Continuous tubular reactor

By performing the balance in the element dV, considering that the cross section of the tube is constant, we obtain  

The molar balance in relation to the reactant A (or B), considering that  

note that in the transformation of the reactant, the rate has negative sign, and in the formation of the product, the rate has positive sign, in accordance with the definition initially adopted. 

In any case, we can integrate with respect to the total volume of the reactor V and the final conversion reached X. If we use the definition of space time t, which relates the volume of the reactor with the volumetric flow  

In this case, it is important to note that the conversion is defined in relation to the limiting reactant A. 

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Fig. 4. Continuous tubular reactor design. Courtesy of BatteUe.

The advantages of continuous tubular reactors are well known. They include the elimination of batch to batch variations, a large heat transfer area and minimal handling of chemical products. Despite these advantages there are no reported commercial instances of emulsion polymerizations done in a tubular reactor instead the continuous emulsion process has been realized in series-connected stirred tank reactors (1, . ... 

Diebold, J. P., The Cracking Kinetics of Depolymerized Biomass Vapors in a Continuous, Tubular Reactor, Thesis T-3007, Colorado School of Mines, Golden, CO, 1985. 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

The theories developed for batch and CSTR reactors do not accurately predict the rate data obtained in a continuous tubular reactor. 

Continuous tubular reactors can also he used to produce emulsion polymers. Such reactors have been used in series with CSTRs (Gonzalez, 1974), as how-through reactors (Rollins et nl., 1979 Ghosh and Forsyth, 1976) and in a ccaitinuous loop process (Lanthier, 1970) in which material is fed and removed from a tubidar loop with a circulating flow greater than the throughput. 

Gonzalez placed a continuous tubular reactor in iront (upstream) of the CSTR. In this case the particle seed was formed in the tube from a recipe that did not contain seed- Gonzalez found the tube-CSTR system to be quite stable so long as the conversion in the tube was adequate to prevent significant particle formation in the CSTR. 

Diebold, J. P. (1985) The Cracking Kinetics of Depoiymerized Biomass Vapors in a Continuous, Tubular Reactor. M. S. Thesis, Dept, of Chemical and Petroleum-Refining Engineering, Colorado School of Mines, Golden, Colorado. Liden, A. G. (1985) A Kinetic and Heat Transfer Modelling Study of Wood Pyrolysis in a Fluidized Bed. MASc Thesis, Dept, of Chemical Engineering, University of Waterloo. 

The discovery of solid catalysts led to a breakthrough of the chemical process industry. Today most commercial gas-phase catalytic processes are carried out in fixed packed bed reactors. A fixed packed bed reactor consists of a compact, immobile stack of catalyst pellets within a generally vertical vessel. On macroscopic scales the catalyst bed behaves as a porous media. The fixed beds are thus employed as continuous tubular reactors in which the reactive species in the mobile fluid (gas) phase are reacting over the catalyst surface (interior or exterior) in the stationary packed bed. Compared to other reactor types or designs utilizing heterogeneous catalysts, the fixed packed bed reactors are preferred because of simpler technology and ease of operation. 

Microwaves should be well suited for continuous tubular reactors, where they might reduce the amount of energy needed, reduce costs, and increase the output of a plant. If water were inert, it might be used to absorb the microwave radiation, the reagents being in solution or in an emulsion. Further research will undoubtedly find many more applications for this technique. 

Continuous processes involving tubular reactors have been reported in the literature (General References 2, 7, and ). Continuous tubular reactors have been used in three ways. Gonzalez (9) used a tubular prereactor to feed a CSTR system. The tubular prereactor served as a particle nucleation system and thus solved the problem of conversion oscillations often observed in CSTR systems. A tubular prereactor also can be used to generate a higher particle concentration than would be produced with the same recipe in a CSTR system. 

Emulsion polymerization reactions have also been studied in reactors consisting only of tubes. Such reactors offer the potential advantage of a large area for heat transfer per unit volume and hence a high polymerization rate. One potential problem with tubular reactors, namely plugging, has discouraged commercial use. A number of studies have been reported on once-through continuous tubular reactors but commercial reactors of this type have not been publicized. 

Formulation of the task or problem, for example, continuous tubular reactor with recycling... 

This nucleation/emulsifier utilization phenomena is one reason why batch kinetics and product characteristics are difficult to extrapolate from batch reactor to continuous stined-tank systems. A comparison of Equations (8.4) and (8.10) illustrates this in a quantitative manner for Smith-Ewart Case 2 kinetics. It should be noted that both formulation and operational variables (such as ) can influence nucleation and polymerization rates differently in the two reactor systems — even for the same kinetic model. One can change some aspects of this potential disadvantage of a CSTR by use of a small particle size seed in the feed stream or by placing a continuous tubular reactor upstream of the CSTR. These techniques can remove the nucleation phenomena tom the CSTR system which can then be used exclusively to grow the seed particles. 

Latex production by miniemulsion polymerizations [172-174] in continuous tubular reactors has also been reported by McKenna and coworkers [175]. 

Ouzine K, Graillat C, McKenna T (2004) Continuous tubular reactors for latex production conventional emulsion and miniemulsion polymerizations. J Appl Polym Sci 91 2195-2207... 

Enright TE, Cunningham MF, Keoshkerian B (2005) Nitroxide-mediated poljrmaization of styrene in a continuous tubular reactor. Macromol Rapid Commun 26 221-225... 

In a continuous tank-type reactor, the flow should not follow preferential paths. In the continuous tubular reactor, the flow can be in extreme cases laminar (not desired) or turbulent (desired), but without dead volume. The type of flow may cause radial and longitudinal diffusion effects causing radial or axial temperature and concentration gradients and consequently affecting the chemical reaction. 

In CSTR reactors, the flow has preferential paths. In continuous tubular reactors, the flow may be laminar, turbulent, and have dead volumes. The flow may cause radial and longitudinal diffusion effects and therefore to result temperature gradients and radial/axial concentration. Therefore, the flow may affect the chemical reaction. 

Dowding, P.J., Goodwin, J.W., and Vincent, B., Production of porous suspension polymer beads with a narrow size distribution using a cross-flow membrane and a continuous tubular reactor. Colloid Surface A, 180 (3), 301-309, 2001. 

Fluidized beds give relatively higher performance, but within a narrow operating window. Another type of reactors, the slurry reactor, effectively utilizes the catalyst because of their small particle size in the micrometer range. However, catalyst separation is difficult and a filtration step is required to separate fine particles from the product. Moreover, when applied in the continuous mode, backmixing lowers the conversion and usually the selectivity [2]. Conventional continuous tubular reactors are used as falling film or wall reactor with catalyst coated on the wall however, supply/removal of heat and often broad residence time distribution because of large reactor diameters are two main drawbacks commonly encountered with such reactors. 

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