Catalysts activity testing

Catalysts - A commercial Raney nickel (RNi-C) and a laboratory Raney nickel (RNi-L) were used in this study. RNi-C was supplied in an aqueous suspension (pH < 10.5, A1 < 7 wt %, particle size 0.012-0.128 mm). Prior to the activity test, RNi-C catalyst (2 g wet, 1.4 g dry, aqueous suspension) was washed three times with ethanol (20 ml) and twice with cyclohexane (CH) (20 mL) in order to remove water from the catalyst. RCN was then exchanged for the cyclohexane and the catalyst sample was introduced into the reactor as a suspension in the substrate. RNi-L catalyst was prepared from a 50 % Ni-50 % A1 alloy (0.045-0.1 mm in size) by treatment with NaOH which dissolved most of the Al. This catalyst was stored in passivated and dried form. Prior to the activity test, the catalyst (0.3 g) was treated in H2 at 250 °C for 2 h and then introduced to the reactor under CH. Raney cobalt (RCo), a commercial product, was treated likewise. Alumina supported Ru, Rh, Pd and Pt catalysts (powder) containing 5 wt. % of metal were purchased from Engelhard in reduced form. Prior to the activity test, catalyst (1.5 g) was treated in H2 at 250 °C for 2 h and then introduced to the reactor under solvent. 10 % Ni and 10 % Co/y-Al203 (200 m2/g) catalysts were prepared by incipient wetness impregnation using nitrate precursors. After drying the samples were calcined and reduced at 500 °C for 2 h and were then introduced to the reactor under CH. 

In a typical procedure, benzene was stirred with freshly activated catalyst sample. Prior to activation, the catalyst samples were ground and sieved, and a fraction of 315-800 pm was used for each catalytic activity test. Catalyst samples were activated by heating in an oven at 185T for 2 h prior to catalyst activity tests. An aliquot of bcn/yl chloride was then added and the reaction mixture stirred for 15 min at room temperature. Mass ratios of the reactants and catalyst were benzyl chloridc/catalyst = 10 and bcn/cne/benzyl chloride = 3.5-4. An excess of benzene resulted in the formation of diphenylmethane as the dominant product. The follow ing reactions occur in the system ... 

As mentioned in Section 2.2 (Fixed-Bed Reactors) and in the Micro activity test example, even fluid-bed catalysts are tested in fixed-bed reactors when working on a small scale. The reason is that the experimental conditions in laboratory fluidized-bed reactors can not even approach that in production units. Even catalyst particle size must be much smaller to get proper fluidization. The reactors of ARCO (Wachtel, et al, 1972) and that of Kraemer and deLasa (1988) are such attempts. 

The first step in E-cat testing is to bum the carbon off the sample. The sample is then placed in a MAT unit (Figure 3-13), the heart of which is a fixed bed reactor. A certain amount of a standard gas oil feedstock is injected into the hot bed of catalyst. The activity i.s reported as the conversion to 430°F (221°C) material. The feedstock s quality, reactor temperature, catalyst-to-oil ratio, and space velocity are four variables affecting MAT results. Each catalyst vendor uses slightly different operating variables to conduct micro activity testing, as indicated in Table 3-2. 

For example, a catalyst with a MAT number of 70 vol% and a 3.0 wt% coke yield will have a dynamic activity of 0.78. However, another catalyst with a MAT conversion of 68 vol% and 2.5 wt% coke yield will have a dynamic activity of 0.85. This could indicate that in a commercial unit the 68 MAT catalyst could outperform the 70 MAT catalyst, due to its higher dynamic activity. Some catalyst vendors ha% c begun reporting dynamic activity data as part of their E-cat inspection reports. The reported dynamic activity data can vary significantly from one test to another, mainly due to the differences in feedstock quality between MAT and actual commercial application. In addition, the coke yield, as calculated by the MAT procedure, is not very accurate and small changes in this calculation can affect the dynamic activity appreciably. 

Tests 2 and 3 were run in the same reactor as Test 1. In order to confirm the initial activity, the catalyst was started up without added sulfur. The catalyst picked up sulfur in both these tests and was deactivated even though no sulfur was added to the feed this indicates that sulfur remained in the reactor after Test 1. This is a common problem encountered when working with sulfur in laboratory test reactors. The sulfur reacts with the steel walls of the reactor. Then, even though sulfur is removed from the feed, sulfur evolves from the walls of the reactor and it is either picked up by the catalyst or it appears in the effluent from the reactor. With continuous addition of sulfur, the CO leakage continues to increase. 

In addition to actual synthesis tests, fresh and used catalysts were investigated extensively in order to determine the effect of steam on catalyst activity and catalyst stability. This was done by measurement of surface areas. Whereas the Brunauer-Emmett-Teller (BET) area (4) is a measure of the total surface area, the volume of chemisorbed hydrogen is a measure only of the exposed metallic nickel area and therefore should be a truer measure of the catalytically active area. The H2 chemisorption measurement data are summarized in Table III. For fresh reduced catalyst, activity was equivalent to 11.2 ml/g. When this reduced catalyst was treated with a mixture of hydrogen and steam, it lost 27% of its activity. This activity loss is definitely caused by steam since a... 

The catalyst (0.15 g) was loaded into a quartz tube reactor (internal diameter = 4 mm). The catalyst was pretreated in nitrogen at 400°C. Simulated gasoline reformate was used for the activity test of the catalyst. The composition of the simulated reformate was 36 wt% H2, 17 wt% CO2, 28 wt% N2, 17 wt% H2O, 1 wt% CO, and air was added additionally as the oxidant. The total flow rate was maintained at 100 ml/min. The test was performed over the temperature range of 120 280°C at various flow rates of inlet air. 

Minimize the effects of transport phenomena If we are interested in the intrinsic kinetic performance of the catalyst it is important to eliminate transport limitations, as these will lead to erroneous data. We will discuss later in this chapter how diffusion limitations in the pores of the catalyst influence the overall activation energy. Determining the turnover frequency for different gas flow velocities and several catalyst particle sizes is a way to establish whether transport limitations are present. A good starting point for testing catalysts is therefore ... 

Presulfiding for the activity tests was accomplished by first heating the catalyst in nitrogen at 204°C. 10% H2S/H2 was intro-... 

Activity Tests. Figure 2 shows results of activity tests for a commercial American Cyanamid HDS-2 catalyst which had been in use for about six years. The catalyst was sampled at various depths and results for three samples containing 0.01% As, 0.6% As, and 3.6% As show a decrease in activity with Increasing arsenic content. 

The activity tests of the catalyst were carried out in a microflow reactor set-up in which all the high temperature parts are constructed of hastelloy-C and monel. The reactor effluent was analyzed by an on-line gas chromatograph with an Ultimetal Q column (75 m x 0.53 mm), a flame ionization detector, and a thermal conductivity detector. The composition of the feed to the reactor can be varied, besides the temperature, pressure, and space velocity. The influence of the recycle components CHCIF2 and methane was tested by adding these components to the feed. In total five stability experiments of over 1600 hours were performed. In each... 

Catalytic activity tests have been performed in a quartz microreactor (I.D.=0.8 cm) filled with 0.45 g of fine catalyst powders (dp=0 1 micron). The reactor has been fed with lean fiiel/air mixtures (1.3% of CO, 1.3% of H2 and 1% of CH4 in air resp ively) and has been operated at atmospheric pressure and with GHSV= 54000 Ncc/gcath The inlet and outlet gas compositions were determined by on-line Gas Chromatography. A 4 m column (I D. =5mm) filled with Porapak QS was used to separate CH4, CO2 and H2O with He as carrier gas. Two molecular sieves (5 A) columns (I D.=5 mm) 3m length, with He and Ar as carrier gases, were used for the separation and analysis of CO, N2, O2, CH4, and H2, N2, O2 respectively... 

Ir catalysts supported on binary oxides of Ti/Si and Nb/Si were prepared and essayed for the hydrogenation of a,P-unsaturated aldehydes reactions. The results of characterization revealed that monolayers of Ti/Si and Nb/Si allow a high metal distribution with a small size crystallite of Ir. The activity test indicates that the catalytic activity of these solids is dependent on the dispersion obtained and acidity of the solids. For molecules with a ring plane such as furfural and ciimamaldehyde, the adsorption mode can iirfluence the obtained products. SMSI effect (evidenced for H2 chemisorption) favors the formation of unsaturated alcohol. 

Calculation of kinetic parameters - In the experiments carried out in the single autoclave the H2 pressure was not maintained and the consumption of H2 controlled the conversion of AcOBu, which could be described by pseudo-first order rate constant. In the activity tests performed in SPR16 the conversion of AcOBu increased linearly up to ca. 50 % with reaction time. Initial reaction rates were calculated from AcOBu conversion vs. reaction time dependence, the initial concentration of substrate and the amount of catalyst or the amount of promoters in 1 g of catalyst. 

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