Straight tube reactor

It is noted that the maximum value of rp in the helically coiled reactor is larger than the maximum observed in the straight tube reactor. The rp increases with increasing Reynolds number while the molecular weight (at a given conversion) decreases. 

Here in Chapter 1 we make the additional assumptions that the fluid has constant density, that the cross-sectional area of the tube is constant, and that the walls of the tube are impenetrable (i.e., no transpiration through the walls), but these assumptions are not required in the general definition of piston flow. In the general case, it is possible for u, temperature, and pressure to vary as a function of z. The axis of the tube need not be straight. Helically coiled tubes sometimes approximate piston flow more closely than straight tubes. Reactors with square or triangular cross sections are occasionally used. However, in most of this book, we will assume that PFRs are circular tubes of length L and constant radius R. 

In such a straight tube reactor, it is clear that the activation of monomer, or the creation of polymerizable species, occurs at the tip of glow where the incoming monomer molecules interact with the luminous gas phase. Thus, the opening of double bond and detachment of F occur at this point, and the further reaction of the free radicals, the species created by the detachment of F, and the detached F s with gas phase species occurs while all gaseous species are moving toward the downstream side of the reactor. Under such a one directional flow conditions, particularly with monomer that contain -CF3, the analysis based on the formation of -CF3 from monomers that do not contain -CF3 might become the focal point of discrepancy. 

The plasma polymerization of tetrafluoroethylene has also been studied in a straight tube reactor. Deposition rates and ESCA results were obtained as a function of location upstream from, within, and downstream from the induction coll [ ]. It was found that fluorine poor polymer was formed downstream fr m the coil even at the relatively low power level of 1.9 x 10 Joules/kg. Fluorine poor pol3rmer was formed at all locations at 7.7 X 10 Joules/kg. 

The computer simulations of chemical kinetics in a straight tube reactor [1065] were based on an equation combining diffusion, convection, and reaction terms. The sample dispersion without chemical reactions gave very similar results to that of Vanderslice [1061], yet the value of that paper is that it expanded the study to computation of FIA response curves for fast and slower chemical reactions. The numerically evaluated equation was similar to that of Vanderslice [1061], however with inclusion of a term for reaction rate. Two model systems were chosen and spectro-photometrically monitored in a FIA system with appropriately con-... 

It is significant that the preceding conclusions of Reijn et al., obtained for SBSR reactor, are in agreement with the results that Wada et al. [1065] obtained with a straight tube reactor, thus confirming the important conclusion that chemical reactions do not alter the dispersio of the analyte in the reactor. Therefore, the experimental values (D, t, T, and ct ), obtained with a nonreacting tracer alone, are well suited for the description of dispersion in any FIA system in the presence or absence of chemical reaction. 

Figure 2.8 Nuclear reactor, straight tube, steam generating boiler.

The difference between the calculated and experimentally determined critical Reynolds number can be explained from the reactor configuration, which consisted of four coils connected by straight tubing section. The straight sections would lower the rela-... 

The maximum rate of polymerization has been confirmed to occur at the laminar-turbulent flow transition. The rate of polymerization was observed to be maximum at the transition for both straight reactors as well as for the helically-coiled reactor for which the transition is at a Reynolds number higher than that of the straight tube. The helically coiled tubular reactor is of industrial interest since it is much more compact and, consequently, the cost and the temperature control problems are more tractable. 

The importance of the linear arrangement of mixer/funnel/tubular reactor is shown when processing in a set-up with a curved flow element (0.3 m long bent Teflon tube of 0.3 mm inner diameter) in between the funnel and tubular reactor [78]. If a straight tube of equal dimensions as given above is used, plugging occius after 30 s. Hence even short curved flow passages are detrimental for micro-chan-nel-based amidation studies. 

Reactors with a packed bed of catalyst are identical to those for gas-liquid reactions filled with inert packing. Trickle-bed reactors are probably the most commonly used reactors with a fixed bed of catalyst. A draft-tube reactor (loop reactor) can contain a catalytic packing (see Fig. 5.4-9) inside the central tube. Stmctured catalysts similar to structural packings in distillation and absorption columns or in static mixers, which are characterized by a low pressure drop, can also be inserted into the draft tube. Recently, a monolithic reactor (Fig. 5.4-11) has been developed, which is an alternative to the trickle-bed reactor. The monolith catalyst has the shape of a block with straight narrow channels on the walls of which catalytic species are deposited. The already extremely low pressure drop by friction is compensated by gravity forces. Consequently, the pressure in the gas phase is constant over the whole height of the reactor. If needed, the gas can be recirculated internally without the necessity of using an external pump. 

Figure 5 Schematic diagrams of reactors used in FIA in order of increasing dispersion (a) single bed string reactor, (b) knitted tube, (c) coiled tube, (d) straight tube, and (e) external mixing chamber with stirring.

After final cooling by air or cooling water, the synthesis gas is compressed (6) and sent to the synthesis loop (7). The synthesis loop is comprised of a straight-tubed boiling water reactor, which is more efficient than adiabatic reactors. Reaction heat is removed from the reactor by generating MP steam. This steam is used for stripping of process condensate and thereafter as process steam. Preheating the... 

FIGURE 5.13 Recorded peaks for different analytical path lengths. A = absorbance S = injection instant. The recording tracings correspond to loop-based injections of 50 pL of a dye solution into a flow injection system with a straight tube (25,75,125,175,250,300 and 350 cm) acting as the main reactor. Adapted from Anal. Chim. Acta 99 (1978) 37, J. Ruzicka, E.H. Hansen, Flow injection analysis. Part X. Theory, techniques and trends, with permission from Elsevier (Ref. [80]). 

A numerical study of the free-radical polymerization of styrene (Scheme 6.15) compared the behavior of an interdigital micromixer with a T-junction and a straight tube [37, 48], The diffusion coefficient of the reactive species was varied to simulate the viscosity increase during a polymerization. The performance of the polymerization turned out to be largely dependent on the radial Peclet number. This dimensionless number is defined as the ratio of the characteristic time of diffusion in the direction perpendicular to the main flow to the characteristic time of convection in the flow direction (i.e., the mean residence time) and, therefore, is directly proportional to the characteristic length of the reactor. 

The coiled tube has so far been the most frequent geometric form of the FIA microreactor. However, it is useful to review all channel geometries (Fig. 2.8). These are straight tube (A), coiled tube (5), mixing chamber (C), single-bead string reactor (D), 3-D or knitted reactor (E)y and imprinted meander (cf. microconduits Section 4.12) or combinations of these geometries. 

Figure 2.10. Dispersion of a dye, injected as a sample zone (Sy = 25 jiL) into A, straight tube By coiled tube C, knitted tube and D, a SBSR reactor. The reactor volumes (Vr = 160 iL) and pumping rates (Q = 0.75 mL/min) were identical in all experiments. The same piece of Microline tubing (L = 80 cm, 0.5 mm inside diameter) was used in experiments Ay By and C. (The injected dye was bromthymol blue, carrier stream 0.1 M borax and wavelength 620 nm, cf. Chapter 6.) The SBSR reactor was made of 0.86 mm inside diameter tube filled with 0.6-mm glass beads. Note that the isodispersion points on the peaks were recorded with microreactors made of identical length and diameter, but different geometry.

---