Reaction tube

The simpler nitrop>arafIins (nitromethane, nitroethane, 1- and 2-nitroproj)ane) are now cheap commercial products. They are obtained by the vapour phase nitration of the hydrocarbons a gaseous mixture of two mols of hydrocarbon and 1 mol of nitric acid vapour is passed through a narrow reaction tube at 420-476°. Thus with methane at 476° a 13 per cent, conversion into nitro methane is obtained ethane at 420° gives a 9 1 mixture of nitroethane (b.p. 114°) and nitromethane (b.p. 102°) propane at 420° afifords a 21 per cent, yield of a complex mixture of 1- (b.p. 130-6°) and 2-nitropropane (b.p. 120°), nitroethane and nitromethane, which are separated by fractional distillation. 

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%. 

Reaction and Heat-Transfer Solvents. Many industrial production processes use solvents as reaction media. Ethylene and propylene are polymerized in hydrocarbon solvents, which dissolves the gaseous reactant and also removes the heat of reaction. Because the polymer is not soluble in the hydrocarbon solvent, polymer recovery is a simple physical operation. Ethylene oxide production is exothermic and the catalyst-filled reaction tubes are surrounded by hydrocarbon heat-transfer duid. 

The formation of acids from heteroatoms creates a corrosion problem. At the working temperatures, stainless steels are easily corroded by the acids. Even platinum and gold are not immune to corrosion. One solution is to add sodium hydroxide to the reactant mixture to neutralize the acids as they form. However, because the dielectric constant of water is low at the temperatures and pressure in use, the salts formed have low solubiHty at the supercritical temperatures and tend to precipitate and plug reaction tubes. Most hydrothermal processing is oxidation, and has been called supercritical water oxidation. 

Vapour phase synthesis may be carried out by passing a mixture of acetylene and acetic acid through a reaction tube at 210-215°C. Typical catalysts for this reaction are cadmium acetate, zinc acetate and zinc silicate. The monomer in each of the above mentioned processes is purified by distillation. 

In practice vapours of the hydrocarbon halide, e.g. methyl chloride, are passed through a heated mixture of the silicon and copper in a reaction tube at a temperature favourable for obtaining the optimum yield of the dichlorosilane, usually 250-280°C. The catalyst not only improves the reactivity and yield but also makes the reaction more reproducible. Presintering of the copper and silicon or alternatively deposition of copper on to the silicon grains by reduction of copper (I) chloride is more effective than using a simple mixture of the two elements. The copper appears to function by forming unstable copper methyl, CUCH3, on reaction with the methyl chloride. The copper methyl then decomposes into free methyl radicals which react with the silicon. 

Under the most favourable reaction conditions when methyl chloride is used the crude product from the reaction tube will be composed of about 73.5% dimethyldichlorosilane, 9% trichloromethysilane and 6% chlorotrimethylsilane together with small amounts of other silanes, silicon tetrachloride and high boiling residues. 

In the case of phenylchlorosilanes some modifications are made to the process. Chlorobenzene is passed through the reaction tube, which contains a mixture of powdered silicon and silver (10% Ag), the latter as catalyst. Reaction temperatures of 375-425°C are significantly higher than for the chloro-methylsilanes. An excess of chlorobenzene is used which sweeps out the high boiling chlorophenysilanes, of which the dichlorosilanes are predominant. The unused chlorobenzene is fractionated and recycled. 

Reaktions-losigkeit,/. absence of reaction, nonreaction. -masse, /. reaction mass, mass resulting from a reaction, -mischung, /. reaction mixture, -mittel, n. reagent, -ord-nung, /. order of a reaction, -ort, m. field or sphere of reaction, -papier, n. test paper, -rohr, n., -rohre,/. reaction tube, -stufe,/. step or stage of a reaction, -teilnehmer, m. participant in a reaction, reactant. 

Fifteen grams of this prepolymer powder in a wide-bore reaction tube (Fig. 3.18b) which is flushed with nitrogen is placed in a heating block. The heating block is warmed over a period of 1 h to 270°C and maintained at this temperature for 4 h, after which the reaction vessel is removed. The yellow polymer obtained has an r]i h of 1.9. The polymer has a melting temperature of 391°C, a heat of fusion of 148 J/g, a Tg dry at 120°C, and a Tg wet at —15°C. 

The gaseous S03 stream (previously diluted with dry air to a concentration ranging from 7% to 2.5% volume) is then fed to the sulfonation/sulfation section which is based on a multitube falling film reactor having a number of tubes proportional to the plant production capacity (Figs. 8 and 9). The S03 gas is fed to the upper part of the reactor and distributed equally to each reaction tube. 

An exception to the above are fatty acid methyl esters, which, due to the reaction mechanism involving molecular rearrangements with excess S03, have to be sulfonated at a slightly higher mole ratio of S03 to methyl esters (namely, 1.15-1.20/L). Outside the reaction tubes, in the reactor jacket, cooling water is circulated to control the liquid-film temperature and removing the reaction heat. 

Before the actual reaction tube, a pre-heating tube is attached to bring the fluids close to reaction temperature [1], Injection of further streams is performed by HPLC-type sample injection valves. 

Both concentric and stacked fluid layer arrangements, corresponding to difler-ent versions of separation mixers, were developed, allowing either a drop- or streamlike injection of liquids in a reaction tube attached to the micro mixer [48],... 

Even inside the controlled conditions of a research laboratory, analyzing clean and standardized test samples PCR procedures requires careful quality control, taking into consideration differences in sample preparation, variation in pipetting, differences in reaction tube thickness, poor calibration or instability of the thermal cycler, and reagent quality. 

Once the reaction tube has been placed in the thermal cycler, there are normally three... 

A typical commercial reactor consists of a vertical tube, up to 10 m in height, into the top of which the monomer is fed continuously. As polymerization proceeds, the increasingly viscous polymer solution travels down the column. Molten polymer is drawn from the bottom of the reaction tube and is subsequently cooled and chopped into pellets. The final manufacturing stage consists of exposing the pellets to a strong vacuum at a slightly elevated temperature to remove residual monomer and water. 

The process of self condensation of co-amino acids involves reactions of the type shown in Fig. 23.6 b). This type of reaction is used to make polymers, such as nylon 11, from molten 11-aminoundecanoic acid, which is stirred at 220 °C. Such specialty nylons are made in much smaller quantities than nylon 6 and are thus more likely to be made in a batch reactor than in a continuous reaction tube. 

As an alternative, it is possible to use a mixture of purified 30S and 50S ribosomal subunits or 70S monomers (0.25 fiMfinal concentration) and 4 to 8 1/reaction tube of SI 00 post-ribosomal supernatant as well as initiation factors IF1, IF2, and IF3 in a 1.5-to-l ratio with the ribosomes. After 30 min incubation at 20°, the activity of the synthesized luciferase is determined as described later. 

The preparation of molybdenum (III) bromide is effected by transferring the reaction tube to a 12-in. split-winding furnace D with a heating zone of 10 to 12 in., so that B is located at the center of the furnace. After the furnace has been heated to 600°, bromine is distilled from A to F simply by moving the ice bath to F and warming A to room temperature. A deposit of molybdenum(III) bromide is obtained at E as the reaction proceeds. When all bromine has been distilled into F, the ice bath is returned to A and the distillation repeated. Once the furnace temperature has been regulated, the reaction does not require further attention except to occasionally transfer the ice bath between A and F. 

On completion of the reaction after 10 to 14 hours, the reaction tube is removed from the furnace. The bromine may be frozen at liquid-nitrogen temperature in either bulb A or F, and both A and F are removed by sealing with the hand torch near the bulb E. The remainder of the reaction tube is transferred to the dry-box under an inert atmosphere (helium, nitrogen, or argon) and opened by breaking at the constrictions between bulbs B and E. 

Multiplex PCR a PCR reaction where more than one primer set is included in the reaction pool allowing 2 or more different DNA targets to be amplified by PCR in a single reaction tube. 

The same concept of volumetric in situ heating by microwaves was also exploited by Larhed and coworkers in the context of scaling-up a biochemical process such as the polymerase chain reaction (PCR) [25], In PCR technology, strict control of temperature in the heating cycles is essential in order not to deactivate the enzymes involved. With classical heating of a milliliter-scale sample, the time required for heat transfer through the wall of the reaction tube and to obtain an even temperature in the whole sample is still substantial. In practice, the slow distribution of heat... 

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