Kinetic study of corn straw pyrolysis: comparison of two different three-pseudocomponent models

With heating rates of 20, 50 and 100 K min(-1), the thermal decomposition of corn straw samples (corn stalks skins, corn stalks cores, corn bracts and corn leaves) were studied using thermogravimetric analysis. The maximum pyrolysis rates increased with the heating rate increasing and the temperature at the peak pyrolysis rate also increased. Assuming the addition of three independent parallel reactions, corresponding to three pseudocomponents linked to the hemicellulose, cellulose and lignin, two different three-pseudocomponent models were used to simulate the corn straw pyrolysis. Model parameters of pyrolysis were given. It was found that the three-pseudocomponent model with n-order kinetics was more accurate than the model with first-order kinetics at most cases. It showed that the model with n-order kinetics was more accurate to describe the pyrolysis of the hemicellulose.     

Pyrolytic and Kinetic Characteristics of the Thermal Decomposition of Perilla frutescens Polysaccharide

The thermal decomposition of Perilla frutescens polysaccharide was examined by thermogravimetry, differential thermogravimetry, and differential thermal analysis. The results showed that the mass loss of the substance proceeded in three steps. The first stage can be attributed to the expulsion of the water from ambient temperature to 182°C. The second stage corresponded to devolatilization from 182°C to 439°C. The residue slowly degraded in the third stage. The weight loss in air is faster than that in nitrogen, because the oxygen in air accelerated the pyrolytic reaction speed reaction. The heating rate significantly affected the pyrolysis of the sample. Similar activation energies of the degradation process (210–211 kJ mol⁻¹) were obtained by the FWO, KAS, and Popescu techniques. According to Popescu mechanism functions, the possible kinetic model was estimated to be Avrami–Erofeev 20 g(α) = [−ln(1–α)]⁴.     

Pyrolysis characteristics and kinetics of oak trees using thermogravimetric analyzer and micro-tubing reactor

In this work, pyrolysis characteristics were investigated using thermogravimetric analysis (TGA) at heating rates of 5-20 degrees C/min. Most of the materials were decomposed between 330 degrees C and 370 degrees C at each heating rate. The average activation energy was 236.2 kJ/mol when the pyrolytic conversion increased from 5% to 70%. The pyrolysis kinetics of oak trees was also investigated experimentally and mathematically. The experiments were carried out in a tubing reactor at a temperature range of 330-370 degrees C with a reaction time of 2-8 min. A lump model of combined series and parallel reactions for bio-oil and gas formation was proposed. The kinetic parameters were determined by nonlinear least-squares regression from the experimental data. It was found from the reaction kinetic constants that the predominant reaction pathway from the oak trees was to bio-oil formation rather than to gas formation at the investigated temperature range.     

Application of the Kinetic Triplets and Geometrical Characteristics of Thermal Analysis Curves in Identifying the Main Bioactive Compounds (BC) that Govern the Thermal and Thermo-Oxidative Degradation Mechanism of <Emphasis Type="Italic">Aronia melanocarpa</Emphasis> (Black Chokeberry)

Thermal and thermo-oxidative kinetics of Aronia melanocarpa fresh samples was investigated. The current investigation was based on the application of kinetic triplets and geometrical characteristics of thermal analysis curves in identifying the main bioactive compounds that govern the thermal and thermo-oxidative degradation mechanisms. From established kinetic model in an argon atmosphere, it was found that released products arise from decomposition of phenolic compounds where autocatalysis may occurs from the inevitable presence of water already in the early stages of the process through the hydrolysis reaction pathway. In the case of thermo-oxidative degradation, it was found that the main mechanistic scheme can be presented with two different forms of reaction mechanism function, such as: nth order reaction model (with n > 1) (in lower heating mode) and ?esták-Berggren autocatalytic model (in higher heating mode). Isoconversional analysis has been shown that neochlorogenic acid represents the governed bioactive compound which has a strong hydrogen-donating activity. Based on the mechanistic conclusions, it was established that in an air atmosphere, the cyanidin-3-glucosylrutinoside (Cy-3-GR) degradation significantly participates in overall complex mechanism.     

Use of autocatalytic kinetics to obtain composition of lignocellulosic materials

Non-isothermal thermogravimetric analysis (TGA) data of biomasses and pulps originating from non-wood and alternatives materials (i.e., Tagasaste or rice straw) have been fitted with refined models, which include autocatalytic kinetics. Data sets were obtained for different experimental conditions, such as variations of heating rate and atmosphere, i.e., inert (pyrolysis) versus oxidative atmosphere (combustion). Besides the access to classical kinetic parameters (pre-exponential factor, activation energy, and reaction order), the improved data analysis enabled the determination of the chemical composition of the samples (cellulose, hemicellulose, extractives, lignin). The latter compared very well with those obtained by conventional methods (chemical analysis, HPLC). Given the reduced environmental impact and rapidness of the method, potential applications for research related to new biomasses and industrial processes can be foreseen.     

Comparative Studies of the Pyrolytic and Kinetic Characteristics of Maize Straw and the Seaweed Ulva pertusa

Seaweed has attracted considerable attention as a potential biofuel feedstock. The pyrolytic and kinetic characteristics of maize straw and the seaweed Ulva pertusa were studied and compared using heating rates of 10, 30 and 50°C min⁻¹ under an inert atmosphere. The activation energy, and pre-exponential factors were calculated by the Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Popescu methods. The kinetic mechanism was deduced by the Popescu method. The results indicate that there are three stages to the pyrolysis; dehydration, primary devolatilization and residual decomposition. There were significant differences in average activation energy, thermal stability, final residuals and reaction rates between the two materials. The primary devolatilization stage of U. pertusa can be described by the Avramic-Erofeev equation (n = 3), whereas that of maize straw can be described by the Mampel Power Law (n = 2). The average activation energy of maize straw and U. pertusa were 153.0 and 148.7 KJ mol⁻¹, respectively. The pyrolysis process of U.pertusa would be easier than maize straw. And co-firing of the two biomass may be require less external heat input and improve process stability. There were minor kinetic compensation effects between the pre-exponential factors and the activation energy.     

Thermal degradation of poly(3-hydroxyalkanoates): preparation of well-defined oligomers

The thermal degradation of the biodegradable bacterial polyesters poly(3-hydroxybutyrate), PHB, poly(3-hydroxyvalerate), PHV, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), 0-21 mol % of hydroxyvalerate, was studied. At moderately low temperatures (170-200 degrees C), the main product is a well-defined oligomer, especially a 500-10,000 g/mol macromolecule, which contains one unsaturated end group, predominantly a trans-alkenyl end group, as well as a carboxylic end group. The process was studied regarding the effect of the copolymer composition and reaction time at 190 degrees C. During the first few hours of reaction, the thermal degradation of PHB and PHV followed a kinetic model of random scission, but eventually auto-acceleration of the pyrolysis was detected, probably due to the influence of the crotonate end groups of the oligomers formed. Ten-time scale-up experiments on a Brabender instrument were successfully undertaken.     

Pyrolysis characteristics and kinetics of Arundo donax using thermogravimetric analysis

The increase of the price of fossil means, as well as their programmed disappearing, contributed to increase among appliances based on biomass and energy crops. The thermal behavior of Arundo donax by thermogravimetric analysis was studied under inert atmosphere at heating rates ranging from 5 to 20 °C min⁻¹ from room temperature to 750 °C. Gaseous emissions as CO₂, CO and volatile organic compounds (VOC) were measured and global kinetic parameters were determined during pyrolysis with the study of the influence of the heating rate. The thermal process describes two main phases. The first phase named active zone, characterizes the degradation of hemicellulose and cellulose polymers. It started at low temperature (200 °C) comparatively to wood samples and was finished at 350 °C. The pyrolysis of the lignin polymer occurred during the second phase from 350 to 750 °C, named passive zone. Carbon oxides are emitted during the active zone whereas VOC are mainly formed during the passive zone. Mass losses, mass loss rates and emission factors were strongly affected by the variation of the heating rate in the active zone. It was found that the global pyrolysis of A. donax can be satisfactorily described using global independent reactions model for hemicellulose and cellulose in the active zone. The activation energy for hemicellulose was not affected by a variation of the heating rate with a value close to 110 kJ mol⁻¹ and presented a reaction order close to 0.5. An increase of the heating rate decreased the activation energy of the cellulose. However, a first reaction order was observed for cellulose decomposition. The experimental results and kinetic parameters may provide useful data for the design of pyrolytic processing system using A. donax as feedstock.     

Kinetics and quantum yield of photoconversion of protochlorophyll(ide) to chlorophyll(ide) a

The kinetics of photoconversion of protochlorophyll(ide) to chlorophyll(ide) a were investigated in dark-grown barley leaves and in a preparation of protochlorophyll holochrome subunits. In the subunits the conversion obeyed first-order kinetics. This indicates that the excitation of protochlorophyll(ide), energy loss through deexcitation, and the reduction of excited protochlorophyll(ide) are all reactions that follow first-order kinetics with respect to protochlorophyll(ide) in protochlorophyll holochrome subunits.In contrast, photoconversion in leaves obeyed neither first- nor second-order kinetics. This prompted the postulation of an additional route within macromolecular units of protochlorophyll holochrome, whereby energy is lost from excited protochlorophyll(ide) by a reaction that is not first order. Such a process might be energy transfer from excited protochlorophyll(ide) to newly-formed chlorophyll(ide) a.A dynamic model describing photoconversion in macromolecular units was derived. The model is consistent with the observed progress of photoconversion in barley leaves and in protochlorophyll holochrome subunits from barley.Determinations of the quantum yield of photoconversion in protochlorophyll holochrome subunits gave values of 0.4–0.5 molecules · quantum^?1. Estimates of the initial quantum yield of the photoconversion process in leaves fell into the same range. The dynamic model allows predictions on the progressively decreasing quantum yield as the photoconversion proceeds in macromolecular units.     

Novel method for determination of phenol degradation kinetics

In this study, we proposed a new method for estimating biokinetic parameters in phenol degradation kinetics. The new method relies on the new formulation of q–S relation where degradation rate q is calculated from the changes of substrate concentration S for each time segment during the course of entire degradation, while in the conventional method q is obtained from the slope of the straight line that is given as substrate concentration changes with time in a semi-logarithmic scale. Thus, this new method provided more data points than the conventional method. The q–S relations obtained from the new method and the conventional method were fitted with three inhibitory kinetic models of Haldane, Yano and Edwards. Simulation of degradation profile with each kinetic model and comparison with the observed profile revealed that the new method offered a better prediction with Edwards model as the best inhibitory model.     

Bioremediation of nitrogenous compounds from oilfield wastewater by Ulva lactuca (Chlorophyta)

Oilfield wastewater (OFW) is a by-product of petroleum production and has a high nitrogen concentration. Bioremediation by macroalgae appears to be an option for OFW, and the genus Ulva (Chlorophyta) has strong potential as an agent of bioremediation because of its high nitrogen absorption capacity. This experimental study evaluated the efficiency of bioremediation of nitrogenous compounds in three concentrations of OFW by Ulva lactuca. One-phase decay models, photosynthetic status (assessed by pulse amplitude–modulated [PAM] fluorometry), and growth rate were used to assess bioremediation efficiency and algal physiology. All nitrogenous compounds were removed during the experimental period. The models that were applied for ammonium showed a stronger bioremediation effect for OFW at a concentration of 25% than at concentrations of 12.5% and 2.5%, and for nitrate, the models showed a stronger bioremediation effect at the 12.5% OFW concentration. The minor effects of OFW on photosynthetic performance and growth, added to high removal of nitrogen, emphasize the bioremediation capacity of U. lactuca, suggesting a new possibility of bioremediation of this waste.     

Common reeds (Phragmites australis) as sustainable energy source: experimental and modelling analysis of torrefaction and pyrolysis processes

The aim of this study is to apply advanced analytical techniques and kinetic modelling to common reeds (Phragmites australis) to characterize its pyrolysis and torrefaction as possible environmental friendly and sustainable pathways of fuel upgrading. Simultaneous thermogravimetric and differential scanning calorimetry analysis have been carried out on common reeds. The evolved gases during the decomposition process have been analysed by a coupled infrared gas analyser and gas chromatograph/mass spectrometer. Different reed origins (China and Italy) and plant parts (stem and leaves) have been compared. The results have been used to calibrate a torrefaction kinetic model. The model has also been tested simulating a reed torrefaction run occurring in a bench‐scale apparatus, supplementing the chemical analysis with a thermal simulation of the reactor carried out through a finite elements approach. The results show that the proposed modelling approach allows the prediction of the reaction products with a satisfying degree of accuracy. Besides its phytodepuration potential, P. australis has proven to be an interesting natural biomass resource for thermochemical conversion processes and energy production both for its suitability and availability.     

Logistic distributed activation energy model--part 2: application to cellulose pyrolysis

The pyrolysis behavior of cellulose has been investigated by using thermogravimetric analysis (TGA). The non-isothermal TGA data obtained at different heating rates have been analyzed simultaneously. Pattern Search Method has been proposed for the estimation of the model parameter values. Predicted values from the logistic distributed activation energy model have been compared with the experimental data and the results have indicated that the model describes the kinetic behavior of cellulose pyrolysis very well. The mean value and standard deviation of the logistic activation energy distribution for cellulose pyrolysis are found to be 258.5718 kJ mol(-1) and 2.6601 kJ mol(-1), the reaction order is 1.1101 and the k(0) is 1.6218×10(17) s(-1).     

Dissecting cardosin B trafficking pathways in heterologous systems

In cardoon pistils, while cardosin A is detected in the vacuoles of stigmatic papillae, cardosin B accumulates in the extracellular matrix of the transmitting tissue. Given cardosins’ high homology and yet different cellular localisation, cardosins represent a potentially useful model to understand and study the structural and functional plasticity of plant secretory pathways. The vacuolar targeting of cardosin A was replicated in heterologous species so the targeting of cardosin B was examined in these systems. Inducible expression in transgenic Arabidopsis and transient expression in tobacco epidermal cells were used in parallel to study cardosin B intracellular trafficking and localisation. Cardosin B was successfully expressed in both systems where it accumulated mainly in the vacuole but it was also detected in the cell wall. The glycosylation pattern of cardosin B in these systems was in accordance with that observed in cardoon high-mannose-type glycans, suggesting that either the glycans are inaccessible to the Golgi processing enzymes due to cardosin B conformation or the protein leaves the Golgi in an early step before Golgi-modifying enzymes are able to modify the glycans. Concerning cardosin B trafficking pathway, it is transported through the Golgi in a RAB-D2a-dependent route, and is delivered to the vacuole via the prevacuolar compartment in a RAB-F2b-dependent pathway. Since cardosin B is secreted in cardoon pistils, its localisation in the vacuoles in cardoon ovary and in heterologous systems, suggests that the differential targeting of cardosins A and B in cardoon pistils results principally from differences in the cells in which these two proteins are expressed.     

Application of artificial neural networks to modelling of starch hydrolysis by glucoamylase

The applicability of neural networks to the dynamic modelling of starch hydrolysis by Aspergillus niger glucoamylase is studied. The advantage of this technique is the possibility of predicting the reaction curves without a detailed kinetic model. Two independent neural models were proposed to predict the concentration of the products and conversion degree of the substrate at the end of the reaction (Model 1) as well as the reaction courses in the first stage when the sharp changes in the reaction rate are observed (Model 2). The results of simulations prove the ability of neural-network models to describe the complex kinetics of starch hydrolysis by glucoamylase.     

Thermal decomposition kinetics of wheat straw treated by Phanerochaete chrysosporium

Combining biological pretreatment with thermal processing may offer an alternative strategy for efficient conversion of lignocellulosic biomass into fuels and chemicals. The thermal decomposition kinetics of biologically pretreated wheat straw by Phanerochaete chrysosporium was investigated in this study using thermogravimetry (TG) - deconvoluted thermogravimetry (DTG) techniques and the Friedman method. This study revealed that biological pretreatment reduced the thermal degradation temperature of the biomass significantly. Relying on the thermal behavior of the biologically pretreated wheat straw, we proposed two biomass degradation phases during the biological degradation of wheat straw. The first phase of biodegradation (within 10 days of biological pretreatment) improved the efficiency of pyrolysis by reducing the temperature demand. In the second phase (after 10 days), although the efficiency of pyrolysis displayed the similar trend as the first phase, it showed a significant increase in activation energy demand. This process is greatly influenced by the residual lignin and cellulose ratios in the biomass. These experimental results will be useful in developing a biological pretreatment based thermochemical conversion process for lignocellulosic biomass.     

Acyl carrier protein (ACP) inhibition and other differences between beta-ketoacyl synthase (KAS) I and II

Escherichia coli beta-ketoacyl synthases (KAS) I and II carry out the elongation steps in fatty acid synthesis. Analyses using the cross-linker BS(3) [bis(sulphosuccinimidyl) suberate] and surface-enhanced laser desorption/ionization-time-of-flight MS disclosed only monomeric and dimeric forms of KAS II, whereas KAS I also forms higher multimers. The binding affinities for KAS I and KAS II to C(14)-acyl carrier protein (ACP) as well as for C(14)-ACP to KAS I and KAS II were determined. KAS I is sensitive to the ACP released during the transfer reaction, with 50% inhibition at 0.17 microM ACP close to the physiological concentration of ACP (0.13 microM). KAS I and II also differ in carrying out the decarboxylation step of the elongation reaction.     

A General Framework for Thermodynamically Consistent Parameterization and Efficient Sampling of Enzymatic Reactions

Kinetic models provide the means to understand and predict the dynamic behaviour of enzymes upon different perturbations. Despite their obvious advantages, classical parameterizations require large amounts of data to fit their parameters. Particularly, enzymes displaying complex reaction and regulatory (allosteric) mechanisms require a great number of parameters and are therefore often represented by approximate formulae, thereby facilitating the fitting but ignoring many real kinetic behaviours. Here, we show that full exploration of the plausible kinetic space for any enzyme can be achieved using sampling strategies provided a thermodynamically feasible parameterization is used. To this end, we developed a General Reaction Assembly and Sampling Platform (GRASP) capable of consistently parameterizing and sampling accurate kinetic models using minimal reference data. The former integrates the generalized MWC model and the elementary reaction formalism. By formulating the appropriate thermodynamic constraints, our framework enables parameterization of any oligomeric enzyme kinetics without sacrificing complexity or using simplifying assumptions. This thermodynamically safe parameterization relies on the definition of a reference state upon which feasible parameter sets can be efficiently sampled. Uniform sampling of the kinetics space enabled dissecting enzyme catalysis and revealing the impact of thermodynamics on reaction kinetics. Our analysis distinguished three reaction elasticity regions for common biochemical reactions: a steep linear region (0> ΔG_r >-2 kJ/mol), a transition region (-2> ΔG_r >-20 kJ/mol) and a constant elasticity region (ΔG_r <-20 kJ/mol). We also applied this framework to model more complex kinetic behaviours such as the monomeric cooperativity of the mammalian glucokinase and the ultrasensitive response of the phosphoenolpyruvate carboxylase of Escherichia coli. In both cases, our approach described appropriately not only the kinetic behaviour of these enzymes, but it also provided insights about the particular features underpinning the observed kinetics. Overall, this framework will enable systematic parameterization and sampling of enzymatic reactions.     

Mapping the genomic regions encoding biomass-related traits in <Emphasis Type="Italic">Cynara cardunculus</Emphasis> L

Cynara cardunculus, a member of the Asteraceae family, comprises the three taxa var. scolymus (globe artichoke), var. altilis (cultivated cardoon) and the ancestral var. sylvestris (wild cardoon). The substantial quantities of lignocellulosic biomass produced by these plants (up to 30.0 t/ha year^?1 dry matter by the cultivated cardoon) can be used either as a source of bioenergy and/or as raw material for paper pulp production. Here, genotyping-by-sequencing to an F₁ population derived from a cross between a globe artichoke (C3) and a cultivated cardoon (ALT) genotypes has been used to perform a genome-wide linkage analysis, leading to the elaboration of a pair of highly dense genetic maps, each derived from one of the two highly heterozygous parental genotypes. In both maps, the number of linkage groups (17) matched the species’ haploid chromosome number. The F₁ population was phenotyped over two seasons with respect to plant height, stem number, capitulum number, leaf and stem fresh weight, and the dry weight of the whole plant, the leaves, the stems, the capitula and the achenes. The phenotypic data were combined with the linkage maps to identify 81 quantitative trait loci, of which 50 were placed on the C3 map and 31 on the ALT map. The loci were scattered over 13 linkage groups, and were clustered within 27 genomic regions, 22 of which harboured two or more QTL. Ten of these regions were specific to the C3 map and six to the ALT map, while the other 11 were represented on both maps. The 27 regions harboured in all 1960 genes, 83% of which could be functionally annotated. An enrichment for certain gene ontology terms was noted for the gene content of the genomic regions harbouring loci influencing seed yield and the number/weight of stems.     

Characterization of primary reactants in bacterial photosynthesis. II. Kinetic studies of the light-induced EPR signal (g = 2.0026) and the optical absorbance changes at cryogenic temperatures

We have shown that the rise and decay kinetics of the light-induced EPR signal are identical to the kinetics of the optical changes at 80 °K. This identity provides independent evidence that the EPR signal is due to the oxidized primary electron donor which is bacteriochlorophyll. The EPR and optical changes could be described by a model photochemical reaction scheme that takes into account spin-lattice relaxation. The optical decay rate was found to be temperature independent between 1.5 and 80 °K and to obey approximately first order kinetics. These results are consistent with the hypothesis that the charge recombination occurs via tunneling through a potential barrier. The decay constants at these temperatures were found to be the same for different bacterial species and strains. No differences were found between purified reaction centers of R. spheroides R-26 and whole cells. Reaction centers treated with sodium dodecylsulfate or urea were still photochemically active but showed a markedly different kinetic behavior. The decay constant may, therefore, serve as a probe to investigate the molecular environment of the primary reactants.