Purity, specification

Reagent-grade urea is used in some pharmaceutical preparations. In these appHcations, urea must meet the purity specifications issued by the ACS. 

Ethylene Stripping. The acetylene absorber bottom product is routed to the ethylene stripper, which operates at low pressure. In the bottom part of this tower the loaded solvent is stripped by heat input according to the purity specifications of the acetylene product. A lean DMF fraction is routed to the top of the upper part for selective absorption of acetylene. This feature reduces the acetylene content in the recycle gas to its minimum (typically 1%). The overhead gas fraction is recycled to the cracked gas compression of the olefin plant for the recovery of the ethylene. 

Large quantities of butane are shipped under contract standards rather than under national or worldwide specifications. Most of the petrochemical feedstock materials are sold at purity specifications of 95—99.5 mol %. Butane and butane—petroleum mixtures intended for fuel use are sold worldwide under specifications defined by the Gas Processors Association, and the specifications and test methods have been pubHshed (28). Butanes may be readily detected by gas chromatography. Butanes commonly are stored in caverns (29) or refrigerated tanks. 

Enzymes are used as feed digestibiUty enhancers for chicken and pigs. They must comply with purity specifications comparable to food-grade enzyme specifications. European Community (EC) guidelines for the assessment of additives in animal nutrition are being revised to make them appHcable for enzymes. Upon completion of these guidelines, the regulatory status of feed enzymes will be estabUshed in EC directive 70/524/EEC. 

In this case, there are n process variables with equality constraints and inequahty constraints. Such problems pose a serious challenge to performing optimization calculations in a reasonable amount of time. Typical constraints in chemical process optimization include operating conditions (temperatures, pressures, and flows have limits), storage capacities, and produc t purity specifications. 

Product purity specifications determine how much soluble corrosion product can be tolerated. 

The introduction of extraneous material can create new problems in achieving product purity specifications. 

Most laboratory chemicals are available in a number of grades, usually according to the concentration of impurities that are present. Generally, the purer the chemical, the more expensive it will be. A supplier s catalogue will indicate the different grades available for a particular chemical, together with the related purity specifications. You should bear in mind that the specification may not identify all of the impurities that are present. The nature of the impurities may or may not be important, depending on how the chemical is to be used. 

Only sweeteners conforming to certain purity criteria are permitted for use in foods. Such purity specifications are normally based on the specifications of the substance used in safety evaluations as byproducts and impurities may affect the toxicological profile of a substance. 

All purity specifications normally list identity tests, an assay, further criteria like loss on drying, general maximum levels for heavy metals and substance-specific limits of byproducts. 

ZeoHte adsorbents play a dominant role in purifications owing to their ability to both adsorb large quantities of material and to achieve extremely low mole fractions of these adsorbed these compounds in product gas. Zeolites are the preferred adsorbent types for dehydration to low levels, purification and in several bulk separations. Zeolites also are employed in a significant portion of the PSA hydrogen purification market segment where they add value to bulk separations by achieving particularly high purity specifications. 

By contrast, the industrial user must view any raw material purchase in terms of its cost effectiveness and in the case of rare earth metals this frequently requires the adoption of low purity specifications. Therefore, in the context of the industrial applications to which reference will be made, the term pure will be taken to include all metals having a purity of not less than 95% - the balance being predominately other rare earths. But before considering the applications in detail it is perhaps of value to have some appreciation of the size of the market for these metals. 

Many of the chemical and physical properties of mineral fillers are important in their application in thermoplastics. These include purity, specific gravity, hardness, electrical, thermal and optical properties, surface area, particle shape and size. The determination and importance of many of these has been covered in several reviews [65,66]. Only a brief coverage is given here for the less ambiguous properties such as specific gravity, hardness and standard thermal and optical properties, with most attention being concentrated on properties such as size and shape which have been found to give particular problems in measurement and interpretation. 

Because ethylbenzene is used almost exclusively to produce styrene, the product specification on ethylbenzene is set to provide a satisfactory feedstock for styrene production. Levels of cumene, -propylbenzene, ethyltoluenes and xylenes in ethylbenzene are controlled to meet the required styrene purity specification. A typical sales specification is as follows purity, 99.5 wt% min. benzene, 0.1-0.3 wt% toluene, 0.1-0.3wt% ort/io-xylene + cumene, 0.02 wt% max. meto-xylene + para-xylene, 0.2 wt% max. allylbenzene + a-propylbenzene + ethyltoluene, 0.2 wt% max. diethylbenzene, 20 mg/kg max. total chlorides (as chlorine), 1-3 mg/kg max. and total organic sulfur, 4 mg/kg max. (Coty et al., 1987). 

Laboratory controls should include the establishment of scientifically sound and appropriate specifications, standards, sampling plans, and test procedures to ensure that raw materials and containers conform to established standards of quality and purity. Specifications, standards, sampling plans, test procedures, or other laboratory control mechanisms, including any minor changes, should be updated by the appropriate organizational unit and reviewed and approved by the QC unit. Laboratory controls should be followed and documented at the time of performance. Deviations from written specifications, standards, sampling plans, test procedures, or other laboratory control mechanisms should be documented and justified. 

Analytical and purity specifications for various grades of Zr and Zr compds of interest to ordnance applications are provided in the following documents ... 

Differential scanning calorimetric methods are applied for the determination of heat of fusion, purity, specific heat and activation energy of decompn for undiluted, unmixed samples of TNT, TNB, Tetryl, RDX, HMX and PETN (Ref 28). The differential thermal analysis thermo-... 

The international consensus is largely that, in principle, authorization for food additives should be given only if justified technologically. This means that without such additives, the required effect could only be achieved either uneconomically or not at all. In every country, food additives are subject to purity specifications which are fixed by law. 

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