Exothermic reaction, temperature and

The stabilization of PAN precursor fibers is highly exothermic. Reaction temperature and amount of heat generated [12] depend upon the precursor composition and on the reaction environment. Optimally, the fiber will take up 8-10 vi. % oxygen without overheating. During stabilization, scission and oxidation reactions result in an evolution of gaseous species, i.e., HCN, CO2, and H2O, and these reactions cause the fiber to shrink [13]. Comonomers exert a catalytic effect. The stabilization of the homopolymer in air is very slow, and requires several hours when run isothermally at 220-230 C. When PAN copolymers are used, the stabilization time can be reduced to less than one hour [1] [3] [13]. 

A sodium stannite solution was prepared by addition of aqueous sodium hydroxide (2.5 mol, lOOg) to aqueous stannous chloride (0.25 mol, 56g). The initially formed precipitate redissolved to form a clear solution. This solution was gradually added to a solution of 16.3g (0.1 mol) phenyl-2-nitropropene in THF at room temperature. A slightly exothermic reaction ensued, and the reaction mixture was stirred for 30 min, a saturated sodium chloride solution was added, and the solution was extracted with ether and the pooled extracts were evaporated under vacuum to give essentially pure P2P oxime in 80% yield. 

To a suspension of a tinc-copper couple in 150 ml of 100 ethanol, prepared from 80 g of zinc powder (see Chapter II, Exp. 18), was added at room temperature 0.10 mol of the acetylenic chloride (see Chapter VIII-2, Exp. 7). After a few minutes an exothermic reaction started and the temperature rose to 45-50°C (note 1). When this reaction had subsided, the mixture was cooled to 35-40°C and 0,40 mol of the chloride was added over a period of 15 min, while maintaining the temperature around 40°C (occasional cooling). After the addition stirring was continued for 30 min at 55°C, then the mixture was cooled to room temperature and the upper layer was decanted off. The black slurry of zinc was rinsed five times with 50-ml portions of diethyl ether. The alcoholic solution and the extracts were combined and washed three times with 100-ml portions of 2 N HCl, saturated with ammonium chloride. 

A mixture of 0.30 mol of the tertiairy acetylenic alcohol, 0.35 mol of acetyl chloride (freshly distilled) and 0.35 mol of /V/V-diethylaniline was gradually heated with manual swirling. At 40-50°C an exothermic reaction started and the temperature rose in a few minutes to 120°C. It was kept at that level by occasional cooling. After the exothermic reaction had subsided, the mixture was heated for an additional 10 min at 125-130°C, during which the mixture was swirled by hand so that the salt that had been deposited on the glass wall was redissolved. After cooling to below 50°C a mixture of 5 ml of 36% HCl and 200 ml of ice-water was added and the obtained solution was extracted with small portions of diethyl ether. The ethereal solutions were washed with water and subsequently dried over magnesium sulfate. The solvent was removed by evaporation in a water-pump vacuum... 

A typical flow diagram for pentaerythritol production is shown in Figure 2. The main concern in mixing is to avoid loss of temperature control in this exothermic reaction, which can lead to excessive by-product formation and/or reduced yields of pentaerythritol (55,58,59). The reaction time depends on the reaction temperature and may vary from about 0.5 to 4 h at final temperatures of about 65 and 35°C, respectively. The reactor product, neutralized with acetic or formic acid, is then stripped of excess formaldehyde and water to produce a highly concentrated solution of pentaerythritol reaction products. This is then cooled under carefully controlled crystallization conditions so that the crystals can be readily separated from the Hquors by subsequent filtration. 

Hydrogenations can be carried out in batch reactors, in continuous slurry reactors, or in fixed-bed reactors. The material of constmetion is usually 316 L stainless steel because of its better corrosion resistance to fatty acids. The hydrogenation reaction is exothermic and provisions must be made for the effective removal or control of the heat a reduction of one IV per g of C g fatty acid releases 7.1 J (1.7 cal), which raises the temperature 1.58°C. This heat of hydrogenation is used to raise the temperature of the fatty acid to the desired reaction temperature and is maintained with cooling water to control the reaction. 

A solution of 61 parts 4-chloro-l,l-di-(4-fluorophenyl)-l-butene in 400 parts 2-propanol is hydrogenated at normal pressure and at room temperature in the presence of 5.5 parts palladium-on-charcoal catalyst 10% (exothermic reaction, temperature rises to about 30°C). After the calculated amount of hydrogen is taken up, hydrogenation is stopped. The catalyst is filered off and the filtrate is evaporated. The oily residue is distilled in vacuo, yielding l-chloro-4,4-di-(4-fluorophenyl)-butane, boiling point 166° to 168°C at 6 mm pressure ... 

The combination of highly exothermic reactions with a sharp increase in viscosity as conversion proceeds controls reactor design and operational conditions in full-scale operations. The art of sulfonation is to maintain the optimal reaction temperature and reaction time, resulting in products with small amounts of byproducts and good color. 

Most of the chemical reactions in the process industry are temperature dependent. They are either exothermic or endothermic. As a consequence, it is often necessary to remove the heat generated by an exothermic reaction to control the reaction temperature and to avoid thermal runaway reactions or to suppress endothermic by-product reactions, for instance [8]. 

Five grams of potassium hydroxide (85% KOH) is dissolved in 100 ml. of Methyl Cellosolve (Note 1) in a 500-ml. flask (Note 2) fitted with a mechanical stirrer, reflux condenser, and a heating mantle. Dicyandiamide (50.4 g. 0.6 mole) (Note 3) and benzo-nitrile (50 g. 0.485 mole) are added, and the mixture is stirred and heated. A solution is formed, and, when the temperature reaches 90-110°, an exothermic reaction begins and the product separates as a finely divided white solid. The vigor of the reaction is kept under control by the refluxing of the solvent (Note 4). 

At an early stage in the preparation of methyl parathion, it is supposed that the phosphorus ester was being chlorinated to give dimethyl thionophosphorochlori-date. Thermocouple failure indicated a low reaction temperature and the process controller boosted the chlorine feed rate, but when this fault situation was realised, the chlorine flow and agitator were stopped. However, an exothermic runaway reaction developed, eventually leading to a violent explosion. 

A 1-1., four-necked, round-bottomed flask equipped with reflux condenser, sealed stirrer, thermometer, and solid addition funnel and protected from atmospheric moisture with a Drierite guard tube is carefully dried and flushed with a dry inert gas (Note I). The flask is charged with 453 g. (3.1 moles) of silver difluoride (Note 2) and 500 ml. of l,l,2-trichloro-l,2,2-trifluoroethane (Note 3), and phenyl disulfide (100 g., 0.458 mole) (Note 4) is weighed into the solid addition funnel. The stirrer is started, and phenyl disulfide is added to the slurry in small portions. An exothermic reaction occurs, and after the addition of several portions the reaction mixture reaches a temperature of 40° (Note 5). By intermittent use of a cooling bath and by adjusting the rate of addition of the disulfide, the reaction temperature may be maintained between 35° and 40°. The addition of the phenyl disulfide requires 45-60 minutes. On completion of the addition the suspension of black silver difluoride has been converted to yellow silver monofluoride, and the exothermic reaction gradually subsides. The reaction mixture is stirred for an additional 15-30 minutes without external cooling and then quickly heated to reflux. 

The reactants are phthalic anhydride, urea and copper(n) chloride, which are heated in a high-boiling aromatic solvent such as 1,2,4-trichlorobenzene, nitrobenzene or m-dinitrobenzene in the presence of a catalyst, usually ammonium molybdate. The solvent also acts as a heat-transfer medium. On heating to 120 °C an exothermic reaction begins and this temperature is maintained for about an hour. The temperature is then raised to 160-180 °C and kept constant for 6-12 hours. During this time ammonia and carbon dioxide are evolved, together with some solvent the reaction is complete when ammonia evolution ceases. The remaining solvent is then removed by either steam or vacuum distillation. The yield is 90-95%. For many years the solvent process was in almost exclusive use. 

A solution of 64.9 g. (I mole) of 86.5% potassium hydroxide (Note I) in 28 ml. of water is cooled in an ice bath, saturated with hydrogen sulfide, and flushed with nitrogen to ensure complete removal of excess hydrogen sulfide (Notes 2 and 3). The freshly prepared potassium hydrosulfide solution is diluted with 117 ml. of water and stirred under nitrogen at 55-60°. Then 95.3 g. (0.5 mole) of finely ground tosyl chloride (Note 3) is introduced in small portions at a uniform rate so that the reaction temperature is maintained at 55-60° (Note 2). A mildly exothermic reaction ensues, and the solution becomes intensely yellow. After about 90 g. of tosyl chloride has been introduced, the yellow color disappears, and the dissolution of the chloride ceases. The reaction mixture is rapidly filtered with suction through a warmed funnel, and the filtrate is cooled several hours at 0-5°. The crystals of potassium... 

The reaction is exothermic, and the heat transfers to the water, creating steam. A backpressure control regulates how much steam is released from the reactor shell. The faster or slower the reaction, the more or less heat transfers, and the more or less steam gets generated. The controls also let in more or less fresh water, all this controlling the reaction temperature and rate ... 

When heat is supplied to a gaseous mixture of oxidizer and fuel components, i. e., a premixed gas, an exothermic reaction occurs and the temperature increases. The reaction may conhnue and proceed into the unreacted portion of the mixture even after the source of the heat is removed. The amount of heat that has to be supplied to the mixture to achieve this is defined as the ignition energy. If, however, the reac-hon terminates after removal of the heat source, ignition of the mixture has failed. This is because the heat generated in the combustion zone is not sufficient to heat the unreacted portion of the mixture from the initial temperature to the ignihon temperature. 

Formation of the zinc carbenoid is exothermic and potentially explosive. The ice bath should be present in order to control the reaction temperature, and methylene iodide should be added gradually rather than all at once. During the addition of the methylene iodide, or shortly thereafter, the reaction mixture should develop a cloudy, white appearance. 

W.A -Diethylaniline (0.70 mol) and redistilled acetyl chloride (0.37 mol) arc placed in the flask. The acetylenic alcohol (0.30 mol) is added over a few min while heating the mixture at ca. 40"C. An exothermic reaction starts and the temperature rises to 120 C in a few min. Occasional cooling is necessary to keep the temperature at that level. After the exothermic reaction has subsided, the mixture is heated for an additional 15 min at 130"C (immersion of the flask in the heating bath is necessary to prevent solidification of the reaction mixture on the glass wall). After cooling to 50 C (stirring has been stopped), a mixture of 300 ml of ice... 

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