Ind. Eng. Chem. Res. 2002, 41, 2529-2534
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GENERAL RESEARCH Experimental Methodology for Heterogeneous Studies in Pulping of Wood Ana P. V. Egas,* Joa˜ o P. F. Sima˜ o, Isabel M. M. Costa, Sandra C. P. Francisco, and Jose´ Almiro A. M. Castro† Department of Chemical Engineering, University of Coimbra, Polo II-Pinhal de Marrocos, 3030 Coimbra, Portugal
The heterogeneous nature of the kraft pulping of wood is experimentally demonstrated in this paper, and a new methodology for kraft pulping investigation is presented. The strategy proposed here enables the measurement of alkali and of lignin concentrations in the pulping liquor, both inside and outside of the wood chips. With this procedure, it is possible to independently determine, in both entrapped and free liquors, the time histories of the concentrations of alkali and lignin as well as total dissolved solids, which are a direct result of the mass transfer and of the chemical reactions that take place during this heterogeneous process. The influence of the chip thickness and of temperature on the relative rates of these two phenomena is also highlighted. This experimental methodology establishes the foundations for the development of a macroscopic heterogeneous kraft pulping model that can be experimentally validated in pulping conditions, even for modified digester processes. 1. Introduction The kraft pulping of wood is essentially based on the simultaneous occurrence of two phenomena: the first, of a physical nature, involves the mass transfer of the cooking chemicals (sodium hydroxide and sodium sulfide) from the bulk liquor surrounding the wood chips to the liquid filling the pores of the wood structure; and the second is related to the chemical reactions between these reactants, inside the chips, and the main wood components (i.e., lignin and carbohydrates). Because of the strong competition between them, it is of great importance for the understanding of the pulping process to quantify their behavior. The lack of experimental data on the alkali concentration in the liquor inside the chips during the kraft pulping of wood has led the majority of the investigators to neglect the heterogeneous nature of the process, trying to build homogeneous models in which the delignification rate is directly related to the conditions in the bulk liquor. In most of these studies and in all experimentally based kinetic models,1-7 the rate of delignification is calculated with respect to the concentration of alkali in the free liquor. This is only realistic if such concentration is the same as the concentration in the entrapped liquid, which requires no internal or external resistances to mass transfer of alkali to the chip. This is far from being true in the kraft pulping of wood. Furthermore, in a diffusion-controlled process such as this, the dynamics of these two liquid systems cannot be ne* To whom correspondence should be addressed. E-mail:
[email protected]. Phone: +351 239 798700. Fax: +351 239 798703. † Deceased.
glected, because they ultimately determine the alkali concentration inside the chips as a result of the competition between mass transfer and chemical reaction. The same happens with the diffusion of dissolved lignin from inside the chip to the bulk phase, as the delignification process takes place. The resistances of wood to mass transfer imply that the concentration of dissolved lignin in the bulk phase will be far lower than that in the liquor inside the chips. Nevertheless, some authors8-10 choose to estimate lignin content in the solid matrix of cooked chips as the difference between the content of lignin in the initial wood and the dissolved lignin in the free liquor. By doing this to determine the delignification rate of wood, the fraction of dissolved lignin that is contained in the entrapped liquor is not properly taken into account, leading to an underestimation of the delignification kinetics. Therefore, from this point of view, the use of high liquor-to-wood ratios (in the order of 50-100) in several delignification studies,1,6-8,11-13 to ensure that the chemical concentrations in the bulk liquor remain almost constant during the cooking, does not seem to be the best methodology. Such a measure does not ensure that the concentration in the liquor inside of the chips, where the reactions take place, remains constant (and equal to that in the bulk). This is because as lignin and carbohydrates in wood are consumed, their reaction rates vary; therefore, the total alkali consumption rate is also strongly affected. As a result of this, there might be important variations of the alkali concentration in the entrapped liquid that cannot be ignored. To pursue the goal of a real heterogeneous pulping model that can be experimentally validated, it is absolutely necessary to measure the alkali concentration in the entrapped liquor within the chips. Some techniques
10.1021/ie010534o CCC: $22.00 © 2002 American Chemical Society Published on Web 04/20/2002
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concerning the diffusion of alkali through wood chips were proposed in order to predict the entrapped liquor alkali profile across the chip. Talton and Cornell14 leached impregnated chips in a water bath and, measuring the resulting alkali concentration change in this bath, estimated the concentration in the liquid inside the chips. A similar method was also adopted by Hultholm et al.15 This method exhibits some disadvantages: first, the dilution of alkali in water makes the measurement of its concentration more difficult and inaccurate, particularly for short reaction times where the concentration is still low; moreover, this is a very time-consuming process (between 8 and 12 h), and as a consequence, it is difficult to avoid further consumption of alkali with the solid components of wood, thus leading to an underestimation of the concentration in the liquor inside the chips. The diffusion studies of McKibbins16 showed a slightly different method, in which samples of wood are taken out of the washing bath at specific times and analyzed for its residual sodium content. However, in this study, the adsorption of sodium in the cellulose fibers, as referred to in some studies (Rosen17 and Eriksson et al.18), is ignored, and the diffusion of sodium ions is assumed to replicate that of hydroxide ions. A third technique to measure diffusion through wood uses diffusion cells in which a chip is placed between two chambers, each filled with liquids of different concentrations of a given chemical. Usually, a chemical solution (sodium hydroxide) is placed in one chamber and water in the other where conductivity is measured online. This method was used by Robertsen and Lo¨nnberg19 and Hultholm et al.15 The problem with this technique is that it does not take into account the reactions that occur between the chemicals in the entrapped liquor and the solid components of the chip (more significant at high temperatures) as diffusion takes place and, therefore, underestimates the amount of chemical diffused into the water chamber. With these methods, the concentration of alkali in the entrapped liquor required to predict the pulping reaction rates can only be estimated using theoretical calculations, and this has never been experimentally validated. Although the direct measurement of the alkali concentration profile along the chip dominant dimension would be ideal for a more rigorous understanding of the mass transfer process in wood pulping, a macroscopic approach of the entrapped liquor phase would still be of significant interest to the characterization of mass transfer as well as chemical reaction kinetics. The objective of this paper is to propose and evaluate a new experimental methodology that complies with the heterogeneous nature of the process. It can be applied to characterize the competing phenomena taking place in an industrial pulping process: mass transfer of inorganic and organic chemicals between the free and entrapped liquid phases and chemical reaction in the solid phase. This is part of a strategy to develop a kinetic model that can be employed in simulation studies of a Kamyr digester, such as the one described by Fernandes and Castro20 and Winewski and Doyle,21 and in the optimization of its operation. This heterogeneous pulping model is based on a lumped parameter approximation, in which the alkali profile inside the chip is represented by a mean concentration, making it simpler to validate in any experimental pulping conditions.
2. Experimental Section Two sets of experiments were carried out, using handmade chips of Eucalyptus globulus with two different thicknesses. The first set represents a mass transfer study using 1 mm thick chips, and each experiment was conducted isothermally at different target temperatures, from 5 to 80 °C. The second set included a series of cooking experiments carried out with 6 mm thick chips and target temperatures varying from 80 to 165 °C. 2.1. Raw Materials. E. globulus chips with dimensions of about 30 × 30 × 1 mm in the first set and 30 × 30 × 6 mm in the second set were used. The chips were preimpregnated with water to a final moisture content of around 50%. White liquors were prepared by mixing sodium hydroxide, sodium sulfide, and sodium carbonate in distilled water. Target values of effective alkali charge, sulfidity, and initial liquor-to-wood ratio were, for the first set, 17.5 g Na2O/100 g odw, 25%, and 6, respectively, and, for the second set, 15 g Na2O/100 g odw, 30%, and 8, respectively. 2.2. Cooking Procedure. All of the experiments with 1 mm chips were carried out in vessels placed in a thermostatic bath adjusted to the desired temperature. Both the chips and the liquors were separately conditioned to the same temperature using a similar bath. After this stage, the vessels were charged with approximately 100 g (oven dry) of wood and about 500 mL of liquor. At prespecified times, a vessel was taken out of the bath, and a sample of free liquor was collected into a flask previously inertized with nitrogen and stored in an ice bath for rapid cooling. The chips were immediately separated from the remaining free liquor, and the excess liquor at the surface was carefully removed with sorption paper. The chips were then pressed to 350 bar for 2-3 min to release the entrapped liquor that was also collected in a previously inertized flask and cooled in a similar ice bath. The contact times between cooking liquor and chips varied from 4 to 60 min. The cooking experiments with 6 mm chips were carried out in a six-vessel batch-digester system with liquor recirculation, as described by Romanenko and Castro.22 Because of the high thermal capacitance of the system, both the liquor and the reaction vessels were preheated separately to a given temperature in order to ensure a rapid setting-up of the initial cooking temperature, often between 80 and 125 °C . The digesters were then charged with approximately 700 g (oven dry) of chips each, and the hot liquor was fed from an auxiliary tank by overpressure. A computer-controlled temperature ramp was imposed to reach the desired cooking temperature, with a rate of around 1 °C/min. At prespecified times, varying from 7 to 300 min, one vessel was isolated from the circulation line, and all of the free liquor in that digester was purged out of the system and a sample taken for chemical analysis after cooling in an ice bath. After this depressurization, the vessel was then opened, and a sample of around 100200 g of chips was taken and pressed to 350 bar for 2-3 min, to collect the maximum volume of entrapped liquor. 2.3. Washing. At the end of each pulping experiment, the chips were washed with water in the six-vessel plant, in successive cycles, between which the washing water was replaced. In the case of the 6 mm chips, water was recirculated during three cycles of 1-h, followed by an overnight cycle without recirculation and two more
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Figure 1. Effective alkali concentration (normalized) in the free (FL) and entrapped (EL) liquid phases versus time for 1 and 6 mm chips in the experiments at 80 °C.
1-h cycles with recirculation. In both cases, the washing cycle was terminated when the washing water conductivity decreased below a given conductivity (0.5 mS/cm). In all situations, the pH was mantained above 11. The weight and moisture content of the chips were determined after washing for yield estimation. 2.4. Chemical Analysis. In both sets of experiments, the white liquor and the free and entrapped liquors were analyzed for sulfide and for active alkali concentrations according to TAPPI T625-cm-85. Lignin concentration in all liquid samples was also analyzed by UV spectrophotometry, according to the method employed by Santos et al.8: liquor samples were diluted in 0.01 N NaOH, and their absorbances measured at 280 nm. The total dissolved solids in the liquors was measured according to TAPPI T625-cm-85. Lignin in wood samples was determined according to TAPPI T222-om-98. 3. Discussion of Results The heterogeneous nature of the process is clearly illustrated in Figure 1, where the concentration profiles for the effective alkali in both the bulk and entrapped liquors are shown for the experiments with 1 and 6 mm chips at the same temperature, 80 °C. In the two cases, the difference between these profiles is remarkable from the beginning of the cooking experiment. For 1 mm chips, the alkali concentration in both liquors becomes similar at about 60 min, while for the case of the 6 mm chips, this never occurs, even after 300 min. As the temperature is the same in both experiments, this difference can only be explained by the lower mass transfer rate of the thicker chips. As expected, the rate of mass transfer of alkali to the interior of the chip decreases as the chip thickness increases, revealling that the global rate of mass transfer is a function of the internal mass transfer resistance. The effect of temperature on this global rate is revealed in Figure 2, that highlights the alkali concentration profiles for experiments performed with chips of 1 mm thickness at temperatures of 5 and 80 °C. As can be seen, temperature plays an important role in the rate of mass transfer, even for chips 1 mm thick. For the lower temperature (5 °C), where the reaction rate is certainly very low, the concentrations of alkali in the two liquid phases are far from each other after a period of 60 min. In this case, the system can be seen as a simple, very slow mass transfer process. When the temperature is changed from 5 to 80 °C, the increase
Figure 2. Effective alkali concentration (normalized) in the free (FL) and entrapped (EL) liquid phases versus time for 1 mm chips in the experiments at 5 and 80 °C.
Figure 3. Effective alkali concentration (normalized) in the free (FL) and entrapped (EL) liquor versus time for 6 mm chips in the experiments at 80 and 165 °C.
in the mass transfer rate is higher than the corresponding increase in the reaction rate, because the temperature (80 °C) is still too low to ignite the main reactions between alkali and lignin. Therefore, despite the higher consumption of alkali at this temperature, the concentrations in the two liquid phases became very close much earlier. From Figure 2, one can demonstrate that the larger disappearance of alkali from the free liquor at 80 °C does not correspond to an equivalent larger rate of reaction, as is assumed in homogeneous-based kinetic models. This is confirmed by the consistently higher profile exhibited by the concentration of alkali in the entrapped liquor, revealling that much of the alkali that disappeared from the bulk liquor is “accumulated” in the liquid inside the pores of the chip and not reacted, as claimed in all previous homogeneous kinetic studies. In the experiments with 6 mm chips, it was decided to increase the level of temperature in order to enhance the rate of chemical reactions. The effect of this change in the temperature of operation is now more pronounced, as shown in Figure 3. For the experiment at 80 °C, the alkali concentration profiles in the free and entrapped liquors approach each other asymptotically in a slow manner and only become similar after 300 min. When the experiment is performed at a cooking temperature of 165 °C, one can observe a sharper decrease in the concentration of alkali in the free liquor mainly during the first 40 min, approximately, although this is not followed by a higher increase of concentration in the entrapped liquor. Such behavior reveals higher
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Figure 5. Total mass of lignin (normalized) in the system (S), in the liquid phases (LIQ), and in the wood chips (W) versus time for 6 mm experiments at 80 and 165 °C.
Figure 4. Concentration profiles of lignin in the free (FL) and entrapped (EL) liquor versus time for 6 mm experiments at 80, 140, and 165 °C.
consumption rates of alkali as a result of the chemical reactions that take place above 140 °C (see figure in Appendix for details of the temperature profiles) between the inorganic chemicals and the main wood components. This also highlights some interesting features of heterogeneous systems. First, different concentration profiles in the bulk phase do not necessarily mean different concentration profiles in the discontinuous phase, as shown by the corresponding profiles up to 40 min of operation. Second, and most typical of heterogeneous processes, chemical reactions strongly affect mass transfer between phases. In fact, despite similar concentration profiles of alkali inside the solid phase, higher temperature profiles give rise to higher reaction rates and to higher mass transfer coefficients, thus enhancing the mass transfer process, even with smaller concentration gradients. It can, therefore, be said that, up to this point (40 min and 140 °C), temperature still favors mass transfer in comparison to chemical reaction. However, above the temperature of 150 °C (around 50 min of operation; see figure in Appendix) the situation begins to change because the rate of chemical reaction becomes slightly higher than the rate of mass transfer into the entrapped liquor and, therefore, the concentration of alkali inside the chip starts to decrease. Assuming that the rates of the chemical reactions taking place in the pulping process depend on the concentration of alkali in the entrapped liquor and also on the concentrations of both lignin and carbohydrates in the solid matrix of the wood, this behavior is even more important because of the progressive reduction of their concentrations in the wood as time goes on. The concentration profiles of dissolved lignin in both free and entrapped liquors for the experiments with 6 mm chips at the temperatures of 80, 140, and 165 °C are illustrated in Figure 4. As expected, the concentration of lignin in the free liquor exhibits a monotonic increasing profile, even at 80 °C. With regard to the entrapped liquid, the pattern changes with temperature. At 80 °C, the concentration of dissolved lignin inside the chip quickly reaches an apparent low steady state, confirming the small extent of delignification at this
temperatures, even for long periods of time. When the experiment is carried out at 140 °C, there is a marked increase in dissolved lignin concentration as a result of the well-known lignin reactions that start to take place at around 140 °C. The profile is, however, of an asymptotic shape, revealing that delignification proceeds at a faster rate than the mass transfer of lignin to the free liquor. At 165 °C, the profile exhibits a maximum at around 80 min (where the delignification rate equals the mass transfer rate of lignin), decreasing thereafter because of the slowdown of the reaction rate and to the high mass transfer of lignin to the free liquor that arises as a result of the large concentration gradients. From the lignin concentration profiles in the entrapped and free liquors and the lignin content in the wood chips, it is possible to compute the total amount of lignin present in this system. This is represented in Figure 5 for the cooking experiments with 6 mm chips at the temperatures of 80 and 165 °C. In this mass balance, the amount of lignin removed at each sampling time in the wood chips and in both the entrapped and the free liquors is taken in account. As can be seen in Figure 5, for both experiments, the total normalized mass of lignin increases with time. The error can be up to 10% of its initial value, and it results mainly from the experimental errors involved in the determination of lignin concentration in the liquors. This was confirmed by performing an experiment in which the wood extractives (removed from the solid samples with an ethanol-toluene mixture, according to TAPPI T204-cm-97) were dissolved in a NaOH solution and analyzed by the same spectrophotometric procedure used for the determination of the concentration of dissolved lignin in the liquors. The resulting solution absorbed in the same wavelength (280 nm) as the lignin, revealing that the extractives dissolved in the liquors contributed to the lignin readings. The effective lignin concentration would then have a value approximately 10% lower than its initial value, to account for the extractives present in the liquor. This effect is more pronounced for the experiments at higher temperatures, where there is a substantial dissolution of extractives from the wood. This set of results clearly shows how misleading the conclusions can be on the kinetics of delignification if the heterogeneous nature of the system is not properly taken into account (i.e., if only the concentration of lignin in the free liquor is used to estimate the rate of delignification).
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Figure 6. Dissolved solids content in the free (FL) and entrapped (EL) liquid phases versus time for experiments at 80 and 165 °C with 6 mm chips.
The total dissolved solids content in both liquors is plotted in Figure 6 for the experiments with 6 mm chips at 80 and 165 °C. The solids content of a liquor represents the sum of the inorganic chemicals and of the organic substances that are dissolved from the wood during the pulping process. In the free liquor, one can observe a slight initial decrease, resulting from the dominant transfer of inorganic chemicals to the interior of the chips in the first period of the process. The intense transfer of dissolved lignin, cellulose, and hemicellulose from the entrapped liquor later compensates for this decrease in the experiment at 165 °C. Because of the values of the liquid-to-wood ratio, the entrapped liquor has a smaller relative volume; therefore, the change in its solids content is faster and more pronounced. For the case of 165 °C, one can see a maximum in the solids content of the entrapped liquor at around 70 min. Such a maximum reveals that the rate of dissolution of organics from the solid phase as a result of the chemical reactions plus the rate of mass transfer of inorganics from the free liquor equals the global rate of mass transfer of organics from the entrapped to the free liquor. As previously mentioned (see Figure 3), after this period, the concentration of alkali inside the chips starts to decrease, and this, together with the reduction of wood components, contributes to diminish all of the reaction rates and, therefore, the dissolution of organic matter into the entrapped liquor. Meanwhile, at this point, the overall rate of mass transfer of organics from the entrapped to the free liquor is very large, as shown in Figure 4 for lignin. The sum of all of these contributions results in a progressive decrease of the dissolved solids content of the entrapped liquor and a slight increase in the free liquor. 4. Conclusions In this study, the proposed experimental methodology made it possible to confirm that both a decrease in chip thickness and an increase in temperature augment the mass transfer of chemical substances between the two liquid phases and, therefore, enhance the rate of chemi-
cal reaction. It also highlighted that, in such a heterogeneous process, different alkali concentration profiles in the free liquor do not necessarily correspond to different alkali concentration profiles in the entrapped liquor and vice-versa. The decrease of alkali in the free liquor does not represent the consumption of alkali by the delignification and carbohydrate degradation reactions because the alkali transferred to the chip is not totally consumed by the wood components in the solid matrix and accumulates in the entrapped liquor. It is possible to show, too, that the dissolution of lignin from the solid matrix of the chips is related to the alkali concentration in the entrapped liquor, thus revealling its importance to the development of a heterogeneous delignification kinetic model. The proposed experimental methodology will make it possible to distinguish between the quantity that is transferred and the quantity that effectively is consumed by chemical reaction, which will allow the confirmation of the mass balances of the pulping process. It also avoids the underestimation of the delignification kinetics that results when the estimation of the residual lignin on wood is based on the lignin present in the free liquor. This heterogeneous approach is based on a lumped parameter approximation that, although not taking into account the real parabolic concentration profile inside the wood chip, enables its experimental validation and the development of simpler but realistic models for the kinetics of wood pulping. 5. Acknowledgment The financial support granted by the Ministry of Science and Technology under Project Praxis 3/3.2/ PAPEL/2327/95 is gratefully acknowledged. J.P.F. Sima˜o is also grateful to the Ministry of Science and Technology for his scholarship PRAXIS_XXI/BD/22236/ 99. The authors are also grateful to RAIZ, Instituto de Investigac¸ a˜o da Floresta e do Papel, for its financial and laboratory support and for supplying all of the wood used in this project. 6. Appendix
Figure 7. Temperature profiles for the experiments with 6 mm chips.
Literature Cited (1) Wilder, H. D.; Daleski, E. J. J. Delignification Rate Studies: Part II of a Series on Kraft Pulping Kinetics. Tappi J. 1965, 48 (5), 293.
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(2) Rekunen, S.; Jutila, E.; La¨hteenma¨ki, E.; Lo¨nnberg, B.; Virkola, N.-E. Examination of Reaction Kinetics in Kraft Cooking. Pap. Puu 1980, 62 (2), 80. (3) Gustafson, R. R.; Sleicher, C. A.; McKean, W. T., Finlayson, B. A. Theoretical Model of the Kraft Pulping Process. Ind. Eng. Chem. Process Des. Dev. 1983, 22 (1), 87. (4) Mirams, S.; Nguyen, K. L. A Predictive Model of Eucalypt Kraft Pulping. Proceedings of the 48th Appita Annual Conference, 1994; p 187. (5) Olm, L.; Nelson, P.; Campbell, S. The Rate of Delignification of Eucalyptus Diversicolor, E. regnans, E. marginata, and E. tetradonta Woods during Kraft Pulping. Appita 1984, 37 (4), 314. (6) Nelson, P.; Gniel, G. Delignification of Eucalyptus Regnans Wood during Soda Pulping. Appita J. 1986, 39 (2), 110. (7) Mirams, S.; Nguyen, K. L. Kinetics of Kraft Pulping of Eucalyptus Globulus. AIChE Symp. Ser. 1996, 92 (311), 1. (8) Santos, A.; Rodriguez, F.; Gilarranz, M. A.; Moreno, D.; Garcı´a-Ochoa, F. Kinetics Modeling of Kraft Delignification of Eucalyptus globulus. Ind. Eng. Chem. Res. 1997, 36 (10), 4114. (9) Vanchinathan, S.; Krishnagopalan, G. Kraft Delignification Kinetics Based on Liquor Analysis. Tappi J. 1995, 78 (3), 127. (10) Sen, S.; Saucedo, V.; Krishnagopalan, G. Modelling of a Modified Kraft Process. Appita J. 2000, 53 (1), 36. (11) Olm, L.; Tistad, G. Kinetics of the Initial Stage of Kraft Pulping. Sven. Papperstidn. 1979, 27 (15), 458. (12) Kondo, R.; Sarkanen, K. Kinetics of Lignin and Hemicellulose Dissolution during the Initial Stage of Alkaline Pulping. Holzforschung 1984, 38, 31. (13) Garland, C.; James, F.; Nelson, P.; Wallis, A. A Study of the Delignification of Eucalyptus Diversicolor Wood during Soda Pulping. Appita J. 1987, 40 (2), 116.
(14) Talton, J. H., Jr.; Cornell, R. H. Diffusion of Sodium Hydroxide in Wood at High pH as a Function of Temperature and the Extent of Pulping. Tappi J. 1987, 70, 115. (15) Hultholm, T.; Robertse´n, L.; Lo¨nnberg, B.; Kettunen, A.; Henricson, K. Impregnation in Alkaline Pulping. Proceedings of the Tappi Pulping Conference, 1997; p 897. (16) McKibbins, S. W. Application of Diffusion Theory to the Washing of Kraft Cooked Wood Chips. Tappi J. 1960, 43 (10), 801. (17) Rosen, A. Adsorption of Sodium Ions on Kraft Pulp Fibers during Washing. Tappi J. 1975, 58, 156. (18) Eriksson, G.; Gre´n, U. Pulp Washing: Sorption Equilibria of Metal Ions on Kraft Pulps. Nord. Pulp Pap. Res. J. 1996, 3, 164. (19) Robertsen, S.; Lo¨nnberg, B. Diffusion in Wood. Part 2: The Effects of Concentration and Temperature. Pap. Puu 1991, 73 (7), 635. (20) Fernandes, N. C. P.; Castro, J. A. A. M. Steady-state Simulation of a Continuous Moving Bed Reactor in the Pulp and Paper Industry. Chem. Eng. Sci. 2000, 55, 3729. (21) Winewski, P. A.; Doyle, F. J. P. Fundamental Continuous Pulp-Digester Model for Simulation and Control. AIChE J. 1997, 43 (12), 3175. (22) Romanenko, A.; Castro, J. A. A. M. An RT-Linux Based Control System of a Pilot Plant for Reaction Kinetics and Process Control Studies. Comput. Chem. Eng. 2000, 24, 1063.
Received for review June 25, 2001 Revised manuscript received December 3, 2001 Accepted January 30, 2002 IE010534O
