171,153 research outputs found
Elettrodi a diffusione di gas per idrodealogenazione elettrocatalitica su argento di composti organici volatili policlorurati
No full textElettrodi a diffusione di gas per idrodealogenazione elettrocatalitica su argento di composti organici volatili policlorurati.
Alberto Vertova,* Gabriele Aricci, Cristina Locatelli, Carlo Pirola, Sandra Rondinini
Dipartimento di Chimica Fisica ed Elettrochimica, via Golgi 19 – 20133 Milano
*e-mail: [email protected]
Gli alogenuri organici volatili rappresentano una delle categorie di inquinanti organici più difficilmente trattabili per la loro elevata tossicità. Queste sostanze essendo dotate di forte resistenza a trattamenti fisici, chimici e biologici si accumulano facilmente nell’ambiente e possono entrare a far parte della catena alimentare.[1] Grande importanza assume quindi lo studio di metodi validi, efficaci ed economicamente sostenibili per la degradazione di tali substrati. Tra i diversi tipi di trattamenti, i processi riduttivi sono particolarmente interessanti perché i prodotti finali ottenibili sono idrocarburi a basso peso molecolare, ad esempio il metano. In particolare, i processi di degradazione riduttiva elettrolitica su elettrodi a base di argento dei composti citati costituisce un processo innovativo molto promettente.[2]
In questa presentazione vengono discussi i risultati di un processo elettroriduttivo con Gas Diffusion Electrode (GDE) a base di argento su molecole organico modello quali il triclorometano e l’1,1,1-tricloroetano, alimentate alla cella tramite un gas inerte.
Lo studio ha previsto due tipi di prove: misure potenziodinamiche, per caratterizzare i GDE in diversi ambienti di reazione; elettrolisi preparative, per verificare il meccanismo di reazione tramite l’analisi dei prodotti gassosi in uscita dalla cella. Nel secondo caso si è proceduto sia con l’impiego di una cella divisa che con cella indivisa, ponendo particolare attenzione all’elettrolita utilizzato.
La degradazione elettroriduttiva del CHCl3 ha portato prevalentemente a metano e in misura minore a prodotti di parziale dealogenazione; nel caso del’1,1,1-tricloroetano il prodotto principale è etano, con tracce di etene e di prodotti di parziale dealogenazione.
[1] C. Costentin, M. Robert, J.M. Seveant, J. Am. Chem. Soc., 125 10729 (2003)
[2] G. Fiori, S. Rondinini, G. Sello, A. Vertova, M. Cirja, L. Conti, J. Appl. Electrochem. , 35 363 (2005
Catalytic conversion of non-food oilseeds into methyl esters : traditional and ultrasound assisted techniques
No full textIntroduction
The most recent challenge concerning the biodiesel production deals with the processing of
non-food, raw oils to make them suitable to be used as biofuels. For these oils several
standardization processes are often required. The search for high efficiency transformation
methods is therefore a key issue in this context. In this work, different kinds of non-edible
oilseeds from crops such as Brassica juncea, Nicotiana tabacum and Cartamus tinctorius have
been selected to be processed processed using traditional and ultrasound (US)-assisted methods.
Experimental
The oilseeds were deacified by free fatty acids (FFA) esterification and then wholly converted
into methyl esters (ME) by transesterification. Sulphonic ion exchange resins Amberlyst®46
(A46) and Purolite®D5081 were used as esterification catalysts. Homemade catalysts of the
kind SO4
=/TiO2-SnO2 (TiO2 loadings from 5 to 20%) and prepared by impregnation were also
tested in the esterification. Both the reactions were carried out in slurry modality using the
conditions reported in the Table 1. US experiments were performed using a tip-type sonicator at
20 kHz. ME yields were monitored through acid base titrations and GC analyses [1,2]. Software
PROII (Simsci Esscor-Invensys) was used to perform process simulations.
Results/Discussion
FFA conversions close to 90% were achieved for all the oils deacidified on A46 and D5081, as
already observed by the authors for other kinds of feedstock [3]. These catalysts were recycled
for several times showing practically no deactivation This stable behaviour is due their
peculiarity of being sulphonated only the external surface. This confers absence to mass
transfer limitations and minimization of side products formation [4]. For these catalysts, a
kinetic pseudohomogenous model [5] was used as for comparison with the experimental data: a
very good correlation for different kinds of oils characterized by different initial acidities was
achieved. This represent an important results for the esterification process scalability.
The catalysts of composition SO4
=/TiO2-SnO2 resulted in less satisfactory performances than
the ones obtained with the ion exchange resins. Moreover, they deactivated after few uses,
probably due to the leaching of the active sulphate groups [6].
In Table 1 the results of both the esterification and transesterification reactions are displayed for
traditional and US-assisted methods.
Table 1. Conversion of an acid rapeseed oil: operative conditions and achieved results.
Esterification catalyst: D5081, transesterification catalyst: NaOCH3.
Reaction Method T (K) MeOH:Oil
(%wt)
Cat:Oil
(%wt)
Time
(min)
Conv. to
ME (%)
Est. Traditional 313a
338b
16:100 10:100 360 52.8a
71.2b
US 313a
338b
16:100 10:100 360 77.3a
76.1b
Trans. Traditional
(2 steps)
333step1
333step2
20:100step1
5:100step2
1:100step1
0.5:100step2
90 step1
60step2
96.9
US (1 step) 293 20:100 1:100 30 86.6
The use of US allows to achieve higher ME conversions in the esterification at lower
temperatures and in the transesterification. In the latter case shorter times and lower amount of
reagents are required.
For the different oils it was in general observed that the positive effect of US is more
pronounced at lower temperatures, whereas at higher temperatures it does not seems to bring
any advantage with respect to the traditional method. This suggests that at lower temperatures
the acoustic cavitation effects are enhanced: it has in fact already been reported the existence of
an optimum temperature for the occurrence of the acoustic cavitation in different reactive
systems, oilseeds included [7]. In the US-promoted FFA esterification, these effects may be
described in terms of the mechanical events enabled by the US waves inside the liquid reaction
medium and in particular in the proximity of the catalyst’s surface. In the case of the
homogeneously catalyzed transesterification, the high reactivity observed with the use of US
may be ascribable to the effects caused by the acoustic cavitation in an homogenous medium,
which generates very high local temperatures and pressures [8].
References
1. C. L. Bianchi, D. C. Boffito, C. Pirola, S. Vitali, G. Carvoli., D. Barnabè and A. Rispoli,
Biodiesel/Book 1. ISBN 978-953-307-713-0, 2011.
2. C. Pirola, D. C. Boffito, G. Carvoli, A. Di Fronzo, V. Ragaini and C. L. Bianchi,
Soybean/Book 2, ISBN 978-953-307-533-4, 2011.
3. C. L. Bianchi, C. Pirola, D. C. Boffito and V. Ragaini, Catal. Lett.., 134, 179 (2010)
4. C. Pirola, C. L. Bianchi, D. C. Boffito, G. Carvoli and V. Ragaini, Ind. Eng. Chem. Res., 49,
4601 (2010)
5. T. Pöpken, T. Götze and J. Gmehling, Ind. Eng. Chem, Res., 39, 2601 (2000)
6. D. C. Boffito, C. Pirola, and C. L. Bianchi, Chem. Today., 30, 42 (2012)
7. H. Lu, Y. Liu, H. Zhou, Y. Yang, M. Chen, B. Liang, Comput. Chem. Eng., 33, 1091 (2009)
8. K. S. Suslick, Science, 247, 1439 (1990
Sonochemical Techniques for the Transformation of Bio-based oils into Fuel
No full textBiodiesel – (FAME – fatty acids methyl esters) is currently produced through the esterification of free fatty acids and the transesterification of triglycerides in multi-stage reactors that are limited by mass transfer. The search for highly efficient transformation methods is therefore a key issue in context of minimizing reactor sizes and accelerating rates, in particular when processing non-edible and raw oils1,2.
We evaluated the esterification rate of FFA to FAME over heterogeneous catalysts subject to either ultrasound (US) or microwaves (MW). Both US and MW remarkably accelerate the esterification reaction rates for temperatures below 313 K. In particular, at 293 K the FFA conversion triples when using US instead of conventionally stirred reactor. The use of MW is beneficial when associated with heterogeneous catalysts3 and contributes to increasing the oil-methanol solubility4.
Process intensification of biodiesel production by transesterification with US horns in batch reactors (traditional vessels and Rosett cell reactors) and continuous flow reactors was studied. Complete conversion within 30 minutes was achieved for most of the US-assisted methods, whereas the mechanically stirred transesterification required two steps and lasted over 150 minutes, in between which the separation of the products was necessary. After only 5 minutes, biodiesel yields higher than 90 % were measured in the Rosett cell reactor, which combines hydrodynamic and acoustic cavitation, when US pulses were applied. The most significant result of this work was achieving biodiesel yields higher than 90% after just one passage of the reagents in the continuous flow reactor in the presence of pulsed ultrasound, corresponding to a reaction time of 18 seconds. In this case the reaction rate of the ultrasound-assisted process accelerated the reaction rate by 300 times versus the conventional synthesis methodology
All the US horns used for the transesterification experiments were provided by Synetude (Chambery – France), including the continuous reactor Sonitube®.
References
1Bianchi. C.L.; Pirola, C.; Boffito, D.C.; Di Fronzo, A.; Carvoli, G.; Barnabè, D.; Rispoli. A.; Bucchi, R. Non edible oils: raw materials for sustainable biodiesel. In Biodiesel Feedstocks and Processing Technologies; Stoytcheva, M. and Montero G., Eds.; Intech, 2011; p. 3.
2Boffito, D.C.; Pirola, C.; Galli, F.; Di Michele, A.; Bianchi, C.L. Free Fatty Acids Esterification of Waste Cooking Oil and its mixtures with Rapeseed Oil and Diesel. Fuel 2012, 10.1016/j.fuel.2012.10.069.
3Chemat, F.; Poux, M.; Galema, S.A. Esterification of stearic acid by isomeric forms of butanol in a microwave oven under homogeneous and heterogeneous reaction conditions. J. Chem. Soc., Perkin Trans. 1997, 2, 2371-2374.
4Patil, P.D.; Gude, V.G.; Mannarswamy, A.; Cooke, P.; Munson-McGee, S.; Nirmalakhandan, N.; Lammers, P.; Deng, S.G. Optimization of microwave-assisted transesterification of dry algal biomass using response surface methodology. Biores. Technol. 2011, 102, 1399-1405
Physics-based large-signal sensitivity analysis of microwave circuits using technological parametric sensitivity from multidimensional semiconductor device models
No full textThe authors present an efficient approach to evaluate the large-signal (LS) parametric sensitivity of active semiconductor devices under quasi-periodic operation through accurate, multidimensional physics-based models. The proposed technique exploits efficient intermediate mathematical models to perform the link between physics-based analysis and circuit-oriented simulations, and only requires the evaluation of dc and ac small-signal (dc charge) sensitivities under general quasi-static conditions. To illustrate the technique, the authors discuss examples of sensitivity evaluation, statistical analysis, and doping profile optimization of an implanted MESFET to minimize intermodulation which makes use of LS parametric sensitivities under two-tone excitatio
Behavioral modeling of GaN-based power amplifiers: impact of electrothermal feedback on the model accuracy and identification
No full textIn this article, we discuss the accuracy of behavioral models in simulating the intermodulation distortion (IMD) of microwave GaN-based high-power amplifiers in the presence of strong electrothermal (ET) feedback. Exploiting an accurate self-consistent ET model derived from measurements and thermal finite-element method simulations, we show that behavioral models are able to yield accurate results, provided that the model identification is carried out with signals with wide bandwidth and large dynamics
Learning distillation by a combined experimental and simulation approach in a three steps laboratory : Vapor pressure, vapor-liquid equilibria and distillation column
No full textDistillation is one of the most important separation process in industrial chemistry. This operation isbased on a deep knowledge of the fluid phase equilibria involved in the mixture to be separated. In par-ticular, the most important aspects are the determination of the vapor pressures of the single compoundsand the correct representation of the eventual not ideality of the mixture. Simulation science is a fun-damental tool for managing these complex topics and chemical engineers students have to learn andto use it on real case-studies. To give to the students a complete overview of these complex aspects, alaboratory experience is proposed. Three different work stations were set up: i) determination of vaporpressure of two pure compounds; ii) the study of vapor-liquid equilibria of a binary mixture; iii) the useof a continuous multistage distillation column in dynamic and steady-state conditions. The simulation ofall these activities by a commercial software, PRO II by AVEVA, allows to propose and verify the thermo-dynamic characteristics of the mixture and to correctly interpret the distillation column data. Moreover,the experimental plants and the data elaboration by classical equations are presented. The students arerequest to prepare a final report in which the description of the experimental plants and experimentalprocedure, the interpretation of the results and the simulation study are critically discussed in order toencourage them to reason and to acquire the concepts of the course.Two different questionnaires each with 7 questions, for the course and for the laboratory, are proposedand analyzed. The final evaluation of the students was strongly positive both for the course as a wholeand for the proposed laboratory activities
EYE4EDU: la realtà virtuale immersiva nell'impianto chimico
No full textUn nuovo progetto didattico basato sulla simulazione di processo dinamica e sulla realtà virtuale immersiva di un impianto di Crude Distillation Unit è stato avviato presso il Dipartimento di Chimica dell’Università degli Studi di Milano nel corso di Laurea in Chimica Industriale in collaborazione con Aveva. Gli studenti possono visitare e svolgere diverse esercitazioni in campo virtuale in questa realtà immersiva aumentata
A Measurement System for On-line Estimation of Weed Coverage
No full textThis paper describes two different solutions for the estimation of weed coverage. Both measuring systems discriminate the weed from the ground by means of the color difference between the weed and ground and can be used to on-line control tractor sprayers in order to reduce weedkiller use. The solutions differ with respect to the sensor type: one solution is based on a digital camera and a computer that analyzes the images and determines the weed amount, while the other simpler solution makes use of two photo detectors and an analog processing system. The camera-based solution provides an uncertainty of a few percentage, while the photo detector-based one, though extremely cheap, has an uncertainty of about 5% and suffers from changes in light conditions, which can alter the estimation
Comparison between experimental and simulated data of a distillation column: evaluation of mass-heat balances and trays efficiency
No full textA laboratory experience concerning a continuous distillation column for Industrial Chemistry and Chemical Engineering students is presented. The experience is based on practical exercise of the column running at infinite and finite reflux and on the elaboration of the collected data by both classical equations and computer simulation. The comparison between experimental and simulated data will help students to understand the theoretical basis of the distillation columns and the importance of a right representation of the phase equilibria representation. The mixture used as example in this work is a binary one of toluene and N-heptane
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