Conversion Countercurrent

A new countercurrent continuous centrifugal extractor developed in the former USSR (214) has the feature that mechanical seals are replaced by Hquid seals with the result that operation and maintenance are simplified the mechanical seals are an operating weak point in most centrifugal extractors. The operating units range between 400 and 1200 mm in diameter, and a capacity of 70 m /h has been reported in service. The extractors have been appHed in coke-oven refining (see Coal conversion processes), erythromycin production, lube oil refining, etc. 

The novel approach finally taken was to conduct the reaction and purification steps in a reactor-distillation column in which methyl acetate could be made with no additional purification steps and with no unconverted reactant streams. Since the reaction is reversible and equilibrium-limited, high conversion of one reactant can be achieved only with a large excess of the other. However, if the reacting mixture is allowed to flash, the conversion is increased by removal of the methyl acetate from the liquid phase. With the reactants flowing countercurrently in a sequence of... 

Performance of a simulated countercurrent moving bed reactor, SCMCR is experimentally investigated for oxidation of CO at low concentration in the absence of hydrogen over Pt/AljOs catelyst/adsorhent. The time-average conversion of CO obtained in the SCMBR was higher than the conversion of CO obtained from a conventional PBR for all over the tested range (period = 2-15 min). For the next step, the effects of operating variables on its performance are planed for both CO oxidation in the absence of H2 and Hz-rich gas system. 

A reactor for the oxidation of S02 is operated adiabatically with heat interchange between feed and product streams in countercurrent. Inlet concentrations are 10% each of S02 and 02 and the balance N2. Preheat temperature is to be 725 K, equilibrium is attained at the outlet and the conversion of S02 is 70%. Pressure is atmospheric. Find the temperatures of the feed and of the outlet. 

Another study was performed on a catalytic hydrogenation of 1,3,5-trimethyl-benzene to 1,3,4-trimethylcyclohexane, which is a typical first-order reversible reaction [168]. By optimizing various operating conditions it was possible to achieve a product purity of 96% and a reactant conversion of 0.83 compared to a thermodynamic equilibrium conversion of only 0.4. The results were successfully described with a mathematical model derived by the same authors [169]. Comparison to a real countercurrent moving bed chromatographic reactor yielded very similar results for both types [170]. 

Fig. 1. Process flow sheet for the continuous conversion of latex in a counterrotating, tangential twin-screw extruder as it might be arranged for the production of acrylonitrile-butadiene-styrene polymer (Nichols and Kheradi, 1982). Polystyrene (or styrene-acrylonitrile) melt is fed upstream of the reactor zone where the coagulation reaction takes place. Washing (countercurrent liquid-liquid extraction) and solids separation are conducted in zones immediately downstream of the reactor zone. The remainii zones are reserved for devolatilization and pumping.

The spreader stoker operated as a continuous system, with ash removal doors. The conversion concept corresponds to updraft-downfeed (countercurrent), moving bed. Secondary air (overfire air) entered at 42 inches above the grate. The overfire air ports were directed slightly downward (12°). 

This section presents a classification of conversion concepts (read section 0), described in the literature on PBC, for example, fuel-bed mode (batch or continuous) and fuel-bed configuration (cocurrent, countercurrent, crosscurrent). Some new conversion concepts, namely fuel-bed movement (fixed, moving and mixed) and fuel-bed composition (homogeneous, heterogeneous), are introduced by these authors, which makes this an extended classification compared with earlier classifications in literature [8,9,10,11], The classification is made in the context of the three-step model. The three-step model, see Figure 14 below, is a system theory, which places the theory of thermochemical conversion of solid fuels into the context of PBC. 

The classification is based on the different conversion concepts cited in the literature, such as fuel-bed mode (batch and continuous), fuel-bed configuration (cocurrent, countercurrent, and crosscurrent), and some new concepts presented by the author, such as fuel-bed movement (fixed, moving, and mixed) and fuel-bed composition (homogeneous and heterogeneuos). The classification resulted in 18 types of updraft conversion systems, according to Figure 32. Some of them are more or less hypothetical, while others are found in practice, see section B 3.4 below. 

According to the three-step model, proposed by the authors, a PBCS can be divided into three subsystems, namely a conversion system, combustion system, and boiler system. It is in the conversion system that the thermochemical conversion of the solid fuel takes place. The conversion system can be designed according to several conversion concepts. The conversion concept can be classified with respect to fuel-bed mode (batch and continuous), fuel-bed configuration (countercurrent, cocurrent and crosscurrent), fuel-bed composition (homogeneous and heterogeneous), and fuel-bed movement (fixed, moving and mixed). 

The Union Carbide Purox system (17) uses municipal solid waste as the feed. Shredded ferrous-free refuse enters the top of the conversion furnace and is contacted countercurrently with hot combustion gases from the reaction occurring in the hearth. 

MPa, corresponding to about 90% conversion, excess monomer is vented off to be recycled. Removal of residual monomer typically involves passing the reaction mixture through a countercurrent of steam. The reaction mixture is then cooled, and the polymer separated, dried in hot air at about 100°C, sieved to remove any oversized particles, and stored. Typical number-average molecular weights for commercial PVC are in the range 30,000-80,000. 

We can design a reactor to separate the products and achieve complete conversion by admitting pure A into the center of the tube with the sohd moving countercurrent to the carrier fluid. We adjust the flows such that A remains nearly stationary, product B flows backward, and product C flows forward. Thus we feed pure A into the reactor, withdraw pure B at one end, and withdraw pure C at the other end. We have thus (1) beat both thermodynamic equilibrium and (2) separated the two products from each other. 

As observed above, in order to quench HMF produced in situ, dealuminated H-form mordenites were investigated in a water/MIBK mixture (1/5) [84, 85]. In this case, a maximum conversion of fructose of 54% (along with 90% selectivity to HMF) was obtained over an H-mordenite with a Si/Al ratio of 11. HMF was continuously extracted with a flow of MIBK circulating in a countercurrent way through a catalytic heterogeneous reactor containing the H-mordenite zeolite. On the continuation of their efforts, the same authors then set up a new continuous solid-liquid-liquid reactor where the zeolite was now in suspension in the aqueous phase while the HMF was continuously extracted with MIBK in a countercurrent way to the aqueous phase and catalyst feed. 

Overhead from D-l is called the raffinate. It is washed countercurrently with water in D-4 for the recovery of the solvent, and then proceeds beyond the battery limits for further conversion to isoprene. Both wash columns operate at substantially atmospheric pressure and 100°F. The product streams are delivered to the battery limits at 100 psig. 

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