Iron removal from reaction vessels

Removal of Iron Oxides from Reaction Vessels... 

A mixture of 15 gms. of phthalic anhydride and 22 gins, of resorcinol is ground in a mortar. It is then transferred to a nickel or cast-iron vessel, and heated in an oil bath to 180°. At this temperature 7 gms. of powdered fused zinc chloride (see p. 509) are added, with stirring, during the course of 10 minutes. The temperature is raised to 210°, and maintained at this point until the liquid, which gradually thickens, becomes solid, for which 1—2 hours are required. The cold melt is removed from the vessel with a knife or chisel, powdered, and boiled 10 minutes with 200 c.cs. of water and 10 c.cs. of cone, hydrochloric acid. This treatment eauses the solution of zinc oxide and basic zinc chloride. The fluorescein is filtered off, washed with water until the filtrate no longer shows an acid reaction it is dried on a water bath. 

The reaction vessel (nitrator) is constructed of cast iron, mild carbon steel, stainless steel, or glass-lined steel depending on the reaction environment. It is designed to maintain the required operating temperature with heat-removal capabiUty to cope with this strongly exothermic and potentially ha2ardous reaction. Secondary problems are the containment of nitric oxide fumes and disposal or reuse of the dilute spent acid. Examples of important intermediates resulting from nitration are summarized in Table 3. 

By manipulating the pressure and removing ammonia from the reaction vessel, Haher successfully increased the yield of ammonia. To increase the rate of the reaction, Haher needed to find a catalyst. A catalyst would allow the reaction to proceed at higher temperatures—a compromise between rate and yield. Some historians claim that Haher performed more than 6500 experiments trying to find a suitable catalyst. He finally chose an iron catalyst. This catalyst works well at the relatively moderate temperature of 400°C that is used for the reaction. It lasts about five years before losing its effectiveness. 

Carbon and sulfur are reacted (Reaction 4.1) in the absence of air in oval or cylindrical vessels called retorts. The vessels are approximately 3 ft in diameter and 10 ft in height [117] and are constructed from chrome alloy steel or cast iron. Usually, 1-4 retorts are installed in a furnace [118]. The furnace is heated by coal, gas or oil. Coal is intermittently added from the top of the retort while vaporized sulfur is continuously fed in from the bottom. Carbon disulfide is formed while the sulfur vapor works its way through the hot coal (800—1000 C) to the top of the retort. The reacted gases exit the top of the retort through a duct. Nonreactive ash and coal dust are periodically removed as they make their way to the bottom while fresh coal is added. Deposits are also removed from the inside walls of the retort, usually on a monthly or bimonthly basis. Because of the corrosive sulfur vapor, the retorts must be replaced every 1—2 years. 

In this reaction, VPA esters can be used with short-chain aliphatic alcohols. The vinylphosphonic dichloride can be obtained from the reaction mixture in a pure state by distillation under reduced pressure. The use of metal halides as catalysts leads to vinylphosphonic dichloride in higher yield. It is advantageous to use iron(III) chloride as catalyst because the residue can be removed easily from the reaction vessel. 

Sonochemical Synthesis of Iron Nanopowders. A dispersion of 15g (0.076 mol) of Fe(CO)s in dry decalin was sonicated at 50% amplitude for 6h at room temperature in a sonochemical reactor as described previously. The color of the solution turned dark and then black within a few minutes and this reaction mixture was sonicated till the formation of shiny metallic particles was observed on the walls of the reaction vessel. The sonication was then stopped and the decalin solvent was removed from the reaction flask via vacuum distillation. The black powders (Yield 3.88 Ig) at the bottom of the reactor was then isolated, transferred to a vial and coated with mineral oil before the compaction. 

Chromium metal is produced hy thermal reduction of chromium(III) oxide, Cr203 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr203 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with A1 powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen. 

Gadolinium is produced from both its ores, monazite and bastnasite. After the initial steps of crushing and beneficiation, rare earths in the form of oxides are attacked by sulfuric or hydrochloric acid. Insoluble rare earth oxides are converted into soluble sulfates or chlorides. When produced from monazite sand, the mixture of sand and sulfuric acid is initially heated at 150°C in cast iron vessels. Exothermic reaction sustains the temperature at about 200 to 250°C. The reaction mixture is cooled and treated with cold water to dissolve rare earth sulfates. The solution is then treated with sodium pyrophosphate to precipitate thorium. Cerium is removed next. Treatment with caustic soda solution fohowed by air drying converts the metal to cerium(lV) hydroxide. Treatment with hydrochloric or nitric acid sol-... 

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