Bioconversion of cellulose into ethanol by nonisothermal simultaneous saccharification and fermentation

The kinetic characteristics of cellulase and beta-glucosidase during hydrolysis were determined. The kinetic parameters were found to reproduce experimental data satisfactorily and could be used in a simultaneous saccharification and fermentation (SSF) system by coupling with a fermentation model. The effects of temperature on yeast growth and ethanol production were investigated in batch cultures. In the range of 35-45 degrees C, using a mathematical model and a computer simulation package, the kinetic parameters at each temperature were estimated. The appropriate forms of the model equation for the SSF considering the effects of temperature were developed, and the temperature profile for maximizing the ethanol production was also obtained. Briefly, the optimum temperature profile began at a low temperature of 35 degrees C, which allows the propagation of cells. Up to 10 h, the operating temperature increased rapidly to 39 degrees C, and then decreased slowly to 36 degrees C. In this nonisothermal SSF system with the above temperature profile, a maximum ethanol production of 14.87 g/L was obtained.     

Kinetics of nonisothermal polymer crystallization

We adopt a cluster size distribution model to investigate the kinetics of nonisothermal polymer crystallization. The time dependencies of polymer concentration, number and size of crystals, and crystallinity (in Avrami plots) are presented for different cooling rates. The incubation period is also investigated at different cooling rates and initial temperatures. The relationship between cooling rates and incubation time is presented graphically and compared with experimental measurements. The initial temperature (relative to melting point) has a significant effect on nonisothermal crystallization. A comparison of moment and numerical solutions of the population balance equations shows the influence of Ostwald ripening. Agreement between modeling results and experimental measurements at different cooling rates supports the application of the distribution kinetics model for nonisothermal crystallization.     

Scaling behavior of nonisothermal phase separation

The phase separation process in a critical mixture of polydimethylsiloxane and polyethylmethylsiloxane (PDMS/PEMS, a system with an upper critical solution temperature) was investigated by time-resolved light scattering during continuous quenches from the one-phase into the two-phase region. Continuous quenches were realized by cooling ramps with different cooling rates kappa. Phase separation kinetics is studied by means of the temporal evolution of the scattering vector qm and the intensity Im at the scattering peak. The curves qm(t) for different cooling rates can be shifted onto a single mastercurve. The curves Im(t) show similar behavior. As shift factors, a characteristic length Lc and a characteristic time tc are introduced. Both characteristic quantities depend on the cooling rate through power laws: Lc approximately kappa(-delta) and tc approximately kappa(-rho). Scaling behavior in isothermal critical demixing is well known. There the temporal evolutions of qm and Im for different quench depths DeltaT can be scaled with the correlation length xi and the interdiffusion coefficient D, both depending on DeltaT through critical power laws. We show in this paper that the cooling rate scaling in nonisothermal demixing is a consequence of the quench depth scaling in the isothermal case. The exponents delta and rho are related to the critical exponents nu and nu* of xi and D, respectively. The structure growth during nonisothermal demixing can be described with a semiempirical model based on the hydrodynamic coarsening mechanism well known in the isothermal case. In very late stages of nonisothermal phase separation a secondary scattering maximum appears. This is due to secondary demixing. We explain the onset of secondary demixing by a competition between interdiffusion and coarsening.     

Some mathematical aspects of nonisothermal kinetics

The results of an attempt to derive correct nonisothermal kinetic equations from isothermal ones through the classical nonisothermal change (CNC) of the postulated primary kinetic equations are presented. An alternative possibility through use of the model of infinitesimal isothermal portions (MIIP) is discussed.

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Zusammenfassung Die Autoren stellen die Ergebnisse eines Versuchs vor, korrekte Gleichungen für die nicht-isotherme Kinetik durch den klassischen nichtisothermen Übergang aus den als primär postulierten isothermen kinetischen Gleichungen abzuleiten. Als alternative Möglichkeit wird das Modell der infinitesimalen isothermen Abschnitte diskutiert.

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A stochastic simulation of nonisothermal nucleation

The results of stochastic simulations of growth and evaporation of small clusters in vapor are reported. Energy dependent growth rates are determined from the monomer-cluster collision rate and decay rates are found from a detailed balance, with the equilibrium size and energy distribution of clusters calculated using the capillarity approximation and the equilibrium vapor pressure. These rates are used in simulations of two-dimensional random walks in size and energy space to determine the fraction of clusters in supersaturated vapor of size (i(min)+1) that reach a size i(max). By assuming that clusters of size i(min) are in equilibrium, this fraction can be related to the nonisothermal nucleation rate. The simulated rates show good agreement with the previously published analytical results. In the absence of an inert carrier gas, the nonisothermal nucleation rates are typically between 1% and 5% of the isothermal rates.     

Nickel oxide reduction under nonisothermal conditions

The interaction of nickel(II) oxide with carbon, polyethylene, and polystyrene in the temperature range 20–1000°C has been investigated by thermal analysis. The interaction of NiO with carbon and polyethylene under these conditions results in complete nickel reduction. In the case of polystyrene, because of its low decomposition temperature, the reduction process is incomplete. As compared to reduction with polyethylene, reduction with carbon takes place at a much higher temperature (750 versus 370°C) and requires a higher activation energy (68 ± 3 versus 41 ± 1 kcal/mol).     

Concentration fluctuations in nonisothermal reaction-diffusion systems

In this paper a simple reaction-diffusion system, namely a binary fluid mixture with an association-dissociation reaction between the two components, is considered. Fluctuations at hydrodynamic spatiotemporal scales when a temperature gradient is present in this chemically reacting system are studied. First, fluctuating hydrodynamics when the system is in global equilibrium (isothermal) is reviewed. Comparing the two cases, an enhancement of the intensity of concentration fluctuations in the presence of a temperature gradient is predicted. The nonequilibrium concentration fluctuations are spatially long ranged, with an intensity depending on the wave number q. The intensity exhibits a crossover from a proportional, variantq(-4) to a proportional, variantq(-2) behavior depending on whether the corresponding wavelength is smaller or larger than the penetration depth of the reacting mixture. This opens a possibility to distinguish between diffusion- or activation-controlled regimes of the reaction by measuring these fluctuations. In addition, the possible observation of these fluctuations in nonequilibrium molecular dynamics simulations is considered.     

Spatial relaxation of electrons in nonisothermal plasmas

The spatial relaxation of electrons to homogeneous states under the action of space-independent electric fields is investigated in helium, krypton, and N₂ plasmas for various electric field strengths. These investigations are based on a new method recently developed for solving the one-dimensional inhomogeneous electron Boltzmann equation in weakly ionized, collision-dominated plasmas. Elastic as well as conservative inelastic collisions of electrons with gas atoms have been included in the kinetic treatment. The spatial relaxation is caused by an imposed direct disturbance in the velocity distribution of the electrons on a spatial boundary. A pronounced dependence of the relaxation structure and the resultant relaxation length on the atomic data of the electron collision processes in different gases has been found. Furthermore the relaxation process sensitively depends on the electric field strength in the region of medium field values.     

Temperature program optimization in a nonisothermal experiment

The optimum temperature program has been determined for a system of independent first-order reactions, which is best in the sense of an identifiability decomposition criterion. Analytic expressions are derived for the optimum programs for the case of two reactions. A computer algorithm is described for the case of any number of reactions. It is suggested that one should use programs combining linear heating with isothermal operation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 716–723, November–December, 1987.     

A new equation for modeling nonisothermal reactions

Based on previously reported approximations of the temperature integral, a new approximation $$\int {\exp ( - E/RT)dT = \frac{{RT^2 }}{E}} \left[ {\frac{{1 - 2(RT/E)}}{{1 - 5(RT/E)^2 }}} \right]\exp ( - E/RT)$$ has been proposed for modeling nonisothermal reactions. It has been found that the equation of Coats and Redfern deviates by less than 1 % from the exact solution forE/RT ratio greater than 23 and by less than 10% forE/RT ratio greater than 6. The exact solution was obtained independently by solving the exponential temperature integral numerically by the Simpson's rule and the Trapezoidal rule. The Gorbachev equation deviates by less than 0.1% forE/RT ratio greater than 41 and by less than 1 % forE/RT ratio greater than 11. The Li equation deviates by less than 0.1 % forE/RT ratio greater than 21 and by less than 1% forE/RT ratio greater than 9. The proposed equation deviates by less than 0.1% forE/RT greater than 7.     

Isothermal and nonisothermal gravimetry of nontronite dehydroxylation

A pure typical nontronite from Czechoslovakia (Sampor) was analysed by the title techniques in the range 570–1070 K. The isothermal dehydroxylation of nontronite, recorded at 630–730 K, was described reasonably, in the decomposition range =0.05–0.95, by diffusioncontrolled mechanismsD ₃ andD ₄. Application of the current solid-state reaction equations to the non-isothermal curve gave very poor results, except in the limited decomposition range =0.10 to 0.55. A unimolecular mechanism equation (Fm ₁) and also a second-order (SO) mechanism gave the best linearization of the curve. The activation energies estimated from the isothermal (D ₃,D ₄) and non-isothermal (F ₁) experiments were 125 and 151 kJ·mol^–1, respectively. Reduced time plots indicate the probable presence of a sequence of different mechanism for both techniques.

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Zusammenfassung Mittels der Titeltechniken wurde im Bereich 570–1070 K ein reines typisches Nontronit aus der SSR (Sampor) untersucht. Die isotherme Dehydroxylierung von Nontronit bei 630–730 K konnte im Bereich der Zersetzung von =0,05–0,95 durch die diffusionsbestimmten MechanismenD ₃ undD ₄ befriedigend beschrieben werden. Eine Anwendung der Gleichungen für Feststoffreaktionen auf die nichtisotherme Kurve ergab mit Ausnahme des Bereiches =0,10–0,55 nur sehr unzureichende Ergebnisse. Eine Gleichung für einen monomolekularen (F ₁) Mechanismus sowie für einen mechanismus zweiter Ordnung (SO) ergaben die beste Linearisierung der Kurve. Die aufgrund der isothermen (D ₃,D ₄) und nichtisothermen (F ₁) Experimente geschätzten Aktivierungsenergien betragen 125 bzw. 151 kJ·mol^–1. Es wird angenommen, daß es sich bei beiden Techniken um eine Sequenz verschiedener Mechanismen handelt.

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570–1070 (). , 630–730 =0,05–0,95, - D ₃ D ₄. , =0,10–0,55. (F ₁), . , (D ₃,D ₄) (F ₁) , , , 125 151 ·^–1. .

     

Breakdown of equivalent-model theory in nonisothermal relaxation

The behavior of Maxwell and of Wagner models with temperature-dependent elements is discussed. It is shown that these models can not be equivalent under nonisothermal conditions. It follows that the theory of equivalence of models does not apply to temperature-induced transients.     

Shear-induced nonisothermal crystallization of two grades of PLA

Shear-induced nonisothermal crystallization of two commercial polylactides (PLAs) differing in optical purity was studied. The molten polymers were sheared at selected temperatures (T_s) and subsequently cooled. The crystallization was followed by a light depolarization method, whereas the specimens were analysed ex-situ by DSC, 2D-WAXS and SEM after etching. It was found that the effect of shear, especially on the crystallinity developed during post-shearing cooling, intensified with a decrease of T_s from 160 to 146 ^°C, and with increasing shear rate and strain. Moreover, the effect of shear on PLA1.5 with d-lactide content of 1.5% was stronger than PLA2.8 with 2.8% of d-lactide, although maximum crystallinity of both polymers was practically the same. A decrease of cooling rate from 30 to 10 ^°C/min increased crystallinity of both PLAs, except for those shearing conditions which induced high crystallinity even during faster cooling. Although SEM examination revealed some row-nucleated forms, no significant crystal orientation was detected by 2D-WAXS, indicating that, under the experimental conditions, the shear induced predominantly point-like nuclei.     

Kinetics of copper slag oxidation under nonisothermal conditions

The kinetics of air copper slag oxidation under nonisothermal conditions is studied using simultaneous TG–DTA at a varying heating rate of slag and flow rate of the oxidizing gas flux. The values of the kinetic parameters, activation energy and pre-exponential factor, have been determined based on: data from DTA by the methods of Kissinger and Ozawa; data from TG using an isoconversion method and the computation procedures of Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose. No relationship between the kinetic parameters and the oxidation gas flow rate has been established. The changes of the phase composition with temperature are investigated by X-ray powder diffraction analysis on the basis of data obtained for the products formed at the different stages of the oxidation process. The morphology of the oxidized slag as well as the elements distribution is studied by electron microscopy and EDS analysis.     

Stress birefringence in amorphous polymers under nonisothermal conditions

The relationship of birefringence to stress in an amorphous polymer was studied, with emphasis on conditions of high stress and rapid cooling. The latter (nonisothermal) conditions are important in connection with studies of polymer processing operations. Polystyrene was pulled at a constant elongation rate (0.075 to 2 sec^?1 in the present and related work) under both isothermal conditions (in the range 120 to 157°C) and nonisothermal conditions (with cooling rates in the range 0.6 to 1.7°C/sec). Generally we conclude that stress in proportional to birefringence under a wide range of conditions, except that a nonlinear regime appears at stresses higher than about 10⁷ dyn/cm². In this regime, stress increases more rapidly with deformation than does birefringence.