Solvents used for the raw material manufacture

As a rule of thumb, the speeifieations set for solvents used for the crystallization step will be more stringent than those used during the synthesis. 

For the intermediates of synthesis, if the origin of the solvent is under eontrol (e.g., existence of contraets/Quality Assurance audits) a simplified monograph is eompletely adequate (see Table 14.21.1.5) as long as the supplier provides a detailed eertifieate of analysis where impurities (ineluding solvents) are properly speeified with aeeeptable limits. If the same solvent is used for the erystallization step additional purity tests are neeessary (Table 14.21.1.6). 

For eeonomic reasons, it may be necessary to recycle solvents. If so, the containers should be fully identified in terms of storage  

We recommend working with reliable solvent suppliers who can give every assurance on the quality of solvents provided to avoid any unpleasant surprises . 

Final crystallization solvents (of well controlled origin) 

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Stereochemistry. Cyclohexane can exist ia two molecular conformations the chair and boat forms. Conversion from one conformation to the other iavolves rotations about carbon—carbon single bonds. Energy barriers associated with this type of rotation are low and transition from one form to the other is rapid. The predominant stereochemistry of cyclohexane has no influence ia its use as a raw material for nylon manufacture or as a solvent. 

Almost all of the cyclohexane that is produced in concentrated form is used as a raw material in the first step of nylon-6 and nylon-6,6 manufacture. Cyclohexane also is an excellent solvent for cellulose ethers, resins, waxes (qv), fats, oils, bitumen, and mbber (see Cellulose ethers Resins, natural Fats AND FATTY OILS Rubber, NATURAL). When used as a solvent, it usually is in admixture with other hydrocarbons. However, a small amount is used as a reaction diluent in polymer processes. 

Process Raw Material. Industrial solvents are raw materials in some production processes. Eor example, only a small proportion of acetone is used as a solvent, most is used in producing methyl methacrylate and bisphenol A. Alcohols are used in the manufacture of esters and glycol ethers. Diethylenetriamine is also used in the manufacture of curing agents for epoxy resins. Traditionally, chlorinated hydrocarbon solvents have been the starting materials for duorinated hydrocarbon production. 

Dyes, Dye Intermediates, and Naphthalene. Several thousand different synthetic dyes are known, having a total worldwide consumption of 298 million kg/yr (see Dyes AND dye intermediates). Many dyes contain some form of sulfonate as —SO H, —SO Na, or —SO2NH2. Acid dyes, solvent dyes, basic dyes, disperse dyes, fiber-reactive dyes, and vat dyes can have one or more sulfonic acid groups incorporated into their molecular stmcture. The raw materials used for the manufacture of dyes are mainly aromatic hydrocarbons (67—74) and include ben2ene, toluene, naphthalene, anthracene, pyrene, phenol (qv), pyridine, and carba2ole. Anthraquinone sulfonic acid is an important dye intermediate and is prepared by sulfonation of anthraquinone using sulfur trioxide and sulfuric acid. 

Sustainability, hazard reduction, and protection of health and the environment remain great concerns for the process industries. Many of the raw materials used—especially those derived from oil, gas, and some plants and animals—have been and in some cases continue to be depleted at rates either large compared to known reserves or faster than replenishment. In addition, there is the desire for products, intermediates, solvents, catalysts, and other materials produced or selected for use in chemical manufacture to be as safe and nontoxic as possible during their use and to be recoverable or benignly degradable after their use. 

Manufacturing processes in which organic products are made are of special interest to green chemists for a variety of reasons, largely because so many of the raw materials used to make such products, the by-products formed in the reactions, and the final products themselves are likely to he toxic or hazardous in other ways. Historically, the problem with such manufacturing processes is that they have required the use of organic solvents, such as carbon tetrachloride, chloroform, tetrachloroethylene, trichloroethylene, 1,1,1-trichloro-ethane, benzene, toluene, and xylene. A major thrust, then, has been to find satisfactory substitutes for these organic solvents. 

The extraction of raw materials, manufacturing processes, use/reuse, and disposal represent the basic stages of a solvent s life cycle. Each stage of a solvent s life cycle generates a variety of environmental burdens. Environmental-impact evaluation qualitatively assesses the life-cycle stages for chemical solvents. The goal of this evaluation is to select environmentally preferable solvents that can best minimize these life-cycle impacts. 

Gun propellants are manufactured by three different methods (i) solvent method (ii) semi-solvent method and (iii) solventless method. The solvent method is that most commonly used for the manufacture of gun propellants. Selection of the method for manufacture basically depends on the properties of the raw materials and the propellant formulation. While there are limitations for the manufacture of gun propellants by solventless and semi-solvent methods, the solvent method may be applied for almost every gun propellant formulation. The solid-liquid ratio of the ingredients and the type of nitrocellulose used usually decide the feasibility of manufacture by the solventless method. Some characteristics of solid gun propellants are given in Table 4.1. 

Ethylene (structure in Figure 13.1) is the most widely used organic chemical. Almost all of it is consumed as a chemical feedstock for the manufacture of other organic chemicals. Polymerization of ethylene to produce polyethylene is illustrated in Figure 13.4. In addition to polyethylene, other polymeric plastics, elastomers, fibers, and resins are manufactured with ethylene as one of the ingredients. Ethylene is also the raw material for the manufacture of ethylene glycol antifreeze, solvents, plasticizers, surfactants, and coatings. 

Pure acrylonitrile may polymerize at room temperature to polyacrylonitrile (PAN), a compound that, unlike polyamides and polyesters, does not melt at elevated temperatures but only softens and finally discolors and decomposes. Nor is it soluble in inexpensive low-boiling organic solvents. Because fibers made from it resist the dyeing operations commonly used in the textile industry, the usual practice is to modify it by copolymerization with other monomers, for example, vinyl acetate, styrene, acrylic esters, acrylamide, or vinyl pyridine in amounts up to 15 percent of the total weight (beyond which the final product may not be termed an acrylic fiber). The choice of modifier depends on the characteristics that a given manufacturer considers important in a fiber, the availability and cost of the raw materials in the manufacturer s particular area of production, and the patent situation. 

The industrial capacity for worldwide production of methanol in 1994 was 2.42 x 10 metric tons per year3 about 85% of which was used as a starting material in the production of other chemicals or as a solvent. Methanol is used as a raw material in the manufacture of formaldehyde. acetic acid, methyl /erf-butyl ether (MTBE), dimethyl terephthalate, methyl chloride, methyl amines, and many other chemicals. It can also be used as a clean-burning fuel. 

Multiple uses. It is desirable to use as the extraction solvent a material that can serve a number of purposes in the manufacturing plant. This avoids the cost of storing and handling multiple solvents. It may be possible to use a single solvent for a number of different extraction processes practiced in the same facility, either in different equipment operated at the same time or by using the same equipment in a series of product campaigns. In other cases, the solvent used for extraction may be one of the raw materials for a reaction carried out in the same facility, or a solvent used in another operation such as a crystallization. 

Chemical reactions normally require a solvent that can dissolve all the raw materials. Reaction kinetics and selectivity may be affected by the choice of solvent. Thermophysical properties of solvents are also very important for endothermic and exothermic reactions. Water, hydrocarbons, alcohols, ketones, chlorinated solvents, and amines are the most widely used solvents in the chemical process industry. In many applications, the solvent is consumed as a raw material. One example is the manufacture of esters, where alcohol takes part in the reaction. 

Kerosene is used as a raw material for the manufacture of keryl benzene sulfonates (38). A close-cut, highly acid treated, or solvent refined material boiling in the range of 425 to 475 F. is used for this purpose. 

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