Acid runaway condition

A relatively sharp transition between oligomerization and alkylation activity has been measured with sulfuric acid at Hq values between — 8.0 and — 8.5 (109). If such low-acidity values occur in an alkylation reactor, oligomerization reactions become so predominant that the acid strength cannot be maintained and the plant is said to be in an acid runaway condition. 

This seems to indicate an "acid runaway" condition and more will... 

Acid runaway" is a term commonly used in commercial alkylation operations and is characterized by a condition of low acid strength and rapid build up of diluents. In certain situations an acid runaway may force olefin feed to be cut out since fresh acid usually cannot be added fast enough to counteract the rapid diluent formation. 

The monomer is sensitive to light, and even when inhibited (with aqueous ammonia) it will polymerise exothermally at above 200° C [1]. It must never be stored uninhibited, or adjacent to acids or bases [2], Polymerisation of the monomer in a sealed tube in an oil bath at 110° C led to a violent explosion. It was calculated that the critical condition for runaway thermal explosion was exceeded by a factor of 15 [3]. Runaway polymerisation in a distillation column led to an explosion and fire [4], See other polymerisation incidents... 

Not even traces of strong acids should be added to high strength solutions of the hydroperoxide [1], The thermal stability and mechanism of cleavage of mixtures with 4-toluenesulfonic acid have been studied under adiabatic conditions, and there is potential for development of a thermal runaway [2]. 

Nitration Chemical reaction of a substance in which the nitro group (-N02) is introduced into the molecule often accomplished under highly reactive conditions using mixtures of nitric and sulfuric acids at high temperatures. Byproducts of the reaction may have explosive properties if reaction control is lost, may lead to vigorous and strongly exothermic runaway reactions due to oxidation of the reactants. 

Liquid ethylene oxide under adiabatic conditions requires about 200°C before a self-heating rate of 0.02°C/min is observed (190,191). However, in the presence of contaminants such as acids and bases, or reactants possessing a labile hydrogen atom, the self-heating temperature can be much lower (190). In large containers, runaway reaction can occur from ambient temperature, and destructive explosions may occur (268,269). 

The explosive hexogen (RDX) is produced according to the SH process. Hexamine is nitrated with an excess of 8-10 times of concentrated nitric acid (98.5 %). The reaction temperature should not exceed 23 °C in order to avoid runaway. Apart from the reacting substances and the product ammonia, formaldehyde and other materials are present in the reactor. The reaction is exothermic and the mixture is chemically unstable. Hence, the reaction temperature and the excess of nitric acid have to be kept within the permissible range in order to avoid an explosion. The reaction takes place in the nitrator whose P l diagram is shown in Fig. 4.11. It represents the first part of a cascade of reactors where the reaction is completed and the product is conditioned. The process is continuous and the process stream progresses from reactor to reactor by overflow. 

Since both acids have relatively high freezing points, 13-14°C, they must be prevented from freezing in cold conditions. If freezing occurs, thawing is a hazardous procedure since the distribution of inhibitor between solid and liquid is difficult to control, and runaway imcontrolled and potentially explosive polymerization of the liquid phase is always a threat. To avoid this potential hazard, monomer storage at temperatures in excess of their freezing points is recommended. 

Most acrylates are polymerized by both radical and anionic initiations, with the former being the more commonly used. In all cases the heat of polymerization must be carefully controlled to avoid runaway reactions. The values of the heat of polymerization for selected methacrylates are listed in literature [18]. In general, the rate of polymerization and the average molar mass must be controlled by the initiator and monomer concentration and the reaction temperature. In all cases the use of high-purity monomers is important for proper polymerization conditions. Therefore, the removal of inhibitors is necessary. Phenolic inhibitors such as hydroquinone, 4-methoxyphenol, or aromatic amines are usually removed by alkaline or acidic extraction [11,19]. Otherwise, the... 

Reaction uniformity in phenol-aldehyde condensations is obtained by careful control of reaction conditions such as temperature of condensation [39], catalyst concentration, and pH. At the early stages the reaction is exothermic, and the temperature must be controlled to prevent a runaway reaction [40]. Gel permeation chromatography offers a means to monitor product uniformity. Specific catalysts (usually 1-6%) are used to obtain either a resole (alkaline catalysts or basic salts) or novolac (acid catalysts). 

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