Effect of mixing on nonuniformly initiated polymerization by radiation

Kawakami, Waichiro; Machi, Sueo

doi:10.1002/aic.690190114

Cited by 6 publications

(7 citation statements)

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“…The degree of mixing can have a profound iduence on monomer conversion as well as the molecular weight distribution (MWD) in radiation-induced polymerization (Chen andHill, 1971, Kawakami andMachi, 1973). Similar effects for photoinitiated chain reactions have been reported by Hill and Felder (1965).…”

Section: Conclusion and Significancementioning

confidence: 66%

Influence of mixing on the performance of periodic chemical reactors

Lee

Bailey

1974

AIChE Journal

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The interaction between imperfect mixing and cyclic operation is examined for several continuous polymerizations in stirred-tank reactors. The reactor is represented by a mixed model involving two interconnected ideal stirred vessels. Cyclic fluctuations in the concentration of a chain transfer agent during Ziegler-catalyzed olefin polymerization can yield molecular weight distributions significantly different from those of a conventional steady state reactor. This result is consistent with the available experimental data. It is especially interesting that the cyclic reactor effluent with a modified molecular weight distribution is of approximately timeinvariant composition when the period of cycling is on the order of the reactor holding time. Imperfect mixing has a lesser effect on cycled reactors for free-radical and polycondensation polymerization than it has on cycled olefin polymerization reactors. C. K. LEE and J. E. BAILEY Department of Chemical EngineeringUniversity of Houston Houston, Texas 77004 SCOPEIt is well known that the degree of mixing within a polymerization reactor can significantly affect the product molecular weight distribution (MWD) and thereby the polymer properties. Similarly, intentional unsteady operation of such reactors by varying such operating parameters as feed concentrations or flow rate can produce different MWD's than any steady state operation. This result has been obtained in modeling studies by Ray (1968) for free-radical and polycondensation polymerizations,.;for example, and demonstrated experimentally by Claybaugh et al. (1969) for Ziegler-catalyzed olefin polymerization. Since commercial reactors may not be perfectly mixed, the objective of this work is to analyze the combined effects of imperfect mixing and cyclic operation.

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Section: Conclusion and Significancementioning

confidence: 66%

Influence of mixing on the performance of periodic chemical reactors

Lee

Bailey

1974

AIChE Journal

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“…As the extent of mixing increases, the peaks move toward each other (M, increases for the low molecular weight fraction and decreases for the high molecular weight fraction) until finally only one species is present. In addition, as mixing increases, the number-average molecular weight of the overall product decreases and the weight-average molecular weight increases, a result predicted theoretically by Chen and Hill (1971) and Kawakami and Machi (1973). Runs 3 to 5 and 6 to 9 show the effect of the extent of illumination at a low mixing rate.…”

Section: Mixing Effects On Product Molecular Weightsmentioning

confidence: 72%

“…Within the limits of the analytical equipment used, no evidence of such a species was found in the present study. Kawakami and Machi (1973) present theoretical expressions for the molecular weight distribution of a polymer formed in a partially illuminated reactor, which predict the occurrence of bimodal distributions under the conditions of the present study. Attempts to fit the MWD data quantitatively by use of Kawakami's model have not been successful.…”

Section: Mixing Effects On Product Molecular Weightsmentioning

confidence: 80%

“…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.…”

Section: Conclusion and Significancementioning

confidence: 93%

“…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).…”

Section: Mixing Effects On Polymerization Ratesmentioning

confidence: 99%

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

1975

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Styrene and methyl methacrylate have been polymerized in a batch photoreactor using two sensitizers-benzoin (C6H5COCHOHC6H5) and benzoin methyl ether (C6H5COCHOCH3C6H5)-and light with a peak intensity at 366 nm. Primary quantum yields have been calculated for each monomer-sensitizer combination. Effects of mixing on the rate of polymerization and product molecular weight distribution have been determined and correlated with a two-region reactor model. Among impediments to the commercial development of photochemical processes have been a scarcity of reliable kinetic data, and the difficulty of accounting in reactor design for imperfect mixing and nonuniform absorption of the reaction-initiating light. The design of photopolymerization reactors is further complicated by the interactive effects of spatial nonuniformities and mixing on both the polymerization rate and the product molecular weight distribution. Theoretical models have been proposed to describe these effects, but few experimental results exist which might either confirm or invalidate the models. MENDIRATTA andThe present study had as its objectives the determination of light absorbances and primary quantum yields for several sensitized photopolymerization reactions, and the experimental confirmation of theoretically predicted mixing effects in photoreactors. Styrene and methyl methacrylate were polymerized in a stirred batch photoreactor by using two sensitizers: benzoin (C6H5COCHOHC6H5) and benzoin methyl ether (C6H5COCHOCH3C6H5). Light from a high pressure short-arc mercury lamp was filtered to pass only the wavelength band with its principal line at 366 nm. Rates were measured dilatometrically, and product molecular weights were determined by gel permeation chromatography. Quantum yields were calculated from measured polymerization rates at full illumination and perfect mixing, and confirmatory estimates of the quantum yields were obtained from the average molecular weights of the polymer products. Rates and product molecular weight distributions were then measured as functions of the fractional illumination of the reactor and the rotational speed of the stirrer, and the observed results were compared with theoretical predictions. CONCLUSIONS AND SIGNIFICANCEPrimary quantum yields for light with a peak intensity at 366 nm are estimated to be 0.011 for styrene sensitized by benzoin, 0.072 for styrene sensitized by benzoin methyl ether, 0.029 for MMA sensitized by benzoin, and 0.32 for MMA sensitized by benzoin methyl ether.The variation of the polymerization rate with the extent of illurnination follows theoretical predictions when the reactor is perfectly mixed, but existing models are only partially successful in correlating the variation of the rate with the degree of mixing. Moreover, even in the absence of stirring, some diffusion of radicals or mixing by natural convection takes place, and so the use of a model consisting of light and dark regions with negligible interchange between them could lead to errors in design or scale-up when the react...

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MWD control in continuous free‐radical polymerizations through forced oscillations of the transfer agent feed

Gugliotta

Couso

Meira

1991

J of Applied Polymer Sci

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SYNOPSISThis paper studies the effect of forced-feed oscillations of a n intentionally added chain transfer agent on isothermal free-radical polymerizations carried out in continuous stirredtank reactors ( CSTRs) . A solution polymerization is first considered. The influence on the molecular weight distribution (MWD) of rectangular waves and impulsive trains of the transfer agent feed is theoretically and experimentally investigated. The main result is that (within certain limits) the average polydispersity can be increased at will with respect to its corresponding steady-state ( SS) value, without affecting the average number average chain length or the instantaneous monomer and initiator conversions. This result is extended to an emulsion copolymerization under sinusoidal oscillations of the transfer agent feed, where the "decoupling" between the average molecular polydispersity and other parameters (conversions, number average molecular weight, average number of branches per molecule, and the particle-size distribution) is also produced.

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Effect of mixing on nonuniformly initiated polymerization by radiation

Cited by 6 publications

References 10 publications

Influence of mixing on the performance of periodic chemical reactors

Influence of mixing on the performance of periodic chemical reactors

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

MWD control in continuous free‐radical polymerizations through forced oscillations of the transfer agent feed

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