The influence of the diffusional phenomena on the apparent kinetics for nth‐order gas‐solid non‐catalytic reactions is studied assuming the unreacted‐core model. Flat‐plate, cylindrical and spherical particles are considered, the size of which may vary with extent of reaction. Specific methods of contacting of fluid with solid are taken into account, but their influence on the results are not remarkable. At high conversions of cylindrical and spherical particles, the process is always chemical reaction controlled.

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The method of polymerization of trioxane solutions during crystallization by cooling is extended to molten trioxane in presence of ethylenoxide, suspended in mineral oil (thickened with polyisobutylene) and activated with small quantities of BF,.Et,O, Operating with quantities of catalyst in the order of 4.0-10-5 moles/mole of trioxane, copolymers with prevailing polyoxymethylene structure are obtained, characterized by high mrjlecular weight (qlnb = 1.5 in 0.5 yo solution in p-chlorophenol at 60 "C;) and good thermal SI aldity (kzzo = 0.03y0/min.), with yields of 45 to 60%. ZUSAMMENFASSUNG: Die Methode, Trioxan, wihrend es aus einer abkiihlenden Losung auskristallisiwt, zu polymerisieren, wird auf die Copolymerisation von geschmolzenem Trioxan mit At hvlenoxid mit tels BF,-hherat in Suspension in mit Polyisobutylen verdicktem Mineraloi ubertragen. Mit ca. 4 Mol Initiator /Mol Trioxan entstehen Copolymere mit iiberwie; :r nder Polyoxymethylen-Struktur in 45 bis 60 Yo Ausbeute, welche sich durch hohe Molrhulargewichte (qinh = 1,s bei 60°C in OJ-proz. Losung inp-Chlorphenol) und durch hoha: thermische Stabilitat (Gewichtsverlust bei 220 "C unter Stickstoff = 0,03 yo /Min.) auszeii4inen. GerieralIn preceding papers 1* 2, a new method of polymerization was described, by which polyoxymethylene of high molecular weight with high yields could be obtained. It consisted essentially in preparing an almost saturated solution of trioxane in a suitable solvent at temperatures above room temperature, adding to it a small quantity of a cationic catalyst and after a certain period of time cooling the reaction mixture gradually.

The preparation of polyoxymethylene of high molecular weight by polymerization of trioxane, starting from concentrated solutions in hydrocarbon solvents (cyclohexane) initiated by addition of a cationic catalyst (BF3 etherate) and inducing the crystallization of trioxane by cooling the system from the initial to room temperature, is investigated. The success of the method depends largely on the time of permanence of the solution at the initial temperature after the induction period (activation time) the initial solution, which can be controlled by following the temperature variations of the system during this stage. The cooling of the activated solution may be performed either continuously, in which case it may be varied from 15 to 200°C./hr., or in two stages: quenching from the initial temperature to the precipitation point followed by controlled cooling at a lower rate from this point to room temperature. The latter method is preferable when initial temperatures higher than the melting point of the pure trioxane are chosen. Products having inherent viscosities ranging from 2.0 to 3.0 dl./g. (in 0.5% solutions in p‐chlorophenol at 60°C.) are obtained.