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.     

氧浓度强制振荡下的丙烯氨氧化反应过程

<正>自从70年代初有学者对催化反应过程的强制振荡操作进行实验研究以来,人们已越来越注意到,对于某些催化反应过程,采用合适的强制周期振荡操作条件比相应的稳态操作产生更优的反应效果,尤其是一些催化氧化反应过程,国内外已有许多研究者开展了大量的实验研究,发现在一定强制振荡周期及振幅操作下能显著提高反应速率（转化率）、主产物的选择性及收率。同时,有许多周期性反应体系的数学模拟理论研究也表明强制振荡操作能     

PERIODIC OPERATION OF ISOTHERMAL PLUG-FLOW REACTORS FOR AUTOCATALYTIC REACTIONS

The performance of isothermal plug-flow tubular reactors under periodic inlet concentration is theoretically analyzed for improvement in yield for liquid phase, homogeneous, autocatalytic reactions of both quadratic and cubic forms. The system of two hyperbolic partial differential equations describing the reactor is solved by the topological method suggested by Bailey (1977). The negligible yield of product obtained at steady-state operation is enhanced to 100 percent yield under periodic operation. The performance of the periodically forced reactor with autocatalytic reactions is compared with that of ordinary simple reactions. The improvement in the yield is much more (at least five times) than that of ordinary simple reactions. The effect of decay of autocatalyst to stable product and the effect of reversibility of reactions on the performance of the periodically forced reactor are evaluated. For irreversible reaction with decay, the yield shows a resonance with inlet pulse width. This is due to complete conversion of the reactant and further only the decay of the autocatalyst.     

Performance Enhancement by Unsteady‐State Reactor Operation: Theoretical Analysis for Two‐Sites Kinetic Model

Theoretical analysis of the reactor performance under unsteady‐state conditions was carried out. The reactions are described by two kinetic models, which involve the participation in catalytic reaction of two types of active sites. The kinetic model I assumes the blocking of one of the active sites by a reactant, and the kinetic model II suggests a transformation of active sites of one type into another under the influence of the reaction temperature. The unsteady‐state conditions on the catalyst surface are supposed to be created (i) by forced oscillations of temperature and concentration in the reactor inlet (periodic operation of reactor) and (ii) by catalyst circulation between two reactors in a dual‐reactor system (spatial regulation). The influence of various parameters like concentration of reactant, cycle split, length of period of forced oscillations, temperatures and the ratio of catalyst volumes in the dual‐reactor was investigated with respect to the yield of the desired product. It is shown that for both cases of unsteady‐state conditions (periodic reactor operation as well as in a dual‐reactor system), a mean reaction rate predicted by the kinetic model I was up to two times higher than the steady‐state value. The kinetic model II shows a 20 % increase of the selectivity towards the desired product.     

Influence of Processing Conditions on the Physicochemical Properties and Shelf-Life of Spray-Dried Palm Sugar (Arenga pinnata) Powder

The influence of spray-drying conditions on some physicochemical properties of palm-sugar powder ( Arenga pinnata ) was studied. Twenty tests were carried out according to a central composite design. Independent variables were: inlet temperature (150–190°C), feed flow rate (9–21 g/min), and maltodextrin concentration (14–25%). Process yield, hygroscopicity, and outlet temperature were analyzed as responses. Results revealed that increasing inlet temperature resulted in higher process yield and outlet temperature and a lower hygroscopicity. Similarly, higher inlet temperature led to lower moisture content, dissolution rate, and total phenolic content of the powder. Conversely, the feed flow rate negatively influenced process yield and hygroscopicity, and positively influenced moisture content. Moreover, maltodextrin exhibited negative influence on process yield and hygroscopicity, respectively. Moreover, storage (30°C, six months) led to noticeable losses in flowability and wettability. Powder morphology was also influenced by the inlet temperature. Lower inlet temperature resulted in particles with shrivelled surfaces while higher temperature produced a greater number of larger particles with smooth surfaces.     

Optimal temperature policies for catalytic transport reactors under periodic operation

The influence of inlet gas concentration cycling on the optimal temperature policy of catalytic transport reactors is studied theoretically. The model considered is based on plug flow of gas and catalyst particles with negligible interand intra-particle diffusional resistances and concentration dependent deactivation kinetics. To utilise the concentration of the reactant and the activity of the deactivating catalyst fully a proper temperature sequence along the reactor is needed. Thus, a general optimal temperature policy using the continuous minimum principle is derived for the reactor under periodic operation. The model equations are solved analytically for gas concentration, activity and temperature profiles. Resonance behaviour (maximum in conversion with pulse width) is obtained using the optimal temperature policy for certain sets of parameters. The effects of activation energy groups, reaction and deactivation constant groups and inlet temperature on the optimal temperature policy under periodic operation are evaluated. In all cases an improvement in conversion with the optimal temperature policy under periodic operation over that with an isothermal policy under periodic operation is obtained. A suboptimal policy, comprising constant temperature over different reactor sections, which is useful for implementation purposes is also discussed.     

Mathematical modelling and experimental validation of a novel periodic flow crystallization using MSMPR crystallizers

The challenges of insufficient residence time for crystal growing and transfer line blockage in conventional continuous mixed‐suspension mixed‐product removal (MSMPR) operations are still not well addressed. Periodic flow crystallization is a novel method whereby controlled periodic disruptions are applied to the inlet and outlet flows of an MSMPR crystallizer to increase its residence time. A dynamic model of residence time distribution in an MSMPR crystallizer was first developed to demonstrate the periodic flow operation. Besides, process models of periodic flow crystallizations were developed with an aim to provide a better understanding and improve the performance of the periodic flow operation, wherein the crystallization mechanisms and kinetics of the glycine‐water system were estimated from batch cooling crystallization experiments. Experiments of periodic flow crystallizations were also conducted in single‐/three‐stage MSMPR crystallizers to validate the process models and demonstrate the advantages of using periodic flow operation in MSMPR stages. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1313–1327, 2017     

Effect of flow rate on temperature in a Bi-P-O catalyst bed: Global enhancement by forced flow rate cycling

Effects of flow rate on reactivity of oxidative coupling of propylene with Bi₂O₃-P₂O₅ were investigated by reaction experiments and by model calculations. Although the conversion is lower at the higher flow rate because of the shorter contact time, there may be a case that when the temperature in the catalyst bed increases and it causes the reaction rate to accelerate. It is thought that the heat was accumulated in the catalyst bed when heat generation rate was much faster than the heat removal rate. The simple calculation based on the assumption of the pseudo-homogeneous phase indicated that the heat was not accumulated at the higher flow rate by the steady-state operation. However, heat wave emerged and accelerated the reaction after the flow rate was changed from the lower flow rate to the higher flow rate. Forced flow rate cycling, an operation where flow rate is changed periodically, was experimentally conducted. The time averaged conversion was slightly enhanced compared with the result from the steady-state operation at the flow rate of . In addition, even in the steady-state operation under the condition where a non-adiabatic reactor packed with only catalyst was used, the conversion and the yield of benzene became higher at the higher flow rate because of the temperature increase in the catalyst bed.     

Polymerization of organic compounds in an electrodeless glow discharge. XI. Pressure in glow discharge

The pressure of a steady-state flow of monomer, p₀, changes to a new steady-state flow pressure, p_g, in glow discharge. The value of p_g is dependent on the flow rate of monomer, the pumping-out rate of the vacuum system for the product gas (which is hydrogen in many cases of plasma polymerization of hydrocarbons), and the characteristic hydrogen yield of a monomer associated with plasma polymerization. The relationships between these factors were established and examined for plasma polymerizations of acetylene, ethylene, and acrylonitrile.     

A Pinched Inlet System for Reduced Relaxation Effects and Stopless Flow Injection in Field-Flow Fractionation

Abstract

The concept of a pinched inlet system for field-flow fractionation (FFF), in which the channel thickness at the inlet end is reduced to hasten relaxation, is introduced and its advantages in simplifying FFF operation and increasing analysis speed are noted. Three forms of FFF operation are described for taking advantage of the split inlet: stopless flow injection, slow flow injection, and stopflow injection. Stopless flow operation is the simplest because flow is neither stopped nor changed to accommodate relaxation. However, stopless flow operation causes band broadening. It is found that the time-based variance of band broadening for many FFF systems is proportional to the fourth power of channel thickness w. Therefore, by reducing w at the inlet end where relaxation occurs, this band broadening can be controlled. The implementation of this concept is discussed for different forms of FFF.     

Numerical and experimental study on the biofiltration of toluene vapor

We have solved both steady state and transient problems on the biofiltration of toluene vapor. The effect of inlet toluene concentration and inlet gas-flow rate on the removal rate of toluene and the elimination capacity of a lab-scale biofilter has been investigated. In this study, the effectiveness factor was a function of pollutant concentration. The dynamic solutions show good agreement with experimental results. At an inlet toluene concentration of 100 ppm, the diffusion of toluene into biofilm was obviously a rate determining step. Above 200 ppm, however, biofilm already showed full activity. The steady-state simulation confirmed that the change of elimination capacity obtained by increasing only inlet toluene concentration was the same as that obtained by increasing only flow rate of contaminated air. The maximum possible performance is about 20 g/m³h with no addition of nutrients.     

A trickling fibrous-bed bioreactor for biofiltration of benzene in air

A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C_gi) was 0·37 g m⁻³, the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1·8 m³ m⁻² h⁻¹. In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was ∽11·5 g m⁻³ h⁻¹ when the inlet benzene concentration was 1·7 g m⁻³ and the superficial air flow rate was 3·62 m³ m⁻² h⁻¹. A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K_l in this model was found to be linearly related to the inlet benzene concentration (K_l=4·64−1·38 C_gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to ∽30 g m⁻³ h⁻¹. Using this model, the maximum elimination capacity for the biofilter was estimated to be 12·3 g m⁻³ h⁻¹, and the critical loading capacity was found to be 14 g m⁻³ h⁻¹. The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m⁻¹ at a high superficial air flow rate of 7·21 m³ m⁻² h⁻¹, indicating a good potential for further scale up for industrial applications. © 1998 Society of Chemical Industry     

连续搅拌釜式丙烯聚合反应器的模拟（Ⅰ）反应器的定态模拟

以实际工业装置为背景，建立了丙烯液相本体聚合连续搅拌釜式反应器的定态数学模型。通过模拟计算，考察了诸工艺参数──进料温度、进料流量、夹套冷却水人口温度和流量、丙烯蒸汽冷凝量、催化剂浓度以及反应器中的氢浓度对聚合反应釜反应结果的影响，并对其定态操作行为作了理论上的解释和分析。     

Influence of forced cycling on the fischer-tropsch synthesis part III. A model for forced concentration cycling over promoted iron catalyst

A model has been developed for the forced feed concentration cycling of a Fischer-Tropsch synthesis reactor containing an iron catalyst promoted with potassium and copper. It was based on an initiation sequence proposed by Vannice (1975) for methanation, a propagation sequence using the CO-insertion mechanism, and termination step based on the desorption of each n-mer, including CH₄. Only surface adsorption, surface reaction and desorption steps were considered; no storage in the catalyst bulk was assumed. Agreement of the model and experimental results permits interpretation of steady-state, as well as the cycling and step-change rate measurements. The model shows that hydrogen is involved in the rate determining step, and further that, except for methane, the results of hydrocarbon production from steady-state, step-change, and periodic experiments could all be reconciled for the results from C₂ to C₉. Failure of the model properly to predict rates of methane formation during cycling operation is attributed to changing carbidization of the catalyst.     

Instationäre Prozeßführung kontinuierlicher Reaktoren

Non-steady-state operation of continuous reactors . The behaviour of continuous chemical reactors can be altered significantly by forced oscillation of the reactor parameters such as feed concentration of the reactants, flow rate, and temperature. In contrast to autonomous oscillations in unstable systems, the forced periodic disturbances are controlled and can be used as a further parameter for process optimization. The dynamic behaviour of individual steps of the overall reaction and of the reactor can be exploited to obtain performances and selectivities which cannot be accomplished in the traditional way on steady-state operation under comparable conditions. This is shown in discussing some simple kinetic schemes published in theoretical studies and comparing them with experimental results for homogeneous and heterogeneous reactions. The physical and chemical causes for the predicted and observed advantages of periodic operation are discussed.     

Unsteady-state operation of trickle-bed reactor for dicyclopentadiene hydrogenation

Unsteady-state operation of a trickle-bed reactor (TBR) was investigated using a multi-step exothermic reaction, hydrogenation of dicylcopentadiene (DCPD) in the presence of Pd/Al₂O₃ catalyst. The influences of five operation strategies on the reactor performance were symmetrically studied and compared with the steady-state operation, including ON-OFF and PEAK-BASE modulations of the liquid flow rate or concentrations, and a novel hybrid modulation of liquid flow rate and concentration. Attempts were also made to develop an unsteady-state operated TBR model based on a plug-flow model incorporating fluid flowing behaviors, three-zone partial wetting catalyst, vapor-liquid phase equilibrium and enthalpy balance, to predict the overall performance under unsteady-state operations. Compared with the experimental observations, it is indicated that the developed model is generally reliable to predict performance enhancement for different modulation strategies.     

Anaerobic catalytic oxidation of hydrocarbons in moving heat waves. Case simulation: Propane oxidative dehydrogenation in a packed adiabatic V-Ti oxide catalyst bed

The model simulation study has shown that the anaerobic process of oxidative dehydrogenation of propane under periodic alteration of feeding between propane and air may be realized in adiabatic catalyst beds in a stable continuous cyclic mode in a two-reactor scheme. In the case of an appropriate choice of process parameters (cycle duration and feeding flow rates) the process appears to be autothermal, i.e. it does not require any inlet gas preheating for stable operation. Compared with a similar steady-state adiabatic process, the proposed process is characterized with much lower maximum catalyst temperatures, giving the way to process pure propane without diluting it with inert gases, thus simplifying the downstream procedure of product separation. Predicted propylene yield is competitive with the one for the steady-state adiabatic process, while sufficient technological benefits of the new technology are expected (decrease in energy consumption and minimization of heat-exchange environment, process safety improvement, suppression of coke formation and efficient coke incineration).     

Physicochemical and nutraceutical properties of barley grass powder microencapsulated by spray drying

ABSTRACT

Barley grass (Triticum aestivum L.) is popular, commonly known as a nutritional supplement in China. To obtain the highest chlorophyll and flavonoid content as well as other physicochemical characteristics, spray drying from barley grass juice was carried out for two different maltodextrin concentrations (10 and 20%, dried basis) and four different inlet air temperatures (140, 150, 160, and 170°C). After drying, color, water activity, odor, taste, density, particle size, glass transition temperature, and chlorophyll and flavonoid contents of the dried product were measured. Highest contents of flavonoid (5.66?mg/kg) and chlorophyll (7.29?mg/kg) were obtained under 150°C inlet air temperature, 10% maltodextrin concentration, at a feed flow rate of 1.8?L/h for the drying. Corresponding particle size was 19.58–13.33?µm. The glass transition temperature (T_g) increased with the increasing of maltodextrin concentration; and two max T_g of powder obtained from 10 and 20% maltodextrin concentration were 74.4 and 77.4°C, respectively. Retention of taste and flavor were highest with 20% maltodextrin. High inlet air temperature was contributed to the large discrepancy of odor and taste substances. The best color (lightness L*?=?64.44 and greenness b*?=??11.53) was obtained at 150°C inlet air temperature and 10% maltodextrin concentration. Both maltodextrin concentrations resulted in poor flowability of the dried product (C_I?≤?32.51).     

Modeling and control of solar‐grade silicon production in a fluidized bed reactor

A multiscale model predicts silicon production yield and powder loss in a fluidized bed reactor for solar silicon production. The reaction module calculates the silicon vapor deposition and powder scavenging rates. A computational fluid dynamics model predicts temperature and bed density. A population balance model calculates the particle‐mass distribution functions on silicon yield. The model results are validated against industrial data. Furthermore, we conduct a sensitivity analysis to investigate the effect of gas flow rate and inlet silane concentration. Finally, a control strategy is proposed to maintain the process at the desired operating point. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1740–1751, 2014     

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.