1,721,338 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
Hydrogen Production by Steam Reforming of Bioethanol: Catalytic Tests and Process Design
No full textAbstract
2nd generation bioethanol was considered as raw material for the sustainable hydrogen production by catalytic steam reforming. An experimental kinetic investigation has been carried out selecting different catalysts synthesized by Flame Spray Pyrolysis, a one step high temperature synthesis able to impart strong metal-support interaction, besides high thermal resistance [1]. Ethanol conversion, selectivity to the main possible byproducts and the CO/CO2 ratio, as a measure of the contribution of the water gas shift reaction, were correlated to the temperature, water/ethanol ratio and space velocity in a central composite experimental design [2]. Two different bioethanol samples, 50 and 90 vol%, produced and supplied by a company (Mossi&Ghisolfi), have been used for at each temperature. Attention was paid to the catalyst resistance towards deactivation by coking.
The kinetic expression was implemented in a software simulation (Aspen Plus), designing a high pressure reactor. A successive process design was investigated considering the hydrogen purification section as well and evaluating the economic feasibility of different plant configurations and operative conditions. Net plant efficiencies and total capital investment will be estimated as well as internal rate of return and payback period.
[1] M. Compagnoni, J. Lasso, A. Di Michele, I Rossetti*, Cat. Sci. & Tech, 6 (2016) 6247
[1] M. Compagnoni, A. Tripodi, I. Rossetti*, App. Cat. B:Environ., 203 (2017) 899–90
H2 production through photoreforming of carbohydrates
Full text linkH2 production through photoreforming of carbohydrates
Gianguido Ramis* 1, Elnaz Bahadori 1, Antonio Tripodi 2, Ilenia Rossetti 2
1 DICCA, Università degli Studi di Genova and INSTM Unit-Genova, Genoa (Italy) * [email protected]
2 Dip. di Chimica, Università degli Studi di Milano, CNR-ISTM and INSTM Unit-Milano università, Milan (Italy)
INTRODUCTION
In this work, we dealt with the production of hydrogen through photoreforming of aqueous solutions of organic compounds.
The photocatalytic reforming occurs through the following general reaction:
which is promoted by a photocatalyst. Different carbohydrates (glucose, xylose and arabinose, as well as levulinic and formic acid) were used as renewable substrates, since they may be rather easily obtained from the hydrolysis of biomass. In particular, we have set up and optimized a new photoreactor operating at pressure up to 20 bar and relatively high temperature (up to 90°C) which allowed to boost the productivity of H2. The possibility to increase the operating pressure allowed to explore unconventional reaction conditions, evidencing an unexpected improvement of hydrogen productivity when increasing temperature in the case of the photoreforming of carbohydrates.
EXPERIMENTAL/THEORETICAL STUDY
The selected photocatalysts were based on TiO2. The materials were prepared by flame spray pyrolysis as dense nanoparticles, or in mesoporous form through a soft template synthesis, and compared with commercial samples of nanostructured TiO2 P25 by Evonik. Different metals, such as Cu and Au, Pt, Pd, Ag, Ni, with loading ranging from 0.1 to 1 mol% were added as co-catalysts (mono or bimetallic formulations. The role of the metals was that of electron sinks, to inhibit the electron-hole recombination and they were also selected due to the formation of a plasmon resonance band which improves visible light absorption. The samples were characterized by N2 adsorption-desorption, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and temperature programmed reduction/oxidation (TPR/TPO).
The photocatalytica activity tests have been carried out in batch mode using a high pressure photoreactor described elsewhere [1,2], using a UVA immersion lamp, coaxial with the photoreactor (max = 365 nm, ca. 77 W/m2).
RESULTS AND DISCUSSION
We have investigated extensively the effect of pressure, temperature, carbohydrate and catalyst concentration, selecting 80°C, 4 bar, 5 g/L of carbohydrate, 0.5 g/L of catalyst and neutral pH as the best operating conditions. The highest productivity was achieved with 0.1 mol%Pt/TiO2 or 1 mol% Au6Pt2/TiO2, leading to ca. 14 mol/h kgcat of hydrogen.
The apparent quantum yield (AQY) has been here calculated as follows:
where (i) is the number of electrons consumed to reduce H+ to 0.5 H2 and is directly calculated from the productivity data here reported. The incident photons flow has been calculated based on the measured intensity of radiation. Considering the productivities here reported we have calculated an AQY much higher than 10% in the best cases.
CONCLUSION
In this work we have investigated the effect of unconventional reaction conditions, i.e high pressure and relatively high temperature, on one of the most challenging photocatalytic processes, such as the production of H2 from carbohydrates. The increase of temperature to 80-90°C revealed beneficial and relatively high productivity has been achieved.
The main achievement, besides the interesting products yields, is the development of a new concept of photoreactor, which can open new unexplored routes in photocatalysis.
REFERENCES
1. F. Galli, M. Compagnoni, D. Vitali, C. Pirola, C. Bianchi, A. Villa, L. Prati, I. Rossetti, Appl. Catal. B: Environmental 200, 386 (2017).
2. E. Bahdori, A. Tripodi, A. Villa, C. Pirola, L. Prati, G. Ramis, I. Rossetti, Catalysts 8, 430 (2018)
ACKNOWLEDGMENTS
I. Rossetti and E. Bahadori are grateful to Fondazione Cariplo and Regione Lombardia for financial support through the grant 2016-0858 – Up-Unconventional Photoreactors.
The financial contribution of MIUR through the PRIN2015 grant (20153T4REF) is gratefully acknowledged (G. Ramis and I. Rossetti)
Flame Spray Pyrolysis: catalysts for the Steam Reforming of bio-ethanol
No full textFlame Spray Pyrolysis (FSP) is a one step high temperature synthesis able to impart strong metal-support interaction [1], besides high thermal resistance. A set of Ni catalysts supported over ZrO2 doped with different basic oxide (CaO, MgO) were prepared by this innovative technique. Steam Reforming catalytic test were carried out for the production of hydrogen using bio-ethanol. The catalytic activity was compared with catalysts of the same composition, but prepared with a traditional precipitation/impregnation method (multistep synthesis). Very high activity has been observed at high reaction temperature (>600°C), but further kinetic studies were done under milder conditions (500-300°C), in order to lower the energy input to the process and to improve H2 productivity favoring the water gas shift reaction [2]. Two different bioethanol samples, 50 and 90 vol%, produced and supplied by Mossi&Ghisolfi, have been used for 8 h-on-stream at each temperature. Attention was paid to the catalyst resistance towards deactivation by coking, besides its activity and selectivity. The acidity of the support was tuned by doping ZrO2 with basic oxides, helping to prevent ethanol dehydration and coking by ethylene polymerization. Fresh and spent samples were characterized by XRD, TPR, TPO, TEM, FE-SEM and Raman analysis.
Figure: scheme and image of Flame Spray Pyrolysis
[1] G. Ramis, I. Rossetti, E. Finocchio, M. Compagnoni, M. Signoretto, A. Di Michele, Progress in Clean Energy, I. Dincer, Ed. Springer, in press.
[2] I. Rossetti, J. Lasso, E. Finocchio, G. Ramis, V. Nichele, M. Signoretto, A. Di Michele, Appl. Catal. B: Environmental, 150-151 (2014) 257-267
Hydrogen production by steam reforming of diluted bioethanol solutions
No full textINTRODUCTION
Bioethanol attracted growing interest as raw material for the production of hydrogen. The latter can be successfully used to feed fuel cells with the aim of combined heat and power (CHP) cogeneration. A demonstrative project has been carried out c/o the Dept. of chemistry of Università degli Studi di Milano 1 by running an integrated CHP unit with residential size, i.e. 5 kWel + 5 kWth. It was constituted by 6 integrated reactors, connected in series, fed with bioethanol and water, to produce reformate gas (prereformer and steam reformer) and to accomplish gas purification from CO (high- and low-temperature water gas shift reactors and two methanators). The purified reformate is suitable to feed a PEM fuel cell with the above mentioned power output.
The aim of this work was to focus on process intensification, to achieve an economically sustainable solution. This was done at first by identifying the effect of bioethanol concentration on process output and proposing suitable means to achieve bioethanol purification. This is particularly straightforward because second generation bioethanol is nowadays proposed as fuel or as blending agent for gasoline, thus requiring deep dehydration. However, if used as feed for steam reforming, much lower concentration is needed, allowing to limit distillation/dehydration cost, which account for 50-80% of bioethanol production expenses 2,3.
EXPERIMENTAL/THEORETICAL STUDY
Process simulation has been carried out by using the Aspen Plus software and economic assessment of the solutions proposed has been carried out by using the Aspen ONE cost evaluation tool.
The experimental apparatus was furnished by Helbio SA and was extensively described elsewhere 1.
Activity resting with bioethanol solutions of different concentration and purity have been carried out by means of a bench scale continuous plant, at 300-750°C, 1 atm, H2O/CH3CH2OH = 3 (mol/mol).
RESULTS AND DISCUSSION
Process layout has been revised by comparing different possible schemes, compared as for heat and power duty (input) and output. Different solutions to account for energy input to the reformer have been also compared. In order to use diluted bioethanol solutions, the reformer was thermally sustained by catalytic combustion of part of the reformate. When using more and more diluted streams, the amount of reformate fed to the combustion line increased (to vaporize more water), so decreasing the electrical output of the fuel cell. However, the spent heat of the generated steam was recovered as thermal energy, so increasing the thermal efficiency.
Additionally, different options for the purification of raw bioethanol beer have been compared, in order to meet the required specifications and to limit the cost of the reformer feed. Depending on the desired ethanol concentration, a flash drum was sufficient and economically feasible to reach intermediate bioethanol concentration (15-25 vol%), whereas for lower desired concentrations, the raw bioethanol flow was partly rectified to the azeotrope and then diluted with the untreated beer. This solution proved convenient to limit the heat input to the column reboiler, provided that no poisons for the reforming catalyst are present in the feed.
To address this latter point, the effect of the purity of the resulting bioethanol stream on reformer performance has been also experimentally addressed. The effect of reactor temperature was considered, and this was set at the minimum level to guarantee optimal product yield, suitable catalyst durability and minimum heat input to the reactor.
CONCLUSION
The possibility to use diluted bioethanol streams as less expensive raw material for hydrogen production by steam reforming has been demonstrated and coupled with suitable bioethanol purification strategies.
REFERENCES
1. I. Rossetti et al, Int. J. Hydrogen Energy, 37, 8499 (2012)
2. I. Rossetti et al, Chem Eng. J., 281, 1024 (2015)
3. I. Rossetti et al, Chem Eng. J., 281, 1036 (2015)
ACKNOWLEDGMENTS
The financial support of Linea Energia, Università degli Studi di Milano, Provincia di Lodi and Parco Tecnologico Padano is gratefully acknowledged
Photocatalytic Approaches to Circular Economy: CO2 Photoreduction to Regenerated Fuels in a three-phase photoreactor
No full textPhotocatalytic Approaches to Circular Economy: CO2 Photoreduction to Regenerated Fuels in a three-phase photoreactor
Francesco Conte1, Antonio Tripodi1, Gianguido Ramis2, Ilenia Rossetti1*
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 Milano, Italy; 2 DICCA, Università degli Studi di Genova and INSTM Unit-Genova, via all’Opera Pia 15A, 16100 Genoa, Italy
*Corresponding author E-Mail: [email protected]
1. Introduction
CO2 photocatalytic conversion towards marketable chemicals such as hydrogen, methanol, methane, formaldehyde and formic acid seems to represent a valid and green method to reduce atmospheric concentration of carbon dioxide [1]. It is less energy demanding than traditional processes and does not produce harmful byproducts. For all these reasons photocatalysis appears to be a smart alternative for effective CO2 conversion. Furthermore, the possibility to exploit solar energy represents a free energy source available worldwide.
We have recently proposed an innovative photoreactor, able to operate up to 20 bar and 100°C for the photoreduction of CO2. The advantage of the approach is found in the possibility to enhance CO2 solubility in water (one of the main physical limitations of the process) and the surface adsorption of the reactant over the heterogeneous catalyst [2-4]. High pressure also allows to increase temperature of operation (while keeping sufficiently high concentration of CO2 in liquid phase), with beneficial effects on all the auxiliary steps of the reaction, i.e. mass transfer, sticking probability, etc. Therefore, the development of a unique high pressure device allows to explore unconventional reaction conditions for both applications, to boost the productivity.
Therefore, in this work, we are reporting some high productivity results for the photoreduction of CO2, collected using simple and inexpensive photocatalysts, trying to focus on the expected efficiency under solar light irradiation. The case study is represented by irradiation in Northern Italy (3.7 kWh/m2), specifically Milan, located on the 45.5° parallel, which is an intermediate situation with respect to the maximum and minimum values across Europe, ranging from 5.0 in Southern Europe to 2.6 in Northern Europe.
2. Methods
The innovative photoreactor used for activity testing has been widely described in previous publications [2-4]. An AISI 316 stainless steel, batch type photoreactor was used, with co-axial immersion lamp and bottom stirrer. Testing is done on 1.2 L of solution, allowing ca. 0.1 L of head space for the gas. A thermal bath circulates water around the external heating wall, setting the operating temperature. A 125 W medium pressure Hg lamp was used as light source, emitting between 254 and 364 nm (main emission peak). A detailed mapping of the irradiance through the reactor is supplied by a radiometer. Irradiance ranged between 133 and 157 W/m2 for different tests. This datum is used as comparison with the sunlight irradiance. The catalyst, 0.03 g/cm3, was suspended in demineralized and outgassed water. The suspension has been saturated with CO2 at 7 bar pressure overnight before starting irradiation. Tests lasted 24 h at 7 bar pressure and 80°C. Na2SO3 0.85 g L−1 has been used as hole scavenger. Sulfite conversion was determined by iodometric titration. The liquid phase products (HCOOH, HCHO and CH3OH) were analysed by HPLC (Agilent 1220 Infinity, column Alltech OA-10308, 300 mm-7.8 mm), with UV and refractive index (Agilent 1260 Infinity) detectors. HCHO, critical to analyse was also quantified in parallel by UV-Vis spectrophotometry through the Nash reactant and UV-Vis analysis (Perkin Elmer, Lambda 35). The gas phase products (H2, CH4 and polar/non polar light gases) were analysed by a gas chromatograph (Agilent 7890) equipped with HP Plot Q and MS columns through a TCD detector.
3. Results and discussion
From preliminary screening on a wide array of samples, we have identified the best results as for productivity of different liquid or gas phase products. In particular, by using commercial TiO2 Evonik P25, with average UVA irradiance of 150 W/m2 (365 nm), we obtained a maximum productivity of HCOOH 39.3 mol / h kgcat.
Data of daily irradiance have been collected for the Metropolitan City of Milan (Northern Italy) relative to year 2018. With an average value of 0.156 kW/m2 day of solar irradiation (of which only a ca. 5% portion can be exploited), the distribution shows a broad variance not only during the seasons, but also within the same time period, depending mainly on weather conditions. This is a first issue with plant sizing, since the huge variability of the primary source induces not only a variable output of the products, but also control problems for the plant, which hardly reaches a stationary condition.
The expected daily and yearly productivity upon solar light exposure has been calculated according to [5] referring to 1 m3 photoreactor volume distributed in a reactor 0.2 m deep and with the extension of 5 m2. Stored power ranging from ca. 1.2 to 1.5 MJ/year kgcat were calculated, corresponding to a yearly productivity of ca. 250 kg/year kgcat of HCOOH. These results refer to a very simple, commercial, inexpensive and durable catalyst. The efficiency of the process is still very low when referred to the whole incident radiation, while it increases to ca. 10% when referred to the useful fraction of radiation exploitable by the photocatalyst. This suggests on one hand the need for improvement of the light harvesting ability of the sample. On the other hand, it leaves wide room for improvement of the intrinsic catalyst efficiency.
4. Conclusions
The photoreduction of CO2 has been investigated in a three-phase high pressure photoreactor. The productivity to HCOOH over-performed most literature data and was set as the basis to check the feasibility of a pilot unit 1 m3/5 m2. The amount of stored energy yearly, though in an almost continental climate region and with a very basic commercial photocatalyst revealed very promising, but suggested further improvement in the light harvesting properties of the material.
References
[1] V. Balzani, A. Credi, M. Venturi, Photochemical Conversion of Solar Energy, 2008.
[2] E. Bahdori, A. Tripodi, A. Villa, C. Pirola, L. Prati, G. Ramis, N. Dimitratos, D. Wang, I. Rossetti, Catal. Sci. Technol. 9 (2019) 2253–2265.
[3] F. Galli, M. Compagnoni, D. Vitali, C. Pirola, C.L. Bianchi, A. Villa, L. Prati, I. Rossetti, Appl. Catal. B Environ. 200 (2017) 386–391.
[4] E. Bahadori, A. Tripodi, A. Villa, C. Pirola, L. Prati, G. Ramis, I. Rossetti, Catalysts 8 (2018) 430.
[5] I. Rossetti, E. Bahadori, A. Tripodi, A. Villa, L. Prati, G. Ramis, Sol. Energy 172 (2018) 225–231
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
Computer aided process design: opportunities and challenges in polymer science and technology
Full text linkThe possibility to exploit in silico process design and modelling tools is ever more attractive in view of the Industry 4.0 and digitalisation strategies, to save time and money for the application oriented discovery of new materials and formulations and the relative production process. The realisation of digital twins allows to replicate the main features of a process to predict the optimal operation points, possible hazards or safety issues, as well as to accompany the experimental development of materials and formulations early exploring the boundaries for technoeconomic feasibility. As well, the currently developing machine learning applications in this field are suitable to identify possible formulations on the basis of the desired properties, thanks to large data available.
All these features are already tested both in the synthesis of polymeric materials and in their disposal cycle.
Some examples of application of computer aided design in this field will be presented to highlight the opportunities offered by these approaches, the correct handling of data and instruments, and the relative challenges
Combined heat and power cogeneration from bioethanol and fuel cells : A brief overview on demonstrative units and process design
No full text- …
