1,721,028 research outputs found
Fractal Kinetic Analysis of Biomass Hydrothermal Carbonization
Full text linkThis paper introduces fractal analysis to study the kinetics of biomass hydrothermal carbonization. The reacting water-biomass slurry is a complex system leading to hydrochar by microscale reactions constrained into fractal topological boundaries. Literature and purpose experimental data check equations adapted from the fractal-like repertoire. More general models are derived from a shortcut, stochastic-based formalism, avoiding the mathematical sophistication of fractal calculus. Fractal equations explain observed data better and with fewer parameters than traditional mass-action network models (0.91202 < R (2) < 0.99998, average 0.97957) over a wide range of biomass and operational conditions. Exploratory experiments highlight the surface fractal dimension of hydrocars and their variation concerning that of parent biomasses (from 2.00 to 2.84). The confluence of fitting success and evidence of HC fractality encourages prosecuting research for making fractal kinetics a fully fledged tool of hydrothermal carbonization studies
Coupling biomass hydrothermal carbonization and green solvent extraction
Full text linkThis paper merges two leading-edge practices of sustainable waste valorization chains – biomass hydrothermal carbonization (HTC) and green solvent extraction – into an integrated process scheme. The innovation is to intersperse two hydrothermal carbonization steps with solvent extraction to recover valuable products from the reaction process water before completing the carbonization. The study uses rice husk as the waste biomass, hydrophobic deep eutectic decanoic acid/thymol (DES) as the green solvent, and furfural and 5-hydroxymethylfurfural as the target chemicals. HTC went batch-wise (230 °C, 1/4 solid/liquid ratio, total reaction time 2 h). DES extraction recovered up to 91 % of the chemicals from the process water. Although only 2 % of the original biomass converts to platform chemicals, the process illustrates a new methodology that is tailorable for other optimized productions. A flowsheet scheme helps quantify mass balances. The many degrees of freedom in the operational parameters allow for the intensification of the industrial-scale process. The new method paves the way for further developments, applying the combined process to other biomasses, solvents, and target chemicals
Modeling biomass hydrothermal carbonization by the maximum information entropy criterion
No full textThis paper demonstrates an innovation in the kinetic modeling of biomass hydrothermal carbonization
based on stochastic techniques. The dynamics of HTC solid-phase transformations is described without
assuming a reaction network. Through the maximum-entropy principle, an equation, which fits data
flexibly, rises to the status of a lumped kinetic model. The time-course of biomass conversion is described
as the macroscopic effect of microreactions, whose frequency is distributed as a continuous
probability density function. The mathematics which defines the density function takes advantage of
the identified analogies with other scientific fields. The corresponding cumulative frequency distribution is
shown to coincide with the empirical fitting equation. The analysis of a wide range of literature data,
concerning various waste biomasses, allows testing the new model. The good accordance between
previsions and experimental evidence encourages the research to follow this way. Sound procedures for
further validating the model are outlined
Membrane reactors for the investigation of product inhibition on enzyme activity
No full textThe use of ultrafiltration cells as membranereactors is extended to the study of enzyme kinetics with productinhibition. This reactor configuration allows the lack of accuracy and instrument limitations typical of differential analysis and of time-course data analysis for experiments performed in batch reactors to be overcome. The hydrolysis of cellobiose to glucose, catalysed by β-glucosidase from Aspergillus niger (E.C. 3.2.1.4), was chosen as model system. The activity of this enzyme is suppressed by glucose according to a mixed-type inhibition pattern.
Attention was paid to the possibility of determining the presence of either reversible or irreversible productinhibition. Details of the apparatus, experimental procedure and data correlation are given. Phenomena such as thermal deactivation, mechanical stress by shear and membraneto-enzyme affinity could alter the system response and mask the effects of inhibition
Investigating the kinetics of the enzymatic depolymerization of polygalacturonic acid in continuous UF-membrane reactorss reactors
No full textA stirred tank membrane reactor is used to study the kinetics of polygalacturonic acid (PGA)
enzymatic hydrolysis. The reactor operates in semicontinuous configuration: the native
biopolymer is loaded at the initial time and the system is continuously fed with the buffer. The
effect of retention time (from 101 to 142 min) and membrane molecular weight cutoff (from 1
to 30 kDa) on the rate of permeable oligomers production is investigated. Reaction products are
clustered in two different classes, those sized below the membrane cutoff and those above. The
reducing power measured in the permeate is used as an estimate of total product concentration.
The characteristic breakdown times range from 40 to 100 min. The overall kinetics obeys a
first-order law with a characteristic time estimated to 24 min. New mathematical data handling
are developed and illustrated using the experimental data obtained. Finally, the body of the
experimental results suggests useful indications (reactor productivity, breakdown induction period)
for implementing the bioprocess at the industrial scale
Studying enzyme-catalyzed depolymerizations in continuous reactors
No full textThe models of Ohmine et al. and Sendra and Carbonell for the enzymatic breakdown of polymers in batch reactors were modified to describe the depolymerization in continuous reactors. The model equations give the time course of the product concentration in the reactor permeate and that of the total product. The model predictions were compared with the experimental results for the hydrolysis of polygalacturonic acid in ultrafiltration membrane reactors. The amount of enzyme in the reactor varied from 0.18 to 1.80 mg. The residence time (100 min), temperature (25 degreesC), and membrane molecular cutoff (30 kDa) were maintained constant in the experiments. The system response was sensitive to the kinetic pattern of the enzymatic attack and was in reasonable agreement only with the predictions of the model based on the kinetic assumption made by Sendra and Carbonell. An induction period and an asymptotic amount of product were detected, which cannot be explained by the model of Ohmine et al
Continuous kinetic lumping of catalytic cracking processes
No full textProcesses, in which a multicomponent mixture of chemically similar compounds undergoes cracking reactions governed by nonlinear kinetics, are analyzed. Cracking reactions in general imply cleavage of chemical bonds between monomeric units. The article focuses on the case of the "uniform" kinetics. To obtain an analytical solution of the kinetic equations describing this process, we present an approach based on a continuous description of the mixture. The resulting nonlinear integro-differential equation has been linearized by a warped time scale, and a formal solution has been obtained via a regular perturbation method. The perturbation parameter is twice the inverse of the initial average number of monomeric units in excess of the minimum number that can be cracked by the reactions considere
Hydrothermal carbonization of mixed biomass: experimental investigation for an optimal valorisation of agrofood wastes
No full textHydrothermal carbonization (HTC) of biomass is a well-known thermochemical process for increasing the energetic density of organic feedstock. Data in the literature mainly concern batch reactor tests and some pilot plants, and do not allow designing flexible processes, nor to move to the continuous. This work starts filling this gap, focusing on products, on mass and energy balances, and on the life cycle assessment for the energetic and environmental effectiveness. Different biomasses are compared in terms of energetic performances and end-products physic-chemical properties.
European silver fir is prevalently used as model biomass in batch tests (200 and 250 °C; from 15 to 300 min). Solids (hydrochar) and liquids (biocrude) are analysed for the key parameters (solid/liquid yields, elemental analysis, calorific value, energetic density). The possible effect of process pressure is investigated up to 50 MPa. The pellets produced in situ demonstrate good hydrophobicity, high mass and energy density and a considerable carbon densification.
LCA analyses of preliminary process layouts give optimal energy recovery and environmental impact: the non-renewable energy request and the emission of CO2eq are reduced of 95 and 93%, respectively.
Hydrochar pellets turn out suitable for heat and power applications, thus allowing the exploitation of matrices such as wastes of the agro-food industry.
PURPOSE OF THE WORK
To develop a new mixed-biomass solid biofuel obtained by HTC and following densification, capable of competing with the traditional woody pellet with regard to calorific value, energetic density and to the environmental impact. Also, this research aims to get additional basic knowledge for designing satisfactory the industrial process, identifying a set of optimal operating parameters, assessing possible layouts and keeping a watch on a possible evolution toward the continuous process.
APPROACH
Batch experimental tests are focused to ascertain the relative influence and the applicable ranges of the process parameters on the characteristics of the final product. The basic information is obtained mainly using the model biomass, while tests for possible process improvements compare different waste biomasses in terms of energetic performances and physic-chemical properties of the end-products. The energetic and environmental effectiveness of the process layout is improved with the LCA methodology.
SCIENTIFIC INNOVATION AND RELEVANCE
The scientific innovation and relevance base on the idea to prove the feasibility of producing industrially an improved solid bio-fuel, comparable to traditional woody pellet, using largely or totally a variety of wastes from different sources: cultivation and maintenance of trees and other agro-industrial activities, non lignocellulosic plants, and possibly the organic fraction of municipal solid wastes.
CONCLUSION AND RESULTS
A solid bio-fuel, obtained from woody material mixed with other vegetables wastes is proposed as an alternative to traditional woody pellet. The technical feasibility was proved experimentally at laboratory scale using a device designed on purpose. A semi-continuous process layout for the industrial production of hydrochar pellet is described, assessed and optimizated by LCA analysis, implemented on a commercial software package, permits the optimization of a first-level process layout specially in terms of net renewable energy value and environmental impact, reducing of 95 and 93% the non-renewable energy request and the emission of CO2eq respectively of the production process.Hydrothermal carbonization (HTC) of biomass is a well-known thermochemical process for increasing the energetic density of organic feedstock, but literature lacks sufficient data for designing flexible processes, possibly operating continuously. This work starts filling this gap, focusing on products, on mass and energy balances, and on the life cycle assessment for the energetic and environmental effectiveness. Attention is paid to energetic performances and end-products physic-chemical properties. European silver fir is prevalently used as model biomass in batch tests (T=200 °C and T=250 °C; t=15÷300 min). Solids (hydrochar) and liquids (biocrude) are analysed for the key parameters (solid/liquid yields, elemental analysis, calorific value, energetic density). The possible effect of process pressure is investigated up to P=50 MPa. The obtained hydrochar pellets demonstrate good hydrophobicity, high mass and energy density and a considerable carbon densification, thus confirming potential heat and power applications of this matrix. Furthermore preliminary tests show that similar results can be obtained a variety of matrices such as wastes of the agrofood industry. LCA analysis of preliminary process layouts gives optimal energy recovery and environmental impact
Nitrile conversion by M. imperiale CBS 498-74 resting cells in batch and UF-membrane bioreactors
No full textThe bio-hydratation of acrylonitrile, propionitrile and benzonitrile catalysed by the NHase activity contained in resting cells of Microbacterium imperiale CBS 498-74 was operated at 5degreesC, 10degreesC, and 20degreesC in laboratory scale batch or membrane bioreactors. The bioreactions were conducted in the presence of buffered media (50 mM Na2HPO4/NaH2PO4, pH 7.0) and in the presence of distilled water or tap-water, to simulate a possible end-pipe biotreatment process. Finally, the integral bioreactor performances were studied varying cell loading, from 0.1 to 16 mg(DCW)/reactor in order to realize near 100% bioconversion of acrylonitrile, propionitrile and benzonitrile without consistent loss of NHase activit
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