Recovery of products

Another example is the purification of a P-lactam antibiotic, where process-scale reversed-phase separations began to be used around 1983 when suitable, high pressure process-scale equipment became available. A reversed-phase microparticulate (55—105 p.m particle size) C g siUca column, with a mobile phase of aqueous methanol having 0.1 Af ammonium phosphate at pH 5.3, was able to fractionate out impurities not readily removed by hquid—hquid extraction (37). Optimization of the separation resulted in recovery of product at 93% purity and 95% yield. This type of separation differs markedly from protein purification in feed concentration ( i 50 200 g/L for cefonicid vs 1 to 10 g/L for protein), molecular weight of impurities (<5000 compared to 10,000—100,000 for proteins), and throughputs ( i l-2 mg/(g stationary phasemin) compared to 0.01—0.1 mg/(gmin) for proteins). 

In recent years alkylations have been accompHshed with acidic zeoHte catalysts, most nobably ZSM-5. A ZSM-5 ethylbenzene process was commercialized joiatiy by Mobil Co. and Badger America ia 1976 (24). The vapor-phase reaction occurs at temperatures above 370°C over a fixed bed of catalyst at 1.4—2.8 MPa (200—400 psi) with high ethylene space velocities. A typical molar ethylene to benzene ratio is about 1—1.2. The conversion to ethylbenzene is quantitative. The principal advantages of zeoHte-based routes are easy recovery of products, elimination of corrosive or environmentally unacceptable by-products, high product yields and selectivities, and high process heat recovery (25,26). 

In-plant controls are perhaps the best approach to eliminate waste generation and pollution problems, and many times good payback exists on recovery of products lost because of poor process controls. If the production department is responsible for the generation and in-plant control of wastes, this will help ensure that initial standards for water use and process loss are reasonable and that they are maintained (33). 

The felted fabrics are generally used for maximum recovery of product and are used at high face velocity for airflow-to-cloth-area ratio. The felt promotes the greatest dust collection surface. 

Nitroethylene, IT2C — CHNCH, is a sensitive compound that must be prepared with great care. Attempted purification of nitroethylene by distillation often results in low recovery of product and a white coating on the inner walls of the distillation apparatus. Explain. 

The retentive power of graphite towards adipic acid and the catalytic effect of the magnetite, especially present in A, are obvious. TEM examinations of a graphite A sample before and after reaction showed that crystallites of Fe304 appeared to be smaller after the reaction. However, the same graphite sample was reused for three successive reactions without significant loss in yield. When applied to the synthesis of other cyclic ketones (Scheme 7.14), less volatile than 74, it was observed that pressure had an effect on the recovery of product (Tab. 7.9, entries 3 and 4). A slightly reduced pressure (300 mm Hg) was necessary to obtain 3-methylcyclopentanone (75) or cyclohexanone (76) in convenient yield (Tab. 7.9, entries 4 and 5). For the cycliza-tion of suberic acid (73), a less favorable structure, the yield in cycloheptanone (77) remained low (Tab. 7.9, entry 6). 

Cocurrent depressurization, purge, and pressure-equalization steps are normally added to increase efficiency of separation and recovery of product. At the end of the adsorption step, the more weakly adsorbed species have been recovered as product, but there is still a significant amount held up in the bed in the inter- and intraparticle void spaces. A cocurrent depressurization step can be added before the blowdown step, which is countercurrent to adsorption. This increases the amount of product produced each cycle. In some applications, the purity of the more strongly adsorbed components has also been shown to be heavily dependent on the cocurrent depressurization step [Cen and Yang, Ina. Eng. Chem. Fundam., 25, 758-767 (1986)]. This cocurrent blowdown is optional because there is always a countercurrent one. Skarstrom developed criteria to determine when the use of both is justified [Skarstrom in Li, Recent Developments in Separation Science, vol. II, CRC Press, Boca Raton, pp. 95-106 (1975)]. 

A mixture of acetone and chloroform is to be separated into pure products [Hostrup et al. (1999)]. Since they also form an azeotrope, one alternative to satisfy the separation objective is to find a suitable solvent for separation by extractive distillation. This type of problem in product design is usually encountered during the purification or recovery of products, by-products, reactants or removal of undesirable products from the process. Also, it can be noted that failure to find a suitable solvent may result in the discard of the product. Alternatively, a functional chemical product manufacturer may be interested to find, design and develop a new solvent. In this case, the solvent is the chemical product. 

Use correct pressures, temperatures, and mixing ratios for optimum recovery of product and rednction in waste prodnced. 

The recovery of products from biotechnological processes has traditionally been focused on bench-scale separation approaches, such as electrophoresis or column liquid chromatography. These methods are dilScult to scale up to production levels and often become prohibitively expensive for medium-and low-value products. 

Reactions carried out on the surface of inorganic oxides allow convenient high-yield and selective syntheses of various metal carbonyl complexes and clusters, starting from easily available materials (Tables 16.1-16.3). The synthetic procedures are straightforward and the recovery of products is easy. Since the use of a solid as reaction medium is not Umited in the manner in solution by boiling points and by the thermal instabiUty of some solvents, it is possible to work at atmospheric pressure even at rather high temperatures. Therefore, in many cases, yields and pressure are better and lower, respectively, than those of the traditional syntheses in solution (Tables 16.4—16.6). 

The ready availability of the starting materials, the lack of special precautions to exclude air and moisture from the reaction mixtures and the ease of recovery of products make these DKR protocols attractive for the preparation of enantiomerically highly enriched A-protected-a-amino acids. 

Adequate dust collection systems point of use are recommended in areas where materials are handled. Where recovery of product is required from the dust collector systems, it is desirable that the system be dedicated to a single process or product line. 

About 30 ml. of warm absolute ethanol readily dissolves 8-9 g. of product. Addition of 15 ml. of water and cooling effect crystallization with about 90% recovery of product. 

For volatile materials vapor phase chromatography (gas chromatography) permits equilibration between the gas phase and immobilized liquids at relatively high temperatures. Tire formation of volatile derivatives, e.g., methyl esters or trimethylsilyl derivatives of sugars, extends the usefulness of the method.103104 A method which makes use of neither a gas nor a liquid as the mobile phase is supercritical fluid chromatography.105 A gas above but close to its critical pressure and temperature serves as the solvent. The technique has advantages of high resolution, low temperatures, and ease of recovery of products. Carbon dioxide, N20, and xenon are suitable solvents. 

As mentioned earlier, the use of a non-condensable, non-adsorbing carrier gas simplifies the task of recovery of products compared to that task in displacement-purge adsorption. At the same time, the scale-up of this process means that the effects of separation-inhibiting thermal gradients accompanying adsorption and desorption have been dealt with successfully. 

A particularly useful reaction of this type involves the direct formation of hexakis(trifluoromethyl)cyclopentadiene (71) (Scheme 31), or the corresponding cyclopentadienide (72), from the diene (38) by a fluoride ion induced reaction with pentafluoropropene [67-69]. Recent work [54] has shown that very active sources of fluoride ion can be generated by direct reaction of amines, especially TDAE (43), with perfluorinated alkenes or perfluorinated aromatic compounds and these essentially solventless systems promote both oligomerisations (see above) and polyfluoroalkylations. The absence of solvent makes recovery of product very easy, e.g. in high-yielding formation of (73), (74) or (75) (Scheme 32). 

Cells which are particularly convenient for work with mercury pool cathodes for both batch and continuous electrolysis were designed by Coleman and Wagenknecht12) and shown in Fig. 3 and 4. In the batch cell (Fig. 3), the mercury placed at the bottom of a cylinder serves as the cathode and the anode is suspended above it in parallel. For experiments in a divided cell the anode is enclosed in a smaller cylinder (also suspended from the top) which serves as the anode compartment. In the continuous electrolysis cell (Fig. 4), the solution was circulated through the system by means of a pump. A repeat-cycle timer device was used to control the addition of reactant and the recovery of products. Anodes of various materials were used (Pt, graphite, platinized C, Ni, Sn, steel and DSA), but the nature of the anode did not seem to affect the reaction. 

To isolate the neat product, the more volatile ether/tri-methylamine combination was used in the reaction, because a higher recovery of product was obtained in trials conducted with the racemic material. However, the neat, distilled, optically active product proved to be stereochemically labile at ambient temperature, and was considerably racemized compared to that obtained directly in the benzene/triethylamine solution. Moreover, the latter was relatively stable when further diluted in benzene solution at ambient temperature, showing only a 14% decrease in optical rotation after 70 hours at 26. For stereochemical studies,... 

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