Catalyst bed temperatures

Combustible masking materials such as organic char may be partially or completely removed by periodic elevations of the catalyst bed temperature. Noncombustible masking materials may be removed by air lancing or aqueous washing generally with a leaching solution (20,21). 

In catalytic incineration, there are limitations concerning the effluent streams to be treated. Waste gases with organic compound contents higher than 20% of LET (lower explosion limit) are not suitable, as the heat content released in the oxidation process increases the catalyst bed temperature above 650 °C. This is normally the maximum permissible temperature to which a catalyst bed can be continuously exposed. The problem is solved by dilution-, this method increases the furnace volume and hence the investment and operation costs. Concentrations between 2% and 20% of LET are optimal, The catalytic incinerator is not recommended without prefiltration for waste gases containing particulate matter or liquids which cannot be vaporized. The waste gas must not contain catalyst poisons, such as phosphorus, arsenic, antimony, lead, zinc, mercury, tin, sulfur, or iron oxide.(see Table 1.3.111... 

The conventional experimental approach to obtaining kinetic data is rather awkward, and it involves varying space velocity as a means for simulating contact, or reaction, time. An alternate approach is to run adiabatic experiments and to obtain catalyst bed temperatures as well... 

The cold gas recycle (CGR) ratio values (Figure 4) are metered values and are more consistent than the HGR and total gas recycle ratio values which were calculated from gas analyses. Although the calculated total recycle gas flow rate was erratic, catalyst bed temperatures were uniform and easily controlled by varying recycle rate and bed inlet tem-... 

The steam reforming of naphthalene was conducted on the fixed bed of catalyst (bed temperature 1173 K, GHSV 3000h ). The detail of the experiment was described in previous papers [7, 8],... 

CO oxidation tests on Au supported on various metal oxides were undertaken at low CO concentrations, where the adiabatic temperature rise in the bed is negligible. Since CO oxidation is highly exothermic, when high CO concentrations are present in the feed 1%), and at high conversions, the adiabatic temperature rise in the catalyst bed due to the heat of reaction may be as high as 100 C. Therefore, it is important to monitor the catalyst bed temperature when high CO concentrations are present in the feed. 

Figure 6 Optimization of catalyst bed temperatures using on-line HPLC.

Parameters such as feed rate, catalyst bed temperature, and reaction pressure were optimized by use of the temporary on-line LC installation. Reactor upsets could also be monitored. Figure 10 demonstrates how continuous monitoring can aid in detection of an upset. Due to a problem with a level control valve, the reactor filled with liquid, preventing the reaction... 

Fig. 3. Time variation of the catalyst bed temperature and the relative S03 signal in the stream leaving the cycled bed for composition forcing of the final stage of a S02 converter with an air stream and effluent from the previous stage (a) half cycle with air feed, (b) half cycle with S03/S02 feed. Feed to the system contains 12.4 vol% S02, conversion in the first stage = 90% and t = 26 min, s = 0.5. (Figure adapted from Briggs etal., 1977, with permission, 1977 Elsevier Science Publishers.)...

Cycloversion A petroleum treatment process which combined catalytic reforming with hydrodesulfurization. The catalyst was bauxite. The process differed from the Houdry process in that the catalyst bed temperature was controlled by injecting an inert gas. Developed by the Phillips Petroleum Company and used in the United States in the 1940s. Pet. Refin., 1960, 39(9), 205. 

In entry 1 to 5 (table 2), the temperature of the oven was kept constant and the increase in the catalyst bed temperature from 241 to 255°C was caused by an exothermic reaction, presumably the formation of water and small amounts of C02 (max. 15 mol% at 255°C). However, increasing the amount of oxygen did lead to an increased yield of the diketone 2 even at lower temperatures (entry 6). 

Figure 3.16 Size effect of Au nanoparticles on the reaction of propylene with 02 and H2 catalyst, Au/Ti02 (P25) 0.5 g catalyst bed temperature, 353 l< feed gas, C3He/02/H2/Ar = 10 10 10 70 space velocity, 4000h-1 mLgca, 1 [121].

Figure 3.19 Propylene oxide (PO) yield as a function of the mean pore diameter of supports catalyst, 0.15 g catalyst bed temperature, 423 K feed gas, C3H6/02/H2/Ar — 10 10 10 70 space velocity, 4000h-1 ml gcat-1. Actual Au loading, about 0.3 wt% [122, 145, 146],...

In the catalyst bed, temperature gradients can develop, analogously to those in a particle. In the axial direction the conversion increases under reaction conditions, causing a temperature gradient. These temperature gradients should be kept as small as possible, otherwise the rate data may not have the value attributed to them. 

The ammonia converter is a demanding engineering and chemical engineering task. To calculate the parameters for the design, including dimensions and number of catalyst beds, temperature profiles, gas compositions, and pressure drop, a suitable mathematical model is required. 

When gum formation proceeds, the minimum temperature in the catalyst bed decreases with time. This could be explained by a shift in the reaction mechanism so more endothermic reaction steps are prevailing. The decrease in the bed temperature speeds up the deactivation by gum formation. This aspect of gum formation is also seen on the temperature profiles in Figure 9. Calculations with a heterogenous reactor model have shown that the decreasing minimum catalyst bed temperature could also be explained by a change of the effectiveness factors for the reactions. The radial poisoning profiles in the catalyst pellets influence the complex interaction between pore diffusion and reaction rates and this results in a shift in the overall balance between endothermic and exothermic reactions. 

Catalyst Activity. Fig. 3 shows the results of the catalyst activity test. The reaction was carried out at standard conditions consisting of a mean catalyst bed temperature of 538°C, atmospheric pressure and LHSV of 2h. The left graph indicates the results for conversion, total aromatics and BTX yields versus time on... 

The pyrolysis unit consisted of an insulated 316 stainless steel preheater tube (1.3 cm i.d. X 50 cm length) which extended 1 in. into a 316 stainless steel fixed bed tubular reactor (2.5 cm i.d. x 46 cm length), which was heated by a cylindrical block heater. Two type J (iron-constantan) thermocouple probes were used to both monitor the internal catalyst bed temperature and maintain a consistent reactor wall temperature in combination with a temperature controller, A syringe pump, condenser, vacuum adapter, receiving flask, nitrogen cylinder, and gas collection system were connected as shown in Fig uTe 2. The reactor midsection was packed with 40 g of activated alumina, which was held in place by a circular stainless steel screen. The preheater and reactor were operated at 180-190 and 450 C, respectively. The entire process remained at normal atmospheric pressure throughout the mn. 

The catalyst bed temperature increases in the direction of gas flow due to the WGS reaction exotherm. Typical temperature gradients in the bed are about 20-30°C. The lifetime and state of activity of the catalyst is conveniently monitored by the temperature profile through the adiabatic bed. As the reaction front moves through the bed when the catalyst ages, so does the temperature rise from the reaction (Fig. 3). 

Carbon monoxide oxidation by pure oxygen on a porous catalyst of the type CuO on A12Os was studied in a laboratory differential recycle reactor. Under certain experimental conditions sustained oscillations of the catalyst bed temperature and CO concentrations in the reactor described in article I of Eckert et al. were observed and reported in article II of the series. 

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