Solvent extraction plant

In a similar appHcation, Cape Industries has announced its intention to commission a solvent extraction plant to recover acetic acid from an effluent generated at its dimethyl terephthalate [120-61-6] faciHty (Wilmington, North Carolina) (44,45). The plant was commissioned in Eebmary 1995. In this case, the solvent will be CYANEX 923 extractant [100786-00-3], CYANEX 923 is also a phosphine oxide, but unlike TOPO is a Hquid and can be used without a diluent (46,47). This has the benefit of reducing plant size, capital, and operating costs. 

K. R. Rawling, Commercial Solvent Extraction Plant Recovers Copper from Leach Liquors, World Min., p. 34, Dec. 1969. 

Blending of Coals. In practice it is unlikely that a coal from a single source will be used as a feed to a large solvent extraction plant and a blend of several coals may have to be used. A preliminary series of tests using blends gave extraction yields in reasonable agreement with those derived from extraction of individual coals (Table VII). 

Cupertino, D. C. Charlton, M. H. Buttar, D. Swart, R. M. Maes, C. J. A study of copper/iron separation in modern solvent extraction plants. Proceedings of the COPPER 99-COBRE 99 International Conference, 4th, Phoenix, Oct. 10-13, 1999, 4, 263-276. 

Much of the optimization of the solvent extraction plant can be achieved in the pilot plant testing. As noted earlier on the subjeet of proeess design, one must investigate the dependence of the dispersion and eoaleseence char-aeteristies and their effect on extraction and phase separation. Also, such variables as metal concentration, equilibrium pH (or free aeidity or free basieity), salt concentration, solvent concentration (extraetant, diluent, and modifier), and temperature have to be studied to determine their effect on mass transfer. Although many of the variables can be tested in the pilot plant, many circuits are not optimized until the full-scale plant is in operation. 

The lack of satisfactory solvent recovery methods prior to 1930 prevented the use of selective solvents more suitable for lubricating oils. The major part of any solvent extraction plant is its complex solvent recovery system. Chemical engineering s contributions to distillation theory and process design resulted in the development of efficient solvent recovery techniques. In 1933, as illustrated by Figure 3, large commercial plants were... 

A flow diagram of an anhydrous phenol solvent extraction plant is shown in Figure 8. Raw distillate is passed through a tower in which it absorbs phenol from the recovery system vapor. The oil is then passed to the treating tower, generally a few sections above the bottom. Anhydrous phenol is introduced at the top of this tower. Phenolic water condensate from the solvent recovery system (about 9.5% phenol) is introduced at the bottom of the tower to effect reflux. A temperature gradient of 10° to 75° F. may be... 

Figure 10. Aqueous Phenol Solvent Extraction Plant...

Many licensors and contractors who must obtain data from which to design and build solvent extraction plants utilize large, elaborate pilot plants which simulate commercial plant conditions. Many refiners have constructed such plants to obtain data from which to guide commercial equipment and prepare samples for engine test evaluations. Plants of this sort cost 200 to 300 daily to operate. An evaluation of a single stock may require weeks and cost thousands of dollars. 

Figure 14 illustrates a comparison between solvent extraction yields predicted from adsorption analyses and actual raffinate yields in commercial solvent extraction plants. Few commercial yields have ever equaled those obtained by adsorption analyses and none has exceeded those values hence, curve A (45° angle) represents the ultimate in solvent extraction. Curve B represents solvent extraction in commercial equipment on stocks ranging in viscosity index from +25 to +110, and for viscosity index improvements ranging from 30 to 130. Extremely viscous stocks or those which require a very large viscosity index improvement have been observed to follow more closely lines C and D. 

Solvent losses constitute an expensive item which must be predicted when designing and evaluating commercial solvent extraction processes. A solvent make-up cost of 250,000 annually would not be unusual for a large lubricating oil solvent extraction plant of this loss, it is likely that only 40 to 60% would be found in the residual streams from raffinate and extract strippers. The balance would disappear as leakage, decomposition, and unexpected upset losses. 

Phillips, C. 1999. The thermal oxide reprocessing plant at Sellafield Four years of active operation of the solvent extraction plant. ISEC 99 Conference on Solvent Extraction for the 21st Century, July, Barcelona, Spain. 

Alonso, A.I. and Gruhn, G. (2002) Flexibility analysis of nondispersive solvent extraction plant. Separation Science and Technology, 37, 161. 

The residue obtained is repeatedly washed with fresh amounts of the same solvent to maximize yield. Solvent is then recovered in a still at reduced pressure, which lowers the solvent s boiling point and permits the use of gentle heat. The concentrated extract is not distilled but is retained in the vessel in a liquid state. When it is removed and cooled, the concentrated extract solidifies to a waxy consistency called a concrete, which is made up of approximately 50% odourless wax. The unwanted wax is removed by washing with alcohol, which extracts the essential oil. The alcohol mixture is then filtered and alcohol is removed by vacuum distillation. The final residue is called the absolute. A typical solvent extraction plant is shown in Fig. 4.4 in this system the solvent is pumped through a bed of the plant material. 

Continuous screw presses are used (1) for extracting fats and oils in small operations where investment capital or supplies of raw materials are limited and installation of a solvent extraction plant is impractical (2) to partially defat high-oil content seeds for easier handling in subsequent solvent extraction or hard pressing and (3) for extraction of animal flesh and bones, fish, and fleshy-type oilseeds such as palm fruit, olives, and copra (dried coconut meat ), and oilseeds. These machines have been generically referred to as expellers, but the Expeller trademark belongs to Anderson International Corporation, Cleveland, OH, successor to the company founded by Valerius D. Anderson who patented the first continuous screw press in 1899. 

Technical Committee on Solvent Extraction Plants, NFPA 36 Standard for Solvent Extraction Plants. NFPA International, Quincy, MA, 2004. 

Dip tanks containing flammable or combustible liquids Plants manufacturing organic coatings Spray finishing areas (residue must be considered) Solvent extraction plants ... 

For this purification process, the crude miscella source may be from (1) the preevaporator of a direct-solvent extraction plant, (2) a blend of prepressed crude oil and solvent-extracted miscella from the press-cake, or (3) a reconstituted blend of crude oil with solvent. In the process, a mixture of approximately 40% to 58% oil in solvent is heated or cooled to 104°F (40°C) and filtered to remove meal, scale, and other insoluble impurities. Two solvents that have been used commercially for miscella refining are hexane and acetone. 

At the solvent extraction plant, the cake (pomace) containing up to 8% residual oil is dried in a rotary kiln before proceeding to the solvent extraction unit, usually a semicontinuous system (Figure 7). The extracted pomace oil is always refined. Spent cake is used as fuel or is separated into two fractions, the pulp (including skin) and the pit. In addition to use as fuel, the pit is occasionally used to produce fiberboard (23). 

Direct solvent extraction is the most widely used oil-recovery method for soybeans, but it also requires considerable capital and large scale to compete. In actual practice, solvent extraction is used to crush over 98% of the soybean processed in the United States. Process flow diagrams are shown in Figures 3 and 4. Most soybean solvent-extraction plants process more than 2,500 MT/day (Figure 5), and some are capable of processing as much as 5,000 MT/day (especially newly constructed plants in Brazil). Direct-solvent-extraction plants smaller than 1,000 MT/day have difficulty competing in the United States. At various times, soybeans have been extracted commercially with petroleum distillate fractions that resemble gasoline, acetone, carbon disulfide, ethanol, trichloroethylene, and even water. 

Hydraulic press oil mills remained in use as late as the 1950s before the last of them were replaced with continuous screw presses and continuous solvent extraction plants, both of which required far less labor and could process at much higher rates. 

In 1951, the V.D. Anderson Company was again the pioneer in mechanical screw pressing, being first to patent the process of using a mechanical screw press to continuously prepress oleaginous materials ahead of continuous solvent extraction plants. The company was awarded U.S. Patent 2,551,254 (5). 

In 1855, Deiss of Marseilles, France, was first to employ solvent extraction (1). He used carbon disulfide to dissolve olive oil retained in spent olive cakes. This technology used batch solvent extraction, where the material was held in a common kettle for both the extraction process as well as the subsequent meal desolventizing process. Deiss obtained a patent for batch solvent extraction of olive oil in 1856 (1). Small batch solvent extraction plants were installed in France and Italy, and by 1870, small batch solvent extraction facilities had spread across Europe. Larger scale solvent extraction plants were supplied by Rose, Downs, and Thompson (2) of Hull, England, starting in 1898. 

---