Rate of distillation

The steam-distillation is continued for 5 minutes after steam can first be seen entering the condenser the ideal rate of distillation is about 4 -5 ml. of distillate per minute, but this is not critical and may be varied within reasonable limits. The receiver J is then lowered from the lip K of the condenser and the steam-distillation continued for a further two minutes, thus ensuring that no traces of liquid containing ammonia are left on the inside of the condenser. At the end of this time any liquid on the lip K is rinsed with distilled water into J, which is then ready for titration. It is important that the receiver and its contents are kept cold during the distillation and it is advisable to interpose a piece of asbestos board or other screen so that it is not exposed to the heat from the burner under the steam generator. 

A simple form of apparatus is that in which a cooled condensing surface is supported a few cm. above a shallow, heated pool of liquid, and the whole is enclosed in a highly evacuated chamber (compare Fig. II, 26, 1) this offers the least hindrance to the flow of vapour from the evaporating to the condensing surface. The rate of distillation is then determined by the rate at which the liquid surface is able to produce vapour. When the evaporating... 

The ethyl acetate is distilled at 70—100°C, leaving spherical particles. This graining operation requires ca 1 to 1.5 h. Grain density and size are determined by the concentration of salt in solution, the temperature and time of the dehydration, agitation speed, and the rate of distillation of the ethyl acetate. 

A solution of potassium hydroxide (5 g) in 8 ml of water is placed in the distilling flask and 25 ml of 95% ethanol is added no boiling chips). The flask is heated in a water bath to 65° and a solution of 21.5 g(0.1 mole) of V-methyl-iV-nitroso-/ -toluene-sulfonamide in 130 ml of ether is added through the dropping funnel over a period of about 25 minutes. The rate of addition should about equal the rate of distillation. When the dropping funnel is empty, another 20 ml of ether is added slowly and the distillation is continued until the distilling ether is colorless. The combined ethereal distillate contains about 3 g (approx. 0.07 mole) of diazomethane and is approximately 0.5 M. 

The use of a clean, dry flask and a moderate rate of distillation help to overcome the tendency of the product to resinify. 

The problem as stated gives no bottom-product composition, so that whilst all flow-rates in the top of the column may be calculated, no information about the lower half can be derived. In the absence of these data, the feed rate cannot be determined, though the rate of distillate removal may be calculated as follows. 

Distilled water is produced from sea water by evaporation in a single-effect evaporator working on the vapour compression system. The vapour produced is compressed by a mechanical compressor of 50 per cent efficiency, and then returned to the calandria of the evaporator. Extra steam, dry and saturated at 650 kN/m2, is bled into the steam space through a throttling valve. The distilled water is withdrawn as condensate from the steam space. 50 per cent of the sea water is evaporated in the plant. The energy supplied in addition to that necessary to compress the vapour may be assumed to appear as superheat in the vapour. Calculate the quantity of extra steam required in kg/s. The production rate of distillate is 0.125 kg/s, the pressure in the vapour space is 101.3 kN/m2, the temperature difference from steam to liquor is 8 deg K, the boiling-point rise of sea water is 1.1 deg K and the specific heat capacity of sea water is 4.18 kJ/kgK. 

The Claisen distillation head was filled with glass wool to avoid formation of foam. The checkers found that constant heating of the distillation apparatus with a heat gun greatly facilitates the rate of distillation and minimizes the column holdup. 

For example, in a distillation column the manipulated variables could be the flow rates of reflux and vapor boilup R — V) to control distillate and bottoms compositions. This choice gives one possible control stmcture. Alternatively we could have chosen to manipulate the flow rates of distillate and vapor boilup D V). This yields another control structure for the same basic distillation process. 

The viscosity of the solution gradually increases and so does the temperature in the flask. In order to maintain a quick rate of distillation (and therefore polycondensation), each time the internal temperature reaches 130 °C about 25 ml of pure toluene are added. After about 25 h the flask is cooled to room temperature and the solution is added drop-wise to a tenfold amount of methanol the polymer is filtered off and dried to constant weight in vacuum at 40 C. Yield about 90%. 

The submitters used a still of the evaporative type, such as a Hickman still. The checkers used a similar still modified to include a magnetic stirring bar. This modification greatly decreases the time required for removal of the last traces of solvent, minimizes the danger of bumping just before evaporative distillation occurs, and increases the rate of distillation of the product. 

The aqueous effluent from the parfait column was exposed to vacuum in a silanized 12-L flask on a high-capacity freeze dryer. The effluent was stirred with a magnetically coupled stirring bar and heated by immersion of the lower half of the flask in a 30 °C constant-temperature water bath. The rate of distillation was controlled to about 8 L/24 h with a needle-valve air bleed. Distillation was continued to a volume of about 500 mL. Then the concentrate was transferred to a smaller flask, and the volume was further reduced to 10 mL on a conventional rotary evaporator. 

The boiling point varies greatly with the rate of distillation and the amount of ebullition. 

---