A new micro-kinetic model is proposed for galacto-oligosaccharide (GOS) synthesis with β-galactosidase from Aspergillus oryzae. Several kinetic models with similar reaction mechanisms, i.e., steps ...and kinetic constants, have been investigated covering a range of initial lactose (20–40 wt %) and enzyme concentrations (0.5–2 mg/mL). The kinetic parameters were estimated simultaneously for all experimental results using a hybrid genetic algorithm. A detailed analysis of the effect of process parameters on the concentrations of lactose and GOS is performed. The proposed model has a very good quantitative fit of the experimental data, with an average error of 9.34%. More importantly, qualitative trends for the change in the concentration of lactose and GOS are predicted excellently, especially if one takes into account the variation of both concentrations of enzyme and lactose in a range wider than reported in the literature to date. Also, the analysis between the two comparative reactions of transglycosylation and lactose hydrolysis confirmed the positive effect of increasing lactose concentration on the production of GOS. On the other hand, a higher enzyme concentration resulted in a faster production of GOS but with more intensive decomposition at longer reaction times.
We investigate effects of catalyst activity, catalyst particle shape (sphere, slab, and hollow cylinder), size (i.e., diffusion length), catalyst distribution (uniform vs eggshell type distribution ...for a spherical particle), and process conditions (temperature, pressure, syngas composition, and conversion level) on catalyst effectiveness factor and methane selectivity inside the catalyst pellet. In numerical simulations we utilize kinetic parameters for CO consumption rate and CH4 formation rate determined from experiments with a highly active Co/Re/γ-Al2O3 catalyst. It is found that the use of small spherical particles (0.2–0.5 mm) or eggshell distribution for larger spherical particles with catalyst layer thickness less than approximately 0.13 mm is needed to avoid negative impact of diffusional limitations on CH4 selectivity under typical Fischer–Tropsch synthesis operating conditions. For monolith reactors with wash-coated catalyst, diffusional limitations can be avoided by using a catalyst layer thickness less than 0.11 mm at base case conditions (473 K, 25 bar, and H2/CO molar ratio of 2).
•Novel helical oscillatory baffled reactor geometry for batch to continuous transition.•Improvement in mixing performance compared to classical oscillatory baffled reactor.•CFD modeling and ...simulations of oscillatory baffled reactors at low Re numbers.•Pulse tracer experiments in 3D printed oscillatory baffled reactor prototype.•Model of residence time distribution based on the tanks-in-series approach.
A helical oscillatory flow reactor with orifice baffles (HOBR) is proposed for use in slow biochemical and pharmaceutical processes. The new reactor geometry with 10 mm diameter was analyzed using the dynamic 3D CFD model and pulse tracer experiments in a 3D printed prototype, for a range of oscillatory and non-oscillatory flowrates (Reo = 25 – 300 and Ren = 20 – 78). Comparison of the HOBR with the classical OBR design using CFD simulations, under the same flow conditions, showed that the new geometry provides near plug flow conditions and notably improves mixing performance. This is due to more complex flow patterns and the enhanced radial mixing, including pairs of Dean vortices, which is related to the baffled tube helical design. A model reduction based on the tanks-in-series approach was examined. The proposed two-parameter correlation can predict the residence time distribution behavior inside of HOBR over the entire range of flow conditions tested.
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•Methane selectivity increases sharply beyond a critical value of Thiele modulus.•Kinetic region extends with increase in pressure or decrease in H2/CO feed ratio.•Methane selectivity ...decreases with increase in conversion and/or decrease in H2/CO.•Multiple steady-state solutions are possible for some values of Thiele modulus.•Hybrid kinetic model was used to predict hydrocarbon product distribution.
In this study we investigate performance characteristics (catalyst effectiveness, CH4 selectivity, and hydrocarbon product distribution) of with a highly active Co/Re/Al2O3 catalyst particle for Fischer-Tropsch synthesis. In numerical simulations we utilize kinetic parameters for CO consumption rate, CH4 formation rate and hydrocarbon formation rates (C2+ hydrocarbons) determined from experiments with this catalyst to study effects of catalyst activity, catalyst particle shape (sphere, slab, solid and hollow cylinder), size (i.e. diffusion length), catalyst distribution (uniform vs. eggshell type distribution for a spherical particle) and process conditions (temperature, pressure, syngas composition and conversion level) on the catalyst performance. With increase in Thiele modulus (i.e. particle size at a fixed set of process conditions) we observe increasing H2/CO ratio profile towards the center of the particle resulting in increase of local and average CH4 selectivity. The goal is to find conditions which allow one to use sufficiently large particles to reduce pressure drop, while avoiding negative influence of diffusional limitations on selectivity and activity. For each catalyst particle shape we determined values of Thiele modulus, i.e. characteristic length of diffusion, corresponding to the upper limit of the kinetic region, and investigated how it changes with operating conditions. We found that simultaneous increase of pressure and the use of syngas with H2/CO feed ratio of 1.4–1.7 is the best strategy for mitigating the negative impact of intraparticle diffusional limitations on CH4 selectivity. For a spherical particle of 1 mm in diameter, one can achieve CH4 selectivity of 5.6% with catalyst effectiveness factor of 1.07 at the reactor inlet by operating at 50 bar, 473 K and H2/CO = 1.4.
The implementation of the liquid organic hydrogen carrier (LOHC) technology for efficient energy storage requires the development of a reliable kinetic model for both hydrogenation and ...dehydrogenation processes. In this research study, the catalytic hydrocarbon saturation for a dibenzyltoluene (DBT) mixture solution, containing dibenzylbenzene (DBB), dibenzylethylbenzene (DBEB) and impurities has been performed in the presence of Ru/Al2O3 particles. The influence of different reaction conditions, such as temperature, pressure, initial reactant concentration, catalyst amount and stirring speed has been examined. A measurement-based system micro-kinetics, based on the Langmuir–Hinshelwood mechanism with dissociative H2 surface adsorption, has been derived. H2 thermodynamic solubility equilibrium was defined through Henry's law. The adsorbing, desorption and reactivity of inert solvent molecules was not considered to be relevant. The mass transfer resistance over 1000 rpm stirring speed was negligible. Relative- and mean squared error of representation were 40.9% and 1.00×10−4, respectively. Expressions gave an excellent data prediction for the profile period trends with a relatively accurate estimation of H2 intermediates' rate selectivity, H2-covered area approximation and pathway rate-determining steps. Due to the lack of commercially available standard chemical compounds for quantitative analysis techniques, a novel experiment-based numerical calibration method was developed. Mean field (micro)kinetics represent an advancement in the mesoscale mechanistic understanding of physical interface phenomena. This also enables catalysis structure–activity relationships, unlocking the methodology for new LOHC reaching beyond traditional, such as ammonia, methanol and formate, which do not release H2 alone. Integrated multiscale simulations could include fluidics later on.
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•Experimental hydrogenation of DBT-based LOHC mixture over Ru/Al2O3 particles.•Influence of temperature, pressure, stirring, initial LOHC and catalyst amount.•Micro-kinetic model with Langmuir-Hinshelwood mechanism and dissociative adsorption.•Parameter estimation using genetic algorithm and Levenberg–Marquardt algorithm.•Excellent concentration profile trends and parameter influence predictions.
A new micro‐kinetic model of the enzyme‐catalyzed synthesis of fructo‐oligosaccharides (FOS) was developed. A commercial enzyme mixture Pectinex® Ultra SP‐L derived from Aspergillus aculeatus was ...used. A variety of initial enzyme concentrations (1–5 vol%) and sucrose concentrations (400–600 g/L) were experimentally investigated and included in kinetic modeling. Several variations of kinetic mechanisms and corresponding models have been examined. A hybrid genetic algorithm was used to predict the kinetic parameters simultaneously for all experimental data. The best fitting model has been adopted, and with an average error of 13.34%, it describes the experimental data very well. The influence of initial concentrations on the conversion of sucrose and production of FOS is being carefully investigated. It was shown that the initial sucrose concentration significantly affects the highest level of FOS concentration, but the enzyme concentration controls the time at which maximum is reached as well as the rate of FOS decomposition.
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•Forced periodic operations in milli-fixed-bed FTS reactor can be beneficial.•High amplitude modulations are optimal for maximization of C5+ productivity.•Optimal forcing of coolant ...temperature resulted in 30% gain of productivity.•Three inputs forcing resulted in highest C5+ productivity improvement of 52%.•Methane selectivity increased relatively less than C5+ productivity in optimal FPO.
One-dimensional pseudo-homogenous dynamic reactor model, incorporating detailed Fischer-Tropsch kinetics, was applied in a theoretical analysis of forced periodic operations. A milli-scale fixed-bed reactor was analyzed, using design and operation parameters, obtained previously in a steady-state optimization. Dynamic optimization and NLP methods were utilized to obtain optimal values of amplitude(s), frequency and phase shift(s) of sine-wave variation of inputs, around the corresponding optimal steady-state values, which maximize the productivity of C5+ hydrocarbons. Inlet variables that were modulated are: coolant temperature, reactants molar ratio, mass flow rate and pressure. In addition to the single input forcing, simultaneous modulations of multiple inputs were also considered, with combinations of the listed inlet variables. Among the single input cases, periodic variation of the coolant temperature resulted in the highest relative improvement of C5+ productivity by 30%. Multiple inputs forcing showed additional potential for improvement, resulting in relative C5+ productivity increase of 52% for synchronized modulation of the coolant temperature, reactants molar ratio and mass flow rate. However, the increase in C5+ productivity is accompanied with relative increase in methane selectivity of 22–33% (relative to the steady-state value). The results suggest that, in the case of multiple input variations with high amplitudes, modulation of the inlet reactants molar ratio mainly contributes to the increase of CO conversion (e.g. reaction rate), the coolant temperature forcing slightly increases selectivity towards the desirable higher hydrocarbons (C5+), while the variation of the inlet mass flow rate enables better reaction temperature control and prevents a thermal runway.
A multiphase fixed-bed reactor (FBR) model for Fischer–Tropsch Synthesis has been developed. A high level of details is considered for description of the phenomena on the reactor and particle scale. ...Detailed kinetics is used, with parameters estimated from experiments with a cobalt-based catalyst. Model robustness has been validated using literature data. Performance analysis was made for a conventional scale FBR with egg-shell distribution of catalyst and a millimeter-scale FBR with small particles and uniform distribution. In both cases, diffusion limitations are almost eliminated due to use of small diffusion lengths. For similar qualitative results, a milli-scaled design would result in a significantly lower reactor volume, but the capital costs could be high due to large wall area and a vast number of tubes. Heat removal is efficient in both cases, and pressure drop in the milli-scale reactor is low due to the use of a shorter bed and lower velocity.
Our previously developed mathematical model is used for parametric sensitivity and optimization study of conventional and milliscale fixed-bed reactors (FBRs) for Fischer–Tropsch synthesis (FTS). ...Five indicators are chosen to analyze the influence of eight parameters on the FBRs’ performance. The results show the scale of the effects caused by changing single parameter values and highlight the most important ones. Subsequently, the model is used to perform a rigorous multivariable optimization of the FBRs’ performance in the steady state. Three optimization functions are used, depicting different reactor costs. Four design parameters (tube length and diameter, particle diameter, and catalyst layer thickness) and five operating parameters (inlet and wall temperature, inlet pressure, H2/CO ratio, velocity) are optimized simultaneously. The results indicate that optimal results, in terms of reactor design and operating parameters and FBR performance, highly depend on the selected objective function and values of constrained parameters (especially methane selectivity and the partial pressure of water).
