1,721,264 research outputs found
Development of innovative photoreactors and photocatalytic processes for hydrogen production
No full textIntroduction
The direct use of solar energy is intriguing for H2 production. The direct photocatalytic water splitting (WS) is thermodynamically limited by the high Gibbs free energy (237 kJ/mol) and very low efficiency is reported for direct WS also for kinetic reasons. Sacrificial reagents, such as methanol or EDTA, can improve hydrogen productivity, but they are non renewable. Compared to WS, the photocatalytic reforming (PR) is a valid approach to produce H2 under ambient conditions and using sunlight, the cheapest energy source available on earth. PR is also thermodynamically more feasible than WS. Thus, the attention is here focused on the use of waste organic compounds to be used as sacrificial agents [1], such as organic compounds obtained through the photoreduction of CO2 or the photoreforming of organic solutions, e.g. carbohydrate containing hydrolysed substrates.
The attention was mainly focused on photoreactor design and the relative process, i.e. on the development of suitable devices that could be rather easily scaled up and that can maximize the hydrogen productivity. In particular, for the photoreduction of CO2 a fully innovative photoreactor was realized, able to operate up to 20 bar pressure. This boosted the solubility of CO2 and, thus, its conversion to regenerated fuels and hydrogen. This approach allowed us to explore high pressure and high temperature operating conditions, which are unconventional for photocatalysis. On the other hand, the optimization of a photocatalytic process based on highly non-ideal, concentrated, sugar-based solutions is non trivial. At last, calculations were done to size a full scale reactor able to harvest solar light for hydrogen production in different geographic zones.
Experimental
Different nanostructured materials were used. Commercial nanometric titanium dioxide P25 by Evonik was used as photocatalyst and suspended in water with a concentration of 0.25-0.75 gL-1. Alternative nanostructured materials were prepared by flame spray pyrolysis (FP) or in mesoporous form by wet template synthesis. Different metals were added as cocatalysts, e.g. Au nanoclusters (0.1-0.5 wt%), Ag and Pd (0.1 mol%). Photocatalytic testing was carried out on a bench scale reactor at ambient pressure, using different carbohydrates and organic model molecules (methanol, glucose, xylose, arabinose, formic acid, methanol, formaldehyde and levulinic acid). These were selected because they represent the basic composition of an acid-hydrolysed fraction from cellulose. On the other hand, CO2 photoreduction was carried out in a dedicated 1.2 L reactor, at high pressure (up to 20 bar) and temperature (up to 80°C), in the presence of Na2SO3 as hole scavenger.
Results and discussion
The photoreduction of CO2 investigated at high pressure is a fully new approach proposed by our group [2-4]. CH4 can be obtained as gas phase product (e.g. with Au/TiO2 catalysts), whereas in liquid phase formic acid, formaldehyde and methanol, can be obtained in variable amount depending on the operating conditions and catalyst used. Unexpectedly, considerable H2 amount in gas phase was also obtained, sometimes as primary product. The hypothesis that it is produced from WS was ruled out by the absence of a corresponding stoichiometric amount of oxygen. Furthermore, by exploring the products distribution as a function of time, we observed that liquid organic products accumulate until Na2SO3 is present, then, organics start to convert through photoreforming generating H2, possibly CO and CO2 [2,3]. Productivity as high as 102 mmol h−1 kgcat−1 for H2, 16537 mmol h−1 kgcat−1 for formaldehyde and 2954 mmol h−1 kgcat−1 for formic acid were achieved when operating at a 7 bar of CO2 over the aqueous solution, 80 °C with 0.5 g L−1 TiO2 by tuning reaction time and pH. The reaction time in batch mode ranged from 3 to 24 h, the longer the reaction time, the higher H2 productivity.
On the other hand, different organic compounds have been tested for the photoreforming under ambient conditions in batch mode by using a 0.1 wt% suspension of the photocatalyst and an amount of 5-20 wt% of different organic compounds in water (Fig. 1 and 2). Irradiation was achieved with an UVA lamp, with maximum emission at 365 nm and measured irradiating power of 113 W/m2. The highest substrate conversion was obtained with 0.1 wt% Au/TiO2-rutile, which however gave a wider spectrum of intermediate products in liquid phase with respect to 0.1 wt% Au/TiO2-P25 and, therefore, lower H2 productivity. The best results obtained with the rutile TiO2 sample were 89 mmol kgcat-1 h-1 of H2, 7 mmol kgcat-1 h-1 of CO, 74 mmol kgcat-1 h-1 of CO2. H2 productivity increased to 276 mmol kgcat-1 h-1 by using P25, whereas it dropped to 40 mmol kgcat-1 h-1 when using anatase as polymorph for TiO2.
The conceptual feasibility of a photoreactor based on these results has been investigated considering both a continuous apparatus with UV irradiation, and solar light. In both cases, the hydrogen productivity and the efficiency of solar light storage seem insufficient for a practical exploitation. However, the same study was based on one of the best hydrogen productivities reported in the literature under visible light and also in such a promising case the feasibility does not seem guaranteed.
The photoreduction of CO2 has been also considered as a process for the fixation of this greenhouse gas to useful fuels by storing solar energy. Hydrogen productivity was insufficient for practical interest, being similar to the results obtained by photoreforming. On the other hand, also reduced organic products accumulate in liquid phase, among which the productivity of formaldehyde is particularly interesting. When using UV lamps 35 kg/day kgcat can be obtained, which decrease to 1.5 under solar light irradiation. This latter value corresponds to a 13% efficiency of solar light storage.
Conclusions
Interesting productivities of regererated fuels and H2 have been obtained by selecting proper nanostructured photocatalysts and operating conditions through photoreduction of CO2 and photoreforming of various organic substrates. The results have been used for photoreactor design and to assess the feasibility of this process. The productivity is still insufficient for the direct exploitation of solar light, but the process is feasible for the fixation of CO2 as different organic compounds to be further transformed into H2.
Acknowledgements
The financial contribution of MIUR through the PRIN2015 grant (20153T4REF) is gratefully acknowledged (G. Ramis and I. Rossetti). I. Rossetti and E. Bahadori are grateful to Fondazione Cariplo and Regione Lombardia for financial support through the grant 2016-0858 – Up-Unconventional Photoreactors.
References
[1] I. Rossetti, ISRN Chemical Engineering, Article ID 964936, (2012). doi:10.5402/2012/964936.
[2] F. Galli, M. Compagnoni, D. Vitali, C. Pirola, C. Bianchi, A. Villa, L. Prati, I. Rossetti, Appl. Catal. B: Environmental, 200 (2017) 386
[3] I. Rossetti, A. Villa, M. Compagnoni, C. Pirola, L. Prati, G. Ramis , W. Wang, D. Wang, Catal. Sci & Technol., 5 (2015) 4481
[4] I. Rossetti, A. Villa, C. Pirola, L. Prati, G. Ramis, RSC Adv., 4 (2014) 2888
Conceptual design of a process for hydrogen production from waste biomass and its storage in form of liquid ammonia
No full textConceptual design of a process for hydrogen production from waste biomass and its storage in form of liquid ammonia
Ilenia Rossetti 1*, Gianguido Ramis 2
1 Chemical Plants and Industrial Chemistry Group, Dip. Chimica, Università degli Studi di Milano, CNR-ISTM and INSTM Unit Milano-Università, via C. Golgi 19, 20133 Milan, Italy, [email protected], presenting author * corresponding author
2 Dip. Ing. Chimica, Civile ed Ambientale, Università degli Studi di Genova and INSTM Unit Genova, via all’Opera Pia 15A, 16145 Genoa, Italy, [email protected]
INTRODUCTION
Many options have been proposed to store energy form intermittent energy sources. Chemical storage presents a unique feature: flexibility. Chemicals can be moved, stored, and distributed easily, with many of them having a mature market already standing for over decades. Hydrogen is currently under assessment as energy vector and numerous paths for its production, distribution and consumption present a complex variation and trade-off between costs, emissions, scalability and requirements. Ammonia has been recently presented as a zero-carbon molecule that can provide the required energy storage medium for renewable sources. It can be stored under easy conditions (i.e., refrigerated at −33 °C at atmospheric pressure or at 0.8−1.0 MPa under atmospheric temperature), thus making it a versatile, easy to store medium. Moreover, liquid ammonia has a greater volumetric hydrogen density than liquid hydrogen itself (i.e., liquid hydrogen at 20 K has approximately 70 kg of H2/m3, while liquid ammonia at 300 K and 1.0 MPa has 106 kg of H2/m3), so that the immediate implementation of an “ammonia economy” can support the futuristic “hydrogen economy”. In this work we present the simulation of a plant for the exploitation of renewable hydrogen (e.g. from biomass gasification) with production of renewable ammonia as hydrogen vector and energy storage medium
EXPERIMENTAL/THEORETICAL STUDY
The simulation and sizing of all unit operations were performed with Aspen Plus® as software. Vegetable biomass is used as raw material for hydrogen production, more specifically pine sawdust.
RESULTS AND DISCUSSION
The hydrogen production process is based on a gasification reactor at high temperature (700-800 °C), in the presence of a gasifying agent such as air or steam. At the outlet, a solid residue (ash) and a certain amount of gas, which mainly contains H2, CH4, CO and some impurities (e.g. sulphur or chlorine compounds) are obtained.
Subsequently this gas stream is purified and treated in a series of reactors in order to maximize the hydrogen yield. In fact, after the removal of the sulphur compounds through an absorption column with MEA (to avoid poisononing of the catalytic processes), 3 reactors are arranged in series: Methane Steam Reforming (MSR), High temperature Water-Gas Shift (HT-WGS), Low temperature Water-Gas Shift (LT-WGS).
In the first MSR reactor, the methane present reacts at 1000 °C in presence of steam and a nickel-based catalyst, in order to obtain mainly H2, CO and CO2. Subsequently two steps of WGS are present to convert most of the CO into H2 and CO2. Also these reactions are carried out in the presence of a catalyst and with an excess of water.
All the oxygenated compounds must be carefully eliminated: the remaining traces of CO are methanated while CO2 is removed by a basic scrubbing with MEA (35 wt%) inside an absorption column. The Haber-Bosch synthesis of ammonia was carried out at 200 bar and in a temperature range between 300 and 400 °C, using two catalysts: Fe (wustite) and Ru/C.
CONCLUSION
In conclusion, from an hourly flow rate of 1000 kg of dry biomass and 600 kg of nitrogen, 550 kg of NH3 at 98.8 wt% were obtained, demonstrating the proof of concept of this newly designed process for the production of hydrogen from renewable waste biomass and its transformation into a liquid hydrogen vector to be easily transported and stored
Kinetic modelling of the biodegradation of polymeric materials
No full textKinetic modelling of the biodegradation of polymeric materials
Francesco Contea, Ilenia Rossettia, Gianguido Ramis b
a Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133, Milano, Italy
b DICCA, Università degli Studi di Genova, via all’Opera Pia 15A, 16149 Genova, Italy
[email protected]
Abstract
Methods to treat kinetic data for the biodegradation of different plastic materials are comparatively discussed [1-4]. Different commercial plastic samples were tested for biodegradation under standard testing methods in different environments. The following standard procedures have been used for kinetic data collection: i) ISO14855 for aerobic biodegradation in compost; ii) ASTM D6691 for aerobic biodegradation in marine environment; iii) ISO 15985 for anaerobic digestion with high solids content and biogas production and iv) ISO 14853 for anaerobic biodegradability in aqueous medium and production of biogas.
Starting from the raw data, the conversion vs. time entries were elaborated using relatively simple kinetic models [5], such as integrated kinetic equations of zero, first and second order, through the Wilkinson model, or using a Michaelis Menten approach, which was previously reported in the literature. The results were validated against the experimental data and allowed to correctly compute the time for half degradation of the substrate and, by extrapolation, to estimate the final biodegradation time for all the materials tested. At the same time, a comparison between the rates of CO2 emission rate during aerobic degradation vs. biogas formation rate could be established.
The reprocessing of the kinetic data by means of a model of the first order was satisfactory in most cases of aerobic biodegradation. By contrast, The reprocessing of the data for test ISO 15985 by means of a model of the first order was unsuitable. Significantly better results were obtained with a Stover-Kincannon model, which, however, has highlighted for all substrates, including cellulose used as reference, the persistence of a fraction of the material not converted. The reliability of the model is confirmed by the data collected for cellulose, for which is estimated reliably the maximum biodegradable fraction. Also in the case of the tests carried out according to ISO 14853 the most appropriate model was found to be the Stover-Kincannon one, which also in this case has highlighted the lack of complete biodegradability of all the three substrates.
Conversion (%) of the three commercial samples and reference cellulose as a function of time.
Linear regression of the conversion data for the A formulate according to a first-order model. Blue diamonds were not included in the regression pertaining to the plateau region.
References
1. S. Ghatge, Y. Yang, J.H. Ahn, H.G. Hur, Appl. Biol. Chem. 2020, 63, 1.
2. S. Fontanella, S. Bonhomme, M. Koutny, L. Husarova, J.M. Brusson, J.P. Courdavault, S. Pitteri, G. Samuel, G. Pichon, J. Lemaire, Polym. Degrad. Stab. 2010, 95, 1011.
3. E. Castro-Aguirre, R. Auras, S. Selke, M. Rubino, T. Marsh, Polym. Degrad. Stab. 2017, 137, 251.
4. F. Kawai, M. Watanabe, M. Shibata, S Yokoyama, Y. Sudate, Polym. Degrad. Stab. 2002, 76, 129.
5. I. Rossetti, F. Conte, G. Ramis, Engineering, 2021, 2, 54
Carbon based materials for H2 storage
No full textWe set up a volumetric method to quantify the amount of H2 “delivered” after saturation of porous solids at high pressure. A complementary dynamic method has been also developed to take into account the reversibility of adsorption and to assess in at least a semi-quantitative way the strength of interaction between H2 and the adsorbent. The method has been applied to compare the H2 storage capacity of very promising carbon-based materials, as supplied, after thermal/chemical treatments or functionalized with metals. The best results, ca. 7 wt% H2 “delivered”, were achieved after saturation at 77 K, 20 kgf/cm2 with an active carbon with ca. 3000 m2/g of apparent specific surface area
Photocatalytic Approaches to Circular Economy: CO2 Photoreduction to Regenerated Fuels and Chemicals and H2 Production from Wastewater
Full text linkSolar energy storage: catalytic and photocatalytic processes for the production of H2
No full textSolar energy storage: catalytic and photocatalytic processes for the production of H2
Ilenia Rossetti*, Gianguido Ramis
H2 is considered a promising energy vector to be used either as fuel in internal combustion engines, or in fuel cells, with overall higher efficiency. More generally, it can be seen as a way to store solar energy, to be used as support for intermittent renewable sources (e.g. photovoltaics or wind). At the moment it is predominantly produced through thermochemical processes based on fossil sources (i.e. exploiting the solar energy stored in such raw materials in the ancient past. Increasing efforts are put in place to adapt such thermocatalytic processes to the conversion of biomass, leading to a virtuous cycle, which exploits the energy sored in biomass during its growth in a shorter time cycle. Examples will be given on the steam reforming of bioethanol, which is a process in very advanced engineering stage.
On the other hand, the direct use of solar energy is intriguing for H2 production. The direct photocatalytic water splitting is thermodynamically limited by the high Gibbs free energy (237 kJ/mol) and very low efficiency is reported for direct WS also for kinetic reasons. Sacrificial reagents, such as methanol or EDTA, can improve hydrogen productivity, but they are non renewable. Compared to thermochemical processes, photocatalytic reforming (PR) is a valid approach to produce H2 under ambient conditions and using sunlight, the cheapest energy source available on earth. PR is also thermodynamically more feasible than WS. Thus, the attention is here focused on the use of waste organic compounds to be used as sacrificial agents, such as organic compounds obtained through the photoreduction of CO2 or the photoreforming of waste organic solutions
Process design issues for hydrogen production : from catalyst design to reactor modelling and process simulation
No full text
Hydrogen Production by Exploiting Diluted Second Generation Bio-ethanol: Process Design and Economic Assessment
No full textINTRODUCTION
Hydrogen is an interesting energy vector and among the various renewable feedstocks, bioethanol is known to be a promising raw material for sustainable hydrogen production through steam reforming. It can be produced through a relatively well assessed biomass fermentation process and it is expected to be industrially available on a large scale in the near future, also starting from 2nd generation biomass, i.e. not competing with the food and food chain. However, in spite of a comprehensive advancement of the research on the related technologies, studies on the real feasibility of its application in economic terms are currently lacking. For this reason, an economic assessment was carried out in this study after the process simulation and optimisation of a bioethanol-to-hydrogen plant. Previous works about the feasibility of power cogeneration through fuel cells (5 kWel + 5 kWth) using bioethanol with different concentration were proposed1. The system was constituted of several reactors in series for hydrogen production (Steam Reforming unit), purification (High-Temperature Water Gas Shift, Low-Temperature Water Gas Shift, Methanator) and by a polymer electrolyte membrane fuel cell with the given power size. However, the process was studied for a small-scale hydrogen production (6.5 Nm3/h), only, to demonstrate the feasibility for a small scale residential use. The bioethanol steam reforming on a large scale represents a route for renewable hydrogen production. To better examine its potentialities, the process was here directed to hydrogen production, only, without considering any power generation downstream or other further uses of hydrogen. The plant was designed, optimised and sized as for the main economic evaluation parameters to estimate its feasibility.
EXPERIMENTAL/THEORETICAL STUDY
The process was assessed using the AspenONE Engineering Suite® (v.9.1). The flowsheet has been designed and optimized using the sequential-modular Aspen Plus® process simulator. A capacity of 40,000 ton/y of bioethanol has been chosen based on the nominal capacity of a second generation bioethanol production plant currently commercialized.
The economic assessment was evaluated using the databanks of Aspen Process EconomicAnalyzer® and updated to the current time using a project capital escalation of 2.
RESULTS AND DISCUSSION
Various economic indicators were used to assess the sustainability of the process. Among them the minimum hydrogen selling price stating from different types and purities of bioethanol was compared as follows (1G, 2G = 1st or second generation bioethanol; 100, 90, 40 = wt% of ethanol in water)2.
CONCLUSION
Concerning the 1st generation bioethanol, the use of 90% purity led to a selling price decreased by 8% compared to the pure Bio100-1G, whereas the use of Bio50 led to a 42% lower price. 2nd generation bioethanol is sustainable only by exploiting diluted solutions. These data refer to a total production of 7,793 ton/year of H2 (9,886 Nm3 h-1) starting from 40,000 ton/year of bioethanol.
REFERENCES
1. I. Rossetti et al., Chem. Eng. J. 281, 1036 (2015)
2. M. Compagnoni et al., Energy&Fuels 31, 12988 (2017
Process design of a direct route from bioethanol to ethylene oxide
No full textPROCESS DESIGN OF A DIRECT ROUTE FROM BIOETHANOL TO ETHYLENE OXIDE
Ilenia Rossetti1*, Antonio Tripodi1 and Gianguido Ramis2
1 Chemical Plants and Industrial Chemistry Group, Dipartimento di Chimica, Università degli Studi di Milano, Via Golgi 19, 20133 Milano (MI) , Italy
2 DICCA, Università degli Studi di Genova, via all’Opera Pia 15A, 16100 Genova, Italy
*[email protected]
Introduction
Currently, ethylene oxide is produced by direct oxidation of ethylene with air or oxygen on supported silver catalysts; annual worldwide production capacity was ca. 1.7 x 107 tons. In the last decades, alternative routes to produce bulk and fine chemicals from renewable sources have been intensely studied. In particular, ethanol seems to be a promising starting reagent and has been used to produce ethylene. The indirect bioethanol-bioethylene-biooxyrane route has already been demonstrated, but it needs two separate plants which, combined with the higher cost of the starting reactant in most countries, would lead to the economic unsustainability of the process. Hence, the aim of this work is to design and simulate the direct one-pot ethylene oxide production starting from bio-ethanol. Starting from the available literature data we have set up a kinetic model and designed the process flow diagram of a completely new production process. Different side opportunities are also discussed for reactants recycles and the valorization of byproducts.
Materials and Methods
Process design and optimization has been based on the experimental investigation reported elsewhere [1,2] for a Au/γ-Al2O3 catalyst promoted by Li2O and CeOx. The available conversion and selectivity data were regressed according to an originally developed kinetic model. Product recovery and separation was designed to allow the valorization of most byproducts. Pinch analysis was carried out for the energetic optimization of the plant.
Results and Discussion
A full flowsheet for the direct one-pot conversion of bioethanol to ethylene oxide has been designed for the very first time. Such plant design is capable of converting more than 99% of the starting ethanol into ethylene oxide into the once-through reactive section, with a selectivity around 84%. The overall yield is limited by the ethanol lost in the beer concentration and stripping operation, but this is a minor issue due to the relatively low cost of the reactant.
The separation section can recover ca. 98% of ethylene oxide produced in the reactive section, 90% as pure ethylene oxide and 8% as pure ethylene glycol. This products recovery section has been also effectively integrated with the raw materials purification line connecting the following steps: a) the concentrated ethanol is split between the reactor feed and the EO absorber, b) the EO left after its distillation is converted into glycol, c) part of the glycol is re-routed to the ethanol concentrator.
With the Pinch Analysis method, the heat consumption achieved after optimization was just 5.5 % higher with respect to the theoretical hot and cold utilities targets. A global as low as 7 °C can be actually achieved considering the substantial contribution of latent heat exchanges.
Figure 1. Layout of the designed plant.
Significance
A novel route for the direct one-pot oxidation of ethanol to ethylene oxide has been designed and scaled-up into a full process: this is the very first design of an innovative one-step conversion route from bioethanol to ethylene oxide. Starting from the review and interpolation of reaction kinetics, a staged, cooled reactor is sized for the air-based oxidation of bioethanol, yielding ethylene oxide in one-step. An efficient strategy for the separation of the product from the gas phase effluent of the reactor is developed, based on absorption in a hydro-alcoholic solution rather than in pure water. This in turn brings a material recycle between the feed and purification section that benefits the atom economy. As the basis of an economic analysis, the energy balances are assessed and analyzed via the Pinch Analysis method. This lets foresee a conversion of 90% of bioethanol into Ethylene Oxide (>99% purity) and 7.7% into marketable ethylene-glycol.
References
1. Lippits, M.J., Nieuwenhuys, B.E. Catal. Today 154, 127 (2010).
2. Lippits, M.J., Nieuwenhuys, B.E. J. Catal. 274, 142 (2010)
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