Gas-lift reactors

Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

Chiyoda and UOP jointly developed an improved methanol carbonyl-ation process on the basis of this supported rhodium complex catalyst the process is called the Acetica process. This process for the production of acetic acid has found several industrial applications in Asia. The process description emphasizes the use of a three-phase reactor, a bubble column, or gas-lift reactor. The reactor column contains a liquid, a solid catalyst, and a bubbling gas stream containing CO efficient dissolution of the gas in the liquid is ensured by the design, which minimizes gas-liquid mass transfer resistance. 

Ghirardini, M., Donati, G., and Rivetti, F. (1992), Gas lift reactors Hydrodynamics, mass transfer, and scale up, Chemical Engineering Science, 47(9-11) 2209-2214. 

Nontraditional types of fixed-bed reactors are begmning to be considered. A gas-lift reactor with monolith type catalyst packing has been described for FT synthesis [40]. It is reported that this reactor has been tested at the laboratory scale with a cobalt... 

Figure 4,12. Schematic diagrams of two types of gas lift reactors and of a venturi-loop reactor.

Bakke R, Trulear MG, Robinson JA, Characklis WG (1984) Activity of Pseudomonas aeruginosa in steady state biofilms. Biotechnol Bioeng 26 1418-1424 Beeftink HH, Staugaard P (1986) Structure and dynamics of anaerobic bacterial aggregates in a gas-lift reactor. Appl Environ Microbiol 52(5) 1139-1146 Beeftink HH (1987) Anaerobic bacterial aggregates variety and variation. University of Amsterdam, Amsterdam... 

Beeftink HH, van den Heuvel JC (1987) Novel anaerobic gas-lift reactor AGLR with retention of biomass, start-up routine and establishment of hold up. Biotechnol Bioeng 30(2) 233-238... 

This problem is solved in the reactor shown in Fig. 10.6. Ethylene and chlorine are introduced into circulating liquid dichloroethane. They dissolve and react to form more dichloroethane. No boiling takes place in the zone where the reactants are introduced or in the zone of reaction. As shown in Fig. 10.6, the reactor has a U-leg in which dichloroethane circulates as a result of gas lift and thermosyphon effects. Ethylene and chlorine are introduced at the bottom of the up-leg, which is under sufficient hydrostatic head to prevent boiling. 

Commercial chlorohydrin reactors are usually towers provided with a chlorine distributor plate at the bottom, an olefin distributor plate about half way up, a recirculation pipe to allow the chlorohydrin solution to be recycled from the top to the bottom of the tower, a water feed iato the recirculation pipe, an overflow pipe for the product solution, and an effluent gas takeoff (46). The propylene and chlorine feeds are controlled so that no free gaseous chlorine remains at the poiat where the propylene enters the tower. The gas lift effect of the feeds provides the energy for the recirculation of the reaction solution from the top of the tower. 

This process, according to the manufacturer,54 has been developed in such a way that space requirements are kept to a minimum. A BIOPAQ IC reactor is used as the initial step in the treatment process. The name of this anaerobic reactor is derived from the gas-lift driven internal circulation that is generated within a tall, cylindrical vessel. These reactors have been operational in the paper industry since 1996. The second step in the purification process is a mechanically mixed and aerated tank. The aerating injectors can be cleaned in a simple way without the need to empty the aeration tank. Potential scaling materials are combined into removable fine particles. At the same time, the materials that may cause an odor nuisance are oxidized into odorless components. The process can be completed by a third and a fourth step. The third step focuses on suspended solids recovery and removal. The fourth step is an additional water-softening step with lamella separation and continuous sand filters in order to produce fresh water substitute. The benefits claimed by the manufacturer are as follows54 ... 

Siegel, M. FL, Merchuk, J. C., and Schugerl, K., Air-Lift Reactor Analysis Interrelationships between Riser, Downcomer, and Gas-Liquid Separator Behavior, including Gas Recirculation Effects, AIChE J., 32 1585 (1986)... 

Schoutens, G. EL, Guit, R. P., Zieleman, G. J., Luyben, K. C. A. M., and Kossen, N. W. F., A Comparative Study of a Fluidised Bed Reactor and a Gas Lift Loop Reactor for the IBE Process Part I. Reactor Design and Scale Down Approach, J. Chem. Tech. Biotechnol., 36 335 (1986a)... 

The low-temperature process, as its name implies, operates at a relatively low temperature where the exothermic heat of the direct chlorination reaction is removed by cooling water. The natural circulation is driven by the gas lift effect of the gaseous feeds before solution and the density differences of a cooler leg that has a relatively higher liquid density than the reactor leg. 

Herri and coworkers (Fidel-Dufour et al., 2005) have developed a flow loop reactor (in Saint Etienne, France) operating at pressures of 1-10 MPa at 0-10°C. The flow section is 36.1 m long, 1.0 cm internal diameter, and has a constant slope of 4°. The unique feature of this flow loop is that the exit of the flow section is connected to a gas lift riser (10.6 m long and 1.7 cm internal diameter) in which gas coming from a separator located at the top of the column is re-injected. The gas lift is thereby able to move an emulsion or suspension slurry without any pump or mechanical system. 

After regeneration, the catalyst enters the first reactor at the top. It passes through the reactor by gravity and is then transferred from the bottom of each reactor to the top of the next by a gas-lift. To minimize the pressure drop across the bed, a cross-flow technology was adopted The catalyst flows downwards from the top of the reactor between two concentric cylinders made up of grids, this allowing the radial passage of the gas phase. 

The first moving-bed process employed countercurrent flow of catalyst and reactants in both vessels and used mechanical bucket elevators to transfer the catalyst from one vessel to the other. This process, originally developed by the Socony-Vacuum Oil Company, was named the Thermo-for Catalytic Cracking (TCC) process (239,295,339). Two major improvements were subsequently developed change from countercurrent to concurrent flow in the reactor (297,298) and substitution of a gas-lift system for transfer of catalyst. In the gas-lift system, the catalyst pellets are conveyed upward through a pipe, or pipes, by a stream of flue gas or air. 

Low coke concentration is desirable in order to maintain satisfactory activity in the reactor and to facilitate operation of the regenerator. Unfortunately, however, catalyst circulation in the TCC units was limited by the bucket elevators. This drawback was not overcome until the development of the gas-lift system for transporting catalyst, as adopted in the Houdriflow and air-lift TCC designs. 

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