Uses of Solvents

The use of solvents having boiling-points below or much above the range indicated by the above examples is inadvisable, for the maintenance of a steady circulation of the boiling liquid may prove difficult. 

The last variation we should discuss is about the use of solvent. Ever-bitching about the rarity and price of chemicals, the bees have thrust their anger at the DMF used in this method. TDK sent Strike an article that gives some credence to this [16]. In it the alcohols methanol, ethanol, 1-propanol, ethanediol and others were used in place of DMF with beautifully high yields. Below is the sample experimental from the article Oust picture using safrole or allylbenzene in place of the 1-hexene) ... 

Throughout the history of the development of fats and oils, many wet chemical methods have been developed to assess the quaUty of the raw materials and products. As sophisticated instmmentation develops, many of the wet methods are being replaced. Particular attention is being given to methods that eliminate the use of solvents which cause an environmental disposal problem. Many in-line sensors are also being developed to allow corrections of critical parameters to be made more quickly in the process. 

Israel Mining Industries developed a process in which hydrochloric acid, instead of sulfuric acid, was used as the acidulant (37). The acidulate contained dissolved calcium chloride which then was separated from the phosphoric acid by use of solvent extraction using a recyclable organic solvent. The process was operated commercially for a limited time, but the generation of HCl fumes was destmctive to production equipment. 

Solution Casting. The production of unsupported film and sheet by solution casting has generally passed from favor and is used only for special polymers not amenable to melt processes. The use of solvents was generally very hazardous because of their flammabiUty or toxic nature. The cost of recovery and disposal of solvents became prohibitive for many lower price film appHcations. The nature of the drying operations leads to problems with solvent migration and retention that are not problems with melt-processed polymers. 

A process has been developed (139) whereby up to 80% of the oil can be removed from whole, raw peanuts without the use of solvent. In this process, the blanched peanuts are brought to a proper moisture content, pressed mechanically, and then reshaped or reconstituted by dipping in hot water subsequently they can be roasted and salted, or used in confections or other formulations. Defatted peanuts may also be ground into meal and added to cookies, cakes, and many other products, where they impart a distinctly nutty flavor and cmnchy texture. On the other hand, the resulting high grade oil is refined and employed in cooking and industrial products. This process can also be used for pecans, walnuts, almonds, Brazil nuts, cashews, and other nuts (140-142). 

Solvent Extraction Technology. The use of solvent extraction technology to replace traditional processes has been the subject of considerable research and development effort since the 1970s (12,14—21). This newer technique was being used commercially as of 1995 in at least three of the principal refineries. 

Water-borne adhesives are preferred because of restrictions on the use of solvents. Low viscosity prepolymers are emulsified in water, followed by chain extension with water-soluble glycols or diamines. As cross-linker PMDI can be used, which has a shelf life of 5 to 6 h in water. Water-borne polyurethane coatings are used for vacuum forming of PVC sheeting to ABS shells in automotive interior door panels, for the lamination of ABS/PVC film to treated polypropylene foam for use in automotive instmment panels, as metal primers for steering wheels, in flexible packaging lamination, as shoe sole adhesive, and as tie coats for polyurethane-coated fabrics. PMDI is also used as a binder for reconstituted wood products and as a foundry core binder. 

AH volatile organic solvents are toxic to some degree. Excessive vapor inhalation of the volatile chloriaated solveats, and the central nervous system depression that results, is the greatest hazard for iadustrial use of these solvents. Proper protective equipment and operating procedures permit safe use of solvents such as methylene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene ia both cold and hot metal-cleaning operations. The toxicity of a solvent cannot be predicted from its chlorine content or chemical stmcture. For example, 1,1,1-trichloroethane is one of the least toxic metal-cleaning solvents and has a recommended threshold limit value (TLV) of 350 ppm. However, the 1,1,2-trichloroethane isomer is one of the more toxic chloriaated hydrocarboas, with a TLV of only 10 ppm. 

The Pott-Broche process (101) was best known as an early industrial use of solvent extraction of coal but was ended owing to war damage. The coal was extracted at about 400°C for 1—1.5 h under a hydrogen pressure of 10—15 MPa (100—150 atm) using a coal-derived solvent. Plant capacity was only 5 t/h with an 80% yield of extract. The product contained less than 0.05% mineral matter and had limited use, mainly in electrodes. 

The ethylene oxidation process can be carried out in either a liquid or a vapour phase but the latter method is often preferred because it avoids corrosion problems and the use of solvents. 

Several alternative methods have been considered in order to increase the energy density of natural gas and facilitate its use as a road vehicle fuel. It can be dissolved in organic solvents, contained in a molecular cage (clathrate), and it may be adsorbed in a porous medium. The use of solvents has been tested experimentally but there has been little improvement so far over the methane density obtained by simple compression. Clathrates of methane and water, (methane hydrates) have been widely investigated but seem to offer little advantage over ANG [4]. Theoretical comparison of these storage techniques has been made by Dignam [5]. In practical terms, ANG has shown the most promise so far of these three alternatives to CNG and LNG. 

Avoidance of use of solvents, abrasive powders or process chemicals for skin cleaning. Provision of overalls of an appropriate type and their frequent laundering either in-house or by an approved contractor, with a prohibition on their unauthorized removal from the workplace or use in e.g. canteens. Disposable overalls are appropriate in some situations. 

In recent years, the use of solvent-borne adhesives has been seriously restricted. Solvents are, in general, volatile, flammable and toxic. Further, solvent may react with other airborne contaminants contributing to smog formation and workplace exposure. These arguments have limited the use of solvent-bome adhesives by different national and European regulations. Although solvent recovery systems and afterburners can be effectively attached to ventilation equipment, many factories are switching to the use of water-borne rubber adhesives, hot melts or 100% solids reactive systems, often at the expense of product performance or labour efficiency. 

Most blocked isocyanates are solids at room temperature and thus may require the use of solvent. The unblocking temperatures are often fairly high and are energy intensive. Furthermore, certain blocking agents may qualify as volatile organic compounds. For these reasons, the blocked isocyanate adhesives occupy a small, but important segment of the adhesive marketplace. 

A careful use of solvent effects should be of great assistance in synthetic chemistry. For example, it may be predicted from the solvent effects described above that in the reaction of 2,4-dichloroquinohne with piperidine the a y ratio should increase in the less polar solvents, although the result might be obscured by the mutual influence of the two chlorine substituents. Nitro-activated benzenes support this prediction since ortho para ratios of 4.2 in methanol and 69 in benzene were observed in the reaction of 2,4-dichloronitrobenzene with piperidine. ... 

The Gabriel synthesis is often carried out by heating the starting materials without a solvent for several hours at a temperature of 150 °C or higher. The use of solvents like dimethylformamide can lead to better results. In a number of solvents—e.g. toluene—the phthalimide is insoluble the reaction can however be conducted in the presence of a phase transfer catalyst." ... 

An on-line supercritical fluid chromatography-capillary gas chromatography (SFC-GC) technique has been demonstrated for the direct transfer of SFC fractions from a packed column SFC system to a GC system. This technique has been applied in the analysis of industrial samples such as aviation fuel (24). This type of coupled technique is sometimes more advantageous than the traditional LC-GC coupled technique since SFC is compatible with GC, because most supercritical fluids decompress into gases at GC conditions and are not detected by flame-ionization detection. The use of solvent evaporation techniques are not necessary. SFC, in the same way as LC, can be used to preseparate a sample into classes of compounds where the individual components can then be analyzed and quantified by GC. The supercritical fluid sample effluent is decompressed through a restrictor directly into a capillary GC injection port. In addition, this technique allows selective or multi-step heart-cutting of various sample peaks as they elute from the supercritical fluid... 

Cold Solvents Solvents, for example, white spirit or paraffin, used either by immersion or by manual application are not to be recommended as effective, or particularly safe methods, of degreasing. When used by immersion, the holding tank can became heavily contaminated with soil, which will remain on the work after the solvent has evaporated. The use of solvent-soaked rags, although a time-honoured procedure, is now being frowned upon on the grounds of operator safety aqueous based pre-wipes are available. 

Almost all urethane materials are synthesized without the use of solvents or water as diluents or earners and are referred to as being 100% solids. This is true of all foams and elastomers. There are many products, however, which do utilize solvents or water, and these are known as solvent-borne and waterborne systems, respectively. In the past, many coatings, adhesives, and binders were formulated using a solvent to reduce viscosity and/or ease application. However, the use of volatile solvents has been dramatically curtailed in favor of more environmentally friendly water (see Section 4.1.3), and now there are many aqueous coatings, adhesives, and associated raw materials. Hydrophilic raw materials capable of being dispersed in water are called water reducible (or water dispersible), meaning they are sufficiently hydrophilic so as to be readily emulsified in water to form stable colloidal dispersions. 

Limitations in the VOCs emissions wUl certainly push the shoe industry to use alternative bonding technologies to the current solvent-based surface preparations. Several limitations are found in the removal or substitution of solvents in shoe bonding, such as the use of new equipments and machinery, the modification in the procedure to produce bonding, costs increase, and difficulty in bonding some materials without the use of solvents. 

Proper ventilation and exhaust system Improved handling Improved handling Controlled use of solvent... 

There are other more recent examples though. In one laboratory, flammable solvents had been used in such small quantities that they required no special storage. As their use of solvents increased, however, there were eventually five-gallon cans of ether casually stored in one comer of a room. When a routine inspection by the fire department uncovered this hazard, the laboratory was forced to install proper storage. 

Avoidance of use of solvents, abrasive powders or process chemicals for cleaning. 

The current state of analytical SPE was critically reviewed and no major changes of the technique have been observed. Overviews of the developments of the extraction technologies of secondary metabolites from plant materials refer to three types of conventional extraction techniques that involve the use of solvents, steam, or supercritical fluids. Each technique is described in detail with respect to typical processing parameters and recent developments. Eollowing the discussion of some technical and economic aspects of conventional and novel separation processes, a few general conclusions about the applicabilities of the different types of extraction techniques are drawn. ... 

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