Two-phase Reactor Research Articles

Axial-dispersion models of fluid-fluid reactors based on the two-film theory

Axial dispersion models of two-phase reactors for fluid-fluid systems are proposed in this paper, based on the two-film theory. The mathematical problem of the two-film mass transfer mechanism accompanied by a chemical reaction is treated in a new way, with the aim of using its results to develop reactor design models conveniently. Analytical solutions can be obtained for the case of constant volumetric flow rates in both phases and an irreversible first-order reaction. The mass balance for the gas phase will be a non-linear differential equation if we take the variation of the volumetric flow rate of the gas phase and the pressure drop into account. In this case an iteration procedure is proposed to integrate the differential equation system. The concentration profile, degree of mass transfer, reactant conversion and reactor capacity can be calculated easily by means of analytical or numerical solutions.

Runaway limits for homogeneous and catalytic reactors

A unified approach that relates and combines the concepts of parametric sensitivity, ignition, extinction, hysteresis and isola formation is presented and used to derive a single universal runaway criterion valid for all homogeneous reactor models. It is also shown that the heat and mass dispersion have very little impact on this runaway locus. Next, the approach is extended to heterogeneous reactor models where interphase gradients strongly influence the runaway boundary. It is shown that the model of a well-mixed two-phase reactor may be used to derive runaway boundaries for a cooled multitubular catalytic reactor influenced by interparticle and intraparticle transport limitations. The validity of the approach is verified by numerical simulations of temperature profiles under safe and runaway conditions for some selected cases. The analysis of the heterogeneous model shows that the heat transfer resistance between the solid and the fluid introduces a qualitative change in the shape of the stability boundary. There exists a limiting value of the dimensionless heat of reaction parameter B, above which the reactor is in a runaway region regardless of the rate of external cooling. This limiting value of B corresponds to the ignition of catalyst particles. It is also shown that within the safe region of operation, there exists an optimal catalyst particle diameter that maximizes the reactor productivity. The main concepts involved and computation of the runaway boundaries for multiple reactions are illustrated by discussing three specific examples of consecutive, simultaneous and consecutive-simultaneous reactions. The important result is that the runaway locus for any multiple reaction network differs significantly from that of the single reaction only when the product λbψ > 0.1. Here, λ, ψ and b, represent, respectively, the ratio of rate constants at feed conditions, heats of reaction and feed concentrations of the primary reaction to that of the main competing reaction. This work also presents slightly conservative analytical results for the determination of the runaway limits of homogeneous and catalytic reactors for most cases of practical interest.

Anaerobic digestion of ice-cream wastewater: A comparison of single and two-phase reactor systems

The anaerobic digestion of ice-cream wastewater, a complex substrate which includes milk proteins, carbohydrates, and lipids, has received little attention. Work using an aerobic contact system showed that at a 7.5-d hydraulic retention time (HRT), with an organic loading rate of 1.7 g COD/Ld and influent TSS (total suspended solids) of 5870 mg/L, the effluent COD was 628 mg/L, BOD was 91 mg/L and TSS was 674. Anaerobic filters have also been used at organic loadings of 6 kg COD/m{sup 3}d applied at a HRT of 0.42 day, with COD removals of 80%. Goodwing showed that this waste was capable of being treated by the UASB process with granulation commencing after 60-70 days, and gas production ranging between 0.73 and 0.93 L CH{sub 4}/g COD removed with loading rates between 0.7 and 3.0 g TOC/Ld. Two-phase anaerobic digestion is an innovative fermentation mode that has recently received increased attention. The kinetically dissimilar fermentation phases, hydrolysis-acidification and acetogenesis-methanation are operated in two separate reactors; the first of which is maintained at a very short HRT. The effluent from the first, acid-forming, phase is used as the substrate for the methane-phase reactor which has a longer HRT or cell immobilization. The aimmore » of this work was to compare the methane production capability and performance of a single-phase upflow fixed bed reactor with a two-phase digestion system. The two-phase digestion system consists of a completely mixed reactor for the acidogenic reaction and an upflow fixed bed reactor for the methanogenic reaction. Because of the high lipid content and COD of ice cream wastewater off site disposal has proved to be both expensive and poses problems to the receiving effluent treatment plant. For this reason the potential for a rapid anaerobic stabilization of the waste, with energy recovery in the form of methane gas, has been investigated in an attempt to minimize plant size and maximize gas production. 9 refs., 2 tabs.« less

Chaos in a simple two-phase reactor

The autocatalytic reaction of Gray and Scott ( A + 2 B→3 B, B→ C is studied in a reactor with two uniform phases. These may be thought of as a reactor communicating with a reservoir and two models are considered corresponding to feeding A or B, respectively, to the reservoir. Both models exhibit chaos reached by the period-doubling route, but the second also shows intermittency.

Effect of copper and lead on the performance of a two-phase anaerobic digester

The effect of metals on the performance of anaerobicidigesters has been examined extensively. However, most of this work has been done withi single-tank reactors where the various phases which constitute the digestion process were fully integrated. The use of two-phase digestion enables the impact of toxins on specific phases to be examined. In this study, a two-phase reactor fed with a starch-based substrate was used to evaluate the effect of copper and lead (0.5 nM) on the individual phases. The metals were added both individually and in combination. The reactros were operated in their normal sequential mode and separately. In the latter case, the methanogenic reactor was fed with an acetate substrate to which copper and lead had been added. The results showed that the most significant impact was on the performance of the acidogenic reactor and that the copper had a greater effect than lead.

Bioconversion of vanillin into vanillic acid byPseudomonas fluorescens strain BTP9

Pseudomonas fluorescens strain BTP9 is used as biocatalyst to produce vanillic acid from vanillin. Several two-phase reactors were investigated and compared to the corresponding one-phase systems in order to optimize this bioconversion.

Anaerobic biotransformation of nitrocellulose

In this investigation, first the toxic effect of nitrocellulose (NC) on anaerobic microorganisms with and without the presence of a supplementary carbon source was evaluated. Then it was observed that with the addition of a supplementary carbon source, such as cellulose or acetate, biotransformation of NC was enhanced. The biodegradation rate of NC in a staged-feed and in a two-phase reactor under anaerobic conditions was evaluated. The results showed that providing cellulose as the supplementary carbon source, NC was degraded at a higher rate in a staged-feed reactor than in a two-phase reactor or in a batch reactor.

Preparation of functionalized polyorganosiloxane spheres for the immobilization of catalytically active compounds

A procedure for the preparation of functionalized polyorganosiloxane spheres is presented. The macroporous beads are suitable supports for covalent immobilization of catalytically active compounds. They are generated by co-condensation of tetraalkoxysilane-organoalkoxysilane droplets in water. A specially designed two-phase reactor permits continuous preparation. To achieve a satisfactory condensation rate, an organotin compound is added. Variation of the reaction conditions allows control of the size (0.2–1.5 mm in diameter), the specific surface area (10–400 m 2/g) and the pore volume (0.1–0.7 ml/g) of the spheres.

Model predictive control of a continuous, nonlinear, two-phase reactor

The Tennessee Eastman challenge problem is simplified to a plant with eight states, four manipulated variables, and 10 outputs. Six regulation/optimization scenarios are proposed. The modified problem retains nonlinearities that cause difficulties in the original, e.g. certain gains can change sign. Steady-state relative-gain analysis suggests variable pairings for multi-loop feedback control that turn out to be inappropriate. A more robust, near-optimal multi-loop design is proposed and tested in simulations. Two model predictive control (MPC) designs are also tested. The first is based on a linear time-invariant (LTI) model of all the plant interactions. Gain variations make it impossible to achieve acceptable performance. The second uses a LTI model in which 10 of the 16 transfer functions are zero, i.e. it includes only the most important plant responses. The resulting MPC performance is comparable or better than the multi-loop design. Alternative MPC strategies are also discussed.

A Bench-Scale, Two-Phase Reactor For Ozone Treatment: Feasibility Studies For High Strength Wastes

Abstract A batch reactor was designed to study the effects of ozone on a complex industrial waste. The objective of the batch reactor was to allow a large mass of ozone to be applied to the waste without losses associated with gas sparging and assure better accuracy than expected from continuously bubbled gas systems. The reactor consisted of two parts: a 478.6 mL cylindrical section for holding effluent and a 1.078 L spherical section for the ozone/oxygen gas mixture. Ozone concentrations were measured at ambient temperature and pressure using the UV absorption method. Ozone diffusion into a reactive test solution in the static condition (during ozone charging of the spherical chamber) was limited to 0.5 mg of the 1,500 mg passed through the spherical chamber. The batch reactor was shown to be capable of 100% ozone mass transfer during the contacting operation. The unit was shown to be a suitable device for evaluation of the effects on high ozone demand solutions.

Extractive bioconversions in aqueous two-phase systems: Enzymatic hydrolysis of casein proteins

Partition coefficients in poly(ethylene glycol)/dextran aqueous two-phase systems are reported for mixed-casein and its components, alpha, beta and kappa casein. Rates of casein proteolysis by alpha-chymotrypsin and by trypsin are reported in single-phase and aqueous two-phase reactor systems. The advantages resulting from selective partitioning of substrates, enzymes, and products are examined in terms of relative volumetric reaction rates.

Choice of Optimal Configurations for Two-Phase Biological Reactors on the Basis of Hydraulic Model Studies of a Wastewater Treatment Plant in Gdańsk

The paper presents procedure, results and conclusions drawn from laboratory studies of nitrification and denitrification chambers of two-phase biological reactors with recirculation system, for a designed wastewater treatment plant of 270 000 m3/day capacity, for the city of Gdańsk. On the 1:17 physical model, observations of stream lines and measurements of the velocity field in some characteristic regions have been performed. The measurements have been carried out for 14 different configurations of the reactor operation, depending on the aerator turbines, mammoth rotors and prototypical mixers with horizontal axle and with guide-ring. Based on these studies, and having introduced some structural innovations aimed at improving flow uniformity around aerators and rotors, a variant optimal from the point-of-view of hydraulic properties and energy consumption has been proposed for realization. Moreover, using results of some other investigations performed on a structure in technical scale, conclusions concerning the following questions have been presented: I/ the importance of uniform velocity distribution in the reactor for final effeot of operation of the wastewater treatment plant, II/ relationships between velocity, discharge and hydraulic efficiency of the wastewater treatment plant chambers, III/ the influence of geometry of chambers and of recirculation on the efficiency of the purification process. The paper includes drawings, figures and short descriptions of the following experimental techniques used in the investigations: the method of varying temperature field, the colorimetric method, the conductometric method and the method using a current micrometer. A video film on the study is available.

Bioconversion of a L-carnitin precursor in a one- or two-phase system

The ability of the yeast Saccharomyces cerevisiae to bioconvert stereo-selectively octyl-4-chloroacetoacetate (OCA) into the corresponding chiral alcohol, precursor of L-carnitin, an important physiological agent, was investigated. In a monophasic system with free cells, more than 90% of OCA (0.018 M) bioconversion have been reached after 6 h (enantiomeric excess for the R form, eeR:97%). Immobilized cells in alginate beads were less efficient in conversion of OCA than free cells. In a two-phase system with free cells, the level of reduction of OCA (0.018 M) reached 85% after 48 h. With a medium containing a higher OCA concentration (0.270 M), 41% of this product were bioconverted after the same period. On the other hand, immobilized cells did not show any significant bioconversion of OCA in two-phase reactors. The limiting factor of these reactors in the regeneration of the cofactors involved in the OCA reduction.

Axial dispersion in the liquid phase in a horizontal two-phase tube reactor

The characteristics of axial dispersion in the liquid phase were measured for two basic flow regimes in a horizontal two-phase tube reactor. The data obtained indicate that in some flow regions, axial dispersion can be quite significant.

Fluidization characteristics of gas fluidized beds at elevated temperatures

The hydrodynamic behavior of a gas-fluidized bed has been investigated at ambient and elevated temperatures. Beds of two mean sizes of sands, 641 and 1312 μm, at temperatures of 298 K and also in the range 913–1173 K have been examined over a wide range of air velocities up to 4 m/s. The bed-pressure drop and its fluctuation over a time period of 18 s were measured as a function of air velocity and bed temperature. Variable temperatures were obtained by burning either coal or propane-air mixtures of different compositions. These data were analyzed to obtain values for the minimum fluidization velocity as a function of temperature, bed voidage as a function of bed height, bed temperature and air velocity, and the time-averaged amplitudes of the fluctuations in the pressure drop, bubble or void-renewal frequency and solids concentration as functions of bed temperature and air velocity. It is shown that the hydrodynamic behavior is in accordance with the powder-classification scheme of Saxena and Ganzha. Furthermore, this work has highlight ed the importance of particle size and bed temperature in the operation of fluidized-bed reactors in general and coal combustors in particular. This work has also pointed to the need for further investigations that will improve our understanding of such two-phase reactors.

Hydrolysis of starch with immobilized glucoamylase

Glucoamylase (E.C.3.2.1.3) covalently immobilized onto chitin particles (dst = 0.37 mm) was examined in two types of continuous bench-scale reactors (180 mL) fed with hydrolyzed manioc starch (15%, w/v): a two-phase reactor (liquid expanded-bed) and a threephase reactor (air expanded-bed). Several conditions of continuous operation were investigated, varying the biocatalyst load (16.7, 37.2, and 54 g/L) into the reactor and the hydraulic residence time. The best results were achieved with the two-phase reactor, which operated continuously for 20 d and showed a decrease of only 6% in conversion (starch to glucose). Conversion levels of 96% were obtained with a hydraulic residence time of about 4 h. A simple mathematical model was able to describe the experimental results of the two types of reactors considering biocatalyst deactivation.

Bioconversion of vanillin to vanillyl alcohol in a two-phase reactor

One of the next challenges in the use of biocatalysts (enzyme or microbial cells) is the upgrading of biological reactions of oxidoreduction. The oxidoreductases need cofactors that must be regenerated. Practical experience shows that this is most readily achieved by using living cells of microorganisms. Living cells ofSaccharomyces cerevisiae are able to bioconvert vanillin to vanillyl alcohol (1). By working with a two-phase reactor (dodecanol—feeding medium) it has been possible to use higher vanillin concentrations without inhibiting the bioconversion (2). Several parameters, such as, volume ratio of aqueous over organic phase, pH, vanillin concentration seem to influence the bioconversion greatly. Bearing this is mind, two-phase reactors have been set up. Productivities exceeded 5000 g/m3/d. On the other hand,Saccharomyces cerevisiae mutants have been selected as vanillyl alcohol hyperproducers: vanillyl alcohol productivity of the best selected mutant is twice as high as wild-type strain productivity. Their specific behavior has been studied.

Stationary states of a two-phase flow reactor

Stationary states of a two-phase flow reactor

Reaction and mass transport in two-phase reactors: Sulfonation of benzene

The objectives of this study were (1) to investigate two phase semibatch reactor operations by determining reaction kinetics and mass transfer characteristics, (2) to use parameters determined from the semibatch data to design a continuous two phase reactor system, and (3) to demonstrate the success of this design.

Analysis of a simple model of a bubble-liquid reactor

A mathematical model which describes the operation of a two-phase bubble-liquid reactor is studied. The model reduces to investigation of the Goursat problem for a hyperbolic system of two partial differential equations. A number of exact solutions to this problem are constructed that describe the operation of the reactor from the time of ignition until the onset of the stationary regime of operation. The problem is also investigated numerically.