Long-Term Catalyst Stability Test

From a practical standpoint, catalyst stability is the most relevant feature of the process as it determines the length of the operational cycle. In this sense, the capacity of the front-end HDM catalyst to store high amonnts of metals from the feedstock is of vital importance. Its purpose is to disaggregate asphaltene molecnles to allow Ni and V removal, so that the downstream catalysts can operate with partially demetallized feed. Since intraparticle diffusion of large molecules such as asphaltenes is a rate-determining step, pore size in this type of catalyst becomes the most relevant characteristic (Furimsky, 1998). If the pore size is too narrow, the catalyst will experience rapid pore-mouth plugging, leading to early shutdown. 

One important aspect of catalyst stability testing is the selection of the operation mode (Marafi et al., 2008) fixed performance or fixed temperature. The former mode, in which reaction temperature is increased periodically to compensate for the activity loss, is more suitable for representing commercial operation. For this reason. 

The evaluation was carried out under the following operating conditions LHSV of 0.25 h , initial temperature of 380°C, pressure of 9.81 MPa, and H2/oil ratio of 891 std mVm. The mass-balance runs were performed consecutively by recovering the products every 12h. Inter-reactor samples were taken every 24h in order to monitor the behavior of the first reactor. The sample size was kept at less than 2% of the total feed rate so as to reduce the disturbance of the system. This small amount is sufficient enough to carry out some analyses, particularly to determine metal content in the products for estimating the metal uptake in the first reactor. 

FIGURE 8.7 Reaction temperature program and API Gravity of the upgraded oil during the catalyst stability test. (—Temperature, (o) API gravity. 

Modeling of Processes and Reactors for Upgrading of Heavy Petroleum 

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Table 8.4 contains the deactivation parameters estimated from the long-term catalyst stability test and the feedstock evaluation with HCO. d and d are the parameters of the hyperbolic function that describes the initial activity decay caused by coke formation, whereas 3 is the exponent of the power-type function that represents the slow deactivation process by metal deposition (see Equation 8.21). Each set of... 

FIGURE 8.9 Comparison between experimental deactivation data and model predictions, (a) Long-term catalyst stability test (b) Feedstock evaluations with HCO (—) 5%. 

Fig. 8.16 Bottom H2-O2 fuel cell polarization plots recorded with 4 mg cm of a PANI-FeCo-C catalyst in the cathode. Performance of an H2-air fuel cell with a Pt cathode (0.2 mgp, cm ) is shown for comparison. Top Long-term perframance stability test of the PANI-FeCo-C catalyst in a H2-air fuel cell at a constant fuel cell voltage of 0.40 V. Anode and cathode gas pressure 2.8 bar, anode loading 0.25 mgp, cm cell temperature 80 °C (reprinted from ref [57] with permission from AAAS)...

Use long-term (>1000 h) tests to determine effects on catalyst stability, poisoning and long-term degradation... 

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

Another important point to guarantee the long-term stability of the electrode is the procedure used to manage shutdowns. The experience gained through the laboratory tests shows that during shutdown the cell must be maintained under polarisation conditions to avoid the probable dissolution of the silver catalyst and its re-deposition... 

For example, with the Co-I-PPh catalyst, methyl acetate reacts with synthesis gas to form ethyl acetate. All of the primary and secondary alcohols tested (C thru C ) decompose during long-term operation. The major decomposition products include aldehydes, alkyl iodides, and ethers. Ketones are readily hydrogenated and the resulting alcohols decompose. Good solvents in terms of stability are diphenyl ether and alkanes. The acetaldehyde rate is somewhat low (1.8 M/hr) in diphenyl ether, and the selectivity is low in alkanes. In addition, these solvents do not have good solubility properties, especially in product refining. 

This test method is commonly utilized throughout the world to rapidly determine the oxidative stability of distillate fuel. Although not as effective at predicting the long-term stability of distillate fuel as ASTM D-4625, this method is useful for measuring the resistance of fuel to rapid degradation by oxidation. Metal catalysts such as copper and iron are sometimes added to the fuel to further accelerate... 

The dispersion method, while not suitable for long-term tests lasting several days, can be used for preliminary trials of electrochemical behavior over a period of several hours. As can be seen from Fig. 13, the activity of CoTAA falls off sharply even within a few hours, in contrast to that of polymeric FePc. The stability of the CoTAA catalyst can however be considerably increased by suitable thermal pretreatment (cf. Section 4.1. .). 

Ion implantation has also been used for the creation of novel catalytically active materials. Ruthenium oxide is used as an electrode for chlorine production because of its superior corrosion resistance. Platinum was implanted in ruthenium oxide and the performance of the catalyst tested with respect to the oxidation of formic acid and methanol (fuel cell reactions) (131). The implantation of platinum produced of which a catalytically active electrode, the performance of which is superior to both pure and smooth platinum. It also has good long-term stability. The most interesting finding, however, is the complete inactivity of the electrode for the methanol oxidation. 

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