Reaction spinning mass transfer

Pant and Chanda [247] report a kinetic study with a sintered V2Os catalyst carried out with a spinning basket reactor. The following selec-tivities are observed at 450—517° C, independent of conversion (20— 40%) and temperature 80% phthalic anhydride, 10% maleic anhydride, 10% carbon oxides. The authors propose a parallel reaction scheme. However, these data, and the absence of tolualdehyde at this conversion level prove that the reactor did not function as a well-stirred reactor, but suffered considerable bypassing (mass transfer limitation with respect to... 

Excellent heat and mass transfer characteristics of the SDR have been confirmed by the study of a phase-transfer-catalyzed Darzens reaction for preparing a drug intermediate. The SDR allowed for a 99.9% reduction in reaction time, 99% reduction of inventory and 93% reduction in the level of impurities [106]. Other possible applications of the SDR include polymerizations and polycondensations (in both cases considerable time savings and more uniform product) as well as precipitation/crystallization (smaller crystals with much narrower size distribution). Two large chemical companies have patented processes based on spinning-disc technology. SmithKline Beecham has claimed a method to epoxidize substituted... 

Meeuwse, M., Lempers, S., van der Schaaf, J. et al. (2010) Liquid-solid mass transfer and reaction in a rotor-stator spinning disc reactor. Ind. Eng. Chem. Res., 49 (1), 10751-10757. Visscher, F., van der Schaaf, J. and de Croon, M. (2012) Liquid-liquid mass transfer in a rotor-stator spinning disc reactor. Chem. Eng. J., 185-186, 267-273. 

High-gravity field Spinning disc reactor Heat transfer from liquid film Mass transfer in liquid film Reaction time Equipment size Impurities level... 

The distinction between them is made by the technique used for solidification. Melt spinning consists of extruding a molten polymer and into an appropriate medium (gas or liquid), where it is solidified by the transfer of heat. Dry spinning involves the extrusion of a polymer solution into a heated gas, where the solvent is removed and the fiber solidified. Wet spinning represents the extrusion of a polymer solution into a liquid chemical bath. The subsequent solidification takes place by mass transfer. In reaction spinning, a prepolymer (partially reacted material) is extruded into a heated fluid medium, where solidification takes place by chemical reaction. 

Fiber-Spinning type Momentum Tranter (Fluid Flow) Energy Tranter (Heat Transfer) Mass Transfer Chemical Reaction... 

The foregoing equations in heat and mass transfer are extremely difficult to handle and, as such, have not as yet been solved analytically. The situation is, in fact, overly complicated, even from the standpoint of numerical analysis. In spite of these considerations, the combination of Eqs. (48) and (52) can assist in analyzing the reaction-spinning situation. 

The chapter on mixers is comparatively short - not because mixers are unimportant, but because mixing is such an integral part of other intensive processes (heat exchange, reactions and crystallisation/precipitation as examples), that the topic is addressed continuously through other equipment and application chapters. The point is well made by Wu et al. (2(X)7) who stresses in their recent review that PI needs to be implemented via increased mixing, as well as heat and mass transfer - hence the success in this area of the spinning disc and the oscillatory baffle reactors. 

It can be seen that the increment in polymerisation following one pass in the SDR corresponds with many minutes of reaction in the small batch reactor used as a reference. This is particularly encouraging because the mass transfer intensity in the laboratory stirred reactor is likely to be much greater than its industrial-scale equivalent, and it therefore provides a demanding benchmark for the spinning disc performance. 

High intensity kLa of order 0.5 s for very fast reactions and short residence times Static mixers in turbulent flow offer plug flow in both phases. Thin-fllm contactors such as wiped-film columns or spinning disks offer large surface per unit volume, giving very rapid mass transfer and evaporative flux. 

Armed with the PFS and the questions for the various process options the team can then discuss the most appropriate way forward. For example considering question 2, production staff may comment that this particular plant only runs on the day shift, so a 10-hour reaction is not viable the chemical engineer may conclude that the problem is likely to be one of mass transfer, and other reactor design options such as a spinning disc reactor should be considered. The SHE advisor may comment that not only is solvent 1 volatile but it is also moderately harmful and would require specialist handling equipment, hence it is very important to find an alternative. As waste minimization starts at the reaction stage it is critical to study this area in particular detail. Questions that can be asked include ... 

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