Bench-scale unit

As an example the use of ceramic membranes for ethane dehydrogenation has been discussed (91). The constmction of a commercial reactor, however, is difficult, and a sweep gas is requited to shift the product composition away from equiUbrium values. The achievable conversion also depends on the permeabihty of the membrane. Figure 7 shows the equiUbrium conversion and the conversion that can be obtained from a membrane reactor by selectively removing 80% of the hydrogen produced. Another way to use membranes is only for separation and not for reaction. In this method, a conventional, multiple, fixed-bed catalytic reactor is used for the dehydrogenation. After each bed, the hydrogen is partially separated using membranes to shift the equihbrium. Since separation is independent of reaction, reaction temperature can be optimized for superior performance. Both concepts have been proven in bench-scale units, but are yet to be demonstrated in commercial reactors. 

Catalytic crackings operations have been simulated by mathematical models, with the aid of computers. The computer programs are the end result of a very extensive research effort in pilot and bench scale units. Many sets of calculations are carried out to optimize design of new units, operation of existing plants, choice of feedstocks, and other variables subject to control. A background knowledge of the correlations used in the "black box" helps to make such studies more effective. 

This study was run in a laboratory bench-scale unit with 0.75-in. reactor tubes. The catalysts were sized to 10 X 12 mesh and diluted nine-to-one with Si02 in order to spread the reaction out through the bed and to permit measurement of temperature profiles, the profile being an... 

Bench-Scale Reactor. The bench-scale reactor is 0.81 in. i.d. and 48 in. long. The nominal feed gas rate for this unit is 30 standard cubic feet per hour (scfh) the feed gas is supplied from premixed, high-pressure gas cylinders. Except for reaction temperature, the bench-scale unit is substantially manually operated and controlled. The catalysts used in these studies were standard commercial methanation catalysts ground to a 16-20 mesh size which is compatible with the small reactor diameter. 

One goal of our experimental program with the bench-scale unit was to develop the necessary correlations for use in the ultimate design of large commercial plants. Because of the complexity inherent in the three-phase gas-liquid-solid reaction systems, many models can be postulated. In order to provide a background for the final selection of the reaction model, we shall first review briefly the three-phase system. 

Figure 2. Conversion vs. contact time with bench-scale unit...

Findings with Bench-Scale Unit. We performed this type of process variable scan for several sets of catalyst-liquid pairs (e.g., Figure 2). In all cases, the data supported the proposed mechanism. Examination of the effect of temperature on the kinetic rate constant produced a typical Arrhenius plot (Figure 3). The activation energy calculated for all of the systems run in the bench-scale unit was 18,000-24,000 cal/g mole. 

In order to overcome these problems, the flow schemes as shown in Figures 1 and 2 were developed. These incorporate the use of Kerr-McGee Corporation s Critical Solvent Deashing and Fractionation Process (CSD) for recovery of the SRC. The Kerr-McGee Process adds extra flexibility since this process can recover heavy solvent for recycle, which is not recoverable by vacuum distillation. EPRI contracted with Conoco Coal Development Company (CCDC) and Kerr-McGee Corporation in 1977-1978 to test these process concepts on continuous bench-scale units. A complementary effort would be made at the Wilsonville Pilot Plant under joint sponsorship by EPRI, DOE, and Kerr-McGee Corporation. This paper presents some of the initial findings. 

Paralleling the work at CCDC were the critical solvent deashing and fractionation studies done on a continuous bench-scale unit at Kerr-McGee Technical Center, Oklahoma City, Oklahoma, Figure 3. The Kerr-McGee Critical Solvent Deashing and Fractionation Process has been previously discussed (3). 

Continuous Bench-Scale Experimentation With encouraging results obtained from microautoclave tests, experimentation emphasis moved to the bench-scale unit Here the concept of adding Light SRC to the recycle solvent on a continuous basis was tested Earlier work (j>) performed on short contact time coal liquefaction showed Indiana V coal to be out-of-solvent balance Also the operability of the continuous bench-scale SRT unit was highly dependent upon the quality of the solvent ... 

The bench-scale unit for the study of catalytic reactions has been designed with features such as accessibility, isothermal operation, and catalyst pretreatment. The use for catalytic screening tests makes easy accessibility a necessity, while the study of kinetics prescribes isothermal operation. 

Bench-Scale Unit eor the Artificial Deactivation OF FCC Catalysts... 

Selection of the chemical, and the proper concentration, requires special knowledge of surface chemistry and laboratory-type testing in bench scale units... 

Laboratory units can be divided into bench-scale, research-, and pilot-scale. Bench-scale units, available in sizes of 20 to 500 ml (up to 400 bar) are used for screening tests, because one can obtain a relatively fast overview of the influence of the diverse major parameters, and only small quantities of raw material are necessary. Optimization duties require research units in sizes of 2 to 10 1, and are available in the pressure range between 325 and 700 (1000) bar. Such units enable quantity- and quality analyses. An illustration of one commercially available unit is shown in Fig. 8.1-1. For scale-up purposes, pilot plants ranging from 20 to 100 1, with design pressures up to 550 (700) bar, are recommendable for use with new products. 

Figure 7. Flow and instrumentation diagram for high temperature, balanced pressure bench-scale unit. LR, level recorder LT, level transmitter TR, temperature recorder FR, pressure recorder FR, flow recording RD, densitometer PC, pressure controller TC, temperature controller GM, gas meter F, filter VSD, variable speed drive PCV, pressure regulator CV, control valve SV, solenoid valve S, gamma ray source.

The above work concentrated most of its attention on the use of zinc chloride as the molten halide and on the use of bituminous coal extract as feed to the process. Hydrocracking of the extract (1) and regeneration by a fluidized-bed combustion technique of the spent catalyst melt (2) from the process were both demonstrated in continuous bench-scale units. 

The melt used in this work was prepared from the residue of hydrogen-donor extraction of Colstrip coal with tetralin solvent in such a way as to simulate the composition of an actual spent melt. The extraction was conducted in the continuous bench-scale unit previously described (17) at 412°C and 50 min residence time. The residue used was the solvent-free underflow from continuous settling (17) of the extractor effluent. The residue was then precarbonized to 675°C in a muffle furnace. The melts were blended to simulate the composition of a spent melt from the direct hydrocracking of the Colstrip coal by blending together in a melt pot zinc chloride, zinc sulfide, and ammonium chloride, ammonia, and the carbonized residue in appropriate proportions. Analysis of the feed melt used in this work is given in Table I. 

Development of technology is generally done using laboratory scale units. Experimental data can be obtained with less expense and with more accuracy and flexibility than by attempting to do the same test on a commercial scale. In the laboratory, smaller quantities of feedstock and catalyst are needed and lower manpower and capital costs are incurred. By necessity, bench scale units must process feedstocks which are at least as difficult as those processed commercially. 

Detoxification of hydrolysates was accomplished in a continuous ion-exchange bench-scale unit. The resins used were Dowex 1 (50/100 mesh, density 0.71 g/cm3), weak basic anion exchanging, and Dowex-50W (50/ 100 mesh, density 0.80 g/cm3), strong acidic cation exchanging. 

Because impurities most often result in reduced crystal growth rate, feedstocks to laboratory and bench-scale units should be as similar as possible to that expected in the full-scale unit. The generation of impurities in upstream process units can depend on the way those units are operated, and protocols of such units should follow a consistent practice. It is equally important to monitor the composition of recycle streams so as to detect any accumulation of impurities that might lead to a reduction in growth rates. 

Such a development would parallel extensive experience in successful commercialization of many fixed-bed processes using similar catalysts and operating conditions. The five licensed processes using ZSM-5 catalyst fall in that category. The simplest fixed-bed MTG system was the one which employed dehydration and ZSM-5 reactors. This system was studied extensively in bench-scale units. These studies in a 3 cm diameter by 30-50 cm length reactors were considered to be sufficient for scale-up. 

Fixed-Bed Demonstration Plant. The major objective of the demonstration test was to verify the bench unit results in a larger plant operating at conditions similar to a commercial-size reactor. The linear velocity of the reactant is the only variable which is significantly different between a bench-scale unit and a commercial-size reactor. The other operating conditions are normally the same for both reactors. 

A bench scale unit for the study of catalyst deactivation, combining an electrobalance with a recycle reactor and operating under completely mixed conditions, is introduced. 

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