Pilot plant deactivation

Table V. Pilot Plant Deactivation of Cerium/Alumina Additive...

Mottola, A.C., Hendrickson, A.P., O Connell, D.E., Palter, R., Kohler, G.O., 1968. Pilot plant deactivation of castor meal allergen. Lime process. J. Agric. Food Chem. 16, 725-729. 

When deactivation occurs rapidly (in a few seconds during catalytic cracking, for instance), the fresh activity can be found with a transport reac tor through which both reac tants and fresh catalyst flow without slip and with short contact time. Since catalysts often are sensitive to traces of impurities, the time-deac tivation of the catalyst usually can be evaluated only with commercial feedstock, preferably in a pilot plant. 

Four pilot plant experiments were conducted at 300 psig and up to 475°C maximum temperature in a 3.07-in. i.d. adiabatic hot gas recycle methanation reactor. Two catalysts were used parallel plates coated with Raney nickel and precipitated nickel pellets. Pressure drop across the parallel plates was about 1/15 that across the bed of pellets. Fresh feed gas containing 75% H2 and 24% CO was fed at up to 3000/hr space velocity. CO concentrations in the product gas ranged from less than 0.1% to 4%. Best performance was achieved with the Raney-nickel-coated plates which yielded 32 mscf CHh/lb Raney nickel during 2307 hrs of operation. Carbon and iron deposition and nickel carbide formation were suspected causes of catalyst deactivation. 

The pilot plant results indicate that the deactivation characteristics of the two catalysts are somewhat different. The same gas pressure, feed composition, and molal feed rate are employed in all cases. If the inlet temperature is 550 °C, the behavior indicated in Figure 12P.2 is observed. If the feed temperature is reduced... 

The major problem of the application of zeolites in alkane-alkene alkylation is their rapid deactivation by carbonaceous deposits. These either strongly adsorb on acidic sites or block the pores preventing the access of the reactants to the active sites. A further problem is that in addition to activity loss, the selectivity of the zeolite-catalyzed alkylation also decreases severely. Specifically, alkene formation through oligomerization becomes the dominant reaction. This is explained by decreasing ability of the aging catalyst to promote intermolecular hydride transfer. These are the main reasons why the developments of several commercial processes reached only the pilot plant stage.356 New observations with Y zeolites reconfirm the problems found in earlier studies.358,359... 

The coke deactivation exponent n, is typically estimated from riser pilot plant experiments at varying catalyst contact time for different catalyst types. A value of n of 0.2 was found for REY catalyst data base. For USY and RE-USY catalysts n was estimated to be 0.4. 

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

Due to the strong interaction between the physical and chemical mechanisms, particularly when catalyst deactivation is present, the parameter estimation becomes very difficult. The kinetic parameters are normally obtained from laboratory scale reactors and when used in pilot plant studies, have to be tuned (1, 2) or even re-evaluated (3, 4) to obtain reasonable predictions. The transport parameters are estimated... 

Here an attempt is made to describe, by means of a simple model, the intermediate deactivation period of HDM catalysts. This is based on pilot plant hidrometallization runs in which a DAO of 180 ppm vanadium was the feedstock. The interpretation of the experimental results led to a procedure which could save considerable expense in the selection of HDM catalysts. 

Accelerated aging tests have been commonly used in facilities ranging from academic bench scale to industrial pilot-plant scale. In such tests, the addition of an accelerant increases the deactivating agent or its precursor, so that a certain Level of deactivation (however measured) is reached at lower run times. In this manner, the performance of a catalyst at a high deactivation level can, in principle, be measured without expending the time and effort required under normal conditions to bring the catalyst to this level of deactivation,... 

The deactivation of a Fischer-Tropsch precipitated iron catalyst has been investigated by means of a novel reactor study. After use of the catalyst in a single or dual pilot plant reactor, sections of the catalyst were transferred to microreactors for further activity studies. Microreactor activity studies revealed maximum activity for catalyst fractions removed from the region situated 20 - 30% from the top of the pilot plant reactor. Catalyst characterization by means of elemental analyses, XRD, surface area and pore size measurements revealed that (1 deactivation of the catalyst in the top 25% of the catalyst bed was mainly due to sulphur poisoning (2) deactivation of the catalyst in the middle and lower portions of the catalyst bed was due to catalyst sintering and conversion of the iron to Fe304, Both these latter phenomena were due to the action of water produced in the Fischer-Tropsch reaction. 

In a laboratory environment it is possible to investigate a general deactivation phenomenon by changing variables one at a time. However, in an industrial plant the deactivation processes usually occur simultaneously and the relative and interrelated importance of the processes are more difficult to assess. In this publication we report on an experimental design that was used to investigate simultaneous deactivation processes in a pilot plant. 

The pilot plant catalyst bed was unloaded in sections after different times on line and the activity of each section was determined in a micro reactor and the activity profiles as a function of position in the catalyst bed determined. The results are shown in Figure 1. In this Figure the activity is plotted relative to the fresh catalyst, i.e. a portion of the catalyst not used in the pilot plant study. The results clearly indicate that at least two different deactivation phenomena are occurring and that the deactivation processes increase with time on line. It can further be seen that the top section of the reactor bed has a low activity, and that the activity increases until a maximum activity is achieved about one quarter distance from the top of the reactor bed. Thereafter a gradual decrease in activity is observed. Figure 1 also indicates that the top section of the catalyst bed deactivates more rapidly than the bottom section of the reactor. 

As shown in Figure 1, the activity profile has an inverted V-shape in which the activity has a maximum value at a position approximately one quarter distance from the top of the pilot-plant reactor. This observation is in agreement with studies reported by Kolbel and Engelhard [11] on a related iron F-T catalyst. The results in Figure 1 indicate thatr as expected, the degree of deactivation increases with time on line. In the discussion which follows studies will concentrate on catalysts that spent the longest time on line since deactivation trends are more clearly observed with this data. 

The feasibility of hydrotreating whole shale oil is demonstrated by means of several long pilot plant tests using proprietary commercial catalysts developed by Chevron. One such test was on stream for over 3500 hr. The rate of catalyst deactivation was very low at processing conditions of 0.6 LHSV and 2000 psia hydrogen pressure. The run was shut down when the feed supply was exhausted although the catalyst was still active. 

Whether the deactivation is separable or non-separable, one normally gets some measure of the activity of a deactivating catalyst by comparing the conversion at zero time to the conversion at some later time. The utility of this type of activity depends in part upon the goal of the study and how fundamentally the data are to be interpreted. For example, the integral reactor shown in Figure 1 is frequently used in pilot plant scale operations and can often produce data of value to interpret and... 

Dautzenberg (6) and many others (1,5) propose guidelines to ensure effective catalyst testing on a laboratory and/or pilot plant scale and ofcourse this area is also the main focus of this symposium. The choice of the proper catalyst pretreatment and/or deactivation conditions obviously also is a key issue to be addressed. 

The deactivation of methanol-synthesis catalyst was studied in laboratory and pilot-plant slurry reactors using a concentrated, poison-free, CO-rich feedstream. The extent of catalyst deactivation correlated with the loss of BET surface area. A model of catalyst deactivation as a function of temperature and time was developed from experimental data. The model suggested that continuous catalyst addition and withdrawal, rather than temperature programming, was the best way to maintain a constant rate of methanol production as the catalyst ages. Catalyst addition and withdrawal was demonstrated in the pilot plant. 

The catalyst deactivation studies described here were carried out in 300 cm.. gas-sparged, stirred autoclaves and in a nominal 10 ton (CH30H)/day pilot-plant, bubble-column reactor. The details of the design and operation of these reactor systems have been reported elsewhere [refs. 4,5]. AH of the present studies were carried out with a feed gas that is referred to as "CO-Rich Gas , with a molar composition of H2 35%, CO-51 %, C02-13% and N2 1%- Its stoichiometric ratio, defined as H2/(CO+1.5002), is 0.5. A typical stoichiometric ratio for the feed to a conventional methanol reactor Is about 2.6, well on the H2-rich side of 2.0, the ratio tor exact stoichiometric equivalence. The feed concentrations of known poisons such as hydrogen sulfide, carbonyl sulfide, chlorine compounds, iron carbonyl and nickel carbonyl were below the limits of detection, 50 ppb, 50 ppb, 10 ppb, 50 ppb and 50 ppb, respectively. 

The results of two catalyst life tests, one in a laboratory autoclave and the other in the pilot plant (Run E-3), are shown in Rg. 1. Both tests were conducted with the same catalyst at a total pressure of 5.27 MPa. (750 psig.) and a temperature of 523X The catalyst concentration was 15 wt.% In the laboratory autoclave and 25 wt. % in the pilot plant the gas hourly space velocities were 5000 and 10,000 liter/kg.(cat.),hr., respectively. Rg. 1 is a plot of a normalized rate constant, k /k (0, versus the time onstream. The normalized rate constant was formed by dividing the rate constant at any time, k, by the rate constant at the beginning of the experiment. k (0). The correspondence between the two sets of data is reasonably good, suggesting that catalyst deactivation is a time-dependent phenomenon that behaves simileu ly in the two reactor systems. 

Samples of catalyst were removed from the pilot-plant reactor at various times during Run >3. Physical and chemical analyses were carried out on these samples and the results were compared with measurements on freshly-reduced catalyst, prior to exposure to synthesis gas. The analyses included BET surface area, S. Cl, Fe and Ni concentration on the catalyst. Cu and ZnO crystallite sizes, and Cu/Zn and Cu VCu ratios on the catalyst surface. The only strong correlation between the rate constant and any of these parameters is shown in Fig. 2, which reveals a striking dependence of the rate constant on the BET surface area. This relationship suggests that sintering of the overall catalyst surface is responsible for a large part of the observed deactivation. 

Experimental studies have demonstrated that conventional methanol-synthesis catalysts deactivate slowly in a slurry reactor, even with a concentrated, CO rich feedstream. The catalyst activity correlates with the BET surface area and the rate of deactivation increases rapidly with temperature. This limits the utility of temperature programming as a means for maintaining a constant methanol production rate as the catalyst ages. Continuous catalyst addition and withdrawal is the preferred means to maintain constant methanol production. The key mechanical and process features of this technique were demonstrated In the pilot plant. 

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