Diffusion in flowing films of dilute polymeric solutions

Mashelkar, R. A.; Soylu, M.

doi:10.1016/0009-2509(74)80107-7

Cited by 48 publications

(21 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similarly, very little is known about the true liquid side mass transfer coefficient kL. Some conclusions can be drawn, however, from the studies of Astarita (1965) and of Mashelkar and Soylu (1974) who found that polymer addition leads to a 10 to 20% increase of the diffusion coeffizient of gases, On the other hand, however, the true liquid side mass transfer coefficient depends also on the surface renewal rate which is likely to be reduced owing to the suppression of turbulence. Following the arguments of Kolmogoroff, the reduction of kL will be proportional to the fourth root of the reduction in power consumption due to polymer additivcs.…”

Section: Gas-liquid Mass Transfermentioning

confidence: 89%

“…The diffusivity and the solubility of carbon dioxide in PAA solutions was reported by Soylu (1974) and his data are reproduced in Table 3. It can be seen that the diffusion coefficient shows a slight upward trend rather than a reduction.…”

Section: Gas-liquid Mass Transfermentioning

confidence: 91%

“…The studies of Perez and Sandall (1974) and of Yagi and Yoshida (1975) conclude the same. Soylu (1974) reports further that whenever surface active agents are present in aqueous solutions together with polyacrylamide, then the polymer has a tendency to suppress the surface activity of the agent. Thus, it may be concluded that the reduction of kLa is not likely to be attributable to any surface activity due to polymer presence.…”

Section: Gas-liquid Mass Transfermentioning

confidence: 95%

“…The surface tension data obtained in this work, however, do not show any surface activity on part of the polymers added (see Table 2 ) . Polyacrylamide was used by Calderbank and Moo-Young (1961) and by Soylu (1974) in their studies of gas-liquid mass transfer, and none of these Page 800 September, 1978 authors report any surface activity due to the polymer presence. The studies of Perez and Sandall (1974) and of Yagi and Yoshida (1975) conclude the same.…”

Section: Gas-liquid Mass Transfermentioning

confidence: 99%

See 3 more Smart Citations

Influence of polymer additives on the gas‐liquid mass transfer in stirred tanks

Ranade

Ulbrecht

1978

AIChE Journal

View full text Add to dashboard Cite

The influence of polymer additives upon the gas-liquid mass transfer in stirred tanks is examined. While the addition of sodium carboxymethylcellulose brings about a reduction of the overall liquid side mass transport coefficient which is in line with the predictions by earlier works, the reduction of kLa in polyacrylamide solutions of equal viscosity is much stronger. This is explained by the viscoelasticity of the PAA solutions, and an empirical correlation is proposed. SCOPERecent research has shown that the addition of small amounts of water soluble polymers can be beneficial in certain biochemical processes. Some of these polymer additives, like polyox and poly acrylamide, which are known to be drag reducing agents, can reduce the power requirement in stirred tanks by about 20yo and in gas-liquid contactors by as much as 7001,. Lucrative incentives thus exist for the addition of polymers in various processes.Mixing is, however, rarely carried out for its own sake, and the influence of polymer additives in stirred tanks must be examined with respect of processes like heat and mass transfer. Further, some polymers will not only influence the viscosity of the aqueous solutions, but they will also make the solution viscoelastic. The manifestations of viscoelasticity can be numerous, ranging from recoil in concentrated solutions to a phenomenon known as drag reduction in very dilute solutions.In a recent paper, Quaraishi et aI. (1977) reported that drag reducing polymers added to stirred aqueous dispersion have no influence upon the performance of the impeller to suspend solid particles and only a limited negative influence upon the liquid phase mixing. The question of the gas-liquid mass transfer was, however, left open in their work. An attempt to find the answer to this question is the scope of this work. CONCLUSIONS AND SIGNIFICANCEPolyacrylamide and sodium carboxymethylcellulose polymers were added in small quantities to the gas-liquid dispersion in a stirred tank, and the overall liquid side mass transfer coefficients were measured using a slow chemical reaction technique.The overall gas-liquid mass transfer coefficient 1cr.n is reduced in diluted aqueous solutions of polyacrylamide far more than one would expect on the basis of increaied viscosity of the solution. Parallel experiments with solutions of sodium carboxymethylcellulose do not show such a drastic reduction. It is argued in this work that this is due to the increased viscoelasticity of the PAA solutions. Following the arguments of Seyer and Metzner (1967), one of the manifestations of the viscoelasticity of diluted polymer solution is the increase of the elongation viscosity. This, in turn, prevents highly deformed gas bubbles from reaching the final stage when they break up. An indirect support for this model is found in the considerably reduced gas holdup in PAA solutions. The consequence of this is a reduction of the specific interfacial area a.When selecting polymer additives for any particular process, one has to bear in mind that the addi...

show abstract

Section: Gas-liquid Mass Transfermentioning

confidence: 89%

Section: Gas-liquid Mass Transfermentioning

confidence: 91%

Section: Gas-liquid Mass Transfermentioning

confidence: 95%

Section: Gas-liquid Mass Transfermentioning

confidence: 99%

See 2 more Smart Citations

Influence of polymer additives on the gas‐liquid mass transfer in stirred tanks

Ranade

Ulbrecht

1978

AIChE Journal

View full text Add to dashboard Cite

show abstract

“…Certain authors have proposed that the diffusivity decreases when the concentration of several polymers increases [16], while other researchers, for aqueous solutions of carboxymethyl cellulose and other polymers, have not found clear behavior [17,18].…”

Section: Full Papermentioning

confidence: 96%

Mass Transfer in a Flat Gas/Liquid Interface using non‐Newtonian Media

Gómez‐Díaz

Navaza

2003

Chem Eng & Technol

View full text Add to dashboard Cite

Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non-Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non-Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients.

show abstract

Diffusion effects in initiator decomposition in highly viscous and macromolecular solutions

Kulkarni¹,

Mashelkar²

1981

AIChE Journal

View full text Add to dashboard Cite

Diffusional limitations in single bond and multibond initiators were experimentally investigated. The concept of "microviscosity" was proposed to account for diffusional resistance in different media. This was then used to obtain a unified correlation of the diffusional phenomena regardless of the nature of viscogen.Parameters related to the kinetic and diffusive processes were evaluated and interpreted giving clear fundamental and pragmatic implications of the findings. There is no prior study which provides a framework for analysis of diffusional limitations in initiator decomposition reactions arising in pragmatically important high viscosity systems, especially in polymer solutions. The present paper bridges this important gap by providing extensive experimental data on decomposition of typical single bond and multibond initiators in a variety of media. It also provides a theoretical framework within which such processes could be analyzed. CONCLUSIONS AND SIGNIFICANCEAn experimental investigation of the decomposition of a typical two bond initiator [AIBN] and a one bond initiator [NAT] was undertaken in three media; viz., polyethylene glycols, polyacrylonitrile solutions in D M F and glycerol solutions in DMF. A kinetic model was proposed for the analysis of the decomposition, recombination and diffusive separation processes. The rate constant for diffusional separation of initiator fragments was proposed to be calculated by Smoluchowski relation.In order to account for the diffusional resistance in different environments created by different types of viscogens, a unifying concept of microviscosity ( v*) was proposed. A method to calculate ( v*) from easily available physico-chemical data wasproposed.The governing kinetic parameters for decomposition reaction and recombination reaction as well as for diffusive separation were evaluated. It was found that for a multibond initiator such as AIBN, the rate constant is independent of the viscosity of the medium. In the case of one bond initiator such as NAT, a number of interesting conclusions emerged. The results in polyethylene glycol media show that increasing chain length above a threshold value has no influence on the diffusion of fragments from the cage, indicating that segmental motion controlled the diffusional process. Comparison of kinetic data for glycerol and polymer solutions in D M F indicated that in the former case the reduction in rate constant was very significant. Use of ( q * ) evaluated by the method proposed in this paper provided unique plots which were helpful in correlating the diffusional effects in decomposition processes irrespective of the nature of viscogen used. The conclusions arrived at are of interest from a fundamental view point since they reveal interesting observations concerning the manner in which diffusional phenomena take place in environments created by different viscogens. These are also of considerable pragmatic interest since in the modelling of polymerization reactors, a simple approach to account for the initiator ...

show abstract

Diffusion in flowing films of dilute polymeric solutions

Cited by 48 publications

References 25 publications

Influence of polymer additives on the gas‐liquid mass transfer in stirred tanks

Influence of polymer additives on the gas‐liquid mass transfer in stirred tanks

Mass Transfer in a Flat Gas/Liquid Interface using non‐Newtonian Media

Diffusion effects in initiator decomposition in highly viscous and macromolecular solutions

Contact Info

Product

Resources

About