Imperial College London

DrMarcosMillan-Agorio

Faculty of EngineeringDepartment of Chemical Engineering

Reader in Chemical Engineering
 
 
 
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Contact

 

+44 (0)20 7594 1633marcos.millan

 
 
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Assistant

 

Mrs Sarah Payne +44 (0)20 7594 5567

 
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Location

 

501Roderic Hill BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

106 results found

Puron H, Pinilla JL, Saraev AA, Kaichev VV, Millan Met al., 2020, Hydroprocessing of Maya vacuum residue using a NiMo catalyst supported on Cr-doped alumina, Fuel, Vol: 263, ISSN: 0016-2361

© 2019 Elsevier Ltd Mesoporous alumina was doped with Cr using a co-precipitation method to prepare a support for hydrocracking catalysts. Ni and Mo were then impregnated on Cr-doped mesoporous alumina (NiMo/Al2O3-Cr). Catalytic activity was tested in hydrodeasphaltenisation (HDA), hydrodesulfurisation (HDS) and hydrodemetallisation (HDM) of Maya vacuum residue in a batch reactor and compared with NiMo supported on mesoporous alumina not doped with Cr (NiMo/Al2O3). Following activation and initial carbon deposition, experiments involving contact of the catalysts with fresh feed were performed. Greater HDA extent and maltene to asphaltene ratios were obtained with NiMo/Al2O3-Cr than NiMo/Al2O3 despite a larger amount of coke deposits. Significant activity of both NiMo/Al2O3-Cr and NiMo/Al2O3 towards HDS and HDM were also observed. Alumina textural properties remained relatively unaffected by the co-precipitation of Cr. X-ray photoelectron spectroscopy (XPS) showed that the catalysts contained Cr3+ and after reduction all Ni was present in metallic state at least in the near-surface region, while Mo6+ was reduced to Mo4+ and Moδ+ (0 ≤ δ ≤ 3) to a larger extent in NiMo/Al2O3-Cr. Lower reduction temperatures in the presence of Cr were determined, suggesting a larger number of metal sites available in reduced form at operating conditions. It was found that Cr aided metal dispersion in catalyst synthesis and coke dispersion during reaction. Spent catalysts showed reductions in surface area and pore volume. However, while spent NiMo/Al2O3 catalysts had a decrease in average pore diameter (APD), NiMo/Al2O3-Cr maintained the fresh material APD, which may explain the sustained catalytic activity.

Journal article

Spiegl N, Berrueco C, Long X, Paterson N, Millan Met al., 2020, Production of a fuel gas by fluidised bed coal gasification compatible with CO<inf>2</inf> capture, Fuel, Vol: 259, ISSN: 0016-2361

© 2019 Elsevier Ltd A continuously fed, laboratory scale spouted bed gasifier has been used to study oxy-fuel gasification of German lignite. In this paper, the influence of different gasification agents and bed temperature on the process performance, during tests at atmospheric and elevated pressure are studied. Two gasification agents have been used, CO2 (with different CO2/C ratios) and mixtures of CO2/steam. The results show that despite the relatively slow CO2-char reaction, good gasification performance could be achieved with German lignite by adjusting the operating conditions at atmospheric pressure: complete carbon conversion, high energy conversion and a medium heating value fuel gas (8–10 MJ m−3). The CO2/C ratio was found to have a large effect on the gasification performance. Increasing the ratio increased the carbon conversion, but the CO2 conversion decreased. At 950 °C, maximum carbon conversion was already achieved with pure CO2, therefore using steam at this temperature could not increase the conversion, but did increase the H2/CO ratio in the fuel gas. At 850 °C, replacing 25% of CO2 with steam increased the carbon conversion to the level achieved at 950 °C without steam. Replacing more than 25% of CO2 with steam increased the H2/CO ratio further. Therefore, with the addition of steam, the operating temperature could be reduced from 950 °C to 850 °C while maintaining the gasification performance. The changes of gasification performance with steam addition at pressures up to 10 bara followed the same trends achieved at atmospheric pressure.

Journal article

Zhu HL, Pastor-Pérez L, Millan M, 2020, Catalytic steam reforming of toluene: Understanding the influence of the main reaction parameters over a reference catalyst, Energies, Vol: 13

© 2020 by the authors. Identifying the suitable reaction conditions is key to achieve high performance and economic efficiency in any catalytic process. In this study, the catalytic performance of a Ni/Al2O3 catalyst, a benchmark system-was investigated in steam reforming of toluene as a biomass gasification tar model compound to explore the effect of reforming temperature, steam to carbon (S/C) ratio and residence time on toluene conversion and gas products. An S/C molar ratio range from one to three and temperature range from 700 to 900 °C was selected according to thermodynamic equilibrium calculations, and gas hourly space velocity (GHSV) was varied from 30,600 to 122,400 h-1 based on previous work. The results suggest that 800 °C, GHSV 61,200 h-1 and S/C ratio 3 provide favourable operating conditions for steam reforming of toluene in order to get high toluene conversion and hydrogen productivity, achieving a toluene to gas conversion of 94% and H2 production of 13 mol/mol toluene.

Journal article

Volpe R, Bermudez Menendez JM, Ramirez Reina T, Volpe M, Messineo A, Millan M, Titirici MMet al., 2019, Free radicals formation on thermally decomposed biomass, Fuel, Vol: 255, ISSN: 0016-2361

© 2019 Pyrolysis provides an attractive alternative for the upgrading of agro-wastes to energy and chemicals. However, consistent quality of the final products is still a goal to be achieved at industrial level. The present study aims at complementing existing results recently published by the authors and investigating the physico-chemical evolution and oxidative reactivity of solid products of pyrolysis of citrus waste. Chars derived from slow pyrolysis (50 °C min−1, 200–650 °C peak temperature) of orange and lemon pulp (OP and LP) in a horizontal batch reactor were characterized by means of Thermo-Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Electron Paramagnetic Resonance (EPR) and Raman spectroscopy. Results show how the onset of breaking of covalent bonds in matrix is triggered by reaching pyrolysis temperatures of 330–350 °C. Around those temperatures, the population of free-radicals significantly increases on solids and chars become more reactive, thereby favoring retrogressive, recombination and secondary solid-vapor reactions. Results also show that the higher content of lignin on LP may facilitate the formation of aromatic networks via lignin fragmentation and condensation above 500 °C. This trend is also confirmed by DSC patterns in which, above 500 °C, significantly more endothermic reactions occur in LP as a comparison to OP. This conclusion is further corroborated by more pronounced G-band Raman shifts shown for LP as a comparison to OP. The present results shed new light on the thermochemical breakdown of solid agro-wastes and provide insights for development of slow pyrolysis technology toward the production of valuable renewable carbonaceous materials.

Journal article

Yu J, Paterson N, Millan M, 2019, The primary products of cellulose pyrolysis in the absence of extraparticle reactions, FUEL, Vol: 237, Pages: 911-915, ISSN: 0016-2361

Journal article

Almeida RSR, Taccini MM, 2019, Effect of Storage Time on the Chemical Characterization of Pyroligneous Liquor From Eucalyptus Wood, Waste and Biomass Valorization, Pages: 1-7, ISSN: 1877-2641

© 2017 Springer Science+Business Media B.V. Abstract: This research focused on the effect of storage time on the chemical composition of the pyroligneous liquor (PL) produced during the pyrolysis of eucalyptus wood in a laboratory furnace at a relatively low heating rate (1 °C min−1) and a maximum temperature of 400 °C. The chemical compounds present in PL were identified through gas chromatography-mass spectrometry. This analysis was repeated over 19 months to observe changes in PL composition. Compounds such as 1,2-butanediol, 2-methoxytetrahydrofuran, 1,2-cyclopentanedione were only detected in the fresh PL and not after 11 or 19 months of storage. On the other hand, in PL stored for 11 and 19 months, new compounds were found, such as propanoic acid, butanediol, 5,9-dodecadien-2-one,6-10-dimethyl cyclopentanone, which were not observed in fresh PL. This suggests that PL from eucalyptus wood pyrolysis contains reactive compounds, mainly oxygenated, that interact during storage. Regarding the moment of stabilization of the qualitative composition of the PL, this research suggests that it is only reached after 11 months of storage. Phenol and furan derivatives were found to be stable, only reacting in their side chains without affecting the central ring. On the other hand, derivatives of tetrahydrofuran showed significant reactivity and tended to disappear with storage time. Graphical Abstract: [Figure not available: see fulltext.]

Journal article

Ji G, George A, Skoulou V, Reed G, Millan M, Hooman K, Bhatia SK, Diniz da Costa JCet al., 2018, Investigation and simulation of the transport of gas containing mercury in microporous silica membranes, Chemical Engineering Science, Vol: 190, Pages: 286-296, ISSN: 0009-2509

© 2018 Elsevier Ltd This work investigates the effect of condensable Hg vapour on the transport of N2gas across cobalt oxide silica (CoOxSi) membranes. Experimental results suggest that Hg significantly affects N2permeation at 100 and 200 °C, though this effect is negligible at 300 °C. This effect was found to have a correlation with Hg adsorption on CoOxSi xerogels. In order to understand the Hg effect in the transport phenomena of N2permeation, the oscillator model was used to model gas transport through pores with different sizes. By including effective medium theory (EMT), the oscillator model fitted well the experimental results and gave good prediction of mass transfer in ultra-microporous materials with a tri-modal pore size distribution, such as silica membranes. It is postulated that Hg seeks lower level potentials in micro-pores, and therefore Hg molecules tend to block small pores (2.5–4 Å from 2.9 Å), or reduce the average pore size of larger pores (6.7–7.8 Å and 12–14 Å). Although N2permeation decreased with the presence of Hg, it did not decrease when the Hg load was increased by a factor of ten; this strongly suggests the adsorption of Hg molecules in the smaller pores (2.5–4.0 Å), or along the pore wall for the larger pore ranges (6.7–7.8 Å and 12–14 Å).

Journal article

Yeletsky PM, Reina TR, Bulavchenko OA, Saraev AA, Gerasimov EY, Zaikina OO, Bermúdez JM, Arcelus-Arrillaga P, Yakovlev VA, Millan Met al., 2018, Phenanthrene catalytic cracking in supercritical water: effect of the reaction medium on NiMo/SiO<inf>2</inf> catalysts, Catalysis Today, ISSN: 0920-5861

© 2018 A series of NiMo/SiO2 catalysts was synthesized by sol-gel method for heavy oil upgrading in supercritical water (SCW). Phenanthrene was used as substrate as it represents polyaromatic structures present in asphaltenes. No phenanthrene conversion was observed in a blank (non‐catalytic) experiment. However, phenanthrene conversions up to 24% after 1 h of reaction in SCW at 425 °C and 230 bar were observed in the presence of NiMo/SiO2, underlining the role of the catalysts in the process. Conversion was found to be dependent mainly on Ni content and the Ni/Mo ratio in the catalysts. The liquid products obtained are thought to be the result of both oxidation and hydrogenation processes. Characterization of the fresh and spent catalysts using X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) was performed. It was revealed that catalysts are not completely stable in SCW, showing that NiMo intermetallic compounds formed the initial catalysts were decomposed, Mo0 and Ni0 were oxidised and the latter formed Ni2SiO4. In addition, MoO2 phase domain size in the catalysts increased and the surface of the spent catalysts appeared to be enriched with Ni and depleted with Mo.

Journal article

Cardoso A, Ramirez Reina T, Suelves I, Pinilla JL, Millan M, Hellgardt Ket al., 2018, Effect of carbon-based materials and CeO<inf>2</inf>on Ni catalysts for Kraft lignin liquefaction in supercritical water, Green Chemistry, Vol: 20, Pages: 4308-4318, ISSN: 1463-9262

© The Royal Society of Chemistry 2018. Kraft lignin (KL) is a by-product from cellulose production typically treated as a waste or used as a low-value fuel in heat and power generation in the pulp and paper industry. This study explores KL upgrading to monoaromatic compounds using supercritical water (SCW) as reaction medium. The effect of Ni-CeO2catalysts supported on carbon nanofibers (CNF) and activated carbon (AC) on the product distribution was investigated. These catalysts were prepared by a wet-impregnation method with acetone, and reduced Ni was observed without the use of H2. CNF presented a high degree of stability in SCW. Ni in its reduced state was still present in all spent catalysts, mainly when CNF were the support. While catalysts supported in AC led to high yields of char and gas, a 56 wt% yield of a light liquid fraction, recovered as dichloromethane (DCM)-soluble product and consisting mainly of (methoxy)phenols (>80 mol%), was obtained in a batch reactor at 400 °C, 230 bar, with Ni-CeO2/CNF as a catalyst. A short reaction time was key to avoid the formation of gas and char. This study demonstrates that high yields of DCM-soluble products from KL and low char formation can be obtained by using only SCW and catalysts, an alternative to widely reported approaches like the addition of organic co-solvents (e.g., phenol) and/or H2.

Journal article

Bermudez JM, Garcia-Fayos J, Reina TR, Reed G, Persoon ES, Görtz D, Schroeder M, Millan M, Serra JMet al., 2018, Thermochemical stability of La<inf>x</inf>Sr<inf>1-x</inf>Co<inf>y</inf>Fe<inf>1-y</inf>O<inf>3-Δ</inf>and NiFe<inf>2</inf>O<inf>4</inf>-Ce<inf>0.8</inf>Tb<inf>0.2</inf>O<inf>2-Δ</inf>under real conditions for its application in oxygen transport membranes for oxyfuel combustion, Journal of Membrane Science, Vol: 562, Pages: 26-37, ISSN: 0376-7388

© 2018 This work addresses the thermochemical stability of ceramic materials –typically used in oxygen transport membranes– under the harsh gas environments found in oxyfuel combustion processes. Specifically, a dual-phase NiFe2O4-Ce0.8Tb0.2O2-δ(NFO-CTO) composite and a single-phase La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF) were studied. The effect of the main contaminants present in this kind of processes (CO2, SO2and H2O) has been tested. NFO-CTO composite remains stable under all the conditions studied whereas LSCF presents a poor stability in the presence of CO2and SO2. Regardless of the treatment, NFO-CTO conserves its crystalline structure, without giving rise to new species due to segregation or incorporation of sulphur and/or carbon. On the contrary, LSCF is prone to degradation in contact with CO2and SO2, segregating Sr in the form of SrCO3and SrSO4and Co and Fe in the form of CoO and Fe3O4. It is also shown that SO2interaction with LSCF is stronger than in the case of CO2. A concentration of just 2000 ppm of SO2in CO2is enough to subdue the formation of SrCO3, promoting the segregation of Sr only in the form of SrSO4. With the results presented in this work, it is possible to conclude that the NFO-CTO is a suitable candidate from the thermochemical viewpoint to be used as membrane material in 4-end modules for oxygen generation integrated into oxyfuel combustion processes whereas the use of LSCF should be dismissed.

Journal article

Bizkarra K, Bermudez JM, Arcelus-Arrillaga P, Barrio VL, Cambra JF, Millan Met al., 2018, Nickel based monometallic and bimetallic catalysts for synthetic and real bio-oil steam reforming, International Journal of Hydrogen Energy, Vol: 43, Pages: 11706-11718, ISSN: 0360-3199

© 2018 Hydrogen Energy Publications LLC Catalysts based on Ni supported on alumina were studied for steam reforming (SR) of a synthetic bio-oil/bio-glycerol mixture and a real bio-oil. Catalyst tests were carried out in a continuous fixed bed reactor at atmospheric pressure and steam to carbon (S/C) ratio of 5.0. In the case of experiments with the bio-oil/bio-glycerol mixture the initial temperature was 1073 K, then it was successively changed to 973 K and 1073 K again to assess catalyst deactivation. Experiments with the bio-oil sample were run at 1073 K. First, the effect of modifications to the alumina support with CeO2 and La2O3 was studied in monometallic catalysts. Ni/CeO2–Al2O3 was identified as the catalyst more resistant to deactivation, likely due to its higher oxygen mobility, and selected for further tests. Then, bimetallic catalysts were produced by impregnation of noble metals (Pd, Pt or Rh) on the Ni catalyst supported on CeO2–Al2O3. Co-impregnation of Rh and Ni on the CeO2–Al2O3 support represented a further improvement in the catalytic activity and stability respect to the monometallic catalyst, leading to stable gas compositions close to thermodynamic equilibrium due to the favourable Rh–Ni interactions. Rh–Ni/CeO2–Al2O3 is therefore a promising catalyst to produce a hydrogen-rich gas from bio-oil SR.

Journal article

Na BT, Ovtar S, Yu JH, Hendriksen PV, Kaiser A, Reina TR, Millan M, Kiebach Ret al., 2018, Performance and stability of (ZrO<inf>2</inf>)<inf>0.89</inf>(Y<inf>2</inf>O<inf>3</inf>)<inf>0.01</inf>(Sc<inf>2</inf>O<inf>3</inf>)<inf>0.10</inf>-LaCr<inf>0.85</inf>Cu<inf>0.10</inf>Ni<inf>0.05</inf>O<inf>3-Δ</inf>oxygen transport membranes under conditions relevant for oxy-fuel combustion, Journal of Membrane Science, Vol: 552, Pages: 115-123, ISSN: 0376-7388

© 2018 Elsevier B.V. Self-standing, planar dual-phase oxygen transport membranes consisting of 70 vol% (ZrO2).89(Y2O3).01(Sc2O3).10(10Sc1YSZ) and 30 vol% LaCr.85Cu.10Ni.05O3-δ(LCCN) were successfully developed and tested. The stability of the composite membrane was studied in simulated oxy-fuel power plant flue-gas conditions (CO2, SO2, H2O). The analyses of the exposed composites by X-ray diffraction (XRD), X-ray fluorescence (XRF), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy revealed an excellent stability. Oxygen permeation fluxes were measured across 1000 µm thick and 110 µm thick self-supported 10Sc1YSZ-LCCN (70–30 vol%) membranes from 700 °C to 950 °C using air as the feed gas and N2or CO2as the sweep gas. The 110 µm thick membrane, prepared by tape-casting and lamination processes, showed oxygen fluxes up to 1.02 mLNcm−2min−1(950 °C, air/N2). Both membranes demonstrated stable performances over long-term stability tests (250–300 h) performed at 850 °C using pure CO2as the sweep gas.

Journal article

Yu J, Sun L, Berrueco C, Fidalgo B, Paterson N, Millan Met al., 2018, Influence of temperature and particle size on structural characteristics of chars from Beechwood pyrolysis, Journal of Analytical and Applied Pyrolysis, Vol: 130, Pages: 127-134, ISSN: 0165-2370

This work investigates the effect of temperature and particle size on the product yields and structure of chars obtained from the pyrolysis of Beechwood Chips (BWC), a lignocellulosic biomass. BWC of three different size fractions (0.21-0.50 mm, 0.85-1.70 mm and 2.06-3.15 mm) were pyrolyzed at atmospheric pressure and temperatures ranging from 300 to 900 °C in a fixed bed reactor. Tar and gas yields increased with increasing temperature, while char yield decreased, particularly between 300 and 450 °C. The effect of particle size was mostly observed at temperatures lower than 400 °C as a larger char yield for larger particles due to intraparticle reactions. At higher temperatures the larger surface area in the char fixed bed favoured reactions increasing char and gas yields from the smaller particles. Pyrolysis chars were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Raman spectroscopy. Loss in oxygenated functional groups and aliphatic side chains with increasing temperature was revealed, along with an increase in the concentration of large aromatic systems, leading to a more ordered char structure but no significant graphitization. The changes in char nature at high temperature led to a loss in their combustion reactivity. Raman spectra indicated that the temperature needed to completely decompose the cellulose structure increased with biomass particle size and the enhanced intraparticle reactions in pyrolysis of large particles was likely to give rise to amorphous carbon structures with small fused ring systems.

Journal article

Torres D, Arcelus-Arrillaga P, Millan M, Pinilla JL, Suelves Iet al., 2017, Enhanced reduction of few-layer graphene oxide via supercriticalwater gasification of glycerol, Nanomaterials, Vol: 7

© 2017 by the authors. Licensee MDPI, Basel, Switzerland. A sustainable and effective method for de-oxygenation of few-layer graphene oxide (FLGO) by glycerol gasification in supercritical water (SCW) is described. In this manner, reduction of FLGO and valorization of glycerol, in turn catalyzed by FLGO, are achieved simultaneously. The addition of glycerol enhanced FLGO oxygen removal by up to 59% due to the in situ hydrogen generation as compared to the use of SCW only. Physicochemical characterization of the reduced FLGO (rFLGO) showed a high restoration of the sp2-conjugated carbon network. FLGO sheets with a starting C/O ratio of 2.5 are reduced by SCW gasification of glycerol to rFLGO with a C/O ratio of 28.2, above those reported for hydrazine-based methods. Additionally, simultaneous glycerol gasification resulted in the concurrent production of H2, CO, CH4and valuable hydrocarbons such as alkylated and non-alkylated long chain hydrocarbon (C12–C31), polycyclic aromatic hydrocarbons (PAH), and phthalate, phenol, cresol and furan based compounds.

Journal article

Pirou S, Bermudez JM, Hendriksen PV, Kaiser A, Reina TR, Millan M, Kiebach Ret al., 2017, Stability and performance of robust dual-phase (ZrO<inf>2</inf>)<inf>0.89</inf>(Y<inf>2</inf>O<inf>3</inf>)<inf>0.01</inf>(Sc<inf>2</inf>O<inf>3</inf>)<inf>0.10</inf>-Al<inf>0.02</inf>Zn<inf>0.98</inf>O<inf>1.01</inf>oxygen transport membranes, Journal of Membrane Science, Vol: 543, Pages: 18-27, ISSN: 0376-7388

© 2017 Elsevier B.V. Dual-phase composite oxygen transport membranes consisting of 50 vol% Al0.02Zn0.98O1.01and 50 vol% (ZrO2)0.89(Y2O3)0.01(Sc2O3)0.10were successfully developed and tested. The applicability of the membrane in oxy-fuel power plants schemes involving direct exposure to flue gas was evaluated by exposing the membrane to gas streams containing CO2, SO2, H2O and investigating possible reactions between the membrane material and these gases. The analyses of the exposed composites by x-ray diffraction (XRD), x-ray fluorescence (XRF), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and Raman spectroscopy revealed excellent stability. Additionally, an electrical conductivity measurement over 900 h confirmed that the composite is stable under prolonged exposure to CO2. However, an instability of the dual-phase membrane under oxygen partial pressures below PO2~10−4atm. was found. Oxygen permeation tests on a 1 mm thick self-standing membrane resulted in an oxygen flux of 0.33 mLNmin−1cm−2at 925 °C in air/N2. Stability tests in CO2with 3 vol% O2demonstrated the potential for the use of 10Sc1YSZ-AZO dual-phase membranes in oxy-combustion processes involving direct exposure to flue gas.

Journal article

Arcelus-Arrillaga P, Hellgardt K, Millan M, 2017, Effect of process conditions on the hydrothermal partial oxidation of phenanthrene as a heavy oil model structure, FUEL, Vol: 209, Pages: 434-441, ISSN: 0016-2361

Journal article

Arcelus-Arrillaga P, Pinilla JL, Hellgardt K, Millan Met al., 2017, Application of Water in Hydrothermal Conditions for Upgrading Heavy Oils: A Review, ENERGY & FUELS, Vol: 31, Pages: 4571-4587, ISSN: 0887-0624

Journal article

Millán M, 2017, Effect of Metal Loading in NiMo/Al<inf>2</inf>O<inf>3</inf> Catalysts on Maya Vacuum Residue Hydrocracking, Energy and Fuels, Vol: 31, Pages: 4843-4850, ISSN: 0887-0624

© 2017 American Chemical Society. Hydrocracking catalysts with large porosity need to be developed to treat heavy oil feedstocks rich in large molecular weight components such as asphaltenes and withstand deactivation due to coke formation. In this work, catalysts were prepared by impregnation of varying NiMo loadings on a mesoporous Al2O3 support. The effect of metal loading on the hydrocracking of a vacuum residue at three temperatures (400, 425, and 450 °C) was studied in a batch microbomb reactor. Catalysts were reutilized in a second reaction with fresh feed to assess their activity following the initial period where results are dominated by a large carbon deposition. The textural properties and the coke content on the spent catalysts were evaluated after both reactions. It was found that the reaction temperature had an important effect on the conversion of the fraction with a boiling point above 450 °C, whereas metal loading had minimal impact. On the other hand, metal loading had a significant effect on hydrodeasphaltenization (HDA); higher asphaltene conversions were obtained with higher metal loading. Reaction temperature had an influence on HDA, particularly for lower metal loadings, as catalysts with higher loadings showed significant activity at the lower temperatures studied. It was observed that coke deposits were mainly formed during the initial hour of reaction with little additional coke being formed in the reutilization of the catalysts. More deposits were obtained at lower reaction temperature, as coke precursors, polyaromatic hydrocarbons, polymerize into coke. No evidence of pore mouth plugging was observed, indicating that catalysts could accommodate coke while retaining most of their textural properties. Catalysts with higher metal loadings took longer to reach a stable amount of deposits, but they stabilized at an overall smaller coke deposition and retained significant HDA activity.

Journal article

Volpe R, Menendez JMB, Reina TR, Messineo A, Millan Met al., 2017, Evolution of chars during slow pyrolysis of citrus waste, Fuel Processing Technology, Vol: 158, Pages: 255-263, ISSN: 0378-3820

Conversion of agro-wastes into energy can be key to a circular-driven economy that could lead to models for sustainable production. Thermochemical processing is an interesting alternative for the upgrading of agro-wastes to energy. However, owing to the complex and largely unknown set of reactions occurring during thermal breakdown, to ensuring consistent quality of the final products is still a goal to achieve at industrial level. The present study investigates the evolution of solid products of pyrolysis, to gain some insights in these complexities. Chars derived from slow pyrolysis (200–650 °C) of citrus pulp in a horizontal reactor have been characterized by means of Fourier Transform Infrared spectroscopy (FT-IR), X-Ray Diffraction (XRD), Thermo Gravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). Results are discussed also in light of similarities with coal thermal breakdown. At temperatures below 300 °C, changes in solid matrix are mainly due to breaking of aliphatic compounds. Significant changes in char structure and behavior then occur between 300 °C and 500 °C mainly related to secondary char-tar reactions. Above 500 °C, changes appear to occur mainly due to recombination reactions within matrix, which thereby becomes progressively less reactive.

Journal article

Remón J, Arcelus-Arrillaga P, Arauzo J, García L, Millan-Agorio Met al., 2017, Pyrolysis bio-oil upgrading to renewable liquid fuels by catalytic hydrocracking: Effect of operating conditions on the process, Mediterranean Green Buildings and Renewable Energy: Selected Papers from the World Renewable Energy Network's Med Green Forum, Pages: 491-500, ISBN: 9783319307459

© Springer International Publishing Switzerland 2017. This work analyses the influence of operating conditions during the catalytic hydrocracking of a bio-oil obtained from the fast pyrolysis of pinewood. The original liquid has a 39 wt.% of water and the following elemental composition in dry basis: 54 wt.% C, 3.3 wt.% H, 41.3 wt.% O, 0.8 wt.% N and 0.6 wt.% S. Experiments were carried out in a batch microbomb reactor employing a co-precipitated Ni-Co/Al-Mg catalyst. They were planned according to a full factorial design of experiments with a statistical analysis of the results in order to analyse the effects of temperature (350-450 °C), hydrogen pressure (70-150 bar), catalyst/bio-oil mass ratio (0-0.25 g catalyst/g organics), reaction time (0-60 min) and all interactions between these operating variables on the process. Statistical analysis of the results indicates that the operating conditions have a statistically significant effect on the results. Specifically, the yields to upgraded bio-oil (liquid), gas and solid vary in ranges of 3-97 %, 0-86% and 3-41% respectively. Depending on the operating conditions, the amount of C, H and O (wt.%) in the upgraded bio-oil varies in ranges of 50-82, 3.5-8.3 and 9-44 respectively. This represents an increase of up to 52 and 150% in the proportion of C and H respectively, as well as a decrease of up to 78% in the proportion of O. The higher heating value of the treated bio-oil varies from 19 to 37 MJ/kg, which is considerably higher than that of the original bio-oil.

Book chapter

Remón J, Arcelus-Arrillaga P, Arauzo J, García L, Millan-Agorio Met al., 2017, Liquid and gas biofuels from the catalytic re-forming of pyrolysis bio-oil in supercritical water: Effects of operating conditions on the process, Mediterranean Green Buildings and Renewable Energy: Selected Papers from the World Renewable Energy Network's Med Green Forum, Pages: 479-490, ISBN: 9783319307459

© Springer International Publishing Switzerland 2017. This work analyses the influence of temperature (310-450 °C), pressure (200-260 bar), catalyst/bio-oil mass ratio (0-0.25 g catalyst/g bio-oil) and reaction time (0-60 min) during the re-forming in sub- and supercritical water of a bio-oil obtained from the fast pyrolysis of pinewood. The original liquid has a 39 wt.% of water and the following elemental composition in dry basis: 54 wt.% C, 3.3 wt.% H, 41.3 wt.% O, 0.8 wt.% N and 0.6 wt.% S. The upgrading experiments were carried out in a batch microbomb reactor employing a co-precipitated Ni-Co/Al-Mg catalyst. Statistical analysis of the re-forming results indicates that the operating conditions and the water regime (sub-/supercritical) have a significant influence on the process. Specifically, the yields to upgraded bio-oil (liquid), gas and solid vary in ranges of 5-90 %, 7-91% and 3-31% respectively. The gas phase, having a medium-high lower heating value (2-17 MJ/STP m3), is made up of a mixture of H2 (9-31 vol.%), CO2 (41-84 vol.%), CO (1-22 vol.%) and CH4 (1-45 vol.%). Depending on the operating conditions, the amount of C, H and O (wt.%) in the upgraded bio-oil varies in ranges of 48-74, 4-9 and 13-48 respectively. This represents an increase of up to 42 and 152% in the proportions of C and H respectively, as well as a decrease of up to 69% in the proportion of O. The higher heating value (HHV) of the treated bio-oil varies from 20 to 32 MJ/kg, which corresponds to an increase of up to 68% with respect to the HHV of the original bio-oil.

Book chapter

Yu J, Paterson N, Blamey J, Millan Met al., 2016, Cellulose, xylan and lignin interactions during pyrolysis of lignocellulosic biomass, Fuel, Vol: 191, Pages: 140-149, ISSN: 0016-2361

The three primary lignocellulosic biomass components (cellulose, xylan and lignin), synthetic biomasssamples (prepared by mixing the three primary components) and lignocellulosic biomass (oak, spruceand pine) were pyrolysed in a thermogravimetric analyser and a wire mesh reactor. Different reactivitieswere observed between the three biomass components. Cellulose mainly produced condensables andwas less dependent on heating rate, while xylan and lignin contributed most char yields and were significantlyaffected by heating rate. While xylan and lignin pyrolysed over a large temperature range andshowed the behaviour characteristic of solid fuels, cellulose decomposition is sharp in a narrow temperaturerange, a behaviour typical of linear polymers. Comparison of the pyrolysis behaviour of individualcomponents with that of their synthetic mixtures showed that interactions between cellulose and theother two components take place, but no interaction was found between xylan and lignin. No obviousinteraction occurred for synthetic mixtures and lignocellulosic biomass at 325 C, before the beginningof cellulose pyrolysis, in slow and high heating rate. At higher pyrolysis temperatures, more char wasobtained for synthetic mixtures containing cellulose compared to the estimated value based on the individualcomponents and their proportions in the mixture. For lignocellulosic biomass, less char and moretar were obtained than predicted from the components, which may be associated with the morphology ofsamples. The porous structure of lignocellulosic biomass provided a release route for pyrolysis vapours

Journal article

Remón J, Arauzo J, García L, Arcelus-Arrillaga P, Millan M, Suelves I, Pinilla JLet al., 2016, Bio-oil upgrading in supercritical water using Ni-Co catalysts supported on carbon nanofibres, Fuel Processing Technology, Vol: 154, Pages: 178-187, ISSN: 0378-3820

This work addresses the preparation, characterisation and screening of different Ni-Co catalysts supported on carbon nanofibres (CNFs) for use in the upgrading of bio-oil in supercritical water. The aim is to improve the physicochemical properties of bio-oil so that it can be used as a fuel. The CNFs were firstly oxidised in HNO3 and afterwards subjected to a thermal treatment to selectively modify their surface chemistry prior to the incorporation of the metal active phase (Ni-Co). The CNFs and the supported catalysts were thoroughly characterised by several techniques, which allowed a relationship to be established between the catalyst properties and the upgrading results. The use of Ni-Co/CNFs for bio-oil upgrading in supercritical water (SCW) significantly improved the properties of the original feedstock. In addition, the thermal treatment to which the fibres were subjected exerted a significant influence on their catalytic properties. An increase in the severity of the thermal treatment led to a substantial reduction in the oxygen content of the CNFs, mainly due to the removal of the less stable oxygen surface groups, which allowed their surface polarity to decrease. This decrease resulted in less formation of solid products. However, it also reduced the H/C and increased the O/C ratios of the upgraded liquid. Therefore, a compromise between the yield and the properties of the upgraded bio-oil was achieved with a Ni-Co supported on a CNF with a moderate amount of oxygen surface groups.

Journal article

Deonarine B, Ji G, Smart S, Diniz da Costa JC, Reed G, Millan Met al., 2016, Ultra-microporous membrane separation using toluene to simulate tar-containing gases, Fuel Processing Technology, Vol: 161, Pages: 259-264, ISSN: 0378-3820

This study investigates the performance of ultra-microporous cobalt oxide silica membranes for processing simulated gas streams containing toluene as a model tar compound in gasification. The performance of the membranes was initially investigated for He (simulating H 2 ), CO 2 , N 2 and Ar in a range of temperatures. Subsequently, toluene was added to a gas mixture containing He and tested to simulate the effect of toluene as a tar compound in gasification. The membranes delivered molecular sieving features, showing activated transport as the permeation of the smaller molecular gas He increased with temperature whilst the permeation decreased for the other larger molecular gases. Prior to toluene exposure, He permeance increased by almost twofold from 3.6 × 10 − 8 to 7.1 × 10 − 8  mol m − 2  s − 1  Pa − 1 as the temperature was raised from 50 to 200 °C. Under a feed gas containing 0.24 mol% toluene, He permeance decreased by an average value of 17%. Upon regeneration of the membrane by heat, He permeance was not fully recovered, a clear indication of tar fouling. A toluene balance calculation showed toluene being retained by the membrane.

Journal article

Volpe R, Messineo A, Millan M, 2016, Carbon reactivity in biomass thermal breakdown, Fuel, Vol: 183, Pages: 139-144, ISSN: 0016-2361

The thermochemical behavior of dry grape residues was assessed during pyrolysis experiments in a horizontal batch reactor. Grape marc (a mix of 50% seeds and 50% skins w/w% db) was pyrolysed during slow heating experiments (50 °C min−1) in a quartz reactor to peak temperatures between 150 and 650 °C, under a continuous flow of nitrogen (1.5 L min−1). Solids recovered after treatments (chars) were then subject to thermo-gravimetric analysis (TGA) in order to assess the reactivity of the carbon contained in them. Results on chars showed a linear increase of fixed carbon (FC) with reaction peak temperature. Elemental analyses on chars showed a consistent linear increase of Carbon (C) and a linear decrease of Oxygen (O) with reaction peak temperature. On the contrary, the Hydrogen (H) content remained relatively constant to approximately 325 °C and then decreased steadily as the reaction temperature was raised further. The reactivity of C in solids was investigated by definition of an index ρ(C), which was shown to remain approximately constant up to 325 °C and then significantly decrease above that temperature. The decrease of C reactivity initially related to the release of the more reactive C within the volatiles and then (for higher reaction temperatures) was shown to be mainly related to deactivation reactions within the solids. A correlation was shown between C reactivity and the release of H from thermal breakdown. As long as H concentration in solids remains constant (for reaction peak temperatures up to 325 °C), C reactivity remains close to the value found for raw feedstock. Then, between 325 and 400 °C, H content in solids decreases by 1.5% (w/w daf) and C reactivity drastically drops by 50%. This trend continues up to the highest reaction peak temperature tested (650 °C), for which the H content in solids is approximately 2% (w/w daf) and C reactivity drops by 70%. Elaboration of results from previous experiments o

Journal article

Reina TR, Yeletsky P, Bermúdez JM, Arcelus-Arrillaga P, Yakovlev VA, Millan Met al., 2016, Anthracene aquacracking using NiMo/SiO<inf>2</inf> catalysts in supercritical water conditions, Fuel, Vol: 182, Pages: 740-748, ISSN: 0016-2361

A series of effective NiMo/SiO2 catalysts for heavy oil upgrading in supercritical water have been developed. Experimental results with anthracene as model compound resembling structures present in heavy oils showed that the catalytic activity as well as the liquid and gas product distributions are governed by catalyst composition. In particular by adjusting the Ni/Mo ratio different physicochemical properties (crystalline phase composition, particle size and catalysts reducibility) are obtained, which have influence on catalytic behavior. A variety of liquid products together with a valuable gas (rich in H2) are produced in this process, which takes place with remarkably low coke deposition on the catalysts. Overall, the results derived from this work confirm the viability of upgrading polyaromatic structures in supercritical water using Ni-Mo catalysts and provides an insight on the main parameters to control in catalyst design.

Journal article

Gargiulo V, Apicella B, Stanzione F, Tregrossi A, Millan M, Ciajolo A, Russo Cet al., 2016, Structural Characterization of Large Polycyclic Aromatic Hydrocarbons. Part 2: Solvent-Separated Fractions of Coal Tar Pitch and Naphthalene-Derived Pitch, Energy and Fuels, Vol: 30, Pages: 2574-2583, ISSN: 0887-0624

Complex polycyclic aromatic hydrocarbon (PAH) mixtures separated from a coal tar pitch (CP) and naphthalene pitch (NP) by sequential extraction with heptane and toluene were characterized in detail by applying a multiarray analytical approach. Gas chromatography-mass spectrometry (GC-MS), size exclusion chromatography (SEC), laser desorption ionization-time-of-flight mass spectrometry (LDI-TOFMS), and thermogravimetry (TG) were used to relate the volatility and coking yield of pitch components to their solubility and molecular weight distribution. Spectroscopic analysis, including infrared (IR), ultraviolet-visible (UV-vis), and fluorescence spectroscopy, proved to be useful for measuring specific features of aromatic systems, such as the aromatic content, degree of aliphatic substitution, and size distribution of PAHs of different molecular weights. In particular, it has been shown that the spectroscopic analysis is an essential tool for characterizing very large PAH systems concentrated in the pitch toluene-insoluble fraction. This fraction constitutes a case study of very large, structurally different aromatic compounds, and it is the pitch fraction more relevant for practical applications because of its higher coking tendency and peculiar optical properties.

Journal article

Millan M, Lorente E, Boldrin P, Brandon Net al., 2016, Integration of gasification and fuel cells: Interaction between the anode and contaminants in the syngas

© 2016 International Pittsburgh Coal Conference. All rights reserved. Fouling due to carbon deposition on the fuel cell anode reduces the performance of the cell. • The addition of steam above S/C of 1 was found to reduce carbon deposition from tars but not fully suppress coke formation. • A combination of high S/C=ratio and current density may effectively inhibit carbon formation, maintaining cell performance. • Benzene and toluene represent a "worst-case scenario" as tar models and light fractions are more likely to produce carbon deposits.

Conference paper

Millan M, Arcelus-Arrillaga P, Hellgardt K, 2016, Coal to liquids by oxidative cracking in near-critical and super-critical water

Conference paper

Gargiulo V, Apicella B, Alfè M, Russo C, Stanzione F, Tregrossi A, Amoresano A, Millan M, Ciajolo Aet al., 2015, Structural Characterization of Large Polycyclic Aromatic Hydrocarbons. Part 1: The Case of Coal Tar Pitch and Naphthalene-Derived Pitch, Energy and Fuels, Vol: 29, Pages: 5714-5722, ISSN: 0887-0624

© 2015 American Chemical Society. The different thermal behaviors and solubilities of large and structurally different polycyclic aromatic hydrocarbon (PAH) mixtures featuring coal tar pitch (CP) and naphthalene synthetic pitch (NP) samples could be read in light of their different molecular weight (MW) distribution and spectroscopic features. The number-average MW obtained by mass spectrometry for CP (417 Da) and NP (691 Da) resulted to be lower in comparison to the values evaluated by size-exclusion chromatography (SEC) (796 and 824 Da for CP and NP, respectively) because of the different response of the detector of mass spectrometry to low- and high-MW components. Hence, SEC showed to be more suitable for the analysis of PAH mixtures overlapping and covering a higher mass range in comparison to mass spectrometry. Insights into structural PAH features were given by means of spectroscopic analysis [infrared (IR), ultraviolet-visible (UV-vis), and fluorescence], allowing for the discrimination between different families of PAHs as ortho-fused PAHs and rylenes interspersed with aliphatic (mainly naphthenic) groups, mainly featuring CP and NP, respectively. Besides showing the different aromaticity and aliphatic/aromatic hydrogen distribution, the improvement of Fourier transform infrared (FTIR) and UV-vis absorption analysis put also in evidence the contribution of carbon-rich particle impurities and PAH aggregates in CP and NP, respectively.

Journal article

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