Vacuum distillation systems

The ice bath is removed after addition of the sodium cyanide, and the mixture is stirred for 4 hours. The organic layer is separated, and the aqueous layer is extracted with three 500-ml. portions of ether. The combined ethereal extracts and organic layer are washed with two 100-ml. portions of cold water and dried over anhydrous magnesium sulfate. The ethereal solution is filtered, and the ether is removed at atmospheric pressure. The residue is transferred to a vacuum distillation system and distilled under reduced pressure (Cauiionl See Note 2). The yield of dlmethylaminophenylacetonitrile boiling at 88-90°/l.9-2.1 tnm. is 842 844 g. (87-88%) (Notes 3 and 4). 

The target for americium concentration in the plutonium is <1000 ppm. This means that a 100-fold reduction of americium concentration is necessary. The vacuum distillation system discussed above seems a likely candidate for this step. 

The crude PA is thermally pretreated (7) and then fed to the vacuum distillation system. Low boiling (LB) impurities are removed in the lights column (8) as LB residues. The high-boiling (HB) residue from the pure PA column (9) is sent to the residue boil-out vessel for PA recovery. Pure PA obtained as a distillate can be stored either in the molten state or flaked and bagged. 

The vacuum-distillation system is improved by distilling with live steam the final 10 per cent of aniline. Such a practice does not introduce a large quantity of water into the system and saves considerable time. The vacuum-distillation system apparently doubles the productivity of the reducers but since the cost of the stills is considerable, the saving is more apparent than real. 

Figure 8.2 Vacuum distillation system with a helium counter-flow leak detector connected.

At ordinary temperatures, the equilibrium favors the concentration of deuterium in the water, but at a temperature of around 130 C the equilibrium favors the concentration of deuterium in the hydrogen sulfide. The tower is therefore divided into two sections, the upper or cold section increasing the concentration of deuterium in the water, which is then used as feed for the lower or hot section, where the exchange leads to a further enrichment, this time in the hydrogen sulfide stream. The enriched gas from this section is then led to the second stage for further concentration. In a final stage, deuterium from the enriched gas is transferred to water, which is then fed to a vacuum distillation system for final enrichment to almost pure D2O (99.75%). 

At high temperatures, active sulfur can directly react with metals at any locations in contact with processing media. This sulfidation attack is a kind of uniform corrosion process. H2S is the most corrosive compound in these sulfides. The typical corrosive environments are located at the bottom of the towers of the atmospheric and vacuum distillation systems, pipelines, atmospheric heavy oil heat exchangers and vacuum residuum heat exchangers, the bottom of the main fractionating columns of catalytic cracking equipment and the coke retarding equipment. 

Heavy crude oils with low sulfur and high TAN were processed within the atmospheric and vacuum units in Refinery B. The average TAN was about 3.0 mg KOH/g and the sulfur content was lower than 0.5%. It was found that severe corrosion occurred in the vacuum distillation systems during the inspection carried out in May 2006. The materials used to fabricate the wall of the third and fourth floors of the tower were carbon steel and 316L stainless steel. The inspection revealed that a lot of pits were formed on the inner wall as shown in Fig. 17.3. 

All the packing materials on the second, third and fourth floors of the vacuum distillation system should be upgraded to 316LSS. The oil collection tank on the third floor should be changed. The load and the velocity of flow must be decreased by process control to decrease the corrosion rate. 

---