Safety exothermic reactions

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). 

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). 

Thiol spills are handled ia the same manner that all chemical spills are handled, with the added requirement that the odor be eliminated as rapidly as possible. In general, the leak should be stopped, the spill should be contained, and then the odor should be reduced. The odor can be reduced by sprayiag the spill area with sodium hypochlorite (3% solution), calcium hypochlorite solution (3%), or hydrogen peroxide (3—10% solution). The use of higher concentrations of oxidant gives strongly exothermic reactions, which iacrease the amount of thiol ia the vapor, as well as pose a safety ha2ard. The apphcation of an adsorbent prior to addition of the oxidant can be quite helpful and add to the ease of cleanup. 

Once a decision to use QRA has been made, you must decide whether frequency and/or consequence information is required (Steps 6 and 7). In some cases you may simply need frequency information to make your decision. For example, suppose you wish to evaluate the adequacy of operating procedures and safety systems associated with a chemical reactor. The main hazard of concern is that the reactor could experience a violent runaway exothermic reaction. You believe that you know enough about the severe consequences of a runaway and nothing more will be gained by quantifying the consequences of potential run-... 

Chemical reactions are sometimes conducted in a dilute solution to moderate reaction rates, to provide a heat sink for an exothermic reaction, or to limit maximum reaction temperature by tempering the reaction. In this example there are conflicting inherent safety goals—the solvent moderates the chemical reaction, but the dilute system will be significantly larger for a given production volume. Careful evaluation of all of the process risks is required to select the best overall system. 

Since the nitrations of interest to us are exothermic reactions that produce expl substances it is obvious that safety is an important consideration in any laboratory nitration and even more so in an industrial nitration process, in the... 

New systems or processes may also need to be qualified from an operational safety perspective. This is particularly relevant in the case of chemical synthesis involving exothermic reactions. Critical safety aspects are usually identified using hazard operability or HAZOP assessments and studies. For example, a HAZOP analysis of an exothermic reaction vessel would involve consideration of the consequence of failure of the motors for mixers or circulation pumps for cooling water. Thus, the qualification of such a system would involve checks and assessment to ensure that the system/process can be operated safely and that pressure relief valves or other emergency measures are adequate and functional. 

Essential modelling for scale-up relates to heat production (ref.4), and the universally applied calculation relates to the disaster calculation where the runaway instant temperature rise is always calculated for any one-shot exothermic reaction. In addition, the normal heat production rate is calculated to determine optimum feed rates, safety margins on cooling coil and condensers, etc. Increasingly, kinetic models are used as these become available. 

Safety PI may drastically increase the safety of chemical processes. It is obvious that smaller is safer. For instance, material inventories will be lower, which is safer in case of hazardous substances. Moreover, keeping processes under control is easier because of PI, for instance, by efficient heat removal from exothermic reactions. 

The high heat capacity associated with the large mass of liquid facilitates control of the reactor and provides a safety factor for exothermic reactions that might lead to thermal explosions or other runaway events. 

For industrial conversion to 5-aminonaphthoquinone derivatives, dinitronaphtha-lene had been mixed cold with sulfuric acid and sulfur (to form sulfur dioxide), then heated to 120°C on over 100 occasions without incident. When dinitronaphthalene from a different supplier was used, the mixture exploded violently. Investigation in the safety calorimeter showed that an exothermic reaction begins at only 30°C, and that the onset and intensity of the exotherm (up to 400° C) markedly depends on quality of the dinitronaphthalene. 

An account of a serious warehouse explosion (15 dead, 141 injured). The two principal detonations were mostly due to ammonium nitrate, of which some hundred tonnes had been present, but the initiating fire was first observed in ammonium persulfate. This had been promiscuously stored alongside potassium permanganate, matches, potassium nitrate and sodium sulphide (or possibly sulphite), inter alia. None of these would improve the safety of ammonium persulfate. It was shown that the persulphate gives an immediate exothermic reaction with the sulphide. This was ascribed as the ultimate initiation. It was concluded that oxidants and... 

Precautions should be taken, especially in a scale-up approach, when dealing with exothermic reactions in the microwave field. Due to the rapid energy transfer of microwaves, any uncontrolled exothermic reaction is potentially hazardous (thermal runaway). Temperature increase and pressure rise may occur too rapidly for the instrument s safety measures and cause vessel rupture. 

The procedure begins with a material factor that is a function only of the type of chemical or chemicals used. This factor is adjusted for general and special process hazards. These adjustments or penalties are based on conditions such as storage above the flash or boiling point, endo- or exothermic reactions, and fired heaters. Credits for various safety systems and procedures are used for estimating the consequences of the hazard, after the fire and explosion index has been determined. 

This section on protective measures discusses three elements (1) containment, (2) instrumentation and detection of a runaway, and (3) mitigation measures. For each element, examples are given to illustrate the principles discussed. This section is basically a summary of protective measures, not an exhaustive treatise. Protective measures are necessary considerations, and in fact, safety requirements, when handling reactive substances and exothermic reactions. 

The Paterson facility was not aware of the decomposition reaction. The Process Safety Information (PSI) package, which was used at the Paterson plant to design the Yellow 96 production process in 1990, served as the basis for a Process Hazard Analysis (PHA) conducted in 1995. The PSI noted the desired exothermic reaction but did not include information on the decomposition reaction. 

Furthermore knowledge of the boundary conditions under which reactions have to run their course is an essential condition for the safety assessment of exothermic reactions. This includes especially ... 

Use of medium-scale heat flow calorimeter for separate measurement of reaction heat removed via reaction vessel walls and via reflux condenser system, under fully realistic processing conditions, with data processing of the results is reported [2], More details are given elsewhere [3], A new computer controlled reaction calorimeter is described which has been developed for the laboratory study of all process aspects on 0.5-2 1 scale. It provides precise data on reaction kinetics, thermochemistry, and heat transfer. Its features are exemplified by a study of the (exothermic) nitration of benzaldehyde [4], A more recent review of reaction safety calorimetry gives some comment on possibly deceptive results. [5],... 

No air should be allowed to come in contact with the hot pot liquid during the distillation, for an exothermic reaction may occur at best this may fill the apparatus with tarry material and the room with noxious fumes at "worst, pressure built up may destroy all or part of the apparatus. As a precaution, this distillation should be carried out behind a safety shield. 

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