Equipment and Techniques

The importance of low pressures has already been stressed as a criterion for surface science studies. However, it is also a limitation because real-world phenomena do not occur in a controlled vacuum. Instead, they occur at atmospheric pressures or higher, often at elevated temperatures, and in conditions of humidity or even contamination. Hence, a major tlmist in surface science has been to modify existmg techniques and equipment to pemiit detailed surface analysis under conditions that are less than ideal. The scamiing tunnelling microscope (STM) is a recent addition to the surface science arsenal and has the capability of providing atomic-scale infomiation at ambient pressures and elevated temperatures. Incredible insight into the nature of surface reactions has been achieved by means of the STM and other in situ teclmiques. 

Most aroma chemicals are relatively high boiling (80—160°C at 0.4 kPa = 3 mm Hg) Hquids and therefore are subject to purification by vacuum distillation. Because small amounts of decomposition may lead to unacceptable odor contamination, thermal stabiUty of products and by-products is an issue. Important advances have been made in distillation techniques and equipment to allow routine production of 5000 kg or larger batches of various products. In order to make optimal use of equipment and to standardize conditions for distillations and reactions, computer control has been instituted. This is particulady well suited to the multipurpose batch operations encountered in most aroma chemical plants. In some instances, on-line analytical capabihty is being developed to work in conjunction with computer controls. 

Knowledge of material-handling techniques is vital to the layout planner, and detailed consideration will need to be given to the various techniques and equipment, which are available. References 2, 8 and 9 contain valuable information and trade journals report the current state of the market. 

Figure 10.1. A particle size selection guide to solid-solid separation techniques and equipment (after Roberts...

The need to separate solid and liquid phases is probably the most common phase separation requirement in the process industries, and a variety of techniques is used (Figure 10.9). Separation is effected by either the difference in density between the liquid and solids, using either gravity or centrifugal force, or, for filtration, depends on the particle size and shape. The most suitable technique to use will depend on the solids concentration and feed rate, as well as the size and nature of the solid particles. The range of application of various techniques and equipment, as a function of slurry concentration and particle size, is shown in Figure 10.10. 

The separation of liquid droplets and mists from gas or vapour streams is analogous to the separation of solid particles and, with the possible exception of filtration, the same techniques and equipment can be used. 

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

The need to provide protective measures will be directly related to the level of potential hazards which may be assessed from the procedures outlined above. Measures concerned with reaction control are frequently mentioned in the following text, but details of techniques and equipment for personal protection, though usually excluded from the scope of this work, are obviously of great importance. 

We will hereafter describe only techniques and equipments of interest for cryogenics. More information can be found in ref. [1-4],... 

Standardized techniques and equipment for such investigations are in widespread use. Unfortunately, the same cannot be said for metabolism investigations in aquatic animals. Most of the world s animals exclusive of the insects —over 200,000 known species -- live at least a part of their lives in water over 100 species have major economic importance and they form the populations most often at risk of exposure to a growing number of chemical pollutants, but science remains largely ignorant of the disposition of xenobiotics by intact, living specimens of even the most common of the aquatic animals. 

Unfortunately, electrochemistry has not been fully embraced by organic chemists, despite the fact that it often provides methodology which may be better suited or superior to a non-electrochemical counterpart. Some of this reluctance is undoubtedly related to the fact that the techniques and equipment are not readily available in each laboratory setting. One hopes that eventually the community will consider electrochemistry simply as another tool, to be explored as routinely as any other. Like all others, it ought to be evaluated in a given context, and used in accordance with its merit. 

High Rate Detonator Production Study. As part of the overall program to modernize the US Govt owned, company operated, Army Ammunition Loading and Assembly Plants, it is planned to develop fully automatic equipment to manuf nonelectric detonators at the rate of 1200 per minute. The survey of literature sources and industry was undertaken to discover techniques and equipment that may be applicable, as described in Ref 1... 

Refs 1) E.E. Hannum, Survey of Techniques and Equipment for High-Volume, Automatic Production of Non-Electric Detonators , PATR 4541 (1974) 2) G. Cohn, Edit, Expls Pyrots 7... 

CCOOC3Ha)2 mw 146.14, col, unstable aromatic liquid combustible but not flammable sp gr 1-079 at 20/4° (Lange), 1.09 at 20/20° (Ref 3), fr P -40.6°, bp 185-4-186° fl p 168°F v si isol in w with gradual deoompn miscible with ale, eth, eth acetate and other common org solvents. Can be prepd by standard esterification procedure using ethanol oxalic acid. The final purification, however calls for specific technique and equipment (Ref 3). Used as solvent for cellulose esters ethers and for synthetic resins also for radio tube cathode fixing lacquers, pharmaceuticals, etc... 

Tests for sterility are to be carried out by trained personnel using techniques and equipment that minimize the risks of accidental microbial contamination of the tests and of the testing environment. 

The march of refining techniques and equipment design during the past 25 years has been matched, step by step, by advances in instrumentation. Twenty-five years ago the few instruments available were used primarily as a guide to operation, and it was perfectly possible to control a batch still with only two or three thermometers and a hydrometer, to yield products adequate for the needs of that period. Today we depend on instruments to control distillation units and anticipate trends with1 greater speed and accuracy than is possible by an operator. 

At the beginning of HPLC use, due to the complexity and variety of matrices that occurred in foods as well as their different properties and the evaluation level of techniques and equipment, it was practically impossible to use a single universal procedure for all SPA determinations. However, contemporary procedures and techniques make it possible to determine all SPA in one procedure. 

Badger-Hickman Centrifugal Distillation Techniques and Equipment/ U. S. Dept. Interior, Saline Water Conversion Program, Progress Rept. 12 (November 1956). 

Substitute for Conventional Vulcanized Rubbers, For this application, the products are processed by techniques and equipment developed for conventional thermoplastics, ie, injection molding, extrusion, etc. The S—B—S and S—EB—S polymers are preferred (small amounts of S—EP—S are also used). To obtain a satisfactory balance of properties, they must be compounded with oils, fillers, or other polymers compounding reduces costs. Compounding ingredients and their effects on properties are given in Table 8. Oils with high aromatic content should be avoided because they plasticize the polystyrene domains. Polystyrene is often used as an ingredient in S—B—S-based compounds it makes the products harder and improves their processibility. In S—EB—S-based compounds, crystalline polyolefins such as polypropylene and polyethylene are preferred. Some work has been reported on blends of liquid polysiloxanes with S—EB—S block copolymers. The products are primarily intended for medical and pharmaceutical-type applications and hardnesses as low as 5 on the Shore A scale have been reported (53). 

Citrus juices that are pasteurized at the lower temperatures, 65-66°C, can undergo clarification, i.e., a process of separation that results in a lower layer of liquid and sediment and an upper layer of clear liquid. This process is brought about by the natural enzyme, pectinesterase, that occurs in citrus fruits. Studies have shown that processing of the juice at temperatures of 170-210°F (76.7-99°C) for a fraction of a second to 40 seconds will destroy the pectinesterase activity in citrus juices (7-10). The temperature necessary to stabilize the juice is pH dependent. Juices at higher pH require higher temperatures for stabilization. With the new high-temperature short-time techniques and equipment, stabilization can usually be effected in a fraction of a second. Flash pasteurization can be accomplished in either a plate-type or a tube-type heat exchanger. 

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