Two-stage reactor

ABB Lummus s RTD consists of a two-stage reactor cyclone system (see Figure 9-2). The riser cyclones (the first stage) are hard-piped to the riser. Attached to the end of each riser cyclone dipleg is a conventional trickle valve as shown in Figure 9-3. Each trickle valve has a small opening to prevent catalyst defluidization, which can be a problem, especially during start-ups. 

Consider a fixed-bed catalytic reactor (FBCR), with axial flow, for the dehydrogenation of ethylbenzene (A) to styrene (S) (monomer). From the data given below, calculate the amount of catalyst required, W/kg, to reach a fractional conversion (fA) of 0.2 in the (adiabatic) first stage (of a two-stage reactor). What is the temperature at this point ... 

At this point there arises the question of whether the two tanks should be the same size or of different sizes. Mathematically, this question needs to be investigated with some care so that the desired objective function is correctly identified. If we wished to design a two-stage reactor we might be interested in the minimum total volume K = K, + K2 required for a given conversion a2. Writing the ratio VJ Vc[ = s, this condition is met by setting ... 

Still another multi-reactor approach is to divide the MTG reaction into two steps as shown in Figure 7. In the first step, methanol is partially dehydrated to form an equilibrium mixture of methanol, dimethyl ether and water over a dehydration catalyst. About 15% of the reaction heat is released in this first step. In the second step, this equilibrium mixture is converted to hydrocarbons and water over ZSM-5 catalyst with the concomitant release of about 85% of the reaction heat. Though this two step approach does not have any of the inherent complications of the previously mentioned multibed reaction systems, it leaves one with a substantial amount of the reaction heat (85%) still to be taken over one catalyst bed. This requires a fairly high recycle stream to moderate the temperature rise over the second reactor. Such a high recycle design would require careful engineering in order to transfer heat efficiently from the reactor effluent to the recycle gas and reactor feed. However, this two stage reactor system is the simplest of the fixed-bed systems to develop. 

DAP solutions have a high partial pressure of ammonia, and the reaction is normally carried out in a two-stage reactor system with feed acid passing countercurrent to the flow of ammonia gas. Incoming acid reacts in the scrubber with ammonia from the main reactor and may also serve as a scrubber for dryer off-gases238. 

The combination of a second unit in peroxidase reactors may be helpful in different situations, depending on the nature of the substrate to be treated. For instance, a two-stage reactor system for the continuous decolorization of direct dyes was used [44]. The first unit consisted on a fixed bed reactor connected to a second column of activated silica, which helped in the adsorption of toxic reactive species, therefore reducing the biotoxicity of the effluent. The same system was applied for the decolorization of textile effluents and was capable of decolorizing 40% effluent even after 2 months of continuous operation [45]. 

Description The Uhde (Edeleanu) technology features a two-stage reactor system of which the first reactor is operated in the recycle mode. With this method, a slight expansion of the catalyst bed is achieved that ensures very uniform concentration profiles in the reactor and, most important, avoids hot spot formation. Undesired side reactions, such as the formation of di-ethyl ether (DEE), are minimized. 

Lion Corporation of Japan developed a continuous transesterification process using unrefined feedstock known as the ES process. The free fatty acid in the oil is pre-esterified by passing the feedstock and methanol through a packed column of a special catalyst resin, after which transesterification is conducted through a two-stage reactor. A high conversion rate of more than 99% is claimed (16). 

Figure 5. Lower olefins and gasohne synthesis using two-stage reactor system [41]...

Rh-Ce catalyst exhibited a high ethanol conversion over 95% and high selectivity to H2 and CO in a very short residence time of <10ms under autothermal condition. Increasing steam/carbon ratio increased the H2 yield due to the participation of WGS reaction. The POE and WGS reactions were also performed in a two-stage reactor. 

Comparison of a Two-Stage Reactor and a Single Reactor for the Synthesis of Isoparaffin-Rich Gasoline from Propylene... 

Figure 2. Synthesis of isoparaffins in the gasoline range from propylene using a two-stage reactor at a much higher flow rate, (propylene GHSV= 5000 h other reaction conditions as in Figure lb).

The notion of gas or melt kinetic studies, free from diflfusional restrictions, is attractive, but experiments by Briggs et al show that if the composition of the feed to the second stage of a two-stage reactor system is cycled the catalyst will absorb sulphur trioxide over a period of several minutes, and this sulphur trioxide can be desorbed by blowing air over the catalyst. It is also claimed by Unni that higher conversions are possible using periodic rather than steady-state operation, an observation which may have important industrial applications. 

Continuous stirred-tank reactors (CSTRs) have been routinely employed for producer gas fermentations. A two-stage reactor system has also been used to maximize ethanol production and minimize the formation of byproducts. Carbon monoxide and hydrogen conversions of 90% and 70%, respectively, were observed in the first reactor, while they were about 70% and 10% in the second reactor. High ethanol-to-acetate ratios were achieved by the use of such a dual reactor system. Bubble colunms are also commonly used for industrial fermentations. A comparative study was performed between a CSTR and a bubble column reactor for CO fermentation using Peptostreptococcus productus. Higher conversion rates of CO were observed with the bubble column without the use of any additional agitation. Producer gas fermentation with packed bubble colunms and trickle bed reactors has also been studied. The trickle bed reactor has a low pressure drop and liquid hold-up, and the conversion rates were the highest compared to CSTRs and bubble columns. 

Table II. Melt-Bulk Process Single vs. Two-Stage Reactor...

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