Continuous exothermic reactions

Fires in mines can be caused by many factors but one of the major causes is spontaneous combustion ( spon com ). Spon com occurs when air is allowed to percolate through organic materials, including coal. Through a progressive series of adsorptive, absorptive, and chemical processes, heat is produced, which causes the temperature of the material to rise. As we discussed in the introduction to this chapter, fires occur when the temperature of the material reaches its minimum self-heating temperature, where a continuous exothermic reaction is sustained and the material goes into thermal runaway. 

In addition to the advantage of high heat transfer rates, fluidized beds are also useful in situations where catalyst particles need frequent regeneration. Under these circumstances, particles can be removed continuously from the bed, regenerated, and recycled back to the bed. In exothermic reactions, the recycling of catalyst can be... 

Reaction temperature. For endothermic reactions. Fig. 2.9c shows that the temperature should be set as high as possible consistent with materials-of-construction limitations, catalyst life, and safety. For exothermic reactions, the ideal temperature is continuously decreasing as conversion increases (see Fig. 2.9c). 

Fit a 1500 ml. bolt-head flask with a reflux condenser and a thermometer. Place a solution of 125 g. of chloral hydrate in 225 ml. of warm water (50-60°) in the flask, add successively 77 g. of precipitated calcium carbonate, 1 ml. of amyl alcohol (to decrease the amount of frothing), and a solution of 5 g. of commercial sodium cyanide in 12 ml. of water. An exothermic reaction occurs. Heat the warm reaction mixture with a small flame so that it reaches 75° in about 10 minutes and then remove the flame. The temperature will continue to rise to 80-85° during 5-10 minutes and then falls at this point heat the mixture to boiling and reflux for 20 minutes. Cool the mixture in ice to 0-5°, acidify with 107-5 ml. of concentrated hydrochloric acid. Extract the acid with five 50 ml. portions of ether. Dry the combined ethereal extracts with 10 g. of anhydrous sodium or magnesium sulphate, remove the ether on a water bath, and distil the residue under reduced pressure using a Claiseii flask with fractionating side arm. Collect the dichloroacetic acid at 105-107°/26 mm. The yield is 85 g. 

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. 

The pilot plant must also be carehiUy designed so that its control and safety systems are "fad-safe" and any unexpected equipment or utdity fadure brings the unit into a safe and de-energized condition. Unexpected or rapid process changes, if they can herald or lead to dangerous conditions (eg, mnaway exothermic reaction), should be continuously monitored by appropriate instmmentation and suitable automatic action provided (1,55—67). 

Later it was synthesized in a batch process from dimethyl ether and sulfur thoxide (93) and this combination was adapted for continuous operation. Gaseous dimethyl ether was bubbled at 15.4 kg/h into the bottom of a tower 20 cm in diameter and 365 cm high and filled with the reaction product dimethyl sulfate. Liquid sulfur thoxide was introduced at 26.5 kg/h at the top of the tower. The mildly exothermic reaction was controlled at 45—47°C, and the reaction product (96—97 wt % dimethyl sulfate, sulfuhc acid, and methyl hydrogen sulfate) was continuously withdrawn and purified by vacuum distillation over sodium sulfate. The yield was almost quantitative, and the product was a clear, colorless, mobile Hquid. A modified process is deschbed in Reference 94. Properties are Hsted in Table 3. 

Regeneration with air can be done with continuous or periodic addition of small amounts of air. Both must be done carefully because of exothermic reaction. Regeneration is never complete, so the beds must be eventually changed out. This must be done carefully because of the pyrophoric (spontaneously combustible) nature of the iron sulfide. The entire bed is wetted first. 

Some batch reactions have the potential for very high energy levels. If all the reactants (and sometimes catalysts) are put into a kettle before the reaction is initiated, some exothermic reactions may result in a runaway. The use of continuous or semi-batch reactors to limit the energy present and to reduce the risk of a runaway should be considered. The term semi-batch refers to a system where one reactant and, if necessary, a catalyst is initially charged to a batch reactor. A second reactant is subsequently fed to the reactor under conditions such that an upset in reacting conditions can be detected and the flow of the reactant stopped, thus limiting the total amount of potential energy in the reactor. 

Hydroxy- 6-diazoandrost-5-en- l-one (96) To a stirred solution of 750 ml of methanol and 144 ml of 5 A sodium hydroxide is added 36 g (0.114 mole) of oximino ketone. Concentrated aqueous ammonia (56.6 ml, 0.850 mole) is then added followed by dropwise addition of 265 ml of cold 3 M sodium hypochlorite at a rate sufficient to maintain the temperature of the exothermic reaction mixture at 20 + 1° while cooling with an external ice bath. At temperatures below 20° appreciable amounts of a-mono- and a-dichloro ketones are obtained above 20° the chloramine decomposes before reacting with the oximino ketone. As soon as all of the sodium hypochlorite has been added, the ice bath is removed and the reaction mixture is allowed to warm to room temperature with continued stirring for 6 hr. The reaction mixture is diluted with an equal volume of water and extracted twice with... 

To 4.9 g of finely pulverized sodium in 50 ml of absolute benzene add dropwise with stirring 12 g of chlorobenzene in 50 ml of absolute benzene. As soon as the exothermic reaction begins, maintain the temperature by cooling between 30° and 35°C, and continue stirring for 2 to 3 hours. To the resulting phenyl sodium add dropwise 19.8 g of thio-xanthene in 120 ml of absolute benzene. The slightly exothermic reaction ceases after about 1 to 1 /j hours. 

A mixture of 540 grams (9.0 mols) of ethylenediamine, 270 grams (1.53 mols) of 1,2,3,4-tetrahydro-alpha-naphthoic ecid, end 360 ml (4.32 mols) of concentrated hydrochloric ecid was introduced into a two-liter, three-necked flask fitted with a thermometer, stirrer, end distillation takeoff. The mixture was distilled under a pressure of about 20 mm of mercury absolute until the temperature rose to 210°C. Thereafter, heating was continued under atmospheric pressure and when the temperature reached about 260°C, an exothermic reaction was initiated. The heat was then adjusted to maintain a reaction temperature of 275° to 280°C for 45 minutes end the mixture thereafter cooled to room temperature. 

Polyurethanes are manufactured by the mixing of various resins, isocyanates and catalysts to produce an exothermic reaction, which liberates the foaming agent and causes the mix to expand. They are made in large block molds as a batch process or are continuously foamed onto a paper or polythene substrate on a conveyor system. 

The choice of a particular type of gas discharge for quantitative studies of ion-molecule reactions is essential if useful information is to be obtained from ion abundance measurements. Generally, two types of systems have been used to study ion-molecule reactions. The pulsed afterglow technique has been used successfully by Fite et al. (3) and Sayers et al. (1) to obtain information on several exothermic reactions including simple charge transfer processes important in upper atmosphere chemistry. The use of a continuous d.c. discharge was initiated in our laboratories and has been successful in both exothermic and endothermic ion-molecule reactions which occur widely within these systems. 

In case of exothermic reactions, the heat-exchange capacities of the reactor allow to rapidly evacuate the heat generated by the reaction and therefore to perform a transposition of a pure batch operating mode into a continuous one. The main point is the ability to avoid, as far as possible, an initial increase of the temperature as soon as the reactants are mixed. 

The feasibility of operating highly exothermic reactions in a HEX reactor has been demonstrated, some considerations can also be given concerning the inherently safer characteristics of an intensified continuous HEX reactor. This type of evaluation has been conducted on the OPR, using the esterification of propionic anhydride by 2-butanol as test reaction [36, 37]. 

Anxionnaz, Z., Cabassud, M., Gourdon, C., and Tochon, P. (2010) Transposition of an exothermic reaction from a batch reactor to an intensified continuous one. Heat Transfer Eng., 31 (9), 788-797. 

Consider a continuous-stirred-tank reactor (CSTR) with cooling jacket where a first order exothermic reaction takes place. It is required to derive a model relating the extent of the reaction with the flowrate of the heat... 

The main driver was to develop a laboratory-scale micro-channel process and transfer it to the pilot-scale, aiming at industrial fine-chemical production [48, 108]. This included fast mixing, efficient heat transfer in context with a fast exothermic reaction, prevention offouling and scale-/numbering-up considerations. By this means, an industrial semi-batch process was transferred to continuous processing. 

Strongly exothermic reactions can be conducted in reactors with a small tube diameter, operated continuously. 

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