Reaction rate from pilot plant data

Detailed models for mixing plus reaction have been presented, and some use computational fluid mechanics to calculate velocities and the local reaction rates throughout the tank [12,13]. Others have developed cell models, with four to six interacting zones to account for different reaction rates [11,14]. These approaches require extensive computations and detailed kinetic data, which may not be available or completely reliable. In industry, multiple reaction systems are generally scaled up from laboratory or pilot-plant data. Mixing theories offer some guidance, but often there is still uncertainty about the correct procedure. 

Pilot-plant studies. The reactors used in these studies are significantly larger than those employed in bench-scale laboratory experiments. One uses essentially the reverse of the design procedures developed later in the chapter to determine the effective reaction rate from the pilot-plant data. In analysis of data of this type, one... 

The proper design of commercial pyrolysis reactors requires a suitable expression for the intrinsic rate of the reactions. As intrinsic rate equations cannot yet be predicted, especially for the ultrapyrolysis regime, experimental data is required. This data is best obtained from bench-scale laboratory reactors, rather than from pilot plants or commercial-scale units. In laboratory scale pyrolysis reactors, the design and operating conditions can be chosen to reduce or eliminate the effects of mass and heat transfer, contaminants and catalytic surfaces from the observed measurements, thus allowing for the development of accurate expressions. It is most advantageous if the laboratory reactor is operated isothermally (in space and time), so that the temperature can be considered as an independent variable. Also, the pressure should be ideally kept constant. 

Collect together all the kinetic and thermodynamic data on the desired reaction and the side reactions. It is unlikely that much useful information will be gleaned from a literature search, as little is published in the open literature on commercially attractive processes. The kinetic data required for reactor design will normally be obtained from laboratory and pilot plant studies. Values will be needed for the rate of reaction over a range of operating conditions pressure, temperature, flow-rate and catalyst concentration. The design of experimental reactors and scale-up is discussed by Rase (1977). 

Model Reaction. The benzene hydrogenation on nickel-kiesel-guhr has been selected as a model reaction. This reaction is well understood and can serve as a typical representative of hydrogenation reactions. Butt (4 5) and Pexider et al.(11) have studied this reaction in laboratory and pilot plant reactors respectively. Pexiderfs data have been obtained from a nonadiaba-tically operated reactor. The reaction rate expression has ... 

Information that has been obtained from this pilot plant includes (1) alkylate quality at simulated commercial operating conditions, (2) alkylate yield, (3) isobutane consumption, (4) catalyst life, (5) maintenance of product quality with catalyst life, and (6) selectivity data (which contributes to the determination of reaction rate constants). 

Laboratory studies are in progress to determine the calcium sulfite precipitation kinetics and the oxidation kinetics of sulfite to sulfate. Until these reaction rate expressions are developed, the experimental data obtained from the pilot plant, prototype, and field units will be used to design the reaction tanks and scrubbers to eliminate calcium sulfite scaling. 

To summarize these last examples, we have seen that in the design of reactors that are to be operated at conditions (e.g.. temperature and initial concentration) identical to those at which the reaction rate data were obtained, we can size determine the reactor volume) both CSTRs and PFRs alone or in various combinations. In principle, it may be possible to scale up a laboratory-bench or pilot-plant reaction system solely from knowledge of as a function of X or Q. However, for most reactor systems in industry, a, scale-up proce.s.s cannot be achieved in this manner because knowledge of solely as a function of X is seldom, if ever, available under identical conditions. In Chapter 3. we shall see how we can obtain = yfX) from information obtained either in the laboratory or from the literature. This relationship will be developed in a two-step process. In Step 1, we will find the rate law that gives the rate as a function of concentration and in Step 2, we will find the concentrations as a function of conversion. Combining Steps 1 and 2 in Chapter 3. we obtain -/-.v =JiX). We can then use the method.s developed in this chapter along with integral and numerical methods to size reactors. 

The differential reactor technique runs showed that, within the explored l ge of reaction conditions, the overall reaction rate Is practically of first order with respect to both reactants. 11) This allows to write an extremely simplified reaction model, in which only five reactions are considered, showing a satisfactory interpretation of the whole set of data, collected by the Integral reactor technique. Ill) No more complex models are needed for practical purposes, since the reaction conditions cannot be very different from the present ones. In order to get good yield and satisfactory catalyst life, as reported [6,10]. Iv) The kinetic equations and parameters so obtained may constitute a safe basis for the design of a pilot plant for the further development of the process. 

Kinetic studies may be used to evaluate the factors affecting the efficiency of removing trace organic pesticides from water by chemical oxidants. The rates of oxidative reactions and the optimum conditions under which the reactions occur are determined in the laboratory before applying them to pilot plant or field studies. Kinetic data also compares the efficiencies of different oxidants with the economy of different treatment processes. 

The gas-phase production of methanol from carbon monoxide and hydrogen is carried out in a small constant-volume batch reactor under isothermal conditions and the pilot-plant operator measures the total pressure within the reactor vs. time for subsequent reaction-rate data analysis. A stoichiometric feed of carbon monoxide and hydrogen is introduced to the reactor at time t = 0, and the total pressure is 3 atm. Sketch (he raw data as total pressme vs. time. Be sure to indicate the appropriate equation that describes the shape of the curve. 

In summary, the stagnancy/catalyst effectiveness model predicts that liquid and/or gas velocity effects on the apparent reaction rate will be observed for catalysts vfliich are at least marginally diffusion limited and run in a trickle bed reactor under low velocity conditions. The model predicts that for scale-up of reactions which are diffusion limited or at least marginally so, the pilot plant should be designed to run at elevated velocities which do not show sensitivity to liquid velocity. Conversely, if a pilot reactor is used for providing data for scaleup showing velocity effects, there is a good likelihood that the catalyst suffers from diffusion limitations. 

The 1984 Chang report is quite comprehensive and presents the results of a series of tests conducted in a 0.1 MW, FGD pilot plant which employs a three-stage turbulent contact absorber (TCA). lii addition to experimental data, the report includes a discussion of the chemical reactions and mass transfer phenomena involved. The theory shows, for example, that increasing the Cl ion concentration from 200 to 100,(XX) ppm (in the form of CaCl2) reduces the total alkalinity (HCOs", CaHC03, SOs , and CaS03) by over 40%. The decreased alkalinity would be expected to decrease the rate of reaction of dissolved SO2, causing a decrease in the liquid phase mass transfer rate and, therefore, a reduction in SO2 removal efficiency. 

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