Purity grades

Modifications of Processes Based on Air Oxidation ofp-Xylene. Since the mid-1970s, starting in Japan, several companies have developed oxidation processes to yield relatively pure forms of terephthaUc acid without a separate purification. These products, normally called medium purity terephthahc acids, contain 200—300 ppm 4-formylbenzoic acid and trace amounts of acetic acid and thus do not meet normal specifications for the highest purity grades available (80,81). 

ANGUS Chemical Company is the only basic manufacturer of technical-grade TRIS AMINO (Tromethamine). However, ANGUS and numerous processors offer recrystallized, high purity grades of this alkanolamine for biomedical appHcations. 

Ferrosihcon production is a nearly slag-free process. Most of the impurities introduced into the furnace via the raw materials and any other sources are transferred to the product. In order to produce high purity grades of ferrosihcon, the tapped ahoy is refined by treating with gas mixtures and slag additions. The principle of ferrosihcon refining is quite similar to that of sihcon. Details on the thermochemistry of ferrosihcon refining and practical examples are available (24). 

High purity 50% ferrosihcon containing <0.1% Al and C is used for production of stainless steel and corded wire for tires, where residual aluminum can cause harm fill alumina-type inclusions. These are also useflil in continuous cast heats, where control of aluminum is necessary. High purity grades of 50 and 75% ferrosihcon containing low levels of aluminum, calcium, and titanium are used for sihcon additions to grain-oriented electrical steels, where low residual aluminum content contributes to the attainment of desired electrical properties, eg, significant reduction of eddy currents. 

Silicate esters are used ia the production of coating and refractories and in some semiconductor manufacturing operations. A broad range of purity grades of silicon tetrachloride are available to meet the requirements of these different appHcations. 

The market price of USP sodium iodide generally follows the price of cmde iodine multiphed by a factor of 1.8—2. Higher purity grades are only marginally related to the price of cmde iodine. 

NaHS, marketed as 71.5—74.5 wt % flakes and 43—60 wt % Hquor ia the high purity grades, is also available as 10—40 wt % Hquor from the oil refining desulfurization process. NaHS is sold commercially ia 22.7-kg bags, 181.4-kg dmms, ia tank tmcks, and ia rail cars. 

Sodium Sulfite Anhydrous, Technical Grade and High Purity Grade, data sheets, Solvay Minerals, Inc., Houston, Tex., 1995. 

Table 3. Imports of Commercial and High Purity Grades of Arsenic Metaf...

Year Commercial grade High purity grade ... 

Calcium carbonate is one of the most versatile mineral fillers (qv) and is consumed in a wide range of products including paper (qv), paint (qv), plastics, mbber, textiles (qv), caulks, sealants (qv), and printing inks (qv). High purity grades of both natural and precipitated calcium carbonate meet the requirements of the Food Chemicals Codex and the United States Pharmacopeia and are used in dentifrices (qv), cosmetics (qv), foods, and pharmaceuticals (qv). 

Phenol, in its various purity grades, is used for phenol—formaldehyde resins to bond constmction materials like plywood and composition board (40% of the phenol produced), for the bisphenol A employed in making epoxy resins (qv) and polycarbonate (qv) (30%), and for caprolactam (qv), the starting material for nylon-6 (20%). Minor amounts ate used for alkylphenols (qv) and pharmaceuticals (10). 

From our point of view, this is exactly what commercial ionic liquid production is about. Commercial producers try to make ionic liquids in the highest quality that can be achieved at reasonable cost. For some ionic liquids they can guarantee a purity greater than 99 %, for others perhaps only 95 %. If, however, customers are offered products with stated natures and amounts of impurities, they can then decide what kind of purity grade they need, given that they do have the opportunity to purify the commercial material further themselves. Since trace analysis of impurities in ionic liquids is still a field of ongoing fundamental research, we think that anybody who really needs (or believes that they need) a purity of greater than 99.99 % should synthesize or purify the ionic liquid themselves. Moreover, they may still need to develop the methods to specify this purity. 

The tantalum strip solution was used for the preparation, by precipitation and thermal treatment, of tantalum oxide. The product was determined to be of high purity grade. Table 62 presents typical analysis results. 

The USA Military Specification (Ref 14) contains the following requirements and criteria (1) a pre-production sample must meet the Spec requirements, (2) silicon monoxide shall be of a high purity grade, (3) chemical compn as detd by the powder—D-C arc semiquantitative technique... 

All programs presuppose the provision of high-quality, fully deaerated FW, with a pH level of 8.5 to 9.5 and appropriately low levels of sodium, silica, copper, iron, nickel, and other contaminants. (Refer to Figure 10.5 for additional details. Also refer to Table 9.3 for MU water purity grades.)... 

The reaction is unfavorable for the production of potassium at 870°C, but the removal of K by distillation drives the equilibrium to the right. A variation in the condenser temperature can be used to produce Na-K alloys or potassium with a typical Na content of 1.0 wt%. A high-purity grade of potassium, with Na contents < 50 ppm, is produced commercially by distillation in a multiplate tower... 

Sold as a solid in pellet and flake forms in several purity grades. Commonly used in commerce as a 50% solution in water. 

But even when single solvents are employed as developing solvents, attention has to be given to purity grade, manufacturer, batch, and stabilizers contained. 

Use of FID and SCD are compatible with SFE-HPLC, since they are flame-based and unaffected by gases in the mobile phase. Unfortunately, SCD can only be used with micro-HPLC (column i.d. <320 (tm), which requires miniaturised equipment not commonly found in most analytical laboratories. When following SFE with HPLC analysis using a spectroscopic detector, a medium-purity grade is usually sufficient. 

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