Static mixer method

Elucidation of degradation kinetics for the reactive extrusion of polypropylene is constrained by the lack of kinetic data at times less than the minimum residence time in the extruder. The objectives of this work were to develop an experimental technique which could provide samples for short reaction times and to further develop a previously published kinetic model. Two experimental methods were examined the classical "ampoule technique" used for polymerization kinetics and a new method based upon reaction in a static mixer attached to a single screw extruder. The "ampoule technique was found to have too many practical limitations. The "static mixer method" also has some difficult aspects but did provide samples at a reaction time of 18.6 s and is potentially capable of supplying samples at lower times with high reproducibility. Kinetic model improvements were implemented to remove an artificial high molecular weight tail which appeared at high initiator concentrations and to reduce step size sensitivity. 

Method A, the Agitated Ampoule Technique, and Method B, the Static Mixer Method, are described below in the experimental section. 

A practical method of predicting the molecular behavior within the flow system involves the RTD. A common experiment to test nonuniformities is the stimulus response experiment. A typical stimulus is a step-change in the concentration of some tracer material. The step-response is an instantaneous jump of a concentration to some new value, which is then maintained for an indefinite period. The tracer should be detectable and must not change or decompose as it passes through the mixer. Studies have shown that the flow characteristics of static mixers approach those of an ideal plug flow system. Figures 8-41 and 8-42, respectively, indicate the exit residence time distributions of the Kenics static mixer in comparison with other flow systems. 

As mentioned above, two experimental methods were examined as a source of kinetic samples Method A Agitated Glass Ampoule and Method B Static Mixer. These are described in turn in the following paragraphs. Analysis of samples was done using high temperature size exclusion chromatography (SEC) under conditions previously described (9.101. 

There are many variants on this simple theme. For instance, many other methods for mixing have found use. In a design offered by Lurgi, the phases are mixed in what is essentially an axial flow pump, and then pass down a relatively long pipe where the turbulence of flow keeps the phases mixed while the extraction takes place. In another design, the individual phases are pumped and then join and pass through a static mixer. There are no particular physicochemical reasons for preferring one type of mixer to... 

Tajima, H. Yamasaki, A. Kiyono, F. (2005b). Process design of a new injection method of liquid C02 at the intermediate depths in the ocean using a static mixer. Fuel Processing Technology, 86 (14-15), 1667-1678. 

This study has shown the possibility to measure segregation problems when discharging mixtures through a funnel. It has also shown the effect of the number of drum revolutions at a fixed speed on the quality of a mixture, as well as the effect of a static mixer. The axial structure of the mixtures through autocorrelation functions could also be studied from these data, but this has not been reported here for clarity of the paper. In addition, it must be remembered that we just studied the evolution of the dielectric permittivity, and that in most cases, we will have to follow the volumetric compositions of each component in order to characterise the homogeneity of the medium. The capacitive method is indeed full of promise for particulate systems, and it would be interesting to explore it much into details, particularly for determining the proportions of each component of the mixture. 

Fig. 7.43 The evolution of concentration distribution after 4, 10, and 20 elements with alternately left and right twisting plates at 140°. [Reprinted by permission from O. S. Galaktionov, P. D. Anderson, G. W. M. Peters, and H. E. H. Meijer, Morphology Development in Kenics Static Mixers (Application of the Extended Mapping Method), Can. J. Chem. Eng., 80, 604-613 (2002).]...

Most manufacturers of static mixers have published (either in sales literature or in the technical literature) design methods for pressure drop. The pressure drop design methods, from Myers et al. (1997) for the Kenics HEM and Kenics HEV mixers are presented. The Darcy friction factor for the standard HEV mixer, Ntr = 2, L/D = 1, (with X/D = 3 downstream pipe) is presented in Figure 10.31. The friction factor is not given below Nrc = 1,000 because the HEV mixer should not be used for Nrc < 3,000. 

The predictive method for drop size is given in the Kenics Bulletin (May 1988, p. 28, Fig. 5-1) and in Figure 10.34. The ratio of Sauter mean drop size to the mixer ID (d/D) is a function of the Weber Number (V Dp/cr) and the ratio of dispersed phase to continuous phase viscosity (p-j/p.,). Now let s do two examples for static mixers. 

Crude oil and brine pumps may be centrifugal or positive displacement, but must be capable of providing steady flow to the mixing device because emulsion properties are highly dependent on the resulting crude-oil-brine ratio. Surfactant may be dissolved in the brine phase on a batch or continuous basis. Static mixers provide a simple method for the preparation step because they require no moving parts, are easy to scale up, and provide an mixing intensity that is suited to preparation of transport emulsions. 

In both experiments, the fuel-air mixture is prepared by separate injection of the reactants and in-line mixing using a proprietary static mixer (type SMV, Sulzer Co.). Other experiments have used this method with good results, but it is not seen as other than a convenience for the laboratory work. 

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