Heating under pressure

If tubes are to be heated not higher than ioo°, the convenient so-called water-bath cannon is used, in which the case enclosing the tube is heated by steam at ordinary pressure in this case overheating is impossible. 

Opening the Tubes.—Sealed tubes must not be opened until after they are completely cold. The protecting case of iron, containing the tube, is removed from the furnace and held in a slightly 

In order to break off the end of a tube after it has been opened, so that the contents may be emptied out, the procedure is as 

Pressure Flasks. Autoclaves. — In order to heat substances under pressure at a moderate temperature which on reacting with each other evolve no gaseous products, so that no pressure due 

Very well adapted to this purpose are the common soda-water or beer bottles, of the kind represented in Fig. 47. In using them they are not immersed in water already heated, but are slowly heated with the water. The water-bath is closed by a loosely fitting cover, so that in case the bottle bursts, one may not be burned by the hot water. The flasks are not opened until after they are completely cold. 

In such cases it is more convenient to use a Kipp or, when nitrogen is employed, a gas-holder filled from a cylinder. 

Experience shows that much gas is wasted because the beginner rarely considers how much is approximately required for his reaction. Nevertheless he should do so. 

With the exception of nitrogen, all commonly used gases can, if necessary, be prepared by simple, well-known methods. 

When it is desired to accelerate a reaction in solution or with undissolved substances at a temperature above their boiling point, the reactants must be shut off from the external atmosphere either by sealing in a glass tube in which they are then heated, or in a closed metallic vessel (autoclave). This is obviously necessary even when we wish a reaction to take place in alcoholic solution at 100° or in aqueous solution at about 120°. Thus the aim is entirely to increase the temperature of the reaction the accompanying increase in pressure has no effect on the reaction velocity, for as a rule it is unaccompanied by any significant change in the concentration. 

The pressure tubes of Jena glass commonly used can be employed with some degree of certainty for pressures of 20 to 25 atmospheres if chemical action on the glass is excluded. 

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C, b.p. 156 C. The most important of the terpene hydrocarbons. It is found in most essential oils derived from the Coniferae, and is the main constituent of turpentine oil. Contains two asymmetric carbon atoms. The (- -)-form is easily obtained in a pure state by fractionation of Greek turpentine oil, of which it constitutes 95%. Pinene may be separated from turpentine oil in the form of its crystalline nitrosochloride, CioHigClNO, from which the ( + )-form may be recovered by boiling with aniline in alcoholic solution. When heated under pressure at 250-270 C, a-pinene is converted into dipentene. It can be reduced by hydrogen in the presence of a catalyst to form... 

SiToniium peroxide, Sr02, is formed from SrO and O2 at dull red heat under pressure. Sr02,8H20 is formed from Sr(OH)2 plus H2O2 in cold aqueous solution. 

Boron nitride is chemically unreactive, and can be melted at 3000 K by heating under pressure. It is a covalent compound, but the lack of volatility is due to the formation of giant molecules as in graphite or diamond (p. 163). The bond B—N is isoelectronic with C—C. 

In manufacture, the abrasive grain is mixed with cmde mbber, sulfur, and other ingredients for curing, then passed through calender roUs to produce a sheet of desired thickness. The wheels are stamped from this sheet and heated under pressure to vulcanise the mbber. 

Up to 0.4 g/L of the iodine stays in solution and the rest precipitates as crystallized iodine, which is removed by flotation (qv). This operation does not require a flotation agent, owing to the hydrophobic character of the crystallized element. From the flotation cell a heavy pulp, which is water-washed and submitted to a second flotation step, is obtained. The washed pulp is introduced into a heat exchanger where it is heated under pressure up to 120°C to melt the iodine that flows into a first reactor for decantation. From there the melt flows into a second reactor for sulfuric acid drying. The refined iodine is either flaked or prilled, and packed in 50- and 25-kg plastic-lined fiber dmms. 

During the press operation, which is actually a form of compression mol ding, the resin-treated laminate pHes are heated under pressure and the resins cured. The initial heating phases cause the resin to melt and flow into voids in the reinforcing ply and bond the individual pHes together. The appHed heat simultaneously causes the resin to polymerize and eventually to cross-link or gel. Therefore, resin viscosity reaches a minimum during the press cycle. This is the point at which the curing process becomes dominant over the melt flow process. Dynamic mechanical and dielectric analyses (11) are excellent tools for study of this behavior. 

At this point in the process, thermoplastic and chlorosulfonated polyethylene (CSPE) membranes are complete and are ready for packaging. In the case of ethylene—propylene—diene monomer (EPDM), the curing step occurs before the membrane is ready for packaging. The curing process is accomphshed by placing the membrane in a large vulcanizer where the material is heated under pressure to complete the cure. 

Manufacture. Several methods have been described for the preparation of -hydroxyben2oic acid. The commercial technique is similar to that of salicylic acid, ie, Kolbe-Schmitt carboxylation of phenol. The modification includes the use of potassium hydroxide in place of caustic (51). The dried potassium phenate is heated under pressure, 270 kPa (2.7 atm) or more, with dry carbon dioxide at 180—250°C. The potassium salt [16782-08-4] of Nhydroxyben2oic acid forms almost quantitatively and can be converted to free acid by using a mineral acid. 

Kraft Process. Wood derived from softwood sources is generally heated under pressure with a 10—20% mixture of NaOH and Na2S for only... 

The simplest unit employing vacuum fractionation is that designed by Canadian Badger for Dominion Tar and Chemical Company (now Rttgers VFT Inc.) at Hamilton, Ontario (13). In this plant, the tar is dehydrated in the usual manner by heat exchange and injection into a dehydrator. The dry tar is then heated under pressure in an oil-fired hehcal-tube heater and injected directly into the vacuum fractionating column from which a benzole fraction, overhead fraction, various oil fractions as side streams, and a pitch base product are taken. Some alterations were made to the plant in 1991, which allows some pitch properties to be controlled because pitch is the only product the distillate oils are used as fuel. 

In wet-air oxidation, the aqueous mixture is heated under pressure ia the presence of air, which oxidi2es the organic material. The efficiency of the oxidation process is a function of reaction time and temperature. The oxidation products are generally less complex and can be treated by conventional biological methods (31). The reactor usually operates between 177 and 321°C with pressures of 2.52—20.8 MPa (350—3000 psig). 

Elemental arsenic normally exists in the a-crystaUine metallic form which is steel-gray in appearance and britde in nature, and in the P-form, a dark-gray amorphous soHd. Other aHotropic forms, ie, yellow, pale reddish-brown to dark brown, have been reported (1), but the evidence supporting some of these aHotropes is meager. MetaUic arsenic, heated under ordinary conditions, does not exhibit a discrete melting point but sublimes. Molten arsenic can be obtained by heating under pressure. 

Calcium Silicate Brick. Sand—lime brick is used ia masonry ia the same way as common clay brick. The bricks, molded from a wet mixture of sand and high calcium hydrated lime, are heated under pressure ia a steam atmosphere. Complex hydrosiUcates are formed that give the bricks high dimensional stabiUty (6). 

Compared to its precursor (HNCO), CA is unusually stable to hydrolysis. It is only slowly hydroly2ed by hot aqueous alkaU and virtually iuert to acidic hydrolysis. Indeed, CA can be heated under pressure iu sulfuric acid solution at 200°C with minimal decomposition. The tria2iae ring, however, can be cleaved by alkaline hypochlorite forming N2 and HCO3 (17). 

Thiophene fails to undergo cycloaddition reactions with common dienophiles under normal conditions. However, when thiophene is heated under pressure with maleic anhydride, the exo adduct (136) is formed in moderate yield (78JOC1471). 

Polyethylene, a linear polymer, is made by an addition reaction. It is started with an initiator, such as FIjOj, which gives free, and very reactive —OFI radicals. One of these breaks the double-bond of an ethylene molecule, C2FI4, when it is heated under pressure, to give... 

Chemical Reactivity - Reactivity with Water Mild reaction, non-hazardous Reactivity with Common Materials Contact with silver or aluminum may cause polymerization Stability During Transport Stable unless heated under pressure Neutralizing Agents for Acids and Caustics Flush with water Polymerization Explosive polymerization can occur when in contact with acids Inhibitor of Polymerization None used. 

When the sludge is heated under pressure to temperatures above 350 F (176.5 C),... 

A similar reaction in which fflnmonia and caibon dioxide aie heated under pressure is the basis of the industrial synthesis of urea. Here, the reactants first combine, yielding a salt called ammonium carbamate ... 

Preparation of 2-( -Diethylaminoethoxy)Ethyl Diethylphenylacetate A mixture of 21 grams of 2-(/3-chloroethoxy)ethyl diethylphenylacetate and 14 grams diethylamine was heated under pressure in a sealed tube at 140°C for 5 hours. After cooling, the mixture was dissolved in dilute hydrochloric acid and extracted with ether to remove traces of neu-... 

Sulfur is pumped out of natural underground deposits in the molten state after it is melted with water heated under pressure to about 170°C. 

The bromodihydrodibenz[/>,/]az.epine-5-carbonyl chloride 41, prepared by radical bromination of the 10,11-dihydro compound, on heating under pressure with ammonia undergoes dehydrobromination and amidation to yield Carbamazepine (42).122... 

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