The purpose of this experiment is to investigate and compare the kinetics of a heterogeneous catalyzed reaction over different nickel-containing catalysts in fixed bed catalytic reactors (essentially plug flow reactors). One reactor contains 1 g of nickel alumina catalyst and the other reactor contains 5 g of nickel alumina catalyst. The remainder of each reactor volume is filled with Cu pellets, which are inert. The reaction is between carbon monoxide and hydrogen to form methane and water. The reaction can be assumed to be irreversible. Why?

Since the mechanism of this reaction is (presumed) unknown, the initial main purpose of these experiments are to determine a rate expression and values for the kinetic parameters (e.g., rate constants, activation energy, etc.). In principle the experiment can be used to perform model discrimination between rival mechanisms or rate expressions (there is a vast literature on this reaction over Ni catalyst). Note that because of stoichiometry, and under conditions of excess H2, that all terms cannot be identified explicitly. It is sufficient to determine the "effective" exponents of carbon monoxide and hydrogen and the "effective activation energy" under the conditions that you investigated.

A schematic diagram showing all thermocouple and valve locations is on the control board of the apparatus.

• The infrared analyzer as well as the reactor have slow dynamics, e.g. may take nearly two hours to warm up. Plan accordingly.
   
• Reactor temperature control has been improved by the implementation of a triac which can be set for any temperature and is continuously monitored by the computer (see Program use). The triac allows you to maintain temperature between 250 and 350 degrees Celsius.

• reactor temperature
   
• volumetric flow rate of CO
   
• volumetric flow rate of H2
   
• volumetric flow rate of N2

• CO concentration at the reactor inlet
   
• CO concentration at the reactor outlet
   
• reactor inlet temperature
   
• reactor outlet temperature
   

The stainless steel tubular reactor, packed with Ni-supported catalyst, is heated with a ceramic heater. Pneumatic valves provide precise volumetric flows of H2, CO and N2, which are mixed upstream of the reactor. An infrared (IR) detector is used to measure the CO concentration in the feed and product streams. Since the reactor operates at a relatively high temperature, a chiller is needed to cool down the gases before entering the IR detector. A LabVIEW interface is used to control the reactor and chiller temperatures, and for data acquisition.

A schematic diagram showing all thermocouple and valve locations is on the control board of the apparatus.

• Read downstream data.
   
  • Open valves A - D.
     
  • Close bypass valve.
     
  • Run reaction gas through reactor.
     
  • Wait for steady state conditions.
     
  • Read downstream data.
     
• Read upstream data.
   
  • Close valve D.
     
  • Open bypass valve.
     
  • Read upstream data.
     
• Alternatively - calculate feed concentration from flow rates.

There are several aspects of this experiment that can be controlled, through which the principals of process control can be studied. Temperature control is crucial in all kinetic processes. This experiment enables you to evaluate various modes of temperature control (at different positions with different control parameters, PID). At a "higher level", it is possible to control composition by control of temperature(s), stoichiometry or flow rate.

The approaches to each control would vary. In each case, you would first determine the dynamics of the process in response to the changed (manipulated) variable. This can then be approximatedby a dynamic model (first- or second-order, wi th or without time-delay, etc.). Various "ideal" control parameters (P, I, and D) can then be estimated from any of several models (Z-N, C-K) available in the literature.

In each case, it is necessary to compare the dynamic response model to the measured response. This relation can be quantified by an evaluation of the measured response versus the model.This is further verified by a comparison of the response with control to the model with control.

1. The IR detector and reactors exhibit slow dynamics, e.g., it may take nearly two hours to warm up; make sure to plan accordingly.
    
2. Reactor temperature control has been improved by the implementation of a triac, which can be set for any temperature and is continuously monitored by the computer. The triac allows the user to maintain a temperature between 270 and 350°C.
    
3. Be careful of coking problems in the reactor. If the temperature fluctuates considerably or becomes elevated, turn off the CO feed and pass pure N2 through the reactor. During cooling, pure N2 should be fed to the reactor.
    
4. Control for the N2 flow is unreliable at times, which may affect the CO concentration reading. If the CO reading is not zero during calibration, the N2 flow should be shut off by switching the toggle valve; the CO concentration should be close to 2%.
    
5. Make sure that the regulators for the compressed gas cylinders are at 20 psi. If this is not the case, consult a TA or laboratory staff member.
    

2. General recommendations