Optimal feed temperature for an immobilized enzyme packed-bed reactor

Optimal feed temperature was determined for a nonisothermal immobilized enzymatic reaction with enzyme deactivation in a packed-bed reactor. The optimal feed temperature was obtained by maximizing the average substrate conversion over a given reaction period. Simulation showed the optimal feed temperature to be strongly dependent on the flow dispersion, the reaction activation energy, the corresponding enzyme inactivation energy and the heat of reaction. It was also observed that in a plug flow reactor the enzyme reaction generally exhibited a lower optimal feed temperature and higher substrate conversion than in a continuously stirred tank reactor.     

Mathematical analysis of the performance of a packed-bed coimmobilized bioreactor

A model has been developed to describe the performance of a packed-bed coimmobilized biochemical reactor. Each step in the consecutive reaction is assumed to follow Michaelis—Menten type kinetics. The model includes all the limiting steps controlling the rate of reaction and the additional effect of axial dispersion of bulk liquid. The model equations are solved by the explicit finite difference method from the transient to steady-state condition. The effects of various parameters of physical importance on the reactor performance are discussed.     

填充床反应器中酶法合成生物蜡酯

研究了填充床式反应器酶法合成生物蜡酯的生产工艺。以大豆油、十六醇为原料,在石油醚体系中,使用实验室自制的固定化Candida sp.99-125为催化剂。对操作参数,如填充高度、进料速度、固定化酶用量、底物摩尔比进行了研究。结果表明,固定化酶质量为47 g,填充高度40 cm（内径3.5 cm）,油醇摩尔比1∶2.4,以4 mL/min速度进料保留时间4 h,产率可达83%。固定化酶在使用16批时,产率仍保持在70%以上。同时,对于填充床的填充方式作了初步探索。     

A computational method for determination of the mass-transfer coefficient in packed-bed immobilized enzyme reactors

A computational method was developed that determined the mass-transfer coefficient k_L or the volumetric mass-transfer coefficient k_La in packed-bed immobilized enzyme (IME) reactors. To study the performance of this method, two experimental systems were considered where an enzyme was immobilized on a non-porous support surface (surface-IME system) or within a porous support (pore-IME system). The values of k_L and k_La determined in these packed-bed IME reactor systems were successfully expressed in terms of the substrate concentration at the reactor inlet and the liquid flow rate. Furthermore, the correlations obtained for k_L and k_La were used to calculate the unconverted fractions of substrate at the reactor outlet. Comparison showed that the calculated results were in satisfactory agreement with the experimental values.     

Wave phenomena in the packed-bed reactor: Their relation to the differential-flow instability

The steady state of a non-isothermal packed-bed reactor (PBR) is convectively unstable in the sense that upstream perturbations are amplified in the course of their downstream propagation before they are washed out by the flow. The differential-flow instability (DIFI) that underlies this dynamics arises from the different rates of transport of heat and matter in the PBR and from the autocatalytic nature of the reaction heat. In the PBR with recycle, the DIFI has an absolute character and it results in self-sustained, periodic wave activity. The DIFI-concept provides a theoretical framework for interpreting and analysing several types of wave phenomena in PBRs.     

Performance analysis of an immobilized yeast packed-bed reactor for ethanol fermentation

The performance of an immobilized packed-bed bioreactor for continuous ethanol fermentation was evaluated. Immobilized yeasts were prepared by entrapment in calcium alginate gel. An axial dispersed plug flow model incorporating the effects of substrate and product inhibition on fermentation kinetics was developed. The model equations were solved by the method of orthogonal collocation and the suitability of the reactor model to predict the conversions obtained in this biocatalytic reaction system was assessed.     

The role of kinetics and heat transfer on the performance of an industrial wall-cooled packed-bed reactor: Oxidative dehydrogenation of ethane

This contribution evaluates systematic but rigorous methodologies to characterize kinetics and heat transfer mechanisms and states statistical and phenomenological criteria to model an industrial-scale wall-cooled packed-bed reactor for the oxidative dehydrogenation of ethane over a MoVTeNbO catalyst. A set of kinetic formalisms was submitted to regression analyses with the reparametrized form of the Arrhenius and van't Hoff equations. Heat transfer parameters (HTP) were determined by evaluating either the effect of hydrodynamics or the type of temperature measurements on reactor simulations. Eley–Rideal formalism led to the most proper approach to describe kinetics, presenting thermodynamic consistency and statistical confidence; whereas the HTP determined out of radial and axial measurements and accounting for hydrodynamics led to the determination of the most reliable transport parameters presenting phenomenological and statistical significance. These results stated criteria to model with confidence the performance of the studied technology, paving the way for its further rigorous design, optimization, or intensification.     

Continuous ethanol production from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor

The continuous production of ethanol from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor has been investigated. At a substrate concentration of 150 g dm^?3, maximum ethanol productivity of 16 g dm^?3 h^?1 was obtained at D = 0·4 h^?1 with 62·3% of theoretical yield and 83·6% sugars′ utilization. At a dilution rate of 0·1 h^?1, optimal ethanol productivity was achieved in the pH range 3·5–5·5, temperature range 30–35·C and initial sugar concentration of 200 g dm^?3. Maximum ethanol productivity of 24·5 g dm^?3 h^?1 was obtained at D = 0·5 h^?1 with 58·8% of theoretical yield and 85% sugars′ utilization when non-sterilized carob pod extract containing 200 g dm^?3 total sugars was used as feed material. The bioreactor system was operated at a constant dilution rate of 0·5 h^?1 for 30 days without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical) and sugars′ utilization were 25 g dm^?3 h^?1, 58·8% and 85·5%, respectively.     

Modelling of simultaneous methanogenesis and denitrification in an upflow packed-bed biofilm reactor

The performance of an upflow packed-bed biofilm reactor was investigated by considering simultaneous methanogenesis and denitrification reactions under step and sinusoidal variations of feed concentration and temperature. For simultaneous step inputs of 20 mg dm⁻³ of NO₃⁻—N and 60 mg dm⁻³ of methanol, the proposed model shows that major conversion of both the substrates takes place in the first half of the reactor. However, when the inlet concentration of methanol is subjected to sinusoidal variation, while that of NO₃⁻—N is maintained stepwise, the exit concentration of both methanol and NO₃⁻—N follow a sinusoidal response. On the other hand, when the inputs are reversed (methanol stepwise and NO₃⁻—N sinusoidal), the response exhibits similar behaviour. For sinusoidal variation of feed temperature the exit concentration profiles of both substrates also follow a sinusoidal pattern. For methanol, the mean steady state conversion under sinusoidal variation is higher than the corresponding steady state concentration when feed temperature is constant at 30°C. The model predictions are in good agreement with the experimental data available in the literature. ©1997 SCI     

Effect of enzyme inhibition on the performance of packed-bed biological reactor - a theoretical study

The performance characteristic of a packed bed reactor has been analyzed by considering diffusional resistance of the biofilm. Model equations were solved by the method of orthogonal collocation for various classical enzyme inhibition kinetics, including partially non-competitive, partially competitive, partially uncompetitive, partially mixed and fully mixed. For all considered modes of inhibition, an increase in the inlet substrate concentration decreases the steady state conversion in the reactor. However, an increase in the Peclet number has been found to improve the conversion. The effects of various other process variables of physical importance were also investigated parametrically.     

Effect of the rotor shape on the mixing characteristics of a continuous flow Taylor-vortex reactor

Macro- and micromixing in a continuous flow Taylor-vortex reactor with novel ribbed rotors were investigated and compared to the features of a classical cylindrical rotor. The characterisation was performed in a wide hydrodynamic range (40<Ta<2500 and 0.03<Re<0.51) through tracer experiments and the analysis of the rotor power consumption. Additionally, the flow patterns were visualised by using a rheoscopic fluid. The results show that the novel rotors equipped with ribs immobilise and stabilise the vortices. As compared to cylindrical rotors, micromixing is clearly enhanced while axial dispersion can be simultaneously reduced. Through the use of ribbed rotors, the operational window can be broadened considerably, in which the reactor runs at very low or moderate extent of macromixing.     

Free radical polymerization of methyl methacrylate: Modeling and simulation under semibatch and nonisothermal reactor conditions

For the bulk free radical polymerization of methyl methacrylate (MMA), equations of the material balance can be written that are based on a kinetic diagram that considers initiation by decomposition of an AIBN initiator, propagation, and termination by disproportionation. To quantify the gel and glass effects simple empirical dependences are used between the rate constants of termination and propagation and monomer conversion. Numerical values for the empirical parameters at different temperatures and initiator concentrations are also given. Conversion history and molecular weights are obtained by simulation when an initiator or monomer are added to the reaction mass and the temperature modifies after some reaction has taken place. These intermediate operations are simulated at different moments with respect to the gel and glass effects. The validation of the model for semibatch and nonisothermal conditions are made by comparing the simulation results with literature experimental data. The most important conclusion of the article is that the empirical model proposed for the gel and glass effects can be successfully used under semibatch and nonisothermal reactor conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2561–2570, 1999     

Modeling of a packed-bed electrochemical reactor for producing glyoxylic acid from oxalic acid

A two-dimensional reactor model was established for a packed-bed electrochemical reactor with cooled cathode (PERCC) for producing glyoxylic acid from oxalic acid based on the system's reaction kinetics, mass conservation equation, and the equation of charge conservation in terms of solution-cathode potential to describe the distributions of glyoxylic acid concentration and electrolyte potential in the cathode compartment of the PERCC. The equation for a circulating mixer was also presented to account for the accumulation of glyoxylic acid in the catholyte of a batch electroreduction process. Using the orthogonal collocation approach, the partial differential equations of the model could be converted into sets of algebraic equations and be numerically solved. The effects of operating temperature, conductivity of catholyte, operating cathode potential, and volumetric flow rate of the catholyte on the current efficiency and concentration of glyoxylic acid were simulated and discussed, with emphasis on the current densities generated from main and side reactions. The model was used in a batch operation process and a continuous operation process, with the predicted results being generally in good agreement with the experimental data for both the cases.     

固定化L-天门冬酰胺酶的性质及其填充床反应器的研究

利用海藻酸钙包埋、戊二醛交联的方法对L-天门冬酰胺酶进行固定化。研究了固定化L-天门冬酰胺酶的最适pH、最适温度、米氏常数、半衰期等酶学性质,并考察了影响固定化酶柱式填充床反应器转化率的因素。结果表明:固定化酶最适pH值为8.5,最适温度为67°C,固定化酶的米氏常数Km增大,固定化酶半衰期随着温度的增加而逐渐减小;温度、反应柱内径、底物溶液浓度、流速等因素对填充床反应器转化率均有显著影响。     

Comparison of the performance of a direct-contact bubble reactor and an indirectly heated tubular reactor for solar-aided methane dry reforming employing molten salt

A theoretical approach is presented for the comparison of two different atmospheric pressure reactors—a direct-contact bubble reactor (DCBR) and an indirectly heated tubular reactor (IHTR)—to evaluate the reactor performance in terms of heat transfer and available catalytic active surface area. The model considers the catalytic endothermic reactions of methane dry reforming that proceeds in both reactors by employing molten salts at elevated temperatures (700–900 °C) in the absence of catalyst deactivation effects. The methane conversion process is simulated for a single reactor using both a reaction kinetics model and a heat transfer model. A well-tested reaction kinetics model, which showed an acceptable agreement with the empirical observations, was implemented to describe the methane dry reforming. In DCBR, the heat is internally transferred by direct contact with the three phases of the system: the reactant gas bubbles, the heat carrier molten salts and the solid catalyst (Ni-Al₂O₃). In contrast, the supplied heat in the conventional shell-and-tube heat exchanger of the IHTR is transferred across an intervening wall. The results suggest a combination system of DCBR and IHTR would be a suitable configuration for process intensification associated with higher thermal efficiency and cost reduction.     

Effects of UV‐irradiation on the nonisothermal crystallization kinetics of polypropylene

The influences of UV‐induced photodegradation on the nonisothermal crystallization kinetics of polypropylene (PP) were investigated by differential scanning calorimetry. The Avrami analysis modified by Jeziorny, Ozawa method, and a method modified by Liu were employed to describe the nonisothermal crystallization process of unexposed and photodegraded PP samples. Kinetics studies reveal that the rates of nucleation and growth may be affected differently by photodegradation. A short‐term UV‐irradiation may accelerate the overall nonisothermal crystallization process of PP, but a long‐term UV‐irradiation should impede it. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Production of structured lipids in a packed-bed reactor with <Emphasis Type="Italic">thermomyces lanuginosa</Emphasis> lipase

Lipase-catalyzed interesterification between fish oil and medium-chain TAG has been investigated in a packedbed reactor with a commercially immobilized enzyme. The enzyme, a Thermomyces lanuginosa lipase immobilized on silica by granulation (lipozyme TL IM; Novozymes A/S, Bagsvaerd, Denmark), has recently been developed for fat modification. This study focuses on the new characteristics of the lipase in a packed-bed reactor when applied to interesterification of TAG. The degree of reaction was strongly related to the flow rate (residence time) and temperature, whereas formation of hydrolysis by-products (DAG and FFA) were only slightly affected by reaction conditions. The degree of reaction reached equilibrium at 30–40 min residence time, and the most suitable temperature was 60°C or higher with respect to the maximal degree of reaction. The lipase was stable in a 2-wk continuous operation without adjustment of water content or activity of the column and the substrate mixture.     

Effect of reactor internal properties on the performance of a flow reversal catalytic reactor for methane combustion

This paper describes the use of a flow reversal reactor for the destruction of lean emissions of methane with ambient temperature feed. The reactor consisted of two parallel sections, each containing a packed bed reactor and inert sections to act as heat traps. In this paper, the effect on reactor performance of the inert properties is illustrated. Three different inert types are described. These are a ceramic monolith of 100 cells per square inch cell density, a metal monolith and a packed bed of Denstone balls. Use of monolith inserts reduces the reactor pressure drop. Inert sections with lower thermal mass give rise to greater movement in temperature fronts, requiring the use of shorter cycles.     

The effect of process nonlinearities on the performance of a periodically operated isothermal catalytic reactor

The periodic behaviour of a heterogeneous isothermal catalytic reactor involving a single irreversible reaction based on the Langmuir-Hinshelwood mechanism is studied. Square-wave concentration cycling of the reactants is used as the reactor input. The nonlinear behaviour of the reactor is analysed by using a special function developed in the present paper. The slope of this special function provides qualitative as well as quantitative information about the enhancement (ratio of periodic and steady-state performance) as a result of periodic operation for large cycle periods. Enhancement as a function of cycle period shows resonance behaviour for one special condition, i.e. for the products to be more strongly adsorbed than the reactants. Only this special condition is found to entail performance improvement over the optimum steady state.     

Analysis of a nonisothermal simulated moving‐bed reactor

Simulated moving‐bed reactor (SMBR) is a multifunctional reactor wherein in situ separation of the products facilitates the reversible reaction to completion beyond thermodynamic equilibrium and at the same time obtaining products of high purity. In this work, we investigate the feasibility of introducing variances in adsorption strength, which has recently been proven to effectively improve SMB performance for pure separation, into an SMB system to include reactions. Synthesis of methyl acetate catalyzed by amberlyst 15 is considered as model system. Numerical simulations were carried out for an SMBR unit consisting of four columns and operated with various temperature distributions in the range of 308–323 K. SMBR productivities were evaluated and compared under the constraints of complete conversion and complete product separation. The effects of kinetics, heat transfer efficiency and adsorption strength of reactant were systematically investigated. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4705–4714, 2013