Processable Materials

Steps such as the substitution of low sulfur fuels or nonvolatile solvents, change of taw materials, lowering of operation temperatures to reduce NO formation or vo1ati1i2ation of process material, and instaHion of weU-designed hoods (31—37) at emission points to effectively reduce the air quantity needed for pollutant capture are illustrations of the above principles. 

Induction heating is used to heat steel reactor vessels in the chemical process industry (5). The heat produced in the walls is conducted to the material within. Multisectioned cods are used to provide controlled heat input to the process material as it passes through the reactor. Figure 6 illustrates a cross section of such a typical installation. 

The first step is to have a complete and detailed description of the system, process, or procedure under consideration. This must include physical properties of the materials, operating temperatures and pressures, detailed flow sheets, instmment diagrams of the process, materials of constmction, other detailed design specifications, and so forth. The more detailed and up-to-date this information is, the better the result of the analysis. 

Fouling of the pH sensor may occur in solutions containing surface-active constituents that coat the electrode surface and may result in sluggish response and drift of the pH reading. Prolonged measurements in blood, sludges, and various industrial process materials and wastes can cause such drift. Therefore, it is necessary to clean the membrane mechanically or chemically at intervals that are consistent with the magnitude of the effect and the precision of the results requited. 

The primary environmental concern for the coating plant is actually the residual material on the anode stmctures being returned for recoating. Therefore the anode user must enact effective cleaning procedures prior to shipment. For example, anodes in chlorine use must be cleaned of all traces of mercury and asbestos (qv). Anodes used in electrogalvanizing or in copper-foil production must similarly be cleaned to remove all traces of process materials. If cleaning at the user s plant is not done effectively, the anode may well be shipped back to the user for appropriate action before it is considered for recoating. 

Principles in Processing Materials. In most practical apphcations of microwave power, the material to be processed is adequately specified in terms of its dielectric permittivity and conductivity. The permittivity is generally taken as complex to reflect loss mechanisms of the dielectric polarization process the conductivity may be specified separately to designate free carriers. Eor simplicity, it is common to lump ah. loss or absorption processes under one constitutive parameter (20) which can be alternatively labeled a conductivity, <7, or an imaginary part of the complex dielectric constant, S, as expressed in the foUowing equations for complex permittivity ... 

Industrial screening is used essentially for separations over 0.2 mm and in conjunction with cmshers because the efficiency decreases rapidly as particle size decreases. The main objective is to remove undersize material that should not be circulated back to the cmshers, or to remove (scalp) oversize material or trash that should not report to the subsequent processing step. Other appHcations of screening include production of a specification size material (as in quarrys), dewatering, and trash removal from processed material. 

Another method of purifying niobium is by distillation of the anhydrous mixed chlorides (29). Niobium and tantalum pentachlorides boil within about 15°C of one another which makes control of the process difficult. Additionally, process materials must withstand the corrosion effects of the chloride. The system must be kept meticulously anhydrous and air-free to avoid plugging resulting from the formation of niobium oxide trichloride, NbOQ. Distillation has been used commercially in the past. 

Manufacturing, analytical, and quaUty control procedures are thus estabhshed. Specifications for taw and in-process materials, as well as for final products per USP/NF and in-house standards are also determined. Process and formula vaUdation assures that each technological procedure in manufacture accomplishes its purpose most efficiently, eg, blending times for powdered mixtures in tableting, and that each formula ingredient is present in optimal concentrations (12). Thus, it serves to ensure process control (qv), reproducibiUty, and content uniformity. 

Phosphoms trichloride is also used in the manufacture of antifoam agents, catalysts, dyes and pigments, as well as pharmaceutical and quaternary compounds, and is commonly used as a chlorinating agent. Phosphoms trichloride is used to make phosphoms oxychloride, which is used in the manufacture of adsorbents for air filters, antifoam agents, dyes and pigments, mineral-processing materials, pharmaceuticals (qv), and solvents. These uses represented 32,000 t of PCl in 1988 and 30,000 t in 1994. 

Table 2 Hsts some of the physical, toxicity, flammabiUty, and reactivity properties of common chemicals (10,13,42,45—51). Also given are some of the quantities specified for reporting spills and for compliance with legislated requirements. The OSHA regulations require that material safety data sheets (MSDS) be developed for all process materials, so that the ha2ard data can be communicated to employees (52). Characteristics of toxicity, flammabiUty, chemical iastabiUty, reactivity and reaction energy, operatiag coaditioas, and corrosive properties of constmction materials must all be considered ia analy2iag ha2ard poteatials of chemicals and chemical operations.

J. W. Cobum, R. A. Gottscho, andD. W. Hess, eds.. Plasma Processing, Materials Research Society, Pittsburgh, Pa., 1986. 

Other factors that favor the choice of the steam ejector are the presence of process materials that can form soflds or require high alloy materials of constmction. Factors that favor the vacuum pump are credits for pollution abatement and high cost steam. The mechanical systems require more maintenance and some form of backup vacuum system, but these can be designed with adequate reflabiUty. 

Quahty control iaspection is a post-, or at best concurrent, manufacture activity. The QC laboratory reports on ia-process and finished product quahty based on testing. Thus QC confirms whether a material has been manufactured in conformance. Sometimes QC also assists the production unit in salvaging process material or reworking off-standard finished product. 

AU processed material is screened to return the coarse fraction for a second pass through the system. Process feed rates are matched to operating variables such as rpm speed and internal clearances, thus minimizing the level of excess fines (—200 mesh (<0.075 mm mm)). At one installation (3) the foUowing product size gradation of total smaller than mesh size (cumulative minus) was obtained ... 

The microstmcture and imperfection content of coatings produced by atomistic deposition processes can be varied over a very wide range to produce stmctures and properties similar to or totally different from bulk processed materials. In the latter case, the deposited materials may have high intrinsic stress, high point-defect concentration, extremely fine grain size, oriented microstmcture, metastable phases, incorporated impurities, and macro-and microporosity. AH of these may affect the physical, chemical, and mechanical properties of the coating. 

High speed machines such as impact mills begin to suffer high wear rates when processing materials above Mohs s hardness 3, unless very special wear-resisting measures can be taken. 

Continuous polymerization systems offer the possibiUty of several advantages including better heat transfer and cooling capacity, reduction in downtime, more uniform products, and less raw material handling (59,60). In some continuous emulsion homopolymerization processes, materials are added continuously to a first ketde and partially polymerized, then passed into a second reactor where, with additional initiator, the reaction is concluded. Continuous emulsion copolymerizations of vinyl acetate with ethylene have been described (61—64). Recirculating loop reactors which have high heat-transfer rates have found use for the manufacture of latexes for paint appHcations (59). 

U.S. imports of calcium metals fluctuate greatiy. Since the mid-1980s, the avadabiHty of very low priced calcium metal from China and the CIS has led to substantial reductions in calcium production by Western producers. This has been compensated to a certain extent by an increase in sales of processed materials, ie, alloys and particulates, by the Western companies. In 1991, more than 700 tons of calcium metal were imported to the United States from the People s RepubHc of China. Significant quantities of calcium alloys and particulates have also been imported from France and Canada. 

Concentration Control. Sequestration, solubilization, and buffering depend on the concentration control feature of chelation. Traces of metal ions are almost universally present in Hquid systems, often arising from the materials of the handling equipment if not introduced by the process materials. Despite very low concentrations, some trace metals produce undesirable effects such as coloration or instabiHty. 

Examination of equation 42 shows that T is directly proportional to the average stage holdup of process material. Thus, in conjunction with the fact that hquid densities are on the order of a thousand times larger than gas densities at normal conditions, the reason for the widespread use of gas-phase processes in preference to hquid-phase processes in cascades for achieving difficult separations becomes clear. 

Utihty needs should be calculated direcdy from the process material and energy balances. Unit costs for the various utihties can be obtained from suppliers or purchasing agents. Although regional variations can be quite large, typical U.S. utihty costs in 1992 are tabulated in Table 3. 

The detergent industry is the largest user of industrial enzymes. The starch industry, the first significant user of enzymes, developed special symps that could not be made by means of conventional chemical hydrolysis. These were the first products made entirely by enzymatic processes. Materials such as textiles and leather can be produced in a more rational way when using enzyme technology. Eoodstuffs and components of animal feed can be produced by enzymatic processes that require less energy, less equipment, or fewer chemicals compared with traditional techniques. 

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