Superatmospheric pressures

In 1968, a French Patent issued to the Sumitomo Chemical Company disclosed the polymerization of several vinyl monomers in C02 [84], The United States version of this patent was issued in 1970, when Fukui and coworkers demonstrated the precipitation polymerization of several hydrocarbon monomers in liquid and supercritical C02 [85], As examples of this methodology, they demonstrated the preparation of the homopolymers PVC, PS, poly(acrylonitrile) (PAN), poly(acrylic acid) (PAA), and poly(vinyl acetate) (PVAc). In addition, they prepared the random copolymers PS-co-PMMA and PVC-co-PVAc. In 1986, the BASF Corporation was issued a Canadian Patent for the preparation of polymer powders through the precipitation polymerization of monomers in carbon dioxide at superatmospheric pressures [86], Monomers which were polymerized as examples in this patent included 2-hydroxyethylacrylate and iV-vinylcarboxamides such as iV-vinyl formamide and iV-vinyl pyrrolidone. 

The polymerization of ethylene in the presence of aluminum chloride is fundamentally changed by the presence of metallic aluminum (Hall and Nash, 72). The product which was obtained at a reaction temperature of 100-200° under superatmospheric pressure was a mobile fuming liquid which was shown to contain diethyl aluminum chloride, a liquid spontaneously inflammable in air. Less conjunct polymerization occurred, the lower-boiling product consisting of olefins mixed with only minor amount of paraffins. 

Mononitration generally occurs when a mixture of vapors of an alkane and nitric acid is heated at 400-500°C under atmospheric or superatmospheric pressure.162 164 165 To overcome the danger of explosion, a molar excess of the hydrocarbon over the acid is used. Oxidation accompanies nitration, which occurs at an increased rate when the reaction temperature is increased.171 The principal nitro compounds produced are those in which the nitro group is on a primary or a secondary carbon 172... 

Alkali lignin was oxidized with alkaline cupric oxide at atmospheric and superatmospheric pressure after first etching the lignin with alumi-... 

The Robbins correlation applies at atmospheric pressure and under vacuum, but not at elevated pressures (90). Equation (8.146) includes a gas density correction term for a preliminary estimate at pressures exceeding atmospheric. Due to the approximation, Eq. (8.146) is unsuitable for design (90). Generally, the Robbins correlation is not recommended for superatmospheric pressures (90). 

In three-phase systems, where the solid catalyst is in contact with a liquid reactant or its solution plus a gaseous reactant, efficient agitation is required to effect dissolution of the gaseous molecule into the liquid and its transport to the catalyst surface. Such systems easily become mass-transport limited, especially when a very active catalyst is used. In a batch reactor, rapid shaking or stirring is needed, and catalyst particles must be small it may operate at atmospheric pressure, or at superatmospheric pressure as an autoclave. Large catalyst particles can however be used with liquid reactants either in a trickle-column reactor or a spinning-basket reactor. 

J The superatmospheric pressure unit was used in these runs (8, 10, 11), the quartz tube unit in the others. 

Polymerization in gas phase must cope with larger entropy change than polymerization in liquid phase. Therefore, polymerization of gas phase monomers such as olefins is carried out in superatmospheric pressure and/or in the presence of heterogeneous catalyst. Polymerization in gas phase in low pressure (in vacuum) does not occur easily due to the limitation of the ceiling temperature of polymerization, and there are only few cases in which the deposition of polymeric material from gas phase starting material occurs in vacuum. Those main exceptional cases are plasma polymerization and parylene polymerization. 

Another cyclical process is the Phillips STAR pro-cess.t ] It uses a fixed-bed fired-tube reactor operating at a positive superatmospheric pressure. In many respeets, it is similar in design to a steam reforming furnaee with the heat of reaction provided by firing outside the tubes, thus operating at near-isothermal conditions. Steam is used as a diluent to lower the partial pressure of the reactants and, thus, to achieve reasonable conversion levels of about 30-40% for propane and 45-55% for butanes. It also helps slow down the deposition of carbon (coke) on the eatalyst, thereby extending cycle time from minutes to hours. 

I am aware that various special methods have been proposed for separating these amines, such as fractional distillation of azeotropic mixtures under superatmospheric pressure, with or without the addition of large quantities of ammonia, and fractional crystallization of the hydrohalide salts from a solvent such as, alcohol. None of these methods is as simple or direct, nor does it produce as sharp a separation, as that which I am about to describe. 

Carbon monoxide at superatmospheric pressure can be reduced electrochemically in a specially designed , high-pressure electrolytic cell. The reaction yields the conjugate base of dihydroxycyclobutenedione (squaric acid) ... 

These reactions are catalyzed by NaOH and NaOMe, respectively, and occur at 170-190°C (formate esters) and at 60-130°C (dimethylformamide) at superatmospheric pressure of CO in the range 5-20 atm. N,N-Dimethylformamide is produced industrially either from the direct reaction (b) or by treatment with Me2NH of the formate ester obtained by the carbonylation reaction (a). 

Hexacarbonyls of molybdenum(O) and tungsten(0 colorless solids with properties similar to those of Cr(CO)fi, are more easily prepared than Cr(CO)g. Zinc or Fe powders reduce molybdenum and tungsten halides in the presence of CO °. Mo(CO)g and W(CO)s were obtained in 46 and 70% yields, respectively, using superatmospheric pressures of CO. 

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