Steam-setting method

Nitrosomethylurea. Acetamide method. To a solution of 59 g. of acetamide in 88 g. (28 ml.) of bromine (1) in a 4-litre beaker add dropwise, with hand stining, a solution of 40 g. of sodium hydroxide in 160 ml. of water. Heat the resulting yellow reaction mixture on a steam bath until eflfervescence sets in (2), after which continue the heating for 2-3 minutes. CrystaUisation of the product from the yellow or red coloured solution usually commences immediately. Cool in an ice bath for 1-2 hours, collect the product by suction filtration, wash with a little ice-cold water, and dry in the air. The yield of colourless acetylmethylurea, m.p. 178-180°, is 50 g. 

The crude liquid acid (about 300 g.) is cooled with running water and 15 cc. of concentrated sulfuric acid is added the clear yellow oil becomes cloudy. The acid is esterified by the method described in Org. Syn. 3, 54, with the following changes all three flasks, the alcohol flask, the trap, and the esterification flask are i-l. round-bottom wide-neck flasks. The alcohol flask and the trap are set on adjacent steam baths. The esterification flask is placed in an oil bath which is heated by a free flame. A safety tube leads from the alcohol flask and dips under 7.5 cm. of mercury contained in a side-arm tube. 

From the point of view of systematic data analysis, it has been found that consistent results can be obtained only with burn-out data produced under stable conditions. The unstable condition leads to considerable scatter, depending on the particular setting of a valve, the size of a compressible volume, the method of preforming a steam and water mixture, and so on. These latter quantities have either been recorded with very low accuracy, or have not been recorded at all. Therefore, the unstable-conditions data appear to be of little value, except for qualitative purposes. In any case, one is usually not interested in instabilities apart from knowing how to avoid them, which is by having a hard inlet. 

Sterilization can be accomplished by several means, including heat, chemicals, radiation (ultraviolet (UV) or y-ray), and microfiltration. Heat is widely used for the sterilization of media and fermentation equipment, while microfiltration, using polymeric microporous membranes, can be performed to sterilize the air and media that might contain heat-sensitive components. Among the various heating methods, moist heat (i.e., steam) is highly effective and very economical for performing the sterilization of fermentation set-ups. 

The impurities present in aromatic nitro compounds depend on the aromatic portion of the molecule. Thus, benzene, phenols or anilines are probable impurities in nitrobenzene, nitrophenols and nitroanilines, respectively. Purification should be carried out accordingly. Isomeric compounds are likely to remain as impurities after the preliminary purifications to remove basic and acidic contaminants. For example, o-nitrophenol may be found in samples of p-nitrophenol. Usually, the o-nitro compounds are more steam volatile than the p-nitro isomers, and can be separated in this way. Polynitro impurities in mononitro compounds can be readily removed because of their relatively lower solubilities in solvents. With acidic or basic nitro compounds which cannot be separated in the above manner, advantage may be taken of their differences in pKg values. The compounds can thus be purified by preliminary extractions with several sets of aqueous buffers of known pH (see for example Table 19, p. 43) from a solution of the substance in a suitable solvent such as ethyl ether. This method is more satisfactory and less laborious the larger the difference between the pK value of the impurity and the desired compound. Heterocyclic nitro compounds require similar treatment to the nitroanilines. Neutral nitro compounds can be steam distilled. 

Figure 3.5. Vacuum control with steam jet ejectors and with mechanical vacuum pumps, (a) Air bleed on PC. The steam and water rates are hand set. The air bleed can be made as small as desired. This can be used only if air is not harmful to the process. Air bleed also can be used with mechanical vacuum pumps, (b) Both the steam and water supplies are on automatic control. This achieves the minimum cost of utilities, but the valves and controls are relatively expensive, (c) Throttling of process gas flow. The valve is larger and more expensive even than the vapor valve of case (a). Butterfly valves are suitable. This method also is suitable with mechanical vacuum pumps, (d) No direct pressure control. Settings of manual control valves for the utilities with guidance from pressure indicator PI. Commonly used where the greatest vacuum attainable with the existing equipment is desired.

Figure 3.14. The lower ends of fractionators, (a) Kettle reboiler. The heat source may be on TC of either of the two locations shown or on flow control, or on difference of pressure between key locations in the tower. Because of the built-in weir, no LC is needed. Less head room is needed than with the thermosiphon reboiler, (b) Thermosiphon reboiler. Compared with the kettle, the heat transfer coefficient is greater, the shorter residence time may prevent overheating of thermally sensitive materials, surface fouling will be less, and the smaller holdup of hot liquid is a safety precaution, (c) Forced circulation reboiler. High rate of heat transfer and a short residence time which is desirable with thermally sensitive materials are achieved, (d) Rate of supply of heat transfer medium is controlled by the difference in pressure between two key locations in the tower, (e) With the control valve in the condensate line, the rate of heat transfer is controlled by the amount of unflooded heat transfer surface present at any time, (f) Withdrawal on TC ensures that the product has the correct boiling point and presumably the correct composition. The LC on the steam supply ensures that the specified heat input is being maintained, (g) Cascade control The set point of the FC on the steam supply is adjusted by the TC to ensure constant temperature in the column, (h) Steam flow rate is controlled to ensure specified composition of the PF effluent. The composition may be measured directly or indirectly by measurement of some physical property such as vapor pressure, (i) The three-way valve in the hot oil heating supply prevents buildup of excessive pressure in case the flow to the reboiier is throttled substantially, (j) The three-way valve of case (i) is replaced by a two-way valve and a differential pressure controller. This method is more expensive but avoids use of the possibly troublesome three-way valve.

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