Bench-scale evaluation unit

In order to prepare the low metal equilibrium catalyst for the bench-scale cracking unit evaluation, the catalyst must be sized, dried, and conditioned. In the following, each of these steps is described. 

Bench-scale evaluation of the feasibility of extracting a nutraceutical is usually accomplished with the aid of a small-scale extractor. Such units are available commercially, but an increased experimental flexibility is achieved by constructing a customized SFE unit. Alternatively, there exists the availability of small-scale SFE equipment, normally intended for analytical uses of critical fluid technology, which can also be used to optimize and assess the extraction of a natural product (28). Both of the above approaches can also incorporate the introduction of a cosolvent into the critical fluid, should this be required in the processing of a nutraceutical source. 

For scale-up, certain tests, such as test for settling rate to evaluate flocculation, design of thickeners, and pressrue-bomb or vacuum-leaf experiments to determine the rate of cake buildup, are easy to perform on a bench scale. On the other hand, for design of centrifuges, small-scale test results are not sufficient, and pilot or full-scale units are necessary for final design. 

Other types of pilot plant, including commercial units embracing this principle, are available. Some selected vendors of pilot plants, although this is not an exclusive list, include UHDE, Thar Designs, Applied Separations, Chematur, and Separex.. Likewise, bench-scale equipment for preliminary evaluations are manufactured by such companies as Autoclave Engineers (now called Snap-Tite), Chematur, Nova Swiss, Applied Separations, Nova Sep, Thar Designs, Pressure Products, Inc., Supercritical Fluid Technologies, and Separex. 

In pilot-scale tests, we used a mobile unit provided by the Envirex division of the Rexnord Company. The drum was four feet in diameter by two feet long. To aid in planning pilot tests, we also carried out some preliminary one-cycle short-time (less than 30 sec) tests of screens in bench-scale apparatuses, designed by manufacturers to evaluate the potential of microscreens. 

The normal composition of the simulated exhaust fed to Union Oil s bench scale NO catalyst evaluation unit is listed in Table I. This composition simulates the auto exhaust obtained with an air/fuel (A/F) ratio of 13.9 (11). At times, catalysts were also evaluated with CO = 1.00 and 3.00 mole % with A/F = 14.2 and 13.7 respectively. This range... 

We have employed some rather simple kinetics, conventional pressure drop and heat transfer formulae, ideal film calculations and some basic empirical correlations to develop a reactor model that quite adequately relates the cracking severity of small bench scale units and commercial furnaces. Thus, evaluation of feedstocks using the bench unit has significantly more meaning. Optimization of operating conditions can be calculated for various cracking coil configurations. 

If the initial feasibility evaluation is successful, it is reasonable to commit additional materials for a spray-drying trial. A laboratory dryer at least 500 mm in diameter is recommended for such tests. Bench-scale spray dryers are available but are limited in their ability to provide adequate atomization or sufficient process air flow for the successful production of dried particles. The laboratory unit, however, eom-bined with very fine atomization (two-fluid or rotary) will often produce aceeptable product for further testing. A series of tests can be performed at different inlet-outlet temperature combinations using small quantities of material and these samples ean be tested for chemieal stability to evaluate thermal effects from process air contact. The relationship between outlet temperature and final product moisture can also be established for this seale. While samples produced in a laboratory dryer are suitable for evaluating the effeet of spray drying on the product, they are not suitable for use in downstream proeessing because the fine particle distribution produced as a result of the small drying chamber dimensions may not be representative of the final spray-dried produet. 

On the basis of the assumptions of model <22> and <23> the Fischer-Tropsch synthesis in a slurry phase BCR has been modeled [37, 38]. As this hydrocarbon synthesis from synthesis gas (CO + H2) is accompanied by considerable volume contraction, it is clear that gas flow variations have to be accounted for. The developed models are useful to evaluate experimental data from bench scale units and to simulate the behavior of larger scale Fischer-Tropsch slurry reactors. Though only simplified kinetic laws were applied, the predictions of the model are in reasonable agreement with data reported from 1.5 m diameter demonstration plant. Fig. 12 shows computed space-time-yields (STY) as a function of the inlet gas velocity. As the Fischer-Tropsch reaction on suspended catalyst takes place in the slow reaction regime, it is understood that STY passes through a maximum in dependence of uqo- The predicted maximum is in striking agreement with experimental observations [37]. 

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