Distillation total takeoff

Discussion—The vapor reaching the top of the column is totally condensed and the resulting liquid is divided into two parts. One part L (reflux), is returned to the column and the other part, D (distillate), is withdrawn as product. The reflux ratio R = L/D), can vary from zero at total takeoff (L = 0) to infinity at total reflux D = 0). 

A8.2.1 A sufficient quantity of the sample is distilled in a low efficiency column under atmospheric pressure at zero reflux ratio (total takeoff) to 130 C, the water decanted, and dry components recombined. 

A8.6.3 Apply heat to the flask, regulating it to attain a moderate reflux rate as specified in 9.2.4 to 9.2.8 for debutanization. Remove distillate slowly at total takeoff (reflux ratio = 0) until a vapor temperature of 130 C is reached. Collect the fraction distilling below 65°C in a receiver cooled to -20 C or lower. 

This test method describes a procedure for distillation of heavy hydrocarbon mixtures having initial boiling points greater than 150 C (300°F), such as heavy crude oils, petroleum distillates, residues, and synthetic mixtures. It employs a potstill with a low pressure drop entrainment separator operated under total takeoff conditions. Distillation conditions and equipment performance criteria are specified and typical apparatus is illustrated. 

Ergotamine tartrate (lOg) is added to a stirred de aerated (nitrogen stream) solution of 38 g potassium hydroxide in 100 ml of methanol and 200 ml of water. The solution turns pink to red. The solution is heated to reflux and the methanol is slowly removed using a partial takeoff. Methanol is allowed to distill until the pot temperature reaches 90-95° C. The mixture is then maintained at total reflux until the evolution of ammonia ceases (hold pH paper in outlet of reflux condenser to test for ammonia). Nitrogen should be bubbled through the mixture to entrain the ammonia. 

Pure ira 5-l-phenyl-l,3-butadiene was obtained by distillation of the twice-distilled product under nitrogen through a 12-plate column of the total reflux-variable takeoff type after adding 0.5% of phenyl-/3-naphthylamine. The packed section of the column was an 18-in. section of Pyrex tubing (10 mm. o.d.) filled with 4-mm. single-turn glass helices. Insulation was provided by means of a vacuum jacket, and heat losses were compensated by resistance wire wound on the jacket. 

The heavier chlorocyclohexanone layer is separated and combined with three 150-ml. ether extracts of the aqueous phase, and washed with 150 ml. of water and then with 200 ml. of saturated sodium chloride solution. After filtration (gravity) through anhydrous sodium sulfate the ether is removed and the residue vacuum-distilled in a modified Claisen flask. The fraction (300-340 g.) boiling below 100° at 10 mm. (Note 5) is collected (Note 6). This material is then fractionated carefully under reduced pressure by means of a 42-in. modified Vigreux column (heated) with a total condensation variable takeoff head (Note 7). The yield of 2-chlorocyclohexanone boiling at 90-91°/14-15 mm. is 240-265 g. (61-66%) (Notes 8 and 9). 

In a flask equipped with a total reflux packed column and a variable takeoff head, 15.0 g of the 2,3-methyl enedioxy-5-nitrotoluene/2,3-methylenedioxy-6-nitrotoluene mix was added to a mixture of 100 mL freshly distilled DMF and 12.8 g of N,N-dimethylformamide dimethyl acetal. The reaction mixture was heated to a controlled reflux that kept the head temperature at 50 to 70 °C, allowing the removal of MeOH. After 4 h, 90% of the theoretical amount of MeOH (7.4 mL) had been distilled off, and the residual solvent (DMF) was removed under vacuum. The dark residue was dissolved in benzene, washed with H2O, dried with anhydrous MgS04, and the solvent removed under vacuum. The crude crystalline product was recrystallized from hexane/benzene to provide 4.8 g (50%) of 2,3-methylenedioxy-6-nitro-beta-dimethylaminostyrene as red needles with a mp 126-128 °C. 

Minimum surges are stepped off when the operating lines Coincide with die diagonal line and have a slope of unity from Eq. (5.3-24) it can be seen that al this condition of minimum stages there can be no net product distillate takeoff. This is the condition of total reflux and is an important condition for starting up columns and for conducting efficiency tests on columns. 

The complicating factor in batch distillation is the transient nature of the process. For a new design, the engineer must be concerned with optimizing the total cycle, which includes chaiging and equilibration, product takeoff at constant or varying rate, and cleanout. 

In a hood, in a three-necked flask fitted with a mechanical stirrer, an empty distillation column, topped with a total reflux-partial takeoff distillation head, an addition funnel, and means to maintain a nitrogen atmosphere are placed 35 gm (0.63 mole) of potassium hydroxide, 30 ml (0.93 mole) of anhydrous hydrazine (95% active), and 60 ml of absolute ethanol. This mixture is cooled in an ice bath while being stirred mechanically. 

---