described by Lauer, Littlewood, and Butler [7/Steel Eng., 46(5), 99 (1969)] with butyl acetate, or with isopropyl ether as described by Wurm [Gliickauf, 12, 517 (1968)], or with methyl isobutyl ketone as described by Scheibel [ Liqmd-Liquid Extraction, in Periy Weiss-... 

Analytical methods for detecting phenol in environmental samples are summarized in Table 6-2. The accuracy and sensitivity of phenol determination in environmental samples depends on sample preconcentration and pretreatment and the analytical method employed. The recovery of phenol from air and water by the various preconcentration methods is usually low for samples containing low levels of phenol. The two preconcentration methods commonly used for phenols in water are adsorption on XAD resin and adsorption on carbon. Both can give low recoveries, as shown by Van Rossum and Webb (1978). Solvent extraction at acidic pH with subsequent solvent concentration also gives unsatisfactory recovery for phenol. Even during carefully controlled conditions, phenol losses of up to 60% may occur during solvent evaporation (Handson and Hanrahan 1983). The in situ acetylation with subsequent solvent extraction as developed by Sithole et al. (1986) is probably one of the most promising methods. 

The pH values of efficient extraction correspond to the pH range where the molecular form of the respective phenol dominates. The recovery of 4-nitro-phenol, 2,4-dinitrophenol, 2,6-dinitrophenol, 4-chlorophenol, 1-naphthol, and 2-naphthol is above 90% (the ratio of aqueous organic phase volume is 3 1). The extraction of naphthol and 4-chlorophenol is significant even at pH > pffa, more than 40 and 24% at pH > 10, respectively. Recovery of picric acid (2,4,6-trinitrophenol) is about 90% at pH 1.5-12.0, where the anionic form of picric acid dominates. Obviously, the high extraction is caused by high hydrophobicity of picrate anions. Recovery of the phenol itself and diatomic phenols, catechol and resorcinol is rather moderate (79,58, and 20%, respectively pH 1-7), which could be explained by relatively high hydrophi-licity of these compounds. 

In the chemical processing industry, extraction is used when distillation is impractical or too costly. Extraction may be more practical than distillation when the relative volatilities of two components are close. In other cases, the components to be separated may be heat sensitive like antibiotics or relatively nonvolatile like mineral salts. When unfortunate azeotropes form, distillation may be ineffective. Several examples of cost-effective liquid-liquid extraction processes include the recovery of acetic acid from water using ethyl ether or ethyl acetate and the recovery of phenolics from water with butyl acetate. 

VC Mason, M Rudemo, S Bech-Andersen. Hydrolysate preparation for amino acid determinations in feed constituents. 6. The influence of phenol and formic acid on the recovery of amino acids from oxidized feed proteins. Z Tierphysiol Tierernaehr Futtermittelkd 43 35-48, 1980. 

Aqueous samples are extracted with methylene chloride. If the sample is not clean or if the presence of organic interference is suspected, a solvent wash should be performed. For this, the pH of the sample is adjusted to 12 or greater with NaOH solution. The sample solution made basic is then shaken with methylene chloride. Organic contaminants of basic nature and most neutral substances partition into the methylene chloride phase, leaving phenols and other acidic compounds in the aqueous phase. The solvent layer is discarded. The pH of the aqueous phase is now adjusted to 2 or below with H2S04, after which the acidic solution is repeatedly extracted with methylene chloride. Phenols and other organic compounds of acidic nature partition into the methylene chloride phase. The methylene chloride extract is then concentrated and exchanged into 2-propanol for GC analysis. For clean samples, abasic solvent wash is not necessary however, the sample should be acidified before extraction. It may be noted that basic solvent wash may cause reduced recovery of phenol and 2,4-dimethylphenol. 

Hydrocarbon waxes produced in a fixed-bed reactor, which has operated since 1955, have found a variety of uses. Also, byproducts from the Sasol Lurgi coal gasifiers are recovered for chemical and solvent applications. These products include phenol, cresols, toluene, xylenes, ammonia, and sulfur. An addition to the spectrum of chemical products from Sasol is polypropylene. Also, ethane is being cracked to supplement ethylene production for sale to polyethylene producers. Additional work is in progress to evaluate the recovery of organic acids from aqueous waste streams. 

Diphenyl carbonate from dimethyl carbonate and phenol Dibutyl phthalate from butanol and phthalic acid Ethyl acetate from ethanol and butyl acetate Recovery of acetic acid and methanol from methyl acetate by-product of vinyl acetate production Nylon 6,6 prepolymer from adipic acid and hexamethylenediamine MTBE from isobutene and methanol TAME from pentenes and methanol Separation of close boiling 3- and 4-picoline by complexation with organic acids Separation of close-boiling meta and para xylenes by formation of tert-butyl meta-xyxlene Cumene from propylene and benzene General process for the alkylation of aromatics with olefins Production of specific higher and lower alkenes from butenes... 

In general, the sample preparation and extraction steps of phenolic acid analysis are very critical to the final result. Solvent or solution composition, extraction temperature, extraction technology, acid, alkaline, or enzymatic hydrolysis, extraction time, and cleanup conditions are all factors that affect the recovery and profile of phenolic acids. Poor sample preparation and extraction result in unreliable outcomes, regardless of the precision of the chromatography quantification method. Table 3.1 lists various sample extraction methods for different types of samples. 

Sample handling is a very important part of the method development for HPLC determination of phenolic acids in natural plants. Because of the great variability of phenolic acids (different polarity, acidity, number of hydroxyl groups, and aromatic rings), the various concentration levels of individual analytes, and the very complex natural matrix with many interfering components, the choice of the technique for their isolation and quantification differs from one described HPLC assay to the next. In some cases, only a one-step extraction and simple clean-up procedure are sufficient before the HPLC analysis, but the most often described HPLC assays include two or more steps of sample preparation, especially in the case of fruits and vegetable samples. It is obvious that each step contributes, on one hand, to the higher sensitivity and selectivity, but, on the other hand, it could increase the number of errors and decrease the recovery of the method. 

Phenol can be removed by weak-base resin (e.g., lonac AFP-329). The capacity of this resin is not affected by the neutral salt. Regeneration of the resin is performed by methanol, isopropanol, or dilute alkah. The use of alcoholic solvents allows the recovery of phenol as the free acid, because the alcohol can be stripped from the regenerant effluent stream, leaving the phenolic concentrate. The recovered alcohol can then be reclaimed and used for subsequent regenerations, and the phenol can be recycled back to the process stream. The use of dilute alkali allows the recovery of the phenol as the sodium salt. 

Extraction of free fatty acids from naturally occurring glycerides removal of HCl from chlorinated organic compounds recovery of aliphatic acids HE and HCl from aqueous solutions nitration of phenol solvent extraction in mineral processing interfacial polycondensation and esterification manufacture of organo-phosphate pesticides. 

Complexation also offers attractive possibilities for selective recovery of dicarboxylic acids, hydroxy-carboxylic acids (luetic, citric, etc.), phenolic carboxylic acids (gallic, vanillic, caffeic. etc.), amino acids, quinolines, and alkaloids from aqueons solution. 

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