Open tubular reactors

A great savings in enzyme consumption can be achieved by immobilizing the enzyme in the reactor (Fig. 12). In addition to the smaller amount of enzyme required, immobilization often increases the stability of the enzyme. Several designs of immobiliz-ed-enzyme reactors (lERs) have been reported, with open-tubular and packed-bed being the most popular. Open-tubular reactors offer low dispersion but have a relatively small surface area for enzyme attachment. Packed-bed reactors provide extremely high surface areas and improved mass transport at the cost of more dispersion. 

Figure 8.39 Comparison of a straight and knitted open tubular reactor of equal length for preserving column resolution. (Reproduced with permission from ref. 6S6. Copyright Dr Alfred Huethig Publishers).

For fast reactions (i.e., < 1 min.), open tubular reactors are commonly used. They simply consist of a mixing device and a coiled stainless steel or Teflon capillary tube of narrow bore enclosed in a thermostat. The length of the capillary tube and the flow rate through it control the reaction time. Reagents such as fluorescamine and o-phthalaldehyde are frequently used in this type of system to determine primary amines, amino acids, indoles, hydrazines, etc., in biological and environmental samples. 

Fig. 2.4p shows three types of post-column reactor. In the open tubular reactor, after the solutes have been separated on the column, reagent is pumped into the column effluent via a suitable mixing tee. The reactor, which may be a coil of stainless steel or ptfe tube, provides the desired holdup time for the reaction. Finally, the combined streams are passed through the detector. This type of reactor is commonly used in cases where the derivatisation reaction is fairly fast. For slower reactions, segmented stream tubular reactors can be used. With this type, gas bubbles are introduced into the stream at fixed time intervals. The object of this is to reduce axial diffusion of solute zones, and thus to reduce extra-column dispersion. For intermediate reactions, packed bed reactors have been used, in which the reactor may be a column packed with small glass beads. 

Open tubular reactor ( ) Segmented reactor Hi) Packed bed reactor... 

Thermolysis of H S was carried out in an open tubular reactor quartz tube with argon/HjS feed over a wide composition spectium (20-100% H S) at four temperatures (1030-1070 K). These experiments show that the reaction is essentially first order in H S partial pressure. Hydrogen yield also increases monotoiucally with feed composition at all temperatures (Adesina et al., 1995). 

Adesina, A.A., Meeyoo, V, Foulds, G. 1995. Thermolysis of hydrogen sulphide in an open tubular reactor. Int J Hydrogen Energy 20 777-783. 

Miniaturizing a conventional-flow screening system (macro-scale system) to a chip-based system comprises a number of changes, such as flow rates, reagent supply, and the material. While the conventional system with the open tubular reactors is restricted to polymer reactors, the choice of materials for the chip is... 

Precolumn derivatization is often inadequate for dirty samples. In these cases, application of a postcolumn reaction detection system will often suffice. Deelder et al. (44) and van der Wal (45) have examined different configurations for postcolumn reactors and defined optimal selections on the basis of reaction time and type and effect on resolution and sensitivity. Both studies preferred the packed-bed reactor to the open tubular reactors when conventional column geometries were employed for separation, that is, 4.6 mm i.d. X 15 or 25 cm. 

B. Postcolumn Derivatization Three types of reactors for postcolumn derivatization are used, depending on reaction kinetics. Straight, coiled, and knitted open-tubular reactors are used for fast reactions, whereas packed-bed reactors are used for intermediate kinetics. Segmented-stream reactors are used for slow reactions. The simplest reactors are the open-tubular reactors a T connector is the most common. Pickering44 has described the performance requirements for instrumental components of HPLC postcolumn systems. 

In single bead string reactors the enzyme is bound both to the reactor wall and to a carrier within the reactor. Compared with open tubular reactors this reactor type provides a higher conversion at lower sample mixing. 

The essence of unsegmented flow analysis is the controlled and, therefore, highly reproducible physical dispersion of an aqueous sample introduced into a continuously flowing carrier stream. For a better understanding of the process, it is advisable to initially consider laminar flow inside a straight open tubular reactor. 

Improved mixing conditions. The use of packed mini-columns or open tubular reactors with a curled inner wall designed in different geometries (see 6.2.3) improves radial mixing. 

Open tubular reactors with the solid phase immobilised on the inner walls of the tubing [245]. 

Detector UV 270 following post-column reaction. The column effluent mixed with 2 M NaOH and 0.05% sodium hypochlorite solution pumped at 0.1 mL/min in a 400 x 0.5 mm hollow fiber membrane reactor at 40° and this mixture flowed through a 1400 x 0.3 mm knitted open tubular reactor at 50° to the detector. 

T. Kojima and F. Morishita, Flow Injection Analysis with Enzyme Immobilized Open Tubular Reactor [in Japanese]. J. Flow Injection Anal., 1(1) (1984) 9. 

M. C. Gosnell, R. E. Snelling, and H. A. Mottola, Construction and Performance of Plastic-Embedded Controlled-Pore Glass Open Tubular Reactors for Use in Continuous-Flow Systems. Anal. Chem., 58 (1986) 1585. 

F. Morishita, Y. Nishikawa, and T. Kojima, Simultaneous Determination of Three Species by Flow Injection Analytical Method Using Enzyme-Immobilized Open-Tubular Reactors. Anal. Sci., 2 (1986) 411. 

The parabolic flow profile in an open-tubular reactor restricts applications to fast reactions if extensive band broadening is to be avoided [244]. The reaction time can be extended by using reactors prepared from optimally deformed capillary tubes [245-247]. The production of secondary flow, even at low flow rates, breaks up the parabolic... 

LLE with dichloromethane has been used before HPLC with LA and fluorescence detection [115]. Dinitrophenols are detected with LA absorption followed by oxidation with cerium(IV) in an open tubular reactor, allowing fluorescence measurement of cerium(III). 

Waiz S, Cedillo BM, Jambunathan S, Holinbolt SG, Dasgupta PK, Wolcott DK. Dispersion in open tubular reactors of various geometries. Anal Chim Acta 2010 428 163-71. 

The same effect seems to be at play in the case of the recently proposed DIFICI mechanism [112] of structure formation. There also the system is convectively unstable and the structure generated is advected away (except in the case of a loop reactor) [108]. The structures observed in the related experiments [113] in an open tubular reactor would thus be a noise generated pattern in a convectively unstable system. 

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