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A Rotating Adsorber for Multistage Cyclic Processes: Principle and Experimental Demonstration in the Separation of Paraffins Igor V. Babich,* A. Dick van Langeveld, Weidong Zhu, Wridzer J. W. Bakker, and Jacob A. Moulijn Delft ChemTech, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
A rotating adsorber, which combines different steps of a cyclic separation process into a single unit, is described. Its design provides for the simultaneous exposure of the various tubular adsorbers of the rotor to the different steps of the process, thus ensuring a continuous operation. The separation of normal and branched paraffins over zeolite 5A is used as a model process to illustrate the experimental performance of the adsorber in comparison to that of a fixed-bed adsorber. Equilibrium adsorption data for n- and i-butane individually were used to determine the optimal experimental conditions. The distribution of the tubular adsorbers over the different sections of the rotating adsorber was based on fixed-bed experiments. Under the experimental conditions chosen, the effluents of the uptake and regeneration sections of the rotating adsorber have a constant composition, containing only i- and n-butane, respectively. The rotating adsorber shows a long-term continuous high efficiency of separation. Introduction Many industrially important processes involving the separation or purification of gas streams require a multistage cyclic operation of the adsorption column(s) that includes at least a sorption and a desorption step. Good examples are the separation of normal and branched paraffins by zeolite 5A1,2 and the regenerative removal of H2S,3-5 SO2,6 and CO27,8 from gas streams by solid sorbents. In the latter cases, the processes are chemical reactions rather than conventional adsorption/ desorption steps. For example, regenerative H2S removal can be based on the following chemical reaction scheme:5
H2S + MnO/Al2O3 f H2O + MnS/Al2O3
(1)
H2O + MnS/Al2O3 f H2S + MnO/Al2O3
(2)
Hence, this process could better be referred to as reactive adsorption. In the production of chemicals, similar process schemes can be considered, e.g., the oxidative dehydrogenation of propane9
C3H8 + cat-O f C3H6 + H2O + cat-*
(3)
cat-* + 0.5 O2 f cat-O
(4)
where cat-O and cat-* refer to oxygen-covered and free sites on the catalyst surface, respectively. All of the above-mentioned processes have in common that the sorbent/catalyst is brought back to its initial state by a regeneration step. To transfer the sorbent from one process step to the next, the conditions at which the adsorber operates (gas flow, pressure, temperature) have to be changed. For instance, the direction and/or composition of the inlet gas can be varied by valves. However, this may result in instabilities in the gas flows, even if a sequence of several adsorbers is * Corresponding author. E-mail:
[email protected]. Fax/Tel.: 31-15-2784452/31-15-2784316.
Figure 1. Schematic diagram of principle of the rotating adsorber. The purge gas is not shown.
used. Novel concepts in experimental setups might circumvent these disadvantages. The integration of the various processes into a single reactor unit is a promising way to realize highly efficient technologies.10 Thus, effective rotary concentrators for the treatment of exhaust air streams containing VOCs (volatile organic compounds) are designed for the continuous adsorption of VOCs from the air stream and discharge of clean air.11,12 Such concentrators are widely produced and sold all over the world [e.g., DEC Impianti Group (Italy); Seibu Giken Co., Ltd (Japan); Du¨rr Environmental, Inc. (U.S.); Waterlink (U.S.); etc.). Also, different types of continuously operated rotary catalytic reactors and sorption bed systems, in which catalyst (sorbent) is subsequently treated at different stages of the cycle process, are described.13-17 In this paper, we present the concept of a rotating adsorber for cyclic chemical processes, which require the regeneration of the sorbent/catalyst and illustrate its advantages over the widely used fixed-bed reactor. The separation of n- and i-butane was used as a model process, as the gas-phase separation of normal and branched paraffins by zeolites, e.g., in the so-called “IsoSiv process”, has been industrially applied since the late 1950s.1,2 2. Experimental Section 2.1. Operating Principle of the Rotating Adsorber. The rotating adsorber shown in Figure 1 is divided into “uptake” and “regeneration” sections separated by “purge” sections. For each section, a separate gas inlet and outlet are provided. Because of the continuous rotation, the sorbent loaded into the adsorber is sequentially exposed to uptake, purge, and
10.1021/ie000456p CCC: $20.00 © 2001 American Chemical Society Published on Web 12/06/2000
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Ind. Eng. Chem. Res., Vol. 40, No. 1, 2001 Table 1. Overview of the Flows and Number of Adsorbers in the Various Sections of the Rotating Adsorber section flow rate composition number of adsorber tubes
Figure 2. Design of the rotating adsorber.
regeneration stages. In the uptake stage, the gas mixture containing the adsorbate passes through the sorbent, and the adsorbate is removed by sorption. Thus, ideally, the outlet gas contains only the nonadsorbing components of the feed gas. Because the capacity of the sorbent is limited, it will become saturated over time. Before breakthrough occurs, the sorbent is transferred from the uptake section to the purge section by rotation of the adsorber. The main task of the purge section is to remove nonadsorbed components from the void volume of the adsorber to increase the purity of the outlet gas from the regeneration section. After purging is complete, the sorbent enters the regeneration section, in which the conditions (composition of the gas flow) are selected such that the adsorbate fully desorbs, thus restoring the capacity of the sorbent. In the subsequent purge stage, the regeneration gas is removed from the void volume of the adsorber, and the sorbent is ready to be used again in the uptake section. In this way, a continuous operation is realized. As for rotary concentrators,11,12 the flows through the uptake and regeneration sections were chosen to have an opposite direction, that is, the uptake and regeneration steps are operated in countercurrent mode. The time during which the sorbent is present in each of the adsorber sections can be adjusted by changing either the rotation speed or the relative size of the corresponding sections. 2.2. Adsorber Design. The design of the rotating adsorber is shown in Figure 2. It consists of the adsorber itself; the so-called rotor (1); and two gas-supply/ distribution plates (2), the so-called stators. The rotor is a ceramic cylinder (30 cm long, 7 cm i.d. and 15 cm o.d.) containing 12 parallel channels (1 cm in diameter) (3), which are filled with the sorbent during adsorber operation. The gas-supply plates (2) introduce the feed streams into the various sections of the adsorber and also provide for the exit of the gases. Four separate segments (4) in the gas-supply plates allow for four independent gas streams to flow from the inlet tubes (5) through the different sections, without any significant cross-interference. The gastightness of the gassupply plates and the rotor is ensured by high-quality polishing of the surfaces in contact, as well as by an additional compression with an external pressure plate (6). Rotation of the adsorber is achieved by a stepper motor (7) via a metal shaft (8), which comprises a mechanism for compensating for differences in thermal
uptake
purge
regeneration
200 cm3 min-1, 80 cm3 min-1, 120 cm3 min-1, 90% N2, 100% N2 100% N2 5% n-butane, 5% i-butane 4 2 6
expansion of the various parts and the frame of the setup. 2.3. Separation Experiments in the Rotating Adsorber. The sorption/desorption experiments were performed over Linde 5A zeolite pellets. About 12 g of Linde 5A zeolite (pellets size ) 3-5 mm), pretreated at 673 K in air, was placed into each tubular adsorber of the rotor. The adsorber was operated in a purge-swing adsorption cycle at constant temperature and total pressure. Regeneration of the sorbent was accomplished by an inert gas purge. The rotating adsorber is operated in a three-section mode, namely, uptake, purge, and regeneration. In principle, the 12 individual adsorbers can be distributed in several ways over the three processes. However, it should be taken into account that, usually, desorption of n-paraffins (regeneration stage) is slower than adsorption (uptake stage) under the same experimental conditions. To reach the same cycle time, the flow rate of the regeneration stage should be greater than that of the uptake.18 However, this results in a diluted effluent from the regeneration section. Alternatively, the time during which the sorbent is present in the regeneration cycle could be longer than that for the uptake section. This approach was used in our experiments. The flow rates and compositions of the feed, purge gas, and regeneration gas are listed in Table 1. The number of adsorbers present in each section is also included. The rotation rate was 0.25 rotation min-1. To ensure a good separation efficiency and to minimize the possibility of the decomposition of i-butane over zeolite 5A, the adsorber was operated at a total pressure of 1.013 × 105 Pa and a temperature 373 K. The compositions of the feed and the effluent gas were determined by GC (Chrompack CP-9001, equipped with CP-Sil-5 column and FID detector). The concentrations of i- and n-butane in the effluent of the uptake, purge, and regeneration sections were used to compare the efficiency of the rotating adsorber with that of the fixed-bed adsorber. 2.4. Equilibrium Adsorption Measurements. A Rupprecht & Patashnick TEOM 1500 pulse mass analyzer was used to measure the equilibrium and transient adsorptions of n-butane and i-butane in Linde 5A zeolite pellets. A detailed description of the TEOM apparatus, its operating principle, and its performance in so-called reference experiments are given elsewhere.19 About 25 mg of the zeolite 5A pellets was crushed and sieved for a particle size of 125-250 µm; it was then loaded into the sample holder. Quartz wool was used at the top and bottom of the sample bed to keep the particles firmly packed, which is essential for a stable measurement. Prior to the experiments, the zeolite was pretreated in the following way: After a temperature rise at a rate of 10 K min-1 in a helium flow of 200 cm3 min-1, the sample was heated at 573 K for 24 h in order to remove adsorbed impurities. Then, three isotherms
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Figure 3. Adsorption isotherms of n-butane in Linde 5A pellets and their corresponding fits with the Langmuir model. Table 2. Fitting Parameters Derived from Experimental Data for n-Butane Adsorption Using the Langmuir Model T (K)
adsorption capacity, qsat (mol/kg)
equilibrium constant, Kc (100 kPa)-1
Henry’s constant, KH [mol kg-1 (100 kPa)-1]
303 338 373
1.42 1.21 0.95
282 81 29
405 99.5 27.6
were obtained by a stepwise increase of the partial pressure of the feed gas at sample temperatures between 303 and 373 K. A mixture of helium and the adsorbate gas was used to create partial pressures of the adsorbate of up to 1.013 × 105 Pa. Most experiments were repeated, and both adsorption and desorption experiments were performed to confirm reversibility. Ultrahigh purity helium (>99.999%), n-butane, and i-butane (>99.95%) were used. 2.5. Separation Experiments in the Fixed-Bed Reactor. Some separation experiments were performed in a fixed-bed reactor (1 cm diameter, 20 cm length) loaded with 10 g of 5A zeolite pellets pretreated at 673 K in air. The fixed-bed reactor operated in a purgeswing adsorption cycle at the same temperature and total pressure as the rotating adsorber. In each step of the fixed-bed reactor operation, the total gas flow was 100 cm3 min-1. The feed of the adsorption section consisted of 5 vol % n-butane and 5 vol % i-butane with the balance N2. Pure nitrogen was used for the purge and regeneration steps. 3. Results and Discussion 3.1. Equilibrium Adsorption Measurements (TEOM Results). The adsorption isotherms of n-butane in Linde 5A zeolite pellets are shown in Figure 3. The observed isotherms are qualitatively in good agreement with earlier published results20-22 and exhibit a Langmuir form (isotherm of type 1, according to the Brunnauer classification23) over the temperature and pressure range studied. All isotherms of n-butane were found to be reversible. The data of n-butane have been fitted by different adsorption isotherms, including those of Langmuir, Dubinin, Virial, and To`th. Of these, the Langmuir model describes the experimental data best over the whole range measured (Figure 3). For engineering purposes, the Langmuir isotherm is quite attractive because of its simplicity. The fitting parameters such as adsorption capacity, equilibrium constant, and Henry constants, are listed in Table 2. The saturation capacity of nbutane decreases with increasing temperature from 1.42
mol/kg at 303 K to 0.95 mol/kg at 373 K, in fair agreement with the data presented by Ruthven and Lounghlin.20 The slightly lower n-butane adsorption capacity found by us can be explained by the different type of zeolite 5A pellets used. Linde 5A zeolite pellets are produced by agglomeration of the crystals in the presence of a binder, followed by mechanical treatments such as extrusion, granulation, etc. As a consequence, the amount of binder may vary between the various batches. The isosteric heat of adsorption at zero coverage derived from the isotherms is 45.6 kJ/mol, which nicely corresponds to the data presented in the literature.21,24 It is difficult to obtain accurate and reproducible adsorption data for i-butane in zeolite 5A pellets, because the equilibrium uptake of i-butane takes much longer than that of n-butane. Under the same conditions, the amount of adsorbed i-butane is much lower than the amount of n-butane. Thus, it can be rationalized that, under our experimental conditions, i-butane is essentially not adsorbed in the cavities of zeolite 5A. To the best of our knowledge, equilibrium adsorption data for i-butane in zeolite 5A pellets are not present in the literature. It was only mentioned by Breck et al. that a very small amount of i-butane, as compared to n-butane, could be adsorbed in zeolite 5A.25 The higher selectivity for n-butane over i-butane in zeolite 5A can be understood from its pore structure, which has a free entry of about 0.45 nm.25 Hence, linear alkanes such as n-butane, whose cross-sectional diameter is ca. 0.42 nm, can enter the pores. In contrast, branched alkanes with cross sections larger than 0.45 nm, like i-butane, cannot enter the pore system of zeolite 5A. The small amount of i-butane adsorbed in Linde 5A pellets is probably due to adsorption in mesopores present because of the binder. Moreover, it has been observed that the adsorption of i-butane is irreversible because of its decomposition even at a temperature as low as of 373 K. After the adsorption procedure, the color of the spent pellets, which were desorbed at 473 K for 2 h, changed to gray. Probably, this was caused by coke formation due to the catalytic cracking by acid sites in the zeolite 5A pellets. Therefore, the adsorption data of i-butane are not presented. 3.2. Fixed-Bed Experiments. To study the separation efficiency of the zeolite 5A pellets at 373 K, uptake and regeneration runs were performed in the fixed-bed adsorber. Figure 4a shows the data for the separation experiment at 373 K with a gas mixture of n-butane, i-butane and nitrogen (the partial pressure of each of the butane isomers was equal to 5 × 103 Pa). The normalized outlet partial pressure of i-butane in the effluent of the fixed-bed adsorber during the uptake step is constant and equal to that in the feed. The normalized outlet partial pressure vs time profile of n-butane is that of a typical breakthrough curve with a diffuse adsorption front, the shape of which is determined by the process conditions such as flow rate, gas-phase composition, temperature, mass and heat transfer rates, and kinetics (Figure 4a). At the beginning of the uptake step, all n-butane entering the adsorber is adsorbed, and the effluent contains only i-butane. In time, the sorbent becomes saturated with n-butane, which results in an increasing partial pressure of n-butane in the effluent. Under the given experimental conditions, the breakthrough time is normally determined by the capacity,
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Figure 5. Distribution of the tubular adsorbers over different sections of the rotating adorber during one cycle of the process. τ* ) t/Tcycle - normalized process time.
Figure 4. Separation of n-butane and i-butane in the fixed-bed reactor: (a) normalized outlet partial pressure in the effluent during the uptake step and (b) partial pressure of i-butane and n-butane in the effluent during the regeneration step. The solid lines are fitting results.
for instance, the amount of the sorbent loaded into the reactor. The adsorption process can continue up to the moment that the criteria for the purity of the effluent gas are reached. Usually, only a limited part of the packed bed is used effectively. In our fixed-bed experiment, only 60% of the sorbent can be used to reach sufficient separation of n- and i-butane (purity of the effluent gas above 95%). Then, the separation process has to be stopped, and the sorbent must be regenerated. Before that, the gas phase in the void volume has to be purged. As a result, i-butane is quickly removed from the adsorber, and its partial pressure in the effluent drops rapidly. These fast changes cannot be followed by the analytical technique that we applied. The i-butane partial pressure measured after about 3 min of purging equals that of the i-butane impurities of in n-butane. Because nitrogen is used as the purge gas, the desorption of n-butane begins simultaneously with the replacement of i-butane in the void volume. To avoid excessive loss of n-butane, the purge time should be short, just long enough to replace the gas phase in the adsorber void volume. As expected, the desorption of n-butane in the fixedbed setup (Figure 4b) is characterized by a transient concentration profile that makes it difficult to utilize the effluent flow without additional treatment. In particular, the last fraction of the adsorbed n-butane is removed slowly. One can see that regeneration of the sorbent takes significantly longer than the uptake process. In related work, a factor of 2 is chosen.18 In this work, such a factor is observed also (Figure 4b). 3.3. Rotating Adsorber Experiments. In the current separation experiments the rotating adsorber is
used in a three-section mode, including uptake, purge, and regeneration. An additional purge section between the regeneration and uptake sections is not necessary as regeneration gas in the void volume of the adsorber consists of pure nitrogen and some desorbed n-butane. The latter does not influence the sorbent ability in the uptake process significantly, nor does it affect the purity of the effluent from uptake section because of the countercurrent operation of the rotating adsorber. The distribution of the tubular adsorbers over the different sections of the rotating adsorber is dictated by some boundary conditions. First, the sorbent capacity should be used as completely as possible. Second, breakthrough of n-butane from the uptake section must be avoided. To attain an effective long and stable operation of the adsorber, the amount of n-butane that enters the uptake section should be equal to the amount of n-butane desorbed in the purge and regeneration sections. As mentioned above, the desorption time was chosen to be twice that of the adsorption step at the same gas flow. Therefore, the amount of tubular adsorbers assigned to the purge and regeneration sections was selected to be twice that of the uptake section. The flow rate through the various sections of the rotating adsorber was chosen rather arbitrarily under requirement of equal gas flow through the uptake section and the purge and regeneration sections. It is clear that gas flow through the purge section should be just enough to replace the void volume in the tubular adsorber during its presence in the purge section. To provide a continuous flow in the purge section, at least two tubular adsorbers should be assigned to it. Because a total of 12 tubular adsorbers were available, the sorbent was treated in the purge section for 1/6 of the full rotation time. Treatment in the regeneration and uptake sections lasted for 1/2 and 1/3 of a full rotation, respectively. Figure 5 illustrates how the adsorbers travel through the different sections of the rotating adsorber during one cycle of the process. The normalized outlet partial pressures of n-butane and i-butane in the effluent of the uptake section vs time are shown in Figure 6a. As can be seen, the i-butane partial pressure in the effluent is very close to that in the initial flow. In contrast, the n-butane partial pressure in the effluent is almost zero during a 220-h run. The performance is much better than that of the fixedbed reactor loaded with the same amount of the sorbent. This means that essentially all of the n-butane entering the uptake section is adsorbed by the sorbent, and a significant breakthrough is not observed because the
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Figure 7. Experimental recovery of the isomers in the rotating adsorber.
recycled without any additional treatments to the uptake section. The purpose of the regeneration section is to restore the ability of the sorbent to adsorb n-butane in the uptake section. As i-butane is not adsorbed by the sorbent and it was removed from the void volume of the adsorber, its concentration in the effluent from the regeneration section is very low and does not exceed the impurity level. The partial pressure of n-butane in the effluent of the regeneration section of the rotating adsorber is constant and relatively high (Figure 6c). When the tube with regenerated sorbent leaves the regeneration section, the next adsorber tube with a saturated sorbent replaces it. In this way, the timeaverage loading of the sorbent with n-butane, present in the regeneration section, is constant. This results in a constant desorption rate and, as a consequence, a constant n-butane partial pressure in the effluent of the regeneration section. The efficiency of the rotating adsorber can be assessed in terms of the n-butane and i-butane recoveries, which can be defined as
n-butane recovery ) n-butane flow leaving the regeneration section (5) n-butane entering the system Figure 6. Separation of a n-butane/i-butane mixture in the rotating adsorber: (a) normalized outlet partial pressures in the effluent from the uptake section, (b) partial pressures of i-butane and n-butane in the effluent of the purge section, and (c) partial pressures of i-butane and n-butane in the effluent of the regeneration section.
sorbent capacity is constantly restored in the regeneration section. During the purge treatment, the gas phase of the void volume of each channel has to be replaced to produce a pure n-butane stream under the regeneration treatment. To minimize the loss of i- and n-butane during the purge, the operation of the rotating adsorber is adjusted in such a way that, because of continuous rotation, the tube is removed from the purge section just after the gas phase in its void volume is replaced. Instead, a new tube containing i-butane in the void volume enters in the purge section (see Figure 5). This results in an almost constant i-butane partial pressure in the effluent (Figure 6b). The presence of small amounts of n-butane in the effluent is caused by its desorption during purging. Because the composition of the effluent of the purge section is constant, it can be
i-butane recovery ) i-butane leaving the uptake section (6) i-butane entering the system Figure 7 presents the results of the experimental determination of the product recoveries during the process. For the chosen experimental conditions, the recoveries of n-butane and i-butane in the rotating adsorber are constant within the experiment time and about 60% for n-butane and 80% for i-butane. These value are relatively high and are achieved at high purity of the effluent streams of the uptake and regeneration section (see Figure 6a,c, normalized outlet partial pressure profiles of n-butane and i-butane, respectively). The main loss of the isomers occurs during the sorbent treatment in the purge section. To avoid this, the effluent of the purge section can be recycled to the uptake section. This option was not tested during the current experiments. The observed variations in the n-butane and i-butane partial pressures in the purge and regeneration sections [about 10% for i-butane and about 15% for n-butane (Figure 6b,c)] are connected with the current design of the rotating adsorber. Because it consists of 12 tubular adsorbers, the sorbent exchange between sections occurs
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in a stepwise mode. After replacement of one tubular adsorber by another, the adsorbers are present in the section during 1/12 of the cycle time (see Figure 5). A “fresh” tubular adsorber at the beginning produces a higher amount of n-butane/i-butane or n-butane in the purge or regeneration section, respectively. As experimental points were measured randomly within the cycle time (Figure 6), the measured values of the n-butane and i-butane partial pressures reflect this phenomenon as data scatter. This is more obvious for the purge section in which only two tubular adsorbers are present and replacement one of them has a big influence on the paraffin’s concentration in the effluent flow. Ideally, a stable composition of the effluent can be achieved only for a rotating adsorber in which a small amount of the sorbent in each section is constantly replaced by the same amount of the sorbent treated in the previous section. For the current design of the rotating adsorber, we have used a ceramic material, namely, aluminum oxide, because in comparison with other construction materials such as stainless steel, metals alloys, and coated alloys, it is more suitable for high-temperature applications and corrosive gas environments. First, ceramics typically have high-temperature stability and long-term corrosion and wear resistance. Second, if the moving parts are made of a ceramic, no additional lubricant or sealing material is needed to make the rotating adsorber gastight. Polishing the surfaces that are in contact to a roughness of less than 0.2 µm appears to be enough to avoid internal gas leakage from one section to another or from the sections to the outside of the adsorber. The current results show that n-butane and i-butane are, within limits of detection, not observed in the effluent of uptake and regeneration section, respectively (Figure 6a,b), although the inlets of the uptake and regeneration sections are adjacent to the outlets of the regeneration and uptake sections, respectively, and are separated only by a ceramic wall of about 10 mm in the gas-supply plates. This means that the total internal leak rate from one section to another is better than 10-3 Pa m3 s-1, which corresponds to quite good sealing between the different sections of the adsorber. To demonstrate the gastightness of the rotating adsorber some test experiments with pure nitrogen as an inlet gas were performed. It was found that the leak rate outside of the adsorber does not exceed 5×10-3 Pa m3 s-1, in good agreement with the internal leak rate. If the rotating adsorber is to be used at high pressure, a better polishing, as well as a higher pressure between the pressure and distribution plates, could be applied to avoid leakage. Another option is to mount the rotating adsorber in a pressurized vessel, which will also reduce the mechanical requirements on the construction. The presented example of the rotating adsorber operation illustrates its efficiency under the applied experimental conditions. It is clear that the operating conditionssgas composition and flow rate of the feed into each section, distribution of the adsorber tubes over the sections, and rotation speedsmust be optimized using a mathematical simulation. A mathematical model, in which equilibrium adsorption data and the data of fixed-bed experiments are used as a background, is currently under development. Because of its high chemical and thermal stability, the rotating adsorber technology is also very promising for other processes. It could be applied, for instance, in
the high-temperature purification of the effluent of a gasifier. The thermodynamic prerequisite is, however, that the uptake and regeneration processes occur at the same temperature. In this respect, the regenerative capture of H2S by a manganese-containing sorbent should be mentioned.5 In this case, uptake and regeneration can be carried out isothermally at about 1123 K, and regeneration could be done with steam, SO2, SO2/ O2, or O2. Other applications are the selective conversion of CH4 to H2 and CO over CeO226 or the regenerative capture of CO2 by calcium-based sorbents.7,8 For each of these processes, the operation of the rotating adsorber has to be modeled, and optimal conditions have to be determined from basic data such as thermodynamic calculations and equilibrium adsorption data. Conclusions The rotating adsorber loaded with a sorbent is an attractive option for the separation and/or purification of gas mixtures. Its high efficiency is demonstrated in the separation of butane isomers. The experimental conditions of the separation process were evaluated from the equilibrium adsorption data for n- and i-butane individually , and the distribution of the tubular adsorbers over the different sections of the rotating adsorber was based on fixed-bed experiments. As compared to the usually applied fixed-bed adsorber, the rotating adsorber has a number of advantages. First, it ensures a long-time continuous operation with a high separation efficiency. Second, it provides a constant composition of the effluent, which simplifies downstream processing. The ceramic used as the construction material for the rotating adsorber looks very promising from the viewpoint of high-temperature resistance and gastightness without the use of lubricants or sealing materials. The rotating adsorber is also attractive for cyclic chemical processes such as regenerative sorption removal of H2S, CO2, and various cyclic catalytic processes provided that all processes are thermodynamically feasible at the same temperature. Acknowledgment This work was financed in part by the European Commission (INCO-COPERNICUS Project IC15-CT980505). Literature Cited (1) Cusher, N. A. UOP IsoSiv Process. In Handbook of Petroleum Refining Processes; Meyers, R. A., Ed.; McGraw-Hill: New York, 1997; p 10.61-10.66. (2) Raghuram, S.; Wilcher, S. A. The Separation of n-Paraffins from Paraffin Mixtures. Sep. Sci. Technol. 1992, 27 (14), 19171954. (3) Elseviers, W. F.; Verelst, H. Transition Metal Oxides for Hot Gas Desulphurisation. Fuel 1999, 78, 601-612. (4) Liang, B.; Korbee, R.; Gerritsen, A. W.; van den Bleek, C. M. Effect of Manganese Content on the Properties of HighTemperature Regenerative H2S Acceptor. Fuel 1999, 78, 319-325. (5) Bakker, W. J. W.; Vriesendorp, M.; Kapteijn, F.; Moulijn, J. A. Sorbent Development for Continious Regenerative H2S Removal in a Rotating Monolith Reactor. Can. J. Chem. Eng. 1996, 74, 713-718. (6) Zeng, Y.; Zhang, S.; Groves, F. R.; Harrison, D. P. HighTemperature Gas Desulfurization with Elemental Sulfur Production. Chem. Eng. Sci. 1999, 54, 3007-3017. (7) Babich, I. V.; van Langeveld, A. D.; Moulijn, J. A. Regenerative CO2 Capture from Gas Streams at High Temperature. In
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Received for review May 4, 2000 Revised manuscript received September 18, 2000 Accepted October 4, 2000 IE000456P
