Periodic operation of a bioreactor with input multiplicities

The performance of a continuous bioreactor under periodic inlet substrate concentration is theoretically analyzed for productivity improvement which under conventional steady-state operation shows input multiplicities in the feed substrate concentration. Two values of feed substrate concentration give identical productivity under conventional steady-state operation. A periodic rectangular pulse is assumed for the feed substrate concentration. It is shown by simulation that under concentration forcing the average productivity is significantly different for these two substrate concentrations. The larger value of feed substrate concentration gives improved average productivity and shows a resonance with the period of oscillation. The effect of periodic operation on the average productivity under the input multiplicities in dilution rate is also analysed.     

Concentration forcing of isothermal plug-flow reactors for autocatalytic reactions

The performance of isothermal plug-flow reactors under feed concentration forcing is analysed for improvement in average yield of product B for a homogeneous autocatalytic reaction, A →k1 A₁ →k2 A_, →k3 B, where A₁ or A₂ has an activity influence on the reaction rate constant k₁. The performance of the periodically forced reactor with the autocatalytic reaction is compared with that of the corresponding uncatalysed reaction.     

Periodic operation of transport reactors for catalytic reactions

Based on plug flow of gas and catalyst particles and concentration dependent deactivation kinetics, the performance of transport reactors under a periodic (rectangular pulse) inlet concentration is analysed for improvement in conversion and extent of catalyst decay. The effects of reaction and deactivation orders, reaction and deactivation constant groups, and γ (cycle split) on the performance of the reactors are evaluated theoretically. For reaction orders greater than one, periodic operation improves conversion. Resonance behaviour is observed for certain combinations of parameters. For identical operating conditions vertical upflow, downflow and horizontal flow reactors are compared. Conversion in upflow reactors is higher than that in either horizontal flow or downflow reactors. However, catalyst decay is the least in downflow reactors.     

Optimization of non-steady-state operation of reactors

Non-steady-state operation of reactors is approached from the optimal control point of view. To find the best type of input, dynamic programming is used. The results show that for some systems, the optimal input is oscillatory in nature as has been found experimentally by others. A modification to conventional dynamic programming is used to avoid the need for interpolation and thus allow high-dimensional systems to be handled more readily. Three chemical engineering systems of different complexity were considered to test the computational aspect of the approach. In all cases, dynamic programming gives the optimum policy with respect to the period, cycle-split and amplitude.     

新型连续乳液聚合反应器

介绍了4种主要连续乳液聚合反应器的研究新进展,包括连续搅拌釜式反应器、连续环管式反应器、脉冲填料塔式反应器及库爱特-泰勒旋流式反应器。提出了连续乳液聚合反应器的发展方向。     

The bifurcation behavior of continuous free-radical solution loop polymerization reactors

The bifurcation behavior of continuous free-radical solution loop polymerization reactors is analyzed in this work. A mathematical model is developed in order to describe the impact of the recycling pump and other external reactor parts upon the process dynamics and stability. Stability analysis is performed using bifurcation theory and continuation methods. It is shown that under certain operational conditions as many as seven steady states are predicted for the loop polymerization reactor. Oscillatory behavior is observed for a wide range of process parameters and onset of oscillations is observed during the transition from operation without material recycling to operation with partial recirculation of the polymer solution. Besides, at certain constrained range of operation conditions, complex dynamics can be observed, including the onset of chaotic behavior. It is also shown that the thermal parameters of the reactor and recycling pump exert a profound effect upon the process stability. For this reason it is shown that oscillatory behavior is very unlikely to occur in actual industrial reactors.     

A study of CrO vapor decomposition in approximated isothermal RF plasma reactors

A simplified RF plasma reaction model has been used for describing the thermal decomposition reaction of chromium oxide (CrO), using an argon RF plasma operated at 2.7 kW. A set of 3 approximated isothermal reactors in series were defined for this purpose within the RF torch. The conversion rate curves were obtained for the respective average isothermal temperatures 4250 K, 3500 K and 2950 K. Reaction order and reaction rate constant were determined at each temperature. Based on the values obtained for the reaction orders, it appears that the kinetics process involved is similar at 2950 K and 3500 K, while a distinctly different process occurs at 4250 K. Assuming that the two former reactions show an Arrhenius type behavior, an activation energy value has been derived, valid between 2900 K and 3500 K. The activation energy for the CrO decomposition reaction has been calculated on the basis of an Eyring and Polanyi model. The calculated and experimental results differ by about 20%. The main point responsible for the large reaction rate constant increase observed at 4250 K is the drastic change of the pre-exponential factor in the Arrhenius equation.     

Factors affecting production of nonaqueous peracetic acid in tubular packed reactors

The synthesis of nonaqueous peracetic acid in acetone by acetaldehyde oxidation was carried out in a tubular packed reactor. The influencing factors of the reacting system including packing material, oxygen carrier, and reactor configuration were investigated. The results show that porous materials are inappropriate for peracetic acid synthesis and only non porous material with appropriate surface area can provide good peracetic acid selectivity and yield. Among the six kinds of packing material investigated, SA-5118 is the best one. As oxidizing gas, pure oxygen is superior to air. The optimum length-to-inner diameter ratio of the reactor is about 40. Under the proper reaction conditions, the highest peracetic acid yield of 84.15% and the highest selectivity of 93.34% can be achieved which indicates that the novel reacting system is effective and economical for nonaqueous peracetic acid production.     

Challenges for the periodic operation of trickle-bed catalytic reactors

Since the earliest publications just over a decade ago, the literature on periodic operation of trickle beds has grown rapidly. There are now over 30 published papers. Two applications, flow and feed composition modulation, for control of hot spots in large-scale reactors are sufficiently advanced for full-scale implementation if that has not already taken place. Models are now available that are capable of representing the time-average performance of periodically operated trickle beds, but these are not detailed enough to reproduce all of the transient behavior observed. Much about performance under periodic operation remains to be discovered. Research challenges are discussed under separate types of periodic operation: flow interruption, flow augmentation for hot spot control, feed composition modulation for hot spot control and to improve rate and/or to modify selectivity, and flow variation for enlargement of the pulse flow regime.     

Evaluation and improvement of dynamic optimality in electrochemical reactors

A systematic approach for the dynamic optimization problem statement to improve the dynamic optimality in electrochemical reactors is presented in this paper. The formulation takes an account of the diffusion phenomenon in the electrode/electrolyte interface. To demonstrate the present methodology, the optimal time-varying electrode potential for a coupled chemical-electrochemical reaction scheme, that maximizes the production of the desired product in a batch electrochemical reactor with/without recirculation are determined. The dynamic optimization problem statement, based upon this approach, is a nonlinear differential algebraic system, and its solution provides information about the optimal policy. Optimal control policy at different conditions is evaluated using the best-known Pontryagin's maximum principle. The two-point boundary value problem resulting from the application of the maximum principle is then solved using the control vector iteration technique. These optimal time-varying profiles of electrode potential are then compared to the best uniform operation through the relative improvements of the performance index. The application of the proposed approach to two electrochemical systems, described by ordinary differential equations, shows that the existing electrochemical process control strategy could be improved considerably when the proposed method is incorporated.     

Forced oscillations of concentration in transport reactors

The performance of a transport catalytic reactor is analysed for an adsorption/desorption type model with Eley-Rideal surface kinetics with square wave oscillations in the feed concentration. The inlet average concentration of both the reactants over a period is assumed to be constant. Significant improvement in the yield of product is obtained by increasing the feed concentration of both the reactants in the first fraction of a period. The effect of adsorption capacity of the catalyst, reaction rate constants, and inlet feed mean concentration of the reactants are evaluated. The deactivation of active sites, due to product inhibition, introduces resonance in the yield versus cycle split. The yield of product shows a minimum with respect to cycle split for the type of forcing where one of the reactant concentrations increases and the second reactant concentration decreases in the first fraction of a period.     

Optimum operation of oxidative coupling of methane in porous ceramic membrane reactors

This paper presents analysis of oxidative coupling of methane on Li/MgO packed porous membrane reactor (PMR) by the fixed-bed reactor (FBR) model with reliable reaction kinetic equations. PMR can improve the selectivity and yield by controlling the oxygen feed to the catalyst bed through manipulating the feed pressure. At a fixed methane feed rate there is an optimal oxygen feed pressure that will achieve the highest yield. With a commercial ultrafiltration ceramic membrane, theoretical analysis shows that PMR can achieve, by operating with both side pressures at 1 bar at 750 °C, a maximal 30% yield at 53% selectivity. The maximal yield achieved in the FBR of identical dimension and temperature is 20.7% at 52.5% selectivity. Parametric study shows that lowering the membrane permeability improves the performance. Higher oxygen feed pressure will reduce the yield as well as the selectivity. Homogeneous reactions at high shell-side pressure can have adverse effect on the performance due to the fact that homogeneous reaction rates are strongly pressure dependent. The shell (oxygen feed) side volume must be minimized to reduce the homogeneous reactions. The results of PMR model calculation fit the published experimental result unexpectedly well.     

Analysis and optimization of cross-flow reactors with distributed reactant feed and product removal

A systematic and general model was proposed for the simulation of cross-flow reactors with product removal and reactant feed policies. Six types of cross-flow reactors were analyzed for reversible series-parallel reaction systems and their optimal feed distributions were determined by maximizing the desired product yield at the outlet of the reactor. The performances of reactors with different types of feed policies were compared at their optimal operating conditions. For irreversible reaction systems with lower order in distributed reactant for the desired reaction than those for undesired reactions, a higher yield and selectivity of the desired product could be achieved with the reactors with staged feed than with conventional co-feed reactors and a sufficiently high residence time was required by staged feed reactors to significantly improve the desired product yields and selectivities over those obtained by a co-feed reactor. However, for reversible reaction systems, the desired product yield always reached a maximum value, and then dropped down as the residence time increased. In addition to the kinetic order and residence time requirements, the rate constants of the reactions involved have to fall within certain ranges for the distributed feed reactor to obtain a higher maximum yield than one-stage co-feed reactors. Optimally distributed feed reactors always give higher maximum product yields than evenly distributed reactors with the same number of feed points. However, the improvement of yields is not as great as that between co-feed reactors and evenly distributed reactors. On the other hand, for reaction systems with higher order with respect to the distributed reactant in the desired reaction than the undesired reactions, co-feed reactors always give higher yield than staged feed reactors.     

The influences of the gas rate dissolution and mass-transfer limitation at the interfaces on selectivity of gas–liquid processes in stirred reactors with a suspended catalyst

A complex mathematical model accounting for the hydrogen dissolution process in suspensions and mass-transfer steps at the liquid–solid interface for the gas and liquid components is given. The calculated data according to the model for the reaction A→B→C shows, that the yield of an intermediate product B is very much affected by the relation of the gas component mass-transfer coefficient on the gas–liquid interface to that on the liquid–solid one. The hydrogenation of chlornitroaromatic compounds was analysed. The kinetics of the catalytic reduction of p-chlornitrobenzene to p-chloraniline via corresponding arylhydroxilamine on the Ir/C catalyst experimentally in a batch reactor has been studied. In this process the first reactions depend on the hydrogen concentration but the second ones are not dependent — this is a disproportion of the intermediate product to the final product — amine.     

An input/output approach to the optimal transition control of a class of distributed chemical reactors

An input/output approach to the optimal concentration transition control problem of a certain type of distributed chemical reactors is proposed based on the concept of residence time distribution, which can be determined in practice by using data from experimental measurements or computer simulations. The main assumptions for the proposed control method to apply are that the thermal and fluid flow fields in the reactor are at pseudo-steady-state during transition and that the component whose concentration is to be controlled participates only in first-order reactions. Using the concept of cumulative residence time distribution, the output variable is expressed as the weighted sum of discretized inputs or input gradients in order to construct an input/output model, on the basis of which a constrained optimal control problem, penalizing a quadratic control energy functional in the presence of input constraints, is formulated and solved as a standard least squares problem with inequality constraints. The effectiveness of the proposed optimal control scheme is demonstrated through a continuous-stirred-tank-reactor (CSTR) network and a tubular reactor with axial dispersion and a first-order reaction. It is demonstrated through computer simulations that the proposed control method is advantageous over linear quadratic regulator (LQR) and proportional-integral (PI) control in terms of control cost minimization and input constraint satisfaction.     

UV absorption by TiO2 films in photocatalytic reactors: Effect of fold curvature

Corrugated reactors are known for their use in applications requiring exposure of a reaction medium or catalyst to UV radiation. During manufacture, the idealized sharp corner of a V‐shaped geometry is replaced with a fold having quantifiable curvature. The effects of this curvature on UV absorption patterns, spatial absorption/incidence patterns and the total absorption efficiency are explored for a broad range of fold curvatures and film angles using a conservative, finite‐element based discrete‐ordinate model. The presence of curvature was found to redistribute radiation from the deepest confines of the V‐shaped geometry to surfaces closer to the light source. The simulations performed suggest that at small film angles, moderate curvature can be incorporated within the fold of the film without significantly affecting the overall absorption efficiency. Detailed absorption data is included for use as a boundary condition for computational fluid dynamics‐based simulations linking UV‐radiation, reaction kinetics, and mass transfer. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

PVC反应釜的高压水清洗

介绍了在PVC生产过程中反应釜附着污垢的危害,分析了几种反应釜清洗方法,指出反应釜高压水清洗装置是目前世界上先进的自动化清釜装置,防粘釜剂有可能会被逐步禁止使用。还介绍了高压水射流的一些基本概念。     

Fabrication of microtubular reactors coated with thin catalytic layer (M=Pd,Pd−Cu,Pt, Rh,Au)

Novel micro tubular reactors composed of Inconel 625 support, TiO₂/Ti intermediate layer and thin catalytic metal film (Pd, Pd−Cu alloy, Pt, Rh, and Au) were fabricated by continuous electroless plating technique. The reactors withstood high temperature (400 °C) and high pressure (30 MPa) water flow without loss of catalytic metals. The high catalytic efficiency of the reactors was demonstrated by the rapid and complete decomposition of organic dye in the flow system.