Platinum stills

In aqueous acetic acid, the disproportionation of the platinum still occurs quite rapidly, and it can be suppressed further by adding mineral acid. Hydrochloric acid is often used, but this has a disadvantage in that the exchange rate is inversely proportional to the chloride ion concentration. Perchloric acid has been found to be more satisfactory (55). The platinum(II) catalyst most used is sodium or potassium tetrachloropla-tinate(II). An aromatic compound added to the reaction mixture also inhibits disproportionation of the platinum(II) complex—benzene, pyrene, and other aromatics have been used. A comparative study of the effect of various aromatics on the H—D exchange in alkanes has been carried out (55). Even under optimum conditions, the disproportionation [Eq. (4)] still takes place, and the catalytic platinum(II) is slowly removed from the reaction mixture. To get useful rates of exchange in alkanes, temperatures of 100° to 120°C have to be used, and the disproportionation rate increases with temperature. 

Colloidal platinum still further resembles organic ferments in its action upon hydrogen peroxide in that its activity is reduced or partially paralysed by the addition of poisons such as hydrogen cyanide, hydrogen sulphide, or mercuric chloride. After a time, however, the metal may recover from these. 

The acid is allowed to collect in the chambers until it bas the sp. gr. 1.55, when it is drawn oK This chamber acidf although used in a few industrial processes, is not yet strong enough for most purposes. It is concentrated, first by evaporation in shallow leaden pans until its sp. gi% reaches 1.746 at this point it begins to act upon the lead, and is transferred to platinum stills, where the concentration is completed. 

In the case of breast cancers, therefore, the inorganic complexes of platinum still do not appear to be cytotoxic agents capable of being successfully coupled to a hormonal delivery system. 

Harrison was also the first to install a new technology to produce concentrated acid. The standard Contact acid was too weak for some applications which required stronger acid but not necessarily fuming. At high concentration, even lead reacted with sulfuric acid. A new distilling technology used platinum stills, a process developed by Erick Bollman, a friend of Lafayette, in 1813. Platinum was not the exotic, expensive element of today. Bollman had found one of the few uses for this material. Platinum was relatively difficult to manipulate and a method had only recently been developed by William Hyde Wollaston (1766 - 1828), whom Bollman knew. Harrison used the original still until 1828. 

The major limitation of the Chamber process was the strength of the acid it produced, even after distillation. Acid from the Chamber process could be concentrated, using platinum stills, but only up to 78%. A special feature of the new Contact process was the ability to make fuming acid still basically the monopoly of the very expensive and limited Nordhausen acid. 

Squire (and Messel) British Patent 3278 (1875) resulted from high oleum price. Used a platinum catalyst supported on pumice with a stoichiometric mixture of SO2/O2 made from decomposing H2SO4 in a platinum still (70% recovery of SO3). Plant at Silvertown produced three tons of SO3 per week. Patent mentioned that this avoided catalyst deactivation with dust and, probably arsenic although poisons were not recognized. 

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

Dual-Pressure Process. Dual-pressure processes have a medium pressure (ca 0.3—0.6 MPa) front end for ammonia oxidation and a high pressure (1.1—1.5 MPa) tail end for absorption. Some older plants still use atmospheric pressure for ammonia conversion. Compared to high monopressure plants, the lower oxidation pressure improves ammonia yield and catalyst performance. Platinum losses are significantiy lower and production mns are extended by a longer catalyst life. Reduced pressure also results in weaker nitric acid condensate from the cooler condenser, which helps to improve absorber performance. Due to the spHt in operating conditions, the dual-pressure process requires a specialized stainless steel NO compressor. 

This international prototype, adopted by the 1st and 3rd CGPM in 1889 and 1901, is a particular cylinder of platinum—iridium kept at the International Bureau of Weights and Measures near Paris. It is the only base unit still defined by an artifact. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

While there are hydroformers still operating, reforming today is generally carried out in fixed bed units using platinum catalysts, because of their superior product yield and distribution. Fluid platinum catalyst processes are not feasible because catalyst losses would be too great. 

In presence of platinum oxide as catalyst in methyl alcohol, it hydrogenates to dihydrowogermine, which darkens >265° and melts at 277-8° (dec.) [a]n ° — 61° (pyridine). The dihydro-base still contains eight... 

Why Do We Need to Know This Material The d-block metals are the workhorse elements of the periodic table. Iron and copper helped civilization rise from the Stone Age and are still our most important industrial metals. Other members of the block include the metals of new technologies, such as titanium for the aerospace industry and vanadium for catalysts in the petrochemical industry. The precious metals—silver, platinum, and gold—are prized as much for their appearance, rarity, and durability as for their usefulness. Compounds of d-block metals give color to paint, turn sunlight into electricity, serve as powerful oxidizing agents, and form the basis of some cancer treatments. 

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