33 research outputs found
On stochastic optimization problems and an application in finance
No full textJosef Anton Strini analyzes a special stochastic optimal control problem. The problem under study arose from a dynamic cash management model in finance, where decisions about the dividend and financing policies of a firm have to be made. Additionally, using the dynamic programming approach, he extends the present discourse by the formal derivation of the Hamilton-Jacobi-Bellman equation and by examining the verification step carefully. Finally, the treatment is completed by solving the problem numerically. Contents Optimal Control of Markov Processes A Singular Stochastic Control Problem Dynamic Programming Approach and Consequences Target Groups Researchers and students in the fields of mathematics, probability theory and applied mathematics in financial and actuarial industry Mathematicians from the financial and actuarial industry The Author Josef Anton Strini wrote his master’s thesis under the supervision of Prof. Dr. Stefan Thonhauser at the Institute of Statistics at Graz University of Technology, Austria
Effects of cracks on chloride‐induced corrosion initiation and propagation of carbon and stainless steel rebar
Get PDFCurrent durability design models for reinforced concrete structures in chloride-contaminated environments do not consider the effects of cracks, which in practice are almost inevitable. Literature reports controversial results on corrosion propagation time of carbon steel (CS) in cracked concrete, while fewer information can be found on stainless steel (SS) rebar, which can be employed as additional protection strategy. In this experimental study, corrosion initiation and propagation of CS and SS rebar in uncracked and cracked concrete are presented. Prismatic specimens, reinforced with CS and 304L SS bars were subjected to a loading procedure to induce longitudinal micro-cracks and exposed to a 3.5% NaCl solution for more than 2 years. Corrosion was monitored with electrochemical techniques and at the end of exposure corrosive attacks were observed. Results demonstrate the fundamental contribution of micro-cracks in accelerating corrosion phenomena for CS, while SS is still in passive conditions also in cracked concrete
Multi-step fractionation as a tool for enhanced valorization of technical lignins
No full textThe valorisation of lignin obtained as a by-product of the pulping and biofuel industries is one of the most promising topics in the bioresource field. Despite its potential value as the only massively available aromatic biopolymer feedstock, technical lignin is nowadays mostly burnt as low cost energy source because of its chemical recalcitrance. The high heterogeneity of this material, largely dependent on the different vegetal sources and the specific biomass recovery methods, restricts its direct use and hinders also the optimization of depolymerisation approaches. The development of effective technical lignin fractionation strategies is therefore today one of the most challenging topic in the green chemistry field.
In this study, the fractionation of two industrial commercial lignins was performed by a three step procedure set-up either in aqueous or in environmentally friendly organic solvents in order to obtain sustainable and scalable processes. The first step consisted in a microfiltration or a Soxhlet extraction in function of the solvent used. Then a cascade membrane ultrafiltration allowed to obtain at the end three refined lignin fractions (see Figure below) which were fully characterized, presenting better defined physico-chemical properties compared to the starting raw material.
The availability of technical lignin fractions with tailored and reproducible characteristics allows the set-up of enhanced lignin valorization strategies for the development of bio-based polymers and preparation of key platform chemicals, thereby paving the way for an effective exploitation and valorization of this remarkable resource.
Allegretti, A.; Fontanay, S.; Krauke, Y.; Luebbert, M.; Strini, A.; Troquet, J.; Turri, S.; Griffini, G.; D’Arrigo, P. ACS Sustainable Chem. Eng. 2018, 6, 9056-9064.
Acknoledgements: ValorPlus Project (grant agreement no FP7-KBBE-2013-7-613802)
LIGNIN VALORIZATION: FROM MOLECULES TO MATERIALS
No full textLIGNIN VALORIZATION: FROM MOLECULES TO MATERIALS
Chiara Allegretti1*, Gianmarco Griffini1, Arno Cordes2, Simon Fontanay3, Alberto Strini4, Julien Troquet3, Stefano Turri1, Paola D’Arrigo1,5
1Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”, Politecnico of Milano,
p.zza L. da Vinci 32, Milano, Italy
2ASA Spezialenzyme GmbH Am Exer 19 C, Wolfenbüttel, Germany
3Biobasic Environnement, Biopôle Clermont Limagne, Saint-Beauzire, France
4Construction Technologies Institute - National Research Council of Italy (ITC-CNR), San Giuliano Mil., Italy
5The Protein Factory Research Center, via Mancinelli 7, Milano, Italy
*Corresponding author: [email protected]
Lignin is a highly complex phenolic matrix that acts as a binder in plants conferring them structural integrity and strength, and is one of the three major subcomponents of lignocellulosic biomass. Although burning lignin is still considered a valuable contribution in saving fossil sources, the exploitation of this extremely abundant natural polymer in terms of higher value-added applications is very appealing as it represents the only viable source to produce aromatic compounds as fossil fuels alternative. Due to the very broad composition in terms of molecular weight of the raw material, a pretreatment strategy becomes necessary for an efficient lignin valorization as macromolecular building block for polymeric materials or as precursor for aromatic small molecules.
To this end, a physical fractionation has been performed in this work, where Lignin (ProtobindTM1000) in a water/ethanol solution is subjected at first to microfiltration under vacuum in order to eliminate the insoluble residues. The permeate then undergoes a cross-flow filtration process using two subsequent membranes with cut-off of 3 kDa and 1 kDa. All the retentates and permeates have been fully characterized by GPC, GC-MS, ESI-MS, DSC, TGA and FT-IR.
This procedure is an essential tool for a thorough exploitation of the main three different fractions recovered, namely a high, an intermediate and a low molecular weight fraction. The first one is characterized by the presence of high molecular weight polymers and is used without further chemical modification for developing bio-based polymeric materials;[1] the last one can be separated by chromatography into small aromatic molecules for preparative organic chemistry; whereas the middle fraction, characterized by an intermediate molecular weight, is the ideal starting material for oxidative depolymerization assays.[2,3] On this fraction, a new cascade process has been investigated involving at first a chemical/photochemical step aiming at a partial conversion of macromolecules to low molecular weight intermediates followed by a biocatalytic step performed by different classes of O2-dependent laccases (EC 1.10.3.2) in the presence of TEMPO as a mediator. Promising results have been obtained and extensive research is now in progress.
Acknoledgements:
COST Action CM1303 Systems Biocatalysis
ValorPlus Project (grant agreement no FP7-KBBE-2013-7-613802
From Waste to Value: Recent Insights into Producing Vanillin from Lignin
Get PDFVanillin, one of the most widely used and appreciated flavoring agents worldwide, is the
main constituent of vanilla bean extract, obtained from the seed pods of various members belonging to the Orchidaceae family. Due to the great demand in the food confectionery industry, as well as in the perfume industry, medicine, and more, the majority of vanillin used today is produced synthetically, and only less than one percent of the world’s vanilla flavoring market comes directly from the traditional natural sources. The increasing global demand for vanillin requires alternative and overall
sustainable new production methods, and the recovery from biobased polymers, like lignin, is an environmentally friendly alternative to chemical synthesis. The present review provides firstly an overview of the different types of vanillin, followed by a description of the main differences between natural and synthetic vanillin, their preparation, the market of interest, and the authentication issues and the related analytical techniques. Then, the review explores the real potentialities of lignin for vanillin production, presenting firstly the well-assessed classical methods and moving towards the most recent promising approaches through chemical, biotechnological and photocatalytic methodologies, together with the challenges and the principal issues associated with each technique
Effect of cracks on the service life of RC structures exposed to chlorides
Get PDFTo move towards a more sustainable concrete, the enhancement of its durability is strongly encouraged and, dealing in particular with reinforced concrete (RC), this mainly means to prevent the damage due to environmental actions, e.g. due to chloride-induced corrosion. Therefore, there is the need of models aimed at designing durable structures. Usually the service life design models consider concrete in uncracked condition. In real structures, however, several phenomena can generate cracks on concrete surface, leading to an acceleration of the corrosion of steel rebar. A number of studies have been recently carried out in order to evaluate the influence of cracks on reinforced concrete durability in chloride-contaminated environment, however the knowledge of the effect of cracks on the initiation and propagation periods is still lacking. Furthermore, few studies have considered additional protection strategies, such as the use of stainless steel rebar. In this work, experimental results are presented concerning the influence of cracks on the service life of reinforced concrete structures in order to evaluate if cracks lead to an earlier corrosion initiation induced by chlorides. Prismatic specimens, reinforced with carbon steel and 304L stainless steel bars, were longitudinally cracked and exposed to ponding with 3.5% NaCl solution. The monitoring of corrosion behaviour showed that when cracks reached the steel surface corrosion initiated immediately
TiO2-based photocatalytic geopolymers for nitric oxide degradation
No full textThis study presents an experimental overview for the development of photocatalytic materials based on geopolymer binders as catalyst support matrices. Particularly, geopolymer matrices obtained from different solid precursors (fly ash and metakaolin), composite systems (siloxane-hybrid, foamed hybrid), and curing temperatures (room temperature and 60 °C) were investigated for the same photocatalyst content (i.e., 3% TiO2 by weight of paste). The geopolymer matrices were previously designed for different applications, ranging from insulating (foam) to structural materials. The photocatalytic activity was evaluated as NO degradation in air, and the results were compared with an ordinary Portland cement reference. The studied matrices demonstrated highly variable photocatalytic performance depending on both matrix constituents and the curing temperature, with promising activity revealed by the geopolymers based on fly ash and metakaolin. Furthermore, microstructural features and titania dispersion in the matrices were assessed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) analyses. Particularly, EDS analyses of sample sections indicated segregation effects of titania in the surface layer, with consequent enhancement or depletion of the catalyst concentration in the active sample region, suggesting non-negligible transport phenomena during the curing process. The described results demonstrated that geopolymer binders can be interesting catalyst support matrices for the development of photocatalytic materials and indicated a large potential for the exploitation of their peculiar features
Two-step fractionation of a model technical lignin by combined organic solvent extraction and membrane ultrafiltration
Get PDFA fractionation method for technical lignin was developed, combining organic solvent extraction and membrane ultrafiltration of the solvent soluble component. This method was validated on a commercial wheat straw/Sarkanda grass lignin (Protobind 1000) using 2-butanone (MEK) as the solvent for both the extraction and the ultrafiltration operations. The parent lignin and the different obtained fractions were fully characterized in terms of chemical composition and physicochemical properties by gel permeation chromatography, gas chromatography/mass spectrometry (GC/MS), pyrolysis-GC/MS, total phenol contents, 31 P nuclear magnetic resonance ( 31 P NMR), thermogravimetric analysis, differential scanning calorimetry analysis, and Fourier-transform infrared spectroscopy. The results show that the proposed process allows a straightforward recovery of the different lignin fractions as well as a selective control over their molecular mass distribution and related dependent properties. Moreover, the operating flexibility of the Soxhlet/ultrafiltration process allows the treatment of lignins from different feedstocks using the same installation just by modulating the choice of the solvent and the membrane porosity with the best characteristics. This is one of the most important features of the proposed strategy, which represents a new fractionation approach with the potential to improve lignin valorization for materials science and preparative organic chemistry applications
Reactive Deep Eutectic Solvents (RDESs): A New Tool for Phospholipase D-Catalyzed Preparation of Phospholipids
Get PDFThe use of Reactive Deep Eutectic Solvents (RDESs) in the preparation of polar head modified phospholipids (PLs) with phospholipase D (PLD)-catalyzed biotransformations has been investigated. Natural phosphatidylcholine (PC) has been submitted to PLD-catalyzed transphosphatidylations using a new reaction medium composed by a mixture of RDES/buffer. Instead of exploiting deep eutectic solvents conventionally, just as the reaction media, these solvents have been designed here in order to contribute actively to the synthetic processes by participating as reagents. RDESs were prepared using choline chloride or trimethyl glycine as hydrogen-bond acceptors and glycerol or ethylene glycol, as hydrogen-bond donors as well as nucleophiles for choline substitution. Specifically designed RDES/buffer reaction media allowed the obtainment of PLs with optimized yields in the perspective of a sustainable process implementation
