Temperature scanning reactor

Not only concentration pulses have been used as input signals. Wojciechowski used temperature ramps with his temperature scanning reactor [99, 103] and Kobayashi and Kobayashi [104] applied concentration step functions. Typical process parameters, which can be changed, are the pressure, the temperature or the composition of the gas mixture. Fast mixture or pressure pulses can be realized by the injection of reaction gas into the system by a micro-dispense valve. An appropriate flow sensor will then record the transition into the next stationary mode. 

Wojciechowski, B., The temperature scanning reactor I reactor types and modes of operation, Catal. Today 1997,... 

The temperature scanning reactor [40] idea goes even further. Here the data collection grid is so dense that interpolations are allowed and even isothermicity along the reactor axis is in principle not a strict requirement any more. 

The metal coupons in the horizontal reactor were exposed at reactor temperature to either acetylene, ethylene, propylene, or butadiene for 120 minutes. The coupons were removed from the furnace, and pictures of the coke were taken using a JSM-U3 scanning electron microscope. Most pictures were taken using a magnification of 10,000. The type of metal in the coke was determined using EDAX Model 707, that was attached to the electron scanning microscope. 

Kinetics and diffusion Steady-state isotopic transient kinetic analysis (SSITKA) Temporal analysis of products (TAP) Tapered element oscillating microbalance (TEOM) Temperature scanning reactor (TSR) Zero length chromatography (ZLC) Pulsed field gradient NMR... 

While combinatorial reactivity testing provides the ability to quickly test and screen catalyst systems and catalyst samples, other kinetic tools are needed to provide deeper understanding. One such tool is the temperature scanning reactor (TSR) system developed by Wojciechowski [4, 5, 6]. The TSR concept allows for the rapid collection of kinetic data. By ramping the reactor temperature at several space velocities, the TSR can cover a wide range of process conditions in a single experiment that would take many runs in a conventional reactor system. Figure... 

Temperature scanning reactors (TSRs) for high throughput serial screening of reaction conditions [8,9,10],... 

B. W. Wojdechowski, The temperature scanning reactor III Experimental procedures and data processing,... 

The temperature scanning technique as currently understood is broadly applicable and can be applied to the study of reactions in all phases, as well as on catalysts, as long as certain readily verified requirements are met. The following text is intended as a guide to kinetic studies of reaction mechanisms. It reviews reactor types that may be applicable in various circumstances, data collection methods, methods of error removal, and the interpretation of data collected using temperature scanning reactors. It is our aim to revive kinetic studies as a useful approach to the understanding of reaction mechanisms, and so put catalyst development on a rational foundation. We dedicate this book to that aid. 

In Chapter 7 we will consider this problem in more detail. In particular we will examine methods of correcting for volume expansion in temperature scanning reactors, where temperature and conversion vary significantly during each experiment. We will see that the conventional use of the linearly dependent epsilon factor to account for volume expansion is by-and-large unsatisfactory. 

One normally analyzes the effluent stream in terms of mole fractions of components present at the reactor outlet. This allows us to perform mass and atomic balances on the effluent and thereby ensure the consistency of the data. On the other hand, mechanistic rate expressions are normally developed in terms of concentrations. What is required is therefore a method of transforming concentration-based rate expressions to a fractional conversion form. This is particularly important in treating data from a temperature scanning reactor (TSR) (see Chapter 5) but is important in dealing with the analytical data from most reactors before the data can be fitted to mechanistic rate expressions. The procedure for doing this is well defined. In liquid and solid phase reactions, where there is no change in volume with reaction, the problem can be ignored in the gas phase one proceeds as follows. 

Gas solid interactions are difficult to study systematically in conventional reactors but can readily be studied in a specialized type of temperature scanning reactor intended for this type of process, the stream swept reactor (SSR). In principle this is a batch reactor containing the solid through which the fluid phase flows sweeping out any desorbed material or reaction products to a detector at the outlet. Reactors of this type are also potentially applicable in adsorption studies and will be discussed in Chapter 5 under the heading TS-SSR. 

In the case of data from a temperature scanning reactor (TSR), the integral method can be used when the temperature scanning reactor is operated in such a way that ... 

Although the TS mode of operation does not require isothermal or steady-state conditions, it is assumed that the reaction is at all times in steady state with respect to certain steps in the reaction. For example, in catalytic TS-PFR operation, it is taken that the adsorption/desorption steady state is achieved much mare rapidly than the time scale involved in the temperature scanning procedure. In the TS-CSTR we assume this, as well as the fact that complete mixing of reactor contents takes place on a time scale much shorter than the temperature ramping. Moreover, although there may be temperature differences and heat flows between various components of the reactor, of the catalyst, and of the reactants, these should not be flow-velocity-dependent, nor should there be any flow-velocity-dependent diffusion effects. 

Notice that this means that the TS-PFR can be operated under isothermal or adiabatic conditions as well as any other. One way to envision this flexibility is to see isothermal reactors as operating under conditions where the heat transfer is infinite, allowing the reaction to track the control temperature perfectly. Adiabatic reactors in that view have zero heat transfer and no heat is lost from the reaction. Temperature scanning reactors operate with any value of heat transfer coefficient, including the above two extremes. 

Temperature Scanning Continuously Stirred Tank Reactor... 

The operation and description of a temperature scanning continuously stirred tank reactor (TS-CSTR) is, in principle, much simpler than for the TS-PFR. It turns out that rates can be calculated from each individual point in each run, and that flow rates and temperature ramping do not need the same careful control as the TS-PFR. Nevertheless, the operation of die reactor should approach the perfectly mixed condition very closely. Although in practice it may be difficult to make the necessary physical arrangements for complete and instantaneous mixing within the reactor, as with other TS reactor types there are verification procedures that will reveal if proper operating conditions are not being met. 

The less well known temperature scanning stream swept reactor (TS-SSR) has features that are particularly well suited to the study of fluid/solid interactions, such as the study of ore roasting or adsorption. The TS-SSR can be constructed in two variants the TS-PF-SSR based on the PFR and the TS-CST-SSR based on the CSTR. Since the data from liquid phase TS-PF-SSR is easier to understand and interpret, we will consider this type of TS-SSR first. 

The TS-PF-SSR can be a very productive instrument for the study of adsorption, as well as other fluid/solid interactions. In adsorption, because the solid sample needs to be reused, completely reversible systems are easiest to handle. If the solid samples need to be replaced after each run, more ingenious instrument designs may be required in order to automate the carrying out of a TS-PF-SSR experiment without stopping to repack the reactor after each run. Even without this level of automation, temperature scanning procedures applied to fluid/solid interactions are sure to increase productivity in the study of fluid/solid interaction kinetics. 

So far we have been considering temperature ramping only, with flow rates held constant. In this section we consider the possibility of varying the flow rate during a run. The TS-CSTR turns out to be very simple to deal with, with marvelous possibilities for interactive control. The TS-PFR, as usual, requires much more careful consideration. In both the plug flow and CSTR reactors, flow scanning can be used alone or in combination with temperature scanning. 

To make full use of the potential of temperature scanning methods, a major realignment of our current view of kinetic experimentation must be coupled with the availability of modem, fully automated, computer controlled, TS reactors. The process would best begin with universities, where fundamental kinetic studies have traditionally been pursued. Such a development would be sure to revive interest and progress in the study of reaction mechanisms using kinetics. 

The large amount of data made available by TS procedures makes it possible, for the first time in kinetic studies, to apply available sophisticated mathematical routines to error correction in raw data, as will be shown in Chapter 7. This, coupled with the productivity of temperature scanning reactors, will make large amounts of better data available, and reduce the tedium associated with conventional studies of reaction kinetics. Moreover, the sophistication and variety of issues involved in TSR experimentation is sure to generate renewed challenges and interest, a development that will attract new talent to kinetic studies. How rapidly the promise of scanning techniques will be fully utilized in practice, remains to be seen. 

Experimental Tests for Diffusion in Temperature Scanning Reactors... 

A comparison between a conventional and a TS-PFR study of methanol reforming is contained in the paper by Asprey et al. (1999) and the associated paper by Peppley (1999). Other workers have used gas phase TS-PFRs in a number of studies carried out in industry. An example of industrial work is given in Investigation of the Kinetics of Ethylbenzene Pyrolysis Using a Temperature Scanning Reactor , Domke et al. (2001). Below we present some of the results and observations from selected studies and relate them to the issues raised above. 

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