Liquid micromixers

Newly developed gas-liquid micromixers are applied in several oxidation reactions, nanopartide synthesis, and size distribution studies [89-91]. 

Guichardon etal. (1994) studied the energy dissipation in liquid-solid suspensions and did not observe any effect of the particles on micromixing for solids concentrations up to 5 per cent. Precipitation experiments in research are often carried out at solids concentrations in the range from 0.1 to 5 per cent. Therefore, the stirred tank can then be modelled as a single-phase isothermal system, i.e. only the hydrodynamics of the reactor are simulated. At higher slurry densities, however, the interaction of the solids with the flow must be taken into account. 

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

Guichardon, P., Falk, L., Fournier, M.C. and Villermaux, J., 1994. Study of micromixing in a liquid-solid suspension in a stirred reactor. American Institute of Chemical Engineers Symposium Series, 299, 123-130. 

WiLLE, C., The potential of micromixers for contacting of disperse liquid phases,... 

Haverkamp, V., Ehreeld, W, Gebauer, K., Hessel, V., Lowe, H., Richter, T, WiLLE, C., The potential of micromixers for contacting of disperse liquid phases, Fresenius J. Anal. Chem. 364 (1999) 617-624. 

Hessel, V, Ehrfeld, W., Golbig, K., Haverkamp, V, Lowe, H., Richter, T., Gas/liquid dispersion processes in micromixers the hexagon flow, in Ehrfeld, W., Rinard, I. H., Wegeng, R. S. (Eds.), Process Miniaturization 2nd International Conference on Microreaction Technology, IMRET 2, Topical Conf. Preprints, pp. 259-266, AIChE,... 

Floyd TM, Schmidt MA, Jensen KF (2005) Silicon micromixers with infrared detection for studies of liquid-phase reactions. Ind Eng Chem Res 44 2351-2358... 

Govindan CK (2002) An improved process for the preparation of benzyl-n-vinyl carbamate. Org Process Res Dev 6 74-77 Gunther A, Jensen KF (2006) Multiphase microfluidics from flow characteristics to chemical and materials synthesis. Lab Chip 6 1487-1503 Gunther A, Jhunjhunwala M, Thalmann M, Schmidt MA, Jensen KF (2005) Micromixing of miscible liquids in segmented gas liquid flow. Langmuir 21 1547-1555... 

Lob P, Lowe H, Hessel V, Hubbard SM, Menges G, Balon-Burger M (2006b) Determination of temperature profile within continuous micromixer-tube reactor used for the exothermic addition of dimethyl amine to acrylonitrile and an exothermic ionic liquid synthesis. In Proceedings of AIChE Spring National Meeting, Orlando, 23-27 April, 2006... 

In general, liquid-phase reactions (Sc > 1) and fast chemistry are beyond the range of DNS. The treatment of inhomogeneous flows (e.g., a chemical reactor) adds further restrictions. Thus, although DNS is a valuable tool for studying fundamentals,4 it is not a useful tool for chemical-reactor modeling. Nonetheless, much can be learned about scalar transport in turbulent flows from DNS. For example, valuable information about the effect of molecular diffusion on the joint scalar PDF can be easily extracted from a DNS simulation and used to validate the micromixing closures needed in other scalar transport models. 

Engler, M. and Kockmann, N. and Kiefer, T. and Woias, P. (2004). Numerical and experimental investigation on liquid mixing in static micromixer. Chemical Engineering Journal, 101, 315-322. 

Ruy et al. have performed a similar reaction under microreactor conditions in a multiphase solvent system containing an ionic liquid as the catalyst carrier and reaction promoter [35]. Their system consisted of two T-shaped micromixers (i.d. 1,000 and 400 pm) and a capillary stainless steel tube as an RTU (1,000 pm i.d. and 18 m length, giving a 14.1 ml volume), equipped with pumps and control valves. Under the optimized conditions, Pd-catalysed carbonylation of aromatic iodides in the presence of a secondary amine provided only the double carbonylated product, ot-ketoamide, while the amide obtained by the single carbonylation was observed in high quantities only when the reaction was performed in batch (Scheme 13). 

The fluidised bed will be considered as a continuous stirred tank reactor in which ideal macromixing of the particles occurs. As shown in the section on mixing (Chapter 2, Section 2.1.3), in the steady state the required exit age distribution is the same as the C-curve obtained using a single shot of tracer. In fact the desired C-curve is identical with that derived in Chapter 2, Fig. 2.3, for a tank containing a liquid with ideal micromixing, but now the argument is applied to particles as follows ... 

If tmicro > Tmeso > Tmacro O 011 the process is micromixing controlled. Micromixing is a complex phenomenon (Section 2.4), but for most liquids engulfment is the longest step. In this case, micromixing time is the inverse of engulfment rate (E) and can be estimated by... 

Because the properties of liquids are essentially different from those of gases, impinging streams with liquid and gas as the continuous phases exhibit totally different performances and it is therefore necessary to discuss them separately. Part II focuses on liquid-continuous impinging streams and related problems, including the features of LIS that efficiently promote micromixing, pressure fluctuation phenomena in LIS, promotion of kinetic processes by LIS, and the application of LIS in the preparation of ultrafine particles, etc. Finally, this we will introduce some important research and development on LIS devices and look forward to the future applications of LIS. 

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