Phosphorus-based vapor-phase

The mode of action of phosphorus-based flame retardants is believed to take place in either the condensed or the vapor phase (refs. 1,2) depending on the type of phosphorus compound and the chemical composition of the polymer. Phosphorus has been reported to be 3 to 8 times more effective than bromine depending on the polymer type (ref. 3). 

Condensed-Phase Mechanisms. The mode of action of phosphorus-based flame retardants in cellulnsic sy stems is probably best understood. Cellulose decomposes by a noncalalyzed route lo tarry depolymerization products, notably levoglucosan, which then decomposes to volatile combustible fragments such as alcohols, aldehydes, ketones, and hydrocarbons. However, when catalyzed by acids, the decomposition of cellulose proceeds primarily as an endothermic dehydration of the carbohydrate to water vapor and char. Phosphoric acid is particularly efficaceous in this catalytic role because of its low volatility (see Phosphoric Acids and Phosphales). Also, when strongly heated, phosphoric acid yields polyphosphoric acid which is even more effective in catalyzing the cellulose dehydration reaction. The flame-retardanl action is believed to proceed by way of initial phosphory lation of the cellulose. 

Adiponitrile is made commercially by several different processes utilizing different feedstocks. The reaction of adipic acid with ammonia in either liquid or vapor phase produces adipamide as an intermediate, which is subsequently dehydrated to adiponitrile. The most widely used catalysts are based on phosphorus-containing compounds. Vapor-phase processes involve the use of fixed catalyst beds whereas, in liquid-gas processes, the catalyst is added to the feed. DuPont currently practices a buiadiene-to-adiponitdle route based on direct addition of HCN to butadiene. 

At Bolton, we also have attempted to introduce volatile and possible vapor phase-active, phosphorus-based FR components in back-coating formulations.60 62 The selected FRs included tributyl phosphate (TBP), a monomeric cyclic phosphate Antiblaze CU (Rhodia Specialties) and the oligomeric phosphate-phosphonate Fyrol 51 (Akzo). When combined with an intumescent char-forming pentaerythritol (PER) derivative (NH1197, Chemtura) and applied as a back-coating on to cotton and polypropylene substrates, significant improvements in overall flame retardancy were observed. 

The fust reaction takes place in the vapor phase, between 330 and 360°C, at low pressure (between 03 and 04.106 Pa absolute), in the presence of air and steam in a r-butanol/air/steam ratio of about 1 10 to 15/6 to 12, on a catalyst based on mixed oxides of molybdenum, cobalt, bismuth, iron, nickel, and additions of derivatives of alkaline metals, antimony, tellurium, phosphorus, tungsten, tin, manganese, etc. With residence times of 2 to 3 s, the molar yield of methacrolein exceeds 85 per cent for virtually total once-throngh conversion of r-butanoLThe main by-products formed are... 

The first industrial plant using n-butane to manufacture maleic anhydride was started up by Monsanto in 1984. At the time, 20 per cent of the maleic anhydride production capacity of this company switched from benzene to butane. Since then, three other manufacturers in the United States (Amoco, Ashland and Denka Chemical), and two in Western Europe (Bayer and Huh) have followed a similar procedure, so that ail maleic anhydride produced today in the United States is based on butane feedstock and nearly 50 per cent of worldwide installed capacity operates by this method. The n-butane is oxidized in the vapor phase, in a multi-tube reactor, on a fixed bed of catalyst based on phosphorus, vanadium and iron, deposited on a silica/alumina support... 

First of all, it is important to evaluate how the phosphorus is allocated between the condensed and vapor phases during the thermal degradation of the polymer, even if the volatilization of phosphorus does not show that it acts in the vapor phase. Vahabi et al. have proposed an original approach to study the efficiency of phosphorus in both condensed and vapor phases. Two indices (called respectively charring efficiency and efficiency in the vapor phase) were calculated to evaluate the influence of phosphorus to improve the charring and to decrease the EHC (measured from TGA and PCFC). These calculations are based on the measurement by elemental... 

---