Solvent extraction processes

Solvent extraction processes are those processes in which coal is mixed with a solvent that is capable of effecting the transfer of hydrogen from the solvent to the coal (or even from gaseous hydrogen to the coal) at temperatures up to 500°C (930°F) and pressures up to 5000 psi. 

Solvent extraction can also be achieved under milder conditions but the product may be a high-nitrogen solid or a heavy oil with only low yields of light oils and gases. The more severe conditions are more effective for sulfur and nitrogen removal to produce a lighter liquid product that is more amenable to downstream processing. 

A more novel aspect of the solvent extraction process type is the use of bitumen and/or heavy oil as process solvents and, in fact, the coprocessing of coal with a variety of petroleum-based 

Consol synthetic fuel (CSF) Conoco Stirred tank 400 750 150-450 1 

Solvent-refined coal (SRC) Pittsburgh and Midway Mining Co. Plug flow - 50 840 1000-1500 1 

---

There are of course liquid-liquid equilibria between hydrocarbons and substances other than water. In practice these equilibria are used in solvent extraction processes. The solvents most commonly used are listed as follows ... 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

The solution leaving the flotation cell, containing about 0.4 g/L iodine, is sent to a kerosene solvent extraction process to recover the dissolved product. After neutralization with soda ash to the initial incoming alkalinity, the solution is returned to the nitrate lixiviation process. The iodine-chaiged kerosene is contacted with an acidic concentrated iodide solution containing SO2, which reduces the iodine to iodide. 

Battery breaking technologies use wet classification to separate the components of cmshed batteries. Before cmshing, the sulfuric acid is drained from the batteries. The sulfuric acid is collected and stored for use at a later stage in the process, or it may be upgraded by a solvent extraction process for reuse in battery acid. 

The electrowinning process developed by Ginatta (34) has been purchased by M.A. Industries (Atlanta, Georgia), and the process is available for licensing (qv). MA Industries have also developed a process to upgrade the polypropylene chips from the battery breaking operation to pellets for use by the plastics industry. Additionally, East Penn (Lyons Station, Pennsylvania), has developed a solvent-extraction process to purify the spent acid from lead—acid batteries and use the purified acid in battery production (35). 

An improved solvent extraction process, PUREX, utilizes an organic mixture of tributyl phosphate solvent dissolved in a hydrocarbon diluent, typically dodecane. This was used at Savannah River, Georgia, ca 1955 and Hanford, Washington, ca 1956. Waste volumes were reduced by using recoverable nitric acid as the salting agent. A hybrid REDOX/PUREX process was developed in Idaho Falls, Idaho, ca 1956 to reprocess high bum-up, fuUy enriched (97% u) uranium fuel from naval reactors. Other separations processes have been developed. The desirable features are compared in Table 1. 

The early developments of solvent processing were concerned with the lubricating oil end of the cmde. Solvent extraction processes are appHed to many usefiil separations in the purification of gasoline, kerosene, diesel fuel, and other oils. In addition, solvent extraction can replace fractionation in many separation processes in the refinery. For example, propane deasphalting (Fig. 7) has replaced, to some extent, vacuum distillation as a means of removing asphalt from reduced cmde oils. 

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. 

The actual solvent extraction processes used, including the specific extractants and the order in which the components are separated, vary from refinery to refinery. However, a typical scheme is shown in Figure 3 (12). 

Polyethers prepared from propylene oxide are soluble in most organic solvents. The products with the highest hydroxyl number (lowest molecular weight) are soluble in water, not in nonpolar solvents such as hexane. The solubihty of 3000 molecular weight triols is high enough in solvents such as toluene, hexane, and methylene chloride that the triols can be purified by a solvent extraction process. 

Screw-pressed oil is aUowed to stand to settle out suspended soUds, filtered through plate filter presses, and then pumped to storage. The oil-rich solvent (miscella) from the solvent-extraction process is filtered or clarified, and most of the solvent is removed in a long tube evaporator. FinaUy, the concentrated oil passes through a stripping column where sparging steam is injected to remove the residual solvent. A metric ton of cottonseed yields ca 91... 

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). 

U.S. EPA, Project Summary Temoval ofPCBs from Contaminated Soil Using the CF Systems Solvent Extraction Process Treatability Study, EPA/540/SR-95/505, Cincinnati, Ohio, 1995. 

A beryUium concentrate is produced from the leach solution by the counter-current solvent extraction process (10). Kerosene [8008-20-6] containing di(2-ethylhexyl)phosphate [298-07-7] is the water-immiscible beryUium extractant. The slow extraction of beryUium at room temperature is accelerated by warming. The raffinate from the solvent extraction contains most of the aluminum and aU of the magnesium contained in the leach solution. 

Selectivity for a single metal of a group is the basis of a solvent extraction process for the recovery of copper (qv) from low concentration ore leach solutions containing high levels of iron (qv) and other interfering metals (16). 

Increasingly more copper is being produced by electrowinning because of economics and technical advances, such as in solvent extraction processes. Certain brands obtained by SX—EW are treated as cathode quahty and are used directly by wire-rod manufacturers. Whereas in 1984 100,180 t of copper was electrowon in SX—EW plants, in 1992, 439,043 t produced by SX—EQ was electrowon (7). 

Three West Virginia coals were supplied by the West Virgmia Geological Survey (WVGS). The particular coals were chosen on the basis of rank, petrographic composition, and mineral matter content The coals were limited to the bituminous rank since these coals are the most amenable to the NMP solvent extraction process and are mdigenous to the Appalachian region. Some of the coal characteristics are listed in Table 2. 

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... 

Vanadium and nickel are poisons to many catalysts and should be reduced to very low levels. Most of the vanadium and nickel compounds are concentrated in the heavy residues. Solvent extraction processes are used to reduce the concentration of heavy metals in petroleum residues. 

Liquid solvents are used to extract either desirable or undesirable compounds from a liquid mixture. Solvent extraction processes use a liquid solvent that has a high solvolytic power for certain compounds in the feed mixture. For example, ethylene glycol has a greater affinity for aromatic hydrocarbons and extracts them preferentially from a reformate mixture (a liquid paraffinic and aromatic product from catalytic reforming). The raffinate, which is mainly paraffins, is freed from traces of ethylene glycol by distillation. Other solvents that could be used for this purpose are liquid sulfur dioxide and sulfolane (tetramethylene sulfone). 

The products of the solvent extraction process are tantalum strip solution, niobium strip solution and raffinate - liquid wastes containing impurities and residual acids. 

The liquid-liquid extraction (solvent extraction) process was developed about 50 years ago and has found wide application in the hydrometallurgy of rare refractory and rare earth metals. Liquid-liquid extraction is used successfully for the separation of problematic pairs of metals such as niobium and tantalum, zirconium and hafnium, cobalt and nickel etc. Moreover, liquid-liquid extraction is the only method available for the separation of rare earth group elements to obtain individual metals. 

The various equilibria involved in the solvent-extraction process are expressed in terms of the following thermodynamic constants ... 

In the solvent-extraction process, the platinum metal concentrate is solubilized in acid using chlorine oxidant. Ruthenium and osmium are separated by turning them into the volatile tetroxides. 

BuUerdiek, Removal of TNT from Waste Water Using a Solvent Extraction Process , TftrhBpnt RQ Riirljjiatrm AFP Plant flQAdA... 

Chelating reagents in solvent extraction processes the present position. A. W. Ashbrook, Coord. Chem. Rev., 1975,16, 285-307 (74). 

We are not aware of any previous studies of the removal of plutonium or americium from (NH )2ZrF6-NHltF-NH N03 solutions. For ready plant-scale application, precipitation, sorption on inorganic materials, or batch solvent extraction processes may all be satisfactory. An inexpensive inorganic material with great selectivity and capacity for sorbing actinides, and with suitable hydraulic properties, would be especially attractive. 

Figure 5.14 Generalized solvent extraction process flowsheet.

---