Reactor Productivity Research Articles

Design and optimisation of a multi-stage bubble column slurry reactor for Fischer–Tropsch synthesis

For carrying out the Fischer–Tropsch synthesis of heavy paraffins starting from syngas (CO+H 2), a multi-stage bubble column slurry reactor design is carried out. The advantages of this reactor configuration with respect to a conventional slurry reactor design, consisting of one well-mixed stage, are (a) increased syngas conversion, and (b) increased reactor productivity. The multi-stage bubble column construction requires installation of additional cooling surface area in order to keep the exothermic reaction within the desired temperature limits.

Comparison of Different Chemoenzymatic Process Routes to Enantiomerically Pure Amino Acids

Five common biocatalytic process platforms for the production of enantiomerically pure amino acids are compared along four different dimensions of merit: i) enantioselectivity, ii) overall yield, iii) biocatalyst operating stability, and iv) reactor space-time yield. All processes practiced on industrial scale utilize biocatalysts of very high enantioselectivity. Short efficient process routes are a necessity, giving an inherent advantage to routes based on lyase reactions or reduction of prochiral keto acids. For processes based on the splitting of a racemate, recycling the unwanted enantiomer is crucial. The pKa value of abstracting the ?-proton serves as a first indication of the difficulty of achieving overall yields far in excess of 50% through dynamic resolution. High solubility of substrates and products was found to favor high reactor productivity (space-time-yield s.t.y. > 1 kg/(I·d)) and high biocatalyst productivity (enzyme consumption number e.c.n. < 500–1000 U/kg of product).

Methanol production from biomass using the Hynol process

In this paper, CO2 hydrogenation to methanol is investigated with three objective functions, i.e. maximization of reactor productivity, CO2 utilization, and hydrogen conversion. Key performance indicators of methanol production via conventional and CO2 hydrogenation routes are compared.The results suggest that the methanol production rate with an inlet H2/CO2 of 3 is ca. 59 % greater than the case with the inlet H2/CO2 composition of 2. The overall hydrogen and CO2 conversion of the cases with the inlet H2/CO2 of 3 is greater than the reactor system with the inlet H2/CO2 of 2.For each objective function criteria, the analysis shows that increasing the H2/CO2 to the methanol reactor increases the natural gas consumption in the conventional route and the higher the inlet H2/CO2 ratio, the higher the CO2 emission is. If the inlet hydrogen is produced via water electrolysis, the CO2 emission of the CO2 hydrogenation process route will be negative.

Acetic acid production from lactose by an anaerobic thermophilic coculture immobilized in a fibrous-bed bioreactor.

An anaerobic thermophilic coculture consisting of a heterofermentative bacterium (Clostridium thermolacticum) and a homoacetogen (Moorella thermoautotrophica) was developed for acetic acid production from lactose and milk permeate. The fermentation kinetics with free cells in conventional fermentors and immobilized cells in a recycle batch fibrous-bed bioreactor were studied. The optimal conditions for the cocultured fermentation were found to be 58 degrees C and pH 6.4. In the free-cell fermentation, C. thermolacticum converted lactose to acetate, ethanol, lactate, H(2) and CO(2), and the homoacetogen then converted lactate, H(2), and CO(2) to acetate. The overall acetate yield from lactose ranged from 0.46 to 0.65 g/g lactose fermented, depending on the fermentation conditions. In contrast, no ethanol was produced in the immobilized-cell fermentation, and the overall acetate yield from lactose increased to 0.8-0.96 g/g lactose fermented. The fibrous-bed bioreactor also gave a higher final acetate concentration (up to 25. 5 g/L) and reactor productivity (0.18-0.54 g/L/h) as compared to those from the free-cell fermentation (final acetate concentration, 15 g/L; productivity, 0.06-0.08 g/L/h). The superior performance of the fibrous-bed bioreactor was attributed to the high cell density (20 g/L) immobilized in the fibrous-bed and adaptation of C. thermolacticum cells to tolerate a higher acetate concentration. The effects of yeast extract and trypticase as nutrient supplements on the fermentation were also studied. For the free-cell fermentation, nutrient supplementation was necessary for the bacteria to grow in milk permeate. For the immobilized-cell fermentation, plain milk permeate gave a high acetate yield (0.96 g/g), although the reactor productivity was lower than those with nutrient supplementation. Balanced growth and fermentation activities between the two bacteria in the coculture are important to the quantitative conversion of lactose to acetic acid. Lactate and hydrogen produced by C. thermolacticum must be timely converted to acetic acid by the homoacetogen to avoid inhibition by these metabolites.

Increasing PVC suspension polymerization productivity by using temperature-programmed reactions

Vinyl chloride polymerizations are known to be autoaccelerating. The reaction rate increases with conversion. Because of this phenomenon, substantial reactor productivity at early conversion can be lost because the heat-removal capacity of the reactor is not fully utilized until near the end of the polymerization. For this reason it is desirable to speed up the polymerization at the beginning and slow it down near the end. This rate adjustment can be achieved by running the polymerization hotter in the beginning and then cooling. We have written a scientifically based computer model of the polymerization designed specifically to simulate such temperature-programmed reactions. The model does a complete heat balance on the polymerization, has a molecular weight predictor, and will be described and demonstrated for a polymerization at 50°C using sec-butyl peroxydicarbonate (SBP) as initiator. By using this single initiator and a very simple straight-line temperature-programmed reaction, the time to 80% conversion can be reduced from 335 minutes to 240 minutes. This is a substantial increase in productivity.

Design and scale-up of the Fischer–Tropsch bubble column slurry reactor

The Fischer–Tropsch (FT) synthesis on a large scale is of interest, as a means of conversion of remote natural gas to high-quality products, particularly, liquid transportation fuels. Recent developments have resulted in reactors of advanced design having production capacities of 2500 bbl/day or higher, which is more than two orders of magnitude higher than the productivity of classical reactors operated before or during World War II. Some fundamental aspects of these reactors, which belong to the classes of gas–solid fluidised beds, multi-tubular trickle-beds, and slurry bubble columns, are discussed to aid the selection and design of reactors for a specific application. Special attention is given to scaling up of slurry bubble columns. Published experimental work is carefully analysed, and procedures are recommended for the estimation of the necessary design and scale-up parameters. Model calculations of a commercial FT reactor are presented in order to underline various important design and operating issues.

Dynamic optimization of hybridoma growth in a fed-batch bioreactor

This study addressed the problem of maximizing cell mass and monoclonal antibody production from a fed-batch hybridoma cell culture. We hypothesized that inaccuracies in the process model limited the mathematical optimization. On the basis of shaker flask data, we established a simple phenomenological model with cell mass and lactate production as the controlled variables. We then formulated an optimal control algorithm, which calculated the process-model mismatch at each sampling time, updated the model parameters, and re-optimized the substrate concentrations dynamically throughout the time course of the batch. Manipulated variables were feed rates of glucose and glutamine. Dynamic parameter adjustment was done using a fuzzy logic technique, while a heuristic random optimizer (HRO) optimized the feed rates. The parameters selected for updating were specific growth rate and the yield coefficient of lactate from glucose. These were chosen by a sensitivity analysis. The cell mass produced using dynamic optimization was compared to the cell mass produced for an unoptimized case, and for a one-time optimization at the beginning of the batch. Substantial improvements in reactor productivity resulted from dynamic re-optimization and parameter adjustment. We demonstrated first that a single offline optimization of substrate concentration at the start of the batch significantly increased the yield of cell mass by 27% over an unoptimized fermentation. Periodic optimization online increased yield of cell mass per batch by 44% over the single offline optimization. Concomitantly, the yield of monoclonal antibody increased by 31% over the off-line optimization case. For batch and fed-batch processes, this appears to be a suitable arrangement to account for inaccuracies in process models. This suggests that implementation of advanced yet inexpensive techniques can improve performance of fed-batch reactors employed in hybridoma cell culture.

Dynamic optimization of hybridoma growth in a fed-batch bioreactor

This study addressed the problem of maximizing cell mass and monoclonal antibody production from a fed-batch hybridoma cell culture. We hypothesized that inaccuracies in the process model limited the mathematical optimization. On the basis of shaker flask data, we established a simple phenomenological model with cell mass and lactate production as the controlled variables. We then formulated an optimal control algorithm, which calculated the process–model mismatch at each sampling time, updated the model parameters, and re-optimized the substrate concentrations dynamically throughout the time course of the batch. Manipulated variables were feed rates of glucose and glutamine. Dynamic parameter adjustment was done using a fuzzy logic technique, while a heuristic random optimizer (HRO) optimized the feed rates. The parameters selected for updating were specific growth rate and the yield coefficient of lactate from glucose. These were chosen by a sensitivity analysis. The cell mass produced using dynamic optimization was compared to the cell mass produced for an unoptimized case, and for a one-time optimization at the beginning of the batch. Substantial improvements in reactor productivity resulted from dynamic re-optimization and parameter adjustment. We demonstrated first that a single offline optimization of substrate concentration at the start of the batch significantly increased the yield of cell mass by 27% over an unoptimized fermentation. Periodic optimization online increased yield of cell mass per batch by 44% over the single offline optimization. Concomitantly, the yield of monoclonal antibody increased by 31% over the off-line optimization case. For batch and fed-batch processes, this appears to be a suitable arrangement to account for inaccuracies in process models. This suggests that implementation of advanced yet inexpensive techniques can improve performance of fed-batch reactors employed in hybridoma cell culture. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 67: 197–205, 2000.

00/00093 Slurry phase Fischer-Tropsch synthesis process development

Fischer-Tropsch synthesis can convert a variety of synthesis gas mixtures produced from both coal and natural gas to obtain hydrocarbons, which can be further processed to manufacture automotive fuels. As the Fischer-Tropsch reaction is highly exothermic, a slurry phase reactor offers a significant advantage over the traditional fixed bed reactor for heat management. Since 1992, Air Products and DOE have been developing the slurry phase Fischer-Tropsch synthesis process with help of a number of industrial partners. This paper discusses the evolution of the technology through four pilot plant campaigns conducted at DOE`s Alternative Fuels Development Unit in LaPorte, Texas. Key issues such as catalyst-wax separation, reactor productivity improvements, reactor temperature control, and in-situ activation are addressed.

Applications of Nonlinear Observers and Control: Improving Productivity and Control of Free Radical Solution Copolymerization

A nonlinear state observer that uses the rate of heat generation due to chemical reaction for the real-time evaluation of key parameters during free radical solution copolymerization is presented. These parameters include the cumulative and instantaneous copolymer compositions, the overall and individual monomer conversions, and the overall termination rate constant associated with the reaction. The information thus obtained is used to control the cumulative copolymer composition and to maintain the productivity of a semibatch reactor for the solution copolymerization of butyl acrylate (BuA) and vinyl acetate (VAc) in ethyl acetate (EAc) at its highest possible level. Both the state and parameter estimation of this observer were then used for the nonlinear control of copolymer composition and optimal reactor productivity.

Fundamentals and selection of advanced Fischer–Tropsch reactors

Fischer–Tropsch synthesis on a large scale is of interest as a means for conversion of remote natural gas to high-quality products, particularly liquid transportation fuels. Recent developments have resulted in reactors of advanced design having production capacities of 2500 bbl/day or higher, which is more than two orders of magnitude higher than the productivity of classical reactors operated before or during World War II. Some fundamental aspects of these reactors, which belong to the classes of gas–solid fluidized beds, multitubular trickle-beds, and slurry bubble columns are discussed to aid selection and design of reactors for a specific application. Special attention is given to scaling up of slurry bubble columns. A scaling-up strategy is proposed which might obviate the inclusion of a costly demonstration stage in the development of a novel process using bubble columns.

Lactic acid production by immobilized Lactobacillus casei in recycle batch reactor: a step towards optimization

Different nutritional and process parameters influencing lactic acid production by Lactobacillus casei, adsorbed to Poraver beads in a recycle batch reactor system, were studied in an attempt to set up a system having a long operational lifetime and permitting use of high substrate concentrations for maximal conversion to the product. The presence of lactose, even as a minor fraction of the total sugar amount, was necessary for complete utilization by the organism for growth and conversion to lactate. Hydrolysed whey protein constituted a richer source of nitrogen compared to yeast extract. Addition of lactate to the medium at the start of the process resulted in severe inhibition compared with the normal process. For a homofermentative process, pH 6.0 was found to be optimal. The overall productivity of the recycle system was higher under all conditions studied in comparison with the batch process using free cells. Enhancement in productivity in the recycle batch reactor was also accompanied by an increase in density of suspended cells. However, the contribution of the suspended cells to the overall reactor productivity was not noticeable. The bead size of the matrix was found to be important for operational stability of the reactor.

Hydrodynamic behavior of slurry bubble column at high solids concentrations

Hydrodynamics of a slurry bubble column have been investigated up to slurry concentrations of 40 vol.% and gas velocities of 0.26 m/s. High slurry concentrations represent high catalyst loading to increase reactor productivity, while high gas velocities would be required to increase reactor throughputs. The solid particles used are 35 μm glass beads representing typical particle size for catalytic slurry reactors. The two important hydrodynamic parameters investigated are gas holdup and solids concentration profiles. The average gas holdups decreased with increasing slurry concentration but the rate of decrease slowed down for higher slurry concentrations. The analysis of axial gas holdup profiles indicated that decrease in gas holdup due to solids addition could be attributed to a decrease in bubble breakup rates. The experimental gas holdups are compared with literature correlations and models. The axial distribution of slurry concentration followed the classical sedimentation–dispersion model. Effects of gas velocity on axial solids distribution are found to be minimal over the range of gas velocities investigated.

99/01966 Hydrocarbon synthesis from dimethyl ether over ZSM-5 catalyst: Sardesai, A. and Lee, S. Prepr. Symp. Am. Chem. Soc., Div. Fuel Chem., 1998, 43, (3), 722–726

The liquid phase synthesis of dimethyl ether from syngas has significant advantages over the liquid phase methanol synthesis in the areas of syngas conversion and reactor productivity. The merits of this dual catalytic process a!lows dimethyl ether to be utilized as a viable feedstock for petrochemical synthesis. In particular, dimethyl ether can be converted to hydrocarbons using H-ZSM-5 type zeolite catalysts. Appropriate choice of the acidity of the zeolite catalyst as well as the operating parameters such as reaction temperature, partial pressure and space velocity of dimethyl ether dictate the product spectrum, ranging from lower olefins (ethylene and propylene) to gasoline-range hydrocarbons. The focus of this paper is to thoroughly study the aforementioned details of this process and compare its merits with methanol conversion.

Continuous production of l-carnitine with NADH regeneration by a nanofiltration membrane reactor with coimmobilized l-carnitine dehydrogenase and glucose dehydrogenase

l-Carnitine dehydrogenase (CDH) was partially purified from Pseudomonas putida IAM12014 for the stereospecific reduction of 3-dehydrocarnitine to l-carnitine. CDH and glucose dehydrogenase (GDH) were coimmobilized in a nanofiltration membrane bioreactor (NFMBR) for the continuous production of l-carnitine from 3-dehydrocarnitine with NADH regeneration. In the NFMBR, NAD was partially immobilized through rejection by the nanofiltration membrane and effectively regenerated by the conjugation reaction of CDH and GDH. Since 3-dehydrocarnitine was unstable at neutral pH, it was maintained under acidic conditions (pH 0.7) and supplied to the NFMBR separately from the other substrates, glucose and coenzyme NAD. As 50 mM 3-dehydrocarnitine in HCl solution, 0.05 mM NAD, and 100 mM glucose in 0.5 M Tris buffer (pH 8) were continuously supplied to the NFMBR with immobilized CDH (200 U/ml) and GDH (200 U/ml) at the retention time of 80 min and temperature of 25°C, the maximum conversion, reactor productivity, and NAD regeneration number were 78%, 113 g/ l/d, and 780, respectively. The half-life of the NFMBR was longer than 500 h.

Strain comparison and medium preparation for the acetone-butanol-ethanol (ABE) fermentation process using a substrate of potato

Several strains of solvent-producing clostridia were investigated for their ability to produce solvents from unsupplemented potato and from potato that had been pre-hydrolysed with amylolytic enzymes. Most of the strains were strongly solventogenic and prior treatment with the enzymes gave no improvement in this property. C. acetobutylicum DSM 1731 showed a reactor productivity of 0·24 g/l/h on unhydrolysed potato, and was the most productive strain tested. In contrast, C. acetobutylicum ATCC 824 was only weakly solventogenic unless the potato was pre-hydrolysed using amylolytic enzymes.

Acetic acid production from fructose by clostridium formicoaceticum immobilized in a fibrous-Bed bioreactor

The fermentation kinetics of acetic acid production from fructose by Clostridium formicoaceticum was studied at pH 7.6 and 37 degreesC. Recycle batch, fed-batch, and continuous fermentations using immobilized cells in a fibrous-bed bioreactor were studied for their potential application in producing acetic acid from fructose, a fermentable sugar commonly found in corn steep liquor and many other food processing wastes. For the immobilized cell fermentation, acetic acid yield from fructose was approximately 1.0 g/g, with a final acetate concentration of approximately 78 g/L and the overall reactor productivity (based on the fibrous bed bioreactor volume) of approximately 0.95 g/(L.h) in the fed-batch fermentation. For a similar fed-batch fermentation with free cells, acetic acid yield was approximately 0.9 g/g, the highest final acetate concentration was approximately 46 g/L, and the overall productivity was approximately 0.12 g/(L.h). In the continuous fermentation with immobilized cells, the reactor productivity decreased from 3.2 to 1. 3 g/(L.h) as retention time increased from 16 to 72 h to reach 100% conversion. Compared to free-cell fermentations, the superior performance of the fibrous-bed bioreactor can be attributed to the high density (>30 g/L) of viable cells immobilized in the fibrous bed. The fermentation product, acetic acid, was found to be a noncompetitive inhibitor to the cells. However, the immobilized cells had a higher maximum production rate (pmax) and a higher value for the inhibition rate constant (Kp) than those for the free cells, suggesting that the immobilized cells in the fibrous-bed bioreactor were less sensitive to acetic acid inhibition than the free cells. This improvement in kinetic behaviors for immobilized cells confirms that the fibrous-bed bioreactor can be used as an effective tool for adapting and screening for acetate-tolerant strains.

Catalytic wet oxidation of substituted phenols in the trickle bed reactor

Continual catalytic wet oxidation of phenol and its derivatives as a suitable chemical pretreatment before a biological treatment process was investigated. The evaluation of (i) the influence of amino-, carboxy- and sulfo- phenol substituents on the course of the oxidation of hydroxyl-aromatics, (ii) the catalytic ability of an active carbon, and (iii) the influence of reaction conditions, viz. temperature (120–160°C) and oxygen partial pressure (2–5 MPa) in the continuous trickle bed reactor, is presented. The active carbon type catalyst seems to be active enough for phenol oxidation, but it is not so effective for aromatic acids. The results of trickle bed operation were strongly influenced by hydrodynamics, viz. wetting efficiency. An insufficient catalyst wetting compensates for an effect of residence time in the bed and undesirable fluctuation of conversion appears at the low liquid velocities which are typical for waste water treatment processes. It is possible to achieve an optimal value of reactor productivity. © 1998 SCI

Periodic Operation of Asymmetric Bidirectional Fixed-Bed Reactors with Temperature Limitations

Possible ways of coupling a solid-catalyzed endothermic reaction with an exothermic reaction in a bidirectionally fed fixed-bed reactor, operated in a periodic steady state, when the maximum allowable temperature is limited by either process, catalyst, or materials constraints, are discussed. Steam reforming of natural gas coupled with methane combustion is considered as an example. The catalyst bed is heated by the combustion reaction during the exothermic semicycle, while the endothermic reaction, with reactants fed from the opposite end, cools the bed during the endothermic semicycles. It is shown that two modes of periodic operation are possible. In the wrong-way process, reactants are fed at temperatures below the initial bed temperature, which results in maximum temperatures that can exceed the allowable limits. To suppress excessive temperature overshoots the fuel feed concentration must be very low, which leads, due to the creeping temperature hot zone, to only a small fraction of the heat produced during the exothermic semicycle being available for the endothermic reaction. Thermal efficiency and the reactor productivity are low. In the normal process, the inlet reactant temperature is above the ignition temperature, leading to a stationary spreadout temperature profile, high thermal efficiency, and high reactor productivity, as well as to controllable maximum temperature. Simulations for the wrong-way and normal processes are described as well as the possibilities of achieving very high thermal efficiencies in a process that integrates the reactor with heat recovery units.

Improved operation of a dextran bioreactor-separator through variation of enzyme activity, viscosity, centrifugal parameters and rotor design

Viscosity regulation allowed the sedimentation of dextran to be increased from 1.89 to 2.89 g.h−1 within a novel centrifugal bioreactor. At an enzyme activity of 187 U, dextran pelleting was 1.66 mg g.h−1. U which was 50% greater than at an enzyme activity of 1344 U. Reactor productivity, at 1.5–2 g.h−1, was similar for both batch and semi-continuous trials. Rotor core design influenced productivity. © Rapid Science Ltd. 1998