Chromatographic column pulse reactor

Several reactors are presently used for studying gas-solid reactions. These reactors should, in principle, be useful for studying gas-liquid-solid catalytic reactions. The reactors are the ball-mill reactor (Fig. 5-10), a fluidized-bed reactor with an agitator (Fig. 5-11), a stirred reactor with catalyst impregnated on the reactor walls or placed in an annular basket (Fig. 5-12), a reactor with catalyst placed in a stationary cylindrical basket (Fig. 5-13), an internal recirculation reactor (Fig. 5-14), microreactors (Fig. 5-16), a single-pellet pulse reactor (Fig. 5-17), and a chromatographic-column pulse reactor (Fig. 5-18). The key features of these reactors are listed in Tables 5-3 through 5-9. The pertinent references for these reactors are listed at the end of the chapter. 

Table 5-10 Key features of a chromatographic-column pulse reactor...

In a typical pulse experiment, a pulse of known size, shape and composition is introduced to a reactor, preferably one with a simple flow pattern, either plug flow or well mixed. The response to the perturbation is then measured behind the reactor. A thermal conductivity detector can be used to compare the shape of the peaks before and after the reactor. This is usually done in the case of non-reacting systems, and moment analysis of the response curve can give information on diffusivities, mass transfer coefficients and adsorption constants. The typical pulse experiment in a reacting system traditionally uses GC analysis by leading the effluent from the reactor directly into a gas chromatographic column. This method yields conversions and selectivities for the total pulse, the time coordinate is lost. 

Chromatographic fixed-bed reactors consists of a single chromatographic column containing a solid phase on which adsorption and reaction take place. Normally a pulse of reactant is injected into the reactor and, while traveling through the reactor, simultaneous conversion and separation take place (Fig. 3). Since an extensive overview of the models and applications of this type of reactor was presented by Sardin et al. [ 132], only a few recent results will be discussed here. Most of the practical applications have been based on gas-liquid systems, which are not applicable for the enzyme reactions, but a few reactions were also reported in the liquid phase. One of these studies, performed by Mazzotti and co-workers [ 141 ], analyzed the esterification of acetic acid into ethyl acetate according to the reaction ... 

The chromatographic column has been used as a reactor to study the kinetics of the dissociation. The reactant is introduced as a pulse at the head of the column and is continuously converted... 

A chromatographic column is arranged upstream of the reactor to produce a pulse of the pure reagent. To narrow the pulse a trap is used if necessary. The column and the reactor are placed in separate thermostats. The most universal is arrangement 2.4... 

With this construction, the reactor could be fed in 5-fil pulses directly from the injection block into a stream of hydrogen or helium flowing at a rate of 282 standard cc per minute. A fraction of the product gases was conducted directly to the chromatograph column. 

A very detailed model of the effect of intraparticle convection inside large-pore catalyts (e.g. selective oxidation catalyts) on the transient behavior of fixed-bed catalytic reactors was published by Quinta Ferreira [75]. Analysis of the transient response data fix>m fixed-bed reactors is in general more complicated than other reactor types as one has to account for the spatial and temporal dependence of the species concentrations and temperature. Catalytic reaction and chromatographic column can be combined in a gas chromatogrqihic pulse reactor. 

The chromatographic column has been used as a reactor to study kinetics of dissociation. The reactant is introduced as a pulse at the head of the column and is continuously converted to product and separated as it travels through the column. The apparent rate constant ( pp) is a function of the rate of the liquid (stationary)-phase reaction (ki), the rate of the gas (mobile)-phase reaction ( g), the residence time in the gas phase (ig), and the residence time in the liquid phase (ii) ... 

In this technique, the sample is heated to a preset temperature in a microfurnace and the pyrolysis products swept as a pulse into the gas chromatograph. Earlier pyrolysis equipmer tended to be somewhat complex in design and operation. Thus, Cox and Ellis [11] described a micro-reactor pyrolyser which they applied to large numbers of polymers. Temperatures increases of 700-1000 °C were used in order to completely pyrolyse 0.1 g samples of the polymers. The pyrolysis products were collected for 15 minutes then swept onto a gas chromatographic column equipped with a flame ionisation detector. This type of equipment has now been displaced by the more recently described equipment as discussed next. 

For chemiluminescence measurements, a postcolumn reactor with a pulse-dampening filter was added to the HPLC apparatus. A 3-cm piece of narrow-bore tubing joined the pulse dampener to a Valeo l-/tl T chemiluminescent reagent with the chromatographic eluent. A C8 ECONOSPHERE (250 X 4.6-mm ID) column was used. Modifications were made with the... 

Some investigators have developed methods in which the reaction proceeds directly in the chromatographic system. The most important of these are the so-called pulse chromatographic methods. In such methods of studying the kinetics of chemical transformations, a pulse of a volatile compound whose transformation provides information on the reaction taking place in the reactor column is fed to the inlet of the reactor column in a flow of carrier gas. In the pulse methods the chemical reaction and separation (analysis) are integrated into a single procedure. 

Some investigators [47] have shown that the kinetics of a reaction in a reactor colunm is often so unusual that some instances call for a specific chromatographic procedure widely different from the static and dynamic ones. For example, in a reaction A B -I- C with pulsed feeding of substance A into the reactor column, substances B and C are continuously generated and separated from A and from each other in zone A (it is assumed... 

The pulse chromatographic method was also used to study the kinetics of the etherification of alcohols of various structures with acetic anhydride [74]. The reaction kinetics were studied for high-boiling alcohols the volatile reagent (acetic anhydride) was fed into the rdactor column in the form of a pulse, and the involatile one (alcohol) was present in the column reactor as the stationary phase. Unlike the pulse method used in studying the reactions involved in diene synthesis, in the etherification of an alcohol with acetic anhydride one of the reaction products (acetic acid) is eluted from the column reactor after the starting component (acetic anhydride). The reaction of alcohol etherification was examined at 80—130 C. The mixture of acetic anhydride with the standard (benzene) was pulsed into the reactor column in which the alcohol under study served as the stationary phase. Various extents of reaction were achieved by varying the carrier gas flow-rate. Table 2.6 summarizes the kinetic characteristics of the etherification of alcohols with acetic anhydrides [74]. The rate constants decrease in the order primary > secondary > tertiary. 

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