Extraction aqueous processing

Cui, W., Mazza, G., Oomah, B.D., and Biliaderis, C.G. 1994b. Optimization of an aqueous extraction process for flaxseed gum by response surface methodology. Lebensm, Wiss. U. Technol. 27, 363-369. 

Aqueous enzymatic oil extraction is another ecofriendly extraction procedure. It is based on simultaneous isolation of oil and protein from oilseed by dispersing finely ground seed in water and separating the dispersion by centrifugation into oil, solid, and aqueous phases. The presence of certain enzymes during extraction enhances oil recovery by breaking cell walls and oil bodies (22). For peanuts, a multistep aqueous extraction process has been described with a recovery of about 98% (23). More recently, the relatively new technique of enzyme-assisted aqueous extraction has been applied to peanuts with a reported oil recovery of 86-92% (24). 

Fig. 19.20. Flowsheet for processing soybeans by aqueous extraction processing (Source Lawhon etal., 1981).

A logical step further is to use a non-aqueous extraction process . For example, in one of them the ore is pugged with sulphuric acid, wetted with a little ammonium nitrate solution and then percolated with 5 per cent TBP in kerosene. Solvent losses are excessive, even after recovery by means of a kerosene wash, although a high purity product is obtained after back-washing. 

Table 12.5 Quality characteristics of oil from enzymatic aqueous extraction process of canola seeds...

The quality characteristics of the oil produced by the enzyme-assisted aqueous extraction process is comparable to that of conventional extraction procedures except in its phosphorus content (Table 12.5). The enzymatic process yields oil with less phosphorus which requires no or limited degumming. The crude oil from this process can be physically refined without further treatment (Laiho et al., 1991). Despite this improved quality of the crude oil which is an apparent cost saving in subsequent downstream processing, the enzymatic process has not been commercially exploited due to problems with yields. Considerable degree of emulsification occurs during the process. Approximately 18-25% of the available oil in the seed remains unrecovered in a standard operation. The discovery that the versatile protein, oleosin, binds approximately 20% of the oil in oil-bearing seeds (Tzen et al., 1990) has implicated this protein in the low yields associated with this process. Thus, the recoveries could be improved by the use of proteases. It has, however, been observed that successful application of proteases to improve oil recovery produces excessively bitter meals, repressing the potential utilization of the meal as feed or food. 

The sulfuric acid hydrolysis may be performed as a batch or continuous operation. Acrylonitrile is converted to acrylamide sulfate by treatment with a small excess of 85% sulfuric acid at 80—100°C. A hold-time of about 1 h provides complete conversion of the acrylonitrile. The reaction mixture may be hydrolyzed and the aqueous acryhc acid recovered by extraction and purified as described under the propylene oxidation process prior to esterification. Alternatively, after reaction with excess alcohol, a mixture of acryhc ester and alcohol is distilled and excess alcohol is recovered by aqueous extractive distillation. The ester in both cases is purified by distillation. 

Supercritical Extraction. The use of a supercritical fluid such as carbon dioxide as extractant is growing in industrial importance, particularly in the food-related industries. The advantages of supercritical fluids (qv) as extractants include favorable solubiHty and transport properties, and the abiHty to complete an extraction rapidly at moderate temperature. Whereas most of the supercritical extraction processes are soHd—Hquid extractions, some Hquid—Hquid extractions are of commercial interest also. For example, the removal of ethanol from dilute aqueous solutions using Hquid carbon dioxide... 

Anhydrous Acetic Acid. In the manufacture of acetic acid by direct oxidation of a petroleum-based feedstock, solvent extraction has been used to separate acetic acid [64-19-7] from the aqueous reaction Hquor containing significant quantities of formic and propionic acids. Isoamyl acetate [123-92-2] is used as solvent to extract nearly all the acetic acid, and some water, from the aqueous feed (236). The extract is then dehydrated by azeotropic distillation using isoamyl acetate as water entrainer (see DISTILLATION, AZEOTROPIC AND EXTRACTIVE). It is claimed that the extraction step in this process affords substantial savings in plant capital investment and operating cost (see Acetic acid and derivatives). A detailed description of various extraction processes is available (237). 

Fractional extraction has been used in many processes for the purification and isolation of antibiotics from antibiotic complexes or isomers. A 2-propanol—chloroform mixture and an aqueous disodium phosphate buffet solution are the solvents (243). A reciprocating-plate column is employed for the extraction process (154). 

Other Metals. Because of the large number of chemical extractants available, virtually any metal can be extracted from its aqueous solution. In many cases extraction has been developed to form part of a viable process (275). A review of more recent developments in metal extraction including those for precious metals and rare earths is also available (262). In China a complex extraction process employing a cascade of 600 mixer—settlers has been developed to treat leach Hquor containing a mixture of rare earths (131). 

The depressed prices of most metals in world markets in the 1980s and early 1990s have slowed the development of new metal extraction processes, although the search for improved extractants continues. There is a growing interest in the use of extraction for recovery of metals from effluent streams, for example the wastes from pickling plants and electroplating (qv) plants (276). Recovery of metals from Hquid effluent has been reviewed (277), and an AM-MAR concept for metal waste recovery has recentiy been reported (278). Possible appHcations exist in this area for Hquid membrane extraction (88) as weU as conventional extraction. Other schemes proposed for effluent treatment are a wetted fiber extraction process (279) and the use of two-phase aqueous extraction (280). 

Soybean concentrate production involves the removal of soluble carbohydrates, peptides, phytates, ash, and substances contributing undesirable flavors from defatted flakes after solvent extraction of the oil. Typical concentrate production processes include moist heat treatment to insolubilize proteins, followed by aqueous extraction of soluble constituents aqueous alcohol extraction and dilute aqueous acid extraction at pH 4.5. 

Processing conditions are closely guarded trade secrets, but manufacturer s Hterature provides some information. The seaweed is extracted with hot water at slightly alkaline pH. The aqueous extract is filtered and recovered by alcohol precipitation, dried, and milled. Dmm-drying provides a less pure product. 

Functional Olefin Hydroformylation. There has been widespread academic (18,19) and industrial (20) interest in functional olefin hydroformylation as a route to polyfiinctional molecules, eg, diols. There are two commercially practiced oxo processes employing functionalized olefin feedstocks. Akyl alcohol hydroformylation is carried out by Arco under Hcense from Kuraray (20,21). 1,4-Butanediol [110-63 ] is produced by successive hydroformylation of aHyl alcohol [107-18-6] aqueous extraction of the intermediate 2-hydroxytetrahydrofuran, and subsequent hydrogenation. 

The purified acid is recovered from the loaded organic stream by contacting with water in another countercurrent extraction step. In place of water, an aqueous alkafl can be used to recover a purified phosphate salt solution. A small portion of the purified acid is typically used in a backwashing operation to contact the loaded organic phase and to improve the purity of the extract phase prior to recovery of the purified acid. Depending on the miscibility of the solvent with the acid, the purified acid and the raffinate may be stripped of residual solvent which is recycled to the extraction loop. The purified acid can be treated for removal of residual organic impurities, stripped of fluoride to low (10 ppm) levels, and concentrated to the desired P2 s Many variations of this basic scheme have been developed to improve the extraction of phosphate and rejection of impurities to the raffinate stream, and numerous patents have been granted on solvent extraction processes. 

Tantalum Compounds. Potassium heptafluorotantalate [16924-00-8] K TaF, is the most important tantalum compound produced at plant scale. This compound is used in large quantities for tantalum metal production. The fluorotantalate is prepared by adding potassium salts such as KCl and KF to the hot aqueous tantalum solution produced by the solvent extraction process. The mixture is then allowed to cool under strictiy controlled conditions to get a crystalline mass having a reproducible particle size distribution. To prevent the formation of oxyfluorides, it is necessary to start with reaction mixtures having an excess of about 5% HF on a wt/wt basis. The acid is added directiy to the reaction mixture or together with the aqueous solution of the potassium compound. Potassium heptafluorotantalate is produced either in a batch process where the quantity of output is about 300—500 kg K TaFy, or by a continuously operated process (28). 

In the tributyl phosphate extraction process developed at the Ames Laboratory, Iowa State University (46—48), a solution of tributyl phosphate (TBP) in heptane is used to extract zirconium preferentially from an acid solution (mixed hydrochloric—nitric or nitric acid) of zirconium and hafnium (45). Most other impurity elements remain with the hafnium in the aqueous acid layer. Zirconium recovered from the organic phase can be precipitated by neutralization without need for further purification. 

Extraction from Aqueous Solutions Critical Fluid Technologies, Inc. has developed a continuous countercurrent extraction process based on a 0.5-oy 10-m column to extract residual organic solvents such as trichloroethylene, methylene chloride, benzene, and chloroform from industrial wastewater streams. Typical solvents include supercritical CO9 and near-critical propane. The economics of these processes are largely driven by the hydrophihcity of the product, which has a large influence on the distribution coefficient. For example, at 16°C, the partition coefficient between liquid CO9 and water is 0.4 for methanol, 1.8 for /i-butanol, and 31 for /i-heptanol. 

As already noted (p. 1073), the platinum metals are all isolated from concentrates obtained as anode slimes or converter matte. In the classical process, after ruthenium and osmium have been removed, excess oxidants are removed by boiling, iridium is precipitated as (NH4)2lrCl6 and rhodium as [Rh(NH3)5Cl]Cl2. In alternative solvent extraction processes (p. 1147) [IrClg] " is extracted in organic amines leaving rhodium in the aqueous phase to be precipitated, again, as [Rh(NH3)5Cl]Cl2. In all cases ignition in H2... 

The combined filtrates or total aqueous extracts are cooled to about room temperature and filtered to remove any residual solids from solution. The clarified aqueous extract is then concentrated to about 70 gallons at a temperature below about 50°C, thus reducing the volume to about one-third the original volume. The resulting concentrate is cooled to room temperature or below and filtered to remove any tar or gum that may have separated. The presence of tar or gum at this stage of the process will vary depending upon the starting material and the manner in which the primary extraction has been carried out. It has baen found, however, that unless any tar or gum present in the initial extract is removed by the procedure described, it will seriously interfere with the further concentration and crystallization steps hereinafter described. 

As the hydrochloric acid salt of the obtained phenothiazine derivative is difficultly soluble In water, the further processing was carried out by way of the acetate. The etheric solution wes extracted several times in e sepereting funnel with dilute ecetic acid. The combined aqueous extracts were basified, extracted with ether, dried with potessium cerbonate end, after removel of the ether, distilled in vecuo. 

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