Effect of agitation on radiation chemical reactions involving chloral hydrate aqueous solutions

Abstract

The location of a radioactive source in the central or inner region of a reactor may be more desirable from the standpoint of the efficiency in use of the source, but it leads to a high nonuniformity in the dose rate distribution. The reaction rates of many radiation chemical reactions are not directly proportional to dose rates and may depend 011 a power of the dose rate less than 1. For this kind of reaction, it is proved (1, 2 ) mathematically by the Cauchy-Schwarz inequality that the more uniform distribution of dose rate in time and space gives the higher reaction rate for the same amount of absorbed energy. If there is a sharp nonuniformity of dose rate in a reactor, the overall reaction rate is expected to be increased by agitation when the lifetime of the intermediate is comparable to a time characteristic of the mixing process.Fredrickson and co-workers (3) have discussed the eficiency of the use of radiant energy by culture of algae as functions of mixing, radiation attenuation, and a nonlinear dependence of growing rate. They have shown theoretically the difference of nonmixing and perfect mixing in growth rate and efficiency of light utilization for algal growth chambers. Hill and co-workers (1, 4, 5) examined theoretically the interaction of mixing, radiation attenuation, and chemical kinetics in a isothermal photoreactor und have discussed time scales of the chemical kinetics and mixing processes by introducing 4, the ratio of the diffusion mean free path of the radical to the radiatioii mean free path. They also reported (6) experimental results of the effect of mixing in a nonuniformly initiated photopolymerization. The relation between 4 and stirring speed or geometry of the agitated vessel, however, remains to be unfolded. The purpose of this note is to explore experimentally the effect of agitation on a radiation induced chemical reaction and to suggest a simplified mechanism for the effect.The radiolysis of chloral hydrate aqueous solutiou (7 to 11) by (3-137 gamma ray was used as a model reaction. EXPERIMENTALThe experimental apparatus is schematically shown in Figure la. Lead blocks were used to form the high dose rate portion in the reactor by providing a slit width of 5 inin., corresponding to 5.0% of the total cross-sectional area of the reactor. However, it was found t?xperimentally that the colliination was poor and yielded a 10% exposure of the reactor. The Pyrex glass vessel could accommodate four baffles (15 inni. width) and was 125 mm. in diameter. Two sizes of stainless steel agitators were used and are illustrated in Figure 16. Tests were run with the two sizes of agitators, with and without baffles in the reactor vessel. One molar aqueous solution of chloral hydrate was used as the reactant, and the volunie WAS 250 cc. corresponding to 20 mm. in height.The concentration of hydrochloric acid, which is the main product of the radiolysis, was measured by using a tungsten electrode with a cell constant of 0.27 cm-l. A 900-curie pencil of Cs-137 was used as the gamma ray source. All e...

Effect of mixing on nonuniformly initiated polymerization by radiation

“…They also found that a low molecular weight species was in appreciable relative amount at low stirring speeds, and its amount became smaller with increasine; stirring speeds. Kawakami and Isbin (1970) reported the effects of agitation on radiolysis of chloral hydrate aqueous solution under nonuniform dose rate distribution. They proposed a simplified analysis based mainly on the intermittent irradiation of fluid elements caused by recirculating flow in a stirred-tank reactor.…”

“…One is based on a diffusion model in which the radicals produced in the higher dose rate area are assumed to be dispersed throughout the reactor by diffusion (Noyes, 1959;Hill and Reiss, 1968). The other is based on a circulation flow model, in which fluid elements are assumed to be irradiated periodically by going around in the reactor (Fredrickson et al, 1961;Kawakami and Isbin, 1970).…”

Benzoin‐ and benzoin methyl ether‐sensitized photopolymerization of styrene and methyl methacrylate: Quantum yields and mixing effects

“…The positive effect of mixing on the rate of a nonuniformly initiated reaction has been shown theoretically in several studies (Hill and Page 1116 November, 1975 Felder, 1965;Hill and Reiss, 1968;Hill, Reiss, and Shendalman, 1968;Chen and Hill, 1971;Shah and Felder, 1971;Shendalman and Hill, 1971) and experimentally by Yemin and Hill (1969), Kawakami and Isbin (1970), Muller, Eichacker, and Hill ( 1971), and Kawakami and Machi ( 1973). Theoretical studies of the effects of mixing on polymer product molecular weights have been carried out by Chen and Hill (1971) and Kawakami and Machi (1973), and an experimental study was carried out by Muller e t al.…”

“…The implication of this result is that axial light attenuation did not have a measurable effect on the polymerization rate, and the averaging procedure used to derive Equation (12) for I,, is accordingly valid regardless of the degree of mixing in the reactor. Kawakami and Isbin (1970) and Kawakami and Machi (1973) propose a model which correlates the overall reaction rate in a nonuniformly irradiated reactor with the rate of stirring. The model postulates distinct light and dark regions-in good correspondence with the conditions of the present system-with a circulation rate between them which depends on the stirrer speed in a manner prescribed by Rushton et al ( 1946).…”