Publications
218 results found
Patel B, Guo M, Chong C, et al., 2016, Hydrothermal upgrading of algae paste: inorganics and recycling potential in the aqueous phase, Science of the Total Environment, Vol: 568, Pages: 489-497, ISSN: 0048-9697
Hydrothermal Liquefaction (HTL) for algal biomass conversion is a promising technology capable of producing high yields of biocrude as well as partitioning even higher quantity of nutrients in the aqueous phase. To assess the feasibility of utilizing the aqueous phase, HTL of Nannochloropsis sp. was carried out in the temperature range of 275 to 350 °C and Residence Times (RT) ranging between 5 and 60 min The effect of reaction conditions on the NO3− , PO43 − , SO42 − , Cl− , Na+ , and K+ ions as well as Chemical Oxygen Demand (COD) and pH was investigated with view of recycling the aqueous phase for either cultivation or energy generation via Anaerobic Digestion (AD), quantified via Lifecycle Assessment (LCA). It addition to substantial nutrient partitioning at short RT, an increase in alkalinity to almost pH 10 and decrease in COD at longer RT was observed. The LCA investigation found reaction conditions of 275 °C/30 min and 350 °C/10 min to be most suitable for nutrient and energy recovery but both processing routes offer environmental benefit at all reaction conditions, however recycling for cultivation has marginally better environmental credentials compared to AD.
Freeman J, Hellgardt K, Markides CN, 2016, Working Fluid Selection and Electrical Performance Optimisation of a Domestic Solar-ORC Combined Heat and Power System for Year-Round Operation in the UK, Applied Energy, Vol: 186, Pages: 291-303, ISSN: 0306-2619
In this paper, we examine the electrical power-generation potential of adomestic-scale solar combined heating and power (S-CHP) system featuringan organic Rankine cycle (ORC) engine and a 15-m2solar-thermal collectorarray. The system is simulated with a range of organic working fluids andits performance is optimised for operation in the UK climate. The findingsare applicable to similar geographical locations with significant cloud coverage,a low solar resource and limited installation areas. A key feature of thesystem’s design is the implementation of fixed fluid flow-rates during operationin order to avoid penalties in the performance of components suffered atpart-load. Steady operation under varying solar irradiance conditions is providedby way of a working-fluid buffer vessel at the evaporator outlet, whichis maintained at the evaporation temperature and pressure of the ORC. Byincorporating a two-stage solar collector/evaporator configuration, a maximumnet annual electrical work output of 1070 kWh yr−1(continuous averagepower of 122 W) and a solar-to-electrical efficiency of 6.3% is reported withHFC-245ca as the working fluid at an optimal evaporation temperature of126 ◦C (corresponding to an evaporation pressure of 16.2 bar). This is equivalentto ∼ 32% of the electricity demand of a typical/average UK home, andrepresents an improvement of more than 50% over a recent effort by the sameauthors based on an earlier S-CHP system configuration and HFC-245fa asthe working fluid [1]. A performance and simple cost comparison with standalone,side-by-side PV and solar-thermal heating systems is presented.
Patel B, Guo M, Shah N, et al., 2016, Environmental Profile of Algal Hydrothermal Liquefaction – A Country Specific Case Study, Algal Research-Biomass Biofuels and Bioproducts, Vol: 16, Pages: 127-140, ISSN: 2211-9264
Microalgae are known to be an important feedstock not just for biofuel but also biochemical production. In this investigation we utilise a cradle-to-biorefinery-gate attributional LCA (aLCA) methodology to evaluate the environmental impacts of Nannochloropsis sp. derived algal biocrude production. A database of primary experimental data for continuous fast Hydrothermal Liquefaction (HTL) and Hydrotreating (HDT) is combined with secondary data from literature to investigate the overall environmental profiles of cultivation, dewatering, HTL and HDT for various scenarios based on the energy generation mix of 5 countries (Brazil, UK, Spain, China and Australia) as well as a comparison with fossil crude. The investigation found that Brazil delivers best environmental profiles for all scenarios, primarily due to its significant contribution from hydropower. Furthermore, the cultivation and HTL processes account for nearly 90% of environmental burdens whereas dewatering and HDT only contribute less than 8%. The research findings highlight the importance of the several factors on the resulting 3G biofuel profiling e.g. energy resource, processing technology choice and the co-product(s) and emissions profiling methodology. Algal biocrude is still undergoing research and development compared to the well-developed fossil crude industry. Via integration and optimisation at process and value chain levels, algae-derived biocrude has the potential to deliver an environmentally sustainable alternative to the fossil crude, provided the energy input for processing is from a renewable source.
Zhu J, Hii KKM, Hellgardt K, 2016, Toward a green generation of oxidant on demand: practical electrosynthesis of ammonium persulfate, ACS Sustainable Chemistry & Engineering, Vol: 4, Pages: 2027-2036, ISSN: 2168-0485
Kalamaras C, Palomas D, Bos R, et al., 2016, Selective Oxidation of Methane to Methanol Over Cu- and Fe-Exchanged Zeolites: The Effect of Si/Al Molar Ratio, CATALYSIS LETTERS, Vol: 146, Pages: 483-492, ISSN: 1011-372X
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- Citations: 55
Newton MA, Brazier JB, Barreiro EM, et al., 2016, Operando XAFS of supported Pd nanoparticles in flowing ethanol/water mixtures: Implications for catalysis., Green Chemistry, Vol: 18, Pages: 406-411, ISSN: 1744-1560
Ethanol-water, a prototypical ‘green’ solvent mixture, cannot be considered as inert toward supported Pd nanoparticles. We establish severe size dependencies in Pd redox behavior, persistent gradients in Pd phase in a plug-flow situation, and that Pd nanoparticles are contaminated with hydrogen derived from the solvent.
Millan M, Arcelus-Arrillaga P, Hellgardt K, 2016, Coal to liquids by oxidative cracking in near-critical and super-critical water
Alshammari YM, Hellgardt K, 2016, Sub and supercritical water reforming of n-hexadecane in a tubular flow reactor, Journal of Supercritical Fluids, Vol: 107, Pages: 723-732, ISSN: 1872-8162
This work investigates the hydrothermal conversion of hexadecane, as a heavy hydrocarbon model for heavy oil upgrading, and syngas generation. This experimental analysis was carried out in tubular flow reactor where water and hexadecane react at 525–605 °C and 150/220 bar under different residence times. Hydrogen and syngas formation was observed and quantified under the current conditions without significant formation of coke in the reactor. Residual hexadecane was also analysed for its contents of cracking products using GCMS. Investigating the temperature and residence time effects enabled determining the reaction kinetic data from which the activation energy, Ea, was determined to 263 kJ/mol (at 220 bar) and 202 kJ/mol (at 150 bar). The determined kinetic data were compared with previously reported results on high pressure pyrolysis of hexadecane and other hydrocarbons. The effects of increasing the water density by increasing the reactor pressure to (220 bar) was found in particular to enhance heat and mass transfer leading to a higher degree of conversion at lower temperatures, and increasing the ratio of n-alkane to 1-alkenes via in situ hydrogenation. Cracking was found to follow the free radical mechanism under both sub and supercritical conditions, producing nearly equi-molar distribution of n-alkanes and 1-alkenes, C7–C13, under lower conversions. Increasing the reaction temperature enhances the formation of 1-alkene via β-scission, while increasing the pressure increases the formation n-alkanes via H-abstraction. In addition, it is found that the hydrothermal conditions have inhibited the formation of higher molecular weight hydrocarbons, C16+, via addition reactions. Results show the potential for a continuous process for hydrogen generation from heavy hydrocarbons using sub and supercritical water with minimised carbon formation.
Patel B, Guo M, Izadpanah A, et al., 2016, A Review on Hydrothermal Pre-treatment Technologies and Environmental Profiles of Algal Biomass Processing, Bioresource Technology, Vol: 199, Pages: 288-299, ISSN: 1873-2976
The need for efficient and clean biomass conversion technologies has propelled Hydrothermal (HT) processing as a promising treatment option for biofuel production. This manuscript discussed its application for pre-treatment of microalgae biomass to solid (biochar), liquid (biocrude and biodiesel) and gaseous (hydrogen and methane) products via Hydrothermal Carbonisation (HTC), Hydrothermal Liquefaction (HTL) and Supercritical Water Gasification (SCWG) as well as the utility of HT water as an extraction medium and HT Hydrotreatment (HDT) of algal biocrude. In addition, the Solar Energy Retained in Fuel (SERF) using HT technologies is calculated and compared with benchmark biofuel. Lastly, the Life Cycle Assessment (LCA) discusses the limitation of the current state of art as well as introduction to new potential input categories to obtain a detailed environmental profile.
Hii KKM, Hellgardt K, 2016, Catalysis in Flow: Why Leaching Matters, ORGANOMETALLIC FLOW CHEMISTRY, Editors: Noel, Publisher: SPRINGER-VERLAG BERLIN, Pages: 249-262, ISBN: 978-3-319-33241-3
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- Citations: 13
Patel B, Hellgardt K, 2015, Hydrothermal upgrading of algae paste in a continuous flow reactor, BIORESOURCE TECHNOLOGY, Vol: 191, Pages: 460-468, ISSN: 0960-8524
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- Citations: 40
del Rio-Chanona EA, Dechatiwongse P, Zhang D, et al., 2015, Optimal Operation Strategy for Biohydrogen Production, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 54, Pages: 6334-6343, ISSN: 0888-5885
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- Citations: 25
Palomas D, Kalamaras C, Haycock P, et al., 2015, Re-evaluating selectivity as a determining factor in peroxidative methane oxidation by multimetallic copper complexes, Catalysis Science & Technology, Vol: 5, Pages: 4108-4115, ISSN: 2044-4753
Zhang D, Dechatiwongse P, del Rio-Chanona EA, et al., 2015, Dynamic modelling of high biomass density cultivation and biohydrogen production in different scales of flat plate photobioreactors, Biotechnology and Bioengineering, Vol: 112, Pages: 2429-2438, ISSN: 1097-0290
This paper investigates the scaling-up of cyanobacterial biomass cultivation and biohydrogen production from laboratory to industrial scale. Two main aspects are investigated and presented, which to the best of our knowledge have never been addressed, namely the construction of an accurate dynamic model to simulate cyanobacterial photo-heterotrophic growth and biohydrogen production and the prediction of the maximum biomass and hydrogen production in different scales of photobioreactors. To achieve the current goals, experimental data obtained from a laboratory experimental setup are fitted by a dynamic model. Based on the current model, two key original findings are made in this work. First, it is found that selecting low-chlorophyll mutants is an efficient way to increase both biomass concentration and hydrogen production particularly in a large scale photobioreactor. Second, the current work proposes that the width of industrial scale photobioreactors should not exceed 0.20 m for biomass cultivation and 0.05 m for biohydrogen production, as severe light attenuation can be induced in the reactor beyond this threshold.
Zhang D, Dechatiwongse P, Del-Rio-Chanona EA, et al., 2015, Analysis of the cyanobacterial hydrogen photoproduction process via model identification and process simulation, CHEMICAL ENGINEERING SCIENCE, Vol: 128, Pages: 130-146, ISSN: 0009-2509
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- Citations: 26
Dechatiwongse P, Maitland C G, Hellgardt K, 2015, Demonstration of a two-stage aerobic/anaerobic chemostat for the enhanced production of hydrogen and biomass from unicellular nitrogen-fixing cyanobacterium, Algal Research-Biomass Biofuels and Bioproducts, ISSN: 2211-9264
Ibadurrohman M, Hellgardt K, 2015, Morphological Modification of TiO<sub>2</sub> Thin Films as Highly Efficient Photoanodes for Photoelectrochemical Water Splitting, ACS APPLIED MATERIALS & INTERFACES, Vol: 7, Pages: 9088-9097, ISSN: 1944-8244
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- Citations: 35
Freeman J, Hellgardt K, Markides CN, 2015, An Assessment of Solar-Thermal Collector Designs for Small-Scale Combined Heating and Power Applications in the UK, Heat Transfer Engineering, Vol: 36, Pages: 1332-1347, ISSN: 1521-0537
Brown NJ, Garcia-Trenco A, Weiner J, et al., 2015, From Organometallic Zinc and Copper Complexes to Highly Active Colloidal Catalysts for the Conversion of CO2 to Methanol, ACS Catalysis, Vol: 5, Pages: 2895-2902, ISSN: 2155-5435
A series of zinc oxide and copper(0) colloidal nanocatalysts, produced by a one-pot synthesis, are shown to catalyze the hydrogenation of carbon dioxide to methanol. The catalysts are produced by the reaction between diethyl zinc and bis(carboxylato/phosphinato)copper(II) precursors. The reaction leads to the formation of a precatalyst solution, characterized using various spectroscopic (NMR, UV–vis spectroscopy) and X-ray diffraction/absorption (powder XRD, EXAFS, XANES) techniques. The combined characterization methods indicate that the precatalyst solution contains copper(0) nanoparticles and a mixture of diethyl zinc and an ethyl zinc stearate cluster compound [Et4Zn5(stearate)6]. The catalysts are applied, at 523 K with a 50 bar total pressure of a 3:1 mixture of H2/CO2, in the solution phase, quasi-homogeneous, hydrogenation of carbon dioxide, and they show high activities (>55 mmol/gZnOCu/h of methanol). The postreaction catalyst solution is characterized using a range of spectroscopies, X-ray diffraction techniques, and transmission electron microscopy (TEM). These analyses show the formation of a mixture of zinc oxide nanoparticles, of size 2–7 nm and small copper nanoparticles. The catalyst composition can be easily adjusted, and the influence of the relative loadings of ZnO/Cu, the precursor complexes and the total catalyst concentration on the catalytic activity are all investigated. The optimum system, comprising a 55:45 loading of ZnO/Cu, shows equivalent activity to a commercial, activated methanol synthesis catalyst. These findings indicate that using diethyl zinc to reduce copper precursors in situ leads to catalysts with excellent activities for the production of methanol from carbon dioxide.
Zhang D, Dechatiwongse P, del Rio-Chanona EA, et al., 2015, Modelling of light and temperature influences on cyanobacterial growth and biohydrogen production, Algal Research, Vol: 9, Pages: 263-274, ISSN: 2211-9264
Dynamic simulation is a valuable tool to assist the scale-up and transition of biofuel production from laboratory scale to potential industrial implementation. In the present study two dynamic models are constructed, based on the Aiba equation, the improved Lambert–Beer's law and the Arrhenius equation. The aims are to simulate the effects of incident light intensity, light attenuation and temperature upon the photo-autotrophic growth and the hydrogen production of the nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142. The results are based on experimental data derived from an experimental setup using two different geometries of laboratory scale photobioreactors: tubular and flat-plate. All of the model parameters are determined by an advanced parameter estimation methodology and subsequently verified by sensitivity analysis. The optimal temperature and light intensity facilitating biohydrogen production in the absence of light attenuation have been determined computationally to be 34 °C and 247 μmol m− 2 s− 1, respectively, whereas for cyanobacterial biomass production they are 37 °C and 261 μmol m− 2 s− 1, respectively. Biomass concentration higher than 0.8 g L− 1 is also demonstrated to significantly enhance the light attenuation effect, which in turn inducing photolimitation phenomena. At a higher biomass concentration (3.5 g L− 1), cyanobacteria are unable to activate photosynthesis to maintain their lives in a photo-autotrophic growth culture, and biohydrogen production is significantly inhibited due to the severe light attenuation.
Sasegbon A, Hellgardt K, 2015, Flux Response Technology (FRT) Applied in Zero Length Column Diffusivity and Adsorption Measurements, TRANSPORT IN POROUS MEDIA, Vol: 107, Pages: 731-744, ISSN: 0169-3913
Sharifzadeh M, Richard CJ, Liu K, et al., 2015, An integrated process for biomass pyrolysis oil upgrading: A synergistic approach, Biomass & Bioenergy, Vol: 76, Pages: 108-117, ISSN: 0961-9534
Zhang D, Dechatiwongse P, Hellgardt K, 2015, Modelling light transmission, cyanobacterial growth kinetics and fluid dynamics in a laboratory scalemultiphase photo-bioreactor for biological hydrogen production, ALGAL RESEARCH-BIOMASS BIOFUELS AND BIOPRODUCTS, Vol: 8, Pages: 99-107, ISSN: 2211-9264
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- Citations: 38
Freeman J, Hellgardt K, Markides CN, 2015, An assessment of solar-powered organic Rankine cycle systems for combined heating and power in UK domestic applications, Applied Energy, Vol: 138, Pages: 605-620, ISSN: 1872-9118
Rix K, Kelsall GH, Hellgardt K, et al., 2015, Chemo- And diastereoselectivities in the electrochemical reduction of maleimides, ChemSusChem, Vol: 8, Pages: 665-671, ISSN: 1864-5631
The electrochemical cathodic reduction of cyclic imides (maleimides) to succinimides can be achieved chemoselectively in the presence of alkene, alkyne, and benzyl groups. The efficiency of the system was demonstrated by using a 3D electrode in a continuous flow reactor. The reduction of 3,4-dimethylmaleimides to the corresponding succinimides proceeds with a 3:2 diastereomeric ratio, which is independent of the nitrogen substituent and electrode surface area. The stereoselectivity of the process was rationalized by using DFT calculations, involving an acid-catalyzed tautomerization of a half-enol occurring through a double hydrogen-transfer mechanism.
Alshammari YM, Hellgardt K, 2015, Partial oxidation of n-hexadecane through decomposition of hydrogen peroxide in supercritical water, CHEMICAL ENGINEERING RESEARCH & DESIGN, Vol: 93, Pages: 565-575, ISSN: 0263-8762
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- Citations: 25
Patel B, Dechatiwongse P, Hellgardt K, 2014, Enzyme-catalysed processes in a potential algal biorefinery, Industrial Biocatalysis, Editors: Grunwald, Publisher: Pan Stanford, Pages: 1065-1099, ISBN: 9789814463881
In this book, renowned scientists discuss the actual developments in these research fields together with a variety of application-oriented topics.
Ibadurrohman M, Hellgardt K, 2014, Photoelectrochemical performance of graphene-modified TiO<inf>2</inf> photoanodes in the presence of glycerol as a hole scavenger, International Journal of Hydrogen Energy, Vol: 39, Pages: 18204-18215, ISSN: 0360-3199
Graphene-modified TiO2 (G-TiO2) photoanode films were successfully prepared by a simple, versatile, and low-cost spray pyrolysis deposition method. The effects of graphene incorporation on the relevant properties of TiO2 films were investigated by means of XRD, SEM, UV-vis absorbance spectroscopy, and photoelectrochemistry-related measurements. Bias-dependant efficiency calculated from linear-sweep voltammograms shows that the presence of graphene within the film networks, despite its low content, could promote a substantial improvement in maximum photoconversion efficiency from 0.39% (at-0.27 V vs HgO|Hg) to 0.65% (at-0.35 V vs HgO|Hg). This improvement is attributable to the enhancement of the electron-transferring ability upon the insertion of graphene, as confirmed by transient photocurrent analysis and Electrochemical Impedance Spectroscopy (EIS). The effectiveness of the photoelectrochemical cell employing G-TiO2 as an excellent photoanode was further examined by running it in the presence of glycerol as a hole scavenger. Glycerol plays an important role as an effective sink for the photogenerated holes so that the surface charge recombination can be significantly suppressed and, subsequently, the photocurrent is enhanced. The additional photocurrent due to glycerol introduction into the cell depends upon the initial concentration of glycerol according to a model resembling a Langmuir-Hinshelwood isotherm. Based upon the results of the present study, further improvements in terms of graphene content, surface morphology modification or the use of other organic wastes as hole scavengers may be important for future investigation.
Alshammari YM, Hellgardt K, 2014, A new HYSYS model for underground gasification of hydrocarbons under hydrothermal conditions, International Journal of Hydrogen Energy, Vol: 39, Pages: 12648-12656, ISSN: 0360-3199
A new subsurface process model was developed using the ASPEN HYSYS simulation environment to analyse the process energy and gasification efficiency at steady-state equilibrium conditions. Injection and production wells were simulated using the HYSYS pipe flow utilities which makes use of the Beggs and Brill flow correlation applicable for vertical pipes. The downhole reservoir hydrothermal reactions were assumed to be in equilibrium, and hence, the Gibbs reactor was used. It was found that high W/C ratios and low O/C ratios are required to maximise gasification efficiency at a constant hydrocarbon feed flowrate, while the opposite is true for the energy efficiency. This occurs due to the dependence of process energy efficiency on the gas pressure and temperature at surface, while the gasification efficiency depends on the gas composition which is determined by the reservoir reaction conditions which affects production distribution. Another effect of paramount importance is the increase in reservoir production rate which was found to directly enhance both energy and gasification efficiency showing conditions where the both efficiencies are theoretically maximised. Results open new routes for techno-economic assessment of commercial implementation of underground gasification of hydrocarbons. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Dechatiwongse P, Srisamai S, Maitland G, et al., 2014, Effects of light and temperature on the photoautotrophic growth and photoinhibition of nitrogen-fixing cyanobacterium <i>Cyanothece</i> sp ATCC 51142, ALGAL RESEARCH-BIOMASS BIOFUELS AND BIOPRODUCTS, Vol: 5, Pages: 103-111, ISSN: 2211-9264
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- Citations: 40
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