Operating the Reactor

This procedure reflects today s technology where, typically, a two- or three-bed reactor is used. Recent investigations by Jacobsen et al. [C.J.H. Jacobsen, S. Dahl, A. Boisen, B.S. Clausen, H. Topsoe, A. Logadottir and J.K. Norskov, J. Catal. 205 (2002) 

] have shown how this concept opens up new and interesting possibilities for combining fundamental insight with detailed process design, improving the overall process by optimizing the catalysts in the beds. 

---

This is an endothermic reaction accompanied by an increase in the number of moles. High conversion is favored by high temperature and low pressure. The reduction in pressure is achieved in practice by the use of superheated steam as a diluent and by operating the reactor below atmospheric pressure. The steam in this case fulfills a dual purpose by also providing heat for the reaction. 

Thus an excess of ammonia in the reactor has a marginal eflFect on the primary reaction but significantly decreases the rate of the secondary reactions. Using excess ammonia also can be thought of as operating the reactor with a low conversion with respect to ammonia. 

In 1974, Monsanto brought on-stream an improved Hquid-phase AIQ. alkylation process that significantly reduced the AIQ. catalyst used by operating the reactor at a higher temperature (42—44). In this process, the separate heavy catalyst—complex phase previously mentioned was eliminated. Eliminating the catalyst—complex phase increases selectivities and overall yields in addition to lessening the problem of waste catalyst disposal. The ethylben2ene yields exceed 98%. 

After exiting tlie riser, tlie catalyst enters the reactor. In modern FCC operations, the reactor serves two basic functions as a disengaging space for the separation of catalyst and vapor, and as the housing for the reactor-internal cyclone. 

After exiting the riser, catalyst enters the reactor vessel. In today s FCC operations, the reactor serves as a housing for the cyclones. In the early application of FCC, the reactor vessel provided further bed cracking, as well as being a device used for additional catalyst separation. 

Tn the synthesis of methane from carbon monoxide and hydrogen, it is desired to operate the reactor or reactors in such a way as to avoid carbon deposition on catalyst surfaces and to produce high quality product gas. Since gas compositions entering the reactor may vary considerably because of the use of diluents and recycle gas in a technical operation, it is desirable to estimate the effects of initial gas composition on the subsequent operation. Pressure and temperature are additional variables. 

The gas motion near a disk spinning in an unconfined space in the absence of buoyancy, can be described in terms of a similar solution. Of course, the disk in a real reactor is confined, and since the disk is heated buoyancy can play a large role. However, it is possible to operate the reactor in ways that minimize the effects of buoyancy and confinement. In these regimes the species and temperature gradients normal to the surface are the same everywhere on the disk. From a physical point of view, this property leads to uniform deposition - an important objective in CVD reactors. From a mathematical point of view, this property leads to the similarity transformation that reduces a complex three-dimensional swirling flow to a relatively simple two-point boundary value problem. Once in boundary-value problem form, the computational models can readily incorporate complex chemical kinetics and molecular transport models. 

Due to the complexity of the problem, it is generally accepted that we will not reach the optimal reactor design and ojjerating variables, but still we would like to design and operate the reactor safely and near the optimum. Further in this section, we will give a general discussion of. scale-up methods for chemical processes, in particular with respect to chemical reactors suitable for the manufacture of fine chemicals. Next, we will discuss how to obtain reasonable quantitative relationships necessary for optimal and safe scale-up according to the art. The reader can find an extensive treatment of scale-up problems in the book of Bisio and Kabel(1985). 

Obviously the aim in operating the reactor cascade is to ensure operation at the most favourable conditions, and for this both the startup policy and control strategy are important. 

For nB2 > Ufib operate the reactor with interactive variation in F to keep Cb low. How is the selectivity influenced by this ... 

Operate the reactor without control using a constant flow of reacta... 

The experiments were performed in a CINC V-02 separator also known as the CS-50 (15). Two Verder VL 500 control peristaltic tube pumps equipped with a double pump head (3,2 x 1,6 x 8R) were used to feed the CCS. In case of the enzymatic reaction, the low mix bottom plate was applied. To operate the reactor at a desired temperature, it was equipped with a jacket which was coimected to a temperature controlled water bath with an accuracy of 0.01°C. The CCS was fed with pure heptane and pure water, both with a flow rate of 6 mL/min. Subsequently, the centrifuge was started (40 Hz, which corresponds to 2400 rpm) and the set-up was allowed to equilibrate for a period of 1 h. At this point, the heptane feed stream was replaced by the organic feed stream (oleic acid (0.6M) and 1-bntanol (0.9M) in heptane). After equilibration for 10 minutes, the reaction in the CCS was started by replacing the water stream with the aqueous feed stream (0.1 M phosphate buffer pH 5.6 containing 1 g/1 of the lipase form Rhizomucor miehei). Samples were taken at regular intervals and analysed by GC. 

Prior to conducting the DOE (design of experiments) described in Table 3, it was established that no reaction took place in the absence of a catalyst and that the reactions were conducted in the region where chemical kinetics controlled the reaction rate. The results indicated that operating the reactor at 1000 rpm was sufficient to minimize the external mass-transfer limitations. Pore diffusion limitations were expected to be minimal as the median catalyst particle size is <25 pm. Further, experiments conducted under identical conditions to ensure repeatability and reproducibility in the two reactors yielded results that were within 5%. 

A 500-gpm pump is used to provide water to a reactor vessel. If the pump continues to operate, the reactor might be overfilled and overpressurized. Determine the relief diameter (in inches) required to protect the vessel. The MAWP of the vessel is 100 psig. Please state clearly any additional assumptions required for your calculation. Assume a 10% backpressure and a 10% overpressure in the relief system. 

Taking Tinto account implies the ability to operate the reactor at a particular T, and hence to measure and control T. A thermostat is a device in which T is controlled within specified and measurable limits an example is a constant-T water bath. 

What are the optimal isothermal temperature for operation and the corresponding reactor volume for a final fractional conversion Zf of 0.68. Is this the best way of operating the reactor ... 

Try to operate the reactor isothermally with the PID-control as programmed to control the heat input rate. 

A variety of control schemes can be employed and are of great importance, since the reactor scheme shows a multiplicity of possible stable operating points. Obviously the aim in operating the reactor cascade is to ensure operation at the most favourable conditions, and for this both the startup policy and the control strategy are important. This example is taken from the paper of Mukesh and Rao (1977). 

Operate the reactor continuously with a KLa value of 40 1 /h. With an ammonia feed concentration of 100 mg/L find the feed flow rate which will give 99% conversion to nitrate. 

An intrinsic, exothermic water-gas shift reaction occurs in the steam reformer reactor. The combined reaction, steam reforming and water gas shift, is endothermic. As such, an indirect high temperature heat source is needed to operate the reactor. This heat source usually takes the shape of an immediately adjacent high temperature furnace that combusts a small portion of the raw fuel or the fuel effluent from the fuel cell. Efficiency improves by using rejected heat from other parts of the system. Note that the intrinsic water-gas shift in the reactor may not lower the... 

It is easy to show that the equilibrium point P2 is unstable, whereas points PI and P3 are stable (in some cases P3 can be unstable) [3], [13], [14], [22]. If the goal is to operate the reactor at point P2 it is necessary to introduce an external control. 

We frequently do not have reliable reaction rate expressions for chain reactions, but we can compensate for this lack by designing and operating the reactor to manage the overall course of the reaction by properly dealing with mixing, mass transfer, promoters and inhibitors, and the presence of surfaces. 

Build and operate the reactor system considering all safety precautions. 

On the other hand, the tubular reactor is a simple and inexpensive apparatus. It s small inner diameter requires a low thickness of the tube-wall to resist high pressure, and facilitates the removal or heating of the feed in order to operate the reactor under isothermal conditions. Solid catalyst can easily be placed in the tubular reactor. 

Aluminum Chloride-Based Alkylation. An improved aluminum chloride-based process was developed by Monsanto in the 1970s. Using a presynthesized aluminum chloride complex and operating the reactor at higher temperature and pressure, the catalyst inventory is reduced to below its solubility in the reaction mixture. The reactants and the catalyst complex are mixed in the reactor to form a homogeneous liquid. The transalkylation... 

One widely used method involves operating the reactor at the boiling point of EDC, allowing the pure product to vaporize, and then either recovering heat fiom the condensing vapoi 01 leplacing one 01 more EDC fractionation column reboilers with the reactor itself. 

---