Catalyst contact time

Paraffin conversion to naphthenes is very unfavorable (last column of Table IV). For paraffins to be converted to naphthenes by ring closure, naphthenes must be at very low concentrations. If appreciable naphthenes exist, such as at short catalyst contact times, naphthene ring opening to paraffins can occur. Again, equilibria improve with carbon number. Eight-and nine-carbon paraffins behave quite similarly. 

This complex system would be difficult to solve directly. However, the problem is separable by taking advantage of the widely different time scales of conversion and deactivation. For example, typical catalyst contact times for the conversion processes are on the order of seconds, whereas the time on stream for deactivation is on the order of days. [Note Catalyst contact time is defined as the volume of catalyst divided by the total volumetric flow in the reactor at unit conditions, PV/FRT. Catalyst volume here includes the voids and is defined as WJpp — e)]. Therefore, in the scale of catalyst contact time, a is constant and Eq. (1) becomes an ordinary differential equation ... 

Equation (16) can then be rearranged to be linear in the catalyst contact time parameters ... 

An isothermal, plug flow, fixed bed reforming pilot plant (shown in Fig. 14) was used to generate the kinetic data. The reactor was U shaped and contained roughly 70 ml of catalyst. Five sample taps were spaced along the reactor length to determine compositions over a wide range of catalyst contact times. The reactor assembly was immersed in a fluidized sand bath to maintain isothermal conditions. 

With respect to catalyst contact time, the effects of temperature and pressure on the yields are shown in Figs. 18, 19, and 20. Activity (as measured by the C5- gas make) is a strong function of temperature, as shown in Figs. 18 and 19. Again, the higher-temperature operation favors benzene formation. KINPTR s prediction of activity as a function of pressure is shown in Fig. 20. Lower-pressure operation favors the yield of benzene. 

Based on Voorhies time-on-stream theory (4), catalytic coke is a function of catalyst contact time ... 

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 fixed bed reactor described by ASTM Method No. D3907 was employed for catalytic testing. A sour, imported heavy gas oil with properties described in Table II was used as the feedstock. Experiments were carried out at a reactor temperature of 800°K and catalyst residence time (9) of 30 seconds. Liquid and gaseous products were analyzed with gas chromatographs. Carbonaceous deposit on the catalyst was analyzed by Carbon Determinator WR-12 (Leco Corp., St. Joseph, MI). The Weight Hourly Space Velocity (WHSV) was varied at constant catalyst contact time to generate selectivity data of various products as a function of conversion. For certain experiments, conversion was also varied by varying the catalyst pretreatment conditions. 

At typical catalyst temperatures of 800°C to 940°C, nitric oxide (NO) is thermodynamically unstable and slowly decomposes into nitrogen and oxygen. Decomposition losses are minimized by avoiding excessive catalyst contact time and by rapidly cooling the gases as they exit the converter. To achieve ammonia conversions of 93% to 98% the catalyst contact time must be as short as 0.0010 to 0.0001 seconds104. 

Figure 6. Variation of the normalized hydrocarbon product distribution as a function of catalyst contact time at 350 °C at a fixed [H2OMC2H2] of 0.6 and added He to vary the total VHSV.

The hydrodenitrogenation activity for both, mono- as well as bidispersed, decreased significantly within 100-150 hr of oil-catalyst contact time. Carbonaceous depositions seem to be the primary cause for catalyst activity decay. 

The Microsimulation test (MST). Modification of the operating procedure and experimental conditions of a convential micro activity test (MAT) has led to the so-called microsimulation test (MST, see Figure 3). Basically, the reactor is a fixed bed with transient operation during the catalyst contact time. A complete description of the operation and design of the MST reactor is given by O Connor in (11). Table I gives an overview of the main differences between the MR and the MST. 

X = number of lb moles of SO, converted in t sec of catalyst contact time per cubic foot of initial gas... 

As in the US, member nations of the European Community will introduce further specifications for transportation fuels over the next few years. Besides other components, the sulfur content of transportation fuels and gasoline in particular will be limited.FCC gasoline can contribute up to 90% of the sulfur in the gasoline pool. The parameters thatcontrol the sulfur levels in gasoline have been described by various authors in the past. The main determinant of sulfur levels in the FCC gasoline is the feedstock. Researchers found that the reactions that converted the feed sulfur compounds in the FCCU were kinetically controlled and were dominated more by catalyst contact time than by catalyst-to-oil ratio [1]. 

Another measure of the efficiency of ammonia conversion is the space velocity which may be used. Space velocity refers to the volume of reactants fed to a reactor per hour, divided by the volume of the reactor. For liquid reaction streams this relationship is straightforward. For gases, however, the space velocity is defined as being the volume of gases corrected to 0°C and 760 mm Hg (1 atm) passing through the reactor (or catalyst) volume/hour. This amounts to a measure of the gas-catalyst contact time for heterogeneous reaction (Eq. 11.7). 

A space velocity of 5,000 hr (corrected to 0°C, 760 mm) corresponds to a gas exchange rate in the catalyst space of 132.4 m of gas/cubic meter of catalyst space/hour at operating conditions (450°C, 100 atm Eq. 11.8), or an actual gas-catalyst contact time of about 27 sec. Increasing the space velocity simultaneously decreases the gas-catalyst contact time and the percentage of nitrogen and hydrogen converted to ammonia. 

Assuming ideal gas behavior what would be the gas-catalyst contact time (seconds) for a space velocity of 5000 hr and a gas mixture at ... 

There has been eonsiderable recent interest in partial oxidation of alkanes for new routes to chemical synthesis from light alkanes, and this research has been summarized extensively[l-3]. While much of this research uses dilution and low flow rates to attain temperatures between 200 and 600°C, another mode of operation involves very short contact times with no dilution to increase the temperature to -1000°C and decrease the catalyst contact time to 1 milUsecond. Recent research with millisecond adiabatic reactors have been carried out by Green et al[4], Lunsford et al[5], Choudhary et al[6], and many other research groups. 

Figure 2. Conversions and selectivities to CO and H2 over Pt (right) and Rh (left) on a-alumina monolith catalysts at atmospheric pressure at catalyst contact times of -1 millisecond.

Chemical oxidation with hydrogen peroxide involves optimization of several controlling variables i.e. pH, catalyst, contact time, application rate and reactivity of compounds (74). 

Figure 1.7 Radial profiles of temperature gradient in a reaction zone AT for 1, 2 - 0.045 m /s 3, 4 - 0.01 m /s for different monomer-catalyst contact times 1,...

On the other hand, the author believes that from the view of dynamics, the ammonia synthesis pressure is determined by the volume of catalyst (contact time) i.e., the loss in the equilibrium of ammonia concentration caused by decreasing... 

The selectivity kinetics describe the rates of production of the chemical species relative to the rate of production of a reference coit5>ound. The activity kinetics modify the selectivity kinetics to describe the absolute rate of production of each chemical species on a "realtime" or actucil catalyst contact time basis. 

The left-hand side integration limit, Tf in equation 7, is the selectivity time at the end of the catalyst bed, v = 1. Since the selectivity time is the result of the independent veiri-edile transformation represented by equation 4, it does not have physical meaning in the sense of catalyst contact time. The selectivity time can only be found by employing the predetermined selectivity kinetics. Xf is determined by a trial and error matching of the selectivity solution from equation 6 to experimental yields at the outlet of the catalyst bed. That is, a value of Xf is converged on when the 05" yield (methane to pentane, inclusive) as predicted by equation 6 agrees with the... 

As in all heterogeneous catalytic processes, the rate of each step will change with the type of catalyst, contact time, temperature, etc. 

The parent rectorite is essentially inactive. Table 2. However, after reacting with Chlorhydrol and calcination in air at 400°C/10h, a pillared product with cracking activity typical of zeolitic fluid cracking catalyst (FCC) and of similarly pillared montmorillonites is obtained. Tables 2,3. The mica-like particles have a bulk density that is less than 502 that of ACH-bentonite granules with similar size, Table 2. Thus, for a given cat/oil ratio longer oil-catalyst contact times are obtained when cracking gas oils at MAT... 

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