Small-scale processing

Addnl Refs (Limited Distribution) A) F.A. Armstrong R.T.M. Fraser, The Silica Gel Process Small Scale Studies. Part 1 Comparison of Catalysts and Labelling Experiments , ERDE TR 113, Waltham Abbey (Engl) (1972)... 

Saffinan and Turner (43) considered collisions between droplets due to turbulence in rain clouds. Under turbulent conditions, droplet collision is governed by two different mechanisms isotropic turbulent shear and turbulent inertia. The choice of regime applicable to a droplet is determined by its size in relation to the Kolmogorov microscale denned earlier. Droplets of diameter d > t are subjected to die former of these processes (small-scale motion). Spatial variations in the flow give neighboring droplets different velocities and fliis result in collisions. Droplets of diameter d > T] are subjected to turbulent inertia. In this case, collisions result from the relative movement of droplets in the surrounding fluid. Droplets of different diameter will have different inertias and this results in collisions. Droplets of equal diameter, however, will not collide under this mechanism as fliey have the same inertia. 

Sublimation. This is a most useful process for small-scale work as the losses are comparatively small. This can be performed (a) In a long narrow tube sealed at one end. The material is shaken to the closed end of the tube, which is then inserted horizontally in a metal-heating block (Fig. 50) (b) In the cold-finger device (Fig. 35, p. 62)-... 

When collecting a sample, for instance, only a small portion of the available material is taken, increasing the likelihood that small-scale inhomogeneities in the sample will affect the repeatability of the analysis. Individual pennies, for example, are expected to show variation from several sources, including the manufacturing process, and the loss of small amounts of metal or the addition of dirt during circulation. These variations are sources of indeterminate error associated with the sampling process. 

A small amount of particleboard is made with a fire-retardant treatment for use in locations where codes require this material, as in some offices and elevators. Particleboards receive overlay and finishing treatments with ease. Wood veneers, melamine overlays, printed paper overlays, vinyl overlays, foils, and direct grain printing can all be done quite simply. A small amount of particleboard is also made in the form of shaped, molded articles such as furniture parts, paper roU plugs, bmsh bases, and even toilet seats. There is another small increment of particleboard made by the extmsion process. These products are made in small captive operations owned by furniture manufacturers which consume all of this production in their furniture. The extmsion process differs from conventional flat-pressed particleboard in that the wood furnish is forced between two stationary heated surfaces. The mats are formed from one edge and this edge is alternately formed and pushed between the heated platens, which are maintained at a distance equal to the thickness of board produced. This is an old, slow, small-scale process, but is stiU in use in at least one location. 

However, chromatographic processes stiH have a considerable appHcabiHty (106) (see Analytical methods). For instance, in small-scale operations, the greater simplicity of the chromatograph may more than compensate economically for the larger adsorbent inventory and desorbent usage. 

Feedstock Development. Most of the research in process in the United States in the early 1990s on the selection of suitable biomass species for energy appHcations is limited to laboratory studies and small-scale test plots. Many of the research programs on feedstock development were started in the 1970s or early 1980s. 

Historically, SOG techniques have been used the most for IMD fabrication, but TEOS/o2one (TEOS/O ) processes are more recent developments that have been increasing in popularity based on excellent step coverage and void-free characteristics. TEOS/O doped with boron and phosphoms (BPTEOS/O ) has replaced BPSG in small-scale devices, and has been used successfully in 4- and 16-Mb DRAM production (16). 

Preparation from Nitrene Intermediates. A convenient, small-scale method for the conversion of carboxyhc acid derivatives into isocyanates involves electron sextet rearrangements, such as the ones described by Hofmann and Curtius (12). For example, treatment of ben2amide [55-21-0] with halogens leads to an A/-haloamide (2) which, in the presence of base, forms a nitrene intermediate (3). The nitrene intermediate undergoes rapid rearrangement to yield an isocyanate. Ureas can also be formed in the process if water is present (18,19). 

Pilot plants are often more hazardous than process plants, even though they are smaller ia size, for many reasons. These iaclude a tendency to relax standard safety review procedures based on the small scale, exceptionally qualified personnel iavolved, and the experimental nature of the research operations the lack of estabhshed operational practice and experience lack of information regarding new materials or processes and lack of effective automatic iatedocks due to the frequendy changing nature of pilot-plant operations, the desire for wide latitude in operating conditions, and the lack of hill-time maintenance personnel. 

Process probably not competitive for small-scale operations (>10 20 t/d product gas). 

Favor adsorption for small-scale desiccation operations soHd-phase desiccant systems are relatively simple to design and operate (generally are lowest cost alternative for processing small quantities of gas). 

Other Methods. Instant tea may also be prepared by directiy extracting fermented leaf before the firing stage. These processes, only suited for practice in the tea-growing countries, have been carried out on a small scale in Sri Lanka, India, and Kenya (101). 

Butylene Oxide. Butylene oxides are prepared on a small scale by Dow by chlorohydrin technology. There appears to be no technical reason why they could not be prepared by the propylene oxide Oxirane process (see Chlorohydrins). 

Potential Use. Processes using butylenes as feedstocks have been developed for a group of industrial chemicals that are not currendy produced by these processes or are produced only on a relatively small scale. Such chemicals are isoprene [78-79-5] maleic anhydride [108-31-6] acetic acid [64-19-7] and until recendy, methyl methacrylate and methyl tert-huty ether. These processes are of interest because they may emerge as important processes with suitable improvements, changes in product values, or development of new markets. 

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