Phenol-Formaldehyde Runaway Reaction

Older cook styles called for addition of phenol, formaldehyde, and water followed by alkali. Once the alkali was added, strict temperature control was the only barrier to a runaway reaction. A power or equipment failure at this point was likely to lead to disaster. Every batch made involved a struggle between the skill of the operator and capability of the equipment to control the exotherm versus the exothermic nature of the reactants. Most of the disasters that have occurred were due to utilization of this cooking method. 

A plant had a runaway reaction with a phenol-formaldehyde polymerization reaction. The result was one fatality and seven injuries and environmental damage. The runaway reaction was triggered when, contrary to standard operating procedures, all the raw materials and... 

The other root causes were (1) the poor understanding of the chemistry, (2) an inadequate risk analysis, and (3) no safeguard controls to prevent runaway reactions. This EPA case history also summarized seven similar accidents with phenol-formaldehyde reactions during a 10-year period (1988-1997). 

Use the paper developed by the EPA (see footnote 27) to describe the phenol-formaldehyde runaway reactions that occurred between 1988 and 1997. 

EPA 1999a. How to Prevent Runaway Reactions, Case Study Phenol-Formaldehyde Reaction Hazards. EPA 550-F99-004. U.S. Environmental Protection Agency. August. 

Phenol. A runaway reaction may be encountered during the preparation of phenol-formaldehyde resins.4... 

It is reported that an industrial explosion was initiated by charging potassium hydroxide in place of potassium carbonate to the chloro-nitro compound in the sulfoxide [1], Dry potassium carbonate is a useful base for nucleophilic displacement of chlorine in such systems, reaction being controlled by addition of the nucleophile. The carbonate is not soluble in DMSO and possesses no significant nucleophilic activity itself. Hydroxides have, to create phenoxide salts as the first product. These are better nucleophiles than their progenitor, and also base-destabilised nitro compounds. Result heat and probable loss of control. As it nears its boiling point DMSO also becomes susceptible to exothermic breakdown, initially to methanethiol and formaldehyde. Methanethiolate is an even better nucleophile than a phenoxide and also a fairly proficient reducer of nitro-groups, while formaldehyde condenses with phenols under base catalysis in a reaction which has itself caused many an industrial runaway and explosion. There is thus a choice of routes to disaster. Industrial scale nucleophilic substitution on chloro-nitroaromatics has previously demonstrated considerable hazard in presence of water or hydroxide, even in solvents not themselves prone to exothermic decomposition [2],... 

For a safe operation, the runaway boundaries of the phenol-formaldehyde reaction must be determined. This is done here with reference to an isoperibolic batch reactor (while the temperature-controlled case is addressed in Sect. 5.8). As shown in Sect. 2.4, the complex kinetics of this system is described by 89 reactions involving 13 different chemical species. The model of the system consists of the already introduced mass (2.27) and energy (2.30) balances in the reactor. Given the system complexity, dimensionless variables are not introduced. 

Fig. 4.11 Safety boundaries for the phenol-formaldehyde reaction according to the runaway criteria of Morbidelli and Varma (7), Thomas and Bowes (2), and for an imposed maximum allowable reactor temperature Tr,ma=98°C(5)...

The primary causes of accidents in the chemical industry are technical failures, human failures and the chemical reaction itself (due to lack of knowledge of the thermochemistry and the reaction kinetics) [156]. As discussed previously, polymerization reactions are subject to thermal runaway, so that it is not surprising to learn that polymerization reactions (64 from 134 cases) are more prone than other processes to serious accidents [157]. Among the polymerization processes, the phenol-formaldehyde resin production seems to be the worst case, although incidents have been reported for vinyl chloride, vinyl acetate and polyester resins polymerization processes. 

---