Deactivation catalytic reactor

Nickel catalysts were used in most of the methanation catalytic studies they have a rather wide range of operating temperatures, approximately 260°-538°C. Operation of the catalytic reactors at 482°-538°C will ultimately result in carbon deposition and rapid deactivation of the catalysts (10). Reactions below 260°C will usually result in formation of nickel carbonyl and also in rapid deactivation of the catalysts. The best operating range for most fixed-bed nickel catalysts is 288°-482 °C. Several schemes have been proposed to limit the maximum temperature in adiabatic catalytic reactors to 482°C, and IGT has developed a cold-gas recycle process that utilizes a series of fixed-bed adiabatic catalytic reactors to maintain this temperature control. 

Deactivating catalytic reaction with Langmuir-Hinshelwood kinetics in a completely mixed reactor. 

In a fixed-bed catalytic reactor for a fluid-solid reaction, the solid catalyst is present as a bed of relatively small individual particles, randomly oriented and fixed in position. The fluid moves by convective flow through the spaces between the particles. There may also be diffusive flow or transport within the particles, as described in Chapter 8. The relevant kinetics of such reactions are treated in Section 8.5. The fluid may be either a gas or liquid, but we concentrate primarily on catalyzed gas-phase reactions, more common in this situation. We also focus on steady-state operation, thus ignoring any implications of catalyst deactivation with time (Section 8.6). The importance of fixed-bed catalytic reactors can be appreciated from their use in the manufacture of such large-tonnage products as sulfuric acid, ammonia, and methanol (see Figures 1.4,11.5, and 11.6, respectively). 

Reaction (13.2) is highly undesired because SO, reacts with water present in the flue gas in large excess and with ammonia to form sulfuric acid and ammonium sulfate salts. The ammonium sulfate salts deposit and accumulate on the catalyst if the temperature is not high enough, leading to catalyst deactivation, and on the cold equipment downstream of the catalytic reactor, causing corrosion and pressure drop problems. The catalyst deactivation by deposition of ammonium sulfate salts can be reversed upon heating. 

In high pressure work, slurry reactors are used when a solid catalyst is suspended in a liquid or supercritical fluid (either reactant or inert) and the second reactant is a high pressure gas or also a supercritical fluid. The slurry catalytic reactor will be used in the laboratory to try different catalyst batches or alternatives. Or to measure the reaction rate under high rotational speeds for assessing intrinsic kinetics. Or even it can be used at different catalyst loadings to assess mass transfer resistances. It can also be used in the laboratory to check the deactivating behaviour. 

The manner in which Ni and V sulfide deposits accumulate on individual catalyst pellets depends on the kinetics of the HDM reactions as influenced by catalyst properties, feed characteristics, and operating conditions. The dynamic course of deactivation of catalytic reactor beds is also determined by the kinetics of the HDM reaction. The lifetime and activity of a reactor bed are directly related to the details of the metal deposit distribution within individual pellets. This section will review deactivation behavior of reactor beds in light of our understanding of the reaction and diffusion phenomena occurring in independent catalyst pellets. Unfortunately, this is an area of research which remains mostly proprietary with too little information published. What has been published is generally lacking in detail for the same reason. 

In contrast to so-called microkinetic analyses, an important aspect of chemical reaction engineering involves the use of semiempirical rate expressions (e.g., power law rate expressions) to conduct detailed analyses of reactor performance, incorporating such effects as heat and mass transport, catalyst deactivation, and reactor stability. Accordingly, microkinetic analyses should not be considered to be more fundamental than analyses based on semiempirical rate expressions. Instead, microkinetic analyses are simply conducted for different purposes than analyses based on semiempirical rate expressions. In this review, we focus on reaction kinetics analyses based on molecular-level descriptions of catalytic processes. 

Activation energy, stability in trickle-bed reactors, 76 Activation overpotential, cross-flow monolith fuel cell reactor, 182 Activity balance, deactivation of non-adiabatic packed-bed reactors, 394 Adiabatic reactors stability, 337-58 trickle-bed, safe operation, 61-81 Adsorption equilibrium, countercurrent moving-bed catalytic reactor, 273 Adsorption isotherms, countercurrent moving-bed catalytic reactor, 278,279f... 

In designing fixed and ideal fluidized-bed catalytic reactors, we have assumed up to now that the activity of the catalyst remains constant throughout the catalyst s life. That is, the total concentration of active sites, C accessible to the reaction does not change with time. Unfortunately, Mother Nature is not so kind as to allow this behavior to be the case in most industrially significant catalytic reactions. One of the most insidious problems in catalysis is the loss of catalytic activity that occurs as the reaction takes place on the catalyst. A wide variety of mechanisms have been proposed by Butt and Petersen, to explain and model catalyst deactivation. 

Catalytic deactivation adds another level of complexity to sorting out the reaction rate law parameters and pathways. In addition, we need to make adjustments for the decay of the catalysts in the design of catalytic reactors. This adjustment is usually made by a quantitative specification of the catalyst s activity, a(t), In analyzing reactions over decaying catalysts we divide the reactions into two categories separable kinetics and nonseparable kinetics. In separable kinetics, we separate the rate law and activity ... 

Fig.2 Deactivation of calcined dolomites-Effect of the type of dolomite(SW = Swedish Sala SP= Spanish Norte I) and of the temperature in catalytic reactor (space-time of this catalytic reactor Q.lS-0,24 kg,h/kg)...

If we adopt this global view, another question arises. Catalysts, as they work in catalytic reactors, are just the intermediary product of a solid state reaction chain which starts with preparation and activation, before the catalysts is contacted with the feed, and is followed by deactivation and, ultimately, "death". The question is what are the relationships among solid-state reactions occurring during the initial activation, catalytic reaction and deactivation ... 

A simple model was also developed to simulate the coking phenomenon and the results compare well with experimental data. The model can be easily coupled into reactor design algorithms to improve the design of catalytic reactors which undergo similar catalyst deactivation. 

Catalyst deactivation is always a problem in catalyst and catalytic reactor design. Empirical equations to represent deactivation rates in design calculations are reported by Weekman (1968), Sadana and Doraiswamy (1971), and Doraiswamy and Sharma (1984). Here, we briefly touch upon the... 

Many of the important catalytic processes are carried out in fixed bed catalytic reactors where the catalyst is experiencing deactivation (Emmett, 1956 Hughes, 1984). 

Optimal Control of Catalytic Reactors Experiencing Catalyst Deactivation... 

INFLUENCE OF DIFFUSIONAL RESISTANCES ON THE OPTIMAL CONTROL OF CATALYTIC REACTORS EXPERIENCING CATALYST DEACTIVATION... 

Other recent work in the field of optimization of catalytic reactors experiencing catalyst decay includes the work of Romero e/ n/. (1981 a) who carried out an analysis of the temperature-time sequence for deactivating isothermal catalyst bed. Sandana (1982) investigated the optimum temperature policy for a deactivating catalytic packed bed reactor which is operated isothermally. Promanik and Kunzru (1984) obtained the optimal policy for a consecutive reaction in a CSTR with concentration dependent catalyst deactivation. Ferraris ei al. (1984) suggested an approximate method to obtain the optimal control policy for tubular catalytic reactors with catalyst decay. 

Elnashaie, S.S.E.R and Abdel-Hakim, M.N., Optimal Feed Temperature Control for Fixed Bed Non-isothermal Catalytic Reactors Experiencing Catalyst Deactivation. A Heterogeneous Model. Computers and Chem. Eng., Vol. 12, pp. 787-790, 1988. 

The most commonly utilized catalytic membrane reactor is the PBMR, in which the membrane provides only the separation function. The reaction function is provided (in catalytic applications) by a packed-bed of catalyst particles placed in the interior or exterior membrane volumes. In the CMR configuration the membrane provides simultaneously the separation and reaction functions. To accomplish this, one could use either an intrinsically catalytic membrane (e.g., zeolite or metallic membrane) or a membrane that has been made catalytic through activation, by introducing catalytic sites by either impregnation or ion exchange. This process concept is finding wider acceptance in the membrane bioreactor area, rather than with the high temperature catalytic reactors. In the latter case, the potential for the catalytic membrane to deactivate and, as a result, to require sub-... 

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